An International Study Tour to Order
Organised for Vedanta Resources by Porter GeoConsultancy
Base Metal Mines of Northern Australia
7 to 10 November 2005
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Mount Isa
This tour was developed and organised by Porter GeoConsultancy Pty Ltd (PGC) to suit the specific requirements of the Hindustan Zinc and Exploration divisions of Vedanta Resources. All mine visit approvals, and the planning and organisation of logisitics (including ground transport and air charters), meals (including special dietary requirements) and accommodation were undertaken by PGC.

The tour visited the following mines in the State of Queensland and the Northern Territory of Australia:
A detailed itinery explaining the arrangements, what logistics items had been arranged, times, pick-up locations, maps, reporting places and times, etc., was presented to the tour members prior to the commencement of the tour to manage themselves.   A technical Literature Compilation and set of geological maps relevant to the deposits visited were also purchased/prepared and presented to the tour party prior to the commencement of the tour.   The group was based in Mount Isa throughout, travelling to the mines by either hire van or by charter aircraft.

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Ernest Henry .......... Monday 7 November, 2005 .......... Travel by hire van from Mt Isa.

The Ernest Henry IOCG style Cu-Au deposit is located 35 km NE of Cloncurry, 150 km east of Mt Isa and 750 km west of Townsville in north-west Queensland (#Location: 20° 26' 40"S, 140° 42' 21"E).

The deposit lies to the east of the Cloncurry Overthrust, within the Cloncurry-Selwyn zone of the Cloncurry Terrane, which comprises the eastern exposed margin of the Mount Isa Inlier of North-west Queensland. It contains IOCG deposits that are hosted by Palaeoproterozoic (1760-1660 Ma) silici-clastic metasedimentary and metavolcanic rocks that were deposited during periods of ensialic rifting.

The Ernest Henry deposit is hosted within the Eastern Succession of the Mount Isa Inlier, that consists of a poly-deformed Palaeo- and Mesoproterozoic volcano-sedimentary succession which is largely composed of evaporite-rich Cover Sequence 2 and silici-clastic-rich Cover Sequence 3 rocks (CS2 and 3). CS2 and 3 were deposited between 1790 and 1690 Ma and from 1680 to 1610 Ma respectively. To the west, these sequences overlie an older crystalline basement and a core of predominantly Cover Sequence 1 felsic volcanic and related intrusive rocks that correspond to the 1870 to 1850 Ma Barramundi Orogeny of northern Australia. Basement is not exposed in the Cloncurry district. Both CS2 and 3 were deposited in intracontinental rift settings, although the relationship between some parts of the sequence is obscured by the deformation history. Both sequences were also accompanied by the emplacement of various intrusive and volcanic rocks.

The first significant deformation to affect CS2 (but not CS3) was the 1750 to 1735 Ma Wonga extensional event. CS2 was extensively intruded by the 1750 to 1730 Ma Wonga Granite to the west, while the coeval Mount Fort Constantine volcanics are found to the NE. Minor tonalites, granitoids and diorite emplaced between CS2 and 3 have been dated at 1686 to 1660 Ma (including the Ernest Henry Diorite).

Thin skinned deformation of the ~1600 to 1520 Ma Isan Orogeny terminated deposition of Cover Sequence 3, and resulted in gross eastward tectonic transport, interleaving of major lithostratigraphic units, and a dominant north-south tectonic grain. This deformation has been divided into: a D1 event, which involved overall north-south compression, and is characterised by large-scale thrusts and isoclinal folds, thrust reactivation of large, km-scale, basin bounding extensional faults with CS3 rocks thrust over CS2, resulting in overturned limbs and a penetrative rock mass foliation; a D2 event, involving horizontal east-west compression producing major north-south upright to isoclinal folding of CS2 and 3 rocks, and a penetrative cleavage, which peaked at 1595 to 1580 Ma with a regional greenschist to upper amphibolite facies metamorphism and the development of anatectic pegmatites; and a D3 event which includes NW- and NE-trending brittle-ductile corridors of faulting, kinking and folding with steep plunges to the NW and NE, and dominantly north-south trending shear and fault zones and associated breccia formation.

Both CS2 and 3 were intruded by the voluminous Williams and Naraku granite batholiths at 1540 to 1500 Ma (including the 1530 Ma Mt Margaret Granite immediately to the east of the E1 deposits; Marshall and Oliver, 2007; Page and Sun, 1998). These represent the youngest felsic intrusions in the inlier, and have an outcrop exposure of >1500 km
2. They were emplaced in an intracratonic environment, and have a pre-, syn- and post-D3 timing, and are largely composed of alkaline to sub-alkaline, K-rich, A-type, magnetite-bearing granitoids. They range from diorite to syenogranite in composition and are typically more oxidised than similar older (~1670 Ma) granitoids in the Western Fold Belt of the Mount Isa Inlier. Sodic intrusions of similar age are rare.

