Namibia´s
varied geology encompasses rocks of Archaen to Phanerozoic age,
thus covering more than 2600 million years of earth history. Nearly
half of the country´s surface area is bedrock exposure, while
the remainder is covered by young surficial deposits of the Kalahari
and Namib Deserts.
Metamorphic inliers consisting of highly deformed gneisses, amphibolites,
metasediments and associated intrusive rocks occur in the central
and northern parts of the country, and represent some of the oldest
rocks of Palaeoproterozoic age (ca. 2200 to 1800 Ma) in Namibia.
The Kunene and Grootfontein Igneous Complexes in the north, the
volcanic Orange River Group and the Vioolsdrif Granite Suite in
the south, as well as the volcanosedimentary Khoabendus Group and
Rehoboth Sequence also belong to this age group.
The Mesoproterozoic (1800 to 1000 Ma) is represented by the Namaqua
Metamorphic Complex, which comprises granitic gneisses, metasediments
and granitic/metabasic intrusions, and by the volcanosedimentary
Sinclair Sequence of central Namibia, with its associated granites
(e.g. Gamsberg Suite).
The coastal and intracontinental arms of the late Proterozoic Damara
Orogen (800 to 500 Ma) underlie large parts of northwestern and
central Namibia, with stable platform carbonates in the north and
a variety of metasedimentary rocks pointing to more variable depositional
conditions further south. Along the southwestern coast, the volcanosedimentary
Gariep Belt is interpreted as the southern extension of the Damara
Orogen. During the later stages of orogenic evolution the shallow-marine
clastic sediments of the Nama Group, which covers much of central
southern Namibia, were derived from the uplifted Damara and Gariep
Belts.
Sedimentary and volcanic rocks of the Permian to Jurassic Karoo
Sequence occur in the Aranos, Huab and Waterberg Basins, in the
southeastern and northwestern parts of the country. They are extensively
intruded by dolerite sills and dyke swarms, which in collusion with
predominantly basaltic volcanism (e.g. Etendeka Plateau) and a number
of alkaline subvolcanic intrusions (e.g. Brandberg, Spitzkoppe,
Erongo), mark the break-up of Gondwana, and the formation of the
South Atlantic ocean during the Cretaceous. The currently last chapter
of Namibia´s exciting geological history is represented by
the widespread Tertiary to Recent (less than 50 Ma) sediments of
the Namib and Kalahari Sequences.
Targets for mineral exploration have been identified throughout
the stratigraphic column. Metamorphic complexes host a variety of
prospective environments, such as copper-molybdenum porphyry, volcano-exhalative
base metals and gold, volcanogenic copper, sedimentary-exhalative
lead-zinc, shear-zone gold and beryllium-niobium-tantalum pegmatites.
Meso- to Neoproterozoic rocks locally contain extensive red-bed
copper, while calc-alkaline granitoid intrusives of that age have
potential for porphyry and hydrothermal copper, as well as for vein-type
gold mineralisation.
In the Neoproterozoic Damara Orogen and Gariep Belt, mineralisation
is associated with successive phases of intracontinental rifting
(copper, graphite), spreading and the formation of passive continental
margins (volcano-exhalative base metals, e.g. Rosh Pinah {1}, Skorpion
{2}; sedimentary-exhalative lead-zinc, eg. Tsongoari {3}; glaciomarine
iron-manganese, e.g. Otjosondu {4}). Besshi-type copper-pyrite (e.g.
Otjihase {5}) is related to mid-ocean ridge development, whereas
subsequent subduction led to the localised enrichment of carbonate-hosted
base metals (e.g. Tsumeb {6} and Kombat {7}), uraniferous granites
(Rössing {8}), rare metal and tin pegmatites (Uis {9}, Rubicon
{10}), as well as skarn tungsten and gold (Navachab {11}).
Coal measures are hosted in Permian rocks of the Karoo Sequence,
while Cretaceous anorogenic complexes, contain a variety of semi-precious
stones, fluorite (Okorusu {12}), apatite, rare earth elements, iron
and base metals. Following the discovery of the offshore Kudu gas
field of Cretaceous age {13}, recent hydrocarbon exploration also
intersected oil-prone source rocks in boreholes. Tertiary epigenetic
uranium mineralisation occurs in calcretes above basement rocks,
while salt is produced by solar seawater evaporation (e.g. Walvis
Bay and Swakopmund Salt Works {14}).
The major growth area of Namibia’s mining industry, however,
is offshore diamond mining, with the country featuring among the
world’s top five producers. The Tertiary to Quaternary diamondiferous
deposits are currently exploited along the southwestern coast, both
off - and onshore {15}, employing techniques, which are used nowhere
else in the world.
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