Metallogeny And Tectonic Evolution Of The Northern Fennoscandian Shield: Field Trip Guidebook

Geological Survey of Finland Guide 54 Metallogeny and tectonic evolution of the Northern Fennoscandian Shield: Field trip guidebook Edited by V. Juhani Ojala, Pär Weihed, Pasi Eilu and Markku Iljina Espoo 2007 Ojala V.J., Weihed P. Eilu P. and Iljina, M. (Eds) 2007 Metallogeny and tectonic evolution of the Northern Fennoscandian Shield: Field trip guidebook. Geological Survey of Finland, Guide 54, xx pages, 52 figures and 7 tables. The Fennoscandian Shield is one of the most important mining areas in Europe. Mineral deposit types include VMS, Kiruna-type apatite-iron, orogenic Au, epigenetic Cu-Au ore, mafic and ultramafic-hosted Cr, Ni-(Cu), PGE and BIF. Palaeoproterozoic parts of the shield are better mineralized than the Archaean areas. The Portimo Complex is exceptional in hosting a variety of styles of PGE mineralization. Economically most potential styles are the contact type and reef-type PGE deposits, and offset base-metal and PGE deposits in the footwall rocks. Other PGE enrichment include in the Portimo Dykes below the Konttijärvi and Ahmavaara marginal series, PGE concentrations near the roof of the Suhanko Intrusion, a Pt-anomalous pyroxenitic pegmatite pipe, and chromite and silicate-associated PGE enrichments in the lower parts of the Narkaus Intrusion and MCU II. Pahtavaara is an active gold mine, with a total in situ size estimate of 15 t gold. It is sited in an altered komatiitic sequence at the eastern part of the Central Lapland greenstone belt and has many of the characteristics orogenic gold deposits, but has an anomalous barite-gold association and a very high fineness (>99.5 % Au) of gold. The Kevitsa Ni-PGE deposit is a large, low-grade disseminated sulphide deposit located in the upper part of the ultramafic zone, in the NE part of the Kevitsa intrusion (2.057±5 Ga). Distribution of Cu, Ni, PGE+Au, and S within the deposit is complex and variable. The deposit has been divided into two bodies, the main ore body (or Main Ore) and the overlying Upper Ore. Four main ore types has been defined, based on the metal and sulphur contents: Regular ore, false ore, Ni-PGE ore, and transitional ore. As distribution of Cu, Ni, PGE+Au, and S within the deposit is complex and variable, the different ore types tend to grade into another. The Suurikuusikko gold deposit is the largest known gold resource in northern Europe. Current resource estimate is about 80 t gold (16 million tonnes at 5.1 g/t). Host rocks are dominantly mafic volcanic rocks within over a 25-kilometre long strike-slip shear zone. Gold is refractory, occurring within arsenopyrite and pyrite. Iron ores in the Kolari area contain significant amounts of copper and gold. The ores are hosted by diopside skarn and quartz-albite rocks. Hannukainen deposit produced 1.96 Mt iron, 40,000 t copper and 4300 kg gold in 1978-1992. The present in situ resource estimate is 16 t Au, 125,000 t Cu and 26 Mt Fe. Typical ore mineral association is magnetite-chalcopyrite-pyrite±pyrrhotite. The Sahavaara iron ore comprises three lenses of skarn-rich iron formation. Resources at Stora Sahavaara are 145 Mt with 43.1 % Fe and 0.076 % Cu. The ore zo