Origin of tin-specialized granites constrained from fluid-absent metapelite melting experiments

Abstract Most tin (Sn) mineralization is associated with Sn–specialized granites. Tin-specialized granites are typically peraluminous and originate from fluid-absent dehydration melting of pelitic sources. Because Sn is supplied primarily by the granitic magma, the concentration of Sn in the anatectic melt is critical for the fertility of granites. Here, we constrained the extent of Sn enrichment in primary magma based on fluid-absent partial melting experiments of a natural metapelite at 750–950 °C, 300 and 900 MPa, and at oxygen fugacities of ∼FMQ−2 and ∼FMQ+2.7. Our experimental results show that muscovite dehydration melting at 750 °C produces a small amount of peraluminous granitic melt (<10 mass%) plus biotite, K-feldspar, and sillimanite as the main peritectic minerals. At 850 °C, biotite dehydration melting results in a higher degree of melting (to 30 mass%), and produces peritectic K-feldspar, garnet, cordierite, osumilite, and spinel. The peraluminous granitic melts derived from biotite dehydration melting are enriched in Sn, W, Li, Be, and depleted in Ti, Zr, Hf, and rare earth elements relative to the source rock, exhibiting a trace element pattern very similar to that of Sn-specialized granites. At 950 °C, melting is extensive (>65 mass%), diluting the contents of Sn in the melts. Importantly, our study reveals that Sn partitions into the melt over the residue across the investigated redox range. Comparison to Sn-specialized granites indicates that they are generated by biotite-dehydration melting in combination with melt fractionation. On a regional scale, favorable protoliths (lithology and pre-enrichment) significantly enhance the potential of Sn deposit and thus tin province formation.