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C-O-H-N fluid inclusions associated with gold-stibnite mineralization in low-grade metamorphic rocks, Mari Rosa mine, Caceres, Spain

Published online by Cambridge University Press:  05 July 2018

L. Ortega ,
E. Vindel  and
C. Beny
L. Ortega
Affiliation:
Dpto. Cristalografía y Mineralogía, Universidad Complutense, 28040 Madrid, Spain
C. Beny
Affiliation:
GIS-BRGM CNRS, 45071 Orleáns Cedex-2, France
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Abstract

The Mari Rosa mine lies within a low-grade Precambrian alternating series of black shales and metagreywackes in the Spanish Hercynian massif. There are two generations of mineralized veins: V2, gold-(stibnite)-bearing quartz veins, parallel to the main cleavage, and V3, stibnite-bearing quartz veins which postdate the main deformation event.

Four main types of inclusions have been identified. Type I, II and IV are aqueous-carbonaceous inclusions, with variable degrees of filling, while type III are non-aqueous and typically single-phase at room temperature. Except for type I (absent in V3), similar inclusions have been observed in both V2 and V3 veins. Gas compositions are always characterised by CH4-N2-CO2 assemblages, ranging from CO2-rich mixtures in the earliest inclusions (type I), to N2-rich mixtures in the latest inclusions (type IV).

Gold precipitation in V2 veins can be related to type I inclusions at T > 380°C (TH = 300–380°C). A subsequent drop in XCO2 and cooling are recorded in type II and III inclusions, interpreted to be the result of unmixing of a previously homogeneous fluid derived from type I. This boiling would provoke the precipitation of stibnite at 300°C and 1 kbar. The type IV inclusions, which are the richest in H2O, represent a late fluid circulation at lower temperatures (TH = 190–280°C).

Keywords

fluid inclusionsgoldstibniteCaceresSpain
Type
Fluid Inclusion Studies
Information
Mineralogical Magazine , Volume 55 , Issue 379 , June 1991 , pp. 235 - 247
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1991

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