INTEGRATED WASTE MANAGEMENT
WASTE ROCK
MANAGEMENT PLAN
PLAN OF OPERATIONS—VOLUME III B
Donlin Gold Project
July 2012
PLAN OF OPERATIONS
Integrated Waste Management Plan
WASTE ROCK MANAGEMENT
PLAN
Donlin Gold Project
July 2012
4720 Business Park Blvd. Suite G-25
Anchorage, Alaska 99503
Prepared By:
SRK Consulting (U.S.), Inc.
4710 Business Park Blvd. Suite F-40
Anchorage, Alaska 99503
Waste Rock Management Plan
Donlin Gold Project
Table of Contents
TABLE OF CONTENTS
Table of Contents .................................................................................................................i
Appendices ................................................................................................................. i
Figures ...................................................................................................................... ii
Tables ....................................................................................................................... ii
Acronyms ................................................................................................................. iii
Units of Measure ...................................................................................................... iv
Elements and Compounds......................................................................................... v
1.0 INTRODUCTION ......................................................................................................1-1
1.1
Authors .......................................................................................................1-1
1.2
Project Location and Summary ...................................................................1-1
1.3
Objective and Scope ...................................................................................1-4
2.0 SITE CONDITIONS ..................................................................................................2-1
2.1
Physical Setting...........................................................................................2-1
2.2
Climate ........................................................................................................2-1
2.3
Geology ......................................................................................................2-3
2.3.1
Regional Geology .........................................................................2-3
2.3.2
Project Geology ............................................................................2-5
2.3.3
Major Rock Types .........................................................................2-7
2.3.4
Geology Underlying the Waste Rock Facility ................................2-8
3.0 WASTE ROCK CHARACTERIZATION ....................................................................3-1
3.1
Waste Rock Geochemical Modeling ............................................................3-4
3.2
Development of Waste Rock Classification System ....................................3-6
3.3
Mine Plan and Waste Rock Distribution ......................................................3-8
4.0 WASTE ROCK MANAGEMENT ...............................................................................4-1
4.1
Waste Rock Classification ...........................................................................4-1
4.2
Waste Rock Mining and Segregation ..........................................................4-1
4.3
Waste Rock Designation and Placement ....................................................4-2
4.3.1
American Creek Valley WRF ........................................................4-4
Isolated Cells on WRF ..................................................................4-5
4.3.2
4.3.3
ACMA Pit Backfill ..........................................................................4-7
4.3.4
Tailings Storage Facility ................................................................4-7
5.0 WASTE ROCK FACILITY DESIGN ..........................................................................5-1
5.1
Waste Rock Facility Construction ................................................................5-1
5.2
Waste Rock Facility Reclamation ................................................................5-2
6.0 MONITORING AND REPORTING ............................................................................6-1
6.1
Operational Monitoring and Reporting .........................................................6-1
6.2
Closure and Post-Closure Monitoring and Reporting ...................................6-1
7.0 REFERENCES .........................................................................................................7-1
APPENDICES
Appendix A
Summary of Mine Production Schedule
Appendix B
Block Model Views
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Waste Rock Management Plan
Donlin Gold Project
Table of Contents
FIGURES
Figure 1-1: Project Location Map .....................................................................................1-3
Figure 2-1: Regional Geology Map ...................................................................................2-5
Figure 2-2: Geologic Map of the Donlin Gold Area ...........................................................2-6
Figure 3-1: Total Waste Rock Material Distribution...........................................................3-9
Figure 4-1: Waste Rock and Stockpile Locations .............................................................4-3
Figure 4-2: PAG 6 Cell Evolution......................................................................................4-6
TABLES
Table 2-1:
Estimated Monthly Precipitation at Donlin ......................................................2-2
Table 2-2:
Potential Evaporation/Sublimation and Mean Temperature ............................2-3
Table 3-1:
Characteristics of Samples Tested Using Sequential MWMP.........................3-3
Table 3-2
Site-specific Calculation of ABA Parameters ..................................................3-5
Table 3-3:
Donlin Gold Waste Rock Management Categories (SRK 2011) .....................3-7
Table 3-4:
Donlin Gold Waste Rock Classification System..............................................3-8
Table 3-5:
Donlin Gold Waste Rock Tonnage Estimates .................................................3-9
Table 4-1:
Waste Rock Tonnage by Facility ....................................................................4-4
Table 5-1:
Waste Rock Facility Design Parameters ........................................................5-1
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July 2012
Waste Rock Management Plan
Donlin Gold Project
Table of Contents
ACRONYMS
ABA
AMEC
AP
ARD
BC
BGC
CIL
CWD
DF
Donlin Gold
GPS
GWK
HCT
ICP
INF
LLDPE
MD
MDAG
ML
MWMP
NAG
NP
OVB
PAG
Plan
RD
RDX
SAG
SHL
SRK
TSF
VPC
WRF
WRMC
Donlin Gold
Acid Based Accounting
AMEC Americas Limited
acid potential
acid rock drainage
British Columbia
BGC Engineering Inc.
carbon-in-leach
Contact Water Dam
Denali-Farewell
Donlin Gold LLC
global positioning system
greywacke
humidity cell test
inductively-coupled plasma
Iditarod-Nixon Fork
linear low-density polyethylene
mafic dykes
Mine Drainage Assessment Group
metal leaching
Meteoric Water Mobility Procedure
non-acid generating
neutralizing potential
overburden
Potentially Acid Generating
Waste Rock Management Plan
Rhyodacite
oxidation reduction potential
semi-autogenous grinding
shale
SRK Consulting (U.S.), Inc.
tailings storage facility
volcano-plutonic complexes
waste rock facility
waste rock management categories
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Waste Rock Management Plan
Donlin Gold Project
Table of Contents
UNITS OF MEASURE
%
<
=
>
°C
°F
cfs
cm
ft
g/t
ha
kg
km
Ktonnes
Ktons
lb
m
Ma
m3
m3/s
mm
Mm3
msl
Mst
Mt
MW
oz/st
st
stpd
t
tpd
yd3
Donlin Gold
percent
less than
equal to
greater than
degree Celsius
degree Fahrenheit
cubic feet per second
centimeters
foot/feet
grams per tones
hectares
kilogram
kilometer
thousand metric tonnes
thousand short tons
pound/pounds
meter
million years
cubic meters
cubic meters per second
millimeter
million cubic meters
mean sea level
million short tons
million tonnes
megawatt
Troy ounces per short ton
short ton
short tons per day
tonne (1,000 kg)
tonnes per day
cubic yard
iv
July 2012
Waste Rock Management Plan
Donlin Gold Project
Table of Contents
ELEMENTS AND COMPOUNDS
H2SO4
NPCO3
ST
CaCO3/t
As/S
Donlin Gold
sulfuric acid
neutralizing potential from carbonate minerals
total sulfur concentration
Amount of Calcium Carbonate (or equivalent) per ton (tonne) required to
neutralize acid generating material
arsenic/sulfur ratio
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July 2012
Waste Rock Management Plan
Donlin Gold Project
1.0
Introduction
INTRODUCTION
This Waste Rock Management Plan (Plan) has been developed by Donlin Gold LLC 1
(Donlin Gold) for the proposed Donlin Gold project to define the procedures and practices
associated with the characterization, management, placement of waste (development) rock,
and final closure at the proposed Donlin Gold mine. The Plan is one volume of the Donlin
Gold Integrated Waste Management Plan.
The Plan may be revised periodically during operations as additional data become available
through the monitoring procedures identified in this report.
1.1
Authors
Preparation of this document was coordinated by SRK Consulting (U.S.), Inc. (SRK), using
information provided by, AMEC Americas Limited (AMEC), ARCADIS U.S. Inc., BGC
Engineering Inc. (BGC), and Barrick Gold U.S.
1.2
Project Location and Summary
Donlin Gold is proposing the development of an open pit, hardrock gold mine in
southwestern Alaska, about 277 miles (446 km) west of Anchorage, 145 miles (233 km)
northeast of Bethel, and approximately 10 miles (16 km) north of the village of Crooked
Creek (Figure 1-1).This document provides an overview of the proposed plans for mining
and milling the ore, water management, waste rock management, and the support facilities
and infrastructure required to support the operation.
The gold resource is hosted in intrusive and sedimentary rock in two main areas of the
property, Lewis and ACMA, with 80% found in intrusive rock. The proven and probable 2
resources total 556.5 Mst (504.8 Mt) with an average grade of 0.061 oz/st (2.09 g/t). With
mill recovery at approximately 90%, the operation would produce an average of over 1
million ounces of gold annually.
The proposed Donlin Gold project would require three to four years to construct, with the
active mine life currently projected to be approximately 27.5 years. The mine is proposed to
be a year-round, conventional “truck and shovel” operation, using both bulk and selective
mining methods. The operation would have a projected average mining rate of 422,000 stpd
(383,000 tpd), or 154 Mst (140 Mt) per year, and an average mill production rate of 59,000
1
Donlin Gold LLC is a limited liability company equally owned by Barrick Gold U.S. Inc. and NovaGold
Resources Alaska, Inc.
2
Based on an assessment of qualitative, non-technical factors, Barrick Gold Corporation treats mineralization
at Donlin Creek as measured and indicated resources, rather than proven and probable reserves for securities
reporting, accounting, and other public disclosure purposes. Mineral reserves are those parts of mineral
resources which, after the application of all mining factors, result in an estimated tonnage and grade which is the
basis of an economically viable project after taking account of all relevant processing, metallurgical, economic,
marketing, legal, environment, socio-economic, and government factors. Mineral reserves are inclusive of
diluting material that will be mined in conjunction with the mineral reserves and delivered to the treatment plant or
equivalent facility. The term ‘mineral reserve’ need not necessarily signify that extraction facilities are in place or
operative, or that all governmental approvals have been received. It does signify that there are reasonable
expectations of such approvals.
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Waste Rock Management Plan
Donlin Gold Project
Introduction
stpd (53,500 tpd). Milling components include a gyratory crusher, semi-autogenous grinding
(SAG) and ball mills, followed by flotation, concentration, pressure oxidation, and carbon-inleach (CIL) process circuits. Onsite retort and gold furnaces would produce an end-product
of gold doré bars, which would be shipped to a custom refinery for further processing.
A tailings storage facility (TSF) would encompass an area of 2,351 acres (951 ha), with a
total capacity of approximately 334,298 acre-ft (412.35 Mm3) of mill tailings, decant water,
and storm water. Total waste rock material is estimated at 3,048 Mst (2,765 Mt), with
approximately 2,460 Mst (2,232 Mt) placed in a waste rock facility (WRF) located outside the
mine pit, 114 Mst (103 Mt) used for construction, and the remaining 467 Mst (424 Mt) of
waste rock backfilled in the pit.
