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

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Presentation on theme: "Characteristics of Porphyry Cu-Au Systems in the Ordovician Macquarie Arc of NSW Bruce Mowat & Stuart Smith."— Presentation transcript:

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

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

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

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

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

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

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

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

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

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

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

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

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

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

15 Northparkes potassic alteration

16 Northparkes Potassic Alt

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

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

19 Albite Sericite Tourmaline Alt

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

21 Central Sericite Alteration E26 & E48 both have a core zone of magmatically derived sericite +/-albite, alunite E26 & E48 both have a core zone of magmatically derived sericite +/-albite, alunite Associated directly with bornite, chalcocite, covellite, digenite, tennantite, enargite 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 One of the greatest unknowns in Macquarie Arc porphyries Cadia has both distal and proximal Cadia has both distal and proximal Northparkes, possibly has distal Northparkes, possibly has distal Strong and very widespread regional assemblage that is definitely unrelated to mineralisation Strong and very widespread regional assemblage that is definitely unrelated to mineralisation Use with extreme caution Use with extreme caution

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

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

26 Regional vs Distal Porphyry Some clues - but a lot more work needed Some clues - but a lot more work needed Fracture control Fracture control Overlap with most distal magnetite-biotite Overlap with most distal magnetite-biotite Any low level Cu Any low level Cu Prehnite/actinolite 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) 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 How well do we understand the controls on magnetite distribution and therefore the types of signatures to expect What are the controls What are the controls Primary magnetite Primary magnetite Magnetite constructive alteration Magnetite constructive alteration Magnetite destructive alteration Magnetite destructive alteration

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

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

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

32 Ore-stage Mt Destruction E26 E26 Major ore stage is associated with intense K-feldspar alteration Major ore stage is associated with intense K-feldspar alteration This overprints and destroys much of the magnetite-biotite alteration This overprints and destroys much of the magnetite-biotite alteration

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

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

35 Metal Zoning Cu-Au Cu-Au Pipe-like systems (eg NPM, Ridgeway) show a strong zoning with Au increasing toward cores 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 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 Systems have traditional Cu, Zn zoning Cu anomaly much larger than the systems Lows within major ?peripheral Zn anomaly From Heithersay & Walshe, 1995

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

38 Temora Porphyry District Goldminco Corporation holds majority of District Goldminco Corporation holds majority of District Junee-Narromine Volcanic Belt Junee-Narromine Volcanic Belt 6 identified systems so far 6 identified systems so far The Dam, Mandamah, Culingerai, Estoril, Harold Bell, Yiddah 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 Porphyry mineralisation clustered around margin of Rain Hill Monzodiorite Similar setting to Northparkes Similar setting to Northparkes Medium to high-K calc-alkaline Medium to high-K calc-alkaline Mineralisation associated with high level porphyritic monzodiorite dykes and plugs Mineralisation associated with high level porphyritic monzodiorite dykes and plugs 435 Ma age on syn to post mineral dyke 435 Ma age on syn to post mineral dyke Andesitic volcanics and volcaniclastics Andesitic volcanics and volcaniclastics No felsic volcanics No felsic volcanics Qtz poor volcanics and intrusives Qtz poor volcanics and intrusives

42

43 Temora Porphyry Mineralisation Mineralisation Mineralisation Early classic qtz-mt-py-cpy seam veins Early classic qtz-mt-py-cpy seam veins Late coarse qtz-carb-chl-cpy veins Late coarse qtz-carb-chl-cpy veins Alteration Alteration Core mt-hm-biot-chl±K-feldspar Core mt-hm-biot-chl±K-feldspar Distal phyllic ab-ser-py Distal phyllic ab-ser-py Late propylitic chl-ep-carb Late propylitic chl-ep-carb Devonian ser-py shear overprint 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 Geological Setting Similar to Northparkes setting Similar to Northparkes setting Age Age Late Ordovician early Silurian Late Ordovician early Silurian Similar alteration facies Similar alteration facies Inner Potassic and overprinting phyllic Inner Potassic and overprinting phyllic Igneous character Igneous character Oxidised High-K intrusives Oxidised High-K intrusives Mineralisation Mineralisation Qtz-mt-cpy seam veins Qtz-mt-cpy seam veins Alteration and ore stage mt Alteration and ore stage mt

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

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


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