examples from China and Russia inform models for Voisey's Bay

Structural controls on nickel sulfide deposits: examples from China and Russia inform models for Voisey’s Bay

Peter C. Lightfoot, PhD, PGeoHutchinson Visiting Industry Professor,

University of Western Ontario

Richard W Hutchinson (1928-2016)

• BSc (Western, 1950), MSc and PhD (Univ Wisconsin, 1951, 1954)

• Three decades in academia (Western and Colorado School of Mines)

• Inducted to Canadian Mining Hall of Fame 2006• Numerous awards (including the Barlow, Duncan Derry,

Penrose Gold and SEG Silver medals)

Field observationsProcess-based models for ore deposits Tectonic controls on metallogenyApplication to exploration• Syngenetic models for VMS – New Brunswick and Cyprus,

(e.g. Econ. Geol., 1973)• Precambrian gold metallogeny – Abitibi and Witwatersrand

(e.g. OGR, 1993; Econ Geol, 1997)• Rare metals in pegmatites – NWT and Mozambique (e.g.

Econ Geol, 1959)• Evaporites and potash (e.g. GSA, 1968)Training, mentoring, and inspiring students with practical geoscience skills• “An army of geological disciples now spread around the

globe” (Poul Emsbo, 2005) A complete bibliography of Dick’s papers will be available from: WWW.LIGHTFOOTGEOSCIENCE.CA

http://www.lightfootgeoscience.ca/

Traditional view of Process Controls in the Formation of Nickel Sulfide Ore Deposits

Craton Margin

Crust

Plume

Mantle

Strike-slipfault zone

2 Sub-ContinentalLithospheric Mantle

30 -

40km

Basalt Lavas

Disseminated Sulphide

Sulphide-richLayers

Mid-CrustalMetamorphic Rocks

Deep Crustal Granitesand Gneisses

Upper CrustalSediments

Generate ultramafic magma from metalendowed source

Ascent of magma

Fractionation and contamination

Emplacement

Sulphide saturation and metal endowment

Sulphide segregation

Syn-tectonic and post-tectonic modification

Key Process Controls

Tetonic Setting Crustal Architecture

1

2

3

4567

1

2

1

765432

After: Lightfoot (2007) and Naldrett (2010)

Begg et al (2011)

PLAN B - Dyke Configuration

PLAN A - Pipe Configuration

PLAN C - Chamber

extensionalbend

contractionalbend

obliquethrust

obliquenormal fault

right-stepping left-stepping

View Along Plane of Stike-SlipShear Zone Plan View

Magma Conduits (pipes, dykes, chambers)at different crustral levels

Kinematics : dextral strike-slip fault zone

Mantle

Chamber

Conduit

Chamber

Chamber

PLAN A

PLAN B

PLAN C

MeltAccumulation

RigidDuctile?

Melting

Heat Source

Cru

st

Surface

Dyke

Magma Conduits(chonoliths)

Extensional spaces in transform fault systems act as “magma highways” from mantle to surface and control many small differentiated intrusions with nickel sulfide deposits

Take-away points

• Widespread importance of strike-slip structures on emplacement of small differentiated intrusions with transported sulphide: Vertical champagne glass-shaped chonoliths (e.g. Huangshan,

Huangshandong, Jingbulake, Limahe, Hong Qi Ling…) Accumulations within sub-horizontal chonoliths (e.g. Noril’sk-Talnakh,

Karatungk, Nkomati, Babel-Nebo…)• A common model for nickel sulfide formation in the roots of large igneous

provinces in craton-margin structures• Case studies of Chinese deposits and Norli’sk help to understand Voisey’s Bay • Chamber geometry, ore distribution, and transport of magmatic sulfide

controlled by dilational space created in a right-lateral fault zone

Distribution and scale of Ni sulfide deposits in China

1000 Km

80°E 90°E 100°E 110°E 120°E 130°E

Hongqiling

Huangshan,Huangshandong

40°N

50°N

30°N

20°N

Jinchuan

Kalatongke

Jingbulake

Limahe

Qingquanshan

Large >1000kt Ni

Medium >100-1000kt Ni

Small >10-100kt Ni

Central Asian Orogenic BeltCentral Orogenic BeltNorth China CratonYangtze CratonTarim CratonCathaysian BlockHimalayan Orogen

