Proceedings.] DISCUSSION ON GOLD-QUARTZREDUCTION. 177 sufficient to pay when the material was properly worked, they Mr. Giles. could see how imperative it was that themachines for reducing the ore should be of the most perfect description. It was remarkable to observe that the discussion had been maintained in many cases by young members; that perhaps proved that mining, though as old as the hills, was still endowed with vitality. For looking at what had taken place at Fort Salisbury, where pre-historic build- ings hadbeen discovered which wereassumed to be connected with the gold-mining industry of the days of King Solomon, they ought to be able to continue that industry, and to make it pay. There was good reason todoubt whether the meansadopted for ex- tracting gold in those days were anythinglike as perfect as those of the present day. In view of the large income derived from gold-mining, a great many consi.derations would be suggested by the Paper, which would be well worth attention in the future.
Correspondence.
Mr. G. ATTWOODwas much struck with the care and general Mr. Attwood. accuracy of the Author’s statements. The subject was a difficult one to handle on account of the numerous inventions which had been made during the last thirty yearsfor the purpose of improv- ing gold-quartz reduction; nearly all the inventions having some good points but failing in the main. The result of practice had reduced the machines most extensively employed to gravitation and steam-stamps, the Erom or similar rolls, and the Blake jaw- crusher. Withregard to the Author’s statement that effective work was done only at the instant that the stamp descended on the ore, it was possible that such was the case in the early days when the stamp was made in square or angular forms ; but when the revolving stamps were brought into use, a rotary motion was givento the stamp as well as the blow, whichcontributed a grinding motion aswell as a pounding one. Thisaction could easily be seen by watching a battery at work with the screens removed. In reply to an objection to stamps brought forward by the Author, hepointed out that modern gravitation-stamps were so arrangedthat, with ordinary care, no oil or greaseshould con- taminate the ore either in the battery or in the feeding-hopper. For the last twenty-five yearshe had been lookingfor a wet- crushing machine that would supersede the gravitation-stamp, and he was still unable to recommend any other appliance. Even for [THE INST. C.E. VOL. CVIII.] N 178 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Minutes of
Mr. Attwood. dry crushing he had found the stamp equal to jaw-breakers and rolls. Indeedat the great Comstock lode in Nevada, wherehe was engaged for nine years, at a time when no expense was spared in trying every newform of machinery, the gravitation-stamp was selected in spite of its many defects. The steam-stamp had been brought to great perfection in the Lake Superior copper district, and he had recently seen at the Calumet and Hecla mines a mill of fifteen stamps pounding 2,500 tons per day of conglomerate,
Fig. 24.
THESCHBANZ STOKE-BREAKER.
containing native copper ; the scrcens in that case being made of steel plates with circular punched holes about inch diameter. Mr. Bellom. Mr. MAuRrCE BELLOM(Paris) wished to compare thestone- breakers described by the Author with a machine, known as the Schranz stone-breaker, he had recently seen at work in Germany. In this machine the ore was subjected to a simultaneous crushing andgrinding motion. The accompanying drawing (Fig. 24) indicated the construction of the machine so clearly that it was merely necessary to add a few details. The two jaws were made Proceedings.] CORRESPONDENCE ON GOLD-QUARTZREDUCTION. 179 of cast-steel, and the space between them might be regulated at Mr. Bellom. will by means of a vertical screw V, which adjusted the wedge C. The short connecting rod B of cast-iron, had been designed with such section that it would be broken before any other part of the stone-breaker, if some veryhard material should find itsway between the jaws.Deta,ils of the different sizes in whichthis machinewas made would beseen from the Table given below. Theadvantages of this machine consisted inthe fineness to w"hich the ore could be brought (8 millimetres), and inthe fact that there was no necessity to employ the trommels usually adopted with Americanstone-breakers. By reason of theacute angle at which the jaws were placed, the Schranz stone-breaker performed the functionof the tromnlel, the jaws beingable to seize and crush the pieces of ore, the size of which prevented them from engaging between t,he surfaces of the cylinders, whose angle could not be reduced below a certain limit without giving to the diameter of these cylinders an exaggerated size. With his contribution to the discussion, Mr. Bellom sent a lengthy statement of the mathe- . matical principles on which the construction of this machine was base&.
- 11. 111. 1V. v.
300 X' 400 X 500 X' 600 X , , I 200 I 250 300 350 Number of revolutionsper minute of thedriving pulley} 250 250 250 250 250 Diameter of the driving pulley 500 650 700 1,000 millimetres} 400 Width of the driving pulley . 125 150 160 180 millimetres} 100 1,450 1,650 1,800 1,950 900 1,150 1,400 1,700 2,000 900 1,150 1,350 1,550 1,650 Weight of the machine . 2,500 4,500 6,500 9,000 kilograms} 8oo Weight of one pair of jaws 200 300 400 500 kilograms} 100 HP...... 1-2 3-4 5-6 8-10 10-12 Quantity of orecrushed . 600-7 '1,500-' 2,000-' 3,000-' 4,000- kilograms per hour} $1,000 J .2,000 , 3,000 J 4,000 , 5,000
Mr. R. BOLTONobserved that the Author gave descriptions of Mr. Bolton. rock-breaking mechanisms in which the breaker-jaw was hinged above and in which it was hinged below, to the advantage of the latter.There was, however, afu.rther form, employed inthe Lancaster stone-breaker, made by Messrs. Penny & Company, of Lincoln. It was largely used in the United States, its peculiarity N2 180 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Bfinutes of
Mr. Bolton. being that the jaw was hungon a toggle, or vibrating link, above and attached to the reciprocating armbelow, whereby a compound motion was attained with very beneficial results as to output and regularity of size. Themachine further possessed simplea mechanical arrangement of driving-gear by a double cam on the driving shaft, upon which wasa broad iron roller fixed to the reciprocating-arm. This had the effect, as compared with eccen- trics or cranks, of doublingthe number of reciprocations at a given speed and of reducing the friction of driving. By a simple mechanism of one lever resting upon another, a control over the stroke of the jaw was attained duringoperation, and the size of the product might be varied in size at will. This machine seemed to possess advantages demanding attention. One of Sholl's pneumatic stamps was worked for some years near St. Austell, and very fine crushing was done with it. The death of the inventor had since then prevented the extension of his system; but there was a good deal to be said in favour of the use of a cushion of air in high- speed stamping.The Huntington mill, with the improvements in detail introduced into it by Mr. Paxman, certainly formed, in Mr. Bolton's opinion, the best fine-crusher in the market. Mr. Chenhall. Mr. J. W. CHEKHALLobserved that,notwithstanding the long indictment of defects adherent to the stamp-mill brought forward by the Author, it still held its own as the most effective machine, and the one most cheaply manufactured and manipulated, in the market. This arose from the fact that the mill-man could always rely-when he had a well-constructed stamp-mill-on the quan- tities he could pulverize, and on the results he could obtain. As a pulverizing-machine no other contrivance could compete with it in effectiveness. Steam-stamps have been very successful intheir application to the crushingof copper ores on Lake Superior, where it was not necessary to carry the stamping to so great a degree of fineness asin the case of gold-quartz reduction. TheHusband quick-speed stamps had also been successful to some extent in the stamping of tin-stone in Cornwall. The stamp-mill, however, could not be considered well adapted for dry stamping, the con- tinued concussion of the stamps making it impossible to collect thedust from the battery-box. This accumulation of dustwas very injurious to the workmen employed in the mill. He had had experience inthe crushing for dressing of largequantities of copper ore by means of modified Erom rolls, used as wet crushing machines. In this case it was unnecessaryto crushvery fine, and, consequently, large quantities could be crushed, the output per day amounting to 1,000 tons with six sets of rolls, each set Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 181 containing three pairs of rolls. The work was very satisfactory ; Mr. Chenhall. butany attempt to increase the fineness influenced theoutput very largely, and the grooving of the surface of the rolls could never be entirelyprevented. All the rolls and roll-shaftswere consequentlymade in duplicate, andthe rollers were removed immediately they showed signs of wear from the last mill to the higher set of rolls, where the crushing was less fine. The cause of the failure of the variousforms of ball pulverizerwas, probably, that gold-quartz, as a rule, was very hard, and the broken pieces hadangular edges. Such materialswhen brought into contact with rubbing surfaces-as was the case in almost all ball pul- verizers-which work at a high speed, the path of the machine and theballs were ground instead of the ore. Whilemany of thesemachines mighthave auseful field of operation inthe pulverizing of soft material, or as purely prospecting machines, they would never come into considerable use in the reduction of gold-quartz. The Huntington mill, whichhas many features to recommend it, could not be regarded as a machine to supersede stamps, particularly where very large quantities of ore had to be dealtwith daily. Althoughinteresting experiments had been made, no satisfactory results had yetbeen accomplished on a large scale with concentration and extraction of gold from quartz by dry methods. Mr. J. H. COLLINSstated that the Author’s general conclusions Yr. Collins. asto gold-quartz reduction might have been more briefly and definitelysummarised inthe followingwords : In thegreat majority of cases, stamps are themost advantageous ; but where the ore is soft and brittle, and thegold is free and coarse, Huntington millsare sometimespreferable, whilstwhere dry-crushing is necessary Krom rolls are better. This, at any rate, had been the conclusion of men of large practical experience hitherto, andit was not likely to be altered for some time to come. But, in the Paper, it seemed to have been tacitly admitted as a disadvantageous cir- cumstance in the use of stamps, that a larger proportion of slime was produced than was the case with other appliances for gold- quartz reduction. Though this was the fact, the conclusion that it is disadvantageous was too general. The production of much slime in gold-ore treatment was sometimes a positive advantage. Slime was merely very finely divided ore, and if the particles of gold in the ore were very fine and very evenly distributed, and if mechanical concentration and subsequent metallurgical treatment werefor any reason out of the question, and thesewere very common conditions indeed, these very fine gold particles must be 182 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Minutes of
