NEWGEN21-Proceedings-Full

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Better data lead to a
big understanding advance




Images: Geoscience Australia


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Cayley & Musgrave, in prep.


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Bootheragandra – Kancoona – Kiewa Fault









































Ross Cayley (GSV) & Robert Musgrave (GSNSW) in prep.


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WOMBAT passive seismic

experiment:

time arrival residuals
(Rawlinson, et al, GR, 2011)










The Bootheragandra Fault:




subvertical



trans-lithospheric (~200km)








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Gray & Foster, 2000




















This strike slip fault is

big enough to explain the

bits of Victorian geology
that don’t make sense

in their current positions..















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Convergent margin key elements and systematics
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Distal back-arc: Magmatic arc: Accretionary wedge: cold, inherent
transition to hot, igneous-dominated strong syn-
intraplate sedimentary shortening
Back-arc basin: deformation, amagmatic

hot, syn-sediment (thickening crust)
magmatism, extension Intraplate: cold,

weak/strong deformation undeformed,
amagmatic































(Stern, 2002)






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Tectonic affinity matrix






















(eg. Greenfield et al., 2011)






























(eg. Reed, 2001)



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arc
distal
back-arc
intraplate

accretionary

















Benchmarking



against modern



systems


















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Matrix rules out ocean-dipping

subduction for the Macquarie Arc

system in the Ordovician






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Complex in Victoria,

with local geometry swaps





























Juxtaposition not

observed in
active systems








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Cayley & Musgrave, in prep.



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Eastern Australian


Tasmanides geology…






…all screwed up….


























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…not like a ‘textbook’



accretionary system..…









‘textbook’ accretionary systems

are often depicted in

‘pseudo-3D’ – which is
2D projected to distance.




Any cross-section through it

will look the same……




























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Analogue modelling…













Early Palaeozoic east-Australia

as a rock ‘warehouse’……



lots of familiar stores,

but pretty messy…..



bits and pieces piled up

all over the place…




…hard to understand….


















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…not like the ‘textbook’ OFFICIAL



warehouse..…

























































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The difference?……









































Appreciation of the huge potential of small colliders introduced into
large, organised, but gravitationally meta-stable system

to trigger a cascade……and the rapid rate of that change…










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The Lachlan Fold Belt

has a potential ‘collider’:

the Selwyn Block:



































Micro-

continent


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Geodynamics of congested subduction zones




Model run time = 60 Million years


Continent Ocean plate
























Possible source of gold:




Cambrian metavolcanics like those exposed
in the Moornambool Metamorphic Complex,

in the Avoca Fault, in the Heathcote Fault Zone and,

farther east, in the Governor Fault Zone








Moresi, Betts, Miller, Cayley, 2014: NATURE NewGenGold Conference 2021 102
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Geodynamics of congested subduction zones





Rifting / basins























Possible source of gold:



Cambrian metavolcanics like those exposed

in the Moornambool Metamorphic Complex,

in the Avoca Fault, in the Heathcote Fault Zone and,
farther east, in the Governor Fault Zone











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H-BZ






















Cayley & Musgrave,

in prep. Possible arc rocks



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Models that suggest strike-slip repetition of

Macquarie Arc segments:















































Packham, 1987 (AGU Geodynamics Series 19); Fergusson, 2009 (AJES)




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New ideas for LFB geodynamics…











Recognition of the critical role of roll-back

in LFB evolution….



Tectonic switching and roll-back in the LFB



Collins, 2002 (Geology)











Extension and the tripartite association:




S-type granites, arcs and back-arc basins



Collins and Richards, 2008 (Geology)










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Models that link extension to sedimentation

in the Lachlan Fold Belt:

























Bindian Orogeny:

extension and translation



Fergusson, 2010: AJES:

Benambran Orogeny:

Lachlan Fold Belt sedimentation: accretion, uplift



Late Silurian-Middle Devonian
plate-driven extension and convergence








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Moresi, Betts, Miller

& Cayley 2014,
NATURE.




Cayley & Musgrave,

in review


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Moresi, Betts, Miller

& Cayley 2014,
NATURE.




Cayley & Musgrave,

in review


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Moresi, Betts, Miller

& Cayley 2014,
NATURE.




Cayley & Musgrave,

in review


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Moresi, Betts, Miller

& Cayley 2014,
NATURE.




Cayley & Musgrave,

in review


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Moresi, Betts, Miller

& Cayley 2014,
NATURE.




Cayley & Musgrave,

in review


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Moresi, Betts, Miller

& Cayley 2014,
NATURE.




Cayley & Musgrave,

in review


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Moresi, Betts, Miller

& Cayley 2014,
NATURE.




Cayley & Musgrave,

in review


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Moresi, Betts, Miller

& Cayley 2014,

NATURE.



Cayley et al., 2011,
Cayley 2011




Cayley & Musgrave,

in review



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continent collision
Moresi, Betts, Miller

NO Lachlan Fold Belt subduction!!! & Cayley 2014,

NATURE.



