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    Clay minerals in hydrothermally altered volcanic rocks, Eastern Pontides, Turkey
    (CLAY MINERALS SOC, 1999) Celik, M; Karakaya, N; Temel, A
    Extensive hydrothermal alteration is observed around volcanogenic massive sulfide deposits. These deposits are related to Late Cretaceous volcanism in various parts of the Eastern Pontide province. Mineral assemblages resulting from alteration consist of mostly clay minerals and silica polymorphs, some sulfate minerals, and scarce zeolite minerals. The clay minerals are kaolinite, illite, and smectite. These minerals were examined using X-ray diffraction (XRD), scanning electron microscopy (SEM)energy dispersive spectrometry (EDS), X-ray fluorescence spectroscopy (XRF), and differential thermal analysis (DTA)-thermal gravimetry (TG) techniques. The illite and the toseki deposits are a result of hydrothermal alteration of dacitic-andesitic volcanites. Two groups of bentonite deposits occur; the first mainly formed by hydrothermal solution whereas the second group resulted from halmyrolysis. The smectite in these alteration zones is generally montmorillonitic in composition and the interlayer cation is mostly Ca and lesser amounts of Na. The SiO2 and Fe2O3 contents of the hydrothermal bentonites are higher than those of the halmyrolysis smectites: however, the MgO content of both groups is similar. The Na2O and K2O contents of both groups are generally <0.5%. The hydrothermal bentonites are not plastic and have open honeycomb microtextures, although the halmyrolitic smectites are plastic with ultrafine and rod-shaped textures. Illite, which contains some smectite layers, is a 1M polymorph, and has an asymmetry to the low-angle side of the XRD peaks. The impure illite deposits contain various combinations of smectite, kaolinite and gypsum, galena, sphalerite, pyrite, goetite, and quartz. The illite has >35 wt. % Al2O3. The toseki raw material, which may be possibly useful as a porcelain raw material, is composed mainly of illite, kaolinite and quartz, or illite and quartz. The crystallinity of the kaolinite is poor.
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    Fibrous foitite from Sebinkarahisar, Giresun Pb-Zn-Cu-(U) mineralized area, northern Turkey
    (MINERALOGICAL ASSOC CANADA, 1999) Yavuz, F; Celik, M; Karakaya, N
    Fibrous foitite occurs in cavities in quartz Veins near Sebinkarahisar town, Giresun mineralized area [Pb-Zn-Cu-(U)], in northern Turkey. Veins of quartz + fibrous tourmaline generally cut monzonitic and syenitic rocks. Acicular and hairlike light gray crystals of foitite have a mean composition of square(0.43)Na(0.52)Ca(0.07), (Fe1.55Mn0.08Mg0.52Al0.67Ti0.01) Al-6 (BO3)(3) Si-6 O-18 (OH,O)(3) (OH)(1). The crystals of this low-temperature tourmaline radiate from irregular patches of schorl in cavities in quartz veins. Each fiber is zoned along its length with respect to Fe, Mn, Mg, Ca, Na, K, and P. The fibrous foitite from the Sebinkarahisar area contains higher Mg, Ca and Na contents than that from southern California and Elba.