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MODULE 1 - AUSTRALASIA
PART B - South West Pacific Laterites,
Sun 28 May to Fri 2 June 2000
This PART commenced on the morning of Sunday 28 May in Sydney, NSW, Australia and comprised a seminar on "New Caledonian Geology and Nickel Deposits", followed by visits to a range of the different ore styles, major and small scale operating mines and new projects under development. An overview of the mineralisation styles visited is detailed below.
This tour was divided into three Modules and five constituent Parts.
The other parts were Yilgarn Sulphides & Laterites, Caribbean Laterites, Canadian Sulphides & Eurasian Sulphides.
MODULE 1 - AUSTRALASIA, PART B, South West Pacific Laterites
New Caledonian Silicate Nickel Laterites
nickel ores of New Caledonia are developed over variably serpentinised
peridotites (predominantly harzburgites and some dunites). Much of the
ore in New Caledonia is now exposed in steep terrane, with deep erosion
of the laterite/saprolite profile on the steep mountainsides. A typical
profile from the SLN deposits for instance, can have up to 40 m or more
of saprolite and laterite developed above bedrock. A generalised profile
is capped by a few meres of iron crust (0.3% Ni, 0.01% Co, 52% Fe,
1% SiO2, 0.1% MgO), underlain progressively by 0 to 10 m thick layers of
red limonite with pisolites in the upper section (0.9% Ni, 0.08% Co, 50%
Fe, 1% SiO2, 0.6% MgO), yellow limonite (1.4% Ni, 0.10% Co, 49%
Fe, 3% SiO2, 2% MgO), earthy ore (2 to 3% Ni, 0.15% Co, 22% Fe,
30% SiO2, 16% MgO), soft saprolite (2.3% Ni, 0.08% Co, 10% Fe, 35%
SiO2, 21% MgO), ore with boulders (2.5% Ni, 0.05% Co, 12% Fe, 39%
SiO2, 28% MgO), rocky ore (3% Ni, 0.02% Co, 8% Fe, 43% SiO2, 33%
MgO), and fresh rock (0.3% Ni, 0.01% Co, 6% Fe, 44% SiO2, 45% MgO).
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The nickeliferous saprolites of New Caledonia are principally silicate 'garnierite' ores.
These silicate ores are preferentially derived from serpentinised ophiolites.
Serpentinite has a higher Ni content than the olivine of the protolith.
Primary serpentinisation in turn is most strongly developed in shear zones,
particularly those related to the late Eocene (37 Ma) over thrusting event
where structures, including serpentinite mylonites, may be several hundred
metres wide. These structures control both the development of serpentinite
and the depth and degree of weathering. The degree of serpentinisation
in the un-weathered rock also determines the type of saprolite produced,
from earthy saprolite over poorly serpentinised peridotite, to smectite
rich greenish earthy saprolites on moderate serpentinisation, to 'hard'
pink to green nickel rich 'garnierite' silicate saprolites from strong
serpentinite development. Colour however is not indicative of grade which
may only be determined by assay. The nickeliferous 'garnierite' ores are
composed of three Ni-Mg sheet silicates, 1). serpentines containing the
bulk of the nickel, both residual primary (lizardite) and secondary (nepouite);
2). talc (willemseite); and 3). smectite-kerolite (pimelite). Nickel is
also contained in limonite derived from the direct weathering of olivine.
The nickel is enriched both through leaching and from concentration of
nickel into serpentine and limonite from downward migrating Ni rich aqueous
solutions leached from the overlying laterites. The original 'garnierite'
ores mined from 1875 and which contained the mineral garnierite, were largely
depleted by the 1930's.
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New Caledonia Oxide Nickel Laterites
A number of major oxide laterite deposits are located in the south-eastern section of the island of New Caledonia. The Goro (West Prony) Project, which is the largest of these oxide laterites, is described here as an example of the deposits
of the district. Goro is located near the south-eastern tip of the island
of New Caledonia, approximately 45 km east of the capital Noumea. The project
is operated by Goro Nickel S.A., which is 100% owned by Compagnie des Mines
de Xere (CMX) registered in France which is in turn 85% owned by Inco Limited.
