DBPapers
DOI: 10.5593/SGEM2015/B11/S1.036

MINERALOGICAL - PETROGRAPHIC AND GEOCHEMICAL INVESTIGATION OF CHROMITE DEPOSITS ASSOCIATED WITH KAYSERI (PINARBASI) OPHIOLITES

A. Sahinoglu, I. Copuroglu, B. Til
Tuesday 4 August 2015 by Libadmin2015

References: 15th International Multidisciplinary Scientific GeoConference SGEM 2015, www.sgem.org, SGEM2015 Conference Proceedings, ISBN 978-619-7105-31-5 / ISSN 1314-2704, June 18-24, 2015, Book1 Vol. 1, 283-290 pp

ABSTRACT
The ophiolite of Pinarbasi covers an approximate area of 500 km2 in the Kayseri-Pinarbasi area, South of the Central Anatolia Region and in the middle section of the Eastern Taurus Mountains. The rocks in this region consist of magmatic, metamorphic and sedimentary blocks enclosed within ophiolitic melanges and serpentinites of Upper Campanian - Maastrichtian age. The magmatic rocks within the melange are serpentinized harzburgite, tectonic dunite, gabroic cumulates, diabase dikes and volcanic rocks. Metamorphic rocks are represented with amphibolites. Sedimentary rocks mostly consist of volcanic sandstone, radiolaritine and shale.
The ophiolites that surface in the vicinity of Kilicmehmet village that is the study area, consist of serpentinized harzburgite, diabase dikes, gabbro with olivine content, listvenites and serpentinites. Dunites and harzburgite in the area are observed to be serpentinized and exhibit sieve texture. Diabases on the other hand are holocrystalline granular textured, consist of plagioclase, pyroxene, low rates of amphibole and opaque minerals and exhibit subophitic texture. Gabbros have holocrystalline-hypidiomorph granular texture and are formed of 68% plagioclase (labrador), 22% clinopyroxene and 6% olivine.
In this region ophiolite-based chromite mineralization are usually observed to be in banded form. Chromite bands are observed to be regular and in parallel zones. Ore-bearing zones stretch in N 10°- 30° D direction and are sloped almost perpendicularly to SE. Ore-bearing zones exhibit thicknesses between 1 and 7 meters, direction lengths between 65 and 150 meters and slope lengths between 50 and 100 meters. Grates of chromites vary between 12.25% and 28.95%. Currently, chromite production activities continue in the region.
In consequence of the interpretation and evaluation of the ratios calculated with trace element (ppm) and oxide % values obtained from chemical analyses, microprobe and SEM analyses, the determinations below were made.
The average Cr2O3, Al2O3 and MgO contents of chromite samples are 22.21%, 6.03% and 22.56% respectively. The banded form of the examined chromites explains the relatively low rates of Cr2O3, Al2O3 and MgO. With the % Fe2O3, Al2O3 and Cr2O3 values obtained from the analysis of chromite minerals, it was determined that while 7 of the samples fall into the ferrochromite area, one sample falls into the chromemagnetite area of Stevens’ triangular diagram that separates between chromemagnetite, ferrospinel, ferrochromite, chromospinel and aluminum magnetite. The interpretation of the 100Cr/(Cr + Al) and 100Mg/(Mg+Fe+2) values found in chemical analyses shows that none of the samples were in the stratiform and podiform chromite area. TiO2 values vary between 0.02% and 0.92%. According to these values, ophiolitic-stratiform chromite separation of chromite minerals was made on the TiO2-Cr2O3 diagram, and chromite minerals were found to be in the ophiolitic chromite area. In addition, since the Cr/Fe rates of the chromites in the study area are between 0.67 and 3.17, and their average Cr ratio is 2.03, it is considered that they also bear the quality of podiform chromite.

Keywords: Pinarbasi ophiolites, chromite, mineralogy-petrography, geochemical interpretation.

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