Fluids from the Neves Corvo massive sulphide ores, Iberian Pyrite Belt, Portugal

Homogenization temperatures lie between 140 and 370 °C. This wide range of Th is typical of VMS deposits from IPB and reflects the evolution of the hydrothermal system with time. Salinity ranges from 3 to 6 wt.% equiv. NaCl, except for a small group of the high-salinity fluid inclusions, which have around 30 wt.% eq. NaCl. These high-salinity fluids are interpreted as brines resulting from sporadic deep subsea-floor boiling that could originate either from seawater or from a magmatic fluid. The carbon dioxide and methane could have been derived from reactions with organic matter enclosed in the metasediments underlying the ores. However, a magmatic origin cannot be precluded.