LOSS OF GOLD IN MILL TAILINGS.

Mount Ida Chronicle, Volume V, Issue 274, 5 June 1874, Page 3

LOSS OF GOLD IN MILL TAILINGS.

In a late article we promised to represent. some of the causes of the loss of gold we have referred loasconjecturednnd partially proved by Mr. Skey. That gentleman states that "the principal couse of loss may shortly be stated, for this (the Thames) and other goldfields where amalgamation is relied on as the want of perfect chemical contact between the gold alloy and the mercury employed. However much of this may be due to defects in the mechanical arrangements adopted for securing the gold, the result of my investigations certainly shows that most of it. is fairly attributable to causes of a ehemieal nature, and which the very best mechanical manipulation could but partially overcome," Mr. Skey then divides these chemical causes into two classes, those which relate to the quicksilver, and those relating to the gold alloy. [ Regarding class 1 he says:—That, quicksilver generally sickens or " flours " when ground up with pyritous rocks is a fact so well known and so frequently experienced by all managers of batteries that it would be superfluous to point out that the true chemical contact we seek is ranch impeded, or even entirely prevented, by such a circumstance Whatever has been affirmed about theme'allie arsenides or sulphides, sulphur and sulphuretted hydrogen being frequently or directly acproducing this flouring, I feel convinced the greatest enemy that has to be contended with on this account upon this Goldfield (the Thames) is protosulphate of iron, or green vitriol. After showing that arsenides or sulphides do not exercise any direct effect upon mercury, and that their products would not have time to act before the whole of the auriferous stuff would have been passed through the mill, and that sulphur and sulphuretted hydrogen ore not in existence, the first in n free state, and the latter at all at the Thames, he concludes that—Taking all this into consideration, I incline to the opinion that, not only in this, but in otli.T Goldfields, the greater part of the flouring or sickening of the mercury used is due to the action of sulphate of iron. Another obstacle to amalgamation is sulphate of copper (blue vitriol), but it occurs,.far loss frequently. This salt is nqt more to be tha sulpha* of. item in.

deed, where the copper salt occurs, the iron salt will also occur, and in prepon-' derating quantity. Both these salts act, I believe, by forming suiisulphates ofmercury and iron or copper, which persistently adheres to its surfaces. With regard to the second cl ss of causes, those affecting the gold alloy, two chief obstacles are alluded to by the ana lyst—one, the preseuce of antimony ; the other to the affinity gold has to absorb sulphur: both these causes are against amalgamation. From an analysis of four Thames specimens it was ascertained that three of them contained antimony in very sensible quautity. Now, Mr. Skey says fairly enough that—He finds by direct experiment antimony is not a metal that readily amalgamates, and it is pretty certain it would communicate some of its uegativeness iu this respect to whatever gold alloy it might occur in ; indeed, I have observed from my own experiments the very slow rate at which these kind of alloys do amalgamate. With regard to the affinity of gold for sulphur, he says —It has become apparent that the surface of native or artificially prepared gold, even of extreme fineness, energetically absorbs sulphur or sulphuretted hydrogen. When thesejsurfaces are so affected thev absolutely fail to have such contact with mercury as to enable the metals to amalgamate—at least such is the case at common temperatures; but they again do so readily when treated with cyanide of potassium, free chromic acid, or chloride of' lime. . . . ... . . The bearing of these results upon the subject 1 under investigation is obviously important, as the exercise of this hitherto unsuspected property of gold must have a very prejudicial effect upon the amalgamation process, as practiced in all reef workings. Sulphuretted hydrogen is too common a substance, or at least the materials required are toojwidely spread, to allow us to hope that any larger portion of the exposed superfhes of oar native gold has not been affected by it to a greater or less extent, and so rendered to a corresponding degree unamaljjamable, REMEDIES AGATNST 1,083. Mr. Skey naturally hesitates to suggest remedies of a practical nature without mature consideration. Ho says Relative to the general mechanical arrangements of the various batteries it would not be easy to propose any improvements in these, and any how i.loas on this sub jt-'ct, the fruit ot such a cursorj r 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 thus tarnished with sulpher, suggests the prolonged grinding of the aurTferous rock as a partial remedy, not so much to ensure finenesses to ensure abrasion of the euclosed gold granules. The results shown by the use of the hand burdan inform us not only how much can be extracted by prolonged. grinding under certain conditions, but 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 made is a question which experience alone can certainly decide, but I think it very probable.

We shall have to hold over Mr. Skey's other suggestions for a third article, or rather transcrip, for we have endeavored to do little more than let the analyst speak tor himself, with due regard to the space at our disposal.