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Buntin, S., Malehmir, A., Koyi, H., Högdahl, K., Malinowski, M., Larsson, S. A., . . . Gorszczyk, A. (2019). Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield. Scientific Reports, 9, Article ID 10498.
Open this publication in new window or tab >>Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 10498Article in journal (Refereed) Published
Abstract [en]

Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30-100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100-300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-391379 (URN)10.1038/s41598-019-46837-x (DOI)000476468700026 ()31324841 (PubMedID)
Funder
Swedish Research Council, 2015-05177
Available from: 2019-09-03 Created: 2019-09-03 Last updated: 2019-09-03Bibliographically approved
Troll, V. R., Weis, F. A., Jonsson, E., Andersson, U. B., Majidi, S. A., Högdahl, K., . . . Nilsson, K. P. (2019). Global Fe-O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores. Nature Communications, 10, Article ID 1712.
Open this publication in new window or tab >>Global Fe-O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores
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2019 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 10, article id 1712Article in journal (Refereed) Published
Abstract [en]

Kiruna-type apatite-iron-oxide ores are key iron sources for modern industry, yet their origin remains controversial. Diverse ore-forming processes have been discussed, comprising lowtemperature hydrothermal processes versus a high-temperature origin from magma or magmatic fluids. We present an extensive set of new and combined iron and oxygen isotope data from magnetite of Kiruna-type ores from Sweden, Chile and Iran, and compare them with new global reference data from layered intrusions, active volcanic provinces, and established low-temperature and hydrothermal iron ores. We show that approximately 80% of the magnetite from the investigated Kiruna-type ores exhibit d56Fe and d18O ratios that overlap with the volcanic and plutonic reference materials (> 800 degrees C), whereas similar to 20%, mainly vein-hosted and disseminated magnetite, match the low-temperature reference samples (<= 400 degrees C). Thus, Kiruna-type ores are dominantly magmatic in origin, but may contain latestage hydrothermal magnetite populations that can locally overprint primary hightemperature magmatic signatures.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Geology
Identifiers
urn:nbn:se:uu:diva-382552 (URN)10.1038/s41467-019-09244-4 (DOI)000464338100023 ()30979878 (PubMedID)
Funder
Swedish Research Council
Available from: 2019-05-10 Created: 2019-05-10 Last updated: 2019-05-10Bibliographically approved
Almqvist, B., Björk, A., Mattsson, H. B., Hedlund, D., Gunnarsson, K., Malehmir, A., . . . Marsden, P. (2019). Magnetic characterisation of magnetite and hematite from the Blötberget apatite-iron-oxide deposits (Bergslagen), south-central Sweden. Canadian journal of earth sciences (Print), 56(9), 948-957
Open this publication in new window or tab >>Magnetic characterisation of magnetite and hematite from the Blötberget apatite-iron-oxide deposits (Bergslagen), south-central Sweden
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2019 (English)In: Canadian journal of earth sciences (Print), ISSN 0008-4077, E-ISSN 1480-3313, Vol. 56, no 9, p. 948-957Article in journal (Refereed) Published
Abstract [en]

Rock magnetic measurements were carried out on drill core material and hand specimens from the Blötberget apatite-iron oxide deposit in the Bergslagen ore province, south-central Sweden, to characterise their magnetic properties. Measurements included several kinds of magnetic susceptibility and hysteresis parameters. Petrographic and scanning electron microscopy (SEM) were used to independently identify and quantify the amount and type of magnetite and hematite. Two hematite-rich samples were studied with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to quantify the trace element chemistry in hematite and investigate the potential influence of trace elements on magnetic properties. Three aspects of this study are noteworthy. 1) Hematite-rich samples display strong anisotropy of magnetic susceptibility, which is likely to affect the appearance and modelling of magnetic anomalies. 2) The magnitude-drop in susceptibility across Curie and Néel temperature transitions show significant correlation with the respective weight percent (wt%) of magnetite and hematite. Temperature dependent magnetic susceptibility measurements can therefore be used to infer the amounts of both magnetite and hematite. 3) observations of a strongly depressed Morin transition at ca -60 to -70 C (200 to 210 K) are made during low-temperature susceptibility measurements. This anomalous Morin transition is most likely related to trace amounts of V and Ti that substitute for Fe in the hematite. When taken together, these magnetic observations improve the understanding of the magnetic anomaly signature of the Blötberget apatite-iron oxide deposits and may potentially be utilised in a broader context when assessing similar (Paleoproterozoic) apatite-iron oxide systems.

