Sulfur isotopes and trace elements of sulfides in gold deposits in the Shuangjianshan-Langwashan area of the Beishan orogenic belt as indicators of metallogenic mechanism

Objective The Shuangjianshan-Langwashan area is situated in the southern margin of the central segment of the Central Asian Orogenic Belt, specifically within the Mingshui magmatic arc of the northern Beishan Orogenic Belt. Currently, critical information regarding the genesis of mineral deposits in this region remains unclear. This study aims to investigate the occurrence state of trace elements in sulfides, fluid characteristics, and metallogenic mechanisms of gold deposits in the Shuangjianshan-Langwashan area, with the ultimate objective of guiding exploration practices.

Methods Based on field geological investigations and ore microscopy studies, LA−ICP−MS analyses of trace elements, rare−earth elements, and sulfur isotopes were performed on pyrite and chalcopyrite from the main metallogenic stages of the Shuangjianshan, Dahongquan, and Langwashan gold deposits in the region.

Results The results show that gold in the Shuangjianshan−Langwashan area gold deposits exists in two forms: visible gold and invisible gold. Invisible gold is mainly hosted in the pyrite lattice in the form of solid−solution gold (Au¹⁺). Pb and Bi are mainly present in galena inclusions, either in the form of bismuthinite or as solid−solution Bi. In the Dahongquan and Langwashan deposits, the positive correlations between Zn and Cd, and between Pb and Sb indicate the presence of mineral inclusions such as sphalerite and galena in pyrite. The Nb/La, Th/La, and Hf/Sm values in the Shuangjianshan−Langwashan gold deposit are mostly less than 1, indicating that the ore−forming fluid is rich in Cl⁻. Likewise, the content and ratio of Co and Ni indicate that the ore−forming fluid has the characteristics of medium−low temperature and low salinity. Moreover, Cu/Au indicates that the overall ore−forming fluid is in a relatively reducing environment. And the Y/Ho, Zr/Hf, and Nb/Ta values indicate the presence of multiple stages of fluid superposition in the metallogenic process. In the late metallogenic stage of the Shuangjianshan gold deposit, the fluid may have mixed with atmospheric precipitation. The average δ³⁴S values of sulfides from the Shuangjianshan, Dahongquan, and Langwashan deposits are 2.58‰, 2.07‰, and 1.22‰ respectively. The range of sulfur isotope values of the Shuangjianshan gold deposit is larger than that of the Dahongquan and Langwashan gold deposits, indicating the mixing characteristics of magmatic sulfur and stratigraphic sulfur. The δ³⁴S values of the Dahongquan and Langwashan gold deposits are all extremely low positive values, indicating the characteristics of magmatic sulfur.

Conclusions Based on field geological phenomena, trace−element characteristics, and sulfur isotopes, it is considered that the Shuangjianshan and Langwashan gold deposits belong to low−sulfidation epithermal gold deposits, while the Dahongquan gold deposit is an orogenic gold deposit, and the metallogenesis in the area has multiple stages.