barents project Summary report on available geological, geochemical and geophysical information for the Nautanen key area, Norrbotten Edward P. Lynch & Johan Jönberger SGU-rapport 2014:34 October 2014 Cover: Historical mine workings at the Nautanen copper-gold deposit, with the 29th (29:an) shaft in the foreground. View looking to the east. Photo: ­Edward Lynch Sveriges geologiska undersökning Box 670, 751 28 Uppsala tel: 018-17 90 00 fax: 018-17 92 10 e-post: [email protected] www.sgu.se CONTENTS Sammanfattning Abstract .............................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 .................................................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Introduction ......................................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geological overview of the Nautanen area 6 .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Available data for the Nautanen area ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bedrock geology information . . ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geology maps and related data layers .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Scanned field maps and other map information .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Outcrop locations ................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Published material (papers and reports) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Drill core ................................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Information on alteration and mineralisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geochemical data . . ...................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geochronology ...................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isotope geology (excluding age dating) .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geophysical data ......................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Airborne measurements . . ..................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ground magnetic data ......................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gravity data ............................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geoelectric and electromagnetic data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Petrophysical data ................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Topographical data ..................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 11 11 12 12 12 19 19 21 23 25 26 26 26 28 29 29 30 Geological summary and some remaining issues ....................................................................................... 31 ........................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 ............................................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Acknowledgments References 3 (40) SAMMANFATTNING Nautanenområdet ligger ca 10 km öster om Gällivare i norra centrala Norrbottens län. Inom området finns en sekvens av Paleoproterozoiska vulkaniska och metasedimentära bergarter som avsatts, deformerats och omvandlats under den Svecofenniska orogenen för ca 1,9 miljarder år sedan. Intrusiva bergarter med gabbroisk, dioritisk och granitisk sammansättning och med likartad ålder förekommer också i området. En regionalt viktig spröd till plastisk deformationszon (Nautanen deformation zone) som klipper områdets bergarter har sannolikt haft ett stort inflytande på lokaliseringen av den granitoida magmatismen, de hydrotermala fluiderna och områdets koppar-guld±järnmineralisering. Många koppar-guldfyndigheter är kända från Nautanenområdet och de har en genetisk affinitet till den löst definierade gruppen av järnoxidkoppar-guldfyndigheter (IOCG). I denna rapport sammanfattas de viktigaste geologiska, geokemiska och geofysiska egenskaperna för Nautanenområdet. Rapporten ger en översikt över tillgängliga kartor, geologiska data och publikationer för området samt en kort sammanfattning av vår nuvarande förståelse av områdets geologiska miljö och utveckling. Vissa olösta geologiska frågor och förslag för framtida forskning presenteras också. Nyckelområdet Nautanen är ett delområde för riktad geologisk kartläggning och utredning inom SGUs Barentsprojekt i Norrbotten som pågår 2012–2015. 4 (40) ABSTRACT The Nautanen area is located about 10 km east of Gällivare in north-central Norrbotten county, Sweden. It is centred on a package of Paleoproterozoic metavolcanic and metasedimentary rocks which were deposited, deformed and metamorphosed during the Svecofennian orogeny at c. 1.9 Ga. Paleoproterozoic intrusive rocks of gabbroic, dioritic and granitic composition also ­occur in the area. The rocks at Nautanen are situated within a regionally significant brittle–­ ductile deformation zone (Nautanen deformation zone) that probably had an influence on the siting of granitoid magmatism, hydrothermal fluid flow and copper-gold±iron mineralisation in the area. Numerous copper-gold prospects are known from the Nautanen area, and they have a genetic affinity to the broad iron oxide-copper-gold (IOCG) family of hydrothermal mineral deposits. This report reviews the main geological, geochemical and geophysical characteristics of the Nautanen area. It presents an overview of available maps, geological datasets and publications and briefly summarises our present understanding of its geological setting and evolution. Some unresolved geologic questions and suggestions for future research are also presented. The Nautanen key area is a subarea for targeted geological mapping and investigation as part of SGU’s Barents Project 2012–2015. 5 (40) nd Gällivare la Fin Nor w ay INTRODUCTION The Nautanen area is located approximately 10 km east of Gällivare, in north-central Norr­ botten County, Sweden (Fig. 1). The area falls within the 1:50 000-scale map sheets 28K Gällivare SO and SV (traditional RT90 map sheet index for Sweden, SO = south-east, SV = southwest) and covers six 5 × 5 km grid squares representing a geographical area of about 150 km2. This report reviews the main geological, geochemical and geophysical characteristics of the Nauntanen area. It presents an overview of available maps, geological datasets and publications and briefly summarises our present understanding of the area’s geological setting. The report also identifies some unresolved geological questions that may further our knowledge of the geology, stratigraphy and mineral potential of this part of Sweden. The Nautanen area (one of fourteen key areas) is a focus for targeted geological mapping and investigation as part of the Norrbotten-based Barents Project (2012–2015) run by the Geological Survey of Sweden (SGU). Access to the Nautanen area is reasonably good, with several paved and gravel roads extending eastward from Gällivare and Malmberget. Route E10/E45 runs north-east through the key area between Gällivare and Svappavaara, continuing northward to Kiruna. In general, most of the mapped outcrop locations can be easily accessed via the road network. Numerous hiking paths and skidoo trails also cross the area. The landscape at Nautanen is a mixture of coniferous and deciduous forests, with marshy and wetland areas located between the forests where rivers and streams occur. The terrain is undulating to hilly in the northern and north-western parts with elevations ranging between 350 and 450 m above sea level. In the central and southern parts the terrain is flatter, averaging about 300 m above sea level (see section Petrophysics). Nautanen Norrbotten County SWEDEN Stockholm 200 km 6 (40) Figure 1. Location of the Nautanen key area (small red polygon) in Norrbotten county, northernmost Sweden. The black square corresponds to map sheet 28K (Gällivare) representing an area of 2 500 km2. 7468000 The Lina river (Linaälven) crosses the southern part of the study area (flowing west to east towards Sammakko) and represents the main hydrographic feature. Several smaller rivers and streams also flow in a general north-west to south-east direction across the study area (subparallel to the dominant structural fabric). Lakes and ponds are mostly located in the central and south-western parts (Fig. 2). 752000 756000 760000 764000 Latnijärvi 79 90 40 87 70 Byxtjärn 60 87 Nautanen 87 35 35 70 20 80 85 60Muorjevaara 58 84 60 29 7464000 60 Pahtavaara 87 Juoigamvárri 88 45 50 90 Koskullskulle 87 28 65 87 Liikavaara 87 85 53 90 Sarkasvaara 87 85 40 7460000 87 65 56 68 60 Rahavaara 70 70 60 70 45 60 60 40 15 15 87 60 90 86 87 87 87 Rahajärvi 85 87 Haltiakoski 50 70 70 20 40 72 90 60 70 30 85 80 70 74 45 87 Sjungberget 87 40 Sorvanen 65 65 76 12 25 Gällivare flygplats 78 87 85 90 60 45 Nunisvaara 87 87 87 40 32 86 Va Vassara sa äl raj ve ok n i 60 70 60 Profile I (Fig. 3) 82 50 55 85 90 7456000 Pienempi Petäjävaara 50 90 Nunisjärvi 25 50 50 53 60 20 eip Sakavaara 10 60 20 ki 90 64 60 60 20 60 87 70 30 ojo 78 60 Suorkkisuvanto 87 Vasaravaara älven Lina ajoki k Link Sakajärvi L Liikavaara Sakajärvi 20 50 50 Nautanen key area Mapped outcrop Aitik Cu-Au-Ag deposit STRUCTURES Fault, fracture zone Ductile deformation zone Kaddivaara METAVOLCANOSEDIMENTARY ROCKS c. 1.88–1.84 Ga Metaarenite Metabasalt–metaandesite c. 1.92–1.87 Ga Form line of fold, dyke Phyllite Syncline, overturned Meta-quartz arenite Synform Metaarenite Layering Metasediment Foliation Metadacite–metarhyolite Bandning Porphyritic texture Fold axis Metabasalt–metaandesite Lineation Geophysical structure 34 34 70 INTRUSIVE ROCKS 4 km c. 1.84–1.77 Ga Dolerite Granite (Lina-type) c. 1.92–1.87 Ga Syenitoid–granitoid (PMS) Gabbroid–dioritoid (HS) Figure 2. Bedrock geology of the Nautanen key area, north-central Norrbotten. Profile line I corresponds to the cross-section shown in Figure 3. Based on Witschard (1996). 