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



295 



existed. A strong odor of H 2 S came from the jar when I withdrew 

 the block ; and I had in its presence an obvious proof that sulphur had 

 found its way from the interior of the cell through the pores of the. 

 rock into the acetate solution. I washed and tested the black precipi- 

 tate and found it to contain sulphur. As the former acetate solution 

 in the jar now contained no lead, I was forced to the conclusion that 

 all the lead originally introduced had been precipitated as sulphide. 

 Still fearing a leakage somewhere, I broke the cement seal and 

 removed the cork from the cell, but while the cork was wet the cement 

 was not only dry where it had been in contact with the rock, but frag- 

 ments of rock came away with it, testifying to the firmness with which 

 it had gripped the surface. Upon breaking the marble block to bits 

 in search of discolored fractures, I found it to be moist, but. to contain 

 no visible fractures nor discolorations such as must have been found 

 had there been any passages larger than the calcite cleavages through 

 which the acetate could have entered the rock to meet the sulphide. 



The conclusion is inescapable that at least the sulphur of the 

 sodium sulphide had passed through one inch of rock in thirty days. 



Mode of Genesis op Veins at Cobalt by Diffusion 



Inception of diffusion. — Inasmuch as segregation of the diabase 

 did not extend beyond the most rudimentary stage, and the margins 

 of the mass were chilled and impervious long before the magma had 

 ceased to flow, it must be supposed that, if ore materials were con- 

 tained in it, they were entrapped there. Having had no time nor 

 opportunity to segregate they must have remained in a dispersed con- 

 dition, probably being imprisoned, perhaps along crystal boundaries 

 or as mineral inclusions ; or, more probably, as components of com- 

 plex molecules, either replacing or aecompaning the essential atoms 

 of rock-forming minerals. The minerals which thus were forced to 

 accommodate the ore. materials in a state which must necessarily 

 rapidly become unstable, may have been the feldspars and pyroxenes. 

 At any rate, such is my supposition; and the. substances of this sort 

 with which we are concerned were sulphur, arsenic, antimony, cobalt, 

 nickel, silver, iron, bismuth, lead, and copper. Mercury and other 

 substances may also have been present, but for the present purpose 

 they may be ignored, since they were very minor constituents of the 

 ores. 



The magma, at some time after the crystallization, but while still 

 hot, was deformed and fractured, and penetrated by the ground water. 



