The Golden Mile Deposit in Kalgoorlie, W Australia

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The Golden Mile Deposit in Kalgoorlie, W
Australia The Kalgoorlie gold field contains
structurally controlled, epigenetic gold deposits
hosted by mafic rocks in the Archean Yilgarn
craton of Western Australia. Its giant size has
prompted much interest in the processes that led
to its formation, particularly of the Golden Mile
mineralization, which hosts over 70 percent of
the gold in the Kalgoorlie gold field. Geology
Adjacent to the city of Kalgoorlie, the giant
Golden Mile deposit is located approximately
595km east of Perth, Western Australia. Gold was
first discovered in Kalgoorlie by Patrick Hannan
in 1893, with underground mining commencing
shortly after. Current gold production is managed
by Kalgoorlie Consolidated Gold Mines, a joint
venture between Normandy Mining Limited and
Homestake Gold of Australia Limited. For the
financial year ending June 30 1999, total gold
production from the Golden Mile "Superpit" was
586,918 ounces, with a head grade of 2.33 g/t.
The Golden Mile is Australias largest gold
producer, and has a proved and probable reserve
of 11.65 million Au ounces.
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Bamboo Creek
Wallaby
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Norseman- Wiluna Greenstone Belt
FIG. 1. Simplified geological map of Western
Australia showing greenstone belts and gold
deposits
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Stratigraphy The upper greenschist lower
amphibolite facies rocks of the Golden Mile
deposit are hosted by the Archean
granite-greenstone Yilgarn craton. Stratigraphy
at the Golden Mile consists of the Paringa Basalt
(26905 Ma), the Golden Mile Dolerite (26752
Ma), and the felsic volcaniclastic and
sedimentary Black Flag Beds (26805 Ma). Multiple
porphyries and lamprophyres have intruded the
greenstones and sediments at the Golden Mile. 
Gold mineralisation is dominantly hosted by the
Golden Mile Dolerite, a internally differentiated
tholeiitic sill, and the high MgO, Paringa
Basalt. Some porphyries are cut by mineralised
zones, however gold tenor is significantly lower
than the greenstones.
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Nth wall Horseshoe pit.  Golden Mile dolerite and
graphitic shale in the Black Flag Beds (BFB). 
The Golden Mile fault (GMF) is located on the
eastern contact of the Black Flag Beds and Golden
Mile dolerite.  An albite porphyry is present to
the east of the fault.  Oxidised stope backfill
is visible in the pit wall to the west of the
Black Flag Beds, indicating the location of
number Three Western lode.  Further west New lode
is cut by the Drysdale stockwork.
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Au Mineralisation Three styles of gold
mineralisation are present at the Golden Mile,
representing at least two gold mineralisation
events. Fimiston style shear zone hosted lode
deposits are economically the most important
source of gold at the Golden Mile. Gold occurs in
solid solution within fine disseminated pyrite,
as coarse "free" gold, and as telluride species
with Ag, Pb, Sb and Hg. Alteration minerals
associated with Fimiston lodes include,
quartz-pyrite-ankerite-sericite-albite-tourmaline.
 
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Highly sheared Fimiston style mineralisation with
abundant "free" gold, No 3 Western lode. Five
cent coin for scale.
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"Greenleader" mineralisation is characterised by
the presence of green vanadium muscovite, and
contains abundant "free" gold and tellurides. The
Oroya shoot is the best example of greenleader
mineralisation, producing 62t of gold.
Greenleader mineralisation, Oroya cutback -130m
level. Pen lid for scale.
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Quartz stockwork gold deposits are present within
and around the Golden mile, mostly confined to
unit 8 of the Golden Mile Dolerite due to
rheological and chemical controls. Stockwork
mineralisation clearly cuts Fimiston style lodes,
indicating that the stockwork deposits were
formed by a younger gold mineralisation event.
Stockwork vein mineral assemblages contain
quartz-albite and carbonates including scheelite.
Wall rock alteration includes pyrite-pyrrhotite-
ankerite-sericite-siderite. The Mt Charlotte
underground mine adjacent to the Golden Mile is
the only stockwork deposit currently in
operation.
