The ore genesis of the Shagou Ag-Pb-Zn deposit in the Southern North China Craton: Constraints from He-Ar-Pb isotopes and trace element compositions of sphalerite

Abstract

Shagou is one of the largest Ag-Pb-Zn deposits with the highest grade of Ag (Ag 1754 t @284 g/t Ag, locally up to 20,000 g/t) in the Southern North China Craton. Four mineralization stages have been identified, with assemblages of: (I) quartz + siderite + pyrite, (II) quartz + dark-brown sphalerite + fine galena + silver minerals, (III) quartz + ankerite + light-brown sphalerite + coarse galena + silver minerals, and (IV) quartz + calcite (IV). Silver minerals were mainly deposited during stage III, in which polybasite and freibergite were the dominant Ag-bearing ore minerals. He-Ar isotope compositions suggest that the ore-forming fluids of the Shagou deposit were derived from a mix of crustal and mantle sources. In situ Pb isotope comparison with regional strata, magmatic rocks, and sulfides from nearby ore deposits indicate that Pb and other metals (e.g., Ag and Zn) of the Shagou deposit originated from both the Mesozoic granite, the surrounding Taihua Group and the Meso-Neoproterozoic marine sediments. LA-ICP-MS analyses revealed that the Ag content of the dark-brown sphalerite was one order of magnitude higher than that of the light-brown sphalerite, suggesting that fluid cooling coupled with decreases in logfO2 and logfS2 were the major factors that promoting extensive Ag deposition. Dark-brown and light-brown sphalerites were enriched in In (up to 474 ppm), consistent with magmatic-related deposits. The newly obtained data in this study, combined with previous results, support a magmatic-hydrothermal origin for the Shagou Ag-Pb-Zn deposit.