The Nautanen deformation zone in the Gällivare area of northern Sweden is a highly Cu-mineralized, magnetite-rich, large-scale shear zone with a long-lived (~100 m.y.) deformation, hydrothermal alteration, and mineralization history. This composite structure hosts the Aitik porphyry Cu-Au-Ag ± Mo deposit and several Cu-Au ± Fe ± Ag ± Mo occurrences assigned to the iron oxide copper-gold (IOCG) deposit class. The Nautanen deformation zone was a locus for polyphase deformation and intermittent metasomatic-hydrothermal activity that overprinted middle Orosirian (ca. 1.90–1.88 Ga) continental arc-related volcanic-plutonic rocks. The deformation zone is characterized by intense shearing fabrics that form a series of subvertical to moderately W-dipping, NNW-SSE–trending, first-order shear zones with oblique reverse kinematics and related NNE-SSW–oriented second-order shear zones that control hydrothermal alteration patterns and Cu-Au mineralization.

Hydrothermal alteration in the study area formed during several phases. Volcanic-volcaniclastic rocks to the east and west of the Nautanen deformation zone display low to moderately intense, pervasive to selectively pervasive (i.e., patchy zones or bands, disseminations) sericite ± feldspar, amphibole + biotite + magnetite ± tourmaline, and K-feldspar + hematite alteration. Both the amphibole + biotite and K-feldspar + hematite associations occur adjacent to NNW- and NE-oriented deformation zones and are locally associated with minor sulfide. Within the deformation zone, a moderate to intense biotite + amphibole + garnet + magnetite + tourmaline + sericite alteration assemblage is typically associated with chalcopyrite + pyrrhotite + pyrite and forms linear and subparallel, mainly NNW-oriented seams, bands, and zones that locally appear to overprint possibly earlier scapolite + sericite ± feldspar alteration. Late-stage epidote ± quartz ± feldspar alteration (retrograde saussuritization) forms selectively pervasive zones and epidote veinlets across the area and is partly related to brittle faulting.

A magnetite-amphibole-biotite–rich, penetrative S₁ foliation records shortening during early Svecokarelian-related deformation (D₁) and can be related to ca. 1.88 to 1.87 Ga arc accretion processes and basin inversion that overlaps with regional peak metamorphism to near mid-amphibolite facies conditions and a potential initial Cu mineralization event. Folding and repeated shearing along the Nautanen deformation zone can be assigned to a second, late-Svecokarelian deformation event (D₂ stage, ca. 1.82–1.79 Ga) taking place at a higher crustal level. This D₂ deformation phase is related to late-stage accretionary processes active during a transition to a stage of postorogenic collapse, and it was accompanied by abundant, syntectonic intrusions. D₂-related magmatism produced high-temperature and low-pressure conditions and represents a regional magmatic-hydrothermal event that controlled the recrystallization/remobilization of magnetite, biotite, and amphibole. Associated shear zone reactivation during D₂ favors the utilization of the Nautanen deformation zone as a fluid conduit, which preferentially controlled the siting and formation of epigenetic Cu-Au mineralization with distinctive IOCG characteristics within second-order shear zones.

