Characterization and in-situmonitoring of large scale heapleach fluid dynamicsDanny Santis Valenzuela, Michael Milczarek, Tzung-mow Yao,Jason Keller

Pilot Heap Leach Design• 500,00 ton copper sulfide heap leach pilot project

– 0.5-inch crushed and agglomerated ore– 18 m height– Approximately 90 m x 90 m leaching area– Drainage system split into 9 modules to monitor outflow– Double aeration system

• Key questions for characterization and monitoring:– Ore permeability?– Solution distribution?– Oxygen content and distribution?– Temperature distribution and evolution?– In-situ solution sampling?

• Operated for 1.3 years

Pilot Heap Leach Characterization

• Daily samples from crusher plant (PSD)– Target < 50% passing the #4 mesh

• Pre-leach and post-leach drilling for deep sub-surface samplecollection– Casing advancement to keep the hole open (and for instrument

placement during pre-leach)

• Sample collection for:– Geochemical/mineralogy testing– Hydraulic and physical property testing (undisturbed samples)

Instrumentation and Monitoring

• 25 monitor well– 0 to 17.5 m below ground surface

• Monitoring parameters– Temperature oxygen/air piezometers (every 3 m)– Moisture content and capillary pressure (tension) (every 6 m)– Water piezometers (one per module)– Suction lysimeters (various)

• Automated data collection w/ telemetry to control room

Leaching Core84 m x 84 m

SolutionCollectionModules30m x 30m

1 4 7

2 5 8

3 6 9

Aeration from East

Aeration from West

Topographic Gradient

Drainage lines

1 4 7

2 5 8

3 6 9

East

West

Slide 6

Suctionlysimeter

In-situ Monitoring InstrumentInstallation

Automated Data Collection

Hourly data collection w/Telemetry to control room

RESULTS

Heap Solution Budget (Average)

0%

5%

10%

15%

20%

25%

30%

11/1/

2007

12/1/

2007

12/31

/2007

1/30/2

008

2/29/2

008

3/30/2

008

4/29/2

008

5/29/2

008

6/28/2

008

7/28/2

008

8/27/2

008

9/26/2

008

10/26

/2008

11/25

/2008

12/25

/2008

Date

Sol

utio

n C

onte

nt (v

/v)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

Irrig

atio

n R

ate

(l/m

2 /hr)

Predicted Solution Content (v/v) Avg Daily Irrigation Rate

Start DoubleAeration

Stop DoubleAeration

Temperature at Depth (Center Borehole)

0

1

2

3

4

5

6

2008

-09-

29

2008

-10-

01

2008

-10-

03

2008

-10-

05

2008

-10-

07

2008

-10-

09

2008

-10-

11

2008

-10-

13

2008

-10-

15

2008

-10-

17

2008

-10-

19

2008

-10-

21

2008

-10-

23

2008

-10-

25

2008

-10-

27

2008

-10-

29

2008

-10-

31

2008

-11-

02

Perc

olat

ion

flow

rate

(L/h

/m2)

Date

Module 4 - East aeration grid Module 6 - East aeration grid

Module 4 - West aeration grid Module 6 - West aeration grid

Percolation vs Aeration (direction)

1 4 7

2 5 8

3 6 9

East

West

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

Single EastAir

Double EastAir

Alt Air-E Alt Air-W No Air

Dra

inag

e/Ir

riga

tion

Mod 1,4,7Mod 2,5,8Mod 3,6,9

North-South Solution Balance(Normalized)

East

West

East

West

4 m bgs Capillary Pressure – DoubleAeration

-40-20

-40

-20

-20

-20

-20

-20

-20

0

00

0

0

0

0

0

0

0

20

20

2020

20

20

20

40 40

40

40

40

40

60

60

60

80 80

80

100

100100

120

120

120140

140

140

160

160

160

180

180

180200

200

200

X (m)

Y(m)

10 20 30 40 50 60 70 80

10

20

30

40

50

60

70

80

200180160140120100806040200-20-40-60-80-100

7/10/2008 - Double Aeration From East, I=3.0 l/hr/m2

4 m bgsCapillary Pressure

(cm)123

456

789

West East

Monitoring Data Summary

• Time dependent behavior– High initial temperatures then temperature decline– Increasing solution balance– Solution samples showed more reducing conditions over time

• Strong preferential solution and air flow• Low aeration efficiency

– Highly variable oxygen contents– Low observed air connectivity under leach

• Positive capillary pressures in heap– Combination of near saturation and CO2 accumulation

Post-leach Ore Sampling andTesting

• Drilled 52 boreholes (sonic drilling)– Samples every 1.5 m– Logging for oxidising and reducing conditions– Physical property and geometallurgical analyses– 12 representative samples for hydraulic property testing

• Determine relationship of PSD, bulk density and hydraulicconductivity

• Results correlated to monitoring data

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100

Perc

ent P

assi

ng

Particle Diameter (mm)

Average of All Core Samples

Average of Crush head

#4 mesh

#100 mesh

Average PSD – Before and After Leaching

Percolation vs < #100 Mesh (module avg)y = -0.061x + 22.015

R² = 0.6559

19.0

19.5

20.0

20.5

21.0

21.5

22.0

22.5

0 5 10 15 20

Perc

ent P

assi

ng #

100

Mes

h

Percent of Total Collected Percolation

Modules 1and 4

Module 7

Module 2Module 5 Module 3

Module 9

Module 8

Module 6

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

Perc

ent o

f Tot

al C

ore

Module 1

Module 2

Module 3

Module 4

Module 5

Module 6

Module 7

Module 8

Module 9

Module Avg

Outside Avg

Yellow (Oxidising) Grey (Reducing)

Eastern Modules

4,5,6 Transect

BETTER AERATION/SOLUTION FLOWModule 9

Relative Oxidising Conditions perModule (52 boreholes)

0

2

4

6

8

10

12

14

16

1.0E

-05

1.0E

-04

1.0E

-03

1.0E

-02

1.0E

-01

1.0E

+00

Dep

th (m

bgs

)

Ksat (cm/sec)

Predicted-AllModules2 L/m2/hr

100X SafetyFactor

0

2

4

6

8

10

12

14

16

1.0E

-06

1.0E

-05

1.0E

-04

1.0E

-03

1.0E

-02

1.0E

-01

1.0E

+00

Dep

th (m

bgs

)

Ksat (cm/sec)

Module 1

Module 2

Module 3

Module 4

Module 5

Module 6

Module 7

Module 8

Module 9

Post-Leach Predicted Permeability (Ksat)

1 4 7

2 5 8

3 6 9

East

West

Other factors:• Decrepitation• Aeration/flow domains (initial fingering)• Aeration pipe damage• Earthquake

High Flow in 4, 5, 6, 8 During No Aeration?

Lessons Learned• Bulk densities higher (permeability lower) than predicted:

– Mostly in initial modules (i.e. 9) where crushing criteria was not beingmet

• Solution movement– Permeability contrasts, preferential flow– Decrepitation, particle orientation (and an earthquake)– Drainage layer pressurization by aeration

• Low aeration efficiency– Air loss from sides, pipe damage– More air may not be better

• Greatest oxidation/copper recovery observed in modules withmost air and solution flow