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  • 201.
    Perttu, Nils
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic Resonance Sounding (MRS) in groundwater exploration, with applications in Laos and Sweden2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Water is essential for all life on the planet, sustaining and ensuring the earth’s ecosystem. Groundwater from a global perspective provides about 50 % of the potable water, 40 % of the industrial water and 20 % of the irrigation water. For drinking water, deep groundwater has many advantages compared to surface water and shallow groundwater, since it demands little or no treatment and the access is secured against temporary droughts. However, drilling wells for deep groundwater is expensive and unprofitable if it is made without knowing the groundwater potential and development of techniques for exploration are therefore of high priority. The petrophysical properties of aquifers are to a large extent influenced by the water content and salinity, e.g. electrical conductivity and electric permittivity, which can be determined from Vertical Electrical Sounding (VES) and Ground Penetrating Radar (GPR) measurements, respectively. Magnetic Resonance Sounding (MRS), based on the principle of nuclear magnetic resonance, is a relatively new, non invasive technique, which in contrast to other geophysical techniques gives a direct measure of the free water content, but also the pore size distribution with depth. With MRS it is possible to determine both storage and hydraulic related parameters far less ambiguously than with classical geophysical techniques. This thesis presents four studies, where the MRS technique have been tested and developed in combination with other geophysical techniques in three different geological environments; (1) The sedimentary basin of Vientiane, Laos, with naturally occurring salt in the bedrock as shallow as 50 m in depth, which inevitably affects drinking and irrigation water from deep wells; (2) In karst limestone, on the island of Gotland, Sweden, where saltwater intrusion, both recent and relic together with pollution from pesticides and fertilizers are major threats to an already exhausted drinking water supply; (3) Test of the MRS spin-echo (SE) technique in Norrbotten, Sweden, where the presence of magnetic rocks and sediments have made it impossible to do MRS with a standard measuring procedure.In Laos (1), MRS and VES have proven to be very efficient in to locate the fresh-salt water interface and distinguish freshwater aquifers from clays. The electrical conductivity (EC) of the aquifers determined from VES correlates well with EC of water collected from shallow and deep wells, which makes the method promising for future water quality estimation in the Vientiane basin. In Gotland (2), the performance of MRS, VES, GPR and Radiomagnetotelluric (RMT) were tested. The use of multiple techniques has shown to give a more coherent interpretation, but MRS and RMT showed to be more efficient in detecting groundwater and characterizing the aquifer. MRS SE measurements have also been conducted in the Bothnian bay (3). It offers a good environment to test the influence of large scale magnetic gradients on the MRS signals but also the reliability of MRS SE result. The MRS SE technique has further been tested for different soil types. The measuring procedure has subsequently been tested and optimized to meet conditions of magnetic environments.

  • 202.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-Åke
    Estimation of water quality parameters of aquifers in the Vientiane Basin, Laos, using MRS and VES2009In: Proceedings, 4th International Workshop on Magnetic Resonance Sounding, MRS 2009, 2009, p. 171-176Conference paper (Refereed)
  • 203.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-Åke
    Evaluation of MRS signals in brackish water with large magnetic gradients2009In: Proceedings, 4th International Workshop on Magnetic Resonance Sounding, MRS 2009, 2009, p. 177-182Conference paper (Refereed)
  • 204.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    New geophysical techniques for determining quantity and quality of ground water: an exemple from the Vientiane basin, Laos2008Conference paper (Other academic)
    Abstract [en]

    The access to clean drinking water in the rural Laos is often restricted. This, together with a poor hygiene, results in serious health problems. In a drilling program for water only around 30% of the boreholes carried water usable for drinking (JICA, 2000). The reason for the poor water quality was often a high content of salt. The aim of this study is to define water bearing geological formation and to test the possibility of using geophysical techniques to determine the quality of the groundwater in the Vientiane basin, Laos. This we do by the use of a combination of Magnetic Resonance Sounding (MRS), Vertical Electrical Sounding (VES) and water quality data gathered from wells in different geological environments. The MRS gives a direct image of the vertical distribution of water content and the electrical measurements are sensitive to the conductivity/quality of the water.The investigation area is part of the Khorat Plateau where rock salt is naturally occurring as shallow as 50 m in depth (Long et al., 1986), which inevitable affects the water quality in some deep wells. The results of the study show that MRS and VES measurements are effective in locating formations carrying fresh water as well as the salt bearing formation. Aquifers are identified in 19 of the 32 sites of measurements. The aquifers are related to specific geological formations and most often located at depths of 20 to 30 m and with water contents varying between 4 to 16 %. The decay times of the MRS signal suggests these aquifers to be predominantly composed of medium grained sand to gravel. The salt bearing formation is usually related to clay or mudstone, with low water contents and high VES  conductivity and can usually be found all over the basin at depths beneath 30 to 50 m.The electrical conductivity (EC) of water samples collected from shallow and deep wells correlates with the conductivities determined with VES and a fairly good correlation can be seen between EC, total dissolved solids (TDS), chloride and hardness. Layers of water with high quality, medium conductivity, are identified at specific depths and in restricted areas. The results demonstrate geophysics to be effective tools for localizing high quality groundwater and the results are important for guiding future drilling.

  • 205.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Persson, Lena
    Geological Survey of Sweden.
    Erlström, Mikael
    Geological Survey of Sweden.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic resonance sounding and radiomagnetotelluric measurements used to characterize a limestone aquifer in Gotland, Sweden2012In: Journal of Hydrology, ISSN 0022-1694, E-ISSN 1879-2707, Vol. 424-425, p. 184-195Article in journal (Refereed)
    Abstract [en]

    Almost all drinking water in Gotland is groundwater and is mainly found in karst limestone. However, the unpredictable location and geometry of the karst cracks and caverns makes it very difficult to estimate groundwater storage and movement, as well as contaminant transport. The aim of this study was to test the performance of different geophysical techniques like Magnetic Resonance Sounding (MRS), Radiomagnetotelluric (RMT), Vertical Electrical Sounding (VES) and Ground Penetrating Radar (GPR) to characterize aquifers in Gotland, in respect to geometry and storage as well as connectivity over a wider area. The investigated area is located on the south-eastern part of Gotland. The geology here is dominated by 50 to 60 m thick successions of limestone that gradually turn into marlstone. The use of multiple techniques has shown to give a more coherent interpretation. However, the shallow penetration depth of GPR and the lack of soil cover in some places of the investigated area limit the use of geoelectrical methods and GPR. With MRS, water are found down to 60 m in depth, with a maximum water content at depths of 20 to 30 m. This coincides with the most resistive sections of the limestone. The water content varies between 0 and 3%, with a relaxation time (T1MRS) less than 400 ms suggesting that the aquifer is hosted in small fractures, molds and vugs rather than larger karst fractures and caverns. Two potential aquifers were identified with MRS, possibly separated by marlstone. From modelling it can be seen that such boundary separating two aquifer apart can be more easily discriminated in the N/S-, than in the E/W direction. In summary, MRS is therefore the only method in this survey that can detect and determine the vertical and lateral distribution of water within the aquifer together with the total volume of free water. The RMT method has shown to be effective in characterizing the limestone/marl interface, but also to locate anomalous low resistive zones, possibly associated with salt water. RMT also helps to constrain the final MRS model by choosing a suitable regularization for the MRS 3D inversion. All together, the combination of MRS and RMT seems most efficient of the tested methods and therefore most promising for future groundwater explorations in geological environments like in eastern Gotland.

  • 206.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Wattanasen, Kamhaeng
    Phommasone, K.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Determining water quality parameters of aquifers in the Vientiane Basin, Laos, using geophysical and water chemistry data2011In: Near Surface Geophysics, ISSN 1569-4445, E-ISSN 1873-0604, Vol. 9, no 4, p. 381-395Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to test the possibility of using magnetic resonance sounding (MRS) and vertical electrical sounding (VES) together with groundwater chemistry data from shallow and deep wells to distinguish freshwater aquifers from salt affected groundwater and moreover determine water quality parameters directly from geophysical data. Three study areas within the Vientiane Basin, including 46 sites and 38 sampled wells, have been chosen for the study. The main water quality parameters affecting the water conductivity in the Vientiane Basin are total dissolved solids (TDS) and hardness and to a minor extent chloride, which all have shown to have fairly high correlation to the electrical conductivity (EC) of groundwater. The resistivity of the aquifers is highly variable but is most often above 4 Ωm, suggesting fresh water. No wells in the investigated areas have water quality parameters exceeding the limit for unacceptable drinking or irrigation water. There is a fairly strong relationship between the conductivity of water from deep wells and the conductivity of the main water bearing layer determined by VES, where the best fit is obtained using: EC[μS/cm] = 0.4694VES[μS/cm], R2 = 0.69. However, due to equivalence in the VES interpretation and the difficulty to estimate the resistivity contribution from finer sediments, the equation may be seen and used as guidance to good water quality only within the Vientiane Basin area or in other areas with similar geology. The MRS results have been used to identify water layers in the VES inversion results to decrease the uncertainty in the interpretation The combination of MRS and VES techniques has been successful in distinguishing high conductive clay and mudstone from water bearing layers and moreover freshwater aquifers from salt affected water. Altogether, this makes MRS and VES very promising tools for guidance of future drilling and water quality estimation.

