ZINC 



703 



district in California (Hall and MacKevett, 1962). 

 Elsewhere in the world significant production has 

 been won from this type of deposit at the Kamioka, 

 Nakatatsu, Chichibu, and other mines in Japan, as 

 well as at mines in northern China and Siberia. The 

 Kamioka mine is the largest zinc-producing mine in 

 Japan, yielding more than 25 percent of the coun- 

 try's annual zinc output. Other contact deposits pro- 

 ducing zinc are in the Trepca district of Yugoslavia 

 and in Sweden and Mexico. 



IRREGULAR REPLACEMENT DEPOSITS AND ASSOCIATED 

 FISSURE FILLINGS 



In many mining districts the typical contact- 

 metamorphic deposits just described are displaced 

 outward or upward from the intrusive contact by 

 deposits of obviously lower temperature. These de- 

 posits are irregularly shaped and are associated 

 closely with filled fissures in either carbonate or 

 clastic rocks. For the most part they appear to be 

 both spatially and genetically related to intrusive 

 igneous stocks of intermediate to acidic composition. 

 Most are confined to zones where favorable strata 

 are crossed by structural breaks. Some lie along 

 veins, but irregular replacement bodies may extend 

 considerable distances into certain beds of the wall 

 rocks away from the veins. Locally, these bedded 

 replacement bodies may be overlain and underlain 

 by impervious shale or other less reactive rocks and 

 may somewhat resemble the various stratabound 

 deposits described below. They differ, however, in 

 that they may occur throughout the local strati- 

 graphic sequence as bedded replacements associated 

 with adjacent veins, or as replacement bodies in 

 pipelike structures that transgress the section. Ore 

 from this type of deposit is more like that of ore 

 in the classic vein deposits (described later) and 

 contains, in addition to zinc and lead, appreciable 

 quantities of copper, silver, and gold. Typical of 

 these deposits in the United States are the silver- 

 lead-zinc ores mined in the Park City, Bingham, and 

 Tintic districts of Utah, at Leadville and Gilman, 

 Colo., and in the Eureka district of Nevada. Else- 

 where, examples include deposits in the Santa Eulalia 

 and similar districts in Mexico, and in central Peru. 

 (See Barnes and Simos, 1968; Rubright and Hart, 

 1968; Bush and others, 1960; Morris, 1968; Em- 

 mons and others, 1927 ; Radabaugh and others, 1968 ; 

 Nolan and Hunt, 1968; Horcasitas and Snow, 1956; 

 and Peterson, 1965.) 



VEIN DEPOSITS 



Veins are tabular ore bodies that fill faults or 

 joints. The ore and accompanying gangue minerals 

 either fill former open spaces along the fractures or 



replace the wall rock; commonly both modes of oc- 

 currence are recognized. Veins are narrow in width 

 as compared with their length and depth; most 

 have sharply defined walls. Zinc-bearing veins are 

 not uniform in their metal content, and many have 

 yielded more significant values in lead, copper, silver, 

 and gold. Zinc-bearing veins are found in most kinds 

 of rocks, although commonly they occur in igneous 

 rocks or in rocks near igneous contacts. Veins con- 

 taining sphalerite apparently form in a wide range 

 of temperature and pressure conditions that are 

 dependent upon the geologic environment. The min- 

 erals of the higher temperature veins may resemble 

 those of the contact-metamorphic deposits, whereas 

 the minerals of the intermediate to lower tempera- 

 ture veins will be generally similar to those in the 

 lower temperature replacement deposits. 



In the United States, important zinc-bearing veins 

 have been mined in the Coeur d'Alene district of 

 Idaho (Hobbs and Fryklund, 1968) , at Butte, Mont. 

 (Meyer and others, 1968), and at numerous locali- 

 ties in Colorado. Additional important zinc vein 

 deposits occur elsewhere in the Western United 

 States in many districts that are perhaps better 

 known for other types of deposits. Well-known simi- 

 lar veins are found in several districts of central 

 Europe, Italy, Mexico, and Peru. As widespread as 

 vein deposits containing zinc apparently are, only 

 a small portion of the world's production has been 

 won from them, and they do not contain a signifi- 

 cantly large part of the world's reserves and re- 

 sources. (See also various papers in Ridge, 1968.) 



STRATABOUND DEPOSITS IN METAMORPHIC ROCKS 



Massive deposits of zinc-lead and zinc-copper ores 

 occur in metamorphic rocks throughout the world. 

 They consist, for the most part, of aggregates of 

 pyrrhotite and pyrite accompanied by sphalerite, 

 galena, and chalcopyrite. The ore bodies are lenticu- 

 lar masses parallel to stratification in enclosing 

 metamorphosed sedimentary and interbedded vol- 

 canic rocks. Although deposits of this type are locally 

 discordant to bedding or fill fissures that cut across 

 the bedding or foliation, many evidently were origin- 

 ally bedded replacement deposits that were subse- 

 quently metamorphosed and folded. Some deposits of 

 this type are in highly folded and faulted rocks, and 

 although the ore replaces the host rock, the domi- 

 nant feature of its control may be the faults and 

 folds. These deposits include the largest concentra- 

 tions of zinc-lead and zinc-copper ores that are 

 known. Typical are those in the Broken Hill and 

 Mount Isa districts of Australia, the Sullivan mine 

 in British Columbia, the Bathurst district in New 



