Know your resources

1. Mineral Exploration and Evaluation (Ersc 607)
Contents:
Introduction to mineral resources and exploration
Historical background of mineral exploration
Types, phases and sequences of mineral exploration planning, and
management of mineral exploration programs.
Sampling and analytical techniques: sampling and sample preparation,
laboratory techniques
Exploration methods
Geological mapping and prospecting;
geochemical prospecting (distribution of elements, primary and
secondary dispersion, treatments of the data and types of geochemical
survey
geophysical prospecting (gravity, magnetic, electric and electromagnetic,
seismic and radiometric surveys)
Presentation and interpretation of exploration data
Resource evaluation (ore reserve estimation, feasibility studies, piloting
of mining operation

2. Part one
Introduction to Mineral Resources and Exploration
• Definition:
 Mineral exploration is the process of finding economically viable
accumulation of minerals/rocks.
 It is a scientific investigation of the earth’s crust to determine if
there are mineral deposits present that may be commercially
developed.
• Minerals: are naturally occurring solid chemical compounds
with definite chemical compositions and characteristic crystal
structures.
• Mineral Resources: Mineral resources can be defined as non-
living, naturally occurring substances that are useful to us,
whether organic or inorganic in origin.

3. Historical Background of Mineral Exploration
What were some of the first resources used?
 Water
 Salt (the mineral Halite) - The word salary comes from the Roman
word for salt. People were paid in salt.
 Rock that could be shaped for making tools for hunting and
gathering.
What were the first metals used by civilization?
 Gold and copper were used before 15,000 B.P. why? Because they
are found in their native state!
What are the metals of antiquity? The metals of antiquity are the
seven metals which mankind had identified and found use for in
prehistoric times. These elements, gold, silver, copper, tin, lead,
iron, and mercury, are the metals from which our modern world
was forged.

5. Mineral Exploration
• Prospecting(finding places where ores occur) and exploration may
discover evidence of a mineral occurrence and outline its size and
character, but ore deposits that support a mining operation are
"made" through the collective efforts of project geologists,
geophysicists, geochemists, metallurgists, engineers, chemists,
lawyers, and even politicians.
• An ore body, strictly speaking, is that part of a mineral deposit
which can be mined and marketed at a profit under contemporary
technological, economic and legal conditions.
Objectives of mineral exploration
• The principal objective of mineral exploration is to find economic
mineral deposits that will appreciably increase the value of a
mining company's stock to the shareholders on a continuing basis,
or to yield a profit to the explorer.

6. Stages in Mineral exploration
• The process of developing mineral resource can shortly be
expressed as a three step process: Prospecting (search and
discover), Exploration (study and evaluate) and Mining (extract
and process).
• However the following can be taken as one of the commonly used
phases/stages in mineral resource development process.
Stage 1 – Exploration Planning: involves five main activities:
a. Commodity selection b. Regional assessment (Desk study) c.
Preliminary result evaluation d. Organization e. Budgeting
Stage 2 - Reconnaissance Stage
• The general objective of reconnaissance stage is selection of small
area (target generation) for detailed (follow-up) exploration
thereby reducing the search area.

7. Stage 3 – Initial Follow-up
• This stage is dedicated to appraise or evaluate the targets selected during
reconnaissance. It involves: Detailed geologic mapping, Detailed
geochemical sampling, Large scale ground geophysics, Limited shallow
drilling, Pitting and trenching.
Stage 4 – Detailed Follow-up
• This stage is devoted to ore body exploration. The methods employed
are the same as previous stages but at detailed scale, close exploration
grid and closer sampling intervals. The purpose of detailed follow-up
phase is to access the deposit in 3D:
• Size, Morphology, Quality, Maximum depth, Extension (along dip
and strike) etc
Stage 5 – Feasibility study
• Feasibility study is a complex phase involving both geologic and
non-geologic issues. The geologic issues concentrate on the nature
and amenability of the ore body for processing. The non-geologic
aspect involves engineering and economic analysis of the mining
operation.

8. • Activities to be conducted during feasibility stage include:
• Drilling for reserve calculation
• Metallurgical test
• Mine design and pilot mining (test mining)
• Select suitable ore dressing method
• Geotechnical studies
• Select type of mining
• Economic analyses, and
• Make ready the deposit to mining.
Stage 6 – Construction and Mine Development
Activities include:
• Site construction
• Further drilling to see ore extension
• Shaft sinking or overburden removal
• Construction of processing plant
• Employment process, and
• Installing mine safety measures.

9. Stage 7 – Extraction
• Extraction is removal of the ore material from the ground and
associated ore beneficiation activities.
Stage 8 – Mine closure
• Every mineral deposit, no matter how large, has a finite life and will
one day be exhausted (i.e. mining will be over at least for that
specific area).
• After the mining life is over, the extraction activity will cease
unless more reserve is discovered through exploration efforts
around the discovered ore. This phase includes:
• Dismantling equipments
• Reduce number of workers, and
• Install/implement environmental rehabilitation & protection
measures.
•

10. prospecting criterion
• In the search for mineral deposits, it is impossible to examine in
details every square km of the area or country by, for example,
drilling (why?).This would be too expensive, time-consuming and
in most cases pointless.
• Recognition of the environment and existence of potentially
economic mineral deposits may be based upon a variety of
geological criteria:
1. Stratigraphic (age) criteria (important in the search for
sedimentary deposits e.g. coal, oil & gas, u, Fe, placer deposits
etc.). Ages of mineralization - e.g. banded iron formation deposits
are characteristic of Precambrian age rocks.
2. Lithological criteria (different rock formations are characterized
by deposits of definite lithological composition). Association with
specific types of igneous rocks -- e.g., copper with quartz-
monzonite porphyry, diamonds with kimberlite pipes, tin with
granites, etc. . Host rock association -- e.g. lead and zinc with
carbonate rocks.

11. 3. Structural criteria. Structural controls -- e.g. laterite deposits
associated with unconformities, replacement deposits associated
with crests of anticlines.
4. Magmatogenic criteria (basic magma, granite magma and
alkaline magma)
5. Metamorphic criteria (metamorphic facies are criterion for
metamorphic deposits)
6. Geochemical criteria (the behavior of elements in the earth’s
crust is governed by certain laws; some are typical of basic rocks
and others of acid igneous rocks sediment. Some elements never
occur together in the same ore province (Cu and Sn), on the
contrary, the presence of other)
7. Geomorphological criteria (mainly for placer deposits, direct
criteria concerns the surface feature of the deposit, which can be
either positive or negative, indirect criteria such as tectonic steps,
hogbacks, cuestas, reveal the tectonic structure of the area.

