OzGold 2011 - Deposit Descriptions

This was a technical tour to precede the major NewGenGold 2011 Conference held in Perth, Western Australia from the evening of 21 to 23 November, 2011.

Geological summaries of the deposits on the itinerary are as follows:

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Cowal - New South Wales .................................... Mon. 14, November, 2011

The Cowal (previously Lake Cowal and Endeavour 42) epithermal gold deposit is located on the western edge of Lake Cowal, approximately 35 km NNE of West Wyalong in central New South Wales, Australia. The deposit falls within the Macquarie volcanic arc of the Palaeozoic Lachlan Fold Belt of southeastern Australia.

Gold mineralisation at Cowal is hosted by the Ordovician Lake Cowal Volcanic Complex, exposed as a north-south elongated 40 x 15 km window of intermediate calc-alkaline intrusives, volcanics and volcaniclastics surrounded by unconformably overlying Siluro-Devonian sediments and volcanics. Immediately to the west of this window a highly deformed north-south zone within the Siluro-Devonian defines the broad Booveri Fault Zone.

The deposit is covered by 30 m of lake sediments and an underlying Tertiary laterite profile with no outcrop of the host volcanics, apart from some minor gossanous float.

The hosts to mineralisation comprise volcaniclastics and coeval extrusives and intrusive magmatic rocks which dip NW at 40 to 45°. This sequence has been subdivided into three conformable units, namely: i). The Great Flood unit of 250 m of monotonous beds, to 72 m of vitric volcaniclastic debris with mass flow structures. The coarser beds are intercalated with less than 3 m thick intervals of laminated shale, siltstone and mudstone, with a 20 m bed of polymictic volcanogenic conglomerate; ii). The Golden Lava unit, comprising 60 to 110 m of trachyandesite interbedded with monomictic sand to breccia with clasts of plagioclase porphyritic fragments - believed to represent a submarine lava with associated hyaloclasite and autobreccia; iii). The Cowal Conglomerate, which is the oldest unit and is around 100 m thick with massive to graded beds of well rounded to very angular, clast supported polymict volcanic debris (andesitic) with interbedded laminated siltstone and mudstone, and evidence of mass flow.

This succession is cut by the 456 ±5 Ma holocrystalline to euqigranular to porphyritic Muddy Lake Diorite (in places a gabbro) and by porphyritic to aphanitic mafic dykes. The latter post date the diorite, are 0.2 to 20 m thick (averaging 1 to 3 m) and were emplaced in active faults.

The gold mineralisation is primarily in narrow dilatant veins of quartz-carbonate-sulphide (with common adularia) and carbonate±quartz-sulphide and narrow, healed faults with a similar mineralogy. Gold occurs to a lesser extent in pyrite stringers and as disseminations, shear chlorite-carbonate veins and chlorite-carbonate-sulphide veins. Approximately 20% of the orebody is in the oxide zone where gold is more erratic, reflecting leaching and dispersion. The veins generally strike at 305° and dip 35°SW and are at their highest density in the Golden Lava, although those in the Muddy Lake Diorite are usually thicker. The veins are typically parallel sided and from <1 to 100 mm thick. Vein alteration haloes are rare and the main sulphides are quartz, sphalerite, chalcopyrite, galena and pyrrhotite, with minor associated visible gold. The best gold accompanies sphalerite and to a lesser extent adularia.

Four alteration styles are recognised, namely i). Propylitic, in the surrounding hosts; ii). Quartz-sericite-carbonate, associated with fault zones and gold mineralisation, and is best developed in the Golden Lava and Great Flood units and grades outward from the faulz zones and associated veining to the propylitic zone - this style usually embraces veins of ankerite-quartz-pyrite-sphalerite-chalcopyrite-galena; iii). Quartz-potassium feldspar - restricted to the Golden Lava as irregular patches and zones usually associated with later chloritisation and occassionally surrounds sulphide bearing dilational veining; iv). Chlorite-carbonate-pyrite, usually associated withe the previous type of alteration and surrounding zones of quartz, K-feldspar, pyrite, sphalerite and chalcopyrite veins.

At December 31, 2003, the pre-mining reserve - resource estimates were:
Proven + probable reserves - 63.6 Mt @ 1.19 g/t Au, for 76 t of contained Au
Mineral resources - 47.53 Mt @ 1.04 g/t Au, for 49 t of contained Au.

Mining commenced in mid 2006. Total production to the end of 2010 was ~34.75 t Au.

At December 31, 2010, the reserve - resource estimates were (Barrick Annual Report):
Proven + probable reserves - 72.5 Mt @ 1.07 g/t Au, for 77 t of contained Au,
Mineral resources - 48.3 Mt @ 0.98 g/t Au, for 47 t of contained Au (in addition to reserves).
Production during 2010 totalled 9.27 t of recovered Au.

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Cadia Valley Operations - New South Wales, .................................... Tue. 15 November, 2011

The Cadia and Ridgeway porphyry gold-copper deposits are located 20 km south of Orange in the central tablelands of New South Wales, Australia, some 200 km WNW of Sydney. Cadia Hill and related adjacent resources are low grade, bulk mining, porphyry style Au-Cu deposits while Ridgeway, 3 km to the north-west of the Cadia Hill open pit and 500 m below surface, comprises quartz veins, sheeted and stockwork quartz and quartz-sulphide veins and disseminated mineralisation with higher grade gold and associated copper mineralisation.

