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  • 1.
    Aiglsperger, Thomas
    et al.
    Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona .
    Proenza, Joaquín A.
    Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona .
    Lewis, John F.
    Department of Earth and Environmental Sciences, George Washington University, .
    Labrador, Manuel
    Departament de Cristal·lografia, Mineralogia i Dipòsits Minerals, Universitat de Barcelona.
    Svojtka, Martin
    Institute of Geology, Academy of Sciences.
    Rojas-Purón, Arturo
    Departamento de Geología, Instituto Superior Minero Metalúrgico de Moa.
    Longo, Francisco
    Falcondo Glencore Nickel.
    Ďurišová, Jana
    Institute of Geology, Academy of Sciences.
    Critical metals (REE, Sc, PGE) in Ni laterites from Cuba and the Dominican Republic2016In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 73, p. 127-147Article in journal (Refereed)
    Abstract [en]

    Ni laterites are considered worthy targets for critical metals (CM) exploration as Rare Earth Elements (REE), Sc and platinum group elements (PGE) can be concentrated during weathering as a result of residual and secondary enrichment. In this contribution geochemical and mineralogical data of CM from two different nickel laterite types (i) from the Moa Bay mining area in Cuba (oxide type) and (ii) from the Falcondo mining area in the Dominican Republic (hydrous Mg silicate type) are presented. Emphasis is given on examining their potential to accumulate CM and on processes involved. Results show that CM are concentrated towards the surface in specific zones: (i) REE in clay minerals rich horizons and within zones composed of secondary Mn oxide(s), (ii) Sc within zones rich in secondary Fe and Mn bearing oxide(s) and (iii) PGE in zones with high concentrations of residual chromian spinel and secondary Fe and Mn bearing oxide(s) at upper levels of the Ni laterite profiles. Concentration factors involve (i) residual enrichment by intense weathering, (ii) mobilization of CM during changing Eh and pH conditions with subsequent reprecipitation at favourable geochemical barriers and (iii) interactions between biosphere and limonitic soils at highest levels of the profile (critical zone) with involved neoformation processes. Total contents of CM in both Ni laterite types are low when compared with conventional CM ore deposits but are of economic significance as CM have to be seen as cost inexpensive by-products during the Ni (+ Co) production. Innovative extraction methods currently under development are believed to boost the significance of Ni laterites as future unconventional CM ore deposits.

  • 2.
    Bark, Glenn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geodynamic settings for Paleoproterozoic gold mineralization in the Svecofennian domain: a tectonic model for the Fäboliden orogenic gold deposit, northern Sweden2012In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 48, p. 403-412Article in journal (Refereed)
    Abstract [en]

    Northern Sweden is currently experiencing active exploration within a new gold ore province, the so called Gold Line, situated southwest of the well-known Skellefte VMS District. The largest known deposit in the Gold Line is the hypozonal Fäboliden orogenic gold deposit. Mineralization at Fäboliden is hosted by arsenopyrite-rich quartz veins, in a reverse, mainly dip-slip, high-angle shear zone, in amphibolite facies supracrustal host rocks. The timing of mineralization is estimated, from field relationships, at ca. 1.8 Ga.The gold mineralization is hosted by two sets of mineralized quartz veins, one steep fault-fill vein set and one relatively flat-lying extensional vein set. Ore shoots occur at the intersections between the two vein sets, and both sets could have been generated from the same stress field, during the late stages of the Svecofennian orogen.The tectonic evolution during the 1.9–1.8 Ga Svecofennian orogen is complex, as features typical of both internal and external orogens are indicated. The similarity in geodynamic setting between the contemporary Svecofennian and Trans-Hudson orogens indicate a potential for world-class orogenic gold provinces also in the Svecofennian domain.The Swedish deposits discussed in this paper are all structurally associated with roughly N-S striking shear zones that were active at around 1.8 Ga, when gold-bearing fluids infiltrated structures related to conditions of E-W shortening.

  • 3.
    Bark, Glenn
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weihed, Pär
    Orogenic gold in the new Lycksele-Storuman ore province, northern Sweden: the Palaeoproterozoic Fäboliden deposit2007In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 32, no 1-2, p. 431-451Article in journal (Refereed)
    Abstract [en]

    Southwest of the well-known Skellefte District, northern Sweden, a new gold ore province, the so called Gold Line, is presently being explored. During the past decade a number of gold occurrences have been discovered in this area. The largest known gold occurrence is the Fäboliden deposit. Late-to post-orogenic, ca. 1.81 to 1.77 Ga, Revsund granite constitutes the main rock type in the Fäboliden area and surrounds a narrow belt of mineralized metagreywackes and metavolcanic rocks. The supracrustal rocks are strongly deformed within a roughly N-S trending subvertical shear zone. The mineralization constitutes a 30 to 50 m wide, N-S striking, steeply dipping zone. The mineralization is commonly hosted by arsenopyrite-bearing quartz-veins within the supracrustal rocks. The quartz veins parallel the main foliation in the shear zone. Gold is closely associated with arsenopyrite-löllingite and stibnite and found in fractures and as intergrowths in the arsenopyrite-löllingite. Gold is also seen as free grains in the silicate matrix of the host rock. The proximal alteration zone displays positive correlation with Ca, S, As, Ag, Sb, Sn, W, Pb, Bi, Cd, Se, and Hg, whereas K and Na show a slightly negative correlation. The hydrothermal mineral assemblage in the proximal alteration zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. This type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide. Garnet-biotite geothermometry indicates amphibolite facies in the Fäboliden area. The ductile fabric that hosts the mineralization is also found in the margin of the surrounding Revsund granitoid. It is therefore suggested that at least the final stages of the gold mineralization are syn- to late-kinematic, and the minimum age for the mineralization is thus constrained at ca. 1.80 Ga (Revsund age).

