Raman Imaging of Multiphase Fluid and "Black" Inclusions in Tourmaline From Kumdy‐Kol Microdiamond Deposit (Kokchetav Massif, Northern Kazakhstan).

Raman spectroscopy, especially Raman imaging, has become a popular technique for fluid inclusion studies. Raman imaging is particularly useful for the study of tiny inclusions appearing in high or ultrahigh pressure (UHP) metamorphic minerals. The small size of daughter phases, as well as the presence of liquid or gas phases, precludes the application of microprobe analysis for unexposed inclusions. Nontransparent inclusions, usually assigned as "opaque", "ore," or "black" accessory minerals, are rarely studied by Raman spectroscopy due to the high absorbance of laser energy by black materials, their unstable behavior at the laser beam, and low Raman signal. Despite these difficulties, a number of documented examples show that multiphase inclusions in these metamorphic rocks may persist. These inclusions provide valuable information on the composition of fluids in deeply subducted environments. For the first time, we demonstrate that "opaque" or "black" inclusions in UHP rocks are multiphase. They contain CO2 + CH4 gas bubbles ± calcite and graphite with different degrees of crystallinity. These multiphase fluid inclusions coexist side by side with "classical" inclusions which also contain CO2 and CH4 gases, as well as liquid water, but no graphite. Our findings demonstrate that Raman imaging of "classical" and "black" fluid inclusions and subsequent data treatment by different techniques may bring important information about their composition. [ABSTRACT FROM AUTHOR]