Geology, fluid inclusion, and stable isotope study of the skarn-related Pb–Zn (Cu–Fe–Sn) polymetallic deposits in the southern Great Xing’an Range, China: implications for deposit type and metallogenesis

In recent decades, several skarn-related deposits have been found and explored in the southern Great Xing’an Range of China. To get a clear understanding of the characteristics and genetics of this type of deposit in this area, three of the largest, most typical, and most famous skarn-related deposits (Haobugao Pb–Zn deposit, Huanggang Sn–Fe polymetallic deposit, and Baiyinnuoer Pb–Zn deposit) are selected for systematically metallogenic study in this paper. The results of ore geology, fluid inclusion, and stable isotopes indicate that (1) most of the ore bodies of each deposit, occurred in the outer contact zone of the magma intrusion and Permian strata, fine vein disseminated mineralization within the intrusions were also found in this study. Mineralization of these deposits all show closely temporal, spatial, and genetic relationships with skarns. (2) Fluid inclusion petrography and microthermometry results show that the fluid inclusion assemblages developed in the different mineralization stages of each deposit changed from Type-S (daughter mineral-bearing three-phase fluid inclusions) + Type-V (vapor-rich fluid inclusions) + Type-L (liquid-rich fluid inclusions) to Type-V + Type-L and eventually evolved into L-Type. Correspondingly, the ore-forming fluids changed from medium to a high-temperature, high-salinity, and boiling fluid system and then to a low-temperature, low-salinity, and uniform fluid system. The types of fluid inclusions in garnets are consistent with those in quartz phenocrysts of Mesozoic granites, indicating that the formation of skarns is directly related to Mesozoic magmatic activity. (3) The δ34S values of ores from the above three deposits all exhibit a narrow variation range (changes are mainly around 0‰) and greatly differ from the SEDEX-type deposits in China. The lead isotope compositions of the sulfide minerals are also consistent with those of Mesozoic granites. These previous characteristics suggest that both of the ore-forming fluids and the ore-forming materials were of magmatic origin. Consequently, the Haobugao, Baiyinnuoer, and Huanggang deposits are all skarn-type deposits, which are related to Mesozoic magmatic activities in terms of ore geology features, ore-forming fluids, and ore-forming material.