230 GEOLOGY OF TONOPAH MINING DISTRICT, NEVADA. 



interest because of their geographic and geologic relations to the Tonopah district. 

 It is found sparingly in the Apollo vein, Unga Island, Alaska (adularia or ortho- 

 clase). It has been described from the Valenciana silver mine, in the State of 

 Guanajuato, Mexico, where it was called valencianite. Lindgren has described 

 it as a common gangue mineral in the Silver City, Idaho, veins (see p. 272). These 

 ores are probably post-Miocene, and Mr. Lindgren gives reasons for considering 

 that the deepest ore bodies were formed at a distance of 700 to 2,000 feet below 

 the original surface. He therefore considers that the temperature at the time the 

 vein was formed can hardly have exceeded 100 C. a 



At Boulder Hot Springs, Montana, 6 are springs of a temperature varying 

 from 120 to 164 F/ which contain a slight amount of sulphureted hydrogen, 

 sodium chloride, soda sulphate, and carbonates of soda, lime, and magnesia. 

 The granite through which they rise is altered in the vicinity of the springs, 

 the most notable products being sericite and kaolinite, the result of the alteration 

 of feldspar and quartz. Calcite does not occur in the altered rock, and has 

 apparently been carried out of it by the altering waters into the fissures, where 

 it has been deposited. Veins which have formed in this granite contain chiefly 

 medium-grained quartz, calcite, and stilbite, and a little adularia. These veins 

 contain slight but perceptible amounts of gold and silver. 



At Cripple Creek, Lindgren found that adularia has been formed in the 

 granite near the veins, together with sericite and chlorite. Within cavities 

 produced by the removal of the granite, iron pyrite, fluorite, and tellurides have 

 been deposited.* 



CHEMISTRY OF THE ALTERATION OF SODA-LIME FELDSPAR TO ADULARIA. 



The chemistry of the change from andesine-oligoclase to adularia seems to be 

 fully explained by the following statements of Bischof," in speaking of observed 

 cases where adularia was altered to albite: 



"The unequal effect of water upon different mineral substances is mainly based 

 upon the fact that it holds materials in solution, which decompose one mineral but 

 not another. Sodium chloride decomposes potassium silicate, and potassium chloride 

 and sodium silicate are formed. Thus waters which hold sodium chloride can 

 decompose potash feldspar, while it leaves soda feldspar undecomposed. 



"In this way it is possible that such water may either change potash feldspar to 

 soda feldspar, or that it may take up and remove the alteration products of the 

 former. We can realize then how water containing sodium chloride (and this is 



a Lindgren, W., Twentieth Ann. Kept. U. 8. Geol. Survey, pt. 3, pp. 165-167. 

 6 Weed, W. H., Twenty-first Ann. Kept. U. 8. Geol. Survey, pt. 2, pp. 236-248. 



e By personal communication with Mr. Weed the writer learns there is evidence that these springs reach the boiling 

 temperature not many feet below the surface. 



<l Lindgren, W., Trans. Am. Inst. Min. Eng., vol. 33, p. 589 

 ' Blue hot, Gustav, Chemlsche Geologic, vol. 2, p. 411. 



