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Garcia Juanatey, Maria de los AngelesORCID iD iconorcid.org/0000-0002-6853-4864
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Publications (10 of 19) Show all publications
García Juanatey, M. d., Hübert, J., Tryggvason, A., Juhlin, C., Pedersen, L. B., Bauer, T. E. & Dehghannejad, M. (2019). 2D and 3D MT in the central Skellefte Ore District, northern Sweden. Tectonophysics, 764, 124-138
Open this publication in new window or tab >>2D and 3D MT in the central Skellefte Ore District, northern Sweden
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2019 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 764, p. 124-138Article in journal (Refereed) Published
Abstract [en]

New broadband magnetotelluric (MT) data have been acquired along two parallel profiles in the central part of the metallogenic Skellefte district in northern Sweden. The data were recorded as part of the Swedish 4D modelling of mineral belts project and cover an area with several economical and sub-economical deposits. The dimensionality and quality of the data were carefully analyzed and new error floors were systematically determined prior to inverse modelling in 2D and 3D. The algorithms used were EMILIA and WSINV3DMT. For the 2D inversion, only the determinant of the impedance tensor was used, while for the 3D inversion all elements were considered. The obtained models fit the inverted data, and image the main regional features. A detailed comparison reveals the superiority of the 3D model, both in model structures and data fit. After assessing the main features in the model, an interpretation is proposed and refined with the support of previous geophysical studies. The most interesting features are large and medium-sized conductors associated with crustal-scale shear zones and faults within the Skellefte Group rocks. These may be depicting a network of fossil pathways for hydrothermal fluid transport and as such, provide new insight into past processes in the area.

Keywords
Magnetotellurics, 3D inversion, Deep exploration, Brownfield, Shear zones, Mineral systems
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-178057 (URN)10.1016/j.tecto.2019.04.003 (DOI)000472697900008 ()
Projects
VINNOVA 4D modeling of mineral belts
Funder
Vinnova
Available from: 2012-07-26 Created: 2012-07-26 Last updated: 2019-08-16Bibliographically approved
Yan, P., Garcı́a Juanatey, M. A., Kalscheuer, T., Juhlin, C., Hedin, P., Savvaidis, A., . . . Kück, J. (2017). A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information. Geophysical Journal International, 208(3), 1465-1489
Open this publication in new window or tab >>A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information
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2017 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 208, no 3, p. 1465-1489Article in journal (Refereed) Published
Abstract [en]

In connection with the Collisional Orogeny in the Scandinavian Caledonides (COSC) project, broad-band magnetotelluric (MT) data were acquired at 78 stations along a recent ca. 55km- long NW-SE directed reflection seismic profile (referred to as the COSC Seismic Profile; CSP), with the eastern end located similar to 30 km to the west of the orogenic Caledonian front. The MT component of the project aims at (i) delineating the highly conductive (similar to 0.1 Omega . m) alum shales that are associated with an underlying main decollement and (ii) calibrating the MT model to borehole logs. Strike and distortion analyses of the MT data show a 3-D structure in the western 10 km of the profile around the 2.5 km deep COSC-1 borehole (IGSN: ICDP5054EHW1001) and a preferred strike angle of N34 degrees E in the central and eastern parts of the profile. 2-D modelling of MT impedances was tested using different inversion schemes and parameters. To adjust the resistivity structure locally around the borehole, resistivity logging data from COSC-1 were successfully employed as prior constraints in the 2-D MT inversions. Compared with the CSP, the model inverted from the determinant impedances shows the highest level of structural similarity. A shallow resistor (> 1000 Omega . m) in the top 2-3 km depth underneath the western most 10 km of the profile around COSC-1 corresponds to a zone of high seismic reflectivity, and a boundary at less than 1 km depth where the resistivity decreases rapidly from > 100 to < 1 Omega . m in the central and eastern parts of the profile coincides with the first seismic reflections. The depth to this boundary is well constrained as shown by 1-D inversions of the MT data from five selected sites and it decreases towards the Caledonian front in the east. Underneath the easternmost part of the profile, the MT data show evidence of a second deeper conductor (resistivity < 1 Omega . m) at > 3 km depth. Based upon the COSC-1 borehole logs, the CSP reflection seismic image, and the surface geologic map, the MT resistivity models were interpreted geologically. In the vicinity of COSC-1, the resistor down to 2-3 km depth pertains to the metamorphic Middle Allochthon. The up to 1000-m-thick shallow resistor in the central and eastern parts of the profile is interpreted to overly an imbricated unit at the bottom of the Lower Allochthon that includes the alum shales. In the MT resistivity model, the 300-500 m thick imbricated unit masks the main Caledonian decollement at its bottom. A second possible interpretation, though not favoured here, is that the decollement occurs along a much deeper seismic reflection shallowing from 4.5 km depth in the west to similar to 600 m depth in the east. An additional borehole (COSC-2) is planned to penetrate the Lower Allochthon and the main decollement surface in the central part of the profile and can provide information to overcome this interpretational ambiguity. Using a synthetic study, we evaluate how resistivity logs from COSC-2 can improve the 2-D inversion model.

