Mineral Composition of the Productive Bed and Features of Chromites in the Lukoyanov Placer District (Nizhny Novgorod Region)

The geological exploration within the Lukoyanov placer district (Nizhny Novgorod region) revealed increased contents of chrome-spinel, reaching a commercial level (up to 100 kg/m³), were detected in complex coastal-marine rare metal–titanium placers, but their source is not obvious. In addition to chrome-spinels, commercial components of placers are composed of ilmenite, zircon, and rutile. Morphological features of ore minerals suggest several sources of ore material (both proximal and distal). Moderately mature mineral composition of the heavy fraction (increased amount of minerals unstable during weathering) indicates that the Permian–Jurassic deposits of this region formed without (or with weak) participation of chemical weathering crusts. During the mobilization of detrital material in the source zone and the formation of intermediate reservoirs (Permian and Early Mesozoic complexes of the sedimentary cover) in the Uralian part of the East European Platform, mechanical processes prevailed with a subordinate influence of weathering crust formation. The study of the chemical composition of chrome-spinels in the most studied and promising Itmanov placer showed that they are mostly similar to counterparts in the ophiolite association and concentric zoned Pt-bearing massifs. Against the background of general impact of regional processes on the sedimentary cover formation in the central and eastern parts of the East European Platform at the Permian–Triassic boundary of the Uralide paleo-orogen, the Puchezh–Katun ring structure, located north of the Lukoyanov dome, had a noticeable influence on the composition of the heavy fraction of sediments in the region.