Potential field and Slingram data alongside rock physical properties, drill‐core information and results from geological field mapping were used to investigate the geometry of the geological structures in the Gällivare area in regional scale. The main purpose of this study was to delineate the vertical and lateral extension of the Malmberget felsic volcanic rocks, the Dundret and Vassaravaara units as well as geological structures related to the crustal‐scale Nautanen deformation zone. Furthermore, we aimed at identifying new magnetite‐hematite and sulphide mineralizations and lithologies related to the mineralizations based on the results from regional‐scale potential field modelling which are delineated with rock physical properties and borehole data. The study result indicated that the dome‐shaped Dundret gabbro extends downwards to ∼4 km depth and has its maximum depth at its centre. Hematite and magnetite assemblages occur within the top 2 km of the Dundret complex. Felsic volcanic rocks in the Malmberget area extend vertically down to a maximum depth of ∼3 km and get considerably thinner towards the west. The model for the known magnetite‐rich mineralizations in Malmberget was inferred from earlier drilling activities and was integrated into the profile models, which indicates a reasonable fit to the measured data, in particular on the magnetic anomaly; whereas the small dimensions of the modelled structures make them invisible on the Bouguer anomaly data. Additional magnetite‐rich mineralizations are suggested within the Malmberget felsic rocks. High real component and low imaginary response of the Slingram data suggests conductive zones within the Nautanen deformation zone towards the NE, which given the geology of the area in the high strain zone can indicate disseminated sulphide mineralizations. Drill‐hole data at the eastern parts of W‐E profiles agreed well with the suggested model inferred from potential field data, suggesting presence of mafic intrusions within the ∼top 1 km of the subsurface. The integrated model based on geophysical, petrophysical and geological data improved earlier understanding about the regional geometry of the key structures in the Gällivare area and indicates new magnetite‐rich and sulphide mineralization prospects which can be used as a guide for future exploration activities in the area.

The northern Norrbotten region in Sweden hosts abundant iron-oxide apatite (IOA) deposits including Kiirunavaara, the type locality for Kiruna-type deposits, and Malmberget. Felsic and intermediate metavolcanic rocks hosting the Malmberget IOA deposit contain oscillatory zoned zircon which yield magmatic U-Pb SIMS ages of 1885±6 Ma and 1881±6 Ma, respectively. Metamorphic rims on zircon from these rocks yield 1797±7 Ma and 1775±6 Ma, respectively, and record the age of the latest Svecofennian regional metamorphic event in the Gällivare area, tentatively interpreted as regional contact metamorphism. Two granite dikes that cut the ore yield U-Pb zircon emplacement ages of 1790±6 Ma and 1791±7 Ma, respectively, overlapping with the metamorphic overgrowths, and set a lower age limit for ore formation in the Malmberget IOA deposit. Rocks hosting the Malmberget IOA deposit have an alkalic to alkali-calcic affinity with a geochemical signature that favors a continental-arc, transitional to extensional setting. These rocks are suggested to have been generated in a back-arc region, in response to subduction beneath the craton margin retreating to the SW or W. The obtained ages and geochemical signatures of these rocks coincide well with the regionally defined Kiirunavaara group rocks, hosting several other IOA deposits in northern Sweden.

Petrographical and lithogeochemical investigations in combination with mapping in the Gällivare area, northern Norrbotten, Sweden, have led to the identification of several igneous intrusive rock types. These include: (1) ultramafic-mafic complexes, (2) mafic-intermediate rocks, (3) dolerites and (4) felsic plutons. The ultramafic-mafic rocks include the ca. 1.88 Ga Dundret complex and ca. 1.80 Ga Vassaravaara complex. The Dundret complex has tholeiitic to calc-alkaline affinity, shows a primitive mineral content and was formed in an extensional tectonic setting. The Vassaravaara complex has a similar chemical signature as the Dundret complex. The mafic-intermediate plutons vary in composition from gabbro to diorite. The chemical signature of the dioritic rocks indicate formation in a volcanic arc setting. Dolerites occur as solitary dikes and have calc-alkaline affinity. The felsic plutons include granite and syenite of ca. 1.88, 1.80 and 1.78 Ga age. The felsic plutons have calc-alkaline to shoshonitic affinity and mostly show a metaluminous I-type character. Results indicate subduction at 1.90 Ga resulting in a volcanic arc system, and including extensional events generating back-arc environments leading to mafic, intermediate and felsic magmatism in the Gällivare area. Subduction at 1.80 Ga is suggested to have caused a similar process generating mafic and felsic magmatic rocks in the same area. A subsequent collision event finally generated 1.78 Ga granitic rocks.

