Typochemistry and possible sources of ferrosaponite with Ce–Cu–Ni from the metabasalts of the Northern Ural

We studied metabasites from metamorphic complexes located in the northern part of the Lyapin anticlinorium of the Subpolar Urals and the Kharbey anticlinorium in the Polar Urals of the Central Ural Uplift, which are part of the Arctic zone. For the first time, ferrosaponite containing copper, nickel, and rare earth metals has been identified in these metabasites. The morphological and typochemical characteristics of ferrosaponite were examined using electron microscopy. In the Polar Urals, ferrosaponite is found in the almandine eclogite of the Marunkeu eclogite-amphibolite gneiss. The mineral is associated with garnet, quartz, pyroxene, muscovite, amphibole, and sulfides. The general formula for the mineral from almandine eclogite: (Ca 0,06–0,27 K 0,01–0,06 Се 0,01 ) ∑0,13–0,31 (Fe 2+ 1,67–2,21 Mg 0,51–0,84 Cu 0,01–0,09 Ni 0,03–0,11)∑2,25–3,08 [(Si 2,84–3,08 Al 0,92–1,16 ) ∑4,00O10 ](OH) 2 ×3,55–3,83H 2 O. In the Subpolar Urals, this mineral was examined in a sample of garnet-amphibole-biotite-plagioclase-quartz shale, where it occurs in association with other minerals: amphibole, plagioclase, quartz, epidote, biotite, zircon, albite, titanite, apatite, and sulfides. The general formula of the mineral: (Ca 0,14–0,22 K 0,01–0,02 Се 0,01 ) ∑0,15–0,23 (Fe 2+ 1,24–2,22 Mg 0,76–0,97 ) ∑2,17–3,15 [(Si 2,86–2,96 Al 1,04–1,14 ) ∑4,00 O 10 ](OH) 2 ×3,41–4,47H 2 O. It is assumed that ferrosaponite forms through a hydrothermal-metamorphic process during the late fluid stage of rock transformation. Feldspars and biotite serve as sources of potassium and aluminum, while hornblende, pyroxenes, and epidote are the primary suppliers of magnesium and iron. In the chemical composition, alongside the main components of the mineral—potassium, calcium, magnesium, aluminum, silicon, and iron—copper, nickel, and rare earth metals were also detected. Under the influence of fluids, copper and nickel may have been derived from replaced sulfides, while cerium could have been introduced from allanite, apatite, and other minerals containing rare earth elements. Continued study of the mineragenic features of metamorphic rocks in the Arctic regions of the Urals is essential for a comprehensive assessment of their resource potential, as well as promising sources and concentrators of rare metals.