Abstract
The Lutang graphite deposit in Chenzhou, Hunan province, China, is a well-known coal seam-derived graphite (graphite formed from coal during its natural evolution) deposit with proven reserves of 9.5 million tons and prospective reserves of around 20 million tons (2015 data). The graphite occurs at an andalusite bearing sericite quartz chlorite metamorphic mudstone around a c. 530 km2 Qitianling granite intrusion. A set of coal seam-derived graphite samples from the Lutang graphite deposit in Hunan was examined by geochemical, crystallographic, and spectroscopic techniques to assess changes in the degree of graphitization approaching the intrusion. The carbon content, degree of graphitization, and Raman spectral parameters of series coal seam-derived natural graphite samples show a fluctuating increase with increasing proximity to the granite intrusion. The profile of geological structural features has a close spatial correlation with the variations in the degree of graphitization of series coal seam-derived natural graphite, and a strain-enhanced graphitization model is proposed. Moreover, the geographical distribution and the degree of graphitization are positively related to changes in the iron content of chlorite, suggesting a graphitization process promoted by mineral catalysis during metamorphism. A close spatial relationship exists between graphite mineral and chlorite occurrences when approaching the intrusive mass. The results of this research are important for understanding the role of tectonic stress and mineral catalysis on the genesis of coal-derived graphite.
Highlights
Contact metamorphism is a typical natural process of transformation of the protolith into a new type of rock under variations of the physico-chemical environment caused by magmatic intrusion
We present results of geochemical analysis and microstructure analysis (X-ray diffraction and Raman spectroscopy) of coal seam-derived graphite sampled at various distances from the intrusion, discussing the relationship between fluctuations in the degree of graphitization of coal seam-derived graphite with tectonic events and chemical composition
X-ray diffraction (XRD) analysis was performed for the coal seam-derived graphite
Summary
Contact metamorphism is a typical natural process of transformation of the protolith into a new type of rock under variations of the physico-chemical environment caused by magmatic intrusion. It is generally believed that the heat radiated from the contact with the intrusion is the highest in the central metamorphic aureole. Contact metamorphism of coal under the influence of intrusive magmatism is a common geological phenomenon. The heat, emanation, and dynamic effects of the intruded rock can induce graphitization in the coal seam and organic matters in the associated rock, forming coal seam-derived graphite. This type of graphite is known as natural graphite derived from coal [7,8] or microcrystalline graphite [9]. As a type of graphite ores, coal seam-derived graphite has attracted significant interest from researchers due to its economic efficiency, ease of mining, and potential utilization as a cutting-edge material
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