Place, publisher, year, edition, pages
Canadian Science Publishing, 2019
Keywords
apatite – iron oxide, magnetic properties, magnetite, hematite, Kiruna-type deposit
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-374225 (URN)10.1139/cjes-2018-0183 (DOI)000486365100007 ()
Funder
Vinnova, 2014-06238The Geological Survey of Sweden (SGU)
Available from: 2019-01-18 Created: 2019-01-18 Last updated: 2019-10-31Bibliographically approved
Jonsson, E. & Högdahl, K. (2019). On the occurrence of gallium and germanium in the Bergslagen ore province, Sweden. GFF, 141(1), 48-53
Open this publication in new window or tab >>On the occurrence of gallium and germanium in the Bergslagen ore province, Sweden
2019 (English)In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 141, no 1, p. 48-53Article in journal (Refereed) Published
Abstract [en]

The presence of the critical and sought-after (semi-)metals gallium (Ga) and germanium (Ge) has previously been reported from mineralisations in the Bergslagen ore province, south central Sweden. Some of these reports were however recently shown to be questionable or erroneous. Here we summarise early analytical work on these metals in mineral deposits of the Bergslagen province, as well as briefly report new analytical data for Ga and Ge from recent, in part on-going work on different mineralisation types. The new data show that the sampled sulphide and iron oxide mineralisations in the Bergslagen province are overall not particularly enriched in Ga, and even less so with regards to Ge. One major exception is the significant Ga enrichment observed in skarn-hosted Fe-REE(-polymetallic) deposits of Bastnas type. Notably, these mineralisations also host increased contents of Ge. Based on this broader suite of sampled deposits, the suggested correlation between Ga and Al contents in previously studied material with relatively increased Ga grades, is in part contradicted, indicating that Ga is only in part sequestered through straightforward Al-substitution into aluminium silicate and oxide minerals. The mineralisations that do exhibit significantly increased Ge contents, in addition to the Bastnas-type deposits, are represented by both sulphide-dominated ones and Fe (-Mn) oxide-rich systems.

Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD, 2019
Keywords
Gallium, germanium, Bergslagen, mineralisation, Sweden
National Category
Geology
Identifiers
urn:nbn:se:uu:diva-385583 (URN)10.1080/11035897.2018.1525619 (DOI)000467182600004 ()
Funder
Swedish Research Council
Available from: 2019-06-17 Created: 2019-06-17 Last updated: 2019-06-17Bibliographically approved
Mattsson, H. B., Högdahl, K., Carlsson, M. & Malehmir, A. (2019). The role of mafic dykes in the petrogenesis of the Archean Siilinjärvi carbonatite complex, east-Central Finland. Lithos, 342-343, 468-479
Open this publication in new window or tab >>The role of mafic dykes in the petrogenesis of the Archean Siilinjärvi carbonatite complex, east-Central Finland
2019 (English)In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 342-343, p. 468-479Article in journal (Refereed) Published
Abstract [en]

