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Yakabindie - Six Mile, David, Goliath, Sheba |
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Western Australia, WA, Australia |
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Ni Cu
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Yakabindie disseminated nickel deposits, which include David, Goliath North, Goliath Central, Goliath South, Sheba and Six Mile Well are distributed over a strike length of >5 km, and are located ~40 km south of Mt Keith in the Archaean Agnew-Wiluna greenstone belt/segment of the Kalgoorlie Terrane, within the Yilgarn craton in Western Australia.
The western Agnew-Wiluna greenstone belt varies from 2 to 17 km in width and comprises an attenuated belt, characterised by major wrench faults traceable over hundreds of kilometres, at least two phases of complex folding, and generally steep dips. In the Yakabindie - Mt Keith area it can be divided into three domains, namely the i). Yakabindie; ii). Agnew; and iii). Mount Keith-Perseverance domains.
Within the overall belt, the sequence has been divided into a Lower and an Upper Greenstone sequence. The Lower sequence is composed of metamorphosed ultramafic, mafic, felsic volcanic, and sedimentary rocks. The Upper Greenstone, which contains all of the significant Ni mineralisation, is composed of meta-basalt, meta-gabbro and meta-sedimentary rocks and comprises i). a basal unit including high magnesian greenstones overlain by thin cherts; ii). a thick sequence of felsic to mafic volcaniclastics and minor pelitic sediments and black shales; followed by iii). a 2500 m thick zone of extensive komatiitic volcanics, predominantly interspersed with layered gabbro units, and high magnesian and tholeiitic basalts with subordinate felsic volcanics; iv). the uppermost unit is composed of fine to medium grained clastic sediments and conglomerates.
The largest of the deposits is the Six Mile, which with David, Goliath North, Central and South occur as a series of pods at the same 'stratigraphic position', in close association with the highly dismembered northern part of the project area. Each pod is enclosed in marginal zones of olivine orthocumulate and have gradational lateral contacts with thinner orthocumulate and spinifex textured layers which link the individual bodies along strike.
Olivine-rich ultramafic orthocumulate rocks also occur to the south of Mount Goode. In both areas, these lenses of serpentinised dunite to olivinite are enclosed by fine-grained clastic meta-sedimentary and felsic metavolcanic rocks.
The detailed sequence is the northern part of the project area, at Six Mile is as follows, from the top:
- Jones Creek Conglomerate - Granitoid arkosic- and mafic-conglomerate and ultramafic para-schist.
- Unconformity.
- Serp Hill meta-peridotite, 100 m thick - Serpentinised olivine peridotite with cumulus texture.
- Cherty meta-sediment marker horizon, a few metres thick.
- Layered series, 600 to 800 m thick - Basaltic to ultramafic flows and intrusive rocks, interlayered meta-basalt and meta-gabbro to pyroxenite prominent in upper part; magnesian meta-basalt and spinifex-textured ultramafic flows prominent in lower part.
- Cherty meta-sediment marker horizon, a few metres thick.
- Dunitic lenses, 300-500 m thick - Serpentinised black dunite-olivinite grading outwards into dark green-grey olivine peridotite which were emplaced into the top of a volcanogenic sediment unit; disseminated nickel sulphides are present in some lenses.
- Volcanogenic meta-sediment, 500-700 m - Poorly bedded quartz, actinolite, garnet, biotite, chlorite and andesine-bearing rocks, some of which are of pyroclastic origin, and with some cherty and slaty horizons.
- Cherty meta-sediment marker horizon, a few metres thick.
- Metabasalt, >500 m thick - Tholeiitic meta-basalt with some lenses of magnesian meta-basalt towards the top.
The mineralised olivine-rich ultramafic orthocumulate lenses form near-vertical, conformable and symmetric bodies composed of a core of dunite-olivinite, now largely converted to a black lizardite-antigorite serpentinite (with minor fresh olivine), enclosed in an envelope of dark-green to black, serpentinised, olivine peridotite. The pseudomorphs after olivine are closely packed in barren dunite-olivinite, are medium to coarse grained and polygonal, but tend to be more rounded and lobate where interstitial sulphides are present. Patchy developments of talc-magnesite alteration are found in the core or envelope rocks, commonly taking the form of reticulated veinlets along which nickel sulphides may also be localised, particularly where the serpentinised olivine peridotite is mineralised.
The bulk of the mineralisation at Yakabindie consists of uniformly distributed interstitial sulphides, principally pentlandite (or violarite) and pyrrhotite, averaging 0.6% Ni and 0.01% Cu, (at a cut-off figure of 0.4% Ni).
