Early Cretaceous Magmatic-Hydrothermal PbZn Mineralization in the Liushutang Deposit, Hengyang Basin, South China

Lead‑zinc mineralization in South China is commonly associated with Mid-Late Jurassic (∼170–150 Ma) magmatic activity. However, the genesis of many deposits lacking direct magmatic connections remains poorly constrained owing to limited geochronological data. The Hengyang Basin, located within the Qin-Hang Metallogenic Belt (QHMB, South China), hosts numerous PbZn deposits whose origins remain debated, with proposed models including magmatic-hydrothermal and Mississippi Valley-type (MVT) styles. The Liushutang deposit (1.36 Mt at 0.85% Pb and 4.49% Zn) is a representative example. Its mineralization comprises three stages: (I) quartz-pyrite, (II) quartz-pyrite-chalcopyrite-galena-sphalerite (main ore stage), and (III) quartz-barite-sphalerite. Integrated geological, mineralogical, and isotopic evidence, including fault-hosted vein geometry, pervasive silicification, a quartz-barite-sulfide assemblage with chalcopyrite and tetrahedrite, magmatic-like HO isotopic signatures, and extremely high Rb/Sr ratios (mean 839) of hydrothermal roscoelite, collectively points to a magmatic-hydrothermal origin for Liushutang. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) data show that Ga enrichment in sphalerite (up to 857 ppm) results primarily from lattice incorporation via Cu-coupled substitution under high-salinity conditions associated with phase separation triggered by rapid fluid depressurization. The Stage II roscoelite RbSr isochron age of 105.8 ± 5.4 Ma (MSWD = 1.3) constrains the timing of PbZn mineralization and clearly distinguishes it from the ∼158 Ma Mid-Late Jurassic magmatic-hydrothermal PbZn deposits (e.g., Kangjiawan and Shuikoushan) in the Hengyang Basin. Although no coeval intrusions are exposed at Liushutang, geophysical data indicate the presence of concealed intrusions beneath the deposit. This ∼106 Ma age coincides with a regional extensional tectonic regime (ca. 135–80 Ma) that caused lithospheric thinning, asthenospheric upwelling, and the formation of NE-trending pull-apart basins, collectively providing the thermal driver and structural permeability for ore formation. Consequently, the Hengyang Basin records two distinct episodes of magmatic-hydrothermal PbZn mineralization: Mid-Late Jurassic and Early Cretaceous, with the Liushutang deposit exemplifying the latter. This finding reveals a previously underrecognized Early Cretaceous magmatic-hydrothermal metallogenic episode in the QHMB and provides a valuable framework for regional exploration by highlighting the roles of concealed intrusions and extensional tectonic settings in PbZn ore formation and critical metal (Ga) enrichment.