The Taivaljarvi Ag-Zn deposit in the Archean greenstone belt, eastern Finland

Abstract

The Taivaljaervi Ag-Zn deposit is associated with felsic metavolcanics in the Archean green-stone belt of eastern Finland. The deposit is stratiform and consists of four ore layers, the A, B, C, and D orebodies. The deposit contains 3.45 million metric tons of ore with 1.27 percent Zn, 0.57 percent Pb, 160 g/metric ton Ag, and 0.37 g/metric ton Au. The content of sulfide ore minerals is low, only 5 percent 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 in high amphibolite facies, and the metamorphic mineral assemblages reflect the variation in chemical compositions of the rock sequence. The intensive hydrothermal alteration associated with the mineralization predated the regional metamorphism, but it can still be recognized in the chemical compositions of the rock sequence. The variation in main and trace element compositions in a traverse of the volcanic formation is presented in tables and diagrams. The delta 34 S values fluctuate from 2.0 to 3.8 per mil, indicating volcanic origin of sulfur. The ore deposit is a product of hydrothermal activity associated with volcanoclastic felsic eruption, and the type of deposition is assumed to be epithermal in character.