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he evaluation and classification on coal resource and reserve in Indonesia has been guided by SNI 1999 which is an Indonesian National Standard on coal resource and reserve estimation. However, this standard does not consider and discuss about any spatial variability an the variable being studied. The coal resource is classified based on the sample spacing and complexiry of geological structures, but not taking into account the coal guantity and guatiry parameters. The complexitv on geological structures does not always correspond to the complexity on coal seam geometric and gualities. Estimation variance in geostatistics i.e. generated by Ordinary Kriging method can be used Io assess the spatial variability on coal geometric and gualities based on variogram modelling and estimation parameters. Therefore geostatistics can be used to evaluate ihe resource estimation and classification which was estimated and classified as well using guidance af SNI 1999. Moreover, estimatian variance can also be used to optimize Ihe drillhole spucing on coal deposit by arranging some spacing and configuration then checking the change an spatial variabiliw of coal variables, The coal resource evaluation takes a case study on two coal seams of Tanjung Formation where the geological structure is considered to be moderate and of Warukin Formation with relatively simple geological structure, both are located at South Kalimantan. The drillhole spacing optimization only lakes a coal seam of Warukin Formation. The result showed that estimation variance by Ordinary Kriging was effective for coal resource evaluation and drillhole spacing optimization.