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Leinster Operations - Perseverance, Rockys Reward, Harmony, Venus |
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Western Australia, WA, Australia |
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Ni
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Leinster Nickel operations are located approximately 330 km north of Kalgoorlie and 90 km south of Mt Keith, in Western Australia and are based on the Perseverance and Rocky's Reward ore deposits which are 2 km apart, and the smaller Harmony deposit, a further 2 km to the north of Rocky's Reward, whilst the more recently mined Venus deposit is ~2.5 km north of Perseverance (#Location: 27° 48' 57"S, 120° 42' 7"E).
These orebodies are found within a regionally extensive ultramafic unit near the eastern margin of the Agnew-Wiluna segment of the more extensive Norseman-Wiluna Greenstone Belt. The greenstone belt in this area has been divided into a structurally repeated eastern and western succession, with all of the known mineralisation in the eastern succession which, in its western sections, comprises a thick tholeiitic basalt, pillowed in places, with abundant sulphidic interflow sediments, spinifex textured komatiite and minor intercalated felsic sediments. Further east the succession is dominated by felsic volcaniclastic sediments and lavas (rhyodacitic to dacitic) with intermittent komatiites and black sulphidic graphitic shales. All of the mineralisation is within the komatiites of this eastern felsic-sediment package dated at around 2700 Ma.
The Perseverance orebody is one of the largest single accumulation of komatiite hosted massive to heavily disseminated sulphides in the world. It occupies the overturned eastern limb of a regional D2 anticline. Regionally, the mineralised komatiite band that hosts Perseverance comprises a thick layer of olivine ortho- to meso-cumulate, capped by a succession of thin spinifex textured flows. At Perseverance the lower cumulate thickens markedly and contains a core of olivine adcumulate, the Perseverance ultramafic complex. This complex comprises a thick, largely intact accumulation of olivine-rich ultramafic rocks (adcumulate to mesocumulate) in which primary igneous cumulate textures are well preserved.
The Perseverance orebody is at the stratigraphic base of the ultramafic complex and is composed of high grade massive and heavily disseminated sulphides, within an extensive sheet of weak sulphides similar to the ore at Mt Keith. The massive sulphides display strong tectonite fabrics and are located in a structurally complex position within the weakly mineralised zone, occurring as a series of steeply dipping, north striking, individual, fault bounded sheets that are the result of physical remobilisation into fault related lodes and dilatant fold hinges. The same structures have divided the main disseminated mineralisation into a series of vertically stacked imbricate lenses. The enveloping disseminated sulphides form a distinct shoot plunging at 70° to the south to more than 1100 m below surface. In contrast the individual structurally controlled massive sulphides shoots strike north and dip steeply to the west.
The heavily disseminated ores of the central zone at Perseverance consistently contain >1.5% Ni (>20 vol.% sulphides) with sulphide aggregates that have a consistent net or semi-net texture and ~4:1 pyrrhotite:pentlandite ratio. The central zone is flanked by the marginal zone which displays systematic decimetre to metre scale layering defined by variations in sulphide content from pyrrhotite to pentlandite dominant bands. These two higher grade zones (the central and marginal) are enclosed by the lower grade dissemination sheet which consists of weakly disseminated sulphides typically containing 0.5 to 0.7% Ni and <5 vol.% sulphides, characterised by lobate aggregates of pyrrhotite:pentlandite (<2:1).
At Rocky's Reward the disseminated and massive sulphides are hosted by two thin komatiite horizons wholly within a package of thick felsic volcanics and sediments. The mineralisation in both lies within a high strain corridor which can be traced to the similar high strain massive sulphides at Perseverance. The ultramafic rocks at Rocky's Reward have been hydrothermally altered, metamorphically recrystallised and serpentinised, with primary igneous textures seldom being preserved. The resultant rock is characterised by coarse grained, randomly oriented metamorphic olivines, now replaced by serpentinites, with carbonate alteration assemblages on the margins of the original ultramafic units. Mineralisation occurs as massive (4 to 6% Ni) and heavily disseminated (0.7 to 4% Ni) sulphides, principally pyrrhotite and pentlandite with trace chalcopyrite. In the massive sulphides the ore minerals are recrystallised into a medium to coarse grained, interlocking granoblastic texture, although sheets of massive sulphide often preserve relict ductile tectonite fabrics. In contrast, disseminated sulphides generally occur as coarse triangular sulphide aggregates interstitial to serpentine pseudomorphs after blade textured metamorphic olivines. Chalcopyrite is common but of a low tenor. Hydrothermal alteration introduced arsenic to produce gersdorffite, cobaltite and niccolite.
