Background information Käymäjärvi-Ristimella key area

Transcription

1 barents project Background information Käymäjärvi-Ristimella key area Susanne Grigull, Robert Berggren & Cecilia Jönsson September 2014 SGU-rapport 2014:30

2 Cover: Strongly deformed limestone wrapping around competent lenses of basic volcanic rock. Near Huuki. Photo: Susanne Grigull. Sveriges geologiska undersökning Box 670, Uppsala tel: fax: e-post:

3 CONTENTS Sammanfattning... 4 Summary... Introduction... 6 Geological overview... 7 Paleoproterozoic supracrustal rocks... 8 Karelian greenstone group... 9 Sammakkovaara group Paleoproterozoic intrusive rocks Deformation and metamorphism Databases and other available information Lithogeochemistry Till geochemistry Alterations and key indicator minerals Mineral deposits... 2 Drilling locations and prospecting reports... 2 Geophysical overview Airborne geophysical data Ground magnetic field data Ground based electromagnetic measurement Ground based electric surveys of induced potential (IP) Ground based gravity measurements Petrophysical samples Further work and target areas References (37)

4 SAMMANFATTNING Berggrunden som utgör den norra fennoskandiska skölden innehåller en stor del av Europas tillgångar av mineralresurser. Av särskild betydelse är norra Norrbotten i nordligaste Sverige med sina stora järn- och koppar±guldmalmer. Trots det stora ekonomiska intresset i området är bildandet av den fennoskandiska berggrunden och den efterföljande geologiska utvecklingen bristfälligt förstådd. Data från tidigare utförda fältarbeten är ofta få och alltför spridda för att erhålla en heltäckande bild. Följaktligen förekommer det flera diskrepanser mellan enheter och strukturer över intilliggande kartbladsområden i skala 1:0 000 och korrelation av geologiska enheter mellan kartblad saknas. Integrering av befintliga data och nya målriktade undersökningar syftar till att utöka förståelsen av den stratigrafiska och tektoniska utvecklingen i Norrbotten, vilket utgör en väsentlig del för framtida prospektering. Barentsprojektet inkluderar undersökningar inom femton nyckelområden i norra Norrbotten. Lokalisering och begränsning av nyckelområdena utgår från att lösa områdesspecifika frågeställningar som har implikationer på en regional skala. Barentsprojektet fokuserar huvudsakligen på de paleoproterozoiska ytbergarterna i regionen och syftar till att inom varje nyckelområde förstå och karaktärisera bergarterna enligt följande: Stratigrafi och avsättningsmiljö vulkanologi, sedimentologi, kemisk karaktär, geokronologi av metamorft omvandlade vulkaniska bergarter, geokronologi av detritiska zirkoner i sediment. Regional strukturgeologi och tektonik geometri och kinematik av veckstrukturer och deformationszoner, metamorf paragenes, åldersbestämning av metamorfos och deformation. Hydrotermiska omvandlingar kemisk och mineralogisk karaktärisering, koppling till stratigrafi och strukturer. Mineraliseringar typ av mineralisering, typ av malmbildande process. Området Käymäjärvi-Ristimella är ett av de femton områden som valts ut för mer detaljerade geologiska och geofysiska undersökningar. Den här rapporten sammanfattar de geologiska och geofysiska data som finns i Käymäjärvi-Ristimellaområdet tillsammans med utförda tolkningar i den mån de finns. Slutligen presenteras också en lista med frågeställningar inför fältarbetet i området. 4 (37)

5 SUMMARY The rocks of the northern Fennoscandian shield host some of Europe s largest mineral resources. The Northern Norrbotten region in northern Sweden is particularly important for its large iron and copper-gold deposits. Despite its economical importance, the formation and subsequent geological development of the Fennoscandian shield is still poorly understood. Field studies of reliable quality are sparse and high-quality age determinations are too few to reveal the stratigraphic and tectonic development, information that is essential for future exploration. The Barents project targets fifteen small key areas distributed over northern Norrbotten which are located at strategic points to resolve regional-scale issues by trying to answer questions that are specific to each key area. The Barents project concentrates on the Paleoproterozoic cover rocks of the region, and in each area aims to understand and characterise the following general points: Stratigraphic organisation and development volcanology, sedimentology, chemical characterisation, dating of metavolcanic rocks, dating of detrital zircons in sedimentary rocks, structural investigation to understand stratigraphy. Regional development of the bedrock large fold structures and deformation zones, metamorphic parageneses, dating of metamorphic events. Hydrothermal alterations chemical and mineralogical characterisation of alterations. Mineralisations characterisation, description of occurrences. The Käymäjärvi-Ristimella key area is one of the chosen areas for detailed geological and geophysical investigations. This report summarises the available geological and geophysical data for the Käymäjärvi-Ristimella key area and an interpretation of the data where possible. Finally, a list of questions and tasks to be addressed during field work in the Käymäjärvi-Ristimella key area are presented. (37)

6 INTRODUCTION The Käymäjärvi-Ristimella key area covers c. 700 km2 and its southern boundary is situated km north of Pajala and the Torne river (Torneälven). It extends c. 40 km east west and c. 20 km north south. The northernmost township in the area is Aareavaara. The eastern boundary is defined by the Muonio river (Muonioälven) which runs along the national border between Finland and Sweden. The western boundary lies c. 10 km to the west of Käymäjärvi. Some major roads allow access to the study area which is covered predominantly by marshes and forest. An overview map is shown in Figure 1. A LiDAR-based digital elevation model (DEM) with 2 m resolution is available for the area (Fig. 2). The DEM shows that the area has a low relief with the highest point being Käymävaara (348 m a.s.l.) in the west. The elevation decreases to about 10 m a.s.l. in the easternmost part of the area. With an area fraction of c. 0.%, outcrop coverage is extremely poor in the key area (Fig. 2). Using geophysical methods to understand the geology underneath the Quaternary SWEDEN FINLAND km Figure 1. Road map of the Käymäjärvi-Ristimella key area. 6 (37)

7 cover will therefore be an essential part of the field campaign planned for the Käymäjärvi-Ristimella key area in GEOLOGICAL OVERVIEW The Käymäjärvi-Ristimella key area is located in the Norrbotten and Överkalix lithotectonic domains of the Fennoscandian shield (Fig. 3). The rocks occurring in the key area are exclusively of Paleoproterozoic age. They are pre- and syn-svecokarelian supracrustal rocks consisting of greenstones as well as clastic sedimentary rocks, volcanic rocks and carbonates. They are intruded by various Paleoproterozoic plutonic rocks (Fig. 4). All rocks but the youngest intrusive rocks have undergone at least greenschist and up to upper amphibolite facies metamorphism Muonioälven Pajala Torneälven Muonioälven SGU bedrock observation points since 199 Bedrock outcrop from 1:0 000 geological map Thin soil cover from 1: soil map Bedrock outcrop from 1: soil map 20 km Figure 2. DEM and outcrop map of Käymäjärvi-Ristimella key area. 7 (37)

