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Geology, Mineralogy, Geochemistry, and Genesis of Bentonite Deposits in Miocene Volcano–Sedimentary Units of the Balikesir Region, Western Anatolia, Turkey
- Selahattİn Kadİr, Tacİt Külah, Hülya Erkoyun, George E. Christidis, Raffİ Arslanyan
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- Journal:
- Clays and Clay Minerals / Volume 67 / Issue 5 / October 2019
- Published online by Cambridge University Press:
- 01 January 2024, pp. 371-398
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The widespread Balıkesir bentonite deposits within the Miocene volcano-sedimentary units in western Anatolia have economic potential; they are important raw materials for the paper and bleaching industries in Turkey. No detailed geological, mineralogical, geochemical, or genesis characterizations of these bentonite deposits have been carried out to date. The present study was undertaken to close this gap. The mineralogical characteristics of the bentonites and their parent rocks were examined using polarized-light microscopy, X-ray powder diffractometry (XRD), scanning- and transmission-electron microscopies (SEM–EDX and TEM), and chemical (ICP–AES and –MS) methods. In the bentonite deposits, smectite is associated with smaller amounts of illite, chlorite, quartz, feldspar, dolomite, calcite, opal-CT, and amphibole. The smectite was identified by sharp basal reflections at 14.42–14.93 Å. Plagioclase and sanidine crystals in volcanic units are altered and sericitized. Biotite and hornblende are partly to completely Fe-(oxyhydr)oxidized and chloritized. Smectite flakes occur on altered feldspar and mica grains and devitrified volcanic glass fragments in association with or without calcite ± dolomite crystals. Increasing Al+Fe+Mg/Si ratios with increasing degree of alteration reveal that hydration of volcanogenic grains (feldspar, mica, hornblende, glass shard) favored precipitation of smectite with montmorillonite composition, with an average structural formula: (Ca0.31Na0.05K0.08)(Al2.72Fe0.17Mg1.27Ti0.011Mn0.01)(Si7.94Al0.06)O20(OH)4. The concentration of Al2O3 and MgO and increase of LREE/HREE ratio, and a distinct, negative Eu anomaly show that smectite was probably formed as a result of the decomposition of volcanic feldspar, mica, amphibole, and volcanic glass. Association of carbonate rocks within the smectite-rich material and the absence of chlorite and detrital materials such as rock fragments in the bentonites suggest that the bentonite deposits formed authigenetically as ‘primary bentonites’ from volcanoclastic materials deposited in a calm lacustrine–palustrine environment during an early diagenetic process.
An Approach to Genesis of Sepiolite and Palygorskite in Lacustrine Sediments of the Lower Pliocene Sakarya and Porsuk Formations in the Sivrihisar and Yunusemre-Biçer Regions (Eskişehir), Turkey
- Selahattin Kadir, Muhsin Eren, Taner İkeç, Hülya Erkoyun, Tacit Külah, Nergis Önalgil, Jennifer Huggett
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- Journal:
- Clays and Clay Minerals / Volume 65 / Issue 5 / October 2017
- Published online by Cambridge University Press:
- 01 January 2024, pp. 310-328
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The Lower Pliocene lacustrine sediments of the Sakarya and Porsuk Formations in the Sivrihisar and Yunusemre-Biçer regions consist of claystone, argillaceous carbonate, carbonate, and evaporites. No detailed studies of paleoclimatic conditions have been performed previously. The present study aimed to determine the depositional environment and paleoclimatic conditions for the formation of these economically important sepiolite/palygorskite/carbonate/evaporite deposits based on detailed mineralogical, geochemical, and isotopic studies. Samples from various lacustrine sediments were examined using polarized-light microscopy, X-ray diffraction, scanning electron microscopy, and chemical and isotopic analysis methods. Dolomites are predominantly of micrite, which is partly recrystallized to dolomicrosparite/dolosparite close to desiccation fractures. The presence of ostracods and dacycladecean algae in the carbonates reflects a restricted depositional environment. The formation of sepiolite and palygorskite fibers, either as cement between/enclosing dolomite and/or as calcite crystals, reflects occasional changes in physicochemical conditions provided by fluctuations in the lake-water level and influx of groundwater in relation to climatic changes during and after dolomite precipitation. The positive correlations of ΣREE with Al2O3, Nb, high-field-strength elements, and transition elements are due to alteration of feldspar and hornblende in the volcanic units. The high values of Ba and Sr relative to Cr, Co, Ni, and V also indicate that felsic rather than ophiolitic rocks were the parent material. The crossplot of whole-rock SiO2vs. Al2O3+K2O+Na2O and V/Cr ratio suggests deposition of carbonate-dolomitic sepiolite-sepiolitic dolomite under arid climate and oxic conditions, whereas the Ni/Co and V/(V+Ni) ratios of the sediments indicate deposition of organic-bearing sepiolite/palygorskite under anoxic-dysoxic conditions. An enrichment in δ13C and δ18O values of dolomite with respect to calcite is probably due to differences in mineral fractionations. The δ34S and δ18O values and 87Sr/86Sr isotope ratios for gypsum suggest an intensely evaporitic lacustrine environment fed by an older marine evaporitic source. The Si, Al, Mg, Ca, and enhanced TOT/C required for periodic precipitation of organic-rich brown sepiolite/palygorskite characterize deposition in a swampy environment, while dolomitic sepiolite and sepiolitic dolomite formed in ponds by partial drying of the main alkaline lake.
