ESTIMASI SEBARAN KUALITAS BATUBARA (ASH CONTENT) MENGGUNAKAN METODE INVERS DISTANCE WEIGHTED (IDW) DAN ORDINARY KRIGING (OK) DI PT. KAYAN PUTRA UTAMA COAL SITE SEPARI, KALIMANTAN TIMUR. geo. sci. kut. bas. [Internet]. 2019 Apr. 12 [cited 2026 Jan. 2];2(1). Available from: https://jurnal.fmipa.unmul.ac.id/index.php/geofis/article/view/330