The Cadia district falls within the Molong Volcanic Belt in the eastern part of the lower Palaeozoic Lachlan Fold Belt of south-eastern Australia where a number of relatively undeformed, shoshonitic, Ordovician volcano-intrusive complexes host porphyry and high sulphidation epithermal gold mineralisation. The largest such deposits are in the Cadia district. The Cadia-Ridgeway cluster of deposits are principally associated with a 3 x 1.5 km late Ordovician composite quartz-monzonite to dioritic porphyry stock and its probable co-magmatic volcanic wall rocks and intercalated volcaniclastics that together form part of an Ordovician volcano-intrusive complex. Overall the stock has an alkaline composition, with mineralisation and alteration being associated with porphyritic quartz-monzonite phases that are altered over an area of 5.5 x 3 km and to a depth of up to 1.6 km, defining a NW trending corridor that encloses the known deposits.

There are five components to the Cadia porphyry system within the mineralised corridor, namely:
  (i) Intrusion- and volcanic wall rock hosted sheeted veins at Cadia Hill. Alteration is principally propylitic with little recognised potassic developments, while a late stage phyllic phase was restricted to zones of faulting and is followed by late carbonates. Mineralisation is mainly chalcopyrite and pyrite with lesser bornite within and disseminated around sheeted 1 to 20 mm thick quartz veins in a 100 to 350 m wide, 65° dipping zone that is 1 km long and has not been closed at depth;
  (ii) Volcanic wall rock hosted disseminated and sheeted vein mineralisation at Cadia East within moderately to strongly altered lavas and volcaniclastic breccias. Alteration and mineralisation is centred on a steeply dipping, 300 m wide, east plunging core of steeply dipping sheeted quartz-calcite ±chalcopyrite ±bornite ±molybdenite ±covellite ±pyrite ±magnetite veins within a disseminated envelope of chalcopyrite, bornite and pyrite. This core persists down plunge for at least 1.6 km. Alteration types include weak propylitic, weak sericite-silica-albite, moderate to strong silica-albite flooding with hematite and K feldspar, and strong sericite-albite with silica-albite flooding ±tourmaline;
  (iii) Intrusion hosted sheeted veins at Cadia Quarry, developed as a 1 km long by 200 m wide package controlled by faulting and fracturing;
  (iv) The up to 70 m thick distal, stratabound hematite-magnetite skarns at Big and Little Cadia. Chalcopyrite is the dominant sulphide, with pyrite and calcite interstitial to the magnetite and hematite blades;
  (v) Probable late stage distal veins.

The Ridgeway deposit is an upright, bulbous body of stockwork quartz veining zoned about a 50 to 100 m diameter plug of porphyritic Cadia Hill Monzonite where it intrudes Ordovician andesitic volcanics to the west of the main Cadia multiple intrusion. The highest grade gold accompanies the most intense alteration and stockwork development immediately adjacent to the monzonite porphyry, with the best being localised directly above the plug compared to grades on its lateral margins. Grades decrease laterally outwards and inwards from the intrusive contact. The ore minerals are predominantly veined, but are also disseminated and comprise native gold, chalcopyrite and bornite, with accessory magnetite. The more intense mineralisation is accompanied by a potassic alteration suite of orthoclase, albite, actinolite, magnetite and biotite, overprinted by a propylitic assemblage of epidote, chlorite, iron carbonates, calcite and hematite dusting. NW-SE trending pre-mineral faults appear to have exerted a strong control on mineralisation.

The total pre-mining resources were:
Cadia Hill in 1977 - 352 Mt @ 0.63 g/t Au, 0.16% Cu for 221.3 t of contained Au;
Cadia Quarry in 2003 - 50 Mt @ 0.40 g/t Au, 0.21% Cu for 21.7 t of contained Au;
Ridgeway in 2002 - 54 Mt @ 2.5 g/t Au, 0.77% Cu for 132.6 t of contained Au.
Cadia East was un-mined in 2010.

The remaining proved+probable reserves in August 2010 (Newcrest website) were:
Cadia Hill - 116 Mt @ 0.60 g/t Au, 0.14% Cu;
Ridgeway underground - 101 Mt @ 0.81 g/t Au, 0.38% Cu;
Cadia East underground - 1073 Mt @ 0.60 g/t Au, 0.32% Cu.
The total measured+indicated+inferred resources at the same date were:
Cadia Hill - 408 Mt @ 0.42 g/t Au, 0.12% Cu;
Cadia Extended - 83 Mt @ 0.35 g/t Au, 0.20% Cu;
Ridgeway underground - 155 Mt @ 0.73 g/t Au, 0.38% Cu;
Big Cadia - 42 Mt @ 0.38 g/t Au, 0.40% Cu;
Cadia East underground - 2347 Mt @ 0.44 g/t Au, 0.28% Cu.