Jinbaosan

Ban Phuc

Baimazhai

Yangliuping

Xiarihamu

Distribution of nickel deposits in Western China

40°N

45°N

Pobei

Korla

Jingbulake

Urumqi

Karatungk

Hami

Hulu Tula’ergenHuangshandong

Huangshan

Jinchuan

Lashuisha

JunggarBasin

TarimBasin

Hami Basin

90°E85°E 95°E 100°E

Mesozoic-Cenozoic Basins Cover

Mesozoic fold-thrust belt

Paleozoic

Precambrian

Border

Nickel Sulfide DepositFaults (strike-slip with thrusting)Town / City

Underlain by Shield

After: Mao et al. (2008), Cunningham (2007)

Xinjiang Gansu

Qinghai

Mongolia

Xiarihamu

Restraining bends and pull-apart basins along the Gobi-Tien Shan fault system in Eastern Xinjiang, China

HuangshanHuangshandong

200km

15km

BogdaShan

Aj Bogd

Barkol Tagh

Turpan Basin

XinjiangAfter: Mann, (2007)

Lightfoot, Evans-Lambswood, (2007)

Geology of the Huangshandong Intrusion and the location of Cu-Ni Sulfide mineralization

A’

A 1km

A’162° 325°A

200m

Gabbro DioriteDiorite

Gabbronorite

Peridotite Country rocks

Ni-Cu sulphidemineralization

FaultsSynformAntiformBoreholes

Gabbro to olivine gabbro

Huangshandong 15km

Xinjiang: Hami Belt – shaft on Huangshandong

Photograph: Peter Lightfoot, 2001

Xinjiang: Hami Belt – exploration under Chairman Mao’s 5 Year Plans


Geology of the Huangshan Intrusion and the location of Cu-Ni Sulfide mineralization

X U

V Y Z

500m

500m

500(m)

0U V

ZYX 50° 90°

0

500(m)

Fault

Basalt and trachyteConglo merate and sandstoneSiltstoneLimestone

Hornblende perido tite

Dunite

Perido titeWebsterite

GabbroDiorite

Gabbrono rite

Disseminated Ni - Cusulfide minerali zation

A

BC

Plan View

Long Section View

CrossSection

View

HuangshanIntrusion

Jingbulake Intrusions, Xinjiang Province

Yang et al., 2012

Sulu

Changawuzi

Jingbulake

81°00 E 81°30 E

42°25 N

42°40 N

40km

Carboniferous BlueschistCarboniferous GreenschistCarboniferous EclogiteEarly-Middle Paleozoic GraniteMafic IntrusionMarbleCarboniferous Volcanicsedimentary rocksProterozoic ComplexFault

Western Xinjiang: the wild west of China

Karatungk Intrusion, Xinjiang Province, China: North-facing long section

1000

500(m)

040 111103958779716359514335271911312162024283236 4

0 500m

#1 #2 #3

Wang et al., 1991

1000 Km

F3

F18

F4

F6 F5

F7F21

F20

F9

150m

Biotite-pyroxene diorite

Biotite-hornblende norite andBiotite-hornblende gabbronoriteBiotite-hornblende olivinegabbronoriteBiotite-hornblende diabase gabbro

Disseminated sulphideHeavy disseminated sulphideCu-rich massive sulphideNi-rich massive sulphide

Karatungk

Karatungk #1,2 and 3 Intrusions, Xinjiang Province, China: West-facing long section#2 Deposit

#3 Intrusion Country rockOlivine gabbronoriteGabbronoriteDioriteQuartz monozoniteOutline ofmineralizationBorehole trace

200m

Wang et al., 1991

Karatungk: the outcrop footprint of the intrusion is ~400x150m

Location Map of the Jinchuan Intrusion, Proterozoic Longshushan Belt, Gansu Province, China

Yongchang

Jinchuan

Qingshijing

ZhangbutaiShandan

1000 Km

39°00’

38°40’

38° 20’

101°00’ 101°30’ 102°00’ 102°30’

10 km Cenozoic

Cretaceous

Devonian-Jurassic

Cambrian-Silurian

Proterozoic

Paleozoic granite

Proterozoic mafic-ultramafic intrusion

FaultMagmatic sulfide mineralization

After Song et al., 2008

Jinchuan Intrusion

Jinchuan

Geological Map and Sections of the Jinchuan Intrusion

Tang Zongli (1993)

