The continuously growing demand for cement in Asia, Africa and South America results in the erection of continuously greater cement plants. The selection of their sites is governed primarily by infrastructural considerations. This means that limestone deposits of increasingly complicated structure have to be worked. 

Consequently, the exploration of these limestone deposits is no longer a purely geological problem but moreover requires a close cooperation between geologists, process engineers and mining specialists. 
 
The task of this team of specialists is properly to evaluate the geological results that have been obtained. It happens repeatedly that no more than a small portion of the comprehensive analytical data included in corresponding studies is evaluated. Such unsatisfactory assessment often results in drawing hasty conclusions for the process layout of cement-producing plants. However, such misinterpretation can be avoided as early as during exploration at extra costs which are significantly lower than expenses for drilling and analyzing. 

While recently, the cement demand did not increase at all or merely insignificantly in Europe, it augmented substantially in Africa, Asia and South America. Table 1 gives information about the cement production in African countries during years 1974 and 1975 as well as about the capacities of the plants under construction (see also Levine, 78). It turns out that an increase in cement production by about 100% can be expected for Africa in the years to come. 

It is particularly striking that the new constructions, - compared to existing plants, - are considerably larger. This trend to large- size plants, implying annual production rates of 500.000t to 2.000.000t, can also be observed in Asian and South American countries. 

Comprehensive geologic examinations will be required for ensuring supply of these large-size plants with the necessary raw materials over an operating period of 25 to 40 years. 

For covering that demand, cement plants are preferably set up in the close vicinity of the ultimate customer to avoid infrastructural difficulties, such as bottlenecks in transportation, traffic restrictions on account of climatic conditions and insufficient traffic facilities. The transport costs, too, are kept low in this way. Therefore, the plant site is less and less governed by the quality of the deposit, which means that deposits are developed, that result in most complicated quarrying and production processes for cement clinker due to the quality of the raw materials. 

Table1: 
Cement production in Africa in 1974/75 (as per Levine) 
 

Earmarking 1-5 % of the investment for the total plant for securing the supply of raw materials, will guarantee that the deposit can be quarried without unexpected major difficulties during the operating period of the cement plant. 

Exploration of a limestone deposit for the production of clinker has the following three objectives: 

1. securing the quality of the raw materials 

2. assessing the fluctuation range of the raw material quality for the life of the deposit 

3. securing the extractable raw material reserves. 

Especially, item 2 is frequently neglected. As regards technologic design of the specific machinery for a cement plant, it is most essential to ascertain the fluctuations of the different raw material components of a deposit for the service span of a plant, since this is the only way to guarantee trouble-free operation, and to yield a final product of good quality. 

The existing fluctuations, must, however, not be ascertained only on a long-term basis; minor variations covering several months up to half a year should be known well in time to allow suitable measures to be taken with regard to machinery and process engineering. Apart from that, economic considerations may suggest quarrying or purchasing correcting agents. 

Seen from the point of view of the plant manufacturers, it has unfortunately to be said that difficulties in connection with the exploration of raw materials for new cement plants, are either not duly considered or neglected completely. This especially applies to the cost of prospection, being, as mentioned earlier, negligible when compared to the total investment for the construction of a new cement plant. 
 

The portion of the limestone component in the mixture ranges between 90 and 50% by weight. Hardly ever so called natural cements are found, which can be burnt to cement clinker without any additives, or for which only additives of 1-3 % weight will be used. As regards the main chemical elements of limestone, the SiO2, Al2O3, Fe2O3 and CaO contents may vary within wide limits, however on the condition that the lime standard (KST = 100 CaO/2.8 Si02 + 1.18 Al2O3 + 0.65 Fe2O3) exceeds 100. For setting the lime standard "KST" to values between 90 and 98, which are customary in practice, the SiO2, Al2O3 and Fe2O3 in the raw mixture will be corrected by suitable clay mineral components or other additives. However, strict restrictions must be requested for MgO, SO3, K2O, Na2O, Cl and P2O5. Local standards have the MgO content limited to 4-6% by weight in the clinker (DIN, ASTM, max., 5.0 % by weight, BSS max. 4.0% by weight. Brazilian standard max. 6.0% by weight max. MgO in the clinker) for avoiding cement expansion due to the presence of magnesia. For precluding delayed setting and delayed strength development, the P2O5-content is generally limited to 1 % by weight at a maximum in the clinker; this value being not based on a standard, but having been ascertained empirically. 

The SO3-content of the cement is likewise restricted by a standard. The values to be met by the raw material must significantly range below the standard values, since fixing of the setting properties requires grinding of the clinker to cement by adding gypsum or anhydrite. The sulfate content of the clinker shall not exceed 1.5 % by weight of SO3, being an empirical value. The SO3-content has to be kept low for reasons of process engineering, too (see below). 

Standards require limited alkali contents only for „low alkali"-cements, being used with concrete additives that are sensitive to alkalies. The limit equals 0.6% by weight of Na-equivalent (Na2O + 0.659 K2O). 

