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Characteristics of Porphyry Cu-Au Systems in NSW Macquarie Arc

Explore the history, distribution, geological aspects, and future challenges of porphyry systems in the Ordovician Macquarie Arc of NSW. Learn about key features, age, Igneous character, alteration types, and mineralization patterns in this economically significant region.

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Characteristics of Porphyry Cu-Au Systems in NSW Macquarie Arc

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  1. 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

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

  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 • 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: • 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. GOONUMBLA Schematic Intrusives - Alteration - Mineralisation G Morrison & P Blevin 3/96 Ap MZp MMZa MMZp ALTERATION MMZm MMZp K Feldspar-quartz MZD K Feldspar destructive MMZc Sericitic 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. Outer Propylitic Inner Propylitic Albite-pyrite Potassic Calc-Potassic Garnet-silica Propylitic Alteration Ridgeway Cadia East 200m 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-OxideDistribution

  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 • E26 • 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 • 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. TemoraGeology

  40. TemoraMagnetics

  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

  42. Temora Porphyry Mineralisation • 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

  43. 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

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

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

  46. 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

  47. 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

  48. Future Exploration • Ordovician Systems • 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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