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Title: EXPLORATION TECHNIQUES


1
EXPLORATION TECHNIQUES
  • Virginia McLemore

2
WHAT ARE THE OBJECTIVES IN EXPLORATION?
3
WHAT ARE THE OBJECTIVES IN EXPLORATION?
  • Establish baseline/background conditions
  • Find alteration zones
  • Find ore body
  • Determine if ore can be mined or leached
  • Determine if ore can be processed
  • Determine ore reserves
  • Locate areas for infrastructure/operations
  • Environmental assessment
  • Further understand uranium deposits
  • Refine exploration models

4
STEPS
  • Define uranium deposit model
  • Select area
  • Collect and interpret regional data
  • Define local target area
  • Field reconnaissance
  • Reconnaissance drilling
  • Bracket drilling
  • Ore discovery

5
(No Transcript)
6
Select Area
  • How do we select an area to look for uranium?

7
Select Area
  • How do we select an area to look for uranium?
  • Areas of known production
  • Areas of known uranium occurrences
  • Favorable conditions for uranium

8
COLLECT DATA
  • Historical data
  • State, federal surveys
  • University research programs
  • Archives
  • Company reports
  • Web sites
  • Published literature
  • Prospectors

9
Methods
  • Magnetic surveys
  • Electromagnetic (EM, EMI), electromagnetic
    sounding
  • Direct current (DC)
  • GPR (Ground penetrating radar potential)
  • Seismic
  • Time-domain electromagnetic (TEM)
  • Controlled source audio-magnetotellurics (CSAMT)
  • Radiometric surveys
  • Induced polarization (IP)
  • Spontaneous potential (SP)
  • Borehole geophysics
  • Satellite imagery
  • Imagery spectrometry
  • ASTER (Advanced space-borne thermal emissions
    reflection radiometer)
  • AVIRIS
  • PIMA
  • SFSI
  • LIBS
  • SWIR
  • Multispectral

10
REMOTE SENSING
11
Remote Sensing Techniques
  • Digital elevation model (DEM)
  • Landsat Thematic Mapper (TM)
  • ASTER (Advanced Spaceborne Thermal Emission and
    Reflection Radiometer)
  • Hyperspectral remote sensing (spectral bands, 14
    and gt100 bands)
  • NOAA-AVHRR (National Oceanic and Atmospheric
    Administration - Advanced Very High Resolution
    Radiometer

12
Remote sensing is the science of remotely
acquiring, processing and interpreting spectral
information about the earths surface and
recording interactions between matter and
electromagnetic energy.
SATELLITE
LANDSAT
AIRBORNE
HYPERSPECTRAL
GROUND
Field Spectrometer
Alumbrera, Ar
Data is collected from satellite and airborne
sensors. It is then calibrated and verified
using a field spectrometer.
CUPRITE, NV
Goldfield, NV
13
Sunlight Interaction with the Atmosphere and the
Earths Surface
Data is collected in contiguous channels by
special detector arrays. Collection is done at
different spectral and spatial resolutions
depending on the type of sensor. Each
spatial element is called a pixel. Pixel size
varies from 1/2 meters in some hyperspectral
sensors to 30 meters in Landsat and ASTER, which
are multispectral. Sensor spatial differences
and band configurations are shown below.
ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum is a distribution of
energy over specific wavelengths. When this
energy is emitted by a luminous object, it can be
detected over great distances. Through the use of
instrumentation, the technique detects this
energy reflected and emitted from the earths
surface materials such as minerals, vegetation,
soils, ice, water and rocks, in selected
wavelengths. A proportion of the energy is
reflected directly from the earths surface.
Natural objects are generally not perfect
reflectors, and therefore the intensity of the
reflection varies as some of the energy is
absorbed by the earth and not reflected back to
the sensor. These interactions of absorption and
reflection form the basis of spectroscopy and
hyperspectral analysis.
Source Bob Agars
14
HYPERSPECTRAL IMAGING SPECTROSCOPY
Imaging spectroscopy is a technique for obtaining
a spectrum in each position of a large array of
spatial positions so that any one spectral
wavelength can be used to make a coherent image
(data cube). Imaging spectroscopy for remote
sensing involves the acquisition of image data in
many contiguous spectral bands with an ultimate
goal of producing laboratory quality reflectance
spectra for each pixel in an image (Goetz,
1992b). The latter part of this goal has not yet
been reached. The major difference from Landsat
is the ability to detect individual mineral
species and differentiate vegetation species.
Source CSIRO
This "image cube" from JPL's Airborne
Visible/Infrared Imaging Spectrometer (AVIRIS)
shows the volume of data returned by the
instrument. AVIRIS acquired the data on August
20, 1992 when it was flown on a NASA ER-2 plane
at an altitude of 20,000 meters (65,000 feet)
over Moffett Field, California, at the southern
end of the San Francisco Bay. The top of the
cube is a false-color image made to accentuate
the structure in the water and evaporation ponds
on the right. Also visible on the top of the
cube is the Moffett Field airport. The sides of
the cube are slices showing the edges of the top
in all 224 of the AVIRIS spectral channels. The
tops of the sides are in the visible part of the
spectrum (wavelength of 400 nanometers), and the
bottoms are in the infrared (2,500 nanometers).
The sides are pseudo-color, ranging from black
and blue (low response) to red (high response).
Of particular interest is the small region of
high response in the upper right corner of the
larger side. This response is in the red part of
the visible spectrum (about 700 nanometers), and
is due to the presence of 1-centimeter-long
(half-inch) red brine shrimp in the evaporation
pond.
15
Exploration Techniques
  • Geologic Mapping
  • Leann M. Giese
  • February 7, 2008

16
Mining Life Cycle (Spiral?)
  • In the mine life cycle, geologic mapping falls
    under Exploration, but it effects all of the life
    cycles

Closure
Ongoing Operations
Post-Closure
Temporary Closure
Exploration
Future Land Use
Mine Development
Operations
?????
(McLemore, 2008)
17
What is geologic mapping?
  • A way to gather present geologic data. (Peters,
    1978)
  • Shows how rock soil on the earths surface is
    distributed. (USGS)
  • Are used to make decisions on how to use our
    water, land, and resources. (USGS)
  • Help to come up with a model for an ore body.
    (Peters, 1978)

18
What is Geologic Mapping? (continued)
  • To better understand the geological features of
    an area
  • Predict what is below the earths surface
  • Show other features such as faults and strike and
    dips.
  • (USGS (a))