The Archean (~2.6 Ga) Siilinjärvi carbonatite complex in east-central Finland is crosscut by a few ultramafic lamprophyre dykes, together with a broad array of more evolved mafic dykes that range in composition from foidites to various types of alkali basalts. A possible genetic link between the primitive lamprophyres and the carbonatite complex has previously been hypothesised, but their exact relations have been unclear due to the regional metamorphic overprint (i.e., greenschist facies). Here we focus on the petrology and petrography of the mafic dykes, and integrate the data to present a coherent model that can explain the genesis of the Siilinjärvi carbonatite complex. Field-relations, in combination with petrography and geochemistry, indicate that there are at least three generations of mafic dykes present. The oldest dykes (Generation I) are strongly deformed, and inferred to have been emplaced shortly after the formation of the complex itself. These dykes can be divided into two groups (i.e., ultramafic lamprophyres and Group A), where Group A comprises foidites characterised by low SiO2 (41.4–51.5 wt%) and high alkali (>10 wt% K2O) content. We interpret the foiditic magmas to have evolved from primitive ultramafic lamprophyres by fractionating a clinopyroxene-olivine dominated mineral assemblage that was devoid of feldspar. This fractionation path forced alkali-enrichment in the magmas belonging to Group A, which pushed them into the miscibility gap, and resulted in liquid immiscibility that produced moderately alkaline conjugate carbonatite(s). Subsequent fractionation of the conjugate carbonatite by predominantly calcite and apatite produced the mineralogically homogeneous carbonatite cumulate that is exposed at Siilinjärvi. Younger, less deformed, mafic dykes (belonging to Generations II and III) exhibit trace element characteristics, broadly similar to basaltic dyke swarms in the region. The younger dykes are characterised by the presence of large plagioclase crystals in thin sections. Crystallisation of a feldspar-bearing mineral assemblage resulted in only moderate enrichment of alkalis with increased fractionation, which caused the younger dykes to evolve along the more common basalt-to-trachyte series. Thus, the magmas belonging to Generations II and III at Siilinjärvi never fulfilled the conditions required to produce carbonatites by liquid immiscibility.

Keywords
Siilinjarvi, Carbonatite, Ultramafic lamprohyre, Archean, Fractional crystallisation, Liquid immiscibility
National Category
Geochemistry
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-385377 (URN)10.1016/j.lithos.2019.06.011 (DOI)000477091500030 ()
Funder
Vinnova, 2014–06238Swedish Research Council, 2018-03702The Geological Survey of Sweden (SGU), 311-1485/2017
Available from: 2019-06-13 Created: 2019-06-13 Last updated: 2019-09-20Bibliographically approved
Buntin, S., Malehmir, A., Malinowski, M., Högdahl, K., Juhlin, C., Thybo, H. & Buske, S. (2016). Seismic reprocessing of the BABEL lines for improved interpretation of the whole crust – preliminary results. In: Ilmo Kukkonen, Suvi Heinonen, Kati Oinonen, Katriina Arhe, Olav Eklund, Fredrik Karell, Elena Kozlovskaya, Arto Luttinen, Raimo Lahtinen, Juha Lunkka, Vesa Nykänen, Markku Poutanen , Eija Tanskanen and Timo Tiira (Ed.), Lithosphere 2016: Ninth Symposium On Structure, Composition And Evolution Of The Lithosphere In Fennoscandia. Paper presented at LITHOSPHERE 2016 Symposium, November 9-11, 2016, Espoo, Finland (pp. 9-12). Helsinki, Finland: University of Helsinki, Institute of Seismology
Open this publication in new window or tab >>Seismic reprocessing of the BABEL lines for improved interpretation of the whole crust – preliminary results
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2016 (English)In: Lithosphere 2016: Ninth Symposium On Structure, Composition And Evolution Of The Lithosphere In Fennoscandia / [ed] Ilmo Kukkonen, Suvi Heinonen, Kati Oinonen, Katriina Arhe, Olav Eklund, Fredrik Karell, Elena Kozlovskaya, Arto Luttinen, Raimo Lahtinen, Juha Lunkka, Vesa Nykänen, Markku Poutanen , Eija Tanskanen and Timo Tiira, Helsinki, Finland: University of Helsinki, Institute of Seismology , 2016, p. 9-12Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

This ongoing study focuses on the reprocessing of the historical BABEL (Baltic and Bothnian Echoes from the Lithosphere, 1989) seismic lines in the Bay of Bothnia in preparation for the acquisition of a 400 km long onshore reflection and refraction profile in central part of Sweden. The main aim of the project is to increase the understanding of the tectonic evolution of the mineral-rich Bergslagen region both offshore and onshore. The seismic data have been recovered and currently being reprocessed using up-to-date processing methods and preliminary results show promising outcome from this work.