Occurrence of Fibrous Chrysotile and Tremolite in the Çankiri and Ankara Regions, Central Anatolia, Turkey
- Tacit Külah, Selahattin Kadir, Hülya Erkoyun, Jennifer Huggett, Eşref Atabey
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- Journal:
- Clays and Clay Minerals / Volume 66 / Issue 2 / April 2018
- Published online by Cambridge University Press:
- 01 January 2024, pp. 146-172
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Numerous occurrences of asbestos minerals, notably chrysotile and tremolite, are to be found on fracture surfaces in thrust fault deformation zones of Cretaceous dunite-harzburgite and pyroxenite in the Çankırı and Ankara regions, central Anatolia, Turkey. Consequently, potential exists for the development of regional malignant mesothelioma. The means of serpentinization, such as reaction of seawater during accretion of the upper ophiolitic mantle crust in a subduction zone and/or following uplift of ophiolitic units and the influence of hydrothermal/meteoric fluids along fractures, were investigated. Cretaceous dunite-harzburgite and localized pyroxenite rocks are mainly composed of serpentinized olivine and pyroxene associated with opaque minerals and Fe-(oxyhydr)oxide phases. Smectite, chlorite, illite, kaolinite, hydromagnesite, goethite, quartz, and opal-CT are also present. Chrysotile and localized tremolite occur either as a mesh, a suboriented to oriented long-fiber bundle, or as fiber-filling millimetric micro-vein textures on relicts of olivine and pyroxene (enstatite, augite). The chrysotile and tremolite have non-pseudomorphic textures developed under high pressure and temperature. The textures suggest authigenic formation of chrysotile and tremolite via a dissolution and precipitation mechanism. Additionally, spherical structures of opal-CT and locally platy hydromagnesite crystals either enclose or are developed within chrysotile/tremolite fiber bundles. The leaching of MgO, Fe2O3, Al2O3, Ni, Cr, and Nb, an increase in the LREE/HREE ratio, and negative Eu anomalies in the dunite-harzburgite and pyroxenite, and asbestos samples suggest that the chrysotile and tremolite were derived from the serpentinization of olivine and pyroxene. The chrysotile and tremolite were developed along fractures by hydrothermal fluid alteration during accretion and/or following the uplift of ophiolitic units of the region under high pressure and temperature conditions. This interpretation is also supported by isotope data and the calculated formation temperature of 170–555°C for chrysotile and tremolite. The average structural formulae for chrysotile and tremolite are (NanK0.03)(Mg5.54Fe0.09Al0.05Ca0.01Mn0.001) (Si3.96Al0.03)O10(OH)8 and (Na0.17K0.07)(Ca1.59Mg0.19Mn0.002)(Mg4.72Fe0.28)(Si7.86Al0.1Fe0.06)O22(OH)2, respectively.
