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10th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Mar 1997 - 26 Mar 1997
- Location: Reno, Nevada, USA
- Published: 23 March 1997
81 - 100 of 106 results
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Characterization Of The Electrical Structure Of An Agricultural Field In Burleson County, Tx
Authors K. Sananikone and M.E. EverettA transient, controlled-source electromagnetic survey has been performed at the Texas
A&M University Hydrogeologic Field Site adjacent to the Brazes River in Burleson County,
central Texas. The experiment is part of a larger, interdisciplinary effort to model the
fate of agricultural chemicals applied to river floodplains. A regularized inversion of the
electromagnetic data show that the sandy alluvial unit which constitutes the main aquifer
for subsurface transport of groundwater is apparent as a resistive zone at depths between
5-20 m. We observe effects in the transient electromagnetic responses that are indicative
of lateral heterogeneity and/or a polarizable Earth.
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Gravity Mapping Of Subsurface Structures In Batholithic Terrain
Authors Jeff S. Zawila, Brian N. Damiata, Shawn C. Biehler and Tien C. LeeA regional gravity survey was conducted in the vicinity of March Air Force Reserve,
southern California with the objective of mapping basement topography that may directly
influence groundwater flow. The data set consists of 3500 gravity stations that cover an area of
670 square kilometers. The raw gravity data were converted to complete Bouguer gravity values
by using standard techniques that included Digital Elevation Models to perform the necessary
terrain corrections. The complete Bouguer values were gridded using a kriging method while
spectral filtering techniques were employed to generate residual anomaly maps. The resulting
anomaly pattern reveals three mappable orders of subsurface structures. Inverse modeling, as
constrained by well-log data and seismic interpretations, indicates that the primary, secondary,
and tertiary structures have axial depths of 1000, 100 to 300, and less than 100 meters,
respectively. The primary structure is a tectonic trough while the secondary and tertiary
structures are erosional channels.
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Airborne Multispectral And Hyperspectral Remote Sensing: Examples Of Applications To The Study Of Environmental And Engineering Problems
Authors Remo Bianchi and Remo BianchiThe availability of a new aerial survey capability carried out by the CNR/LARA (National
Research Council - Airborne Laboratory for the Environmental Research) by a new
spectroradiometer AA5000 MIVIS (Multispectral Infrared and Visible Imaging Spectrometer) on
board a CASA 212/200 aircraft, enable the scientists to obtain innovative data sets, for different
approach to the definitions and the understanding of a variety of environmental and engineering
problems.
The 102 MIVIS channels spectral bandwidths are chosen to meet the needs of scientific research
for advaced applications of remote sensing data.
In such configuration MIVIS can offer significant contributions to problems solving in wide
sectors such as geologic exploration, agricultural crop studies, forestry, land use mapping,
idrogeology, oceanography and others.
LARA in 1994-96 has been active over different test-sites in joint-venture with JPL, Pasadena,
different European Institutions and Italian University and Research Institutes.
These aerial surveys allow the national and international scientific community to approach the use
of Hyperspectral Remote Sensing in environmental problems of very large interest.
The sites surveyed in Italy, France and Germany include a variety of targets such as quarries,
landfills, karst cavities areas, landslides, coastlines, geothermal areas, etc.
The deployments gathered up to now more than 300 GBytes of MIVIS data in more than 30 hours
of VLDS data recording.
The purpose of this work is to present and to comment the procedures and the results at reasearch
and at operational level of the past campaigns with special reference to the study of environmental
and engineering problems.
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Ip And Resistivity Survey At The Inel Cold Test Pit
More LessInduced polarization (IP) is a technique for detection of diffuse occurrences of
metallic material. The Idaho National Laboratory (INEL) Cold Test Pit (CTP) has been
carefully constructed to simulate stored hazardous waste occurrences. IP and resistivity
surveys of the CTP show a very strong IP response and a modest resistivity response
associated with the simulated waste. Several false positive resistivity anomalies are noted.
2-D inversion of the data accurately determine the lateral limits of the waste zone.
The depth of burial indicated is deeper than reported by the construction engineers.
Limited depth extent is recognized, in distinction to results from other, resistivity-based,
methods, but it also appears too deep. IP holds promise as a method for locating buried
waste.