Electrical power would be supplied by 12 onsite natural-gas fueled reciprocating engines
with heat recovery and steam generation (a combined cycle system to supply power for a
total connected load of 227 MW, with an average running load of 153 MW, with a peak load
of 184 MW.
The natural gas would be transported via a 313-mile (503 km), 14-inch (35.5 cm) diameter
buried pipeline from an existing 20-inch (51 cm) natural gas pipeline near Beluga, Alaska, to
the proposed Donlin Gold mine site.
General cargo for operations would be transported from terminals in Seattle; Vancouver,
British Columbia (BC); or Dutch Harbor via marine barge to Bethel. At Bethel, it is expected
that cargo would be transferred to the dock for temporary storage or loaded directly onto
river barges for transport up the Kuskokwim River to a port constructed at Jungjuk Creek. A
30-mile (48 km), all-season access road would be constructed from the proposed Jungjuk
(Angyaruaq) Port to the mine site.
Fuel would be transported to Dutch Harbor by tanker, then to Bethel via marine barge. At
Bethel fuel would either be transferred directly to double-hull river barges, or off-loaded for
temporary storage. From Jungjuk Port, fuel would be transferred to the mine site fuel
storage facility via tank trucks.
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July 2012
Chukchi Sea
Hamilton
Nome
Chuloonawick
Emmonak
Alakanuk
Nunam Iqua
A
AD
N
CA
Anchorage
Bethel
Bering Sea
Takotna
ammon Bay
r
Nikolai
Juneau
Shageluk
Anvik
Talkeetna
Iditarod
Flat
DONLIN
GOLD
HolyPROJECT
Cross
iv
Yukon R
er
Skwentna
Georgetown
Crooked
Creek
Russian Mission
Upper Kalskag
Lower Kalskag
Ohogamiut
R i ve
Petersville
Gulf of Alaska
Marshall
McGrath
Grayling
Donlin Gold
Mountain Village
Pitkas Point
Saint Mary's
Pilot Station
Medfra
Ophir
Stony River
Red Devil
River
Fairbanks
Denali National Park
& Preserve
Innoko National
Wildlife Refuge
Susitna
ALASKA
Kotlik
Bill Moores Slough
Telida
im
IA
Barrow
Kuskok
w
S
er
S
Stebbins
Saint Michael
Riv
U
Yuk
on
Susitna
Sleetmute
Willow
Houston
Palme
Wasilla
Big
Lake
Knik
Eklutna
Chuathbaluk
Aniak
River
Anchorage
Napaimute
Lime Village
Yukon Delta National Wildlife Refuge
Beluga
Tyonek
Hope
Tuluksak
Newtok
Kasigluk
Atmautluak
Toksook
Bay
Nunapitchuk
Bethel
Akiak
Salamatof
Kenai
Lake Clark National
Park & Preserve
Ku
sk
ghtmute
Port Alsworth
Ninilchik
K
Eek
Soldotna
Kasilof
Clam
Gulch
IN
Tuntutuliak
Chefornak
Cooper
Landing
Nikiski
Kwethluk
Oscarville
Napaskiak
ok
w
im
Napakiak
Akiachak
LE
T
Mertarvik
Nondalton
Pedro Bay
Kwigillingok
Quinhagak
Newhalen
Koliganek
KUSKOKWIM BAY
Nikolaevsk
O
Wood-Tikchik
State Park
Kongiganak
O
Kipnuk
Togiak National
Wildlife Refuge
mn
Illi a
New Stuyahok
ke
a La
Iliamna
Anchor Point
C
R
Cantwell
Kachemak
Homer
Seldovia
Kokhanok
Nanwalek
Port Graham
Igiugig
Portlock
Ekwok
Aleknagik
Populated Places
Goodnews Bay
SCALE:
Proposed Natural Gas Pipeline Alignment
Proposed Infrastructure Layout
Federal Administrative Boundaries
State Administrative Boundaries
Seward Meridian, UTM Zone 5, NAD83
FIGURE:
Levelock
0
12.5
25
50 mi
0
20
40
80 km
PROJECT LOCATION MAP
1-1
DONLIN GOLD PROJECT
DG: PER0130.mxd, 07/11/12, R05
Moo
Waste Rock Management Plan
Donlin Gold Project
1.3
Introduction
Objective and Scope
This Plan documents the procedures for characterizing, classifying, and managing waste
rock associated with the proposed Donlin Gold project for surface disposal. The first step in
developing a Plan is to characterize the geochemical behavior of the various waste rock
material types associated with the project. This characterization defines the potential for the
waste rock material to generate acid or leach deleterious constituents. The characterization
is used to develop a classification system that can be used during implementation of a
waste rock handling plan that manages waste rock materials for different facilities.
Specifically, this Plan includes:
•
a summary of the geochemical characterization programs that define the
geochemical behavior of the waste rock
•
the volume of waste rock to be produced according to the current long-range
mine plan
•
waste rock classification according to operational criteria for waste rock
management
•
waste rock placement design and procedures to minimize potential oxidation and
solute generation
•
reclamation and closure activities planned for the waste rock disposal facilities.
This Plan incorporates acid-base accounting and solute generation information, and general
waste rock volumes and types, in order to optimize the development of waste rock disposal
facilities and minimize the potential for constituent release, while supporting final closure
actions.
This Plan will periodically modified to integrate data from ongoing geochemical studies, mine
modeling changes, mine planning, WRF performance monitoring, or other information.
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Waste Rock Management Plan
Donlin Gold Project
2.0
SITE CONDITIONS
2.1
Physical Setting
Site Conditions
The proposed Donlin Gold project is located in an area of low-lying, well-rounded ridges on
the western portion of the Kuskokwim Mountains, with elevations ranging from 500 to 2,100
ft (152 to 640 m). Area vegetation is typically hard shrubs and small trees. Hillsides are
forested with black spruce, alder, birch, and larch. Soft muskeg and discontinuous
permafrost can be found in poorly drained areas at lower elevations. The current exploration
project has an all-season camp with facilities to house a workforce of up to 160 to
accommodate exploration, environmental, geotechnical, and engineering studies. There is
currently no overland access to the site. All equipment, supplies, and personnel are
currently transported by air. An adjacent 5,000 ft (1,524 m) airstrip is capable of handling
aircraft as large as a C-130 Hercules. The project is serviced by charter air services out of
Anchorage and Aniak.
2.2
Climate
Based on a detailed analysis of regional precipitation data from McGrath and Crooked
Creek, and limited site data, a synthetic dataset was generated by BGC (2011) for the
proposed Donlin Gold project site. The area has a relatively dry interior continental climate,
with an average annual precipitation of 19.6 inches (50 cm) as shown on Table 2-1.
Summer temperatures are relatively warm and may exceed 83°F (28°C). Minimum
temperatures may fall to -45°F (-43°C) during the winter months.
Rainfall generally occurs from May through September and snowfall from November through
March. October and April are transition months, with both rainfall and snowfall. On average,
snowmelt starts April 1 and ends May 4.
Table 2-2 presents the potential evaporation/sublimation and mean temperature in the
proposed project area (BGC 2011). Table 2-2 shows that annual average potential
evaporation/sublimation for the site is estimated to be 14.56 inches (36.9 cm). Annual
average runoff for the site is 13.39 inches (34.0 cm), indicating that actual
evaporation/sublimation is 6.26 inches (15.9 cm), or approximately 43% of the potential
evaporation.
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July 2012
Waste Rock Management Plan
Donlin Gold Project
Table 2-1:
Site Conditions
Estimated Monthly Precipitation at Donlin
Total Precipitation
Snowfall
Rainfall
Month
(in)
(mm)
(in)
(mm)
(in)
(mm)
January
1.16
29.4
1.16
29.4
0.00
0.0
February
0.89
22.6
0.89
22.6
0.00
0.0
March
0.80
20.3
0.64
16.2
0.16
4.1
April
0.40
10.1
0.04
1.1
0.36
9.0
May
1.05
26.7
0.00
0.0
1.05
26.7
June
2.15
54.7
0.00
0.0
2.15
54.7
July
2.61
66.2
0.00
0.0
2.61
66.2
August
3.70
93.9
0.00
0.0
3.70
93.9
September
2.66
67.6
0.00
0.0
2.66
67.6
October
1.74
44.3
0.85
21.7
0.89
22.6
November
1.17
29.7
1.17
29.8
0.00
0.0
December
1.30
33.1
1.30
33.1
0.00
0.0
Annual
19.6
499
6.1
154
13.6
345
Source: BGC 2011
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Waste Rock Management Plan
Donlin Gold Project
Table 2-2:
Site Conditions
Potential Evaporation/Sublimation and Mean Temperature
Potential
Evaporation/Sublimation
(in)
Millimeters
(mm)
Mean
Temperature (ºF)
Centigrade
(ºC)
January
0.09
2.3
-7.4
-21.9
February
0.11
2.8
0.7
-17.4
March
0.19
4.8
10.4
-12.0
April
0.55
14
27.9
-2.3
May
2.84
72
45.3
7.4
June
3.58
91
56.5
13.6
July
3.31
84
59.2
15.1
August
2.09
53
54.5
12.5
September
1.50
38
44.2
6.8
October
0.12
3
25.5
-3.6
November
0.11
2.8
5.9
-14.5
December
0.07
2
-6.0
-21.1
Total
14.56
370
-
Month
2.3
Geology
2.3.1
Regional Geology
The Kuskokwim region of southwestern Alaska is predominately underlain by the Upper
Cretaceous Kuskokwim Group. These include coarse- through fine-grained clastic rocks that
reach an estimated thickness of greater than 6.2 miles (10 km) (Decker et al., 1994). Minor
basin margin andesitic tuff and flows are also present near the top of the sequence and may
represent an initiation of volcanism that later culminated in widespread Late Cretaceous and
early Tertiary igneous activity (Goldfarb et al., 2004). These basin margin volcanic rocks
also suggest that deep penetrating structures controlled basin subsidence. A regional
geologic map is provided as Figure 2-1.
Kuskokwim Group sediments were deposited between 100 and 77 million years (Ma) ago in
a 93-mile (150 km) long, northeast-trending basin that subsided between a series of
amalgamated terranes including Mesozoic marine volcanic rocks, Paleozoic clastic and
carbonate rocks, and Proterozoic metamorphic rocks. This basin is interpreted to have
formed as a post-accretion foreland basin in a strike-slip environment. Kuskokwim Group
rocks show evidence of only the lowest grades of regional burial metamorphism (Goldfarb et
al., 2004).