The total declared measured+indicated+inferred resource in the Cadia district was estimated in 2010 to contain 1360 tonnes (43.7 Moz) of gold and 7.99 Mt of copper. The Cadia-Ridgeway mines are operated by Newcrest Mining Ltd.

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Boddington - Western Australia, .................................... Wed. 16 November, 2011

The Boddington gold deposit is located approximately 130 km SSE of Perth in Western Australia and lies within the Saddleback greenstone belt, part of the Western Gneiss terrane, on the far south-western extremity of the Archaean Yilgarn Craton. The Saddleback greenstone belt is some 35 km long and 5 to 10 km wide.

The deposit was discovered in 1980 in the Darling Ranges Bauxite district and mining commenced in 1987. The original operation commenced on a resource of 60 Mt @ 1.6 g/t Au which occurred as very fine, generally <5 µm, gold grains spread through the 4 to 25 m thick lateritic weathering profile, sections of which are mined on a large scale for bauxite elsewhere in the district.

The lateritic gold mineralisation at Boddington occurred as a semi-continuous blanket over a strike length of more than 5 km and a width of around 1 km. Some 30% of the Some 30% of the gold was hosted by the same vertical zones as the bauxite, namely the upper lateritic gravels, the hardcap and the B-zone laterite. The remaining 70% was found in the underlying clay and saprolite zone, which was 10m, and locally up to 120 m in thickness.

The laterite resource was exhausted in 2001 and the mine placed on care and maintenance, after having produced 105 Mt @ 1.4 g/t recovered Au for 147 t Au and 6500 t Cu.

Beneath the lateritic ore, there are a variety of other ore types present in the greenstone belt bedrock, including rich lode deposits and the large low grade, hard-rock Wandoo body.

The Wandoo deposit occurs as disseminations and stockworks hosted by 2715 to 2690 Ma dyke and stock-like dioritic intrusives and andesitic volcanic rocks of the Saddleback Greenstone belt. The element chemistry of the host intrusions indicates an island arc tectonic setting. The host rocks underwent a ductile deformation event (D1-D2), followed by a second period of supracrustal deposition comprising intermediate volcaniclastic rocks and intrusion of coeval granodiorite-tonalite rocks dated at around 2675 Ma. The chemistry of the latter rocks is again consistent with formation in an arc setting. All of these rocks were then metamorphosed to upper-greenschist to lower-amphibolite facies at around 2640 Ma, and deformed by brittle-ductile faults (D3-D4). A late monzogranite intrudes the greenstone belt just east of the Boddington mine. This intrusion, dated at 2612Ma, is distinct in terms of its K feldspar-phyric texture, associated aplites and rare pegmatites, distinctive magnetic low signature, and its elevated U-Th and K radiometric character.

The core of the mineralised hydrothermal system is characterised by overlapping Cu, Au, Mo, Bi and W concentrations, with marked enrichments in Pb, Zn and Ag on the periphery.

Two stages of mineralisation are recognised at Boddington, namely:

i). An early widespread silica-biotite alteration, and complex quartz+albite+molybdenite ±clinozoisite ±chalcopyrite veins variably deformed by ductile shear zones. Re-Os ages from molybdenite in these veins indicates a formation age ofapproximately 2700 Ma.
ii). A second, main stage of mineralisation which cuts all of the above, and comprises,
a). complex quartz+albite+molybdenite ±muscovite ±biotite ±fluorite ±clinozoisite ±chalcopyrite veins (controlling the Mo distribution);
b). clinozoisite-sulphide-quartz-biotite veining (controlling the bulk of the lowgrade Au-Cu mineralisation);
c). actinolite ±sulphide ±quartz, carbonate-chlorite-sulphide, and sulphide veins (controlling high grade mineralisation). Re-Os dates from these mineral assemblages yields ages of around 2625 to 2615 Ma, broadly synchronous with the monzogranite to the east of the deposit.

Structurally, mineralisation is controlled by the following, in increasing order of importance: i). a late ductile WNW to NW striking, sub-vertical fault network with elevated mineralisation and alteration; ii). intersection of this fault network and competent lithologies; iii). intersection of these late faults and early ductile quartz-sericite shear zones; and iv). NE striking corridors which appear to compartmentalise the deposit by offsetting favourable hosts prior to mineralisation.

The Wandoo basement gold mineralisation is therefore interpreted to represent a structurally-controlled, intrusion-related Au-Cu deposit, paragenetically associated with both ~2700 and 2612 Ma events, with the main stage, higher grade mineralisation being apparently synchronous with the late, K-rich post-magmatic monzogranite suite.

The basement mineralisation in 2004 comprised (Newcrest Annual Report, 2005):
Proven + Probable Reserve - 395 Mt @ 0.87 g/t Au, 0.13% Cu; (reserves included in resources),
Measured + Indicated Resource - 505 Mt @ 0.86 g/t Au, 0.12% Cu, for 435 t Au;
Inferred Resource - 232 Mt @ 0.80 g/t Au, 0.09% Cu, for 185 t Au.

