The nature of transition from adakitic to non-adakitic magmatism in a slab window setting:A synthesis from the eastern Pontides,NE Turkey

The eastern Pontides orogenic belt provides a window into continental arc magmatism in the Alpine-Himalayan belt. The late Mesozoic-Cenozoic geodynamic evolution of this belt remains controversial. Here we focus on the nature of the transition from the adakitic to non-adakitic magmatism in the Kale area of Gumushane region in NE Turkey where this transition is best preserved. The adakitic lithologies comprise porphyries and hyaloclastites. The porphyries are represented by biotite-rich andesites, hornblende-rich andesite and dacite. The hayaloclastites represent the final stage of adakitic activity and they were generated by eruption/intrusion of adakitic andesitic magma into soft carbonate mud. The non-adakitic lithologies include basaltic-andesitic volcanic and associated pyroclastic rocks. Both rock groups are cutting by basaltic dikes representing the final stage of the Cenozoic magmatism in the study area. We report zircon U-Pb ages of 48.71 ± 0.74 Ma for the adakitic rocks, and 44.68 ± 0.84 Ma for the non-adakitic type, suggesting that there is no significant time gap during the transition from adakitic to non-adakitic magmatism. We evaluate the origin, magma processes and tectonic setting of the magmatism in the southern part of the eastern Pontides orogenic belt. Our results have important bearing on the late Mesozoic-Cenozoic geodynamic evolution of the eastern Mediter- ranean region.

The genesis of the slab window-related Arzular low-sulfidation epithermal gold mineralization(eastern Pontides,NE Turkey)

The Arzular mineralization is one of the best examples of epithermal gold deposits in the eastern Pontides orogenic belt. The mineralization is hosted by the subduction-related basaltic andesites and is mainly controlled by E W and NE SW trending fracture zones. The main ore minerals are galena. sphalerite, pyrite, chalcopyrite, tetrahedrite and gold. Homogenization temperatures of fluid inclu- sions are between 130 and 295 C for quartz and between 90 and 133 C for sphalerite. Sulphur isotope values obtained fiom pyrite, galena and sphalerite vary between 1.2‰ and 3‰ indicating that sulphur belongs to magmatic origin and was derived from the Lutetian non-adakitic granitic intrusions in the region. Oxygen isotope values are between 15.0‰, and 16.7‰ and hydrogen isotope values are between -87‰ and 91‰ The sulphur isotope thermometer yielded temperatures in the range of 244-291 C for the ore formation. Our results support the hypothesis that the Arzular mineralization is a low-sulfidation epithermal gold deposit associated with non-adakitic subduction- related granitic magmas that were generated by slab window-related processes in a south-dipping subduction zone during the Lutetian.

Prediction of mine drainage generation potential and the prevention method of the groundwater pollution in the Gümüskoy(Kütahya)mineralization area,NW Turkey

One of the leading factors of seepage contamination is mine drainage,which creates serious ecological risks on the environment both during operation and post-mining times.In this study,experimental processes have been carried out to determine the occurrence of mine drainage in the Gümüskoy(Kütahya)mineralization area(Northwest Turkey).The prevention method for potential mine drainage occurrence has been also discussed.High enrichment was observed which are directly related to mineralization in trace element concentrations,especially in potentially toxic metals such as Ag,Cd,Mo,Ba,Bi,and Zn.Based on short-term tests,mine drainage formation has not been expected according to the p H(7.36-9.38),contact leaching,and acid-base accounting studies.However,in the long-term,acid generation potential has been expected because of weathering and oxidation in terms of rock type and mineralization in the area.Therefore,in order to prevent groundwater contamination in the event of a possible formation of mine drainage,the hydraulic conductivity of the stock area bedrock was evaluated by the in situ tests performed in the field and it was found to be moderately permeable(K=1.9×10^-6 m/s).In order to make the stock area bedrock impermeable,natural clay will be laid and compressed at the base of the stock area.When the finite elements were modeled by seepage analysis,the seepage discharge to be formed on the base rock at a depth of 5 m was determined as 3.17×10^-19 m^3/s.Since the discharge value determined in the seepage analysis after modeling is very close to zero,contamination of possible ground and surface water will be prevented.