Metallogenesis at the Carris W-Mo-Sn deposit (Geres, Portugal): Constraints from fluid inclusions, mineral geochemistry, Re-Os and He-Ar isotopes

• Type: Another Publication in an International Scientific Journal
• Date: 2014

Authors

Moura, A (Author) FCUP; Doria, A (Author) Other; Neiva, AMR (Author) Other; Leal Gomes, CL (Author) Other; Creaser, RA (Author) Other

Journal

Title: Ore Geology Reviews

Vol. 56

Pages: 73-93

ISSN: 0169-1368

Publisher: Elsevier

Indexing

ISI Web of Knowledge - 34 Citations

Scopus - 38 Citations

Scientific classification

FOS: Engineering and technology > Environmental engineering

Other information

Authenticus ID: P-008-GNH

DOI: 10.1016/j.oregeorev.2013.08.001

Abstract (EN): The Carris orebody consists of two partially exploited W-Mo-Sn quartz veins formed during successive shear stages and multipulse fluid fillings. They cut the Variscan post-D3 Geres I-type granite. The most important ore minerals are wolframite, scheelite, molybdenite and cassiterite. There are two generations of wolframite. The earlier generation of wolframite is rare and has the highest WO4Mn content (91 mol%) and the most common wolframite contains 26-57 mol% WO4Mn. Re-Os dating of molybdenite from the ore quartz veins and surrounding granite yields ages of 279 +/- 1.2 Ma and 2803 1.2 Ma, respectively which are in very good agreement with the previous ID-TIMS U-Pb zircon age for the Cards granite (280 +/- 5 Ma). He-3/He-4 ratio of pyrite ranging between 0.73 and 2.71 Ra (I Ra = 139 x 10(-6)) and high He-3/Ar-36 (0.8-5 x 10(-3)) indicate a mixture of a crustal radiogenic helium fluid with a mantle derived-fluid. The fluid inclusion studies on quartz intergrown with wolframite and scheelite, beryl and fluorite reveal that two distinct fluid types were involved in the genesis of this deposit. The first was a low to medium salinity aqueous carbonic fluid (CO2 between 4 and 14 mol%) with less than 1.95 mol% N-2, which was only found in quartz associated with wolframite. The other was a low salinity aqueous fluid found in all the four minerals. The homogenization temperatures indicate minimum entrapment temperatures of 226-310 degrees C (average 280 degrees C) for the H2O-CO2-N-2-NaCl fluid and average temperatures of 266 degrees C for scheelite and 242 degrees C, 190 degrees C and 160 degrees C for the last generations of beryl, fluorite and quartz, respectively. It was estimated that wolframite was deposited similar to 7 km depth, assuming a lithostatic pressure, probably due to strong pressure fluctuation caused by seismic events triggered by brittle tectonics during the exhumation event. Precipitation of scheelite and sulphides took place later, at the same depth, but under a hydrostatic or suprahydrostatic pressure regime, and probably caused by mixing between the magmatic-hydrothermal fluid and meteoric waters that deeply penetrated the basement during post-Variscan decompression.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 21