A regionally extensive Na-Ca hydrothermal system in the Cloncurry district (>1000 km
2) affected all rock types, especially the resultant calc-silicate-rich lithologies of cover sequence 2. This alteration appears to have been formed by multiple periods of hydrothermal activity that locally overlapped and is most intense in breccia zones along large structural conduits and within calc-silicate-rich units. The bulk of the sodic-calcic alteration, dominantly regional albite and scapolite, was associated with fluids that were initially mostly sedimentary formation waters with lesser magmatic components, prior to and during peak metamorphism (Kendrick et al., 2008; Oliver et al., 2008; Baker et al., 2008). Subsequent more structurally controlled albite-actinolite-magnetite-titanite±clinopyroxene assemblages, were synchronous with major granite (e.g., Williams-Naraku batholiths) emplacement (Baker et al., 2008), involving a larger magmatic fluid component, and coincided with formation of the majority, but not all of the significant oxide Cu-Au deposits. These deposits may have some stratigraphic control, but are usually associated with brittle and brittle-ductile shear and fault structures which acted as conduits for the transport of high temperature (300 to 500°C) saline fluids into the host rocks (Williams, 1998).

The Ernest Henry deposit is concealed by 35 to 60 m of extensive Phanerozoic cover and does not outcrop. While the exact stratigraphic position of the host rocks is not known, they have been tentatively correlated with the 1730 ±10 Ma Mount Fort Constantine Meta-volcanics towards the top of Cover Sequence 2. The Mount Fort Constantine metavolcanics comprise dacite and andesite with subordinate metabasalts and calc-silicate metasedimentary rocks. The only other outcrop in the district is the 1480 Ma Mount Margaret granite some 12 km to the east. Within Cover Sequence 2, volcanism is common between 1790 and 1780 Ma, and 1760 to 1720 Ma, with later 1540 to 1450 Ma granitoids.

Within the immediate orebody area the principle lithologies encountered are: i). altered plagioclase phyric andesitic volcanic/hypabyssal rocks (ca 1740 Ma) which host the orebody where they are brecciated; ii). various siliciclastic, calc-silicate-rich and graphitic metasedimentary rocks that occur as <10 m thick intercalations within the metavolcanic rocks; and, iii). medium-grained metadiorite (ca 1660 Ma).

Structural analysis suggests that ore deposition accompanied reverse-fault movement between two northeast trending bounding shear zones and formed a pipe-like zone of dilation in the K-feldspathised metavolcanic rocks. The breccia pipe, plunges at ~45° to the SSESSE, nested between the ductile shear zones (Rusk et al., 2010). The orientation of this dilational zone is consistent with the shape and dip of the Ernest Henry ore breccia.

Four stages of alteration are recognised at Ernest Henry:
i). Regional pre-ore Na-Ca alteration, occurring mainly as albitic plagioclase-, magnetite-, clinopyroxene- and amphibole-rich veining and fault-related breccia-fill.
ii). Pre-mineralisation potassic-(manganese-barium) alteration which only contains minor sulphides, and is typified by multiple stages of K feldspar-, biotite-, amphibole-, magnetite-, garnet- and carbonate-bearing veins, and by fault-related breccia and alteration.
iii). Mineralisation associated alteration, characterised by K feldspar veining and alteration. K feldspar alteration is most intense in the vicinity of copper-gold mineralisation, but forms a halo extending from several hundred meters up to 2 km beyond the ore body (Mark et al., 2006), although this outer halo may represent part of pre-ore regional alteration zone. Mineralisation is divided into two main stages, characterised by similar mineral assemblages. The first stage of economic Cu-Au mineralisation was the main ore-forming event, associated with a matrix-supported hydrothermal breccia that is enveloped by crackle veined K feldspar altered meta-volcanic rocks. The second stage of mineralisation occurs as a network of veins cutting earlier infill-supported ore-breccias, and contains a largely identical mineralogy to earlier stage. The ore-bearing assemblage dominantly comprises magnetite, pyrite, chalcopyrite, carbonate and quartz, with lesser apatite, barite, titanite, actinolite, biotite and fluorite. In the upper levels of the deposit, the bulk of the ore is present as hypogene chalcopyrite infilling between K feldspar-altered breccia clasts, while at greater depths, it both infills between, and replaces clasts. Electrum and native gold are closely associated with pyrite and chalcopyrite (Foster et al., 2007).
iv). Post-ore, volumetrically minor, multiple stage calcite-dolomite- and/or quartz-rich veining and alteration which lacks magnetite, and only carries a little gold. Deeper in the deposit, breccias include rounded clasts of previously mineralised breccias containing magnetite, pyrite and chalcopyrite, indicating multiple superimposed brecciation events (Rusk et al., 2010).

