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  • 1.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Torklid Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Project: Development, Evaluation and Optimization of Measures to Reduce the Impact on the Environment from Mining Activities in Northern Regions2016Other (Other (popular science, discussion, etc.))
    Abstract [en]

    Min-North is a transnational project financed by the Interreg Nord program and coordinated by LTU. The project is a cooperation between Geological survey of Finland, GTK, Oulo University (Finland), The Arctic University of Norway, UiT and several (>17) small and large enterprises and mining companies in the northern region with expertise within geology, waste management, geophysics and geochemistry. The overall goal is to reduce the environmental impacts of mining in the northern regions by developing, evaluating, optimizing environmental techniques. In Sweden, geophysical and geochemical techniques will be integrated to develop a 4D model for tracing pollution transport in the mine waste, mine areas and in(to) the surroundings.

  • 2.
    Alakangas, Lena
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Salifu, Musah
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Heino, Neea
    Geological Survey of Finland, Finland.
    Hyvönen, Eija
    Geological Survey of Finland, Finland.
    Karlsson, Teemu
    Geological Survey of Finland, Finland.
    Panttila, Hannu
    Geological Survey of Finland, Finland.
    Pietilä, Raija
    Geological Survey of Finland, Finland.
    Tornivaara, Anna
    Geological Survey of Finland, Finland.
    Turunen, Kaisa
    Geological Survey of Finland, Finland.
    Lu, Jinmei
    UiT The Arctic University of Norway, Norway.
    Fu, Shuai
    UiT The Arctic University of Norway, Norway.
    Bui, Minh Tuan
    UiT The Arctic University of Norway, Norway.
    Heiderscheidt, Elisangela
    University of Oulu, Finland.
    Postila, Heini
    University of Oulu, Finland.
    Leiviskä, Tiina
    University of Oulu, Finland.
    Ronkanen, Anna-kaisa
    University of Oulu, Finland.
    Kujala, Katharina
    University of Oulu, Finland.
    Khan, Uzair
    University of Oulu, Finland.
    Gogoi, Harshita
    University of Oulu, Finland.
    Min-North: Development, Evaluation and Optimization of Measures to Reduce the  Environmental Impact of Mining Activities in Northern Regions2019Report (Other academic)
    Abstract [en]

    The Min-North (Development, Evaluation and Optimization of Measures to Reduce the Environment Impact of Mining Activities in Northern Regions) project was a trans-national cooperative project, with participants from the Geological Survey of Finland (GTK), University of Oulu (UO), UiT The Arctic University of Norway (UiT), Luleå University of Technology (LTU) and SMEs from Sweden, Finland and Norway. The project was funded by Interreg Nord and Norrbottens länsstyrelse. The participants have expertise in mine waste management, mine water treatment and geophysics. The overall aim of the project was to enhance the development of environmental protection technologies. An associated goal was to deepen cross-border cooperation by creating a larger critical mass of researchers in mine waste management and local SMEs in the Northern regions with greater capacities to disseminate and implement new methods, products and services. The project ran for 36 months from the 1st of January 2016 to the end of December 2018.

     

  • 3.
    Appel, Peter W.Uitterdijk
    et al.
    Geological Survey of Denmark and Greenland.
    Abrahamsen, Niels
    Geophysical Laboratory, Aarhus University.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Unusual features caused by lightning impact in West Greenland2006In: Geological Magazine, ISSN 0016-7568, E-ISSN 1469-5081, Vol. 143, no 5, p. 737-741Article in journal (Refereed)
    Abstract [en]

    Two lightning impacts are described from an area near the Inland Ice in West Greenland. The first lightning blasted an outcrop of metacherts. It subsequently split into two branches, which traversed rock outcrops and boulders, leaving behind two white almost straight lines, 30 m and 14 m long, respectively, where all lichens and plants were burned away. On the white lines the upper few millimetres of the traversed boulders were melted to a glass which subsequently peeled off by thermal expansion to leave a rough surface. Magnetic investigation of an amphibolite boulder found on the white line showed that a strong electric current indeed traversed the boulder. A few years later a second lightning impacted on a mountaintop close to the first impact. The second lightning left a trail on the rock surface covered by a thin layer of glass. The glass displays spectacular colours ranging from metallic blue to red, yellow and green.

  • 4.
    Basokur, Ahmet Tuǧrul
    et al.
    Ankara Universitesi.
    Rasmussen, Thorkild Maack
    University of Uppsala, Solid Earth Physics.
    Kaya, Cemal
    MTA Genel Mudurlugu .
    Altun, Y.
    Demir Export A.S.
    Aktas, K.
    MTA Genel Mudurlugu .
    Comparison of induced polarization and controlled-source audio-magnetotellurics methods for massive chalcopyrite exploration in a volcanic area1997In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 62, no 4, p. 1087-1096Article in journal (Refereed)
    Abstract [en]

    In this paper, we compare and contrast the results of field experiments with the dipole-dipole-induced polarization (IP) and controlled-source audio-magnetotellurics (CSAMT) methods, along the same survey profiles, at a test area that was subject to extensive drilling and detailed geological investigation. The ore bodies are interbedded between two series of dacitic tuff. The depth and thickness of the massive chalcopyrite-pyritesphalerite body vary between 25 and 100 m and 0.5 and 16 m, respectively. Resistivity and IP phase measurements on the core samples collected from the test area provide some idea of the relative differences between the background rock units and the target. The resistivity of the chalcopyrite samples varies between 0.6 to 2 ohm-m and provides sufficient resistivity contrast with surrounding volcanic rock units for target detection. The results of dipole-dipole IP profiling with a 50-m dipole length conducted along two profiles are presented in the form of apparent resistivity and phase pseudosections. CSAMT measurements were made at 13 frequencies from 2 Hz to 8192 Hz along three profiles. The receiver dipole length was 25 m. The CSAMT data are presented in the form of pseudosections using conventional and new definitions of apparent resistivity. The elliptical contours of low apparent resistivity generated by the transition-field notch can be misleading with respect to the real anomaly of the ore body. These artificial anomaly patterns are suppressed by making use of an alternative apparent resistivity definition derived from the frequency-normalized impedance. The qualitative interpretation based on the IP and CSAMT pseudosections shows that the location and the extension of the ore body are indicated better in the CSAMT apparent resistivity data computed from the alternative definition. The qualitative interpretation of the IP data is difficult because of the 3-D effect arising from the neighboring thicker parts of the ore body and pyrite particles within the basement. At the final stage, the far-field range of the CSAMT apparent resistivity and phase data is identified by the visual inspection of the individual sounding diagrams. The models derived from the 2-D Occam inversion carried out on the far-field data are compared with the drill-hole information and are found to describe the actual geological situation.

