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76th EAGE Conference and Exhibition - Workshops
- Conference date: 16 Jun 2014 - 19 Jun 2014
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73834-90-3
- Published: 16 June 2014
21 - 40 of 142 results
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Seismic Exploration for Volcanogenic Massive Sulphides - The DeGrussa Copper-gold Mine, Western Australia
Authors J. Kinkela, S. Ziramov, A. Dzunic, M. Urosevic and P. HilliardTraditional geophysical prospecting techniques used for mineral exploration rarely provide the resolution required to accurately target orebodies at depth. Based on this, the seismic reflection method was trialled over a known VMS orebody at the DeGrussa copper-gold mine, Western Australia, in the hope of providing a viable exploration tool for deeper depths of investigation. However, a structurally complex geologic setting and a thick, highly variable regolith caused significant challenges in the processing of the seismic data. This paper addresses these challenges and looks at strategies used to overcome them eventually leading to the direct imaging of the orebody.
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In-Mine Seismic Imaging Revisited
Authors B.M. Milkereit, R. Saleh, J.W. Huang and B.V. ValleyCurrently, only microseismicity is used as a proxy for stress near deep mines. However, most of the physical properties of crystalline rocks are highly stress dependent. As such, the nonlinear and anisotropic variability of the in situ P- and S-wave velocities can potentially be linked directly to changes in the stress field. At an in-mine seismic laboratory, multi-component sensor arrays are deployed in multiple locations (3D) allowing for both controlled source and passive recordings. Previous in-mine seismic observatories have experienced a number of challenges with regards to sensitivity and longevity. Hence, the geothermally cool but highly stressed Sudbury mining camp offers a favourable setting for fundamental research in to time-lapse monitoring of seismicity, stress, and stress dependent physical properties at a deep mine.
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Direct VMS Targeting through Preserved Relative Amplitude Processed Seismic Imaging at Neves Corvo, Portugal
Authors S. Yavuz, J. Kinkela, M. Penney, V. Araujo, R. Neto, A. Dzunic and M. UrosevicExploration of deep VMS deposits at the Neves Corvo mine on the Iberian Pyrite Belt was further advanced through a specialised application of surface seismic techniques. The contrast in impedances from elastic property measurements of core samples showed that there should be a significant difference in the seismic response of mineralisation compared to the surrounding host rocks. These results indicated that relative amplitude preservation processing may be of importance to help reduce the ambiguity in direct, seismic amplitude anomaly based targeting of Volcanogenic Massive Sulphides. However, such processing was not easy to implement due to an intrinsically low signal to noise ratio, complex 3D geology, high scattering level and often patchy and poor reflectivity. The newly obtained 3D seismic cube was calibrated with the existing boreholes to show superior ore zonation and precision required for the subsequent deep drilling campaign.
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Mineralization Indicators from Seismic and Full Wave Sonic Data in the Athabasca Basin, Saskatchewan, Canada
More LessSeismic reflection method was successfully introduced, as an exploration tool, in the Athabasca Basin in 2003. Investigations demonstrated that the mineralized zones are associated with basement located shear zones, complex variable sandstone-basement unconformity intervals, and significant alteration zones within the sandstone fill and the basement. All these anomalous zones consistently were associated with diagnostic seismic images, providing a set of primary indicators of mineralization for regions of future exploration interest. Recent Full Wave Sonic surveys illustrated that not only the longitudinal (P) waves, which were exclusively utilized to date, but detectable transverse waves (S) can also observed from the geologic setting of the basin. In most instances, the responses of these elastic disturbances, to geologic irregularities, are recognizably dissimilar. This duality of the specific responses permits derivation of characteristic elastic properties of the lithological units within the investigated area. The knowledge of the depth variations of the P and S wave velocities permits the computations of elastic parameters of rocks such as shear modulus (µ), Lame’s modulus (λ) and Poisson’s ratio (σ). Combinations of these elastic properties facilitate the recognition of fractures with different sizes and their properties, as well as alteration and meta-somatic zones.
