School of Environmental Sciences
Department of Mining and Environmental Geology
STUDENT NUMBER
FULL NAMES
COURSE
LECTURER
11602169
MBEDZI ADAM
MEG3641: EXPLORATION AND MINING GEOLOGY
PROF. J.S. OGOLA
TOPIC: MINERAL PROSPECTING AND EXPLORATION ENCOMPASSES THREE MAIN AREAS:
GEOLOGICAL, GEOCHEMICAL AND GEOPHYSICAL. WITH EXAMPLES, EXPLAIN THE
APPLICATION OF THESE TECHNIQUES THE SEARCH OF AND ASSESSMENT OF MINERAL
RESOURCES.
CONTENTS
1. Introduction……………………………………………………………………………………………. 2
2. Background of mineral prospecting and exploration………………………………. 2
3. Mineral prospecting and exploration techniques……………………………………. 3
3.1. Geological technique……………………………………………………………………….. 3
3.2. Geophysical technique…………………………………………………………………….. 4
3.3. Geochemical technique……………………………………………………………………. 5
4. Conclusion……………………………………………………………………………………………… 6
5. References……………………………………………………………………………………………… 7
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1. Introduction
Prospecting involves searching a district for mineral deposits with the view to mine it at a
profit i.e. to transform a mineral occurrence into an orebody. The object of search is to
establish the presence of a deposit and evaluate its promise from the geological point of
view. This includes study of the local geological and economic conditions to the extent
necessary to answer the main questions concerning further, exploration. Exploration, while
it sounds similar to prospecting, is the term used for systematic examination of a mineral
occurrence. After a mineral occurrence has been identified from different potential areas,
an application for exploration permit is made.
Approval by officials is needed before exploration activities can commence. It is not easy to
define the point where prospecting turns into exploration, but the scale at which each of
these processes are conducted and the factors taken into consideration are the basis of
distinction between the two processes. The main objective in mineral exploration is to be
fairly certain that the mineral occurrence is economically viable by providing a detailed
knowledge of the geology for a clear financial picture. Ore is an economic concept, defined
as a concentration of minerals, which can be economically exploited and turned into a
saleable product. Before a mineral deposit can be labelled as an orebody, full knowledge is
required about the mineralization, proposed mining technology and processing methods.
2. Background of mineral prospecting and exploration
Many fundamental principles of geology and chemistry were known in antiquity, and
references to the use of chemistry in the search for mineral deposits are not infrequent in
both classical and Renaissance literature. The techniques of modern geochemical
prospecting originated in the Soviet Union and Scandinavia, where extensive research into
methodology was conducted during the 1930s. After World War II these techniques spread
to the western world and were further developed; by 1960 they had become widely used by
both government agencies and mining companies. By 1970 geochemistry had become firmly
established as one of the most effective tools of mineral exploration.
Several factors contributed to the rapid development of geochemical prospecting during the
twentieth century. It was found that most metallic mineral deposits are surrounded by halos
of abnormal trace-element concentrations in the adjacent and enclosing rocks. Also,
abnormal trace-element concentrations in materials such as glacial sediment, soil, spring or
stream water, and stream sediment were recognized as being derived from the weathering
of mineral deposits. Precise and rapid methods of chemical analysis suitable for the
detection of low concentrations (a few parts per million, or even parts per billion) of
elements and compounds in natural media were developed.
These methods include use of the emission spectrograph, specific and sensitive colorimetric
reagents, atomic absorption spectrometry, and development of polyethylene laboratory
equipment. The effectiveness of geochemical exploration has been greatly enhanced by the
use of computer-aided statistical techniques for processing and evaluation of data. Sampling
techniques have become steadily more effective with the use of helicopters and devices
such as overburden drills.
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Understanding of the significance of landscape in geochemical exploration has progressed
considerably, permitting the most effective set of field techniques and interpretive
procedures to be selected for any given set of field conditions. Geochemical prospecting is
employed extensively in all regions of the world from the Arctic to the tropics, and has
contributed significantly to the success of many important mineral exploration programs.
3. Mineral prospecting and exploration techniques
The first step is to conduct a review of historical and existing data from maps, aerial photos,
satellite images and other sources, data can also be taken from closed down mines and
terminated exploration there often exist core samples and other relevant information
which can be accessed. This can result in great savings in time and money required for new
activities. One of the cheapest phases of property exploration is preparation of a
comprehensive, detailed and accurate geological map which often starts with basic
instruments such as tape and compass. The accuracy can be enhanced by using air photos
to help locate outcrops, major fault zones and basic topographic control. Each step adds
some more costs, but it also improves the accuracy and detail of the resulting map.