  • 5.
    Bedini, Enton
    et al.
    Federal Institute for Geosciences and Natural Resources (BGR), Hannover. Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Geological Survey of Denmark and Greenland (GEUS), Copenhagen, Denmark.
    Use of airborne hyperspectral and gamma-ray spectroscopy data for mineral exploration at the Sarfartoq carbonatite complex, southern West Greenland2018In: Geosciences Journal, ISSN 1226-4806, Vol. 22, no 4, p. 641-651Article in journal (Refereed)
    Abstract [en]

    The Sarfartoq carbonatite complex occurs in the transition zone between Archaean and Paleoproterozoic gneisses in southern West Greenland. The Sarfartoq carbonatite complex hosts ore deposits and occurrences of rare earth elements and niobium. In this study, airborne HyMap hyperspectral imagery and coincident airborne gamma-ray spectroscopy data were analysed for mineral exploration of Sarfartoq carbonatite complex. The study area included the carbonatite core zone and a hydrothermally altered shear zone prospective for rare earth elements mineralization in the southern margin of the carbonatite complex. The analysis of the hyperspectral imagery was focused on the mapping of the spatial distribution of carbonatite, fenite and limonite. Significant anomalies of uranium, thorium and potassium were outlined from the gamma-ray spectroscopy data. Decision trees were used to combine the results from the hyperspectral image analysis and airborne gamma-ray spectroscopy. Significant anomalies of thorium at the hydrothermally altered shear zone coinciding with the presence of carbonatite rocks are generally indicative of outcropping rare earth element mineralization. The study indicates the benefits of coincident airborne hyperspectral and gamma-ray spectroscopy surveys for the mineral exploration of carbonatite complexes.

  • 6.
    Belay, R.
    et al.
    University of Uppsala, Department of Geophysics.
    Rasmussen, Thorkild Maack
    University of Uppsala, Department of Geophysics.
    One‐dimensional non‐linear inversion of magnetotelluric data: the importance of data errorrs1995In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 43, no 7, p. 905-918Article in journal (Refereed)
    Abstract [en]

    Inversion of noisy magnetotelluric data over a horizontally stratified earth has no unique solution. Instead, the resistivities and thicknesses of the layers can only be specified to lie within certain bounds at a particular confidence level. The significance of having correctly estimated data errors when calculating the parameters and parameter bounds is discussed. Emphasis is put on the very corrunon problem of not being able to obtain models which can be considered acceptable with a reasonable certainty from a statistical point of view. A method is presented to obtain a pragmatic data error description by adjustment of wrongly estimated data errors while keeping the suppression of 1D data features at a minimum. A comparison is made between calculation of the parameter bounds based on approximating the confidence surface by hyperellipsoids and a calculation based on a full non‐linear most‐squares analysis. In general it is found that the approximation works very well when the confidence limit is small. However, significant deviations are found in some cases.

  • 7.
    Brethes, Anais
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Geological Survey of Denmark and Greenland (GEUS), Department of Petrology and Economic Geology, Denmark.
    Guarnieri, Pierpaolo
    Geological Survey of Denmark and Greenland (GEUS), Department of Petrology and Economic Geology.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Bauer, Tobias Erich
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Interpretation of aeromagnetic data in the Jameson Land Basin, central East Greenland: Structures and related mineralized systems2018In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 724-725, p. 116-136Article in journal (Refereed)
    Abstract [en]

    This paper provides a detailed interpretation of several aeromagnetic datasets over the Jameson Land Basin in central East Greenland. The interpretation is based on texture and lineament analysis of magnetic data and derivatives of these, in combination with geological field observations. Numerous faults and Cenozoic intrusions were identified and a chronological interpretation of the events responsible for the magnetic features is proposed built on crosscutting relationships and correlated with absolute ages. Lineaments identified in enhanced magnetic data are compared with structures controlling the mineralized systems occurring in the area and form the basis for the interpretations presented in this paper. Several structures associated with base metal mineralization systems that were known at a local scale are here delineated at a larger scale; allowing the identification of areas displaying favorable geological settings for mineralization. This study demonstrates the usefulness of high-resolution airborne magnetic data for detailed structural interpretation and mineral exploration in geological contexts such as the Jameson Land Basin.

  • 8.
    Brethes, Anais
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Guarnieri, Pierpolo
    GEUS.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    3D modelling of the base-metal mineralized Jameson Land Basin (central East Greenland) using geologically constrained inversion of magnetic data2015Conference paper (Other academic)
  • 9.
    Brethes, Anaïs
    et al.
    Geological Survey of Denmark and Greenland.
    Guarnieri, Pierpaolo
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Integrating 3D photogeology with aeromagnetic data as a tool for base-metal exploration in East Greenland2014In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 31, p. 71-74Article in journal (Refereed)
  • 10.
    Brethes, Anaïs
    et al.
    Geological Survey of Denmark and Greenland.
    Guarnieri, Pierpaolo
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    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.
    3D-Modelling of the Early Triassic Base-Metal Mineralized Syn-Rift Sequence in the Jameson Land Basin (East Greenland)2015In: Mineral Resources in a Sustainable World / [ed] A.S. Andre-Mayer; M. Cathelineau; P. Muchez; E. Pirard; S. Sindern, 2015, p. 1701-1704Conference paper (Refereed)
    Abstract [en]

    The Jameson Land Basin in central East Greenland is mineralized in Pb, Zn and Cu. Mineralization occurs in several stratigraphic horizons and along structures in Upper Permian and Triassic sediments. A good understanding of the basin architecture and evolution is therefore essential for mineral exploration in this area. 3D-Photomapping from high resolution aerial photos along with a structural interpretation of aeromagnetic data, electromagnetic data, and results from fieldwork and drilling were integrated into a 3D-structural model. This data integration allowed modelling the rift architecture in the eastern margin of the Jameson Land Basin.

