Iron Oxide Cu-Au (IOCG) Mineralizing Systems: The Eastern Yakutia (Russia) Perspective

Abstract

Iron-Oxide-Copper-Gold (IOCG) are the worldwide economically attractive deposits with significant amount of iron oxides, copper minerals, gold and ± silver and REE. In order to obtain more gold resources in Eastern Yakutia (Russia) we provide a descriptive model for IOCG style mineralization for several new prospective sites, which were initially discovered on satellite images and subsequently certified by prospecting. We allocate three basic Fe-oxide-Cu-Au deposit styles in Eastern Yakutia. First is related to Mesozoic hypabyssal intrusions of granodiorites (Kis-Kuel, Kysyltas and Rep-Yure deposits). As follows from the REE behavior in magmatic rocks, the fractionation of the magmatic melt during cooling was extremely insignificant. Due to this, a substantial part of the iron did not fractionate into high-iron melts, and separated into hydrothermal solutions with rich iron oxide mineralization. Second is related to flows of the basaltic and andesitic lavas of the upper Devonian – lower Carboniferous age (Khurat, Rosomakha and Jalkan deposits). Significant accumulations of hematite with copper and gold are associated with calc-alkaline basalts. The appearance of iron oxides in basaltic lavas is a result of decomposition of ilmenite into hematite and pseudorutile. Third style belongs to magnetite rich lavas of upper Jurassic age (Kildyam deposit). Variolithic lava flows saturated with native iron, magnetite, troilite and pyrite, native iron usually spherical in shape. Intrusion related ore bodies are irregular shaped breccias with arrays of variably mineralized veins and veinlets inside intrusives and veins in the host rocks. Associated with basaltic and andesitic lavas deposits occur as massive, tabular bodies, stratified, pyroclastic ores. The gold grade in IOCG ore varies from less than 1 to more than 50 g/t, base metals are optional. Differences in gold’ fineness and admixtures characterize the genetic features of ore formation and is represented by a system of alloys: Au-Ag, Au-Ag-Cu and Au-Fe-Pd. Discovered iron-oxide copper gold mineralization in Eastern Yakutia analogous to several World class deposit types. Related to Mesozoic hypabyssal intrusions of granodiorites Kis-Kuel, Kysyltas and Rep-Yure deposits are close to Olympic Dam type. IOCG mineralization in basaltic and andesitic lavas of the Khurat, Rosomakha and Jalkan deposits looks similar to deposits of the Mount-Isa region (Eastern North-West Queensland, Australia). The Kildyam deposit rich iron-oxide ore bodies resemble lava flows and have share many common features with El Laco deposit in High Andes.