BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 14, pp. 269-276 July 15, 1903 



SYNTHESIS OP CHALCOCITE AND ITS GENESIS AT BUTTE 



MONTANA 



BY HORACE V. WINCHELL 



{Read before the Cordilleran Section of the Society December SO, 1902) 



CONTENTS 



Page 



Copper production of Butte . . 269 



Principal ore mineral ... 269 



Paragenesis of chalcocite in Butte 270 



Chemistry of copper sulphide 270 



Literature of copper glance 271 



Chalcocite on coins 272 



Artificial formation of chalcocite 272 



Chemistry of oxidation of pyrite . 275 



Chalcocite a secondary mineral and primary ore 276 



Copper Production op Butte 



Since 1880 the mines of Butte, Montana, have produced approximately 

 1,250,000 tons of fine copper. They are now yielding about 200,000,000 

 pounds per annum, and have attained a maximum depth of 2,200 feet. 



Notwithstanding the statements of some writers on ore deposits,* the 

 copper ore of this mining camp is not chalcopyrite, nor is this mineral 

 at all common here. Indeed, it is about as rare as covellite, and a good 

 specimen of either is difficult to procure. 



Principal Ore Mineral 



Chalcocite is the principal copper mineral, although bornite and 

 enargite are common ; and it is probable that more than 75 per cent of 

 the total output of Butte copper has come from the smelting of the 

 mineral chalcocite or copper glance. It is found in all the mines and 

 on all levels from the highest unoxidized level to the bottom workings. 

 It occurs in small crystalline specks, in black powder, and in massive 



*Ed. Fuchs et L. De Launay : Traite des Gites Mineraux et Metallif^res, vol. ii, pp. 263, 265. 

 Eissler : Hydro-Metallurgy of Copper, p. 29. 



XXXIX— Bull. Geol. Soc. Am., Vol. 14, 1902 (269) 



