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 WvcbQiwQ tor 
 (3ol6 ^ ^ ^ ^ 
 
 36? a. m. IRoblnsoii 
 
 Ob. Bm. Soc. C. £., /l^. am. Soc. /Ift. E. 
 
 IRcprlntcD fiom 
 
 Cassier's /lDaoaj»inc 
 
 "Mew JJorh 
 
^ 
 
 CoUecUorv 
 
(Reprinted from Cassier's Magazine.) 
 
 DREDGING FOR GOLD 
 
 By A. W. Robinson, M. Am. Soc. C. E. and M. E. 
 
 "PANNING iiI'T" 
 
 C()I.\C1I3KXT with the dedine 
 of hydraulic niininj^ for gohl 
 in the Oeat West of the 
 L'niterl States, is the rise and velop- 
 ment of a new ])rocess for recoverinji; 
 the precious metal from the alluvial 
 bottoms and river beds which have 
 heretofore been deemed inaccessible. 
 It is the later an<l more perfect process 
 succeeding:: the earlier and cruder one, 
 and it makes available vast deposits of 
 gold-bearinj; j^^ravel which is beyond 
 the reach of hydraulic mining. 
 
 1 lydraulic mining is at once the sim- 
 l)lest and most effective method of sav- 
 mg the bulk of the gold where the con- 
 ditions exist for its use : but more or 
 less loss occurs in the tailings. Hy- 
 draulic mining is the disintegration 
 and washing down of a bank of au- 
 riferous gravel by mean- of a jiowerful 
 jet of water, and the jiassing of the re- 
 sultant water and tichris off through a 
 sluice-box containing riffles in which 
 the gold is caught. Two essential con- 
 tliti<»ns are necessarv to successfullv 
 
 operate this system : — First, the water 
 must be available in large quantity and 
 under heavy pressure ; and secondly, 
 there must be a "dump." or natural 
 grade, for the w ater to run ofif and de- 
 posit the tailings without interrui)tion. 
 
 These con<liti(jns are found in many 
 places along the banks of rivers and 
 creeks and in the valley sides, situated 
 so that the water can be laid on by a 
 ditch or Hume, which taps the stream 
 near its head waters, and, following 
 down the contour of the valley at a 
 gentle grade, is soon far above the 
 river bottom, which has descended 
 more ra]Mdly. A pipe line car'-ies the 
 water down to a "giant" nozzle, which, 
 bv the f(3rce of a stream, sometimes as 
 much as 6 inches in diameter, from a 
 pipe-line i8 inches in diameter, and 
 with a pressure of several hundred 
 pounds per square inch, does tremen- 
 dous execution in washing down whole 
 hillsides and spreading them out in the 
 valley below. This harnessing of the 
 forces of nature is so simple and eflfi- 
 cacious, so free from complication, and 
 so cheap as to operating expanses, 
 that handsome returns are obtained, 
 notwithstanding its wastefulness. 
 
 This simple and attractive system 
 soon began to decline for the reason 
 that the localities favored by nature 
 became grailuallv exhausted and 
 worked out. Furthermore, the vast 
 volumes of debris, washed down into 
 the rivers and fruitful valleys below, 
 became a menace to agriculture and 
 other occupations, so much so that the 
 United States Government ap])ointed 
 the "California Debris Commission" 
 to investigate and regulate the con- 
 rticting interests. The i)roceedings of 
 this commission, and the record of the 
 strife between th<' gold miners and 
 the land and navigation interests, fur- 
 nish an interesting chapter in the his- 
 tory of American gold mining, par- 
 ticularlv in California. 
 
