SEGSEG NEWSLETTERNEWSLETTER SOCIETY OF ECONOMIC GEOLOGISTS JULY 2003 NUMBER 54

S.A. Gleeson (SEG 1999), 1 C.R.M. Butt,2 and M. Elias3

ABSTRACT INTRODUCTION economically exploitable concentra- tions of nickel, but not to a specific hori- Nickel are an important resource Nickel deposits are formed by zon or unit. Although the profiles of of Ni and ferronickel and account for the prolonged and pervasive weather- most Ni laterites do have an upper fer- approximately 40% of world annual Ni ing of Ni -bearing ultramafic ruginous duricrust, they rarely contain production (Fig. 1). Of the 130 million rocks, generally in tropical to subtropi- economically significant enrichments of tonnes (Mt) of Ni in land-based resources cal climates. The deposits can be fur- Ni. “Nickel laterite,” therefore, is used ther classified as hydrous silicate containing over 1% nickel, approxi- loosely and does not conform to con- deposits (e.g., SLN Operations, New mately 60% is in laterite deposits (USGS ventional definitions; similarly, the ter- Caledonia), clay silicate deposits (e.g., Commodity Summary, 2002). minology used for different parts of the Murrin Murrin, Australia), and oxide These deposits are produced by the pro- profile varies widely in the literature. deposits (e.g., Moa Bay, Cuba; Cawse, longed and deep weathering of Ni sili- In general, a “typical” Ni lateritic Australia) on the basis of the ore min- cate-bearing ultramafic rocks, generally profile has three or four components eralogy. The physical and chemical in humid tropical to subtropical cli- nature of a nickel laterite deposit is a (Fig. 3). The base of the profile, the pro- mates. In consequence, many recently tolith, is the parent ultramafic rock, function of many factors, including the formed, and actively forming deposits composition of the parent rock, the tec- most commonly harzburgite (orthopy- are situated in equatorial latitudes roxene-rich ), or other types of tonic setting, climate, topography (Fig. 2). The major-producer countries of (specifically, laterite morphology), and peridotite or dunite (e.g., Colin et al., Ni laterite ores include New Caledonia, drainage. Nickel laterite ore is 1990). Nickel occurs within the silicate Cuba, Philippines, Indonesia, Colombia, extracted using both selective and bulk mineral structure of magnesium-rich and, increasingly, Australia (Table 1). mining methods in open cast mining (or its serpentinized alteration operations. The mined ore has tradi- products) in these units. ... tionally been processed either by THE LATERITE SOIL PROFILE AND Olivine is not stable in to page 10 hydrometallurgical leaching technol- CLASSIFICATION ogy (pressure acid leach or Caron pro- OF DEPOSITS cesses) to produce oxides of nickel and cobalt or mixed Ni-Co sulfides for mar- The term “laterite” has ket, or by pyrometallurgical smelting to been used very loosely in produce ferronickel granules or nickel the literature, both to matte. However, recent advances in describe specific soil high-pressure acid leaching and con- horizons, including some tinued testing of atmospheric leach having quite different technology should lead to a reduction properties, or even to in overall operating costs and increased define the entire weath- exploitation of Ni laterite resources in ering profile. More the future. specifically, the term now generally refers to 1 Department of Earth and Atmospheric the iron oxide-rich, sil- Sciences, University of Alberta, Edmonton, ica-poor upper soil hori- Alberta, Canada T6G 2E3; e-mail, zon of intensely weath- [email protected] ered regoliths found in 2 CSIRO Exploration and Mining, tropical climates PO Box 1130, Bentley, WA, Australia 6102 3 Mick Elias Associates, CSA Australia Pty (Eggleton, 2001). “Nickel FIGURE 1. World nickel production from 1988 to 2001 by Ltd., Level 1, 47 Burswood Road (PO Box 139), laterite” refers to a ore type (after Elias, 2002). In 2001, Ni laterites Burswood, WA, Australia 6100. regolith that contains accounted for approximately 40% of world production. 10 SEG NEWSLETTER No 54 • JULY 2003

... from 1 Nickel Laterites: A Review (Continued)

TABLE 1. Summary of Major Ni Laterite Mines and Prospects, Grades, and Processing Techniques (after Elias, 2002)

Main Rated ore Ni in % Ni Project capacity Processing Project Country Ownership type resource grade status (t/yr Ni) route1

