Jacky CHAN S.L. Department of Earth Sciences, HKU
The Central African Meso- and Neoarchean Greenstone Belt extends ca. 3000 Km from Tanzania extends westward to the Democratic Republic of Congo (DRC) and into Central African Republic. This unexplored greenstone belt is highly prospective for gold. This study focuses on the Kebigada 30 Km west of the 17-million-ounce Kibali gold deposit.
In the Giro region, the prolonged magmatism commenced at ca. 2801 Ma and ceased around 2196 Ma. A group of felsic to intermediate granitoid plutons with relatively high Sr/Y ratio was formed and intruded the volcano-sedimentary rocks in the region. A stage of dextral ductile shearing along the 30km-long NNW-trending Kebigada Structure Corridor (KSC) occurred between ca. 2583 and ca. 2512 Ma which resulted in the pervasive NNW-trending foliation in the volcano-sedimentary rocks in the region. During this 70 million years period, the rock units were uplifted shortly after the ductile deformation and experienced another stage of sinistral brittle deformation along the KSC which opened up fissures sub-parallel to the foliations. The first phrase of gold mineralization deposit.
A geochemically- distincy phase of intermediate deoleritic intrusions with low Sr/Y ratios emplaced at ca. 2512 Ma and the magmatism ceased at ca. 2497 Ma. Afterwards, the Kebigada deposits and the surrounding region experienced another phrase of sinistral brittle deformation resulting in a number of high-grade vein-type gold deposits.
Geophysics, soil sampling and lithostructural analysis are very effective exploration tools for gold in the region. With extensive drilling during the course of this study, a minimum of 4-million0counces of gold was estimated. Following the same exploration strategies, another Kebigada-type gold deposit, which is just 10 Km further south of Kebigada, has newly been discovered.