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Bauer, Tobias, Associate professorORCID iD iconorcid.org/0000-0003-1627-7058
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Publications (10 of 68) Show all publications
Allen, R., Bauer, T. E., Persson, M. F., Jansson, N. F. & Mercier-Langevin, P. (2023). Base, Precious, and Critical Metal Deposits of the Paleoproterozoic Skellefte District, Sweden: September 25 –30, 2022. Society of Economic Geologists, Inc.
Open this publication in new window or tab >>Base, Precious, and Critical Metal Deposits of the Paleoproterozoic Skellefte District, Sweden: September 25 –30, 2022
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2023 (English)Book (Other academic)
Place, publisher, year, edition, pages
Society of Economic Geologists, Inc., 2023
Series
Guidebook Series, ISSN 2374-6955 ; 65
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-99667 (URN)978-1-629495-02-6 (ISBN)
Available from: 2023-08-14 Created: 2023-08-14 Last updated: 2023-08-14Bibliographically approved
Logan, L., Veress, E. C., Andersson, J. B. H., Martinsson, O. & Bauer, T. E. (2023). Structural framework and timing of the Pahtohavare Cu ± Au deposits, Kiruna mining district, Sweden. Solid Earth, 14(7), 763-784
Open this publication in new window or tab >>Structural framework and timing of the Pahtohavare Cu ± Au deposits, Kiruna mining district, Sweden
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2023 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 14, no 7, p. 763-784Article in journal (Refereed) Published
Abstract [en]

As part of the larger mineral systems approach to Cu-bearing mineralization in northern Norrbotten, this study utilizes structural geology to set the classic Pahtohavare Cu ± Au deposits into an up-to-date tectonic framework. The Pahtohavare Cu ± Au deposits, situated only 5 km southwest of the Kiirunavaara world-class iron oxide–apatite (IOA) deposit, have a dubious timing, and their link to IOA formation is not constrained. The study area contains both epigenic Cu ± Au (Pahtohavare) and iron oxide–copper–gold (IOCG; Rakkurijärvi) mineral occurrences which are hosted in bedrock that has been folded and bound by two shear zones trending northeast to southwest and northwest to southeast to the east and southwest, respectively. Structural mapping and petrographic investigation of the area reveal a noncylindrical, SE-plunging anticline. The cleavage measurements mirror the fold geometry, which characterizes the fold as F2 associated with the late phase of the Svecokarelian orogeny. Porphyroclasts with pressure shadows, mylonitic fabrics, and foliation trails in porphyroblasts indicate S0/S1  is a tectonic fabric. The epigenetic Pahtohavare Cu ± Au mineralization sits in brittle–ductile structures that cross-cut an earlier foliation and the F2 fold, indicating that the timing of the deposits occurred syn- to post-F2 folding, at least ca. 80 Myr after the Kiirunavaara IOA formation. A 3D model and cross-sections of the Pahtohavare–Rakkurijärvi area and a new structural framework of the district are presented and used to suggest that the shear zones bounding the area are likely reactivated early structures that have played a critical role in ore formation in the Kiruna mining district.

Place, publisher, year, edition, pages
Copernicus Publications, 2023
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-100661 (URN)10.5194/se-14-763-2023 (DOI)001031584400001 ()2-s2.0-85170210557 (Scopus ID)
Projects
New Exploration Technologies – NEXT
Funder
EU, Horizon 2020, 776804
Note

Validerad;2023;Nivå 2;2023-08-21 (hanlid)

Available from: 2023-08-21 Created: 2023-08-21 Last updated: 2023-10-11Bibliographically approved
Logan, L., Andersson, J. B. H., Whitehouse, M. J., Martinsson, O. & Bauer, T. E. (2022). Energy Drive for the Kiruna Mining District Mineral System(s): Insights from U-Pb Zircon Geochronology. Minerals, 12(7), Article ID 875.
Open this publication in new window or tab >>Energy Drive for the Kiruna Mining District Mineral System(s): Insights from U-Pb Zircon Geochronology
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2022 (English)In: Minerals, E-ISSN 2075-163X, Vol. 12, no 7, article id 875Article in journal (Refereed) Published
Abstract [en]

