Mineralogy, micromorphology, geochemistry and genesis of a hydrothermal kaolinite deposit and altered Miocene host volcanites in the Hallaçlar area, Uşak, western Turkey

Abstract

The Hallaçlar kaolinite deposit of the Uşak Province (western Turkey) is hosted by dacite, andesite and siliceous materials of the Miocene Karaboldere volcanites. Mineralogical zonation, such as the prevalence of kaolinite at the centre of the deposit, coexisting with silica polymorphs such as quartz and cristobalite along with feldspar and hornblende, and a relative increase of smectite, illite, chlorite, and Fe-oxide/-hydroxide phases outward and upward, demonstrate that hydrothermal-alteration processes resulted in kaolinization. Micromorphologically, kaolinite occurs as pseudohexagonal blocky kaolinite with coarse-grained quartz in microfractures, and the presence of relatively fine-grained vermiform kaolinite that edges volcanic materials indicates that kaolinite developed in several phases coexisting with goethite, lepidocrocite, hematite, pyrite, jarosite, alunite, and gypsum/anhydrite with smectite in fractures. The highly crystallized Hallaçlar kaolinite is identified by: (1) sharp reflections at 7.23 and 3.57 Å, with triplet and doublet non-basal reflections; (2) sharp infrared spectral bands at 3687, 3651 and 3620 cm-1; (3) well defined, pseudohexagonal and hexagonal kaolinite crystal growth; (4) a chemical index of weathering of 98.6-100; and (5) SiO2/Al2O3 ratios between 1.04 and 1.45. Enrichment of Sr and depletion of Rb+Ba, Ti, and HREE relative to LREE, with a distinct negative Eu anomaly, are responses to the fractionation of feldspar and hornblende by the hydrothermal fluid; these results are also supported by the O- and H-isotopic character and formation temperatures of the Hallaçlar kaolinite and smectite; namely, 134.1-183.4°C and 65.6°C, respectively. The negative δ34S (-20.7‰) value of gypsum/anhydrite reflects its formation from geothermal-water-derived sulphur. Under the influence of a tectonically controlled hydrothermal process, feldspar, hornblende and volcanic glass were altered, resulting in the conservation of Al and depletion of Si, Na, Ca, K, Mg and Fe in an open hydrological system such that formation of kaolinite in the central part of the deposit under acidic conditions and development of smectite and illite upward and outward under basic conditions were favoured.

Sediment-Hosted Kaolin Deposit from Çakmaktepe (Uşak, Turkey): its Mineralogy, Geochemistry, and Genesis

“…the deposit, the presence and distribution of certain mineral phases such as alunite and Fe-Ti oxide, the major and trace elements, and the stable isotope compositions of kaolinite may provide information regarding the origin of kaolinization (Kelepertis and Esson, 1987;Boulvais et al, 2000;Siddiqui and Ahmed, 2008). Unlike the primary kaolin hypothesis of Erkoyun and Kadir (2011), the present authors suggest that Ç akmaktepe kaolins are secondary-type kaolins. The following data support our argument: (1) the stratified shape of the deposit;…”

“…The genesis of the Ç akmaktepe kaolin deposit has been debated. The genesis of the kaolin deposit was linked by Fujii et al (1995) to sedimentary processes, but kaolinization was stated by Erkoyun and Kadir (2011) to have occurred as a result of acidic hydrothermal fluids and controlled by tectonic activity. The aims of the present study were to resolve the controversy regarding the genesis of the Ç akmaktepe kaolin deposit and to contribute to discussions on geology, mineralogy, geochemistry and the origin of kaolin deposits in western Anatolia and around the world.…”

Mineralogy and technological characterization of two kaolin deposits from the Borborema Pegmatite Province, northeastern Brazil

“…The XRD traces of the <2 μm fractions indicate that kaolinite is the predominant phase present, with traces of illite. The high values of Al 2 O 3 are related to the replacement of Si 4+ by Al 3+ in tetrahedral sites, and the low values of Fe 2 O 3 indicate limited replacement of Al 3+ by Fe 3+ in octahedral sites in comparison with other studies (Kadir & Akbulut, 2009;Erkoyun & Kadir, 2011). The Na + and P 5+ detected (Table 4) are attributed to the sodium hexametaphosphate used as a deflocculant during separation of the <2 μm fraction, while K + is attributed to trace illite.…”

Alteration of glassy volcanic rocks to Naand Ca-smectites in the Neogene basin of Manisa, western Anatolia, Turkey

“…In general, seafloor alteration and/or atmospheric weathering processes are considered to be responsible for the formation of most smectites. While silica polymorphs, kaolinite, gypsum, opaque minerals and alunite form under strong acidic conditions, smectite may form under slightly acidic to slightly alkaline conditions (Wirsching et al, 1990;Kadir & Akbulut, 2009;Erkoyun & Kadir, 2011). Thus, the pH of the solution gradually becomes alkaline with the release of the alkalis and montmorillonites may precipitate from the solution (Karakaya et al, 2011a,b).…”