  • 207.
    Perttu, Nils
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Wattanasen, Kamhaeng
    Phommasone, Khamphouth
    Department of Physics, National University of Laos.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Characterization of aquifers in the Vientiane Basin, Laos, using magnetic resonance sounding and vertical electrical sounding2011In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 73, no 3, p. 207-220Article in journal (Refereed)
    Abstract [en]

    The aim of this study is to define and characterize water bearing geological formation and to test the possibility of using geophysical techniques to determine the hydrogeological parameters in three areas in the Vientiane basin, Laos. The investigated areas are part of the Khorat Plateau where halite is naturally occurring at depths as shallow as 50 m in the Thangon Formation. Magnetic Resonance Sounding (MRS) has been used in combination with Vertical Electrical Sounding (VES) in different geological environments. In total, 46 sites have been investigated and the MRS and VES recognized the stratigraphic unit N2Q1-3, consisting of alluvial unconsolidated sediments, as the main water bearing unit. The aquifer thickness varies usually between 10 and 40 m and the depth to the main aquifer range from 5 to 15 m. The free water content is here up to 30%, and the decay times vary between 100 and 400 ms, suggesting a mean pore size equivalent to fine sand to gravel. The resistivity is highly variable, but usually around 10-1500 Ω-m, except for some sites in areas 1 and 2, where the aquifer is of low resistivity, probably related to salt water. Hydraulic and storage-related parameters such as transmissivity, hydraulic column, have been estimated from the MRS. The MRS together with VES has been shown to be a useful and important tool for identifying and distinguishing freshwater from possible salt-affected water as well as the salt-related clay layer of the Thangon Formation. This clay layer is characterized by very low free water content and a resistivity lower than 5 Ω-m and can be found in all 3 areas at depths from 15 to 50 m

  • 208.
    Pesonen, L. J.
    et al.
    Laboratory for Palaeomagnetism, Geological Survey of Finland.
    Bylund, G.
    Department of Geology, University of Lund.
    Torsvik, T. H.
    Department of Earth Sciences, University of Oxford.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mertanen, S.
    Laboratory for Palaeomagnetism, Geological Survey of Finland.
    Catalogue of palaeomagnetic directions and poles from Fennoscandia: Archaean to tertiary1991In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 195, no 2-4, p. 151-207Article in journal (Refereed)
    Abstract [en]

    Palaeomagnetic data from Fennoscandia ranging from the Archaean to the Tertiary have been compiled into a catalogue. The data are presented in table format, listing Precambrian data according to tectonomagmatic blocks and Late Precambrian-Phanerozoic data according to geological periods. Each pole is graded with the modified Briden-Duff classification scheme. The catalogue (complete to the end of 1988) contains 350 entries from 31 tectonomagmatic blocks and/or geological periods. Normal and reversed polarity data are listed separately to allow polarity asymmetries to be studied. Each entry also has an indexed abstract summarizing relevant information, such as the age of the rock, the age of the natural remanent magnetization and the basis for the assigned reliability grade. All the data are stored in the palaeomagnetic data bank, which will be updated annually with new data. The catalogue is the basic source of data for the microcomputer-based palaeomagnetic database for Fennoscandia now being compiled.

  • 209.
    Pesonen, L. J.
    et al.
    Division of Geophysics, Department of Physical Sciences, University of Helsinki.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mertanen, S.
    Geological Survey of Finland.
    Pisarevsky, S.
    Tectonics Special Research Centre, The University of Western Australia.
    D'Agrella-Filho, M. S.
    Institute of Astronomy, Geophysics and Atmospheric Sciences, University of São Paulo.
    Meert, J. G.
    Department of Geological Sciences, University of Florida.
    Abrahamsen, N.
    Department of Earth Sciences, University of Aarhus.
    Bylund, G.
    Lunds universitet.
    Palaeomagnetic configuration of continents during the Proterozoic2003In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 375, no 1-4, p. 289-324Article in journal (Refereed)
    Abstract [en]

    Palaeomagnetic data are used to study the configurations of continents during the Proterozoic. Applying stringent reliability criteria, the positions of the continents at 12 times in the 2.45- to 1.00-Ga period have been constructed. The continents lie predominantly in low to intermediate latitudes. The sedimentological indicators of palaeoclimate are generally consistent with the palaeomagnetic latitudes, with the exception of the Early Proterozoic, when low latitude glaciations took place on several continents. The Proterozoic continental configurations are generally in agreement with current geological models of the evolution of the continents. The data suggest that three large continental landmasses existed during the Proterozoic. The oldest one is the Neoarchaean Kenorland, which comprised at least Laurentia, Baltica, Australia and the Kalahari craton. The protracted breakup of Kenorland during the 2.45- to 2.10-Ga interval is manifested by mafic dykes and sedimentary rift-basins on many continents. The second ‘supercontinental' landmass is Hudsonland (also known as Columbia). On the basis of purely palaeomagnetic data, this supercontinent consisted of Laurentia, Baltica, Ukraine, Amazonia and Australia and perhaps also Siberia, North China and Kalahari. Hudsonland existed from 1.83 to ca. 1.50-1.25 Ga. The youngest assembly is the Neoproterozoic supercontinent of Rodinia, which was formed by continent-continent collisions during ≈1.10-1.00 Ga and which involved most of the continents. A new model for its assembly and configuration is presented, which suggests that multiple Grenvillian age collisions took place during 1.10-1.00 Ga. The configurations of Kenorland, Hudsonland and Rodinia depart from each other and also from the Pangaea assembly. The tectonic styles of their amalgamation are also different reflecting probable changes in sizes and thicknesses of the cratonic blocks as well as changes in the thermal conditions of the mantle through time.

  • 210.
    Pesonen, L. J.
    et al.
    Geological Survey of Finland.
    Torsvik, T. H.
    Department of Earth Sciences, University of Oxford.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bylund, G.
    Department of Geology, University of Lund.
    Crustal evolution of Fennoscandia: palaeomagnetic constraints1989In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 162, no 1-2, p. 27-49Article in journal (Refereed)
    Abstract [en]

    Palaeomagnetic poles from Fennoscandia, ranging in age from Archaean to Tertiary, are compiled and graded using a modified Briden-Duff classification scale. An new "filtering" technique is applied to select only the most reliable poles for analysis. The filtering takes into account the following information: 1. (1) source block of rock unit,2. (2) age of rock,3. (3) age of magnetization component,4. (4) scatter of palaeomagnetic directions,5. (5) information from multicomponent analysis of natural remanent magnetization (NRM),6. (6) whether the pole considered belongs to a cluster or subcluster of poles,7. (7) magnetic polarity and8. (8) the author's original assignment of results.Data are still insufficient for the drawing of separate Apparent Polar Wander Paths (APWP) for different blocks or cratons of Fennoscandia. Treating Fennoscandia as a single plate, a new APWP from Archaean to Permian is constructed. From the five previously drawn APWP loops (or "hairpins"), only one, the Jatulian loop (2200-2000 Ma), disappears in filtering. The loops during 1925-1700 Ma and during 1100-800 Ma ago are linked to Svecofennian and Sveconorwegian orogenies, respectively. Palaeomagnetic data support the concept that these orogenies took place episodically; three distinct orogenic pulses (early, middle and late) can be distinguished in the cluster plots of palaeopoles. The drift history of Fennoscandia from Archaean to Permian is presented. During most of geological history, Fennoscandia has occupied low to moderate latitudes and undergone considerable latitudinal shifts and rotations. The Svecofennian and Sveconorwegian orogenies have different kinematic characteristics. During the Svecofennian orogeny, Fennoscandia drifted slowly while rotating a large amount in an anticlockwise sense. During the Sveconorwegian orogeny, it drifted rapidly and rotated first clockwise and then anticlockwise. The most striking feature in the drift velocity curves is, however, the pronounced maxima in the latitudinal drift and rotation rates (˜ 9 cm/yr and ˜ 0.8°/Ma, respectively) during the late Subjotnian-Jotnian anorogenic magmatism and rifting phase (˜1450-1250 Ma ago), possibly reflecting the passage of Fennoscandia across a thermal upwelling (hotspot) at equatorial latitudes. The use of palaeomagnetism in delineating and dating movements between blocks is demonstrated with three examples from the POLAR Profile area, the northernmost section of the European Geotraverse.