Goro New Caledonia INCO-BRGM Oxide- >5 Mt 1.56 Feasibility study HPAL silicate Sorowako Indonesia INCO-Sumitomo- Silicate >5 Mt 1.80 Producer 68000 Matte Others smelting Sampala Indonesia Rio Tinto Oxide >5 Mt 1.34 Exploration HPAL Koniambo FeNi New Caledonia Falconbridge- Silicate 3-5 Mt 2.58 Feasibility study FeNi smelting SMSP Sipilou Cote d’Ivoire Falconbridge- Oxide- 3-5 Mt 1.48 Feasibility study HPAL SODEMI silicate Murrin Murrin Western Australia Anaconda- Clay 3-5 Mt 0.99 Producer 45000 HPAL Glencore Gag Island Indonesia BHP Billiton- Oxide- 3-5 Mt 1.35 Feasibility study HPAL Aneka Tambang silicate Bahodopi Indonesia INCO-Sumitomo- Silicate 3-5 Mt 1.77 Feasibility study Matte Others smelting SLN Operations New Caledonia Eramet-SLN Silicate 3-5 Mt 2.40 Producer 60000 Smelting Weda Bay Indonesia Weda Bay- Oxide- 2-3 Mt 1.37 Exploration HPAL Aneka Tambang silicate Pinares de Cuba Cuban Oxide 2-3 Mt 1.07 Exploration HPAL Mayari Government Pomalaa East Indonesia INCO-Sumitomo- Silicate 2-3 Mt 1.83 Exploration FeNi smelting Others and other Camaguey Cuba BHP Billiton Clay 2-3 Mt 1.30 Exploration HPAL Musongati Burundi Argosy Oxide- 2-3 Mt 1.31 Exploration HPAL silicate Moramanga Madagascar Phelps Dodge Oxide 2-3 Mt 1.11 Feasibility study HPAL Prony New Caledonia Inco (Goro Ni) Oxide- 2-3 Mt 1.40 Exploration HPAL Silicate Euboea- Greece Larco Oxide 2-3 Mt 1.00 Producer 20000 FeNi smelting Larymna Onca-Puma Brazil INCO-Canico Silicate 1-2 Mt 2.20 Exploration Smelting Cerro Matoso Colombia BHP Billiton Silicate 1-2 Mt 2.35 Producer 55000 FeNi smelting Falcondo Dominican Falconbridge Silicate 1-2 Mt 1.23 Producer 34000 FeNi smelting Republic

1 HPAL = high-pressure acid leaching.

the presence of water during chemical along joints and fractures, resulting in of the upper collapsed portion may be weathering and breaks down, leaving a blocks of fresh parent rock surrounded as little as ~15% of the original parent residue of amorphous ferric , by altered material (known informally rock (Golightly, 1981). A dense indurated with minor amorphous and as boulder saprolite). As weathering ferruginous duricrust (also referred to as other phases hosting immobile ele- proceeds, the Mg in the protolith is cuirasse, canga, ferricrete, or lateritic ments (such as Cr). The initial stages of almost totally leached, and Si is par- residuum) may develop at the top of the weathering produces saprolite, in which tially removed from the profile by the profile and protect portions of the the unweathered rock fabric is pre- ground waters. This results in the com- underlying laterite profile from erosion. served, although most of the original plete destruction of primary silicates and, In the literature, and here, these pro- may have been altered. The higher in the profile, collapse and loss files are commonly represented as sim- boundary between the saprolite and the of primary fabric. In consequence, Fe ple columns. In three dimensions, how- bedrock—the weathering front—is oxides dominate in the upper saprolite ever, the relationship between the extremely irregular and may be grada- and the overlying horizon. This oxide- various units can be very complex. tional; many Ni laterites are character- rich part of the profile is referred to Figure 4 is an example of Ni grade dis- ized by spheroidal weathering initiated informally as limonite and the volume tribution in a cross section of part of the JULY 2003 • No 54 SEG NEWSLETTER 11

Cerro Matoso mine, as documented by Lopez-Rendon (1986). The complexity of Ni grade distribution shown by this diagram, relative to other features such as topography, suggests that the size, morphology, and composition of the deposits is a function of many geologic and climatic variables. Nickel laterite deposits can be broadly classified into three types based on mineralogy of principal ore-bearing phases (Brand et al., 1998; see Fig. 3).

Hydrous silicate deposits In hydrous silicate deposits, the lower saprolite is the ore horizon and the ore minerals are hydrous Mg-Ni silicates. These are the highest-grade Ni laterite deposits with mean Ni grades ranging FIGURE 2. Distribution of Ni laterite deposits worldwide. Most deposits are within 20° of from 1.8 to 2.5%. Locally, within the the Equator. Those outside the present tropics (e.g., Balkans, former USSR) were formed saprolite, areas of intense secondary during earlier episodes of tropical climates. veining and box-works can be devel- oped. These, typically, follow relic struc- tures, fractures, and grain boundaries, and can contain neo-formed and Ni-rich minerals such as the distinctive green mineral “” (see below), which can have Ni content up to 40% (e.g., Gleeson, Herrington, Durango, Velasquez, and Koll, in prep.). In these deposits, Ni has been leached from the limonite Fe oxyhydroxide phases and moves down the profile before rede- positing either in hydrous silicate min- erals or substituting for Mg in altered serpentine (Pelletier, 1996). Therefore, although Ni laterites are classified as residual deposits, Ni enrichment by supergene processes is important for the formation and economics of the hydrous silicate deposits. Most of the large producing Ni laterite deposits are of this type with examples found in New Caledonia, Indonesia, Philippines, Dominican Republic, and Colombia.

