Geology, Geochemistry And Genesis Of The Caijiaping Lead-Zinc Deposit, North Wuyi Area, Jiangxi Province

The Caijiaping lead-zinc deposit, located in north Wuyi area, Jiangxi Province, is a newfound medium-sized deposit. Sandstones of the Jurassic Shuibei Formation(J1s) and Zhangping Formation(J2z) are the wall rocks of orebodies. The lead-zinc orebodies usually occur in the crush belts beside the fractures, and often exist in boundary surfaces of rhyolite porphyries and sandstones. On the basis of field work, by means of observation of microscope and analysis of electron probe, this paper researches main sulfide minerals of the deposit at great length. Ore-forming process is preliminarily divided into sedimentary mineralization period, magmatic hydrothermal period and hypergene period. Magmatic hydrothermal period consists of medium-high temperature pyrite-sphalerite stage, medium-low temperature quartz-polymetallic sulfide stage and carbonate stage. Medium-high temperature pyrite-sphalerite stage is characterized by medium and large-grained hypautomorphic-automorphic pyrite+ christophite, which can reflect higher formation temperature. The alteration of this stage is epidotization. Medium-low temperature quartz-polymetallic sulfide stage, which is major metallogenetic stage, has a major ore mineral association consisting of pyrite+sphalerite+chalcopyrite+galena. The major alteration of this stage is silification, chloritization and sericitization. The data of electron probe indicates that following the mineralization, sulfur was more and more deficient.According to the trace element geochemistry of galena and sphalerite, mineralization mainly resulted from magmatic hydrothermal process superimposed on layer-controlling action and sedimentation- metamorphism, what indicates that the mineralization of this deposit is polygenous. The bedding and incision orebodies we found in the field imply that the origin and the type of the lead-zinc orebodies are not single. Sulfur isotopic analysis indicates that the sulfur of the Caijiaping deposit is mainly magmatic sulfur in origin, possibly mixed with mantle-derived magma, and the sulfur isotope was approximately on balance when metallogenic materials were precipitated. Lead isotopic analysis reveals that ore-forming materials are derived from rhyolite porphyries and sandstones, and the metallogenic elements are crust-mantle mixed type.Geochemical analysis indicates that the tectonic setting of provenance of sandstones is continental margin, and diagenetic provenance is related with Wuyi metamorphosed basement. Rhyolite porphyries are high potassium calc-alkaline S-type granite, which come from remelting of Wuyi metamorphosed basement.The geologic thermometers of chlorite, cadmium and sulfur isotope show that the temperature of mineralization is 292.3℃~490.6℃, which is medium-high temperature and is consistent with the result of the trace element analysis.Additionally, it is found that the fault F4 cuts orebodies in the field, and the potash feldspar selected from felsic vein within F4 yields a 40Ar /39Ar age of 120±4 Ma, implying the mineralization of the Caijiaping deposit should be occurred before 120±4 Ma. Combining with the former research results of predecessors, the authors speculate the age of mineralization was 138~120 Ma, corresponding with extensional mineralization stage of the South China area.According to the researches above, the Caijiaping lead-zinc deposit, was formed in Lower Cretaceous during extensional mineralization stage of the South China area. It is a medium temperature hydrothermal deposit, which mainly resulted from magmatic hydrothermal process. According to the basis of field work, the former research results of predecessors and isotope analysis, we think the sandstones are source bed, and layer-controlling action also controlled the formation of the deposit. Wuyi metamorphosed basement contributed a great deal to the diagenetic and metallogenic process.