Keywords
Inverse theory, Downhole methods, Magnetotellurics, Continental tectonics: compressional, Europe
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-303495 (URN)10.1093/gji/ggw457 (DOI)000396818900016 ()
Funder
Swedish Research Council, 2013-5780The Geological Survey of Sweden (SGU)
Available from: 2016-09-20 Created: 2016-09-20 Last updated: 2017-04-27Bibliographically approved
Yan, P., Kalscheuer, T., Hedin, P. & Juanatey, M. d. (2017). Two-dimensional magnetotelluric inversion using reflection seismic data as constraints and application in the COSC project. Geophysical Research Letters, 44(8), 3554-3563
Open this publication in new window or tab >>Two-dimensional magnetotelluric inversion using reflection seismic data as constraints and application in the COSC project
2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 44, no 8, p. 3554-3563Article in journal (Refereed) Published
Abstract [en]

We present a novel 2-D magnetotelluric (MT) inversion scheme, in which the local weights of the regularizing smoothness constraints are based on the envelope attribute of a reflection seismic image. The weights resemble those of a previously published seismic modification of the minimum gradient support method. We measure the directional gradients of the seismic envelope to modify the horizontal and vertical smoothness constraints separately. Successful application of the inversion to MT field data of the Collisional Orogeny in the Scandinavian Caledonides (COSC) project using the envelope attribute of the COSC reflection seismic profile helped to reduce the uncertainty of the interpretation of the main decollement by demonstrating that the associated alum shales may be much thinner than suggested by a previous inversion model. Thus, the new model supports the proposed location of a future borehole COSC-2 which is hoped to penetrate the main decollement and the underlying Precambrian basement.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-324629 (URN)10.1002/2017GL072953 (DOI)000401847500015 ()
Funder
Swedish Research Council, 2013-5780
Available from: 2017-06-16 Created: 2017-06-16 Last updated: 2017-06-16Bibliographically approved
Yan, P., Andersson, M., Kalscheuer, T., Garcı́a Juanatey, M. A., Malehmir, A., Shan, C., . . . Almqvist, B. S. G. (2016). 3D magnetotelluric modelling of the Alnö alkaline and carbonatite ring complex, central Sweden. Tectonophysics, 679, 218-234
Open this publication in new window or tab >>3D magnetotelluric modelling of the Alnö alkaline and carbonatite ring complex, central Sweden
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2016 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 679, p. 218-234Article in journal (Refereed) Published
Abstract [en]