Soil-covered ground is inaccessible to the prospector, whose first check would be to look
for an outcrop of the mineralization. Where the ground cover comprises a shallow layer of
alluvial material, trenches can be dug across the mineralized area to expose the bedrock. A
prospector will identify the discovery, measure both width and length, and estimate the
mineralized area. Samples from the trenches are sent to the laboratory for analysis. Even
when minerals can be found on the surface, determining any extension in depth is a matter
of qualified guesswork. If the prospector's findings and his theorizing about the probable
existence of an orebody are solid, the next step would be to explore the surrounding
ground. Exploration is a term embracing geological, geophysical, geochemical, and finally
the more costly activities which drilling into the ground for obtaining samples from any
depth.
3.1.
Geological technique
Geological prospecting criteria mean such geological settings, which point to the possibility
of discovering various mineral deposits. The geological observations and analysis recorded
on geological, tectonic and geomorphological maps are very important for prospecting.
However, geological maps give too general idea of a district and outline too vast area where
deposits of one mineral or another may possibly be discovered. Besides the various
geological maps, different satellite imageries and aerial photos are widely used in geological
exploration. At present, use of computers and digitised data is also gaining an impact in
developed countries. Though interdependent, geological mapping and prospecting are not
the same operation, and therefore should be considered and planned separately. In view of
this it is necessary to develop and apply various prospecting methods based on the
geological map.
The geological technique itself encompasses many methods: for example, River Float
Tracing which is one of the oldest prospecting methods. This method consists in finding and
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tracing ore-bearing fragments and fragments of the country rocks. A rough idea of distance
the float has travelled is given by the degree of wear. If float is found in the channel, or on
the banks of a stream, it is followed along a certain line known as a traverse. Fragments
usually become more and more numerous and less water-worn. When float is no longer
found in the alluvium, this is taken as an indication that this is the spot where it begins to
come from hillside waste. The search is then continued up-slope, and trenches and shallow
test pits are dug near the spot where the last pieces of float were found. Traverses are
sometimes planned across the strike of the rocks rather than parallel to a river or
approximately along a single contour line around a hill if the object is to find ore-bearing
debris at its foot.
Another example include, Panning which is similar to float tracing, this is based on the
recognition and tracing of small pieces of metal and ore minerals which have migrated from
outcrops and appear in concentrates obtained by panning alluvial and colluvial material
taken at regular intervals along the sides of valleys and rivers and streams, and on tracing
them to their source. Three main tasks are accomplished by panning:
 the location of primary deposits of various minerals;
 the location of areas of alluvium, colluvium and eluvium carrying increased
concentrations of economic minerals, i.e. placer deposits;
 Ascertaining the general geological and mineralogical characteristics of the area
(usually by panning crushed material and further study of concentrates).
3.2.
Geophysical technique
The science of geophysics applies the principles of physics to the study of the Earth.
Geophysical investigations of the interior of the Earth involve taking measurements at or
near the Earth’s surface that are influenced by the internal distribution of physical
properties. Analysis of these measurements can reveal how the physical properties of the
Earth’s interior vary vertically and laterally. The natural field methods utilize the
gravitational, magnetic, electrical and electromagnetic fields of the Earth, searching for local
perturbations in these naturally occurring fields that may be caused by concealed geological
features of economic or other interest. Artificial source methods involve the generation of
local electrical or electromagnetic fields that may be used analogously to natural fields, or,
in the most important single group of geophysical surveying methods, the generation of
seismic waves whose propagation velocities and transmission paths through the subsurface
are mapped to provide information on the distribution of geological boundaries at depth.
Geophysical exploration is usually supported by geological data to able to identify potential
areas and have an expectation of what to encounter in the field.
The five important geophysical methods relate to five most common characteristics of the
earth, which can be determined from the surface, viz. (1) electrical conductivity, (2) density,
(3) magnetism, (4) elasticity and (5) radio activity. These can be detected using geophysical
methods related to their properties and are presented in the table below.
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Method
Seismic
Measured Parameter
Travel
times
of
reflected/refracted seismic
waves
Gravity
Magnetic
Electrical
Resistivity
Induced polarization
Self-potential
Electromagnetic
Radar
Operative Physical Property
Density and elastic moduli,
which
determine
the
propagation velocity of
seismic waves
Spatial variations in the Density
strength of the gravitational
field of the Earth
Spatial variations in the Magnetic susceptibility and
strength of
remanence
the geomagnetic field
Earth resistance
Electrical conductivity
Polarization voltages or
frequency-dependent
ground resistance
Electrical potentials
Response to electromagnetic
radiation
Travel times of reflected
radar pulses
Electrical capacitance
Electrical conductivity
Electrical conductivity and
inductance
Dielectric constant
Examples of application of these methods include:
 Self-Potential or S.P. Method: This method utilises the natural flow of current and
oerates on fundamental principle that an ore body, undergoing oxidation, is a source
of electric current. If a tabular sulphide ore body is present in the ground, oxidation
at the upper levels near P induces greater chemical activity than at Q. Hence a
potential difference is induced; and a current flows from P towards Q. Two types of
circuits are employed to measure the weak earth currents: (1) potentiometer and (2)
micro-ammeter.
