Sampling and analysis for feasibility studies and mineral processing

Basdew Rooplal
Mining & Metallurgical consultant
http://mineralprocessingconsultant.com/

SAMPLING -
Mineral Processing Deposits & Process Plants, Bench Scale
testwork with a view for flowsheet development.

CONTENTS
• Sampling Introduction
• Sampling for feasibility studies
• Types of sampling and samplers
• Types of Analysis
• Bench scale testwork
• Flowsheet development and ore dressing studies
• Ore characterisation and understanding the ore body

SAMPLING -
INTRODUCTION
• The objective of sampling in
mineral processing is to
estimate grades and
contents of sampling units
in an unbiased manner and
with an acceptable and
affordable degree of
precision.
• Mineral deposits are
sampled for several reasons
including:
• Resource evaluation
• Determination of the
physical and chemical
characteristics of material,
• And process amenability.

SAMPLING
• Generally sampling is the
process of selecting a part
of a whole such that the
measured value for the part
is an unbiased estimate for
the whole.
• In mineral processing a
whole is referred to as a
sampling unit such as mill
feed, dewatered
concentrate or bullion.
• A sampling unit is classified
as a dynamic stochastic
system when sampled
during transfer, and as
static stochastic system
when sampled whilst
stationery.

DEFINITIONS: ACCURACY
• A generic term that implies
closeness of agreement,
between a single measured
value or the central value of
a set (arithmetic mean or
weighted average), and the
unknown true value of a
stochastic variable.
• This definition reflects
that accuracy is an
abstract concept.
• By contrast a lack of
accuracy can be
measured and quantified
in terms of a bias or a
systematic error.
• Webster defines accuracy
as free from error.

DEFINITIONS: BIAS
• A statistical significance
difference between a single
measured value or the
central value of a set, and
an unbiased estimate of the
unknown true value of the
stochastic variable.
• Testing for absence or
presence of bias is an
essential part of
• sampling in mineral
processing.
• Terms such as random error
or error without adjuncts or
adjectives, will not be used
to avoid confusion with
randomly distributed
variations for which the
variance is the fundamental
and unambiguous measure.

DEFINITIONS: PRECISION
• A generic term that refers to
the magnitude of randomly
distributed variations
(random variations) in the
measurement procedure
applied to estimate the
central value of the
stochastic variable of
interest.
• Quantitative measures of
precision are:
• Confidence intervals in
absolute values or
• Relative percentages
• Symmetric and asymmetric
confidence ranges in
absolute values,
• Derived from the variance
of the central values for
the variable

DEFINITION: SAMPLE
• A part of a sampling unit or
sample space selected such
that a measured value for
the part is an unbiased
estimate for the sampling
unit or the sample space.
• A sample is often referred
to as a representative part
of a population or a whole.

SAMPLING FOR
FEASIBILITY STUDIES
• Sampling for plant design
during the feasibility phase
of a project can be critical
to the overall success of the
project but this is all too
often minimized.
• Sampling at this stage is
usually carried by geologists
and mining engineers for
• Identification and
quantification of ore
reserves.
• Sampling for comminution
and the amenability of the
ore for processing is left for
later bulk sampling
programs.

SAMPLING FOR
FEASIBILITY STUDIES
• Precise quantification of the
processing characteristics of
the plant feed material does
require the additional
sampling, much information
can be obtained from the
initial feasibility sampling
program that can guide and
even determine
• The testwork program and
even final design.
• Due to budget constraints
the initial team is limited to
geologist, mining engineers,
geotechnical engineers and
environmentalists.

TYPES OF SAMPLES
• Core Drilling
• Reverse circulation drilling
• Auger Drilling
• Other drilling methods
• Channel Sampling
• Trench sampling
• Geochemical and
environmental Sampling
• Water samples
• Run of mine ore feed
• Crusher product sampling
• Sampling of pulps
• Sampling of loaded carbon,
slags flue dust, etc.
• Sampling of bullion
• Sampling of liquids/

CORE DRILL SAMPLES
• This is the preferred method
of recovering material from
within the ore body and is
also the most expensive.
• Generally between 27 mm
to 100 mm in diameter.
• Cores are generated using a
circular drill bit that allows a
cylinder of rock to rise
• Within the interior of the
drill steel as the drill
progresses.
• The resulting drill core
generally has a smooth
surface and is consistent in
diameter along its length.