8 Lithotectonic domains Neoproterozoic and Phanerozoic platformal cover and igneous rocks Post-Svecokarelian, Proterozoic rocks Rödingsfjället Nappe Complex Köli Nappe Complex Seve Nappe Complex Jämtlandian, Offerdal and Särv Nappes Eastern Segment, lower unit Eastern Segment, middle unit Eastern Segment, upper unit Idefjorden terrane Blekinge Bornholm orogen Småland lithotectonic domain Ljusdal lithotectonic domain Bergslagen lithotectonic domain Överkalix lithotectonic domain Bothnia Skellefteå lithotectonic domain Norrbotten lithotectonic domain Figure 3. Lithotectonic domains of Sweden (SGU, unpublished). The Käymäjärvi-Ristimella key area is marked in red. Deformation in the area is polyphase and greatly influenced by the so-called Pajala shear zone as well as earlier folding phases. The area lies within the Pajala-Kolari Fe-Cu-Au metallogenic district and contains the wellknown Kaunisvaara ore belt with its stratiform skarn-hosted iron ore deposits Sahavaara and Tapuli. The geological map sheets 28M Pajala NV, NO (Padget 1977) and 29M Huuki SV, SO (Lindroos & Henkel 1981) cover the key area at a scale of 1: The area is also part of the regional mapping that was done at a scale of 1: by Bergman et al. (2001). Paleoproterozoic supracrustal rocks Due to the restricted outcrop accessibility, reliable information on the stratigraphy of the supracrustal rocks in the Käymäjärvi-Ristimella key area is scarce. The following summary of the stratigraphic succession in the area is compiled from map descriptions in Padget (1977), 8 (37)

9 Kiruna KADZ Boden PSZ Deformation zones Brittle-ductile deformation zone, reverse, symbols in upthrown block Brittle-ductile deformation zone, dextral Brittle-ductile deformation zone, normal, symbols in downthrown block Brittle-ductile deformation zone, dip slip, symbols in downthrown block Brittle-ductile deformation zone, unspecified kinematics FENNOSCANDIAN SHIELD Caledonian orogen Margin to the continent Baltica Terranes from outboard of the continent Baltica Cryogene-Eocene cover rocks on the Fennoscandian Shield Svecokarelian orogen syn-orogenic rock Mostly non-metamorphic GSDG-GP and subordinate GDG intrusive suites, supracrustal rock (1.8 Ga; cycle 4) Variably metamorphosed GSDG-GP and subordinate GDG intrusive suites, supracrustal rock (1.88 or Ga; cycle 3) Metamorphosed GDG intrusive suite ( or 1.87 Ga; cycle 2) Metamorphosed volcanic rock, carbonate rock and skarn ( Ga, cycle 2) Metamorphosed volcanic rock and GDG intrusive suite ( Ga, cycle 1) Metamorphosed clastic sedimentary and volcanic rocks Svecokarelian orogen pre-orogenic rock Metamorphosed sedimentary rock, basic ultrabasic volcanic rock and gabbro ( Ga) Metamorphosed supracrustal rock, orthogneiss, granitoid and dioritoid ( Ga) reworked after a c. 2.7 Ga event Luleå Piteå 0 km Figure 4. Simplified lithological map (SGU, unpublished). The Käymäjärvi-Ristimella key area is marked in red. KADZ: Karesuando-Arjeplog deformation zone. PSZ: Pajala shear zone. GSDG: Granite-syenitoid-dioritoid-gabbroid, GP: granite-pegmatite, GDG: granitoid-dioritoid-gabbroid. Lindroos & Henkel (1981) and Bergman et al. (2001), as well as work done by Gustafsson (1993), Kumpulainen (2000), Martinsson (2004), Hallberg et al. (2007) and Martinsson et al. (2013). The supracrustal rocks occurring in the key area can be divided into two major formations. From oldest to youngest these are the Karelian greenstone group and the Sammakkovaara group (Martinsson 2004, Martinsson et al. 2013). Karelian greenstone group The base of the Karelian greenstone group is not exposed and the greenstone group itself is here divided into the Käymäjärvi formation which is overlain by the Vinsa formation (Martinsson et al. 2013). The Käymäjärvi formation corresponds to the Kolari greenstones by Padget (1977) and occurs mainly in the western parts of the key area around Käymäjärvi (Fig. ). It includes greenstones consisting of basic pyroclastic and volcaniclastic rocks and lava. The lithogeochemi- 9 (37)

10 cal character can be picritic. Bergman et al. (2001) report an MgO content of 19.2% for a picritic basalt near Käymäjärvi. Radiometric U-Pb dating of zircon resulted in an age of Ma for the picrite (Bergman et al. 2001). It is unclear what caused the large errors and whether this age can be interpreted as a reliable protolith age. The overlying Vinsa formation (Martinsson et al. 2013) is equivalent to the Iron ore formation (Lindroos 1974, Hallberg et al. 2007) and the Käymäjärvi group (Padget 1977). At its base, basic tuffites with intercalated graphitic layers (M1 in Table 1) overlie the greenstones of the Käymäjärvi formation. These are overlain by iron-rich sedimentary rocks (BIF, M2 in Table 1) consisting of cherts and silicate bands (Bergman et al. 2001). The silicate bands consist mainly of pyroxene, amphibole and fayalite with grünerite being the dominant iron rich Mg-Fe-Mn amphibole in these bands (Geijer 192). The BIF member is followed by another unit with basic tuffites and graphite and calc-silicate bearing rocks (M3 in Table 1). Member M4 of the Vinsa formation consists of an up to 200 m thick dolomite unit with skarn-hosted iron ores. This is the main iron ore bearing unit of the Karelian greenstone group and hosts the economically important deposits Stora Sahavaara, Runtijärvi, Tapuli and Palotieva. Rocks of the Vinsa formation make up the eastern half of the key area. They occur predominantly within and to the east of the Kaunisvaara ore belt and to a lesser extent close to the core of the Käymäjärvi anticline (Fig. ). The four members of the Vinsa formation are summarised after Martinsson et al. (2013) and presented in Table 1. Sammakkovaara group The Karelian greenstone group is overlain by lower Svecofennian metamorphosed clastic sedimentary rocks belonging to the Sammakkovaara group (O. Martinsson unpublished data and Martinsson 2004). According to Martinsson (2004), the Sammakkovaara group represents an equivalent to the Kurravaara conglomerate and the Porphyrite group in western Norrbotten, e.g. around Kiruna. Until the definition of the Sammakkovaara group by Martinsson (2004), the Svecofennian rocks in the Käymäjärvi-Ristimella key area were separated into the so-called Pahakurkkio group and the Porphyrite group (e.g. Padget 1970, Witschard 1970, Padget 1977, Kumpulainen 2000). The type of contact between the rocks of the Sammakkovaara group and the underlying greenstone group is not described by Martinsson (2004), however, Padget (1977) reports the contact between the former Pahakurkkio group and the greenstones to be Table 1. Members M1 to M4 of the Vinsa formation (after Martinsson et al. 2013). Member Rock types and minerals Thickness M4 M3 M2 M1 Dolomite Skarn iron ore Basic tuffites Includes graphitic and calc-silicate bearing units Partly laminated on a mm-scale Scapolite common + diopside (major component in some beds) Disseminated graphite and Fe-sulphides BIF with locally developed oxide facies Distinct 30 cm thick bands of recrystallised chert alternating with silicate beds (px, amp, gt, fa), grünerite most dominant in silicate bands Magnetite locally as micro-scale banding or disseminated Top: Scapolite alteration Tuffites, basic composition, locally graphite-bearing Fe-sulphide quite high; graphite only a few percent Middle part: beds rich in garnet porphyroblasts m c. 100 m m >0 m (?) 10 (37)

