The black calcite gangue in Herja marks the final ore deposition stage of this ore deposit related to Neogene volcanism in the Baia Mare district, Eastern Carpathians, Romania. The mineral assemblage containing black calcite was studied by optical microscopy combined with scanning electron microscopy, X-ray diffraction and electron-probe microanalysis. It is composed of sphalerite, galena, marcasite, pyrite, stibnite, berthierite, jamesonite, boulangerite, fülöppite, calcite, ankerite and siderite. Several unidentified sulfosalts (X1 to X6) have also been encountered and analysed. The colour variation of calcite, from translucent to milky-white, creamy white and black is closely related to the presence of mineral impurities, i.e. ankerite, siderite, jamesonite and/or berthierite.

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