Yurdal GENÇ, M. Tekin YÜRÜR

Savcılıebeyit (Kaman-Kırşehir) Altın Cevherleşmesi ve Cevherleşmenin Orta Anadolu’nun (Türkiye) Çarpışma Sonrası Yükselme ve Genleşme Tektoniği ile Olan Kökensel Ilişkisi

Orta Anadolu’da altın aramaları son on yılda artmış ve önemli potansiyel altın cevherleşmeleri keşfedilmiştir. Bölgede, metamorfik ve granitik kayaçlar içinde önemli altın bulguları batıda Savcılıebeyit ve Terziali (Kırşehir), orta kesimlerde Himmetdede ve Mahmatlar (Kayseri), Akçataş (Nevşehir), ve güneydoğuda Gümüşler (Niğde) cevherleşmeleridir. Savcılıebeyit altın cevherleşmesi daha çok altınlı kuvars damarlarında görülmekte ve Orta-Batı Anadolu’da metamorfik kayaçlar içinde keşfedilen ilk altın zenginleşmesidir. Bu damarlar Kırşehir’in 60 km batısındaki Cefalıkdağ-Baranadağ granit-migmatit domunun güneydoğu eteklerinde bulunmaktadırlar. Bu çalışmada bu altınlı kuvars damarlarının jeolojik ve yapısal ön çalışmaları sunulmuştur.İnceleme alanı, Senozoyik çökellerle örtülü ve çoğunlukla yüksek dereceli metamorfik ve derinlik kayaçlarının yeraldığı Paleozoyik-Mezozoyik Kırşehir Masifi içinde yer almaktadır. Altınlı kuvars damarları migmatitler, migmatitik gnayslar, gnays-şist-mermer ardalanmaları, kalk-silikatik gnayslar ve mermerler içinde bulunmaktadırlar. Kuvars damarları metamorfik yan kayaçların yapraklanma ve önemli litolojik düzlemleriye uyumsuz olup damarların yankayaçlarla dokanakları keskindir. Damarlar, tek veya damar sistemleri şeklinde gözlenmekte olup, devamlılıkları doğrultu yönünde 2 km ye, eğim yönünde ise en az 200 m ye ulaşmaktadır. Damar kalınlıkları birkaç mm den 2 metreye kadar değişmektedir. Altınlı kuvars damarları başlıca kuvars, arsenopirit, pirit ve ikincil hematit ve limonitten oluşmaktadır. Diğer yaygın mineraller kalsit, muskovit, biyotit, klorit ve epidottur. Damarlar içinde altının dağılımı düzensiz olup damarların sadece oksitlenmiş, hematit ve limonitçe zengin yüzeye yakın kesimlerinde yüksek altın değerleri elde edilmektedir.. Kuvars damarlardaki sıvı kapanımlarının homojenleşme sıcaklıkları 160° C’den 400° C’nin üzerinde geniş bir aralıkta dağılım göstermektedir. Sıvı kapanımları genelde karbon dioksitçe zengin olup yüksek tuz içeriklidirler (% 20-33 NaCl eşdeğeri). Altınlı kuvars damarları, metal içeriği, yan kayaç alterasyonu, mineraloji, oluşum koşulları ve yapısal kontrol açısından orojenik altın yatakları ile benzer özelliklere sahiptir. Damarların migmatitlerle, yüksek dereceli metamorfik kayaçlar ve granitoidlerle olan mekânsal birlikteliği bunların oluşumunun Orta Anadolu’daki metamorfizma, yükselme ve/veya migmatitik domlaşma ve granitoid yerleşimi ile ilgili olduğunu ifade etmektedir.

Savcılıebeyit (Kaman-Kırşehir) Gold Mineralization and Its Genetic Relationship With Post-Collisional Exhumation and Extensional Tectonics in Central Anatolia, Turkey

Gold exploration works in central Anatolia, Turkey, were intensified during the last decade, and potentially important gold mineralizations were discovered. In the region, important gold discoveries hosted by metamorphic and granitic rocks are, in the west, Savcılıebeyit and Terziali (Kırşehir), in the middle part, Himmetdede and Mahmatlar (Kayseri), Akçataş (Nevşehir), and at the southeast, Gümüşler (Niğde) mineralizations. The Savcılı gold mineralization consists mainly of gold-quartz veins, and is the first discovered gold enrichment hosted by metamorphic rocks of west-central Anatolia. These veins are situated at the southeastern margin of the Cefalıkdağ-Baranadağ granite-migmatite dome, at 60 km west of the city of Kırşehir. In this study, preliminary results of geological and structural investigations of the gold-quartz veins are presented. The study area is part of the Palaeozoic-Mesozoic Kırşehir Massif that comprises mainly high-grade metamorphic and plutonic rocks covered by Cenozoic sediments. The gold-quartz veins are hosted by migmatite, migmatitic gneiss, gneiss-schist-marble intercalations, calc-silicate gneiss and marble. Quartz veins are discordant with respect to the foliation and major lithologic boundaries, and have sharp contacts with the enclosing metamorphic wall rocks. Veins occur as single or composite, relatively continuous veins that are up to about 2 km long and extend for at least 200 m down dip. Their thickness ranges from a few millimetres to two metres. The gold-quartz veins consist mainly of quartz, arsenopyrite, pyrite and secondary haematite and limonite. Other common minerals in the veins are calcite, muscovite, biotite, chlorite and epidote. The distribution of gold is erratic, and only weathered, haematite- and limonite-rich parts of the veins near the surface consistently display higher gold contents. Homogenisation temperatures obtained from fluid inclusions in the quartz vein have a wide range, from 160˚C to well above 400˚C. The fluid inclusions are generally rich in carbon dioxide and also have high salinities (20-33 % NaCl equivalent). The gold-quartz veins have many similarities to orogenic gold deposits in terms of metal associations, wall-rock alteration assemblages, mineralogy, formation conditions and structural control. The spatial association of the veins with migmatites, high-grade metamorphic rocks and granitoids suggests an origin related to metamorphism, uplift and/or migmatite doming and granitoid emplacement in central Anatolia.

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