Figure 1. Graphic representation of typical
information in a general purpose geologic map
that can be used to identify geologic hazards,
locate natural resources, and facilitate land-use
planning. (After R. L. Bernknopf et al., 1993)
19
Simplified Geologic Map of New Mexico
Topographic Map of the Valle Grande in the Jamez
Mountains
(from NMBGMR).
20
Geologic Mapping Equipment
  • Field notebooks
  • Rock hammer
  • Hand Lens (10x or Hastings triplet)
  • Pocket knife
  • Magnet
  • Clip board
  • Pencils (2H-4H) and Colored Pencils
  • Rapidograph-type pens and Markers
  • Scale-protractor (10 and 50 or 11000 and 14000)
  • Belt pouches or field vest
  • 30 meter tape measurer
  • Brunton pocket transit
  • GPS/Altimeters
  • Camera
  • (Compton,1985)

21
Mapping types
  • Aerial photographs
  • Topographical bases
  • Pace and Compass
  • Chains

(Compton, 1985)
22
Map scales
  • A ratio that relates a unit of measure on a map
    to some number of the same units of measure on
    the earth's surface.
  • A map scale of 125,000 tells us that 1 unit of
    measure represents 25,000 of the same units on
    the earth's surface. One inch on the map
    represents 25,000 inches on the earth's surface.
  • One meter or one yard or one kilometer or one
    mile on a map would represent 25,000 meters or
    yards or kilometers or miles, respectively, on
    the earth's surface.

(from USGS (b))
23
Map scales (continued)
(from USGS (b))
24
What to do first?
  • Most mineral deposits are found in districts
    where there has been mining before, an earlier
    geologist has noticed something of importance
    there, or a prospector has filed a mineral claim
  • Literature Search
  • Library (University, Government, Engineering, or
    Interlibrary loans)
  • State and National bureaus of mines and
    geological surveys (may have drill core, well
    cuttings, or rock samples available to inspect)
  • Mining company information
  • Maps and aerial photographs
  • Is the information creditable? Is it worth
    exploring?

(Peters, 1978)
25
Where to go from here?
  • Mapping is costly and time consuming, so an area
    of interest needs to be defined
  • Reconnaissance helps narrows a region to a
    smaller area of specific interest
  • Reconnaissace in the U.S. usually begins at
    1250,000-scale
  • This large scale mapping can zone-in on areas of
    interest that can then be geologically mapped in
    detail (this is usually done on a 110,000 or
    112,000-scale).
  • Individual mineral deposits can be mapped at a
    12,000 or 12,400-scale to catch its smaller
    significant features.
  • (Peters, 1978)

26
Detailed Geological Mapping
  • When mapping, we want to be quick, because time
    is money, but not too quick as to make a mistake
    or miss something.
  • Along with mapping occurs drilling, trenching,
    geophysics, and geochemistry
  • Samples can be analyzed for Uranium
    concentrations. This gives a better idea of where
    to explore more or drill in an area.

27
Uranium Deposit Types
  • Unconformity-related deposits
  • Metasedimentary rocks (mineralisation, fauletd,
    and brecciated) below and Proterozoic SS. Above
    (pitchblende)
  • Breccia complex deposits
  • Hematite-rich breccia complex (iron, copper,
    gold, silver, REE)
  • Sandstone deposits
  • Rollfront deposits, tabular deposits,
    tectonic/lithologic deposits
  • Surficial deposits
  • Young, near-surface uranium concentrations in
    sediments or soils (calcite, gypsum, dolomite,
    ferric oxide, and halite)
  • Volcanic deposits
  • Acid volcanic rocks and related to faults and
    shear zones within the volcanics (molybdenum
    fluorine)
  • Intrusive deposits
  • Associated with intrusive rocks (alaskite,
    granite, pegmatite, and monzonites)
  • Metasomatite deposits
  • In structurally-deformed rocks altered by
    metasomatic processes (sodium, potassium or
    calcium introduction)

(Lambert et al., 1996)
28
Uranium Deposit Types (continued)
  • Metamorphic deposits
  • Ore body occurs in a calcium-rich alteration zone
    within Proterozoic metamoprphic rocks
  • Quartz-pebble conglomerate deposits
  • Uranium recovered as a by-product of gold mining
  • Vein deposits
  • Spatially related to granite, crosscuts
    metamorphic or sedimentary rocks (coffinite,
    pitchblende)
  • Phosphorite deposits
  • Fine-grained apatie in phosphorite horizons mud,
    shale, carbonates and SS. interbedded
  • Collapse breccia deposits
  • Vertical tubular-like deposits filled with coarse
    and fine fragments
  • Lignite
  • Black shale deposits
  • Calcrete deposits
  • Uranium-rich granites deeply weathered,
    valley-type
  • Other

29
Some Minerals Associated with Uranium
  • Uraninite (UO2)
  • Pitchblende (U2O5.UO3 or U3O8)
  • Carnotite (uranium potassium vanadate)
  • Davidite-brannerite-absite type uranium titanates
  • Euxenite-fergusonite-smarskite group
  • Secondary Minerals
  • Gummite
  • Autunite
  • Saleeite
  • Torbernite
  • Coffinite
  • Uranophane
  • Sklodowskite

(Lambert et al., 1996)
30
Example of exploring a sandstone Uranium deposit
  • When looking for a sandstone-type uranium deposit
    in an area that has had a radiometric survey, our
    first place to focus in on the areas where
    radioactivity appears to be associated with SS.
    Beds. (We will disregard potassium anomalies,
    below-threshold readings, unexplained areas, and
    radioactive noise.)
  • We will then map the radioactive SS. units and
    other associations with our model of a SS.
    uranium deposit.
  • We will look for poorly sorted, medium to coarse
    grained SS. beds that are associated with
    mudstones or shales.
  • Detailed mapping of outcrops on a smaller scale
    is now appropriate. Stratigraphic sections can
    be measured and projected to covered areas.
  • Other radioactive areas that were disregarded may
    be given a second look for other possibilities
    for further investigations.