12. 8. Paleoclimatic criteria (particularly important in prospecting for
deposits related to weathering crust)
9. Weathering effects -- e.g. oxidation of pyrite leaves a residue of
iron oxide gossan marking possible underlying deposits.
10. Wall rock alteration -- e.g. a concentric pattern of
feldspathization, sericitization and propylitization around
porphyry copper deposits, and dolomitization around lead-zinc
replacement deposits.
11. Gangue mineral association -- e.g. gold associated with quartz-
ankerite veins.
12. Trace metal association -- e.g. gold associated with arsenic and
mercury in trace amounts.
13. Ore and gangue mineral in fresh or oxidized states in outcrop
of derived sediments may give surface evidence of underlying or
adjacent deposits.

13. 14. Products of alteration zones from residual deposits like
gossan
15. The presence of pathfinders
16. The presence of sulfide minerals in outcrops
17.Identification of suitable structures favorable for
mineralization: major shear zone and contacts between various
lithological units, volcano-sedimentary units, conglomerates

14. Chapter Two
Geological Mapping and Prospecting
Geological Method, why make a map?
• Conceptual tools can then help in the interpretation of isolated
outcrops and drill hole intercepts that might be available in and
adjacent to covered areas.
• The geological observations and analysis recorded on geological,
tectonic and geomorphologic 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.
• Though interdependent, geological mapping and prospecting are
not the same operation, and therefore should be considered and
planned separately.
• the following working scales are generally taken for geological
prospecting.

15. The geological prospecting method (apart from the geological
mapping) considers the river and glacial float tracing and panning.
River Float Tracing: It is one of the oldest prospecting methods.
This method consists in finding and tracing ore-bearing fragments and
fragments of the country rocks.
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.

16. • Glacial Float Tracing: The prospector is guided by the material
brought down by glaciers.
• The movement direction of glaciers (especially the last movement)
is important. It is determined by striations on the rocks
• they are often found by local residents, or in excavation made for
canals and roads.
• Panning: Like 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.

17. Why we make a Map?
• A geological map is a graphical presentation of geological
observations and interpretations on a horizontal plane.
• A geological section is identical in nature to a map except that data
are recorded and interpreted on a vertical rather than a horizontal
surface.
• geological mapping is a method of recording and organizing
observations, much of its power in targeting lies in providing
conceptual insight of value.
• Depending on scale there are different kinds of geological map.
With large-scale maps, the geologist generally aims to visit and
outline every significant rock outcrop in the area of the map.
• In a small-scale map, visiting every outcrop would be impossible;
generally only a selection of outcrops are examined in the field and
interpolations have to be made between the observation points.

18. • By convention, large-scale refers to maps with a small scale ratio
(that is, a large fraction) – e.g. 1:1,000 scale or 1:2,500 scale.
• Small-scale refers to large scale ratios (a small fraction) such as
1:100,000 or 1:250,000. Generally, anything over 1:5,000 should
be considered small-scale, but the terms are relative.
Intelligent Mapping
• Most of the time of the intelligent mapper is thus spent in the areas
of “fertile” outcrop where there is most to be learned, and less time
is spent in those areas where the rocks are uniform – in the latter
areas a lower density of observation will serve.
Geological prospecting includes:
• Studying documentation ( archives , geological and topographical
maps , aerial photo interpretation, bibliography and other
information)
• Choosing or selecting of an area
• Inspecting of mining field (eg. Quarry) which have been
abandoned , or even of fields still under operation

19. • Even from scratch based on reports of minerals
• Geological mapping
• From satellite images
• Aerial photographs
• Topo map
• Field checking aided by ground investigation (gossan, rock
alteration, sampling out crops etc.)
• Geological methods rely on the identification of rocks and minerals
and an understanding of the environment in which they formed.
• Based on known "environments for mineralization" or models for
mineralization, regional geological surveys can be used to define
smaller areas in which more detailed studies can be undertaken.
A geological survey can be undertaken using a number of methods
depending on the size of a region and the amount of information
that is required.

20. • Remote Sensing-some geological mapping can be done using
satellite remote sensing methods. While most of these methods
rely on geophysical rather than pure geological data, the use of
this method can give broad scale views of surface geological
structures such as folding, faulting, igneous intrusions etc.
• Air photo interpretation-this can give a broad overview of the
geological relationships of an area with no detailed knowledge of
the mineral composition or fabric of the rocks.
• Outcrop surveys-this is normally achieved by geologists driving
along roads and walking traverses along creeks and rivers
mapping the outcropping rock types.
Geological mapping includes:
• a) Geological indications of a possible mineral body include
presence of gossans or leached capping, rock alteration.
• b) Structural intersections, breccia, fold axes.
• c) Favorable rock types.
• d) Topographic features suggesting anomalous rock conditions.

21. • IN GEOLOGICAL exploration methods the following works
could be the technical methods: Trenching, Pitting , and Drilling

22. Chapter Three
Sampling and sample preparation
• Economic mineral deposits are sampled to ascertain the grade of
minerals, which is sometimes important for the commercial
evaluation of a deposit.
• This is achieved by taking samples from mine openings, boreholes
and natural exposures.
• The results of sampling furnish the necessary information for
determining:
 the mean thickness of mineral bodies
 the technical and technological properties of useful minerals
 delineate the mineral bodies
 correlation of individual constituents and elements in the ore
 establish the priority in mining the minerals
 their losses and dilution during exploitation

23. Different types of sampling for different purposes
• Sampling may be chemical, mineralogical, technical and
technological.
1. Chemical: Samples are taken for determining the content of
useful and secondary components.
2. Mineralogical: It is done to ascertain the mineral and
Petrographical composition of the mineral. It helps to establish
the origin of the deposit, the dependences governing grade
variations and also to plan the ore dressing and beneficiation.
3. Technical: Samples are taken to study the technical properties of
the raw material, which does not require metallurgical or
chemical treatment. Thus in the case of building stone, it is their
bearing capacity, in the case of asbestos – the length, strength and
flexibility of fibers; mica – the size; sand and gravel – grain size
distribution, etc.

24. 4. Technological: Samples are collected for the study of the
technological properties of the raw material in the course of its
beneficiation and processing.
Sites of sampling
• Surface
- surface outcrops of any possible rock types having ore indication,
- old working and old dumps, soil, broken ore,
- bottom or the walls of pits and trenches,
• Underground :
• walls and /or roofs of adits, cross-cuts, drifts, raises, winzes and
sometimes shafts.
• In drill holes:
• either core or cuttings from bore holes
• During mining activities:
- they are taken as bulk samples from blasted material

25. Methods of sampling: point or spot, face or lump, channel or trench,
drill or shot hole, chip and bulk sampling.
Point or Spot Sampling consists of taking a number of equal
portions of a mineral at points distributed in a regular grid over a
work face ore mineral exposure.