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On The Application Of Radiomagnetotellurics To Waste Site Exploration In Germany
More LessSince several years, the environmental geophysics department of the University of Cologne
uses the radiomagnetotelluric method (RMT) extensively in connection with waste site
exploration successfully (Tezkan et al., 1996, Zacher et al., 1996, Dautel, 1995).
The RMT-method uses transmitters from powerful civilian and military radio stations in
the frequency range 10 to 240 kHz with possible extension to few Mhz. Horizontal
components of the magnetic field are measured by a coil and of the electric field by using
two grounded electrodes spaced 5 m apart. Apparent resistivity and phase data can be
derived from these data for several selected frequencies. These data are then interpreted by
using 2D conductivity models which give excellent information about the vertical and
lateral borders of the waste site and about the top layer.
Two case histories about waste site exploration from Germany will be demonstrated.
Depending on the accessability of the survey areas for geophysical measurements the
lateral borders of the waste sites are located in the field very accurately. They are
characterized by strongly decreasing apparent resistivities observed at nearly all
frequencies at the border between waste site and undisturbed geology. The information
about the thickness of the top layer and the resolution of the bottom of the waste site can
be obtained by 1D and 2D model calculations quantitatively. They give also information
about different areas of the waste site containing different materials.
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Geophysical Data Integration To Delineate Rupture Extension In A Urban Tunnel
São Paulo City, located in the southeast region of Brazil, is home to a population of 13 million
people and about 3 million vehicles. The megalopolis characteristic causes enormous traffic
problems, with combined daily average traffic jams of about 120 km.
One of the alternatives which has been adopted to minimize such a problem is the construction of
urban tunnels connecting important avenues of the city. One of these tunnels, which lies below
Ibirapuera Park (the city’s main park), links the Juscelino Kubitschek, Sena Madureira and 23 de
Maio Avenues.
During the construction of this tunnel, a roof rupture occurred involving an volume of about 20
m3. Despite the stabilization procedures taken by the contractors, there was doubt as to what
extent the massive had been compromised, giving rise to the need for more intensive support
treatment.
In an emergency character, a geophysical study was conducted with the aim of defining the
extension of the affected zone and, eventually, of helping in the proposition of recovering
solutions. Due to time constraints, limitation of surface space and mainly the scale and depth of
the rupture, high resolution seismic and detailed geoelectric mapping were carried out. To
overcome the natural noise of the city, the range of frequencies used by the seismic study was
between 200 Hz and 1,000 Hz, and a geophone spacing of 1 .O meter. Three profiles were taken,
one on the intact massive, the second on the known disturbed massive and the last crossing the
rupture zone.
The geoelectric studies encompassed time domain induced polarization (IP) - resistivity and
spontaneous potential (SP). A gradient array was utilized with an AB of 60 and 50 meters and
measurements were taken every 2 meters in a grid of 20 x 20 m.
The results allowed for the definition of a 3 m x 5 m zone in which the massive was disturbed,
consequently requiring treatment to improve the support. Boreholes confirmed the exactness of
the conclusions taken. AtIer the treatment and the reopening of the tunnel excavation, it was
possible to see that the rupture zone had been limited to about 3 x 3 m.
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Geophysical Imaging Of Transient Ground Water Flow In Partially Saturated Aquifers
Authors Ran Bachrach and Amos NurThe relation between the subsurface water table, saturation, and the hydraulic
conductivity is often used for estimating hydraulic conductivity by the use of
different inversion methods. We show that the ability to image the water table
and the saturation, using surface geophysical methods, together with flow
simulations, can significantly improve the characterization of a site. Our approach
also provides a useful tool for evaluating the performance of seismic and ground
penetrating radar (GPR) in different field conditions.
