prospecting& exploration
TRANSCRIPT
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Prospecting
Introduction
Prospecting Steps
eologic ExaminationsG
airborne Geophysics Groundgeophysical surveys
Exploration
Sampling Techniques
Channel sampling
Exploration Drilling
Drill Hole Patterns
Bulk Sampling Types
of analysis of samples
Pilot Testing
Feasibility Studies
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Introducti
on: Most modern metal production comes from large efficient operations requiring huge capital investments. Considering the nature of oredeposits, minerals, and the enclosing wall rocks, it is obvious that the fundamental basis for all prospecting is the science of geology. To
be effective, the prospector must possess considerable geologic knowledge and insight. It does not follow, however, that the prospector
must be a geologist. Corporate geologists involved in the search for minerals most often work as a part of a team of professional
specialists, technicians, contractors, and consultants.
A prospector and his equipment
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Prospecting Steps:
Search old reports & geological literature.
Study geologic & surface maps.
Study aerial & satellite photographs.
Conduct airborne geophysical survey if required.
Set up ground mapping procedures.
Conduct, geophysi al, geo-chemical and geological sampling surveys as required.c
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Geologic outcrop map of the North Empire Mining District
Geologic Examinations:
Photographic study Aerial
examinations Outcrop
mapping Trenching
Reverse circulation drilling
Core drilling
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Geo-chemical Sampling:
Soil sampling
Water sampling
Stream sediment sampling (panning)
Vegetation sampling
All of these samples are
subjected to chemical analysis
for low level concentrations.
The results are plotted on a
contour map of concentration.
The Viscaria copper mine in northern Sweden was discoveredwhen a prospecting geologist noticed concentrations of the
Viscaria flower, known to prefer copper rich soils.
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airborne Geophysics
Magnetic surveys
Electromagnetic surveys
Radiometric surveys
Remote sensing
Ground geophysical surveys
Gravity surveys
Magnetic surveys
Radiometric surveys Seismic surveys
Resistivity surveys
Self-potential surveys
Induced polarization surveys
VLF (Very Low Frequency Radio)
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Geophysics
Geophysics is the branch of science which studies the physical properties of the Earth.
In a typical geophysical survey, a physical property like the gravitational or magnetic field is measured on a grid of locations over
the survey area. The value found at each grid position is plotted on a plan view or section views of the property and contour maps
created.
Magnetic Methods
In magnetic surveying, the geophysicist measures the strength of the earth's magnetic field, which will vary locally depending on the
amount of magnetic material in the underlying rocks.
Where the rocks have high magnetic susceptibility the local magnetic field will be strong; where they have low magnetic
susceptibility it will be weaker.
Deposits with magnetic minerals iron,pyrrhotite bearing nickel, and skarns can be detected directly.
Magnetic surveying can be used as an aid to geological mapping; units with higher susceptibility will show up as areas of high
magnetic field strength.
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Resistivity
In this method, an electric current is generated and forced into the ground from widely spaced electrodes.
The current flows through the earth to complete the circuit, and the amount of current that flows depends on the resistance the rock
offers. This can be measured by probing the ground with pairs of electrodes connected to sensitive voltmeters. A conductive orebody
containing economic metallic sulphides will cause an anomalously low resistance. So, too, will a fault plane
lined with graphitic material, a barren sulphide, or a water course containing brackish solution.So results from this method must be interpreted using geological evidence.
Induced Polarization
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The Gravity Method
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The force of gravity is not uniform over the whole surface of the earth; it is actually slightly stronger where the underlying
rocks are more dense, and slightly weaker where they are less dense. The difference is tiny, but it can be measured and mapped.
Gravity surveys use extremely sensitive balances to detect the variations in density of the underlying rocks.
They can be useful in conducting a rapid reconnaissance survey of an area to delineate major rock types.
This information can help to indicate areas favorable to exploration by other methods.
They can also be used in more detailed exploration to detect mineral deposits, which are commonly denser than the rocks that surround
them.
