EIA-REP-325d-12 _BB_ - 201.09.14.pdf - SAHRA

The typical sequence of mining will entail the stripping of all unsuitable soil and subsoil and the stockpiling
thereof at dedicated topsoil and subsoil stockpiles, sited specifically for the purpose. The hard overburden
material will be blasted utilising throw blasting techniques. Waste material overlying the coal seam will be
removed by truck and shovel and these waste materials will be backfilled immediately behind the coal strip
currently being mined. The backfilled waste and subsoil will be profiled, topsoil added and re-vegetated as part of
the mining operation, and hence rehabilitation will be undertaken concurrently with the mining process. The final
void and mine ramps will be backfilled to proximate pre-mining topography.
The extent of Vunene Mining (Pty) limited Mining Right application is approximately 13 540 hectares; however
the extent of the proposed opencast mining area is approximately 200 hectares. The total minable in-situ coal
located within the opencast area is approximately eight million Run Of Mine (ROM) tons of coal.
Based on the quality of the coal within the Usutu Colliery proposed opencast mining project area and the
production rate, the life of mine for the Usutu Colliery proposed opencast mining project is estimated to be
approximately five years.
3.1 Underground mining
The seam thickness varies between 1.20 to 3.00 meters in thickness, which lends itself to bord and pillar mining
using continuous miners. It is planned to take the maximum extraction allowed in primary mining to a safety
factor of 1.6, which will give a 65% yield. There is no plan to extract any pillars at this stage. It is expected that
there will be some dolerite intrusions, thus a dyke development section will be deployed for the purpose of mining
through these and preparing new mining sections.
The underground production is planned to commence on the West Underground Main high wall and will produce
at a rate of 90,000 ROM tons per month from a single production section.
The B and C coal seams reserve at the proposed mining area extends over an area of approximately 13 540
hectares. The seam thicknesses varied between 1.20 metres and less than 3 metres at the depth of 55 to 90
metres. It is estimated that the B and C coal Seam is 84 Million In-Situ Tonnes; as a result the mine is expected
to remain in production for thirty years (30 years).
The terms of reference for underground bord and pillar mining includes:
• No secondary extraction may be undertaken;
• A minimum safety factor of 3,0 must be maintained at all times; and
• A minimum pillar width to mining height ratio of 4,0 must be maintained at all times.
The main factors that influence pillar stability in underground coal mines are the pillar width to height (w:h) ratio
and the pillar safety factor (SF). In order to better understand these concepts, the background relating to these
aspects needs to be understood.
W:H Ratio
The width of the pillar to the height of the seam mined is given as the width to height ratio. This ratio can be read
as the manner in which the pillar will fail. A ratio smaller than 3, indicates that the failure can be violent and
EIA-REP-325d-11
October 2012
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