REMEDIES AGAINST OF GOLD.

Bruce Herald, Volume VI, Issue 403, 31 January 1872, Page 7

REMEDIES AGAINST OF GOLD.

Much 'valuable scientific information relative to gold-saving- may be gathered from the following extract of a report recently made by Mr W. Skey, Government Analyst, respecting quartz mining at the Thames Goldfields :—

1. Relative to the general mechanical arrangement of the various batteries : — it would not be easy fo propose any improvements in these ; and any new ideas on this subject, the fruit of such a cursory or superficial inspection as I had an opportunity of making, could scarcely have any practical utility. The absorbent property of gold for sulphuretted hydrogen, and the great likelihood that much of the Thames gold is, as it were, thas 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 of the hand berdan inform us how, much can be extracted by prolonged grinding- under certain conditions, bur that most of the residual gold from the batteries is in a free state. Doubtless the good results are mostly attributable to the greater extent of new clean surface thus exposed to the mercury. Whether any extensive change in favor of apparatus having greater grinding action could be profitably marie, is a question which experience alone can certainly decide, but I think it very probable. The Chilian mill seems too slow ; besides, much complaint is made that the loss of mercury is very great by this mill. With the berdan, though certainly an excellent apparatus for rich hand samples or blanketinffs, there is evidently on the part of a few managers who use them, such a disposition to run them either ton fast or with so much water — in fact, to give them too much work — that one does not like to recommend them afc all. They are rather deficient in grinding power for profitable use on a large scale, as at present constructed ; but if some means could be devised for increasing this considerably, say by fixed shoes instead of balls, or a mixture of the two, they might be found to work well.

Concentration of the heavier portions of the auriferous rock, and the treatment of the residues by special processes, certainly merits great attention. 2a. Losses occasioned by the condition of mercury used for the amalgamation. As the principal cause of the flouring or sickening of mercury upon these goldfields is the presence of sulphate of iron in the reef stuff, and as this salt is freely soluble in water it will naturally occur that one way of preventing the mercury being affecred in this manner is to wash the auriferous .-stuff impregnated with this salt, prior to stamping. Whether such a process could be profitably used is a question for experience to determine. It could only bfi applied with any considerable saving effect in those cases where the reef is porous and incoherent. To a certain extent, where good water is used for th« stampers and tables, the ill effects of the metallic sulphates present in the reef's are diminished.

In reference to the kind of water for these purposes, I would desire here to remark how necessary it is to abstain from lh*} use of mine or 'shaft water for the crushing or amalgamating apparatus of the battery, except, indeed, it is quite, or at least nearly free from metallic sulphates, a circumstance only rarely occurring". The use of water for these purposes containing any notable quantity of sulphates, acts even more prejudicially than the sulphates naturally existing- in the stuff itself, were they ever so abundant; flouring-, in such a c.-iae, becomes, as it were, a chronic complaint. The greatest possible quantify of good water that the incline of thu 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 otber substances} but for stampers and table.*, where such immense quantities of matter are used, it would scarcely pay to manipulate the water itself. For this reason, in the case of the battery tables* it :s only the merciir}' we can profitably influence by the addition to it of so Hum, 'or the sodium amalg-.«m, as suggested by Mr Orookes. 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 ix flouring condition. Cyanide of potassium, which appears to be the only agent yet administered to the water for keeping the mercury bright, acts admirably. It is a solvent for the metals gold, silver, and mercury $ singly ; but I have lound, experimentally^ that in the

presence of theiWe. together it only dissolves the silver Mid mercury (at least, to an appreciable extent) ; and therein, therefore, not that loss ot gold incurred fro nil its use which some persons, have^ anticipated. Its expense, however, requires that it only be applied to that work which a cheaper salt cannot effect. Thus the neutralising 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 in sight in the -veil-stirred liquid are bright and sharply defined.

