Search

Many of the sandstones at cultural heritage sites around the world are susceptible to chemical weathering, and long-term monitoring of the chemical weathering would be of great value for heritage conservation and would also provide reference data for environmental protection policies and projects. Reflectance spectroscopy is a potential tool for monitoring sandstone weathering due to its non-destructive characteristics. In this paper, we present the results of an investigation into the reflectance spectra of sandstones at the Yungang Grottoes, China, where the sandstones are variously fresh, calcite-dissolved, or argillitic-altered. We found several spectral absorptions, including those at 490, 675, 900, 1410, 1918, 2205, 2330, 2350, and 2380 nm. The absorptions at 490, 675, and 900 nm are related to hematite cement, while that at 2330 nm is associated with calcite cement. The absorptions at 1410, 2205, 2350, and 2380 nm are induced by the Al-OH vibration of kaolinite, and that at 1918 nm is related to crystal water. The calcite-dissolved sandstones have lower absorption intensities at 2330 nm than fresh sandstones, and the argillitic-altered sandstones have lower absorption intensities at 490, 675, and 900 nm than the fresh sandstones. In the 1st-derivative reflectance plots, the absorption peaks at ∼1400 nm shift towards shorter wavelengths with increasing kaolinite contents. The spectral features of the fresh, calcite-dissolved, and argillitic-altered sandstones are all different, and this means they can be distinguished spectroscopically, which demonstrates the usefulness of reflectance spectroscopy for the long-term monitoring of sandstone weathering in the Yungang Grottoes. [ABSTRACT FROM AUTHOR]

[Display omitted] • VNS spectroscopy are used to investigate mineralogy and geochemistry of drill cores rapidly and non-destructively. • K-M values are negatively correlated with Fe 2 O 3 , Fe3+/Fe2+, TOC, and carbonates, and positively with clay and kaolinite. • Redox is found to be the key U enrichment factor, and kaolinite and organic matter may cause limited U enrichment. The Qianjiadian deposit is the first late Mesozoic–Cenozoic sandstone-type uranium deposit discovered in the Songliao Basin, northeast China. It remains uncertain whether high-temperature hydrothermal fluid or low-temperature groundwater dominated the mineralization process that led to uranium enrichment in this deposit. We investigated the gamma ray intensity and semi-quantitative mineralogical and geochemical characteristics of drill cores from the Qianjiadian deposit. A total of 60 gamma ray anomalies were identified; most of these anomalies are associated with negative Fe 2 O 3 and Fe3+/Fe2+ anomalies, four are associated with positive total organic carbon (TOC) anomalies, and none are associated with positive carbonate (calcite + dolomite) anomalies. The absence of positive carbonate anomalies, together with low kaolinite crystallinities, rules out the influence of high-temperature fluid on uranium enrichment. The dominant negative Fe 2 O 3 and Fe3+/Fe2+ anomalies and the occurrence of pyrite in thin section and gray-red sandstone and native sulfur in some U-rich drill cores indicate that redox reactions in low-temperature groundwater may have been the principal control on uranium enrichment. In addition, two gamma ray anomalies are associated with positive TOC, Fe 2 O 3 , and Fe3+/Fe2+ anomalies and another two are associated only with positive kaolinite anomalies, suggesting that carbonaceous debris and kaolinite could also cause limited uranium enrichment. [ABSTRACT FROM AUTHOR]