Boddington Gold Mine
|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.
|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
|The Ranger Uranium Mine|
Location: Kakadu National Park, Northern Territory, Australia.
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%.
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.
|Local stratigraphy of The Ranger Mine|
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.
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.
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
|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.
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.
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.
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).
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 .
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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