Kısacık (Biga metalojenik provensi, KB Türkiye) epitermal altın sisteminin cevherleşme karakteristiklerinin incelenmesi
Investigation of the mineralization characteristics of Kısacık (Biga metallogenic province, NW Turkey) epithermal gold system
Yazar: ALİ ERDEM BAKKALBAŞI
Danışman: DR. ÖĞR. ÜYESİ ZEYNEP DÖNER
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Jeoloji Mühendisliği Ana Bilim Dalı / Jeoloji Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2023
Konu: Jeoloji Mühendisliği = Geological Engineering
Dizin: Altın = Gold ; Epitermal = Epithermal ; Jeoloji = Geology ; Jeolojik inceleme = Geological survey ; Çanakkale-Biga = Çanakkale-Biga

Özet:
Biga Yarımadası (KB, Türkiye), damar tipi Pb-Zn, epitermal Au-Ag, skarn ve porfiri Cu-Mo gibi çok sayıda polimetalik tipte maden yatağını açısından zengindir. Bu cevherleşmeler esas olarak Oligo-Miyosen dönemindeki yüksek kalk-alkalen magmatizma ile ilişkilidir. Bunlardan ekonomik açıdan önemli olan Au-Ag mineralizasyonlu epitermal damarlar genellikle dasitler, andezitler ve piroklastik kayaçlar gibi volkaniklerde bulunur. Volkanik kayaçların porozitesinin yüksek olması, maruz kaldıkları hidrotermal aktivite sonucunda metalik içeriği yüksek geniş alterasyon alanları oluşmasına sebep olmuştur. Kısacık (Ayvacık-Çanakkale) volkanik kayaçlarında (tüf, altere riyolit-dasit, andezit) gözlemlenen yoğun alterasyon zonları Au cevherleşmeleri açısından önemli bir potansiyeldir. 
İnceleme alanının temelini Kazdağ Metamorfikleri oluşturmaktadır. Onları uyumsuzlukla üzerleyen Çetmi Ofiyolitik Melanjı bulunmaktadır. Bunların üzerine yine uyumsuzlukla gelen Miyosen volkanikleri (Hüseyinfakı, Arıklı ve Ayvacık) gelmektedir. Miyosen yaşlı İlyasbaşı Fm. Miyosen yaşlı volkanikler ile geçişli dokanak göstermektedir. En genç birimler ise Pliyosen yaşlı Bayramiç Fm. ve Kuvaterner yaşlı alüvyondan oluşmaktadır. Cevherleşmenin ve alterasyonun özelliklerini anlamak amacıyla mineralojik ve jeokimyasal çalışmalar yapılmıştır. 21 adet kayaç örneğinde mineralojik ve petrografik tayinler için ince-parlak kesit ve XRD çalışmaları, jeokimyasal çalışmalar için XRF (majör-iz element), ICP-MS (Au-Pt grubu) analizleri ve sıvı kapanım çalışmaları yapılmıştır. İnce kesitlerde ve XRD çalışmalarında alterasyonla ilişkili mineraller adularya, kaolin, montmorillonit, fenjit ve kuvars olarak tespit edilmiştir. Au-Pt grubu element analizlere göre altere volkaniklerin Au içeriği 0.03-21.34 ppm arasında değişim gösterirken, Ag değerleri ise 0.3-19.8 ppm arasında değişim göstermektedir. 
Cevher petrografisi çalışmaları sonucunda parajenezde altın, markazit, pirit, arsenopirit, kalkopirit, götit ve hematit tespit edilmiştir. Altın esas cevher mineralini temsil ederken, arsenopirit ve markazit ise altını taşıyan olası sülfid mineralleri olarak öne çıkmıştır. Alterasyon özelliklerini belirlemek adına, tez çalışması kapsamında hesaplanan altere volkanik majör oksit değerleri kullanılarak ve altere olmayan Ayvacık volkaniklerinin majör oksit verileri literatür çalışmalarından alınarak Alterasyon İndeksi (AI) ve Klorit-Karbonat-Pirit İndeksleri (CCPI) hesaplanmıştır. Hesaplanan değerler ile oluşturulan alterasyon diyagramlarında altere-altere olmayan volkanikler karşılaştırılmış ve klorit-pirit-serizit alterasyon yönelimi gösterdikleri tespit edilmiştir. 
