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TOUR SUMMARY & ORE DEPOSIT DESCRIPTIONS Image: Mount Isa, NW Queensland. 
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:
- Ernest Henry Au-Cu, Queensland.
- Cannington Ag-Pb-Zn-Cu, Queensland,
- McArthur River Zn-Pb-Ag, Northern Territory,
- Mt Isa - George Fisher Zn-Pb-Ag, Queensland,
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 north-east of Cloncurry, 150 km east of Mt Isa and 750 km west of Townsville in north-west Queensland.
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 succession is largely composed of evaporite-rich cover sequence 2 rocks and silici-clastic-rich cover sequence 3 rocks (ca 1740 Ma and ca 1670 Ma, respectively) which overlie crystalline basement formed during the Barramundi Orogeny (ca 1880-1850 Ma). Basement is not exposed in the Cloncurry district. The deposition of cover sequence 2 and 3 rocks was also accompanied by the emplacement of various intrusions and volcanic rocks. The cover sequences were deformed and metamorphosed during the Isan orogeny, which peaked with a regional greenschist to upper amphibolite facies metamorphism associated with a major horizontal east-west compression (D2).
The Williams and Naraku Batholiths (ca 1550-1500 Ma) that largely post-date D2 represent the youngest felsic intrusions in the inlier, and have an outcrop exposure of >1500 sq. km. 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 oxidized than similar older (ca. 1670 Ma) granitoids in the Western Fold Belt of the Mount Isa Inlier. Sodic intrusions of similar age are rare. The K-rich igneous rocks are similar to the intrusions that host Olympic Dam, and form part of a larger series of geochemically-similar Proterozoic intrusions that have a global distribution.
A regionally extensive Na-Ca hydrothermal system in the Cloncurry district (>100 sq. km) affected all rock types, especially the calc-silicate-rich rocks within cover sequence 2, and formed over the same period as the Williams and Naraku Batholiths. The regionally extensive Na and Na-Ca (e.g. actinolite, albite and diopside) 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. It affects the host rocks to all major Cu-Au deposits prior to sulphide mineralisation.
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 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 bounding shear zones and formed a pipe-like zone of dilation in the K-feldspathised metavolcanic rocks. 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 Na-Ca alteration, occurring mainly as albitic plagioclase-, magnetite-, clinopyroxene- and amphibole-rich veining and fault-related breccia-fill. ii). Pre-mineralisation 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. 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. iv). Post-ore multiple stage calcite-dolomite- and/or quartz-rich veining and alteration.
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,
The operation is controlled by Ernest Henry Mining Pty Ltd, a subsidiary of Xstrata Ltd.Return to top
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.
The Cannington deposit lies below 10 to 60 m of Phanerozoic cover 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 hosted by a sequence of garnetiferous psammite within a migmatitic quartzo-feldspathic gneiss terrain. The sequence strikes north-south and is cut by two major NW trending structures. 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 hangingwall.
The sulphide mineralisation is associated with a diverse package of siliceous and mafic rocks. Gangue minerals include pyroxmangite, manganese-fayalite, fluorapatite, fluorite and hedenbergite in the mafic associations, and blue-quartz, feldspar and carbonate in the siliceous lodes. The sulphide assemblage comprises galena and sphalerite, with minor pyrrhotite, marcasite, arsenopyrite and chalcopyrite, and a range of silver minerals, predominantly freibergite. Magnetite is found in some lodes. A number of different strongly folded and faulted lode horizons have been delineated.
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.
The mine is operated by BHP Billiton.
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McArthur River .......... Wednesday 9 November, 2005 .......... Travel by private air charter from Mt Isa.
The HYC orebody at McArthur River is located 50 km SSW of Borroloola and 725 km SE of Darwin in the Northern Territory, Australia (#Location: 16° 26' N, 136° 06'E).
It 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 resource is 227 Mt @ 9.2% Zn, 4.1% Pb, 41 g/t Ag, 0.2% Cu.
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.
Open pit resources in 2006 totalled - 124 Mt @ 13% Zn, 6% Pb, 60 g/t Ag (Xstrata Zinc, 2006).
The McArthur River operation is owned by McArthur River Mines, a subsidiary of Xstrata Zinc.
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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.
Reserves and resources (at June 2006) are as follows (X-Strata 2007):
Proved reserves George Fisher South - 12.5 Mt @ 8.3% Zn, 5.7% Pb, 127 g/t Ag
Probable reserves George Fisher South - 5.9 Mt @ 7.8% Zn, 5.8% Pb, 126 g/t Ag
Measured resources George Fisher South - 25.3 Mt @ 9.7% Zn, 6.9% Pb, 150 g/t Ag
Indicated resources George Fisher South - 10.6 Mt @ 9.2% Zn, 6.6% Pb, 139 g/t Ag
Inferred resources George Fisher South - 10 Mt @ 10% Zn, 6% Pb, 100 g/t Ag
Proved reserves George Fisher North - 11.3 Mt @ 8.9% Zn, 4.7% Pb, 91 g/t Ag
Probable reserves George Fisher North - 15.1 Mt @ 8.3% Zn, 3.9% Pb, 75 g/t Ag
Measured resources George Fisher North - 14.5 Mt @ 10.4% Zn, 5.2% Pb, 101 g/t Ag
Indicated resources George Fisher North - 27.9 Mt @ 9.5% Zn, 4.0% Pb, 74 g/t Ag
Inferred resources George Fisher North - 45 Mt @ 9% Zn, 4% Pb, 80 g/t Ag
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 Ð 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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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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Porter GeoConsultancy Pty Ltd 6 Beatty Street LINDEN PARK 5065 South Australia Telephone: +61 8 8379 7397 Facsimile: +61 8 8379 7397. |
  
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