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Seismic across Different Mineral Deposits - Does It Work?
By M. UrosevicMany years of application of seismic for mineral exploration in Western Australia provided very rich data base which is used to test and optimise data processing and analysis. High signal to noise ratio enabled investigation into the performance of partial and full pre-stack imaging techniques. On the other end of the scale, very complex geologies and poor seismic response inspired the use of novel technologies and also concurrent use different geophysical techniques. Various case histories are presented and discussed.
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Application of Seismic Interferometry in Crystalline Rocks - A Case Study From the Lalor Mining Area, Canada
Authors S. Cheraghi, J. Craven and G. BellefleurApproximately 300 hours of ambient noise data covering an area of 4 km² were acquired over the Lalor mining area, Canada, to test the capability of seismic interferometry to image ore deposits in the crystalline rock environment. The interferometry survey consists of 336 receivers located along 9 parallel lines oriented southwest-to northeast and 7 southeast-to-northwest lines. Alongside the ambient noise survey, a larger 3D active source seismic survey was also acquired in the area and used to evaluate the interferometry results. The seismic wave field is retrieved by crosscorrelating the noise between all receiver locations in each hourly segment of passive seismic data. The crosscorrelated results of all segments are spatially summed to generate virtual shot gathers. The virtual data is processed along all 2D lines with conventional methods similar to those applied to active 3D data. The DMO-stacked section obtained reveals a number of events, some more coherent than observed on the similarly processed active seismic section. Of particular interest is an event possibly associated with the massive sulphides. A comparable event is also observed on the active seismic data. These results demonstrate the benefits of ambient noise measurements in crystalline rock environment for mineral exploration purposes.
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High-resolution Multicomponent Hardrock Seismic Imaging of Mineral Deposits and their Host Rock Structures
Authors A. Malehmir, S. Wang, J. Lamminen, M. Bastani, C. Juhlin, K. Vaittinen, L. Dynesius and H. PalmAlthough applied in the past, there are only a few cases demonstrating the advantages of multicomponent seismic data for mineral exploration. To illustrate this, a test survey using sixty 3C-digital sensors, spaced between 2 to 4 m and assembled in a 160 m long landstreamer, was carried out to provide information on shallow structures hosting mineralization and also a magnetic lineament with an unknown origin. The survey, totally about 1.3 km long, was complemented by Radio MagnetoTelluric (RMT) measurements. Although an explosive source was used to generate the seismic signal, the seismic data show good quality for all the three components. Supported by the RMT results, clear reflections are observed in the horizontal component data at about 25 m depth, one of them steeply dipping, likely associated with the magnetic lineament. Field static corrections were well estimated thanks to the close shot and receiver spacing and the broadband frequency content of the data. This study demonstrates that multicomponent seismic data can be useful for providing information on shallow structures and linking them to the surface geology. The vertical component data, however, show deeper penetration and better image the crystalline basement and its undulated/faulted surface at about 50 m depth.
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Application of Curvelet Denoising to 3D Post-stack Data Acquired in Hardrock Environment
Authors A. Górszczyk and M. MalinowskiSeismic data acquired in hardrock environment are demanding for processing. Frequently occurring lack of clear coherent events hinders imaging and interpretation. Additional difficulty arises from the presence of significant amount of cultural noise (e.g. associated with exploration and processing of ore) which corrupt the data. For this purpose we demonstrate our noise attenuation approach based on 2D Discrete Curvelet Transform (DCT) by applying it to 3D post-stack seismic data from active mining camp. DCT introduce minimal overlapping between coefficients representing signal and noise in the curvelet domain, hence being well-suited for data denoising. Forward DCT is applied in sequences to inline, crossline and time slice sections. 3D DMO volume after curvelet denoising is much easier to interpret, e.g. it’s easier to follow diffracted energy originating at ore lenses. We believe that the presented approach of running 2D DCT for 3D data might be also a sufficient substitution for a more expensive 3D DCT.