26. Face or Lump Sampling: This method of sample taking may be
referred to the group of point sampling. It is a very simple, quick
and cheap procedure, but the taking sample is often done
subjectively and for this reason, the accuracy of the method is
rather low.
Channel or Trench Sampling: It is most widely used and consists of
scooping out a rectangular channel across the entire thickness of a
mineral deposit or a certain part there of.
• Drill and Shot Hole Sampling: It is applied on ore deposits. This
is employed in collecting samples for chemical assaying. The
samples are taken from blast holes drilled in driving mine
workings, or from special sampling bore holes.
• Drill holes intended for taking samples are disposed along the line
of the greatest regularity or across the thickness of mineral body.
• The number of drill holes depends upon the degree of the
irregularity: a uniform ore may be sampled from a single drill
hole; with an extremely variable (irregular) ore samples are taken
from 3 to 4 holes per each advance of the face.

28. • This type of sampling (irregular) has the merit of a possible
collection of specimens beyond the range of a mine opening, i.e. it
enables thick ore bodies unexposed by the opening to be sample-
tested.
• The method has, however, substantial disadvantages, such as: (1)
it is not always possible to locate drill holes along the line of the
maximum irregularity, (2) thin ore bodies cannot be test-sampled,
(3) sectional sampling is lacking.
• Chip Sampling consists of chipping off a uniform 3 to 10 cm
thick layer of ore from the entire work face.
• This method is not widespread and has limited use, chiefly in the
exploration and extraction of thin veins and deposits with a most
regular distribution of values (Au, Platinum group of minerals,
rare earth elements).
• Bulk Sampling consists of taking large (up to 10,000 kg) sample,
their volume not infrequently reaching scores of cubic meters.
Bulk samples are collected for making technological laboratory
and sampling mill and smelter tests

29. Sampling of Exploratory Bore Holes
• In the case of core drilling, the sampling material comes from the
core, and sludge. To make sure of complete core recovery and
obtain representative samples double core barrels are used.
Recovery (C.R.) = l/L * 100% Where l = length of the core, and L =
bore hole length.
• Sludges are less valuable material than the core samples because of
their being contaminated and incomplete catching. Therefore, when
the core recovery is as high as 70 to 80% no sludge samples are
taken.

30. Core sample

31. Sample Spacing
• The distance between the sampling sites is determined by the
variability of mineralization and the size of the deposit as well as
by the objectives and detailed nature of the investigation.

32. Treatment of Samples
• Bulk samples of 50 to 10,000 kg for pilot and mill tests are usually
shipped in their natural state.
• Sieve and fractional analyses are usually carried out right on the site.
• A representative samples a specimen in which the content of the
constituents in the reduced sample accord well with their content on
the face.
• In order that a mineral sample of minimum but satisfactory weight it
is recommended to take into consideration the following factors:
a) The structure or the texture of the ores; when sampling ores of
brecciated and mottled textures, the required samples must be of a
greater weight than in sampling ores of massive structure and banded
texture,
b) The grain size of the ore minerals; the coarser the grains, the greater
should be the weight of the sample,

33. c) The number of ore mineral grains in the sample; with the sample
containing a large number of the ore mineral grains the reduction
error is minimized.
d) The unit weight of the useful component; the greater the difference
in the unit weights of the ore and gangue minerals, the heavier
must be the sample.
e) The higher in the average metal content in the ore and the more
uniform in the distribution of the component therein.
f) The degree of the chemical assay precision; the greater the
accuracy demands on the analysis, the heavier should be the
sample. Generally:
• Treatment of samples consists of crushing, sieving, mixing and
reduction. A sample is treated in several stages. Crushing is done to
the following sizes: coarse 100-30 mm, intermediate 12-5 mm, fine
0.7 mm, superfine 0.15 0.07 mm. A sample is passed through
standard sieves of different sizes.
• Before reducing a sample, it is mixed several times to obtain a
homogenous mixture. A most common reduction procedure is
quartering.

34. SAMPLE PREPARATION
Rock samples
• The objective of a precise sample preparation scheme is to produce
a representative and meaningful test sample (regularly about 100 -
150 g) from a large bulk sample.
• The grain size of the prepared sample must be so fine that the
element of interest (or host mineral) can be properly liberated from
the bulk matrix and distributed in the pulp to produce a
homogeneous distribution sufficiently representative for
preceding analytical methods.
• This is particularly important for low-concentration ores (e.g. Au
and PGE’s) where the number of mineral particles producing ore
concentration is always low.
• Different minerals behave differently during pulverization – most
(brittle) minerals will easily breakdown to small particles while
some (e.g. native gold) will just change their shape if proper
sample preparation methods are not used.

35. Drying
• Drill cores are always dried no matter what the earlier
sample preparation history is. Exceptionally wet and large
samples (RC-, chip-samples etc.) require longer drying in elevated
temperature.
Crushing
• The standard scheme consists of direct one–stage fine crushing
using a special type jaw crushers
Pulverizing
• Pulverizing will always cause unavoidable contamination of
wear metals at trace level from the grinding surfaces. This
contamination may vary depending on material of the bowl,
hardness of the sample material, pulverizing time etc.

36. Soil and sediment samples
Sample preparation methods
• For soil samples (e.g. till), is recommended drying at 110 °C and
sieving to < 0.06 mm fraction. If mercury or other volatile
components are to be determined, lower drying temperatures must
be used.
• drying temperatures may also cause oxidation of some minerals.
• For some purposes, the entire soil sample (weathered bedrock) or a
coarse sieved fraction of the sample can also be crushed and/or
pulverized.
SAMPLE ANALYSIS
• Base metal assays
• To obtain the best quality and cost-efficiency in a particular
geological project it is important to decide the strategy of
analysis by selecting the appropriate analytical methods
(element suit, digestion / pretreatment method, detection limits,
optimum measurement area etc.) to fit the objectives of the
project.

37. • Selecting a wrong method may end up in attaining optimized
results in wrong concentration levels and introducing problems
in laboratory (contamination, additional sample dilutions)
which may deteriorate accuracy and precision.
• The specialists of laboratory will also assist you in selecting the
optimized methods of analysis for your project.
• For geochemical exploration for the base metals, were commend
aquaregia digestion of the sample and multi-element analysis by
ICP-OES. The package can be upgraded by ICP-MS- analysis to
include larger set of elements and lower detection limits.
• Although aquaregia is a powerful leaching agent, it still produces a
partial dissolution for many elements. The dissolution of silicates
and refractory minerals (e.g.barite, chromite and other spinelles,
zircon, cassiterite, tourmaline) varies depending on various
factors.

38. The process of sampling falls into several stages:
1. Taking of samples,
2. Their processing,
3. Laboratory studies of the sample (assaying), and
4. Analysis of the laboratory findings.

39. Chapter Four
Geochemical Prospecting
• The use of chemical properties of naturally occurring substances
(including rocks, glacial debris, soils, stream sediments, waters,
vegetation, and air) as aids in a search for economic deposits of
metallic minerals or hydrocarbons.
• In exploration programs, geochemical techniques are generally
integrated with geological and geophysical surveys.
• involve the collection and geochemical analysis of geological
materials, including rocks, soils and stream sediments. The
results mapping and sampling may suggest patterns indicating
the direction where an ore deposit could be present underground
or at the surface.

