Ring Blasting Mine to Mill Optimization

Transcription

1 Ring Blasting Mine to Mill Optimization Benjamin Cebrian, Blast Consult S.L. & Roberto Laredo, MATSA mine Mubadala-Trafigura Group Joel Chipana, MATSA mine Mubadala-Trafigura Group Abstract Ring blasting is a common production method in underground metal mines. As a drill and blast process, it presents particular features that do not correspond with bench blasting in open pit or underground mining. In this paper, a six month mine-to-mill optimization program performed in a Cu-Pb-Zn underground mine is presented, showing the steps followed from initial assessment and baseline definition to the specific approach to obtain high-energy ring blasting designs that would suit other important goals in sublevel stoping. Apart from fragmentation optimization, these goals are to increase ore recovery, preserve drift integrity, minimize dilution (from damage to adjacent backfilled stopes and pillars), displacement control to minimize remote-controlled LHD loader use and minimize damage to already drilled rings. Special high economic value was detected by increasing ore recovery through high energy blasting. Three types of ore are processed at the mill: Massive-Cu, Massive-Polymetallic and Stockwork. Assessment of the blastability and processing characteristics of each was performed in order to customize high energy or high efficiency blasting. Ore tracking at the mill was considered in order to correlate throughput when mine-to-mill blasts or blending of those were being processed. Different explosives were tested including cartridge emulsion and bulk uphole emulsion, as well as electronic and non-electric detonators. Burden was the primary variable adjusted, along with spacing and explosive load to ensure toe breakage.

2 Introduction Ring blasting is perhaps one of the most complex blasting techniques for mining. In addition to long holes, small diameters and underground working conditions, uphole loading requires proper techniques to efficiently achieve their goals. These typically are: achieve proper fragmentation, reduce dilution, reduce ore loss, control vibrations, protect drift integrity and avoid toe formation at the floor of production stopes. preserve drift integrity Preserving Drift Integrity reduce ore loss Reducing ore loss proper rock fragmentation Proper Rock Fragmentation reduce dilution Reducing dilution control vibrations Controlling vibrations avoid toes Avoiding toes Figure 1. Uphole and downhole ring blasting pursue typical goals of rock fragmentation, ore loss reduction, drift integrity, dilution control and avoiding toes at the stope floor. At Matsa mine, ring blasting is used to create open stopes of different size and shapes, both by uphole and downhole blasting. It is a 4,4 Mt/year metal mine (Cu-Pb-Zn) located at the pyrite belt in southern Spain. In 2016 a blast optimization process was conducted on a 6 month mine-to-mill trial. Potential savings of several million euros per year were detected by using higher energy blasting, mainly through better ore recovery. This paper presents the design evaluation, implementation control and monitoring process as well as results of the optimization of ring blasting at Matsa mine.

3 Initial state, starting from the beginning An audit was conducted to properly assess the baseline for later comparison once the changes were implemented in the blasting process. This audit included both the design procedures and the physical implementation of designs at the mine KPIs for this project were: - D80, D50, D20 (mm) - Ore recovery / Ore Loss on primary stopes (%) - Mill throughput on crushing and ball mill (t/h) - info finally not provided by mill due inability of tracking different ore Initially, there were only two blast designs used for all production blasts, regardless of ore type, rock hardness, RMR of rock mass and other geotechnical constraints (Table 1). This means some rock was being overshot with excess energy while some rock masses had blast designs with insufficient explosive energy. At the time the audit was performed, engineers at the mine had recently conducted a first optimization of blast designs based on geotechnical domains (DG) of Massive Ore, Polymetallic Ore and Stockwork Ore. Thus, burden and spacing variables were the first ones that had been adapted to better suit the different geotechnical units at the mine (Table 2). Table 1. Classification of Geotechnical Domains (DG) at primary stopes Geotechnical Domain UCS (MPa) Structure DG Highly Jointed DG Blocky DG Blocky DG Massive Table 2. Blasting variables B=Burden, E=Spacing for different geotechnical domains for 102mm bulk explosive-uphole (left) and 89mm-catridged explosive downhole rings (right) BURDEN/SPACING/STEMMING CALCULATION at 102 mm BURDEN/SPACING/STEMMING CALCULATION at 89 mm POLY B max B max design B S POLY B max B max design B E DG2 2,96 3,00 2,8 3,6 DG2 2,73 2,70 2,5 3,1 DG3 2,93 2,90 2,7 3,5 DG3 2,70 2,70 2,5 3,1 DG4 2,93 2,90 2,7 3,5 DG4 2,69 2,70 2,5 3,1 DG5 2,85 2,80 2,6 3,3 DG5 2,49 2,50 2,3 2,8 CU B max B max design B E CU B max B max design B E DG3 2,93 2,90 2,7 3,5 DG3 2,69 2,70 2,5 3,1 DG4 2,93 2,90 2,7 3,5 DG4 2,69 2,70 2,5 3,1 DG5 2,85 2,80 2,6 3,3 DG5 2,61 2,50 2,3 2,8 STW B max B max design B E STW B max B max design B E DG3 3,01 3,00 2,8 3,6 DG3 2,62 2,70 2,5 3,1 DG4 2,93 2,90 2,7 3,5 DG4 2,55 2,50 2,3 2,8 DG5 2,92 2,90 2,7 3,5 DG5 2,55 2,50 2,3 2,8

