Geologian tutkimuskeskus, Opas —
Geological Survey of Finland, Guide 42

Abstract:

The excursion visits some of the most important metallic and non-metallic ore deposits in the Proterozoic of eastern Finland, as well as providing an introduction to exploration history and respective geological environments. Archean geology and mineralization are also represented by the Pampalo gold deposit within 2.75 Ga sediment-dominated Hattu schist belt (Stop 6) and the major soapstone operations at Nunnanlahti (Stop 4), while a kimberlite pipe near the abandoned Luikonlahti Cu-Zn-Co deposit (Stop 1) provides an opportunity to examine some the youngest events to affect the Fennoscandian shield in Finland.

The main theme of the excursion is the mineralization associated with episodic rifting of the Karelian craton, particularly after 2.1 Ga, when there was a major phase of rifting and predominantly mafic volcanism, followed by more quiescent passive margin deposition; the exhausted sediment-hosted Hammaslahti Cu-Zn deposit and the 300 Mt low grade Ni-Cu-Zn mineralization at Talvivaara (Stop 7) appear to have formed during this time. Renewed rifting culminated in the formation of oceanic crust at 1.97–1.95 Ga, which was subsequently thrust back on to the craton margin, together with the passive margin sequence and overlying monotonous turbidites, during the Svecofennian Orogeny, between 1.92–1.85 Ga. The Jormua ophiolite complex (Stop 8) is the best preserved and exposed example of oceanic crust and mantle lithosphere, while the Outokumpu region is characterized by a distinctive metamorphic assemblage comprising serpentinites, quartz rocks, calcsilicate skarns and black schists, and hosting major Cu-Co-Zn deposits which were mined until recently at Luikonlahti (Stop 1), and at Outokumpu itself (Stop 2). This distinctive assemblage is also well-represented at Horsmanaho (Stop 3), where talc is mined commercially.

A review of exploration, genetic models and metallogeny of the Outokumpu region, and of black schists in eastern Finland is given, including a synopsis of petrophysical properties, supplemented by appended maps of regional geophysical data.

Excursion held on: August 8–10, 1997

Key words (GeoRef Thesaurus, AGI): metal ores, metallogeny, mineral exploration, Precambrian, field trips, guidebook, Eastern Finland

Kirsti Loukola-Ruskeeniemi, Geological Survey of Finland, P.O. Box 96, FIN-02151 Espoo, Finland
e-mail: kirsti.l-r@gsf.fi

Peter Sorjonen-Ward, Geological Survey of Finland, P.O. Box 96, FIN-02151 Espoo, Finland
e-mail: peter.sorjonen-ward@gsf.fi

ISBN 951-690-658-3
ISSN 0781-643X

Price: 50 FIM (incl. VAT)

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