Contrasting origins of Sn-W mineralization in western Thailand

Investigations of pegmatite, stockwork and replacement deposits, using geological, whole-rock and mineral chemistry, fluid inclusion, and stable isotope data, were undertaken to establish some of the controls of mineralization in the western Thai Sn-W belt.Cassiterite was saturated in the late-stage melt in the Nong Sua granitic pegmatite and subsequently with wolframite in orthomagmatic fluids. The latter mixed with external aqueous and aqueous-carbonic fluids of evolved meteoric or metamorphic origin at $ le$650$ sp circ$C and $ le$3.8 kbar. Hydrothermal cassiterite and wolframite crystallized as a result of increasing $fO sb2,$ fluid mixing, and cooling. At the Pilok stockwork deposits tourmalinization was followed by successive wolframite-K-feldspar deposition and cassiterite-sulphide greisen mineralization. Tin was remobilized by reduced metamorphic or evolved magmatic-meteoric aqueous-carbonic fluids. Cassiterite was deposited at 300-450$ sp circ$C in response to increasing $fO sb2,$ pH, or decreasing temperature. Limited data on the Takua Pit Thong replacement suggest that cassiterite was deposited from aqueous fluids at $ ge$500$ sp circ$C, but metamorphic aqueous-carbonic fluids were also involved.The depth of emplacement was one of the major controls on mineralization style. Aqueous-carbonic fluids in the western Thai, and other Sn-W belts, are a consequence of a moderately deep level of emplacement; hypersaline orthomagmatic fluids are associated with sub-volcanic Sn-W mineralization