SILVER 



589 



productive mines in North America that supply 

 silver as a byproduct are massive sulfide deposits. 

 They are abundant in the following regions: (1) 

 The Appalachian region of the United States and 

 Canada (Bathurst, New Brunswick; Buchans and 

 Tilt Cove, Newfoundland; Maine and Vermont; 

 Ducktown, Tenn.) (Kinkel, 1967; Heyl and Bozion, 

 1971) ; (2) the Precambrian Shield of eastern and 

 central Canada (Kidd Creek, Timmins, Ont. ; No- 

 randa, Quebec), including the Adirondack uplift in 

 New York and the Wisconsin dome in Wisconsin and 

 Michigan; (3) the Pacific coast region of California 

 (Kinkel and Hall, 1952), British Columbia, and 

 Alaska; and (4) the Basin and Range province and 

 Rocky Mountains (Iron King, Bagdad, and Jerome, 

 Ariz. (Anderson, 1969), Pecos, N. Mex., and the 

 Sedalia mine, Colorado) . 



At the United Verde mine, Jerome, Ariz., 57 mil- 

 lion ounces of silver was recovered between 1883 

 and 1952 (Anderson and Creasey, 1958, p. 101). This 

 represents 214 ounces of silver per ton of ore, or 31 

 ounces of silver per ton of copper. The Iron Moun- 

 tain mine, in the West Shasta district, California, 

 was first mined for silver in the gossan, which 

 locally averaged about 8 ounces of silver per ton of 

 ore ; the primary ore contained less than 1 ounce of 

 silver per ton (Kinkel and Albers, 1951, p. 8). The 

 massive sulfide deposits with substantial amounts 

 of sphalerite and galena carry more silver than the 

 pyrite-chalcopyrite ore. At the Iron King mine, 

 Arizona, the ore averaged 4 ounces of silver, 2.2 

 percent lead, and 6.4 percent zinc (Anderson and 

 Creasey, 1958, p. 155) . At the Mammoth mine, Cali- 

 fornia, the massive sulfide ore that was mined for 

 copper contained 2.2 ounces of silver whereas the 

 ore mined for zinc averaged 5.8 ounces of silver per 

 ton (Kinkel and Hall, 1952, p. 6). 



LEAD-ZINC REPLACEMENT DEPOSITS 



Lead-zinc replacement ore deposits are one of the 

 principal sources of silver. Most argentiferous lead- 

 zinc replacement deposits formed from hydrother- 

 mal solutions of deep-seated origin at the margin of 

 or within intrusive bodies of granitic to dioritic 

 composition. In the margins of the intrusive bodies, 

 limestone is a particularly favorable host rock, but 

 quartzite, argillite, and schist also host major de- 

 posits. Many deposits are localized near or within 

 the intrusive by structural features such as a favor- 

 able bed near a feeder fissure, a fracture or fissure, 

 a brecciated zone near the intrusive, or a favorable 

 bed in a roll in the structure. Especially favorable 

 geologic settings are found near Mesozoic and Ter- 

 tiary instrusives in the circum-Pacific belt and near 



Tertiary intrusives in the Great Basin and Rocky 

 Mountains, eastern Canada, and central Europe. 



Much of the rich silver ore is produced from lead- 

 silver-zinc replacement deposits in limestone. These 

 include such famous camps as Park City and Tintic, 

 Utah ; Leadville and Red Cliff, Colo. ; Silver City and 

 Magdalena, N. Mex. ; Eureka, Nev. ; and Cerro de 

 Pasco and Casapulca, Peru. The bedded replacement 

 deposits at Park City are in many places contiguous 

 with vein deposits that occupy feeder fissures in 

 which the ore solutions moved. Silver-rich lode de- 

 posits were exploited in the early years of the dis- 

 trict. The Ontario lode provided high-grade silver 

 ore over a strike length of approximately 5,000 feet 

 and to a depth of 1,300 feet (Barnes and Simos, 

 1968, p. 1116). Where the vein is in the Weber 

 Quartzite, it contains high-grade ore, but in the 

 underlying limestone the ore is discontinuous and 

 lower grade. Extensive bedded limestone replace- 

 ment ore bodies are found in the overlying Park City 

 Formation; these deposits have been the major 

 source of production since the early exploitation of 

 the high-grade lodes. The Jenney limestone bed of 

 economic usage, which is 100 feet above the Weber 

 Quartzite-Park City Formation contact, is the host 

 rock for most of the large bedded deposits (Garmoe 

 and Erickson, 1968, p. 34). It was mineralized over 

 a strike length of more than 6,000 feet, with a maxi- 

 mum width of 150 feet, and ranged in thickness 

 from 25 to at least 100 feet. The ore averaged 25.3 

 ounces per ton of silver, 14 percent lead, and 12 

 percent zinc. 



At Tintic, Utah, much of the ore mined during 

 the early history of the district averaged 30-40 

 ounces of silver per ton (Lindgren and Loughlin, 

 1919, p. 105-112) and some of it assayed more than 

 100 ounces per ton. At Darwin, Calif., much of the 

 near-surface primary ore averaged 50 ounces of sil- 

 ver per ton whereas the deeper replacement ore 

 averaged about 6 ounces per ton (Hall and Mac- 

 Kevett, 1962). Oxidation and supergene enrichment 

 of these argentiferous galena ores produced the shal- 

 low-depth bonanza ore bodies that were mined dur- 

 ing the latter part of the 19th century. 



Lead-zinc deposits with appreciable silver occur 

 in quartzite, argillaceous rocks, and schist, as veins 

 or veinlike replacements along steep fissures or in 

 fractures along bedding. Veins of this type consti- 

 tute much of the formerly productive mineral belt 

 of Colorado, particularly in the Montezuma, Idaho 

 Springs, and Silver Plume districts, where they occur 

 in fault zones in Precambrian gneisses (Lovering 

 and Goddard, 1950, p. 138-178) . 



