EAGE Research Workshop - Advances in Seismic Acquisition Technology, 2004
A01 COMPLEXITIES OF MODERN SEISMIC REFLECTION INVESTIGATIONS IN ISOLATED MINING DISTRICTS OF NORT... more A01 COMPLEXITIES OF MODERN SEISMIC REFLECTION INVESTIGATIONS IN ISOLATED MINING DISTRICTS OF NORTHERN SASKATCHEWAN CANADA Summary 1 Multifaceted Vibroseis surveys established fundamental data acquisition parameters for implementation of the reflection method under severe climatic and logistical settings. The integrated results generated novel comprehensive high-quality subsurface images of the subsurface from near-surface to Moho depth around the McArthur mine the location of the world’s highest grade uranium deposit. The surveys utilized 3-C component Vectorsies detectors in 2-D and 3-D survey configurations. Special operational procedures were created to guarantee functionality of the data acquisition system in an extremely low temperature -35 to
The geologic origin of crustal subhorizontal reflections are investigated by establishing metamor... more The geologic origin of crustal subhorizontal reflections are investigated by establishing metamorphic facies and strength of rocks in depth, and correlating these properties to seismic reflection sections from eastern Hungary. Estimation of the depths of metamorphic mineral stability zones utilized the principles developed by Fyfe et al. and known geothermal data of the area. The strength versus depth profile was derived by relating local seismic P-wave interval velocities to Meissner et al.'s activation energy. The results show that the series of subhorizontal reflections, observed in the Pannonian basin, are a consequence of combined metamorphic and rheologic changes in depths. The synthesis of the integrated dataset suggests that the retro-grade alteration of the pre-Tertiary basement above the percolation threshold was made possible by the softening effect of shear zones and their water conducting capacity. The subhorizontal reflections of highest energy, of the consolidated...
... and a tele seismic feasibility study using travel time differen tials, receiver function anal... more ... and a tele seismic feasibility study using travel time differen tials, receiver function analysis and ... The seismic profile offers no evi dence for the extension of the Superior craton base ... Lim ited rapidly undertook a program based largely on aeromagnetic techniques (LehnertThiel et ...
Within the Hungarian segment of the Pannonian basin, a 100-km-long seismic reflection profile ima... more Within the Hungarian segment of the Pannonian basin, a 100-km-long seismic reflection profile images the sedimentary fill of two major depressions and their associated crustal signatures. These deep (~7000 m) subbasins are asymmetric half grabens, bounded along their western margins by low-angle crust-penetrating subparallel listric faults. The hanging walls are intensely fractured and comprise pre-Tertiary basement and upper-crustal rocks. The footwalls are formed by uplifted and ductilely deformed middle to lower crust. The crust is relatively thin (25-27 km) and decoupled by well-defined detachment faults. The Moho has a gentle northeasterly dip and a spatially variable seismic signature. The seismic images imply that the present crustal setting of the area was developed contemporaneously through the northeastward extension of the Pannonian basin.
A practical and simple method is developed for tile selection of computational parameters to be u... more A practical and simple method is developed for tile selection of computational parameters to be used when the re"ectivity method is applied to generate synthetic seismagrams for a horizontally layered Earth. The actual sedimentary-strata-based design of paramef~o. which are easily comp"ted. eliminateb the n"merica, noise that generally cO"taminateS seislnic records produced by using the! Standard trial-error proceci"res to &tine tile best parame- ters. I" rile selecrion process. special attention is given here ,O tile typical hydrocarbon exploration environment. me r:omp"tatio"s a"t"matically provide a,, P-wave arriYa,s. including multiples, in a single calculation, for any number of traces and offsers. Examples illustrate the types of numerical ani- facts created by poor parameter or kern&function selection. The derived seismograms are clean and are computed without costly experimental computer runs. The control of numerical art- fa...
Various data show the 'influence of unusual processes occurring beneath the Jan Mayen, Iceland, a... more Various data show the 'influence of unusual processes occurring beneath the Jan Mayen, Iceland, and Azores shallow volcanic plateaus'; regional morphotectonics and the petrochemistry of the erupted basalts reflect these processes. Typical MORB's are erupted from LILE-depleted mantle; however, these MAR hotspots are supplied by mantle apparently enriched in large incompatible elements, halogens, and water. It is suggested that these areas be called 'hotspots as well as wetspots' and that these melts 'have segregated from partial melting zones extending deeper than along adjacent normal ridge segments.' Whether the basalt major element compositional differences reflect mantle heterogeneity or varying pressure-temperature dynamics remains to be seen. Includes 6 pages of references. Grad.
