『Abstract
Despite its importance within environmental management strategies,
little concern is shown to sulfide oxidation and/or hardpan formation
at neutral pH were 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 homogeneous
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.
Keywords: Gold mine; Tailings; Thickened deposition; Hardpan;
Column experiments』
Introduction
Study area
Climate
Materials and methods
Results and discussions
Geochemical properties
Bulk rock chemistry
Paste-water extraction
Physical and mineralogical properties
Particle size distribution
Specific surface area (BET)
Bulk mineralogy (XRD)
Detailed mineralogy by mineral liberation analyzer (MLA)
Conclusions and environmental concerns
Acknowledgments
References