Keşkek tepe altın cevherleşmesinin kökeni, akışkanının kaynağı ve yapısal kontrolleri (Gördes, Manisa)

This thesis aims to identify the origin of alteration - mineralization, source of ore fluid, and the relationship between mineralization and host rock characteristics along with constraints on structural controls in Keşkek Hill prospect in Gördes, Manisa. The mineralization is hosted by jasperoids hosted by gray recrystallized limestones as blocks within ophiolitic mélange. Ophiolitic mélange consists of serpentinized peridotites, epi-ophiolitic sequences including mudstone, radiolarite, light gray laminated limestones, beige-colored laminated limestones (wall rock of mineralization) and dark gray recrystallized limestones. Basement rocks of the study area belong to metamorphic rocks of Menderes Massif. Jasperoid is the main host rock which is mapped and identified by petrographic studies. It is formed by pervasive silicification and decarbonatization of the carbonate rocks. Silicification and decarbonatization are the first stage of the alteration in the study area. Jasperoid consists of very fine grained-massive quartz. It is cut by or infilled by comb textured quartz, and locally exhibit boxwork texture in decarbonized limestones. Calcification and oxidization are also characteristic alterations formed at the late stages of alteration. Calcification is typically observed in oxidized jasperoids and occur either as veins or as filling the empty spaces between the comb and boxwork textured quartz crystals. Oxidization of jasperoids is very common at surface outcrops, and intersections at drill holes showed that the degree of oxidation decreases with depth. The most significant texture observed on oxidized jasperoids is the liesegang texture. Mineralization in the area only observed in jasperoidal rocks associated with disseminated fine-grained pyrite, arsenopyrite, and stibnite. Gold is the only precious metal in the study area. Base metal abundances are very low in jasperoidal rocks. Jasperoid occurrences observed in high angle normal faults with NW-SE direction. High angle (73° to 90°) normal faults in NW-SE direction truncating the thrust faults within the ophiolitic mélange acted like a conduit for the ore fluids and mineralization. Mineralized jasperoids are cut by post mineralized normal and strike slips faults. The fluid inclusion studies include analyses of primary fluid inclusions on the samples from pre-syn ore stage quartz and syn-ore stage quartz crystals. The primary inclusions are of type-2 inclusions that refers to two-phase inclusions with variable amounts of liquid-vapor (L-V) inclusions. These inclusions subdivided into two as type 2a and type 2b depending on the relative abundance of liquid-vapor ratio in the inclusions. The microthermometric analyses of the inclusions showed that the mean homogenization temperature for pre-syn ore stage quartz minerals is 295.83 °C (ranging between 288.7 °C and 313 °C), and the salinity values range from 5.71 to 7.59 wt. % NaCl eq. The mean homogenization temperature for the inclusions from ore-stage quartz is calculated to be 169 °C (ranging from 136 °C to 182.7 °C) with salinity ranging from 0.70 to 15.86 wt. % NaCl eq. The salinity values for both samples are measured as relatively low salinity for inclusions. The calculated value δ18O(fluid) values for syn-ore stage quartz sample ranging between –5.69‰ and -1.77‰. δD(fluid) calculated values for syn-ore stage whole rock (jasperoid) sample ranging between -105.79‰ and -101.87‰. Stable isotope data suggest that the hydrothermal fluids that formed jasperoid have been originated by mixing of meteoric water mixing and formation water. The δ34S isotope value for stibnite is -0.6‰. δ34S, and suggests magmatic sulfur, due to the deep circulation of the meteoric water within the ultramafic rocks in ophiolitic mélange. The decarbonatization followed by pervasive silicification along with collapse breccia is typical for many sediments hosted gold deposits such as Carlin-type gold deposits. Additionally, the normal faults formed during a regional extension just after the main thrusting (compression), and silicification along the faults within the carbonate rocks also resemble to structural controls and mechanism of silicification for the Carlin-type deposits. Therefore, the similarities in nature and morphology of the jasperoidal rock hosting the main gold mineralization, and geologic-structural setting suggest that of the gold mineralization at the Keşkek Hill prospect is a Carlin-type gold mineralization. Keywords: Carlin-Type, Jasperoid, Decarbonatization, Fluid Inclusions, O And H Stable Isotope