Mine area #2 – no trace of sulfide or country rock xenoliths inside the intrusion at surface


Jinchuan Model

Sequential Emplacement of Sulfide-bearing silicate melts

Hongqiling – Geology, Structure and Mineral Occurrences

1000 Km

Hulan Group Gneiss (older)Hulan Group Gneiss (younger)

Granitoid rocksMafic-ultramafic Intrusions

Mesozoic sedimentary rocks

Fault

0 5

km

Hongqiling

Jilin #1Deposit

Jilin #7Deposit

After Zhou et al., 2000

Hongqiling

Hongqiling: Jilin Province

A’

100m100m

200

100

-100

-200(m)

0

A A’

Number 7Deposit

A

C D

Othopyroxenite andhybrid zone

Massive sulphideConglomerate

Disseminated and massiveSulphide in orthopyroxenite

SchistMarbleGneissOutline of open pit

UnconformityFaults and shear zones

WesternIntrusion

200

-200

-400

-600

0

Shaft

EasternIntrusion

250m 150m

A GabbroPyroxeniteOlivine PyroxeniteDisseminated sulfidein olivine pyroxeniteWeakly mineralizedperidotiteAmphiboliteGneissFaultPit outline

B

Plan View

Plan View Section View

Section View

Number 7Deposit

EasternIntrusion

WesternIntrusion(projected toSurface)

Intrusions controlled by structures beneath the ~260 Ma Emeishan Flood Basalt, SW China

1000km

200km

Chengdu

SICHUAN

YUNN AN

Kunming

Yangliuping

Qingquan shan

Limahe

Pan

xi“R

ift”

Baimazhai

Jinbaosan

Yangtze craton

Himalayan orogen

Emeishan flood basalt

Underlain by manysmall intrusions

Fault zone

Nickel and PGE sulphidedeposits

Provincial boundary

A

Geology of the Limahe and Qingquanshan Cu-Ni Sulfide Deposits (Sichuan Province)

50m

A'A

200m

A A’

50m

1700

1800

(m)

1600

70o

B C D E

Mined-out

Hekou formation

Gabbro

Peridotite

Overburden

Diorite and gabbro

Pyroxenite and peridotite

Massive and disseminatedNi - Cu sulfide

Section View Section ViewSection ViewPlanView

Huili group quartzite

Huili group limestone

Fault

High grade massive sulfide

Dissemintated sulfide

Diabase

Fault

Distribution of Siberian Trap Basalts

Crustally-contaminated andNi-Cu-PGE-depletedbasalts

Stratigraphic equivalent ofLow Talnakh Type Intrusions

Stratigraphic equivalentof Talnakh Type Intrusions

~3500m

Ivakinsky

Syverminsky

Gudchikhinsky

Khakhanchansky

Tuklonsky

NadezhdinskyNd3

Nd2

Nd1

Morongovsky

Mokulaevsky

Kharaelakhsky

Kumginsky

Samoedsky Tholeiitic basaltsPicrictic basaltsAlkalic and sub-alkalic basalts

KHARAELAKHINTRUSION

TALNAKHINTRUSION

50km

Basalt trapSedimentary rocks

Isopach map thickness ofNadezhdinsky Formationbasalts (in meters)

Economically mineralizedintrusions projected tosurface

Naldrett et al (1995)

OmskNovosibirsk

Kara Sea

MongoliaKazakhstan

Russia

Noril’sk

Margin ofSiberianShield

West SiberianLowlands

Siberian Trap basaltWest Siberian basalts

www.largeigneou sprovi nces.org/LOM.html

Noril’sk

Panoramic view from Bear’s Brook towards north


Footprint of ~20 million tonnes of nickel at Talnakh


Morphology of the Talnakh and Kharaelakh chonoliths

1000

500

0

(m)

0 1km

SkalistyMine

GlubokyMine

TaimyrskMine

OktyabryskMine

EW

Kharaelakh Intrusion

Noril’sk-KharaelakhFault

TalnakhIntrusion

Siberian Trap basalt

Permian sedimentary rocksDevonian sedimentary rocks(including evaporites and shales)Kharaelakh and TalnakhIntrusions and their apophyses