  • 4. Edfelt, Åsa
    et al.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Fennoscandian Shield: iron oxide-copper-gold deposits. Tjårrojåkka, northern Sweden: Lat 67° 40′ N, Long. 19° 10′ E2005In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 27, no 1-4, p. 328-329Article in journal (Refereed)
  • 5.
    Eilu, Pasi
    et al.
    Geological Survey of Finland.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Fennoscandian Shield: Orogenic gold deposits2005In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 27, no 1-4, p. 326-327Article in journal (Refereed)
  • 6.
    Frietsch, Rudyard
    et al.
    Luleå tekniska universitet.
    Perdahl, Jan-Anders
    Luleå tekniska universitet.
    Rare earth elements in apatite and magnetite in Kiruna-type iron ores and some other iron ore types1995In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 9, no 6, p. 489-510Article in journal (Refereed)
    Abstract [en]

    An investigation has been conducted to determine the content and distribution of REE in apatite and magnetite in the iron ores of Kiruna type and some other iron ores. The purpose of this article is to discuss the results obtained from the investigation. In particular, it will be shown that REE in apatite and magnetite in different ore types exhibit characteristic patterns related to different modes of formation of the ores

  • 7.
    Frietsch, Rudyard
    et al.
    Luleå tekniska universitet.
    Tuisku, Pekka
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Perdahl, Jan-Anders
    Luleå tekniska universitet.
    Early Proterozoic Cu-(Au) and Fe ore deposits associated with regional Na-Cl metasomatism in northern Fennoscandia1997In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 12, no 1, p. 1-34Article in journal (Refereed)
    Abstract [en]

    Scapolite is widely distributed in 1.9-2.5 Ga volcano-sedimentary rocks and 1.77-2.2 Ga igneous rocks over several hundred square kilometres in northern Fennoscandia, comprising northern Sweden, northern Finland and adjacent parts of Norway and Russia. This region is one of the largest scapolite-bearing Precambrian terranes in the world. Albitization, and to a lesser extent carbonatization, phyllic and tourmaline alteration, are spatially associated with scapolite. A number of epigenetic Cu-(Au) sulphide and Fe oxide deposits in northern Fennoscandia show a spatial and genetic relationship to this type of alteration, mainly scapolitization and albitization. The main metal occurrences are in 2.0-2.5 Ga mafic volcanics and sediments of the Lapponian Greenstone group and in 1.9 Ga intermediate-composition volcanic and volcaniclastic rocks of the Svecofennian Porphyry group. The scapolite is mainly a dipyre-mizzonite with Cl and CO3 and small amounts of SO4 and F, indicating high Na and Cl activity at the time of crystallization. Fluid inclusion data of the Lapponian Pahtohavare and similar Cu-Au deposits indicate formation temperatures of about 300°C and ore deposition from highly saline aqueous solutions. The deposition of copper and gold was in places regulated by a redox barrier; graphite in associated schists controlled the reduction reactions of the ore fluids and metals were precipitated. The Lapponian and Svecofennian sulphide deposits contain tourmaline of the schorl-dravite series. Aitik-Nautanen Cu-(Au) style deposits and in particular some deposits with vein-style iron ore, contain dravite-schorl deficient in Al and enriched in Fe3+, which is due to Fe-Al substitution in an oxidizing, relatively iron-rich environment. Scapolite and, probably also tourmaline, formed by a complex, multistage process. The source of the components in scapolite may have been evaporitic sequences or high salinity brines in Lapponian rift basins that contain 2.0-2.5 Ga mafic volcanics. During low to medium-grade (low P) regional metamorphism, the components that formed scapolite and tourmaline were mobilized and transported to their present positions in several metasomatic phases. Fault zones with fractures and breccias channeled the fluids, resulting in locally developed intense alteration. Gold and copper was transported by saline, high fO2, high temperature solutions as metal-chloride complexes. The ultimate source of fluids and heat sources is uncertain, but deep-seated crustal magmatic processes seem prerequisite. The alteration occurred mainly around 1.9 Ga at the peak of the main regional metamorphism and the intrusion of granitoids through to around 1.8 Ga. Cu-(Au) sulphide and Fe oxide ore deposits associated with large-scale scapolite-forming metasomatic processes are found elsewhere in the world (e.g., Australia, Kazakhstan, Russia) and show similarities with the Cu-(Au) deposits in northern Fennoscandia. However, the close genetic connection between scapolite-albite and ore formation of Fennoscandian deposits is not a common feature in other belts

  • 8.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Multistage ore formation at the Ryllshyttan marble and skarn-hosted Zn-Pb-Ag-(Cu) + magnetite deposit, Bergslagen, Sweden2015In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 69, p. 217-242Article in journal (Refereed)
    Abstract [en]

