Australia
Boddington Gold Mine
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| Boddington Gold Mine |
Location: Boddington ,Western Australia.
Ore Type: Lode Deposits.
Products: Gold. Secondary Copper.
Owner: Newmont Mining.
Reserves: By the end of 2011,
proven ore reserves at Boddington were 20.3 million ounce (moz) of gold and
2.26 billion pounds (blbs) of copper.
Overview: Boddington Gold Mine
(BGM) is located about 130km south-east of Perth in Western Australia. The
largest gold mine in the country, it is poised to become the highest producing
mine once production ramps up over the next few years. The $2.4bn project was
initially a three-way joint venture between Newmont Mining, AngloGold Ashanti
and Newcrest Mining. In 2006 Newmont bought Newcrest's 22.22% share, bringing
its interest to 66.67% and ending any Australian ownership. AngloGold owned the
remaining 33.33%. In June 2009, Newmont became the sole owner of the mine by
acquiring the 33.3% interest of AngloGold. The original, mainly oxide open-pit
mine was closed at the end of 2001.
The project has an
attributable capital budget of between A$0.8bn and A$0.9bn. On 23 July 2009,
the project, including the construction of the treatment plant, was completed.
Production began in the third quarter of 2009. The first gold and copper concentrate
was produced in August 2009.
Approximately 100,000t
of ore was processed by mid-August. Gold production began on 30 September 2009.
By 19 November 2009, the mine achieved commercial production. The mine was
officially inaugurated in February 2010. The project had an attributable
capital budget of between A$0.8bn and A$0.9bn. It employs 900 workers.
Based on the current
plan, mine life is estimated to be more than 20 years, with attributable
life-of-mine gold production expected to be greater than 5.7Moz.
In May 2012, Newmont
decided to seek the expansion of mine life to 2052 by combining the north and
south Wandoo open pits. It also plans to expand the waste rock facility to two
billion metric tons.
Newmont and Anglo had
focused their exploration activities on the poorly explored areas of the
greenstone belt outside the already identified Boddington Expansion resource.
The exploration strategy was to identify the resource potential of the
remainder of the greenstone belt, with the emphasis on high-grade lode-type deposits.
Geological settings & Mineralization:
The Boddington gold
mine is hosted in Archean volcanic, volcaniclastic, and shallow-level intrusive
rocks that form the northern part of the Saddleback greenstone belt, a
fault-bounded sliver of greenstones located in the southwestern corner of the
Yilgarn craton, Western Australia. Total Au content of the Boddington gold mine
(past production plus in situ resource) exceeds 400 metric tons, making the
Boddington gold mine one of the largest Au mines currently operating in
Australia.Geologic mapping and radiometric dating indicate that five phases of
igneous activity occurred during development of the Saddleback greenstone belt.
Basaltic, intermediate, and minor felsic volcanism occurred between
approximately 2714 and 2696 Ma and again at approximately 2675 Ma. An older
suite of ultramafic dikes was emplaced between approximately 2696 and 2675 Ma
and a younger suite was emplaced between approximately 2675 and 2611 Ma.