Igneous activity was coeval with Late Cretaceous sedimentation in the Kuskokwim basin
and continued into early Tertiary. Intermediate composition volcano-plutonic complexes
(VPCs) intrude and overlie Kuskokwim Group rocks throughout the region. The igneous
rocks are predominantly tuffs, flows, and composite comagmatic monzonite to granodiorite
Donlin Gold
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Waste Rock Management Plan
Donlin Gold Project
Site Conditions
plutons. Volcanic and plutonic rocks range in age from 76 to 63 Ma and 71 to 66 Ma,
respectively. Kuskokwim Group sedimentary rocks are often extensively hornfelsed near
plutons. Volumetrically minor Late Cretaceous intermediate to mafic intrusive bodies are
also common and often associated with mercury and antimony occurrences (Goldfarb et al.,
2004). Felsic to intermediate hypabyssal granite to granodiorite porphyry dikes, sills, and
plugs are also widely distributed and often associated with placer and lode gold occurrences
(e.g., Donlin Gold deposit). Many dikes were emplaced within or near northeast-trending
fault zones. Contacts between porphyry igneous rocks and Kuskokwim Group sedimentary
rocks are generally sharp and do not display hornfelsed margins. Age dates range from 70
to 65 Ma, but a genetic association with the VPCs is uncertain.
The proposed Donlin Gold project area lies between two regional, northeast-trending,
dextral slip faults that dominate the structural setting of southwest Alaska – the Holitna
segment of the Denali−Farewell (DF) fault system to the south and the Iditarod−Nixon Fork
(INF) fault system to the north (Goldfarb et al., 2004). The region contains numerous NE to
ENE- and NW to WNW-trending lineaments that probably represent steeply dipping strikeslip faults. Fault movement in the Donlin Creek region appears to be right lateral on
northeast structures and left lateral on northwest structures. The proposed Donlin Gold
project is located along a splay of the INF fault system (Goldfarb et al., 2004). A regional
NNE-SSW compression event, lasting from approximately 80 Ma to approximately 65 Ma,
caused folding, tilting, and low-angle reverse faulting of Kuskokwim Group sedimentary
rocks and culminated with emplacement of granite porphyry dikes and sills. Compressional
deformation in the region probably occurred soon after sedimentation, because folds are
truncated by the volcano-plutonic complexes. East-trending open folds are prominent east of
the proposed Donlin Gold project area but appear truncated to the west by the proposed
Donlin Gold project fault, a splay of the INF fault. Local post-intrusion folding developed as
accommodation of intrusive events or as drag folds along faults.
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Waste Rock Management Plan
Donlin Gold Project
Figure 2-1:
2.3.2
Site Conditions
Regional Geology Map
Project Geology
Property-scale geology is largely interpreted from trenches and drill holes because outcrop
is limited and of generally poor quality. Figure 2-2 illustrates the property-scale igneous
geology, including the resource area, which is located between the Queen deposit area on
the northeast and the airstrip on the southwest. Undivided Kuskokwim Group sedimentary
rocks (uncolored), and several phases of granite porphyry associated with the 70 to 65 Ma
igneous events, are the main rock units. Sedimentary bedding strikes SE and dips
moderately to the SW. Overall, sedimentary structure in the northern resource area is
monoclinal, while sedimentary rocks in the southern resource area display apparent open
easterly-trending folds.
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Waste Rock Management Plan
Donlin Gold Project
Figure 2-2:
Site Conditions
Geologic Map of the Donlin Gold Area
Note: Shows igneous rocks, faults, and gold prospects.
RDA – aphanitic porphyry
RDX – crowded porphyry
RDXL– lathe rich porphyry
RDXB – blue porphyry
The oldest igneous rocks at the proposed Donlin Gold project are 74 to 72 Ma intermediate
to mafic dikes and sills. They are not abundant but occur widely throughout the property as
generally thin and discontinuous bodies. The later and much more voluminous 70 to 65 Ma
granite porphyry dikes and sills vary from a few feet to 200 ft (60 m) wide and intrude the
sedimentary rocks along a 5-mile long by 2-mile wide (8 x 3 km) NE- trending corridor. The
granite porphyry units occur as WNW-trending sills in the southern resource area and NEtrending dikes farther north. The felsic dikes and sills have similar mineralogy and the
porphyry texture indicates relatively shallow emplacement. These rocks belong to the
regionally important granite porphyry igneous event and are classified into five textural
varieties of rhyodacite. Rhyodacite is a term normally reserved for felsic to intermediate
composition volcanic to sub-volcanic rock types, but it is also used informally for igneous
rocks emplaced at a shallow depth. These units are chemically similar, temporally and
spatially related, and probably reflect textural variations of related intrusive events.
Differences include phenocryst size and abundance, groundmass texture, and overall color.
The earliest deformation (pre-74 through 68 Ma) includes flexural slip folding and southward
tilting of the sedimentary sequence. Continued compression further advanced the fold-thrust
response and formed ESE-trending and plunging folds or monoclinal warps. Shallow to
moderately north-dipping reverse or thrust fault structures developed along bedding slips
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Waste Rock Management Plan
Donlin Gold Project
Site Conditions
and competency breaks and ramped through fold hinge areas. Mafic dikes and sills (74 to
72 Ma) were intruded into compressional structures prior to intrusion of rhyodacite dikes and
sills (72 to 70 Ma) into NE extensional faults and layer-parallel weaknesses, respectively.
NE- and NW-striking oblique slip faults formed near the end of the compression event and
displaced earlier low-angle reverse faults, as well as intrusive rocks. As intrusive activity
decreased, gold bearing hydrothermal fluids utilized NNE fractures formed during ESEWNW extension (72 to 65 Ma, averaging 70 Ma).
2.3.3
Major Rock Types
The proposed Donlin Gold project deposit is hosted by rhyodacitic sills and dikes intruded
into a sedimentary package consisting of calcareous and non-calcareous shale and
greywacke. The sedimentary host rocks contain diagenetic iron sulfide mineralization, as
well as iron, arsenic, antimony, and mercury sulfide minerals introduced with the gold
mineralization. The intrusive rocks contain the same sulfide minerals introduced by
mineralizing processes. Mineralogical analyses have shown that carbonate minerals occur
variably in both rock type groups. Carbonate minerals are dominated by magnesium- and
iron-enriched varieties such as dolomite, ankerite, and siderite, rather than pure calcium
carbonates such as calcite.
The following sections provide a description of the major rock types associated with the
proposed Donlin Gold project based on observations made by SRK geologists (SRK 2007).
Shale
The majority of shale examined in core contained no visible sulfide minerals. In the intervals
where pyrite was observed, it occurred mainly as very fine disseminated grains but also as
larger blebs and veinlets. Generally, carbonates did not occur in the matrix of the shale in
the intervals examined, but rather as veinlets, which appeared to be zones of weakness that
would break preferentially. Sparry dolomite was rarely observed, and no arsenopyrite was
observed.
Greywacke
Similar to the shale, the majority of greywacke examined contained no visible sulfide
minerals. Pyrite, where observed, was not commonly disseminated, but instead occurred as
blebs and veinlets associated with carbonate.
The iron content of carbonates was commonly apparent by iron staining on veinlets in core.
Similarly, brown weathering indicative of iron carbonates was also observed in road cuts
throughout the project area. In intervals where the carbonate veinlets were not stained by
iron, the white carbonate minerals were identified as dolomite, based on its slow reaction
with dilute hydrochloric acid. Like the shale, arsenopyrite was not observed in the
greywacke. Coarse vuggy stibnite and coarse disseminated realgar were observed.
Rhyodacite
The term “Rhyodacite” is broadly used for the various porphyries that are observed within
the project area. Both pyrite and arsenopyrite were observed in the rhyodacite in a variety of
forms. Pyrite occurs in finely to coarsely disseminated sulfide veinlets and in mixed
carbonate and sulfide veinlets. Carbonates occur mainly as veinlets and rarely as part of the
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Site Conditions
matrix. Natural weathering of rhyodacite in outcrop has resulted in orange brown mottles,
suggesting oxidation and leaching of sulfides, but no sulfide minerals were observed in the
fractures. In one outcrop of rhyodacite (possibly crowded porphyry), green staining was
observed, which appeared to be malachite.
2.3.4
Geology Underlying the Waste Rock Facility
Several field investigations have been carried out within the proposed footprint of the WRF.
The investigations started in 2004 and included test pit excavations, auger hole drilling, core
drilling, ground reconnaissance, seismic refraction surveys, and resistivity surveys. The
overburden consisted of peat, loess, colluviums, alluvium, and terrace gravel deposits to
shallow levels. The bedrock in the area consists of greywackes, siltstones, and shales of the
Cretaceous Kuskokwim Group.
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3.0
Waste Rock Characterization
WASTE ROCK CHARACTERIZATION
Several extensive geochemical characterization studies have been completed that define
the geochemistry of waste rock materials associated with the proposed Donlin Gold project.
Geochemical data collected during these waste rock characterization programs were
evaluated to characterize and predict the potential reactivity and stability of waste rock that
would be extracted from the pit. The two main considerations of the waste rock
characterization programs include:
•
acid generation due to oxidation of sulfide minerals, which, when mixed with
water, can form sulfuric acid (H2SO4), leading to acid rock drainage (ARD)
•
potential for leaching of metals and metalloids (e.g., arsenic) and salts (e.g.,
sulfate).
The processes of acid generation and leaching can operate independently, although the
development of acidic conditions enhances the leachability of many constituents.
The characterization programs completed for the proposed Donlin Gold project utilized the
following testing methodologies:
•
mineralogy, including optical and quantitative (Rietveld method) x-ray diffraction
mineralogy on 40 samples and microprobe analysis of 617 carbonate mineral grains
•
bulk geochemical analysis using four-acid digest and Inductively-Coupled Plasma
(ICP) mass spectrometry analysis to determine total metal and metalloid chemistry
•
Acid-Base Accounting (ABA) including paste pH, total sulfur analysis using a LECO
sulfur analyzer and neutralization potential (NP) testing by titration using the
standard Sobek method (Sobek et al., 1978) of 2,312 samples
•
sequential Meteoric Water Mobility Procedure (MWMP) with geochemical analysis of
the leachate for specific constituents on 20 composite samples
•
kinetic testing using standard humidity cell test (HCT) procedures designed to
simulate water-rock interactions and predict the rate of reaction for acid generation
and metals mobility.
The ARD and metal leaching potential of the proposed Donlin Gold project waste rock has
been characterized in several phases.
In 2005, an initial suite of over 700 widely spaced core samples was collected by Placer
Dome from 162 drill holes and analyzed for ABA to evaluate the potential for ARD. Sixteen
samples from this suite were selected for kinetic testing using humidity cells to evaluate both
ARD and metal leaching (ML) potential. The 16 humidity cell samples were selected to
represent the main rock types (host sediments and intrusives), and the range of sulfur and
arsenic content in the two main mineralized areas (ACMA and Lewis). The geochemical
assessment from this database is described by the Mine Drainage Assessment Group
(MDAG) in a report dated February 12, 2006. Subsequent review of the report by SRK
(2007) confirmed that a thorough assessment of the ARD and metal leaching potential had
been completed for the project.
