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

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

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

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

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

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

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

Macquarie arc - Australia's only economic porphyry province

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

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

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

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

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

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

Northparkes potassic alteration

Northparkes Potassic Alt

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

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

Albite Sericite Tourmaline Alt

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

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

E48 Proximal He-Se-Carb

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

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

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

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

Fe-Oxide Distribution

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

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

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

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

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

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

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

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

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

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

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

Temora Geology

Temora Magnetics

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

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

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

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

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

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

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

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)