DETAILS OF CYANIDE PRACTICE 
 
McGraw-Hill Book Company 
 
 Electrical World The Engineering and Mining Journal 
 Engiaeering Record Engineering News 
 
 R ailway Age G aze tt<? American Machinist 
 
 Signal Elngin<?9r American Engineer 
 
 Electric Railway Journal Coal Age 
 
 Metallurgical and Chemical Engineering P o we r 
 
DETAILS OF 
 CYANIDE PRACTICE 
 
 BY 
 HERBERT A. MEGRAW 
 
 MINING AND METALLURGICAL ENGINEER. MEMBER OF THE AMERICAN 
 
 INSTITUTE OP MINING ENGINEERS. MEMBER OF EDITORIAL STAFF 
 
 OF THE "ENGINEERING AND MINING JOURNAL." AUTHOR 
 
 OF "PRACTICAL DATA FOR THE CYANIDE PLANT." 
 
 FIRST EDITION 
 
 McGRAW-HILL BOOK COMPANY, INC. 
 239 WEST 39TH STREET, NEW YORK 
 
 6 BOUVERIE STREET, LONDON, E. C. 
 1914 
 
T/y 
 A/.-f 
 
 COPYRIGHT, 1914, BY THE 
 McGRAW-HiLL BOOK COMPANY, INC. 
 
 
 
 
 THE. MAPLE- PRESS- YOKK. PA 
 
PREFACE 
 
 The chapters presented in this book are the record of an investigative 
 tour of the principal cyaniding mills of North America, taken with the 
 idea of presenting detailed facts about the present state of the process to 
 the readers of the Engineering and Mining Journal, in which periodical 
 they have already appeared. Actual description has been considered of 
 less importance than discussion and correlation of facts gathered from 
 widely different places, the intention having been to present facts and 
 personal opinions, clearly indicated as such, in a form calculated to 
 inform the profession in general and to promote discussion respecting 
 details involving diverging practice. Some pages of the discussion 
 elicited have been included as illuminating the subjects. 
 
 One article, that constituting Chapter II, has been included that I 
 did not write. Although I had visited and studied the plant discussed, 
 and had formulated a paper treating of its interesting points, the de- 
 scription and explanation submitted by Mr. R. B. Watson, manager of 
 the Nipissing Mining Co , was used, a manager being more thoroughly 
 familiar with his own plant than anyone else could be. Some points 
 which particularly attract the attention of the outsider, however, were 
 mentioned in my discussion of the subject, and these are to be found 
 constituting Chapter III. Those points thoroughly covered by Mr. 
 Watson have been removed from my article, which makes it somewhat 
 disjointed, but anyone reading the two chapters will be at no trouble to 
 understand the references 
 
 The original itinerary of this technical journey included a visit to the 
 important plants of Mexico, but the condition of affairs in that country 
 when the trip was undertaken, made it necessary for that part to be 
 postponed until such time as there will be more to study and greater 
 safety in traveling. 
 
 Any benefit which the profession may derive from the matter pre- 
 sented is to be credited to Mr. Walter Renton Ingalls, Editor of the 
 Engineering and Mining Journal, to whose energy and progressive 
 spirit the undertaking is due. 
 
 H. A. MEGRAW. 
 NEW YORK, 
 February 10, 1914. 
 
CONTENTS 
 
 CHAPTER PA OR 
 
 PREFACE v 
 
 I. THE COBALT DISTRICT, ONTARIO 1 
 
 II. THE NIPISSING HIGH-GRADE MILL, COBALT. 14 
 
 III. THE NIPISSING HIGH-GRADE MILL, COBALT, Concluded . 23 
 
 IV. THE HOLLINGER MILL, PORCUPINE, ONTARIO 28 
 
 V. THE DOME MILL, SOUTH PORCUPINE, ONTARIO 39 
 
 VI. PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 50 
 
 VII. THE LIBERTY BELL MILL, TELLURIDE, COLORADO 67 
 
 VIII. PRACTICE AT CRIPPLE CREEK, COLORADO 79 
 
 IX. CONTINUOUS DECANTATION OF SLIME 96 
 
 X. PRACTICE AT TONOPAH 102 
 
 XI. PRACTICE AT TONOPAH, Continued 114 
 
 XII. PRACTICE AT TONOPAH, Concluded 129 
 
 XIII. THE NEVADA HILLS MILL AT FAIRVIEW 153 
 
 XIV. PRACTICE AT THE NEVADA WONDER MILL 161 
 
 XV. METHODS AT REPUBLIC 168 
 
 XVI. THE MILLS OF GRASS VALLEY, CALIFORNIA 177 
 
 XVII. THE BLACK OAK PLANT, CALIFORNIA 188 
 
 XVIII. THE GOLD ROAD MILL, ARIZONA 195 
 
 XIX. Two ARIZONA MILLS 203 
 
 INDEX . . 213 
 
 Vll 
 
DETAILS OF CYANIDE PRACTICE 
 
 CHAPTER I 
 THE COBALT DISTRICT, ONTARIO 
 
 The mining district of Cobalt in Ontario, Canada, is one of the 
 newer areas in which economic mining has proved possible. In common 
 with most new camps the first output was high-grade material, but it 
 differs from many in the fact that the average content of the mineral 
 has continued up to this time to be higher than is usually the case when 
 work has been carried to the extent that it has here. The valuable 
 metal is silver which occurs native and in combination. It is found 
 as sulphide, arsenide, antimonide and in combination with manganese, 
 nickel and cobalt. Small proportions of copper are also found in some 
 of the ores and in at least one, the Nipissing, mercury has been definitely 
 proved to exist. In regard to the latter many engineers are skeptical, 
 having never encountered any indications of it even in the higher grade 
 mineral but the work of the metallurgists who experimented upon the ores 
 of the Nipissing mine has been sufficient for them to state positively that 
 a small quantity of mercury does exist as a mercury-silver amalgam. 
 
 Character of Ore. The ores occur in narrow fissures in a country 
 rock of fine-grained conglomerate, slate or diabase. They are all hard 
 and tough and are not easily ground to a fine state. The experience 
 of the camp has been that when the ores are ground extremely fine, even 
 to a point where they will pass a 200-mesh screen, the product is largely 
 granular and has the property of settling quickly, the light, flocculent 
 product generally called true slime being conspicuous for its rarity. In 
 addition to this, the mineral is extremely heavy, so that the difficulty 
 of obtaining a product which may be treated as a total slime is greater 
 than is usually the case with silver ores. The power and care required 
 to keep it in suspension is comparatively great. 
 
 Most of the mills in the Cobalt camp are concentrators and due to 
 the character of the mineral, which is favorable to concentration, good 
 results have been obtained from this system of treatment. The silver 
 occurs, as has been mentioned, in heavy minerals which give up a large 
 percentage of their silver content on the concentrating table. Never- 
 theless, the tailing discarded by the concentrating mills contains sufficient 
 silver so that its extraction, or partial extraction, by cyanidation while 
 the pulp is in motion through the mill, might be expected to repay more 
 
 1 
 
2 DETAILS OF CYANIDE PRACTICE 
 
 than the additional expense of cyanide treatment. It is altogether likely 
 that the average tailing from a concentrator treating 25- to 35-oz. ore 
 will contain not less than five to eight ounces of silver per ton. Most 
 of the operators will not admit that the tailing runs so high, but a con- 
 sideration of the conditions, together with some frank conversation with 
 operators leads me to believe that these figures do not overstate the case. 
 If this is true, then cyanide treatment of the table tailing should be 
 economical in view of the fact that most of the work has already been 
 done on the ore and the additional cost of regrinding plus the cost of 
 chemicals and labor would be more than met by the additional silver 
 recovered. I have already said that the ore, even when finely ground, 
 is difficult to agitate, but this does not conflict with the idea that cyanida- 
 tion would be economical, because it is conceivable that the fine sand 
 might be leached at a cost which would be less than that of agitating 
 it. I am unable to discover that any exhaustive experiments have been 
 carried out on leaching a concentrate tailing, but I do not know of any 
 good reason why it would not be possible, particularly in those mills where 
 concentration has already been installed. It may be true that a new mill 
 designed for cyaniding the entire product would give the most economical 
 result eventually, but that is no reason why mills now operating as con- 
 centrators could not increase their profits by cyaniding the table tailing 
 in some way. The analysis of the ores support this view in so far as show- 
 ing that the higher grade ores contain most of the elements considered 
 rebellious, while the lower grade ores are comparatively free from them, 
 making cyanidation cheaper on the low-grade minerals. In the accom- 
 panying table is presented a statement of the comparative content of the 
 extraordinary elements in Cobalt ores of various grades, A representing 
 the high-grade, B the medium-grade and C the low, or milling-grade ores. 
 
 TYPICAL ANALYSES OF COBALT ORES OF DIFFERENT GRADES 
 
 
 A 
 
 B 
 
 C 
 
 SiO 2 
 
 4 51 
 
 2 88 
 
 
 Fe 
 
 2 34 
 
 2 80 
 
 7 00 
 
 CaO.. 
 
 9 05 
 
 10 00 
 
 Q 00 
 
 A1 2 O 3 
 
 1 42 
 
 87 
 
 15 00 
 
 MgO 
 
 6 22 
 
 7 13 
 
 
 Ni 
 
 6 62 
 
 8 78 
 
 
 Co 
 
 7 11 
 
 8 42 
 
 
 As.. 
 
 29 88 
 
 34 48 
 
 <=;o 
 
 Ag. (oz. per ton) 
 
 4786.1 
 
 2014.00 
 
 71.27 
 
 Present Cyaniding Mills. Four of the Cobalt companies have under- 
 taken cyanidation in some form and degree. These are the Nipissing 
 Mining Co., the Buffalo Mines Co., the Dominion Reduction Co. and 
 
THE COBALT DISTRICT, ONTARIO 3 
 
 the O'Brien. 1 The Buffalo mill 2 treats partly by concentration and partly 
 by cyanidation. The ore is broken through crusher and rolls and is 
 partly reground in a high-speed Chilean mill, the crushing and grinding 
 being done in water. The slime is separated, thickened in a Dorr 
 thickener and cyanided in Pachuca tanks, the sand being concentrated 
 in water. The tailing is stacked and may be retreated at some future 
 time. Of the sand reground in the Chilean mill, only about 5% is slimed, 
 the total quantity of slime cyanided being only 18 to 20% of the total 
 ore crushed. The 200-mesh product is considered as slime and it is 
 largely a granular product, there being very little colloid in it. 
 
 NEW LOW GRADE-MILL AT THE NIPISSING. 
 
 The mill of the Dominion Reduction Co., formerly known as the 
 Nova Scotia, 3 crushes with stamps in cyanide solution. The mill was 
 erected for cyanide treatment alone, small allowance being made for 
 concentration, but having lately entered the custom-milling field it was 
 found necessary to reconstruct the mill, due to the different character 
 of ore to be treated, and this work is now in progress, a system of careful 
 concentration being interposed between the grinding and cyaniding 
 departments. The regrinding in this mill is done in tube mills. Under 
 the reformed system the pulp will be passed through a Callow screen 
 with a 30- or 40-mesh wire cloth, the under size going to sand tables and 
 
 1 The O'Brien is the property of one man, is not incorporated and is known simply 
 as the O'Brien mine. 
 
 2 Eng. and Min. Journ., Aug. 3, 1912. 
 3 Eng. and Min. Journ., June 8, 1912. 
 
4 DETAILS OF CYANIDE PRACTICE 
 
 the oversize being reground and returned to the Callow screen. Thus 
 all the pulp will have to pass the screen eventually. From the concen- 
 
 MILL OF THE DOMINION REDUCTION CO. 
 
 THE O BRIEN MILL. 
 
 trators it will be sent to a modified Dorr classifier where the sand will be 
 drained and taken out, receiving a wash of cyanide solution in the classi- 
 fier, and will then be discarded. The slime, which carries the greater 
 
THE COBALT DISTRICT, ONTARIO 5 
 
 part of the valuable content, will be subjected to cyanidation by agitation. 
 
 At the O'Brien mill the ore is crushed, jigged and stamped, jigging 
 being done in water and stamping in solution. Recrushing is done in 
 Hardinge conical mills. Concentration is practised, but to a less extent 
 than usual in the Cobalt mills, the pulp receiving only one passage over 
 the tables. The reground pulp is treated as slime, about 75% of it 
 passing a 200-mesh screen. 
 
 New Mill for Low-grade Ores. The Nipissing company has under 
 construction a mill for treating its so-called low-grade ores which assay 
 from 25 to 35 oz. silver per ton. This mill, which is scheduled to begin 
 operations in November of the present year, will be a purely cyaniding 
 one, the only variation being a jigging of the crushed ores. The high- 
 grade rock will be removed on a picking belt, and this, together with the 
 rich jig product, will be treated in the present high-grade mill which will 
 be maintained in operation, as at present, for taking care of the high- 
 grade mine ores and the rich product obtained by the picking and jigging 
 methods. There will be no concentration, no tables or vanners having 
 been included in the design of the mill. There will be 40 stamps of 1500 
 Ib. each and four tube mills, 6 J X 20 ft. Dorr classifiers are to be used 
 for removing the- sand which will be tube milled, the entire product being 
 treated by agitation as slime. Zinc-dust precipitation will be used, the 
 standard Merrill triangular press being installed to collect the precipitate. 
 The standard Butters filter will be used for filtering the residue. 
 
 The agitation tanks to be used have the flat bottoms and mechanical 
 agitators usually employed by the Butters engineers. The tanks are 
 fitted with decanters and treatment will be by the intermittent or charge 
 system. It is stated that these agitators, while not perfect, will give 
 as good results as can be obtained by the newer forms at costs which are 
 entirely satisfactory in comparison. It is noteworthy that in the face 
 of the more modern forms of agitators, for which higher efficiency and 
 lower costs have been claimed, the older type of agitators are being in- 
 stalled in this modern mill, and also that in spite of the advantages 
 claimed for continuous processes, the charge system will be employed, 
 and all of this sanctioned by a body of engineers which, while not in- 
 fallible, is fully competent to weigh the advantages of all classes of 
 machinery and make use of the best. The difference of opinion is re- 
 markable and goes to show that neither form of machinery nor method 
 has been able to demonstrate so clearly its superiority as to make it 
 universally accepted. It seems almost certain that one or the other of 
 two forms of machinery, or even of processes, must be the better, the only 
 explanation of the varying opinions being that different ores must give 
 different results when handled by the different processes. Neither is 
 the personal equation to be eliminated, for operators accustomed to a 
 
6 DETAILS OF CYANIDE PRACTICE 
 
 certain class of machinery and certain methods of working, do not re- 
 linquish them with facility, and it is often the most difficult thing in the 
 world to convince an operator that there is some better way of doing 
 things than the particular one he is using. 
 
 Primary-crushing Devices. -The persistent use of stamps for re- 
 ducing rock to various degrees of fineness is an example of the general 
 disinclination to dispense with a form of machinery which has been in 
 use a considerable length of time and which, all things considered, has 
 given a vast amount of satisfactory service. It is difficult to censure 
 the profession for sticking to a device which has served well, but it is 
 nevertheless true that circumstances alter cases, and a machine ought 
 to be considered in the light of the work it is expected to do. When the 
 primary object was to crush ore to a point necessary to liberate its mineral 
 and make it susceptible to amalgamation, then the stamp was a good 
 medium to use. It did the work at one step, and had advantages for 
 amalgamation. It made comparatively little slime, and this was an 
 advantage, particularly in the days when cyanidation was first used and 
 leaching was the accepted practice. The slime was a nuisance and was 
 hard to handle and therefore any machine which produced a minimum 
 of it was considered efficient. With the advent of the total-slime treat- 
 ment it would seem likely that some other machine might be used which 
 would do the work of reducing ores to a fine state quicker and cheaper, 
 it not being necessary to keep the production of slime down to a minimum. 
 
 In spite of this circumstance, the stamp continues to be the standard 
 machine for primary crushing, although there is little doubt but that 
 some other form of machine would be more economical in use. This con- 
 dition exists all over the mining world and Cobalt is no exception. In 
 preparing ores for cyanidation there is no other object but to crush them 
 to the required point, usually a total slime, in the quickest and cheapest 
 way. Yet most mills use stamps for the purpose and in Cobalt the stamp 
 is used except in one instance, the Buffalo mill. All over the world in- 
 vestigations are being made on this detail and in some cases the stamps 
 have been displaced with distinctly good results. I think that if some 
 trials were ma'de on the Cobalt ores these economies would be manifested 
 there also. The Cobalt ores are hard, but not too hard to be crushed 
 through rolls, and a stage crushing through crushers, rolls and tube mills 
 would seem to indicate the most economical method. It is to be hoped 
 that the system will be given thorough trials on the ores of the camp for 
 such a system would remove many vexations in addition to introducing 
 economies. 
 
 Regrinding the Ores. Tube mills are used for regrinding in the 
 majority of the mills in the Cobalt camp. The Nipissing, new and old 
 mills, the Dominion and the O'Brien mills have installations of them 
 
THE COBALT DISTRICT, ONTARIO 7 
 
 while the Buffalo, as has already been mentioned, uses a high-speed 
 chilean mill. There is no data at hand for comparing the results of the 
 two forms of machines, but it is probable, on this ore, that the tube mill 
 will give more consistent results. The Hardinge conical mill, as used 
 at the O'Brien mill, has not proved to be altogether satisfactory. The 
 mill is apparently good as a granulator, reducing the rock to a state of 
 medium fine sand with efficiency, but it does not grind fine enough. 
 In this regard the ordinary tube mill is more satisfactory. It is possible 
 to slime the rock in the Hardinge mill, but to do so would reduce its 
 capacity so far as to remove it from consideration as an economical 
 machine. It is possible that the hardness of the ore has something to do 
 with this result for, as has been mentioned, the ore is extremely difficult 
 to slime. 
 
 Methods of Agitation. Pachuca tanks are used generally for agita- 
 tion except in the cases of the Nipissing company, and at the Dominion 
 mill where Trent agitators are at present in use. The Pachuca tanks used 
 in the district are somewhat modified, not conforming exactly with the 
 standard sizes and proportions used in Mexico and in the United States, 
 the difference being that they are not so high in proportion to the diam- 
 eter. While this reduces the capacity, there is no effect upon the agita- 
 tion except, perhaps, that it requires less power to accomplish the desired 
 result. The Parral type of agitator is to have a trial in the camp at thf 
 new high-grade mill of the Buffalo company, now under construction. 
 This plant, which is, in the main, similar to the corresponding plant of 
 the Nipissing company, contains some details which are considered to be 
 improvements and will be referred to later. In view of the fact that it 
 has been difficult for metallurgists to agree upon the most satisfactory 
 tank for agitation, it will be interesting to have a comparative exhibition 
 of the three classes, Pachuca, Parral and mechanical, at work in the same 
 camp and upon the same material. It is to be hoped that full details of 
 the results will be obtainable. 
 
 Use of Chemicals. Lime in some form is used at all the cyanide mills 
 in the camp. At the O'Brien mill the dry lime is added in the batteries 
 and in addition caustic soda is used in the solutions. Caustic soda is 
 not usually considered a good agent to use for securing alkalinity as it 
 tends toward dissolving some compounds which would be better left 
 untouched. There are, however, some cases where its use is justified 
 in spite of its chemical conduct and its cost. The alkalinity at the 
 O'Brien is carried at 3 Ib. in terms of NaOH. At the Dominion mill dry 
 lime is added to the ore going to the mill at the rate of about 6 or 7 Ib. 
 per ton. The lime is in fine lumps, not powdered, as it is desired to take 
 advantage of the alkalinity developed by the slow solution of the lumps. 
 
 At the Buffalo mill lime is added in powdered form to the treatment 
 
8 DETAILS OF CYANIDE PRACTICE 
 
 tanks at the rate of 7 to 8 Ib. per ton of dry ore. The addition of the 
 lime to the treatment tanks in this case is due to the fact that the pulp 
 here meets the cyanide solution for the first time, the preceding opera- 
 tions being carried out in water. 
 
 It will be noted that there is a great deal of difference in the manner of 
 using lime in this district, every operator having some special ideas of 
 the most efficient way. Naturally, the lime will be used in the way which 
 seems to be best adapted to each particular ore, but in this case the use of 
 it typifies the state of cyanide practice in the district. It is as yet unset- 
 tled, and the best methods for economical results have not yet been defi- 
 nitely determined. 
 
 The use of lead salts is varied and spasmodic. There seems to be no 
 definite information as to whether or not they are required and their use, 
 even in the same mill, is not systematized. The general tendency 
 seems to be to dispense with their use. At the Buffalo mill it is claimed 
 that there is no noticeable difference in results whether the lead salts are 
 used or not, and the same is true at the O'Brien mill. Solution analyses 
 at the O'Brien have convinced the operators that the sulphur, which 
 exists in appreciable quantity in solution, is in the form of sulphocyanide. 
 This would indicate that the soluble sulphides, which are undoubtedly 
 first formed, have been transformed by action of the metal elements 
 extracted from the ore and subsequently by the cyanide solutions them- 
 selves. If this is true it shows that a portion of the cyanide is removed 
 from its primary object of dissolving silver and is tied up with the sulphur 
 forming a compound which, while having a certain solvent action 
 upon silver, would certainly not be intentionally formed for such pur- 
 pose. It would apparently be more economical to remove the sulphur 
 definitely from the solution, if possible, leaving the cyanides free to carry 
 out their designed function. It is probably true that the Cobalt ores carry 
 elements which themselves form insoluble sulphides with the dissolved 
 sulphur and remove them, at least partially, from the solutions. 
 
 The consumption of cyanide is much the same in all the mills, leav- 
 ing out, of course, the Nipissing high-grade mill, which is not to be con- 
 sidered with the mills treating large quantities of lower grade ores. 
 From 3 to 6 Ib. of KCN per ton of ore treated is the average con- 
 sumption, when treating ores running from 20 to 35 oz. of silver. At 
 the O'Brien mill the consumption for the year 1911 was 5 Ib. KCN per 
 ton of ore treated, while for the present year the records up to date show 
 a consumption of 3.8 Ib. per ton. At the Buffalo and Dominion mills 
 the consumption will average about the same and at the Nipissing high- 
 grade mill the figures are reserved from publication, but the consump- 
 tion is probably high. 
 
 Metal Recoveries. The percentage recovery of silver seems to vary 
 
THE COBALT DISTRICT, ONTARIO 9 
 
 a great deal in the different mills of the camp. From 80 to 90% is about 
 the saving that is attained by cyanidation, except in the Nipissing mill. 
 In the latter a saving is made by amalgamation of 97% and in the subse- 
 quent cyanidation a small additional saving is made. The head content 
 of silver at this mill runs about 2500 oz. silver and the tailing is said to be 
 as low as 20 to 30 oz. per ton. The extraordinary percentage of extraction 
 is, of course, accounted for by the richness of the ore treated. At the 
 O'Brien mill concentration and cyanidation reduce 20-oz. heads to a 
 tailing which averages 1 to 1.5 oz. per ton in silver. At the Buffalo mill 
 where only the slime is cyanided the extraction on the material is from 
 80 to 85%, but this is by the cyanide treatment alone and no comparisons 
 can be made between this result and the results obtained at the other 
 mills in the district. At the Dominion mill no extraction results are 
 obtainable at this time due to the fact that a change of method is being 
 made, and while the mill is actually in operation, the newer method is 
 not yet fully installed and no statement can be made. 
 
 It is generally conceded that the percentage extraction depends largely 
 upon the fineness to which the ore is ground, the finer grinding giving a 
 better recovery of metal than the coarser. This is to be expected in view 
 of the density of the ore which does not permit penetration of the cyanide 
 solutions into the ore particles and requires extreme subdivision in order 
 to expose the maximum amount of the silver to the action of solutions. 
 
 Temperature has also a great effect upon extractions. In the winter 
 season the cold solutions lower extractions to a large extent and it is often 
 necessary to warm the solutions in order to obtain normal results. At 
 the Buffalo mill steam coils are placed in the treatment tanks in order to 
 bring the solutions up to normal efficiency. In this case the warming is 
 particularly necessary, for there is a constant introduction of cold water 
 into the treatment circulation from the grinding department. At other 
 mills where the circulation is entirely cyanide solution, a thorough heating 
 of the mill during the winter season suffices to keep the solutions active. 
 
 Precipitation Systems. The precipitant most favored is zinc dus+ 
 which will ultimately be used in practically all the mills. At the Buffalo 
 mill the precipitation is at present by zinc shavings, three wooden boxes 
 of the ordinary type being used. At the Dominion mill zinc dust is used 
 and the regular Merrill triangular filter press is installed for collecting the 
 precipitate. The consumption is in this case If of zinc to one of silver 
 precipitated, by weight. At the new mill of the Nipissing company the 
 same process will be used and the resultant precipitate will be sent to the 
 refinery of the high-grade mill which has already been described. 
 
 At the O'Brien mill the process is the same mechanically, but zinc 
 dust is replaced by aluminum powder. It is stated that the aluminum 
 powder will precipitate three times its weight of silver and has a lesser 
 
10 DETAILS OF CYANIDE PRACTICE 
 
 fouling effect upon the solutions. The claim is also made that the result- 
 ing precipitate may be melted in the ordinary oil-fired tilting furnace 
 without any flux, giving a bullion of high purity. The cost of the alumi- 
 num dust, which is 32c. per lb., compared with the cost of zinc, about 7c. 
 per lb., does not indicate any appreciable economy in the use of aluminum 
 even with its increased efficiency, unless there are some advantages not 
 clearly understood. It is probable that further experiments will be made 
 on the use of this material so that some definite facts may become known 
 and comparisons established with the results accomplished with zinc dust. 
 
 Vacuum Filtration. Vacuum filters are at present in use in all the 
 mills, the Butters and Moore types being the ones preferred. At the 
 Nipissing, both the high-grade mill and the new low-grade mill are 
 equipped with Butters filters of the standard type. The Dominion mill 
 has a Moore filter as has also the O'Brien mill. In all these mills a 
 high efficiency is claimed for the filters in washing out dissolved silver, 
 but from the looks of the installations it is rather difficult to understand 
 how high efficiencies can be claimed on any of them. The great weight 
 of the pulp and its granular condition make it necessary that the filter 
 tank be equipped with air lifts in order to keep the solids in suspension, 
 and a rather violent action is necessary to do the work. The filters cannot 
 be operated at all without the air lifts as the heavy solids would- settle 
 immediately making operation impossible. From the nature of the ore 
 and the condition of the filters in the Cobalt camp I should think that 
 pressure filters would be likely to give much better results than those 
 operated on the vacuum system. Pressure systems, like the Merrill, 
 would take a definite quantity of pulp and make a fairly homogeneous 
 cake at once, and would tend toward a condition which would facilitate 
 proper washing of the cake. With the vacuum filters some segregation 
 must naturally take place, and a filter cake which is not homogeneous 
 cannot be washed perfectly. The pressure filter would, in my opinion, 
 be a decided improvement over vacuum systems in the Cobalt camp, due 
 to the weight and granular character of the solids in the pulp treated. 
 
 Cost of Operations. The cost of treatment in the Cobalt camp is not 
 obtainable in the majority of cases, due to the fact that some of the mills 
 are treating custom ores and consequently do not care to make public 
 that essential part of the business. It may be stated that the treatment 
 of the mill or low-grade ores costs from $2.50 to $4.50 per ton. This 
 seems to be a rather wide variation of cost on ore which is practically 
 identical and which is treated on more or less the same scale. The varia- 
 tion is wide indeed, but, as has already been mentioned, there are so many 
 different ideas and so many different methods in use in the camp that 
 there is bound to be a variation in cost. Probably the cost for cyanida- 
 tion is less at the Buffalo mill because of the small extent and simplicity 
 
THE COBALT DISTRICT, ONTARIO 
 
 11 
 
 of the treatment, most of the charge for reduction being made against the 
 concentration department. At the Buffalo, the cost may be said to be 
 about the lower figure given, while at the other two mills costs varying at 
 or about the higher figure may be taken as representing the average. At 
 the Nipissing no costs at all are divulged, but the report of the company 
 for the year 1911 shows that the cost per ounce of silver at the high-grade 
 mill was 1.14c. At this rate, considering the average ore treated as 
 assaying 2500 oz. per ton, the cost per ton of treatment would be $28.50, 
 which seems to be a fair average figure for an operation of this sort. It 
 seems likely that the majority of this cost consists of cyanide consumed and 
 mercury lost, the other charges being of comparatively less importance. 
 
 The cost of material at Cobalt is about as follows: Cyanide (KCN 
 universally used) 15c. per lb.; zinc dust (90% metallic zinc) 6.5 to 7c. per 
 lb.; pebbles (imported) $20 per ton. Power varies somewhat in cost, 
 the original contracts being made on a basis of $50 per horsepower-year, 
 but the contracts now being made are at the rate of one cent per kilowatt- 
 hour, due. I understand, to a change in the policy of the power companies 
 which serve the district. The cost items in general are not excessive and 
 work should be done at reasonable cost. 
 
 Buffalo High-grade Mill. The Buffalo company is erecting a small 
 mill to treat its high-grade mine product and concentrates, similar to the 
 
 MATERIAL FOR REFINING FURNACE AT BUFFALO MINES, LTD. 
 
 Material 
 
 Dimensions 
 
 Quantity 
 
 Red brick 
 
 
 4000 
 
 Firebrick 
 Firebrick 
 
 4|X9X2 in. 
 44 and 4X9X3 
 
 1200 
 375 
 
 Firebrick "A" 
 Firebrick "AA" 
 
 4| and 5^X9X21 
 4 and 5^X9X2^.3^ 
 
 14 
 1 
 
 Firebrick "B"...' 
 
 1\ and 3|X9X4| 
 
 12 
 
 Firebrick "C" 
 Firebrick "CC" 
 
 
 26 
 
 2 
 
 Firebrick "D" 
 
 
 28 
 
 Firebrick "DD" 
 Firebrick "E". 
 
 
 2 
 2 
 
 Firebrick "EE" 
 
 
 2 
 
 I-beams 
 I-beams . 
 
 3 in. X 5ft. 6 in. 
 4 in. X6 ft. 6 in. 
 
 6 
 12 
 
 Angle iron 
 
 3 in. X3 in. X8 ft. 6 in. 
 
 2 
 
 Angle iron 
 Rods 
 
 3 in.XS in.X6 ft. 3 in. 
 f in.XS ft. 
 
 2 
 
 8 
 
 Rods 
 
 \ in. XlO ft. 3 in. 
 
 4 
 
 Plates 
 Oil burners, "Monarch" 
 
 f in.X4in.X6 in. 
 
 12 
 
 2 
 
 Fire clay, cu. ft 
 
 
 
 10 
 
 Sheet iron (pan) ' 
 
 3 ft. 8in.X5ft. ll|in.Xl4 
 in. high 
 
 
12 
 
 DETAILS OF CYANIDE PRACTICE 
 
 *t**f*4k- .,$..> 
 
 /,fZ'' * U-.t// -H 
 
THE COBALT DISTRICT, ONTARIO 13 
 
 installation at the Nipissing. The differences are that the tube mill is 
 larger, 5JX22 ft.; the agitation will be performed in tanks of the Par- 
 ral type; a concentrator with a copper top will be installed over which the 
 pulp will be passed after amalgamation in order to recover any floured 
 quicksilver, and filtration will be performed in a large Perrin plate-and- 
 frame filter press having a capacity of about 20 tons of dry solids. Refin- 
 ing will be performed as at the Nipissing, in a reverberatory furnace, 
 which by courtesy of H. G. S. Anderson, superintendent of the Buffalo 
 mill, I am able to present in detail in the accompanying drawing. The 
 system seems to be well adapted for this class of work and it is not im- 
 possible that its use might be profitably extended to other cyaniding 
 installations. 
 
 Future Development. The details of cyanidation of the Cobalt 
 ores have not yet been definitely settled and the metallurgy is in a state of 
 evolution such that little is really known. There have been few points 
 definitely settled and I expect to see most of the mills make radical 
 changes before settling down to routine work. Many methods are in 
 use which do not seem altogether suited to the conditions and it is likely 
 that these will be gradually changed as some systems prove their super- 
 iority. Results obtained in extraction are not yet reliable, as most of 
 them are based on estimates, and the same is true of costs, which are so 
 varied and indefinite as to be not suitable for comparison. There are 
 many skillful metallurgists at work in the district who may be relied upon 
 to work out the processes in time and I have no doubt that the district 
 will reach a state of settled and satisfactory cyanidation after time has 
 been given to allow the problems, which are many and difficult ; to be 
 worked out. 
 
CHAPTER II 
 NIPISSING HIGH-GRADE MILL, COBALT 
 
 The high-grade ores of the Cobalt district consist mainly of the arsen- 
 ides of cobalt and nickel in a calcite gangue with a large quantity of 
 silver in the metallic state. A typical ore carries 10% silver, 9% cobalt, 
 6% nickel and 39% arsenic; the rest is lime, silica and smaller amounts of 
 antimony, iron, sulphur, tellurium, etc. 
 
 Ore Character. The complex nature of the ore and its high content 
 in arsenic make it an undesirable ore for the ordinary custom smelter, 
 
 NIPISSING HIGH-GRADE MILL. 
 
 who is compelled to charge a high price for its reduction. The general 
 practice is to smelt in a blast furnace where a large part of the silver is 
 recovered at once as base bullion; the resulting speiss is roasted and 
 treated in the wet way for the recovery of the cobalt, nickel and the rest 
 of the silver. This process is slow; the necessary plant costs several 
 hundred thousand dollars, and a large working capital must be available 
 to carry on the business. 
 
 Another serious problem in shipping to a smelter was the difficulty in 
 obtaining a fair sample of the ore. This is always a tender point when a 
 mine is marketing ore, but when the ore carries several thousand ounces of 
 
 14 
 
NIPISSING HIGH-GRADE MILL, COBALT 15 
 
 silver per ton and the silver occurs in the metallic state, ranging in size 
 from the smallest particles up to nuggets the size of one's hand, the diffi- 
 culty of sampling is enormously increased. 
 
 Great improvement, however, has been made in this part of the mar- 
 keting by the building of the Campbell & Deyell custom sampling works 
 at Cobalt, where the ore is crushed in a ball mill fitted with 10- to 20- 
 mesh screens. All metallics coarser than this mesh remain in the mill and 
 are subsequently removed and melted down to bullion. The pulp 
 can then be sampled with a reasonable degree of accuracy. 
 
 The marketing expense is made up of smelter deduction, treatment, 
 freight, assaying, representation at smeltery, etc. On 23 carloads of ore 
 averaging 2560 oz. per ton, the marketing expense was 5.57% of the gross 
 value (with silver at 60 c. per oz.) or $83.55 per ton. In addition to 
 the above direct charge, there is a loss of interest from the date of ship- 
 ment to the date of payment, which averages 65 days on shipments to 
 Canadian smelters, and all ore is settled for on the commercial assay, 
 which is about 1 % lower than the actual assay on this grade of -ore. 
 
 As the largest producer in the district, the Nipissing Mining Co., Ltd., 
 had been trying for several years to find a simple process by which ite 
 high-grade ores could be treated at the mine without going to the largs 
 expense of building the usual smeltery. To this end a great many proc- 
 esses had been investigated and one small experimental plant was 
 built; the trouble with most of the processes is the complication of the 
 operations and the consequent tying up of a large amount of money. 
 
 An Original Process. It remained to Charles Butters and G. H. 
 Clevenger, finally to work out a process which promised to be so simple 
 and effective that the Nipissing company decided to build the necessary 
 plant at once. James Johnston designed and constructed theplant 
 which went into operation February, 1911, and has run successfully ever 
 since. 
 
 The high-grade ore from the picking tables is delivered to the sampling 
 plant at the top of the mill where it is put through a 9 X 15-in. Blake 
 crusher and elevated to a steel receiving bin. From this it is fed auto- 
 matically into a No. 3 6-ft. Krupp ball mill carrying 1000 Ib. of steel balls 
 and fitted with 20-mesh screens. The metallics or silver nuggets which 
 will not pass the screen are removed periodically by taking off a screen, 
 and are melted down in the refinery. From the ball mill the pulp is 
 delivered by a spiral feed to a Vezin sampler and elevated to two 60-ton 
 steel storage tanks, from which it is drawn as needed for treatment in the 
 mill. 
 
 The main operation consists of amalgamating the silver in a 5% 
 cyanide solution while the 20-mesh material is being ground in a tube mill. 
 The mill used is a Krupp mill 3 ft. 11 in. in diameter and 19 ft. 8 in. long, 
 
16 
 
 DETAILS OF CYANIDE PRACTICE 
 
 fitted with silex liners and run at 37 r.p.m. The weight of ore per charge 
 depends somewhat on the silver content, but with 2500-oz. ore the ordi- 
 nary tube-mill charge is 6500 Ib. of ore; 8500 Ib. of mercury; 3800 Ib. of 
 cyanide solution, and six tons of pebbles. 
 
 The materials are charged through a manhole on the top of the mill, 
 and after the cover has been replaced the mill is revolved for 9J hr., 
 when 99 % of the pulp will pass a 200-mesh screen. This fine grinding is 
 necessary to liberate the fine particles of silver and permit of complete 
 amalgamation. A screen analysis of the final tailing shows that the 
 coarser particles are much richer than the slime; this is also shown by the 
 accompanying screen tests on ore crushed through a 10-mesh screen. 
 
 It was found advantageous to have a certain quantity of silver go into 
 solution in the cyanide, and to this end more air had to be supplied to the 
 charge. 
 
 Each gudgeon of the mill is fitted with a stuffing box through which 
 passes a heavy cast-iron pipe, four inches outside diameter, with a 1J- 
 in. hole through the center. The casting is held stationary by bolts to 
 
 GRADING ANALYSIS OF NIPISSING ORE CRUSHED THROUGH 10-MESH 
 
 Mesh 
 
 Percentage 
 by weight 
 
 Silver oz. 
 per ton 
 
 + 20 
 + 40 
 
 12.7 
 26 2 
 
 6837 
 3375 
 
 + 60 
 + 80 
 
 11.6 
 6 3 
 
 2330 
 1954 
 
 + 100 
 + 120 
 
 6.3 
 
 2 7 
 
 1654 
 1348 
 
 + 150 
 + 200 
 
 1.3 
 
 3O 
 
 1182 
 1202 
 
 - 200 
 
 29.1 
 
 706 
 
 the concrete foundation, and the mill revolves about the pipe. Com- 
 pressed air under 25 Ib. pressure is introduced through one of the hollow 
 castings. At the outlet end there is a right-angle turn in the hollow 
 casting just inside the mill and the upper end reaches to within \ in. 
 of the lining. The heavy cast-iron elbow, therefore, remains stationary, 
 the inside leg stands vertical, and the upper end remains above the level 
 of the charge at all times, allowing the compressed air to escape while the 
 mill is in motion. The casting is heavy enough to withstand the batter- 
 ing of the pebbles falling against it. This arrangement allows the mill to 
 be filled well above the center with a consequent decrease in the power 
 used, but it is found that the best results are obtained by filling the 
 mill to a point two inches above the center. 
 
 Handling the Tube-mill Product. At the end of the grinding period 
 the three manhole covers are replaced by coarse screens and the mill is 
 
NIPISSING HIGH-GRADE MILL, COBALT 17 
 
 turned over; the charge falls into a sheet-iron hopper which delivers it 
 into an all-iron settler, eight feet in diameter, fitted with wooden shoes. 
 The tube mill is then washed out twice by revolving it with a ton of solu- 
 tion and 1500 Ib. of mercury. These washes are added to the charge and 
 the settler filled with solution; the charge is kept in agitation by the mu - 
 ler while the amalgam is drawn off into an iron clean-up pan, and from 
 there into canvas amalgam filters, of which there are 24, each holding 400 
 Ib. of amalgam. The pulp is gradually run out of the settler by drawing 
 the top plug, the balance of the charge being washed twice with solution. 
 When the flow of amalgam has ceased, the mercury, as it drains out of 
 the canvas filters, is pumped back to the settler to wash out any remaining 
 amalgam. The bottom plug is finally drawn and the balance of the pulp 
 discharged. It requires two hours to dump the charge and get the amal- 
 gam into the filters. 
 
 It was soon found that the amalgam must be kept exceedingly thin, 
 otherwise it would stick in the tube mill and cake under the muller of the 
 settler; hence the mercury used is 15 times the weight of the silver in the 
 ore. After draining in the sacks, the amalgam still carries 78% mercury. 
 The remarkable part about the whole process is that 97% to 98% of 
 the total silver in the ore yields to amalgamation in the tube mill. An 
 ore assaying 2500 oz. per ton is reduced to 50 to 75 oz. per ton when it 
 leaves the settler. 
 
 The Role of Cyanide. The cyanide treatment of the pulp which 
 follows is comparatively unimportant as it deals only with six or seven tons 
 of 50-oz. ore daily. There are four 16X7-ft. wooden tanks for the col- 
 lection and treatment of the pulp, and the necessary tanks for storage of 
 solution and water. A charge for agitation is made up of four tube-mill 
 charges or 13 tons of dry pulp. Five pounds of lime per dry ton of pulp 
 are added and the charge is agitated for 36 hr. ; the tanks are fitted with 
 mechanical agitators, and the pulp is circulated through a pump as well. 
 The cyanide strength is 0.75 per cent. 
 
 After settling, the solution is decanted, and the pulp, having a specific 
 gravity of 2, is run to a Butters filter of 10 leaves. The specific gravity of 
 the ore is 6, and to avoid the settling of the pulp in the bottom of the filter 
 box while the cake is forming, the charge is kept in circulation by an 
 air lift drawing out of the bottom of the box and delivering at the top. 
 The cake is washed 2 1/2 hr. with weak solution and then discharged. 
 The arsenides of cobalt and nickel go through the process practically 
 unchanged; the residue for the first seven months of this year contained 
 9% cobalt and 4.5% nickel. 
 
 Analysis of Ore. The complex nature of this residue is shown by the 
 following analysis by Johnson & Sons on some of last year's product: 
 Nickel, 9.72%; cobalt, 5.85%; .iron, 2.58%; antimony, 3.80%; bis- 
 
18 DETAILS OF CYANIDE PRACTICE 
 
 muth, 0.09%; copper, 0.06%; tellurium, 1.39%; arsenic, 29.50%;'sul- 
 phur, 1.59%; silica, 11.44%; lime, 8.63%; magnesia, 2.91%; carbonic 
 acid, 13.55%; combined water, 5.74%; mercury, alkali, oxygen, gold and 
 silver, traces of zinc, tin and manganese, 3.15%. Determinations of 
 mercury consumption indicated the presence of mercury in the ore itself. 
 Investigation along this line showed that the ordinary high-grade ore of 
 the district usually carries from two to five pounds of mercury per ton of 
 ore, depending upon the amount of metallics contained. Tests were then 
 made on the metallics alone; 21 samples of metallics taken from various 
 Nipissing veins and from three other mines, showed mercury in every case ; 
 the result varied from eight to 95 Ib. mercury per ton of metallics and 
 averaged 35 pounds. 
 
 The presence of mercury in the metallics was proved on a large scale 
 when the refinery was built; the first charge melted down in the rever- 
 beratory when the furnace and flues were clean, was a ton of metallics. A 
 small bottle full of mercury was taken from the condenser and globules of 
 mercury could be plainly seen through the flue dust. 
 
 Method of Precipitation. There are two zinc precipitation boxes, 
 one for strong and one for weak solution. The precipitate from both 
 boxes goes to an 18-in. Johnson filter press with 12 frames; the press 
 holds 500 Ib. of precipitate which assays 15,000 oz. silver per ton. The 
 product of the cyanide plant amounts to 8000 to 10,000 oz. silver per 
 month. 
 
 The solution going to the zinc box carries 14 oz. silver per ton, 0.028% 
 mercury and 0.6% zinc. By passing through the box the mercury in 
 solution is reduced to 0.015%, so it is necessary to retort the precipitate to 
 recover the mercury. As no solution is thrown away, it has become very 
 foul; after passing through the zinc box it runs to a storage tank in the 
 bottom of which a precipitate collects. An analysis of this precipitate 
 follows: Silver, 0.394%; mercury, 2.51%; antimony, 3.30%; sulphur, 
 16.13%; arsenic, 32.64%; silica, 5.362%; zinc, 2.257%; iron, 5.04%; 
 nickel, 9.06%; cobalt, 7.03%; lime, 9.24%; carbon dioxide, 7.259%; 
 manganese, trace. 
 
 The sacks of amalgam are hoisted into a car with a cast-iron body, 
 weighed and taken to the refinery which adjoins, but is separate from the 
 mill building. There are six 14X60-in. retorts mounted in batteries of 
 two. They are fired by oil, and the waste gases are conducted through 
 a condenser before discharging them; this is to catch any mercury which 
 might get into the flue on account of a cracked retort. 
 
 The retorts are filled three-quarters full of amalgam, fired for nine 
 hours, and allowed to cool for six hours. The resulting sponge and 
 mercury are weighed and compared with the weight of amalgam put in 
 the retort; a cracked retort will sometimes be detected by the loss in 
 
NIPISSING HIGH-GRADE MILL, COBALT 19 
 
 weight when it has not been noticed by the man in charge. The sponge 
 is 79% silver; the impurities are mainly arsenic, cobalt, nickel, antimony 
 and bismuth. 
 
 The average life of a retort is 34 charges. As soon as the slightest 
 crack appears the retort must be discarded at once. Occasionally a 
 retort will break on the first firing, and retorts have been received which 
 would not hold mercury when cold. Various grades of iron have been 
 tried but the makers have not succeeded in turning out a cast-iron retort 
 
 RUNNING THE SILVER FROM FURNACE INTO MOLDS. 
 
 which will stand up to the hard and continuous work required. A soft 
 gray iron, low in phosphorus, gives the best results. 
 
 Recently a cast-steel retort was installed; it is still in good condition 
 after having been fired 82 times. A specially made wrought-iron retort 
 with sides 3/8 in. thick is now on order; this will be slipped into a 
 cast-iron cylinder which will take the weight of the charge and bear the 
 brunt of the firing. 
 
 Melting of the Sponge. The sponge from the retorts is melted down 
 in -a reverberatory furnace in charges containing 28,000 oz. of refined 
 silver. The hearth is stationary and is made of brick contained in an 
 iron pan, 5 ft, X5 ft. 6 in., supported on rails. Heat is supplied by two 
 
20 
 
 DETAILS OF CYANIDE PRACTICE 
 
NIPISSING HIGH-GRADE MILL, COBALT 21 
 
 oil burners; the waste gases pass first through a series of dust chambers, 
 then through two iron pipes 3 X 27 ft. and to a fan which exhausts into the 
 stack. Sprays of water are introduced into the last dust chamber and 
 into the first iron pipe, the object being to cool the gases and condense 
 any mercury that is driven off in melting the sponge, or that comes from 
 a leaky retort. 
 
 As soon as the charge in the reverberatory is melted, air under 15 Ib. 
 pressure is blown on the surface through two iron pipes introduced at the 
 back of the furnace. The oxides of cobalt, nickel and the other impurities 
 rapidly rise to the surface and are scraped off through the charging door. 
 No flux of any kind is added. The air blown on the surface of the metal 
 has been heated by carrying the pipe through the dust chambers; this 
 materially shortens the operation which usually takes 18 to 20 hr. After 
 the surface of the metal has become mirror-like it must still be blown sev- 
 eral hours to expel the last traces of impurities. 
 
 Dip samples are taken and when the bath is 999 fine the air is shut off 
 and the metal is covered with charcoal to absorb the included oxygen 
 and thus avoid sprouting of the bars. The furnace is tapped through the 
 side; the charge fills 25 molds which are run along under the spout on a 
 car. 
 
 The first hearth was made of common firebrick; it lasted five months 
 during which time 1,860,000 oz. were refined. The present hearth 
 made of magnesite brick is still in good repair after nine months' use and 
 has turned out to date 3,236,000 fine ounces. 
 
 Smelting the Precipitate. For the purpose of working up the skim- 
 ming from the melting furnace, the flue dust and the zinc precipitate 
 from the cyanide plant, a 20-in. round water-jacketed blast furnace was 
 installed. The jacket is hung from the feed floor to allow removal of the 
 curb. The flue is connected with the dust chambers. Before being 
 charged to the blast furnace the flue dust and precipitate are retorted, 
 then mixed with sugar water, briquetted and dried. 
 
 The skimming assays about 15,000 oz. silver per ton, the flue dust 
 700 oz., and the precipitate 15,000 to 18,000 oz. The charge is calculated 
 according to the material to be put through; some of the mixtures used 
 are as follows: Charge 1: 250 Ib. of skimming; 300 Ib. of slag; 100 Ib. of 
 coke. Charge 2: 100 Ib. of skimming; 100 Ib. of flue dust; 300 Ib. of 
 slag; 40 Ib. of iron ore; 100 Ib. of coke. Charge 3: 10 Ib. of flue dust; 
 20 Ib. of precipitate; 30 Ib. of slag; 25 Ib. of iron ore; 15 Ib. of lime- 
 stone. These charges gave a slag carrying from five to 11 oz. of silver 
 per ton. 
 
 The charge being so rich in silver no lead is necessary. As soon as the 
 crucible is half full of bullion the metal is drawn off into molds. A small 
 amount of speiss is also formed. The bullion runs 800 fine and is melted 
 
22 
 
 DETAILS OF CYANIDE PRACTICE 
 
 down in the reverberatory with the sponge. It is only necessary to run 
 the blast furnace one day in every 10, to clean up all the by-products. 
 
 The only product marketed is fine silver. It is shipped direct to 
 London and sold at the daily quotation without refining charge. Ship- 
 
 DryOre inSack$ 
 
 F~ 
 
 Blake Crusher 
 
 
 Elevator 
 
 OreBiri 
 
 Ball Mill (BO Mesh) 
 
 ^ 
 Vezin Sampler 
 
 Dum 
 
 Butters Filter 
 Tail Solution Y/eakSolution 
 
 Amalgam Mercury 
 Tram Cars 
 6-fetorts (Oil) 
 Sponge Mercury 
 
 -\ ' 
 
 Reve r be rcttory Furnace (Oil) 
 
 ?/fer Press ' Skimmings Fumes Fine Si I ve r(999) 
 
 (Retort and Briquet) \ 
 
 .-4- 
 
 Blast -Furnace 
 
 (Pe tort and Briquet) 
 
 FLOW SHEET OF HIGH-GRADE MILL, 
 
 ments this year have amounted to 370,000 oz. per month. The bullion 
 carries 0.0043% gold, equal to about $1 per 1200-oz. bar. The total cost 
 of the plant was $67,757, which includes sampler, mill and refinery. 
 
CHAPTER III 
 NIPISSING HIGH-GRADE MILL, COBALT Concluded 
 
 The works of the Nipissing Mining Co., Ltd., is situated on the east 
 side of Cobalt Lake, nearly opposite the town of Cobalt in Ontario. The 
 company has had to solve a metallurgical problem that presented unusual 
 features, and has resulted in a unique plant for milling the high-grade 
 silver ore. 
 
 Ore Character. The ore to be treated contains a large variety of 
 elements, among which may be mentioned about 40% arsenic, 6% cobalt, 
 6 to 7 % nickel and varying percentages of antimony, manganese and a 
 large amount of sulphur 
 
 In addition to the elements already mentioned, the ore is extremely 
 rich in silver, being indeed one which is not usually considered in any 
 sense a milling ore. It carries from 2000 to 4000 oz. per ton, an average of 
 2500 oz. silver per ton being usual over long periods of time. 
 
 The suggestion of treating an ore of this grade, running nearly 80 kg. 
 per ton in silver, by any milling process would be treated warily by most 
 metallurgists, the difficulties certain to be encountered being more than 
 most would care to face. The first impulse would be to ship this rich 
 ore to a smeltery in the confidence that a nearly total extraction might be 
 obtained at a cost lower than could be hoped for under milling conditions. 
 
 After careful consideration, however, the Nipissing Mining Co., Ltd., 
 of which R. B. Watson is manager, came to the conclusion that the high- 
 est economy lay in treating the ore on the ground, making only one prod- 
 uct bullion. The problems of metallurgy were placed in the hands 
 of Charles Butters, consulting metallurgist for the company, assisted by 
 G. H. Clevenger and James Johnston, who built the mill and has since been 
 in charge of it. The result is the so-called high-grade mill 
 
 Ore of this character, containing as it does, pieces of rock of varying 
 grade from nothing up to native silver, cannot be satisfactorily sampled in 
 a coarse state. At the Nipissing mill the sampling is done after the ball 
 mill has crushed the entire material to pass a 20-mesh screen, when it can 
 be done with accuracy 
 
 As all the breaking and grinding up to this point is performed on the 
 dry ore, there is naturally some dust formed, and it follows from the grade 
 of the material that this dust contains a valuable quantity of silver. In 
 order that this rich dust shall not be lost, pipes from a small exhaust fan 
 
 23 
 
24 DETAILS OF CYANIDE PRACTICE 
 
 are led to places where it can best be collected, the fan delivering into a 
 baghouse from which point it may be returned to the treatment system. 
 
 The fine ore is taken to a platform over a 4X20-ft. 
 
 Krupp tube mill. This portion of the metallurgy is unique and somewhat 
 astonishing. 
 
 Extraordinary Amalgamation. The tube mill has its axial entrances 
 sealed up except for a small compressed-air pipe which enters it at one 
 end and a corresponding air exit at the other end. The mill has the usual 
 manholes in the tube, but these are seldom used. Instead there are three 
 handholes with the usual covers equally spaced over the length of the 
 mill on the same horizontal line. Through these holes the mill is charged 
 and discharged, the larger holes being necessary only when relining or 
 repairing inside the tube 
 
 Here, then, is a tube mill used as an amalgamating barrel, but under 
 conditions which were probably never before sought for amalgamating 
 purposes. The combination of an extremely high cyanide solution, a 
 complex ore which contains all sorts of elements, and mercury all ground 
 violently in a pebble mill, would seem to induce conditions quite the 
 reverse of satisfactory. The natural expectation is that the mercury 
 would become floured and that a large loss of it would be incurred. 
 Particularly would this seem to be the case after the absorption of a 
 quantity of silver would have resulted in the formation of amalgam with 
 a tendency toward granulation, an ideal condition to be thoroughly 
 " sickened" by the foreign elements in the ore. 
 