Clay silicate deposits In these deposits, Si is only partially removed from the weathering profile by ground water. Remaining Si com- bines with Fe, Ni, and Al to form clay minerals such as Ni-rich nontronite in the mid to upper saprolite. Nickel-rich serpentine can also be replaced by smectite or quartz if the profile remains in contact long enough with the ground waters for the solutions to become supersaturated in these min- erals. In general, the mean Ni grades FIGURE 3. Generalized profile for the three types of Ni laterites (after Trescases, 1986; Elias, in these deposits are slightly lower 2002). The profile for the silicate deposits shows the four major weathering zones and than in hydrous silicate deposits summarizes the terminology used for each zone in the literature. Also shown for this type (1.2%; Brand et al., of deposit is the major element geochemistry and Ni distribution throughout this profile. 1998). to page 12 ... 12 SEG NEWSLETTER No 54 • JULY 2003

... from 11 Nickel Laterites: A Review (Continued)

FIGURE 5. The mineralogy of the “gar- nierites” of New Caledonia (after Brindley et al., 1979; Brindley, 1978; Trescases, 1986). These minerals can have compositions ranging from kero- lite to (Mg, Ni -like miner- als), and from serpentine to Ni-bearing serpentine (nepouite). FIGURE 4. Nickel grades in a cross section from the Cerro Matoso deposit, Colombia, redrawn from Lopez-Rendon (1986). This section indicates the variability within a Ni laterite deposit. example, a recent study of natural and synthetic goethite found that 75% of Ni is substituted for Fe in the goethite structure, Oxide deposits with affinities to Ni-bearing talc and with the remainder associated with the In oxide deposits, also known as serpentine-structured minerals (Brindley, asbolane structure (Manceau et al., 2000). limonite deposits, Ni is associated with 1978; Brindley et al., 1979; Fig. 5). Fe oxyhydroxides, principally goethite. Analyses of “garnierite” veins from Some also contain abundant Mn oxides Cerro Matoso in Colombia showed all enriched in Co. Average Ni grades are these minerals to be pimelite, a poorly CONTROLS ON THE GENESIS commonly about 1.2%, but there are defined Ni-rich talc, although the main OF NICKEL LATERITES many examples of subeconomic occur- ore mineral in the Cerro Matoso sapro- Composition of the protolith rences overlying both hydrous silicate lite is Ni (Gleeson, Herrington, and smectite clay deposits. The Moa Durango, Velasquez, and Koll, in prep.). The protoliths for Ni laterite deposits are Bay deposit in Cuba is the best known In the oxide deposits, Ni is mainly predominately ultramafic rocks origi- example of an oxide deposit in com- associated with goethite and, to a lesser nally containing a high proportion of mercial production. extent, Mn oxides. The possibility of Ni forsteritic olivine with a Ni content of adsorption on the surface of goethite or between 0.2 and 0.4 wt %. Some small other Fe and Mn oxides and oxyhydrox- deposits in Greece are developed from MINERALOGY ides has been widely discussed in the sedimentary rocks, themselves derived literature (e.g., Trivedi and Axe, 2001). In from ultramafic rocks. Rarely, the regolith The ore in Ni laterite deposits occurs recent years many studies have examined on other rock types may be enriched in either as silicate or oxide minerals. The the possibility that the Ni is structurally nickel. At Cawse, for example, dolerite ionic radius of the Ni2+ is similar to incorporated in these minerals. For dikes that crosscut ultramafic units have Mg2+, allowing Ni substitution in Mg sil- icate minerals. Accordingly, many of the ore minerals are hydrous silicates TABLE 2. A Summary of the Common Ni Silicate Minerals Found in Ni Laterite Deposits such as serpentine, talc, smectite, sepio- (mineral names in italics are mineral species recognized by the Commission on New lite, and chlorite, formed during low- Minerals and Mineral Names) temperature metamorphism and subse- Mg + Ni series end members Mineral type Formula quent weathering of the parent rock (Table 2). Commonly, these minerals Lizardite-Nepouite Serpentine (Mg, Ni)3Si2O5(OH)4 have variable Ni to Mg ratios. The green Talc-Willemseite Talc (Mg, Ni)3Si4O10(OH)2 silicate “garnierites,” first described Kerolite-Pimelite ?Talc Variable compositions from New Caledonia, do not have a Sepiolite-Falcondoite Sepiolite (Mg, Ni)4Si6O15(OH)2.6H2O well-defined composition or structure Clinochlore-Nimite Chlorite (Mg, Ni, Al)6(Si, Al)4O10(OH)8 and are not a recognized specific min- eral species. They are poorly crystalline, JULY 2003 • No 54 SEG NEWSLETTER 13

