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Geochronology and structural relationships of mesothermal gold mineralization in the Palaeoproterozoic Jokisivu prospect, southern Finland

Published online by Cambridge University Press:  18 January 2010

K. SAALMANN ,
I. MÄNTTÄRI ,
P. PELTONEN ,
M. J. WHITEHOUSE ,
P. GRÖNHOLM  and
M. TALIKKA
K. SAALMANN*
Affiliation:
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
I. MÄNTTÄRI
Affiliation:
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
P. PELTONEN
Affiliation:
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
M. J. WHITEHOUSE
Affiliation:
Laboratory for Isotope Geology, Swedish Museum of Natural History, P.O. Box 50 007, SE-104 05 Stockholm, Sweden
P. GRÖNHOLM
Affiliation:
Polar Mining Oy, Kummunkatu 34, 83500 Outokumpu, Finland
M. TALIKKA
Affiliation:
Polar Mining Oy, Kummunkatu 34, 83500 Outokumpu, Finland
*
†Author for correspondence: [email protected]
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Abstract

The palaeoproterozoic Svecofennian orogen in southern Finland contains a number of orogenic gold occurrences. The Jokisivu gold deposit, comprising auriferous quartz veins, is hosted by syn-tectonic quartz diorites to gabbros. Mineralization occurs in approximately WNW–ESE- and WSW–ENE-trending shear zones, which probably branch from regional-scale NW–SE-trending shears. Ore zone fabrics post-date regional-scale folding and the metamorphic peak, and can be correlated with late Svecofennian regional shear tectonics (D6; 1.83–1.78 Ga), indicating that mineralization formed during the late stages of orogenic evolution. SIMS and TIMS U–Pb dating of three samples place tight constraints on the age of gold mineralization. Zircons from both unaltered and altered quartz diorites have ages of 1884±4 Ma and 1881±3 Ma, respectively. These are interpreted as the crystallization age of the rock and as providing the maximum age for mineralization. Zircon rims from an altered quartz diorite from the ore zone give ages of c. 1802±15 Ma, which overlap with the 1801±18 Ma titanite (mean Pb–Pb) age from the ore zone. The ages are similar to the age of the pegmatite dyke that cuts the ore zone and whose zircon age of 1807±3 Ma is approximately the same as the 1791±2 Ma monazite age (TIMS) giving the minimum age of the gold mineralization. The mineralization and its structural framework can be correlated with coeval late Svecofennian shear tectonics related to WNW–ESE-oriented shortening in southern Finland. Extensive c. 1.8 Ga granite magmatism, shear zone development and associated gold mineralization are of regional importance also in the northern and western Fennoscandian Shield (Finnish Lapand and Sweden). A Cordilleran-type setting can explain the widespread distribution of magmatism and gold mineralization associated with shortening, as well as the required heat source triggering hydrothermal fluid flow along shear zones.

Keywords

U–Pb geochronologyorogenic goldstructural geologySvecofennian orogenytectonic modelFinland
Type
Original Article
Information
Geological Magazine , Volume 147 , Issue 4 , July 2010 , pp. 551 - 569
Copyright
Copyright © Cambridge University Press 2010

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