[WALLACE] SECONDARY PROCESSES IN PRE-CAMBRIAN OREBODIES 171 



erals are covellite, native copper and, doubtfully, chalcocite. To this 

 list of metallic minerals there should be added the non-metallic oxi- 

 dation product gypsum, which occurs in cavities in the oxidized zone, 

 which were presumably occupied previously by pyrite. In the case 

 of the Flin-Flon orebody, which has been more accessible for study 

 by reason of the exposures obtained by mining operations, the most 

 extensive weathering occurs immediately east and north of a high 

 horse of unmineralized fairly massive greenstone at the south end of 

 the property. '^ In this weathered area a rather peculiar type occurs. 

 Immediately east of the horse a highly porous, pumice-like silica rock 

 is exposed. From the underground sections of this rock it would 

 appear to have been a quartz porphyry in which, on mineralization, 

 the feldspar had been replaced by pyrite and secondary silicification had 

 taken place. On oxidization, the pyrite has been removed, leaving 

 a vesicular rock which is mainly silica. 



Much of the oxidation material has doubtless been removed from 

 the vicinity of the sulphide bodies by surface agencies. Some of it 

 has, however, penetrated downwards, and has in lower levels been 

 reduced to other minerals. Covellite is rare, but was found in the 

 Mandy orebody. Native copper is not uncommon in fine scales in the 

 rock fissures even at the surface of several sulphide bodies, and was 

 found in a flat dendritic mass of crystals when sinking the shaft near 

 section "D" of the Flin-Flon orebody at a depth of 60 feet. At this 

 depth the shaft, which had been sunk in greenstone, encountered solid 

 sulphides. The native copper lay on the surface of the solid sulphide, 

 the copper bearing solutions having evidently migrated downwards 

 in the water bearing zone between the greenstone and solid sulphides. 

 As this zone has not been sectioned elsewhere except at the 100 and 

 200 feet levels,^ the probability remains that considerable masses of 

 native copper may have been deposited in this zone. Chalcocite has 

 not been found in the Flin-Flon orebody, but was seen by the writer 

 in the Sunbeam group, west of Hook Lake, where the mineral occurs 

 mixed with chalcopyrite at the bottom of a pit 12 feet deep. There 

 is no suggestion of secondary enrichment in the mineral association, 

 and the occurrence is considered by the writer to be primary. 



In studying in further detail the process of oxidation, one notes 

 that the action is most complete where pyrite- — or pyrrhotite — has 

 been crystallized in the original replacement process in association 

 with considerable country rock. Where the replacement process has 

 gone further, and an intimate mixture of sulphides with relatively little 

 country rock has been the result, oxidation is not so pronounced. 

 iSee Wallace, Bull. Can. Min. Inst., Feb., 1921, p. 106. 