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Seismic Methods
Small artificial shock waves are generated at a selected point by either firing a charge of explosives in a shallow drill hole or dropping a
heavy weight. The speed of the shock waves is measured by timing their arrival at sensitive receivers (geophones) placed along the survey
line.
Shock waves are acoustic waves, and like sound waves, they travel faster in rigid and dense bodies than they do in less rigid and less
dense ones.
They also reflect from the boundaries between different rock types, allowing the geophysicist to measure the time they take to travel and
determine the structure of the rocks below.
Seismic prospecting is the most widespread geophysical method in petroleum exploration.
Radiometric Methods
The presence of radioactive elements can be determined by the familiar Geiger counter. The instrument measures the energy released
during the process of radioactive decay. As a uranium molecule decays, for instance, three kinds of rays are given off: alpha, beta and
gamma rays.
Of these, the gamma ray is the most penetrating and is therefore the most likely to be detected by the Geiger counter. Gamma-ray
spectrometers are an even more advanced version of the scintillation counters. They an distinguish between radiation from the three
main radioactive elements that occur in nature -uranium, potassium, and thorium -by measuring the energy of the radiation.
Ground radiometric surveys are most useful to detect showings of radioactive minerals directly.
Airborne radiometric surveys are often used for geological mapping, because the radioactive elements occur in greater
abundance in granitic rocks. Down-hole probes are frequently used to measure the radioactivity of rock units encountered in
drill holes.
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Exploration
Exploration determines the geometry, extent, and worth of a mineral deposit using techniques similar to but more precise than
those in prospecting.
Sampling Techniques
Extensive sampling and analysis must be performed before a mineral deposit may be evaluated.
Types of sampling:
surface outcrop sampling
channel samples in underground workings
drilling
percussion
drilling
rotary
drilling
reverse
circulationdrilling
rilling
(diamond
drilling)core bulksampling
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Channel sampling
Channel samples consist of cuttings collected from a grove cut into the
rock about 4 inches wide and 0.75 in deep.
Various tools such as a hammer and moil or a pneumatic chisel can be
used to cut the sample.
Rock fragments are collected on a canvas tarp on the floor and sent forassaying.
Exploration Drilling There are two basic types
of rock drills:
Percussivedrilling by hammering
Rotaryrotation and thrust drilling by
crushing, cutting, and wearing
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Rotary Percussion Drilling for Exploration
One of the simplest and least expensive methods
Depth limited to about 300- 500 ft.
Pneumatic or hydraulic drive.
Air or water circulation for cuttings removal.
Samples relatively fine cuttings.
Works best in competent and dry rock.
Good sample quality above water table.
Below water table, poor to fair quality.
Most common method Down-the-Hole hammer.
Cyclone for sample collection.
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Disadvantages-potential problemsraveling of hole walls
water inflow in clayey
materials
hole erosion causing sample
contamination
loss circulation
less recovery with increasing
hole depth
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Rotary Drilling
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Most commonly a tricone bit.
Generally faster and cheaper than percussion.
Greater depths, up to about 2000 ft.
Air or drilling mud circulation.
Fine-grained cuttings.
Fair sample quality for mud drilling.
Good sample quality for air drilling.
Usually the same disadvantages as percussion.
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Reverse Circulation Drilling
Double-wall drill pipe
Air or water or combination down the annulus
Cuttings carried up the inside pipe
Cuttings recovered by cyclone
Most applications: tricone bit
Hard formations: Down-the-Hole hammer
Accurate geologic sampling
Good quality samplesCasing serves to minimize contamination
Used widely in low grade gold and oxide copper
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Most useful and accurate sampling.Most versatile of all drilling methods.
Designed for mineral exploration.
Truck mounted, skid mounted or hand-portable.
Wire line preferred, but smaller core diameter.
In shallow holes, wire line may not provide any time savings.
Disadvantages of diamond core drilling More costly than other methods Slower than other
methods Produces a relatively smaller sample
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Drill Hole Patterns
a) random, b) str atified random c)
regular, d) biased