Abstract:

 A regional depression cone exists in groundwater level in the deep confined water owing to a long- term exploitation of groundwater in Zhanjiang, Guangdong. The formation of the depression cone has a certain effect on the chemical nature of groundwater in the deep confined water, resulting in low concentration of Fe in the western and northwestern parts, high concentrations of Fe in the northern part and medium concentrations of Fe near the center of the depression cone. Geochemical simulation was carried out for the Fe occurrence in groundwater in the depression cone. The results show that groundwater in the depression cone in the deep confined water  may be supplied from groundwater in the north, northwest and west, or from groundwater in the shallow confined aquifers.Groundwater in the deep confined water  is a mixture of the supplied groundwater, and the high Fe groundwater is a main source. Groundwater exploitation of large quantity in the deep confined water  causes an increase in Fe contents in the groundwater. In the course of groundwater towards the center of the depression cone, not only the dissolution of calcite, dolomite and hematite, the precipitation of siderite and melanterite may occur, but also the cation exchange between Na⁺ and Ca²⁺, Fe oxidation- reduction of Fe may occur.

Key words: Fe occurrence, depression cone, groundwater in deep confined water, water-rock reaction, geochemical simulation, Zhanjiang