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MODULE 1 - AUSTRALASIA
PART A - Yilgarn Sulphides & Laterites,
Sun 21 to Fri 26 May 2000
This MODULE and PART commenced on the evening of Sunday 21 May, 2000, in Perth, Western Australia, and included a full day workshop, followed by a field traverse and detailed visits and briefings to the following nickel mines and projects:
- Perth Seminar
- Overview of Yilgarn Nickel and its occurrence
- Komatiite hosted massive & disseminated sulphides
- Silver Swan - Very high grade Komatiite hosted massive sulphides
- Komatiite hosted massive & disseminated sulphides
- Mt Keith - Komatiite hosted large low grade disseminated sulphides
- Murrin Murrin - Silicate laterite, pressure leach
- Cawse - Oxide laterite, pressure leach
MODULE 1 - AUSTRALASIA, PART A, Yilgarn Sulphides & Laterites
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Perth Seminar - "The Setting & Occurrence of Nickel in the Yilgarn Craton"
The workshop included presentations covering the following topics:
- The Geological and Tectonic Framework of Western Australia, with Particular Emphasis on the Archaean Nickel Bearing Greenstone Belts - Tim Griffin, Assistant Director, Geological Mapping, Geol. Survey of WA.
- The Processes Involved in the Development of Komatiitic Hosted Nickel Sulphide Deposits - Dr Rob Hill, CSIRO.
- The Distribution, Styles & Controls of Nickel Mineralisation in the Yilgarn Craton - Dr Rob Hill, CSIRO.
- Deep Weathering & the Formation & Classification of Ni Laterite Deposits - Dr Charles Butt, CRC-LEME.
- An Overview of Australian Nickel Laterite Deposits - Mick Elias, WMC Resources.
- The Regolith Expression of Nickel Sulphide Deposits in the Yilgarn Craton - Dr Charles Butt, CRC-LEME.
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Kambalda - Western Australia
The Kambalda nickel mines lie within the south-central section of the Archaean Norseman-Wiluna greenstone belt, 60 km SSE of Kalgoorlie in Western Australia. The lowest member of the host succession is the Lunnon Basalt which is overlain by
the host 2710 Ma Kambalda Komatiite, followed by the Devon Consols Basalt
and a package of basalts and sediments (slates and greywackes) deposited
from 2710 to 2670 Ma. These are intruded by a 2662 Ma granitoid stock which
forms the core of the oval shaped Kambalda Dome around which the individual
orebodies are distributed in an annular zone of approximately 8 x 3 km,
elongated in a NNW direction. Peripheral porphyry dykes associated with
the granitoid stock cut both the hosts and ore. The sill like Kambalda
Komatiite, which lies more or less conformably between the two basalts,
is composed of the upper Tripod Hill Member and the lower Silver Lake Member,
with Fe-Ni mineralisation being generally restricted to the lowermost sections
of the latter. In each, flow, lateral and vertical variations in composition,
degree of differentiation and distribution of interflow sediments define
channel flow and sheet flow facies. Channel flows may be up to 100 m thick,
500 m wide and 15 km long, occupying channel structures in the underlying
Lunnon Basalt. The Fe-Ni sulphides are usually restricted to the base of
the lowermost channel flows - contact orebodies - but are occasionally
also in higher flows - hangingwall orebodies. The contact orebodies,
which account for 80% of the reserves, occur as elongate, lensoid and tabular
ribbon like bodies up to 3 km long and 300 m wide and usually <5 m thick,
containing <0.5 to 10 mt ore lenses. The individual orebodies grade
upwards from the around 2 m thick basal massive (>80%) sulphides to around
2 m of matrix (40 to 80%) sulphide, to disseminated and blebby sulphides.
