1 Sensitivity unit cost analysis of a surface marble quarry George Exadaktylos Professor of Rock Mechanics & Mining Engineering November 2006

2 Motivation of work  Construction of a reliable algorithm for the calculation of unit cost of surface marble quarrying based on state-of-the-art marble exploitation techniques (i.e. sufficient mechanization of production of good quality commercial marble blocks at the quarry) and appropriate size of personnel and equipment for the respective production level.  Creation of a flexible spreadsheet in Excel® for unit cost analysis of surface marble quarrying. Flexibility refers to the quick calculation of unit cost by varying a sensitive parameter (e.g. recoverability, working days per year, working hours per day, oil price, quarry productivity etc.)

3 Structure of the spreadsheet 1. General data opening phase (or production phase) 2.Equipment data opening phase (or production phase) 3. Consumables 4. Personnel 5.Unit cost estimation for opening phase (or production phase) The structure of the calculation Spreadsheet created in Microsoft Excel® has the form:

4 Main assumptions at this phase of design 1. As the in situ exploration survey and subsequent laboratory analysis indicated the quality of marble is very good (both physico-chemical and mechanical properties) with white to grey-white color variations and good recoverability. The in situ exploration consisted of geological mapping, georadar logging, core drilling and laboratory testing. 2. Two distinct phases of quarrying have been considered in the present cost analysis, namely:  An “opening phase” with 5,000 m 3 /year that will be necessary at the initial stage of quarrying at the upper bench; this is the preparatory stage where also the “initial risk” will be reduced to a “residual risk” by optimizing the various quarrying activities.  The “full production phase” that will follow the opening phase, has been set arbitrarily to 30,000 m 3 /year, i.e. 1-2 operating benches. Note that the selected equipment with proper use can lead to considerable increase of productivity.

5 Excavation technique and shape of unit block at bench Since the marble is not transected by multiple joints, and the bench height will be 6 m, the best size and shape of the ‘unit production block’ falling after separation from the orebody at the bench is indicated in Fig. 1. Fig. 1. Dimensions of unit marble block extracted from the quarry phase and the 3 cuts for squaring at the bench floor. Terminology in marble quarrying: - Opposite sides hxw are called grain or secondo in Italian or mourelo in Greek. -Opposite sides dxdh are called head- grain or contro in Italian or kefali in Greek -Opposite horizontal sides wxd are called rift or verso in Italian or prosopo in Greek. This terminology is used hereafter.

6 Fig. 1a. Initiation of bench exploitation by making a “U” cut with diamond wire saw & dense drilling at the bottom and back of the block with pre-splitting (ABHΘ & ΓΖΕΔ with saw and ΒΓZH & ΗΘΕΖ with pre-split blasting). Depending on the topography the free faces of a bench initially are only two, i.e. a “grain” and a “rift”. The first cut we make to obtain thereafter the 3 free faces is shown in Fig. 1a and the photo. Initial excavation (opening) at bench

7 Excavation activities (quarrying cycle after initial opening)  The first task is to prescribe the dimensions of the 3 primary wire cuts (2 vertical and 1 horizontal) from which the various unit blocks will be obtained. In the present case we assume that these dimensions will be 12m (width)x 8m (depth)x6m (height).  The three surfaces GRAIN or SECONDO (‘mourelo’ in Greek), RIFT OR VERSO (‘prosopo’ in Greek) & HEAD-GRAIN or CONTRO (‘kefali’ in Greek) are free; we have to separate the block from the other 3 surfaces. The first two activities after cleaning and grading the bench floor is the drilling of two mutually intersecting horizontal drillholes as is indicated in Fig’s 2,3 below. Fig st activity of drilling the horizontal hole with DTH or top-hammer. Fig nd activity of drilling the horizontal hole with DTH or top-hammer.