The drill indicated resource is 165 mt @ 1.6% Ni, 0.16% Co, with an initial
proven mining reserve of 47 mt. The deposit is an oxide laterite in contrast
to the silicate laterites of most of the other significant mines on the
island. As such it is amenable to treatment by pressure acid leach treatment,
rather than the ferro-nickel and matte smelters used for the silicate ores.
Goro is developed over the same peridotite mass as the other main deposits
on New Caledonia. It is composed of a thick limonite and thin underlying
saprolite, and occurs on a plateau with deep lateritisation, protected
by an iron cap cover. It has a lower MgO and higher Co content than the
silicate ores of the island. A typical profile comprises an upper thin
iron cap, generally <5 m thick, overlying a limonite over burden layer
that may be 15 m thick, with a zone of iron shop in its upper sections.
This limonite overburden carries around 0.8 to 1.2% Ni, 0.01 to 0.06% Co,
40 to 50% Fe, 1 to 2% SiO2, 0.5 to 2% MgO. Below this zone there is more
than 10 m of limonite carrying 1.2 to 1.7% Ni, 0.1 to 0.5% Co, 40 to 50%
Fe, 3 to 10% SiO2, 0.6 to 3% MgO. This is followed by a transition to the
saprolite, which together are less than 10 m thick. The saprolite to sap-rock
carries 1.2 to +3% Ni, 0.05 to 0.5% Co, 15 to 40% Fe, 20 to 40% SiO2, 10
to 30% MgO.
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Noumea Seminar - "New Caledonian Geology and Nickel Deposits"
The seminar included presentations covering the following topics:
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SMGM Tomo Mine at Tontouta
The small mines of New Caledonia produce a large percentage of the nickel from the island, commonly as high grade direct shipping ore. Tomo is one of the efficient, high grade operations visited to provide an insight into this important part of New Caledonia's nickel industry.
- The tectonic, geologic and structural framework of New Caledonia - Pierre Maurizot, (BGRM),
- The distribution,
controls and styles of Nickel mineralisation in New Caledonia> - Pierre
Charlent (INGEMINE), jointly prepared with Bernard Pelletier (SLN) &
Christian Picard (UNC),
- The nickel industry in New Caledonia - Laurent Bergeot (Director, Services des Mines et de
- The regulatory regime for exploration and mining in New Caledonia - Laurent Bergeot (Director,
Services des Mines et de l'Energie).
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SLN (Société le Nickel) Thio
le Nickel operates a 60 000 tpa smelter at Doniambo, near Noumea in New
Caledonia which it feeds from its current four mines at Thio, Kouaoua,
Népoui-Kopéto and Etoile du Nord. This facility produces
both ferro-nickel and nickel matte. The smelter treats around 3 mt of ore
per annum. SLN, which was formed in 1880 to mine lateritic nickel in New
Caledonia is the dominant producer on the island. It is 90% owned
by the French company Eramet, which is in turn 55% owned by the French
State. The lateritic ores mined by SLN are principally silicates within
nickel enriched saprolites. Inclusion of established mines such as those
of SLN allows access to information on well known and understood mineralisation
and allows a close study of the ore, overburden and bedrock. The
Plateau Mine at Thio was visited and studied in detail.
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Falconbridge - SMSP Koniambo
their local partners have completed 35000 m of drilling testing a large
silicate lateritic nickel deposit in the northern half of New Caledonia.
This project was included to allow an appreciation of the testing and surface
expression of such deposits, and as a further very important example of
the major silicate laterites of New Caledonia.
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Goro / Prony / Plaine des Lacs District
A geological tour of the Prony / Plaine des Lacs district which hosts a number of large oxide laterite deposits in south-eastern New Caledonia, including Goro and Prony
(a large tested resource that is currently available for tender) which are amenable to Pressure Leach Technology. The tour comprised a comprehensive breifing and field inspection of the Inco, Goro Project, by Inco geologists, and a field visit to the Penamax pit at Prony led by Pierre Charlent of Ingemine.
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For more information contact: T M (Mike) Porter, of Porter GeoConsultancy (email@example.com)
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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