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"Free" gold in a stockwork quartz vein. 
Fe-carbonate wall rock alternation.  Drysdale
stockwork, -160m level.  Pen for scale.
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Mining In 1903, 10 years after the discovery of
gold at Kalgoorlie peak annual production was
reached with 1 225 700 Oz (38.124 t) of gold
produced. Over 30 shafts were operating at this
time. In May 1989 Kalgoorlie Consolidated Gold
Mines was formed with the intention of operating
a large single "super" pit at the Golden Mile.
Mining contractors Roche Bros were hired for
earth moving and drill and blast operations. By
mid 1991 underground mining at the Golden Mile
had ceased due to the expanding Fimiston open
pit. At the time of closure, some of the shafts
had reached depths greater than 1,300m below
surface, and over 1181 t of gold had been
recovered. Chaffers shaft is still used as an
exploration platform for diamond drill hole
delineation of the ore body.
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TELLURIDE MINERALOGY OF THE GOLDEN MILE DEPOSIT,
KALGOORLIE, WESTERN AUSTRALIA The Golden Mile is
a giant orogenic lode gold deposit located within
the Norseman-Wiluna Belt in the Yilgarn Craton,
Western Australia. It is a unique deposit because
of its size (having produced greater than 1200
tonnes of Au) and in that telluride
mineralization is responsible for 15 to 20 of
gold production. Gold mineralization is hosted
primarily by Archean-aged dolerites and basalts
that have been metamorphosed to the greenschist
facies. This mineralization occurs within
hundreds of shear zones as auriferous and
telluride-bearing lodes, which have been
classified into three structural types based on
orientation (main (trending NNW), caunter
(trending NW) and cross lodes (trending NE)).
Three distinct styles of mineralization are
present within the area. The older Fimiston
(characterized by main, caunter and cross lodes)
and Oroya (vanadium and telluride rich cross
lodes) styles are overprinted by younger Mount
Charlotte (quartz vein stockwork) style
mineralization.
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Native tellurium and sixteen tellurides
(calaverite (AuTe2), krennerite ((Au,Ag)Te2),
sylvanite ((Ag,Au)Te4)), montbrayite
((Au,Sb)2Te3), petzite (Ag3AuTe2), coloradoite
(HgTe), hessite (Ag2Te), stuetzite (Ag5-xTe3),
altaite (PbTe), tellurantimony (Sb2Te3),
nagyagite (Au(Pb,Sb,Fe)8(S,Te)11), melonite
(NiTe2), weissite (Cu2-xTe), tetradymite
(Bi2Te2S), rickardite (Cu4Te3), and one poorly
identified gold-arsenic telluride occur in the
Golden Mile. Calaverite, petzite, coloradoite,
altaite, and native gold are commonly found
throughout the Golden Mile. Tellurantimony,
melonite, hessite, stuetzite, krennerite and
sylvanite are rarely found in the main and
caunter lodes. Additionally, hessite is found in
trace amounts in the cross lodes and montbrayite
is found in trace amounts in the main lodes.
Krennerite is restricted to the central part of
the deposit whereas montbrayite has been found
only along the margins of the Golden Mile. First
generation tellurides in the Fimiston and green
leader ores formed at logfTe2 -11.4 and logfS2
-12.6, approximately (assuming a T of ore
formation of 300oC). Ultimately the results
obtained from this study will be useful as
potential guides to ore on mine, local, and
regional scales.
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The Fimiston Open Pit, colloquially known as the
Super Pit, is Australia's largest open cut gold
mine. The Super Pit is located off the Goldfields
Highway on the south-east edge of
Kalgoorlie-Boulder, W Australia. Most of the
gold mined in the Super Pit occurs within ore
lodes formed by ancient shears in a rock unit
called the Golden Mile Dolerite. As a result, the
area is known as the Golden Mile even though the
lodes occur in an area over 2 km in width and 1
km in depth. This renowned Kalgoorlie-Boulder
land mark will eventually stretch 3.8 km long,
1.4 km wide and reach a depth over 500 m. Since
1893, when Irishman Paddy Hannan first made his
famous discovery, more than 50 million ounces
(1,550 t) of gold have been harvested from the
Golden Mile.
