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The neglected involvement of organic matter in forming large and rich hydrothermal orogenic gold deposits

Gaboury Damien. (2021). The neglected involvement of organic matter in forming large and rich hydrothermal orogenic gold deposits. Geosciences, 11, (8), p. 344.

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URL officielle: http://dx.doi.org/doi:10.3390/geosciences11080344

Résumé

Orogenic gold deposits have provided most of gold to humanity. These deposits were formed by fluids carrying dissolved gold at temperatures of 200–500 °C and at crustal depths of 4–12 km. The model involves gold mobilization as HS− complexes in aqueous solution buffered by CO2, with gold precipitation following changes in pH, redox activity (fO2), or H2S activity. In this contribution, the involvement of carbonaceous organic matter is addressed by considering the formation of large and/or rich orogenic gold deposits in three stages: the source of gold, its solubilization, and its precipitation. First, gold accumulates in nodular pyrite within carbonaceous-rich sedimentary rocks formed by bacterial reduction of sulfates in seawater in black shales. Second, gold can be transported as hydrocarbon-metal complexes and colloidal gold nanoparticles for which the hydrocarbons can be generated from the thermal maturation of gold-bearing black shales or from abiotic origin. The capacity of hydrocarbons for solubilizing gold is greater than those of aqueous fluids. Third, gold can be precipitated efficiently with graphite derived from fluids containing hydrocarbons or by reducing organic-rich rocks. Black shales are thus a key component in the formation of large and rich orogenic gold deposits from the standpoints of source, transport, and precipitation. Unusual CO2-rich, H2O-poor fluids are documented for some of the largest and richest orogenic gold deposits, regardless of their age. These fluids are interpreted to result from chemical reactions involving hydrocarbon degradation, hence supporting the fundamental role of organic matter in forming exceptional orogenic gold deposits.

Type de document:Article publié dans une revue avec comité d'évaluation
Volume:11
Numéro:8
Pages:p. 344
Version évaluée par les pairs:Oui
Date:17 Août 2021
Sujets:Sciences naturelles et génie > Génie
Sciences naturelles et génie > Sciences appliquées
Sciences naturelles et génie > Sciences naturelles > Sciences de la terre (géologie, géographie)
Département, module, service et unité de recherche:Départements et modules > Département des sciences appliquées > Unité d'enseignement en sciences de la Terre
Unités de recherche > Laboratoire de métallogénie expérimentale et quantitative (LAMEQ)
Mots-clés:orogenic gold deposits, carbonaceous organic matter, hydrocarbons, graphite, CO2-rich fluids, gisements d'or orogénique, matière organique carbonée, hydrocarbures, graphite, fluides riches en CO2
Déposé le:21 oct. 2021 00:11
Dernière modification:21 oct. 2021 00:11
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