Nickel Laterite Classification and Features by Brand Et Al. [PDF]

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AGSO Journal of Australian Geology & Geophysics, 17(4),81-88



© Commonwealth of Australia 1998



Nickel laterites: classification and features



N,W Brandl, c'RM, Butt2, & M, Elias 3



I WMC Leinster Nickel Operations, PO Box 22, Leinster, Western Australia 6437. 2 Cooperative Research Centre for Landscape Evolution and Mineral Exploration, CSIRO Exploration and Mining, Wembley, Perth, Western Australia. J Western Mining Corporation Ltd, QVl Building, 250 St George's Terrace, Perth, Western Australia.



EXPLORATION MODEL: The Cawse shear-controlled Ni-oxide and associated Mn-Co--Ni deposit, Western Australia Examples of oxide deposits Wingelinna (Western Australia); Claude Hills (South Australia); Moa Bay, Nicaro (Cuba); Guri Kuq (Albania); Kosovo Region (Balkans); Moramanga (Madagascar); Ramu River (Papua New Guinea); Santa Isabel (Solomon Islands); Dinagat (Philippines); Sebuku Island (Borneo); Goro (New Caledonia).



Target • • • • •



Pervasive free silica



Typical size: 0.85 Mt of contained Ni, (0.01 - 5 Mt). Smaller deposits combine to make an economic region. Average grade 1.2% Ni, rarely exceeds 1.4% Ni. Low Si & Mg concentrations. High Fe (>40%) and Co (> 700 ppm) contents.



Mining and treatment • Shallow enrichment «50 m) allows cost-effective assessment and mining. • Treatment includes pyrometallurgy (i.e. Ni recovered from siliceous flux or as direct feed, e.g. Siberia, Western Australia), and hydrometallurgy (i.e. alkaline leach , e.g. Cuba; acid leach, proposed for Cawse, Western Australia). • Screening of silica to enrich oxide feed. • High-Mg clays (e.g. nimites) may cause problems by consuming acid.



Saprock



Olivine adcumulate pratore Absolute enrichment of Nt (and Co) associated with Mn oxides Absolute enrichment of Ni associated with chlorites Relative enrichment of NI associated wIth the dlso/utian of S,



Figure 2, Model for shear-controlled Ni-oxide deposits,



-----'2\1~ •



•



OliVine



meso-adcumulate



IC]



OliVine



orthocumulale



I[J



Regional geological criteria



I Granlle



• Developed over unaltered or serpentinised ultramafic lithologies: never developed over talc carbonate lithologies. • Formed both in stable cratonic platforms (e.g. Yilgarn Block, Western Australia) and accretionary terrains (e.g. Cuba). • Limonite deposits developed over Mg-rich lithologies, (i.e. high MgO, low AI 20) • Shear-hosted mineralisation controlled by primary high• angle strike-slip faults that transgress in-situ regolith horizons and are perpendicular to ultramafic stratigraphy. • Other styles of supergene mineralisation present in district• stratabound Mn- Co- Ni (e.g. Siberia, Western Australia),



Cross



section %Ni



Figure 3. Interpreted geo logical setti ng of t he Cawse shear• controlled Ni-ox ide deposit, Western Australia,



nontronite-hosted nickel laterite (e.g. Bulong and Murrin Murrin, Western Australia) and num ero us supergene Au deposits.



Mineralisation features -20



IE] Lateritic duricrust



1



Ore



> 1.0% Ni



Figure l, Interpreted section of th e Cawse, shear-controlled, Ni-oxide deposit, Western Australia,



• Enrichment ofNi in shear-controlled stac ked lenses devel• oped along strike of fault. Intimately associated with flat• lying, goethite-rich pods. • Mn enrichment associated with permeability contrast in upper regolith profile. • Main mineralisation developed above the Fe redox boundary and confined to the ferruginous sapro lite. Ni enrichment below redox boundary associated with silicate and carbonate, (highly variable in concentration and abundance ). • Depth control to mineralisation: lenses and pods, IS and 50 m depth; Mn-Co-Ni , 5-15m depth . • Strong regolith control, with enriched Ni confined to ferruginous saprolite. • Ni associated with goethite, nimites, various Mn oxides and minor magnetite. • High free-silica content in ferruginous saprolite.



82



N.W. BRAND ET AL.



Geophysical criteria



Regolith profile Zone (* ore zones)



Duricrust Mn-Co- Ni horizon* Mottled zone Collapsed Fe saprolite* Fe-saprolite Saprolite Saprock Protore Oxidised shear zone* Shear zone



Thickn ess (m)



Mineralogy



Av. Ni



3



Si-mgt-gt Mn oxides- SiFe oxides Si--clay- gt gt- Si



0.08 0.96 0.12 Co 0.02 1.26



Si- gt mgs- serp-Si-dom serp- mgt- dom- mgs serp, fo, mgt, chr talc- nimite



0.46



talc- phl-mgs



0.30



up to 14 m 5 13



24 18 4



up to 16 m wide



(%)



0.41 0.20 0.27 1.50



up to 8%



• Chromites may be enriched in goethite pods. • Magnetite preserved through in-situ regolith profile.



Weathering



• Silica envelope to ore system developed in the ferruginous saprolite and immediately surrounding the ore pods. • Carbonate, magnesite and dolomite developed in the saprock and saprolite. • Complete in-situ profile developed at Cawse.



Geochemical criteria



• Widespread Ni (>0.5%) ± Co- Mn regolith anomalies developed along strike and overlying the dunite unit. • Elevated Fe (>40%), Si:Mg ratio (>200) and high Ni :Cu ratio (>40: 1). • Elevated light-PGEs (Ir, Os, Ru) . • Trace elements include Cr, Zn ± Mn, ± Co.



• Regional airborne magnetics can be used to define high-Mg cumulate stratigraphy, favourable structures, and intrusions that act as impermeable hydromorphic barriers. • Electromagnetics can assist in geomorphic interpretation.



Fluid chemistry and source • • • •



Limited data available. Present-day meteoric water at Cawse, Ci--rich. Solubility constant for nickel, ct 10-0 25, OH 10- 19 • Lack of primary sulphides indicates low S02- in meteoric waters.



Climate and geomorphology • Developed in seasonally humid regions and modified by dry arid climates. • Low to moderate topographic relief. • Proximal to alluvial systems.



Comments on genesis



• Dunitic lithology structurally prepared before weathering. • Formed under seasonally humid climate; modified under later arid climates. • Meteoric waters leach Ni from the upper profile and from olivine/serpentine in saprock and saprolite. • Main Ni enrichment is shear controlled. • Enrichment confined to .a



Contained Ni (Mt)



> 50



* -



~10 50



e



5 -10



Figure 4. World distribution or nickel laterite resources (by country).



o



1-5



•