Genesis of Smectites associated with a Coal Seams Succession in the Neogene Orhaneli and Keles Coal Deposits (Bursa), NW Turkey
- Hülya Erkoyun, Selahattin Kadir, Tacit Külah
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- Journal:
- Clays and Clay Minerals / Volume 70 / Issue 5 / October 2022
- Published online by Cambridge University Press:
- 01 January 2024, pp. 628-659
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The Bursa-Orhaneli and Keles-Harmanalan coal deposits were developed in swampy and fluvial-lacustrine environments in western Anatolia under the E–W-trending graben zone during the Neogene. The present study aimed to determine the mineralogical and geochemical properties of clays interlayering the coal seams to define the origin of clay minerals, in particular, smectite. These deposits, comprising argillaceous sediment, marl, coal seam, mudstone, organic-rich shale, and sandstone, were deposited in a lacustrine environment accompanied by volcanogenic materials. The characteristics of sediments and their parent rocks were examined using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, palynology, and chemical analyses. The association of abundant smectite with quartz, amphibole, accessory chlorite, and a decrease in feldspar in fluvial-lacustrine sediments compared to those in the smectite accompanied by feldspar and volcanic glass and the absence of quartz and amphibole in the pyroclastic units suggest that smectite had detrital and authigenic origins. Flaky smectite shows either detrital, irregularly outlined coating and filling pores of terrigenous sediments or in situ precipitation edging resorbed feldspar and devitrified volcanic glass. Chemical analyses of the smectite-rich fraction show montmorillonite compositions with an average structural formula of: (Ca0.42Na0.25K0.08)(Al2.76Fe0.47Mg0.59Ti0.07Mn0.002)(Si7.65Al0.35)O20(OH)4.
The positive correlation of Al2O3 vs. TiO2 and K2O vs. Rb may be related to the abundant detrital input. Feldspar and biotite were replaced by illite during diagenesis.
An increase in the Ni/Co and V/(V + Ni) ratios in the altered units also suggest oxic, suboxic to anoxic conditions, under the control of a dry, warm to subtropical climate in fresh water and lakes during the Late Eocene to Middle Miocene. The slight enrichment of light rare earth elements (LREE) compared to heavy rare earth elements (HREE) with positive Eu and positive/negative Ce anomalies reflect fractional crystallization of feldspar. The δ18O and δD values of smectite and illite fractions and the wide range of δ34S isotope values (–1.5 to 15‰) for pyrite and chalcopyrite associated with coal indicate a signature of both diagenetic and partial hydrothermal origin.
Genesis of the Yarikçi Hydrothermal Clay Deposit Within the Mesozoic Metamorphic Units, Mihaliççik, Eskişehir, Turkey
- Selahattİn Kadİr, Hülya Erkoyun, Tacİt Külah
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- Journal:
- Clays and Clay Minerals / Volume 68 / Issue 6 / December 2020
- Published online by Cambridge University Press:
- 01 January 2024, pp. 553-579
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Hydrothermal alteration led to development of the Yarıkçı clay deposit within the Mesozoic chlorite-, muscovite-, chlorite-muscovite-schist, and garnet-graphite phyllite units along NW–SE- and N–S-trending faults in Mihalıççık in western central Anatolia. The geological, mineralogical, and geochemical characteristics and genesis of this economically important clay deposit have not been examined in detail previously. The present study has attempted to fill this gap. Green smectitic and cream kaolinitic claystones are abundant with smaller amounts of gray illite, dark brown Fe oxides, and silica phases occurring as stockwork/fracture infill and stain/coating. These units are covered by a dark, hard, sharp-edged, and thick silica cap. Metamorphic units exhibit cataclastic texture due to tectonic activities. Muscovite is mostly degraded to kaolinite, and feldspars show sericitization and argillization. Kaolinite typically has a platy form with irregular margins and locally sub-rounded, book-like texture suggesting hydrolysis during the hydrothermal injections. The association of Fe oxides, cristobalite/tridymite/quartz, gypsum/anhydrite, and jarosite are indicative of intense hydrothermal activities and development of kaolinite under acidic geochemical conditions. The local enrichment of SiO2, Fe2O3, S, Cu, and Au also supports this suggestion. The leaching of Sr, Rb, Ba, and Zr, and the slight increase in LREE/MREE+HREE ratios together with the negative Eu and Ce anomalies suggest the selective dissolution of muscovite, garnet, feldspar, and pyroxene by the hydrothermal fluids. Thus, abundant claystones of smectite and kaolinite were formed via the increase in Al+Fe+Mg/Si and Al±Fe/Si ratios in the alkaline and acidic environment, respectively, under the tectonic control of hydrothermal activity as seen in the alteration of chlorite, muscovite, and feldspar in metamorphic units.
