| 1. |
- Rivera, Javier, et al.
(författare)
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Platinum-group element and gold enrichment in soils monitored by chromium stable isotopes during weathering of ultramafic rocks
- 2018
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Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 499, s. 84-99
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Tidskriftsartikel (refereegranskat)abstract
- Weathering of ultramafic rocks can lead to the formation of soil profiles with high contents of Fe, Ni, Co, platinum-group elements (PGE) and gold. Traditionally, these metal-rich soils are known as “laterites” and are formed under tropical climates and stable tectonic conditions. However, little is known about their possible development in cold/humid regions, and the factors governing PGE and gold mobility and enrichment under these weathering conditions are poorly constrained. In this study, five soil profiles developed on serpentinized, chromite-bearing ultramafic rocks at La Cabaña, located in the Coastal Range of south-central Chile (38° S) were studied by combining major and trace element geochemistry with chromium stable isotope data. The results show that the soils developed at La Cabaña have higher PGE and Au contents than the parent serpentinite rock, with ∑PGE and Au reaching up to 160 ppb and 29 ppb in a limonitic soil horizon and clay saprolite, respectively. Most soil samples have slightly negative δ53/52CrSRM979 values, within a range of −0.089 ± 0.012‰ to −0.320 ± 0.013‰ (average of −0.178‰), and are in agreement with previous data reported for modern soils. A noteworthy relation between δ53/52Cr data and PGE + Au contents is observed in the studied soil horizons, where isotopically lighter values of δ53/52Cr match the higher contents of PGE and gold. These results show that pedogenetic processes operating at the cold and humid La Cabaña area are capable of increasing the total PGE and Au contents of certain soil horizons. Such processes are complex and multivariate but are primarily modulated by chromite dissolution and the formation of secondary phases such as clay minerals and oxy-hydroxide phases in the soil. These findings provide evidence that important weathering and PGE + Au supergene accumulation are not only restricted to tropical latitudes, and that the chromium isotope system is a useful proxy to track surface redox process and noble metal enrichment during pedogenesis.
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| 2. |
- Jansson, Nils, et al.
(författare)
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Controls on cobalt and nickel distribution in hydrothermal sulphide deposits in Bergslagen, Sweden : constraints from solubility modelling
- 2020
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Ingår i: GFF. - : Taylor & Francis. - 1103-5897 .- 2000-0863. ; 142:2, s. 87-95
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Tidskriftsartikel (refereegranskat)abstract
- We address controls on Co and Ni distribution, based on their solubility in hydrothermal fluids as functions of pH, ƒO2 and T, in two end-member types of sulphide deposits in Bergslagen, Sweden. Oxidized hydrothermal fluids, as have been suggested for the formation of the Zinkgruvan deposit, would efficiently transport Co and Ni in solution, even at 150 oC. Formation of Co and Ni sulphides and sulphosalts supersedes or overlaps the precipitation of other sulphides along a reduction or H2S-mixing path. This is consistent with the presence of Co and Ni sulphides and sulphosalts in vent-proximal Cu-Zn mineralization at Zinkgruvan.Reduced, acidic and hot (≥250 oC) hydrothermal fluids that have been invoked for the formation of deposits like Falun and Stollberg could also transport Co and Ni in solution. However, their solubility is strongly dependent on high T and low pH. Cooling and neutralization are here proposed as likely key triggers for the deposition of Co and Ni, yet, unlike in the Zinkgruvan scenario, saturation will occur within the pyrite stability field, whereby these metals may be sequestered as stoichiometric lattice substitutions in pyrite and other sulphides rather than forming minerals of their own.We conclude that at any T or realistic pH, hydrothermal systems involving oxidized brines have a greater ability to traverse and leach large rock volumes of Co and Ni. Consequently, areas hosting deposits that formed from such brines have a significant exploration potential for these metals, even in areas where Co-enriched source rocks are lacking or subordinate.
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| 3. |
- Ecke, Frauke, et al.
