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DIMENSIONAL STONE QUARRYING

AND

RECOVERY PERCENTAGE

By

A. Rajan Babu

Principal Scientist, Centre for Testing Services & HOD, Dimensional Stone Technology,

National Institute of Rock Mechanics, KGF – 563 117

1.0 INTRODUCTION

The Indian granites for use as dimensional stones have been recognizedworldwide for their aesthetic beauty and availability in innumerousvariety in different colours and shades. The usage of granite blocks forvarious applications both within and outside the country has increased therevenue generation manifold.

The export of dimensional stones is steadily contributing to theGovernment’s exchequer over many years and today, dimensional stonesalone share about 20% of the revenue generation. The prospect of thebusiness has easily attracted many businessmen and as a result countlessquarries were mushroomed in a splash of time.

The scientific and engineering application for stone quarrying wassidelined except for a few major companies. The end result was thatmajority of the quarries have run on loss and closed down due to poorquality of the blocks and very less recovery. The mushrooming of quarrieshas never ended and is continuing though, at a slower pace.

The process has undoubtedly, left several quarry operators in a state ofconfusion apart from generating huge revenue losses for want of someguidelines related to risk component. A general assessment of quarryperformance reveals that about 70 – 80 % of them are unsuccessful.

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The USBM defines dimension stone as “Naturally occurring

rock material cut, shaped or selected for use in blocks, slabs,sheets or other construction units of specialized shapes andsizes”.

A dimension stone block thus has value as a result of itsdimensions and appearance, underlain by a set of minimumphysical properties (among these are various strengthparameters, workability, ability to take a polish, andresistance to physical and chemical weathering).

The major application of dimension stone is within theconstruction sector, which accounts for over 80% ofconsumption, with the funerary monumental industryaccounting for 15%, and various special applications foraround 3%.

A common sub-classification scheme separates dimensionstone into Calcareous materials (marbles, travertines,limestones etc), Siliceous materials (granites, quartzites andsandstones) and Slate.

2.0 PRODUCTION

Granite is declared as a “Minor Mineral,” under the MMDR Act, 1957 and

therefore falls under the purview of the State Governments.

India has major resources of marble, granite, sandstone, Kota stone,quartzite & slate. Granite resources are largely in South India and Marbledeposits are largely in Western India (Rajasthan & Gujarat).

Granite has a 95% share in India’s dimensional stone export.

The Dimension Stone Industry employs a workforce of over one million atits various sectors. This Industry plays a vital role in the economy of thestates like Tamil Nadu, Andhra Pradesh, Karnataka and Rajasthan. Ruraleconomy of many developing States like Madhya Pradesh, Uttar Pradesh,Odisha and North-Eastern States is dependent on this Industry.

Within the country, granite used for decorative purposes is consideredcostly when compared with other materials, hence, its utilisation and tradein the domestic front has been relatively low when compared to its exportpotential.

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2.1 Critical Parameters for Block Extraction

Number of case studies has been conducted by the authors (A. Rajan Babuetal) solving various problems associated with the exploitation of graniteblocks. Data generated during the studies has been recorded and criticallyassessed with respect to their response to various aspects of blockextraction. All parameters influencing the extraction of blocks have beenconsidered to define the critical parameters that control the production ofsaleable blocks. Certain parameters are to be simultaneously compensatedduring the block extraction process. The critical parameters are shown infigure 1.

2.1.1 Mode of Occurrence of the Deposit

Once the commercial validity of the stone has been proved, the nextoperation will be to open the quarry to make it amenable for blockproduction.

Opening up of a quarry at the right location with sufficient provision fordevelopment of working faces, haul roads, expansion of benches etc., isan important process in the quarrying for dimensional stones. Thelocation and methods of opening up depends mainly on topography ofthe area.

A major problem of Indian quarries are that most of the quarries (ofany topography) were not developed in a systematic way and veryfrequently either needs to be abandoned or reopened from a differentlocation.

Abandoning or reopening of a quarry involves huge losses/investmentsand often discourage/curtail further advancements due to shortage ofworking capital.

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2.1.2 Geological-cum-Geotechnical Characteristics

The block splitting technique for a site largely depends on the physico-mechanical properties of the rock and the nature & orientation of thejointing system.

Splitting becomes easy when prominent loose joints are present in verticaland horizontal planes. Loose or filled joints are very rarely encounteredand only tight joints are commonly present. The following properties shallbe studied to assess the quality of stone for their commercial viability.

• Structure,

• Texture

• Colour,

• Intrinsic designs etc.,

• Discontinuities,

• Fractures,

• Joints

• Bedding planes etc.,

• Physico-mechanical properties of the rock

2.1.3 Quarry Configuration

The orientation of faces significantly influences the recovery ofsaleable blocks. The orientation of faces in favourable direction, usuallyalong the strike of the foliation or the major joint set is desired.