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3D Seismic Imaging of the Ghost-Carbon Leader Reef of the World's Deepest Gold Mine - Mponeng Gold Mine, South Africa
By M. ManziThe re-interpretation of the old 3D seismic data from the world’s deepest gold mine of the Witwatersrand basin, have proven to be effective in enhancing the detection of fault zones and unstable lithologies that are potential mining hazards. Most of the structures identified seem to offset the gold-bearing horizons such as the Ventersdorp Contact Reef (VCR) and Carbon Leader Reef (CLR) with throws below seismic resolution limit (equivalent to one-quarter dominant seismic wavelength (λ/4)). To derive or ghost the seismically transparent Carbon Leader Reef model, we used more than 2000 drillholes that intersect the CLR (within the Central Group), VCR (top of the Central Rand Group) and Crown lava (top of the West Rand Group). The final ghosted CLR shows a very consistent dip with the VCR and Crown lava. The model also shows that 60% of the structures imaged at the VCR level at 2-3 km depth continue and displace the ghosted-CLR at 3.5-4.5 km depth in a similar manner. This model represents the gross-structural architecture that was formed following the massive Platberg age extension on the first-order scale structures.
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3D Seismic Survey in Crystalline Rocks of Saxony, Germany
Authors E. Lueschen, F. Rost, G. Hoecht and R. Thomas3D seismic measurements have been performed in 2012 to explore a petrothermal reservoir in a crystalline environment (granite intrusion, metamorphic cover) within the Erzgebirge in Saxony. The intention and challenge is to image and characterize a steeply dipping fault zone with potentially permeable fracture zones at target depths of 5-6 km and temperatures well above 150 °C. The vibroseis technique was used in the experiment. A suite of imaging methods has been applied, from conventional CMP-stacking, CRS processing to pre-stack migrations.
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Application of the 3D CRS Workflow in Crystalline Rock Environment
Authors K.A. Ahmed, B. Schwarz and D. GajewskiSeismic data from crystalline environments usually exhibit a poor signal-to-noise (S/N) ratio due to low acoustic impedances. Moreover, instead of continuous reflections we observe a lot of steeply dipping events and diffractions. The conventional seismic processing (CMP stack and DMO) is not ideally suited for imaging such type of data. CRS processing considers more traces during the stack than CMP processing and the resulting image displays a better quality. CRS workflow was established as a powerful tool to provide improved images, especially for low fold and S/N data. The application of the workflow to the 3D Schneeberg crystalline rock seismic data shows that images of coherence provided the best results for an initial analysis compared to the CRS stack with poor image quality not suitable for interpretation. For data from environments with low acoustic impedance the coherence may provide an alternative way to image the subsurface. The analysis of the data has shown that without pre-stack data enhancement methods it may not be possible to generate satisfactory stacked images. The first time migration results helped to identify several major fault structures in the data volume which coincide with geological features of the considered area.
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Structural Characterization of a Geothermal Reservoir Using Seismic Depth Imaging Methods
More LessGeothermal reservoirs can be characterized by the analysis of heat transport and fluid migration throughout the target rock volume. A hydrothermal simulation which provides insights into these processes, however, first requires detailed knowledge of the structural parameters of the reservoir. Those can be obtained from reflection seismic measurements. For this purpose, we apply two different prestack depth migration methods, namely the familiar Kirchhoff Prestack Depth Migration (KPSDM) and the recently developed Fresnel Volume Migration (FVM) on five seismic reflection profiles in a target region in Southern Tuscany, Italy. The resulting migrated images capture the important reflectors of the target region and provide a good insight in the potential extend of the geothermal reservoir. Moreover, we demonstrate that FVM produces cleaner images than KPSDM due to its “intelligent” aperture limitation. The obtained results provide the structural base on which a hydrothermal evaluation will be performed.
