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- MakaleAçık Erişim2020Nature of clays in late cretaceous dacitic rocks in the eastern sakarya zone (Ne turkey): A geochemical and isotopic approach
Sipahi, Ferkan; Gücer, Mehmet Ali; Sadiklar, Münür Burhan
Late Cretaceous felsic rocks are common in the eastern Pontides (NE Turkey). These rocks developed as an island arc from the Jurassic to the Miocene; they also host numerous volcanogenic massive sulfide deposits. The Late Cretaceous dacites that outcrop around Zigana Mountain (Gümüşhane, NE Turkey) were exposed to intensive hydrothermal alteration. Widespread hydrothermal alteration of Late Cretaceous dacite in Zigana Mountain has led to the formation of well-developed clay minerals. Their main alteration products are sericite, chlorite, and carbonates (ankerite and calcite). The clay minerals identified by X-ray diffraction and differential thermal analysis include illite, chlorite, small amounts of kaolinite, and smectite. The polytype of illite is 2M1. Illites formed as a result of hydrothermal alteration of feldspars; they are also Fe-and Mg-poor. Chlorite is characterized by decreasing Fe/(Fe+ Mg) ratio with increasing alteration grade and has a trioctahedral structure. Chlorite geothermometer calculations (100–300°C) reflect the activities of hydrothermal solutions. Chlorite forms in more alkaline conditions compared with illite, as its formation is associated with the presence of carbonates. Oxygen and hydrogen stable isotope values, K-Ar dating of illites, and textural and chemical evidence suggest that clays might have formed mainly by alteration of minerals in dacitic rocks with hydrothermal fluids of magmatic origin during the Campanian under acidic–weak alkaline conditions.
- Yüksek Lisans TeziAçık Erişim2013Kıbletepe (Araklı, Trabzon) yöresindeki volkanik kayaçların petrografik, jeokimyasal ve maden yatakları açısından incelenmesi
Sema Akyürek
Doğu Karadeniz Bölgesi'nde, Kıbletepe (Araklı, Trabzon) ve çevresindeki volkanik kayaçlar Geç Kretase yaşlı olup, tabanda bazalt, andezit ve piroklastları, bunların üstünde bulunan dasit, riyolit ve piroklastları ile bunları kesen bazalt ve andezit dayklarından oluşmaktadır. Çalışma alanının tabanını oluşturan bazalt, andezit ve piroklastlarının üst seviyelerinde kireçtaşı tabakaları bulunmaktadır. Bu birimleri yer yer Kuvaterner yaşlı yamaç molozları örtmektedir.Geç Kretase yaşlı volkanik kayaçlar genel olarak ayrışmış olup, Zn-Cu cevherleşmesi ve cevherleşmeyle ilişkili alterasyonlar asidik piroklastik kayaçlar içerisinde izlenmektedir. Dasitik ve riyolitik kayaçlar hyalo-porfirik ve sferulitik dokuda olup, başlıca plajiyoklas, kuvars ve hornblendden oluşmaktadır. Cevher ağsal, saçınımlı ve breşik yapıda bulunmaktadır. Pirit, sfalerit, kalkopirit ve daha az oranda fahlerz, dijenit, kovellin ve malahit cevher minerallerini oluşturmaktadır. Gang mineralleri ise kalsit, kuvars ve kil mineralleridir. Sfalerit ile kalkopirit arasında ayrılım dokusu görülmektedir.Cevherin içinde bulunduğu kayaçlar toleyitik-geçiş özelliğe sahip olup, yüksek BİYE (büyük iyon yarıçaplı elementler) ve düşük YÇAE (yüksek çekim alanlı elementler) içerikleri ve yüksek BİYE/YÇAE oranları ile yitim ilişkili kayaçların jeokimyasal özelliğini yansıtmaktadır. Cevherleşmelerin etrafındaki yan kayaçlarda genellikle serizitleşme, silisleşme, killeşme ve daha az karbonatlaşma, kloritleşme, hematitleşme ve limonitleşme türü alterasyonlar izlenmektedir. Kil mineralleri olarak illit, kaolinit, klorit, simektit ve az oranda da illit/simektit aratabakalısı belirlenmiştir.Sonuç olarak, Kıbletepe'deki volkanitler, Doğu Karadeniz Bölgesi'ndeki masif sülfit yataklarının gösterdiği ayrışma özelliklerine benzer ayrışmalar göstermekte ve bunlardaki cevherleşme Doğu Karadeniz ada yayı volkanizmasına bağlı olarak gelişen hidrotermal kökenli sıvılarla ilişkilidir.Anahtar Kelimeler: Geç Kretase, Hidrotermal Alterasyon, Kıbletepe, Masif Sülfit, Volkanitler
- MakaleYalnız künye2010The Alteration Mineralogy and Mass Change of the Zigana (Gumushane) Volcanics of NE Turkey
Sipahi, Ferkan; Sadiklar, M. Burhan
The Late Cretaceous volcanic rocks around Zigana Mountain (Gumushane) in the eastern Black Sea metallogenic province in NE Turkey show intensive hydrothermal alteration but less weathering alteration. The basement of the study area is formed by Late Cretaceous basalt, andesite and their pyroclastics. These rocks are overlain by dacitic rocks of the same age, namely Dacite-I and Dacite-II. These volcanic rocks are bimodal in character and have developed in a volcanic arc environment. The volcanic rocks in the study area have been altered to the sericite/illite-chlorite facieses, and contain sericite/illite, chlorite, quartz, carbonate minerals (ankerite and calcite), iron-oxide, and rare kaolinite, smectite and epidote as the products of alteration. Sericitization/illitization is the most common type of hydrothermal alteration associated with these volcanics, and chloritization is the most common alteration type after illitization; pyritisation is seen in all volcanics, and is the most common in dacites. In some fields limonitisation is occasionally present. Epidotization is rare, and especially seen in basalt and andesite. Isocon analysis was undertaken to estimate the mass gains and losses of the Zigana Volcanics as a result of hydrothermal alteration. In general terms, the results shows that, basalt and andesite have 2-61% mass gain, Dacite-I 71% mass gain and 42 % mass loss, and Dacite-II 44% mass gain and 32% mass loss. Namely, both mass gain and mass loss occurred in the volcanics during the hydrothermal alteration of the parent materials. From less altered rock to highly altered rock there was an increase in illite-chlorite-kaolinite whereas there was a decrease in carbonate minerals. In the volcanics, fluids which cause sericitization and chloritization did not increase metals like Cu, Pb and Zn and, in fact, it can be said that these fluids are poor in point of these metals. This also shows that the metals developed under different hydrothermal conditions.