ГЕОХИМИЯ, 2010, № 10, с. 1079-1092
MINERALOGY AND MAJOR-TRACE ELEMENT GEOCHEMISTRY OF THE HAYMANA MANGANESE MINERALIZATIONS, ANKARA, TURKEY
© 2010 A. Karakus*, B. Yavuz*, Ko?**
*Ankara University Graduate School of Natural and Applied Sciences, 06100, Tandogan, Ankara, TURKEY; e-mail: alpaykrks@gmail.com **Ankara University, Engineering Faculty Department of Geological Engineering, 06100,
Tandogan, Ankara, TURKEY Поступила в редакцию 12.12.2008 г.
Abstract—The study area comprises ^ayirli, Harapagillari and Ortabel (^HO) districts in the Haymana town 25 km SW of the Ankara city. In this study, geologic setting, mineralogical and geochemical characteristics of manganese mineralizations are examined and their origin is discussed. Data were obtained from field observations, various polished and thin section determinations and chemical analyses of 25 ore samples. Major and trace element analyses were conducted with ICP-ES and ICP-MS methods at ACME Laboratories (Canada). ^HO manganese ores are found in reddish radiolarites and partly interbedded marls of the Ankara ophi-olitic melange of lower Cretaceous-upper Senonian age. In these extremely folded rocks, manganese is observed as band and lenses. All samples are composed of pyrolusite and quartz. Circular pyrolusites around the gangue form a ring texture and radiolarite ores yield spherical sections. In addition, breccia-like texture is observed between pyrolusite and quartz. Geologic setting, mineralogical and textural data indicate an exogene environment. Major and trace element abundances and correlation among them imply that ^HO mineralizations are of hydrothermal origin and linked to the same source. Evaluation of all these data shows that ^HO manganese mineralizations are of hydrothermal type sedimentary mineralization and they were deposited in distal part of the source.
Key words: Manganese, Trace element, Major element, radiolarite, Haymana, Turkey.
INTRODUCTION
The study area comprises Çayirli, Harapa gillari and Ortabel (ÇHO) sites in Haymana 25 km SW of Ankara (Fig. 1).
There are several manganese mineralizations in the Central Anatolia particularly around Ankara. Most of these mineralizations are uneconomic occurrences. The manganese mineralizations are found in pelagic sediments of the Ankara ophiolitic melange that is known as the Ankara Mélange [1]. Mn mineralizations under investigation are one of these manganese ores. Studies conducted so far suggested various explanations for the origin of mineralization. Some workers [2—5] stated that mineralization is closely related to Tertiary andesites in the region and Mn was added to the environment by metasomatism of the lavas. Helke [6] suggested that mineralization which is alternated with radiolarites is derived from a submarine volcanism and he described the occurrence as a volcanic extrusive formation. On the basis of relation with sedimentary rocks at the base and top of the manganese deposition, Ozkoçak [7] stated that mineralization could be in hypogenetic character. All these works outlined above are the results of field observations. The most recent work on Çayirli Mn mineralization was conducted by Oygur et al. [8] and Oygur
[9]. In these works, detailed geologic maps were made and geochemical characteristics of mineralization were examined, and the mineralization was described to be a hydrothermal occurrence which was formed as a result of submarine volcanism. In the present study, first the ore microscopic features and the major and trace element contents of the mineralization were determined and then these data were used for genetic evaluations and correlation relations.
MATERIAL AND METHOD
The materials of this study are 25 ore samples of which 11 are collected from the Qayirli, 8 from the Harapa gil and 6 from the Ortabel area. For mineralogical investigations, polished sections were prepared and examined on the Nikon (Labophot-Pol) brand reflection microscope. In addition to mineralogical descriptions, XRD analyses were conducted on 7 samples. XRD analyses were carried out at the Laboratories of the Mineral Research and Exploration of Turkey (MTA). Diffractograms were obtained with Rigaku D/max-2200 Ultima+/PC XRD device using copper tube and at 40 Kv, 20 mA, 1.54059 A (CuZa1 wave length and 2°/min scanning rate. Major and trace element analyses
Fig. 1. Geological and location map of the study area (9).
were conducted with ICP-ES and ICP-MS methods at ACME Laboratories (Canada). Analyses which were performed with the Inductively Coupled Plasma Mass Spectrometry (ICP-MS) method comprise a number of 53 elements. Analyses which were carried out with the Inductively Coupled Plasma Emission Spectrometry (ICP-ES) method comprise major and trace elements. Some geostatistical methods such as correlation coefficient calculations and cluster analyses were applied to determine the geochemical behavior of major and trace elements in the samples collected from studied areas.
