University of California Berkeley Technical Paper 90 DEPARTMENT OF THE INTERIOR BUREAU OF MINES JOSEPH A. HOLMES, DIRECTOR METALLURGICAL TREATMENT &*& OF THE LOW-GRADE AND COMPLEX ORES OF UTAH A PRELIMINARY REPORT BY D. A. LYON, R. H. BRADFORD, S. S. ARENTZ, O. C. RALSTON, and C. L. LARSON ISSUED JOINTLY BY THE BUREAU OF MINES AND THE DEPARTMENT OF METAL- LURGICAL RESEARCH OF THE ENGINEERING STATION OF THE UNIVERSITY OF UTAH WASHINGTON GOVERNMENT PRINTING OFFICE 1915 The Bureau of Mines, in carrying out one of the provisions of its organic act to disseminate information concerning investigations made prints a lim- ited free edition of each of its publications. When this edition is exhausted, copies may be obtained at cost price only through the Superintendent of Documents, Government Printing Office, Wash- ington, D. C. The Superintendent of Documents is not an official of the Bureau of Mines. His is an entirely separate office, and he should be addressed : SUPERINTENDENT OF DOCUMENTS, Government Printing Office, Washington, D. C. The general law under which publications are distributed prohibits the giving of more than one copy of a publication to one person. The cost of this publica- tion is 5 cents. First edition. March, 1915. CROI 1 I IBKARY CONTENTS. Page. Introduction, by D. A. LYON 5 The problem of Utah's low-grade ore, by ROBERT II. BRADFORD 7 Review of mining in Utah 7 Gold 7 Silver 7 Lead 8 Copper 8 Zinc 8 Improvements in mining and methods of treatment 8 Porphyry mining at Binghain 9 Treating stope fillings at Park City 10 Low-grade ore in the Tintic district 10 Situation and extent of the low-grade ores, by S. S. ARENTZ 10 Examination of the mining districts 11 Bingliam and Garfield 11 Park City district 11 The milling problem in the Park City district 13 The metallurgical problem in the Park City district 14 Tintic district 14 Stockton district 1C Dry Canyon and Ophir district , 17 Deep Creek district 17 Milford district 17 Silver Reef district _ 19 Eastern Utah 20 Chemical characteristics of the Utah ores, by O. C. RALSTON 21 Results of analyses 21 Types of ores analyzed 22 Metallurgical treatment of the ores, by D. A. LYON, R. H. BRADFORD, S. S. ARENTZ, O. C. RALSTON, and C. L. LARSON 24 Processes of treatment 24 Oxidized ores i 24 Complex sulphide ores 25 Removal of copper 26 Chief metallurgical problems 26 Treatment of oxide and carbonate ores 26 Treatment of zinc-bearing ores 26 Chloridizing processes 28 Holt-Dem process . 28 Principal features of process 29 Factors affecting the process '. 29 Summary 30 Knight-Christensen process 31 3 CONTENTS. Metallurgical treatment of the ores Continued. p age . Processes having a possible application to Utah ores 32 Lead carbonates carrying silver 32 Murex process 32 Sulphidizing and flotation 32 Electrostatic separation 32 Oxidized copper ores carrying gold and silver 33 Chloridizing and leaching 33 Sulphidizing and flotation 33 Mosher-Ludlow process 33 Slater process 33 Other processes 33 Oxidized zinc ores, occasionally carrying gold and silver 34 Igneous concentration 34 Leaching with ammonium carbonate solution 34 Bisulphite process 34 Leaching with acid solution and electrolytic precipitation of zinc 34 Oxidized zinc-lead ores, carrying occasionally gold and silver 36 Bisulphite process 35 Leaching with ammonium carbonate solution 35 Sulphidizing and flotation 35 Oxidized ores of zinc and copper, carrying gold and silver 35 Leaching with ammonium carbonate solution 35 Bisulphite process 36 Leaching with acid solution and electrolytic precipitation 36 Igneous concentration 36 Oxidized ores carrying zinc, copper, lead, silver, and gold 36 Partly oxidized sulphide ores. 36 Raw materials for use as reagents 36 Iron for precipitation 37 Sodium sulphate (mirabilite) 38 Allied problems 38 Conclusion 39 Publications on treatment of minerals 40 METALLURGICAL TREATMENT OF THE LOW-GRADE AND COMPLEX ORES OF UTAH. INTRODUCTION. By D. A. LYON. In the performance of its duty of conducting investigations to increase safety, efficiency, and economic development in the mining and treatment of ores and minerals the Bureau of Mines is cooperat- ing with various State organizations in order that the necessary work may be done to best advantage and without duplication of effort. At its tenth regular session in 1913 the Legislature of the State of Utah provided for the establishment of a metallurgical research department in connection with the State School of Mines of the University of Utah. The act providing for this department stated : The purposes of this research department shall be to conduct experiments and researches, either alone or in cooperation with the National Bureau of Mines and other agencies, with a view of finding ways and methods of profit- ably