首页|Electrical resistivity tomography for characterization of carbon-rich rocks (shungites)
Electrical resistivity tomography for characterization of carbon-rich rocks (shungites)
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NSTL
Elsevier
Electrical resistivity tomography (ERT) is rightly considered an effective tool for studying subsurface, but some particular geological conditions can lead to results that are difficult to explain. Carbon-rich rocks undoubtedly belong to such cases because of their very high resistivity contrast compared to the host rock. Shungite-bearing rocks have total organic carbon (TOC) in the range of 5 to 95 weight percentage (wt%), and such a range ac-counts for a wide variety of electrical rock properties. We used ERT at three shungite deposits to study their internal structure and to evaluate the reliability of the resulting geoelectrical models. The study of carbon-rich rocks (shungites) of the Zaonega Formation in the Onega basin is interesting in the Precambrian carbon accu-mulation and the exploration of shungite deposits. As a result, we clarified the main features of geological sections, such as topsoil base, primary shungite-rich successions, individual zones of metasomatic rocks, and gabbro intrusions. Drilling data and geological reference sections show the reliability of the ERT cross-sections and accuracy of main geological boundaries with an average discrepancy of 1-2 m. Laboratory studies of drill cores samples revealed the nonlinear relationship between resistivity and TOC, which, in the future, may facilitate identifying rocks with relatively low carbon. However, it was impossible to quantitatively assess TOC by ERT models due to the resolution-dependent correlation loss. Comparison of synthetic model with natural field one shows that the significant considerable contrast of resistivity for geological layers about 1:1000 ratio and more produces lower sensitivity and higher uncertainty parts of the inverse models. At the same time, despite high RMS errors, all obtained models retain their geological validity. Our research results demonstrate the ef-ficiency of ERT for mineral exploration of shungites and reveal its internal limitations when the survey these specific highly conductive carbon-rich rocks.
NSTL
Elsevier