4 Optimization process by simulation Blast simulation with 2DRing software offers a useful evaluation of explosive energy distribution on each individual ring as well as interaction of several rings in 3D. This information, prior to blasting, was used to refine blast design though adjusting: - Hole spacing and positioning of corner holes - Explosive load on each hole and interacting energy - Energy reduction in the proximity of top drift - Contour energy levels Figure 2. Before (left) and after (right) optimization of explosive energy levels (MJ/t). Observe energy increase at the toe and a more homogeneous distribution at the middle of the ring Implementation control As with any blast improvement process, supervision of the implementation of the blasting design is key to ensure full control of results. Controls during drilling revealed hole deviation levels beyond design assumptions, hole length inconsistency (holes shorter or longer than design) and hole positioning (collaring) Also, explosives loading supervision showed a clear difference between design and reality at production blasts, affecting rock fragmentation, ore recovery and toe formation. Mainly, differences came though lower loading density values (kg/m), explosives up hole not sticky enough, holes not loaded because of blockages and different from design loaded/stemming lengths. Figures 3, 4, 5 and 6 illustrate some of the field measurements performed to control drilling and loading quality

5 Figure 3. Hole length and integrity control prior to loading at rings B1 and B2 on Stope g. Design (left) and actual (right) Figure 4. Design (left) vs actual explosive load of production ring (right) at stope h. Explosive energy levels and distribution in MJ/t are illustrative of why toes appear, loss of ore occurs at the roof of the stope and fragmentation is poorer than expected from design.

6 Figure 5. Explosive energy design (top) vs actual (bottom ) on stope 984. A 5% ore loss resulted in this stope due to inconsistencies in explosive distribution Figure 6. Field supervision included up-hole boretrak deviation control, collar accuracy and explosive quality and loading techniques.

7 Figure 7. Field notes of blast at stope b. This blast presented lack of proper loading. Pinkmarked holes are not loaded and the loaded (green marked) present different loading lengths In order to quantify these inconsistencies, four KPIs were measured: hole length, explosive linear density, powder factor and energy factor. From one month of audits of production stopes with different ore types revealed the following values were determined (Figure 8) Figure 8. An audit of blasting of Massive, Stockwork and Polymetallic ore types revealed clear differences between design variables and real implemented values. These were especially high on the stockwork ore.