Together with sulfates and chlorides, the alkalies are of specific importance for the burning process. Easy volatilization of the alkali chlorides implies the danger of circuits of the corresponding compounds building up inside the kiln system, which may entail accretions and cloggings. This likewise applies to sulfate circuits. In such cases special facilities should be incorporated in the kiln system (e.g. a bypass for withdrawing alkali-bearing dusts and gases), or a long kiln should be installed instead of a preheater system. The presence of organic substances or of graphite in the limestone will result in particular difficulties for the layout of a kiln system. Therefore, selecting the most suitable kiln will require thorough investigations, in particular with regard to combustibles contained in the limestone. 

The mineralogic composition of the limestone is less important than its chemism for cement production. Petrographic and mineralogic investigations are of interest mainly with respect to the rock nomenclature and to the layout of crushing- and grinding systems. 

On request, information can be given about the burning properties. 

Thus, exploration of limestone for cement production, is substantially a geochemical examination of the deposit. In this respect, the specific structural conditions will be of decisive importance for later quarry working duly considering the limestone demand of the cement plant.

Apart from the limestone quality mentioned above, comprehensive requirements have to be met by the deposit, particularly with regard to the specific mode of extraction. 

Cement plants, producing 1000 t/d to 6000 t/d of cement clinker, require 2000 t/d to 12 000 t/d of raw materials (taking into account 330 days of clinker production and a working time in the quarry of 260-280 days), with 50% to 90% of that quantity being limestone. 

Quarrying of such quantities is done in large-scale opencast working, by benches, or by large-scale ripping. The objective of exploration, has to be furnishing proof of the extractable reserves for ensuring their economic quarrying. Apart from evidencing the limestone grade, comprehensive examinations have to be made as to structural conditions, faults and hydrologic situation duly taking into account quarry working. 

It will above all be required to prepare an advance plan for quarrying already during the exploration, so as to provide for selective investigations on the basis of the specific site problems. 

Demands raised due to reasons of environmental control, excavation regulations and the like, are not dealt with in this paper. 
 

Any prospecting operation will be matched to the specific conditions of the deposit, so that merely general outlines are given below. Normally, prospecting is made up of three phases: 

phase 1: touring several deposits, surface sampling, isolated drilling, core drilling, if any, simple hydrologic and tectonic examinations, large-scale mapping. 

The objective of the first phase of limestone prospecting is selecting one or several deposits for further detail exploration. Here the quality of the deposit is of major importance, while mining problems are only dealt with marginally. 

phase 2: After completion of the first phase, one or several deposits are selected for detailed investigations. During that phase the deposit is substantially explored by way of an extensive drilling programme, to obtain information on the chemism of the deposit. 

Along with the drillings, investigations are carried out for structural conditions, ground water and mining to enable site assessment for open-pit mining. The objective of the second phase is to select from a deposit the most suitable area for location of an open-pit mine, or to select the most favourable out of several suitable areas. 

phase 3: Detailed examinations are carried out during the third phase of an exploration. A close-meshed drilling network is set up for thoroughly investigating the limestone chemism and subsequently matching the plant layout to these findings. 

Moreover, special investigations are carried out for planning mining operations. The deposits' structure is explored over narrow areas. It will likewise be possible to investigate e.g. the possibility of extracting by way of ripping. The investigations are accompanied by evaluating the available results, so that clearly recognized problems can be duly considered under the current prospecting work. After completion of the third phase of geological exploration, all aspects of the deposit will be thoroughly known, i.e. as to quality, quantity and mining, so that it can be prepared for quarrying. 
 

The samples for investigating a limestone deposit are extracted from the surface, either directly from the exposed rock trenches or from penetrating the limestone- or weathered layer, or from deeper strata of the deposit by means of drilling. In general, both processes are applied. 

Conditions that merely allow surface testing are found very rarely. It will, of course, be possible to do trenching without sampling or surface sampling, and merely apply drilling, however this will not be done during phase 1 of the investigation on account of the cost involved. 
 

6.1 Trenching and surface sampling  

Extracting samples from test pits, will mostly be surface sampling, since the limestone will hardly ever allow putting down trenches to greater depths economically. 

Trenches are put down wherever material covering the limestone must be removed for limestone sampling, enabling a simultaneous sampling of the top layer and testing its usability. 

As soon as the limestone surface has been freed or if it is exposed without top layer, sampling can be done in two different ways: either individual samples are taken from a small outcrop or continuous samples are taken along a contour or along the length of a trench. 

It is essential for continuous sampling that the samples are representative of the rock mass that has been penetrated which can most simply be ensured by a channel, yielding a constant sample quantity per unit of length at approximately constant cross section. 

If preparing a channel is too expensive or not feasible at all, a sample (quantity) must be taken from the rock mass being at correct proportion to the thickness of the pertinent rock mass. 

If possible, not only the surface of the limestone should be trenched but the trench should be put down at least to the lower weathering edge of the limestone, which in most cases is done with the aid of a heavy excavator or with road breakers and compressors; a ripping crawler or even lighter appliances will be suitable for young chalky limes or coral limestones. 

It will have to be decided in each specific case whether the samples taken at the surface or originating from trenches, are reliable. 

At any rate it will have to be examined, whether compared with the samples the chemism may have been changed by atmospheric influences, weathering or by circulating waters or near-surface ground water. In the latter case, the chemism of the ground water, too, will be of great importance (illustration 1). 