However, further assessment was recommended to address the following factors
considered critical to the project:
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•
adjustment of ABA parameters (primarily NP) to reflect the minerals expected to
contribute to generation and neutralization of acid
•
actual criterion or criteria that define potential for ARD and ML
•
overall distribution of Potentially Acid Generating (PAG) and Non-Acid
Generating (NAG) rock
•
feasibility of waste segregation during full-scale mining
•
chemistry of runoff in contact with waste rock.
As part of this assessment, an additional set of 360 samples from 12 holes was selected to
fill gaps identified in the MDAG characterization. The samples were obtained from
continuous intervals to evaluate “mining block-scale” geochemical variations, and were
analyzed for similar parameters as the MDAG suite. Data obtained in 2006, under the
direction of SRK, were combined with the MDAG database for a comprehensive evaluation.
At the same time, four large composite samples were prepared from drill core to fill large
barrels holding approximately 660 lb. (300 kg) each for onsite testing designed to evaluate
leaching under site conditions. The sample composites representing the two main lithologic
units (sediments and intrusive rocks) have distinctive sulfur and arsenic populations
observed in the geochemical dataset (SRK 2007). In 2008, two 1,200 lb. (544 kg) crushed
core composite samples, representing two waste rock categories, were prepared. One
barrel each was filled with 200 lb. (91 kg), 400 lb. (181 kg), and 600 lb. (272 kg) of each
composite resulting in six additional barrels (three for each composite). Assuming the test
materials were relatively homogeneous and conditions within the barrels were uniform in
terms of exchange with the atmosphere, this design is a surrogate for evaluating
concentration changes at three equally spaced points along a flowpath. These new barrels
were then monitored on the same schedule as the four existing barrels.
In addition, 20 composite samples containing a representative range of sulfur and arsenic
concentrations were tested using a modification of the Nevada Division of Environmental
Protection’s MWMP. Table 3-1 show rock types, sulfur, and arsenic content of the 20
composites. The sequential extraction procedure involves re-application of leachate from a
single step of the MWMP to a new column loaded with fresh sample; this procedure involves
six steps with a full analysis of leachate at each step. The method allows the assessment of
the build-up of solutes along a flow path to be made and provides a better indication of the
solubility of rock components than the conventional MWMP test that has a single extraction
step. The procedure is best performed on weathered or oxidized materials where soluble
products are present; therefore, older core was selected for MWMP testing. The results of
the supplemental testing and analysis are described in the Waste Rock Metal Leaching and
Acid Rock Drainage Assessment for Feasibility Study (SRK 2007) and were factored into
predictions of water chemistry for full-scale waste rock facilities and pit walls.
The kinetic geochemical characterization results reported by MDAG (2006), including 16
humidity cells operated for 74 weeks, were used by SRK (2007) to predict waste rock
drainage chemistry and determine the potential for segregating and blending NAG rock and
PAG rock. In 2008, 24 new humidity cells were started. Twenty samples were selected to
provide broader coverage of the range of geochemical characteristics (ARD potential and
arsenic content) of waste rock matching the seven waste rock management categories
(WRMCs). Two of the new cells were duplicates, and two were the same material used to fill
two additional onsite test barrels also installed in 2008 (SRK 2011).
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The geochemical prediction calculations were made using Geochemist’s Workbench and
provided an estimate of the concentrations of constituents that would likely be released from
the waste rock material. It was assumed that the waste rock material would be managed
according to the geochemical properties of the material (i.e., NAG versus PAG) for wellmixed and poorly mixed scenarios.
Table 3-1:
Characteristics of Samples Tested Using Sequential MWMP
Column
Year
Rock Type
Arsenic (mg/kg)
Sulfide (%)
1
1996-2002
GWK
47.3
0.09
2
1996
GWK
77.2
0.12
3
1996
SED
1495
0.18
4
1996-2002
SED
94.8
0.94
5
1996
SED
1020
0.76
6
1996-2002
GWK
2850
1.03
7
1996
ARG
75
0.2
8
1996
ARG
259
0.25
9
1996
SED
1545
0.1
10
1996
SED
145.5
1.1
11
2002
SHL
1785
1.61
12
2002
SHL
3100
1.47
13
1996
RD
79.5
0.27
14
1996-2002
RD
92.2
0.21
15
1996-2002
RD
1685
0.43
16
2002
RD
102
0.64
17
2002
RD
1610
1.19
18
1996
RD
2660
1.05
19
2002
MD
230
0.19
20
1996
MD
619
0.15
GWK = Greywacke, RD = Rhyodacite, SHL = Shale, MD = Mafic dykes
Also as part of the SRK geochemical evaluation (SRK 2007), carbonate mineralogy was
characterized using x-ray diffraction from the 16 humidity cells samples from MDAG (2006).
The objective of the carbonate mineral characterization was to estimate a correction factor
for NP that accounts for NP due to carbonates. Since NP by the Sobek method (Sobek et
al., 1978) is determined by reaction of the rock with boiling hydrochloric acid, the resulting
NP reflects the dissolution of calcium and magnesium carbonates and silicates. While the
former reflects minerals that would contribute NP to buffer pH near neutral under field
conditions, the latter is not likely to consume acid until pH drops below 5 if the silicates are
associated with aluminum. The resulting correction factor derived from mineralogical
interpretation is recommended for the purpose of waste rock classification and management
(SRK 2007).
Both the MDAG and SRK suites of ABA samples were drawn largely from rock defined as
waste, but in the vicinity of mineralization. This resulted in a slight bias of the assessment
toward a higher potential for ARD and metal leaching. During 2006, five additional holes
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Waste Rock Characterization
were drilled near the proposed final pit walls, producing 483 additional samples for ABA
testing. These additional samples were selected from waste areas outside of the highly
mineralized areas to refine the block-model, and from estimates of waste rock volumes with
distinct ARD characteristics. Results of this sampling were used as input into subsequent
block modeling and waste management planning for the project.
The following conclusions made by SRK (2007) were based on a review and evaluation of
the geochemical database for the proposed Donlin Gold project. These conclusions were
updated further to reflect new data obtained by SRK (2011) from ongoing static testing of
waste rock, continuing waste rock field and laboratory kinetic tests, new field and laboratory
kinetic tests, and additional mineralogical characterizations (x-ray diffraction and microprobe
of carbonates and sulfides). Conclusions include the following:
•
The majority of the waste rock at the project has a low potential for ARD with
neutralization potential/acid generating potential (NP/AP) well above 2. However,
some samples fall in the uncertain range (i.e., 1<NP/AP<2) or are PAG based on
a site-specific criterion of NP/AP <1.3.
•
Concentrations of arsenic, antimony, and mercury are above global crustal
averages due to the introduction of these elements during mineralization. Arsenic
concentrations are weakly correlated with sulfur concentrations for all major rock
units, and both arsenic and sulfur show a bimodal distribution that corresponds to
weakly and strongly mineralized populations. The sedimentary rocks had large
weakly mineralized populations, whereas the rhyodacite was mostly strong
mineralized. The overall distribution of arsenic is similar to sulfur.
•
Water quality predictions for waste rock indicate arsenic has the potential to be
leached from waste rock under both acidic and non-acidic conditions.
•
Acid generation potential and metal leaching is controlled to some degree by
rock type, but the over-printing effect of sulfide mineralization results in variable
sulfur content, variable potential for ARD, and ML in all rock types. Therefore,
rock type alone is not a reliable indicator of metal leaching or ARD potential.
•
Results from continuous sample intervals showed that geochemical
characteristics tend to show uniform NP/AP and arsenic concentrations over
intervals spanning tens of meters, indicating that waste segregation based on
ARD and ML characteristics is feasible. No large-scale spatial trends in these
parameters have been observed.
•
Characterization of carbonate mineralogy resulted in development of a sitespecific correction factor for NP that accounts for the presence of carbonates that
would not contribute to the actual neutralizing potential of the material. This
correction factor is to prevent overestimation of the waste rock NP.
3.1
Waste Rock Geochemical Modeling
A waste rock block model has been developed to provide a basis for the initial planning and
the long-range mine plan for the proposed Donlin Gold project. The waste rock block model
uses the waste rock management categories defined by SRK (2007, 2011), as summarized
in Table 3-3, to define the ARD characteristics of the deposit.
Variables that were incorporated in the block model to aid with the geochemical
classification of waste rock at the proposed Donlin Gold project include NP from carbonate
minerals (NPCO3), and AP.
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AP is calculated from the total sulfur concentration (ST) where:
AP = 31.25 x estimated ST (%)
NP from carbonate minerals (NPCO3) was estimated from:
NPCO3 = 0.76·NP + 4.8
To avoid a bias at low NP values, the calculated NPCO3 should not exceed analytical NP
when NP is below 50 lb. (22.7 kg) CaCO3/t. Therefore, the following rules were applied to
the calculation of NP:
If NP≤22.7 kg CaCO3/t:
NPCO3 = NP
If NP>22.7 kg CaCO3/t:
NPCO3 = 0.85·NP + 3.4
Table 3-2 summarizes the site-specific calculation of ABA parameters developed for
characterization and block modeling. These variables were estimated for each block to
calculate NPCO3/AP. In addition, the block model estimates for arsenic and sulfur values
were used to calculate the ratio of arsenic to sulfur (As/S) for each block. The ARD potential
as defined by the ratios NPCO3/AP and As/S was then used to preliminarily classify blocks
into the waste rock management categories that are subdivided into PAG and NAG groups.
The two NAG categories are each split into two sub-categories to allow for identification of
arsenic leaching.
Table 3-2
Site-specific Calculation of ABA Parameters
Acid Potential (AP)
kg CaCO3/t
Neutralization Potential (NP)
kg CaCO3/t
SRK (2006)
31.25 x ST (%)
If NP ≤16.3 NP = NP
If NP >16.3 NP = 0.94.NP + 0.98
Updated (2011)
31.25 x ST (%)
If NP ≤22.7 NP = NP
If NP >22.7 NP = 0.85.NP + 3.4
Source
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3.2
Waste Rock Characterization
Development of Waste Rock Classification System
With respect to waste management and classification of material, SRK (2011) concluded the
following:
1
•
Kinetic tests have shown that rates of sulfide mineral oxidation are strongly and
positively correlated with sulfur content, and arsenic release is strongly
associated with arsenic content of the rock. This suggests that bulk rock
characteristics can be related to leaching behavior.
•
Kinetic test results have demonstrated that NP/AP values below 1.3 define PAG
rock, and that NP/AP values above 1.3 define NAG rock. Therefore, segregation
of PAG waste rock can be based on a NP/AP value less than 1.3. 1
•
A relationship between NP/AP and the delay to onset of ARD has been
developed using humidity cell results. For rock with elevated NP/AP near 1.3, the
delay to onset is estimated to be of the order of a decade or more. For rock with
NP/AP less than 1, ARD may be produced in less than a decade or several
years.
