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Utilizing a tectonic framework to constrain the mineral system and remobilization in the Kiruna mining district, Sweden
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.ORCID iD: 0000-0003-1583-502x
2022 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The Kiruna mining district, located in the northern Norrbotten ore province, Sweden, is a geologically and economically important area, being the type-locality for Kiruna iron oxide-apatite (IOA) deposits and also host to a variety of other deposits including syngenetic stratiform exhalative Cu-(Fe-Zn) (Viscaria, Eastern Pahtohavare), epigenetic stratabound Cu ± Au (Pahtohavare), and iron oxide-copper-gold (IOCG, Rakkurijärvi) deposits. However, the timing of IOA versus IOCG within the tectonic evolution is in question based on structural investigations showing Cu- and Fe-sulfides occur in late-orogenic structures. Here we use an established tectonic framework to constrain mineral systems (tectonic/thermal drives, metal and ligand sources, fluid pathways, traps, remobilization mechanisms) related to the early and late phases of the Svecokarelian orogeny in the Kiruna mining district. U-Pb zircon geochronology of intrusions in the district indicates a thermal drive was present during the early phase of the Svecokarelian orogeny from ca. 1920-1865 Ma, however remains enigmatic for the late Svecokarelian orogeny. Zircon grains from a magnetite-ilmenite gabbro yielded an age of 1881 ± 8 Ma, coeval with the Kiirunavaara IOA deposit and suggested to represent an important generation of mafic magmatism related to the ore. Lithogeochemistry of early bimodal Svecokarelian intrusions in the district indicates a within-plate to active continental margin environment with a volcanic arc affinity, pointing to a back arc environment. Epsilon Ndi and 87Sr/86Sri values calculated from the U-Pb ages for the igneous intrusions were compared to samples of ore-related alteration from epigenetic Pahtohavare and Rakkurijärvi deposits, district greenstone, and Archean samples. Results show that each deposit sourced Sr and Nd from a variety of rocks suggesting broad fluid transport. Each deposit has a distinct Sr mixing trend suggesting they formed from different ore-forming fluids and pathways. This is supported by new structural data that constrain the folding event and the ore-related quartz-carbonate-sulfide veins in the Pahtohavare area to a late orogenic timing, compared to the early orogenic timing of Rakkurijärvi. Sulfide trace element and sulfur isotope data from structurally constrained ores within the tectonic framework also record distinct characteristics between early and late deposits. However, remobilization of early Pahtohavare sulfides associated to an increase in Co content and heavier sulfur isotope compositions is recorded. The results of this study illustrate that using a structural framework approach to constrain the ingredients of mineral systems is a powerful strategy for interpreting ore deposit processes in tectonically complex terrains where both IOA and IOCG deposits occur.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2022.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords [en]
Kiruna, tectonic framework, mineral system, IOCG, IOA, remobilization, sulfur isotopes, trace elements, geochronology, Pahtohavare, Viscaria, Rakkurijärvi
National Category
Geology
Research subject
Ore Geology
Identifiers
URN: urn:nbn:se:ltu:diva-88406ISBN: 978-91-7790-995-8 (print)ISBN: 978-91-7790-996-5 (electronic)OAI: oai:DiVA.org:ltu-88406DiVA, id: diva2:1619752
Presentation
2022-02-01, F1031, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Funder
EU, Horizon 2020, 776804Available from: 2021-12-14 Created: 2021-12-14 Last updated: 2023-09-05Bibliographically approved
List of papers
1. A mineral systems-scale investigation into the Kiruna mining district and implications for the timing of ore forming processes within a regional tectonic framework
Open this publication in new window or tab >>A mineral systems-scale investigation into the Kiruna mining district and implications for the timing of ore forming processes within a regional tectonic framework
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The formation of iron oxide apatite (IOA) and iron oxide-copper-gold (IOCG) deposits and their relation to each other is currently strongly debated. Recent characterization of the polyphase Svecokarelian orogeny in the northern Norrbotten ore province provides a tectonic framework that can be used to assess the timing of IOA and IOCG genetic processes from a broader mineral systems perspective. This study combined whole rock lithogeochemistry, whole rock Sr and Nd isotopes, U-Pb zircon geochronology, and structural data to gain insight into the Kiruna mining district mineral system. Results show that the igneous intrusions range from mafic to felsic in composition and developed in an active continental margin with both volcanic arc and within-plate affinities. The intrusions have ages ranging from 1891 ± 6 Ma to 1876 ± 11 Ma. One magnetite-ilmenite gabbro gives a concordia age of 1881 ± 8 Ma. These ages indicate a thermal drive for the mineral system can be recognized occurring during an early-orogenic deformation phase (D0-D1) but remains enigmatic for a late-orogenic phase (D2). 87Sr/86Sri and εNdi data from ore-related alteration (Na-alteration and late K-Fe overprint) at Pahtohavare Cu ± Au and Rakkurijärvi IOCG deposits as well as district igneous, greenstone, and Archean rocks indicate that the deposits have distinct Sr-mixing trends and that both sourced Sr and Nd from a wide variety of protoliths. Alteration results show a prominent Na-metasomatism with certain areas showing a K-overprint. New structural analysis of the Pahtohavare area indicates the main ore-related generation of quartz-carbonate-sulfide veins cross cut foliation and were introduced during F2 folding in the late Svecokarelian (D2), suggesting that a late Cu-Au mineralization/remobilization occurred in the Kiruna mining district ca. 80 m.y. after the emplacement of the Kiirunavaara IOA deposit. In brief, our data show that IOA and IOCG systems can be of different ages and sources within the same district.

