The Supergene Alteration of Pyrrhotite-Pentlandite Ore at Kambalda, Western Australia

The measurement of ignition temperatures and extents of reaction on iron and iron-nickel sulfides

“…EPMA also indicated the presence of 1.5-2% of nickel within the pyrite particle on average, a maximum of 4% being measured. This agreed with EPMA results reported by Nickel et al [6] for pyrite of a similar origin. Hence the solution from which pyrite was precipitated was obviously nickel enriched.…”

“…Some of the iron released during alteration is thought to precipitate as a carbonate, hence it is likely that the grey phase in Fig. 2 is siderite [6]. A second type of violarite is observed in Fig.…”

“…This has resulted from pentlandite alteration and it is porous due to the associated volume reduction. The violarite-pyrite assemblage is known to be a supergene alteration product of the primary ore [6,7]. Alteration commences with the appearance of specks of violarite throughout the pentlandite grain.…”

“…This mineral has formed by reaction of pyrrhotite with nickel released during the formation of violarite. The 'saw-tooth' appearance has been inherited from the twin lamellar structure of pyrrhotite [6]. This phase is reported to be iron rich compared with the blocky form and is far less abundant due to the limited quantity of nickel available.…”

“…Obviously the polished section was not representative of the bulk material. Marcasite is known to occur in violaritepyrite assemblages [6], being porous and frequently colloform as is secondary pyrite. For the purpose of convenience in this paper, the pyritemarcasite sample will be simply referred to as pyrite, while the violaritepyrite mixture will be labelled violarite.…”