 It is stated that this does not occur, which must be largely due to the 
 strong cyanide solution keeping the mercury clean and allowing the fine 
 particles to coalesce without hindrance from a coating of foreign sub- 
 stances. The heat formed in the mill may also have some effect in a 
 beneficial way by tending to keep the mercury fluid and active. There is 
 a great deal of heat generated in the mill, in fact steam would be formed 
 were it not for the stream of compressed air which enters one axis of the 
 mill and is discharged through a standing pipe at the other. This keeps 
 down the temperature, though even with this cooling assistance the tem- 
 perature of the mixture after completion of the agitation period is about 
 90 degrees. 
 
 Use of Chemicals. It ie noteworthy that neither lime nor lead salts 
 are used during this process, and that after the agitation is complete, there 
 is still sufficient cyanide to carry on the subsequent operations without 
 further addition. The amount originally added to the tube mill is 
 sufficient to produce a very strong solution, which is capable of partially 
 outlasting the destroying effect encountered within the mill. 
 
 The agitation is continued for nine hours, after which time 97% of 
 the contained silver has been extracted from the ore. The tube mill 
 
NIPISSING HIGH-GRADE MILL, COBALT 25 
 
 makes 37 r.p.m. and, contrary to the general practice of the day, is lined 
 with silex brick. 
 
 Power. The charge which is put into the mill fills it more than 
 half full; there is little space left after putting in the total charge. This 
 results in balancing the mill so that during the agitation process it requires 
 only about 17 hp. to keep it in motion. When the mill is emptied 
 of the charge and contains only the pebbles, it requires nearly 40 hp. to 
 move it 
 
 Cyaniding the Pulp. The agitating tanks are of the flat-bottomed 
 type, having mechanical agitating appliances. These consist of a vertical 
 shaft, to which arms are fixed, reaching nearly to the periphery of the 
 tank. The vertical shaft is moved at a rate of 30 r.p.m., by means of 
 crown wheel and pinion gearing. The high speed of these agitators 
 is worthy of note, the necessity for it being found in the high specific 
 gravity of the ore, which is almost equal to an ordinary concentrate. 
 Besides, the ore is so hard that only a small portion of it ever becomes a 
 true slime, but remains in a granular form and has that tendency to settle 
 characteristic of such material. The high speed is necessary to keep the 
 solids in suspension 
 
 The striking feature of the cyanidation of the pulp is not in the method 
 followed, which is the usual one, but in the fact that it is carried out in 
 solutions, which must necessarily be in a state which is not usually 
 regarded as being efficient for cyanidation. A consideration of what these 
 solutions must contain, coming, as they do, from intimate contact with 
 the conglomeration of elements found in the tube mill, will indicate that 
 they must be more or less foul and in a condition which is not favorable to 
 maximum efficiency. This matter will be referred to later 
 
 Precipitating the Solution Content. The solutions are precipitated 
 by means of zinc shavings in a box of the usual design, which has eight 
 compartments, each compartment having room for about six cubic feet 
 of zinc. The shaving used is rather coarser than that usually used, 
 resembling a stout wire, the width of the shaving being nearly equal to 
 the thickness of the sheet from which it is cut 
 
 The refinery department presents some unusual features. There are 
 six retorts of the horizontal tubular type set in brick, each retort measur- 
 ing 14 X 60 in. These retorts are heated by oil burners, thus making the 
 operation simpler, cleaner and easier than when wood or coal is used. The 
 oil burners are capable of generating a degree of heat which is entirely 
 satisfactory and the operation is not troublesome 
 
 The precipitate from the cyanide department is mixed with a borax- 
 soda flux of the composition usual for precipitate, briquetted and melted 
 in a small blast furnace, together with the skimmings from the reverbera- 
 tory furnace and other cleanings of value. This blast-furnace system of 
 
26 DETAILS OF CYANIDE PRACTICE 
 
 melting is not new, having been practised before in different places. It is 
 a good system when properly followed, but is not to be promiscuously 
 recommended 
 
 From the standpoint of cyanidation there are several points about this 
 metallurgy which attract attention. The first one is the use of a solution 
 high in cyanide content for the amalgamation process. Of course, the 
 intention is to use the cyanide entirely as an aid in amalgamation, there 
 being not the least effort to put silver into solution during this stage. 
 Nevertheless a portion of the silver must be dissolved along with a large 
 number of other elements. The wonder is that there is any available 
 cyanide left at all after the amalgamation period is over. 
 
 Considerations of Theory. A question which is naturally suggested is 
 whether the mercury is dissolved to any extent, and if so, what becomes of 
 it. Some authorities claim that mercury in the native state is not dis- 
 solved by cyanide solutions while others take the opposite view. I 
 am inclined to believe that it depends a great deal upon conditions. A 
 volume of mercury in quiet contact with cyanide solution will probably 
 not dissolve to any great extent, but mercury in a finely divided state and 
 amalgamated with other metals will be likely to go into solution. Such a 
 finely divided and amalgamated state is certain to exist inside the tube 
 mill during the amalgamation period when it is subjected to the grinding 
 action of the pebbles, and it seems quite likely that a portion of the mer- 
 cury would be dissolved. In any case it is well known that some com- 
 pounds of mercury are readily soluble in ordinary cyanide solutions and 
 it is not at all unlikely that some such compounds are formed during the 
 amalgamation period, so that it seems reasonable to assume that there 
 would be some mercury in the solution. 
 
 If this is agreed upon it is easy to see why lead salts are not necessary 
 in subsequent cyanide treatment, for the mercury would decompose the 
 soluble sulphides precipitating HgS. In addition, the double cyanide of 
 mercury, K2Hg(CN) 4, formed is an active solvent of silver and might 
 assist in recovering additional amounts of it. 
 
 While it has been stated that no lime is added to the tube mill during 
 the amalgamation period, the fact that mill solutions are used makes it 
 necessary that lime in solution be present, at least at the initial period, 
 though it is conceivable that it would be destroyed soon after agitation 
 had been started. 
 
 In addition to the mercury there are elements in the ore, such as 
 nickel, cobalt, manganese, sulphur, and arsenic, which would enter solu- 
 tion. This presents an opportunity for all sorts of chemical reactions 
 to take place which would be exceedingly difficult to follow. The well 
 known affinity of mercury for sulphur would account for its removal from 
 solution and it seems likely that the other elements would be precipitated 
 
NIPISSING HIGH-GRADE MILL, COBALT 27 
 
 in some form at some stage of treatment. It is only reasonable to expect 
 that the solution of the metallic elements as cyanides and their consequent 
 transformation into other forms would act as reducers to the solution, 
 robbing them of some of the oxygen which would otherwise be available 
 and retarding the dissolution of silver. 
 
 Character of Solutions. A peculiarity of the solutions used in this 
 treatment is that they contain quantities of a brownish-black precipitate 
 floating in them. This precipitate is not noticeable until the solutions 
 enter the precipitation box where so much of it is liberated that it obscures 
 the zinc. In spite of this condition, which would apparently be fatal to 
 good precipitation, the results are good, as shown by the solution assays 
 already given, and the action in the zinc box is lively and normal, shown 
 by the evolution of gas. 
 
 The floating precipitate is light in weight and does not remain on the 
 zinc to any large extent, but does settle in the sump tank, an analysis of 
 it showing that it contains practically all the elements mentioned as 
 existing in the ore, together with portions of zinc and mercury. 
 
 The zinc in the zinc box does not show much effect of mercury, 
 which has the property of amalgamating with the zinc and causing it to 
 break up into a soft mass of short, amalgamated zinc. There may be 
 some slight indication of it, but not enough to account for the presence of 
 any considerable quantity of mercury in the solution 
 
CHAPTER IV 
 
 THE HOLLINGER MILL, PORCUPINE 
 
 The plant of the Hollinger Gold Mines, Ltd., is situated east of Miller 
 Lake, near the town of Timmins in the Porcupine district of Ontario, 
 Canada. The mill occupies a site on the side of a hill in proximity to the 
 main shaft from which the ore is hoisted from the mine. The ore is 
 broken to a size appropriate for stamp milling at the shaft head and 
 is then conveyed by means of an inclined belt conveyor to the mill bins, 
 where it begins the process of reduction. The accompanying engraving of 
 an east view of the mill shows the conveyor which carries the broken ore 
 to the mill bins. 
 
 Ore Classification. The ore, in which gold is the valuable constituent, 
 is comparatively soft and is easily crushed, the crushing and grinding 
 
 THE HOLLINGER MINE AND MILL. 
 
 machinery having a high rate of efficiency, as will be shown. The mill 
 run consists of about two-thirds sericitic schist and about one-third quartz, 
 all the rock being highly schistose and for this reason easily crushed and 
 ground. While a good proportion of slime is formed, there is also a large 
 proportion of fine sand in the product which passes a 200-mesh screen. 
 Thus a product for treatment is formed which is largely granular in 
 character and which presents the difficulties usually encountered in a 
 pulp of this character. The mineral is heavy, the dry slime having a 
 specific gravity of about 2.85. A pulp of this character always is trouble- 
 
 28 
 
THE HOLLINGER MILL, PORCUPINE 29 
 
 some to handle on account of its tendency to settle at every opportunity, 
 and the machinery for handling it has to be designed particularly with the 
 idea of obviating, as far as possible, every chance for the heavy, granular 
 solids to settle and give trouble in treatment. 
 
 The ore from the mine is first passed through a No. 7 Kennedy gy- 
 ratory crusher, after which it goes through a trommel having 2j-in. 
 openings, the undersize going directly to the 20-in. inclined belt conveyor, 
 which carries it to the mill, while the oversize is passed through a 20 X 10- 
 in. Allis-Chalmers Blake crusher, which reduces all the rock to 2| in. 
 The crushed ore joins the undersize from the trommel on the conveyor 
 belt. 
 
 The incline conveyor delivers the ore to a cross conveyor which 
 reaches over the top of the mill bin and, by means of a Bobbins tripper, 
 the ore can be delivered at any desired point in the bin. The bin is of 
 wooden construction with flat bottom and has a capacity of 1000 tons of 
 rock. 
 
 Suspended Challenge feeders deliver the ore to the stamps, of which 
 there are 40 of 1500 Ib. each, dropping in a narrow mortar of the type used 
 for speed crushing. The height of drop is 6i in. and the frequency is 
 100 drops per minute. 
 
 The screens used in the battery are of the slot form of wire cloth, the 
 size used being about six mesh in width and about J in. long. 
 
 Experiments made on crushing capacity show that through a 14-mesh 
 screen of this type a capacity of eight tons per stamp per 24 hr. is obtained; 
 with 6-mesh, 9| tons and with 4-mesh, 12| tons. The screen normally 
 used at the present time is the 6-mesh and a regular crushing of 9| tons, 
 possibly a little in excess of this figure, is obtained. 
 
 Crushing is done in cyanide solution of 1J Ib. KCN per ton, the 
 ratio being five of solution to one of ore. The mortars are arranged so that 
 the height of discharge is two inches. 
 
 Classifier and Tube-mill Arrangement. From the stamps the ore is 
 carried by gravity to four Dorr duplex classifiers of the Belmont type. 
 This type of machine is fitted with a crank arrangement with which the 
 rakes may be lifted above the bed of sand and the machine started. 
 This is of great service when a large amount of sand has settled in the 
 classifier after a shutdown, the rakes being gradually lowered into the 
 settled sand and raking it out by degrees. ' 
 
 The sand from the classifiers is reground in four Allis-Chalmers tube 
 mills each 5 X 20 ft. They are lined with silex brick, the brick being set 
 on edge in the mill, thus giving thickness which aids in giving long life 
 of the lining. At present no idea of the life of these linings can be obtained 
 because the original linings are at work and do not show any great indi- 
 cations of wear. 
 
30 
 
 DETAILS OF CYANIDE PRACTICE 
 
 The tube mills are fitted with special spiral scoop feeders, 22 in. in 
 diameter. Through these feeders the daily addition of pebbles is also 
 put into the mill. The pebble charge is about six tons to each mill and 
 the consumption is approximately two pounds per ton of ore ground. 
 The consumption of pebbles was higher at first, reaching four pounds per 
 ton at one time, but is gradually becoming less and it is expected that the 
 normal consumption will remain at about two pounds per ton. 
 
 The consistency of the pulp fed to the tube mills varies somewhat 
 from that usually considered most efficient and is the result of experiments 
 undertaken to determine the most efficient dilution. The weight of the 
 solids in this case makes it most efficient to use a thick pulp, 33 % moisture 
 having proved to give the best results. The mills make 28 r.p.m., use 
 No. 1 Danish pebbles and grind 90 tons per 24 hr. to a point such that 
 90% passes a 200-mesh screen. The illustration shows the arrangement 
 of the stamps, classifiers and tube mills. 
 
 Driving the Stamps and Tube Mills. At this mill an original device, 
 by means of which a unit of 10 stamps and one tube mill is driven from one 
 motor, is installed. The motor, of 100 h.p., is connected with a 3fi-hi. 
 line shaft by means of a Reynolds silent-chain drive, and this shaft passes 
 
 STAMPS AT THE HOLLINGER MILL. 
 
 to stamp-mill line shaft, of 2f| in., at right angles, moving it by means of 
 a miter gear. The motor shaft continues to the front of the batteries and 
 is directly geared to the tube mill. The advantage claimed for this 
 arrangement is that the full power of the motor may be utilized for start- 
 ing the tube mill after a shutdown; the power is sufficient to overcome the 
 inertia of the loaded mill, the stamps being hung up while this is done. 
 The cam shaft for the 10 stamps, six inches in diameter, is in two parts 
 and is driven by a pulley on each end. The arrangement of the driving 
 
THE HOLLINGER MILL, PORCUPINE 31 
 
 motor and shafts is shown in the accompanying plan of the mill. This ar- 
 rangement, while having the advantage claimed for it, has also the appar- 
 ent disadvantage of being subject to breakage due to the crystallization 
 of the metal of the gears from the constant vibration caused by the stamps. 
 As a matter of fact some of these gears have already broken, but it is 
 considered that the advantages of the system outweigh the disadvantages. 
 
 Removing Gold by Concentration. The slime product from the classi- 
 fiers is led to a series of wooden dewatering boxes, 20 in number, each 
 6X6X6 ft., having pointed bottom and goose-neck discharge. This de- 
 watering plant is really two 10-compartment spitzkasten, and is used 
 to obtain a pulp thick enough for efficient concentration. The underflow 
 from the spitzkasten, at a dilution of three of solution to one of solids, is 
 led to 40 No. 3 Deister slime concentrators. The concentrators are in- 
 stalled for the sole purpose of removing from the pulp the comparatively 
 coarse particles of gold which would require a long time to dissolve in the 
 cyanide solutions used. There is not a great deal of this gold that ever 
 appears on the tables, most of it being retained in the tube mill and 
 ground until it is dissolved in the solution. 
 
 Gold, even in fine state, does not show on the tables unless there has 
 been an unusual quantity of extremely high-grade ore milled, which is 
 exceptional. The expectation, when the mill was designed, was that there 
 would be a large quantity of comparatively coarse gold, which would 
 come out of the tube mill and would take such a long time to dissolve in 
 cyanide solution that there would be danger of its being incompletely dis- 
 solved and discharged in the tailing. This idea has proved to be generally 
 incorrect, the coarser particles of gold being ground up and dissolved to a 
 great extent in the tube mill. The concentrate recovered, however, is 
 high in gold and is treated separately on the ground. 
 
 Amalgamation of Concentrate. The concentrate from the tables 
 drops directly into conduits in the floor, which are equipped with spiral 
 steel conveyors by means of which it is conveyed to the end of the con- 
 centrator room, where it is received by a cross conveyor of the same type 
 and delivered into the boot of a belt-and-bucket elevator. This spiral 
 conveying system would seem to be a rather expensive way of conveying 
 concentrate on account of the large amount of power usually consumed by 
 machinery of that class. Screw conveyors are usually not considered 
 altogether satisfactory on that account. 
 
 The concentrate is elevated to a launder which delivers it into four 
 wooden, flat-bottom bins, each 4X7 X5 ft., where it is stored and shoveled 
 out as required in the amalgamation treatment. 
 
 There are installed four Chalmers & Williams standard Wheeler pans, 
 five feet in diameter, and into each of these is charged 1.5 tons of concen- 
 trate, 100 Ib. of mercury and some lye for keeping the mercury clean, the 
 
32 
 
 DETAILS OF CYANIDE PRACTICE 
 
 pan being filled up with solution. The mullers of the pan are let down and 
 grinding is continued for one hour, after which three hours are devoted to 
 amalgamation. The pulp is then passed to two 8-ft. settlers, where 
 settling is completed in four hours, the amalgam being drawn off and 
 cleaned up in a small clean-up pan. In this way about 97J% of the 
 gold contained in the concentrate is recovered, the amalgam being sent to 
 the refinery, where it is retorted and the resultant sponge added to the 
 bullion obtained from the regular cyanide treatment. 
 
 As already mentioned, the original scheme of treatment included this 
 concentration and amalgamation for the purpose of taking care of the 
 expected quantity of coarse gold, but that has not been encountered in 
 practice and it is altogether probable, according to the management, that 
 
 m ; 
 
 | ; V } ITI . i . jj 
 
 HgiS9 %ffffig$- - Waw^MBi*^ I^^B 
 
 EEGRINDING AND AMALGAMATING PANS AT THE HOLLINGER MILL. 
 
 this step in the process can be left out, the straight cyanide treatment 
 being able to recover as much gold without it. Experiments toward this 
 end are being undertaken and a decision will be made within a few months 
 as to the course which will be pursued. The illustration shows the pres- 
 ent installation of bins, pans and settlers, together with the elevator 
 which brings the concentrate from the level of the concentrator room. 
 
 Mechanical Pulp Thickening. The tailing from the concentrators is 
 joined by the solution which was taken from it by the spitzkasten and 
 goes to two Aldrich triplex slime pumps, each 10X12 in., which deliver 
 to four Dorr thickeners. These thickener tanks are 30X12 ft. and the 
 scraper arms make f revolution per minute. 
 
 Each triplex pump is operated by a 10-hp. motor and lifts the slime in 
 an 8-in. spiral-riveted pipe through 30 ft. to deliver into the thickeners. 
 The pulp from the amalgamation treatment joins the concentrator tailing 
 and goes through the regular cyanide treatment in the mill. The Dorr 
 
THE HOLLINGER MILL, PORCUPINE 33 
 
 thickeners deliver an underflow containing 48% moisture which is ele- 
 vated in two belt-arid-bucket elevators with 10-in. buckets into the treat- 
 ment tanks. 
 
 The pulp going into the Dorr thickeners receives the lime which is 
 required for treatment. The dry lime in a fine state is put into a small 
 pan and an emulsion is made, which is fed continuously into the pulp as 
 it enters the thickeners. A portion of the lime is so coarse that it does not 
 dissolve or float out of the emulsifying pan, and this portion is recovered 
 and put into the mortars of the battery, where it is soon ground up and 
 dissolved. The total quantity of lime added is at the rate of five pounds 
 per ton of dry ore. 
 
 Agitation of Heavy Solids. There are four agitating tanks each 30 X 15 
 ft. with flat bottoms which are equipped with Trent agitators operated 
 by 6-in. Morris centrifugal pumps. The pulp is treated continuously 
 through three of these tanks, the length of time of this passage being 
 about 48 hr., experience having shown that this is sufficient time for 
 treatment; the fourth tank is reserved as a spare. Due to the high spe- 
 cific gravity of the solids these agitators have been unsuccessful in hand- 
 ling the pulp in the agitation tanks. The pulp cannot be successfully 
 agitated if this is thicker than 3:1, the power for moving the arms running 
 as high as 18 hp. per tank. 
 
 At the 3 : 1 dilution the sand and granular slime settle in the tanks, 
 stopping the agitator arms and giving an endless amount of trouble. This 
 trouble extends to the filtration department where, on account of having 
 to filter a dilute pulp, the operation cannot be performed in an efficient 
 manner. On account of the difficulty experienced with these agitators it 
 has been decided to remove them and install an agitator of a different 
 type, which will be described. With the Trent agitators, in addition to 
 the difficulty inside the tank, there is the difficulty experienced with the 
 use of centrifugal pumps. With the pumps used this consists principally 
 in the difficulty and time required to take them apart and examine the 
 interior. 
 
 The agitators to be installed are the Dorr type, which is simply a 
 mechanism with four revolving arms equipped with rakes exactly as in 
 the Dorr thickener but revolving at a higher speed. The slime is raked 
 down to the center of the tank and is then lifted by means of an air lift 
 situated in the center of the tank, circulation being down through the 
 tank and up through the air lift in the center. The system has been 
 tried in an experimental way at this mill and there is now under way the 
 equipment of the spare agitation tank, with the agitation mechanism 
 which will be given a thorough trial on a working scale. The arms will 
 make 12 r.p.m. The solution used in treatment is 1.5 Ib. KCN per ton, 
 as is all the solution used in the mill. 
 
34 
 
 DETAILS OF CYANIDE PRACTICE 
 
THE HOLLINGER MILL, PORCUPINE 
 
 35 
 
36 DETAILS OF CYANIDE PRACTICE 
 
 Vacuum Filtration of Pulp. The pulp from the treatment tanks is 
 sent to the filter plant by gravity. The filter plant consists of a Moore 
 installation of four baskets of 60 leaves each, the leaves being 6X8 ft. 
 each. There are six tanks in two units, each tank measuring 28 ft. 4 in. 
 wide and 9 ft. 6 in. long, and having sides nine feet deep for the vertical 
 part, beside hopper bottoms which have 7 ft. 6 in. additional depth. 
 There are five 10X7-in. Buffalo vacuum pumps, one for each basket and 
 one for the acid washing of the leaves. One crane handles the four bas- 
 kets, having a capacity of 35 tons total load. The crane has two motors, 
 one of 40 hp. for the lift and one of 15 hp. for the lateral travel. Some 
 trouble has been experienced with the crane, it apparently having been 
 designed somewhat light for the work it has to perform. 
 
 The cycle of operations is longer than should be necessary, one hour 
 being allowed for loading, during which time a cake If in. thick is 
 formed. One hour is allowed for solution wash and five minutes for 
 the water wash. Transferring the basket takes about two minutes 
 and discharging the cake, which is done in the water washing tank, about 
 15 min. The discharge is continuous, the tailing containing about 25% 
 moisture. 
 
 It is extremely difficult to get efficient washing under the conditions 
 obtaining with this filter because the slime is so dilute and the solids so 
 heavy that they will not stay in suspension, the result being that there is 
 a segregation in the cake, the lighter and more impenetrable slime being- 
 at the top of the leaf, while further down it is more and more mixed with?:' 
 granular product until the bottom of the leaf contains a porous, granulated^ 
 material which is to all intents sand, and through which the wash solution 
 will pass, leaving the upper part of the leaf, which contains the true slime, 
 practically unwashed. The filter tanks are supplied with air lifts to 
 assist in keeping the solids suspended, but they are not altogether efficient 
 and are rather troublesome to take care of. 
 
 The major part of this filter difficulty is traceable to the inefficiency 
 of the Trent agitators. With a properly thickened slime, as has been 
 proven in this case, less trouble will be experienced in keeping the solids 
 in suspension and the homogeneous cake thus formed can be washed with 
 a 97 \% efficiency. It is expected that with the installation of the new 
 system of agitation a thick pulp, 1:1, will be maintained throughout the 
 agitation and filtration system with beneficial results to both. 
 
 The loading solution from the filter plant, together with a part of the 
 solution from the Dorr thickeners, is passed through two 20-leaf 36-in. 
 Merrill clarifying filters and to the pregnant-solution sumps, of which 
 there are two, each 22 X 20 ft. This solution is pumped out by means of 
 a 7X9-in. Aldrich triplex solution pump, into which zinc dust is fed 
 through a Merrill feeder at the rate of 0.2 Ib. per ton of solution, into two 
 
THE HOLLINGER MILL, PORCUPINE 37 
 
 20-leaf 52-in. Merrill triangular precipitate presses, where the precipitate 
 is recovered. The regular addition of cyanide is made to the gold 
 solution before precipitation, the cyanide being ground up and dissolved 
 in the flow of solution. No cyanide is added in any other way in this 
 mill. The solution precipitated is about four tons to every ton of ore 
 treated, the consumption of zinc being 0.8 Ib. per ton of ore milled. The 
 precipitated solution is sampled for tonnage and assay purposes by a 
 tilting-bucket device. 
 
 The resulting precipitate from the cyanide treatment is- fluxed in the 
 following proportions: Precipitate, 100; borax, 20; soda, 7; and silic , 3. 
 It is melted in a Monarch tilting furnace using oil fuel, in a No. 275 
 graphite crucible, the bullion being remelted in a No. 60 crucible. The 
 resulting bullion is about 760 fine in gold. It is contemplated that later 
 a lead stack will be installed for the purpose of melting down the precipi- 
 tate with litharge and then cupelling it in an appropriate test. By this 
 means a finer bullion will be produced. 
 
 A plant for sampling the ore going to the mill will be erected at some 
 time in the near future. At present every car of ore is weighed and a 
 sample of it taken so that some idea of the work done may be obtained. 
 The new plant will contain Snyder and Vezin samplers and a proportion of 
 the entire ore will be cut out, reduced in small rolls and crushers and the 
 ensuing sample reserved for assay. 
 
 The total power required to operate the mill is about 500 h.p., elec- 
 trical current being used for all purposes. The mill is of wood construc- 
 tion, well built, and is covered with corrugated iron. It is sheathed 
 inside with wood over a layer of tarred paper and is amply heated with 
 . steam, making a comfortable mill to work in during the winter season. 
 
 Metallurgical Simplicity. There are no great metallurgical diffi- 
 culties, those that were expected before operations were commenced 
 having failed to materialize. The ore is clean and contains no rebellious 
 elements and the gold dissolves easily in the weak cyanide solutions used. 
 The ore does not develop much acid as is shown by the small quantity 
 of lime used during the treatment. It might be safely said that the only 
 problems which have been encountered are the mechanical ones already 
 mentioned as due to the high specific gravity and granular character of the 
 solids in the pulp. 
 
 The recovery of gold is thoroughly satisfactory, a total extraction of 
 93% being obtained even under the present circumstances of mechanical 
 imperfection. Of the gold recovered, about 85 % is dissolved in the grind- 
 ing operations, which are intended to include stamping, classifying and 
 tube milling, and 15% in the agitation department. The high percent- 
 age of gold dissolved in grinding is worthy of note. It is usually true 
 that a large proportion of metals is dissolved in the grinding department, 
 
38 DETAILS OF CYANIDE PRACTICE 
 
 but not much attention has been given to a study of the fact and utiliza- 
 tion of the opportunity presented. 
 
 The dissolving rate is largely due to the efficiency of the tube mill as 
 an agitating machine, the grinding action of pebbles liberating and clean- 
 ing the gold and getting it in contact with solution in a condition most 
 conducive to prompt dissolution. For this reason it is good practice to 
 make the most of the tube-mill action and do everything to assist the 
 extraction of metal at this point. I believe it is a good thing to freshen 
 up the solution just before going into the tube mill either by adding fresh 
 cyanide, part or all of the addition that is regularly made, or by using a 
 solution which has been freshly rejuvenated by means of some one of the 
 accepted methods. 
 
 The general run of ore milled has a value of about $20 per ton, of which 
 about 98% is recovered in the mill. The mill started operations in June 
 of this year and the greater part of the elapsed time has been taken up in 
 systematizing the operation, making necessary minor changes and in 
 general tuning up the mill so that a normal basis of cost could be obtained. 
 The mill is now running well and the cost is not excessive, but the manage- 
 ment desire to establish the costs firmly before publishing any data. 
 
 The mill is well built, compact and convenient, and reflects credit on 
 its constructing engineer, A. G. Kirby. The operations of the Hollinger 
 Gold Mines, Ltd., are under the direction of P. A. Robbins, manager, and 
 the mill is superintended by Noel Cunningham. 
 
CHAPTER V 
 CYANIDING AT THE DOME MILL 
 
 The property of the Dome Mines Co., Ltd., is situated about 2J 
 miles west of the town of South Porcupine, Ont The property is famous 
 as the first discovery in the district, and has been the subject of great in- 
 terest and discussion among mining men. It has been developed for some 
 time, and is now equipped with a modern mining plant, a power plant, a 
 modern 40-stamp mill and cyanide plant, started in March, 1912. 
 
 Typical Porcupine Ore. The ore is white quartz and schist, the quartz 
 occurring as stringers and veins of various width running in different direc- 
 tions through the schist country. Within the payable zone the rock is so 
 impregnated with gold that no attempt is made to separate it, the whole 
 product being sent to the mill as mined. The ore is similar in character 
 to that of the Hollinger mine, but the Dome ore is harder, though it does 
 not reach a point where it could be called difficult to crush. In common 
 with the ores of the camp and district in general, it has a high specific 
 gravity, the dry slime treated in the mill having a specific gravity of about 
 2.8, and the resultant slime is largely granular in character. It has been 
 determined that the pulp under treatment contains about 35% colloid 
 slime, the rest of the product being granular and heavy. 
 
 The mill is a modern structure with steel frame, concrete foundations 
 and floors, and, a feature which is often forgotten in mill construction, 
 excellently lighted with windows and skylights, making it easy and con- 
 venient to work in any part of the mill without artificial light in the day 
 time. In view of the prevailing gloomy weather of the district, this is a 
 distinct advantage tending toward more and better work and has a real 
 value in dollars and cents. The building is heated by steam, a separate 
 boiler installed in the mill for that purpose being of sufficient size to make 
 the building comfortable at all times. 
 
 The ore going to the mill comes from two different places, two sets of 
 tracks entering the crusher house. The crusher house is separate from the 
 mill and is on the ground level. The ore, entering in cars moved by a 
 hoist with an endless wire rope, is thrown first into a No. 7J Kennedy 
 gyratory crusher. This crusher discharges to a grizzly with IJ-in. open- 
 ings. The oversize is put through two No. 3 Kennedy gyratory crushers. 
 All the ore, after passing through these crushers, will pass a IJ-in. ring. 
 This is somewhat smaller than is usually necessary for feeding stamps, but 
 in the case of the Dome ore experience has proved that if crushing is not 
 
 39 
 
40 
 
 DETAILS OF CYANIDE PRACTICE 
 
CYANIDING AT THE DOME MILL 
 
 41 
 
 rather fine, slab-shaped pieces of ore are likely to pass through the crushers 
 without being sufficiently reduced. To avoid this condition, the crushers 
 are set rather close, and the result is that the product is all of a good size to 
 go through the feeders and into the mortars. 
 
 Ore Delivery from Mine to Mill. The ore from the final crushers 
 falls upon an inclined belt conveyor by means of which it is carried into 
 the mill bins. The belt is 20 in. wide and rises at an incline of about 
 20i, the belt traveling at the rate of 350 ft. per min. At the point where 
 the conveyor enters the mill the conveyor way is closed with an iron 
 door and a heavy iron wall is interposed between it and the mill build- 
 ing, only a small opening being left through which the belt passes. This 
 
 DOME MILL CRUSHER HOUSE AND INCLINE IN FOREGROUND. 
 
 arrangement is for protection against fire, the crusher house and the 
 conveyor way not being constructed in a way to resist fire as the rest of 
 the mill is. The half-tone engraving shows the conveyor reaching from 
 the crusher house to the mill. 
 
 The inclined conveyor delivers the ore to a second conveyor which 
 reaches across the bins. The second conveyor is provided with a tripper 
 so that the ore can be delivered into any desired part of the bins. This 
 belt is also 20 in. wide. 
 
 The mill bin is of steel construction and has a flat bottom. It has a 
 capacity of about 1500 tons of ore and is placed back of the stamps. The 
 ore going to the bins is not weighed, but carloads are weighed at intervals 
 and an estimation of the quantity is made. A rough sample of the coarse 
 
42 DETAILS OF CYANIDE PRACTICE 
 
 ore is taken, also one of the pulp issuing from the battery at the lip of 
 the mortar, but no absolute system has been devised to record the 
 content of the ore milled. According to the general results obtained it 
 may be said that the ordinary milling ore averages about J oz. in gold. 
 
 Crushing in Water. From the bins the ore is fed into 40 1250-lb. 
 stamps by means of suspended Challenge feeders. The stamps drop 
 through 6J in. 100 times per minute and crush through a rolled slot wire 
 screen equal to 10 mesh. On this ore and with the screen mentioned the 
 stamps have a capacity of 10 tons per stamp per day, but owing to the 
 limitations of the cyanide plant the actual crushing is a little under that 
 figure, the 40 stamps crushing generally about 380 tons per day. Water 
 is used in crushing at the rate of about 6 J : 1 of ore. 
 
 Just outside the batteries are the primary amalgamating plates, one 
 for each ten stamps, 54X144 in., in two sections, the grade being 1J 
 in. per ft. These plates are intended to recover coarse gold coming from 
 the batteries, in which there is no provision for amalgamation, but due to 
 the scouring effect of the heavy rush of coarse pulp they are of little use. 
 One of these plates has already been experimentally discontinued and it 
 is likely that the others will be put out of commission. 
 
 From the primary plates the pulp is passed through four Dorr duplex 
 classifiers where the sand is taken out and sent to four Allis-Chalmers 
 tube mills, each 5X22 ft., having spiral scoop feeders and reverse-spiral 
 discharge, which tends to prevent pebbles issuing from the mill and also is 
 convenient for the introduction of the regular daily addition of pebbles 
 which can thus be fed into the discharge end of the mill without trouble. 
 From the tube mills the pulp is returned to the Dorr classifiers by means 
 of five Frenier pumps, each 8X54 in., the tube mills and classifiers thus 
 being in a closed circuit. The tube mills make 32 r.p.m. which is some- 
 what excessive, the general speed of mills of this size being about 28 r.p.m. 
 Due to the weight of the pulp it may be fed into the tube mills somewhat 
 thicker than in usual practice. 
 
 From the classifier the fine pulp, or slime, goes over a second series 
 of plates, called the secondary plates, where amalgamation takes place. 
 These plates are 108 X 144 in. with a slope of J in. per foot. On these 
 plates under present conditions of operation about 60 to 65% of the gold 
 content of the ore is recovered. 
 
 The whole of this crushing and grinding operation is carried out in 
 water, the reason being that a flow of cyanide solution is believed to be 
 prejudicial to good work on the amalgamating plates. 
 
 From the secondary plates the pulp is led to three Dorr thickeners, 
 each 30X10 ft., where the pulp is thickened as much as possible, the 
 usual effluent being about 1:1. From the thickeners it goes to the 
 boot of a duplex belt-and-bucket elevator, 70 ft. between centers and 
 
CYANIDING AT THE DOME MILL 43 
 
 carrying 7Xl6-in. buckets. This elevator delivers to the agitation 
 system. 
 
 In the boot of the elevator the cyanide necessary for treatment is 
 added, the material in lump form being suspended in the flow of pulp 
 where it dissolves. The solution is made to a strength of one pound per 
 ton of solution, the average consumption in total being about 0.8 Ib. 
 per ton of ore treated. The dilution ratio varies between 1: 1 and 1J: 1. 
 
 The classification of the pulp going to agitation is about as follows: 
 + 100 mesh, 8%; +200 mesh, 32%; -200 mesh, 60%. The fineness of 
 grinding is controlled entirely by the comparison of cost and recovery, 
 and the most efficient condition for both considerations has been found 
 to be the condition above stated. 
 
 The water from the pulp is returned to the battery circuit for further 
 use, the circulation being maintained separate. It is of course necessary 
 to take out as much water as possible from the pulp which is to go to 
 cyanidation treatment, in order that the consumption of cyanide shall 
 be as low as possible. 
 
 Pachuca-tank Agitation. For agitation of the pulp Pachuca tanks 
 are used, but the design varies from the usual standard. These tanks 
 are 8 ft. in diameter and 40 ft. deep, resembling a chimney more than a 
 tank. This form was adopted in view of the especially heavy character 
 of the slime to be treated, it being considered that in a wider tank there 
 would be danger of settling of the solids. It is stated that 35 to 40 Ib. 
 of air pressure is sufficient to secure satisfactory agitation in these tall 
 tanks. They seem a peculiar form of agitator, but if they are, as is 
 claimed, the most satisfactory form, for agitating this heavy pulp, no 
 criticism can be made of them. 
 
 The agitation is continuous through the Pachuca tanks, of which 
 there are four, the last tank being arranged so that its overflow may take 
 out a quantity equal to that which enters the tank, or may be changed 
 so as to take out more or less, according to the desirability of increasing or 
 reducing the amount of material in the tank. The dilution of the pulp 
 during this treatment is from 1:1 to 1|:1 and varies somewhat in 
 accordance with the work of the thickeners. The height of these tanks 
 results in an advantage in that a considerable fall is secured to the filters, 
 allowing them to be filled by gravity. 
 
 The pulp from the agitation system goes into two Dorr thickeners, 
 each 25 X 10 ft., where the pulp is thickened for filtration and then into a 
 mechanical agitator tank where the slime for filtering is stored, the slow 
 agitation preventing the solids from settling in the tank. The overflow 
 from these two thickeners is passed through a Merrill clarifying press and 
 is precipitated. 
 
 Glass bottoms are used in many of the launders at the Dome mill in 
 
44 DETAILS OF CYANIDE PRACTICE 
 
 order to facilitate the flow of pulp. It has been shown that with the same 
 grade a launder having a glass bottom runs cleaner and easier and at the 
 same time lasts longer than one without it. The glass seems to reduce 
 friction, so that often a launder which gives trouble when made of wood or 
 iron will flow easily and without trouble when glass bottoms are put in. 
 A sudden drop or fall of the pulp on glass must be avoided, for in such 
 cases the glass grinds out sooner than when iron is used. The cost is 
 low, scrap plate glass being used, which may be bought for about seven 
 cents per foot for pieces of various length 12 in. wide. 
 
 Pressure Filtration. The pulp is led from the mechanical agitator 
 to two Merrill slime presses, standard type, having 76 frames 4 inches 
 thick. The press is filled by gravity and the slime being thick, there 
 is no segregation and a homogeneous cake is made. Once made, the cake 
 is washed with barren solution, an amount equal to the weight of the cake 
 being used. During this wash there is an appreciable additional solution 
 of gold. After the solution wash the cake is discharged, there being no 
 actual water wash in the press, but as it requires four or five parts of 
 water under 80 Ib. pressure to discharge the slime, there results a form of 
 washing, as most of the water is afterward recovered in the two Dorr 
 thickeners, each 30X10 ft., through which the sluicing mixture is passed. 
 
 Only an equal amount of water is discharged with the slime, the rest 
 being recovered from the thickeners and used again to sluice out the 
 presses. The amount of wash water discharged is about equal to the 
 quantity of water taken into treatment from the crushing system. The 
 slime is discharged from the thickeners by gravity. This system is well 
 adapted to the character of the pulp, the heavy solids having no time to 
 settle previous to filling the press, with the result that a cake which can 
 be thoroughly washed with solution is formed. 
 
 Zinc -dust Precipitation. The Merrill system of zinc-dust precipita- 
 tion is used, the zinc being added to the solution from the clarifying press 
 which passes to the two pregnant-solution sumps, from where it is 
 pumped into the precipitation press, which has ten 2-in. frames. The 
 zinc is added by a spiral-screw conveyor which feeds the dust into a 
 miniature tube mill were an emulsion of solution and zinc is formed, this 
 emulsion going into the stream of solution entering the pump. 
 
 The amount of zinc added is approximately J Ib. for every ton of 
 solution. As there are about two tons of solution precipitated for every 
 ton of ore treated, the consumption of zinc is about i Ib., or approxi- 
 mately two cents per ton of ore milled. 
 
 A small amount of lime is used in the treatment, the system being the 
 formation of milk of lime by placing the dry pulverized lime in a barrel 
 and adding a constant stream of solution, the outgoing solution, or milk 
 of lime, entering the treatment at the desired points. About three- 
 
CYANIDING AT THE DOME MILL 
 
 45 
 
 fourths of the total lime consumption is added to the thickeners which 
 prepare the pulp for the agitation treatment, this being to assist settle- 
 ment and aid in the production of a thick pulp; the remaining one-fourth 
 is added to the thick pulp going to treatment. The total consumption of 
 lime is a little under three pounds per ton of ore treated, as the ore is not 
 extremely acid, and the lime is used more to assist settlement than for any 
 other purpose. 
 
 Hoi si- 
 
 No. 7i Kennedy Gyratory 
 Crushers 
 
 Grizzly /^ " Openings 
 No. 3 Kennedy Crushers 
 
 Inclined Belf Conveyor 
 20"- Belt 
 
 20" Cross Con.^,, 
 with Tripper 
 
 1500 Ton Flat- bottom 
 Steel Ore Bin 
 
 Suspended Challenge 
 Feeders 
 
 40- 1250 lt>. Stamps 
 
 Primary A malgamating 
 Plates 54"x144" 
 
 Four Dorr Duplex 
 
 Classifiers 
 
 Four 5x22 ft. Tube -V; 
 Mills 32 r.p.m. "> 
 
 Five Frenier Pumps 
 
 S econdary Amalgamating 
 Plates 108"xl44" 
 
 Three Dorr Thickener's 
 30x 10 ft. 
 
 Duplex n Bucket Elevator 
 7x 16" Buckets 
 
 Four continuous Pachuca 
 Agitators 8x40 ft 
 
 Zinc -dust Emulsified 
 Precipitation Pump 
 
 Precipitation Press 
 Blast Furnace 
 
 Cupel Furnace Oil 
 
 Burner 
 
 Oil-fired Tilting Furnace 
 
 FLOW SHEET OF DOME MILL. 
 
 A total of approximately 95% of the gold content of the ore is re- 
 covered, about 65% of which is recovered on the plates as has been men- 
 tioned, and the remaining quantity in the cyanide treatment. The 
 percentage recovery is governed by the economic question, there being 
 no difficulty in recovering 98 or 99% of the gold if it is desired to do so. 
 
46 DETAILS OF CYANIDE PRACTICE 
 
 Experience has shown that it is more advisable to stop at the point now 
 established than to attempt to extract more of it. The costs established 
 are proportionately less than if the higher extractions were obtained. 
 
 The power used by the company is generated in its own power 
 house by steam, using coal as fuel, and is higher than would be the case 
 were hydro-electric power available. It is expected that such power will 
 be delivered at the plant within the next few months, when a corre- 
 sponding reduction of cost is expected. Detailed treatment costs are not 
 given at this time as such figures to be of any service should be repre- 
 sentative of permanent conditions. 
 
 Smelting the Precipitate. The precipitate is melted in a small blast 
 furnace with litharge, the resulting lead bullion being afterward cupelled 
 in an appropriate test. The cost of this system of refining seems to be 
 less than the older method of direct melting and a practically fine 
 bullion is obtained, with the advantages which come with a product of 
 that kind. The lead stack is easy to operate and does not entail the 
 severe labor attendant upon pot melting, and the cupelling operation is 
 also comparatively clean and convenient. A comparison of the cost will 
 add the deciding factor, and I expect to give especial attention to this 
 matter in future papers on the subject. 
 
 At the Dome mill the cupelled bullion is melted and made into bars in 
 a small oil-fired tilting furnace. For this purpose the tilting furnace is 
 satisfactory. 
 
 The cupel furnace is heated by means of an oil burner, but tne operators 
 consider that it is not as satisfactory as when wood fuel is used. The 
 cupel itself is made of a mixture of ground limestone and Portland cement 
 in the porportions of about 1 : 3, which makes a properly absorbent 
 test. The saturated protions are melted down in the blast furnace to- 
 gether with scraps, sweepings, etc., in a scavenger run which is made at 
 intervals. 
 
 Points for Discussion. The first point in the Dome mill which is 
 open to criticism of any kind is the fact that no accurate weighing or 
 sampling is done on the ore which enters the mill. Estimations are 
 made, but these can hardly be considered an effective substitute for 
 absolute methods and probably much more satisfaction would be ob- 
 tained with accurate weighing and sampling systems such as are being 
 installed in the newer mills. The pulp from the Dorr thickeners going 
 to the agitation treatment is estimated by measurement and specific 
 gravity determinations which are taken at regular intervals and the 
 operators believe that in this way a good estimate of the tonnage is 
 obtained. 
 
 Pachuca tanks as here used seem to be a subject for some discussion, 
 but personally I think there might be some more satisfactory and 
 
CYANIDING AT THE DOME MILL 47 
 
 economical method of obtaining the same result. I am not convinced 
 that Pachuca tanks are most efficient agitators, particularly where the 
 time of contact is short and where great agitation is not necessary. 
 The fall for the filters could as well be secured by using tanks of different 
 form, even if the elevation were made equal to that now obtained. 
 
 A comparison of the design of the Hollinger and Dome mills presents 
 a good illustration of two ways of doing the same thing. In both mills 
 the original design contemplated the removal of coarse gold which 
 might not be dissolved in the cyanide solutions and which, it was feared, 
 might be discharged undissolved with the residues. At the Hollinger 
 the attempt was made to extract this coarse gold on concentrators, while 
 at the Dome mill the same result is sought through the medium of 
 amalgamating plates. It is probable that neither system is necessary. 
 
 At the Hollinger mill it has been demonstrated that this coarse gold 
 is more than likely to be retained in the tube mill as long as it is coarse, 
 and being there scoured and subjected to attrition it is generally reduced 
 and dissolved. The concentration system is already under suspicion of 
 being useless and may be dispensed with. At the Dome the system of 
 amalgamation on plates is ( done in water which has to be carried through 
 the whole grinding system and this presents the serious defect of losing 
 the dissolving effect of the solution during crushing and grinding, and 
 particularly the highly efficient dissolving action of the tube-milling 
 operation. 
 
 I am of the opinion that the simplification of the mill through the 
 discarding of the plates and grinding directly in cyanide solutions would 
 obtain a result as good or better than the one now in use and perhaps at 
 less cost. A great advantage about the latter system is that not so much 
 water would be necessarily taken into the circulation. None would be 
 taken in through milling and what water is required could be taken into 
 circulation through giving the filter cake a water wash. This would 
 reduce the loss in dissolved gold and also the mechanical loss of cyanide, 
 which constitutes at present about two-thirds of the total loss. 
 
 The logical addition of water to milling systems is through the filter 
 cake where it will do the most good, and not into the agitation circuit 
 where it merely dilutes solutions and necessitates the addition of cyanide 
 to keep strengths up to normal. 
 
 It is still an open question whether or not economies could be in- 
 troduced by using a system of partial leaching, agitating only the natural 
 slime formed during grinding and passing the fine, granular solids to a 
 leaching system. This question can only be solved by a series of ex- 
 periments establishing the point to which grinding must be carried to 
 liberate the maximum quantity of gold and the desirability of either 
 leaching or agitating the fine sand, according to cost. 
 
48 DETAILS OF CYANIDE PRACTICE 
 
 The filtration system at the Dome mill, using the Merrill pressure 
 filter, is the best I have seen in Canada. The character of the pulp 
 makes the machine especially applicable to handling it, and filtration is 
 performed at a minimum expense and with beautiful simplicity. The 
 pressure system ought to be installed in all mills to be built even if it 
 does not displace vacuum plants already installed. With the change 
 from the Dome practice of adding a water wash to the cake, it seems to 
 me that most admirable results might be obtained. 
 
 At the Dome mill the metallurgical difficulties are negligible. The 
 problems are all mechanical, due to the handling of the heavy pulp and 
 the devising of a system of manipulation which will give the highest 
 economy. 
 
 DISCUSSION 
 
 Cyaniding at the Dome Mill 
 
 I read with interest the article by Mr. Megraw in the JOURNAL of 
 Nov. 23, 1912, describing the milling practice of the Dome Mines Co., 
 at Porcupine, Ont. I notice that the writer seems to consider the ratio 
 between the width and height (8 : 40) of the Pachuca agitators unusual, 
 but in an all-sliming process such as followed at the above-mentioned 
 property it is doubtful if efficient agitation could be obtained with a 
 more shallow, wider tank. F. C. Brown, in giving specifications for 
 Pachuca tanks (Min. and Sci. Press, Sept. 26, 1908), placed the ratio 
 between the width and height of standard tanks at 1 : 4 \ or 5, hence that 
 observed at the Dome plant does not appear to be excessive. 
 
 In Pachuca construction there seems to be a general tendency to 
 build a lower, wider tank, either from motives of economy in construction, 
 or from the fact that in many cases the tanks are simply remodeled agita- 
 tors of some other type. While a tank of this kind will give fair results 
 when working on a pure slime, in all-sliming practice where a large per- 
 centage of material consists of fine angular grains of sand, trouble is 
 bound to be experienced in the close packing of these particles. In fact, 
 I believe that the greater part of the difficulty encountered in this 
 system of agitation is due to the reason that the proper ratio of width to 
 height has been neglected in the construction of the tanks. 
 
 With respect to the Dome plant, and taking into consideration the 
 all-sliming method in use there, I do not see how any other system would 
 handle successfully such a heavy pulp, containing, as it certainly must, a 
 large percentage of angular, fast-settling particles. Mechanical agitation 
 under the above conditions would entail an extremely high repair cost, 
 resulting from the strain on the machinery. The only alternative to the 
 
CYANIDING AT THE DOME MILL 49 
 
 present treatment, it seems to me, would be to divide the mill product 
 into sand and slime, and treat each separately. Considering the matter 
 from this viewpoint, and from the fact that the time spent in leaching 
 would be offset by a lower power cost, I do not see why the older method 
 would not be successful. 
 
 As regards amalgamation, I am quite in accord with Mr. Megraw; it 
 appears to me unnecessary. 
 
 J. A. REID. 
 Kingston, Ont., Dec. 1, 1912. 
 
CHAPTER VI 
 PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 
 
 The mineral district of the Black Hills, in South Dakota, has long; 
 occupied a prominent position in the mining world, due to the extent of 
 its deposits and their original richness. In the early days ores of high 
 grade were obtained and as these gradually disappeared, ores of lower 
 grade had to be depended upon to keep up production. The ingenuity 
 of the metallurgical world was taxed to the utmost in devising methods 
 by means of which profits might be obtained from rebellious ores contain- 
 ing only small quantities of gold and silver. The whole gamut of 
 metallurgical methods has been played upon in the effort to treat the ores 
 economically. 
 
 Victory of Cyanidation. Such processes as smelting, pan amalga- 
 mation, bromination, chlorination, plate amalgamation, all had their day 
 and were thoroughly tried, but nothing made any noteworthy success 
 until cyanidation was tried, proved available, and applied on a large 
 scale to the treatment of the ores. Cyanidation has been the means by 
 which enormous quantities of low-grade ores have been made economic- 
 ally available and millions of dollars have been taken from ores which 
 by no other means could be beneficiated at a profit. It is probable that 
 in no other mining district has cyanidation had a greater beneficial 
 effect. 
 
 The first application of cyanide in the Black Hills was at the Rossiter 
 plant in 1892, but great and decided success was not demonstrated until 
 1900, since which time the applications of the process have increased, 
 until at present there is no successful installation which does not make 
 use of the process in some form. 
 
 The ores are in the main siliceous, containing silica in the form of 
 quartz and in proportions varying between 75 and 90 %. The unaltered 
 blue ores contain less than the red oxidized mineral. The blue ores 
 contain also an average of from 6 to 8% of pyrites, fine and evenly 
 distributed, though some of them contain as high as 20%. In the red 
 ores the pyrite has been oxidized to form the iron oxides which give the 
 ore its color. Tellurium has been found in some minerals and the exist- 
 ence of tellurides of gold and silver is maintained by some authorities 
 Copper occurs in minute proportions in many of the minerals. At 
 some of the larger mills, notably the Homestake, copper is always present 
 
 50 
 
PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 51 
 
 in the precipitate, but this is believed to be due principally to the caps 
 used in detonating the charges of explosives and from other similar 
 sources, although copper does exist in the ore. The gold is in an ex- 
 tremely fine state and is rarely found jree. The ores are fairly hard, in 
 some instances extremely so, but there is also much clayey material which 
 produces a large amount of colloid slime. All grades of hardness are 
 found between the extremes of clay and extremely hard and close- 
 grained rock. In most cases the mineral is heavy, the specific gravity 
 of the solids in mill pulp often running as high as 3, while there are many 
 graduations under that figure, all, however, being comparatively heavy. 
 
 Dry Crushing at Wasp No. 2. One of the most interesting installa- 
 tions in the Black Hills is that of the Wasp No. 2 Mining Co., where a 
 flat quartzite deposit carrying extremely small quantities of gold is being 
 milled at a substantial profit. The ore, after passing the usual crusher 
 system, is broken through four sets of rolls, two of which are used for 
 roughing and two for finishing. This crushing is all performed on the 
 dry ore. After passing the finishing roll the material will all pass a 
 screen having J.in. openings. A large proportion of the material is, of 
 course, much finer, varying between fine sand, there being little slime, 
 and the maximum size of |-in. The crushing is carried no farther, the 
 ore being treated in this condition. This finished product is stored in 
 bins and is drawn out as required to charge the treatment tanks. The 
 tanks are charged from these bins by means of a system of belt con- 
 veyors which receive the material at the bins and deliver it at about the 
 center of the treatment tanks, where it is distributed by hand. The 
 leaching tanks are six in number, each 32X12 ft., and hold a little over 
 400 tons of ore. 
 
 Treatment by Leaching. The cyanide treatment of this ore is 
 entirely by leaching. The practice is to add first a bath of solution carry- 
 ing five pounds KCN per ton in sufficient quantity to impregnate the 
 charge thoroughly and leave a solution covering of about an inch over it. 
 This bath remains in contact with the charge for 12 hours, when it is 
 drained off. The mixture of fine and coarse material offers little re- 
 sistance to the passage of solutions and the leaching rate is exceptionally 
 high, which facilitates the treatment to no small degree. It will be seen 
 that this condition of porosity of the charge also facilitates treatment, 
 for the reason that air for aeration of the charge readily penetrates the 
 entire charge, following the solution through the mass. 
 
 After the strong solution has been drained off, a weaker solution is 
 added, the strength being 2J Ib. KCN per ton, and this treatment is 
 continued for 48 hours, there being seven separate additions of the 
 solution during this time. A subsequent water wash is given in quantity 
 only sufficient to displace the solution held by the ore. The gold-bearing 
 
52 DETAILS OF CYANIDE PRACTICE 
 
 solutions from this treatment are passed over zinc shavings, the resulting 
 precipitate being dried and melted in a crucible furnace using oil fuel in 
 the usual way. 
 
 Tonnage Estimations. No attempt is made to sample or estimate the 
 quantity of ore handled before it enters treatment, all calculations being 
 made on the filled tanks before the cyanide solutions are added. In the 
 general run of mills this would be considered faulty practice, but in this 
 case where the ore is crushed dry and loaded into treatment tanks without 
 any preliminary treatment or separation of any kind, it is probably as 
 accurate as any way could be and is extremely simple. The tanks can 
 be sampled satisfactorily by means of the pipe sampler, taking a large 
 number of tests in different portions of the tank, and a good estimate 
 of the weight can be made from it as well as a satisfactory sample for 
 determining the content of the charge in gold and silver. 
 
