Magnetic separation tests on a braunite-rich manganese ore, Eskisehir, Turkey

Turkey is an important manganese ore producer and exploration for new manganese deposits is ongoing. One of the prospected areas is the melange zone of the Eskisehir ophiolite. Some samples from the Taycilar deposits, located in the Eskisehir ophiolite melange, were used in this study to assess the feasibility of magnetic enrichment of manganese ore. The Eskisehir ophiolite is located in the western part of the Izmir-Ankara-Erzincan Suture Zone (IAESZ) that crosses Turkey from the west (Izmir area) to the east (border with Georgia) (Uysal et al., 2009). Manganese deposits within the IAESZ are classified by Ozturk (1997) as radiolarian chert-hosted deposits. They are related to Neo-Tethyan suture and form the epi-ophiolitic sediment succession together with associated radiolarite, radiolarian chert, siliceous shale and brown claystone. The deposits show high Mn, Si variable and low Al contents. The most important of these deposits is the Cayirli Mn deposit in central Anatolia. The Taycilar deposit has never been mined and the local geology is not well known due to paucity of outcrops and absence of investigation. Mn-rich rocks are mainly strongly deformed braunite-rich quartzites, with NW-SE trend of layering. As a whole the Taycilar deposit belongs to the IAESZ Mn deposits but it is characterized by a strong metamorphic overprint that changed its mineralogy and texture. Mineralogy and texture of the Taycilar deposit show conditions that can favour magnetic enrichment of ore at relatively fine grainsize, providing the opportunity to produce a high grade final product. Magnetic properties of Mn ore have been assessed in magnetic prospecting (Bhimasankaram and Rao, 1957). Braunite shows a paramagnetic behaviour that is strongly affected by incorporation of elements, like Mg and Fe, substituting Mn. In addition the Taycilar deposit shows a metamorphic re-crystallization with grainsize increase that allows good separation of Mn-rich phases and quartz at relatively fine grainsize of crushed ore. For the experiment samples, about 25 kg each, were taken from two outcrops (ESK1 and ESK2) and mixed in equal proportion. Ore was crushed at grain size < 4mm. Magnetic separation tests were carried out with a Permroll dry magnetic separator at University of Eskisehir, using constant roll speed and magnetic field. First test, on the whole sample, crushed at < 4 mm, shows that separation of a Mn-rich sand is possible with a high metal recovery. Efficiency is higher for the finest fraction (< 1 mm), with an MnO content increase from 15 to 30 wt% at a very high metal recovery of more than 96 wt%. For coarser grainsizes, without any change of setting, metal recovery decreases due to stronger effect of gravity (78 wt% at > 2 mm) but MnO enrichment increases up to 35 wt%. A second test was carried out dividing beforehand the feeding sand in three grainsize classes, in order to study the effect of sorting on separation. Results show that metal recovery does not change meaningfully and hence previous separation of feeding sand in different grainsize classes is useless. In conclusion tests show that braunite-rich metamorphic manganese deposits can be successfully enriched magnetically, with a metal recovery that is inversely correlated to grainsize. Minimum grainsize is hence chosen on the basis of crushing costs and market demand.