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

Abstract

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 southdipping 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.

Diversity of supergene gold expressions and implications for gold targetting in an equatorial regolith (AMG's Couriège Exploration Prospect, French Guiana)

“…Within this tectonic-lithological framework, four types of gold-bearing deposits are currently identified: (1) Au-rich VMS (Volcanogenic Massive Sulphide) deposit as characterised by Franklin et al (2000) and Guiraud et al (2017Guiraud et al ( , 2020 at Montagne d'Or; (2) stratiform/stratabound gold-bearing tourmalinites with disseminated sulphides as observed at Dorlin (Milesi et al, 2003) with an overprinting of late orogenic gold mineralisation dated at ca. 2.06 Ga (Marcoux & Milési, 1993); (3) gold-bearing polygenic conglomerates hosted by the Upper Detrital Unit, exampled at Montagne Tortue (Milesi et al, 1995) where the mineralisation is multi-stage with an orogenic gold overprinting expressed by quartztourmaline veining (Milesi et al, 2003) and (4) orogenic gold deposits as observed at Yaou, Esperance, Loulouie, Boulanger and Camp Caïman (Milesi et al, 2003).…”

“…The Guiana Shield (Fig. 1A) in South America is an important mineral province hosting significant gold resources which are attractive for the exploration of gold deposits (Voicu et al, 2001;Milesi et al, 2003;Daoust et al, 2011;Velasquez et al, 2014;Tedeschi et al, 2018a;Guiraud et al, 2020, Combes et al, 2021. However, due to its low latitude geographic position, the Guiana Shield is covered mainly by a well-developed regolith and equatorial rainforest, representing a challenging environment for exploration (Freyssinet et al, 1989(Freyssinet et al, , 2005Butt, 1998;Butt et al, 2000;Anand & Butt, 2010;Theveniaut & Freyssinet, 2002;Butt, 2015;Sunkari et al, 2019).…”

Challenging the traceability of natural gold by combining geochemical methods: French Guiana example

“…Four types of primary gold deposits have been identified (Marcoux and Milési, 1993;Milesi et al, 1995Milesi et al, , 2003Franklin et al, 2000;Guiraud et al, 2020): (i) gold-rich volcanogenic massive sulphide (VMS, e.g. Montagne d'Or); (ii) stratiform/stratabound gold deposits hosted by volcano-sedimentary rocks, where gold is associated with disseminated sulphides (e.g.…”