The Artova Ophiolitic
Complex (AOC), which formed in association with Alpine Ophiolites, is exposed
in the NE part of central Anatolia, in the interior of the central Black Sea
region and within the borders of Çorum and Yozgat. The Derbent-Eymir manganese-
oxide deposit under investigation occurs within this ophiolitic complex. The mineral
association in Derbent ore is composed chiefly of pyrolusite, manganite and
lesser amounts of ramsdellite, magnetite and goethite. Calcite is the main
gangue mineral. The mineral association in Eymir ore is represented by
pyrolusite, braunite, neltnerite, jacobsite, psilomelane and trace amount of
limonite accompanied by some gangue minerals such as quartz and calcite.
Electron microprobe analysis was carried out on pyrolusite, braunite and
psilomelane minerals. While pyrolusite from Eymir has higher Si, Al, Mn and Ca,
pyrolusite from the Derbent ore has lower Fe, K and Ba contents. Pyrolusite in
the Eymir ore has higher Si, Al, Mn and Ca (10.28-7.06; 3.19-1.28; 87.98-81.88;
2.38-1.97 respectively) and lower Fe, K and Ba (0.31-0.16; 0.02-0.00; 0.07-0.00
respectively) contents in comparison to pyrolusite in the Derbent ore. Element
variations in core-rim zones of spherical pyrolusites and manganite crystals
elongated towards the gangue are quite noticeable. Both Eymir and Derbent ore
deposits are low-temperature hydrothermal deposits. Geochemical variations
recorded in various manganese minerals are found to be strongly dependent on
the changes in pH and temperature of the ore-forming solution and distance to
the spreading center.
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