Investigation of the geological, geochemical and gemological characteristics of diaspores formations of the Menderes Massif in the southwest side (Aydin-Muğla)

The study covers an area of approximately 174 km2, which includes the Yatağan district in the west of Muğla province and the areas in the south of Aydın province. The study area consists of bauxite quarries and diaspore deposits in the Menderes Massif. Within the framework of this thesis, a total of 45 different diaspore samples were compiled from 10 different regions with the aim of determining the mineralogical and crystallographic properties of the diaspore and other accompanying minerals in the bauxite mines in the region, examining the formation conditions-form, and determining the gemological properties/characteristics and coloration of the diaspore. Bauxite deposits in the study area within Göktepe and Yatağan formations are observed along the unconformity in the contact of white crystallized limestone (Lower/Late Triassic) and gray-grey colored crystallized limestone (Upper/Jura-Cretaceous). The deposits generally extend in the NW - SE direction and the samples show massive, pisolithic and oolitic texture features. Diaspore crystals, which are found in different sizes and colors in bauxite deposits starting from Bafa Lake and progressing in the form of an intermittent arc towards Yatağan, are unique to our country. In the study area, diaspore formations were observed in macro scale, generally as lenticular, brecciated, cracked and pockets in crystallized limestones, bauxite and altered zones together with calcite, muscovite and chloritoid minerals. Diaspores are generally observed in the form of plates around Milas, and generally in small and swallow-tail structure around Yatağan. In order to reveal the bauxite formation processes, the properties/characteristics and distributions of major and trace elements were examined and it was revealed that the clayey/clastic metamorphic-igneous rocks with higher Al content according to the Al2O3/SiO2 ratio (1.0-61.3) were the source of bauxite formation and the enrichment was repeated more than once. In addition, the comparison of Zr, Cr and Ga contents of bauxite and diaspore samples in the study area showed that bauxite formations have a bedrock with medium magmatic or clayey composition, and diaspore formations provide data close to ultrabasic-basic properties outside the areas. According to the rare earth element (NTE) evaluation of the samples in the study area, the La/Y ratio in bauxite samples is over 1, and the La/Y ratio in diaspore samples is over 1 in Pınarcık (PI) region; it was determined below 1 in Sodra (SO) and Yatağan (YA) regions. According to these data, it has been determined that bauxite and Pınarcık diaspore formations are formed in alkaline environment conditions, and diaspore formations in Sodra (SO) and Yatağan (YA) regions are formed in acidic environment conditions. According to the Ce/Ce* (NASC) evaluation on bauxite and diaspore formations, it was determined that both formations occurred in an oxygen-poor environment (anoxic), and bauxite formation processes were slowly and diaspore formation processes were rapidly. In addition, according to the Eu/Eu* (PASS) assessment, the formations/solutions were thought to be a mixture/predominant clastic material product (magmatics, schist-phyllite and mafic intrusions of the Menderes massif) of wind/water (?) borne magmatic material, possibly derived from a distant volcanic source. Various geological formations occurred in the Permo-Triassic and Late Cretaceous (Cenomanian-Turonian) ranges in the Alpine-Himalayan orogenic belt (including the Mediterranean region, from Southeastern France to Iran), including the study area. The evolution of the Menderes platform; it is expressed as events related to the subduction and thrusting process of ophiolitic rocks related to the beginning of the closing of the Neo-Tethys ocean during a northward dipping, intraoceanic subduction in the Late Cretaceous. It is thought that the bauxites in the region were buried due to tectonic movements and underwent metamorphism at a depth of approximately 10-25 km, pressure of 5-10 kb and temperature of 500-620 °C. It is thought that with this metamorphism, gibsite and boehmite transformed into diaspore and corundum, ferrous compounds turned into magnetite, and clays into such as minerals muscovite and chloritoid. It was determined that rare earth elements (HREE>REE) and chromophore elements (Cr3+, V3+ and Fe2+-Ti4+ pairs) were effective in color changes in diaspores in the study area. As a result of SEM imaging and EDS analyzes, it was observed that the samples of Sodra, Yatağan and Pınarcık region mainly contain O, Al and Si, and in addition to these elements the presence of K, Na, Fe, Ca and Mg was detected in close-ups. The collected specimens were identified as gemstones, for this reason the specimens were shaped and the causes of wastage were observed.