Keywords
Kiruna, U-Pb zircon geochronology, Rb-Sr isotopes, Sm-Nd isotopes, IOA, IOCG
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-88402 (URN)
Funder
EU, Horizon 2020, 776804
Available from: 2021-12-13 Created: 2021-12-13 Last updated: 2022-02-01Bibliographically approved
2. Signatures of sulfide remobilization in the Kiruna mining district: a SIMS sulfur isotope and LA-ICP-MS trace element study
Open this publication in new window or tab >>Signatures of sulfide remobilization in the Kiruna mining district: a SIMS sulfur isotope and LA-ICP-MS trace element study
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The Kiruna mining district in northern Norrbotten, Sweden, is situated in a region that is broadly described as an iron oxide-copper-gold (IOCG) district. Kiruna is well known for the iron oxide-apatite (IOA) deposits (Kiruna-type), but also hosts several Cu-bearing prospects including the Viscaria and Eastern Pahtohavare stratabound-stratiform Cu-(Fe-Zn), the Rakkurijärvi IOCG, and the Pahtohavare epigenetic Cu ± Au prospects. However the genesis of the Cu mineralization in the district has not been studied from a structural perspective in relation to the tectonic evolution of the region. Utilizing recent structural characterization of the Svecokarelian orogenic cycle as a framework, Cu- and Fe-bearing sulfides have been identified from the pre-, early, and late orogenic phases and assessed for primary and overprinting signatures with in situ δ34S and trace element data. Results indicate that the youngest stage of epigenetic mineralization (late orogenic) in the Pahtohavare area precipitated vein-hosted pyrite from a strongly Co-enriched hydrothermal fluid with δ34S values between 2‰ and 6 ‰. The late mineralization event occurred syn- to post-folding of the host rocks together with remobilization of sulfides from the younger Eastern Pahtohavare deposit. This remobilization is characterized by a fractionation of sulfur isotopes towards heavier values and dispersion of Co and Ni data towards higher and lower concentrations, respectively, and indicates redistribution of metals occurred as a result of the late orogenic mineralization and deformation. This implies a distinct Cu-forming event occurred in the late Svecokarelian orogeny both that introduced new metals and redistributed (and possibly incorporated) metals from a preexisting source. Metamorphic and low temperature remobilization is also recorded in samples from the district characterized by increases in Co and Ni, respectively. 

Keywords
SIMS sulfur isotope, LA-ICP-MS trace element, Kiruna, sulfides, IOCG
National Category
Geology
Research subject
Ore Geology
Identifiers
urn:nbn:se:ltu:diva-88404 (URN)
Funder
EU, Horizon 2020, 776804
Available from: 2021-12-13 Created: 2021-12-13 Last updated: 2022-02-01Bibliographically approved

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