 |
May 27th, 2008
The Rukwa Coalfields comprise two areas of downfaulted Lower Karoo coal measures in western Tanzania, the Namwelle-Mkomolo Coalfield and the Muze Coalfield. They are located about 15km apart, some 40-50 km by road north of the regional capital, Sumbawanga, and approximately 130km and 220km respectively from the Mpanda (Central Line) and Tunduma (Tazara Line) rail heads.
Namwelle-Mkomolo Coalfield lies high on the Ufipa Plateau at an altitude of some 1,750m and takes the form of two elongated, northwest trending, Karoo sediment wedges extending over a strike length of 17km and average width of 2km. The coal measures dip to the southwest off Ubendian basement gneisses and terminate to the dip against a major boundary fault system. Cross faults separate the Namwelle block in the southeast from the Mkomolo-Wankulwe block to the northwest by raising a horst of basement gneiss, called the Wimi Ridge. Locally the stratigraphic sequence typically comprises a thin basal sandstone about 10-15m thick, 20-30m of coal measures, which include a 6m thick "coal zone", a calcareous section up to 60m in thickness, and more than 600m of overlying arkosic and red sandstones.
Potentially workable coal within the upper part of the Namwelle-Mkomolo coal zone occurs in seams up to 1m thick, commonly aggregating 2.0-2.5m, separated by carbonaceous mudstone partings. Initial exploration, including shaft sinking and the drilling of three boreholes, was conducted in the Coalfield in the 1920s and 1930s, but it was not until the 1940s that systematic evaluation was undertaken (McConnell, 1947). McConnell reports on the results of 985m of pitting plus 1,009m of underground exploration development in the Namwelle block. Four shafts were sunk, from two of which the seam was driven down and a number of headings and crosscuts developed. Mkomolo was assessed from old 1935 shafts and pits and trenches. McConnell estimated total coal resources at Namwelle and Mkomolo at 5Mt and 2.5Mt, respectively (currently unclassified). The coal can be described as high volatile bituminous coal, with high ash, high sulphur and a moderate to low specific energy.
In 2004, Tanzanian company Upendo Group Ltd obtained 26 PMLs (Mining Leases) over the main Namwelle-Mkomolo coal zone and began small scale opencast production at an average annual rate of about 2,500t/yr. The coal is trucked to Mbeya and sold to Mbeya Cement and local industries. No recent exploration work has been undertaken.
Muze Coalfield is less well defined than Namwelle-Mkomolo, occurring as a fault margin inlier on the southwestern floor of the great Rukwa Rift Valley, and although close to Namwelle, Muze lies at an altitude of just 850m, or 900m below Namwelle, at the foot of the Rukwa rift escarpment. The stratigraphic column at Muze is very similar to that at Namwelle, with the Karoo sediments largely dipping to the northwest off an upthrown basement gneiss block in the floor of the rift. In close proximity to the main rift fault the coal measures appear to be highly disturbed structurally, but they may flatten with distance from the rift.
Historical exploration at Muze comprised shaft sinking in the 1930s(?), followed by the drilling of two diamond drill holes in 1945. The latter showed that the main Muze coal zone
extends below the Neogene Rukwa Lake Beds cover towards the northeast. Potentially workable coal occurs in at least one seam of thicknesses of up to 3.2m, containing perhaps 2.4m of coal, and is generally of better quality than Namwelle coal, being lower in sulphur and possessing higher specific energy. Apart from a bulk sample of coal having been obtained from a new shaft sunk in 1947 by Williamson Diamonds Ltd, the Muze Coalfield has never been worked.
Coal resources in the exposed part of the Muze Coalfield were estimated by McConnell (1950) at about 10Mt. In 1965 McKinlay re-estimated this resource at just 3.0-3.5Mt. However, he acknowledged that the deposit is open to the north and therefore could be larger. By contrast, Stockley (1947) estimated resource potential at “….. 10,000,000 tons ….. but it is possible that the actual amount might reach 50,000,000 tons”. These estimates are currently unclassified. Exploration drilling through the Rukwa Lake Beds would resolve the extent of the coalfield.
Upendo Group Ltd has registered 40 PMLs over the main part of the Muze Coalfield.
November 16th, 2007
In a previous article in THE MINING MAGAZINE, the writer (G.M. Sockley) gave a brief summary of the history of the search for coal in East Africa. That article was written after the completion of the reconnaissance geological survey of the coalfields in the Ruhuhu Basin east of Lake Nyasa and the present article is to put on record the results of exploration in 1946.
During reconnaissance geological work in the Songea District, situated east of Lake Nyasa, the writer located two new coalfields in teh northern section of the upper Ruvuma Basin. Previous information showed that coal probably could be found somewhere in the region.
A review of the coal deposits of East Africa will be given in a succeeding article and it will be shown that the largest coal=fields of East Africa lie in teh Lake Nyasa region and, although situated a considerable distance from present main communications, the deposits constitute an important source of coal and their influence on teh future economy of this region cannot be long ignored...more
|
|
