Multiply deformed Paleoproterozoic foreland fold and thrust belt in northern Fennoscandia – The peripheral Kuusamo belt as a key example

Lahtinen, Raimo; Köykkä, Juha

doi:10.1016/j.precamres.2020.105825

Cited by 13 publications

(7 citation statements)

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“…b Stratigraphic column of KB showing stratigraphic setting of Au-Co mineralization. Modified after Huhma et al (2018) with additions from Köykkä et al (2019) and Lahtinen and Köykkä (2020). Section of Au-Co mineralization in the stratigraphy is taken from Vanhanen (2001).…”

Section: Regional Settingmentioning

confidence: 99%

“…Rock descriptions in this geological map are based solely on alteration mineralogy as described by Vanhanen (2001). Modified after Pankka (1992) and Vanhanen (2001) stratigraphy of the KB was further refined (Köykkä et al 2019;Lahtinen and Köykkä 2020) and now includes a formation belonging to the Kumpu Group as the uppermost unit (Fig. 1b).…”

Section: Regional Settingmentioning

confidence: 99%

“…1b). Total thickness of the volcano-sedimentary sequence in the KB varies from 5 to 7 km (Lahtinen and Köykkä 2020).…”

Section: Regional Settingmentioning

confidence: 99%

“…The stratigraphic sequence of the KB underwent deformation and regional metamorphism during the Svecofennian orogeny (1. 93-1.76 Ga;Silvennoinen 1972Silvennoinen , 1992Lahtinen and Köykkä 2020). Deformation occurred in four stages (D1-D4; Lahtinen and Köykkä 2020), starting with an E-W compressional phase (D1), followed by a N-S shortening (D2) that produced F2 folds.…”

Section: Regional Settingmentioning

confidence: 99%

“…Higher metamorphic grade is also present in the northern and eastern parts of the KB. Lahtinen and Köykkä (2020) suggested that the gradual metamorphic zonation from greenschist facies in the south to amphibolite facies in the north can be explained by the presence of a long wavelength (70-100 km) major D4 anticlinorium, with the metamorphic grades increasing towards the hinge zone. This interpretation was partly based on results of wide-angle reflection and refraction surveys (Tiira et al 2014) that showed ca.…”

Section: Regional Settingmentioning

confidence: 99%

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Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland

et al. 2021

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The Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.

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Section: Regional Settingmentioning

confidence: 99%

Section: Regional Settingmentioning

confidence: 99%

“…1b). Total thickness of the volcano-sedimentary sequence in the KB varies from 5 to 7 km (Lahtinen and Köykkä 2020).…”

Section: Regional Settingmentioning

confidence: 99%

Section: Regional Settingmentioning

confidence: 99%

Section: Regional Settingmentioning

confidence: 99%