Thirty-four broadband magnetotelluric stations were deployed across the Alno alkaline and carbonatite ring intrusion in central Sweden. The measurements were designed such that both 2D models along existing seismic profiles and a 3D model can be constructed. Alno Island and surrounding areas are densely populated and industrialized and in order to reduce the effect of noise, the remote reference technique was utilized in time series processing. Strike and dimensionality analyses together with the induction arrows show that there is no homogeneous regional strike direction in this area. Therefore, only the determinant of the impedance tensor was used for 2D inversion whereas all elements of the impedance tensor were used for 3D inversion. Representative rock samples were collected from existing outcrops and their resistivities were measured in the laboratory to facilitate interpretation of the inversion models. The results from these measurements show that coarse grained (sovite, white color) and fine-grained (dark color) carbonatites are the most conductive and resistive rock types, respectively. In accordance with the interpretation of the reflection seismic images, the 2D and 3D resistivity models depict the caldera-related ring-type fault system and updoming faulted and fractured systems as major 10-500 Omega m conductors, extending down to about 3 km depth. A central similar to 4000 Omega m resistive unit at about 3 km depth appears to correspond to a solidified fossil magma chamber as speculated from the reflection seismic data and earlier field geological studies.

Keywords
Alnö; Carbonatite; Alkaline; 3D; Magnetotelluric; Resistivity
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-292604 (URN)10.1016/j.tecto.2016.05.002 (DOI)000378177700017 ()
Funder
Swedish Research Council, 621-2009-4439
Available from: 2016-05-04 Created: 2016-05-04 Last updated: 2017-11-30Bibliographically approved
Tavakoli, S., Dehghannejad, M., Garcia Juanatey, M. d., Bauer, T. E., Weihed, P. & Elming, S.-Å. (2016). Potential Field, Geoelectrical and Reflection Seismic Investigations for Massive Sulphide Exploration in the Skellefte Mining District, Northern Sweden. Acta Geophysica, 64(6), 2171-2199
Open this publication in new window or tab >>Potential Field, Geoelectrical and Reflection Seismic Investigations for Massive Sulphide Exploration in the Skellefte Mining District, Northern Sweden
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2016 (English)In: Acta Geophysica, ISSN 1895-6572, E-ISSN 1895-7455, Vol. 64, no 6, p. 2171-2199Article in journal (Refereed) Published
Abstract [en]

Multi-scale geophysical studies were conducted in the central Skellefte district (CSD) in order to delineate the geometry of the upper crust (down to maximum similar to 4.5 km depth) for prospecting volcanic massive sulphide (VMS) mineralization. These geophysical investigations include potential field, resistivity/induced polarization (IP), reflection seismic and magnetotelluric (MT) data which were collected between 2009 and 2010. The interpretations were divided in two scales: (i) shallow (similar to 1.5 km) and (ii) deep (similar to 4.5 km). Physical properties of the rocks, including density, magnetic susceptibility, resistivity and chargeability, were also used to improve interpretations. The study result delineates the geometry of the upper crust in the CSD and new models were suggested based on new and joint geophysical interpretation which can benefit VMS prospecting in the area. The result also indicates that a strongly conductive zone detected by resistivity/IP data may have been missed using other geophysical data.

Keywords
potential field data, seismic reflection, resistivity, induced polarization, magnetotelluric, 3D modeling
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-316139 (URN)10.1515/acgeo-2016-0088 (DOI)000391967700009 ()
Available from: 2017-03-03 Created: 2017-03-03 Last updated: 2017-11-29Bibliographically approved
Muhamad, H. A., Juhlin, C., Lehnert, O., Meinhold, G., Andersson, M., Juanatey, M. d. & Malehmir, A. (2015). Analysis of borehole geophysical data from the Mora area of the Siljan Ring impact structure, central Sweden. Journal of Applied Geophysics, 115, 183-196
Open this publication in new window or tab >>Analysis of borehole geophysical data from the Mora area of the Siljan Ring impact structure, central Sweden
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2015 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 115, p. 183-196Article in journal (Refereed) Published
Abstract [en]

