where do we find magmatic sulfide ore deposits? · seminar june 20 2011 1 magmatic nickel sulphide...

15/06/2011

Steve Barnes AIG Base Metals seminar June 20 2011 1

Magmatic nickel sulphide deposits in Australia

Steve BarnesCSIRO Earth Science and Resource EngineeringFeb 2011

Where do we find magmatic sulfide ore deposits?

• Komatiites• Subvolcanic intrusions in flood basalt

provinces (Norilsk, Duluth)• Mafic/ultramafic intrusions in anorogenic

plume settings, often at craton margins or in intracontinental rifts (Voisey’s Bay, Jinchuan?)

• Large differentiated mafic/ultramafic layered intrusions (Bushveld, Stillwater) and feeder zones to same (Uitkomst/Nkomati)

• (Rarely) mafic intrusions in continental arcs (Finland, Caledonides)

• Impact melt sheets (Sudbury)• Almost never: alkalic mafic or ultramafic

intrusions

Lava flows

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Australian deposits

Radio Hill

HoatsonGA 2004

Ni resources in Australia

HoatsonGA 2004

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2002 Global Ni Mines Reserves & Resources

Extrusive Reserve (3895kt)

Extrusive Resource (6214kt)

Intrusive Reserve (11593kt)

Intrusive Resource (22787kt)

Lateritic Reserve (18670kt)

Lateritic Resource (23075kt)

4.50%7.20%

13.40%

26.40%21.70%

26.80%Komatiite reserve

Komatiite resource

HoatsonGA 2004

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Volcanic rocks with >18% MgO in the liquid

Characteristic dendritic olivine and pyroxene textures- “spinifex”

Predominantly Archaean

Eruption temperatures up to 1600C

Komatiites: an introduction

Komatiite VolcanosKomatiite VolcanosKomatiite VolcanosKomatiite Volcanos

Extremely high T (1600C), extreme low viscosity lavasProbably built low-aspect shield volcanoes, lava fields

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Komatiite (and HMB) localities worldwide

Archaean/Early Prot cratons

Yilgarn 2.7-2.9

Superior 2.7-2.8

Zimbabwe 2.7

Kaapvaal 3.25-3.55

Sao Francisco 2.7

Baltic 1.9, 2.4, 2.7

Pilbara 2.7, 2.9, 3.4

Gorgona .09

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Type 1 Ore profiles

Matrix 0-50m

Massive 0-10m

Komatiite hosted

Kambalda Dome

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Barnes et al., reviews in Economic Geology, in press

Origin of komatiite-hosted ores – the substrate erosion model

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Ore formation by thermo-mechanical erosion of sulfidic substrate along the flow channel; formation, transport and accumulation of immiscible sulfide ore magma

Type 1 (Kambalda-style) sulphide-rich contact ores

Sulphide assimilation, entrainment and transport

Thermal and mechanical erosion

Contaminatedkomatiite lava

Sulfidic substrate

Olivine

THERMAL AND MECHANICAL EROSION AND THE

FORMATION OF TYPE I NICKEL DEPOSITSREHs012-98

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Australian deposits

Radio Hill

HoatsonGA 2004

Halls Creek Orogen, WA (after Hoatson, GA)

HoatsonGA 2004

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HoatsonGA 2004

Sally Malay - Savannah


HoatsonGA 2004

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Nebo-Babel Ni-Cu-PGE sulfide depositLocation

Modified after Glickson et al., 1995

HoatsonGA 2004

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Nebo-Babel Ni-Cu-PGE sulfide depositLocation

Modified after Seat et al., 2007

Nebo-Babel Ni-Cu-PGE depositLithologies

Variably-textured leucogabbronorite Massive sulfides

Mineralized gabbronorite (MGN)

5 cm5 cm

5 cm 5 cmModified after Seat et al., 2007

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Nebo-Babel dykesDifferent types

5 different dyke types

Low-Ti basalts

High-Ti basalts

Alkali basalts

Not

sca

led

Modified after Seat et al., 2007, 2011; Godel et al 2011 (Econ Geol)

divided into 3 groups

(González-Álvarez et al., 2010)

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(Lygin et al., 2010)