11 conformable in the Kaunisvaara and Käymäjärvi areas, but unconformable elsewhere on the Pajala map sheet. The Sammakkovaara group is relatively well exposed in the Käymäjärvi area and is interpreted to have formed during simultaneous volcanic and clastic sedimentation. Based on petrographic studies, Martinsson (2004) subdivides the group into three formations: from base to top these are the Muotkamaa, Hosiokangas and Hosiovaara formation (Table 2). What defines the distinct boundary between these three formations is, however, somewhat unclear. The Muotkamaa formation is a lower volcanic unit with intercalated clastic sedimentary rocks exhibiting rapid facies changes expressed in varying fractions of volcanic and sedimentary rocks (Martinsson 2004). Variations in grain size in the more clastic sediment-dominated rocks of the Hosiokangas formation also indicate rapid facies changes (Martinsson 2004). The Hosiovaara formation represents an upper volcanic unit. The composition of the sedimentary-dominated facies of the Sammakkovaara group is usually pelitic to arenitic. Heavy mineral layers occur locally. Monomict conglomerates consisting of clasts of vein quartz and arkosic quartzite can occur locally as up to 10 m thick beds (Kumpulainen 2000, Martinsson 2004). Typical sedimentary structures are horizontal lamination, lowangle cross-bedding, and hummocky cross-bedding (Kumpulainen 2000). Ripple marks and rill marks indicate a shallow marine environment for the deposition of these sediments (Martinsson 2004). Martinsson (2004) interprets local intercalations of carbonate rocks, graphite schists and tourmalinites as the result of temporary anoxic and hydrothermal events in low-energy areas. Volcanic rocks of the Sammakkovaara group have an andesitic composition in the lower stratigraphic positions (Muotkamaa formation) and often show pseudomorphic growth of amphibole after pyroxene (Martinsson 2004). In upper stratigraphic positions (Hosiovaara formation), the rocks show andesitic to dacitic composition and may contain plagioclase phenocrysts in the range mm (Martinsson 2004). Gustafsson (1993) describes the andesitic rocks as generally fine-grained, grey rocks containing hornblende and plagioclase phenocrysts and locally pyrite. The dacites are described as fine-grained, reddish-grey rocks which locally contain epidote and magnetite. Locally, clast-supported conglomerates occur within the volcanic successions. The clasts consist of locally derived andesite pebbles (Eriksson 194, Padget 1977, Martinsson 2004). Geochemical analyses of three samples of volcanic rocks in the key area show an andesitic to trachyandesitic composition (SGU unpublished). Bergman et al. (2001) derived a protolith age for a metadacite near Hosiokangas of 1880±3 Ma using U-Pb radiometric dating of zircon. In general, the volcanic rocks of the Sammakkovaara group have a calc-alkaline signature, and are interpreted as the extrusive equivalents of an early volcanic arc magmatism (Haparanda suite, see below) during north-eastward directed subduction under an Archaean paleocontinent. Martinsson (2004) interprets the conglomerates with andesite-clasts as resulting from erosion of subaerial volcanic cones. The arenitic sedimentary rocks and the quartzite-rich conglomerates are suggested to originate from a granite-gneiss area further to the north-east (Martinsson 2004). The Sammakkovaara group is the youngest supracrustal unit exposed in the Käymäjärvi- Ristimella key area. In the key area, metasedimentary rocks of the Sammakkovaara group occur in the flanks of the Käymäjärvi anticline, to the west of the greenstones in the Kaunisvaara belt, and in the core of a syncline south-west of Ristimella (Ristimella syncline in Fig. ). Volcanic rocks of the Sammakkovaara group occur only to the west of the Kaunisvaara ore belt. Here, they seem to build the limbs of folds related to the Käymäjärvi folding. A stratigraphic column of the Paleoproterozoic supracrustal rocks in the key area in correlation to other greenstone-bearing areas in Norrbotten is provided in Martinsson (199) and is here presented in Figure (37)

12 Table 2. Stratigraphic overview of the Kaunisvaara domain. The Vinsa formation is mostly known from exploratory drilling (Martinsson et al. 2013). Formation Subunit Main rock types Thickness Mineral deposits Notes Sammakkovaara group ( Ga) (Martinsson 2004) Equivalent to combination of Paha kurkkio group and Porphyrite group (e.g. Padget 1970) Karelian greenstone group (c. 2.1 Ga) (Martinsson et al. 2013) Hosiovaara fm. Volcanic rocks. Andesitic to dacitic composition. Locally clast-supported conglomerates; clasts mostly andesitic pebbles of local origin. Hosiokangas fm. Dominated by clastic sediments deposited in shallow water. Arenitic to pelitic composition. Locally up to 10 m thick quartzite pebble conglomerates. Crossbedding, ripple marks. Muotkamaa fm. Volcanic rocks with minor intercalated clastic sediments. Andesitic composition. Vinsa fm. (Martinsson et al. 2013) Equivalent to Käymäjärvi group (Padget 1977) Equivalent to Iron ore formation (Lindroos 1974, Hallberg et al ) Käymäjärvi fm. (Martinsson et al. 2013) Equivalent to Kolari greenstone (Padget 1977) Marble, magnetite, skarn, dolomite m Tapuli, Stora Sahavaara, Runtijärvi, Palotieva Mainly mafic tuffites and graphite units c. 100 m none BIF* m Sahavaara Södra, Mainly mafic tuffites and graphitic units >0 m Greenstones consisting of partly graded picritic lapilli >10 m tuff. Basaltic rocks (volcaniclastic and basaltic lava), mafic sills and dykes.??? Sahavaara Östra*, Käymäjärvi* *Only in Käymäjärvi. Seems to be missing in Kaunisvaara belt. Instead replaced by Sahavaara Östra skarn iron ore 12 (37)

