Mayum: an orogenic gold deposit in Tibet, China

Abstract

Located in western Tibet, China, the Mayum orogenic gold deposit was discovered in 2002 with estimated resources of > 80 tonnes gold. The gold mineralization is hosted by Neoproterozoic–Cambrian schists, and is controlled by nearly parallel E–W trending bedding-concordant fracture zones. The Au orebodies are composed of auriferous quartz veins and altered rocks, with the Au grades ranging from 2.23 g/t to 69.56 g/t, and containing < 3 vol.% sulfides. The δ 34S values of 18 separates of sulfides from auriferous quartz veins show a large variation from − 0.2 to + 16.8‰. The lead isotope compositions of sulfides from the gold ore are characterized by highly radiogenic values and very wide ranges of ratios: 18.324 to 20.819 for 206Pb/ 204Pb, 15.679 to 15.856 for 207Pb/ 204Pb, and 38.401 to 41.204 for 208Pb/ 204Pb. These data indicate that lead and sulfur in the quartz veins have multiple sources, and were derived from the different wall rocks as the fluid flowed through them. Fluid inclusions indicate that the ore fluid was CO 2-rich, with salinities mainly between 1 and 6 wt.% NaCl equiv, and homogenization temperatures predominantly ranging from 260 to 280 °C. The δ 18O values for quartz from auriferous veins range from 13.7 to 16.3‰, and the calculated δ 18O H2O values in equilibrium with quartz vary from 5.54 to 9.48‰. It suggests that the ore fluid may be derived from deep, metamorphic deep-crustal gold-transporting fluids, although a contribution from magmatic source cannot be ruled out. 40Ar/ 39Ar age dating on the sericite from the alteration associated with the auriferous quartz veins in the Mayum gold deposit gives a plateau-like age of 59.34 ± 0.62 Ma, later than the onset of the Indo-Asian collision. It is believed the gold mineralization was related to the Indo-Asian collision, and was formed during the early stage of orogenesis.