A preliminary evaluation method for coal-based graphite

Coal-based graphite is a type of strategic mineral resource and has unique advantages in the fields such as nuclear graphite and military aircraft tires. The evaluation of coal-based graphite is crucial to its exploration and development, upgrading and storage increase, and strategic resource security. Owing to the continuous transition between coal-based graphite and highly metamorphosed coals, some coal-based graphite tends to be wrongly treated as blind coal, and, accordingly, the identified resources of existing coal-based graphite may have been greatly underestimated. In fact, the resources of coal-based graphite are directly related to those of high-rank coals. Therefore, it is significant to survey and evaluate coal-based graphite in the exploration areas of high-rank coals (e.g., blind coal) in the expectation of discovering new areas with potential for coal-based graphite. By analyzing the distribution of typical coal-based graphite resources in Hunan, Fujian, and Jilin in China, this study summarized the prospecting indicators of coal-based graphite, including horizons, mineralization, rock masses, structures, and wall rock alteration. Based on data on coal field structures, the sedimentary environment of coal-bearing strata, magmatic activity, characteristics of coal petrology and coal quality, and coal distribution and metamorphism, as well as the prospecting indicators of coal-based graphite, this study surveyed and evaluated these typical coal-based graphite resources. Accordingly, on the evaluation principle of scientificity, systematicness, and operability, this study proposed a preliminary evaluation method for coal-based graphite based on three parameters, namely exploration level, geological conditions, and mineral conditions, and seven indicators, namely sampling point density, the degree of tectonic deformation, tectonic stress, rock mass scale and thermal action intensity, the distance between rock masses and coal seams, basic identification, and precise identification. In this method, the measured data are compared with the preset values of the corresponding indicators first, then the characteristic values of the indicators are calculated using a fitting equation for planar straight lines, and finally, coal-based graphite is evaluated based on the seven evaluation indicators and their weights. The purpose is to provide a scientific basis for the evaluation of coal-based graphite resources in China. Using the proposed evaluation method, this study evaluated the coal-based graphite resources in the Kekeng mining area in Zhangping, Longyan Yongding coalfield, southwest Fujian, determining an evaluation value of (A1, A2, A3) = (0.735,0.793,0.838). This value indicates that the Kekeng mining area has a high exploration level, favorable geological conditions, minor difficulties with mining, and mineral condition of coal-based graphite No. 1. It is recommended to further densify sampling points and deploy resource exploration.