Optimisation of Drill and Blast for Mill Throughput Improvement at Ban Houayxai Mine

Jon Gaunt, Dwayne Symonds, Glenn McNamara Lachlan Kennelly, Ewan Sellers, Sarma Kanchibotla, Lee Julian

Ban Houayxai Mine Laos

Gold-silver mine operated by Phu Bia Mining Limited

Ore schedule and design TPH – 20 months

650 tph

500 tph 410 tph

Strength and Structure Oxide

Transition

Fresh

Fragmentation

Oxide Transition Primary?

Blasting and Processing

• Blasted in 5m benches • Mined in 3 flitches

– Heave – Middle – Bottom

• 0.8 kg/BCM PF in transition material • Using BVIs to measure blast movement • Direct Feed to crusher • Process mostly SAG Mill limited • Significant throughput drops with hard ores

5m Bench

Feed Effect

700 TPH

300 TPH

1st Trial Objectives

• To monitor the impact of higher benches (10m) on blast movement, fragmentation and plant performance in transitional ore.

• Develop methods to minimise ore loss and dilution

• Generate calibrated models to predict effects of design

alterations to improve plant performance

Trial Blast Designs

106 107

105 104

127 126

TB #3

TB #1

TB #2

TB #4

10m

5m The initiation pattern and timing is similar for all blasts (67ms control row and 42ms echelons)

Design Implementation

• Observation of blast crew – Excellent practices • Hole depth accuracy – Very accurate • Stem length – Very accurate • Product density checks – Within spec • VOD – Within Spec

High speed video

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

100.00

10 100 1000

Cum

ulat

ive

% P

assi

ng

Size (mm)

Heave vs 2nd Flitch (Split)

Ave Heave Ave Flitch 2

Fragmentation Results

• In all blasts, the fragmentation is significantly finer in the 2nd flitch compared to the heave flitch as a result of increased confinement and more of the rock mass being in contact with explosives

• By increasing the bench height to 10m there is 27% less stem zone which improves the fragmentation in the upper portion of the blast block

5m Bench 10m Bench

44% Stem Zone

32% Stem Zone

Weighted average throughput from10m benches was ~ 24% higher than the weighted average throughput from 5m bench blasts.

Plant Throughput

513 498

586 641

Heave Flitch TPH 2nd Flitch TPH

Specific Energy

Specific energy during the ‘steady state’ period 2hrs prior to the plant surveys shows that the 5m benches required more energy and were more variable compared to 10m bench blasts.

D&B cost comparison of 5 and 10m benches

~ 5.9M dollars savings due to reduced drilling and Initiating systems costs

FY2014 cost comparison Unit 5m 10m Difference (10m-5m)

Percentage Improvement

Volume in contact with Explosive m3 154,916 185,346 30,430 20% Increased throughput TPH 505 627 122 24% Number of holes 93,649 21,609 -72,039 77% Total percussion hours hours 4,350 2,122 -2,228 51% Total Drill Metres m 491,270 237,703 -253,568 52% Total Drilling Costs US$/m $7,501,217 $2,771,861 -$4,729,356 63%

US$/BCM $1.54 $0.57 -$0.97

US$/t $0.57 $0.21 -$0.36

Total IE Cost US$ $1,469,347 $339,050 -$1,130,297 77%

2nd Trial blast set • Powder factors were:

– 1.4 kg/BCM – Blast 116

– 1.4 Kg/BCM – Blast 117

– 1.2 Kg/BCM – Blast 118

• The same initiation timing was used for all blasts

– 65ms control row and 42ms echelons

Parameter Unit Blast 104 Blast 105 Blast 106 Blast 107 Blast 126 Blast 127 Blast 116 Blast 117 Blast 118

