The document outlines the process a geologist would follow to evaluate raw material reserves for a proposed cement plant. This includes: 1. Conducting a literature review and reconnaissance visits to identify potential sites. 2. Performing detailed field mapping, drilling, and core logging at priority sites to understand the geology below surface. 3. Interpreting drilling results to determine the deposit's structure, quality, and overall reserves that could supply the plant long-term. The goal is to prove that sufficient reserves exist of chemically suitable materials that can be economically extracted to meet the plant's needs.

1. 3
EVALUATION OF RAW
MATERIALS
D W POOK

2. EVALUATION OF RAW MATERIALS
CONTENTS
1. INTRODUCTION
2. LITEIWTURE SEARCH
3. RECONNAISSANCE
4. GEOLOGICAL INVESTIGATION
4.1 Detailed Field Mapping and Sampling
4.2 Drilling
4.3 Core Logging
4.4 Sample Preparation
4.5 Planning of Drilling Programme
5. INTERPRETATION OF BOREHOLE RESULTS
6. RESERVES ASSESSMENT

3. 1. INTRODUCTION
Imagine that a business consortium wishes to build a new cement works and they engage a
consultant geologist to advise them on raw material aspects. The geologist will employ some or
all of the methods described below to produce a report, which should meet the following criteria
if a sound judgement is to be made in flu-theringthe project:
i) The proposed raw materials are, en masse, chemically suitable.
ii) Sufficient reserves are availableto meet the raw material requirements for at least the
minimum work’s life specified by the investors.
iii) The reserves are economically extractable.
iv) The resewes, if quarried correctly, will provide an acceptably uniform feed for the life of
the works.
The procedures described below are largely referred to investigations for limestone reserves; they
apply equally to finding and proving reserves of secondary materials.
2. LITERATURE SEARCH
Today there is published geological information about most countries, so it is usually possible to
gain at least an impression of the extent of limestone occurrences in any country. Where these
are few in number then locations for a fist visit may choose themselves. In cases where limestone
outcrops are extensive, commercial factors such as infhstmcture and main markets may determine
the areas of interest.
Where countries have been geologically mapped there are often detailed descriptions of the rock
types which can indicate suitability of the limestone for use in cement manufacture.
Topographical plans and aerial photographs are also usefi.d, as can be information on any cement
companies already operating.
Whatever inflorrnationis available, it usually enables you to target regions which you would wish
to visit.
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4. 3. RECONNAISSANCE
This could be, at first a brief visit to all sites of interest in order to confirm the correctness of the
i.niiormationderived from the literature search. Some sites may have to be eliminated because of
non-geological reasons, e.g. property development, National Park or military installation. If a
number of sites remai~ it may be necessary to put them in order of priority and concentrate
fin-ther efforts on the top 2 or 3 sites.
The aim of that tier effort is to assess rapidly the geology of an area in relation to its economic
significance. This essentiallyinvolves the preparation of a basic geological map and initial
sampling in order to determine whether or not the material being studied filfils, in general terms,
the quaMative and quantitative requirements for the project.
The efficiency of the reconnaissance depends very much upon the skill of the geologist. It is
essential to know which features are important, and those that will affect the long term value of
the deposit. Accurate topographical maps are not required, and although in certain, areas, it may
be necessary to make rough topographical surveys, it is often found that existing maps suffice;
enlarged road maps can be used as reconnaissance base maps where no others are available.
Apart from collecting as much relevant geological information as possible, the geologist during
the reconnaissance will also be considering how much fi.u-therwork will be required to obtain the
information necessary to prove the deposit. This will enable him not only to report on the
potential economic value of the deposit, but also on the amount of development work which
would be required.
In the reconnaissance survey the area will be traversed for rock exposures, in particular strews
and rivers will be followed and the soils, together with their contained rock fragments, will be
studied. The effects of the rocks on topography will be noted; in areas where the land-form is due
to sub-aerial weathering processes only, and such factors as glaciation have not been effective,
the nature of the terrain is largely determined by the underlying rock. The vegetation is noted,
since this is often dependent on the soil type. For example, unexposed lenses of limestone in
schist have been successfully mapped in Portugal using the distribution of trees, the limestone
supporting oaks whereas the schist is covered by pines. In limestone country, unexposed or
grass-covered areas will be carefidly recorded as they may well be underlain by low-grade or
magnesian horizons. As well as the ground reconnaissance, an aerial survey by light aircraft or
helicopter may be made. This may well help the geologist to form a coherent picture out of the
mass of data he has collected on the ground.
Once the potential deposit under consideration has been generally mapped and some samples
taken for analysis,the geologist is in a position to prepare a reconnaissance report and map. This
would describe the areas most suitablefor fhrther detailed investigations, the potential qwdity and
size of the deposits and the possible ease or otherwise of extraction.
Assuming that the results of the reconnaissance survey are favorable and that the project is to
go ahead, then a decision has to be made as to which specific area(s) are to be investigated in
much fi.u-therdetail.
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5. 4. GEOLOGICAL INVESTIGATION
4.1 Detailed Field ?vfi3DDhIfZ %rrmling
and
Having chosen a site which has the potential to provide the required limestone tonnage,
then the geologist carries out surf ace mapping as in the reconnaissance survey but in
much greater detaii. A decailea topographic map is required and is usually prepared by
professional surveyors. All detail of the rock exposures is noted, such as the dip of the
beds, and where feasible some trenching or pitting can be carried out to expose the
rocks; systematic and well recorded sampling can be extremely useful. The geologist
needs to gain as much information as possible from the surface as this will determine
how much investigation is required by other methods such as drilling.
4.2 Drilling
When assessing a deposit, it is necessary to know the disposition and quality of the
strata at depth. Although this can be inferred from the surface information recorded
during detailed mapping, it is invariably necessary to confirm those inferences, usually
by means of drilling although geophysics can provide an alternative method for
determining the thickness of overburden.
Drilling boreholes to provide samples for identification and analysis of strata is usually
carried out by one of three main methods.
Augering can be used on soft rocks such as clays and shales which would be quarried for
secondary materials. For satisfactory results a powered auger is required, which will
