1922] Whitman: Genesis of the Ores of the Cobalt District 



269 



A few stopes of high-grade ore were developed on the Cobalt Lake 

 fault, where at first glance it would seem that, according to the rule, 

 ore of that quality could not occur; but on close study it was recog- 

 nized that these kidney-shaped ore bodies occurred where the fault 

 surface had been warped by a subsequent minor .synclinal fold, as a 

 result of which the stress conditions in the fault walls must have been 

 locally disturbed, the transverse compression being relieved on the 

 limbs of the fold, thus making a favorable situation for the deposition 

 of ore according to the stress rule. 



The mineralization of faults even with calcite is usually discon- 

 tinuous, and ore is very sparsely distributed. Another very significant 

 relationship lies in the fact that the richness of veins is related with 

 fairly pronounced consistency to the number and strength of shear 

 joints or flat faults which intersect them, as if these had served as 

 feeders for the supplying of ore materials to the veins. 



Space relations. — In a region deformed as this was, it may prop- 

 erly be assumed that the folds, major and minor, with their various 

 associated joints and faults, would not be limited to a particular hori- 

 zon, but would be general throughout all known horizons ; and this 

 has been proved at Cobalt. The structurally favorable sites for ore 

 deposition have, therefore, no immediate relationship to the diabase 

 sheet. In view of this fact it is significant that only those favorable 

 structures are mineralized which occur within 350 feet of the margins 

 of the diabase, both in' the diabase itself and in the adjacent Kee- 

 watin, or within 550 feet of the diabase in the Cobalt Series. This 

 applies at both upper and lower margins of the sheet, indifferently, 

 to 187 stoped veins and many nonproductive ones, including all the 

 veins of the district without exception, as well as all known veins of 

 the South Lorrain, Casey, and Gowganda areas, not to mention other 

 known occurrences of either silver or cobalt ores in northern Ontario. 

 In connection with this, it is an interesting fact that the ore bodies 

 show no distribution witli reference to steep faults or other deep- 

 seated structures or contacts, while either commercial or non-commer- 

 cial veins of silver ore, cobalt ore, or calcite with traces of cobalt or 

 nickel are coextensive, over large areas, with the Nipdssing diabase. 



On a smaller scale, a very peculiar and interesting phenomenon 

 is the relation of joint veins in the Cobalt Series to the bedding joints 

 and faults, presenting the aspect of post-vein dislocations. Probably 

 geological observers at^irst sight would almost unanimously pronounce 

 most of these cases as prima facie evidence that the veins had been 