(Peters, 1978)
31
References
  • Compton, R. R. (1985). Geology in the Field.
    United States of America and Canada John Wiley
    Sons, Inc.
  • Bernknopf, R. L., et al., 1993Societal Value of
    Geologic Maps, USGS Circular 1111.
  • Lambert,I., McKay, A., and Miezitis, Y. (1996)
    Australia's uranium resources trends, global
    comparisons and new developments, Bureau of
    Resource Sciences, Canberra, with their later
    paper Australia's Uranium Resources and
    Production in a World Context, ANA Conference
    October 2001. http//www.uic.com.au/nip34.htm
    (accessed February 6, 2008).
  • McLemore, V. T. Geology and Mining of
    Sediment-Hosted Uranium Deposits What is
    Uranium?. Lecture, January 30, 2008 pp. 1-26.
  • New Mexico Bureau of Geology and Mineral
    Resources. http//geoinfo.nmt.edu/publications/map
    s/home.html (accessed February 1, 2008).
  • Peters, W. C. (1978). Exploration and Mining
    Geology. United States of America and Canada
    John Wiley Sons, Inc.
  • U.S. Geological Survey (a).
  • http//ncgmp.usgs.gov/ncgmpgeomaps (accessed
    February 1, 2008).
  • U.S. Geological Survey (b). http//id.water.usgs.g
    ov/reference/map_scales.html (accessed February
    6, 2008).

32
GEOPHYSICAL TECHNIQUES
33
Gravity and magnetic exploration
  • Pedram Rostami

34
Gravity TechniquesIntroduction
  • Lateral density changes in the subsurface cause a
    change
  • in the force of gravity at the surface.
  • The intensity of the force of gravity due to a
    buried mass difference (concentration or void) is
    superimposed on the larger force of gravity due
    to the total mass of the earth.
  • Thus, two components of gravity forces are
    measured at the earths surface first, a general
    and relatively uniform component due to the total
    earth, and second, a component of much smaller
    size which varies due to lateral density changes
    (the gravity anomaly).

35
Applications
  • By very precise measurement of gravity and by
    careful correction for variations in the larger
    component due to the whole earth, a gravity
    survey can sometimes detect natural or man-made
    voids, variations in the depth to bedrock, and
    geologic structures of engineering interest.
  • For engineering and environmental applications,
    the scale of the problem is generally small
    (targets are often from 1-10 m in size)
  • Station spacings are typically in the range of
    1-10 m
  • Even a new name, microgravity, was invented to
    describe the work.

36
  • Gravity surveys are limited by ambiguity and the
    assumption of homogeneity
  • A distribution of small masses at a shallow depth
    can produce the same effect as a large mass at
    depth.
  • External control of the density contrast or the
    specific geometry is required to resolve
    ambiguity questions.
  • This external control may be in the form of
    geologic plausibility, drill-hole information, or
    measured densities.
  • The first question to ask when considering a
    gravity survey is For the current subsurface
    model, can the resultant gravity anomaly be
    detected?.
  • Inputs required are the probable geometry of the
    anomalous region, its depth of burial, and its
    density contrast.
  • A generalized rule of thumb is that a body must
    be almost as big as it is deep.

37
Rock Properties
  • Values for the density of shallow materials are
    determined from laboratory tests of boring and
    bag samples. Density estimates may also be
    obtained from geophysical well logging
  • Table 5-1 lists the densities of representative
    rocks.
  • Densities of a specific rock type on a specific
    site will not have more than a few percent
    variability as a rule (vuggy limestones being one
    exception). However, unconsolidated materials
    such as alluvium and stream channel materials may
    have significant variation in density.

38
Field Work General
  • Up to 50 percent of the work in a microgravity
    survey is consumed in the surveying.
  • relative elevations for all stations need to be
    stablished to 1 to 2 cm. A firmly fixed stake or
    mark should be used to allow the gravity meter
    reader to recover the exact elevation.
  • Satellite surveying, GPS, can achieve the
    required accuracy, especially the vertical
    accuracy, only with the best equipment under
    ideal conditions.
  • High station densities are often required. It is
    not unusual for intervals of 1-3 m to be required
    to map anomalous masses whose maximum dimension
    is 10 m.

39
Field Work General
  • After elevation and position surveying, actual
    measurement of the gravity readings is often
    accomplished by one person in areas where solo
    work is allowed.
  • t is necessary to improve the precision of the
    station readings by repetition.
  • The most commonly used survey technique is to
    choose one of the stations as a base and to
    reoccupy that base periodically throughout the
    working day.
  • The observed base station gravity readings are
    then plotted versus time, and a line is fitted to
    them to provide time rates of drift for the
    correction of the remainder of the observations.

40
Interpretation
  • Software packages for the interpretation of
    gravity data are plentiful and powerful.
  • The geophysicist can then begin varying
    parameters in order to bring the calculated and
    observed values closer together.
  • Parameters usually available for variation are
    the vertices of the polygon, the length of the
    body perpendicular to the traverse, and the
    density contrast. Most programs also allow
    multiple bodies.

41
Magnetic MethodsIntroduction
  • The earth possesses a magnetic field caused
    primarily by sources in the core.
  • The form of the field is roughly the same, as
    would be caused by a dipole or bar magnet located
    near the earths center and aligned sub parallel
    to the geographic axis.
  • The intensity of the earths field is customarily
    expressed in S.I. units as nanoteslas (nT) or in
    an older unit, gamma (g) 1 g 1 nT 10-3 µT.
    Except for local perturbations, the intensity of
    the earths field varies between about 25 and 80
    µT over the coterminous United States

42
  • Many rocks and minerals are weakly magnetic or
    are magnetized by induction in the earths field,
    and cause spatial perturbations or anomalies in
    the earths main field.
  • Man-made objects containing iron or steel are
    often highly magnetized and locally can cause
    large anomalies up to several thousands of nT.
  • Magnetic methods are generally used to map the
    location and size of ferrous objects.
    Determination of the applicability of the
    magnetics method should be done by an experienced
    engineering geophysicist.
  • Modeling and incorporation of auxiliary
    information may be necessary to produce an
    adequate work plan.

43
Theory
  • The earths magnetic field dominates most
    measurementsz on the surface of the earth.
  • Most materials except for permanent magnets,
    exhibit an induced magnetic field due to the
    behavior of the material when the material is in
    a strong field such as the earths.
  • Induced magnetization (sometimes called magnetic
    polarization) refers to the action of the field
    on the material wherein the ambient field is
    enhanced causing the material itself to act as a
    magnet.
  • The field caused by such a material is directly
    proportional to the intensity of the ambient
    field and to the ability of the material to
    enhance the local field, a property called
    magnetic susceptibility. The induced
    magnetization is equal to the product of the
    volume magnetic susceptibility and the inducing
    field of the earth

44
Theory(continue)
  • I k F
  • k volume magnetic susceptibility (unitless)
  • I induced magnetization per unit volume
  • F field intensity in tesla (T)
  • For most materials k is much less than 1 and, in
    fact, is usually of the order of 10-6 for most
    rock materials.
  • The most important exception is magnetite whose
    susceptibility is about 0.3. From a geologic
    standpoint, magnetite and its distribution
    determine the magnetic properties of most rocks.
  • There are other important magnetic minerals in
    mining prospecting, but the amount and form of
    magnetite within a rock determines how most rocks
    respond to an inducing field.
  • Iron, steel, and other ferromagnetic alloys have
    susceptibilities one to several orders of
    magnitude larger than magnetite. The exception is
    stainless steel, which has a small susceptibility.

