ABSTRACT
Groundwater plays a vital role for satisfying water requirements for local populations in Wadi Hodein area. The main objective of the present article is to recognize in detail the relation of groundwater composition to alterations and weathering of silicate minerals in the basement aquifer. To achieve that, 36 rock samples (18 fresh and their altered equivalent) were collected nearby the water wells for petrographical and geochemical studies. Besides, eleven groundwater samples were also collected and chemically analyzed.
The petrographical and geochemical studies revealed that the basement rocks in the investigated area comprise different rock units each of them has its own mineralogical and geochemical characteristics. Some effective secondary minerals were formed due to water-rock interactions phenomena (e.g. Kaolin, sericite, chlorite, and saussurite and carbonate veins). Such minerals play the most important role in the mobility of major component (e. g. Na, K, Ca, Mg, Fe, and Si02) and in turn affect on groundwater composition.
The study of groundwater composition in the different rock units of basement local aquifers reflects that each hydrogeologic unit has its own hydrogeochemical characters according to the mineralogical composition, weathering and alterations of silicate minerals. The saturation indices of relevant mineral were calculated using WATEQ-F computer-program. The results show that, the saturation indices of talc, trimolite, sepiolite, actinolite, diopside and quartz minerals are highly positive, indicating a strong super-saturation and precipitation of these minerals. Also, the saturation indices of iron and manganese minerals (goethite, hematite, magnetite and manganite) are positive values, reflecting super-saturation and precipitation of such minerals. This is confirmed by the presence of iron-stains on feldspar minerals and alteration of iron rich biotite in most of rock samples.
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