Drill Hole Diameter mm 152 152 152 152 102 102 152 127 152

Bench Height m 10 10 10 10 5 5 10 10 10

Burden m 4.2 4.2 4.2 4.2 2.8 2.8 3.3 2.8 3.5

Spacing m 4.8 4.8 4.8 4.8 3.3 3.3 3.8 3.2 4.0

Subdrill m 1 1 1 1 1 1 1.5 1.0 1.0

Stemming Height m 3.3 3.3 3.3 3.3 2.2 2.2 3.0 2.6 3.2

Powder Factor Kg/BCM 0.8 0.8 0.8 0.8 0.8 0.8 1.4 1.4 1.2

High speed video

Fragmentation results heave comparison

Fragmentation curves from the heave flitches of trials 1 and 2

0.8 0.8 1.4

SAG Mill TPH

• Throughput during the trial period was 621 TPH (including breakdowns)

• Blast 117 produced more consistent throughput for each flitch

0

100

200

300

400

500

600

700

800

Heave Top Middle Bottom

Median TPH

116

117

118

TPH Blast Bench PF Diameter Burden Spacing Heave Top Middle Bottom Weighted Ave

126/127 5 0.8 152 2.8 3.3 513 498 505 105 10 0.8 152 4.2 4.8 595 614 605 107 10 0.8 152 4.2 4.8 600 697 649

104/106 10 0.8 152 4.2 4.8 574 626 600 118 10 1.2 152 3.5 4 591 580 657 700 632 117 10 1.4 127 2.8 3.2 646 639 663 646 649 116 10 1.4 152 3.3 3.8 546 613 605 639 601

(Steady state 2 hrs)

(Campaign & different mill conditions + 24hrs)

• Fragmentation improved from both increasing the bench height and increasing the powder factor

• Plant performance from high energy blasts – Average TPH is 621TPH which is 24% higher than target 500TPH – 20% of the time the plant reached its downstream bottleneck

(>700TPH)

• Smaller diameter with tighter pattern produces consistently higher TPH for the same powder factor

Conclusions from trials

• Ore dilution occurs when low grade or waste material is miscategorised as ore and sent for processing or stockpiling, diluting the run of mine head grade and recovery.

• Ore loss takes place when valuable mineral is miscategorised

as waste and sent to the waste dumps, thus never being processed and recovered.

Blast induced dilution and ore loss

Cho

ked

face

Min. distance 15 - 20 m

Min. distance 15-20 m

Monitoring holes

Plan view

Blasthole section view

1st f

litch

2n

d flit

ch

Crushed aggregate

~5 m

~3 m

Pol

ypip

e 1

(4m

) P

olyp

ipe

2 (2

m)

BMMs

Pol

ypip

e 3

(2m

)

> 70m

> 60m

Grade

Pol

ypip

e 4

(2x2

m)

10m

10.5m

(May include more than 4 BMMs depending on the geometry)

3rd f

litch

~7 m

3m

2m

2m

3m

BMT System

Typical movement - section view

Flitch Pf 0.8 Pf 1.2 Pf 1.4

Heave 1.6 2.7 3.6

Top 5.6 6.4 8.9

Middle 6 7.2 10.5

Bottom 4.9 5.1 8.4

Loss and Dilution management 1. Where possible plan to blast with either all ore or all waste

2. Ensure high grade/low grade boundaries do not occur near edges and power

troughs

3. Drill and Blast design blast to maximise energy distribution and minimise edge

effects

4. initiation timing which promotes movement parallel to strike to increase the

likelihood of ore moving into ore and waste moving into waste

5. Engineering to ensure that blast boundaries are choked

6. Drill and blast crews implement the blast plan accurately

7. Concentrate QA/QC effort around high grade and waste boundaries

8. Geologists move polygons based on initiation timing, powder factor and rock

characteristics

9. Production excavates and ensures correct allocation of material

High energy blasting damage

Significant back-break and damage behind high energy blasts Back-break

Trials - Active Split to isolate faults

Result

• Minimised fault activation into trim

• Good high wall conditions after trim

Questions