Influence of climate, mineralogy and mineral processing on the weathering behaviour within two, low-sulfide, high-carbonate, gold mine tailings in the Eastern Desert of Egypt |
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Authors: | Mostafa Redwan and Dieter Rammlmair |
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Institution: | (1) Bundesanstalt f?r Geowissenschaften und Rohstoffe (BGR), Stilleweg 2, 30655 Hannover, Germany;(2) Department of Geology, Faculty of Science, Sohag University, Sohag, 82524, Egypt |
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Abstract: | Despite its importance within environmental management strategies, little concern is shown to sulfide oxidation and/or hardpan
formation at neutral pH where dry condition prevails. Two gold mine tailings in Egypt, El Sid and Barramiya, were studied
for their geochemical/mineralogical properties, and climate influence on hardpan formation. The tailings are characterised
by homogeneous silt-sized sediments (>42%), have high carbonate, predominantly as calcite for El Sid and dolomite-ankerite
for Barramiya, and low-sulfide contents, chiefly as pyrite, galena and sphalerite for El Sid, and arsenopyrite–pyrite for
Barramiya. El Sid is characterised by high average concentrations of Pb (2,758 mg/Kg) and Zn (2,314 mg/Kg), its lower part
dominated by mafics, overlaid by granitoids. Barramiya has higher As (average 2,836 mg/Kg) content and represents a mixture
of mica-schists/mafics-ultramafics. During field investigations, no hardpans were identified, only bassanite and gypsum were
found at the surface of El Sid tailings, forming thin layers and desiccation crack fillings. Column experiments showed a thin
crust consisting of gypsum, halite and sodium sulfate formed at the top of the column of El Sid tailings after 2 weeks, this
was not recognized in the column from Barramiya. The homogenous thickened tailings deposition in both areas did not favour
hardpan formation, since the critical amounts of reacting sulfides were never achieved in individual lamina, due to missing
mineral/grain size fractionation. The high-temperature/low-water availability, characteristic for desert climate regions did
not allow significant sulfides oxidation. Therefore, both tailings will suffer from continuous erosion and spreading out of
contaminants to the environment for a prolonged period of time by sporadic flash floods. |
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