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Hybrid nature of the platinum group element chromite-rich rocks of the Norilsk 1 Intrusion: genetic constraints from Cr spinel and spinel-hosted multiphase inclusions

Citation

Chayka, IF and Kamenetsky, VS and Zhitova, LM and Izokh, AE and Tolstykh, ND and Abersteiner, A and Lobastov, BM and Yakich, TY, Hybrid nature of the platinum group element chromite-rich rocks of the Norilsk 1 Intrusion: genetic constraints from Cr spinel and spinel-hosted multiphase inclusions, Economic Geology, 115, (6) pp. 1321-1342. ISSN 0361-0128 (2020) [Refereed Article]


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DOI: doi:10.5382/ECONGEO.4745

Abstract

The Norilsk 1 intrusion (Russia), renowned for its abundance of sulfide ores, contains an upper contact zone, which hosts sulfide-poor and Cr spinel and platinum group element (PGE)-rich discontinuous reefs with significant economic potential. Located within strongly inhomogeneous contact rocks of various compositions, the origin of these reefs is complex and debated. Enrichment in PGEs in these rocks is distributed heterogeneously, occasionally occurring in extremely dense disseminations of Cr spinel, which are unusual for other rocks of the Norilsk 1 intrusion. The compositions of Cr spinel vary significantly between individual samples, even within the same samples across clusters of several Cr spinel grains and single grains. Chromium spinel grains are broadly characterized by low Mg# (350 mol %), moderate to extremely high TiO2 content (118 wt %), diverse Fe2+/Fe3+ ratios, and elevated V and Zn. Multiphase silicate inclusions hosted by Cr spinel are dominated by orthopyroxene, alkali-feldspar, clinopyroxene, Na phlogopite, high-Al amphibole, chlorite, and albite, along with minor felsic glass, sulfide, apatite, baddeleyite, titanite, calcite, halite, and cordierite. Heating experiments (1,250C) on the silicate inclusions failed to produce homogeneous glasses but showed evidence of partial melting and reactions with precursor minerals that crystallized new phases. The experimentally obtained glasses are characterized by compositions that strongly differ from any known igneous rock in the Norilsk region, and the assemblage of phases in these inclusions is not supportive of the entrapment of a homogeneous silicate melt. Trace element patterns of the glasses of the experimentally heated inclusions are compositionally distinct from the Norilsk trap basalts, and instead are closer to the sedimentary rocks of the Norilsk region. We suggest that an in situ interaction between the mafic melt and the sedimentary rocks was responsible for Cr spinel mineralization and the formation of the host rocks. The subsequent subsolidus modification of the initial rocks expanded the Cr spinel compositional range and formed muscovite-albite-chlorite assemblages, which replaced the original silicate minerals.

Item Details

Item Type:Refereed Article
Keywords:Norilsk, Cr-spinel, noble metals
Research Division:Earth Sciences
Research Group:Geology
Research Field:Igneous and metamorphic petrology
Objective Division:Mineral Resources (Excl. Energy Resources)
Objective Group:Mineral exploration
Objective Field:Precious (noble) metal ore exploration
UTAS Author:Kamenetsky, VS (Professor Vadim Kamenetsky)
UTAS Author:Abersteiner, A (Mr Adam Abersteiner)
ID Code:143707
Year Published:2020
Web of Science® Times Cited:1
Deposited By:CODES ARC
Deposited On:2021-03-30
Last Modified:2021-06-22
Downloads:0

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