The Kiruna mining district, Sweden, known for the type locality of Kiruna-type iron oxide-apatite (IOA) deposits, also hosts several Cu-mineralized deposits including iron oxide-copper-gold (IOCG), exhalative stratiform Cu-(Fe-Zn), and structurally controlled to stratabound Cu +/- Au. However the relationship between the IOA and Cu-systems has not been contextualized within the regional tectonic evolution. A broader mineral systems approach is taken to assess the timing of energy drive(s) within a regional tectonic framework by conducting U-Pb zircon geochronology on intrusions from areas where Cu-mineralization is spatially proximal. Results unanimously yield U-Pb ages from the early Svecokarelian orogeny (ca. 1923-1867 Ma including age uncertainties), except one sample from the Archean basement (2698 +/- 3 Ma), indicating that a distinct thermal drive from magmatic activity was prominent for the early orogenic phase. A weighted average Pb-207/Pb-206 age of 1877 +/- 10 Ma of an iron-oxide-enriched gabbroic pluton overlaps in age with the Kiirunavaara IOA deposit and is suggested as a candidate for contributing mafic signatures to the IOA ore. The results leave the role of a late energy drive (and subsequent late Cu-mineralization and/or remobilization) ambiguous, despite evidence showing a late regional magmatic-style hydrothermal alteration is present in the district.

Place, publisher, year, edition, pages
MDPI, 2022
Keywords
Kiruna, mineral system, U-Pb zircon geochronology, IOA, IOCG
National Category
Geophysics Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-92436 (URN)10.3390/min12070875 (DOI)000833356600001 ()2-s2.0-85137380223 (Scopus ID)
Funder
EU, Horizon 2020, 776804Swedish Research Council, 2017-00671
Note

Validerad;2022;Nivå 2;2022-08-11 (hanlid)

Available from: 2022-08-11 Created: 2022-08-11 Last updated: 2024-01-17Bibliographically approved
Bauer, T., Lynch, E., Sarlus, Z., Drejing-Carrol, D., Martinsson, O., Metzger, N. & Wanhainen, C. (2022). Structural Controls on Iron Oxide Copper-Gold Mineralization and Related Alteration in a Paleoproterozoic Supracrustal Belt: Insights from the Nautanen Deformation Zone and Surroundings, Northern Sweden. Economic geology and the bulletin of the Society of Economic Geologists, 117(2), 327-359
Open this publication in new window or tab >>Structural Controls on Iron Oxide Copper-Gold Mineralization and Related Alteration in a Paleoproterozoic Supracrustal Belt: Insights from the Nautanen Deformation Zone and Surroundings, Northern Sweden
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2022 (English)In: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 117, no 2, p. 327-359Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Society of Economic Geologists, 2022
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-83978 (URN)10.5382/econgeo.4862 (DOI)000743559000003 ()2-s2.0-85121295941 (Scopus ID)
Projects
Multi-scale 4-dimensional geological modeling of the Gällivare area
Funder
Vinnova
Note

Validerad;2022;Nivå 2;2022-03-11 (sofila);

Funder: Boliden AB; LKAB

Available from: 2021-05-03 Created: 2021-05-03 Last updated: 2023-09-05Bibliographically approved
Andersson, J. B. .., Logan, L., Martinsson, O., Chew, D., Kooijman, E., Kielman-Schmitt, M., . . . Bauer, T. E. (2022). U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden. Precambrian Research, 372, Article ID 106613.
Open this publication in new window or tab >>U-Pb zircon-titanite-apatite age constraints on basin development and basin inversion in the Kiruna mining district, Sweden
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2022 (English)In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 372, article id 106613Article in journal (Refereed) Published
Abstract [en]

To constrain the tectonothermal evolution of the type locality for iron oxide-apatite deposits, we have obtained U-Pb zircon, titanite, and apatite age data for the Kiruna mining district in northernmost Sweden. The results indicate that the host basin initiated in an overall extensional regime as indicated by the deposition of alluvial conglomerates and greywackes. A volcanic intercalation in a conglomerate unit northwest of the Luossavaara iron oxide-apatite deposit yields a U-Pb zircon age of 1887 ± 3 Ma representing the timing of the earliest Orosirian volcanism in the central Kiruna mining district coinciding with the onset of basin development. In-situ analysis of titanite on hydrothermally altered fracture planes within a cataclastic fault damage zone (c. 270 m from the fault core system associated to the Luossavaara iron oxide-apatite deposit) yields complex U-Pb data. Applying a strict discordance filter yields a 207Pb/206Pb age of 1889 ± 26 Ma. The age implies that the fault probably has a syn-volcanic origin and that syn-volcanic faults may have played an important role during iron ore emplacement. The mineralized basin was subsequently buried and metamorphosed under upper greenschist-facies conditions and later tectonically exhumed and cooled below the apatite closure temperature at 1805 ± 26 Ma indicated by apatite from the Nukutus iron oxide-apatite deposit. Basin inversion is temporally constrained by syn-tectonic titanite as part of sodic-calcic + Fe + Cl hydrothermal alteration along a brittle-ductile reverse shear zone to the east of the study area. Titanite grains that show sector and oscillatory zoning yield an age of 1812 ± 3 Ma, which we interpret as the onset of basin inversion. Homogeneous (relatively unzoned) titanite in the same sample yields an age of 1802 ± 8 Ma, tentatively indicating that the tectonothermal activity lasted up to c. 20 m.y.

