In-Situ Crystallization and Continuous Modification of Chromian Spinel in the "Sulfide-Poor Platinum-Group Metal Ores" of the Norilsk-1 Intrusion (Northern Siberia, Russia)

• Published in: Minerals
• Main Authors: Chayka, Ivan F., Zhitova, Liudmila M., Antsiferova, Tatiana N., Abersteiner, Adam, Shevko, Artem Ya, Izokh, Andrey E., Tolstykh, Nadezhda D., Gora, Marina P., Chubarov, Valery M., Kamenetsky, Vadim S.
• Other Authors: Department of Geosciences and Geography
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI 2021
• Subjects: Cr-spinel; chromite; layered intrusion; Norilsk-1; BUSHVELD COMPLEX; OPHIOLITIC COMPLEXES; STILLWATER COMPLEX; MELT INCLUSIONS; OMAN OPHIOLITE; KOLA-PENINSULA; MAFIC ROCKS; KILAUEA IKI; ORIGIN; 1171 Geosciences; Kola Peninsula; Norilsk; kola peninsula; norilsk; Siberia
• Online Access: http://hdl.handle.net/10138/326914

Layers rich in chromian spinel (Cr-spinel) occur in numerous differentiated and layered intrusions. These layers are often characterized by elevated and even economic concentrations of platinum-group-elements (PGEs), but only scarce sulfide mineralization. One particular type of such lithology occurs in the roof parts of the Norilsk-type differentiated intrusions (Russia) and is referred to as the "sulfide-poor PGE ores". We investigated rocks containing variable enrichments in Cr-spinel, sulfides, and platinum-group minerals (PGMs) from two sections of the upper zone of the Norilsk-1 intrusion, with a focus on Cr-spinel. The rocks are dominated by two lithological types: (1) leucogabbro/troctolitic and (2) olivine-gabbro. Fine-grained (5-100 mu m) disperse disseminations with varying modal abundances of Cr-spinel are characteristic for the rocks studied. Those abundances range from scarce mineralization through to very dense (up to 30 vol. % Cr-spinel) cloud-like accumulations. However, compact-grained accumulations and cumulate-like textures, which are typical for chromitites of layered intrusions, are not characteristic for the studied rocks. Instead, the disseminations exhibit chain- and trail-like alignments of Cr-spinel grains, which cross the boundaries between enclosing silicates, and sub-circular arrangements. The study revealed millimeter-scaled patchy distribution of Cr-spinel compositions within a given dissemination with Cr-spinel chemistry being strongly correlated with a kind of the enclosing silicate. (1) In unaltered rocks, plagioclase hosts more magnesian Cr-spinel (Mg# 30-60), while Cr-spinel in mafic minerals is less magnesian (Mg# 18-35). (2) In altered rocks, more magnesian Cr-spinel is hosted by less altered silicates, while strongly altered silicates mainly host less magnesian Cr-spinel. Systematics of trivalent cations exhibits divergent trends, even on a scale of a thin section, and depends on a kind of hosting lithology. Leucogabbro/troctolite lithologies contain Cr-spinel with ...