either bring the sample to the surface continuously or require the auger to be brought
back up the borehole periodically. On site logging of the sample as it is recovered is
highly desirable. Advantages are rapid progress from hole to hole, disadvantages can
be the presence of harder material such as boulders preventing effective penetration.
A second method is a percussive one, suitable only for hard rocks, where a chisel bit is
driven into the rock and the rock chips are cleared from the borehole and collected.
Compressed air is used to operate a hammer device which both rotates and hits the
chisel biG the hammer can be located on the rig and the bit is located on the end of
specialised drill rods or it can be designed with an integral bit and located on the end
of the drill rods in which case it progresses down the hole as it is drilled.
Whichever type of hammer is used, it is necessary to clear the rock chippings from the
hole so that the chisel bit can operate efficiently, and compressed air is passed down
the drill pipe to blow the chippings back up the borehole to the surface where they can
be collected.
The third method is core drilling in which a purpose designed barrel, about 3 metres long
and from 76 to 115mm in diameter, is used to obtain a cylindrical sample of rock called
core.
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6. A diamond impregnated bit is fitted to the end of the barrel so that, when rotated, it
will cut out a ring or annular shape thus creating a cylinder of rock over which the
barrei will pass. Once the barrel is full the core can be retrieved by bringing the barrel
back to the surface; a catch spring in the barrel facilitates both snapping off and
retaining the core as the barrel is brought back up the hole.
Barrels are usually double ones; the inner barrel is designed to stand still and thus
minimise disturbance to the core. The barrel is progressed down the hole by adding
sections of drill pipe and is rotated via a clutch mechanism driven by a diesel engine.
Downward pressure is applied by hydraulic rams. A means of both cooling and flushing
any rock debris is necessary; usually water is pumped down the drill string and this
returns up the borehole to the surface. Additives can be used’ to improve perf orrnance
or reduce water usage if necessary; compressed air is an alternative to water.
The advantages of chip sampling are that it. is cheaper and faster than core drilling, and
to reduce costs could be done with a {lam-y drill rig used for blasthole ~illing.
Disadvantages are that the chips can become contaminated when passing back up the
hole and some of the dust is lost to the atmosphere. Use of cyclones to collect the
samples can improve representativeness, and there are rigs purpose designed with drill
pipes which incorporate an extra tube to carry the chippings to the surface. Coring,
although more expensive, provides not only more representative samples but also an
opportunity to describe the strata in considerable detail.
However, much depends on the integrity of the driller who must record the depth drilled
to obtain the core samples and also the occurrence of cavities. The softer, clayey bands
that are often present in limestone strata may be flushed away during drilling so that
although the core barrel is drilled 3 metres into the strata the recovered core lend I
will be less. It is extremely important that the geologist interprets this loss when
logging the core, as described in the next section.
4.3 Core Logg@
When core is removed from the core-barrel, its depth is noted and it is placed in a box
and appropriately labelled. This core will then be studied by the geologist who will not
only make a careful description of the strata and note such iterns as the angle of dip~
but will also calculate core losses. This is necessary since although the depths from
which the top and bottom of a section of core were recovered are known, it is’only by
calculating losses within the core that the accurate depth of any point within the
sequence can be determined. In his description of the core, the geologist will
differentiate carefully between all the rock types present and describe in detail each
of these rock types and the exact depth down the borehole of each junction between
them. It is essential that as much information as possible is obtained from the
boreholes since it is by correlation of individual strata, or groups of strata, in different
boreholes that the structure of the unexposed rocks is worked out.
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7. If a core is to be analysed chemically, the geologist will divide the core into suitable lengths for
analysis. Such sample lengths are normally based on differences in the rock which indicate a
change in the chemistry regarding its use as a cement raw material, although if a large thickness
of identical material occurs it will be divided at regular intervals.
Two important considerations when choosing sample lengths are (1) the analyses will be used to
predict the quality of the limestone for stages in quarry development and therefore the chosen
lengths should not span boundaries between strata which may be quarried separately (2) where
core losses have occurred the quality of the limestone as quarried may differ from that indicated
by the recovered core (e.g. loss of softer, clayeybands means the recovered core analysis is higher
grade than would have been the case if all the strata drilled had been recovered) and this must be
recognised when assessing the deposit.
4.4 SamRle Preparation
The aim of sampling and sample preparation is to obtain small portions of bulk material, such as
sections of borehole core, for chemical a.dor physical tests. Such samples must represent the
bulk material as closely as possible.
Where it is necessary to not only analyse the core but also either retain a fill core record of a
borehole or use the core for physical testing, the first stage in sample preparation is to split the
core longitudinally, this being carried out either by splitting with a chisel or preferably using a
diamond saw. The split core which is to be analysed is then crushed, using a laboratory jaw
crusher, to a maximum size of 6mm. The crushed material is then thoroughly mixed and a sample
representing about 2°/0 of the total taken. Accurate sampling of the crushed material can only be
petiormed mechanically, and the use of a riffle or rotary splitting device is highly recommended.
The small sample of crushed material can now be ground, ready for analysis, using either a pestle
and mortar or a ring roller mill (e.g. a Tema Mill).
Efficient sampling is a task which must be performed conscientiously; accuracy and cleanliness
are essential as is clear, unambiguous labelling. The sample for analysis will only be of the order
of 30 grams, whereas the initialcore from which it was obtained may have been over 6 kilograms
in weight. Much time and money spent on recovering borehole cores or other samples can be
entirely wasted if insufficient attention is paid to the preparation of representative samples for
analysis.
4.5 Planning of Drilling ProEramme
Dnillingprogrammed ii.dfiltwo needs; one is to determine the structure of the strata and the other
is to provide samples. The number of boreholes required is, therefore, a consequence of the
nature of the deposit. A simple structure with very little variation in grade requires a few
boreholes to confirm the predictions made from surface information. Boreholes maybe required