Place, publisher, year, edition, pages
Elsevier, 2022
Keywords
Geochronology, Kiruna, IOA, basin development, basin inversion
National Category
Geology
Research subject
Ore Geology; Centre - Centre for Advanced Mining & Metallurgy (CAMM)
Identifiers
urn:nbn:se:ltu:diva-87738 (URN)10.1016/j.precamres.2022.106613 (DOI)000807894300001 ()2-s2.0-85125532558 (Scopus ID)
Funder
EU, Horizon 2020, 776804
Note

Validerad;2022;Nivå 2;2022-03-31 (hanlid);

Funder: Centre of Advanced Mining and Metallurgy (CAMM) (2450-2009); Science Foundation Ireland (SFI) (13/RC/2092 and 13/RC/2092_P2)

Available from: 2021-11-03 Created: 2021-11-03 Last updated: 2023-09-05Bibliographically approved
Tavakoli, S., Sarlus, Z., Kronsell, I. & Bauer, T. E. (2021). 2.5D geophysical model of the Gällivare mining area: An integrated study to model the top 4km of the subsurface and guide for future exploration activities. Geophysical Prospecting, 69(4), 821-841
Open this publication in new window or tab >>2.5D geophysical model of the Gällivare mining area: An integrated study to model the top 4km of the subsurface and guide for future exploration activities
2021 (English)In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 69, no 4, p. 821-841Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
John Wiley & Sons, 2021
Keywords
Gällivare area, potential field data, 2.5D modeling, Slingram data, geophysical investigation, rock physical properties
National Category
Geophysics
Research subject
Ore Geology; Exploration Geophysics; Soil Mechanics
Identifiers
urn:nbn:se:ltu:diva-82810 (URN)10.1111/1365-2478.13077 (DOI)000626154500001 ()2-s2.0-85102201190 (Scopus ID)
Projects
Multi‐scale 4‐dimensional geological modeling of the Gällivare area
Funder
Vinnova
Note

Validerad;2021;Nivå 2;2021-04-20 (alebob);

Finansiär: Boliden Mineral AB, LKAB

Available from: 2021-02-08 Created: 2021-02-08 Last updated: 2021-04-20Bibliographically approved
Lishchuk, V., Haller, E., Martinsson, O. & Bauer, T. E. (2021). Analytical Modeling of a Synthetic VMS Deposit Data: a Proxy Tool for Education and Initial Research. Mining, Metallurgy & Exploration, 38(2), 863-874
Open this publication in new window or tab >>Analytical Modeling of a Synthetic VMS Deposit Data: a Proxy Tool for Education and Initial Research
2021 (English)In: Mining, Metallurgy & Exploration, ISSN 2524-3462, Vol. 38, no 2, p. 863-874Article in journal (Refereed) Published
Abstract [en]

Freely accessible and non-confidential real-life geological data sets from mineral deposits are desirable for the wide range of applications in research and education. However, publicly available statistical data are limited in their number and quality-they contain reduced information about geological, geophysical, geotechnical, chemical, mineralogical, and other relevant properties of deposits. This makes such data insufficient for scientific purposes. However, the amount of geological knowledge obtained for a variety of deposits in the past allows the construction of an idealized synthetic ore body model using analytical approach. Such a model could be used for education purposes and testing basic scientific theories, e.g., visualization of deposit structure; teaching sampling strategies; testing new algorithms for mine planning; or comparing geostatistical modeling methods. This paper presents an analytical approach to simulate volcanic massive sulfide (VMS) deposits and shows how synthetic deposit model can be constructed and further used for studying sampling with drilling and simulating folding and faulting.

