Diagenesis of Dawsonite bearing Tuffite in Beier Sag, Hailar Basin

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Abstract: The dawsonitebearing pyroclastic rock from DamoguaiheYimin Formation in Beier Sag of Hailar Basin was taken as the research object. Polarization microscope, Scanning Electron Microscope, Energy Disperse Spectroscope, alizarin redS staining, Cathode Luminescence and Xray Diffractomer are used in this research to study its rock type, types of authigenic minerals and paragenetic sequences. It is ascertained that the host rock type of dawsonite is tuffite and carbonates are the main authigenic mineral such as dawsonite, ankerite and siderite. Content of dawsonite is up to 25%. The paragenetic sequence is shown as sideriteⅠ→ kaolinite, overgrowth quartz → dawsonite → microcrystalline quartz → calcite → ankerite → sidriteⅡ→ bitumen. Dawsonite is characterized by replacing feldspar, quartz, debris and kaolinite matrix, which is different from porefilling dawsonite found in other field, implicating that these mass in tuffite could provide origin of metal ions, and reacting with diagenetic fluid under the participation of CO2 which results in precipitation of dawsonite. Large amount of carbonates (15%~44%) developed proves that pyroclastic rock owns a relatively well capacity of CO2 fixation.