Fikret Suner

Geology, mineralogy and fluid inclusion data of the Kizilcaören fluorite–barite–REE deposit, Eskisehir, Turkey

The Kizilcaoren fluorite–barite–Rare Earth Element (REE) deposit occurs as epithermal veins and breccia fillings in altered Triassic metasandstones and Oligocene–Miocene pyroclastics adjacent to alkaline porphyritic trachyte and phonolite. This deposit is the only commercial source of REE and thorium in Turkey. Most of the fluorite–barite–REE mineralisation at Kizilcaoren has been formed by hydrothermal solutions, which are thought to be genetically associated with alkaline volcanism. The occurrence of the ore minerals in vuggy cavities and veins of massive and vuggy silica indicate that the ore stage postdates hydrothermal alteration. The deposit contains evidence of at least three periods of hypogene mineralisation separated by two periods of faulting. The mineral assemblage includes fluorite, barite, quartz, calcite, bastnasite, phlogopite, pyrolusite and hematite as well as minor amounts of plagioclase feldspar, pyrite, psilomelane, braunite, monazite, fluocerite, brockite, goethite, and rutile. Fluid inclusion microthermometry indicates that the barite formed from low salinity (0.4–9.2 equiv. wt% NaCl) fluids at low temperatures, between 105 and 230 °C, but fluorite formed from slightly higher salinity (<12.4 equiv. wt% NaCl) fluids at low and moderate temperatures, between 135–354 °C. The depositional temperature of bastnasite is between 143–286 °C. The local coexistence of liquid- and vapour-rich inclusions suggests boiling conditions. Many relatively low-salinity (<10.0 equiv. wt% NaCl), low and moderate temperature (200–300 °C) inclusions might be the result of episodic mixing of deep-saline brines with low-salinity meteoric fluids. The narrow range of δ34S (pyrite and barite) values (2.89–6.92‰ CDT)suggests that the sulphur source of the hydrothermal fluids are the same and compatible with a volcanogenic sulphate field derived from a magmatic sulphur source.

Occurrence and properties of natron in the Miocene lacustrine Beypazari basin, Turkey

Natron, Na 2 CO 3 .10H 2 O, is a rarely forming evaporite mineral, which precipitates under the unique physicochemical conditions of Na wt. %, temperature and HCO 3 /CO 3 . Natron is observed in the upper parts of the lower trona level of the Beypazan Neogene volcanosedimentary sequences, where exist two trona beds between 260 m and 285 m depths. In this study, natron and some other soda minerals were examined by detailed geochemical, physicochemical and experimental studies. Euhedral natron crystals were determined sporadically within sedimentary beds. Based on our studies, it is postulated that white, soft and platy-fibrous natron minerals formed in the microenvironments within the rhythmic series of marls and claystones, are precipitated from pore solutions under the conditions of low temperature and high CO 3 /HCO 3 ratio during the end of the first precipitation of the trona deposits. The contents of the trace elements were measured using wet chemical analyses; XRD, DTA and SEM techniques were performed, and the results were evaluated based on the formation conditions of the mineral.

Origin of galena and sphalerite mineralization in the Koru Volcanics, Biga Peninsula, Turkey: insights from MELTS modelling and SUPCRT calculations

Tertiary volcanism (34.3 ± 1.2 Ma and 0.4 ± 0.7 Ma) in NW Turkey produced lead + zinc bearing trachyte, latite, dacite and rhyodacite tuffs, and agglomerates, as well as basaltic andesite, andesite, dacite, and rhyolite lavas. The primary objective of this study is to develop quantitative models for the evolution of magmas that produced these rocks and for the dissolution, transport, and deposition of disseminated ore as sphalerite and galena vein deposits. Our petrogenetic modelling using the MELTS algorithm (Ghiorso, M.S., and Sack, R.O., 1995, Chemical mass transfer in magmatic processes IV: a revised and internally consistent thermodynamic model for the interpolation and extrapolation of liquid-solid equilibria in magmatic systems at elevated temperatures and pressures: Contributions to Mineralogy and Petrology, v. 119, p. 197–212) indicates that the ore-bearing volcanic rocks reflect mixing of a basaltic andesite parental magma with a rhyolite magma. In addition, our aqueous geochemistry modelling using the SUPCRT indicates that controlling parameters of the vein deposits were pH = 5.3–9.2, fO2 = 10−55–10−46 at 150°C and ∑S = 10−3 molal. At 250°C, compared with 150°C, the mineral stability field is more oxidized, yet the pH range is not significantly different (pH = 5.8–9.8, fO2 = 10−34–10−43).

Varying depositional environments of gypsum successions in the Upper Miocene Eskişehir-Sivrihisar lacustrine basin, NW Turkiye

The basement rocks of Eskisehir-Sivrihisar basin are made of Upper Paleozoic metamorphic rocks and Upper Cretaceous ophiolite complex. These rocks are overlain by Middle Miocene sedimentary rocks the base. Upper Miocene-Pliocene stratigraphic succession consists of basal conglomerates, sandstones, claystones, limestones, dolomites and tuffs are thinly interbedded with cyclic evaporites. The main clay mineral assemblage consists of smectite, illite and sepiolite that are enriched in different percentage in different horizons. The Upper Miocene-Pliocene stratigraphic succession consists of alterations of gypsum, clayey carbonates and unconsolidated very soft dolomite beds, which are conformably underlain by sepiolite-bearing clayey carbonates and disconformably overlain by alluvium and conglomerate series of Pleistocene age. The Upper Miocene unit includes three different facies, based on sedimentary properties of gypsum from the base to the top; (I) laminated gypsum beds are thinly interbedded with dolomites and green clays; (2) gypsum rosettes within thin reddish and greenish clays and carbonates; and (3) scattered gypsum mainly within carbonates. Gypsums had been deposited in somewhat different depositional conditions in the same basin where multi-periodic evaporative episodes, ranging from saline to schizohaline environments, had been involved. During these episodes, under high Eh-pH intervals and high salinity conditions, three different types of gypsum formations had been developed in a meromictic-type lake under the influence of varying paleoclimatologic conditions and pore water chemistry of brines. All these gypsum morphologies respectively reflect the different conditions of environments of deposition in a Miocene playa lake basin: (1) subaqueous environments in playa lakes with short evaporation episodes; (2) marginal swamps with cyclic fluctuation of lake level; and (3) extended closed-lake with evaporatic lake water. These different gypsum morphologies are associated with distinctive sedimentary subfacies, which are also primarily related to cyclic climatic changes, alternating semi-arid and evaporite conditions, fluctuation of lake water level and sulphate input in the chemistry of lake water from runoff and hydrothermal source adjacent to basin.