8. to locate faults or major folds, although they may not be necessary for quality reasons. Conversely, a
deposit which could have the simplest structuremight vary laterallyto such an extent that a series of
boreholes on a grid system is requiredto be drilled.
5. INTERPRETATION OF BOREHOLE RESULTS
,’
A geologist, having decided that enough boreholes have been drilled, must interpret the itiormation to reach
a conclusion as to the disposition of the strata at depth. The simplest explanation is applied first, and
increasing complexity is added only if justified by both the borehole and sutiace information. Figure 1
serves to illustrate how two borehole records could be interpreted; it will be appreciated that whichever
interpretation the geologist chooses it will be put to the acid test once quarrying begins.
In cases where the boreholes have only encountered one major stratigraphical unit, e.g. a major limestone
or chalk body, then correlation of the boreholes would have to be by studying detailed features such as shell
bands, minor clay lenses and textures.
The second important use of borehole informationis that of raw materialquality. Average analysescan be :
calculatedfor chosen stratain each borehole (hence the need for carefid selection of samplelengthsduring
core logging) and these, in relationto theirlocations, can be used to calculate an overall average analysis
for theraw material deposits. Furthermore, redictionscanbe madeas to the chemistryof the raw materials
p
as theywillbe deliveredto theworks, particularly ith regardto variations over the life of the works. Such
w
qualityinformation% togetherwith the physicalnatureof the materials(e.g. moisture content and hardness)
will be factors in choosing the type of process for the new works.
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—

