ГЕОХИМИЯ, 2013, № 2, с. 156-170
GEOCHEMISTRY, MINERALOGY AND GENESIS OF PYROPHYLLITE DEPOSITS IN THE POTURGE REGION (MALATYA, EASTERN TURKEY)
© 2013 F. ONER* and A. TA S **
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*Mersin University, Faculty of Engineering, Department of Geological Engineering, Ciftlikkoy
33342 Mersin, Turkey e-mail: foner@mersin.edu.tr *M.T.A. Directorate of East Mediterranean Region, Adana, Turkey Поступила в реакцию 11.03.2011 г. Принята к печати 19.10.2011 г.
Abstract—In the Potflrge (Malatya, Turkey) area pyrophyllite occurrences are common in the shear zones, mostly in the form of lenses along faults. Mineralogical investigations (XRD, FTIR and SEM) revealed that pyrophyllite, kaolinite (dickite) and quartz are present in the form of major phases and muscovite (sericite), kyanite, chlorite, and alunite are only present in the form of minor phases.
This study revealed that the existence of the kyanite phase points out to high pressure and temperature conditions which the rocks were underwent. On the other hand, the minerals such as pyrophyllite, kaolinite, and alunite are products of a low degree metamorphism (retrograde). The mineral paragenesis in the pyrophyllite deposits suggests that the formation of minerals took place in two ways: (1) the transformation of kyanite into pyrophyllite and quartz through retrograde metamorphism by a high degree temperature, (2) then pyrophyllite and probably muscovite were transformed into kaolinite and alunite through reactions with relatively low temperature hydrothermal fluids.
The geochemical data indicate that during the retrograde metamorphism the elements K, Rb, Sr, Ba, S, and Fe were mobile, the elements Si, Al, P moderately mobile to immobile and the HFS elements (Zr, Ti, and Nb) were immobile. It was shown that the formation of pyrophyllite, kaolinite and alunite was associated with depletion in alkalis, Mg, Fe and enrichment of elements including Sr, Ba, and S. Mineralogical and geochemical data suggest that parent rocks (premetamorphism) of the Potflrge pyrophyllite were probably kaolinite, Al-rich clays or bauxites.
Keywords: Alunite, Pötürge Metamorphic Rocks, Retrograde, Pyrophyllite, SEM.
DOI: 10.7868/S0016752513020088
INTRODUCTION
The industrial mineral pyrophyllite is an economically important raw material which is used particularly due to its exceptional thermal-mechanical characteristics among others, especially in certain type of ceramics, fireproof materials and cement industry. Important pyrophyllite deposits are found in Japan, USA, South Korea, China, Brazil and India [1, 2]. The pyrophyllite deposits in Japan are usually products of acidic volcanic rocks, such as rhyolite, dacite or metavolcanic rocks which were decomposed and/or converted by hydrothermal or metasomatic processes [3]. In South Korea, the pyrophyllite occurs in the southern part of the country and was formed through hydrothermal alteration of intermediate and acidic volcanic rocks and tuffs, respectively [4]. The pyrophyllite deposits in the USA are located in North Carolina (Carolina Slate Belt) and are characterized by high-alumina minerals such as kaolinite, sericite, andalusite, topaz, diaspore and pyrophyllite [5]. The
pyrophyllite deposits in Canada show similarity to the occurrences in North Carolina.
There are approximately 25 economically important Pyrophyllite occurrences in the Poturge massif (Malatya, Turkey) in the eastern Taurus Mountains. Pyrophyllite occurrences are mostly present as lens-shaped bodies and occur predominantly in the shear zones. Pyrophyllite has been mined in Turkey since 1976 and used primarily in ceramic and refractory industries. Pyrophyllite has been used since 1990, to a great extent (100—120 thousand tons per year), as a raw material for the production of the white cement in CIMSA (Cement Factory in Mersin) due to the fact that it contains minute amounts of Fe and Cr elements.
Previously, the mined region has been studied very intensively by the General Directorate of Mineral Research & Exploration Institute (MTA) concerning the available reserves, as well as the quality of the pyro-phyllite occurrences. Nevertheless, none of these
studies provide data on the genesis of the pyrophyllite deposits in Poturge region (Malatya).
The aim of this study is to shed light on the genesis of the pyrophyllite occurrences in Poturge region by utilizing geochemical data (especially, trace and rare earth elements). For this purpose, in addition to min-eralogical investigations, 26 samples of pyrophyllite and wall rock material were analyzed for their major and trace element contents. Additionally, 17 samples from altered zone and unaltered wall rock were selected and analyzed for their rare earth element contents.
