Prospecting& Exploration

7/31/2019 Prospecting& Exploration

1/24

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


2/24

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


3/24

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


4/24

Geologic outcrop map of the North Empire Mining District

Geologic Examinations:

Photographic study Aerial

examinations Outcrop

mapping Trenching

Reverse circulation drilling

Core drilling


5/24

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.


6/24

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)


7/24

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.


8/24

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


9/24

The Gravity Method


10/24


11/24

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.


12/24

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.


13/24

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


14/24

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


15/24

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.


16/24

Disadvantages-potential problemsraveling of hole walls

water inflow in clayey

materials

hole erosion causing sample

contamination

loss circulation

less recovery with increasing

hole depth


17/24


18/24

Rotary Drilling


19/24

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.


20/24


21/24

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

http://www.midnightsundrilling.com/reverse_circulation_anim.html
http://www.midnightsundrilling.com/reverse_circulation_anim.htmlhttp://www.midnightsundrilling.com/reverse_circulation_anim.html


22/24

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


23/24


24/24

Drill Hole Patterns

a) random, b) str atified random c)

regular, d) biased

Prospecting& Exploration

Documents

Transcript of Prospecting& Exploration