Mineralogy and Sedimentation of the Sabantuy Chromite Beach Paleoplacer of the Southern Pre-Urals: Provenance and Origin of Cement

A mineralogical study of sandstones from the ore bed of the Sabantuy paleoplacer was completed. Using EDS scanning electron microscopy, the composition of grains of ore-bearing sandstones (chromitolites) and interbedded, conventionally barren sandstones (chert graywackes) was studied. Using EDS mapping, the ratios of ore minerals in the chromitolites and barren sandstones of the productive bed were estimated. Chromite was found to be the most quantitatively prevalent ore mineral (53 vol.%), followed by magnetite (25%, including chromium-magnetite – 29%) and ilmenite (12%). Variations in ore element contents were found to be related to the position of a particular sample within the section relative to the wave energy zones. Chromite preferentially accumulated in the supratidal zone along the line of relative energy dissipation of breaking waves. A combination of geological, lithological, and morphodynamic factors indicates distal sources of ore detritus for the Sabantuy paleoplacer. The primary sources of detrital material for the host sandstones could have been sedimentary and metamorphic complexes of the Bashkir Meganticlinorium and the Uraltau Zone, while additional (ore-bearing) material could have come from ultramafic-mafic massifs currently present in the axial Urals – ophiolitic allochthons (such as the Krakinsky and Khabarninsky) and tectonites of the Main Ural Fault. The source of cement was limestones from the overlying unit, which dissolve and redeposit.