Department of Geology
P.O. BOX 27, ZOMBA, MALAWI.
A Paper by Z.
Dulanya
Malawi lies between 33°E and 36°E longitude and between latitudes 9°S and 17°S within the great East African
Rift Valley that stretches from Ethiopia.
The geology is dominated
by crystalline Precambrian to Lower Palaeozoic rocks that have been affected
by the polycyclic Mozambique orogeny (700 – 400my; Carter and Bennett, 1973)
and generally referred to as the Basement Complex (Carter and Bennet, 1973).
Pelitic to semi-pelitic rocks including banded hornblende-biotite gneisses with
intercalations of marbles, calc-silicate gneisses, quartzites and mica schists
cover much of the country. Two-pyroxene granulites and gneisses also known as
charnockites make a good proportion of the geology in the south of the country.
These rocks have been metamophosed under amphibolite to granulite facies
metamorphism. Granitoid orthogneisses and basic and ultrabasic rocks are
scattered throughout the country rocks.
Sedimentary and subordinate volcanic
rocks such as basalts and dolerites of Permo-Triassic to Quartenary overlie
unconformably the Basement Complex rocks together with intrusive rocks of
Jurassic to Lower Cretaceous which
are ascribed to the Chilwa Alkaline Province. The Chilwa series includes
syenites, nepheline syenites, carbonatites and agglomerates, solvsbergites,
trachytes and phonolites.
Large parts around the
major drainage systems such as the Lake Malawi and the Shire River, the
Lilongwe, Kasungu and Mzimba plains are overlain by superficial deposits.
The structural and
metamorphic history of the country is complicated. A number of orogenies such as
the Ubendian (2200 – 1900 my), the Irumide (~1350 – 1000 my) and the
Mozambican are known to have affected the country the first two being restricted
to the northen part of the country. Faulting which is mostly related to the
rifting has played a greater part in the post-orogenic development of the
country.
With such variety of
rocks, a number of minerals are known to occur. At the time of writing this
manuscript (January, 2002), detailed information on most of these minerals is
lacking and much is known about the geological evolution of the Malawi basement
complex which was not the case in the past. Re-evaluation work on some of the
known minerals has or might render some of these prospects workable under the
present economic conditions. For example gypsum which was known to occur as an
occurrence exists in abundance for exploitaion. Carter and Bennett (1973)
categorized the minerals into three groups the first group being deposits with
highest exploitation potential and the third group with the least potential.
Such categorization is maintained here for clarification and classification
purposes only. Some work has been done on some of the Group I and II minerals.
These include phosphates
(apatite), bauxite, kaolinitic clays, coal, kyanite, limestones, rare earths
(including strontianite and monazite), graphite, sulphides (pyrite and
pyrrhotite), titanium minerals, vermiculite,
and uranium minerals.
Barytes, Chromite,
Copper, Corundum (includes the gem varieties), Fluorite, , Mica, Nepheline
Syenite, Niobium, Gypsum, Iron Ore, Talc, gemstones (agates, garnets,
aquamarine, aegerine, smoky quartz, etc) and Ornamental or dimension stones (sodalite
and amazonite among others).
This group includes
mostly mineral occurrences and very little to no work has been done to assess
their viability for exploitation.
Known occurrences include
Asbestos, Beryl, Diatomite, Galena, Gold, Magnesite, Manganese minerals, Molybdenite, Nickel minerals,
Platinoids, Semi-precious and Tantalum minerals, Zinc Minerals and Zircon.
REFERENCE
Carter, G.S.; Bennett,
J.D. (1973). The Geology and Mineral Resources of Malawi. Bull Geol. Surv. Malawi, 6.