DIMENSIONAL STONE QUARRYING AND RECOVERY PERCENTAGE

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1 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 INTRODUCTION The Indian granites for use as dimensional stones have been recognized worldwide for their aesthetic beauty and availability in innumerous variety in different colours and shades. The usage of granite blocks for various applications both within and outside the country has increased the revenue generation manifold. The export of dimensional stones is steadily contributing to the Government s exchequer over many years and today, dimensional stones alone share about 20% of the revenue generation. The prospect of the business has easily attracted many businessmen and as a result countless quarries were mushroomed in a splash of time. The scientific and engineering application for stone quarrying was sidelined except for a few major companies. The end result was that majority of the quarries have run on loss and closed down due to poor quality of the blocks and very less recovery. The mushrooming of quarries has never ended and is continuing though, at a slower pace. The process has undoubtedly, left several quarry operators in a state of confusion apart from generating huge revenue losses for want of some guidelines related to risk component. A general assessment of quarry performance reveals that about % of them are unsuccessful. 1

2 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 and sizes. A dimension stone block thus has value as a result of its dimensions and appearance, underlain by a set of minimum physical properties (among these are various strength parameters, workability, ability to take a polish, and resistance to physical and chemical weathering). The major application of dimension stone is within the construction sector, which accounts for over 80% of consumption, with the funerary monumental industry accounting for 15%, and various special applications for around 3%. A common sub-classification scheme separates dimension stone into Calcareous materials (marbles, travertines, limestones etc), Siliceous materials (granites, quartzites and sandstones) 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 Marble deposits 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 at its various sectors. This Industry plays a vital role in the economy of the states like Tamil Nadu, Andhra Pradesh, Karnataka and Rajasthan. Rural economy 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 considered costly when compared with other materials, hence, its utilisation and trade in the domestic front has been relatively low when compared to its export potential. 2

2.1 Critical Parameters for Block Extraction Number of case studies has been conducted by the authors (A. Rajan Babu etal) solving various problems associated with the exploitation of granite blocks.

3 2.1 Critical Parameters for Block Extraction Number of case studies has been conducted by the authors (A. Rajan Babu etal) solving various problems associated with the exploitation of granite blocks. Data generated during the studies has been recorded and critically assessed with respect to their response to various aspects of block extraction. All parameters influencing the extraction of blocks have been considered to define the critical parameters that control the production of saleable blocks. Certain parameters are to be simultaneously compensated during the block extraction process. The critical parameters are shown in figure Mode of Occurrence of the Deposit Once the commercial validity of the stone has been proved, the next operation will be to open the quarry to make it amenable for block production. Opening up of a quarry at the right location with sufficient provision for development of working faces, haul roads, expansion of benches etc., is an important process in the quarrying for dimensional stones. The location and methods of opening up depends mainly on topography of the area. A major problem of Indian quarries are that most of the quarries (of any topography) were not developed in a systematic way and very frequently either needs to be abandoned or reopened from a different location. Abandoning or reopening of a quarry involves huge losses/investments and often discourage/curtail further advancements due to shortage of working capital. 3

4 2.1.2 Geological-cum-Geotechnical Characteristics The block splitting technique for a site largely depends on the physicomechanical properties of the rock and the nature & orientation of the jointing system. Splitting becomes easy when prominent loose joints are present in vertical and horizontal planes. Loose or filled joints are very rarely encountered and only tight joints are commonly present. The following properties shall be 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 Quarry Configuration The orientation of faces significantly influences the recovery of saleable blocks. The orientation of faces in favourable direction, usually along the strike of the foliation or the major joint set is desired. Unfavorable orientations very frequently result in damage to the rockmass and wastage of valuable material through development/propagation of cracks/fractures and toe formations. Sometimes it becomes compulsory to orient the faces across the foliation to produce block patterns most liked by the buyers. In such cases; a matching technology should be adopted to combat any adverse 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 4