The Siljan impact structure is the largest known impact structure in Europe, the result of a Late Devonian meteorite impact (380.9 +/- 4.6 Ma). It is outlined mainly by a ring of lakes and Palaeozoic sedimentary rocks of Ordovician to Devonian age. The Palaeozoic successions are generally poorly exposed, but often well preserved with clear stratigraphy. At some locations they are strongly tectonised with sharply inclined or nearly overturned packages of crystalline basement and/or sediments. Down-hole logging data were acquired in the western part of the Siljan impact structure to determine some of the physical properties of the Palaeozoic sedimentary rocks in the area. Boreholes Mora 001 (356 m logged depth), Vattumyra Production (420 m logged depth), Mora VM 2 (94 m logged depth) and Mobillyft (437 m logged depth) were logged for temperature, sonic velocity and electrical resistivity. Logging data were compared to the lithology in the Mora 001 core, which had been mapped in detail, and information from other cores in the area. Good agreement between the natural gamma log and the core lithology was found. The sonic log shows a marked difference in velocity for the more clastic Silurian succession compared to the Ordovician succession and the Precambrian basement. A synthetic seismogram shows that a high amplitude reflection is expected at the Silurian-Ordovician boundary, raising some questions concerning interpretation of a seismic profile located about 6-7 km north of the study area. Correlation of the borehole logs shows that the thickness of the Silurian succession varies rapidly in the area and that its composition differs over distances of less than 1 km. These rapid variations suggest that the study area may be located in a megablock zone that was highly influenced by the impact Caledonian tectonics and changing depositional environments may also play a role in explaining the present-day borehole lithologies. Even though the boreholes are relatively far from the seismic profile and the geology is complex, the new data confirm that the Silurian has significant thickness along parts of the seismic profile. Potentially, the Silurian can be up to 450 m thick on parts of the profile. Further geophysical investigations in the area, including seismic surveying and gravity measurements, may help in mapping the complex structures away from the boreholes and discriminating between possible geological models.

Keywords
Siljan impact structure, Sweden, Down-hole logging, Palaeozoic rocks
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-258831 (URN)10.1016/j.jappgeo.2015.02.019 (DOI)000351646900018 ()
Available from: 2015-07-23 Created: 2015-07-20 Last updated: 2017-12-04Bibliographically approved
Bauer, T. E., Tavakoli, S., Weihed, P., Skytta, P., Hermansson, T., Allen, R., . . . Juhlin, C. (2013). A regional scale 3D-model of the Skellefte mining district, northern Sweden. In: Proceedings of the 12th SGA Biennial Meeting 2013.: . Paper presented at 12th Biennial SGA Meeting (pp. 62-65). Uppsala
Open this publication in new window or tab >>A regional scale 3D-model of the Skellefte mining district, northern Sweden
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2013 (English)In: Proceedings of the 12th SGA Biennial Meeting 2013., Uppsala, 2013, p. 62-65Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Uppsala: , 2013
Series
MINERAL DEPOSIT RESEARCH FOR A HIGH-TECH WORLD, VOLS. 1-4
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-259497 (URN)000337983900013 ()978-91-7403-207-9 (ISBN)
Conference
12th Biennial SGA Meeting
Available from: 2015-08-05 Created: 2015-08-05 Last updated: 2017-08-16
Skytta, P., Bauer, T., Hermansson, T., Dehghannejad, M., Juhlin, C., Juanatey, M. d., . . . Weihed, P. (2013). Crustal 3-D geometry of the Kristineberg area (Sweden) with implications on VMS deposits. Solid Earth, 4(2), 387-404
Open this publication in new window or tab >>Crustal 3-D geometry of the Kristineberg area (Sweden) with implications on VMS deposits
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2013 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 4, no 2, p. 387-404Article in journal (Refereed) Published
Abstract [en]

