Multiple sources for the Baoshan polymetallic Cu–Mo–Pb–Zn deposit, southern Hunan Province, China: Insights from in situ LA–MC–ICP–MS sulfur isotopic compositions

Abstract

Southern Hunan Province, China, is characterized by extensive Mesozoic magmatic rocks and coeval polymetallic deposits, including granite-related W–Sn and granodiorite-porphyry-related Cu–Mo–Pb–Zn mineralization. It is commonly accepted that ore-forming materials for Cu–Mo–Pb–Zn mineralization in the southern Hunan area were generally dominated by granodiorite porphyry, owing to the close spatial and temporal relationship between the two. However, the detailed mineralization process for this type of deposit remains unclear, especially with respect to the relationship between the proximal skarn-hosted Cu–Mo and distal carbonate-hosted Pb–Zn mineralization. In this study, high-resolution in situ LA–MC–ICP–MS sulfur isotopic compositions for different types of sulfide from the typical Baoshan polymetallic Cu–Mo–Pb–Zn deposit are used to investigate the characteristics of mineralization in this area. Our results show that three endmembers with distinct δ34S values contributed to the formation of the Baoshan deposit: (1) granodiorite porphyry with moderate δ34S values (2.6‰ to 3.7‰), (2) carbonate strata with high δ34S values (3.8‰ to 22.7‰), and (3) metamorphic or crystalline basement with low δ34S values (−7.0‰ to 4.5‰). Molybdenite from the proximal skarn-hosted Mo mineralization has high δ34S values ranging from 3.6‰ to 6.6‰, whereas pyrite (−1.0‰ to 4.8‰), chalcopyrite (−1.1‰ to 4.4‰), sphalerite (1.9‰ to 4.2‰), and galena (0.2‰ to 4.8‰) from both the proximal skarn-hosted and distal carbonate-hosted Cu–Pb–Zn mineralization have wide-ranging δ34S values depending on their locations. These values suggest that the granodiorite porphyry and carbonate sources dominated the sulfur input for the entire Mo mineralization and that the granodiorite porphyry source dominated most of the Cu–Pb–Zn mineralization with similar or higher δ34S values in the Baoshan deposit, with some contribution from the carbonate strata for the latter mineralization. Deep-seated metamorphic or crystalline basement likely provided sulfur for the other parts of the Cu–Pb–Zn mineralization with low δ34S values. In addition to the contributions by granodiorite porphyry and carbonate strata, our study emphasizes the substantial contribution of basement rock materials to Cu–Mo–Pb–Zn mineralization. The ore-forming materials accumulated in the basement by the intrusion of early mafic magmas, which were then added to the Baoshan granodioritic magmas by remelting and mingling with these magmas. Ore-forming materials may also have been extracted from the basement by hydrothermal circulation triggered by the intrusion of these late granodioritic magmas.