Mohave County miner., 1907-05-11
Genesis of Ores of the Cobalt District.


 genesis of the ores of the Cobalt dis
 trict, presented at the Toronto meet
 ing of the Canadian Mining Institute
 Prof. Van Hise said that the metallic
 silver was due to secondary enrich
 ment.
 His argument was based on the gen
 eral principle that all veins have a
 zone of secondary enrichment, and
 when this zone is passed the ore be. comes poorer. This is true of veins occurring in countries where there has not been great amount of glaciation. In Ontario and particularly in the Co., bait district, glaciation has removed several hundred and possibly thou sands of feet of the surface, and the veins as they Outcrop at present are but the remains of larger ones that have been glaciated off.
 There has been very little oxidation or secondary enrichment since the glacial period as evidenced by the me- tallic silver at the outcrop presenting glacial striae just as plainly as the rocks in which it is or was inclosed. MT. Timmons, of the La Rose mine. and l were shown vein of metallic silver two to six inches wide outcrop- ping on the hill back of the mine. The clay loam had been stripped off and for a distance of POO fee. the me- tallic silver presented all the glacial markings as plainly as the inclosing Huronian rocks.
 This is conclusive proof that the sil- yer was there at the close of the glac- ial period and it is very unlikely that it could have been formed from sec. ondary enrichment during the glacial period.
 In the sulphide deposits of the Sud bury region, the zone of secondary en- richment is entirely absent, having been cut off during the glacial period l and sufficient time not having elapsed | since that period D produce another. | The sulphides art at the surface only covered by few inches of gossan. As the same general conditions prevailed at the Cobalt district during the yla- cial period it is reasonable to assume that whatever zones of secondary en- richment have existed in the veins that they have been removed, and that the ores as mined few feet be- low the surface are in the same con- dition ln which they were deposited.
 It therefore becomes necessary to account for the deposition of metallic silver from ascending hot solutions in order to explain the presence of the metallic silver in these ores. Its pres ence requires an explanation that is sound from a chemical standpoint and not subject to the accidental introduce tion of reducing matter from the sur face. The writer opposed the explanation by secondary enrichment and suggest ei the presence of graphite deposits along with the ore due to the decom- position of hydrocarbon gases asso- ciated with the mineralizing solutions at the time the ore was deposited. These hydrocarbons would act as DOW | erful reducing agents on the silver salts and preciptate metallic silver : during the time of mineralzation. $ Professor Miller stated that such car- | | oonaceous or graphite deposits were present, and were associated with the | pres, some of this material being piled V 'n the dumps at the mines. This evidence was further strength . ened by the information furnished by Messrs. Coste and Ingall that in the ! Silver Islet mine, near Port Arthur, lydrocarbon gases were encountered n the lower levels in sufficient auan- I ities to burn under rock pressure. It d vas also stated that metallic silver il vas found in the bottom of the mine " tt depth of 600 feet. As the glacia- t ion was fully as great in that region c IS in the Sudbury district it seems i'm e that secondary enrichment h ould account for the metallic silver a n the Silver Islet mine. S, The ores of that mine and of the Co., r. 'alt district are said to be practically 9 he same in character, and the condi- ti ions in each case point to the depo- b nf cl, c