been deeply weathered and are com- poor drainage characteristics, which In areas of low relief, drainage is posed of smectites that have concen- has significance in smectite genesis. impeded and the water table is high. trated Ni derived from adjacent weath- Nickel laterites are rare or absent on Such situations are common in cratonic ering ultramafic rocks (Elias et al., 1981; talc carbonate rocks. settings and occur locally in accreted Stephen Denn, pers. commun., 2002). Tectonic setting terrains. The reduced water flow slows The most common protoliths appear the rates of leaching and removal of to be harzburgitic that have Ni laterites can develop over Phanerozoic weathering solutions, so that Ni concen- been partially or wholly serpentinized. ophiolite complexes, with many deposits trations are largely residual, with little The nature of the protolith has a funda- in Cretaceous to Miocene accreted ter- absolute accumulation except where mental control on the genesis of the rains (e.g., Schellman 1989; de Oliveira faults have led to increased leaching. deposits. In general, these rocks are et al., 1992). These complexes tend to be However, local restrictions and ponding mineralogically and chemically pervasively faulted and jointed, and also behind impervious weathered dolerite restricted in composition, and the prin- affected by tectonic uplift that enhances dikes may give locally high grades (e.g., cipal minerals—olivine, serpentine, and relief and lowers the water table, all of Elias et al., 1981). Over peridotites, high pyroxene—are highly prone to weather- which increase the through-flow of water water-tables and impeded drainage ing in tropical environments (Fig. 6). and intensity of weathering. Other, gen- result in the formation of low-grade Only a small proportion of the primary erally lower grade, deposits are found in smectite clay deposits in the saprolite rock is insoluble, allowing for strong stable Archaean and Proterozoic cratons, (e.g., Murrin Murrin on the Yilgarn cra- residual concentration of stable sec- associated with layered mafic complexes ton, Western Australia). Over dunite, ondary oxides and silicates, many of and komatiites (Butt, 1975). In both set- impeded drainage tends to favor the which may contain Ni. Nevertheless, tings, the deepest zones of enrichment and formation of oxide deposits (e.g., neither a higher primary Ni abundance the highest grades are commonly associ- Cawse, Western Australia) and the local nor a more reactive mineralogy directly ated with steep faults and shear zones. accumulation of silica. Tectonic uplift influences the Ni grade in the deposits. Conversely, major thrust faults associ- plays an important role in some For example, Ni grades in laterite are ated with the emplacement of ophiolite deposits by rejuvenating the topogra- subeconomic at Mt. Keith, Western complexes and with stable greenstone phy and, in some locations, lowering Australia, although the protolith con- platforms tend to form mylonitic zones previously high water tables, resulting tains about 0.6% Ni, of which some of serpentine- or talc-carbonate-altered in the reworking of zones of enrich- 0.4% is hosted by sulfides (Butt and ultramafic rocks. These are less perme- ment. Typically, this enhances the accu- Nickel, 1981; Brand and Butt, 2001). able and may form hydromorphic barri- mulation of high Ni grades at the base The type of Ni laterite deposit is only ers that do not concentrate Ni in the of the saprolite. Such processes are partially controlled by the lithology. regolith. likely to have been important in New Each of the three deposit classes may be Caledonia where many of the ophiolites developed on peridotites, but on dunite Geomorphology and topography have multiple terraces and the deposits protoliths, oxide deposits predominate. Topography plays an important role in are commonly found in the bases of The role played by serpentinization of the formation of Ni laterite deposits, eroded plateaux (Golightly, 1981). the protolith on the formation of these primarily because of the relationship deposits is fully discussed by Golightly with structure, drainage, and the posi- Climate tion of the water table. In areas of high (1981) and Pelletier (1996). Nickel lat- Climate plays an important role in the relief, many deposits, and the zones of erites on unserpentinized olivine-rich formation of Ni laterite deposits. Most highest enrichment, are located on rocks are not as well documented, but are formed in savanna (e.g., New tend to form oxide deposits with a thin, upper hill slopes, crests, spurs, and Caledonia, Cuba) or humid tropical rocky saprolitic unit (see Golightly, 1981). plateaux and/or terraces. The water (rainforest) climates (e.g., Colombia, Partially or wholly serpentinized protoliths table in these topographic positions is Indonesia). The warm temperatures and are much more common and generally low in the profile and, coupled with high rainfall, combined with high bio- produce a much thicker saprolite zone, mine scale structures such as faults and genic activity, allows for the rapid but grades tend to be lower with increas- joints, results in the maximum rates of chemical weathering necessary to form ing alteration. Clay silicate deposits are leaching and drainage of solutions, the deposits in areas of high relief reported only from serpentinized peri- enhancing both residual concentration where erosion rates are also high. dotites; they have only recently been and accumulation deep in the saprolite. There are, however, many deposits in identified as potentially economic. Such topographic situations are sites for other climatic zones, including temper- Serpentinization may also contribute to the generally high-grade, hydrous sili- ate (Urals, Russia; Kazakhstan), cate deposits Mediterranean (Oregon, United States; formed on peri- Greece; Albania) and warm semi-arid dotitic rocks in (Western Australia). These deposits are Indonesia, probably much older, having formed New under similar climates to those of the Caledonia, present savannas or rainforests, at vari- Colombia, ous times in the late Palaeozoic, Oregon Mesozoic, and early Cenozoic. Many FIGURE 6. Solubility of the common minerals in the lateritic profile at (United States), deposits in the Balkans and central Asia near neutral pH. The solubility of silica is independent of pH at these and the Urals have been buried by ... conditions (after Golightly, 1981). (Russia). later sediments to page 14 14 SEG NEWSLETTER No 54 • JULY 2003

