Investigation of ore occurences related to Dümrek (Sivrihisar-Eskişehir) ophiolites

ABSTRACT Listwaenite, is a hydrothermal alteration product generated by the low temprature (17-200°C) fluids moving along the joints of serpantinized ultrabasic rocks. It's mineralogy consists of quartz, carbonate (magnesite, ankerite and dolomite) and/or fuchsite. Accessory minerals are aragonite, calcite, chromite, cinnabar and metacinnabar. Mesh structure is rarely protected and can be seen as relicts. Also the mineral associations of original serpantinites can be observed. Outcrops of the listwaenite occurences that create lenses and dike-like structures are typically highly reliefed, hard and yellowish or light brown colored. Listwaenization is a tectonic and lithologic controlled process. Listwaenitization process that generates precious metal epithermal deposits in the areas which ultrabasic units are located, shows spatial relationship with Au, As, Co, Ni, W and Hg deposits. The study area, is located in the blueschist belt on south of İzmir- Ankara suture, southeast of Mihalıççık (Eskişehir). Geology of the area consists of Mihalıççık metamorphics, ophiolitic units and asidic magmatic rocks overlying the latter, listwaenite occurences that are created by the fluids and located in the major faults and cracks of serpantinites, Tertiary Porsuk Formation overlying all of these units and Quaternary alluvium above all. Lackness of contact metamorphism zone on the contact of ophiolites and acidic magmatics and foliated appearence of both rock units show that tonalite and granodiorites which symbolize asidic magmatics are introduced in study area during obduction of ophiolitic sequence. VIListwaenite outcrops in the study area are divided into two groups, "SDL" (silica dominated) type and "CDL" (carbonate dominated) type. Pyritized and over- silicified areas are regarded as sub-group of "SDL" type and are named "PSDL" (pyritized silica dominated) type. "SDL" type listwaenites typically include quartz, dolomite and calcite while "CDL" type dominantly consist of dolomite and "PSDL" type are characterised by the high silica content. Fuchsite has not been found in the listwaenite occurences in the study area. Ore minerals that are observed in listwaenites are chromite, pyrite (I and II), bravoite (nickelliferrous pyrite), gersdorffite ((Ni, Co, Fe)AsS), magnetite, marchasite, skutterudite ((Co, Ni,Fe)As3,x)(?), arsenopyrite, glaucodot ((Co, Fe)AsS), hematite and goethite. Chromite grains reflect the ultrabasic origin of these rocks. Secondary sulphide mineralizations are products of the fluid income. The following supergene stage has lead the occurence of hematite and goethite. Chemical analysis show that the main major oxides of of listwaenites are SİO2, Fe2C<3, AI2O3, MgO and CaO. Cr203 values cite the origin of the original lithology as an ultrabasic rock. Similar trace element values and trends have been observed in listwaenite and serpantinite and this situation reflects that these rocks are genetically related. Also these evidence offer that different fluid and ophiolitic units of different chemistry leads to occurence of different listwaenite types. Keywords: Eskişehir-Mihalıçcık, ophiolite, listwaenite, silica carbonate alteration VU