Background variation of ore-related elements in the Tampere area, southern Finland

Lahtinen, Raimo & Lestinen, Pekka 1996. Background variation of ore-related elements and regional-scale mineralization indications in Palaeoproterozoic bedrock in the Tampere–Hämeenlinna area, southern Finland. Geological Survey of Finland, Bulletin 390. 38 pages, 8 figures, 2 tables and one appendix.

Abstract

A total of 403 bedrock samples, covering all main rock types, were collected from an area of 9600 km2. Rock types were classified into different geochemical and areal subgroups and the data of ore-related elements Ag, As, Au, B, Bi, Cs, Co, Cu, Hg, Li, Mo, Ni, Pd, S, Sb, Se, Sn, Te, Tl, Zn and W were collected and interpreted.

Sedimentary rocks show an increase in ore-related elements from psammites to pelites with highest values in black schists, which are particularly enriched in Ag, Bi, Mo, Ni, Pd, S, Te and Zn. Tellurium abundances are in pelites 5–20 times and in black schists 20–100 times those in non-assimilated igneous rocks. Tholeiitic mafic volcanics exhibit highest values of copper, while Sb is enriched in intermediate calc-alkaline volcanics. The granitoid groups with an assimilated sedimentary component reflect this character: the contents of elements typically enriched in sedimentary rocks are about 2–3 times the normal level in granitoids. The S/Se ratios vary between rock types and subgroups, but typically form areal anomalies of high (> 10 000) and low (< 5000) S/Se ratios spanning different rock types.

Gold, As and Te data indicate mineralized areas already known but also some new prospecting areas. The Li and Cs data reveal several anomalies, including two earlier unknown areas, and the anomalous Sn values are associated with S-type microcline granites. Cu±Mo±W anomalies indicate porphyry-type mineralizations, known to occur in the area. Although direct indications of magmatogenic Ni–Cu occurrences were not found, a favourable zone is proposed. This zone is characterized by MORB-affinity volcanics, sedimentary rocks with low S/Se ratio and DM-affinity mafic–ultramafic plutonics.

The study showed that large and wide mineralization processes can be detected, but low sampling density and an unevenly spaced sampling grid prevent the detection of discrete mineralizations.

Key words(GeoRef Thesaurus, AGI): geochemical surveys, bedrock, metamorphic rocks, plutonic rocks, chemical elements, metals, geochemical anomalies, mineral exploration, Proterozoic, Paleoproterozoic, Tampere, Hämeenlinna, Finland

Raimo Lahtinen,
Geological Survey of Finland,
P.O. Box 96, FIN-02151 ESPOO, FINLAND
E-mail: raimo.lahtinen@gsf.fi

Pekka Lestinen,
Geological Survey of Finland,
P.O. Box 1237, FIN-70211 KUOPIO, FINLAND
E-mail: pekka.lestinen@gsf.fi

ISBN 951-690-666-4
ISSN 0367-522X

Price: 56 FIM (incl. VAT)

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