Mineralisation at Rocky's Reward is localised in three ultramafic layers. The two eastern layers contain heavy disseminations and lesser massive sulphides and are folded about a steep, north trending fold axis to form two vertically stacked mineralised layers that plunge at 10 to 15° N. These are truncated to the west by a north-trending, steeply dipping high strain zone that contains abundant remobilised massive sulphide.
The smaller Harmony deposit is located 2 km NNW along strike from the Rocky's Reward orebody. The mine stratigraphy trends NNW, is overturned, dipping at 30 to 80°W and has been metamorphosed to middle amphibolite facies. The stratigraphic footwall to the west is composed of 2720 to 2725 Ma volcano-sedimentary rocks and rhyodacite volcanic and volcaniclastic rocks, which are overlain by the host nickel-bearing komatiitic unit. Pyrite rich pelitic units are found in the immediate footwall. The stratigraphic hanging wall is represented by reworked sedimentary or volcaniclastic interlayered with at least two barren spinifex textures komatiite units. The host komatiite is thickest in the centre of the deposit, thinning to both the north and south. Massive and lesser disseminated sulphides are largely concentrated near the western sheared footwall, although lesser concentrations occur throughout the host komatiite at structural locations. Mineralisation has both 'stratigraphic' magmatic and structural controls. Massive sulphides comprise 85% of the resource and disseminated the remaining 15%. The massive sulphides are composed of 80% pyrrhotite and <7% pentlandite with lesser pyrite, violarite, chalcopyrite and magnetite. Ni grades range from 3 to 8%. The less deformed massive sulphides occur along the footwall of the host komatiite and contain 0.1 to 1 cm pentlandite and magnetite surrounded by pyrrhotite. More deformed sulphides are composed of banded pyrrhotite and pentlandite parallel to the elongation of the mineralised lens, enclosing angular clasts of wall rocks. Disseminated sulphides are mainly to the east of the massive sulphides in the hanging wall of the massive sulphides and include pyrrhotite, pentlandite, pyrite and violarite. Stringers of 1 to 10 cm thick remobilised massive sulphides and metamorphosed komatiites and are interpreted to represent post metamorphic remobilised massive sulphides.
The small Venus deposit is located ~2.5 km north of Perseverance. It occurs at the base of the Perseverance Ultramafic Unit, in a host sequence that is bounded to the the west and east respectively by the Hanging Wall 1A Shear Zone/East Fault System and the Perseverance Fault. It is just to the south of Rocky's Reward but on the opposite (eastern) side of the East Fault System. Mineralisation occurs at the base of the Perseverance Ultramafic Unit as massive, matrix and disseminated Ni sulphides with a tenor of ~8% Ni. It is associated with a slight, <100 m, thickening of the ultramafic host, and with the local development of olivine mesocumulate and adcumulate lithologies. The in situ mineralisation has in a primary tube-like shape within the Perseverance Ultramafic Unit, but has been significantly structurally modified. It comprises a high grade core of disseminated sulphides, typically with >1.9% Ni, surrounded across an abrupt change by lower grade disseminations carrying 1.9 to 0.4% Ni. The orebody plunges at ~30° with an azimuth of 340°. The overall shape of the mineralised contact defines an open fold. The basal contact is dislocated by a series of west dipping thrusts with throws of ~50 m. Local remobilisation within these structures result in the formation of massive sulphide ore, including that found up to 300 m along the late, north trending, dextral Venus fault where it impinges on the mineralised base of the Perseverance Ultramafic Unit. This resulted in the development of remobilised massive nickel sulphide within the Venus fault at the northern margin of the defined orebody, with mineralisation occurring with little to no associated host ultramafic. The footwall lithology is dominantly dacite. Near the mineralised contact, the dacite has commonly been intruded by dolerite dykes of variable thickness of ~1 to 25 m. The mineralisation is severely disrupted by at least two east-west trending pegmatite dyke swarms that dip at ~65°W. The information from this paragraph is drawn from Perring et al. (2017).
