| 1. |
- Bauer, Tobias, Associate professor, 1982-, et al.
(författare)
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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
- 2022
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 117:2, s. 327-359
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Sarlus, Zimer, 1984-, et al.
(författare)
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Character and tectonic setting of plutonic rocks in the Gällivare area, northern Norrbotten, Sweden
- 2019
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Ingår i: GFF. - : Taylor & Francis. - 1103-5897 .- 2000-0863. ; 141:1, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- Petrographical and lithogeochemical investigations in combination with mapping in the Gällivare area, northern Norrbotten, Sweden, have led to the identification of several igneous intrusive rock types. These include: (1) ultramafic-mafic complexes, (2) mafic-intermediate rocks, (3) dolerites and (4) felsic plutons. The ultramafic-mafic rocks include the ca. 1.88 Ga Dundret complex and ca. 1.80 Ga Vassaravaara complex. The Dundret complex has tholeiitic to calc-alkaline affinity, shows a primitive mineral content and was formed in an extensional tectonic setting. The Vassaravaara complex has a similar chemical signature as the Dundret complex. The mafic-intermediate plutons vary in composition from gabbro to diorite. The chemical signature of the dioritic rocks indicate formation in a volcanic arc setting. Dolerites occur as solitary dikes and have calc-alkaline affinity. The felsic plutons include granite and syenite of ca. 1.88, 1.80 and 1.78 Ga age. The felsic plutons have calc-alkaline to shoshonitic affinity and mostly show a metaluminous I-type character. Results indicate subduction at 1.90 Ga resulting in a volcanic arc system, and including extensional events generating back-arc environments leading to mafic, intermediate and felsic magmatism in the Gällivare area. Subduction at 1.80 Ga is suggested to have caused a similar process generating mafic and felsic magmatic rocks in the same area. A subsequent collision event finally generated 1.78 Ga granitic rocks.
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| 3. |
- Sarlus, Zimer, 1984-
(författare)
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Timing and Origin of Igneous Rocks in the Gällivare area, Northern Sweden
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Gällivare area is one of Europe’s top mining regions. The area is located in the northern Norrbotten ore district which hosts ore deposits such as the Malmberget underground iron ore mine, the Aitik open pit Cu-Au mine and the currently explored Nautanen Cu-Au deposit. In addition, several small, mineralized bodies are found. These deposits are hosted by volcanic and volcanosedimentary rocks intruded by intrusive rocks. Previous studies of intrusive and volcanic rocks have often been of local scale and restricted to the major deposits, or of regional scale including entire northern Norrbotten. Minor attention has been paid to rocks of the Gällivare area on a semi-regional scale, especially the intrusive rocks. Very few studies have presented radiometric data of the intrusive and volcanic rocks. In addition, the choice of radiometric method or the re-sults have been lacking confidence. A multidisciplinary approach combining structural geology, geochemistry, geochronology and geophysics is commenced to understand the geological history, crustal geometries and geological evolution of the Gällivare area. This forms basis for future exploration of ore deposits. This study presents geochemical, geochronological and Hf-isotope results with the purpose to characterize and classify major intrusive and volcanic rocks, their timing, source magmas and tectonic environment.Petrographical and geochemical investigations reveal that the intrusive rocks range in composition from ultramafic-mafic to felsic. The ultramafic-mafic rocks comprise dominantly gabbroic layered complexes with peridotitic sequences and have tholeiitic to calc-alkaline affinity. The intermediate and felsic intrusive rocks show calc-alkaline to shoshonitic affinity. Volcanic rocks of the Malmberget deposit show alkali to alkali-calcic character. The geochemical character of the intrusive and volcanic rocks favors a continental arc, transitional to extensional setting (late- to post-collisional).Radiometric in situ U-Pb zircon analyses indicate that mafic and felsic intrusive rocks were generated during magmatic episodes at 1.88, 1.80 Ga and 1.78 Ga. Volcanic rocks hosting the Malmberget deposit belong to the 1.88 Ga magmatic episode. Hydrothermal overgrowth rims from the analyzed zircon crystals indicate extensive reworking and high-T metamorphism of the area around 1.81-1.78 Ga.The mafic-intermediate rocks show minor internal variations in Hf-isotopic signature as well as minor variations inbetween the samples indicative of relatively homogenous source regions beneath the Archean basement. The felsic rocks show a wider range in their Hf-isotopic signature suggesting multiple sources with contribution from old Archean crust.It is here suggested that a subduction process active at 1.9 Ga resulted in a volcanic arc system and ex-tensional environments (back-arc environments) leading to mafic, intermediate and felsic magmatism in the Gällivare area at 1.88 Ga. The mafic-intermediate rocks were extracted from a rather homogenous source reservoir. The c. 1.80 Ga and 1.78 Ga intrusive rocks indicate a complex tectonic evolution of the area at that time. The early 1.80 Ga mafic rocks are suggested to have been generated as a result of extensional magmatism related to an east-directed 1.80 Ga subduction system. Subsequent compression followed by uplift, resulted in the generation of 1.78 Ga felsic rocks.
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| 4. |
- Sarlus, Zimer, 1984-, et al.
(författare)
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Timing and tectonic setting of host rocks to the Malmberget AlO deposit, Sweden
- 2017
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Ingår i: Mineral Resources to Discover. - : Society for Geology Applied to Mineral Deposits. - 9782981689801 ; , s. 959-962
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Konferensbidrag (refereegranskat)abstract
- Host felsic and intermediate meta-volcanic rocks to the Malmberget apatite iron ore (AlO) deposit have been investigated geochemically and geochronologically, the latter using the U-Pb method on a set of zircons. Results indicate emplacement age of 1.9 Ga for the felsic and intermediate volcanic rocks, potentially in an extensional environment. The zircon U-Pb radiometric ages are among the first conclusive ages with implicit constraint on the geological evolution of the northern Norrbotten ore district and Malmberget deposit.
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