S. M. Zhmodik, E. A. Zhegallo, E. V. Lazareva, E. A. Saprykin, M. I. Kapralov, N. V. Grubova, A. Yu. Rozanov

The biogenic factor impact on rare earth element accumulation in the Tomtor complex rocks (Yakutia)

Abstract. The authors analyzed a sample of an ore rock from the unique Tomtor REE-Nb ore deposit, using scanning electron microscopy and energy-dispersive X-ray spectroscopy. A high rare earth element (REE) potential of the rocks should have been previously related to microorganisms’ activity and specific physical and chemical conditions of their habitat. To confirm the hypothesis, the authors conducted a bacterial and paleontological study of the goethite horizon (int. 58.0–58.1 m) rock sample from the borehole Г2 (Buranny site). The findings revealed microfossil remains of various morphologies in the rock sample, which correspond with rare earth element accumulation zones. The results described morphology of the discovered microfossils and identified both prokaryotic and eukaryotic forms. The study demonstrated that in the manganese iron oxide rock rare earth element accumulation occurs exclusively in microfossil remains, with the fossilization process involving replacement of the organic matter with plumbogummite-group minerals. It was determined that, during their lifetime, microorganisms in the studied sample primarily accumulated cerium and lanthanum, and to a lesser extent, praseodymium and neodymium, provided that the qualitative composition of rare earth elements relates to the fossilized microorganisms’ morphological type.

Keywords: Tomtor REE-Nb ore deposit, light lanthanides, SEM-EDX, bacterial paleontology, ore-bearing rock prospecting