GEOLOGICA CARPATHICA CLAYS - Abstract

Volume 5, number 2/1996, pages 55-63

MINERALOGY OF Fe-OCHRE DEPOSITS FORMED FROM ACID MINE WATER IN THE SMOLNIK MINE (SLOVAKIA)

OTILIA LINTNEROVA

Department of Mineral Deposits Geology, Faculty of Sciences, Comenius University, Mlynska dolina G, 842 15 Bratislava, Slovak Republic

Abstract: When the acid mine drainage water, formed as the result of massive pyrite oxidation in the flooded Smolnik mine, mixes with surface water of Smolnik Stream, characteristic brown-ochre precipitates are formed. These ochres continue to form in the strong acidic aqueous environment: stream water pH values are in range 3–5, and ochre deposit pore water has a pH< 3. The ochre samples have been studied by X-ray diffraction and electron microscopy methods (TEM, SEM) with elemental microanalysis. Large amounts of the fresh precipitates are X-ray amorphous. The SEM and TEM investigations have shown that there are a few mineral crystalline phases in ochre hardpan samples consisting of crystals some tens to several hundred nm large in size. The Fe-sulphates, jarosite (KFe₃(OH)₆(SO₄)₂) and probably schwertmannite (Fe₈O₈(OH)6S0₄) are found in the precipitates and have formed from high SO₄^2- and acid solutions. Goethite (α-FeOOH) has also been identified in the ochre deposits, and is the dominate mineral when the pH value increases and the SO₄^2- concentration decreases in the water-ochre deposit system. In acid conditions aluminosilicate minerals have been dissolved or degraded and amorphous Si-Al phase and possibly neoformed halloysite have formed as a result.

Keywords: oxidation, pyrite, mineral identification, goethite, jarosite, schwertmannite, X-ray diffraction, electron microsc

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