Dry Stacking Operation at Pogo Mine, Alaska

Dry Stacking Operation

at Pogo Mine, Alaska June 12, 2014

Sumitomo Metal Mining Pogo LLC

Contents

1. About Pogo Mine

• Geology

• Mining and paste backfill

• Process

2. Dry Stacking Operation

• About Dry Stack Tailings Facility (DSTF)

• Flotation tailings geotechnical characteristics

• Monitoring

3. Operational Challenges

• Filter plant issues

• DSTF construction design

• Lessons learnt

Tokyo

Tokyo

Chiba

Kanagawa

Kagoshima

Toyo Smelter Ehime

Hyogo

SMM’s Core Facilities in Japan

SMM’s Overseas Assets

Tintina Gold Belt

N. W. T.

Y U K O N

B. C.

A L A S K A

DONLIN CK.

11.4 M oz

TRUE NORTH

1.3 M oz DUBLIN GULCH

3.1 M oz

POGO/LIESE ZONE

5 Moz Au

FORT KNOX

8.8 M oz

TINTINA GOLD BELT

SIGNIFICANT GOLD DEPOSIT

GOLD DEPOSIT or OCCURRENCE400 kilometers

Geologic Map

Orebodies

Looking NE

Liese Zone

Pogo Mine as of 1999

Goodpaster River

Pogo Mine as of 2005

Drift & Fill Mining Method

15m

Paste Plant Process Flow

Recycle Tailing Pond

(RTP)

Floatation tailing thickener

CIP tailing thickener Overflow

UnderflowUnderflow

Cement silo

Filter press

Filter cake stock pile

UndergroundHigh-Pressure Paste Pump

Paste

FCU/FCIP tailing

BFD waterCement

RTP water

tanktank

tank

tank

Flotation tailing thickener

Paste Backfill in Stope

Stope void

Barricade Blast off

Plan view

Cross section

Paste pipe

Breathing pipe

Blast off point

Paste Backfill - Barricade

Paste

Backfill

Cut 1

Cut 2

Exposed Paste Backfill Wall

Processing

Pogo Process Flow

Surface Disposal

Flotation TailingCIP Tailing

Filtering

Paste Backfill

ILR

Regrind Leach/CIP/Stripping

EW

CN Destruct

Cyanide ContactGrinding

Gravity

Flotation

Non Cyanide Contact

90%10%

60%

40%

Concentrate

ILR: Intensive Leach Reactor

EW: Electrowinning

CIP: Carbon-in-Pulp

Production

0.0

0.5

1.0

1.5

2.0

2.5

0

100

200

300

400

500

600

700

800

900

1000

2006 2007 2008 2009 2010 2011 2012 2013

Cu

mu

lati

ve A

u P

rod

uct

ion

(Mo

z)

Ore

Pro

cess

ed

(kt

pa)

Au Production - Cumulative (oz)

Ore Processed (ktpa)

Dry Stack Tailings Facility (DSTF)

Why DSTF?

• Geographical and geotechnical restrictions for

conventional tailings dam:

• Narrow and steep valleys;

• Deep alluvial valley infillings;

• Permafrost.

• Lowest operational risks:

• Non-susceptible to liquefaction failures;

• Less impact on surface and ground water quality.

DSTF – Plan & Cross Section

(as of Sep. 2013)

60m

Recycle

Tailings

Pond

Inlet 1

Inlet 2

Inlet 3 Inlet 4

New Diversion Ditch

New Haul Road

Flow-through Drain

Recycle Tailings Pond (RTP)

Diversion Ditch Construction

Inlet Construction

Insulation Board

New South Flume

Filtering Process Open Filter Plate Pack

Filter Press

• Filter Plates: 6m2 x 24/each

• Cycle Time: Approx. 15 min.

