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This article evaluates the known rare earth elements (REE), Ti and Li occurrences and exploration potential in Finland, based on existing data combined with new geochemistry and mineralogy, heavy mineral studies, geophysical measurements, geologic mapping and recent drilling of new targets.The potential rock types for REE include carbonatite (Sokli, Korsnäs), alkaline rocks (Otanmäki, Lamujärvi, and Iivaara), rapakivi granite and pegmatite (Kovela), and kaolin-bearing weathering crusts in eastern and northern Finland. The highest REE concentrations occur in late magmatic carbonatite veins in the fenite area of the Sokli carbonatite complex. Detailed mineralogical investigations have revealed three distinct types of REE mineralization as phosphates, carbonates and silicates in the studied areas. Mineralogical and mineral chemical evidence demonstrates that hydrothermal processes are responsible for the REE mineralization in the studied rocks and confirms that such processes are predominant in the formation of REE minerals in carbonatite, calc-silicate rocks and albitite. Titanium occurs as ilmenite in hard rock deposits in Paleoproterozoic subalkaline mafic intrusions. The Otanmäki ilmenite was mined together with vanadium-rich magnetite from 1953 to 1985 from a small gabbro-anorthosite complex, which still contains potential for Ti resources. Other major ilmenite deposits are within the Koivusaarenneva ilmenite gabbro intrusion and Kauhajärvi apatite-ilmenite-magnetite gabbro complex. Possible Ti resources are included in Ti-magnetite gabbro of the large layered mafic intrusions in northern Finland, such as at the former Mustavaara vanadium mine. For several years, Rare Element (RE)-pegmatite of the Kaustinen and Somero-Tammela areas has been the objective of Li exploration by the Geological Survey of Finland (GTK). At Kaustinen, Li-pegmatite occurs as subparallel dyke swarms in an area of 500 km 2 within Paleoproterozoic mica schists and metavolcanic rocks. Li pegmatite contains more than 10% spodumene as megacrysts (1-10 cm), albite, quartz, K-feldspar, muscovite and accessory minerals such as columbite-group minerals, apatite, tourmaline, beryl, Fe-oxide minerals and garnet. The Kaustinen spodumene pegmatite and Somero-Tammela petalite-spodumene pegmatite contain potential Li resources for the battery industry in EU countries.

The Wiborg rapakivi batholith (1.64 Ga) in southeastern Finland with documented occurrences of REE, indium and Zn-Cu-Pb sulphide mineralization was studied. Hydrothermal greisen and quartz vein type Fe-Sn and Zn-Cu-Pb are found in the Kymi granite stock as intrusions. They are enriched with indium and rare earth elements, with roquesite (CuInS 2 ) being a major indiumcarrier, whereas monazite (Ce), allanite (Ce), bastnäesite (Ce), xenotime-(Y) and thorite are the main REE carriers. Combination of optical and field emission scanning electron microscopy (FE-SEM) and electron probe microanalysis (EPMA) were used to study the indium and REE-bearing mineral assemblages. EPMA of roquesite found in galena had a composition of 26.16% S, 0.02% Fe, 25.06% Cu, 0.03% Zn, 1.06% As, 0.31% Sb and 47.14% In. Substitution reaction Pb 2+ S 2− ↔ Cu + In 3+ S 2− is the cause of the incorporation of indium in the galena structure. The majority of the LREE are carried by monazite, bastnäesite and allanite, and the HREE by xenotime and zircon. There is a partial solid solution between monazite and xenotime with minor or trace amounts of LREE in xenotime grains (6.0 wt%). LREE (>95 mol% LREE) and less than 5 mol% HREE + Y reflects the enrichment of chondrite-normalized REE of the monazite grains of the Kymi granite stock. The xenotime grains (small and irregular) main composition contains 71 -76 mol% YPO 4 , 16 -27 mol% HREE, and 6 -8 mol% LREE. It is believed that indium and REE-mineralization presence is due to the combination of magmatic and postmagmatic processes, particularly at later stages by fluid fractionation.

More than 40 m length of drill cores were collected from four boreholes drilled by Geological Survey of Finland (GTK) and Outokumpu Oy in high-grade metamorphic rocks of Rautalampi and Käypysuo, Central Finland. The hosted rocks of the graphite mineralization were mica–quartz schist and biotite gneiss. The graphite-bearing rocks and final concentrated graphite powder were studied with petrographic microscope, scanning electron microscope (SEM-EDS), Raman spectroscopy, and X-ray analysis (XRD and XRF). A majority of the studied graphite had a distinctly flakey (0.2–1 mm in length) or platy morphology with a well-ordered crystal lattice. Beneficiation studies were performed to produce high-purity graphite concentrate, where rod milling and froth flotation produced a final concentrate of 90% fixed carbon with recoveries between 67% and 83%. Particle size reduction was tested by a ball and an attritor mill. Graphite purification by alkaline roasting process with 35% NaOH at 250 °C and leached by 10% H2SO4 solution at room temperature could reach the graphite purity level of 99.4%. Our analysis suggested that purifying by multistage flotation processes, followed by alkaline roasting and acid leaching, is a considerable example to obtain high-grade graphite required for lithium-ion battery production.

Na-metasomatic augite and aegirine-augite episyenites are hosted by subalkaline amphibole granites in the 1.644 Ga Suomenniemi rapakivi granite complex, southeastern Finland. In an examined drill core, episyenites are bordered by up to 50cm-wide zones of Na-enriched augite-bearing granite in which alkali feldspar forms rims on plagioclase, and aggregates of augite and magnetite have formed by fluid-induced dehydration of hastingsite and biotite. In the episyenites, quartz has been partially removed, alkali feldspar (An <1 Ab 50 Or 50 ) and plagioclase have been partially recrystallized to granoblastic polygonal aggregates, and clinopyroxene (augite or aegirine-augite) has coarsened and been enriched in the aegirine component. Mass balance modeling implies addition of mainly Na, depletion of Si, F, Rb, Ba, Sr and 10-20% volume loss (by quartz dissolution) in the episyenitized zones in the drill core. Quartz-depletion and recrystallization may have been caused by several superimposed stages of alteration, probably related to voluminous dike-and A-type granite magmatism in the Suomenniemi area 10-15 m.y. after the emplacement of the Suomenniemi complex. Because of the coarse recrystallization textures and near-solidus recrystallization temperatures, distinguishing these fenite-like metasomatic rocks from igneous syenites is not trivial. In epizonal A-type granite complexes, high-temperature episyenites may be more common than currently thought.