Potensi Pembentukan Air Asam Tambang Pada PIT 3000, Blok Toraja, PT Trubaindo Coal Mining Berdasarkan Studi Karakteristik Geokimia dan Mineralogi Batuan Overburden dan Underburden

Abstract

Coal mining in Indonesia is mostly applied by an open pit system which causes the rocks in the mining location to be exposed to the surface, so that it will be easy to react with air and water directly. The high content of sulphide minerals such as pyrite and marcasite in coal mining site, has the potential to produce mine acid water. Mine acid water causes environmental pollution and a threat to aquatic and soil ecosystems by increasing the concentration of other heavy metal ions. This study aims to identify the mineral content of the overburden rock layers to determine the type of sulfide minerals forming acid mine and neutralizing minerals in rocks. The methods used in this study are field investigations, mineralogical content analysis, geochemical characteristics and measured stratigraphic to evaluate mineralogical content, geochemical characteristics and depositional environmental facies of overburden and underburden rocks from the Pit 3000 coal seam. The results showed that overburden rocks were composed by claystone with the thickness ranges 1.60 m – 5.15 m, whereas underburden rocks are characterized by diverse lithology such as claystone, siltstone and sandstone with the thickness ranges from 0.20 m – 4.50 m. Based on geochemical analysis on 18 overburden rock samples, it is known that overburden layers have characteristics that are dominated by Non Acid Forming (NAF) rocks with 83% NAF, 11% Potential Acid Forming (PAF) and 6% uncertain. The characteristics of the underburden layer are dominated by PAF rocks with 45% PAF, 19% NAF and 36% uncertain.