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ORIGIN OF VARIATIONS IN NICKEL TENOR ALONG THE STRIKE OF THE EDWARDS LODE NICKEL SULFIDE OREBODY, KAMBALDA, WESTERN AUSTRALIA

2001; Mineralogical Association of Canada; Volume: 39; Issue: 2 Linguagem: Inglês

10.2113/gscanmin.39.2.655

1499-1276

Charles Heath, Yann Lahaye, W. E. E. Stone, David D Lambert,

Hydrocarbon exploration and reservoir analysis

Nickel tenor (Ni concentration in 100% sulfides) varies from 12.5 to 14.5 wt% on the eastern flank, and from 16 to 18 wt% on the western flank of the Edwards lode orebody, Kambalda, Western Australia. The center of the orebody exhibits a large internal variation in tenor, from 9.6 to 18.7 wt% Ni. Tenor variation of this magnitude within a single orebody has not previou sly been documented at Kambalda. Three models were evaluated for the observed variation. (1) Variation in R factor. This model is supported by a higher nickel tenor within the matrix ores than the massive ores. Pyrolite-mantle-normalized abundances of the platinum-group elements (PGE) are consistent among massive, matrix and disseminated ores. This does not support an R-factor model for tenor variation, because sulfide liquid / silicate melt partition coefficients for the PGE are higher than for Ni (D PGE >> DNi). (2) Variations in oxygen fugacity f(O2). The f(O2) control on Ni tenor is not supported by geochemical or petrographic observations. The proportion of magnetite is relatively consistent within the orebody, demonstrating no correlation with Ni ten or. (3) Partial redistribution and sulfidation of the nickel ores during upper-greenschist- to lower-amphibolite-facies metamorphis m. Evidence includes increased pentlandite abundance correlating with an increase in the abundance of secondary metasomatic pyrite. Some pentlandite grains demonstrate a genetic relationship with carbonate veining, indicating nickel mobility. The larg e variation in Ni tenor observed within the central domain of the Edwards lode orebody correlates with the ore surface that exhib its the greatest degree of metamorphic heterogeneity. A laser-ablation ICP–MS study of the PGE distribution within sulfides shows that the Ir-group PGE (IPGE) are homogeneously distributed, in contrast to the Pt-group PGE (PPGE). The distribution of Pd reflects the distribution of pentlandite, and the other PGE (Rh, Ru, Pt) and Au seem controlled by PGM and Au-bearing phases. The IPGE show a strong primary magmatic control with distance along the strike of the orebody. Nickel does not demonstrate a correlation with the IPGE, indicating that post-volcanism processes of remobilization partly control the distribution of Ni alo ng strike.