An Interpretive Study of a Nickel-Iron Sulfide Ore Intersection, Lunnon Shoot, Kambalda, Western Australia

Abstract

A section through Archeart nickel-iron sulfide mineralization of Western Mining Corporation's Lunnon Shoot, Kambalda, consists of a footwall of pillow basalt, a narrow contact zone comprising magnetite-rimmed chromite enhedra in silicates, massive ore with 95 percent sulfide, matrix (disseminated) ore with 60-20 percent sulfide, and hydrated and carbonated ultramafic rocks in the hanging wall. The sulfides were selectively dissolved for analysis using a bromine attack (see Appendix) giving an average composition of the sulfide portion of Ni = 9.37%, Fe -50.56%, Cu = 0.87%, Co = 0.20% and S = 39.01%. The major sulfides are pyrrhotite, pentlandite (with minor alteration to violarite), pyrite and chalcopyrite. The pyrite is concentrated near the top of the massive ore. Magnetite is irregularly distributed through the ore, and is more abundant in the matrix ore than in the massive ore.The data are consistent with the ore having been eraplaced at elevated temperatures as an ultramafic crystal mush containing olivine and chromite crystals, magnesia-rich silicate melt and immiscible sulfide-oxide liquid. Gravity segregation, probably in flow. has resulted in an ore zone comprising a quenched chromite-bearing zone, a sulfide-rich massive ore zone and a matrix ore in which olivines were set in continuous sulfide. The hanging wall represents the original silicate crystal mush with only minor sulfides.Solidification of sulfide commenced at about 1,140 ø C near the contact, resulting in magnetite-poor massive ore and oxide-enriched matrix ore. Pyrite was the first subsolidus sulfide mineral to crystallize at about 400 ø C and grew to give bands and subhedra near the top of the massive ore (with rejected Ni and Fe diffusing away). Cobalt was preferentially concentrated in this pyrite and depleted from the surrounding sulfide (Mss). Pentlandite exsolving at lower temperatures, however, competed favorably with lateforming pyrite for available cobalt. Nickel is low in the early-formed pyrite but concentrated in pyrite formed at low temperatures.

Supergene alteration of the Mt Windarra nickel sulphide ore deposit, Western Australia

“…Hence, although the material studied comes from two separate ore shoots, the general conclusions derived from the sequence of alteration is believed to be valid as these and indeed many other massive/matrix sulphide nickel orebodies throughout the Yilgarn are characterised by their mineralogical, textural and chemical monotony both with regard to the primary ore and the weathering profile. (HaNcOCK et al 1970;EWERS and HUDSON 1972;FARDON 1970;HUDSON, 1972;NICKEL, Ross and TI-IORNBER 1973;OLIVER and WARB 1970;ROBERTS (in press);WATMUFF 1970;WooDALL and TRAVIS 1969;company reports and oral communications). Modal analyses of the opaque and non-opaque mineralogy were made on samples from the A (Shirley) Shoot exploratory winze.…”

“…Most of these orebodies appear to be syngenetic stratiform deposits having crystallised from an immiscible sulphide (oxygen) silicate melt (e.g. EweRs and HUDSON 1972;N~SUITT 1970). The ore types can be classified into three broad categories viz.…”

Boudinage on radial fractures: An alternative to magmatic models for the emplacement of nickel ores, Lunnon Shoot, Kambalda, Western Australia

“…694), or both (McNaughton et al 1988); (v) ores being seen as forming either by gravitational settling of immiscible sulfides (Ewers & Hudson 1972;Naldrett 1973) or by separate emplacement of sulfidic flows (Ross & Hopkins 1975); and (vi) flows being seen as channelising downwards Huppert & Sparks 1985) or channelising upwards ('constructional' lava piles: Cowden 1988;Cowden & Roberts 1990).…”

Depositional Environments of Volcanic Peridotite-Associated Nickel Sulphide Deposits with Special Reference to the Kambalda Dome

“…2. Relationships of massive/matrix/disseminated sulphides at base of host unit and interpillow sulphides within underlying basalts (Woodall and Travis 1969, Ewers and Hudson 1972, Hudson 1972, Naldrett 1973, Gresham and LoftusHills 1981. 3.…”