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Super Pit gold mine
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Originally consisting of a number of small
underground mines, consolidation into a single
open pit mine was attempted by Alan Bond, but he
was unable to complete the takeover. The Super
Pit was eventually created in 1989 by Kalgoorlie
Consolidated Gold Mines Pty Ltd, a joint venture
between Normandy Australia and Homestake Gold of
Australia Limited. As of 2005 Kalgoorlie
Consolidate Gold Mines Pty Ltd is owned by the
Australian subsidiaries of the Barrick Gold
Corporation and Newmont Mining Corporation and
produces up to 900,000 ounces (28 t) of gold
every year.
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The Age of the Giant Golden Mile Deposit,
Kalgoorlie Open-pit and underground mines in the
Golden Mile at Kalgoorlie, Western Australia,
have produced more than 1,475 metric tons (t) of
gold since 1893. Despite the economic importance
of the deposit, the age of the mineralized shear
zone array and its temporal relationship to other
structures and to porphyry intrusions in the host
greenstone terrane are poorly constrained. The
SHRIMP ion microprobe has been used to date
zircons and monazites recovered from a
chlorite-carbonatealtered, synmineralization
lamprophyre dike intruded into sericite-ankeritea
ltered Paringa basalt below the high-grade Oroya
hanging-wall shear zone. Analyses of
magmatic-hydrothermal zircons define a weighted
mean 207Pb/206Pb age of 2642 6 Ma (n 37, MSWD
0.88). Analyses of cogenetic hydrothermal
monazites yield a concordant 207Pb/206Pb age of
2637 20 Ma (n 9, MSWD 1.8).
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The world-class Wallaby gold deposit, Laverton,
Western Australia An orogenic-style overprint on
a magmatic-hydrothermal magnetite-calcite
alteration pipe Gold mineralisation at the
Wallaby gold deposit is hosted by a 1,200 m thick
mafic conglomerate. The conglomerate is intruded
by an apparently comagmatic alkaline dyke suite
displaying increasing fractionation through
mafic-monzonite, monzonite, syenite, syenite
porphyry to late-stage carbonatite. In the mine
area, a pipe-shaped zone of actinolite-magnetite-e
pidote-calcite (AMEC) alteration overprints the
conglomerate. Gold mineralisation, associated
with dolomite-albite-quartz-pyrite alteration, is
hosted in a series of sub-horizontal,
structurally controlled zones that are largely
confined within the magnetite-rich pipe. The
deposit has a current ore reserve of 2.0 Moz Au,
and a total resource of 7.1 Moz Au.
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TIMS UPb analysis of magmatic titanite and
SHRIMP UPb analysis of gold-related phosphate
minerals are used to constrain the timing of
magmatism and gold mineralisation at Wallaby.
Monzogranite and carbonatite dykes of the
Wallaby syenite intruded at 2,6643 Ma, at least
5 m.y. and probably 14 m.y. before gold
mineralisation at 2,6506 Ma. The significant
hiatus between proximal magmatism and gold
mineralisation suggests that gold-bearing fluids
were not derived from magmas associated with the
Wallaby syenite, particularly since intrusive
events are unlikely to drive hydrothermal systems
for more than 1 m.y.
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Analysis of the C and O isotopic compositions of
carbonates from regional pre-syenite alteration
and AMEC alteration at the Wallaby gold deposit
suggests that AMEC alteration formed via
interaction between magmatic fluids and the
pre-syenite wallrock carbonate. The C and O
isotopic composition of gold-bearing fluids, as
inferred from ore-carbonate, are isotopically
distinct from proximal magmatic fluids, as
inferred from magmatic carbonate in carbonatite
dykes. Thus, detailed isotopic and
geochronological studies negate any direct
genetic link between proximal magmatic activity
related to the Wallaby syenite and gold
mineralisation at Wallaby.