treating low-grade ores, of obtaining other information that shall have for its object the benefit of the mining industry and the utilization and conserva- tion of the mineral resources of the State, and to publish and distribute bulle- tins and articles relating to the department and its work. The station has effected a working arrangement with the Federal Bureau of Mines by which the bureau is furnishing the metallurgist, who has charge of the research department, and an assistant metal- lurgist. The University of Utah is providing the buildings and equipment and also five metallurgical research fellowships of the yearly value of $720 each. The fellowships are awarded to gradu- ates of colleges, and preferably mining schools, who have shown special aptitude for research investigations. Holders of the fellow- ships are required to work on the bureau time schedule, except Sat- urday, when they quit at noon. Their employment extends over the entire 12 months. The fellows selected by the university authorities for the fiscal year 1913-14 were: L. F. Pattison, A. B., University of Utah; W. G. Laws of Utah, 1913, ch. 102, sec. 2, pp. 199-200. 6 TREATMENT OF LOW-GRADE ORES. Woolf , A. B., University of Utah ; O. H. Pierce, A. B., University of Nebraska ; A. E. Gartside, A. B., University of Oklahoma ; and C. Y. Pfoutz, E. M., University of California. Messrs. Pattison, Gartside, and Pfoutz resigned their fellowships at the end of the fiscal year, and those selected, from a large number of applicants, to take their places for the fiscal year 1914rl5 were: R. M. Isham, Ph. D., Columbia University; C. L. Larson, E. M., University of Minnesota; and H. J. Morgan, A. B., Stanford Uni- versity. All of the men mentioned actively aided in obtaining the data used in preparing this report. Attention is called to the fact that this report is a preliminary statement only. Much work must be done to determine the applica- bility or the precise value of most of the different methods of ore treatment that are mentioned. THE PROBLEM OF UTAH'S LOW-GRADE ORE. By ROBERT IT. BRADFORD. REVIEW OF MINING IN UTAH. When the ores from the head of Little Cottonwood Canyon were shipped by wagon to San Francisco and by boat from there to Swansea, Wales, their value per ton was necessarily high. These were surface ores, and the value decreased with depth. However, at the Emma and neighboring mines at Alta, the ores continued of sufficient value to warrant shipping by team to Omaha and thence by train to the smelters at Chicago. Early mines in other districts added to the amounts shipped to the distant smelters, but none of the mines of these districts yielded ores of enormous value, as have many of the mines of the neighboring States. Utah's high standing as a mining State has resulted from her enormous supply of medium and low grade ores. GOLD. Utah has produced some free-gold ores, but these were seldom very rich and were never found in any considerable quantity. The gravels of Bingham Canyon yielded placer gold for a time, as did also gravels near some other early mining camps. Mines near Rich- field, in Sevier County, produced some " picture rock " and ore con- taining enough finely disseminated free gold to pay handsomely when cyanided. A few other districts have produced some gold, but Mercur has given by far the greatest returns as a strictly gold camp. The gold ore of Mercur was low grade and could not have been treated profitably but for the advent of the cyanide process, just when all old processes had failed. So even in the case of gold ores the State of Utah has produced the lower grades. SILVER. Silver ore richer than that now mined was common at most of the early camps. Later developments showed increased tonnage, but of lower grade. From the first mining efforts in Utah the State has ranked high in silver production. To-day much low-grade silver ore awaits some cheap method of treatment. 8 TREATMENT OF LOW-GRADE ORES, LEAD. Lead ore mined for lead alone must carry a high percentage of the metal to have much value per ton. In Utah the lead ores mined have been rich in silver, and it was the combined lead and silver content that made the ores valuable. Much low-grade lead ore and lead- zinc-silver-gold ore is awaiting some cheaper method of treatment. COPPER. For the first 20 years of the State's mining history the red metal, copper, was not considered valuable. In the last 20 years the copper production has increased until now Utah ranks a close fourth among the States of the Union in the production of that metal. Low-grade copper ores are the source of the copper. ZINC. Up to date no zinc smelter has been built in Utah, but not because the ores mined contained no zinc. To keep down the zinc content, because of the penalty