Itä-Suomen yksikkö CM 60/2006/3 8.12.2006 Kuopio M60/2006/3 Structural and hydrothermal event history of the Koli-Kaltimo-Eno region - a preliminary regional framework Peter Sorjonen-Ward FINU1 2006 Karelian structural studies Commercial - in - confidence, Public 1.1.2013 GTK Report CM 60/2006/3 GEOLOGICAL SURVEY OF DOCUMENTATION PAGE FINLAND Date / Rec. no. 8.12.2006 Authors Type of report Peter Sorjonen-Ward Commercial - in - Confidence Commissioned by COGEMA/GTK Contract 2004/Tender 2006 (K129/53/2004) Title of report Structural and hydrothermal event history of the Koli-Kaltimo-Eno region – a preliminary regional framework Abstract A preliminary structural framework and geological event history is outlined, as a basis for considering uranium mobilization, transport and deposition in the Koli-Eno area in eastern Finland. The study area represents a well-preserved, though tectonically modified and metamorphosed Paleoproterozoic sedimentary sequence overlying a Neoarchean basement comprising granitoids and greenstone belts, some of which appear to be relatively enriched in uranium and thorium. Accordingly, the area may be evaluated in terms of diagenetic to metamorphic mobilization of uranium, as well as primary depositional enrichment. It is necessary to establish whether the lowest formations in the stratigraphical sequence were deposited before or after redox shift in atmosphere and regolith. Further scenarios may be considered, such as extrapolation of Riphean basins across the study area, with potential for mineralization if the present erosion level is close to that in the Mesoproterozoic. However, current isotopic and paleomagnetic data favour late Svecofennian rather than younger hydrothermal activity. A late Svecofennian event can also be reconciled with the interpreted kinematic framework, involving partitioning of deformation into strike-slip zones subparallel to the craton margin, and associated small scale thrusts and duplex systems. Keywords Uranium, mineral system, stucture, hydrothermal, granite, paleoregolith, Archean, Svecofennian Geographical area Finland, North Karelia Map sheet 4223, 4224, 4232, 4241, 4242, 4313, 4331 Other information Report serial Archive code Unpublished reports CM 60/2006/3 Total pages Language Price Confidentiality 16 English Public 1.1.2013 Unit and section Project code 401 1901006 Signature/name Signature/name Peter Sorjonen-Ward FinU1 2006 Karelian structures and hydrothermal event history Peter Sorjonen-Ward FINU1 2006 Karelian structural studies Commercial - in - confidence, Public 1.1.2013 GTK Report CM 60/2006/3 Contents 1 OUTLINE OF REGIONAL STRUCTURAL FRAMEWORK AND PRINCIPAL GEOLOGICAL EVENTS 1 2 OUTLINE OF EVENTS AND PROCESSES POTENTIALLY RELEVANT FOR MOBILIZATION, TRANSPORT AND PRECIPITATION OF URANIUM IN THE KOLI-ENO AREA 10 3 REFERENCES 14 FinU1 2006 Karelian structures and hydrothermal event history Peter Sorjonen-Ward GTK Report CM 60/2006/3 1 Commercial - in - confidence, Public 1.1.2013 1 OUTLINE OF REGIONAL STRUCTURAL FRAMEWORK AND PRINCI- PAL GEOLOGICAL EVENTS The purpose of this study was to provide a structural framework and outline a history of geologi- cal and hydrothermal events, to assist in defining a more detailed research and exploration pro- gram. The report therefore provides a preliminary synthesis based on regional geological and geophysical data, checked against outcrop observations in key areas, but no microscopic or ana- lytical studies have been undertaken. For documentation and descriptions of known uranium mineralization in the area, please refer to Äikäs (2000). 21°E 24°E 27°E 30°E FIRE 1 64°N 64°N Kokkola FIRE 3a 63°N 63°N FIRE 3 Kuopio Joensuu 62°N 62°N 61°N 61°N FIRE 2 100 km Helsinki 27°E 30°E 1.87 Ga ”post-kinematic” granodiorite, tonalite, Mesoproterozoic rapakivi granite quartz diorite; locally olivine and pyroxene 1.89-1.87 Ga porphyritic granodiorite and granite 1.85-1.80 Ga biotite granites, asociated predominate over mafic granitoids with migmatites and granulite metamorphism 1.89-1.87 Ga tonalite and quartz diorite 1.88 Ga pyroxene-bearing, K-feldspar phyric predominate over granite and granodiorite Granodiorite, mostly in granulite facies terrain Figure 1 Location of the Koli-Eno study area in eastern Finland, indicated by rectangle north of Joen- suu. Ochre dotted line defines western limit of exposed Archean rocks. Image superimposes Proterozoic granitoids on grayscale DEM, to indicate the absence of Svecofennian orogenic magmatism in the study area, in contrast to the Itä-Uusimaa study area (to NE of Helsinki). Note also the orthogonal trends of the craton margin and the northern boundary of the late orogenic migmatite and granite zone in southern Finland (adapted from Sorjonen-Ward, 2006). FinU1 2006 Karelian