Elastic and electromagnetic wave velocities in porous media are sensitive to the
presence of fluids in the pore space. Consequently, monitoring velocity changes
in porous systems can serve to image time variations of saturation in the
subsurface, and to extract hydraulic transport properties. To investigate the
feasibility of monitoring we model the response of an unconfined aquifer to
shallow seismic and GPR surveys during pumping. We use a 3D radial flow
model to compute partial saturation profiles in a heterogeneous, unconfined
aquifer at different times of the pumping. We then compute the corresponding
time varying seismic and GPR images of the subsurface for these saturation
profiles. We use the Biot-Gassmann theory to extract the seismic velocity field of
the subsurface from the saturation. The electromagnetic response of the
subsurface is computed using an empirical regression relation between the
saturation and the dielectric constant of the medium. These are widely supported
by laboratory and field observations. The simulated results show that velocity
analysis of both the seismic and the GPR sections can be used for estimating the
saturation variations in an uncontined aquifer during pumping tests: High
permeability zones result in sharper images of the water table with both GPR and
seismic sections. Low permeability zones are detectable because of the relatively
high partial saturation values left behind the down drawn water table.
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Airborne Measured Analytic Signal For Uxo Detection
Authors T. Jeffrey Gamey, J. Scott Holladay and Reinhold MahlerThe Altmark Tank Training Range north of Haldensleben, Germany has been in
operation since WWI. Weapons training and testing has included cavalry, cannon,
small arms, rail guns, and tank battalions. Current plans are to convert the area to a
fully digital combat training facility. Instead of using blank or dummy ordnance, hits will
be registered with lasers and computers. Before this can happen, the 25,000 ha must
be cleared of old debris. In support of this cleanup operation, Aerodat Inc., in
conjunction with IABG of Germany, demonstrated a new high resolution magnetic
survey technique involving the measurement of 3-component magnetic gradient data.
The survey was conducted in May 1996, and covered 500 ha in two blocks. The
nominal line spacing was 10 m, and the average sensor altitude was 7 m. The geologic
column consisted of sands over a sedimentary basin. Topographic relief was generally
flat with approximately 3 m rolling dunes and occasional man-made features such as
fox holes, bunkers, tank traps and reviewing stands. Trees were sparse and short (2-3
metres) due to frequent burn off and tank activity. As such, this site was nearly ideal for
low altitude airborne surveying.
The geophysical sensors included four Cesium vapour magnetometers in a irregular
tetrahedron (Figure 1). The average spacing between sensors was 1.5 metres.
Reading from these sensors provided the basis for measuring three components of
gradient (G,, G,, G,). The vector sum of the gradients was calculated to create a
measured total gradient (G), or analytic signal (AS). A real time differentially corrected
Global Positioning System (RT-DGPS) was used to provide navigation and data
positioning information. A laser altimeter provided height control, and a multi-antenna
GPS unit monitored system attitude.
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Multi-Sensor Ordnance Signatures For Algorithm Development And Model Training
Authors H.H. Nelson, J.R. McDonald and Richard RobertsonThe Naval Research Laboratory is developing a Multi-Sensor Towed Array
Detection System, MEADS, for ordnance detection and site characterization, One
component of this task is construction and validation of algorithms for target
characterization and location for use in the data analysis system. In support of this
task, we have collected an extensive set of ordnance signatures using total field
magnetometers, total field magnetometers deployed as vertical gradiometers and
specially modified Geonics EM-61 pulsed induction sensors. The ordnance items
characterized range from Mk 42 submunitions to Mk 82, 500 lb bombs at depths
ranging from the surface to 20 ft. Where appropriate, signatures are recorded as a
function of azimuth and inclination. We discuss the details of the sensor systems and
the data collection methodologies. Typical signatures are presented and compared
to simple models. We anticipate that this data set will become one of the standards
for passive and active sensor algorithm development and training in the ordnance
detection community.
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Whole-Field Geophysical Measurements Using Coherent Optics
By Edgar ConleyThis paper describes powerful methods of optics and mechanics brought to bear on important geomechanical
problems. Whole-field surface glacier ice flow and mine-wall strains were mapped in two separate feasibility
studies using high-resolution photography and coherent light to interrogate the images. Young’s fringe patterns
result when a double-exposed transparency of a deforming surface is illuminated by a narrow beam of coherent
light. Geometry gives a relationship between the surface displacement vector and the interference fringe patterns.
