Scandium Ore Occurrences in the Ancient Weathering Crust in the Nakyn Kimberlite Field of Yakutia

Abstract

In the Malo-Botuobinsky, Sredne-Markhinsky, and Ygyattinsky diamond-bearing areas of the Western Yakutian kimberlite province, the prerequisites and signs of scandium deposits in ancient weathering crusts overlying Lower Paleozoic rocks and associated with zones of ancient reservoir and soil oxidation. According to X-ray fluorescence and ICP MS analyses, in the Nakyn kimberlite field of the Sredne-Markhinsky diamond-bearing region, promising ore occurrences and scandium concentration halos have been established in clay deposits of redeposited weathering crusts of the Dyakhtar Formation of Late Triassic–Early Jurassic age. They are confined to the erosional surface of Lower Paleozoic carbonate rocks and Middle Paleozoic traps, with monzonite porphyries and kimberlites cutting through them, covered on top by a sedimentary cover of Jurassic terrigenous deposits. Concentration anomalies of scandium in clays of the Dyakhtar Formation are localized mainly in deluvial clay deposits of paleowatersheds and gravitate to the intersections of tectonic disturbances. The depth of their occurrence does not exceed 100 m, which is quite favorable for the extraction of scandium by borehole in situ leaching. Concentrations of scandium were detected at one of the sites before 262 g/t in Late Triassic weathering crust, including material from a Middle Paleozoic gabbro dike, as well as overlying colluvial clays of the Dyakhtar formations with a maximum of 462 g/t.