The largest of the Yakabindie lenses, the Six Mile deposit, comprises a north-south elongated serpentinised dunite-olivinite core with dimensions of >1400 m x 200 m at the surface. If the peridotitic envelope is included, the whole lens is up to 400 m wide. Igneous textures grade from olivine adcumulate to olivine orthocumulate westward and upward across the igneous stratigraphy, consistent with the primary igneous laminations. Four main igneous zones with gradational margins are recognised, as follows: i). cyclic layers up to several metres thick of medium grained olivine orthocumulate to mesocumulate; ii). a 100 m thick zone of closely packed olivine orthocumulate and olivine-sulphide cumulate, with sulphides mainly in finer grained layers; iii). essentially sulphide free, coarse grained, olivine adcumulate; and iv). predominantly layered, medium to coarse grained olivine adcumulate with lesser medium grained olivine-sulphide mesocumulate layers.
The indicated resources within the Six Mile lens are more than 60 Mt @ 0.6% Ni and 0.01% Cu at a cut-off of 0.4% Ni. This lens is south plunging, steeply westdipping to vertical, and persists to a vertical depth of > 600 m in the south. The eastern contact is partly intrusive and partly faulted, while the western contact is comfortable with overlying west-dipping meta-sediments. The serpentinised olivine peridotite (35 to 45% MgO) envelope contains lizardite or antigorite, plus minor brucite, tremolite, talc, magnesite and chromite. A narrow 850 x 25 m zone of mineralisation is present in the western part of the envelope comprising pentlandite+pyrrhotite with lesser niccolite, maucherite, cobaltite and pyrite, which occur mainly in carbonate veinlets forming networks in the peridotite in the south, whereas ragged blebs of pentlandite and pyrrhotite characterise the peridotite to the north. The dunite-olivinite (45 to 51% MgO) core which is host to the bulk of the mineralisation, is almost completely serpentinised to lizardite or antigorite, although areas of relict olivine remain. Zoned chromite grains with magnetite rims are an accessory phase. Pentlandite and pyrrhotite with minor pyrite and chalcopyrite occur interstitially to the olivine pseudomorphs in a zone 50 to 100 m wide running the full length of the dunitic core, and beyond into peridotitic rocks to the north. The mineralization in the dunitic core tends to be of slightly lower tenor than that in the peridotitic envelope. Where disseminated sulphides are only very poorly developed, millerite, heazlewoodite and godlevskite may be present. Supergene alteration occurs to a depth of around 150 m, while the oxidised zone is 30 to 70 m thick.
The Goliath North deposit is 3 km south-southeast of Six Mile and is contained within a similar, but smaller lens of black serpentinised dunite-olivinite, mantled by serpentinised olivine peridotite. A marker unit on the west of the lens dips at 50 to 80°NW, while its eastern contact dips at 80°E. At the surface the lens has dimensions of 1000 x 200 m wide, tapering northwards. It contains black serpentinite containing low-grade disseminated Fe-Ni sulphide mineralisation similar to that described at Six Mile deposit.
The Sheba deposit is 7 km south-southeast of Six Mile and occurs as a 1600x 150 m serpentinised green peridotite to dunite ultramafic lens that strikes slightly west of north. This deposit, unlike the others of the project area also contains a thin vein of massive nickel sulphides (violarite, pyrrhotite, pyrite, chalcopyrite) on the sheared eastern contact between serpentinised peridotite envelope of the dunitic core and the adjacent meta-sediments.
The quoted resources for the Yakabindie project (DOIR 2006) total 289 Mt @ 0.58% Ni. Yakabindie resource is now part of BHP Billiton's Mt Keith operation.
Published JORC compliant ore reserves and mineral resources at 30 June 2012 (BHP Billiton Annua Report 2012) were:
Measured resource - 156 Mt @ 0.59% Ni;
Indicated resource - 113 Mt @ 0.62% Ni;
Inferred resource - 171 Mt @ 0.61% Ni;
TOTAL resource - 439 Mt @ 0.61% Ni.
The deposit title is owned by BHP Billiton - 100%.
The most recent source geological information used to prepare this decription was dated: 2006.
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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Barnes S J, 2007 - Cotectic Precipitation of Olivine and Sulfide Liquid from Komatiite Magma and the Origin of Komatiite-Hosted Disseminated Nickel Sulfide Mineralization at Mount Keith and Yakabindie, Western Australia: in Econ. Geol. v102 pp 299-304
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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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Perring, C.S., 2016 - Yakabindie Revisited - Volcanological and Structural Controls on the Komatiite-Hosted Six Mile Well and Goliath North Deposits and Implications for the Architecture of the 2.7 Ga Rift Event in the Agnew-Wiluna Belt, Yilgarn Craton, Western Australia: in Econ. Geol. v.111, pp. 1159-1185.
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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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