Mineralogy, diagenesis and hydrochemical evolution in a probertite–glauberite–halite saline lake (Miocene, Emet Basin, Turkey)

The Emet basin is one of the Neogene basins in western Turkey containing significant amounts of borate minerals, mainly colemanite. The petrologic study of core samples from two exploratory wells in the Doğanlar sector, under optic and electron microscopy, reveals a complex mineral association in which probertite, glauberite, and halite constitute the major primary phases (without mineral precursors) precipitated in a saline lake placed in a volcano-sedimentary context. Other sulfates (anhydrite, gypsum, thenardite, celestite and kalistrontite), borates (colemanite, ulexite, hydroboracite, tunellite, kaliborite and aristarainite), and sulfides (arsenopyrite, realgar and orpiment) are attributed to early diagenesis. So far, the Doğanlar deposit is the most important deposit of probertite known up to now. al changes in the groundwater inflow led to the precipitation of Ca-bearing borates (colemanite) in the tuff-flat environment surrounding the lake, while Na–Ca sulfates and borates (glauberite and probertite) precipitated in the center of the lake. Fluid inclusion compositions in halite indicate that the advanced brines correspond to the Na-K-Cl-SO4 type. During restricted stages of the saline lake, the residual brines seeped through the tuff-flat sediments, leading to transformations of previous precipitates that resulted in the formation of K-bearing minerals. undance of coccoid-like biogenic dolomite, colloidal arsenopyrite and the isotopic composition of sulfates are indicative of bacterial sulfate reduction. In contrast, arsenic sulfides are attributed to acidophilic micro-organisms in oxidizing conditions. Fluctuations of redox conditions in both free and interstitial brines control the biological influence in some diagenetic transformations.