Abstract:Located in northwest Liaoning, the Baijiazi lead-zinc deposit occurs at the contact between the Yanshanian biotite-quartz diorite and dolomite of Sinian Gaoyuzhuang Formation as well as in the NW-trending fault zone within the neighbouring carbonate wall rocks.The ore-related biotite-quartz diorite is of calcic-alkaline series rich in alkali and volatiles, with the whole-rock K-Ar age being 170 Ma, indicating that the alkaline metasomatism must have played an important role in mineralization. Based on a study of spatial distribution of skarns, mineral assemblage and geochemical characteristics of skarn minerals, the author, has divided the skarns in ore district into magnoskarn, calciskarn and manganese calcskarn from the contact outward, with their representative minerals being forsterite-diopside-chondrodite, andradite-salite-epidote, and thodonite-spessartine respectively, and their associated mineralization being magnetization, magnetite-pyrite and pyrite orebodies and pyrite-lead, zinc and lead-zinc orebodies, respectively. They show zoned distribution from the contact outward or from the fault zone northwestward. From magnoskarn zone to manganese calciskarp zone, crystalline form of pyrite in ores varies from xenomorphic irregular grains through pentagonal-dodecahedron to cube; metallogenic element assemblages gradually change from Fe-Mo to Fe-Cu-Zn-Pb and finally to Pb-Zn-Ag, and with the increasing lead-zinc contents, manganese also uninterruptedly increases, whose content may the refore indicates lead-zinc grade in the ore; skarn mineral assemblage evolve from forsterite-diopside to andradite-salite and end in spessartine-rhodonite, accompanied by the variation of mineral assemblages in order of magnetite-molybdenite→magnetite -pyrrhotite-pyrite –chalcopyrite→pyrite-galen a-sphalerite→galena-sphalerite-silve- bearing minerals. According to the relationship of skarnization to mineralization, the minerogenic process might be divided into skarn, hydrothermal and supergene phases with the second phase subdivided into magnetite, quartz-sulfides and carbonate-sulfate stages. As for the formation temperature, it is inferred that the skarn stage is above 500℃ with manganese calciskarn somewhat lower, the magnetite stage 400℃ or so, the quartz-sulfides stage 300-400℃, and the carbonate-sulfate stage 170-300℃. From temperature, mineral assemblage and FeS content, LogfO2 is estimated to be some -25 at the magnetite stage, -26- -30 at the quartz-sulfides stage and lower than -30 at the sulfate stage, implying the slight decrease of log fO2 in solutions from the magnetite stage to the sulfate stage. An integrated analysis of the above data has led the author to believe that the Bajiazi lead-zinc deposit is of skarn type. The progressively decreasing temperature, the regular variation of fO2 and other physicochemical conditions, and the differential behaviors of magnesium, calcium, manganese, and iron, molybdenuir, copper, zinc, lead and silver during the evolution of ore fluids resulted in the spatial zonation of mineralization and alteration.
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董永观.1986.八家子铅锌矿矿化蚀变分带特征[J].矿床地质,5(4):82~93.1986.Characteristics Of Alteration And Mineralization Zoning In The Bajiazi Skarn Lead-Zinc Deposit[J].Mineral Deposits5(4):82~93
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