Table 2 shows different prospecting results, for which trench and drilling samples had been taken. Prospecting in the Middle East yields samples that perfectly correspond to each other. For instance, a continuous channel sample was taken as surface sample at the natural hillside outcrop of a pile of limestone. Due to the climate, the rock has been exposed only to high temperatures, entailing thin desert varnish encrustations only on the topmost rock layer; these can easily be excluded from sampling. There are almost no rain fails and ground water is lacking, too. 

Table 2 
Comparison of Si02- and CaO-contents in the samples 
taken from drills and trenches 
 

	Middle  east drill	Middle  east rench	Central America drill	Central America trench	Central America drill	Central America Trench
SiO2	1,6	1,4	8,8	7,0	17,2	8,7
CaO	53,9	54,3	46,3	50,0	39,4	41,1

  
 

 

For preventing such errors, at least one drill should be put down during phase 1 of a prospecting job for each deposit to be examined. 

A prospection, merely based on sampling of trenches - as is practiced in several countries - should be accepted with great care and serve as a basis for the layout of machinery with certain restrictions only.  
 

6.2 Drilling work  

Selection of the most suitable drilling process, also with regard to economical aspects, is a precondition for a successful prospection. Mainly three drilling processes are available for limestone prospecting: 

solid drilling incl. discharge of the wet drill cuttings by flushing core drilling with continuous bore sections rotary impact drilling incl. discharge of the drilling dust. 

Solid drills with rotating drilling chisel and discharge of the drillings by the flushing medium followed by collection of the drillings are considered exploration drillings and are suitable only in exceptional cases. It must be known prior to start 

of the drilling work, whether the sample chemism may be subject to changes, either by washing out soluble compounds (e.g. alkali chlorides) or by loss of marl layers or intermediate clay layers in the deposit. Moreover, solid drilling with the aid of cone bits requires mostly large drill hole diameters, which in turn, necessitates a correspondingly heavy drill unit, thus increasing the capital expenditure for the drilling work. 

Rotary impact drilling with the aid of a crawler-type drilling unit, also used for drilling of blasting holes in quarries, implies similar difficulties for sampling as solid drilling. The drillings are lifted with the flushing air. This mode of drilling, too, implies the danger that soft, moist intermediate layers (e.g. clay layers) are displaced by the drill bit to the rim of the drill hole so that no dust is entrained by the flushing air from these layers which could be used as sample. 

Duly taking into account these factors, application of this economic process is certainly suitable for supplementing a core drilling programme. 

The most safe and reliable method for evaluation is the core drilling method. A continuous core is drawn through the total drill hole depth, so that - subject to a properly experienced operating staff - the geologist will get a comprehensive idea of all details of the limestone deposit as regards its depth. 
 

6.2.1 Core drilling 

Today, a great variety of core drilling units of varying outfit and easy to handle are offered. These units are frequently mounted on all-wheel drive vehicles, thus enabling their being manoeuvred even in most difficult terrains. Moreover, core drilling units are offered, that can easily be dismantled, thereby ensuring the availability of easily handable individual systems for transportation by bulldozers or even helicopters. 

A proper selection of drill bits, core barrels and flushing appliances will be decisive for a successful exploration. 

The diameter required for core drilling in limestone shall not be smaller than 75 mm. Smaller diameters imply the danger that clogged cores break down thin, soft intermediate layers by grinding, that the drill hole is easily jammed by failing down material and that layers are lost by flushing. 

The maximum diameter of the cores is limited due to economic considerations. Diameters of 120 mm and more are very rare, except for critical situations, which require drilling with water flushing for porous rocks and where washing out of soluble compounds can be prevented (see below) due to the large diameter inside the core. Drill cores that are too small, imply inconvenient working conditions for the evaluating geologist. Moreover, core halves set aside for record purposes are inappropriate for subsequent or supplementing examinations if they have a small diameter. 

Selection of the appropriate drill bit much depends on the rock, proper, on its thickness, fissures and tectonics of the deposit as well as on the abrasivity of the rock. Tungsten carbide- and diamond drill bits are used. In case of large diameters and very weak rock, hard metal bits entail the danger that core elements get clogged in the core barrel. Moreover, drilling with tungsten carbide bits, has the core more exposed to the flushing medium than in case of diamond drill bits. Actually, proper selection of the drill bit depends on the skill of head driller. 

  
 6.2.1.1 Core barrels  

For selecting the core barrel, the geologist should precisely define the requirements to be met by the core. 

Three core barrel types are available: the single tube core barrel, the double tube barrel, and the wire line core barrel. Moreover, there are special core barrels, being suitable for use under extremely difficult conditions. 

Illustration 2 is a schematic presentation of the three core barrel types. The single tube core barrel bottom part a accomodates a coretrap ring above the bit, retaining the drill core when pulling the string of drill pipes, thus avoiding its being dropped into the drill hole. A precondition for using a single tube core barrel is that a core can be cut out of the material to be drilled. Thin flaky limestone, tending to break during drilling, implies the danger that a portion of the sample fails back into the drill hole upon pulling the drill core. This makes geological and geochemical treatment of the sample cumbersome, since only fractions come to hand as sample material. These fractions do not allow the necessary detailed examinations. Another essential drawback of the tube core barrel is that the drill core is surrounded by the flushing medium over its entire length, so that sandy, silty and clayey inclusions and rock chippings may be washed away when flushing. 