Massive sulphide

Low Talnakh Intrusion

Faults

1 km

E

W

KHARAELAKHINTRUSION

TALNAKHINTRUSIONNE BRANCH

TALNAKHINTRUSION

SW BRANCH

Skalisty and Gluboky Mines, Talnakh and Kharaelakh Intrusion: North-facing Section

Intrusion

Noril’skKharaelakhFault zone

GlubokyDeposit

KharaelakhIntrusion

Surface

SkalistyDeposit1500 m

0 m

250m

Talnakh

West East

Siberian Trap basaltCarboniferous and Permiansedimentary rocksDevonian sedimentary rocksIntrusionsNi-rich sulphideFault zone

Lightfoot and Evans-Lamswood (2014)

TalnakhIntrusion

NE Branch

KharaelakhIntrusion

SectionLine

TalnakhIntrusion

SW Branch1

km

“Horns and Ears” of the KharaelakhIntrusion

Lightfoot and Zotov (2006)

Sandstone

C'C

Dolomite and limestone

Dolomite, anhydrite and marl

Shale and marl

Ti-augite dolerite

Massive sulphide

Cuprous breccia ores

Olivine-free and olivine-bearing gabbrodolerite

Disseminated sulphide in taxitic gabbrodolerite

Ti-augite dolerite

Troctolite

Disseminated sulphide in picritic gabbrodolerite

0

100

m 0 100

m

Contact metamorphism and apophyses of the Kharaelakh Intrusion

Kharaelakh Intrusion: Spotted Hornfels 952m; Drill Core TG21 (Lightfoot and Zotov, 2006)

5 cm5 cm

Kharaelakh Intrusion: Apophyses of Chilled Gabbrodolerite (Lightfoot and Zotov, 2013)

Morphology of the Kharaelakhchonolith

2km

25 100 150 250m

Contact betweenKharaelakh Intrusion andLow Talnakh Intrusion

2km

Thickness of massiv esulf ide orebodies nearlower contact

0 20m 40m

Contact betw eenKharaelakh Intrusionand low Talnakh Intrusion

B C

Thickness of Kharaelakhintrusion

Lower Talnakh intrusionthickness >40 m

Margin of the Intrusionwhere thickness <50m

Noril ’sk – Kharaelakh fault

A B

C D

1000 um

1 cm 1 cm

2 cm

Ligh

tfoot

, 201

6

334g/t Pd; 72 g/t Pt

Noril’sk-Talnakh: Massive Ni-rich contact ores

Disseminated sulfide ores in taxites; Noril’sk and Talnakh

Cuprous Ores at Kharaelakh and Talnakh

0 1

km Mk and Mk-Cub massive sulfide

Cpy-Cub massive sulfide

Cpy-Po vein sulfide

Country rocks


Cuprous breccia sulfide

X Y

~ 100m

Masive Ni-rich ores

DisseminatedPo-Cpy-Pn

sulfides

Cuprous ores

X

Y

Cuprous mineralization of thehanging wall and breccia zones

Cuprous mineralization of thefootwall

Talnakh Intrusion


Outcrop

Noril’sk Kharaelakh Fault

Kharaleakh and TalnakhCuprous ores (Lightfoot and Zotov, 2013) – hosted in adjacent country rocks (skarns, metasomatism, and replacement textures in associated with magmatic sulfides)

Talnakh: Komsomolsk Mine; Lower Exocontact

Breccia Ore

Komsomolsk Mine: Lower Exocontact Cuprous Breccia Ore

Oktyabrsky MineUpper contact –mineralisation in ahhydrite; metasediment inclusions

Talnakh Intrusion: Skalisty Mine. Cuprous Ore along bedding in footwall hornfels

A B

C DSiltstone

Po-Pn-Cpy

Po-Pn-Cpy

Po-Pn-Cpy

Po-Pn-Cpy

Siltstone

ChurchillProvince

(Rae craton)

Nain Plutonic Suite

Kogaluk RiverLineament

Nain

100km

Gardar Province

Torngatorogen

ArcheanNorth Atlantic

craton

Voisey’s Bay - Gardarfault zone

GREENLANDLABRADOR

Myers et al., 2008

Location of the Voisey’s Bay - Gardar fault zone

Voisey’s Bay

TasisuakLake

Tugtutoq augite troctolite dykes (Upton and Thomas, 1980)