Unfavorable orientations very frequently result in damage to therockmass and wastage of valuable material throughdevelopment/propagation of cracks/fractures and toe formations.Sometimes it becomes compulsory to orient the faces across thefoliation to produce block patterns most liked by the buyers. In suchcases; a matching technology should be adopted to combat anyadverse affect arising out of unfavorable face orientation.

The following parameters largely govern the quarry configuration.

• Dimensions of the quarry

• Number of quarry-faces

• Orientation of faces and direction of advance

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2.1.4 Technology for quarrying

The rockmass response to various techniques of extraction is seldom considered during theprocess of machinery selection that has a vital role to play in the economics of operation.

Unlike other mining operations, the quarrying of granite demands for site-specific selection ofmachineries owing to large variations in their geological, geotechnical and physico-mechanicalcharacteristics.

A successful extraction technology in one quarry may not yield good results in another quarry.

: Scarce

: Frequent : Occasional

: Wide spread

CONSOLIDATED

TECHNOLOGIESALTERNATIVE TECHNOLOGY

INNOVATORY

TECHNOLOGY

ES Explosive splitting LD Line drilling WJ Water jet

FJ Flame jet CDAChemical demolition

agentsDBS Diamond belt saw

WS Wedge shearing

DW Diamond wire saw CS Chain saw

2.1.5 Block geometry

Determination of block geometry and hence the correct block size iscritical in the extraction process. Detailed geotechnical mapping must beconducted on the area identified to record the strike, dip of foliation,joints etc.

Visible cracks and material defects such as black patches, moles, quartzveins etc. shall be recorded.

The theoretical volume and volume estimated by projections of joints,visible material defects etc., should be compared for varying benchgeometry.

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3.0 RISK ASSOCIATED WITH VARIOUS QUARRY ACTIVITIES

Considering the critical parameters, performance evaluation of availableextraction technologies and applicability of different techniques for variousnature of deposit, the most important activities of the quarry were derived. Thevarious activities are listed in Table 2 and ratings are given on a scale of 0 – 10 in

the increasing order of influence from lowest to highest.

Parameters Application Rating

Topographic survey Location of the quarry 5

Geological investigation Assessment of rock quality and quantity with respect to

commercial viability10

Geotechnical investigation Estimation of recovery of saleable blocks in terms of volume,

shape and size8

Quarry lay out Design of approach roads, block geometry, etc 7

Quarrying techniquesSelection of suitable exploitation technique(s) 6

Quarrying machinery Selection of suitable machinery for various activities of

exploitation9

Production plan Design of number of benches, production faces, etc 5

Quarrying plan Development/expansion schedules, 4

Environmental plan Pollution control, waste management, etc 5

Economic analysis Loss/profit assessment, 10

Table: Degree of influence of various activities on granite exploitation

4.0 RECOVERY

The extraction of saleable blocks is one of the most critical processes inthe quarrying of dimensional stones.

The quarry operators are constantly under pressure to produce goodquality and required quantity of saleable blocks to meet their productiontarget and market demand.

The continuation of a quarry and hence the profitability of blockproduction is mainly controlled by the recovery of saleable or marketablevolume.

In reality the rockmass by its nature is bound to exist with severalgeological weak planes and other material defects imposing restrictionson investments for full pledged quarry operations.

However, a few rare deposits provide a relatively more recoverablevolumes leading to profitable operations.

On a whole, irrespective of the method of extraction including the moderntechniques, about 85% of the quarries are facing problems withdiscouraging recoveries leading to abandoning of the operations quitefrequently.

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Joint mapping is applicable for mapping on exposed rock surfaces and itis difficult to measure the fractures within a rock mass usingconventional measuring methods.

In general the production from the quarry will be irregular andcontinuous record of low recovery and substantial damage to the rockmass poses a serious threat to the continuance of the mining operationsin most of the quarries.

The processes of recovery and waste generation from various activitiesof stone production are shown in figure .

Authors/Agency Recovery (%)

Ashmole (2008) 10-12

IBM (2013) 5-15

Rajgor (2013) 5-15

Crackmite (2015) 30

University of

Tennesse (2006)7-97

Other Studies 22-85

The scientific exploitation of the given deposit is a key for improving therecovery. The average recovery percentage world over by various authorsis presented in Table .

When the intention is to merely blast and remove stone for its physical properties, therecovery can be almost 100% of the volume removed,

while when the same stone is quarried with the intention of producing dimension stoneblocks, recovery of saleable blocks is typically between 3% and 30%.

The cost of removal of the material is typically of the order of 10 to 15 times the cost in theformer case.

