Abstract
Granite-related W-Sn ore systems are commonly associated with coeval Pb-Zn mineralization.It remains unclear whether these metals are derived from the same sources or not.Mercury(Hg)is a common minor component in such systems.Hg isotopes undergo unique mass-independent fractionation(expressed as A199Hg values),which is mainly generated during Hg photochemical reactions on Earth's surface and not affected by magmatic-hydrothermal processes,offering an excellent op-portunity to trace metal sources in hydrothermal systems.We observed near-zero Δ199Hg values in wolframite(-0.10‰ to 0.08‰,n=11),and in skarn-(-0.17‰ to 0.12‰,n=48)and greisen-type(-0.12‰ to 0.10‰,n=11)bulk tin-tungsten ore from eight major ore deposits in South China.These values are identical to those of coeval highly evolved granites(-0.13‰ to 0.12‰,n=49),supporting that Hg in W-Sn ores were sourced from granite.However,sulfides(e.g.,pyrite,chalcopyrite,arsenopyrite,galena,and sphalerite)in these deposits exhibit negative to near-zero Δ199Hg values(-0.42‰ to 0.09‰,n=124),which indicates a contribution of Hg and by inference other metals from both Precambrian basement rocks(A199Hg＜0)and ore-related granites.The study demonstrates that multiple sources of metals were involved in the formation of the polymetallic W-Sn deposits,and further highlights that extraction of metals from basement rocks may be a critical control on the formation of economically important mineralization of base metal sulfides(e.g.,Pb,Zn)in granite-related magmatic-hydrothermal systems.
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