Gardar Province, Greenland


Geology of the Voisey’s Bay Deposit

Voisey’s Bay2 km

AshleyIntrusion

WesternDeeps

Chamber

Reid BrookDyke

Eastern DeepsChamber

Ovoid

568000E556000E544000E

6237

000N

6245

000N

Makhavinekh Lake GraniteSuiteVoisey’s Bay Granite SuiteAnorthosite SuitesMushuau IntrusionOutcrop of VBISubsurface extent of VBIChurchill ParagneissEnderbite OrthogneissArchean GneissRegional FaultsSection LineOre deposits

Y

X

100km

GREENLANDLABRADOR

Voisey’s Bay

Nain Plutonic SuiteGardar IntrusionsOrthogneissParagneiss

Voisey’s Bay: location of mineral zones

Eastern Deeps

Ovoid

Far Eastern Deeps

Discovery Hill

Western Extension

Reid Brook Zone

Voisey’s Bay: Arrival at Camp Pond, 1996


1996 Camp, Voisey’s Bay (Ovoid)

Exploration defined 31.7 m tonnes 2.83%Ni, 1.68%Cu, and 0.12% Co

Pho

togr

aph:

Pet

er L

ight

foot

, 199

6

Voisey’s Bay: Camp pond


Geological relationships in the OvoidC

Northing(m)

Ovoid Deposit

Line55985E

SoutheasternExtensionDeposit Southeastern

ExtensionDyke

Ovoid

5000

4800

VB95-010 VB95-014

Northing(m)

Ovoid DepositVB95-013

Line55945E

OvoidDyke

SoutheasternExtensionDyke

4800

4200

Northing(m)

SoutheasternExtensionZone

EasternDeepsChamber

Eastern endof Ovoid Deposit

OvoidDyke

Line56044E

EasternDeepsDyke

Elev

(m)

4250

0

4300

0

4280

0

4330

0

Elev

(m)

5000

4800

Elev

(m)

4250

0

4300

0

A

B

Lightfoot et al (2011)

0 1000

Threewest-facing sections

ABCD

Massive SulphideEnderbitic Orthogneiss

OverburdenDyke Mafic RocksDisseminated Sulphide

Ovoid Deposit

Pho

togr

aph:

Pet

er L

ight

foot

, 200

7

Geology of the Voisey’s Bay Deposit

Makhavinekh Lake GraniteSuiteVoisey’s Bay Granite SuiteAnorthosite SuitesMushuau IntrusionVoisey’s Bay IntrusionSubsurface extent of VBI

400m

200

0

-200

-400

-600

-800

3400

N

3600

N

3800

N

4000

N

4200

N

4400

N

4600

N

4800

N

5000

N

5200

N

5400

N

North ofEastern Deeps

Zone

EasternDeepsDeposit

FeederConduitGneiss

Lip

Depth(m)

VB95-266 VB95-194 Weakly - mineralized VTTHeavily - mineralized VTTSemi-massive sulfideMassive sulfide

A B

Section View

GneissWall

EasternDeeps

Churchill ParagneissEnderbite OrthogneissArchean GneissRegional FaultsSection LineOre deposits

Y

Eastern Deeps Intrusion

Western DeepsIntrusion

0m

500m

1000m

1000m

X

Reid BrookZone

EasternDeeps

Ovoid

Southeast Extension ZoneOvoid DepositDiscovery Hill ZoneReid Brook Zone

DykeEastern Deeps IntrusionNorth Eastern Deeps ZoneEastern Deeps Deposit

Long Section ViewFrom Lightfoot & Evans Lamswood (2012)

Voisey’s Bay: Drill rig on Eastern Deeps, 1997


Exploration defined indicated resource of 50 m tonnes 1.63%Ni, 0.67%Cu, and 0.09% Co

Voisey’s Bay: Eastern Deeps, 1997


1999: Anakhtalak Bay CampP

hoto

grap

h: P

eter

Lig

htfo

ot, 1

999

2007: Voisey’s Bay Mine P

hoto

grap

h: P

eter

Lig

htfo

ot, 2

007

Geology of the Reid Brook Zone

Contactdip 45°

20° to 50°

45° plungeof mineral zone

Mini-Ovoid

Ovoid

Mafic EnderbiteFelsic EnderbiteChurchill paragneiss

Leopard troctoliteMassive sulfide

Troctolite

Variable troctolite with heavydisseminated sulfide

FaultsPlunge of mineral zone

Ferrogabbro

500 m

Granite

Tasiuyak Gneiss

W E

Evidence for syn-magmaticdextral transtension1. Displaced contacts2. Magnetic fabric3. Morphology of intrusion4. Shear zones with granite5. Fabric of gneiss rotated into

north wall of Eastern DeepsFrom Lightfoot & Evans Lamswood (2012)