 The cost of discharging the tanks is low, approximating only about 
 five cents per ton. The work is accomplished by seven men, four of 
 whom are employed inside the tank shoveling out the charge through 
 bottom doors, and three employed in tramming out the cars, which are 
 loaded directly under the discharge gates. The men inside the tank do 
 not have to lift the charge at all, the process being simply to scrape the 
 material to the discharge gates. The proportion of moisture is small and 
 the material runs readily enough and gives no trouble. Due to this 
 facility the tanks may be emptied in about seven hours. The tanks 
 are charged at a rate which gives the mill a daily capacity of 500 tons. 
 
 Addition of Lime. Lime at the rate of six pounds per ton of dry ore 
 is added at the crushers, and is carried through the crushing system 
 with the ore, being thus thoroughly mixed with it. The treatment 
 solutions carry about one pound dissolved CaO, which is sufficient to 
 protect them against any small amount of acid which the ore might 
 develop. 
 
 The method of adding lime seems to me to be somewhat wasteful in 
 this instance, as the ore is not entirely reduced to a fine state and it is 
 reasonable to suppose that the lime, at least in part, will be in coarse 
 particles. The time of treatment is not sufficient to dissolve the coarser 
 pieces of lime entirely and it is likely that an appreciable percentage of it 
 is discharged undissolved, occasioning a slight loss. I am of the opinion 
 that some method of adding the lime in emulsion in the quantity actually 
 required for protection might result in a slight reduction of the cost of 
 lime used. A hint would be to consider the method used at the Home- 
 stake mills for adding lime to the leaching tanks. While this method 
 might not be applicable in exactly the same form, some simple variation 
 of it might be productive of good results. 
 
 The extraction averages about 70% of the precious metals contained, 
 
PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 53 
 
 sometimes a little more and occasionally a little less, depending on the 
 grade of the ore handled. The cost of the treatment is exceptionally 
 low. The entire costs of the operations are: Mining, 53.48c. per ton; 
 milling, 66.82c.; general expense, 4.35c. The principal items in the mill- 
 ing cost are: Labor, 21. 3c. per ton; cyanide, 6.3c.; zinc, 3.3c.; lime, 
 1.2c.; power, 8.4c., and supplies and repairs, 12. 6c. per ton milled. 
 
 Simple Treatment at Wasp Mill. It will be seen that the metallurgy 
 of the Wasp ore is extremely simple. The simplicity is probably due, in 
 a great measure, to the fact that the gold is contained in cleavage planes 
 which are fractured and opened by the coarse crushing, thus exposing a 
 maximum quantity to the action of cyanide solutions. Besides, the rock 
 itself is porous and the solutions can readily enter and act upon a 
 large portion of the gold, bringing it out without entailing the expense of 
 fine crushing. 
 
 A large number of experiments have been made on this ore by com- 
 petent metallurgists in order to determine whether an economical higher 
 extraction could be obtained by grinding finer, but the conclusion has been 
 that the maximum profit is being obtained by the system now followed. 
 The ore carries only about $2 per ton and will not stand a higher operation 
 expense. It is likely that there are few examples of a similar nature in 
 existence where a profit ranging from 50 to 75c. per ton can be obtained 
 on ore of this low gold content. I have seen one other example, a 
 Mexican mine which contained an ore having a good gold content. 
 The ore was so porous that pieces \ in. in size would readily surrender 
 their content to weak cyanide solutions, but this ore was in the surface 
 zone of a vein and was soon exhausted. 
 
 Wet Crushing in Chilean Mills. An example of conditions differing 
 from those obtaining at the Wasp is found at the mill of the Golden 
 Reward Mining Co. at Dead wood. This company owns mines in 
 different districts and the ores delivered at the mill for treatment differ 
 widely in character. Some of them are hard, while others are at the 
 other extreme of the scale, being soft and clayey, many variations be- 
 tween the two being submitted for treatment. The ore is delivered to 
 the mill in railway ore cars and is always carefully weighed before being 
 put into the mill bins. The ore is crushed dry through a series of crushers 
 and rolls, an automatic sample being taken during the process which is 
 reduced in a small crushing roll, put through several quartering samplers, 
 and finally divided in a small hand sampling machine, which delivers a 
 sample appropriate for assaying purposes. The reject from the sampling 
 all goes into the mill bins with the milling ore. 
 
 From the mill bins the ore is taken to Chilean mills of the modern, 
 high-speed type, making 30 r.p.m., and is milled in cyanide solution. 
 The feeders for these mills are similar to the challenge feeders used for 
 
54 
 
 DETAILS OF CYANIDE PRACTICE 
 
 feeding stamps, but are continuously moved by power, belt and pulley, 
 and the feed is arranged so that a practically continuous stream of ore is 
 fed into the mills. The ore is milled to pass a 16-mesh screen. 
 
 Pulp Classification. From the Chilean mills the pulp goes to drag 
 classifiers of the so-called Esperanza type, which differ from the Dorr 
 machines in that the series of scrapers is connected to a link belt, which 
 moves continuously over sprockets, large at the slime-discharge end of 
 the machine and smaller at the sand end. These machines are more or 
 less efficient, but the general consensus of opinion among those who use 
 them is that the absence of the reciprocal motion, which is obtained in the 
 Dorr machine, allows more slime to be carried over with sand product. 
 The reciprocal motion of the latter seems to turn over the sand, loosen it 
 
 GOLDEN REWARD MILL. 
 
 and offer facilities for washing out the greater portion of the slime mixed 
 with it. 
 
 The separation of slime and sand is about half and half, the sand being 
 delivered into leaching tanks, each 20X10 ft., where it is treated in the 
 usual way by successive solution washes, followed by a final water wash. 
 The slime is passed through Dorr thickeners and pumped into slime- 
 storage tanks, the simple passage through the thickeners being sufficient 
 to dissolve the economical maximum of the contained gold. 
 
 Vacuum Filtration. From the slime-storage tanks the pulp is drawn 
 by gravity into the Moore filter at an average dilution of about one of 
 solid to 1J of solution, this rate varying with the exigencies of the oc- 
 casion. The Moore plant contains two 40-leaf baskets, each leaf measur- 
 
PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 55 
 
 ing 6 X 8 ft. A 1-in. cake is formed on the leaf in from 40 to 60 minutes, 
 depending on the condition of the leaves. The cake is washed with 
 solution and water and discharged following the usual practice, the 
 application presenting no novelties. 
 
 The proportion of colloid slime existing in the pulp makes it par- 
 ticularly applicable to filtration by this system and efficient results are 
 procured with comparative ease. The problem of filtration is not a simple 
 one in any case and it cannot be said that any of the processes in use at 
 the present time approximate perfection to any great extent, but by apply- 
 ing the machine and method best adapted to any particular ore fairly 
 satisfactory results may be obtained, 
 
 The ores treated at this mill vary widely in grade, running from a 
 minimum of about $5 per ton to a maximum of about $12. An average 
 extraction of slightly under 80% is obtained at a cost of less than $1.50 
 per ton milled. The lime used in treatment, the quantity varying with 
 the ore at hand, is added at the crushers and amounts usually to four to 
 six pounds per ton milled. The milling capacity is about 275 tons per 
 day. 
 
 The practice of the Golden Reward mill is typical of the modern 
 tendency to mill in cyanide solutions, in this case the strength being about 
 1 J Ib. KCN per ton, and although the mill is old and not particularly well 
 adapted for securing low operation costs, the work is nevertheless 
 efficiently done and the costs, under the circumstances, do not seem to be 
 exorbitant. 
 
 Experimenting with Roasting Process. The Golden Reward company 
 possesses a large quantity of ore which has resisted the efforts of met- 
 allurgists to treat it by any of the straight milling processes and an effort 
 is now being made to render it amenable to cyanidation by giving it a 
 preliminary roast. Experiments have shown that after being roasted 
 the ore is amenable to cyanidation and high extractions can be obtained 
 without excessive consumption of cyanide or other chemicals. The 
 cost of roasting will not be excessive as it is proposed to utilize the sulphur 
 content as fuel as far as possible, thus reducing the consumption of 
 extraneous fuel. 
 
 A roasting furnace is now in course of erection and will be in operation 
 in the near future. The results obtained by this departure in metallur- 
 gical practice will be awaited with interest. 
 
 Wet Crushing through Rolls. Another mill employing a wet crushing 
 process and using cyanide solutions throughout is that of the Trojan 
 Mining Co. at Portland, probably one of the most modern installa- 
 tions in the Black Hills. This mill formerly was the property of the 
 American Eagle company, but was acquired by the Trojan company and 
 remodeled to suit modern practice. The ore from the mines is dumped 
 
56 
 
 DETAILS OF CYANIDE PRACTICE 
 
 into bins at the crusher house and from these bins is drawn over 
 grizzlies, the undersize going to a belt conveyor, the oversize passing 
 through gyratory crushers and then joining the undersize on the belt 
 conveyor. This conveyor has a slope of about 16 and delivers ore into 
 mill bins having a capacity of about 450 tons. An automatic sampling 
 arrangement was at first installed to cut a sample from the ore stream 
 falling into the bins, but the arrangement did not give a representative 
 sample and was dismantled. 
 
 The ore is drawn from the mill bins and fed by disk feeders into two 
 sets of crushing rolls, strong cyanide solution being added at this point. 
 These rolls were probably not intended for wet crushing, for the housing 
 leaks a good deal and the almost constant attention of an attendant is 
 necessary to keep the leaks stopped up. 
 
 The product of the rolls flows through a launder to two Monadnock 
 Chilean mills, each seven feet in diameter. These mills gave some trouble 
 
 TROJAN MILL. 
 
 due to slight mechanical imperfections, but these have been remedied 
 so that the mills now give good results. The product of the mills is 
 elevated to Dorr classifiers where the sand and slime are separated. The 
 sand is delivered to 200-ton leaching tanks, 28X8 ft., through automatic 
 revolving arm distributors. The sand treatment presents no novelties, 
 being the same as that usually followed in the district. 
 
 Air Agitation of Slime. The slime from the classifiers is taken to 
 three tanks for air agitation, these tanks being said to be of the Pachuca 
 type. They measure 17 ft. 6 in. in diameter and 16 ft. in height, and it 
 will be readily seen that they differ a great deal from the Pachuca idea in 
 their proportions. A true Pachuca tank should have about 40 ft. of 
 height for a diameter of 15 ft. and the Trojan tanks have a greater 
 diameter with much less height. They are, however, doing excellent 
 work. The dilution of the slime under treatment is about 1 or 1J : 1, the 
 
PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 57 
 
 object being to maintain a fairly thick pulp suitable for subsequent 
 filtering. 
 
 A detail of these tanks which is of interest is the central air-agitation 
 tube, which is not a tube at all, but a succession of cone sections set one 
 above another through the entire height of the tank. The idea is that, 
 whatever the height of the pulp in the tank, it can be successfully agitated 
 because the central tube will discharge itself at almost any point. 
 
 The slime treatment is continuous through two of the agitation tanks, 
 the slime from the first one being transferred either to the second or third 
 tank, as desired, by air lifts, and from these secondary tanks it is drawn 
 off into the filter plant. The average agitation time of the slime is five 
 to six hours, no solution being decanted but the entire pulp going to the 
 filter. 
 
 The solution fed into the primary crushing rolls with the ore averages 
 three pounds of KCN per ton and is added in the proportion of four to six 
 tons of solution to one of ore. The sand in the leaching tanks is treated 
 with this same solution for about three days, and this treatment is 
 followed by treating two days with weak solution, which has been 
 precipitated, containing about one pound of KCN per ton. A light 
 water wash is given before discharging the sand, the treatment usually 
 extending over about five days. 
 
 The filter is the ordinary Butters stationary, semi-gravity type which, 
 while more or less satisfactory, entails a high cost for pumping pulp and 
 solutions. From the filter the solution effluent from making cake is sent 
 to the precipitation department, the weak barren-solution wash and the 
 water wash not being precipitated. 
 
 Precipitation is accomplished in the usual way, using zinc shavings 
 and the ordinary form of steel box. The boxes have a total capacity of 
 384 cu. ft. of zinc. At the cleanup the precipitate is run into an acid- 
 treatment tank where the sulphuric-acid process, customary in the Black 
 Hills plants, is carried out. The precipitate is collected, dried, partly 
 roasted, fluxed and melted in crucibles in a coke furnace. 
 
 The capacity of the Trojan mill is about 175 to 180 tons per day, but 
 steps are being taken to increase this tonnage materially. The extraction 
 secured by the combined slime and sand treatment is in the neighborhood 
 of 75%, somewhat more on the slime than on the sand product. 
 
 Unusual Crushing Practice. The practice of crushing with cyanide 
 solution through rolls is not usual, although it is practised in a few cases 
 and in one other instance in this district, as will be noted. It has been 
 productive of good results, probably due to the increased time of contact 
 between the ore and cyanide solutions, and the agitation secured in the 
 rolls and Chilean mills. 
 
 The Chilean mills are efficient crushing machines and are capable of 
 
58 DETAILS OF CYANIDE PRACTICE 
 
 handling large quantities of ore, but being high-speed machines they 
 naturally incur a maintenance cost which is high compared to the results 
 obtained with slow-speed mills. In this connection it might be men- 
 tioned that the Minnesota mill, at Maitland, is equipped with slow-speed 
 mills of the Lane type, and it is claimed that these mills have demon- 
 strated their ability to crush an equal or greater quantity of ore with less 
 expense both for operation and maintenance. 
 
 The Chilean mill is said to have been introduced into Black Hills 
 practice by J. V. N. Dorr, who first installed them at the Lundberg, Dorr 
 & Wilson mill and afterward included them in the design of the Mogul 
 mill, where they gave good results. The Mogul mill was recently 
 destroyed by fire and rebuilding is now under consideration, but the new 
 plant will probably be built on a site more convenient to the mining 
 properties owned by the company. 
 
 Dry Crushing of Hard Ores. As an example of extremely hard ores 
 found in the Black Hills district, the material handled by the Victoria 
 mill in the Spearfish Canon region may be mentioned. The ore here is 
 extremely hard and the mill equipment has been designed with this 
 characteristic in view. The ore is delivered into the mill bins by a tram- 
 way and from these bins is passed through a gyratory crusher which 
 delivers a product that will pass a l|-in. ring. This crusher product is 
 passed through a set of rolls which delivers a product having a maximum 
 size of f in. ; the crushed ore drops into a 100-ton bin. 
 
 From this bin the ore passes a set of fine-crushing rolls and through a 
 trommel, carrying 6-mesh, No. 14-wire screen. The oversize from the 
 trommel passes to a second set of fine-crushing rolls, and through another 
 trommel like that already mentioned. The oversize from this trommel 
 goes back to the same rolls and the screened product from both trommels 
 drops into a finished-product bin having a capacity of 200 tons. 
 
 The ore is so hard that its passage through the rolls is accompanied 
 by a great deal of noise which sounds much like cannon shots, but the 
 rolls handle the material in a satisfactory manner without undue wear. 
 
 The finished product is drawn from the bin and taken to leaching 
 tanks by means of a belt-conveyor system. The conveyor deposits the 
 ore into the center of the leaching tanks, each 27J ft. in diameter by eight 
 feet deep, with a capacity of about 200 tons, and the distribution is 'by 
 hand. 
 
 Leaching is practised in the ordinary way by first treating with a 3-lb. 
 cyanide solution, for 72 hr. During this treatment about 70% of the 
 gold content is dissolved. An additional 10 or 12% is obtained by 
 leaching for a further period of 48 hr. with cyanide solution containing 
 1J Ib. KCN per ton, the latter being finally displaced with a minimum 
 water wash. 
 
PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 
 
 59 
 
 Precipitation on Zinc Shavings. Precipitation is accomplished in the 
 usual way, using zinc boxes of the ordinary type made of sheet steel. 
 There are two six-compartment boxes, each compartment measuring two 
 by three feet. Each compartment is connected by a pipe to a main which 
 leads into the acid-treatment tank. At the cleanup the zinc is thoroughly 
 washed and the precipitate, after settlement, is drawn through the pipes 
 directly to the acid tank without further handling. The acid tank is 
 lead lined and furnished with a hood by means of which the gases gen- 
 erated are carried off. The acid-treated product is pumped through a filter 
 press and washed. This precipitate, after being partially dried and mixed 
 with the usual borax-soda flux, is melted in graphite crucibles. The 
 resulting bullion is a little more than 900 fine, of which 50 is silver. 
 
 LUNDBERG, DORR AND WILSON MILL. 
 
 The ore treated at this mill varies in value from $4 to $7 per ton. The 
 mill has not been in operation for a sufficient time to standardize the costs, 
 but it is expected that these will not average higher than those obtained 
 at other similar mills in the district. The mill is at present treating about 
 200 tons per day, perhaps the average being a little under that figure. 
 
 A Mill of Historical Interest. At Terry is situated the Lundberg, 
 Dorr & Wilson wet-crushing cyanide mill, owned by a partnership 
 composed of John Lundberg, J. V. N. Dorr and A. D. Wilson. For 
 several reasons this plant is unique. It was started in January, 1904, 
 and was the first mill in the world to operate continuously and successfully 
 a leaf-filter plant. It was in this plant that the first filter plant designed 
 by George Moore was installed, its difficulties encountered and over- 
 
60 DETAILS OF CYANIDE PRACTICE 
 
 come; the original plant is today operating and doing good work. 1 In 
 this plant also the well known Dorr classifier and the equally well known 
 Dorr thickener were developed. In addition this was the first plant in 
 the Black Hills to use the improved Chilean mill for crushing in cyanide 
 solution. The plant has operated steadily since January, 1904, except 
 during the labor troubles of 1907 and 1910, and it has the best record for 
 continuous operation of all the Black Hills cyanide plants. The mill has 
 a capacity of 110 tons per day and, due to the fact that it is treating 
 custom ores as well as ores belonging to the partnership, few details of the 
 practice have been made public and no information as to costs has been 
 given out. 
 
 The ore from the mines belonging to the company is held in three bins 
 having a capacity of 135 tons and the custom ore is dumped from mining 
 cars on the Chicago & Northwestern R.R. tracks in the rear of the mill 
 into bins holding 80 tons, from which point it is trammed to the crushers. 
 After passing over grizzlies with openings of 1J in. the ore passes through a 
 Gates gyratory crusher and thence to a 12-in. vertical belt elevator which 
 delivers it into a 75-ton crushed-ore bin. As the ore drops into this bin 
 an automatic sample is cut from the stream. 
 
 Wet Crushing Rolls. From the crushed-ore bin the material is fed 
 by a cam feeder into a Carterville geared roll together with solution 
 carrying 1| Ib. KCN per ton. The solution is run in sufficient quantity 
 to sluice the product satisfactorily through a launder into the Chilean 
 mill. This product, which will average about f in. in size, passes to a 
 6-ft. Monadnock Chilean mill, and is reduced so that practically all of 
 it passes a 30-mesh screen. At this point sufficient clear overflow from 
 the thickeners and cones is added to bring the quantity up to three or 3 J 
 tons of solution to one of ore. 
 
 The ground product from this mill is taken to a standard Dorr classi- 
 fier, the sand product of which passes to one of four leaching tanks, 
 each 18 ft. in diameter by 11 ft. deep, holding 105 tons of sand. In 
 addition to the 32 hours required to fill each tank, the charge is given a 
 further 12-hr, treatment with mill solution. The balance of the five-day 
 treatment is with barren solution carrying 1J Ib. cyanide per ton, fol- 
 lowed by a weak-solution treatment and finally a minimum water wash. 
 The leaching rate starts at five tons per hour and gradually diminishes 
 toward the end of treatment at which time it is one to 1J tons per hour. 
 
 Slime Treatment. Slime from the classifier, which amounts to 50 
 to 55% of the dry weight of the ore, is divided between two cones, one 
 18 ft. in diameter and the other 22 ft., and one standard 18-ft. continuous 
 Dorr thickener. The two cones are so placed as to give a gravity flow 
 
 1 This mill was closed down late in July, 1913, which was subsequent to the date of 
 the present article. 
 
PRACTICE IN THE BLACK HILLS, SOUTH. DAKOTA 61 
 
 of clear solution to the roll supply tank while the overflow of the thick- 
 ener goes to the Chilean mill. The thickened slime containing about 55 % 
 moisture is transferred by air lifts from the thickener and the 18-ft. cone 
 to the 22-ft. cone. From the latter it goes to a small cone agitator and 
 into the loading vat of the Moore filter, usually carrying about 55% 
 moisture and containing from five to 10% of 200-mesh material. 
 
 First Moore Filter. This original Moore filter plant was designed in 
 the beginning to handle 30 tons of slime per day, but it has been crowded 
 until it now handles 60 tons daily, using two baskets. With minor 
 changes in the construction of the plant and a change in the bottom of one 
 tank the installation is practically the same today as when it was designed 
 in 1903. 
 
 The crane for the transfer of the basket is operated by water at 105-lb. 
 pressure, the water being pumped into an accumulator. It gives little 
 trouble and costs almost nothing for maintenance. The mill solution 
 and most of the barren-solution wash from the filter process and sand 
 leaching go to the gold tanks and are precipitated. Solutions assaying 
 less than $1 per ton are not precipitated unless the treatment happens to 
 demand additional barren-solution, or the supply of high-grade solution 
 is insufficient to keep the precipitation department busy. 
 
 The solutions are precipitated by means of zinc shavings. In this 
 plant barrels have always been used instead of zinc bozes, the plant having 
 a total of 30 barrels in 10 rows of three each. They are cleaned up twice 
 a month, the rule being to take all the contents of the head barrel, part 
 from the second barrel and still less from the third barrel, sorting all the 
 coarse zinc and returning it to the second barrel. The fine zinc and 
 precipitate thus sorted out are placed directly in the acid tank. The 
 barrels are all moved up one step, the second barrel before cleaning up 
 becoming the first and the first barrel moved down to the foot. The 
 second barrel, now the head of the series, is repacked, the next partially 
 repacked; all of the fine material taken out is put in the acid tank. As 
 the cleanup usually consists of about 100 Ib. of dry product, all the figures 
 which follow apply to a cleanup of that size. 
 
 To the product in the acid tank 415 Ib. of commercial sulphuric acid 
 are added and allowed to remain in contact for six to seven hours, or 
 until chemical action has nearly ceased. Water in equal volume is then 
 added and the contents are heated with live steam and allowed to stand 
 10 or 12 hr., usually over night. The following morning the solution is 
 siphoned into a settling tank where any flocculent matter is settled. An- 
 other water wash is added and live steam again introduced to heat the 
 charge thoroughly. The charge is then allowed to stand about an hour. 
 The clear solution is drawn off into a vacuum tank and filtered. When 
 the acid tank is nearly empty the contents are energetically stirred to 
 
62 DETAILS OF CYANIDE PRACTICE 
 
 bring all of the product into suspension and the charge is transferred to a 
 vacuum tank and filtered. 
 
 When the moisture contained is brought down to 4 or 5 % the product 
 is taken from the tank, broken so that no piece is larger than a 1-in. cube 
 and placed in flat, iron roasting pans. These pans are placed in a soft- 
 coal furnace and the fire is started. The furnace has a total capacity of 
 four 18X3-in. pans in two layers; 1J to two hours' time is sufficient to 
 drive off nearly all the zinc, and the resulting bullion is comparatively 
 clean. The product in the pans is not touched or stirred during the roast- 
 ing and experiments have proved that mechanical losses are thereby 
 eliminated. The size to which the product is broken is small enough to 
 insure a good clean roast. 
 
 The roasted precipitate is placed in a No. 100 graphite crucible in a 
 coke furnace together with five to seven pounds of flux composed of f 
 borax glass and -J sodium carbonate. Melting is usually completed in 
 about 1| hr., using 80 to 100 Ib. of coke. The bar is poured into a bullion 
 mold as it is not necessary to remelt. The resulting bullion is 950 to 
 970 fine. Bars have been made as high as 984 fine, but the average is as 
 stated above. 
 
 Although the mill was built seven years ago it is kept in the best repair 
 and is still uptodate in most of its features. The machinery is driven by 
 electricity throughout, using alternating current at 440 volts; a total of 
 104 hp. is used. 
 
 Other Mills in the District. Among the mills now operating in the 
 Black Hills district may be mentioned the new Reliance, which has just 
 been remodeled and has started operation along lines unusual in the camp, 
 treating slime by a continuous decantation process and making use of 
 Dorr thickeners for the purpose. This mill has also installed a Portland 
 continuous filter for filtering the slime tailing. The mill has been in 
 operation only a short time, remodeling is not yet complete and no 
 information is available for publication. 
 
 The Bismark Mining Co. is building a mill near the Wasp No. 2 in 
 which the system of treatment will be identical with that of the latter. 
 The mill is approaching completion and should be in operation in the 
 near future. 
 
 In this paper no mention has been made of the metallurgy of the 
 Homestake installations. This is a matter which is so extensive that it 
 should be treated alone and I hope in a later paper to discuss that practice. 
 The Homestake is treating ores on a scale which is not equaled at the 
 present time and has attained an astonishingly low cost for mining and 
 milling. An ore of low grade is being treated and the methods, original 
 in many instances as they are efficient, are a lasting credit to the energy 
 of the technical men who are responsible for their devising. 
 
PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 63 
 
 There are many mills in the Black Hills which are not now operating, 
 but it would serve no useful purpose to speak of these at the present time 
 in spite of the fact that some of them may resume operations in the near 
 future. 
 
 Conclusions. It is with no little hesitation that one ventures to call 
 attention to details in the practice of this district which seem capable of 
 improvement, in view of the fact that capable operators have studied 
 the problems and undoubtedly are aware of the solutions of them even if 
 they are not put into practice at the present time. A little criticism, 
 however, may be helpful from a constructive point of view and the few 
 suggestions that I venture to make are offered in a friendly spirit, with a 
 
 NEW RELIANCE MILL. 
 
 desire only to add a little to the present practice. It is possible that a 
 perspective view may be appreciated by those whose vision has been 
 limited by long contact and short focus. 
 
 The first impression is that in few of the operating plants is there any 
 efficient means of estimating with accuracy the tonnage treated. The 
 importance of the point will be readily appreciated by those familiar with 
 the problem, so that it needs no discussion. It will be sufficient to say 
 that mill estimations are not sufficiently accurate upon which to base 
 comparative calculations except in such extraordinary cases as has al- 
 ready been mentioned in the Wasp No. 2 mill. A system of weighing the 
 mill ore, while expensive to install, will repay, in information acquired and 
 in satisfaction, any financial outlay which may be necessary. 
 
 The same is true of sampling. Sampling plants are expensive to install 
 but are productive of much good. In some mills in the district samples of 
 mill run are taken by means of a large elevator bucket fixed to a chain 
 belt which periodically crosses the stream of ore falling into the mill 
 bins. This device is more than likely to give erratic results. The 
 area of the bucket opening is too small, and large pieces of ore strike the 
 
64 
 
 DETAILS OF CYANIDE PRACTICE 
 
PRACTICE IN THE BLACK HILLS, SOUTH DAKOTA 
 
 65 
 
66 DETAILS OF CYANIDE PRACTICE 
 
 edges of the bucket and bounce off, leaving a sample which is not repre- 
 sentative. Often the capacity of the bucket is not sufficient to hold the 
 entire quantity of ore which belongs to it and it piles up and overflows, 
 again resulting in an erratic sample. I believe it is recognized that to 
 secure a proper sample it is necessary to take the whole stream of ore at 
 regular intervals, the oftener the better, and to reduce the size of the 
 sample by successive operations of the same kind. A part of the stream 
 for all or part of the time is not sufficient and leads to a sample which is 
 not accurate, and this, in the opinion of those who have most carefully 
 studied the subject, is worse than no sample at all. 
 
 Crushing Hard Ore with Rolls. The practice of crushing through 
 rolls in this district should be an object lesson to some metallurgists who 
 have maintained that rolls are not adaptable to hard ores. Some of the 
 roll installations here are crushing extremely hard, close-grained ores and 
 doing it efficiently and at low cost. The controversy as to the supremacy 
 of rolls or stamps might receive considerable light if a thorough comparison 
 of the different practices in the camp were made. The greatest difficulty 
 is that only one company, the Homestake, is using stamps, and this is 
 on such an enormous scale that the extremely low costs obtained there 
 cannot be compared with those obtained by rolls on a much smaller scale. 
 The Homestake mills are treating more than 4000 tons daily and by. 
 reason of the extent of the operation are able to institute economies 
 which would be impossible in smaller plants, the largest of which treats 
 but 500 tons daily. Comparison of results without a long period of 
 study and analysis is obviously out of the question. 
 
 High-speed Chilean mills are operated in a number of plants and are 
 giving good results. I have for some time believed that the slow-speed 
 mill is capable of giving more economical results and a comparison of the 
 cost of these and the cost obtained by the slow-speed mills at the Minne- 
 sota mill would be of greatest interest. In view of the fact that the latter 
 will probably begin operations soon I hope to see this comparison made. 
 
 The use of lime is accompanied by some losses which might possibly be 
 avoided by some slight change of method. This is typified in the case 
 of the Wasp No. 2 which has already been mentioned and a similar 
 procedure is followed at some of the other mills. The use of lime should be 
 carefully watched, as it has been clearly proved at the Homestake that 
 excessive lime has a retarding effect on the solution of gold in the ores of 
 the Black Hills. 
 
 On the ores in general it is said to be true that fine grinding increases 
 extraction, and where the ores have sufficient value to justify additional 
 expense it would seem to be good business to determine accurately at just 
 what point grinding can be carried to return the maximum economical 
 extraction. 
 
CHAPTER VII 
 THE LIBERTY BELL MILL, TELLURIDE, COLORADO 
 
 The mill of the Liberty Bell Mining Co. is situated near the town of 
 Telluride in San Miguel County, Colo. It is an old -mill, operations 
 having commenced in 1898 and continued up to the present time with 
 only a few interruptions due to reconstruction and improvement of 
 the plant and the unavoidable loss of time on account of labor troubles. 
 The mill began operations with 10 stamps and the scale has gradually 
 been increased until at present there are 80 stamps in operation, crushing 
 a total of about 485 tons of ore per 24 hours. 
 
 Type of Ore. The ore consists of quartz or calcite, banded, occurring 
 either alone or together, and often having bunches of the feldspathic 
 country rock. The vein material is generally fractured and contains large 
 quantities of clay which produces a colloid slime in the milling process. 
 The ore is not hard and milling is comparatively simple. 
 
 Cyanidation was early installed. In 1899 an experimental plant was 
 built and tested and, success having been demonstrated, a 250-ton leaching 
 plant was erected in 1900. It was soon shown that a substantial profit 
 could be obtained by this method, although at that time it was about the 
 lowest grade of ore being profitably handled by such process. Conditions 
 were facilitated by the delivery of power from the plant of the Telluride 
 Power Co., which had just begun operations. All these conditions aided 
 in securing the satisfactory result which has been continuously improved 
 upon up to the present time. 
 
 Ore Breaking. The primary crushing plant is installed at the mine 
 and consists of two HXl8-in. Blake sectional crushers. The ore is 
 delivered above the crushers on to a grizzly having 3-in. openings. The 
 pitch of the grizzly is steep, about 52, in order to secure a satisfactory 
 run of the ore, which is wet, averaging in general about 8% moisture. 
 The crushers break the ore to the same approximate size as the product 
 which has passed the grizzly, so that the material delivered to the mill is 
 sufficiently small in one direction to pass the 3-in. opening. It should 
 be noted, however, that this is a much different thing from passing a 3-in. 
 ring, as material having one 3-in. dimension, no matter what its length 
 and breadth may be, will go through the grizzly and large slabs of rock 
 are frequently run into the mill. 
 
 The ore is carried to the mill by means by an aerial cable tramway 
 
 67 
 
68 
 
 DETAILS OF CYANIDE PRACTICE 
 
THE LIBERTY BELL MILL, TELLURIDE, COLORADO 69 
 
 1| miles long. The cableway crosses a high divide between the mine 
 and mill, which necessitates a more substantial construction than when 
 the whole line is on one approximate level. The highest point on the 
 tramway is 1800 ft. higher than the mill. At the mill a steam-heated 
 detention room is provided, which is useful in winter for thawing the 
 buckets which have been loaded between shifts. Each bucket carries 
 about 700 to 800 Ib. of ore. 
 
 Amalgamation in Cyanide Solution. There are 80 stamps of 850 Ib. 
 each in the mill, having a 7-in. drop and 106 drops per minute. Four 
 of the five-stamp batteries are equipped with 12-mesh screen, due to a 
 difference in construction, but the rest carry 14-mesh wire screen. The 
 milling is done in cyanide solution carrying two pounds of KCN per ton. 
 The sodium salt is used but the records are kept in terms of KCN as is 
 customary practice at present. 
 
 In front of each five-stamp battery is placed a copper amalgamating 
 plate, 4 ft. 7 in. wide and 8 ft. long, with a slope of 2| in. to each foot. Over 
 this plate the pulp passes and is amalgamated. This detail is worthy of 
 particular attention, as some authorities have maintained that amalgama- 
 tion cannot be successfully carried out in cyanide solutions. It is done 
 successfully at the Liberty Bell mill. Care and attention are essential 
 to good results and a knowledge peculiar to this particular work must be 
 obtained to operate it successfully. 
 
 The plates are maintained in a rather " wet" state, for if they are run 
 fairly dry as is usual when milling in water, they soon become too hard 
 and crusted to be of any use in recovering the gold. Keeping the plates 
 wet avoids the excessive hardening of the amalgam and allows the 
 retention of a large percentage of the gold. In view of the fact that some 
 quicksilver and amalgam may be scoured off the plates while in this wet 
 condition, traps are used to recover any particles which may escape. 
 It is not claimed that the extraction under these conditions is as high as 
 when the operation is carried out in water, but the object of the operation, 
 which is the recovery of any coarse gold which might not readily dissolve 
 in cyanide, is attained and the system has obvious advantages over milling 
 in water where cyanidation is to follow. 
 
 When milling is done in water there is an appreciable amount of it 
 introduced into the cyaniding system and it follows that an equal amount 
 must be discharged with the residues. 
 
 It is almost impossible to get rid of the residual moisture without losing 
 some cyanide and dissolved metal along with it. To avoid the discharge 
 of excessive moisture with residues as far as possible is an important item 
 in cutting down losses and by milling in cyanide solution, wherever it is 
 possible, this discharge and its valuable content is saved to a large extent. 
 
 One development of milling in water, where that measure seems 
 
70 DETAILS OF CYANIDE PRACTICE 
 
 unavoidable, is the system in use at the mill of the Smuggler-Union 
 company, where the pulp delivered to the cyanide plant has previously 
 been crushed and concentrated in water and contains an enormous pre- 
 ponderance of the liquid. This pulp is here thickened and then filtered, 
 from which point it begins cyanide treatment containing a minimum of 
 moisture. This is a system which cannot be generally recommended and 
 its use in special cases will be considered later. 
 
 Classification and Concentration. The pulp from the batteries is 
 carried to Richards hindered-settling classifiers, which make a coarse, 
 middling and fine product in addition to the slime overflow. The latter 
 is taken to 6X6-ft. settling cones, the underflow of which is concentrated 
 on Wilfley tables, the overflow going to Dorr thickeners. 
 
 The underflow product from "the Richards classifiers is concentrated 
 separately on Wilfley tables, the tailing going to an Akins classifier and the 
 middling passing over a Bunker Hill screen which is fitted with 16-mesh 
 No. 22 wire screen. The oversize from this screen also goes to the Akins 
 classifier, the undersize being concentrated on a Wilfley table the tailing 
 of which goes to the same classifier. The accompanying flow sheet gives 
 the details of the pulp flow and machinery in operation. 
 
 The Akins classifier delivers the sand to a 5X22-ft. tube mill of the 
 Abbe tire type, the mill feed containing about 40% moisture. The dis- 
 charge from this mill is raised to a diaphragm cone where a separation is 
 made, the overflow going to a simple cone and the underflow from both 
 of them going to a second tube mill identical with the first one mentioned. 
 The overflow from the simple cone, together with the product of the 
 second tube mill, is elevated to a second series of amalgamating plates, 
 and from the plates to cones, the underflow being led to Deister slime 
 concentrators and the overflow to Dorr thickeners. Kidney pulp dis- 
 tributors are largely used in the mill. These machines have already 
 been described. 1 
 
 The tube mills are of the tire type, which is convenient in allowing any 
 desired size of inflow and outflow openings. In some cases mills of this 
 type have proved more or less unsatisfactory, due to difficulty in keeping 
 the tires running true on the supporting rollers, but here this difficulty 
 has been overcome by careful installation on heavy, rigid concrete blocks 
 and the use of a deep flange. No difficulty is now experienced >and the 
 mills run true and without vibration. 
 
 The mills are lined with silex blocks four inches thick set on edge. 
 The lining lasts from nine to ten months without renewal and the type 
 has been found generally satisfactory. In order, however, to take 
 advantage of any economy which might be available, experiments are 
 now being made with a lining of the Komata type, but as yet this work 
 1 Eng. and Min. Journ., Nov. 26, 1910, p. 1046. 
 
THE LIBERTY BELL MILL, TELLURIDE, COLORADO 71 
 
 has not been carried far enough to give any conclusive results. Danish 
 pebbles are used in the mills, about 130 Ib. per mill per day being the 
 consumption. The mills require about 43 hp. to keep them moving. 
 The feeders are of the usual spiral-dip type. 
 
 There are three of these mills installed, but only two are in regular 
 use, the third being held in reserve. This reserve mill is so arranged that 
 it can be used in place of either of the other mills when one is cut out for 
 relining or repair. 
 
 Agitation of the Slime. The Dorr thickeners deliver a pulp thickened 
 to about 2 : 1 to the Hendryx agitators, of which there are six. The pulp 
 flow is continuous through the Dorr thickeners and the agitators, de- 
 livering continuously into the equalizer tank which feeds the filter. The 
 agitators were originally installed to take advantage of the Hendryx 
 specialties in cyanide metallurgy, but these having been found of ques- 
 tionable value, were abandoned and the tanks retained simply as agitators. 
 They agitate by elevating the material in a central tube in the tank by 
 means of a propeller screw. The system is considered expensive of power 
 consuming 7 hp. each for the tanks, which hold about 33 tons of dry 
 slime. 
 
 Grinding Requirements. Due to the soft and clayey character of the 
 ore, extremely fine grinding is not necessary. The statement would 
 probably be more accurate were it said that grinding the ore through 
 an 80-mesh screen is sufficient to reduce it to such fineness that it may be 
 treated as slime. The battery grinding alone produces a pulp of the 
 following analysis: On 20 mesh, 2.9%; on 40 mesh, 20%; on 60 mesh, 
 10.6%; on 80 mesh, 7.3%; on 100 mesh, 5.6%; on 200 mesh, 7.6% and 
 through 200 mesh, 46.6%. After regrinding, the pulp which is subjected 
 to agitation treatment has the following analysis: On 80 mesh 7.5%; on 
 100 mesh, 4.9%; on 200 mesh, 14.2% and through 200 mesh, 73.4%. 
 
 The pulp is easy to keep in suspension and is sufficiently fine to give 
 the maximum economical extraction. The pulp as treated contains 
 about 30% of colloid slime and one of the principal problems is the 
 handling of the product and inducing settlement. In order to promote 
 satisfactory settlement a milk of lime is prepared and added to the 
 inflow to the Dorr thickeners, an average of seven or eight pounds per ton 
 of ore being required. The average specific gravity of the dry slime is 
 about 2.68, a figure which indicates no extreme either way, but about an 
 average ore density. 
 
 Filtering the Slime Pulp. The Moore filter plant is one of the earliest 
 examples. The tanks are of wooden construction, but are well put 
 together and are still in good condition. For filtering there are four baskets 
 of 66 leaves each, the leaves measuring 6 X 8 ft. These baskets are operated 
 in two groups of three tanks each, the middle tank being the one in which 
 
72 
 
 DETAILS OF CYANIDE PRACTICE 
 
 loading is carried out and the others used for washes and discharging. 
 The cycle is as follows: Loading, 50 min.; drying and transferring, 
 10 min.; washing, strong solution, 15 min.; washing, weak solution, 30 
 min.; discharging, 10 min.; transferring, five minutes. 
 
 4 Richards 
 Hindered Sett Una 
 Cla<;Kifte a 
 
 QDDDQDDC 
 
 ~8x.4-~3 Amalgam at I net 
 2-6'Seitnng 
 
 Cones Overflo 
 
 l~ ' 9- Dorr Continuous PulpThichenen 
 
 t-r* '$ -Tp ^ ~TZ^I: j ^ -y_ 
 
 I Stronq Solution Decanted Solution 
 
 I WeakSolution - / 
 
 Pulp 
 
 \ /\ / | i i \ / , t> nenaryx ngira 
 
 \/ \/ l{i:r!*~. =^_ ^eakSolutior,_S-hraae in Series 
 
 ?^--^ : WrFii"X:rri 
 
 9*SXtf 
 
 *!0"<->oula '-5 
 
 DIAGRAM OF TREATMENT AT LIBERTY BELL MILL. 
 
 The thickness of the cake made varies from seven-eighths to one inch, 
 approximating 10 tons per basket of dry slime. The plant was con- 
 structed to treat a much smaller tonnage than is now being put through 
 
THE LIBERTY BELL MILL, TELLURIDE, COLORADO 73 
 
 it, but has been forced up to its present capacity by increasing the ef- 
 ficiency of each operation. One of the refinements is the installation of a 
 vacuum pump of high efficiency to expedite the filtering. This machine 
 is of the type usually used for obtaining a vacuum in the manufacture of 
 incandescent electric lamps. The system is a dry-vacuum operation, no 
 solution passing through the vacuum pump. The solution discharge is 
 into a specially constructed deep pit for securing a barometric discharge. 
 
 The loss in dissolved metal amounts to about three cents per ton of dry 
 ore and the cyanide mechanically lost to about 0.3 Ib. per ton. The 
 filtered pulp has an average dilution of 2 : 1 and air lifts are used to as- 
 sist in maintaining an even consistency vertically in the tank. The 
 solids do not settle rapidly, as has already been mentioned, but the 
 air lifts are used as an additional assurance of homogeneity. Solution 
 under 18 Ib. pressure is used for discharging the cake and the operation 
 is concluded with air under 10 Ib. pressure. 
 
 The filter leaves require acid treatment about every three months, and 
 to facilitate this operation without delay of filtration, a separate basket 
 is always kept in readiness for instant use. The basket requiring acid 
 treatment is removed from service and the extra one immediately put 
 into action. A separate tank is provided for containing HC1 for treating 
 the leaves, and the cost of the acid-treating operation mounts to about 
 0.6 c. per ton of ore. 
 
 Precipitation is accomplished by means of zinc shavings, using boxes 
 of the ordinary type. It is recognized that the use of zinc dust offers 
 conveniences and in many cases economies, but the question has been 
 given careful study here without seeming to justify a change of system. 
 
 The precipitation at the Liberty Bell mill gives no trouble in any way, 
 the only requirement being that the clarified solution be allowed to pass 
 over the zinc at the stated rate of about 0.7 ton per cu. ft. of zinc shaving 
 per 24 hr. Precipitation is good, head solutions carrying SI per ton give 
 tailing assays of one to two cents per ton. The solution going into the 
 pregnant-solution tanks is metered by the use of a device similar to that 
 described in the article on the Hollinger mill at Porcupine, Ontario. 
 
 The precipitate is melted in oil-fired tilting furnaces, one Steele-Harvey 
 and one Donaldson furnace being installed. The operation is extremely 
 simple and presents no difficulties. The precipitate is lightly acid treated,, 
 fluxed and melted, the bullion obtained averaging over 900 fine. 
 
 A small blast furnace is used for cleaning up all waste product such as 
 flue dust, slag, sweepings, etc. This material is all briquetted with 
 Portland cement in such proportion that a satisfactory slag will result 
 and periodical runs are made which eliminate all waste products. The 
 results are altogether satisfactory, there being a substantial saving over 
 selling such material to the smelters. 
 
74 
 
 DETAILS OF CYANIDE PRACTICE 
 
 Use of Heated Solutions. The heating of solutions has been found of 
 assistance in the mill. This measure was adopted primarily for the pur- 
 pose of bringing extractions up to the normal point in cold weather, but 
 it was considered advisable to continue to warm the solutions through- 
 out the year in order to take advantage of the additional recovery of 
 the silver. The effect upon the gold is not noticeable. 
 
 The matter of warming solutions is one that has received some atten- 
 tion from metallurgists in various countries and in many cases has not 
 shown any particular benefits. At any rate there has been no con- 
 sistency in the results obtained. The silver mills in Mexico, particularly, 
 have experimented with solutions of various temperatures and generally 
 speaking the improvement has been so small and variable that benefits 
 have been considered not proven. In case of the Liberty Bell, the action 
 
 Pipe Cap 
 
 Sample 
 
 Disk free fo 
 
 moveonshaff 
 
 Tailing . 
 
 AUTOMATIC TAILING SAMPLER AT LIBERTY BELL MILL. 
 
 of the warm solution has not been studied for sufficient time to warrant 
 final conclusions. The benefit, if any, may not be confined to the dissolving 
 effect of the solutions but may extend to the amalgamation and con- 
 centration, as will be mentioned later. 
 
 The ore delivered to the mill is not regularly sampled nor weighed. 
 In order to approximate the weight, a number of the tram-way buckets 
 are weighed each day and the total weight of ore delivered is calculated 
 from this information, together with the number of buckets coming into 
 the mill. The latter are counted automatically by means of an electrical 
 device which records each bucket as it enters the mill, the counter being 
 installed in the mill office. No sample is taken of the ore, the average 
 content being obtained by summing the total mill production and the 
 
THE LIBERTY BELL MILL, TELLURIDE, COLORADO 
 
 75 
 
 content of the tailing leaving the mill. The latter is sampled auto- 
 matically by a device invented and perfected by W. E. Tracy, mill super- 
 intendent. The sampler has been described before 1 but a sketch of it is 
 herewith presented as it is worthy of note. 
 
 It consists of a disk mounted on. a shaft and moved by means of a 
 worm gear. A pipe is fixed to the disk, the pipe having a slot through 
 which the sample enters. The worm gear moves the disk slowly until a 
 point is reached where the weight fixed to the disk over-balances the pipe 
 and the disk swings around rapidly, the slot in the pipe passing the 
 tailing stream and taking a sample of it. The momentum is sufficient 
 to carry the disk far enough to raise the pipe into a vertical position 
 again and the sample runs out of the curved end of the sampling pipe into 
 a small launder which is properly placed to receive it and conduct it into the 
 sample receptacle. The movement is so rapid that the solids in the sample 
 do not settle and the pipe drains cleanly. A pawl engaging a ratchet cut 
 in the disk prevents a return swing of the disk. 
 
 This system of estimation of ore content cannot be recommended at all 
 times. It may be fairly satisfactory if every care is taken to avoid mis- 
 haps and losses within the mill, but its great weakness is that such losses 
 and shortages of production cannot be readily detected. 
 
 CHEMICAL CONSUMPTION AND COST AT LIBERTY BELL MILL 
 
 Material 
 
 Consumption per 
 ton ore Ib. 
 
 Cost 
 
 Unit 
 
 Zinc 
 
 5 
 
 $0 115 
 
 Ib. 
 
 Lime 
 
 7-8 
 
 0.005 
 
 Ib. 
 
 Cyanide (KCN) 
 
 1.3 
 
 215 
 
 Ib. 
 
 Litharge 
 Pebbles.. 
 
 0.3 
 0.54 
 
 0.085 
 37.75 
 
 Ib: 
 ton. 
 
 The period of agitation which the pulp receives in the mill is about 14 
 hr. in the mill circulation and about 12 hr. in the Hendryx tanks. The 
 consumption of chemicals and the cost per unit is about as given in the 
 accompanying table. 
 
 Metallurgy of the Ores. The metallurgy of the Liberty Bell ore is not 
 complicated, as there is no rebellious element to be reckoned with. The 
 fact that silver exists in sufficient quantity to make is extraction an object 
 introduces an element which is somewhat more complicated than when 
 only gold is to be extracted. In this case, however, the quantity of silver 
 is small and strong solutions do not have to be resorted to. A 2-lb. KCN 
 solution is used throughout the mill. The use of a lead salt, however, has 
 been found advantageous. At first lead acetate was used, added to the 
 
 1 Trans. A. I. M. E., October, 1911. 
 
76 
 
 DETAILS OF CYANIDE PRACTICE 
 
 agitators, but now litharge is in regular use, the addition being made to 
 the tube mills where it is readily ground up and put into solution. 
 
 The thorough system of concentration used is based upon the belief 
 that it does not pay to attempt to extract the contents of the sulphides in 
 contact with the remainder of the ore as the strong solution required and 
 the long time would entail a loss of cyanide and cost of agitation out of 
 proportion with the recovery. By removing the sulphides the siliceous 
 ore may be treated, as has been shown, with weak solutions and short 
 time of agitation and the sulphides may be handled in some satisfactory 
 way. 
 
 Up to the present the sulphides have been sold to the smelters, but 
 experiments are under way looking toward a cyanidation of the product 
 on the ground. While these experiments have not been carried to con- 
 clusion, it may be said that the indications are that the process is feasible, 
 and if this is true an additional saving will be made possible. The idea is 
 to treat the concentrate in a separate system using stronger solutions and 
 more time. The residues from the concentrate .treatment will be thrown 
 in with the regular siliceous ore and will thus be given an additional treat- 
 ment, with the possibility that the total recovery, compared with its cost, 
 will show a greater profit than the method now followed will produce. 
 
 Special Metallurgical Features. The two special metallurgical 
 features, as have been described, are first, amalgamation on plates in 
 cyanide solutions, and second, the heating of mill solutions in order to in- 
 crease extraction of silver. 
 
 PERCENTAGE EXTRACTION AT LIBERTY BELL MILL DURING FISCAL 
 
 YEAR 1912 
 
 Gold 
 
 First half 
 
 Second half 
 
 Amalgamation 
 
 48.98 
 
 50.20 
 
 Cyanidation 
 
 35.71 
 
 34.40 
 
 Concentration 
 
 7.52 
 
 8.40 
 
 
 
 
 T^fal 
 
 09 91 
 
 OQ on 
 
 Silver 
 
 Amalgamation 
 
 7.12 
 
 11.30 
 
 Cyanidation 
 Concentration ' 
 
 37.67 
 17.24 
 
 39.70 
 21.60 
 
 Total 
 
 62.03 
 
 72.60 
 
 The first of these items is one that has been called unsuccessful and 
 impossible in many cases, but it has here demonstrated its value, and 
 there can be no reasonable doubt that it is useful in some cases. I should 
 
THE LIBERTY BELL MILL, TELLURIDE, COLORADO 
 
 77 
 
 consider it a valuable system to adopt in cases where amalgamation was 
 considered essential for the purpose of recovering coarse gold which would 
 not dissolve in cyanide solutions in any reasonable length of time, 
 and which existed in such large quantities that the regrinding process 
 would not reduce it to some form readily dissolved. It should be pref- 
 erable to milling in water, which has manifest disadvantages. 
 
 Extraction and Cost. Due to certain changes which took place in 
 about the middle of the present fiscal year and the changes in mill results 
 which followed, the ore content and recovery are given as types for these 
 periods. The ore content for the first half of the year was . 27 oz. of gold 
 and three ounces of silver; for the second half, 0.27 oz. of gold and two 
 ounces of silver. 
 
 TABLE I. LIBERTY BELL MILLING COSTS 
 
 
 Labor 
 
 Supplies 
 
 Genera] mill labor. 
 
 $0 0901 
 
 $0 5811 
 
 Crushing 
 
 0531 
 
 0194 
 
 Stamping 
 Regrmding 
 Settling and agitating 
 Filtering 
 Concentrating 
 Amalgamati ng 
 
 0.0935 
 0.0104 
 0.0150 
 0.0372 
 0.0476 
 0426 
 
 0.0973 
 0.0665 
 0.0390 
 0.0509 
 0.0199 
 0224 
 
 Precipitating 
 
 0.0137 
 
 0.0755 
 
 Total labor 
 Total supplies. . 
 
 0.4032 
 9720 
 
 Total 0.9720 
 
 
 
 
 Total cost 
 Depreciation 
 Realization 
 
 1.3752 
 0.1200 
 0.3100 
 
 
 Total mill cost of production 
 
 1.8052 
 
 
 The increase in silver extraction in the second half is noteworthy in 
 view of the fact that the ore content is one-third less, a situation which is 
 opposed to general experience. There are two factors which have changed, 
 either of which, or both, may be in part or wholly responsible for the dif- 
 ference in results. The first change, the mining of the ore from a different 
 and deeper level, may have its effect, and the second change, the increase 
 in solution temperature, would naturally influence results to some extent. 
 
 Of a total gain of 10. 57% only 2. 03% is due to improved recovery in 
 the cyanide solution. The coincident alteration of two important factors 
 makes it impossible to say without further study just what part each has 
 played in producing the final result. The temperature of the solution in 
 agitators and filter plant has been raised to about 80 F. and that on plates, 
 
78 
 
 DETAILS OF CYANIDE PRACTICE 
 
 concentrators and settlers to about 70. The cost of operation, based on 
 the milling of 104,460 tons in seven months, is shown in the accompany- 
 ing tables. 
 
 TABLE II. DISTRIBUTION OF GENERAL EXPENSES AT LIBERTY BELL 
 
 MILL 
 
 Labor 
 
 Per ton 
 
 Supplies 
 
 Per ton 
 
 Superintendence 
 Heating 
 
 $0.0268 
 0.0129 
 
 Pipe lines 
 Bins . .... 
 