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The Use of Outcrop Analogue Basement Rocks to Help Seismic Imaging of Buried Reservoirs
Authors L. Bertrand, B. Walter, G. Perry, Y. Geraud and M. DiraisonBasement rocks are well studied nowadays for their exploitation as geothermal reservoirs or for mineral exploration. In these rocks, the matrix permeability is poor and the fluid flow (geothermal resource or linked to mineral precipitation) is mainly controlled by the natural fracture and fault network and associated weathered materials. Unconfortunately, the fracture and fault pattern at reservoir scale in the basement is not well known and is difficult to characterize with the actual geophysical tools. The use of analogue rocks at the outcrop is therefore an important tool for helping to the reservoir characterization. This study present a synthesis of basement outcrops studies in different geological setting linked to crustal extension. The method used was to combine satellite pictures, field studies and laboratory measurement in order to define the faults, fractures and cracks network at the largest range of scales as possible. That have lead us to construct a reservoir’s model composed by blocks of different orders depending on their size bounded themselves by faults with decreasing thickness and lengths. This model is a key tool for the characterisation of fractured buried reservoirs by seismic imaging.
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Volumetric Interpretation of 3D Seismic Data from the Hillside IOCG Deposit in South Australia
Authors M.S. Hossain, M. Urosevic and A. KepicA 3D high-resolution reflection seismic data were acquired to investigate its utilisation for exploration of typically excessively complex IOCG deposits in Hillside, South Australia. Full 3D pre-stack imaging produced results where seismic character well resembled different rock types. Further assessment of the value provided by seismic data required borehole calibration. Unfortunately only core samples were available. These information were enriched by utilising a specific gravity voxet that was extracted from the Rex supplied database. Core sample tests (velocity) and specific gravity information were utilised during the process of volumetric interpretation. We show that faults extracted from variance attribute correlate with the faults extracted using guided-tracking method. However, petrophysical data shows that the boundaries between gabbro and metasediments may not generate acoustic impedance contrast to be clearly detected by seismic reflection method. The tops to the main rock formations however are mappable in depth slices and agree very well with magnetic data. Further work involves correlation of seismic interpretation with the geological cross sections and lithological logs collected from the site.
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Reflection Seismic Characterization of the Grängesberg Iron Deposit and Its Mining-induced Structures, Central Sweden
Authors J.A.P. Place, A. Malehmir, K. Högdahl, C. Juhlin and K. Persson NilssonReflection seismic investigation has been conducted on the Grängesberg apatite iron deposit. At the time of closure in 1989, the mine was operated at about 650 m below the surface. Mining activities might be resumed in the next years, which require better understanding of (1) the ore geometry and (2) the fault network which has developed up to the surface from excavated zones at depth. Two E-W oriented reflection lines with a total length of 3.5 km were acquired. The seismic lines intersect the Grängesberg ore body and open pit, as well as several of the mining-induced faults. A weight drop mounted on an hydraulic bobcat truck was used as a seismic source; both cabled and wireless receivers were used for the data recording. Preprocessing of the data first required the cable- and wireless- recorded datasets to be merged before stacking all data available at each shot point. The dataset exhibits several shallow reflections which are likely to occur on steep lithologic or tectonic structures. Other deeper reflections are recorded; careful processing will be carried out in order to preserve such events in final stacked sections and help with refining the geological model of the area.
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Seismic Exploration for Volcanogenic Massive Sulphides - The Rosebery Zinc, Lead, Copper Mine, Tasmania
Authors J. Kinkela, A. Dzunic, M. Urosevic, R. MacRae and L. WebbAn experimental 3D seismic survey conducted in extreme topographic and weather conditions in Rosebery, Tasmania, Australia -a known VMS province - was aimed at validating the technique for this region as well as prospecting further down dip for additional mineralisation. Significant challenges were faced during the survey design stage stemming from trying to image dipping structures while taking into account extreme topographical variation of up to 400 m using a limited survey grid of approximately 1.5 km². Initial processing results were less than satisfactory with the majority of the target geology being migrated outside of the conventional 3D space. By expanding the geometry additional space for migration was provided, allowing seismic events to migrate to their true spatial position. This unambiguously imaged the controlling structures and achieved the major objectives of the trial survey.