The outer tube of the double tube core barrel accommodates a tube being connected to the former by a ball bearing, thus ensuring that the outer tube does not join rotation of the drill bit. In this way, the drill core remains at rest position, thereby substantially avoiding breaking up of the core halves by grinding against each other. The most essential advantage of the double tube core barrel can be attributed to the fact that the core is not surrounded by the flushing medium, the latter being transported in the annular space between inner and outer tube. The drill core comes into contact with the flushing medium only in the bottommost part of the drill tube, i.e. where the inner tube terminates, and where a gap exists for passage of the flushing medium between the inner tube and drill bit. Although this arrangement practically avoids losing of material, soluble matter may still be entrained with the water. 

Special double tube barrels are equipped with drill bits, which have the flushing liquid not escape between inner-and outer core barrel in the drill bit, but have it discharged in front of or on the cutting surface of the drill bit. Inside the drill bit (figure 2), the inner tube has been fitted so closely to the bit, that the core practically does not come into contact with the flushing water. 

Drilling in very soft and brittle material, which however, allows a stable drill hole, enables inserting a plastic tube into the inner tube of special double core barrels which is to take the core. The core will be removed together with the plastic tube, thus enabling an examination of the undisturbed rock. 

If the deposit consists of a material not guaranteeing a stable drill hole, even when providing for drilling mud, drilling can be done by way of a wire line barrel. 
 

 

The drill pipe of a wire line barrel has the same diameter as the core barrel. However, the inner tube is not rigidly connected to the outer tube over a ball bearing, but retained in the outer tube by a ratchet. As soon as the required length of the core barrel has been drilled off, a rope with a fishing taper is lowered into the drill pipe, which releases the ratchet and serves for lifting the core barrel with the core. This method offers the advantage that the string of drill pipes will not have to be pulled when pulling the core, thus avoiding a follow-up of material, caving, and clogging of the drill hole. Core pulling requires less time than other core barrels. Again, wire line barrels are available, where the flushing medium escapes in front of the cutting edge of the drill bit of the inner tube, so that the core hardly comes into contact with the flushing medium. Since a wire line core equipment is expensive compared to the other core equipment, mentioned above, there are unfortunately only a few non-European firms, who own that appliance. The cost of drilling with a wire line core barrel is higher than with double- or single tube barrels. 
 

6.2.1.2 Flushing  

Selection of the flushing medium for drilling jobs in limestone, is of particular importance for later geochemical treatment of the samples. As has been mentioned repeatedly, flushing with liquids implies the danger of washing out clayand marl layers as well as sandy-and silty inclusions and having soluble components in the limestone entrained with the liquid. Basically, distinction can be made between air and liquid flushing. Air flushing shall be preferred in any case, since this safely prevents solving and discharge of components and material. Air flushing will in many cases not require the use of a double tube core barrel, since the sample is only surrounded by air in the single tube barrel. Many drilling contractors abroad refuse to work with air flushing, since they fear great wear at the drill bit and often are unable to provide the necessary large compressors. Comparing the costs of liquid flushing with provision of a compressor, the expenditure for liquid flushing is substantially higher. Apart from a pump, a tank vehicle for the required water will have to be available, too. Due to quality problems, the water must often be procured from far away. 

Nevertheless, most drillings are carried out with liquid flushing. Therefore, utmost care shall be taken right from the start of the works. 

In any case the flushing water pressure must be kept at a minimum. Increasing the flushing water pressure augments the danger of washing out material. 

Illustration 3 shows a cutout of a working face of a limestone deposit. There are alternate layers of approx. 1.0 to 1.5 m thickness of limestone with marl layers. Exploring the deposit had been done with water flushing and a high flushing water pressure, so that most of the marl layers was discharged. An examination of the cores revealed that the deposit was suitable for winning limestone for the production of cement. Marl layers of high MgO contents were noticed only after actual quarrying had been started so that this deposit had to be given up. 
 

The porosity of the limestone, too, is of major importance for water flushing. At any rate the water to be used shall be analyzed to allow drawing conclusions as to the influence of the flushing water on the sample. In case of e.g. salt water, it will anyway by difficult to distinguish between the alkali content of the limestone and the alkali quantities originating from the flushing water. In this context, it must be pointed out that especially the alkalies are of great signifiance for layout of a rotary kiln system for the production of cement clinker. 

Duly considering the factors described above, water flushing with the aid of a double tube core barrel will yield good results, on the condition that properly trained and well-experienced personnel, including modern equipment, is available. 

If, however, a limestone of high porosity has to be worked which, moreover, suggests high alkali-, chlorine- and sulfate contents, core drilling with air flushing will be the only way of extracting samples for geochemical examinations. Table 3 shows a comparison between samples taken by drilling with water flushing and trench samples from young coral limestones at the East coast of the Red Sea. 

Table 3 Comparison between the Cl-contents of trench samples and samples taken during core drillings, with fresh water flushing in coral limes at the East coast of the Red Sea. 
 
 

6.2.1.3 Describing the drilling cores  

The drilling cores are stored in suitable boxes. If the cores must be transported over long distances, the boxes must be made of very strong material and must be fitted with irons, A collection of loose drill cores after transportation will ruin all previous work. 