... from 13 Nickel Laterites: A Review (Continued)

(Glazkovsky et al., 1977; Valeton et al., termites in disturbing the laterite profile rate of lateritization is between 140 and 1987); they are, thus, protected from by carrying saprolitic material to the 125 m in 1 m.y. in the mountains and subsequent erosion. Nevertheless, minor surface has been discussed (e.g., at least an order of magnitude less in diagenetic alteration and interaction Truckenbrodt et al., 1991). However, the plateaux areas, due to less efficient between the ore and sediments can there have been few specific studies of drainage. The more rapid weathering in occur, including reduction to Ni sulfides the role of biogenic processes in the for- mountainous areas is offset by faster and chamosite (Glazkovsky et al., mation of Ni laterites. At present, many rates of erosion, which may result in the 1977), and redistribution of Ni into experimental and field-based studies in destruction of deposits. Golightly (1981) chlorite because hydroxides are altered geomicrobiology are focused on identi- suggested that between 20 and 100 m of to chlorite (Albandakis, 1981). Deposits fying the role of biogenic processes in peridotite must be leached to form in Western Australia are preserved mediating the phase changes between saprolite ores, which can be achieved in because of the stability, low relief, and amorphous Fe phases, Fe oxyhydrox- about 1 m.y. However, rates of weather- minimal erosion of the Yilgarn craton. ides, and hydroxides. There are a small ing are dependent on local processes Some modification of the deposits has number of recent studies on the role of and are likely to be highly variable occurred due to slow, ongoing weather- bacteria in the mobilization of Ni from from place to place. ing under semi-arid conditions, princi- Fe oxides (e.g., Quantin et al., 2001; pally manifested as silicification and Zachara et al., 2001). Numerous papers the precipitation of magnesite (Brand et on the role of organic agents in leach- MINERAL PROCESSING al., 1998). ing Ni laterite ores in the mineral pro- AND EXTRACTION cessing literature (e.g., Alibhai et al., Groundwater and organic matter 1993; Sukla and Panchanadikar, 1993) There are currently three commercial The chemistry of waters that have inter- suggest this may be an interesting methods of processing Ni lateritic ores. acted with Ni laterite profiles is quite avenue for future research. Because of the variability of the miner- distinctive. At the base of the profile, alogy in these deposits, different pro- they are characterized by high concen- Rates of weathering cessing techniques are generally better trations of dissolved Mg and Si and rela- The rate of formation of lateritic profiles suited to particular parts of the profile. tively high pH, as shown in Figure 7 for is not well constrained. Mass balance However, this variability also permits waters from the in calculations suggest weathering rates of some beneficiation of the ore before Colombia. Analyses of waters from New 5 to 50 mm per 1,000 yr, with an aver- processing. In silicate ores, for example, Caledonia and Colombia suggest that age of 20 mm per 1,000 yr, so that a less-weathered remnants of parent rock bicarbonate, rather than sulfate and lateritic profile may develop in 1 to 6 can be removed mechanically. In chloride, is the dominant anion. This m.y. (Nahon, 1991; Nahon and Tardy, mixed silica-oxide deposits, in which observation suggests that biogenic 1992). These authors also note that the ore is associated with Fe and Mn activity and organic compounds in basic and ultrabasic rocks weather two oxides, barren silica can be removed by these tropical soils may have a role in to three times faster than other rock screening after crushing. Basic descrip- the development of at least the upper types. Trescases (1975) had estimated tions of nickel laterite processing tech- part of these profiles. The role of that, in New Caledonia, the downward nologies were reviewed by Simons (1988), although this work does not include more recent developments, such as high-pressure sulfuric acid leaching. Most of the major Ni laterite produc- ers are mining predominantly hydrous silicate ore for energy-intensive pyrometallurgical processing (partial reduction and smelting of dried ore). The main products are ferronickel gran- ules and nickel matte, which are used in stainless steel production. High Ni recoveries are achieved by these opera- tions, but Co is not recoverable as a by- product. Many deposits have their own electrical generating plants (e.g., Cerro Matoso) because of the high-energy requirements that are arguably the sin- gle most important factor in determin- ing the economic viability of hydrous silicate Ni laterite deposits. Access to low-cost hydroelectric power is a distinct FIGURE 7. Plot of Mg concentration vs. pH for the ground waters in and around the advantage (e.g., Soroako, Indonesia). Cerro Matoso mine. Waters from within the mine can be clearly distinguished by their The less common Caron process is alkalinity and high Mg contents. used for treating oxide ores. This process JULY 2003 • No 54 SEG NEWSLETTER 15

