SECOND CONCENTRATION BY DESCENDING WATERS. 1141 



this hypothetical case, as shown by the work of Anthon" and Schiirmann, 6 

 omitting the less important elements, is therefore manganese, arsenic, iron, 

 cobalt, nickel, zinc, lead, tin, antimony, copper, silver, mercury. It is, 

 however, understood that the oxidation of an easily destroyed sulphide is 

 not complete before the oxidation of a more refractory sulphide has begun. 

 All of the sulphides are being oxidized all the time, but the more readily a 

 sulphide is oxidized the more rapidly it is destroyed. 



The sulphur of a sulphide may be oxidized without the oxidation of 

 the metal, in which case a metal is produced by the process of oxidation. 

 At the same time the sulphur is oxidized, or subsequently, the metal may 

 also be oxidized, and thus oxides be formed. As soon as the oxides are 

 produced they may unite with carbon dioxide and form carbonates, or with 

 silicic acid and form silicates. If water also unites with the compounds the 

 carbonates and silicates are hydrated. But the carbonates and silicates 

 may also be produced in a different manner. The sulphides as originally 

 oxidized may be tranformed to sulphates. If thus changed, the sulphates 

 may immediately react upon carbonates or silicic acid, producing carbonates 

 or silicates, at the same time forming sulphates of other elements, such as 

 barium, strontium, or calcium. The evidence that reactions of this kind 

 have taken place upon an extensive scale in veins is perfectly clear. In 

 mine waters sulphates of copper, zinc, and iron occur very frequently. In 

 some cases the amount of sulphate of copper in such water is so great that 

 it is worth while to run it over iron and thus precipitate the copper. 

 Further evidence of the formation of the sulphates is shown by the frequent 

 precipitation of basic ferric sulphates in the veins, as, for instance, at 

 Cripple Creek. That the sulphates produced by oxidation of the sulphides 

 react upon the other elements is shown by the frequent development in the 

 upper part of the veins of such gangue minerals as barite, celestite, gypsum, 

 and occasionally even magnesium sulphate. 



An admirable case illustrating this principle is described by James 

 Douglas. In speaking of the Arizona mines he says that gypsum is abun- 



« Anthon, E. F., Ueber die Anwendung der auf nassem wege dargestellten Schwefelmetalle bei der 

 chemischer Analyse: Jour. f. Prak. Chem., vol. 10, 1837, pp. 353-356. 



& Schiirmann, E., Ueber die Verwandtschaft der Schwermetalle zum Schwefel: Liebic's Ann. d. 

 Chem., vol. 249, 1888, pp. 326-350. 



c Penrose, R. A. F., jr., Mining geology of the Cripple Creek district: Sixteenth Ann. Kept. U. S. 

 Geol. Survey, pt. 2, 1895, p. 130. 



