RESUMEN
Garnets that common constituent of skarn type iron deposits are wide ranges of chemical compositions, and they are also important as a semi-gemstone mineral. This study has been investigated garnets and inclusions of its formed in contacts of Pertek granitoid and Keban marble by using a combination of multiple techniques including Raman spectrum, electron microprobe, petrography and LA-ICP-MS. The main mineral assemblage observed in the skarn formation is diopside, garnet, quartz, magnetite, calcite and pyrite. The garnets are in size between 1 and 7 cm and have reddish, greenish and light-dark brown colour. The compositions of the garnets are mainly grossular-andradite, andradite-grossular, less grossular and andradite. Increased porosity and horizontal flow of hydrothermal fluids during metasomatism resulted in the formation of garnets of different sizes. Raman spectroscopy studies on garnets show to be that the idiomorphic and semi-idiomorphic garnets are predominantly grosular, andradite and uvarovite in the core. Raman spectroscopy studies on garnets showed to have predominantly grossular, andradite and uvarovite composition in the core of the idiomorphic and semi-idiomorphic garnets. As for the rare earth element (REE) analysis and distribution model, the chondrite-normalized REE patterns of all garnets in the study area have similar trends and generally in the right-slopping shape depleted in HREE and enriched in LREE, mostly controlled by adsorption. High Fe2O3, CaO and MgO contents may cause to high mobility during skarn formation associated with contact metamorphism and cation exchange via hydrothermal fluids (eg uvarovite in the core). All garnets have generally positive Ce and positive Eu anomalies. These results suggest that the garnets in the studya area formed in conditions showing increase in pH and high oxygen fugacity or decrease in temperature in the source of the hydrothermal fluids.
RESUMEN
The mineralogy, trace and minor element geochemistry and different color changes of Bitlisignimbirite (eastern Turkey) were measured with Neutron Activation Analysis and Confocal Raman spectrometr methods. From these analyzes, were determined three levels as lower, middle and upper according to texture, color, welded degree, component and chemical differences in Bitlis ignimbrites in study area. The most distinguishing feature observed in black, red and grey color ignimbirite levels are partially mineralogical compositions, fiamme geometry and appearance of different colors. The mineralogical compositions of all levels are plagioclase, feldspar, augite, fayalite, biotite, sanidine, hematite and Fe-Ti oxide (titanomite, ilmenite) minerals. The matrix consists of quartz, anorthoclase, Fe-Ti oxide and sanidine. In addition, the matrix rarely contains glassy and dispersed mineral microliths, apart from intermediate levels of iron oxide/hydroxides. The intermediate levels have higher Fe-Ti oxide composition than others. The hydrous minerals in all ignimbrite levels have been partially replaced by devitrification minerals. The fayalite, which rarely seen in ignimbrites is determined by Raman spectroscopy method in Bitlis ignimbrite. The Raman spectra of different colored ignimbirites obtained using Confocal Raman spectroscopy showed different spectra between 869 and 3062 cm-1 for the grey, black, and reddish colored ignimbirites. In spectral ID are determined anorthoclase, fayalite, hematite, bitovnite minerals. The REEs patterns of ignimbrites normalized to chondrite are similar each other. All of them show a decrease from high LREE to HREE. The LREE enrichment and Lan/Ybn ratios (7.95-9.07) in ignimbrites is the sign of the liquid-rich calalkaline magmatic source. The cerium anomaly shows the decrease in solubility accompanying the oxidation of Ce (+3) to Ce (+4). The different color levels of ignimbrites can be summarized as cooling, iron oxide/iron hydroxides ratios (high in middle level), volatile elements (U,Th,Cl) (low in middle levell), devitrification of volcanic glass and chemical reactions.