Heterogeneity in the SCLM - energymining.sa.gov.au · Heterogeneity in the SCLM Multiple mantle source components identified from 1590 Ma mafic intrusions, Gawler Craton Claire Wade

Heterogeneity in the SCLM

Multiple mantle source components identified from 1590 Ma mafic intrusions, Gawler Craton

Claire Wade1,2, Justin Payne3, Anthony Reid1,2, Karin Barovich2

1Geological Survey of South Australia2 School of Physical Sciences, University of Adelaide3School of Natural and Built Environments, University of South Australia

AGCC Adelaide, 2018

SCLM in the Gawler Craton

• The SCLM at 1590 Ma is complex and heterogeneous

• At least four compositional groups can be observed

• Resulting from partial melting of a metasomatised SCLM

• Role of a metasomatised SCLM for Cu and Au mineralisation IOCG

Province

Central Gawler

Gold Province

Province

(1590 Ma)

(1590 Ma)


• Geochemical connection between SCLM and metals by association of juvenile isotopes with increasing Cu and Au abundance

• Mantle connection important

References: Johnson and McCulloch, 1995. Chem. Geol.,

121, 177-199; Budd and Skirrow, 2007. Eco. Geol., 102,

1541–1563; Skirrow et al. 2007. Eco. Geol., 102, 1441-1470.

εNd vs Cu at Olympic Dam

(Skirrow et al. 2007)

SCLM in the Gawler CratonConductivity

pathways within the

mantle and crust

revealed in new MT

data and inversions

which link the lower

crust with major

IOCG-U deposits.

Heinson et al. 2018. Sci. Rep., 8:10608

2D seismic showing

zones of reduced

reflectivity under all

the major mineral

deposits.

A

A’

WW: Wirda Well; OD Olympic Dam; VC: Vulcan

• Lithospheric mantle is hydrous and metasomatised

• A heterogeneous and enriched mantle existed at 1590 Ma

• Previous work have been isolated studies, often limited by restricted geographical extent or limited data sets

• No systematic approach


References: Wade et al., 2012. Precam. Res., 206–207, 17–35; Thiel and

Heinson 2013, Geophys. Res. Lett., 40, 2947–2952; Huang et al., 2016.

Precam. Res., 281, 185-199; Rogers et al., 2018. Lithos, 314-315, 216-235;

Skirrow et al. 2018. G3, 19.

Interpreted metasomatised SCLM in the Gawler Craton

inferred from geophysical, geochemical and geochronological

datasets from Skirrow et al. 2018. G3, 19.

• Lithospheric mantle is hydrous and metasomatised

• A heterogeneous and enriched mantle existed at 1590 Ma

• Previous work have been isolated studies, often limited by restricted geographical extent or limited data sets

• No systematic approach


References: Wade et al., 2012. Precam. Res., 206–207, 17–35; Thiel and

Heinson 2013, Geophys. Res. Lett., 40, 2947–2952; Huang et al., 2016.

Precam. Res., 281, 185-199; Rogers et al., 2018. Lithos, 314-315, 216-235;

Skirrow et al. 2018. G3, 19.

Interpreted metasomatised SCLM in the Gawler Craton

inferred from geophysical, geochemical and geochronological

datasets from Skirrow et al. 2018. G3, 19.

• Variable compositions


• Filter for most mafic compositions

• Removes obvious crustal contamination


• Filter for most mafic compositions

• Removes obvious crustal contamination

• Emergence of four compositional groups

Th/Nb ratios for the mafic Hiltaba Suite and basalts from the lower GRV

Lower GRV

100 km

Group 1

Group 1

Largely juvenile

εNd(1590 Ma) =

-1.3 to 1.1

Th/Nb < 0.10

Flat trace element and REE profiles

Absence of negative Nb-Ta-Ti anomalies

Upper continental crust

εNd(i) = -1.3

εNd(i) = 0.2–1.1

IOCG

Province

Central Gawler

Gold Province

Province

Variable Nd

εNd(1590 Ma) =

-5.5 to 0.2

Th/Nb = 0.11–

0.25

Lower GRV


100 km

Group 1

Group 2

εNd(i) = -0.2

εNd(i) = 0.2

εNd(i) = -2.3

and -5.5

εNd(i) = -5.5

Flat to moderate trace element and REE profiles

Negative Nb-Ta anomalies

Group 2


IOCG

Province

Central Gawler

Gold Province

Province

Lower GRV


100 km

Group 1

Group 2

Variable Nd

εNd(1590 Ma)