53700 E

Line

of s

ectio

n

Reid Brook Zone: 53700E Section –Looking West

2.43, 1.1933

VB-12-941B

Western DeepsIntrusion

VB-05-653VB-07-8272.64, 1.11

35 2.76, 1.0626

0 m

100 m

200 m

300 m

400 m

500 m

600 m

700 m

Rapakivi Granite

Massive SulphideSulphide

Troctolite

Host Rock

Overburden

Garnetiferous ParagneissParagneiss / Quartz Paragneiss

FaultHistoric Drilling

Troctolite

Amphibolite

Breccia

Mineralized Troctolite

Granite / Pegmatitic

Leopard Textured Troctolite

Troctolite Chamber

% Ni, % Cucore meters

Reid BrookDyke

Section prepared byDanny Mulrooneyand Sheldon Pittman

100 m

Geological Mode: Reid Brook Zone

Leapfrog model showing Ni grade distribution in the Reid Brook Zone projected onto W-E long section

Model prepared byLisa Gibson

Discovery Hill zone

Mini-Ovoid

Reid Brook zone

Mineralization in paragneisscontrolled by structureplunging ~10° East.

Mineralization in dykecontrolled by chonolithplunging ~45° East.

Top of WesternDeeps Chamber

Isosurface Ni>0.5wt%Isosurface Ni>1wt%Isosurface Ni>1.5wt%Isosurface Ni>2wt%Trend of mineral system

Kinematics: Summary for Voisey’s Bay

From Lightfoot & Evans Lamswood (2012)

3D model:rotational movementon a “scissor” fault

3D modelnegative flower structureon dextral strike-slip fault withrotational movement to createspace for Eastern Deeps chamber

Offset

Offset

Pivot OffsetPosition ofReid BrookDyke

Position of Eastern DeepsChamber

Summary

• Magmatic Ni-Cu-(PGE) sulphide ore bodies: often not the product of simple in-situ gravity settling within a magma chamber.

• Sulphide-laden magma ascended through a sub-vertical conduit system in a structural zone from a parental source/chamber at depth.

• Common theme now recognised in a spectrum of Ni sulphide ore deposits that underpin process models for their formation

– Funnel-shaped intrusions– Chonoliths– Dykes

• Conduit morphology is controlled through the intersection of regional structures that create space, and are localized by dilations and traps created by transtension in strike-slip fault zones:

Global Examples of magma conduits (red – this talk):

• FUNNEL MORPHOLOGY: Jinchuan, Hong Qi Ling #1, Jingbulake, Huangshan, Huangshandong, Limahe, Qingquanshan, Lengshuiqing, Zhubu, Ban Phuc, Ovoid, Discovery Hill, Eastern Deeps, Eagle, Double Eagle, Aguablanca, Maksut, Santa Rita, Suwar, Savanah, South Raglan

• PIPE (CHONOLITH) MORPHOLOGY: Baimazhai, Tongdongzi, Talnakh, Kharaelakh, Noril’sk I, Karatungk, Noril’sk II, Chernagorsk, Maslovskoe, Tamarack, Current Lake, Babel-Nebo, Nkomati, Limoeiro, Chibasong, Wellgreen, Voronezh, Zhouan, Xiarihamu

• DYKE MORPHOLOGY: Reid Brook, NED, Worthington (Sudbury), Copper Cliff (Sudbury), Hong Qi Ling #7, Tong Dong Zi

Controls on emplacement and morphology of komatiites (Yilgarn, Thompson, Pechenga, and Raglan) may also share primary structural controls.

Thank You: Vale

Graphic design: Alex Gagnon

Dawn-Evans LamswoodRogerio MonteiroIan FieldhouseLisa Gibson

Danny MulrooneySheldon PittmanVivian FengIgor Zotov


examples from China and Russia inform models for Voisey's Bay

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Transcript of examples from China and Russia inform models for Voisey's Bay