Microcomponents, Macro- and Mesoporosity, and Genesis Features of Zeolite-Bearing Rocks from the Tatarsko-Shatrashanskoye Deposit (Republic of Tatarstan)

Studies were conducted on the morphology of the void space, structural-textural characteristics, composition, and mineral formation conditions of Upper Cretaceous (Turonian– Santonian stages) carbonate-clay-siliceous zeolite-bearing rocks exploited at the Tatarsko-Shatrashanskoye deposit. The deposit is located in the northern part of the Ulyanovsk-Saratov Depression. The objects of study were zeolite-bearing siliceous marls from the first bed (t-1) of the productive sequence. A total of 40 samples represented by calcined and uncalcined coarsegrained fractions (0.5–1 mm) were examined. The research was performed using X-ray microtomography (micro-CT) and scanning electron microscopy with energydispersive spectroscopy. The samples are represented by intergrowths of mineral aggregates and detritus, forming medium-, fine-, and very fine-grained, biogenic, scaly, and lepispheric microstructures. The microcomponent composition includes: a paragenesis of authigenic minerals (Opal-CT, the clinoptilolite-Ca – heulandite-Ca isomorphous series, glauconite, clay minerals, volcanic glasses), defined as “camouflaged pyroclastics”; allothigenic minerals (manganoilmenite, zircon); and fossilized remains of calcareous and siliceous biota (foraminifera, coccolithophores, rhabdoliths, diatoms, stomatocysts). Calcined and uncalcined samples exhibit similarity in all characteristics, except for secondary cracks and a rounded surface in calcined samples. The morphology of the primary void space is represented by rounded and elongated biovoids (>1 µm) and tortuous intergranular pores (<1 µm), of open and closed types. By size, pore types are divided into mesopores (<25 nm) and macropores (>25 nm), with the latter predominating. The basis for the unique sorption properties of the zeolitebearing rocks exploited at the Tatarsko-Shatrashanskoye deposit, used in various economic sectors, is their mineral composition in combination with macro- and mesoporosity, and the isomorphism within the clinoptilolite-Ca – heulanditeCa series, which enhances bioorganic sorption. The formation of the zeolite-bearing rocks is the result of the interaction of endogenous and exogenous processes under the conditions of a stable shelf basin with a developed carbonate buffer system.