  • 211. Pesonen, Lauri
    et al.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pisarevsky, S
    Mertanen, S
    Agrella-Filho, M
    Meert, J
    Schmidt, P
    Bylund, G
    A pre-Rodinia supercontinent?: a paleomagnetic survey2000In: European Geophysical Society, 25th general assembly, 2000Conference paper (Other academic)
  • 212.
    Pesonen, L.J.
    et al.
    Laboratory for Palaeomagnetism, Geological Survey of Finland.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Fennoscandian continental drift: a new paleomagnetic and paleoclimatological analysis1993In: Abstracts of lectures and posters: 21:a Nordiska geologiska vintermötet 10-13 Januari 1994 Luleå / [ed] Jan-Anders Perdahl, Luleå: Högskolan i Luleå , 1993, p. 158-Conference paper (Other academic)
  • 213.
    Pesonen, L.J.
    et al.
    University of Helsinki.
    Mertanen, S.
    University of Helsinki.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Reconstructions of continents during the Proterozoic: a way towards Rodinia2001In: From basins to mountains: Rodinia at the turn of the century / Chris Powell Memorial Symposium / [ed] K.N. Sircombe; Z.X. Li, University of Western Australia , 2001, p. 82-84Conference paper (Other academic)
  • 214.
    Pesonen, L.J.
    et al.
    Geological Survey of Finland, Geophysical Department, Espoo.
    Mertanen, S.
    Geological Survey of Finland, Geophysical Department, Espoo.
    Torsvik, Trond H.
    University of Bergen.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bylund, Göran
    University of Lund.
    Accretion history of Fennoscandia: a paleomagnetic view1987In: Abstracts and timetable for the inter-disciplinary symposia: International Union of Geodesy and Geophysics (IUGG), XIX general assembly, Vancouver, BC, Canada, Aug. 9-22, 1987, 1987, p. 105-Conference paper (Other academic)
  • 215.
    Pisarevsky, Sergei A.
    et al.
    Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtain University.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pesonen, Lauri J.
    Division of Geophysics and Astronomy, Department of Physics, University of Helsinki.
    Li, Zheng-Xiang
    Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtain University.
    Mesoproterozoic paleogeography: Supercontinent and beyond2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 244, p. 207-225Article in journal (Refereed)
    Abstract [en]

    A set of global paleogeographic reconstructions for the 1770–1270 Ma time interval is presented here through a compilation of reliable paleomagnetic data (at the 2009 Nordic Paleomagnetic Workshop in Luleå, Sweden) and geological constraints. Although currently available paleomagnetic results do not rule out the possibility of the formation of a supercontinent as early as ca. 1750 Ma, our synthesis suggests that the supercontinent Nuna/Columbia was assembled by at least ca. 1650–1580 Ma through joining at least two stable continental landmasses formed by ca. 1.7 Ga: West Nuna (Laurentia, Baltica and possibly India) and East Nuna (North, West and South Australia, Mawson craton of Antarctica and North China). It is possible, but not convincingly proven, that Siberia and Congo/São Francisco were combined as a third rigid continental entity and collided with Nuna at ca.1500 Ma. Nuna is suggested to have broken up at ca. 1450–1380 Ma. West Nuna, Siberia and possibly Congo/São Francisco were rigidly connected until after 1270 Ma. East Nuna was deformed during the breakup, and North China separated from it. There is currently no strong evidence indicating that Amazonia, West Africa and Kalahari were parts of Nuna.

  • 216.
    Planke, Sverre
    et al.
    Volcanic Basin Petroleum Research (VBPR), Oslo Research Park.
    Rasmussen, Thorkild Maack
    Volcanic Basin Petroleum Research (VBPR), Oslo Research Park.
    Rey, Sebastian Scheel
    Volcanic Basin Petroleum Research (VBPR), Oslo Research Park.
    Myklebust, Reidun
    TGS-NOPEC.
    Seismic characteristics and distribution of volcanic intrusions and hydrothermal vent complexes in the Vøring and Møre basins2005In: Petroleum Geology Conference Proceedings, ISSN 2047-9921, Vol. 6, p. 833-844Article in journal (Refereed)
    Abstract [en]

    A voluminous magmatic complex was emplaced in the Vøring and Møre basins during Paleocene/ Eocene continental rifting and break-up in the NE Atlantic. This intrusive event has had a significant impact on deformation, source-rock maturation and fluid flow in the basins. Intrusive complexes and associated hydrothermal vent complexes have been mapped on a regional 2D seismic dataset (c.150 000 km) and on one large 3D survey. The extent of the sill complex is at least 80 000 km2, with an estimated total volume of 0.9 to 2.8 × 104 km3. The sheet intrusions are saucer-shaped in undeformed basin segments. The widths of the saucers become larger with increasing emplacement depth. More varied intrusion geometries are found in structured basin segments. Some 734 hydrothermal vent complexes have been identified, although it is estimated that 2-3000 vent complexes are present in the basins. The vent complexes are located above sills and were formed as a direct consequence of the intrusive event by explosive eruption of gases, liquids and sediments, forming up to 11 km wide craters at the seafloor. The largest vent complexes are found in basin segments with deep sills (3-9km palaeodepth). Mounds and seismic seep anomalies located above the hydrothermal vent complexes suggest that the vent complexes have been re-used for vertical fluid migration long after their formation. The intrusive event mainly took place just prior to, or during, the initial phase of massive break-up volcanism (55.0-55.8Ma). There is also evidence for a minor Upper Paleocene volcanic event documented by the presence of 20 vent complexes terminating in the Upper Paleocene sequence and the local presence of extrusive volcanic rocks within the Paleocene sequence

  • 217.
    Rasmussen, Jon
    Luleå tekniska universitet.
    Non destructive testing methods for integrity determination of concrete structures2003Licentiate thesis, monograph (Other academic)
    Abstract [en]

    The ageing of concrete structures can be a threat to human safety as well as being a huge economical factor in the near future. Lifetime prediction and damage assessment of concrete structures will be a growing part of infrastructure planning. Thus the field of Non Destructive Testing (NDT) of concrete structures is an important part of the future in civil engineering. A substantial amount of Ground Penetrating Radar (GPR) data has been measured on concrete structures to define some of the limiting factors that prevent GPR from being used more extensively in connection with NDT of concrete. A Ramac CU2- GPR system with three sets of high frequency antennas has been used to collect data. The main difficulties found in concrete GPR surveys are: limiting depth penetration; large amount of spurious signals causing difficulties when interpreting the data; significant low frequency "noise" blurring the appearance. A concrete test block containing various reinforcement-meshes and cable ducts situated at different depths was constructed. The result of the initial GPR study on the test block showed that the resolution of an 800MHz antenna was poor and that there was a need for a better understanding of the ray paths involved. To explore the ray paths involved one of the GPR antennas was split into a separate transmitting, Tx and receiving, Rx antenna and the electronics were modified to transmit energy at a higher frequency. Initial measurements also suggested that the varying properties of different concrete structures have a significant influence on the response and thus complicate comparison between structures. To overcome this negative influence of the varying properties a simulation tank was built. The matrix used to simulate concrete was a mixture of rapeseed oil, water and table salt. During measurements in the simulation tank it was found that a surprisingly large portion of the energy in the radar wave is transmitted through the reinforcement mesh. The result suggests that ground penetrating radar should be more successful than measurements on real concrete structures has indicated. Part of this difference is likely to be caused by complex ray paths in the concrete that distorts the received data and makes it difficult to interpret. One of these ray paths was found when measuring on a single reinforcement bar, which produced a "ghost" hyperbola situated at the bottom interface of the simulation-tank. This ghost response could have the shape of a "double" hyperbola or a horizontally stretched hyperbola depending on the geometry and permittivity of the host medium. The simulation tank also revealed that the antenna used has two perpendicular polarisation directions. The additional polarisation will have a huge influence on the measured response in concrete measurements since concrete structures involves linier targets such as reinforcement bars and cable ducts. From the measurements done it is clear that there is a need to use different antenna configuration, particularly the in-line mode, as well as different antenna offset when measuring on reinforced concrete. Measurements on real world structures suggest that GPR can be successful but the technique should be applied with caution due to its sensitivity of host environment.