REGIONAL GEOLOGY
The eastern Taurus chain, where the study area lies, represents a complete geological cross section of the area between Arabian platform in the south and Mun-zur nappes in the north (Fig. 1). Ricou et al. [7], Mi-chard et al. [8] and Yazgan [9] have divided the area into seven tectonic units according to its lithological and structural characteristics. These units, which are located between the Arab platform and the North Anatolian suture zone, are folded autochthon Arabian series; Poturge thrust belt; Poturge metamorphic massif including the volcanosedimentary cover rocks (the Maden complex); Ispendere-Komurhan metaophio-lite; Baskil igneous rocks; Keban metamorphics and Munzur platform limestone. The Poturge metamor-phic massif is found in the north of the Poturge and Bitlis thrust zone as allochthonous units metamorphosed into the green-schist and amphibolite facies and shows indications of a syn-metamorphic tectoge-nesis [10, 11]. Augen-gneisses occur within the Poturge metamorphic massif as lower unit. It is composed of relatively clear porphyroclasts of alkali feldspar, plagioclase, quartz, biotite, muscovite and chlorite and can be very easily identified in the field by well developed augen texture. In the area, biotite and amphibole schist exist as next series and it is green-yellow colored and composed of amphibole (hornblende), bi-otite, muscovite, quartz and plagioclase [10]. In the central part of the study area, rocks designated as granite-gneiss (gneissic granites) outcrop, which are mainly consist of albite, quartz, K-feldspar, muscovite, tourmaline, rutile, zircon, apatite, and garnet. Granite-gneiss neither macroscopically nor microscopically shows a clear texture. All these series are defined by Erdem and Bingol [12] as lower unit. Within this unit, a 50 to 100 m wide shear zone is found, which contains the minerals such as muscovite (sericite), pyrophyllite and quartz. The pyrophyllite occurs in those series in lens-shaped bodies and contains thin quartzite layers and schist, where muscovite or sericite are present as wall rocks. On top of the Poturge metamorphic unit the calc-schist series lays and is covered discordantly by volcano-sedimentary rocks (Maden complex) of the middle Eocene age.
MATERIAL AND METHODS
About twenty six samples of pyrophyllite and wall rock material were analyzed for mineralogical composition by Fourier Transform Infrared (FTIR). The FTIR analyses were made using a Jasco 5300 FTIR spectrometer and performed on pressed powders mixed with KBr (2 mg sample diluted by 200 mg KBr). Data were collected over the range 4000—400 cm-1. After that, 10 powdered bulk samples were selected for further investigation of mineralogical composition by X-Ray diffraction (XRD) using a Philips Analytical X-Ray B.V. with CuKa radiation at the Laboratories of Technical University of Berlin and by Mineral Research & Exploration Institute (MTA) in Ankara. The XRD data were recorded at 50 kW and 30 mA over the range 3 to 80°20. Additionally, four samples were analyzed by scanning electron microscopy (SEM) to reveal micromorphological and textural features. Thin sections were also prepared from some samples and investigated under transmitted and reflected light microscopes to show the textural relationship between the minerals and their host rocks. Major element composition of samples was determined by X-Ray fluorescence (XRF) at the laboratories of Technical University of Berlin. In addition to this, 17 selected samples were analyzed for their trace and rare earth element compositions by ICP-MS method at the ACME laboratories in Canada.
RESULTS OF MINERALOGICAL ANALYSES Microscopic Investigations
The pyrophyllite bearing samples display lepido-granoblastic texture and are characterized by quartz, kyanite, muscovite, sericite and pyrophyllite. The ky-anite porphyrobalasts are often decomposed and converted into pyrophyllite (Fig. 2a). Muscovites are also partially altered to pyrophyllite and kaolinite along fractures and at the outer parts of grains (Fig. 2b).
XRD Analyses
Mineral assemblages were determined by X-Ray analyses and the results are presented in Table 1. The granite-gneiss (GG) samples contain quartz, feldspar and muscovite as expected. However, the samples of pyrophyllite deposits show a very variable mineralogi-cal composition. The major minerals in the samples are pyrophllite, kaolinite, dickite and quartz and the minerals like natro-alunite, feldspar, illite and kyanite exist as minor phases (Fig. 3). The polymorph kaolin group minerals kaolinite and dickite are characterized by intensive first- and second-order basal reflection and possess main peaks at 12.5 and at 25° 20 in the XRD pattern. Therefore, for the determination of these minerals, the characteristic peaks between 2050° 20 can be used. The strongest diagnostic reflections for dickite would appear at 3.79, 3.34, 2.32 and
Stream Road
Fault (probable) Fault
Schistosy Strike and dip Alluvium
Basalt, Splite, Diabase complex
Calc shcist Marble
Undifferentiated Shcist
Pyrophyllites
Graniric gneiss
Biotite schist Amphibolite schist
Augen gneiss
Fig. 1. Location and Geological map of the (Poturge-Malatya) area (modified from
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