Authigenic Titanium and Zirconium Minerals at the Verkhnekamskoe Salt Deposit

Аннотация

The salt-bearing and suprasalt units at the Verkhnekamskoe salt deposit contain newly formed Ti oxides and zircon. The minerals may have been produced at the decomposition of clay material and release of colloid Ti and Zr hydroxides during diagenesis, catagenesis, and supergenesis because of sulfate reduction and an acidic environment caused by Fe²⁺ oxidation in the sylvite and carnallite. Anatase was found in both the suprasalt units and the salt-bearing ones, whereas rutile occurs exclusively in the bottom part of the salt-bearing unit. The possible reasons for this distribution may have been intensification of the catagenetic transformations with depth and the composition of the coexisting sulfate or chloride brines, respectively. The anatase typically forms pinacoidal crystals, which give way to dipyramidal ones in the carnallite zone (whose solutions are the most acidic). The rutile shows twins of three types, whose origin was caused by the growth of the mineral in the fine-grained material of dehydrated Ti hydroxide colloid. The Ti oxides contain V, Cr, Zr, and (Al, Si, and Fe) admixtures, which reflect the geochemistry of the erosion regions which provided the aluminosilicate material.