involves the drying and roasting of ore and Cawse (oxide ore) came on stream may act as impermeable hydromorphic in a reducing atmosphere, followed by in 1999, but all have had serious capi- barriers. Within appropriate areas, pre- low-pressure ammonia leaching. Both tal and operating cost problems, as well liminary geomorphological, regolith- Ni and Co are recovered by solvent as engineering and construction materi- landform, and structural maps can be extraction and then further refined. als problems. A novel HPAL plant is prepared from aerial photography, a Again, like smelting, ore drying and also being planned for Goro in New variety of remote sensing techniques, reduction roasting consume significant Caledonia to treat both oxide and and magnetic surveys to determine the amounts of energy. As a result, this tech- hydrous silicate portions of the profile most prospective sites for potential Ni nology is unlikely to be chosen in the (e.g., Mihaylov et al., 2000). Despite the accumulation. Airborne electromag- future for new nickel laterite projects. difficulties that have been experienced netic surveys may also assist in 3D There has been a recent resurgence by this new generation of HPAL plants regolith mapping. Follow-up by inspec- in processing oxide deposits by high- (see Elias, 2002), economics favor this tion, field mapping, and drilling are pressure acid leach (HPAL) technology. technology over the Caron leaching used to outline the potential resource. Sulfuric acid at temperatures of 250°C and the smelting technologies and it is Soil geochemical surveys are inappro- or more and pressures of 4,500 kPa likely that more HPAL plants will be priate precursors to drilling, because leach Ni and Co from predominantly constructed in the future to meet the they respond to the regolith “stratigra- oxide ores (Krause et al., 1998). The growing demand for nickel as sulfides phy” exposed by dissection, rather than metals are extracted from the leach resources become depleted. providing an indication of Ni distribu- solution by precipitation as sulfides (by tion at depth. Mine-scale exploration is addition of H2S) or as hydroxides (by essential in order to delineate different addition of lime), or by solvent extrac- EXPLORATION ore types based on mineralogy and tion and electrowinning. This process is Exploration for Ni laterites does not pre- mineralogical assemblages rather than also applied to clay silicate ores but the sent significant technical problems. In using Ni (and/or Co) grades alone. relatively high levels of Si in these the past, a variety of conventional Properly planned exploration may dif- deposits can cause problems at the prospecting and geochemical tech- ferentiate ores, such as silica and/or Fe- autoclave stage and the process niques (e.g., stream sediment surveys) Mn oxides, that can be physically becomes more expensive. The dominant have found Ni laterites, and prospective upgraded, or may delineate varieties operating cost components of HPAL are ultramafic rocks commonly have dis- inappropriate for processing and that associated with bulk supply of sulfur tinctive soils and plant communities. should be blended or discarded. Multi- and the production of sulfuric acid. For However, these techniques now have lit- element analysis is commonly used for many years, the only HPAL producer tle practical relevance in modern explo- the latter purpose, including attempts was Moa Bay in Cuba (operating at ration. The occurrence and distribution at calculating normative mineralogy, slightly lower pressure and tempera- of ultramafic rocks is now well known but there is scope for further improve- ture). Recent decreases in the cost of sul- in most, if not all, deeply weathered ter- ments in this field to maximize the effi- fur and improved solvent extraction rains. They can be readily and more ciency of HPAL and other processes. As and autoclave technologies have led to precisely delineated at regional to local noted above and illustrated in Figure 4, increased interest in this processing scales by airborne magnetic surveys, Ni laterite deposits show great variation technology. Three new plants in which can also be used to outline litho- in the distributions of Ni and other ele- Western Australia at Bulong and logical variation and stratigraphy, ments, profile thickness, ... Murrin Murrin (smectite silicate ores) favorable structures, and intrusions that and other characteristics to page 16 EXPLORATION TRAINING ON CD-ROM Self-paced, practical exploration simulations delivered in the workplace Courses in the EXPLORE! series include: • Introduction to Exploration Practice • Mapping and Interpreting Alteration • Geophysics for Geologists Contact LEARNING CURVE • Exploration Geochemistry • Interpretation of Airborne Magnetic Data Fax Int’l + (612) 6281 5909 Phone Int’l + (612) 6281 5899 • Structural Mapping for Mineral Exploration [email protected] • Resource Assessment http://www.learning-curve.com.au/explore

