COAL
Tanzania possesses a considerable
resource of low sulphur coal. This resource is currently exploited only on
a small scale at Kiwira Coal Mine, but is potentially suitable as a source
of energy or coal-based materials for domestic industries. There is
potential for export to neighbouring African and Indian Ocean countries.
Coalfields with the highest potential
are Ketewere-Mchuchuma in the Ruhuhu basin and Songwe-Kiwira, both located
near the shores of Lake Nyasa in Southwest Tanzania. Coal
characterisation, has been undertaken by the Geological Survey of Tanzania
in collaboration with other local and foreign institution, based on coal
petrology, quality studies and depositional environments (Semkiwa 1992;
Semkiwa et al. 1998; and Semkiwa et al. 2003). The coalfields are
contained in the rocks of the Karoo Super group. Eight Karoo basins
containing eleven recognized coalfield occur in the south-west part of the
country (Fig. 49). A few occurrences of lignite have been reported in the
Tertiary coastal plain sediments and in the region of Jurassic outcrop
near the coast. Lignites deposits are generally poorly investigated.
Isolated from the coastal industrial
areas and from most major mineral deposits, coal has not yet contributed
to the economy of the country. With the extension of paved highways and
railroads into the interior, economic prospects for the coalfields have
improved considerably. Drilling in all the coalfields has proved resources
in the order of 500 Mt of coal, but only 40% can be extracted by surface
mining methods. The total coal resource in Tanzania may be as high as 1500
Mt. Seam continuity and quality are generally comparable with the Karoo
(Permo-Triassic) coal of Zimbabwe and South AFRICA. Coal quality data on
the Tanzanian coalfields re summarised in the Tables 8 and 9.
In common with Karoo coals elsewhere
in African, the Tanzanian seams investigated low in methane and other
gases. Very little formational gas was encountered in drilling within the
Ruhuhu basin.
Geology.
The coalfields of Tanzania occur in
disconnected Karoo basins, which extend along a northwest-southeast
trending corridor near Lakes Nyasa and Rukwa (Fig 49). Coal seams are
contained in two formations; a lower and upper formation, which have been
formerly named as Mchuchuma Formation and Mhukuru Formation (Ssemkiwa,
1992). The coal is of Permian age and is equivalent to the coals occurring
in the Ecca Group of the main Karoo Super group in South Africa.
Coal seams occurring in the Mchuchuma
Formation are of commercial significance. Those seams within the Mhukuruu
Formation are not economic in all the coalfields except in the Mhukuru
coalfield where marginally economic seams occur.
The major and most economic
coalfields are the Ketewaka-Mchuchuma and Ngaka fields located in the
Ruhuhu basin, in the southwest of Tanzania. In these coalfields, the
Mchuchuma Formation has been sub-divided into two distinct facies
(Semkiwa, 1992). The lower or sandstone-coal facies has thick coal seams
with relatively low sulphur and ash contents. It consists of succession
thick high-energy sandstone and arkoses separated by coal seams of
commercial interest ranging in thickened from less than 1-m to7.5m with
good continuity. The coal seams have relatively low sulphur and ash
contents. The upper or shale-coal facies consists of succession of shale,
coaly shale and mudstone bands separated by thin, impersistent seams
generally of poor quality. The coal seams have relatively high sulphur and
ash contents compared to those in the lower sandstone-coal facies. The
succession is generally about30-50 m thick with about10% composed of coal.
The underlying contact between rocks
of the Karoo Super group and the Precambrian is
Figure 49: Distribution of Karoo
Super group and Coalfields of Tanzania
Irregular with relief up to 300
metres. Coal seams associated with the lower sandstone-coal facies are
better developed over the palaeo-valleys of this surface. Thick and
persistent seams occur at the Mchuchuma-Ketewaka coalfield and Mbalawala
in the Ngaka coalfield. Dips of the seams of interest are less than 15
degrees. The coal seams are disturbed by block faulting.
The coal of Tanzania was deposited in
fluviatile to lacustrine depositional environments (Kreuser et al., 1987,
Semkiwa, 1992). They vary in rank from sub-bituminuos to
medium-volatile bituminous (mvb). They are generally low in sulphur (less
than 2%), but high in ash content between 15%and 20%, with some as
sulphide in pyrite and marcasite. Much of the ash content in the shale
coalfacies is related to shale stringers included within the coal seams,
and it is probable that washing would yield a higher-quality product. The
resulting product would be a good quality steam coal or, in some cases, a
cooking coal.
Generally the coal has high content
of inertinite minerals similar to other Gondwana coals. Coal seams
associated with sandstone-coal facies have relatively high vitrinite
contents while the coal seams in the shale-coal facies have relatively
high lipnite contents.
Songwe-Kiwira Coalfield.
Songwe-Kiwira coalfield is located
near the Tanzania/Malawi border at the Northwest end of Lake Nyasa. This
is the only coalfield producing coal using mechanised underground coal
mining (Kiwira Coal Mine). The coalfield is in a relatively small outlier
of Karoo and is 100km from Mbeya, the railhead of TAZARA Railway and only
45km from Itungi port on Lake Nyasa. The Kiwira Coal Mine (KCM) was
developed in 1988 by STAMICO with Chinese assistance; to replace a former
small privately owned Ilima Colliery. Kiwira Coal Mine has a rated
production capacity of150, 000 tonnes of coal per annum or 93,000 tonnes
of washed bituminuos coal. At present, the mine produces only96, 000
tonnes annually and an additional 103,000 tonnes a year from the nearly
Ilima Colliery. Proven reserves at IVOGO Ridge (KCM) amounts to 35Mt while
those at Ilima Hill are 280,000 tonnes. The nearly Kabulo Ridge has
surface mineable proven reserves of 85Mt with ash content ranging from 25%
to 45%.
All the production is consumed
locally. A coal-fired power generating plant at the mine site has a
designed capacity of Mw. Four MW are supplied to the National Grid and the
mine uses 1 MW. Expansion to 18 MW is planned.