The Malmberget iron oxide-apatite (IOA) deposit in northern Sweden is one of the largest underground iron ore mine operations in the world with estimated ore reserves in 2015 of 346 million metric tons (Mt) at 42.5% Fe. The underground operation is concentrated in 10 orebodies of 5 to 245 Mt each, which currently produce 17.4 Mt of apatite iron ore per year. Structural investigations were combined with data on hydrothermal mineral assemblages in order to reconstruct the relative timing of ore-forming, deformation, and overprinting hydrothermal events. The results improve the understanding of structural geometries, relationships, and control on orebody transposition in the deposit. A first compressional event (D1) around 1.88 Ga represents the main metamorphic event (M1) in the area and was responsible for a strong transposition of potential primary layering and the orebodies and led to the formation of a composite S0/1 fabric. A subsequent F2 folding event around 1.80 Ga resulted in the formation of an open, slightly asymmetric synform with a steeper southeast limb and a roughly SW-plunging fold axis. The result of structural modeling implies that the ore formed at two separate horizons. The folding was accompanied by stretching, resulting in boudinage of the iron orebodies. D2-related high-strain zones and syntectonic granites triggered the remobilization of amphibole, biotite, magnetite, and hematite and controlled the formation of iron oxide-copper-gold (IOCG)-type hydrothermal alteration, including an extensive K-feldspar alteration accompanied with sulfides, scapolite, and epidote. This shows a distinct time gap of at least 80 m.y. between the formation of iron oxides and sulfides. Brittle structures and the lack of an axial planar parallel fabric in conjunction with previous results suggest upper crustal, low-pressure, and high-temperature conditions during this D2 deformation phase, indicating a hydrothermal event rather than a purely regional metamorphic compression. It is proposed in the present study that the Malmberget IOA deposit was deformed and metamorphosed during a 1.88 Ga crustal shortening event. Moreover, the Malmberget IOA deposit was affected by a 1.8 Ga folding and hydrothermal event that is related to a regional IOCG overprint.

The Gällivare area is one of Europe’s top mining regions. The area is located in the northern Norrbotten ore district which hosts ore deposits such as the Malmberget underground iron ore mine, the Aitik open pit Cu-Au mine and the currently explored Nautanen Cu-Au deposit. In addition, several small, mineralized bodies are found. These deposits are hosted by volcanic and volcanosedimentary rocks intruded by intrusive rocks. Previous studies of intrusive and volcanic rocks have often been of local scale and restricted to the major deposits, or of regional scale including entire northern Norrbotten. Minor attention has been paid to rocks of the Gällivare area on a semi-regional scale, especially the intrusive rocks. Very few studies have presented radiometric data of the intrusive and volcanic rocks. In addition, the choice of radiometric method or the re-sults have been lacking confidence. A multidisciplinary approach combining structural geology, geochemistry, geochronology and geophysics is commenced to understand the geological history, crustal geometries and geological evolution of the Gällivare area. This forms basis for future exploration of ore deposits. This study presents geochemical, geochronological and Hf-isotope results with the purpose to characterize and classify major intrusive and volcanic rocks, their timing, source magmas and tectonic environment.

Petrographical and geochemical investigations reveal that the intrusive rocks range in composition from ultramafic-mafic to felsic. The ultramafic-mafic rocks comprise dominantly gabbroic layered complexes with peridotitic sequences and have tholeiitic to calc-alkaline affinity. The intermediate and felsic intrusive rocks show calc-alkaline to shoshonitic affinity. Volcanic rocks of the Malmberget deposit show alkali to alkali-calcic character. The geochemical character of the intrusive and volcanic rocks favors a continental arc, transitional to extensional setting (late- to post-collisional).

Radiometric in situ U-Pb zircon analyses indicate that mafic and felsic intrusive rocks were generated during magmatic episodes at 1.88, 1.80 Ga and 1.78 Ga. Volcanic rocks hosting the Malmberget deposit belong to the 1.88 Ga magmatic episode. Hydrothermal overgrowth rims from the analyzed zircon crystals indicate extensive reworking and high-T metamorphism of the area around 1.81-1.78 Ga.

