Abstract
Rare earth elements (REE) have critical importance in the manufacturing of many electronic products in the high-tech and green-tech industries. Currently, mining and processing of REE is strongly concentrated in China. A substantial growth in global exploration for REE deposits has taken place in the recent years and has resulted in considerable advances in defining new resources. This study provides an overview of the mineralogical and petrological peculiarities of the most important REE prospects and metallogeny of REE in Finland. There is a particularly good potential for future discoveries of carbonatite hosted REE deposits in the Paleozoic Sokli carbonatite complex, as well as in the Paleoproterozoic Korsnäs and Kortejärvi Laivajoki areas. This review also provides information about the highest known REE concentration in the alkaline intrusions of Finland in the Tana Belt and other alkaline rock hosted occurrences (e.g., Otanmäki and Katajakangas). Significant REE enrichments in hydrothermal alteration zones are also known in the Kuusamo Belt (Uuniniemi and Honkilehto), and occurrences of REE-rich mineralisation are also present in granite pegmatite bodies and greisens in central and southern Finland (Kovela monazite granite and the Rapakivi Granite batholith at Vyborg, respectively). REE minerals in all of the localities listed above were identified and analyzed by scanning electron microscopy (SEM) and electron microprobes (EMPs). In localities of northern and central Finland, both primary rock forming and epigenetic-hydrothermal REE minerals were found, namely phosphates (monazite-Ce, xenotime-Y), fluorcarbonates (bastnäsite-Ce, synchysite), and hydrated carbonates (ancylite-Ce), hydrated aluminium silicates (allanite-Ce, Fe-allanite, cerite, chevkinite), oxides (fergusonite, euxenite) and U-Pb rich minerals. The chondrite normalized REE concentrations, the La/Nd ratios and the REE vs. major element contents in several types of REE bearing minerals from prospects in Finland can be used to identify and define variable REE fractionation processes (carbonatites), as well as to discriminate deposits of different origins.
Highlights
The demand for rare earth elements has spiked in recent years due to their increasing usage in numerous high-technology applications that touch many aspects of modern life and culture.Specific Rare earth elements (REE) are used individually or in combination to make phosphors—substances that emit luminescence—for many types of ray tubes and flat panel displays, in screens that range in size from smart phone displays to stadium scoreboards
Significant REE enrichments in hydrothermal alteration zones are known in the Kuusamo Belt (Uuniniemi and Honkilehto), and occurrences of REE-rich mineralisation are present in granite pegmatite bodies and greisens in central and southern Finland (Kovela monazite granite and the Rapakivi Granite batholith at Vyborg, respectively)
The most significant REE deposits and occurrences in Finland are associated with highly fractionated carbonatite intrusions and dikes, alkaline rocks, hydrothermal alteration zones in metamorphic rocks and greisens and pegmatites in granite intrusions
Summary
The demand for rare earth elements has spiked in recent years due to their increasing usage in numerous high-technology applications that touch many aspects of modern life and culture. (3) the Kortejärvi carbonatite and Laivajoki silicocarbonatite complexes; (4) the alkaline gneissic granite in the Otanmäki area; (5) the REE-Au mineralization at Mäkärä and Vaulo in the Tana Belt; (6) the metasomatic-hydrothermal Au-Co-Cu-Fe-U and REE deposits with intense albitization in the Kuusamo belt; (7) the Kovela monazite granite in southern Finland and (8) the Vyborg rapakivi granite batholith in south eastern Finland We classify these deposits and occurrences on the basis of their origin and geological settings (Figure 1), and summarize their characteristics into four REE deposit types on the basis of the age, host rock type and mineral associations (Table 1). Modified after Korsman et al and Nironen et al [18,19] respectively
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