 S0.0061 1 
 0.0085 1 
 
 Electric plant 
 
 0106 
 
 Building 
 
 0628 1 
 
 Lubrication 
 Pumping plant 
 Watchman 
 
 0.0034 
 0.0212 
 0083 
 
 Electric plant 
 Pumping plant 
 Fuel and heating 
 
 0.0111 
 0.0198 
 0471 
 
 Examination and tests 
 
 0068 
 
 Tools 
 
 0.0043 1 
 
 
 
 
 2fi 14 1 
 
 
 0901 
 
 Lime 
 
 0.0426 1 
 
 
 
 Lead salts 
 
 0.0330 
 
 
 
 Light and power 
 Oil and waste 
 
 0.0378 2 
 0.0091 
 
 
 
 Assaying and melting 
 Examination and tests 
 Miscellaneous 
 
 0.0347 1 
 0.0027 
 0.0001 
 
 
 
 
 0.5811 
 
 1 Combined labor and supply. 
 
 2 The power in this item is that used in pumping between departments. 
 
CHAPTER VIII 
 PRACTICE AT CRIPPLE CREEK, COLORADO 
 
 The Cripple Creek district of Colorado is one of the most famous gold 
 camps of the world and has, at times, been called the richest gold district 
 in existence. Although this can hardly be said to be true at present, 
 still the district is of great importance and continues to produce gold in 
 large quantities. Its minerals are too well known to require any detailed 
 description at the present time. The occurrence of tellurides of gold is 
 distinguishing and is the principal feature which opposes simple reduction 
 methods. 
 
 The metallurgy of the ores of the district has passed through all the 
 changes common to most of the gold camps of the United States, plate 
 amalgamation, chlorination, concentration and finally cyanidation having 
 been applied to the minerals with varying degrees of success, not to 
 mention the procession of patented and secret processes which have made 
 one brief appearance and then vanished forever. At the present time 
 cyanidation, occasionally alone but more generally in combination with 
 concentration or some other metallurgical means, notably roasting, is 
 applied to all the ores which are too low grade to smelt, and the process 
 has become essential to the life of the district. 
 
 Many Mills in Operation. There are a number of mills at work in the 
 district and in addition to these a quantity of ore is shipped to the two 
 large custom mills operating at Colorado Springs. The richer ores are 
 smelted but the quantity of this product is not so important as it was in 
 earlier days. By far the greater quantity of ore is milled and the cyanide 
 process is responsible for the recovery of a large part of the gold. 
 
 Most of the mills in the district, or at any rate the most important 
 ones, use a combination of concentration and cyanidation, the idea being 
 to remove, as far as possible, the tellurides, sulphides and other refractory 
 compounds which do not yield readily to cyanide treatment, leaving a 
 tailing which is satisfactorily treated with cyanide solutions of low 
 strength and at reasonable cost. " Some of the plants are simple leaching 
 installations treating ore or waste of low grade and in different degrees of 
 fineness, but these present no metallurgical novelties and are simply 
 efforts to extract a profit from material available without reference to 
 technical niceties or conservation of resources. 
 
 Of the more important mills which are following modern practice and 
 obtaining results which are satisfactory in various degrees, may be meh- 
 
 79 
 
80 
 
 DETAILS OF CYANIDE PRACTICE 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 81 
 
 tioned those of Stratton's Independence, Ltd., the Portland Gold Mining 
 Co., the Ajax-Colburn and the Blue Flag Mining Co. Of these the 
 Ajax is the principal one which has made serious attempts to obviate the 
 use of both concentration and roasting and use the cyanide process 
 direct, making use of chemical means in combination with the cyanide 
 solutions to dissolve the refractory gold compounds. This mill has 
 installed the Clancy electrochemical method of procedure and is now in 
 process of ascertaining what benefits may be expected from it. At pres- 
 ent there is not sufficient information available to enable a statement 
 which will definitely prove either success or failure for the system, but 
 it is hoped that within a few months data for the settlement of the question 
 may be forthcoming. The serious attempt of the operators of this plant 
 to solve a difficult problem along scientific lines is worthy of the complete 
 success that they hope to obtain. 
 
 Separate Dry Crushing at Ajax. The Ajax has installed a plant 
 entirely separate from its cyanide mill in which the ore is crushed dry and 
 mechanically sampled. The ore is brought into this plant in electrically 
 moved cars and is passed through a series of crushers, rolls, screens, etc., 
 being sampled during the process, and is finally delivered in a condition 
 sufficiently fine to be mixed with the cyanide solutions and classified, any 
 oversize being led directly into the tube mills for regrinding. This, I 
 believe, is the first attempt in the Cripple Creek region to slime all the 
 milling ore and . treat it directly by cyanide. The statement of proven 
 results will be awaited with interest. 
 
 The Blue Flag mill is another which is making a trial of a compara- 
 tively new development of cyanidation. It is equipped with machinery 
 for the continuous-decantation process using Dorr thickeners in con- 
 junction with agitation tanks of a well-known design. This process 
 presents some innovations which are of great interest at this time and 
 will be discussed in a separate article. 
 
 Portland and Independence Mills. The mills of the Portland Gold 
 Mining Co. and Stratton's Independence, Ltd., are similar in many ways, 
 the principal difference being that the Portland makes a total slime prod- 
 uct, while at the Independence the sand and slime are treated separately. 
 Due to the fact that the Portland company does not desire to make public 
 any details of its practice at the present time, no information can be given, 
 but it will be safe to accept the practice followed at the Independence as 
 typical of successful work in the Cripple Creek district and its system, 
 which is made public without reserve, will form the bulk of this article. 
 
 At this mill a long series of experiments was conducted by Philip 
 Argall and it was decided that the most feasible method was careful con- 
 centration of the ores followed by cyanidation of the tailing. The adapta- 
 bility of this system was due to the fact that the ore contained a quan- 
 
82 
 
 DETAILS OF CYANIDE PRACTICE 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 83 
 
 tity of gold in the form of telluride which is not easily cyanied by direct 
 methods and it was considered advisable to remove this constituent and 
 extract its gold content by some means more satisfactory. A mill to 
 treat 5000 tons per month was erected to make use of this method. The 
 mill was afterward increased to handle 10,000 tons per month, at which 
 capacity it is now operating. 
 
 The ore supply comes mainly from the dumps, a large accumulation 
 of this material having resulted during the long life of the mine. The 
 average content has a value of about $3 . 50 per ton as milled. An elec- 
 tric shovel is used for moving the material, which is loaded into 4-ton cars, 
 hoisted up an inclined plane and delivered into the crusher house. 
 
 COSTS AT STRATTON'S INDEPENDENCE MILL 
 
 Per ton 
 treated 
 Dump breaker: 
 
 Power $0.0436 
 
 Operation 0.0516 
 
 Repairs. 0.0681 
 
 Total $0. 1633 
 
 Crushing and concentrating: 
 
 Power 0. 1946 
 
 Operation 0.1192 
 
 Repairs 0. 1982 
 
 Loading concentrate . 0097 
 
 Total 0.5217 
 
 Cyaniding: 
 
 Power 0.0484 
 
 Operation 0.3420 
 
 Repairs 0.0549 
 
 Total ' 0.4453 
 
 Miscellaneous: 
 
 Heating 0.0050 
 
 Water service 0.0048 
 
 Liability insurance . 0057 
 
 'Fire insurance 0.0298 
 
 Taxes.. 0.0465 
 
 Total 0.0918 
 
 Mine breaker 1 0.0169 
 
 Total cost $1 .2390 
 
 1 The mill receives one-tenth of its supply from a small breaker plant where mine 
 ore is crushed to \ in. and taken directly to the Chilean mills. 
 
84 DETAILS OF CYANIDE PRACTICE 
 
 From the head of the crusher house the ore is delivered to a No. 7 J 
 Gates gyratory crusher, which delivers its crushed product to a picking 
 belt three feet wide. Here the larger boulders of barren rock are thrown 
 out as much as possible and the belt carries the remaining material to a 
 No. 5 Gates crusher, in which the ore is reduced to about 1 f-in. cubes 
 and conveyed, by means of an 18-in. conveying belt, to the steel storage 
 bin. The sorting does not materially increase the value of the ore, less 
 than 3% being removed in the process, which is of more importance on 
 account of the quantity of pieces of wood, steel and much other foreign 
 matter which comes from the dump. 
 
 The steel mill bin is of special design and was installed with the idea 
 of obviating blocking or sticking of the ore, which object has been attained. 
 It consists of a steel cylinder, the bin proper, terminating in a cone-shaped 
 bottom. The apex of the cone is cut off leaving a circular opening four 
 feet in diameter. This opening is set down into another smaller cone, the 
 feed cone, which has a 12-in. opening delivering the ore to a revolving 
 disk feeder. The opening in the bin bottom is large enough to prevent 
 blocking and is small enough to relieve the feed cone of excessive pressure. 
 The device works successfully and the bin can be entirely emptied of its 
 contents without shoveling. The ore stored in the bin is all reduced to 
 smaller than 2-in. cubes. 
 
 From the storage bin the ore is fed through two sets of 16X36-in. 
 rolls which reduce it to about J-in. size. Due, however, to the flaky 
 character of the ore, largely phonolite, the size is more nearly f in., 
 although its thickness is generally less than J in. 
 
 Addition of Lime. The ore coming from the storage bin is slightly 
 moistened with cyanide solution which tends to settle the dust and also 
 to slake the lime which is added at this point. By means of this procedure 
 it is calculated that the lime shall be in good condition to render effective 
 service, and by the passage through the rolls normal character of ore feed, 
 they crush almost exactly five tons per hour with an expenditure of 55 hp. 
 With the mill in average condition the pulp delivered from it has the fol- 
 lowing approximate composition: On 50 mesh, 21%; on 100 mesh, 12%; 
 on 150 mesh, 5%; through 150 mesh, 62 per cent. 
 
 The total steel consumed per ton of ore milled, using Midvale or 
 Latrobe brands, amounts to 0.62 Ib. The crushing pressure of the' mill 
 amounts to about 900 Ib. per sq. in., which is probably somewhat increased 
 by centrifugal force. 
 
 The Chilean mill has been generally considered a sliming machine, 
 but the operators at the Independence mill have found that within certain 
 limits it is able to give a fine, yet granular product. The adjustment, 
 however, must be made with a view to the result desired. In some cases, 
 of which the Independence is typical, a fine, granular product is desired 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 85 
 
 for concentration efficiency, while in other instances, typified by the total- 
 sliming mills, the highest economy is secured by producing an extremely 
 fine product as quickly and simply as possible. In the latter case the 
 Chilean mill has been able to prove its adaptability, and when construc- 
 tion includes the Mantey offset I should be inclined to consider the large 
 diameter, slow-speed mill both cheaper and more efficient than the higher- 
 speed mills such as are used at the Independence. In connection with 
 this subject it will be interesting to refer to my article on Chilean mills 1 
 and also the paper by Walter H. Urbiter 2 on the same subject. 
 
 The ore coming from the storage bin is slightly moistened with 
 cyanide solution which tends to settle the dust and also to slake 
 the lime which is added at this point. By means of this procedure 
 it is calculated that the lime shall be in good condition to render 
 effective service, and by the passage through the rolls becomes 
 thoroughly mixed in with the ore and probably reaches every part 
 of it. Being in a damp condition, the time of passage through the rolls 
 to the mill bins and the time it remains in the latter should be sufficient 
 for a thorough neutralization of any latent or developed acidity in the ore. 
 The system of adding lime to ores in cyanide milling has been the subject 
 of much discussion and the methods used are extremely varied. It is 
 of considerable interest to note the methods and reasons adopted at the 
 different plants, and a final comparison of them will be valuable and of 
 technical interest. 
 
 Chilean Mills for Fine Crushing. From the rolls the ore is taken to 
 the storage bins above the Chilean mills, which are used for fine crushing. 
 The fine-crushing plant consists of four 6-ft. Akron Chilean mills. Three 
 of these are kept in operation all the time, easily crushing the required 
 amount of 10,000 tons per month, the third being held in reserve and 
 ready for use at any time. The mills can each crush from 100 to 130 tons 
 per day, according to the feed they receive. The ore is fed into them by 
 means of revolving-disk feeders which may be adjusted to any required 
 capacity. 
 
 The mills are fitted with square wire screen having 0.046-in. aperture 
 and 0.054-in. wire. The speed is about 33 r.p.m., and with this adjust- 
 ment, using the normal character of ore feed, they crush almost exactly 
 five tons per hour with an expenditure of 55 hp. With the mill in aver- 
 age condition the pulp delivered from it has the following approximate 
 composition: On 50 mesh, 21%; on 100 mesh, 12%; on 150 mesh, 5%; 
 through 150 mesh, 62 per cent. 
 
 The total steel consumed per ton of ore milled, using Midvale or Lat- 
 robe brands, amounts to 0.62 Ib. The crushing pressure of the mill 
 amounts to about 900 Ib. per sq. in., which is probably somewhat increased 
 by centrifugal force. 
 
 1 "Eng. and Min. Journ.," Nov. 12, 1910. 
 
 2 "Eng. and Min. Journ.," Aug. 5, 1911. 
 
86 
 
 DETAILS OF CYANIDE PRACTICE 
 
 Concentration a Feature. From the Chilean mill the pulp is led to the 
 Ovoca classifiers, which are double spiral-screw machines designed by 
 Philip Argall. The milling is done in cyanide solution containing \ Ib. 
 
 KCN per ton, and from that point the ore is constantly in solution. The 
 Ovoca classifiers give a sand practically free from slime with from 15 to 
 25% moisture, thus' performing the operations of separation and sand 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 87 
 
 de watering. The sand is sent to 20 Card concentrators. There are 22 
 installed and the pulp is distributed to the tables by means of an auto- 
 matic distributor which has been perfected in use at this mill. 
 
 The slime from the classifier is thickened in cones and sent to the slime 
 concentration department, which is equipped with 13 Deister tables and 
 four vanners. The Deister slime concentrator here performs equally as 
 good work as the vanners and the maintenance expense is less than one- 
 tenth of that of the vanners. 
 
 From the sand concentrators two products are obtained, a high-grade 
 concentrate, which is shipped direct, and a middling, which is reground 
 and reconcentrated. Originally it was designed to treat the concentrate 
 on the ground and a roasting plant for that purpose was erected, but it 
 was finally decided, on account of the character of the concentrate, which 
 is desired by the smelters, to ship it. The concentrate can now be con- 
 sidered as having its gold content definitely recovered as the other ele- 
 ments contained pay all its expenses, leaving the gold net. Under such 
 circumstances it would not be wise to attempt its local treatment. 
 
 High Value of Finer Material. In the case of the Independence ores 
 it is invariably true that the finest material carries the most gold. The 
 gold occurs mainly in films along the fracture planes or in small cavities, 
 the sulphide in the body of the rock being of low grade and often worth- 
 less. It is due to these basic facts that the crushing system in use was 
 devised and followed, it being briefly an attempt to liberate the sulpho- 
 tellurides to sufficient extent that they might be removed by concentra- 
 tion, leaving a sand tailing of low grade that might be lightly cyanided 
 and discarded. 
 
 The slime, containing the higher value, is also concentrated as closely 
 as possible and cyanided carefully by more efficient methods. .The slime 
 tailing has never been reduced as low as the sand. The guide now chosen 
 is to keep the sand tailing below $1 per ton in value, making a slime that 
 runs in the neighborhood of $2 per ton after concentration. The coarse 
 sand produces a high-grade concentrate, running from five to seyen ounces 
 per ton, a middling which is reground, in turn producing rich concentrate 
 and a proportion of slime, and a tailing of extremely low gold content, as 
 has been mentioned. This procedure enables the comparatively coarse 
 crushing to be practised in the Chilean mills and renders obtainable a 
 crushing cost which would be out of the question were total sliming re- 
 sorted to. 
 
 Sand Leaching. The sand and slime tailings are both pumped to the 
 cyanide plant where a pair of Ovoca classifiers separate them finally, the 
 sand being moved by a special conveyor into the sand-leaching tanks. 
 This conveyor is the usual "grasshopper" type, a long bar, supported on 
 wheeled trucks, having a number of hinged pusher blades working in a 
 
88 DETAILS OF CYANIDE PRACTICE 
 
 trough or launder. The launder is arranged so that openings can be 
 made into each tank at several different places. The sand is distributed 
 practically automatically, the final leveling of the top of the tank being 
 about the only hand labor required. A stream of solution is led into the 
 tank along with the sand, which is so free from slime that no trouble with 
 channeling or segregation of slime is experienced. 
 
 The sand thus laid into the tanks is treated with i-lb. cyanide solu- 
 tion for four days and is then sluiced out and run to waste. The sand 
 treatment is extremely simple; but since the precious-metal content is 
 small, the economical maximum of extraction is reached in this way. 
 
 Bromocyanidation of Slime. The separated slime from all depart- 
 ments is led into four continuous thickening tanks, the products being a 
 clear overflow and a thick slime which is pumped into a treatment tank 
 where it receives a six-hour treatment with f-lb. cyanide solution, and 
 afterward a four-hour treatment with bromocyanide in a separate tank. 
 The bromocyanide treatment is in accordance with the general practice, 
 the solvent being made from the usual "miners salt" in the ordinary way. 
 The only departure from generally accepted practice is that it is found 
 necessary to maintain a comparatively high alkalinity during the treat- 
 ment, general practice insisting on a neutral solution in most cases. 
 
 The tanks used for agitation are a special design, the features of which 
 are a pointed cone bottom and a cylindrical section of little height, a cen- 
 tral agitation pipe, into which air is admitted at the bottom, and having a 
 cone over its outlet, which is in about the middle of the vertical height of 
 the tank. The cone is open, with its vertex pointed down and is designed 
 to spread the outcoming pulp over the area of the tank. It is simply 
 another method of taking advantage of pneumatic agitation, the varia- 
 tions of which are without number. The accompanying flow sheet shows 
 the movement of pulp and solution and the machinery installed. There 
 is little novelty in the methods used in cyaniding the concentrate tailing. 
 
 The pulp is fed from a storage tank into a vacuum filter of the station- 
 ary or Butters type, in which the leaves are fixed and the movement is of 
 pulp and solutions. This filter is built after the Cassell design and was 
 one of the first of the kind to be used. It shows its early construction, 
 but is ^still doing efficient work. The leaves are made of canvas with a 
 filling of cocoa matting, and are stitched with wire instead of the usual 
 thread. This is said to prevent'ripping and'obviate a large portion of the 
 usual repair bills. Solutions for precipitation are clarified by passing 
 them through a filter press of the plate-and-frame type. 
 
 Precipitation on Zinc Shavings. Precipitation is in the ordinary man- 
 ner by the use of zinc shavings. There is little difficulty with the opera- 
 tion. The barren solution produced is used first on the concentration 
 tables as wash. The precipitate is not melted or refined at the plant, it 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 89 
 
 having been proved more economical to ship it to smelters for final treat- 
 ment. The precipitate is thoroughly dried, sampled and sealed up in cans 
 for shipment. The fact that precipitate of this class can be shipped at a 
 less cost than treating it on the ground is worthy of comment, for it is 
 generally considered better practice to handle it at the plant, where there 
 is less chance for loss due to differences of sampling, to say nothing of 
 transportation charges. This matter ought to be investigated, particu- 
 larly by plants situated conveniently to smelting installations, as I be- 
 lieve that generally no investigations are seriously made, it being taken 
 for granted that treatment on the ground is cheaper. 
 
 Extraction and Consumption of Material. The extraction totals 
 71.5% of the content, of which 43.65% is obtained by concentration and 
 27.85% by cyanidation. The consumption of chemicals is about 0.45 Ib. 
 of NaCN per ton, 0.3 Ib. of zinc, 2 2 Ib. lime and 0.4 Ib. of the bromine 
 salt. The mill consumes about 320 hp. and employs 35 men regularly in 
 the operations. The costs are moderate for the method followed and are 
 shown in the accompanying table. 
 
 [DISCUSSION 
 
 The Shipment of Cyanide Precipitate. In the JOURNAL of Feb. 8, 
 1913, Mr. Megraw comments on the shipment of cyanide precipitate -to 
 smelters as being cheaper than home treatment, and advises other plants 
 to investigate the matter. However, he seems to state the vital objec- 
 tion to it in the same paragraph, "the chance of loss due to difference in 
 sampling." 
 
 I have seen this thing tried out where I knew that every effort was 
 being made to give the shipper a square deal, and as a check, the shipper 's 
 material was treated by itself, as far as producing bullion and byproducts 
 went. The bullion alone carried more metal than the assays showed in the 
 original precipitate, while there was a whole string of metalliferous by- 
 products still to be heard from. 
 
 Of course the balance might be in favor of the shipper, I remember 
 hearing that one of the difficulties of the old Seattle Smelting & Refining 
 Co. was due to erroneous sampling on exceedingly high-grade material, 
 giving the shippers more than was coming to them, but usually the 
 sampler will err, although perhaps unconsciously, on his own side. 
 
 Considering the expense of tight coopering or bagging, freight, the 
 danger of theft in transit, and errors in sampling and assaying, it seems 
 that a plant shipping cyanide precipitate, silver sulphides, or like material, 
 is taking a long chance. 
 
 K. T. WHEELER. 
 
 Pittsburgh, Penn., Feb. 10, 1913. 
 
90 DETAILS OF CYANIDE PRACTICE 
 
 In the JOURNAL of Feb. 8, 1913, Mr. Megraw, in his excellent article 
 upon "Cyanidation at Cripple Creek," refers to the practice pursued at 
 the Independence mill of shipping the precipitate to smelters, saying: 
 "The fact that precipitate of this class can be shipped at a cost less than 
 that for treating it upon the ground is worthy of comment, for it is gen- 
 erally considered better practice to handle it at the plant where the chance 
 of loss, due to differences in sampling, is less, to say nothing of transporta- 
 tion charges. This matter ought to be investigated, particularly by 
 plants situated conveniently by smelting installations, as I believe that 
 generally no investigations are seriously made, it being taken for granted 
 that treatment on the ground is cheaper." 
 
 In commenting upon this feature of Mr. Megraw's article, Mr. 
 Wheeler, in the JOURNAL of Feb. 15, 1913, doubts the wisdom of this 
 course for various reasons, although he gives no definite figures to support 
 his opinion. Surely so experienced an operator as Mr. Argall is not 
 shipping his precipitate, in preference to local reduction, without good 
 reason. The fact that this plant is situated convenient to smelteries, and 
 that gold precipitate is produced, may have its influence. In general, 
 smelters do not buy this material upon the result of corrected assays, and, 
 as it is a well known fact that the percentage of correction upon the assay 
 of a product carrying largely gold is not so great as upon one in which sil- 
 ver predominates, it will be readily seen that the difference in favor of the 
 smelter, arising from this cause, would not be so great as in the latter case. 
 
 The transportation problem is a serious one and, perhaps, is at its 
 worst when long distances have to be covered by mule back or ox cart and 
 steamer. I have seen various methods of packing tried, such as sacking 
 in canvas and burlap, paper sacks inside of canvas protected by burlap, 
 boxing, etc., but the only satisfactory method is to pack it in hermetically 
 sealed tin cans protected by wooden cases. A satisfactory container for 
 this purpose can be readily obtained at any cyanide plant by carefully 
 opening and preserving the tin-lined wood cases in which the cyanide is 
 received. These should be washed and dried. The precipitate is then 
 placed in them, the tin cover soldered on, and the wood top securely 
 fastened by nails or screws. A binding of light strap iron greatly 
 strengthens the package and is desirable if it is to go any distance. 
 
 Cyanide operators would welcome comparative figures from Mr. 
 Argall, showing the advantage of shipping precipitate instead of bullion. 
 Various plants, with which I have been connected in the past, have 
 shipped precipitate and then have later installed melting furnaces and 
 shipped bullion. In every case it was felt that there was a distinct advan- 
 tage, although no accurate comparisons were made, in favor of producing 
 bullion, and in no case did any of these plants return to shipping precipi- 
 tate after having once produced bullion. 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 91 
 
 A number of years ago I had an opportunity of making a thorough and 
 fair comparison between the relative merits of shipping precipitate and 
 the production and shipping of bullion, when Charles Butters requested 
 me to go to Virginia City, Nev., and thoroughly investigate this feature 
 of their practice. At this time the Virginia City plant was treating a 
 considerable tonnage of Tonopah ore and old Comstock tailing. Both 
 electrical and zinc precipitation were in use and the precipitate resulting 
 from the two methods was quite different in character. The electrically 
 precipitated material was high in lime and copper and also contained 
 some lead. The zinc-box precipitate was similar to that produced in 
 plants employing that method of precipitation when treating a silver-gold 
 ore, except that it was not quite so high grade as that produced by present- 
 day practice. The precipitate from the electric boxes formed the bulk of 
 the product. Both classes of precipitate contained mercury and it 
 was the practice to retort for its recovery until the Comstock tailing, 
 which was its source, finally became exhausted, when retorting was 
 discontinued. 
 
 From the beginning of operations at this plant it had been the practice 
 to ship the precipitate, and this was continued long after the other Butters 
 plants had found it to their advantage to ship bullion. It was generally 
 supposed, owing to the refractory nature of the precipitate, and its low 
 gold and silver content, that there was every advantage in favor of ship- 
 ping precipitate rather than bullion. 
 
 I have no reason to doubt the accuracy of the sampling and assaying 
 of the smelters to whom the precipitate was usually shipped, as their 
 results generally agreed with the independent sampling and assaying at 
 the mill; but, of course, it is to be understood that neither party made 
 corrected assays. It will, therefore, be seen that the factor of dealing 
 with an unscrupulous smelter does not necessarily enter into the case in 
 hand. 
 
 For the purpose of experimentation there was erected, under my direc- 
 tion, a single stationary pot furnace and a small cupeling furnace. It was 
 planned to carry on experiments to determine the relative advantages of 
 fluxing and melting directly in graphite crucibles, producing a bullion 
 containing most of the copper; and melting in the cupel furnace with 
 litharge and other fluxes, running off the slag and cupeling the lead, thus 
 producing a high-grade bullion. A number of experiments were carried 
 out along both lines and it was finally decided that it would be more 
 advantageous to adopt the method of melting in pots. 
 
 The results obtained with the cupel furnace all showed a substantial 
 gain over shipping, but as the pot method was the one finally adopted it 
 will suffice to give comparative figures for that method and shipping. 
 For that purpose I will give the results of two experiments made upon two 
 
92 DETAILS OF CYANIDE PRACTICE 
 
 samples taken from the precipitate comprising two separate and distinct 
 shipments to the smelter. 
 
 These large samples were taken at the time that the precipitate was 
 being sampled for assay prior to shipment. Every precaution was taken 
 to have them truly representative of the mass of the material shipped, and 
 in my opinion they were even more representative of the whole mass than 
 the small samples taken independently at the mill and smeltery for assay. 
 Assays upon these independent samples generally checked closely. 
 
 In the first shipment the fine ounces of silver and gold realized by 
 smelting 460 Ib. of precipitate and marketing bullion were 2302.60 and 
 40.3595, respectively. The fine ounces in 460 Ib. of precipitate, as shown 
 by the assays at the smeltery and mill, and upon which basis the lot of 
 precipitate was sold, were 2250.01 of silver and 39 . 857 of gold. The gain 
 in favor of shipping bullion was, silver, 52.59 fine ounces; gold, 0.5025 
 fine ounce. 
 
 COMPARATIVE COST OF SHIPPING 460 LB. OF PRECIPITATE AND 
 PRODUCING AND SHIPPING THE BULLION FROM 460 LB. OF 
 
 PRECIPITATE 
 
 Sampling and preparing for shipment $2. 16 
 
 Drayage . 55 
 
 Express 15 . 94 
 
 Sampling at smeltery 1 . 15 
 
 Treatment charges 22 . 55 
 
 Deductions, gold. 16 . 64 
 
 Deductions, silver , 25 . 86 
 
 Total cost of shipping 460 Ib. precipitate $84.85 
 
 Cost of melting at I0.01 1 per oz. dore bullion $32.55 
 
 .Canvas on bars, etc . : 0.30 
 
 Drayage . 48 
 
 Express 1 1 . 86 
 
 Refining charges 33 . 38 
 
 Total cost of melting 460 Ib precipitate and shipping 
 
 as bullion $78.57 
 
 Net amount realized shipping bullion was $2074.04, and that realized 
 shipping precipitate was $2026.88, a difference in favor of shipping 
 bullion of $47.16. 
 
 This would amount to a saving of $0.02079 per fine oz. of dore bullion 
 (fine ounces gold plus fine ounces silver) . 
 
 In the second shipment the fine ounces of silver and gold realized by 
 melting 300 Ib. of precipitate and marketing bullion were 1297.71 oz. 
 silver, and 21 . 532 oz. gold respectively. The fine ounces in 300 Ib. of 
 
 1 This figure includes the cost of treating the byproducts. It is unusually high on 
 account of the nature of the precipitate. 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 93 
 
 precipitate, as shown by the assays at the smeltery and mill, and upon 
 which basis the lot of precipitate was sold, were of silver, 1236.94 and of 
 gold, 21 . 61. The gain in favor of shipping bullion was 33.77 oz. of silver 
 and 0.078 oz. of gold. 
 
 COMPARATIVE COST OF SHIPPING 300 LB. OF PRECIPITATE AND 
 PRODUCING AND SHIPPING THE BULLION FROM 300 LB. OF 
 
 PRECIPITATE 
 
 Sampling and preparing for shipment $1.41 
 
 Drayage . 36 
 
 Express 11 . 14 
 
 Sampling at smeltery . 80 
 
 Treatment charges 12 . 83 
 
 Deductions, gold 9 . 08 
 
 Deductions, silver 14 . 66 
 
 Total cost of shipping 300 Ib. precipitate $50.28 
 
 Cost of melting at $0.01 per oz. dore bullion $12. 11 
 
 Canvas on bars, etc 0.10 
 
 Drayage 0.17 
 
 Express 5 . 19 
 
 Refining charges 12 . 51 
 
 Total cost of melting 300 Ib. precipitate and shipping 
 
 as bullion , $30.08 
 
 The net amount realized when shipping bullion was $1167.66, and the 
 net amount realized when shipping precipitate was $1129.49, a difference 
 in favor of shipping bullion of $38.17. This would amount to a saving of 
 $0.02969 per fine oz. of dore bullion. 
 
 The saving for four consecutive months, when the shipments of dore 
 bullion amounted to over 50,000 oz. per month, was in July, $1090.52; 
 August, $1056.21; September, $1178.67; October, $1003.61; a total of 
 $4329 saving for the four months. 
 
 Although the cost of melting (Ic. per ounce) was unusually high at this 
 plant, due to the refractory nature of the precipitate, the saving in favor of 
 local melting and the shipping of bullion is apparent. I have obtained 
 costs of melting as low as O.lc. per ounce in Central America, and others 
 have done much better than this where a large volume of high-grade silver 
 precipitate was melted under the most favorable conditions. 
 
 Within certain limits the treatment charge upon bullion is usually 
 based upon a flat rate per gross ounce, so that while apparently the rate 
 is no higher upon bullion containing considerable base material, as a 
 
94 DETAILS OF CYANIDE PRACTICE 
 
 matter of fact as the amount of base material increases, the rate per fine 
 ounce of dore also increases in direct proportion to the increase of base. 
 To illustrate how this might affect the saving due to melting, I have cal- 
 culated the saving which would have resulted if bullion 950 fine had been 
 shipped instead of the base copper bullion from the plant in question. 
 During the four months mentioned, the saving in July would have been 
 $1557.36, that in August $1508.40, in September $1683.24, and in Oc- 
 tober $1433.25. It will, therefore, be seen that where a high-grade pre- 
 cipitate is produced which can be converted into comparatively high-grade 
 bullion at a low cost, the saving by local melting in a large plant is greater 
 than that indicated by the figures which I have given. 
 
 The saving indicated in this case is plainly due to two causes : First, 
 that the ordinary cyanide plant can actually convert silver-gold precipi- 
 tate into bullion cheaper than the charge made by the smelters for this 
 service; second, that with local melting and the proper treatment of the 
 byproducts, more bullion is realized than that indicated by the ordinary 
 uncorrected assays. 
 
 It is only fair to say that these comparisons were made a number of 
 years ago and that the rates of treatment for precipitate and bullion taken 
 are those obtaining at that time. 
 
 G. H. CLEVENGER. 
 
 Palo Alto, Calif., Mar. 16, 1913. 
 
 In the discussion regarding the shipment of cyanide precipitate, I 
 would like to direct attention to one reason which may account, in some 
 cases, for low results when shipping bars. This is the shipment of imper- 
 fectly refined bars, which yield such erratic assay results that the pur- 
 chaser must necessarily put a low valuation on them for his own protec- 
 tion. In the annual report of the British Mint for 1896, Roberts-Austen 
 describes a cyanide bar weighing 393 oz., which was paid for at 965. 
 This bar was refined by itself and yielded gold worth 1028. The 
 shipper of the bar lost 63 or over $300. After paying for the refining, 
 such a loss might easily be fatal to shipment of bars as against precipitate 
 in a comparison of costs. 
 
 In the JOURNAL for Apr. 13, 1912, 1 have given.a table of erratic assays 
 of cyanide bars from the Mercur mine. It would be a hazardous under- 
 taking to determine from these assays just how much gold these bars 
 contained. Some bullion deposited by the Mercur mine just before 
 closing down was better refined and higher grade. Samples from three 
 bars of these later shipments were assayed in duplicate in three labora- 
 tories with the following results: 
 
PRACTICE AT CRIPPLE CREEK, COLORADO 
 
 95 
 
 . 
 
 1st Bar gold 
 
 2d Bar gold 
 
 3d Bar gold 
 
 1st Laboratory 
 
 920 1 fine 
 
 916 3 fine 
 
 884.2 fine 
 
 2d Laboratory 
 3d Laboratory 
 
 .2 fine 
 920.8 fine 
 .8 fine 
 920.1 fine 
 .3 fine 
 
 .7 fine 
 916.8 fine 
 .5 fine 
 916.5 fine 
 .6 fine 
 
 .^fine 
 884.5 fine 
 885. fine 
 884.0 fine 
 .3 fine 
 
 These results show a vast improvement over the former assays of 
 Mercur bars. 
 
 FKEDERIC P. DEWEY, 
 
 Assay er, Mint Bureau. 
 Washington, D. C., Apr. 28, 1913. 
 
CHAPTER IX 
 CONTINUOUS DECANTATION OF SLIME 
 
 The advent of a new process is not regarded with excitement in the 
 metallurgical world. Too many of them have appeared, led a struggling 
 existence for a few months, or longer in some cases, and then disappeared 
 without leaving many ripples in the places where they existed. Develop- 
 ment of existing and proved processes, however, is regarded with interest, 
 and as each step in advance proves its worth it is incorporated into the 
 system of approved and satisfactory methods. 
 
 In the days when the decantation method of treating slime was the 
 only one known, operators made serious efforts to improve it, particularly 
 
 OPHIR MILL, OPHIR, COLO. 
 
 to find some way of avoiding the losses which occurred in discharging 
 residues containing moisture charged with both cyanide and valuable 
 metal in dissolved form. The necessity for improvement brought forth 
 the slime filters, and for a long time experiments in decantation were 
 discontinued. After many years of filtering, however, the suspicion 
 remains that the decantation process might be improved so as to compete 
 with filtration, the cost of operation and maintenance of existing filtering 
 apparatus going far toward strengthening that suspicion. It may be said 
 
 96 
 
CONTINUOUS DECANTATION OF SLIME 97 
 
 that the cost of slime filtration varies from lOc. to maximum figures which 
 would be regarded with suspicion were I to mention them. Including 
 cost of operation, maintenance and loss in dissolved metal, the minimum 
 figure above mentioned is extremely low and I doubt whether there are 
 any number of plants in existence attaining it. It will be seen that there 
 is, then, an opportunity for improvement, for if any procedure can suc- 
 cessfully reduce these costs or losses, or even equal them without the use 
 of complicated and expensive machinery, it will stand a good chance for 
 approval and success. 
 
 Development of Proposed System. Lately some progress has been 
 made toward developing a process of continuous decantation, which is 
 nothing new, but a development of the methods used before the filters 
 came into use. In the old intermittent decantation process the slime 
 after being agitated with a quantity of solution was allowed to settle, the 
 solution decanted off and a new bath of solution put on. This was in 
 turn agitated, allowed to settle and again decanted, the process being 
 carried on as many times as was thought necessary. The efficiency of 
 fresh solution washes was recognized, particularly when this solution was 
 barren or freshly made up or regenerated, but the difficulty with this 
 system was the enormous quantities of solution to be handled in addition 
 to the impossibility of reducing the moisture content of the final pulp to 
 such a point that too much dissolved metal and valuable cyanide should 
 not be thrown away. This new development attempts to accomplish a 
 solution of both difficulties by means of a* continuous-decantation and 
 thickening process using solutions flowing opposite to the course of the 
 pulp. The fact that this method has seemed feasible to a number of 
 competent metallurgists and is actually in operation in a number of in- 
 stances makes it worthy of attention and in this paper two such plants 
 will be described. 
 
 Milling in Cyanide Solution. The plants in question are the mills of 
 the Ophir Gold Mines, Milling & Power Co., at Ophir, San Miguel County, 
 Colorado, and of the Blue Flag Gold Mining Co., in the Cripple Creek 
 district. Both are of recent construction, and while operations have not 
 been carried on long enough to provide satisfactory details of cost and 
 maintenance, the metallurgy has shown sufficient promise of success to 
 warrant consideration. 
 
 The Ophir mill crushes ore with stamps, the installation including 20 
 of 850 Ib. each with 6-in. drop and 104 drops per min. From the stamps 
 the pulp goes to a Dorr classifier, where the slime is passed to a Dorr Thick- 
 ener and the sand reground in a Hardinge mill, from which it is pumped 
 back to the classifier, the circuit being closed and only solids of sufficient 
 fineness reaching the thickener. 
 
 A point of interest is that the overflow solution from the first thickener 
 
98 
 
 DETAILS OF CYANIDE PRACTICE 
 
 is the only one precipitated. It is passed through a clarifier and precipi- 
 tated with zinc dust. The thickened pulp is passed to two agitation tanks 
 of the Dorr type, through which it passes in series and where it is calcu- 
 lated that the extraction is practically completed. Leaving the agitators, 
 
 Tank 
 
 
 
 [ Stamps 
 
 
 ISOWreKCNI.O\ 
 
 
 \dOOT.5oI.P A J.O 
 
 
 r "* 
 
 A 
 
 ISOT.Wa-t-er 
 
 No.4Dorr 
 Thickener 
 33x12' 
 
 -O /OI//.JO/. | 
 
 " V 
 
 No.SDorr^ 
 
 Thickener 
 33'xl2' 
 
 -of--$" 
 /AU. 0.035 
 
 tycrt.o.31 
 
 PA.O.Zl 
 
 
 ^ \L> $ 
 \U.O.Q1 
 KCN.0.62 
 PA.QC2 
 
 i, 
 
 .740 T.SIime \I50 T.SIimeAU. 0.20 KCN.0.31. 
 
 ISOT.Sol. 
 
 ISOT.Sol. AU.0.03SP.A.0.3T Tai ' S 
 
 FLOW SHEET OF OPHIR MILL. 
 
 the pulp is delivered to the first of a series of four thickeners, through 
 which it passes with successive dilutions until it is finally discharged from 
 the last one, washed practically free of gold in solution. 
 
CONTINUOUS DECANTATION OF SLIME 99 
 
 The overflow solution from the first of these thickeners is returned to 
 the mill solution tank, where it is used in milling and classifying, the 
 result being a concentrated solution for precipitation. The barren 
 solution from precipitation goes to dilute the inflow into the second 
 thickener, the overflow from which goes back into the first. The accom- 
 panying flow sheet shows the movement of pulp and solution throughout 
 the mill. It will be noted that water is taken into circulation at the 
 end of the washing period, the logical point of entry for it, and prac- 
 tically replaces the solution which comes with the solids to that point. 
 
 Progress of Solutions. It will also be noticed that the progress of 
 solutions is contrary to the direction of pulp flow, the solutions being 
 constantly enriched. The figures given in the flow sheet are based on ore 
 carrying $5 in gold and the contents of solutions are given in pounds of 
 KCN and lime. The calculations of thickening are based on withdrawing 
 a pulp from each thickener which consists of half solids and half solution. 
 This is accomplished in practice, in fact a slightly thicker pulp can be ob- 
 tained, thus increasing the efficiency of the process. It has been in opera- 
 tion only a short time but the results obtained have been in complete 
 accordance with the figures shown. It will be seen that the installation is 
 simple and inexpensive, may be operated by a minimum amount of labor 
 and accomplishes a washing of pulp and removal of dissolved metals that 
 is, to say the least, comparable with good filtration work. 
 
 The lime in this mill is added at the bins and goes through the circula- 
 tion with the pulp. The consumption amounts to about 0.9 Ib. per ton 
 of ore. The value of the process depends a great deal on using solutions 
 of low cyanide content and the existence of a plentiful water supply, which 
 conditions are satisfactorily met in this case. The flow sheet shows all 
 the details of the process and apparatus and no further explanation is 
 needed. 
 
 The Cripple Creek Installation. The Blue Flag mill is situated be- 
 tween Cripple Creek and Victor in Colorado. The ore averages between 
 $5 and $6 and is to a great extent from the dumps. The coarse ore is 
 dumped on to a steel conveying and picking belt where a portion of the 
 barren rock is removed. From the picking belt it is passed through^ a 
 12X18-in. Dodge crusher and through a Symons disk crusher from which 
 it emerges reduced to about f-in. cubes. The finely crushed ore is then 
 delivered to a special form of Chilean mill which consists of a concave die 
 ring 7 ft. in diameter, over which convex rollers pass. The rollers are 
 small, weighing only 700 to 800 Ib. each. The mill makes 36 r.p.m. and 
 grinds the ore, in cyanide solution of 1J per ton strength, through a 30- 
 mesh screen. Solution used at the rate of about five to one. 
 
 The pulp as it comes from the mills is delivered to the series of agi- 
 tating tanks through which it passes continuously. These tanks are 14 
 
100 
 
 DETAILS OF CYANIDE PRACTICE 
 
 ft. diameter and 16 ft. deep having cone bottoms at an angle of 55. The 
 agitation is pneumatic, elevating the pulp through a central tube. 
 
 This point in the process is open to criticism, as the pulp from the 
 mills is in too coarse condition for economical agitation, to say nothing 
 of the metallurgy of it. If it is true that finer crushing is not necessary, 
 then it would seem reasonable to separate the coarse portion of the solids 
 and treat it separately by some more economical means. The pulp under- 
 going agitation has the following approximate grading analysis: On 30 
 mesh, to 0.5%; on 40 mesh, 4 to 9%; on 60 mesh, 22 to 24%; on 80 
 mesh, 35 to 36%; on 120 mesh, 58 to 60% and through 120 mesh, 40 to 
 42%. The grading statement is cumulative. Pulp of this class requires 
 excessive power to keep it in circulation. 
 
 Solution 
 
 Overflow 
 
 Clarifier 
 Precipji-ai-ion 
 
 Wear 
 Overflow 
 
 DIAGRAM OF CONTINUOUS COUNTER-CURRENT DECANTATION AT BLUE FLAG MILL. 
 
 Continuous Washing. The pulp is in circulation through the agita- 
 tion tanks for about nine hours and the extraction in them amounts to 
 about 70%. In considering the extraction results it must be remem- 
 bered that this is on the refractory ore of the Cripple Creek district. 
 The cyanide consumed in the process is about 0.35 Ib. of which 0.15 Ib. 
 is mechanical loss. Lime is added to the ore bins and progresses with the 
 pulp, the consumption being about 2? Ib. per ton milled. 
 
 The pulp from the agitators is taken to a series of four thickeners and 
 is washed through them after the manner described in the Ophir mill. 
 The accompanying diagram shows the flow of pulp and solutions through 
 them. In the case of the Blue Flag mill, also, it has been found possible 
 to secure a thickened pulp containing less than 50% moisture. In this 
 instance, also, it has been found that the calculations, based on 50% 
 thickening, are borne out in practice. 
 
 Other Combinations. It should be remembered that this development 
 is not recommended to cure all the ills that cyaniders are heir to, but 
 is a progression along conservative lines and one that should eventually 
 lead to a fixed system available in cases where the character of the ore 
 
CONTINUOUS DECANTATION OF SLIME 101 
 
 will bear such treatment and where other local conditions are favorable. 
 It is a system which, while not yet perfected, will be well worth following. 
 It is easy to see that other combinations are possible, such as using a 
 greater number of thickeners, of this type or any other satisfactory one, 
 and by precipitating two or more different solutions. The two installa- 
 tions mentioned are not by any means the only ones using it. They may 
 not even be the ones where it is most advanced, the idea in presenting the 
 matter being principally to draw attention to the fact that there is a 
 system in course of development which may possibly lead to decided 
 economies in the cases of ores to which it is applicable. 
 
CHAPTER X 
 PRACTICE AT TONOPAH 
 
 The Tonopah district offers to the student of contemporary metal- 
 lurgy what is probably the most interesting demonstration of the efficiency 
 of the cyanide process applied to silver ores. This is not to say that the 
 general methods in use are original, as they are not, but the application 
 of these methods has been attuned to the requirements of the particular 
 ores to be treated and the problems have been attacked and solved with 
 praise worthy conservative judgment. It is both interesting and note- 
 worthy that in all the Tonopah district there is not one idle reduction 
 plant, nor one which has been designed by a tyro to include exaggerated 
 ideas or " freaks." All the plants conform to standard practice, are 
 built after tried and proved plans and embody only such variations as 
 have seemed best adapted to care for the characteristics of the local ores. 
 
 It is also noteworthy that there is not a mill in Tonopah which has not 
 paid for itself out of profits won from the ores of the mine it was designed 
 to treat, the only exception at the present time being one, or possibly two, 
 of the most recently built mills which have not yet had time to accomplish 
 this feat, but which will, without any question, complete the requirements 
 within a few months. Possibly the most noteworthy accomplishment of 
 this kind is that of the West End mill, which returned sufficient profit 
 within seven months to pay for the installation. It is to be remembered 
 that this is an old mill, rebuilt twice before reaching its present condition, 
 but still performing admirable work at a cost which is comparable with 
 that attained by the more recent plants. 
 
 The Ores of Tonopah. The geology and character of the Tonopah 
 ores have been sufficiently described in the technical press from time to 
 time and it will be sufficient to consider them here only in Delation to 
 their attitude toward cyanidation. They may be said to be of medium 
 hardness and crush without any great amount of trouble. This statement 
 is made not so much in considering the ores as a single problem, but as 
 comparing them with the rock treated in the cyanide plants of other 
 districts. For instance, it might be said that the Tonopah ores are some- 
 what harder than that of the Porcupine district, which differ essentially, 
 of course, in character, and not so hard as many of those of the Cobalt 
 district. They are perhaps about equal to most of the ores of the Pozos dis- 
 trict of Guanajuato and some of those of the Guanajuato and Pachuca 
 
 102 
 
PRACTICE AT TONOPAH 103 
 
 districts of Mexico. They may, briefly, be said to be medium ores as 
 far as resistance to fine reduction is concerned. 
 
 There are under treatment, as is usual in districts as comparatively 
 recent as Tonopah, both oxidized and sulphide ores. The oxidized ores 
 have not presented any great difficulties of metallurgy, but the sulphides 
 have, in many cases, presented a complexity of nature which is not so 
 simply handled. Reference to the current descriptions of these ores will 
 show their character, but it is probably not superfluous to call attention 
 to the fact that in some of the high-grade sulphide ores mercury has been 
 found in small quantities. I have seen a specimen of sulphide ore which 
 shows a quantity of cinnabar. These sulphides are not always simply 
 treated and in some cases, as will be noted, it was found advisable to 
 remove them by concentration before proceeding to the cyanidation of 
 the bulk of the ore. 
 
 The mill of the West End Consolidated Mining Co. is situated at the 
 southeast edge of the town of Tonopah. At the mine shaft the ore is 
 crushed to break up all large boulders. The ore is brought to the mill in 
 auto trucks and delivered into a bin, from which it passes through a 
 10X20-in. Blake crusher. A bucket elevator delivers the crushed ore 
 into a 32X72-in. trommel with 1-in. apertures, the oversize going to a 
 No. 3 Kennedy crusher. The crusher product joins the undersize from 
 the trommel and is carried by a belt conveyor with 14 incline, 14-in. 
 belt, to the 200-ton battery bin. 
 
 Stamp Installation. There are 10 stamps of 1200 Ib. and 10 of 1300 
 lb., fed by means of suspended Challenge feeders. The stamps drop 
 through 6J in. 101 times per minute. The stamp duty at present is 
 about 7.5 tons per day per stamp. 
 
 From the stamps the pulp is fed into two Dorr classifiers, which deliver 
 into two 5 X 18-ft. tube mills. The classifiers are placed close in front of 
 the batteries, and the tube mills are ranged with their long axes parallel 
 to the batteries, the discharge end of one of them fronting the feed end 
 of the other. This has been done with the idea of occupying the least 
 possible space in the direction of the mill fall. As the mill is a recon- 
 structed one, having formerly been the first amalgamating mill in the 
 district, a free hand in designing the arrangement was not obtainable, 
 but the advantages have been well handled and the arrangement is 
 such as to permit economical handling of the material. 
 
 Tube-Mill Linings. It will be noticed that the tube mills in use are of 
 large diameter and short length. It seems that this type is meeting with 
 almost universal approval from metallurgists of the present day, the con- 
 clusion being that in the former long mills there was a great deal of space 
 at the discharge end which did not perform any useful work. The change 
 toward larger diameters and less length has resulted in an increased pro- 
 
104 
 
 DETAILS OF CYANIDE PRACTICE 
 
PRACTICE AT TONOPAH 105 
 
 duction of slime at a power consumption, per ton of ore, equal to or less 
 than with the long tubes. There is an added advantage in the smaller 
 floor space occupied. 
 
 At the West End mill the linings used in the tube mills are of the 
 smooth, cast-iron type, as hard as they can be made. The operators 
 claim that with this lining the power consumption is less than when silex 
 is used or any of the ribbed types and that the output is satisfactory in 
 quantity and character. In this point the investigator has to face a 
 peculiar problem which seems to have no direct solution. Smooth linings 
 for tube mills were used in the days long ago and were discarded in most 
 places for silex or the ribbed types, where the wear does not come directly 
 upon the lining, or at any rate, is not supposed to do so. Yet we have 
 here a recurrence to the older type, with the claim of better results. This 
 circumstance would not be so strange if the operators in the district 
 working upon the same character of ore were in accord, but they are not. 
 The Belmont mill has made tests using silex in competition with smooth 
 linings and giving preference to the silex. Tests have also been made at 
 the West End mill, and the result is said to be in favor of the smooth 
 lining. 
 
 In cases of this kind no definite conclusions can be drawn at the 
 present time, the only recourse being to await developments, it being 
 more than probable than the operators in the district will eventually 
 agree upon the most effective form. It is noteworthy that both the 
 smooth cast-iron linings and the silex linings were tried out in Mexico 
 years ago and discarded in favor of ribbed linings. The Komata form 
 was tested here, but the increased power required, together with its 
 high cost, have prevented its use. At the Goldfield Consolidated mill, 
 however, these linings are in use and it is stated that they are the most 
 economical and effective ever tried. It is true that there is an increase 
 in the power required to drive the mill, but the increased production 
 more than compensates for the additional power used. 
 
 When the West End plant was first started both of the tube mills were 
 moved by a 100-hp. motor and the pebble charge was carried at or slightly 
 below the center of the mill. The power was ample with this arrange- 
 ment. With the desire to increase capacity, experiments were made with 
 the object of securing greater capacity by increasing the charge of pebbles 
 in the tube mills. It was soon found that the power was insufficient, but 
 as a result of many tests, the 100-hp. motor formerly driving the two mills 
 was replaced by a 150-hp. motor and the pebble charge carried six inches 
 above the mill center. 
 
 Solely by this change the capacity of the plant was increased from 100 
 to 150 tons per day, the increased work performed by the tube mills 
 allowing a coarser screen to be used on the batteries. The actual power 
 
106 DETAILS OF CYANIDE PRACTICE 
 
 taken by the two mills is from 120 to 125 hp. This result is noteworthy* 
 and has the effect of rendering the use of the counter-spiral discharge un- 
 suitable for a mill of the kind, as the high pebble charge is likely to force 
 out some of the pebbles through the discharge end. A grating is usually 
 used in mills of the kind, which, of course, precludes the feeding of pebbles 
 at the discharge end. Experiments with tube mills of large diameter and 
 varying pebble charges ought to be productive of interesting results. 
 
 Concentrating the Slime. The tube-mill product is returned to the 
 classifiers by means of a bucket elevator and the slime from the classifier? 
 is taken to the concentrating department of the mill which is of recent in- 
 stallation. The slime is led to four 8-ft. Callow thickening cones, the 
 thickened slime being concentrated on 12 Deister slime concentrators. 
 After concentration the slime tailing from the concentrators is returned to 
 four Dorr thickeners, 16X10 ft. each, part of the overflow being used for 
 the concentrator-table washes and returning with the pulp to the thick- 
 eners. The slime pulp contains about 90% through a 200-mesh screen. 
 
 Four diaphragm pumps are used for lifting the thickened slime from 
 the thickeners into the agitation tanks. The suction of these pumps is 
 connected directly to the outlet from the thickeners and consequently any 
 regulation of thickener discharge has to be made by varying the adjust- 
 ment of the pumps. Personal experience has not been such as to inspire 
 a great deal of confidence in diaphragm pumps, as they have usually 
 proved unreliable and likely to lose their priming or break the diaphragms 
 at most inopportune times, but at the West End mill they are working 
 successfully and have given entire satisfaction. Due to the fact that they 
 are essentially a suction pump, they have been placed at a height where 
 their delivery can flow by gravity into the agitation tanks. 
 
 The system of having the pump suction connected directly to the 
 thickener has the advantage of avoiding spilling of the pulp and makes a 
 direct and tight connection from the thickeners to the agitation tanks, but 
 the disadvantage is that adjustment or change of the thickener discharge 
 has to be made on the pumps, either by changing the throw or speed, 
 making the operation slow and necessarily performed at a distance from 
 the thickener itself. It seems possible that a preferable arrangement 
 would be to allow the thickened slime to fall directly into an appropriate 
 sump from which it could be picked up and delivered to the elevation re- 
 quired. This change would allow of prompt and effective regulation of 
 the thickener outflow. 
 