(författare)
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Landscape structure and the long-term decline of cyclic grey-sided voles in Fennoscandia
- 2010
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Ingår i: Landscape Ecology. - : Springer. - 0921-2973 .- 1572-9761. ; 25:4, s. 551-560
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Tidskriftsartikel (refereegranskat)abstract
- Changes in forest landscape structure have been suggested as a likely contributing factor behind the long-term decline in the numbers of cyclic grey-sided voles (Clethrionomys rufocanus) in northern Fennoscandian lowland regions in contrast to mountain regions due to the absence of forest management in the mountains. This study, for the first time, formally explored landscape structure in 29 lowland (LF) and 14 mountain forest (MF) landscapes (each 2.5 x 2.5 km) in northern Sweden, and related the results to the cumulated spring trapping index of the grey-sided vole in 2002-2006. The grey-sided vole showed striking contrasts in dynamics close in space and time. The MF landscapes were characterized by larger patches and less fragmentation of preferred forest types. The grey-sided vole was trapped in all of 14 analyzed MF landscapes but only in three out of 29 of the LF landscapes. MF and LF landscapes with grey-sided vole occurrence were characterized by similar focal forest patch size (mean 357 ha, minimum 82 ha and mean 360 ha, minimum 79 ha, respectively). In contrast, these MF compared to the LF landscapes were characterized by larger patches of preferred forest types and less fragmented preferred forest types and by a lower proportion of clear-cut areas. The present results suggest that landscape structure is important for the abundance of grey-sided voles in both regions. However, in the mountains the change from more or less seasonal dynamics to high-amplitude cycles between the mid 1990s and 2000s cannot be explained by changes in landscape structure.
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| 4. |
- Juhlin, C., et al.
(författare)
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Crustal reflectivity near the Archean-Proterozoic boundary in northern Sweden and implications for the tectonic evolution of the area
- 2002
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 150:1, s. 180-197
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Tidskriftsartikel (refereegranskat)abstract
- Sm–Nd isotope ratios of 1.9–1.8 Ga granitoids delineate the Archaean–Proterozoic boundary in northern Sweden, an important feature in the Fennoscandian Shield. The boundary strikes approximately WNW–ESE and is defined as a c. 20 km wide zone with juvenile Palaeoproterozoic rocks to the SSW and Archaean and Proterozoic rocks, derived to a large extent from Archaean sources, to the NNE. It therefore constitutes the strongly reworked margin of the old Archaean craton. Extrapolation of the boundary offshore into the Bothnian Bay and correlation with the marine reflection seismic BABEL Lines 2 and 3/4 indicates that the boundary dips to the south-southwest, consistent with interpretation of the Sm–Nd data. In order to tie the BABEL results with onshore surface geology and obtain detailed images of the uppermost crust a short (30 km of subsurface coverage) pilot profile was acquired in the Luleå area of northern Sweden during August 1999. The profile consisted of a high-resolution shallow component (1 kg shots) and a lower-resolution deep component (12 kg shots). Both components image most of the reflective crust, with the deep component providing a better image below 10 s. Comparison of signal penetration curves with data acquired over the Trans-Scandinavian Igneous Belt (a large batholith) indicate the transparent nature of the crust there to be caused by geological factors, not acquisition parameters. Lower crustal reflectivity patterns on the Luleå test profile are similar to those observed on the BABEL lines, suggesting the same lower crust onshore as offshore. Interpreted Archaean reflective upper crust in the NE extends below more transparent Proterozoic crust in the SW. This transparent crust contains a number of high-amplitude reflectors that may represent shear zones and/or mafic rock within granite intrusions. A marked boundary in the magnetic field in the SW has been interpreted as being the result of a gently west-dipping contact zone between meta-sediments and felsic volcanic rocks, however, the seismic data indicate a near-vertical structure in this area. By correlating the onshore and offshore seismic data we have better defined the location of the Archaean–Proterozoic boundary on the BABEL profiles. Our new interpretation of the crustal structure along the northern part of the BABEL Line 2 shows a more bi-vergent geometry than previous interpretations. Comparison of the re-interpreted crustal structure in northern Sweden with that found in the Middle Urals shows several similarities, in particular the accretion of a series of arcs to a stable craton. Based on this similarity and geological data, we deduce that a continental arc accreted to the southwestern margin of the Archaean craton at c. 1.87 Ga. Shortly thereafter, the Skellefte island arc underthrust the continental arc owing to a collision further to the southwest resulting in the bi-vergent crustal structure observed today.
