256 University of California Publications in Geology [Vol. 13 



Cobalt deposits of not only Cobalt proper, but of Eabbit Lake 30 miles to the 

 south, Casey Township 15 miles to the northeast, South Lorrain to the southeast, 

 and others. 



Believing that the occurrence of ore is in some way connected with the north- 

 east-southwest lines of weakness, .the writer advised prospectors to search for 

 deposits in the vicinity of Animanipissing. This resulted in the first finds of 

 cobalt there. 



It was also recognized that folding occurred along NE-SW axes, 

 and that Cobalt Lake lies in a syncline ruptured along its axis on 

 what is known as the Cobalt Lake fault. 



Cobalt-silver veins. — The deposition of the ores was considered by 

 Miller to have occurred along joints and joint-like fissures, which, he 

 suggested, may represent cracks resulting from the contraction of the 

 diabase shortly after its intrusion. 



The genesis of the ores was variously assigned by different writers 

 to ascending juvenile waters or to descending meteoric waters. 

 According to Miller : 



The relation of the veins to the intrusive flat-lying sill of Nipissing diabase is 

 unique. The veins have not been filled by waters ascending vertically, as some 

 writers on the Cobalt area have assumed ; neither are the veins that are being 

 worked the narrow parts of wide veins that penetrated the now eroded overlying 

 rocks. It can not be proved that any of the veins in the Cobalt area reached the 

 surface as it existed at the time of the intrusion of the Nipissing diabase. The 

 occurrence of ' ' blind veins ' ' makes it doubtful whether or not all the veins 

 associated with the sill did not have a comparatively short vertical extension. 



The material in these veins has, in all likelihood, been deposited from highly 

 heated impure waters which circulated through the cracks and fissures of the 

 crust and were probably associated with .... followed .... the Nipissing dia- 

 base eruption. It is rather difficult to predict the original source of the metals — 

 silver, cobalt, nickel, arsenic, and others — now found in these veins. They may 

 have come up from a considerable depth with the waters,- or they may have leached 

 out of what are now the folded and disturbed greenstones and other rocks of the 

 Keewatin. Analysis of various rocks of the area have not given a clew as to 

 the origin of the ores. However, the widespread occurrence of cobalt veins in 

 the diabase or in close association with it, shown by discoveries during the last 

 seven or eight years, throughout a region over 3000 square miles in extent, appears 

 to be pretty conclusive proof that the diabase and the ores come from one and 

 the same magma. 



The veins, as is generally known, occur chiefly in the Cobalt sedi- 

 mentary series beneath the diabase sill ; but good veins are also found 

 in the sill itself, and in the adjacent Keewatin, both above and below it. 



The essential minerals of the veins as given in Miller's report, in 

 what he considers their order of deposition, are: smaltite, niccolite, 

 (period of moving and fracturing), calcite, argentite, native silver, 

 native bismuth, (period of decomposition), erythrite, annabergite. 