In the field, the drill cores should preferably be described by the geologist after having been removed from the core barrel. Afterwards, a colour photograph is taken of each box with the lid removed. 

Field describing should be as comprehensive as possible, so that the specific site conditions encountered during sampling, can later on be correlated with supplemental drilling or after exploration of the deposit. 

The drilling record shall quote drilling- and geological data, thus ensuring a complete log for each drill after the geochemical examinations have been supplemented. 

Location, altitude of the drill hole collar and identification of the drill must be included in each drill log. Drill hole diameter, type of core barrel, type of drill bit and drill bit change, core lifting, loss of returns and drilling progress, must be entered in the log with due reference to the corresponding drilling depth. Provided these data are available, they may later on serve as a basis for considering whether it would be advisable to use other tools for drilling. Moreover, the master driller should state, whether the rock is hard or easy to drill. Although this statement will always be subjective, it will, however, facilitate a correlation of the profiles at macroscopically uniform rock. 

The correct geological description of the samples comprises the identification of the examined rock, the rock colour, its granular texture, data on inclusions of foreign rock or mineral inclusions, porosity and hardness as well as thickness, fissures and data on existing faults. 

Moreover, extraction of samples from the core section should be entered in each drill log, unless the core is split and one half remains for record purposes. If data on an approximate stratigraphic classification are available, these should likewise be included in the log. Field tests may already be carried out at the cores, for assessing the CaC03- content or for checking presumed MgO-contents. These investigations, too, must be entered in the drill log. A graph giving information about the specific conditions will in any case be required. 

The complete drill logs are always added to the final report on the examinations, to have others get an idea of the original data of a geologic report. 
 

6.2.1.4 Sampling of drill cores  

For drill core sampling these are split into sections by macroscopic aspects, which then represent a larger analyzed section. Generally, when exploring limestone deposits for the production of clinker, the smallest analyzed section may equal approx. 1 m core section, but the largest should not exceed 5 m. 

Wherever feasible, the core should be split, having one half preserved for further treatment and the other directed to the laboratory. The core may be quartered in case of very large core diameters. If the core cannot be split, but is reduced in a laboratory crusher, the sections should not exceed 1 m to save cost in laboratory analyzing. 

6.2.2 Rotary impact drilling with the crawler drilling unit 

An economical way of supplementing core drilling and of ensuring a closed-meshed drilling network is rotary impact drilling with the aid of a crawler drilling unit. 

Crawler drilling units are used in quarries for drilling blast holes. They are mounted on a crawler unit, which allows manoeuvring the drilling facility even under most difficult circumstances, thanks to oscillating tracks of the crawler. The machine is moved by hydraulic motors, the hydraulic pump is supplied with compressed air by a compressor. The compressor is either towed as trailer or the unit is connected to the compressor via a correspondingly long line. The compressor supplies both the air for drilling as well as for flushing. There are also units where the hydraulic pumps are operated with a diesel engine of their own, requiring, however, also a compressor for the supply of flushing air and possibly of air for drilling. 

The drilling units are equipped with a swivel-type and tiltable cradle, onto which the feed device has been mounted. The feed mostly has a length of about 3 m. The drive for rotation of the auger stems is in any case mounted on a slide, provided on top of the cradle. The hammer may either be mounted on the cradle, too, for transmitting the blows via the string of drill pipes, or a down hole drill hammer can be used inside the drill hole fitted to the end of the string. This hammer substantially relieves the string of drill pipes. 

Cross-or pin drill bits can be used as drill bits, with the latter requiring less attention. 

The rotary impact drill bit shatters the rock, the flushing air emerging from the bit lifts the drilling dust to the drill hole rim. 

A dust separator enables collection of the discharged dust This dust- separating unit is mounted to the drilling unit. It comprises a cyclone, meant for separating coarse particles, whereas the smaller particles are retained in special filters. The suction unit is connected to a hose, terminating in a plastic sleeve which tightly seals the drill hole rim. This guarantees collecting all dust. It is essential for sampling that not only the dust separated in the cyclone is analyzed, but also the fines of the sample separated in the filter. 

Also this drilling method allows drilling by sections, having, e.g., dust that accumulated when drilling along one length of the rod taken as sample and having cyclone and filter cleaned upon an exchange of the drilling rod. 

During drilling operations of this type, it is noticed repeatedly that the dust is collected without a suction unit, by placing a plastic sheet around the drill hole collar, for collecting the dust originating from the drill hole. This method is not recommended, since the fines portion will be blown away. These drillings can merely offer guide values, or provide quick information on approximate chemical composition of a specific zone inside a known deposit. 

The results of these dust analyses are reliable only if it is known that the drilled layers are compact and exist as limestone rock over the entire depth. 

Intermediate clay layers, sand inclusions, or soft, wet limestone are pushed to the side by a rotary impact drill bit and stick to the wall of the drill hole. No sample is extracted from these layers. 

This method will not give information on cavities in the rock either. Above all, there is no way of sampling the rock proper, and of getting an idea about the existence of the limestone in the deposit which actually has been the objective of prospecting. 
 