  • 11.
    Brethes, Anaïs
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Guarnieri, Pierpaolo
    GEUS.
    Rasmussen, Thorkild Maack
    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.
    Geological Analysis of Aeromagnetic Data over the Blyklippen Lead-zinc Mine at Mesters Vig, Central East Greenland2016In: First Conference on Geophysics for Mineral Exploration and Mining: Near Surface Geoscience 2016, Barcelona, Spain, 4-8 September 2016, Houten, 2016, article id Mo MIN 05Conference paper (Refereed)
    Abstract [en]

    In the Mesters Vig area epithermal Pb-Zn sulphide-bearing quartz veins are associated with the border faults of a NNW-SSE elongated graben down-faulting Carboniferous to Lower Triassic sediments. The analysis of the total magnetic field, tilt derivative, vertical derivative and analytic signal allowed to define subcropping magnetic domains and identify structural trends. Doleritic dykes, sills and faults were mapped and structural relationships were established between them. Finally, aeromagnetic data allowed here to delineate structural trends along and in the vicinity of which mineralized quartz veins are mapped.

  • 12.
    Brethes, Anaïs
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Guarnieri, Pierpaolo
    GEUS.
    Bauer, Tobias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Mapping and characterization of Induced Polarization in airborne TEM data from central East Greenland: application of a Self-Organizing Map procedure2016Conference paper (Refereed)
    Abstract [en]

    nduced Polarization (IP) effects were observed in airborne Time Domain EM (TEM) data acquired in central East Greenland in the context of exploration for disseminated sulphides in a sedimentary basin. Some of the IP anomalies were targeted by drilling which revealed the absence of mineralization. In order to understand the possible causes of the IP effects we first identified them in the TEM data. IP indicators were extracted from the shape of the transient curves at every measurement location and were analysed by using a Self-Organizing Map (SOM) procedure. Results from K-mean clustering of the SOM are visualized on a geographical map showing the transient curves’ characteristics. Some of the clusters are clearly correlated with the geology whereas others merely reflect recordings below the noise level. In order to interpret the cause of the IP anomalies the airborne TEM data were inverted for the Cole-Cole parameters.

  • 13.
    Chouliaras, Gerassimos
    et al.
    Department of Seismology, University of Uppsala.
    Rasmussen, Thorkild Maack
    Department of Solid Earth Physics, University of Uppsala.
    The application of the magnetotelluric impedance tensor to earthquake prediction research in Greece1988In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 152, no 1-2, p. 119-135Article in journal (Refereed)
    Abstract [en]

    Continuous short period (0.1-3600 s) measurements of the magnetotelluric field components were conducted simultaneously at two sites in Greece for a period of 5 weeks. The estimation of the impedance tensor elements from 8-hr windows of recorded data, at each station, is found to describe the local electromagnetic induction with great accuracy. The computation of the residual electric field, obtained as the difference between the observed and estimated inductive part of the electric fields, clearly improves the detection of any local electric field anomaly. This method was used in an attempt to detect precursory Sci smic electrical signals (SES) that have been reported to precede earthquakes in Greece. The results indicate the success of this method in resolving ambiguities about the nature of the reported SES, i.e. whether it has an external or internal source. Although during the recording period no large earthquake occurred, five with a magnitude of between ML = 4.0 and ML = 4.3 occurred within a radius of 150 km from one of the stations. The magnetotelluric recordings and the computed residual electric fields for the time intervals reported to contain the SES precursors to these events were analysed in some detail. In two of the cases it was found that the sources could not be related to earthquake processes. In the other three cases the nature of the source of the suspected SES, although electric, could not be established with certainty. These results indicate that for earthquakes of small magnitude (ML ≤ 4.3) or of large epicentral distance (r ≥ 100 km), the detection of a SES is extremely difficult.

  • 14.
    Darwesh, Ali K.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Maack Rasmussen, Thorkild
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Kicks controlling techniques efficiency in term of time2017In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 5, p. 482-492Article in journal (Refereed)
    Abstract [en]

    Kicks are the result of under balance drilling operation. Time consumed to control the kicks will be different in depending on the controlling technique. Drilling fluid considered as a first barrier to control formation pressure and well kicks. Any advance in drilling fluids leads to more controlled operation in term of time. This paper will follow the general increasing profile of pressure before entering the reservoir. Both methods of well controlling technique; circulating techniques and non-circulating have been implemented in many oil blocks. The process of designing and casing selection, setting depth and many other issues is predominately dependent on the utilization of accurate values of formation pressure. Formation pressures used to design safe mud weights to overcome fracturing the formation and prevent well kicks. Hence the emphasis has been placed on the practical utilization of kicks pressure near the reservoir. The presented relationships will help the engineer to better understand lithological columns and reduce potential hole problems during the kick appearance. Selecting the best well controlling practical method can lead to not harming the reservoir and more production later. Changes in some drilling fluid properties have been proposed with increasing the depth without damaging the reservoir. Suggestions in relation to the casing setting point of the intermediate section are also proposed. Standard equations with proper modification for gases and safety margin have been proposed for the future drilling operation in oil fields above the reservoir.

  • 15.
    Darwesh, Ali K.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Time Optimizing near the Pay Zone2017In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 9, no 10, p. 848-858Article in journal (Refereed)
    Abstract [en]

    Well control techniques are used in oil and gas drilling operations to control bottom hole pressure and avoid any fluid influx from formation to the well. These techniques are highly important near the pay zone in term of time. Controlling formation fluid pressure and thereby the formations behavior in a predictable fashion will help toward more optimized environmental friendly drilling operation. Time consumed to control the formation fluid pressure will range between few hours to many days. This paper discusses hydrostatic pressure distribution and changes near the pay zone for one oil blocks in Kur- distan, in the northern part of Iraq. Obtaining homogeneous increase in some drilling fluid properties will help the engineer to better interpret sampling of the lithological columns and reduce potential hole problems and operationtime.

