In-situ S and Pb isotope constraints on an evolving hydrothermal system, Tianbaoshan Pb-Zn-(Cu) deposit in South China

Abstract

The Upper Yangtze Pb-Zn metallogenic province in South China consists of >400 carbonate-hosted Pb-Zn deposits within Neoproterozoic to Paleozoic strata. Origin of these deposits has been a matter of debate and is thought to be related to Proterozoic basement rocks, Paleozoic sedimentary rocks and the late Permian flood basalts of the Emeishan large igneous province (ELIP). The Tianbaoshan Pb-Zn-(Cu) deposit contains ~22Mt Pb-Zn ores @ 1.43 wt% Pb and 10.4 wt% Zn, and ~0.1Mt Cu ores @ 2.55 wt% Cu. Copper sulfide ores are composed dominantly of chalcopyrite and tetrahedrite, whereas Pb-Zn sulfide ores consist mainly of sphalerite and galena with minor chalcopyrite and tetrahedrite. In-situ δ34S values (+3.2–+4.6‰) of chalcopyrite in the Cu ores are similar to the bulk δ34S values (+3.9–+5.4‰) of chalcopyrite separates from the Cu ores and sphalerite separates (+1.7–+3.9‰) from the Pb-Zn ores. Such a sulfur isotope signature indicates that reduced sulfur of both the Cu and Pb-Zn ores was derived from a mixed source of magmatic sulfur (derived from igneous rocks) and sedimentary sulfur or evaporated marine sulfate by thermochemical sulfate reduction (TSR). In-situ Pb isotopic ratios of chalcopyrite grains in the Cu ores are similar to those of galena grains from both the Cu and Zn-Pb ores, suggesting that they have the same metal sources. Hence, our study demonstrates that both the Cu and Pb-Zn ores were co-genetic and their mineralizing elements were derived from or flowed through a mixed source of basement rocks and sedimentary rocks, and even basalts. The Tianbaoshan Pb-Zn-(Cu) deposit is an epigenetic sulfide deposit hosted in carbonate rocks and was formed from an evolving hydrothermal system from Cu to Pb-Zn.