•
Arsenic leaching is a potentially significant concern for almost all waste rock, due
to widespread elevated concentrations in the rock and leachability indicated by
testwork.
•
By combining the PAG criteria, delay to onset timeframes, and arsenic content,
seven WRMCs have been defined (SRK 2007), updated to four categories (NAG
1, 2, 3, and 4 are the same for practical purposes), and are summarized in Table
3-3.
•
Waste rock mixing or blending has merit, though mainly to combine rock with a
very long delay to onset of ARD (i.e., 1<NP/AP<1.3) with NAG rock (NP>1.3).
•
Water chemistry modeling indicates that blending would need to be managed to
ensure that sufficient alkalinity is available to neutralize acid. The calculated
tonnage of Category 5 rock that can be blended with Categories 1 -4 is 81%,
provided that active management measures result in intimate contact between
Categories 1-4 and 5. The remaining 19% of PAG 5 waste rock mined will be
used for construction of the TSF causeway and as backfill into the ACMA pit.
The theoretical NP/AP that defines the potential for acid generation is between 1 and 2. The range depends
on the completeness of the acid neutralization reactions by carbonates. Regulators in various jurisdictions
have proposed higher screening threshold values in the absence of site-specific information. These
thresholds have, for example, ranged at times up to 3 in California and 4 in British Columbia. The higher
values reflect uncertainty in the chemical measurements particularly of NP, which can include acid
neutralizing components of the rock that are not sufficiently reactive under field conditions. The approach
used to address this uncertainty at Donlin Gold has been to (a) calculate a site-specific NP based on
mineralogical studies, which is lower than or equal to the laboratory-determined NP values; and (b) use
kinetic weathering studies to determine the site-specific NP/AP threshold of 1.3 consistent with the sitespecific NP approach.
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Table 3-3:
Waste Rock Characterization
Donlin Gold Waste Rock Management Categories (SRK 2011)
SRK 2007
Waste Rock
Management
Category
Revised 2011
Category
Description
NP /AP Range
and AP
As/S
(As in mg/kg
and S in %)
NAG 1
Very unlikely to
generate ARD and
"low" arsenic leaching
AP<3 kg CaCO3/t or
NP*/AP > 2
As/S<196
and As<250
Not Used
NAG 2
Very unlikely to
generate ARD and
arsenic leaching
potentially significant
AP<3 kg CaCO3/t or
NP*/AP > 2
As/S>196
or As>250
AP<3 kg
CaCO3/t or
NP*/AP > 2
NAG 3
Unlikely to generate
ARD and "low"
arsenic leaching
1.4<NP* /AP≤2
As/S<196
and As<250
Not Used
NAG 4
Unlikely to generate
ARD and arsenic
leaching potentially
significant
1.4 < NP*/AP ≤ 2
As/S>196
or As>250
1.3 < NP*/AP ≤
2
PAG 5
PAG but with very
long delays (several
decades) to onset of
ARD
1.0 < NP*/AP ≤ 1.4
All
1.0 < NP*/AP ≤
1.3
PAG 6
PAG in the life of the
mine (possibly less
than a decade)
0.2 < NP*/AP ≤ 1.0
All
0.2 < NP*/AP ≤
1.0
PAG 7
PAG but with shorter
delays to onset (less
than a few years)
NP*/AP ≤ 0.2
All
*
*
NP /AP Range
and AP
*Revised site-specific NPCO3 = 0.76·NP + 4.8 (SRK 2011)
In the characterization of waste rock geochemistry, the material is segregated according to a
series of detailed chemical characteristics that are diagnostic of metal leaching and acid
generation potential. The classification of the waste rock according to operational criteria for
waste rock management requires a site-specific criterion or criteria that are sufficiently
sensitive to the indicators of metal leaching and acid generation but simple enough for
operational waste rock management. The geochemical characterization programs (SRK
2011) completed for the proposed Donlin Gold project have confirmed that NPCO3/AP can be
used as the main diagnostic indicator of metal leaching and acid generation potential.
Consequently, this parameter has been selected as the site-specific criterion to segregate
PAG waste rock. Therefore, the four revised waste rock management categories defined by
the Donlin Gold geochemical evaluation can be grouped into the following four material
types for the purposes of waste rock management during operations (see Table 3-4):
1.
2.
3.
4.
Non-acid generating (NAG 1-4 and overburden [OVB])
Potentially acid generating with a very long onset to ARD (PAG 5)
Potentially acid generating with a moderate onset to ARD (PAG 6)
Potentially acid generating with a short onset to ARD (PAG 7)
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The classification of waste rock in relation to these characterizations is as follows:
1. Materials with a NPCO3/AP value greater than 1.3 are considered non-acid
generating, and include NAG 1-4 waste rock and OVB. NAG 2 and NAG 4 waste
rock have the potential to leach significant arsenic even though the acid generating
potential is low (Table 3-3).
2. For material with a NPCO3/AP value less than 1.3, but greater than 1, the delay to
onset is estimated to be on the order of a decade or more and is classified as PAG 5.
3. For material with a NPCO3/AP value less than 1, but greater than the lowest value
(0.2), the delay to onset is estimated to be less than a decade and may occur within
the life of mine. This material is classified as PAG 6.
4. Material with the lowest NPCO3/AP values (i.e., <0.2) is classified as PAG 7 and is
considered the most reactive material with ARD predicted to take place within a few
years.
Table 3-4:
Donlin Gold Waste Rock Classification System
Waste Rock
Classification
Description
Delay to Onset of ARD
NAG 1-4 and OVB
Non-acid generating
--
1.0 < NPCO3/AP ≤ 1.3
PAG 5
Potentially acid generating
Several decades
0.2 < NPCO3/AP ≤ 1.0
PAG 6
Potentially acid generating
Less than a decade
≤ 0.2
PAG 7
Potentially acid generating
Less than a few years
NPCO3/AP
>1.3
NPCO3 = NP CO3 = 0.76·NP + 4.8, where NP is determined using the Sobek method (Sobek et al., 1978)
AP =Total Sulfur (wt%) x 31.25
3.3
Mine Plan and Waste Rock Distribution
The current proposed Donlin Gold mine plan predicts there would be a total of about 3 billion
tons (2.7 billion tonnes) of waste rock. The amount of each type of waste rock to be mined is
summarized in Table 3-5 and illustrated in Figure 3-1. A summary of mine production
schedule for the life of the mine is provided in Appendix A.
As shown in Figure 3-1, NAG 1-4 and OVB make up almost 92.6% of the total waste rock
tonnage. PAG 5 waste rock is estimated to be less than 3% of the total waste rock tonnage
that would be generated during the project. Furthermore, the rate at which PAG 5 would be
extracted from the pit is fairly consistent throughout the life of mine and never exceeds 5%
of the total waste rock mined during any one year. Therefore, the quantity of PAG 5 waste
rock is considered to be within the range that could be accommodated by blending with
NAG 1-4 rock to create an overall mixture that does not produce ARD. However, for the
blended approach described in Section 4.3 below to be successful in mitigating ARD, waste
rock must be managed to ensure that PAG 5 and NAG 1-4 waste rock is intimately mixed at
a small enough scale. This has been confirmed by water quality predictions based on HCT
results that indicate acidity is mitigated by reaction with acid-consuming minerals for wellmixed conditions (SRK 2007).
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Table 3-5:
Waste Rock Characterization
Donlin Gold Waste Rock Tonnage Estimates
Tonnage
Waste Rock Classification
NAG 1-4 and OVB
PAG 5
PAG 6
PAG 7
Total Waste Rock
Figure 3-1:
Mst
Mt
Percent of Total
2,823.153
87.113
135.065
2.555
3,047.886
2,561.121
79.028
122.529
2.318
2,764.996
92.63
2.86
4.43
0.08
100
Total Waste Rock Material Distribution
In order to gain a better understanding of the modeled distribution of the various waste rock
types, a series of snapshots throughout the life of mine schedule was produced from the
block model. End-of-period status maps (section view, along with a selected bench plan
view) are provided in Appendix B. In the model views, the pit design for the current year is
shown as a black line, NAG 1-4 waste rock in grey, PAG 5 waste rock in orange, and PAG 6
and PAG 7 waste rock in blue. The grid lines are 250 m in plan, with elevation lines every
24 m in the section view.
The series of status maps provided in Appendix B illustrate that the PAG 5 waste rock (in
orange) is disseminated throughout the deposit with very few large contiguous zones
indicated. For the most part, PAG 5 waste rock, as mined and placed in the WRF, would be
naturally mixed with the surrounding NAG waste rock and would in effect, produce a
desirable blend to negate the reactivity of the PAG 5 rock. For those periods where PAG 5 is
the predominant waste rock material type mined, the material would be dispersed on the
WRF to produce a well-mixed blend. This would require operational controls (as described in
Section 4.2 below) in order to ensure the PAG 5 rock is not repeatedly placed on the same
dump location. Where the PAG 5 rock in the pit is surrounded by more reactive PAG 6 or
PAG 7 waste rock, and is too small a zone to be selectively mined, it would be incorporated
in the management of the PAG 6 or PAG 7 waste rock.
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Waste Rock Management
4.0
WASTE ROCK MANAGEMENT
4.1
Waste Rock Classification
The proposed Donlin Gold project waste rock classification system would consist of four
waste rock material types that are defined by the ratio of NPCO3 to AP according to Table 34.
Total sulfur would be measured in the onsite laboratory using a LECO analyzer. AP is then
calculated from the total sulfur concentration where:
AP = 31.25 x total sulfur (wt%)
NP would be measured in the onsite laboratory according to the standard Sobek method
(Sobek et al., 1978). The rock is digested with boiling hydrochloric acid, and then the base
equivalent amount of acid consumed is determined by titrating the acid solution to a pH of 7
and converting the measured quantities to NP expressed as kg CaCO3/t. Once NP is
calculated, a correction factor would be applied to account for the presence of carbonates
that do not contribute to the actual neutralizing potential of the material as described in
Section 3.1. NPCO3 would be estimated from the following equations:
NPCO3 = NP (for NP≤22.7 kg CaCO3/t)
NPCO3 = 0.85·NP + 3.4 (for NP>22.7 kg CaCO3/t)
The ratio NPCO3/AP would then be calculated and used to classify waste rock according to
Table 3-4.
4.2
Waste Rock Mining and Segregation
The current mine schedule targets an average mining rate of approximately 422,000 stpd
(383,000 tpd) of total material that would be mined by bulk open pit mining methods. Waste
rock alone would be extracted from the open pit at an average mining rate of 345,000 stpd
(313,000 tpd). This mining rate is subject to change based on operational considerations
during the life of the project. Large hydraulic face shovels with a 50 yd3 (38 m3) capacity,
along with 400 st (360 t) haul trucks, would be used for primary pit production. Mining would
occur on 40 ft (12 m) benches in waste, and 20 ft (6 m) split benches in selected primary ore
zones.