AveburyAvebury cross sectioncross section

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AveburyAvebury

�� 170k Ni t, 1.02 wt% global Ni grade170k Ni t, 1.02 wt% global Ni grade��Western Tasmania within the Dundas TroughWestern Tasmania within the Dundas Trough��Host by an EHost by an E--W ultramafic unit, striking 2 km, dips steeply to the NW ultramafic unit, striking 2 km, dips steeply to the N��Within a hosted volcanoclastic sequence of turbidites, carbonates and brecciasWithin a hosted volcanoclastic sequence of turbidites, carbonates and breccias��Located within the metamophic aureole of the Late Devonian Heemskirk granite Located within the metamophic aureole of the Late Devonian Heemskirk granite ��Associated granite with Sn, PbAssociated granite with Sn, Pb--Zn depositsZn deposits��Magnetite rich mineralization up to 18%Magnetite rich mineralization up to 18%��Ore: pentlandite, minor pyrrhotite and rare millerite, mackinawite, niccolite, gersdorffite Ore: pentlandite, minor pyrrhotite and rare millerite, mackinawite, niccolite, gersdorffite and maucheriteand maucherite��Associated with an ultramafic unit formed in a Cambrian island arc settingAssociated with an ultramafic unit formed in a Cambrian island arc setting��Deposit age ~370 MaDeposit age ~370 Ma

(Keays and Jowitt, 2009)

Australian deposits

Radio Hill

HoatsonGA 2004

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What’s special about the Kalgoorlie Terrane?

Con

tain

edN

imet

al,t

hous

ands

ofto

nnes

10

100

1000

10000E

GS

Agn

e w-

Wilu

na

Tho

mp

s on

Be l

t

EG

SK

a lgo

orli

eTe

rrain

Rag

lan

For

r-La

keJ-

Rav

Abi

tibiW

est

EG

SK

urna

lpi

terra

ne

EGS combined

Thompson Belt

Pechenga

Abitibi

Raglan

Zimbabwe

Forr-LakeJ-Rav

S

Subvolcanic conduits (Mt Keith)

Channel fed compound flow fields (Kambalda)

Conceptual reconstruction of komatiite flow fields, Kalgoorlie Terrane

S-rich Ni ores

S-poor dissem Ni ores

Modified from Fiorentini, Rosengren, Beresford et al, Hill, Barnes et al

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maximum MgO content of komatiites at each locality

>4535-4525-35

East Yilgarn again...

E Yilgarn nickel sulfide deposits

Strong association of ore deposits with most magnesian (olivine-rich) rocks

Adcumulates are the key...• Prolonged eruption• Very high magma flux• Mature conduits,

focussed flow

Why here?

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Ni deposits and craton margins

Superior

Thompson belt

Sudbury

Raglan (Cape Smith) belt

Voisey’s Bay


Begg et al 2010

Jinchuan

Kabanga

Selibe-Phikwe

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Begg et al 2010

NORIL’SK

Nebo-Babel

Sally Malay

Champion and Cassidy Sm/Nd model age in granites – proxy for age of lower crust

>3.2 Ga

<2.7Ga

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Major nickel deposits close to margin of stable “Archon” (Begg et al 2010)

Craton margin model (Begg et al 2010)

f low age o f plu me alon gslop ing b ase o f li t hos phere

inc reased p art ialm el t ing

int erac t io n bet w een m agm aand sedim ent d efo rm at ion of t he lit hosp here,

p assag e of m ag mas alo ng f r act u res

lit ho sph eric mant le

crust

plume

sed im ent s

Reasons why Ni deposits might form at craton margins

1. Thinner lithosphere promotes high-degree melting

2. Sloping lithosphere base focuses flow of plume or magma beneath the lithosphere

3. Deformation of the lithosphere by the plume fractures the lithosphere

4. Ascending magma encounters sediments (S source)

5. Deformation uplifts base of volcanic pile exposing intrusions

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Targeting in komatiite terranes –Applications of geochemistry

• Ni-Cr-Ti ratios• Platinum Group elements (PGEs)

RECENT CSIRO + CET developments

• Ni-Cr-Ti ratios –mineralised flow units often Cr-deficient

Ni/Cr vs Ni/TiApplicable to mildly weathered material Elements can be analysed by portable XRF

Targeting in komatiite terranes

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Subvolcanic conduits (Mt Keith)

0.01

0.1

1

10

10 15 20 25 30 35 40 45 50 55 MgO wt %

Pt/T

i n

Sulfide-free samples

C

Background

Enriched

Depleted

Other lithogeochemical indicators:Platinum Group Elements (PGE)

Fiorentini, Barnes et al. Economic Geology 2010

Platinum group elements as exploration indicators

Thanks to Independence Group NL

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Heggie PhD, and Heggie et al. (in review)