Rusk et al. (2010) interpret the data from Ernest Henry to be consistent with the following genetic trend:
i). Rapid devolatilisation (of possibly both chloride-rich brines and CO
2-rich fluids) within the source magma chamber;
ii). Fluid over-pressuring in the roof of the magma chamber as a result of volatile exsolution and vapour expansion, assisted by a seal created by magma solidification, sodic-calcic alteration and/or contact metamorphism in the carapace of the igneous complex;
iii). Possible leakage of over-pressured magmatic fluid along structures controlling the location of the later breccia pipe, producing a pre-ore potassic alteration halo;
iv). The eventual failure of the seal and sudden release of fluid pressure, resulting in a high-energy fluid flow event driving brecciation and upward transported and milled clasts. The resultant breccia mass permitted the mixing and/or subsequent ingress of basinal brines circulating within fractured rocks several kilometres above the magma chamber. Fluid mixing, rapid depressurisation and resultant cooling led to ore precipitation within the matrix porosity between breccia clasts at the top of the orebody, where, as the fluid flow, temperature and pressure declined the breccia was sealed;
v). At depth, closer to the heat source, the temperature and pressure gradient degraded more slowly, allowing for fluid-rock reaction to be more protracted, such that prolonged chemical interaction between K feldspar-rich host rocks and ore fluids led to replacement style mineralisation within clasts, with the same mineral assemblage as observed in the shallower parts of the deposit.
vi). At the deepest levels, repetition of the cycle may have resulted in the release of a new pulse of fluids which brecciated and tapped earlier formed magnetite-chalcopyrite rich rocks, telescoping mineralised clasts upwards into the orebody along narrow channels, thereby upgrading ore.

The brecciated volcanic mass that hosts the ore forms a plunging elongate body, some 250 m thick, 300 m average length and extending at least 1000 m down plunge to the SSE. The breccia ranges from the unbrecciated volcanics, to crackle fracture veining to clast supported and matrix supported breccia to total clast digestion (massive matrix). The breccias typically contain 5-20 mm subrounded to rounded meta-volcanic and rare biotite altered meta-sedimentary clasts. The matrix is largely composed of magnetite, calcite, pyrite, biotite, chalcopyrite, K feldspar titanite and quartz. Accessory minerals include garnet, barite, molybdenite, fluorite, amphibole, apatite, monazite, arsenopyrite, a LREE fluorcarbonate, galena, cobaltite, sphalerite, scheelite, uraninite and tourmaline. The bulk of the economic mineralisation is restricted to breccia zones with more than 10% matrix.

The total reserve + resource prior to the commencement of mining in 1998 was 166 Mt @ 1.1% Cu, 0.54 g/t Au.
As of June 2003 the remaining resource totalled 117.9 Mt @ 1.13% Cu, 0.52 g/t Au.
At 30 June 2006, the reserves and resources were (Xstrata, 2007):
    Open cut proved reserves - 41 Mt @ 0.9% Cu, 0.5 g/t Au + probable reserves of 20 Mt @ 0.8% Cu, 0.4 g/t Au,
    Open cut measured + indicated resources were the same as, and included the proved and probable reserves,
    Open cut inferred resources - 1 Mt @ 0.4% Cu, 0.2 g/t Au,
    Underground indicated resources - 21 Mt @ 1.5% Cu, 0.7 g/t Au + inferred resources of 23 Mt @ 1.4% Cu, 0.7 g/t Au,

Open pit as at December, 2011 (Xstrata, 2012):
    Total resource and reserve - depleted during 2011 from 17 Mt @ 1.0% Cu, 0.5 g/t Au, 23% magnetite at December 31, 2010
Underground as at December, 2011 (Xstrata, 2012):
    Measured resource - 4 Mt @ 1.3% Cu, 0.7 g/t Au, 32% magnetite
    Indicated resource - 71 Mt @ 1.3% Cu, 0.7 g/t Au, 28% magnetite
    Inferred resource - 13 Mt @ 1.2% Cu, 0.6 g/t Au, 26% magnetite
    Total resource - 88 Mt @ 1.3% Cu, 0.7 g/t Au, 28% magnetite
    Total ore reserve (all probable) - 74 Mt @ 0.95% Cu, 0.5 g/t Au, 23% magnetite.

The operation is controlled by Ernest Henry Mining Pty Ltd, a subsidiary of Glencore Xstrata Ltd.

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Cannington .......... Tuesday 8 November, 2005 .......... Travel by private air charter from Mt Isa.

The Cannington lead - zinc - silver deposit is located 135 km SSE of Cloncurry, 200 km south-east of Mt Isa and 750 km west of Townsville in north-west Queensland (#Location: 21° 52' 9"S, 140° 55' 23"E).

The Cannington deposit occurs in the south eastern corner of the Mt Isa Inlier, to the east of the Cloncurry Overthrust, within the Eastern Fold Belt. The hosts belong to the strongly metamorphosed 1677±9 Ma Fullarton River Group, which have been extensively intruded by the 1560 to 1480 Ma granitoids. The deposit is overlain by 10 to 60 m of Cretaceous and more recent overburden, and was discovered as result of an aeromagnetic survey which identified a sharp magnetic high.

The deposit is hosted by a sequence of garnetiferous psammite within a migmatitic quartzo-feldspathic gneiss terrain. The sequence strikes north-south and is bounded by two major NNW trending structures, the Hamilton and Trepell Faults to the SW and NE respectively, and is cut by similar intervening faults. Four periods of deformation are recognised. The host migmatite gneiss contains intercalated bands of fine grained schistose biotite-sillimanite-quartz bands and pegmatitic quartz-feldspar, while a thick sequence of quartz-garnet-sillimanite and foliated garnet psammite (almandine) is developed in the hanging wall.

