1. Bruce Mowat & Stuart Smith
Characteristics of Porphyry Cu-Au Systems in the Ordovician Macquarie Arc of NSW
Bruce Mowat & Stuart Smith

2. Outline
Introduction
History of exploration and research
Distribution of systems
Review key geological aspects of the major deposits
Characteristics of the Temora porphyry systems
Future challenges of exploration
Introduction
History

3. History
1976 Geopeko/North identifies porphyry style Cu-Au in the Goonumbla area
Initial Research, (Paul Heithersay, John Walshe)
AGSO, NSW DMR (Doon Wyborn)
Newcrest identify Cadia Hill porphyry system
AMIRA P425 (Gregg Morrison, Phil Blevin)
SPIRT (Dave Cooke, Tony Crawford, Dick Glen)
Ongoing research by Newcrest team

4. Macquarie Arc Macquarie Arc is a component of the Lachlan Orogen
Sydney
Melbourne
Macquarie Arc is a component of the Lachlan Orogen
Ordovician to early Silurian Volcanic Province

5. Macquarie Arc Four Separate Belts Junee-Narromine (JNVB) Molong (MVB)
Rockley-Gulgong (RGVB)
Kiandra (KVB)
JNVB
MVB
RGVB
KVB

6. Distribution of Systems
24 porphyry systems
Most (22) occur within definable districts
17 including all operations within Cadia and Northparkes
Districts defined by coherent geological character
Clustered
Northparkes District
Cowal District
Cadia District
Rain Hill District

7. Temporal Distribution
Macquarie Arc – Summary Time-Space Plot
Northparkes District
Cadia
Lake Cowal
Copper Hill
Cargo

8. Macquarie arc - Australia's only economic porphyry province

9. Key Features of the Districts
Higher proportion of intrusive rocks
More complex (but not unique) magnetic signatures - most related to intrusive activity
Gravity lows
Overall more felsic
Overall more potassic

10. Age of the Systems 455 Ma 440 Ma E43, Cargo, Copper Hill,
Low K, dacite association
adakites
440 Ma
Cadia District, Northparkes, Rain Hill
Medium to High K, monzonite association

11. LFB Late intrusive shoshonites (monz) 440
Evolved shoshonitic lavas suites
Copper Hill-type adakitic dacite-gdt suites
450
Middle Ord high-K to (higher) shoshonitic lavas
Narromine and Cowal Middle Ord Intrusive Monzodiorites etc (hi-K CA)
465
480
Nelungaloo Volcs and Mitchell Fmn- - Hi-K calc-alk and shoshonitic

12. Igneous Character
Macquarie Arc dominated by basalts and andesite compositions
Productive districts tend to be more felsic on average
E43, Cargo and Copper Hill low-K Calc-alkaline
Dacite porphyry association (adakites)
Rain Hill District medium to high-K Calc-alkaline
Cadia and Northparkes districts are high-K to shoshonitic in character, the most potassic regions in the arc
Monzonite, syenite, latite, trachyte

13. Alteration Core: Distal: Late faults:
potassic (biotite-mt; orthoclase-qtz-sulphide-hematite)
calc-sodic (act-mt-ab)
Phyllosilicate (sericite, hm, ab)
Distal:
propylitic (chl-carb-epi-ab-hm)
sodic (ab-chl-tm)
Phyllosilicate (sericite, albite)
Late faults:
phyllic (QSP-carbonate-base metals)
Distinctive pink rock hematite alt of intrusions & volcanics

14. Schematic Intrusives - Alteration - Mineralisation
GOONUMBLA
Schematic Intrusives -
Alteration - Mineralisation
G Morrison & P Blevin 3/96 Ap
MZp
MMZa
MMZp
ALTERATION
MMZm
MMZp
K Feldspar-quartz
K Feldspar destructive
MZD
Sericitic
MMZc
Kf network +
biotite spots
MMZp
MMZc DI
MMZa
MZD
GRp

15. Northparkes potassic alteration

16. Northparkes Potassic Alt

17. Sericite Albite Alteration
Cadia East, Ridgeway, E26, E48 have sericite and/or albite bearing zones
These can be
Central and directly associated with ore
Proximal and directly associated with ore
Peripheral and not associated with ore
Minor associated with narrow fault zones
Distinguishing these is critical but can be very difficult

18. Cadia East Extensive alb-ser-tour-py-hem zone
Above and peripheral to orebody
Obscures outcrop of the orebody
After Tedder et al., 2001

19. Albite Sericite Tourmaline Alt

20. E26 Widespread and generally high level qtz-ser-py-alb Highly bleached
Unaltered or Propylitic
Qtz-ser-py-alb
Weak K-fs
Strong K-fs
Weak mt-bi
Strong mt-bi

21. Central Sericite Alteration
E26 & E48 both have a core zone of magmatically derived sericite +/-albite, alunite
Associated directly with bornite, chalcocite, covellite, digenite, tennantite, enargite
Generally > 2%Cu

22. E48 Proximal He-Se-Carb

23. Propylitic Alteration
One of the greatest unknowns in Macquarie Arc porphyries
Cadia has both distal and proximal
Northparkes, possibly has distal
Strong and very widespread regional assemblage that is definitely unrelated to mineralisation
Use with extreme caution

