ORIGIN OF HOT SPRINGS. 259 



quantities of the rare metals silver and gold, and unusually small ones of the 

 commoner ones copper, lead, and zinc. The amount of silver by weight in these 

 primary ores, so far as they have been developed, seems to exceed that of 

 either of the three last-named metals. No such results as this could be expected 

 were the metals derived from leaching of the andesite. Plainly some process of 

 separation and concentration has furnished the noble metals contained in the 

 mineralizing waters, separating them from the baser metals. Nickel is present in 

 the fresh later andesite (p. 34) and was detected in the fresh earlier andesite of 

 Eureka; yet this metal has not been detected in the ores in either camp. In the 

 rocks near the Comstock lode analyses conducted by Dr. G. F. Becker* showed 

 small quantities of silver and gold, whence it was concluded that the ores of the 

 lode had been derived from the wall rocks (by lateral secretion). But later 

 investigations on the subject of the presence of the precious metals in rocks 

 show that these metals are very frequently present in rocks not associated with 

 ore deposits, as well as in those that are; and the results of the assays tabulated 

 by Becker do not, to the writer's mind, indicate any connection between these 

 traces of metals and the ores of the Comstock lode. At Washoe, as at Tonopah, 

 the theory of leaching from wall rocks, or lateral secretion, indeed, leaves 

 unexplained the presence of silver and gold in such large quantities, relatively 

 to the commoner metals. The view concerning this problem at the Comstock, 

 expressed by von Richthofen,'' seems to the writer especially illuminating, and 

 applicable, as well, to the similar situation at Tonopah. Von Richthofen remarks: 



" We have in the elements evolved during the first two periods of solfataras 

 namely, fluorine, chlorine, and sulphur all the conditions required for filling the 

 Comstock fissure with such substances as those of which the vein is composed. 

 Steam, ascending with vapors of fluosilicic acid, created in its upper parts (by 

 diminution of pressure and temperature, according to well-known chemical agencies) 

 silica and silicofluohydric acid, the former in solid form, the latter as a volatile gas, 

 which acts most powerfully in decomposing the rocks it meets on its course. The 

 chloride of silicon in combination with steam forms silica and chlorhydric acid. 

 Fluorine and chlorine are the most powerful volatilizers known, and form volatile 

 combinations with almost every substance. Besides silicon, the metals have a great 

 affinity with them. All those which occur in the Comstock vein could ascend in a 

 gaseous state in combination with one or the other of them. * 



"It is a fact worthy of notice that there is scarcely a single chemical agent, 

 excepting fluorine and chlorine, which would not carry metallic substances into 



a Since the above was written the important discovery of the presence of selenides has been made by Doctor Hillebrand. 

 See pp. 89, 90. Doctor Hillebrand remarks that the presence of selenides, and the absence of their closely associated 

 element, tellurium, indicated some unusual process of separation. Tellurides have been found at Goldfield, 28 miles 

 south of Tonopah, also in Tertiary volcanic rocks; and from that camp selenides have not yet been reported. 



6Mon. U. 8. Geol. Survey, vol. 3, pp. 184, 155, 223. 



c As examples, see Wagoner, Luther, Trans. Am. Inst. Min. Eng., vol. 31, pp. 798-810. 



dMon. U. S. Geol. Survey, vol. 3, pp. 19, 20. 



