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Russian Geology and Geophysics

2018 year, number 10

Cr-SPINEL ASSEMBLAGE FROM THE UPPER TRIASSIC GRITSTONES OF THE NORTHEASTERN SIBERIAN PLATFORM

E.I. Nikolenko1, A.M. Logvinova1,2, A.E. Izokh1,2, V.P. Afanas’ev1, O.B. Oleynikov3, A.Ya. Biller3
1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
2Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia
3Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
Keywords: Шпинель, карнийский ярус, алмаз, щелочной магматизм, осадочный коллектор, триас, Сибирская платформа, Spinel, Carnian Stage, diamond, alkaline magmatism, sedimentary reservoir, Triassic, Siberian Platform

Abstract

An assemblage of Cr-spinels widespread in Carnian (Upper Triassic) diamondiferous deposits in the northeastern Siberian Platform is studied. Analysis of their morphology and chemical composition has revealed two dominant varieties of Cr-spinels and has demonstrated certain regularities in their distribution in the study area. Correlations have been established between the areal distribution of the recognized types of Cr-spinels and diamond varieties typical of kimberlite sources and between the distribution of Cr-spinels and rounded diamond dodecahedrons. The phase and chemical compositions of polyphase inclusions in the Cr-spinels are studied. The spatial arrangement of inclusions along the crystal growth zones indicates their primary genesis and trapping from the melt during crystallization. Compositional features of some minerals in the inclusions-SiO2 impurity in apatite and high CaO contents (0.2-0.8 wt.%) in olivines-point to a nonkimberlite source of these Cr-spinels. The presence of K- and Na-containing phases and calcite in the inclusions indicates saturation of the initial melt with alkalies, Ca, and CO2. The data obtained suggest that the numerous Late Vendian diatremes in K-rich alkaline basites of the Olenek Uplift area are the source of the dominant Cr-spinel variety.