Surface Formations in the Weathering Crusts of Carbonatites: Implication for the Genesis of Unique Rare Metal Ores in the Tomtor Deposit, Russia

A comparative analysis of the composition and structure of the surface facies of carbonatite weathering crusts (profiles) in the Chuktukon (Russia) and Seis Lagos (Brazil) deposits and ultra-rich rare metal ores in the Tomtor deposit (Russia) is presented. It is shown that the main geochemical trends in the formation of the Tomtor-type ultra-rich rare metal ores and the surface facies of weathering profiles are opposite. The obtained results do not confirm the genetic link between the unique Tomtor ores and the surface facies of the crust of carbonatites, but serve as evidence of their later formation due to the reductive epigenesis of carbonatite weathering products under the influence of solutions draining the overlying coaliferous rocks. Wide distribution of the phenomena of colloidal liquid layering into manganese and ferruginous fractions was established for the first time in surface facies of the weathering crust of carbonatites, and active lateral colloidal migration of Ti from the host rocks was revealed.