Geology, geochemistry, and petrology of the alkaline subvolcanic trachyte-hosted iron deposit in the karakuz area, northwestern hekimhan-malatya, turkey

Abstract

The Karakuz iron deposit is hosted by Maastrichtian subvolcanic trachyte-trachyandesite, which has a total alkali content of 9-13 wt%, with Na2O less than 1% of the total alkalies. SiO2, Al2O3, and Fe2O3, in order of relative abundance, are other common oxides, whereas the P2O5 concentration is less than 0.5% in all of the host-rock samples. The trachytic host rock has an indistinct flow structure in the field and a subvolcanic porphyritic texture in thin sections. The tectonomagmatic environment of the trachytic subvolcanic host rock is intraplate and is derived from alkaline basaltic magma in the Hasancelebi-Hekimhan area. The iron deposit at Karakuz occurs as stringers, stockworks, lenses, and less disseminated ores. A characteristic feature of the deposit is martitization. Dominant iron minerals in the paragenetic sequence are magnetite-hematite-martite-goethite ± lepidocrocite ± limonite. Quartz, calcite, and barite are the main gangue minerals in the ore zone. The ore zone proper is characterized by silicification; however, mineralized alkaline rocks that surround the ore zone are kaolinitized. Average Fe2O3 of the ore is a little over 50%. SiO2 is the second most abundant oxide in the ore zone. Other oxides are negligible (less than 1%) in all of the iron-ore samples. Base-metal concentrations are as follows, in ppm: As = 11 to 1500, Ba = 25 to 300,000, Ni = 67 to 2337, Zn = 13 to 302, and Cu = 15 to 662. Other base metals, such as Co, Cr, Sb, and Pb, are present in very low ppm concentrations. Au and Ag occur in ppb (Au) to fractional ppm (Ag) concentrations. Hematite-magnetite growth zoning, a common textural feature in the ore zone, probably was formed by a change in oxygen fugacity during crystallization. The low sodium and phosphorus contents of the Karakuz iron deposit would appear to disallow any correlation of the Karakuz deposit with Kiruna in Sweden or Kiruna-like deposits elsewhere in the world. Rare-earth-element concentrations in both iron ore and host rock have similarities that suggest that the trachytic host rock and the iron ore formed from the same magma. © 1996 Taylor & Francis Group, LLC.