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Application of the Seismic Reflection Method in Mineral Exploration and Crustal Imaging: Contributions to Hardrock Seismic Imaging
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The seismic reflection method has been used extensively in mineral exploration and for imaging crustal structures within hardrock environments. In this research the seismic reflection method has been used and studied to address problems associated with hardrock settings. Papers I and II, address delineating and imaging a sulfide ore body and its surrounding rocks and structures in Garpenberg, central Sweden, at an active mine. 3D ray-tracing and finite-difference modeling were performed and the results suggest that although the detection of the ore body by the seismic reflection method is possible in the area, the presence of backfilled stopes in the mine makes seismic imaging of it difficult. In paper III the deeper structures of the Pärvie fault system in northern Sweden were revealed down to about 8 km through 2D seismic reflection profiling. The resulting images were interpreted using microearthquake data as a constraint. Based on the interpretation, some locations were suggested for future scientific deep drilling into the fault system. In paper IV, the seismic signature of complex geological structures of the Cue-Weld Range area in Western Australia was studied using a portion of a deep 2D seismic reflection profile. The pronounced reflections on the seismic images were correlated to their corresponding rock units on an available surface geological map of the study area. 3D constant velocity ray-tracing was performed to constrain the interpretation. Furthermore, the proposed structural model was tested using a 2D acoustic finite-difference seismic modeling method. Based on this study, a new 3D structural model was proposed for the subsurface of the area. These studies have investigated the capability of the seismic reflection method for imaging crustal structures within challenging hardrock and complex geological settings and show some its potential, but also its limitations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 76 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1269
Keyword [en]
Seismic reflection, Hardrock, Mineral exploration, Crustal imaging, Interpretation, Modeling
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-259396ISBN: 978-91-554-9290-8 (print)OAI: oai:DiVA.org:uu-259396DiVA: diva2:844513
Public defence
2015-09-25, Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2015-08-26 Created: 2015-08-02 Last updated: 2015-10-01
List of papers
1. High-resolution 2D seismic imaging and forward modeling of a polymetallic sulfide deposit at Garpenberg, central Sweden
Open this publication in new window or tab >>High-resolution 2D seismic imaging and forward modeling of a polymetallic sulfide deposit at Garpenberg, central Sweden
2013 (English)In: Geophysics, ISSN 0016-8033, E-ISSN 1942-2156, Vol. 78, no 6, B339-B350 p.Article in journal (Refereed) Published
Abstract [en]

We acquired a high-resolution 2D seismic profile to test the capability of the seismic method in imaging a sulfide ore body at Garpenberg, central Sweden. Delineation of the geologic structures, which surround and host the ore body, is another goal of the survey. Due to the 3D geology of the structures, a cross-dip correction performed to image out-of-the-plane reflections, resulting in a clear high amplitude anomaly at a time and location to that to be expected from near the top of the ore body. Furthermore, DMO processing and migration are applied to the data, providing images of four main reflection groups. The reflections have been interpreted as corresponding to geologic rock units in the area that partly interfere with the potential ore body signal. To further investigate the seismic response of the ore body, forward modeling by ray-tracing is applied using the ore body geometry as mapped by drilling. We use two ray-tracing approaches: standard 3D ray-tracing and an exploding reflector approach. Seven representative samples from the mine area are used to determine P-wave velocities. The measurements show a considerable contrast between the ore body and host rock. By comparing the modeled and observed data, we find that the high amplitude signal in the real seismic section most likely emanates from near the top of one concentrated ore which lies inside the larger mapped ore body that has been modeled as a resource. The base of the ore body is only observed on the synthetic data whereas a signal penetration analysis suggests that the seismic signal penetrated efficiently along the entire survey line. Presence of disseminated ore and lower fold toward the northern end of the profile could be combined reasons that make imaging the base of the ore body difficult.

