Keçiborlu (Isparta-Türkiye) opal oluþumlarýnýn jeolojik-jeokimyasal özellikleri

Isparta civarýndaki Geç Miyosen’de baþlayan ve Pliyo-Kuvaterner boyunca devam eden asidik volkanizmanýn son ürünleri þeklinde gözlenen silisçe zengin çözeltiler Keçiborlu (Isparta) kükürt yataðý çevresinde gözlenen ana fay boyunca etkilidir. Bundan dolayý, opal oluþumlarý bu zayýf zonun yakýn çevresinde yoðun olarak gözlenir. Opal oluþumlarý, gri, bej, sarýmsý, kýrmýzýmsý, siyahýmsý gibi çeþitli renklerdedir. Masif yapýlý, yer yer bant þeklinde gözlenen opaller keskin kenarlý, konkoidal kýrýnýmlý, yarý saydam, mat, yaðýmsý parlak yüzeyli opaller ise yer yer demiroksitleþmiþtir. Bazý opallerin breþik kayaç parçalarý içerdiði gözlenmektedir. Opal oluþumlarýnýn sahadaki lokasyonlarý tespit edilmiþ ve temsili örnekler kullanýlarak, söz konusu örneklerin ince kesit, SEM analizleri ile yapýsal ve dokusal özellikleri, XRD ve FTIR analizleri ile mineral birliktelikleri belirlenmiþtir. Jeokimyasal bulgular ile kimyasal bileþimleri ortaya konmuþtur. Ýncekesitleri çalýþmalarýnda hidrotermal çözeltilerin etkisiyle ilksel özelliklerini kaybederek opalleþmiþ örneklerin yer yer demiroksitleþmiþ, laminalanma kazanmýþ olduklarý ve killeþmenin de olduðu gözlenmiþtir. Manyetit ve hematit gibi opak mineral içermektedirler. SEM görüntülerinde amorf, taneli, çöl gülü ve lepisfer gibi farklý mikro dokular gözlenmiþtir. XRD ve FTIR analizlerinde opallerin çoðunun Opal CT ve bir kýsmýnýn da Opal C türünde olduðu tespit edilmiþtir. Jeokimyasal analizler sonucunda Ba <120 ppm ve Ca >200 ppm miktarlarý, LOI deðerlerinin dikkate deðer deðiþimi, gerekse de C/T oraný ile Ga arasýndaki nispi iliþki ile hidrotermal alterasyonlar dikkate alýndýðýnda Keçiborlu opallerinin magmatik kökenlidir.

Geological-geochemical signatures of opal occurrences in Keçiborlu (Isparta-Turkey)

Silica-rich solutions, observed as the final products of acidic volcanism, which started in the Late Miocene around Isparta and continued throughout the Plio-Quaternary, are effective along the main fault observed around the Keçiborlu (Isparta) sulfur deposit. Therefore, opal occurrences are intensely observed in and around this weak zone. Opal formations are in various colors such as gray, beige, yellowish, reddish, blackish. Opals with a massive structure, observed as bands, are sharp-edged, conchoidal diffraction, translucent, matte, oily glossy surface opals are iron oxidized. Some opals are observed to bear brecciated rock fragments. The locations of the opal occurrences in the field were determined in this study. Using representative samples, structural and textural properties of opals were determined by thin section, SEM analyses, and mineral associations determined by XRD and FTIR analyses. Geochemical findings revealed chemical compositions. Based on the thin-section studies, it was observed that the opalized samples lost their primary properties due to the effect of hydrothermal solutions and they became iron oxidized, laminated, and argillized. In addition, they contain opaque minerals such as magnetite and hematite. Different micro textures such as amorphous, granular, desert rose, and lepisphere quartz associations were observed in SEM images. In the XRD and FTIR analyzes, it was determined that most of the opals were Opal CT and some of them were defined as Opal C type. Based on the geochemical analyses considering Ba <120 ppm and Ca >200 ppm, the remarkable changes in LOI values, and the relative relationship between C/T ratio and Ga, such hydrothermal alterations in opals the Keçiborlu opals were found to have the magmatic origin.