Following further drilling and development, the reserve and resources in 2010 (Newmont 2011) were:
Proven + Probable Reserve - 1089 Mt @ 0.58 g/t Au, 0.11% Cu, for 631 t Au, (reserves additional to resources)
Measured + Indicated Resource - 469 Mt @ 0.40 g/t Au, 0.08% Cu, for 187 t Au,
Inferred Resource - 163 Mt @ 0.43 g/t Au, 0.11% Cu, for 70 t Au.

The current hard rock Boddington project is owned and operated by Newmont Australia. The laterite mine was operated by Worsley Alumina Pty Ltd for the original joint venture owners.

The hard rock description was based on McCuaig et al., 2001 available from the GeoScience Australia website.

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Kalgoorlie Superpit - Western Australia .................................... Thu. 17 November, 2011

The KCGM Super Pit lies within the Kalgoorlie Gold Field, some 600 km east of Perth. It exploits the Golden Mile string of deposits.

The Kalgoorlie Gold Field is developed within the Archaean Norseman-Wiluna greenstone belt of the Eastern Goldfields province in the eastern Yilgarn craton. It is hosted by greenschist facies, marine volcano-sedimentary rocks, divided into narrow blocks by NNW-trending regional wrench faults. The volcanic succession comprises, from oldest to youngest: (1) the Lunnon Basalt (~2720 Ma) - pillowed to massive tholeiitic lavas; (2) Kambalda Komatiite (2709±4 Ma) - ultramafic flows; and (3) Devon Consols and Paringa Basalts - two pillowed to massive magnesian lavas, separated by the 10 m thick, 2692±4 Ma, Kapai Slate marker horizon of sulphidic and tuffaceous shale.

This volcanic succession is overlain by black shales, greywackes, and volcaniclastic rocks of the Black Flag Group. To the south of Kalgoorlie, near Kambalda, this latter unit is intruded by the 2680±8 Ma Condenser Dolerite sill and 2678±8 Ma rhyolite porphyry dykes. In the Kalgoorlie district it is intruded by the 750 m thick Golden Mile Dolerite, which is the principal host rock to lode structures, and comprises a folded and metamorphosed, differentiated sill, emplaced at the same stratigraphic position as the Condensor Dolerite. The youngest mineralised rocks in all gold mines located between Kalgoorlie and Kambalda are 2675 to 2660 Ma stocks and dykes of hornblende-plagioclase porphyry.

Deformation of the volcano-sedimentary succession in the Kalgoorlie-Kambalda area was subdivided by Swager (1989) into four events: D1, characterised by recumbent folding and nappe-style thrusting; D2, which comprises upright folding that produced regional northwest-trending folds; D3, a post ~2660 Ma episode of sinistral wrench faulting in a transpressional regime, with major NNW-trending faults; and D4 which involved dextral wrench faulting, mostly NNE-trending.

The Kalgoorlie Gold Field comprises more than 1000 discrete lodes, controlled by brittle-ductile shear zones, clustered in a geometric array on both sides of the steeply dipping, NW to NNW-trending, sinsitral Golden Mile fault, which transects folded Golden Mile Dolerite in the centre of the mining district. The most significant of the lodes make up the Golden Mile, Mt Charlotte, Mt Percy and Hannan's South ore zones. An envelope of chlorite-calcite alteration, surrounds the entire mining area, replacing metamorphic actinolite and albite in all mafic rocks. The main lode systems are contained within a volume of these altered rocks, which is up to 5 km in length, by 1 to 2 km in width, and to a depth of 1000 m. They are controlled by a complex series of steeply dipping shears, and are largely hosted by ultra-mafic and mafic rocks and sills, the most important of which is the composite mafic sill, the Golden Mile Dolerite, and to a lesser extent the Paringa Basalt.

Two groups of structures, the Fimiston and Oroya lodes have been recognised. The Fimiston Lodes occur in steeply dipping (70 to 90°) shear zones, commonly parallel to the main Golden Mile fault, although others have different strike orientations. Individual lodes are up to 2 km long by 1.3 km in vertical extent, with high-grade shoots located at the intersections of shear zones. They are characterised by breccia bodies and cavity-fill veins surrounded by (1) an inner sericite-ankerite-siderite-quartz-hematite-pyrite±telluride alteration zone, containing most of the gold, and (2) an outer ankerite-sericite-quartz-pyrite zone where chlorite and calcite are progressively replaced. The ores are mineralogically refractory and complex, containing free native gold (often intimately associated with gold-bearing arsenical pyrite) and a significant proportion of Au-Ag-Hg-Pb telluride minerals. These Fimiston Lodes are subdivided into the Eastern and Western Lode System on the flanks of the Kalgoorlie Syncline. The Eastern Lodes System comprises a swarm of lodes (areas of pyritic and hydrothermal alteration) with mineralisation confined to shoots at lode-lode and lode-fault intersections. The Western Lode System is less complex, although the lodes are more persistent and well defined. Individual lodes occupy 20 to 50% of a lode channel and may be 30 to 1800 m long, 0.1 to 10 m thick and extend 30 to 1160 metres down dip. Mueller et al. (1988) suggest that the Fimiston Lode shear zones formed during D3 sinistral wrench faulting, whereas Bateman et al. (2001a) and Bateman and Hagemann (2004) conclude that the mineralised shear zones formed as flat, late D1 thrusting structures, subsequently rotated into their present subvertical position during D2 folding.

