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Kunwarara |
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Queensland, Qld, Australia |
| Main commodities:
Mg
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The Kunwarara magnesite deposit is located 60 km NW of Rockhampton in central Queensland, Australia.
The Kunwarara magnesite deposit was discovered in 1985 by Queensland Metals Corporation. Pancontinental Mining Limited subsequently acquired a 40% interest in the venture, and the Austrian company Radex Heraklith purchased 10%. A series of acquisitions, mergers, sales and consolidation resulted in 100% of the operation being held by a new company, Australian Magnesium Corporation. However, AMC was to sell the mine to Resource Capital Funds in December 2004 and renamed the holding company operating the mine and controlling the magnesia and magnesite assets, to QMAG Limited. Global, Belgium based industrial and minerals company, Sibelco, purchased 100% of QMAG Limited from Resource Capital Funds in April 2012.
Mining began at the Kunwarara mine in 1991 at the KG1 open pit where the beneficiation plant is situated. The KG 3 began operation in 1999 and the following year, KG2 open pit, 6.5 km SE of KG1, commenced production. The Oldman South and Oldman North deposits, ~5 km further to the SE, were developed in later years. In 2000 a second pre-concentration plant was was constructed at the KG2 open pit. This concentration plant involved the crushing, scrubbing and screening of the magnesite. The two beneficiation plants treat the low silica, low calcium magnesite before it is trucked to the company's processing plant at Parkhurst in north Rockhampton. By the end of 2006 the Kunwarara operation had mined 43 Mt of ore that in turn had produced >5.7 Mt of top grade beneficiated magnesite.
Regionally, the Kunwarara deposit is located on the boundary between the Marlborough and Wandilla Terranes, and is located in a Tertiary basin that occupies a 22 km long, arc shaped depression, possibly a half graben, bounded to the east by the Tungamull Fault. The deposit occurs as sheet like lenses of magnesite developed in the upper portions of a Tertiary to Quaternary sedimentary sequence. These sediments were deposited in a shallow fresh water basin and were derived from a surrounding basement of metamorphic rocks of the Curtis Island Group and Carboniferous to Devonian ultramafic rocks, mainly altered to serpentinites by thrusting, and by Permian granitic intrusives.
The deposit is covered by a 0.3 to 12 m (averaging 4.6 m) thick humus rich black clay layer and does not outcrop. It occurs as 4 high grade zones of 'bone type', low iron, cryptocrystalline magnesite covering an area of 49 sq. km that is 15 km long, elongated NW-SE. The magnesite zone averages 11 m in thickness and it is defined by a 5% magnesite cut-off. The typical profile through the sequence in the orebody area comprises, from top to bottom (after Searston, 1998):
• Humus rich black clays and silts - which overlie the sandy siltstones with a sharp contact and form the ubiquitous black soil cover on the Kunwarara area. This unit is generally massive, but can contain local layers of dark manganiferous silty material and fine grained sands. It is devoid of magnesite. It was probably deposited on a low energy floodplain all by sheet flooding.
• Olive to green sandy siltstone - a poorly cemented sandy siltstone with a thickness of between 3 and 15 m. The courser are classic component of this unit comprises quartz and feldspar in a matrix of silt and smectite. The silt is mainly finely crystalline illite. Manganese veinlets and globules our common. Magnesite occurs as small porous nodules up to 40 mm in diameter. This unit is interpreted to have been deposited in a low energy fluvial environment.
• Fine grained sandstone - marking a sharp transition from unconsolidated gravel into weakly indurated sandstone that is reddish in colour, grading upwards to grey. It has a thickness of between 5 and 20 m, and is generally fine to medium grained and composed of feldspar, quartz, minor magnetite and clay. It contains wispy, dendritic veinlets and small globules of manganese within the sandstone mass. Magnesite nodules are common, especially in the upper portion of the sandstone. The bulk of the magnesite is porcelainous and occurs in nodules of up to 300 mm in diameter. Fluvial channels have been recognised, indicating deposition on a fluvial floodplain.
• Unconsolidated gravels and sand of fluvial channel fill or beach origin, not always present. The thickness of this unit averages 10 m with the average depth from surface varying from 20 to 40 m. Gravels comprise unconsolidated, well rounded quartz pebbles and cobbles in a fine-grained sandy matrix. The sandy units are fine grained, not cemented and are composed of reddish sandy mud with wispy white layers of magnesite rich mud.
• Basement granite or serpentinite.
The magnesite occurs as irregular nodules from 1 to 500 mm in diameter, usually within the mudstones and weakly indurated sandstone units to depths of 20 m but rarely deeper.
Two types of magnesite are found, namely bone magnesite which is white, dense, compact, extremely hard and porcelainous with a rough surface and conchoidal fracture that forms the biggest nodules up to 50 cm in diameter, sometimes forming aggregates up to 1 m across, and porous magnesite which is more common, softer and more porous, lacking the porcelainous texture and conchoidal fracture, and more likely to contain inclusions of non-magnesite material. The latter tends to be lighter, with cavities and porosity of 10 to 20% and in extreme cases >50%, resembling volcanic scoria. Characteristic magnesite nodules assayed: 94 to 98% MgO, 0.8 to 2% CaO, 0.7 to 2.7% SiO2, 0.1 to 0.3% Fe2O3, 0.1 to 0.3% Al2O3, 0.002% B2O3, 0.06 to 0.2% MnO.
The original resource in 1989 was of the order of 800 Mt of sediment hosted in situ material of which 400 Mt was estimated to be low iron nodular cryptocrystalline magnesite.
Reserve and resource figures in 2000 were stated as (QMag website):
Proven+probable reserve - 122.3 Mt containing 34.8 Mt of magnesite,
Measured+indicated resource - 142.6 Mt containing 41.9 Mt of magnesite,
Inferred resource - 1.2 Gt containing 400 Mt of magnesite,
Information in this summary is partly drawn from: Searston, S.M.,1988 - Resource estimation and the Kunwarara magnesite deposit; A thesis submitted in fulfilment of the requirements of a Master of Economic Geology, University of Tasmania, 356p.
For more detail consult other reference(s) listed below.
The most recent source geological information used to prepare this summary was dated: 1998.
Record last updated: 24/2/2019
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.
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Selected References:
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Burban B 1990 - Kunwarara Magnesite deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v2 pp 1675-1677
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