Mineralisation is crudely stratabound, occurring along the limbs of a large-scale, tight, recumbent D2 isoclinal synform with an easterly dip and a southerly plunge. The core of the synform is composed of amphibolites with encompassing silver-lead-zinc sulphide mineralisation. It is divided by faulting into a shallow, low-grade Northern Zone and a deeper, higher grade Southern Zone.

Within the Southern Zone, the isoclinal synform appears to control broad repetition patterns between ore lenses. Grade distribution within individual ore zones can also be related to zones of ductile strain and metasomatism influenced by strain partitioning around the termination of the Core Amphibolite. Within this Southern Zone, five main economic lode horizons and nine mineralisation types have been recognised. The mineralisation types are defined on the basis of distinctive zonations in Pb/Zn ratios, and Fe-rich versus siliceous gangue lithologies. The Fe-rich mineralisation types are characterised by coarse-grained, equigranular hedenbergite, Mn-Fe pyroxenoid, magnetite, olivine and fluorite mineralogies. Zones of extensive post-peak metamorphic metasomatism and retrogression contain assemblages of amphibole, almandine, ilvaite and pyrosmalite-dominant mineralogies with sulphide- and fluorite-rich ductile breccias. The siliceous mineralisation types represent late-stage metasomatism, with further modification of the mineralisation and retrogression of Fe silicates. These siliceous types have a distinctive low abundance of magnetite and fluorite (Walters and Bailey, 1998). Gangue minerals include pyroxmangite, manganese-fayalite, fluorapatite, fluorite and hedenbergite in the mafic associations, and blue-quartz, feldspar and carbonate in the siliceous lodes.

Dominant sulphides are galena and sphalerite, with multiple generations and variable intergrowth relationships. Subordinate magnetite-pyrrhotite with minor marcasite and arsenopyrite-lollingite-chalcopyrite are characteristic of the Fe-rich mineralisation types. Pyrite is generally absent and is only locally associated with late structural and low-temperature metasomatic overprints. All of the mineralisation types in the Cannington deposit show a consistent extreme Ag enrichment, occurring as argentiferous galena with freibergite inclusions. High levels of Sb, Cd, As, Cu and F are also a feature of specific mineralisation types. Magnetite is found in some lodes (Walters and Bailey, 1998).

The total resource in May 2007 (Bailey, 1998) comprised - 43.8 Mt @ 11.6% Pb, 4.4% Zn, 538 g/t Ag.
Production in 2003-04 totalled 64 183 tonnes of Zn, 263 305 tonnes Pb and 1206.364 tonnes Ag.

Reserve and resource figures as at 30 June 2007, published by BHP Billiton (2008) include:
    Total measured + indicated + inferred resource - 44 Mt @ 383 g/t Ag, 8.9% Pb, 4.2% Zn, including
    Total proved + probable reserve - 22 Mt @ 402 g/t Ag, 9.3% Pb, 4.1% Zn.

Remaining JORC compliant mineral resources as at 30 June 2015, published by South32 (2015) include:
    Measured resource - 47 Mt @ 201 g/t Ag, 5.53% Pb, 3.66% Zn,
    Indicated resource - 14 Mt @ 127 g/t Ag, 3.91% Pb, 2.81% Zn,
    Inferred resource - 10 Mt @ 82 g/t Ag, 3.00% Pb, 1.95% Zn,
  Total underground resource - 71 Mt @ 170 g/t Ag, 4.86% Pb, 3.26% Zn, including
  Open pit
    Measured resource - 13 Mt @ 90 g/t Ag, 3.66% Pb, 2.21% Zn,
    Indicated resource - 7.9 Mt @ 58 g/t Ag, 2.51% Pb, 1.83% Zn,
  Total open pit resource - 20.9 Mt @ 78 g/t Ag, 3.23% Pb, 2.07% Zn.

The mine was originally operated by BHP Billiton, but was included in the South32 demerger from BHP Billiton in 2015.

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McArthur River .......... Wednesday 9 November, 2005 .......... Travel by private air charter from Mt Isa.

The HYC stratabound, sediment-hosted zinc-lead-silver deposit at McArthur River is located 50 km SSW of Borroloola and 725 km SE of Darwin in the Northern Territory, Australia (#Location: 16° 24' 41"S, 136° 5' 41"E).

  The HYC deposit was first indicated by the discovery of a small outcrop of jasper containing acicular crystals of hemimorphite by Mount Isa Mines Ltd in 1955. After testing more promising targets in the district, a follow-up drill hole in 1959 revealed this outcrop was part of an otherwise barren breccia bed 20 m above the main flat lying, zinc- and lead-bearing pyritic shales of the HYC orebody which is largely concealed below alluvial cover. The deposit was subsequently delineated, but due to the very fine grained nature of the sulphides that precluded an adequate metallurgical recovery was not developed. After extensive testing, MIM Ltd started mining and processing ore from an underground mine in 1995. In August 2005, McArthur River Mining (MRM) commenced a test open pit that was subsequently expanded into full production in April 2007, when underground mining ceased.

