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

• Type: Article in International Scientific Journal
• Date: 2005

Authors

Moura, A (Author) FCUP

Journal

Title: Chemical Geology

Vol. 223

Pages: 153-169

ISSN: 0009-2541

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 20 Citations

ISI Web of Science

Scopus - 18 Citations

Scientific classification

FOS: Natural sciences > Earth and related Environmental sciences

Other information

Authenticus ID: P-000-0EM

DOI: 10.1016/j.chemgeo.2004.12.025

Abstract (EN): The Neves Corvo Cu-Sn-(Zn) mine is probably the richest VMS deposit in the world. The research was conducted in order to know if pristine volcanogenic fluids are present in the massive sulphide ores and proceeds to their characterization and interpretation. The samples were collected inside thick massive sulphide bodies that are undoubtedly of primary origin. Petrographic relations between quartz and sulphide phases (mainly pyrite + chalcopyrite) suggest that the quartz and the sulphides were formed simultaneously. Three types of fluid inclusions were observed: 1 - low salinity aqueous fluid inclusions either isolated, in clusters, or along trails; 2 - low salinity H2O-CO2-CH4- NaCl fluid inclusions in intergranular arrays or intracrystalline trails (some in growth zones), some of which form clathrates on freezing; and 3 - (only in one sample) high-salinity fluid inclusions with halite, without any regular distribution in the crystals. The aqueous low Salinity fluid is the most abundant, consisting of modified seawater resulted from convection through the basement. Homogenization temperatures lie between 140 and 370 degrees 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.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 17