Surface, borehole, and laboratory acoustic measurements all confirm the existence of a near‐surfa... more Surface, borehole, and laboratory acoustic measurements all confirm the existence of a near‐surface low‐velocity zone in metavolcanic, metasedimentary, and plutonic rocks of the Flin Flon region of Canada. This zone is caused by a high frequency of open fractures and extends from the surface to depths of between 5 and 44 m, although occasional open fractures extend to at least 60 m. There is a linear decrease in sonic velocity with increasing frequency of large fractures; the details, however, vary for different sites, depending upon several geologic features including rock type and nonfracture porosity. Laboratory sonic data indicate very low microcrack densities in the volcanic and plutonic rocks. Synthetic seismograms derived from sonic log information from the center of the granitic pluton have been compared with a nearby multifold seismic profile. This shows that the near‐surface low‐velocity zone attenuates most of the high‐frequency seismic energy. However, the remaining low‐...
Understanding of the unexposed link between the Trans-Hudson orogen in Canada and Early Proterozo... more Understanding of the unexposed link between the Trans-Hudson orogen in Canada and Early Proterozoic terrains in the U.S. midcontinent is critical to overall modeling of Early Proterozoic evolution of North America. Green et al.'s (1985a, 1985b) interpretation of geophysical data for this region is a welcome and important contribution. However, much of their subsurface extrapolation is poorly constrained by geologic evidence and indeed conflicts with recently acquired subsurface data. It thus provides a tenuous basis for geotectonic modeling. We acknowledge problems of subsurface extrapolation of lithotectonic domains lying between the Superior and Wyoming-Churchill cratonic platforms and do not dispute Green et al.'s location of major geophysical boundaries. However, much of their interpretation of the nature of domains lying between those boundaries is questionable.
Figure 1. Simplified geology (where exposed) and shaded relief total field aeromagnetic image (wh... more Figure 1. Simplified geology (where exposed) and shaded relief total field aeromagnetic image (where Phanerozoic cover exists) showing Superior boundary zone (SBZ) at eastern margin of Trans-Hudson orogen. Locations of three Lithoprobe deep seismic reflection profiles across SBZ are indicated: 1, 2 (White et al., 1999a), and S3B (this study). Dashed lines on map indicate interpreted southward continuation of SBZ based on extrapolation using magnetic field signature and limited drill core from sub-Phanerozoic basement. Abbreviations: CSB, Cape Smith belt; FFB, Flin Flon belt; FRB, Fox River belt; PGD, Pikwitonei Granulite domain; SBF, Superior boundary fault; T,
The seismic structure of the British Columbia continental margin has been investigated using four... more The seismic structure of the British Columbia continental margin has been investigated using four reversed refraction profiles. The profile across strike extended 350 km from the volcanic arc on the continent to the deep ocean of the Juan de Fuca Plate; the three profiles along strike were located on Vancouver Island, on the continental shelf, and in the deep ocean on the Juan de Fuca Plate. Interpretation of the profile along Vancouver Island yields a well constrained model for the upper crust with velocity increasing from ~5.3 km/s at the surface to ~6.4 km/s at 2 km depth to ~6.75 km/s at 15.5 km depth where the velocity increases sharply to ~7 km/s. The velocity structure of the deep crust and the crustal thickness are poorly constrained. Four possible velocity functions, based on ambiguous first arrivals and (or) secondary phases interpreted as Moho reflections, are presented. The preferred one includes a deep crustal low velocity zone with a crustal thickness of 37 km; models ...
A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen... more A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen, based on the interpretation of 590 km of deep-sounding seismic reflection data and a comparable length of existing seismic reflection information, is presented. The seismic images identify the regional geometry of the basal detachment zone (Pelican thrust) that separates juvenile allochthonous terranes from the underlying Archean microcontinent (Sask craton). The Sask Craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike. During terminal collision, complete convergence of the RaeHearne and Superior continental blocks was precluded by the presence of the Sask Craton, resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material. Along regional tectonic strike, consistency of crustal structure across the RaeHearne margin Reindeer zone boundary is establi...
