324 



UNITED STATES MINERAL RESOURCES 



and other metals, or for fluorite, barite, or calcite. 



In addition to the great Coeur d'Alene district of 

 Idaho and the North Pennine district of England, 

 other examples of highly productive vein-type lead 

 deposits include the classic districts of Clausthal, 

 West Germany, Freiberg, East Germany, and Pri- 

 bram, Czechoslovakia (Berg, 1927), Santa Barbara, 

 Fresnillo, and Taxco in Mexico (Gonzales Reyna, 

 1950), Morococha, Casapalca, San Cristobal, and 

 others in Peru (Peterson, 1965), Butte, Mont. 

 (Meyer and others, 1968), Montevecchio, Italy 

 (Zuffardi, 1950), and many others. It should be 

 noted, however, that some districts that are well 

 known for other types of lead deposits, such as the 

 Tintic, Park City, Leadville, and Pioche districts 

 of the United States, and a great many others, also 

 contain vein deposits of considerable importance. 



The apparent environments of deposition of lead- 

 bearing veins are generally as widely varying as 

 the depositional environments of replacement de- 

 posits. They range in character from high-tempera- 

 ture veins containing galena in association with 

 tourmaline (Knopf, 1913) and with garnet, heden- 

 bergite, actinolite, fluorite, and quartz (Spurr and 

 Garrey, 1908) to crustified epithermal veins that 

 were deposited at low temperatures and shallow 

 depths, commonly in association with fluorite, cal- 

 cite, and quartz. The extreme temperature range 

 may extend from 50°C to 550°C, and the pressure 

 range from 1 to 1,000 atmospheres or more. Some 

 veins, such as those of the Kentucky-Illinois fluor- 

 spar and lead district and possibly those of the 

 North Pennine district of England (Dunham, 1949), 

 are classified with the Mississippi Valley type 

 deposits. 



CONTACT PYROMETASOMATIC DEPOSITS 



Although the irregular or pod-form lead deposits 

 that occur in the aureoles of granitic plutons may 

 have importance locally, particularly in Japan, they 

 are relatively unimportant in terms of gross pro- 

 duction. These deposits are localized chiefly in limy 

 or dolomitic rocks that have become bleached, re- 

 crystallized, and silicated by solutions that were 

 associated with intrusions of intermediate compo- 

 sition. Some deposits also occur in calcareous shales, 

 tuffs, and sandstones. In general the contact depos- 

 its range in form from tabular bodies and masses 

 of unpredictable shape to veins. The more common 

 metallic minerals include galena, typically less abun- 

 dant than iron-rich sphalerite, chalcopyrite, pyrite, 

 pyrrhotite, arsenopyrite, and magnetite. In some 

 deposits, bismuth, molybdenum, and tungsten min- 

 erals and native gold may also be present. The 



gangue minerals include diopside, hedenbergite, gar- 

 net, fluorite, epidote, actinolite, ilvaite, tremolite, 

 quartz, and a variety of other silicates. 



The deposits range in size from insignificant 

 veins and lenses to large pods, one of which, at the 

 Kamioka mine, Japan, is 850 feet long, 230 feet 

 wide, and has been proven to a depth of 1,575 feet 

 (Japan Geol. Survey, 1960, p. 182). This mine 

 annually produces more than 1.5 million metric tons 

 of ore containing 1.12 percent lead, 5.80 percent 

 zinc, and 0.84 ounce per ton of silver. A somewhat 

 similar but relatively lead-poor ore body in the 

 Central district. New Mexico, 2,500 feet long, 30 

 feet wide, and 80 feet high (Lasky and Hoagland, 

 1950, p. 106), contained sphalerite and small 

 amounts of galena and chalcopyrite, in association 

 with andradite, salite, hedenbergite, ilvaite, and 

 other minerals (Hernon and Jones, 1968, p. 1229). 

 The average grade of this ore was probably close to 

 14 percent zinc, 0.13 percent lead, 6.19 percent iron, 

 and 10.19 percent sulfur (Lasky and Hoagland, 

 1950, p. 106). Other contact pyrometasomatic de- 

 posits that produce lead include the Chichibu, Naka- 

 tatsu, Obori, and other deposits of Japan (Japan 

 Geol. Survey, 1960, p. 180-183), Tetyukhe in Si- 

 beria (Grigor'yev, 1936), Parroquia-Magistral and 

 La Sirena in Mexico (Gonzalez Reyna, 1950), Falun, 

 Garpenberg, Saxberget, Stollberg, Ammeberg, and 

 other mines in Sweden (Magnussen, 1950), Trepi^a 

 in Yugoslavia (Forgan, 1950), and possibly the 

 Darwin mine in California (Hall and MacKevett, 

 1962). In some of these deposits lead is merely a 

 coproduct or byproduct of zinc, copper, silver, or 

 other metal. 



The spatial and temporal relations of contact 

 pyrometasomatic ore deposits with nearby intru- 

 sions indicate that hot, metal-enriched solutions rose 

 steeply within the fractured margins of the plutons 

 and spread laterally into the fractured and brecci- 

 ated wallrocks. Where these wallrocks consisted of 

 argillaceous and arenaceous limestone and dolomite, 

 they were commonly converted to skarn and were 

 also locally replaced by sulfide minerals and mag- 

 netite. The intimate association of galena, spha- 

 lerite, chalcopyrite, and other sulfide and oxide min- 

 erals with anhydrous garnet and pyroxene minerals 

 and the thermodynamic stability of these metallic 

 minerals above 600°C (Holland, 1965, p. 1140-1147) 

 both indicate a depositional environment with 

 temperatures and pressures not far below the solidi- 

 fication temperatures and pressure of the associated 

 igneous rocks. These temperatures and pressures 

 are above the critical constants for water, indicating 

 deposition from supercritical solutions. It is recog- 



