Violarite

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Violarite
General
Category Sulfide mineral
Thiospinel group
Spinel structural group
Formula
(repeating unit)		(Fe2+Ni23+S4)
IMA symbol Vio [1]
Strunz classification 2.DA.05
Crystal system Isometric
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space group Fd3m
Unit cell a = 9.46 Å; Z = 8
Identification
References [2] [3] [4]

Violarite (Fe 2+ Ni 23+ S 4) is a supergene sulfide mineral associated with the weathering and oxidation of primary pentlandite nickel sulfide ore minerals.

Contents

Violarite crystallises in the isometric system, with a hardness of 4.5 to 5.5 and a specific gravity of about 4, is dark violet grey to copper-red, often with verdigris and patina from associated copper and arsenic sulfides, and is typically in amorphous to massive infill of lower saprolite ultramafic lithologies.

Violarite has a characteristic violet colour, hence the name from the Latin 'violaris' alluding to its colour especially when viewed in polished section under a microscope.

Paragenesis

Violarite is formed by oxidisation of primary sulfide assemblages in nickel sulfide mineralisation. The process of formation involves oxidation of Ni2+ and Fe2+ which is contained within the primary pentlandite-pyrrhotite-pyrite assemblage.

Violarite is produced at the expense of both pentlandite and pyrrhotite, via the following basic reaction;

Pentlandite + Pyrrhotite --> Violarite + Acid

(Fe,Ni)9S8 + Fe(1-x)S + O 2 → Fe2+Ni23+S4 + H2SO3

Violarite is also reported to be produced in low-temperature metamorphism of primary sulfides, though this is an unusual paragenetic indicator for the mineral.

Continued oxidation of violarite leads to replacement by goethite and formation of a gossanous boxwork, with nickel tending to remain as impurities within the goethite or haematite, or rarely as carbonate minerals.

Occurrence

Violarite is reported widely from the oxidised regolith above primary nickel sulfide ore systems worldwide. It is of particular note from the Mount Keith dunite body, Western Australia, where it forms an important ore mineral.

It is also reported from open cast mines around the Kambalda Dome, and Widgiemooltha Dome, in association with polydymite, gaspeite, widgiemoolthalite and hellyerite, among other supergene nickel minerals.

Economic importance

Violarite is an important transitional ore in many nickel sulfide mines, as it has increased nickel tenor (Ni% as a total of sulfide) and occupies a position within the mineralised profile where it must be extracted to pay for development down to the most valuable fresh mineralisation.

Violarite mineralisation requires different metallurgy to primary nickel sulfides, due to the different nature of its gangue and its flotation properties. This may require additional treatment and processing, so in some cases low-grade violarite mineralisation is considered refractory ore.

Related Research Articles

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<span class="mw-page-title-main">Pentlandite</span> Iron–nickel sulfide

Pentlandite is an iron–nickel sulfide with the chemical formula (Fe,Ni)9S8. Pentlandite has a narrow variation range in Ni:Fe but it is usually described as having a Ni:Fe of 1:1. It also contains minor cobalt, usually at low levels as a fraction of weight.

<span class="mw-page-title-main">Nickeline</span> Nickel arsenide mineral

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<span class="mw-page-title-main">Pyrrhotite</span> Magnetic iron sulfide mineral

Pyrrhotite is an iron sulfide mineral with the formula Fe(1-x)S. It is a nonstoichiometric variant of FeS, the mineral known as troilite. Pyrrhotite is also called magnetic pyrite, because the color is similar to pyrite and it is weakly magnetic. The magnetism decreases as the iron content increases, and troilite is non-magnetic.

<span class="mw-page-title-main">Trevorite</span>

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Kambaldaite, NaNi4(CO3)3(OH)3·3H2O, is an extremely rare hydrated sodium nickel carbonate mineral described from gossanous material associated with Kambalda type komatiitic nickel ore deposits at Kambalda, Western Australia, and Widgie Townsite nickel gossan, Widgiemooltha, Western Australia.

<span class="mw-page-title-main">Polydymite</span>

Polydymite, Ni2+Ni23+S4, is a supergene thiospinel sulfide mineral associated with the weathering of primary pentlandite nickel sulfide.

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The Widgiemooltha Komatiite is a formation of komatiite in the Yilgarn Craton of Western Australia.

<span class="mw-page-title-main">Mackinawite</span> Iron nickel sulfide mineral

Mackinawite is an iron nickel sulfide mineral with the chemical formula (Fe,Ni)
1+xS. The mineral crystallizes in the tetragonal crystal system and has been described as a distorted, close packed, cubic array of S atoms with some of the gaps filled with Fe. Mackinawite occurs as opaque bronze to grey-white tabular crystals and anhedral masses. It has a Mohs hardness of 2.5 and a specific gravity of 4.17. It was first described in 1962 for an occurrence in the Mackinaw mine, Snohomish County, Washington for which it was named.

<span class="mw-page-title-main">Browns polymetallic ore deposit</span>

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<span class="mw-page-title-main">Saprolite</span> Chemically weathered rock

Saprolite is a chemically weathered rock. Saprolites form in the lower zones of soil profiles and represent deep weathering of the bedrock surface. In most outcrops its color comes from ferric compounds. Deeply weathered profiles are widespread on the continental landmasses between latitudes 35°N and 35°S.

<span class="mw-page-title-main">Millerite</span> Nickel sulfide mineral

Millerite is a nickel sulfide mineral, NiS. It is brassy in colour and has an acicular habit, often forming radiating masses and furry aggregates. It can be distinguished from pentlandite by crystal habit, its duller colour, and general lack of association with pyrite or pyrrhotite.

References

  1. ↑ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi: 10.1180/mgm.2021.43 . S2CID   235729616.
  2. ↑ Mindat.org
  3. ↑ Webmineral.com
  4. ↑ Handbook of Mineralogy
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