blr. Collins. saved by some form of amalgamation. It was obvious that the gold could not be satisfactorilyliberated from the veinstone except by bringingthe ore intothat extremely fine state of division termed slime. He had microscopicallxexamined tin ores, inwhich the particles of tin oxide were less than of an inch long, of aninch wide, and of aninch thick. In gold ores the metallic particles were often far finer than this. It was evident, therefore, that unless such ores were reduced to an almost impalpable powder, the minute particlesof gold could not be seized and retained by the amalgamated plates. This fine state of division must be obtained either by stamping through a very fine screen, or by subsequent grinding in a mill capable of doing finer work than could be done by a Huntington mill or byKrom rolls. Mr. Commans. Mr. R. E, COMMAXSremarked that there was one form of stone- breaker, the “ Schranz ” crusher (Fig.24), which was not referred to by the Author. It was of interest, as it formed a link between the ordinary stonebreaker with reciprocating jaws, and the crushing rolls. The outward appearance of this crusher was not unlike an ordinary stone-breaker, butthe action was quite different and resembled more that of crushing rolls. The movable jaw, instead of having a reciprocating motion, had a rocking one somewhat similarto the motion of a circularblotting-pad. Anumber of thesecrushers were at work, takingthe place of rolls, and givingevery satisfaction. One advantagethis machine had, in common with the ‘‘ Dodge ” fine crusher, was that the opening atthe bottomwas constant,thereby securing a uniform-sized product.Apoint of some importance, where stone-breakers hadto be sent abroad andlong distances up country, was to keep down the weight of the various parts as much as possible, without at the same time reducing the strength of the machine. This object had been attained(by building up the machines, either with solid steel frames, or by the employment of strong tie- bolts to take up the thrust), with thebest results, and the weight of the machinereduced about 50 per cent. Howfar crushing- rolls were suitable for very fine pulverizing had yet to be proved. Even the best designs of these machines had many weak points. It was, forexample, almost impossible to keep the shells from wearing hollow inthe centre, even when one of the rolls was given a slight longitudinal motion. The number of wearing parts was considerable, and when crushing dry, whatever precautions were taken, it was very difficult to keep a certain amount of the sharp grit from getting into the bearings. The shells and other parts of the rolls were further very costly to replace, and it was a Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 183
question whether, especially for dry crushing, equallygood results, Mr. Commans. with considerably less wear and tear, could not be obtained by the employment of one or other of the numerous forms of ball-crushers in which the ore is crushed down by heavy balls revolving in a drum of more or less cylindrical form, the fine-crushed product passingout through sieves as soon as sufficiently reduced. The material crushed by rolls was broken down in a granular form, without the production of so much fine powder as would be the case if stamps were employed and, therefore, for ore-concentration and chlorination purposes, whereextreme fineness was not re- quired,the employment of rolls was no doubt advantageous. Without doubt, inorder to crush properly with rolls, at least two pairs should always be employed, so as to gradually reduce the material, and a very good plan was to have a set of spare rolls, SO that as soon as the lower pair of finishing rolls showed signs of wearing hollow these could be inserted in their place, and the pair of finishingrolls used some timelonger as roughing rolls before being re-faced. A plan sometimes adoptedfor turning heavy rolls was to have a slide-rest fixed to the frame of the rolls, which permittedof the tires being turnedup in position, and saved the rolls havingto be lifted in and out. Although the Chilian mills had given exceedingly good results, the employment of ordinary edge-runnerswas hardlylikely to extend for quartz-crushing abroad; because, not only was the output with these mills small, but also because the weight andsize of the runners rendered their transport up country very difficult. Another objection was that, however narrowthe face of therunners might be, it wasim- possible toprevent the grinding action, dueto the slip of the runner on thepath. This reduced thematerial to a fine im- palpable powder, rather than to a fine granular condition. This grinding action, as well as the heavy weight of the runners, had been overcome in the Schranz fine-crusher, which was employed at Lauremburg, on theLahn, in conjunction withthe coarse- crusher above described, for reducingthe mixedproducts from the fine jigs. This mill consisted of a revolvingpan and three conical rollers. The rolls revolved on spindles fixed radiallyat an angle toeach other of 120'. The inner ends of the spindles were rigidly fixed. The outer ends moved in aframe, and were capable of being pressed down by means of set-screws and rubber buffers on to the revolving pan, or annular crushing ring. As the pan revolved the rolls were driven by frictional contact, the fact that they were conical prevented any grinding action and con- sequent production of slimes. The ore, which had been reduced 184 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [bfinutes of
)fr. Cornmans. in therocking crusherwas fed evenlyinto the machine, and passed successively beneath each of the three rolls. The pressure of each successive roll was adjusted so as to be a little greater than the preceding one, with the result that after the material had passed under the third roll it was sufficiently finely reduced and waswashed off intothe launder by a spray of water for further treatment. All high-speedcrushers were, without doubt, unsuited for quartzcrushing atthe mines and out-of-the-way places, where breakdowns were difficult to repair. As long as all went well, the output of several of these high-speed crushers was satisfactory; but should a piece of drill steel, a bolt or hammer- head once getinto the machine,a breakage of the flyers or beatersinvariably took place, the renewal of which wasa matter of considerable delayand expense, and would cause the stopping of the whole plant.With reference tothe Crawford millwhich was notmentioned bythe Author, it might be pointed outthat this mill undoubtedly possessed severalnorel features,and as fine-crushera hadgiven wonderfully good results. Topretend that any mill would crushand treat every class of material wasa mistakethat was often made, andin many instances blame had been laid on the machine, where it wasreally due tothose employingit. To attemptto crush material finely in one operation was a very great mistake, and whereverattempted had invariably ended in failure. The Crawford mill was pre-eminently a fine-crusher, and in order to obtainthe best results the material fed into it should have been previously reduced by a stonebreaker, which was the most economical form of coarse-crusher for reducing material down to say &-inchto i-inch size. The special features of the Crawford mill (Fig. 25) were:-The feed wascentral, not to one side, therebyensuring an even wear of the roller-path. No screens whatever were employed, and a constant source of expense and trouble was thus removed. The crushed material instead of being discharged at the periphery of the machine where the swirl was great, passed out in a steady flow near the centre, so that there was no danger of any particles of gold being carried over with the tailings. A natural concentration was carried on in the machine itself by a current of clear water being admitted at the centre, passing over the surface of the mercury, and rising up through an annular slot below the crushing-path of the balls. The action of this rising current of water was to carry off all the material as fast as it was sufficiently finely reduced, and was light enough to pass out at the centre of the machine. Any gold that had been Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 185 freed from the quartz, or from sulphurets, owingto its greater Mr. Cornmans. specific gravity, could not be lifted by the risingcolumn of water and sank down through the slot below the roller path, and became amalgamated with the quicksilver in the annular well. Further as the mercury-well was out of the swirl of the pulp, and as the water flowing over it keptany base mineral fromcoming in
Fig. 25.
