Lignite resource estimations and seam modeling of Thar Field, Pakistan

Thar lignite field in Pakistan contains more than 175 billion tons thus far not exploited. To date, the coalfield has been divided into 12 exploration blocks and each block is studied and investigated separately by different agencies. As a result of exploration programs, a large exploration database containing geological and coal quality information is constructed, but geostatistical studies regarding to quantify entire Thar lignite resources is not available yet. This paper aims to generate 3D solid model of main Thar seam and to produce spatial distribution maps for various coal quality attributes by geostatistical method, ordinary kriging. 3D seam model has a volume of 17.71 billion m3. The resulting spatial map of ash content shows structured distribution and LCV map shows fair agreement with ash map except in block VI where high and low values of ash and LCV occur in close proximity. The moisture distribution reveals higher values in northern and southern parts whereas the central portion possesses lower moisture values. The sulfur content shows homogenous distribution with some higher sulfur patches at places. The kriging variance maps are generated to delineate areas of higher uncertainty. These maps could be helpful to devise further exploration programs. Blocks were checked on the basis of global averages and swath plot comparison.