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Greenvale |
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Queensland, Qld, Australia |
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Ni Co
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Greenvale lateritic nickel - cobalt deposit is located in tropical north Queensland, Australia, and is 190 km WNW of the coastal city of Townsville. Ore was railed to the Yabulu refinery near Townsville. The mine operated from 1974 to 1993 when economic reserves were exhausted (#Location: 18° 58' 41"S, 144° 55' 26"E).
The Greenvale deposit is developed over ultramafic rocks emplaced within the major Burdekin River fault zone that defines the boundary between the Proterozoic metamorphics of the Georgetown Inlier to the NW and the Palaeozoic sediments of the Broken River Embayment to the SE. Three major ultramafic bodies are known in the Greenvale area, namely the Precambrian (?) Sandalwood Serpentinite and the Devonian Boiler Gully Complex, both within the Georgetown Inlier and the Devonian Gray Creek Complex in the Broken River Embayment rift sediments.
The Devonian Boiler Gully Complex is the basement or protolith to the Greenvale deposits, comprising a 5.5 sq. km. core within a mantle of gabbro, with no evidence of layering. The serpentinite is dark grey to green, fine grained and soft with veins of chrysotile and disseminated crystals of chromite, and is entirely made up of serpentine. Around 80% is fresh mesh serpentine after olivine, while 15% is platy-textured after enstatite. The fresh serpentinite carries around 37.1% SiO2, 39.2% MgO, 0.63% Al2O3, 6.7% Fe2O3, 0.47% FeO, 0.28% Ni and 0.01% CoO.
The laterite profile over the ultramafics is deep and mature, and fully developed over about one third of the serpentinite, which with the partially eroded remnants has resulted in an area of 3.3 sq. km. of ore development. The laterite profile has been divided into four zones, as follows, from the base:
i). Weathered serpentinite laterite - the transition from fresh to weathered serpentinite corresponds to an SG change from 2.7 to 1.4 and the development of a saprolitic clay mineralogy with retained texture. Limonites (goethite) increase higher in this zone, as does the redeposition of silica in chalcedonic veins with asscoaited chrysoprase, with Ni enrichment reaching a peak near the top of the zone of up to 10x that in the fresh serpentinite. This zone is up to 10 m thick. Nearly half the reserve was from this zone with 1.5 to 1.7% Ni, lower Co (0.05%), low Fe (15 to 20%), high Mn (15%) and average silica (30 to 40%). The ore component of this zone averages 5 m in thickness.
ii). Limonitic laterite - characterised by the loss of the original texture, with a mineralogy primarily of yellow to brown ochreous coloured geothite, accompanied by massive secondary silicification as horizontal bands and irregular pods, particularly at the boundary with the weathered serpentinite (saprolite) zone. Ni concentration is generally less than in the weathered serpentinite zone, although Co reaches peaks of 0.5% (25x enrichment). Cr2O3 and MnO2 are also enriched. This zone is around 5 m thick.
Limonitic ore in the upper part of this zone accounted for around 25% of the reserve with lower average Ni (1.2 to 1.4%), while Co reaches its peak of up to 0.5%, averaging 0.25%, Fe is high (15 to 20%), MgO is low (1 to 5%), and silica is low (15 to 20%). The limonitic ore in this zone is usually in the low central area and averages 3 m in thickness.
Siliceous ore - accounted for a further 25% of the reserve in the upper weathered serpentinite and lower limonitic zone as a). massive siliceous ore with lower Ni (1.2 to 1.3%), lower Co (0.05 to 0.08%), low Fe (15 to 20%), variable MgO and high silica (50 to 60%), and b). boxwork ore in 10 cm to 5 m wide zones of intense fracturing (occurring anywhere in the orebody) where chalcedonic boxes 10 to 50 cm across form, filled with decomposed serpentinite and carrying the highest Ni grades (up to 6%), above average Co (0.15 to 0.2%), low Fe (15%), low MgO (5 to 10%) and high silica (40 to 50%).
iii). Pisolitic laterite - composed of ferruginous concretions, partially or un-consolidated, as pisolites, oolites or irregular plates which increase in diameter upwards to 4 to 5 cm. Ni and Co is depleted to background levels, with a marked increase in Al2O3. This zone is around 7 m thick.
iv). Surface soils - red-brown unconsolidated residual soil with clayey layers, up to 10 m thick, but averaging 3 m.
The initial reserve/resource in 1969 was: 40 Mt @ 1.57% Ni, 0.12% Co.
Production from commencement in 1974 to 1990 totalled: 0.383 Mt of Ni and 32 165 t Co metal respectively.
Reserves + resources in 1990 were: approx. 8 Mt @ 1.35% Ni, 0.11% Co.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1990.
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd. Unauthorised copying, reproduction, storage or dissemination prohibited.
Greenvale
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Selected References:
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Fletcher K, Couper J 1975 - Greenvale nickel laterite, north Queensland: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne Mono 5 pp 995-1001
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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