structures and hydrothermal event history Peter Sorjonen-Ward GTK Report CM 60/2006/3 2 Commercial - in - confidence, Public 1.1.2013 The Koli-Eno area is perhaps the most intensively studied area in Finland, not only in terms of uranium mineralization (Piirainen, 1968), but also with respect to lithostratigraphic and sedimen- tological (Gaál, 1964; Piirainen, 1968; Laiti, 1983, 1985; Marmo, 1992; Kohonen and Marmo, 1992; Kohonen, 1995, Pekkarinen et al., 2006). Figure 1 shows the location of the study area, together with the distribution of various groups of Paleoproterozoic granitoids. It is immediately apparent, in contrast to the Uusimaa region for example, that Paleoproterozoic granitoids are ab- sent from this region, and have played no part in uranium mobilization and enrichment. On the other hand, late Archean crustal evolution in eastern Finland shows many parallels with Sve- cofennian orogenic events (Sorjonen-Ward and Luukkonen, 2005), including the intrusion of widespread late orogenic monzogranites with conspicuous radiometric signatures. Therefore, a primary magmatic enrichment of uranium during late Archean time is at least theoretically pos- sible. It is also evident from Figure 2 that the Koli-Eno region is distinctive in terms of Protero- zoic geology, including quartzites and arkoses of the Herajärvi Group and the Koli mafic sill complex, which sills intruded across the unconformity between Archean basement and Paleopro- terozoic cover. 29°15´E 30°00´E Late Archean rock units Felsic volcanic and volcaniclastic rocks Turbiditic metagraywackes Mafic and ultramafic volcanics and sills Nurmes Complex supracrustal gneisses, migmatites, Koli granodiorites and late orogenic monzogranites Biotite tonalitic and hornblende/pyroxene granodioritic plutons; locally granulite facies PaukkajaPaukkaj a 6980 400 Riutt a Kon Outokumpu Ilomantsi 1200 So t 6950 2000 Jo e n s u u 6000 4000 5200 400 Ju o 3200 Kovero 1200 Kiihtelysvaara 6920 4460 4500 4540 Paleoproterozoic rock units Proterozoic granodiorites and granites, typically with isotopic Höytiäinen Province marine shelf to deep basin evidence for derivation from underlying Archean crust sedimentary and mafic volcanic units (< 2.1 Ga) Turbidites and black schists enclosing Outokumpu assemblage Autochthonous terrigenous quartzites and (khaki), emplaced onto Karelian domain at 1.9 Ga layered mafic sills(2.4-2.2 Ga) Figure 2. Regional geological context of the Koli-Eno region. Note in particular the 2.2 Ga Koli mafic sill complex (dark brown) and westwards dipping Herajärvi Group, between the Archean basement to the east and Kalevian (2.1-1.9 Ga) turbidites (blue). Location of the FIRE 3 seismic reflection profile is also indicated. FinU1 2006 Karelian structures and hydrothermal event history Peter Sorjonen-Ward GTK Report CM 60/2006/3 3 Commercial - in - confidence, Public 1.1.2013 Whether this spatial association has any significance with respect to uranium transport during weathering and deposition, or redox processes at mafic sill contacts, remains to be confirmed, although these concepts played a role in previous exploration targeting (Piirainen, 1968; Koho- nen and Marmo, 1992). Further work clearly needs to focus on the possible structural controls on mineralization, and in particular, dating of minerals; there is some indication of uraninite precipi- tation at Riutta (Ristimonttu) coincident with late Svecofennian metamorphism (Michel Cuney, pers. comm. 2006). Ko li Paukkaja RiutRiutt t a Kiihtelysvaara Huhtilampi Värtsilä Jänisjärvi Figure 3. Total magnetic intensity image combined for eastern Finland and adjacent Russia (data compi- lation from joint project between GTK and Minerals Sp., purchased also by AREVA; this image proc- essed by Jouni Lerssi, GTK Kuopio). Note the tendency for high magnetic response in many Archean granitoids (and also the Puruvesi Granite in the southwestern part of the image). For explanation see text. FinU1 2006 Karelian structures and hydrothermal event history Peter Sorjonen-Ward GTK Report CM 60/2006/3 4 Commercial - in - confidence, Public 1.1.2013 The total magnetic intensity images in Figures 3 and 4 clearly reveal the prominent positive anomalies associated with the Koli sill complex, and analogous intrusions along and immediately east of the national border (Koidanvaara in Figure 4). Intercumulus titanomagnetite is the pri- mary mineral phase responsible for the magnetic signature (Vuollo, 1994; Vuollo and Huhma, 2005). Note however, that these distinctive intrusions are not present south of Riutta. Instead, between Kiihtelysvaara and Värtsilä (and further across the border to Jänisjärvi), the Archean- Koidanvaara Havukka Paukkaja Riutta Mustavaara mv Huhtilampi Värtsilä Jänisjärvi Figure 4. Total magnetic intensity