7 (40) 7468000 752000 756000 760000 764000 Latnijärvi Byxtjärn Nautanen Nautanen-Hoppet Muorjevaara södra Mariagruvan skärpning 1 Muorjevaara 7464000 Mariastollen Koskullskulle Pahtavaara Sarkasvaara Pienempi Petäjävaara Nautanen skärpning Juoigamvárri Milian Nautanen xx Ferrum4 Nautanen-Bratt Nautanen xx Ferrum Ferrum9 Nautanen xx Myrheden Liikavaara Liikavaara A Liikavare-8:an Liikavaara C Liikavaara-Tor Liikavaara B Liikavaara13 Liikavaara22 *Liikavare* Liikavare-Nya Fyndet Snålkok Liikavare-28:an Fridhem Snålkok-D Liikavaara-Friheten Snålkok-A Snålkok-B Liikavare-Masen Snålkok-C Sjungberget 7460000 Juoikama Sorvanen Rahavaara Sorvanen-norra Sorvanen-östra Rahajärvi Sorvanen-mellersta Nunisvaara Sorvanen-södra Gällivare flygplats Haltiakoski 7456000 Nunisvare 2 Nunisvare 1 Nunisjärvi Vassaravaara V a Vassara sa äl raj ve ok n i Suorkkisuvanto älven Lina ajoki k Link Sakakoski-norra Sakavaara Sakakoski-västra Vasaravaara Sakakoski-södra ki ojo Sakajärvi ip Le Liikavaara Sakajärvi Liikavaara Östra Kaddivaara Iron ore, trial pit or prospect 4 km Sulphide mineralisation, trial pit or prospect Quarry, industrial mineral, abandoned Drill core (Malå) Figure 3. Geological map showing the locations of known mineral prospects in the Nautanen area. The locations of drill core related to the various Cu-Au deposits, which is available at SGU’s Malå office, is also shown. From a geological perspective, the Nautanen area is best known for hosting numerous copper prospects with associated gold and iron mineralisation (e.g. Nautanen). The area is located just north of the Aitik mine, one of Europe’s largest copper-gold-silver producers, and east of the Malmberget iron-(phosphorous) mine which is Sweden’s second largest (after the Kiirunavaara deposit). The rocks at Nautanen host a regional-scale, Proterozoic deformation zone that has probably played a significant role in the area’s metallogenic evolution. GEOLOGICAL OVERVIEW OF THE NAUTANEN AREA The following geological summary is based on Witschard (1996), Bergman et al. (2001) and Martinsson & Wanhainen (2004a). The Nautanen area is centred on a linear zone of north to north-west-aligned, deformed and metamorphosed volcanic and volcanosedimentary rocks (Fig. 2). These units form part of a regionally extensive supracrustal succession occurring across 8 (40) Svecofennian porphyrite group W Granitic dykes, veins Dolerite Linaälven Intensely deformed and altered metavolcanic rocks Metaarenite NDZ Metasedimentary rocks (schistose, skarn banded) Metavolcanic rocks (trachytes, andesites) E sea level Lina-type granite (c. 1.77 Ga) Diorite–granodiorite (Haparanda suite, c. 1.87 Ga) 1 km Figure 4. Schematic geologic cross-section (profile I) through the Nautanen deformation zone (modified after Witschard 1996). The profile line is shown on the bedrock map in Figure 2. northern Sweden that was deposited, deformed and metamorphosed during the Svecofennian orogeny (c. 1.96–1.75 Ga). A major ductile–brittle deformation zone transects the area and hosts numerous occurrences of copper±gold±iron mineralisation (cf. Fig. 3). The rocks in the Nautanen area consist of a mylonitic and foliated volcanic and volcaniclastic sequence that has undergone extensive deformation, metamorphism, recrystallisation and hydro­thermal alteration. In the eastern part of the area, metaarenite, carbonates (metamorphosed calc-silicate rocks), phyllites and schists dominate, with subordinate basalt, andesite and tuff. In the west, within a high strain deformation zone (see below), andesite, basaltic andesite, basalts and tuffs occur (Figs. 2 & 4). Thin, lamellar, metasomatic-related magnetite banding is a common feature of the volcanic units to the west. While the primary characteristics of many of the rock units at Nautanen are difficult to assess due the multiple metamorphic, deformation and alteration events, the rocks are generally considered to have been deposited by volcanic, volcaniclastic and sedimentary (epiclastic) processes. Limited attempts have been made to establish a stratigraphic classification for the rocks at Nautanen and make correlations with analogous supracrustal sequences elsewhere in Norrbotten (Zweifel 1976, Ros 1980). Thus, the assignment of the succession to both a regional or local stratigraphic framework has varied over the years (e.g. Ödman 1957, Witschard 1996, Bergman et al. 2000, Bergman et al. 2001, Martinsson & Wanhainen 2004a). Presently, the metamorphic rocks within the key area are assigned to the Muorjevaara group (Martinsson & Wanhainen 2004a) which incorporates the previously established Aitik, Liikavaara and Nautanen formations (Zweifel 1976). In addition, Bergman et al. (2000, 2001) assign the meta-volcanosediment­ ary rocks at Nautanen to the regionally extensive Porphyrite group comprised of calc-alkaline to alkaline meta-volcanosedimentary rocks (cf. McGimpsey 2010). Thus, the rock sequence in the Nautanen area is regarded to lie stratigraphically below Kirunavaara (Porphyry) group rocks that occur further to the east and host the Malmberget iron-phosphorus deposit. The Nautanen area is bound to the east and west by Paleoproterozoic intrusive rocks of both mafic and felsic compositions. They primarily consist of gabbroids, peridotites, dioritoids and granitoids assigned to the Haparanda suite of intrusive rocks (c. 1.88–1.86 Ga, e.g. Witschard 1984, 1996) and younger granitoids of the Lina suite (c. 1.77 Ga, e.g. Bergman et al. 2001, 2011). Perthite monzonite suite intrusions are less prevalent in this area. Numerous doleritic dykes and sills of presumed Mesoproterozoic age intrude Lina suite granite to the east of the study area (Fig. 2). Apart from investigations conducted on the intrusive rocks at the Aitik deposit to the south of the Nautnaen area (e.g. Wanhainen et al. 2006), detailed petrographic, geochemical and isotopic investigations of the intrusive rocks in the area have not been conducted. In addi9 (40) tion, efforts to establish any temporal or genetic links between the intrusive phases and spatially coincident Cu-Au mineralisation in the area have presently not been undertaken. The bedrock at Nautanen is situated within a major north to north-west orientated deformation zone termed the Nautanen deformation zone (NDZ, Bergman et al. 2001). The NDZ is c. 1–3 km wide in the study area and represents a high strain zone comprised of intensely tecto­ nised and altered rocks that display sub-vertical, mylonitic fabrics and laminar magnetite±garnet alteration bands (profile I, Figs. 2 and 4). The NDZ is spatially and structurally constrained along its east and west margins by two major fault zones, while in the south-west part of the key area (Suorkkisuvanto-Sakajärvi area) the zone deflects to the south-east, possibly due to the emplacement of granite in the area (Fig. 2). The NDZ transects a sub-vertical, north-north-west orientated, fold sequence where the fold axes generally plunge to the south-south-east. This earlier ductile deformation is overprinted by numerous brittle faults that are generally sub-vertical and predominately orientated north-north-west. At present, few detailed structural investigations have been made for the NDZ and thus the kinematic and deformational properties of the area are not well constrained. The absolute timing and duration of the various deformational events is also not known, although the area has probably undergone several phases of deformation and reworking during its geological evolution. Likewise, the control of deformational processes on Cu-Au mineralisation is, while recognised by previous workers (e.g. Ros 1980), poorly understood. Metamorphism in the Nautanen area is estimated to have reached medium to high grades (amphibolite facies) based on mineral assemblages, with the metamorphic grade generally increasing from east to west across the NDZ (cf. Fig. 60 in Bergman et al. 2001). A well developed north-north-west orientated, sub-vertical schistosity, locally grading into a gneissic banding, ­occurs in the metavolcanic rocks and tends to parallel primary depositional features (e.g. bedding contacts) and major deformational structures. Sillimanite porphyroblasts developed in metasedimentary horizons indicate local contact metamorphism associated with granitoid magmatism. Tollefsen (2014) reports pressure-temperature estimates for regional, contact and retrograde metamorphic conditions for the Nautanen area, based on mineral chemistry and thermodynamic modelling. A regional metamorphic event is constrained from c. 550 to 660 °C and 2 to 5 kbar. Contact metamorphism adjacent to Lina granite (forming a sillimanite-biotitemuscovite assemblage) occurred from c. 630 to 710 °C and 2 to 4.4 kbar. Retrogression is constrained between c. 430 and 570 °C, and 3 to 3.5 kbar. Mineralisation in the Nautanen area predominantly consists of numerous, relatively small (<1 million tonnes) copper±gold±iron prospects. Within the NDZ, mineralisation is mainly disseminated (replacement?) to semi-massive (strataform lenses) in nature, with fewer vein-hosted occurrences. Further away from the high strain zone, relatively undeformed, vein-type mineralisation dominates with sub-vertical, north to north-north-east orientations. This latter veinhosted mineralisation is considered to represent the youngest mineralisation event in the area (e.g. Martinsson 2004). Chalcopyrite and bornite are the principal ore minerals, with minor chalcocite, magnetite, sphalerite, galena, molybdenite and scheelite. Gold generally occurs as inclusions or overgrowths associated with chalcopyrite, pyrite and bismuthenite, and as electrum (cf. Ekström 1987; Bark et al. 2013). Hydrothermal alteration mainly consists of pervasive and vein-related potassic (K-feldspar) alteration, scapolitisation, sericitisation and tourmalinisation. Garnet, amphibole and epidote are also important alteration minerals in the area. AVAILABLE DATA FOR THE NAUTANEN AREA The following sections present a summary of available geological, geochemical and geophysical data covering the Nautanen key area. Some useful topographic datasets are also listed. 