40. General Principles
• Mineral deposits represent anomalous concentrations of specific
elements, usually within a relatively confined volume of the Earth's
crust.
• Most mineral deposits include a central zone, or core, in which the
valuable elements or minerals are concentrated, often in percentage
quantities, to a degree sufficient to permit economic exploitation.
• The valuable elements surrounding this core generally decrease in
concentration until they reach levels, measured in parts per million
(ppm) or parts per billion (ppb), which appreciably exceeds the
normal background level of the enclosing rocks. This zone
surrounding the core deposit is known as a primary halo or
anomaly, and it represents the distribution patterns of elements,
which formed as a result of primary dispersion.
• In general, it is formed at, or near, the same time as the central ore
body.

41. • Mineral deposits at/or near the surface are subject to chemical and
physical agencies of weathering.
• Many of the ore minerals undergo decomposition or disintegration,
and their chemical constituents become dispersed into weathering
debris, soils, ground water, and plant tissue.
• Abnormal chemical concentrations in weathering products are
known as secondary dispersion halos or anomalies and are more
widespread.
• All of these halos afford means whereby mineral deposits can be
detected and traced; they form the geochemical anomalies, which
are the objects of search of all geochemical prospectors.
Primary Environment
• Most igneous rocks have formed by a differentiation process. This
starts with a parent magma, often of basaltic composition, and as
cooling proceeds, early crystallizing minerals are separated to form
cumulate rocks.

42. • The remaining melt, having lost elements that are concentrated in the
early minerals, becomes changed in composition. Through such a
process the magma may pass through a differentiation series, such as
gabbro-diorite-granodiorite-granite-pegmatite, in which each point
has a distinctive composition of both major and minor chemical
elements.
• In general, as differentiation proceeds, there is an overall decrease in
iron, magnesium, calcium, and titanium in the rocks combined with
an increase in silicon, aluminum, sodium, and potassium.
• Trace-element concentrations also change considerably with this
sequence of rock type and major element alteration. The occurrence
of trace elements in rock-forming minerals is generally controlled by
a combination of ionic size, valency, and type of chemical bond.
• Some elements, however, including lithium (Li), boron (B),
beryllium (Be), niobium (Nb), tantalum (Ta), tin (Sn), uranium (U),
thorium (Th), tungsten (W), zircon (Zr), and the rare earths, do not
enter rock-forming silicate minerals to any significant degree during
magmatic crystallization.

43. • These elements tend to be concentrated in residual aqueous fluids
together with compounds such as hydrogen fluoride (HF),
hydrogen chloride (HCl), and carbon dioxide (CO2), and remain in
solution until the final stages of magma crystallization,
exemplifying primary mobility.
• They eventually may become concentrated in pegmatites, and may
play an important role in hydrothermal alteration and ore
formation.
• Primary dispersion halos vary greatly in size and shape as a result
of the numerous physical and chemical variables that affect fluid
movements in rocks.
• Some halos can be detected at distances of hundreds of meters
from their related ore bodies; others are no more than a few
centimeters in width.
• Some of the factors controlling the development of primary halos
are presence or absence of fractures in the host rock, porosity and
permeability of the host rock, tendency of mineralizing fluids to
react chemically with the host rock, and volatility of the ore
elements.

44. • The main types of primary halos are syngenetic and epigenetic.
• Syngenetic primary halos are formed essentially at the same time
with the enclosing rocks.
• Epigenetic primary halos are formed after the host rock has
solidified, and result from the introduction of mineralizing
solutions to open spaces such as fractures.
• Many elements occur in hydrothermal mineralizing solutions, and
some may be more mobile than others.
• In some cases, however, the element give up the most extensive
primary dispersion halo, which is not that of greatest economic
significance in the ore body, even though it is closely associated
geochemically.
• Such an element is referred to as a pathfinder, and is of value in
prospecting because its halo is broader than that of the element of
primary interest

45. • E.g. Arsenic is frequently used as a pathfinder element in
geochemical exploration for gold; radon is frequently utilized in
similar manner in uranium exploration.
Secondary environment
• Rocks and minerals that are stable in the primary environment are
frequently unstable in the secondary; they undergo disintegration
and modification through a variety of chemical and physical
processes that are known collectively as weathering.
• Trace elements of ore bodies and their associated primary halos are
frequently released by weathering processes to soils, overburden,
and vegetation, with consequent generation of secondary halos.
• There are two primary types of weathering, chemical and
physical.
• Chemical weathering requires abundant water, oxygen, and
carbon dioxide; it involves the breakdown, by chemical
means, of rocks and minerals with consequent release of their
contained trace elements to the environment.

46. • Physical weathering comprises all processes of rock disintegration,
which do not involve chemical changes; it is most common in
extremely cold or arid regions where frost shattering and sand
blasting occur.
• Secondary dispersion halos, or anomalies, are sometimes referred
to as dispersion trains. The shape and extent of secondary
dispersion trains depend on a host of factors, such as topography
and ground-water movement.
• Ground waters frequently dissolve some of the constituents of
mineralized bodies and may transport these for considerable
distances.
• Further dispersion may develop in stream sediments when soil or
weathering debris that has anomalous metal content becomes
incorporated through erosion in stream sediment.
 Geochemical mobility in the secondary environment depends on
certain inherent properties of the elements:

47. • electronic configuration, ionic potential, stability relations with
variation in acidity and oxidation potential (pH and Eh), tendency
to form complexes with organic matter, and tendency to be co-
precipitated or absorbed with iron or manganese hydroxides.
Survey Design of geochemical prospecting
• The degree of success of a geochemical survey in a mineral
exploration program is often a reflection of the amount of care
taken with initial planning and survey design.
• This phase of activity is often referred to as an orientation survey.
• When a geochemical prospecting survey is studied, four basic
considerations must be addressed: the nature of the mineral deposits
being sought; the geochemical properties of the elements likely
to be present in the target mineral deposit; geological factors
likely to cause variations in geochemical background; and
environmental, or landscape, factors likely to influence the
geochemical expression of the target mineral deposit

48. • Wherever possible, an orientation survey should include a study of
the geochemical expression of a known mineral deposit similar to
that which is the target of the proposed prospecting program, and
which occurs in a geological and environmental setting similar to
that of the proposed search.
Sampling techniques
• Wherever possible, sampling should be confined to one type of
material for any particular survey, such as one rock type in
lithogeochemical surveys, one horizon in soil surveys, or one plant
organ and plant species in biogeochemical surveys.
• Selection of analytical procedures for a geochemical prospecting
survey is one object of the initial orientation survey.
• Samples collected during the orientation survey are often subjected
to multi-element analysis which will show the techniques most
likely to yield maximum contrast between anomaly and
background.