4 
 
 CASSIER'S MAGAZINE 
 
DREDGING FOR GOLD 
 
 5 
 
 >» 
 
 'I'hc ^old ill those placer deposits is 
 in the form of tiiielv (hvided ])afticles, 
 scattei-'.'d throiij^h the j^'ravel. The 
 vahie is very variable, lo to 15 cents 
 per cid)ic yard heint;' accounted ])oor 
 ^roitnd, while 50 cents to $1 \V(nild be 
 rich ])ay. ( )ccasionally pay streaks 
 are found which will run $5 and even 
 $20, or more, per cubic yard, but such 
 streaks do not represent the f^eneral 
 averajn'e of a deposit. 
 
 A cubic yard of ,i;'ravel and sand will 
 weij^h. about 2,800 ])oun(ls, or nearly a 
 ton and a half, h'ifty cents' worth of 
 i^o](\, scattered through this (piantity, 
 at $20 an ounce, will wcijj^h only 12 
 .qrains. The proportion of ^^M to 
 jL;ravei i)y weit^ht is, therefore, 1 to 
 1,630,000. Inasmuch as sold is eleven 
 times as heavy as t;favcl, the pro- 
 portion bv volume would be 1 to 
 I 7,000,000. 
 
 This 50 cents' worth of ^old is 
 found usually in finely divided par- 
 ticles. If the particles weijL^h only a 
 j^rain apiece, it is called "coarse" fi-old 
 and can lie readily saved in a sluice- 
 box, altliout^h the ])articles are not 
 larji^cr than ordinary sand. Fine j^'old 
 is of various de.ti^rees of fineness down 
 to minute floating; ])articles, scarcely 
 visible to the naked eye, and of whicli 
 it re(piires several hundred to make a 
 cent's value. 
 
 The marvelous ease with which the 
 apparemly infinitesimal and elusive 
 yellow jj^rains, lost amid millions of 
 tons of earth and stones, can be recov- 
 ered is due to the t^^reat specific j.jrav- 
 ity of ^o\(\. ISeintj eleven times 
 heavier tlian sand and nineteen times 
 heavier than water, it is only neces- 
 sary to wash the two together, when 
 the gold sinks to the bottom and the 
 lijrhter sand and tjravel are carried ofif 
 by the rushinji^ water. 
 
 The beautiful simplicity o{ the hy- 
 draulic sluicing process in all its forms 
 causes it to be the most widely adopted 
 of any method of jjold saving. Its 
 efficiency in fine gold is from 40 to 
 60 per cent., and in coarse gold, from 
 70 to 100 per cent. If the gold is 
 wlioUy coarse, it will save it all. 
 
 This lack of cf^iciencv has led manv 
 
 invciUors to devise means to :,ave that 
 fraction of the tine gold that is lost in 
 sluicing, but thus far with indifferent 
 success. Several methods of amal- 
 gamation have been successfully used, 
 but for thorough work their capacity 
 is so limited that they do not pay. 
 
 The gradual erosion of the gold- 
 bearing banks by the streams and 
 rivers naturally causes a deposition of 
 strata lower down, containing more or 
 less gold. These alluvial bottoms, 
 sedimentarx bars and beds of streams 
 have, until recently, been considered 
 as beyond the reach of any ordinary 
 method of working. 
 
 They were not capable oi being 
 washed or sluiced, because they were 
 alreadv at the lowest level. X'arious 
 
 THE ROCKER 
 
 attempts to dig the material up and 
 elevate it into sluices, from which it 
 could be worked, were made ; but the 
 constant presence of water in such 
 workings and the great cost, or impos- 
 sibility of drainage, rendered such 
 efforts abortive. Miners were com- 
 ])elled to be content with scratching 
 the surface or sinking shallow pits 
 until overcome by the water, and 
 speculating upon the unknown and 
 untold riches that lay just beneath 
 their feet. 
 
 The bottom of the alluvial deposit, 
 or "bed rock," as it is termed, is gen- 
 erally where the richest pay is found, 
 
• 
 
 CASSIER'S MAGAZINE 
 
 (hit' to the natural ^gravitation of the 
 gohl. Thus it comes about tliat atten- 
 tion has been turned to dredtrintj as a 
 method of reachinjj;' these deej) and 
 submerged deposits effectively. ( )n 
 the face of it a simple enough problem. 
 