13 Ritna Rantakarvosenvaara Tulemajoki Siikavaara Anttis Antinrova Sarvikero Salmi Tervavuomansaajo Käymäjärvi anticline Pellirova Huhta Seiviönniemi Lumivaara Toravaara Käymävaara Käymäjärvi Isokoijukko Kursuniskanmaa Marjarova Välipirtti Pellijoki Karijoki Aareajoki Huornanen Palovaara Peräjävaara Sevänlaki Kursulehto Kursulehonoja Lamuvaara Sammakkovaara Käymäjoki Vittalaki Kaunisjoki Tervajoki Kiimamaa Liviöjoki Vännijänkänjupukka Pilkkasaajo Jupukka Kaarlahonmaat Ristivaara Kaalamalaki Sivakkajoki Kaunisvaara Suksijoki Muotkamaa Ranta- Peräjävaara Pajala flygplats Kenttä- Kuusivaara Aareavaara Kieksiäisvaara Lompolovaara Rytivaara Maalari Autio Juhonpieti Erkheikki Mukka- Tuohmaanniemi kangas Salo Mukkavaara Ahot Rova Liviövaara Rasi Liviöjärvi Penäjäoja Pajala Muonioälven Aareajoki Vaararinta Sahavaara Aihkivinsa Kihlanki Kaunisvaara ore belt Järvenvinsa Käryvaara Nivanlehto Torneälven Muotkapalo Laatas Honkavaara Poitajarova Sammalvaara Koijuvaara Poitajavaara Laatas Suksivaara Mettä- Peräjävaara Kengis Huukki Perävaara Parkkijoki Törmäsniva Kallio Köngäsenranta Kengis bruk Vittaniemi 20 km Ristimella Ylinen Airivaara Airivaara Airivaara Nuottaniemi Kolari Mella Ristimella syncline Hippalehto Kaunisjoensuu Muonioälven Structural formline, bedding or layering Anticline, overturned Synform Antiform Brittle deformation zone (fault, fracture, fracture zone) Plastic deformation zone Plastic deformation zone, dextral Plastic deformation zone, symbols in down-thrown block Structural formline, plastic deformation PALEOPROTEROZOIC INTRUSIVE ROCKS Intrusive rocks <1.8 Ga Ultramafic, mafic or intermediate intrusive rock (gabbro, diorite, dolerite etc.) Gabbro, metagabbro, dolerite Intrusive rocks, c Ga Granite syenitoid gabbroid assoc. Granite Syenitoid granite Gabbroid dioritoid Granite-pegmatite assoc. (Lina suite) Granite Intrusive rocks, c Ga Granitoid syenitoid, partly metamorphic and migmatitic Intrusive rocks, c Ga (Haparanda suite) Tonalite granodiorite, metamorphic Syenitoid granite, metamorphic Gabbroid dioritoid, metamorphic Figure. Regional geological map of the Käymäjärvi-Ristimella key area. Map based on SGU s 1: map database. PALEOPROTEROZOIC SUPRACRUSTAL ROCKS Sammakkovaara group Basalt andesite to dacite, metamorphic Wacke, metamorphic Arenite, metamorphic Karelian greenstone group Vinsa formation Carbonate rock, marble Metallic mineral deposit Iron ore mineralisation Mica-rich metamorphic rock (phyllite, schist, paragneiss etc.) Schist, metamorphic Basalt-andesite, metamorphic Arenite, metamorphic Käymäjärvi formation Ultramafic volcanic rock, picrite, metamorphic 13 (37)

14 (km) 9 Kiruna? Carbonate rock Andesite / redeposited Mafic sill / albite diabase Basalt / pillow lava 8 Soppero Tärendö?? Quartzite micaschist 7 Pajala? Basement granitoids Conglomerate Rhyodacite tuff 6 Kovo? Vittangi? Trachyandesite lava Iron formation Black schist Mafic tuff tuffite Komatiite / picrite 4 3? 2 1 0??? Figure 6. Stratigraphic column of the Pajala area in correlation with other greenstone-bearing areas in Norrbotten. After Martinsson (199). Paleoproterozoic intrusive rocks Everywhere in the Fennoscandian shield, Paleoproterozoic supracrustal rocks are intruded by numerous suits of magmatic rocks. The subdivision and description of the Paleoproterozoic intrusive rocks occurring in the key area are here summarised from the geochemical classification work done by Ahl et al. (2001), an introduction to Paleoproterozoic magmatism by Bergman et al. (2007), and the latest subdivision in Martinsson & Wanhainen (2013), and are not only specific to the Käymäjärvi-Ristimella key area. Table 3 gives an overview of the characteristics of the various intrusive rocks of northern Sweden. The distribution of the different intrusive suites in the key area is shown in Figure 7. The oldest rocks belonging to the Haparanda suite include a granodiorite tonalite body in the eastern part and an extensive syenite body in the western part of the key area. No outcrop or drilling information exists for the granodiorite body in the eastern part. It seems to be solely based on geophysical interpretation. An extensive syenite body of the Haparanda suite is exposed in the north-western part of the key area. A larger ultrabasic gabbro or diorite body occurs to the west of Aareavaara, also belonging to the Haparanda suite. Rocks of the Perthite monzonite suite have not been reported within the key area. However, Jonsson & Kero (2013) report the occurrence of kali-feldspar porphyritic quartz monzonites and monzogranites in the Korpilom- 14 (37)

