Abstract
The Ildeus ore-magmatic basite-ultrabasite system in the central part of the Stanovoy superterrane formed in the Triassic as a result of subduction of the Mongol-Okhotsk basin oceanic lithosphere. In the Jurassic and Early Cretaceous, it underwent hydrothermal-metasomatic alterations during collision and post-collision processes within the southern margin of the Siberian continent. Hydrothermally altered ultrabasites and acid-alkaline albite-quartz-biotite-K-feldspar-apatite (with calcite and barite) metasomatites of Ildeus contain rare earth element (REE) minerals, represented by monazite in association with apatite, xenotime, oxides, REE carbonates, and REE silicates. Native metals and alloys of Ag, Au, Cu, Ni, Zn, Pt and sulfides of Fe, Co, Ni, Cu, Pb, and Zn are associated with REE minerals in rocks of the massif. The total REE content in these rocks varies from 10 to 1938 g/t positively correlating with the concentrations of barium (up to 5876 g/t) and thorium (up to 74.5 g/t). Alkaline-silicate metasomatites with REE minerals are spatially associated with adakite dikes and veins (Sr/Y from 27 to 1716) and were formed in the presence of aqueous-carbonate-sulfate-phosphorus-potassium fluids with hybrid properties characteristic of the fluid phase of mantle alkaline-ultrabasic-carbonatite complexes, on the one hand, and lower crustal adakitic melts, on the other. It is assumed that the enrichment of ultrabasites and metasomatites of Ildeus with rare earth minerals, metals and sulfides is associated with the melting of the sulfidized thickened lower crust under the influence of deep mantle fluids and the intrusion of Early Cretaceous metal-bearing adakites into Triassic supra-subduction igneous complexes.
Published Version
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