In Situ Rb‐Sr Dates of Muscovite and Sulfur Isotope of Pyrite from the Yangshan Gold Deposit in Western Qinling, China

Abstract

Located along the southern part of the West Qinling, Yangshan gold deposit is one of the largest gold deposits in China. The major gold ores of the Yangshan are disseminated in metasedimentary host rocks with minor native golds amounts in stibnite‐gold quartz veins. Pyrite and arsenopyrite are the major Au‐bearing minerals. Hydrothermal muscovite from gold‐bearing quartz vein was dated by in situ Rb‐Sr method to determine the formation age of the Yangshan gold deposit. The Rb‐Sr isochron age of the muscovite yielded 210.1 ± 5.6 Ma (MSWD = 1.2). This age is near the lower end of the period of the mineralized granitic dykes (210.49–213.10Ma). Two stages of gold‐rich process are recognized in gold bearing pyrite. The first gold enrichment process is incorporated with the Co, Cu, As, Ni enrichment. And the second stage of gold enrichment is accompanied by Bi, Co, Ni, Pb, Cu, Sb concentration. The in‐situ sulfur isotopic values of pyrites show a restricted δ34S range of ‐1.43 to 2.86 ‰ with a mean value of 0.43 ‰. Trace‐element mapping and in‐situ sulfur isotopic analysis of pyrite suggest that the sulfur sources are likely derived from magmatic source and likely assimilated by sulfur from the sedimentary bedrock. The magmatism plays a critical role in the formation of the Yangshan gold deposit.