45
  • The importance of magnetite cannot be
    exaggerated. Some tests on rock materials have
    shown that a rock containing 1 percent magnetite
    may have a susceptibility as large as 10-3, or
    1,000 times larger than most rock materials.
  • Table 6-1 provides some typical values for rock
    materials.
  • Note that the range of values given for each
    sample generally depends on the amount of
    magnetite in the rock

46
Theory(continue)
  • Thus it can be seen that in most engineering and
    environmental scale investigations, the
    sedimentary and alluvial sections will not show
    sufficient contrast such that magnetic
    measurements will be of use in mapping the
    geology.
  • However, the presence of ferrous materials in
    ordinary municipal trash and in most industrial
    waste does allow the magnetometer to be effective
    in direct detection of landfills.
  • Other ferrous objects which may be detected
    include pipelines, underground storage tanks, and
    some ordnance.

47
Field Work
  • Ground magnetic measurements are usually made
    with portable instruments at regular intervals
    along more or less straight and parallel lines
    which cover the survey area.
  • Often the interval between measurement locations
    (stations) along the lines is less than the
    spacing between lines.

48
  • The magnetometer is a sensitive instrument which
    is used to map spatial variations in the earths
    magnetic field.
  • In the proton magnetometer, a magnetic field
    which is not parallel to the earths field is
    applied to a fluid rich in protons causing them
    to partly align with this artificial field.
  • When the controlled field is removed, the
    protons precess toward realignment with the
    earths field at a frequency which depends on the
    intensity of the earths field. By measuring this
    precession frequency, the total intensity of the
    field can be determined.
  • The physical basis for several other
    magnetometers, such as the cesium or
    rubidium-vapor magnetometers, is similarly
    founded in a fundamental physical constant. The
    optically pumped magnetometers have increased
    sensitivity and shorter cycle times (as small as
    0.04 s) making them particularly useful in
    airborne applications.

49
  • The incorporation of computers and non-volatile
    memory in magnetometers has greatly increased the
    ease of use and data handling capability of
    magnetometers.
  • The instruments typically will keep track of
    position, prompt for inputs, and internally store
    the data for an entire day of work.
  • Downloading the information to a personal
    computer is straightforward and plots of the
    days work can be prepared each night.

50
  • To make accurate anomaly maps, temporal changes
    in the earths field during the period of the
    survey must be considered. Normal changes during
    a day, sometimes called diurnal drift, are a few
    tens of nT but changes of hundreds or thousands
    of nT may occur over a few hours during magnetic
    storms.
  • During severe magnetic storms, which occur
    infrequently, magnetic surveys should not be
    made. The correction for diurnal drift can be
    made by repeat measurements of a base station at
    frequent intervals.
  • The measurements at field stations are then
    corrected for temporal variations by assuming a
    linear change of the field between repeat base
    station readings.

51
  • The base-station memory magnetometer, when used,
    is set up every day prior to collection of the
    magnetic data.
  • The base station ideally is placed at least 100 m
    from any large metal objects or travelled roads
    and at least 500 m from any power lines when
    feasible.
  • The base station location must be very well
    described in the field book as others may have to
    locate it based on the written description.

52
  • The value of the magnetic field at the base
    station must be asserted (usually a value close
    to its reading on the first day) and each days
    data corrected for the difference between the
    asserted value and the base value read at the
    beginning of the day.
  • As the base may vary by 10-25 nT or more from day
    to day, this correction ensures that another
    person using the SAME base station and the SAME
    asserted value will get the same readings at a
    field point to within the accuracy of the
    instrument.

53
Interpretation.
  • Total magnetic disturbances or anomalies are
    highly variable in shape and amplitude they are
    almost always asymmetrical, sometimes appear
    complex even from simple sources
  • One confusing issue is the fact that most
    magnetometers measure the total field of the
    earth no oriented system is recorded for the
    total field amplitude.
  • The consequence of this fact is that only the
    component of an anomalous field in the direction
    of earths main field is measured.
  • Figure 6-1 illustrates this consequence of the
    measurement system
  • Anomalous fields that are nearly perpendicular to
    the earths field are undetectable

54
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55
  • Additionally, the induced nature of the measured
    field makes even large bodies act as dipoles
    that is, like a large bar magnet.
  • If the (usual) dipolar nature of the anomalous
    field is combined with the measurement system
    that measures only the component in the direction
    of the earths field, the confusing nature of
    most magnetic interpretations can be appreciated

56
  • To achieve a qualitative understanding of what is
    occurring, consider Figure in the next page.
  • Within the contiguous United States, the
    magnetic inclination, that is the angle the main
    field makes with the surface, varies from 55- 70
    deg.
  • The figure illustrates the field associated with
    the main field, the anomalous field induced in a
    narrow body oriented parallel to that field, and
    the combined field that will be measured by the
    total-field magnetometer.
  • The scalar values which would be measured on the
    surface above the body are listed.
  • From this figure, one can see how the total-field
    magnetometer records only the components of the
    anomalous field.

57
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58
Uranium Exploration
59
Magnetic
  • Magnetic. Palaeochannel magnetic (either positive
    or negative) anomalies may be defined if
    high-resolution surveys are used and if there are
    sufficient magnetic minerals in the channels or
    measurable magnetic contrast between the channel
    sediments and bedrock.
  • Cainozoic palaeochannels are not usually visible
    on regional magnetic data, as they are relatively
    shallow features, but careful use of detailed
    surveys may assist in locating channel deposits.

60
Gravity
  • Gravity anomalies in the earths gravitational
    field can in some cases be used to define the
    thickness and extent of the fluvial sediments,
    and hence palaeochannels, due to the contrast in
    density between the sediments and fresh bedrock.
    For example, the density of sand and clay is
    1.8g/cc and granitic basement is 2.7 g/cc
    (Berkman 1995).

