Sensitive high-resolution ion microprobe U-Pb Zircon and 40Ar-39Ar muscovite ages of the Yinshan deposit in the northeast Jiangxi province, South China

The Yinshan deposit in the Jiangnan tectonic belt in South China consists of Pb-Zn-Ag and Cu-Au ore bodies. This deposit contains approximately 83Mt of the Cu-Au ores at 0.52% Cu and 0.8g/t Au, and 84Mt of the Pb-Zn-Ag ores at 1.25% Pb, 1.02% Zn and 33.3 g/t Ag. It is hosted by low-grade metamorphosed sedimentary rocks and mafic volcanic rocks of the lower Mesoproterozoic Shuangqiaoshan Group, and continental volcanic rocks of the Jurassic Erhuling Group and dacitic subvolcanic rocks. The ore bodies mainly consist of veinlets of sulfide minerals and sulfide-disseminated rocks, which are divided into Cu-Au and Pb-Zn-Ag ore bodies. The Cu-Au ore bodies occur in the area close to a dacite porphyry stock (No. 3 stock), whereas Pb-Zn-Ag bodies occur in areas distal from the No. 3 stock. Muscovite is the main alteration mineral associated with the Cu-Au ore bodies, and muscovite and chlorite are associated with the Pb-Zn-Ag ores. A zircon sensitive high-resolution ion microprobe U-Pb age from the No. 3 dacite stock suggests it was emplaced in Early Jurassic. Three 40Ar-39Ar incremental-heating mineral ages from muscovite, which are related to Cu-Au and Pb-Zn-Ag mineralization, yielded 179-175Ma. These muscovite ages indicate that Cu-Au mineralization occurred at 178.2+/-1.4Ma (2 sigma), and Pb-Zn-Ag mineralization at 175.4+/-1.2Ma (2 sigma) and 175.3+/-1.1Ma (2 sigma), which supports a restricted period for the mineralization. The Early Jurassic ages for the mineralization at Yinshan are similar to that of the porphyry Cu mineralization at Dexing in Jiangnan tectonic belt, and suggest that the polymetallic mineralization occurred in a regional transcompressional tectonic regime.