The mafic-intermediate rocks show minor internal variations in Hf-isotopic signature as well as minor variations inbetween the samples indicative of relatively homogenous source regions beneath the Archean basement. The felsic rocks show a wider range in their Hf-isotopic signature suggesting multiple sources with contribution from old Archean crust.

It is here suggested that a subduction process active at 1.9 Ga resulted in a volcanic arc system and ex-tensional environments (back-arc environments) leading to mafic, intermediate and felsic magmatism in the Gällivare area at 1.88 Ga. The mafic-intermediate rocks were extracted from a rather homogenous source reservoir. The c. 1.80 Ga and 1.78 Ga intrusive rocks indicate a complex tectonic evolution of the area at that time. The early 1.80 Ga mafic rocks are suggested to have been generated as a result of extensional magmatism related to an east-directed 1.80 Ga subduction system. Subsequent compression followed by uplift, resulted in the generation of 1.78 Ga felsic rocks.

Zircon ion probe (secondary-ion mass spectrometry or SIMS) data from a set of intrusive rocks emplaced in the vicinity of major ore bodies, as well as from large igneous intrusions in the Gällivare area, gave the following results: (1) the Dundret ultramafic–mafic layered complex (1883±5 Ma), the Aitik granite (1883±5 Ma), the Nautanen diorite (1870±12 Ma), the Vassaravaara ultramafic–mafic layered complex (1798±4 Ma), the Aitik dolerite (1813±9 Ma), the Bergmästergruvan and Sikträsk syenites (1795±4 Ma and 1801±3 Ma, respectively) and the Naalojärvi granite (1782±5 Ma). These data broadly fall within the ranges 1.89–1.87 Ga (early Svecofennian) and 1.80–1.78 Ga (late Svecofennian), but geochronologically allow further subdivision into pulses at 1885–1880, 1875–1870, 1800 and 1780 Ma. During these events, large layered ultramafic–mafic and felsic plutonic rocks were generated with distinct overlap in time suggesting coeval felsic–mafic magmatism. Results also indicate the presence of inherited c. 1.87 Ga zircon crystals in the plutonic rocks at 1.78 Ga, supporting reworking of the previous crust. These data indicate the importance of mantle-derived mafic underplating in the process of crustal magma generation in the region. The c. 1.88 Ga event that generated ultramafic–mafic layered complexes is tentatively suggested to have played an important role in the formation of the Aitik Cu–Au porphyry system. The later event at c. 1.80 Ga, generating voluminous mafic–felsic units, is suggested to be coupled to the regional iron-oxide-copper-gold (IOCG) overprint.

Host felsic and intermediate meta-volcanic rocks to the Malmberget apatite iron ore (AlO) deposit have been investigated geochemically and geochronologically, the latter using the U-Pb method on a set of zircons. Results indicate emplacement age of 1.9 Ga for the felsic and intermediate volcanic rocks, potentially in an extensional environment. The zircon U-Pb radiometric ages are among the first conclusive ages with implicit constraint on the geological evolution of the northern Norrbotten ore district and Malmberget deposit.