2.1.4 Technology for quarrying The rockmass response to various techniques of extraction is seldom considered during the process of machinery selection that has a vital role to play in the economics

5 2.1.4 Technology for quarrying The rockmass response to various techniques of extraction is seldom considered during the process 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 of machineries owing to large variations in their geological, geotechnical and physico-mechanical characteristics. A successful extraction technology in one quarry may not yield good results in another quarry. : Wide spread : Frequent : Scarce : Occasional CONSOLIDATED INNOVATORY ALTERNATIVE TECHNOLOGY TECHNOLOGIES TECHNOLOGY ES Explosive splitting LD Line drilling WJ Water jet Chemical demolition FJ Flame jet CDA DBS Diamond belt saw agents WS Wedge shearing DW Diamond wire saw CS Chain saw Block geometry Determination of block geometry and hence the correct block size is critical in the extraction process. Detailed geotechnical mapping must be conducted on the area identified to record the strike, dip of foliation, joints etc. Visible cracks and material defects such as black patches, moles, quartz veins etc. shall be recorded. The theoretical volume and volume estimated by projections of joints, visible material defects etc., should be compared for varying bench geometry. 5

6 3.0 RISK ASSOCIATED WITH VARIOUS QUARRY ACTIVITIES Considering the critical parameters, performance evaluation of available extraction technologies and applicability of different techniques for various nature of deposit, the most important activities of the quarry were derived. The various 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. Table: Degree of influence of various activities on granite exploitation Parameters Application Rating Topographic survey Location of the quarry 5 Geological investigation Geotechnical investigation Assessment of rock quality and quantity with respect to commercial viability Estimation of recovery of saleable blocks in terms of volume, shape and size Quarry lay out Design of approach roads, block geometry, etc 7 Quarrying techniques Quarrying machinery Selection of suitable exploitation technique(s) 6 Selection of suitable machinery for various activities of exploitation 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, RECOVERY The extraction of saleable blocks is one of the most critical processes in the quarrying of dimensional stones. The quarry operators are constantly under pressure to produce good quality and required quantity of saleable blocks to meet their production target and market demand. The continuation of a quarry and hence the profitability of block production is mainly controlled by the recovery of saleable or marketable volume. In reality the rockmass by its nature is bound to exist with several geological weak planes and other material defects imposing restrictions on investments for full pledged quarry operations. However, a few rare deposits provide a relatively more recoverable volumes leading to profitable operations. On a whole, irrespective of the method of extraction including the modern techniques, about 85% of the quarries are facing problems with discouraging recoveries leading to abandoning of the operations quite frequently. 6

$Joint mapping is applicable for mapping on exposed rock surfaces and it is difficult to measure the fractures within a rock mass using conventional measuring methods.$

7 Joint mapping is applicable for mapping on exposed rock surfaces and it is difficult to measure the fractures within a rock mass using conventional measuring methods. In general the production from the quarry will be irregular and continuous record of low recovery and substantial damage to the rock mass poses a serious threat to the continuance of the mining operations in most of the quarries. The processes of recovery and waste generation from various activities of stone production are shown in figure. The scientific exploitation of the given deposit is a key for improving the recovery. The average recovery percentage world over by various authors is presented in Table. Authors/Agency Recovery (%) Ashmole (2008) IBM (2013) 5-15 Rajgor (2013) 5-15 Crackmite (2015) 30 University of Tennesse (2006) 7-97 Other Studies When the intention is to merely blast and remove stone for its physical properties, the recovery can be almost 100% of the volume removed, while when the same stone is quarried with the intention of producing dimension stone blocks, 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 the former case. This increased cost results from the techniques used to split or cut the stone without damage and the special attention that must be given to carefully extracting rectangular blocks of material from between flaws in the stone (such as cracks, joints, veins, banding or accumulations of a single mineral or colour) which render it unsuitable in terms of the market requirements, rather than just simply extracting blocks of a standard size without regard to these flaws. 7

