ALBERT

Description: Gold mineralization at the Damang deposit is unique among currently known orogenic gold deposits in Ghana, comprising gold hosted within metasediments of the Tarkwaian System and contained in a subhorizontal, extensional quartz vein array that formed during regional compression. The Damang region has an extended paragenesis involving numerous structural, metamorphic, igneous, and metasomatic events. Orogenic gold mineralization occurred late in the geologic paragenesis at Damang, postdating regional metamorphism and an earlier episode of hydrothermal alteration, locally termed "pink hematite" alteration, associated with the intrusion of mafic sills and dikes. This earlier pink hematite alteration event involves extensive silicification that changed the rheology of the altered rocks and promoted later fracturing. Following peak regional metamorphism at around 2005 Ma, the Damang region underwent a short period of rapid exhumation, as constrained through numerical thermal modeling of existing pressure-temperature-time data. This exhumation triggered the generation of a subhorizontal fracture array that was fed by fluids released through decompression-driven metamorphic devolatilization. The interaction between these fluids and the host rock resulted in precipitation of gold in association with sulfide-carbonate-potassic alteration halos around quartz veins. Such postpeak metamorphic, exhumation-driven, devolatilization is unlikely to be a singular occurrence and represents a potentially important source of fluid for orogenic gold deposits elsewhere in Ghana, West Africa, and globally.