Structural controls of özyurt shear-hosted gold deposit, ;Niğde, central Türkiye

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Thesis Type: Postgraduate

Institution Of The Thesis: Middle East Technical University, Graduate School of Natural and Applied Sciences, JEOLOJİ MÜHENDİSLİĞİ ANABİLİM DALI, Turkey

Approval Date: 2022

Thesis Language: English

Student: KAAN ONAT

Supervisor: NURETDİN KAYMAKCI

Open Archive Collection: AVESIS Open Access Collection

Abstract:

Shear-hosted Özyurt Gold Deposit is located in the Niğde Massif, a metamorphic core complex at the southern tip of Kırşehir Block, in Central Türkiye. The massif is composed of alternations of gneiss, schist, quartzite, marble, and amphibolites. It is tectonically overlain by Neotethyan ophiolites and intruded by Üçkapılı Granite. Gold mineralization is hosted along the foliation surfaces, by oxidized cataclastic breccias formed in schists along a high-angle fault network, as well as the gossans at the contacts of schist and overlying marbles. The pre-existing fault network was cut by syn-tectonic dikes that are coeval with the exhumation. The deposit undergone supergene stage causing the breakdown of all sulfide minerals and liberating the gold in oxide zones. Two mineralization stage was observed in the polished thin sections. The primary mineralization is composed of disseminated marcasite-pyrrhotite-chalcopyrite±pyrite within the foliation surfaces. The secondary mineralization consists of pyrite±carbonate veins and veinlets followed by cross-cutting arsenopyrite-pyrite-chalcopyrite±tetrahedrite in carbonate±chlorite±sericite veins. The low-grade primary mineralization is the hypogene ore while high-grade secondary mineralization is formed due to supergene enrichment. Since schists were less competent than quartzites and marbles between ∼5-13 km depths, they deformed intensely during the exhumation of the massif. This deformation along foliation planes of schists provided fluid pathways for hydrothermal fluids. The spatial association of syn-tectonic dikes and gold mineralization within the foliation planes suggests that the intrusion might have played a role in mineralization. The possible age of the hydrothermal activity is interpreted as ∼75 Ma considering the youngest dike age in the massif. The mineralization occurred at ∼11 km depth and the peak temperature was ∼350℃, under brittle-ductile to brittle conditions.