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Stratigraphic setting and timing of the Montagne d’Or deposit, a unique Rhyacian Au-rich VMS deposit of the Guiana Shield, French Guiana.

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Guiraud, James; Tremblay, Alain; Jébrak, Michel; Ross, Pierre-Simon; Lefrançois, Rock (2020). Stratigraphic setting and timing of the Montagne d’Or deposit, a unique Rhyacian Au-rich VMS deposit of the Guiana Shield, French Guiana. Precambrian Research , vol. 337 . p. 105551. DOI: 10.1016/j.precamres.2019.105551.

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Résumé

In French Guiana, the Montagne d’Or gold deposit (5 Moz at 1.5 g/t Au) is located in the northern branch of the Rhyacian Paramaca Greenstone Belt. The sulphide deposit is hosted by a south-facing bimodal volcanic and volcaniclastic sequence that is highly strained and affected by a penetrative E-W striking and steeply south-dipping foliation. The volcanic sequence is composed of three members, (1) the Lower unit in the stratigraphic footwall, (2) a bimodal mafic-felsic formation hosting the orebody, and (3) the Upper sedimentary and volcanic rocks unit in the stratigraphic hanging-wall. The bimodal formation is dominated by calc-alkaline felsic volcanic rocks in the west, interbedded/interdigitated with tholeiitic mafic rocks in the east. Pillowed mafic flows and graded-bedded felsic volcaniclastic rocks collectively indicate effusive to explosive volcanic activity in a submarine environment. The mineralization consists of thick and laterally extensive sulphide zones forming (1) stratiform sulphide disseminations, (2) structurally-transposed stringer stockworks, and (3) thin layers of deformed semi-massive sulphides. The gold-rich sulphide mineralization consists mainly of pyrite, pyrrhotite and chalcopyrite with minor sphalerite, magnetite, galena and arsenopyrite, hosted by chlorite-sericite-rich alteration zones mainly developed in the felsic tuff facies. U-Pb zircon geochronology shows that most of the Montagne d’Or volcanic and intrusive sequence has crystallized during a multi-cycle magmatic event, from ca. 2152 Ma to ca. 2130 Ma. A porphyry intrusion crosscutting the ore yields a U-Pb zircon age of 2117.6 ± 5.1 Ma, hence constraining a minimum age for the auriferous sulphide mineralization. This also indicates that the sulphide mineralization was coeval with arc magmatism, demonstrating the volcanogenic nature of the Montagne d’Or gold deposit.

Type de document: Article
Mots-clés libres: Rhyacian; Guyane Française; Montagne d’Or; Au-rich VMS; geochronology; transamazonian orogeny; Paramaca greenstone belt; gold
Centre: Centre Eau Terre Environnement
Date de dépôt: 30 janv. 2020 22:02
Dernière modification: 30 janv. 2020 22:02
URI: http://espace.inrs.ca/id/eprint/9697

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