Place, publisher, year, edition, pages
Springer, 2021
Keywords
VMS, Synthetic data, Simulation, Deformation
National Category
Geology
Research subject
Applied Mathematics; Ore Geology
Identifiers
urn:nbn:se:ltu:diva-82665 (URN)10.1007/s42461-020-00377-5 (DOI)000607776500001 ()2-s2.0-85100098823 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-04-20 (alebob)

Available from: 2021-01-28 Created: 2021-01-28 Last updated: 2023-09-05Bibliographically approved
Andersson, J. B. .., Bauer, T. & Martinsson, O. (2021). Structural Evolution of the Central Kiruna Area, Northern Norrbotten, Sweden: Implications on the Geologic Setting Generating Iron Oxide-Apatite and Epigenetic Iron and Copper Sulfides. Economic geology and the bulletin of the Society of Economic Geologists, 116(8), 1981-2009
Open this publication in new window or tab >>Structural Evolution of the Central Kiruna Area, Northern Norrbotten, Sweden: Implications on the Geologic Setting Generating Iron Oxide-Apatite and Epigenetic Iron and Copper Sulfides
2021 (English)In: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 116, no 8, p. 1981-2009Article in journal (Refereed) Published
Abstract [en]

To guide future exploration, this predominantly field based study has investigated the structural evolution of the central Kiruna area, the type locality for iron oxide-apatite deposits that stands for a significant amount of the European iron ore production. Using a combination of geologic mapping focusing on structures and stratigraphy, petrography with focus on microstructures, X-ray computed tomography imaging of sulfide-structure relationships, and structural 2D-forward modeling, a structural framework is provided including spatial-temporal relationships between iron oxide-apatite emplacement, subeconomic Fe and Cu sulfide mineralization, and deformation. These relationships are important to constrain as a guidance for exploration in iron oxide-apatite and iron oxide copper-gold prospective terrains and may help to understand the genesis of these deposit types. Results suggest that the iron oxide-apatite deposits were emplaced in an intracontinental back-arc basin, and they formed precrustal shortening under shallow crustal conditions. Subsequent east-west crustal shortening under greenschist facies metamorphism inverted the basin along steep to moderately steep E-dipping structures, often subparallel with bedding and lithological contacts, with reverse, oblique to dip-slip, east-block-up sense of shears. Fe and Cu sulfides associated with Fe oxides are hosted by structures formed during the basin inversion and are spatially related to the iron oxide-apatite deposits but formed in fundamentally different structural settings and are separated in time. The inverted basin was gently refolded and later affected by hydraulic fracturing, which represent the last recorded deformation-hydrothermal events affecting the crustal architecture of central Kiruna.

Place, publisher, year, edition, pages
Society of Economic Geologists, 2021
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-87685 (URN)10.5382/econgeo.4844 (DOI)000707200500001 ()2-s2.0-85122448953 (Scopus ID)
Note

Validerad;2021;Nivå 2;2021-10-29 (beamah);

Forskningsfinansiär: Centre of Advanced Mining and Metallurgy

Available from: 2021-10-29 Created: 2021-10-29 Last updated: 2023-09-05Bibliographically approved
Vadoodi, R., Rasmussen, T. M., Smirnov, M. & Bauer, T. (2021). Towards an understanding of mineral systems – Contributions from magnetotelluric data from the Fennoscandian Shield in northern Sweden. Tectonophysics, 808, Article ID 228816.
Open this publication in new window or tab >>Towards an understanding of mineral systems – Contributions from magnetotelluric data from the Fennoscandian Shield in northern Sweden
2021 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 808, article id 228816Article in journal (Refereed) Published
Abstract [en]

Magnetotelluric data from 104 new stations in northern Sweden together with previously available MaSca project data are analysed with respect to a hypothesised genetic relation between mineral occurrences and commonly reported deep crustal electrically conductive structures in Precambrian Shield areas. A total of 165 stations from the north-eastern part of the Norrbotten ore province are modelled from an area characterised as having an Achaean basement with later reworking during the Paleoproterozoic. The data cover an area of 200 × 250 km2 and provide a significant improvement of spatial resolution compared to previously available data. The derived 3D model reveals the presence of strong crustal conductors with conductance of more than 3000 S at depth of tens of kilometres within a generally resistive crust. A subdivision into a central more conductive domain bounded towards north and south by resistive domains is revealed. The boundaries between these three domains are oriented NW-SE. The southern boundary coincides roughly with the boundary between Archaean and Paleoproterozoic crust defined by εNd data. The northern boundary coincides with an interpreted 2.4–2.3 Ga coastline of a marine rift basin, which is spatially defined by the occurrence of the Kovo group rocks. The location of major conductors within the central domain correlates with the presence of mapped Paleoproterozoic metasupracrustal belts. A significant part of the middle crust conductors is elongated in directions that coincide with major deformation zones that have been mapped from airborne magnetic data and geological fieldwork. Some of these conductors have near-surface expression where they spatially correlate with the location of known mineralisation. In these cases, the conductive structures may mark the pathways for metal-bearing hydrothermal fluids. Interpretations involving enhanced quantities of magnetite or graphite in the middle crust are discussed but the magnetotelluric data alone are not conclusive with respect to cause of observed high conductivities.

