4 BULLETIN 131, UNITED STATES NATIONAL, MUSEUM 



The veins are contained in a great number of districts situated in 

 and around the borders of the central granitic mass. Most of them 

 carry gold and silver in a quartz gangue with abundant sulphides. 

 Among the best known districts are those of the Idaho Basin and the 

 vicinity of Boise, adjoined on the east by the Sawtooth, Atlanta, and 

 Rocky Bar districts. To the northeast are a number of minor dis- 

 tricts in Lemhi County. To the north are those of Warren, Florence, 

 Buffalo Hump, Dixie, Elk City, and Pierce. Still farther north, 

 surrounding a smaller granitic intrusive mass, cluster the lead-silver 

 bearing veins of the Coeur d'Alene district. The late Cretaceous 

 gold-bearing veins have usually yielded placer deposits of importance, 

 many of which are still producing. The placer districts of greatest 

 present importance are in the Idaho Basin, along the eastern bound- 

 ary of Lemhi County, and at Pierce. The now largely exhausted 

 placers of Warren, Florence, Elk City, and the Coeur d'Alene region 

 should also be mentioned. The fine gold occurring in the sands of 

 Snake River has been described frequently, but the actual production 

 from these deposits is very small. Placers of diminishing importance 

 are situated along Salmon and Boise Rivers. 



Among the Tertiary veins those near Silver City and De Lamar, 

 in Owyhee County, have been and are still important producers. 

 These veins cut through early Tertiary rhyolites and basalt and bear 

 clear evidence of having been formed within short distances of the 

 present surface. 



Less well known are the veins at Custer, and also those ot a few 

 districts like Singiser, in Lemhi County, which occur under similar 

 conditions. Low-grade gold ores have been mined at Thunder 

 Mountain, in Idaho County, and are said to form disseminations in 

 rhyolitic tuffs. The Tertiary veins carry gold and silver with a very 

 small amount of sulphides and no important amount of base metals. 



Idaho contains few deposits of iron, and none of them is mined 

 at present. Iron Mountain, in Washington County, near Snake 

 River, is the principal locality. No rare-metal deposits of importance 

 occur in Idaho. 



METAL PRODUCTION OF IDAHO 



It is deemed appropriate to here give a few figures on the amount 

 and value of the metal production of the State in order to convey 

 some idea of the importance of the mining industry which, after all, 

 is concerned entirely with obtaining and marketing minerals. The 

 following figures are taken from State Mine Inspector Robert N. 

 Bell's annual report for 1918. 



Estimated total value of metals mined previous to 1898, 

 $381,315,312. 



