Mineralogy and metal distribution in the copper-tungsten deposit at Ylojarvi, southwest Finland

Abstract

The Yloejaervi Cu-W deposit in southwest Finland is located at the western end of the Svecokarelidic Tampere schist zone, which consists of argillaceous sediments and volcanics. The deposit was mined from 1942 to 1966. During that time a total of 4,013,500 tons of ore were hoisted, from which 128,343 tons of copper concentrate, 894 tons of scheelite concentrate, and 2,100 tons of arsenopyrite concentrate were produced.The mineralized rock is confined to a tourmaline breccia close to the Haemeenkyroe granodiorite, both some 1,850 m.y. in age. The breccia fragments, which are tuffite and porphyrite, are enveloped by a quartzose alteration seam about 1 cm thick. The matrix is composed of tourmaline with variable amounts of chalcopyrite, arsenopyrite, pyrrhotite, scheelite, and some accessory ore minerals.