Structural analysis of the Palaeoproterozoic volcanogenic massive sulfide (VMS) hosting Kristineberg area, Sweden, constrained by existing magnetotelluric (MT) and seismic reflection data, reveals that the complex geometry characterized by non-cylindrical antiformal structures is due to transpression along the termination of a major high-strain zone. Similar orientations of the host rock deformation fabrics and the VMS ore lenses indicate that the present-day geometry of the complex VMS deposits in the Kristineberg area may be attributed to tectonic transposition. The tectonic transposition was dominantly controlled by reverse shearing and related upright to overturned folding, with increasing contribution of strike-slip shearing and sub-horizontal flow towards greater crustal depths. Furthermore, the northerly dip of the previously recognized subsurface crustal reflector within the Kristineberg area is attributed to formation of crustal compartments with opposite polarities within the scale of the whole Skellefte district. The resulting structural framework of the main geological units is visualized in a 3D model which is available as a 3-D PDF document through the publication website.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-214060 (URN)10.5194/se-4-387-2013 (DOI)000328256200013 ()
Available from: 2014-01-07 Created: 2014-01-07 Last updated: 2017-12-06Bibliographically approved
García Juanatey, M. d., Hübert, J., Tryggavson, A. & Pedersen, L. B. (2013). Imaging the Kristineberg mining area with two perpendicular magnetotelluric profiles in the Skellefte Ore District, northern Sweden. Geophysical Prospecting, 61(1), 200-219
Open this publication in new window or tab >>Imaging the Kristineberg mining area with two perpendicular magnetotelluric profiles in the Skellefte Ore District, northern Sweden
2013 (English)In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 61, no 1, p. 200-219Article in journal (Refereed) Published
Abstract [en]

New magnetotelluric (MT) data from two perpendicular profiles in the Kristineberg area, northern Sweden, were analysed and modelled. In the Skellefte Ore District, the Kristineberg volcanic hosted massive sulphide (VHMS) deposit mine is one of the largest and deepest (1250 m). Seventeen broadband magnetotelluric stations were installed along two existing seismic reflection lines. The profiles were 6 and 12 km long with 500 m and 1 km site spacing, respectively. The obtained MT transfer functions in the period range of 0.0015–200 s are of fairly good quality. Detailed strike and dimensionality analysis reveal consistent but period dependent, strike directions, indicating a change in the geoelectrical strike with depth. From the two-dimensional inversion of the determinant of the impedance tensor, two stable conductivity models with good data fit were obtained. The addition of seismic reflection information from the co-located survey, improved the data fit of one of them. Extensive sensitivity analyses helped to delineate the well resolved regions of the models and to determine the position of pronounced boundaries. The results are in good agreement with previous studies, especially regarding the presence of a deep conductor interpreted as a structural basement to the district. They also reveal with more detail the configuration of the main geological units of the Skellefte Ore District, especially of the ore bearing volcanic rocks and the embedded alteration zones.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2013
Keywords
Mining, Magnetotelluric, 2D inversion
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-163596 (URN)10.1111/j.1365-2478.2011.01040.x (DOI)000312548300015 ()
Projects
VINNOVA 4D modeling of the Skellefte District
Available from: 2011-12-13 Created: 2011-12-13 Last updated: 2017-12-08Bibliographically approved
García Juanatey, M. d., Hübert, J., Tryggavson, A., Juhlin, C., Pedersen, L. B., Dehghannejad, M., . . . Skytta, P. (2013). Magnetotelluric measurements in the Skellefte ore district, northern Sweden. In: : . Paper presented at 12th Biennial SGA Meeting on Mineral Deposit Research for a High-Tech World (pp. 138-141).
Open this publication in new window or tab >>Magnetotelluric measurements in the Skellefte ore district, northern Sweden
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2013 (English)Conference paper, Published paper (Refereed)
Abstract
Series
MINERAL DEPOSIT RESEARCH FOR A HIGH-TECH WORLD, VOLS. 1-4
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-259499 (URN)000337983900032 ()978-91-7403-207-9 (ISBN)
Conference
12th Biennial SGA Meeting on Mineral Deposit Research for a High-Tech World
Available from: 2015-08-05 Created: 2015-08-05 Last updated: 2017-08-11
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-6853-4864

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