The key to the success of this Plan would be the identification of the various material types
in the field and, in particular, at the active mining face. This approach would require a
material identification system that is built into the ore control system. Sources of information
include:
•
daily survey control
•
•
maintaining an up-to-date 3-D block model
blasthole sampling and logging to assist in this waste characterization
•
possibly face sampling including mapping, visual inspections, and sampling.
Donlin Gold
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July 2012
Waste Rock Management Plan
Donlin Gold Project
Waste Rock Management
Blasthole cuttings would be collected during blasting operations for analysis at the onsite
laboratory. The number of blasthole samples collected would depend on the geologic
conditions within the blast area and the blasthole pattern. However, it is anticipated that a
sample density of 1 in 12 would be adequate to perform the required waste rock
segregation. These samples would be submitted to the onsite laboratory for ABA testing and
calculation of NPCO3/AP. Based on the results, the material would be classified as one of the
four waste rock material types as described above. The sampling and testing would be
completed on the same schedule as ore determination in order to be effectively included in
the short-term mine planning process.
The resulting information would be used to assign material types to the areas of the active
bench. Each area would be assigned a destination code based on classification of the
material. An automated routing and tracking system would be used that integrates the ore
control data with a global positioning system (GPS)-enabled loading and hauling fleet to
route and track material. Each of the shovels working in ore and waste at the proposed
Donlin Gold project would be equipped with GPS positioning to allow real-time updates of
the digging face in relation to ore grades and waste rock types.
An electronic map would be developed by the short range planner to differentiate between
the ore and waste types. This electronic map would be available to the shovel operator in
real time via an on-board computer screen so the type of material loaded into the truck
would be known at all times. Furthermore, all the trucks would be equipped with a GPS
dispatch system (AMEC 2009). When equipment is loading from a particular area, a code
would be assigned to the truck being loaded and the designation would appear on the
operator’s screen. The system would record the volume of each waste rock type mined
during each shift and its ultimate destination. This mining methodology would ensure that
ore and waste rock types are mined and delivered to the correct location.
4.3
Waste Rock Designation and Placement
The waste rock for this project would be routed to one of four destinations including (Figure
4-1):
1.
2.
3.
4.
American Creek drainage WRF (east of the pit)
isolated cells on WRF
ACMA pit backfill
TSF construction.
The estimated tonnage of each waste rock type is summarized in Table 4-1 has the
methods of waste rock placement described in the following sections for each facility.
Donlin Gold
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July 2012
ee
Cr
oo
Cr
NORTH OVERBURDEN
STOCKPILE
k
d
ke
Creek
ULTIMATE PIT
WASTE ROCK FACILITY (WRF)
2,460 Mst, 2,232 Mt
Omega
Gulch
Croo
ked
SOUTH OVERBURDEN
STOCKPILE
0.5 mi
Natural Gas Pipeline
Ultimate Pit
Solid Waste
Laydown Area
Streams
Waste Rock Facility
Berm
Overburden Stockpile
Ore Stockpile
Building
Pond
Material Site
Facility
Ramp
Potentially Acid Generating Rock (PAG) #6
WASTE ROCK FACILITY AND
OVERBURDEN STOCKPILES
FIGURE:
4-1
DONLIN GOLD PROJECT
DG: PER0033.mxd, 07/17/12, R07
Waste Rock Management Plan
Donlin Gold Project
Table 4-1:
Waste Rock Management
Waste Rock Tonnage by Facility
ACMA Backfill
Waste Rock Facility
Isolated Cells
Tailings Dam
Material
Type
Ktons
Ktonnes
Ktons
Ktonnes
Ktons
Ktonnes
Ktons
Ktonnes
NAG 1-4
429,091
389,265
2,252,501
2,043,434
--
--
95,129
86,300
OVB 8
45
41
46,387
42,082
--
--
--
--
PAG 5
11,833
10,735
70,587
64,035
--
--
4,694
4,258
PAG 6
11,744
10,654
--
--
123,320
111,874
--
--
PAG 7
47
43
2,508
2,275
--
--
--
--
452,761
410,738
2,371,983
2,151,826
123,320
111,874
99,823
90,558
Total
a
a
This tonnage reflects the total PAG 7 waste rock that would be temporarily placed in the low-grade stockpile at the toe of the
WRF and relocated to the ACMA pit backfill once space is available.
4.3.1
American Creek Valley WRF
The waste rock types that would be placed on the WRF would consist of NAG 1-4 waste
rock and PAG 5 and isolated cells of PAG 6, as described in Section 4.3.2. Waste rock
classified as NAG 1-4 has no potential to generate acid and would be placed in WRF
without any constraints on placement. This material would be blended with the PAG 5
material. The final cover of each lift of the WRF would consist of NAG 1-4.
Waste rock classified as PAG 5 has the potential to become acid generating over a long
period of time (several decades). In order to mitigate this potential, PAG 5 waste rock would
be blended with the NAG 1-4 waste rock in the WRF. However, PAG 5 rock would need to
be intimately blended with the NAG rock in order for its reactivity to be negated. As such, the
vertical dimension (or deposited thickness) of PAG 5 rock can be no more than
approximately 3 ft (1 m) when placed in the WRF (SRK 2007). This requires operational
controls to ensure the PAG 5 material is not repeatedly placed at the same dump location,
but is staggered or spread across the operational dump face.
The advancing dump crest of any lift would be several hundred feet across to facilitate safe
haul truck turnaround. The dump crest would be maintained by a dozer in a typical “dumpand-doze” waste rock handling operation. The dozer operator would be instructed to shift
position with each incoming load of waste to allow spreading of successive loads across the
entire dump face. The effective blending of PAG 5 material with NAG 1-4 material is
possible due to the disseminated occurrence of PAG 5 in the deposit, the small overall
percentage of PAG 5, and the staggered placement approach.
To further mitigate the potential for PAG 5 to generate acid, the last 80 ft (24 m) of the dump
crest advancement of any lift would be limited to only NAG 1-4 waste rock. This would
ensure the final regraded slopes of the WRF would consist of NAG 1-4 waste rock with an
average thickness of about 30 ft (9 m). Mine engineers would develop a PAG/NAG
boundary beyond which only NAG waste rock can be placed. This would ensure no PAG 5
material is placed beyond the PAG/NAG boundary and the regraded final slopes of the WRF
would consist entirely of NAG material.
This type of waste rock placement methodology has been successfully applied at other
mines that operate at a similar scale with similar equipment. Extra management is required
Donlin Gold
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Waste Rock Management Plan
Donlin Gold Project
Waste Rock Management
at the end of the mine life to ensure no PAG 5 material is dumped on a final face, and there
is sufficient NAG material in the mine plan or in prepared stockpiles to cap the top surfaces
of the WRF.
Waste rock classified as PAG 7 is highly mineralized material (below the economic cut-off
grade) that has the potential to become acid-generating in the shortest timeframe. As a
result, PAG 7 would be segregated from the other waste rock material types and placed on
the low-grade stockpile area for temporary storage. Once the final limits of the ACMA pit are
reached, PAG 7 stored in the low-grade stockpile would be relocated to the bottom of the
ACMA pit.
The low-grade stockpile area is located at the toe of the WRF near center of American
Creek Valley. During operations, surface water from this area, including stormwater from the
PAG 7 waste rock, would report to the Lower Contact Water Dam (CWD) and any seepage
that enters groundwater would be intercepted below the Lower CWD for mill make-up water
or pumped to the Upper CWD for future mill use.
4.3.2
Isolated Cells on WRF
Waste rock classified as PAG 6 has the potential to become acid-generating in a short
period of time. To mitigate this potential, PAG 6 would be segregated from the other waste
rock types.
Isolating the PAG 6 in this area will result in reduced amounts of water coming into contact
with these materials, and will minimize their potential to become acidic. The foundation of
NAG rock would be placed beneath the PAG 6 materials in Rob’s Gulch would limit the
potential for water running along the drainage to rise and fluctuate within the PAG 6 waste
cell. The NAG material will also act as a rock drain to convey the runoff and perennial flows
out of this drainage.
The materials in each PAG 6 cells will be placed in 33 ft (10 m) intermediate lifts, until a lift
height of 100 ft (30 m) is reached. Each 100 ft (30 m) cell will then be covered with a low
permeability “cap” to minimize infiltration of surface water (Figure 4-2). For the permanent
isolated cells, an engineered intermediate cap, consisting of 3.3 ft (1 m) thick mixture of
terrace gravel or colluvium (in-situ hydraulic conductivity of approximately 1.3 x 10-6 (4 x 107 m/s), would be placed on top of the PAG 6 material in the waste rock facility as each lift is
completed. This would limit the amount of runoff and precipitation entering the PAG cells.
NAG 1-4 waste rock would be dumped around the PAG waste rock to isolate the material
from the final surface of the WRF and from the surrounding natural ground.
During the early years of operation, PAG 6 would be placed in these permanent, isolated
cells in the Rob’s Gulch and Unnamed Gulch sections of the WRF. Once the ACMA pit
becomes available for backfilling in Year 22, any new PAG 6 waste rock that is mined would
go directly into the ACMA pit as backfill.
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July 2012
Waste Rock Management Plan
Donlin Gold Project
4.3.3
Waste Rock Management
ACMA Pit Backfill
Once the final limits of the pit are reached in Year 22 of the mine life, waste rock would be
placed as backfill in the ACMA Pit. At this point, all PAG 6 or PAG 7 mined in the Lewis Pit
would be placed in the ACMA pit backfill and no additional waste rock would be placed in
the low-grade stockpile or isolated cells. Material classified as PAG 5 and NAG 1-4 would
also be placed in the ACMA pit backfill as the material is mined from the Lewis Pit, with the
majority of the waste rock consisting of NAG 1-4. The deepest portion of the ACMA pit
would be backfilled to approximately 695.5 ft below mean sea level (msl) (212 m below msl)
elevation, at which, a pit lake can be maintained at an approximate maximum depth of
1,023.5 ft (312 m). Other portions of the Lewis and ACMA pits would be backfilled to
approximately 111.5 ft amsl (34 m amsl) to maintain a depth of approximately 216 ft (66 m).
This maximum recommended backfill for the ACMA pit is based on the pit lake study
completed by Lorax Environmental (2011) and is necessary to keep the pit lake stratified
and PAG backfill anoxic.