 CLEANING UP A SLUICE BjX 
 
 yet what vast sums have been sjient 
 in the mistaken efforts of those who 
 did not fully appreciate all the condi- 
 tions involved, and how elusive the 
 little yellow grains are when attacked 
 under water ! The seductiveness of 
 the gold attracts many to engage in a 
 mad and determined search f. r it. and 
 it is not strange that, like moths 
 around a candle, some should come 
 to grief. 
 
 The truth is that gold mining is a 
 business which must be learned, like 
 any other business, and it is just as 
 amenable to the natural laws which 
 govern it as any other of the practical 
 sciences. What would be said of a 
 tailor who engages in watch making, 
 or of a merchant who endeavours to 
 design a bridge or a locomotive? Yet 
 we see the merchant, the manufac- 
 turer, and the business man launch 
 
 out into gold mining, and make sim- 
 ple calculations of the enormous 
 wealth that can be taken out of their 
 claims at so nnich i)er cubic yard, ;'tid 
 assume all the resi)onsil)ility of tiie 
 practical and technical work. The 
 primitive mode of hand wash- 
 ing is by the "pan," — a shal- 
 low dish of sheet steel about 
 18 inches across and 3 inches 
 dee]), witli a tlat bottom and 
 daring sides. Tlie little cut 
 at tlie head of this article 
 shows a uiiner panning out 
 some samples witli which lie 
 seems well satisfied. The 
 nuich-uscd ex])ression, "pan 
 out" has its origin in the 
 early gold - mining days, 
 when, after careful washing 
 down to the last fine par- 
 ticles, the results in the pan 
 were eagerly looked for. In- 
 asmuch as there are about a 
 hundred ])ans to the cubic 
 yard, it will be seen that a 
 cent's worth of gold to the 
 pan would be valuable 
 ground when worked by 
 modern wholesale methods. 
 
 "Panning" gold is a sim- 
 ])le and rapid oi)eration to 
 an exj)enenced miner, but to 
 the novice it is slow and la- 
 borious, liy a few gyratory move- 
 ments with the li]) of the pan under 
 water the bulk of the gravel is 
 (juickly washed over the i.^i\gi:: of the 
 pan, while the gold settles to the bot- 
 tom. The jjrocess is then continued, 
 with repeated lap])ings of the water 
 carrying off a little sand and gravel 
 each time, until there remains only a 
 small (|uantity of the heavy magnetic 
 "black sand" always found in gold- 
 bearing gravel. In this sand the occa- 
 sional gleam of a "golden colour" is 
 seen, and then conies the interesting 
 and delicate part of the operation. 
 Every grain of black sand must be 
 carefully washed away, leaving the 
 grains of gold perfectly clean. 
 
 The determination of values can be 
 made only by weighing the results of 
 a large number of pans, .or from a 
 definite volume of material, but the 
 
 f 
 
DREDGING FOR GOLD 
 
 f 
 
 iiutiihcr of "rolours" to a pan is (jftcn 
 usi'd ti> indicate values. A "colour" 
 is a particle of ^-old apparent to the 
 eye. and as the visible ])articles vary 
 in size from a pin's p(jint upward, they 
 can have no detinite value. 
 
 Xext followinj,'- the "ijan" is the 
 "rocker." Tliis is the ])ainiin_ij;- o])era- 
 tion ])erfonned continuously in a 
 wooden box mounted on rockers, and 
 fitted with a sieve and shelves helow 
 which serve as sluice-boxes for catch- 
 inj^- the ^old. 'i'he miner, as shown on 
 I'''.i^^«-' .^5. J^hovels the t;ravel into the 
 rocker, then rocks it with one Iiand. 
 and di])s water into it with the other. 
 Many wanderinj;- miners make a livinj^ 
 by "rockinj;" out the surface gravel 
 in selected spots along' river bars and 
 in favourite points in valley-bottoms. 
 
 type of (lre(l).je was evolved and per- 
 fected. 
 
