Remedies against Loss of Gold.

Cromwell Argus, Volume III, Issue 113, 9 January 1872, Page 3

Remedies against Loss of Gold.

1 Much valuable scientific information relative to gold-saving may be gathered from the following Extract of a report recently made °° t>y Mr W. Skey, Government Analyst, reed ipactings quartz-mining at the Thames Goldad adds : L lj " : 1. Rolative to the general mechanical arrangement of the various batteries:—it would not be easy to propose any improvements in >et these ; and any new ideas on this subject, the fruit of such a cursory or superficial inspection as I had an opportunity of making, J could scarcely have any practical utility. The absorbent property of gold for sulphu-1 Isited hydrogen, and the great likelihood j ~ that much of the Thames gold is, as it were, JQ thus tarnished with sulphur, suggests the prolonged grinding of the auriferous rock as a partial remedy, not so much to ensure fineness as to ensure abrasion of the enclosed gold granules. The results shown by the use tof the hand berdan inform us how much j can be extracted by prolonged grinding under j certain conditions, but that most of the resi- 1 dual gold from the batteries is in a free state. \ Doubtless the good results are mostly attri-1 butable to the greater extent of new clean! surface thus exposed to the mercury, j Whether any extensive change in favour of j apparatus having greater grinding action "" could be profitably made, is a question which experience alone can certainly decide, but I think it very probable. The Chilian mill seems too slow ; besides, 1 > much complaint is made that the loss of mercury is very great by this mill. With the iberdan, though certainly an excellent apparatus for rich hand samples or blanketings, there is evidently on the part of a few mall igers Avho use them, such a disposition to ' ran them either too fast or with so much , water —in fact, to give them too much Work, Y j—that one does not like to recommend them at all. They are rather deficient in grinding le power for profitable use on a large scale, as s [it present constructed ; but if some means \ could be devised for increasing this consider- i id* kbly, sav by fixed shoes instead of balls, or a I mixture of the two, they might be found to work well. a .- C i.'kv.Ji/'ra'rf'oji of the heavier portions of the auriferous rock, and the treatment of the residues by special processes, certainly merits great attention. 3 2i. Losses occasioned by the condition of I mercury used for the amalgamation. _ As the principal ciuse of the flouring or sickening o; mercury upon these goldfields is the presence of sulphate of ir.m in the reef 3, stu-f, and as this salt is freely soluble in J water, it will naturally occur that oneway of preventing the mercury being a Tec-ted in this manner is to wash the auriferous stuff ini-p-'jgn 'ted with this silt, prior to stamping. Whether such a process could be profitably .used is a question for experience to determine, ft could onlv be applied with any considerable saving effect in those cases where the reef is porous and incoherent. To a cer- :_. tiin extent, where good water is used for the , stampers and tables, the ill effects of the -'•■ metallic sulphates present in the reefs are diminished. te In reference to the kind of water for these le purposes, I would desire here to remark how necessary it is to abstain from the use of * nipie or shaft water for the crushing or amalrfiating apparatus of the battery, except, •frfred, it i 3 quite, or at least nearly free ; metallic sulphates, a circumstance only :y occurring. The use of water for these !. ~ poses containing any notable quantity of 1 aphates, acts even more prejudicially than •§~/e sulphates naturally existing in the stud" itself, were they ever so abundant ; flouring, in such a case, becomes, as it were, a chronic complaint. The greatest possible quantity of good water that the incline of the copper plates "will safely allow should be employed, since the solution of the metallic slates is thereby weakened, and so, correspondingly, less productive of harm. In a manner more strictly chemical, it is easy to destroy or overpower this tendency of mercury to flour in the presence of these or any other substances ; but for stampers and tables, where such immense quantities of matter are used, it would s-arcelypay to manipulate the water itself. For this reason, in the case of the battery tables, it is only the mercury we can profitably influence by the addition to it of sodium, - or the sodium amalgam, as suggested by Mr [_ Crookes. In working up the blanketings, either the water or mercury should certainly be treated chemically ; the blanket slimes being generally very pyritous, and the amalgam present in a flouring condition. Cyanide of potasK sunn, which appears to be the only agent yet t- administered to the water for keeping the _; mercury bright, acts admirably. It is a solj vent for the metals gold, silver, and mercury, ' . singly ; but I have found, experimentally, that in the presence of the three together, it oily dissolves the silver and mercury (at 1 least, to an appreciable extent) : and there * is, therefore, not that loss of gold incurred from its use which some persons have anticilJ pated. Its expense, however, requires that A it only be applied to that work which a ii cheaper salt cannot effect. Thus the neutra<j lising of the acid substances in the blanketings may be safely and cheaply performed by washing soda, and after the liquid and solid matters are feebly alkalined, then the cyanide can be added, till any mercurial globules iii sight in the well-stirred liquid are bright and sharply defined. 2b. With reference to the remedies to be employed against the newly-discovered absorptive property of gold for sulphuretted hydrogen. I would rem irk, that the frequency