 Induced Polarisation (I.P.) Method: It has been observed, in resistivity surveys, that
on disconnecting the battery from current electrodes, the voltage in potential
electrodes does not drop to zero immediately, but persists for some time with a
continuously decreasing magnitude. This phenomenon is termed as induced
polarisation or IP. IP measurements can be made by (a) Time domain method, and
(b) Frequency domain method.
3.3.
Geochemical technique
Geochemical prospecting is concerned primarily with the examination of the earth’s
crust, comprising not only the rocks, but also the waters and the gases, with a view to
locate mineral deposits. Geochemical prospecting for minerals includes any method of
mineral exploration based on systematic measurement of the chemical properties of a
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naturally occurring material. The purpose of the measurements is the location of
geochemical anomalies or of areas where the chemical pattern indicates the presence of
ore in the vicinity. Anomalies may be formed either at depth by igneous and
metamorphic processes or at the earth's surface by agents of weathering, erosion, and
surficial transportation. Geochemical anomalies of deep-seated origin primary
anomalies may result from (1) apparent local variation in the original composition of the
earth's crust, defining a distinctive "geochemical province" especially favourable for the
occurrence of ore, (2) impregnation of rocks by mineralizing fluids related to ore
formation, and (3) dispersion of volatile elements transported in gaseous form.
Examples of application methods include:
 Hydrogeochemical Method: It is based on the study of hydrchemical haloes of
dispersion and consists of analysing the chemical composition of subterranean
waters, which in the vicinity of ore bodies show increased concentrations of ore
constituents (chiefly U, Mo, Zn and Cu). And then to trace their flow up to the
source.
 Biogeochemical Method: The root system of plants, which sometimes pierces the
soil to a considerable depth, assimilates many metals (Mn, Cu, Zn and others)
together with nutritive substances. Such metals cumulate in the plant tissues
(bark, wood, leaves). The samples are taken from plants of a single species,
better from one and the same part, being then reduced to ashes, which then go
for a spectral analysis. Its finding undergoes the same processing as in the case of
metallometric surveying.
 Gas Surveying: It is used to outline the dispersion haloes of different gases, which
seep through from depth to the surface. Samples are taken from sampling points
located in a dense regular pattern by means of hand augers adapted to
withdrawing gas from a depth of 1.5-2 m.
4. Conclusion
Many prospecting and exploration techniques are commonly used in discovering and
evaluating mineral occurrences, and help to quantify these mineral occurrences by
providing enough information to allow mine development or to give the actual value of a
mineral occurrence. Although these techniques have the potential to identify mineral
occurrences, the full quantification of a mineral resource cannot be finalised based on one
method i.e. the complete application of the techniques works collectively to achieve or to
provide necessary information about a mineral deposit to allow mining. These techniques
can also be used to identify pollutants and record their dispersion from mine areas; their
application is not limited to studies of this sort. For instance, geophysical monitoring of
pollutant activity, which requires significantly greater study, is another aspect of
geoenvironmental investigations. Monitoring differs from detection chiefly in recurrent use
of geophysical methods in specific. The effort required extending application of prospecting
and exploration techniques to naturally occurring pollutants related to mineralized, but
unmined, rock or to other Cultural concentrations of toxic or assistance in meeting national
needs for healthy national environmental conditions of potentially toxic substances is
minimal.
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References
Birnie, R.W., Francica, J.R., 1981, Remote detection of geobotanical anomalies related to
porphyry copper Mineralization: Economic Geology, v. 76, p.637-647.
Brown, G.C., Cassidy, J. Oxburg, E.R., Plant, J., Sabine, P.A., and Watson, J.V., 1980,
Basement heatflow and Metalliferous mineralization in England and Wales: Nature, v. 288,
p. 657-659.
Corwin, R.F., 1990, The self-potential method for environmental and engineering
applications, in Ward, S.W., Geotechnical and environmental geophysics, v.I: p. 127-145.
Durrance, E.M., 1986, Radioactivity in geology, principles and applications: Ellis Horwood
Ltd., 441 p.
Guerin, Roger, and Benderitter, Yves, 1995, Shallow karst exploration using MT-VLF and DC
resistivity methods: Geophysical Prospecting, v. 43, no. 5, p. 635-654.
Paterson, Norman, 1995, Application of geophysical methods to the detection and
monitoring of acid mine drainage, in Bell, R.S., ed., Proceedings of the Symposium on the
application of geophysics to engineering and environmental problems, Orlando, Florida,
April 23-26, Environmental and Engineering Geophysical Society, p. 181-189.
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