61
Hoover et al. (1992)
62
Hoover et al. (1992)
63
GEOCHEMICAL SAMPLING
  • Ground water
  • Surface water
  • Stream sediments
  • Soils
  • Biological
  • Ore samples
  • Radon
  • Track etch (identify radiaoactivity)

64
Surface Sampling in Exploration
  • Introduction
  • Sample? Sampling?
  • Sampling Programs
  • Bias and Error in Sampling
  • Quality Control
  • Surface Sampling Methods
  • Sample Handling
  • Documentation Requirements
  • Conclusion
  • References

65
Introduction
  • Sampling methods vary from simple grab samples on
    existing exposures to sophisticated drilling
    methods.
  • As a rule, the surface of the mineralization is
    obscured by various types of overburden, or it is
    weathered and leached to some depth, thereby
    obscuring the nature of the mineralization."

66
What is a sample? What is sampling?
  • A sample is a finite part of a statistical
    population whose properties are studied to gain
    information about the whole (Webster, 1985).
  • Sampling is the act, process, or technique of
    selecting a suitable sample,
  • or
  • a representative part of a population for the
    purpose of determining parameters or
    characteristics of the whole population.
  • Why Sample?

67
Sampling Programs
  • Reconnaissance
  • (1) check status of land ownership, (2)
    physical characteristics of area, (3) mining
    history of the area.
  • Field inspection
  • surface grab sampling over all exposures of
    gravel, few seismic cross section, geobotanical
    study, and survey for old workings.
  • Sampling Plan
  • Special Problems Associated with Sampling
  • Sample Processing or Washing
  • Data Processing
  • Data processing consists of record keeping,
    reporting values, and assay procedures.

68
Sampling Plan
  • Defining the population of concern
  • Specifying a sampling frame, a set of items or
    events possible to measure
  • Specifying a sampling method for selecting items
    or events from the frame
  • Determining the sample size
  • Implementing the sampling plan
  • Sampling and data collecting
  • Reviewing the sampling process

69
Sample Size
  • The question of how large a sample should be is a
    difficult one. Sample size can be determined by
    various constraints such as
  • Cost.
  • nature of the analysis to be performed
  • the desired precision of the estimates one wishes
    to achieve
  • the kind and number of comparisons that will be
    made,
  • the number of variables that have to be examined
    simultaneously

70
Bias and Error in Sampling
  • A sample is expected to mirror the population
    from which it comes, however, there is no
    guarantee that any sample will be precisely
    representative of the population from which it
    comes.
  • biased
  • when the selected sample is systematically
    different to the population.
  • The sample must be a fair representation of the
    population we are interested in.
  • Random errors
  • The sample size may be too small to produce a
    reliable estimate.
  • There may be variability in the population,
    the greater the variability the larger the sample
    size needed.

71
Quality Control
  • Responsibility for maintaining consistency and
    ensuring collection of data of acceptable and
    verifiable quality through the implementation of
    a QA/QC program.
  • All personnel involved in data collection
    activities must have the necessary education,
    experience, and skills to perform their duties.

72
Selecting Methods and Equipment
  • Soil and sediment samples may be collected
    using a variety of methods and equipment
    depending on the following
  • type of sample required
  • site accessibility,
  • nature of the material,
  • depth of sampling,
  • budget for the project,
  • sample size/volume requirement,
  • project objectives

73
Surface Sampling Methods
  • Near-surface samples can be collected with a
    spade, scoop, or trowel.
  • Sampling at greater depths or below a water
    column may require a hand auger, coring device,
    or dredge.
  • As the sampling depth increases, the use of a
    powered device may be necessary to push the
    sampler into the soil or sediment layers.

74
Sampling Equipments
  • Tube Sampler
  • Churn Drills
  • Tube Corers
  • Hand Driven Split-Spoon Core Sampler
  • Hand-Dug Excavations
  • Backhoe Trenches Bulldozer Trenches
  • Other Machine-Dug Excavations
  • Augers
  • Bucket or Clamshell Type Excavators

75
Surface Sampling
Floodplain sampling in southwestern Finland
(Photo Reijo Salminen, GTK).
Figure 13. Wet sieving of a stream sediment
sample in the UK (Photo Fiona Fordyce, BGS from
Salminen and Tarvainen et al. 1998,
76
Surface Sampling
Figure 16. Humus sampling in Finland using
cylindrical sampler, and the final humus sample.
(Photographs Timo Tarvainen, GTK).
77
Surface Sampling
The alluvial horizons at the floodplain sediment
sampling site 29E05F3, France.
The soil sample pit at the site 41E10T3, Finland.
78
Sample Handling
  • Samples should be preserved to minimize chemical
    or biological changes from the time of collection
    to the time of analysis. Keep samples in air
    tight containers. Sediment samples should also be
    stored in such a way that the anaerobic condition
    is preserved by minimizing headspace.
  • If several sub samples are collected, soil and
    sediment samples should be placed in a clean
    stainless steel mixing pan or bowl and thoroughly
    homogenized to obtain a representative composite
    sample.

79
Sample Handling
  • Sample Label Information
  • Label or tag each sample container with a unique
    field identification code. If the samples are
    core sections, include the sample depth in the
    identification.
  • Write the project name or project identification
    number on the label.
  • Write the collection date and time on the label.
  • Attach the label or tag so that it does not
    contact any portion of the sample that will be
    removed or poured from the container.
  • Record the unique field identification code on
    all other documentation associated with the
    specific sample container.
  • Ensure all necessary information is transmitted
    to the laboratory.

80
Documentation
  • Thorough documentation of all field sample
    collection and processing activities is necessary
    for proper interpretation of results. All sample
    identification, chain-of-custody records,
    receipts for sample forms, and field records
    should be recorded using waterproof, non-erasable
    ink in a bound waterproof notebook.
  • All Procedures must be documented.

81
Sample Data
  • From Sampling to Production Pyramid

3RD FLOOR
2ND FLOOR
1ST FLOOR
FOUNDATION
82
Conclusion
  • There are many ways to sample and many methods to
    calculate the value of a deposit. It is important
    to remember to use care in sampling and to select
    the method that best suits the type of occurrence
    that is being sampled.

