Iron-nickel Sulfide Research Articles

Spinel phases associated with metamorphosed volcanic-type iron-nickel sulfide ores from Western Australia

Previous interpretations of spinels in Archean Fe-Ni sulfide ores from Western Australia must be revised in view of widespread metamorphic effects. When these effects are isolated, however, the spinels remain useful genetic indicators.Modified igneous chromites occur in the metamorphosed ultramafic host rocks but show no tendency toward gravity-induced basal accumulation. They may be distinguished from chromites of metasomatic origin in contact reaction zones and from Cr-bearing magnetites produced during serpentinization. Ragged magnetites also attributed to serpentinization reactions occur in disseminated and matrix ores. In addition, the ores contain large subhedral ferrochromites and more euhedral magnetites which appear to be relict crystallization products of sulfide-oxide melts; their presence provides supporting evidence for an initially magmatic origin of the ores. Despite changes in their distribution during deformation, some gravitational concentration of the ferrochromites within ore is apparent; this concentration is incompatible with a single-stage magmatic model.Both the lithophile and chalcophile chromites in mineralized ultramafic rocks are unusually rich in zinc, a feature apparently inherited from the magmatic stage, and one which may be useful in exploration.

The replacement of chrome spinel by chromian valleriite in sulphide-bearing ultramafic rocks in Western Australia

Chromian valleriite occurs as a replacement product of chrome spinel in the Nepean and Perseverance nickel-iron sulphide deposits of Western Australia. Compositions determined for chromian valleriites are variable due to intergrowth with spinel and to substitution of Fe and Ni for Cu. At Perseverance, valleriite, with minor admixed chrome spinel, has a composition expressed by the formula Fe1.18Cu0.81Ni0.01S2.00·2.03[Mg0.50Cr0.37Mn0.08Fe0.03Ti0.01Al0.01(OH)2.00]. Nepean valleriites are similarly intergrown with spinel, with the purest chromian valleriites varying in composition from a nickel-poor Fe1.21Cu0.78Ni0.01S2.00·1-46.[Mg0.43Cr0.18Mn0.05Fe0.30(OH)2] to Fe1.58Cu0.28Ni0.15S2.00·1.79[Mg0.51Cr0.30Fe0.16Ti0.03(OH)2]. Conversion of chrome spinel to valleriite is attributed to addition of Cu and S from the breakdown of chalcopyrite, addition of Mg from serpentinising olivine and limited addition of Ni from the breakdown of pentlandite to mackinawite. These processes are thought to occur as post-metamorphic hydrothermal reactions in nickel sulphide ores that have been subjected to high grade regional metamorphism.

Modification of Iron-Nickel Sulfides During Serpentinization and Talc-Carbonate Alteration at Black Swan, Western Australia

Disseminated nickel-iron sulfides in Archean serpentinite at Black Swan consist of the relatively uncommon assemblage millerite-pyrite-magnetite-violarite, with the previously unrecorded assemblage pyrite-vaesite-violarite occurring in some talc-carbonate rocks. Although interstitial sulfide textures and relic pyrrhotite-pentlandite aggregates suggest a primary magmatic origin for at least part of the mineralization, the sulfide assemblages are too sulfur-rich to have crystallized directly from a sulfide liquid. Progressive serpentinization and carbonation of a dunite body during an essentially static, upper greenschist to lower amphibolite facies metamorphism has clearly controlled the composition of sulfide aggregates and has resulted in at least limited mobilization and concentration of nickel and sulfur. Whether larger scale mobilization of nickel and sulfur resulted in significant concentration of sulfides is problematical, although sufficient silicate nickel does appear to have been released during carbonation to provide the observed concentration of nickel in the mineralized serpentinite.During an early-stage serpentinization iron-poor lizardite with clinochrysotile rims and magnetite dust, all pseudomorphous after olivine, coexisted with pyrite-millerite-magnetite in mineralized serpentinite and with disseminated violarite in near-barren serpentinite. Progressive release of silicate nickel and extensive textural modification of sulfide aggregates without significant change in their composition accompanied the replacement of lizardite by antigorite, and its subsequent recrystallization in response to increasing temperature. Carbonation of serpentinites was penecontemporaneous with recrystallization of antigorite in areas where carbon dioxide fugacity of the serpentinizing fluid was high. Sulfide aggregates in contact with carbonate were strongly recrystallized and more sulfur-rich assemblages were generated in talc-carbonate rocks, the final products of carbonation. Sulfide assemblages continued to re-equilibrate after final recrystallization of serpentine and carbonate minerals.

