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Bruce Mowat & Stuart Smith

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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)

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