83
References
  • Journal of the Mississippi Academy of Sciences,
    v. 47, no. 1, p. 42.
  • http//www.evergladesplan.org/pm/pm_docs/qasr/qasr
    _ch_07.pdf
  • http//www.gtk.fi/publ/foregsatlas/article.php?id
    10
  • http//www.socialresearchmethods.net/tutorial/Mugo
    /tutorial.htm
  • http//www.policyhub.gov.uk/evaluating_policy/mage
    nta_book/chapter5.asp

84
  • Thank you

85
Radiometric Survey
Shantanu Tiwari Mineral Engineering Feb 07, 2008
86
Outline
  • Introduction to Radiometric Survey
  • Radioactivity
  • Use of Radiometric Survey
  • Process
  • Case Study
  • Conclusion
  • Refrences

87
Introduction
  • Radiometrics Measure of natural radiation in
    the Earths surface.
  • 2. Also Known as Gamma- Ray Spectrometry (why?).
  • 3. Who uses it?- Geologists and Geophysicists.
  • 4. Also useful for studying geomorphology and
    soils.

88
Radioactivity
  • 1. Process in which, unstable atom becomes
    stable through the process of decay of its
    nucleus.
  • Energy is released in the form of radiation
  • (a) Alpha Particle (or helium nuclei) - Least
    Energy- Travels few cm of air.
  • (b) Beta Particle (or electrons)- Higher Energy-
    Travels upto a meter in air
  • (c) Gamma Rays- Highest Energy- Travels upto 300
    meters in air.

89
Radioactivity (Contd.)
  • Energy of Gamma Ray is characteristic of the
    radioactive element it came from.
  • Gamma Rays are stopped by water and other
    molecules (soil Rock).
  • A radiometric survey measures the spatial
    distribution of three radioactive elements
  • (a) Potassium
  • (b)Thorium
  • (c) Uranium
  • 6. The abundance of these elements are measured
    by gamma ray detection.

90
Use of Radiometric Survey
  • Radioactive elements occur naturally in some
    minerals.
  • Energy of Gamma Rays is the characteristic of the
    element.
  • Measure the energy of Gamma Ray- Abundance.

91
Process
  • How we do radiometric survey?- By measuring the
    energy of Gamma Rays.
  • Can be measure on the ground or by a low flying
    aircraft.
  • Gamma Rays are detected by Spectrometer.
  • Spectrometer- Counts the number of times each
    Gamma Ray of particular energy intersects it.

92
Process
93
Process
  • The energy spectrum measured by a spectrometer is
    in MeV.
  • Range- 0 to 3 MeV.
  • The number of Gamma Ray counts across the whole
    spectrum is referred as the total count (TC).

94
Process
Number of Gamma Rays (per second)
Energy of Gamma Rays
95
Process
High
Low
96
Case Study
Gold Canyon Inc. (USA)- Bear Head Uranium
Project Bear Head Uranium Project- Red Lake
Mining Camp(north-west Ontario) Covers a 23 km
strike-length of Bear Head Fault Zone 0.05 U3O8
97
Conclusion
  • Good Technique
  • Large Area.
  • Better for plane areas.

98
References
  • http//www.goldcanyon.ca/
  • Suzanne Haydon from the Geological Survey of
    Victoria (Aus).

99
Thank you
100
GROUND GEOPHYSICS
101
EXPLORATION TECHNIQUES BY METALLURGICAL SAMPLING
  • GERTRUDE AYAKWAH
  • MINERAL ENGINEERING DEPARTMENT
  • NEW MEXICO INSTITUTE OF MINING AND TECHNOLOGY
  • LEROY PLACE
  • SOCORRO NM
  • February, 7th, 2008

102
Outline
  • Introduction
  • Purpose
  • Sampling
  • Sample Preparation
  • Types of Metallurgical Sampling
  • Geochemical Analysis
  • Assay Techniques
  • Conclusion
  • References

103
Introduction
  • Exploration geology is the process and science of
    locating valuable mineral or petroleum which has
    a commercial value. Mineral deposits of
    commercial value are called ore bodies
  • The goal of exploration is to prove the existence
    of an ore body which can be mined at a profit
  • This process occurs in stages, with early stages
    focusing on gathering surface data which is
    easier to acquire and later stages focusing on
    gathering subsurface data which includes drilling
    data, detailed geophysical survey data and
    metallurgical analysis

104
Purpose
  • The purpose of this presentation is to discuss
    metallurgical sampling in exploration geology

105
Soil and Stream Sample Preparation
  • Samples are reduced and homogenized into a form
    which can easily be handled by analytical
    personnel
  • Soil and stream sediment samples are usually
    sieved so that particles larger than fine sand
    are removed.
  • The fine particles are mixed and a portion is
    removed for chemical analysis

106
Rock Sample Preparation
  • Rock samples are treated in a multi-step
    procedure
  • Rocks, cuttings, or core are first crushed to
    about pea-size in a jaw crusher, then passed
    through a secondary crusher to reduce the size
    further - usually 1/10 inch
  • This crushed sample is mixed, split in a riffle
    splitter and reduced to about one-half pound or
    250 grams. This 250 grams is placed in a
    pulverizer where it is reduced further to -150
    mesh for analysis

107
Metallurgical Sampling
  • Types
  • Geochemical Analysis
  • Assay Techniques

108
Geochemical Analysis
  • Involves dissolution of approximately one gram of
    sample by a strong acid
  • The solution which contains most of the base
    metals is aspirated into a flame as in atomic
    absorption spectroscopy (AAS) or into an
    inductively coupled (ICP)
  • AAS measures one element at a time to a normal
    sensitivity of about 1 ppm

109
Geochemical Analysis (Contd)
  • Whilst ICP 20 measure more elements at a time
    to ppm levels
  • The technique is low-cost, rapid, reasonably
    precise and can be more accurate if the method is
    controlled by standards.
  • However accuracy is minor importance in
    geochemistry as the exploration geologist seeks
    patterns rather than absolute concentration
  • Hence making geochemical analysis methods are
    considered to be indicators of mineralization
    rather than absolute measurement of
    mineralization.

110
Assay Techniques
  • Wet Chemistry
  • Fire Assay
  • Aqua Regia Acid Digestion

111
Assay Techniques
  • Assay procedures uses accurate representation of
    the mass of the sample being analyzed than in
    geochemical analytical techniques.