  • 218.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Current trends in geophysical exploration for minerals2016Conference paper (Other academic)
  • 219.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Section of Solid Earth Physics, Department of Geophysics, University of Uppsala.
    Magnetotellurics in southwestern Sweden: evidence for electrical anisotropy in the lower crust?1988In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 93, no B7, p. 7897-7907Article in journal (Refereed)
    Abstract [en]

    Magnetotelluric data from measurements conducted on the SW part of the Baltic Shield are analyzed with respect to crustal and upper mantle structures. The interpretations have been done using ordinary 2-D and transverse anisotropic layered models in which distortions of the impedance tensors due to near-surface electrical structures are included in the interpretation procedures. The anisotropic model is able to explain the gross features of the data, whereas the 2-D model only displays features observed at long periods. The 2 main results from the study with anisotropic models are the interpretation of a possible transverse anisotropic lower crust and a depth to the uppermost conductive layer within the mantle of more than 200 km. The minimum depth to the conductive mantle layer is found from a most squares analysis

  • 220.
    Rasmussen, Thorkild Maack
    Department of Solid Earth Physics, Uppsala University.
    Two-Dimensional Occam Model of COPROD2 Data: First Order Description of Resolution and Variance1993In: Journal of Geomagnetism and Geoelectricity, ISSN 0022-1392, Vol. 45, no 9, p. 1027-1037Article in journal (Refereed)
    Abstract [en]

    A two-dimensional Occam model of crustal electrical conductivity is derived based on data from 35 magnetotelluric stations on a profile in Saskatchewan, Canada. The model is discussed in relation to a first order description of the resolution and variance of the model parameters. Prior to the two-dimensional Occam's inversion, the data are analysed with respect to underestimated data errors. The analysis is based on separate D+ inversions of the E- and H-polarization responses and a procedure for adjusting the data errors is presented. The main features of the model are the presence of two conductive structures with vertically integrated conductivity exceeding 30,000 S and 100, 000 S respectively. In addition to these main features, some minor conductive structures are inferred.

  • 221. Rasmussen, Thorkild Maack
    et al.
    Dawes, Peter Robert
    Kennedy Channel and its geophysical lineaments: New evidence that the Wegener Fault is a myth2011In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 23, p. 69-72Article in journal (Refereed)
  • 222.
    Rasmussen, Thorkild Maack
    et al.
    Section of Solid Earth Physics, University of Uppsala.
    Pedersen, Laust Börsting
    Section of Solid Earth Physics, University of Uppsala.
    Zhang, Ping
    Section of Solid Earth Physics, University of Uppsala.
    Roberts, Roland G.
    Section of Solid Earth Physics, University of Uppsala.
    Magnetotelluric investigations of the lithosphere in scandinavia1992In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 113, no 2-3, p. 264-Article in journal (Refereed)
  • 223. Rasmussen, Thorkild Maack
    et al.
    Thorning, Leif
    Olesen, Arne Vestergaard
    National Space Institute, Technical University of Denmark.
    Schjøth, Frands
    Quality control of airborne geophysical data from the EU mining Sector Support Programme, Ghana2011In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 23, p. 81-84Article in journal (Refereed)
  • 224.
    Renström, Viktor
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    The influence of weakness zones on the tunnel stability based on investigations in Bodøtunnelen2016Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When planning for a tunnel, the ground conditions in which the tunnel is going to be excavated through will be investigated to different extent. Lack of relevant pre-investigation data or misinterpretations of the available data can cause both economical and/or unexpected stability problems.

    Weakness zones that are expected to cross the tunnel could be investigated thoroughly with a variety of methods. Refraction seismicity survey and 2D resistivity survey are two geophysical methods that are common in Norway for obtaining information about the rock quality in weakness zones. In this work, a twin tunnel under construction in Bodø (northern Norway) called the Bodøtunnel is studied. The predictions based on the pre-investigation for crossing of some expected weakness zones are compared to the actual conditions encountered during tunneling. Tunneling observations (Geological mapping and photos), rock samples and measurement while drilling (MWD) were used to describe the weakness zones that were encountered during tunneling.

    Rock samples were collected from two weakness zones and the general rock mass. These samples were tested in a point bearing machine for determination of their uniaxial compressive strength (UCS). These results indicated that the rock samples gathered from the weakness zones had significantly lower UCS than the samples from the rock mass. This was exceedingly clear for the samples of fault rock gathered in connection with a shear zone. The results from this work demonstrate that refraction seismicity had a high success rate for locating weakness zones, with the exception for the crossed narrow zones that were interpreted lacking a shear component. Empirical formulas relating Q-value and UCS with the seismic wave speed were used for calculating these factors for some interesting locations. The empirically calculated UCS was similar to the obtained UCS from the point bearing tests, while the empirically calculated Q-value showed large deviations from the mapped Q-value.

    The resistivity measurements had a low success rate so far in this project; the reason for this could be disturbances in the ground and the location of the resistivity profiles, which had to adapted to the nearby railroad. It should be noted that only one full resistivity profile has been crossed and the rest of the profiles are expected to be more accurate. Based on the results from the crossed profile(s), the suitability of resistivity survey 2D in urban areas can be brought to question. This work also stumbled upon problems regarding the definition of weakness zones. Shear/fault zones are one of the more common type of weakness zones encountered in tunneling. These kind of zones often consists of different parts. Depending on which parts are regarded as a weakness zone by the responsible engineers, the Q-value might differ due to the SRF.

    Different scenarios were also evaluated with numerical modeling for the expected remaining major weakness zones. This analysis highlights the importance of differentiation between more fractured zones and zones containing fault rock, such as breccia. The width of the zone had a major impact on the stability while the dip for wide zones had a minor impact on the stability, as long the zones dip is not so small that both tunnels are intersected at the same time. The rock mechanical parameter of the weakness zones that had the most impact on the overall stability was the cohesion.

  • 225.
    Riisager, Peter
    et al.
    Danmarks og Grønlands Geologiske Undersøgelse, GEUS.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Aeromagnetic survey in south-eastern Greenland: project Aeromag 20132014In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 31, p. 63-66Article in journal (Refereed)
  • 226.
    Sandrin, Alessandro
    Luleå tekniska universitet.
    Geophysical and petrophysical characterisation of the Tjårrojåkka IOCG mineralisation, Sweden2003Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A geophysical-petrophysical study has been performed in an area WSW of the city of Kiruna, northern Sweden. Particular attention has been dedicated to the Tjårrojåkka iron oxide copper gold (IOCG) mineralisations. The bedrock is characterised by intermediate to mafic meta-volcanites, metamorphosed intermediate to mafic dykes, gabbroic-dioritic and granitic intrusions of Svecofennian ages (ca. 1.96-1.75 Ga). The aim of the study is to put the deposits into a tectonic framework, to test existing hypotheses for their occurrences and to produce a database of physical properties of rocks, in an attempt to define a petrophysical signature of the mineralisations. Glacial deposits cover almost the entire area, which means that outcrops are sparsely occurring and that geophysical data are crucial for the geological studies. For the tectonic analysis also anisotropy of magnetic susceptibility (AMS) was studied. More than 150 oriented samples were collected in a number of outcrops along a profile intersecting the major structures in the Tjårrojåkka area. From the airborne magnetic data two major linear features are interpreted as deformation zones. The strike of the deformation zones is approximately NW- SE and E-W, respectively. The same trend has been defined from other geophysical data, as airborne VLF and ground gravity data. A third important structural trend striking SW-NE has also been identified. Very good agreement has been found between geophysical lineaments, AMS directions and geological field observations. Magnetic foliations determined by AMS measurements confirm the existence of three major trends in the study area: SW-NE, E-W, NW-SE. Ground magnetic data indicate that the major mineralised bodies have a ca. SW-NE strike direction, which is parallel to the strike of magnetic foliation determined in outcrops ca. 1 km northwest of the mineralisations. This, together with the epigenetic nature of the mineralisations and their spatial relationship with deformation zones, suggests a structural control of the mineralisations. A later tectonic episode resulted in an E-W trending deformation in the central part of the area. Other SW-NE compressive deformation is indicated by petrophysical, geophysical and geological analysis. It resulted in a probable thrust in proximity of a granitic intrusion. The presence of such a thrust is supported by modelling of gravity data. A good spatial correlation has been observed between Cu-mineralisations and high K/Th values from radiometric data, values that are expressions of potassic alteration. Thermomagnetic measurements indicate that iron oxides (Ti-magnetite) are widely common in the area, while iron sulphides are almost absent. Multi- domain magnetite has been identified as the most common Fe-oxide in different rock types. An unstable magnetic mineral has been detected in metamorphosed volcanites and it may have originated from oxidation of (Ti)- magnetite in submarine/subaerial environments or from oxidation related to hydrothermal activity and metamorphism.

