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Diamond-Bearing Root Beneath the Northern East European Platform (Arkhangelsk Region, Russia): Evidence from Cr-Pyrope Trace-Element Geochemistry

1
Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia
2
Proex Service Ltd., Arkhangelsk 163071, Russia
3
AGD Diamonds, Arkhangelsk 163000, Russia
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(5), 261; https://doi.org/10.3390/min9050261
Received: 3 April 2019 / Revised: 22 April 2019 / Accepted: 26 April 2019 / Published: 30 April 2019
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Abstract

In this study, we reconstruct the composition and metasomatic evolution of the lithospheric mantle beneath the poorly-studied southern Arkhangelsk region, based on the geochemistry of 145 Cr-pyrope grains recovered from samples of modern rivers and stream sediments, to evaluate the diamond exploration potential of these territories. Based on the concentrations of Cr2O3, CaO, TiO2, and rare earth elements (REEs), the garnets are divided into four groups: (1) low-chromium lherzolitic pyropes with fractionated heavy REE patterns; (2) low- to medium-chromium pyropes of lherzolitic and megacryst associations with flat heavy REE patterns; (3) high-chromium lherzolitic pyropes with “humped” REE patterns; and (4) high-chromium and low-chromium lherzolitic and harzburgitic pyropes with sinusoidal REE patterns. The pyrope geochemistry suggests a multi-stage model for the evolution of the lithospheric mantle, including partial melting to different degrees and further metasomatic overprints by silicate and carbonatite melts. The results confirm that the lithospheric mantle beneath the study area is suitable for the formation and preservation of diamonds. The significant percentage of diamond-associated pyropes (15%) emphasizes the likelihood of high diamond contents in kimberlites to be discovered within the study area. View Full-Text
Keywords: diamond exploration; kimberlite indicator mineral; pyrope geochemistry; mantle metasomatism; lithospheric mantle; kimberlite diamond exploration; kimberlite indicator mineral; pyrope geochemistry; mantle metasomatism; lithospheric mantle; kimberlite
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Shchukina, E.V.; Agashev, A.M.; Shchukin, V.S. Diamond-Bearing Root Beneath the Northern East European Platform (Arkhangelsk Region, Russia): Evidence from Cr-Pyrope Trace-Element Geochemistry. Minerals 2019, 9, 261.

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