Stone coal is defined as a combustible, low-heat value, high-rank black shale of early Paleozoic (in a few cases, Permian) age, widely distributed in southern China. Attention has been focused on stone coals because (1) they can be used as fuel energy (for power plants and daily use in some villages) mainly in southern China; (2) they are enriched in critical elements and are currently industrially (economic extraction of V) and agriculturally (such as Se) utilized or have such a great potential (e.g. Au, platinum group elements, Mo, and Ni); (3) they are the sources for some toxic elements that have caused environmental pollution (e.g. SO₂ emission during their combustion) and endemic diseases such as selenoisis and fluorosis; and (4) they can provide useful information for geological events and regional geological setting (e.g. hydrothermal activities). This article reviews stone coal’s definition; occurrence and distribution; petrologic properties, mineralogy, and geochemistry; adverse impacts on environment and human health; and by-products of critical elements as well as major challenges remaining from point of view of determining element enrichment mechanisms, utilization of critical elements, and control of toxic elements released during stone coal utilization.

This paper presents the mineralogical and geochemical compositions of coal benches and non-coal (carbonaceous rock benches, parting, roof and floor) samples from the No. 1 Coal in the Longtan Formation of the Permian-Lopingian epoch from the Shugentian Coalfield, eastern Yunnan Province, southwestern China. The coal is rich in Nb, Ta, Zr, and Hf, which were derived from the Kangdian Upland with the dominant compositions of the Emeishan basalt. The minerals identified in the samples include mixed-layer illite-smectite, kaolinite, quartz, siderite, and minor calcite, pyrite, anatase and ankerite. Albite and chamosite occur in the roof and floor samples. The parting sample (SGT1-2p) is characterized by abundant siderite (64.9%) and calcite (20.1%), and one carbonaceous rock sample SGT1-11 contained a large amount of pyrite (26.1%). Four factors were responsible for the geochemical and mineralogical compositions in the samples; namely, the terrigenous detrital materials transported from the Kangdian Upland, direct volcanic ash inputs, multi-stage inputs of hydrothermal fluids, and marine influences. The co-existence of siderite and pyrite was attributed to a continental-marine transitional environment.

Coal and oil shale are both organic matter-rich sedimentary rocks. However, their sources of organic matter and their depositional environments are different. The present study focuses on the Palaeogene Lijiaya Formation sequence in the Huangxian Basin, Shandong Province, East China, which has oil shales showing marine geochemical indicators overlain by coals indicating marine regression. We investigated the C1 coal seam and underlying OS2 oil shale layers, compared their geochemical and mineralogical characteristics, clarified the details of their constituents, in order to elucidate the features of their sources, their depositional environments, and the post depositional processes in the context of the geological evolution of the basin. The Al₂O₃/TiO₂ (18.1–64.9) and TiO₂/Zr ratios (28.2–66.5) in the C1 coals and OS2 oil shales, respectively, suggest a felsic to intermediate source, and the Mesozoic granite on the South of Huangxian Fault may be one of the provenances of these sediments. The low sulphur content (0.53–0.59%) and low Sr/Ba ratios (0.32–0.67) suggest a freshwater depositional environment for the C1 coals. In contrast, the higher total sulphur contents (0.60–1.44%), the higher Sr/Ba ratios (0.31–1.11%), and the occurrence of calcareous shells, indicate seawater intrusions during deposition of the oil shales. The V/Ni, V/(V + Ni), and V/Cr ratios of the OS2 oil shale suggest oxic to suboxic conditions with a distinct change in palaeo-redox between the lower and upper parts of OS2 seam. The high boron contents in C1 coals (average, 504 ppm) is related to the high content of analcime (with the correlation coefficient of 0.96), and the high concentration of boron was attributed to a secondary enrichment by epigenetic hydrothermal solutions. The occurrence of idiomorphic-authigenic albite in association with analcime and quartz in veins in the coals suggests that albite is a product of a reaction between analcime and silica, both of volcanic origin. The reaction takes place at about 190 °C, indicating that the area was affected by hydrothermal fluids.

The overlying strata of the stope can be divided into low ( immediate roof ), medium and high strata according to the degree of influence of the mine pressure behavior of the working face. Among them, the pressure step distance of low rock strata can be judged according to the roof pressure appearance of hydraulic support, and the middle and high rock strata can not be accurately and intuitively determined only by theoretical calculation. Therefore, IMU is used to monitor the motion state and fracture distance of different layers, so as to study the relationship between them and periodic weighting. Firstly, the accuracy of monitoring effect and the error of monitoring data are determined by indoor test. Then, taking the 52507 working face of Daliuta as the engineering background, 3DEC software is used to assist the verification. The research shows that the IMU monitoring data meets the requirements of error and accuracy, and can accurately monitor the rock movement ; the movement period of rock strata at different heights is different. As the height of rock strata increases, the displacement distance of rock strata gradually increases, and the median rock strata play a key role in the movement of overlying rock strata. The periodic pressure monitored is twice the actual periodic pressure.

Coal and its associated minerals are vital geological resources, holding significant value for both energy security and the supply of strategic materials