Chemical and stable isotopic compositions of Proterozoic metamorphosed evaporites and associated tourmalines from the Houxianyu borate deposit, eastern Liaoning, China

Abstract

An integrated major element, trace and rare earth element, and stable isotope (B, Si, O and S) study has been carried out on the Houxianyu borate deposit, eastern Liaoning, China. The present-day mineralogy of the deposit is closely similar to that of magnesian skarn deposits and the borates are underlain by granite; however, the geochemical and isotopic evidence does not favour a skarn-type origin. In particular, the boron isotopic compositions of the borate minerals and associated tourmalines preclude their origin from fluids derived from the granite. Rather, the data are compatible with the borate deposit being a metamorphosed evaporite. The mineralogy and chemistry of the deposit are most compatible with a non-marineorigin, although the high δ 34S- and δ 11B-values suggest that there may have been some marine components to the evaporitic brines. Overall, the premetamorphic origin of the Houxianyu borate deposit is similar to that of the Tertiary non-marine evaporite borate deposits of western Turkey. There are also similarities with other Proterozoic early rifting environments (e.g., the Upper Proterozoic Damaran Orogen of South Africa) that have implications for the structural evolution and mineral potential of the region.