Zirconium-titanium placers of the Voronezh Anteclise: Types, epochs and factors of formation, and forecast

The early and late Frasnian, Barremian-Aptian, Cenomanian, early Santonian, early Campanian, and Oligocene-Miocene epochs of the formation of various types of zirconium-titanium placers are distinguished in the Voronezh Anteclise. The factors of their formation are considered, and a forecast of prospecting has been made. Lower Frasnian sedimentary rocks occur in the southeast, where the placers are related to the ilmenite-bearing volcanosedimentary rocks of the Yastrebovo Sequence. The upper Frasnian productive quartz sand of the Petino Sequence occurs in the central part of the Voronezh Anteclise. The Barremian-Aptian productive quartz sand and kaolinite clay occur in the northern and northeastern parts of the anteclise (Ryazan and Lipetsk oblasts). The placers formed in the Cenomanian are known in the Tambov oblast in the northeast of the Voronezh Anteclise and are related to phosphate-bearing glauconite-quartz sand. The early Campanian phosphorite-glauconite-quartz formation is widespread in the northwest of the Voronezh Anteclise at the junction with the northeastern wall of the Dnieper-Donets Basin (Bryansk oblast). The Oligocene-Miocene epoch was characterized by quartz sands abundant in the northwestern and south-western areas. The formation of zirconium-titanium placers is controlled by structural-tectonic, facies, volcanic, paleogeographic, stratigraphic, and evolutional factors. The indispensable condition for heavy mineral concentration is existence of positive forms of underwater topography. These are mostly structural elements of the third and fourth orders on the slopes of the Voronezh Anteclise at the boundaries of the adjacent negative structures. As concerns the facies factor, the occurrence of coastal and shallow-water marine facies with alternating and medium hydrodynamic activity and predominance of sand fractions 0.25–0.05 mm are criteria of elevated concentration of heavy minerals in sand. One of the conditions providing concentration of heavy minerals is a multiple rewashing of sands close to a relatively stable shoreline. The volcanic factor is determinant for the lower Frasnian marine placers fed by volcanic sources. The Cretaceous and Paleogene zirconium-titanium placers were formed owing to scouring of the older Paleozoic and Mesozoic sedimentary rocks of the Voronezh Anteclise, as well as the Baltic Shield, Moscow Syneclise, and the Volga-Ural Anteclise. The age of placers was estimated with accuracy up to substages (lower Aptian, lower Santonian, lower Campanian). The evolution factor is expressed in variation of localization and composition of placers in time and space. The forecast of potentially ore-bearing areas is based on optimal combinations of favorable factors.