New seismic reflection data collected by Lithoprobe across the Trans-Hudson Orogen (Manitoba and ... more New seismic reflection data collected by Lithoprobe across the Trans-Hudson Orogen (Manitoba and Saskatchewan) provide striking images of juvenile paleo-Proterozoic arc rocks (Flin Flon and Kisseynew belts) juxtaposed against the deformed northwestern margin of the Archean Superior craton. Crustal imbrication on a scale imaged in few other orogens is observed within the Flin Flon Belt where a package of shallowly east-dipping reflections extends from the surface to 14 s. These reflections are attributed to middle to lower crustal arc rocks that appear to have been stacked below a major detachment that underlies the upper crustal rocks of the Flin Flon Belt. Surprisingly, the seismic images show the juvenile arc rocks dipping moderately eastward beneath the craton in apparent contradiction to existing tectonic models. Geological and geochronological evidence suggest that the observed crustal imbrication probably reflects late-collisional or postcollisional convergence rather than ear...
The seismic refraction method was used in 1981 to study the crust under the northern half of the ... more The seismic refraction method was used in 1981 to study the crust under the northern half of the Williston Basin, in Saskatchewan. A new method of spatial seismic recording, based on a triangular arrangement of receivers, was used for the first time to obtain three-dimensional structure and velocity information. The broadside seismic refraction and wide-angle reflection data obtained by the technique were of particular value in defining several faulted blocks. These blocks are also characterized by aeromagnetic anomalies trending in a northerly direction. The crustal thickness in the southern part of the western provinces shows large variation ranging from 35 to 50 km. Much of the area is also notable for the presence of one or more low-velocity layers and a high-velocity lower crust. There is good evidence for significant lateral heterogeneity, and detailed deep seismic reflection and refraction studies would likely yield information on dips and strikes of beds and faults around th...
Within Lithoprobe’s 10 transects, data from more than 20 000 km of multichannel seismic (MCS) ref... more Within Lithoprobe’s 10 transects, data from more than 20 000 km of multichannel seismic (MCS) reflection profiling and 12 refraction – wide-angle reflection (R/WAR) surveys were acquired. While the main results related to crustal structure, the data also indicated substantial heterogeneity in the lithospheric mantle. Images of fossilized subduction zones from the Eocene to the Neoarchean demonstrate that current plate tectonic processes have been active for more than 2.6 Ga. The Canadian Cordillera has a thin (50–60 km) lithosphere that is likely receiving some dynamic support from the asthenosphere below. Vestiges of the last stage of accretionary tectonic processes that formed the Archean Superior craton are indicated by an unusual anisotropic high velocity layer that may represent relic oceanic lithosphere. Within the Paleoproterozoic Trans-Hudson Orogen, a restricted region of upper mantle P-wave velocity anisotropy is identified with the continental collision between the boundi...
Modern multifold reflection techniques were introduced to the Athabasca Basin through the activit... more Modern multifold reflection techniques were introduced to the Athabasca Basin through the activities of the Canadian National LITHOPROBE Program in the mid 1990's. Since then, several very successful 2D and 3D surveys were carried out, mainly in the eastern segment of the uranium exploration and mining district. Within this region of the basin, predominantly horizontal sandstones and conglomerates of the Manitou Falls Formation constitute the sedimentary fill. The crystalline basement lithologies comprise highly folded and interleaved Paleoproterozoic meta-sediments and Archean orthogneisses. Despite this apparently simple geology, complex seismic signatures are generated within the sedimentary fill, at the sandstone- basement unconformity and within the underlying basement rocks sequences. Results from in-situ geophysical and geological logs, and rock-property measurements reveal that the reflectivity within the basin fill strata is dominantly controlled by porosity variations; and also, in part, by post-depositional hydrothermal alteration zones and grain-size lithological changes. Internal, lithology-based reflectivity properties and their variations within the sandstone column, although weak, are still identifiable in many cases. The seismic waveforms related to the unconformity are highly variable. Contact(s) between fresh sandstone and comparable basement rocks generate strong and simple seismic signals. Interfaces between altered sandstone and variably-altered basement segments (regolith) all reduce the strength of the reflectivity; and in combination with zones of fracture density variations, lead to complex multi-cycle wave patterns. Core sample analyses reveal that certain, moderately dipping lithological variations in the basement can be recognized seismically. Numerous examples from different regions of the basin illustrate that the seismic method is not only capable of imaging the sub-surface structural environments, but also can map lithological changes within the Athabasca Basin. All seismically mapped mineralized areas are associated with prominent basement fracture zones. Seismic attribute analyses of 2D sections and 3D data volumes have great potential in providing additional constraints in mapping and identifying the structurally complex mineralizing systems of the Athabasca unconformity-type uranium deposits.