Production at Perseverance to 1997 was 10.6 Mt @ 2.1% Ni, with 31 Mt @ 1.65% Ni remaining. At Rocky's Reward the production + reserve was of the order of 9.6 Mt @ 2.4% Ni. (production to 1997, 3.2 Mt @ 2.85% Ni - Proved + probable reserve 6.4 Mt @ 2.22% Ni). In addition there are indicated open cut resources of 79 Mt @ 0.8% Ni and inferred resources of 144 Mt @ 0.7% Ni.
At the end of 2004, the Leinster Nickel Operations had reserves + resources of underground ore totalling 53.2 Mt @ 2.15% Ni and open pit ore amounting to 157 Mt @ 0.6% Ni. During 2004 the operation treated 2.73 Mt of ore at a head grade of 1.88% Ni to produce 44 577 tonnes of Ni. In 2003, the Harmony deposit contained a resources of 3.2 Mt @ 2.31% Ni.
Published JORC compliant ore reserves and mineral resources at the Leinster Operation 30 June 2012 (BHP Billiton Annual Report 2012) were:
Open pit massive sulphide resource - 7.0 Mt @ 1.40% Ni;
Underground massive sulphide resource - 21 Mt @ 2.40% Ni;
TOTAL massive sulphide resource - 28 Mt @ 2.15% Ni;
Open pit disseminated resource - 173 Mt @ 0.52% Ni;
including
Open pit reserve - 3.1 Mt @ 1.3% Ni;
Underground reserve - 10 Mt @ 1.8% Ni;
TOTAL reserve - 13.1 Mt @ 1.7% Ni;
Mineral Resources estimated at Rocky's Reward at 30 June, 2016 (Perring et al., 2017) were:
Measured Resource - 3.7 Mt @ 1.4% Ni;
Indicated Resource - 1.1 Mt @ 1.1% Ni;
Inferred Resource - 2.1 Mt @ 1.1% Ni;
TOTAL Resource - 6.9 Mt @ 1.3% Ni.
Remaining JORC compliant Ore Reserves and Mineral Resources at the Leinster deposit at 30 June 2020 (BHP Limited Annual Report 2021) were:
Open Pit
Measured resource, Disseminated - 4.1 Mt @ 0.72% Ni; Massive sulphide - 0.25 Mt @ 4.4% Ni;
Indicated resource, Disseminated - 77 Mt @ 0.58% Ni; Massive sulphide - 1.0 Mt @ 4.9% Ni;
Inferred resource, Disseminated - 52 Mt @ 0.64% Ni; Massive sulphide - 0.37 Mt @ 4.7% Ni;
TOTAL resource, Disseminated - 133 Mt @ 0.60% Ni; Massive sulphide - 1.6 Mt @ 4.8% Ni;
Underground
Measured resource, Disseminated - 15 Mt @ 1.9% Ni; Massive sulphide - 0.63 Mt @ 4.5% Ni;
Indicated resource, Disseminated - 10 Mt @ 1.3% Ni; Massive sulphide - 2.4 Mt @ 4.9% Ni;
Inferred resource, Disseminated - 3.2 Mt @ 1.2% Ni; Massive sulphide - 1.1 Mt @ 4.1% Ni;
TOTAL resource, Disseminated - 28 Mt @ 1.6% Ni; Massive sulphide - 4.2 Mt @ 4.6% Ni;
including
Open pit reserve - 3.4 Mt @ 0.63% Ni;
Underground reserve - 5.0 Mt @ 1.6% Ni;
TOTAL reserve - 8.4 Mt @ 1.2% Ni;
Remaining JORC compliant Ore Reserves and Mineral Resources at the Venus deposit at 30 June 2020 (BHP Limited Annual Report 2021) were:
Underground
Measured resource, Disseminated - 1.2 Mt @ 1.5% Ni; Massive sulphide - 0.11 Mt @ 6.0% Ni;
Indicated resource, Disseminated - 5.4 Mt @ 1.8% Ni; Massive sulphide - 0.7 Mt @ 6.4% Ni;
Inferred resource, Disseminated - 1.1 Mt @ 1.1% Ni; Massive sulphide - 0.35 Mt @ 6.2% Ni;
TOTAL resource, Disseminated - 7.7 Mt @ 1.7% Ni; Massive sulphide - 1.2 Mt @ 6.3% Ni;
including
Probable reserve - 8.6 Mt @ 1.5% Ni;
TOTAL reserve - 8.6 Mt @ 1.5% Ni.
