A geological, geochemical and isotopic study of primary diamond deposits in the Siberian craton

Abstract

We present an overview of published and newly obtained data, which provides general information about the diamond deposits, geochemical and isotopic of kimberlites from all primary diamond deposits of the Siberian craton (20 kimberlite pipes). These deposits are predominantly composed of pyroclastic kimberlites, typically forming as complex, multi-phase, and multi-channel intrusions. Age determinations, based on U-Pb dating of zircon and perovskite, place these deposits between 370 and 350 Ma. A discernible south-to-north gradation in diamond grade across the Siberian craton, particularly in the Yakutian Province correlates with variations in the chemical composition of the kimberlites. The richest diamondiferous deposits are predominantly high-Mg kimberlites. Strikingly, some of the largest deposits by size (such as Jubileynaya, Zarnitsa, and Mir) are Mg-Fe kimberlites and are noted for their lower proportions of high-quality diamonds. Pyroclastic kimberlites, which constitute most Siberian primary diamond deposits generally have higher diamond grades than coherent kimberlites.Apart from the Nakyn field, the distribution of incompatible elements within Siberian diamondiferous kimberlites appears to be independent of their MgO, total FeO, and TiO₂ content. The kimberlites exhibit ɛNd values ranging from + 1.9 to + 7.0 and initial ⁸⁷Sr/⁸⁶Sr ratios (denoted as ⁸⁷Sr/⁸⁶Sr_i) from 0.702 to 0.706 (except for the Nakyn field deposits), suggesting a provenance from a slightly depleted mantle source, akin to the prevalent mantle. The kimberlites of the Nakyn field deposits differ from other Siberian diamond deposits by an abnormally low content of incompatible elements, higher ⁸⁷Sr/⁸⁶Sr_i (0.706 to 0.710), and low ɛNd (-3.1 to + 2; Kononova et al. 2005). It is assumed that the kimberlites of the Nakyn field were derived from a mantle source, with an intermediate composition between prevalent mantle and enriched mantle I.