In addition to the deposits of the Kambalda Dome, similar bodies have recently
been outlined and mined in the surrounding district as part of the Kambalda
Nickel Operations. These include the Helmut deposit in the Tramways Belt,
45 km to the south, Mariner on the Widgiemooltha Dome, 70 km to the SW,
and the Blair mine at the Golden Ridge-Carnilya Hill Belt 40 km to the
north. Production has come from a series of separate orebodies or 'shoots'.
Pentlandite is the principal Ni sulphide, accompanied by varying amounts
of pyrrhotite, pyrite, chalcopyrite, chromite and magnetite. Lesser millerite
zones are also present. Mining commenced in 1967, and from 1972 to 1988
exploration maintained resources at an almost constant level of around
25 mt @ 3.2% Ni. Production in 1996 was 1.27 mt of ore @ 3.27% Ni, 0.21%
Cu for 40 000 t of Ni. In 1997 proven and probable reserves totalled 10.5
mt while resources amounted to more than 20 mt of comparable grades, with
an output of 32 391 t of Ni in the previous 12 months. To 1999, reserves
plus production amounted to 70 mt @ 2.9% Ni. The 8 biggest orebodies varied
in size from 0.9 to 10 mt at grades of 2.3 to 3.9% Ni. The operation is
owned by WMC Limited - 100%.
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Mount Hunt Traverse - Western Australia
This traverse allows an overview of the stratigraphy and lithologies of this important greenstone belt which hosts many of the more important gold and nickel
deposits of the Yilgarn Craton. It also allows an appreciation of the degree
of exposure a nd weathering experienced over the Yilgarn Craton.
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Silver Swan - Western Australia
The Silver Swan orebody, 43 km NNE of Kalgoorlie, comprises a steeply plunging high grade massive sulphide shoot that extends from a depth of 200m, to past 700m
below the surface. Prior to mining the Probable Ore Reserve was 655 000
t @ 9.5% Ni. Some 35 diamond core holes drilled to 1995 on a 20x50m grid
returned uniform grades of 12 to 16% Ni and defined the orebody, prior
to production commencing in 1997. The deposit lies within the Norseman-Wiluna
Greenstone Belt of the Yilgarn Craton and is hosted by the Archaean Black
Swan Komatiite which dips steeply and is 150 to 600 m thick, extending
over a strike length of 3 km. Large volumes of the komatiite have been
altered to carbonate-talc±quartz-sericite. The footwall is predominantly
a thick felsic suite. The Silver Swan shoot is composed of massive pyrrhotite-pentlandite-pyrite±chalcopyrite-magnetite-ferrochromite
mineralisation on the footwall of the Black Swan Komatiite. It has a 550
m down plunge extent, 20m maximum thickness and strike length of 75 m.
The sulphides are typically coarse grained without any consistent compositional
banding or layering. The low grade, disseminated Black Swan resource with
7 mt @ 0.8% Ni, and the 3.4 mt @ 1.42% Ni of the Cygnet deposit are adjacent
to the high grade Silver Swan shoot. Cygnet includes a discrete zone of
930 000t @ 2.47% Ni. The mine is owned and operated by Outokumpu Mining
Australia Pty Ltd.
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Cawse - Western Australia
The Cawse project
area comprises a corridor up to 500 m wide that extends for around 25 km
containing lateritic nickel and cobalt mineralisation. This corridor reflects
a fault structure related surface "channel" cutting the Siberia Komatiite
within the Archaean Norseman-Wiluna greenstone belt, 25 km to the north
of Kalgoorlie. Around 80% of the mineralisation in the main Cawse Central
tenements consists of a shallow, flat lying zone associated with limonitic
clays in the upper 40 m of the weathering profile in this structure, overlying
a barren saprolite. Immediately above the saprolite a smectite layer is
developed, followed by the limonite zone with 1.7% Ni, 0.09% Co. A distinctive
interval of high grade silica-cobalt with 1.6% Ni, 0.73% Co and 5% Mn is
located at the top of the limonite zone, below the gravel cover of the
channel. A narrow zone of manganiferous cobalt ore occurs at the transition
from the limonite to siliceous ores and carries similar grades of Ni and
Co, but higher Mn. Around 90% of the resource at Cawse has <0.5% Mn,
although the Co rich zones may contain up to 20% Mn. A deeper nontronitic
clay and talc zone is found on the margins of bedrock structures. The oxide
(limonite) ore at Cawse is the result of a second phase of weathering that
oxidises the first stage nontronite formed from the protolith, which at
Cawse was a dunite, not a peridotite. In 1997 the total resource amounted
to 213 mt @ 0.7% Ni, 0.04% Co, over the 25 km interval, with a proven+probable
reserve of 30.3 mt @ 1% Ni, 0.11% Co. The ore deposit is an oxide laterite.
