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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!
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