CRAWFORD’SMILL. (LATESTTYPE.) contactwith it, therewas no loss due to “sickening,”and it was possible in these mills to treat refractory ores, which could not be treated in an ordinary stamp battery, with copper tables. The mercury was easily withdrawn from time to time to remove any amalgam, and fresh mercury added to the machine by means 186 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [hfinutes of
IJr. Con-mans. of the pipe and funnel. In many ores the gold was SO exceedingly finely disseminated that no amount of pulverizing in an ordinary stamp battery would eliminate this from its surrounding matrix. For such ores the Crawford mill was, undoubtedly, most suitable, since by it there was no difficulty in reducing the ore, so that it could pass a No. 120-mesh sieve. Stamps seldom pulverized finer than 40 to 45-mesh. The wearing-parts of thesemachines were rough castings, which could easily be renewed, and at far less expense than the tires of ordinary roller-mills.These machines were self-contained, easy of transport, and on arrival at the mine could be erected and put to work in a day or two. Clayey ores, which were very difficult to treat in a stamp battery owing to the slime produced, had been very successfully reduced by these mills, little or no gold being carried over with the tailings. JIr. Ednarde. Mr. R. EDWARDSpointed out that the ordinary gravitation-stamp wasnot such a clumsy and unmechanicalmachine as so many thought it to be. It was quitetrue that the total weight of il 10-head batterywas considerable, and entailed in consequence heavy cost for carriage, besides that for the foundations and for erection. Buteven if S1,OOO wereallowed for these costs, the interest on that sum might easily be covered by the simplicity, freedom frombreakdowns, and lessened wearand tear, which were the chief advantages that had made the stamp-battery an illustration of the survival of the fittest. Besides the advantages of its extreme simplicity, and of the fact that the stem of one stamp could be repairedwithout interrupting the work of the battery,the stamp-mill had the further advantage of being capable of dealing with any class of ore from the softest to the hardest. Xr. Hadfield. Mr. R. A. HADFIELDstated that, according to the Author, Krom rolls, said to be made of the best open-hearth forgedsteel, had crushed more than 20,000 tons of ore before being worn out. It would be of considerable interest if the Author could give the chemical composition of suchsteel, especially as regardedthe carbon contents ; and, further, if he could state whether the rolls were put to work just as received from the makers, that is, beyond being machined, being used in theunhardened state. The firm with which Mr. Hadfield was associated had for several years been making considerable numbers of experiments with special mate- rial (manganese steel) for crushing-purposes, and although, for reasons in the manufacture, its introduction had not been on a large scale, the initial difficulties were now being rapidl,v over- come, and this manganesesteel wasbeing applied specially for Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 187 purposes where it was necessary tohave hardness andgreat Mr. Hadfield. durability.Trials of stamp-castings of thismaterial at the Tregurtha Downs mines, in Cornwall, hadgiven exceedingly satisfactory results. Another special application of this material wastested atthe well-known Penmaenmawrgranite quarries, where much troublehad beenexperienced throughthe rapid wearing of the plates inserted at each side of the Blake stone- breaker to protect the parts of the machine between which the moving jaw works. A pair of ordinary steel sides was worn out in less than two months, whilst the manganese steel, after being in service for more than twelve months, had only worn a inch, and was still at work. These trials referred to manganese steel in its cast state; in its forged state it had also given excellent results. Anymaterial, which would enable more work to be obtainedwith less renewals, was of great importance in these times of severecompetition inall branches of industry,and, therefore, these results obtained with manganese steel might be of interest. It would be of great service if the Author could give any further details as to the quality of steel hitherto found to be best adapted for crushing-work, and as to the particular points which seemed to him of most importance in preparing a material suitable to form parts of crushing and other machineryexposed to excessive wearand tear. Thehardest material did not always prove to be the most durable. Mr. H. N. HARVEY,having been intimately associated with the Mr. Harvey. manufacture of variouskinds of crushing,pulverizing and stamping machinery, wished to supplement the Paper by a few notesregarding the Husband stamper. Thisstamper had now been in use on various mines at home and abroad for upwards of twenty years, and thus it might be considered tohave passed successfully throughthe experimental stage. In order toarrive at trustworthy data, he had gone closely into the performance of a battery of 4-heads of Husband's stampers, which were erected at Tregurtha Downs Tin Aline, Afarazion, Cornwall, in 1883. These 4-heads were the only stampers on the mine. Various trials made from time to time on thesestampers, over an extended period, showed thatthe four headswere togetherequal to crushing 100 tons per day of twenty-four hours, including all stoppages. The horse-power sequired foreach head asindicated on the engine was23.4. The size screens used were No. 36. The ore might be considered to be moderately hard, taking the Cornish ores as a standard. The cost of repairs and renewals for twelve months, including new shoes and dies, amounted to 4Jd. per ton 188 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Minutes Of
Mr. Harvep. of stuff stamped. This, he thought, compared in a most favourable manner with any similar typeof machine in the market. Again a, pair of lighter stamps erected at Callington tin mines, Cornwall, to supplement others of the same type previously erected there, had worked duringthe year ending February, 1892, withthe following results :-Output per head per day of twenty-four hours, 212 tons;repairs of stampersthroughout the year,nil. The character of the ore was hard tin capel, practically the hardest rock found inthe county. The size screens used was No. 32. Taking the old Cornish gravitation-stamp as a standard ofcom- parison, with the 4-heads of stampers at Tregurtha Downs Mine, it would require about 120 heads of the former, to obtain thesame results. These heads would require 120 indicated HP. to drive them, would occupy a building 150 feet long, and would weigh, with wood framing, about 120 tons. The four Husband stampers required 93 * 6 indicated HP. occupied a building 25 feet long, and, with iron framing, weighed 30 tons. In the Table showing cost, capacity, &C., of stamps furnished by the Author, no record was given of the hardness of the ore stamped; but where asingle head of 750 lbs. gravitation-stamps could pulverize 2 tons of ore per day, it might be safely asserted that the Husband stampswould pulverize 30 tons. With regard to the fineness of stamping, the Husband stampers would work well with any size perforations,provided the screens were made of best Russian iron or of copper. Screens of woven wire did not appear to standwell. Mr. Jenkins. Mr. RHYSJENKINS thought that, although the classification of the machines described was perhaps a minor detail in theAuthor’s Paper, it might be well to point out that that adopted appeared to be defective in some respects. In view of the fact that the term “ roller-mill ” was so extensively applied, in flour-milling and in millinggenerally, to the machines known in ore-millingas crushing-rolls, its use to denote mills of theHuntington type was objectionable. A newterm, such as roller and ring mills, which would lead to no confusion, might readily be found for the latter. This class might include the Globe and similar mills, as well as theHowland pulverizers, but should notinclude edge runners.The term ball mill, or pulverizer,should be reserved for machines of the tumbling-barrel type, whilst the term pneu- matic pulverizer did not cover the machines included in Class 6. “Impactpulverizer ” would, perhaps, be a more suitable de- signation. Mr. Iiitto. Mr. C. W. HITTOurged that the objections to the Cyclops mill brought forward by the Authorwere not borne out by experience. Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 189
