SEAMIC Newsletter Vol. 10

Mesozoic to Paleozoic sediments
equivalent to the Karoo Supergroup
occur mainly in the Cassanje Graben, a
north-central to north-western
geographical depression. Diverse subvolcanic
and volcanic bodies occur
including kimberlites and carbonatites
along a major south-west to north-east
trend line across Angola, as well as
basalt, dolerites, syenites, trachytes and
phonolites.
Upper Proterozoic fold belts (Pan
African age) occur along the margins of
Angola's Precambrian shield, the most
important being the West Congo,
Damara and Maiombe-Macongo. They
are characterized by the occurrence of
base metal mineralisation and a variety
of industrial minerals.
Lower Proterozoic to Archean rocks
form the Angolan, Maiombe, Cassai and
Bangweulo shields and the Kwanza
horst. Granite-gneissic terrain, metavolcano-sedimentary
and metasedimentary
(greenstone) belts are
present in south-central Angola
(Cassinga and Menonogue). The
Cunene basic (ultrabasic) complex
occupies 20,000 km 2 of the southwestern
part of the Angolan shield.
MINERAL DEPOSITS
Angola has considerable mineral wealth. Currently diamond is the most important mineral
resource after oil. Precambrian shield areas, which cover a large part of the country, have
reported mineral occurrences of gold, copper, platinum group metals and other minerals which
could be commercially exploited.
Diamonds occur in kimberlites and in a variety
of placer deposits. Around 700 kimberlites of
varying sizes (65-190ha) and shapes (rounded
to elongate) are known, the grade increasing
with depth. The kimberlites are aligned along a
SW to NE trend across Angola into DRC.
Alluvial diamonds are produced from the
erosion of kimberlites of Cretaceous age (80-
120Ma). The richest diamond fields are located
in the north-eastern corner of Angola in Lunda
Norte. Past and present production is
principally from recent alluvial river deposits,
but some deposits occur in older alluvial terraces or Cretaceous conglomerates.
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