24. Propylitic Alteration
Ridgeway
Cadia East
200m
Potassic
Calc-Potassic
Inner Propylitic
Outer Propylitic
Garnet-silica
Albite-pyrite
After Tedder et al., 2001
After Wilson et al., 2003

25. eg. Cadia East
Extensive alb-ser-
tour-py alteration

26. Regional vs Distal Porphyry
Some clues - but a lot more work needed
Fracture control
Overlap with most distal magnetite-biotite
Any low level Cu
Prehnite/actinolite
Distal Porphyry ep-chl-preh
Regional ep-chl-calc

27. Fe-Oxide Distribution

28. Magnetite Distribution
Magnetics is the second most common targeting tool (behind simple Cu & Au geochemistry)
How well do we understand the controls on magnetite distribution and therefore the types of signatures to expect
What are the controls
Primary magnetite
Magnetite constructive alteration
Magnetite destructive alteration

29. Alteration Magnetite Magnetite constructive alteration
Occurs in ALL systems, but location is not always the same
All Macquarie arc systems share an early mt alteration stage
Associated with early intrusions - can be widespread -several 100 m from intrusions
Distal magnetite-biotite

30. Magnetite & Alteration
Cadia systems
Ridgeway - direct association with ore
Ridgeway Cross Section
Contoured Magnetic Susceptibility values; 10-5SI
After Harper, 2000

31. Northparkes Fundamentally different character
In all known systems the ore-bearing stage overprints and destroys earlier magnetite constructive stage
Amount of early magnetite AND the degree of magnetite destruction is variable
Mt alteration is in part function of host rock composition
Intermediate hosts develop large mt halos
In felsic hosts low 1o Fe content results in lesser mt

32. Ore-stage Mt Destruction
Major ore stage is associated with intense K-feldspar alteration
This overprints and destroys much of the magnetite-biotite alteration

33. E26 - magnetite destructive K-feldspar
Weak
Remnant bi-mt alteration
Moderate
Intense

34. Magnetite and Ore Directly associated with Ore
Ridgeway
Magnetite destruction with Ore
E26
Felsic host less Mt
Northparkes
Mafic to intermediate host more Mt
Cadia Region

35. Metal Zoning
Cu-Au
Pipe-like systems (eg NPM, Ridgeway) show a strong zoning with Au increasing toward cores
Can be used as an exploration tool - slight systematic increase in Au:Cu should encourage further drilling

36. Metal Zoning Systems have traditional Cu, Zn zoning
From Heithersay & Walshe, 1995
Cu anomaly much larger than the systems
Lows within major ?peripheral Zn anomaly

37. Preservation Remarkably intact, little deformation Northparkes Cadia
Intrusives vertical, 30 degree dip volcanics
Cadia
Intrusives vertical, stratigraphy flat
Cowal
intact
Rain Hill
Devonian shear zone overprint

38. Temora Porphyry District
Goldminco Corporation holds majority of District
Junee-Narromine Volcanic Belt
6 identified systems so far
The Dam, Mandamah, Culingerai, Estoril, Harold Bell, Yiddah

39. Temora Geology

40. Temora Magnetics

41. Temora Porphyry Characteristics
Porphyry mineralisation clustered around margin of Rain Hill Monzodiorite
Similar setting to Northparkes
Medium to high-K calc-alkaline
Mineralisation associated with high level porphyritic monzodiorite dykes and plugs
435 Ma age on syn to post mineral dyke
Andesitic volcanics and volcaniclastics
No felsic volcanics
Qtz poor volcanics and intrusives

43. Temora Porphyry Mineralisation
Early classic qtz-mt-py-cpy seam veins
Late coarse qtz-carb-chl-cpy veins
Alteration
Core mt-hm-biot-chl±K-feldspar
Distal phyllic ab-ser-py
Late propylitic chl-ep-carb
Devonian ser-py shear overprint

44. Estoril porphyry Au-Cu system
Qz-mt-ksp-cpy veins
Chl-mt-bi alt volc
Qz-mt-cpy seam vein
Ep-chl overprinting
Early mt-ksp alt

45. Estoril porphyry Au-Cu system
Qz-mt-cpy veins in
Diorite host rock
Sheeted qz-mt-cpy veins
Andesite and MZDR
Intrusive host rock

46. Qz-mt-ksp-cpy veins
He-mt alt MZDR
Local intense He-mt
Alteration
MZDR

47. Similarities to other systems
Geological Setting
Similar to Northparkes setting
Age
Late Ordovician early Silurian
Similar alteration facies
Inner Potassic and overprinting phyllic
Igneous character
Oxidised High-K intrusives
Mineralisation
Qtz-mt-cpy seam veins
Alteration and ore stage mt

48. Differences to current economic systems
No Felsic rocks
Lack of the felsic suites (monz, trach, latite)
Limited hematite
Much less alteration hematite than Northparkes
Post mineral tectonics
Overprinted by Devonian shear zones

49. Future Exploration Ordovician Systems Other Ages
Current model prefers the current 4 productive districts (tightly held)
Under cover Narromine-Junee
Variations on current model (Less oxidised systems)
Other Ages
Siluro-Devonian Systems (Yeoval, Bald Hill, Vic, Bushranger)