10 (40) Bedrock geology information The Nautanen area is covered by a number of bedrock geology maps and digital datasets. Several of these are available as vector layers and georeferenced raster images for use in geographical information system (GIS) and mapping software. The GIS data are mainly derived from digitised versions of bedrock maps published at 1:50 000, 1:250 000 and smaller scales. Additional bedrock sampling and analyses (e.g. lithogeochemistry, age determinations) by SGU and other workers are generally represented as point layers that show the sample location and associated analytical results (see the sections Geochemistry and Geochronology). Geology maps and related data layers Tables 1 and 2 list some important results of bedrock mapping for the Nautanen area along with additional bedrock information derived from SGU’s internal databases. The maps listed Table 1. Published bedrock maps and related GIS data covering the Nautanen area. Code Ai 100 Title Bedrock map 28K SV Scale 1:50 000 Reference Witschard 1996 Ai 101 Bedrock map 28K SO 1:50 000 Witschard 1996 1:250 000 1:400 000 Bergman et al. 2000 Ödman 1957 Ba 56:1 Regional bedrock map Ca 41 Berggrundskarta över urberget i Norrbottens län K 423 Bedrock map of Sweden n/a Nordkalott bedrock geology map n/a Metallic mineral deposit map of the Fennoscandian Shield n/a Geology of the Fennoscandian Shield. n/a Lokal berggrundsinformation n/a Regional berggrundsinformation Map or data extent Western Nautanen key area Eastern Nautanen key area Northern Norrbotten Norrbotten County 1:1 000 000 Bergman et al. 2012 1:1 000 000 Silvennoinen et al. 1987 1:2 000 000 Eilu et al. 2008 Sweden N. Sweden Fennoscandia 1:2 000 000 Koistinen et al. 2001 Fennoscandia 1:50 000 1:250 000 Nautanen key area Nautanen key area SGU GIS data SGU database Table 2. Other geology-related layers and datasets covering the Nautanen area. Layer or dataset Häll, ytor ur Jordartskartan 1:250 000 Norrbotten Jordarter 1:250 000, Nordligaste Sverige Berggrundsobservationer Geology_1M Swedish Radiometric Age Database Fennoscandian Shield (komplett WGS84 TM) Förenklad jordartsindelning (JBAS) Norrbotten NBDIG Sveriges berggrund 1:1M Description GIS polygon layer showing outcrop and thin soil cover areas from soil maps. Digital layer showing outcrop and soil cover types. Ice flow directions also. Point dataset of location and description of outcrop and structural observations. 8 points in key area. 1:1 000 000 scale vector data showing bedrock geology. No colour coding. Point locations of age dating samples with methods and results Digital polygon layer showing small scale bedrock geology soil/till geology map of Norbotten 1:250 000 Location Nautanen key area Digital polygon layer showing small scale bedrock geology with outcrops highlighted also Digital polygon layer showing small scale bedrock geology Norrbotten Nautanen key area Southern Nautanen key area Sweden Two locations, north NKA Fennoscandia Norrbotten Sweden 11 (40) in T ­ able 1 represent both georeferenced, scanned paper maps and vector databases. The most detailed SGU mapping for Nautanen is two 1:50 000-scale bedrock maps from SGU’s Ai series covering map sheets 28K Gällivare SV and SO (map sheet nomenclature relates to the old RT90 map index system). Scanned field maps and other map information Table 3 lists scanned field maps produced during the 1:50 000 mapping campaigns in and around the Nautanen area (mostly from the 1960s). The field sheets show the location of outcrops, areas of thin soil cover, mineralised boulders and other geological information. The majority of information was recorded at the scale 1:20 000. Scanned field diaries (45 in total) recorded by SGU geologists are also available for consultation. Additional scanned geological maps can be found within several Brap and Prap reports (historical SGU, SGAB, NSG and LKAB exploration reports), particularly for mineralised areas (see Table 4). For example, Jonasson (1988) and Petersson (1988) present several drill hole profiles through the metavolcanic rocks at the Muorjevaara and Sorvanen copper prospects, respectively. Likewise, several reports by Gustafsson (1986a to g) contain detailed (typically 1:5 000 and 1:1 000-scale) geological maps and drill hole profiles for the Liikavaara, Muorjevaara, Snålkok, Sakakoski and Sorvanen copper prospects located within the NDZ. Furthermore, Danielsson (1984, 1985) and Daniels­son & Lindroos (1986) present geological maps, drill hole profiles (with associated assay data) and interpreted geological cross-sections for the Nautanen Cu-Au deposit. Zweifel (1976) presents a geological map of the Aitik area showing stratigraphic and lithological units that extend into the southern part of the Nautanen area (e.g. Aitik and Nautanen formations). Outcrop locations Figures 2–6 show the location of mapped outcrops and exposed rock across the Nautanen area. By Norrbotten standards, the Nautanen area has reasonable outcrop exposure. Metavolcanic and metasedimentary rocks in the southern, eastern and north-western parts appear to be the best exposed. Several large areas of exposure within the Nautanen deformation zone also o­ ccur. Outcrop exposure for intrusive rocks to the east and west of the deformation zone is more scattered and intermittent. Exposures along the banks of the river Linaälven (southernmost Nautanen area) provide an opportunity to assess the stratigraphy, deformation and alteration of the metavolcanic rocks orthogonal to a high strain deformation zone. The hinge zone of an overturned syncline comprised of metasedimentary rocks in the south-eastern part of the study area is poorly exposed (Fig. 2). Likewise, intrusive rocks in the south-east corner of the area are generally not exposed. Historical drill core, retained at SGU’s Malå office, provides an additional source of bedrock information that may fill in areas with relatively poor exposure (e.g. northeast Nautanen area, south of Snålkok prospect, cf. Fig. 3). In addition, several aggregate quarries in the Nautanen area may also provide access to exposed bedrock (e.g. in the Mourjevaara area, north-east of Nautanen). Published material (papers and reports) A list of some relevant papers and reports for the Nautanen key area is presented in Table 4. This literature compilation should be viewed as a starting point for obtaining information on the geol­ogy and mineralisation of the Nautanen area. A short synopsis of each publication is presented in the “Brief overview” column. Several of the publications are review papers that summarise on a regional scale the broad geological, tectonic and metallogenic setting of Norrbotten within the context of the geological evolution of northern Fennoscandia. 12 (40) Table 3. Scanned field maps and other map information for the Nautanen area. Scanned map or information (not rectified) G10906 G10909 G10910 G10915 G10920 G10921 G10924 G10925 G10926 G10935 G10937 G10941 G10950 G10952 G10953 G10954 G10955 G10959 G10960 G10963 G10967 G10968 G10969 G10970 G10973 G10975 G10976 G12603 G12605 G12606 G12607 G12609 G12610 G12612 G12613 G12615 G12616 G12617 G12618 G12619 G12620 G12635 G12636 G12638 G12640 G12644 G12645 G12647 G12648 Diaries_28K_various named workers Boulders_28K Description and coverage (RT90 map system) Scale Scanned outcrop field map, 28K SO Scanned outcrop field map, 28K Scanned outcrop field map, 28K SV Scanned outcrop field map, 28K SV Scanned outcrop field map, 28K Geology regional interpretation, 28K Scanned outcrop field map, 28K 0–1 e–f Scanned outcrop field map, 28K 2–3 c–d Scanned outcrop field map, 28K 2–3 e–f Mineral deposits and prospects, 28K Mineral deposits and prospects, 28K Drill hole overview map, 28K Outcrops with observation numbers, 28K SV Mineralised boulders and outcrops, 28K SV Mineralised boulders and occurrances, 28K SV Mineralised boulders and occurrances, 28K SV Mineralised boulders and occurrances, 28K SV Outcrop observation no map, 28K SV Mineral deposit overview, 28K SV Outcrops with contacts, 28K SV Mineral deposit areas, 28K SO Mineral deposit areas, 28K SO Boulders and mineralised outcrops, 28K SO Boulders and mineralised outcrops, 28K SO Boulders and mineralised outcrops, 28K SO Outcrops with observation numbers, 28K SO Outcrops with observation numbers, 28K SO Outcrop map, 28K 0–1 c–d Outcrop map, 28K 0–1 c–d Outcrop map, 28K 0–1 c–d Outcrop map, 28K 0–1 c–d Outcrop map, 28K 0–1 c–d Outcrops and samples Outcrops and observation numbers Outcrop map, 28K 0–1 e–f Outcrop map, 28K 0–1 e–f Outcrop map, 28K 0–1 e–f Outcrop map, 28K 0–1 e–f Outcrops with contacts, 28K 0–1 e–f Outcrops and observation numbers, 28K 0–1 e–f Boulder locations, 28K 0–1 e–f Economic map, 28K 2–3 c–d Outcrop map, 28K 2–3 c–d Outcrop map, 28K 2–3 c–d Outcrops with observation numbers, 28K 2–3 c–d Outcrops with observation numbers, 28K 2–3 e–f Outcrops with observation numbers, 28K 2–3 e–f Outcrops with observation numbers, 28K 2–3 e–f Outcrops with observation numbers, 28K 2–3 e–f Field notebooks from SGU geologists. 45 field diaries in total. 1:50 000 1:100 000 1:50 000 1:50 000 1:100 000 1:100 000 1:20 000 1:20 000 1:20 000 n/a n/a 1:100 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:50 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 1:20 000 Varies Gives location and description of mapped boulders (map sheet 28K, no maps) n/a 13 (40) Table 4. Publications and reports relating to the geology of the Nautanen area. Reference Tollefsen 2014 Title Thermal and chemical variations in metamorphic rocks in Nautanen, Gällivare, Sweden Martinsson & Wanhainen 2013 Fe oxide and Cu-Au deposits in the northern Norrbotten ore district Hydrothermal fluid evolution and metal transport in the Kiruna District, Sweden: Contrasting metal behaviour in aqueous and aqueous–carbonic brines Smith et al. 2013 Brief overview and relevance to Nautanen area M.Sc. study on metamorphic conditions in the Nautanen area. Petrography, mineral chemistry, wholerock chemistry and PT modelling. Metasomatic fluids are Ba, Mn and Fe enriched. Review of the geology and metallogeny of northern Norrbotten. Fluid inclusion study (LA and crush leach analysis) of IOCG-type mineralisation in Kiruna district. Includes samples from Nautanen deformation zone. Coexisting aqueous–carbonic, carbonic and saline fluid inclusions in deposits associated with the NDZ indicate a fluctuating pressure regime, potentially with periods of phase separation. Cl/Br ratios of inclusion fluids determined by crush-leach are consistent with a range of fluid sources including both magmas and halitebearing evaporites. Sarlus 2013 Geology of the Salmijärvi Cu-Au MSc thesis on the Salmijärvi Cu-Au deposit. Geology deposit and geochemistry focus on host rocks and hydrothermal veins. Hallberg et al. Metallogenic areas in Sweden. Review of some of the main mineral deposits across 2012 Sweden. Divided into metallogenic areas. Covers Gällivare-Nautanen-Aitik. Wanhainen et al. Modification of a PalaeoproIntegrated study of the Aitik deposit. Modified (meta2012 terozoic porphyry-like system: morphosed) porphyry system. Integration of structural, geochemical, petrographic, and fluid inclusion data from the Aitik Cu–Au–Ag deposit, northern Sweden Bergman et al. Geological and tectonic evolu- Regional scale review of the geological and tectonic 2011 tion of the northern part of the setting of the Fennoscandian Shield. Fennoscandian Shield McGimpsey 2010 Petrology and lithogeochemis- Study of the Nautanen deposit. Review of geological try of the host rocks to the Nau- setting. tanen Cu-Au deposit, Gällivare area, northern Sweden Smith et al. 2009 In Situ U-Pb and trace element Titanite and alanite U-Pb geochronology study. analysis of accessory minerals in Samples from the Nautanen deposit gave ages of the Kiruna district, Norrbotten, 1777 ± 20 Ma and 1785 ± 21 Ma. Corresponds to some Sweden: new constraints on the age dating results at Aitik. Mineral chemistry data also timing and origin of mineraliza- presented. tion Gleeson & Smith The sources and evolution of Fluid inclusion study using halogen and Cl isotope 2009 mineralising fluids in iron oxide- data as tracer for ore forming fluids in IOCG systems, copper-gold systems, NorrNorrbotten. Some focus on deposits in the Nautanen botten, Sweden: Constraints deformation zone. Cl data suggests crustal fluids from from Br/Cl ratios and stable either meta-evaporites or Lina-type granites. Cl isotopes of fluid inclusion leachates Storey et al. 2007 In situ LA-ICP-MS U–Pb dating Titanite and apatite U-Pb ages. Malmberget sample of metavolcanics of Norrbotten, gives titanite cores dated at 2073 ± 19 Ma; rims = Sweden: Records of extended c. 1900 to 1700 Ma. Apatite gives 1583 ± 10 Ma. Results geological histories in complex used to infer age of Porphyry Group magmatism at c. titanite grains 2.0 Ga and not 1.9–1.8 Ga (i.e. pre-Svecokarelian). Nordin et al. 2007 Stop 2. Aitik Cu-Au-Ag mine Field excursion guide covering the Gällivare-Aitik areas. Geology and mineralisation review. 