    Numerous magnetite skarn deposits and marble- and skarn-hosted base metal sulphide deposits occur in polydeformed and metamorphosed, felsic-dominated metavolcanic inliers in the Palaeoproterozoic Bergslagen region of south-central Sweden, including the Ryllshyttan magnetite and Zn-Pb-Ag-(Cu) sulphide deposit, approximately 2.5 km SW of the large Garpenberg Zn-Pb-Ag-(Cu-Au) deposit. The Ryllshyttan deposit, from which approximately 1 Mt of Zn-rich massive sulphide ore and 0.2 Mt of semi-massive magnetite were extracted, is located near a transition between magnesian skarn and dolomitic marble. The host unit consists of a 10-20 m-thick former calcitic limestone of likely stromatolitic origin that is commonly pervasively altered to skarn, locally hosting magnetite skarn deposits. The ore-bearing unit is one of several mineralised marble units within a more than 1 km-thick, felsic-dominated metavolcanic succession that includes a metamorphosed, large caldera-fill pyroclastic deposit, 800 m stratigraphically above the Ryllshyttan host succession. The Garpenberg stratabound Zn-Pb-Ag-(Cu)-(Au) deposit is located higher in the stratigraphy, just below the caldera fill deposits. The metavolcanic succession is bounded to the NW by a large granitoid batholith and intruded by a microgranodiorite pluton less than a 100 m from the Ryllshyttan deposit. Magnetite laminae in bedded skarns and metavolcanic rocks in the hanging wall of Ryllshyttan indicate an early (syngenetic) accumulation of Fe-rich exhalites. In contrast, the sulphide mineralisation consists of stratabound replacement-style ore associated with dolomitisation of the host and with discordant K-Mg-Fe±Si alteration of volcanic rocks and early porphyritic intrusions in the footwall and hanging wall. The microgranodiorite that intrudes the host succession crosscuts the K-Mg-Fe±Si alteration envelope and is overprinted by Na-Ca alteration (diopside and plagioclase-bearing mineral associations) that also overprints K-Mg-Fe±Si-altered rocks. The Na-Ca alteration is interpreted to be associated with the formation of calcic and magnesian iron skarn deposits semi-regionally at a similar stratigraphic position. Despite superimposed amphibolite facies regional metamorphism and substantial syn-D2-D3 remobilisation of sulphides concurrent with retrograde alteration of skarn assemblages, cross-cutting field relationships indicate that the Ryllshyttan magnetite and Zn-Pb-Ag-(Cu) sulphide deposit results from protracted VMS-style hydrothermal activity including early seafloor mineralisation (Fe-rich exhalites), closely followed by sub-seafloor carbonate-replacement-style mineralisation (base metal-bearing massive sulphides). Both mineralisation styles were overprinted by contact metasomatism associated with the formation of abundant magnetite skarn deposits during the emplacement of granitoid intrusions. As for other deposits in the Bergslagen region, the ore-forming system at Ryllshyttan thus has similarities to both metamorphosed VMS deposits and metasomatic Fe and Zn skarn deposits. Our results suggest that the sequence of volcanic, intrusive and hydrothermal events in this region is compatible with prograde heating of a long-lived hydrothermal system, wherein a shift from a convective seawater-dominated system to a contact metamorphic and/or metasomatic environment occurred during the early stage of the 1.9-1.8 Ga Svecokarelian orogeny. This model partly resolves the controversy regarding genesis of the iron oxide and base metal sulphide deposits in Bergslagen, as we recognise that these deposits have a complex history of alteration, metamorphism, deformation and (re)mobilisation, and no unique established genetic model can account for all their features.

  • 9.
    Jansson, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Zetterqvist, Anders
    Zetterqvist Geokonsult AB.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Billström, Kjell
    Swedish Museum of Natural History.
    Malmström, Lars
    Zinkgruvan Mining AB.
    Genesis of the Zinkgruvan stratiform Zn-Pb-Ag deposit and associated dolomite-hosted Cu ore, Bergslagen, Sweden2016In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 82, p. 285-308Article in journal (Refereed)
    Abstract [en]

    Zinkgruvan, a major stratiform Zn-Pb-Ag deposit in the Paleoproterozoic Bergslagen region, south-central Sweden, was overprinted by polyphase ductile deformation and high-grade metamorphism (including partial melting of the host succession) during the 1.9-1.8 Ga Svecokarelian orogeny. This complex history of post-ore modification has made classification of the deposit difficult. General consensus exists on a syngenetic-exhalative origin, yet the deposit has been variably classified as a volcanogenic massive sulfide (VMS) deposit, a sediment-hosted Zn (SEDEX) deposit, and a Broken Hill-type (BHT) deposit. Since 2010, stratabound, cobaltiferous and nickeliferous Cu ore, comprising schlieren and impregnations of Cu, Co and Ni sulfide minerals in dolomitic marble, is mined from the stratigraphic footwall to the stratiform Zn-Pb-Ag ore. This ore type has not been fully integrated into any of the existing genetic models. Based on a combination of 1) widespread hematite-staining and oxidizing conditions (Fe2O3>FeO) in the stratigraphic footwall, 2) presence of graphite and reducing conditions (Fe2O3<FeO) in the ore horizon and hangingwall and 3) intense K-feldspar alteration and lack of feldspar-destructive alteration in the stratigraphic footwall, we suggest that both the stratiform Zn-Pb-Ag and the dolomite-hosted Cu ore can be attributed to the ascent and discharge of an oxidized, saline brine at near neutral pH. Interaction of this brine with organic matter below the seafloor, especially within limestone, formed stratabound, disseminated Cu ore, and exhalation of the brine into a reduced environment on the sea floor produced a brine pool from which the regionally extensive (> 5 km) Zn-Pb-Ag ore was precipitated.

    Both ore types are characterized by significant spread in δ34S, with the sulphur in the Cu ore and associate marble-hosted Zn mineralization on average being somewhat heavier (δ34S = -4.7 to +10.5 ‰, average 3.9 ‰) than that in the stratiform Zn-Pb-Ag ore (δ34S = -6 to +17 ‰, average 2.0 ‰). The ranges in δ34S are significantly larger than those observed in syn-volcanic massive sulphide deposits in Bergslagen, for which simple magmatic/volcanic sulphur sources have been invoked. Mixing of magmatic-volcanic sulfur leached from underlying volcanic rocks and sulfur sourced from abiotic or bacterial sulfate reduction in a mixing zone at the seafloor could explain the range observed at Zinkgruvan.

