Programme OS1m Water quality 1
Hydrogeochemistry and balance between minerals and solutions in the
mercurial zone of Azzaba, N-E Algeria
Author(s): Moussa Benhamza(1) , Nacer Kherici(1) , Francoise Picard-
Mokhtar, Faculty of Science of the Earth - Department of Geology - B.P 12, Annaba Algerie Tel., Fax:
038.87.65.62 - E mall: email@example.com
(2) Laboratory of Sciences of the Environment and
Amenagement, Faculty of Science, Univers
Keyword(s): water, metallic micropolluants, pollution, simulation, model PhreeqC
Session: OS1m Water quality 1
The mercury ore deposit of Azzaba is located on the northern
flank of the Limestone Chain, south of Azzaba town, North East Algeria.
The Northern numidian zone is divided
in two parts of different litho chemical composition. The Northern part is made of sandstone and clays of Oligocene
age , the Southern part is formed by limestones, calcareous micro breccia and carbonated sandstones of the Kabyle
ridge (calcareous mountain range).
The different indices of mineralization which outcrop in the kabyle ridge are
classified as polymetallics (Pb, Zn, Cu) and mercurial polymetallics (Hg, Pb, Zn, Cu).
Clays and sandstones of
the Oligocene present a Hg, Pb, Zn geochemical background contents of respectively 0.6 ppm, 30 ppm, and 60
ppm ; on the other hand, the Copper content is relatively high (80 ppm). As for limestones and carbonated
sandstones of the ridge, the Hg background contents range from 0.2 to 1.5 ppm ; the Cu, Pb and Zn contents are
high as well.
In this region, two aquifers were recognized. The Oligocene phreatic aquifer is composed of fissured
sandstone alternating with argillaceous layers whereas the deep aquifer is of Paleocene-Eocene age and is made of
sandstone, limestone and conglomerate-breccia.
The two aquifers are separated by impermeable clay,
microbreccia and limestone of Palaeozoic and Lutetian-Priabonian. The latter is the host of the cinnabar
The results of the analyses of nine drilling wells and two springs of both aquifers show three main
facies: the bicarbonated calcic, the sulphated calcic and the chlorided magnesian facies
The contamination of the
Oligocene aquifer by Hg and Pb is much higher than that of the Paleocne-Eocene.
using the simulation of the concentration of the major ions, under the effect of isothermal evaporation (25 °C) by the
thermodynamic software "PhreeqC" in terms of balances salt/solution, shows that water of the area is under
saturated compared to halite, leading to its dissolution and the enrichment of water by Na of Cl.
Water is in
balance and in some locations is in super saturation compared to the gypsum and anhydrite, which causes the
precipitation of these evaporitic minerals.
The carbonated minerals are supersaturated and tend to precipitate as
calcite, aragonite and mainly as dolomite.
Water of the area is under saturated with Pb(OH)2 and PbSO4 , which
causes the dissolution of these minerals, resulting in a Pb enrichment .
Water is supersaturated with PbCO3,
which, in the zones of oxidation, causes a precipitation as PbCO3.
Water is supersaturated compared to ZnCO3
and Zn(OH)2, the consequence of which is the enrichment of water by Zn following the dissolution of these