Abstract
Abstract. Scanning electron microscopy-cathodoluminescence (SEM-CL) imaging of vein quartz in the Cu-mineralised, Shuteen Complex (South Gobi, Mongolia) has revealed a complex history of crystal growth, dissolution and microfracture healing, associated with several hydrothermal events that could not be detected using other observational techniques (e.g. transmitted/reflected light microscopy, back-scattered electron imaging, or secondary electron imaging). The quartz initially grew as CL-bright/grey crystals in a 345±30d̀C liquid reservoir, as inferred by the analysis of primary liquid fluid inclusions (average Th of 343d̀C; 6.6∼7.7 wt% NaCleq). Quartz precipitation occurred at the edge of the crystals as reservoir fluids cooled to 260±25d̀C, as indicated by micron-scale CL-dark/CL-bright quartz growth bands containing abundant fluid inclusions (with an average Th values of 261d̀C). Pressure fluctuations were the likely cause of dissolution, as SEM-CL imaging reveals the quartz have corroded or rounded crystal edges, and precipitation of later quartz into open space. SEM-CL imaging shows the quartz contains healed microfractures that trapped low salinity fluids (3.9 wt% NaC1eq) with Th values of 173±15d̀C. SEM-CL imaging provides a means of deciphering the thermal and chemical evolution of the fossil Shuteen hydrothermal system, and the nature of hydrothermal quartz vein-forming processes, by facilitating the correlation of distinct fluid inclusion populations and their relative chronology, with specific hydrothermal events.
Published Version
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