Granitoid plutons crystallized at approximately 2611 Ma and cut all the other
Archean rocks in the Saddleback greenstone belt.Regional upper greenschist
facies metamorphism accompanied the earliest phase of ductile deformation (D 1
). Sericite-quartz + or - arsenopyrite-altered shear zones developed during
subsequent ductile deformation (D 2 ). Crosscutting relationships indicate that
D 1 and D 2 predate approximately 2675 Ma. Further ductile shear zones
characterized by quartz-albite-sericite + or - pyrite alteration developed
during D 3 , after approximately 2675 Ma. Narrow brittle faults (D 4 ) with
biotite + or - clinozoisite alteration halos, active between approximately 2675
and 2611 Ma, cut the three generations of ductile shear zones.Rare
quartz-albite-fluorite-molybdenite + or - chalcopyrite + or - pyrrhotite veins
developed prior to D 1 and the regional metamorphism. These veins are not
associated with any Au mineralization or significant Cu. Quartz + or - pyrite +
or - molybdenite + or - Au veins and crosscutting clinozoisite-biotite + or -
actinolite + or - quartz-chalcopyrite-pyrrhotite + or - galena + or -
molybdenite + or - scheelite Au veins developed during movement on the D 4
faults between approximately 2675 and 2611 Ma. Mineralized veins crosscut the
three generations of ductile shear zones but are not foliated. Movement on the
D 4 faults controlled the location of mineralization within the Boddington gold
mine. Higher grade mineralization occurs along the D 4 faults and coplanar
pyroxenite dikes and where the faults intersect older shear zones, and quartz
veins. Widespread lower grade stockwork mineralization is concentrated in the
general vicinity of the D 4 faults. The orientation of veins within stockworks
is consistent with vein development during sinistral strike-slip movement on
the D 4 faults. Au-Cu + or - Mo + or - W mineralization at the Boddington gold
mine, therefore, occurred late in the tectonic evolution of the Saddleback
greenstone belt.The timing of mineralization at the Boddington gold mine is
analogous to many other structurally late Au deposits in the Yilgarn craton,
e.g., Mount Magnet, Mount Charlotte, and Wiluna. Movement on the D 4 faults and
mineralization may have been coeval with the emplacement of granitoid
intrusions at approximately 2611 Ma. Whereas these granitoids are unaltered and
therefore unlikely to have been the source of significant volumes of
hydrothermal fluids, they may have provided the thermal energy necessary to
drive circulation of auriferous hydrothermal fluids through D 4 faults that may
also have accommodated their intrusion.Previous workers at the Boddington gold
mine have inferred that mineralization is genetically linked to subvolcanic
intrusions emplaced between approximately 2714 and 2696 Ma. However, this
inference is inconsistent with the crosscutting relationships of structures and
mineralized veins which indicate that mineralization occurred between
approximately 30 and 80 Ma after emplacement of these rocks.
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| General Geological Map of Boddington Gold Mine |
Note From Dr. Walter L. Pohl
"Lateritic gold deposits as
a class are a relatively recent discovery. One of the largest representatives
of this group was the Boddington bauxite mine in Western Australia, which until
closure in 2001 was the biggest gold mine in Australia with an annual gold
production of 2500 kg. Premining resources amounted to 60 Mt of ore at 1.6 ppm
Au, apart from bauxite with gold contents <1 ppm. Exploitable gold was
located in near-surface, iron-alumina hard crusts that reached a thickness of 5
m and in additional 8 m thick lumpy Fe-Al laterite of the B-horizon. Sources of
the gold in soil at Boddington are quartz veins and hydrothermally altered
bodies of Archaean greenstone bedrock. Since 2009, resources of 400 Mt of this
primary ore with a grade of 0.9 g/t Au and 0.12% Cu are exploited in a new
mine. Worldwide, numerous lateritic gold deposits are worked. They are
attractive because exploration, extraction and processing of soil is less
costly compared with hard rock mining."
The Ranger Uranium Mine
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| The Ranger Uranium Mine |
Location: Kakadu National Park, Northern Territory, Australia.
Products: Uranium.
Owner: Energy Resources of Australia
Limited.
Deposit Type: Unconformity-related uranium deposits.
Overview: In 1969 the Ranger
orebody was discovered by a Joint Venture of Peko Wallsend Operations Ltd (Peko)
and The Electrolytic Zinc Company of Australia Limited (EZ). In 1974 an
agreement set up a joint venture consisting of Peko, EZ and the Australian
Atomic Energy Commission (AAEC).
In 1978, following a
wide ranging public inquiry (the Ranger Uranium Environmental Inquiry) and
publication of its two reports (the Fox reports), agreement to mine was reached
between the Commonwealth Government and the Northern Land Council, acting on
behalf of the traditional Aboriginal land owners. The terms of the joint
venture were then finalised and Ranger Uranium Mines Pty Ltd was appointed as
manager of the project.
