Process Technology and Innovation PTI

Blast Fragmentation Impacts on Downstream Processing at Gold Fields Cerro Corona Kimberly Caron David La Rosa Walter Valery Ronald Diaz Hyder Mamani

© Metso

Project Objective • Goldfields La Cima (Cerro Corona operation) engaged Metso Process Technology and

Innovation (PTI) to conduct a Process Integration & Optimisation (PIO) project for the blasting, crushing and grinding processes.

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“Maximize the plant throughput when treating the hardest ore ”

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Rock Mass Characterisation Benchmark Material

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Polygon 3810007

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Rock Mass Characterisation Rock Structure (RQD)

RQD > 75 high quality massive rock RQD < 50 low quality, jointed/fractured rock

Siro

visi

on

2010

Dril

l Cor

e

RQD ~ 30 %

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Rock Mass Characterisation Rock Strength

Point Load Tests (PLi to estimate UCS)

DWi (Impact breakage)

Finger Axb ta Density Dwi (kWh/m3)

FS 1 76.3 0.52 2.73 3.58

FS 2 87.1 0.72 2.73 3.13

Sample FS 1 (Survey Ore) Results

BWI @ 150 µm closing screen 11.73 kWh/t F80: 2436 µm, P80: 124 µm

BWi (Abrasion breakage)

Overall Hardness Category 4 (50-100 MPa) Moderately Hard Ore

DWi/BWi (resistance of the material to crushing and grinding): Soft to Medium ore for milling

71.2 MPa

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Brief Description of Overall Process

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(9)

24’ x 14.5’ 3800 kW

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24’ x 34’ 7600 kW

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Cu

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tive

Ore

Ble

nd

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(%)

Mixed

Supergene

Hypogene

Treated Ore: Hypogene: 80 % (P3810007) Supergene: 12 % Mixed: 8 %

19,200 tpd 6.6 mtpa

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Drill and Blast Audit Benchmarking Phase

Parameter Value

Bench Height (m) 10

Hole Diameter (mm) 200

Burden (m) 5.2

Spacing (m) 6.0

Stemming (m) Drill cuttings/mill scats (m)

4.5 2.0/2.5

Subdrill (m) 1.0

Number of Holes Area (m2)

132 36.6

Explosive Type HA 46/HA 64

Explosive Density (g/cm3) 1.2/1.28

Detonator system Non-electric

Downhole (ms) Inter-hole (ms) Inter-row (ms)

600 17 25

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SmartTagTM Ore Tracking System

Antenna 1

Antenna 2

RFID Tag

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Comminution Circuit Review and Survey Review of Crushing and Grinding Operations

600525450375300225150750

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0600525450375300225150750

kW-CR1

Perce

nt

kW-CR2

N 4059StDev 89.01Mean 129.5

N 4346StDev 96.45Mean 132.5

Histogram of Power Draw - Crushers CR1 & CR2

Nomin

al Pow

er

Nomin

al Pow

er

Available Power Available Power

Hypogene: 800-850 tph

Crushers : •Operating below installed power 225 kW of 373 kW 60 % Grinding Mills: •Wide range of bearing pressure and power levels (overloading) •60 % critical speed

Historical Operational Data

Average Daily Production: •Hypogene tph lower than overall distribution

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Modelling & Simulations Blast Fragmentation Model Calibration

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Blast Model Average ROM

Model Inputs

•Rock mass characterisation data •Audit blast parameters •ROM image analysis (coarse end of the curve) •Primary crusher product belt cut sample (fine end of the curve)

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Modelling & Simulations Blast Model Simulations

*Use 20 mm crushed angular material for the full stemming length

Benchmark P3810007

Simulation Scenario 5

Bench (m) 10 10 Diameter (mm) 200 200 Burden (m) 5.2 4 Spacing (m) 6.0 4.7 Subdrill (m) 1 1 Stemming (m) 4.5 *3.5 Explosive Type HA 46 HA73 Density 1.20 1.30 Primer (Booster) (g) 450 450 Charge/hole (kg) 245.0 306.3 Detonator Non Electric Electronic Surface (holes) 17 20 Surface (holes) 42 100 PF (kg/m³) 0.79 1.63 PF (kg/t) 0.31 0.65 Difference (%) 107

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Blast Simulations

Benchmark P3810007

Scenario 1

Scenario 2

Scenario 3

Scenario 4

Scenario 5

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Modelling & Simulations Comminution Circuit Model and Simulations

Model •Survey samples were analysed and used to mass balance and model fit. Simulations •Explore the effects of the primary crusher and SAG mill operating conditions. •Assess the effect of modified blast fragmentation. •Combined effect of all changes Primary Crusher Recommendations Improve primary crusher power utilisation by reducing crusher gap (increases thickness of teeth) SAG Mill Recommendations Higher SAG mill ball charge, lower operational speed, run the mill at a stable feed rate. Ball Mill Recommendations Increase ball top size. Increase ball charge to fully utilise the installed power.