Regional setting

  The McArthur River deposit lies within the McArthur Basin, part of the NW-SE trending Carpentaria Zinc Belt, which extends for >1200 km, from Mount Isa in Queensland to the south, to Arnhem Land in the Northern Territory in the north.
  The Palaeo- to Mesoproterozoic McArthur Basin contains a 5 to 10 km package of mostly unmetamorphosed sedimentary and volcanic rocks deposited between ~1800 and 1575 Ma, and covers an area of ~180 000 km
2. This succession unconformably overlies 1890 to 1820 Ma metamorphosed and deformed igneous and metamorphic basement rocks of the Pine Creek and Arnhem Province to the NW and NE repectively, and the 1860 to 1840 Ma Murphy tectonic ridge to south. The latter was likely a palaeogeographic high, partially separating the McArthur Basin from the South Nicholson Basin and Lawn Hill Platform of the Isa Superbasin in Queensland (Plumb and Wellman 1987; Wygralak et al., 1988; Ahmad et al., 2013). Palaeozoic and younger sedimentary sequences of the Georgina, Arafura and Carpentaria basins unconformably overlie the McArthur Basin succession to the SW, north and SE repectively. The McArthur Basin may be continuous, beneath the Georgina basin, with the Tomkinson Basin in the Tennant Creek area, >300 km to the SW (Ahmad et al., 2013).
  The McArthur Basin is punctuated by two main, 50 to 100 km wide and ~300 km long asymmetric zones of faulting, the Walker and Batten fault zones that lie along the same north-south trend, but are separated and marginally offset by the ~20 km wide, ESE-trending Urapunga Fault Zone. This latter cross-cutting fault zone also divides the larger basin into the northern and southern McArthur basins. A deep seismic reflection survey (Rawlings et al., 2004) showed that the entire succession within these basins is essentially horizontal and ~8 km thick with no significant variation on either side of or within the Walker and Batten fault zones (Rawlings 1999; Rawlings et al., 2004; Ahmad et al., 2013). This is contrary to the long held interpretation that these two zones represented grabens, the Walker and Batten troughs, flanked by thinner shelf sequences (e.g., Plumb and Derrick 1975; Plumb et al., 1980, 1990, Plumb and Wellman 1987).
  The McArthur River deposit is located immediately to the west of the major Emu Fault on the eastern margin of the Batten Fault Zone in the Southern McArthur Basin (Ahmad et al., 2013).
  The sequence within the McArthur Basin is part of the broader Mt Isa-McArthur succession, which is, in turn, is part of the Northern Australian Platform cover. This 5 to 15 km thick volcano-sedimentary pile was deposited during the period 1800 to 1580 Ma in an intracontinental setting. Deposition took place in three super-basins which represent three nested cycles of deposition and exhumation, specifically the Leichhardt (1798 to 1738 Ma), Calvert (1728 to 1680 Ma) and Isa (1667 to 1575 Ma) super-basins, terminated by the 1590 to 1500 Ma Isan Orogeny, which was followed by the fourth and younger, ~1500 to ~1400 Ma Roper super-basin (Jackson et al., 1999, 2000; Betts et al., 2003; Withnall and Cranfield, 2013; Stewart, GeoScience Australia 2015). Each of these super-basins corresponds to a period of extension, and each is ended by a basin inversion, although less intense inversions are also recorded within the duration of these super-basins, affecting the stratigraphic packages deposited within them.
  All of the major stratabound Zn-Pb-Ag deposits of the Carpentaria Zinc Belt, including McArthur River, are hosted by 2 to 8 km thick successions of the Isa Superbasin, ranging in age from ~1660 to 1650 Ma (Dugald River, Lady Loretta), ~1650 Ma (Mt Isa), ~1640 (McArthur River) to 1595 Ma at Century (Queensland Department of Mines and Energy, 2000; Chen et al., 2003).
  Rawlings et al. (1997) and Rawlings (1999) divided the McArthur Basin succession into five basin-wide depositional 'packages', each of which is disconformity or unconformity bounded and characterised by similarities in age, stratigraphic position, lithofacies composition, style and composition of volcanism, and basin-fill geometry across the McArthur Basin. These packages can be related to the super-basins of Jackson et al. (1999, 2000).
  Within the Southern McArthur Basin, the packages, stratigrapic units and super-basins are as follows:
Redbank package which comprises the Tawallah Group that corresponds to the Calvert super-basin succession. The Tawallah Group unconformably overlies basement metamorphic rocks of the Murphy tectonic ridge, with the Leichhardt super-basin not being represented. It is composed basal conglomerates overlain by shallow marine and fluvial sandstones, with lesser mudstones, dolostone, basaltic and rhyolitic volcanic rocks, and coeval and younger, doleritic and granitic intrusive bodies. Available SHRIMP U-Pb zircon dates from near the centre of the succession range from 1708 to 1730 Ma (Page et al., 2000; Page and Sweet, 1998; Rawlings, 2002).
Goyder package of the upper Calvert super-basin, which is largely absent from the Southern McArthur Basin, but may include some sandstones included in the upper Tawallah Group (Ahmad et al., 2013; Rawlings, 1999).
Glyde package, which corresponds to the lower Isa super-basin, and is represented by the McArthur Supergroup that hosts the McArthur River deposit. In contrast to the unconformably underlying Tawallah Group, that is predominantly arenaceous, the up to 5 km thick McArthur Group comprises a succession of platformal stromatolitic dolostone and clastic sedimentary rocks with local pyritic and carbonaceous siltstone units (Winefield 1999). Although exposures of the McArthur Group are confined to Batten Fault Zone, seismic data indicates that it continues at depth beyond the inferred limits of that fault zone (Rawlings et al., 2004). It is subdivided into the Umbolooga and overlying Batten subgroups, separated by a possible unconformity. The lower half of the Umbolooga Subgroup is characterised by alternating thick (200 to 650 m) units of sandstones, dolostones and dolomitic arenites. This succession fines upwards to dolostones and dololutites, including the 10 to 900 m thick, 1640±4 Ma Barney Creek Formation, composed of finely bedded to laminated, dolomitic, carbonaceous and pyritic siltstone, shale and dololutite, with locally abundant tuff beds and breccias, that hosts the McArthur River deposit within the HYC Pyritic Shale Member. This unit is underlain by the dololutites of the Teena Dolostone and is overlain by the uppermost unit of the Umbolooga Subgroup, the 30 to 350 m thick Reward Dolostone composed of dololutite, silty dololutite and lesser bedded to cross-bedded dolarenite. A local inversion and reactivation of faulting is recorded at ~1640 Ma. The overlying Batten Subgroup is largely composed of shallow marine to tidal and emergent dolostones, dololutite, dolomitic siltstones and lesser dolarenites and a few beds of quartz sandstone. The uppermost unit is dated at 1614±4 Ma (Ahmad et al., 2013).
Favenc package, which corresponds to the upper Isa super-basin, and within the Southern McArthur Basin is represented by the up to 1600 m thick Nathan Group. This sequence, which unconformably overlies the McArthur Group, was deposited in shallow marine to terrestrial setting, and comprises a relatively thin and lenticular basal siliciclastic and often conglomeratic unit, overlain by thicker carbonate and siliciclastic rocks containing tuff beds that have yielded a date of 1589±3 Ma. The Nathan Group includes the quartz arenite and dolarenite with cross-beds, ripple marks and commons gypsum and halite casts of the widespread, up to 700 m thick Karns Dolostone (Ahmad et al., 2013).
Wilton package of the Roper super-basin, represented by the widespread Roper Group which covers an area of ~145 000 km
2 and comprises an upward-coarsening cyclic succession of mainly marine mudstone alternating with sandstone, with minor micritic and intraclastic limestone, and ooidal ironstone (Ahmad et al., 2013).

