Çayırbağı-Meram (Konya) yöresindeki manyezit yataklarının jeolojik ve ekonomik özelliklerinin araştırılması

Abstract

Menderes-Toros Zon'u içerisinde kalan çalışma alanında yer alan birimler; tabanda Paleozoyik üzerine diskordan olarak gelen Alt Triyas yaşlı Ardıçlı formasyonu ile başlar. Bunun üzerinde sırasıyla, Orta Triyas yaşlı Loras kireçtaşı, Berriasiyen-Alt Maastrihtiyen yaşlı Midos Tepe formasyonu uyumlu olarak yer almaktadır. Daha sonra, kireçtaşı, diyabaz, radyolarit blokları içeren serpantinit hamurlu Hatip ofiyolitli karmaşığı tektonik bindirmeli olarak bu birimler üzerine gelmiştir. Çayırbağı ofiyoliti de bölgeye itilerek gelmiş ve Hatip ofiyolitli karmaşığı üzerinde bulunmaktadır. Bütün birimlerin üzerim ise, Neojen yaşlı birimler diskordan olarak örtmektedir. Çayırbağı ofiyolitini, çalışma konusu olan manyeziti içinde bulunduran serpantinitler ile steril serpantinitler oluşturmaktadır. Manyezitli serpantinit, steril serpantinit üzerinde yer almaktadır. Bu kayaçların mikroskopik incelemelerinde iddingsit, krizotil, bastit ve serpantinleşmeden kalan olivin ile enstatit içerdikleri görülmüştür. Ayrıca bu kayaçlar içerisinde, opak minerallerden kromit ve manyetite rastlanmaktadır. Çayırbağı ofiyolitini oluşturan serpantinitlerin ilksel kayaları, yapılan incelemeler sonucunda dunit ve harzburjit olarak belirlenmiştir. Serpantinitlerin ayrışması sonucu oluşan manyezitler, kriptokristalen dokuludur. Alınan bazı örneklerin ince kesitlerinde, makroskopik olarak da gözlenen kuvarsa rastlanmaktadır. Bu kuvars manyezite göre ikincildir. Ancak manyezitlerle aynı zamanlı olarak oluşan kuvarslar da vardır. Kuvars dışında serpantin ve ikincil kalsitleşmeler gözlenmektedir. Manyezitler, birincil manyezitler ve bunları kesen ikincil manyezitler olarak ikiye ayrılmışlardır. Birincil manyezitler daha sert ve genellikle konkoidal kırılmalı iken, ikincil olanlar silis içermediklerinde daha yumuşaktır. Bir üçüncü manyezit ise, Neojen çökeller içerisinde yüzeysel koşullarda, Miyosen' de oluşmuş manyezittir. Manyezitlerin oluşumu, ofiyolitin bölgeye yerleşimi sırasında Üst Kretase sonlarında başlamış, Miyosen' de devam etmiş ve günümüzde de devam etmektedir. Ofiyolitlerin, altta bulunan karbonatlı kayaçların üzerine bindirmesiyle bir ısı artışı olmuş ve bu ısı da CO2 çıkışına neden olmuştur. Bundan başka hidrotermal ve yüzeysel kökenli C02'li sular da manyezit oluşumunda etkili olmuştur. Bu C02'i içine alan sular, serpantinitlerin içerisinde yukarı doğru tektonik kırıklar boyunca dolaşarak, serpantiniti ayrıştırmış ve Mg+2 iyonunu mobilize etmiştir. CO2 taşıyan su, mobilize olan Mg+2 iyonu ile birleşerek, büyük kırıklarda damar, değişik yönlerde gelişen küçük çatlak aralarında stokverk cevheri çökeltmiştir. Manyezitler görünüşlerine göre masif, yumrulu ve bireşik olarak ayrılmıştır. Manyezitlerin tamamı kriptokristalen olmakla birlikte, mikroskopik ölçekte yine breşik ve stokverk dokular saptanmıştır. Bölgede bulunan manyezitlerin rezervi görünür+muhtemel türden 301 137 413 ton, tenörü % 46. 12 MgO olarak belirlenmiştir.