charged by the smelters, has been the im- portant aim of the ore shipper. Now the proportion of zinc is in- creasing and the zinc must be considered as a possible source of profit in mixed sulphide ores and also in oxidized ores. Occasion- ally the percentage of zinc is sufficient to make the ore worth ship- ping direct to zinc smelters, but the amount of such ore found has been small. Zinc ores, so long considered as of no value, now bid fair to become a big source of income if methods of profitably treat- ing the low-grade ores can be discovered. IMPROVEMENTS IN MINING AND METHODS OF TREATMENT. The first smelting furnace was erected at Bingham with the hope that the cost of mining and smelting would be less than $100 per ton, which had been the cost of mining, shipment to Chicago, and smelting there. Actually, the cost with this furnace was kept down to $89 per ton, and as improvements in design and operation were made the cost was still further reduced. As the mining and treatment costs were lowered, ores of less value were mined at a profit. During the seventies ores valued below $40 to $50 per ton were considered too low grade to save. In the early nineties methods had been so improved that $20 ore was successfully handled, and under favorable conditions $16 ore. Ten years later $8 to $9 ore was worked and under certain conditions a profit was made on $6 ore. With the enormous deposits of low-grade ores the principal prob- lem demanding attention is still, as before, the devising of cheaper methods of mining and treatment. THE PROBLEM OF UTAH'S LOW-GRADE ORE. 9 PORPHYRY MINING AT BINGHAM. It is interesting to note the results of the improvements already made. Compare, for instance, the costs for mining and smelting high-grade ore at Bingham in 1872 $89 per ton with the costs for ores at the same camp 41 years later, when the porphyry copper ores were mined, milled, and smelted for $1.25 per ton. In order to bring the costs down to this figure the Utah Copper Co. is conducting work on a mammoth scale. The company is min- ing an entire mountain, the largest developed ore body in the world, and has an enormous equipment. Fifty-one locomotives and 22 steam shovels are day and night engaged in tearing down the ore. Every 24 hours about 24,000 tons of ore and nearly double this amount of overburden are moved, the pay ore to mill bins, the waste to near-by gulches. The feat of solving the problem of treating these ores was accom- plished by careful and painstaking experimental research on the part of the management of the company. Success was largely due to its ability to anticipate the results of mining and milling on a scale commensurate Avith the immensity of the low-grade ore body in the monzonite-porphyry it had carefully prospected. The company has expended $25,000,000 in improving its property, and produces yearly 8,000,000 tons of ore, from which it extracts over 150,000,000 pounds of copper. These results illustrate the application on an enormous scale of methods devised for one class of Utah's low-grade ores. However, the Utah Copper Co. still has its problems. Enormous quantities of monzonite are mined and treated at remarkably small cost per ton, but the fact remains that the saving is low. For each 2 pounds of copper recovered by milling, a third pound goes to the dump. To better this saving while keeping the cost of treatment at a minimum is the company's constant effort. Considerable of the ore shows a mixture of sulphides and oxides of copper. To keep the oxides from going to the tailings and being wasted requires a different treatment from that now employed in the two mammoth mills. A method of leaching combined with flotation is being worked out for this ore. The oxidized capping as a rule carries considerable copper, in many places as much as the porphyry ore, and the copper-bearing capping is kept separate from the more barren waste rock that has to be removed. The treatment of the enormous amount of low- grade ore in this capping is a gigantic problem. More than 40,000,- 000 tons of such ore is awaiting treatment by a process that will successfully and economically recover the contained metal. If such Boutwell, J. M., Economic geology of the Bingham mining district, Utah : Prof. Paper 38, U. S. Geol. Survey, 1905, p. 90. 