This mill would treat harder ore than the Huntington mill or the Mr. Kitto. Krom rolls would, and as its action was concussive and rolling, and not a grinding one, the gold was liberated from its matrix under the best conditions for amalgamation. Further, in the case of wet pulverizing, the cyclonic action in the mill, caused by the revolution of the ball and disks, induced a wave-action against the screens, so that the pulp was discharged as fast as ground, loss dueto float gold being thus avoided. In dry pulverizing, the quartz was sucked out of the mill by the fan, the speed of which was regulated to suit the degree of fineness required. There was
Sectional elevation, with ball in position. A, path ; B, ball ; C Cl, driving-diaks.
L‘ L‘ CYCLOPB”MILL. no sieving, whether the fineness was 30 or 120. An independent authority, Mr. M. Eissler, in his treatiseon the Metallurgy of Gold, stated that this was the only mill in which full advantage was derived from centrifugal action, andthat by no other system could the workbe done at so low a cost. Theball of thismill did effective work during the whole of its circuit. Though the Globe mill, in its original form, was undoubtedly complicated, this was not the case with the Cyclops mill, which numbered twenty parts as compared withtwenty-six with rolls. The millwas adapted for both wet and dry pulverization. The principal feature in this mill was that the ball B, Fig. 26, which varied in weight from 190 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [l\;liuutes of
Mr. Kitto. 16 to 300 lbs. according to the size of the machine, was caused to revolve at from 250 to 600 revolutions per minute in a vertical plane by the frictional gripof the driving disks C C', which' were held by elastic buffers so as to permit the ball a certain amount of play in case it should in its trajectory encounter unusual sized pieces of quartz; and also by gripping the ball at different places or transverse diameters to cause it to constantly change its axis, thusinsuring evenness of wearall over its surface. Whenthe machine was set in motion, the ball by centrifugal €orce kept in
Fig. 27.
Sectional elevation, showing driring-disk slid hack and hall removed.
" CYCLOPS" MILL.
close contact with the internal heof the path A A, crushing in its course the material interposed between it and the path. The rapidity with which the balltravelled, which, in a No. 1 sized mill runningat 250 revolutions perminute was equal to nearly 3,000 feetper minute, caused thematerial to be carriedround with theball, thus insuring a continuance of effective work during the whole of its circuit. Theworking parts of themill were enclosed, in the dry pulverizing mill, in an airtight casing, from which a fan sucked out the crushed material, the speed of the fan beingregulated to suit the degree of fineness required. The material to be crushed was fed into the top of the mill through a proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 191 hopper which was fitted with an arrangement for regulating the Mr. Kitto. feed. To avoid having to dismantlethe mill when it was necessary to change a ball, the main shaft of the mill was fitted with a split sleeve which could be easilr removed, andwhich permitted the driving disk on that side to be slid back and the ball removed, as shown in Fig. 27. The following Table gave the principal details of the three sizes of “ Cyclop ” mills made.
Internal diameter of crushing path . 45 ins. 36 ins. 18 ins. Width of crushing path ...... 10 ins. 8 ins. 44 ins. Diameter of ball ...... 13 ins. 10 ins. 5 ius. Weight of ball ...... 300 Ibs. 130 lbs. 16 Ibs. Size of machine ...... 88 X 58 ins. 78 X 48 ins. 44 X 24 ins. Weight of heaviest piece .... 35 cwt. 18 cwt. 3 cwt. Totalweight ...... 9 tons 5 tons 18 cwt. Horse-power . ... 16 9 3 Outputper hour (60 mkshj . . , 35 cwt. 20 cwt. 4 cwt. Price for dry pulverizing .... E450 2250 E60 ,,wet for ,, ...... E510 X300 E75 ,, combined wct anddry machine E510 E300 €75
Mr. S. R. KROM(New York) thoughtthat the Author had Mr. Iirom. endeavoured to be fair in hiscriticism of the merits of the vario~~s pulverizing machines under review. He could not, however, fully endorse theAuthor’s remarks in relation to the Gates crusher. Thewearing parts of that machine could not be considered durable. The objection was not to the large first cost, but to the trouble and expense of repair. In thematter of capacity, the Gatescrusher had no advantage over a high-speed Blake ore- breaker. He was convinced that the best constructed ore-breaker and properlydesigned rolls were the most economical machines for crushing ore, and that all efforts to improvesuch machines should be directed to these, in order to bring them to the highest state of efficiency. In estimating the relative merits of rolls and other machines, it mustnot be forgottenthat the screening capacity of pulverizing-mills and stamps was very small, and that the screens were subject to hard usage and rapid destruction. In the roller system, however, the screening was done independently of the crushing, and ample provision could be made for it. The Author’s criticism of the Sturtevant mill was well founded. The power required was very great in comparison with that required in the case of rolls. The wear on the mill was excessive, and the grinding was effected by attrition-a feature which at once con- 192 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Minutes of
Mr. h'rom. demned it for pulverizing in cases where a granular condition of the pulp was requiredfor lixiviation or for concentration. JIr. Louis. Mr. D.A. LOUISdoubted whether the Author's objection bo the Blake ore-breaker, thatthe product leaving the machine was of various and not uniform sizes, did not apply equally well to other crushing-machines. In the favourable opinion expressed on the Gates machine, the product was stated to be finer than that produced by a Blake ore-breaker; but there were no numerical data given to support this statement, or to show that the product was more uniform in size. Details as to the size of material fed in, and as to theproportion of various sizes obtained, would be of interest, as they would also be in the case of the Krom rolls, which were stated to pulverize 2 tons of gold-quartz per hour, without, however, any information being given as to the character of the comminution. Thedegree of fineness to which the rock couldbe pulverized by theserolls depended, according to the Author, on the number of times the coarser parts of the product werereturned to the hopper. Thisstatement was surely also applicableto Cornish rolls. In reference tothe introduction of stamps into Cornwall, Carew, writing at theclose of the sixteenth century, pointed out that dry-stamping was in vogue, but wet- stamping appeared to have been introduced into Cornwall shortly afterwards. Agricolamade a statementthat in 1512 a certain Duke George, of Saxony, liberally rewarded Sigismund Malthitz for replacing a dry-stamping plant by wet stamps invented by himself. Althoughthe Author stated that the fine dustwas unlikelyto carry any estimable quantity of gold with it, Mr. Louis had seen fine dust collected from high ledges in a dry con- centrating mill, and this proved to be richin silver. Perhaps gold would not behave in this manner ; but it was difficult to see why it should differ in this respect from silver, especially when the gold was finelydisseminated in pyritic ores. In considering thevarious baIl mills of thepresent day, one could nothelp thinking of thefate of their predecessors, all of whichhad eventually to give way to stamps. Among such mills might be cited the von Hermann mill, with balls in a revolving vertical drum; the Cochrane mill, with balls rolled in a horizontal path of cup-like section; the Wright mill, with rollers in a revolving vertical path; and the Stephan mill, similar in character to the last mentioned, but with rollers and path corrugated. &h. Xeinicke. Mr. MEINICKE(Clausthal) was