Petrography and Geochemistry of Igneous Rocks in Amoanda Damang Mine and its Relationship with Gold

Abstract

Economic gold mineralization at Amoanda project area is hosted mainly in the footwall quartzite of the Banket series of the group. Igneous rocks generally are barren in both Amoanda project area and Greater Damang project area. However, core logs and sections from extensive deep drilling at Greater Damang has identified a deep-seated mineralized diorites body whereas igneous intrusive rocks in Amoanda which is suspected to be having similar characteristics show no gold mineralization so far. The question asked is whether the intrusives are the same for the two different project areas and if so why one is mineralized and the other not. Two methods were employed, namely petrography and geochemistry Petrographically, two uniquely weak foliated and fractured igneous rocks, the Meta Diorite and the Meta Dolerite. Major alteration minerals in the selected samples were the cubic pyrites whereas that of the mineralized was euhedral. Geochemically, the average abundance of trace elements such as As,Mn,Fe,Cu,Mg and Ag in selected igneous rocks which form pathfinders to gold mineralisationin in the Birimian were below the background values of average elemental abundance of As, Mn,Fe,Cu,Mg and Ag in normal igneous rocks. This suggests that the intrusives in the Amoanda project area is unmineralised according to Green (1959). Structurally, deformation is weak in the unmineralised igneous rocks where deformations in the mineralized rocks are extensive. The extensive deformation of mineralized deep seated igneous rocks may be as a result of the presence of a structural regime that ruptured and provided enabling environments for the permeation, cooling and subsequent deposition of gold mineralization from the ore bearing hydrothermal fluids.