Elemental and Mineralogical Characterization of Permo-Carboniferous Coal in the Ngaka Coalfield, Southwest Tanzania: Implications for Coal Quality Variation

Abstract

Coal from heterolithic seams exhibits distinct chemical characteristics due to interbedded non-coal beds, which influence its quality and usability. Despite extensive research in these settings, the elemental and mineralogical characteristics of the heterolithic sequences of the Mchuchuma Formation (K2) in the Ngaka Coalfield remain poorly documented. This study provides the first detailed assessment of K2 seams across five active mine sites. Eleven representative samples were analyzed using proximate, elemental, and mineralogical techniques, supported by Pearson correlation, binary analysis, and Principal Component Analysis. Proximate analysis revealed that ash content varies across mine sites, with values ranging from 9.17 to 25.03%, volatile matter from 24.06 to 27.49%, inherent moisture from 1.07 to 1.89%, fixed carbon from 48 to 64.78%, and calorific value from 5,766.2 to 7,457.35 kcal/kg, classifying the coal as medium-volatile bituminous. Most minor elements are below 100 ppm, except sulfur, chlorine, and strontium, which are enriched, particularly in Sites 3 and 4. Potassium, calcium, and iron also exceed 1,500 ppm. Mineralogical analysis shows a diverse range of minerals with abundant quartz, clays, feldspars, carbonates, and minor sulfides. Integration of chemical and mineralogical data indicates that ash content and traceelement enrichment strongly influence coal quality, with Site 3 exhibiting the lowest quality