COLLECTIONS TN ECONOMIC GEOLOGY AND METALLURGY. 7 



They consist of (luartz ol" several kinds, jionerally anioiphons, but 

 frequently crystallized, and generally milk white to colorless, but very 

 often colored by iron ; this coloring may be due to the stains from the 

 recent decomposition of iron minerals, especially pyrite, or it may be 

 an original ingredient of the (luartz. Through this quartz gold is scat- 

 tered, varying from invisibly tine particles to coarse gold plainly visible. 

 Sometimes considerable masses are found. 



The <iuartz frequently contains other minerals, especially silicates 

 and sulphides : these latter sometimes occur iu large amounts, and are 

 generally auriferous, in fact quartzose ores graduate insensibly into the 

 sulphuret ores. 



The ores occur in several kinds of veins and also as rock strata, but 

 the richness of the various parts of a deposit may be very different, 

 and under some conditions certain parts may not be rich enough to be 

 profitably mined, with the appliances at hand. 



The universal process for extracting the gold from quartzose ores is 

 to crush the ore and submit it to the action of mercury, which forms a 

 heavy amalgam with the gold, and separates it from the gangue mate- 

 rial. After the gold has been extracted, the auriferous sulphides are 

 generally separated and treated for the gold they contain. Although 

 this process is not rei)resented in the collections, it is essentially the 

 same as the sulphuret process, illustrated by a collection from the Black- 

 hawk Mill, Blackhawk, (xilpin County, Colorado. 



Besides the specimens of gold quartz in the mineral series, which are 

 simply rich (juartzose ores with visible gold, the following characteristic 

 specimens of quartzose ores are shown. The series begins with pure 

 white quartz containing a very small amount of pyrite, and continues 

 with increasing amounts of pyrite and slate to the last two specimens 

 which are only about one-half quartz. 



(1) CoDtainiug a few crystals of pyrite. Wasbingtou Mine, Mariposa County, 

 Califoruia. (14506.) 



(2) Containing- pyrite and slate. Chariot Mine, Banner di.strict, Inyo County, Cali- 

 fornia. (14850.) 



(3) Crystallized, coutaiuiuc- pyrite and galena. New York Hill Mine, Grasa Val- 

 ley, Nevada County, Califoruia. (149.59.) 



(4) Containing galena and slate. Salsig Mine, Auburn district, Placer County, 

 California. (1505().) 



(5) Containing a little pyrite and decomposed silicates. Pennsylvania Mine, Ne- 

 vada City, Nevada County, Califoruia. (14928.) 



(()) Stained by decomposition products. Sierra Butte Mine, Sierra Butte district, 

 Butte County, California. (15021.) 



(7) Containing several slaty veins. Chariot Mining Company, Banner district, 

 Inyo County, California. (65355 ) 



(8) Intimate mixture of (luartz, pyrite, and slate. Keystone Mine, Sutter Creek 

 district, Amador County, Ciliforuia. (14994.) 



(9) Containing large amounts of various snlphurets, pyrite, chalcopyrite, galena, 

 blende (sulphides of copper, ir.)n, lead, and zinc). Plumas Eureka Mine, Plumas 

 Connty, Califoruia. (,1.5049.) 



