Characterisation of the quality of the Main Seam at the Ngwabe Shaft of the Zululand Anthracite Colliery, Northern KwaZulu-Natal

Mbonambi, Ntuthuko Blessing
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The Nongoma Coalfield in KwaZulu-Natal is currently one of the least well-known coal deposits in South Africa, yet it is of critical importance as it contains the best quality anthracite in South Africa. The coalfield is still set to remain the country’s major source of anthracite and high-quality metallurgical source for local industry. Coal rank increases from west to east within the Karoo Basin in South Africa. Coal maturity stages include peat, lignite, bituminous and anthracite. Previous work has focused mainly on the structural controls of the coal deposits of the Nongoma Coalfield; no work has been undertaken on quantifying the nature of the seams-particularly the principal economic Main Seam. Thirteen channel samples were collected for this research at several localities at Section 30 of the Ngwabe Shaft at Zululand Anthracite Colliery. Here the Main Seam may be divided into three plies: (i) Coal mainly Bright, Dull (CBD), (ii) Coal mainly Dull, Bright (CDB) and (iii) Coal Bright (CB). Proximate, washability and petrographic (maceral analyses and vitrinite reflectance) analyses were conducted on each ply, thereby allowing for the first description of the physio-chemical and petrographic constituents of the Main Seam in the Nongoma Coalfield. The proximate analyses indicate that the CBD, CDB, and CB plies are characterised by low Inherent Moisture of 1.4-4.2%, Ash of 7.6-20.7%, Volatile Matter of 5.1-6.8%, and a high Fixed Carbon content of 71.4-84.5%.The Total Sulphur analysis revealed low values of Total Sulphur ranging from 0.74-1.62%.The maceral analysis reflected that the CBD, CDB, and CB plies are rich in inertinite and vitrinite, with no liptinite content. The basal CB ply and the top CBD ply exhibits the same maximum reflectance value(5.17%), but the minimum reflectance values recorded for the CB ply (2.40%) and the CBD ply (2.03%) are different. The CBD ply has the highest percentage of mineral matter, mainly sulphides (2.3-3.8%), clay(3.2-8.0%), quartz (0.2-1.0%), and carbonates(0-5.6%).The CB ply reflects the lowest percentage of mineral matter, mainly sulphides (0.8-2.8%), clay (0.2-1.6%), and carbonates (0-0.2%). Quartz is not present in the CB ply. The Main Seam is overlain by two well-defined marker horizons, namely the Upper anthracite marker and the Wave rippled cross laminated marker. The Upper anthracite marker occurs 45m above the Main Seam and is a thin shaly anthracite seam. The Wave ripple marker lies some 80m above the Main Seam. Because this horizon is slightly calcareous it has a distinctive appearance when weathered. This marker is very useful in defining target areas in this structurally complex environment. In most areas the roof consists of competent sandstones, and the floor comprises siltstones and carbonaceuous shale
A dissertation submitted in partial fulfilment of the requirements for the degree of MSc (Economic Geology), in the Faculty of Science, University of the Witwatersrand