Deposit geology


This record is currently being progressively updated and expanded.

  HYC is a shallow dipping, shale hosted, stratabound deposit hosted by the Middle Proterozoic (1643±10 Ma) HYC Pyritic Shale Member of the McArthur Group, in the McArthur Basin, just south of the Gulf of Carpentaria in the Northern Territory.

The McArthur Group is a sequence of interbedded dolostones (massive dolomite, stromatolitic dolomite, thinly bedded dolomite and dolomitic siltstones), gypsum rich beds, red beds and quartz arenite, with minor lutite, sedimentary breccia, siltstone and tuff.

The ore occurs as seven conformable, well banded, semi massive sulphide units separated by thicker, barren sedimentary breccias with clasts up to 1 m across.

The major sulphides are pyrite, sphalerite and galena, with lesser chalcopyrite, arsenopyrite and marcasite. The mineralisation covers an area of 2 sq km and averages 55 m in thickness. It is elongated parallel to the major Emu growth Fault which is 1.5 km to the east, but is separated from the ore by carbonate breccias of the Cooley Dolomite Member.

The total geological resources prior to mining - 227 Mt @ 9.2% Zn, 4.1% Pb, 41 g/t Ag, 0.2% Cu (Logan et al., 1990).

Reserves and resources as of mid 2004 (Xstrata Zinc) totalled:
  Proven reserve - 5.2 Mt @ 31.0% Zn, 5.3% Pb, 53 g/t Ag,
  Probable reserve - 26.0 Mt @ 11.0% Zn, 5.1% Pb, 53 g/t Ag
  Measured resource - 80.0 Mt @ 13.0% Zn, 5.8% Pb, 57 g/t Ag,
  Indicated resource - 41.0 Mt @ 12.0% Zn, 5.5% Pb, 57 g/t Ag,
  Inferred resource - 0.7 Mt @ 17% Zn, 5% Pb, 60 g/t Ag.

Production from McArthur River in the 12 months to June 2004 totalled - 1.59 Mt @ 13.1% Zn, 5.6% Pb, 55 g/t Ag, representing the final stages of the underground mine before commencement of the open operation in 2005.

