The Couriège prospect (French Guiana) provides key examples of the diversity of gold distribution related to supergene processes. The nature of gold in two contrasted weathering profiles is examined as a function of the weathering lithofacies. The autochthonous profile hosts weathered Au-bearing quartz veins whereas the pediment profile is enriched in free gold issued from dismantled gold-bearing quartz veins. The gold distribution is controlled by: (i) the preservation of primary gold as free gold in both transported and autochthonous horizons and as electrum inclusions in detrital pyrite, and (ii) the formation of secondary gold through dissolution/precipitation processes, expressed as gold spherulites on free gold grain surface, Ag-depleted rim around transported free gold grains and Ag-depleted gold micro-inclusions hosted by oxidised autochthonous pyrite. Gold enrichment through supergene chemical processes remains limited within the truncated autochthonous profile. A new conceptual model is proposed for the area, defining the role of chemical and physical processes in gold endowment, and accounting for the geomorphological context. The overall evolution includes (i) deep weathering and peneplenation, (ii) dismantlement and transport of lateritic material, and (iii) development of a latosol cover. This study highlights that gold exploration in tropical environments must consider the residual vs transported nature and the inheritance of targeted pedogenic horizons.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5476187

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The Yaou deposit, located in French Guiana within the Guiana Shield, is one of the most promising gold deposits of the regional Palaeoproterozoic greenstone belt. It displays numerous quartz monzodiorite bodies aligned along a sinistral shear zone where a five-deformation phases model is established at the camp scale. The ductile D1/2YA phase is responsible for the main penetrative foliation while the D3YA phase is related to shearing. An intrusive event is identified as being pre to syn-D3YA. The following phase D4YA represents a brittle quartz-carbonate veining set hosted preferentially within intrusive bodies and along the shear zone. A local D5YA brecciation event crosscuts the D4YA veins. Among this deformation history, two auriferous events (D3YA and D4YA) control the overall grade of the Yaou gold deposit. More specifically, most of the Au grade is associated with the main economic D4YA veining event, where the gold is visible and linked to Py4 within an ankerite/hematite rich alteration halo. At the microscopic scale, results of in situ analyses using LA-ICP-MS on pyrite show that metasediment-hosted Py0 is a primary source of submicroscopic gold having a low contribution to the total endowment. Py3 shows some gold content due to possible remobilisation of AuD0YA. Gold in Py4 is found as submicroscopic gold, as micro-inclusions and as infilling fractures in association with elements such as Te, Ag and Bi. Most contribution to the Au grade is from micro-inclusions and, to a lesser extent, from free and submicroscopic gold. The ore shoot locations are lithologically controlled for AuD0YA (metasedimentary unit-hosted), structurally controlled (shear zone-hosted) for AuD3YA and rheologically controlled for the AuD4YA (intrusion-hosted). The deposit is clearly polyphase both at the macroscopic and the microscopic scales, invisible gold is associated with As whereas visible gold is observed as inclusions in pyrite with high contents of Ag, Te and Bi. We define an early low-grade enrichment of AuD0YA to AuD3YA followed by a later high-grade event, AuD4YA supporting polyphase mineralisation processes. This study confirms that orogenic gold deposits can be formed by remobilisation and/or new gold inputs during multiple deformation, veining and hydrothermal events.