Keyword
2D, processing, ray tracing, modeling
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-210135 (URN)10.1190/geo2013-0098.1 (DOI)000330223800003 ()
Available from: 2013-11-01 Created: 2013-11-01 Last updated: 2017-12-06
2. The effect of the backfilled stopes on seismic imaging of a sulfide deposit in Garpenberg, central Sweden
Open this publication in new window or tab >>The effect of the backfilled stopes on seismic imaging of a sulfide deposit in Garpenberg, central Sweden
2015 (English)Manuscript (preprint) (Other academic)
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-259140 (URN)
Available from: 2015-07-27 Created: 2015-07-27 Last updated: 2015-08-28
3. Revealing the deeper structure of the end-glacial Parvie fault system in northern Sweden by seismic reflection profiling
Open this publication in new window or tab >>Revealing the deeper structure of the end-glacial Parvie fault system in northern Sweden by seismic reflection profiling
2015 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 6, no 2, 621-632 p.Article in journal (Refereed) Published
Abstract [en]

A new seismic reflection survey for imaging deeper levels of the end-glacial Parvie fault system in northern Sweden was acquired in June 2014. The Parvie fault system hosts the largest fault scarp so far documented in northern Scandinavia, both in terms of its length and calculated magnitude of the earthquake that generated it. Present-day microearthquakes occur along the length of the fault scarp on the eastern side of the scarp, in general agreement with an east-dipping main fault. In the central section of the fault system, where there is a number of subsidiary faults east of the main Parvie scarp, it has been unclear how the earthquakes relate to the structures mapped at the surface. A seismic profile across the Parvie fault system acquired in 2007, with a mechanical hammer as a source, showed a good correlation between the surface mapped faults and moderate to steeply dipping reflections. The most pronounced reflectors could be mapped to about 3 km depth. In the new seismic survey, for deeper penetration an explosive source with a maximum charge size of 8.34 kg in 20 m deep shot holes was used. Reflectors can now be traced to deeper levels with the main 65A degrees east-dipping fault interpreted as a weakly reflective structure. As in the previous profile, there is a strongly reflective 60A degrees west-dipping structure present to the east of the main fault that can now be mapped to about 8 km depth. Extrapolations of the main and subsidiary faults converge at a depth of about 11.5 km, where current earthquake activity is concentrated, suggesting their intersection has created favorable conditions for seismic stress release. Based on the present and previous seismic reflection data, we propose potential locations for future boreholes for scientific drilling into the fault system. These boreholes will provide a better understanding of the reflective nature of the fault structures and stress fields along the faults at depth.

National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-259138 (URN)10.5194/se-6-621-2015 (DOI)000357128400020 ()
Available from: 2015-07-27 Created: 2015-07-27 Last updated: 2017-12-04Bibliographically approved
4. Seismic signatures of complex geological structures in the Cue-Weld range area, Murchison domain, Yilgarn Craton, Western Australia
Open this publication in new window or tab >>Seismic signatures of complex geological structures in the Cue-Weld range area, Murchison domain, Yilgarn Craton, Western Australia
2016 (English)In: Tectonophysics, Vol. 689, 56-66 p.Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

The Murchison domain forms the northwest part of the Youanmi Terrane, a tectonic unit within the Neoarchean Yilgarn Craton in Western Australia. In the Cue-Weld Range area the Murchison domain has experienced a complex magmatic and deformation history that resulted in a transposed array of greenstone belts that host significant iron, gold, and base metal deposits. In this study, we interpret the upper 2 s (about 6 km) of a deep crustal seismic profile TOGA-YU1, near the town of Cue, and correlate rock units and structures in outcrop with corresponding reflections. We performed 3D constant velocity ray-tracing and calculate the corresponding travel times for the reflectionsfor time domain pre-stack and post-stack seismic data. This allows us to link shallow reflections with mafic volcanic rocks of the Glen Group and basaltic rocks of the Polelle Group in outcrop. Based on our interpretation and published geological maps and data, we propose a model in which the local stratigraphy represents a refolded thrust system. To test our hypothesis, we applied 2D acoustic finite difference forward modeling. The corresponding synthetic data were processed in the same way as the acquired data. Comparisons between the acquired and the synthetic data show that the model is consistent with observations. We propose a new model for the subsurface of the Cue-Weld Range area and argue that some of the lithologies in the area are repeated structurally at different levels. Our approach highlights the benefit of imaging and modeling of deep seismic transects to resolve local structural complexity in Archean granite-greenstone terrains.

Keyword
Seismic interpretation; 3D structural model; Ray-tracing; Finite difference modeling; Weld range; Murchison domain
National Category
Geophysics Geology
Research subject
Geophysics with specialization in Solid Earth Physics; Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
urn:nbn:se:uu:diva-259139 (URN)10.1016/j.tecto.2016.02.020 (DOI)000387522100006 ()
Available from: 2015-08-01 Created: 2015-07-27 Last updated: 2017-01-25Bibliographically approved

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