Metallogenic system of Shapinggou porphyry molybdenum-hydrothermal lead-zinc deposit in Dabie orogeny belt: Constraints from fluid inclusions and stable isotope

The Shapinggou molybdenum deposit, located in Jinzhai County, Anhui Province, China, is the second largest porphyry molybdenum deposit in the world. Several Pb-Zn deposits have been discovered in the periphery of Shapinggou Mo deposit, such as Yinshan and Gaijing deposits, but their genetic relationship with porphyry Mo deposit is misunderstood. In this work, we base on data from field work investigation combined with laboratory analyses data such as fluid inclusions petrography, microthermometry, laser Raman microprobe and stable isotopes to characterize the source and evolution of Shapingguo porphyry Mo deposit and surrounding Yinshan Pb-Zn deposits in order to establish a genetic relationship between both deposits. Petrography fluid inclusion of lithofacies from Shapinggou porphyry Mo deposit reveals 3 types of fluid inclusions including gas-liquid phase inclusions (AV), CO2-rich three phase inclusions (AC), and crystalline-bearing inclusions (ADV), developed in three stages of mineralization. In the early stage of mineralization, the homogeneous temperature of fluid inclusions ranges from 325 to 420℃ with relatively low salinity of AV and AC types ranging from 0.8% to 15.4% NaCleqv and moderately high salinity of ADV type ranging from 33% to 46% NaCleqv. In the middle stage of mineralization, AV, AC and ADV have uniform temperature at around 226-367℃ with low salinity of AV and AC types ranging from 0.4% to 13.2% NaCleqv and relatively high salinity of ADV type ranging from 33.3% to 39.6% NaCleqv. The late stage of mineralization develops AV type of fluid inclusion with homogeneous temperature ranging from 185 to 300℃, and the salinity ranges from 0.7% to 8.4% NaCleqv. However, in the Yinshan Pb-Zn deposits, only one stage of mineralization has been developed and displaying AV fluid inclusions. The homogeneous temperature of fluid ranges from 175 to 315℃ with salinity of 0.6%-4.9% NaCleqv, which correspond to the late stage of Shapinggou porphyry Mo deposit. It clearly appear that the homogeneous temperature and salinity decrease from the earlier to the late stage of mineralization. H-O isotope results of water in fluid inclusions show that the early stage fluid of Shapinggou Mo deposit is principally originated from magmatic source, while in the late stage of Pb-Zn mineralization, the ore-forming hydrothermal fluid is a mixture of magmatic water and meteoric water, similar to H-O isotopes of water in quartz fluid inclusions in the main metallogenic stage of Yinshan Pb-Zn deposit. It appears that the early hydrothermal fluid was originated from magmatic source with a small amount of meteoric water, which has, therefore, gradually increased during the middle and late stage of mineralization. S-isotope data indicated that sulfur of the two deposits derives from deep magmatic source and Pb-isotope, however, has characteristic of crust-mantle mixed source. The characteristics of S, Pb, H, O isotopes and fluid inclusions indicate that, the Mo deposits and Pb-Zn deposits in the study area have the same material sources. The ore-forming fluid has an evolution trend from high-temperature-high-salinity magmatic hydrothermal fluid to low-temperature-low-salinity magmatic-meteoric mixed fluid and from CO2-rich to CO2-poor. The Yinshan Pb-Zn deposits around Shapinggou are part of the porphyry metallogenic system. © 2019, Science Press. All right reserved.