The Oroya Lodes represent the high-grade "green leader" ores, characterised by green vanadian muscovite, ankerite, quartz, pyrite, native gold, and gold-silver tellurides, the principal example of which is the 1500 m long Oroya shoot on the Paringa mine leases of the Golden Mile. This lode is controlled in large part by the 50°W dipping, reverse Oroya shear zone system. This style of ore also occurs in the brecciated cores of steeply dipping Fimiston lodes, and may represent a late-stage of the D3 transpressional regime that generated the Fimiston lodes (Mueller et al., 1988), or a separate mineralisation event (Bateman et al., 2001).

Mount Charlotte occurs as a quartz vein gold deposit, present as a series of steeply plunging, pipe-like vein stockwork orebodies in massive 2692±2 and 2678 to 2670 Ma metagabbro of the Golden Mile Dolerite. These, and other related quartz-vein stockworks cross-cut the Fimiston and Oroya lodes, and are apparently controlled by district-scale NNE-trending strike-slip D4 faults. The Mt Charlotte mine exploits the main Charlotte and Reward orebodies and the satellite Maritana and Northern bodies. The Charlotte orebody extends more than 800 m vertically, from the surface to -1000 m RL, 250 m north-south along strike and over a width of 50 to100 m east-west. Reward extends from the surface to -800 m RL, 250 m north-south along strike and 50 m east-west. The orebodies are restricted to the most differentiated (and competent) unit of the host sill and are usually found adjacent to major steeply dipping faults where these cut the sill. The stockworks have two sets of veins that were developed as hydraulic fractures and were filled simultaneously and are of equal significance. Gold is in pyrite or pyrrhotite bearing metagabbro around the stockwork veins and to a lesser degree as free gold in the veins and along vein margins.

The final 'Super Pit' open pit is designed (as of 2008) to have dimensions of 3.8 x 1.35 km and a depth of 500 m below the surface by 2018. Production in 2006 was 85 Mt of mined rock, 12 Mt of which was milled. The remaining tonnage was stockpiled low grade mineralisation and waste. In 2007, the underground Mt Charlotte mine produced 1 Mt of ore @ 3 g/t Au.

Total production from 1893 to 2005 was ~1475 t Au (47.5 Moz), with a further ~110 t from 2005 to 2010.

The total open pit and underground reserves plus resources at December 31, 2010 were (Barrick, Newmont, 2011):
Proved + probable reserves - 153 Mt @ 1.71 g/t Au, for 260 t Au; (reserves in addition to resources)
Measured + indicated resources - 95.6 Mt @ 0.76 g/t Au, for 72 t Au;
Inferred resource - 2.24 Mt @ 4.47 g/t Au, for 10 t Au.

The Kalgoorlie Super Pit open pit and Mt Charlotte underground operations are owned by KCGM, a 50:50 JV between Newmont Mining and Barrick Australia. Production in 2010 totalled approximately 24.5 t of recovered Au (Barrick and Newmont, 2011).

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Sunrise Dam - Western Australia .................................... Fri. 18 November, 2011

The Sunrise Dam operation is approximately 55 km to the south of Laverton, 220 km NNE of Kalgoorlie, and 770 km NE of Perth, in the Eastern Goldfields province of the Archaean Yilgarn craton, in Western Australia.

The deposit originally straddled the title boundary between the AngloGold Ashanti Ltd Cleo mine and the adjacent Sunrise leases of the Placer Pacific Granny Smith operation, (see the Granny Smith record), with the pits of the two operations overlapping. AngloGold Ashanti subsequently took control of the complete deposit.

The ore at the ~2670 Ma Sunrise Dam deposit is developed within both Archaean basement and the overlying transported cover. The basement ore lies within the Laverton Tectonic Zone of the Yilgarn craton, characterised by major north-south shears and associated faults. The dominant host is strongly deformed, greenschist facies andesitic to basaltic/mafic-ultramafic volcaniclastic rocks and magnetite-rich shales and turbidites (banded iron formation), which have been intruded by both quartz-feldspar porphyry sills and dykes (e.g., Dolly porphyry) and localised ultramafic and lamprophyre dykes. The timing of gold mineralisation relative to the metamorphic peak has not been ascertained, although similar deposits elsewhere in the Yilgarn craton are inferred to have formed syn- to post- peak metamorphism. Gold mineralisation is found intermittently within a NE trending corridor over a length of 4.5 km, coincident with a strongly magnetic BIF rich sequence.

