Lithology and mineralogy recognition from geochemical logging tool data using multivariate statistical analysis

The availability of a deep well that penetrates deep into the Ultra High Pressure (UHP) metamorphic rocks is unusual and consequently offers a unique chance to study the metamorphic rocks. One such borehole is located in the southern part of Donghai County in the Sulu UHP metamorphic belt of Eastern China, from the Chinese Continental Scientific Drilling Main hole. This study reports the results obtained from the analysis of oxide log data. A geochemical logging tool provides in situ, gamma ray spectroscopy measurements of major and trace elements in the borehole. Dry weight percent oxide concentration logs obtained for this study were SiO₂, K₂O, TiO₂, H₂O, CO₂, Na₂O, Fe₂O₃, FeO, CaO, MnO, MgO, P₂O₅ and Al₂O₃. Cross plot and Principal Component Analysis methods were applied for lithology characterization and mineralogy description respectively. Cross plot analysis allows lithological variations to be characterized. Principal Component Analysis shows that the oxide logs can be summarized by two components related to the feldspar and hydrous minerals. This study has shown that geochemical logging tool data is accurate and adequate to be tremendously useful in UHP metamorphic rocks analysis. - Highlights: • Cross plot and PCA were applied for lithology characterization and mineralogy description. • Oxide logs provide information for accurate lithological and mineralogical description. • Geochemical log can be an outstanding complement to in situ physical logs and core data for geological interpretation.