DRILL CORE SAMPLES

BAUER LARGE DIAMETER
DRILL RIG

REVERSE CIRCULATING
DRILLING
• Operates in the same
manner as holes drilled for
general purpose viz.
boreholes
• Less expensive than core
drilling
• The samples from each drill
interval are logged
separately as they come
from the hole.
• RC is not recommended
when the exact transition
from one rock to another is
required viz. coal.

AUGER DRILL

AUGER DRILLING
• When material is
unconsolidated Auger
drilling method is used.
• Soils, placer deposits of
river gravel, and previously
placed material such as
mine waste dumps and
impoundments.
• The sample may consist of
the entire amount of
material extracted from the
hole or a hollow tube in the
middle of the drill stem can
be used to collect materials
from only desired depths.

OTHER DRILLING
METHODS
• Other specialized drilling
methods are also used to
recover samples of material
and to make holes within
which in situ measurement
can be made.
• Chip and mud samples are
collected from ordinary
rotary drilling
• Which are less expensive
but also less reliable and
are used for indicative
purposes only.
• Specialized drills for
collection of large pieces of
rock such as placer
sampling are also used.

CHANNEL SAMPLING
• Where the material to be
sampled is exposed to the
surface or in underground
workings, channel sampling
is used.
• In this procedure a channel
of dimensions similar to the
diameter of the core or RC
hole is excavated.
• The resulting samples are
chips similar to those
recovered through RC
drilling.
• Channel samples have the
advantage over RC samples
in that the material can be
geologically logged prior to
excavation.

TRENCH SAMPLING
• Where the material to be
sampled is close to the
surface, trenches are
excavated to gain access to
the material and samples
are taken either as channel
samples within the trenches
or as selected samples of
the excavated material.
• This results in broken
material

GRAB SAMPLING
• When material is exposed
on surface or underground,
it is possible to grab
samples on a random basis
as it is mined or
transported.
• Such samples maybe useful
for obtaining overall
averages for large amounts
of material but not
• Useful for identifying
material characteristics at a
specific location.

STOP BELT SAMPLING FOR
ROM MATERIAL
• The feed belt is stopped, a
former placed on it and all
the material within the
former is removed into a
bucket before restarting the
belt.
• This method is recognized
by certain national and
international standards as
the reference sampling
method when checking for
bias in automatic samplers.

AUTOMATIC SAMPLING OF
RUN OF MINE ORE
• Due to problems occurring
during stop belt sampling
the process can be
automated.
• Primary increments from
the discharge of the head
pulley are taken and
increments and sub-
divisions are further
processed by crushing.
• Automatic samplers have
now been developed where
the samples are taken in the
direction of the material
flow.

PRIMARY CROSS BELT
SAMPLERS
• Easily – mounted on
conveyor stringers along
length of conveyor
• Guaranteed not to damage
the conveyor belt when
correctly installed

CRUSHER PRODUCT
SAMPLING
• Rotary Plate Divider
• For continuous or timed dry
material splitting
• Suitable for primary
sampling and secondary
division
• Must be consistently fed by
vibratory feeder or feeder
conveyor
• Ideal sample divider for
bulk materials handling
systems

SAMPLING OF PULPS
• Manual sampling is usually
employed but is not
reliable:
• There is no guarantee that
the samples will be
unbiased
• Precision of the
measurement is much
lower than can be
obtained with mechanical
methods.
• The mechanical systems are
usually of two types, viz.
• Those with cross stream
cutters
• And the arc type rotary
cutters.

