Fluid Inclusion Geothermometry Used to Recognise an Ancient "Silica Sinter"

Abstract

The Da Yuwan "silica sinter" in the Shui Koushan Mining District was described by Haynes (1989)who attempted to prove that a hot spring system existed here in the early Cretaceous. The deposit has been reassessed using fluid inclusion geothermometry. The "sinter", in fact, is a silicified breccia without any flow textures or plant fossils. Study shows that it contain two generationsof fluid inclusions. The earlier fluidwas trapped in primary or pseudo secondary inclusionsalong growthzones in quartz at about and with apparent salinities of 2.4-7.0 eqv NaCl. Most secondary inclusions are single phase or necked. The results suggests that the Da Yuwan silicified breccia body is unlikely to be a subaerial deposit but formed below m depth in an epithermal system interpretedto be of meteoric origin but are probably mixed with connatewater.