Application of the Global Estimation Variance and Sill Variogram Methods in Determining the Optimum Drill Hole Distance for the classification of Measured Coal Resources
DOI:
https://doi.org/10.11137/1982-3908_2025_48_60123Keywords:
Geostatistics, Geological Complexity, SNI standardAbstract
In the implementation of effective and efficient exploration of mineral and coal resources, it is required to carry out geostatistical analysis to determine the relative error value of the optimum spacing of the drilling and its thickness and quality distribution. This study uses the application of geostatistics with the sill variogram method and global estimation variance (GEV), based on the relative value of the error of the thickness of the coal seam. This research was conducted in the concession area of PT. Kaltim Prima Coal. Based on the case study, the coalfield consisted of two seams, namely the North BE and South BE seams, with moderate geological conditions. From the variogram analysis of the thickness of the northern BE layer, the range is 151, the sill is 0.65, and the Nugget Effect is 0.04, while the BE South has a range value of 209, the sill is 0.16, and the nugget effect is 0.26. Based on field data, the average drill hole distance in the North BE seam is 131 meters. The distance of 1/3 of the sill gets a value of 50 meters (measured resource), while for the South BE seam it is 126 meters. The distance of 1/3 sill gets a value of 60 meters (measured resource), the distance of 2/3 sill gets a value of 122 meters (resource indicated), and the distance of 3/3 sill gets a value of 210 meters (inferred resource). Based on global estimation variance analysis. For the North BE Seam, the drill hole spacing for the measured resource category was 350 meters with a total of 29 drills, while for the South BE Seam, the drill hole spacing for the measured resource category was 350 meters with a total of 104 drills. The results of this classification produce an area of influence that is smaller than the SNI standard of moderate geological complexity. By using the sill variogram analysis, the results of the drill hole spacing are dense when compared to the results of the GEV analysis. The results of this GEV classification produce an area of influence that is relatively like to the SNI standard of moderate geological complexity.
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