 .\hnost every known type of dredge 
 has been tried for gold dredging. One 
 of the most attractive types is the suc- 
 tion, or hydraulic dredge, which sucks 
 up the sand and gravel with a large 
 (piaiUity of water. The water, thus 
 pum])ed up, thereafter serves the pur- 
 ])ose of sluicmg, being [vractically one 
 ojjeration. There is ;i difference of 
 opinion concerning the utility of using 
 a ceiUrifugal pumj), or suction dredge, 
 for handling gold-bearing gravel. It is 
 claimed by some that grains of gold 
 can be elevated and carried through 
 the discharge i)ipe of the pump, be- 
 cause the velocity of flow is so nuich 
 greater than the velocity at which 
 grains of gold will fall through the 
 
 PLAN AND SKCTION OF A GOLD UKEUGER 
 
 I'Vom these primitive methods can.c 
 the suggestion of the larger and more 
 wholesale methods of dredging. It 
 was otily necessary to combine a 
 <lredging machine and a sluicing and 
 washing' a])paratus in order to reach 
 at once these precious deposits. The 
 problem proved, however, much less 
 simple than it seemed, and many ex- 
 periments were tried before the final 
 
 water. This is true, and if the grains 
 of gold could be introduced mto the 
 mouth of the suction pipe they would 
 assuredly be elevated and passed 
 through the pump into the riffles, and 
 would there be caught. 
 
 But this is not the difficulty with this 
 form of dredge. The difficulty is that 
 the force of the suction, being intense 
 close to tlie suction pipe and rapidly 
 
• 
 
 CASSIER'S MAGAZINE 
 
DREDGING FOR GOLD 
 
 (k'criasitiLj in iiitt'iisity a short distanco 
 from tlu' siuiimi, causi-s all tlu' sand 
 and f^^avi'l to \k' \nc\<vt\ up and Iravos 
 till' ^old hrliind, <hu' to its j^rcatir 
 spi'cilic {gravity. iMirthcnnorc, lin' 
 surtinn drrdi,^' cannot work in stones 
 or howld' rs. The nse of a oentrifuffal 
 ])innp. tlierefore. for cleanint:^ np tlic 
 hoitoin and piokini^ nji the ^old is ini- 
 p.actieahle, especially if the f^old he 
 coarse and the bed rock uneven. A 
 rotary cutter on the suction pi|)e does 
 not remedy the difticulty, h. . ."^c it 
 oidy ajj^itates the f^ravcl and in her 
 precipitates the j^old. 
 
 'I'he dii)per dredj^e has nlso heen 
 used, hut in most cases hrs mccii aban- 
 doned, althout^h it is an admirahU ma- 
 chine as a dredj^e and will handle any 
 ordinary material. It is noi adapted 
 for placer-mining', hecause it disturbs 
 the ).;ravel in the act of di^.^Lnuj;, so 
 that a considerable portion of the jjold 
 is lost. It is well known that atjitation 
 of ,tj()ld-l)earint^ .gravel imder water in- 
 duces the i)reci])itatinn of the qcild ; in 
 fact, it is ])recisely this (pialily on 
 which the whole operation of sluicini; 
 and j.j()ld washinj^' depends. 
 
 it is, moreover, mechanicailv impos- 
 sible to construct a dip])er dot^r which 
 will be absolutely water-ti^ht. Natur- 
 ally, therefore. luuch of the tine j^ravel 
 in the bottom of the (lii)per leaks out 
 and carries .q'old with it. X'arious 
 packiuj.js and devices for makin.u: tiie 
 dip])er door water-tij.^ht Inive been 
 tried, but none are successful. A cer- 
 tain amount of hK)seness is necessary 
 to its proper workinjjf. .V bit of j.jravel 
 would prevent a tij^htly fitted door 
 from closinjjT, and it would inevitably 
 become loose by wear in any case. 
 
