Giraudite-(Zn)

giraudite-(Zn)

chameanite

geffroyite

berzelianite

Images

Formula: Cu6(Cu4Zn2)As4Se13
Selenide, giraudite subgroup, tetrahedrite group, arsenic-bearing mineral
Crystal system: Isometric
Specific gravity: 5.75 calculated
Hardness: 3½ to 4
Colour: Pale grey, with a creamy tint in reflected light
Common impurities: Hg,Fe
Environments

Plutonic igneous environments
Hydrothermal environments

Giraudite-(Zn) is a rare late-stage mineral with other selenides and sulphides in uranium deposits (HOM).

Localities

At the type locality, the Chaméane Uranium Deposit, Le Vernet-Chaméane, Issoire, Puy-de-Dôme, Auvergne-Rhône-Alpes, France, three new (in 1982) selenides occur, chaméanite, geffroyite and giraudite-(Zn). They occur in a complex quartzitic vein cutting granite. Three stages of mineralisation, separated by tectonic movements causing brecciation, are recognised.
In the first stage pitchblende was deposited with copious baryte gangue.
In the second stage quartz occurred with löllingite, arsenopyrite, pyrite, chalcopyrite, tetrahedrite, tennantite and clausthalite, with partial replacements of baryte by quartz, pitchblende by chalcopyrite, and chalcopyrite by clausthalite.
In the third stage the selenides bukovite, athabascaite, umangite, eucairite, eskebornite, more clausthalite, together with chaméanite, geffroyite and giraudite-(Zn), occur with an ankerite gangue, followed by a second generation of chalcopyrite. Giraudite-(Zn) sometimes occurs alone and may reach 400 microns in size AM 67.1074-1075).
Giraudite-(Zn) from the Chaméane Uranium Deposit - Image

At Alberoda, Aue-Bad Schlema, Erzgebirgskreis, Saxony, Germany, among the minerals of the selenide assemblage at the uranium deposit, members of the giraudite-(Zn)hakite-(Hg) solid solution intergrown with berzelianite and galena have been identified. They form complexly zoned, anhedral, minute (<350 micron) grains embedded in a dolomite matrix (CM 40.4.1161-1170).

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