PRECIOUS METALS :, 



evidence that their walls form part of a channel through which 

 the ore em-rents came up fnun below. 



Since the work of Mr. Emmons was done at Leadville, other 

 eminent geologists have been in the field with better opportunity 

 to study the origin of the ore deposits. The finding of fissure 

 ores in the Cambrian quartzite leads them to the conclusion 

 that the ores may have been brought in by solutions ascending 

 directly from the intrusives. 



In 1859, placer gold was found in California Gulch, worked out 

 in 1863 and deserted. The owners were much troubled with 

 heavy rock, the composition of which was unknown to the miners, 

 but later discovered to be cerussite, the carbonate of lead, rich 

 in its silver content. 



In 1875 these deposits were reopened and worked for their 

 silver content. The silver occurs as argentite, native silver, 

 cerargyrite and embolite at the surface and in galenite at greater 

 depths. Masses of auriferous galenite have been found 100 ft. 

 in thickness. 



At Aspen, oxidized lead and silver ores occur in highly folded 

 and faulted Carboniferous limestone. According to W. H. Weed, 

 the accumulation of ore at the intersection of fault planes is the 

 result of a secondary enrichment rather than of primary concen- 

 tration. At Creede, the silver ores occur in fissure veins pene- 

 trating igneous rocks. At Red Mountain the silver ores occur 

 in true fissure veins traversing Jura-Trias terranes. 



Utah. Third in order of importance as a silver producer is 

 Utah. In both Cottonwood canons, oxidized lead-silver ores 

 occur near the surface in bedded veins in Carboniferous lime- 

 stone. In Beaver County oxidized lead and silver ores occur in 

 contact fissures in the Horn Silver mine; in "chamber deposits" 

 in Carboniferous limestone at the Cave mine; in fissures at the 

 Carbonate mine; in Park City, as silver and lead oies in 

 Carboniferous limestone, sandstone; and shales. The ores 

 bearing lead and copper are oxidized, the others appear mostly 

 as bedded deposits in the limestone, often with siliceous walls 

 separating one deposit from another. These are frequently 

 associated with porphyritic igneous rocks. In Idaho at Coeur 

 d' Alene the ore galenite is found with siderite gangue in highly 

 folded quartzites and mica schist. 



Nevada The Comstock lode, Nevada, represents the largest 

 auriferous silver- bearing deposit ever discovered. It lies in a 