    A distinct discontinuity in the stratigraphy, at which key stratigraphic units stop abruptly, is interpreted as a syn-sedimentary fault. Metal zonation in the stratiform ore (decreasing Zn/Pb from distal to proximal) and the spatial distribution of Cu mineralization in underlying dolomitic marble suggest that this fault was a major feeder to the mineralization. Our interpretation of ore-forming fluid composition and a dominant redox trap rather than a pH and/or temperature trap differs from most VMS models, with Selwyn-type SEDEX models, and most BHT models. Zinkgruvan has similarities to both McArthur-type SEDEX deposits and sediment-hosted Cu deposits in terms of the inferred ore fluid chemistry, yet the basinal setting has more similarities to BHT and felsic-bimodal VMS districts. We speculate that besides an oxidized footwall stratigraphy, regionally extensive banded iron formations and limestone horizons in the Bergslagen stratigraphy may have aided in buffering ore-forming brines to oxidized, near-neutral conditions. In terms of fluid chemistry, Zinkgruvan could comprise one of the oldest known manifestations of Zn and Cu ore-forming systems involving oxidized near-neutral brines following oxygenation of the Earth’s atmosphere.

  • 10.
    Kampmann, Tobias Christoph
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Jansson, Nils F.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Stephens, Michael B.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Olin, Paul H.
    CODES ARC Centre of Excellence and TMVC ARC Research Hub, University of Tasmania.
    Gilbert, Sarah
    CODES ARC Centre of Excellence and TMVC ARC Research Hub, University of Tasmania.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Syn-tectonic sulphide remobilization and trace element redistribution at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen, Sweden2018In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 96, p. 48-71Article in journal (Refereed)
    Abstract [en]

    Mineralization types at the Palaeoproterozoic Falun base metal sulphide deposit are predominantly pyritic Zn-Pb-Cu-rich massive sulphide mineralization, disseminated to semi-massive Cu-Au mineralization, auriferous quartz veins, and mineralized shear zones of talc-chlorite-dominated schist. The massive and disseminated to semi-massive sulphide mineralization types were subject to polyphase ductile deformation (D1 and D2) and metamorphism under low-P, lower-amphibolite facies conditions, which led to the development of ore textures and paragenetic relationships indicating both mechanical and chemical remobilization of sulphides. In the massive sulphide mineralization, rare inclusion-rich pyrite occurs as relic cores inside inclusion-poor metamorphosed pyrite. Imaging and spot analysis using multielement laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) reveal that inclusion-poor pyrite was depleted in trace elements, which were originally present as non-stoichiometric lattice substitutions or in mineral inclusions. The inclusion-rich pyrite was shielded from depletion and, at least partly, retained its initially higher trace element concentrations, including Au.

    Gold is also associated with chalcopyrite in the disseminated to semi-massive Cu-Au mineralization and in the system of auriferous quartz veins hosted therein, the latter being also affected by the D2 ductile strain. It is inferred that emplacement of the vein system took place after the peak of metamorphism, which occurred between D1 and D2, but prior to and possibly even shortly after completion of the D2 deformational event. Similarities in trace element signatures in chalcopyrite are compatible with the interpretation that the quartz veins formed by local chemical remobilization of components from the Cu-Au mineralization. Transport of liberated Au from pyrite during grain growth in the massive sulphide mineralization may have upgraded the Au endowment in the quartz veins, leading to the additional formation of native gold in the veins. A strong correspondence between elements liberated from pyrite (e.g. Pb, Bi, Se and Au) and those forming discrete and characteristic mineral phases in the quartz veins (Pb-Bi sulphosalts, native gold) supports this hypothesis.

    Trace element signatures for the main sulphide minerals pyrite, chalcopyrite, sphalerite and galena are similar to previously published data from other metamorphosed massive sulphide deposits. The association of the Falun mineralization with elevated Bi is reflected by its occurrence in sulphide minerals (e.g. galena) and in abundant mineral inclusions of Pb-Bi sulphosalts (e.g. weibullite), especially in the disseminated to semi-massive Cu-Au mineralization. Elevated Sn concentrations in the lattice and/or as cassiterite inclusions in chalcopyrite, sphalerite and galena are compatible with a hot, acidic and reducing fluid during formation of the syn-volcanic, base metal sulphide mineralization and associated host-rock alteration.

  • 11.
    Martinsson, Olof
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Billström, Kjell
    Laboratory for Isotope Geology. Swedish Museum of Natural History, Stockholm, Laboratoriet för Isotopgeologi, Naturhistoriska Riksmuseet, Stockholm, Swedish Museum of Natural History, Department of Geosciences.
    Broman, Curt
    Department of Geology and Geochemistry, Stockholm University, Stockholms Universitet, Stockholm University, Department of Geological Sciences, Stockholm University.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Metallogeny of the Northern Norrbotten Ore Province, northern Fennoscandian Shield with emphasis on IOCG and apatite-iron ore deposits2016In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 78, p. 447-492Article in journal (Refereed)
    Abstract [en]