Place, publisher, year, edition, pages
Elsevier, 2021
Keywords
Magnetotellurics, 3D Inversion, Electrical Conductivities, Mineralisation
National Category
Geophysics
Research subject
Ore Geology; Exploration Geophysics
Identifiers
urn:nbn:se:ltu:diva-83304 (URN)10.1016/j.tecto.2021.228816 (DOI)000674649000005 ()2-s2.0-85103982326 (Scopus ID)
Funder
Luleå University of Technology
Note

Validerad;2021;Nivå 2;2021-04-20 (alebob)

Available from: 2021-03-18 Created: 2021-03-18 Last updated: 2023-09-05Bibliographically approved
Andersson, J., Bauer, T. & Lynch, E. P. (2020). Evolution of structures and hydrothermal alteration in a Palaeoproterozoic supracrustal belt: Constraining paired deformation–fluid flow events in an Fe and Cu–Au prospective terrain in northern Sweden. Solid Earth, 11(2), 547-578
Open this publication in new window or tab >>Evolution of structures and hydrothermal alteration in a Palaeoproterozoic supracrustal belt: Constraining paired deformation–fluid flow events in an Fe and Cu–Au prospective terrain in northern Sweden
2020 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 11, no 2, p. 547-578Article in journal (Refereed) Published
Abstract [en]

An approximately 90 km long Palaeoproterozoic supracrustal belt in the northwestern Norrbotten ore province (northernmost Sweden) was investigated to characterize its structural components, assess hydrothermal alteration–structural geology correlations, and constrain a paired deformation–fluid flow evolution for the belt. New geological mapping of five key areas (Eustiljåkk, Ekströmsberg, Tjårrojåkka, Kaitum West, and Fjällåsen–Allavaara) indicates two major compressional events (D1 and D2) have affected the belt, with each associated with hydrothermal alteration types typical for iron oxide–apatite and iron oxide Cu–Au systems in the region. Early D1 generated a regionally distributed, penetrative S1 foliation and oblique reverse shear zones that show a southwest-block-up sense of shear that formed in response to NE–SW crustal shortening. Peak regional metamorphism at epidote–amphibolite facies broadly overlaps with this D1 event. Based on overprinting relationships, D1 is associated with regional scapolite ± albite, magnetite + amphibole, and late calcite alteration of mafic rock types. These hydrothermal mineral associations linked to D1 structures may form part of a regionally pervasive evolving fluid flow event but are separated in this study by crosscutting relationships.

During D2 deformation, folding of S0–S1 structures generated F2 folds with steeply plunging fold axes in low-strain areas. NNW-trending D1 shear zones experienced reverse dip-slip reactivation and strike-slip-dominated movements along steep, E–W-trending D2 shear zones, producing brittle-plastic structures. Hydrothermal alteration linked to D2 structures is a predominantly potassic–ferroan association comprising K-feldspar ± epidote ± quartz ± biotite ± magnetite ± sericite ± sulfides. Locally, syn- or post-tectonic calcite is the main alteration mineral in D2 shear zones that intersect mafic rocks. Our results highlight the importance of combining structural geology with the study of hydrothermal alterations at regional to belt scales to understand the temporal–spatial relationship between mineralized systems. Based on the mapping results and microstructural investigations as well as a review of earlier tectonic models presented for adjacent areas, we suggest a new structural model for this part of the northern Fennoscandian Shield. The new model emphasizes the importance of reactivation of early structures, and the model harmonizes with tectonic models presented by earlier workers based mainly on petrology of the northern Norrbotten area.

Place, publisher, year, edition, pages
Copernicus publications, 2020
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-78783 (URN)10.5194/se-11-547-2020 (DOI)000527805400001 ()2-s2.0-85083756752 (Scopus ID)
Note

Validerad;2020;Nivå 2;2020-05-05 (johcin)

Available from: 2020-05-05 Created: 2020-05-05 Last updated: 2023-09-04Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-1627-7058

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