49. • Techniques used for the analysis of geochemical sampling media
are varied; some are intended for use in mobile field laboratories,
and some are intended primarily for well-equipped permanent
laboratories such as those operated by commercial firms or
government agencies.
Field Analysis
• Analytical techniques for on-site sampling of water, soil, stream
sediment, and lake sediment are usually based on colorimetry;
they utilize a specific selective organic reagent, such as dithizone,
which produces a characteristic color in the presence of a given
metal in solution.
• Field analytical techniques generally determine loosely bonded,
or exchangeable, metal ions, which are extracted by a citrate,
acetate, or dilute acid.

50. Laboratory Analysis
• When it is desirable to determine the total content of a given
metal in a sample, analysis is generally performed in a laboratory.
• The most common techniques used for lab. Analysis are emission
spectrography and atomic absorption spectrophotometry.
• Other geochemical analytical procedures include x-ray
fluorescence spectrography, chromatography, and polarography.
Gas chromatography is frequently used for analytical
determination of hydrocarbons.
Geochemical prospecting Surveys
• Geochemical prospecting surveys fall into two broad categories,
strategic or tactical, which may be further subdivided according
to the material samples.
• Strategic survey simply coverage of a large area (generally several
thousands of square kilometers) where the primary objective is to
identify districts of enhanced mineral potential.

51. • Tactical surveys comprise the more detailed follow-up to strategic
reconnaissance.
• The sample medium most commonly used for strategic
geochemical prospecting is stream sediment.
• Stream sediment sampling offer a relatively rapid and reliable
method of appraising the mineral potential of a large area.
• A variety of sample media may be used for the more detailed
sampling required at the tactical level of prospecting; soil is the
most common medium, but rock and vegetation are also frequently
used.
Geochemical survey of natural water
• Accurate and sensitive analytical methods are a requirement in
water surveys. Most water analyses are done by sensitive
colorimetric methods or by atomic absorption spectrometry.
• Either surface waters or ground waters may be tested in water
surveys, depending on local conditions. Surface waters are
sampled at regular intervals along the drainage net, and a map of
the value is prepared. An increase in the metal content of the water
upstream may indicate approach to a mineralized zone.

52. • Surveys based on ground waters can be done only where there is a
good distribution of wells, springs, or diamond drill holes.
• Higher than normal contents in the water system may indicate sites
or zones of mineralization.
Geochemical survey of Sediments
• Samples are collected from the fresh sediment in the bottoms of
streams and also from old sediment on the terraces and floodplains.
For chemically dispersed elements, the fine fraction is generally
used for analysis; for mechanically dispersed heavy minerals, a
coarser fraction is panned from the sediment.
• An increase in the metal content of the stream sediment upstream
may indicate approach to a mineralized zone.
Soil Geochemical Surveys
• Soils are the product of weathering of bedrock, decomposition of
organic material at the surface, and deposition of other materials
which have been transported.

53. • Generally speaking the soils tend to form certain layers called
“horizons”.
• The lowermost horizon consists largely of decomposed bedrock
and is called the “C” horizon. The uppermost horizon, called the
“A” horizon, is variable in composition.
• In vegetated areas the “A” horizon consists largely of organic
material. The “B” horizon is between the “A” and “C” horizons,
and is essentially a mixed zone.
• Dispersion is generally greatest in the “A” and “B” horizons. For
this reason, soil samples collected from the “B” horizon can detect
a mineral deposit from a greater distance.
Biogeochemical Surveys
• These surveys are of two types. One type utilizes the trace-element
content of plants to outline dispersion halos, train, and fans related
to mineralization;

54. • the other uses specific plants or the deleterious effects of an excess
of elements in soils on plants as indicators of mineralization. The
latter type of survey is often referred to as a geobotanical survey.
• Some biogeochemical surveys of a research nature have been
conducted by utilizing various animals as the sampling media.
• The animals used have been fish (livers), mollusks (soft parts), and
insects (whole organisms).
• Dogs can locate mineral deposits by sniffing out boulders of ore
occurring in the dispersion trains and fans of sulfide deposits.
Rock geochemical Surveys
• Most reconnaissance surveys are carried out on a grid or on
traverses of an area, with samples taken of all available rock
outcrops .
• One or several rock types may be selected for sampling and
analyzed for various elements. The distribution of the volatiles
such as chlorine (Cl), fluorine (F), water (H2O), sulfur (S), and
CO2 in intrusive with associated mineralization has received some
attention as an indicator.

55. Isotopic Surveys
• Used to indicate certain types of mineral deposits, which may
share a common origin. Isotopic ratios may also be used to
determine the ages of minerals or given rock types and may thus
assist in elucidating questions of ore formation.
Hydrocarbon Prospecting
• Geochemistry may be applied at several stages during exploration
of sedimentary basins for hydrocarbons.
• geochemistry can provide valuable information on the petroleum-
generating potential of a basin and permit recognition of major
source rocks. This is chiefly accomplished by extraction, analysis,
and microscopic study of kerogen from rocks sampled by drilling.
• Kerogen is a complex polymer, formed from organic matter
originally incorporated in sedimentary rocks, and is an
intermediate stage in the formation of oil and gas.

56. • What are the controlling factors of primary dispersion halos?
– presence or absence of fractures in the host rock,
– porosity and permeability of the host rock,
– tendency of mineralizing fluids to react chemically with the host rock, and
– volatility of the ore elements.
• Discuss about the two types of primary dispersion halos?
– Syngenetic primary halos are formed essentially at the same time with the
enclosing rocks.
– Epigenetic primary halos are formed after the host rock has solidified, and result
from the introduction of mineralizing solutions to open spaces such as fractures.
• What are pathfinders mean in geochemical prospecting?
– Elements that are associated with the ore elements in the target ore type and
are used because of a more favorable geochemistry.
 Geochemical mobility in the secondary environment depends on certain
inherent properties of the elements:
• electronic configuration, ionic potential, stability relations with variation
in acidity and oxidation potential (pH and Eh), tendency to form
complexes with organic matter, and tendency to be co-precipitated or
absorbed with iron or manganese hydroxides.

57. Chapter Five
Geophysical prospecting
• Geophysical techniques are usually used in an exploration
program to help the project geologist delineate areas favorable for
the type of target being pursued.
• They can be used to directly detect some minerals, indirectly
detect others, and to map geological and structural features in
exploration programs.
• Direct detection includes using induced polarization (IP) to find
disseminated sulfides, magnetics to delineate magnetite hosting
rocks, and gravity and electrical techniques for massive sulfides.
• Examples of indirect detection of targets include using IP to detect
pyrite in association with sphalerite and gold (both non-responders
to IP geophysical techniques), and copper and molybdenum in
porphyry systems.

58. • The five important geophysical methods relate to five most
common characteristics of the earth, which can be determined
from the surface are: (1) electrical conductivity, (2) density, (3)
magnetism, (4) elasticity and (5) radio activity.
Electrical Method
• All the electrical methods are widely used in the exploration work
connected with metalliferous deposits, in groundwater exploration
and engineering geological investigations.
Self-Potential or S.P. Method: This method utilizes the natural flow
of current and operates 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 induces greater chemical activity than at lower. Hence
a potential difference is induced; and a current flows from upper
level towards lower level.

