the greenfield grapple and bumblebee discoveries of the ... · bumblebee grapple. aileron province...
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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