The most recent source geological information used to prepare this decription was dated: 2017.
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.
Perseverance Rocky's Reward
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Barnes S J, Gole M J, Hill R E T 1988 - The Agnew Nickel deposit, Western Australia: Part II. Sulfide geochemistry, with emphasis on the Platinum-group elements: in Econ. Geol. v83 pp 537-550
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Barnes S J, Gole M J, Hill R E T 1988 - The Agnew Nickel deposit, Western Australia: Part I. Structure and stratigraphy: in Econ. Geol. v83 pp 524-536
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De-Vitry C, Libby J W, Langworthy P J 1998 - Rockys Reward Nickel Deposits: in Berkman D A, Mackenzie D H (Eds), Geology of Australian and Papua New Guinean Mineral Deposits The AusIMM, Melbourne pp 315-320
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Duuring P, Bleeker W and Beresford S W, 2007 - Structural Modification of the Komatiite-Associated Harmony Nickel Sulfide Deposit, Leinster, Western Australia : in Econ. Geol. v102 pp 277-297
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Fiorentini, M., Beresford, S., Barley, M., Duuring, P., Bekker, A., Rosengren, N., Cas, R. and Hronsky, J., 2012 - District to Camp Controls on the Genesis of Komatiite-Hosted Nickel Sulfide Deposits, Agnew-Wiluna Greenstone Belt, Western Australia: Insights from the Multiple Sulfur Isotopes : in Econ. Geol. v.107, pp. 781-796.
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Hills R E T, Barnes S J, Gole M J, Dowling S E 1990 - Komatiites in the Agnew-Wiluna Greenstone Belt (Extracts for OzTour 99 Compilation): in Physical Volcanology of Komatiites, A Field Guide to the Komatiites of the Norseman-Wiluna Greenstone Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia GSA (WA Division), Perth Excursion Guide Book No. 1 pp 36-42, 67-76
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Libby J W, Stockman P R, Cervoj K M, Muir M R K, Whittle M, Langworthy P J 1998 - Perseverance Nickel Deposits: in Berkman D A, Mackenzie D H (Eds), Geology of Australian and Papua New Guinean Mineral Deposits The AusIMM, Melbourne pp 321-328
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Libby J W, Stockman P R, Langworthy P J 1997 - Nickel Mineralisation and Geology in the Perseverance-Mount Keith Segment of the Agnew-Wiluna Greenstone Belt: in AGSO Record 1997/41 pp 97-101
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Mamuse A, Porwal A, Kreuzer O and Beresford S, 2010 - Spatial Statistical Analysis of the Distribution of Komatiite-Hosted Nickel Sulfide Deposits in the Kalgoorlie Terrane, Western Australia: Clustered or Not?: in Econ. Geol. v105 pp 229-242
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Marston, R.J., Groves, D.I., Hudson, D.R. and Ross, J.R., 1981 - Nickel sulfide deposits in Western Australia: a review: in Econ. Geol. v.76, pp. 1330-1363.
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Martin J E, Allchurch P D 1975 - Perseverance nickel deposit, Agnew: in Knight C L, (Ed.), 1975 Economic Geology of Australia & Papua New Guinea The AusIMM, Melbourne Mono 5 pp 149-155
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Naldrett A J 1999 - World Class Ni-Cu-PGE Deposits: Key Factors in their Genesis: in Mineralium Deposita v34 pp 227-240
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Perring, C.S., Rieuwers, M.T., Westernm E.E., Menicheli, M.M., Greenwood, W,F. and Gole, M.J., 2017 - Nickel deposits of the Mount Keith and Leinster regions, Agnew-Wiluna Belt: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The Australasian Institute of Mining and Metallurgy Mono 32 pp. 127-132.
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Trofimovs J, Tait M A, Cas R A F, McArthur A, Beresford S W 2003 - Can the role of thermal erosion in strongly deformed komatiite-Ni-Cu-(PGE) deposits be determined? Perseverance, Agnew-Wiluna Belt, Western Australia: in Australian J. of Earth Sciences v50 pp 199-214
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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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