PAID ADVERTISEMENT 16 SEG NEWSLETTER No 54 • JULY 2003

... from 15 Nickel Laterites: A Review (Continued) over short distances. Advanced explo- Alibhai, K.A.K., Dudeney, A.W.L., Leak, D.J., Colorado State University, 378 p. ration for accurate estimation of Agatzini, S., and Tzeferis, P., 1993, Manceau, A., Schlegel, M.L., Musso, M., Sole, Bioleaching and bioprecipitation of nickel V.A., Gauthier, C., Petit, P.E., and Trolard, resources and reserves, and for reliable and iron from laterites: FEMS Microbiology F., 2000, Crystal chemistry of trace elements mine planning, therefore, relies on hav- Reviews, v.11, p. 87–96. in natural and synthetic goethite: Geochimica ing an adequate drilling density; gener- Brand, N.W., and Butt, C.R.M., 2001, et Cosmochimica Acta, v. 64, p. 3643–3661. ally a 25- to 50-m grid is used. Weathering, element distribution and geo- Mihaylov, I., Krause, E., Colton, D.F., Okita, Subsequently, precise grade control and chemical dispersion at Mt. Keith, Western Y., Duterque, J.P., and Perraud, J.L., 2000, Australia: Implication for nickel sulphide The development of a novel hydrometallur- careful blending of mined ore categories exploration: Geochemistry: Exploration, gical process for nickel and cobalt recovery are required to minimize variation in Environment, Analysis, v.1, p. 391–407. from Goro laterite ore: Canadian Institute the composition of plant feed and thus Brand, N.W., Butt, C.R.M., and Elias, M., of Mining, Metallurgy and Petroleum optimize plant operating conditions. 1998, Nickel laterites: Classification and Bulletin, v. 93, p. 124–130. features: AGSO Journal of Australian Nahon, D.B., 1991, Introduction to the Grade control commonly requires Geology and Geophysics, v.17, p. 81–88. petrology of soils and chemical weathering: drilling on grids of 5 to 10 m. Brindley, G.W., 1978, The structure and New York, John Wiley, 313 p. chemistry of hydrous nickel-containing sili- Nahon, D.B., and Tardy, Y., 1992, The fer- cate and aluminate minerals: Bulletin du ruginous laterites, in Butt, C.R.M., and Bureau de Recherches Geologiques et Zeegers, H., eds., Regolith exploration geo- CONCLUSIONS Minieres Section 2, v. 3, p. 233–245. chemistry in tropical and subtropical ter- Presently, most Ni production comes Brindley, G.W., Bish, D.L., and Wan, H.M., rains: Handbook of exploration geochem- from sulfide deposits. In the future, the 1979, Compositions, structures and proper- istry 4: Amsterdam, Elsevier, p. 41–55. ties of nickel containing minerals in the Pelletier, B., 1996, Serpentines in nickel silicate increasing cost of mining sulfide ores kerolite-pimelite series: American ores from New Caledonia, in Grimsey, E.J., underground, diminishing economic Mineralogist, v. 64, p.615–625. and Neuss, I., eds. Nickel ’96, Australasian sulfide resources, and increasing envi- Butt, C.R.M., 1975, Nickel laterites and baux- Institute of Mining and Metallurgy, Mel- ronmental compliance costs may have ites: Perth, CSIRO Australia, Division of bourne, Publication Series 6/9, p. 197–205. Mineralogy, Report FP12, 34 p. Quantin, C., Becquer, T., Rouiller, J.H., and a strong impact of the economics of Butt, C.R.M., and Nickel, E.H., 1981, Berthelin, J., 2001, Oxide weathering and mining these deposits in the future. The Mineralogy and geochemistry of the weath- trace metal release by bacterial reduction economic viability of Ni laterite deposits ering of the disseminated nickel sulfide in a New Caledonia Ferralsol: is controlled not only by the nature of deposit at Mt. Keith, Western Australia: Biogeochemistry, v. 53, p. 323–340. Economic Geology, v. 6, p.1736–1751. Schellman, W., 1989, Composition and the resource but also by other factors Colin F., Nahon, D., Trescases, J.J., and Melfi, origin of lateritic nickel ore at Tagaung such as infrastructure, location, and A.J., 1990, Lateritic weathering of pyroxen- Taung, Burma: Mineralium Deposita, v. access to low cost energy sources. ites at Niquelandia, Goais, Brazil: The 24, p. 161–168. Environmental issues that need to be supergene behavior of nickel: Economic