Stratigraphic examinations are of sub-ordinate importance when prospecting raw materials for the production of cement as the suitability of a specific limestone depends primarily ~n its chemism; moreover, suitable raw materials may exist either in the form of precambrian marble or as more recent coral deposits. Consequently, limestone deposits of this type are not bound to specific ages. 

Hence, stratigraphic examinations are mostly limited to macroscopic classification of the drill cores and to assigning characteristic guidelines so as to correlate the different core drillings to each other. 

However, the chemo-stratigraphic examination of the drilling profiles is of greater importance, in particular, if the deposit appears fairly uniform as to the terrain and judged by the drill cores. 

These tests will often allow noticing facies differences which would otherwise not be recognizable. These differences may be of great importance for the quarry working schedule to be prepared later, e.g., with average CaO contents of the limestone of no more than about 46% and upon pronounced shifting to calcareous lime facies. That situation often requires special arrangements for quarrying to balance the fluctuations in the CaO content since great fluctuations can hardly be made good for, in particular not in the long run. 

Biostratigraphic examinations or micro-facies tests will be necessary in very rare cases only. 

It would be of advantage if the sample material left after completion of the tests and originating from drilling and prospecting were made available to interested research and university institutes. They could carry out stratigraphic examinations and other investigations. 
 

Investigations about conditions and structure of the deposit are more comprehensive than stratigraphic examinations. An exact assessment of conditions and structure of the deposit are the basis of reliable planning for quarry working and for a geo-chemical evaluation of the results of drilling. 

The examinations begin with recording the outcrops that exist within the area of the deposit. These enable measuring sequence of strata and faults, if any. Special attention has to be paid to micro-tectonics which measures decimetre and metre dimensions, since these structures are of oustanding importance for the later orientation of the quarry face. Moreover, these outcrops permit observation of zones that have been affected by stress which is reflected by changing thickness of the layers or by foliation of the lime material. 

Faults require special examination. Similarly, fractures without displacements which are found flat-spread throughout the limestone are of importance for future planning. Frequently, younger limestone deposits (e.g. Westphalian upper Cretacious) are interspersed by such fractures. Their surfaces are often covered with calcite and a thin clay layer. These phenomena have to be watched particularly careful when planning quarry working since blasting shocks will easily result in rock sliding so that portions of the quarry face may suddenly slide down over great widths. 

In the event that the outcrops of the deposit do not suffice for complete plotting of the structural elements, a photogeologic plotting may be of help. However, a prerequisite is that aerial photographs are available of a scale of about 1 :5 000 to 1: 15 000 and that vegetation will allow such photogeologic evaluation. 

Another important aid for assessing structural conditions are the drilling results. A first correlation can be made on the basis of the stratigraphic description of the different drillings. However, such correlation must not be carried out only after completion of the drilling work but has to be done along with drilling, thus having a possibility of correcting the location chosen for the new points of drilling on the basis of the evaluations made. 

Evaluation of the macroscopic stratigraphic description of the drill cores is done by profile sections along the drilling network and by maps which indicate the depth of specific stratigraphic horizons. These data will permit developing a good representation of the structure of a deposit which will be supplemented by entering the findings of the geochemical tests 

Such supplementing is the second step towards structural examination of a deposit. The chemical data of each drilling and the stratigraphic details are entered in profiles and depth contour maps. A combination of these two evaluating procedures will then give a clear definition of the tectonic and geo-chemical structure of the deposit. 

The results of these two analyses must not necessarily coincide. Particularly cretacious deposits frequently show facies shifting which does not correspond to the tectonic structure and which will be reflected in the results of chemical analyzing. 

Planning of quarry working can be started only after all conditions of these two aspects are known. Such planning will include working by quantity of the rock to be won and by the chemical composition of that quantity per unit of time. Such assessment is of specific importance whenever faults exist where, due to secondary effects, the chemism of the limestone has been changed in front of and behind that trouble. Although such change will be localized, the raw material properties will be different for a certain operating period. Such alteration has to be known well in advance to have working organized in such a way that unhindered production operation will be ensured. Moreover, a possible influence on deposits due to magmatic activities in their vicinity or metamorphous changes have to be investigated with particular care. 
 

The top layer of the deposit has to be included in the investigation to decide on whether that layer will have to be discarded or included in the production, e.g. as portion of the clay mineral component or as sand additive. 

This requires chemical examination of the top layer and checking its thickness. These tests can be combined. Investigating the thickness can be done with core drilling, just like taking samples for chemical analyzing. 

Apart from that samples can be taken and the thickness determined during prospecting. 

An inexpensive and quick method are drillings for ground investigation where a channel-type drill steel is driven in with the aid of a heavy hammer or a motor-powered road breaker. Upon withdrawing the drill steel material is retained in the channel which can then be used as sample. 

If nothing but thickness shall be investigated, geo-physical procedures have proved successful. Seismic analyzing i's especially suitable for top layers consisting of mantle rock; this is a quick and inexpensive method. However, it requires a fairly plane limestone surface. It cannot be applied for strongly carstic surfaces. A combination of seismic analysis and drilling for ground investigation will be particularly advantageous. 

For thicker overburdens it is likewise possible to use the resistivity method which yields good results when combined with seismic analyzing. 

A map with contours of identical overburden thickness will be best suitable for evaluating the overburden examinations provided the overburden is not uniform and very thin. 
 
