594 



UNITED STATES MINERAL RESOURCES 



silver-bearing lead-manganese oxides have been 

 identified from black silver-bearing manganiferous 

 calcite samples (Radtke and others, 1967). 



One of the richest of the oxidized silver-manga- 

 nese deposits was mined in the Lake Valley district, 

 New Mexico, from 1878 to 1893, during which time 

 it yielded 5 million ounces of silver (Jicha, 1954, p. 

 71). Half of the silver came from one stope where 

 the silver occurred in cerargyrite and one 4-foot face 

 averaged 15,000 ounces of silver per ton. Lower 

 grade silver ore consisted of silver-bearing manga- 

 nese and iron oxides in cherty limestone. The nature 

 of the primary ore is not known inasmuch as all the 

 mined ore was manganese oxides and silver chlorite 

 in limestone ; only a small amount of galena, almost 

 completely oxidized, was found. Sulfide cavities are 

 uncommon. 



EPITHERMAL SILVER-LEAD-ZINC REPLACEMENT DEPOSITS 



Epithermal silver-lead-zinc replacement deposits 

 are not common, but a few have been very produc- 

 tive. One of the largest and most productive districts 

 with such deposits is Aspen, Colo., where large veins 

 and replacements along bedding-plane faults and 

 cross faults in Mississippian carbonate rocks contain 

 large, rich, pocketlike hypogene ore bodies of barite, 

 pearceite, and native silver near the surface. In 

 places these bodies grade into fine-grained collof orm 

 silver-rich galena and sphalerite. Other silver re- 

 placement deposits occur at Eureka and Cortez, 

 Nev. ; Tombstone, Ariz. ; Hermosa and Kingston, N. 

 Mex. ; and Shaffer, Tex. 



Variants of this type are the Tertiary volcanic 

 breccia pipes or chimneys of silver, gold, lead, zinc, 

 copper, and tungsten ores that formerly were pro- 

 ductive in the Red Mountain district in the core of 

 the Silverton caldera of the San Juan Mountains, 

 Colo. (Burbank and Luedke, 1968). The ore was de- 

 posited at shallow depth and replaces the breccia, or 

 it forms cylindrical replacement envelopes around 

 the pipes along the contact with wallrocks and fills 

 the interstices. These epithermal ores are rich in 

 silver and copper, and in places include pipes of 

 shallow-depth high-temperature deposits containing 

 heubnerite. The best silver ore consists mostly of 

 stromeyerite and bornite. 



At Mercur, Utah, the Carlin-type very fine grained 

 limestone-shale gold-arsenic replacement ores grade 

 into silver ores geologically similar to the Carlin, 

 Nev., gold ores. The first mining was for silver, and 

 the gold ore was found after the highest grade silver 

 ore had been mined out and the camp abandoned for 

 a decade (Gilluly, 1932). 



EPITHERMAL SILVER-COPPER-BARITE DEPOSITS 



Rich silver-copper-barite deposits of Triassic age 

 were found in the 1960's at Walton, Nova Scotia 

 (Boyle, 1963; 1972). At the surface, pipe deposits 

 were mined for barite and manganese. Subsequent 

 deep drilling for barite revealed deposits, beneath 

 the barite in the same pipe, that consist of chalcocite 

 and at least 10 other copper and silver sulfide min- 

 erals. Similar barite deposits with silver-bearing 

 chalcocite are known in the Triassic shales of the 

 Connecticut Valley. Hewett (1968) suggested that 

 the Walton deposit is a type of silver occurrence that 

 might be expected beneath the manganese-silver ores 

 previously mined. 



MESOTHERMAL SILVER-BASE METAL VEINS 



The Coeur d'Alene district of Idaho is the coun- 

 try's leading silver producer, one of the few active 

 mining districts in the world in which a significant 

 part of the ores are mined chiefly for their silver 

 content. Through 1968 its mines have yielded ap- 

 proximately 754,300,000 ounces of silver, 7,010,000 

 short tons of lead, 2,555,000 short tons of zinc, and 

 125,000 short tons of copper, in addition to sub- 

 stantial amounts of cadmium and antimony. The 

 total value of the metals produced exceeds $2.3 

 billion. 



The ore is in replacement veins in weakly meta- 

 morphosed argillites, siltites, and quartzites of the 

 Precambrian Belt Supergroup. Coeur d'Alene ore 

 shoots are characteristically longer in vertical di- 

 mension than in horizontal dimension. Ore has been 

 mined over a vertical range of 8,000 feet. Many ore 

 shoots have been bottomed, but others continue 

 below the lowest mine levels, with no evidence to 

 suggest their bottom limit. The principal producing 

 mines are found in two groups, one north of the 

 Osborn fault, the other south of the fault. The east- 

 ern part of the southern group is known as the 

 "Silver Belt" because of the higher silver content of 

 the ore. 



In most mines in the Silver Belt, the ore averages 

 about 25 ounces of silver per ton and 0.75 percent 

 copper. In the other mines the combined lead-zinc 

 content averages 10-12 percent, and the silver con- 

 tent is variable. 



The Chewelah district, which has been the leading 

 producer of silver in Stevens County, Wash., is in an 

 entirely different geologic setting from the Coeur 

 d'Alene district. The silver is in braided quartz- 

 carbonate veins in shear zones in argillite of the Belt 

 Supergroup. Chalcopyrite is the principal ore min- 

 eral. All the mines are within 2 miles of outcrops of 

 the Flowery Trail Granodiorite (Clark and Miller, 