15 Table 3. Subdivision of Paleoproterozoic intrusive rocks in northern Norbotten after Ahl et al. (2001), Bergman et al. (2007) and Martinsson and Wanhainen (2013) and references therein. TIB: Transscandinavian igneous belt. Suite Age (Ga) Geochemical character Lithologies Haparanda suite Calc-alkaline Granite, granodiorite, tonalite, diorite, gabbro Perthite monzonite suite Granite-pegmatite association or Lina suite Granite-syenitoidgabbroid association or A-, I-type intrusions Alkali-calcic Granite, monzonite (dominant), diorite, gabbro, peridotite Calcic(?) Monzogranite, syenogranite, adamellite Alkaline Granite, monzonite, granodiorite, diorite, gabbro Tectonic setting I-type, volcanic-arc, co-magmatic with extrusive phases of early Svecofennian arc magmatism (Sammakkovaara group) I-to A-type, probably intra-plate setting, mantle-plume origin Continentcontinent collision or contemporaneous to TIB-1 magmatism Part of TIB; TIB inferred to have formed in an extensional phase in subduction setting; OR may be related to final orogenic collapse Field appearance More or less gneissose, medium-grained to fine-grained Perthite granites usually red and mediumcoarse grained, pyroxene-bearing monzonites locally, typically isotropic but may have foliation at pluton margins Red-grey, medium-grained, weakly porphyritic; red fine-grained varieties; weakly foliated; few mafic components; biotite common, muscovite rare; fragments of country rocks common; dykes and veins of granite, pegmatite, aplite common Very similar to Perthite monzonite suite; quartz-poor; occurrence of augite and locally orthopyroxene and olivine, Sharp boundary to rocks that are cut by this suite References Ödman (197), Skiöld (1988), Bergman et al. (2001), Mellqvist et al. (2003) Skiöld (1981), Skiöld & Öhlander (1989), Martinsson et al. (1999) Skiöld et al. (1988), Öhlander & Skiöld (1994), Bergman et al. (2001) Romer et al. (1994), Bergman et al. (2001), Lahtinen (2003, 200) bolo map area (SGU K 394) further south of Pajala. U-Pb dating of zircon resulted in ages of c Ga for these rocks (Jonsson & Kero 2013) and could therefore be attributed to the Perthite monzonite suite. Additionally, intrusive rocks that were marked as tonalites belonging to the Haparanda suite (Bergman et al. 2001) to the south-west and just outside of the key area are now attributed to a large body of the Perthite monzonite suite (Bergman et al. 2012). The second youngest intrusive rocks occurring in the key area are syenites, granites, pegmatites and gabbro bodies belonging to the Granite-pegmatite association, also known as the Lina suite. These rocks occur in both limbs of the Käymäjärvi anticline as well as folded and sheared to the west of a major north-east to south-west striking shear zone in the eastern part of the key 1 (37)

16 area. Here, the rocks of the Granite-pegmatite association appear as coarse-grained granites to pegmatites and form the topographic highs Honkavaara, Jatkovaara and Käryvaara (Padget 1977, Fig. 7). Other intrusive rocks belong to the granite-syenitoid-gabbroid association and occur in large amounts mostly to the south-west of Käymäjärvi. No radiometric age data is available for any of the intrusive rocks within or near the key area. Deformation and metamorphism The Pajala shear zone (e.g. Kärki et al. 1993, Bergman et al. 2006) extends through parts of the key area. This major deformation zone is also known as the Baltic-Bothnian megashear (Berthelsen & Marker 1986) and its northern continuation as the Bothnian-Seiland shear zone Ritna Rantakarvosenvaara Tulemajoki Siikavaara Anttis Antinrova Sarvikero Salmi Tervavuomansaajo Pellirova Huhta Seiviönniemi Lumivaara Toravaara Käymävaara Käymäjärvi Isokoijukko Kursuniskanmaa Marjarova Välipirtti Pellijoki Karijoki Aareajoki Huornanen Palovaara Peräjävaara Sevänlaki Kursulehto Kursulehonoja Lamuvaara Sammakkovaara Käymäjoki Vittalaki Kiimamaa Liviöjoki Kaunisjoki Tervajoki Vännijänkänjupukka Pilkkasaajo Jupukka Kaarlahonmaat Ristivaara Kaalamalaki Sivakkajoki Kaunisvaara Suksijoki Muotkamaa Ranta- Peräjävaara Pajala flygplats Kenttä- Kuusivaara Aareavaara Kieksiäisvaara Lompolovaara Rytivaara Maalari Autio Juhonpieti Erkheikki Mukka- Tuohmaanniemi kangas Salo Mukkavaara Ahot Rova Liviövaara Rasi Liviöjärvi Penäjäoja Pajala Muonioälven Aareajoki Vaararinta Sahavaara Aihkivinsa Kihlanki Järvenvinsa Käryvaara Nivanlehto Torneälven Muotkapalo Laatas Honkavaara Poitajarova Sammalvaara Koijuvaara Poitajavaara Laatas Suksivaara Mettä- Peräjävaara Kengis Huukki Perävaara Parkkijoki Törmäsniva Kallio Köngäsenranta Kengis bruk Vittaniemi Ristimella Ylinen Airivaara Airivaara Airivaara Nuottaniemi Kolari Mella Hippalehto Kaunisjoensuu Muonioälven PALEOPROTEROZOIC SUPRACRUSTAL ROCKS Porphyrite group Pahakurkkio group Karelian greenstone group 20 km Figure 7. Distribution of Paleoproterozoic intrusive rock suites in the Käymäjärvi-Ristimella key area. Map based on SGU s 1: map database. 16 (37)

