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- Cheraghi, Saeid, 1973-
(författare)
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Seismic investigations in the Brunswick No. 6 area, Canada – Imaging and heterogeneity
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Brunswick No. 6 area, which is located in the Bathurst Mining Camp, New Brunswick, Canada, is the focus of this thesis. Almost a decade ago, in order to improve the understanding of the crustal structures and explore for new mineral deposits at depth, three 2D seismic profiles totaling about 30 km and 3D seismic data covering an area of about 38 km2 were acquired from the study area. Petrophysical properties including compressional-wave velocity and density were also measured in two deep boreholes in the area. These data were recovered and reanalyzed, and the improved seismic images interpreted as the main part of this PhD thesis.A prestack DMO and poststack migration algorithm was considered for processing both 2D and 3D data. Processing of 2D data revealed shallow and deep reflections, which correlate well with surface geology. Steeply-dipping reflections, some of which could host mineral deposits, were imaged down to a depth of 6-7 km. Processing of 3D data showed similar results to the processed 2D profiles. Nevertheless, the non-orthogonal nature of the 3D survey, combined with irregular distribution of offsets, azimuths and trace midpoints, caused a severe acquisition footprint masking reflections in the DMO-corrected unmigrated stacked cube. An FK-dip filter in the wavenumber domain was designed to reduce the effects of the acquisition footprint.To better understand wave propagation and scattering effects, calculated acoustic impedance log from the available borehole data was used to estimate vertical scale length using a von Karman autocorrelation function. 2D synthetic models representative of heterogeneity in the area were generated accounting for the estimated scale length. Numerical modeling was used to study the scattering effects on the synthetic models, where some predefined targets were superimposed in the provided 2D heterogeneous medium. The effects of variable source frequency, longer horizontal scale length and petrophysical fluctuations of heterogeneous medium were also investigated. The modeling results indicate that, in the presence of large horizontal, but small vertical scale lengths (structural anisotropy), the identification of mineral deposits is possible in the unmigrated stacked sections, but can be challenging in the migrated sections.
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| 2. |
- Ahmadi, Omid, 1980-
(författare)
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Application of the Seismic Reflection Method in Mineral Exploration and Crustal Imaging : Contributions to Hardrock Seismic Imaging
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 3. |
- Markovic, Magdalena
(författare)
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Seismic Exploration Solutions for Deep-Targeting Metallic Mineral Deposits : From high-fold 2D to sparse 3D, and deep-learning workflows
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mineral exploration has in recent years moved its focus to greater depths than ever before, particularly in brown fields. Exploring new deposits at depth, if economical, would not only expand the life of mine but also provide minimal environmental impacts. It allows the existing mining infrastructures to be used for a longer period. Exploration at depth, however, is challenging and requires a multidisciplinary team and methods, and innovative thinking for generating new targets and effective exploration expenditure. The application of seismic methods for mineral exploration has increasingly been conducted over the past 20 years because they provide high-resolution subsurface images, and retain good resolution with depth as compared with other geophysical methods. Nevertheless, and despite challenges in hardrock settings, only limited attention has been given to seismic interpretations, often performed subjectively. With the growing application of machine-learning solutions, hardrock seismic data can benefit these for improved interpretations and target generations.This thesis showcases different workflows developed for deep-targeting metallic mineral deposits, starting from high-fold 2D, through sparse 3D reflection imaging and the implementation of deep-learning algorithms for diffraction pattern recognitions. Three different deposits were studied from Sweden and Canada. The Blötberget iron-oxide mineralization in central Sweden was first targeted in 2D, followed-up, a sparse 3D dataset was acquired enabling to image the mineralization both laterally and with depth, providing good knowledge on subsurface structures controlling the geometry of the deposits. In Canada, Halfmile Lake and Matagami mining sites were studied due to the accessibility to 3D seismic datasets, which contained diffraction signals as deposit responses. Deeplearning algorithms were utilized for the proof-of-concept and at the same time helped to generate new potential targets from other diffraction signals that were not obvious to an interpreter’s eye due to their incomplete tails originated outside of the seismic volume. The studies in this thesis show the effectiveness of seismic methods for mineral exploration at depth, especially in 3D, as they provide, among others, structural interpretation for future mineplanning purposes. Deep-learning solutions provide improved results for diffraction delineation and denoising and have great potential for hardrock seismics.
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