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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

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 ► Ordovician to early Silurian Volcanic Province

Melbourne Sydney

► ► ► ► ► Four Separate Belts Junee Narromine (JNVB) Molong (MVB) Rockley Gulgong (RGVB) Kiandra (KVB)

Macquarie Arc

JNVB

-3 2 °

Narromine

MVB

 -3 4 ° 

Temora

Parkes

RGVB

Orange

KVB

0 km 100

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 -3 2 ° -3 4 °

Narromine

 Northparkes District

Orange

Cowal District   Cadia District

Parkes

Temora

 Rain Hill District

0 km 100

Temporal Distribution

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

► 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    E43, Cargo, Copper Hill, Low K, dacite association adakites ► 440 Ma   Cadia District, Northparkes, Rain Hill Medium to High K, monzonite association

440

LFB

450 465 480

Late intrusive shoshonites (monz) Evolved shoshonitic lavas suites Copper Hill-type adakitic dacite-gdt suites Middle Ord high-K to (higher) shoshonitic lavas Narromine and Cowal Middle Ord Intrusive Monzodiorites etc (hi-K CA) 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:  potassic (biotite-mt; orthoclase-qtz-sulphide-hematite)   Distal:  propylitic (chl-carb-epi-ab-hm)   calc-sodic (act-mt-ab) Phyllosilicate (sericite, hm, ab) sodic (ab-chl-tm) Phyllosilicate (sericite, albite) Late faults:  phyllic (QSP-carbonate-base metals) Distinctive pink rock hematite alt of intrusions & volcanics

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

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

500m

Reg Prop Skarn Skarn Prop Alb-ser Alb-qz-hem Calc-sodic Inner Prop Outer calc-pot Inner calc-pot

Albite Sericite Tourmaline Alt

► Widespread and generally high level qtz-ser-py-alb ► Highly bleached

E26

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 Outer Propylitic Inner Propylitic Albite-pyrite Potassic Calc-Potassic Garnet-silica

After Wilson et al., 2003

200m

After Tedder et al., 2001

500m

Reg Prop Skarn Skarn Prop Alb-ser Alb-qz-hem Calc-sodic Inner Prop Outer calc-pot Inner calc-pot

► eg. Cadia East

Extensive alb-ser tour-py alteration

500m

Reg Prop Skarn Skarn Prop Alb-ser Alb-qz-hem Calc-sodic Inner Prop Outer calc-pot Inner calc-pot

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 -5 SI

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

magnetite destruction is variable the degree of ► Mt alteration is in part function of host rock composition ► Intermediate hosts develop large mt halos ► In felsic hosts low 1 o Fe content results in lesser mt

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

► 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  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

Belimebung Volcanics Boonabah Volcanics Currumburrama Volcanics

Temora Magnetics

Gidginbung Volcanics Rain Hill Monzodiorite Gidginbung 0 kilometres 5 10

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

► 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    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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