0.01

0.1

1

10

10 15 20 25 30 35 40 45 50 55 MgO wt %

Pt/T

i n

Sulfide-free samples

C

Enriched

Depleted

Enriched

Depleted

Distance from nearest 0.6% Ni grade shell

Limit of anomalous

Ni

Spinifex flow tops

B-zone cumulates

S-

Sulphide-poor samples only

Ruthenium in chromite

(Locmelis PhD thesis 2010, Geochimica 2011. MERIWA funded)

Laser ablation - ICPMS data

Komatiites

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Pt (Red)-Ni (Green)-Fe (Blue)

Millerite

Pentlandite

Pyrrhotite

Platinum-

group minerals

Pt (Red)-Os (Green)-Ni (Blue)Fresh Dunite-

Betheno

Olivine

Next slide

1 mm

5 microns

200 microns

BSE images

PtSynchrotron X-ray fluorescence mapping

Extremely Ni-rich sulphide assemblages in fresh (unserpentinised) dunite, Betheno – synchrotron XFM

Fe Pt Ni

millerite

pnpy

Synchrotron XFM

High-Ni mineralogy is PRIMARYNatural sulphide liquids can contain >30% Ni

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Low-energy channel, abundant sulfide = low R

Sed S source Entrained bed-load sulfide liquid – Ni, PGE poor

Sed S source Entrained sulfide liquid droplets – Ni, PGE rich

High-energy channel, less sulfide = high R

The next research challenge: sulfide transport and deposition mechanisms

Sulfide liquid droplets entrained and transported

What is the accumulation mechanism – coalescence and settling?New clues from 3D microtomography...

Disseminated ores in komatiitic olivine cumulates – size and shape of sulfide blebs in 3D

1 mm3

Smaller blebs are more spherical – lower Bond number (Godel and Barnes, in prep)

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Coalescence of droplets - Manga and Stone 1994

Coalescence via entrainment

Non-coalescence – small droplets flow around big ones

Favoured by low surface tension, large drops, similar droplet sizes

Big drops coalesce, small drops don’t...

Disseminated sulfide mineralogy –serpentine/carbonate alteration

mill py pn

QEMSCAN image

1 mm

Ultramafic rocks as sensitive recorders of complex alteration histories – applications in Au systems

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Low-energy channel, abundant sulfide = low R

Sed S source

Sulfide transport and deposition mechanisms

Rapid heat loss through highly conductive sulphide layer

Solid sulphide

Entrained sulfide freezes on to basal sulfide layer

Crustal scale Ni mineral systems

Blind Alley

Crustal S source

Ore-body

Orebody

Magma Freeway

Questions:• Is crustal S always necessary?• Does the magma source matter? Is the SCuM involved?• How to distinguish magma freeways? (e.g. use of resistate

detrital minerals such as Ti-rich chromite)

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What’s new in komatiite-hosted Ni?

1. Flow-sill complex model for Agnew-Wiluna Belt (Beresford, Fiorentini, Rosengren et al papers)

2. Multi-S-isotope data – external S source model is confirmed – particular sources are important – VMS-type sulfides in felsic rift associations (Bekker et al, Science, 2010)

3. Variety of lithogeochemical prospectivity indicators and vectors including Ni-Cr-Ti, FeO-MgO, REE (Barnes et al papers)

4. Platinum group elements as prospectivity indicators and vectoring tools (Barnes, Fiorentini et al papers)

5. Disseminated (Mt Keith style) ores are not genetically distinct –part of a continuum

6. Extremely Ni-rich sulphide liquids exist in nature and are very attractive exploration targets

7. Tectonic setting and craton margins localise major ore camps (Begg et al)

Shameless plug…

Chapters on:•Exploration history•Komatiites and volcanology•Sulfide ore deposits•Mt Keith-type deposits•Weathering and geochem exploration•Geophysical exploration•Nickel laterite deposits

Order from

http://store.agiweb.org/seg/pubdetail.html?item=SP13

Or just Google <SEG CSIRO Nickel>

15/06/2011


Thank you

Contact UsPhone: 08 6436 8645Email: [email protected] Web: www.csiro.au

There stood a hill not far; whose grisly top

Belched fire and rolling smoke; the rest entire

Shone with a glossy scurf - undoubted sign

That in his womb was hid metallic ore

The work of sulphur. Thither, winged with speed,

A numerous brigade hastened… Mammon led them on

John Milton, Paradise Lost, 1670

where do we find magmatic sulfide ore deposits? · seminar june 20 2011 1 magmatic nickel sulphide...

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