EAGE Research Workshop - Advances in Seismic Acquisition Technology, 2004
A01 COMPLEXITIES OF MODERN SEISMIC REFLECTION INVESTIGATIONS IN ISOLATED MINING DISTRICTS OF NORT... more A01 COMPLEXITIES OF MODERN SEISMIC REFLECTION INVESTIGATIONS IN ISOLATED MINING DISTRICTS OF NORTHERN SASKATCHEWAN CANADA Summary 1 Multifaceted Vibroseis surveys established fundamental data acquisition parameters for implementation of the reflection method under severe climatic and logistical settings. The integrated results generated novel comprehensive high-quality subsurface images of the subsurface from near-surface to Moho depth around the McArthur mine the location of the world’s highest grade uranium deposit. The surveys utilized 3-C component Vectorsies detectors in 2-D and 3-D survey configurations. Special operational procedures were created to guarantee functionality of the data acquisition system in an extremely low temperature -35 to
The geologic origin of crustal subhorizontal reflections are investigated by establishing metamor... more The geologic origin of crustal subhorizontal reflections are investigated by establishing metamorphic facies and strength of rocks in depth, and correlating these properties to seismic reflection sections from eastern Hungary. Estimation of the depths of metamorphic mineral stability zones utilized the principles developed by Fyfe et al. and known geothermal data of the area. The strength versus depth profile was derived by relating local seismic P-wave interval velocities to Meissner et al.'s activation energy. The results show that the series of subhorizontal reflections, observed in the Pannonian basin, are a consequence of combined metamorphic and rheologic changes in depths. The synthesis of the integrated dataset suggests that the retro-grade alteration of the pre-Tertiary basement above the percolation threshold was made possible by the softening effect of shear zones and their water conducting capacity. The subhorizontal reflections of highest energy, of the consolidated...
... and a tele seismic feasibility study using travel time differen tials, receiver function anal... more ... and a tele seismic feasibility study using travel time differen tials, receiver function analysis and ... The seismic profile offers no evi dence for the extension of the Superior craton base ... Lim ited rapidly undertook a program based largely on aeromagnetic techniques (LehnertThiel et ...
Within the Hungarian segment of the Pannonian basin, a 100-km-long seismic reflection profile ima... more Within the Hungarian segment of the Pannonian basin, a 100-km-long seismic reflection profile images the sedimentary fill of two major depressions and their associated crustal signatures. These deep (~7000 m) subbasins are asymmetric half grabens, bounded along their western margins by low-angle crust-penetrating subparallel listric faults. The hanging walls are intensely fractured and comprise pre-Tertiary basement and upper-crustal rocks. The footwalls are formed by uplifted and ductilely deformed middle to lower crust. The crust is relatively thin (25-27 km) and decoupled by well-defined detachment faults. The Moho has a gentle northeasterly dip and a spatially variable seismic signature. The seismic images imply that the present crustal setting of the area was developed contemporaneously through the northeastward extension of the Pannonian basin.
A practical and simple method is developed for tile selection of computational parameters to be u... more A practical and simple method is developed for tile selection of computational parameters to be used when the re"ectivity method is applied to generate synthetic seismagrams for a horizontally layered Earth. The actual sedimentary-strata-based design of paramef~o. which are easily comp"ted. eliminateb the n"merica, noise that generally cO"taminateS seislnic records produced by using the! Standard trial-error proceci"res to &tine tile best parame- ters. I" rile selecrion process. special attention is given here ,O tile typical hydrocarbon exploration environment. me r:omp"tatio"s a"t"matically provide a,, P-wave arriYa,s. including multiples, in a single calculation, for any number of traces and offsers. Examples illustrate the types of numerical ani- facts created by poor parameter or kern&function selection. The derived seismograms are clean and are computed without costly experimental computer runs. The control of numerical art- fa...
Various data show the 'influence of unusual processes occurring beneath the Jan Mayen, Iceland, a... more Various data show the 'influence of unusual processes occurring beneath the Jan Mayen, Iceland, and Azores shallow volcanic plateaus'; regional morphotectonics and the petrochemistry of the erupted basalts reflect these processes. Typical MORB's are erupted from LILE-depleted mantle; however, these MAR hotspots are supplied by mantle apparently enriched in large incompatible elements, halogens, and water. It is suggested that these areas be called 'hotspots as well as wetspots' and that these melts 'have segregated from partial melting zones extending deeper than along adjacent normal ridge segments.' Whether the basalt major element compositional differences reflect mantle heterogeneity or varying pressure-temperature dynamics remains to be seen. Includes 6 pages of references. Grad.
