760 C. 7?. VAN HISE 



But let us follow the matter still farther. In the majority of 

 cases, as denudation continued, the parts of the ore deposits 

 produced by the second concentration rise into the belt of weath- 

 ering. They may there be partly or wholly transformed into rich 

 oxidized products, or they may be depleted to extend the rich 

 deposits below. In the concentration by descending waters the 

 chief chemical reactions are believed to be between the oxides 

 or salts of copper and the sulphide of iron. The precipitation 

 of copper sulphide resulting may occur in various ways. 



The reaction may produce chalcopyrite, as shown by the fol- 

 lowing equations : 



CuS0 4 + 2FeS =CuFeS 2 + FeS0 4 , or 



CuS0 4 + 2FeS 2 +0 4 =CuFeS 3 + FeS0 4 +2S0 3 . 



The reactions may produce bornite, as shown by the follow- 

 ing equations : 



Cu 2 S0 4 + CuS0 4 + 3FeS = Cu 3 FeS 3 +2FeS0 4 , or 



Cu 2 S0 4 +CuS0 4 + 3FeS 2 +60 = Cu 3 FeS 3 + 2FeS0 4 + 3S0 2 . 



Or the reactions may directly produce chalcocite, as shown 

 by the following equations : 



Cu 2 S0 4 + FeS = Cu 3 S + FeS0 4 , or 



Cu 3 S0 4 + FeS 3 +0 3 =Cu 2 S + FeS0 4 +S0 2 . 



If the reactions are between a copper salt and sulphide bear- 

 ing copper various reactions throwing down the copper may 

 also occur. The reactions may be upon chalcopyrite producing 

 bornite, as shown by the following equation : 



2CuFeS 3 +CuS0 4 + 2 =Cu 3 FeS 3 + FeS0 4 +S0 3 . 



It may be the reaction of copper sulphate upon chalcopyrite 

 or bornite producing chalcocite, as shown by the following: 



CuFeS s +CuS0 4 + 2 =Cu 2 S + FeS0 4 +S0 2 , or 



Cu 3 FeS 3 +CuS0 4 + 3 = 2Cu 2 S+FeS0 4 +S0 2 . 



It may be by the reaction of copper oxide or copper sulphate 

 upon covellite producing chalcocite, as shown by the following 

 equations : 



6CuS+2Cu 2 0=5Cu 3 S + S0 3 , and 



6CuS+2Cu 3 S0 4 + 3H 3 0=5Cu 3 S+2H 3 S0 4 + H 3 S0 3 . 



