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 gossaniferous 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

Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.

<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 nickel to iron ratios (Ni:Fe), but it is usually described as 1:1. In some cases, this ratio is skewed by the presence of pyrrhotite inclusions. 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

Nickeline or niccolite is the mineral form of nickel arsenide. The naturally-occurring mineral contains roughly 43.9% nickel and 56.1% arsenic by mass, but composition of the mineral may vary slightly.

<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. Pyrrhotite is generally tabular and brassy/bronze in color with a metallic luster. The mineral occurs with mafic igneous rocks like norites, and may form from pyrite during metamorphic processes. Pyrrhotite is associated and mined with other sulfide minerals like pentlandite, pyrite, chalcopyrite, and magnetite, and has been found globally.

<span class="mw-page-title-main">Volcanogenic massive sulfide ore deposit</span> Metal sulfide ore deposit

Volcanogenic massive sulfide ore deposits, also known as VMS ore deposits, are a type of metal sulfide ore deposit, mainly copper-zinc which are associated with and produced by volcanic-associated hydrothermal events in submarine environments.

<span class="mw-page-title-main">Sulfide mineral</span> Class of minerals containing sulfide or disulfide as the major anion

The sulphide minerals are a class of minerals containing sulphide (S2−) or disulphide as the major anion. Some sulfide minerals are economically important as metal ores. The sulphide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulpharsenides and the sulphosalts. Sulphide minerals are inorganic compounds.

<span class="mw-page-title-main">Ore genesis</span> How the various types of mineral deposits form within the Earths crust

Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.

Kambalda type komatiitic nickel ore deposits are a class of magmatic iron-nickel-copper-platinum-group element ore deposit in which the physical processes of komatiite volcanology serve to deposit, concentrate and enrich a Fe-Ni-Cu-(PGE) sulfide melt within the lava flow environment of an erupting komatiite volcano.

In inorganic chemistry, mineral hydration is a reaction which adds water to the crystal structure of a mineral, usually creating a new mineral, commonly called a hydrate.

In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene processes include the predominance of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater, and react with hypogene sulfides at the supergene-hypogene boundary. The reaction produces secondary sulfides with metal contents higher than those of the primary ore. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite (Cu2S), covellite (CuS), digenite (Cu18S10), and djurleite (Cu31S16) are deposited by the descending surface waters.

<span class="mw-page-title-main">Gaspéite</span> Nickel carbonate mineral

Gaspéite, a very rare nickel carbonate mineral, with the formula (Ni,Fe,Mg)CO3, is named for the place it was first described, in the Gaspé Peninsula, Québec, Canada.

<span class="mw-page-title-main">Kambaldaite</span> Carbonate mineral

Kambaldaite, NaNi4(CO3)3(OH)3·3H2O, is an extremely rare hydrated sodium nickel carbonate mineral described from gossaniferous 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> Supergene thiospinel sulfide mineral

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

<span class="mw-page-title-main">Mineral redox buffer</span> Geochemical assemblage

In geology, a redox buffer is an assemblage of minerals or compounds that constrains oxygen fugacity as a function of temperature. Knowledge of the redox conditions (or equivalently, oxygen fugacities) at which a rock forms and evolves can be important for interpreting the rock history. Iron, sulfur, and manganese are three of the relatively abundant elements in the Earth's crust that occur in more than one oxidation state. For instance, iron, the fourth most abundant element in the crust, exists as native iron, ferrous iron (Fe2+), and ferric iron (Fe3+). The redox state of a rock affects the relative proportions of the oxidation states of these elements and hence may determine both the minerals present and their compositions. If a rock contains pure minerals that constitute a redox buffer, then the oxygen fugacity of equilibration is defined by one of the curves in the accompanying fugacity-temperature diagram.

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">Cubanite</span> Copper iron sulfide mineral

Cubanite is a copper iron sulfide mineral that commonly occurs as a minor alteration mineral in magmatic sulfide deposits. It has the chemical formula CuFe2S3 and when found, it has a bronze to brass-yellow appearance. On the Mohs hardness scale, cubanite falls between 3.5 and 4 and has a orthorhombic crystal system. Cubanite is chemically similar to chalcopyrite; however, it is the less common copper iron sulfide mineral due to crystallization requirements.

<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">Djerfisherite</span> Sulfide mineral

Djerfisherite is an alkali copper–iron sulfide mineral and a member of the djerfisherite group.

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

Millerite or nickel blende 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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