The displacement occurring during the time-lapse interval is thus known. When applied to the surface of the
Nisqually Glacier, Mt Rainier National Park, WA, the speckle method yielded ice flow data that was compared with
similar flow data acquired by surveying techniques. In the areas for which results can be compared, our experiments
yield a flow of .6 meters/day where conventional methods yield about .4 meters/day. The same photographic
technique was applied to measure the visco-plastic deformation of a proposed nuclear waste repository carved into
bedded salt deep in the earth’s crust Data reduction concluded with the differentiation of the displacement vector
map to obtain the two-dimensional strain rate field which correlated well with extensometer-gathered data. The
research demonstrates the feasibility of using whole-field optical techniques to map ice flow and mine-wall strains,
and confirms certain, but not all, measurements of point-by-point instruments. Field work, data analysis, and
additional potential applications of the speckle photography method are indicated.
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Effective Electrical Resistivity Tomography Surveys For Environmental Monitoring
Authors Douglas J. LaBreque, Gianfianco Morelli and Paul LundegardThe paper emphasizes the need for careful design of ERT surveys for reliable, high resolution
imaging of subsurke processes. In this paper we discuss the use of the resolution radius matrix to
compare the resolution achieved with difkrent configurations of electrodes.
The most critical factor in designing ERT surveys is the aspect ratio of the image plane The aspect
ratio is the length of the boreholes fitted with electrodes divided by the separation of the boreholes.
With a large aspect ratios the resolution in the center of the image plane is about the same as the
resolution near the boreholes. As the aspect ratio decreases the resolution drops in the center of the
image plane but stays roughly the same near the edges. Data collected with ratios less than about
1.5: 1 have an unacceptably low resolution in the center of the images. This problem can be partly
offset by including surface electrodes as well as borehole electrodes.
The resolution does appear to improve with increased numbers of electrodes. However, using
large numbers of electrodes with large aspect ratios tends to produce only limited improvements in
resolution while greatly increasing the data acquisition time.
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Three-Dimensional Electrical Resistivity Tomography And Its Application To Larderello-Valle Secolo Geothermal Field In Tuscany, Italy
Authors Weiqun Shi, William Rodi, M. Nafi Toksoz, F. Dale Morgan, Adolfo Fiordelisi and G. Mauro CameliThe Valle Secolo region in the Larderello geothermal field in western Italy is a vapor-dominated
reservoir producing steam primarily from shallow, highly fractured Tuscan anhydrites. In this
area, water re-injection into various wells has been carried out for many years. During this period,
electrical resistivity surveys have been conducted for the purpose of monitoring distribution of
re-injected water and steam displacement through changes in subsurface electrical properties.
This paper describes a 3-D d.c. electrical resistivity inversion algorithm and its application to
data obtained from two surveys conducted in 1991 and 1993, respectively. The objective of this
effort is to relate the variations in resistivity with position and time to the injection history. Our
inversion models indicate that the primary resistivity variations in the Larderello geothermal field
are of structural origin, e.g., the variation of conductivity of the geologic section. However, the
models from both surveys contain a low resistivity anomaly at a depth of a few hundred meters that
does not correlate with structure. From its location relative to the injection wells, and from changes
in its properties between the two surveys, we infer that the anomaly is related to the injection and
is probably a zone of high permeability or high water saturation.
These preliminary results show that it is possible to detect and monitor the re-injection of fluid
through the systematic observation of electrical resistivity at the site. The method is also suitable
for the detection of environmental contaminant movement. However, field measurements must be
repeated using the same geometry and uniform calibration over time.
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Joint Refraction Traveltime Migration And Tomography
Authors Jie Zhang and M. Nafi ToksözMigration and tomography represent two major techniques in state-of-the-art seismic imaging technology.
Migration maps interfaces in the subsurface by reconstructing physical raypaths from a downward continuation
process, while tomography reconstructs a physical model by inverting recorded data. For interpreting
refraction traveltimes, we present two approaches that combine migration and tomography in one joint imaging
process in an iterative manner. The slowness parameters on a regular grid can be updated on the basis
of fitting traveltimes as well as defining interfaces associated with the migrated traveltime image. The first
method, model-interface method, assumes that the migration image corresponds to a slowness discontinuity
in the model. Therefore, an a priori curvature constraint is emplaced at the image location by way of
Tikhonov regularization. The second approach places a discontinuity in the regularization (Laplacian) operator
according to the location of the migration image, thus it is called derivative-interface method. The first
method gives a stronger model constraint, while the second one relies more on the data. We demonstrate
that both methods are capable of reconstructing a reliable velocity model with sharp features.