59. Equipotential Line Method: when an electric current is applied,
between two points or between two parallel line conductors on the
surface of the ground, an electric current will flow across from one
conductor to other.
• The potential distribution produced by the flow of current in
homogenous medium can be calculated. Where the ground is not
homogenous, the potential distribution will not follow the pattern
obtained by calculation. Hence, it is possible to detect any variation
in homogeneity in the ground by comparing the measured potential
distribution with the calculated theoretical distribution.
Electromagnetic Method: The principal use of EM surveys is in the
exploration for metalliferous mineral deposits, differ significantly
in their electrical properties from their host rocks.
• On a small scale, EM methods can be used in geotechnical and
archaeological surveys to locate buried objects such as mine
workings, pipes or treasure trove.

60. Induced Polarization (I.P.) Method: In spite of its drawbacks, the IP
method is extensively in base metal exploration as it has a high
success rate in locating low-grade ore deposits such as
disseminated.
• Although the deposit is of low grade, containing less than 2%
conducting minerals, the chargeability anomaly is well defined and
centered over the ore body.
Gravity Method: Gravity measurements define anomalous density
within the Earth; in most cases, ground-based gravimeters are used
to precisely measure variations in the gravity field at different
points.
• Positive gravity anomalies are associated with shallow high density
bodies, whereas gravity lows are associated with shallow low
density bodies.
• Thus, deposits of high-density chromite, hematite, and barite yield
gravity highs, whereas deposits of low-density halite, weathered
kimberlite, and diatomaceous earth yield gravity lows.

61. Magnetic Method: is a rapid and cost-effective technique and
represents one of the most widely-used geophysical methods in
terms of line length surveyed.
• Magnetic surveys are used extensively in the search for
metalliferous mineral deposits.
• Magnetic surveys are capable of locating massive sulphide
deposits especially when used in conjunction with electromagnetic
methods.
• Magnetic surveys are the quickest, and often the cheapest, form of
geophysics that can provide useful exploration information. A few
minerals, of which magnetite is by far the most common, produce
easily detectable anomalies in the Earth’s magnetic field because
the rocks containing them become magnetized.
• However, the principal target of magnetic surveying is iron ore.

62. Seismic Methods: Seismic techniques have had relatively limited
utilization, due to their relatively high cost and the difficulty of
acquiring and interpreting seismic data in strongly faulted and
altered igneous terranes, in mineral assessments and exploration at
the deposit scale.
• Reflection seismic methods provide fine structural detail and
refraction methods provide precise estimates of depth to
lithologies of differing acoustic impedance.
• The refraction method has been used in mineral investigations to
map low-velocity alluvial deposits such as those that may contain
gold, tin, or sand and gravel.
Radioactive Method:
• This method is based on measurement of radioactive radiation.
Upon fissioning radioactive elements (U, Th, Ra, etc.) give off α,
β, γ rays. These rays ionize gas, which becomes electrically
conductive as a result.

63. Chapter Six
Underground Sampling Methods
• In areas where soil cover is thin, the location and testing of
bedrock mineralization is made relatively straightforward by the
examination and sampling of outcrops.
• However, in locations of thick cover such testing may involve a
deep sampling program by pitting, trenching, or drilling.
• Pitting to depths of up to 30 m is feasible and, with trenching,
forms the simplest and least expensive method of deep sampling
but is much more costly below the water table.
• Drilling penetrates to greater depth but is more expensive and
requires specialized equipment and expertise that may be supplied
by a contractor.
• Despite their relatively shallow depth, pits and trenches have some
distinct advantages over drilling in that detailed geological logging
can be carried out, and large and, if necessary, undisturbed
samples collected.

64. Pitting
• In areas where the ground is wet, or labor is expensive, pits are best
dug with a mechanical excavator. Pits dug to depths of 3–4 m are
common and with large equipment, excavation to 6 m can be
achieved.
• In wet, soft ground, any pit deeper than 1 m is dangerous and
boarding must be used. Diggers excavate rapidly and pits 3–4 m
deep can be dug, logged, sampled, and re-filled within an hour.
Trenching
• Trenching is usually completed at right angles to the general strike
to test and sample over long lengths, as across a mineralized zone.
Excavation can be either by hand, mechanical digger, or by
bulldozer on sloping ground.
• Excavated depths of up to 4 m are common.

65. Auger drilling
• Augers are hand-held or truck-mounted drills, which have rods
with spiral flights to bring soft material to the surface. They are
used particularly to sample placer deposits.
• In soft ground, augering is rapid and sampling procedures need to
be well organized to cope with the material continuously brought
to the surface by the spiraling action of the auger.
• Augers are light drills and are incapable of penetrating either hard
ground or boulders. For this purpose, and holes deeper than about
60 m, heavier equipment is necessary.
Percussion drilling
• In percussion drilling, a hammer unit driven by compressed air
imparts a series of short rapid blows to the drill rods or bit and at
the same time impart a rotary motion.
• The drills vary in size from small hand-held units (as used in road
repair work) to large truck-mounted rigs capable of drilling large
diameter holes to several hundred meters depth.

66. • The units can be divided broadly into two types:
1. Down-the-hole hammer drills. The hammer unit is lowered into
the hole attached to the lower end of the drill rods to operate a
noncoring, tungsten carbide-tipped, drill bit.
• Holes with diameters of up to 20 cm and penetration depths of up
to 200 m are possible, but depths of 100–150 m are more usual.
2. Top hammer drills. As the name suggests the hammer unit, driven
by compressed air, is at the top of the drill stem and the energy to
the noncoring drill bit is imparted through the drill rods.
• They are used for holes up to 10 cm diameter and depths of up to
100 m, but more usually 20 m.
• Percussion drilling is a rapid and cheap method but suffers from
the great disadvantage of not providing the precise location of
samples, as is the case in diamond drilling.
• However, costs are one third to one half of those for diamond
drilling and this technique has proved particularly useful in
evaluating deposits which present more of a sampling problem
than a geological one, e.g. a porphyry copper

67. Chapter Seven
Mineral Resource and Ore Reserve Estimates
• The credibility of database and geological interpretations are more
important than the methodology used for estimates.
• Database credibility depends on the sampling and sample
preparation procedures and on the adequate and reliable analyses
• Geological interpretations should include a credible evaluation of
the database and adequate models derived from the processing of
data.
Three important principles should be realized:
1. All the phases of estimation must be transparently documented so
that the grounds for all choices and all conclusions are visible as
well as the methods of research and calculations.