9. Bomhole Results
:::
:::
;::
;::
;::
,,.
;::
:::
A. A horizontal bed B. A faulted horizontal bed C. Faulted dipping beds
Fault
...----#
F. Deeply eroded G. Repetition of
similar successions H. Latemi facies changes
FIGURE 1: POSSIBLE INTERPRETATIONS OF TWO BOREHOLES

10. 6. RESERVES ASSESSMENT
Having built up a picture of how the limestone occurs at depth, an estimate of the
reserves can be made as follows:-
(i) Area of limestone deposit multiplied by its thickness will produce a volume.
(ii) Multiplying this volume by the density of the limestone (typically 2.6 tonnes per
cubic metre) will give a tonnage
i.e. Area x thickness = volume
Volume x density = tonnage
The above calculations will provide a reserve for an area of interest, but it is also
gross
necessary both to design a quarry and to estimate how much of that gross reserve will
be won by operating the designed quarry.
Quarry design is illustrated by a simplified example shown in Figures 2 to 6.
The rectangular property shown in Figure 2 is known, from surface investigations in the
region, to contain limestone beneath a cover of soil and weathered material which will
have to be removed and tipped/dumped. Contours (i.e. lines of equal height or elevation
in metres above a fixed point e.g. sea level) on the ground surface are also shown in
Figure 2.
A series of boreholes were drilled to determine the thickness of overburden and their
locations are shown on Figure 3. For each borehole a thickness of overburden has been
recorded and this can be subtracted from the ground surface elevation to deduce the
elevation of the top of the limestone. This point information can be interpreted as an
unseen surface representing the top of the limestone and contours drawn as shown in
Figure 4; these contours will be useful in both designing the quarry and calculating
volumes
A slice or section drawn through the middle of the property gives a profile showing the
overburden overlying the limestone - see Figure 5.
When designing a quarry, allowances have to be made for:-
A margin to the company boundary.
A slope angle in the overburden for reasons of stability.
A bench, for access, between the base of the overburden and the top of the first
face in the limestone.

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Figure 5
.

13. Deciding at what elevation the first bench should be to avoid excessive face
heights (not greater than 15 metres).
.
Benches between the vertical (or near vertical) faces in the limestone for reasons
of stability.
Figure 6 compares two views of the proposed quarry - one is in section, the other in
plan view. Note that the sloping face in the overburden is shown with squiggles and the
limestone faces with cliff symbols.
What can be seen is that, because of the need to maintain stability, the area over which
overburden is to be moved is greater than that which will be quarried for limestone.
Volumes can be calculated for the overburden required to be removed and also the
limestone to be won. Note that when calculating the overburden volume, the average
thickness required could be averaged from the borehole results or by the better method
of estimating the thickness of overburden at points on a grid by comparing the ground
surface and the surface representing the top of the limestone. This latter surface would
have to be used to average the limestone thickness to be won from the top bench.
These volumes of overburden and limestone can be expressed as a ratio which is a useful
guide to the viability of working a limestone deposit. For example, having to remove
1 part of overburden for 1 part of limestone to be won might be an acceptable cosu if
this ratio rises to 2 parts overburden to 1 part limestone then it may be preferable to
quarry elsewhere.
It is these basic principles of maximum bench heights and the need for each bench to
be inside the area of the one above which are applied to the examples of quarry design
discussed in the next paper.
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Figure 6
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