  • 16.
    Darwesh, Ali
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Evaluation of Limestone Interval in the Drilled Surface Section of Bn-1 Oil Well2016In: Engineering, ISSN 1947-3931, E-ISSN 1947-394X, Vol. 8, no 8, p. 515-524Article in journal (Refereed)
    Abstract [en]

    The first exploration oil well in any oil block consumes in general more time and cost than the other wells in the same block. Evaluating the drilled wells serves to improve the future operations. This paper evaluates the drilled surface section through real field data for the first exploration oil well drilled in one of the oil blocks, in Kurdistan north of Iraq. The surface section of the well was drilled with the conventional method to penetrate many different geological formations with tight intervals. Drilling efficiency and the difficulties encountered are discussed and explained using various data sources. All daily drilling reports concerning a specific interval were studied. This includes weight on bit, string rotation, mud pump flow and penetration rate. Evaluation was carried out by analyzing the used controllable drilling parameters with the formations features. Penetration of the Pila Spi formation (Middle Eocene) was the most difficult formation in the drilled section. Microsoft Office 365 Pro Plus used in making graphs and Excel tables. Evaluations showed that the conventional technology used left many negative effects, like increase in None Productive Time NPT, cost and ground water pollution. Simultaneous Casing Drilling method proposed as an alternative method for the future campaign.

  • 17.
    Darwesh, Ali
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Al-Ansari, Nadhir
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Wiper Trips Effect on Wellbore Instability Using Net Rising Velocity Methods2018In: Open Petroleum Engineering Journal, ISSN 1874-8341, Vol. 11, p. 14-28Article in journal (Refereed)
    Abstract [en]

    Background: This paper discusses the wiper trip effects on well instability in shale formations.Objectives: Problematic shale interval sections have been studied for the time spent on the wiper trip operations. Lifting efficiency and well wall instability change with the time analyzed. Detailed drilling operation, formation heterogeneity, rheological and filtration characteristics of polymer water-based mud are discussed. Physical and chemical properties of the drilled formation and drilling fluid are also studied.Materials and Methods: Wiper trips are analyzed using a typical drawing program to find the relations between the most controllable parameters. For that, two calculation models have been implemented to find the net rising cutting particles velocity in the annular. The relation between the net rising velocity and wiper trips is analyzed. Laboratory works have been done to support the findings of field work.Results: Strong relations have been found between the wiper trip impacts and lithology types of the penetrated shale.Conclusion: A modified drilling program is proposed in relation to changes in casing setting depth and drilling fluid properties that make the operations more efficient in cost and time.

  • 18.
    Døssing, Arne
    et al.
    DTU Space, National Space Institute, Technical University of Denmark.
    Hopper, John R.
    Geological Survey of Denmark and Greenland (GEUS), Copenhagen.
    Olesen, Arne Vestergaard
    DTU Space, National Space Institute, Technical University of Denmark.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland (GEUS), Copenhagen.
    Halpenny, John F.
    Natural Resources Canada, Ottawa, ON.
    New aero-gravity results from the Arctic: Linking the latest Cretaceous-early Cenozoic plate kinematics of the North Atlantic and Arctic Ocean2013In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 14, no 10, p. 4044-4065Article in journal (Refereed)
    Abstract [en]

    The tectonic history of the Arctic Ocean remains poorly resolved and highly controversial. Details regarding break up of the Lomonosov Ridge from the Barents-Kara shelf margins and the establishment of seafloor spreading in the Cenozoic Eurasia Basin are unresolved. Significantly, the plate tectonic evolution of the Mesozoic Amerasia Basin is essentially unknown. The Arctic Ocean north of Greenland is at a critical juncture that formed at the locus of a Mesozoic three-plate setting between the Lomonosov Ridge, Greenland, and North America. In addition, the area is close to the European plate, resulting in complicated interactions between all these areas that are difficult to resolve. In 2009, the 550,000 km2 LOMGRAV aero-geophysical survey produced the first collocated gravity and magnetic measurements over the area, significantly increasing the data coverage. We present an interpretation of a new free-air gravity compilation, which reveals a regionally consistent structural grain across the Lomonosov Ridge, the Ellesmere and Lincoln Sea shelves, and the Alpha Ridge. We interpret the grain as evidence of latest Cretaceous (∼80 Ma) regional extension in response to the northward propagation of Atlantic and Labrador Sea opening into the Arctic, west of Greenland. This interpretation is consistent with coincident alkaline volcanic activity evident in the borderlands of the Lincoln Sea. We further suggest that Eurekan crustal shortening contributed to the formation of the distinct Lomonosov Ridge plateau against an important fault zone north of Greenland. Our results provide new constraints for Cretaceous-Cenozoic plate reconstructions of the Arctic. Key Points Presentation of the largest aero-gravity survey acquired over the Arctic Ocean Plate tectonic link between Atlantic and Arctic spreading west of Greenland New plate reconstruction models are presented for the area north of Greenland

  • 19.
    Døssing, Arne
    et al.
    DTU Space, National Space Institute, Technical University of Denmark.
    Jackson, H. Ruth
    Geological Survey of Canada Atlantic (GSCA), Halifax.
    Matzka, Jürgen
    National Space Institute, DTU Space.
    Einarsson, Indridi
    National Space Institute, DTU Space.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland (GEUS) .
    Brozena, John M.
    Naval Research Laboratory.
    On the origin of the Amerasia Basin and the High Arctic Large Igneous Province-Results of new aeromagnetic data2013In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 363, p. 219-230Article in journal (Refereed)
    Abstract [en]

