Occurrence

The bulk of the nickel mined comes from two types of ore deposits. The first are laterites
where the principal ore minerals are nickeliferous limonite: (Fe, Ni)O(OH) and garnierite
(a hydrous nickel silicate): (Ni, Mg)3Si2O5(OH). The second are magmatic sulfide
deposits where the principal ore mineral is pentlandite: (Ni, Fe)9S8.

In terms of supply, the Sudbury region of Ontario, Canada, produces about 30 percent of
the world's supply of nickel. The Sudbury Basin deposit is theorized to have been created
by a massive meteorite impact event early in the geologic history of Earth. Russia
contains about 40% of the world's known resources at the massive Norilsk deposit in
Siberia. The Russian mining company MMC Norilsk Nickel mines this for the world
market, as well as the associated palladium. Other major deposits of nickel are found in
New Caledonia, Australia, Cuba, and Indonesia. The deposits in tropical areas are
typically laterites which are produced by the intense weathering of ultramafic igneous
rocks and the resulting secondary concentration of nickel bearing oxide and silicate
minerals. A recent development has been the exploitation of a deposit in western Turkey,
especially convenient for European smelters, steelmakers and factories. The one locality
in the United States where nickel is commercially mined is Riddle, Oregon, where several
square miles of nickel-bearing garnierite surface deposits are located.

Based on geophysical evidence, most of the nickel on Earth is postulated to be

concentrated in the Earth's core.

Applications
Nickel is used in many industrial and consumer products, including stainless steel,
magnets, coinage, and special alloys. It is also used for plating and as a green tint in glass.
Nickel is pre-eminently an alloy metal, and its chief use is in the nickel steels and nickel
cast irons, of which there are innumberable varieties. It is also widely used for many other
alloys, such as nickel brasses and bronzes, and alloys with copper, chromium, aluminum,
lead, cobalt, silver, and gold.

Nickel consumption can be summarized as: nickel steels (60%), nickel-copper alloys and
nickel silver (14%), malleable nickel, nickel clad and Inconel (9%), plating (6%), nickel
cast irons (3%), heat and electric resistance alloys (3%), nickel brasses and bronzes (2%),
others (3%).

In the laboratory, nickel is frequently used as a catalyst for hydrogenation, most often
using Raney nickel, a finely divided form of the metal.

Extraction and purification

Nickel can be recovered using extractive metallurgy. Most sulfide ores have traditionally
been processed using pyrometallurgical techniques to produce a matte for further refining.
Recent advances in hydrometallurgy have resulted in recent nickel processing operations
being developed using these processes. Most sulphide deposits have traditionally been
processed by concentration through a froth flotation process followed by
pyrometallurgical extraction. Recent advances in hydrometallurgical processing of
sulphides has led to some recent projects being built around this technology.

Nickel is extracted from its ores by conventional roasting and reduction processes which
yield a metal of >75% purity. Final purification in the Mond process to >99.99% purity is
performed by reacting nickel and carbon monoxide to form nickel carbonyl. This gas is
passed into a large chamber at a higher temperature in which tens of thousands of nickel
spheres are maintained in constant motion. The nickel carbonyl decomposes depositing
pure nickel onto the nickel spheres (known as pellets). Alternatively, the nickel carbonyl
may be decomposed in a smaller chamber without pellets present to create fine powders.
The resultant carbon monoxide is re-circulated through the process. The highly pure
nickel produced by this process is known as carbonyl nickel. A second common form of
refining involves the leaching of the metal matte followed by the electro-winning of the
nickel from solution by plating it onto a cathode. In many stainless steel applications, the
nickel can be taken directly in the 75% purity form, depending on the presence of any
impurities.

The largest producer of nickel is Russia which extracts 267,000 tonnes of nickel per year.
Australia and Canada (particularly the Sudbury Basin) are the second and third largest
producers, making 207 and 189.3 thousand tonnes per year.

Compounds
 Kamacite is a naturally occurring alloy of iron and nickel, usually in the
proportion of 90:10 to 95:5 although impurities such as cobalt or carbon may be
present. Kamacite occurs in nickel-iron meteorites.

Isotopes
Naturally occurring nickel is composed of 5 stable isotopes; 58Ni, 60Ni, 61Ni, 62Ni and 64Ni
with 58Ni being the most abundant (68.077% natural abundance). 18 radioisotopes have
been characterised with the most stable being 59Ni with a half-life of 76,000 years, 63Ni
with a half-life of 100.1 years, and 56Ni with a half-life of 6.077 days. All of the
remaining radioactive isotopes have half-lives that are less than 60 hours and the majority
of these have half-lives that are less than 30 seconds. This element also has 1 meta state.

