Geochemistry of metamorphic-hosted iron ore deposit and associated silica caps in Mt. Arı, Bitlis, Eastern Anatolia: preliminary records and pathfinder elements for hydrothermal origin

Abstract

Iron ore (magnetite-hematite) is one of the common ore deposits occurred in Bitlis and surrounding areas from Eastern Anatolia. A new Fe occurrence have recently been discovered in Mt. Arı (locally called as Gultik Mountain) at SE of Bitlis city. Fe ore presents in metamorphic basement rocks as predominantly disseminated-type and to lesser amount massive ore. The area also hosts silica-rich alteration zones. Here, the bulk samples from both disseminated Fe-ore and siliceous alteration zones have been geochemically analysed by XRF method. Obtained results show that the grade of Fe-ore as total Fe2O3 (wt.%) increase from 2 wt.% to 42 wt.%, together with MgO (from 0.01 to 5.3 wt.%,), CaO (from 0.13 to 1.90 wt.%) and Na2O (from 0.42 to 4.93 wt.%), as a function of decreasing SiO2 (from 68 to 39 wt.%) and Al2O3 (15 to 8 wt.%). Significant amount of Co (36-160 ppm), Mo (4-13 ppm), As (0.5- 3.7 ppm), Hg (2.3-4.0 ppm) and Sb (0.8-1.3 ppm) was determined in analyzed disseminated iron ore samples. Similarly, in the samples of silica caps, SiO2 range between 88 wt.% and 74 wt.%, and decrease with increasing Al2O3 (from 0.01 to 20.85 wt.%) and TiO2 (from 0.015 to 1.05 wt.%). Other oxides do not show regular trends. Such siliceous zones also include remarkable amount of Au (from 7.8 gr/t to 17.6 gr/t in some samples), Co (30-200 ppm), Mo (2-10 ppm), As (0.9-3.2 ppm), Hg (1.7-6.7 ppm) and Sb (0.7-73 ppm) contents. LREE enrichment also exist in high-grade Fe-ore. Based on the first preliminary geochemical results, it is concluded that the metamorphic-hosted Fe ore and Au-bearing silica caps from Mt. Arı have most likely hydrothermal in origin, and leaching of silica and the removal of iron, formed the iron ore (hematite-magnetite) in the metamorphic basement rocks. As a new target area, the region has a powerful potential. The uplifting of the metamorphic massif and related postmetamorphic tectonics (possibly in Neo-tectonic period) gave way the prominent channels for emplacement of hydrothermal fluids in the area. Due to an episode of regional extensional tectonic, the Au-Co-As-Hg-Sb-Mo-bearing silica-rich hydrothermal fluids relocated into the metamorphic basement