with which natural surfaces of native gold must be tarnished by this substance renders it a matter of importance to ascertain the state of these surfaces, and in the case of their being sulphurised, to take every practical means for effecting, the exposure of the pure metal to the action of the various amalgamators. vv e may have the mercury ever so clean, ever so positive, as it were, to the gold,—we may even put it in an electrical state, as was proposed to me by an enterprising gold-min-ing manager ; but if the gold is coated with j a continuous film of any negative substance, | however thin, it is certain there could be no ! contact between the two metals, and consei quently amalgamation could not proceed. I Indeed, we have a far better chance of obtaining amalgamation when of the two metals mercury is the tarnished one, since even then it yields a tolerably clean surface to the slightest pressure or friction. There is no doubt tint the operation of extracting the stone from the reef, and the pre- | sent method of working it at the mills, tend j greatly, by mere abrasion, to remove old surJ faces, and thus expose clean metal. These | should be powerful remedial measures in j themselves, though their utility in this re- | spech has not been before suspected. I do i not know that we can push this mechanical ! abrasion much further than it is at present done, for it seems there is a point, or rather a degree of fineness, past which the proportion of mercury and amalgam which escapes is so large as to neutralise the good effects. The ea°e with which gold is scratched by hard and angular surfaces, such as those of crushed quartz, make it probable, however, that the mere stirring of the auriferous sand after it has left the stampers, without reducing its coarseness sensibly, should be sufficient to clean the surfaces of any exposed gold granules that had escaped with an adherent film of sulphide. Chemically, this abrasion may be performed with a greater diversity of re-agents than I those which are available for the brightening i or cleansing of mercury. Some of the methods i for accomplishing this have been already ini cidentally stated, but the same objections j against treating the water, to prevent flour- | ing of the mercury, also apply here. Crooke's sodium amalgam effects the im J mediate removal of the sulphurised film, | metallic sodium combining energetically with ! sulphur, and decomposing its compounds j rapidly. This accomplished, then there is nothing to intervene between the gold and the mercury, and amalgamation commences. It is pretty certain the good effects frequently attending the use of this amalgam, are proI perly referable to this action on the thin films of sulphur compounds attached to the j surfaces of the gold to which it is aoplied, | and not to the action of the sodiu a upon the j mercury. It has been stited that except in case of I the more cupreous native golds, the process j of roasting these sulphurised ores removes j the sulphur, and render.s the enclosed gold I more am.tlgamable. But though these good affects upon sulphurised gold are palpable i enough on a stu ill sell ■, it is conceived that ; on a large scile it would not; bo e.p.vdly easy, j but in fact likely, by the application of a j sim lar process, to make the gold worse than I it was afc first, Pnl:s> the roasting be thoroughly done, the whole of the sulphur driven i oh? or oxydised, and the temperature towards j the end of the process raised or kept at a dud ! red heat, it is certain that gold which might : | have been cleaned or exposed by the first ' i part of the process would be more or loss , resulphurised towards the end of it. Bat "j the subject of the natural salphurisat'.on of I gold has been so recently opened, that it i would be as yet premature to speculate as to ) the precise elects of any process wy mav . (employ as a remedial" measure. The first II step should certainly be to ascertain whether : i there are any natural processes no.v in opora- ■ jtion, or that could be brought to operate, for I the removal of this sulphur. We want to learn the elects on such gold of long expo- • I sure to air, and to the various oxydised and oxydising substances which occur in superficial strata and workings. When we have i fully investigited those, and learned what . action, if any, they exert, we can see better I what would be proper to proscribe as anti- ■ ! dotes. Meanwhile it may not be out of place here to conclude this part of the subject by j indicating the results obtained in the laboratory to this date, bearing upon these various j points. For convenience of future reference ! 1 1 will number the experiments consecutively. • 1. Pure gold, kept in strong solution of • j protosulphafce of iron for one week, in an open > j vessel, and then washed, amalgamated very j well at the end of the term. ' I . 2. Sulphurised gold, treated in manner ! 'detailed above, would not am dg.v.nate in the | least. 3. Pure gold, freely exposed to the air for three days, at a distance from labora ory, <' readily anvil ; invited. i| 4. Sulphurised g dd, exposed as in So, 3, -for six davs, would not imalgauite. • j s % Parogo!.l, plasod in sUatiou of proto--1 sulphite of ir>n. along with sulphide of aoti- '• niony, was rendered m im ilgauvi dein fcwoutyt; four hours. ■] (5. The sa.no effects followed when iron -pyrites (slightly cupreous) were substituted ' i for the antimony suinhid \ 1 j The experiments detailed ;ve obviously ton ■ limited in scope and number to all >w o; any ; very specific deduction bong founl.m o'i :■ them, but their general tendency is greatly ; to confirm me in my couvicnou, that in most s1 cases gold must be sulphurised ; besides ibis, ■jit unfortunately appears- as if .here is bul 1 : little chance »? s-ny natural or agents ' in an ordinary way •vn'cigmi.ntic ■•'■ the pe:

manertcy of stbli surface • deposits. But fo the proper and general investiga ion of this subject, the co-operation of those having charge of the mines and batteries is most! necessary, as circumstances which could j . hardly be obs3rved by. any outsider, require to be accurately recorded. It is the chemical I condition, of the natural, iiot the abraded! surface, we want to test, and this necessitates I extreme care in the collection of samples. | further investigations are required, however, in this direction, particularly to inform j us as to the chemical condition o: these natural! surfaces ; it is not often that they can be ob-! . j tabled with such certainty that their chemical I examination would be useful; a touch ol the j finger might render clean surfaces unamil- { gamable, while the accidental contact with , any moderately hard substance, might on tli3 j other hand so abrade a sulphurised or dirty I surface, as to reader it amalgamable.