The origin and formation of metamorphic microdiamonds from the Kokchetav massif, Kazakhstan: a nitrogen and carbon isotopic study

Discrimination of metamorphic diamond populations by Raman spectroscopy (Kokchetav, Kazakhstan)

“…Comparing this band with our spectra, we can conclude that there is clearly an offset of about 50 cm −1 with the C O peak; the Raman band which is reported here is at a different position and is much broader. Among all different diamond types, diamonds from garnet-pyroxene rocks were shown to bear up to 11,000 ppm of nitrogen, the highest amount recorded [19][20][21]. The 1700 cm −1 band may be associated with the very high content of double bounded N N or N C groups [35,36].…”

“…De Corte et al [19] classified these diamonds as Ib-Ia types and suggested that nitrogen is incorporated in the diamond lattice as single atoms (carbon defect) or pairs of nitrogen atoms [37][38][39]. However, a significant quantity of nitrogen (up to 7000 ppm) has been found as an infrared-inactive form and may represent fluid inclusions [21], where nitrogen occurs as N 2 fluids and not as platelet defects [20,21]. This tends to suggest that the presence of this ∼1700 cm −1 Raman band may be assigned to the presence of N 2 -fluid inclusions with an average size of less than 1 m [35,36].…”

“…Previous studies demonstrated that the diamond morphology and the content and aggregation state of its nitrogen impurities are related to the lithology [19][20][21]. Relying on this information, intragranular diamond included in garnets from representative samples of garnet-biotite gneiss, garnet-zoisite gneiss, carbonate rock (marble) and garnet-clinopyroxene (Grt-Cpx) rock were selected.…”

“…1. Details on these lithologies, their mineral assemblages and their diamond properties were published elsewhere [17,21,[23][24][25]. Besides these intragranular diamonds, diamonds in Kokchetav rocks might occur intergranular [26].…”

“…Kokchetav microdiamonds have been widely investigated by other analytical methods and it has been shown that their morphology, nitrogen impurities and inclusion contents change depending on the lithology [18][19][20][21]. Assuming that these changes in their characteristic properties should also be reflected in their Raman spectra, it is the second aim of this work to attempt to discriminate distinct diamonds from different rock types of the Kokchetav massif, by means of Raman spectroscopy.…”