The nickel sulfide deposits of Western Australia in global perspective

Abstract

Fifty-six nickel sulfide deposits in the Archean and lower Proterozoic terrains of Western Australia have been included in a global assessment of the geologic and economic characteristics of 145 Ni sulfide deposits. Essentially all deposits can be classified into one of two classes: (1) the dunite-peridotite class, which embraces deposits associated with host rocks of komatiitic affinities (usually Archean) and is subdivided into the intrusive dunite association and the volcanic peridotite association; and (2) the gabbroid class, which is subdivided by host rock characteristics into intrusive mafic-ultramafic complexes, large, layered intrusions, and the Sudbury Irruptive. Deposits in the gabbroid class are the most important source of Ni, even if Sudbury is excluded.Most original resources of sulfide Ni occur in stable platforms, but when the non-Sudbury component of ores with > or = 0.8 percent Ni is considered, Precambrian mobile belts are most important followed by Precambrian (mainly Archean) greenstone belts and Phanerozoic fold belts. The highest grades occur in the greenstone belts (volcanic peridotite-associated deposits) and the Phanerozoic fold belts (gabbroid intrusive mafic-ultramafic deposits of the Noril'sk region). The latter deposits are the most widespread and occur in all environments except the stable platforms. About 95 percent of the original resources in Western Australia occur in Archean greenstone belts and contribute about 11.4 percent of total original resources in ores with > or = 0.8 percent Ni. This contribution is split almost equally between intrusive dunite-associated and volcanic peridotite-associated deposits and has an advantageous grade distribution.Nickel sulfide deposits occur through geologic time, with most resources being lower Proterozoic in age. However, in the non-Sudbury component of ores with > or = 0.8 percent Ni, Archean deposits are the most important, followed by lower Proterozoic and Phanerozoic deposits. Gabbroid intrusive mafic-ultramafic complex deposits occur in each of these time intervals.The tonnage-grade distribution of original resources clearly shows the higher grade characteristics of volcanic peridotite-associated deposits (particularly those in Western Australia). Grade characteristics in gabbroid intrusive mafic-ultramafic complex deposits are improved considerably by allowance for their substantial Cu content, whereas recovery of their platinum-group element and Co content offers further scope for improvement. Intrusive dunite association deposits are characterized by a favorable size distribution, but commonly at low grades in contrast to the relatively small, high-grade volcanic peridotite-associated deposits.Mine production of sulfide Ni since 1900 has been largely derived from Sudbury, but the important contributions of intrusive dunite and volcanic peridotite-associated deposits since 1960, and major expansion of production from the Noril'sk region of the USSR has led to considerable diversification of ore sources. Gabbroid intrusive mafic-ultramafic complex deposits are now the principal source of sulfide Ni production. Current mine production from Western Australia represents about 12 percent of total mine production of sulfide Ni and is in balance with its 14.5 percent share of identified resources in ores with > or = 0.8 percent Ni.It is estimated that total identified resources of sulfide Ni in ores with > or = 0.8 percent Ni are adequate to maintain the existing rate of world mine production of sulfide Ni for about 40 years. The much larger component of identified resources in ores with < 0.8 percent Ni show a trend of increasing metric tons of Ni with decreasing grade, and it is likely that, in the long term, economic factors, rather than resource availability, will constrain production of sulfide Ni.