Nickel-56 is produced in large quantities in type Ia supernovae and the shape of the light
curve of these supernovae corresponds to the decay of nickel-56 to cobalt-56 and then to
iron-56.

Nickel-59 is a long-lived cosmogenic radionuclide with a half-life of 76,000 years. 59Ni

has found many applications in isotope geology. 59Ni has been used to date the terrestrial
age of meteorites and to determine abundances of extraterrestrial dust in ice and sediment.
Nickel-60 is the daughter product of the extinct radionuclide 60Fe (half-life = 1.5 Myr).
Because the extinct radionuclide 60Fe had such a long half-life, its persistence in materials
in the solar system at high enough concentrations may have generated observable
variations in the isotopic composition of 60Ni. Therefore, the abundance of 60Ni present in
extraterrestrial material may provide insight into the origin of the solar system and its
early history.
Nickel-62 has the highest binding energy per nucleon of any isotope for any element.
Isotopes heavier than 62Ni cannot be formed by nuclear fusion without losing energy.

Nickel-48, discovered in 1999, is the most proton-rich nickel isotope known . With 28
protons and 20 neutrons 48Ni is "doubly magic" (like 208Pb) and therefore unusually stable.

The isotopes of nickel range in atomic weight from 48 u (48-Ni) to 78 u (78-Ni). Nickel-
78's half-life was recently measured to be 110 milliseconds and is believed to be an
important isotope involved in supernova nucleosynthesis of elements heavier than iron.

Precautions
Exposure to nickel metal and soluble compounds should not exceed 0.05 mg/cm³ in
nickel equivalents per 40-hour work week. Nickel sulfide fume and dust is believed to be
carcinogenic, and various other nickel compounds may be as well.

Nickel carbonyl, [Ni(CO)4], is an extremely toxic gas. The toxicity of metal carbonyls is a
function of both the toxicity of a metal as well as the carbonyl's ability to give off highly
toxic carbon monoxide gas, and this one is no exception. It is explosive in air.

Sensitised individuals may show an allergy to nickel affecting their skin. The amount of
nickel which is allowed in products which come into contact with human skin is regulated
by the European Union. In 2002 researchers found amounts of nickel being emitted by 1
and 2 Euro coins far in excess of those standards. This is believed to be due to a galvanic
reaction.

Metal Value
As of March 28, 2007 nickel was trading at 45,500 $US/mt (45.5 $US/kg, 20.6 $US/lb or
1.29 $US/oz). Interestingly, the US nickel coin contains 0.04 oz of nickel, which at this
new price is worth 5.2 cents. Since a nickel is worth 5 cents, this made it an attractive
target for melting by people wanting to sell the metal at a profit. However, the United
States Mint, in anticipation of this practice, implemented new interim rules on December
14, 2006, subject to public comment for 30 days, which criminalize the melting and
export of pennies and nickels. Violators can be punished with a fine of up to $10,000
and/or imprisoned for a maximum of five years.

References
1. Jaouen, G., Ed. Bioorganometallics: Biomolecules, Labeling, Medicine; Wiley-
VCH: Weinheim, 2006
2. Szilagyi, R. K. Bryngelson, P. A.; Maroney, M. J.; Hedman, B.; Hodgson, K. O.;
Solomon, E. I."S K-Edge X-ray Absorption Spectroscopic Investigation of the Ni-
Containing Superoxide Dismutase Active Site: New Structural Insight into the
Mechanism" Journal of the American Chemical Society 2004, volume 126, 3018-
3019.
 3. Thornalley, P. J., "Glyoxalase I--structure, function and a critical role in the
enzymatic defence against glycation", Biochemical Society Transactions, 2003,
31, 1343-8.
4. Production and consumption figures are from, The Economist: Pocket World in
Figures 2005, Profile Books (2005), ISBN 1-86197-799-9
5. W., P. (October 23, 1999). Twice-magic metal makes its debut - isotope of nickel.
Science News. Retrieved on {{#time:F j, Y|2006-09-29}}.
6. KS Kasprzak, FW Sunderman Jr, K Salnikow. Nickel carcinogenesis. Mutation
Research. 2003 Dec 10;533(1-2):67-97.
7. JK Dunnick, MR Elwell, AE Radovsky, JM Benson, FF Hahn, KJ Nikula, EB
Barr, CH Hobbs. Comparative Carcinogenic Effects of Nickel Subsulfide, Nickel
Oxide, or Nickel Sulfate Hexahydrate Chronic Exposures in the Lung. Cancer
Research. 1995 Nov 15;55(22):5251-6.
8. O Nestle, H Speidel, MO Speidel. High nickel release from 1- and 2-euro coins.
Nature. 419, 132 (12 September 2002).

