1056 A TREATISE ON METAMORPHISM. 



an ore consisting of chalcopyrite and pyrite associated with the gang'ue 

 of quartz and tourmaline. He here places the Copperopolis mine and 

 Jessie vein. The ores are intergrown with quartz and tourmaline. At the 

 Jessie vein the other gangue materials are calcite, dolomite, and specula- 

 rite." Lindgren says the copper deposits of the Seven Devils and tourma- 

 line types "are of rare occurrence." 6 



In the South Mountain district of Idaho, an argentiferous g-alena, with 

 some zinc blende and copper minerals, occurs in crystalline limestone and 

 in schist. The gangue minerals are quartz, calcite, actinolite, brown garnet, 

 and ilvaite, the gangue minerals and ores being intergrown." 



Weed states that the Jimenez copper deposits of Mexico follow a line 

 of contact between limestone and granite, the limestone being largely con- 

 verted into massive garnet. d He further states that the Porvenir gold- 

 copper vein in the Sierra Azul mining district of Mexico occurs in granite, 

 and has tourmaline as an abundant gangue mineral." 



Yung and McCaffery describe the copper deposits of San Pedro, in 

 New Mexico, as contact deposits in limestone. The limestone has been 

 largely replaced by garnet. Chalcopyrite is intimately associated with the 

 garnet, and with subordinate amounts of specular hematite, epidote, vesu- 

 vianite, wollastonite, quartz, and calcite. They say " the ore is always 

 accompanied by garnet, although the garnet does not in all places carry 

 ore. When the garnet carries the ore the chalcopyrite is disseminated 

 throughout its mass, and appears to be of synchronous origin." f 



In those instances in which it is clearly shown that heavy anhydrous 

 minerals, such as topaz, tourmaline, garnet, and biotite, develop simulta- 

 neously with the deposition of the ores by metamorphic processes, it seems 

 highly probable that they formed under the conditions of the zone of ana- 

 morphism and that the temperature at the time of the deposition was above 

 the critical temperature of water. 



«Lindgren, Waldernar, The gold belt of the Blue Mountains of Oregon: Twenty-second Ann. Kept. 

 U. S. Geol. Survey, pt. 2, 1901, pp. 629-630. 



6Loc. cit., p. 629. 



''Lindgren, Waldemar, The gold and silver veins of Silver City, De Lamar, and other mining 

 districts in Idaho: Twentieth Ann. Eept. U. S. Geol. Survey, pt. 3, 1900, p. 189. 



d Weed, Walter Harvey, Notes on certain mines in the States of Chihuahua, Sinaloa, and Sonora, 

 Mexico: Trans. Am. Inst. Min. Eng., vol. 32, 1902, p. 404. 



« Loc cit., p. 440. 



/ Yung, Morrison B., and McCaffery, Richard R., The ore deposits of the San Pedro district, New 

 Mexico: Trans. Am. Inst. Min. Eng., vol. 33, 1903, p. 355. 