Cayley et al., 2011,
Cayley 2011




Cayley & Musgrave,

in review



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Moresi, Betts, Miller
& Cayley 2014,

NATURE.



Cayley & Musgrave,

in review



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Cayley & Musgrave,

in review


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E79 Resources 14 July 2021.



Drillhole HDV003 intersected:




11.10m @ 160 g/t Au, including:
0.6m @ 2430 g/t Au,

0.60m @ 147 g/t Au,

0.70m @ 99 g/t Au,



140m below historic workings.




4 other intersections >3g/t Au




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The Lachlan Orocline:



an alternative explanation of apparent

vergence reversals in Ordovician LFB:







































Cayley & Musgrave,

in review


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Parkes



Cadia


































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Parkes



Cadia Most of these potential

Macquarie Arc rocks

are hidden under cover




























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1. Base Metals 6. Gold-Base Metals
2. Nickel-PGE’s 7. Tin-Tantalum
3. Copper-Base Metals-Gold 8. Gold-Base Metals
4. Gold 9. Gold-Base Metals
5. Gold-Antinomy 10. Base Metals























The value add:





Mineral Systems map






– Key Commodities













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Talk outline






• Geological setting for Victorian orogenic gold




• Competing tectonic models for the Early Palaeozoic – confusing for gold explorers




• Structural / stratigraphic mapping + potential field geophysics: powerful

tools…

• …but Deep Seismic Reflection data drives systems-scale understanding



• Application to mineral systems models at crustal scale…



• Constrained retrodeformation scenarios – critical to take geological systems

analysis from crustal scale to lithospheric scale



• Towards a Unifying Theory for Eastern Australian Early Palaeozoic geology and
mineral systems




• Wrapping up






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Victorian gold: new opportunities





























































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Wrapping up…. OFFICIAL







• Data, technology, concept and confidence advance: a new dawn for Victorian orogenic gold
exploration…but the big practical lesson for success is: Drill, drill often, and drill DEEP.





• One virtually blind world-class discovery (Fosterville) has added ~12 m OZ+ to Victoria’s gold
inventory. How may others can there be? (the geology suggests several)





• The Stavely Arc – new opportunities for primary and epigenetic base metals + gold in a swath
of western Victoria, most undercover and untested. Hill 800 – ditto in the Selwyn Block in

Central Victoria.




• The Lachlan Orocline hypothesis: a constrained and testable tectonic concept for Early

Palaeozoic Australia – potentially explains the fully diversity of observed orogenic gold

and base/critical metal styles. Explains epic Bendigo Zone gold endowment + linkages




• Predictive capacity for the styles and locations of gold (and base/critical metals)

systems, including under cover – and more precompetitive research is underway!




• Victoria has crossed a threshold of data and understanding

. to what looks like sustained success
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New Constraints on the evolution of the



Paterson Orogen and basement to the




Canning Basin






Simon Johnson, Klaus Gessner, Paul Duuring, Peter



Haines, Lucy Brisbout and Huaiyu Yuan

‘The Gap’








• The Gap: remote desert country



• Hints of prospectivity



– geology mostly under cover

– a major geofrontier in mapping



• Drillcore and drill chips are the new

outcrop



• No boots-on-the-ground work in the


Paterson (drilling itself)





Government of Western Australia Department of Mines and Petroleum
Government of Western Australia Department of Mines and Petroleum

The Paterson Orogen







• Exploration is challenging



– geology is undercover, both regolith and sedimentary basin


• Recent discoveries at Winu → Havieron → Obelisk etc



– major Tier 1 sediment-hosted copper (+/- gold) province?



– alongside Telfer suggest more than one mineral system?


• Crustal architecture, stratigraphy and events critical for


understanding the mineral system(s)



• Petrophysics critical for connecting geology to geophysics




Government of Western Australia Department of Mines and Petroleum
Government of Western Australia Department of Mines and Petroleum

The Paterson Orogen - new datasets






• Regional stratigraphic setting (MRIWA M0521)


• Crustal architecture


– deep crustal seismic lines
– passive seismic data

– major crustal structures and isotopic maps


• Geochronology of rocks beneath the Canning Basin


• Rock petrophysics (not going to talk about these - eBookshop)


– improved 2D and 3D models

– which geophysical techniques are best for exploration


• Timing of mineralization at Obelisk Cu–Au deposit





Government of Western Australia Department of Mines and Petroleum
Government of Western Australia Department of Mines and Petroleum

Global context and stratigraphic setting

Sediment hosted deposits





A B

Canning

McR Yeneena

AB
MI B Pilbara

A






OD
BH











Hoggard et al. 2020 (Nature Geoscience)


Government of Western Australia Department of Mines and Petroleum
Government of Western Australia Department of Mines and Petroleum

The Paterson Orogen













































Government of Western Australia Department of Mines and Petroleum
Government of Western Australia Department of Mines and Petroleum