68. 2. When something is outlined, the framework must be described as
well. So, when a mineral deposit is outlined, the criteria for
separating the deposit material from the geological frames, their
structures, lithology, and grades, must be presented. Also all
information supporting shape, size and structure interpretations
should include a reference to a larger geological framework.
3. All estimate methods have their faults and shortcomings. For the
best results, at least three basically different methods should be
applied for each estimation. A reasonable sensitivity analysis of
parameters should be applied to each case.
Terms and definition
Core loss (core recovery): Soft, non-coherent rock may flow out
from the hole leaving empty spaces in between hard rock samples.
• These spaces are core loss. Core loss locations should be marked
accurately as if they were samples. Core loss data may lead to
important structural information.

69. Country rock (wall rock, mother rock): Country rock means the rock
next to the ore and its host, or the rock enclosing or traversed by a
mineral deposit.
Cutoff grade (analytical cutoff, geological cutoff, economic cutoff,
monetary cutoff)
• Economic cutoff grade means the lowest grade of mineralized
material that qualifies as ore.
• Analytical cutoff means the lowest grade accepted to be processed
or estimated.
• Cutoff grades are normally expressed in percentages of metal for
base metals and in grams per metric tons for precious metals.
• Generally, cutoff grade is a grade below which the value of
contained metal/mineral in a volume of rock does not meet certain
specified economic requirements.

70. • Cutting factor: is the highest metal assay accepted in
resource/reserve estimates.
• Dilution (waste rock dilution): Dilution may come from internal
waste, planned waste (intentional dilution), accidental waste or
geologic waste.
• Internal waste, when detected, is usually included at assay grade.
• Planned waste is what belongs to the stop to be mined. It can be
foreseen and thus it can be added to the ore reserve estimation at the
assayed grade.
• Accidental waste is a surprise caused by caving, slough, etc. It may
be caused by the incomplete control on the rock mechanics of a
mine or by unrecognized zones of weakness.
• Geologic waste is caused by the incomplete knowledge on the
shape of ore bodies.

71. Effective grade: the apparent grade averaged to a deposit may be
true but misleading. The effective grade is generally lower than
the apparent one, seldom higher.
Extraction ratio (mine recovery): The proportion of the total insitu
reserve that is actually extracted during stoping.
Feed: is the mined material that is transported to the concentration
plant for enrichment. In practice an ore reserve estimate means a
grade and tonnage estimate of the average feed(s).
Gangue (matrix): The valueless rock in ore body or in an ore sample.
Host rock: The rock hosting an ore; especially with low-grade ores,
host rock and its properties are important to know and to control.
Mineral deposit: is general name for an outline able and quantifiable
natural mineral enrichment possibly of economic value.
Mineral occurrence (mineral showing): Mineral enrichment not
quantified nor otherwise evaluated.

72. Mineral resource (measured, indicated and inferred): a mineral
resource is an accumulation of material of intrinsic economic
interest in such form and quantity that economic exploration of a
mineral from the deposit may be feasible.
• A measured mineral resource has been explored, sampled and
tested (lab. scale) through appropriate techniques with observations
and samples spaced closely enough to confirm geological
continuity.
• An indicated mineral resource is defined like above except that
samples are too widely spaced to confirm geological continuity
but they are spaced closely enough to assume geological
continuity.
• An inferred mineral resource is indirectly or, without systematic
sampling, assumed to be a part of a total mineral resource.
Nugget: it means a lowered reliability of sample analyses due to the
uneven or sparse distribution and/or large grain size of minerals
hosting assayed elements.

73. Ore: economically valuable enrichment of mineral(s). Also:
mineralized rock type that is typical to economic mineral deposits.
Ore body: A three dimensional continuous mass of ore, either an ore
deposit or an outlined part of an ore deposit. Also: a technically
definable unit of an ore deposit.
Ore loss: the part of an ore body (in percentages) that is not blasted
or loaded during a mining process. Usually this happens because of
unexpected outlines of ore or as a consequence of unsuccessful
blasting. Instead of ore loss, ore recovery may be used.
Ore mineral: The essential and usually smallest constituent of ore to
be enriched.
Ore reserve (proved, probable): The economically minable part of a
mineral resource, inclusive of diluting materials and allowing for
losses.
A proved ore reserve is that part of measured mineral resource
that can be exploited.

74. • A probable ore reserve is that part of measured or indicated
mineral resource that can be exploited under appropriate technical
and economic conditions.
• Ore value is the value of mineral concentrate per ore ton. The
price or value of concentrate depends on the agreement between
mine and refinery (smelter).
• Recovery (mining recovery, concentration recovery, metallurgical
recovery): The percentage of valuable minerals derived from an
ore at a stage of mining: blasting R, loading R, concentration R,
smelter R, etc.
• Waste rock (dilution): Valueless (but not necessarily useless) rock
that must be removed in mining.

75. Resource estimation
The evaluation is a continuing process applied to every step in the
exploration and development process.
• A resource estimate is based on the prediction of the physical and
chemical characteristics of a mineral deposit.
• Done through collection of data, analysis of the data, and
modeling of the predicted size, shape and grade of the deposit.
• Physical characteristics of the mineralized zone must be predicted
and include:
1) the size, shape and continuity of the mineralized zone
2) the frequency distribution of the metal grade
3) the special variability of the metal grade
4) recoverability of metal values.

76. Methods of ore reserve calculation
1. Method of sections
2. Polygonal methods
3. Triangular method
4. Regular grid, random stratified grid
5. Inverse distance weighting
6. Contouring methods.
• Methods 1 through 3 involve estimation of volumes; methods 4
through 6 concern point samples on which properties (e.g., grades)
have been estimated and that are commonly used to estimate
points on a regular grid.
Method of Sections
• applied most successfully in the case of a deposit that has sharp,
relatively smooth contacts, as with many tabular (vein and
bedded) deposits.

77. Polygonal Methods
• polygons are defined in several ways, one of the more common
being by a series of perpendicular bisectors of lines joining sample
locations (when on 2D).
• Each polygon contains a single sample location and every other
point in the polygon is nearer to the contained datum than to any
external datum.
• The third dimension, the “height” of the polygonal prism,
represents the thickness of the deposit or bench and is
perpendicular to the projection plane.

78. Figure 7.2: Details of the construction of a polygonal area to which a single contained grade
is applied (i.e., the contained sample grade is extended to the polygon). Circles are data
points; dashed lines join adjacent data points and form Delaunay triangles; thick lines
defining a polygon are perpendicular to the dashed lines and divide the dashed lines into
two equal segments

82. Method of Triangles
• Triangular prisms are defined on a two-dimensional projection
(e.g., bench plan) by joining three sample sites such that the
resulting triangle contains no internal sample sites.
• The average of the three values at the apices of a triangle is
assigned to the triangular prism (block).
• in which each hole is taken to be at one corner of a triangle, or a
number of them, with a width and grade assumed to be the average
of its three corner holes.

