Is there superimposed mineralization occurring within the Longshan Sb-Au deposit, South China? A perspective from U-Pb dating of apatite and in-situ S isotopes of pyrite and stibnite

Abstract

The Longshan deposit, located in the Xiangzhong metallogenic Province (XZMP), South China, is a large-scale Sb-Au deposit with substantial reserves (Sb: 143,000t, Au: 15.5 t). Despite its economic importance, the genesis of the deposit remains enigmatic and the subject of ongoing debate, primarily due to uncertainties regarding its mineralization age and its link with regional granitic magmatism. Mineralogical investigations have revealed the occurrence of apatite within the Sb ore veins, where it is closely associated with scheelite and stibnite. Apatite displays elevated REE contents, MREE-enriched patterns with positive Eu anomalies, which suggest its hydrothermal origin. Consequently, the apatite U-Pb age provides a robust constraint on the timing of Sb mineralization at the Longshan Sb-Au deposit. Cathodoluminescence (CL) images reveal that apatite typically exhibits a core-rim texture, comprising an early-stage core apatite (Ap1) and late-stage rim apatite (Ap2). U-Pb dating of Ap1 proved unsuccessful due to high common Pb concentrations, while LA-ICP-MS U-Pb dating of Ap2 yielded a Tera-Wasserburg lower intercept age of 159 ± 13 Ma, which likely reflects the timing of late-stage mineralization at the Longshan deposit. The new data indicate that the Longshan deposit experienced the superposition of Late Jurassic mineralization, in addition to the previously documented Late Triassic mineralization event. In-situ sulfur isotope measurements of stibnite and pyrite from different mineralization periods revealed δ³⁴S values ranging from −2.37 ‰ to + 6.04 ‰, which indicate that sulfur in the ore-forming fluids at Longshan likely originated predominantly from buried magmas. A weak upward trend in δ³⁴S values from deeper to shallower levels indicates the minor contributions from host rock sulfur. Integrated with early chronological data and mineralogical observations, these findings suggest that the Longshan is a magmatic-hydrothermal Sb-Au system formed through the superposition of Late Triassic and Late Jurassic mineralization events.