Features of calcite from kimberlite rocks

Abstract

Introduction: A characteristic feature of kimberlite bodies, established on the ancient platforms of the world, is the significant variability of the parameters of their material composition. The high gradient of variability of material features in the volume of kimberlite bodies is largely associated with the polygenicity and heterochnonism of the components of the rocks that make up the pipes, covering the range of formation conditions from the upper mantle (through the pneumatolytic-hydrothermal stage) to hypergenesis. A significant role in the formation of the final appearance of kimberlites belongs to the environment containing the diatreme (composition and mechanical properties of the host rocks). The dependence of the petrophysical, petrochemical, geochemical, and mineralogical features of kimberlites on the composition and mechanical properties of the host rocks should be taken into account when predicting and searching for primary diamond deposits. Under the influence of host rocks, the chemical composition of kimberlites can become significantly different from the usual primary composition, and therefore the chemical criterion can lose its diagnostic role. The petrophysical properties of kimberlite rocks largely depend on the degree of postmagmatic and supergene alterations, the main mineral among which is calcite. In the present study, the characteristics of calcite, the dominant, rock-forming mineral of the carbonate class in kimberlites, are provided. Materials and Methods, Results: Calcite is one of the most common carbonates in the kimberlite rocks of the Siberian Platform. Such common distribution was largely facilitated by the terrigenous-carbonate composition of the strata containing the diatremes. The mineral is detected in kimberlites in the form of grains and aggregates in the rocks, veins and bonny, spherical segregations, druses, geodes, and brushes. Several varieties of the mineral dominate in the pipes: a) early (deep) primary magmatic calcite (inclusions in deep minerals); b) deep metasomatic calcite - a product of upper mantle metasomatism of rocks and minerals; c) kimberlite calcite, the crystallization of which is associated with various stages of postmagmatic and supergene transformation of rocks. Calcite can be attributed to the continuous polygenic minerals of the kimberlite process, a comprehensive study of which can provide new information about the nature and specifics of this process at different stages of the formation of kimberlite bodies (pipes, dikes, and sills). The heterogeneous nature of Ca and СО2 in calcites and multi-stage processes of calcite formation in kimberlites was noted. The process of crystallization of calcite in kimberlites is very complex and multistage. Often, within a single geode, several generations of calcite are distinguished, differing in size, morphological features, set of inclusions, zoning type, colour, and luminescent properties. The obtained typomorphic features of calcite from kimberlites can be successfully used to improve technological methods for extracting diamonds from rocks, and in redeposited form in sedimentary strata as an additional search criterion. Conclusions: Now, the information content and typomorphic significance of the microcomposition and properties of calcite from kimberlite rocks, which to a certain extent complicates their use as genetic indicators of the conditions of kimberlite formation are important and fundamental issues. The quantitative relationships between the mineral phases and the form of calcite segregations can differ significantly. Regularities in the distribution of both rock-forming neoformations of the groundmass (including calcite) and hydrothermal mineralization of veins were established at the depth of the studied diatremes. Features of the distribution of calcite in terms of diatremes are often associated with the degree of postmagmatic and hydrothermal alteration of rocks.