This study discusses the ore
geology and origin of the Kesikköprü (Bala- Ankara) iron deposit. The basement
composed of gneiss, schist, and quartzites of Paleozoic- Mesozoic Kırşehir
massive is overlain by sedimentary and volcanicvolcaniclastic rocks that
consist of spilitic basalt, basaltic tuff, diabase dikes, cherty limestone,
radiolarite, and mudstonelimestone lenses which are transitional with an
ophiolitic melange made of crystallized limestone blocks and ultramafic-mafic
rocks in a basin that was formed during the upper Cretaceous time. Rocks of the
basin are cut by granitoids such as granite, granodiorite, and porphyries of
Maastrichtian-Paleocene age. These units are unconformably covered by Eocene
Çayraz formation consisting of sandy, clayey, fosiliferous limestone,
Miocene-Pliocene (?) İncik formation composing of siltstone, claystone,
anhydrite-gypsum alternations, and sandstones with limestone and fosiliferous
limestone blocks, volcanic rocks made of rhyolite and tuffs,
Pliocene-Quaternary Kızılırmak formation consisting of gravel, sand and mud
deposits, and finally posttectonic basin sediments of Quaternary alluvium.
Possible lithologies for source and country rocks of mineralization are
examined under two main groups as ultramafic rocks consisting of crystallized
limestone blocks, peridotite, pyroxenite, and serpentinites and mafic rocks
consisting of gabbro and diabases while in more detail, they are investigated
as serpentinites and mafic rocks subjected to hydrothermal alteration. The
association among olivine, pyroxene, and plagioclase minerals is distinctive in
field, thin section, and XRD studies. Petrographic works conducted on mafic and
ultramafic rocks yield occurrences unique to ultramafic cumulates. Ore samples,
in the order of abundance, consist mainly of magnetite and lesser amounts of
pyrite, chalcopyrite, chromite, siderite, ankerite, and trace amounts of
pentlandite, pyrrhotite, gersdorffite, ilmenite, and sphene. In addition,
olivine, pyroxene, tremolite, and actinolite also accompany the ore and calcite
and dolomite are also observed in crack and fracture fillings. Geochemical
studies performed on the ore samples indicate that granitic fluids have no
direct effect in the ore formation. The processes of granitic intrusions
associated with hydrothermal convection cell affect the mafic rocks and shape
the hydrothermal alteration modes formed by "skarn type minerals" and
fels-like textures". Expelling of iron element as a result of
serpentinization of ferromagnesian minerals within the ultramafic rocks, such
as olivine and pyroxene, is the primary source of iron. Their secondary
enrichment by the granitic intrusions indicates another important stage in the
formation of Kesikköprü iron deposit. Present study favors the idea that
Kesikköprü iron deposit is similar to the Divriği type deposit, in other words,
as also stated by previous works, iron was derived directly from the granitic
rocks.
Primary Language | English |
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Subjects | Engineering |
Journal Section | Articles |
Authors | |
Publication Date | January 1, 1998 |
Published in Issue | Year 1998 Volume: 120 Issue: 120 |
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