Balıkesir-Dursunbey skarn yataklarının jeolojik, mineralojik ve jeokimyasal özellikleri
Geological, mineralogical and geochemical characteristics of the Balikesir-Dursunbey skarn deposits
Yazar: EMRE İSTANBULLU
Danışman: DOÇ. DR. MUSTAFA KUMRAL ; DOÇ. DR. MURAT BUDAKOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2013
Konu: Jeoloji Mühendisliği = Geological Engineering
Dizin: Jeokimya = Geochemistry ; Jeoloji = Geology ; Skarn = Skarn ; Skarn zonu = Skarn zone

Özet:
Bu çalışma Dursunbey (Balıkesir) ilçesinin doğusunda yer alan Tersiyer yaşlı Çataldağ Graniti ile Mesozoyik Kayacıklar Kireçtaşı dokanağı boyunca gelişmiş kontak metasomatik skarn zonlarının oluşum ve kökenini belirlemek amacıyla yapılmıştır.İnceleme alanındaki birimler stratigrafik olarak tabandan itibaren Paleozoyik Kocadere Metamorfitleri, Mesozoyik Kayacıklar Kireçtaşları, Üst Kretase renkli melanj ve Tersiyer Çataldağ Graniti ile temsil edilmektedir. Çalışma alanında melanjın yerleşmesi esnasında gerçekleşen şariyaja bağlı olarak oluşan ters ve doğrultu atımlı faylar genç tektonizmaya bağlıdır. Bununla birlikte bölgenin yükselimi sırasında kazanılmış düşey faylar gözlenmektedir. Kuzeydoğu-güneybatı uzanımlı en büyük bindirme fayı Kayacıklar Kireçtaşları ile renkli melanjın dokanağını oluşturmaktadır. Bu nedenle melanjın kireçtaşları üzerine bindirme ile itildiği anlaşılmaktadır.Bölgenin doğusunda yer alan Çataldağ Graniti monzogranit-granodiyorit bileşimli, subalkalen ve kalk-alkalen karakterli, I-S tipi bir plutondur. Tersiyer yaşlı Çataldağ Graniti sokulumu neticesinde çevre kayaçlarda kontakt metamorfizmaya neden olmuştur. Manastır Tepe'nin kuzeybatı ve güneydoğusunda karbonatlı kayaçlar içerisinde gelişen Fe, Cu cevherleşmeleri kontak metasomatik niteliktedir. Manastır Tepe civarındaki cevherleşmeler düzensiz oluşumlar şeklinde olup granit ile mermer veya granit ile skarn mineralleri arasındaki dokanak geçişleri keskindir. Cevherleşmeler; granit içerisinde, granit ile mermer arasında ve mermer içersinde düzenli zonlanmalar/bantlaşmalar ve yer yer genişliği birkaç metreyi bulan düzensiz damarlar şeklinde oluşmuştur. Skarn olarak nitelendirilen bu oluşumların metasomatik akışkanlarının evrimi ve jeokimyasal özelliklerini belirlemeye yönelik mineraloji ve petrografi, major ve iz element analizleri yapılarak şu sonuçlara ulaşılmıştır.Çataldağ Graniti'ne ait örneklerin cevher mikroskopisi incelemelerinde metalik fazların >%1 civarında olduğu ve başlıca magnetit, hematit, limonit ve götitten oluştuğu tespit edilmiştir. Gang olarak pirit, kalkopirit ve zirkona rastlanmıştır. Martitleşmeye uğrayan magnetitler, yaygın magnetit-hematit dönüşümü ve limonitleşme birimdeki alterasyonun önemli göstergeleridir. Bununla birlikte Çataldağ Graniti'ne ait numunelerde Cu minerallerine rastlanmamıştır.Çataldağ Graniti'ne ait örneklerin major oksit değişimleri Harker diyagramlarında incelendiğinde SiO2 artıştı ile Fe2O3, MgO, CaO ve MnO konsantrasyonlarının azaldığı, Al2O3, Na2O, K2O, Ti2O, P2O5 konsantrasyonlarının arttığı gözlenir. Skarn zonlarından alınan örneklerde CaO bileşimindeki artış karbonatlı kayaçlarla etkileşime, MgO ve MnO bileşimindeki artış ise kontak metasomatizma varlığına işaret etmektedir. TiO2-Zr değişim diyagramı Fe-tipi, Rb-Rb/Nb değişim diyagramı tüm skarn oluşumlarına, Rb/Sr-Zr değişim diyagramı ise Fe-Cu-Zn tipi skarn oluşumlarına işaret etmektedir. Kayacıklar Kireçtaşlarına ait TiO2-SiO2/Al2O3, SiO2-Ce, Al2O3-Ce ve TiO2-Ce değişim diyagramları ise net bir ilişki sergilememekle birlikte karbonat çözülümünün Al ve Ce mobilitesine etki edebilecek sıcaklıklarda gerçekleşmediğini göstermektedir.Skarn zonundan alınan cevher örnekleri %4,52-8,22 SiO2, %41,04-80,29 Fe2O3 içeriğine sahiptir. Örnekler 1042-2551 ppm arasında değişen kuvvetli Cu anomalisi sergilemektedir. 259 A örneği 8840 ppm S ve 1918 ppm Zn anomalisi ile dikkat çekmektedir. Cevher numunelerindeki diğer önemli anomaliler ise Co (254 ppm) ve W (586 ppm) olarak tespit edilmiştir.