  • 227.
    Sandrin, Alessandro
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Luleå tekniska universitet, Geological Institute, Luleå University of Technology, Maersk Olie og Gas AS.
    Geophysical targeting of Fe-oxide Cu-Au deposits in the northern fennoscandian sheild2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the last decades Fe-Oxide Cu-Au deposits have been discovered and developed in Australia, South America and Canada. This class of mineral deposits is also present in northern Sweden and thus represents a potential target for improving the mineral production of the country. The project aims at defining a geophysical signature of IOCG deposits from regional scale to local scale by using available geophysical data and newly measured petrophysical data. The Kiruna district was selected for regional investigations, while the Tjårrojåkka prospect was selected as testing site for the local study. The Tjårrojåkka prospect is located around 50 km west of Kiruna and is constituted by an apatite-iron ore (Kiruna type) and an associated Cu(-Au) deposit. The host rock is an altered andesite of Palaeoproterozoic age. The working hypothesis to be tested was that a spatial relationship exists between IOCG deposits and major tectonic lineaments and between IOCG deposits and alteration zones and that geophysical data can be used to delineate prospective areas. Gravity and magnetic data were used to map faults and associated fracture zones at regional scale, whereas airborne radiometric data were used to map potassic alteration, which appears to be related to the Cu(-Au) mineralising event. The K/Th ratio maps at both regional and local scale seem to be able to define prospective areas for IOCG deposits. Magnetic maps are also used to indicate presence of highly magnetic bodies associated to high concentrations of Fe-minerals. In the Tjårrojåkka area, Anisotropy of Magnetic Susceptibility on oriented samples was used as tectonic indicator for the geological study of the area. Three major tectonic events were identified, one of which is interpreted to be related to the main mineralising event. Density, bulk susceptibility and Natural Remanent Magnetisation were measured for oriented samples and for borehole specimens at the main Cu deposit. Thermal demagnetisation cycles were applied to the specimens to define the main magnetic mineral, which is mostly multidomain magnetite as confirmed by Königsberger ratios lower than one. Haematite is also present and is caused by oxidation of magnetite. The haematitisation of magnetite is contemporaneous to the Cu(-Au) ore deposition and to potassic alteration. At local scale, high magnetic anomalies define magnetite bodies, while intermediate magnetic anomalies mark areas that were affected by haematitisation. These areas also show high K/Th ratios and are associated to Cu-(Au) occurences. The proposed model for IOCG exploration begins with the analysis at regional scale of potential field data to define the major tectonic lineaments and fracture zones that may have acted as pathways for mineralising fluids. The second step is to identify high/intermediate magnetic anomalies caused by magnetite/haematite deposits. High values of K/Th ratio from airborne radiometric data show areas affected by potassic alteration, which often accompanies Cu-(Au) deposition.

  • 228.
    Sandrin, Alessandro
    et al.
    Geological Institute.
    Berggren, Robert
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geophysical targeting of Fe-oxide Cu-(Au) deposits west of Kiruna, Sweden2007In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 61, no 2, p. 92-101Article in journal (Refereed)
    Abstract [en]

    Ore deposits are frequently associated with various types of rock alteration that may affect the physical properties of rocks, and result in a characteristic signature of the deposits. The present work focuses on the use of geophysical data in targeting areas hosting Fe-oxide Cu-Au (IOCG) deposits west of the Kiruna mining district, northern Sweden. It is noted that IOCG deposits in different areas worldwide (e.g., Australia, Canada) are preferentially located in proximity to faults associated with deformation zones of regional relevance, and that the deposits are hosted in areas affected by potassic to sodic alteration. This study shows that at a semi-regional scale IOCG deposits occur within areas of high positive gravity anomalies, high values of estimated potassium content and high K/Th ratios, which is an expression of potassic alteration. High magnetic anomalies are associated with magnetite occurrences, while low linear magnetic anomalies mark fault/shear zones, in proximity of which the majority of the IOCG deposits occur.

  • 229.
    Sandrin, Alessandro
    et al.
    Luleå tekniska universitet.
    Edfelt, Åsa
    Waight, Tod E.
    University of Copenhagen.
    Berggren, Robert
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Physical properties and petrologic description of rock samples from an IOCG mineralized area in the northern Fennoscandian Shield, Sweden2009In: Journal of Geochemical Exploration, ISSN 0375-6742, E-ISSN 1879-1689, Vol. 103, no 2-3, p. 80-96Article in journal (Refereed)
    Abstract [en]

    The Tjårrojåkka Fe-Cu prospect in northern Sweden is considered an example of a Fe-oxide Cu-Au (IOCG) deposit and is hosted in metamorphosed Paleoproterozoic volcanic and intrusive rocks. Rock samples from 24 outcrops were collected for petrophysical analysis (magnetic susceptibility, remanent magnetization, variation of magnetic susceptibility with temperature, Curie temperature and density). The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four selected rock samples. The samples are from an exploration well that intersects the main Cu-mineralized body.The magnetic analyses show that magnetite is the dominant magnetic mineral, while hematite and other Fe-minerals are present in minor amounts. The electron microprobe observations confirm the presence of magnetite and further indicate that hematite is an alteration product of magnetite. Moreover, microprobe observations indicate that Fe-sulfides are present in negligible amounts in the samples from the Tjårrojåkka area. The strong spatial relationship of Cu-minerals (e.g., chalcopyrite) and the oxidation of magnetite to hematite suggest that the presence of rocks with low magnetic susceptibility in areas dominated by high susceptibility rocks may be a signal of related Cu-prospects.

  • 230.
    Sandrin, Alessandro
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geophysical and petrophysical study of an iron oxide copper gold deposit in northern Sweden2006In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 29, no 1, p. 1-18Article in journal (Refereed)
    Abstract [en]

    A geophysical-petrophysical study has been performed in an area WSW of the city of Kiruna, northern Sweden. The sub-regional tectonic setting is dominated by two important shear zones, which define the boundary of a granitic body. Many Cu-Fe-occurrences are located in proximity of faults related to these major deformation zones. Particular attention has been given to the Tjårrojåkka iron oxide copper gold (IOCG) deposit. Here the bedrock is characterised by intermediate to mafic meta-volcanics, metamorphosed intermediate to mafic dykes, and gabbroic-dioritic intrusions of Svecofennian ages (1.96-1.75 Ga). The major Cu- and Fe-occurrences are hosted by the meta-andesites. The aim of the study is to put the deposits into a tectonic framework and test existing hypotheses for their occurrences.Glacial deposits cover almost the entire area, leading to a scarcity of outcrops and inferring that geophysical data are fundamental for geological understanding. In addition to this, petrophysical analysis is vital for the interpretation of geophysical data (gravity, airborne magnetics and radiometrics, very low frequency) and for the definition of geophysical signatures of the deposits. The anisotropy of magnetic susceptibility (AMS) was also studied for the tectonic analysis. More than 150 oriented samples were collected in a number of outcrops along a profile intersecting the major structures in the Tjårrojåkka area.From the airborne magnetic data, two major linear features are interpreted as deformation zones. The strike of these deformation zones is approximately NW-SE and E-W, respectively. The same trends have been defined from other geophysical data such as airborne VLF and ground gravity data. A third important structural trend striking SW-NE has been defined by K/Th data and ground magnetic data. Very good agreement has been found between geophysical lineaments and AMS directions. Magnetic foliations determined by AMS measurements confirm the existence of three major trends in the study area: SW-NE, E-W and NW-SE. The major Fe-orebody shows approximately a SW-NE strike direction as defined from ground magnetic data. This is parallel to the strike of magnetic foliation determined in outcrops 1 km NW of the deposit. The epigenetic nature of the Cu and Fe occurrences in Tjårrojåkka and their spatial relationship with deformation zones suggest a connection between the formation of the deposits and a tectonic event. A later tectonic episode resulted in E-W trending deformation in the central area, affecting the orebodies themselves. Other, probable, compressive deformations have been indicated from petrophysical and geophysical analyses.Thermomagnetic measurements indicate that Fe-oxides (Ti-magnetite) are common in the area, while Fe-sulphides are almost absent. Multi-domain magnetite has been identified as the most common Fe-oxide in different rock types, while an unstable magnetic mineral has been detected in metamorphosed volcanics. A good spatial correlation has been observed between Cu-deposits and high K/Th values from radiometric data, values that are expressions of potassic alteration.

  • 231.
    Sandrin, Alessandro
    et al.
    Luleå University of Technology.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Physical properties of rocks from borehole TJ71305 and geophysical outline of the Tjårrajåkka Cu-prospect, northern Sweden2007In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 30, no 1, p. 56-73Article in journal (Refereed)
    Abstract [en]

    In the last decades Fe-oxide Cu–Au (IOCG) deposits attracted the interest of exploration geologists and geophysicists. General geophysical descriptions of IOCG deposits have been published in the recent past, but there is still a lack of detailed geophysical investigations. We present a petrophysical study of rock samples from exploration borehole TJ71305, which intersects the Cu-prospect in the Tjårrojåkka IOCG mineralised area, northern Sweden. Furthermore geophysical data are compiled and analysed to tentatively define a geophysical signature, at local scale, for this type of deposit. The study area is dominated by intrusive and volcanic rocks of Middle Proterozoic age, the latter hosting the Cu and Fe occurrences. The Fe occurrences are clearly defined from both aeromagnetic and ground magnetic data, and are also indicated by gravity, geoelectric and electromagnetic data. Enrichment in ferromagnetic minerals in the area is suggested by the high values of magnetic susceptibility commonly obtained for different rock types; magnetite and Ti-magnetite are the dominant magnetic minerals. Haematite with variable contents of Ti was detected and it is probably a result of oxidation of magnetite in alteration zones. In Tjårrojåkka a clear spatial relationship is noted between Cu occurrences and high K/Th ratios. This ratio is calculated from airborne radiometric data and is an expression of enrichment in potassium, due to alteration. The Cu-prospect is also indicated by high gravity and magnetic anomalies, by clear positive anomalies in induced polarisation data and by negative anomalies for the imaginary part of ground electromagnetic (Slingram) data. However, high-density/high-susceptibility/low-resistivity (Ti)-magnetite is associated with the Cu-prospect and this may lead to misinterpretation of potential field, electromagnetic and geoelectric data.

