Abstract

The Karouni orogenic gold deposit is located in north-central Guyana, 35 km to the west of the 5 Moz Omai gold mine. The deposit is hosted within 2.2 to 2.1 Ga volcano-sedimentary rocks of the Barama-Mazaruni Supergroup, part of the Paleo- to Neoproterozoic Guiana Shield. Karouni consists of two zones, Smarts and Hicks, located 2 km apart along the NW-striking Smarts-Hicks shear zone, a second-order splay of the regional-scale Makapa-Kuribrong shear zone. The Karouni camp is composed of a lower sequence of mafic volcanic rocks, overlain by a lower sequence of immature sandstone and conglomerate, and an upper sequence of sandstone and laminated carbonaceous siltstone, intruded by several generations of felsic plutons and dikes. Whole-rock geochemical analysis indicates their formation in oceanic island-arc environment, and mantle-like characteristics of the high MgO basalts may indicate the presence of deep-seated structures during the early history of the camp. Regional-scale deformation during the Trans-Amazonian orogeny led to tectonic inversion of the volcano-sedimentary basins, greenschist facies metamorphism, and the development of strike-slip shear zones. Late movement on these shear zones is interpreted to be responsible for hydrothermal fluid flow, alteration, and gold mineralization within the Karouni gold camp. The Smarts and Hicks orebodies are localized within dilatational bends formed at changes in strike of the Smarts-Hicks shear zone during late dextral transcurrent movement. Rheological contrast played a dominant role in the formation of the deposits with shear-hosted, NW-striking, and steeply dipping quartz-carbonate-chlorite ± tourmaline-pyrite-gold (V2a) veins preferentially hosted in ductilely deformed, high MgO basalts, whereas mineralized N-S, quartz-carbonate-chlorite ± tourma-line-pyrite-gold (V2b) veins are hosted within rheologically competent high TiO2 dolerite sills and granodiorite dikes. The interaction of these structures with favorable lithology is key for localizing high-grade orebodies.

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