Specific features of the distribution and genesis of some carbonate minerals in kimberlite rocks (on the example of the Siberian Platform)

Abstract

In addition to previously individually characterized calcite that, along with serpentine, is the main rock-forming mineral of kimberlite rocks of the Siberian platform (SP), such carbonates as dolomite, aragonite, pyroaurite, strontianite, magnesite, hydromagnesite, and huntite are also widely, although variably, distributed in diatremes of this type. Dolomite was diagnosed in substantial amounts in the SP diatremes, where it associated with calcite and serpentine, occasionally even as a rock-forming mineral. The dolomite formation covers a sufficiently wide temporal interval, from the beginning of metasomatism of the upper mantle rocks through the final stage of hydrothermal-metasomatic processes within cavity-fissure features of the cooling kimberlite melt. Aragonite forms veinlets, radial-beam and sheaf-like reniform aggregates, and druses of acicular crystals in the kimberlites. Pyroaurite was distinguished in the kimberlite rocks in form of the veinlets and nests of fibrous and crystalline appearance, associated with calcite, magnetite, and serpophyte. Pyroaurite often composes large greenish-grey geodes together with serpentine. Pyroaurite is a typical mine-ral for the groundmass of kimberlites at deep horizons of some SP diatremes. This mineral sometimes occurs in form of concentrically zoned concretions in association with serpentine and calcite, as well as individual crystals. Other carbonates are represented by variable amounts of huntite, strontianite, magnesite, and hydromagnesite. Based on mineralogical-geochemical and luminescent properties of the carbonates from the hydrothermal-metasomatic cavity-fissure features in the kimberlite rocks, their stable and regular paragenetic associations were distinguished, reflecting the character of physical-chemical processes at the postmagmatic and supergene stages of the kimberlite formation.