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University of California Publications in Geology 



[Vol. 13 



the emanation of the superheat of the magma, and the heat gradient 

 has become relatively flat. It may reasonably be expected, therefore, 

 that although the diabase and its neighborhood did not long remain 

 at their initial temperature, the diabase itself must have remained 

 hot for a considerable length of time. 



In the course of that time the ore materials must be conceived to 

 have found their way from mineral cleavage to crystal boundary, 

 thence to shear joint and flat fault, and to the flatly inclined diabase 

 and Keewatin contacts where shearing was chiefly concentrated, and 

 thence to split joint and steep fault, where deposition occurred. At 

 certain points here and there the journey of the ore ions may have 

 been hastened by water circulation, but probably in general that was 

 a negligible factor in their dispersion. Finally, a given ion may be 

 supposed to have arrived at a point in the adjacent conglomerate 

 where it was removed from the solution by precipitation. At once the 

 neighboring ions, being relieved of its active presence, moved to take 

 its place in the solution and were themselves precipitated in the same 

 manner. As precipitation progressed at that point, thus impoverish- 

 ing the neighboring solution, the diffusion gradient was steepened 

 there, and a general migration to the point occurred throughout a 

 larger and larger region about, until it finally extended to the source 

 of the ions in the diabase, reduced their concentration there, and thus 

 hastened the solution of others. In this manner solution and diffusion 

 were accelerated throughout a considerable space about the point of 

 precipitation, and the movement of ions from their source became 

 increasingly direct to the point of precipitation. As one point of pre- 

 cipitation after another was established, the entire locality and mass 

 of diabase became impoverished in ore ions, and these ions were ex- 

 clusively concentrated in the veins. 



Miller and Knight 22 made many careful analyses of the Nipissing 

 diabase and found it to contain no silver. If the mother-magma of 

 the diabase had been the source of the ores, surely some silver should 

 be found in the diabase. One might say, if the visible diabase itself 

 were the source of the ores, why does it show no silver? The answer 

 is, that if the silver came from the diabase it could not still be in the 

 place from which it came. One might object to this that a residiuum 

 of silver should remain at its source ; but that would imply that the 

 extraction was only partial. What right have we to assume that ? If 

 some agency was able to extract and remove the silver, why should it 



22 Ont. Bur. Mines, Report, vol. 19, pt. 2. 