Abstract:
The aim of this work is to determine the style of occurrence and origin of contact metasomatic skarn zones which occur along the boundary between the Tertiary Çataldağ Granite and Mesozoic Kayacıklar Limestone exposing at east of the Dursunbey town (Balıkesir).The stratigraphy of the study area is characterized by these following units; Paleozoic metamorphic rocks (Kocadere Metamorfitleri), Mesozoic carbonate rocks (Kayacıklar Kireçtaşı), Upper Cretaceous tectonic units (Renkli Melanj) and Tertiary Çataldağ Granite.Paleozoic metamorphic rocks, the stratigraphic base, are mainly consist of muscovite-quartzite, quartz-albite-sericite-clorite schist, quartz-albite-muscovite schist, calc schist and biotite schist. Due to the intensive mechanical deformation large shear zones and joint systems are formed in this unit. In Tokmaklı Tepe region iron minerals, brought by the iron rich hydrothermal fluids, fill the joint systems and crack zones. On the east, near Manastır Tepe and on the west, near Tokmaklı Tepe regions the carbonate content of these rocks progressively increase and the formation reveals a petrographic transition into Kayacıklar Limestone.Kayacıklar Limestone, Jura-Early Cretaceous crystalized carbonate rocks are white-cream and gray in color and approximately 400-500 meters in thickness. The bedding in lower levels is mainly thin-medium whereas in high levels it gets thicker and more massive. Also the crystal size gets coarser towards the Çataldağ Granite. Due to the high tension and compression tectonic activities large thrust faults and fold systems are common in the study area. The NE-SW trending thrust fault creates the tectonic contact zone between carbonates and mélange. This contact zone suggests that the mélange has been pushed over the carbonate rock via faulting.Upper Cretaceous tectonic units (Renkli Melanj) mainly consist of radiolarite, mudstone, serpentine, gabbro, dunite and harzburgite. Due to the overlapping tectonism, rocks in this unit don?t show primal relations. The different lithologies within the unit have tectonic contact zones. Gabbro and serpentine are both dark green, green, green-white, green-black in color and contain calcite minerals in crack fillings. Peridotites and primitive preserved olivines contain chromite and iron-oxide fillings. Carbonate and dolomite blocks within the melange also contain thin coal layers.According to K-Ar cooling dating, the age of Çataldağ Granite is determined as Early Miocene-Oligo Miocene (21,2-25,9 m.y). On the outer zones between Kayacıklar Limestone boundary and the granite-granodiorite reveal significant foliation. The formation has offently cut by aplitic and pegmatite dikes which are the products of hydrothermal stage.In NW and SE of Manastır Tepe region, along the boundary between Çataldağ Granite and Kayacıklar Limestone contact metasomatic skarn zones with Fe-Cu rich minerals were formed. These mineralisations tend to occur in irregular shapes. The boundaries between granite-marble and granite-skarn minerals generally display sharp transitions. The evolution of skarn zones took place inside granite, on the granite-marble contacts and inside marbles as zones/bands. The width of these zones can reach several meters. Eventhough magnetite is formed as the primal mineral, due to intense alteration it turns into hematite near the surface.Ore microscopy involves not only the identification of individual mineral grains but also the interpretation of ore mineral textures, the relationship between grains. Ore mineral textures may provide information on process of initial ore deposition, post-depositional re-equilibriation or metamorphism, deformation, annealing and meteoric weathering. Better mineral characterisation is required for reliable and quantitative characterisation of iron ore sources. Studying mineral liberation of hematite and magnetite is important to predict iron extraction behaviour. Therefore polished sections of 8 samples from study area were prepared.The ore microscopy studies of Kayacıklar Limestone samples show that the limestones contain pyrite in calcic matrix with approximately <5 µ in grain-size. On the other hand marble samples contain monozite, ilmenite and Fe-oxihidroxides (<20 µ) in silisic matrix.Highly altered samples of Çataldağ Granite are composed of pyrite, zircon, ilmenite and monozite in silisic and silicate matrix. The metallic phases within these samples are nearly 1% in volume. Less altered samples contain magnetite in grain-size of 40-50 µ within the silisic matrix. Magnetites made of <1% of total volume of the samples. In addition, it has seen that magnetites were oxidized and partialy transform into limonite.The granitic-granodioritic samples from skarn zones contain larger amounts of metallic phases such as