Balya(Balıkesir)Yöresindeki Porfiri Bakır-Molibden Cevherleşmesi ile İlişkili Magmatik Kayaçların Mineralojik ve Jeokimyasal Özelliklerinin İncelenmesi
Özet
Within the scope of this thesis, the mineralogical, petrological and geochemical properties of igneous rocks in Balıkesir-Balya region were examined, the origin of the magma that formed these rocks, was determined and the processes that were effective in their formation were revealed. Since the igneous rocks observed in the study area, are associated with Cu-Mo mineralization, in the light of the obtained geochemical results, in addition to revealing the petrogenesis of igneous rocks, it is aimed to determine the Cu-Mo metal enrichment associated with magmatism in the studied area, to determine the chemical changes in igneous rocks caused by the solutions that are effective in the formation of mineralization, to examine the relations between wall rock alteration zone, and ore deposits, to determine the formation environment and conditions of the ore deposit and to reveal the relationship between magmatism and ore mineralization with this study.
The volcanic rock samples of the Balya vary from basaltic trachyandesite to dacitic composition and the core samples from the borehole are dacite and andesite in character. All of the samples are sub-alkaline and all of the Balya volcanic rocks have calc-alkaline characteristics.
According to the results of mineral chemistry analyses performed on three samples of basaltic, andesitic and dacitic volcanic rocks, it was determined that pyroxenes in basaltic rocks are augite and plagioclases are labrador, pyroxenes in andesite and dacite rocks are diopside and plagioclase are andesine in composition, amphiboles are pargasite, edenite and micas are biotite in the dacite sample. The crystallization pressure and temperature conditions of the labradors and andesines in these samples were calculated using the equations determined by Putirka (2008). The calculated temperatures were found to vary between 1070–1090 °C for basaltic samples, 1010–1020 °C for andesite and 980–990 °C for dacite. The depth estimation calculations based on basaltic, andesitic and dacitic volcanic rocks from the obtained pressure and temperature values revealed that feldspars crystallized at a depth range of ~15–30 km.
Partial melting modeling was performed to determine the origin of the magma and the melting environment. With the geochemical data obtained, it was revealed that all of the samples, except having the highest MgO content sample for Balya volcanic rocks, derived from a shallow lithospheric source due to their high La/Ta (32–76), high Nb/La (0.18–0.45), low Zr/Ba (0.09–0.16) ratios and low TiO2 (0.54–0.91%) contents. With these geochemical data pointing to a lithospheric source, a hypothetical partial melting modeling was performed to determine whether this melting is derived from spinel peridotite or garnet lerzolite. This modeling revealed that the Balya volcanic rocks were intensively formed by low-grade (<5%) partial melting of spinel peridotite.
The mineralization processes associated with this magmatism were determined by examining the drill core samples in the region. In the Balya borehole, argilic, phyllic, propylitic and potassic hydrothermal alteration types were identified as transitional within the granodiorite porphyry unit. The A and B, D and M veins, which are porphyry system indicators, were also cut. The molybdenite, chalcopyrite, magnetite, pyrite and hematite minerals were identified as ore minerals with the thin sections.
In order to reveal the age of the ore mineralization, Re-Os age determination was performed on the molybdenites and the age of minerals were identified as 25.61 ± 0.02 Ma, 25.67 ± 0.01 Ma and 25.56 ± 0.01 Ma. Accordingly, it was revealed that the mineralization occurred in the Late Oligocene period and was coeval with magmatism.
With this study, it has been revealed that porphyry alteration and Cu-Mo mineralizations formed with the magmatic activities that continued during the Oligocene period were formed in the early stages of the transformation of the compressive regime into an extensive regime in the region.
