[WALLACE] SECONDARY PROCESSES IN PRE-CAMBRIANOREBODIES 173 



The oxidation of ferrous sulphate to ferric sulphate and the subsequent 

 hydrolysis of the latter with formation of limonite has undoubtedly 

 been widespread. If the reversible equation 



Cu S04+Fe S04^Cu2S04+Fe2 (504)3 



be considered a closed system, it is fairly certain that at no time in the 

 history of the orebody since the original replacement, least of all since 

 glacial times, have the temperatures been sufficiently high to permit 

 of any considerable amount of cuprous sulphate being formed. The 

 explanation here suggested is that cuprous sulphate was formed, but 

 not in a closed system. In any balanced action, at any temperature, 

 all the constituents are represented, even though the constituents 

 on one side of the equation may be present in very small amount. 

 The hydrolysis of Fe2 (804)3, and the precipitation of native copper 

 from CU2SO4, would by the removal of both constituents from the 

 system permit of further formation of CU2SO4 and Fe2 (804)3, as 

 a continuous process even at ordinary temperatures. The associations 

 of native copper in the Flin-Flon orebody would indicate that the 

 process 



Cu804=Cu+Cu804 



takes place most readily in the presence of pyrite and chalcopyrite. 



The Age of the 8econdary Processes 



In recent years the question of the possible existence of pre-glacial 

 weathered surfaces in Canadian Pre-Cambrian territory has frequently 

 been raised. The discussion of Whitehead and Bateman on the one 

 hand, and of Tyrrell on the other, on this matter, as arising from the 

 oxidation in the Cobalt territory, may be cited in this connection.^ 

 Cross- has noted the existence of a kaolinized syenite in the 

 Mattagami River which may possibly have been weathered in pre-glacial 

 times. Keele^ has described unconsolidated sands of probably 

 Mesozoic age in the northern fringe of the Pre-Cambrian in Ontario, 

 which were untouched by glaciation. Coleman'' had found, how- 

 ever, that unoxidized sulphides immediately underlie the glacial drift 

 in the 8udbury field and relegated the oxidation in that field entirely to 

 post-glacial times. The conclusive evidence in any field is, of course,, 

 that furnished in the relationship of the oxidized material to the glacial 

 drift, where such exists. In the Flin-Flon district, glacial drift is 



^Econ. Geol. 15, 1920, pp. 103, 453; 16, 1921, p. 558. 

 "Ont. Bur. Mines, xxix, 1920. Pt. II, p. 17. 

 'Trans. Roy. Soc. Can. xv, 1921, p. 43. 

 ^Ont. Bur. Mines, xiv, 1905, pp. 101, 163. 



