The greenfield Grapple and Bumblebee discoveries of the western Aileron Province: First constraints on sulfide mineralising processes

Matt McGloin1, Barry L Reno1, Natalie Kositcin2, Simon Cornwell3, Doug Winzar3, Eloise E Beyer1, David Huston2, David Champion2

and Anthony Crawford41NTGS, 2Geoscience Australia, 3Independence Group, 4A&A Crawford Geological Consultants

NTGS Aileron Province Copper StudyProject under the CORE initiative to study the temporal and genetic relationship between the copper-endowed mineral systems in the Aileron Province

Grapple & Bumblebee

Aileron Province

after McGloin et al (2016) AGES Abstract

WA

QLD

Aileron Province (simplified):• Sedimentary rocks with maximum depositional ages between ca 1.86 and 1.79 Ga• Extensive magmatism and metamorphism between ca 1.82 and 1.69 Ga• Localised magmatism in the southeast during the ca 1.64–1.63 Ga Liebig Orogeny• Periodic localised metamorphism and deformation until ca 1.56 Ga, and during

younger events including the Alice Springs Orogeny and Larapinta Event

Aileron Province

Amadeus Basin

Warumpi Province (simplified):• Bound to the Aileron Province by the Central Australian Suture• Metasedimentary successions at ca 1.66–1.64 Ga and 1.64–1.60 Ga• Magmatic rocks at ca 1.68–1.66 Ga, 1.64–1.63 Ga, and 1.61–1.60 Ga• Extensive magmatism associated with the Liebig Orogeny at ca 1.64 Ga.

Aileron Province

Amadeus Basin

BumblebeeGrapple

Aileron Province

Warumpi Province

Independence Group’s Lake Mackay ProjectGreenfields polymetallic sulfide mineralisation (Cu-Zn-Au-Ag-Pb)

Central Australian Suture

after Winzar (2016) AGES Abstract

BumblebeeGrapple

Aileron Province

Warumpi Province

Lander Rock Formation

Andrew Young Igneous Complex

Lander Rock Formation

NyirripiBeds

Du Faur Suiteafter Meixner et al (2004) Mount Rennie, interpreted geology

Du FaurSuite

10 km

Independence Group’s Lake Mackay Project

• Metasedimentary host rock (Lander Rock Formation)

Independence Group’s Lake Mackay Project

• Intruded by mafic igneous rocks

Independence Group’s Lake Mackay Project

• Mineralisation occurs mainly in layered brecciated lenses in the Lander Rock Formation between two large mafic sills

Mineralisation at Grapple and Bumblebee

Net-textured pyrrhotite within S2 fabric in the Lander Rock Formation – interpreted as metamorphosed diagenetic pyrite

Chalcopyrite–pyrite-bearing quartz vein that cross cuts a foliated amphibole–quartz mafic rock

5 mm 2 cm

Galena

Amphibole

Quartz

Chalcopyrite

PyrrhotitePyrrhotite

Hornblende

Arsenopyrite within a pyrrhotite breccia. The brecciaengulfs clasts of altered country rock.

Sulfide stringers overprinting mafic rock with a amphibole–quartz–clinopyroxene–carbonate assemblage. Garnet is common, but not shown in this photomicrograph.

Mineralisation at Grapple and Bumblebee

1 cm 2 mm

Pyrrhotite Arsenopyrite

Amphibole Chalcopyrite Clinopyroxene Carbonate

Sulfide

Amphibole–Quartz

Commonly: Pyrrhotite (dominant), chalcopyrite, sphalerite, arsenopyrite, pyrite, galena

Pyrrhotite breccia mineralogy

Arsenopyrite within a pyrrhotite breccia. Intergrowths within the arsenopyrite grains.

Pyrrhotite

Arsenopyrite GalenaChalcopyrite

Sphalerite

Löllingite Pyrrhotite Chalcopyrite

Arsenopyrite500 μm 100 μm

Sulfide mineralisation

Lander Rock Formation

Brecciated Lander Rock Formation hosting the sulfide mineralisation

Two possible explanations:• Durchbewegung texture• Intrusion-related

Lander Rock Formation – Timing of deposition

U–Pb SHRIMPMaximum Depositional Age

ca 1855 Ma

• Regionally, maximum depositional ages span the range ca 1.87 – 1.84 Ga and earliest metamorphism recorded at ca 1.81 Ga.

