Tectonic setting of the Gawler Craton iron oxide-copper-gold mineral systems

Anthony Reid

Senior Principal Geoscientist

Geological Survey of South Australia

Iron oxide-copper-gold workshop

2-3 December 2019

South Australia Drill Core Reference Library, Adelaide

Hydrothermal zircon with sulphide inclusions, Olympic Dam

Hiltaba Suite granite, Hiltaba Station

• Main stratigraphic units relevant to IOCG systems in South Australia

• Interpretations of tectonic setting for IOCG systems

Looking east from the central Gawler CratonRubble is silicified Jurassic sandstone

GawlerCraton

Curnamona Province

GawlerCraton

Curnamona Province

IOCG event

GawlerCraton

Curnamona Province

BasementSleafordianOrogeny

5cm

GawlerCraton

Curnamona Province

Basement

TDM (Ga) contour

Data from many sources. GIS layer and compilation by Champion, 2014Geoscience Australia Record 2013/044 http://www.ga.gov.au/metadata-gateway/metadata/record/77772/

http://www.ga.gov.au/metadata-gateway/metadata/record/77772/

GawlerCraton

Curnamona Province

Basement

Devils Playground Volcanics, c.2555 Ma • magnesian, calc-alkali• basalt – eNdt ~ -1

Enriched lithospheric mantle

Basalt, andesitic basalt, andesite; 51 – 59 % SiO2

GawlerCraton

Curnamona Province

Basement

Donington Suitec. 1850 Ma

GawlerCraton

Curnamona Province

Basement

Cover

• c. 1790 – 1740 Ma• Sedimentary and volcanic rocks, • Key unit for the eastern Gawler Craton: Wallaroo Group• Widespread distribution• Variable metamorphic grade

GawlerCraton

Curnamona Province

Basement

Cover

Wallaroo Group

GawlerCraton

Curnamona Province

Basement

Cover

c. 1730 - 1690 MaKimban Orogeny

• High strain; transpression• HT-MP metamorphism

crd-bearing leucosome

GawlerCraton

Curnamona Province

Basement

Cover Cover

Hores Gneiss, meta-volcanic unit host to Broken Hill orebody.View towards Broken Hill mullock heap

Willyama Supergroupc. 1710 – 1640 Ma

c. 2440 Ma

c. 1730 –1690 Ma

Empirical observation: distribution of pre-1590 Ma metamorphism

Olympic Dam

Pre-1740 Ma lowmetamorphic grade rocks

c. 1730 –1690 Ma

c. 2440 Ma

Olympic Dam

Empirical observation: distribution of pre-1590 Ma metamorphism

~1730 – 1690 MaHigh-T;

TranspressionKimban Orogeny

Low –grade or no metamorphism

~1730 – 1690 MaHigh-T;

TranspressionKimban Orogeny

Broken Hillmineralisation:broadly coevalwith deposition~1685 Ma

~1720 – 1640 Ma sedimentation;

extension~1730 – 1690 Ma

High-T;TranspressionKimban Orogeny

Low –grade or no metamorphism

Gawler – Curnamona setting ca. 1710–1690 Ma

Gawler – transpression – transtension:•Metamorphism and deformation – Kimban Orogeny•Subdued topography•Local sedimentation (e.g. Labyrith Fmn)

Curnamona – extension:•Sedimentation ~ Lower Willyama Supergroup•Magmatism – e.g. Ameroo Subsuite

‘Gawler’ crust ‘Curnamona’ – thinned crust

Kalinjala Shear Zone Broken Hill Zn-Pb-Ag

GawlerCraton

Curnamona Province

Basement

Cover Cover

St Peter Suite

St Peter Suite, c. 1620 Ma• Mantle-derived, enriched• Interpreted subduction-related

Reid et al 2019 AJES

Magnesian to ferroan composition

St Peter Suite, c. 1620 Ma• Mantle-derived, enriched• Interpreted subduction-related

Enriched mafic rock composition

Reid et al 2019 AJES

Skirrow et al. 2019

GawlerCraton

Curnamona Province

Basement

Cover

Large igneous province:• Hiltaba Suite• Bimbowrie Suite• Gawler Range Volcanics• Benagerie Volcanics

Cover

Hiltaba Suite, c. 1595- 1575 Ma• A- and I-type• High temperature, oxidized

magmas

Gawler Range Volcanics, c. 1590 Ma• Compositional variation in Lower• Large volume felsic lavas in Upper• High temperature• Benagerie Volcanic Suite – virtually identical

Lower GRV; basalt, flow banding, volcanicalstic units

Eucarro Ryholite, Upper GRV

GawlerCraton

Curnamona Province

Basement

Cover Cover

1630 – 1590 Ma

Olarian Orogeny:

• Early HT-LP metamorphism & subsequent

compression

• Deformation and metamorphism in parts of

Gawler Craton

Upright late folding, Olary

High T metamorphism, Coober Pedy Ridge, Gawler Craton.

950 °C, 6.5 kbar

Cutts et al. 2011

UPPER CRUST

Decreasing metamorphic grade

Olarian Orogeny:

• Spatial arrangement of higher metamorphic grade exhumed at margins of Gawler Craton and Curnamona Province

• Upper crust preserved in central Gawler Craton…

• …where most of the mineral deposits are, including the hematite IOCG systems

• Main stratigraphic units relevant to IOCG systems in South Australia

• Interpretations of tectonic setting for IOCG systems

Early model – plume-related magmatism1993, Bulletin 54, Geological Survey of South Australia

Geodynamic setting for IOCG deposits: Skirrow et al., 2019 Ore Geology Reviews

Key points

• IOCG systems associated with c. 1590 Ma large igneous province and major

tectonometamorphic event: active tectonic setting

• Pre- c. 1590 Ma crust included low metamorphic grade sequences in the

eastern Gawler Craton and Curnamona Province – regions with most IOCG

deposits

• Gawler Craton mantle shows multiple stages of enrichment/metasomatism

including in Archean

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