Geologic and Metallogenic Framework of North Africa

Abstract

North Africa is noteworthy for having a great diversity of geology and mineral resources. Geologically, the region contains numerous terranes that contain rocks ranging in age from Archean to Quaternary, including diverse igneous, sedimentary, and metamorphic lithologies. Major geological features were built during the main phases of Proterozoic and subsequent Phanerozoic orogenies, the break-up of the supercontinents Rodinia, Gondwana, and Pangea, and during the opening and closing of major ocean basins such as the Iapatus, Atlantic, Pacific, and Tethys. Three major tectono-stratigraphic domains are recognized (1) the Precambrian province that includes the African-Nubian Shield (ANS) to the east and the West African Craton (WAC) to the west, and the intervening Tuareg Shield and “Saharan Metacraton”; (2) the Variscan (Paleozoic) fold belt; and (3) the Atlas-Alpine (Mesozoic-Cenozoic) system. Mineral deposits of North Africa formed in a variety of geologic settings at different time periods from Archean to Quaternary. Mineral commodities including gold, silver, cobalt, nickel, chromium, arsenic, copper, lead, zinc, iron, and many other elements. Major deposit types present in the region are (1) orthomagmatic Cr-Ni-platinum group elements (PGE); (2) rare-metal granites and related rare-element pegmatites; (3) volcanic-hosted massive sulphide (VHMS); (4) sedimentary-exhalative (SEDEX); (5) orogenic and intrusion-related gold; (6) iron oxide-copper-gold (IOCG); (7) banded iron formation (BIF); (8) Mississippi Valley-type (MVT) lead-zinc; (9) sediment-hosted stratiform copper; (10) sediment-hosted U, Mn, and phosphate; (11) five-element veins containing nickel-cobalt-arsenic-silver-bismuth(-uranium); (12) epithermal gold-silver veins; (13) skarn and replacement tungsten, tin, and/or base-metals; (14) residual manganese, phosphate, salt, potash, bentonite, etc.); and (15) mechanically concentrated deposits (e.g., paleoplacer gold). Some deposits are world class in terms of size, grade, and ore production, including phosphate deposits and the Imiter silver deposit in Morocco, Precambrian BIF deposits in Mauritania, orogenic gold deposits in Mali and Mauritania, uranium deposits in Niger, and MVT lead-zinc deposits in the High Atlas system of Morocco and Tunisia. Resources and exploration potential are also known for gold, diamonds, strategic metals, and other commodities within the Precambrian cratonic terranes of most North African countries. Based on absolute ages for mineralization, or alternatively for ages of the host rocks (where radiometric age determinations are lacking), seven major time periods of mineralization defining distinct metallogenetic epochs are recognized. Each has different metal associations, mineralogical and geochemical features, spatial distributions, and geodynamic environments that collectively discriminate time periods and related metallogenic provinces. These are: (1) Archean (>2500 Ma), (2) Paleoproterozoic (2500–1600 Ma), (3) Neoproterozoic (630–542 Ma), (4) Hercynian (540–290 Ma), (5) Permian-Triassic (~300–200 Ma), (6) Late Cretaceous-Paleogene (100–23 Ma), and (7) Late Miocene-present (<16 Ma).