The units Which are found within the study area in Menderes-Toros Zone begin with Lower Triassic age Ardıçlı formation which overlies the Paleozoic disconformably at the base. The overlying formations are, in turn, Middle Triassic age Loras limestone, Berriasian-Maastrichtian age Midos Tepe formation. Hatip ophiolithic complex made of limestone, diabase, radiolarian blocks with serpentinite matrix thrust over these units tectonically. Çayırbağı ophiolite which rest on Hatip ophiolithic complex is also found as a thrust block in the region. All these units are covered by Neogene age units disconformably. In the study area Lower Triassic age Ardıçlı formation and overlying Loras limestone and Midos Tepe formation, in turn, represent supratidal, shallow continental shelf, continental platform environments, and uppermost formations deposited in conditions representing continental slope and abyssal plain. Taking this into consideration the environment were observed deepened gradually from Lower Triassic to Upper Cretaceous ( Figure 1 ). This characteristics of Lower Triassic-Upper Cretaceous carbonate sequence reflect rather transgressive carbonate series. Ardıçlı İm Lores kireçtaşı ^gel seviyesi normals deniz seviyesi Midos Tepe fm. Figure 1. The deposite environments of carbonate rocks in the study area. The Lower Triassic-Upper Cretaceous carbonate sequence in the study area are made of carbonate rock components continuously comprehensive but may have been laterally discontinuous and generally deposited in continental platform. This carbonates belongs rather to Taurid Carbonate Belt, representing carbonates deposited in Atlantic Type continental edge platform. vu Hatip ophiolite complex which emplaced tectonically in the region, is in the form of a tectonic complex which consists of clay, sand, and radiolarite, peridotite, serpentinite, diabase in a mylonitized serpentinite matrix together with limestone blocks in varying ages, claystone in smaller dimensions, sandstone blocks and approximately has a 350 m thickness. The emplacement age of Hatip ophiolite complex were found to be Upper Maastrichtian by studying lower-upper boundary relations. If the blocks within the complex are taken into consideration, it was established that the formation age of Hatip ophiolite complex may have been Late Turonian-Senonian. Due to melange character and the content of the oceanic crust material such as peridotite, diabase blocks in the unit, it is believed in that the unit was formed either in trench or in subduction zone. During the subduction of the oceanic crust, complex was formed by mixing of fragments of oceanic crust and oceanic sediments like radiolarite and limestone. This complex has been thrusted to the environment in which exposed to day. Due to the thrusting matrix has been deformed, in places, drag folds has been developed and schistose appearance has been gained. Çayırbağı ophiolite which includes magnesites within the study areais seen as a nappe in the region. The unit has been formed of generally green, in places brown, serpentinized, rather fractured peridotite ( dunite, harzburgite ). Since this ophiolite include the magnesite under investigation, is important and has been studied in three different headings seperately : barren " serpentinite ( less altered serpentinite ), magnesite-bearing serpentinite ( altered serpentinite ), and silicified serpentinite. Barren Serpentinite Barren serpentinite has been exposed extensively in the study area. This unit is, in general, hard, green coloured, and has apolished appearance. Since subjected to tectonic movements has been gained a fractured structure. Is found below the magnesite-bearing serpentinite and is easily recognized by its colour, absence of magnesite or in lesser amounts. Magnesite-Bearing Serpentinite These are found on top of basement serpentinites; are yellowish brown and brown coloured, in general, are limonitized, incompetent and brittle. This serpentinites in the study area, relative to underlying barren serpentinite, is less exposed. Slicified Serpentinites This is the uppermost serpentinite consist of lateritic sections formed by the alteration of the ultrabasic rocks. The excess silica formed during the alteration infiltrates the rock through the fractures in the upper levels and sometimes make the wall rock completely silicified. So results with the completely silicified serpentinites and reddish brown serpentinites coloured by the iron-bearing minerals found in the fluids. Although may contain some magnesite these silicified formations called as "silica cap" due to their magnesite grade and existing silica is not economic. With its reddish and brownish colours this easily recognised unit, outside the silicified sections, is not hard, is friable and soft. Within the peridotitic rocks exist in Çayırbağı ophiolite chromite and, in lesser amounts are observed as opaque minerals. Another unit exposed within the study area is Middle Miocene-Pliocene age Dereköy formation. This formation begins with yellowish brown-greenish grey conglomerates at the base, towards top continuing with claystone, clayey limestone and limestone. The unit, in general, is observed at the plains and small hills and covers the underlying units discomformably. Dereköy formation is represented with fluviatile, lacustrine and partly brakish water sediments. The existence of coal in neighbouring areas, fossils in limestones, and fauna and flora associations in the terrestrial sediments are accepted as evidences of terrestrial ( fluviatile ) and lacustrine character of the deposition environment. Magnesites were began to form after the emplacement of ophiolites in the late Upper Cretaceous, and continued in Miocene even to date. Serpentinites including magnesite which is the subject of this study and barren serpentinites make up Çayırbağı ophiolite altogether. In the microscopic study of these serpentinites iddingsite, crysotile, bastite and olivine relicts result of serpentinisation together with enstatite have been observed. Besides these minerals, chromite and magnetite are found as opaque minerals in these rocks. The magnesites, which are found as a result of alteration of the serpentinites, have a cryptocrystalline texture. In thin sections of some collected samples quartz, which can be observed macroscopically, is also encountered. This quartz is secondary when correlated with magnesite. There are also secondary calcifications and serpentinisations in addition to quartz. Magnesites are classified primary and secondary which cut across the primary ones. While primary magnesites are harder with concoidal fracturing, secondary magnesites are softer due to the absence of silica. The formation of magnesites commence with the emplacement of the ophiolites (Upper Cretaceous) in the region and are also continuing to date. After the thrust of ophiolites over the underlying carbonate rocks a temperature increase is seen and this event led to the seperation of CO2. Besides this, C02- bearing waters of hydrotermal origin are also effective in magnesite formation. The waters which include this CO2 by circulating upwards along the fractures within the serpentinites alter it and mobilise Mg ion. Waters transporting CO2 combining with Mg2+ ion from veins along fractures and deposit stockwork ore in between small fractures. To correlate with Çayırbağı-Meram (Konya) magnesite some samples were also collected from Denizli (Çambaşı-Hırsızdere) sedimentary magnesites. Thin sections of these magnesites were studied and geochemical analysis were made. As a result of investigations made it was found that Denizli magnesites are also cryptocrystalline like that of Konya. However there are differences in the mode of formation together with some major oxides and trace elements ( Table 1- 2) Table 1. The ICP analyse results of magnesite samples in the study area. Al, N48- Vein magnesite samples. Anothers- Stockwerk magnesite samples. Table 2. The ICP analyse results of two samples in the Denizli ( Çambaşı- Hırsızdere ) magnesite depo site.