 .\nother objection to the dipper 
 dredge is that it deposits tlie material 
 intermittently, several tons at a time, 
 and at a lontj distance from the centre 
 of the dredi^e, so that it is ditVicult to 
 take care of the material delivered in 
 this way. It is necessary to have a 
 lar,i;e hojjper either on the bank or on 
 an auxiliary scow, and to feed the 
 .i^ravel out of this hopper into sluice- 
 l)oxes or other a])l)lianccs. 
 
 The same objections a])]ilv to tlie 
 
 clamslu'll form of dredi,^' to an even 
 f^reater de}.;ree, as it is by no means 
 water-ti^ht, and loses most of the q;old 
 in the act of brin^'inj.j up the ^i^'ivel. 
 
 In the elevator dredge none of the 
 forej.;()in)4' objections are found. The 
 action of the endless chain of buckets 
 is slow and (piiet. and the material is 
 picked up clean from the bottom with 
 the smallest amount of a};itation, ami 
 in a maimer best calculated to retain 
 the Ji'old. The buckets are water-tinht, 
 and retain their entire contents until 
 emptied by inversion at the top. The 
 delivery of material is continuous and 
 at the centre of the boat, instead of be- 
 iiij; intermittent and at a distance over 
 the side of the boat, as in the dii)per 
 dredge. The elevator buckets also 
 brin^ up a considerable proportion of 
 water, which facilitates the washing? 
 operation, and the material is broujuht 
 U]) in smaller masses than in the case 
 of the dipper (lredj.je, and, hence, is 
 ..lore easily broken and disiutej^rated 
 in the screen. For all of these reasons 
 it is the ideal type of drcd^t for river 
 minin.LT. This conclusion is confirmed 
 by the fact that all the c'redges in the 
 Australian and New Zealand i^old 
 fields are of tiiis type, and a larj^e 
 number of them are successfully in 
 use there. 
 
 The elevator or chain - bucket 
 dredq'e, is not new ; in fact, it is one of 
 the earliest known types. Some very 
 good dredf^es of ihis type were 
 broujtjht to America from the Clyde 
 in 1832 for use on the river St. Law- 
 rence. They had em^ines of the side- 
 lever ty])c. and did very effective work 
 with 6 pounds of steam. 
 
 On the opposite pagfe is shown a 
 typical jTold drcdcfe. This machine 
 consists of the f( illowint? elements : — 
 1st. the dred^inq' apparatus proper. 
 comprisin,q" the chain of buckets and 
 means for driviui^ them ; 2(1, a steel 
 ho]iper into which the material is dis- 
 charjn;ed ; 3d, a revolving' screen in 
 which it is washed and by means of 
 which the coarse stones arc rejected ; 
 4th. a sluice-box for carryin.q' oi¥ the 
 fine tailings and dischargincf them 
 astern; and 5th, a centrifugal pump 
 
t 
 
 # 
 
 10 
 
 CASSER'S MAGAZINE 
 
 i) 
 
 AN ELKCTHICALLY OPERATED URKDr.E 
 
 for furnishing' the necessary water for 
 sluicing' and washing purposes. All 
 these details have been successfully 
 combined so as to make a complete 
 machine, capable of dredging and 
 treating 3,000 cul)ic yards of material 
 per day. The operations are simple and 
 contiiuious, and tmder perfect control. 
 
 The vastness of the field thus opened 
 up is incalculable. Thousands of miles 
 of good gravel deposits, beyond the 
 reach of all other known methods, can 
 now be made available at a low work- 
 ing cost. One of these dredges can do 
 the work of a thousand men working 
 in the old way ; and not only that, it 
 can reach depths and clean up l)ed 
 rock that would be totally inaccessible 
 by the cond)ined labour of any num- 
 ber of men. The work of gold dredges 
 has already become a perce[)tible fac- 
 tor in the world's production of gold, 
 and it is yet in its infancy and bound 
 to increase. 
 
