MANGANESE CRICHTONITE IN KIMBERLITE BRECCIA

Abstract

The persistent occurrence of diverse forms of manganese crichtonite in kimberlite breccias of the Mir, the Aykhal, the No. 3 and the Dal'nyaya pipes, Yakutia has been proven. The coexisting forms of this mineral detected here are as follows: 1) inclusions in xenoliths of sedimentary carbonate rock; 2) segregations in the mesostasis of breccia-cementing kimberlite; 3) phenocrysts in breccia-cementing kimberlite; 4) inclusions in picroilmenite nodules; 5) segregations of the vein type. The concentration of admixed components in manganese crichtonite is rather variable, but there are no patterns either in the variations themselves, or in their relationship to forms in which the mineral is segregated. Manganese crichtonite even within a rock type as specific as kimberlite breccia may exhibit great diversity in its forms and mineral associations. There are marked fluctuations in chromium content of a whole series of these forms and association. The chemical composition of the medium that generated the manganese crichtonite must have varied widely in the kimberlite process, and such crichtonite properties could not have developed in the same magmatic melt. These and other aspects of the subject are discussed.