  • 232.
    Sandrin, Alessandro
    et al.
    Luleå tekniska universitet.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tectonophysical study of an epigenetic Cu-Fe mineralisation in northern Sweden2003In: Program with Abstracts : Joint Annual Meeting, Geological Association of Canada; Mineralogical Association of Canada , 2003, Vol. 28Conference paper (Other academic)
    Abstract [en]

    A tectonophysical study has been performed on the Tjårrojåkka Cu-Fe mineralisations, WSW of the city of Kiruna, northern Sweden. The bedrock is characterized by intermediate to mafic meta-volcanites, mafic dykes and monzo-dioritic intrusions, with ages of c. 1.9-1.88 Ga. The epigenetic copper and iron mineralisations occur within the meta-andesitic rocks. The aim of the study is to define structures that may have controlled the deposition of the mineralisations using combined geophysical and petrophysical data. Magnetic, gravity and VLF (Very Low Frequency) datasets have been analysed for the delineation of geophysical domains and lineaments. Subsequently, in spite of the glacial sediments, a number of outcrops along a profile, that intersects major structures, has been sampled for petrophysical studies. These also include Anisotropy of Magnetic Susceptibility (AMS) measurements that are used for the tectonic interpretation. 21 outcrops were drilled in the Tjårrojåkka area, for a total of more than 150 samples. We defined three major geophysical domains reflecting different rock types: meta-basalts, meta-andesites and an intrusive body. Geophysical lineaments of tectonic significance, striking E-W, SW-NE, NW-SE, occur in the area and at least one of them (SW-NE) seems to be related to the mineralisations. Examination of ground-geophysics datasets gives a SW-NE strike for the major mineralised bodies. The small number of structural elements visible in outcrop makes the analysis of AMS necessary for a comprehensive tectonic study. Magnetic foliations and lineations, defined for both meta-volcanic and intrusive rocks, confirm the trends obtained from other geophysical and geological observations and allow more detailed information about the character of the different geophysical lineaments and domains. Besides, magnetic foliations defined for meta-andesitic rocks, weakly Cu-mineralised, in proximity of the major Cu-deposit, mark two major tectonic events, one of them parallel to that defined for the orebodies. This result reinforces the thesis of a tectonic control on Cu-Fe mineralisations, reflected by a petrophysical inprint of this tectonic episode.

  • 233.
    Sandrin, Alessandro
    et al.
    Maersk Olie og Gas AS.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Berggren, Robert
    Geophysical and petrophysical characterisation of IOCG prospects in northern Sweden2008Conference paper (Other academic)
    Abstract [en]

    In the last decade the importance of Fe-oxide Cu-Au deposits has been increasing constantly and a relevant effort was put on the creation of efficient exploration models. Among the other disciplines, geophysics is a vital tool for the first definition of IOCG leads. Airborne/field geophysical surveys are widely used fro preliminary exploration and they can be further exploited to characterise mineral alterations and to indicate the presence of magnetic or density anomalies. The link between the geophysical signature of altered or mineralised rocks and the alterations/mineralisations themselves is given by the physical properties of rocks. In this study we review this link by investigating in very detail the petrophysical (i.e. magnetic and density) properties of the Tjårroåkka IOCG prospect together with its geophysical expression at the surface. Moreover, we put this prospect in a more regional context with a study that makes use of available airborne magnetic and radiometric data, coupled with ground gravity measurements and petrophysical databeses.Our study suggests that, at semi-regional scale, the Fe-Cu prospects are located at major gravity highs that bound granitic intrusions. The prospects appear to be linked to main faulting and to positive magnetic anomalies caused by magnetite enrichment. At prospect scale, the magnetic print of IOCG deposits may be subdivided as follows: the Fe-prospect is characterised by high magnetic anomalies due to a high content of magnetite, whereas the Cu-mineralised rocks show hematitisation of magnetite, which causes a decrease in magnetic susceptibility. The occurrence of IOCG mineralised rocks is also indicated by the associated potassic alteration, which can be mapped through analysis of airborne radiometric data. In this case, the potassium/thorium ratio has been proven to be a viable attribute to locate K-altered zones.

  • 234.
    Sandrin, Alessandro
    et al.
    Maersk Olie og Gas AS.
    Waight, Tod
    University of Copenhagen.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic and electron microscope identification of Fe-minerals in four selected samples from the Tjårrojåkka Cu-prospect, Sweden2008Conference paper (Other academic)
    Abstract [en]

    The Tjårrojåkka area in northern Sweden hosts a number of Fe-oxide Cu-Au (IOCG) occurrences.The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four selected rock samples. The samples are from an exploration well that cuts the main Cu-mineralised body. Magnetic susceptibility thermal treatment of samples indicates that magnetite (and maghemite) are the dominant magnetic minerals, while haematite and other Fe-oxides and Fe-hydroxides are present in minor amounts. Fe-sulphides are not detected in the selected samples. The electron microprobe observations confirm the presence of magnetite and further indicate that haematite is present as an alteration product of magnetite at its rims.The formation of the highly magnetic minerals is possibly contemporaneous with deposition of the Tjårrojåkka Fe-prospect, which is a "Kiruna type" iron deposit. However, our study shows that highly oxidised Fe-minerals (i.e., haematite, goethite and/or lepidocrocite) occur in spatial association with the mineralised rocks of the main Cu prospect. The relatively low magnetic susceptibility of these minerals, compared to the high susceptibility of magnetite and maghemite, and their spatial relationship with the Cu-mineralised rock, may be used as a tool for targeting Cu-deposits. Low magnetic anomalies within areas showing generally strongly magnetised rocks may indicate oxidised areas associated with Cu deposits.

  • 235.
    Sarlus, Zimer
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nordin, Roger
    Boliden Mineral AB, Boliden AB, Boliden Mineral, Exploration Department, Boliden.
    Andersson, Joel
    LKAB, Exploration Department, Malmberget.
    Geochemistry of Ultramafic-Mafic Units Related to Fe-, Cu-, and Au Deposits in the Gallivare Region, Northern Norrbotten, Sweden2015In: Mineral Resources in a Sustainable World / [ed] A.S. Andre-Mayer; M. Cathelineau; P. Muchez; E. Pirard; S. Sindern, 2015, p. 1123-1126Conference paper (Refereed)
    Abstract [en]

    Geochemical investigations were carried out in the Gallivare area as a part of a larger project aiming to understand the crustal architecture of the region in 3D. Major igneous suites such as the Dundret and Vassaravaara intrusions with additional smaller mafic intrusions have been identified as key localities and investigated. Results indicate two distinct rock units. The first suite is assigned to ultramafic-mafic layered intrusions with a calc-alkaline to a more tholeiitic composition belonging to the Dundret and Vassaravaara intrusions. The second suite is mainly of mafic to intermediate composition with a clear ophitic texture. This paper investigate the source and origin of the key rock suites, playing a major role on the evolution of the Gallivare region, a region which is characterized by porphyry Cu, IOCG, and Al0 deposits including some of Europe's top producing Fe and Cu-Au-Ag (-Mo) mines.

  • 236.
    Sarlus, Zimer
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Wanhainen, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nordin, Roger
    Boliden Mineral, Exploration Department, Boliden.
    Andersson, Joel
    LKAB.
    Geochemistry of Ultramafic-mafic Units Related to Fe-, Cu-, and Au Deposits in the Gällivare Region, Northern Norrbotten, Sweden2015Conference paper (Refereed)
  • 237.
    Seigel, Harold
    et al.
    Colorado School of Mines, Golden.
    Nabighian, Misac
    Colorado School of Mines, Boulder.
    Parasnis, Dattatray
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Vozoff, Keeva
    University of Sydney.
    The early history of the induced polarization method2007In: The Leading Edge, ISSN 1070-485X, E-ISSN 1938-3789, Vol. 26, no 3, p. 312-321Article in journal (Refereed)
    Abstract [en]

    This paper traces the early development of the induced polarization method, starting with field observations by Conrad Schlumberger in a mining region in France, about 1913. Starting about 1929 he introduced this technique into hydrocarbon borehole logging in the USSR, and this resulted in further development in eastern and western Europe.

