Girelbelen (Bodrum, Muğla) skarn cevherleşmesinin jeolojisi, jeokimyası ve kökeni

This study aims to present the petrographical, geochemical and alteration-mineralization characteristics of the Girelbelen (Dağbelen) skarn prospect at Bodrum peninsula (Turkey). Lower Cretaceous dolomitic limestones and flysch blocks of the Upper Çaldağ Formation are intruded by Middle Miocene Girelbelen pluton in the Girelbelen. The intrusion resulted in a prominent calc-silicate hornfels mostly on the flysch type fine grained clastic rocks and skarn at dolomitic limestones. Both endo and exoskarns were developed. The endoskarn was observed in a limited area and mainly comprises garnet and pyroxene. Actinolite and epidote overprints in this zone represent retrograde stage assemblages. The exoskarn was observed in a relatively broader zone and displays zonation pattern from intrusion to dolomitic limestone as of garnet skarn, garnet-pyroxene skarn, pyroxene-garnet-vesuvianite skarn and forsterite-pyroxene-vesuvianite skarn. Actinolite, tremolite, epidote, calcite and quartz form the retrograde stage assemblages in the exoskarn zone. Predominance of magnesium-bearing assemblage including forsterite, actinolite and diopside indicate that Girelbelen is a magnesian skarn. The sulfide mineralization is hosted by both endoskarn and exoskarn. Chalcopyrite mineralization is hosted and closely associated by the garnet and pyroxene formed at the prograde stage in the endoskarn zone, and its ratio decreases toward to exoskarn contact. Chalcocite replaces chalcopyrite. Galena and sphalerite are synchronous and are hosted by actinolite, tremolite and epidote in the exoskarn. Electron microprobe analyses showed that garnets are grossularite (Gro44.97-93.4-Ad0-35.36-Pyr0.42-21.7) in composition and display enrichment in the grossularite towards the rim. The pyroxenes are rich in diopside (Di85-94Hd5.6-15Jo0.3-5.4) with a low hedenbergite end member composition. Composition of the calc-silicate minerals and Mn/Fe ratios of the pyroxenes are indicative of oxidized Au-Fe and Cu skarns. Intrusions at the Girelbelen are mostly monzodiorite in composition and have calc-alkaline, metaluminous, I type character. They are enriched in large ion lithophile elements (LILE e.g, Ba, Cs, Rb, Th, U), and depleted in high field strength elements (HFSE e.g, Nb, Ta, Y, Zr, Ti) normalized to primitive mantle. These characteristics suggest that Girelbelen is a subduction related intrusion. Total alkali contents of the intrusions at Girelbelen correlate well with those of average with Au, Fe and Cu skarn granitoids. Fluid inclusion analyses conducted on the primary type 1, type 2 and type 3 inclusions on the exoskarn zone minerals. Homogenization temperatures (Thº) and salinity values (wt.% NaCI equivalent) of the fluid inclusions on the garnets from prograde stage are yielded Thº and salinity values 496 to > 600ºC and 10.86 to 16.99 wt.% NaCI equivalent, respectively. The homogenization temperatures (Thº) and salinity values (wt.% NaCI equivalent) of the fluid inclusions on vesuvianite referring to early stages of retrograde stage are 338 to 394ºC and 7.45 to 9.60 wt.% NaCI equivalent, respectively. Those on calcite formed at the syn-ore stage are 287 to 343ºC and 2.24 to 7.45 wt.% NaCI equivalent, respectively. Homogenization temperatures and salinity values of the fluid inclusions from the skarn zones are compatible with the world-wide Pb-Zn skarns. The calculated δ18O(fluid) values of the garnets at the exoskarn zone are 12.04‰ and 11.94‰, respectively. Skarn isotopic compositions of the garnets show that, prograde stage minerals were mostly produced by magmatic fluids through preliminary skarn forming metasomatism. δ34S values of galena in the exoskarn zone is -1.6‰ indicating that sulfur was originated from magmatic rocks. Assessment of stable isotope and fluid inclusion data reveals that, magmatic fluids were mixed with meteoric water during the retrograde stage. Keywords: Monzodiorite, Endoskarn, Exoskarn, Fluid Inclusion, Stable Isotope