Geology of Zimbabwe

Stratigraphy

Precambrian

The oldest supracrustal rocks are the Sebakwian Group (3.5 Ga) exposed around Shurugwi and Mashava, and northwest of Gweru, within the central craton. This group consist of metavolcanic rocks, including komatiite and basalt, banded iron formation, and clastic metasedimentary rocks. The Sebakwian Group is succeeded by the Bulawayan Group, further differentiated by the Lower Greenstones (2.9 Ga) and Upper Greenstones (2.7 Ga). The Lower Greenstones include felsic volcanic and volcaniclastic rocks, komatiites, and komatiitic basalts with interbedded iron-formations and polymict clastic sediments. Overlying the Bulawayan Group is the Shamvaian Group (2.7 Ga), and it is these two groups which constitute the main greenstone belts. The tonalitic Sesombi Suite and granitic Chilimanzi Suite granitoids intruded the Upper Greenstones and Shamvaian Group between 2.7 Ga to 2.6 Ga. The last major Archaen event was the intrusion of the Great Dyke (2.5 Ga).

By 1982, 123 mines had produced 155 tonnes of gold from the stratabound iron-formations of the Sebakwian, and Lower and Upper Greenstones. Of these mines, 31 had produced more than 311 kg, with the Wanderer Mine near Shurugwi producing the most at 36 tonnes. Non-stratabound gold production included 128 tonnes from the Que Que Ultramafic Complex within the Mashaba Ultramafic Suite of the Upper Greenstones, while the Upper Greenstone Basaltic and Bimodal Units had produced 400 and 161 tonnes respectively. Granitoid host rocks had produced a total of 132 tonnes of gold, and include the Rhodesdale Batholith at 53 tonnes, the Sesombi Suite at 36 tonnes, and the Penhalonga quartz diorite at 10 tonnes.