MECHANISM FOR KOSMOCHLOR SYMPLECTITE AND COMPOSITIONAL VARIATION ZONING IN JADEITE JADE

At present, different views on the compositional variation and origin of the kosmochlor, a new mineral, are held out. In this paper，the petrographic and EPMA analytical testing technologies are employed with an emphasis on the investigation into mineral microfacies，m icrofabric and microscopic chemical elements. The research indicates that kosmochlor is mainly in the form of symplectite substi- tutes or surrounds chromite, a primary mineral in jadeite. Part of kosmochlor is metasomatized with chromite adjacent to jadeite ，resulting in the three-layer symplectitic zoning of kosmochlor-calcic kos- mochlor-uvarovite. In this way, the chemical com positional variation zoning occurs ，revealing the mul- ti-stages and complexity of the imbalanced metasomatic reaction. It can be concluded that the coupling of ion diffusing bimetasomatism with flow percolating metasomatism between the mineral particles is the major cause of kosmochlor symplectite and compositional variation zoning.