A comparison between the China Clay deposits of China and Cornwall

In the People's Republic of China kaolin deposits are found in a wide range of geological settings both in the coastal and the inland provinces of southern China. Major deposits, predominantly kaolinitic, were produced by alteration of arkosic sediments in the Tertiary Basin of Maoming in Guangdong Province, while extensive halloysitic-kaolinitic assemblages are located on acid intrusive and volcanic sequences formed during the Yanshanian magmatic cycle (Late Mesozoic) throughout southern China. A brief description of the chemistry and mineralogy is given and shows a great deal of variation often reflecting the differing host rocks. The morphology of the sedimentary Maoming kaolinites is platy in nature with a typical pseudo-hexagonal shape and is very similar to the morphology of kaolins from Devon and Cornwall. The morphology of the altered volcanics and granites is dominated by tubular halloysite and stacky to platy kaolinite. Halloysite is not found in deposits from Devon and Cornwall. A stable isotope study (δD, δ¹⁸O) from Chinese deposits shows that the sedimentary derived kaolinites with a platy morphology have isotopic compositions clustered along the 'kaolinite line' but they show a considerable range. Samples from the other deposits with a mixed tubular and platy morphology have isotopic morphology have isotopic compositions that fall above this line. Previous isotopic work on kaolins with a platy morphology studied from Cornwall and the Czech Republic plot near the 'kaolinite line'. It is tentatively suggested that the occurrence of kaolinites and halloysites shows a close relationship with isotopic compositions and is governed by the origin and formation of the deposit in question.