 Among the earliest successful 
 dredges are those at Bannock, Mon- 
 tana, on Grasshopper Creek, in the 
 I'nited States, where three dredges are 
 at work. The ground is not phenom- 
 enally rich, varying from 10 cents to 
 
 40 cents per cubic yard ; but the 
 dredges have maintained a steady 
 average of work which has yielded 
 "clean-ups" varying from $500 to 
 S3000 ])er day. 
 
 On ])age 34 is shown a bird's-eye 
 view of the valley of the Grasshopper 
 with one of the dredges in the dis- 
 tance. The creek is cjuite small, aver- 
 aging 20 feet wade by a foot deep ; but 
 the dredges work out the whole area 
 of the valley bottom and work at dif- 
 ferent levels controlled by dams. 
 
 The whole field of dredging for gold 
 is yet in its infancy, and it offers a 
 promising field for investment under 
 ])ro])er conditions. A large amount of 
 ))lacer-mining ])roperty yet remains to 
 be opened up that can be worked only 
 by dredging. The improvement of 
 modern methods, by which large 
 capacity can be maintained at low 
 operating cost, renders the vvorking of 
 iow-grade ground possible at a good 
 profit. The proverbial uncertainty of 
 mining is largely eliminated, and by 
 taking ])roper precaution and prv)ceefl- 
 ing on business principles, dredging 
 for gold becomes sini|)ly a uianufac- 
 turing proposition. 
 
 u^ 
 
DREDGING FOR GOLD 
 
 tt 
 
 f 
 
 There are many good claims and 
 river leases lying undeveloped for 
 want of capital and for want of knowl- 
 edge of how to produce certainty of 
 results. ]f the results can be assured 
 with reasonable certainty, capital will 
 not be slow to embrace the opportu- 
 nity. Many costly experiments have 
 been made, some of which have been 
 total failures, some partial failures and 
 some successes. Capitalists, naturally 
 and wisely, are reluctant to put money 
 into schemes that may result in similar 
 failure. An intelligent examination of 
 these cases shows that in every in- 
 stance failure has been due to some 
 evident cause. 
 
 Some of these causes are the fol- 
 lowing : — 
 
 1st, the ado])tion of the wrong type 
 
 eral arrangement or detail, so that it 
 fails in point of insufficient capacity, 
 frequent breakdowns, inability to dis- 
 pose of tailings, inability to clean "bed 
 rock," inability to save the gold, and 
 excessive cost of operation in propor- 
 tion to work done; 4th, poor manage- 
 ment ; 5th, not enough gold in ground 
 to pay ; 6th, organisation by a "pro- 
 moter" for stock jobbing purposes ; 
 7th, operation by an "inventor" who 
 has a new machine, and can do what 
 no one else has ever done; 8th, lack 
 of capital to efficiently carry on the 
 enterprise ; 9th, ground not suitable 
 for dredging; and, 10th, character of 
 gold such that it cannot be commer- 
 cially saved. 
 
 "Forewarned is forearmed," and to 
 avoid these and other rocks and shoals 
 
 ^ ^ 
 
 HVORAIXIC SLLICING 
 
 of dredge, such as suction, clamshell, 
 and otlior tuisiiitable types, which, for 
 specific reasons, cannot be made a suc- 
 cess for dredging gold; 2d, erroneous 
 diagno'qs of the conditions to be ful- 
 fiilc' as to the character of material 
 and method of working, and the conse- 
 (|uent lack of a(lai)tability of the ma- 
 chine to those conditions; 3d, faulty 
 design of the machinery, either in gen- 
 
 it 1.-= necessary to have a knowledge of 
 them. It is i)ractically impt)Ksil)le for 
 any one but an ex])ert to determine all 
 the points that must be covered from a 
 mechanical, connnercia! and legal 
 point of view ; but enough has been 
 said to indicate the general character 
 of this new industry and ihe lines on 
 which it can be successfully carried 
 on.