 

The ground-water level in the area of the deposit has to be known for planning quarry working. That level will best be observed by watching the water level in the drillings that have been put down. Of course, a certain period will have to be considered for water steadying when flushing is applied, i.e. to allow the flushing water to be distributed. However, such observations should at any rate cover a whole year to include seasonal fluctuations. 

Hydrogeological investigations will be particularly comprehensive in carstic deposits which frequently require a wide network of levels of observation. If the drillings do not suffice for determining the ground-water level, it will also be possible to have an examination with electrical geophysical tests made; it can be supplemented by plotting the ground- water surface on the basis of electrical geophysical tests. However, similarly complicated investigations will be made only if the ground-water level is at the height of the quarry floor or just below it or if several aquifers shall be approached. 
 

If it becomes obvious as early as during exploration that the material cannot be worked by conventional bench methods, but if ripping crawlers have to be used instead, it will be necessary to examine rippability of the limestone. This can be done by a ripping test with a suitable crawler. If that is impossible, it has proved successful to have the travelling speed of seismic waves determined by seismic analyzing. The results of these tests and the technical data given by the crawler manufacturers will permit a decision as to whether ripping will be possible and which appliance will be suitable for that job. 
 

Apart from drilling, chemical analyzing causes most of the cost accumulating for prospecting work of that type. T fore, all opportunities should be utilized to ensure eco working by a clever arrangement of the sampling sectiions. 

As a general rule, the contents of SiO2, Al2O3, Fe2O3, (TiO2) CaO, MgO, S03, K2O, Na2O, Cl and P2O5 of a specific limestone have to be known for assessing its suitability for the production of cement. It may likewise be necessary to check the content of organic substances since they will tend to oxidize in the preheater and - because of the reduction of Fe2O3 - result in the formation of accretions. 

As mentioned earlier, the portions analyzed and made up of bore sections should not be longer than 5 m. If the samples are macroscopically uniform, 5 m could be combined to one analysis. However, this implies the danger that fluctuations existing in the analyzed section will not be noticed although they may be decisive for planning quarry working. Therefore, the halved cores should preferably be sub-divided into sections of 1 m and these prepared to one sample. For these combined 1 m samples the total carbonate is determined first to get an idea of possible fluctuations by the main portions of CaO and MgO. However, that test should at any rate also include determination of the insoluble HCI residues as these may contain minerals that will essentially influence the MgO content. 

Table 4 compares these values. It turns out that the difference between the two analyzing methods increases with rising clay portion in the limestone. Therefore, this test method has to be considered with care, in particular for marly limestones and calcareous marls. 

Table 4 Comparison of the contents of MgCO3 and CaCO3 having been determined by titration and complete chemical analysis: 
 

The X-ray emission gauge has proved most successful for handling large sample quantities as it permits coping with large amounts within short periods. However, alkali and sulfate contents have to be examined by wet chemical analyzing since, when ascertained by the X-ray method, they will be reliable only when found by most experienced staff. Chlorides will at any rate have to be determined by wet chemical methods. Needless to say that a prerequisite for a successful application of the X-ray emission gauge will always be a good calibrating curve which is continuously checked by wet analyzing of reference samples. 

When prospecting limestone deposits for ascertaining the existence of raw materials for the production of cement, mineralogic and petrographic investigations are less important than chemical tests.  

Frequently, the limestone exists as lime- clay mixture. If so, it is defined on the basis of the chemical analysis for the "Kühl" nomenclature (1958) (table 5). Mineralogic tests will be of interest if the raw materials shall be separated into components rich in lime and components rich in clay mineral (e.g. for the production of white cement clinker when the Fe203-bearing components have to be separated).  

These investigations are of importance for siliceous limestone deposits. It will then be necessary to ascertain the quartz distribution in the lime matrix. Type of intergrowth and grain size of the components can be determined by way of polished sections. The mineralogic test will then also be of interest for identifying the rock. 
 

Table 5 
Kühl nomenclature proposal (1958). These terms are normal practice in today's cement industry. 
 

Apart from that, the distribution of dolomite can be investigated by staining the polished sections. However, examining deposits will be easier by chemical analyses. 

In addition, mineralogic data will be of specific interest as to expected wear in crushing and grinding equipment. 

In many cases, the quickest way of getting information on the mineralogic composition will be the X-ray powder method. 
 

The test results available have to be processed such that any fluctuation as regards chemism, quantities to be worked, changes in the mixture and use of equipment will be recognizable from the evaluation. 

The first decision to be made will be for what periods average values have to be formed by the results obtained. An average analysis for a deposit of 5 x 10^6 tons of limestone will not be of any use for fixing the machine pool required for a cement plant. 

The length of these periods is governed essentially by the homogeneity of the deposit. After the periods have been fixed, evaluation can be started along with planning quarry working. This combination is decisive for calculating the existing reserves. 

14.1 Geochemical evaluation and planning of quarry working  

Along with planning of quarry working, the first thing to do is determining the average chemical composition of the first section to be worked. This is followed by calculating the raw mixture for the production of cement. That calculation will reveal the limestone portion in the mixture, i.e. the limestone originating from the first part to be worked. That value will permit calculating the exact service span of the pertinent quarry section. 

