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.

Korpela is a Cu-Zn-Au VMS occurrence hosted by bimodal, sub-alkaline, volcanic and volcaniclastic rocks. It is part of a Svecofennian supracrustal sequence 1.93–1.91 Ga in age. In this study, lithogeochemical evidence is used to assess the VMS-prospectivity in the Korpela area to serve regional-scale exploration and provide detailed information on chemostratigraphy and hydrothermal alteration within the Korpela succession. Korpela is understood to have been formed in an evolved arc rift, possibly in a continental back-arc environment. The felsic rocks of the sequence are FII-FIIIa, HFSE-enriched (A-type) rhyolites overlain and, locally cross-cut, by mafic rocks with MORB/BABB signatures and felsic synvolcanic porphyry dykes. In the vicinity of Korpela, tonalitic subvolcanic intrusions intrude the supracrustal rocks which share textures common with local shallow VMS-related intrusion complexes. The Korpela area comprises a volcanic succession where primary volcanic textures are completely destroyed by multiple deformation, metamorphism and alteration. Using detailed volcanic chemostratigraphy established from downhole geochemical profiles, 12 chemostratigraphic units and 21 chemical rock types could be identified ranging from basalt to rhyolite. Several metamorphic mineral assemblages were identified which were further classified into six alteration types, i.e. Mg-Fe-S, K-Al-Fe-(± S), K-Al-Mg-Fe-S, K, Si-K-Ca-(± S) and Ca-(± Na), using a combination of mineralogy and geochemistry. The chemostratigraphy and alteration studies help in understanding the volcanic stratigraphy and in recognising a potential VMS-related alteration.

In mineral exploration, reliable and comprehensive petrophysical groundwork helps evaluate the success rate of applying geophysical methods to the target and thus improves the quality of decision-making related to geophysical surveys. Petrophysical data for potential field exploration can be efficiently collected from drill cores together with portable XRF data that provide insight into rock compositions. We acquired and analysed a multi-parameter portable-instrument drill core data set (2036 samples) with portable XRF, magnetic susceptibility and density measurements from the Metsämonttu Zn-Pb-Cu deposit, one of the base metal deposits in the Orijärvi Belt, southern Finland, with little post-mining exploration during the last 50 years. Our study applied a machine learning technique (Gaussian Mixture Model clustering) to the portable XRF data to provide a pseudo-lithological reclassification of the drill cores and used this as a basis for characterization of the deposit in petrophysical terms. We also used thermomagnetic measurements to inspect the magnetic mineralogy of the drill cores. Finally, we estimated the success of using potential field methods (magnetic and gravity) for brownfield exploration of analogous deposits in the area. With the portable XRF data clustering we were able to distinguish between barren mafic and felsic volcanic rocks, altered rocks and three different ore mineral enriched rock types. The petrophysical measurement data and thermomagnetic results were combined with the clusters to define the petrophysical characteristics for future mineral exploration with potential field methods. At Metsämonttu, the highest densities are related to the ore and iron sulphide-bearing rocks. High natural remanent magnetization intensities are related to the iron sulphide-bearing ore, and remanent magnetization is a significant magnetic anomaly source. Based on synthetic modelling results, both magnetic and gravimetric data could be used in direct exploration in the Metsämonttu area.