Genesis of the Taolin Pb-Zn deposit in northeastern Hunan Province, South China: constraints from trace elements and oxygen-sulfur-lead isotopes of the hydrothermal minerals

Abstract

Located in the northeastern Hunan Province of South China, the Taolin Pb-Zn deposit is one of many metallic deposits structurally controlled by extensional faults in the central segment of the Jiangnan Orogen. The deposit occurs in a tectonic breccia zone between the Mufushan pluton and the Neoproterozoic Lengjiaxi Group. Field and microscopic observations reveal that the hydrothermal ore-forming processes at Taolin can be divided into five stages, from early to late: (1) coarse-grained quartz, (2) quartz + fluorite + chlorite + claybank sphalerite (Sp1) + galena + chalcopyrite, (3) quartz + barite + pale-yellow sphalerite (Sp2) + galena + chalcopyrite, (4) quartz ± chalcopyrite, and (5) fine-grained quartz, in which the stages 2 and 3 are regarded as the main Pb-Zn-forming events. LA-ICP-MS analyses show that Sp1 has higher contents of Fe, Mn, Co, In, and Sn, but lower contents of Ge and Sb, relative to the Sp2. Trace element concentrations of the sphalerite suggest a medium-low temperature hydrothermal event dominated in the Taolin deposit and that the ore fluids gradually decreased in the estimated average temperature and became relatively oxidized from stages 2 to 3. The δ18O values of ore fluids calculated from in situ analysis on the stages 2 and 3 quartz suggest the ore fluids are from a mixture of magmatic and meteoric waters. The δ34S values of sulfides/sulfates from stages 2 and 3 mineralization indicate a dominating magmatic affinity for sulfur. Further, lead isotope compositions for the stages 2 and 3 sulfides are similar to those of the Mufushan pluton, indicating that the ore metals may have been derived from the latter. We thus propose that the Taolin deposit precipitated from a medium-low temperature magmatic-hydrothermal system most likely related to the Mufushan pluton.