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| 5. |
- Logan, Leslie, 1992-, et al.
(författare)
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Energy Drive for the Kiruna Mining District Mineral System(s): Insights from U-Pb Zircon Geochronology
- 2022
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Ask, Maria, et al.
(författare)
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Proposed Drilling into Postglacial Faults : The Pärvie Fault System
- 2021
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Ingår i: Glacially-Triggered Faulting. - Cambridge : Cambridge University Press. - 9781108779906 - 9781108490023 ; , s. 151-174
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Bokkapitel (refereegranskat)abstract
- Postglacial faults in northern Fennoscandia have been investigated through geophysical methods, trenching, and mapping of brittle deformation structures. Very little is known about postglacial faults through direct measurements. A few short, up to 500 m deep, boreholes exist. Plans for a scientific drilling program were initiated in 2010. The drilling target has been identified: The Pärvie Fault system is the longest known postglacial fault in the world and has been proposed to have hosted an M8 earthquake near the end or just after the last glaciation. Further, this fault system is still microseismically active. The drill sites are north of the Arctic Circle, in a sparsely populated area. Existing site survey data, established logistics, and societal relevance through the fault’s proximity to mining and energy operations make this fault system an appropriate target. The International Continental Scientific Drilling Program approved a full drilling proposal in October 2019. This chapter presents an abbreviated version of the approved proposal.
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| 7. |
- Andersson, Ulf Bertil, et al.
(författare)
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Emendment to the term complex in: “Guide for geological nomenclature in Sweden” (Kumpulainen 2016)
- 2022
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Ingår i: GFF. - : Taylor & Francis. - 1103-5897 .- 2000-0863. ; 144:3-4, s. 151-151
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Since the publication of Kumpulainen (2016), the Committeehave been alerted by the investigation and subsequent changesto the North American Stratigraphic Code concerning thelithodemic unit“complex”(Easton et al.2016; North Ameri-can Commission on Stratigraphic Nomenclature (NACSN)2017). These changes concern the introduction of the nomen-clature unit“Intrusive Complex”. In the original version(NACSN1983), as well as in the Swedish Guide for nomencla-ture (Kumpulainen2016), the unit“complex”is defined ascontaining at least two genetic classes of rocks, i.e., igneous,sedimentary, or metamorphic.
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| 8. |
- Dehghannejad, Mahdieh, et al.
(författare)
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Reflection seismic imaging of the upper crust in the Kristineberg mining area, northern Sweden
- 2010
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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 71:4, s. 125-136
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Tidskriftsartikel (refereegranskat)abstract
- The Kristineberg mining area is located in the western part of the Palaeoproterozoic Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 3D geologic modeling project, two new reflection seismic profiles were acquired with a total length of about 20 km. One profile (HR), parallel to previous seismic profiles, was acquired using a 10 m receiver and source interval and crosses the steeply dipping structures of the Kristineberg mine. The other profile (Profile 2) runs perpendicular to all existing profiles in the area. Although the structural geology is complex, the processed seismic data reveal a series of steeply dipping to sub-horizontal reflections, some of which reach the surface and allow correlation with surface geology. Our general interpretation of the seismic images is that the Kristineberg mine and associated mineral horizon are located in the northern part of a series of steeply south dipping structures. Overall, main structures plunge to the west at about 30 degrees-40 degrees. Cross-dip analysis and reflection modeling were carried out to obtain the 3D orientation of the main reflections and to provide insight into the possible contribution of out-of-the-plane reflections. This helped, for example, to obtain the 3D geometry of a deep reflection that was previously interpreted as structural basement to volcanic rocks. The new reflection seismic profiles have improved our understanding of shallow geological structures in the area and in conjunction with recently acquired potential field data, magnetotelluric data and geological observations will help to refine previous 3D geologic modeling interpretations that were aimed at larger scale structures.