 Agitation System. There are four agitation tanks, each 24X8 ft., 
 arranged for continuous agitation and carrying Trent agitators. The 
 continuous arrangement is such that in the passage from tank to tank the 
 pulp is required to pass through the pump suction and enter each tank 
 through the Trent agitators, thus insuring the maximum agitation and 
 
PRACTICE AT TONOPAH 
 
 107 
 
 avoiding short circuits across the top of the tank. The centrifugal pumps 
 used are the Kelly & Campbell, a local make which has been designed to 
 make replacement of worn parts easy and rapid, and the wearing part or 
 
 200 Ton R.R. Bin 
 1-10x20 "Blake Crusher 
 Be It a net Bucket Elevator 
 
 l-32x iz"jrommel, /"Apertures, Undersize l'/ 4 n 
 
 Battery 
 Solution 
 Storage 
 
 u 
 
 J 
 
 J-No.3 Kennedy Crusher 
 I- 14" Be It Conveyor, Id" Incline 
 
 200-ton Battery Bin 
 
 4- Suspended Challenge Feeders 
 
 4-5 Stamp Batteries (2-!200/b. 2-l300lb\ l l ' n Dr0 P 5 
 
 / Qp- Drop 
 
 2~ Dorr Duplex Classifiers 
 
 \ 2-5x18 Tube Mills 
 
 \ 
 
 > 
 
 h Bettand Bucket Elevator 
 
 4-8' CaKow Cones 
 
 12- Dei sfer Slime Concentrators 
 
 4-l6xIO'Dorr Thickeners 
 
 4~ Ho.Z Could Diaphragm Pumps 
 
 4-24x8' Trent Ag if atorTanh, 4"Centrifugal 
 
 Pumps 
 l-28'x22' Dorr Thickener 
 
 1-8x28' Stock Tank 
 
 I.-IOO Leaf Butters Filter, 5%"x8"Cycloidal 
 
 Vacuum Pump 
 Slime to Waste ^ 
 
 o 
 
 Solution 
 
 Pregnant Solution Tank 
 l-Ba-ltery Solution Sump 
 Pregnant Solution Storage 
 6-6'Compartnienf Zinc Boxes 
 
 I- Dry ing Pan 
 I -Fa her du Faur fie If ing Furnace 
 
 \Bullion 
 
 SlagtoSmeltei 
 
 FLOW SHEET OF WEST END MILL. 
 
 liner is designed to require no machining so that it can be chilled all over. 
 These pumps are used throughout the mill and, in fact, throughout the 
 district, and have given entire satisfaction. 
 
108 DETAILS OF CYANIDE PRACTICE 
 
 The difficulties encountered with Trent agitators at other mills, 
 notably the Hollinger, at Porcupine, Canada, and at the Mexican, in 
 Virginia City, Nev., are not found at the West End mill, nor in some other 
 mills in the district where they are largely used, as will be noted. Here 
 they give satisfactory results and the operators are well pleased with their 
 performance. The centrifugal pumps used have 4-in. delivery and give a 
 pressure of from 14 to 16 Ib. per sq. in. The agitator arms make 3J 
 r.p.m. and the operation of the agitator is said to require from 7 to 9 hp., 
 varying, naturally, with the consistency of the pulp and somewhat on 
 other temporary variations. 
 
 From the agitation tanks the pulp is elevated by means of a 6- in. 
 centrifugal pump of the type already mentioned into a 28X22-ft. 
 Dorr thickener, the overflow solution going to the pregnant-solution 
 tank and the thickened slime into an 8X28-ft. stock tank, which feeds 
 the filter. 
 
 The filter is a 100-leaf installation of the usual stationary vacuum type 
 and presents no novelties in the system of operation. The slime is of 
 such character that a light, soft, spongy cake can be made which is easy 
 to wash, a cake 1J in. thick being readily made and washed. As 
 proof of the ready washing character of the material the operators have 
 shown that shortly after one replacement of the contained solution is 
 made, the value of the effluent solution drops down nearly to the value of 
 the wash solution used. By a " replacement " is meant the passing 
 through the cake of a quantity of solution equal to the amount contained 
 as moisture in the cake. By passing another replacement of water 
 through the cake the cyanide-bearing solution is nearly entirely displaced, 
 the water taking its place. It should be remembered, however, that a 
 cake of this homogeneity and porosity is unusual and it would be difficult 
 to point to many examples of the kind. A IJ-in. cake is made in 
 from 45 to 60 minutes and is given a three-hour solution wash in order to 
 take advantage of the additional extraction noted below. Due to the 
 local conditions, the residue from the filtering operation has to be repulped 
 with a minimum of water and pumped away, there being no available 
 method of running to waste by gravity. 
 
 Rotary Vacuum Pump. The vacuum pump is a type I have not seen 
 used for this purpose, and as it has advantages which are material, it is 
 well worth mention. It is a Connersville cycloidal machine, 5JX8 in., 
 and has 2j-in. suction and discharge. It consumes only three to four 
 horsepower and maintains a vacuum of 19 in. at this altitude (6000 ft.) 
 The machine is low in first cost, occupies an exceedingly small floor space 
 and has an admirable maintenance cost, there having been no repairs on 
 it since its installation. Machines of this class ought to be investigated 
 for this work, as the record of this particular installation is admirable 
 
PRACTICE AT TONOPAH 109 
 
 in the extreme. It is constructed like a positive blower, having two Jobes 
 revolving in conjunction with each other. 
 
 The filter tank is equipped with air lifts to aid in keeping the material 
 in suspension. After forming the cake on the filter it is given a solution 
 wash for three hours, during which time an additional extraction of silver 
 of from 1 to 2% is gained. The point of additional extraction is extremely 
 interesting and is one which has been verified in several of the mills in 
 the district, the additional metal dissolved varying from 1 to 3% in vari- 
 ous plants. 
 
 Of the filter leaves, five are acid-treated each day, using HC1 of 0.5 
 to 1 % strength. It has been shown in many mills of late that the fre- 
 quent treatment of filter leaves in dilute acid lengthens their life con- 
 siderably and does not tend to harden the canvas as does more concen- 
 trated acid. 
 
 Zinc shavings are used in the usual way for precipitating the metal 
 from solutions, the installation consisting of six boxes of six compart- 
 ments each. The precipitate is collected, partially dried and melted in 
 Faber du Faur furnaces, which are equipped with a special low-pressure 
 burner. 
 
 The ore treated varies in value from $18 to $20 per ton, the propor- 
 tion of silver to gold being about as 100:1. The extraction in the mill 
 varies from 90 to 92% of the contained metal. The power consumed is 
 two horsepower per ton of ore treated, and the regular force of operatives 
 consists of 18 men. 
 
 The consumption of the principal supplies used in cyaniding is as 
 follows: KCN, 3 Ib. per ton of ore treated; CaO, 3 lb.; lead acetate, 
 0.5 lb; zinc, 1.8 lb.; pebbles, 6 lb. The total cost of treatment amounts 
 to about $3.30 per ton of ore treated. The accompanying flow sheet 
 gives the details of the mill operation and the machinery used. 
 
 The Montana-Tonopah Mill. The Montana-Tonopah mill is one of 
 the original mills in the district to treat ores by total sliming. It was 
 constructed to make use of concentration, but this has been partially 
 eliminated and now is using only a partial concentration system. 
 
 The ore is first put through a No. 5K Gates* gyratory crusher, from 
 which it is elevated and passed through two No. 3D short-head crushers 
 of the same make, thence going by means of a 14-in. belt elevator into 
 the battery bin. 
 
 There are 40 stamps of 1100 lb., dropping 102 times per minute 
 through 7J in. The screen used is a " ton-cap" equal to about 25 
 mesh. Stamp crushing is universal in the camp and the Montana- 
 Tonopah is in line with general practice. 
 
 From the batteries the pulp is classified in cone classifiers, the slime 
 going to the settlers and the sand being concentrated on eight Wilfley 
 
110 
 
 DETAILS OF CYANIDE PRACTICE 
 
PRACTICE AT TONOPAH 111 
 
 sand tables. The sand from the concentrators passes to two Dorr duplex 
 classifiers operating in closed circuit with two Allis-Chalmers tube mills, 
 each 5 X 22 ft. The grinding capacity of this mill is in excess of its leach- 
 ing and agitating capacity and only one of the tube-mill sets is in use, the 
 other being held in reserve so that no time is lost on account of relining 
 or repairing the tube mill. 
 
 It will be noticed that the tube mills in this installation are the long 
 type, which is due to the fact that they were installed before the general 
 opinion turned toward the short, large-diameter mills. Most of the tube 
 mills used at present in the district are the latter type, which is most gen- 
 erally favored. Smooth cast-steel linings are used in the tube mills, this 
 arrangement having proved satisfactory in efficiency and economy. 
 
 Types of Agitators in Use. The slime is settled in cone-bottom tanks, 
 of which there are four, each 30X10 ft., with a 9 pointed bottom. The 
 thickened slime is taken to one of eight agitation tanks, which are operated 
 on the intermittent-charge system. There are six 22X15-ft. tanks, con- 
 taining Hendryx agitators; one 22X12-ft. tank, and one 27Xl2-ft. tank, 
 each equipped with a Trent agitator. 
 
 In this plant an opportunity has been had to compare the work and re- 
 sults accomplished with the Trent and Hendryx systems, and it is note- 
 worthy that the operators prefer the Hendryx, although admitting that 
 it requires a greater amount of power to drive it, resulting in a greater 
 expense. It is claimed that the extraction results are better with the 
 Hendryx device and that it gives a great deal less trouble than the Trent. 
 The main difficulty with the latter seems to be that it is extremely likely 
 to become stopped up with splinters or caked slime and also that it is not 
 so efficient in getting extraction results. This matter of difference of 
 opinion in reference to agitators will be mentioned again in discussing 
 further the practice in this district. 
 
 The agitation in these tanks is continued for 54 hr. in a solution con- 
 taining 5 Ib. KCN per ton. Lime is added to the agitators in powdered 
 form, the consumption being three pounds per ton of ore. The treatment 
 solutions are kept heated to 110, by which means the extraction of silver 
 is said to be materially increased. 
 
 Stationary Vacuum Filter. The filter installation consists of a sta- 
 tionary plant of the Butters type, containing a total of 140 leaves, of 
 which only 100 are required to handle the capacity of the mill. The filter, 
 is worked in five cycles per 24 hr., three hours being used for taking out 
 and acid-treating the leaves, the filtering operation ceasing for that period. 
 Each day six leaves are treated, and weak acid is used for the process, the 
 average being about 2% HC1. Frequent treatment with weak acid keeps 
 the filter leaves in good condition, avoids accumulation of large quantities 
 of lime on the canvas and notably lengthens the life of the leaf. The weak 
 
112 
 
 DETAILS OF CYANIDE PRACTICE 
 
 acid does not destroy the thread used in sewing the leaf and does not 
 harden the canvas as strong acid does. In treating the leaves frequently, 
 only a small quantity of lime is allowed to accumulate on the leaves and 
 the weak acid is effective in removing it. 
 
 () l-Ho.5K.6ates Crusher 
 
 Q Elevator 
 (f 2-Ho.3D.Shorthead. 6ates Crushers 
 
 Battery 
 Storage Tank 
 
 1-14 ' Belt Elevatot 
 
 _J Battery Bin 
 
 40-llOOIb. Stamps, 102 Drops- 7j Drop.Challenge 
 25 flesh Ion-cap Screen feeders 
 
 8~Cone Classifiers 
 
 8- Wifley Sand Concentrators 
 
 2~ Duplex Dorr Classifiers 
 ^ 
 
 ^ '2-5x22 Allis-Chalmers tube mills, 
 2" Smooth Chi I led Liners 
 
 4 - 30x10 'done-bottom Settlers, 
 
 6-/sJ(22 r Hendryx Agitators^ Intermittent 
 I -12x22' Trent Agitators \ Charge 
 I- 12x27' Trent Agitators I System 
 
 1-500 ton Stock Tank 
 1-100 Leaf Butters Fitter 
 
 Slime to Waste 
 
 Pregnant Solution Tank 
 I- Zinc-dust Feeder 
 
 2- Merrill P.recipitate Presses 
 l~SumpTank 
 
 l~0il Fired Furnace 
 FLOW SHEET OF MONTANA-TONOPAH MILL. 
 
 The time of forming the cake is 45 min., a IJ-in. cake being built up 
 in this time. Solution wash is continued for three hours and a slight addi- 
 tional extraction is gained in this time. The additional extraction gained 
 on the filter is so small in this case as to be almost negligible, thus differing 
 from the experience of some plants in the district, where appreciable 
 quantities of metal are dissolved during the solution-washing period. 
 
PRACTICE AT TONOPAH 113 
 
 Due to the fact that a railroad spur runs through the property, it was 
 necessary to design the mill in two units, one of which includes the crush- 
 ing, grinding and concentrating units and the other the cyanide plant. 
 This disadvantage is somewhat offset by the advantage gained in receiv- 
 ing supplies directly at the mill and the loading of concentrate without 
 haulage expense. The concentrate is shipped to a smelting plant. 
 
 Zinc -dust Precipitation. The Merrill system of zinc-dust precipitation 
 is used, the consumption of zinc being equal weight with the bullion re- 
 covered. The precipitate is melted in oil-fired furnaces, no acid treat- 
 ment being practised. 
 
 The total extraction resulting from the ore treatment is about 92.6% 
 and this total is divided into 20% in concentration, 20% in contact with 
 solutions and 52.6% in agitation. The cost of benefication is placed at 
 $3.09, which figure does not include the general expense items. The con- 
 sumption of material is 8 Ib. lime per ton of ore treated, 3 Ib. cyanide, 
 0.75 Ib. lead acetate; pebbles, 1J Ib. per ton treated. The mill treats 
 from 145 to 150 tons per day, and the ore contains 20 oz. silver and about 
 $4 gold. The mill requires 320 hp. for its operation and employs 19 men 
 regularly. 
 
 As this is the oldest mill in the district maintaining its original con- 
 struction and treatment plan, some of the later ideas are not included. 
 This is to be especially noted in the case of the tube mills, the long type 
 being used instead of the shorter ones, which conform to later ideas. 
 
CHAPTER XI 
 PRACTICE AT TONOPOH Continued 
 
 The mill of the Tonopah Extension Mining Co. is situated at the 
 edge of the town of Tonopah. It is one of the later mills and embodies 
 more recent ideas in metallurgy of the Tonopah ores. Some of these 
 departures are of much interest, among them the use of tube mills in 
 tandem. 
 
 The ore is first crushed through a No. 4 Kennedy gyratory crusher and 
 is then taken by an inclined belt conveyor to the mill bins. From these 
 it is fed through suspended Challenge feeders into the stamps. There 
 are thirty 1050-lb. stamps having 7-in. drop and 100 drops per min. 
 Four of the batteries are equipped with 12-mesh screens and two with 
 3-mesh screens of the "ton-cap" type, the object of the use of these 
 different screens being to furnish a pulp of varied coarseness with the idea 
 of increasing the efficiency of the tube mills. It is maintained that the 
 coarser portion of the pulp not only provides a means of satisfactorily 
 using a part of the grinding action of the pebbles which is expended in 
 crushing upon themselves, but actually assists in grinding the finer 
 portions into slime. 
 
 Tube-mill Arrangement. From the batteries the pulp is received 
 by a duplex Dorr classifier, which removes the slime and delivers the 
 sand and coarser rock into the first tube mill. This is a machine 5 ft. 
 diameter and 18 ft. long, following the recent accepted design. It is 
 equipped with spiral scoop feeder and Komata lining, and makes 27 r.p.m. 
 In this mill there is but one passage of the pulp, there being no return of 
 oversize to it. It performs a heavy duty in reducing the larger particles 
 of the pulp, as the analysis shows. 
 
 From this first tube mill the pulp is received by a second Dorr classifier, 
 the slime is taken out and joins the stream from the first, and the sand 
 requiring regrinding is led into the second tube mill. This mill is the 
 same size as the first one, but is equipped with a smooth cast lining, in 
 distinction to the first which has a Komata lining. Here the fine sand is 
 ground into the slime required for total pulp. The product issuing from 
 the mill is returned to the second classifier, thus forming a closed circuit 
 from which only the portion light enough to pass over the discharge of 
 the Dorr classifier issues. The accompanying table shows the classifica- 
 tion of the entering and issuing pulp of each mill and also the classifier 
 overflows. 
 
 114 
 
PRACTICE AT TONOPAH 
 
 115 
 
116 
 
 DETAILS OF CYANIDE PRACTICE 
 
 The Agitation System. From the regrinding system the pulp is 
 taken to four cone-bottom settling tanks, each 24X16 ft., where the col- 
 lection of slime is made, the overflowing solution being either pumped 
 back for further use or sent to the precipitation department, according to 
 conditions. This bulk of solution is used to maintain the balance 
 between precipitation and the total solution used in the mill. 
 
 From the settlers the slime is drawn off into the agitation tanks, of 
 which there are four, each 24X16 ft., all equipped with Trent agitators. 
 At the Extension mill the Trent agitators are regarded as highly efficient 
 and satisfactory devices, although it is acknowledged that they are not 
 without their faults. They do give some trouble, due to plugging of the 
 nozzles, and it is also found that the bearing upon which the arms revolve 
 is not entirely grit proof and is subject to grinding action of the pulp 
 
 SCREEN ANALYSES OF TUBE MILL AND CLASSIFIER PRODUCTS AT 
 TONOPAH EXTENSION MILL 
 
 
 + 10 
 mesh 
 
 +20 
 mesh 
 
 +60 
 mesh 
 
 + 100 
 mesh 
 
 + 150 
 mesh 
 
 +200 
 mesh 
 
 -2 
 
 mesh 
 
 Tube mill No. 1 intake 
 (Komata lining). 
 Tube mill No. 2 intake 
 (smooth lining). 
 Tube mill No. 1 discharge . 
 Tube mill No. 2 discharge . 
 
 15.45 
 
 1.77 
 1.00 
 
 16.90 
 1.06 
 0.80 
 
 40.00 
 
 18.08 
 
 17.20 
 2.60 
 
 14. OC 
 35.82 
 
 26.60 
 20.60 
 
 4.19 
 14.35 
 
 8.60 
 14.00 
 
 4.62 
 13.83 
 
 11.20 
 16.80 
 
 4.91 
 15.09 
 
 35.60 
 46.00 
 
 Classifier No. 1 overflow. 
 
 
 
 
 16 
 
 1.00 
 
 2.8 
 
 96 81 
 
 Classifier No. 2 overflow. 
 
 
 
 
 1.89 
 
 5.91 
 
 14.60 
 
 77.60 
 
 which gets into it. Some experiments have been made lately by removing 
 the nozzles from the air and pulp-delivery pipes, which constitute the 
 arms, and it has been found that while the speed of revolution has been 
 diminished, there is no other ill-effect and the agitation continues as 
 usual. This procedure is calculated to lessen the probability of stoppage 
 from plugged nozzles. Another experiment to avoid the wear occasioned 
 by grit entering the bearings and grinding them out has been made by 
 removing the bearing altogether from the tank and suspending it above 
 the tank, connecting it with the revolving arms by means of a pipe. It 
 seems probable that both these variations may be productive of econo- 
 mies, and a final decision on the matter will be of interest. 
 
 The power required to move the Trent agitators is stated to be 6 hp. 
 for each agitator, plus the power required for furnishing compressed air, 
 which in this case is 13 hp. for five agitators, including the four treatment 
 agitators and the stock tank. 
 
 Vacuum Filtration. From the agitators the pulp is taken to a stock 
 tank, 30 X 20 ft., which serves to feed the filter. The stock tank is equip- 
 ped with a Trent agitator to keep its contents in suspension. From the 
 
PRACTICE AT TONOPAH 117 
 
 stock tank the pulp is taken to a stationary vacuum filter of the Butters 
 type having 100 leaves. The filter is operated in the usual way, a cake of 
 1J in. is made and given a 2-hr, solution wash. The usual cycle is six 
 hours in total. An additional extraction is made on the filter, which at 
 times reaches 3%. The slime at the Extension mill is easy to filter, as is 
 generally the case with the Tonopah ores. 
 
 Zinc shavings are used for precipitation. The solution is clarified by 
 passing it through excelsior and is precipitated in eight 6-compartment 
 zinc boxes, each compartment being 30X36X30 inches. 
 
 The precipitate resulting is partially dried and fluxed and melted in 
 Steele-Harvey furnaces. The slag is allowed to accumulate until suffi- 
 cient is at hand for treatment when it is crushed in one of the batteries, 
 concentrated to remove the metallic particles and the remainder added a 
 little at a time to the tube mill, where it is crushed to a slime and cyanided 
 along with the regular mill run of ore. By treating the slag in this man- 
 ner only a small portion is added to the mill run every day, and it is soon 
 used up without any detrimental effect. It avoids the expense of shipping 
 the material to smelters and it is probable that the ultimate economy of 
 the scheme is as good or better than when it is shipped. 
 
 There is some controversy over the relative merits of zinc shavings and 
 zinc dust as a precipitant in the Tonopah district, and the operators at the 
 Extension mill believe that the process using shavings is as satisfactory 
 and economical as when the dust is used. They point to the fact that their 
 consumption of zinc is as low as is usual when zinc dust is used and that 
 their cost of cleanup is no more than in such cases and also that their 
 resulting bullion is better and barren solutions are easily secured. This 
 question is one which will stand a good deal of argument, and there seems 
 to be something of advantage for each system. It is, however, difficult to 
 overlook the great advantage in simplicity and safety obtained by the use 
 of zinc dust. This matter will be referred to again in considering the 
 metallurgy of Tonopah in a general way. 
 
 Extraction Data. The extraction obtained at the Extension is consist- 
 ently high and may be said to be about the limit obtainable on Tonopah 
 ores. The material treated contains silver and gold in the proportion of 
 about 90 : 1, the heads averaging 16 oz. silver. 
 
 The pulp is given 40-hr, agitation in the tanks with solution of about 
 three pounds of KCN per ton. The extraction obtained averages about 
 94 to 95 % of the total content. As an example of the division of extrac- 
 tion a typical month showed 25.77% in milling, 67.57% in agitation and 
 1.74% in the stock tank and in filtering. Solutions are warmed at this 
 mill, as is the general practice at all Tonopah mills, to 120, and it is 
 claimed that a clear and definite additional extraction is obtained over 
 working with normal temperatures. 
 
118 
 
 DETAILS OF CYANIDE PRACTICE 
 
 No 4- Kennedy Gyratory Crusher 
 
 Inclined Belt Conveyor 
 Hill Bin 
 
 . , , (I 50 Stamps 105V Ib.-l drop, lOOdroi 
 1-24x16 Solution J permin.4-l2meshand2-3meshto 
 
 Tank Joooool cap screens. Suspended Challenge 
 
 9"" 
 
 H| I- Dorr Duplex Classifier 
 
 
 1- 5x/8 ' Tube Mill 
 
 | 
 \ 
 
 y 
 
 1- Dorr Duplex Classifier 
 V 
 
 \ 
 
 n 
 
 
 1-5x18 Tube Mil f 
 
 ^-7~T"* 
 
 ' / > ^V 5 - 
 ES^J-v J^/" 
 
 Intermedi- ^ . 
 
 Tl 
 frj'^) 4 - <?4^/6 'Cone bottom seWers 
 
 <arfe Solution Tank v i 
 
 i ^ /^\ 
 
 
 ( jf ) 4~24xl6 Agitation Tank 
 
 
 ^ V__J/ Trent Agitators 
 
 
 ^ T' 
 
 ran* j | ^ 
 
 X'^^v 1-30x20' StockTanh, Trenf 
 J Ag_itator> 
 
 I A ^~r^ 
 
 ;fi 
 
 
 1-100 Leaf Butters Filter 
 
 )Yfer 
 
 
 
 
 
 1 \~^ Slime to Waste 
 i ^ 
 
 t 
 i 
 
 1 
 1 
 
 
 Ol-30x8 'Pr.eqnant Solution 
 Tank 
 
 1 
 
 
 1 
 
 i 
 
 
 I 
 
 1 
 
 
 r 
 
 i 
 
 i 
 
 
 8~6 Compartment ZmcBoxes 
 
 | 
 
 
 
 
 ! 
 "o 1 
 
 1 
 
 
 g 
 
 $Jt 
 >^ . 
 
 UJ_..i<^ 
 
 -/ J 2-26x8' Sumps 
 
 SlagCrushed Q^Steele -Harvey Furnaces 
 andConcent rated j 
 
 | *" ^' > Bull ion 
 
 ^~~7 Silver 
 
 Residue to 
 Tube Mill 
 
 OreandPutp 
 
 Solution 
 
 FLOW SHEET OF TONOPAH EXTENSION MILL. 
 
PRACTICE AT TONOPAH 
 
 119 
 
 The consumption of material is as follows: Cyanide, 2.78 lb.; lead 
 acetate, 0.963 lb.; lime, 3.398 lb., and pebbles, 4.423 lb., all calculated 
 per ton of ore milled. The consumption of zinc is 0.052 lb. per oz. of 
 bullion recovered. The mill treats about 155 tons of ore per day with 400 
 hp., and employs 14 men regularly, including the superintendent. The 
 accompanying flow sheet shows the details of the system followed. 
 
 An Installation of Heavy Stamps. The mill of the MacNamara 
 Mining Co. is one of the most recent of the Tonopah installations, and 
 originally contained a number of innovations, most of which, however, 
 have made room for devices conforming to standard practice. 
 
 THE MACNAMARA MILL. 
 
 The ore is brought into the mill over a conveying and sorting belt, and 
 that part of the waste which is easily recognizable is thrown out. A 
 Kennedy gyratory crusher is used for primary crushing and the ore is then 
 dropped into the battery bins. 
 
 There are 10 stamps in the mill, fed by suspended Challenge feeders, 
 the stamps weighing 1400 lb. each. They are set in a special heavy-duty 
 mortar, the screen being only three inches from the dies. This type of 
 mortar is designed for rapid crushing and, in fact, at the MacNamara mill 
 a duty of 7.5 tons per stamp per day is attained. With stamps of this 
 weight this could not be considered an exceptionally high duty, but the 
 crushing capacity is limited by the following regrinding installation which 
 will not permit any greater output. The stamps make 98 drops per min- 
 ute through 8 in., and the mortars are equipped, one with 8-mesh and the 
 other with 12-mesh screens. The different screens are used with the idea 
 
120 DETAILS OF CYANIDE PRACTICE 
 
 of furnishing a varied feed for the tube mill, as has been mentioned in the 
 case of the Tonopah Extension mill, although the efficiency of this pro- 
 cedure in the case of the MacNamara would seem to be limited by the use 
 of a single tube mill. 
 
 The tube mill used is 5 ft. diameter and 16 ft. long, which is carrying 
 the shortness to the extreme. As has been mentioned, the tendency at the 
 present time is to limit the length of the tube mill, and this instances the 
 progression of that tendency. It is stated that with the 16-ft. mill the 
 results are the same, as far as fineness of output is concerned, as if the 22-ft. 
 length were used and the wear on the lining and the power and pebble 
 consumption are less. This mill is equipped with smooth cast lining and 
 runs at 26 r.p.m. and uses about 60 hp. for its operation. The cast lining 
 is stated to wear 11 months, and as it is locally cast, hard iron, the renewal 
 cost is not high. The mill is equipped with a scoop feeder of the spiral 
 type. The discharge is taken up by an 8 X 52-in. Frenier pump and re- 
 turned to the classifier, making a closed circuit. 
 
 The Agitation System. The slime from the classifier is collected 
 and thickened in a Dorr thickener, 26X12 ft., the overflow solution 
 being returned for battery use and the thickened slime proceeding 
 to the agitators. There are two agitator tanks, each 26 X 16 ft., equipped 
 with Trent agitators' actuated by 4-in. centrifugal pumps of the local make 
 already mentioned. Originally the arrangement of these agitators was 
 somewhat different, the bearing was situated outside and below the bot- 
 tom of the tank and connected with the revolving arms by means of a 
 pipe which also revolved. This pipe passed through a stuffing box in the 
 bottom of the tank, but it was found that when the gland was tightened 
 sufficiently to prevent leakage, the free revolution was prevented and the 
 agitator was likely to stop at any time. Recourse was had to the stand- 
 ard Trent device and subsequent trouble has been confined to the points 
 previously mentioned. 
 
 Agitation in these tanks is continued for a total of 55 hr., which 
 includes the time required for filling the tank. The filling time is 18 to 
 20 hr., during which the agitators are in use and the pulp receives efficient 
 agitation. A 2-lb. KCN solution is used for treatment. 
 
 After the completion of agitation the pulp from the agitators is 
 received in a stock tank, 27.5X19.5 ft., also equipped with a Trent agi- 
 tator. From this tank the pulp is drawn off to a 50-leaf vacuum filter of 
 the Butters type. In the construction of the tank for this filter it was 
 intended to discharge it from a single point, and the bottom was not 
 divided into separate hoppers, but consisted of a single V-bottom, in 
 which was placed a spiral screw conveyor to convey the discharged slime 
 to the point of exit. This arrangement was found to be decidedly unsat- 
 isfactory, as the slime stuck and piled up on the side of the tank and even- 
 
PRACTICE AT TONOPAH 
 
 121 
 
 1-24x12' 
 
 Batf-erySolutio 
 Tank 
 
 Overflow 
 
 1-20x10' 
 Water Tank 
 
 l-20xIO'Wash 
 Solution \^/ 
 Tank 
 
 1 \ 
 
 
 Co nve yirtg and Sor ting Be I 
 
 Kennedy by ratory Crusher 
 
 200 Ton Battery Bin 
 Suspended Challenge Feeders 
 
 10-1400 Ib. Stamps, 98 drops 
 &"drop.8and 12, mesh screens 
 
 I- Dorr Duplex Classifier 
 
 Cast Liner 
 f-8 f Jf 52 "prenier Pump 
 
 9 t 
 
 u'ckener 
 
 VM 2- 26 x!6 r f f Trent Agitator 
 ^ V Tanks 4'Centri-fuga! 
 
 Pumps 
 
 Treat Agitator 
 1-SOLeafBu-fters F//tei 
 
 I* I \Slfmetoqasfe 
 
 l~2Qx!2 PregnantSolution 
 
 I! 
 t 
 
 1 
 I 
 
 I- 2 Ox I 2' Lower ( ) 
 
 Battery Tank \J 
 
 1- Excelsior C/ar/fier 
 
 -6 -Compartment Steel 
 Zinc Boxes 
 
 1-20x12 Barren Solution 
 Sump 
 
 Slag Crushed 
 and Screened 
 
 Residue 
 Ore and Pulp 
 
 (\ l-Steele - Harvey Furnace 
 I ^ L Bui /ton 
 
 FLOW SHEET OF MACNAMARA MILL. 
 
122 DETAILS OF CYANIDE PRACTICE 
 
 tually the screw was tunneling under the mass of slime. In order to 
 remedy this defect the bottom was divided up into separate hoppers by 
 inclined partitions, and is now conforming to usual construction. 
 
 The filter cycle occupied a total of 4J hr., which includes a 2-hr, 
 solution wash and 5- to 10-min. water wash as final treatment. The cake 
 is formed in from 60 to 80 min., and usually has a thickness of about 1J 
 in. In common with most Tonopah slimes, this cake is easily washed. 
 
 Precipitation on Zinc Shavings. In accordance with the usual Tonopah 
 practice, zinc shavings are used for precipitation, there being four 6-com- 
 partment boxes preceded by a special box containing excelsior for clarify- 
 ing the solutions. It is to be noted that several plants in Tonopah are 
 using this excelsior clarifying system and it seems to do the work in a 
 satisfactory manner. It is undoubtedly a simple and cheap process and 
 for small plants seems to be a cheaper method than installing clarifying 
 presses. A box is made on the principle of the zinc precipitator box, the 
 size varying with the requirements, and is filled with excelsior through 
 which the solution passes in the same manner as thourgh a zinc box. The 
 excelsior is packed rather tightly and effectually prevents suspended 
 slime from entering into the zinc box. The excelsior is easily and cheaply 
 cleaned when there is sufficient accumulated slime to make cleaning 
 necessary. 
 
 The precipitate is partially dried, fluxed and melted in a Steele-Harvey 
 furnace, the slag crushed and screened to separate the metallics which are 
 returned to the bullion melts. A flow sheet of the mill is given, showing in 
 detail the metallurgical procedure. 
 
 The extraction secured is 90 to 92%, in conformity with that secured 
 by most of the other tube mills of the district. The consumption 
 of cyanide is about 1J to If lb., and of lime about three pounds. 
 The lime is added to the classifier in dry form. Of lead acetate the 
 consumption is 0.55 lb. per ton milled, and of pebbles, four pounds 
 per ton milled. The mill crew consists of seven men, not including the 
 superintendent. 
 
 The MacNamara is the smallest mill in the district and its operating 
 costs are not to be fairly compared to those obtained by the larger mills. 
 It is stated, however, that the costs are not materially more than those 
 of the mills which most nearly approximate its capacity. The mill is 
 situated in the town of Tonopah, and is convenient to sources of supplies 
 and finds it easy to secure labor sufficient for its needs. The details of 
 the treatment are shown in the accompanying flow sheet. 
 
 Separate Treatment at the Desert Mill. Besides the mills in Tono- 
 pah proper, there are two that are, or have been, milling Tonopah ores 
 with success. The most important of these is the mill of the Desert 
 Power & Mill Co., at Millers, 13 miles from Tonopah. This has been 
 
PRACTICE AT TONOPAH 123 
 
 reducing ores of the Tonopah Mining Co. for some years, it being the 
 original cyanide mill of the Tonopah district, constructed in 1906. The 
 mill contains 100 stamps of 1050 Ib. each and regrinding is performed in 
 Huntington and Chilean mills of the Monadnock type. The ore is 
 crushed in solution, as is the practice in all mills of the Tonopah district, 
 and is concentrated on Wilfley tables in order to recover the sulphides 
 which are not so easily cyanided. 
 
 The sand and slime at this mill are treated separately after the older 
 method in use before treatment as total slime became universal. In 
 
 MILL AND SAND TAILING PILE OF THE DESERT POWER & MILL CO., MILLERS, NEV. 
 
 this plant the slime is treated in tanks having mechanical agitation by 
 means of revolving arms moved by gears at the top of the tanks. The 
 sand is subjected to double treatment, being collected in 33X8-ft. 
 leaching tanks and afterward removed by means of Blaisdell excavators 
 and distributed with distributors of the same make into secondary 
 leaching tanks of the same type and size. 
 
 It is noteworthy that although crushing is in solution and concentra- 
 tion is practiced in the same solution, the amount of metal dissolved dur- 
 ing these operations is proportionally small, and it is found necessary to 
 take advantage of every possible means of increasing the dissolution of the 
 metal after that point. 
 
124 
 
 DETAILS OF CYANIDE PRACTICE 
 
 O) No. 7j Gates Gyratory 
 v ) * Crusher 
 
 26 Belt Elevator 
 Trommel I^Ho/es 
 
 O ) 2- No. 4 Gates Crushers 
 
 18 Be It Conveyor 
 Robbins Ore Tripper 
 
 1500 Ton Storage B 
 20-Challenge Feeder 
 100 Stamps 1050 1 b. 
 
 50 Sand Wheel 
 20"Cone Classifiers 
 
 3-5' Huntingdon Mills and 
 2-6'ChileanmHs 
 
 18 Belt Elevator 
 14 Wilfley TablS 
 
 10 Deli Elevator 
 hS^ Huntingdon Hill 
 30 'Sand hee/ 
 20"Cone Classifiers 
 
 Butters Distributer 
 4-33x8'Cotlecting. Tanks 
 Excavtrfarand BeltConve yo 
 
 (--.-..>) 18 -33* 8 Leach ing Tanks 
 Dump 
 
 FLOW SHEET OF DESERT MILL. 
 
PRACTICE AT TONOPAH 125 
 
 The plant in general is much like the South African plants of an 
 early period, containing tailing-wheel elevators, separate treatment with 
 its consequent large area of tanks for leaching and slime treatment, and 
 comparatively great area under the mill roof. The mill is extremely inter- 
 esting as a comparison with modern mills of the same or greater capacity 
 now operating in Tonopah and a flow sheet of it is herewith presented. 
 The mill treats 500 tons per day, of which 60% is treated as slime 
 and the remainder as sand, the sand requiring about 15 days' leaching to 
 extract the maximum economical percentage. It requires 770 hp. and 
 64 men for its operation. 
 
 Detailed descriptions of the Desert mill have been published in the 
 technical press, and it is not necessary to review its methods in detail at 
 this item, as they are sufficiently well known. It would, of course, be 
 impossible for a mill of this kind to beneficiate ores at a cost comparable 
 to that attained in modern mills, but it may be said that for a mill of its 
 type, the Desert plant is still performing good work. A comparison of 
 the Desert mill with the new Belmont plant forms a good object lesson a? 
 to what great changes have taken place in the cyanidation of silver ores 
 within six years. 
 
 At Millers there is also the old mill of the Belmont company, having 
 60 stamps and built after the separate treatment plan, much like the 
 Desert mill. This mill is now treating a small quantity of custom ore 
 and retreating some of its sand tailing. A description of it would be 
 unnecessary at this time. 
 
 DISCUSSION 
 
 Cost of Cyanidation at Tonopah 
 
 In the synopsis of Herbert A. Megraw's article on " Silver Cyanidation 
 at Tonopah II," in the JOURNAL of Mar. 1, with reference to the Desert 
 mill at Millers, Nev., the statement is made that, " Costs are higher than 
 those obtained with modern all-slime plants," and in the text of the arti- 
 cle, one reads: "It would, of course, be impossible for a mill of this kind 
 to beneficiate ores at a cost comparable to that attained in modern mills." 
 
 It is possible that what I believe to be an erroneous impression may be 
 gained from the above statements. If Mr. Megraw refers to the modern 
 mills of Mexico or modern mills of the United States, treating straight 
 gold ore, the statements are correct, but if he would only refer to the mills, 
 both modern and antiquated, of the Tonopah district, which would 
 be a fair basis for a comparison of costs, I believe an investigation 
 would show that the operating costs of the Desert mill, granted to be 
 antiquated, have been, and are still, lower than those of any other 
 mill in the district. 
 
126 DETAILS OF CYANIDE PRACTICE 
 
 For the eleven months of the present fiscal year the direct costs at 
 the Desert mill are, $2.489 per ton, indirect $0.146, total $2.635 per ton. 
 Direct costs include all labor, power and supplies used in operating the 
 mill together with all costs of repairs, renewals, and upkeep of plant and 
 equipment. Taxes, insurance, legal and home office expense are included 
 in the indirect costs. 
 
 A. R. PARSONS. 
 
 Tonopah, Nev., Mar. 8, 1913. 
 
 It is possible that Mr. Parsons has misinterpreted the statements to 
 which he refers in my article dealing with cyanide practice at Tonopah. 
 What I meant was that a plant operating on the old separate-treatment 
 system, without the most modern machinery and appliances, cannot 
 possibly reach the low level of cost attainable in all-slime plants where 
 every improvement is at hand. Of course, to make any comparisons of 
 value, the scale of operations must be approximately the same, and for 
 this reason the Desert mill, treating 500 tons, cannot be compared to the 
 other mills in Tonopah which handle 150 tons or less per day. An instruc- 
 tive contrast might be made between the Desert mill and the new Belmont 
 mill, which treats approximately the same tonnage of the same kind of 
 ore. Undoubtedly the Belmont, a modern and efficiently operated 
 installation, is treating its ore at less cost than the Desert mill, or will be 
 doing so when normal conditions can be maintained. My statement was 
 not limited to the Tonopah district alone. 
 
 I am aware of the cost of milling at the Desert mill and consider it 
 exceptionally low for a mill of that kind. I think Mr. Parsons will agree 
 with me, however, in believing that a mill equipped with every modern 
 improvement can treat the same ore as efficiently and at less cost. 
 
 H. A. MEGRAW. 
 
 New York, Mar. 18, 1913. 
 
 On reading Mr. Megraw's article on " Silver Cyanidation at Tonopah 
 II" in the JOURNAL of Mar. 1, a reference to the slime discharge of the 
 MacNamara mill will be noted, which seems to condemn that type of 
 installation generally as a method of removal of tailings. 
 
 Quoting briefly, he says: "The mill of the MacNamara 
 
 originally contained a number of innovations, most of which have been 
 
 made for devices conforming to standard practice The 
 
 filter bottom was not divided into separate hoppers, but consisted of a 
 single V-bottom, in which was placed a spiral screw conveyor to convey 
 the discharged slime to the point of exit. The arrangement was found to 
 be decidedly unsatisfactory, as the slime stuck and piled up on the side of 
 the tank and eventually the screw was tunneling under the mass of slime. 
 
PRACTICE AT TONOPAH 127 
 
 In order to remedy this defect the bottom was divided up into separate 
 hoppers by inclined partitions, and is now conforming to usual con- 
 struction." 
 
 Though without first-hand knowledge of the conditions prevailing 
 at the MacNamara, I wish to state that this failure of a screw conveyor 
 readily to clean a filter hopper is not to be considered a typical perfor- 
 mance, nor should it be a sufficient reason to revert to the common 
 practice. 
 
 As evidence, I would submit the results obtained at El Tigre, Sonora, 
 where a screw conveyor is transporting heavy filter slime-cake that is 
 dropped into a hopper that contains no water whatever. The equip- 
 ment, as first set up, was a screw of ribbon type, revolving in the bottom 
 of a horizontally set discharge hopper, the sheet-iron walls of which are 
 inclined at an angle of 45. The residues discharged are filter cakes from 
 Kelly presses, which range from 25 to 30% moisture, and more often 
 approach the former figure than the latter. Inasmuch as the cakes are 
 stiff and sticky, the leaves are washed with water from a high-pressure 
 hose, after having dropped the cake by internal water pressure, but the 
 total discharge from the hopper has not exceeded a moisture ratio of 
 0.5 of water to 1.0 of solids, more frequently being 0. 4 :1, and there 
 is no accumulation of water in the hopper at any time, to serve as a 
 flushing medium. 
 
 When first put in use, the conveyor behaved as described by Mr. 
 Megraw, and " tunneled" through the slime-cake, making the prompt 
 discharge of residues impossible. After some time elapsed, the following 
 alterations were made, which changed the screw from a source of annoy- 
 ance and lost time, to a smoothly working mechanism. First, the bottom 
 plates were taken out, and a trough, 22 in. wide, was bult into the bottom, 
 of similar gage iron. The hopper bottom was originally level, but this 
 trough has an inclination of 12% on a 50-ft. length. 
 
 The ribbon shaft was lowered as well, but not as much, and is now a 
 foot above the bottom of trough at discharge end, while at the other ex- 
 treme it is only 'about 5 or 6 in. above it. 
 
 The result of the change is that all the slime slides into the trough and 
 is at once cut up by the worm, and pushed forward before it has time to 
 lag and hold back the succeeding fragments of cake that fall. The small 
 amount of hose water that is used acts as a lubricant and the slime cakes 
 shoot out of the discharge end of the hopper as though on a greased 
 skid way. 
 
 No fall or head room was sacrificed, as the hopper is at the head of the 
 tailings ditch. In passing, it might be said that without the aid of the 
 screw conveyor, it is impossible to discharge the hopper save by long-con- 
 tinued sluicing with much water. The conveyor is driven by a small 
 
128 DETAILS OF CYANIDE PRACTICE 
 
 motor that takes about 3 hp. under the new arrangement, and as it is in 
 operation about 4 hr. in all per day, the power requirements are extremely 
 small. 
 
 Cake discharges are now made in 1.5 to 18 min., counting from the 
 time that the presses are opened until the time that they are beginning to 
 fill again with slime. In this time five presses of the "Parral" size are 
 cleaned. Occasional discharges have been made in 10 or 12 minutes. 
 
 The above statement shows that screw conveyors will remove filter 
 slime under the proper conditions, even though much denser than the 
 average vacuum filter_cake, and at no noticeable expense for power or 
 repairs. 
 
 Conditions at El Tigre preclude the use of much water or water in 
 large quantities at recurring intervals. At other plants they might be 
 such as to offer no field for the screw conveyor for a variety of reasons, 
 but it is certainly possible to make it work well as a means of transport for 
 slime cake in a filter plant. Furthermore, it does not leave masses of 
 heavy slime in the corner of hopper, as is frequently the case when using 
 rectangular boxes and dropping the cake in water or barren solution. 
 
 DONALD F. IRVIN. . 
 
 Yzabal, Sonora, Mar. 15, 1913. 
 
CHAPTER XII 
 PRACTICE AT TON OPAH Concluded 
 
 The ores of the Tonopah district have not as yet been subjected to 
 thorough tests in order to determine the advisability of sorting the ore 
 before milling it. Some of the plants have adopted sorting in a desultory 
 way and two have taken some pains to accomplish a more or less thorough 
 sorting. These latter are the West End Consolidated and the new Bel- 
 mont. The first of these has installed a mechanical washing machine 
 which screens and washes the ore in hot water and then delivers it upon a 
 wide sorting belt running at slow speed. This belt is so arranged that 
 the sorters work on one side of it, throwing the waste not off the belt, but 
 to one side of it. At the end of this belt there is a splitter which bivides 
 the stream delivery, the milling ore going to its proper bin while the 
 waste is delivered into a waste bin from which it can be readily discarded. 
 
 There are several advantages about this sorting system. The ore to be 
 sorted is passed over a trommel with small: holes and is given a thorough 
 rasping which dislodges much of the sticking clay and mud and also gets 
 rid of the fine portion of the ore which does not require sorting but which 
 goes directly into the mill. The coarser ore thus is passed through into 
 the washer proper, which is a large steel cylinder set on an incline with its 
 lower, or receiving end, set into a tank of water which is heatedly steam. 
 The inside of the cylinder contains a spiral, or reverse screw arrangement, 
 which obliges the ore to ascend through the cylinder until it is finally dis- 
 charged at the higher, or discharge end. Near the discharge end there is 
 a section of the cylinder perforated with small holes through which the 
 washing water returns to the tank below. The coarse ore delivered to the 
 sorting belt is in perfect condition for sorting, as the operator can see at a 
 glance its character and can eliminate all absolute waste without hesita- 
 tion. The mud and clay washed from the ore are collected in the wash- 
 ing tank and can be recovered at convenient intervals. It is usually of 
 high grade and is sent to the mill along with the regular milling ore. 
 
 The practical utility of this system has been thoroughly tested and 
 calculated at the West End plant and the conclusion is that there is a 
 clear and definite saving by its use. A large portion of rock that will 
 not pay its way 'through the mill is discarded, saving the milling cost of 
 putting it through the process and enriching the portion of payable ore. 
 In other words, the same amount of silver is concentrated into a smaller 
 
 129 
 
130 
 
 DETAILS OF CYANIDE PRACTICE 
 
 bulk for milling, the economies being evident. The new Belmont mill 
 has installed a similar machine for washing the ore. 
 
 Sorting in some form is practiced by several of the operating companies 
 at Tonopah, but only at the above mentioned plants is it carried out in 
 thorough form. It has been stated that a great many of the Tonopah 
 dumps would pay well for sorting them over if it were possible to lift 
 the material economically and get rid of the waste. If this statement is 
 true, it seems likely that sorting while the ore was originally in motion 
 might have repaid the trouble necessary to do it. It is a question which 
 requires some study and it is impossible to make any statement which 
 would certainly cover all cases. 
 
 NEW MILL AT TONOPAH, NEV., AND OLD MILL AT MILLERS, OF THE TONOPAH- 
 BELMONT DEVELOPMENT CO. 
 
 Crushing in Solution. All the operating mills at Tonopah use solu- 
 tion throughout the mill operations. At the same time there are certain 
 of the operators who believe that better metallurgical results could be 
 obtained if it were possible to do the crushing and grinding in water 
 without incurring a loss of cyanide and dissolved metal. It is evident 
 that in treating silver ores where solution of comparatively high cyanide 
 content must be used, crushing in water is not usually practicable. The 
 amount of water taken in unavoidably from the grinding system to the 
 
PRACTICE AT TONOPAH 131 
 
 cyanide plant would have to be discharged as moisture with the residues, 
 and at that time would contain both cyanide and metal in solution, a 
 combination that could not be thrown away. The only system by which 
 it might be managed would be to filter the pulp from the grinding system, 
 whereby it could be introduced into the cyanide plant with approximately 
 the same quantity of water as the residues would contain in moisture. 
 Whether the advantages obtainable would justify the additional expense 
 is a question which would have to be solved in each particular case. The 
 procedure is followed at the mill of the Smuggler-Union Mining Co., at 
 Telluride, Colo., as has already been mentioned in these papers. 
 
 Crushing in Water at Goldfield. The advantage of crushing in water 
 is believed to be a saving of cyanide by removing cyanicides from the ores, 
 resulting also in an improved extraction. This matter has received 
 much attention from^the operators at the Goldfield Consolidated mill 
 and experiments covering several months' work have convinced them that 
 water crushing has decided advantages over crushing in solution. Natu- 
 rally enough, the conditions at the Goldfield mill are decidedly different 
 from those obtaining at Tonopah and the results of experiments cannot be 
 transferred bodily. The former is treating a gold-bearing ore and using 
 solutions much weaker than those necessary for the ores of Tonopah. 
 
 At the Goldfield Consolidated, it has been satisfactorily proved that 
 when crushing in water is followed the consumption of cyanide is less and 
 the extraction of metal better than when crushing in solution. It is 
 shown, also, that when crushing in solution is practiced, there is likely to 
 appear in the mill a light gelatinous product which refuses to settle and 
 causes a great deal of trouble in mill operating. The substance appears 
 much like an alumina product, which it may be, but that has not been 
 proved. On the contrary, when water is used in the crushing system, this 
 product does not appear. 
 
 It is extremely difficult to account for this difference and many theories 
 have been invented in the attempt to do so. The theory has been 
 advanced that no matter how alkaline a crushing solution may be, and all 
 solutions containing cyanide must be kept alkaline, there will be a certain 
 length of time, however short, when the acid liberated from the ore will 
 overbalance any alkalinity immediately available at any one point, and 
 that during this short time a chemical change might take place which 
 would render soluble some elements which would not be put into solution 
 with water and which would be removed by washing before reaching the 
 cyanide department, were water used in crushing. This momentary 
 acid condition might also introduce certain combinations prejudicial to 
 high extractions. Of course, there has been no research which would 
 prove that this condition does exist and is responsible for the results 
 shown, but the results are plain* Commercial operators rarely have 
 
132 DETAILS OF CYANIDE PRACTICE 
 
 the opportunity to solve questions of this kind, but it is just such prob- 
 lems which most need solving in the cyanide field. 
 
 Whether or not similar conditions to those found at Goldfield would 
 obtain at Tonopah is not certain, but with this example in mind there are 
 many who would like to have the opportunity of trying it. 
 
 The use of gravity stamps for crushing is universal at Tonopah and it 
 seems that nothing else has been considered in the design of the plants. 
 This seems unfortunate, for the ore does not appear to be too hard to give 
 good results with rolls or Chilean mills, either of which might be applied 
 with economy. It is true, however, that stamps have been considered the 
 conservative crushing machine for a long time and the design and con- 
 struction of plants at Tonopah have been eminently conservative. To 
 install a machine which will surely do the work, even though at a cost 
 somewhat higher than that of one which might be satisfactory, is a sound 
 basis upon which to reason and designers can hardly be censured for 
 following that system. At the same time the results obtained by the 
 other machines, rolls and Chilean mills, both as to efficiency and cost, are 
 no less definite and clearly proved, the obstacle to their use being simply 
 that the results are not so well known. One cannot say with certainty 
 that either of the machines above mentioned would satisfactorily take 
 the place of stamps at Tonopah, but it is not too much to say that I 
 believe either of them would introduce economies. 
 
 Lining for Tube Mills. The matter of tube mills at Tonopah intro- 
 duces some interesting variations which are worthy of attention. First 
 attention is called by the shortness of the mills generally used, especially 
 in the later installations. This progression has apparently been along 
 conservative lines and there is reason to believe that the theory is sound. 
 Certainly it has resulted in a reduction of power for the same production. 
 
 The mills recently installed are generally 5 ft. diameter and 18 ft. 
 long, in one case the length has been reduced to 16 ft. with satisfactory 
 results. It will be interesting to watch this development and see what 
 it brings forth. It is not impossible that the tube mills of the future may 
 be more like drums of large diameter and short length than the long, 
 narrow tubes first used. 
 
 The lining of the tube mills has given rise to much argument. The 
 contrast here to Mexican practice is noteworthy. In all the Tonopah 
 installations I have not seen a single instance of the use of the El Oro 
 ribbed lining, but everywhere there is the use of the smooth cast lining 
 and the silex blocks, both of which had been tried and discarded in 
 Mexico before the El Oro lining came into use. The smooth cast lining 
 would seem, theoretically, to be the most inefficient of all possible linings, 
 as it would appear that the pebbles would be more than likely to slide 
 over it and reduce the ore by rubbing it between the lining and the 
 
PRACTICE AT TONOPAH 133 
 
 pebbles. The matter of the dropping or tumbling of pebbles would 
 apparently be reduced to a minimum, and while it is clear that the 
 power requirements would be reduced to the lowest possible point, 
 apparently the efficiency would go down with it. That this is not the 
 case is what several of the operators declare positively. They claim to 
 get better results, both as to character of product, its quantity and cost 
 of production. And it is also stated positively that the pebbles do not 
 wear flat in the smooth-lined mills. It is a fact that if one is careful he 
 can avoid seeing flat pebbles on the scrap heaps of these mills. 
 
 The silex lining has its advocates also, the installation at the new 
 Belmont mill containing silex lining except in experimental cases. Silex 
 has proved to be a good lining in many cases, and except for the item of 
 cost has done good work in Mexico. The objections there to its use are 
 the cost and the time necessary to reline the mill when it wears out. 
 This usually puts a tube out of commission for from five to seven days 
 and where there is no reserve capacity it seriously interferes with the mill 
 operation. 
 
 The Komata lining has had trials at Tonopah and in the case noted 
 in the Tonopah Extension mill, is doing satisfactory work. Komata 
 linings have also been installed at the Goldfield Consolidated with 
 satisfactory results and are now used altogether. It is claimed that 
 these linings increase the power consumption, which is undoubtedly 
 true, but that the ultimate efficiency is increased. This is even more 
 definitely shown when the revolutions of a mill into which they are 
 placed are reduced considerably. For instance, a 5Xl8-ft. tube mill 
 using smooth or silex lining and revolving at 26 or 27 r.p.m. can be re- 
 duced, when the Komata lining is used, to about 22 or 23 r.p.m., resulting 
 in a lower power consumption and no great reduction of efficiency. 
 
 The height at which the load of pebbles is carried also varies a good 
 deal. The variation is from somewhat below the center line of the 
 mill to 6 or 8 in. above it, calculating with the mill not running, of 
 course. In cases where the load is carried above the center line of the 
 mill a grating has to be used in the discharge in order to prevent the 
 issuing of pebbles. At the West End mill a difference of pebble load 
 made an enormous difference in the efficiency of the tubes so that the 
 whole mill was affected. This question of lining will probably be 
 solved in the near future when there will be some agreement among the 
 operators as to which type best suits their needs. At present there 
 seems to be a great difference of opinion. 
 
