Cahit Helvacı

Geochemical constraints for the origin of thermal waters from western Turkey

The combined chemical composition, B and Sr isotopes, and the basic geologic setting of geothermal systems from the Menderes Massif in western Turkey have been investigated to evaluate the origin of the dissolved constituents and mechanisms of water–rock interaction. Four types of thermal water are present: (1) a Na–Cl of marine origin; (2) a Na–HCO3 type with high CO2 content that is associated with metamorphic rocks of the Menderes Massif; (3) a Na–SO4 type that is also associated with metamorphic rocks of the Menderes Massif with H2S addition; and (4) a Ca–Mg–HCO3–SO4 type that results from interactions with carbonate rocks at shallow depths. The Na–Cl waters are further subdivided based on Br/Cl ratios. Water from the Cumali Seferihisar and Bodrum Karaada systems are deep circulated seawater (Br/Cl=sea water) whereas water from Canakkale–Tuzla (Br/Cl<sea water) are from dissolution of Messinian evaporites. Good correlations between different dissolved salts and temperature indicate that the chemical composition of the thermal waters from non-marine geothermal systems is controlled by: (1) temperature dependent water–rock interactions; (2) intensification of reactions due to high dissolved CO2 and possibly HCl gasses; and (3) mixing with overlying cold groundwater. All of the thermal water is enriched in B. The B isotopic composition (δ11B=2.3‰ to 18.7‰; n=6) can indicate either leaching of B from the rocks, or B(OH)3 degassing flux from deep sources. The large ranges in B concentrations in different rock types as well as in thermal waters from different systems suggest the water-rock mechanism. 87Sr/86Sr ratios of the thermal water are used to differentiate between solutes that have interacted with metamorphic rocks (87Sr/86Sr ratio as high as 0.719479) and carbonate rocks (low 87Sr/86Sr ratio of 0.707864).

FC-AFC-FCA and mixing modeler: A Microsoft® Excel© spreadsheet program for modeling geochemical differentiation of magma by crystal fractionation, crustal assimilation and mixing

Several petrological processes, such as (1) fractional crystallization (FC), (2) combined and decoupled fractional crystallization and assimilation (AFC and FCA), and (3) mixing processes, which modify the geochemical composition of the magma, are graphically programmed using Microsoft^(R) Excel^(C) spreadsheet on the basis of differentiation equations. The FC-AFC-FCA and mixing modeler is an interactive program that models the consequent theoretical vectors of FC, AFC, FCA, and mixing processes, which are frequently used in modern petrology. The program enables the user to export outputs of linear- or logarithmic-scaled bivariate diagrams and also rare earth elements (REE)- and multi-element spider diagrams of the modeling results. It also plots some classification diagrams as well as bivariate Harker variation diagrams. Because the program is interactive in nature, changes in any parameters are simultaneously updated onto all diagrams.

The boron isotope geochemistry of the neogene borate deposits of western Turkey

Abstract We have analyzed the boron isotope composition of 80 borate minerals (major minerals: borax, colemanite, and ulexite; minor minerals: veatchite-A, tunellite, kernite, terrugite, probertite, meyer-hofferite, inderite, inyoite, hydroboracite, howlite, and pandermite) from the main deposits (Kirka, Bigadic, and Emet) and two smaller deposits (Kestelek and Sultancayir) in the western Turkish borate deposits. Forty-three samples were also analysed for their Sr isotope composition. The data span a wide range in δ11B values from -1.6%o to -25.3%o. The δ11B values of the main borate minerals are largely controlled by their mineralogy and the pH of the brines from which they precipitated. An inverse correlation between the average δ11B and 87 Sr 86 Sr ratios of colemanite in the different deposits suggests there is some variation in the sources of boron and Sr to the deposits. Emet has the highest contribution from aluminosilicates and Kirka the highest contribution from Eocene carbonates, with Bigadic occupying an intermediate position. The δ11B values of the minor borate minerals distinguish between those which are primary precipitates from the original brines (or formed from primary borates without boron loss from the system) and those which formed from alteration of preexisting borate minerals with substantial loss of boron from the system.

The boron isotope geochemistry of the Kirka borate deposit, western Turkey

Abstract We have measured the boron isotope composition of seventeen samples of borate minerals (colemanite, ulexite, and borax) and the 87 Sr/ 86 Sr ratio in thirteen borate samples from the Kirka borate deposit in western Anatolia, Turkey. These Neogene deposits were formed by evaporation of playa lakes fed by geothermal springs. The δ 11 B values range from −14.9% o in colemanite to −1.6% o in borax. To a first approximation the relative differences in the δ 11 B values of the borate minerals are consistent with their basic boron atomic configuration, but the magnitude of the boron isotope fractionation between the three minerals precludes their simultaneous precipitation from a brine with the same boron isotope composition and pH. Rather the data are consistent with precipitation of colemanite from a brine with lower pH than that required for ulexite precipitation, which in turn requires a lower pH than is needed for borax precipitation. The boron isotope data also suggest that the borate minerals did not maintain boron isotopic equilibrium with the brine after they precipitated. Rayleigh fractionation models indicate that during borax precipitation the δ 11 B value of the brine was slightly heavier than during precipitation of ulexite and colemanite.