79474 15 2 10 TREATMENT OF LOW-GRADE ORES. ores be leached, as they probably will be, it will be necessary to employ a process that can be applied on a scale commensurate with the size of the deposit. TREATING STOPE FILLINGS AT PARK CITY. In the Ontario mine at Park City, Utah, the material of too low a grade to be treated at a profit was either not mined or was stored in stopes, or rooms, underground. To-day, because of improved methods of treatment, these old stope fillings and the low-grade ores in place are being profitably mined and milled. The management states that the new mill of the Mines Operating Co. treats 150 tons of ore a day. Similar ores in the near-by mines are amenable to the same process of treatment and will no doubt be economically worked in mills now being designed. LOW-GRADE ORE IN THE TINTIC DISTRICT. In the Tintic district the better-grade ores have been shipped to the smelters in the Salt Lake Valley, or else have been milled. Some of the early methods of milling were quite crude. Ores high in silica, and hence hard to smelt, that carried a metal content valued at less than $10 per ton, were either left in the mine or stored on the dumps. These low-grade deposits are known to be large. Of late much research has been conducted with a view to devising some method of treating these ores. A mill is now being tested in Silver City which bears promise of giving desired results. The three districts mentioned are the largest in Utah, and their untreated ores have been measured in tons. Ores in smaller camps promise much profit when cheap methods of handling and treating are worked out. The " porphyry ores " of the mammoth deposits at Bingham remained uninviting for years. Ore, after all, is a relative term, one definition being as follows: "A metalliferous mineral containing metals in sufficient proportions to be profitably extracted." Hence minerals that once were dis- carded as waste may later be classed as ore, and material that is con- sidered valueless in one region may be deemed ore in a region more favorably situated. The deciding factor in the classification is the cost of treating the material to obtain its marketable product. SITUATION AND EXTENT OP THE LOW-GRADE ORES. By S. S. ARENTZ. In considering what investigations would be most profitable to take up in connection with the low-grade ore problem it at once became evident that each low-grade ore presents its own problem and that a survey of the State to determine the location and extent of the developed low-grade ore deposits was necessary. Considerable time SITUATION AND EXTENT OF THE LOW-GRADE ORES. 11 and attention have been given to the examination of reported large low-grade ore deposits and tailings dumps. Some of them have proved to be most inviting, whereas others have not. A report of the results of the examinations made of the mining districts visited is given here. EXAMINATION OF THE MINING DISTRICTS. BINGHAM AND GARFIELD. The mammoth deposits of moiizonite porphyry at Bingham, previously mentioned, carry small percentages of copper, silver, and gold. The ore is low grade, but is mined in great quantity and is treated by concentration and smelting. The tailings, which carry 0.6 per cent copper, make an enormous pile. Over 30,000,000 tons of this material now collected may yet be re-treated. The ore under the capping and above the sulphides, consisting of oxides and sulphides intermixed, will need special treatment. A combination of flotation and leaching is suggested. The oxidized ore of the capping has been carefully saved and will doubtless be leached. The treatment of pyritiferous ores with a low copper content has long been a problem of the mines in this district. When the zinc content is below 8 per cent this material smelts well in blast furnaces running " pyritically." Ores high in silica and low in copper are sold to the smelters for flux in the basic-lined copper converters. If these ores could be leached to a better advantage, the district no doubt could supply a large tonnage of such ore. Complex sulphide ores are also produced in this district. Their treatment has long been a much-discussed problem. At the Midvale mill of the United States Co. the ore is concentrated, then the middlings are dried and treated electrostat- ically. The company ships a zinc concentrate east to the " gas belt>" but smelts the lead concentrates and also the pyrite. Much ore of this class is demanding attention. PARK CITY DISTRICT. Mining has been conducted at Park City 1 since 1869, and many dividend-paying mines have been developed, so that operators in that district are rather averse to admitting that anything like a low-grade or complex ore problem exists there. a For a discussion of the geology of the ore deposits, see Boutwell, J. M., Economic geology of the Bingham mining district : Prof. Paper 38, U. S. Geol. Survey, 1905, 413 pp. 6 For a description of the geology of the ore deposits, see Boutwell, J. M., Geology and ore deposits of the Park City district : Prof. Paper 77, U. S. Geol. Survey, 1912, 231 pp. 12 . TREATMENT OF LOW-GRADE ORES. In this district there are three classes of ore, as follows : 1. Shipping ore. Sulphide : (a) Silver-lead ore. (b) Silver-lead-zinc ore. (