Cathodoluminescence of Microdiamond in Dolomite Marble from the Kokchetav Massif—Additional Evidence for Two-Stage Growth of Diamond

Abundant microdiamonds occur as inclusions in garnet and diopside in dolomite marble from the Kumdy-kol area of the Kokchetav Massif. These microdiamonds have been classified by previous work into three types (S type, R type, T type) according to their morphology. S-type diamond, the most abundant type in Kokchetav dolomite marble, was examined using microcathodoluminescence (CL) spectroscopy to detect the difference between core and rim. Cathodoluminescence was obtained as spectra and intensity images at the peak of the main CL band using two kinds of CL spectrometer combined with a scanning electron microscope (SEM). Strong broad bands of the CL spectra at 514 to 537 nm were detected at the rim of all S-type microdiamond grains. The core also has the same broad band, but its intensities are very weak. The weak broad band at about 393 nm was detected at the rim of some grains; another weak broad band at about 440-450 nm was also detected both in the core and the rim of several grains by the MP-32 spectrometer system. The intensity images of CL spectra at the peak wavelength (514-537 nm) of the main broad band showed a clear difference between core (weak) and rim (strong). These CL data indicate different geochemical environments for the growth of core and rim of S-type microdiamonds, and provide additional evidence for the two-stage growth of microdiamond in dolomite marble, as previously proposed.