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A fluid-inclusion study and genetic model of wolframite-bearing quartz veins, Garganta de los Montes, Spanish Central System

Published online by Cambridge University Press:  05 July 2018

E. Ouilez
Affiliation:
Departamento de Cristalografia y Mineralogia, Facultad de C.C. Geologicas, Universidad Compiutense, 28040 Madrid, Spain
J. Sierra
Affiliation:
Departamento de Cristalografia y Mineralogia, Facultad de C.C. Geologicas, Universidad Compiutense, 28040 Madrid, Spain
E. Vindel
Affiliation:
Departamento de Cristalografia y Mineralogia, Facultad de C.C. Geologicas, Universidad Compiutense, 28040 Madrid, Spain

Abstract

Wolframite-bearing quartz veins from Garganta de los Montes, Madrid province, are hosted by banded gneisses that have undergone intense migmatization processes. The ore deposit is closely related to the La Cabrera granitic batholith. The veins strike 075° and dip 75°S. The mineral association includes wolframite, quartz and minor amounts of scheelite and sulphides (sphalerite, chalcopyrite, pyrrhotite, stannite and marcasite). The fluid phases associated with quartz from the vein margin (early barren quartz) and from the vein centre (late wolframite-bearing quartz) have been studied using microthermometry, scanning electron microscopy and crushing test analyses. Four hydrothermal stages have been distinguished.

The earliest fluids, only recognized in the barren quartz, contain brine, daughter phase (halite) and trapped minerals. The second hydrothermal stage is characterized by complex carbonic-aqueous inclusions of low salinity (3 to 7 wt.% eq. NaC1) and low density (0.4 to 0.7 g.cm−3). They mainly homogenize into liquid between 300 and 420°C. The third stage is represented by low to moderate salinity inclusions (<9 wt. % eq. NaCl) of moderate density (0.8 to 0.96 g.cm−3), homogenizing between 120° and 330°C. The latest fluids correspond to aqueous solutions of higher salinities (H2O-NaCl, with Ca2+ and Mg2+) and densities (>1 g.cm−3), with TH ranging between 50 and 130°C. The role of the complex-carbonic aqueous fluids in the transport and precipitation of tungsten is highlighted.

Type
Ore environments—gold mineralization
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1990

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