  • 238.
    Shumlyanskyy, Leonid
    et al.
    Institute of Geochemistry, Mineralogy and Ore Formation of the National Academy of Sciences of Ukraine, Kyiv.
    Billström, Kjell
    Laboratory for Isotope Geology. Swedish Museum of Natural History, Stockholm.
    Hawkesworth, Chris
    University of St. Andrews.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    U-Pb age and Hf isotope compositions of zircons from the north-western region of the Ukrainian shield: mantle melting in response to post-collision extension2012In: Terra Nova, ISSN 0954-4879, E-ISSN 1365-3121, Vol. 24, no 5, p. 373-379Article in journal (Refereed)
    Abstract [en]

    The North-Western region of the Ukrainian shield represents Palaeoproterozoic continental crust formed essentially during two orogenic events at ca. 2.1–2.05 and 2.0–1.95 Ga. At 1.8–1.74 this area was intruded by huge Korosten anorthosite–mangerite–charnockite granite complex. At least three generations of mafic dykes can be distinguished in the region. We report new U-Pb data obtained for a suite of Ni-enriched dolerite dykes and layered gabbroic intrusions. Our results indicate that the Tomashgorod dyke was formed at 1787.4 ± 6.4 Ma, the Prutivka intrusion at 1777.0 ± 4.7 Ma and the Kamenka massif at ca. 1.79 Ga. This time coincides with the collision of the Fennoscandian and Sarmatian segments of the East European craton and it is contemporaneous with the initial stages of evolution of the Korosten complex. Hf isotopic compositions of zircons indicate that these rocks originated due to melting of moderately depleted mantle material.

  • 239.
    Singsoupho, Sounthone
    et al.
    Geophysics Unit, Department of Physics, Faculty of Science, National University of Laos.
    Bhongsuwan, Tribop
    Geophysics Research Center, Department of Physics, Faculty of Science, Prince of Songkla University, Hatyai.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Palaeocurrent direction estimated in Mesozoic redbeds of the Khorat Plateau, Lao PDR, Indochina Block using anisotropy of magnetic susceptibility2015In: Journal of Asian Earth Sciences, ISSN 1367-9120, E-ISSN 1878-5786, Vol. 106, p. 1-18Article in journal (Refereed)
    Abstract [en]

    Mesozoic redbeds in the western part of central and southern Laos are the most abundant rocks of the Khorat Plateau. In earlier studies, palaeocurrent directions of the Mesozoic redbeds in the Khorat Plateau were mapped, but for the Upper Cretaceous sediments no palaeocurrent data was presented. The purpose of the present study is to test previous models of sedimentary source areas and propose palaeocurrent flow directions for Upper Cretaceous sediments in the Khorat Plateau. This we do by characterization of the rocks on the basis of their magnetic properties and anisotropy parameters. Integrated magnetic properties, including susceptibility, NRM, Q-value, and S-ratio, have been used for classification of the stratigraphies of the redbeds. A clear difference in magnetic properties was observed between the Jurassic and Cretaceous rocks, while some sites of the Lower and Upper Cretaceous were similar. From magnetic analyses the Champasak redbeds could be defined statigraphically as an unconformity beneath the Khorat Group. On the basis of the AMS interpretation, the rocks can be divided into undeformed and deformed rocks. The palaeocurrent directions in the undeformed redbeds are predominantly from the NNE and NE of the Khorat Basin. For the Upper Jurassic-Lower Cretaceous redbeds, we argue that the sources rocks of the sediments were located in the northern and eastern margin of the Khorat Plateau, probably in the Truong Son Belt zone in the northeastern Laos and central Vietnam. While, the source rock of the Upper Cretaceous redbeds in the Khorat Plateau was located in the Qinling Belt in China or in the Loei-Luang Prabang Fold Belt in northeastern Thailand and northern Laos.

  • 240.
    Singsoupho, Sounthone
    et al.
    Geophysics Unit, Department of Physics, Faculty of Science, National University of Laos.
    Bhongsuwan, Tripob
    Geophysics Research Center, Department of Physics, Faculty of Science, Prince of Songkla University, Hatyai.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tectonic Evaluation of the Indochina Block during Jurassic-Cretaceous from Palaeomagnetic Results of Mesozoic Redbeds in Central and Southern Lao PDR2014In: Journal of Asian Earth Sciences, ISSN 1367-9120, E-ISSN 1878-5786, Vol. 92, p. 18-35Article in journal (Refereed)
    Abstract [en]

    Rock magnetic and palaeomagnetic studies were performed on Mesozoic redbeds collected from the central and southern Laos, the northeastern and the eastern parts of the Khorat Plateau on the Indochina Block. Totally 606 samples from 56 sites were sampled and standard palaeomagnetic experiments were made on them. Positive fold tests are demonstrated for redbeds of Lower and Upper Cretaceous, while insignificant fold test is resulted for Lower Jurassic redbeds. The remanence carrying minerals defined from thermomagnetic measurement, AF and Thermal demagnetizations and back-field IRM measurements are both magnetite and hematite. The positive fold test argues that the remanent magnetization of magnetite or titanomagnetite and hematite in the redbeds is the primary and occurred before folding. The mean palaeomagnetic poles for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous are defined at Plat./Plon. = 56.0oN/178.5oE (A95 = 2.6o), 63. 3oN/170.2oE (A95 = 6.9o), and 67.0oN/180.8oE (A95 = 4.9o), respectively. Our palaeomagnetic results indicate a latitudinal translations (clockwise rotations) of the Indochina Block with respect to the South China Block of -10.8 ± 8.8o (16.4o ± 9.0o); -11.1 ± 6.2o (17.8 ± 6.8o); and -5.3 ± 4.7o (13.3 ± 5.0o), for Lower Jurassic, Lower Cretaceous, and Upper Cretaceous, respectively. These results indicate a latitudinal movement of the Indochina Block of about 5 - 11o (translation of about 750 - 1700 km in the southeastward direction along the Red River Fault) and clockwise rotation of 13 - 18o with respect to the South China Block. The estimated palaeoposition of the Khorat Plateau at ca. 21 - 26°N during Jurassic to Cretaceous argues for a close relation to the Sichuan Basin in the southwest of South China Block. These results confirm that the central part of the Indochina Block has acted like a rigid plate since Jurassic time and the results also support an earlier extrusion model for Indochina.

  • 241.
    Singsoupho, Sounthone
    et al.
    Geophysics Unit, Department of Physics, Faculty of Natural Sciences, National University of Laos. Geophysics Research Center, Department of Physics, Faculty of Science, Prince of Songkla University, Hatyai, Thailand.
    Bhongsuwan, Tripob
    Prince of Songkla University, Department of Physics, Hatyai, Thailand.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Deformation in Jurassic-Cretaceous redbeds from Champasak and Khammouane, Lao PDR, revealed by anisotropy of magnetic susceptibility2018In: Chang Mai journal of science, ISSN 0125-2526, Vol. 45, no 1, p. 576-587Article in journal (Refereed)
    Abstract [en]

    The anisotropy of magnetic susceptibility measurement technique was applied to the Jurassic-Cretaceous redbeds in the Champasak and Khammouane provinces of the southern and central part of Lao PDR, in order to define the correlation between the magnetic anisotropic data and degree of deformation in redbeds due to tectonic stress field focusing on the mountain belt and fault areas. The results show that the alignment of Kmax axes is predominantly parallel to the trending of the mountain belts (or fold axis) and the strike of faults. The orientation patterns of the principal axes of the susceptibility ellipsoid did not show the typical pattern usually found in undeformed sedimentary rocks. It can be concluded that the development of the triaxial and pencil structure patterns of secondary magnetic fabric correlates well with the degree of rock deformation which is caused by tectonic compression acting on the rocks.

  • 242.
    Skyttä, Pietari
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hermansson, Tobias
    Boliden Mineral AB.
    Andersson, Jenny
    Geological Survey of Sweden.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pre-1.87 Ga development of crustal domains overprinted by 1.87 Ga transpression in the Palaeoproterozoic Skellefte district, Sweden2012In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 206–207, p. 109-136Article in journal (Refereed)
    Abstract [en]

    The complex structural evolution within the VMS-hosting Skellefte district, Sweden, has been investigated to provide a solid structural framework for the known mineral deposits in the area. The area occurs in a transition zone between dominantly N-S to NNE-WSW striking structures in the north and approximately WNW-ESE oriented structural trends in the south. The presence of high-strain zones with both the above orientations in the Skellefte district allows constraining their mutual relationship, as well as their significance for the build-up of the Svecokarelian orogen at around 1.89 Ga and for the following tectonic overprint between 1.87-1.80 Ga. The methods used in this study include structural analysis complemented by potential field modelling and SIMS U-Pb geochronology on zircon. Based on the results of this study, the earliest deformation (D1) is constrained at 1.89–1.88 (1.87) Ga and tentatively attributed to crustal extension occurring synchronously with volcanism. Deposition of the Skellefte Group metavolcanic rocks is inferred to have occurred in a pull-apart basin developed due to dextral strike-slip shearing along approximately N-S striking regional-scale shear zones. Variations in the development of deformation fabric across the district indicate that the crust was divided into an upper, un-metamorphosed domain and a lower, strongly metamorphosed domain during D1. We further infer that the transition from the upper to lower crust was locally coupled with development of low-angle crustal-scale detachment zones during D1. The heterogenous crust was subsequently overprinted by transpressional deformation which may be explained by two alternative models. According to the first model, one single SSE-NNW transpressional event with distinct strain partitioning between the coaxially deformed upper crust and the non-coaxially deformed lower crust is largely responsible for the present-day structural geometry. A post-folding rhyolite dyke, here dated at 1871 ± 4 Ma, constrains the minimum age of this event (D2). The alternative model includes two separate transpressional events: a SW-NE one at (1.88-) 1.87 Ga, followed by SSE-NNW transpression at 1.86 Ga. Recognition of the early-orogenic detachment zones allow us to suggest that many of the major crustal-scale shear zones in the central Fennoscandian Shield have originated as 1.89-1.87 Ga crustal detachment zones, i.e. earlier than typically considered.