This increased cost results from the techniques used to split or cut the stone without damageand the special attention that must be given to carefully extracting rectangular blocks ofmaterial from between flaws in the stone (such as cracks, joints, veins, banding oraccumulations of a single mineral or colour) which render it unsuitable in terms of the marketrequirements, rather than just simply extracting blocks of a standard size without regard tothese flaws.

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Ashmole (2008) depicts atwo dimensionalrepresentation of a face in agranite quarry, wheredefects such as veins orjoints cross the bench at anangle to the cuttingdirections of the stone(parallel to the edges of thebench) which aredetermined by the naturalgrain or cleavage of thetone.

In the first case, the initialcutting is made on astandard grid of 3 m by 1.5m, as depicted by the dottedlines, while in the secondcase, the initial cuts areplanned in such a way as toyield an optimum recoveryand size of blocks produced.

The second case yields a total volume offinal blocks 15% higher than the first case,but with a total value that is 43% higherdue to a higher proportion of large blocks.

In addition, in the second case, 88% of theproduction is in large block sizes which arein greater demand in the market, comparedto only 44% in the first case.

1 2

4.1 Defects

The quarrying of dimension stone is one of the most exacting processes in theextraction industries. A major problem is the inability to predict the jointing, beddingplane, and fault systems, which control block layout on a given bench. Anunanticipated joint or fault may upset the most careful planning for block layout.Another major problem is the need to divide blocks to required dimension withoutcreating microscopic fractures in the quarried stone. Such cracks can cause the lossof finished product.

Some of the major defects which control the recovery of saleable blocks include;

• Mole (segregation of darker minerals or inclusions).

• Flowers (concentration of quartz in black granite).

• Green lines or streaks (due to alteration of pyroxene in to chlorite).

• Inclusion of secondary minerals.(quartz, calcite, zeolite).

• Pitted surface (due to removal of soft mica and platy minerals).

• Hairline cracks (due to natural! tectonic disturbances or blasting effects )

• Cracks at the contact of quartz veins with ferromagnesium minerals (due to

injection effects and differences in hardness)

• Occurrence of crystals of pyrite or marcasite.

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The jointing pattern Uneven distribution of minerals

Uneven distribution of fine to medium grain minerals

Criss-cross quartz veinsMica and

amphibole layer around

Enclave

Criss - cross veins of quartz and pegmatite intruded into the Mafic Enclaves

Pegmatite veins

Pegmatite veins

Pegmatite distribution

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Enclaves found in full height of quarry face

Foliation band, pegmatite intrusion and mafic rock

5. CASE STUDIES ON RECOVERY (After Rajan Babu et al, 2011)

Estimation of recoverable reserves involves evaluation of geotechnical aspects,volume, quality, size and shape of deposit.

Structural mapping using scan line method was carried out to estimate the volumeof recoverable blocks.

Surface observations related to structural features like strike & dip of joints,lineation, folds and faults, variation in mineral component, variation in texturalfeature, variation in color, quartz veins, and amphibolites was observed in thedeposit.

Blocks of varying size was considered for reserve estimation; three dimensionalblock diagram was prepared for three blocks according to the scale of geologicalmapping where all the information is projected (figures a, b & c).

Figure a: Three dimensional view of block-I

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Figure b: Three dimensional view of block-II

Figure c: Three dimensional view of block-III

The theoretical volume and estimated recovery was calculated as shown in the following Tables.

Sl. No. Block size (m3)Theoretical

volume (m3)

Estimated recoverable volume

with natural defects (m3)

Percentage (%)

(Estimated recoverable volume /

Theoretical volume)

1 25*20*5 2500 440 17.6

2 25*10*5 1250 148 11.84

3 25*20*5 2500 488 19.52

Total 6250 1076 17.21

Sl. No. Block size (m3)Theoretical

volume (m3)

Estimated recoverable volume

with natural defects (m3)

Percentage (%)

(Estimated recoverable volume /

Theoretical volume)

1 10*8*8 640 87 14

2 8*8*7 448 168 38

3 10*16*10 1600 215 13

4 10*8*8 640 45 7

Projected average recovery for the whole quarry (%) 18

1

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Sl. No. Block size (m3)Theoretical

volume (m3)

Estimated recoverable volume

with natural defects (m3)

Percentage (%)

(Estimated recoverable volume /

Theoretical volume)

1 6*3.3*5 99 16 16

2 9*6*5.5 297 98 33

3 6*5.5*5 165 50 30

Projected average recovery for the whole quarry (%) 26

3

Sl. No.Block size

(m3)

Theoretical

volume (m3)

Estimated recoverable volume

with natural defects (m3)

Percentage (%)

(Estimated recoverable volume /

Theoretical volume)

1 6*5*4 120 21.6 18

2 6*5*5 150 24 16

3 6*5*3 90 27 30

Projected average recovery for the whole quarry (%) 21

4

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Apart from the natural defects present in the rock mass, poor recovery and excessivewaste generation is a quite common feature in majority of the Indian quarriesmainly due to unscientific approach in locating the quarries and conventional ortraditional methods of exploitation.

