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



279 



As the diabase sheet cooled and contracted, it tended to accentuate its 

 own undulations parallel to each of the major tectonic lines ; and when 

 this process was completed the force exerted by the cooling magma 

 was greatly exceeded by the contraction of the inclosing rocks. This 

 shrinkage, conformable with the two controlling tectonic axes of the 

 region, gave rise to folds parallel to them, and at the same time gave 

 rise to associated faults and joints. The Cobalt Lake fault reopened 

 as a rupture along the axis of the Cobalt Lake syncline, displacing 

 the Cobalt Series a distance of 500 feet diagonally upward, dislocat- 

 ing certain of the easterly-westerly faults, and being followed by fold- 

 ing parallel to the other axis. As these deformations began, the first 

 effects were the inception of NE-SW folds accompanied by the 

 development of shear joints and reverse faults, then by split joints 

 and the E-W faults, then by dislocation on the Cobalt Lake fault ; 

 then came minor folding superimposed on the other, parallel to the 

 NW-SE axes, and the warping of the surface of the Cobalt Lake fault 

 where two of these minor synclines cross it. There followed further 

 intensification of all the folds, and the considerable dislocation of 

 many split joints on shear joints and flat dip-slip reverse faults. Then 

 came the ore. 



Current Theories op Vein Genesis at Cobalt 



Descending solutions. — In view of the fact that these veins con- 

 tain large percentages of native silver, dyscrasite, argentite, and 

 proustite, easy first thought supposes that they may have originated 

 through processes of downward secondary enrichment. Some writers 

 have suggested that the veins at Cobalt may be the roots of vertically 

 more extensive veins of cobalt and nickel poor in silver, which have 

 been enriched through the solution of the silver of the upper portions 

 of the veins in the products of their oxidation, and its redeposition 

 in their lower portions through the precipitating agency of smaltite 

 and niccolite. Research may have demonstrated the feasibility of this 

 precipitation process ; but it is more relevant to the problem in hand 

 to consider whether such solutions could ever have been delivered to 

 the cobalt veins. 



The consideration of any one of a number of conspicuous con- 

 ditions would suffice for the rejection of any idea of downward 

 secondary enrichment. First of all, the products of oxidation of the 

 veins would be preponderantly arsenious and scarcely at all sulphur- 

 ous; and at no place in the district are the lower portions of the 



