A mantle origin for Paleoarchean peridotitic diamonds from the Panda kimberlite, Slave Craton: Evidence from 13C-, 15N- and 33,34S-stable isotope systematics

In order to address diamond formation and origin in the lithospheric mantle underlying the Central Slave Craton, we report N- and C-stable isotopic compositions and N-contents and aggregation states for 85 diamonds of known paragenesis (73 peridotitic, 8 eclogitic and 4 from lower mantle) from the Panda kimberlite (Ekati Mine, Lac de Gras Area, Canada). For 12 peridotitic and two eclogitic sulfide inclusionbearing diamonds from this sample set, we also report multiple-sulfur isotope ratios. The 73 peridotitic diamonds have a mean delta C-13-value of -5.2 parts per thousand and range from - 6.9 to - 3.0 parts per thousand, with one extreme value at -14.1 parts per thousand. The associated delta N-13-values range from -17.0 to +8.5%. with a mean value of -4.0 parts per thousand. N-contents range from 0 to 1280 ppm. The 8 eclogitic diamonds have delta C-13-values ranging from -11.2 to -4.4 parts per thousand with one extreme value at -19.4 parts per thousand. Their delta N-13 ranges from -2.1 to +7.9%. and N-contents fall between 0 and 3452 ppm. Four diamonds with an inferred lower mantle origin are all Type II (i.e. nitrogen-free) and have a narrow range of delta C-13 values, between -4.5 and - 3.5 parts per thousand. The delta S-13 of the 14 analyzed peridotitic and eclogitic sulfide inclusions ranges from -3.5 to +5.7 parts per thousand. None of them provide evidence for anomalous delta S-13-values; observed variations in delta S-13 are from +0.19 to -0.33 parts per thousand, i.e. within the 2 sigma uncertainties of mantle sulfur (delta S-33 = 0 parts per thousand). At Panda, the N contents and the delta C-13 of sulfide-bearing periclotitic diamonds show narrower ranges than silicate-bearing peridotitic diamonds. This evidence supports the earlier suggestion established from eclogitic diamonds from the KaapvaaI that sulficle- (+/- silicate) bearing diamonds sample a more restricted portion of sublithospheric mantle than silicate-(no sulfide) bearing diamonds. Our findings at Panda suggest that sulfidebearing diamonds should be considered as a specific diamond population on a global-scale. Based on our study of delta S-34, Delta S-33, delta N-13 and delta C-13, we find no evidence for subduction-related isotopic signatures in the mantle sampled by Panda diamonds. (C) 2009 Elsevier B.V. All rights reserved.