W. Skey. — Auriferous Alloys. 371 



occurrence in our reefs), we obtain that mixed deposit or alloy we are seeking 

 to produce. 



The only condition which appears to me from the results of numerous 

 experiments necessary in regard to such metallic solutions is that they should 

 be not only alkaline, but alkaline from presence of a fixed alkali or alkaline 

 earth, and it will be remembered, perhaps, in connection with this circum- 

 stance, that this alkaline condition is one which I have recently shown* to 

 be that of our' silicates generally, whether simple or compound, with the 

 exception of silicate of alumina and other corresponding silicates of the 

 sesqui- oxides, while quartz itself, whether free or in combination, is either 

 quite neutral or of such very feeble acidic powers as regards intensity that 

 when united, even in very greatly disproportionate quantity, with alkalies or 

 alkaline earth the resulting compound gives an alkaline reaction. 



If such then are the conditions (alkalinity or neutrality) of our surface 

 rocks generally, it is clear that the condition of the water permeating them 

 at some distance from the surface would be alkaline, the intensity of which 

 would be largely increased were the retaining rock subjected to those hydro- 

 chemical influences popularly supposed to have operated for the deposition 

 of their older vein matters and their metallic contents. 



The fact that many mine waters are acid does not affect the truth of the 

 conclusion thus drawn as to the general alkaline condition of the waters 

 charging our rocks, since this acidity is, as is well known, brought about by 

 the contact of air with pyritous matters, metallic sulphates thus being formed 

 which communicate an acid reaction to water dissolving them. This is a 

 mere surface affair as it were, and is besides in its manner of production 

 entirely distinct from, if not antagonistic to that by which gold has been 

 deposited in the pyritous portions, for a slight examination of these shows 

 that the gold present in them has been deposited there before they were 

 oxidized by atmospheric agency. 



Alkalinity being then certainly the general condition of our waters per- 

 meating rocks, closed, or partially so, against the atmosphere, and this con- 

 dition of liquids appearing essential for the production of alloys by humid 

 methods, as shown here, it does seem highly probable that our native alloys 

 of gold and silver have been deposited from alkaline solutions, and by such 

 agents as I have suggested, viz., the metallic sulphides. 



I will only add, in reference to the mode in which our deposits of native 

 gold have been formed, that while the number of substances capable of pre- 

 cipitating this metal from solution is many, the number of those at all likely 

 to have been actually concerned in the production of these deposits is very 

 small indeed. As far as at present appears, the substances capable of reducing 

 * Trans. N.Z. Inst., Vol. IV., Art. LVI. 