Kambalda type komatiitic nickel ore deposits

Kambalda type nickel ore deposits are a class of magmatic nickel-copper ore deposit in
which the physical processes of komatiite volcanology serve to enrich, concentrate and
deposit nickel-bearing sulfide within the lava flow environment of an erupting komatiite
volcano.
Classification

The classification of the type of ore environment sets these apart from other similar nickel
sulfide ore deposits, which share many of the same source and transport criteria for
nickel mineralization, according to the trap mechanism. Kambalda-type ore deposits are
distinctive in that the deposition of nickel sulfides occurs within the lava flow channel
upon the palaeosurface. This is distinct from other komatiite and ultramafic associated
NiS ore deposits, where nickel sulfide accumulates within the lava conduit or upon the
floor or within a subvolcanic lava chamber.

Genetic model

The genetic model of Kambalda-type NiS ore deposits is similar to the broader category
of magmatic Ni-Cu-PGE ore deposits.

 Source: Highly magnesian ultramafic melts which become sulfur saturated during
ascent, or upon contact with the surface
 Transport: Typically, the transport of the komatiitic melts in the Kambalda type
NiS ore deposits is considered to represent a mantle plume tail impinging on a
continental rift or margin. The nickel is transported within the highly ultramafic
high-temperature melt.
 Trap: Kambalda-type NiS ore is considered to be trapped at the surface by the
following physical and chemical processes;
o The sulfur capacity of mafic silicate melts increases with decreasing
pressure, meaning that the pressure decrease during the ascent of a
komatiitic melt will drive the melt to sulfur undersaturation (Mavrogenes
and O'Neill, 1999), irrespective of the sulfur content of the melt at source.
Thus, sulfur-saturation of komatiites requires changes in the composition
of the melt either by assimilation of siliceous substrate material, diluting
the FeO content of the melt and thus reducing sulfur solubility, or by
simple assimilation of sulfurous material. Sulfidic sediments typically
form part of the substrate sedimentary sequence in deposit districts.
However, recent research into sulfur isotopic composition of komatiitic
sulfides has revealed that they lack the non-mass dependent isotope
fractionation typical of sulfides formed at the surface during the Archaean,
as would be expected if much of the sulfur was sourced from the
sedimentary substrate. Indeed, the sulfur isotope signature of the samples
investigated was found to be more similar to that of hydrothermal
exhalative massive sulfides hosted by the footwall felsic volcanics
associated with komatiite sequences (Fiorentini et al, 2006).
o Sulfides within the komatiite lava flows are denser than the silicate melt
and tend to pool within topographic lows, which may be enhanced in the
lava channel by proposed thermal erosion of the substrate by the komatiite
lava
o Nickel tenor is enhanced by the flushing of voluminous komatiitic melt
across the sulfide accumulation. The tenor is enhanced because nickel,
copper and platinum-group metals are chalcophile and will preferentially
partition from the silicate melt into the sulfide melt

Morphology
The morphology of Kambalda-type Ni-Cu-PHE deposits is distinctive because the nickel
sulfide can be shown to be associated with the floor of a komatiite lava flow, concentrated
within a zone of highest flow in the lava channel facies.

The lava channel is typically recognised within a komatiite sequence by;

 Thickening of the basal flow of the komatiite sequence

 Increased MgO, Ni, Cu, and concomitant decrease in Zn, Cr, Fe, Ti as compared
to 'flanking flows'
 A 'sediment free window' where sediment has been scoured or melted from the
basal or footwall contact of the komatiite with the underlying substrate
 A trough morphology, which is recognisable by a reentrant flat and steep-sided
embayment in the footwall underlying thickest cumulate piles

The ore zone typically consists, from the base upwards, of a zone of massive sulfides,
matrix sulfides, net-textured ore, disseminated and cloud sulfide.

Massive nickeliferous sulfide is composed of greater than 95% sulfide occasionally with
exotic enclaves of olivine, metasedimentary or melted material derived from the footwall
to the lava flow. The massive sulfide ideally sits upon a footwall of basalt or felsic
volcanic rock, which the massive sulfide may intrude into vertically. This forms a carrot-
structured ore, interpreted to represent either thermal erosion of the underlying substrate
by the ultra-high temperature komatiite lava, or physical remobilisation during
deformation.

The massive sulfide is in some cases overlain by a zone of matrix sulfide. The ideal
Kambalda type-section lacks matrix sulfides, which is interpreted to be because of either
physical remobilisation, or because matrix ore will only form in quiescent magma
conditions, and thus does not form in active channel zones except, perhaps, late in the
eruption. However, most other komatiitic nickel ore sections contain matrix to net-
textured ore.