Altın cevherleşmesiyle ilişkili kuvars damarlarından yapılan sıvı kapanım çalışmalarında homojenleşme sıcaklıkları Th(oC) 148.8-369.4 oC arasında değişim gösterirken tuzluluk oranları (NaCl%) 0.42-25.02 arasındadır. Farklı kökene sahip akışkanlar için sıcaklık-tuzluluk oranları kıyaslandığında cevherleşmenin hem magmatik-meteorik hem de metamorfik sıvılardan etkilendiği tespit edilmiştir. Yapılan çalışmalar sonucunda arazi gözlemleri, cevherleşme-yan kayaç ilişkisi, kuvars dokuları ve alterasyon-cevher mineralleri dikkate alındığında düşük sülfidasyon tip epitermal sistemin etkin olduğu gözükse de jeokimyasal veriler değerlendirildiğinde Kısacık altın cevherleşmesinin çok fazlı bir sisteme sahip metamorfik kökenli bir yapı olduğu ve en geç evre olarak metamorfik kaynaktaki altını tekrardan mobilize eden daha yüksek tenörlü epitermal cevherleşmenin meydana geldiği belirlenmiştir.

Abstract:
The Biga peninsula (NW, Turkey) hosts numerous polymetallic mineral deposits including skarns, porphyry Cu-Mo, vein type Pb-Zn, and epithermal Au–Ag. These mineralizations are mainly associated with widespread high-K magmatism in the Oligo-Miocene period. Economic epithermal veins with Au-Ag mineralization are generally found in volcanics such as dacites, andesites and pyroclastic rocks. The high porosity of volcanic rocks has led to the development of large alteration halos with high metallic content as a result of the hydrothermal activity. The intense alteration zones observed in the Kısacık (Ayvacık-Çanakkale) volcanic rocks (tuff, altered rhyolite-dacite, andesite) are an important potential for Au mineralizations. Kazdağ Metamorphics are the basement of the study area. The Çetmi Ophiolitic Melange uncormably overlies them and the Miocene volcanics and clastics are representing the late stage. Miocene aged İlyasbaşı formation shows transitional contact with Miocene aged volcanics. The youngest units are Pliocene Bayramiç Fm. and Quaternary aged alluvium. 
Mineralogy and geochemistry studies were carried out in order to understand the properties of mineralization and alteration. Thin-polished section, XRD, XRF major-trace element, ICP-MS Au-Pt group and fluid inclusion studies were performed on 21 rock samples. In thin sections and XRD studies, minerals associated with alteration were determined as adularia, kaolin, montmorillonite, phengite and quartz. Kaolin and adularia minerals detected in XRD studies represent a steam-heated alteration zone in epithermal systems. This zone can be seen in both high-sulphidation and low-sulphidation systems but commonly represents low-sulphidation. Especially adularia mineral is characteristic for low sulfation systems. Montmorillonite can occur in both low and high sulfidation but is usually associated with advanced argillic alteration in high-sulfidation systems. The coexistence of alteration minerals belonging to different systems indicates the existence of a multi-phase mineralization. 
On the other hand, phengite mineral represents sericite group in quartz-sericite alteration. The presence of phengite indicates that a high-sulfidation system may have worked at a higher temperature, as well as a low-sulfidation system. In high-sulfidation systems, phengite mineral is closely located with Alunite-Au associations. It also indicates a metamorphic origin. In order to determine the alteration characteristics of the Kısacık Au mineralization, 18 volcanic rock samples were taken during the field studies. The presence of unaltered, altered or mineralized rocks together with fresh bedrocks in the database, creates a more reliable database for interpretation. Since almost all of the volcanic rocks associated with mineralization are altered, the major oxide values of the unaltered volcanic rocks have been compiled from previous literature studies. In this review, the study of Günaydın (2017) on the Arıklı Ignimbrite and the database shared by Karacık (1998) on the Ayvacık volcanics were used. From these two studies, a total of 48 samples were created, 25 from the Arıklı Ignimbrite, 5 from the Ayvacık volcanics, and 18 from the altered and gold-containing volcanics made within the scope of this thesis. 
