Signature characteristics of coal geochemistry from the Eocene Tanjung Formation and the Miocene Warukin Formation, Barito Basin: Insights into geological control on coal deposition and future critical element prospection

In conjunction with implementing the Indonesian Act on coal downstream research and development, the geochemical characterization of the Barito Basin coals and an evaluation of the critical elements in coal and coal ashes compared with those found in conventional deposits must be fulfilled. This study documented the signature characteristics of the coal geochemistry in the Barito Basin. Coals from Tanjung Formation mainly comprise huminite macerals and inorganic constituents are mainly dominated by kaolinite, pyrite, quartz, carbonate minerals (i.e., calcite, Sr-bearing carbonate), Ti-oxide minerals (anatase or rutile), chlorite, and apatite. Meanwhile, the Warukin Fm is characterized by high contents of inertinite and inorganic materials comprising kaolinite, pyrite, and quartz. Moreover, the B3 seam from the Tanjung Fm shows normal slight enrichments for Hf, Zr, and V, demonstrating the highest REY content of up to 194.56 ppm. Meanwhile, coal samples from the Warukin Fm show depletion in all the trace elements and REY. The provenance source of the Barito Basin coals is derived from epiclastic mafic-intermediate volcaniclastic rocks, including the Early Cretaceous Pitap and Haruyan Fm, which are mainly derived from low-Ti mafic magmas. Subsequently, marine water infiltration during peat accumulation is subjected to the influence of the geochemical characteristics of coals from the Eocene Tanjung Fm, showing the transgressive settings. On the other hand, the Miocene Warukin Fm. represents a non-marine regressive setting during peat accumulation. Furthermore, local geological controls in the Eocene Tanjung Fm. may lead some roof, floor, parting and coals from B3 seam to critical elements enrichment (such as REY, Zr, Hf, and V), and their affinity is related to Ti-oxide minerals, aluminosilicates, and organic matter.