Matrix sulfide ore, in high-grade metamorphic areas, is characterised by jackstraw

texture, composed of bladed to acicular metamorphic olivine which resembles spinifex
textured olivines, within a matrix of nickel sulfide. This texture is formed by
metamorphism of the ore, which is interpreted to have been composed of olivine crystals
floating in massive sulfide.

Net-textured ore is rarely observed, being the ideal condition of sulfide-silicate

immiscibility. This texture is difficult to prove from the majority of komatiite
mineralisation profiles, but is known from the Jinchuan intrusive, China, where nickel
sulfide forms a network textured groundmass liquid in which olivine floats. Most net-
textured ores in komatiites are considered metamorphic overprints.

Disseminated sulfide zones occasionally overly the matrix sulfide zone, grading upwards
into barren ultramafic olivine adcumulate. These zones are rarely economic to mine in the
majority of komatiites, except when close to surface.

The massive sulfide sits within the B3 flow horizon of a typical komatiite lava flow
system.
Ore Positions

The typical position of massive sulfide ore in a komatiitic nickel sulfide deposit, and in
shoots and trends within a mineralised belt, is for the sulfide to occupy the disconformity
between the komatiitic lava and its underlying substrate. This is known as contact ore.

In most cases, for instance at the type-locality Kambalda Dome, the contact ore sits upon
the footwall basalt, and is flanked by sulfidic and graphitic sediment with which it can be
structurally comingled or grades laterally into (eg; Wannaway). However, it is not
unknown for basal contact ore to be developed on a basement of felsic volcanics, as at
Emily Ann and Maggie Hays, or sedimentary formations thick enough to resist the
thermal erosion of the main lava channel, an example being in the region of the Blair
nickel deposit, on the Pioneer Dome.

Other ore types are known, which do not sit on the basal contact.

 Interformational sulfides; So-called serp-serp ore which is developed off a

thrust pinchout, or via remobilisation of massive sulfide along a shear surface or
thrust which drags ore up off the contact into the serpentinitised komatiite. Serp-
serp ore may, in some cases, be similar to interspinifex ore, the diagnostic spinifex
textures often absent due to thermal erosion or metamorphic overprint, and can
only be determined as such by comparison of chemistry of the ultramafics above
and below.

 Basalt-basalt pinchout, or pinchout or Bas-bas ore, is developed during

deformation by remobilisation of massive sulfide into the footwall via attenuation
of the trough and structural re-closing. Bas-bas ore can be found up to 40-60m
into the footwall leading from a trough position.

 Interspinifex ore, developed on the upper contact of the basal flow and on the
basal contact of a fertile second flow. In some cases, liquid sulfide from the
second flow is seen intermingled intimately with spinifex-textured ultramafic flow
tops of the basal flow (eg; Long-Victor Shoot, Kambalda) and may be present
above remnant sediments and intermingled with remnant sediments (eg; Hilditch
Prospect, Wannaway, Bradley Prospect, Location 1 and likely others).

 Remobilised ore. In rare cases, ore may be remobilised into a bas-bas or serp-serp
position geometrically variant to the stratigraphy. Such examples include
Waterloo-Amorac, Emily Ann, Wannaway and potentially other small pods of
remobilised and structurally complicated sulfides (eg, Wedgetail, in the
Honeymoon Well complex). In most cases, sulfides move less than 100m,
although in the case of Emily Ann, over 600m of displacement is known.

Metamorphic overprint

Metamorphism is nearly ubiquitous within Archaean komatiites. The type locality for
Kambalda-type Ni-Cu-PGE deposits has suffered several metamorphic events which have
altered the mineralogy, textures and morphology of the komatiite-hosted ore.

Several key features of the metamorphic history affect the present-day morphology and
mineralogy of the ore environments;
Prograde metamorphism

Prograde metamorphism to either greenschist facies or amphibolite facies tends to revert

igneous olivine to metamorphic olivine, serpentinite or talc carbonated ultramafic schists.

In the ore environment, the metamorphism tends to remobilise the nickel sulfide which,
during peak metamorphism, has the yield strength and behaviour of toothpaste as
conceptualised by workers within the field. The massive sulfides tend to move tens to
hundreds of meters away from their original depositional position into fold hinges,
footwall sediments, faults or become caught up within asymmetric shear zones.

While sulfide minerals do not change their mineralogy during metamorphism as silicates
do, the yield strength of the nickel sulfide pentlandite, and copper sulfide chalcopyrite is
less than that of pyrrhotite and pyrite, resulting in a potential to segregate the sulfides
mechanically throughout a shear zone.

Retrograde metamorphism

Ultramafic mineralogy is especially susceptible to retrograde metamorphism, especially

when water is present. Few komatiite sequences display even pristine metamorphic
assembages, with most metamorphic olivine replaced by serpentine, anthophyllite, talc or
chlorite. Pyroxene tends to retrogress to actinolite-cummingtonite or chlorite. Chromite
may hydrothermally alter to stichtite, and pentlandite may retrogress into millerite or
heazlewoodite.