8 Mine to Mill optimization without the mill A series of stopes of the hardest ore were selected to perform a mine-to-mill program by increasing fragmentation through higher energy blasting. Consequently, powder factor and energy factor were increased by 30% from about 1000 kj/t up to 1400 kj/t, depending on geological domains. This was achieved by adjusting burden, spacing and explosive load on each hole (Table 2) with the help of blast simulation. Although an investigation conducted with the plant manager showed potential savings from finer fragmentation of euros/year net profit, several problems affected the evaluation of the test blasts. First, blending of material from other parts of the mine as well as other deposits in the complex made the isolation of results difficult. Traceability was not possible without Ore Tracker microchips, which were not used at that time. Second, several stops and maintenance works at the mill prevented the correct feeding of the crusher at full capacity, therefore not obtaining full benefit of better fragmentation. However, a far better benefit was obtained by applying software modeling to mine-to-mill blasting processes. The fact that each ring had more energy, with better distribution, contributed to better breakage of the toes and to the limits of each ring, thus reducing ore loss. This proved to be a 3% gain in ore recovery with a net value for the mine of several M per year. Figure 9. Energy distribution simulation of mine to mill blasting designs on DG5 (hard, massive ore) for uphole rings (left) and downhole rings (right). Note how high energy concentrations on the center (red) are prone to creating finer fragmentation while mid level energy concentrations (green) provide a more complete cut on the ore body contours of the stope

9 The mine to mill blasts implemented at the mine had an overall increase of energy of around 20% but different adjustments had to be done depending on: drill diameter, rock type and explosive types. Table 3 shows the main designs on each case. Table 3. Blasting parameters of high energy blasting at primary stopes Hole Powder Energy Ring Blast / Geological diameter B (m) E (m) factor Factor explosive type Domain (mm) (kg/t) (kj/t) Up hole Bulk Emulsion 102 DG ,225 Up hole Bulk Emulsion 102 DG ,485 Down hole Cartridged 89 DG ,160 Emulsion Down hole Cartridged Emulsion 89 DG ,335 Fragmentation and Ore Loss Results Mine to mill fragmentation was compared to a previous fragmentation study performed on all of the mine ore stock piles with Split Desktop. Also, two stopes were partially shot with standard pattern and partially shot with high energy blasts in order to compare fragmentation under the same conditions. A total of 143 valid pictures were processed and produced fragmentation curves. Results of fragmentation differences through the use of high energy, optimized and supervised blasting vs standard blasting can be seen in Table 4 and Figure 10. Also Table 4 reflects the percent difference of ore loss compared to historical reference values. Table 4. Comparison on rock size and ore loss Standard Blasting Mine to Mill Blasting Size Reduction ORE LOSS REDUCTION % Passing Size[mm] Size[mm] F10 3,23 2,74 15% F20 15,18 11,73 23% F30 34,51 25,64 26% F40 60,36 43,6 28% F50 93,31 65,79 29% F60 130,81 92,96 29% F70 177,7 127,86 28% F80 244,14 180,75 26% F90 360,47 279,89 22% Topsize (99.95%) 1488,18 779,52 48% 38% Overall, average reduction in D80 reached 26%, while ore loss decreased an average of 38%

10 Figure 10. Fragmentation curves of copper and polymetallic ores comparing mine to mill (red) to standard blasting designs Except for the blasts where operational problems happened during loading of the explosives (uphole bulk), results show consistently a decrease in all key size numbers (D80, D50, D20). A maximum decrease of 50% size for downhole and 51% uphole blasts was achieved on D80 sizes and, in D20, this was even more evident with reductions on the fine portion up to 63%. Conclusion and Future Work Blasting optimization, control of implementation and high energy blasting proved to be a great technical and economical approach for the mining operation at MATSA. A reduction of 38% on P80 and 63% on P20, higher ore recovery rates (38% reduction of ore loss) and reduction of toes lead to a profit of several M per year. The potential benefit of additional /y in the mill crushing and grinding processes still needs to be measured with the help of Ore Tracker microchips inserted in high energy blasting stopes or through statistical analysis, since Operations at the mine has decided to apply mine-to-mill blasting in hard ore domains. Acknowledgements Mr Joel Chipana, head of Engineering of MATSA is acknowledged for making this study happen at the mine. Also the geotechnical team at MATSA for their kind assistance. Co-author Roberto Laredo for his leadership and support with his great underground mining know-how. Blasting engineers at Blast Consult: Antonio Morato, John Baker and fragmentation expert Maria Rocha for their passion and commitment on this not-easy-to-perform job. References Onederra, I Fragmentation Modelling for Underground Production Blasting Aplications IRR Drilling and Blasting Conference, 2004 Perth Hartwig, David The Application of the Mine to Mill Concept to Large Scale Underground Mining, Bachelor of Engineering Thesis, The University of Queensland, 2005