Optimizing of Drill Hole Spacing For Coal Resources Classification in Kelay Blok 3 Area, Labanan Formation, Berau Regency, East Kalimantan

Optimizing of drill hole spacing for coal resource classification is a method for optimizing and evaluating coal resources in a seam within a coal mining area. The Kelay Block 3 area is included in the concession of PT Berau Coal, Berau Regency, East Kalimantan. The main coal-bearing formation is the Labanan Formation. The Labanan Formation is known to have fairly thick and low-quality coal seams. Exploration drilling has been conducted at 69 drilling locations, consisting of 34 core drilling locations and 35 open-hole drilling locations. The coal resource classification in the study area falls into the moderate geological condition category according to SNI 5015:2019. This research was conducted to analyze the optimal borehole spacing in the Labanan Formation for coal resource evaluation and classification in the study area using the global estimation variance (GEV) approach. The results obtained from optimizing borehole spacing in the study area were taken at a spacing of 350 m for the measured category, 600 m for the indicated category, and 1200 m for the inferred category, based on the thickness variable. This is because the global estimation variance (GEV) method considers population and variation, which are values that approximate variance thru GEV analysis. Optimizing borehole spacing using the global estimation variance (GEV) method showed wider and more optimal results than the provisions of SNI 5015:2019 under the same geological conditions.