Transcript ppt - Sydney Mineral Exploration Discussion Group

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
Sydney
Melbourne
► Four
149 °
147 °
Macquarie Arc
Separate
Belts
► JuneeNarromine
(JNVB)
► Molong (MVB)
► RockleyGulgong
(RGVB)
► Kiandra (KVB)
JNVB
MVB
-3 2 °
Narromine

RGVB
Orange


Parkes
-3 4 °

Sydney
Temora
100
0
KVB
km
24 porphyry
systems
► Most (22) occur
within definable
districts
► 17 including all
operations within
Cadia and
Northparkes
► Districts defined by
coherent geological
character
► Clustered
149 °
147 °
Distribution of Systems
►
-3 2 °
Narromine

Northparkes District
Orange
Cowal District


Cadia District
Parkes
-3 4 °

Temora
Sydney
Rain Hill District
100
0
km
Temporal Distribution
Northparkes District
Cadia
Lake Cowal
Copper Hill
Cargo
Macquarie Arc – Summary Time-Space Plot
► Macquarie
province
arc - Australia's only economic porphyry
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
LFB
440
Late intrusive shoshonites
(monz)
Evolved shoshonitic lavas suites
Copper Hill-type adakitic
dacite-gdt suites
450
465
480
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)
 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
volcanics
pink rock hematite alt of intrusions &
GOONUMBLA
Schematic Intrusives Alteration - Mineralisation
G Morrison & P Blevin 3/96
Ap
MZp
ALTERATION
MMZa
MMZm
MMZp
K Feldspar-quartz
MZD
K Feldspar destructive
MMZc
Sericitic
Kf network +
biotite spots
MMZp
MMZc
DI
MZD
MMZa
GRp
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-tourpy-hem zone
500m
 Above and peripheral to
orebody
 Obscures outcrop of the
orebody
Reg Prop
Skarn
Skarn Prop
Alb-ser
Alb-qz-hem
Calc-sodic
Inner Prop
Outer calc-pot
Inner calc-pot
After Tedder et al., 2001
Albite Sericite Tourmaline Alt
► 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
E26
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
500m
Reg Prop
Skarn
Skarn Prop
Alb-ser
200m
Alb-qz-hem
Calc-sodic
Inner Prop
Outer Propylitic
Inner Propylitic
Albite-pyrite
Potassic
Calc-Potassic
Garnet-silica
After Wilson et al., 2003
Outer calc-pot
Inner calc-pot
After Tedder et al., 2001
► eg.
Cadia East
500m
Reg Prop
Skarn
Skarn Prop
Alb-ser
Extensive alb-sertour-py alteration
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; 10-5SI
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
► 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
Boonabah
Volcanics
Belimebung
Volcanics
Gidginbung
Volcanics
Rain Hill
Monzodiorite

 Gidginbung
0
5
kilometres
10
Currumburrama
Volcanics
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
► 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)