Mineral characteristics and geological significance of coal gangue inHanpoao Coal Mining Area，Hunan Province

The increase of coal metamorphism and the transformation of minerals in the gangue are closely related to the change of the surrounding deformation environment.The mineralogy characteristics and illite crystallinity of coal gangue in Hanpoao Coal Mining Area of Hunan Province were studied by means of polarizing microscope and X-ray diffraction (XRD).The characteristics of clay minerals directly or indirectly indicate the degree of coal metamorphism and its response to temperature and pressure changes were discussed.The results show that the clay mineral,a layered silicate mineral,is very sensitive to the change of deformation environment in the study area.The andalusite (chiastolite) in the coal seam is symbiosis with illite,phyllite and chlorite,etc.The crystallinity of illite is high,and the crystallinity is distributed in 0.140 6°～0.090 9°△2θ,the average crystal thickness (Lc) is greater than 566×10-1 nm.The crystalline order degree of illite was consistent with the organic structural evolution,compared with the peak area,half height and width of illite (001) and the γ peak of irregular part.Vitrinite reflectance and Raman spectra of coal geological thermometer revealed graphite formation of the metamorphic temperature of 400～500 ℃ or higher,indicating the study area of coal seam by low-level epimetamorphism,illite in coal gangue is more than 2M1 model,b0 distributed in 8.883 6～9.030 5×10-1 nm,indicates the deformation environment of coal seam and surrounding rock under low and medium pressure,the pressure conditions formed are 250～400 MPa or higher.According to the change of XRD structure parameters of coal with different metamorphism degree with formation temperature,it shows that higher heating condition is an important factor of organic matter evolution and mineral transformation in gangue.However,the d002 spacing of organic matter structural basic units in coal continues to decrease in the range of similar temperature changes,indicating that the strong tectonic stress in the geological process can catalyze the graphitization process significantly.