= -3.4 to 4.0

Th/Nb > 0.25

εNd(i) = -1.7 to 1.0

εNd(i) = -2.6 to -2.1

εNd(i) = -2.4

to -0.9

εNd(i) = -3.4

to -3.3

εNd(i) = -1.1

Group 3

Flat to steep trace element and REE profiles

Negative Nb-Ta-Ti anomalies

Group 3

εNd(i) = -0.4 to 1.9

εNd(i) = 4.0

εNd(i) = -3.3


IOCG

Province

Central Gawler

Gold Province

Province

Group 1

Group 2

Lower GRV


100 km

Flat to steep trace element and REE profiles

Negative Nb-Ta-Ti anomalies

Evolved Nd

εNd(1590 Ma)

= -8.2 to -4.3

Th/Nb > 0.25

εNd(i) = -8.2 to -4.3

Group 4

Group 3

Group 4 εNd(i) = -4.8 to -4.3


IOCG

Province

Central Gawler

Gold Province

Province

Mantle source components

Subduction modified lithosphere

OIB modified lithosphereDepleted unmodified lithosphere

AM

EMII

LC

UC

E-MORB

N-MORB

OIB

After Pearce et al. 2015. Geol.

Assoc. of Can. 38. and Pearce

et al. 2017. GSA Abstracts with

Programs. 49, No. 6.

UC: Upper Crust; LC: Lower Crust; EMII; Enriched Mantle 2; OIB: Oceanic Island

Basalt; AM: Asthenospheric Mantle; N-MORB: Normal Mid-Ocean Ridge Basalt;

E-MORB: Enriched Mid-Ocean Ridge Basalt

• Th/Nb as a proxy for crustal input

• Subducted component stored in SCLM or assimilation during fractionation

• Ti/Yb proxy for depth of melting

• Define mantle source regions




AM

EMII

LC

UC

E-MORB

N-MORB

OIB




Group 1: ~E-MORB








AM

EMII

LC

UC

E-MORB

N-MORB

OIB




Group 1: ~E-MORB

Group 2: Enriched

mantle








AM

EMII

LC

UC

E-MORB

N-MORB

OIB




Group 1: ~E-MORB

Group 3: Subduction

modified SCLM

Group 2: Enriched

mantle








AM

EMII

LC

UC

E-MORB

N-MORB

OIB




Group 1: ~E-MORB

Group 4: Subduction

modified SCLM plus

crustal contamination

Group 3: Subduction

modified SCLM

Group 2: Enriched

mantle





Mantle source components and metals

Group 1: ~E-MORB

Group 4: Subduction

modified SCLM plus

crustal contamination

Group 3: Subduction

modified SCLM

Group 2: Enriched

mantle

Association of subduction

modified SCLM and higher

Cu abundances


Sub. Mod.

SCLM

Sub. Mod. SCLM + AFC

Enriched

Mantle

~E-MORB

c. 2520–1608 Ma c. 1590 Ma

Partial melting of SCLM in response to

asthenospheric upwelling due to extension,

lithospheric foundering or mafic underplating of

mantle plume

Multiple metasomatic events affecting the

composition and structure of the SCLM

Mantle source componentsc. 2520–1608 Ma c. 1590 Ma

Magmas derived from the metasomatised SCLM

may constitute a fertile and hydrous source.

Subduction as a mechanism to create siderophile

and chalcophile-rich zones in the SCLM,

similar to post-subduction porphyry Cu and

epithermal Au deposits of Richards 2009,

Geology, 37, 247–250.

Sub. Mod.

SCLM


Enriched

Mantle

~E-MORB

Mantle source componentsc. 2520–1608 Ma c. 1590 Ma

Generation of Cu and Au mineralisation related to

remelting of subduction metasomatised SCLM or

lower crust hydrous zones.

Subduction as a mechanism to create siderophile

and chalcophile-rich zones in the SCLM,

similar to post-subduction porphyry Cu and

epithermal Au deposits of Richards 2009,

Geology, 37, 247–250.

Au Cu AuCu

Sub. Mod.

SCLM


Enriched

Mantle

~E-MORB

Acknowledgements

Contacts

Claire Wade, Senior Geologist

Department for Energy and Mining

11 Waymouth StreetAdelaide, South Australia 5000

GPO Box 320Adelaide, South Australia 5001

T: +61 8 8429 2571

E: [email protected]

mailto:[email protected]

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Heterogeneity in the SCLM - energymining.sa.gov.au · Heterogeneity in the SCLM Multiple mantle source components identified from 1590 Ma mafic intrusions, Gawler Craton Claire Wade