Redox states and protoliths of Late Mesozoic granitoids in the eastern Jiangnan Orogen: Implications for W, Mo, Cu, Sn, and (Au) mineralization

Abstract

• Late Mesozoic granites in eastern Jiangnan Orogen include 154–136 and 136–126 Ma. • Zircon and biotite parameters reveal redox state of Late Mesozoic granitoids. • Early stage granitoids originate from metasedimentary & volcanic–sedimentary rocks. • Late stage granitoids originate from anatexis with various mantle-derived melts. • Magmatic redox states and protoliths controlled the diverse mineralization . Late Mesozoic magmatism is extensively developed in the eastern Jiangnan Orogen and is closely related to W, Mo, Cu, Au, and Sn mineralization. Late Mesozoic granitoids show various petrological and mineralizing features that vary spatially (northern Jiangxi Province and southern Anhui Province) and temporally (early stage: 154 to 136 Ma, late stage: 136 to 126 Ma). In this study, we analyzed zircon trace element data from four Late Mesozoic granitoids. Together with published zircon trace element data and biotite compositions from granitoids in the eastern Jiangnan Orogen and W–Sn, Mo and Cu deposits, we use these data to determine the magmatic redox state of the Late Mesozoic granitoids, which is useful in determining mineralization competency and is instructive during exploration. The results show that early stage granitoids of southern Anhui Province are oxidized, characterized by high zircon Ce 4+ /Ce 3+ (median = 278), Ce/Nd (median = 17.1), and Eu N /Eu N * (median = 0.42) ratios, and high biotite Fe 3+ /Fe 2+ ratios (median = 0.23) and X Mg values (median = 0.48). The late stage granitoids of southern Anhui Province are relatively reduced, showing lower zircon Ce 4+ /Ce 3+ (median = 49.7), Ce/Nd (median = 12.7), and Eu N /Eu N * (median = 0.16) ratios, and lower biotite Fe 3+ /Fe 2+ ratios (median = 0.11) and X Mg values (median = 0.38). The early stage granitoids of northern Jiangxi Province show a somewhat reduced redox state. They have comparatively low zircon Ce 4+ /Ce 3+ (median = 17.28), Ce/Nd (median = 4.50), and Eu N /Eu N * (median = 0.17) ratios, and comparatively low biotite Fe 3+ /Fe 2+ ratios (median = 0.07, N = 160) and X Mg values (median = 0.35). The late stage granitoids of northern Jiangxi Province are strongly reduced, characterized by low zircon Ce 4+ /Ce 3+ (median = 17.03), Ce/Nd (median = 0.72), and Eu N /Eu N * (median = 0.02) ratios, and low biotite Fe 3+ /Fe 2+ ratios (median = 0.06) and X Mg values (median = 0.25). Geochemical and isotopic data reveal that early stage granitoids in northern Jiangxi Province were sourced from Neoproterozoic metasedimentary rocks, whereas those in southern Anhui Province originated from Neoproterozoic volcanic–sedimentary sequences. The late stage granitoids in the eastern Jiangnan Orogen formed under an extensional regime and were generated by anatexis with various mantle inputs. The results suggest that early stage granitoids of southern Anhui Province have the potential for Cu (>1 Mt) and Mo (>0.3 Mt) mineralization, whereas late stage granitoids are related to W, Cu (<1 Mt), and Mo (<0.3 Mt). In northern Jiangxi Province, the highly evolved and relatively reduced early stage granitoids have more potential to form large- to super-large-scale W mineralization, with subordinate Cu (<1 Mt) and Mo (<0.3 Mt) mineralization, whereas the similarly reduced and evolved late stage granitoids are closely associated with large- to super-large-scale Sn and W mineralization, with subordinate Cu (<1 Mt) and Mo (<0.3 Mt) mineralization. Different magmatic redox states and protoliths have controlled diverse mineralization in the eastern Jiangnan Orogen.