CHEMICAL-COMPOSITION OF CHROME SPINELLID AND THE HETEROGENEITY OF THEDALDYN KIMBERLITE FIELD

Analyses of chrome spinellid monomineral separates from a number of ki mberlite pipes in the Daldyn kimberlite field point to remarkable diff erences between objects (individual pipes and pipe soups). For example , the average contents of Cr2O3 vary from 38.44 to 58.35%. A comparati ve analysis of the average (of 18 objects) compositions reveals the fo llowing regularities: a negative correlation between Cr and Ti (r = -0 .572), Cr and Al (r = -0.704), and Cr and Mg (r = -0.866) and a positi ve correlation of Cr with the Mn/Fe ratio (r = +0.775). The content of Ti in the kimberlites (data on 17 objects) is correlated with the com position of chrome spinellid from respective pipes: a positive correla tion was revealed with Ti (r = +0.570) and Mg (r = +0.710), and a nega tive correlation occurs with Cr (r = -0.780) and the Mn/Fe ratio (r = -0.780). A positive correlation (r = +0.67) was detected between the c ontents of Cr in the chrome spinellid and chrome diopside (average of 11 objects). It was determined that the area distribution of chrome sp inellid of various composition also shows a systematic pattern: the. c ontents of Cr and Mn are higher in this mineral from pipes of the nort heastern portion of the field; the contents of Al are somewhat higher and those of Fe are lower in the Sibirskaya and Polunochnaya pipes (no rthwestern part of the field); low-Ti chrome spinellid is typical of t he nearby Osennyaya, Zimnyaya, and Letnyaya pipes. The composition of chrome spineliid provides additional information on the heterogeneity of the Daldyn field, The correlations between the chemical composition of chrome spinellid and the bulk-rock chemistry of the host kimberlit e are generally consistent with the theoretical scheme for the crystal lization of chrome spinellid from kimberlite magma.