Colusite

colusite

enargite

germanite

sulvanite

Images

Formula: Cu13VAs3S16
Sulphosalt, germanite group, forms a series with sulvanite, vanadium-bearing mineral
Crystal System: Isometric
Specific gravity: 4.2 to 4.5 measured, 4.63 calculated
Hardness: 3 to 4
Streak: Black
Colour: Bronze, pinkish bronze
Common impurities: Zn,Fe,Te
Environments

Hydrothermal environments

Colusite is widespread in small amounts with other sulphides and sulphosalts, typically in hydrothermal veins and disseminated copper deposits. Associated minerals include pyrite, tetrahedritetennantite, enargite, luzonite, stannoidite, goldfieldite, germanite, renierite, bornite, chalcocite, covellite, chalcopyrite, sphalerite and galena (HOM).

Localities

There are two co-type localities, the Lebedinoe Au Deposi, Aldan, Sakha Republic, Russia, and the East Colusa mine, Butte Mining District, Silver Bow County, Montana, USA.

At the Waterloo deposit, Charters Towers Region, Queensland, Australia, bornite-bearing ores of the volcanic rock massive sulphide deposit host germanium-bearing colusite. Associated minerals include pyrite, chalcopyrite, sphalerite, tennantite and bornite. It is suggested that the colusite-group minerals formed under moderately oxidised conditions in the ore-forming hydrothermal fluids (CM 43.655-669).

Lorano Quarry, Torano quarrying basin, Carrara, Massa-Carrara Province, Tuscany, Italy.
Numerous quarries of the well known Carrarra marble can be found in the surroundings of Carrara, but colusite was found only in the Lorano quarry, as small crystals up to 1 mm in size. The snow-white matrix of marble makes a considerable contrast for epitactic overgrowths of the colusite on sphalerite or on wurtzite, forming beautiful specimens. The colusite crystals are bronze-brown with a metallic lustre. Two small crystals were found in vugs in marble. One was found associated with quartz, albite, fluorite and dolomite, and the second from a different vug was found associated with quartz, dolomite and sulvanite (CM 19.423-427).

At the Geis Mine, Cone Butte Sub-District, Warm Springs District, Fergus county, Montana, USA, the epithermal deposit consists of gold-silver telluride veins that occur along the contact between alkaline intrusive rocks (quartz monzonite, syenite and tinguaite porphyries) and sedimentary rocks (shale, sandstone, conglomerate, limestone and dolostone).
Four stages of mineralisation have been identified; colusite occurs in the third, which is dominated by quartz, gold-silver tellurides and roscoelite. It is suggested that stage 3 mineralisation formed between 185 and 237oC. Anhedral colusite up to 1.5 mm in size is intergrown with chalcopyrite, tetrahedrite, pyrite, hessite, enargite, and chalcocite (AM 79.750-762).

At the East Colusa Mine, Butte Mining District, Silver Bow County, Montana, USA, colusite is associated with pyrite, tetrahedrite, bornite, chalcocite and quartz. The colusite is found almost entirely within an area of intensely altered quartz-monzonite.
The sequence of deposition was as follows:
(1) pyrite and early quartz
(2) colusite
(3) enargite
(4) tennantite-tetrahedrite
(5) chalcocite and bornite
(6) late quartz
Evidently the precipitation of pyrite had ceased before the chalcocite-bornite solutions arrived since no chalcopyrite is observed. Had copper been present while iron and sulphur were forming pyrite it no doubt would have entered into the reaction in the form of chalcopyrite (AM 18.528-533, AM 24.369-376).

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