Ashmole (2008) depicts a two dimensional representation of a face in a granite quarry, where defects such as veins or joints cross the bench at an angle to the cutting directions of the stone

8 Ashmole (2008) depicts a two dimensional representation of a face in a granite quarry, where defects such as veins or joints cross the bench at an angle to the cutting directions of the stone (parallel to the edges of the bench) which are determined by the natural grain or cleavage of the tone. In the first case, the initial cutting is made on a standard grid of 3 m by 1.5 m, as depicted by the dotted lines, while in the second case, the initial cuts are planned in such a way as to yield an optimum recovery and size of blocks produced. 1 2 The second case yields a total volume of final blocks 15% higher than the first case, but with a total value that is 43% higher due to a higher proportion of large blocks. In addition, in the second case, 88% of the production is in large block sizes which are in greater demand in the market, compared to only 44% in the first case. 4.1 Defects The quarrying of dimension stone is one of the most exacting processes in the extraction industries. A major problem is the inability to predict the jointing, bedding plane, and fault systems, which control block layout on a given bench. An unanticipated joint or fault may upset the most careful planning for block layout. Another major problem is the need to divide blocks to required dimension without creating microscopic fractures in the quarried stone. Such cracks can cause the loss of 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. 8

9 The jointing pattern Uneven distribution of minerals Uneven distribution of fine to medium grain minerals Mica and amphibole layer around Enclave Criss-cross quartz veins Criss - cross veins of quartz and pegmatite intruded into the Mafic Enclaves Pegmatite veins Pegmatite veins Pegmatite distribution 9

Enclaves found in full height of quarry face Foliation band, pegmatite intrusion and mafic rock 5.

geotechnical aspects, volume, quality, size and shape of deposit.

Surface observations related to structural features like strike & dip of joints, lineation, folds and faults,

10 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 volume of recoverable blocks. Surface observations related to structural features like strike & dip of joints, lineation, folds and faults, variation in mineral component, variation in textural feature, variation in color, quartz veins, and amphibolites was observed in the deposit. Blocks of varying size was considered for reserve estimation; three dimensional block diagram was prepared for three blocks according to the scale of geological mapping where all the information is projected (figures a, b & c). Figure a: Three dimensional view of block-i 10

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. 1 2 3 4 Sl.

6 2 25*10*5 1250 148 11.84 3 25*20*5 2500 488 19.52 Total 6250 1076 17.21 Sl. No.

168 38 3 10*16*10 1600 215 13 4 10*8*8 640 45 7 Projected average recovery for the whole quarry (%) 18 Sl. No.

11 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 (m 3 ) Theoretical volume (m 3 ) Estimated recoverable volume with natural defects (m 3 ) Percentage (%) (Estimated recoverable volume / Theoretical volume) 1 25*20* *10* *20* Total Sl. No. Block size (m 3 ) Theoretical volume (m 3 ) Estimated recoverable volume with natural defects (m 3 ) Percentage (%) (Estimated recoverable volume / Theoretical volume) 1 10*8* *8* *16* *8* Projected average recovery for the whole quarry (%) 18 Sl. No. Block size (m 3 ) Theoretical volume (m 3 ) Estimated recoverable volume with natural defects (m 3 ) Percentage (%) (Estimated recoverable volume / Theoretical volume) 1 6*3.3* *6* *5.5* Sl. No. Projected average recovery for the whole quarry (%) 26 Block size (m3) Theoretical volume (m3) Estimated recoverable volume with natural defects (m3) Percentage (%) (Estimated recoverable volume / Theoretical volume) 1 6*5* *5* *5* Projected average recovery for the whole quarry (%) 21 11