According to Ahmad et al. (2013), ore reserves and mineral resources at McArthur River at 30 June 2007 were:
  Total reserves - 46.3 Mt @ 9.6% Zn, 4.2% Pb, 43 g/t Ag;
  Total resources - 144 Mt @ 11.2% Zn, 4.8% Pb, 48 g/t Ag.

Remaining JORC compliant ore reserves and mineral resources as at 31 December, 2016 (Glencore, 2017) were:
  Ore reserves
    Proved reserve - 71.2 Mt @ 10.6% Zn, 5.00% Pb, 50.1 g/t Ag;
    Probable reserve - 45.0 Mt @ 7.4% Zn, 3.6% Pb, 37 g/t Ag;
    Total reserve - 117.0 Mt @ 9.4% Zn, 4.5% Pb, 45 g/t Ag.
  Mineral resources which are inclusive of reserves
    Measured resource -123 Mt @ 9.94% Zn, 4.64% Pb, 46.9 g/t Ag;
    Indicated resource - 64 Mt @ 8.9% Zn, 4.1% Pb, 43 g/t Ag;
    Measured + indicated resource - 190 Mt @ 9.6% Zn, 4.5% Pb, 46 g/t Ag;
    Inferred resource - none reported.
The current mine capacity is 5 Mt of ore per annum.

The McArthur River operation is owned by McArthur River Mining, a subsidiary of Glencore.

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George Fisher Zn-Pb-Ag .......... Thursday 10 November, 2005 .......... Travel by hire van from Mt Isa.

The George Fisher South (Hilton) and George Fisher North are located approximately 20 km north of the city of Mt Isa, in north-western Queensland, Australia and 975 km west of Townsville.

The George Fisher orebodies lie within the Mt Isa-McArthur basin system that are part of the Northern Australian Platform cover which is a 5 to 15 km thick volcano-sedimentary succession deposited during the period 1800 to 1580 Ma. Deposition took place in three super-basins which represent three nested cycles of deposition and exhumation, specifically the Leichhardt (1800 to 1875 Ma), Calvert (1735 to 1690 Ma) and Isa (1670 to 1580 Ma) super-basins, terminated by the 1590 to 1500 Ma Isan Orogeny, which was followed by the younger Roper super-basin. All of the major stratabound Zn-Pb-Ag deposits of the system, including George Fisher deposits, are hosted by the Isa super-basin.

Both of the George Fisher orebodies lie within the Middle Proterozoic (1653 Ma) pyritic, dolomitic siltstone of the approximately 1000 m thick Urquhart Shale, which is near the top of the Mt Isa Group. The Mount Isa Group was deposited within the Leichhardt River Fault Trough, and belongs to Cover Sequence 3 of the Isa super-basin in the Western Fold Belt of the Mt Isa Inlier.

The Western Fold Belt lies immediately to the east of the Lawn Hill Platform that embraces the Century deposit some 250 km to the NNW, hosted by the McNamara Group, also part of the Isa super-basin. The McNamara Group temporally overlaps the Mt Isa Group, but is generally younger than the Mt Isa Group. Both groups unconformably overlie the rift phase sediments and lesser volcanics of the Calvert super-basin.

Cover Sequence 3 platform and sag phase sediments of the Isa and Calvert super-basins unconformably overlies the thick mafic volcanics and quartzites of Cover Sequence 2 of the Leichhardt super-basin, which includes the 7 km thick Eastern Creek Volcanics.

In the George Fisher mine area, the Mt Isa Group strikes north-south and has a persistent moderate to steep westerly dip. It is around 4500 m in thickness and comprises a succession of siltstone and shale which are commonly dolomitic, calcareous or pyritic, with minor sandstone and conglomerate, mainly at the base, thickening to the east, and minor felsic tuff. The overall sequence is dated at approximately 1670 Ma.

The George Fisher mines are some 20 km to the north along strike from the Mt Isa orebodies, and are located immediately to the east of the major, north-south trending Mt Isa fault system. Both are hosted by similar facies in the upper sections of the same host Urquhart Shale which also embrace the Mt Isa Zn-Pb ores, although the orebodies are generally thinner and more disrupted by faulting than the similar ores at Mt Isa. Little copper is known in association with the zinc lead ores at both Hilton and George Fisher.

The George Fisher South (Hilton) deposits occur as 7 to 10 stacked ore lenses within a 250 m stratigraphic interval, which have been complicated by intense shortening associated with the Isa Orogeny. The George Fisher North deposit is present as 11 stacked lenses within a 350 m stratigraphic interval. Bedding-parallel, fine-grained pyrite is abundant, with from 10 to >50%, throughout the host stratigraphy, over a thickness of 800 m, enveloping both deposits and extending over a strike length of >10 km.

The Zn-Pb ores occur as individual stratabound, well banded sphalerite-galena-pyrite ore lenses separated into hangingwall and footwall orebody groups by a barren zone. Sub-economic mineralisation follows the strike of the Urquhart Shale for 4 km to the north and south of the economic orebodies.

Within the deposits there is a zonation such that the Zn/Pb ratio varies from 4 to 10 in the lowermost lenses to 1 to 4 in the uppermost ore lenses.