In August 1979 the
Commonwealth Government announced its intention to sell its interest in the
Ranger project. As a result of this, Energy Resources of Australia Ltd (ERA)
was set up with 25% equity holding by overseas customers. In establishing the
company in 1980 the AAEC interest was bought out for $125 million (plus project
costs) and Peko and EZ became the major shareholders. Several customers held 25%
of the equity in non-tradable shares. Ranger Uranium Mines Pty Ltd became a
subsidiary of ERA. During 1987-8 EZ's interest in ERA was taken over by North
Broken Hill Holdings Ltd and that company merged with Peko. Consequently ERA
became a 68% subsidiary of North Limited, and this holding was taken over by
Rio Tinto Ltd in 2000. In 1998 Cameco took over Uranerz, eventually giving it
6.69% of ERA, and Cogema took over other customer shares, giving it (now Areva)
7.76%.
Late in 2005 there was
a rearrangement of ERA shares which meant that Cameco, Cogema and a holding
company (JAURD) representing Japanese utilities lost their special unlisted
status and their shares became tradable. The three companies then sold their
shares, raising the level of public shareholding to 31.61%.
Geological Features:
Features associated with some of the
unconformity-related uranium deposits in the Alligator Rivers, Rum Jungle and
South Alligator Valley uranium fields are as follows (modified after Ewers
& others, 1984; Mernagh, Wyborn & Jagodzinski, 1998): The host rocks
occur in intracontinental or continental margin basins; the deposits are near
to a late Palaeoproterozoic oxidised thick cover sequence (>1 km) of quartz-rich
sandstone;
The basement is chemically reduced,
containing carbonaceous/ferrous iron-rich units or feldspar-bearing rocks;
The deposits are associated with a
Palaeoproterozoic/late Palaeoproterozoic unconformity and with dilatant brecciated
fault structures, which cut both the cover and basement sequences and separate
reduced lithologies from the oxidised cover sequence;
Most of the large deposits in the
Alligator Rivers and the Rum Jungle fields are in stratabound ore zones and
have a regional association with carbonate rock/pelitic rock contact, but an
antipathetic relationship with carbonate in the ore zones;
The major Australian deposits lie
close to an unconformity although the Jabiluka deposit is still open some 550 m
below the unconformity;
The known major uranium deposits are
present where the oxidised cover sequence is in direct contact with the
reducing environments in the underlying pre-1870 Ma Archaean–Palaeoproterozoic
basement and not separated by an intervening sequence, as by the El Sherana and
Edith River Groups in the South Alligator Valley uranium field.
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| Local stratigraphy of The Ranger Mine |
Alteration
Alteration features associated with
the deposits are:
Alteration extends over 1 km from the
deposits,
Alteration is characterised by
sericite–chlorite ± kaolinite ± hematite,
Mg metasomatism and the formation of
late-stage Mg rich chlorite are common,
Strong
desilicification occurs at the unconformity.
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Source of Uranium mineralization
Archaean and
Palaeoproterozoic granites of the Alligator Rivers and South Alligator Valley
uranium fields have uranium contents which are well above the crustal average
of 2.8 ppm U (Wyborn, 1990a). Granites and granitic gneisses of the Nanambu
complex contain 3–50 ppm U; tonalites, granitic gneisses and granitic migmatites
of the Nimbuwah complex have 1–10 ppm U. The Nabarlek Granite that has been
intersected in drill holes below the Nabarlek deposit has 3–30 ppm U, and the
Tin Camp and Jim Jim Granites also have high uranium contents. The Malone Creek
Granite (South Alligator Valley) has 11–28 ppm U. Wyborn (1990b) suggested that
the underlying crust in the region of these uranium fields is enriched in
uranium. Maas (1989) concluded from Nd–Sr isotopic studies that for Jabiluka,
Nabarlek and Koongarra, the uranium was derived from two sources: the
Palaeoproterozoic metasediments and a post-unconformity source, probably highly
altered volcanics within the Kombolgie Subgroup. Maas (1989) also proposed that
these orebodies formed when hot oxidising meteoric waters, which contained
uranium derived from volcano-sedimentary units within the Kombolgie, reacted
with reducing metasediments of the Palaeoproterozoic basement.