    The Northern Norrbotten Ore Province in northernmost Sweden includes the type localities for Kiruna-type apatite iron deposits and has been the focus for intense exploration and research related to Fe oxide-Cu-Au mineralisation during the last decades. Several different types of Fe-oxide and Cu-Au ± Fe oxide mineralisation occur in the region and include: stratiform Cu ± Zn ± Pb ± Fe oxide type, iron formations (including BIF's), Kiruna-type apatite iron ore, and epigenetic Cu ± Au ± Fe oxide type which may be further subdivided into different styles of mineralisation, some of them with typical IOCG (Iron Oxide-Copper-Gold) characteristics. Generally, the formation of Fe oxide ± Cu ± Au mineralisation is directly or indirectly dated between ~ 2.1 and 1.75 Ga, thus spanning about 350 m.y. of geological evolution.The current paper will present in more detail the characteristics of certain key deposits, and aims to put the global concepts of Fe-oxide Cu-Au mineralisations into a regional context. The focus will be on iron deposits and various types of deposits containing Fe-oxides and Cu-sulphides in different proportions which generally have some characteristics in common with the IOCG style. In particular, ore fluid characteristics (magmatic versus non-magmatic) and new geochronological data are used to link the ore-forming processes with the overall crustal evolution to generate a metallogenetic model.Rift bounded shallow marine basins developed at ~ 2.1–2.0 Ga following a long period of extensional tectonics within the Greenstone-dominated, 2.5–2.0 Ga Karelian craton. The ~ 1.9–1.8 Ga Svecofennian Orogen is characterised by subduction and accretion from the southwest. An initial emplacement of calc-alkaline magmas into ~ 1.9 Ga continental arcs led to the formation of the Haparanda Suite and the Porphyrite Group volcanic rocks. Following this early stage of magmatic activity, and separated from it by the earliest deformation and metamorphism, more alkali-rich magmas of the Perthite Monzonite Suite and the Kiirunavaara Group volcanic rocks were formed at ~ 1.88 Ga. Subsequently, partial melting of the middle crust produced large volumes of ~ 1.85 and 1.8 Ga S-type granites in conjunction with subduction related A −/I-type magmatism and associated deformation and metamorphismIn our metallogenetic model the ore formation is considered to relate to the geological evolution as follows. Iron formations and a few stratiform sulphide deposits were deposited in relation to exhalative processes in rift bounded marine basins. The iron formations may be sub-divided into BIF- (banded iron formations) and Mg-rich types, and at several locations these types grade into each other. There is no direct age evidence to constrain the deposition of iron formations, but stable isotope data and stratigraphic correlations suggest a formation within the 2.1–2.0 Ga age range. The major Kiruna-type ores formed from an iron-rich magma (generally with a hydrothermal over-print) and are restricted to areas occupied by volcanic rocks of the Kiirunavaara Group. It is suggested here that 1.89–1.88 Ga tholeiitic magmas underwent magma liquid immiscibility reactions during fractionation and interaction with crustal rocks, including metaevaporites, generating more felsic magmatic rocks and Kiruna-type iron deposits. A second generation of this ore type, with a minor economic importance, appears to have been formed about 100 Ma later. The epigenetic Cu-Au ± Fe oxide mineralisation formed during two stages of the Svecofennian evolution in association with magmatic and metamorphic events and crustal-scale shear zones. During the first stage of mineralisation, from 1.89–1.88 Ga, intrusion-related (porphyry-style) mineralisation and Cu-Au deposits of IOCG affinity formed from magmatic-hydrothermal systems, whereas vein-style and shear zone deposits largely formed at c. 1.78 Ga.The large range of different Fe oxide and Cu-Au ± Fe oxide deposits in Northern Norrbotten is associated with various alteration systems, involving e.g. scapolite, albite, K feldspar, biotite, carbonates, tourmaline and sericite. However, among the apatite iron ores and the epigenetic Cu-Au ± Fe oxide deposits the character of mineralisation, type of ore- and alteration minerals and metal associations are partly controlled by stratigraphic position (i.e. depth of emplacement). Highly saline, NaCl + CaCl2 dominated fluids, commonly also including a CO2-rich population, appear to be a common characteristic feature irrespective of type and age of deposits. Thus, fluids with similar characteristics appear to have been active during quite different stages of the geological evolution. Ore fluids related to epigenetic Cu-Au ± Fe oxides display a trend with decreasing salinity, which probably was caused by mixing with meteoric water. Tentatively, this can be linked to different Cusingle bondAu ore paragenesis, including an initial (magnetite)-pyrite-chalcopyrite stage, a main chalcopyrite stage, and a late bornite stage.Based on the anion composition and the Br/Cl ratio of ore related fluids bittern brines and metaevaporites (including scapolite) seem to be important sources to the high salinity hydrothermal systems generating most of the deposits in Norrbotten. Depending on local conditions and position in the crust these fluids generated a variety of Cu-Au deposits. These include typical IOCG-deposits (Fe-oxides and Cu-Au are part of the same process), IOCG of iron stone type (pre-existing Fe-oxide deposit with later addition of Cu-Au), IOCG of reduced type (lacking Fe-oxides due to local reducing conditions) and vein-style Cu-Au deposits. From a strict genetic point of view, IOCG deposits that formed from fluids of a mainly magmatic origin should be considered to be a different type than those deposits associated with mainly non-magmatic fluids. The former tend to overlap with porphyry systems, whereas those of a mainly non-magmatic origin overlap with sediment hosted Cu-deposits with respect to their origin and character of the ore fluids.

  • 12.
    Sandrin, Alessandro
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geophysical and petrophysical study of an iron oxide copper gold deposit in northern Sweden2006In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 29, no 1, p. 1-18Article in journal (Refereed)
    Abstract [en]