George Fisher North is concealed and is partially connected to George Fisher South (Hilton) on its northern margin.   Both mines are underground operations and are owned and operated by Xstrata Zinc.

The original resources were estimated as follows (Forrestal 1990, Valenta 1994, Chapman 2004):
    George Fisher South (Hilton):  120 Mt @ 10.2% Zn, 5.5% Pb, 100 g/t Ag,
    George Fisher North:               108 Mt @ 11.1% Zn, 5.4% Pb, 93 g/t Ag.

JORC compliant ore reserves and mineral resources (at June 2006) were as follows (X-Strata 2007):
  George Fisher South underground
      Proved reserves - 12.5 Mt @ 8.3% Zn, 5.7% Pb, 127 g/t Ag
      Probable reserves - 5.9 Mt @ 7.8% Zn, 5.8% Pb, 126 g/t Ag
      Measured resources - 25.3 Mt @ 9.7% Zn, 6.9% Pb, 150 g/t Ag
      Indicated resources - 10.6 Mt @ 9.2% Zn, 6.6% Pb, 139 g/t Ag
      Inferred resources - 10 Mt @ 10% Zn, 6% Pb, 100 g/t Ag
  George Fisher North underground
      Proved reserves - 11.3 Mt @ 8.9% Zn, 4.7% Pb, 91 g/t Ag
      Probable reserves - 15.1 Mt @ 8.3% Zn, 3.9% Pb, 75 g/t Ag
      Measured resources - 14.5 Mt @ 10.4% Zn, 5.2% Pb, 101 g/t Ag
      Indicated resources - 27.9 Mt @ 9.5% Zn, 4.0% Pb, 74 g/t Ag
      Inferred resources - 45 Mt @ 9% Zn, 4% Pb, 80 g/t Ag

JORC compliant ore reserves and mineral resources (at 31 December, 2011) were as follows (X-Strata 2012):
  George Fisher South underground
      Proved + probable reserves - 19.6 Mt @ 6.5% Zn, 4.4% Pb, 96 g/t Ag
      Measured + indicated resources - 49.8 Mt @ 8.6% Zn, 5.9% Pb, 125 g/t Ag
      Inferred resources - 23 Mt @ 8% Zn, 5% Pb, 113 g/t Ag
  George Fisher North underground
      Proved + probable reserves - 61.8 Mt @ 7.5% Zn, 3.6% Pb, 62 g/t Ag
      Measured +indicated resources - 106.2 Mt @ 8.6% Zn, 3.7% Pb, 63 g/t Ag
      Inferred resources - 65 Mt @ 8% Zn, 4% Pb, 69 g/t Ag
  Handlebar Hill open pit primary
      Proved + probable reserves - 2.1 Mt @ 7.6% Zn, 3.4% Pb, 54 g/t Ag
      Measured +indicated resources - 6.9 Mt @ 6.9% Zn, 2.3% Pb, 43 g/t Ag
      Inferred resources - 1 Mt @ 5% Zn, 2% Pb, 30 g/t Ag
  Handlebar Hill open pit oxide
      Proved + probable reserves - 0.5 Mt @ 0.4% Zn, 8.5% Pb, 89 g/t Ag
      Measured +indicated resources - 0.6 Mt @ 0.4% Zn, 7.8% Pb, 85 g/t Ag
      Inferred resources - Nil

Mine production in 2005 totalled 2.7 Mt @ 8.3% Zn, 5.0% Pb, 115 g/t Ag.

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Vedanta Resources - background

Vedanta Resources plc is a London listed diversified and integrated FTSE 250 metals and mining group with annual sales of USD 1.9 billion. The company's principal operations are located in India, where it has a major market share in each of its main metals: aluminium, copper, zinc and lead. Its principal zinc assets include three main mines, Rampura-Agucha (reserves+resources approx. 75 Mt @ 12.7% Zn, 1.8% Pb), Rajpura-Dariba (reserves+resources approx. 42.5 Mt @ 6.3% Zn, 2.1% Pb) and Zawar (reserves+resources approx. 42 Mt @ 4.4% Zn, 2.3% Pb), all in Rajasthan. These mines supply the company's three smelters, two in Rajasthan and one in Andhra Pradesh (with a combined capacity of 400 000 tpa Zn and 35 000 tpa Pb). The company's annual mine production has been around 210 000 t. of contained Zn, but is currently being expanded to 400 000 tpa, and is managed through its subsidiary Hindustan Zinc Ltd. Vedanta's Indian copper interests are principally smelting (300 000 tpa Cu metal capacity) through its subsidiary Sterlite Industries. There are also substantial copper operations in Zambia (51% of Konkola Copper Mines 250 000 tpa Cu) and 2 copper mines in Australia (Thalanga and Mt Lyell). The company's aluminium mining and smelting capacity is currently being expanded to 400 000 tpa, supported by its own power stations.

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For more information contact:   T M (Mike) Porter, of Porter GeoConsultancy   (

This tour was organised by:
T M (Mike) Porter of Porter GeoConsultancy Pty Ltd on behalf, and to the specification, of the client.

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