Place, publisher, year, edition, pages
Helsinki, Finland: University of Helsinki, Institute of Seismology, 2016
Series
Report - Institute of Seismology, University of Helsinki, ISSN 0357-3060 ; S-65
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-307696 (URN)978-952-10-5081-7 (ISBN)
Conference
LITHOSPHERE 2016 Symposium, November 9-11, 2016, Espoo, Finland
Funder
Swedish Research Council, 2015 – 05177
Available from: 2016-11-20 Created: 2016-11-20 Last updated: 2019-09-03Bibliographically approved
Eklöf, S., Högdahl, K., Jonsson, E., Malehmir, A. & Michael, S. (2016). Towards a structural framework for apatite-iron oxide deposits in the Grängesberg-Blötberget area, Bergslagen, Sweden. In: : . Paper presented at 32nd Nordic Geologic Winter Meeting.
Open this publication in new window or tab >>Towards a structural framework for apatite-iron oxide deposits in the Grängesberg-Blötberget area, Bergslagen, Sweden
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2016 (English)Conference paper, Poster (with or without abstract) (Refereed)
National Category
Geology
Identifiers
urn:nbn:se:uu:diva-288898 (URN)
Conference
32nd Nordic Geologic Winter Meeting
Available from: 2016-04-28 Created: 2016-04-28 Last updated: 2016-04-28
Jonsson, E., Högdahl, K., Persson Nilsson, K. & Hellström, F. (2015). Apatite-iron oxide-hosted REE mineralisation at Kopslahyttan, NW Bergslagen, Sweden. In: A-S André-Mayer (Ed.), Mineral Resources In A Sustainable World: . Paper presented at Mineral deposits in a sustainable world. 13th SGA biennial meeting 2015 (pp. 781-784). , 1-5
Open this publication in new window or tab >>Apatite-iron oxide-hosted REE mineralisation at Kopslahyttan, NW Bergslagen, Sweden
2015 (English)In: Mineral Resources In A Sustainable World / [ed] A-S André-Mayer, 2015, Vol. 1-5, p. 781-784Conference paper, Published paper (Refereed)
Abstract [en]

Of the different types of REE mineralisation known from the Fennoscandian shield, the Palaeoproterozoic apatite-iron oxide ores of Kiruna type represent one resource type with significant potential. Here we describe an REE-rich apatite-magnetite mineralisation from the classic Bergslagen ore province in south central Sweden. Associated with moderately to weakly REE-enriched magnetite mineralisation of banded and vein types, the most apatite-rich occurrence at Kopslahyttan shows REE enrichment that is similar in both magnitude and pattern to other Kiruna type deposits. Yet, the present REE mineralogy is wholly dominated by monazite-(Ce), allanite-(Ce) and LREE-enriched epidote, the latter two often occurring as zoned crystals or aggregates. Minor xenotime-(Y) also occurs, and titanite locally hosts minor Y+HREE. The abundant fluorapatite is suggested to have been an additional, original host for REE, prior to fluid-mediated alteration leading to wholesale remobilisation of REE from the apatite. This remobilisation included dissolution-reprecipitation processes that lead to the nucleation of monazite in fluorapatite, but probably also further transport and precipitation as e.g. allanite/REE-epidote, through reactions with locally common silicates. In addition, we suggest that very coarse grained, variably Th-bearing monazite present in the mineralisation may have been a primary REE phase, in marked contrast to most other deposits of this type.

Keywords
REE; apatite-iron oxide; Kiruna type; Kopslahyttan; Bergslagen; Sweden
National Category
Geology
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-271009 (URN)000374801300177 ()9782855550664 (ISBN)
Conference
Mineral deposits in a sustainable world. 13th SGA biennial meeting 2015
Available from: 2016-01-05 Created: 2016-01-05 Last updated: 2016-07-26Bibliographically approved
Place, J., Malehmir, A., Högdahl, K., Juhlin, C. & Nilsson, K. P. (2015). Seismic characterization of the Grangesberg iron deposit and its mining-induced structures, central Sweden. Interpretation, 3(3), SY41-SY56
Open this publication in new window or tab >>Seismic characterization of the Grangesberg iron deposit and its mining-induced structures, central Sweden
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2015 (English)In: Interpretation, ISSN 2324-8858, E-ISSN 2324-8866, Vol. 3, no 3, p. SY41-SY56Article in journal (Refereed) Published
Abstract [en]