The operation is operated by Centaur Mining & Exploration Ltd.
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Mt Keith - Western Australia
The Mount Keith
orebody is one of the worlds largest low grade, economically mined, disseminated
nickel sulphide deposits. It is some 425 km north of Kalgoorlie and lies
within the Agnew-Wiluna segment of the regional Archaean Norseman-Wiluna
greenstone belt. Mt Keith is developed near the centre of the narrowest
part of the belt, which ranges from 5 to 25 km in width. In this segment
the greenstone belt comprises a lower succession of interbedded volcanics,
pyroclastics, shale and chert, overlain by an upper thick sequence composed
of pillowed basalt, a thick suite of volcaniclastic rocks, a zone dominated
by komatiite and an upper series of thin komatiite flows, layered gabbro,
and high magnesian and tholeiitic basalt. The komatiitic interval is up
to 2500 m thick while the individual komatiite bands can be correlated
for more than 100 km along strike. Three west facing komatiite units, the
Eastern, Central and Western ultramafic units and a thin early flow are
identified at Mt Keith. Nickel mineralisation is hosted by a thickened
zone within the regionally extensive, orthocumulate-rich Eastern Ultramafic
Body, known locally as the MKD5. The MKD5 has a maximum thickness of 650
m and has been subdivided into three lithologically distinct zones: 1).
a basal olivine orthocumulate to the east; 2). a lensoid central zone containing
un-mineralised coarse grained adcumulate, grading upwards into a layered
olivine-sulphide adcumulate-mesocumulate which is the Mt Keith orebody;
and 3). an upper orthocumulate to the west, containing zones of gabbroic
ultramafic differentiate. Both the hangingwall and footwall of the MKD5
unit have been strongly sheared. Ultramafic rocks of the MKD5 have been
completely serpentinised and the overlying mafics and volcaniclastics have
been altered to albite-actinolite-epidote-chlorite assemblages. No relict
olivine remains. In addition there is strong structurally controlled alteration,
with intense carbonate±talc on the outer margins of the MKD5, and
along faults. This carbonate alteration decreases away from the fractures
& shears. Primary nickel bearing sulphides occur as lobate aggregates
in the interstices between former olivine grains, generally 1 to 2 mm across,
locally up to 6 mm. The highest grades are in the least carbonated rocks.
The predominant nickel sulphide is pentlandite accompanied by pyrrhotite±magnetite,
while about 20% of the orebody is pentlandite-millerite±heazlewoodite±magnetite
found in the eastern or stratigraphically lower sections. Nickel mineralisation
extends for over 2 km along strike and continues steeply down dip to a
depth of at least 500 m. Ore grade mineralisation is developed over 250
to 300 m of the 650 m thickness of the MKD5 unit. In mid 1999 the total
reserve + resource was 517 mt @ 0.54% Ni, at a 0.2% recovered Ni cutoff.
Of this the economic reserve was 269 mt @ 0.58% Ni. The operation, which
treats around 12 mt of ore per annum, produced 43 000 t of Ni in 1998.
The mine is owned and operated by WMC Resources Limited - 100%.