    The history of the 2.5 million km2 Amerasia Basin (sensu lato) is in many ways the least known in the global tectonic system. Radically different hypotheses proposed to explain its origin are supported only by inconclusive and/or indirect observations and several outstanding issues on the origin of the Basin remain unaddressed. The difficulty lies in the geodynamic evolution and signature of the Basin being overprinted by excess volcanism of the Alpha-Mendeleev Ridge complex, part of the High Arctic Large Igneous Province (HALIP) and one of the largest (>1 million km2) and most intense magmatic and magnetic complexes on Earth. Here, we present the results of a 550,000km2 aerogeophysical survey over the poorly explored Lomonosov Ridge (near Greenland) and adjoining Amerasia and Eurasia Basins that provides the first direct evidence for consistent linear magnetic features between the Alpha and Lomonosov Ridges, enabling the tectonic origin of both the Amerasia Basin and the HALIP to be constrained. A landward Lower Cretaceous ( ~ 138 - 125(120) Ma) giant dyke swarm (minimum 350×800km2) and tentative oceanward Barremian (or alternatively lower Valanginian-Barremian) seafloor spreading anomalies are revealed. Prior to Cenozoic opening of the Eurasia Basin the giant dyke swarm stretched from Franz Josef Land to the southern Alpha Ridge and possibly further to Queen Elisabeth Islands, Canada. The swarm points towards a 250-km-wide donut-shaped anomaly on the southern Alpha Ridge, which we propose was the centre of the HALIP mantle plume, suggesting that pronounced intrusive activity, associated with an Alpha Ridge mantle plume, took place well before the Late Cretaceous Superchron and caused continental breakup in the northern Amerasia Basin. Our results imply that at least the southern Alpha Ridge as well as large parts of the area between the Lomonosov and southern Alpha Ridges are highly attenuated continental crust formed by poly-phase breakup with LIP volcanic addition. Significantly, our results are consistent with an early ( ~ pre-120 Ma) overall continental scale rotational opening of the Amerasia Basin in which the Eurasian continental margin is rifted from the Canadian-southern Alpha Ridge margin about one or more poles in the Mackenzie Delta (Alaska). The findings provide a key to resolving Arctic plate reconstructions and LIPs in the Mesozoic.

  • 20.
    Elming, Sten-åke
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Danmarks og Grønlands Geologiske Undersøgelse, GEUS.
    Results of magnetotelluric and gravimetric measurements in western Nicaragua, central America1997In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 128, no 3, p. 647-58Article in journal (Refereed)
    Abstract [en]

    Studies a ca. 170 km long traverse running from the Pacific coast of Nicaragua in the west to the Nicaraguan Highland in the east. This part of Nicaragua is characterized by sedimentary rocks of the Pacific Coastal Plain, separated from the Tertiary volcanic rocks of the Highland by the NW-SE-trending Nicaraguan Depression. The purpose of this study is to provide electric conductivity and density constraints on geological crustal structures along the transect. This may then serve as a base for the understanding of the tectonic evolution of this part of Central America. Questions to be answered are: (1) is the Pacific coastal province an accreted terrane? (2) What is the character of the depression? Is this a hidden contact between an accreted terrane and the continental Chortis block? (3) If so, is there a different physical signature for the crust of the Pacific province compared to that of the Highlands?

  • 21.
    Fyhn, Michael B.W.
    et al.
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Dahl-Jensen, Trine
    Geological Survey of Denmark and Greenland.
    Weng, Willy
    Geological Survey of Denmark and Greenland.
    Bojesen-Koefoed, Jørgen A.
    Geological Survey of Denmark and Greenland.
    Nielsen, Tove
    Geological Survey of Denmark and Greenland.
    Geological assessment of the East Greenland margin2012In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 26, p. 61-64Article in journal (Refereed)
  • 22.
    Gaina, Carmen
    et al.
    Geological Survey of Norway.
    Werner, Stephanie C.
    PGP, School of Geosciences, University of Oslo.
    Saltus, Richard W.
    USGS, Denver, CO.
    Maus, Stefan
    CIRES, University of Colorado, NOAA's National Geophysical Data Center, Boulder, CO.
    Circum-Arctic mapping project: New magnetic and gravity anomaly maps of the Arctic2011In: Geological Society Memoir, ISSN 0435-4052, E-ISSN 2041-4722, Vol. 35, p. 39-48Article in journal (Refereed)
    Abstract [en]

    New Circum-Arctic maps of magnetic and gravity anomalies have been produced by merging regional gridded data. Satellite magnetic and gravity data were used for quality control of the long wavelengths of the new compilations. The new Circum-Arctic digital compilations of magnetic, gravity and some of their derivatives have been analyzed together with other freely available regional and global data and models in order to provide a consistent view of the tectonically complex Arctic basins and surrounding continents. Sharp, linear contrasts between deeply buried basement blocks with different magnetic properties and densities that can be identified on these maps can be used, together with other geological and geophysical information, to refine the tectonic boundaries of the Arctic domain.

  • 23.
    Guarnieri, Pierpaolo
    et al.
    GEUS, Geological Survey of Denmark and Greenland, Copenhagen.
    Brethes, Anaïs
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Geometry and kinematics of the Triassic rift basin in Jameson Land (East Greenland)2017In: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 36, no 4, p. 602-614Article in journal (Refereed)
    Abstract [en]

    The Triassic rift basin along the east Greenland margin described in this paper is represented by NE-SW trending basins and highs segmented by NW-SE trending transfer zones. Coarse-grained sediments along the eastern side of Jameson Land are shown to be hosted in half-graben structures belonging to the Carlsberg Fjord Basin that is bounded by NW dipping normal faults mapped and described after fieldwork in the Klitdal area in Liverpool Land. New aeromagnetic and electromagnetic data together with new drill cores allow the reinterpretation of available seismic lines showing the continuation of the Triassic rift basin toward the SW where it is buried under the Upper Triassic postrift sediments and the Jurassic successions of the Jameson Land Basin. The N-S trending Liverpool Land, interpreted as the boundary block of the Triassic basin, is shown to represent a structural high inherited from the Late Carboniferous tectonics and faulted during the Triassic rifting. The Carlsberg Fjord Basin and the Klitdal Fault System described in this paper should be seen as analogues to the Helgeland Basin in the Norwegian offshore that is bounded by the Ylvingen Fault Zone and to the Papa and West of Shetlands Basins that are bounded by the Spine Fault. The Triassic rift zone and transfer faults on both conjugate margins show a straightforward correlation with the trends of the initial spreading line and fracture zones of the northeast Atlantic indicating a possible inheritance of the Triassic rifting

