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The historical stockpile of chromium slag in China is large, and the hexavalent chromium in slag leachate is highly toxic and migratory. In order to investigate the migration and transformation pattern of Cr(Ⅵ) in groundwater under the combined effect of pollution source, site hydrogeological condition and hydrogeochemical process, a hexavalent chromium contaminated site was taken as an example in this study, the spatial distribution, hydrogeochemical characteristic, occurrence form and proportion of Cr(Ⅵ) in groundwater, and the main factors affecting migration and transformation of Cr(Ⅵ) are analyzed by sampling and testing groundwater samples, and the combination using of methods such as Kriging interpolation, factor analysis, hydrogeochemical calculation, Piper diagram and ion ratio. The results show that (1) the two aquifers below ground surface 40 m are polluted by Cr(Ⅵ), but the size and degree are different obviously. (2) The main forms of Cr(Ⅵ) in groundwater are \begin{document}${\mathrm{CrO}}_4^{2-} $\end{document} and \begin{document}${\mathrm{HCrO}}_4^- $\end{document}, \begin{document}${\mathrm{Cr}}_2{\mathrm{O}}_7^{2-} $\end{document} content is extremely low, and the anions of samples with high Cr(Ⅵ) concentration are mainly \begin{document}${\mathrm{HCO}}_3^- $\end{document} and \begin{document}${\mathrm{SO}}_4^{2-} $\end{document}, the cations are mainly Na+ and Ca2+. (3) Precipitation leaching and seepage result in the leachate containing large amounts of Na+, \begin{document}${\mathrm{SO}}_4^{2-} $\end{document} and Cr(Ⅵ) entering groundwater. The increasing pH, high concentrations of \begin{document}${\mathrm{HCO}}_3^- $\end{document} and dissolution of iron oxides under low oxidizing environment in groundwater can facilitate the migration of Cr(Ⅵ). Manganese oxides and organic matter are able to change Cr(Ⅵ) content through redox reaction. Evaporation also plays an important role on the enrichment of Cr(Ⅵ) in groundwater. The results of this research can provide strong support for risk management and post remediation of chromium slag contaminated sites.

Objective The Chishan rare earth deposit in Weishan County, Shandong Province is located on the southeastern edge of the North China Plate. It is a magmatic hydrothermal rare earth deposit mainly composed of light rare earths, and is currently the third largest light rare earth deposit in China. There is still controversy over its mineralization age. Methods Therefore, taking the latest exploration borehole ore samples from Chishan rare earth deposit as the research object, the mineralization age of Chishan rare earth deposit was accurately determined through field investigation, mineralogy, and chronology research, using Th-Pb isotope dating of fluorocarbon cerium ore. Results The Th-Pb isotope dating results of 5 fluorocarbon cerium deposits indicate that the mineralization age of the Chishan rare earth deposit can be divided into two periods: the early period is (125.5±0.5)-(122.2±0.5)Ma, and the late period is (112.3±0.6) Ma. Conclusion The early age is basically consistent with the mineralization age of the deposit determined by previous studies, while the late mineralization age is the first report, indicating that there may be two periods of mineralization activity in the Chishan rare earth deposit, which is worthy of attention and further work.