Today, the mine is closed but the dumps were bought by the Geological Club of l'Arbresle which conducts regular searches. The "blue Mine": highly oxidized ore (azurite, cuprite, malachite and smithsonite) in clays and sandstones of Middle and Upper Triassic. The "red Mine": oxidized ore (cuprite, limonite) released into the red clay of the Lower Triassic The "black Mine": reduced ore (tenorite, native copper) in black nodules in the altered dacites (contact dacites / Triassic) The "yellow Mine": native ore (chalcopyrite, pyrite) in speckles or nodules in the dacites At the time of operation, engineers distinguished four different parts in the deposit: This reputation has been built from 1811 when the miners opened the famous "Blue Mine" which contained many vugs of azurite. It is these secondary minerals that have built the celebrity of the Chessy mines, thanks to superb specimens of azurite (called here "chessylite") displayed in many collections today. Then, primary sulphides were oxidized (during Eocene?) allowing the formation of secondary minerals of lead, zinc and especially copper (azurite, cuprite, malachite, agardite, chrysocolla. This orebody was covered by Triassic sediments (clay and sandstone) which were mineralized in turn by hydrothermal fluids during their deposit. It's a "stockwerk" mineralization with barite, galena, sphalerite, and chalcopyrite hosted in altered soda-dacitic lavas near the Devonian Brévenne rift. ![]() ![]() The ore deposit of Chessy-les-Mines was mined for copper in the Middle Ages until 1875. Amphibole, dendrites, chessyite nodules and cuprite on the dumps of the mines."
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