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3D-3C Reflection Seismic Imaging of the Lalor VSM Deposit, Manitoba, Canada
Authors G. Bellefleur, E. Schetselaar, K. Miah and D. WhiteA 3D-3C seismic data set was acquired over the Lalor Lake VMS deposit, located near Snow Lake Manitoba, to provide images of the ore zones and host rocks, and to assess the applicability and potential benefits of P-S waves for deep mineral exploration. An analysis of borehole logging data shows that ore zones associated with pyrite and diorite should produce strong reflection on seismic data. Clear reflections are locally observed at the location of shallower ore zones. Alteration and post-metamorphism increased the P-wave velocity and density of felsic volcanic rocks but the impact of this change has not been clearly identified on seismic data. Many prominent and continuous reflections of lithological origin are observed close to the base of the Chisel sequence. P-S results are not discussed here but will be presented at the workshop.
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Deep Ore Exploration of Sulfides with Seismic Reflection Profiling in Outokumpu, Finland
Authors S.E. Heinonen, S. Aatos, P.J. Heikkinen, N. Hellqvist, M. Kurimo, H. Leväniemi and I.T. KukkonenA network of high resolution seismic reflection profiles was acquired in Outokumpu, Finland. Outokumpu is one of the most important mining regions in Finland where active sulphide exploration is ongoing. Over 5 km long spread with 402 active channels and nominal vibroseismic source point interval of 25 m guarantee high fold and good signal-to-noise ratio of the seismic data. These high quality data have been commercially processed by Vniigeofizika, Moscow with standard hardrock seismic processing flow including careful static corrections. Seismic sections were migrated and depth converted with constant velocity (5400 m/s) that corresponds approximately to the seismic P-wave velocity in the main lithology of the area, mica schist. Additionally to seismic velocities, also densities of the main lithologies have been measured from the 2.5 km long drill hole. This enables estimation of the main sources of reflectivity in the Outokumpu area. Encouragingly, typical ore hosting lithological assemblage was found to be brightly reflective both externally and internally due to interlayers of high acoustic impedance skarns and low acoustic impedance serpentinites. All together nine interconnected seismic profiles combined with the drill hole logging data and other geophysical data, including ZTEM survey, enable the 3D-modeling of the Outokumpu subsurface structures.
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High Resolution Seismic Reflection for Imaging Metamorphic Rocks
By M. JudTo optimize the exploitation of ore deposits it is necessary to know the exact geometry of the ore body, as well as the geometry of any barren rock. In the course of this project the principal applicability of high resolution 2D seismic reflection should be tested. For this purpose we have chosen a magnesite quarry where the geology is known from outcrops and deep mining.
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3D Seismic Processing of Crooked Line 2D Data in the Vicinity of the COSC 2.5 Km Deep Scientific Borehole
More LessTwo crooked line 2D seismic profiles were acquired in the vicinity of the location of the first scientific borehole of the Collisional Orogeny in the Scandinavian Caledonides (COSC) project. The planned depth of the borehole is 2.5 km and drilling will start in mid-Spring 2014. The data were previously processed in 2D and the borehole was located based on the results of this processing. In order to obtain a better image of the subsurface and provide better predictions of the expected lithology at depth the data have been reprocessed as a sparse 3D data set. The 3D processing suggests that a larger mafic lense is expected to be penetrated at about 1000 m depth and the base of a high grade metamorphic unit at about 2.2-2.3 km depth. The upper 500 m is not well imaged due to the acquisition geometry.
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