14 (40) Reference Wanhainen et al. 2005 Title 160 Ma of magmatic/hydrothermal and metamorphic activity in the Gällivare area: Re–Os dating of molybdenite and U–Pb dating of titanite from the Aitik Cu–Au–Ag deposit, northern Sweden Weihed et al. 2005 Precambrian geodynamics and ore formation: The Fennoscandian Shield Character of Cu-Au mineralization and related hydrothermal alteration along the Nautanen deformation zone, Gällivare area, northern Sweden Cu-Au deposits in the Gällivare area Martinsson & Wanhainen 2004a Martinsson & Wanhainen 2004b Martinsson 2004 Bergman et al. 2001 Ahl et al. 2001 Martinsson & Wanhainen 2000 Billström & Martinsson 2000 Pitkänen 1997 Frietsch 1997 Frietsch et al. 1997 Billström et al. 1997 Witschard 1996 Brief overview and relevance to Nautanen area Geochronology study at the Aitik Cu deposit. Re–Os dating of molybdenite from deformed barite and quartz veins yielded ages of 1876 ± 10 Ma and 1848 ± 8 Ma, respectively. A deformed pegmatite dyke yielded a Re–Os age of 1848 ± 6 Ma, and an undeformed pegmatite dyke an age of 1728 ± 7 Ma. U–Pb dating of titanite from a diversity of alteration mineral associations defines a range in ages between 1750 and 1805 Ma with a peak at c. 1780 Ma. Broad review paper of metallogeny and geotectonic setting of mineral deposits in N Sweden. Review and field guide of Cu-Au mineralisation in the Gällivare-Nautanen area. Review and field guide of Cu-Au mineralisation in the Gällivare-Nautanen area. Includes description of mineralisation at Aitik and Nautanen deposits. Geology and metallogeny of the Review paper of metallogeny and geological setting northern Norrbotten Fe-Cu-Au of IOCG deposits Norrbotten. Includes description of province mineralisation at Aitik and Nautanen areas. Description of regional geoSynthesis report on the bedrock geology and geophyslogical and geophysical maps of ics of Norrbotten based on 1:250 000 regional maps. northern Norrbotten County … Geochemical classification of Classification and petrogenesis of various plutonic plutonic rocks in central and suites based on whole-rock geochemistry. northern Sweden The Gällivare area Excursion guide that reviews geology and metallogeny of the Gällivare area. Nautanen area covered. Links between epigenetic Cu-Au Abstract suggesting Cu mineralisation at Nautanenmineralizations and magmaAitik area is c. 1800–1750 Ma based on U-Pb titanite tism/deformation in the Norrgeochronology. No actual data presented however. botten county, Sweden Anisotropy of magnetic susAMS study on mylonitic rocks from two deformation ceptibility of mylonites from zones. AMS fabrics trend parallel to dominant tectonic the Kolkonjoki and Nautanen foliations, particularly at Nautanen area. deformation zones in Norrbotten, Sweden The iron ore inventory proReview of mineral deposits of Norrbotten. Includes degramme 1963–1972 in Norrbot- scription of Aitik and Nautanen deposits (i.e. sulphide ten county ores in Porphyry Group). Early Proterozoic Cu-( Au) and Study of scapolite and related alteration associated Fe ore deposits associated with with Cu-Au and Fe mineralisation across Norrbotten. regional Na-Cl metasomatism Reviews scapolite-tourmaline alteration in Nautanenin northern Fennoscandia Aitik areas. Scapolite tends to be more Cl-poor here. Regional variations in the Pb Study on galena Pb isotope systematics. Galena linked isotopic compositions of ore to epigenetic Cu deposits in Porphyry Group rocks is galena across the Archaeannon-radiogenic. This is similar signature to galena from Proterozoic border in northern deposits in Skellefte district. Includes samples from Sweden Muorjevare and Snålkok (Nautanen area). Berggrundskartan 28K Gällivare SGU map sheet for area 28K Gällivare SV (Ai 101). The SO 1:50 000 back side of this map contains a description in English of the geology of map sheet 28K which includes the Nautanen area. Mineralisation is also described. 15 (40) Reference Romer 1996 Title U-Pb systematics of stilbitebearing low-temperature mineral assemblages from the Malmberget iron ore, northern Sweden Martinsson 1995 Greenstone and porphyry hosted ore deposits in northern Norrbotten Frietsch & Perdahl Rare earth elements in apatite 1995 and magnetite in Kiruna-type iron ores and some other iron ore types Lilljequist 1991 OV-Projektet. Basemetaller i Norrbotten Gaal 1990 Petersson 1988 Tectonic styles of early Proterozoic ore deposition in the Fennoscandian shield Stora prospekeringsmål i Gällivareområdet, Sorvanen gravimeteranomali. “The Mother Lode to Aitik.” The geology and genesis of the Aitik copper-gold deposit, Arctic Sweden: Sorvanen. Borrningar 1988 Johansson 1988 Muorjevaara. Borrfas III, 1987 Carlson 1989 Monro 1988 Danielsson 1987 Geologisk beskrivning över Nautanen–Aitik – Jårbojoki­ stråket i Gällivare Ekström 1987 Mineralogisk undersökning av häll och blockprover från Gällivareområdet Skiöld 1987 Aspects of the Proterozoic geochronology of northern Sweden Fredriksson 1986 Projekt Nordöstra Norrbotten Etapp 111 (1985). Sammanfattning av utförda prospek­ teringsarbeten och resultat Lindholm 1986 28J Fällåsen och 28K Gällivare, sammanställning av myrtorv­ analyser 1982–1984 Gustafsson 1986a Projekt 5515 Malmberget Prospekteringsarbeten 1985 Rekommendationer för 1986 Lägesrapport 1986-01-15 Gustafsson 1986b Liikavaara, nya fyndet. Borr­ ningar 1986 Gustafsson 1986c Snålkok. Borrningar 1986 16 (40) Brief overview and relevance to Nautanen area Geochronology of low temperature mineral assemblages at the Malmberget Fe deposit. Includes regional geologic setting. Age of c. 1740 Ma for fracture-filling monazite may constrain late brittle faulting in the area. Review of geology and mineral deposits of northern Norrbotten. Includes description of the Nautanen Cu deposit. Study on mineral chemistry from various localities across Norrbotten. One sample from Malmberget deposit, west of Nautanen. Overview report covering area 28K SV Nautanen. Gives background to base metal mineralisation in the area. Several maps - regional geochemical anomalies and location of mineral prospects in Nautanen area. Big picture, regional review of tectonic and metallogenic evolution of the Fennoscandian Shield. Mostly geophysical modelling in the Nautanen deformation zone. Comparisons made to the Olympic Dam deposit in Australia. PhD thesis on the Aitik Cu deposit (within Nautanen trend). Geology and geochemistry focus. Review of exploration activity at the Sorvanen prospect (Nautanen area). Includes drill core data. Review of exploration activity at the Muorjevaara Au prospect. Includes drill core data. Geological description of the Nautanen–Aitik–Gällivare areas. Mineralogical study from the Snålkok, Sorvanen, Sakakoski and Likavaara prospects (Nautanen area). Review of age dating results and general stratigraphy of northernmost Sweden. Overview of LKAB exploration activity across northeastern Norrbotten. Discusses mineralisation in the Malmberget–Nautanen areas. Report on peat bog sampling and analysis results. Contains map showing sampling and analysis for sheet 28K with anomalous metal values. Review of exploration activity in the general Gällivare area. Contains geological and geophysical maps of the Gällivare–Nautanen areas, sample descriptions, some assay data. Exploration report on the Liikavaara deposit, Nautanen deformation zone. Includes drill hole logs and profiles Exploration results at Snålkok prospect. Drill hole sections, logs and assay data. Reference Title Gustafsson 1986d Projekt nordöstra Norrbotten delprojekt Malmbergetomradet lägesrapport för tiden 1986-0812–1986-11-10 Gustafsson 1986e Muorjevaara borrfas II 1986 Gustafsson 1986f Sorvanen. Borrningar 1986 Gustafsson 1986g Sakakoski. Borrningar 1986 Danielsson & Lindross 1986 Arkko 1986 Lundh 1985 Nautanen copper-gold deposit The Nordkalott project. Geophysical aspects of large mafic intrusions in northern Sweden Dikesgrävning Sakakoski 1985 Brief overview and relevance to Nautanen area Review exploration activity in the Nautanen area with focus on Sakajärvi–Muorjevaara prospects. Exploration report on the Muorjevaara prospect. Includes drill hole logs, assay data, profiles. Exploration results at Sorvanen prospect. Drill hole sections, logs and assay data. Exploration report on the Sakakoski Cu prospect. Includes drill hole logs, assay data, profiles. Review and field excursion guide to the Nautanen deposit. Includes map and cross section through deposit. Study on the geophysical properties of several mafic intrusions including the Gällivare area. MSc thesis. Summary of trenching work at the Sakakoski Cu-Au prospect. Contains maps and assay data. Gustavsson 1985 Fältarbeten 1984 inom delpro- Overview of exploration at Gällivare and Nautanen. jektområde Gällivare SV och SO. Contains geology maps with observation numbers and Slutrapport outcrops at Nautanen area, and presents stratigraphy overview. Discusses characteristics of the Nautanen and Muorjevaara formations. Danielsson 1985a Nautanen. Borrhålsprotokoll Detailed exploration report for activity at the Nauoch analysintyg från 1985 års tanen deposit. Drill hole profiles, logs and assay data. arbeten Danielsson 1985b Nautanen. Borrförslag på TEM- Nautanen deposit. Contains drill hole locations and anomalier 1985 schematic logs. Danielsson 1984 Cu-Au-fyndingheten