He, Pb and S isotopic constraints on the relationship between the A-type Qitianling granite and the Furong tin deposit, Hunan Province, China

The Furong tin deposit, located in southern Hunan Province, China, is a large, newly discovered deposit with an estimated Sn reserve of about 700,000 tons. The deposit is spatially and temporally associated with the A-type Qitianling granite. The 3He/4He ratios of fluid inclusions trapped in sulfides from the deposit range from 0.13 to 2.95 Ra, indicating a mixed crust-mantle source, similar to that of the Qitianling granite complex. Lead isotopes in feldspars of the granite (mostly in the range of 206Pb/204Pb = 18.547–19.180, 207Pb/204Pb = 15.598–15.825, 208Pb/204Pb = 37.912–39.068) and in sulfide minerals (206Pb/204Pb = 18.467–18.836, 207Pb/204Pb = 15.503–15.772, 208Pb/204Pb = 38.607–39.099) are essentially the same, indicating that the lead in both was derived mainly from the upper crust, with a small mantle component. The sulfur isotopic values of the ore minerals vary widely, ranging from − 26.1‰ to + 10.4‰, but are mainly within the range of + 0.2‰ to + 10.4‰, implying that the S in the hydrothermal fluids was derived mainly from magmatic fluids, with minor contributions from the mantle, sedimentary rocks and biogenic material. The He, Pb and S isotopes all confirm that the ore-forming fluids of the Furong deposit were magmatic in origin, derived from the melts that produced the Qitianling A-type granite. The tin mineralization occurs within, or along the margins of, the Qitianling granite complex, and the timing of the mineralization coincides with the intrusive age of the granite. The available data suggest that the emplacement of the granites and the mineralization was related to mantle upwelling and extension of the lithosphere in South China during the Mesozoic.