科研之友
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摘要
The Dabaozhuang pyrite deposit is located in the western margin of the Luzong Mesozoic volcanic basin in eastern China and has distinct metallogenic characteristics compared to known types of massive pyrite deposits. In addition to pyrite, ores of the deposit contain a significant amount of gypsum/anhydrite. However, the mineralization processes are poorly understood and the genesis of the deposit remains controversial. In an attempt to better understand the deposit, we conducted SHRIMP in-situ oxygen and sulphur isotope analysis for quartz, anhydrite, and pyrite, as well as LA-ICP-MS trace element analysis for pyrite. The & delta;18O value of quartz in the silicified tuff indicates inheritance of oxygen isotope characteristics from host volcanic rocks. The & delta;18O values of quartz grains from massive pyrite ores suggest the involvement of a substantial amount of meteoric water in the ore-forming fluids. The sulphur isotopes of the pyrite in the deposit were affected by thermodynamic and redox kinetic fractionation, making the pyrite-anhydrite S isotope thermometer unsuitable for determining the ore-forming temperature. The mineral assemblages of fluorite and native sulphur suggest that the transition from pyrite to anhydrite occourred at temperatures above 130 celcius, with a pH value between 2 and 5. The Dabaozhuang deposit shares similarities with VMS deposits in terms of orebody shape, ore structure, mineralization temperature, pH value, and oxygen fugacity. The main difference lies in the fertility of the magmatic-hydrothermal fluid. Further research is necessary to explore this type of deposit in the volcanic apparatus near polymetallic deposits.