Gold mineralisation is structurally controlled and vein hosted, occurring in two main styles, namely: (1) gently dipping shear-related and high strain veins; and (2) stockwork zones in steeply dipping planar faults with brittle characteristics, commonly concentrated at lithofacies contacts within the volcanic stratigraphy or porphyry margins, and within hinge domains in the magnetite shales (BIF). Gold is found in all lithologies, but is best developed in the Fe rich bands, in association with pyrite replacement of BIF. These mineralisation styles occur as:
Group I orebodies, which occur in shallowly dipping foliation parallel veins within a strong penetrative fabric that consists of a sericite±chlorite cleavage and/or schistosity. Veins typically contain quartz-carbonate±pyrite±arsenopyrite and quartz-sericite-carbonate-pyrite-chlorite alteration.
Group II lodes are steeply dipping and characterised by steep veins and breccias up to a few metres in width. Breccias comprise angular clasts of sericite-altered host-rock volcanics up to several cms across, locally with jigsaw fits, set in a quartz and quartz-carbonate matrix. Veins may be up to 5 m wide, and consist of carbonate-pyrite-arsenopyrite-quartz. Gently NW-dipping, laminated quartz-carbonate veins containing gold, arsenical sulphides and tellurides are also observed within Group II orebodies, and are interpreted to have formed during D4 dextral normal faulting.
Group III orebodies are hosted within steeply dipping stockwork breccia zones up to 20 m wide, and less commonly as vein zones. Stockwork veins commonly contain carbonate-chlorite-quartz±sericite±pyrite±arsenopyrite, with adjacent alteration typically consisting of sericite-quartz-pyrite-ankerite±arsenopyrite. The breccia is characterised by sericite-altered host-rock volcanics clasts and quartz and carbonate matrix.
Group IV lodes are hosted within the quartz-feldspar Dolly porphyry, with mineralisation being typically arsenic rich, occurring and within steep narrow (0.2 to 0.5 cm wide) gold-bearing quartz-pyrite-arsenopyrite veins.

These variably oriented gold-hosting structures and mineralisation styles are the result of a complex structural and mineralisation history involving at least six phases of deformation, namely:
D1 - formed several major shallow- to moderately dipping northwest-trending shear zones (Cleo, Margies, Mako, Sunrise, Midway-GQ, and Carey). These include low-angle ductile shear zones, characterised by a penetrative S1 fabric, mostly parallel to the structures, are up to 40 m wide, and are vertically stacked above one another. Steeply dipping shear zones are also interpreted as initial D1 structures that subsequently underwent D3 reactivation.
D2 - produced north- and south-plunging upright folds with steep axial surfaces, in response to east-west to WNW-ESE shortening, and S2 cleavage which crenulates S1. No mineralisation is associated with D2 structures, although the bulk of the ore accompanied D3 and D4.
D3 - characterised by thrusting along gently dipping D1 shear zones and sinistral shearing along steeply dipping structures, accompanied by Group I and II orebodies (see below) in the respective structures. Quartz-feldspar porphyries (e.g., the Dolly dyke) are interpreted to have intruded during late D2 to D3 and locally host narrow gold-bearing quartz-pyrite veins (Group IV orebodies). These quartz porphyries are deformed by D3 shear zones and cut by S3 fabrics.
D4 - resulted in dextral faults as a response to NE-SW shortening accompanied by steeply dipping stockwork vein (D4a) and breccia systems (D4b) that comprise the Group III orebodies.
D5 - produced strike-slip faults as a result of SE compression.
D6 - characterised by dextral conjugate faults caused by east-west shortening. Neither D5 nor D6 structures are mineralised.

In the transported cover, secondary (supergene) gold with extremely high gold grades was hosted by fluvial sediments within two distinct horizons, each of 2 to 12 m in thickness over a 600 x 200 m area and at a depth of from 5 to 40 m. These were developed near the base of Tertiary palaeochannels and horizontal blankets of mineralisation related to iron redox fronts and associated palaeo-water table.

The ore below the unconformity is developed in both oxidised and fresh bedrock, occurring as a shallow west dipping zone covering a plan area of 1600 x 700 m, and extending to more than 700 m below the surface.

In December 2000 the AngloGold Cleo resource totalled 40.8 Mt @ 3.39 g/t Au, while in December 1998 the Placer Dome Granny Smith section of the deposit had a resource of 11.3 Mt @ 3.2 g/t Au. Together these total more than 170 t of contained Au.

Extensions of the ore at depth comprise the Sunrise Deeps discovery.

Total production to 2010 was 149 t (4.8 Moz) of gold at an average grade of 4.2 g/t Au.

At December 2010, (AngloGold Ashanti reserve statement):
Proved + Probable Reserves were: 13.89 Mt @ 3.08 g/t Au, and
Measured + Indicated + Inferred Resources were: 36.68 Mt @ 2.85 g/t Au (which includes the reserves, and totals 104.38 t of Au),
Additional low grade resources and stockpiles were: 22.8 Mt @ 2.70 g/t Au (for an additional 61.55 t Au)
Production in the year 2006 totalled 14.463 tonnes of Au and by 2010, 12.316 tonnes Au.

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Telfer - Western Australia .................................... Sat. 19 November, 2011

The Telfer gold deposits are within the Paterson Tectonic Province, in the Great Sandy desert, 400 km ESE of Port Hedland, and 1000 km north of Kalgoorlie, in Western Australia (#Location: 21° 46' 08" S, 122° 12' 30" E).

The orebodies are hosted by quartzites, sandstones and siltstones of the Telfer Formation, a member of the late Mesoproterozoic to early Neoproterozoic Yeneena Group. The Yeneena Group (which was metamorphosed at 1130 Ma) unconformably overlies the Palaeo- to early Mesoproterozoic metamorphics of the Rudall Complex which were metamorphosed between 1530 and 1330 Ma.