Simons, C.S., 1988, The production of nickel: addressed in the development of a Geology, v. 85, p. 1010–1023. Extractive metallurgy—past, present and de Oliveira, S.M.B., Trescases, J.J., and Melfi, future, in Tyroler, G.P., and Landolt, C.A., deposit include the rehabilitation of A.J., 1992, Lateritic nickel deposits of Brazil: eds., Extractive metallurgy of nickel and large open pits, disposal of tailings, and Mineralium. Deposita, v. 27, p. 137–146. cobalt: Pennsylvania, The Metallurgical revegetation. As outlined above, Eggleton, R.A., ed., 2001, The Regolith Society, p. 91–134. improvements in mineral processing Glossary CRC for Landscape Evolution and Sukla, L.B., and Panchanadikar, V., 1993, Mineral Exploration: Floreat Park, Western Bioleaching of lateritic nickel ore using a technologies may have a large impact Australia, 144 p. heterotrophic microorganism: on viability of lateritic deposits, particu- Elias, M., 2002, Nickel laterite deposits-geo- Hydrometallurgy, v. 32, p. 373–379. larly for oxide deposits. These issues, logical overview, resources and exploita- Trescases, J.J., 1975, L’evolution geochimique along with the large resource base, tion, in Cooke, D., and Pontgratz, J., eds., supergene des roches ultrabasiques en zone Giant ore deposits: characteristics, genesis tropicale; formation des gisements nickelif- make the future of laterite mining and exploration: Centre for Ore Deposit eres de Nouvelle-Caledonie: Memoires potentially very important. Research, University of Tasmania, Special Office de la Recherche Scientifique et Publication 4, p. 205–220. Technique Outre-Mer (ORSTOM), Paris, Elias, M., Donaldson, M.J. and Giorgetta, N., France, v. 78, 278 p. 1981, Geology, mineralogy, and chemistry ——1986, Nickeliferous laterites: A review of the ACKNOWLEDGMENTS of lateritic nickel-cobalt deposits near contributions of the last 10 years: Geological SG would like to acknowledge Gordon Kalgoorlie, Western Australia: Economic Survey of India Memoirs, v. 120, p. 51–62. Koll, Richard Herrington, and the staff Geology, v. 76, p.1775–1783. Trivedi, P., and Axe, L., 2001, Ni and Zn sorp- Glazkovsky, A.A., Gorbunov, G.I., and Sysoev, tion to amorphous versus crystalline iron of the Cerro Matoso mine and BHP- F.A., 1977, Deposits of nickel, in Smirnov, oxides: Macroscopic studies: Journal of Colloid Billiton for giving her the opportunity to V.I., ed., Ore deposits of the USSR, Volume and Interface Science, v. 244, p. 221–229. study these fascinating deposits. CRMB II: London, Pitman Publishing, p. 3–79. Truckenbrodt, W., Kotschoubey, B., and Schell- and ME thank Nigel Brand for many Golightly, J.P., 1981, Nickeliferous laterite mann, W., 1991, Composition and origin of deposits: Economic Geology 75th the clay cover on North Brazilian laterites: valuable and stimulating discussions. Anniversary Volume, p. 710–735. Geologische Rundschau, v. 80, p. 591–610. Thanks are also due to Paulina Gromek Krause, E., Blakey, B.C., and Papangelakis, Valeton, I., Biermann, M., Reche, R., and for drafting many of the diagrams. V.G., 1998, Pressure acid leaching of nicke- Rosenberg, F., 1987, Genesis of nickel lat- liferous laterite ores: Alta 1998 erites and bauxites in Greece during the Nickel/Cobalt Pressure Leaching & Jurassic and Cretaceous, and their relation REFERENCES Hydrometallurgical Forum (Day 3), Perth, to ultrabasic parent rocks: Ore Geology Western Australia, Blackburn South, Alta Reviews, v. 2, p. 359–404. Albandakis, N., 1981, The nickel-bearing iron- Metallurgical Services. Zachara, J.M., Fredrickson, J.K., Smith, S.C., ores in Greece, in Augustithis, SS, ed., Inter- Lopez-Rendon, J.E., 1986, Geology, mineral- and Gassman, P.L., 2001, Solubilization of national Symposium on Metallogeny of ogy and geochemistry of the Cerro Matoso Fe(III) oxide-bound trace metals by a dissimu- Mafic and Ultramafic Complexes, UNESCO, nickeliferous laterite, Cordoba, Colombia: latory Fe(III) reducing bacterium: Geochimica Athens, October 1980, v. 1, p. 194–213. Unpublished M.Sc. thesis, Fort Collins, CO, et Cosmochimica Acta, v. 65, p. 75–93.