We have conducted a reflection seismic investigation over the apatite-iron deposit at Grangesberg in central Sweden. At the time of closure in 1989, the mine was operated using the sublevel caving method down to approximately a 650-m depth. This mining technique caused subsidence and generated a network of faults that propagated from excavated zones at depth up to the surface. The Grangesberg deposit is the largest iron oxide mineralization in central Sweden and is planned to be mined again in the coming years. It is therefore imperative to have a better understanding of the ore geometry and the fault network. A reconnaissance survey consisting of two seismic lines with a total length of 3.5 km was carried out to address these issues. The profiles intersect the Grangesberg deposit and open pit, as well as the major mining-induced fracture zone present in this area. A drop-hammer source mounted on a hydraulic truck was used to generate seismic signals; cabled and wireless receivers were used for the data recording. Preprocessing of the data first required the cable-and wirelessrecorded data sets to be merged before stacking all data available at each shot point. Source gathers exhibit reflections from the near surface, probably generated at lithological boundaries hosting the iron mineralization and other geologic structures. Deeper reflections were also observed. The metavolcanic assemblage hosting the mineralization and the anthropogenic fault network were depicted in the stacked sections, bringing in new elements to refine the geologic model of the area. This study also illustrated the ability of reflection seismic methods to delineate mining-induced structures in hard-rock environments. Low-velocity anomalies from the open pit and adjacent structures were depicted in tomographic sections along the two lines, which showed good agreement with known geologic features and the reflection seismic results.

National Category
Geophysics Geochemistry
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-269284 (URN)10.1190/INT-2014-0212.1 (DOI)000364362900051 ()
Funder
Sida - Swedish International Development Cooperation AgencySida - Swedish International Development Cooperation Agency
Available from: 2015-12-15 Created: 2015-12-15 Last updated: 2017-12-01Bibliographically approved
Högdahl, K., Jonsson, E., Kritikos, A. & Sahlström, F. (2015). Turning yesterday´s waste into tomorrow´s treasure: searching for base and critical metals in central Sweden´s ancient mine dumps. In: A-S André-Mayer (Ed.), Mineral Resources In A Sustainable World: . Paper presented at Mineral deposits in a sustainable world. 13th SGA biennial meeting 2015 (pp. 757-760). , 1-5
Open this publication in new window or tab >>Turning yesterday´s waste into tomorrow´s treasure: searching for base and critical metals in central Sweden´s ancient mine dumps
2015 (English)In: Mineral Resources In A Sustainable World / [ed] A-S André-Mayer, 2015, Vol. 1-5, p. 757-760Conference paper, Published paper (Refereed)
Abstract [en]

Mine dumps the abundant by-products of centuries of mining in Europe have potential to become sources of a wide range of metals and minerals. Despite their variable volumes and the geometallurgical challenges involved, they are a raw material resource to include among other, not least in the context of the present societal demand to increase recycling. Until the mid-1900s the applications and therefore the markets for many metals were limited. Additionally, many were difficult to identify, and thus often missed. In numerous mining districts this resulted in rocks hosting such metals to end up as waste, that is, on the mine dumps. The present pilot project is aimed at testing the potential for such secondary resources in the classic and ancient Bergslagen ore province in south central Sweden, with a special focus on metals presently identified as "critical" for industry. The Bergslagen province, with its 1000-year-history of mining is a suitable testing ground to find out what may actually be out there. Results so far include the detection and mineralogical characterisation of variable amounts of precious and critical as well as base metal minerals, along with the main ore commodity in many old mining fields.

Keywords
Mine dumps; mine waste; recycling; critical metals; Bergslagen; Sweden
National Category
Geology
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-271008 (URN)000374801300172 ()9782855550664 (ISBN)
Conference
Mineral deposits in a sustainable world. 13th SGA biennial meeting 2015
Available from: 2016-01-05 Created: 2016-01-05 Last updated: 2016-07-26Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5581-3613

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