The Yeneena Group comprises, from the base:
Lower Yeneena Group
Coolbro Sandstone - around 2500 m of planar and trough cross bedded grey, massive and thickly bedded sandstone.
Broadhurst Formation - up to 2000 m of dark grey to black carbonaceous quartz mica siltstone to shale to pelitic schist which conformably overlies the Coolbro Sandstone.
Upper Yeneena Group
Isdell Formation - which comprises around 1000 m of fine grained, well bedded dolomitic and calcareous rocks.
Malu Quartzite - up to 1000 m of mainly massive and uniform metamorphosed quartz sandstone with increasing quantities of pelitic interbeds at both the top and bottom, indicating gradational contacts with the Isdell and Telfer Formations respectively. Much of the quartzite is pyritic and stratabound quartz veins are locally gossanous.
Telfer Formation - which is 600 to 700 m thick and is largely a transition zone between the Malu Quartzite and the overlying, mainly carbonate rich Puntapunta Formation. With the Isdell Formation and Malu Quartzite, it is the main Au bearing formation in the region and comprises an alternating sequence of quartzite, siltstone and shale, subdivided into four quartzite and four shale/siltstone units in the Telfer area, as follows, from the base:
- Lower Vale Siltstone, 2 to 5 m thick - thinly bedded and silicified siltstone with disseminated pyrite and siderite.
- Footwall Sandstone, 20 to 50 m thick - commonly poorly sorted quartz sandstone.
- Middle Vale Siltstone, 5 to 9 m thick - fine grained and thin bedded argillaceous siltstone, claystone, mudstone, minor carbonaceous limestone and calcareous sandstone. It is pyritic and the main ore host in the original Telfer open pits hosting the Middle Vale Reef. Abundant shortite pseudomorphs are evident in this unit.
- Median Sandstone, 25 to 40 m thick - poorly stratified and thick bedded, fine grained and well sorted quartz sandstone with silty or muddy interbeds.
- Upper Vale Siltstone, 1 to 4 m thick - thinly bedded sideritic siltstone with minor fine grained sandstones, containing disseminated pyrite in places.
- Rim Sandstone, 30 to 40 m thick - a stratified sequence of interbedded quartz sandstone to subarkose and argillaceous siltstone.
- Outer Siltstone, up to 500 m thick - well stratified, thin bedded, argillaceous, calcareous and minor carbonaceous siltstones with interbedded sandstone. The lower sections host the 'E Reefs' at Telfer. In the Karakutikati Ranges this unit has laminated dolomite and dolomitic shale prominent near the top.
- Camp Sandstone, 10 to 90 m thick - similar to the Median Sandstone and is commonly pyritic.
Puntapunta Formation - 2000 m thick, comprising an extensive unit of dolomite, limestone, calcarenite and sandstone. The dominant rock type is a well-bedded medium- to coarse-grained clastic dolostone with detrital quartz and lesser muscovite. Fine to coarse grained dark grey calcarenite interbeds within the dolostone, commonly contain pyrite. Siliceous quartz sandstone beds up to 10 m thick are distributed through the unit while cleaved shale and interbedded shale and sandstone are found near the top of the formation to the north of Telfer, marking a transition to the overlying Wilki Quartzite.
Wiki Quartzite - 1000 m thick, conformably overlies the Puntapunta Formation and comprises a continuous sequence of thick bedded, medium grained quartzites.

The structure in the mine area is dominated by broad, gentle, domal structures, with shallow bedding dips on their flanks. The domes are intruded by 680 to 620 Ma granitoids, which on the basis of isotope studies may be related to the emplacement of mineralisation. Granitoids in the district are also associated with porphyry-like Cu-Au, Au and W-Pb-Zn skarn mineralisation, as well as stratibound Au replacemenr reefs (Rowins, et al., 1998).

The ore deposit occurs as a series of silicified, generally conformable, reefs around 2 m thick, and stockwork zones within units of claystone, mudstone, carbonaceous limestone and argillaceous siltstone. These reefs are generally localised along the base of individual siltstone beds each of which overlies a sandstone unit in the lower sections of the Telfer Formation. The Middle Vale Reef (MVR), the main ore zone in the original open pits, lies within the lower 2 m of the Middle Vale Siltstone (MVS). The underlying Footwall Sandstone carries quartz veinlets with 0.1 to 1.5 g/t Au to a maximum of 20 m below the MVS. The other main ore zone, the E Reefs, are localised in the lower sections of the Outer Siltstone. The Middle Vale and E reefs, which comprised the bulk of the ore in the original pits, are remarkably conformable thin sheets of auriferous quartz-pyrite-chalcopyrite mineralisation, or their oxidised equivalents, that extend over an area of at least 20 sq. km. They are conformable in general, but transgressive in detail. The reefs are everywhere within distinctive calcareous, carbonaceous and argillaceous sediments. Significantly large pods are also associated with cross faulting. Primary mineralisation is mainly pyrite and quartz with gold, chalcopyrite and pyrrhotite, and minor bornite and chalcocite, as well as lesser galena, sphalerite, scheelite and Pb-Co-Ni sulphides. Pyrite may locally reach concentration of 20% and extend up to 20 to 30 m into the footwall. Sulphides are present as disseminated blebs and euhedral crystals of pyrite replacing metasedimentary host rocks and as disseminated and locally massive zones in quartz veins, both concordant and discordant. Pyrite and quartz commonly occur as crudely banded, conformable zones of coarse euhedral and fine anhedral grains that mimic the bedding structure in the host siltstones. Common gangue minerals include quartz, sericite, calcite, dolomite, ankerite, tourmaline and albite. Gold occurs as inclusions in pyrite, often associated with small amounts of chalcopyrite. The underground orebodies comprise a series of vertically stacked stratabound, high grade quartz-sulphide (±secondary iron oxides) centred on anticlinal hinges. The reefs are linked by lower grade stockwork vein arrays and sheeted vein sets, with a similar mineralogy to the conformable reefs. At least 8 main reefs are distributed over a stratigraphic interval of >500 m below the MVR and E Reefs (Dimo, 1990; Rowins, et al., 1998; Newcrest, 2006).