Mineralogy of the Marbridge No. 3 & No. 4 nickel-iron sulfide deposits; with some comments on low temperature equilibration in the Fe-Ni-S system

The Marbridge No. 3 and 4 deposits are associated with lens-like bodies of serpentinized ultramafic rock that occur within a sequence of interbanded felsic volcanic rocks and graywackes. Both deposits consist of sulfide disseminated within the host peridotite, together with smaller amounts of stringer ore. Ore at the No. 3 deposit occurs towards the top of its associated serpentinite while that at the No. 4 occurs towards the base.The major sulfide minerals at the No. 4 deposit are pyrite and pentlandite together with minor amounts of millerite. At No. 3, the ore is zoned parallel to the contact with the host volcanics. The major part consists of pyrite, pentlandite and millerite, but close to the contact the assemblage pyrite-pentlandite-pyrrhotite is developed. Small amounts of pentlandite and heazlewoodite occur at the center of the serpentinite lens at the No. 3 deposit. Pentlandite is extensively altered to violarite throughout much of this deposit.Electron microprobe analyses of pentlandite from the Marbridge deposits, together with samples from the Alexo mine, the Texmont mine and the Sudbury ores indicate that the Fe:(Ni + Fe) ratio of pentlandite varies directly with the minerals with which it is associated, ranging from 0.518 for that in association with troilite and intermediate hexagonal pyrrhotite to 0.341 in association with heazlewoodite. This relationship indicates that equilibrium has been established between pentlandite and its associated minerals and is supporting evidence for the existence of a stable tie-line between pentlandite and pyrite at low temperatures in the Fe-Ni-S system.

The central portion of the Fe-Ni-S system and its bearing on pentlandite exsolution in iron-nickel sulfide ores

A detailed study of the central portion of the Fe-Ni-S system between 600 degrees and 250 degrees C has been conducted by means of silica-tube techniques. Particular emphasis has been placed on defining the limits of the mono-sulfide solid solution (Mss) that extends across the system from Fe (sub 1-x) S to Ni (sub 1-x) S; the sulfur-poor limit is significant with respect to the formation of pentlandite in iron-nickel sulfide ores.At 600 degrees C the Mss appears on the phase diagram as a nearly straight-sided band, thinner at the nickel-rich than at the iron-rich end. The band becomes narrower as the temperature falls: the sulfur-rich limit remains nearly straight but moves towards the sulfur-poor limit; the sulfur-poor limit moves rapidly towards the sulfur-rich limit in the center but not at the ends of the solid solution, so that at lower temperatures the Mss is concave outwards on the sulfur-poor side. The temperature at which the Mss becomes incomplete and below which the pyrite-pentlandite assemblage is stabilized is not known precisely, although it is below 300 degrees C.Magnetite and chalcopyrite, which often occur with pyrrhotite and pentlandite in ores, do not change significantly the temperature at which pentlandite exsolves from Mss of any given composition. When projected from chalcopyrite onto the Fe-Ni-S face of the Cu-Fe-Ni-S system, compositions of most pyrrhotite-pentlandite-chalcopyrite ores fall within the boundaries of the Mss at 500 degrees C. If these deposits were formed as equilibrium assemblages at or above this temperature, the pentlandite must have exsolved from Mss.The shape of the pentlandite-pyrrhotite solvus is such that pentlandite exsolution is more dependent on the metal: sulfur ratio than the nickel content of the Mss. Two copper-poor deposits serve as examples: pentlandite exsolution would have started at the Alexo deposit ( approximately 6.5 percent Ni in sulfides, 38-38.2 percent S in pyrrhotite) at 350 degrees -400 degrees C, but in the massive ore at the Marbridge deposit ( approximately 6.5 percent Ni in sulfides, 39.2-39.8 percent S in pyrrhotite) it would not have begun above 300 degrees C. Since most if not all of the nickel in iron-nickel sulfide deposits is in solid solution as nickeliferous pyrrhotite at temperatures as low as 300 degrees C, the pyrrhotite-pyrite solvus is invalidated as a geothermometer in these ores.

A Study of the Strathcona Mine and Its Bearing on the Origin of the Nickel-Copper Ores of the Sudbury District, Ontario

A Study of the Strathcona Mine and Its Bearing on the Origin of the Nickel-Copper Ores of the Sudbury District, Ontario

The Sulphide Phase in Some Iron Meteorites

METALLIC meteorites are composed in, varying proportions of two iron–nickel metallic solid solutions, kamacite, which has a low nickel content, and taenite, which has a higher nickel content. The structure and distribution of these phases have been extensively examined on a macro- and on a micro-scale. Many iron meteorites also contain non-metallic inclusions of an iron–nickel phosphide (schreibersite) or an iron–nickel sulphide (troilite). Troilite has not been subject to very detailed microscopic examination for two reasons. First, it shows a great tendency to chip and disintegrate during preparation and, secondly, it is very reactive towards most etching agents ; hence, when metallic meteorites are deeply etched for museum exhibition the troilite is usually protected from the etching agent by a suitable stopping-off compound.

The discovery of nickel in Egypt

Nickel was discovered in the ancient Ab Swayel copper mine, Egypt, in 1940, in the form of a nickel iron sulfide, identified as violarite. X-ray analyses are given.

Bravoite from a new locality [Missouri

The discovery of a new locality for bravoite (Ni, Fe) S 2 has provided material for a study of this rare nickel-iron sulphide and has established the Missouri occurrence as the first in North America. The minuteness of grain size and the manner of the occurrence with pyrite precludes any determination of the optical, chemical or physical properties of the mineral. Nevertheless the remarkable zonal structure and the violet color which it exhibits in polished section agrees with that described from Mechernich, 3 Germany, and serves very well to establish its identity. Certainly, without the aid of the metallographic microscope and its accessories for high magnification, this mineral would have gone unrecognized and chemical assays would have established the pyrite merely as nickeliferous.