SLURRY SAMPLING
• Primary Rotary Samplers • Vezin Samplers & Launder
Samplers

TYPES OF ANALYSIS: IN
SITU MEASUREMENTS
A down hole survey is carried
out in order to locate the
position of the sample that
has been taken since drill
holes are seldom straight
over long distances.
Other types of probes that
are inserted into open drill
holes include:
callipers to measure the
diameter of
• The hole along its length
• Resistance sensors to detect
the presence of water,
carbonaceous material, and
gamma sources,
• And detectors to measure
density and normal
radiation levels,

TYPES OF ANALYSIS: IN
SITU MEASUREMENTS
• Expandable cylinders to
measure rock strengths and
stresses,
• Gauges to measure ground
water levels
• .Sophisticated tomographic
techniques use sensors
placed in multiple drill holes
to provide detailed
information on the material
between the drill holes.
• Work is underway to
develop sensors that will be
able to detect the presence
of metals.

TYPES OF ANALYSIS:
GEOLOGIC LOGGING
• Drilling samples both core
and chips are logged by
geologists in order to
record the material
characteristics along the
drill hole.
• Samples are logged for:
• Rock types
• Alteration types
• Association of various
minerals
• And estimated content of
the desired commodity
• Core samples are also
logged for:
• fracture spacing and
intensity,
• Rock quality designation
• And fracture orientation
• Photographs are also taken
of the core.

TYPES OF ANALYSIS:
CHEMICAL ANALYSIS
Representative samples of the
core are subjected to
chemical analysis.
The analysis includes:
• moisture content
• Total metal content
• Soluble metal content
• Content of non-metal
commodities
• Heat content for coal and
oil shale
• Ash content after
combustion
• In some cases multiple
samples are combined to
give composite metal
values.

TYPES OF ANALYSIS:
MINERALOGICAL
ASSESSMENT
• Direct measurement of
mineral types is possible
using QEM*SEM.
• QEM*SEM uses a computer
controlled scanning
electron microscope which
can distinguish minerals
and their attributes in
individual ore particles.
• These images can also be
processed to provide
information on:
• modal abundance
• Grain size
• Mode of occurrence
• Liberation characteristics
• And quantity of mineral
phase recoverable.

TYPES OF ANALYSIS:
PHYSICAL CHARACTERISTICS
• Direct measurement of
physical parameters of the
materials sampled are also
performed. These include:
• In situ density
• Porosity
• Permeability
• Compressive strength
• Compaction
• Grinding index
• In some commodities it is
the physical characteristics
that determine value e.g.
kaolin where the value is
determined by brightness
and slurry viscosity.

METALLURGICAL TESTWORK -
BENCH SCALE TESTWORK
Introduction
• The resistance of ore samples
to breakage (or hardness) is
measured through grindability
tests.
• Several grindability tests have
been developed over the years
for different applications and
each test has its own strengths
and weaknesses
• Grindability tests are a
compromise between test
costs and its deliverables.
• The highest degree of
deliverables and certainty is
achieved in a pilot plant, which
is also the most reliable test
procedure to determine the
resistance of ore samples to
grinding or hardness and is
also the most expensive.

SUMMARY OF
GRINDABILITY TESTS

GRINDABILITY TESTS
Bond Ball mill
Grindability
• The AG/SAG mill or HPGR
circuit products, which have
non-standard particle size
distribution.
• One of the keys of the Bond
work index success over
time has been its reliability
and reproducibility.
• The figure below shows that
the Ball Mill work index is
normally distributed with
AVG 14.6 and Median 14.8

GRINDABILITY TESTS
Bond Rod mill work
Index
• The rod mill work Index is
also normally distributed
with and average and
median of 14.8kWh/t
• It is common to observe
difference between the ball
and rod mill caused by
variation in ore hardness
• The test has been mainly
used for the design of rod
mill or primary ball mills.

