The Sapan Dalam coal deposit of Indonesia consists of ten steeply
dipping seams with thicknesses varying between 0.1 and 3.5 m and split
by shale, clay, silt and sandstone. The area contains four faults dipping
about 75 with four to 85 m vertical displacements. The complex nature
of the deposit coupled with limited 27 exploration drillholes at an average
spacing of 200 m made it difficult to create a realistic geological model. A
three-dimensional gridded seam model gave a fair representation of the
deposit. Attempt to create an optimum pit using the WHITTLE 3D pit
optimiser proved unsuccessful since the pit optimiser is restricted to
standard regular or fixed blocks. The gridded seam model was converted
to a fixed block model prior to the optimum pit design. Smoothing and pit
base controlling were also introduced to obtain a smoother pit. A mining
scenario produced 3.6 million tonnes of coal, 28.4 million bcm of waste
and US$18.1 million revenue.