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| Uranium mineralization |
Processing: Following crushing,
the ore is ground and processed through a sulfuric acid leach to recover the
uranium. The pregnant liquor is then separated from the barren tailings and in
the solvent extraction plant the uranium is removed using kerosene with an
amine as a solvent. The solvent is then stripped, using an ammonium sulphate
solution and injected gaseous ammonia. Yellow ammonium diuranate is then
precipitated from the loaded strip solution by raising the pH (increasing the
alkalinity), and removed by centrifuge. In a furnace the diuranate is converted
to uranium oxide product (U3O8).
Reserves & Resources: The Ranger 1 orebody,
which was mined out in December 1995, started off with 17 million tonnes of ore
some of which is still stockpiled. The Ranger 3 nearby is slightly larger, and
open pit mining of it took place over 1997 to 2012.
In 1991 ERA bought
from Pancontinental Mining Ltd the richer Jabiluka orebody (briefly known as
North Ranger), 20 km to the north of the processing plant and with a lease
adjoining the Ranger lease. ERA was proposing initially to produce 1000 t/yr
from Jabiluka concurrently with Ranger 3. The preferred option involved
trucking the Jabiluka ore to the existing Ranger mill, rather than setting up a
new plant, tailings and waste water system to treat it on site as envisaged in
an original EIS approved in 1979. However, all these plans are now superseded –
see Australia's Uranium Deposits and Prospective Mines paper.
In the Ranger 3 Pit
and Deeps the upper mine sequence consists of quartz-chlorite schists and the
lower mine sequence is similar but with variable carbonate (dolomite, magnesite
and calcite). The primary ore minerals have a fairly uniform uranium mineralogy
with around 60% coffinite, 35% uraninite and 5% brannerite. In weathered and
lateritic ores the dominant uranium mineralogy is the secondary mineral
saleeite with lesser sklodowskite.
In the second half of
2008 a $44 million processing plant was commissioned to treat 1.6 million
tonnes of stockpiled lateritic ore with too high a clay content to be used
without this pre-treatment. Following initial treatment the treated ore is fed
into the main plant, contributing 400 t/yr U3O8 production for seven years. A
new $19 million radiometric ore sorter was commissioned at the same time, to
upgrade low-grade ore and bring it to sufficient head grade to go through the
mill. It will add about 1100 tonnes U3O8 to production over the life of the
mine, and be essential for beneficiating carbonate ore from the lower mines
sequence of the Ranger 3 Deeps.
A feasibility study
into a major heap leach operation for 10 Mt/yr of low-grade ore showed the
prospect of recovering up to 20,000 t U3O8 in total. Column leach trials were
encouraging, yielding extractions of greater than 70% at low rates of acid
consumption. The facility would consist of fully lined heaps of material about
5m high and covering about 60-70 ha. These will be built and removed on a
regular cycle and the residues stored appropriately after leaching is
completed. The acid leach solutions would be treated in a process similar to
that used in the existing Ranger plant and recycled after the uranium is
removed from the pregnant liquor. ERA applied for government (including
environmental) approval for the project, which was expected to begin operation
in 2014, but in August 2011 ERA announced that the plan was shelved due to high
capital costs and uncertain stakeholder support. As a result, ore reserves of
7,100 tonnes of uranium oxide were reclassified as resources.