GRINDABILITY TESTS
Bond low energy
impact test
• Consists of an apparatus with
two pendulum hammers
mounted on two bicycle
wheels, so as to strike equal
blows simultaneously on
opposite sides of each rock
specimen.
• The height of the pendulum is
raised until the energy is
sufficient to break the rock
specimen
• The test is generally performed
on 20 rocks
• One of the strengths of the
test is to measure the natural
dispersion in the sample.
• Another advantage of the test
is the coarse size 2 – 3 inches
which makes it unique in the
series of tests.
http://mineralprocessingconsultant.c
om/

GRINDABILITY TESTS
SAG power index (SPI)
• SPI expressed in minutes , is
the time T necessary to
reduce the ore from P80 of
12.5mm to P80 of 1.7 mm
• The SPI has the advantage of
requiring low weight and is
suited for geometallurgical
mapping of ore deposits
• SPI is widely used and
deposits can be compared
in terms of hardness and
variability, see fig below.

GRINDABILITY TESTS
JKTECH drop weight
test
• Developed by JKMRC
• Divided into 3 components:
• Test measures the resistance
to impact breakage of
coarse particles in the range
63 – 13.2 mm
• Then evaluates the
resistance to abrasion
breakage in the range 53 –
37.5 mm
• Finally the rock density of
20 particles is measured to
asses the average ore
density as well as its
dispersion.

GRINDABILITY TEST
JKTECH drop weight
test
• The test generates the
appearance function –
• E.g. the breakage pattern of
the ore under a range of
impact and abrasion
breakage conditions
• The appearance function can
be used in the JKSimMet
modelling and simulation
package to predict the ore
response to comminution
process

GRINDABILITY TESTS
JKTECH Drop weight
test
• Also part of these procedure is
the density determination of
20 rock samples, using water
displacement techniques.
• Figure 5 shows an ore
displaying a wide range of
densities.
• The density distribution of the
ore is important in AG/SAG
milling because
• It affects the bulk density of
the charge and associated
power draw

GRINDABILITY TESTS
JKTECH drop weight
test
• A great number of rock
weight tests have been
performed over the years
which allows for
comparison of ore types in
a data base.
• The frequency distribution
of the function ‘A x b’ from
JKTech is depicted in Fig 6

GRINDABILITY TESTS
JKTECH drop weight
test
• One of the interesting
features of the drop weight
test procedure is that it
provides a variation in rock
hardness by size from 13.2
to 63 mm.
• Fig 7 illustrates this at 3
different energy levels.
• 0.25 1.0 and 2.5 kWh/t
• For a very competent ore, the
curve will be nearly horizontal,
a non-competent fractured ore
will show a high gradient with
increasing size

GRINDABILITY TESTS
SAG Mill
comminution test
• This is an abbreviated drop
weight test, which can be
performed at low cost on
small samples 19 – 22 mm
or drill cores.
• 5 kg of sample is normally
sufficient.
• The advantage of the SMC test
is that it generates the energy
versus breakage relationship
with as small quantity of
sample of a single size fraction.
• Because the test can be
performed on small rocks, it is
well suited for
geometallurgical mapping.

GRINDABILITY TESTS
MacPherson Autogenous
Grindability tests
• This is a continuous test
performed in a 46 cm semi-
autogenous mill with an 8%
ball charge.
• The pilot plant consists of a
feed hopper, cyclone, screen
and dust collector with a
control system to regulate the
charge volume and circulating
load.
• 100 to 175 kg of sample is
required with a top size
greater than 25 mm.
• The test is run continuously for
6 hours.
• The importance of reaching a
steady state in a grinding mill
is widely accepted, this test is
the only small scale test that
offers the option.

GRINDABILITY TESTS
MacPhersons Autogenous
grinding tests
• Throughput rates • Specific Energy

GRINDABILITY TEST
Media Competency
test
• There has been some
variations of media
competency test developed
over the years with the
assessment of media
survival in autogenous
milling being the main
objective.
• 104 to 165 mm rocks are
subjected to a tumble test
using 10 large rock in 5 size
fractions.
• The surviving rocks are
submitted to fracture energy
test procedure.
• This provides the relationship
between the first fracture
energy requirement and rock
size.

