Carbon isotopic composition of diamonds from the Archangelsk diamond province

The first data are reported on the carbon isotopic composition of diamond crystals from the Grib pipe kimberlite deposit of the Archangelsk diamond province (ADP). The δ 13 C value of the crystals ranges from −2.79 to −9.61‰. The isotopic composition of carbon was determined in three zoned crystals (δ 13 C of −5.8 −6.96 ‰, −5.64/ −5.85 ‰, and −5.94/ −5.69 ‰), two “diamond in diamond” samples (diamond inclusion with δ 13 C of −4.05 and −6.34 ‰ in host diamond crystals with δ 13 C of −8.05 and −7.54 ‰, respectively), and two samples of coated diamonds (cores with δ 13 C of −6.98 and −6.78‰ and coats with δ 13 C of −7.51 and −8.01 ‰, respectively). δ 13 C values were obtained for individual diamond crystals from bort-type aggregates (δ 13 C of −4.24/ −4.05 ‰, −6.58/ −7.48 ‰, and −5.48/ −6.08 ‰). Correlations were examined between the carbon isotopic composition of diamonds and their crystal morphology; the color; the concentration of nitrogen, hydrogen, and platelet defects; and mineral inclusions content. It was supposed that the observed δ 13 C variations in the crystals are most likely related to the fractionation of carbon isotopes rather than to the heterogeneity of carbon sources involved in diamond formation. The isotopic characteristics of diamonds from the Grib pipe were compared with those of previously investigated diamonds from the Lomonosov deposit. It was found that diamonds from these relatively closely spaced kimberlite fields are different; this also indicates the existence of spatially localized peculiarities of isotope fractionation in processes accompanying diamond formation.