AI and CCPI values were calculated separately for each sample and these values were interpreted on the diagrams. In the alteration diagrams created according to the Al-CCPI values, it was determined that the volcanics undergoing alteration were in the chlorite-pyrite-sericite trend. This hydrothermal alteration trend is typical of the footwall of mineralizations associated with chlorite-rich highly acidic volcanics. Negative correlation was detected in the Tl-K2O diagram. Anomaly can be expected in trace elements such as Hg, Au, Ag and Tl towards the surface in epithermal system mineralizations. In the near-surface parts of the mineralization, depletion in Na can be expected, while an enrichment in K can be expected. The main reason for this is that K-Feldspars, which are alteration products, replace sodium feldspars under the influence of acidic solutions. The best example of this type of feldspar is the mineral Adularia (KAlSi3O8), which is characteristic of low sulphidation epithermal systems and was also detected in XRD results. In such low-sulfidation systems, Tl usually acts with adularia. 
Volcanic rocks outcropping around Kısacık and Baharlar villages can be divided into two groups in terms of lithology, alteration and mineralization: the first group is almost completely altered acidic volcanics, pyroclastics and tuffs; The second group is basaltic andesite, andesites, which are not associated with mineralization and generally give fresh outcrops. The mineralizations are generally associated with quartz veins that cut the porous acidic volcanics and the alteration zones created by them. Quartz veins do not show a certain direction, but they cut the volcanic rocks irregularly. It is observed more frequently in tuff and pyroclastic units and their thickness varies from 5 cm to 40-50 cm. Along with the quartz veins, another element associated with gold is the intense silica alteration of the volcanics. This silicification is sometimes accompanied by sericite and often clay minerals. In the elemental analyzes of the ICP-MS Au-Pt group, the Au content of altered volcanics varies between 0.03 and 21.34 ppm, while Ag values vary between 0.3-19.8 ppm. As a result of ore mineralogy studies, while gold, marcasite, pyrite, arsenopyrite, chalcopyrite are determined as primary stage ore minerals, goethite and hematite were determined as supergene stage. In the fluid inclusion studies carried out from quartz veins associated with gold mineralization, homogenization temperatures vary between Th(oC) 148.8-369.4 oC, while salinity ratios (NaCl%) are between 0.42-25.02. 
When salinity and homogenization temperatures are examined in microthermometric measurements made within the scope of fluid inclusion studies, it is seen that mineralization occurs in more than one phase. In the fluid inclusion fluid origin diagram, the samples are located in the metamorphic and magmatic-meteoric regions. In the Ore deposit diagram, 3 groups were detected in the Lode-Au (High-S), Epithermal and Sn-W domains. In particular, homogenization temperatures of 300 oC and above indicate that a mesothermal system is also a source of the system, apart from the epithermal system. 
Apart from this, isothermal mixing and mixing with surface waters, which show that more than one system is active, seem to be dominant in the fluid evolution trends diagram. Metamorphic waters and basement rocks theoretically form the origin of the Au source in most epithermal type mineralizations. As a result of magmatism and tectonic activity that may develop after these metamorphic fluids, Au can be mobilized again and form a new mineralization within an epithermal system. 
As a result of the studies, when the field observations, mineralization-host rock relationship, quartz textures and alteration-ore minerals are taken into account, low sulphidation type epithermal system seems to be effective, but when geochemical data are evaluated, it has been determined that the Kısacık gold mineralization has a metamorphic origin with a multi-phase system. Geochemical data and the field observations shows that higher grade epithermal mineralization occurred in the late phase and it re-mobilizes the gold from metamorphic origin.