  • 243.
    Skyttä, Pietari
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Hermansson, Tobias
    Boliden Mineral AB.
    Andersson, Jenny
    Sveriges Geologiska Undersökning, Geological Survey of Sweden.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Evolution of early-orogenic deformation zones and their significance for the development of contrasting structural domains within the Palaeoproterozoic Skellefte District, Sweden2012Conference paper (Refereed)
  • 244.
    Skyttä, Pietari
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Boliden Mineral AB.
    Dehghannejad, Mahdieh
    Uppsala University, Uppsala universitet, Department of Earth Sciences, Uppsala University.
    Juanatey, Maria A. Garcia
    Department of Earth Sciences, Uppsala University, Uppsala University.
    Hübert, Juliane
    Uppsala University, Department of Earth Sciences, Uppsala University.
    Multiscale 3/4D-modelling of mineral belts: examples from the Skellefte Mining District, Sweden2011Conference paper (Refereed)
  • 245.
    Skyttä, Pietari
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Tavakoli, Saman
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Weihed, Pär
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Allen, Rodney
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dehghannejad, Mahdieh
    Juanatey, Maria Garcia
    Hübert, Juliane
    4-dimensional geological modelling of mineral belts2011Conference paper (Other academic)
  • 246.
    Skyttä, Pietari
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Hermansson, Tobias
    Boliden Mineral AB.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Magnetic fabrics as constraints on the kinematic history of a pre-tectonic granitoid intrusion, Kristineberg, northern Sweden2010In: Journal of Structural Geology, ISSN 0191-8141, E-ISSN 1873-1201, Vol. 32, no 8, p. 1125-1136Article in journal (Refereed)
    Abstract [en]

    Outcrop-scale correlations of deformation fabrics with low-field anisotropy of magnetic susceptibility (AMS) measurements revealed a two-stage structural evolution of the pre-tectonic, Palaeoproterozoic Viterliden intrusion in the Skellefte District, Sweden. The first deformation event reflected ˜N-S compression during basin inversion, and comprised reverse dip-slip shearing along major ˜E-W faults, whereas the low-strain lenses in between experienced penetrative deformation with a component of NE-SW elongation along the main foliation. This event is largely responsible for the present structural geometry regionally and locally, and also for the magnetic fabric of the rocks. In particular, the sub-vertical maximum principal susceptibility axes (Kmax) within the high-strain zones are related to early dip-slip deformation, and were virtually unaffected by subsequent dextral strike-slip reactivation, which is recorded by sub-horizontal rock lineations. The strike-slip deformation reflects ˜E-W bulk shortening and may regionally be correlated with reverse faulting along a ˜N-S trending major shear zone east of the study area.

  • 247.
    Steenfelt, Agnete
    et al.
    Geological Survey of Denmark and Greenland.
    Stendal, Henrik
    Geological Survey of Denmark and Greenland.
    Nielsen, B.M.
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Gold in central West Greenland: Known and prospective occurrences2004In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 4, p. 65-68Article in journal (Refereed)
  • 248.
    Stendal, Henrik
    et al.
    Geological Survey of Denmark and Greenland.
    Frei, Robert
    Geological Institute, University of Copenhagen.
    Muhongo, Sospeter M.
    Department of Geology, University of Dar es Salaam.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark, Greenland GEUS.
    Mnali, Saidi
    Department of Geology, University of Dar es Salaam.
    Petro, Faustin Nyanda
    Geological Survey of Tanzania.
    Temu, E. Brian
    Geological Survey of Tanzania.
    Gold potential of the Mpanda Mineral Field, SW Tanzania: Evaluation based on geological, lead isotopic and aeromagnetic data2004In: Journal of African Earth Sciences, ISSN 0899-5362, Vol. 38, no 5, p. 437-447Article in journal (Refereed)
    Abstract [en]

    Gold and base metals of the Mpanda Mineral Field (MMF) is the focus of this paper. Gold veins and gold-bearing base metal occurrences are structurally controlled by conjugate sets of NW-SE and E-W trending faults and/or shear zones that crosscut high-grade metamorphic rocks and post-kinematic intrusions. It was anticipated that Palaeoproterozic country rocks could have been potential host rocks for the gold mineralisation in this area. This argumentation was based on Pb model ages of various deposits from the MMF. Recent fieldwork and Pb isotopic results presented herein indicate that epigenetic gold and base metal vein-type mineralisation in the MMF is post-Palaeoproterozoic. Our Pb isotope study concentrates on constraining the sources of metals in gold-bearing quartz reefs and base metal occurrences. Pb isotopes of whole rocks and minerals indicate that mineralisation was emplaced during the Neoproterozoic, contemporaneous with the intrusion of alkaline granites and carbonatite complexes (e.g., Sangu-Ikola carbonatite complex) at ∼720 Ma. The source of Pb in the mineral occurrences is compatible with that characteristic of the Palaeoproterozoic host rocks. Aeromagnetic data suggest that the gold-bearing, NNW-SSE trending area continues to the north beyond Mpanda town. Pb isotope results and aeromagnetic data have significant implications for future exploration programs within the region, in that the search should potentially focus on the defined geophysical borders and trendlines, and on Neoproterozoic, rather than Palaeoproterozoic vein systems

  • 249.
    Stensgaard, Bo Møller
    et al.
    Geological Survey of Denmark and Greenland.
    Chung, Chang-Jo
    Geological Survey of Canada.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Stendal, Henrik
    Geological Survey of Denmark and Greenland.
    Assessment of mineral potential using cross-validation techniques and statistical analysis: A case study from the paleoproterozoic of West Greenland2006In: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 101, no 7, p. 1397-1413Article in journal (Refereed)
    Abstract [en]

    An ideal mineral exploration program characterizes all types of data by describing its relationship to an integrated mineral deposit and exploration model. The model is used to interpret the mineralization and plays a role in the decision making for exploration activities and investments. Successful application of the model depends on validated techniques that quantify the signatures of geologic features, combine data, and lead to parameters that can be expressed in economic terms. A step-by-step procedure for assessment of mineral potential is proposed here based on probabilistic models, on empirical analysis, and on location and quantitative characterization of known mineral occurrences. Mineral potential maps are constructed as a part of the procedure. The reliability of the results is evaluated mathematically by cross validations and prediction rate curves. Estimations of the probability for new discoveries are made and the results are discussed in economic terms. To illustrate the procedure we apply the method to exploration f or volcanogenic massive sulfide deposits in a poorly to moderately explored area of about 25,800 km2 within the Paleoproterozoic Nagssugtoqidian orogen of West Greenland. The input data for the analysis include 67 noneconomic occurrences and 15 different types of geophysical and geochemical data. Based on statistical characterizations, 36 of the occurrences were divided into three groups (the Naternaq, Arfersiorfik, and Ataneq groups). The remaining 31 occurrences did not have consistent characteristics in terms of the 15 geophysical and geochemical parameters, and these were excluded from further statistical study. A consistent set of geophysical and geochemical characteristics was established for each of the three groups and used to construct mineral potential maps of the exploration area. Each potential map was divided into 200 equal-size classes of 129 km2 each (0.5% of the entire study area). The probability that the most favorable 129 km2 will host an occurrence of the type assigned to a particular group is estimated as 71, 32, and 100 percent for the three groups (Naternaq, Arfersiorfik, and Ataneq). The probabilities of new discoveries within a specific minimum prospective area targeted for exploration are also discussed. The probabilities of new discoveries within 1 km2 of the 129 km2 most favorable area were estimated as 1.0, 0.3, and 23 percent, respectively for the three types of occurrences

  • 250.
    Stensgaard, Bo Møller
    et al.
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Steenfelt, Agnete
    Geological Survey of Denmark and Greenland.
    An integrative and quantitative assessment of the gold potential of the Nuuk region, West Greenland2006In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 10, p. 37-40Article in journal (Refereed)
23456 201 - 250 of 288
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