A preliminary stable isotope study on Mogok Ruby, Myanmar

The primary occurrence of ruby in the Mogok area, northern Myanmar is exclusively found in marble along with spinel-forsterite-bearing marble and phlogopite-graphite marble. These marble units are enclosed within banded biotite-garnet-sillimanite-oligoclase gneisses. Samples of these marbles collected for C-O stable isotope analysis show two trends of δ 13C-δ 18O variation resulting most likely from fluid-rock interactions. Ruby-bearing marble and phlogopite-graphite marble follow a trend with coupled C-O depletion, whereas spinel-forsterite-bearing marble follows a δ 18O depletion trend with relatively constant δ 13C values. Ruby formation might have resulted from CO 2-rich fluid-rock interaction, while spinel-forsterite-bearing marble was genetically related to CO 2-poor fluid-rock interaction. Both fluids may have arisen from external sources. Based on graphite Raman spectral thermometry, the estimated temperature for phlogopite-graphite marble, and probably ruby-bearing marble, was lower than 607°C, and for spinel-forsterite-bearing marble, lower than 710°C. Contrasting C/O diffusion between graphite/ruby/spinel/forsterite and calcite, local variations of isotopic compositions of newly formed minerals as a result of non-pervasive fluid infiltration, and open-system isotopic disturbance during cooling may have affected C-/O-isotopic fractionations between minerals. The estimated high formation temperatures for ruby and spinel/forsterite imply that the parental fluids may have been related to nearby igneous intrusions and/or metamorphic processes. Whether these two types of fluid were genetically related is unclear based on the present data. © 2008 Elsevier B.V.