Presence and Distribution of Lithium in Borate Deposits and Some Recent Lake Waters of West-Central Turkey

The presence and distribution of lithium, which is used in a variety of applications in current technology and will be a strategic component in near future technology, has been investigated within the scope of some of Turkeys borate and non-borate Neogene basins and recent lakes. Clay samples from the Turkish borate deposits, Soma lignite basin, and Beypazari trona basin, and water samples from Acigöl, Salda, Yarisçi, Burdur, Egirdir, Tersakan, Bolluk, Karapinar (Acigöl), and Tuzgölü lakes were studied. Analytical results show that the lithium values obtained from clays of borate deposits vary between 0.17 and 0.58% Li2O, and lake water samples contain between 0.30 and 325 mg/l Li+. Lithium is mostly bounded in the clay minerals at the borate deposits. While, the Beypazari trona deposit has lithium between 10 and 46 ppm, the Soma lignite basin does not contain lithium. Therefore, lithium is mainly related to evaporatic formations. These lithium amounts indicate that both the waters of Tuzgölü lake and the clays associated with borate deposits are potential lithium resources, and that they may be considered for economic use in the near future. In western Turkey, geothermal sources mostly depend on the graben faulting system; they also contain minor amounts of lithium.

Sodium sulphate deposits of Neogene age: the Kirmir Formation, Beypazari Basin, Turkey

The Evaporite Member of the Kirmir Formation was deposited in shallow lacustrine environments during the upper Miocene. The most soluble minerals of this member can be currently observed in the Cayirhan mine. The Evaporite Member, which is composed of secondary gypsum at outcrop, can be subdivided into a bedded lower unit and a massive upper unit. In the bedded lower unit, most of the gypsum throughout the basin can be identified as having been transformed from glauberite. In the glauberite layers of the Cayirhan mine, some glauberite textures (‘clear glauberite’) suggest a primary, subaqueous, free precipitation on a depositional floor. More common, however, are the glauberite textures indicating an interstitial growth within a clayey-magnesitic matrix. In the thenardite layers accompanying the glauberite in the Cayirhan mine, some disruption structures can be assigned to synsedimentary dissolution. These structures together with the textures of the thenardite suggest that the original sodium sulphate was mirabilite, thenardite being a secondary phase, which formed during early to moderate burial diagenesis. The massive upper unit, in which evidence of sodium-bearing minerals is absent, is characterized by laminated to banded gypsum and nodular gypsum in the marginal areas of the evaporitic basin, whereas thick, clast-supported gypsum breccias prevail in the northern, deeper part of the basin. The brecciation of these calcium sulphate layers occurred as a result of synsedimentary, gravitative slumping under tectonic control. Although the sulphur isotopic values (d 34 S) of the sulphates of the Kirmir Formation suggest a marine-derived brine supply, the oxygen isotopic values (d 18 O) and the strontium ratios ( 87 Sr/ 86 Sr) do not support such a supply. The origin of the mother brines, the glauberite genesis, the depositional model of the sodium sulphates, and the salinity evolution are discussed. D 2002 Elsevier Science B.V. All rights reserved.

Occurrence of rare borate minerals: Veatchite-A, tunellite, teruggite and cahnite in the Emet borate deposits, Turkey

The Emet borate deposits were formed in two separate basins, possibly part of an interconnected lacustrine playa lake, in areas of volcanic activity, fed partly by thermal springs and partly by surface streams. The borates are interlayered with tuff, clay and marl. Limestone occurs above and below the borate lenses. Sediments in both basins are similar but borate minerals show different mineralogical and geochemical features in the two basins.The Emet borate deposits are the only deposits known to contain any of the minerals veatchite-A, tunellite, teruggite and cahnite. Principal minerals are colemanite, with minor ulexite, hydroboracite and meyerhofferite.Thermal springs associated with local volcanic activity are thought to be the source of the borates. The initial brines from which the borates crystallized are deduced to have been high in sulphite and sulphate, low in chloride, and hence it is assumed that the initial brines were fed at all times by abundant calcium and boron with minor amounts of arsenic, strontium and sulphur. Realgar, celestite and native sulphur are almost ubiquitous in borates and sediments, and appear to have formed at all stages during deposition and diagenesis.The early colemanite, meyerhofferite, ulexite and teruggite nodules were probably formed directly from brines penecontemporaneously within the unconsolidated sediments below the sediment/water interface, and continued to grow as the sediments were compacted. Later generations of colemanite occur in vugs, veins and as fibrous margins to colemanite nodules. Tunellite appears to have formed during diagenesis with enrichment of Sr in some places. Diagenetic alterations include the partial replacement of colemanite by veatchite-A, cahnite, hydroboracite and calcite.

