172 THE ROYAL SOCIETY OF CANADA 



The starting point for the oxidation is undoubtedly pyrite, and that 

 because of the acid liberated on taking up oxygen. 



Fe S,+H2O + 70= Fe SO4+H2SO4 

 This has already been fully emphasized in the literature of second- 

 ary enrichment. The free acid acts on chalcopyrite and cupric sulphate 

 is formed and carried downwards, with further formation of acid: — 



Cu Fe S2+2 H2S04= Cu S04+FeS04+2 H2S 

 2H2S+80 = 2H2SO4 



Whether the greater porosity of the disseminated sulphide rock, 

 thus admitting of freer entry of oxygen, and readier downward move- 

 ment of the sulphate solutions, is the only important factor in the 

 readier oxidation of the scattered sulphide bodies, has not yet been 

 definitely determined. In some experiments which they carried out 

 with various sulphides, Gottschalk and Buehler^ found that when 

 the sulphides were in intimate contact, the electromotive force which 

 was established on oxidation of the pyrites (or marcasite) led to the 

 protection of the pyrite (or marcasite) from further oxidation. The 

 writer is of the opinion that differences of porosity cannot sufficiently 

 account for the differences in oxidation, and that the principle which 

 Gottschalk and Buehler established in their experimental mixtures 

 may hold in the intimately mixed sulphides of parts of the Mandy or 

 Flin-Flon orebodies, and that the active source of oxidation processes 

 • — pyrite' — may thereby be protected from further oxidation. 



The most interesting phase of the reduction process is the 

 formation of native copper. As already noted, native copper is 

 found not only in minute scales in the ftssures at or near the surface 

 in many properties, but has been found in comparatively large crystal 

 aggregates at a depth of 60 feet in the Flin-Flon orebody. It is 

 known that the chemical action 



2 Cu SO4+2 Fe S04;=iCu2S04+Fe2(S04)3 

 is reversible,^ and that the action goes almost entirely towards the 

 right at a temperature of 200° C. The hydrolysis of Fe2 (804)3 

 doubtless affects the balance of this action, even at lower 

 temperatures, as ferric sulphate is thus removed from solution by the 

 precipitation of ferric hydrate. It is also known that from cuprous 

 sulphate copper is readily deposited according to the equation 



Cu,S04=Cu-f-CuS04 

 more particularly, it would appear, in the cooler parts of the system.^ 



lEcon. Geol. 7, 1912, p. 15. 



2See R. C. Weils. Econom. Geol. 5, 1910, p. 205. 



'Stokes: Journ. Geol. I, 1905-06, p. 647. 