Nautanen. Geology and exploration work at the Nautanen deResultat av 1983 års diaposit. mantborrning Witschard 1984 The geological and tectonic Overview and tectonic synthesis of the geological evolution of the Precambrian evolution of northernmost Sweden. Presents revised of northern Sweden. A case for lithostratigraphy. basement reactivation? Skiöld & Cliff Sm-Nd and U-Pb dating of early Dating of felsic volcanic rocks assigned to the Porphyry 1984 Proterozoic mafic-felsic volcan- Group. Age of 1909 ± 17 Ma which appears on the ism in northernmost Sweden 1:50 000 bedrock map of Witschard (1996) is partly based on a sample collect to west of Nautanen area. Zircon populations from several samples were mixed. Gustavsson 1984 28J Fjällåsen SO-NO 28K Reviews exploration and field work in Gällivare–NauGällivare. Prospekteringsförslag tanen area. Contains maps with location of mineral1984 ised. Gustavsson 1984 Fältarbete 1984 inom delproReviews exploration and field work in Gällivare–Naujektområde Gällivare. Gällivare tanen area. Includes a review of regional stratigraphy. SV och SO. Underhandsrapport Includes overview maps with outcrop observation points. Gustavsson & Ferrum kopparfyndighet geoOverview of exploration work at the Ferrum deposit. Johansson 1984 fysik och geologi 1984 Contains drill hole logs, geologic maps and cross sections and assay data (Cu, Au, Ag). Carlson 1984 Nautanen. ProspekteringsOverview of geology and exploration at Nautanen deförslag 1984 posit. Contains drill hole sections showing mineralised Cu-Au horizons. Hålenius 1983 En mineralogisk undersök­ning Mineralogical investigation of sulphide-bearing av Cu-Au-mineraliseringen samples from Nautanen deposit drill holes. Describes Nautanen sulphide-gold mineralogy, paragenesis. Cobolt also discussed. 17 (40) Reference Lagerbäck 1982 Carlson 1982 Frietsch 1980 Ros 1980 Wilson & Sundin 1979 Title Isrörelser inom kartbladen 26L Pålkem SV, NV, 27L Lansjärv SV, NV, 28J Fjällåsen SV, NV, SO, NO, 28K Gällivare SV, NV, SO, NO, 28L Tärendo SV, NV, 29K Vittangi SV, NV, SO, NO, 29L Lainio SV, NV Guld i Norrbotten. Del 2 Precambrian ores of the northern part of Norrbotten County, northern Sweden Nautanenområdet. Rapport över SGU:s arbeten utförda under 1966–1979 Isotopic age determinations on rocks and minerals in Sweden 1960–1979 SGU (no author), Projekt Norra Norrbotten Brap 00682, 1978 Zweifel 1976 Frietsch 1974 Svensson 1971 Ödman 1957 Geijer 1948 Aitik. Geological documentation of a disseminated copper deposit The occurrence and composition of apatite with special reference to iron ores and rocks in northern Sweden Nunisvaara molybdenförekomst Beskrivning till berggrunds­karta över urberget i Norrbottens län Sveriges malmtillgångar Ödman & Werner Likavaara-Salmivaara-Vuod1940 najaure-Svappavaara. Rapport över SGUs prospeckeringsverksamhet i Norrbotten 1940 Geijer 1931 Pre-Cambrian geology of the iron-bearing region Kiruna– Gällivare–Pajala Geijer 1924 Geijer 1918 Geijer 1917 18 (40) Brief overview and relevance to Nautanen area Iceflow directions and geomorphology analysis for 20 map sheets covering various areas across central Norrbotten. Covers map sheet 28K Gällivare. Compilation of gold showings and prospects in Norrbotten. No.5, 6, 7 and 8 related to Cu-Au mineralisation in general Gällivare area. Review of metallogeny of northernmost Sweden. Contains section on Aitik deposit and general Nautanen area. Summary report on the geology of the Nautanen area. Contains geologic descriptions, drill hole locations and some assay data. Ferrum prospect discussed. Summary report reviewing age dating for whole of Sweden during period 1960–79. Item 30 relates to a recalculated Rb-Sr whole-rock age (inaccurate) for a granite sample close to the Nautanen area (Lina granite = 1530 ± 35) and taken from Welin et al. 1971. Overview of the geology and mineral potential of northern Norrbotten. Includes Nautanen and Sjaunja deposits. Study of the Aitik Cu deposit. Includes geological and stratigraphic description of rocks at the Nautanen area. Apatite geology and chemistry in Norrbotten. Discusses metasomatic iron ores of the Nautanen area. Report on the molybdenum mineralisation at Nunisvaara, to the west of Nautanen. Synthesis report on the regional bedrock geology of Norrbotten County accompanying the 1:400 000 published map. Early summary of Sweden’s mineral resources. Includes map and information on Norrbotten deposits and Nautanen area. Geological and geophysical exploration activity at several mineral prospects in the general Gällivare– Nautanen area. Early synthesis report on the bedrock geology of the Kiruna–Gällivare–Pajala area and related mineralisation. Includes Nautanen area. Discusses significance of scapolite alteration. Some Swedish occurrences of Early report on Cu-sulphide mineralisation for Sweden bornite and chalcocite including the Nautanen area of northern Sweden. Includes Nautanen area. Nautanenområdet. En malmge- Early report on the geology and mineral deposits of ologisk undersökning the Nautanen area. Includes Nautanen and Ferrum prospects. Om landisens avsmältningsEarly report on the Quaternary geology of the Nauförhållanden inom Nautatanen area. Discusses paleo-ice flow directions. nenområdet vid Gällivare Table 5. Drill core associated with mineral prospects within the Nautanen area. Deposit or prospect No. of holes available in Malå Liikavaara Cu 9 holes (1979, 86, 2003; NSG, Phelps Dodge) Nautanen Cu-Au 109 holes (1966–2003; SGAB, NSG, North Atlantic Natural Resources AB, Phelps Dodge) Janstorp (Nautanen 18 holes (1997, 1998, 2003; North N) Atlantic Natural Resources AB, Phelps Dodge) Ferrum Cu 6 holes (1969, SGAB) Fridhem none Juoikama Cu-Mo none Muorjevaara 13 holes (1986, 87; NSG) Sakakoski Cu 28 holes (1986, 1987; NSG) Snålkok Cu-Au 10 holes (1986, 2005; SGAB, Phelps Dodge) Sorvanen Cu-Au 32 holes (1951–1998; SGAB, NSG, LKAB, North Atlantic Natural Resources AB) Kirunakorset Cu-Au 1 hole (1986, SGAB) Jappe Cu-Au 3 holes (1998, North Atlantic Natural Resources AB) Nunisvaara Mo none Total length >755 m Logs, assay data, reports Gustafsson 1986b 23 310 m Ros 1980, Danielsson 1984, Danielsson 1985a, b 1 516 m not known 751 m n/a n/a 1 324 m 2 851 m 922 m Ros 1980 n/a n/a Gustafsson 1986e Gustafsson 1986g Gustafsson 1986c >2 486 m Gustafsson 1986f, Petersson 1988, Ros 1980 not recorded Gustafsson 1986f 280 m not known n/a Svensson 1971 The publications in Table 4 are listed from most recent to oldest. References quoted in the main text of this report refer to those in Table 4 and the reference list at the end of this report. Drill core Table 5 lists the exploration drill holes and drill core associated with the various mineral deposits and prospects in and around the Nautanen area that are available for inspection at SGU’s Malå office. Drill hole collar locations are plotted in Figure 3. The majority of the holes were drilled in the 1980s as part of Sweden’s state exploration activity for Cu-Au deposits in the Gällivare area. Some relevant information about more recent drilling activity within the NDZ (since the mid2000s and onwards) may be available from SGU’s Malå and Luleå (Bergsstaten) offices. Information on alteration and mineralisation The Nautanen area hosts numerous, generally small-scale (<1 million tonnes, excluding the ­A itik Cu-Au deposit), disseminated and vein-hosted Fe, Cu and Au prospects and occurrences. The area has been a historical target for Cu-Au exploration since the discovery of copper mineralisation at Nautanen in 1898 (Geijer 1918), and is presently considered part of an important IOCG-style mineral deposit district (e.g. Carlon 2000, Billström et al. 2010, Williams 2012). Reviews of the setting and style of mineralisation in the Nautanen area is provided by Bergman et al. (2001) and Martinsson & Wanhainen (2004a, b, 2013). In general, Cu-Au mineralisation is spatially associated with favourable structural and lithological depositional sites within the high strain NDZ. A genetic link to granitoid magmatism, or contemporaneous metasomatism that drove metal remobilisation and enrichment, has also been proposed (e.g. Gleeson & Smith 2009, Smith et al. 2013). The area also displays a degree of district-scale metal and alteration zonation along the NDZ. Fe- and Cu-rich (Au-poor) occurrences associated with scapolite-albiteK-feldspar alteration are found in the north-west close to Malmberget (e.g. Nautanen, Ferrum, Fridhem prospects), while Au/Cu ratios increase (Fe-poor) towards the south-east in association 19 (40) Table 6. Datasets relevant to mineral resources and exploration within the Nautanen area. Layer or dataset Borrkärna_20110405 Description Location and description of drill core available at SGU’s Malå office Borrhål_20110405 Historical drill holes including Malå drill core and drill core no longer available at Malå Mineralresurser_mdep Location and description of mineralisation prospects, showings and deposits alteration_minerals Location and description of alteration type minerals Point database of location and basic description of mineralised boulders boulders_mineralized Ballast och industrial mineral Undersökningstillstånd_beviljade Mineralrättsregistret (MRR10) prospekteringsdata_ Bergsstaten undersökningstillstånd_beviljade Riksintressen mineral undersökningstillstånd FMIS_Norrbotten_L_ SWEREF_point FMIS_Norrbotten_L_ SWEREF_area Location and description of aggregate and industrial mineral sources Granted prospecting licence blocks (polygons) Polygons of metallic mineral resource blocks with current and past licence holders Polygons of exploration blocks with current and past licence holders Exploration permits granted Polygons covering areas with a state mineral interest Exploration permits Swedish national heritage board. Points of national interest Swedish national heritage board. Areas of national interest Coverage or location Covers mainly northern and southeastern Nautanen area (205 drill holes available in total) Covers mainly northern and southeastern Nautanen area (207 drill holes recorded in total) Location of 39 mineral prospects recorded (excludes Aitik and Liika­ vaara Östra to the south of key area) Northern and SE Nautanen key area Generally proximal to known prospects and deposits (likely reflects exploration activity) NE Nautanen area Western Allavaara area Nautanen key area Nautanen key area Nautanen key area Southern Nautanen area and Malnberget Nautanen key area Nautanen key area Nautanen key area with more prevalent phyllic-type (biotite-sericite) alteration (e.g. Jårbojoki and Puolalaki prospects south-east of the Nautanen area). Some 40 mineralised localities are recorded in SGU’s mineral deposits database (Mineralresurser_Mdep) for the Nautanen key area and its surroundings. The locations of these mineralised areas are shown in Figure 3. Several of the mineralised localities represent neighbouring prospects that can be grouped under a single deposit or prospect name (e.g. Nautanen deposit, consisting of Nautanen-Maria, Nautanen-Bratt areas etc.). Some additional datasets relevant to mineralisation and exploration are listed in Table 6. These data include GIS layers relating to drill hole locations, available drill core (at SGU’s Malå office), mineralised boulders and the ­status of exploration licences. The location of mineralised boulders and alteration minerals is shown in Figure 5. Gustafsson (1984) also presents information on mineralised boulders in the Nautanen area. Many of the boulder locations appear to cluster close to known Cu-Au prospects (cf. Figs. 3 and 5). This may reflect a greater level of geological mapping and prospecting activity in these areas. Alteration in the areas is dominated by potassic and sodic assemblages (K-feldspar, scapolite, albite). Tourmaline, epidote and sericite are also important alteration indicator minerals. 