 Types of Agitators. Opinions in regard to agitators seem to differ 
 as widely as they do in tube-mill linings. There are examples of the 
 Pachuca, Hendryx, Trent and other systems in use. The original mills 
 of the district, the Desert and Belmont mills at Millers, used mechanical 
 
134 DETAILS OF CYANIDE PRACTICE 
 
 agitators for their slimes, the Hendryx type is in use at the Montana- 
 Tonopah mill and several installations are using the Trent system, while 
 the new Belmont mill at Tonopah is using the Pachuca system. 
 
 Particularly the Trent agitator seems to be a bone of contention. 
 Some users say it is perfect and others delcare it has no merit in it, that 
 it is a nuisance and not satisfactory in any way. The truth lies somewhere 
 between these two extremes, no doubt, but at what exact point is im- 
 possible to state. 
 
 The Hendryx agitator has been previously mentioned in these 
 columns, but it is a machine which has never become popular on account 
 of its high power consumption. There is no doubt that it is a good 
 agitator, but it will probably never become a serious factor in the agita- 
 tion of slime for the reason of its high operating cost. 
 
 Pachuca tanks have been the subject of investigation for some time 
 and many operators claim that they offer no advantages in economy nor 
 in additional extraction obtained. 
 
 Referring back to the new Nipissing mill at Cobalt, in which the 
 slime agitators are the old-style mechanically moved arms, the designers 
 stated that they had been able to find no device which would assure 
 them either better results or lower costs. In such event the Pachuca 
 tank would be entirely out of the reckoning, for if it presents no such 
 advantages, its high cost of installation and the additional cost of pump- 
 ing in a mill, occasioned by the height of the tanks, would certainly 
 preclude its installation. I am of the opinion that the Pachuca tank is 
 likely to be replaced by some other more satisfactory design. 
 
 Concentration Practice. It will be noticed that some of the Tonopah 
 mills practise concentration while others do not. The two at Millers, 
 the Montana-Tonopah, the West End and the New Belmont practise 
 concentration, while the Tonopah Extension and the MacNamara mills do 
 not. In those mills which do concentrate, the object has been to make 
 as little concentrate as possible consistent with removing the objection- 
 able elements from the ore. With low- or medium-grade ores con- 
 centration is not necessary but with the rise in silver content, attendant 
 upon the increase in the proportion of sulphides, concentration must 
 be resorted to. Many of the mills using the process have reduced the 
 number of tables, the point being that it is more expensive to market 
 concentrate than bullion; therefore as large ^a proportion as possible 
 should be taken out in bullion form. This is sound reasoning, par- 
 ticularly where the concentrate has to be shipped to smelters where 
 losses may be multiplied by many means. 
 
 There is no instance of local treatment of concentrate at Tonopah. 
 In this connection it is interesting to review the situation at Goldfield, 
 where the Consolidated treats all of its concentrate by an elaborate proc- 
 
PRACTICE AT TONOPAH 135 
 
 ess. Experiments on concentrate treatment showed that by treat- 
 ing the concentrate raw a certain percentage could be saved; that by 
 first roasting the concentrate and then cyaniding it, a better extraction 
 would result, but that by treating it raw, then roasting it and retreating 
 by cyanide, an extraction about equal to the sum of the results of the 
 other two methods could be obtained. That system has been installed 
 and is followed with success. After the cyanidation of the roasted 
 concentrate, the residue is delivered into the tank which feeds the filter 
 and is discharged with the filtered tailing. By this means the con- 
 centrate tailing is reduced to a value nearly equal to that of the regular 
 mill tailing. The process is interesting and unusual. 
 
 Use of Heated Solutions. Operators universally agree that the 
 extraction of silver from the Tonopah ores is increased by heating the 
 solutions. The point to which this is carried is generally about 120. 
 There seems to be no difference of opinion on this point and all the mills 
 are doing this with good results. The question naturally occurs as to 
 whether the Mexican operators have been overlooking anything in the 
 matter of heating solutions. I have seen the scheme tried several times 
 and made experiments on it, but without any beneficial result. That this 
 is not unusual will be shown in a later paper, when I will call attention to 
 another silver mill which has made repeated experiments and found no 
 increase of extraction through heating the solutions. Still, this is a 
 point which ought to be worked out for each particular ore, no general 
 rule governing it. 
 
 Heating solutions seems to have no effect whatever on the extraction 
 of gold. This means, of course, solutions of normal temperature, as 
 extraction of both metals falls off in abnormally cold solutions. 
 
 The use of lime and lead acetate at Tonopah does not vary widely 
 from accepted practice at most other camps. The addition of these 
 materials varies, and the practice is governed principally by convenience. 
 The filters in use at Tonopah are all of the stationary vacuum type. 
 The present condition of the filter problem makes it advisable for dis- 
 cussion to be postponed until there shall be more liberty to publish 
 statements. 
 
 Calculation of Extraction. At Tonopah, as in most of the mills at 
 the present time, the calculation of extraction is performed by using the 
 content of bullion produced plus the content of tailing discharged as the 
 value of head samples. Some of the older operators look with envy on 
 the mill men of the present day and think of the monthly recurrence of 
 attacks of heart disease that came with the attempt to reconcile pro- 
 duction and tailing content with head samples taken at or before the 
 batteries. Extractions of 120% were not unusual in those days, nor were 
 drops to 60 and 70% unexpected, but the mill man was continuously in 
 
136 DETAILS OF CYANIDE PRACTICE 
 
 hot water about it, particularly if he differed with the general manager 
 about the accuracy of the head samples. This later method is much 
 simpler and tends to avoid worries. At the same time it is hard to agree 
 with a method of solving a problem by means of which any answer is 
 the right one. I am anxious to have this matter discussed and hope that 
 there will be someone kind enough to take it up and extract opinions 
 about it. 
 
 DISCUSSION 
 Silver Cyanidation at Tonopah III 
 
 In Mr. Megraw's article, " Silver Cyanidation at Tonopah III," 
 in the JOURNAL of Mar. 8, 1913, it is suggested that crushing in water 
 might be accomplished without an additional or prohibitive cyanide loss 
 if the pulp were filtered after grinding, introducing it into the cyanide 
 plant at practically the same moisture contained by the residue on 
 discharging. As the amount of water taken into the mill without 
 building up the quantity of solution is governed entirely by the amount 
 of moisture contained in the residue at the time of discharging, and can 
 only be equal to this amount, the water added ahead of cyanidation would 
 preclude the use of water for final wash. It would allow the discharge to 
 go out containing 33% of standard cyanide solution, which is in our 
 case three pounds per ton of ore. When the cost of dewatering with 
 filters is considered together with the mechanical loss of cyanide, and 
 the trouble and expense of again thoroughly mixing a pulp dewatered 
 to such a point of dryness, the additional extraction above 94.44%, the 
 average obtained by the Belmont Milling Co. for the last eight months, 
 it would hardly seem to be an attractive undertaking, even when con- 
 sidering the cyanide which might be saved by crushing in water. 
 
 As to the mechanical-stirrer type of agitator being efficient on silver 
 sulphide ore, I will state that the type of agitator called the " Butters" 
 was originally installed at our Millers plant and only a fair extraction 
 could be obtained from it until a 6-in. air lift was added, taking pulp 
 from bottom of the vat and discharging it over the top, in addition to the 
 mechanical stirring. 
 
 At the Tonopah mill where solution during agitation is kept at 100, 
 the air for agitation is furnished by a steam-driven compressor and the 
 exhaust steam is used for heating the solutions. As there is only 7% 
 loss between live steam at 125-lb. pressure and exhaust at five pounds, in 
 heating efficiency, we can figure only 7% of cost of producing steam 
 against agitating medium or method, so that if air were not beneficial 
 to extraction, and I am of the opinion that it is, another method or 
 medium could hardly be had at the same or lower cost per ton. 
 
PRACTICE AT TONOPAH 137 
 
 At the Millers plant where live steam is used for heating solution, the 
 cost averages about 18c. per ton, while at the Tonopah plant, with, of 
 course, a better equipment, heating and air for agitation together amount 
 only to 12c. per ton of ore treated. 
 
 The benefits to be derived from the heating of solutions used with 
 Tonopah ores, are shown in the following tailing assays from tests made 
 identically, except in temperature. They typify the results obtained in 
 practical mill work. 
 
 Warm solutions, 100 Cold solutions, 65 
 
 48 hr. 0.015 oz. Au. 2.1 oz. Ag. 0.02 oz. Au. 3.8 oz. Ag. 
 
 60 hr. 0.01 oz. Au. 1.4 oz. Ag. 0.02 oz. Au. 3.0 oz. Ag. 
 
 I think that Mr. Megraw's assertion that the addition of lead and lime 
 in Tonopah practice is " principally by convenience" is a little broad. 
 In this mill at least, the lime content is very closely watched, it having 
 been proven, not only by laboratory tests, but on a working scale, that 
 extraction is very erratic, due to reprecipitation when either too high or 
 too low alkalinity is carried. The lime is maintained between 1 Ib. and 
 1.5 Ib. of CaO per ton of solution. 
 
 The amount of lead giving best result is at all times somewhat of a 
 conjecture, but in order that it may not be understood that lead is added 
 at random and that we have some fixed ideas, even though they may be 
 wrong, the practice and theory followed at this plant are here stated. 
 
 It is figured that sulphur, alkaline sulphides, and other reducers have 
 a retarding action and are detrimental to the highest dissolving power 
 of the solutions, and in order to keep alkaline sulphides under control, 
 lead acetate is added to precipitate the lead sulphide. The amount used 
 is determined by experimental tests with clean solution. Zinc in solution 
 will act to a great extent, especially in hot solution, the same as lead, 
 forming zinc sulpkide, but is not as amenable to the combination as lead. 
 If an excess of lead is present the zinc will tend to accumulate in the 
 solutions, and then the amount of lead is reduced, allowing the zinc to 
 take care of the alkaline sulphides. In this way a kind of a balance of 
 zinc contents is maintained. 
 
 In regard to tube-mill lining, 14 tests, under varying conditions of 
 feed and moisture, conditions in both mills being as nearly identical as 
 possible at all times, showed an average of 5% more product of minus 
 200-mesh with silex than with the smooth iron liner. 
 
 In regard to El Oro lining, which according to Mr. Megraw's Mexican 
 experience is an improvement over all other linings, and which he in- 
 timates has never been tried at Tonopah, I think he failed to go thor- 
 oughly into what had been tried or considered, and why, in the opinion 
 10 
 
138 DETAILS OF CYANIDE PRACTICE 
 
 of the operator, the practice being followed is best suited to their condi- 
 tions. 
 
 The Montana-Tonopah Mining Co. tried El Oro liners, finding their 
 life to be between seven and eight months, while the cost of the lining 
 installed was over twice that of silex. At this plant the cost of silex 
 lining per mill, when lining seven mills, was as follows: Labor at $4.50 
 per day, $42.25; cement, 28 sacks at $1.035, $28.89; silex, six tons at 
 $42.80, $256.80, or a total of $327.94. To Mar. 20, these mills have 
 been in operation eight months, crushing 13,269 tons per mill, or an 
 average of 55 tons per day with the following average discharge screen 
 analysis: On 100-mesh, 1.33%; on 150-mesh, 5.05%; on 200-mesh, 
 6.42%; through 200-mesh, 87.20%. This is an average of 36 tests made 
 during eight months. 
 
 To this date none of these mills has had to be relined, but it is figured 
 that the first mill will have to be lined in about two weeks and the entire 
 installation during the next 60 days. Allowing eight months, which 
 is very good life for this style of liner, the cost compares more than 
 favorably with any available figures of El Oro liners. In "A Textbook 
 of Rand Metallurgical Practice," Vol. II, p. 151, the following statement 
 is made: " While the El Oro liner has a longer life than the silex liner, 
 the difference is not great enough to compensate for the extra cost." 
 
 In the original plans for our Tonopah mill, rolls were seriously con- 
 sidered by comparison of all data to be had at that time and were only 
 abandoned after an extended visit to Mammoth Copper Co.'s plant at 
 Kennett, Calif., where 27,000 tons of Belmont ore were sampled as 
 custom ore and crushed with rolls. The excessive wear of roll shells 
 and total cost per ton resulting in the eminently conservative installation 
 of stamps. The general manager of one of the late large cyanide mill 
 installations, where rolls are used, told the writer after six months' 
 operation, that he was sorry stamps had not been installed instead of rolls. 
 
 , A. H. JONES. 
 Tonopah, Nev., Mar. 18, 1913. 
 
 In this letter, Mr. Jones adds some interesting facts to the discussion 
 of cyanide problems and his statements will be accepted as authoritative 
 on Tonopah practice. Except in those instances where he has misin- 
 terpreted the meaning of my remarks, we are substantially in accord. 
 
 Regarding crushing in water, I agree with Mr. Jones' reasoning. 
 In my article, the matter is referred to in a discussive way and not as a 
 recommendation. Reference to the article in question will show this. 
 
 The remarks on agitators and temperature of treatment solutions are 
 interesting additions to the general data on Tonopah practice. 
 
PRACTICE AT TONOPAH 139 
 
 Mr. Jones' objection to my remarks referring to addition of lime and 
 lead acetate is justified by his misinterpretation of the text of my article. 
 " Principally by convenience" referred to the method of addition, not 
 to the quantity of the chemicals used. 
 
 Regarding tube-mill lining, it seemed worth while to call attention 
 to the difference between practice at Tonopah and in Mexico. I did not 
 attempt to convey the impression either that the El Oro lining was the 
 best, or that it had not been tried at Tonopah. What I wished to say 
 was that it is not considered the best in Tonopah and is not in use there, 
 although it has been proved by repeated tests to be best suited to condi- 
 tions in some other districts. 
 
 Stamps versus rolls may be the subject of interesting and lengthy 
 discussion. I hope that Mr. Jones may be induced to publish the facts 
 and figures which led to the decision in favor of stamps at the Belmont 
 mill. Some others have adopted rolls and do not announce any regret. 
 
 H. A. MEGRAW. 
 New York, Mar. 24, 1913. 
 
 Crushing Tonopah Ores 
 
 The following data relative to crushing Tonopah, Nev., ore by rolls 
 may be of interest in the discussion of the subject invited by H. A. Megraw 
 in his article, recently published in the JOURNAL. A set of 10X30-in. 
 Allis-Chalmers rolls was among the equipment of the crushing and 
 sampling department of the Desert Power & Mill Co. These rolls were 
 in operation four years, from December, 1906, to January, 1911, and 
 during that time reduced 29,873 tons of ore, which was 5% of the entire 
 tonnage, cut out by a Snyder sampler. The roll feed was the same as 
 that going to the stamp batteries, varying in size from slime to pieces of 
 ore 2 in. in diameter, this size depending upon the condition of the 4D 
 crushers. The maximum size of the roll product varied between J and f 
 in., depending upon the opening between faces of the rolls. However, 
 usually the reduction would be about 50%. The average time run per 
 day was 5 hr. for a total of 1195 days in operation. 
 
 The power is estimated at 10 hp. and on that basis would amount to 
 a total of 44,573 kw.-hr., which, at $0.0152 per kw.-hr., gives the total 
 power cost $677.52, or $0.0227 per ton of ore reduced by rolls. It is 
 estimated than one-fourth of one man's time at $4.50 per 8-hr, shift, or 
 $0.703 for five hours, a total of $840.09, or $0.0281 per ton, is a fair 
 allowance for the labor of operating the rolls during the 1195 days. 
 Roll shells were refaced in a lathe and five changes were made; 2J sets 
 were worn out during the period of operation. The roll shells weighed 
 
140 
 
 DETAILS OF CYANIDE PRACTICE 
 
 757 Ib. each, so that the total consumption of steel amounted to 4163.5 lb., 
 or 0.14 lb. per ton of ore reduced. The rolls were operated at 103 r.p.m., 
 which gives a peripheral speed of about 800 ft. per minute. 
 
 REPAIR COST FOR ROLL OPERATION 
 
 Labor changing rolls @ $20 . 00, per set 
 
 10 roll shells turned, 6 hr., each @ 69 cents per hr 
 
 80 ft. of 10-in. belt @ 96 cents 
 
 General repairs to feeder, belt liners, etc 
 
 8 bearings babbitted @ $5 . 00 for labor 
 
 Cost of babbit @ $10.00 each 
 
 2f sets of shells @ $146. 62 per set. . 
 
 Total 
 
 Per ton of ore reduced 
 
 $100.00 
 41.40 
 77.20 
 100.00 
 40.00 
 80.00 
 
 $403 . 20 
 
 $841 . 80 
 0.0282 
 
 SUMMARY 
 
 
 Total 
 
 Per ton 
 reduced 
 
 Repairs and upkeep 
 
 $841 80 
 
 $0 0282 
 
 Labor of operating 
 Power used 
 
 840.09 
 677 52 
 
 0.0281 
 0227 
 
 
 
 
 Total 
 
 $2359.41 
 
 $0.0790 
 
 It will be noticed that some of the* above figures are based upon 
 estimates, but it is believed that the estimates are liberal. I have had 
 the impression that rolls can be used to advantage in the milling of 
 Tonopah ore and am of the opinion that a thorough test and comparison 
 would show a saving in initial cost of installation as well as in operating 
 expense, and would welcome the publication of the figures obtained by 
 A. H. Jones when he was investigating the subject of roll crushing before 
 stamps were decided upon for the new Belmont mill. 
 
 A. R. PARSONS. 
 Monrovia, Calif., May 13, 1913. 
 
 Calculation of Extraction 
 
 In the third article on " Silver Cyanidation at Tonopah," by Herbert 
 A. Megraw, in the JOURNAL for Mar. 8, 1913, there is expressed some 
 doubt as to whether the method of calculating extraction is better than 
 the old system based on samples of the mill heads. We are familiar 
 with the trouble between the millman and the general manager, when 
 the head samples indicate extremes of extraction varying from 70% to 
 120%, but it is my opinion that the fault lies not in the mill, but in the 
 assay office. 
 
 When treating a gold ore it is possible, due to the slight mixing the 
 
PRACTICE AT TONOPAH 141 
 
 samples receive in crushing from 1J in. to the size that will pass a 60-mesh 
 screen, for a particle of gold the size of the screen opening to pass in excess 
 into the final assay sample or to be retarded and thrown away with the 
 discard, causing an appreciable error in either case. 
 
 A 60-mesh Tyler screen has an opening of 0.221 mm., and the cube 
 of this aperture is 0.01079 cu.mm. Assuming the gold in the ore to be 
 700 fine, silver, 250, and base, 50 (sp. gr. 7), then the specific gravity of 
 the gold as it goes into the assay will be 16.61, and the value of the 
 same per ounce, $14.62, when the silver has a value of $0.60 per oz. 
 The weight of one of the cubical particles of gold that will pass a 60-mesh 
 screen would be 0.01079X16.61, or 0.1792 mg. For assay 29,166 mg. is 
 taken, and if a particle of gold the size of the aperture passes in excess 
 into the final assay sample, or is retarded with the discard, there is 
 0.1792X14.62, or a value of $2.62 difference from the true assay, repre- 
 senting .26% on $10 ore. 
 
 In an all-sliming plant the screen tests will usually show about 80% 
 through 200 mesh, 19 to 20% on 200 mesh, and 1% or so on 100 mesh. 
 The tailing sample is certainly more intimately mixed in its passage 
 through launders, agitators and filters, than would be economically 
 possible for the head sample. For comparison I shall assume the 
 cubical size of the screen opening, although it is certain that with effective 
 treatment the metal in tailing is not fully exposed to the dissolving 
 effect of the cyanide solution, but exists in the grains of quartz or sulphide 
 in quantities much smaller than the inclosing grains. The cubical 
 opening of a Tyler 200-mesh screen is 0.0004052 cu.m., and its weight, 
 if a gold cube, 0.00673 mg., with a value of $0.098, 80% by weight 
 being taken as through 200 mesh, the value affecting the sample is $0.0784. 
 The cubical opening in a 100-mesh screen is 0.002744 cu.mm., and its 
 value is $0.67. This, with 20% of the sample on 100 mesh, gives a value 
 which may affect the final result of $0.13. The small portion on 100 
 mesh, all of which will pass 80 mesh, cannot account for a difference of 
 more than $0.01. The sum total giving a value of $0.22, which would 
 have an effect of only 2.2% on extraction. 
 
 Having shown the value of the particles, it would not be amiss to 
 show the number of sand, and gold particles in each case, arid their 
 proportions. The specific gravity of tailing being about 2.6, the weight 
 of a cubical particle that will pass a 60-mesh screen is 0.01079X2.6, or 
 0.02805 mg. In one assay ton there are 1,039,809 possible particles of 
 this size. In ore assaying $10 and bullion worth $14.62 per oz., we have 
 0.684 mg. in one-assay ton, which divided by 0.1792, gives 3.817 particles 
 of gold. Having 3.817 particles of gold that will pass the 60-mesh 
 screen, there will be, to complete the assay ton, 1,039,785 particles of 
 sand. 
 
142 DETAILS OF CYANIDE PRACTICE 
 
 In the case of the slime the value is assumed proportional to the 
 screen tests by percentage. With a total value of $0.50, the value of 
 the minus 200-mesh material is $0.40, and the weight 25,332.8 mg. The 
 weight of a gold cube equal in size to the aperture in a 200-mesh screen is 
 0.00673 mg., and $0.40 represents 0.02736 mg. Therefore, there are 4,065 
 particles of gold, and, consequently, 25,327.735 mg., exclusive of the gold. 
 Then 25,327.735 divided by 0.0004052X2.6 gives 24,083,772 particels, 
 exclusive of the gold. 
 
 With 19% on 200 mesh, the weight is 5541.5 mg., and the weight of 
 the gold cube the size of the screen opening is 0.04558 mg., giving actually 
 0.1462 particles of gold in this part of the sample; 5541.54 mg., minus 
 0.0065 mg., gives 5541.5335 mg., which, divided by 0.002744X2.6 gives 
 776,734 particles, exclusive of the gold. 
 
 On 100 mesh there is 1% containing $0.005, and weighing 0.00034 
 mg., the cubical opening of an 80-mesh screen is 0.005178 cu.mm., and 
 the weight of the same cube of gold is 0.0756 mg. Therefore, 0.00034 
 divided by 0.0756 gives 0.0045 particles of gold, which may remain on 
 100 mesh. There are then 291.66 mg. minus 0.00034 mg., or 291.6596 
 mg. of sand, and 291.6596 divided by 0.005178X2.6, or 21,664 particles 
 besides those of the gold. 
 
 To sum up these facts, we have, in heads, 3.817 particles of gold, 
 and 1,039,785 particles of sand, or a ratio of 1 to 271,800, and in tailing 
 4.2115 particles of gold, and 24,882,170 particles of sand, or a ratio of 1 
 to 5,908,000. From the ratio of gold particles to sand particles, the 
 chances of having an error in the head sample as compared with the tail 
 sample is about 21 J times as great. 
 
 Of the usual head sample only one is taken, while with tailing a sample 
 is generally taken from each cycle, at least four samples a day, and any 
 discrepancy in one is partly compensated by the assayer when he takes 
 the mean of the four. 
 
 Tons stamped, and tons discharged may not be the same, but under 
 proper operating conditions the results over a period of 12 months will 
 not indicate enough of a difference to justify a suspense account. 
 
 Providing there are no mechanical wastes of slime or solution, except 
 in the regular filter discharges, then the value of bullion, plus the value of 
 tailing discharged, divided by the number of tons treated, should give a 
 closer true value of each ton of ore than the older methods. 
 
 A. G. CADOGAN. 
 Puntarenas, Costa Rica, Apr. 25, 1913. 
 
 In the JOURNAL of Mar. 8, 1913, H. A. Megraw, in his article, " Silver 
 Cyanidation at Tonopah III," states that in most of the mills there, the 
 
PRACTICE AT TONOPAH 143 
 
 calculation of extraction is performed by using the content of bullion 
 produced plus the content of tailing discharged as the content of head 
 samples. This, no doubt, is excellent from the point of view of the 
 millman in charge of the plant and doubtless saves him much worry, 
 but from the point of view of accuracy it leaves something to be desired. 
 
 There may be serious errors constantly occurring, which, with the 
 above-mentioned method of calculation, would never be suspected. 
 Quite considerable quantities of bullion might be stolen and no one be 
 any the wiser. Moreover, there is no way of finding out if there is any 
 serious unnoticed leakage in the plant. 
 
 No doubt the assayer can be checked with duplicate samples, but the 
 greatest test on his work and on the tonnage calculation is whether the 
 output of bullion tallies with the theoretical quantity required. With 
 careful work there should be no reason why the bullion output should 
 not check within reasonable limits. This gives satisfaction to every one 
 concerned and then, should there be any serious discrepancies, the cause 
 will probably be noticed almost at once, whereas with an adjusted method, 
 such as that used at Tonopah, there can only be an accumulation of 
 error. 
 
 The fact of crushing in solution complicates the mill-head sample 
 slightly, owing to metal being dissolved while in the mortar box, and also 
 by the bullion content of the cyanide solution in circulation. However, 
 a fair sample of the mill-head can be obtained from the pulp on leaving 
 the mortar boxes. If this is assayed, and also the solution before and 
 after it comes in contact with the ore, the proportion of solution to ore 
 being known and its bullion content allowed for, the original content of 
 the ore can easily be calculated. The pulp, of course, will have to b 
 washed before assaying. 
 
 Extractions varying between the limits of 60% and 120% are cer- 
 tainly annoying, but this sort of thing is almost inevitable. However, 
 these variations only happen from month to month and the important 
 matter is what the annual result is going to be; the monthly reports are 
 only to see how the production is progressing. It stands to reason if 
 for several months an unusual quantity of bullion is taken from the zinc 
 boxes and extra zinc acided, which usually happens at the end of a 
 financial year in order to balance accounts, that the actual production 
 for those months will be in excess of the theoretical. 
 
 Later, owing to less short zinc being present in the boxes, the bullion 
 distributes itself over a larger proportion of long zinc than usual, with 
 the result that not so much bullion is cleaned up and there is an apparent 
 shortage. Conversely if there is an apparent shortage of, say, 20% on a 
 90% extraction, if calculations are correct and there is no other source 
 of error, there is no reason why a month or two later, taking the extraction 
 
144 DETAILS OF CYANIDE PRACTICE 
 
 as being 90%, there should not be an actual extraction of 110%, making 
 up for the original 20% left in the boxes. About the middle of the 
 financial year, the boxes would be in normal condition and one would 
 expect the theoretical and actual extractions to be about the same. 
 
 Taking the year 1912 at the Mijnbouw Maatschappij Ketahoen, the 
 cyanide plant treated 47,597 tons of ore with a total content of 7160.7 oz. 
 gold for a theeortical extraction of 88.7%, calling for 6350.55 oz. The 
 actual gold recovered was 6325.22 oz., or an actual extraction of 88.3%, 
 the difference being 25.33 oz. The silver called for was 19,315.46 oz., 
 whereas 19,224.46 oz. were recovered, a shortage of 91 oz. 
 
 Monthly actual extractions varied between 59.5% and 123.3%. 
 This has also been the case for the years 1909, 1910 and 1911 with 
 equally close yearly results. 
 
 GEORGE SIMPSON, JR. 
 
 Mijnbouw Maatschappij Ketahoen, 
 Lebong Soelit, Benkoelen, Sumatra^ 
 
 May 1, 1913. 
 
 An article, by Herbert A. Megraw, in the JOURNAL of Mar. 8, on 
 " Silver Cyanidation at Tonopah III," has just come to my notice and 
 I am somewhat surprised to learn that the method of calculation of 
 extraction referred to is in use in any of our " up-to-the-minute-in- 
 efficiency" milling plants, and I am inclined to at once agree with Mr. 
 Megraw that the question of such method should be discussed. The 
 estimation of mill-head contents by adding bullion content to tailing 
 content and dividing by tonnage, is not a method worthy of a metal- 
 lurgist, and, as Mr. Megraw so fittingly puts it, is certainly l< & method of 
 solving a problem by means of which any answer is the right one." 
 
 Such methods are not, I believe, in general use, but are being mostly 
 used by operators for stock companies. There are two classes of mining 
 shareholders; those holding shares as an income-gaining investment, 
 and those holding them for the purpose of speculation. Dividend- 
 receiving shareholders do not exact highest efficiency. They are glad 
 to get a dividend instead of an assessment and seldom question the 
 methods. Those holding shares for stock operating are not interested. 
 If the mine is paying its way, with an occasional dividend, declared at 
 the right time to stimulate a dull market, nothing more is expected or 
 wanted. However, from an engineer's standpoint, or from a business 
 man's standpoint, the system leaves much to be desired. 
 
 Not only is the system referred to the source of inaccurate statements 
 and fictitious results, but it is unscientific and unbusinesslike, and tends 
 to show a lack of moral courage on the part of the well-paid specialists 
 
PRACTICE AT TONOPAH 145 
 
 in charge of operations. Advocates of the system will claim that they 
 are continually watching results and working toward better extractions, 
 and that they get everything possible out of the ore anyway, so why 
 undertake additional work which would result in no benefit and only 
 confuse the records. How do they know they are getting everything 
 possible out of the ore, if they do not know what the ore contains to start 
 with? They tell by the tailing assays; if these are low they assume results 
 to be correct. How do they know that the bullion recovered is the true 
 difference between head and tail content? Tailing content may be low 
 and still the bullion produced may not represent what should have been 
 recovered from the ore, or perhaps what really was extracted, Losses 
 may occur through carelessness, faulty treatment, or dishonesty. These 
 losses, which may amount to much, are entirely unguarded under such a 
 system. 
 
 If an operator is afraid of his mill head, why is he not afraid of his mill 
 tailing? He probably is not afraid of either alone, but does not care to 
 meet both together, particularly when he is standing between them with 
 the " brick." There is no reason why the tailing sample or assay should 
 be more reliable than the head sample or assay. In many cases, it is 
 much less reliable. Who ever heard of a correct tailing sample during the 
 time anything was going wrong in the mill, especially when there was no 
 record of heads? How can tonnage represented by tailing samples be as 
 accurately established as tonnage represented by head samples? In 
 cases where sand and slime are treated separately, the calculation of 
 proportionate tonnage increases such inaccuracy. 
 
 When the head content is known, an efficient system of solution 
 sampling will check both bullion and tailing, but when the head is un- 
 known, this will only check the bullion. It is true that bullion plus tailing 
 content is equal to the head content if no losses or errors occur, but they 
 do occur, and hence the formula instead of being B + T = H, should 
 be written B + T + L = H. But H and L being both unknown 
 quantities, "any answer is the right one." 
 
 By having the head assay, precipitation record from solution assays, 
 tailing assays and correct tonnage record, results are positive and any 
 discrepancy represents loss or error, the two most important things the 
 metallurgist is paid to guard against. He is not necessarily careless or 
 incompetent when such discrepancies occur, but displays his ability when 
 he finds and removes the causes for such losses or errors. Having no 
 head assay, it requires no ability on the part of the metallurgist to keep 
 his records free from discrepancies except that he must be able to add 
 correctly. 
 
 By one method the treatment is controlled or regulated by a knowl- 
 edge, before treatment, of what is being treated. By the other method 
 
146 DETAILS OF CYANIDE PRACTICE 
 
 the treatment is controlled or regulated by a knowledge, after treatment, 
 of what was treated. By one method the operator is able to arrange his 
 treatment so as to secure the best results, by the other he makes a guess 
 and then, after treatment is finished, he determines how far he was off 
 and makes his answer right by fitting his original problem to it. He 
 never does know what per cent, extraction is being made (a $2 tailing 
 may be the result off better per cent, extraction than a $1 tailing), not 
 that it makes any material difference, as the actual amount of bullion is 
 the main thing, but he reports his percentages just the same; how? 
 
 The method is also unfair to the mine. The mill keeps its record clean 
 and all contained values that come to it are accounted for and reported 
 either in bullion or tailing, but the mine must stand its own losses as 
 well as those of the mill. The mine may be sending $20 ore to the mill, 
 but the B + T system may only show $18 as mill head, which is all the 
 mill will acknowledge receiving. What becomes of the $2? Where is 
 it charged? Who loses it? It flutters about unaccounted for, for a 
 time, and then finally settles unowned and unnoticed in the little nest of 
 " shrinkage of previously estimated ore reserves," shown in no report, a 
 most convenient hiding place for inaccuracies, losses and results of the 
 inefficient method of " calculation of extractions." If a careful in- 
 vestigation were made into the cause of discrepancies in mill results, on 
 account of which this " any-answer-is-the-right-one " method has been 
 adopted, it will be found that an incorrect tonnage record is a greater 
 factor in the matter than will be generally conceded. 
 
 A. SIDNEY ADDITON. 
 San Francisco, Calif., June 14, 1913. 
 
 The custom of using the content of bullion produced plus the content 
 of tailing discharged as the value of the feed in milling operations, as 
 stated by Mr. Megraw in the JOURNAL of Mar. 8, 1913, easily accounts 
 for the High percentages of extraction frequently reported. Occasionally 
 more reasonable estimates 1 may be found in the reports published by 
 
 A-B When 
 
 X100 C A = Assay value of feed; 
 
 C B B = Assay value of tailings ; 
 
 = % extraction. C = Assay value of concentrates. 
 
 A 
 
 This formula would give correct results if the assays of feed and tailings could be 
 relied upon, but with an assay of settled tailings, i.e., tailings minus float, the extrac- 
 tion percentages so obtained may be more than 18% above the actual extraction and 
 
 J A formula much used for calculating the extraction, and which is stated to be 
 convenient for approximate estimations when it is impracticable to weigh the prod- 
 ucts, is the following: 
 
PRACTICE AT TONOPAH 147 
 
 it is therefore undesirable to make use of this formula. Ashcroft "The Flotation 
 Process," "Trans.," I. M. M., 1912, and "Eng. and Min. Journ.," Dec. 7, 1912, p. 
 1085. 
 
 large mining companies working low-grade ores, as such companies 
 generally make use of sampling devices and employ their own assayers, 
 but no calculation into which the assay value of the tailing enters can be 
 of value because, under working conditions, it is impossible to ascertain 
 directly the real value of the tailing. 
 
 From the moment concentration commences the water made use of 
 carries off mineral of value, and this continues all through the process. 
 The amount of floating mineral will vary with the fineness of division of 
 the particles, degree of concentration, amount of water used, and in- 
 clination of the tables, or with the rapidity of concentration. The 
 effect of these circumstances is to cause the settled tailing to be invariably 
 of lower assay value than if there were no float. 
 
 The subject of extraction percentages is one which occupied my 
 attention for several years, owing to my having been engaged by a 
 mining company to carry out investigations with a view to ascertaining 
 the amount and manner of loss in the wet concentration of silver ores. 
 No trouble or expense was to be spared and ample opportunity was 
 afforded to make experiments on whatever scale seemed advisable. 
 
 To estimate the extraction it was clearly necessary to know either the 
 correct value of the mill feed or of the tailing. To obtain the tailing value 
 was difficult on account of the constant loss in the overflow and the 
 impossibility of collecting the whole of the material under ordinary 
 circumstances of working, and it was therefore decided to depend on the 
 assay value of the feed. 
 
 During the tests, samples of the settled tailing were taken and 
 assayed, but in no instance did their value agree with the theoretical 
 value obtained by difference. Their value was invariably lower and 
 the difference greater with higher degrees of concentration. At first, it 
 was supposed that some error had been made in sampling or assaying, 
 and check samples were taken and assayed, but these only confirmed the 
 low value of the settled tailing. In the opinion of the operators, the 
 water only carried off the more soluble portion of the waste. It seemed, 
 however, that the mineral accompanying this might account for the low 
 value of the settled tailing. After this, a number of tests were made to 
 ascertain the extraction in jigging, in sand treatment, and in concen- 
 trating slime, by concentrating in the usual manner about 10 tons of ore 
 in the same condition as fed to the different machines, it being possible 
 in concentrating a moderate quantity of ore to collect the entire tailing in 
 tanks. As a result of many tests it appeared that the percentage of 
 floating material was proportional to the fineness of the particles treated 
 
148 DETAILS OF CYANIDE PRACTICE 
 
 and that its value was more than twice the theoretical assay value of the 
 tailing. Thus, the discrepancy between the theoretical and actual assay 
 value of settled tailing was accounted for. 
 
 The tests referred to were made with the same care in weighing, 
 sampling and assaying the ore and products of concentration as would 
 be exercised by a smelter purchasing ore, and were under my constant 
 personal inspection, the object being to arrive at the actual rate of loss 
 per degree of concentration of value in each of the three operations 
 mentioned. The assumption was that with this data it would be possible 
 to calculate with precision the probable results to be obtained in con- 
 centrating ores of different assay value to different degrees of value, 
 by the methods of concentration made use of at the establishment under 
 consideration, without the necessity of weighing the feed or the tailing. 
 
 Loss in concentration appears to arise from : First, the unavoidable 
 loss characteristic of the particular ore concentrated, arising from the 
 degree of natural concentration of the value in the gangue, its combina- 
 tion with various sulphides, and the nature of these; and second, the 
 degree of division of the particles, which is the main cause of loss. 
 
 Some minerals are more friable than others, but the percentage of 
 mineral to gangue is so small that it would not materially affect the general 
 friability of the mass, and it may be assumed that ore of different minerals 
 will crush in a similar manner and that the effect of division would be 
 similar, although the float slime might be of higher value with friable 
 ore. Hence, the weight of float arising from a certain degree of crushing 
 an ore may be taken to be a measure of the percentage of float in crushing 
 any ore to a similar degree, and this appears to be confirmed by the few 
 examples which it has been possible to obtain. 
 
 The accompanying scale of extraction percentages obtained in 
 concentrating a silver ore, crushed to pass a 30-mesh screen, aperture 
 0.0166 in., will illustrate the application of the results of some of the 
 tests made. The silver was associated mainly with iron pyrites and a 
 small amount of blende and occasional small quantities of galena, and 
 occurred as pyrargyrite and in combination with copper (fahlerz). 
 The matrix was quartz of average hardness. 
 
 The extraction by formula based on the assay value of the settled 
 tailing was 4.2669% at 2 : 1 concentration, and 18.3545% at 12 : 1 con- 
 centration, in excess of the actual extraction. 
 
 It will be observed that* the difference in the assay value of the 
 settled tailing and the total tailing is so small in low degrees of con- 
 centration that, with ores of little value, it might escape attention 
 unless great care were taken in sampling and assaying. 
 
 The method adopted for finding the percentages of extraction and 
 loss incurred, weight and value of concentrates and tailings, for any 
 
PRACTICE AT TONOPAH 
 
 149 
 
 degree of concentration or value of feed, according to results obtained in 
 carefully made tests, was as follows: 
 
 ii 
 
 
 -o 
 
 K) O U3 u 
 
 00 00 00 X X 
 
 (N i-H 1-H i-H 
 
 Degree 
 concentrati 
 values 
 
150 
 
 DETAILS OF CYANIDE PRACTICE 
 
 The total possible loss being 100%, the loss due to different degrees 
 of concentration of the values will be proportionate percentages of this 
 loss according to the degree of concentration: 
 
 PERCENTAGE OF LOSS IN VARIOUS DEGREES OF CONCENTRATION 
 Degree = % of total loss Degree = % of total loss 
 
 0=0 
 
 2=50.0 
 
 3=62.5 
 
 4 = 75. 
 
 5=78.125 
 
 6=81.25 
 
 7=84.375 
 
 8=87.5 
 
 9 = 88.28 
 10 = 89.06 
 11=89.84 
 12 = 90.625 
 13=91.41 
 14 = 92.19 
 15=92.97 
 16 = 93.75 
 
 To find the total loss, first divide the assay of the concentrate by the 
 assay of the feed to find the degree of concentration, then by means of the 
 table find the relative percentage and, from this, the total loss. When the 
 total loss is found by means of a test, the loss in concentrating similar 
 ore of any assay value, and in a similar state of division, may be found, as 
 it will correspond to the percentage of the total loss for that degree. 
 In this manner the percentage weight of tailing and concentrate may be 
 found and the actual value of the tailing. 
 
 The total loss may exceed 100% when the rate of loss is great, due to 
 water used in concentration being excessive or there is a reversal of 
 concentration. 
 
 A knowledge of what the actual value of the tailing may be at different 
 degrees of concentration is of great importance, as concentration may be 
 carried to such an extent as to become negative, that is to say, the discard 
 will be of greater value than the feed, owing to the tailing increasing in 
 value in proportion to the degree of concentration. The first tailing 
 discarded, up to a concentration of 2 : 1, is the largest in amount and the 
 least valuable. After this it becomes richer and less in quantity; this, 
 however, is liable to pass unnoticed, as the amount being small in com- 
 parison with the first tailing, the average value of the whole of the tailing 
 is not greatly increased. The following example of concentrating cop- 
 per ore, sand and slime, with bubbles will illustrate this: 
 
 Degree 
 of 
 concentration 
 
 Tons 
 concentrate 
 
 % 
 
 Tons 
 tailing 
 
 % 
 
 Extraction 
 
 % 
 
 Loss 
 
 % 
 
 Average value 
 of tailing 
 units 
 
 2 
 4 
 8 
 
 22.56 
 4.42 
 0.495 
 
 77.44 
 95.58 
 99.505 
 
 45.12 
 17.68 
 3.96 
 
 54.88 
 82.32 
 96.04 
 
 7.0868 
 8.6127 
 9.6518 
 
 The unit has been taken as 10 for feed. 
 
PRACTICE AT TONOPAH 151 
 
 In this scale of concentration the total loss found by experiment was 
 109.76%, so that there was a reversal of concentration at some point. 
 Concentrating 22.56 tons to 4 : 1 would produce 4.42 tons concentrate 
 with 18.14 tons tailing at 15.127 units, but concentrating to 2.5 deg. the 
 tailing would be worth 9.463 units, the limit to which concentration could 
 be carried without reversal. 
 
 In the vanner treatment, the total possible loss, found by experiment 
 was 106.66, about the same as with the buddies; consequently it was not 
 possible to concentrate beyond 2.5 degrees ih either case. The con- 
 centration, however, was carried to 4.9471 degrees by vanners and 
 2.6277 degrees by buddies. The combined concentration was, by jigs, 
 12.734 degrees, extraction, 57.095%; by vanners, 4.9471 degrees, extrac- 
 tion, 17.589%; and by buddies, 2.6277 degrees, extraction, 36.545%; 
 and combined, 8.4692 degrees, extraction, 69.575%. Assuming the data 
 given to be correct, the tailing would have an average content per ton, 
 0.70443% copper, of which, according to the loss in float resulting in 
 tests of silver ores, 35% of the weight of tailing would have been carried 
 off with 57% of the calculated contents of same, and the value of the 
 settled tailing would have become reduced to 0.46594% copper, equal to 
 a reduction of 0.23849% in the percentage value. 
 
 Calculating the percentage of extraction by the formula, with value 
 of settled tailing 0.4659%, an extraction of 80.10% would be obtained or 
 15.127% in excess of the actual combined extraction. The excess, how- 
 ever, would be much more in calculating separate recoveries by vanners or 
 buddies. 
 
 The relative extraction by the different machines at the same degree of 
 concentration was: Jig, 76.48%; vanner, 46.67; buddle, 45.12%. This 
 must not be considered as a measure of efficiency but, if anything, a 
 measure of the fineness of division of the particles. The float percentage 
 on the tailing was: Jig, 10 to 15%; sand tables, 30%, due to a portion 
 being reground; buddies, 45%, due to nearly all being reground. 
 
 A single test was not found to be sufficient as a test of the recovery or 
 of the amount of float occurring in the operations of a mill, because, in 
 working, buddle heads are sent to tables, and table seconds and slime 
 go to buddies, and these combinations alter the conditions. It was 
 found that the regrinding greatly increased the loss and this without 
 doubt was the main cause of lower results being obtained under working 
 conditions than in single tests. The main loss arises from float whatever 
 machine is used and there appears to be little chance of overcoming this 
 difficulty. The great loss of tin slimes in Cornwall is evidence of this 
 but it may be possible to improve extraction by paying more attention 
 to coarser crushing and jigging. It is not sufficient to infer from observa- 
 tion only that an ore requires to be crushed fine to obtain the best results 
 
152 DETAILS OF CYANIDE PRACTICE 
 
 in its concentration and the possibility of obtaining better results from 
 coarse crushing may well repay the trouble of carefully ascertaining the 
 most favorable degree of crushing in each case, as even adjacent veins 
 vary much in the natural concentration of their values. With silver 
 ores, the tailing is hardly ever of lower value than 8s. per ton; conse- 
 quently, every ton of waste picked out by hand before concentration 
 results in a considerable saving, as it raises the value of the remainder, 
 thereby reducing the degree of concentration required and, at the same 
 time, reducing the loss in treatment of the whole. 
 
 WILLIAM S. WELTON. 
 London, Eng., Apr. 8, 1913. 
 
CHAPTER XIII 
 THE NEVADA HILLS MILL, AT FAIRVIEW 
 
 The plant of the Nevada Hills Mining Co. is situated at Fairview, 
 about 45 miles southeast of Fallon, Nev., the nearest railroad station. 
 Due to the lack of immediate railroad communication the entry of 
 supplies is slow and somewhat expensive. A line of automobile stages, 
 however, makes passenger and mail transportation more easy and 
 simple. The situation of the plant, so far removed from the railroad 
 point, makes the obtaining and retaining of competent labor somewhat 
 difficult. The fact that the company is the only one operating actively 
 in the district does not help matters in this respect, and it is stated that 
 the labor question is one of the important ones to be handled. 
 
 Varied Character of the Ores. The ores milled at the Nevada Hills 
 mill vary in both character and hardness, but on the average may be 
 said to be somewhat harder than the usual Nevada silver ores. In 
 character they vary from clean, easily treated mineral to complex 
 deposits, which give some trouble in beneficiation. The oxidized ores 
 contain a certain quantity of manganese and are generally more difficult 
 to cyanide than the sulphides, an extraction of 87% being usual on the 
 former and on the latter 94% or more. Calculating on a basis .of the 
 average mill run an extraction of 92% is obtained. The mill treats from 
 120 to 140 tons per day, depending on the character of the rock. The 
 proportion of silver is about as 100 : 1, the ordinary mill heads averaging 
 $20 to $22 per ton. 
 
 The mill is situated at the shaft head, thus obviating transportation 
 difficulties, the mine skips dumping directly into a bin at the head of the 
 mill. The mill building is a steel-frame structure covered with iron, 
 substantial and well built. 
 
 Sampling and Weighing Plant. The ore coming from the mine is 
 dumped into a 300-ton bin from which it is fed to a Blake crusher, the 
 product of which passes over a shaking grizzly into an elevator. This 
 elevator lifts the rock to a sorting and conveying belt, where the waste 
 is taken out after the whole has been given a spraying wash, to facilitate 
 the sorting operation. 
 
 The original design of the mill included at this point an automatic 
 weighing device and sampling plant, but both of these have now been 
 eliminated from the operating plan and the passage of ore is as above 
 11 153 
 
154 
 
 DETAILS OF CYANIDE PRACTICE 
 
THE NEVADA HILLS MILL, AT FAIRVIEW 155 
 
 stated. The reasoning leading to the abandonment of these steps is 
 that the expense of operating them was more than any advantages gained 
 from them. It is noteworthy that practically the same condition obtains 
 at the mill of the Goldfield Consolidated, at Goldfield, where the ex- 
 tensive sampling plant originally built was never replaced after its 
 destruction by fire. 
 
 Whether a sampling and weighing plant is worth its cost of installation 
 is a question which seems to have been decided in the negative in recent 
 years, although in former times such refinements were considered indica- 
 tions of approximate perfection. The system of calculating extraction 
 percentages by using the sum of bullion output plus tailing content as the 
 content of ore entering the mill has rendered sampling unnecessary and 
 weights can be approximated in some other more economical manner 
 than by actually passing the mill run over scales. In speaking of the 
 Tonopah mills I have already referred to this method and in writing on 
 conditions at the Black Hills I mentioned the advisability of sampling 
 and weighing plants for these mills. These later facts brought out 
 by the investigation of further plants will modify the conclusions made 
 earlier, but even at this time I do not feel altogether convinced that the 
 methods so universally used at the present time are the best ones. 
 
 Methods of Calculating Extractions. The arguments used by ad- 
 herents of the latest method of calculating extractions are that even with 
 elaborate sampling plants it is difficult to obtain an. accurate sample; 
 that even if accurate samples are secured, they are liable to corruption 
 through the inaccuracies of assaying, the fact being advanced that there 
 is always a certain loss in assays and that the loss on the higher-grade 
 samples, heads, is greater than on the lower-grade samples, tailing; and 
 that the varying amount of metal contained in mill pulp and solutions 
 makes accurate calculation an impossibility in any case. All these argu- 
 ments, no doubt, have weight, although it does seem that some method 
 of calculating a check could be devised. 
 
 As concerns sampling and weighing, I am convinced that by using 
 properly designed apparatus in^the hands of competent operators an 
 accurate sample is possible. And also that chemical science is not so 
 limited but that an exact estimation of the contained metal in any sample 
 can be made. As to the conditions within the mills themselves, that is an 
 entirely different matter and a question not so easily solved. In the older 
 style of mill where sand and slime are treated separately, the slime going 
 through the mill in three or four days while the sand portion remains in 
 process of treatment as much as 15 days, it is evidently impossible to 
 calculate extractions over a short period of time, although if the period 
 be long enough a fair approximation of accuracy should be obtainable. 
 In the newer mills treating all the ore as one product, calculations ought 
 
156 DETAILS OF CYANIDE PRACTICE 
 
 to be considerably simplified. In its present condition this question can 
 hardly be considered definitely settled and I believe operators ought to dis- 
 cuss it publicly and see if some satisfactory solution cannot be advanced. 
 Chemical Consumption and Operating Cost. The consumption of 
 material is about as follows: Cyanide, 2.7 lb.; lime, 9 lb.; lead acetate, 
 0.8 lb.; zinc, 1.5 lb. per ton; pebbles, 3 lb. per ton of ore milled. The cost 
 of operation at the Nevada Hills mill is given completely in the accom- 
 panying table: 
 
 OPERATING COSTS AT NEVADA HILLS MILL 
 
 Per ton 
 Crushing: ore milled 
 
 Labor $0.052 
 
 Repairs 0.003 
 
 Power 0.016 $0.071 
 
 Stamping : 
 
 Labor 0.106 
 
 Repairs 0.024 
 
 Power 0.117 . 247 
 
 Concentrating : 
 
 Labor 0.087 
 
 Material 0.011 
 
 Power 0.021 0.119 
 
 Elevating and separating: 
 
 Labor... 0.042 
 
 Material 0.004 
 
 Power v . 0.025 0.071 
 
 Assaying and sampling: 
 
 Labor.. 0.134 
 
 Material 0.001 
 
 Power 0.008 0.143 
 
 Tube milling: 
 
 Labor 0.040 
 
 Material 0. 104 
 
 Power 0.149 0.293 
 
 Settling and agitating: 
 
 Labor 0.105 
 
 Material 0.655 
 
 Power 0.062 0.822 
 
 Continuous dficantation: 
 
 Labor . 020 
 
 Material 0.004 
 
 Power 0.008 0.032 
 
 Filtering: 
 
 Labor 0.096 
 
 Material 0.028 
 
 Power.. 0.052 0.176 
 
THE NEVADA HILLS MILL, AT FAIRVIEW 157 
 
 OPERATING COSTS AT NEVADA HILLS MILL (Continued) 
 
 Per ton 
 ore milled 
 
 Discharging : 
 
 Labor 0.066 
 
 Material 0.046 
 
 Power 0.013 0.125 
 
 Precipitation: 
 
 Labor 0.057 
 
 Material 0.191 
 
 Power 0.032 0.280 
 
 Refining: 
 
 Labor 0.073 
 
 Material. . . '. 0.077 
 
 Power 0.003 0.153 
 
 Heating: 
 
 Labor 0.004 
 
 Fuel (oil) 0.052 0.056 
 
 Water 0.005 
 
 Surface equipment: 
 
 Labor ' 0,007 
 
 Material 0.003 
 
 Power 0.004 0.014 
 
 General expense : 
 
 Labor 0.015 0.015 
 
 Total $2.622 
 
 Note Cost based on milling 4030 tons of ore in 30 days. 
 
 The ore ready for the mill is dumped into a 600-ton mill bin back of 
 the batteries, into which it is fed through feeders of the Challenge type, 
 but driving by means of a wire rope instead of the usual grip used on them. 
 
 There are 20 stamps, each 1250 Ib. in weight, making 107 drops 
 through 6J in. and crushing through 8-mesh screen. The pulp from the 
 stamps is delivered into two cone classifiers, each 36 in. diameter, where 
 it is divided into two portions, one containing the coarser sand and the 
 other the finer part of the pulp. 
 
 Classified Concentration. The underflow, or sandy portion, from the 
 classifiers is passed to a pulp distributor, whence it is distributed to six 
 No. 2 Deist er concentrators, the overflow of the cone passing around this 
 concentration system into a second battery of two hydraulic cone 
 classifiers. 
 
 The tailing from the sand concentrators is passed to Akins classifiers. 
 The overflow from the first classifiers passes to the second battery, where 
 the underflow, containing the heavier part of the .pulp, goes to another 
 pulp distributor and thence to eight No. 3 Deister concentrators. The 
 
158 DETAILS OF CYANIDE PRACTICE 
 
 overflow, consisting of slime ready for agitation treatment, goes directly 
 to the first thickener, as will be mentioned. 
 
 From the slime concentrators, the pulp with the concentrate removed, 
 flows to a distributor which divides it in two and delivers to two 48-in. 
 Akins classifiers, these being of the well-known interrupted spiral flight 
 type, the overflowing slime joining that coming from the second battery 
 of hydraulic classifiers, while the sand is passed to another distributor 
 which delivers to two tube mills, each 5 X 18 ft. The reground product 
 from these mills is returned to the second battery of classifiers, where the 
 slimed portion is taken out and the remaining pulp follows through the 
 concentration and mechanical classification process. This procedure is 
 shown in the accompanying flow sheet. 
 
 Continuous Agitation. The slime for agitation is taken first to one 
 Dorr thickener, 34X12 ft., where it is thickened from about 6:1 to 1:1. 
 Issuing from this thickener, the pulp goes to the agitation series, before 
 reaching which, however, it is diluted to 2 or 2J : 1 by solution made up to 
 treatment strength, which contains 5 Ib. KCN per ton. The solution 
 used throughout the mill averages 3 Ib. per ton,' all crushing being in 
 solution. 
 