8 Quarrying cycle (3 rd activity: wire cutting)  The 3 rd activity is the diamond wire leading through the holes and the subsequent wire cutting of the lower horizontal plane of 12mx8m as is indicated in Fig. 4 below. The total length of the diamond wire in this case is approx. 55 m. Fig rd activity of wire leading through the holes and horizontal wire cutting (see photo at the right). Diamond wire machine Pulley in horizontal position wire

9 Quarrying cycle (4 th -10 th activities): horizontal+vertical holes for cutting head-grains or ‘kefalia’)  The 4 th – 10 th activities is the drilling first of horizontal and then of the vertical holes as is indicated in Fig’s 5,6 below. The total number of holes is 7 or 8 depending if the 1 st horizontal hole (activity #1) can be used at this phase. Fig. 5. Drilling horizontal holes for cutting later 4 head-grain (‘kefalia’) planes. Fig. 6. Drilling vertical holes for cutting later 4 head-grain or ‘kefalia’ planes.

10 Quarrying cycle (11 th -14 th activities: vertical cuts along head-grain or contro or ‘kefalia’)  The subsequent 4 activities (11 th – 14 th ) refer to diamond saw cutting of the 4 vertical head-grain or contro (‘kefalia’) planes. Procedure for wire leading through the drillholes Procedure for cutting of vertical planes

11 Quarrying cycle (15 th -28 th ) activities: horizontal & vertical holes along grain or secondo or ‘mourela’ planes)  The 15 th – 19 th activities is the drilling first of horizontal and then of the vertical holes (20 th to 23 rd activities) for the subsequent cutting of grain or secondo (‘mourela’) planes as is indicated in Fig’s 7,8 below. The total number of holes is 9 or 10 depending if the 1 st horizontal hole (activity #7) can be used at this phase. Finally, the rest of the 5 activities refer to the diamond saw cutting of the 5 vertical grain (‘mourela’) planes. Fig. 7. Drilling horizontal holes for cutting later 5 grain or secondo or ‘mourela’ planes. Fig. 8. Drilling vertical holes for cutting later 5 grain or secondo or ‘mourela’ planes.

12 Quarrying cycle activities: Overturning of each released marble block and squaring into commercial sizes The released from the bench block is overturned on a bed of rubble previously prepared on the quarry floor with the backhoe’s (excavator, wheel, or track loader), push (Fig. 9). The fallen block is cut again into commercial sized blocks (i.e. according to Fig. 1) using the diamond saw machine (Fig. 10). Fig. 9. Overturning of the block with backhoe excavator. Fig. 10. Production of commercial block sizes by further cutting with wire saw unit at bench floor.

13 Quarrying cycle activities: Overturning of each released marble block and squaring into commercial sizes Fig. 9. Overturned block at the quarry floor (left side) ready for squaring with small size portable diamond wire unit (right side).

14 Quarrying cycle activities: Loading of commercial marble blocks Finally, the blocks are loaded onto trucks by wheel or track loaders (or lifting machines, derricks) for transportation downhill (Fig. 11). Fig. 11. Loading of commercial blocks with derrick (or with loader CAT-980 with forks replacing the bucket).

15 Equipment dimensioning (for the ‘opening phase’) Track front loader (CAT963) Air compressor DTH drill for vertical drillholes Chain-saw Backhoe excavator, 150 hp Crawler drill

16 Equipment dimensioning for the production phase Wheel loader, CAT 988 (left) & Dump truck (dumper) CAT 769D for hauling of waste (right)

17 Basic consumables in marble quarrying Diamond wireDrill rods and drill button bits

18 Calculation of ‘Unit ‘dry’ cost for production’ ‘General data production phase’ Note: Cells with green color may be arbitrarily altered to see the effect on unit cost

19 In ‘General data production phase’ – Formulae for unit costs Depreciation ([€/year]): Operating cost (Fuel) ([€/year]): Maintenance cost ([€/year]): i=rate of interest, y=years for depreciation C=capital cost Operating cost (lubricating oil) ([€/year]):

20 Unit cost estimation for production

21 Distribution of unit costs at production phase

22 Example: Influence of commercial marble recovery on unit cost and unit net earning at production phase