The Metallogenic Mechanism Of Zijinshan Cu-Au Deposit, Fujian

Zijinshan mineral field is a large porphyry-epithermal Cu-Au-Mo-Ag mineralizationsystem located in thesouthwestern Fujian province, which containsLuoboling porphyry Cu-Mo deposit, Zijinshan high-sulfidation epithermalCu-Au deposit and Yueyang low-sulfidationepithermalAg-Au-Cu deposit, etc. The ZijinshanCu-Au depositis the China’s largest high-sulfidation epithermal Cu-Au deposit, with the Zijinshan granite being the wall rock and vocanic rocksof the late Yanshanian related to mineralization. LA-MC-ICP-MS zircon U-Pb dating results and petrol geochemical characteristicsshow that the Zijinshan graniteformed in Middle-Late Jurassic (165-157Ma), and belongs to high potassium or shoshonitic series, with the characteristics of volcanic-arc granite or active continental margin granite. Sr-Nd-Pb-Hf isotopic features show that the granite was originated from Paleoproterozoic basement crust material. The intrusive-volcanic rocks related to the Cu-Au-Mo-Ag mineralization were formed in102to112Ma, and belongs to high potassium or shoshonitic series, with the characteristics of volcanic-arc granite or active continental margin granite. Sr-Nd-Pb-Hf isotopic features suggested that they were derived from the mixing of partial melting of the Mesoproterozoic basement and mantle-derived melts.According to the analysis of fluid inclusions in quartz veins, the ore-forming fluids of copper ore body in Zijinshan Cu-Au deposit was CO2-H2O-NaCl system, with the late stage of evolution simple H2O system. The homogeneous temperatures of ore fluid change from320～380℃to240～320℃. and finally to160～200℃, with the salinities from3.06～14.57NaCl.eqv to1.91～33.48NaCl.eqv, and to3.87-10.49NaCl.eqv respectively. Higher homogenization temperature display deep copper mineralization may not belong to the epithermal-type and reflect mineralization may be directly related to magmatic. The hydrogen and oxygen isotopic composition of quartz in Zijinshan Cu-Au deposit suggest that the ore-forming fluid was mainly derived from magmatic water, mixing a small amount of meteoric water, while the hydrogen and oxygen isotopic composition inYueyang deposit imply that the ore-forming fluid was mainly derived from meteoric water, mixing a small amount of magmatic water. The sulfur and lead isotopic characteristics of various metallic sulfides in Zijinshan Cu-Au deposit suggest that the ore-forming materials were mainly dereived from the magma, mixing a small amount of crustal base material, and the ore-forming materialsof Yueyang deposit derived from the magma and sedimentary wall rocks or crustal basement. It is therefore suggested that the Middle-Late Jurassic and the Early Cretaceous magmatic rocks in the Zijinshan region are the result of an active continental-margin setting related to the subduction of thePaleo-Pacific Plate beneath the Eurasian continent. Because of the continuous subduction andmixing of mantleand ancient oceanic crustmaterial, it makes a large-scale mineralization beganin the Zijinshan regionfrom106Ma (Re-Os age of the molybdenite from the Luoboling Cu-Mo deposit) to92Ma.