Abstract

The Mäkärä Au-rare earth element (REE) prospect area is located in the Tana Belt, south of the 1.9 Ga Lapland Granulite Belt, in northern Finland. The Belt has prominent lanthanum (La) and yttrium (Y) anomalies in regional till and bedrock geochemical data. High Y indicates enrichment of heavy REE in the bedrock. At Mäkärä, promising narrow Au-hematite-quartz veins occur in connection with tensional fractures in the great shear zone.

Under the latest ice divide of the last glaciation, subglacial erosion was weak and glacial transport distance short. High Au contents in saprolite and till together with deep weathering have a strong positive correlation with the positive electromagnetic anomalies caused by the sulphidic gneisses. The highest La and Y contents in till correlate well with the Th maxima of airborne-radiometric datasets. Locally, the <0.06 mm till size fraction contains up to 0.4% REE. A recent exploration project in Mäkärä revealed a 13 m wide Au-hematite-quartz vein with a mean of 3 ppm Au and 0.04–0.1% REE in kaolinitic saprolite derived from arkosic gneiss. The elevated REE content resembles that of ionic adsorption clays in China. Typical REE-rich minerals are monazite, rhabdophane, xenotime and kaolinite. Till geochemistry proved useful in REE exploration.

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