 There are nine agitation tanks of the Pachuca type, each 12 ft. diame- 
 ter by 32 ft. deep. The pulp for treatment passes through six of these 
 tanks in series, the flow being continuous. From these tanks it is taken 
 to a Trent agitator tank, of the same size as the thickener, and thence to 
 a 34Xl2-ft. Dorr thickener. Here the pulp is thickened again to about 
 1 : 1, and subsequently diluted with fresh made-up solution. The pulp 
 then passes to another series consisting of three Pachuca tanks, of the 
 same size as those formerly mentioned, through which it passes con- 
 tinuously. 
 
 This interrupted agitation series is especially worthy of note, as it 
 accomplishes a continuous agitation and also a change of solution, a 
 condition making for better extraction and one which I advocated some 
 years ago for silver ores when continuous agitation was proposed but not 
 generally practised. 1 The advantage of a change of solution during a 
 long agitation period is generally recognized and this method of ac- 
 complishing it can hardly fail to produce beneficial results. 
 
 Washing by Decantation. From the second agitation series the pulp 
 is passed to a tank 29.5 ft. diameter by 13.5 ft. deep, in which is installed 
 a Dorr agitating mechanism. In passing it is worth while to mention the 
 working of this machine. It has two agitating arms which revolve at 
 4J r.p.m., and the central air-lift pipe is 12 in. diameter. This air lift 
 delivers the pulp to two arms suspended above the surface of the pulp in 
 the tank and which revolve in unison with the submerged arms. The 
 
 1 "Continuous Processes," Mex. Min. Journ., August, 1910. 
 
THE NEVADA HILLS MILL, AT FAIRVIEW 
 
 159 
 
 Solution 
 
 Skip 
 
 I -500 Ton Bin 
 l-l2"x20"B)ake Crsher 
 
 /-Shaking Grizzly 
 
 Elevator 
 SortingBelt 
 
 1-600 Ton Milt Bin 
 4-Suspended Feeders 
 
 20-1250 1 b.Stemps,6jr"drop, I07drops 
 8 MeshScreen 
 
 2~36 Hydraulic Cone Classifiers 
 
 I -36" Pulp Distributor 
 
 / 6- Ho. 2 De/'ste r Concentrators 
 
 Concentrate 
 
 2-36" Hydraulic Cone Classifiers 
 1-36 "Pulp Distributor 
 
 8-No.3 Deister Concentrators 
 
 entrate 
 
 1-36 Pulp Distributer 
 
 2-48" 'Ak ins Classifiers 
 1-36 "Pulp Distributor 
 2-5x18' Tube Mil Is 
 
 1-34x12 'Dorr Thickener 
 
 6~l2x32'Pachuca Tanks inSeries 
 I- 34x12 'Trent 'Agitator Tank 
 l-34'x!2' Dorr Thickener 
 *3-l2x32' Pachuca Tanks in Series 
 l-2exlSj Dorr Agitator Tank 
 3-34x12' Dorr Thickeners 
 
 rrre/7 Solution 
 
 2-12' Oliver Filters 
 
 Residue 
 
 l~PregnantSolution Tank- 
 
 2-36 f '~40 Frame Clarifying Presses 
 
 2-2 inc Dust Feeders 
 
 Pumps 
 
 . 2- Merrill Precipitation Presses 
 
 f" 
 
 *i) 
 
 ^ Barren Solution Tanks 
 
 Bullion Furnaces 
 FLOW SHEET OF NEVADA HILLS MILL. 
 
160 DETAILS OF CYANIDE PRACTICE 
 
 outside arms consist of a launder which carries the pulp from the air lift 
 and drops it at various points over the tank surface, an arrangement of 
 slots or openings allowing an equal distribution. It is stated that tests 
 have shown that the pulp within this agitator maintains its homogeneity 
 at all points within 2% when tested by specific gravity, pulp assay or 
 screen test. 
 
 From this agitator the pulp passes to three Dorr thickeners, operated 
 as a continuous-decantation system. The flow sheet illustrates the 
 .operation of this series which, it will be noticed, takes in barren solution 
 at the final thickener and passes it back through successive tanks until 
 it overflows at the first one, enriching itself and impoverishing the pulp. 
 This is an exemplification of the proper working of the counter-current 
 decantation method, of which I have already spoken. By its use an 
 effective washing of the solids is accomplished and also a lightening of 
 the burden upon the filtering machine. 
 
 From the final thickener of the series the pulp is taken to two 12-ft. 
 Oliver filters where final dewatering is done. A water wash is applied to 
 the ascending side of the filter, but, none on the descend-side, as economy 
 of water is necessary and by this means the discharged pulp contains a 
 minimum of moisture. The slime is discharged upon a conveyor belt, 
 by which it is carried clear of the mill and deposited on the tailing pile. 
 It contains an average of 27% moisture. At this mill, in distinction 
 to the experience of the Tonopah mills, no advantage is found from 
 heating the solutions above normal. 
 
 The solution to be precipitated is passed through clarifying presses and 
 zinc dust is used to precipitate the metals. The precipitate is partially 
 dried, fluxed and melted in oil-fired furnaces. 
 
 The lime used in treatment is added as an emulsion at the slime col- 
 lector, the quantity being about 10 Ib. per ton of ore milled. 
 
CHAPTER XIV 
 PRACTICE AT THE NEVADA WONDER MILL 
 
 The mine and plant of the Nevada Wonder Mining Co. is situated at 
 Wonder, Nev., at a distance of about 63 miles from Fallon, which is its 
 nearest railroad station. Communication is by means of wagons for 
 freight, and automobile stage for passengers and mail. As has already 
 been mentioned in the case of the Nevada Hills company at Fairview, the 
 isolated situation is responsible for high transportation charges and 
 some measure of labor difficulties, the same condition applying at 
 Wonder as at Fairview, but with somewhat more force due to the greater 
 distance from communication. 
 
 The ores treated at Wonder are clear quartz of medium hardness and 
 offer no special difficulties in crushing. The plant treats an average of 
 about 110 tons per day of 24 hours, the mill run assaying about 18 oz. 
 silver and 0.25 oz. gold. 
 
 For convenience the property is operated by two companies, the 
 mining being carried on by the Nevada Wonder Mining Co. and the 
 milling by the Churchill Milling Company. 
 
 In its present condition the mill embodies a great many changes from 
 its original treatment plan, some of these changes having necessitated 
 ingenuity in installing additional apparatus in space which was not 
 designed to receive it. Such changes often force awkward arrangements, 
 but in this mill most of them have been planned and instituted without 
 mechanically embarrassing results. 
 
 Crushing Practice. The ore from the mine, after being weighed, is 
 passed through a 10Xl6-in. Blake rock crusher which delivers to an 
 inclined belt conveyor, the latter delivering into the battery bin. The 
 battery bin is of 2550 cu.ft. capacity and holds about 120 tons of ore. 
 
 From the bin the ore moves by gravity through gates into suspended 
 Challenge feeders delivering into the mortars. It is noted by the op- 
 erators that the one-stage crushing through a Blake-type breaker throws 
 a somewhat heavy burden upon the stamps. The crusher allows a 
 proportion of large pieces of rock to get through into the battery bins and 
 these may at times cause difficulty in the mortars. Probably a better 
 course is to crush in two stages, insuring a uniform feed of proper size for 
 stamp crushing. 
 
 There are ten stamps of 1400 lb., each dropping 96 times per min. 
 
 161 
 
162 
 
 DETAILS OF CYANIDE PRACTICE 
 
PRACTICE AT THE NEVADA WONDER MILL 163 
 
 through 8 in. The mortars are of the narrow, rapid-crushing type and 
 are equipped with screens of the square-mesh variety having an aperture 
 of f in. These stamps are relied upon in this instance to bear the heavy 
 work of reduction, and the pulp from them is passed to one Monadnock 
 Chilean mill for the second stage. This mill makes 28 r.p.m. and is fitted 
 with " ton-cap" screens having an aperture 0.08 in. wide. 
 
 Comparison of Time Loss with Stamps and Chilean Mills. It is 
 worth while at this point to consider the relative time lost on account of 
 repairs to batteries and the Chilean mill. "One of the strong points made 
 by objectors to Chilean mills is the time required to make repairs to them, 
 the claim being that stamps keep on working all the time without any 
 great loss due to renewals and repairs. A great many operators fail to 
 take into consideration the fact that while the stamps seem to be work- 
 ing steadily and making a great deal of noise about it, it is rare in a mill 
 containing any great number of them that there is not one or more hung 
 up for adjustment, setting tappets, putting on a dropped shoe, aligning, 
 or doing any one of a number of operations that are necessary with that 
 class of machinery. When a small proportion of stamps are hung up it 
 does not make any apparent difference in operations, for the mill is mak- 
 ing just about as much noise as if they were all running, but it must be con- 
 sidered that each individual stamp is relied upon to crush a certain defi- 
 nite number of tons of ore in a year and every hour one stamp is out of 
 commission has its effect upon the total product. On the contrary, if a 
 Chilean mill is stopped for repair the whole work is hung up, there is no 
 noise and it seems necessary to .make every effort to get it running again. 
 The effect is to make it appear that the Chilean is taking much more time 
 for repairs than the stamps, whereas, if all the minor delays of stamps are 
 added up they will usually approximate as much or more than those made 
 necessary by the Chilean mill. As an instance, at the Wonder mill during 
 a period of a year the time lost for battery repairs amounted to 7.70 days 
 and the Chilean mill, 3.66 days. There is a 1QO% difference in favor of 
 the Chilean mill. And in this case it is to be remembered that the feed 
 delivered to the Chilean is too fine to insure maximum efficiency or econ- 
 omy of wearing parts. Personal experience has been that the Chilean re- 
 quires a percentage of coarser feed to do its best work and I believe most 
 operators agree with that theory today. 
 
 Tube-mill Grinding. From the Chilean mill the pulp passes to a 
 duplex Dorr classifier where the already slimed portion is taken out and 
 the sand passed to a tube mill. This mill is 5 X 22 ft. and makes 28 r.p.m. 
 It will be noted that this mill is of the long type, due to the fact that it was 
 installed before the advantages of shorter tubes of the same diameter were 
 recognized. The mill contains a lining of the El Oro type, one of the very 
 few of these linings I have seen in use in the West. 
 
164 
 
 DETAILS OF CYANIDE PRACTICE 
 
 Classification of the tube-mill product is somewhat involved and is an 
 illustration of one of the changes made in the original mill design already 
 mentioned. The stream from the mill is split into two parts, each going 
 to a separate belt elevator, one of which sends its portion directly back to 
 the Dorr classifier and the other delivering to a 5-ft. classifying cone. 
 The underflow of this cone is returned to tube-mill feed and the overflow 
 is taken to a 7-ft. classifying cone which takes out the coarser part as 
 underflow and returns it to the elevator leading back to the Dorr classifier, 
 and passes its overflow, slime, directly to the slime collector. The accom- 
 panying flow sheet shows the movement of the pulp and solution. 
 
 Continuous Agitation System. Slime is collected in a Dorr thickener, 
 24X14 ft., and the overflow solution passes to the precipitation depart- 
 ment or to the battery tank. The thickened pulp is agitated intermit- 
 tently in four Pachuca tanks, each 15 X45 ft. The pulp receives about 40 
 
 COST OF MILLING AT WONDER, NEVADA 
 
 (Tons milled, 25,186 Period of one year.) 
 
 | Labor Supplies Power 
 
 Total 
 
 Superintendence $3,686 . 65 
 Crushing and conveying 1,651 . 14 
 Stamps 3,173.41 
 Chilean mill 1 435 97 
 
 
 800.40 
 2,658.55 
 1,722.62 
 2,213.44 
 476 . 65 
 1,660.12 
 1,161.52 
 
 $3,686.65 
 3,070.05 
 7,409.94 
 5,173.55 
 5,357.39 
 1,988.50 
 24,158.04 
 4,793.78 
 8,031.74 
 8,940.40 
 632.50 
 2,248.55 
 3,126.93 
 883 . 02 
 1,100.90 
 1,337.33 
 7,014.76 
 171.81 
 
 618.51 
 1,577.98 
 2,014.96 
 2,126.37 
 566 . 84 
 15,775.08 
 953.25 
 7,044.47 
 5,736.84 
 88.87 
 1,120.53 
 503 . 97 
 508.91 
 383 . 42 
 617.79 
 5,293.14 
 32.13 
 
 Tube mill 1,017.58 
 Elevating and separating 945.01 
 Agitating 6,722 . 84 
 Filtering 2,679.01 
 Precipitating 987 . 27 
 Refinery ; 3,048 . 98 
 Concentrating 543 . 63 
 Assaying | 1,086.10 
 Surface and plant 1 2,101.77 
 General 374.11 
 Storehouse 677 . 59 
 Water and fire line 719 54 
 
 154.58 
 
 41.92 
 521.19 
 
 39.89 
 
 Steam heat.. 1,721.62 
 Traction engine 139 . 68 
 
 Total direct 32,711 .90 
 Indirect 
 Office expense j 1,371 . 48 
 Company house 86 . 06 
 Taxes and insurance 
 
 44,963 . 06 
 
 822 . 39 
 105.48 
 
 11,450.87 
 
 89,125.84 
 
 2,193.87 
 191.54 
 2,933.61 
 267.54 
 5,586.56 
 3.538 
 0.222 
 3.760 
 
 Legal and traveling i 
 Total indirect -. . . | 1,547.54 
 Direct cost per ton 
 Indirect cost per ton. 
 
 927.87 
 
 
 
 
 Total cost per ton 
 
 
 
 1 Refers to building repairs, outside lighting, removal of debris, etc. 
 
PRACTICE AT THE NEVADA WONDER MILL 165 
 
 hours' agitation in these tanks and the solution used is heated to about 80. 
 Solution used for treatment contains 4.5 Ib. KCN and 4 Ib. lime per ton. 
 Due to the fact that the ore is clean and docile, high extractions are 
 the rule, the average over the past year being 94.49% of the gold and 
 94.74 of the silver. This percentage of recovery is good, especially so on 
 the silver, due to the raising of the temperature of the solutions. It has 
 been proved, in this mill that the extraction falls off approximately 2% 
 when the solution temperature is allowed to fall to or below 50 F. during 
 treatment. 
 
 Continuous Filtration. Pulp from the Pachuca agitation tanks is 
 delivered to a stock tank, 28 X 14 ft., which is equipped with a mechanical 
 agitator, and is diluted by the addition of 2 ft. of barren solution, and 
 from this tank it is taken to a Dorr thickener. The overflow of this 
 thickener goes to the precipitation department and the underflow of 
 thickened slime is returned to the stock tank again. By this means the 
 pulp is given a light washing and the content of the stock tank is main- 
 tained at a proper thickness for filtering. 
 
 Oliver niters are used, and the pulp, having already received the pre- 
 liminary washing mentioned, is filtered continuously, receiving a final 
 wash at the filter. The wash water applied at the filter is led through 
 hoses to a shaking pipe where it is sprayed on the cake in a constantly mov- 
 ing stream. By this means the delivery of the wash to any one point is 
 avoided and a better distribution is accomplished. The discharge from 
 the filter is said to contain about 50% moisture. 
 
 In this mill, as in many others, the centrifugal pump has proved a 
 more economical and satisfactory method of moving slime pulp than the 
 triplex slime pumps. 
 
 Solutions from the Dorr thickeners and from the filters are passed to 
 the pregnant-solution tank from which the precipitation system is fed. 
 There are six zinc boxes, each with seven compartments 30X27 in. area. 
 Only five of these compartments are used for precipitation and the other 
 two, at the heads of the boxes, are filled with excelsior and used for clarify- 
 ing the solutions. Many of the Nevada mills are using excelsior for 
 clarifying, as has already been mentioned in the case of the Tonopah mills, 
 and it seems to do the work in a satisfactory manner. 
 
 The precipitate cleaned up is dried in a pah which is fitted with elec- 
 trical means for heating, and is then fluxed and melted in Faber du Faur 
 furnaces burning oil. In order to avoid the melting of short zinc which 
 accumulates, an acid tank has been installed and this material finds its 
 way into the regular bullion production. 
 
 Material Consumption and Cost. Consumption of material at the 
 Wonder mill is of cyanide, 1.6 Ib. per ton of ore milled; of lime, 5 Ib.; 
 of acetate, 0.8 Ib.; of pebbles, 3 Ib. and of zinc 1.8 Ib. A feature of in- 
 
166 
 
 DETAILS OF CYANIDE PRACTICE 
 
 Storage Tank for 
 /-~^ Barren Solution 
 
 V\\ BatterySof. 
 Tank 
 
 Optional 
 return to 
 battery tank 
 
 I- Mine Car Scale 
 I- 10x16" Blake Crusher 
 Inclined Belt Con veyor 
 
 ti&ton Storage Bin 
 
 2-Suspended Choi lie nge 
 -^ IO-l400Ib.Stamps- feeders 
 Over to 8"drop, 16 drops j Scree n 
 l-VBox 
 
 I- Trent- Monadnock Mill, 
 
 28 r.p.m.0.08"Ton CapScreen 
 
 J- Duplex Dorr Classifier 
 
 1-5x22' Gates TubeMill,21r.p.m. 
 ElOro Lining 
 
 2 -Belt Elevators 
 2- Riffled L aunders 
 
 l~5 Classifying Cone 
 I- 7 Classifying Cone 
 l-24xl4 f Dorr Thickener 
 
 4-~l5x45 Pachuca Tanks 
 
 !-2oxl4 Stock Tank, mechanical 
 Agitator 
 
 I- 28x10' Dorr Thickener 
 
 2'8x II Oliver Filters 
 
 Pregnant Solution Tank 
 
 i-^ 6-Zinc Boxes, / 'Compartments 50x27 
 
 i 
 
 Bar re n Solution S ump 
 
 LIJ Electric Drier 
 
 C) 2-faber au Faur Furnaces 
 
 > Bull ion 
 
 FLOW SHEET OF NEVADA WONDER MILL. 
 
PRACTICE AT THE NEVADA WONDER MILL 167 
 
 terest is that the cyanide, lead acetate and lime required in treatment are 
 all ground up together in a small Chilean mill and added to the pulp flow 
 between the Chilean mill and the Dorr classifier. This is shown on the 
 flow sheet. 
 
 The cost of milling is shown in the accompanying table, but it is to 
 be remembered that the period of one year covered by these figures 
 included 115 days lost due to lack of power and other less important 
 causes, expenses naturally continuing to a large extent during that time. 
 These expenses falling on the reduced tonnage show a cost abnormally 
 high and it should be said that during the last two months when the mill 
 was operating at its maximum rated capacity of approximately 110 tons 
 per day, the expense dropped to about $2.75 per ton. 
 
 Considering the situation of the mill and the difficulties under which 
 the operators have been working, the results obtained are extremely 
 creditable. 
 
CHAPTER XV 
 METHODS AT REPUBLIC, WASHINGTON 
 
 The mining camp of Republic is situated in the northwest section of 
 Ferry County, Wash., about 25 miles south of the Canadian line. In 
 common with most mining camps it has been the scene of intermittent 
 activity and decline, and has had a hard time to demonstrate its value. 
 The district, originally a part of the Colville Indian reservation, was 
 opened in 1896 and its history since that time has been a checkered one of 
 alternating interest and indifference. Lately, however, its mines have 
 begun to be developed in a methodical manner which, if slow, is at least 
 more satisfactory and certain than can be obtained by a succession of 
 booms. 
 
 Metallurgical History of the Camp. Republic- has seen a series of 
 mills built within her boundaries, none of which seems to have made any 
 remarkable success. The first one was built for the Republic Gold Min- 
 ing & Milling Co., and made use of the Pelatan-Clerici process. Natu- 
 rally, this was not much of a success, the saving amounting to perhaps 50% 
 of the contained . silver and gold. Then followed a series of plants 
 embodying the chlorination process, combined amalgamation and cya- 
 nide, the Hendryx cyanide system, and finally the plant constructed by 
 D. C. Jackling for the Republic Power & Cyanide Co.,. built in 1900. 
 This plant operated for about 10 months and was then shut down. It 
 was patterned after the old Mercur plant in Utah, and included crushing 
 by means of rolls and Griffin mills, roasting and leaching. Precipitation 
 was attempted by the old method of using zinc dust in tanks, as was done 
 at Mercur. This mill is reported to have saved about 91 % of the gold in 
 the ore but only about 15 % of the silver. 
 
 Due to the many methods of treatment and the apparent failure of all 
 of them to accomplish any commercially successful results, the camp 
 received a bad name and the ores, while the quantity and grade were 
 acknowledged, were thought impossible to treat by any means sufficiently 
 cheap to insure profit. As a matter of fact, the trouble appears to have 
 been the persistent attempts to fit a process which had proved useful 
 somewhere else to the ores at hand, which happened to be not in the least 
 appropriate for it. 
 
 There seems to have been a remarkable lot of misinformation pub- 
 lished about the character of the ores. Some experimenters went to a 
 
 168 
 
METHODS AT REPUBLIC, WASHINGTON 
 
 169 
 
 12 
 
170 DETAILS OF CYANIDE PRACTICE 
 
 great deal of trouble to prove that they were not treatable cheaply, and 
 apparently satisfied themselves and a large portion of the mining public. 
 That the mineral itself does not justify this conclusion, the two plants 
 now in operation prove. 
 
 Description of the Ore. The ore is described as being a fine grained, 
 close textured quartz, but there is also some white quartz which is not so 
 hard and which is easily distinguished from the blue, flinty, hard material 
 mentioned. Ore from some portions of the camp is more like a clay and 
 contains an extremely large amount of colloid matter. It will be seen 
 that there is a great variety of ore, but that at present worked by the mills 
 consists largely of the blue quartz and white quartz, and is, in general, 
 hard. 
 
 While it has been repeatedly stated that this ore contains elements 
 which make it rebellious to cyanide treatment, such as tellurium, selen- 
 ium and copper, repeated tests have failed to detect tellurium, selenium 
 exists only in minute traces in ores of milling grade, and copper only in 
 small quantities. Neither of these last two elements presents any insuper- 
 able obstacle to cyanidation as selenium compounds are usually soluble 
 and exist in quantities too small to consume excessive amounts of 
 cyanide, and the same is true of copper, which occurs in somewhat larger 
 quantities. 
 
 It is undoubtedly true that the ores did not prove amenable to the 
 processes applied to them, but as has been stated, these methods were not 
 adapted to the ores. Later methods and careful experimentation has, 
 however, opened up an entirely new viewpoint. 
 
 In discussing the matter, H. W. Newton, superintendent of the mill of 
 the North Washington Power & Reduction Co., at Republic, who is 
 familiar with the ores, having studied them and experimented on them for 
 years, and who is responsible for their present successful treatment, stated 
 that he had made a number of experiments on roasted samples and in- 
 variably found that while a slight increase of gold extraction was obtained 
 on subsequent cyanidation, invariably the extraction of silver decreased 
 and almost disappeared. This was undoubtedly one of the reasons why 
 the mill built by Jackling was not successful as the silver is in quantities 
 too great to be ignored and constitutes a large proportion of the value. 
 
 Another point which has been detected and pointed out by Mr. New- 
 ton is that the gold occurs in such fine particles as to be rarely visible, is 
 scattered through an extremely close-grained rock so that the finest 
 grinding is necessary to liberate it and expose it to the action of cyanide 
 solutions. 
 
 The silver probably occurs as a sulphide, or sub-sulphide, and is soluble 
 readily enough in stronger cyanide solutions, though when roasted it is 
 converted into some other form, probably metallic silver, which is not 
 
METHODS AT REPUBLIC, WASHINGTON 171 
 
 readily soluble in cyanide solutions. The reasonable treatment, then, 
 would appear to be sliming of the total ore and agitation in cyanide solu- 
 tions without roasting or any other auxiliary treatment. And this has 
 proved to be the case. 
 
 The Crushing System. The mill of the North Washington Power & 
 Reduction Co. was commenced in 1911 and has now been in operation 1 
 something more than seven months. It handles ore from the Surprise and 
 Lone Pine mines, a rather hard run of ore. Railroad cars deliver the ore 
 to the mill where it passes through a system of crushing and sampling as 
 shown by the accompanying flow sheet. 
 
 From the first bin, the ore passes over a grizzly to a Blake crusher and 
 then over another grizzly to a set of 16X22-in. rolls. From this set of 
 rolls it is passed through a wire-screen trommel, the apertures of which are 
 |Xj in. The oversize is taken to a set of 14X30-in. rolls, after passing 
 which it joins the undersize from the trommel and passes through the 
 sampling plant to the mill bin. 
 
 From the mill bin the ore, now reduced to such size that the largest 
 pieces are about T \ in., is passed to a Chilean mill, where it is crushed 
 to pass a 16-mesh screen, then through a 45-in. Akins classifier and the 
 sand to a tube mill, 5X22 ft., where it is slimed. 
 
 There is some difficulty with this crushing system, the crucial point 
 being in the Chilean mill. The capacity of the plant is about 100 tons per 
 day of 24 hr., and yet there is extreme difficulty in getting the Chilean mill 
 to crush the amount of coarse material contained in the feed, which is not 
 large, through the 16-mesh screen. This condition should not exist, for 
 the material is all small, as has been mentioned, and the screen is coarse. 
 The difficulty probably depends on two factors, one of which is the fine- 
 ness of the feed. A feed of this fineness is usually considered too small to 
 give maximum efficiency with a Chilean mill, although at some plants 
 large capacities are obtained with similar material. This is exemplified at 
 the Portland and Independence mills at Cripple Creek. Too fine feed in a 
 Chilean mill usually results in building a bed on the die ring, the rollers rid- 
 ing over it without doing much grinding, and the operators at the North 
 Washington mill state that this is what occurs in this case, but they also 
 state that increasing the size of the material decreases the capacity, and 
 conversely, though with a very fine feed there is not much left for the 
 mill to do but pulp the material and put it through the screen. 
 
 The probability is that there is something wrong with the design of this 
 Chilean mill and that it is not adapted to ores of this kind. I feel con- 
 vinced that under normal conditions there would be no difficulty in hand- 
 ling a sufficient tonnage of this material. It is reduced with greatest ease 
 in the rolls. 
 
 1 At date of this article. 
 
172 
 
 DETAILS OF CYANIDE PRACTICE 
 
 Tube-mill Practice. At present there is one tube mill in operation, 
 as has been mentioned, but serious consideration is being given to the 
 installation of a second one, and the replacement of the Chilean mill with 
 a short tube mill of large diameter, having ribbed lining of the Komata type. 
 This would probably be an advantageous change and by it the capacity of 
 the mill could be materially increased. A short mill of large diameter 
 
 f 1 Storage Bin 
 
 Shaking Grizzly 
 /Ox 20 "dlake Crushe r 
 Shaking Grizzly 
 16x42" Rolls 
 
 4x6' Trom me !-$ XjrApe rtures 
 
 Solution 
 Tank 
 
 14x30 RbHs 
 
 18" Belt Conveyor 
 
 2~ Vezin Samplers 
 Mill 5in 
 
 1-6' Trent Chi lean Mill 
 
 (16 Mesh Ton Cap Screen) 
 
 1-45" A kins Classifier 
 
 1-5x22' Tube Hill .ElOrolinmc. 
 
 4- Trent Agitators 3$'x 20 '-Series 
 Settling E>ox 
 
 r Tl I- 11. 
 
 ^O \ L_ _ >. 
 
 - 11.5x16' Oliver Filter 
 
 --~ i Slime Tails 
 
 tJ Excelsior Cla r ifie r 
 
 Zinc Dust 
 
 Solution 
 
 Pregnant Solution Tanks 
 2~24-" Per rin Presses 
 
 t-Steele Harvey Furnace 
 
 Bullion 
 FLOW SHEET OF THE NORTH WASHINGTON POWER & REDUCTION CO.'s MILL. 
 
 equipped with the ribbed lining would efficiently break up the coarser 
 portion of this mill-run of ore and leave a product sufficiently varied to be 
 efficiently slimed in the succeeding two fine-grinding mills. 
 
 Closed circuit between the classifier and tube mill is effected and the 
 slime which leaves the classifier is taken to the first of a series of four 
 
METHODS AT REPUBLIC, WASHINGTON 173 
 
 agitation tanks, 33X20 ft., which are equipped with the Trent 
 agitator. 
 
 The operators claim that every satisfaction is obtained from the use 
 of these agitators even in the large, deep tanks installed. They perform 
 their work with a minimum of trouble and give good results in extraction. 
 The aeration of the pulp is said to be good and extraction proceeds 
 satisfactorily. 
 
 The first tank is used as a thickener as well as agitator, the overflow 
 going to the precipitation department. Agitation is continuous through 
 the series of tanks, the passage through them being accomplished in 
 about 36 to 40 hours. 
 
 It will be noted that the agitation capacity of these tanks is sufficient 
 for a good deal more tonnage than can be delivered by the crushing and 
 grinding department. The slight changes necessary for increase of that 
 part of the mill would be well worth making. 
 
 Use of Cyanide and Other Chemicals. The strength of the cyanide 
 solution in these agitation tanks is kept at about 5 Ib. KCN per ton of 
 solution. While a solution containing 2 Ib. per ton would be ample for 
 the extraction of the gold, in less time also, the strength is kept up to 5 Ib. 
 in order to make the best possible extraction of silver. The lime is added 
 to the first of the series of agitation tanks at which point also the solution 
 is standardized in cyanide content. 
 
 Lead acetate is used intermittently. It has been found that after 
 several days' use of the acetate it can be discontinued for a long time, the 
 relation being approximately, using it for one week and omitting it for 
 three weeks. If it is discontinued for much more than this time, trouble 
 develops which is believed to be due to soluble sulphides, the condition 
 being immediately remedied by the addition of the lead salt. 
 
 From the agitation system the pulp is either taken directly to the 
 Oliver filter or is first passed through a settling box for thickening it. 
 The procedure is usually to omit the settling box as the pulp is already 
 in good condition for filtering. 
 
 The Oliver filter is a large one, 11.5X16 ft., and is said to be doing 
 excellent work. 
 
 Precipitation Details. Zinc dust is used for precipitation, this being 
 the most acceptable method when treating ores containing copper, as 
 the metal is recovered immediately from the solution and does not tend 
 to make useless a large amount of zinc, as is the case when shavings are 
 used. The Bosqui system of agitating zinc dust in tanks with the preg- 
 nant solution and then pumping the mixture through a filter press, is 
 followed. 
 
 There is not a large amount of copper present, but what little there is 
 may be removed in this way from solution. A statement of the compara- 
 
174 DETAILS OF CYANIDE PRACTICE 
 
 tive content of the ores milled is given as follows: From the Surprise 
 mine, gold, 0.51 oz.; silver, 5.80 oz.; copper, 0.2%, and from the Lone 
 Pine Mine, gold, 0.32 oz.; silver, 2.20 oz.; copper, 0.1%. It will be 
 seen from this statement that the copper is not in sufficient quantity to 
 cause any great difficulty. 
 
 The average grade of ore treated at the mill for six months has been 
 $9.55, and the extraction of gold during this time was 92.8% and of silver 
 90.5%. The consumption of cyanide is 1.3 Ib. per ton of ore treated, of 
 lime, 4.5 Ib., and of Zn, 0.6 pound 
 
 The mill consumes 2 hp. for each ton of ore milled and employs 12 
 men in its actual operation in addition to six men at the power plant. 
 Power is electric, generated by a not very efficient steam plant at the mill, 
 and is expensive. It is expected that hydro-electric power will be avail- 
 able within the near future when, based on the expenses at the present 
 time, the total cost of treating the ore will not exceed $2 per ton. 
 
 Extraction percentages are based on the samples taken at the head of 
 the mill by the sampling plant and calculated against the tailing samples 
 taken below the filter. It is said that the bullion return checks closely 
 with these calculated results. 
 
 The precipitate is not acid treated, but is melted with flux in a Steele 
 Harvey furnace. The refinery department is situated at the head of the 
 mill and in a separate building. 
 
 A New Crushing Machine. The mill of the SanPoil Consolidated Co., 
 the only other plant operating at the present time in the Republic district, 
 is situated in a canon some little distance north of the town. The mill has 
 been recently completed and is operating on ores of much the same 
 character as those referred to in connection with the North Washington 
 mill, hard, close-grained quartz. 
 
 Railroad cars deliver the ore into the bin at the head of the plant and 
 from this bin an 18-in. belt conveyor delivers it to a Williams hammer 
 trommel mill. This machine is unusual in milling plants. It is constructed 
 much like the Quenner dry placer machine which was devised at the 
 Altar field in Sonora, Mexico. It consists of a trommel built of heavy bars 
 spaced yV in. apart, revolving at 100 r.p.m., and a central shaft running 
 through it revolving at 600 r.p.m. Upon the central shaft are 32 hammers 
 weighing 16 Ib. each connected with the shaft by heavy chains. The 
 hammers swing so that there is no danger of their touching the trommel. 
 Ore is introduced at one end of the machine and the hammers, flying out 
 by centrifugal force, strike the pieces of rock and shatter them. Several 
 kinds of metal have been used in making these hammers, which receive the 
 major part of the wear, and at present the most available material has 
 proved to be mild steel, sawn from the bar, and drilled to receive the chain 
 connections. Wear of the hammers has diminished from an original two 
 
METHODS AT REPUBLIC, WASHINGTON 
 
 175 
 
 or more pound per ton of rock crushed to a point where it is not much more 
 than 0.5 Ib. per ton. 
 
 The machine certainly does an immense amount of work, reducing 
 mine run to a granular product at one operation. The product is supposed 
 to come out through the trommel bars at y\ m -> the distance between 
 the bars, but there is a good deal of it which is considerably larger, pre- 
 sumably due to wearing of the bars, thus enlarging the openings. In 
 
 Ore Bin -600 Tons 
 !8" Belt Conveyor 
 
 Sol. Storage 
 
 Solution 
 
 Sump 
 
 l-Williams Hammer 
 Trommel Mill 
 
 l-Elevator-Belt8cBucket-20Ton-hrCap 
 
 Storage Bin 
 
 14-24 Rolls. Mils-Chalmers "C " 
 
 t- 5x22" Gates Tube Mi!l,smooth 
 
 g /-Sana" Wheel 
 > 
 
 I- Duplex. Dorr Classifier 
 
 1-25 x 10 'Dorr Thickener 
 
 9-l2x 18' Agitators, tirLiftSeries 
 ^ Cone Bottom Thickener 
 ^ I- 16' Oliver Filter 
 
 Slime Tailing 
 
 C/an'-f/er 
 
 Zinc Boxes 
 
 Melting Furnace 
 Bullion 
 
 FLOW SHEET OF THE SAN FOIL CONSOLIDATED MILL. 
 
 operation the machine makes an enormous amount of dust as the dry ore 
 is broken up. When damp ore is used the quantity of dust is not so great 
 and the general product is finer, but its capacity is much reduced. Sizing 
 tests on the product show as high as 40% of the product passing a 20- 
 mesh screen, of which 65% is finer than 10-mesh and 6% through 200- 
 mesh screen. About 70 tons per day are being milled through the 
 machine. Its capacity is 10 tons per hour. 
 
 It is acknowledged that this machine is still in the experimental stage, 
 although the operators believe it will continue to perform its work as at 
 
176 DETAILS OF CYANIDE PRACTICE 
 
 present. The machine now installed is to be exchanged for another 
 similar one built much heavier, but designed to do the same work in the 
 same way. It will, however, require incontestable proof to show that a 
 machine of this kind can be built strong enough to stand the enormous 
 strain of reducing mine-run ore to J in. or even J in. at one operation by 
 such strenuous means and be economical. 
 
 Sampling the fine ore is done automatically, and after passing the rolls, 
 as shown in the accompanying flow sheet, it is sent to a 5X22-ft. tube mill 
 which is in closed circuit with a duplex Dorr classifier. 
 
 Air Agitation Methods. -The slime from the classifier is thickened in a 
 Dorr thickener 25 X 10 ft., and the thickened pulp taken to a series of nine 
 agitator tanks, each 12 X 18 ft., with cone bottoms and using air agitation. 
 In addition to the central air lift in these agitators, which are cut off below 
 the surface as is done in the tanks at Grass Valley, to be mentioned in the 
 following paper, there are three additional lifts in each tank, designed to 
 avoid settling of slime on the cone bottoms which are too flat to do this 
 automatically. Treatment through the tanks is continuous and solution 
 from 5 to 7 Ib. KCN per ton is used. At this mill the stronger solutions 
 are used in the tube mill, the weaker ones being made up at the agitators. 
 The time of agitation is 50 to 70 hr. in the tanks. 
 
 From the final agitator of the series the pulp is taken to a cone-bottom 
 thickener and thence to an Oliver filter, 16-ft. drum, where filtration is 
 effected. The pregnant solution is passed through zinc boxes using shav- 
 ings and the barren solution issuing is passed back to the final agitator of 
 the series of nine, thus diluting the pulp and giving it a wash before going 
 to the thickening box and filter. Solution overflowing from the thickener 
 is pumped back to storage to be used over again. 
 
 The ore averages $8 per ton in value and 92 to 95% is extracted. 
 Consumption of KCN is 1 . 5 Ib. per ton and CaO 2.3 Ib. per ton. 
 
 There is nothing particularly novel about this plant with the exception 
 of the Williams mill above mentioned, but it is another link in the chain of 
 recent events which have shown clearly that the ores of jthe Republic do 
 not deserve the reputation they have received for being difficult to treat 
 and that when use is made of the means which have been developed within 
 the last few years for the better working of the cyanide process, together 
 with the essential and vital point of the metallurgy as applied to this 
 particular rock, extremely fine grinding, there is no difficulty in benefi dat- 
 ing it cheaply and efficiently. 
 
 Neither of the mills at present in operation is perfect nor is to be taken 
 as a model of its kind, but considering the difficulties in the way of getting 
 sufficient capital to treat ores which had already been tagged as hopeless, 
 they are good, and too much credit cannot be given to the men who have 
 made a metallurgical success where inevitable failure was freely foretold. 
 
CHAPTER XVI 
 THE MILLS OF GRASS VALLEY, CALIFORNIA 
 
 The North Star Mines Co., situated near the town of Grass Valley in 
 Nevada County, Calif., operates two mills, one built at the shaft of the 
 mine, known as the North Star mill, and one situated in a canon near the 
 town, known as the Central mill. The Central is the newer mill, built 
 much later than the old North Star mill. They are both 40-stamp instal- 
 lations and treat about the same quantity of ore in exactly the same way, 
 the only difference being that the older mill does not attempt to treat the 
 concentrate made in it, but sends it to the Central mill for reduction. 
 Owing to these facts the Central mill will be discussed in his paper, its 
 system typifying the practice established by the company and illustrating 
 the method of concentrate treatment. 
 
 Occurrence of Gold. The ore is a free-milling quartz in which quan- 
 tities of sulphides occur, and it is principally in these sulphides that its 
 value lies. The principal valuable metal is gold; silver exists in small 
 proportion, but not sufficient to justify any special metallurgical efforts to 
 recover it. The gold is principally in mechanical association with the 
 sulphides, only a small proportion being in chemical combination. In 
 crushing, the ore may be said to be of medium hardness. It consists 
 principally of quartz. 
 
 Each of the mills of the company contains 40 stamps, and the com- 
 bined capacity of the two is about 9000 tons per month, or about 300 
 tons per day. The average ore treated in the mill is valued at about $10 
 to $12 per ton. 
 
 Stamp -crushing Practice. The ore is brought to the Central mill in 
 small cars drawn by a light electric locomotive. It is dumped into a 
 general bin from which it passes over a grizzly, the coarse rock being 
 reduced in size in crushers of the Blake type and the whole finally received 
 in the battery bins. 
 
 The construction of these bins is noteworthy in that they are entirely 
 of masonry, forming a massive and solid foundation for the crushers. 
 They are built directly on the hillside and are a fine example of permanent 
 construction. 
 
 From the battery bins the ore is drawn through disk feeders into the 
 mortars. There are 40 stamps of 1000 Ib. each dropping 110 times per 
 min. through 7 in. Inside amalgamation is practised, using chuck plates, 
 
 177 
 
178 
 
 DETAILS OF CYANIDE PRACTICE 
 
 and^there is also an outside lip plate. The regular apron plates follow as 
 is usual. 
 
 The screen in use is somewhat unusual, consisting of a light sheet- 
 steel plate punched with small round holes. These holes are grouped in 
 small squares of about 1 in. on a side, and the squares are separated by 
 ribs of the solid metal, about as shown in the illustration. The size of 
 
 CENTRAL MILL. 
 
 CENTRAL CYANIDE PLANT. 
 NORTH STAR MINES, GRASS VALLEY, CALIF. 
 
 the holes is such that they approximate the opening generally found in a 
 30-mesh wire screen. The separating ribs add strength to the screen. 
 The whole length of the mortar, with a width of about one foot, is occupied 
 by the screen which has no strengthening strips aside from the ordinary 
 wooden frame used to retain it. 
 
 The battery framing is entirely of steel. The driving arrangement is 
 a little out of the ordinary as the motor is situated above the batteries and 
 
THE MILLS OF GRASS VALLEY, CALIFORNIA 
 
 179 
 
 STAMP BATTERY AND PLATES, CENTRAL MILL OF NORTH STAR MINES. 
 
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 SCREEN USED AT NORTH ST^AR MILL. 
 
180 DETAILS OF CYANIDE PRACTICE 
 
 the driving belts lead down, with one reduction, to the camshaft. The 
 accompanying illustration shows this arrangement. By this means the 
 battery motor is given a firm foundation on the masonry of the bins and 
 all belts and pulleys are easily reached when desired. 
 
 From the plates the pulp is led to a series of concentrators which are 
 round, of the buddle type, but have a reciprocating motion, revolving 
 back and forth about a central point, through a small arc. The concen- 
 trate is removed at a point on the edge of the circle. An arrangement is 
 made for reconcentrating the middling of a number of these tables on 
 others. The machine is known as the Dodd buddle. 
 
 From the concentrators the pulp flows to the cyanide plant, which is 
 separate from the mill and situated at some distance from it. All crush- 
 ing and concentration is done in water and the pulp flows by gravity to 
 the cyanide-treatment plant. 
 
 Cone System of Classification. All the pulp is received at the cyanide 
 plant in a roughing cone, 7X6 ft. The overflow from this cone goes 
 immediately to the cyanide department as slime, the object being to take 
 out the majority of the slime, and slime only, leaving the cone underflow 
 to be further classified in a separate system. This system consists of 
 three cones, each 5X5 ft., using an upward current of water to assist in 
 the classification. One of these cones has straight sides, but of approxi- 
 mately the same size as the other two, and its operation is the same. 
 Clean separation is accomplished in these cones and their overflow joins 
 the stream of slime, from the roughing cone and forms the slime portion of 
 the pulp. 
 
 Separate Sand and Slime Treatment. The underflow of the cones is 
 taken directly to the leaching tanks where the first cyanide solution is 
 put in contact with it. 
 
 The leaching tanks are six in number, each 22 ft. 5 in. by 87 in. and 
 are served by distributors of the Butters type. The cyanide treatment 
 occupies about seven days in total. At first a wash of lime water is 
 applied to neutralize any acidity in the ore and prepare it for the cyanide 
 solution which follows. After this has been drained away a bath of 30 
 tons of pregnant solution from the filters is applied which has strength of 
 about 0.035% KCN. This is immediately drained and is followed by a 
 bath of barren solution containing 0.1% KCN. The tank is filled with 
 this solution, which is allowed to remain in contact with the charge for 
 24 hr. with the tank outlets closed meanwhile. After this soaking period, 
 the solution is allowed to drain into a special solution tank until it shows 
 a strength of 0.06% KCN, when it is turned into the strong sump, where 
 it finally reaches a strength of about 0.09% KCN. Other strong washes 
 are followed by washes of sblution from the filters and finishes with the 
 barren solutions which are to be wasted, after being precipitated, and 
 
THE MILLS OF GRASS VALLEY, CALIFORNIA 181 
 
 finally a water wash is applied. The sand, after treatment, is sluiced out 
 of the tanks. There is no scarcity of water. 
 
 The slime is all collected in a series of cone-bottomed settling tanks, 
 assisted by one Dorr thickener. There are six of these settling tanks, 
 three of which are 14 X 15 ft. and three 13.3 X9 ft. The Dorr thickener is 
 19.5X13.5 ft., and is arranged to make one revolution in 3 min. 50 sec. 
 The slime is thus dewatered, leaving a pulp having specific gravity of 
 about 1.3 and a dilution of 2 : 1, approximately. 
 
 In a system of this sort, where an appreciable amount of water is taken 
 into the cyaniding system, it is evident that it will have to be discarded 
 at some point. This introduces a condition somewhat difficult to handle 
 and it is only where weak solutions are used that it is practicable. At the 
 Central mill weak solutions are used in slime treatment and for leaching 
 the sand. With sand treatment by leaching it is possible to reduce the 
 incoming moisture to about the same quantity discharged with the tail- 
 ings, so that in this department there is little or no accumulation of sur- 
 plus solutions. This can be accomplished with slime also, but is an expen- 
 sive process, in fact it was tried at the Central mill at one time but it 
 was soon found to be more economical to waste a selected, precipitated 
 solution, with its cyanide content reduced to the lowest possible point, 
 than to undertake the expense of more complete dewatering. 
 
 Slime Treatment System. The partially dewatered slime is recovered 
 in a stock tank, from which it is taken to the agitation department and 
 the necessary cyanide added to bring up the strength to the treatment 
 standard of 0.035% KCN. The slime, with its added cyanide and solu- 
 tion, goes then to the treatment tanks. 
 
 The tanks used for agitation are 8 ft. diameter and 18 ft. deep and 
 have cone bottoms of 60 inclination. The agitation is by means of a 
 central lift pipe. It will be noted that these tanks are practically Pachuca 
 tanks, except that the lift pipe does not reach the surface of the pulp, a 
 feature which has been adopted with some advantage in a few Pachuca 
 installations. Air is used for operating the lifts. It is of interest to note 
 that these tanks are said to have been installed and in use before the 
 Pachuca type, as such, came into existence. 
 
 The agitation of the slime pulp is continuous through the three 
 agitators, the time of passage being calculated at approximately 14 hours. 
 
 Continuous Filter System. The pulp from the agitators is collected 
 in two settlers, used alternately, each 8X13 ft., equipped with cone bot- 
 toms. Settling and decantation proceed simultaneously, the thickened 
 pulp meanwhile being drawn off for nitration. In about eight hours, one 
 settler is filtered so that the overflow is not clear, when the pulp is trans- 
 ferred to the other settler, the first one being allowed to settle, the solution 
 decanted, and the thickened underflow drawn off as it settles. 
 
182 
 
 DETAILS OF CYANIDE PRACTICE 
 
 Ore from Mine 
 
 Water Waste or 
 ^ ^ Auxiliary Use 
 ^~s E; 
 
 Rough- ore Bin 
 
 Grizzly 
 
 2-9x15' Blake - type Crushers 
 8- Disc Feeders 
 
 40- 1000 Ib. Stamps- 7" Drop- 110 
 Drops -30- -flesh Screen, Chuck and 
 Lip Amalgamation Plates 
 8 -Outside Amalgamation Plates 
 
 12 -D odd Buddies, Pipe Line to 
 Cyanide Plant 
 
 1-7x6' Roughing Cone 
 3-5x5 Hydraulic Classifying 
 
 6-22-Jx 7-3" Leaching Tanks 
 Butters Distributors 
 
 J 6- Settling C 
 \l-Dorr Thic 
 
 ones 
 Thickener 
 
 SI i me Stock Tank 9-6 "x JO' 
 
 3-%'xlQ'A ir Agitation Tanks, 60 
 Cone bottoms,continuous rlow 
 
 2-8x12 'Settlers, alternate Use 
 
 2-102x7' fiver Filters 
 , Slime Tails 
 
 Barren , .->* 
 Solution L 
 
 \ i Tube Zinc Grinder and 
 Feeder 
 
 Sump Tanks 
 
 2- 36 '-6 Frame Merrill Precipi ta te 
 Presses 
 
 "Precipitate 
 
 Oil - fired Sta tionory Furnaces 
 
 Bullion 
 
 FLOW SHEET OF CENTRAL MILL. 
 
THE MILLS OF GRASS VALLEY/CALIFORNIA 183 
 
 The thickened pulp is taken to the filters, this installation consisting of 
 two 10 J X7-ft. Oliver continuous revolving machines. It was at this mill 
 that the Oliver filter was conceived and developed and the two machines 
 now in use are the first of their type to be built. 
 
 The tailing is sluiced away from the filter and run to waste. About 
 60 tons of slime- daily are treated on the two filters. 
 
 The Merrill system of precipitation is used. Zinc dust added to the 
 pregnant solution is pumped through two Merrill presses, each of which 
 contains eight frames, the frames being the 36-in. triangular type. These 
 presses originally had the solution discharge at the bottom of the frame, 
 but pipes have been fitted to the discharges and carried above the level of 
 the frames so that the press always remains full even in case of cessation of 
 operations of the plant. The frames thus kept full of solution prevents 
 oxidation of the zinc consequent upon an empty frame and resulting con- 
 tact of air with the zinc. All solutions to be precipitated are first used as 
 washes on the sand-leaching tanks, enriching the solutions and effectually 
 clarifying them. The precipitate is melted in stationary, oil-fired fur- 
 naces without any preliminary treatment whatever. A small tube mill is 
 used for emulsifying the zinc dust with solution before its addition to the 
 solution to be precipitated, and a mechanical feeder introduces the zinc 
 into the tube mill. 
 
 Concentrate Treatment. The concentrate treatment is unusual and 
 worthy of particular note. The two mills of the company make six to 
 seven tons of concentrate daily, all of which is treated at the Central mill. 
 It is brought to the mill in cars and is dumped into a concentrate bin, 
 being meanwhile mixed with lime at the rate of about nine pounds per 
 ton. From this bin the concentrate is mechanically fed into a tube mill of 
 the Abbe type. The mill is 4.5 ft. in diameter and 20 ft. long and revolves 
 at 19 r.p.m. The concentrate is reground in this mill, and issuing, it is 
 classified in a cone classifier: The fine overflow all goes over an amalga- 
 mating plate and the underflow is returned to the tube mill, forming a 
 closed circuit from which there is no exit save through the overflow of the 
 reclassifying cone. All of the reground concentrate pulp, after having 
 passed this regrinding and amalgamating system, is taken directly to the 
 large roughing cone, before mentioned, at the head of the cyanide plant, 
 where it enters treatment along with the bulk of the ore. 
 
 Thus the concentrate, after having been removed from the pulp, is 
 ground, amalgamated, and returned to it and undergoes exactly the same 
 treatment as the siliceous part of the ore. This treatment is said to be 
 altogether satisfactory, the regrinding being sufficient to liberate most 
 of the contained gold, a part of which is recovered on the plate and the 
 remainder in the cyanide treatment. The portion which goes to the 
 cyanide plant is amenable to the short-time and weak solutions used there. 
 
184 
 
 DETAILS OF CYANIDE PRACTICE 
 
 The explanation, of course, is that the gold is only mechanically com- 
 bined with the sulphides and is liberated by the additional grinding. 
 In the case of chemical combinations other means would be necessary for 
 its satisfactory extraction. 
 
 This is a good illustration of the utility of experimental work, for it has 
 here fitted an inexpensive process to a material which needs nothing else. 
 A separate treatment, such as is usually considered necessary with sul- 
 phides, might have been considered necessary in this case and an expensive 
 plant and treatment system might have been installed had not thorough 
 experiment shown the exact requirements of the material. 
 
 The concentrate varies in value from $30 to $80 per ton and the ex- 
 traction is about as complete as with the siliceous portion of the ore. As 
 has already been said, the mill head averages $10 to $12 per ton, and the 
 head of the cyanide plant averages about $2 per ton, before the concen- 
 trate is added. The total extraction obtained from mill and cyanide 
 plant approaches 98%. In the cyanide plant alone, about 94% of the 
 gold in slime is recovered and 85 to 90% of that in the sand. The tailing 
 contains on the average about $0.20 in gold value. 
 
 Consumption of Material and Cost. The consumption of cyanide is 
 0.61 Ib. per ton milled; of zinc, 0.216 Ib. per ton; of lime, 4.21 Ib. per ton, 
 and of pebbles, 4.5 Ib. per ton of sulphides ground. 
 
 The cost of treatment is given in the accompanying table. 
 
 
 Milling 
 
 Concentration 
 
 Cyaniding 
 
 Labor 
 
 $0 176 
 
 $0 087 
 
 $0 166 
 
 Material 
 Power 
 
 0.075 
 129 
 
 0.017 
 027 
 
 0.186 
 116 
 
 
 
 
 
 Total 
 
 $0 380 
 
 $0 131 
 
 $0 468 
 
 
 
 
 
 Milling 
 
 
 $0.380 
 
 
 Concentration 
 
 
 131 
 
 
 Cyanidation 
 Total. . 
 
 
 0.468 
 10.979 
 
 
 The Empire Mill. The Empire mill is also near the town of Grass 
 Valley. The mine and mill are close together, although as in the case 
 of the Central, the milling and cyanide departments are in separate 
 buildings. 
 
 The ore at the Empire mill is like that at the North Star, a free-milling 
 quartz containing sulphides. The mill is similar, and in fact, the treat- 
 ment is almost identical, so that it will not be necessary to make a detailed 
 study of that practice, but attention will only be called to the few points 
 of difference. 
 
 The Empire mill contains 40 stamps of 1050 Ib. each and amalgama- 
 tion is practised both inside and outside the mortars. The quantity of 
 
THE MILLS OF GRASS VALLEY, CALIFORNIA 
 
 185 
 
 ore milled is from 140 to 150 tons per day, about the same as the North 
 Star mills. Concentration is practised as is the case at the other mills. 
 
 The mill pulp flows through a pipe line to the cyanide plant, where 
 it is received in two roughing cones, the slime overflowing and going di- 
 rectly to settlers and the underflow passing for further classification to 
 four hydraulic classifying cones, which make the final separation into 
 sand and slime. 
 
 EMPIRE MILL. 
 
 EMPIRE CYANIDE PLANT. 
 GRASS VALLEY, CALIF. 
 
 The sand is taken directly to the leaching tanks and is delivered into 
 them by means of Butters distributors. A feature of the practice both at 
 the Empire and Central mills is that the Butters distributors are used 
 both in filling the tanks and also in sluicing out the residue. For sluicing 
 out the sand, water is admitted through the distributor, the bottom gate 
 
 13 
 
186 DETAILS OF CYANIDE PRACTICE 
 
 opened, and sluicing proceeds automatically. The filter bottom of the 
 tank is made slightly inclined, in order to facilitate the discharge. The 
 sand tanks are 14 ft. by 9 ft. 4 in., and contain approximately 155 tons. 
 The treatment occupies six days and the strong solution is 0.10% KCN, 
 as in the case of the Central mill. 
 
