Does gold in orogenic deposits come from pyrite in deeply buried carbon-rich sediments; insight from volatiles in fluid inclusions

The origin of volatiles in fluid inclusions was reviewed for testing the involvement at depth of carbonaceous-pyritic sedimentary rocks as the source for orogenic gold mineralization. Fluid inclusions from selected deposits were analyzed by solid-probe mass spectrometry. Fluids are mostly aqueous-ca...

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Bibliographic Details
Published in:Geology (Boulder) 2013-12, Vol.41 (12), p.1207-1210
Main Author: Gaboury, Damien
Format: Article
Language:English
Subjects:
Africa
aliphatic hydrocarbons
alkanes
aqueous solutions
Canada
carbon
Carbon dioxide
carbonaceous composition
case studies
Computational fluid dynamics
Degradation
Deposition
Economic geology
ethane
Fluid flow
Fluid inclusions
Fluids
gases
Geochemistry
Gold
gold ores
hydrocarbons
inclusions
Mass spectrometry
metal ores
methane
mineral deposits, genesis
mineralization
nitrogen
organic compounds
pyrite
rock, sediment, soil
Rocks
Sedimentary rocks
Sediments
sulfides
volatiles
water
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Summary:The origin of volatiles in fluid inclusions was reviewed for testing the involvement at depth of carbonaceous-pyritic sedimentary rocks as the source for orogenic gold mineralization. Fluid inclusions from selected deposits were analyzed by solid-probe mass spectrometry. Fluids are mostly aqueous-carbonic, with variable amounts of N2, CH4, C2H6, Ar, H2S, H2 and He. For fluids with CH4 and C2H6, their ratios (C1/C2) range from 2.6 to 25.5, indicating that C2H6 is sourced from thermally degraded organic matter. Proportions of CO2, CH4, C2H6 and H2 are highly variable and can be explained by hydrothermal reactions where C2H6 is degraded to CO2 by water consumption. Such reactions may account for the problematic CO2-rich, H2O-poor fluids associated with some of the richest gold districts. Conditions needed for C2H6 degradation are also fundamental for forming gold deposits, such as HS--enriched fluids for carrying gold and local weakly oxidizing conditions for promoting gold precipitation. The C2H6 content is recorded in fluids from Mesoarchean to Cretaceous gold deposits, providing support for a general model where fluids and gold were sourced from deeply buried, carbon-rich, and pyrite-gold-bearing sedimentary rocks.
ISSN:0091-7613
1943-2682
DOI:10.1130/G34788.1