Chessy copper mines, Chessy-les-Mines, Le Bois d'Oingt, Rhône, Rhône-Alpes, France

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Anciennes mines de cuivre de Chessy

The ore deposit of Chessy-les-Mines was mined for copper in the Middle Ages until 1875. It's a "stockwerk" mineralization with barite, galena, sphalerite and chalcopyrite hosted in altered soda-dacitic lavas near the devonian Brévenne rift. This orebody was covered by Triassic sediments (clay and sandstone) which were mineralized in turn by hydrothermal fluids during their deposit. Then, primary sulphides were oxidized (during Eocene?) allowing the formation of secondary minerals of lead, zinc and especially copper (azurite, cuprite, malachite, agardite, chrysocolla ...). It is these secondary minerals that have build the celebrity of the Chessy mines, thanks to superb specimens of azurite (called here "chessylite") displayed in many collections today. This reputation has been built from 1811 when the miners opened the famous "Blue Mine" which contained several vugs of azurite in which a man could enter! At the time of operation, engineers distinguished four different parts in the deposit:

The "yellow Mine": native ore (chalcopyrite, pyrite) in speckles or nodules in the dacites

The "black Mine": reduced ore (tenorite, native copper) in black nodules in the altered dacites (contact dacites / Triassic)

The "red Mine": oxidized ore (cuprite, limonite) released into the red clay of the Lower Triassic

The "blue Mine": highly oxidized ore (azurite, cuprite, malachite and smithonite) in clays and sandstones of Middle and Upper Triassic.

Today, the mine is closed but the dumps were bought by the Geological Club of l'Arbresle who conducts regular searches.

Mineral List

Actinolite Adamite var: Cuprian Adamite Agardite-(Nd) Agardite-(Y) Allophane Andalusite Andradite var: Melanite Anglesite Anhydrite 'Apatite' Aragonite Arsenolite Arsenopyrite Aurichalcite Autunite Azurite (TL) Baryte 'Biotite' Bismuth Bismuthinite Boothite Bornite Boulangerite Bournonite Breithauptite Brochantite Cacoxenite Calcite Cassiterite Cerussite

Chalcanthite Chalcocite Chalcophyllite Chalcopyrite Chrysocolla Clinochlore Cobaltite Conichalcite Connellite Copper Corundum Cosalite Covellite Cubanite Cuprite var: Chalcotrichite Devilline Digenite Duftite Epidote Epsomite Euchroite ? 'Feldspar Group' Gahnite Galena 'Garnet' Goethite Gold var: Electrum Goslarite Goudeyite Gypsum

Halite 'Halloysite' Hematite Hemimorphite Hydrozincite Ilmenite Kaolinite Langite Lepidocrocite Libethenite 'Limonite' Linarite Mackinawite Magnetite Malachite Manganite Marcasite Melanterite var: Cuprian Melanterite Meneghinite Mercury Mimetite Molybdenite Montmorillonite Muscovite Olivenite Opal Orthoserpierite (TL) Pearceite Plancheite Polybasite Pseudomalachite

'Psilomelane' Pyrite Pyrolusite ? Pyrrhotite Quartz var: Chalcedony Rosasite Rutile Scheelite Serpierite Siderite Silver Smithsonite var: Cuprian Smithsonite Sphalerite Stannite Stephanite Sulphur Tennantite Tenorite Tetrahedrite Titanite 'Tourmaline' Turquoise Tyrolite Vesuvianite Wulfenite Zálesíite Zircon

125 entries listed. 110 valid minerals. 2 type localities (valid minerals).

References