Epochs of formation of titanium-zirconium placers in the Phanerozoic of the Voronezh anteclise

Abstract

Introduction: titanium-zirconium placers of different ages are known in the sedimentary cover of the Voronezh anteclise. They are considered in a number of publications. At the same time, over the past fifteen years, as a result of geological survey and thematic work carried out by employees of the Voronezh State University, new data on the distribution and composition of placers have been obtained, which formed the basis of this article.

Methodology: field and laboratory studies of Mesozoic and Cenozoic sands were carried out to study titanium-zirconium placers. Sampling was carried out using the furrow method, thin interlayers were sampled pointwise. The main attention in the description and sampling was paid to the structural and textural features of the rocks. In the laboratory, the granulometric and mineral composition of sand deposits was determined. Samples were quartered, the clay fraction was washed out, and the silt-sand fraction was dispersed. A quantitative analysis of heavy and light fraction minerals was carried out. Based on the complex data, lithological-facies and mineragenic constructions were made.

Results and discussion: six placer formation epochs were distinguished − Early Frasnian (Yastrebovskaya), Barremian-Aptian, Cenomanian, Early Santonian, Early Campanian and Oligocene-Miocene. In the Early Frasnian, volcanogenic-sedimentary placers were formed in the southeast of Voronezh anteclise, in which the main mineral is ilmenite. Cretaceous and Paleogene-Neogene placers are titanium-zirconium, usually occur on watersheds and have a small overburden thickness. Useful components are ilmenite, rutile, leucoxene, and zircon. In the Barremian-Aptian, long-distance placers were formed in quartz sands in the northern part of the Voronezh anteclise territory. In the Cenomanian epoch, a large placer deposit Central with a high content of heavy-fraction minerals was formed in glauconite-quartz sands on the northeastern slope of the Voronezh anteclise. Complex placers with heavy minerals and nodular phosphorites are typical there for the Santonian age. In the Campanian placers of the northwest of the Voronezh anteclise, heavy minerals, like quartz grains, can have a phosphate shell. Oligocene-Miocene placers are developed in the southwest of the Voronezh anteclise, are associated with quartz sands and are distinguished by an increased content of zircon and rutile.

Conclusions: in the history of the Voronezh anteclise, conditions for the formation of titanium-zirconium placers repeatedly arose. The most important factors were tectonic and facies, secondary -− stratigraphic and paleogeographic. The evolution of placer formation over time is also traced, which is expressed in the migration of useful component accumulation areas across the Voronezh anteclise territory and among them in the increase in the share of the most stable heavy minerals as a result of recycling processes.