Re-Os dating of auriferous pyrite from the Zhenyuan super-large gold deposit in Ailaoshan gold belt, Yunnan Province, Southwestern China

Zhenyuan gold deposit is the largest super large gold deposit in the Ailaoshan gold belt, but its precise mineralization age is still lack. Re-Os isotopic age of the auriferous pyrite from the Zhenyuan gold deposit was determined by using a high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). The pyrite samples were decomposed in carius tubes, Os was separated by distillation and Re was extracted by acetone, respectively. The results show that the Re-Os isochron age is 229 +/- 38 Ma (MSWD=2.0, confidence level is 95%), with an initial Os-187/Os-188 value of 0.68 +/- 0.24 and a corresponding gamma Os value of 442 +/- 91. The Re/Os ratios of the pyrite vary from 40.8 to 100.5. The data suggest that at least one important ore-forming event was occurred during Indosinian epoch, and the ore-forming materials probably derived from mixed sources of crustal and mantle, while the later dominated. The Ailaoshan composite orogen experienced complicated evolutional processes, including formation of Precambrian-Early Paleozoic basement, subduction and orogenesis of Late Paleozoic era, collisional orogenesis of Late Hercynian-Indosinain epoch, and extensional or striking orogenesis of Yanshainan-Cenozoic epoch. The polycycle tectonic evolution and magmatism in this area caused multi-stage and superposition metallization characteristics of the Zhenyuan gold deposit: the mineralization probably occur mainly during the Indosinian collisional orogeny, while the minor gold ores of altered granite-porphyry and altered lamprophyre may be formed in the late superposition metallization.