Deciphering the ore-forming process of Sb-W deposits through scheelite and stibnite trace element geochemistry

Abstract

Antimony (Sb) and tungsten (W) and deposits typically form in distinct and unrelated ore-forming environments. However, in rare cases, ore deposits may present combined Sb-W mineralization within a single deposit. These contrasting occurrences introduce uncertainty within the Sb-W ore deposit model, which ultimately guides mineral exploration strategies. Scheelite and stibnite are prevalent ore minerals in Sb-W deposits, making their trace element compositions valuable for enhancing our understanding of the genesis of Sb-W ore systems. In this study, we conducted a systematic investigation of trace element compositions in scheelite and stibnite samples from the Chashan and Zhazixi Sb-W deposits in South China to decipher the primary ore-forming processes. Scheelite from the Sb-W deposits is characterized by low Na, Nb, Ta and Mo contents, and variable Nb/Ta ratios. These results present a remarkably different geochemical signature when compared with granite-related W deposits, indicating that W mineralization in Sb-W deposits was derived from a non-magmatic origin. Moreover, when combining the trace element signature with reported fluid inclusion and isotopic data, it can be concluded that ore-forming fluids of the Chashan and Zhazixi Sb-W deposits were primarily composed of deep-circulating meteoric groundwater. Scheelite from the Chashan deposit presents relatively flat REE patterns with large positive Eu anomalies, whereas the Zhazixi deposit is characterized by bell-shaped REE patterns with weak Eu anomalies. This suggests that the two Sb-W deposits may differ slightly in their source rock composition, which is also supported by the different trace element compositions of stibnite. Stibnite from the Zhazixi deposit is relatively enriched in As, Se and Pb, whereas stibnite from the Chashan deposit contains higher Sn, Zn, Mo, Ag, In and Sr, further indicating that the initial fluids of the two deposits may have undergone different degrees of fluid-rock interaction with their distinctive source rocks. This study demonstrates that the genesis of the Zhazixi and Chashan Sb-W deposits significantly differ when compared to the ore-forming processes that control granite-related W or metamorphic W deposits. Moreover, the formation of these Sb-W deposits appears to share a similar genetic model consistent with low-temperature Sb deposits in South China. In this model, deep-circulating meteoric groundwater infiltrates and leaches Sb and W from fertile source rocks through fluid-rock interaction. Concealed granites may have solely served as a thermal source for the convection and upward migration of ore-forming fluids, while the fertility of source rocks and the intensity of fluid-rock interaction are expected to have played a crucial role in the formation of Sb-W deposits.