The Gällivare area is situated in northern Norrbotten, Sweden, and hosts the Aitik Cu-Au deposit and the Malmberget Fe deposit. In addition, more than 17 mineral prospects and mineralizations are present, among these the currently developed Nautanen Cu-Au deposit. All deposits are hosted within Paleoproterozoic volcanic and volcano-sedimentary successions intruded and surrounded by multiple generations of intrusive suites, including large bodies of ultramafic to mafic layered complexes. Detailed field mapping combined with geochemical and petrological investigations and geochronology have revealed suites of igneous rocks ranging in composition from ultramafic-mafic, intermediate to felsic. Main key igneous rocks include 1) tholeiitic, ultramafic-mafic layered intrusive complexes; 2) calc-alkaline mafic to intermediate plutonic and volcanic units; 3) calc-alkaline, mafic-intermediate dykes and sills; 4) calc-alkaline and shoshonitic granitoids. U-Pb multigrain zircon SIMS analysis combined with lithogeochemical investigations suggest two magmatic episodes at 1.88 and 1.80 Ga, respectively, with coeval mafic-felsic magmatism including the generation of voluminous layered complexes. Based on their MORB-type, tholeiitic character, these layered complexes are suggested to have formed in an extensional setting, preferentially in a back-arc environment. U-Pb multigrain zircon SIMS analysis and field mapping also reveal that granitoids in the area range from 1886 to 1779 Ma with the oldest granitoids containing mafic enclaves. This suggests magma interaction between basic and felsic magma sources. Geochemical data suggest generation of granitoids in a volcanic arc environment in a mainly post-collisional setting. Results suggest the formation of layered complexes and a volcanic arc system in an extensional setting followed by a subsequent compressional phase of arc accretion producing post-collisional granitoids. The 1.88 Ga event that generated the ultramafic-mafic layered complexes is associated with a back-arc setting generated in response to 1.90 Ga NNE trending subduction. The later event at ~1.80 Ga generating voluminous mafic-felsic units is associated with the TIB event which is also coupled to the regional IOCG overprint.

The Gällivare area is situated in northern Norrbotten, Sweden, and hosts the Aitik Cu-Au deposit and the Malmberget Fe deposit. In addition, more than 17 mineral prospects and mineralizations are present, among these the currently developed Nautanen Cu-Au deposit. All deposits are hosted within Paleoproterozoic volcanic and volcano-sedimentary successions intruded and surrounded by multiple generations of intrusive suites, including large bodies of ultramafic to mafic layered complexes. Detailed field mapping combined with geochemical and petrological investigations and geochronology have revealed the role of intrusive igneous events and their control on ore formation. Main key igneous rocks include 1) tholeiitic, ultramafic-mafic layered intrusive complexes; 2) calc-alkaline mafic to intermediate plutonic and volcanic units; 3) calc-alkaline, mafic-intermediate dykes and sills; 4) calc-alkaline and shoshonitic granitoids. U-Pb multigrain zircon SIMS analysis combined with litho-geochemical investigations suggest two magmatic episodes at 1.88 and 1.80 Ga, respectively, with coeval mafic-felsic magmatism including the generation of voluminous layered complexes. Based on their MORB-type, tholeiitic character, these layered complexes are suggested to have formed in an extensional setting, preferentially in a back-arc environment. U-Pb multigrain zircon SIMS analysis and field mapping also reveal that granitoids in the area range from 1886 to 1779 Ma with the oldest granitoids containing mafic enclaves. This suggests magma interaction between basic and felsic magma sources. Geochemical data suggest generation of granitoids in a volcanic arc environment in a mainly post-collisional setting. Results suggest the formation of layered complexes and a volcanic arc system in an extensional setting followed by a subsequent compressional phase of arc accretion producing post-collisional granitoids. The 1.88 Ga event that generated the ultramafic-mafic layered complexes is is associated with a back-arc setting generated in response to 1.90 Ga NNE trending subduction. The later event at ~1.80 Ga generating voluminous mafic-felsic units is associated with the TIB event also coupled to the regional IOCG overprint.

Geochemical investigations were carried out in the Gallivare area as a part of a larger project aiming to understand the crustal architecture of the region in 3D. Major igneous suites such as the Dundret and Vassaravaara intrusions with additional smaller mafic intrusions have been identified as key localities and investigated. Results indicate two distinct rock units. The first suite is assigned to ultramafic-mafic layered intrusions with a calc-alkaline to a more tholeiitic composition belonging to the Dundret and Vassaravaara intrusions. The second suite is mainly of mafic to intermediate composition with a clear ophitic texture. This paper investigate the source and origin of the key rock suites, playing a major role on the evolution of the Gallivare region, a region which is characterized by porphyry Cu, IOCG, and Al0 deposits including some of Europe's top producing Fe and Cu-Au-Ag (-Mo) mines.