• The maximum depositional age provides a maximum constraint on timing of mineralisation.

Mineralisation is hosted within the Lander Rock Formation

Direct dating of mineralisation

• Re–Os age of ca 1.96 Ga of arsenopyriteyielded ages that were older than the timing of maximum deposition of the host ca 1.84–1.81 Ga Lander Rock Formation.

• Pb model ages of ca 1.84–1.83 Ga were obtained for sulfides within the breccias at Grapple – this is a plausible deposition age

• Pb model ages support possibility that sulfide mineralisation formed syn-genetically.

• No rocks at Grapple or Bumblebee are currently interpreted as metaexhalites or metavolcanics.

Löllingite

Pyrrhotite

Chalcopyrite

Arsenopyrite100 μm

Mafic rock intruding the Lander Rock Formation• Spatially associated with sulfide mineralisation• Interpreted to intrude the Lander Rock Formation

1600

1800

2000

2200

2400

2600

0.08

0.10

0.12

0.14

0.16

0.18

1.8 2.2 2.6 3.0 3.4 3.8

207 P

b/20

6 Pb

238U/206Pb

unnamed amphiboliteGA 2704878all data, n = 11

• Main population at ca 1867 Ma is older than the host Lander Rock Formation (Max dep ca 1855 Ma)

• Single analysis at 1629 ± 21 Ma

Lander Rock Formation – Timing of deformation

Monazite that overprints mylonite fabric has age of 1668 ± 7 Ma.

Abundant monazite overprints the main S2 fabric, and has an internal microstructure consistent with hydrothermal dissolution–reprecipitation

Figures after Reno et al (2018) NTGS Record 2018-013

AndalusiteBiotite

Muscovite

Monazite

10 μm

5 mm

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1.5 2.5 3.5 4.5

207 P

b/20

6 Pb

238U/206Pb

data-point error ellipses are 68.3% conf.

0.06

0.10

0.14

0.18

0.22

0.26

1 3 5 7 9 11

207 P

b/20

6 Pb

238U/206Pb

data-point error crosses are 1σ

Intercept1635 ± 12 Ma

Intercept1627 ± 31 Ma

Mafic rock – early phase pre-dating main S2 fabric

Zircon in the mafic rocks show evidence for disturbance at ca 1.64–1.63 Ga

Mafic rock – late phase cross-cutting main S2 fabric

0.08

0.10

0.12

0.14

0.16

0.18

1.8 2.2 2.6 3.0 3.4 3.8 4.2

207 P

b/20

6 Pb

238U/206Pb

data-point error crosses are 1σ

Lander Rock Formation

Mafic intrusive rock

Intercept1634 ± 30 Ma

• Intrudes deformed Lander Rock Formation

• Show evidence for disturbance at ca 1.64–1.63 Ga

• Host Lander Rock Formation was deposited after ca 1.84 but prior to ca 1.81 Ga.

• Sulfides in the breccia have Pb isotope model age of ca 1.84–1.83 Ga

• At least two phases of mafic rock; one phase intruded pre-deformation, and a second phase intruded between ca 1.67 Ga and 1.64 Ga.

• Lander Rock Formation was deformed at or before ca 1.67 Ga.

• The breccia that hosts the sulfide mineralisation was apparently brecciated post-deformation, after ca 1.67 Ga. This breccia hosts sulfide mineralisation.

• Extensive magmatism and associated fluid influx at ca 1.64 Ga.

Timing of sulfide mineralisation

Model 1: Syn-depositional• Volcanic or sediment-hosted massive sulfide

mineralisation formed syngenetically at ca 1.84 Ga.

• Sulfide mineralisation was deformed or remobilised after ca 1.67 Ga.

• No rocks at the prospects are currently interpreted as metavolcanics or metaexhalites.

Model 2: Epigenetic (intrusion related)• The host-breccia cross-cuts the fabric of the

Lander Rock Formation, suggesting this brecciation occurred after ca 1.67 Ga.

• Breccia formation and mineralisation has a magmatic-hydrothermal origin associated with regional ca 1.64 Ga magmatism.

Timing of sulfide mineralisation