Supergene modificaction

Kambalda style komatiitic nickel mineralisation was initially discovered by gossan

searching in ~1965, which discovered the Long, Victor, Otter-Juan and other shoots
within the Kambalda Dome. The Redross, Widgie Townsite, Mariners, Wannaway,
Dordie North and Miitel nickel gossans were identified generally at or around the time of
drilling of the Widgiemoltha area beginning in 1985, and continuing till today.

Gossans of nickel mineralisation, especially massive sulfides, are dominated in the arid
Yilgarn Craton by boxworks of goethite, hematite, maghemite and ocher clays. Non-
sulfide nickel minerals are typically soluble, and preserved rarely at surface as carbonates,
although often can be preserved as nickel arsenates (nickeline) within gossans. Within
subtropical and Arctic regions, it is unlikely gossans would be preserved or, if they are,
would not contain carbonate minerals.

Minerals such as gaspeite, hellyerite, otwayite, widgiemoolthalite and related hydrous

nickel carbonates are diagnostic of nickel gossans, but are exceedingly rare. More usually,
malachite, azurite, chalcocite and cobalt compounds are more persistent in boxworks and
may provide diagnostic information.

Nickel minseralisation in the regolith, in the upper saprolite typically exists as goethite,
hematite, limonite and is often associated with polydymite and violarite, nickel sulfides
which are of supergene association. Within the lower saprolite, violarite is transitional
with unaltered pentlandite-pyrite-pyrrhotite ore.
Exploration for Kambalda Ni-Cu-PGE Ores

Exploration for Kambalda-style nickel ores focuses on identifying prospective elements

of komatiite sequences via geochemistry, geophysical prospecting methods and
stratigraphic analysis.

Geochemically, the Kambalda Ratio Ni:Cr/Cu:Zn identifies areas of enriched Ni, Cu and
depleted Cr and Zn. Cr is associated with fractionated, low-MgO rocks and Zn is a typical
sediment contaminant. If the ratio is at around unity or greater than 1, the komatiite flow
is considered fertile. Other geochemical trends sought include high MgO contents to
identify the area with highest cumulate olivine contents; identifying low-Zn flows;
tracking Al content to identify contaminated lavas and, chiefly, identifying anomalously
enriched Ni (direct detection). In many areas, economic deposits are identified within a
halo of lower grade mineralisation, with a 1% or 2% Ni in hole value contoured.

Geophysically, nickel sulfides are considered effective superconductors in a geologic

context. They are explored for using electromagnetic exploration techniques which
measure the current and magnetic fields generated in buried and concealed mineralisation.
Mapping of regional magnetic response and gravity is also of use in defining the
komatiite sequences, though of little use in directly detecting the mineralisation itself.

Stratigrahic analysis of an area seeks to identify thickening basal lava flows, trough
morphologies, or areas with a known sediment-free window on the basal contact.
Likewise, identifying areas where cumulate and channelised flow dominates over
apparent flanking thin flow stratigraphy, dominated by multiple thin lava horizons
defined by recurrence of A-zone spinifex textured rocks, is effective at regionally
vectoring in toward areas with the highest magma thoughput. Finally, regionally it is
common for komatiite sequences to be drilled in areas of high magnetic anomalism based
on the inferred likelihood that increased magnetic response correlates with the thickest
cumulate piles.

General Morphological Phenomena

Parallel Ore Trends

One notable phenomena in and around the domes which host the majority of the
komatiitic nickel ore deposits in Australia is the high degree of parallelism of the ore
shoots, especially at the Kambalda Dome and Widgiemooltha Dome.

Ore shoots continue, in essential parallelism, for several kilometres down plunge;
furthermore in some ore trends at Widgiemooltha, ore trends and thickened basal flow
channels are mirrored by low-tenor and low-grade 'flanking channels'. These flanking
channels mimic the sinuous meandering ore shoots. Why extremely hot and superfluid
komatiitic lavas and nickel sulfides should deposit themselves in parallel systems is
unknown.

Subvolcanic feeder vs. mega-channels

One of the major problems in classifying and identifying komatiite-hosted NiS ore
deposits as Kambalda type is the structural complication and overprint of metamorphism
upon the volcanic morphology and textures of the ore deposit.
This is especially true of the peridotite and dunite hosted low-grade disseminated nickel
sulfide deposits such as Perseverance, Mt Keith MKD5, Yakabindie and Honeymoon
Well, which occupy peridotite bodies which are at least 300m and up to 1200m thickness
(or more).

