Sulfur Sources of the Tulargen Ni-Cu Deposit in the Eastern Tianshan, Xinjiang

Ni-Cu deposits are an important category of strategic metal resources in China. In recent years, a large number of magmatic Ni-Cu sulfide deposits have been discovered in the eastern Tianshan, Xinjiang, among which the Tulargen deposit is a typical example. Previous studies have suggested that crustal contamination may have played an important role in sulfide mineralization at the Tulargen deposit. In this study, laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) was used to perform systematic vertical sampling of drill hole ZK1304 at the Tulargen deposit, and in-situ sulfur isotope analysis was conducted on sulfide minerals, providing high-resolution sulfur isotope data at the drill-hole scale. The results show that the δ34S values of the ore sulfides at the Tulargen deposit range from 0.63‰ to 1.43‰, which are highly consistent with the typical values of mantle sulfides in mid-ocean ridge basalts (MORB; 0 ± 2‰). This indicates that the ore-forming sulfur mainly originates from a deep mafic magmatic system. The δ34S values of different mineral phases show very little variation, suggesting that the sulfides formed from a homogeneous and stable magmatic sulfur reservoir, without significant sulfur isotope fractionation or temporal changes in sulfur sources. In contrast, the δ34S values of pyrite from the surrounding tuffaceous rocks range from 2.00‰ to 5.27‰, which are significantly heavier than those of the ore sulfides, indicating that the contribution of crustal sulfur to the ore-forming sulfur is minimal. Therefore, this study suggests that the precipitation of Ni-Cu sulfides at the Tulargen deposit was likely controlled mainly by the evolution of the mafic magmatic system itself. The magma-dominated sulfur control mechanism can also form Ni-Cu sulfide deposits of considerable scale.