surprised to find that the Author had regarded crushing rolls as unsuitable for fine crushing by the wet process. That was not in accord with his own experience. In Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 193 a dressing floor belonging to the Mosel-Lahn Company at Trier, Mr. Meinicke. he had employed rolls which crushed per hour 3 to 38 tons of wet ore from the size of a bean down to 2 millimetres, all the ore that remained too coarse and did not pass through the circular holes, 2 millimetres in diameter, of the trommels being returned to the same rolls. The capacity was thus considerable, and the crushing of wet ores presented no inconvenience, if care was taken to submit them to a preliminary sifting so as to remove slime and to keep the rolls clean by playing on them with a jet of water. Rolls of 72 centimetres (288 inchesj in diameter and 29 centimetres (114 inches) in width, made 80 revolutions per minute, andwere pressed togetherby very strong and long india-rubber buffer-cushions, which in consequence of their length prevented a fracture of the rolls if a large unbreakable substance should happen to getbetween them. The rings might be turned in a short time without taking the crusher to pieces, while the rest of the machinery was still working. The rolls, which worked without cogwheels, cost S230.. and weighed 82 tons. The construction of the machinewas so solid that rolls 15 inches inwidth could beinserted. If these figures were compared with those given by the Author in relation tothe Kromrolls, it would beseen thesatisfactory results obtainedby the latter were probably less dueto the special construction than to the fact that therolls were very solidly built, and permitted a powerful pressure together of the rolls. The same result wouldalso bearriyed at ifthe various points brought forward by the Author favourin of the Krom rolls,were considered. (1) Good and well-fixed steel rings were also used in other crushing rolls. Further, the arrangement for turning the rings on the rolls mentioned above rendered that machine suitable for fine crushing, even if thebest material for the rings was notavailable. (2) Toothed wheels had for many years been dispensed with in other crushing rolls, if they were required torevolve rapidly or if their diameter was sufficiently great. (3) The employment of theswinging pillow-blocks perhaps presented some smalladvantage to the manufacturer, but it had no appreciable influence on the action of the rolls, because the sliding friction of the pillow-blocks of" other construction was extremely small in comparison with the forces exerted in pressingtogether the movable rolls. Thefact thatwith swinging pillow-blocks the rolls always remained parallel, had a favourable action, inasmuch as the pressure oc a speciallyhard piece of ore was somewhatincreased, butan unfavourable one if the hard fragment did not give, because in that case the pieces in proximity were subjected to less pressure [THE INST.CVIII.] C.E. VOL. 0 194 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Minutes of
Mr Meinicke. than was the case in a crusher, the rolls of which could be placed somewhat inclined. (4) Powerful springs were also employed in other crushing-rolls in the same manner. (5) Satisfactory methods of feeding were also provided in other crushing-rolls. (6) Lastly, the housing for the rolls was unessential. From these grounds he concluded that, though he was completely at one with the Author in his opinion of the advantages of crushing by rolls, good results could also be obtained by rolls of other constructions than that of Krom, and he would go still farther inexpressing the opinion that fine crushing was advantageouseven for the treatmentof wet ores, and of ores thatare comparatively poor. In these cases,too, it was often advisable to effect the crushing by degrees, and either to avoid the production of fine slime or only to permit it after the valuabl;? ore had been separated from the sands and coarse slimes. A mode of procedure such as this, which should give good results inthe treatment of ores containingauriferous pyrites, would necessitatea carefuldressing of thesands and slimes, and in consequence the erection of a large and costly dressing-floor, and the dread of such an expenditure was probably often the reason why, in spite of the attendant great loss, a simpler and cheaper method was preferred. This was obviously right when the life of the mine was short or uncertain. With reference to gravitation- stamps, he might mention that at Clausthal in the Mountains Hartz for fine stamping of the ore that hasbeen crushed in rolls, gravita- tion-stamps with nine toeleven stamps in a battery were adopted. They were placed very close together (10 millimetres interval), and with a rectangular section the stamp heads had quite as great a capacity as rotating stamps, seeing that in the mortar-box there was but little free space, and with good material the amount of wearwas comparatively small. By this arrangement, there was the advantage that a couple of batteries of eleven stamps each did not take up more space than two batteries of five stamps each. Care was taken to Beep the height of water behind the screen the same as that in the mortar-box. This secured an economy in the consumption of water, and alonger life for the screen without diminishingthe output of thebattery. The stamps were, asa rule, of the single-discharge type. With two screens 20 per cent. more material could be stamped, but the consumption of water was greater. JIr. Faxman. Mr. JAMESPAXXAN wished to confine his remarks particularly to the Huntington mill, with which he had had some little ex- perience. Thequartz tobe used shouldbe reduced to the size of a smallwalnut, or, betterstill, to that of a cob-nut. The Proceedings.] CORRESPONDENCE OX GOLD-QUARTZ REDUCTION. 195
feed at all times should beautomatic and regular. Careshould &fr.Paxman. be taken that the mill was not overfed. It should be fed so that it would comfortably clear itself. A sufficient quantity of water must be fed into the mill with the material to be dealtwith. After a little experience the millman would know exactly how to treatthe material, as very often two samples of ore required dealing with in different manners. No damage could arise to the millitself from over-feeding, andhe had never known a case where a mill had been broken through anaccumulation of material inthe centre. Theaction of theHuntington mill was one of crushingrather than grinding, and it was suchthat it would liberate the particles of metal without destroying their grain or turning them into float-gold. This mill was suitable not only for argillaceous and soft quartz, but also for thehardest and most brittle varieties. It had other great advantages, particularly that of delivery. As soon as the material was crushed it was delivered through the screens, and this constant delivery enabled the mate- rial to get thoroughly away. The millcould be made to discharge nearly all round, if desired, and in this case it would present a discharging surface very much greater than that which could be given toa ten-stampbattery. With reference tothe saving of gold in the pan, this did not depend upon the quantity of gold contained in the quartz, but on the nature of the material. With quartzcontaining perfectly free gold, the proportion of gold retained was rarely less than 60 per cent., generally being from about 60 to 80 percent. The Huntington mill could be easily put together at the mines, and fixed and started by a mechanic, understanding his work, in two to three days after its arrival. In this mill, as made at Colchester, the ring dies were of rolled steel, and he had never yet known one to break. The mill was, therefore, inall respectsa thoroughlytrustworthy one. The power used in the crushing of material through plates equivalent to about 30-mesh screen, was 10 indicated HP. This was crushing at the rate of 15 cwt. per hour; but, when indicating the engine- driving shafting only, the mill standing idle, he found it to be 3.73 indicated HP. Thusshowing that the mill itself requires 6.37 indicated HP. In working the mill it was necessary to have an operator who thoroughly understood the use of such machinery, as the resultdepended very largely upon the way in which the mill was worked, and the quantityof water permitted to enter themill. If too much was used the materialbecame too thin, and did not work well upon the plates. Again, if an insufficiency of water was used, the discharge was too slow, and the result was notso satisfactory. 02 196 CORRESPONDENCE ON GOLD-QUARTZREDUCTION. [Minutes Of