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| 9. |
- Malehmir, Alireza, et al.
(författare)
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Regional structural profiles in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden
- 2007
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 159:1-2, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- The Kristineberg mining area is situated in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden, and is well known for its VHMS base-metal and gold deposits. This paper presents five upper crustal geological cross sections that have been constructed and mainly constrained by seismic reflection data, potential field modeling as well as geological field observations. These profiles are visualized in 3D to highlight the three dimensionality and internal consistency of structures across the region. The resulting structural model for the Skellefte volcanics and overlying metasediments comprises two thrust-sheets that expose the Skellefte volcanics in the cores of hanging-wall anticlinal structures. A shear-zone is imaged as a band of seismic reflectivity terminated by the southern Revsund granite unit. Another shear-zone, possibly a continuation of the Skellefte Shear Zone (SSZ) runs through the centre of the region and accounts for some of the structural complexity and shearing observed between the two anticlinal exposures of the volcanics. Additional smaller scale shear-zones have been identified from geological and geophysical mapping within the main structural blocks of the Skellefte volcanics. The Mala volcanic rocks in the north are separated from the Skellefte volcanics by a fault that cuts discordant to the strike of the Mala volcanics. A structural basement has been proposed to the Skellefte volcanics, constrained by seismic reflection data. Exposures of Bothnian Basin rocks south of the Revsund granite outcrops, suggest that the domain beneath the north dipping reflectivity is associated with Bothnian Basin stratigraphy. The preferred interpretation for the contact between the Skellefte volcanics and the Bothnian Basin rocks is a thrust fault that brings the felsic volcanic rocks over the metasedimentary domain. The Revsund granites are divided into two major groups based on their present day thickness and shapes. Although parts of the Viterliden intrusion are almost undeformed, it is cut by a series of shear-zones, causing the magnetic lineations seen within these rocks. The structural profiles presented demonstrate that the Kristineberg ore is situated in the northern limb of a local synformal structure. The new crustal-scale structural model demonstrates the potential of integrating geophysical and geological data when modelling structures hosting mineralization in a complex region like the Skellefte District. The structural profiles presented in this paper, have greatly improved our understanding of the 3D tectonostratigraphy and architecture of the poly-deformed ca. 1.9 Ga the Skellefte Ore District.
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| 10. |
- Malehmir, Alireza, et al.
(författare)
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Seismic imaging and potential field modeling to delineate structures hosting VHMS deposits in the Skellefte Ore District, northern Sweden
- 2006
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 426:3-4, s. 319-334
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Tidskriftsartikel (refereegranskat)abstract
- The Skellefte District in northern Sweden is a roughly 150 by 50 km2 large early Proterozoic massive sulphide belt. Based on high-resolution reflection seismic data along two parallel seismic profiles, potential field modeling has been carried out and two geologic cross sections have been constructed that are consistent with the available geophysical data as well as surface geologic observations. The combined modelling suggests that the Kristineberg deposit occurs on the northern limb of a regional E–W striking syncline. The interpretations help to identify new prospective areas, both down-plunge from known ores, and on the ore-bearing horizon on the southern limb of the syncline. The new results suggest that the post-orogenic Revsund granites can be divided into two major types of intrusives, those which are intruded as domes/stokes with a maximum present day thickness of about 3–3.5 km and those which are intruded as thin sheets, with a maximum thickness of a few hundred meters. The margins of the intrusions are generally inclined inwards, suggesting that the current erosion level is near the middle, or toward the base, of the granites. The contact between the Skellefte volcanic rocks and the Bothnian Basin has been interpreted as a thrust fault. We also suggest that crustal thickening predates the Skellefte volcanism and that the interpreted Bothnian Basin rocks are either a structural basement or a separate terrane to the Skellefte volcanism. Diffraction patterns in the reflection seismic data can be interpreted as originating from either a mafic–ultramafic intrusion or a mineralization zone, similar to observations elsewhere in the world. The results obtained in this study have greatly improved our understanding of the tectonostratigraphic framework and architecture of the poly-deformed c. 1.9 Ga Skellefte VHMS belt and is a key step towards building a 3D geological model in the area.
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