112
Wet Chemistry
  • It's just an informal term referring to
    chemistry done in a liquid phase. When chemists
    talk about doing "wet chemistry," they mean stuff
    in a lab with solvents, test tubes, beakers, and
    flasks (Richard E. Barrans Jr., Ph.D)
  • It utilizes a physical measurement, either the
    color of a solution, the weight or volume of a
    reagent, or the conductivity of a solution after
    a specific reaction
  • It is a preferred technique to determine element
    concentration in ore samples

113
Fire Assay
  • It is used to analyzed precious metals in rock
    or soil
  • Assay ton portion of the sample is put into a
    crucible and mixed with variety of chemical (lead
    oxide)
  • The mixture is fused at high temperature
  • During fusion, beads of metallic lead are
    released into the molten mixture

114
Fire Assay
  • The lead particles scavenge the precious metals
    and sink to the bottom of the crucible due to the
    difference in density between lead and the
    siliceous component of the sample known as slag.
  • On completion, the molten mixture is poured into
    a mold and left to solidify
  • After cooling, the slag is removed from the lead
    and the lead bottom is transferred into a small
    crucible known as cupel and placed back into a
    furnace

115
Fire Assay
  • The lead is absorbed by the cupel leaving a bead
    of the precious metals at the bottom of the cupel
  • Gold and silver is measured by weighing the bead
    on a balance
  • Silver is dissolved in nitric acid and the bead
    is weighed again to determine the undissolved
    gold
  • Silver is calculated by the difference

116
Aqua Regia Acid Digestion
  • The same procedure is used as in fire assay but
    different method of measuring gold and silver
  • Atomic absorption is used to measure gold and
    silver
  • Other forms of measurement include neutron
    activation analysis and flameless atomic
    absorption

117
Conclusion
  • Geochemical analysis is considered to be
    indicators of mineralization during the earlier
    stages of exploration
  • Assay techniques is used to determine absolute
    measurement of mineralization
  • It also determines if the ore deposit can be
    processed by conventional milling or in situ
    leaching or some other way

118
References
  • http//www.alsglobal.com/Mineral/ALSContent.aspx?k
    ey31metallics
  • http//www.amebc.ca/primer3.htmsampling
  • http//www.newton.dep.anl.gov/askasci/chem00/chem0
    0868.htm

119
DRILLING
120
DRILLING
Samuel Nunoo New Mexico Bureau of Geology and
Mineral Resources New Mexico Institute of Mining
and Technology, Socorro, NM 7TH FEBRUARY 2008
121
Outline
  • Introduction
  • Purpose
  • Types

122
Introduction
123
  • Drilling is the process whereby rigs or hand
    operated tools are used to make holes to
    intercept an ore body.
  • Drilling is the ultimate stage in exploration.

124
Purpose
125
  • The purpose of drilling is
  • To define ore body at depth
  • To access ground stability (geotechnical)
  • To estimate the tonnage and grade of a discovered
    mineral deposit
  • To determine absence or presence of ore bodies,
    veins or other type of mineral deposit

126
Types
127
  • Drilling is generally categorized into 2 types
  • Percussion Drilling
  • This type of drilling is whereby a hammer
  • beats the surface of the rock, breaks it into
    chips.
  • -Reverse Circulation Drilling (RC)
  • Rotary Drilling
  • This is the type of drilling where samples are
    recovered by rotation of the drill rod without
    percussion of a hammer.
  • - Diamond Drilling
  • - Rotary Air Blast (RAB)
  • - Auger Drilling

128
  • Percussion Drilling
  • Reverse Circulation Drilling (RC)
  • This type of drilling involves the use of high
    pressure compressors, percussion hammers that
    recover samples even after the water table.
  • The end of the hammer is a tungsten carbide bit
    that breaks the rock with both percussion and
    rotary movement .This mostly follows a RAB
    intercept of an ore body.
  • The air pressure of a RC rig can be increased by
    the use of a booster. This allows for deeper
    drilling.
  • Samples are split by special sample splitter that
    is believed to pulverize the samples. This is
    done to avoid metal concentrations at only
    section of the sample. Contamination is checked
    by cleaning the splitter after every rod change
    either by brush or high air pressure from rigs
    air hose.
  • RC drilling is mostly followed by diamond
    drilling to confirm some of the RC drilling ore
    intercept.
  • This type of drilling is faster and cheaper than
    diamond drilling

129
http//www.midnightsundrilling.com/ reverse_circul
ation.html
130
  • Rotary Drilling
  • Rotary Air Blast Drilling (RAB)
  • This type of drilling is common in green-field
    exploration and in mining pits.
  • This drilling mostly confirms soil, trench or pit
    anomalies.
  • It involves an air pressure drilling and ends as
    soon as it comes into contact with the water
    table because the hydrostatic pressure is more
    than the air pressure.
  • Samples cannot be recovered after the water
    table is reached.
  • Mostly a 4meter composite sampling is conducted.
    Every 25th sample is replicated to check accuracy
    of the laboratory analysis.
  • RAB drilling in the mine is mostly done for blast
    holes.

131
  • Rotary Drilling (Contd)
  • Diamond Drilling
  • This type of drilling uses a diamond impregnated
    bit that cuts the rock by rotation with the aid
    of slimy chemicals in solution such as
  • - DD200, expan-coarse, expan-fine, betonite and
    sometimes mapac A and B for holes stability.
  • Drill sample are recovered as cores sometimes
    oriented for the purpose of attitude measurement
    such as dip and dip directions of joints,
    foliation, lineation, veins.
  • Sampling involves splitting the core into 2
    equal halves along the point of curvature of
    foliations or along orientation lines. One half
    is submitted to the lab for analysis and the
    other left in the core yard for future sampling
    if necessary.
  • Standards of known assay values are inserted in
    the samples to check laboratory accuracy. Mostly
    high grade standards are inserted at portions of
    low mineralization and low grade standards into
    portions of high mineralization.
  • Diamond drilling is usually the last stage of
    exploration or when the structural behavior of an
    ore body is to be properly understood.

http//en.gtk.fi/ExplorationFinland/images/ritakal
lio_diamond_drilling.jpg
http//www.almadenminerals.com/geoskool/drilling.h
tml
http//www.istockphoto.com/file_closeup/
132
  • Rotary Drilling (Contd)
  • Auger Drilling
  • This is a type of superficial drilling in soils
    and sediments. It could machine powered auger or
    hand powered (manual).
  • It is mostly conducted at the very initial stage
    of exploration. That is after streams sediments,
    soils or laterite sampling.

http//www.geology.sdsu.edu/classes/geol552/sedsam
pling.htm
133
Thank You !!!!
134
GEOPHYSICAL LOGGING
  • Frederick Ennin
  • Department of Environmental
  • Engineering

