Chalcopyrite

minerals

chalcocite

molybdenite

covellite

Formula: CuFeS2
Sulphide
Specific gravity: 4.1 to 4.3
Hardness: 3½ to 4
Streak: Greenish black
Colour: Brass yellow, often with an iridescent tarnish
Solubility: Moderately soluble in nitric acid
Common impurities: Ag,Au,In,Tl,Se,Te
Environments:

Plutonic igneous environments
Carbonatites
Metamorphic environments
Hydrothermal environments

Chalcopyrite is the most widely occurring copper mineral. It is a primary mineral.
In contact metamorphic environments it may be associated with molybdenite.
In hypothermal (high temperature) and mesothermal (moderate temperature) veins and replacement deposits it occurs associated with galena, sphalerite and dolomite. It may contain gold or silver. Chalcopyrite is often present in large bodies of pyrite. Primary chalcopyrite readily alters to the secondary minerals bornite, covellite and brochantite, and also malachite, azurite, langite and numerous other secondary copper minerals.

Localities

At Mount Moliagul, Moliagul, Central Goldfields Shire, Victoria, Australia, chalcopyrite is present as coatings on pyrite crystals in granodiorite and as anhedral masses in quartz veins (AJM 21.1.42).

In Bulgaria pyrite pseudomorphs after chalcopyrite have been found (R&M 95.3.275).

At the Blue Points mine, Thunder Bay, Ontario, Canada, chalcopyrite is associated with galena, and minor pyrite and marcasite (R&M 94.4.319).

At the Thunder Bay Amethyst Mine, Thunder Bay District, Ontario, Canada, chalcopyrite has been found as inclusions in quartz variety amethyst (R&M 94.4.332).

At Herrensegen, Schapbach, Schartzwald, Germany, chalcopyrite occurs with covellite (FM 2318).

At Guanajuato, Mexico, acanthite-chalcopyrite pseudomorphs after polybasite have been found (KL p124).

At Palabora, South Africa, chalcopyrite occurs in a carbonatite (R&M 92.5.436-437).

At Redruth, Cornwall, England, UK, chalcopyrite has been found with tetrahedrite and calcite (FM 47545).

At Alderley Edge, Cheshire, England, UK, copper mineralised solutions percolated through porous sandstones and deposited barium, cobalt, copper, lead, vanadium and zinc minerals between the sand grains. Anhydrite formed as cement in permeable rocks, then baryte was deposited, followed by pyrite, chalcopyrite, sphalerite and galena. Subsequently a second generation of baryte and iron-rich calcite followed. These minerals crystallised from highly saline, sulphate-rich brines, at a temperature of 50 to 60o C (RES pps 49-50). A specimen of chrysocolla with a pseudomorph of goethite after chalcopyrite has been found (RES p55).

At Croft quarry, Blaby, Leicestershire, England, UK, chalcopyrite has been found as inclusions in analcime and also disseminated in the host diorite. Chalcopyrite crystals to 1 mm have also been found associated with fluorite, calcite and analcime (JRS 20.13-14, RES 189).

At Breedon quarry, Breedon on the Hill, Leicestershire, England, UK, chalcopyrite occurs with calcite (RES p202, 208).

At Cloud Hill Quarry, Breedon on the Hill, Leicestershire, England, UK, chalcopyrite occurs with calcite, dolomite and baryte (RES p205)

At Earl Ferrers' mine, Staunton Harold, Leicestershire, England, UK, chalcopyrite occurs with galena, sphalerite, calcite, dolomite and baryte (RES p222, 223).

At Wotherton mine, Chirbury, Shropshire, England, UK, chalcopyrite occurs with calcite and pyrite (RES p285).

At the Shadwell quarry, Much Wenlock, Shropshire, England, UK, chalcopyrite occurs with calcite on limestone (RES p296).

At the Pennerley mine, near Worthen, Shropshire, England, UK, chalcopyrite occurs with calcite, quartz and baryte (RES p290).

At the Ecton mine, Staffordshire, England, UK, chalcopyrite occurs with calcite, baryte, pyrite, galena and malachite (RES p302-307).

At Judkins quarry, Nuneaton, Warwickshire, England, UK, chalcopyrite has been found as pseudomorphs after chalcocite, with calcite (RES p324)

At the Magma mine, Pioneer District, Pinal county, Arizona, USA, chalcopyrite crystals have been collected with a purple bornite surface, and also on quartz crystals; crystalline masses of chalcopyrite have been found in association with sphalerite (R&M 95.1.84).