17 (Henkel 1991), Bothnian-Kvænangen fault complex (Olesen & Sandstad 1993) or Kolari shear zone (Niiranen et al. 2007). The Pajala shear zone is a 10 0 km wide, north south trending brittle-ductile deformation belt. Deformation is localised to several smaller shear zones within this belt, placing intensely strained rocks next to nearly undeformed ones (Berthelsen & Marker 1986). The Pajala shear zone separates rocks of different metamorphic grades (Bergman et al. 2001). On its eastern side, metamorphic rocks of upper amphibolite facies occur, and on the western side, rocks have undergone greenschist to lower amphibolite metamorphism (Gustafsson 1993, Bergman et al. 2001, Bergman et al. 2006). Martinsson et al. (2013) refer to the eastern side as the Kolari domain and to the western side as the Kaunisvaara domain. Migmatisation, strong recrystallisation and quartzofeldspathic veining has affected many of the supracrustal rocks in the eastern part of the key area as well as some metasedimentary rocks on the western side of the Pajala shear zone (e.g. Bergman et al. 2001). The abrupt change in metamorphic grade across the Pajala shear zone as well as kinematic studies east of Tärendö indicate overall eastern-side-up kinematics (Bergman et al. 2001, Bergman et al. 2006). In Bergman et al. (2001), the shear sense of the Pajala shear zone is described as opposite to the one of the Karesuando-Arjeplog deformation zone further west which has a dextral strike slip component and shows eastern-side-down movement. Based on the interpretation of geophysical and geological investigations in the Kautokaino greenstone belt in Norway, Olesen & Sandstad (1993) also determined sinistral movement for the Pajala shear zone. Sinistral shear may also be deduced from the magnetic anomaly pattern south of Pajala. Here, ductile deformation formed what may be interpreted as mega-sc-structures which are reflected in the magnetic anomaly pattern (Fig. 8). In the western part of the Käymäjärvi-Ristimella key area, the structural grain is oriented predominantly north-west to south-east, whereas in the eastern part it is oriented north-east to south-west. In general, the north-west to south-east trending structures correspond to folds with north-west to south-east trending fold axes. These folds generally verge north-east and their north-eastern limb may be overturned. An example of this type of folding occurs at Käymäjärvi in the form of a north-east vergent anticline and is seen as a first folding phase, F1 (e.g. Padget 1977). Here, picritic pyroclastic volcanic rocks of the Käymäjärvi formation (Bergman et al. 2001, Martinsson et al. 2013) build the core of the anticline (Fig. 9). Using garnet-biotite and garnet-biotite-plagioclase-quartz geothermobarometry, Bergman et al. (2001) were able to constrain the metamorphic conditions in a tuffitic basic volcanic rock of the Vinsa formation to c. 10 C at 260 MPa (Fig. 9). It is unclear which deformation phase these values reflect since the MnO zoning profile in the garnet was bell-shaped and rim measurements were used (Bergman et al. 2001). Another sample taken of a metagreywacke of the Pahakurkkio group within the Pajala shear zone south-west of Pajala township yielded 1 C at 410 MPa. Whereas a tuffitic basic metavolcanic rock from the Vinsa formation, taken close to Ristimella within a north-east striking shear zone, yielded metamorphic conditions of 690 C at 620 MPa (Bergman et al. 2001). The sampling sites for pressure-temperature measurements as well as for radiometric dating are shown in Figure 9. Bergman et al. (2006) performed radiometric U-Pb analyses on rocks from north-eastern Norrbotten. One of their sample sites lies within the key area near Huuki. Here, Bergman et al. (2006) analysed a paragneiss sample belonging to the Vinsa formation and consisting mainly of quartz, feldspar, biotite, sillimanite and secondary muscovite overgrowing biotite. Accessory monazite is associated with biotite, whereas titanite is associated with the secondary muscovite. Bergman et al. (2006) report intercept ages of 1788±8 Ma for the monazite and 1743±21 Ma for titanite. The latter age is somewhat younger than the other peak metamorphic ages reported 17 (37)

18 Käymäjärvi-Ristimella MasugnsbynTakanenvaara Pajala Liviöjärvi 0 km Figure 8. Magnetic anomaly map (SGU, 1: geophysical map) covering the area south of Pajala and indicating sinistral shear within the Pajala shear zone. The white thicker lines mark ductilely deformed rocks, whereas the grey, thinner lines represent magnetic minima which are interpreted as brittle faults. Red and blue colours indicate rocks with high and low magnetic susceptibility, respectively. for this region (Fig. 10) which cluster around Ma in the eastern domain and it is interpreted as representing a deformation event which, in the rest of the northern Fennoscandian shield, is usually characterised by brittle deformation (Bergman et al. 2006). The north-east to south-west oriented shear zones in the key area are seen as a deviation from the general north south trend of the Pajala shear zone (e.g. Bergman et al. 2006), but nonetheless as a continuation of this megashear. On most maps available for the Käymäjärvi-Ristimella key area, the north-east striking narrow shear zones are therefore connected to the Pajala shear zone to the south (e.g. Figs. 9, 10). Additionally, the total width of the shear zone seems to de- 18 (37)

19 Käymäjärvi anticline 20± MPa 10 C Käymäjärvi 1880±3 Kaunisvaara Pajala Sahavaara ± MPa 690 C 410 MPa 1 C Sampling site PT conditions Sampling site for radiometric dating Protolith age Metamorphic age Not known Stretching lineations and fold axes (plunge in degrees) km N stretching lineation fold axis Figure 9. Sampling sites for radiometric dating and determination of PT conditions. The orientation of stretching lineations and fold axes is also shown. Map is based on SGU 1: scale map database. 19 (37)

20 186±8 24 E 1880±28 Saivomuotka 1796±7 1778±2 180± N 68 N Muonio 1797±3 1792± Lainio 183± ±9 1873±23 Kitkiöjärvi Kursumaa 1784± ± 1817± Parkalompolo 1791± 1796± ± 1862±3 1783, 1748±7 188± ±6 1849±16 Masugnsbyn 1786± ±9 186± PSZ Kolari 1861±3 1800±2 Pajala Tärendö 1813± ±6 1797±4 M 1788±3 1800±8 67 N 22 E 24 E 67 N M Sample location: monazite/titanite Metamorphic/igneous zircon Structural domain boundary Deformation zone Structural form line or magnetic connexion Intrusive rocks, c. 1.8 Ga Intrusive rocks c Ga, left, ditto, metamorphosed, right Pre-1.86 Ga rocks, low- to medium-grade Pre-1.86 Ga rocks, high-grade 0 km Figure 10. Map summarising the distribution of metamorphic ages around the Pajala shear zone (PSZ). Bergman et al. (2006, their Fig. 4). 20 (37)

21 D U 10 km Figure 11. Magnetic field (tilt derivative) of north-east striking deformation zone north-east of Pajala. Structural formlines are shown in white and red. The outline of the folded, sheared and dismembered granite from the Granite-pegmatite association is indicated in skin colour. crease within the study area (Figs. 9, 10). However, renewed interpretation of magnetic anomalies, as well as an analysis of stretching lineations and fold axes along the major north-east to south-west striking deformation zone in the eastern part of the key area reveals that this set of shear zones has a major dextral strike-slip component, i.e. opposite to the shear sense of the Pajala shear zone. Additionally, the north-east to south-west oriented shear zones seem to cut the Pajala shear zone and to offset pre-existing structures in a dextral motion. A coarse granite body of the Granite-pegmatite association that intruded the basic and sedimentary rocks of the Karelian greenstone formation has been folded together with its host rocks. This granite body is also sheared and dismembered along the north-east trending shear zone north of Pajala (Fig. 11). It is unclear whether folding of the granite took place before or during shearing along the north-east striking shear zone. However, the deformation pattern most defi21 (37)

