Mwyngloddfa Nant-y-cagl (Eaglebrook Mine)
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Geology & landscape
Rock Type: Dolomite
Description
Description This old copper-lead-zinc mine, situated just north-west of Nant-y-moch Reservoir, is of particular interest owing to the well developed gossan (the part of the vein nearest the surface where the ores have been weathered and, in particular, oxidised). The ore, as first deposited, consisted of galena, chalcopyrite and sphalerite contained in a gangue of quartz, dolomite and calcite in a brecciated country rock, but supergene oxidation, forming much gossany material, has resulted in the formation of an unusually wide array of secondary minerals. Commonly found phases are green velvety malachite, acicular cerussite and serpierite, as well as leadhillite, hemimorphite, native copper with cuprite, brochantite, langite, linarite, devilline and the recently reported rare copper sulphate, wroewolfeite. Additional occurrences of pyromorphite, covelline, chrysocolla, chalcocite and bindheimite have also been reported. Many of these secondary phases are well crystallised, but microscopic, specimens.