Structural controls on granitoid-hosted gold mineralization and paleostress history of the Edikan gold deposits, Kumasi Basin, southwestern Ghana

The > 9 Moz total aggregate gold endowment at the Edikan mine, Kumasi Basin, Ghana, is contained within a cluster of orogenic gold deposits located along the Akropong fault zone. The granitoid-hosted orebodies at Edikan (e.g., AG2, AG3, Fobinso, Esuajah), essentially an interconnected mesh of gold-bearing quartz veins, formed during deformation event D3Edk, which postdates the penetrative regional D2Edk deformation. The gold-bearing quartz veins developed in, and adjacent to, N-S- and NW-SE-trending, low-angle thrust faults that crosscut lithological contacts and earlier formed, steeply dipping D2Edk faults. Our paleostress analysis shows that the D3Edk deformation, during which the mineralized fault system developed, was characterized by a WNW-ESE “hybrid” compression that evolved to a strike-slip regime. This progressive deformation is best described with the following stress regimes: WNW-ESE transpression-pure compression (T1) associated with low-angle thrusting, subsequent transpression-strike-slip (T2), and later strike-slip-transtension (T3) associated with steeply dipping strike-slip faulting. The bulk of the granitoid-hosted gold mineralization at Edikan is associated with two principal sets of gold-bearing quartz veins, including low-angle fault-fill veins controlled by thrusts and shallow dipping oblique-extension veins that developed during T1. The activation of the reverse and sinistral strike-slip faults led to the development of restraining jogs characterized by abundant shallow and steeply dipping gold-quartz veins with moderately NE-plunging ore shoots. The geometry of the mineralized fault-fracture meshes is consistent with fault-valve behavior in a horizontal compressive stress regime under sustained conditions of supralithostatic fluid pressures at low differential stress.