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Regularizing Data In 3D Dc Resistivity Tomography
By Jie ZhangBecause of the ill-posedness and high non-uniqueness of the 3D d.c. resistivity inverse problem, we cannot
find a stable and unique solution solely on the basis of fitting data. To stabilize the inverse problem and find a
minimum-structure solution, Tikhonov regularization is often applied. This usually involves the minimization
of the second-order model derivatives, which is equivalent to the application of nonlinear interpolation in
model space. For the same purpose, we propose to regularize data and invert a large number of interpolated
measurements with an estimated data covariance matrix. Because the potential field distribution is generally
smooth, interpolation can be an effective tool to fill in the missing data on the surface and construct 2D data
slices. Inverting 2D data slices along with the use of model regularization turns out to be more attractive,
because it can more tightly constrain the near-surface structure roughnesses. It also gives parameterization
for the model regularization more flexibility. In addition, inverting a large number of interpolated data with
an efficient algorithm does not require additional computational effort.
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3D Visualization Of A Resistivity Data Set - An Example From A Sludge Disposal Site
Authors Christian Bernstone, Torleif Dahlin and Peter JonssonA relatively large 2D inverted CVES resistivity data set from a waste pond area in southern Sweden was
visualized as an animated 3D model using state-of-the-art techniques and tools. The presentation includes a
description of the hardware and software used, outline of the case study and examples of scenes from the
animation’.
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A Roll-Along Technique For 3D Resistivity Data Acquisition With Multi-Electrode Arrays
Authors Torleif Dahlin and Christian BernstoneA roll-along technique for 3D data acquisition using standard multi electrode equipment, designed for
engineering and environmental applications, allow measurement of large true 3D resistivity data sets. Results
from a field test at a closed sludge disposal site display consistent data, with marked differences between
measurement directions. The data was inverted to form a resistivity-depth model of the ground using a 3D quasi-
Newton technique. The results achieved with the technique can be highly useful for engineering and
environmental applications, but would require the use of multi channel measurement to speed up the data
acquisition process for routine application.
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The Shallow Porosity Structure Of The Continental Shelf Off Humboldt Bay, California: Results Of A Towed Electromagnetic Survey
Authors Rob Evans, Lawrie Law, Benoit St Louis, Steve Cheesman and Khamla SananikoneWe have completed a towed electromagnetic survey, mapping the electrical resistivity of the seafloor across
an area of the Californian continental shelf. The area has been designated as a natural laboratory by the
Office of Naval Research as part of the STRATAFORM initiative. More than 120km of tow-lines were
completed, making measurements of resistivity over the top 20m of sediment every 20m or so along track
and from water depths of 1OOm to around 30m. We identify three distinct depositional environments based
on the resistivities recorded and the porosities inferred from them: one, a mid-shelf depo-center also
associated with recent flood deposits; another an uplifted, buried anticline system; and the third associated
with the Eel river delta.
We present the electromagnetic method used as a technique that can provide valuable information about
facies conditions across the littoral zone. Such information can be used for a variety of purposes, but from
an environmental perspective these include: identifying sand and gravel deposits; monitoring the effects of
storms on continental shelf erosion; finding suitable locations for the siting of offshore cables and pipelines;
quantifying the transport of material from river estuaries across and along the shelf; and mapping areas of
fine grained sediment that might preferentially scavenge pollutants from the water column.
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Borehole Velocity Logging For The Caltrans Bridge Retrofit Program
Authors William P. Owen and Darby K. VickeryThe influence of local soil conditions on ground shaking and the potential for resulting
structural damage has long been recognized. Two of the primary soil properties affecting the
intensity of ground motion are shear- and compressional-wave velocity. As part of a multidisciplinary
approach to the seismic retrofit of toll bridges, the California Department of
Transportation uses a suspended borehole probe to measure in situ compressional- and shearwave
velocity, both for onshore and offshore environments. These data are used as input for
ground-motion and foundation response analysis. The probe contains a dipole source that
directly produces compressional waves. Shear-wave velocity is measured via the low-frequency
component of the borehole flexural mode. A new empirical relationship between P-wave
velocity and density improves the fit to observed data. Experiments with logging through freehanging
plastic casing produced mixed results. Although resolution is low compared to
conventional sonic logs, the velocity data provide good delineation of gross stratigraphy (bed
thickness > 1 meter).
