THE PROBLEM OF THE METALLIFEROUS VEINS. 205 



igneous rocks, well knoAvn to exist in the locality, was believed to be 

 the source of the springs. The same general line of investigation 

 has led Dr. Eudolf Delkeskamp, of Giessen, and other observers to 

 similar conclusions for additional springs, so that magmatic waters 

 have assumed a prominence in this respect which leaves little doubt 

 as to their actual development and importance. 



All familiar with western and southwestern mining regions know 

 as a matter of experience that the metalliferous veins are almost 

 always associated with intrusive rocks, and that in very many cases 

 the period of ore formation can be shown to have followed hard upon 

 the entrance of the eruptive. The conclusion has therefore been 

 natural and inevitable that the magmatic waters have been, if not the 

 sole vehicle of introduction, yet the preponderating one. 



With regard to their emission from the cooling and crystallizing 

 mass of molten material we are not perhaps entirely clear or well 

 established in our thought. So long as the mass is at high tempera- 

 tures the water is potentially j^resent as dissociated hj'^drogen and 

 oxygen. AVe are not well informed as to just what is the chemical 

 behavior of these gases with regard to the elements of the metallic 

 minerals. Hydrochloric acid gas is certainlj^ a widely distributed 

 associate. If, as seems probable, these gases can serve, alone or with 

 other elements, as vehicles for the removal of the constituents of the 

 ores and the gangiie, the possibilities of ubiquitous egress are best 

 while the igneous rock is entirely or largely molten. In part even 

 the phenomena of crystallization of the rock-forming minerals them- 

 selves may be occasioned by the loss of the dissolved gases. Through 

 molten and still fluid rock the gases might bubble outward if the 

 pressure were insufficient to restrain them and woidd, were their 

 chemical powers sufficient, have opportunity to take up even sparsely 

 distributed metals. 



On the other hand, if their emission, as seems more probable, is 

 in largest part a function of the stage of solidification and takes place 

 gradually while the mass is congealing or soon thereafter, then they 

 must depart along crevices and openings whose ratio to the entire 

 mass would be similar to those given above. They might have and 

 probably do have an enhanced ability to dissolve out in a searching 

 and thorough manner the finely distributed metallic particles as com- 

 pared with relatively cold meteoric waters which might la tpr permeate 

 the rock, but as regards the problem of leaching, the general relations 

 of crevices to mass are much the same for both, and it holds also true 

 that the discovery of the metals by assay of igneous rocks proves 

 that all the original contents have not been taken by either process. 



We may, however, consider an igneous mass of rock as the source 

 of the water even if not of the ores and gangue, and then we have 



