Accessory Minerals in the Chromitite Ores of Dzharlybutak Ore Group of Kempirsai Massif (Southern Urals, Kazakhstan): Clues for Ore Genesis

Abstract

The paper provides results of a detailed mineralogical study of some chromitite ores from two deposits in the Southern Urals of Kazakhstan: Almaz-Zhemchuzhina and Geofizicheskoe-VII. It is revealed that the main ore minerals are Cr-spinel with high Cr# (Cr/(Cr + Al) = 0.8–0.83), as well as serpentine and chlorite, replacing primary olivine. Chromium spinel grains contain mineral inclusions, which are distributed rather unevenly. The most common mineral inclusions are olivine (serpentine) and amphibole; phlogopite, pyroxenes, and base metal sulfides are rare. Olivine from inclusions in chromite is the highest in magnesium (Fo97–98), and is anomalously high in nickel (up to 1.8 wt.% NiO). The closure of exchange reactions between olivine and chromite occurred in the temperature range of 700–850 °С and in the oxygen fugacity range of −1.04 … +2.8 ΔFMQ, which most likely corresponds to the upper mantle settings of the fore-arc basin. A few tens of monomineral grains and polymineral intergrowths of platinum group minerals (PGMs) were found in chromite aggregates. Notably, monomineral grains are mainly represented by Ru, Os, and Ir disulfides, while in polymineral inclusions, iridium prevails (with widespread native phases, sulfides, and sulfoarsenides). PGM grains included in chromite are often associated with hydrous silicates: amphibole, and less often with phlogopite or chlorite. Discussed in the paper is the possible genesis of ores and inclusions. As a preliminary conclusion, we suggest that the solid-phase processes played the most significant role in the crystallization of Cr-spinel in the investigated chromitite ores.

Genesis of the Sartohay Podiform Chromitite Based on Microinclusions in Chromite

“…Furthermore, the mechanism of chromite concentration as ore bodies is substantiated in the melt-peridotite reaction model insufficiently [90]. This has been interpreted by the rheomorphic model [7,8,61], which provides thermodynamic reasons for the compaction or sintering mechanism of chromitites.…”

“…The lack of petrographical evidence for plastic deformation in Sartohay chromitites is possibly due to the unattained high pressure required for pressure sintering [8], which may have enabled the retention of primary mineral inclusions in the chromite. However, the high mantle temperature needed for chromitite compaction as proposed by the rheomorphic model [90] is recorded in Sartohay chromitites. Hence, progress similar to sintering under a tectonic setting at high temperatures is a possible hypothesis for the coalescence of ore grains to form chromitite aggregates.…”

Research on the Production of Pigments Based on Composite Pellets in the Recycling of Industrial Waste

“…The chromite ore of the Kempir say massif is a fine-grained rock with a massive texture. Porphyritic crystals of amphibole and laths of plagioclase stand out against the fine-grained background of the main ore mass [20,21].…”