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

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Halkoaho , T , Ahven , M , Ramo , O T , Hokka , J & Huhma , H 2020 , ' Petrography, geochemistry, and geochronology of the Sc-enriched Kiviniemi ferrodiorite intrusion, eastern Finland ' , Mineralium Deposita , vol. 55 , no. 8 , pp. 1561-1580 . https://doi.org/10.1007/s00126-020-00952-2

Title: Petrography, geochemistry, and geochronology of the Sc-enriched Kiviniemi ferrodiorite intrusion, eastern Finland
Author: Halkoaho, Tapio; Ahven, Marjaana; Ramo, O. Tapani; Hokka, Janne; Huhma, Hannu
Contributor: University of Helsinki, Department of Geosciences and Geography
University of Helsinki, Department of Geosciences and Geography
University of Helsinki, Department of Geosciences and Geography
Date: 2020-11
Language: eng
Number of pages: 20
Belongs to series: Mineralium Deposita
ISSN: 0026-4598
URI: http://hdl.handle.net/10138/320837
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-Ti-P-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 (iron-enriched) 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 epsilon Nd 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.
Subject: Ferrodiorite
Scandium
Zirconium
Yttrium
Bimodal
Svecofennian
Finland
SILICATE LIQUID IMMISCIBILITY
SKAERGAARD LAYERED SERIES
POST-KINEMATIC MAGMATISM
RARE-EARTH-ELEMENTS
ANORTHOSITE COMPLEX
SVECOFENNIAN OROGEN
GRANITOID COMPLEX
SCANDIUM SILICATES
BEARING MINERALS
IGNEOUS ZIRCON
1171 Geosciences
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