Differentiating Styles of Alteration within Kaolin-Alunite Hydrothermal Deposits of Çanakkale, NW Turkey

Abstract

The Biga Peninsula of NW Turkey is host to many kaolin and halloysite deposits with mineralization occurring at the intersections of fault zones in contact with Late Eocene-Miocene calc-alkaline volcanic rocks. Distinguishing between the relative overprinting of hypogene by supergene processes in these deposits is a challenge and important because they affect the physical-chemical properties of minerals and their potential for industrial applications. This study examines the Sarıbeyli-Sığırlı and Bodurlar kaolin deposits in NW Turkey, which were formed from similar volcanics as evidenced by 40Ar/39Ar. Late Eocene (34.2 ± 0.20 Ma) to Early Oligocene (32.7 ± 0.17 Ma) ages for both primary volcanic rocks and alunites are consistent with surrounding rocks in the Çanakkale region. Criteria used to distinguish hypogene alteration from supergene alteration processes come from X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Raman spectroscopies, thermal gravimetric analysis (TGA), scanning and transmission electron microscopy (SEM, TEM), and elemental analyses. Isotopic δ18O depletion and δD enrichment of the Sarıbeyli-Sığırlı deposit suggests that it was more influenced by magmatic waters than was the Bodurlar deposit. The Bodurlar deposit contains a paucity of dickite compared to the Sarıbeyli-Sığırlı deposit, which is evidenced by lower TGA endotherms, higher ratios of XRD intensities for reflections at 1.316 Å and 1.307 Å, distinctive FTIR absorbance bands at 3620 cm− 1 and 3652 cm−1, and relative Raman intensities of the γ1 and γ5 vibrational modes.A genetic model is proposed whereby these deposits are mainly formed through an acid-sulfate hydrothermal alteration, in what appears to be a volcanic-hydrothermal system. The extent of hydrothermal alteration was controlled by fault density and the initial texture of the volcanic rocks. These steam-heated environments included sulfide-enriched vapors and groundwater mixed to varying degrees in the vadose zone. The Sarıbeyli-Sığrlı and Bodurlar deposits, respectively, contain mineral assemblages that reflect both hypogene (kaolinite, alunite, dickite) and supergene (kaolinite, halloysite, jarosite) processes. These observations offer a basis for comparing and discriminating the relative influence of these two important alteration processes responsible for the formation of kaolin deposits in NW Turkey and around the world.

Correlations among the mineralogical and physical properties of halloysite nanotubes (HNTs)

“…In other cases small cylindrical tubes intersect at an angle with larger prismatic ones, and occasionally curved moulds of these intersections are also visible in some prismatic particles where intersecting tubes have presumably become detached during sample preparation. A final feature is the angular terminations of the larger tube edges and the outlines of pseudo-hexagonal forms on the surfaces of some tubes similar to features observed for example by Ünal-Ercan et al (2016). Further details of several of these features are revealed in TEM images (see below).…”

The acid sulfate zone and the mineral alteration styles of the Roman Puteoli (Neapolitan area, Italy): clues on fluid fracturing progression at the Campi Flegrei volcano

“…Emitted gases include H 2 S, CH 4 , N 2 , H 2 and CO, in addition to the dominant water vapor and the secondary abundance of CO 2 reaching a flux of at least 1500 t d −1 and a maximum value of 3000 t d −1 (Allard et al, 1991; et al., 2013;Chiodini et al, 2016). Previous studies further report a Hg flux between 0.9 and 4.5 g d −1 (Ferrara et al, 1994;Bagnato et al, 2014), a detectable (yet very low) abundance of SO 2 (Ferrara et al, 1994;Aiuppa et al, 2013), the occurrence of light hydrocarbons (Capaccioni and Mangani, 2001), and the presence of As and Hg (17-5200 and 1-30 µL, respectively; Valentino and Stanzione, 2003) in the pools and waters. High NH 4 concentrations are described for waters at Pisciarelli (Martini et al, 1991;Celico et al, 1992;Valentino and Stanzione, 2003), but an understanding of the nitrogen source and cycling at the Phlegraean area, showing a unique isotopic composition with δ 15 N at 6.3 ± 0.3 % (Chiodini et al, 2010), remains elusive.…”

“…Anthropogenic contributions are obviously possible (Alloway, 2013), e.g., when considering that NH 4 is generally attributed to agricultural (i.e., fertilizer) and urban soils. However, Hg and As have been detected at the main fumaroles with similar concentrations today and in the last century (Ferrara et al, 1994;Bagnato et al, 2014). These fumaroles continuously emit H 2 S and CO 2 (Allard et al, 1991;Aiuppa et al, 2013;Chiodini et al, 2016) and are the preferred location of the crystallization of native S and alunite.…”

“…Selection of sampling sites (hereinafter referred using the abbreviations in Fig. 1d, e) is based on variable macroscopic features including outgassing "magnitude", tectonics and fracturing evidence, mineral occurrences, and exhalative vent locations, as visible in the field and described in the literature (Allard et al, 1991;Ferrara et al, 1994;Valentino and Stanzione, 2003;Aiuppa et al, 2013;Bagnato et al, 2014;Chiodini et al, 2016). A thermocouple digital probe 51/52 II by Fluke with precision of ±0.3 • C was used to measure temperature in the field, contextually to sample collection.…”

Hydrothermal alteration products in the vicinity of the Ahırözü kaolin deposits, Mihalıççık-Eskişehir,Turkey

“…The geological, mineralogical and chemical characteristics, origin and technological properties of the most important Turkish kaolin deposits were summarized by Fuji et al (1995). Most deposits originated from the hydrothermal alteration of andesitic and dacitic rocks and their associated tuffs, granitic intrusions and less commonly, metamorphic rocks (Seyhan, 1978;Sayın, 1984Sayın, , 2007Sayın, , 2016Ünal-Ercan et al, 2016), but sedimentary kaolins are also present (Gençoglu and Bayhan, 1989). Okut & Gök (1975) and Okut et al (1984) reported the geology and hydrothermal origin of the Düvertepe kaolin deposits in the Balıkesir region which were formed by the fault-controlled hydrothermal alteration of Miocene rhyolites-rhyodacites and contain kaolin-type and alunite-type mineral paragenetic groups (Ece et al, 2013).…”