Constraints on the genesis of the Wangjiawan gold deposit, northeast Hunan district, Jiangnan Orogen: Evidence from fluid inclusions and H-O-S-Pb isotopes

Abstract

The recently discovered Wangjiawan gold deposit in NE Hunan, central Jiangnan Orogen, primarily features orebodies composed of quartz veins and altered slates. The orebodies are controlled by faults and hosted by low-grade metamorphosed Neoproterozoic Lengjiaxi Group. Mineralization can be divided into three stages: quartz–pyrite–arsenopyrite, quartz–dolomite–polymetallic sulfide–gold, and quartz–carbonate veins. Three types of fluid inclusions were identified using fluid inclusion microthermometry and Raman spectroscopy: H2O-CO2-NaCl (type 1), CO2-rich aqueous (type 2), and aqueous fluid inclusions (type 3). Petrographic and microthermometric analysis revealed that the homogenization temperatures for stages 1, 2, and 3 were 308–340, 219–285, and 154–198 °C, respectively, with corresponding salinities of 4.1–7.8, 2.2–8.3, and 2.0–4.0 wt% NaCl equiv. δ18Ofluid values vary from 0.0 ‰ to 10.3 ‰, and δD values from –57.9 ‰ to –50.0 ‰, suggesting a metamorphic source. Fluid immiscibility and fluid-rock interactions likely played a crucial role in gold precipitation during the main ore stage. For stage 1 and stage 2, the δ34S values of sulfides are –4.49 ‰ to –0.66 ‰ and –9.20 ‰ to –6.24 ‰, respectively,indicating sulfur isotopes originate from the Neoproterozoic metasedimentary rocks. The sulfides Pb isotope compositions (206Pb/204Pb = 17.722–18.490, 207Pb/204Pb = 15.650–15.810, and 208Pb/204Pb = 37.732–39.343) imply that the lead originated from deep metasedimentary rocks. H-O-S-Pb isotopic data suggest that the ore-forming fluids and materials of the Wangjiawan gold deposit were sourced from a deeper and higher metamorphic grade source. The Wangjiawan deposit exhibits characteristics of orogenic gold deposits.