Geochronological constrains on the timing of magmatism, deformation and mineralization at the Karouni orogenic gold deposit: Guyana, South America

The Karouni deposit is located in central Guyana 35 km to the W of the former producing 5 Moz Omai mine and is interpreted to be an orogenic gold deposit. It is hosted in Rhyacian aged (2.2 to 2.1 Ga) volcano-sedimentary and intrusive rocks metamorphosed to greenschist facies. Detailed structural and crosscutting relationships, coupled with robust, new U-Pb geochronology on intermediate to felsic intrusive rocks and hydrothermal minerals from the Karouni camp have constrained the structural evolution of the deposit and provided a new age for gold mineralization with important implications for the structural framework and timing of gold mineralization throughout the region. Magmatism within the 200 km ² of the Karouni camp progressed from early, synvolcanic intermediate composition dikes at ∼2147 Ma to a major voluminous pulse of felsic magmatism coeval with regional deformation during the Trans-Amazonian Orogeny between 2120 and 2088 Ma. A late pulse of granitic magmatism at ∼1950 Ma may be related to a post orogenic event. Inherited zircons within the felsic intrusive rocks indicate assimilation of crust as old as 2223 ± 32 Ma. Gold mineralization associated with camp scale D ₂ deformation has been dated to 2084 ± 15 Ma on the basis of U-Pb geochronology of hydrothermal titanite. These results show gold mineralization is coeval with felsic magmatism and contemporaneous with a major pulse of orogenic gold mineralization in the Birimian Province of West Africa.