Geological controls on mineralogy and geochemistry of the Late Permian coals in the Liulong Mine of the Liuzhi Coalfield, Guizhou Province, Southwest China

Abstract

This paper investigates the mineralogical and geochemical compositions of the Late Permian coals in the Liulong Mine, Liuzhi Coalfield, Western Guizhou Province, China, by using XRD, SEM-EDX, ICP-AES and ICP-MS. Both the No.3 and No.7 Coals are classified as low volatile bituminous coal. However, the No.3 Coal is a medium-ash (29.8% on average) and high-sulfur (4.76% on average) coal while the No.7 Coal is a low-ash (12.4% on average) and medium-sulfur (2.16% on average) coal. Major minerals in both coal seams include quartz, pyrite, marcasite, kaolinite, calcite, and to a lesser extent, gypsum and anatase. Illite, chlorite, rectorite, albite, ankerite and siderotil are only present in the No.3 Coal. The No.3 Coal contains higher elemental concentrations than the No.7 Coal probably due to the higher mineral contents in the No.3 Coal, and is enriched in Nb and Ta, and to a lesser extent in K, Ti, Li, V, Co, Cu, Sr, Zr, Mo and Ba.The mineralogical and geochemical data presented in this study have shown that the No.3 Coal was formed under a higher degree of marine-influenced coal-forming environment than the No.7 Coal. However, the both Coals have the Kangdian Upland (made of mafic igneous rocks, such as basalt rocks) as sediment-source region like other coals from Guizhou Province. Three geological factors control the geochemical patterns of the No.3 and No.7 Coals, namely: (1) the high detrital input in the No.3 Coal causing high ash yields; (2) the sediment-source region (Kangdian Upland basalt) causing high Ti, Nb and Ta contents, and a minor proportion of Co, Cr, V and Cu, when combined with the high detrital input in the No.3 Coal; (3) the higher degree of marine influenced depositional environment in the No.3 Coal causing a high S, Sr and Ba contents.