The base of supergene ore is approximately 240 to 290 m below the current surface, occurring as both leached gossan and the supergene enriched sulphide mineralisation. The supergene sulphide and primary zones of the Middle Vale Reef are similar in texture and appearance, except that chalcocite has extensively replaced pyrite along grain boundaries and fractures in the former. In some places all pyrite has been replaced, resulting in grades of up to 90 g/t Au and 20% Cu.

The initial mining exploited oxidised and higher grade supergene ore in the top 100 m below the present surface, which were underlain by hypogene mineralisation that rarely exceeded 3 g/t Au in the upper levels. The Telfer sequence is generally oxidised to a depth of 200 m below surface and to as deep as 1000 m along permeable structures. Underground, high grade hypogene ore is also exploited, with individual reefs around 50 cm thick which have grades of up to 60 g/t, diluted to 10 to 12 g/t Au, 0.8% Cu over mining widths.

Mineralisation has been defined in the Main and West domes to a depth of 1300 and 1500 m below the surface respectively. Both deposits remain open at depth and are subject to ongoing exploration (Newcrest, 2011).

The Telfer deposit was discovered in 1971 and brought into production in 1977. After producing 186 t of Au, operations were suspended in late 2000 due to commodity prices and metallurgical problems. The resource was re-assessed and re-developed, and the new open pit mine commenced operations in 2004, followed by the underground extraction in early 2006. The projected mine life (in 2008) was for the open pit to operate until 2023 and the underground mine to 2015 (Newcrest, 2008).

In 1988 reserves + production accounted for 146 t Au at an average grade of 2.35 g/t Au.
In 1996 open pit resources totalled 92 Mt @ 1.1 g/t Au, while
underground resources were 3.9 Mt @ 11 g/t (indicated) + 7.5 Mt @ 6 g/t Au (inferred).
In 1997, the total measured + indicated + inferred resource was - 173 Mt @ 1.4 g/t Au.

The original mine operated from 1977 to 2000, over which period it produced almost 185 t of recovered gold. The redeveloped operation commenced with two open pit mines (Main and West domes) in November 2004 and February 2005 respectively and underground (4 Mtpa) in February 2007.

In June 2005, published reserves and resources totalled (Newcrest reserve statement, 2006):
Total reserves: 360 Mt @ 1.5 g/t Au, 0.18% Cu for 535 t Au,
Total resources: 520 Mt @ 1.57 g/t Au, 0.18% Cu for 815 t Au,
including Open pit - 444 Mt @1.39 g/t Au, 0.13% Cu; Underground 59 Mt @ 2.8 g/t Au, 0.52% Cu; plus satellites and stockpiles.

At the end of June 2011, published reserves and resources totalled (Newcrest website, 2011):
Main Dome open-pit reserves: 240 Mt @ 0.80 g/t Au, 0.10% Cu for 190 t Au,
West Dome open-pit reserves: 190 Mt @ 0.64 g/t Au, 0.06% Cu for 120 t Au,
Underground reserves: 46 Mt @ 1.3 g/t Au, 0.33% Cu for 59 t Au.
Main Dome open-pit resources: 390 Mt @ 0.66 g/t Au, 0.08% Cu for 260 t Au,
West Dome open-pit resources: 370 Mt @ 0.50 g/t Au, 0.05% Cu for 185 t Au,
Underground resources: 100 Mt @ 1.2 g/t Au, 0.31% Cu for 120 t Au.
Other resources resources: 16 Mt @ 0.42 g/t Au, 0.33% Cu for 6.2 t Au,
Ore Reserves are included within Mineral Resources. Total gold in resources in June 2011 was 575 t,

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The summaries above were prepared by T M (Mike) Porter from a wide range of sources, both published and un-published. Most of these sources are listed on the "Tour Literature Collection", soon to be available from the OzGold 2011 Tour options page.

		Another PGC International Study Tour Developed & Managed by Porter GeoConsultancy OzGold 2011 Major Australian Gold Deposits 14 to 19 November, 2011
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	Image: Section of the Kalgoorlie Super Pit, Western Australia.