GEOLOGIC SETTING OF MINERALIZATION
In the study area, Mesozoic and Cenozoic units are exposed (Fig. 1). The Tertiary mélange with metamor-phic blocks comprises the basement. This is overlain with an angular unconformity by marl-bearing limestone. The base of this unit which is aged as. This ophi-
olitic mélange is made of spilite, peridotite, limestone, radiolarite and greywacke blocks and the matrix materials of serpantinite, shale and sandstone. Serpantinite and radiolarite comprise the most part of the ophiolitic mélange.
Triassic, Jurassic and Cretaceous units are described as the Ankara Mélange [1]. Granite porphyries that were emplaced cutting all these units are linked to the Central Anatolia granite plutons [13] and their age is accepted as Paleocene. Oligo-Miocene volcanites [Erol, 1954] called as the Ankara Andesites [12] unconformably overlie the older units. They are covered with Pliocene [5] lacustrine deposits that consist of limestone and marls.
Manganese mineralizations are mostly found within reddish radiolarites of the ophiolitic melange and partly in marls which are interlayered with radiolarites within the of lower Cretaceous-upper Senonian Ankara Mélange which is one of the most important ophiolitic se-
ries in Turkey. In these extremely folded rocks, the thickness of manganese band and lenses is 1—20 mm (Fig. 2a). In comparison to the Ortabel and Harapa gil-lari areas, thickness is higher in Qayirli.
ORE MICROSCOPY STUDIES
Ore characteristics were examined with numerous polished and thin sections. It was determined that mineralization in three areas has similar paragenetic and structure-texture features. All samples are composed of pyro-lusite and quartz which is also supported with XRD analyses. Pyrolusite is observed around the gangue minerals and as filling the spaces between them. In addition, pyrolusite is also found as veinlets of varying thickness forming by filling of fractures and fissures within the gangue (Fig. 2b and 2c). Pyrolusites show anhedral and subhe-dral sections. Euhedral grains display triangular, rectangular and square (some are lenticular) shapes (Fig. 2d and 2e). Pyrolusite grains within the gangue show needle, flake and wedge-shaped sections (Fig. 2f and 2g). Circular pyrolusites square (some are lenticular) shapes (Fig. 2d and 2e). Pyrolusite grains within the gangue show needle, flake and wedge-shaped sections (Fig. 2fand 2g). Circular pyrolusites around the gangue form ring texture (ring-forming) (Fig. 2h) and completely mineralized pyrolusites display spherical structures (Fig. 2i). Breccia like texture between pyrolusite and quartz is also common (Fig. 2j). Parallel shrinkage fractures are developed in most of pyrolusites. Some openings are observed in areas offracture development (Fig. 2k).
MAJOR AND TRACE ELEMENT
GEOCHEMISTRY OF MINERALIZATION
Major and trace element contents of 25 samples collected from the Qayirli, Harapa gillari and Ortabel areas were used in determining of mineralization type. Then geochemical behavior of these elements was examined and the element groups showing similar characteristics were determined.
EVALUATIONS ON THE ORIGIN
Major element contents of ore samples are given in Table 1. Fe, Mn, Al, Si and Ti concentrations are helpful for evaluations on the origin.
For example, hydrothermal deposits associated with the active ocean spreading centers display low Fe/Mn ratios [14—16]. According to Nicholson [15], Fe-Mn concentrations in exhalative sedimentary deposits vary in a wide range (0.1 < Fe/Mn < 10) reflecting a strong Fe-Mn fractionation and this ratio in hydrogenetic deposits is around 1. Fe/Mn ratios of samples from the study area change in a wide interval (0.005—0.314). Such a range indicates that mineralization is not hydro-genetic but could be a hydrothermal type. In their detailed geochemical study on the Tokoro manganese oxide deposits in Japan, Choi and Hariya [16] describe the
deposit as the hydrothermal type and found the Fe/Mn ratio to be 0.017—6.41. Submarine hydrothermal manganese deposits have low Fe/Mn ratios. In early stages of deposition, Fe/Mn ratios are higher [17] Fe-Mn deposits are generally formed around the center of active submarine hydrothermal sites while manganese oxide deposits are mostly developed in distal parts of the center [18; 16]. In ore microscopy investigations, no iron mineral was observed. Low Fe/Mn ratios and manganese oxide (pyrolusite) type deposits are indicative of distal parts of the spreading center. It is known that iron is the first dissolved element and manganese could be in solution for a long time and also pH required for separation of iron and manganese should change slowly and gradually [19; 20].
Like Fe and Mn, Al and Ti contents could also be used to evaluate the origin of mineralization. These two elements are abundantly found in sedimentary formations. High Al and Ti contents may indicate the sedimentary contribution to mineralization [17, 21, 22, 15, 16]. Fo
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