56 BULLETIN 131, UNITED STATES NATIONAL MUSEUM 



ADA COUNTY 



Although the Black Hornet district contains no important placers, a 

 number of veins of gold-bearing quartz occur. Chief among these is 

 the Black Hornet or Ironsides mine which had made a gold produc- 

 tion of about $30,000 previous to 1897. The ore consists of quartz 

 containing about 8 per cent of sulphides, chiefly arsenopyrite with 

 less pyrite and sphalerite. Arsenopyrite also occurs in disseminated 

 form in the altered (sericitized) granite of the walls immediately 

 adjacent to the vein. 



In the Boise (Mclntyre) district a number of auriferous veins have 

 been developed, although there has never been any very great pro- 

 duction. Some of the lodes are quartz veins and others are merely 

 altered streaks in the granite along a fault plane. In some cases 

 the values are entirely in gold but some small deposits of rich silver 

 ore have been mined. 



In the Snake River placers desultory operations have been carried 

 on from year to year in this county. A dredge capable of handling 

 1,500 cubic yards of gravel daily was installed in 1907. 



BINGHAM AND BONNEVILLE COUNTIES 



In the Mount Pisgah district some hydraulic mining has been done 

 at Gray. The gold is 960 fine (96 per cent Au) and is worth $19.84 

 an ounce. 



In the Snake River placers there are a considerable number of 

 small mines. Six operators were working in 1905; a production of 

 185.22 ounces of gold was reported for 1907, while the output for 

 1908 and 1909 was worth $2,717 and $1,448, respectively. The gold 

 is 951 fine (95.1 per cent Au) and is valued at $19.66 an ounce. 



A sample of heavy concentrate from a Snake River placer mine 

 at Rosa, Bingham County (Cat. 53625 U.S.N.M.) has an average 

 grain diameter of 0.1 mm. and contains a few minute rounded grains 

 of gold associated with abundant ilmenite and augite, occasional 

 almandite and quartz, and rare zircon and olivine. 



BLAINE COUNTY 



In the Camas district fissure veins in granite carry free native 

 gold with pyrrhotite, pyrite, and chalcopyrite, and less galena, 

 sphalerite and arsenopyrite in a gangue of quartz with some siderite. 

 The principal mines are the Camas No. 2 and the Tip Top. The 

 Camas No. 2 vein produced gold to the value of $58,392. 



In the Mineral Hill (Hailey) district the Croesus, Hope, and neigh- 

 boring veins of what is known as the Hailey gold belt contain their 

 principal values as free gold which is associated with considerable 

 quantities of sulphides, mainly pyrrhotite and chalcopyrite with less 

 galena and sphalerite in a quartz and siderite gangue. These are 



