Petrology and Geochemistry of the Jurassic Coals in Southwestern Ordos Basin, China

Abstract

This study is related to seven Jurassic bituminous coal samples collected from four mines of the Huanglong coalfield, southwestern Ordos Basin, China. Petrological and geochemical characteristics of these samples were investigated. The results show that these Jurassic coals are high in inertinite (54 vol. %), followed by vitrinite (31.7 vol.%) and liptinite (3.7 vol.%). The mineralogy of the coals is dominated by illite, kaolinite, quartz, calcite, pyrite, and less siderite, feldspar, goyazite, anatase, illite-smectite, dolomite, and marcasite. These coals are low in sulfur (0.18–0.71%). With the exception of the No. 4 coal from the Dafosi mine, in which the total sulfur is 1.32% and the pyritic sulfur is up to 0.78%. Compared to common Chinese coals, the Jurassic coals are much high in CaO (2.12%), MgO (0.26%), P2O5 (0.21%), Sr (591 μg/g), Ba (476 μg/g), and F (187 μg/g). The excess P, Sr, and Ba in the BMF-2 and BMF-4 are mainly present in goyazite-gorceixite series minerals (goyazite). The content of rare earth elements ranges from 32.2 to 154 μg/g (mean 80.6 μg/g). The chondrite-normalized distribution pattern is typically characterized by the enrichment of LREE over HREE. And the high anomaly Eu value (0.86) of these Jurassic coals was probably inherited from its source detrital rocks.