Surface, borehole, and laboratory acoustic measurements all confirm the existence of a near‐surfa... more Surface, borehole, and laboratory acoustic measurements all confirm the existence of a near‐surface low‐velocity zone in metavolcanic, metasedimentary, and plutonic rocks of the Flin Flon region of Canada. This zone is caused by a high frequency of open fractures and extends from the surface to depths of between 5 and 44 m, although occasional open fractures extend to at least 60 m. There is a linear decrease in sonic velocity with increasing frequency of large fractures; the details, however, vary for different sites, depending upon several geologic features including rock type and nonfracture porosity. Laboratory sonic data indicate very low microcrack densities in the volcanic and plutonic rocks. Synthetic seismograms derived from sonic log information from the center of the granitic pluton have been compared with a nearby multifold seismic profile. This shows that the near‐surface low‐velocity zone attenuates most of the high‐frequency seismic energy. However, the remaining low‐...
Understanding of the unexposed link between the Trans-Hudson orogen in Canada and Early Proterozo... more Understanding of the unexposed link between the Trans-Hudson orogen in Canada and Early Proterozoic terrains in the U.S. midcontinent is critical to overall modeling of Early Proterozoic evolution of North America. Green et al.'s (1985a, 1985b) interpretation of geophysical data for this region is a welcome and important contribution. However, much of their subsurface extrapolation is poorly constrained by geologic evidence and indeed conflicts with recently acquired subsurface data. It thus provides a tenuous basis for geotectonic modeling. We acknowledge problems of subsurface extrapolation of lithotectonic domains lying between the Superior and Wyoming-Churchill cratonic platforms and do not dispute Green et al.'s location of major geophysical boundaries. However, much of their interpretation of the nature of domains lying between those boundaries is questionable.
Figure 1. Simplified geology (where exposed) and shaded relief total field aeromagnetic image (wh... more Figure 1. Simplified geology (where exposed) and shaded relief total field aeromagnetic image (where Phanerozoic cover exists) showing Superior boundary zone (SBZ) at eastern margin of Trans-Hudson orogen. Locations of three Lithoprobe deep seismic reflection profiles across SBZ are indicated: 1, 2 (White et al., 1999a), and S3B (this study). Dashed lines on map indicate interpreted southward continuation of SBZ based on extrapolation using magnetic field signature and limited drill core from sub-Phanerozoic basement. Abbreviations: CSB, Cape Smith belt; FFB, Flin Flon belt; FRB, Fox River belt; PGD, Pikwitonei Granulite domain; SBF, Superior boundary fault; T,
The seismic structure of the British Columbia continental margin has been investigated using four... more The seismic structure of the British Columbia continental margin has been investigated using four reversed refraction profiles. The profile across strike extended 350 km from the volcanic arc on the continent to the deep ocean of the Juan de Fuca Plate; the three profiles along strike were located on Vancouver Island, on the continental shelf, and in the deep ocean on the Juan de Fuca Plate. Interpretation of the profile along Vancouver Island yields a well constrained model for the upper crust with velocity increasing from ~5.3 km/s at the surface to ~6.4 km/s at 2 km depth to ~6.75 km/s at 15.5 km depth where the velocity increases sharply to ~7 km/s. The velocity structure of the deep crust and the crustal thickness are poorly constrained. Four possible velocity functions, based on ambiguous first arrivals and (or) secondary phases interpreted as Moho reflections, are presented. The preferred one includes a deep crustal low velocity zone with a crustal thickness of 37 km; models ...
A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen... more A three-dimensional model of the regional crustal architecture of the western Trans-Hudson Orogen, based on the interpretation of 590 km of deep-sounding seismic reflection data and a comparable length of existing seismic reflection information, is presented. The seismic images identify the regional geometry of the basal detachment zone (Pelican thrust) that separates juvenile allochthonous terranes from the underlying Archean microcontinent (Sask craton). The Sask Craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike. During terminal collision, complete convergence of the RaeHearne and Superior continental blocks was precluded by the presence of the Sask Craton, resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material. Along regional tectonic strike, consistency of crustal structure across the RaeHearne margin Reindeer zone boundary is establi...