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The gold endowment of the Wallaby gold deposit,
combined with the relatively low solubility of
gold as thiosulfide complexes in low-salinity ore
fluids at temperatures of about 300C, implicates
the influx of very large volumes of auriferous
hydrothermal fluids. No large-scale shear-zones
nor faults through which such large fluid-volumes
could pass have been identified within the
immediate ore environment, so fluid influx most
probably occurred largely in a unit-confined,
brittle-ductile fracture system. This was the
500-m diameter AMEC alteration pipe, which was a
brittle, iron-enriched zone in an otherwise
massive conglomerate. During compressional
deformation, the competency contrast between
unaltered and AMEC-altered conglomerate created a
zone of increased fracture permeability, and
geochemically favourable conditions (high
Fe/FeMg ratio), for gold mineralisation from a
distal source.
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Oldest Gold Deformation and Hydrothermal
Alteration in the Early Archean Shear Zone-Hosted
Bamboo Creek Deposit, Pilbara, Western Australia
The Early Archean Bamboo Creek gold deposit
contrasts with most other orogenic deposits
because of its relatively early timing in the
tectonic evolution of the Pilbara
granitoid-greenstone terrane.
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Lead-lead model ages for galena, together with
the relationships between the Bamboo Creek shear
zone and dated granites, indicate a relatively
early age of gold deposition of ca. 3400 Ma.
Correlation of structures associated with gold
deposition and regional structural phases shows
that gold deposition was most likely related to
an extensional tectonic phase. The early timing
and association with extension is unlike the
tectonic setting of other Archean gold deposits,
which tend to form during the final,
compressional or strike-slip stages of
orogenesis. The Bamboo Creek gold mineralization
may have been related to an Early Archean lower
crustal delamination event. This may explain the
anomalous timing and the low gold endowment of
the Pilbara relative to Late Archean greenstones.
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The Bamboo Creek deposit is situated in a
bedding-parallel, brittle-ductile shear zone (the
Bamboo Creek shear zone) within a komatiite
sequence. The laminated quartz-carbonate gold
lodes occur in carbonate-altered boudins within
the Bamboo Creek shear zone and are associated
with early sinistral, northeast-up deformation in
the shear zone, whereas dextral reactivation of
the zone postdates gold deposition. Gold-related
alteration zones reflect an increase in XCO2
toward the mineralized zone. Variations in
original host-rock composition give rise to
asymmetric alteration zoning, with a
fuchsite-carbonate zone in the more Mg- and
Cr-rich cumulate-textured footwall and a
chlorite-quartz zone in the more aluminous
spinifex-textured hanging wall.
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The alteration envelope is enriched in Na2O, K2O,
Rb, Pb, As, and Sb. Whereas pyrite and minor
chalcopyrite occur in all alteration zones,
tetrahedrite, galena, and sphalerite are strongly
associated with gold in the lodes. The alteration
and metal enrichment of the Bamboo Creek gold
deposit are indistinguishable from those of other
orogenic (mesothermal) lode gold deposits in
Archean terranes. Carbonate 13C(PDB) and
18O(SMOW) isotope signatures are consistent
throughout the alteration envelope at 0.2 0.6
and 14.6 0.6 per mil, respectively. The 13C
value, in particular, is higher than typical
values for orogenic gold deposits, implying
interaction of auriferous fluids with preexisting
marine carbonates that formed during an early
sea-floor alteration event. The temperature of
deposition, estimated from chlorite thermometry
and alteration assemblages, is about 250C, which
is within the lower part of the range for
orogenic gold deposits.
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Supplement
Refractory gold ores in Archaean greenstones,
Western Australia mineralogy, gold paragenesis,
metallurgical characterization and classification
J. P. Vaughan and A. Kyin Western Australian
School of Mines, Curtin University of Technology,
Western Australia
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Norseman- Wiluna Greenstone Belt
FIG. 1. Simplified geological map of Western
Australia showing greenstone belts and gold
deposits
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FIG. 2. Processing subdivision of Archaean gold
ores
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FIG. 3. As content of gold ores plotted against
gold recovery.
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FIG. 4. Bands of fine-grained rhomb-shaped
arsenopyrite (asp) cutting coarser-grained pyrite
(py), Lancefield ore. Reflected light (x100).