22 nitely indicates ductile, dextral-oblique deformation along this shear zone (Fig. 11). The northeast to south-west trending deformation zone is therefore interpreted as representing a ductile deformation event that occurred after deformation in the Pajala shear zone. DATABASES AND OTHER AVAILABLE INFORMATION Lithogeochemistry There is information on twenty-seven lithogeochemical samples of which sixteen have been collected in the 1970s and eleven in the years Figure 12 shows the lithogeochemistry sampling sites within and around the key area Ritna Rantakarvosenvaara Tulemajoki Siikavaara Anttis Antinrova Sarvikero Salmi Tervavuomansaajo Pellirova Huhta Seiviönniemi Lumivaara Toravaara Käymävaara Käymäjärvi Isokoijukko Kursuniskanmaa Marjarova Välipirtti Pellijoki Karijoki Aareajoki Huornanen Palovaara Peräjävaara Sevänlaki Kursulehto Kursulehonoja Lamuvaara Sammakkovaara Käymäjoki Vittalaki Tervajoki Kiimamaa Liviöjoki Kaunisjoki Vännijänkänjupukka Pilkkasaajo Jupukka Kaarlahonmaat Ristivaara Kaalamalaki Sivakkajoki Kaunisvaara Suksijoki Figure 12. Sampling sites within the key area. Colours refer to publications presenting the lithogeochemical analysis results. Map is based on SGU s 1: scale map database. Muotkamaa Ranta- Peräjävaara Pajala flygplats Kenttä- Kuusivaara Aareavaara Kieksiäisvaara Lompolovaara Rytivaara Maalari Autio Juhonpieti Erkheikki Mukka- Tuohmaanniemi kangas Salo Mukkavaara Ahot Rova Liviövaara Rasi Liviöjärvi Penäjäoja Pajala Muonioälven Aareajoki Vaararinta Sahavaara Aihkivinsa Kihlanki Järvenvinsa Käryvaara Nivanlehto Torneälven Muotkapalo Laatas Honkavaara Poitajarova Sammalvaara Koijuvaara Poitajavaara Laatas Suksivaara Mettä- Peräjävaara Kengis Huukki Perävaara Parkkijoki Törmäsniva Kallio Köngäsenranta Kengis bruk Vittaniemi Ristimella Ylinen Airivaara Airivaara Airivaara Nuottaniemi Kolari Mella Hippalehto Kaunisjoensuu Muonioälven Unknown SGU SGU Af 21, 22, 23, 24 SGU Af 3, 36, 37, 38, 39 SGU Af, 6, 7, 8 SGU Af 9, 10, 11, km 22 (37)

23 Till geochemistry Throughout the years, several geochemical surveys, mainly on till, have been carried out in northern Norrbotten and within the Käymäjärvi-Ristimella key area. The most modern data was produced in when 83 till samples were taken in the key area and analysed by SGU (Fig. 13). Samples were taken at approximately 1 m depth in the C-horizon, and the <0,063 mm fraction was analyzed by XRF for total composition and by aqua regia leaching fol Till geochemistry samples 20 km Soil type Moraine, 0,063 2 mm Peat Moraine, <0,063 mm Fluvial sediment, sand Moraine, <2 mm Clay silt Patterned ground Moraine, >2 mm High frequency of surficial boulders Sediment, <2 mm Glaciofluvial sediment Sediment, >2 mm Moraine Boulder depression Glaciofluvial deposit with ridges and hummocks Glaciofluvially eroded area Bedrock Drumlin or drumlinoid Frost shattered bedrock Hummocky moraine Landform Figure 13. Sampling sites for till geochemistry. Quaternary geology map in the background. Source: SGU s 1: scale Quaternary map database. 23 (37)

24 Scapolite Epidote Albite Olivine Albite-ankerite, albite-carbonate Pyroxene Leucodiabase Epidote, garnet Ankerite, carbonate Skarn, actinolite, tremolite, amphibole, diopside, hornblende 20 km Figure 14. Types of mineral alterations and key indicator minerals in the Käymäjärvi-Ristimella key area. Map is based on SGU s 1: scale bedrock map database. lowed by ICP-MS. Earlier surveys include data produced in 1991 by the State Mining Property Commission (NSG) where 38 till samples from the key area was analysed. Prior to that, the Nordkalott Project presented a few analyses in 1986, and in a heavy mineral survey on till produced around 10 analyses from the key area. Alterations and key indicator minerals Figure 14 shows the distribution and types of alterations occurring in the key area. Skarn alteration has affected the carbonate rocks of the Vinsa formation. Scapolite alteration is com- 24 (37)

25 mon in the basic rocks of the Vinsa formation. Epidote alteration seems to have affected the entire region. Mineral deposits All iron ore deposits in the key area are skarn hosted and of the IOCG type. In the Kaunisvaara domain, all skarn iron deposits are stratiform and occur as lenses or layers. The most important iron deposits are Käymäjärvi, Sahavaara and Tapuli. The Tapuli deposit occurs as stratabound lenses made up of skarn iron ore. It has a low sulphide content and is situated at the top of the Karelian greenstones. The footwall rocks to the ore are dolomitic marbles that change gradually into skarn as well as tuffites and graphitic tuffites of the Vinsa formation (Martinsson et al. 2013). The hanging wall to the ore consists of quartzites and mica schist of the Sammakkovaara group. Mining of the Tapuli deposit by Northland Resources began in The Sahavaara deposit occurs at the contact between rocks of the Vinsa formation and the overlying Sammakkovaara group. It is usually subdivided into three major deposits: Stora Sahavaara situated in a serpentine-diopside-tremolite skarn more or less directly at the contact between the two stratigraphic formations, and the Södra and Östra Sahavaara deposits, which occur in a stratigraphically lower position (Hallberg et al. 2012, Martinsson 2013). The Roskajokki and Annaniva deposits are the only two sulphide deposits in the key area. Figure 1 shows the location of mineral deposits. Drilling locations and prospecting reports Figure 1 also shows drilling sites within and around the key area. Table 4 lists these sites according to location name, drilling period and ownership. Prospecting reports relevant to the Käymäjärvi-Ristimella key area are summarised in Table. Overall, diamond drilling has taken place at 300 sites in and around the Käymäjärvi-Ristimella key area. The most recent drilling was done by Northland Exploration Sweden AB in the Kaunisvaara ore belt within the framework of the development of the Tapuli deposit. 2 (37)

