Abstract
A detailed study of sandstones recovered from the upper part of the recently discovered KL-01 magmatic pipe in the southern part of the Arkhangelsk diamondiferous province (ADP), containing magmatic material and rare kimberlite indicator minerals, is presented in this paper. Results are compared to the composition of crater samples of the highly diamondiferous Vladimir Grib kimberlite pipe and several poorly to non-diamondiferous ADP pipes. To identify the type of magmatic material admixture, a model of binary mixing between country Vendian sandstones and typical ADP magmatic rocks based on correlations of La/Yb and Zr/Nb ratios and Ni contents is proposed. The modeling results show that the type of magmatic component in the KL-01 samples can be identified as kimberlite, with a maximum admixture of 20 vol.%. Kimberlite indicator mineral geochemistry did not exclude the interpretation that the composition, structure, thermal state and metasomatic enrichment of the lithospheric mantle sampled by the KL-01 pipe were suitable for the formation and preservation of diamonds. The lower boundary of the sampled lithospheric mantle could be in the depth range of 175–190 km, with a diamond window width of 55–70 km. Thus, the sandstones could represent the upper level of the crater of a new kimberlite pipe.
Highlights
The Arkhangelsk region, located in the northern portion of the East European Platform (Figure 1), is one of the major industrial diamondiferous areas in Russia
The sandstones of the KL-01 pipe have variable major element compositions; SiO2 and other main oxides correlate negatively, which indicates the ratio of sandstone to magmatic material (MM) constituents (Figure 7A)
The widespread distribution of montmorillonite in the KL-01 pipe sandstones can indicate that these sandstones may be predominantly a component from the upper level of the kimberlite pipe crater and that the lower boundary of the crater may be deeper than 300 m from the surface, with a thickness of at least 160 m
Summary
The Arkhangelsk region (with an area of ~590,000 km2 ), located in the northern portion of the East European Platform (Figure 1), is one of the major industrial diamondiferous areas in Russia. To date, ~100 magmatic bodies of mafic and ultramafic compositions are known within the northern part of the region and form the Arkhangelsk diamondiferous province (ADP, with an area of ~19,000 km2 [1]). Two major diamond deposits are found within the ADP: the Lomonosov and Grib mines [2]. Grib kimberlite pipe in 1996, no new diamondiferous kimberlites have been identified either within the ADP or within the region. Recent studies [1,3] show that several areas, both within the ADP and outside it, have high potential to host local diamondiferous kimberlite sources
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