| Abstract |
The Mnanka area is situated within the Archean age of Musoma Mara Greenstone Belt in NNE of Tanzania in East Africa, the area is near to Nyabigena, Gokona and Nyabirama Gold mines owned by African Barrick Gold. The Mnanka volcanics are found within the Kemambo group that comprises of the sequence of predominant rhyolitic volcanic rocks, chert and metasediments south of the Nyarwana fault. Archaean rocks in the North Mara region form two geologically distinct domains separated by the Nyarwana Fault. South of the Nyarwana Fault the geology is dominated by granitoids and gabbroic rocks with lesser amounts of rhyolitic. Early mapping and interpretation suggests that the basement geology of northern domain (an area north of Nyarwana fault) comprises sedimentary and volcanogenic packages. The basement geology of the area immediately between the Nyarwana Fault and the Utimbaru (Escarpment) is largely obscured by Tertiary phonolite cover somewhat limiting geological knowledge of this area. North of the Utimbaru (Escarpment) Fault the geology is dominated by a distinct sequence of sedimentary rocks that includes a basal conglomerate, overlying basaltic volcanics, sandstone, greywacke, and ferruginous shales. Subordinate cross cutting intrusions include dacitic porphyries, syenite, granite and minor gabbro/dolerite dikes. Many of these intrusive rocks are texturally and petrologically distinct from those south of the Nyarwana Fault. Gold mineralizations in Mnanka area is structure controlled and occur mainly as hydrothermal disseminated intrusion related deposits. Hence the predominant observed structures are joints and flow banding. Measurements from flow banding plotted on stereonets using win-TENSOR software has provided an estimate for the general strike of the area lying 070o to 100o dipping at an average range angle of 70o to 85o while data from joints plotted on stereonets suggest multiple deformation events one of which conforms to the East Africa Rift System (striking WSW-ENE, NNE-SSW and N-S) |