 Settling Area. The slime from the classifiers is taken to the settlers. 
 There are four of these, each 24 ft. in diameter and 22 ft. deep, with cone 
 bottoms. The pulp is distributed among them as conditions dictate. 
 This settling capacity seems extensive for the quantity of slime handled, 
 about 65 to 70 tons daily, but it is stated that the settling, even with this 
 great capacity, is accomplished only with great difficulty. A large quan- 
 tity of lime is added to assist settlement, most of this lime being lost in the 
 overflow water, which is either run to waste or used in auxiliary opera- 
 tions about the plant, there being none returned for further use in milling. 
 
 It is an object to draw the slime from these settlers with as little mois- 
 ture as possible, the dilution usually being about 1:1. As the thickened 
 pulp reaches the agitation department it is diluted to about 2:1 with 
 fresh solution and is made up to 0.04% cyanide strength. 
 
 The agitation is continuous through four tanks of the Pachuca type, 
 each 10X18 ft. The cyanide strength is made up in the first and last 
 tanks of the series and a low protective alkalinity maintained. There is 
 no thickening or washing of the pulp after agitation except that given in 
 the filters, to which the pulp is taken directly from the agitation tanks. 
 The filter installation consists of two Oliver machines of the 8-ft. size. 
 
 As at the Central mill, all solutions to be precipitated are first 
 used as washes on the sand tanks in order to clarify them. The Merrill 
 system of zinc-dust precipitation is used, and there are two triangular 
 frame presses, 36-in. frames, having nine and ten frames respectively. 
 These presses have pipe connections for the solution outlets which deliver 
 above the level of the top of the frames. The precipitate is acid treated 
 and melted. 
 
 The concentrate treated, about four tons daily (part of which is pur- 
 chased), is reground in a 4 X 8-ft. Allis-Chalmers tube mill, run over plates 
 and classified at the cyanide plant in a separate cone, the overflow of 
 which joins the stream of slime to the settlers and the underflow, the 
 product going to the sand-leaching tanks. This separate classification is 
 the only detail in which the concentrate treatment differs from that in 
 use at the Central mill. 
 
 The general arrangement at the Empire mill is somewhat less com- 
 plicated, as it is understood that the mill stands exactly as designed and 
 the necessity for inconvenient remodeling has been avoided. 
 
 The Grass Valley properties present mining in its most attractive form. 
 Situated in a fertile agricultural district, free from climatic extremes and 
 
THE MILLS OF GRASS VALLEY, CALIFORNIA 187 
 
 surrounded by luxuriant vegetation, the aspect differs widely from the 
 usual mining camp. The district is ola, the first discovery was in 1850, 
 and proven, so that makeshifts and cheap construction have long since 
 given place to substantial installations, an artistic eye having evidently 
 been concerned in the general plans. This is especially true at the Empire 
 where stone buildings and pleasant foliage give an appearance more like 
 that generally presented by well designed and permanent habitations than 
 mining camps. Those concerned in the operation of these mines are 
 fortunate indeed in their habitation. 
 
CHAPTER XVII 
 THE BLACK OAK PLANT, CALIFORNIA 
 
 Near the town of Soulsbyville, in Tuolumne County, Calif., is situated 
 the plant of the Black Oak Development Co., said to be the only mill at 
 the present in the State of California which employs the total-sliming, 
 continuous-agitation process of treatment. The property is in an agree- 
 able district where climatic conditions are good and the natural surround- 
 ings pleasant. 
 
 Ore Character. The plant is near the town of Tuolumne, the terminus 
 of the branch line railroad by means of which the district is reached, from 
 Stockton, via Oakdale. 
 
 Gold and silver both occur in the ore of the Black Oak mine, and the 
 proportion is 2 or 3 parts of silver, by weight, to one of gold. In this 
 proportion the gold is, of course, by far the most important factor to be 
 considered in the metallurgy of the ore, but, as will be mentioned later, 
 the silver is in sufficient quantity to make advisable a special effort to 
 recover a goodly proportion of it. 
 
 Most of the valuable metal is in quartz which occurs in a granite-diorite 
 country rock, and sulphides contain the greater part of the silver and gold. 
 As often happens in California ores, this gold does not seem to be chemi- 
 cally combined with the sulphides, but only mechanically, so that fine 
 grinding liberates the greater part of it. The silver is, of course, largely in 
 combination as sulphide, in which condition it is amenable to cyanidation 
 after having been subjected to fine grinding. 
 
 Comparison with Other Ores. It is noteworthy that the ore deposits 
 of the Black Oak mine, and of the surrounding district similar in a general 
 way to the mineral already described at Grass Valley, are said to be similar 
 to the majority of ores in the mines on the Mother Lode, and identical 
 with some of them. If this is true, the question immediately is suggested 
 as to why the other Mother Lode mines, or at least some of them, do not 
 make use of cyanidation, a process which has demonstrated its efficiency 
 and economy on similar material. Mother Lode ores are still being 
 beneficiated by old methods, amalgamation and concentration. While 
 both of these systems are simple and cheap, it is undeniable that neither of 
 them approaches cyanidation in the amount of recovery from simple ores. 
 Some have informed me that Mother Lode ores are not treatable by cyani- 
 dation, while others have assured me quite as emphatically that they are. 
 
 188 
 
THE BLACK OAK PLANT, CALIFORNIA 
 
 189 
 
190 DETAILS OF CYANIDE PRACTICE 
 
 In view of results obtained at Black Oak and Grass Valley, the preponder- 
 ance of evidence would seem to be in favor of the latter statement. Per- 
 haps the experience of these two camps will be of value to those opera- 
 tors on the Mother Lode who desire to increase the efficiency of their 
 installations. 
 
 The Crushing System. Ore from the mine is first delivered to the mill 
 bin- which has a capacity of about 185 tons. Four Challenge feeders 
 deliver it into the mortars of a 20-stamp crushing plant, each stamp weigh- 
 ing 1250 Ib. and dropping 102 times per minute through 6 in. Mortars 
 are of the narrow pattern designed for rapid crushing. Three of them are 
 equipped with ton-cap screens having 19 apertures per inch, and the re- 
 maining mortar has a 6-mesh, square aperture screen. This coarse screen 
 adds sufficient granular material to increase the efficiency of subsequent 
 tube mill work. Many of the recently constructed mills are adopting the 
 system of varied feed for tube mills and the results thus far seem to have 
 amply justified the practice. 
 
 The Black Oak mill was originally a 40-stamp plant, containing the 
 old-style stamps of light weight, but it has been entirely rebuilt with new 
 and appropriate machinery. There is still room for 40 stamps under the 
 present room, in fact 20 of the original stamps are still there in a more or 
 less dismantled condition. With further mine development all available 
 space may be required. 
 
 Classifying and Regrinding. Pulp from the stamps flows by gravity 
 to a Dorr classifier of the usual type in which the slime is separated and 
 taken directly to treatment and the sand is delivered to a tube mill 
 for further grinding. This tube mill is 5 X 18 ft. and is of the type made 
 by the Power & Mining Machinery Co. It is operated at 26 r.p.m. and 
 requires 48 hp. to keep it moving. Imported pebbles are used, the con- 
 sumption of which is 5 Ib. per ton of ore crushed. The hardness of the 
 ore is attested by this consumption of pebbles which is extraordinarily 
 high. 
 
 Ground product from the tube mill is returned to the classifier by 
 means of a bucket elevator, thus forming a closed circuit, the only exit 
 from which is the slime in condition for agitation treatment. 
 
 Upon its exit from the classifier, the slime proceeds to a 10X20-ft. 
 Dorr thickener, where a portion of the solution is decanted and a thick- 
 ened pulp delivered of proper consistency for the subsequent cyanidation. 
 
 Agitation of the Slime. Slime treatment is performed in tanks of the 
 Pachuca type of which there are three, each 10X30 ft. Passage of the 
 pulp is continuous through these tanks and during the time of agitation 
 the extraction of the contained gold is practically complete. 
 
 The Dorr thickener, which prepares the pulp for the agitation tanks, 
 delivers a pulp in which the proportion of slime to solution is about 1 : 1 J. 
 
THE BLACK OAK PLANT, CALIFORNIA 
 
 191 
 
 The thickener is operated at about one revolution in six minutes, and in 
 common with these machines, requires an extremely small expenditure of 
 power. 
 
 185 -Jon Ore Bin 
 4-Challenge Feeders 
 
 20- 1250 1 b. Stamps, narrow 
 Mortars, 102 Drops.- 6 "drop 
 
 I- Duplex Dorr Classifier 
 
 /- 5x18 ' Tube Mill, 26 R.p.m. 
 Bucket Elevator 
 
 I- 10x20' Dorr Thickener 
 
 3-10x30 Pachuca-Type Agitators 
 (Continuous System) 
 
 I-10x20'Dorr Thickener 
 
 H2' Oliver Filter 
 Slime Residue 
 
 \ 
 
 Solution Collecting Tank 
 
 2 ~5 6 Frame, 24 "Clarify 'ing Presses 
 Pregnant Solution Tank 
 Zinc Feeder 
 
 1-16 Frame, 52"t1er rill Precipitation 
 
 Press 
 ~t- 
 -^. Solution Sump 
 
 Drying Pan 
 
 Oil Fired Tilting Furnace 
 
 Bullion 
 FLOW SHEET OF BLACK OAK MILL. 
 
 The material agitated is true slime, or colloid, only in small proportion, 
 the major part consisting of extremely fine granular matter. About 78% 
 
 \ 
 
192 DETAILS OF CYANIDE PRACTICE 
 
 of it is sufficiently fine to pass a 200-mesh screen, while 98 to 99% will 
 pass a 150-mesh aperture. Pipe connections for the continuous passage 
 of the pulp are 4 in. in diameter. 
 
 Continuous Filtration. Issuing from the agitation treatment in the 
 Pachuca tanks, the pulp is received in a second Dorr thickener, identical 
 in its dimensions with the one first mentioned. Just before reaching this 
 thickener, the pulp is diluted with the overflow product of the first 
 thickener and the mixture thickened to a point where the underflow of 
 pulp issuing contains solution and solid in a 1 : 1 proportion. 
 
 This thickened pulp is delivered to a 12-ft. Oliver continuous filter. 
 The slime residue is dewatered and discarded and the solution, together 
 with the overflow from the final Dorr thickener, is gathered in a collecting 
 tank from which it is taken to the precipitation system. 
 
 For precipitation the Merrill system, using zinc dust, is followed. A 
 special zinc-dust feeder drops the precipitant into the stream of pregnant 
 solution going from the tank to the suction of the pump, and the mixture 
 is forced through al6-frame filter press of the Merrill type. The frames of 
 this press are 52 in. across the top and are triangular in shape as is usual. 
 
 Solution, after precipitation, is received in a sump from which it is 
 pumped up to the solution storage tank for further use in the mill. 
 
 Precipitate from the press is partially dried in a drying pan, fluxed and 
 melted in a tilting, oil-fired furnace. The accompanying flow-sheet dia- 
 gram illustrates the metallurgical process followed in the mill and the 
 principal machinery installed. 
 
 Character of the Dry Slime. The Black Oak ore is hard, as has 
 already been mentioned, and remains largely in the granular state even 
 after continued grinding. The specific gravity of the dry slime in the 
 condition in which it is subjected to agitation treatment, is about 2.8, a 
 figure which is rather high in comparison with ordinary siliceous slimes, 
 which generally contain a greater proportion of colloid matter. 
 
 The mill will treat about 100 tons per day of 24 hours, but at present 
 the rate of crushing is near 85 tons daily. Average run of ore will contain 
 a combined gold and silver value of $15 per ton in the proportions which 
 have already been mentioned. 
 
 Of the gold, 97% is usually extracted without difficulty, and about 
 92% of the silver. Treatment solutions contain 0.2% KCN and 0.15% 
 CaO. Lime is added at the batteries and in the agitators. Litharge is 
 used as a source of lead for removing soluble sulphides from solution and 
 is added at the tube mill in order to facilitate solution. 
 
 Chemical Consumption. The consumption of chemicals and supplies 
 is low, as is usual when treating an ore whose value is largely in its gold 
 content. The cyanide consumption is 1.0 Ib. per ton; of litharge, 0.35 lb.; 
 of lime, 3 lb.; of zinc, 1 lb., and of pebbles, 5 lb. per ton. 
 
THE BLACK OAK PLANT, CALIFORNIA 193 
 
 TABLE OF COSTS AT THE BLACK OAK MILL, CALIF., BASED ON MILLING 
 
 2202.5 TONS 
 
 Supplies Per Ton 
 
 Rock crusher $0.0121 
 
 Batteries 0.0158 
 
 Tube milling 0.0349 
 
 Tube-mill liners 0.0266 
 
 Classification 0.0039 
 
 Refining 0.0195 
 
 Repairs 0.0131 
 
 Office and general superintendent . 0042 
 
 Assaying 0.0241 
 
 Marketing bullion: 
 
 Control $10.45 
 
 Treatment. . . 167.38 
 
 Express 25.25 0.0922 
 
 Cyanide 0.2018 
 
 Lime 0.0111 
 
 Litharge . 0507 
 
 Zinc 0.0970 
 
 Pebbles.. 0.0780 $0.6850 
 
 Power and lights $0. 3500 
 
 Insurance 0.0200 
 
 Labor 
 
 Rock crusher. $0.0453 
 
 Tramming 0.0844 
 
 Batteries . 0968 
 
 Tube milling 0.0184 
 
 Classification 0. 0192 
 
 Agitation 0. 0223 
 
 Thickening 0.0223 
 
 Pumping and elevating 0. 0244 
 
 Filtration . 0246 
 
 Clarification 0.0224 
 
 Precipitation 0.0236 
 
 Refining 0.0305 
 
 Repairs 0.0523 
 
 Office and general superintendent. 0.0715 
 
 Mill superintendent 0.0681 
 
 Power and light 0.0165 
 
 Assaying 0.0315 $0.6741 
 
 Total mill costs $1 .7291 
 
 Seven men, excluding the superintendent, are required for mill opera- 
 tion, and 130 hp. is the average consumption of energy for moving the 
 machinery. While the mill is small and handles only a limited quantity 
 of ore, costs have been reduced to an extremely reasonable figure as is 
 
194 DETAILS OF CYANIDE PRACTICE 
 
 shown by the accompanying tabulated list of items. During the two 
 months following that in which this report was made, a general reduction 
 of costs has been accomplished, the total being reduced to about $1.61 
 per ton. The operators are fortunate in having an ample supply of water 
 and conditions generally favorable for successful operation. 
 
CHAPTER XVIII 
 THE GOLD ROAD MILL, ARIZONA 
 
 The mill of the Gold Road Mines Co. is situated at Gold Road, about 
 20 miles from the town of Kingman in western Arizona. Railroad com- 
 munication is established at Kingman and connection with the mine is by 
 wagon road over which freight is hauled by horses, and passengers by 
 automobile stage. The region is arid, water is scarce and has to be con- 
 served with care. 
 
 Local ores have gold as the principal valuable constituent, the metal 
 being finely divided and distributed through a gangue consisting of quartz 
 
 GOLD ROAD MILL, GOLD ROAD, ARIZ. LOOKING TOWARD THE CRUSHING PLANT. 
 
 and some calcite in a country of andesitic rock. There is no great quan- 
 tity of sulphides, the gold being free and principally fine. On account of 
 the fineness and wide distribution of the gold, a rather high degree of 
 crushing is required and the total-sliming process is followed. 
 
 The mill is not an original construction, but rather a development, the 
 remnants of machinery used in various processes, now relinquished, remain 
 as reminders of the older systems of metallurgy. This changing of sys- 
 tems has also resulted in a scattering of the reduction plant over a good 
 
 195 
 
196 
 
 DETAILS OF CYANIDE PRACTICE 
 
 deal of territory, a fact which may be seen by a study of the accompany- 
 ing engravings. Notwithstanding this circumstance, a plant of ex- 
 ceedingly good metallurgical performance is now in operation, the details 
 of which are explained in this paper. 
 
 Preliminary Breaking. Installed at the mine is a No. 5 Gates gyratory 
 crusher where the ore receives its preliminary breaking. From the 
 crusher it is trammed to the mill, where it is delivered into a 1540-ton bin 
 which supplies the mill as required. During the preliminary breaking at 
 the mine, the required portion of lime is added to the ore so that by the 
 time the material has passed through the bin and entered the stamp-crush- 
 
 GOLD ROAD MILL, GOLD ROAD, ARIZ. UPPER SIDE VIEW. 
 
 ing department, the lime has performed a great deal of its essential work, 
 neutralizing the developed acidity and becoming more or less slaked and 
 ready to offset the acids which may be formed later in the course of its 
 treatment. This method of lime addition is advocated by many operators 
 because of the advantages enumerated above, and further, because the 
 lump form is progressively crushed as is the ore, and develops alkaline 
 conditions, when the addition is at the appropriate rate, just as the ore 
 develops acidity. Others advocate the powdered form of lime, sometimes 
 previously slaked, and make additions at the point and time when acidity 
 develops. No doubt a greater percentage of CaO can be dissolved by 
 careful slaking under favorable conditions, but whether the highest ulti- 
 mate economy and efficiency are reached by so doing, is a question which 
 will have to be solved for every problem after consideration of all the 
 conditions. 
 
THE GOLD ROAD MILL, ARIZONA 197 
 
 Crushing and Grinding. From the bin, Challenge feeders deliver 
 the ore into a battery of forty 1050-lb. stamps, making 104 drops per min. 
 through 7 in. The stamp crushing is done in solution. Screens of 4- 
 mesh are used on the batteries, the stamp duty being about nine tons per 
 stamp per day, or a total of 3"60 tons daily for the mill. 
 
 Pulp from the stamps is led to two distributing cones, one 4 ft. and 
 one 6 ft. in diameter, from which it goes to six duplex Dorr classifiers, 
 where the overflow slime is removed and the sand dewatered and delivered 
 to the tube mills for regrinding. 
 
 There are four tube mills, each 5X22 ft, used in closed circuit with 
 the classifiers, the delivery from the tube mills being elevated with 10X54- 
 in. Frenier pumps and returned to the classifiers where any sand not 
 sufficiently fine for treatment by agitation, is removed and returned to the 
 tube mill for further grinding. El Oro linings are used in these mills and 
 are said to be entirely satisfactory, each lining lasting a year before it is 
 replaced. Imported pebbles are used in the mills, the consumption being 
 4 Ib. per ton crushed. 
 
 It has been practically found unnecessary to grind this ore through 
 a 200-mesh screen, the product passing a 100-mesh screen giving as good 
 extraction results. In practice, the pulp delivered to the agitation treat- 
 ment contains about 86 to 87% which will pass a 150-mesh screen. The 
 specific gravity of the dry slime has been determined and is stated to 
 be 2.63, a figure denoting about medium weight. 
 
 Thickening and Agitation. The entire pulp from the grinding system 
 is received in two 30 X 10-ft. Dorr thickeners, the overflow solution going 
 to clarifying tanks and the underflow of thickened pulp being taken to the 
 agitation system. This agitation installation consists of three 17X44-ft. 
 Pachuca tanks which were used in series, but, having found that so long 
 a time for agitation was not necessary to secure highest extraction, this, 
 together with the inherent inconveniences of this kind of tank, resulted 
 in cutting out two of them and the using of only one. 
 
 With the pulp of the grade and character customary at Gold Road, it is 
 somewhat difficult to prevent settling of a portion on the solids, and in such 
 cases the Pachuca tank has often been found unsatisfactory. Here the 
 settlement became so great that the time of agitation was reduced to 
 practically nothing. It is stated that the settlement was so hard and solid 
 that one could step over the edge into the tank and walk about, keeping 
 away from the center, without any inconvenience. 
 
 Thickened pulp, that coming from the thickeners into the agitation 
 department, has the dilution ratio of about 1 to 1, and retains this con- 
 sistency until after finishing the agitation treatment. Contact between 
 the ore and cyanide solution was 36 to 48 hr. in the mill, counting from its 
 first pulping at the cones, to its discharge. Owing to a change in the 
 
198 
 
 DETAILS OF CYANIDE PRACTICE 
 
 metallurgical system, this time of contact may have become somewhat 
 protracted, but not because of any necessity of increasing the per cent, ex- 
 
 THE GOLD ROAD MILL, AGITATION AND FILTRATION PLANT. 
 
 THE GOLD ROAD MILL, THICKENERS AND SOLUTION TANKS. 
 
 traction. The greater part of the extraction is secured before the agita- 
 tion treatment, and practically none after it. 
 
 Issuing from the agitation system in the Pachuca tanks, the pulp is 
 
THE GOLD ROAD MILL, ARIZONA 199 
 
 delivered to a series of thickeners where the pulp is successively dewatered 
 and rediluted, thus washing out the dissolved metal in the pulp. 
 
 This treatment is not that which has been generally followed at the 
 Gold Road mill. The former method, followed until a few months ago, 
 involved delivering the slime from the agitation system into a slime-storage 
 tank whence it was taken by a 120-leaf Butters filter installation and 
 handled in the usual way. After the cake had been dropped from the 
 filter leaves, it was mixed thoroughly in a tank containing mechanical 
 agitators and discharged by gravity after passing an automatic mechanical 
 sampler. 
 
 For many reasons, this system has been dispensed with and the pulp 
 from the agitation system is delivered to two thickeners. 
 
 Filtration vs. Decantation. The solution overflow from these thick- 
 eners is pumped back to the head of the mill and used as mill solution, 
 while the thickened underflow goes to two more thickeners, before reach- 
 ing which, however, it is diluted with solution previously precipitated. 
 The solution overflow from this second pair of thickeners is sent back to 
 dilute the pulp entering the first pair of thickeners. This solution, over- 
 flowing from the first pair of thickeners, does not require immediate pre- 
 cipitation as it consists largely of precipitated solution as has been shown, 
 The first solution for precipitation is taken from the overflow of the Dorr 
 thickener, through which the pulp passes before reaching the agitation 
 system in the Pachuca tanks. 
 
 Second Thickening System. As a final result, then, the pulp from the 
 agitation system going into the first thickening unit, consisting of two 
 pairs of thickeners, issues from it in form of a thick pulp of about the same 
 consistency at which it entered, having been meantime diluted with 
 barren solution, and twice thickened. The barren solution has passed 
 through the pulp, diluted the metal-bearing solution, and carried most of 
 its value to the mill solution circulation. From this circulation a great 
 proportion of the solution passes to precipitation from the first Dorr 
 thickener, which follows the tube mills, avoiding any extensive building 
 up of value in solution. 
 
 Underflowing from the first thickening system, the thick pulp goes to a 
 second system, which consists of three pairs of thickening tanks. In this 
 unit the pulp is repeatedly thickened and washed , water in this case being 
 the washing medium. The counter-current system is followed, water 
 entering at the final thickener and progressing backward to the first of the 
 series, the solids taking the opposite direction. 
 
 There is provided a separate precipitation circuit to accompany this 
 washing unit, with facilities for diverting the solution either into the mill- 
 solution circuit, before precipitation, or into the washing circuit itself 
 after precipitation. The precipitate joins the bulk of that from the main 
 
200 DETAILS OF CYANIDE PRACTICE 
 
 precipitation system, which is carried to the refining department. The 
 movement of pulp and solution is graphically shown in the accompanying 
 flow sheet. 
 
 Preference for Decantation. Undoubtedly, the adoption of this 
 system will be regarded with interest by everyone connected with the 
 process. Not merely is it interesting as an example of continuous coun- 
 ter-current decantation, noteworthy as it is from that point of view, but 
 more particularly because that system has supplanted a large, modern, 
 vacuum-filter installation with results, according to statement of the 
 operators, better than those obtained under former method of operation. 
 
 There is food for considerable serious thought in this change, but there 
 is danger of falling into popular form of error, and regarding the procedure 
 as a reversion to a system already discarded, or, in other words, a step 
 backward. A little thought, however, will make clear the fact that it is 
 nothing of the kind, but rather a refinement of an earlier process, than 
 which no change can be more progressive. It is clear to the most casual 
 observer that the system used at the Gold Road mill is not applicable to 
 all mills, although it may, as in the present instance, be applied occasion- 
 ally with favorable results both as to percent of recovery and cost of 
 operation. It is applicable in its present form only where solutions carry- 
 ing low cyanide percentages can be used and where the amount of metal 
 in solution is comparatively small, conditions which are manifestly present 
 when low or medium-grade gold ores are treated. Where high-grade 
 solutions are used, it would be impossible to use the system in this form 
 because a large loss of cyanide would be entailed, but by following up 
 the decantation with a form of continuous filtration which would reduce 
 the moisture content of the residue to about 25%, the system is not only 
 feasible, but advantageous. To steer clear of generalities is necessary for 
 the intelligent consideration of any innovation, so that in estimating the 
 value of this one, it must not be considered revolutionary nor reactionary, 
 nor anything more than a simple, clear application of a newly developed 
 system to a particular case. 
 
 Precipitation by Zinc Dust. Solutions of both circuits are precipi- 
 tated with zinc dust, the special feeders and presses being provided in each 
 case, as is shown in the flowsheet. Square-frame presses are used, and not 
 the triangular form usually found in Merrill installations. A variation of 
 the general filter-press practice is the use of three filter coverings for each 
 plate. The layer next the cake of precipitate is of filter paper, the inter- 
 mediate one of light muslin, and the outer one of the usual canvas. The 
 paper is removed and burned with each precipitate cake, the intermediate 
 sheet lasts for several clean-ups, while the canvas, by careful cleaning, is 
 made to last indefinitely. 
 
 The method of adding zinc dust to the solution is the Bosqui system, 
 
THE GOLD ROAD MILL, ARIZONA 
 
 201 
 
 Water Storage Tanks^/^-f-, 
 
 C\Tanks 
 
 No. 5 Gates Crushers 
 
 atM'-ne 
 Tram -to Bin 
 
 1540 Ton Ore Bin 
 
 8 Challenge feeders 
 
 104 brops.+Mesh Screens 
 
 ^-Clarifying Tanks 
 Clarifying Press His:! fc ^ 
 
 Clarifying Press '5 
 Zinc feeder 
 
 Precipi-ra-re 
 ' Press 
 
 Tilting furnace 
 
 Bullion 
 FLOW SHEET OF GOLD ROAD MILL. 
 
 14 
 
202 DETAILS OF CYANIDE PRACTICE 
 
 controlled by the Merrill Metallurgical Co. and, as is usual, the Trent 
 agitator is used for emulsifying. The consumption of zinc dust amounts 
 to about 0.4 Ib. per ton of solution precipitated. 
 
 Precipitate is handled in the usual way Formerly acid treatment was 
 not resorted to, but at present a preliminary acid " cutting-down" is 
 made and the mass of precipitate is then roasted. The dry product of the 
 roasting pan is fluxed and melted in a Steele-Harvey oil-fired furnace. 
 
 Experience at this plant has been such, as to demonstrate that solutions 
 containing exceptionally low percentages of cyanide can be precipitated 
 successfully when the percentage of lime carried is sufficiently high. Solu- 
 tions containing as little as 2c. to 15c. in gold and very weak in cyanide, 
 solutions from washing systems, are successfully precipitated by carrying 
 high alkalinity. 
 
 As has already been mentioned, the lime is added at the mine crushing 
 plant. The consumption amounts to about 0.65 Ib. per ton treated. 
 Treatment solutions usually carry 2 to 2J Ib. CaO, per ton of solution. 
 
 Cyanide in the Tube Mill. The regular addition of cyanide for 
 keeping up the strength of mill solutions, is at the tube mill. This 
 is often considered an excellent point for addition of cyanide, as it is 
 immediately crushed and put into solution; besides, the energetic agita- 
 tion in the mill, together with the somewhat elevated temperature, gives 
 the best opportunity for dissolving the greatest possible quantity of metal. 
 
 Solutions, at the Gold Road mill, are carried at about 2 to 2J Ib. KCN 
 per ton, only one strength being in use. The consumption is about 0.4 Ib. 
 per ton of ore treated. 
 
 Extraction of gold is usually about 94% or more, and is calculated by 
 using the combined content of bullion produced and tailing discharged as 
 the content of the ore milled. Recognizing the limitations of this system, 
 careful duplication and check samples are taken continuously in various 
 parts of the mill. 
 
 The total milling process requires 530 hp. for its operation and 20 
 men are employed continuously, two of these being repair men. 
 
 Detailed cost data on this installation would be exceedingly inter- 
 esting, but unfortunately the policy of the company is adverse to such 
 publication, and for that reason no figures can be given. It may, how- 
 ever, be said that the expenses are altogether reasonable and in conformity 
 with those found satisfactory in the best installations of its kind. 
 
CHAPTER XIX 
 TWO ARIZONA MILLS 
 
 The property of the Tom Reed Gold Mines Co. is situated in the 
 western part of the state of Arizona, not far from the California line. The 
 village of Oatman, which consists principally of the officers and employees 
 of the Tom Reed Co., is not reached by the railroad, but communication 
 is established at Kingman, about 20 miles distant. With Kingman, 
 
 GENERAL VIEW OF TOM REED MILL, OATMAN, ARIZ. 
 
 transportation is by means of automobile stage for passengers; machinery 
 and supplies are brought in on wagons and occasionally pack animals. 
 
 The situation is in a rocky, desert country, comparatively isolated, the 
 nearest activity being at the Gold Road mine of the U. S. Smelting, Re- 
 fining & Mining Co., about 1| miles distant. Aside from this large mine, 
 there is nothing within a much greater distance. Water is scarce and its 
 use has to be governed by great economy. The name of the company^is 
 taken from the name of one of the claims which comprise the property. 
 
 203 
 
204 
 
 DETAILS OF CYANIDE PRACTICE 
 
 Character of the Ore. Gold is the principal valuable metal in the ore, 
 and it occurs generally free in quartz and, to a smaller extent in calcite. 
 The ore is not particularly hard, but requires fairly fine grinding to free 
 the gold and expose it to the action of cyanide solutions. 
 
 From $15 to $25 per ton is the general variation in the value of the ore 
 treated in the mill and the average for several months at a time has been 
 near the higher figure. While there is a small amount of silver occurring 
 with the gold, it is not significant and no effort to save it would be worth 
 while. At present the mill treats about 150 tons daily of dry ore, crush- 
 ing with stamps and regrinding with tube mills. The total-sliming system 
 
 FILTER PLANT DISCHARGE AT TOM REED MILL. 
 
 of cyanidation is followed, crushing in cyanide solution containing 2 Ib. 
 KCN per ton. At the point where it is ready for the agitation treatment, 
 the solids in the pulp will average about 70% through a 200-mesh screen 
 and remaining on 100 mesh the quantity is about 1 to 2%, the whole 
 making a product not particularly difficult to agitate. 
 
 Character of Material. While pulp of this class may be difficult to 
 agitate in those cases when it is largely heavy, granular and devoid of 
 colloid constituent, the governing factor is usually, or ought to be, the 
 fineness necessary to liberate the economically maximum amount of gold. 
 The question of fine grinding has prompted vigorous partisanship for or 
 against it by those metallurgists who believe strongly in extremes of fine 
 grinding or no regrinding at all. Some maintain that extremely fine 
 
TWO ARIZONA MILLS 205 
 
 grinding is wasteful and costly, and that if the grinding is not carried to 
 extremes, agitation of the entire pulp is unnecessary and extravagant. 
 Certainly there are several factors which must be given consideration. 
 Primarily, of course, the cost of fine grinding must be weighed against the 
 additional income furnished by it, and, to be truly profitable, this 
 increased income must be sufficient to cover the cost of regrinding, interest 
 and depreciation on the grinding plant, and leave a profit in addition. 
 Even this comparison alone, however, is not sufficient to justify a proper 
 decision. Part of the material reduced to the so-called state of slime is 
 likely to be granular, though fine, and its agitation will cost more than if 
 a true slime, or colloid matter, were being handled. This extra cost of 
 agitation is not to be ignored in an exhaustive search for definite facts. 
 
 Contrary to what seems to be the general belief a large proportion of 
 this fine granular material might be successfully leached provided only 
 that it is well cleaned, that is, entirely freed of colloid material. If, 
 and when, this granular material is sufficiently fine to liberate the con- 
 tained metal and expose it to the action of cyanide solutions, it is more 
 than likely that leaching will provide for recovery of an amount equal to 
 that which could be obtained by agitation, at much less cost. Leach- 
 ing will take longer to accomplish the same result, but the cost will be 
 less and extraction will be as good in many cases. Also, the installation 
 of a leaching plant costs less than that for agitation, and maintenance 
 expenses and interest are therefore lower. In calculating the cost of 
 leaching plants, however, it should not be forgotten that the separation, 
 meaning a definite and clearly marked separation, of fine, granular mater- 
 ial from a slime pulp is not a simple operation and is likely to cost an 
 appreciable sum per ton treated. The most natural deduction is that 
 every problem should receive separate study and be solved according to its 
 requirements. At the Tom Reed plant, the grinding is carried to a fine 
 point where the product is comparatively easy to agitate and gives 
 better extraction; hence the total-sliming treatment. 
 
 Stamp -crushing. At the Tom Reed mine the ore is hoisted and passed 
 over a grizzly and through a No. 2 Austin gyratory crusher. Thus pre- 
 pared, the ore is delivered to a long 16-in. conveyor belt which delivers it 
 to the mill bin. From the bin, Challenge feeders supply a battery of 20 
 stamps of 1250 Ib. each, dropping 105 times per minute through 6 in. 
 The material is crushed to pass a 12-mesh screen. Crushing is done in 
 cyanide solution containing 2 Ib. KCN per ton and alkalinity equal to 
 about 2 Ib. CaO per ton of solution is carried. 
 
 From the stamps the pulp is received in a 6-ft. hydraulic cone, the 
 slime overflowing to a circuit which will be described, and the sand going 
 directly into the first tube mill. 
 
 Tube -milling and Classification. Sand, or underflow, from the 6-ft. 
 
206 DETAILS OF CYANIDE PRACTICE 
 
 cone is fed into the first tube mill which is 5X22 ft., and equipped with 
 El Oro lining. From this mill the entire pulp is delivered into a Dorr 
 duplex classifier, from which the slime overflow joins the overflow from 
 the 6-ft. cone first mentioned and the sand is delivered to an 8X54-in. 
 Frenier pump, and thence to the second tube mill. This mill is a 
 small one, 3|X 16 ft., and is also fitted with the El Oro lining, which has 
 given good results at this mill. The pebble consumption in these mills is 
 4 Ib. per ton of ore crushed. This small tube mill delivers its product into 
 another hydraulic cone, this one 5 ft. in diameter, whose overflow com- 
 prises the stream of total slime going to the agitation system. Its under- 
 flow is fed into a second duplex Dorr classifier, the overflow from which 
 returns to the cone and overflows from there into the treatment circuit, 
 while the sand product is taken to the Frenier pump which elevates it, for 
 further grinding, into the small tube mill. It will be noted that the 
 rather complicated flow of pulp through the grinding and separating 
 machines is merely an exceptionally careful system of separating sand and 
 slime so that the pulp for agitation may be uniformly and finely reground. 
 
 Agitation of Slime. A 10X30-ft. Dorr thickener receives the slime 
 pulp now prepared for agitation, thickens it to a consistency of about 1 : 1 
 and delivers the thickened product to a battery of four 38 X 10-ft. Pachuca 
 tanks which are operated in series. During agitation treatment the 
 solution is maintained at 3 Ib. KCN per ton and 2 Ib. CaO per ton. Due 
 to the character of the ore, the chemical consumption of cyanide is so 
 small that it may be disregarded. The total cyanide loss is J Ib. per ton of 
 ore milled and is almost entirely mechanical. The lime consumption is 
 about J Ib. per ton of ore treated. 
 
 Discussion of Filtration. Pulp from the agitation tanks is received in 
 another 10X30-ft. Dorr thickener which delivers thickened pulp into a 
 series of stock tanks which are equipped with mechanical agitators, in 
 which the pulp is kept thoroughly mixed until ready for filtration. The 
 overflow is returned to dilute the inflow into the first thickener, the solu- 
 tions being disposed of, as shown in the accompanying flow sheet. A 48- 
 leaf filter of the stationary vacuum type, or Butters system, is used for 
 filtration, and, although it has proved satisfactory, it will probably be re- 
 placed by continuous decantation in the near future, experience and experi- 
 ments having shown that system to be more economical and quite as 
 efficient. Tailing from the filtering tanks is discharged by gravity into a 
 dam, where the material is skimmed at intervals, as has already been 
 described. 1 
 
 Solutions from the filtration plant are precipitated and returned to a 
 treatment-solution storage tank, from which the solution for treatment is 
 drawn. Any surplus at this point may be returned to the mill-solution 
 
 1 "Eng. and Min. Journ.," Mar, 22, 1913; p. 618. 
 
TWO ARIZONA MILLS 
 
 207 
 
 Mill Solution 
 Tank' 
 
 Q- ',. 
 
 I! -} 
 
 Overflow 
 
 Ore from Mine 
 
 No. 2 Austin 6yrcttory Crusher 
 
 IJ-tfRobins BettConveyor 
 Mill Bin 
 
 4- Automatic Feeders 
 
 20, 1250-1 b. Stomps 105 Drops . 
 6" Drop. 12-Mesh Screen 
 
 6' Hydraulic Cone 
 1. 5x22' Tube Mil I 
 I- Duplex DorrCtassifier 
 
 1-8x54 'Frenier Pump 
 \ I- 5^16' Tube Mill 
 
 I 
 
 l-5'Hydrau/ic Cone 
 
 I- Duplex Dorr Classifier 
 
 Pumps 
 
 l-10x$0 Dorr Thickener 
 
 P 
 
 . 4-38xlO'Pachuca Tanks 
 ! Series System 
 
 * HOxSO' Dorr Thickener 
 rflo* 
 
 3-27x5 'Stock Tanks, Mechanical 
 Agitators 8 K.p.m. 
 
 I, 46-Leaf Butters Filter 
 Slime Residue, 
 
 2 Clarifying Tanks 
 Zinc-dust Feeder 
 Pumps 
 
 Pmc'ipitate\ 
 
 Pumps 
 
 FLOW SHEET OF TOM REED MILL. 
 
208 
 
 DETAILS OF CYANIDE PRACTICE 
 
 tank at the head of the mill, thus maintaining a solution balance without 
 difficulty. 
 
 Precipitation Method. Zinc shavings have been used for a long time 
 for precipitating the gold from cyanide solutions at the Tom Reed mill, 
 but recently the system was changed and the Merrill zinc-dust apparatus 
 installed. The system gives entirely satisfactory results, 420 tons of 
 solution being precipitated in a plant designed to handle only 300 tons. 
 With zinc shavings, the consumption of zinc amounted to 0.25 Ib. per ton 
 of ore treated, while with zinc dust only 0.15 Ib. is necessary. 
 
 The mill crushes an average of 150 tons per day, requires 134 hp. for its 
 operation, and employs 16 men for its regular control. Pebble consump- 
 tion in the tube mills amounts to 4 Ib. per ton of ore crushed. While 
 itemized cost data is not obtainable, the aggregate is $2.50 per ton milled, 
 including the depreciation account. Average extraction is 95% of the 
 gold in the ore. 
 
 THE VULTURE MILL, WICKENBURG, ARIZ. 
 
 The Vulture Mill. The property of the Vulture Mines Co. is situated 
 about 14 miles southwest of Wickenburg, in central Arizona. The coun- 
 try is practically desert, and water is scarce. There is no available wood 
 for fuel, and, as coal is extremely expensive laid down at the mine, distil- 
 late and oil are used entirely to furnish motive power. Power for the mill 
 is furnished by two 150-hp. Nash engines, which are entirely satisfactory. 
 
 The valuable metal is gold, which occurs in white quartz, together 
 with pyrite and small quantities of galena and chalcopyrite, sometimes 
 banded and sometimes occurring in masses with the pyrite. The present 
 
TWO ARIZONA MILLS 209 
 
 orebody is one which was discovered in 1911, the vein having been faulted 
 and the ore entirely lost. The mine is an old one, having been discovered 
 by H. Wickenburg in 1863. Surrounding country rock is dioritic schist, 
 no igneous intrusions having any influence on the ore deposition. The 
 average milling ore contains gold to the value of approximately $20 per 
 ton. Mine ore is trammed a short distance from the working shaft to the 
 crusher bins, from which it is fed to a gyratory crusher. The crushed ore, 
 which passes a 2-in. ring, drops to a conveyor belt, and is elevated to 
 another ore bin. From this the ore is hoisted over a trestle 700 ft. long 
 to the mill bins by means of a friction hoist on the mill line shaft. 
 
 Regrinding in Pans. The stamp installation consists of twenty 1600- 
 Ib. stamps, dropping 98 times per minute through 6J in., and crushing 
 through a 40-mesh round-aperture screen. Chuck blocks are used, and 
 the ore is subjected to amalgamation inside the mortars. 
 
 A Dorr duplex classifier follows the stamps, and separates the pulp into 
 sand and slime. Solution is used throughout the mill, including the stamp 
 crushing department. The slime portion of the ore is elevated to three 
 Deister slime concentrators, the tailing from which is taken to a series of 
 thickeners. The classified sand is reground in two 5-ft. Wheeler pans, 
 which make 42 r.p.m., and each is capable of grinding 35 tons per day, 
 85% of which passes a 100-mesh screen. The consumption of iron 
 amounts to about one pound per ton of ore treated. 
 
 Continuous Decantation without Filtration. From the two grinding 
 pans, the ground pulp passes to four Wilfley concentrators, the high-grade 
 sulphide being here removed, and the tailing from the tables is again 
 reground in a third Wheeler pan, identical with the other two. The prod- 
 uct of this third pan is sent directly into the first of a series of continuous 
 thickening tanks, together with the slime from the Deister concentrators. 
 In this series of thickeners, there is continuous decantation and thickening 
 of pulp, followed by a thinning by means of weaker solutions. Water for 
 final washing enters the last thickener and progresses to the first in a direc- 
 tion contrary to that of the moving pulp. The accompanying flow-sheet 
 diagram shows the movement of the pulp and solutions in the thickener 
 series, as well as in the rest of the mill. No filter is in use and the final 
 thickener is required to discharge the pulp at the maximum possible 
 thickness. It will be noted that there are no tanks for agitation of the 
 pulp, the operation being practically grinding, concentrating, washing 
 and discharging. The operators, however, believe that better results 
 could be obtained by using one or two agitation tanks ahead of the thick- 
 ener series, and such tanks will probably be installed in the near future. 
 
 Zinc dust is used as a precipitant, a feeder of the belt type being 
 installed. A precipitate press of the Merrill triangular type having sixteen 
 36-in. frames is used to collect the precipitate, which is not acid treated, 
 
210 
 
 DETAILS OF CYANIDE PRACTICE 
 
 but is melted directly in an oil-fired tilting furnace and the bullion shipped. 
 Slags formed in the melting are periodically smelted in a small blast fur- 
 nace, the lead bullion cupelled and the product added to the regular output 
 of the mill. 
 
 It is of particular interest to note that in the two modern and efficient 
 
 battery 'Solution 
 'Tank 
 
 Gyratory Crusher 
 Be/ f and Tram to.fli/l 
 
 Mi I I Bin 
 Challenge Feeders 
 
 20- 1600-1 b.Stamps 
 
 98 Drops, 6j "Drop, 40- Mesh Screen 
 
 l-Duplex Dorr Classifier 
 2~ 5' WheeJerGrind/ng Pans. 42 R.p.m. 
 
 4-Wilfley Concentrators 
 I- 5 ' Wheeler Grinding fan , 42 Rp.m. 
 
 4 -Dorr Thickeners 
 
 l-2B'xl5' 
 
 3-32x12' 
 
 Continuous Counter-current Decantation 
 
 Wafer, 
 
 \Slime fesf'afi/e 
 
 line-dust Feeder 
 Precipitate Press 
 
 Oil- fired Tilting Furnace 
 jllfon 
 
 FLOW SHEET OF VULTURE MILL. 
 
 plants described here, experiment has shown that expensive filtration 
 plants may be considered superfluous. At the Tom Reed mill, where a 
 filtration plant was originally installed, it will be superseded by contin- 
 uous decantation, resulting in a material economy, while at the Vulture, 
 no filter has been installed, the series of four thickeners satisfactorily doing 
 
TWO ARIZONA MILLS 211 
 
 the work. In practice the thickeners deliver a product which is accep- 
 table from the point of view of contained moisture. The first of the series 
 at the Vulture mill delivers a product containing 31% moisture; the 
 second, 43%; the third, 42%; and the fourth and final one, 35% mois- 
 ture. If necessary, the thickener can deliver a product containing as 
 little as 25% moisture on a slime which settles rapidly. It is not too 
 much to say that on the same material, the vacuum filter cannot do a 
 great deal better than the thickener, considering all points at their real 
 value. In the statements that are made here in this connection, reference 
 is made solely to the treatment of gold ores of milling grade. Silver ores, 
 requiring solution of greater cyanide strength, may be treated by a varia- 
 tion of the system which will be mentioned in a later article. 
 
 Extremely fine grinding is not required on the Vulture ore to secure 
 the economically maximum extraction. Classification stated in the 
 accompanying table shows the condition of the pulp undergoing treat- 
 ment. 
 
 CLASSIFICATION OF SLIME PULP 
 
 + 80 mesh 12.0% 
 
 + 100 mesh 2.5% 
 
 + 150 mesh 23.5% 
 
 +200 mesh 46 . 5% 
 
 -200 mesh 45.5% 
 
 Solution is used throughout the mill, usually maintained at about 2.1 
 Ib. KCN per ton of solution. Lime is added at the mortars in sufficient 
 quantity to maintain an alkaline condition. 
 
 About 1 Ib. of KCN is consumed in treatment, 2 Ib. of lime and 0.4 
 Ib. zinc, in the form of zinc dust. Costs, while not at present available for 
 publication, are reasonable in view of the adverse conditions already men- 
 tioned. These Arizona plants are particularly instructive as examples of 
 first-class operation under difficulties. 
 
INDEX 
 
 Acid treatment of precipitate, 59, 61 
 Additon, A. Sidney, 144 
 Agitation methods, 7, 33, 43, 56, 71 
 
 system, 106, 111, 116, 120, 133, 164, 
 
 176, 190, 191, 206 
 Ajax mill, 81 
 
 Akins classifiers, 70, 157, 171 
 Aluminum as precipitant, 9 
 Amalgamation, 15, 18, 19, 24, 31, 42, 
 69, 177 
 
 B 
 
 Belmont mill, 105, 125, 130 
 Bismark mill, 62 
 Black Hills, Practice in, 50 
 Black Oak mill, 188 
 Blue Flag mill, 81, 97 
 Bromocyanidation, 88' 
 Butters, Charles, 15, 23 
 Buffalo mine, cobalt, 2, 6 
 refining furnace, 11 
 Butter's filter, 5, 10, 17, 57 
 discharge, 126 
 
 Cadogan, A. G, 140 
 
 Calculation of extractions, 140, 142, 144, 
 
 146, 155 
 
 Central mill, 177 
 Chilean mills, 53, 56, 60, 85 123, 163, 
 
 171 
 
 Churchill Milling Co., 161 
 Clevenger, G. H., 15, 23, 94 
 Cobalt District, Ontario, 1 
 
 ore character, 1, 14 
 Concentrate treatment, 31, 183, 186 
 
 of slime, 106 
 Concentration, 31, 86, 109, 134, 157, 180, 
 
 209 
 
 Continuous decantation, 96, 209 
 Cost of cyanidation at Tonopah, 125 
 
 Costs of milling, 10, 77, 83, 156, 164, 184, 
 193 
 
 of shipping precipitate and bullion, 
 
 92,93 
 
 Cripple Creek, Colo., 79 
 Crushing in solution, 136 
 
 advantages and drawbacks, 130 
 
 Tonopah ores, 139 
 Cunningham, Noel, 38 
 Cyanide, consumption of, 8 
 
 at Nipissing mill, 17 
 
 Liberty Bell mill, 75 
 
 Stratton's Independence, 89 
 
 West End mill, 109 
 
 Montana-Tonopah, 113 
 
 Tonopah Extension, 119 
 
 MacNamara, 122 
 
 Nevada Hills, 156 
 
 Nevada Wonder, 165 
 
 North Washington P. & R. Co., 173 
 
 San Foil mill, 176 
 
 North Star, 184 
 
 Black Oak, 192 
 
 Gold Road, 200 
 
 Vulture, 211 
 
 1) 
 
 Decantation washing, 158 
 Desert mill, 122 
 Dewey, Frederick P., 95 
 Dome mill, Porcupine, 39 
 Dominion Reduction Co., 2 
 Dorr J. V. N., 59 
 agitators, 31, 158 
 
 classifiers, 42, 54, 60, 97, 103, 111, 
 
 114, 120, 164, 176, 190, 197, 206 
 
 thickener, 32, 33, 42, 54, 60, 71, 97, 
 
 108, 120, 158, 165/176,181,190, 
 
 197, 206 
 
 E 
 
 Empire mill, 184 
 
 Extension, Tonopah, mill, 114 
 
 213 . 
 
214 
 
 INDEX 
 
 Extraction percentage, 8, 45, 52, 58, 76, Linings for tube mills, 132 
 
 89, 109, 113, 117, 122, 135, 140, Lundberg, Dorr & Wilson mill, 59 
 
 142, 144, 146, 155, 165, 174, 
 
 176, 184, 192 M 
 
 Faber du Faur furnace, 109 
 Filter, Butter's, 111, 117, 120, 199, 206 
 Filters, pressure, Merrill, 10 
 vacuum, 108 
 
 Butters, 5, 10, 17, 57, 88 
 
 Moore, 36, 54, 59, 71 
 
 G 
 
 Golden Reward mill, 53 
 
 Goldfield Consolidated mill, 131 
 
 Gold Road mill, 195 
 
 Grading analysis, 16, 71, 84, 85, 100, 116, 
 
 211 
 Grass Valley, Calif., 177 
 
 II 
 
 Hardinge conical mills, 5, 7 
 Hendryx agitators, 71, 111, 133 
 Hollinger mill, Porcupine, 28 
 Homestake mill, 50, 62 
 
 MacNamara mill, 119 
 Mechanical agitator, 136 
 Merrill filter, 10, 44 
 
 precipitation press, 5, 37, 44, 183, 
 
 186, 200, 209 
 
 Metallurgical history of Republic, Wash- 
 ington, 168 
 Minnesota mill, 66 
 Montana-Tonopah mill, 109 
 Moore filters, 10 
 Mother Lode ores, Calif., 188 
 
 X 
 
 Nevada Hills mill, 153 
 
 Wonder mill, 161 
 Newton, H. W., 170 
 Nipissing, mine, Cobalt, 1, 5 
 
 grading analysis, 16 
 
 high-grade mill, 14, 23 
 North Star mill, 177 
 
 North Washington Power and Reduction 
 Co., 170 
 
 Irvin, Donald, F. 126 
 J 
 
 Johnston, James, 15 
 Jones, A. H., 136 
 
 K 
 
 Kirby, A. G., 38 
 
 Leaching, 51, 58, 87, 123, 180 
 
 Lead salts, use of, 8, 75, 109, 113, 119, 
 122, 137, 156, 165, 173, 192 
 
 Liberty Bell mill, 67 
 
 Lime, use of, 7, 44, 52, 75, 84, 85, 109, 
 111, 113, 119, 122, 137, 156, 160, 
 165, 173 176, 184, 192, 202, 211 
 
 O 
 
 O'Brien mill, Cobalt, 3 
 Oliver filters, 160, 165, 181 
 Ophir mill, 97 
 Ovoca classifier, 86 
 
 Pachuca tanks, 7, 43, 56, 133, 158, 164, 
 
 181, 186, 197, 206 
 Parral agitator, 7 
 Pans, regrinding, 209 
 Parsons, A. R., 125, 139 
 Porcupine, Dorr mill, 39 
 Hollinger mill, 28 
 ore character, 28 ,39 
 Portland mill, 81 
 Precipitation systems, 9, 18, 25, 37, 57, 
 
 59, 73, 88, 109, 113, 122, 160, 
 
 173, 183, 199, 208 
 
INDEX 
 
 215 
 
 11 
 
 Refining, 18, 19 
 
 furnace at Buffalo mill, 11 
 Reid, J. A., 49 
 Reliance mill, 62 
 Republic, Washington, 168 
 Reverberatory furnace, 12, 21 
 Robbins, P. A., 38 
 Roll crushing, 51, 55, 60, 66, 138, 139, 171 
 
 Tonnage estimations, 46, 52, 74 
 Tonopah ores, of, 102 
 
 practice at, 102 to 152 
 Treatment, cost of, 10 
 Trent agitators, 33, 36, 106, 116, 120, 133, 
 
 158, 172 
 Trojan mill, 55 
 Tube mills, 6, 16, 24, 29,"42, 70, 103, 114, 
 
 120, 132, 163, 172, 182, 190, 
 
 197, 205 
 
 S 
 
 San Foil mill, 174 
 Settling area, 186 
 Shipping precipitate, 89, 90 
 Simpson, George, Jr., 142 
 Smelting precipitate, 46, 73 
 Smuggler-Union mill, 70 
 Solutions, 27 
 
 heated, 74, 111, 117, 135, 136 
 
 progress of, 99 
 Sorting ore at Tonopah, 129 
 Stamps and Chilean mills, comparison 
 
 of lost time in, 163 
 Stratton's Independence mill, 81 
 
 Vacuum pump, 73, 108 
 Victoria mill, 58 
 Vulture mill, 208 
 
 W 
 
 Wasp No. 2 mill, 51 
 
 Watson, R. B., 23 
 
 Welton, Wm. S., 146 
 
 West End mill, 103 
 
 Wheeler, K. T., 89 
 
 Williams' hammer trommel mill, 174 
 
 Wonder, Nevada, mill, 161 
 
 Temperature of solutions, 9 
 Thickness, 32 
 
 Tigre, El. Yzabal, Sonora, 126 
 Tom Reed mill, 203 
 
 Zinc dust, as precipitant, 9, 44, 113, 160, 
 
 173, 183, 186, 199, 208, 209, 
 shavings, 9, 18, 52, 57, 59, 73, 88, 
 109, 122 
 
293556 
 
 UNIVERSITY OF CALIFORNIA LIBRARY