Anomalously high Sc contents in ore minerals from Sn–W deposits: Possible economic significance and genetic implications

An investigation on Sn–W and W deposits and associated granites in the Erzgebirge region, central Kazakhstan, Mongolian Altai, and central Mongolia reveals anomalously high Sc contents up to several thousands of parts per million in wolframite and cassiterite from Sn–W deposits in the eastern Erzgebirge; even though whole-rock samples of granites from these localities have low Sc contents typical of high-silica granitic rocks.It is possible to trace the distribution of Sc in rocks and veins using data on accessory and ore minerals enriched in Sc (columbite, rutile, cassiterite, wolframite, zircon, scheelite, and mica). There are no indications for an enrichment of Sc during the magmatic evolution of the granite intrusions. Magmatic fractionation causes rather low Sc contents in evolved granites. On the other hand, Sc enrichment in zircon found in these rocks is clearly related to processes of secondary alteration leading to high U, Ca, and Fe besides Sc enrichment in the mineral. Enhanced Sc contents were also found in whole-rock samples from the greisen.The occurrence of Sc-rich wolframite and cassiterite is mainly restricted to endocontact orebodies (greisen and veins). Outside the rare metal-bearing granites, the Sc content in wolframite drops off if host rocks are formed by schist and gneiss. Correlation between Sc and Nb concentrations in wolframite found in endocontact orebodies also disappears in the exocontact veins except if the vein system provides a focused fluid flow.Sc enrichment in Sn–W mineralisation is accompanied by strong Y/Sc, Y/Yb, and Th/U fractionation in Sc-bearing minerals as indicated by trace-element contents in wolframite and scheelite. Y/Sc ratios in wolframite below 0.1 are typical of Sn deposits. It is suggested that certain conditions of complexation, pH, and Eh in F-rich fluids are necessary prerequisites for Sc enrichment and deposition. Our results hint for a Sc input into the ore-forming system by an external F-rich fluid carrying also U and heavy REE and possibly derived from a mantle-related source. Although whole-rock samples of rare metal-bearing topaz granite have low Sc contents, the related Sn–W ores may represent an interesting source for Sc extraction because of their enrichment in Sc.