Sulfur isotope characteristics of the Yangshan gold belt, West Qinling: Constraints on ore-forming environment and material source

The main crystal habit of diagenetic pyrite in the Yangshan gold belt is cube-xenomorphic, indicating a diagenetic environment with low temperature (<200 degrees C), low degree of supersaturation of diagenetic fluid, fast cooling, low oxygen fugacity and sulfur fugacity, and insufficient supply of material. The delta S-34 value varies in a large range (-4. 2 parts per thousand similar to 12. 5 parts per thousand), indicating that the sulfur came from Devonian stratum, within which sulfur of pyrite in limestone originated from reduction of sulfate ion in sea water and sulfur of pyrite in phyllite experienced bacterial reduction. The ore pyrite has various morphologies, but with few cubes, indicating that the metallogenic system is under conditions of medium-low temperature (200 similar to 300 degrees C), high degree of supersaturation of ore-forming fluids, slow cooling, high oxygen and sulfur fugacity, and sufficient supply of material, which are favorable for metallogenesis. The delta(34) S value of sulfides in the early and main ore stages varies from -4. 2 parts per thousand to 3 parts per thousand, which is close to the delta S-34 ranges of magmatic sulfur. Pyrite in the main ore stage has more combination forms of pyritohedron, octahedron and cube. The delta S-34 value of the combination forms concentrates in -2. 1 parts per thousand similar to 1. 2 parts per thousand, which is more likely to be of magmatic origin. The delta S-34 value of stibnite in the late ore stage varies from -6. 6 parts per thousand to -4. 5 parts per thousand, while the pyrite which coexists with stibnite has delta S-34 value of 7. 6 parts per thousand and -12. 1 parts per thousand, showing that besides magmatic sulfur, Devonian stratum provided partial sulfur for the system.