Genesis of the Huangshaping W–Mo–Cu–Pb–Zn polymetallic deposit in Southeastern Hunan Province, China: Constraints from fluid inclusions, trace elements, and isotopes

Abstract

The Huangshaping polymetallic deposit is located in southeastern Hunan Province, China. It is a world-class W–Mo–Pb–Zn–Cu skarn deposit in the Nanling Range Metallogenic Belt, with estimated reserves of 74.31Mt of W–Mo ore at 0.28% WO3 and 0.07% Mo, 22.43Mt of Pb–Zn ore at 3.6% Pb and 8.00% Zn, and 20.35Mt of Cu ore at 1.12% Cu. The ore district is predominantly underlained by carbonate formations of the Lower Carboniferous period, with stocks of quartz porphyry, granite porphyry, and granophyre. Skarns occurred in contact zones between stocks and their carbonate wall rocks, which are spatially associated with the above-mentioned three types of ores (i.e., W–Mo, Pb–Zn, and Cu ores).Three types of fluid inclusions have been identified in the ores of the Huangshaping deposit: aqueous liquid–vapor inclusions (Type I), daughter-mineral-bearing aqueous inclusions (Type II), and H2O–CO2 inclusions (Type III). Systematic microthermometrical, laser Raman spectroscopic, and salinity analyses indicate that high-temperature and high-salinity immiscible magmatic fluid is responsible for the W–Mo mineralization, whereas low-temperature and low-salinity magmatic-meteoric mixed fluid is responsible for the subsequent Pb–Zn mineralization. Another magmatic fluid derived from deep-rooted magma is responsible for Cu mineralization.Chondrite-normalized rare earth element patterns and trace element features of calcites from W–Mo, Pb–Zn, and Cu ores are different from one another. Calcite from Cu ores is rich in heavy rare earth elements (187.4–190.5ppm), Na (0.17%–0.19%), Bi (1.96–64.60ppm), Y (113–135ppm), and As (9.1–29.7ppm), whereas calcite from W–Mo and Pb–Zn ores is rich in Mn (>10.000ppm) and Sr (178–248ppm) with higher Sr/Y ratios (53.94–72.94). δ18O values also differ between W–Mo/Pb–Zn ores (δ18O=8.10‰–8.41‰) and Cu ores (δ18O=4.34‰–4.96‰), indicating that two sources of fluids were, respectively, involved in the W–Mo, Pb–Zn, and Cu mineralization.Sulfur isotopes from sulfides also reveal that the large variation (4‰–19‰) within the Huangshaping deposit is likely due to a magmatic sulfur source with a contribution of reduced sulfate sulfur host in the Carboniferous limestone/dolomite and more magmatic sulfur involved in the Cu mineralization than that in W–Mo and Pb–Zn mineralization. The lead isotopic data for sulfide (galena: 206Pb/204Pb=18.48–19.19, 207/204Pb=15.45–15.91, 208/204Pb=38.95–39.78; sphalerite: 206Pb/204Pb=18.54–19.03, 207/204Pb=15.60–16.28, 208/204Pb=38.62–40.27; molybdenite: 206Pb/204Pb=18.45–19.21, 207/204Pb=15.53–15.95, 208/204Pb=38.77–39.58 chalcopyrite: 206Pb/204Pb=18.67–19.38, 207/204Pb=15.76–19.90, and 208/204Pb=39.13–39.56) and oxide (scheelite: 206Pb/204Pb=18.57–19.46, 207/204Pb=15.71–15.77, 208/204Pb=38.95–39.13) are different from those of the wall rock limestone (206Pb/204Pb=18.34–18.60, 207/204Pb=15.49–15.69, 208/204Pb=38.57–38.88) and porphyries (206Pb/204Pb=17.88–18.66, 207/204Pb=15.59–15.69, 208/204Pb=38.22–38.83), suggesting Pb206-, U238-, and Th 232-rich material are involved in the mineralization. The Sm–Nd isotopes of scheelite (εNd(t)=−6.1 to −2.9), garnet (εNd(t)=−6.8 to −6.1), and calcite (εNd(t)=−6.3) from W–Mo ores as well as calcite (εNd(t)=−5.4 to −5.3) and scheelite (εNd(t)=−2.9) from the Cu ores demonstrate suggest more mantle-derived materials involved in the Cu mineralization.In the present study we conclude that two sources of ore-forming fluids were involved in production of the Huangshaping W–Mo–Pb–Zn–Cu deposit. One is associated with the granite porphyry magmas responsible for the W–Mo and then Pb–Zn mineralization during which its fluid evolved from magmatic immiscible to a magmatic–meteoritic mixing, and the other is derived from deep-rooted magma, which is related to Cu-related mineralization.