[miller-knight] PRE-CAMBRIAN OF ONTARIO 245 



Michipicoten island in Lake Superior and in the area tributary to 

 Port Arthur, 500 miles distant from Cobalt. With the effusive rocks 

 of Michipicoten island is also found native copper under conditions 

 similar to those of Michigan and the Coppermine River region; (3) 

 Some of these ores, those of Sudbury, are considered by certain authors 

 to be a direct segregation from the magma, while the cobalt-silver 

 deposits are less direct, having been deposited from aqueous solu- 

 tions, although a few veins partake to some extent of the character of 

 deposits formed by segregation from a molten magma. ^ 



The Animikean — Interbedded with the Animikean clastic sedi- 

 ments are vast quantities of iron formation, a chemical deposit. 

 Through the action of aqueous solutions concentration of the iron has 

 taken place, giving rise to ore bodies of economic importance. 



While the iron deposits of Ontario in the Animikie series of the 

 north shore of Lake Superior have not proved to be of much economic 

 value, across the international boundary in Minnesota they are 

 represented by the great Mesabi ore bodies. 



The Algoman — Gold deposits, that are found in numerous 

 localities in the Province, from the Quebec boundary on the east to 

 that of Manitoba on the west, are, in many cases at least, genetically 

 connected with granites to which the name Algoman is applied. 

 In a few cases the granites are represented by more basic rocks. 

 The gold occurs in quartz veins, being associated usually with iron 

 pyrites, but occasionally the ore carries considerable arsenical pyrites 

 or mispickel. Certain of these veins have been worked as a source 

 of arsenic. There are thus two epochs in which arsenic has been 

 deposited in economic quantities, the Algoman and the Keweenawan, 

 represented by the cobalt-silver arsenical ores of Cobalt 



The gold deposits are found chiefly in Keewatin schists, but a few 

 occur in Timiskamian clastic rocks. It is worthy of note that the only 

 gold deposits of the Province that have been proved to be of great 

 economic importance are found in, or in the vicinity of, these Timis- 

 kamian fragmentai rocks. 



Most of the gold, at least, in the important deposits belongs to a 

 later generation than the mass of the veins, having been deposited 

 after the veins were disturbed and fractured. 



Basic intrusives that appear to immediately precede the Algoman 

 granite are genetically connected with important nickeliferous pyrrho- 

 tite deposits in the township of Dundonald and with small deposits 

 of chromitc and pyrrhotite that have not proved to be of economic 

 value in the township of Reaume. These intrusives have not been 



1 Ont. Bureau of Mines, Vol. XIX, Part 2. 



Sec. IV, 1915—16 



