North of the Gokcesu (Bolu/Mengen) along the Bolu River geochemical prospecting and investigating possible economic potentials

The aim of this study is to investigate possible economic potentials and geochemical prospecting along the Bolu River, located at the north of the Gökçesu at the western part of Mengen/Bolu. During the study, the units located in this area were distinguished according to the lithological features and a field of study approximately 115 km2 was carried out and a special scale geological map of the study area has prepared. The study field is located in Bolu G27 – b2 sheet. In general, this studywas carried out along the Bolu River, which is located at the north of the Gökçesu, with samples taken systematically. The basement rocks in the north of the study area are Precambrien metamorphic rocks. These basement rocks are unconformably covered by Middle/Late Devonian – Early Carboniferous dolomitic limestones. In generalized stratigraphic section, this unit is covered unconformably by Permian – Triassic terrestrial clastic sediments which are conglomerates, sandstones and mudstones. The units thought to be harmonious in themselves which are Eocene semi-pelagic limestones, nummulitic limestones, neritic limestones and terrestrial clastics covered the Permian – Triassic units unconformably. Laboratory studies were made on samples taken systematically from the study area. Geochemical (major and trace elements) analyzes of all collected samples were made and CIA, CIW, AI and CCPI indexes were calculated with using these datas. Diagrams which are prepared with these indexes, helped to make some comments about the type and the grade of the alteration. Moreover, the sample which is thought to be skarn (contact metasomatic) is used for XRD analysis. These obtained datas from XRD were interpreted. In the light of such informations and datas, an advanced study is proposed to reveal possible economic potential. As a result of the mineralogical and petrographic studies; According to thin section studies on Lok 3.9, Lok 3.10 and Lok 3.12 samples taken from the metagranodiorites belonging to the Precambrian aged Yedigöller formation, actinolites and chloritization caused by metamorphismhave been observed and it has been concluded that hydrothermal activity in the region is effective. Garnet, chlorite and muscovite minerals paragenesis in Lok 3.9 indicate the presence of a contact metasomatic zone. Quartz, albite and clinochlorite minerals were similarly detected in the XRD study carried out on the same sample. In thin - section studies of recrystallized (dolomitic) limestones belonging to Yılanlı formations, white - gray in single nichols, white in black and gray in double niches, some calcite crystals have temperate color and some calcite crystals have waxy twist textures. In the study of thin sections (Lok 2.16 and Lok 2.19) from the Çakraz formation (Permian-Triassic) samples, amphibole and microklin were observed along with chlorites formed by the hydrothermal activity, and the samples taken from metacachite were found to contain calcite cement along with crushed quartz. When the samples taken from carbonated sandstones belonging to Akveren formation (Upper Campanian-Lower Eocene age) are examined, it is determined that Lok 2.14 sample is carbonate cement, kataplastic tissue metachlorite sample and Lok 2.15 sample is mixed sandstone and carbonate cementitious sandstone. This suggests that the region is tectonically active, and that the presence of sandstones of different origin is also influenced by wear and tear. In the thin section studies of the samples taken from the Soğanlı formation (Middle Eocene aged), yellowish - white colors dominate, and in the double nichrome, gray colored, different origins were observed. Quartz arenites containing secondary quartz veins were identified in thin section studies of the samples taken from the Yunuslar formation (Middle - Upper Eocene). According to the geochemical results of the samples collected from the study area; Major element determinations were made in 27 samples in total, and the samples of 9 Precambrian aged metamorphic rocks were between 41-64% SiO2, Al2O3 12-18%, Fe2O3 5.5-16, K2O 0.4-5.6, Na2O Of the dolomitic limestones of Lok 2.20, Lok 3.2 and Lok 2.1 are between 27-54.1% of the CaO and 8.6-20.4% of the MgO, respectively The other CaO values of the other limestones were changed between 52.9-55.2% and the MgO content was changed between 0.3-1.04%, the other 7clastic rocks were 40.9-64% SiO2 content, 8% Al2O3 content -15.5%, Fe2O3 contents 1,3-%, K2O content 0.3-4.6% and Na2O content 0.2-4%, respectively. According to the CIA, CIW, alteration and chlorite-carbonate-pyrite indices assessments made during the prospecting studies carried out along the Bolu Stream line, the majority of the study area is covered, it is thought that hydrothermal activity is similar to thin section studies of the samples in the region. It was also found that the CIA values of the investigated samples ranged from 0.2 to 71.5 (approx. CIA 33), the samples had less severe alteration and the CIW values ranged from 0.15 to 83.5 (approx. CIW 36) and weakly weathered. Normalization according to EMORB performed on 9 samples thought to affected by low temperature fluid effect alteration (Lok 2.1, Lok 2.20, Lok 3.1a, Lok 3.2, Lok3.5, Lok 3.8, Lok 3.9, Lok 3.12 and Lok 3.14), contact metasomatism HREE elements were enriched in a similar pattern to the formation of a classical skarn in Lok 3.9 where contact metasomatism was observed in the resulting pattern. Pb anomalies indicate that the rocks are derived from continental magmatics or continental clastics and metamorphosed. In the normalization patterns made according to the NMORB and the primitive mantle, the examined specimens were enriched in LILE elements. If it is patterned normalized to REE chondrite, the Lok 3.9 has a relative HREE enrichment in the sample, and it is thought that this enrichment is in the garnet minerals in the contact metasomatic formation. As a result, according to all these results obtained within the scope of this study, it is thought that the study area is likely to host a tectonic controlled mineralization. The absence of any economic enrichment in the samples exposed to hydrothermal alteration strengthens the idea that the solution does not contain enough elements. It is probable that a potential mineralization will be detected with further investigations. A detailed sampling study of Lok 3.9, which is thought to be a contact metasomatic formation with thin section and XRD studies, has led to the conclusion that Mg is intended to reveal the presence of a rich iron skarn.