Thème ETUDE GEOCHIMIQUE ET MINERALOGIQUE DES ...

Abstract
Résumé
Water is an essential source for a permanent development, in the substance of all the alive
organisms, animals, vegetables and the biosphere because it is necessary to insure the life in
our planet as well for the health and the socio-economic progress of the societies with the
respect of the environment. Chott and sebkha is characterized with water content. Allot of
study was made to see spatio-tomporelle evolution of brine in these area. Chott Baghdad is
our objective in this study which located in Algerian Sahara part.
Chott Baghdad is situated in septontrional Algerian sahra basin (northern of Africa).these
small depression is fall dawn about 31m below sea level. One of characteristic of this zone is
dry climate in summer when temperature reach 45°C and decrease in winter to less zero °C.
chott Beghdad irrigate with surface water zone, continental saharien aquifer and precipitated
water. Geologics and gitologic carcteristics of deposed evaporits in Baghdad basin, small
closed lagon take place with brines rich in Ions SO4 2- , Ca 2+ , Na + , Cl - and under the effect of
evaporation generate the rock salt and gypsum precipitation.
The objective of this study is to simulate evolution the geochemical cycle inside of chott
Baghdad, in addition try to interpreter behavior of major element which constructs this small
depression. The most important thing is to calculate saturated index of evaporated mineral and
compare it with DRX result.
To reach this study, monthly brine samples were collected from January to December.
Different analytic methods were used: physicchemical analytic (PH, temperature and
conductivity). In addition, spectrophotometer and titration, phlame emission was done to
calculate major element concentration.
From this study, we can conclude that major element behavior (Na + , Cl - , SO4 2- , Mg + , K + ,
HCO3 - , and Ca 2+ ) is as follow:
Chlore and sodium was decreasing at end of geochemical cycle.
Bicarbonate, potassium and magnesium have characteristic evolution, where they increase at
the beginning of geochemical cycle till summer then decrease steadily at the end of cycle.
Calcium is quit steady during year cycle.
Precipitation of: firstly halite and gypsum with calcium carbonate followed by anydrite
Epsomite.
Key words: hydrochemical, hydrogeological, sebkha, evaporates.