Fluid inclusion volatiles as an exploration guide to black shale-hosted gold deposits, Dolgellau gold belt, North Wales, UK

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doi: 10.1016/0375-6742(91)90058-3
Authors:Shepherd, T. J.; Bottrell, S. H.; Miller, M. F.
Author Affiliations:Primary:
Br. Geol. Surv., Geochem. Dir., Nottingham, United Kingdom
Other:
Univ. Leeds, United Kingdom
Volume Title:Fluid inclusion gas analyses in mineral exploration
Volume Authors:Kesler, Stephen E., editor
Source:Fluid inclusion gas analyses in mineral exploration, edited by Stephen E. Kesler. Journal of Geochemical Exploration, 42(1), p.5-24. Publisher: Elsevier, Amsterdam-New York, International. ISSN: 0375-6742
Publication Date:1991
Note:In English. 23 refs.; illus. incl. 5 tables, geol. sketch maps
Summary:MS analysis allows a distinction to be made between auriferous and non-auriferous fluids. Samples of auriferous quartz from ore shoots at the Clogau-St Davids and Gwynfynydd mines are significantly enriched in CH4 and N2 compared to quartz from barren veins. Variation in the composition of inclusion volatiles strongly supports a spatial link between the distribution of high-grade ore zones, the presence of graphitic shale wall rocks and CH4-N2 fluids. During mineralization, C and N are released to the ore fluids as a result of fluid-rock interaction; the process generating CH4, CO2 and N2. It is the generation of N2, however, thought to be due to the oxidation of NH+4 substitution in wall-rock phyllosilicates, that gives rise to auriferous fluids with a distinctive 'CH4-N2' signature. Ore deposition is thought to have been triggered by destabilization of the Au(HS)-2 complex caused by the flashing of H2S into an immiscible (CH4-N2)-rich fluid phase generated during mineralization. Hence, volatile signatures, Au deposition and fluid unmixing can be related to reactions producing CH4 and N2. In view of the worldwide occurrence of black shale/schist-hosted Au deposits in greenschist facies metamorphic terrains, the recognition of fluid inclusions with enhanced levels of CH4 + N2 constitutes a potential reconnaissance exploration technique. [This, and the papers represented by 10 additional abstracts, form a Special Issue on Fluid inclusion gas analyses in mineral exploration.] [R.E.S.]
Subjects:Analysis; Black shale; Clastic rocks; Economic geology; Fluid inclusions; Gases; Geochemical methods; Gold ores; Inclusions; Metal ores; Mineral exploration; Ore guides; Ore-forming fluids; Sedimentary rocks; Volatiles; Europe; Great Britain; United Kingdom; Wales; Western Europe; Clogau-Saint Davids Mine; Dolgellau Belt; Dolgellau District; Gwynfynydd Mine; Northern Wales
Abstract Numbers:92M/3167
Record ID:1992014682
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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