    A geophysical-petrophysical study has been performed in an area WSW of the city of Kiruna, northern Sweden. The sub-regional tectonic setting is dominated by two important shear zones, which define the boundary of a granitic body. Many Cu-Fe-occurrences are located in proximity of faults related to these major deformation zones. Particular attention has been given to the Tjårrojåkka iron oxide copper gold (IOCG) deposit. Here the bedrock is characterised by intermediate to mafic meta-volcanics, metamorphosed intermediate to mafic dykes, and gabbroic-dioritic intrusions of Svecofennian ages (1.96-1.75 Ga). The major Cu- and Fe-occurrences are hosted by the meta-andesites. The aim of the study is to put the deposits into a tectonic framework and test existing hypotheses for their occurrences.Glacial deposits cover almost the entire area, leading to a scarcity of outcrops and inferring that geophysical data are fundamental for geological understanding. In addition to this, petrophysical analysis is vital for the interpretation of geophysical data (gravity, airborne magnetics and radiometrics, very low frequency) and for the definition of geophysical signatures of the deposits. The anisotropy of magnetic susceptibility (AMS) was also studied for the tectonic analysis. More than 150 oriented samples were collected in a number of outcrops along a profile intersecting the major structures in the Tjårrojåkka area.From the airborne magnetic data, two major linear features are interpreted as deformation zones. The strike of these deformation zones is approximately NW-SE and E-W, respectively. The same trends have been defined from other geophysical data such as airborne VLF and ground gravity data. A third important structural trend striking SW-NE has been defined by K/Th data and ground magnetic data. Very good agreement has been found between geophysical lineaments and AMS directions. Magnetic foliations determined by AMS measurements confirm the existence of three major trends in the study area: SW-NE, E-W and NW-SE. The major Fe-orebody shows approximately a SW-NE strike direction as defined from ground magnetic data. This is parallel to the strike of magnetic foliation determined in outcrops 1 km NW of the deposit. The epigenetic nature of the Cu and Fe occurrences in Tjårrojåkka and their spatial relationship with deformation zones suggest a connection between the formation of the deposits and a tectonic event. A later tectonic episode resulted in E-W trending deformation in the central area, affecting the orebodies themselves. Other, probable, compressive deformations have been indicated from petrophysical and geophysical analyses.Thermomagnetic measurements indicate that Fe-oxides (Ti-magnetite) are common in the area, while Fe-sulphides are almost absent. Multi-domain magnetite has been identified as the most common Fe-oxide in different rock types, while an unstable magnetic mineral has been detected in metamorphosed volcanics. A good spatial correlation has been observed between Cu-deposits and high K/Th values from radiometric data, values that are expressions of potassic alteration.

  • 13.
    Sandrin, Alessandro
    et al.
    Luleå University of Technology.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Physical properties of rocks from borehole TJ71305 and geophysical outline of the Tjårrajåkka Cu-prospect, northern Sweden2007In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 30, no 1, p. 56-73Article in journal (Refereed)
    Abstract [en]

    In the last decades Fe-oxide Cu–Au (IOCG) deposits attracted the interest of exploration geologists and geophysicists. General geophysical descriptions of IOCG deposits have been published in the recent past, but there is still a lack of detailed geophysical investigations. We present a petrophysical study of rock samples from exploration borehole TJ71305, which intersects the Cu-prospect in the Tjårrojåkka IOCG mineralised area, northern Sweden. Furthermore geophysical data are compiled and analysed to tentatively define a geophysical signature, at local scale, for this type of deposit. The study area is dominated by intrusive and volcanic rocks of Middle Proterozoic age, the latter hosting the Cu and Fe occurrences. The Fe occurrences are clearly defined from both aeromagnetic and ground magnetic data, and are also indicated by gravity, geoelectric and electromagnetic data. Enrichment in ferromagnetic minerals in the area is suggested by the high values of magnetic susceptibility commonly obtained for different rock types; magnetite and Ti-magnetite are the dominant magnetic minerals. Haematite with variable contents of Ti was detected and it is probably a result of oxidation of magnetite in alteration zones. In Tjårrojåkka a clear spatial relationship is noted between Cu occurrences and high K/Th ratios. This ratio is calculated from airborne radiometric data and is an expression of enrichment in potassium, due to alteration. The Cu-prospect is also indicated by high gravity and magnetic anomalies, by clear positive anomalies in induced polarisation data and by negative anomalies for the imaginary part of ground electromagnetic (Slingram) data. However, high-density/high-susceptibility/low-resistivity (Ti)-magnetite is associated with the Cu-prospect and this may lead to misinterpretation of potential field, electromagnetic and geoelectric data.

  • 14.
    Tornos, Fernando
    et al.
    Centro de Astrobiología - Consejo Superior de Investigaciones Científicas, Ctra Ajalvir km.4.5. 28850 Torrejón de Ardoz.
    Peter, Jan M.
    Geological Survey of Canada.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Conde, Carmen
    c/Vilar Formoso 66. 37008 Salamanca.
    Controls on the siting and style of volcanogenic massive sulphide deposits2015In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 68, p. 142-163Article in journal (Refereed)
    Abstract [en]