GRINDABILITY TESTS
High Pressure
Grinding Rolls
• HPGR are emerging as an
energy efficient alternative to
AG/SAG circuits.
• The traditional method for
testing is processing large
samples in a pilot scale.
• Several tests are performed to
asses the effect of operating
pressure and moisture content
on HPGR performance
• The power input is recorded
and presented below.

CRUSHABILITY TEST
Impact Crushability
• Gives a WI that can be applied
to 3 types of crushers
• Gyratory – WI can be used to
determine the horse power.
• Impactors – WI is an indication
of hardness
• Cone Crusher – rate the
material to determine the duty
of the crusher

CRUSHABILITY TESTS
Paddle Abrasion
• Results are in the form of
Abrasion Index and chemical
makeup of the material
• Tests are used to determine
whether an Impactor or cone
crusher is suitable.
• Can also be used to calculate
the approximate liner life for
the crusher

CRUSHABILITY TESTS
French Abrasion
• Gives an Abrasion and
Crushability Index
• Mainly used to estimate
hammer wear in the
Impactor application
Dynamic
Fragmentation
• Conducted for Impactor
application
• Measures the friability of
the material
• Dynamic fragmentation
number will indicate if the
Impactor is feasible for a
particular application.

FLOWSHEET
DEVELOPMENT - ODS
Introduction
• Ore dressing studies the
characterisation of the ore
body with respect to
metallurgical properties.
• In conjunction with the project
requirements, geologists and
mineral resource
management, a sampling
program is compiled for the
specific ore body.
• These samples are characterised
with respect to various
flowsheet and data obtained
from the characterisation work
is analysed and evaluated to
improve the process recovery .
• This provides information with
regards to risk minimisation, for
both plant design envelopes as
well as operational efficiency

ODS - KNOWLEDGE FLOW

ODS - IN AN ORE BODY
DEVELOPMENT

ODS - GENERIC DIAGRAM
FOR SAMPLE
CHARACTERISATION

ODS - COMMINUTION
CHARACTERISATION
• Test work consists of a suit of
laboratory and pilot plant scale
tests
• Laboratory tests are typically
rock mechanic tests as used
by equipment manufacturers
to provide performance
guarantees for comminution
equipment.
• These also include drop
weight tests , a
methodology used to
determine the extent of
breakage resistance due to
impact and abrasion.
om/

ODS - COMMINUTION
CHARACTERISATION
• Depending on the
requirement of the specific
ore dressing study, i.e.
feasibility study , pilot scale
tests can be conducted on
various comminution
equipment to validate
laboratory scale test results
and generate plant design
information.
• Samples can also be
provided to equipment
manufactures to conduct
their own tests
om/

ODS - DATA ANALYSIS
AND INTERPRETATION
• The data generated from the
characterisation tests is
analysed and interpreted by
process specialists.
• This is a collaborated effort
amongst in-house specialists,
proprietary and commercial
software, research institutes,
and equipment manufactures
and suppliers.
• Interpretation in this context
means that key metallurgical
parameters are determined
and operating envelopes are
established.
• Also potentially problematic
ore types are identified and
process recommendations are
made.
om/

ODS - DATA ANALYSIS
AND INTERPRETATION
• The output results in key
plant design information.
• E.g. comminution
characterisation predicts the
product size distribution
and mass balance via
simulation for scrubbing
and each of the crushing
stages.
om/

ODS - INTEGRATION
• The role of the metallurgist is
key in generating the
flowsheet design knowledge
package through the
interaction with a variety of
process specialists and process
engineers.
• Important major ore related
problem areas within a specific
ore type are also highlighted.
• This means that such problem
areas and solutions are
integrated within the overall
process design.
• Depending on the phase of the
project the integration process
also includes a level of
simulation of the ore dressing
study, and derived flowsheet
options that resulted from the
characterisation of the various
ore types.
om/

ODS - INTEGRATION
• Simulation enables critical
investigation of all system
attributes, and the ability of
the circuit design to deliver
finished product with out
recycling.
• Raw ore dressing information
and knowledge is traded off
against practical operational
constraints, which leads to a
fit-for-purpose design
• That has the best chance of
maximizing recovery of
minerals from in-situ
resources.
om/

