Main types and conditions for the formation of kaolinites from clays of the sedimentary cover of the Voronezh anteclise

Abstract

Introduction: Kaolinite is the main mineral of refractory and refractory ceramic clays, a valuable and at the same time deficient raw material. In addition, this mineral is included in polymineral clays as one of the components. 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 goal of this article was to establish the distribution and genesis of this mineral in the clays of the sedimentary cover of VA in order to predict their deposits as ceramic raw materials in the territory of this structure. Methodology: A complex of techniques was used to study kaolinites. Field research, desk construction of facies maps and sections, and laboratory and technological tests were carried out. During the performed work, core samples of more than 50 wells were documented and tested, rocks from over 90 observation points (outcrops and quarries) were described and tested within the Voronezh, Kursk, Lipetsk, and Oryol regions. Samples were prepared, and the mineral and chemical composition of clays from about 200 samples was studied using precision methods (diffractometric and electron microscopic). Results and discussion. It has been established that kaolinite clays are confined to the deposits of the Mamon stratum of the upper Devonian, the Aptian tier of the lower Cretaceous, and the formations of the Kiev Eocene, the Berek Oligocene, the Shapkinskaya Miocene, and the Usman Pliocene. Six genetic types of kaolinite clays have been identified: primary kaolin weathering crust (WC); secondary kaolins; rusk clays of the “flint-glue” type; lake-swamp fire-resistant; lagoon-sea refractory; coastal-marine polymineral ceramic, mainly fusible, clays. Primary kaolins were formed during the weathering of crystalline basement rocks and were subsequently eroded. Secondary kaolins were formed during the Mamonian period of the Late Devonian during the erosion of the WC. The formation of Early Carboniferous clays of the “flintglue” type in lake reservoirs was associated with synchronous weathering in the sources of demolition. From there, dissolved components were transported by underground surface waters and Al and Si precipitated from them in the form of kaolinite. In the Early Cretaceous and Neogene, on alluvial plains in raised bogs with a reducing-acidic environment, polymineral clayey sediments underwent processes of “flowing diagenesis” with the formation of fire-resistant kaolinite clays. Clays of lagoon-marine origin were formed in the Aptian Age and have an illite-kaolinite composition. They inherited their composition from the source rocks and are refractory varieties. Finally, shallow marine clays were formed in the Paleogene, they have a kaolinite-montmorillonite-illite composition and belong to low-grade fusible raw materials. These conditions were not favourable for the accumulation of kaolinite, resulting in the formation of low-grade ceramic clays. Conclusions: Secondary kaolins, lake-swamp refractory and lagoon-sea refractory clay are the most important for increasing the mineral resource base of ceramic raw materials.