87. Inverse Distance Weighting Methods
• Inverse distance weighting methods generally are applied to a
regular three-dimensional block array superimposed on a deposit
• each block is estimated independently from a group of nearby
data selected on the basis of distance criteria relative to the point

88. Contouring Methods
• Contouring methods of reserve/resource estimation generally
depend on estimation of a regular grid of points by some type of
interpolation procedure (e.g., one of the traditional estimation
methods described previously) followed by contouring of the data.
CHAPTER EIGHT
• Mineral resources are accumulations, occurrences or showings in
such form and quantity that economic exploitation of a mineral or
substance from the deposit may be currently or potentially feasible.
• cost of exploration is relatively easy to count or even to foresee. But
the evaluation of results is much more difficult.
• Quantification of success means the calculation of the price of
exploratory results.
• We can say that quantifying has been well done, when we are able
to sell our project with a reasonable profit.

89. • It is one of the alternate economic strategies of mining companies
to buy successful projects instead of starting new ones from the
grassroots level.
• Sequential approach makes above quantification easier. For each
sequence, targets have been defined on the basis of cumulated
information.
• After completing a sequence, the expenditure is known. Target
definition actually includes a rough estimate of the worth of
deposits possibly detectable.
• The first sequences end with screenings. Screenings or tentative
feasibility studies or viability studies are based on indirect
observations, extrapolations, analogies, and simulations and on
general market and work pricing.
• Ore evaluation in the early phases of an exploration project is more
or less based on speculations and may be rather called 'project
evaluation'.

90. • Ore evaluation will then be started by the evaluation of:
observation quality
sampling quality
sample preparation quality
assay quality
• After quality evaluations, the evaluator can start quantifying:
• assay value treatment
• geological modeling
• ore geological interpretations
• The only concrete element in the evaluation process is the
collection of remaining geological samples including core
remnants, pulver bags, thin sections, etc.

91. CHAPTER NINE
Exploitation of Mineral Resources
Ore dressing comprises the following processes:
1. Crushing,
2. Sizing,
3. Grinding
4. Concentration,
5. Storage.
Crushing and Grinding
• Crushing is done either manually or by using different types of
crushers. For grinding, different mills are utilized. While crushing
yields a relatively coarse product, grinding produces finer material.
• the parts of the machine, which are used for grinding, come into
contact with each other, while crusher jaws and rolls do not touch
each other.

93. • The purpose of crushing is generally, to reduce the size of the run of
mine product, but grinding is essential for liberating valuable
minerals from the gangue.
• Grinding is also necessary in order to liberate minerals, where the
minerals occur as intergrowths, e.g. galena and chalcopyrite, so that
these ores may be render amenable to ore dressing processes, e.g.
floatation.
• In the case of non-metallics, e.g. feldspar, sillimanite, limestone,
coal, etc. grinding is done to make them marketable.
Sizing
• Purposes of sizing are: (1) to remove the coarser fractions, (2) to
remove the finer material from the grinding circuit, (3) to obtain
commercially marketable sizes of material, e.g. sand, rock chips,
etc., (4) to obtain suitable sizes for further beneficiation, and (5) to
separate different minerals, which occur together, but each mineral
being characterized by a particular grain size.

94. • Requirements and conditions for proper sizing are:
(1) All particles should be brought to the screen opening, oriented in
such a way, and moved at such a rate, that the undersize particles
will pass through freely unhampered, without rebounding, from
the edges of the screen opening,
(2) Ideally, every undersize particle should be at standstill and
centrally placed, in respect of the aperture
(3) Larger tonnage can be obtained if the particles of the material
move over the screen,
(4) Even though screen, made of extremely fine wire or metal, they
are ideal for efficiency, in practice, these cannot be employed as
they are mechanically too weak.

95. Concentration
• This aspect of beneficiation takes advantages of the differences in
specific gravity, which come into play under the influences of
forces impressed upon various particles.
 Hand-Picking
 There are many primitive mining operations in various parts of the
world where groups of men, women, and children break up pieces
of ore with hand hammers on hard stones or blocks of steel and, by
sorting and re-sorting, discard the gangue and garner pieces of
valuable mineral into separate piles.
 Primitive as it is, hand-sorting can be the most economical method
of ore-dressing when circumstances favour it.
 In its modern form, hand-picking is facilitated by mechanical aids;
the ore, after coarse crushing, goes over a screen to separate the
fines and under a spray to wash off dust and mud.

96. Gravity Concentration
 This method is based on mechanical refinements of the simple
processes of washing and panning.
 effectiveness depends on the difference in specific gravity between
different minerals; naturally, the greater the difference the better the
separation.
 Large particles of light minerals settle as fast as small particles of
heavy minerals; thus, a quartz particle 4 mm in diameter settles at
about the same rate as a galena particle of 1 mm.
 Among particles of very small size, gravity separation is not
efficient. Great varieties of machines have been used in gravity
concentration, but much the commonest are jigs and vibrating
tables.

97. Heavy-Fluid Separation
• This method uses the heavy fluid, which is a pseudo-liquid
consisting of a finely ground heavy solid in suspension in water.
• Galena and ferrosilicon are the solids most commonly used.
• Ferrosilicon has the advantage of being ferromagnetic so that it
can be recovered and cleaned for re-use by means of a magnetic
separator.
• This method uses sink-and-float process
Floatation
• a particle of sulphide, suitably treated, would float at the surface of
the water while a particle of quartz would sink.
• This is because the quartz, unlike the sulphide, is “wetted” by the
water.

98. Magnetic Separation
• Magnetic methods have long been used for concentrating
magnetite ores. The other iron oxides (hematite and goethite) as
well as siderite are virtually non-magnetic, but they may be
converted into artificial magnetite by controlled roasting.
• Magnetic methods may be used “in reverse” to purify non-ferrous
ore by removing the undesired magnetic minerals. Such methods
are used on a large scale for removing magnetite from the titanium
ore.
• Wolframite or tantalite can be separated from cassiterite by this
means.
Amalgamation
• Mercury forms an amalgam with metallic gold or silver. This
principle is utilized in the recovery of precious metals by passing a
layer of pulp over a table consisting of a plate of silvered copper,
which has been coated with mercury.

99. • The mercury holds and partially absorbs the particles of precious
metals, while gangue and sulphides pass onward.
Cyaniding
• The cyaniding process is applicable commercially only to ores of
gold and silver. Any base metals in the ore are not recovered.
• The solvent is a weak solution of sodium or calcium cyanide
which, when aerated, readily dissolves the precious metals.
4Au + NaCN+ O2+ 2H2O = 4NaAu(CN)2+ 4Na OH
Leaching
• Some copper ores can be treated by leaching, using a solvent
ammonia, ferric sulphate, or sulphuric acid, according to the
nature of ore.
• Ammonia in presence of CO2dissolves native copper and is used
in retreating tailings.
• Sulphuric acid readily dissolves copper carbonates and sulphates
but is uneconomical for ores with limestone gangue because of the
high acid consumption.