• Capacity: 9dt/batch

Dry Stacking Process

①

②

③

④

Flotation Tailings – Grain Size Distribution

• Permeability (saturated): 1.6～7.8×10-6 cm/sec

Grain Size (mm)

Pe

rce

nt

Fin

er

80%

75μm

Geotechnical Properties of Flotation Tailings

Water Content (%)

Dry

Density (

pcf) 15.8%, 109.8 pcf

Standard Proctor Test

90%

95%

Direct Shear Test (Normal Stress: 24~120kPa)

100%

35

36

37

38

39

40

41

42

43

90% 95% 100%

Fric

tio

n A

ngl

e (

de

gre

e)

Compaction Effort

1.75 g/cm3

1.3

1.4

1.5

1.6

1.7

1.8

4 6 8

Dry

De

nsi

ty (

g/cm

3)

No. of Passes

1 Day

2 Days

3 days

7 Days

Dry Stacking under Cold Weather

Air Temp. during Compaction Test: -23 ~ -7℃

90%

100%

Frozen Dewatered Tailings

Stability Evaluation (18Mt Facility)

Material Name ColorUnit Weight

(g/cm3)

Sat. Unit

Weight

(g/cm3)

Cohesion

(kPa)

Internal

Friction Angle

(deg)

Compacted Tailings 1.68 2.05 0 34

Tailings@GPA 2.00 2.40 0 34

Rock Shell 2.00 2.40 0 38

Flow-through Drain 2.00 2.40 0 38

Starter and Toe Berm 2.00 2.40 0 32

Overburden 2.00 2.40 0 32

Bedrock 2.50 2.50 0 40

Pseudostatic analysis, considering:

• Vertical ground acceleration

(upward)

• Excess pore pressure

Geotechnical Monitoring at Shells

Nuclear Densometer

Shell 2

Water Quality Monitoring at DSTF

:Surface water sampling point

:Ground water monitoring wells

:Flumes with pressure transducer (Flow measurement)

Piezometer Installation

SB-1 GP-1 RR-1

SB-1 GP-1

RR-1

2012 DSTF Extent

18Mt DSTF Extent

2012 DSTF Extent

18Mt DSTF Extent

Piezometer Installation - Major Findings

• Permafrost exists within

DSTF;

• Phreatic surface exists near

the base of DSTF;

• Density and geotechnical

properties of in-situ samples

coincide well with past

laboratory test results;

• Potential of acid rock

drainage from DSTF is

minimal.

Vibrating Wire Piezometer

Operational Challenges

Filter Plant Issues

• Poor performance of filter

presses:

• Plan: 2,040tpd with two filters

• Actual: 1,360tpd

• Causes:

• Longer cycle time

• Lower mechanical availability:

• Excess wear of filter cloths

• Frequent mechanical failure

Pinhole on the cloth

0

2

4

6

8

10

12

14

16

18

Plan Actual

Cyc

le T

ime

(m

in)

Cake Discharge

Air Blowing

Press

Filtration

Cycle Time for Dewatering

• More fine particles

(<20µm) than plant

test

• Higher dilution of

waste rock?

0

500

1000

1500

2000

2500

3000

20

07

20

08

20

09

20

10

20

11

20

12

20

13

Cycles per cloth

Excess Wear of Filter Cloths

Causes

• Debris in slurry → Pinholes

• Folding of cloths

Solutions

• Trash removal screen and

strainers

Target

60%

65%

70%

75%

80%

85%

90%

95%

100%

20

07

20

08

20

09

20

10

20

11

20

12

20

13

Mechanical Availability of

Filters (%)

Mechanical Availability of Filters

Causes

• Excess parts wear

Solutions

• Washing & Maintenance!

• Dayshift:

Two filters in operation,

one in maintenance

• Nightshift:

Three filters in operation

Target

DSTF Construction Design Issues

60m

Extent of 2015

STARTER

BERM

FLOW THROUGH

DRAIN

GENERAL PLACEMENT

AREA SHELL DEPOSITION

AREA

ROCKFILL TOE

BERM

DSTF Construction – Plan vs. Actual

Rock Shell

Shell Deposition Area General Placement Area

Plan

Actual

DSTF Placement Tonnage - Plan vs. Actual

Plan Actual

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

Pre

-200

6

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

Cu

mu

lati

ve T

on

nag

e (

Mt)

Flotation TailingsWaste Rocks

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

11.0

12.0

13.0

Pre

-200

6

2006

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

Cu

mu

lati

ve T

on

nag

e (

Mt)

Flotation TailingsWaste Rocks

Lessons Learnt on Dry Stacking

• Dewatering:

• Expect more fine particles;

• Consider abrasiveness of

tailings;

• Remove debris from feed.

• DSTF Construction Design:

• General Placement Area with

Rock Shell;

• Haul road planning with the

raise of GPA;

• Conservative placement plan.

Thank you for your attention!