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

Abstract

AbstractLocated along the southern part of the West Qinling orogenic belt, the Yangshan gold deposit is one of the largest in China. The major gold ores of Yangshan are disseminated in metasedimentary host rocks with minor native gold amounts in stibnite‐gold quartz veins. Pyrite and arsenopyrite are the major Au‐bearing minerals. Hydrothermal muscovite from gold‐bearing quartz veins was dated using the in situ Rb‐Sr method to determine the formation age of the Yangshan gold deposit. The Rb‐Sr isochron date of the muscovite yielded 210.1 ± 5.6 Ma (MSWD = 1.2). This date is near the lower end of the period of the mineralized granitic dykes (210.49–213.10 Ma). Two stages of gold enriching process are recognized in the gold‐bearing pyrite: the first is incorporated with the Co, Cu, As, Ni enrichment; and the second 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 deposits are likely derived from a magmatic source and likely assimilated by sulfur from the sedimentary bedrock. Thus, magmatism plays a critical role in the formation of the Yangshan gold deposit.