Petrography, geochemistry, and geochronology of the Sc-enriched Kiviniemi ferrodiorite intrusion, eastern Finland

Abstract

The Kiviniemi mafic intrusion, near the eastern margin of the Paleoproterozoic Central Finland Granitoid Complex, is both spatially and temporally associated with post-kinematic Fe-TiP enriched Svecofennian orogenic mafic magmatism. The main rock types in this small (~15 ha) intrusion are garnet-bearing fayalite ferrodiorite, leucoferrodiorite, ferromonzodiorite, and pyroxene diorite. The garnet-bearing fayalite ferrodiorite and leucoferrodiorite contain 50-281 ppm Sc, 275-5600 ppm Zr, and 58-189 ppm Y (n = 42), delineating a mineralized deposit some 2.5 ha in extent. Overall, these rocks show an evolved (ironenriched) tholeiitic character; low values of Ni (< 20-40 ppm), Cr (< 20 ppm), and Cu (< 20-80 ppm); and high contents of Zn (213-700 ppm). The rock-forming minerals in the ferrodioritic rocks are (ferro)hedenbergite, plagioclase (~An 40), ferropargasite and ferroedenite, almandine garnet, and fayalite (Fo 1-4). Accessory minerals include zircon, ilmenite, fluorapatite, biotite, pyrite, pyrrhotite, potassium feldspar, grunerite, and clinoferrosilite. Some relict cumulate textures have been preserved, but primary magmatic features have largely been overprinted by strong recrystallization and corona formation. The main carriers of Sc are amphibole, clinopyroxene, and apatite. The remarkably strong enrichment of Sc in ferromagnesian silicates and apatite, rather than in specific Sc-minerals, implies magmatic enrichment. Post-kinematic mafic intrusions in central Finland constitute a bimodal association with co-existing granitoid counterparts. The Kiviniemi mafic intrusion is associated with a coarse megacrystic granite and the two rock type display mingled contacts, indicative of contemporaneity of the two magmas. This conclusion is in accord with the coincident U-Pb zircon ages for the ferrodiorite, at 1857 ± 2 Ma (multigrain ID-TIMS) and the megacrystic granite, at 1860 ± 7 Ma (single-crystal LA-MC-ICP-MS). The initial εNd value of the ferrodiorite and the granite are + 0.1 and − 2.5, respectively. These Nd isotope compositions probably reflect a chondritic mantle source for the ferrodiorite and suggest incorporation of some Archaean crustal material into the granite in the course of magmatic evolution. The resource estimation calculated for Kiviniemi intrusion by using 40 g/t Sc cut off value is 13.4 Mt of rock with an average grade of 162.7 g/t scandium, 1726 g/t zirconium, and 81 g/t yttrium.

Magnetic Preconcentration and Process Mineralogical Study of the Kiviniemi Sc-Enriched Ferrodiorite

“…The Kiviniemi mafic intrusion (Figure 2A,B) is located in the municipality of Rautalampi, approximately 70 km SW of the city of Kuopio in Finland [11,16]. Altogether, nine holes were drilled between 2008 and 2010.…”

“…As illustrated in Figure 2A, the Kiviniemi intrusion has a zoned structure, in which an Fe-and Sc-rich, medium-to coarse-grained garnet-bearing fayalite ferrodiorite body is surrounded by transitional ferrodiorites and pyroxene ferromonzodiorites. The country rock of the intrusion is composed of porphyritic granite [11]. The preliminary mineral resource estimation calculated with the inverse distance method is 13.4 Mt, with an average grade of 163 g/t Sc [11,16].…”

“…According to Wang et al (2020) [10], magmatic rocks with average Sc concentrations > 60 ppm can be regarded as Sc deposits. Table 1 includes the Kiviniemi ferrodiorite-hosted Sc deposit discovered recently in eastern Finland [11]. [11,16] With respect to REE production from ore to end products, after the traditional beneficiation of REE minerals, individual elements are extracted by hydrometallurgy, electrometallurgy or pyrometallurgy, of which hydrometallurgy is the most widely used technique.…”

“…Table 1 includes the Kiviniemi ferrodiorite-hosted Sc deposit discovered recently in eastern Finland [11]. [11,16] With respect to REE production from ore to end products, after the traditional beneficiation of REE minerals, individual elements are extracted by hydrometallurgy, electrometallurgy or pyrometallurgy, of which hydrometallurgy is the most widely used technique. The purified bulk product is often a solid oxide, carbonate or chloride with very low impurity content, which is then further processed into desired end-products [17][18][19].…”

Iron Isotope Constraints on the Mineralization Process of Shazi Sc-Rich Laterite Deposit in Qinglong County, China

“…The grade of Sc in these primary deposits is in the range of 0.005-0.04 wt.% [3]. Only 12 terrestrial minerals are known to contain Sc as an essential component, and thortveitite [Sc 2 Si 2 O 7 ] is the most important among these minerals [4,5]. Significant proportions of Sc can be hosted in ferromagnesian silicate minerals (including clinopyroxene and garnet) and in a number of high-field-strength-element (HFSE) minerals such as wolframite baddeleyite, rutile, etc.…”