  • 24.
    Jokat, Wilfried
    et al.
    Ayred Wegener Institute for Polar and Marine Research.
    Uenzelmann-Neben, Gabriele
    Ayred Wegener Institute for Polar and Marine Research.
    Kristoffersen, Yngve
    Ayred Wegener Institute for Polar and Marine Research.
    Rasmussen, Thorkild Maack
    Ayred Wegener Institute for Polar and Marine Research.
    Lomonosov Ridge: a double-sided continental margin1992In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 20, no 10, p. 887-890Article in journal (Refereed)
    Abstract [en]

    The first two traverses of marine multichannel seismic data across the Lomonosov Ridge (central Arctic), by the German research icebreaker Polarstern and the Swedish icebreaker Oden, demonstrate a prograded margin toward the Amerasian side and fault-bounded half grabens toward the Eurasian side of the ridge. Nearly 450m of undisturbed flat-lying strata have been deposited on top of the peneplaned ridge since it rifted from the Barents-Kara Sea margin and subsided below sea level in early Tertiary time (64-56 Ma) .

  • 25.
    Jokat, Wilfried
    et al.
    Ayred Wegener Institute for Polar and Marine Research.
    Weigelt, Estella
    Ayred Wegener Institute for Polar and Marine Research.
    Kristoffersen, Yngve
    University of Bergen, Institut for Solid Earth Physics.
    Rasmussen, Thorkild Maack
    University of Uppsala.
    Schöne, Tilo
    University of Uppsala.
    New geophysical results from the south‐western Eurasian Basin (Morris Jesup Rise, Gakkel Ridge, Yermak Plateau) and the Fram Strait1995In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 123, no 2, p. 601-610Article in journal (Refereed)
  • 26.
    Jokat, Wilfried
    et al.
    Ayred Wegener Institute for Polar and Marine Research.
    Weigelt, Estella
    Ayred Wegener Institute for Polar and Marine Research.
    Kristoffersen, Yngve
    University of Bergen, Institut for Solid Earth Physics.
    Rasmussen, Thorkild Maack
    University of Uppsala.
    Schöne, Tilo
    University of Uppsala.
    New insights into the evolution of the Lomonosov Ridge and the Eurasian Basin1995In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 122, no 2, p. 378--392Article in journal (Refereed)
  • 27.
    Korja, Toivo
    et al.
    Department of Geophysics, University of Oulu.
    Hjelt, Sven-Erik
    Department of Geophysics, University of Oulu.
    Koivukoski, K.
    Department of Geophysics, University of Oulu.
    Rasmussen, Thorkild Maack
    Department of Geophysics, University of Uppsala.
    Roberts, Roland G.
    bDepartment of Geophysics, University of Uppsala.
    The geoelectric model of the POLAR Profile, Northern Finland1989In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 162, no 1-2, p. 113-133Article in journal (Refereed)
    Abstract [en]

    Electromagnetic soundings have been made in order to construct a geoelectrical (conductivity) model of the crust along the European Geotraverse (EGT) POLAR Profile. Forty magnetotelluric (MT) soundings, eighteen audiomagnetotelluric (AMT) soundings and ten magnetohydrodynamic (MHD) soundings were made on the main POLAR Profile (POLAR I) and ten more MT soundings on a parallel profile (POLAR II), 40 km to the southeast of the main profile. Analysis of simultaneous recordings by the EISCAT magnetometer chain, and thin-sheet modelling of the effect of the Barents Sea, indicate that neither the source field effects nor the presence of the ocean are significant at periods below 200 s in the measurement area. The magnetotelluric data have been modelled with two-dimensional models representing the regional structure along the profiles. In addition to the regional structure, a thin inhomogeneous surface layer is included in the models in order to explain some local features of the measured response functions. Although details of the surface electrical structures are poorly resolved, the gross features of the geoelectrical cross section are considered to be reliable. The results divide the POLAR Profile into three different blocks. The better conducting Karasjok-Kittilä Greenstone Belt in the south has an average resistivity of less than 10 Ωm. The more resistant Lapland Granulite Belt, with a resistivity between 100 and 200 Ωm, is underlain by conductive (< 5 Ωm), N-dipping layers. The depth for the uppermost conductive layer varies from a few kilometres in the southwestern part of the granulite belt to 13 km in the northeastern part, from where it rises steeply towards the surface close to the boundary between the Lapland Granulite Belt and the Inari Terrain. These features appear to be continuous between the two parallel MT profiles. Within the Inari Terrain a conductive zone at an approximate depth of 10 km and with a resistivity of about 20 Ωm was identified in a resistive upper crust. The geoelectric cross section agrees, in gross detail, with the corresponding gravity, refraction seismic and reflection seismic cross sections of the POLAR Profile. All methods indicated a similar shape for the southwestern part of the Lapland Granulite Belt i.e., granulites have a gently NE-dipping boundary against the underlying Karelian Province. In the northeastern part of the granulite belt the geoelectric model and the gravimetric model show a rather steep S-dipping boundary against the Inari Terrain northeast of the granulite belt.

  • 28.
    Korstgård, John A.
    et al.
    Department of Earth Sciences, University of Aarhus.
    Stensgaard, Bo Møller
    Geological Survey of Denmark and Greenland.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    Magnetic anomalies and metamorphic boundaries in the southern Nagssugtoqidian orogen, West Greenland2006In: Geological Survey of Denmark and Greenland Bulletin, ISSN 1811-4598, E-ISSN 1604-8156, Vol. 11, p. 179-184Article in journal (Refereed)
    Abstract [en]

    Within the southern Nagssugtoqidian orogen in West Greenland metamorphic terrains of both Archaean and Palaeoproterozoic ages occur with metamorphic grade varying from low amphibolite facies to granulite facies. The determination of the relative ages of the different metamorphic terrains is greatly aided by the intrusion of the 2 Ga Kangâmiut dyke swarm along a NNE trend. In Archaean areas dykes cross-cut gneiss structures, and the host gneisses are in amphibolite to granulite facies. Along Itilleq strong shearing in an E-W-oriented zone caused retrogression of surrounding gneisses to low amphibolite facies. Within this Itivdleq shear zone Kangâmiut dykes follow the E-W shear fabrics giving the impression that dykes were reoriented by the shearing. However, the dykes remain largely undeformed and unmetamorphosed, indicating that the shear zone was established prior to dyke emplacement and that the orientation of the dykes here was governed by the shear fabric. Metamorphism and deformation north of Itilleq involve both dykes and host gneisses, and the metamorphic grade is amphibolite facies increasing to granulite facies at the northern boundary of the southern Nagssugtoqidian orogen. Here a zone of strong deformation, the Ikertôq thrust zone, coincides roughly with the amphibolite-granulite facies transition. Total magnetic field intensity anomalies from aeromagnetic data coincide spectacularly with metamorphic boundaries and reflect changes in content of the magnetic minerals at facies transitions. Even the nature of facies transitions is apparent. Static metamorphic boundaries are gradual whereas dynamic boundaries along deformation zones are abrupt.

