Guo, F.-F., Maier, W. D., Heinonen, J. S., Hanski, E., Vuollo, J., Barnes, S.-J., Lahaye, Y., Huhma, H., & Yang, S. (2023). Geochemistry of 2.45 Ga mafic dykes in northern Finland: Constraints on the petrogenesis and PGE prospectivity of coeval layered intrusions. In Lithos (Vols. 452–453, p. 107206). Elsevier BV. https://doi.org/10.1016/j.lithos.2023.107206
Geochemistry of 2.45 Ga mafic dykes in northern Finland : constraints on the petrogenesis and PGE prospectivity of coeval layered intrusions
|Author:||Guo, Fang-Fang1; Maier, Wolfgang D.2; Heinonen, Jussi S.3;|
1Oulu Mining School, Faculty of Technology, University of Oulu, Oulu 90014, Finland
2School of Earth and Environmental Sciences, Cardiff University, Cardiff CF10 3AT, Wales, UK
3Department of Geosciences and Geography, University of Helsinki, Helsinki 00014, Finland
4Geological Survey of Finland, Rovaniemi 96100, Finland
5Science de la Terre, Université du Québec à Chicoutimi, Chicoutimi, QC G7H 2B1, Canada
6Geological Survey of Finland, Espoo 02150, Finland
|Online Access:||PDF Full Text (PDF, 10.9 MB)|
|Persistent link:|| http://urn.fi/urn:nbn:fi-fe20231003138517
|Publish Date:|| 2023-10-03
The Karelian craton contains abundant ∼2.45 Ga mafic dykes that are compositionally, temporally and, in some cases, spatially related to PGE-mineralised mafic-ultramafic layered intrusions. The dykes can be sub-divided into four groups, namely siliceous high-magnesian basalts (SHMB), gabbronorites (GBNO), low-Ti tholeiites and Fe-rich tholeiites. In this study, we group the SHMB and GBNO dykes to one group as SHMB group, and the two tholeiitic group dykes as tholeiite group, based on their similar geochemical and mineralogical features. In the SHMB group dykes, plagioclase has initial 87Sr/86Sr ratios of 0.7028 to 0.7036 and initial bulk-rock εNd values vary from −2.5 to −1.0, indicating moderate degrees of contamination with Archaean basement. Tholeiitic dykes show a less-radiogenic Sr isotope composition with an average initial 87Sr/86Sr ratio of 0.7024 and higher initial εNd values ranging from +0.3 to +1.7. Thermodynamic and geochemical modelling suggests that the SHMB group dykes could have formed by crustal contamination of a komatiitic magma at deeper crust followed by fractional crystallisation at shallower depth, whereas the tholeiitic group mainly experienced fractional crystallisation with less crustal contamination. Alternatively, the SHMB dykes may have been derived from a SCLM mantle whereas tholeiitic dykes from a plume mantle, or the two types of dykes derived from different part of a mantle plume with different melting degrees, though these latter two models are not favoured in this study. Based on trace element and isotope characteristics, the SHMB dykes are suitable candidates for the parental magmas to some of the Finnish PGE-mineralised intrusions (e.g., Penikat and Portimo), whereas the tholeiitic dykes may represent the parental magma of the Tsipringa layered intrusion in Russia. Both the SHMB and tholeiitic dyke types are fertile with regard to PGE, with up to 10–20 ppb Pt and Pd and mantle-like Cu/Pd ratios in their least evolved members, suggesting that the magmas remained sulphide undersaturated during mantle melting and en route to the upper crust. This interpretation is consistent with the fact that most of the ∼2.45 Ga Fennoscandian layered intrusions contain PGE mineralisation. Sulphide melt saturation in the dykes and layered intrusions was mostly attained after their final emplacement, likely due to crystal fractionation.
|Type of Publication:||
A1 Journal article – refereed
|Field of Science:||
This work was co-funded by the K.H. Renlund Foundation, European Union and UK Research and Innovation (SEMACRET, 101057741), Korlactic CBC, Academy of Finland for J.S. Heinonen (Grant no. 295129) and a scholarship from the Finnish Graduate School of Geology to F.-F. Guo.
|EU Grant Number:||
(101057741) SEMACRET - Sustainable exploration for orthomagmatic (critical) raw materials in the EU: Charting the road to the green energy transition
|Academy of Finland Grant Number:||
295129 (Academy of Finland Funding decision)
© 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).