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FIG. 5. Native gold in arsenopyrite
microfracture, Paddington ore. Width of gold is
1 µm. Reflected light (x500).
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FIG. 6. Co-existing pyrite (py), arsenopyrite
(asp) and pyrrhotite (po), Coolgardie ore.
Reflected light (x100).
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FIG. 7. Native gold in arsenopyrite (asp)
microfractures, Coolgardie ore. Adjacent
pyrrhotite (po) microfractures contain no gold.
Reflected light (x200).
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FIG. 8. Large arsenopyrite crystal containing
rounded inclusions of pyrrhotite (po) and pyrite
plus marcasite aggregates (py mc). Exhibition
deposit. Reflected light (x50).
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FIG. 9. Arsenopyrite crystal with deformed,
poikiloblastic core zone and clear rim
overgrowth. Exhibition deposit. Reflected light
(x50).
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FIG. 10. Detail of arsenopyrite crystal in Fig. 9
, showing inclusions of idioblastic metamorphic
silicates and chalcopyrite (cp), and rounded gold
grains (Au). Exhibition deposit. Reflected light
(x200).
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FIG. 11. SIMS images of pyrite crystal, Wiluna
gold deposit, Western Australia. (a) As
distribution, concentrated in rim zone. (b)
Submicroscopic Au distribution, concentrated in
similar, but not exactly the same, rim zone as
arsenic.
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FIG. 12. SIMS image of submicroscopic Au
distribution, arsenopyrite crystal, Wiluna
deposit, Western Australia. Gold is concentrated
in rim zone.
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FIG. 13. Arsenopyrite compositions.
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Rock-Buffering of Auriferous Fluids in Altered
Rocks Associated with the Golden Mile-Style
Mineralization, Kalgoorlie Gold Field, Western
Australia It is generally agreed that the
widespread presence of hematite and the
moderately negative sulfur isotope composition of
some of the pyrite (34S of 10 to 2) in the
Golden Mile lodes and associated alteration
indicate the presence of a relatively oxidizing
(SO2 4 HS H2S, with hematite stable)
fluid during gold deposition and wall-rock
alteration, but the origin and evolution of this
fluid are not well constrained. A piece of
evidence that has not been fully integrated into
interpretations is the low variance of mineral
assemblages in the alteration haloes of the
Golden Mile lodes (e.g., coexisting
magnetite-hematite-siderite-pyrite-ankerite-albite
-muscovite-ilmenite rutile-quartz chlorite).
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Thermodynamic modeling, using HCh and a
purpose-built code that facilitates investigation
of systems that involve complex mineral solid
solutions, CO2-rich fluids, and open-system
chemical behavior was used to investigate the
constraints that the low variance assemblages
place on the source and evolution of mineralizing
fluids. Results of the modeling show that
fluid-rock reaction with decreasing temperature
can drive pyrrhotite-magnetite assemblages, in
equilibrium with a fluid that contains aqueous
sulfide, to hematite-pyrite-magnetite assemblages
in equilibrium with a fluid that contains aqueous
sulfate. This modeled shift arises from
cooling-driven oxidation of sulfides and reduced
sulfur-bearing aqueous species by ferric iron in
magnetite and formation of hematite and siderite
from magnetite and CO2 there is no requirement
for electron acceptors other than those provided
by the rock.
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The implication of the model results for the
Golden Mile mineralization is that hematite
growth and sulfate-bearing fluids could have
resulted from fluid-wall rock interaction without
involvement of an externally derived oxidizing
fluid. The change from aqueous-sulfide dominated
to aqueous-sulfaterich solutions would
destabilize gold sulfide complexes in solution
and lead to gold precipitation. Formation of
aqueous sulfate species would also result in the
precipitation of pyrite with negative 34S. Mass
balance calculations show that production of
hematite in the carbonate zone of the Golden Mile
mineralization could have occurred without any
requirement for addition of fluid-derived
electron acceptors although open-system behavior
is not precluded. Overall, the characteristics of
the carbonate zone alteration are consistent with
electron redistribution caused by interaction
between a reduced auriferous fluid and the host
dolerite.
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