  • 29.
    Lyngsie, Stig B.
    et al.
    Geological Institute, University of Copenhagen.
    Thybo, H.
    Geological Institute, University of Copenhagen.
    Rasmussen, Thorkild Maack
    bGeological Survey of Denmark and Greenland.
    Erratum to "Regional geological and tectonic structures of the North Sea area from potential field modelling" [Tectonophysics Volume 413/3-4 (2006) 147-170] (DOI:10.1016/j.tecto.2005.10.045)(2006In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 413, no 3-4, p. 303-306Article in journal (Refereed)
  • 30.
    Lyngsie, Stig B.
    et al.
    Geological Institute, University of Copenhagen.
    Thybo, H.
    Geological Institute, University of Copenhagen.
    Rasmussen, Thorkild Maack
    bGeological Survey of Denmark and Greenland.
    Regional geological and tectonic structures of the North Sea area from potential field modelling2006In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 413, no 3-4, p. 147-170Article in journal (Refereed)
    Abstract [en]

    The spatial distribution of large-scale crustal domains and their boundaries are investigated in the North Sea area by combining gravity, magnetic and seismic data. The North Sea is situated on the plates of three continents, Avalonia, Laurentia and Baltica, which collided during the Caledonian orogeny in the middle Palaeozoic. The location and continuation of the collisional sutures are debated. We apply filters and transformations to potential field data to focus on the crystalline crust and uppermost mantle on a regional scale in order to extract new information on continental sutures. The transformations reveal intrinsic features of crustal transitions between the Caledonian plates and their relation to later extensional structures. The transformations include the Hough Transform applied to the gravity field, calculation of fractional derivatives and integrals of the gravity and magnetic fields, the pseudogravity field and the horizontal gradient field as well as upward continuation. The results indicate a fundamental difference between the lithosphere of Avalonia, Laurentia and Baltica. The location of the Mesozoic rift system (the Central Graben and Viking Graben), may have been partly determined by the presence of the sutures between these three plate, indicative of extensional reactivation of compressional structures. A significant lineament across the entire North Sea between Scotland and North Germany indicates that the lower crust of Baltica provenance may extend as far south-westward as to this lineament. Comparison of the power spectra of the gravity field in five selected areas shows significant differences in the long wavelength components between the areas north and south of the lineament corresponding to differences in crustal properties. This lineament could represent the suture between lithosphere of Caledonian origin (Avalonia) versus lithosphere of Precambrian origin (Baltica) in the lower crust and upper mantle. If this is the case, the lineament is the missing link in the reconstruction of the triple plate collision

  • 31.
    Matzka, Jürgen
    et al.
    DTU Space.
    Rasmussen, Thorkild Maack
    GEUS.
    Olesen, Arne Vestergaard
    DTU Space, National Space Institute, Technical University of Denmark.
    Nielsen, Jens Emil
    DTU Space.
    Forsberg, René
    DTU Space.
    Olsen, Nils
    DTU Space.
    Halpenny, John F.
    Natural Resources Canada, Ottawa, ON.
    Verhoef, Jacob H.
    Natural Resources Canada, Ottawa, ON.
    A new aeromagnetic survey of the North Pole and the Arctic Ocean north of Greenland and Ellesmere Island2010In: Earth Planets and Space, ISSN 1343-8832, E-ISSN 1880-5981, Vol. 62, no 10, p. 829-832Article in journal (Refereed)
    Abstract [en]

    We present a preliminary analysis of more than 50,000 km of aeromagnetic survey lines flown in the Arctic Ocean, acquired in 2009 with an optically pumped scalar magnetometer as part of the airborne geophysical survey 'LOMGRAV'. From the observations we removed main and magnetospheric fields as given by the CHAOS-3 field model (Olsen et al., 2010) and remaining external fields as monitored by the Canadian magnetic observatory Alert. The reduced data were levelled based on cross-over differences at line intersections. Finally, a grid was computed, upward continued by 3500 m and compared with the EMAG2 grid (Maus et al., 2009), showing a good general agreement but also areas with systematic differences. The obtained data are expected to be part of the next version of the World Digital Magnetic Anomaly Map (WDMAM).

  • 32.
    Pedersen, Laust Börsting
    et al.
    Uppsala Universitet, Department of Earth Sciences.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University.
    Rasmussen, Thorkild Maack
    Uppsala Universitet, Department of Earth Sciences.
    Electric resistivity in the Gravberg-1 deep well, Sweden1992In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 97, no 6B, p. 9171-9182Article in journal (Refereed)
    Abstract [en]

    The Siljan impact structure located in central Sweden has been the object of intense geophysical and geological studies for several decades. This paper presents the results of electrical resistivity measurements on the surface, in the hole, and on core samples from shallow coreholes distributed over the whole impact structure. Magnetotelluric data constrain the central part of the structure to be essentially one-dimensional with an upper crustal unit of about 10 000 Ωm followed by a less resistive impact related unit of 1000 Ωm from a depth of about 6 km to a depth of 20 km. The lower crust is a homogeneous unit of about 300 Ωm extending down to about 40 km, where the upper mantle is marked by an increase in resistivity of about 1000 Ωm. Major fracture zones, some of which coincide with the horizontal dolerite sills, known to extend over tens of kilometers, are probably the main carriers of current. Saline fluids recovered below 5.4-km depth and the magnetotelluric results lead us to conclude that pore fluids are highly saline below this depth even on a regional scale.

