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.

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.

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.

preserve drift integrity Preserving Drift Integrity

reduce ore loss Reducing ore loss

proper rock fragmentation Proper Rock Fragmentation

avoid toes Avoiding toes

reduce dilution Reducing dilution

control vibrations Controlling vibrations

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

DG2 64.7 Highly Jointed

DG3 60.7 Blocky

DG4 70.5 Blocky

DG5 100.8 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)

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

BURDEN/SPACING/STEMMING CALCULATION at 102 mm BURDEN/SPACING/STEMMING CALCULATION at 89 mm

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

Figure 3. Hole length and integrity control prior to loading at rings B1 and B2 on Stope 810 63g.

Design (left) and actual (right)

Figure 4. Design (left) vs actual explosive load of production ring (right) at stope 810-370h.

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.

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.

Figure 7. Field notes of blast at stope 660-984b. This blast presented lack of proper loading. Pink-

marked 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.

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 660.000 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

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

Ring Blast / explosive type

Hole diameter

(mm)

Geological Domain

B (m) E (m) Powder factor (kg/t)

Energy Factor (kJ/t)

Up hole Bulk Emulsion

102 DG 2-4 2.7 2.9 0.37 1,225

Up hole Bulk Emulsion

102 DG 5 2.3 2.6 0.45 1,485

Down hole Cartridged Emulsion

89 DG 2-4 2.3 2.6 0.26 1,160

Down hole Cartridged Emulsion

89 DG 5 2.0 2.6 0.3 1,335

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

Overall, average reduction in D80 reached 26%, while ore loss decreased an average of 38%

Standard

Blasting

Mine to Mill

BlastingSize 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%

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 660.000 €/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