Mr. Reimers. Mr. E. REIMERSthought that the Author had not done sufficient justice to ballpulverizers, and notably to the ball mill constructed by Mr. Gruson, of Magdeburg-Buckau. During thepast three years over fourhundred of thesemills had beenmade for Freiberg, Huanchaca, Potosi, and other mines in various parts of the world. The mill consisted briefly of a cylindrical drum, made internally of hardchilled cast-ironplates. Thisrotated on a shaftand wassurrounded by double sieves. Themill was filled with a number of very hard steel balls. The ore was automatically fed intothe hopper, andthe pulverizedproduct, which could be regulated to any degree of fineness, according to the number of the outer sieves with which the millwas supplied, came out below ready for being treated by amalgamation or concentration. This mill,he claimed, had successfully surmountedthe objections raised by the Authoras to the great wear and tearof such mills- objections which at first sight would seem natural enough, but whichthe careful construction of thewearing-parts, and the judicious selection of the material of which they were made, ha& completely overcome. Very satisfactory results had been obtained with these mills in the reduction of basic slag, and hard gold quartz, and the advantages of this mill would be evident from the following data :-A ball mill, 72 inches in diameter, could turn out from 25 to 30 tons of pulverized material of medium fineness per day, and required only 10 to 12 HP. to drive; it made about 25 revolutions per minute, and cost about 5275. A mill, 84 inches in diameter, had an output of 45 to 48 tons perday, required 16 to 17 HP., made 20 revolutions per minute, and cost about 5360. These results compared very favourably with those given by the Author for Erom rolls, and for the Huntington mill. The repairs, too, in the case of the ball millmerely consisted in supplementing the balls from time to time when they become worn. This mill, he considered, fulfilled most of the requirements named by the Author for an ideal pulverizer. Mr. Smith. Mr. HAMILTONSMITH, jun., pointedout that gravitation-stamps have been employed for pulverizing ores from times of great antiquity; they were probably used by the Romans in the Iberian Peninsula, andwere fully described in the earliestGerman literature on Metallurgy. At first the stem of the stamp was of hard wood, shod with iron, and had a square section. Soon after gold-quartz mining commenced in California-about the year1856-round iron stems, to which a rotary movement was given by themoving cam, were employed in a mill at Grass Valleyunder the charge of Mr. Melville Attwood, father of Mr. George Attwood, Assoc. M. Inst. proceedings.1 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 197
C.E. The great merit of this invention was at once appreciated Mr. Smith. by gold and silver miners, and this form of gravity-stamp was now almost universally in use, except in Cornwall. In addition to this radical improvement, details in stamping hadbeen so improved that .a modern California gold mill would now pulverize per stamp in twenty-four hours 3 tons of hard quartz to a size which would pass Shrough a slot of an inch across ; whereas when he first became a resident of California in 1869, a duty of 13 tons per diem was con- sidered excellent work. Many other methods hadof late years been invented for the purpose of pulverizing ores ; but to-day, by far the larger portionof gold, silver, and copper ores in theworld was reduced by stamps, andin his opinion no other method of pulverizinghard rock orore was likelyto supersedestamping. This, he thought, was also the opinion of almost every practical man of large mining-experience. He therefore thought that the Author had attached undue importance to the merits of rolls, and variousnew methods of crushing,and had underestimated the advantages of stamping.Every few months one heard of some wonderful new invention by which quartz was to be crushed at the cost of a song, and by the aidof which worthless mines would become valuable ; but at all the good mining camps, the stamps were still pounding away as they hadbeen for centuries past, and as they would probably continue to do for centuries to come. The only rival of merit which the gravity-stamp had thus far encoun- tered was the steam-stamp, which was really a steam-hammer, and which was now largely used in the reduction of copper ores on Lake Superior and in Montana. The Calumet and Hecla, and the Anacondacopper companies both used these stamps, andthese two pulverizing-plants were by far the largest ever constructed, each of them having now a capacity of over 3,000 tons per diem. Neither of thesetwo companies published accounts, SO hewas unable to give the costs of stamping per ton, but from personal observation he was convinced that this cost was very considerably larger at the Calumet and Hecla than it was with modern first- classgravity-stamps. The Treadwell Gold Mining Company in Alaska had a mill of 240 gravity-stamps, and for the year 1890-91 stamped 220,686 tons of hard quartz at an expense of 42 cents. (about 21 pence)per tonincluding costs of concentration. The screensemployed had slots about & of aninch across; water- power was used for about nine months of the year, and steam for the otherthree months. Themill was hardlya first-class one, the I steam-engines were not of high class, coal cost 52 per ton, and white labour was paid about 14s. per day. The conditions for 198 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. minutes of
Mr. Smith. cheap work were hence not particularlyfavourable. At theCalumet and Hecla mill, on the other hand, fuel was verycheap, the cost of labourwas much more reasonable, andthe screens in use had apertures 4 of aninch in diameter. The Calumet officials, in comparingthe two methods of stamping,insisted that, even admitting the superior economy of the gravity-stamp, for such a huge plant, the large amount of space required would be almost a fatal objection. This, by the way, was, he thought, the only well- founded objection to thegravity-stamps in the listof ten " defects " enumerated by theAuthor. The cost per tonof stamping-capacity for a steam-stamp plantwas not verymuch larger than thatof a gravity- stamp mill. The operatingeconomical advantages of the latter were chiefly :-(l) The motor could be of large power, and of the mosr economical type known, whether of water or steam, while there must necessarily be asimple separate enginefor each steam-stamp ; (2) the wear and tear was much less; (3) minor accidents only delayed the workingof a small fraction of the entire mill; (4) for fine stamping with a steam-stamp it was difficult to protect the screens. There could be no better proof of theadvantages of first-class milling-machinery, coupled with judicious management, than the results obtained at El Callao. The old El Callao mill was of 60 stamps, and during the year1882 pulverized 22,405 tons of quartz at a cost of 78.30 francs per ton. In 1885 a Fraser and Chalmers mill was erected. It consisted of 60 stamps weighing when new about 890 lbs. each ; the drop was about 8 inohes, and there were 94 drops per minute. The quartz was firm and hard, and was stamped through slots & inch across. The total cost of milling for the year 1891 was 6.29 francs or 5s. per ton. Con- sidering the high cost of labour, supplies, and fuel at El Callao this was an exceedingly low rate, including as it did 0.60 franc forshare of general expenses, a chargenot generally made to milling accounts. On the usual basis, therefore, the cost per ton for milling was 5.69 francs or 48. 6d. Theengine used wasa compound-condensing tandem, supplied with steam by locomotive boilers with combustion-chambers, the steam-pressure being 145 lbs. During the year 1891,1,589 English cords of wood were used for fuel, costing 23,492. This was equivalent to about 800 tons of good coal at 24 7s. per ton. In addition to supplying the power for stamping 58,949 tons of quartz, the engine did other work, so thatonly three-fourths of the power employed was used for milling. Consequently the fuel used per ton of ore stamped was equivalent to about 22 lbs. of good coal. Mr. Taylor. Mr. HERBERTE. TAYLOR thoughtit was desirableto have some Proceedings.] CORRESPONDENCEON GOLD-QUARTZ REDUCTION. 199
