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    Chemical composition of tourmaline from the Asarcik Pb-Zn-Cu +/- U deposit, Sebinkarahisar, Turkey
    (SPRINGER WIEN, 2008) Yavuz, F.; Fuchs, Y.; Karakaya, N.; Karakaya, M. C.
    Abundant tourmaline, commonly as rosettes up to 1.5 cm in diameter, is present in the Upper Cretaceous Asarcik granitoid (Sebinkarahisar), Northeastern Turkey. The tourmalines also occur in quartz-tourmaline veins up to 4 m thick that cut the Asarcik granitoid. This granitoid was emplaced in the eastern Pontide Metallogenic Belt, where accompanying tourmalines are found in close association with a vein-type, uranium-bearing Pb-Zn-Cu deposit. Tourmaline crystals are generally optically zoned from core to rim with a bluish green core. Electron-microprobe studies show that tourmalines from the Asarcik granitoid and quartz-tourmaline veins display mainly dravite-schorl solid solutions with a tendency to schorl compositions. The tourmaline from the Asarcik granitoid has Fe/(Fe+Mg) ratios from 0.28 to 0.69 (mean=0.52) and Na/(Na+Ca) ratios from 0.57 to 0.93 (mean=0.76). In contrast, tourmaline in the quartz-tourmaline veins has Fe/(Fe+Mg) ratio from 0.14 to 0.92 (mean=0.59) and Na/(Na+Ca) ratio from 0.78 to 1.00 (mean=0.96). Tourmaline in the veins has a more alkali-deficient trend than that in the granitoid. Substitution mechanisms for the chemical evolution of tourmalines at Asarcik are the MgFe-1, (Fe2+Fe3+)(MgAl)(-1), square Al(NaR)(-1), AlOR2+ (-1)(OH)(-1), square Al2ONa-1R2+ (-2)(OH)(-1), Ca-0.5 square Na-0.5(-1), CaMg2 square Al--1(-2), CaMgO square Al--1(-1)(OH)(-1), CaMg3OH square-1Al-3O-1, CaMgNa-1Al-1, CaONa(OH)(-1), CaMg2OHNa-1Al-2O-1, CaMg2 square Al--1(-2), and CaMg3OH square-1Al-3O-1 exchange vectors. Chemical zoning in the tourmalines is consistent with these substitutions. Stoichiometric calculations of electron-microprobe data in the Asarcik granitoid suggest a relatively oxidizing environment during tourmaline crystallization.
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    Relation between spring-water chemistry and hydrothermal alteration in the Saplica volcanic rocks, Sebinkarahisar (Giresun, Turkey)
    (ELSEVIER, 2007) Karakaya, N.; Karakaya, M. C.; Nalbantcilar, M. T.; Yavuz, F.
    Widespread and intense zones of hydrothermal alteration are present in the Cretaceous Saplica volcanics of NW Turkey. ropylitic, phyllitic (quartz-sericite, pyrite-sericite) and argillic types of alteration, along with hematite, silica polymorphs and two different types of tourmaline mineralization, have developed as products of these intense alteration processes. In addition, many springs have been detected in the vicinity of the alteration zones. Moderately warm, generally acidic, sulfate-dominated and meteoric in origin, the highly conductive and oxidizing spring waters of Saplica (Giresun,Turkey) were sampled at different times over the past 2 years, especially for chemical and isotopic analyses. Molalities, activities, activity coefficients and log activity ratios of ionic species and mineral saturation indices have been calculated for the sampled spring waters. Minerals actually observed in rocks of the alteration zones yield positive saturation indices in corresponding water samples, while mineral species absent in the alteration zones accordingly display negative saturation indices in corresponding water samples. In other words, the presence/absence of minerals in the field corresponds well to the mineral saturation indices determined from our water samples. Based on delta(18)0 and H-2 data, the spring waters observed in the argillic alteration zones are generally meteoric in origin. The TU value of the spring waters is between 3.40 and 11.2, indicating that young waters have mixed with older waters from different sources. Some of the analyzed samples show high Fe3+, Al3+, Na, Ca, K and Mg concentrations, but their cationic contents vary over time. Amongst the trace elements, the highest dissolved concentrations were those of Sr, Ba, B, Mn, Zn and U. The lowest concentrations were measured for Me, V, Cd, Be and Ce. Increases in Al and Fe concentrations parallel increases in total and mineral acidity values. Significantly, precipitation of recent gypsum, alunite, native sulfur, and goethite has been observed around the spring-water sources. (c) 2006 Elsevier B.V. All rights reserved.
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