A fluid inclusion model for the genesis of the ores of the Dolgellau Gold Belt, North Wales

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doi: 10.1144/gsjgs.145.1.0139
Authors:Bottrell, S. H.; Shepherd, T. J.; Yardley, B. W. D.; Dubessy, J.
Author Affiliations:Primary:
Univ. Leeds, Dep. Earth Sci., Leeds, United Kingdom
BGS Geochem. Div., United Kingdom
CREGU, France
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, 145(1), p.139-145. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1988
Note:In English. 17 refs.; illus. incl. 6 tables, geol. sketch map
Summary:The results of a detailed study of fluid inclusions in a zone of auriferous quartz veins in the Clogau-St Davids gold mine are presented. Both aqueous and an immiscible pair of H2O-CH4 fluids were present during the mineralizing event. Calculations based on laser Raman and bulk inclusion volatile analysis data indicate that the ores were formed at approx 300-320°C and approx 1.6 kbar. A model is developed which is consistent with both the fluid inclusion data and other considerations. This involves the introduction of aqueous fluid into the graphitic shales hosting the mineralized veins, which reacts with graphite to produce H2O-CH4 fluids. As H2O is consumed to produce CH4, an increase in salinity is observed in the residual aqueous inclusion fluids. Deposition of gold is ascribed to destabilization of either 042AuCl-2 or 059Au(HS)2- complexes in the incoming fluid as a result of interaction with graphite. Auriferous zones within the veins are defined by high CH4 values and low CO2/CH4 ratios in bulk inclusion analyses. These effects are thought to be the result of increased fluid-rock interaction in these zones, related to structural features in the wall-rocks. [R.A.H.]
Subjects:Aliphatic hydrocarbons; Alkanes; Carbon dioxide; Economic geology; Fluid inclusions; Genesis; Geochemistry; Gold ores; Hydrocarbons; Inclusions; Metal ores; Methane; Ore-forming fluids; Organic compounds; Paleosalinity; Salinity; Water; Europe; Great Britain; United Kingdom; Wales; Western Europe; Clogau-Saint Davids Mine; Dolgellau Gold Belt; North Wales
Abstract Numbers:88M/1904
Record ID:1988020505
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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