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Borehole Geophysics In Gold Exploration
Authors K.A. Pflug, P.G. Killeen and C.J. MwenifumboThe Borehole Geophysics Section of the Geological Survey of Canada has acquired
multiparameter borehole geophysical logs in several holes in gold deposits in Ontario. These
measurements were made to document the geophysical signatures of the ore zones and host rocks,
and to determine which physical properties may be used to outline zones favourable for gold
mineralization. The geophysical logs acquired include: spectral gamma-ray, density, spectral gammagamma
ratio (heavy element indicator), resistivity, induced polarization, self potential, magnetic
susceptibility, temperature and temperature gradient.
Although gold in economic quantities does not occur in high enough concentrations to be
directly detected by geophysical methods, geophysics may be used to delineate certain lithologic
units known to host the gold as well as structural features or alteration associated with gold
mineralization. In many gold deposits, an increase in the concentration of potassium is associated
with gold mineralization, due to sericite alteration. The potassium log (which is derived from the
spectral gamma-ray log) can be used to outline zones of potassium enrichment. The resistivity and
induced polarization logs also show characteristic responses to pyrite, which is frequently associated
with gold mineralization. Increases in other elements, such as the barium enrichment associated with
some of the Hemlo gold deposits, can also be detected by geophysical methods. Enrichment of
barium, which is a ‘heavy’ element, is detectable by the spectral gamma-gamma method. In areas
where gold is known to occur in certain lithologic units, the geophysical logs can be used to map
lithology. The use of multiparameter borehole geophysics to map lithology and to detect alteration
associated with gold mineralization is illustrated using examples from boreholes in the Kirkland
Lake and Hemlo mining areas.
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Towards Prediction Of Geological Drill Core Logs Using Geophysical Logs In Volcanic Stratigraphy
Authors P.G. Killeen, B.E. Elliott and C.J. MwenifumboIn base metal exploration projects in greenstone belts, geological logging of the drill core can be
difficult because different volcanic and volcaniclastic rocks are often visually similar. Geophysical
logging tools measure physical and chemical properties that are not visible and therefore complement
observations made in geological logs. The geophysical data can provide a more complete (e.g. no
missing drillcore) and objective geologically-related interpretation of the lithology intersected by the
drillholes and can be used as an aid to geological logging of the drill core.
The Borehole Geophysics Section of the Geological Survey of Canada has conducted multiparameter
geophysical logging in areas of massive sulphide exploration, for more than ten years. Excellent
correlation of geophysical logs with geological logs has been observed in boreholes associated with
volcanogenic massive sulphide deposits, at locations from Newfoundland to British Columbia. The
application of borehole geophysical logs to the problem of core logging in areas of volcanogenic
massive sulphide deposits, is illustrated with examples.
The first example is a geological hole-to-hole correlation problem at the McConnell Nickel Deposit
near Sudbury. A simple case of the obvious relation between geophysical logs and geological logs
at the Mudhole base metal prospect near Buchans, Newfoundland, is presented next. The third
example is from the Brazil Lake area of Nova Scotia, where the potential for development of a
pseudo-geological log based on the use of multiparameter logs is shown. In another example, in the
Kam-kotia Mine area near Timmins, Ontario, the pseudo-geological log was derived by using three
geophysical logs (gamma-ray, magnetic susceptibility and density). In all cases, the geological
interpretation from the geophysical logs was subjective, However, initial investigations suggest an
objective, computer-based method of deriving the pseudo-geological log, as a tool for the geologist,
is feasible. Some early trials of this semi-automated ‘pre-picking’ of the geology by computer, based
on the geophysical logs at the McConnell deposit, are presented, illustrating the difficulties and the
possibilities.
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