Petrology, geochemistry, and evolution of the iron skarns along the northern contact of the Eğrigöz Plutonic Complex, Western Anatolia, Turkey

Authors: TOLGA OYMAN, İSMET ÖZGENÇ, MURAT TOKCAER, MEHMET AKBULUT

Abstract: The Çatak and Küreci skarn districts are located approximately 10 km NW of Emet (Kütahya) in Western Turkey. The skarn and associated ore formations mainly occur at the contact between intrusive rocks of the Eğrigöz Plutonic Complex (EPC) and calcareous pelitic schists with limestone lenses of the Sarıcasu Formation and meta-carbonate rocks of the Arıkaya Formation. The major, trace, and rare earth element analysis of the igneous rocks indicate that they are high level, subalkaline, calc-alkaline, peraluminous to metaluminous I-type intrusions, generated in a continental arc setting. Three distinct skarn-type mineralization, differing in their host rocks and distance from the intrusive body, were chosen to establish the ore-forming conditions in different episodes of skarn formation. The Küreci iron mineralization is hosted in a skarn zone with well-developed zoning from unaltered granodiorite and endoskarn, andradite-diopside exoskarn, to diopside-wollastonite exoskarn towards a marble reaction front. In Sakari, the iron mineralization and associated skarn have formed due to successive fracturing and infiltration processes. From early contact metamorphic rocks to late prograde skarn at the Sakari prospect, the composition of clinopyroxene ranges from (Di_{50-70} Hd_{28-53} Jo_{1-2}) to (Di_{19-73} Hd_{26-77} Jo_{2-6}) and the composition of garnet ranges from (Ad_{95-99} Gr_{1-5}) to (Ad_{40-61} Gr_{36-58}), respectively. The presence of anisotropic grossular garnet with high Fe^{2+}/Fe^{3+} in crosscutting pyrrhotite-pyrite-bearing veinlets coupled with hedenbergitic pyroxene (Mg-poor clinopyroxene with higher Fe^{2+}/Fe^{3+}) is consistent with reducing conditions during the later stage of prograde skarn alteration. The Çatak iron skarn is characteristic, with its high sulphide content due to the presence of pyrrhotite, pyrite, and arsenopyrite, and low proportion of garnet to pyroxene. The sulphur isotope (\delta^{34}S) compositions in the pyrrhotite-dominant skarn zones range between +0.84 to -2.23&permil. We interpret the bulk of the sulphur in the system as of igneous derivation and there has not been any significant sulphur contribution from a crustal source. Fluid inclusion measurements conducted on skarn minerals of the proximal zone and distal zone+vein skarn revealed high homogenization temperatures (371 to >600°C) and varying salinity values (10.5 to >70 wt% NaCl). The fluid inclusion data indicate that there are at least three fluids associated with the genesis of the proximal skarn where the high garnet/pyroxene ratios are found. Fluid inclusions that represent the early stages both in garnet and pyroxene plot in 'Primary Magmatic Fluid' and 'Metamorphic Fluids' fields. A magmatic fluid, presumably located at deeper parts of the system, mixed with a metamorphic fluid during its ascent. Over all the Eğrigöz skarn a weak or moderate retrograde skarn alteration envelope formed, dominated by the incursion of meteoric waters in the system, indicating limited fluid-rock interaction. Hydrofracturing resulted in pressure decrease and inclusions with Type III (L+V+S) inclusions that plot in the 'Secondary Magmatic Liquid' and 'Magmatic Meteoric Mixing' fields.

Keywords: geochemistry, iron skarn, calc-silicate, Eğrigöz, Turkey

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