magnetite, hematite, limonite, goethite with silisic-silicate gang minerals and trace amounts of pyrite. Most of the metallic phase consist of magnetites. Due to oxidation of hematite prismatic magnetites were formed. Although rocks collected from skarn zones have high Cu content, Cu-minerals couldn?t be detected under microscopic studies.Skarn deposits occur throughout the world and have been mined for a varity of elements including Fe, W, Cu, Pb, Zn, Mo, Ag, Au, U, REE, B and Sn. Skarns can occur on all continents and in rocks of almost all ages. Skarns can form during regional and contact metamorphism and from a variety of metasomatic processes involving fluids of magmatic, metamorphic, meteoric or marine origin. Therefore understanding the mineralogical and geochemical characteristics of skarn formation is critical for determination of origin and type of skarn deposit.In order to determine the geochemical features of the Balıkesir-Dursunbey skarn deposits major oxide and trace element analysis of 29 samples collected from the study area has been done. Harker variation diagrams are commonly used for correlation of major oxides for fractional cyristallisation, partial melting, magma mixing and crustal contamination interpretations.The SiO2 content of Çataldağ Granite varies between 38,9-69,4%. Major oxide Harker variation diagrams for Çataldağ Granite indicate that the Fe2O3, MgO, CaO and MnO concentrations tend to decrease with increasing SiO2 content. On the other hand Al2O3, Na2O, K2O, Ti2O, P2O5 concentrations show positive correlation with increasing SiO2 content. Higher CaO content of Manastır Tepe skarn zone samples indicates the reaction with host carbonate rocks. Furthermore, the increase in MgO and MnO contents confirm that the contact metasomatic processes have taken place.The Çataldağ Granite with monzogranite-granodiorite composition (according to QAP diagram) is a sub-alkaline (according to TAS diagram), calc-alkaline (according to AFM diagram) and peraluminum I-S type pluton. Determination of I-S type of Çataldağ Granite is controversional. Therefore P2O5 and Pb behaviors against SiO2 content have to be compaired. According to this comparison P2O5 content tends to increase whereas Pb content tends to decrease with SiO2 content. This behavior suggests that Çataldağ Granite shows S-type characteristics more dominantly.Trace elements, like major oxides, can be used to determine fractional crystallisation processes and the controlling factors of these processes. Trace elements like Nb, Zr, Y, Th and Hf are important indicators of magmatic differentiation stages. Because these elements penetrate both major rock forming minerals and accessory minerals.Trace element behavoirs like major oxides change towards the skarn zones. Harker variation diagrams of trace elements show that W, Zn and Nb contents tend to decrease with increasing SiO2 content. On the other hand Y, S, Ni don?t show a correlation whereas Ba, Sr and Rb contents show positive correlations with SiO2.The fractionation degree of granitic rocks is an important parameter to determine the skarn mineralisation type. It is known that Fe-type skarns have high Sc and low Rb contents. V and Ni, like Rb, tend to decrease during magmatic differantion. The high Rb and low V-Ni contents of Çataldağ Granite indicate that the pluton was formed in later stages of magmatic differentiation.TiO2-Zr, Rb-Rb/Nb and Rb/Sr-Zr variation diagrams can be also used to determine the skarn types. TiO2-Zr diagram indicates Fe-type, Rb-Rb/Nb diagram indicates all skarn types and Rb/Sr-Zr variation diagram indicates Fe-Cu-Zn type skarns.The SiO2 content of Kayacıklar Limestones and marbels varies between 0.07-2,78%. The major oxide vs. SiO2 variation diagrams reveal positive correlations with Fe2O3, Al2O3 ve K2O contents. The positive correlation in the Al2O3-SiO2 variation diagram indicates that the silica content of carbonate rocks is consistant with a detrital source. Morever it shows that the passif trace element enrichment is related to hydrothermal activities.TiO2-SiO2/Al2O3, SiO2-Ce, Al2O3-Ce and TiO2-Ce variation diagrams help to determine the immobile or least-mobile elements in the system. These variation diagrams of Kayacıklar Limestone show that the carbonate dissolution never reached to significant temperatures which would effect the Al and Ce mobility.The analysis performed on skarn zone ore samples show that the SiO2 content vary between 4,52-8,22% and Fe2O3 content vary between 41,04-80,29 %. The samples also show a strong Cu-anomaly (1042-2551 ppm). Sample 259 A shows S-anomaly (8840 ppm) and Zn-anomaly (1918 ppm). Co (254 ppm) and W-anomalies (586 ppm) are also detected in ore samples. In addition to these enrichments Mo, Ni, Sn, Zr, Rb, Pb and Ag contents are also at important levels.