ODS - PLANT DESIGN
• To reduce the risk of selecting
incorrect equipment from a
vast array of possibilities a
formalised set of tools to
guide equipment selection and
plant design have been
developed
• These tools consist of
commercially available as well
as proprietary tools
• Process engineers are
provided with basic flow
diagrams and related
metallurgical parameters.
• The process engineer will then
expand on the original ore
dressing flowsheet provided
and develop a number of
flowsheet based on the project
requirements.
om/

ODS - PLANT DESIGN
• Completed ore dressing
study assists the process
engineer to rapidly evaluate
scenarios using existing
models and create an
understanding of how the
metallurgical envelope of
characteristics develop
through the ore body.
• An evaluation of proposed
solutions against a
background of knowledge
derived from the study is then
conducted.
• The knowledge derived from
the study supports the
engineer in the design phase
and assists in reducing project
risk and increases confidence
in the approved flowsheet.
om/

ORE CHARACTERISATION -
UNDERSTANDING THE ORE
BODY AND THE METALLURGY
• The best possible
body will enhance the
ability to extract better
outcomes from a mine to
mill application.
• The greater data, the better
body Properties.
• This characterisation is
important in developing
extraction and processing
strategies which enhance
the productivity gains
possible from a mine to
mill application (JKMRC
1998)

CHARACTERISATION -
• At its simplest ,
characterisation is about
developing the best possible
understanding of the ore body
, in particular its variability.
• One of the first
comprehensive
characterisation studies was
reported by Simkus and Dance
(1998) at the Highland Valley
Mine
Highlands Valley
• Had developed a program
mapping the hardness of
different ore types, since the
late 1970’s.
• By late 1990’s , drill monitors
were being used to provide an
estimate of ore hardness of
subsequent blasted ore.
• Ore was then tracked to
stockpiles using mine dispatch
systems and movement
through stockpiles was
modelled.
om/

CHARACTERISATION -
• An image analysis system
was used to provide an
estimation of the feed size
distribution to the SAG
mills.
• Relationships were
developed between ore
hardness, feed size and mill
throughput.
• This approach provided a
strong ability to predict
expected mill throughput
information which could
then be utilised in process
control.
om/

CHARACTERISATION -
Rock Mass Properties
• Standard rock mass
properties are usually
obtained as geotechnical
information from drill core
and include:
• Rock Mass Rating
• Rock quality designation
• Point load Index
• Young’s Modulus
• Poisson’s Ratio
• Unconfined Compressive
stress
• In-situ block size
• Joint spacing
om/

CHARACTERISATION -
Metallurgical Process
Parameters
• These data typically include:
• Grades, including the grades
of gangue minerals and minor
elements
• Grindability data, principally
related to ore hardness, as
measured by bond work
indices and JKMRC grinding
model parameters,
• Flotation grade and
recovery data as
determined by laboratory
flotation tests
• Mineral liberation
• Lithology
• Geological Alteration
• Acid forming potential of
ore
om/

CHARACTERISATION -
Predictive Models
• Models frequently used in
mine to mill studies include
• Mine block models
incorporating geotechnical
and geometallurgical
parameters.
• Blast fragmentation models
• Muck pile models
• Comminution models
• Models which predict the
final stockpile shape
resulting from open pit
blast are increasingly useful
when it is desirable to
understand where material
of different properties,
notably grade, reside in the
muck pile after blast.
om/

CHARACTERISATION -
Conclusions
• The literature analysis suggests
that the tools required to
implement Mine to mill
approach are available in
acceptable form.
• Many of these hardware and
software tools are provided by
established suppliers and have
been successfully
implemented.
• Most tools are also subjected
to research and further
development
• The area of greatest need is
the availability of tools to
monitor mine to mill
outcomes.
• To date these have been
developed at individual sites
• More generic software tools
would be useful.
om/

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