20 (40) 7468000 752000 756000 760000 764000 Latnijärvi Byxtjärn Nautanen Muorjevaara 7464000 Pienempi Petäjävaara Juoigamvárri Koskullskulle Pahtavaara Liikavaara Sarkasvaara 7460000 Sjungberget Sorvanen Rahavaara Rahajärvi Nunisvaara 7456000 Gällivare flygplats Haltiakoski Nunisjärvi Va Vassara sa äl raj ve ok n i älven Lina ajoki k Link Suorkkisuvanto Sakavaara Vasaravaara ki ojo Sakajärvi ip Le Liikavaara Sakajärvi Kaddivaara Mineralised boulder Carbonate Skarn assemblage Amphibole Sericite Tourmaline Epidote Skapolite Garnet 4 km Feldspar Figure 5. Bedrock map of the Nautanen area showing locations of key alteration minerals and sulphide-­ bearing boulders. In terms of exploration activity, the following companies have held historical exploration permits covering the Nautanen area: Teck Cominco Ltd, SGU, State Mining Property Commission (NSG), Golden Eagle Mines AB, Geoforum Scandinavia AB, Phelps Dodge Exploration Sweden AB, Boliden Mineral AB and North Atlantic Natural Resources AB. At present, Boliden Mineral AB (Nautanen and Liikavaara areas), LKAB (Malmberget area) and Norrbotten Exploration AB (Sjungberget area) hold exploration permits within and adjacent to the Nautanen key area. Geochemical data Table 7 lists several geochemical datasets available for the Nautanen area. 34 whole-rock geochemical analyses are available for several of the rock units in the area (Fig. 6). Many of these analyses were made as part of the 1:50 000-scale bedrock mapping programme (e.g. Witschard 21 (40) 1996). The analyses comprise major element oxide, trace element and rare earth element ­concentrations. Several additional studies within or adjacent to the Nautanen area have incorporated geochemical analyses of various rock units and mineral assemblages, with a particular focus on mineralisation processes. For example, Smith et al. (2013) conducted a fluid inclusion study on IOCG-type mineralisation across northern Norrbotten, which included several samples from mineralised localities within the NDZ. The results indicate that complex fluid flow regimes has operated in the area with fluids probably derived from several sources (e.g. magmatic, meta­somatic ± basinal brines). Sarlus (2013) investigated the genesis of the Salmijärvi Cu-Au prospect, located south-east of the Nautanen area. This study included whole-rock and mineral chemical analyses of rock units analogous to those within the Nautanen area. Wanhainen et al. (2012) present lithogeochemical and fluid inclusion data for the Aitik Cu-Au deposit, while McGimpsey (2010) presents lithogeochemical data for altered rock units at the Nautanen Cu-Au deposit. Tollefsen (2014) presents whole-rock (n = 21) and mineral chemistry data for rock units within and adjacent to the NDZ to constrain chemical and compositional variations during metasomatism. Additional lithogeochemical (major elements, selected trace elements) and assay data (typically Cu, Au and Ag) for several of the rock units at Nautanen are presented in many of the historical SGU, SGAB and NSG exploration reports compiled during the 1980’s (e.g. Ros 1980, Carlson 1982, Carlson 1984, Gustavsson & Johansson 1984, Danielsson 1985b, Gustafsson 1986b, c, e). These data typically represent down-hole analysis of altered and mineralised sections through several of the known Cu-Au deposits and prospects in the Nautanen area. The exploration reports are available as scanned versions of paper documents. However, the analytical data they contain are not at present available in digital format. Table 7. Geochemical datasets (for bedrock and overburden) covering the Nautanen area. Layer or dataset Description Location or coverage Litogeokemi, analysdata 34 lithogeochemical analyses of plutonic, metavolcanic and metasedimentary rocks. Consists of major, trace and rare earth elements. Point locations and descriptions of moraine samples used for till geochemistry analysis Raster dataset of shaded till geochemistry data for the elements Au, Cd, Co, Cr, Cu, Ni, Pb, V, Zn. Circular Cu anomalies in the NDZ Point locations of heavy mineral samples with analysis of 11 metal concentrations Point data from Nordkalotten moraine geochemistry dataset (NAA analysis method) Point data from Nordkalotten moraine geochemistry dataset (OES analysis method) Point data from Nordkalotten moraine geochemistry dataset (XRF analysis method) Various locations across Witschard 1996, the Nautanen area Perdahl & Frietsch 1993 Markgeokemi_ fysiska prov Markgeokemi, raster 250m Heavy mineral geochemistry till_geochem_NK_ naa till_geochem_NK_ oes till_geochem_NK_ xrf 22 (40) Reference Nautanen key area Ladenberger et al. 2009 Nautanen key area Ladenberger et al. 2009 Nautanen key area NE Nautanen key area NE Nautanen key area NE Nautanen key area Some lithogeochemical data for intrusive rocks is presented by Ahl et al. (2001). These workers provide a regional summary of lithogeochemistry of various intrusive rocks occurring across northern Sweden. The study includes analyses of Haparanda, Perthite monzonite and Lina suite granitoids similar to the intrusive rocks occurring around the Nautanen area. The majority of other geochemical analyses in the area relate to till geochemistry measurements determined as part of SGU’s regional till geochemistry programme (e.g. Ladenberger et al. 2009). Mapped anomalies of Cu, V and Zn represent the main geochemical anomalies in the area and probably reflect their elevated concentrations in the metavolcanics rocks. 7468000 Geochronology Table 8 lists the results of age dating in the Nautanen area while Figure 6 shows the location of the dating samples. Few geochronology studies have been made for the bedrock in or around 752000 756000 760000 764000 Latnijärvi Byxtjärn Nautanen 7464000 Muorjevaara 1785 1777 1777 +/-21 +/-20 +/-20 1785 +/-21 Pienempi Petäjävaara Juoigamvárri Koskullskulle Pahtavaara Liikavaara Sarkasvaara 7460000 Sjungberget Sorvanen Rahavaara Rahajärvi Nunisvaara Gällivare flygplats Haltiakoski älven Lina ajoki k Link 7456000 +/Nunisjärvi Va Vassara sa äl raj ve ok n i Suorkkisuvanto Sakavaara Vasaravaara ki ojo Sakajärvi ip Le Liikavaara Sakajärvi Kaddivaara Nautanen key area Lithogeocehmistry sample Mapped outcrop Bedrock observation Aitik Cu-Au-Ag deposit Hydrothermal age 4 km Figure 6. Geological map showing the location of age dating and lithogeochemistry samples at Nautanen. Historical bedrock observations by SGU are also plotted. 23 (40) Table 8. Geochronology for the Nautanen and surrounding areas. Age (Ma) 1777 ± System (method) U-Pb (LAICP-MS) U-Pb (LAICP-MS) Material Host rock Unit or suite Area Reference titanite & allanite titanite Schist Nautanen deposit Nautanen deposit Smith et al. 2009 Smith et al. 2009 19 U-Pb (LAICP-MS) titanite (core) Scapolite-altered unit (not clear) Altered metavolcanic rock Alteration assemblage linked to Lina-type magmatism Alteration assemblage linked to Lina-type magmatism 1785 21 2073 Porphyry group Storey et al. 2007 1920 23 U-Pb (LAICP-MS) titanite (rims) Altered metavolcanic rock Porphyry group 1708 20 U-Pb (LAICP-MS) titanite (rims) Altered metavolcanic rock Porphyry group 1583 10 U-Pb (LAICP-MS) apatite Altered metavolcanic rock Late thermal event at c. 1.6 Ga, or uplift/cooling age 1887 8 U-Pb zircon 1878 7 U-Pb (LAICP-MS) zircon Quartz monzo- Haparanda-PMS Suites diorite Porphyritic Porphyrite group metaandesite Malmberget deposit (hanging wall) Malmberget deposit (hanging wall) Malmberget deposit (hanging wall) Malmberget deposit (hanging wall) Aitik deposit 1875 10 1848 6 1848 8 Re-Os (TIMS) Re-Os (TIMS) Re-Os (TIMS) U-Pb (TIMS) molybdenite molybdenite molybdenite titanite 20 c. 1780 1776 8 U-Pb (TIMS) titanite 1728 7 1811 6 Re-Os molyb(TIMS) denite U-Pb (TIMS) zircon 1771 +7 –5 U-Pb (TIMS) titanite 1873 24 c. 1740 U-Pb U-Pb zircon monazite 1909 17 U-Pb (TIMS) zircon 1530 35 Rb-Sr wholerock Storey et al. 2007 Storey et al. 2007 Storey et al. 2007 Wanhainen et al. 2006 Tjårrojåkka Cu Edfelt et al. (c. 90 km NW 2006 of Nautanen) Barite vein Hydrothermal, HaparandaAitik deposit Wanhainen et PMS Suites al. 2005 Pegmatite dyke Jyryjoki granite and related Aitik deposit Wanhainen et magmatism al. 2005 Quartz vein Hydrothermal, Jyryjoki gran- Aitik deposit Wanhainen et ite and related magmatism al. 2005 Alteration asHydrothermal event, LinaAitik deposit Wanhainen et semblages type magmatism al. 2005 Metaandesite Alteration/metasomatic 8 km west of Wanhainen et event, Lina-type magmatism Aitik deposit al. 2005 pegmatite Lina suite Aitik deposit Wanhainen et dyke al. 2005 Granite Lina suite c. 35 km NW Bergman et al. of Nautanen 2002 area Granite Lina suite c. 35 km NW Bergman et al. of Nautanen 2002 area Monzodiorite Haparanda suite Aitik deposit Witschard Fracture fill Late-orogenic brittle deforMalmberget Romer 1996 (with silbite) mation, fluid flow deposit Porphyritic Porphyry group Close to Gälli- Skiöld & Cliff rhyodacite vare airport 1984 (part of mixed sample) Granite Lina suite c. 30 km NW Wilson and of Gällivare Sundin 1979 the study area. Thus, the absolute timing of the various magmatic, metamorphic, mineralisation and deformation events is poorly constrained. Table 8 includes age dating conducted at the neighbouring Aitik Cu-Au deposit, where most of the recent geochronology has been obtained. Smith