The major difficulty in identifying adcumulate peridotite piles in excess of 1km as being
entirely volcanic is the difficulty in envisaging a komatiitic eruptive event which is
prolonged enough to persist long enough to build up via accumulation such a thickness of
olivine-only material. It is considered equally plausible that such large dunite-peridotite
bodies represent lave channels or sills through which, perhaps, great volumes of lava
flowed enroute to the surface.

This is exemplified by the Mt Keith MKD5 orebody, near Leinster, Western Australia,
which has recently been reclassified according to a subvolcanic intrusive model.
Extremely thick olivine adcumulate piles were interpreted as representing a 'mega' flow
channel facies, and it was only upon mining into a low-strain margin of the body at Mt
Keith that an intact intrusive-type contact was discovered.

Similar thick adcumulate bodies of komatiitic affinity which have sheared or faulted-off
contacts could also represent intrusive bodies. For example the Maggie Hays and Emily
Ann ore deposits, in the Lake Johnston Greenstone Belt, Western Australia, are highly
structurally remobilised (up to 600m into felsic footwall rocks) but are hosted in folded
podiform adcumulate to mesocumulate bodies which lack typical spinfex flow-top facies
and exhibit an orthocumulate margin. This may represent a sill or lopolith form of
intrusion, not a channelised flow, but structural modification of the contacts precludes a
definitive conclusion.

Example ore deposits

Definitive Kambalda-type

 Kambalda Dome, Western Australia

 Otter-Juan, Lunnon, Coronet, Long, Victor, Loreto, Carneliya orebodies
 Widgiemooltha Dome, Western Australia
o Miitel, Mariners, Redross, Wannaway mines
 Flying Fox, Forrestania Greenstone Belt, Western Australia
 Black Swan, Eastern Goldfields, Western Australia

Probable Kambalda-type

 Maggie Hays and Emily Ann, Lake Johnstone Greenstone Belt, Western Australia
 Waterloo Nickel Deposit, Agnew-Wiluna Greenstone Belt, Western Australia

References

 Gresham, J.J., and Loftus-Hills, G.D., 1981, The geology of the Kambalda nickel
field, Western Australia, Economic Geology, v. 76, p. 1373-1416.
 W.E. Stone, M. Heydart and Z. Seat, 2004. Nickel tenor variations between
Archaean komatiite-associated nickel sulphide deposits, Kambalda ore field,
Western Australia: the metamorphic modification model revisited. Mineralogy and
Petrology, (2004).
  Hess, P. C. (1989), Origins of Igneous Rocks, President and Fellows of Harvard
College (pp. 276-285), ISBN 0-674-64481-6.
 Lesher, C.M., Arndt, N.T., and Groves, D.I., 1984, Genesis of komatiite-
associated nickel sulphide deposits at Kambalda, Western Australia: A distal
volcanic model, in Buchanan, D.L., and Jones, M.J. (Editors), Sulphide Deposits
in Mafic and Ultramafic Rocks, Institution of Mining and Metallurgy, London, p.
70-80.
 Hill R.E.T, Barnes S.J., Gole M.J., and Dowling S.E., 1990. Physical volcanology
of komatiites; A field guide to the komatiites of the Norseman-Wiluna Greenstone
Belt, Eastern Goldfields Province, Yilgarn Block, Western Australia., Geological
Society of Australia. ISBN 0-909869-55-3
 Blatt, Harvey and Robert Tracy (1996), Petrology, 2nd ed., Freeman (pp. 196-7),
ISBN 0-7167-2438-3.
 S. A. Svetov, A. I. Svetova, and H. Huhma, 1999, Geochemistry of the Komatiite–
Tholeiite Rock Association in the Vedlozero–Segozero Archean Greenstone Belt,
Central Karelia, Geochemistry International, Vol. 39, Suppl. 1, 2001, pp. S24–
S38. PDF accessed 7-25-2005
 Vernon R.H., 2004, A Practical Guide to Rock Microstructure, (pp. 43-69, 150-
152) Cambridge University Press. ISBN 0-521-81443-X
 M.L. Fiorentini, A. Bekker, D. Rumble, M.E. Barley and S.W. Beresford (2006)
'Multiple S isotope study indicates footwall hydrothermal exhalative massive
sulfides were the major sulfur source for Archean komatiite-hosted magmatic
nickel-sulfides from Western Australia and Canada.' Geochimica et
Cosmochimica Acta, Volume 70, Issue 18, Supplement 1, August-September
2006, Page A174
 J A. Mavrogenes and H. St. C. O’Neill (1999) 'The relative effects of pressure,
temperature and oxygen fugacity on the solubility of sulfide in mafic magmas.'
Geochimica et Cosmochimica Acta, Volume 63, Issues 7-8, April 1999, Pages
1173-1180

Lateritic nickel ore deposits

Lateritic nickel ore deposits are surficial, weathered rinds formed on ultramafic rocks.
They comprise 73% of the continental world nickel resources and will be in the future the
dominant source for the winning of nickel.

