TY - JOUR
T1 - Hybrid Nature of the Platinum Group Element Chromite-Rich Rocks of the Norilsk 1 Intrusion
T2 - Genetic Constraints from Cr Spinel and Spinel-Hosted Multiphase Inclusions
AU - Chayka, Ivan F.
AU - Kamenetsky, Vadim S.
AU - Zhitova, Liudmila M.
AU - Izokh, Andrey E.
AU - Tolstykh, Nadezhda D.
AU - Abersteiner, Adam
AU - Lobastov, Boris M.
AU - Yu. Yakich, Tamara
N1 - Funding Information:
The authors are very grateful to many people who assisted this study: Artem Shevko and Marina Gora (field work and sampling), Maya Kamenetsky and Nadezhda Belkina (sample preparation), Valery Chubarov (electron microscopy), and Sergey Smirnov (Raman spectroscopy). Elena Nigmatullina and Victoria Danilovskaya are particularly thanked for the high-quality EMPA data they supplied. Sergey Sluzhenikin, Viktor Ryabov, Valery Kalugin, Marina Yudovskaya, and Anton Kutyrev discussed the results and helped to make implications. The paper benefited from comments by two anonymous reviewers and the guest editor, Steve Barnes. The study was performed on state assignment of IGM SB RAS and is largely supported by the Russian Science Foundation (grant 16-17-10145). Field and analytical works were partly supported by the Russian Foundation for Basic Research (RFBR; 16‐05‐00945a) and the Tomsk Polytechnic University Competitiveness Enhancement Program, respectively.
Publisher Copyright:
©2020 Society of Economic Geologists, Inc.
Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.
PY - 2020/9
Y1 - 2020/9
N2 - 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# (3–50 mol %), moderate to extremely high TiO2 content (1–18 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 (1,250°C) 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.
AB - 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# (3–50 mol %), moderate to extremely high TiO2 content (1–18 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 (1,250°C) 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.
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U2 - 10.5382/ECONGEO.4745
DO - 10.5382/ECONGEO.4745
M3 - Article
AN - SCOPUS:85085868947
VL - 115
SP - 1321
EP - 1342
JO - Economic Geology
JF - Economic Geology
SN - 0361-0128
IS - 6
ER -