Based on outcrop observation, microscopic identification and EPMA, it is determined that the mineral association complexes in the Pingchau Formation of the Pingchau Island, Hong Kong, are glauberite pseudocrystals replaced by analcime, acmite and calcite, which show bipyramid shapes and scattered occurrence in mud beds. It is proposed that hydrothermal alteration and replacement processes played a main role for the glauberite to have been changed to analcime, acmite and calcite, as the primary glauberite provided Na 2O and CaO and the hydrothermal activity produced SiO 2-bearing fluid. This result suggests that the Pingchau Formation is a salt-bearing sequence, and that the Mirs Bay was once a highly saline evaporate basin during the late Cretaceous to Eogene.