particulars of the aotual work done by the different machines &fr.Taylor. usedfor gold-quartz reduction. He had, there€ore, noteda few particulars respecting the work of stamps and Huntington mills. Thegreat variations in practice, whichhad beensuccessfully adopted in different districts or under varying conditions, showed the necessity for a most careful consideration of the nature of the ore and of its gangue, before any decision could be arrived at as to thedetails of themachinery to be adopted. In California the weight of thestamps in general use varied from 250 lbs. to 1,100 Ibs., the drop from 2g inches to 12 inches, the number of blows per minute from sixty to one hundred and twelve, and the screensfrom a 20-mesh to 60-mesh. In several cases, however, the screens were as large as $-inch square mesh. The output of the mills varied from 15 cwt. per stamp-head to 13 tons, and the cost of renewals from lid. to 2s. Ohd. per ton of ore stamped. The average figures for one hundredand thirty-three mills, having two thousand two hundred and thirty-twostamps, were as follows : weight of stamp, 806 lbs. ; drop, 6.06 inches; number of blows per minute, eighty-six and a-half; orecrushed (1 ton 19 cwt.), per stamp per day of twenty-four hours; the height of the dis- charge above the dies was 4 to 4& inches; the average screen used 37 mesh;and the averagecost of renewals 54d. In Colorado, where the ore had to be stamped much finer in order to free it from pyrites,the stamps weighed about 650 lbs.;they made twenty-six to twenty-eight blows per minute ; they had a drop of 16 to 18inches, a height of discharge of 13 inches, a 50 to 60-mesh screen, and an output of from 15 to 16 cwt. per day of twenty- four hours. Turning to Huntington mills, he found that at the Quaker mine, Calaveras County, California, a G-foot mill driven at 50 to 55 revolutions per minute pulverized from 15 to 20 tons per twenty-four hours, so as topass through angle-slot screens(equal1ing 25 to 40-mesh screens. The lode-stuff was stated to be of a black, slaty nature, with quartz and asoft black gouge. At the Shaw mine, El Dorado County, a &foot mill, making 50 revolutions per minute, pulverized 10 to 12 tons per twenty-four hours, so as to pass through a screen equal to a 25 or 30-mesh. At the Mathines Creek mine, in the same county, a S-fOOt mill pulverized 9 to 10 tons per twenty-four hours, so as to pass a screen equal to a 40- mesh. Atthe Monte Christ0 mine, Mono County, two 5-foot Huntington mills, runningat from 65 to 75 revolutions per minute, pulverized 2 tons of ore per hour to pass a screen equal to a 40-mesh; 25 Ibs. of quicksilver being charged into each mill at the commencement of the run, and about 3 oz. more being added 200 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. minutes of
Mr. Taylor. each half-hour. The tailings ran over 50 feet of blankets, and the concentrates were returned to the mill with the ore. The cost of renewals was not noted, but was believed not to exceed that in the case of stamps. At the Central mine, Shasta County, twomills pulverized 25 tons of ore per day of twenty-four hours, through a screen equal to 25-mesh; but whether 25 tons each, or for the two, was notstated, and no further particulars weregiven. At the Golden Treasure mine, in Tolumne County, one Huntington mill, 5 feet in diameter,was in use. The orewas crushed very fine before going to the mill, whichtreated 15 to 25 tonsper twenty-four hours, using a slot-screen equal to a 35-mesh, about nine-tenths of the amalgam being recovered in the milland one- tenth on the outsideplates. The cost of renewalsamounted to lad. per ton of ore treated. At the Spanish mine, Nevada County, California, therewere four Huntington mills, three of 5 feet diameter and one of 4 feet diameter. They had treated a large quantity of material, and were reported to be doing good work, so that it might be interesting to go a little more into detail. The pay ore was found in a soft talcose slate, which contained many smallveins and streaks of ferruginousquartz, carrying gold. The vein was worked by means of two tunnels and an open cut. The cost of mining in this way was 2s. Ohd. per ton of ore broken. The ore, a free-milling one, passed first to a Blake stone-breaker and then to the mills. The four mills ran at 58 revolutions per minute and pulverized about 4,000 tons of ore per month, or, in other words, 33 or 34 tons of ore for each mill per day of twenty- four hours, so as to pass through a slot-screen equal to a 20-mesh. After being charged at the starting of the run, quicksilver was put into the mills at the rate of B oz. to each ton of ore, and the pulp passed, on leavingthe mills, over theusual amalgamated plates. Of t,he amalgam recovered, 60 per cent. was obtained from themills and 40 per cent.from the plates. The gold recovered from the mills was of a coarse grain, and the amalgam retortedabout 40 per cent. The gold from the plates was very fine, and the amalgam yielded only 20 per cent. of its weight in gold on retorting. The loss of quicksilver was about 31r oz. per ton of ore. There was a tendency, if a large piece of rock hp- pened to get into the mill, for quicksilver to be thrown out on to the apron. The cost of wear and tear of the ring-dies and roller- shellsamounted to2 * 05d. perton of ore worked. The cost of screens was 0.6d. perton, and this was considered heavy. The total cost of milling was 29. per ton. The frequent necessity for readjusting the feed was stated to be the greatest difficulty in 1Proceedings.l CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 201
workingthese mills, asthere was no means of automatically Mr. Taylor. regulating the feed according to the quantity of ore in the mill, .as is the case withstamp batteries. Thevalue of theaverage yield of the ore was 3s. per ton; but, during a test-run that was made for one month, when 4,126 tons of ore were pulverized, the ,yield was 28. 12d. per ton, the superintendent stating that this was less than had ever been the case, while the loss of quicksilver wasgreater than usual. Thetailings, which were thoroughly sampled throughout the run, assayed 3s. per ton in gold, showing therefore a working result of only 42.4 per cent. of the total gold -contents of the ore. Whenthe tailings were carefullyground and washed in an agate mortar, a few bright specks of gold were visiblewith a lens, but no quicksilver. Whetherthis loss was ,caused by trying toforce too great a quantity of stuff through the mill, by the ore not being brought down fine enough, or by an ,excessive flow of water, whether in fact it was the fault of the mill or of the millman, there was no evidence to show; but the result of 42 per cent. saved could not be considered satisfactory. AS bearing on the question of uniformity of size in the output,it might be noted that, whereas the mill-screens were equal to it '20-mesh, at least 50 per cent. of the tailingswould pass through a 30- mesh sieve. Coming nearer home, he had taken the followingfigures ,from the daily returns of the running of three 5-feet Huntington mills on Cornish tin ore over a period of about twelve months. These mills were not worked to the best advantage, as they were driven from line-shafting, from which also power was taken to drive astone-breaker, and a wire ropewayto bring up the ore from the adit-level's mouth. This line-shaft was driven by power transmitted by means of a wire-rope driven from a turbine, fixed some 600 feet distant, and this turbine also served to work the pumpsto a depth of 60 fathoms. It was, consequently,almost impossible to keep up a uniform speed on the mills. The stone- breaker, too, did not do its work thoroughly satisfactorily, and frequently passed flatstones much larger than it should have done. The three mills pulverized 907 tons of lode-stuff (hard tin capel, with quartz), to pass a No. 36 Cornish gauge punched grate (equal to about a 15-mesh screen), in two thousand one hundred and nineteen hours, or at the rate of 85 cwt. per mill per hour. The same millspulverized 3,890 tons of lode-stuff, consisting mostly of chlorite or peach, with quartz, to pass Nos. 38 and 40 Cornishgauge punched grates (equal to 25 to 35-mesh screen) in four thousand six hundred and ninety-nine hours, or at the rate of 3 6%cwt. per mill per hour. The average of the whole of 202 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. [Minutes 01
