Chapter 9.3 - The Taivaljärvi Ag-Au-Zn deposit in the Archean TipasjÄrvi greenstone belt, eastern Finland

Abstract

The Taivaljärvi Ag-Au-Zn deposit is associated with felsic metavolcanic rocks in the Archean Tipasjärvi greenstone belt of eastern Finland. The current owner, Sotkamo Silver Oy, has named it the Silver Mine deposit. The deposit is stratiform and consists of four mineralized layers: the A, B, C, and D bodies. The deposit contains 3.34 Mt of ore reserves (according to the JORC 2012 code) with 0.71% Zn, 0.34% Pb, 102 g/t Ag, and 0.29 g/t Au, as part of 3.5 Mt measured and indicated resource. The content of sulfide ore minerals is low, 5% on average. The main ore minerals are sphalerite, galena, chalcopyrite, pyrite and pyrrhotite, dyscrasite, freibergite, electrum, and native Ag. The deposit displays disseminated and vein-type ore textures. The volcanic host rocks are deformed and metamorphosed at upper amphibolite facies conditions, and the metamorphic mineral assemblages reflect the variation in chemical compositions of the rock sequence. The intense hydrothermal alteration associated with mineralization predated the regional metamorphism, but it can still be recognized in the chemical compositions of the rock sequence. The δ34S values fluctuate from 2.0–3.8 per mil, indicating a volcanic origin of sulfur. The deposit is a product of hydrothermal activity associated with volcanoclastic felsic eruption, and the type of deposition is assumed to be epithermal in character.