New seismic reflection data collected by Lithoprobe across the Trans-Hudson Orogen (Manitoba and ... more New seismic reflection data collected by Lithoprobe across the Trans-Hudson Orogen (Manitoba and Saskatchewan) provide striking images of juvenile paleo-Proterozoic arc rocks (Flin Flon and Kisseynew belts) juxtaposed against the deformed northwestern margin of the Archean Superior craton. Crustal imbrication on a scale imaged in few other orogens is observed within the Flin Flon Belt where a package of shallowly east-dipping reflections extends from the surface to 14 s. These reflections are attributed to middle to lower crustal arc rocks that appear to have been stacked below a major detachment that underlies the upper crustal rocks of the Flin Flon Belt. Surprisingly, the seismic images show the juvenile arc rocks dipping moderately eastward beneath the craton in apparent contradiction to existing tectonic models. Geological and geochronological evidence suggest that the observed crustal imbrication probably reflects late-collisional or postcollisional convergence rather than ear...
The seismic refraction method was used in 1981 to study the crust under the northern half of the ... more The seismic refraction method was used in 1981 to study the crust under the northern half of the Williston Basin, in Saskatchewan. A new method of spatial seismic recording, based on a triangular arrangement of receivers, was used for the first time to obtain three-dimensional structure and velocity information. The broadside seismic refraction and wide-angle reflection data obtained by the technique were of particular value in defining several faulted blocks. These blocks are also characterized by aeromagnetic anomalies trending in a northerly direction. The crustal thickness in the southern part of the western provinces shows large variation ranging from 35 to 50 km. Much of the area is also notable for the presence of one or more low-velocity layers and a high-velocity lower crust. There is good evidence for significant lateral heterogeneity, and detailed deep seismic reflection and refraction studies would likely yield information on dips and strikes of beds and faults around th...
Within Lithoprobe’s 10 transects, data from more than 20 000 km of multichannel seismic (MCS) ref... more Within Lithoprobe’s 10 transects, data from more than 20 000 km of multichannel seismic (MCS) reflection profiling and 12 refraction – wide-angle reflection (R/WAR) surveys were acquired. While the main results related to crustal structure, the data also indicated substantial heterogeneity in the lithospheric mantle. Images of fossilized subduction zones from the Eocene to the Neoarchean demonstrate that current plate tectonic processes have been active for more than 2.6 Ga. The Canadian Cordillera has a thin (50–60 km) lithosphere that is likely receiving some dynamic support from the asthenosphere below. Vestiges of the last stage of accretionary tectonic processes that formed the Archean Superior craton are indicated by an unusual anisotropic high velocity layer that may represent relic oceanic lithosphere. Within the Paleoproterozoic Trans-Hudson Orogen, a restricted region of upper mantle P-wave velocity anisotropy is identified with the continental collision between the boundi...
Modern multifold reflection techniques were introduced to the Athabasca Basin through the activit... more Modern multifold reflection techniques were introduced to the Athabasca Basin through the activities of the Canadian National LITHOPROBE Program in the mid 1990's. Since then, several very successful 2D and 3D surveys were carried out, mainly in the eastern segment of the uranium exploration and mining district. Within this region of the basin, predominantly horizontal sandstones and conglomerates of the Manitou Falls Formation constitute the sedimentary fill. The crystalline basement lithologies comprise highly folded and interleaved Paleoproterozoic meta-sediments and Archean orthogneisses. Despite this apparently simple geology, complex seismic signatures are generated within the sedimentary fill, at the sandstone- basement unconformity and within the underlying basement rocks sequences. Results from in-situ geophysical and geological logs, and rock-property measurements reveal that the reflectivity within the basin fill strata is dominantly controlled by porosity variations; and also, in part, by post-depositional hydrothermal alteration zones and grain-size lithological changes. Internal, lithology-based reflectivity properties and their variations within the sandstone column, although weak, are still identifiable in many cases. The seismic waveforms related to the unconformity are highly variable. Contact(s) between fresh sandstone and comparable basement rocks generate strong and simple seismic signals. Interfaces between altered sandstone and variably-altered basement segments (regolith) all reduce the strength of the reflectivity; and in combination with zones of fracture density variations, lead to complex multi-cycle wave patterns. Core sample analyses reveal that certain, moderately dipping lithological variations in the basement can be recognized seismically. Numerous examples from different regions of the basin illustrate that the seismic method is not only capable of imaging the sub-surface structural environments, but also can map lithological changes within the Athabasca Basin. All seismically mapped mineralized areas are associated with prominent basement fracture zones. Seismic attribute analyses of 2D sections and 3D data volumes have great potential in providing additional constraints in mapping and identifying the structurally complex mineralizing systems of the Athabasca unconformity-type uranium deposits.
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