1922] Whitman: Genesis of the Ores of the Cobalt District 285 



of water under atmospheric pressure which will be absorbed by gran- 

 ites, diabases, and gabbros is equal to from one ninetieth to one one- 

 hundred-and-tenth of the volume of the rock, and that this ratio would 

 be sufficient to bring the water in contact with only from 1 to 15 per 

 cent of the leachable ore material contained. It would therefore be 

 very difficult for the descending water to leach any significant metallic 

 content from any formation along its deeper course, no matter how 

 hot and chemically potent it might be. 



It has been impossible in these few paragraphs to do full justice 

 to both of these views of eminent disputants ; but I trust no injustice 

 has been done in thus partially quoting them. They seem in the main 

 to agree that the circulation of ground water must be chiefly and 

 almost exclusively through fissure conduits ; for its circulation is 

 excluded from the rock pores, in which it is generally admitted to be 

 present in a state of virtual stagnation, by the influence of adhesion 

 and the loss of head energy through friction in the capillary and sub- 

 capillary spaces of most firm rocks, increased mobility due to heat 

 notwithstanding. 



Partisans on both sides have indicated their belief that the mobility 

 of fluids in small pore spaces may be greatly increased by heat; but 

 none of them makes a strong point of it nor mentions the fact that in 

 the passage of any fluid, no matter how highly heated, through capil- 

 lary and subcapillary openings, its progress would be so slow that it 

 could not be presumed to carry heat above that of the rocks through 

 which it is passing. In fact, its initial pressure would probably be 

 converted by friction into heat and thus lost to the surrounding rock. 



In spite of this fact both schools conceive water circulation to be 

 the principal agency by which the ore materials are transported and 

 deposited, apparently overlooking the fact that crustification deposits 

 are in the minority, most ore bodies being due to replacement and 

 impregnation of wall rocks. On the hypothesis of deposition from 

 circulating solutions they are obliged to interpret metasomatic deposits 

 as due to the passage of immense volumes of dilute mineral waters 

 through the pore spaces of the wall rocks, from which the disputants 

 have excluded themselves by their own arguments. If a fissure too 

 narrow to exhibit the phenomena of crustification becomes sealed in 

 the first stages of vein formation, as must be the case since the major 

 circulation and easiest deposition would be along the open channel 

 rather than in its walls, why should the mineral-bearing solutions 

 thereafter prefer to circulate along its frozen and irregular walls 



