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The alteration degree of the metacrystalline rocks based on UAI, Bolu (Turkey)

Recep Kilic • Koray Ulamis • Metin Yurdakul • Yusuf Kagan Kadioglu

The geomechanical properties of the metacrystalline rock masses vary due to alteration. The Devonian aged Yedigoller formation crops out in the Asarsuyu valley (Bolu, Turkey). The aim of this study is to investigate the alteration degree of the amphibolite and metagranodiorites based on their geomechanical and petrographical properties. The P-wave velocity is 1,613–5,588 m/s and the unconfined compressive strength varies between 12.75 and 99.86 MPa. Several weathering products occurred due to carbonisation, oxidation and sericitation. These rocks, subjected to hydrothermal effects, are classified as ‘‘fresh’’ to ‘‘completely altered’’ according to the unified alteration index (UAI). In addition, the values of the loss on ignition, modified weathering potential index and chemical index of alteration were taken into account for supporting the alteration process. Since the main process is hydrothermal alteration, the rocks which were exposed to alteration are weathered on the slopes after excavation. Weathering classification and the chemical indices indicate this process. Thus, UAI is concluded to be more suitable and credible in order to evaluate the hydrothermal alteration process of such crystalline rocks numerically.