COMPUTER AIDED THREE DIMENSIONAL GEOLOGICAL MODELING AND RESOURCE ESTIMATION OF MULTIPLE LIGNITE SEAMS AT THE BADIN COAL FIELD, BLOCK-I, PAKISTAN, USING THE INVERSE DISTANCE WEIGHTING METHOD

Abstract

The Badin Coal Field hosts considerable lignite resources in the south eastern part of Sindh, Pakistan. A two hundred square kilometre area of the field subdivided into four blocks. The preliminary investigation of Block-I was completed by drilling thirty three boreholes, and the resources were originally reported as about 275.998 million tons using the conventional Bore Hole Influence Method (BHIM). The conventional approach carries a high level of uncertainty because it disregards the spatial continuity of seam thickness, which can lead to both overestimation and underestimation of the deposit. This study replaces the conventional procedure with a computer aided workflow. A validated digital geological database of the thirty three boreholes was developed and imported into Geovia Surpac, and the Inverse Distance Weighting Method (IDWM) was applied to estimate the resource and to generate spatial distribution maps for moisture content, ash, gross calorific value, and sulfur. Four consistent seams, namely Seam-1, Seam-2, Seam-3, and Seam-5, were encountered with thickness ranging from 0.3 m to 6.2 m. The solid model returned a combined volume of about 160.023 million cubic metres, and the constrained block model, populated using IDWM with a power of eight and a coal density of 1.25, estimated about 206.15 million tons of lignite resource across Block-I. Seam-4 and Seam-6 were excluded because they were intersected in only three and one boreholes respectively. The spatial maps reveal systematic directional trends in quality for each seam and an alternating correlation between gross calorific value and sulfur that reflects depositional control. The results provide a reliable and reproducible basis for mine planning and offer policy makers an improved picture of the resource than the conventional estimate.