2b. With reference to the "remedies to be employed against the newly-discovered absorbtive property of gold tor sulphuretted hydrogerifc, I Would remark, 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 pur« meral to the action of the various amalgamators. We 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 enterprisinggold mining manager ; but if the gold is coated with a continuous film of any negative substance, however thin, it is certain there could be no contact between the two metals, and consequently 'amalgamation could not proceed. Indeed, we have a 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 that the operation of extracting the stone from the reef, and the present method of working it at the mills, tend greatly, by mere abrasion, to remove old surfaced, and thus expose clean metal. These should be powerful remedial measures in themselves, though thpir utility in this respect has not been before suspected. Ido not know that we can push this mechanical abrasion much further than it is at present done, for it seems, there is a pointy 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 ease 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 abnts'on may be performed with a greater diversity of re-agents than those which are available for the brightening or cleansing of mercury. Some of the methods for accomplishing this have been already incidentally stated, but the same objections against treating the water, to prevent flouring of the mercury, also apply here. Crooke's sodium amalgam effects the immediate removal of the sulphansed film, metallic sodium combining energetically with sulphur, and decomposing- its compounds 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 ot tliis amalgam, are properly referable to this action on the thin films of sulphur compounds attached to the surfaces of the gold to which it is applied, and not to the action of the sodium upon the mercury. It has been stated that except in case of the more cupreous native golds, the process of roasting- these sulphurised ores removes the sulphur, and renders the enclosed gold more sunalgamable. But thong-h these good effects upon sulphurised gold are palpable enough on a small scale, it is conceived that on a large scale iwould not be equally ea*y, but in fact likely, by the application of a similar process, to make the gold worse than it was at first. Unless the roasting be thoroughly done, the whole of the sulphur driven off or oxydised, and the temperature 10 wards the end of the process raised or kept at a dull red heat, it is certain that gold which might have been cleaned or expo-ed by the first part of the process would be more or Ipss resulphurised towards the end of it. But the subject of the natural sulphurisation of gold has been so recently opened, that it would be as yet premature to speculate as to the precise effects of any process we may employ as a remedial measure. The first step should certainly be to ascertain whether there are any natural processes now in operation, or that could be brought to operate, for the removal of tliis sulphur. We want to learn the effect on such gold of long exposure to air, and to the various oxydised and oxydising substances which occur in superficial strata and workings. When we have, fully investigated these, and learned what action, it any, they exert, we can see better what would be proper to prescribe as antidotes; Meanwhile it may not be out. of place here to conclude this part of the subject by indicating- the results obtained in the laboratory to this date, bearing- upon these. various points. For convenience of future reference I will number the experiments consecutively.

1. Pure gold, kept in strong solution of protosnl[>hate'of iron for one week, in an open vessel, and rhen washed, amalgamated very well at the end of the term. 2. Sulphurised gold, treated in manner derailed above, would not amalgate in the least. 3 Pure gold, freely exposed to the air for three days, at a distance from laboratory, readily amalgamated. 4. Sulphurised gold, exposed as in No. 3, for six days, would not amalgamate. 5. Pure gold, placed in solution of pro- i tosulphate of iron> ulong with sulphide of

'antimony, \vas rendered unamalgamable ; in rwenty -four hours.

6. Tho same effects followed when iron pyrites (slightly cupreous) were substituted for the antimony sulphide. The experiments detailed are obviously too limited in. scope and number to allow of any very specific deduction being founded on them, bat their general tendency is greawy to confirm me in ray conviction, that in most cases gold must be sulphurised ; busines this, it unfortunately appears a,s if there is but little chance of any natural process or agents in an ordinsry way antagonistic to the permanency of such surface deposits. But tor the proper and general investigation of this subject, the co-operation of those having charge of the mines and batteries is most necessary, as circumstances which could hardly be observed by any outsider, require to be accurately recorded. It is the chemical condition of the natural, not the abraded surface, we want *o test, and this necessitates extreme care in the collection of samples. Further investigations are required, however, in this direction, particularly to inform us as to the chemic al condition of these natural surfaces ; it is not often that they can be obtained with such certainty that their chemical examination would bf> useful ; a touch of the finger might render clean surfaces unamalgamable,while the accidental contact with any moderately hard substance, might on the other band so abrade a sulphurised or dirt}' surface, as to render it amnloMmable.