Chromite Paleoplacer in the Permian Sediments at the East Edge of the East European Platform: Composition and Potential Sources

• Main Authors: Ildar R. Rakhimov, Evgenii V. Pushkarev, Irina A. Gottman
• Format: Article
• Language: English
• Published: MDPI AG 2021-06-01
• Series: Minerals
• Subjects: composition of chromspinel; solid-state inclusions; melt inclusions; chromite placer; provenance sources; ophiolite
• Online Access: https://www.mdpi.com/2075-163X/11/7/691

A chromite occurrence called the Sabantuy paleoplacer was discovered in the Southern Pre-Ural region, at the east edge of the East-European Platform in the transitional zone to the Ural Foredeep. A ca. 1 m-thick chromite-bearing horizon is traced at a depth of 0.7–1.5 m from the earth’s surface for the area of ca. 15,000 m². The chromspinel content in sandstones reaches 30–35%, maximum values of Cr₂O₃ are 16–17 wt.%. The grain size of detrital chromspinel ranges from 0.15 to 0.25 mm. Subangular octahedral crystals dominate; rounded grains and debris are rare. The composition of detrital chromspinel varies widely and is constrained by the substitution of Al³⁺ and Cr³⁺, Fe²⁺ and Mg²⁺ cations. Chemically, low-Al (Al₂O₃ = 12 wt.%) and high-Cr (Cr₂O₃ = 52–56 wt.%) chromspinel prevail. The compositional analysis using discrimination diagrams showed that most chromites correspond to mantle peridotites of subduction settings. Volcanic rocks could be an additional source for detrital chromites. It is confirmed by compositions of monomineralic, polymineralic and melt inclusions in chromspinels. The presented data indicates that ophiolite peridotites and related chromite ore associated with oceanic and island-arc volcanic rocks, widespread in the Ural orogen, could be the main sources of the detrital chromspinel of the Sabantuy paleoplacer.