Mineralogy, Geochemistry, and Genesis of Bentonites in Miocene Volcanic-Sedimentary Units of the Ankara-Çankiri Basin, Central Anatolia, Turkey
- Selahattin Kadir, Tacit Külah, Nergis Önalgil, Hülya Erkoyun, W. Crawford Elliott
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- Journal:
- Clays and Clay Minerals / Volume 65 / Issue 2 / April 2017
- Published online by Cambridge University Press:
- 01 January 2024, pp. 64-91
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Widespread alteration in the Miocene lacustrine volcanic/sedimentary rocks of the Ankara-Çankiri basin of central Anatolia has resulted in the formation of sizeable (economic) quantities of bentonite deposits. No detailed characterization of the geological, mineralogical, and geochemical properties or the depositional environments of these primary and secondary bentonite deposits has been carried out to date. The present study was undertaken to close this knowledge gap. Two possible hypothetical processes were examined to explain the genesis of the bentonites: 1) The bentonites were formed by the devitrification of volcanic glass in a lacustrine setting; and 2) The bentonites were formed by the chemical weathering of previously deposited volcaniclastic sediments and ophiolitic materials. The characteristics of the bentonites were examined using X-ray diffractometry, scanning and transmission electron microscopy, energy dispersive spectroscopy, and chemical analyses of major and trace elements. The Ankara-Çankırı bentonites are found gradationally interbedded with parent Miocene volcanic and volcaniclastic rocks. These bentonites were deposited in a shallow lacustrine setting based on observed desiccation cracks, locally enclosed coal seams, plant rootlets, gypsum lenses, yellow sulfate-like fracture infillings, and ferric iron oxide stains. Smectite resulted from the chemical weathering of feldspar and possibly also the weathering of biotite and hornblende. This smectite was precipitated in situ on partially dissolved glass and feldspar. The average major-element composition of the smectite-rich clay fractions yielded the following montmorillonitic smectite structural formula: (Na0.33Ca0.31K0.18) (Al2.35Fe0.80Mg0.78)(Si7.79Al0.21)O20(OH)4.
The interlayer cation occupancy in the smectite-rich clay fractions was based on the use of Na+/(Na++Ca2+) ratios and showed a composition between a Ca-smectite and a Na-smectite. The relative increases in several groups of elements according to the LREE/(MREE+HREE) ratio, Al2O3, the sum of Ni+Co+Cr, the sum of Fe2O3+MgO+TiO2, the positive correlation between Rb+Ba and Na2O+K2O, Sr and Rb, Rb/Sr and Zr, Zr/Sm and SiO2, the negative Eu anomaly, and the field and petrographic observations further showed that the Si, Al, Fe, and Mg required to form smectite were mainly supplied from the decomposition of feldspars, amphiboles, and volcanic glass from volcanic materials and were partially supplied from the chemical weathering of ophiolitic basement units. The bentonite deposits examined in this study are mainly primary bentonites derived from volcanics and local secondary bentonites from previously deposited volcaniclastic sediments and ophiolitic materials.