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Leinster - Western Australia
The Leinster Nickel
Operations of WMC Resources Ltd are approximately 330 km north of Kalgoorlie
and 90 km south of Mt Keith, and are based on the Perseverance and Rocky's
Reward ore deposits which are 2 km apart. 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 an eastern and western succession,
with all of the known mineralisation in the eastern which comprises from
east to west, a thick tholeiitic basalt unit with interflow sediments and
komatiites. Further east is a felsic unit of volcanics and sediments and
intermittent komatiites and black sulphidic graphitic shales. All of the
mineralisation is within the komatiites of this felsic-sediment package
dated at around 2700 Ma in age. 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 orebody is on the stratigraphic base of the ultramafic complex and
is composed of high grade massive and disseminated sulphides, within an
extensive sheet of weak sulphides, similar to the ore at Mt Keith. The
massive sulphide occurs as a series of steeply dipping, north striking,
individual, fault bounded sheets. The disseminated sulphides form distinct
north plunging shoots to more than 1000 m below surface. The disseminated
and massive sulphides at Rocky's Reward are hosted by two thin komatiite
horizons wholly within thick felsic volcanics and sediments. The mineralisation
at both lies within a high strain corridor. The sulphides are principally
pyrrhotite and pentlandite. Production at Perseverance to 1997 was 10.6
mt @ 2.1% Ni, with 31 mt @ 1.65% Ni remaining, while at Rocky's Reward
the production + reserve was of the order of 9.6 mt @ 2.4% Ni. In addition
there are indicated open cut resources of 79 mt @ 0.8% Ni and inferred
resources of 144 mt @ 0.7% Ni.
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Murrin Murrin & Mt Margaret - Western Australia
The Murrin Murrin
group of deposits overlie the Archaean Norseman-Wiluna greenstone belt,
some 200 km north of Kalgoorlie. Lateritisation of extensive ultramafic
sequences in the Murrin Murrin district has resulted in enrichment of nickel
and cobalt within limonite and nontronite clays in at least 10 zones. The
deposits overlie serpentinised Archaean, medium to coarse grained olivine
cumulate peridotites of komatiitic origin near the centre of the greenstone
belt. The lateritic profile passes upwards from the unweathered ultra-mafic,
through mixed saprolite and ultramafic, to siliceous saprolite, saprolite,
ferruginous saprolite, smectite, ferruginous smectite, to the upper ferruginous
zone. The Ni-Co mineralisation, as indicated by the 0.5% Ni cutoff, is
primarily confined to the smectite, saprolite and ferruginous smectite
zones, and may be up to 25 m thick below the ferruginous zone. The total
resource is 142.5 mt @ 1.01% Ni, 0.06% Co. It will be treated by acid pressure
leach hydrogen reduction autoclave technology at a rate of 3.75 mtpa to
produce 45 000 t of Ni and 3000 t of Co. The stage 2 expansion will produce
up to 70 000 tpa Ni, with additional planned expansion to 100 000 tpa.
The Murrin Murrin operation is owned by Anaconda Nickel Ltd in which Anglo
American Investments holds 23% and Glencore 19.5%.
Last minute changes by Anaconda Nickel meant that the Murrin Murrin operation could not be
visit as promised. Instead a visit was conducted made the Mt Margaret
deposit near Leinster. This project was in the test pit stage.
Anaconda were able to demonstrate the key features of the deposit in the
field supported by detailed data, sections and plans.
In addition similar plans, sections and images for Murrin Murrin were reviewed,
as were details of the plant which was circled at low altitude en route
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For more information contact: T M (Mike) Porter, of Porter GeoConsultancy (firstname.lastname@example.org)
This was another of the International Study Tours designed, developed, organised and escorted by T M (Mike) Porter of Porter GeoConsultancy Pty Ltd (PGC) in joint venture with the Australian Mineral Foundation (AMF). While the reputation and support of the AMF contributed to the establishment of the tours, after it ceased trading at the end of 2001, PGC has continued to develop, organise and manage the tour series.
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