Late Devonian magmatic-hydrothermal Pb–Zn system in South China: redefining the paleozoic metallogenic framework

The Mesozoic tectono-magmatic events have long defined the primary metallogenic framework of South China, whereas the Late Devonian hydrothermal history is sparsely documented, and corresponding ore-forming mechanisms remain poorly understood. This study challenges this paradigm by documenting the Xianping Pb–Zn deposit in Southeast Guangxi, situated within the Qin-Hang Metallogenic Belt (South China). Its hydrothermal evolution consists of four stages: (I) quartz‑sericite stage, (II) quartz‑chalcopyrite‑tetrahedrite‑pyrite, (III) quartz‑pyrite‑galena‑sphalerite, and (IV) quartz‑calcite‑dolomite stages. Stage II is dominated by chalcopyrite and tetrahedrite, with two generations of pyrite: early homogeneous pyrite (Py1) and later porous, inclusion-rich pyrite (Py2) that overgrows and corrodes Py1. Stage III is characterized by Pb–Zn mineralization, featuring core-rim pyrite consisting of a porous, galena-hosting core (Py3) and a compact rim (Py4). Critically, Re–Os geochronology of Stage II chalcopyrite yields an isochron age of 382.5 ± 1.0 Ma (MSWD = 3.1), unequivocally defining a previously underappreciated Late Devonian metallogenic epoch within South China. In-situ sulfur isotope analyses of pyrite reveal a two-stage evolution: early Py1 and Py2 exhibit heavy δ 34 S values (+20.5‰ to + 30.3‰), reflecting sulfur extraction via extensive fluid-rock interaction. In contrast, Py3 and Py4 display a sharp shift to negative δ 34 S values (down to –6.5‰). This dramatic isotopic shift, together with hydrothermal breccias and coexisting barite, indicates that boiling-induced phase separation and sulfate-sulfide isotope fractionation jointly controlled the sulfur isotopic evolution, ultimately triggering the rapid precipitation of Pb–Zn sulfides. Moreover, the Xianping mineralization exhibits diagnostic magmatic-hydrothermal characteristics, as mainly evidenced by the fault-hosted vein geometry, pervasive silicification, magmatic-like H–O isotopic signatures, and sphalerite geochemistry (enriched in Fe–Mn–Co–In–Sn and depleted in Ga–Ge–Cd). Although no coeval intrusions are exposed at Xianping, geophysical data indicate the possible presence of concealed intrusions beneath the deposit. Our findings demonstrate that Late Devonian post–orogenic extension drove large–scale hydrothermal circulation, culminating in economically significant magmatic-hydrothermal mineralization in South China and highlighting the fertility of such extensional settings for exploring concealed magmatic-hydrothermal Pb–Zn deposits globally.