Mineralogical and Geochemical Characteristics and Genesis of the Gülzelyurt Alunite-Bearing Kaolinite Deposit Within the Late Miocene Gödeles Ignimbrite, Central Anatolia, Turkey
- Selahattın Kadır, Tacıt Külah, Muhsın Eren, Negrıs Önalgıl, Alı Gürel
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- Journal:
- Clays and Clay Minerals / Volume 62 / Issue 6 / December 2014
- Published online by Cambridge University Press:
- 01 January 2024, pp. 477-499
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The Güzelyurt kaolinite deposit is an important source of raw material for the ceramics industry in Turkey. No detailed mineralogical or geochemical characterizations of this deposit have been undertaken previously and these were the goals of the present study. The Güzelyurt alunite-bearing kaolinite occurs along a fault zone in the Late Miocene Gödeles ignimbrite, which consists of dacitic and andesitic tuffs. Horizontal and vertical mineralogical zonations with gradual transitions were observed within the alteration zone. The inner kaolinite, alunite, and 7 Å halloysite zones progress horizontally outward to a smectite zone; and native sulfur- and cinnabar-bearing alunite with 7 Å halloysite and porous silica zones increase as one progresses up through the profile. Fe-(oxyhydr)oxide phases associated with native sulfur and cinnabar demonstrate that multiple hydrothermal-alteration processes resulted in kaolinization and alunitization of the deposit. The kaolinization of feldspar, Fe-(oxyhydr)oxidation of hornblende and mica, the presence of kaolinite as stacked and, locally, book-like forms, and of 7 Å halloysite tubes, and smectite flakes as a blanket on altered volcanic relicts indicate an authigenic origin for this deposit. The leaching of Si + Mg + K and Ba + Rb, the retention of Sr, the enrichment of light rare earth elements relative to the heavy rare earth elements, and the negative Eu anomalies suggest that fractionation of plagioclase and hornblende occurred within the volcanics. The oxygen- and hydrogen-isotopic values of the kaolinite, 7 Å halloysite, smectite, and smectite + kaolinite fractions reflect a steam-heated environment at temperatures in excess of 100°C. An increase in the δD and δ18O values of 7 Å halloysite relative to kaolinite suggests its formation under steam-heated magmatic water, the mixing of steam and meteoric water near the surface, and evaporation. The oxygen- and sulfur-isotopic compositions of alunite suggest the direct influence of steam-derived sulfur. The Güzelyurt alunite-bearing kaolinite deposit is inferred to have formed after an increase in the (Al±Fe)/Si ratio and the leaching of alkali elements, which are driven by the sulfur-bearing low-temperature hydrothermal alteration of feldspar, hornblende, and volcanic glass under acidic conditions within the Neogene dacitic and andesitic tuffs.
Mineralogy, Geochemistry, and Genesis of Mudstones in the Upper Miocene Mustafapaşa Member of the Ürgüp Formation in the Cappadocia Region, Central Anatolia, Turkey
- Tacit Külah, Selahattin Kadir, Ali Gürel, Muhsin Eren, Nergis Önalgil
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- Journal:
- Clays and Clay Minerals / Volume 62 / Issue 4 / August 2014
- Published online by Cambridge University Press:
- 01 January 2024, pp. 267-285
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The Upper Miocene Mustafapas-a member of the Ürgüp Formation in the Cappadocia region consists predominantly of mudstones, sandstone, and conglomerate lenses with ignimbrite and basalt intercalations. The mudstones are an important source of raw materials for the ceramics industry in Turkey. A detailed mineralogical, geochemical, and genesis study of these materials has not been performed previously and the present study aims to fill that gap. The characteristics of mudstones of the Mustafapas-a member were examined using X-ray diffraction, scanning and transmission electron microscopy, energy dispersive spectroscopy, and chemical analyses. Weathering products of ophiolitic and pyroclastic rocks were transported into the tectonically subsided zone where they accumulated as fluvial and lacustrine deposits.Weathering in the mudstones is evidenced by smectite flakes associated with relict pyroxene, rod-like amphibole, feldspar, and volcanic glass. The chemical composition of mudstones and their distribution suggest that the depositional basin was supplied with ophiolitic material in the south and ignimbrite material in the north. This interpretation is based on an increase in the quantity of feldspar and opal-A and a decrease in the Fe2O3+MgO/Al2O3+SiO2 ratio from south to north in the study area. The northward increases in Light Rare Earth Elements/Heavy Rare Earth Elements, La/Yb, Zr/Ni and Zr/Co ratios and Nb, Ba, Rb, Sr, and Eu in the mudstones of the Mustafapas-a member with positive Eu anomalies suggest that the Fe, Mg, Al, and Si required to form smectite were supplied mainly through the decomposition of amphiboles, pyroxenes, feldspars, and volcanic glass during weathering processes. After the deposition of mudstones, relative increases in evaporation-controlled Ca, K, and Al in pore water favored the partial dissolution of Ca-bearing minerals and smectite flakes and in situ precipitation of calcite and traces of illite fibers under alkaline micro-environmental conditions during early diagenesis.