135
INTRODUCTION
  • Geophysical logging is the use of physical,
    radiogenic or electromagnetic instruments lowered
    into a borehole to gather information about the
    borehole, and about the physical and chemical
    properties of rock, sediment, and fluids in and
    near the borehole
  • Logging make record of something
  • First developed for the petroleum industry by
    Marcel and Conrad Schlumberger in 1972.
  • Schlumberger brothers first developed a
    resistivity tool to detect differences in the
    porosity of sandstones of the oilfield at
    Merkwiller-Perchelbrom, eastern France.
  • Following the first electrical logging tools
    designed for basic permeability and porosity
    analysis other logging methods were developed to
    obtain accurate porosity and permeability
    calculations and estimations (sonic, density and
    neutron logs) and also basic geological
    characterization (natural radioactivity)

136
THE BOREHOLE ENVIRONMENT
  • Different physical properties used to
    characterized the geology surrounding a
    borehole-drilling
  • Physical properties porosity of gravel bed,
    density, sonic velocity and natural gamma signal
  • Drilling can perturb the physical properties of
    the rock
  • Factors influencing properties of rocks
  • Porosity and water content
  • Water chemistry
  • Rock chemistry and minerology
  • Degree of rock alteration and mineralisation
  • Amount of evaporites
  • Amount of humic acid
  • Temperature

137
APPLICATIONS
  • Became and is a key technology in the petroleum
    industry.
  • In Mineral industry
  • Exploration and monitoring grade control in
    working mines.
  • Ground water exploration
  • delineation of aquifers and producing zones
  • In regolith studies
  • provides unique insights into the
    composition, structure and variability of the
    subsurface
  • Airborne electromagnetics
  • used for ground truthing airborne
    geophysical data sets.

138
GEOPHYSICAL LOGGING METHODS
  • MECHANICAL METHODS
  • caliper logging
  • sonic logging
  • ELECTRICAL METHODS
  • resistivity logging
  • conductivity logging
  • spontaneous potential logging
  • induced polarisation
  • RADIOATIVE METHODS
  • natural gamma rays logging
  • neutron porosity logging

139
MECHANICAL METHODS
  • Caliper logging
  • caliper used to measure the diameter of a
    borehole and its variability with depth.
  • motion in and out from the borehole wall is
    recorded electrically and transmitted to surface
    recording equipment
  • Sonic logging
  • works by transmitting a sound through the rocks
    of the borehole wall
  • Consists of two parts
  • transmitter and receivers separated by
    rubber connector to reduce the amount of direct
    transmission of acoustic energy along the tool
    from transmitter to receiver

Crosshole Sonic Logging method with various kinds
of defects.  (Blackhawk GeoServices, Inc.)
140
ELECTRICAL METHODS
  • Used in hard rock drilling
  • Resistivity
  • probes measure voltage drop by passing current
    through rocks
  • Conductivity
  • measurements induction probes via
    electromagnetic induction
  • either in filled or dry holes
  • Spontaneous potential (SP) - oldest E-method
  • Measures small potential differences between down
  • hole movable electrode and the surface earth
    connection
  • Uses wide range of electrochemical and
    electrokinetic processes
  • Induced polarisation (IP)
  • Commonly used in surface prospecting for minerals
    and downhole applications.
  • Uses transmitter loop to charge the ground with
    high current
  • Transmitter loop turned off and voltage change
    with time is recorded.

141
(No Transcript)
142
RADIOATIVE METHODS
  • Natural Gamma logging
  • simplest, high penetration distance through
    rocks (1-2 m)
  • Depends on initial energy level and rock density
  • Records levels of naturally occurring gamma rays
    from rocks around borehole
  • Signals from isotopes K-40, Th-232, U-238
  • and daughter products-
  • provides geologic information
  • Sophisticated tools records emission from Bi-214
    and
  • Tl-208 instead of U-238 and Th-232
  • provides detailed chemistry of rocks in
    borehole
  • Successfully used to search for roll front
    uranium deposit in regolith

Secondary uranium minerals associated with
Gulcheru quartzite from Gandi area, Andhra
Gamma-ray Borehoole Logging Probe (Lead
Shielded)/System for measurement of high-grade
ore in borehole
143
RADIOATIVE METHODS
  • Neutron Porosity Logging
  • Measures properties of the rock close to the
    borehole
  • Very useful tool for measuring porosity
  • free neutrons almost unknown in the Earth
  • Neutron emission source
  • Active source emits into rocks around a borehole
  • Flux of neutrons recorded at the detector is used
    as indicator of conditions around surrounding
    rocks.
  • Neutron logging provides data under a variety of
    conditions in cased and uncased boreholes. .

144
RADIOATIVE METHODS
  • Effects
  • Hydrogen Exception
  • neutrons rapidly loose energy due to
    collision with hydrogen nuclei
  • (thermal neutron-like diffusing gas)
  • Changes in Diameter of boreholes affects results
  • Calibrated with limestone samples of differing
    water-filled porosities (equivalent limestone
    porosities)
  • Used in conjunction with other logging
  • methods in mineral geophysical logging in
    hard rock (lower porosities)

145
PROBLEMS AND LIMITATION
  • Problems
  • Biggest is the need for a well (ie. a borehole)
    to operate
  • High cost of drilling meaning boreholes are
    always
  • not available hence GWL will not be possible for
    a particular study.
  • Colapse of holes in regolith systems
  • while wireline logs are running solved with foam
    drilling
  • or plastic casing insertion.
  • Limitations
  • Recognition that each method has weaknesses and
    strengths.
  • PVC casing- prevents electrical logging neutron
    logging (hydrogen)

146
CONCLUSIONS
  • Geophysical well logging provides many different
    opportunities to investigate the material making
    up the wall of a borehole, be it regolith or
    crystalline rock.
  • A widen range of different sensors provide
    information which complementary in nature. Best
    results are obtained by running a suite of logs
    and analyzing their similarities and differences.

147
REFERENCES
  • Hallenburg, J.K., 1984. Geophysical logging for
    mineral and engineering applications. PennWell
    Books, Tulsa, Oklahoma, 254 pp.
  • Keys, W.S., 1988. Borehole geophysics applied
    groundwater investigations. U.S Geol. Surv. Open
    File Report 87-539, Denver.
  • McNeill, J.D., Hunter, J.A and Bosnar, M., 1996.
    Application of a borehole induction magnetic
    susceptibility logger to shallow lithological
    mapping. Journal of Environmental and Engineering
    Geophysics 2 77-90
  • Schlumberger, 2000. Beginnings. A brief history
    of Schlumber
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