Petrochemical evaluation of the diamond potentials of Yakutian kimberlite fields

Abstract

The diamond potentials of nine kimberlite bodies occurring in the Mirnyi, Nakyn, AlakitMarkha, and Daldyn fields were studied by examination of 2026 10-m core intervals. Most typical rock samples of about 1 kg were taken from each interval for X-ray fluorescence analysis of silicates. A total of 6715 kimberlite samples were analyzed. Pairwise correlation coefficients between mean compositions of kimberlites and their diamond contents were calculated. Correlations with diamond presence (99%) were found only for TiO2, Al2O3, and K2O. The negative correlation with TiO2 and the positive correlation with K2O can serve as criteria for diamond presence. These dependences are in good agreement with the petrochemical population model. According to this model, the decrease in TiO2 contents in the range 3.0–0.01% and the increase in K2O content to 0.85% are related to larger depths of parental melting zones. Contents of K2O exceeding 0.85% are determined by the presence of garnet pyroxenites, associated with processes accompanying oceanic crust subduction, in magma formation zones. Formation of parental melts at larger depths determines higher diamond potentials of kimberlite bodies. Our results confirm the hypothesis that kimberlite parental melts are selective melts of lithospheric peridotites saturated with water and carbon dioxide.