At Joplin, Jasper county, Missouri, USA, tetragonal crystals of chalcopyrite have been found epitaxial on sphalerite (FM 47452).

At the Sweetwater Mine, Ellington, Reynolds county, Missouri, USA, chalcopyrite pseudomorphs after galena have been found (KL p131).

Alteration

chalcopyrite to goethite
The first stage of copper supergene mineral formation is the oxidation of a primary copper-containing ore mineral, such as chalcopyrite. This is a complex process, but the reaction can be summarised as:
chalcopyrite + oxygen + water → copper ions + sulphate ions + goethite + sulphuric acid
4CuFeS2(s) + 17O2(g) + 6H2O(l) → 4Cu2+(aq) + 4SO42-(aq) + 4FeO(OH)(s) + 4H2SO4(aq)
The copper and sulphate ions are then free to react with carbonate ions in solution to form a range of supergene copper sulphates and carbonates (JRS 18.12).

chalcopyrite to sulphur
Oxidation of pyrite forms ferrous (divalent) sulphate and sulphuric acid:
pyrite + oxygen + water → ferric sulphate + sulphuric acid
FeS2 + 7O + H2O → FeSO4 + H2SO4
The ferrous (divalent) sulphate readily oxidizes to ferric (trivalent) sulphate and ferric hydroxide:
ferrous sulphate + oxygen + water → ferric sulphate + ferric hydroxide
6FeSO4 + 3O + 3H2O → 2Fe2(SO4)3 + 2Fe(OH)3
Ferric sulfate is a strong oxidizing agent; it oxidises chalcopyrite according to the reaction:
chalcopyrite and ferric sulphate to copper sulphate, ferrous sulphate and sulphur
CuFeS2 + 2Fe2(SO4)3 → CuSO4 + 5FeSO4 + 2S
(AMU b3-3.7)

chalcopyrite, arsenopyrite, CO2 and O2 to Fe-tennantite, siderite and sulphur
10CuFeS2 + 4FeAsS + 4CO2 + 8O2 = Cu10Fe2As4S13 + 4Fe(CO3) + 11/2S2
(CM 28.725-738)

chalcopyrite, arsenopyrite and pyrite to Fe-tennantite and troilite
10CuFeS2 + 4FeAsS + FeS2 = Cu10Fe2As4S13 + 13FeS
(CM 28.725-738)

chalcopyrite, arsenopyrite and sulphur to Fe-tennantite and pyrite
10CuFeS2 + 4FeAsS + 13/2S2 = Cu10Fe2As4S13 + 12FeS2
This reaction occurs at a comparatively low temperature (CM 28.725-738).

chalcopyrite, arsenopyrite and sulphur to Fe-tennantite and troilite
l0CuFeS2 + 4FeAsS + l/2S2 = Cu10Fe2As4S13 + l2FeS
(CM 28.725-738)

chalcopyrite and chalcocite to bornite
CuFe3+S2 + 2Cu2S = Cu5FeS4
This reaction occurs in the supergene enrichment zone (JRS 18.14).

chalcopyrite, stibnite and sulphur to Fe-tetrahedrite and pyrite
10 CuFeS2 + 2 Sb2S3 + 3/2 S2 = Cu10Fe2As4S13 + 8FeS2
(CM 28.725-738)

enargite and pyrite to Fe-tennantite, chalcopyrite and sulphur
4Cu3AsS4 + 4FeS2 = Cu10Fe2As4S13 + 2CuFeS2 + 7/2S2
(CM 28.725-738)

Fe-tetrahedrite, berthierite and sulphur to chalcopyrite and stibnite
Cu10Fe2Sb4S13 + 2FeSb2S4 + 11/2S2 = 10CuFeS2 + 4Sb2S3
(CM 28.725-738)

Fe-tetrahedrite, siderite and sulphur to chalcopyrite, stibnite, CO2 and O2
Cu10Fe2Sb4S13 + 8Fe(CO3) + 13/2S2 = 10CuFeS2 + 2Sb2S3 + 8CO2 + 4O2
(CM 28.725-738)

The diagram below is a Pourbaix diagram for Cu-Fe-S-H2O (IJNM 07(02).9.23). It shows the relationship between copper Cu, chalcopyrite CuFeS2, tenorite CuO, covellite CuS, cuprite Cu2O, chalcocite Cu2S, pyrite FeS2 and hematite Fe2O3.

Pourbaix Cu-Fe-S-H<sub>2</sub>O.jpg
























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