云南白牛厂超大型银多金属矿床叠加成矿的地质地化特征

GEOLOGICAL AND GEOCHEMICAL CHARACTERISTICS OF THE BAINIUCHANG SUPERLARGE SILVER POLYMETALLIC DEPOSIT OF SUPERIMPOSED MINERALIZATION, YUNNAN PROVINCE

白牛厂银铅锌硫化物矿体赋存在中寒武统海相细碎屑岩中，白垩纪花岗岩体接触带附近。矿床的形成经历了中寒武世海底喷溢沉积成矿作用和燕山期酸性岩浆热液叠加成矿作用，具多源、多成因和多旋回演化的特点，兼有外生和内生矿床的特征，是我国极具特色的细碎屑岩建造中Ｓｅｄｅｘ型矿床。

Located in the western flank on Nanling Metallogenic Zone, the Bainiuchang deposit was controlled by Middle Cambrian aulacogen and Yanshanian magmatic activities. Orebodies occur in fine grained clastic formation of Middle Cambrain. There are both characteristic features of exogenic and endogenic origins in the Bainiuchang deposit. The main orebodies are in the forms of both stratiform and veins of various dimensions, and some slump structures occur in sulfide accumulations. The mineralogical composition is very complex, and the kinds of the minerals are more than 90. The ore texture and structure are variouss: massive, laminated, clastic related to sedimentary and veinlike, stockwork and brecciated realted to deuterogenic. The sulfides in sedimentary orebodies often show interbedded and rhythmetic textures. The pyrites and the sphalerites are often in the form of granular aggregates with clastic and/or intraclastic features. Some aggregates show abrasion and impaction features, and some show an even more complex history of sedimentation-diagenesis-rewash and redeposition and recementation by microlitic quartz, argillite, sulfide of different generation. The pyrite is characterized by low contents of Co and Ni, and the avarage of the Co/Ni ratio is lower than unity. The S.Se ratio is lower than 2×106. The contents of Fe and In in the splalerites is high but the contents of Ga and Ge is low. The assiterite related to the sedimentation is characterized by high content of In, and the avarage of In is 1.84%. The decrepitation temperatures of the fluid inclusions range from 60℃ to 410℃, and the contents salts range from 3.1% to 10%. the δ34S values of sulfids in orebodies are about -4‰ - +5.5‰ but +18.6‰ - +23.4‰ insrata. The lead is normal lead and anomal lead. Majority of mineralization hydrothermal solution are from seawater and rainfall.