Martadi; Pambudi, S.; Verdiansyah, O. Optimizing of Drill Hole Spacing For Coal Resources Classification in Kelay Blok 3 Area, Labanan Formation, Berau Regency, East Kalimantan. IJBAS 2026, 14 (8), 667-675. https://doi.org/10.14419/nbt0tq29.