A new Tertiary borax deposit in the Andes

The Loma Blanca borate deposit was formed in the muds of playa-lake environments during the Late Miocene and is the fourth Tertiary commercial borax deposit discovered within the borate districts of the world. It is the only South American deposit known to contain any of the minerals colemanite, inyoite, ulexite, borax, tincalconite and teruggite with a unique and characteristic mineral sequence among the other Argentinian borate deposits. The Loma Blanca deposit is characterized by abundant Ca, Na and B, very low Cl and relatively high As, S and Mg concentrations compared with other borate deposits. Thermal springs and hydrothermal solutions associated with local volcanic activity are thought to be the source of the borates. The early colemanite, inyoite, ulexite, borax and teruggite nodules and crystals appear to have been formed directly from brines penecontemporaneously within the unconsolidated sediments, and they continued to grow as the sediments were compacted. Later generations of borate minerals occur in vughs, veins and as thin layers. Diagenetic alterations include the partial replacement of borax by ulexite and tincalconite; when weathered, borates are often almost completely replaced by calcite.

Hydrogeochemical and hydrogeological investigations of thermal waters in the Emet area (Kütahya, Turkey)

Metamorphic rocks host the majority of the thermal waters of the Emet area. Only Dereli springs are hosted by nonmetamorphic carbonates and ophiolitic rocks. The carbonated rocks of the lower parts of the Neogene sequence are also secondary reservoir rocks. The measured surface temperatures of thermal waters are between 33 and 54 C. Most of the thermal waters are characterized as Ca–Mg–SO4–HCO3 type although there are a few Ca–Na–HCO3, Na–Ca– SO4 and Ca–Mg–HCO3 waters. Calcium concentrations in the thermal waters are 89–354 mg/kg. High SO4 contents of the thermal waters (up to 1309 mg/kg) are related to rocks and minerals in the Red Unit below the Emet borate deposits. Although the SO4 concentrations are high and SO4 is the major anion, gypsum and anhydrite are undersaturated for all of the thermal waters indicating that dissolution of SO4 is still taking place in the reservoir. Thermal waters are oversaturated at outlet conditions with respect to calcite, chalcedony, dolomite and quartz. According to the activity diagrams thermal waters are likely to form illite as an alteration product in the reservoir and Ca and Mg contents are controlled by exchange with smectite. Reservoir temperatures obtained by silica geothermometers and assessments of the saturation states of minerals are more appropriate for Emet geothermal waters. Assessments of the various geothermometers suggest that reservoir temperature is around 75–87 C.

SAPONITE FROM THE EMET COLEMANITE MINES, KÜTAHYA, TURKEY

Clay mineralogy and whole-rock chemistry of the borate-bearing layers of the Hisarcik and Esbey mines were examined. The Hisarcik clays occur as laminated or unlaminated clay layers with sharp contacts. Unlaminated layers contain quartz derived from metamorphic rocks and carbonate fragments in a clay matrix, and are interpreted as reworked tuffs deposited in playa-lake environments. An important feature is that the unlaminated clays contain little MgO (3–15 wt. %) as compared with the laminated clays (15–30 wt. %). As previous studies have shown, the clay fraction of the studied profile contains predominantly Li-bearing saponite, and accounts for 60–90 wt. % of the clay fraction (<2 μm). Illite in the clay fraction varies from 0 to 67 wt. % and the average illite percentage never exceeds 40 wt. %. Chlorite is scarce (2–5 wt. %). Illite-smectite interstratified clays (illite at 70%, smectite at 30%) were only found in low concentrations in the laminated clay layers of the upper limestone unit (above the borate zone), where illite-2M of detrital origin is also present. The Esbey clays occur interstratified with colemanite layers and envelope colemanite nodules. Calcite is the major mineral of the clays whereas quartz, plagioclase, feldspar, colemanite, and cahnite are minor components. The MgO contents vary between 4.70–13.95 wt. % in the clays interstratified with colemanite layers, between 7.24–11.89 wt. % in the enveloping clays, and between 10.27–21.25 wt. % in clays located above the colemanite zone. The composition of the clay fraction (<2 μm) in all samples is similar. Smectite represents between 40–90 wt. % of the clay fraction in the upper portion of the stratigraphic profile and decreases towards the lower part of the stratigraphic profile. Smectite always occurs with illite which may vary from 20 to 90 wt. % of the clay fraction, and a small amount of kaolinite and chlorite. Illite-2M polytype is abundant. The d(060)-reflection position suggests that the smectite minerals from the Hisarcik and Esbey colemanite mines contain both dioctahedral and trioctahedral smectites to form a transitional zone. These smectites are a product of a magnesium-rich alkaline playa-lake environment.