Morphological Features and Spectral Comparisons of Diamonds from Three Kimberlite Belts in Mengyin, China

Abstract

Striking differences in potentiality of diamond mineralization are shown in the three kimberlite belts of Changmazhuang, Xiyu and Poli in Mengyin, Shandong Province. Previous studies of diamonds have focused on the Changmazhuang belt; however, genesis of diamonds from the other two belts, as well as comparative studies on diamonds from the three belts, are relatively scarce. In this paper, the morphological and spectral features of 44 diamonds ranging from 0.03 mg to 16.46 mg in weight from the three belts are investigated systematically by microscopic observation, Fourier-transform infrared spectroscopy (FTIR) and Raman spectroscopy. The results show that the formation temperature is 1118–1251 °C for Changmazhuang diamonds, 1091–1167 °C for Xiyu diamonds, and 1132–1172 °C for Poli diamonds. Diamonds in the three belts exhibit uniform pre–kimberlite surface features of multiple serrate, triangular laminae and small trigons, suggesting a similar condition of diamond destructive metasomatism caused by carbonatitic and silicate-carbonatitic melts. However, Poli diamonds probably suffered from a silicate component-enriched carbonatitic melt in the deep mantle. Nitrogen contents (0–539 ppm) of diamonds from the three belts have a slight impact on their morphological features.