12 Poor recovery.., Apart from the natural defects present in the rock mass, poor recovery and excessive waste generation is a quite common feature in majority of the Indian quarries mainly due to unscientific approach in locating the quarries and conventional or traditional methods of exploitation. No efforts or inclination is shown for the initial exploration of the deposit. Studies for understanding the geological and geotechnical features covering the physiographic details 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 specific conditions often leading to heavy losses or closure of the quarry. The environmental aspects including air, noise & water pollution, damage to structures, consolidation of waste dumps, afforestation etc were not considered or assessed before starting a quarry. The rough calculation of techno-economics of operation based on assumptions is still continuing to dominate the minds of quarry owners. 6. SUGGESTIONS FOR IMPROVING RECOVERY In order to improve the recovery and minimise the waste generation, certain basic principles to be followed are given below (After Rajan Babu et al, 2011): Initial exploration for assessing the quality and reserves of the stone should be carried out using scientific tools. An expert agency on the subject should be consulted before commencing actual quarrying operations. The removal of topsoil should be planned in such a way to stack it separately for re-handling at a later stage. Topsoil should be removed to completely expose the rockmass over the area intended for quarrying. Partial exposure of the rock mass will hamper the progress of work and may lead to improper planning thereby generating huge waste. Application of proper extraction technologies and selection of suitable machineries shall pave way for improved recovery. Extreme care shall be adopted during drilling and blasting of overburden or host rock for exposing the deposit. Indiscriminate blasting often-produced cracks or fractures in the sound blocks rendering them waste. About 30% of wastes are attributed due to blasting cracks. Site specific controlled blasting techniques should be developed and executed by competent persons to avoid damage to the potential saleable blocks and safety of operations. 12

13 A detailed geological and geotechnical study on the exposed rock mass will aid in proper planning and designing of the quarry. The development of benches, favourable face orientation, extraction sequence, face advance, selection of block size, selection of exploitation technique etc largely depend on the vital information on the geological and geotechnical properties. The bench dimensions shall be designed in such a way that desirable blocks sizes can be obtained freely taking advantage of the jointing systems. The possibility of utilising joints as free faces and merging of benches shall be explored. The number of benches and working faces should be planned to meet the production target and balancing of quality from various faces. Guided or mounted drills can drill perfect holes thereby improving the performance of splitting and hence the recovery. Secondary block splitting, Squaring, shaping and sizing of the blocks shall be done using proper techniques. Hydraulic rock splitters can be used with less risk of damage. Feather and wedges and detonating cord splitting can also be used with careful split designs. Properly maintained approach roads, ramps etc would minimise the maintenance 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 exchange earnings. The industry is passing through a transition period of technological advancements that requires quick readjustments in the system to meet the needs of the global market. The process of orientation towards new quarrying standards incorporating high quality stone products and enhanced production has caused a great deal of confusion. In this paper the risk elements related to successful quarrying has been discussed and some suggestions are made for scientific exploitation. The critical parameters, which prevails on the decision for opting of a quarry for extraction are identified and explained. The performances of various available techniques have been assessed with respect to crucial parameters of production. The causes for poor recovery and high waste generation were highlighted. The literature review and the experiences in several investigated quarries has revealed a maximum of overall recovery of saleable blocks to about 30% and is ranging from 5 to 15%. However, by adapting to scientific methods, the recoverable volumes can be maximized. The applicability of suitable techniques for various types of deposit has been suggested. The critical activities of the quarrying system have been identified and are rated on the risk factor associated with them. The ratings are based on qualitative assessment and were arrived at after carefully studying their influence in several quarries. The ratings suggested would be useful for the entrepreneurs in meticulous planning & scheduling of various quarrying activities. Thus the risk of wrong investments can be minimised to a great extent. The issues related to design of the quarries and strata control measures shall be addressed prudently along with eco-friendly quarrying practices. 13

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ANNEXURE I Site Location map of M/s. Stone Plus quarry lease A-1

ANNEXURE I Site Location map of M/s. quarry lease A-1 Quarry Lease boundary map of M/s. A-2 a. Introduction M/s. proposes to conduct semi mechanized open cast method quarrying for Colour granite extraction