Abstract

A Precambrian mobile zone rimming an ancient craton in central Finland is host to a number of ore deposits. Two of these, Vihanti and Pyhaesalmi, are currently being exploited.The ores are stratabound zinc-copper ores whose country rocks consist of volcanics and sediments with volcanogenic weathering products. Hydrothermal alteration expelled Na and Ca from the rocks; accordingly, the contents of Mg, Fe, and Al increased. The area has undergone high-grade regional metamorphism accompanied by intense movements. In the altered rocks metamorphism resulted in the formation of sericite, cordierite, and anthophyllite.The ores at Vihanti and Pyhaesalmi are products of volcanic activity. The other deposits are metamorphosed to such an extent that their mode of formation cannot with certainty be established.

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