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GEOLOGY. — Tungsten deposits of northwestern Inyo County, Cali- 

 fornia. Adolph Knopf. U. S. Geological Survey Bulletin 

 640-L. Pp. 21. 1917. 



Tungsten deposits were found in northwestern Inyo County, Cali- 

 fornia, in 1913 but remained practically unknown until the spring of 1916, 

 when they began to be energetically developed. By midsummer two 

 mills, having a total daily capacity of 400 tons, had been completed 

 and were in active operation. 



The ore consists of scheelite associated mainly with garnet, epidote, 

 and quartz. The country rock is prevailingly granitic, but in it are 

 isolated masses of limestone which became mineralized shortly after 

 the granitic rocks were intruded. The limestones were altered to 

 masses of garnet carrying subordinate scheelite by the metallic vapors 

 then given off, and these altered rocks are the tungsten deposits now 

 under exploration. The ore bodies that are being mined are from 20 

 to 60 feet wide and from 150 to 260 feet long. They carry from 1.5 

 to 2 per cent of tungsten trioxide (WO3) . The area in which scheelite- 

 bearing deposits have been found forms roughly a belt 20 miles long, 

 but it is likely that the prospecting now going on will extend the 

 dimensions of the field. 



These deposits, like those discovered in recent years in Humboldt 

 County, Nevada, belong to the contact-metamorphic class, a well-known 

 source of copper and iron but not widely recognized as a possible 

 source of tungsten. A. K. 



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