8 BULLETIN 12, UNITED STATES NATIONAL MUSEUM. 



SULPHURET (lOLD ORES. 



These ores consist of the sulphide of iron, pyrite, the sulphide of 

 iron aud copper, chalcopyrite, aud the sulph-arseuide of iron, niispickel, 

 the two former are by far the most common aiul always occur to- 

 gether. Occasionally other sulphides are associated in small amounts 

 with those uamed. The sulphides of iron and copper generally occur in 

 a gangue of quartz, which is also auriferous, and these ores are some- 

 times simpl}' portions of quartzose veins, containing large amounts of 

 sulphides. Mispickel generally occurs with a gangue of calcite or dolo- 

 mite. The general occurrence of these ores is the same as the quartz- 

 ose ores. 



The gold in sulphuret ores occurs in practically two distinct forms; 

 the first form amalgamates readily with mercury and can thus be sep- 

 arated by that means ; but after most prolonged and careful treatment 

 with mercury there will always remain some gold in the sulphides. 

 It is claimed that the gold that amalgamates occurs as free gold in the 

 sulphides, while that which will not amalgamate occurs in a chemically 

 combined condition, but this distinction has not been fully proved, and 

 it seems more probable that all the gold occurs in the free state, but 

 that the portions that will not amalgamate are protected by the phys- 

 ical condition of the sulphides. 



For the extraction of the gold the ores are first crushed aud sub- 

 jected to amalgamation. The sulphides are then separated from the 

 gangue, and further treated. 



Sometimes the concentrates are simply roasted to remove the sulphur 

 and again amalgamated ; sometimes after roasting the gold is dissolved 

 by chlorine gas in water, the solution containing the gold is filtered 

 off and the gold recovered from the solution. Sometimes the roasted 

 ore is used in some of the smelting processes, and this is especially the 

 case when it contains copper. Aside from the gold value these roasted 

 sulphides are very useful in fusion processes on account of the iron they 

 contain, which acts as a basic flux. 



Mispickel ores are generally roasted previous to amalgamation to 

 remove the arsenic as well as the sulphur. 



The following ten specimens illustrate sulphuret gold ores: 



(1) Pyrite in qnartz. Curraha Miue, Gainesville, Hall Coimty, Georgia. (30834.) 



(2) Pyrite, crystallized iu quartz. Gold Tunnel Mine, Nevada City, Nevada County, 

 California. (14940.) 



(3) Pyrite in quartz. Gold Dirt Miue, Gold Dirt district, Gilpin County, Colo- 

 rado. (19209.) 



(4) Pyrite and chalcopyrite, with a little quartz. Gregory Mine, (Gregory district, 

 Gilpin County, Colorado. (19223.) 



(5) Chalcopyrite in quartz. Bowery Mine, Ward district, Boulder County, Colo- 

 rado. (19060.) 



(6) Intimate mixture of pyrite, chalcopyrite, galena, and blende. (Sulphides of 

 copper, iron, lead, and zinc.) Bates Mine, Gilpin County, Colorado. (60.356.) 



