The Characteristics and Classification of Spinel Group Minerals in Kimberlite in Wafangdian, Liaoning Province

According to crystal mineralogy theory, under the diagenetic environments with different physical and chemical conditions, crystal structure and chemical composition of spinel group minerals in kimberlite will be obviously different. Through the determination of the lattice parameters and chemical compositions of spinel group minerals from non-lean ore mines and Bonanza kimberlite pipe, the study of internal relations of chemical composition and lattice parameter changes in spinel group minerals among no ore, lean ore and bonanza kimberlite plays an important role for kimberlite diamond deposits prospecting. In order to determine the species of spinel group minerals, MgO, FeO, TiO₂, Al₂O₃, MnO and Cr₂O₃ of 50 spinel group minerals were analyzed by using micro area chemical analysis with Electron Microprobe. The lattice parameters of 136 spinel group minerals were determined by single-crystal X-ray Diffraction. The results show that spinel group minerals in kimberlite Wafangdian of Liaoning province are magnesium-rich chromite. Based on the main cations occupying chemical formulae groups A and B, the spinel group minerals in mining can be divided into 10 subspecies. If the ratio of Cr₂O₃/(Cr₂O₃+Al₂O₃) content (Cr' values) in spinel group minerals represent the degree of mineralization of kimberlite ore-bearing deposit, the Cr' values in high-grade ore, medium-grade ore and lean ore of kimberlite rock in Wafangdian Liaoning are 89.5%, 83.4%-87.1% and 70.2%, respectively. Lattice parameters of the spinel group minerals were 0.831-0.832 nm, 0.834-0.836 nm and larger than 0.837 nm from non-rock, lean ore rock, medium-grade ore and high-grade ore. A case that the spinel mineral lattice parameter of the first generation and Cr' value are the indicators of the ore bearing in Wafangdian kimberlite, Liaoning province is described.