Metasomatic diamond growth: A multi-isotope study (13C, 15N, 33S, 34S) of sulphide inclusions and their host diamonds from Jwaneng (Botswana)

Mantle Sulfides and their Role in Re–Os and Pb Isotope Geochronology

“…Although a subduction origin for the carbon from which some diamonds form may be controversial (cf. Cartigny et al 2001), a subduction-related origin for diamond formation and for the supply of material to Archean SCLM roots is independently supported by (i) both S and Pb isotope systematics of BMS grains in eclogitic diamonds (Eldridge et al 1991;Rudnick et al 1993b;Farquhar et al 2002;Thomassot et al 2009), (ii) by diamondbearing eclogite xenoliths whose oxygen isotopic systematics are not consistent with a mantle origin (e.g., Jacob 1994; Shirey et al 2001Shirey et al , 2004aShirey et al , 2008, and (iii) by the correlation between isotopically light C in diamond and the isotopically heavy O in eclogitic silicate inclusions (Ickert et al 2013(Ickert et al , 2015Schulze et al 2013). The S-saturated nature of the eclogitic protolith is less controversial and is based on the occurrence of BMS globules in MORB (e.g., Roy-Barman et al 1998) and the absence of evidence for wholesale melting of the eclogitic protolith that would have removed the sulfur during subduction.…”

Homogenisation of sulphide inclusions within diamonds: A new approach to diamond inclusion geochemistry

“…Sulphur isotopic compositions (particularly d 34 S) may also be affected by partial sampling of inclusions, as instrumental mass-fractionation is sensitive to the endmember sulphide analysed (e.g., Chaussidon et al, 1987;Thomassot et al, 2009). Sulphide inclusions in Orapa diamonds show a range in d 34 S from +2.1 to +9.5‰ (pyrrhotite, Chaussidon et al, 1987) to À11 to +2‰ (Mss and pyrrhotite, Eldridge et al, 1991).…”

“…Because of this fractionation, it is incumbent that all of the mass of the inclusion be extracted intact to ensure a completely unbiased estimate for the composition of the original bulk sulphide Taylor and Liu, 2009;Harvey et al, 2016). However, the 'flaking' or disintegration of the sulphide during inclusion extraction by breaking open the diamond, is a frequently documented and inherent problem (e.g., Deines and Harris, 1995;Pearson et al, 1998;Richardson et al, 2001Richardson et al, , 2009Thomassot et al, 2009). Thus, partial sampling of BMS inclusions is common and may introduce a serious bias to geochemical and/or isotopic results and classifications.…”

“…Mass-independent fraction D 33 S in the Farquhar et al (2002) study reported a range from À0.1 to + 0.6‰. In all cases, the range of d 34 S and D 33 S has been used to infer an isotopic signature for both younger (<2.45 Ga) and older (>2.45 Ga) subduction of S-bearing sediments, as recorded in the mantle (e.g., Farquhar et al, 2002;Thomassot et al, 2009).…”

“…BMS occur in both major diamond parageneses, being relatively Nirich in peridotitic (P-type) diamond and relatively Nipoor when associated with eclogitic (E-type) diamonds. Their relative abundance may itself be informative for understanding diamond mineralisation where transient volatile-rich (C, H, O, N, S) metasomatic agents have been suggested as key to diamond formation (e.g., Deines and Harris, 1995;Westerlund et al, 2004;Thomassot et al, 2007Thomassot et al, , 2009Stachel and Luth, 2015). Thus studies of BMS inclusions within diamonds have become a major line of enquiry; for the timing and genesis of diamond growth, for models of crustal and mantle development during the Archaean and the Earth's deep carbon cycle (e.g., Hart et al, 1997;Pearson et al, 1998;Richardson et al, 2001Richardson et al, , 2009Shirey et al, 2004;Stachel and Harris, 2008;Dasgupta and Hirschmann, 2010;Harvey et al, 2016).…”