Of course, the composition of the materials included in the mixture apart from limestone many change in the period concerned which will result in altered component portions. Needless to say that such changes have to be duly considered when quarrying the first batch, as this may entail alterations of the quantity of limestone to be won daily. Similar statements apply to changes in the limestone composition. If a strongly marly limestone is approached near a fault zone it 

will have to be investigated what quantity of limestone of higher quality has to be recovered at another point of the quarry for arriving at the required raw mixture. It may even happen that changes of this kind in the chemism of the limestone will make the addition of clay unnecessary over extended periods of time. That will, of course, necessitate an adequate number of machines to allow winning and conveying that additional quantity of limestone. Moreover, that additional demand of material will reduce the service life of the deposit. 

Influences of that kind can be assessed only if geochemical evaluation and quarry planning are done at the same time. Table 6 shows an example of such planning. A change in the limestone chemism entails an alteration in the amounts of limestone, clay and sand that have to be recovered. Moreover, it will imply changes in the machine pool necessary for quarrying. 

The changes in daily production of limestone shown in table 6 are not very large because the fluctuations of the CaO content range between 47.0 % by weight and 50.5 % by weight only. Furthermore, the clay deposit is of very homogenous structure. 

Table 6 
Raw material demand as a function of the range of fluctuations of the raw materials with proceeding working of the quarry 
 

In the event that average values are used for calculations over long periods it may happen that the machine design capacity will no longer be sufficient for the requirements of every day's operation. In that case a crushing section will only be capable of reaching such capacity by an extension of the daily operating time. 

Moreover, calculations of that type reveal that a plant which has originally been operated with no more than two rawmaterial components, may require additional components after some years, i.e. after the average composition has undergone changes. Similarly, it may be necessary to install a bypass system because chloride and alkali contents have increased. If that is known right from the beginning, such installations can be included in project planning or the plant is designed such that these facilities can be fitted without major expenditure or extended plant shutdowns. 

This kind of evaluation of the geologic examinations also permits including rock portions in quarrying by suitable mining 
measures which are above the permissible limit values for some of their constituents. For instance, the quarry can be adapted in such a way that by changing the floor level of a specific bench or by providing for an intermediate bench, the limit concentrations will in no case be exceeded. 

Unfortunately, examinations of this type are done only rarely. This is all the more regrettable since an adequate number of drillings and analyses has been made and as the extra cost is little compared with the expenditure for drilling and analyzing. 
 

14.2 Calculating reserves and classifying reserves  

Information on the reserves of limestone in a final report of prospecting should always refer to quantities that can be recovered. It happens repeatedly that the calculation of reserves includes zones existing at the margins of the main deposit which after preparation of the quarry for working have practically been removed and which will not yield the material quantity required per day judged by aspects of mining. 

Material that has to be excluded from winning because transporting routes, manoeuvering areas, access ramps and safety spaces have to be provided there, should have been deducted from the quantities given in the report. Apart from that, there will be losses during quarrying. 

Provided prospecting is evaluated as described above, calculating the reserves that can be recovered will actually be nothing else than an addition of values already determined. The quantity figures quoted for the different quarry sections are available for chemical evaluation of the individual working operations. The contents of the different sections are in most cases easy to calculate as the working face is straightly oriented. Therefore, deductions have to be made only for the traffic and safety areas mentioned above. 

The overall reserve results when adding the contents of the different quarry sections and the service span of the individual blocks. That calculation will have to be made for all of the safe reserves. 

The reserve classification for non-metallic minerals is based on that for ores (GIDIVIB 1972). "Safe reserves" (category A) are thoroughly investigated reserves as regards chemism and its range of fluctuations, structural conditions, tectonics, preparation, hydro-geological as well as legal aspects of mining. "Probable reserves" of category B are zones adjacent to deposits with reserves of category A. They have been explored by drilling to such an extent that conclusions can be drawn as to chemism, structural conditions, hydro-geological situation and preparation on the basis of the experience gained with the reserves of category A. 

Reserves of category A shall be determined as a result of phase 3 of deposit prospecting when also those of category B became known. 

"Suggested reserves" (category C 1) will be known upon completion of the second phase of prospecting a deposit for cement raw materials. They have been explored by a widemeshed drilling network; the existing rock types and their chemism are basically known; similarly, structure and conditions of stratification are essentially known. 

The "presumed reserves" (category C 2) will be known after prospecting phase 1. The deposit will have been explored by individual outcrops or drillings thus giving a rough survey of chemism and structure of the deposit. 
 

The operations necessary for prospecting limestones as raw material for the production of cement are no longer the job of only geologists or geologic institutions. To guarantee promising work right from the beginning, a team of experts will have to be included in the investigating job.  

One of the main prerequisites is that right from the start the team includes a mining expert and a process technician of cement production. This will be the only way of precluding serious errors as early as during the planning stage. Cooperation of the process technician is of specific importance so as to have the geo-chemical tests oriented by the requirements of the cement industry.  

Even well-known geologic institutions carry out comprehensive test work with its evaluation and test methods being far away from the practical demands. It would be welcomed if colleges and universities would teach - particularly to foreign students - the know-how required for prospecting work in the line of non-metallic minerals. This will be a prerequisite for having geologic investigations become even more successful by cooperating with a team of experts from other scientific divisions.