Study on the Source of Ore-Forming Materials of the Sangmuchang Barite Deposit in Northern Guizhou

Abstract: The study of fluid inclusions and sulfur isotope characteristics of barite deposits is crucial for tracing the source of ore-forming materials and predicting prospecting targets. Current research indicate that the Sangmuchang barite deposit in northern Guizhou is primarily hosted within the joint fractures of dolomites in the Sinian Dengying Formation and Cambrian Qingxudong Formation. The contact between ore bodies and surrounding rocks is distinct, with the orebodies occurring as veins and lenticular. The ore textures are mainly veinlets, stockworks, massive, and banded, while the ore structures consist of inequigranular tabular-columnar blastic, fine-crystalline, and arenaceous texture.  Fluid inclusion studies reveal that  the inclusions are single-phase aqueous inclusions. Microthermometric measurements of 33 inclusions show that their homogenization temperatures range from 81°C to 182°C, with an average of 132°C; Salinity values vary from 9.61 wt.% NaCl eqv to 20.63 wt.% NaCl eqv, with an average of 17.53 wt.% NaCl eqv. Ten sulfur isotope analyses from the deposit show that the δ³⁴SV-CDT values range from 40.89‰ to 46.95‰, with a mean of +44.51‰.The characteristics of fluid inclusion salinity, temperature and sulfur isotopes suggest that the ore-forming fluids of this barite deposit are characterized by moderate-low temperature and moderate-high salinity. These ore-forming fluids were mainly derived from basin brines, with contributions from meteoric water. The significant enrichment of heavy sulfur isotopes and homogeneous sulfur isotope composition reveal that the sulfur source of ore-forming materials in this barite deposit is a relatively singular source for the sulfur in the ore-forming materials, which is similar to the δ³⁴S characteristics of Sinian marine evaporites, suggesting a close genetic relationship between the sulfur source and evaporites. Therefore, the Sangmuchang barite deposit is interpreted as a moderate-low temperature hydrothermal deposit.  It was formed by the migration of moderate -low temperature hydrothermal fluids in the sedimentary basin, which leached ore-forming materials from underlying and surrounding barium-rich evaporite sequences, followed by precipitation within structural fracture zones under the mixing of meteoric water. The structural fracture zones and areas indicative of fluid migration pathways along the basin margin are important targets for exploration prediction. Keywords: ore-forming fluid; fluid inclusion; sulfur isotope; barite; northern Guizhou