Architectural controls on porphyry Au-Cu mineralization in the Cadia Valley, NSW

23 Pages·2010·1.84 MB·English

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CCaaddiiaa HHiillll,, DDeecceemmbbeerr 22000055
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CCaaddiiaa ddiissttrriicctt –– rreessoouurrcceess
CCaaddiiaa HHiillll,, NNoovveemmbbeerr 22000088
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Newcrest Mining Ltd 2009 Resources & Reserves Statement –August 2010
CCaaddiiaa ddiissttrriicctt –– ggeeoollooggyy
Tertiary
Basalt
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Middle Silurian
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Waugoola Group
Ordovician - Silurian
Cadia Intrusive
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Complex
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Ordovician
Forest Reefs Volcanics
CCCaaadddiiiaaa HHHiiillllll
Weemalla Formation
CCCaaadddiiiaaa EEEaaasssttt
NNeeww SSoouutthh WWaalleess
NN MMiinnee NN CCaaddiiaa
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Evolving low-relief, multiple vent
volcanic complex developed
across an area of active marine
sedimentation
• Vents comprised mafic to intermediate lava flows, cryptodomes,
dykes and sills
• Stacked lava sequences, including hyaloclastites, massive lavas
and their reworked equivalents, are up to 1 km thick
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• The volcaniclastic units contain rare mid-
t
s
e
Darriwilian (Da2-3) to late Gisbornian (Gi2)
r
o
graptolites (reworked?) F
• There are also conodonts, brachiopods,
fragmentary coral and trilobites
• Detrital zircons from the Weemalla Fm have U-
Pb ages ~454 Ma
m
• Faunal ages that are diagnostically Eastonian
F
(Ea3 – ca. 452 Ma) have been recognized in the a
l
l
a
upper parts of the FRV
m
e
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W
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22400mE 22800mE 23200mE
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mmiinneerraalliissaattiioonn
• Mineralisation and
alteration was centred on
monzonite pipes at
Ridgeway, and dykes at
Cadia East
• Mineralisation occurred
Ridgeway
within larger monzonite
Intrusive
plutons at Cadia Hill and
Complex
Cadia Quarry
• Quartz – sulfide –
carbonate veins are the >0.2 g/t Au
Weemalla
predominant
Formation
mineralisation style
>1.5 g/t Au
(sheeted and stockwork)
Ridgeway Section 11050E -unpubl. Cuison(2010)
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6000 RL
Tertiary basalt Waugoola Group
Upper FRV
Lower FRV 5000 RL
Weemalla Cadia
Formation Intrusive
Complex
4000 RL
• The Cadia district has been dismembered by steeply-dipping
faults, some with offsets of 100s of metres…
• This has juxtaposed different levels of the magmatic-
hydrothermal system, and disrupted the cover sequence
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EE WW
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• Deformed Silurian sub-basins cover the dismembered Cadia Hill deposit
• Scale of thrust-related movement differs between the basement
and cover rocks
Washburn (2008)
CCaaddiiaa EEaasstt
–– aa 3333 MMoozz ggoolldd rreessoouurrccee
• Largest known gold deposit
CCaaddiiaa in eastern Australia
LLiittttllee
HHiillll
CCaaddiiaa
• World’s sixth largest
CCaaddiiaa
porphyry deposit in terms of
EEaasstt
contained Au
• Total resources of 2.3 billion
tonnes at 0.44 g/t Au and
0.28 % Cu
• Contains more than 70% of
the Cadia district Au
resource
• Mineralised zone ~2 km long, 600 m wide and >1500 m in
vertical extent
• Significant variations in mineralisation and alteration styles with
depth
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CCaaddiiaa EEaasstt –– GGeeoollooggyy
Host rocks:
21,000 m N 21,500 m N 22,000 m N 22,500 m N
• Polymict volcanic conglomerates
and intermediate to basic lavas
6,000 m
and associated autobreccia RL
Pre-mineralisation intrusions:
• Basaltic-andesite dikes and sills
5,500 m
RL
Mineralising intrusions:
• Early Silurian (c. 437 Ma) alkalic
monzonite – monzodiorite dikes 5,000 m
RL
surrounded by concentric zones of
mineralisation and alteration
Styles of mineralisation:
4,500 m
RL
• Deep-level W-NW- trending sheeted
quartz-sulphide vein array
• Shallow level, disseminated stratabound
orezone
CadiaEast section 15220mE; Fox et al., 2009