SOLUTION OF SILVER. 1099 



organic material, and since the gold is more intimately associated with the 

 sulphides, it seems probable that, in proportion to its mass, pyrite is a more 

 important precipitating agent than the organic matter; but undoubtedly 

 both are effective. 



In many cases it is probable that the precipitation is due fundamentally 

 to carbonaceous material, but that the influence of the organic matter is one 

 step removed. That is to say, the organic matter first precipitated the 

 baser sulphides by reducing them from sulphates, as explained under the 

 succeeding section, and then the base sulphides precipitated the gold. This 

 would seem to be the natural explanation which accounts for the close 

 connection of the gold of some deposits with both carbonaceous materials 

 and pyrite and other base sulphides." 



SILVER. 



Metallic silver as a product of the first concentration by ascending 

 waters is not an abundant source of the metal. One of the most notable 

 occurrences of metallic silver of this origin is that of the Keweenawan 

 of Lake Superior, where the silver, in subordinate amounts, is closely 

 associated with copper. 



solution. — The form in which silver most extensively occurs is sulphide. 

 It is well known that oxidizing waters change silver sulphide to a sulphate 

 which is a readily soluble compound. It is therefore probable that the silver 

 is very largely transported as a sulphate. It is also certain that silver is 

 transported as a chloride, which may be produced either by the direct action 

 of the chlorides or of hydrochloric acid on the sulphides of the metal, or by 

 the interaction of the chlorides and sulphates. Silver carbonate is also 

 somewhat readily soluble in carbonated solutions. Silver also occurs as a 

 metal. It is well known that metallic silver is soluble in ferric sulphate, 

 the reaction being: 



2Ag+Fe 2 (S0 4 ) 3 =Ag 2 S0 4 +2FeS0 4 



This reaction takes place in proportion as the ferric sulphate is abundant, 

 and it has already been pointed out that such sulphates are likely to 

 be abundant in the early part of the journey of the underground waters 

 where they are descending. Stokes has shown that after this reaction has 



"Don, J. R., The genesis of certain auriferous lodes: Trans. Am. Inst. Min. Eng., vol. 27, 1898, 

 pp. 569, 612. 