Mr. Taylor. the above crushing was 14 cwt. per mill per hour, the rate varying from 8 cwt. to 22 cwt. per hour according to the stone treated, the speed of the mills, and the care of the attendant in regulating the feed. Themills worked at speeds varying from 45 to 62 revolutions per minute, with an average for the twelve months of 55 revolutions. The wear and tear of the ring-dies and roller- shells was as follows: for the first 1,650 tons treated (mostly the hard stone), load. per ton; and for the next 3,766 tons crushed (the softer stone), 44d. per ton, or an average for the twelve months of 64d. per ton. In none of the above cases was the actual power required to drive the mill given, but he hadbeen informed that, in one instance, where a mill was treating 16 tons of medium gold- quartz per twenty-fourhours, it required 11 indicated HP. to run it. &fr.Wilkinson. Mr. W. F. WILKINSONcommented on the absence from the Paper of a detailed description of the methods employed for obtaining the gold from the pulverized ore. There were a variety of ways for extractingthe gold fromgold quartz. Some advocated the practice of endeavouring to amalgamate as much gold as possible during pulverizing, naturally at the expense of ithe pulverizing capacity;others maintained that pulverizing shouldbe carried outwithout regard to amalgamation. Some recommended rapid or coarse pulverizing and a concentration of the coarse sand, which might still have gold included or attached, by hydraulicclassifiers for retreatment. The success of this method, presuming the ex- traction of the gold to beequal, would depend on whether the cost of collecting and retreating the coarse sands was less than the difference of cost between coarse and fine stamping. The pulveriz- ing machinewould be influenced bythe requirements of the system of amalgamation adopted. With regard to the Huntington mill, he agreed with the Author that for certain ores, particularly soft ones, and for small mines, this mill was of great value. AS evidence of its practical success, he might mention that he had seen it working on silver ores at the Santa Eulalia Mill, Mexico, where gravitation-stamps were formerly used. Here the Hunting- ton mill was said to work more economically than stamps. There was one point connected with the Huntington mill not mentioned by the Author, and that was the difficulty of feeding it properly withautomatic feeders, when the ores varied in hardness. The Huntingtonmill, unlike the stamp-battery, had nothing to regulatethe feed. If the ore wasnot regular in hardness, it followed that the mill was liable to get choked when hard rock was being fed in ; for though the automaticfeeder would continue to feed hard and soft rock equally fast, the millwould not be able Proceedings.] CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. 203
to pulverize the hard so quickly as the soft. With regard to the Yr.Wilkinson. question of the superiority between stamps and rolls, the point of chief interest in the Paper, he had been much disappointed that no practicalworking-results of rolls in a gold-quartzcrushing . mill had been brought forward. He agreed with the Author’s list of objections to the stamp battery, andwas glad that among these objections he had not thought the great noise attending their use beneath notice. In a stamp-battery, to gve directions or to gain information,except by dumb show, were equally impossible. In spite, however, of their disadvantages stamps had proved, in all parts of the world, most useful and efficient machines, and before rollswere introduced to take their placefor fine crushing,he thoughtfurther proof was needed to show thatthey were as economical as stamps. The figures of the Bertrand mill,quoted in the Paper, figures which had been repeatedly quoted before in similar Papers in favour of Krom rolls, were apt to be misleading, as far as they were used for making a comparison with stamps. The Bertrand ores were crushed through a 16-mesh screen for the lixiviation process, whilst gold-quartzes required tobe passed through it much finer screen, not usually less than 30-mesh and more often 40-mesh. Moreover, atthe Bertrandmill, the rolls were tried with finer screens, but the results were unsatisfactory, the reason beingthat the capacity was reduced, owingto the difficultyexperienced ingetting the ore to pass the screen. Again, at the Haile Gold Mine, South Carolina, the Krom rolls were tried for fine crushing and proved a failure. They became surcharged, threw their belts, and wore badly. Although for very fine crushing Krom rolls did not appear to have been a success- fulrival to stamps, there could be no doubtthat, where very fine crushingwas not essential, they provided a most efficient machine. They could also be used with advantage in crushing gold-quartz in mills where some system was employed for concen- trating the coarse sands for retreatment. It was well known that in crushing ore through a screen of any size, a large percentage would pass through a much finer screen. In crushing, therefore, through a 16-mesh screen, which Krom rolls could do satisfactorily, it was probable that a large amount would be as fine as if it had beencrushed bystamps through a 40-mesh. The coarse sands would have to be concentrated and reground ; but would probably form only a smallpercentage of theoriginal bulk of ore. In conclusion, he was of opinion that the losses that occurred in gold- milling were more likely to be reduced by improvements in the amalgamation part of the process rather than in its crushing part. 204 CORRESPONDENCE ON GOLD-QUARTZ REDUCTION. pinutea of
Mr. Wilkinson. The losses wouldbe reduced by a more careful attentionto statistics than was, except in the case of a few mines, at present given.Careful sampling inall parts of themill wouldshow where improvements might be made.
ADDENDUM, APRIL 22,1892.
The Royal THEROYAL COMMISSIOX, appointed on July 15, 1889, toenquire asto the best mode in which assistance could berendered to develop the auriferous resources of the colony of Victoria, has re- cently published a voluminous report, a copy of which has been presented to the library of the Institution since the reading of the Paper on “ Gold-Quartz Reduction.” As the evidence set forth in the report was tenderedby some of the most experienced mining- engineers in thecolony, it has been thought that a brief summary of theinformation given in relation to gold-quartz reduction wouldbe of valueas representing the opinions of Australian experts on this subject. The reduction of the auriferous gan,pe should, the report states, first be effected, where possible, by the use of stone-breakers, andthe broken-up ore shouldbe fed automaticallyinto the reducing appliances, eitherwet stamps, Huntington’scentrifugal roller quartz-mill, Husband’smedium pneumatic stamps, the Ball direct-acting steam-stampsfor poor, hard stone, or a wet-working Globe mill (Lansell’s Bendigo mill). Instead of wet-stamping, dry pulverizing in stampsor rolls might possiblybe resorted to with good results in districts in which there is a scarcity of water. The Commission makes no definite recommendation in regard togold-quartz reduction, except that stone-breakers should be more generally employed. Their value, from an economical point of view, has beenestablished beyond question, andthey should be used in all cases where large quantities of ore have to be treated.
9 February, 1892. HARRISON HAYTER, Vice-President, in the Chair.
16 February, 1892. ALFRED GILES, M.P., Vice-President, in the Chair.
Both of the above meetings were devoted to the discussion of the Paper by Mr. A. H. Curtis on ‘‘ Gold-Quartz Reduction.”