Fluids related to tungsten ore deposits in Northern Portugal and Spanish Central System: a comparative study

A comparative study of P-T-X fluid evolution in several Iberian tungsten deposits has been carried out using microthermometric and Raman data on representative deposits of Northern Portugal (Panasqueira and Borralha) and Spanish Central System (San Rafael, Cabeza Mediana, Cabeza Lijar). ThTee main types of fluids have been distinguished: (i) magmatic hypersaline aqueous fluids (only present in Spanish Central System); (ii) "metamorphic" aqueous-carbonic fluids (H20-NaCI-C02- CH4); and (iii) aqueous fluids (H20-NaCI). The fluid evolution is characterized by dilution of aqueous carbonic fluids, accompanied by a decrease of the volatile phase density and cooling. The W-mineralisation IS always related to aqueous-carbonic fluids, resulting from the interaction between water and C-hearing metamorphic host rocks. The Hercynian granites of Iberia are thus considered to have played a role on ore forming processes rather distinct than that previously thought, as no typical magmatic signature is found except in the earliest stages responsible for the greisen formation in the Spanish Central System. The main role of the granites appears to be a heat supply at the origin of fluid convection, rather than a fluid or a metal source.

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