Fluid characteristics from shallow magmatic environments: A contribution to danburite bearing Luc Yen pegmatites, northern Vietnam
Keywords:Pegmatites, danburite, fluid inclusions, necking down, Luc Yen
Danburite as a member of the Luc Yen pegmatite mineral assemblage has been studied using fluid inclusion microthermometry and Raman spectroscopy. Data characterize well-preserved fluid inclusions which originate from primary large tubular inclusions as result of necking down. Same modifications underwent a second inclusion generation that evolved during healing of a later crack. Both generations of fluid inclusions show the same chemistry (H2O-CO2) characterizing 3-phase inclusions with additional solids (calcite, sassolite and danburite). Inclusions consist of pure CO2 and H2O with additional NaCl ± KCl comprising a salinity of about 4.5 mass%. Internal fluid inclusion pressures as well as bulk inclusion densities have been calculated using the fermi diad split method of pure CO2 at clathrate melting temperatures of the system and total homogenization temperatures, respectively. Mean internal pressures of ca. 4.5 MPa as well as a bulk density around 0.60 g/cm3 represent a low-dense fluid with XH2O~0.86 and XCO2~0.14 in composition that was present during formation of danburite. Data characterize danburite as a late stage crystallization member of the pegmatite in a shallow magmatic environment.
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