    Volcanogenic massive sulphide (VMS) deposits form in subaqueous environments from circulating hydrothermal fluids heated by volcanic activity. These deposits form as sulphide mounds, stratiform exhalative and/or replacive bodies and commonly have stockwork/vein mineralization in their immediate footwall. These various “styles” are essentially facies of mineralization, each one being the product of a particular set of conditions that control the ore-forming processes and the consequent geometry and architecture (style) of the deposits. These controls include the physical and/or chemical nature of the host rocks, the temperature and composition of the hydrothermal fluids and the redox state of the depositional environment.The style of exhalative deposits is controlled by the salinity of the vented fluids and the redox state at the seafloor. Hydrothermal fluids with salinities less than twice that of seawater that vented into open, oxic oceanic environments, typically formed small mound and chimney complexes, unless they were rapidly covered by sediments or volcanic rocks. The massive sulphides were rapidly oxidized and partly dissolved by seawater. In contrast, stratiform sheet-like deposits are typically formed in anoxic bottom waters. Anoxic marine conditions were periodically of global extent, – particularly prior to 2.4 Ga – or of a regional nature. Local anoxic conditions can also be self-induced by the exhalation of saline and reducing hydrothermal fluids that ponded in bathymetric depressions such as second- or third-order basins to form a brine pool. These exhalative systems may have been initiated as chimney vent complexes and subsequently overlain by stratiform sulphides formed under the self-induced anoxic conditions. Deposits formed in anoxic environments can be significantly larger than those in oxic settings, and this is attributed to several factors that include longer-lived hydrothermal circulation, more efficient sulphide precipitation and reduced or inhibited oxidation thereof.Replacement of volcanic and sedimentary strata by sulphide typically occurs within the feeder zones beneath the exhalative mineralization. However, successions with abundant porous, permeable and/or reactive rocks such as glassy and/or pumiceous volcaniclastic rocks, and in some cases limestone, favoured the development of large replacive deposits, that may have had little surficial expression on the sea floor.VMS deposits at spreading centres within oceanic crust formed almost exclusively as mounds. Most of them have not been preserved, likely due to oxidation of the sulphides in the prevailing oxic environment and/or destruction of oceanic crust during subsequent subduction. Intra-continental rifts, arc rifts and back-arc rifts commonly have more complexity in their structure, and facies architecture and environments and can host all styles of VMS mineralization. In these settings, early extension favoured the formation of restricted basins with ideal conditions for the onset of hydrothermal activity and development of anoxic bottom waters, whereas in mature rifts the conditions were less conducive for the formation of regionally extensive anoxic environments. Formation of replacive deposits was permissible in all settings with porous or reactive subsea-floor strata. Replacive mineralization is the most likely to be preserved in the geological record due to the sulphides being physically shielded from oxidative weathering and mechanical erosion at the seafloor.The various styles of VMS mineralization can rarely be distinguished using a single criterion; in most cases multiple criteria are required.Mound style mineralization is distinguished by: (a) mound- or lens-shaped morphology; (b) presence of chimney fragments; (c) presence of abundant sedimented sulphide breccias; (d) location on a stratigraphic boundary (ore horizon); and, (e) association with a thin horizon or thicker stratigraphic interval of fine-grained clastic rocks (e.g., shale, mudstone) that accumulated at slow sedimentation rates.Stratiform exhalative mineralization is distinguished by: (a) sheet-like morphology prior to deformation; (b) presence of fine-grained clastic host rocks that accumulated at relatively slow rates (e.g., mudstone); (c) presence of local or extensive planar stratification.Replacive mineralization is characterized by: (a) irregular geometry and distribution of sulphide bodies; (b) gradation from massive sulphides to semi-massive sulphides and disseminated mineralization with relict textures of the host rock; and, (c) originally pumiceous, glassy or reactive host rocks emplaced at high depositional rates (mass flow deposits, lavas, carbonate-altered mass flow deposits) or limestone.One deposit or district may comprise two or more of these main styles of mineralization. In many cases the main styles of VMS mineralization present in a particular region can be predicted from examination of the facies architecture and depositional environments of the host succession. Recognition of the style(s) of mineralization that occur in a particular basin or mineral belt enables exploration models to be improved and should influence the strategy of exploration for VMS deposits.

  • 15.
    Torró, L.
    et al.
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain; Universidad Tecnológica del Cibao Oriental (UTECO), Cotuí, Dominican Republic.
    Proenza, J. A.
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain.
    Aiglsperger, Thomas
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain.
    Bover-Arnal, T.
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain.
    Villanova-de-Benavent, C.
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain.
    Rodrí­guez-García, D.
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain.
    Ramí­rez, A.
    Servicio Geológico Nacional, Av. Winston Churchill 75, Edificio “J. F. Martínez”, Santo Domingo, Dominican Republic.
    Rodríguez, J.
    Servicio Geológico Nacional, Av. Winston Churchill 75, Edificio “J. F. Martínez”, Santo Domingo, Dominican Republic.
    Mosquea, L. A.
    Universidad Tecnológica del Cibao Oriental (UTECO), Cotuí, Dominican Republic.
    Salas, R.
    Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Martí i Franquès s/n, 08028 Barcelona, Spain.
    Geological, geochemical and mineralogical characteristics of REE-bearing Las Mercedes bauxite deposit, Dominican Republic2017In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 89, p. 114-131Article in journal (Refereed)
    Abstract [en]

    Bauxite deposits, traditionally the main source of aluminum, have been recently targeted for their remarkable contents in rare earth elements (REE). With ∑REE (lanthanoids + Sc + Y) concentrations systematically higher than ∼1400 ppm (av. = 1530 ppm), the Las Mercedes karstic bauxites in the Dominican Republic rank as one of the REE-richest deposits of its style.

    The bauxitic ore in the Las Mercedes deposit is mostly unlithified and has a homogeneous-massive lithostructure, with only local cross-stratification and graded bedding. The dominant arenaceous and round-grained texture is composed of bauxite particles and subordinate ooids, pisoids and carbonate clasts. Mineralogically, the bauxite ore is composed mostly of gibbsite and lesser amounts of kaolinite, hematite, boehmite, anatase, goethite, chromian spinel and zircon. Identified REE-minerals include cerianite and monazite-Ce, whose composition accounts for the steady enrichment in light- relative to medium- and heavy-REE of the studied bauxites.

    Considering the paleo-geomorphology of the study area, we propose that bauxites in the Las Mercedes deposit are the product of the erosion and deposition of lithified bauxites located at higher elevations in the Bahoruco ranges. Based on the available data, we suggest a mixed lithological source for the bauxite deposits at the district scale: bedrock carbonates and an igneous source of likely mafic composition.

