MAJOR-ION GEOCHEMISTRY AND MINERALOGY OF THE SALT-LAKE (TUZ-GOLU) BASIN, TURKEY

In the Salt Lake basin of Turkey, chemical composition of inflow surfa ce waters defines a continuous trend from Ca-HCO3-rich spring waters t o Na-SO4-Cl-rich brines. Considerable compositional variation exists a mong the surface waters. Water-rock interaction governs compositional variations in springs, streams and rivers, and is enhanced by evaporat ion and precipitation of calcite and protodolomite. Solute concentrati ons of the streams and the rivers are partially controlled by the mine ralogy of the playa deposits. The concentration increase from inflow s urface waters to a Na-Cl-type lake surface brine is not accessible to direct observation. The principal cause of the evolution from SO4-rich brine to Cl-rich brine in the lake is interpreted as the recycling of solutes through the differential dissolution of efflorescent crusts. In the lake, major-ion concentrations generally exhibit an evaporation -dependent evolution trend that is further modified by precipitating h alite, gypsum, aragonite and calcite. Sediments of the lake are predom inantly composed of gypsum, dolomite, huntite, magnesite, and subordin ately of polyhalite minerals. Magnesite and huntite are mostly early d iagenetic minerals that have been formed by the transformation of dolo mite in the presence of pore fluids with a high Mg/Ca ratio.