et al. (2009) dated titanite and allanite grains from altered host rocks at the Nauta­ nen Cu-Au deposit (described as a deformed IOCG deposit). Two samples yielded ages of 1777 ± 20 and 1785 ± 21 Ma. These dates were interpreted to correspond to metamorphic and 24 (40) hydrothermal events coincident with late-orogenic deformation and Lina-type magmatism in the area. Storey et al. (2007) dated titanite grains from Porphyry group altered metavolcanic rocks from the hanging wall of the Malmberget iron deposit. In situ analysis of reworked titanite rims produced a spread of ages between c. 1920 and 1708 Ma that was interpreted to represent protracted hydrothermal-metasomatic processes. In situ analysis of the titanite cores yielded an age of 2073 ± 19 Ma at Malmberget. This age was interpreted to represent the first phase of regional metamorphism of the volcanic rocks. Thus, these workers proposed that the formational age of the host volcanic rocks to the Malmberget deposit is older than the regionally inferred age of c. 1.89 Ga (i.e. Svecofennian) and may be contemporaneous with intermediate volcanism assigned to the middle to upper Kiruna greenstone group. Several geochronology studies have been made at the Aitik Cu-Au deposit, just to the south of the Nautanen area. Wanhainen et al. (2005) conducted several analyses using U-Pb and Re-Os techniques that record a prolonged, 160 Ma period of overprinting magmatic and hydrothermal processes at Aitik. Molybdenite within a barite vein was dated at c. 1875 Ma and was inferred to represent hydrothermal processes associated with Haparanda or Perthite monzonite type magmatism. Molybdenite hosted within a pegmatite dyke and a quartz vein gave identical ages of c. 1848 Ma. These ages were linked to regional magmatic events represented by the Jyryjoki granite. Titanite and molybdenite ages between c. 1780 and 1728 Ma were interpreted to represent alteration and metasomatic processes associated with Lina-type granite magmatism. In an additional study, Wanhainen et al. (2006) produced a U-Pb zircon age of c. 1887 Ma for a quartz monzodiorite intrusion at the Aitik deposit. This age is similar to the c. 1873 Ma age shown on the 28K Gällivare SV bedrock map (Witschard 1996) determined for a monzonitic intrusion in the footwall of the Aitik deposit. However, analytical details relating to this latter date are not available. Bergman et al. (2002) determined a magmatic age of c. 1771 Ma for a Lina-type granite to the north-west of Nautanen using U-Pb dating of titanite. In the same study, a zircon population was dated at c. 1811 Ma. This latter result was interpreted to represent the age of inherited zircons within the granite. The ages in Table 8 presented by Skiöld & Cliff (1984) and Edfelt et al. (2006) represent ages of metavolcanic rocks to the north-west of the Nautanen area that are partly analogous to the metavolcanic sequence at Nautanen. These U-Pb dates (1909 Ma and 1878 Ma, respectively) are included here to provide some regional age constraint for the timing of volcanism at Nautanen (i.e. Svecofennian volcanism at c. 1.89 Ga). An older, imprecise and inaccurate Rb-Sr age for Lina-type granite is also listed in Table 8 for completeness (Wilson & Sundin 1979). Isotope geology (excluding age dating) There have been few dedicated tracer isotope studies (either radiogenic or stable isotopes) on rocks and minerals within the Nautanen area. As part of a broader fluid inclusion study, Gleeson & Smith (2009) used δ37Cl values to investigate the source of hydrothermal fluids associated with Cu-Au mineralisation in the NDZ. Measured δ37Cl values (ranging between +0.5‰ and –2.4‰) suggest that mineralising crustal fluids were derived from seawater, meta-evaporite horizons (i.e. surficial brines) or fluids exsolved from Lina-type granites that had assimilated a crustal δ37Cl signature within the melt (cf. Williams 2012). Wanhainen & Martinsson (2003) conducted a stable sulphur isotope (δ34S) study of sulphide and sulphate minerals from the Aitik Cu-Au deposit (just south of the Nautanen area). These data broadly indicate a single magmatic source of sulphur for main-stage mineralisation at Aitik, based on a narrow range of sulphide values that cluster around 0‰. The δ34S signature of sulphate min25 (40) erals (c. 10‰) indicates that sulphate sulphur may have been derived from an external source. The results are consistent with an earlier sulphur isotope study at Aitik by Yngström et al. (1986). Some lead isotope data for galena, sampled from the Muorjevare and Snålkok copper prospects and measured as part of a regional study, are presented in Billström et al. (1997). These data suggest that radiogenic lead in Norrbotten was remobilised during the Caledonian orogeny at c. 0.4 Ga). Geophysical data The following sections provide a summary of available geophysical data (e.g. magnetic, gravity, electromagnetic and petrophysic) covering the Nautanen key area. Airborne measurements Five airborne geophysical campaigns have been made over the Nautanen key area. A list of these measurements can be found in Table 9. In 1962, SGU conducted an airborne magnetic survey covering map sheet 28K Gällivare using a fluxgate magnetometer. In 1965, SGU conducted a smaller airborne magnetic survey mainly over the south-western part of the same map sheet. This survey coincides with the northern part of the Nautanen key area. In 1974, SGU conducted an airborne survey over map sheets 28K Gällivare SV and 27K Nattavaara NV, further to the south. This survey used a Trums magnetometer, a gamma-ray spectrometer and a VLF-receiver, capable of collecting data from one transmitter. In 1984, LKAB conducted an airborne geophysical survey over map sheets 28K Gällivare SV and SO. They acquired magnetic data along with slingram data, gamma-ray spectrometry and VLF data using two transmitters. However, the VLF data is incomplete along several flight lines, especially over the southern part of the Nautanen key area. This lack of information can be seen as white areas in the map which shows the apparent resistivity (Fig. 11). The last airborne survey was conducted by NAN (North Atlantic Natural Resources AB) in 1995 when they acquired magnetic data along the Nautanen shear zone, keeping the flight lines orthogonal to the main strike direction of the zone (i.e. north-north-east). A magnetic anomaly map over the Nautanen key area derived from airborne data is shown in Figure 7. Ground magnetic data Historical ground magnetic measurements have been made over most of the Nautanen key area. Table 10 lists information about these surveys. Magnetic maps showing the geographical extent and result of the ground magnetic measurements are presented in Figures 8 and 9. Table 9. Airborne geophysical surveys conducted over the Nautanen key area. Year 1962 1965 1974 1984 1995 26 (40) Company Geophysical methods Area used SGU Magnetics Entire 28K SGU Magnetics Parts of 28K SV and SO SGU Magnetics, gamma- Entire 28K SV and ray spectrometry, VLF parts of 27K NV (1-transmitter) LKAB Magnetics, gamma- Entire 28K SV and ray spectromSO (project R71) etry, slingram, VLF (2-transmitters) NAN Magnetics Along the Nautanen shear zone Flight direction East–west East–west Flight line separation (m) 200 200 Flight altitude (m) 30 30 East–west 200 30 East–west 200 30 60 degrees to the east 200 120 750000 755000 760000 765000 770000 7450000 7455000 7460000 7465000 7470000 7475000 745000 Anomaly (nT) 1446 703 434 278 174 102 50 6 –33 –69 –105 –140 –175 –213 –257 –312 –382 –468 –573 –735 –1072 Figure 7. Magnetic anomaly map (airborne data) covering the Nautanen key area (black polygon) and its surroundings. The magnetic data is expressed as the difference between measured data and an upward continuation to 1 km. Table 10. Magnetic ground surveys within the Nautanen key area. The numbers in column “Polygon nr” refer to those found in Fig. 8. Polygon nr Name Method Operator Year of measurement 1 2 3 4 5 6 7 Nautanen Liikavaara Ferrum Nautanen Nautanen Sorvanen Sakakoski Magnetometer Z-anomaly Magnetometer Magnetometer Magnetometer Z-anomaly Magnetometer Z-anomaly Magnetometer Magnetometer total field No information No information No information SGU SGU No information SGU 1968 1986 1984 1966–1967, 1978 1966–1967 1985 1987 27 (40) 755000 760000 765000 7455000 7460000 7465000 750000 Anomaly (nT) 1446 703 434 278 174 102 50 6 –33 –69 –105 –140 –175 –213 –257 –312 –382 –468 –573 –735 –1072 Figure 8. Airborne magnetic anomaly map of the Nautanen key area showing the geographical extent of existing ground magnetic measurements (red polygons). Explanations for the numbered polygons can be found in Table 10. Gravity data In general, the Nautanen key area has a good coverage of gravity measurements with less than 1 km between each measured gravity point (Fig. 10). However, in the central western part, the gravity measurement coverage is more sparse, with a station spacing of roughly 2.5 km. The majority of the gravity measurements within the Nautanen key area were acquired during the years 1967–1970. 28 (40) 755000 760000 765000 7455000 7460000 7465000 750000 Anomaly (nT) 1446 703 434 278 174 102 50 6 –33 –69 –105 –140 –175 –213 –257 –312 –382 –468 –573 –735 –1072 Figure 9. Magnetic anomaly map of the Nautanen key area showing ground magnetic measurements (higher resolution) overlain on the airborne magnetic data (coarser resolution). Geoelectric and electromagnetic data Most of the Nautanen key area is covered by ground slingram measurements. Several geoelectric surveys have also been done, primarily in the south-western part of the area. Table 11 lists information about the various geoelectric and electromagnetic surveys. Petrophysical data There are currently 241 petrophysical bedrock samples from the Nautanen key area (Fig. 12). Information on rock density, magnetic susceptibility and Königsberger ratio exist for these 29 (40) 755000 760000 765000 7455000 7460000 7465000 750000 Residual (mGal) 7 6 5 4 3 2 1 0 –1 –2 –3 –4 –5 Figure 10. The residual gravity field in the Nautanen key area, expressed as the difference between the ­Bouguer anomaly and an upward continuation to 3 km. Black dots represent gravity measurement stations. s­ amples. Some samples also have information on remnant magnetisation directions with respect to the Earth’s magnetic field. Topographical data Table 12 lists several topographic datasets covering the Nautanen area. The most useful information can be derived from orthophotos (both visible and infrared images) and LiDAR elevation data acquired at a height resolution of 50 m and 2 m. The map Vägkartan, produced by Lantmäteriet (Sweden’s topographic mapping agency), contains vector polygon height contours with a 10 m interval. The Nautanen area is not covered by the Terrängkartan topographic map series. 