Main Types and Conditions for the Formation of Kaolinites from Clays of the Sedimentary Cover of the Voronezh Anteclise

Kaolinite is the main mineral of refractory and high-melting ceramic clays, a valuable and at the same time deficient raw material. In addition, this mineral is a component of polymineral clays. In the sedimentary cover of the Voronezh anteclise (VA), clays of sediments of different ages differ in terms of formation conditions, material composition, and quality. Therefore, the main purpose of this work was to establish the distribution and genesis of this mineral in the clays of the VA sedimentary cover in order to predict their deposits as ceramic raw materials on the territory of this structure. A complex of techniques was used to study kaolinites. Field research, desktop construction of facies maps and sections, and laboratory and technological tests were carried out. During the works, core samples from more than 50 wells were documented and tested; rocks from over 90 observation points (outcrops and quarries) were described and tested within Voronezh, Kursk, Lipetsk, and Orel oblasts. Samples were prepared, and the mineral and chemical composition of clays from about 200 samples was studied using precision methods (XRD and electron microscopy). It is established that kaolinite clays are confined to the deposits of the Mamon stratum of the Upper Devonian, the Aptian stage of the lower Cretaceous, and the formations of the Kievskii Eocene, the Berek Oligocene, the Shapkinskii Miocene, and the Usmanian Pliocene. Six genetic types of kaolinite clays are identified: primary kaolins of the weathering crust (WC); secondary kaolins; kaolin clays of the “flint-glue” type; lacustrine–boggy refractory; lagoon–marine high-melting; and coastal–marine polymineral ceramic, mainly low-melting, clays. Primary kaolins were formed during the weathering of crystalline basement rocks and were subsequently eroded. Secondary kaolins were formed during the Mamon period of the Late Devonian during the WC erosion. The formation of Early Carboniferous clays of the “flint-glue” type in lacustrine reservoirs was associated with synchronous weathering in the provenance areas. Dissolved components were transported from there by underground surface waters, and their Al and Si precipitated in the form of kaolinite. In the Early Cretaceous and Neogene, polymineral clay sediments underwent processes of “flowing diagenesis” with the formation of refractory kaolinite clays on alluvial plains in raised bogs with a reducing-acidic environment. Clays of lagoon–marine genesis were formed in the Aptian and have an illite–kaolinite composition. They inherited their composition from the rocks of the provenance area and are high-melting varieties. Finally, shallow marine clays were formed in the Paleogene; they have a kaolinite–montmorillonite–illite composition and belong to low-grade low-melting raw materials. These conditions were unfavorable for the accumulation of kaolinite, which resulted in the formation of low-grade ceramic clays. Secondary kaolins, lacustrine–boggy refractory, and lagoon–marine high-melting clay are the most important for increasing the mineral resource base of ceramic raw materials.