Helium isotopic ratios in fluid inclusions from fluorite-rich Mississippi Valley-Type district of Asturias, northern Spain

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Helium isotopes have been measured in fluorite and sulphides from fluorite-rich Mississippi Valley-type (MVT) deposits from Asturias, Spain, in order to assess the involvement of mantle and crust-derived volatiles in the genesis of the deposits. The ³He/⁴He of the ore fluids are ≤0.1 R_a ruling out a contribution of mantle-derived magmatic helium in the inclusion fluids. Data support a crustal source for the volatiles and is consistent with the existing basinal model for the genesis of the Asturias MVT mineralization by mixing of sedimentary brines with infiltrating superficial fluids.