  • 16.
    Wanhainen, Christina
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Broman, C.
    Department of Geological Sciences, Stockholm University.
    Martinsson, Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnor, B.
    Vattenfall.
    Modification of a Palaeoproterozoic porphyry-like system: integration of structural, geochemical, petrographic, and fluid inclusion data from the Aitik Cu-Au-Ag deposit, northern Sweden2012In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 48, p. 306-331Article in journal (Refereed)
    Abstract [en]

    The Aitik Cu-Au-Ag deposit in the Gällivare area in northern Sweden is Sweden´s largest sulphide mine with an annual production of 35 Mt of ore, and the biggest open pit operation in northern Europe. It is proposed in the present study that the Aitik deposit represents a Palaeoproterozoic, strongly metamorphosed porphyry copper deposit that was affected ca. 100 Ma later by a regional IOCG-type hydrothermal event. Consequently, the Aitik deposit might represent a mixed ore system where an early copper mineralisation of porphyry type has been overprinted by later regional IOCG mineralisation.Several attempts have previously been made to genetically classify the Aitik Cu-Au-Ag deposit as a distinct ore type. New geochemical, petrographic, structural, and fluid inclusion results combined with published data have provided the opportunity to present new ideas on the genesis and evolution of the Aitik Cu-Au-Ag deposit. The emplacement of a ca. 1.9 Ga quartz monzodiorite that host the ore at Aitik was related to subduction processes and volcanic arc formation, and synchronous with quartz vein stockwork formation and porphyry copper mineralisation. Highly saline aqueous (38 wt.% NaCl) fluid inclusions in the stockwork veins suggest entrapment at 300 °C and a pressure of nearly 3 kbar, a high pressure for a typical porphyry copper ore, but consistent with conditions at associated deep root zones of intrusion-related magmatic-hydrothermal systems. The highly saline fluid formed disseminated and vein-type ore of mainly chalcopyrite and pyrite within comagmatic volcaniclastic rocks, and caused potassic alteration (biotite, microcline) of the host rocks. The early porphyry copper mineralising event was followed, and largely overprinted, by CO2 and aqueous medium- to high-salinity (16–57 wt.% salts) fluids related to a ca. 1.8 Ga tectonic and metamorphic event (peak conditions 500–600 °C and 4–5 kbar). Extensive deformation of rocks and redistribution of metals occurred. Magnetite enrichment locally found within late veins, and late amphibole-scapolite and K feldspar alteration within the deposit, are some of the features at Aitik implying that aqueous fluids responsible for IOCG-mineralisation (200–500 °C and ~ 1 kbar) and extensive Na-Ca alteration in the region during the 1.8 Ga tectonic event also affected the Aitik rocks, possibly leading to addition of copper ± gold.

  • 17.
    Weihed, Pär
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Arndt, Nicholas
    Université Joseph Fourier, Grenoble.
    Billström, Kjell
    Swedish Museum of Natural History.
    Duchesne, Jean-Clair
    University of Liège.
    Eilu, Pasi
    Geological Survey of Finland.
    Martinsson, Olof
    Papunen, Heikki
    University of Turku.
    Lahtinene, Raimo
    Geological Survey of Finland.
    Precambrian geodynamics and ore formation: the Fennoscandian Shield2005In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 27, no 1-4, p. 273-322Article in journal (Refereed)
    Abstract [en]

    Compared with present-day global plate tectonics, Archaean and Palaeoproterozoic plate tectonics may have involved faster moving, hotter plates that accumulated less sediment and contained a thinner section of lithospheric mantle. This scenario also fits with the complex geodynamic evolution of the Fennoscandian Shield from 2.06 to 1.78 Ga when rapid accretion of island arcs and several microcontinent–continent collisions in a complex array of orogens was manifested in short-lived but intense orogenies involving voluminous magmatism. With a few exceptions, all major ore deposits formed in specific tectonic settings between 2.06 and 1.78 Ga and thus a strong geodynamic control on ore deposit formation is suggested. All orogenic gold deposits formed syn- to post-peak metamorphism and their timing reflects the orogenic younging of the shield towards the SW and west. Most orogenic gold deposits formed during periods of crustal shortening with peaks at 2.72 to 2.67, 1.90 to 1.86 and 1.85 to 1.79 Ga. The ca. 2.5 to 2.4 Ga Ni–Cu ± PGE deposits formed both as part of layered igneous complexes and associated with mafic volcanism, in basins formed during rifting of the Archaean craton at ca. 2.5 to 2.4 Ga. Svecokarelian ca. 1.89 to 1.88 Ga Ni–Cu deposits are related to mafic–ultramafic rocks intruded along linear belts at the accretionary margins of microcratons. All major VMS deposits in the Fennoscandian Shield formed between 1.97 and 1.88 Ga, in extensional settings, prior to basin inversion and accretion. The oldest “Cyprus-type” deposits were obducted onto the Archaean continent during the onset of convergence. The Pyhäsalmi VMS deposits formed at 1.93 to 1.91 Ga in primitive, bimodal arc complexes during extension of the arc. In contrast, the Skellefte VMS deposits are 20 to 30 million years younger and formed in a strongly extensional intra-arc region that developed on continental or mature arc crust. Deposits in the Bergslagen–Uusimaa belt are similar in age to the Skellefte deposits and formed in a microcraton that collided with the Karelian craton at ca. 1.88 to 1.87 Ga. The Bergslagen–Uusimaa belt is interpreted as an intra-continental, or continental margin back-arc, extensional region developed on older continental crust. Iron oxide–copper–gold (IOCG) deposits are diverse in style. At least the oldest mineralizing stages, at ca. 1.88 Ga, are coeval with calc-alkaline to monzonitic magmatism and coeval and possibly cogenetic subaerial volcanism more akin to continental arcs or to magmatic arcs inboard of the active subduction zone. Younger mineralization of similar style took place when S-type magmatism occurred at ca. 1.80 to 1.77 Ga during cratonization distal to the active N–S-trending subduction zone in the west. Possibly, interaction of magmatic fluids with evaporitic sequences in older rift sequences was important for ore formation. Finally, the large volumes of anorthositic magmas that characterize the Sveconorwegian Orogeny formed a major concentration of Ti in the SW part of the Sveconorwegian orogenic belt under granulite facies conditions, about 40 million years after the last regional deformation of the Sveconorwegian Orogeny, between ca. 930 and 920 Ma.

  • 18.
    Weihed, Pär
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Eilu, Pasi
    Geological Survey of Finland.
    Fennoscandian Shield: proterozoic VMS deposits2005In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 27, no 1-4, p. 324-325Article in journal (Refereed)
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