Genesis and types of nickel laterites

Lateritic nickel ores formed by intensive tropical weathering of ultramafic rocks above all
serpentinites which consist largely of the magnesium silicate serpentine and contains
approx. 0,3% nickel. This initial nickel content is strongly enriched in the course of
lateritization. Two kinds of lateritic nickel ore have to be distinguished: limonite types
and silicate types.
Limonite type laterites (or oxide type) are highly enriched in iron due to very strong
leaching of magnesium and silica. They consist largely of goethite and contain 1-2%
nickel incorporated in goethite. Absence of the limonite zone in the ore deposits is due to
erosion.

Silicate type (or saprolite type) nickel ore formed beneath the limonite zone. It contains
generally 1.5-2.5% nickel and consists largely of Mg-depleted serpentine in which nickel
is incorporated. In pockets and fissures of the serpentinite rock green garnierite can be
present in minor quantities, but with high nickel contents - mostly 20-40%. It is bound in
newly formed phyllosilicate minerals. All the nickel in the silicate zone is leached
downwards (absolute nickel concentration) from the overlying goethite zone.

Ore deposits
Typical nickel laterite ore deposits are very large tonnage, low-grade deposits located
close to the surface. They are typically in the range of 20 million tonnes and upwards (this
being a contained resource of 200,000 tonnes of nickel at 1%) with some examples
approaching a billion tonnes of material. Thus, typically, nickel laterite ore deposits
contain many billions of dollars of in-situ value of contained metal.

Ore deposits of this type are restricted to the weathering mantle developed above
ultramafic rocks. As such they tend to be tabular, flat and areally large, covering many
square kilometres of the Earth's surface. However, at any one time the area of a deposit
being worked for the nickel ore is much smaller, usually only a few hectares. The typical
nickel laterite mine often operates as either an open cut mine or a strip mine.

Extraction
Nickel laterites are a very important type of nickel ore deposit. They are growing to
become the most important source of nickel metal for world demand, and are second for
now to sulphide nickel ore deposits.

Nickel laterites are generally mined via open cut mining methods with ore extracted via
some form of hydrometallurgy process, with two main process routes; high-pressure acid
leach (HPAL) and for some types of limonite type nickel laterites, heap leach-SX-EW
process routes are viable.

HPAL Processing

High Pressure Acid Leach processing is required for nickel laterite ores with a
predominantly nontronitic character where nickel is bound within clay or secondary
silicate substrates in the ores. The nickel (+/- cobalt) metal is liberated from such minerals
only at low pH and high temperatures, generally in excess of 250 degrees celsius.

The advantages of HPAL plants are that they are not as selective toward the type of ore
minerals, grades and nature of mineralisation. The disadvantage is the energy required to
heat the ore material and acid, and the wear and tear hot acid causes upon plant and
equipment. Higher energy costs demand higher ore grades.
Heap (Atmospheric) Leach

Heap leach treatment of nickel laterites is primarily possible only for clay-poor oxide-rich
ore types where clay contents are low enough to allow percolation of acid through the
heap. Generally, this route of production is much cheaper - up to half the cost of
production - due to the lack of need to heat and pressurise the ore and acid.

Ore is ground, agglomerated, and perhaps mixed with clay-poor rock, to prevent
compaction of the clay-like materials and so maintain permeability. The ore is stacked on
impermeable plastic membranes and acid is percolated over the heap, generally for 3 to 4
months, at which stage 60% to 70% of the nickel-cobalt content is liberated into acid
solution, which is then neutralised with limestone and a nickel-cobalt hydroxide
intermediate product is generated, generally then sent to a smelter for refining.

The advantage of heap leach treatment of nickeliferous laterite ores is that the plant and
mine infrastructure are much cheaper - up to 25% of the cost of a HPAL plant - and less
risky from a technological point of view. However, they are somewhat limited in the
types of ore which can be treated.

Pig iron oxide ores

A recent development in the extraction of nickel laterite ores is a partcular grade of

tropical deposits, typified by examples at Acoje in the Philippines, developed on ophiolite
sequence ultramafics. This ore is so rich in limonite (generally grading 47% to 59% iron,
0.8 to 1.5% nickel and trace cobalt) that it is essentially similar to low-grade iron ore. As
such, certain steel smelters in China have developed a process for blending nickel
limonite ore with conventional iron ore to produce stainless steel feed products. This pig
iron process short-circuits the typical costly hydrometallurgical route for producing
nickel, which is then used in stainless steel anyway.

