Gold-bearing volcanogenic massive sulfides and orogenic-gold deposits in the Nubian Shield

Abstract

The Nubian Shield is a large region of juvenile Neoproterozoic rocks that, together with its counterpart in the Arabian Shield, is part of a major accretionary orogen. It originated as late Tonian-Cryogenian island arcs on the site of the Mozambique Ocean formed by breakup of Rodinia. Arc collisions, subsequent magmatism, volcanism, sedimentation, and orogeny, associated with Cryogenian-Ediacaran convergence of cratonic blocks during the assembly of Gondwana, converted the region into the East African Orogen. The Nubian Shield region also has important Paleozoic-Neogene strata, including significant flood basalt, that conceal large areas of the basement. The Shield contains hundreds of gold occurrences and evidence of a 5,500-year history of gold mining. The main deposit types are orogenic gold and gold associated with volcanogenic massive sulfides (VMS). The juvenile subduction-related origin of the Shield rocks and the pervasiveness of shearing and greenschist-to-amphibolite facies metamorphism associated with late Neoproterozoic orogeny are geologic features highly favorable for the development of these types of deposits, and make the combined Arabian-Nubian Shield the Earth’s largest Neoproterozoic gold resource. Gold-bearing VMS deposits are currently mined at Bisha (Eritrea) and are soon to be mined at Hassai (Sudan). Orogenic gold is mined at Sukari and Hamash (Egypt), Qbgbih and Kamoeb (Sudan), Koka (Eritrea), and Lega Dembi and Sakaro (Ethiopia), and mining is due to start at Gupo (Eritrea) and Tulu Kapi (Ethiopia) in the near future. More than twenty companies are actively exploring for gold in the region and potentially important deposits are known in Egypt (Hamama-VMS), in northern Sudan (orogenic gold and VMS), along strike from Bisha and in the Asmara area, Eritrea (VMS and orogenic gold), in northern Ethiopia (VMS), and in western and southern Ethiopia (orogenic gold and sparse VMS).