In 2006 the projected operating life of the
Ranger plant was extended to 2020 due to an improvement in the market price
enabling treatment of lower grade ores, and in 2007 a decision to extend the
operating Ranger 3 open pit at a cost of $57 million meant that mining there
continued to 2012. However, reassessment of the low-grade stockpile in 2011
resulted in downgrading reserves by 6100 t U3O8. The #3 pit is now being
backfilled, and to mid-2014, 31 million tonnes of waste material had been moved
there. It will then be used as a tailings dam.
Sunrise Dam Gold Mine
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| Sunrise Dam Gold Mine |
Location: Laverton,
Western Australia.
Geological Settings: The deposit is hosted by the Archaean Norseman-Wiluna belt, in the Eastern Goldfields Province of the Yilgarn Craton. The deposit falls within the structurally complex Laverton Domain, which is characterized by tight folding and thrusting. A number of other Au deposits lie within or near the margins of the Laverton Domain, including Laverton, Granny Smith (this volume), Red October (this volume), Childe Harold, Lancefield and Keringal. Most of these deposits are hosted by metasedimentary rocks, a distinctive feature of the Laverton region relative to other parts of the Yilgarn Craton.
Mineralization: The Sunrise Shear, within the Archaean rocks, controls geometry of the mineralization and is thought to have been the main conduit for Au-bearing hydrothermal fluids (Newton et al., 1998). Pyrite replacement of BIF accounts for most of the primary mineralization and is well developed where the shear zones, parallel to bedding, follow the contact of BIF with less competent units. Gold is also associated with quartzankerite- pyrite veins and pervasive ankerite-silica-sericite-pyrite alteration of intermediate volcaniclastic host rocks. Thin quartz-carbonate veins also host Au, but are mostly located in the Sunrise part of the deposit. Supergene mineralization has developed in the weathered bedrock and in transported cover in the eastern part of the study area.
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Cadia-Ridgeway Mine
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| Cadia-Ridgeway Mine |
Location: Orange, New South Wales,is one of three gold mines Newcrest currently operates in Australia.
Products: Copper & Gold. A series of large underground and open-cut gold and copper mines
Ore Minerals: Ore minerals are native gold, chalcopyrite and bornite, mostly occurring within veins, but also disseminated. Magnetite is a major accessory mineral in veins. Hydrothermal alteration associated with the strongest mineralisation is potassic: orthoclase, albite, actinolite, magnetite, biotite. This is overprinted by later propylitic assemblages: epidote, chlorite, Fe-carbonate, calcite, hematite dusting.
Geological
setting: The Cadia
deposits are part of a Late Ordovician – Early Silurian porphyry alteration-mineralisation
system that extends over an area of at least 6 X 2 km within the Ordovician Molong
Volcanic Belt of the Palaeozoic
Lachlan Fold Belt (Newcrest Mining Staff, 1997). The Molong
Volcanic Belt comprises a suite of intermediate to basic volcanics,
volcaniclastics,
comagmatic
intrusions, and limestones. The
suite is probably part of a subduction-related island arc disrupted by later
tectonism (Glen et al, 1997). In the Cadia
area the volcanics
and intrusions are shoshonitic
(Blevin,
1998).
Mineralization: Sheeted quartz vein, stockwork quartz vein, disseminated and skarn, all of which are genetically related to a relatively small (3 X 1.5 km in outcrop) composite intrusion of predominantly monzonitic composition, with a monzodioritic to dioritic rind (Cadia Hill Monzonite). The Cadia Hill Monzonite intruded Forest Reefs Volcanics (volcaniclastics, lavas, subvolcanic intrusions, and minor limestone) and Weemalla Formation (siltstone, mudstone, minor volcaniclastics). Emplacement of the Cadia Hill Monzonite was probably facilitated and localised by the development of a major north-west (NW) to south-east (SE) trending dilational structural zone, which is well evident in magnetic data.
Kalgoorlie Superpit Gold Mine
The
Australia's largest open cut gold mine
Location: Kalgoorlie,
Western Australia.
Products: Gold.