No efforts or inclination is shown for the initial exploration of the deposit. Studies forunderstanding the geological and geotechnical features covering the physiographicdetails like the structural features, ground water conditions, quality of the rock,reserves etc were not given importance.

The physico-mechanical properties of the rock such as the compressive strength,tensile strength, P-wave velocity, hardness, density, porosity, abrasion resistance,elastic properties, gloss reflectivity etc have been grossly neglected.

The technical aspects covering the design & quarry layout, equipment selection,production schedules, exploitation techniques were not examined for site specificconditions often leading to heavy losses or closure of the quarry.

The environmental aspects including air, noise & water pollution, damage tostructures, consolidation of waste dumps, afforestation etc were not considered orassessed before starting a quarry.

The rough calculation of techno-economics of operation based on assumptions is stillcontinuing to dominate the minds of quarry owners.

Poor recovery ……..,

6. SUGGESTIONS FOR IMPROVING RECOVERY

In order to improve the recovery and minimise the waste generation, certainbasic principles to be followed are given below (After Rajan Babu et al, 2011):

•Initial exploration for assessing the quality and reserves of the stone shouldbe carried out using scientific tools. An expert agency on the subject should beconsulted before commencing actual quarrying operations.

•The removal of topsoil should be planned in such a way to stack it separatelyfor re-handling at a later stage. Topsoil should be removed to completelyexpose the rockmass over the area intended for quarrying. Partial exposure ofthe rock mass will hamper the progress of work and may lead to improperplanning thereby generating huge waste.

•Application of proper extraction technologies and selection of suitablemachineries shall pave way for improved recovery.

•Extreme care shall be adopted during drilling and blasting of overburden orhost rock for exposing the deposit. Indiscriminate blasting often-producedcracks or fractures in the sound blocks rendering them waste. About 30% ofwastes are attributed due to blasting cracks. Site specific controlled blastingtechniques should be developed and executed by competent persons to avoiddamage to the potential saleable blocks and safety of operations.

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• A detailed geological and geotechnical study on the exposed rock mass will aidin proper planning and designing of the quarry. The development of benches,favourable face orientation, extraction sequence, face advance, selection of blocksize, selection of exploitation technique etc largely depend on the vital informationon the geological and geotechnical properties.

• The bench dimensions shall be designed in such a way that desirable blockssizes can be obtained freely taking advantage of the jointing systems. Thepossibility of utilising joints as free faces and merging of benches shall beexplored. The number of benches and working faces should be planned to meetthe production target and balancing of quality from various faces.

• Guided or mounted drills can drill perfect holes thereby improving theperformance of splitting and hence the recovery.

• Secondary block splitting, Squaring, shaping and sizing of the blocks shall bedone using proper techniques. Hydraulic rock splitters can be used with less risk ofdamage. Feather and wedges and detonating cord splitting can also be used withcareful split designs.

• Properly maintained approach roads, ramps etc would minimise themaintenance of loading and transport machinery and save on time.

7. CONCLUSIONS

The dimensional stone industry of the country is one of the major sources of foreign exchangeearnings. The industry is passing through a transition period of technological advancementsthat requires quick readjustments in the system to meet the needs of the global market. Theprocess of orientation towards new quarrying standards incorporating high quality stoneproducts and enhanced production has caused a great deal of confusion. In this paper the riskelements related to successful quarrying has been discussed and some suggestions are made forscientific exploitation.

The critical parameters, which prevails on the decision for opting of a quarry for extraction areidentified and explained. The performances of various available techniques have been assessedwith respect to crucial parameters of production.

The causes for poor recovery and high waste generation were highlighted. The literature reviewand the experiences in several investigated quarries has revealed a maximum of overallrecovery of saleable blocks to about 30% and is ranging from 5 to 15%. However, by adaptingto scientific methods, the recoverable volumes can be maximized.

The applicability of suitable techniques for various types of deposit has been suggested. Thecritical activities of the quarrying system have been identified and are rated on the risk factorassociated with them. The ratings are based on qualitative assessment and were arrived at aftercarefully studying their influence in several quarries. The ratings suggested would be useful forthe entrepreneurs in meticulous planning & scheduling of various quarrying activities. Thus therisk of wrong investments can be minimised to a great extent.

The issues related to design of the quarries and strata control measures shall be addressedprudently along with eco-friendly quarrying practices.

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