OVERVIEW OF FENNOSCANDIAN SHIELD METALLOGENY AND TECTONIC EVOLUTION WITH SPECIAL EMPHASIS ON FE-OXIDE-CU-AU DEPOSITS

The Fennoscandian Shield, one of the major base metal provinces in Europe, is composed of an Archean nucleus, largely unmineralized, in the northeastern part of the Shield. This nucleus is bordered to the southwest by Paleoproterozoic rocks. At c. 2.5-2.3 Ga sedimentary and volcanic rocks were deposited on the Archean basement during an extensional event. Further rifting of the continent at c. 2.1 Ga gave rise to tholeiitic and komatiitic lavas and dikes. At the end of this extensional event MORB-type pillow lavas were erupted. At c. 1.9 the tectonic regime shifted to compressive and subduction related volcanic and sedimentary rocks were deposited in a terrestrial to shallow water environment. Southwest of these intracratonic complexes, 1.95-1.87 Ga old volcanic arcs were accreted towards the craton during the Svecokarelian orogeny. This orogeny involved voluminous early calc-alkaline magmatism and ended with migmatization, S-type magmatism and large batholithic intrusions of A- to I type granitoids.

Mineralization related to these Proterozoic early extensional and later comressional tectonic regimes include VMS (including Outokumpu Cu-Zn-Co±Ni type) to epithermal VMS, sediment-hosted Zn-Pb, porphyry style Cu, gold lode style deposits, BIF´s, mafic and ultramafic Ni±Cu±PGE deposits as well as Kiruna type apatite-Fe deposits, epigenetic Cu-Au deposits and syngenetic Cu deposits. The latter three types of economic deposits are included in the diverse group of Fe-oxide-Cu-Au style mineralizations: The Kiruna type apatite iron ores are hosted by 1.88 Ga felsic alkaline porphyries emplaced during compressional tectonics. The epigenetic Cu-Au deposits is a diverse group of mineralizations including vein style structurally controlled Cu-Au, probably both 1.87 Ga and 1.77 Ga in age, and intrusive hosted, porphyry style Cu-Au±Fe, related to both calc-alkaline and alkaline magmatism in a compressional regime between 1.9-1.8 Ga. The syngenetic Cu±Zn deposits restricted to the c. 2.1 Ga greenstones, formed during extensional tectonics in intracratonic rift basins.