30 (40) Table 11. Summary of the geoelectric and electromagnetic ground surveys made within the Nautanen key area. The numbers in column “Polygon nr” refer to those found in Figure 11. Polygon nr 1 2 3 4 5 6 7 8 9 10 11 12 13 Name Nautanen Liikavaara Ferrum Liikavare statsgruvefält Sorvanen Liikavaara Sakakoski Liikavaara Liikavaara Sorvanen Liikavaara Liikavaara Sakakoski Method Slingram Slingram Slingram El. indikation Operator SGU SGU SGU No information Year of measurement 1967 1986 1984 No information Slingram Slingram Slingram IP, SP, resistivity IP, SP, resistivity IP, resistivity SP, resistivity IP IP, resistivity No information SGU SGAB No information SGU LKAB/SGU SGU SGU SGAB 1985 1940–1942 1987 1971 1970 1985 1971 1971 1985–1987 Table 12. Topographic datasets covering the Nautanen area. Layer or datset Indexrutor RT90 2,5 gon V Description RT90 map sheet index polygons Rutor_5x5_km RT90 map sheet index 5x5 km subdivision squares Översiktskartan 2007, Overview vector topographic map (small SWEREF99 TM scale) Vägkartan Overview vector topographic map (medium scale) Visningstjänst allmänna Overview raster topographic map (mekartor dium scale) Sverigekartan 1 milj. (2012) Overview vector topographic map (small scale) GSD-Höjddata, grid 2+ Raster LiDAR digital elevation model. Slope and aspect data also included. GSD-Höjddata, grid 50+ Raster LiDAR digital elevation model. Svenska Marktäckedata Sveriges landskap Visningstjänst ortofoton Vector dataset for landuse classification Swedish landskap administrative boundaries Raster layer of visible and near infrared orthophotography Scale 25 x 25 km squares 5 x 5 km squares Reference Lantmäteriet Lantmäteriet Lantmäteriet Lantmäteriet Lantmäteriet 1:1 000 000 Lantmäteriet 2 m height resolution 50 m height resolution Lantmäteriet Lantmäteriet Lantmäteriet Lantmäteriet Lantmäteriet GEOLOGICAL SUMMARY AND SOME REMAINING ISSUES The metamorphic rocks at Nautanen were assigned to the Porphyry group by Witschard (1996) as part of SGU’s 1:50 000-scale bedrock mapping programme (in part due to an abandonment of the original Porphyrite group subdivision proposed by Offerberg in 1967 for the Kiruna area). This lithostratigraphic unit, also known as the Kiirunavaara group or Kiruna porphyries (see Table 2 in Bergman et al. 2001), hosts economically important iron oxide-apatite deposits in the Kiruna and Malmberget areas. Subsequently, Bergman et al. (2000, 2001) reassessed the sequence for their 1:250 000-scale regional compilation and assigned the meta-volcano­ sediment­ary units in the Nautanen area to the stratigraphically lower Porphyrite group (thus 31 (40) 755000 760000 765000 7455000 7460000 7465000 750000 Apparent resistivity (ohmm) 4341 3916 3695 3547 3434 3336 3249 3167 3091 3018 2950 2883 2819 2754 2689 2618 2532 2432 2312 2121 1708 Figure 11. Apparent resistivity map over the Nautanen key area. The apparent resistivity is derived from airborne VLF data from two transmitters. The black polygons with hatches represent areas where ground electro­magnetic surveys have been made while the filled black polygons show the extent of previously made geoelectric surveys. Numbers correspond to those shown in Table 11. reinstating Offerberg’s subdivision). This assignment was largely based on lithological characteristics, geochemical properties and regional rock comparisons and distributions (cf. Martinsson & Perdahl 1995). In terms of the local stratigraphy, the rocks at Nautanen have been assigned to the Muorjevaara group and correlated with the volcanosedimentary rocks of the Sammakkovaara group in the Pajala area in north-eastern Norrbotten (Martinsson & Wanhainen 2004a). However, detailed accounts of the internal lithological, geochemical and structural characteristics of the Nautanen rock units, as well as their depositional and stratigraphic inter-relationships, are 32 (40) 755000 760000 765000 7455000 7460000 7465000 750000 Elevation (m) 488 459 441 425 414 397 383 371 360 349 339 329 319 312 306 301 297 295 291 286 270 Figure 12. Location of existing petrophysical bedrock samples from the Nautanen key area and surroundings. The background elevation model is based on LiDAR data (2x2 m resolution). presently not available. The absolute timing and duration of volcanism in the Nautanen area are also not known. Porphyrite group rocks are considered to have formed during regional-scale tectonic compression within a subduction zone setting at c. 1.90–1.87 Ga, with subduction directed towards the north-east (present-day coordinates). Volcanic rocks in the area typically have an intermediate (andesitic), calc-alkaline chemistry and display continental arc-type characteristics. More alkaline varieties also occur, however. This may reflect local tectonic or magmatic variations, or the effects of subsequent hydrothermal alteration (cf. McGimpsey 2010). The occurrence of 33 (40) epiclastic deposits in part suggests a relatively dynamic environment with an active depositionerosion-burial system. Two main intrusive suites occur in the Nautanen area: (1) Haparanda suite intrusive rocks, ranging from gabbro to monzodiorite and granodiorite, representing an older c. 1.90–1.87 Ga phase of subduction-related, calc-alkaline, syn-orogenic magmatism, and (2) Lina suite granitoids, representing a younger, 1.79–1.77 Ga phase of late- to post-orogenic, granitic magmatism. Detailed petrographic and geochemical data for these suites, as well as information on their degree of deformation and the relationship between the NDZ and intrusive magmatism in the area, is presently not available. Bergman et al. (2001) placed the rocks at Nautanen within their structural domain “H” and recognised the NDZ as a regionally significant deformation zone. Mylonitic fabrics, foliations, schistosity and alteration banding are generally sub-vertical and north-north-west orientated, coincident with the main trend of the deformation zone. An early phase of folding also affects the area, suggesting a prolonged deformational history. Detailed deformation and kinematic investigations along the length of the NDZ are presently lacking, although new investigations are ongoing (e.g. Bauer et al. 2014). Likewise, details about which structures are important for Cu-Au mineralisation are sill poorly constrained. In general, the study area has experienced multiple, overlapping metamorphic-metasomatic events during a prolonged deformational history (e.g. Wanhainen et al. 2005, Tollefsen 2014). The Nautanen area hosts numerous disseminated and vein-type Cu-Au occurrences which display some geological characteristics similar to the Cu-Au-Ag mineralisation at the Aitik d ­ eposit to the south. Like the intrusive rocks at Nautanen, two generations of copper mineralisation are recognised. An older phase is represented by the disseminated and semi-massive mineralisation within locally deformed lenses, and a younger phase associated with quartz-tourmaline veins. The following points identify some remaining tasks and unresolved geological questions for the Nautanen key area. Investigating some of these issues will help develop a more comprehensive understanding of the geological evolution of the area and establish regional lithological and stratigraphic correlations with other parts of Norrbotten. In addition, focused geological and geophysical investigations in the area will have positive implications for the development of local and regional metallogenic models and further our understanding of Cu-Au mineralising processes. • What are the geological characteristics of the various Cu-Au prospects in the Nautanen area and can a broader relationship with the Malmberget Fe-P and Aitik Cu-Au deposits be established? Since few modern deposit-scale investigations have been conducted in the Nautanen area (e.g. McGimpsey 2010), further investigations are needed on the Cu-Au mineralisation to establish possible genetic links with the nearby mineralisation at Malmberget and Aitik. Assessing the nature of the host rocks, structural controls on mineralisation, characterising mineralisation and alteration assemblages, and constraining the timing of Cu-Au mineralisation (single event, or multiple events driving metal remobilisation) should be a priority. • Do the two main intrusive suites in the Nautanen area (i.e., older Haparanda dioritoids, younger Lina granitoids) have a genetic link with stages of Cu-Au mineralisation? Petrographic descriptions, isotopic characteristics and age constraints for the Haparanda and Lina suite intrusions are required to better establish the intrusive history of the area and to identify temporal and genetic links between intrusive magmatism, deformation and Cu-Au mineralisation. • Is there a genetic link between the metasedimentary rocks in the Nautanen area (Muorje­ vaara group) and other locally or regionally occurring volcanic units? Can a link be established by geochemical and geochronological methods, or are the epiclastic rocks derived 34 (40) from a more external, distal source? An assessment of the internal lithological and stratigraphic characteristics of the Muorjevaara group rocks, including the establishment of a type locality, will help constrain the volcanic and sedimentary history of the Nautanen area. Lithogeochemical sampling and analysis will help ascertain the relative abundance of calc-alkaline versus alkaline rock types. New age dating, concentrating on samples from the base and top of the volcanosedimentary sequence, would help to establish regional correlations with other areas in Norrbotten and enable the assignment of the various rock units to their correct stratigraphical position. Furthermore, potential lithological controls on (older?) disseminated to strataform style Cu-Au mineralisation in the Nautanen area are not well documented. • What are the geological factors that determine the potential for Cu-Au mineralisation within analogous regional-scale deformation zones? The NDZ contains numerous epigenetic-type Cu-Au occurrences located in structurally favourable zones and hosted by Porphyrite group meta-volcanosedimentary rocks. Investigations of the rocks and structures in the NDZ provide an opportunity to compare and contrast this type of mineralisation setting with other key areas in Norrbotten. 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