Isotope geochemistry, chronology and genesis of the Yangshan gold deposit, Gansu

Abstract：The Yangshan gold deposit, located in the Sichuan-Shaanxi-Gansu border region, is a superlarge finely disseminated gold deposit recently found in China. δD and δ18OH2O analysis of quartz veinlets in ores shows that the ore fluids of the deposit are dominated by magmatic water, and the δ34S analysis of various sulfides indicates that sedimentary sulfur and magmatic sulfur coexist in the gold district and show significant difference in δ34S, while the sulfur in metal sulfides in the ores is mainly of magmatic origin. δ13C analysis indicates that both magmogenic carbon and sedimentary carbon exist in the gold deposit. K-Ar, 39Ar-40Ar, Rb-Sr and U-Pb isotopic datings show that plagiogranite porphyry dikes originated in the Early Jurassic, and in addition, Early Cretaceous and early Paleogene buried intrusions do also exist in the gold district and their related hydrothermal activities also exhibit the feature of repeated occurrence. Based on the data and other analyses, the authors further discuss the genesis of the deposit and think that：a sequence of hydrothermal carbonaceous, siliceous and argillaceous sediments formed in the area in the Devonian and gold was primarily concentrated in the process of regional low-grade metamorphism in the Indosinian metamorphism; afterwards multiple magmatic activities occurred in the district and their related ore fluids and materials migrated along the Anchanghe-Guayinba fault and were concentrated and stacked in favorable structural sites, thus resulting in the formation of the Yangshan gold deposit.