PROSPECTS OF SEARCH FOR DIAMONDiferous KIMBERLITES IN THE NORTHEASTern SIBERIAN PLATFORM
N.V. Sobolev1,2, A.V. Sobolev3, A.A. Tomilenko1, D.V. Kuz’min1,2, S.A. Grakhanov4, V.G. Batanova3, A.M. Logvinova1,2, T.A. Bul’bak1, S.I. Kostrovitskii5, D.A. Yakovlev5, E.N. Fedorova1, G.F. Anastasenko6, E.I. Nikolenko1, A.V. Tolstov7, V.N. Reutskii1
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
3V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, ul. Kosygina 19, Moscow, 119991, Russia
4Diamond and Precious Metal Geology Institute, Siberian Branch of the Russian Academy of Sciences, pr. Lenina 39, Yakutsk, 677980, Russia
5A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia
6St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russia
7AK ALROSA Scientific Research and Geological Exploration Enterprise, ul. Lenina 6, Mirnyi, 678170, Republic of Sakha (Yakutia), Russia
Keywords: Литосферная мантия, гипабиссальный кимберлит, оливин, алмаз, мезозой, U/Pb изотопное датирование, циркон, перовскит, рутил, Сибирская платформа, Литосферная мантия, гипабиссальный кимберлит, оливин, алмаз, мезозой, U/Pb изотопное датирование, циркон, перовскит, рутил, Сибирская платформа, Lithospheric mantle, hypabyssal kimberlite, olivine, diamond, Mesozoic, U/Pb isotope dating, zircon, perovskite, rutile, Siberian Platform
Abstract
The objects of study are Triassic hypabyssal diamondiferous kimberlites with an age of 220-245 Ma, containing macrocrysts of unaltered olivine. The latter are close in the time of formation to the main stage of intrusion of the Siberian Trap Province (252 Ma), which lasted less than 1 Myr. A comparative high-precision analytical study of the Ti, Ca, Cr, and Al impurity patterns of about 1000 olivine macrocryst samples with a forsterite content Fo = [100Mg/(Mg + Fe)] of 78 to 93 has demonstrated the effect of traps on the lithospheric composition. A comprehensive comparative study of diamonds from northern placers and Triassic kimberlites, including determination of their carbon isotope composition, was performed. Chromatography-mass-spectroscopic analysis of submicron fluid inclusions in diamonds from northern placers and kimberlites has shown prevailing hydrocarbons of a wide range of compositions and subordinate contents of N2, H2O, and CO2. These findings, together with the results of previous studies of subcalcic Cr-pyropes and diamonds found in the Lower Carboniferous gritstones of the Kyutyungde graben, lead to the conclusion that the Toluopka kimberlite field is promising for Paleozoic kimberlites. The results of comprehensive studies of diamonds and indicator minerals and U/Pb isotope dating of numerous detrital zircon samples from the basal horizon of the Carnian Stage (Upper Triassic) of the Bulkur site in the lower reaches of the Lena River suggest the presence of diamondiferous kimberlites within the northeastern Siberian Platform. The age of the probable primary diamond sources in the study area can be evaluated by an integrated U/Pb isotope dating of zircons, perovskites, and rutiles from the developed diamond placers and from the basal horizon of the Carnian Stage.
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