4.3.4
Tailings Storage Facility
The TSF would be a fully lined impoundment located in the Anaconda Creek Valley, 2.2
miles (3.5 km) south of the open pit. Waste rock from the pit would be used in the
construction of the TSF as rockfill, filter zones, riprap, and underdrain rockfill. NAG 1-4
waste rock would be used for all portions of the TSF that are not within the lined
containment. Some PAG 5 waste rock would also be placed in the TSF, but would only be
placed in the portions of the TSF within lined containment (e.g., reclaim causeway).
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Waste Rock Management Plan
Donlin Gold Project
Waste Rock Facility Design
5.0
WASTE ROCK FACILITY DESIGN
5.1
Waste Rock Facility Construction
The WRF has been designed to maximize reclamation efficiency, utilize the neutralizing
capacity of NAG materials, add flexibility to the site water balance, and minimize the cost of
closure. The design parameters for the American Creek Valley WRF are summarized in
Table 5-1. Slope stability and rock drain designs were completed by AMEC (2009).
Table 5-1:
Waste Rock Facility Design Parameters
Crest Elevation
Authorized Tonnage
Footprint
Waste Rock
Facility
ft
amsl*
m
amsl
Mst
Mt
acres
ha
American Creek
Valley WRF
1,705
520
2,460
2,232
3,020
1,222
*above mean sea level
The American Creek Valley WRF would have a maximum height of 1,150 ft (351 m). It
would be constructed by end-dumping material in lifts up to 100 ft (30 m) in height. The toe
of each dump lift would be set back 155 ft (47 m) from the crest of the previous lift to
achieve the 3.0H:1.0V dump slope angle. This method of construction would result in the
most cost-effective configuration for regrading and reclamation of the WRF.
As described above, waste rock types that would be placed on the American Creek Valley
WRF would consist of NAG 1-4 and PAG 5 waste rock and isolated cells of PAG 6. Waste
rock classified as NAG 1-4 would be blended with the PAG 5 material in the WRF and the
last 80 ft (24 m) of the dump crest advancement of any lift would be limited to only NAG 1-4
waste rock. Waste rock classified as PAG 6 would be segregated from the other waste rock
types and would be placed in permanent, isolated cells in the Rob’s Gulch and Unnamed
Gulch sections. An intermediate cover, consisting of an engineered, compacted cover
consisting of a 3.3 ft (1 m) thick mixture of terrace gravels or colluvium would be placed on
the isolated cells in the WRFs as each lift is completed. NAG 1-4 waste rock would be
dumped around the PAG waste rock to isolate the material from the final surface of the WRF
and from the surrounding natural ground.
The WRF would be constructed entirely from the bottom up. During the initial construction of
the WRF, the organic materials, loess, and ice-rich overburden would be removed from the
footprint of the first and third lift (AMEC 2009). The stripped materials would be replaced
with coarse waste rock. This would result in a high degree of stability at the WRF toe and a
very low likelihood of instability in the early stages of construction and through the life of the
WRF. The materials removed from the foundation would either be placed in temporary
overburden stockpiles or mixed with waste rock in the WRF.
The foundation of the WRF would require drainage control. The potential magnitude of flow
in the American Creek drainage, as well as discharging springs in the valley bottoms,
warrants construction of engineered rock drains in the valley bottom, with connecting
secondary rock (finger) drains constructed in the smaller contributing drainages. These
upstream water collection and diversion measures would be constructed during the
preproduction period, and the first segments of the rock drain would be placed using
Donlin Gold
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July 2012
Waste Rock Management Plan
Donlin Gold Project
Waste Rock Facility Design
NAG 1-4 rock. Utilizing larger block sizes of the broken rock from blasting in the open pit, the
rock drain beneath the WRF would be sized to contain the peak instantaneous flow
associated with the 100-year, 24-hour duration rainfall event for the American Creek
catchment. A Lower CWD would be constructed in the American Creek valley downstream
of the WRF to collect runoff and seepage water from the WRF. The surface and
groundwater flow path along American Creek between the Lower CWD and ACMA pit would
be toward the ore stockpile and pit dewatering wells. Surface and groundwater from this
area would be pumped back to the Lower CWD and would be managed as mine contact
water.
5.2
Waste Rock Facility Reclamation
The WRF would be progressively reclaimed during operations by placing a cover designed
to minimize infiltration over the WRF 2,347 acres (950 ha). The cover would consist of a
minimum 14 inches (0.35 m) of growth medium (peat mineral mix) over a minimum 12
inches (0.3 m) of terrace gravel and/or colluvium. The growth medium cover would be
vegetated, and the underlying waste rock would be contoured prior to placement of the
cover to provide natural drainage toward the south margin of the WRF. Contouring would
also produce a natural drainage pattern of swales. The base of the swales would be allowed
to develop naturally and self-armor after cover placement. Ongoing maintenance of these
swales (e.g., riprap or cobble and boulder placement) would ensure the cover integrity is not
compromised. Progressive reclamation during operations is expected to result in
reclamation of the majority of the WRF prior to the end of mining; however, at a minimum,
reclamation of haul roads and ramps would be necessary during the closure period. A more
detailed description of the site-wide reclamation procedures is contained in the Reclamation
and Closure Plan, Donlin Gold Project (SRK 2012a).
Post-closure, all surface and groundwater would be collected and directed (piped) into the
lower levels of the pit lake. A majority of the reclaimed WRF would convey surface runoff to
a major runoff collection channel that would be constructed along the south margin of the
facility. The purpose of the channel is to collect runoff from the WRF cover system and
convey it to the ACMA pit lake at closure. The collection channel would be lined to mitigate
the potential for channeling of the cover and minimize potential seepage losses during lowflow periods. The channel would be lined with 40 mil linear low-density polyethylene
(LLDPE) and would have a base width of 13 ft (4 m), 2H:1V sideslopes, and a depth of 6.6 ft
(2 m). The base of the channel would be lined with a lift of sand/pea gravel (1 ft [0.3 m]) and
natural cobbles and boulders or riprap (-24 in [600 mm]). A 1 ft (0.3 m) bedding layer would
be placed on top of the waste rock before the LLDPE liner is deployed. The lining would
extend one-third of the way up the side to allow sideslope and tributary runoff to enter the
channel rather than being forced below the lined channel. The channel would have an
approximate total length of 2.2 miles (3.5 km).
Modeling of the pit lake geochemistry indicates that water quality is significantly improved
when the surface runoff from the WRF and upslope areas is separated from the seepage
runoff that infiltrates the cover because this seepage runoff includes the subsurface runoff
component (slow runoff) from undisturbed areas upslope. This seepage would come into
contact with the waste rock, with subsequent additional metal loading to the pit lake. The
seepage flows would, therefore, be isolated by constructing four small, concrete
containment structures at the outlet of the rock drains for American Creek and Rob’s Gulch.
A gravity-fed pipe would then direct these seepage flows to the bottom of ACMA pit, with
surface runoff draining naturally to the surface of the pit lake. This segregation of flow would
Donlin Gold
5-2
July 2012
Waste Rock Management Plan
Donlin Gold Project
Waste Rock Facility Design
encourage pit lake stratification. The combined flow pipeline would require a maximum
capacity of 12 cfs (0.34 m3/s), which equates to a 24-inch (61 cm) diameter pipe. An
approximate pipe length of 2.92 miles (4.7 km) would be required to convey the combined
seepage flows to the edge of the pit lake. Here, the seepage water would feed into the
pipeline used to convey TSF water to the base of the pit.
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Waste Rock Management Plan
Donlin Gold Project
Monitoring and Reporting
6.0
MONITORING AND REPORTING
6.1
Operational Monitoring and Reporting
The quantities and destinations of waste rock and ore would be recorded during operations,
and these data would be tabulated monthly. Laboratory analyses for total sulfur and NPCO3
and ABA calculations would be maintained on site. This geochemical data would be
processed on a monthly basis to calculate the average NPCO3/AP for placed waste rock, and
to record final destinations. In order to verify designated waste rock is managed as
proposed, surveys of the advancing WRF lifts would be conducted to make sure the 80 ft
(24.4 m) set-back of PAG material is maintained. In addition, the final slopes would be
inspected for evidence of ARD to determine if PAG material was placed on the final WRF
surfaces. Additional NAG 1-4 material would be placed on the surface to thoroughly cover
any exposed PAG material.
Visual inspections of the WRF and associated storm water controls would be conducted to
evaluate the performance and condition of the facility. Excluding the isolated cells, the toes
of the WRF would be checked for seepage, and if seepage is observed, the specific location
and flow rate would be recorded, and a sample would be collected for water quality analysis.
These inspections would be conducted on a monthly basis and as soon as practicable after
significant precipitation events.
Site staff would carry out weekly visual inspections on each area of the WRF that is
undergoing active development or concurrent reclamation. The general condition of the
WRF would be recorded. Items to be observed would consist of physical stability, presence,
or absence of erosion, confirmation that lifts and slopes are within design limits, and status
of any reclamation (e.g., revegetation success). Inspection of non-active areas of the
facilities would be carried out on a monthly basis. Upon completion of a portion of the
facility, inspections would be carried out annually until closure. The results of the inspections
would be incorporated into the inspection recording and document storage system
developed for the site.
Groundwater and surface water monitoring would be conducted in accordance with the
Monitoring Plan, Donlin Gold Project (SRK 2012b).
6.2
Closure and Post-Closure Monitoring and Reporting
Post-closure monitoring would consist of visual inspection of the WRF, including but not
limited to covered areas, areas of potential stormwater concentration, storage facility base
areas where seepage would have the highest potential to occur, and storm water control
facilities. Inspections would be carried out for a period of not less than five years. The
frequency of inspections would be at least once annually in the spring and following any
storm events exceeding the 25-year, 24-hour storm event. The purpose of the inspections
would be to observe and document the following:
•
the physical integrity of the soil cover including areas of erosion
•
the extent of vegetation establishment and density
•
evidence of any staining, discoloration, streaking or moisture conditions
indicating significant geochemical reactivity of disposal facility surfaces
•
the condition of stormwater control structures
Donlin Gold
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July 2012
Waste Rock Management Plan
Donlin Gold Project
•
Monitoring and Reporting
the location and extent of any ponded stormwater.
Conditions observed that require repair, maintenance, or further evaluation would be
documented and scheduled for requisite action as soon as possible. Inspections, repairs,
and evaluations would be documented and submitted to the Alaska Department of
Environmental Conservation on an annual basis.
Donlin Gold
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July 2012
Waste Rock Management Plan
Donlin Gold Project
7.0
References
REFERENCES
AMEC Americas Limited, 2009. Donlin Creek Gold Project, Alaska, Feasibility Study Update.
October.
Barrick Gold Corporation, 2007. Water Quality Monitoring and Data Management
Procedures Manual. Barrick internal manual, November.
BGC Engineering. Inc., 2011. Donlin Creek Gold Project, Feasibility Study Update 2, Waste
Rock Facility Design-Final Report, July.