  • 33.
    Pedersen, Laust Börsting
    et al.
    Section of Solid Earth Physics, University of Uppsala.
    Rasmussen, Thorkild Maack
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Section of Solid Earth Physics, University of Uppsala.
    Inversion of magnetotelluric data: a nonline least-squares approach1989In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 37, no 6, p. 669-695Article in journal (Refereed)
    Abstract [en]

    The inverse problem of magnetotellurics over a horizontally stratified earth is described, with emphasis on practical application. The inversion is divided into basically two steps. The construction of some best solution, and the analysis of that solution with regard to uncertainty and complexity. For the construction of best solutions a robust non‐linear solver was developed, and for the estimation of parameter errors a modified eigenvalue‐eigenvector analysis is performed to better describe non‐linear effects. The choice of the number of layers is shown to be intimately connected with the structure of data errors and the misfit between model and data. An example from the Siljan impact structure in Sweden illustrates the power of the technique.

  • 34.
    Pedersen, Laust Börsting
    et al.
    Uppsala Universitet, Department of Earth Sciences.
    Rasmussen, Thorkild Maack
    Uppsala Universitet, Department of Earth Sciences.
    Some techniques for enhancement of gravity and magnetic maps1991In: GFF, ISSN 1103-5897, E-ISSN 2000-0863, Vol. 113, no 2-3, p. 264-Article in journal (Refereed)
  • 35.
    Pedersen, Laust Börsting
    et al.
    Uppsala Universitet, Department of Earth Sciences.
    Rasmussen, Thorkild Maack
    Uppsala Universitet, Department of Earth Sciences.
    The gradient tensor of potential field anomalies: some implications on data collection and data processing of maps1990In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 55, no 12, p. 1558-1566Article in journal (Refereed)
    Abstract [en]

    The full gradient tensor is presently not measured routinely onboard airplanes or on land. This paper describes some improvements that can be made in strategies of data collection and in processing of potential field maps if such tensor measurements were available. We suggest that, in addition to producing for example standard total field anomaly maps, the invariants of the tensor be mapped

  • 36.
    Pedersen, Laust Börsting
    et al.
    Department of Geophysics, Section of Solid Earth Physics, University of Uppsala.
    Rasmussen, Thorkild Maack
    Department of Geophysics, Section of Solid Earth Physics, University of Uppsala.
    Dyrelius, Dan
    Department of Geophysics, Section of Solid Earth Physics, University of Uppsala.
    Construction of component maps from aeromagnetic total field anomaly maps1990In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 38, no 7, p. 795-804Article in journal (Refereed)
    Abstract [en]

    Total field anomalies as defined from normal aeromagnetic surveys give good approximations of the anomalous components along the direction of the main geomagnetic field, which is generally much larger than the anomalous field. Using the relations between vertical and horizontal components of the field, the total field anomaly is related to any vertical or horizontal component and the corresponding horizontal and vertical derivatives. An example from the Siljan impact structure indicates that such directional filters may be applied to extract useful information from magnetic maps.

  • 37.
    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

  • 38.
    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)
  • 39.
    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

  • 40.
    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.

  • 41. 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)
  • 42.
    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)
  • 43. 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)
  • 44.
    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)
  • 45.
    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)
  • 46.
    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

  • 47.
    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

  • 48.
    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)
  • 49.
    Tavakoli, Saman
    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.
    Rasmussen, Thorkild Maack
    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.
    Elming, Sten-åke
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Deep massive sulphide exploration using 2D and 3D geoelectrical and induced polarization data in Skellefte mining district, northern Sweden2016In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 64, no 6, p. 1602-1619Article in journal (Refereed)
    Abstract [en]

    Geoelectrical and induced polarization data from measurements along three profiles and from one 3D survey are acquired and processed in the central Skellefte District, northern Sweden. The data were collected during two field campaigns in 2009 and 2010 in order to delineate the structures related to volcanogenic massive sulphide deposits and to model lithological contacts down to a maximum depth of 1.5 km. The 2009 data were inverted previously, and their joint interpretation with potential field data indicated several anomalous zones. The 2010 data not only provide additional information from greater depths compared with the 2009 data but also cover a larger surface area. Several high-chargeability low-resistivity zones, interpreted as possible massive sulphide mineralization and associated hydrothermal alteration, are revealed. The 3D survey data provide a detailed high-resolution image of the top ∼450 m of the upper crust around the Maurliden East, North, and Central deposits. Several anomalies are interpreted as new potential prospects in the Maurliden area, which are mainly concentrated in the central conductive zone. In addition, the contact relationship between the major geological units, e.g., the contact between the Skellefte Group and the Jörn Intrusive Complex, is better understood with the help of 2010 deep-resistivity/chargeability data. The bottommost part of the Vargfors basin is imaged using the 2010 geoelectrical and induced polarization data down to ∼1-km depth.

  • 50.
    Watermann, Jürgen F.
    et al.
    Le Studium and LPC2E/CNRS.
    Gleisner, Hans
    Danish Meteorological Institute.
    Rasmussen, Thorkild Maack
    Geological Survey of Denmark and Greenland.
    A geomagnetic activity forecast for improving the efficiency of aeromagnetic surveys in Greenland2011In: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 47, no 12, p. 2172-2181Article in journal (Refereed)
    Abstract [en]

    In recent years several aeromagnetic surveys were carried out in Greenland and more will be carried out in the future. We describe some of the characteristics pertinent to surveys in Greenland and the problems faced and experiences made by the survey teams working there, with special emphasis on the west coast where most surveys were conducted. Both unfavorable terrestrial weather and space weather appear to complicate survey planning. We discuss possible options available to the survey teams for mitigating the adverse effect of part of the problems, namely survey data contamination by intense geomagnetic activity. The implementation of a prototype geomagnetic activity forecast service as an aid to planning survey flights is discussed in more detail. The forecast service was tested by an independent observer, and the performance of the scheme is evaluated by a subsequent comparison between forecast and actual measurements. The comparison rendered largely acceptable results, but their validity is limited by the fact that the two-month test interval was characterized by a mostly relatively quiet magnetic field

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