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Factors Controlling Low Uranium and Thorium Concentrations in the Çayirhan Bituminous Shales (ÇBS) in the Beypazari (Ankara) Area, Turkey
Author(s) -
PEHLIVANLI Berna Yavuz,
KOÇ Çükrü,
SARI Ali,
ENGIN Hilal
Publication year - 2014
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12195
Subject(s) - uranium , geology , sedimentary depositional environment , geochemistry , thorium , oil shale , sedimentary rock , uranium ore , gneiss , clastic rock , mineralogy , structural basin , geomorphology , metamorphic rock , paleontology , materials science , metallurgy
In this study uranium and thorium contents and depositional characteristics of Çayirhan bituminous shales (ÇBS), west of Ankara (central Anatolia), are investigated. Samples used were collected from boreholes opened by Park Holding Ltd. A total of 25 samples were taken from bituminous shale levels in boreholes drilled at 6 different locations in the study area. The Hirka formation which hosts bituminous shale deposits is a volcano sedimentary sequence and all lithofacies indicate that a lacustrine environment where the water level was continuously changed. In addition to hydrocarbon generation potential, bituminous shales also accumulate significant amount of radioactive elements such as uranium and thorium. The average uranium and thorium concentrations of ÇBS (1.83/2.62 ppm) are much lower than averages of UC, NASK and PAAS (uranium: 2.70/2.66/3.10 ppm; thorium: 8.50/12.30/14.60 ppm). Low uranium contents in comparison to those of similar lacustrine environments might be attributed to that waters of depositional environment of ÇBS contain low concentration of dissolved uranium and redox conditions were of oxic and dioxic character. Correlation data indicate that U and Th have a similar source and are associated predominantly with clays and phosphates and dominantly with organic material. Radioactive elements in the basin might be derived from Paleozoic granites and metamorphites (e.g. gneiss, schist) which comprise the basement and volcanism which was active in the region throughout the Miocene period. These elements are probably associated with uraniferous phosphate minerals (e.g. autunite, torbernite) which occur in granite, gneiss and schist. ÇBS with average TOC content of 10.96 % shows very good/perfect source rock potential. Positive correlations between Gamma‐Ray values and U, Th and K concentrations imply that radioactivity might be originated from these three elements.