BGC Engineering Inc., 2009. Donlin Creek Gold Project Feasibility Study Update 2 Water
Management Plan – Final Report, July.
Decker, J., Bergman, S.C., Blodgett, R.B., Box, S.E., Bundtzen, T.K., Clough, J.G.,
Coonrad, W.L., Gilbert, W.G., Miller, M.L., Murphy, J.M., Robinson, M.S., and
Wallace, W.K., 1994. Chapter 9: Geology of southwestern Alaska, in Plafker, G., and
Berg, H.C., eds., The geology of Alaska: The Geology of North America, Geological
Society of America, Boulder, Colorado, v. G1, p. 285-310.
Goldfarb, R.J., Ayuso, R., Miller, M.L., Ebert, S.W., Marsh, E.E., Petsel, S.A., Miller, L.D.,
Bradley, D., Johnson, C. and McClelland, W., 2004. The late Cretaceous Donlin
Creek Gold Deposit, Southwestern Alaska: Controls on Epizonal Ore Formation.
Economic Geology, 99:643-671.
Lorax Environmental, 2011. Donlin Creek Gold Project Feasibility Study Update II Pit Lake
Modeling Assessment, June.
Mine Drainage Assessment Group (MDAG), 2006. DRAFT Donlin Creek Project –
Environmental Geochemistry Report for Prefeasibility. Prepared for Placer Dome
America.
Sobek A.A., Schuller W.A., Freeman J.R., and Smith R.M., 1978. Field and Laboratory
Methods Applicable to Overburden and Minesoils, USEPA Report No. 600/2-78-054,
203 pp.
SRK Consulting (U.S.), Inc., 2012a. Reclamation and Closure Plan, Donlin Gold Project,
Alaska.
SRK Consulting (U.S.), Inc., 2012b. Monitoring Plan, Donlin Gold Project, Alaska.
SRK Consulting (U.S.), Inc., 2012c. Project Description, Donlin Gold Project, Alaska.
SRK Consulting (U.S.), Inc., 2011. Metal Leaching and Acid Rock Drainage Assessment for
Feasibility Study, Donlin Gold Project, Alaska, Update Report, February.
SRK Consulting (U.S.), Inc., 2007. Waste Rock Metal Leaching and Acid Rock Drainage
Assessment for Feasibility Study, Donlin Creek Project, Alaska. September.
SRK Consulting (U.S.), Inc., 2006. Memorandum: Donlin Creek Guidance for Block
Modeling of ARD and Metal Leaching Potential – UPDATE DRAFT, September.
Donlin Gold
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July 2012
Appendix A
Summary of Mine Production Schedule
Waste Rock Management Plan
Donlin Gold Project
Appendix A
Summary of Mine Production Schedule
Material Type
Unit
Ore-Mine to Crusher
kt
Ore-Mine to Stockpile
kt
Ore-Long Term Stockpile to Crusher
kt
Waste - Mine to WRF
kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Foundation Prep. kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Rock Drains
kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Roads
kt
Waste-Mine to Backfill
kt
Waste-Mine to Tailings Dam
kt
Overburden-Mine to WRF
kt
Overburden-Mine to Backfill
kt
Overburden-Mine to Tailings Dam
kt
Overburden-Mine to North Overburden Stockpile
kt
Overburden-Mine to South Overburden Stockpile
kt
MTO's Ovb. Excavated Fundation Preparation
kt
MTO's Ovb. Excavated Rock Drains
kt
MTO's Ovb. Excavated Roads
kt
Waste-WRF to Tailings Dam
kt
Total Movement
kt
Donlin Gold
2018
Q1
506
539
784
421
46
2,913
5,209
2018
Q2
62
1,603
506
354
162
1,788
335
1,212
362
729
7,112
2018
Q3
451
3,126
506
100
2,665
1
272
986
362
637
9,105
2018
Q4
1,211
2,289
2,672
287
1,041
7,500
A-1
2019
M1
255
1,399
230
1,306
0
44
161
12
3,407
Preproduction
2019
2019
M2
M3
1,658
370
2,028
230
230
1,306
1,306
12
12
3,575
3,575
2019
M4
2,579
5,447
1,305
0
145
524
10,000
2019
M5
326
8,009
1,308
0
21
77
9,742
2019
M6
2,931
5,383
1,308
82
296
10,000
2019
M7
915
13
7,736
197
984
286
79
10
10,221
Production
2019
2019
M8
M9
482
1,210
1,705
647
8,056
5,614
197
197
984
984
375
382
103
105
10
10
10,854
10,207
July 2012
Waste Rock Management Plan
Donlin Gold Project
Appendix A
Summary of Mine Production Schedule (Continued)
Material Type
Ore-Mine to Crusher
Ore-Mine to Stockpile
Ore-Long Term Stockpile to Crusher
Waste - Mine to WRF
Waste(NAG)-Mine/Quarry to Rockfill MTO's Foundation Prep.
Waste(NAG)-Mine/Quarry to Rockfill MTO's Rock Drains
Waste(NAG)-Mine/Quarry to Rockfill MTO's Roads
Waste-Mine to Backfill
Waste-Mine to Tailings Dam
Overburden-Mine to WRF
Overburden-Mine to Backfill
Overburden-Mine to Tailings Dam
Overburden-Mine to North Overburden Stockpile
Overburden-Mine to South Overburden Stockpile
MTO's Ovb. Excavated Fundation Preparation
MTO's Ovb. Excavated Rock Drains
MTO's Ovb. Excavated Roads
Waste-WRF to Tailings Dam
Total Movement
Donlin Gold
Unit
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
kt
2019
M10
646
734
7,798
312
984
449
124
440
16
11,502
2019
M11
1,432
789
6,366
312
984
336
93
440
16
10,768
2019
M12
1,274
184
7,403
312
984
266
73
440
16
10,952
A-2
2020
Q1
4,663
12
21,248
3,219
3,195
882
145
33,364
2020
Q2
4,617
1,249
22,654
1,160
320
30,000
2020
Q3
4,633
55
25,023
270
75
30,055
2020
Q4
4,727
1,165
23,639
369
102
30,000
2021
Q1
4,746
806
24,420
1,093
1
6
22
55
31,148
2021
Q2
4,841
2,148
24,176
0
18
67
31,250
2021
Q3
4,825
1,967
24,382
17
60
31,250
2021
Q4
4,791
2,634
23,770
12
43
31,250
2022
15,701
17,418
3,711
91,631
1,934
6,074
1,676
99
138,244
July 2012
Waste Rock Management Plan
Donlin Gold Project
Appendix A
Summary of Mine Production Schedule (Continued)
Material Type
Unit
Ore-Mine to Crusher
kt
Ore-Mine to Stockpile
kt
Ore-Long Term Stockpile to Crusher
kt
Waste - Mine to WRF
kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Foundation Prep. kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Rock Drains
kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Roads
kt
Waste-Mine to Backfill
kt
Waste-Mine to Tailings Dam
kt
Overburden-Mine to WRF
kt
Overburden-Mine to Backfill
kt
Overburden-Mine to Tailings Dam
kt
Overburden-Mine to North Overburden Stockpile
kt
Overburden-Mine to South Overburden Stockpile
kt
MTO's Ovb. Excavated Fundation Preparation
kt
MTO's Ovb. Excavated Rock Drains
kt
MTO's Ovb. Excavated Roads
kt
Waste-WRF to Tailings Dam
kt
Total Movement
kt
Donlin Gold
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
19,553
13,043
5
88,940
13,952
6,427
585
142,505
18,190
12,318
1,344
121,390
841
472
130
44
154,729
18,719
17,498
118,457
0
70
255
155,000
16,487
6,834
2,135
126,798
245
886
153,385
19,548
1,974
35
110,724
17,517
30
51
156
150,035
19,663
8,530
120,930
190
687
150,000
19,455
6,541
121,796
478
1,730
150,000
19,321
6,930
122,097
159
199
1,295
150,000
19,791
180
70
109,777
19,523
565
164
150,070
15,339
13
3,457
134,104
118
427
153,457
14,076
112
4,319
135,222
152
438
154,319
11,848
7,210
137,737
401
157,196
A-3
July 2012
Waste Rock Management Plan
Donlin Gold Project
Appendix A
Summary of Mine Production Schedule (Continued)
Material Type
Unit
Ore-Mine to Crusher
kt
Ore-Mine to Stockpile
kt
Ore-Long Term Stockpile to Crusher
kt
Waste - Mine to WRF
kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Foundation Prep. kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Rock Drains
kt
Waste(NAG)-Mine/Quarry to Rockfill MTO's Roads
kt
Waste-Mine to Backfill
kt
Waste-Mine to Tailings Dam
kt
Overburden-Mine to WRF
kt
Overburden-Mine to Backfill
kt
Overburden-Mine to Tailings Dam
kt
Overburden-Mine to North Overburden Stockpile
kt
Overburden-Mine to South Overburden Stockpile
kt
MTO's Ovb. Excavated Fundation Preparation
kt
MTO's Ovb. Excavated Rock Drains
kt
MTO's Ovb. Excavated Roads
kt
Waste-WRF to Tailings Dam
kt
Total Movement
kt
Donlin Gold
2035
2036
2037
2038
2039
2040
15,059
4
4,380
111,329
5,000
17,998
609
154,380
11,619
7,880
120,033
1,348
140,880
14,559
4,978
110,146
1,294
130,978
15,469
6
4,160
62,505
72,000
20
154,160
15,633
2,774
2,983
4,342
127,230
8
13
152,983
11,162
4,327
7,129
104,011
126,629
A-4
2041
2042
2043
2044
2045
8,725
10,476
65,523
84,723
16,135
201
3,057
1
40,663
60,057
4,308
15,182
2
8,676
28,168
19,550
19,550
16,956
16,956
Total
384,162
120,649
120,650
2,209,901
1,518
10,198
1,046
423,103
89,856
24,734
13
779
6,234
10,362
2,464
504
4,279
3,410,452
July 2012
Appendix B
Block Model Views
Figure 1: Year 2018 – N6878500, elevation 142 m. Ore is yellow
Figure 2: Year 2019 – N6878500, elevation 136 m. Ore is yellow
Figure 3: Year 2020 – N6878500, elevation 136 m. Ore is yellow
Figure 4: Year 2021 – N6878500, elevation 124 m. Ore is yellow
Figure 5: Year 2022 – N6878500, elevation 124 m. Ore is yellow
Figure 6: Year 2024 – N6878500, elevation 160 m. Ore is yellow
Figure 7: Year 2025 – N6878500, elevation 104 m. Ore is yellow
Figure 8: Year 2030 – N6878500, elevation 104 m. Ore is yellow
Figure 9: Year 2035 – N6878500, elevation 104 m. Ore is yellow
Figure 10: Year 2040 – N6878500, elevation 104 m. Ore is yellow