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Combined Predicted Results Modelling & Simulations

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l Pro

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SAG

Thro

ughp

ut, t

ph

Throughput

P80

Powder factor increased to

1.4kg/m3

Powder factor increased to

1.6kg/m3

Optimised SAG milling

Optimised ball milling

Base Case

+8.3%

+12.1%

+15.9% +15.9%

Blast Scenario 5

Blast Scenario 4

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Recommendations for the Validation Trial Drilling and Blasting Recommendations //~ Implement larger diameter holes Implementation of Electronic Detonators Decrease the stemming length from 4.5 m to 3.5m Use 20 mm crushed angular material for the full stemming length Avoid using drill cuts for stemming; if crushed material is unavailable use mill scats Use explosive HA 73 with 1.3 g/cm³ in all holes Use parameters PF: 1.6 kg/m³, Burden: 4 m, Spacing: 4.7 m, HD:200 mm ~ Use delays of 20 ms between holes and 100 ms between rows. Primary Crusher Recommendations Increase primary crusher power utilisation by reducing the crusher gap SAG Mill Recommendations Higher SAG mill ball charge and lower operational speed Run the mill at a stable feed rate. Ball Mill Recommendations Increase ball top size to compensate the increased ball mill feed size. Increase ball charge to 35 % to fully utilise the installed power.

Implemented Not implemented Partially implemented ~

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Validation Trial Rock Mass Characterisation Overall Rock strength: Moderately Hard Ore P3800017: Similar strength to benchmark P3800018: Higher range of ore hardness Rock structure: Low quality, jointed/fractured rock Breakage Characteristics: Soft to medium ore for milling (very similar)

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Validation Trial Blast Design Parameters

Polygon 3800017

• Reduced stemming in only soft lithology holes

• Reduced PF

Polygon 3800017 & 3800018

• GF’s preferred use of HA55/HA64 for dry/wet holes

• Stemming plugs

• Electronic detonators

• 25 ms and 83 ms

*Stemming plugs used in both validation trial polygons

Benchmark P3810007

Simulated Scenario 5

Validation P3800017

Validation P3800018

Burden (m) 5.2 4 4 4 Spacing (m) 6 4.7 4.7 4.7 Stemming (m) 4.5 3.5 *3.5/4.5 *3.5/4.5 Explosive HA 46 HA 73 HA 55/64 HA 55/64 Density (g/cm3) 1.2 1.3 1.28/1.3 1.28/1.3

Powder Factor (kg/m3) 0.79 1.63 1.31 1.62 Powder Factor (kg/t) 0.31 0.65 0.52 0.65 Detonator Non Electric Electronic Electronic Electronic Inter-hole (ms) 17 20 25 25 Inter-row (ms) 42 100 83 83

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Validation Trial

Polygon 3800017 •More fines •Lower range hardness levels •Lower PF Polygon 3800018 •Higher range of ore hardness

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Validation P3800018 Validation P3800017Benchmark P3810007 PTI Recommendations

Fragmentation for Benchmarking and Validation Polygons

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Validation Trial Fragmentation Impact on Crushing and Grinding

ValidationBenchmark

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Project Phase

SAG

Mill

Thro

ughp

ut (t

ph)

928.95

808.935

Comparison of SAG Mill Throughput for the Specific Ore Type

+ 14.84%

P80: 154 µm

P80: 141 µm

SAG Feed: % F80: Very similar % Fines Increase: 18 % Avg tph increase: 14.8 % Specific Energy Reduction: 9.2 % Ball Mill: Reduced final product P80 = 141 µm

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Validation survey, July 2012

Benchmark survey, Oct 2011

Crushing:

•Increased tph due to finer blast fragmentation

• Reduced wear on crusher

• Increased power utilisation (scope to improve)

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Metso PTI’s PIO methodology demonstrated that Cerro Corona may increase the plant throughput by 14.8 % (same ore type as in validation trial) and at least 5.7 % for all ore types.

Knowledge and understanding of ore properties is critical during execution of PIO projects.

Optimised blast design produced finer ROM fragmentation therefore finer feed to primary crusher which impacted the plant throughput.

By combining the optimised blast design and optimised comminution processes it is possible to increase the plant throughput and reduce energy and costs.

An integrated process integration and optimisation approach from mine to mill results in highest impact and benefits in terms of operational efficiency and profitability.

Conclusions

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Metso PTI would like to thank everyone at Cerro Corona who assisted in this project.