Laterite
 Picture 1. Cutting of laterite brickstones at Angadipuram, Kerala, India

Laterite is a surface formation in hot and wet tropical areas which is enriched in iron and
aluminium and develops by intensive and long lasting weathering of the underlying
parent rock. Nearly all kinds of rocks can be deeply decomposed by the action of high
rainfall and elevated temperatures. The percolating rain water causes dissolution of
primary rock minerals and decrease of easily soluble elements as sodium, potassium,
calcium, magnesium and silicon. This gives rise to a residual concentration of more
insoluble elements predominantly iron and aluminium.

Overview
Laterites consist mainly of the minerals kaolinite, goethite, hematite and gibbsite which
form in the course of weathering. Moreover, many laterites contain quartz as relatively
stable relic mineral from the parent rock. The iron oxides goethite and hematite cause the
red-brown color of laterites.

Laterite covers have mostly a thickness of a few meters but occasionally they can be
much thicker. Their formation is favoured by a slight relief which prevents erosion of the
surface cover. Laterites occurring in non-tropical areas are products of former geological
epochs. Lateritic soils form the uppermost part of the laterite cover; in soil science
specific names (oxisol, latosol, ferallitic soil) are given for them.

In geosciences only those weathering products are defined as laterite, which are
geochemically - mineralogically most strongly altered. They must be distinguished from
less altered saprolite which has often a similar appearance and is also very widespread in
tropical areas. Both formations can be classified as residual rocks.

Laterites can be as well soft and friable as firm and physically resistant. Indurated
varieties are sometimes cut into blocks and used as brickstones for house-building. The
term laterite which is derived from the Latin word later = brickstone is given because of
this usage. History of laterite monuments dates back to 200 B.C. with megaliths of
Kerala, South India. Most of the third generation Khmer temples at Angkor are built with
laterite and have survived for over 1000 years. Later, world heritage sites such as
Churches of Old Goa (India) and Walls in G5 monuments of My Son, Vietnam are also
built in Laterite. Till today it is a common vernacular building material and profoundly
used in road construction. Nowadays solid lateritic gravel is readily put in aquaria where
it favors the growth of tropical plants.

Hardened laterite varieties are also used to construct laterite roads (also known as laterite
pistes), especially in Africa. Such roads range from local roads to major highways. If
well-constructed with attention to compacting the roadway base and drainage, and well
maintained by grading, reasonably high average speeds and smooth travel can be
achieved on them when dry. In East Africa, a softer laterite locally called murram is used
for road building.

Lateritization is economically most important for the formation of lateritic ore deposits.
Bauxite which is an aluminium-rich laterite variety can form from various parent rocks if
the drainage is most intensive thus leading to a very strong leaching of silica and
equivalent enrichment of aluminium hydroxides above all gibbsite.

Lateritization of ultramafic igneous rocks (serpentinite, dunite, or peridotite containing

about 0,2 - 0,3% nickel) often results in a considerable nickel concentration. Two kinds of
lateritic nickel ore have to be distinguished: A very iron-rich nickel limonite or nickel
oxide ore at the surface contains 1-2% Ni bound in goethite which is highly enriched due
to very strong leaching of magnesium and silica. Beneath this zone nickel silicate ore can
be formed, frequently containing > 2% Ni that is incorporated in silicate minerals
primarily serpentine. In pockets and fissures of the serpentinite rock green garnierite can
be present in minor quantities, but with high nickel contents - mostly 20-40%. It is bound
in newly formed phyllosilicate minerals. All the nickel in the silicate zone is leached
downwards (absolute nickel concentration) from the overlying goethite zone. Absence of
this zone is due to erosion.

Picture 2. Close up of bricks

References
 Aleva,G.J.J.(Compiler) (1994): Laterites. Concepts, Geology, Morphology and
Chemistry.169 pp. ISRIC, Wageningen, The Netherlands, ISBN 90-6672-053-0

 Bardossy, G. and Aleva, G.J.J.(1990): Lateritic Bauxites. 624 pp. Developments

in Economic Geology 27, ELSEVIER, ISBN 0-444-98811-4

 Buchanan, F. (1807): A Journey from Madras Through the Countries of Mysore,

Canara and Malabar, T. Cadell and W. Davies, London. (reprint: Asian
Educational Services,New Delhi, India), ISBN 8120603869

 Golightly, J.P. (1981): Nickeliferous Laterite Deposits. Economic Geology 75,

710-735

 Schellmann, W. (1983): Geochemical principles of lateritic nickel ore formation.

Proceedings of the 2. International Seminar on Lateritisation Processes, Sao Paulo,
119-135

 Sutapa Das (2007): Laterite Monuments of India. Construction History Society

Newletter May 2007, UK, 15-19