Geochemistry of source rock-controlled Late Triassic coal: An example from the Dabaoding Coal Mine in Panzhihua, Sichuan Province, southwestern China

The geochemistry of source rock-controlled coals from the Late Triassic Daqiaodi Formation in the Dabaoding Coal Mine of the southwestern Sichuan Province was investigated. A total of 15 coal samples, 6 parting samples, and 4 roof and floor rock samples from the D15-3 and D18 coals were subjected to proximate and ultimate analyses for coal quality, by using LTA-XRD with Siroquant software for minerals, XRF for major element oxides, ICP-MS for trace elements, ICP-CCT-MS for As and Se, ISE for F, and a DMA-80 analyzer for Hg. Results indicate that the Dabaoding D15-3 and D18 coals are classified as low ash and low-volatile bituminous coal. Minerals in coals are dominated by quartz, kaolinite, illite, and dolomite. Most trace elements in the Dabaoding coals are depleted or at normal levels relative to Chinese coals or world hard coals (except for Cr with slight enrichment). The Dabaoding coals and host rocks are characterized by weakly positive Ce and Y anomalies, strongly positive Gd anomalies, and weakly negative Eu anomalies. Based on paleogeographical, mineralogical, and geochemical evidence, the sediment source rocks of the Daqiaodi coal-bearing strata are identified as the Panzhihua trachyte at the top of the Kangdian Upland, which exerted crucial impacts on the Dabaoding coals.