26 Mellangruvan Lumivaara Roskajokki-Cu Roskajokki Käymajärvi Muotkavuoma Pellivuoma Isonkivenmaa Marjarova Salovuoma Peräjävaara Peräjävuoma Lumivaara Karhujärvi Erkheikki Erkheikki söder Tapulivuoma Ruutijärvi 2 Ruutijärvi 1 Kaunisjoki Sahavaara Stora Palotieva Tapuli Sahavaara Östra Sahavaara Södra Suksivuoma Jupukka Jupukka Erkhekki-Cu Erkhekki-BIF Aareajoki Käryjärvi Rytivaara Aareavaara Kirkonlahti Kursunoja Pajala Södra Liviövaara Liviövaara-graphite Huuki Kalliomaa Al. Airivaara Muotkapalo-graphite Muotkapalo-Mg Sarvisto Kieksiäisvaara Annaniva Drill holes Drill cores Iron mine, in operation Iron ore, trial pit or prospect Iron mineralization Sulphide mineralisation, trial pit or prospect Sulphide mineralisation Sulphide ore known from core drilling Quarry, industrial mineral, abandoned Industrial mineral, mineralisation Industrial mineral, trial pit or prospect Quarry, abandoned Drilling 20 km Figure 1. Ore deposits, industrial mineral deposits and drill sites in the Käymäjärvi-Ristimella key area. Yellow crosses indicate drill cores that are available at the Malå drill core archive. The map is based on SGU s 1: scale bedrock map database. 26 (37)

27 Table 4. Drill sites in alphabetic order with drilling period and ownership. NÖN: Nordöstra Norrbotten project. Drill site Drilling period Owner Aarearova Northland Exploration Sweden AB Erkheikki SGU Honkavaara 1986 NÖN/LKAB/NSG/VOLVO Honkavaara 2002 Anglo American Kalliomaa 1986 NÖN/LKAB/NSG/VOLVO Karhujärvi Kiruna last Kaunisjoki 1984? Kaunisvaara South 2008 Northland Exploration Sweden AB Kaunisvaara South 2008 Northland Exploration Sweden AB Kivirova 1997 Geopartner HB Käryjärvi 1971 SGU Käryjärvi Anglo American Käymäjärvi 196 SGU/Lst BDlän Käymäjärvi 1960 Stora Käymäjärvi 1984 NÖN/LKAB/NSG/VOLVO Käymäjärvi 200 Phelps dodge Liviövaara 1986 NÖN/LKAB/NSG/VOLVO Liviövaara Anglo American Lompolovaara 1984 NÖN/LKAB/NSG/VOLVO Marjajärvi SGU Muotkapalo 198 NÖN/LKAB/NSG/VOLVO Navettamaa 2010 Northland Exploration Sweden AB Pajala 2003 Boliden Mineral Pajala Syd 1967 SGU Palotieva 2004 Anglo American Palotieva N HWY 2008 Northland Exploration Sweden AB Pellivuoma SGU Peräjävuoma 1970 SGU Plant Site Main Line 2008 Northland Exploration Sweden AB Roskajoki 1984 NÖN/LKAB/NSG/VOLVO Rässingpalo 2008 Northland Exploration Sweden AB Sahavaara Hill 2008 Northland Exploration Sweden AB Sahavaara S SGU Sahavaara St SGU Sahavaara W 2010 Northland Exploration Sweden AB Sarvisto? NÖN/LKAB/NSG/VOLVO Stora East Dump Northland Exploration Sweden AB Suksivuoma 1963 Kiruna last Suksivuoma 2002 Anglo American Tailings Area Northland Exploration Sweden AB Tapuli SGU Tapuli Road 2008 Northland Exploration Sweden AB Waste Rock Area Northland Exploration Sweden AB Välikuusikko 2008 Northland Exploration Sweden AB Välivaara 1996 Viscaria AB Exploration/Outokumpu 27 (37)

28 Table. Prospecting reports relevant to the Käymäjärvi-Ristimella key area. Report Author Year Location Relevance SRK report Baker et al Kaunisvaara ore belt Prospecting summary; cross-sections through Tapuli deposit; 3D models of ore bodies at Tapuli and Sahavaara; SRK report Baker et al Pellivuoma Pellivuoma deposit geology; cross-sections through ore body; information on alteration Brap SGU 1973 Pajala community Description of occurences of carbonate rocks in Huuki, Aareavaara, Aareajoki, Kaunisvaara, Sahavaara Brap 0070 Lundberg 1962 Kaunsivaara-Aareavaara-Huuki Brap 0072 Lundberg & Werner Cross-section Sahavaara; detailed outcrop sketches and maps along Muonio river; description of rocks in outcrop 196 Stora Sahavaara Drill core descriptions; some maps; cross sections based on drill core interpretation Brap Ros et al Pellivuoma Detailed (1:2 000) maps of Pellivuoma iron ore deposit at different depths and cross sections based on drill cores Brap Shaikh et al Norrbotten Industrial minerals; description of metamorphic pelitic schist at Al. Airavaara and occurrence of sillimanite K Hansson & Martinsson 1986 Honkavaara, Kalliomaa, Muotkapalo Some maps; drill core descriptions and sections K Hansson et al Pajala, Käymäjärvi Detailed description of outcrop geology GEOPHYSICAL OVERVIEW In the 1960ies the Geological Survey of Sweden (SGU) surveyed the Käymäjärvi area in order to find ore bodies. Airborne surveys revealed prospects such as Huuki, Jokikarhakka, Käryjärvi, Honkavaara, Lehto, Kalliomaa, Liviöjärvi, Muotkapalo, Sarvisto and Käymäjärvi. Most of these prospects were followed up by ground surveying with geophysical methods during the 1960s to 1980s. During the mid 2000s the exploration company Northland Resources followed up on the earlier exploration efforts by performing their own surveying. The collected data belongs to Northland Resources. At the time of writing it is mainly Northland Resources that own exploration licenses in the area but there are a few regions that are now marked with a temporary denial of exploration, since they have been recently dropped by Northland Resources. Viewed historically there have been a few companies who explored the area, such as Rio Tinto, Phelps Dodge Exploration Sweden, Viscaria AB and Anglo American Exploration. Their efforts were started during the years 1986, and Earlier exploration in the area has been done by companies such as NSG, Boliden and JCC. Airborne geophysical data Airborne geophysical data in the region have been collected mainly by SGU and LKAB with 200 m line spacing and 30 m flight altitude. In 1961, SGU collected airborne data in the Tärendö area. The magnetic field was measured using a fluxgate magnetometer. In 1963, the Huuki area was surveyed in the north-eastern part of the Käymäjärvi-Ristimella key area. The Huuki and Tärendö areas are covered by magnetic measurements only and no other geophysical methods were applied. In 1982, LKAB conducted an airborne geophysical survey covering the whole area. They aquired magnetic data along with slingram data, gamma-ray spectrometry and VLF data using two transmitters. This survey was followed up in 1983 when a smaller area (Kaunisjoki) was measured using the same methods but with 100 m line spacing. The magnetic field was measured using the instrument G803 which had the precision of ±1 nt. 28 (37)