Owner: Kalgoorlie
Consolidated Gold Mines Pty Ltd.
Overview: The
Super Pit is located off the Goldfields Highway on the south-east edge of
Kalgoorlie, Western Australia. The pit is oblong in shape and is approximately
3.5 kilometres long, 1.5 kilometres wide and 570 metres deep. At these
dimensions, it is large enough to be seen from space.
The Super Pit is owned by Kalgoorlie
Consolidated Gold Mines Pty Ltd, a company owned 50/50 by Barrick Gold Corporation
and Newmont Mining Corporation. The mine produces 850,000 ounces (28 tonnes) of
gold per year, and employs around 550 employees directly on site.
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.
Barrick Gold acquired its share of the mine in
December 2001, when it took over Homestake Mining Company. Newmont became
part-owner of the mine three months later, when it acquired Normandy Mining in
February 2002.
Geological Setting: Most of the good gold mined in the
Super Pit occurs within ore lodes formed by ancient shears in a rock unit
called the Golden Mile Dolerite. The gold mining area of
Kalgoorlie-Boulder-Fimiston has long been called the Golden Mile because of the
geographical concentration of rich mines in that area, even though the lodes
occur in an area over 2 km in width and 1 km in depth.
Kalgoorlie Terrane.
1. Pre- to syn-D, granitoids were emplaced as
broadly conformable sheet-like bodies at the base of, or within, the greenstone
succession, probably during
2. Post-D, to syn-D, granitoids were
diapirically emplaced, and are concentrated in a zone along the western side of
the Kalgoorlie Terrane.
3. Late-tectonic to post-tectonic granitoids
were emplaced late in the history of the Terrane. Limited geochronological data
suggest the granitoids were emplaced at 2690-2680 Ma (group I), 2665-2660 Ma
(group 2) and 2650-2600 Ma (group 3) (Hill ef al.,
1992). Small porphyry intrusions, including
lamprophyres
(Rock et aL, 1989), are widespread and petrologically
diverse; they may be genetically related to some of the I-type granitoid suites
(Witt, 1992). They are common in and near regional deformation zones, and are
associated with many gold deposits (Perring et al., 1988,1989).
GOLD MINERALIZATION:
All rock types in the Kalgoorlie Terrane host
gold mineralization, but most production has come from fractionated quartz-dolerite
zones of mafic-ultramafic sills and from tholeiitic basalt.
The dominance of quartz-dolerite and
tholeiitic basalt remains even if bias introduced by the "giant"
Kalgoorlie deposits (Golden
Mile, Mount Charlotte) is eliminated. A
similar picture emerges when host rocks to gold mineralization throughout the
Yilgarn Craton are considered (.1B; Groves & Barley, 1988). Quartz-dolerite
and tholeiitic basalt host rocks are characterized by high FeO* contents and
FeO*/(FeO*+MgO) (Tables II.1,11.2), where FeO* is total iron expressed as FeO.
Although mafic rocks are the dominant hosts, other rock types (e.g.,
granitoids, porphyry, ultramafic rocks) host important deposits, and can even
be the dominant host rock on a camp scale (e.g., porphyries at New
Celebration). All rock types in the Kalgoorlie Terrane host gold mineralization,
but most production has come from fractionated quartz-dolerite zones of
mafic-ultramafic sills and from tholeiitic basalt .
Production:
Mining is via conventional drill and blast
mining via face shovels and dump trucks. Around 15 million tonnes of rock is
moved in any given year, consisting primarily of waste rock.
Gold within the Golden Mile lode system is
unusual in that it is present as telluride minerals within pyrite. In order to
recover the gold, the ore must be crushed, passed through a gravity circuit to
recover the free gold present in some of the higher-grade lodes, and then
subjected to flotation to produce an auriferous pyrite concentrate. This is
then roasted at a small smelter outside Kalgoorlie-Boulder to liberate the gold
from the tellurides, with doré bars poured.
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