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Uz. Bektas ¹, Fahri Esenli ¹, Senel Ozdamar ¹, Vildan Esenli ¹, Fikret Suner ¹

Affiliations
1 Istanbul Technical University, Department of Geology, Maslak, 80626, Istanbul, TR

Abstract

The geological and chemical compositional heterogeneties of the two different types of bentonite occurrence, from the Hoylu and Caltumar areas in Fatsa of Ordu province (NE Turkey), were discussed in terms of silica polymorph structure The Hoylu occurrence was formed by means of in situ alteration, the Caltumar bentonite was deposited within a volcano-sedimentary sequence and it has undergone diagenetic process The samples of both areas contain smectite and opal (cristobalite/tndymite) as the main minerals Feldspar, quartz and calcite are the other minerals observed in the Caltumar samples while the latter two minerals are not observed in the Hoylu samples The cristobahtcs in Caltumar samples have strongly ordered microstructure and high crystalhnity The d-spacings of 101 line (4A band) of these enstobahtes are lower than 4 07A and these silica polymorphs were identified as opal C But the opals from the Hoylu samples have disordered microstructure and probably rich in trydimite layers The d values of 4A band of these opal-CT are higher than 4 08 A.

Keywords

Structural ordering, Bentonite, Opal-C Opal-CT, Silica polymorphs, Ordu Provinces, NE Turkey.

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Fikret Suner ¹, Fahri Esenli ¹, Bektas Uz ¹, Vildan Esenli ¹, A. Haydar Gultekin ¹

Affiliations
1 Istanbul Technical University, Department of Geology, 80626, Maslak, Istanbul, TR

Abstract

Pattern of REE distribution in various types of magnesite ore occurring within the Late Cretaceous ultramafics in Orhaneli Region (Western Anatolia) were studied to interpret their genetic significance. The samples were classified into three different groups viz. massive, lentiform and pignolite or stockwork. Individual groups exhibit distinctly different REE distribution pattern with variable Eu, Ce and Yb anomalies. Three types of REE distribution patterns are recognizable with the following characteristics: (1) high LREE/HREE ratios without having Ce and Eu anomalies, (2) similar LREE and HREE abundance with uncertain positive and negative Eu and Ce anomalies, and (3) low REE abundance with markedly positive Eu, negative Ce and slightly negative Yb anomalies. It is postulated that the redox conditions in the primary mineral formation system was subjected to change and as a result, subsequent mobilization followed by recrystallization took place in the formation of primary magnesite minerals. Although a low temperature environment is indicated for magnesite formation, it is possible that REE-Poor solutions derived from the fluid-Rock interaction had caused mobilization and later recrystallization of magnesite ore.

Keywords

Geochemistry, Magnesite, Massive, Lentiform, Pignolite, Stockwork, Sparry, Rare Earth Elements, Turkey.

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