Kärenlampi, K., Kontinen, A., Hanski, E., Huhma, H., Lahaye, Y., Krause, J. & Heinig, T.. (2020) Age and origin of the Nb-Zr-REE mineralization in the Paleoproterozoic A1-type granitoids at Otanmäki, central Finland. Bulletin of the geological society of Finland, 92(1), 39-71. https://doi.org/10.17741/bgsf/92.1.003
Age and origin of the Nb-Zr-REE mineralization in the Paleoproterozoic A1-type granitoids at Otanmäki, central Finland
|Author:||Kärenlampi, Kimmo1; Kontinen, Asko2; Hanski, Eero1;|
1Oulu Mining School, P.O. Box 3000, 90014 University of Oulu, Finland
2Geological Survey of Finland, P.O. Box 1237, 70211 Kuopio, Finland
3Geological Survey of Finland, P.O. Box 96, 02151 Espoo, Finland
4Helmholtz Center Dresden—Rossendorf, Helmholtz-Institute Freiberg for Resource Technology, Chemnitzer Str. 40, D-09599 Freiberg, Germany
|Online Access:||PDF Full Text (PDF, 5.4 MB)|
|Persistent link:|| http://urn.fi/urn:nbn:fi-fe2020071047206
The Geological Society of Finland,
|Publish Date:|| 2020-07-10
The Otanmäki area in central Finland hosts two occurrences of Nb-Zr-REE mineralization, Katajakangas and Kontioaho, within a suite of ca. 2.04–2.06 Ga (A1-type) gneissic granites, syenite and monzonite-monzodiorite. They exhibit trace element characteristics and whole-rock εNd(2050 Ma) values (from +2.6 to -1.3) consistent with derivation by differentiation of mantle-derived mafic magmas with variable interaction with crustal material. The mineralization is localized in 0.1- to 1.4-m-thick dikes (Kataja-kangas) and a 30- to 50-m-thick sheet-like body (Kontioaho), containing allanite-(Ce), zircon, titanite, and Nb-REE-Th-U oxides. Their wall rocks are composed of ca. 2.06 Ga peraluminous monzogranite, which is genetically unrelated to the mineralized rock units, as evidenced by whole-rock chemical and Sm-Nd isotope data and zircon U-Pb geochronology. Instead, the mineralization is linked to the nearby peralkaline to metaluminous alkali feldspar granite magmatism dated at ca. 2.04–2.05 Ga. The development of REE-HFSE enrichment in the mineralized rock units required extensive crystallization of a peralkaline granite magma, producing residual metaluminous, high-silica melts enriched in REE-HFSE, Ca, and Fe relative to Na, K, and Al. The REE-HFSEand Ca enrichment was further promoted by volatile complexing with dissolved F-, CO₃²⁻ and SO₄²⁻. These highly evolved melts were parental to the mineralized dikes and the sheet-like intrusive body, which were emplaced into the monzogranite capping the intrusions of peralkaline granite.
Bulletin of the Geological Society of Finland
|Pages:||39 - 71|
|Type of Publication:||
A1 Journal article – refereed
|Field of Science:||
Financial support for this study was provided by the Advanced Materials Doctoral Programme (ADMA-DP) of the University of Oulu, the K.H. Renlund Foundation, and the Tauno Tönning Foundation. The field work was profoundly supported by Otanmäki Mine Oy (www.otanmaki.fi) and the CEO of the company, Jouko Jylänki, which is gratefully acknowledged. The NordSIMS facility is funded by the Swedish Research Council (infrastructure grant # 2017-00671), the Swedish Museum of Natural History and the University of Iceland; this is NordSIMS publication 647. Martin Whitehouse is thanked for U-Pb data reduction and Lev Ilinsky and Kerstin Lindén for laboratory assistance at NORDSIM. Andreas Bartzsch and Roland Würkert from the HIF and Sari Forss from the University of Oulu are thanked for the preparation of the samples used in MLA and EPMA. Leena Järvinen from the GTK is acknowledged for laboratory assistance. An anonymous reviewer, Tapio Halkoaho and the handling editor Ferenc Molnàr are thanked for their constructive comments that helped to improve this manuscript.
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