The Karouni Gold Deposit, Guyana, South America: Part I. Stratigraphic Setting and Structural Controls on Mineralization

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 one, 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 orogenv led to tectonic inversion of the volcano-sedimentary basins, greenschist fades 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 l licks 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 (V-2a) veins preferentially hosted in ductilely deformed, high MgO basalts, whereas mineralized N-S, quartz-carbonate-chlorite +/- tourmaline-pyrite-gold (V-2b) veins are hosted within theologically competent high TiO2 dolerite sills and granodiorite dikes. The interaction of these structures with favorable lithology is key for localizing high-grade orebodies.