174 THE ROYAL SOCIETY OF CANADA 



relatively unimportant, and furnishes no clue, so far as ascertained, 

 in the immediate vicinity of the orebody. The direction of flow of 

 the ice-sheet in this district was approximately south westwards, and 

 the high horse of unmineralized rock immediately west of the most 

 highly oxidized part of the sulphide body could, therefore, have formed 

 no protection against the erosion of the gossan in the valley. How 

 deep the gossan cap may have been in the valley before the ice-sheet 

 advanced there is now no means to determine. Conditions were 

 favourable for deep weathering in late Pre-Cambrian time, in late 

 Palaeozoic and early Mesozoic times, and again in late Tertiary times, 

 representing periods of high elevation in this area with maximum 

 differences between surface and water-table levels. During Ordovi- 

 cian, Silurian, Devonian, and again in Cretaceous times, the sulphide 

 bodies were probably under water, and protected from erosion. 

 Even if the earlier history of the orebody be left out of consideration, 

 conditions during the later periods in Tertiary times were such as to 

 give rise to widespread disintegration of elevated orebodies, and 

 doubtless a deep capping of gossan covered the Flin-Flon and other 

 disseminated sulphides in trench-like valleys. Under such condi- 

 tions it is at least possible that the ice-sheet would not pick up the 

 oxidized sulphides of the lower levels. It might be expected, however, 

 that if the erosive power of the ice were lessened to that extent some 

 glacial drift would be deposited in the trench over the untouched 

 gossan as the ice passed on. 



This drift has not been found in any section of the weathered 

 sulphides. The conclusion has been reached, after comparing the 

 unprotected solid sulphides of the Mandy orebody, which are un- 

 weathered, with the disseminated sulphides elsewhere in the district, 

 which are deeply weathered, that the secondary processes are post- 

 glacial in age, and that their relative magnitude is due to the porous 

 nature of the rock in which the disseminated sulphides occur, and 

 to the fact that the pyrite— or pyrrhotite — ;is less intimately in contact 

 with the other sulphides than is the case in the solid ores. 



