New Identity of the Kimberlite Melt: Constraints from Unaltered Diamondiferous Udachnaya – East Pipe Kimberlite, Russia - Advances in Data, Methods, Models and Their Applications in Geoscience - page 184

zemkorite (Na, K) 2 Ca(CO 3 ) 2 ), chlorides (halite and sylvite), and minor phlogopite and
opaque minerals (e.g. spinel group minerals, perovskite, Fe±(Ni,Cu,K) sulphides) (Golovin
et al., 2007; Golovin et al., 2003; Kamenetsky et al., 2004; Kamenetsky et al., 2007a; Sharygin
et al., 2003; Sobolev et al., 1989). Groundmass olivine is very abundant (up to 40 vol%),
completely unaltered, and contains crystal, fluid and melt inclusions (Fig. 3; Golovin et al.,
2003; Kamenetsky et al., 2004; Kamenetsky et al., 2007a; Kamenetsky et al., 2008;
Kamenetsky et al., 2009a).

1 00  m

Mg

Ca

Cl

Na

Fig. 2. Backscattered electron image and X-ray element maps showing intimate association
of euhedral zoned olivine, Na-K chlorides, alkali carbonates, calcite, and sodalite in the
groundmass of Udachnaya-East kimberlite

The bulk rock compositions are also characterised by low Al 2 O 3 (1.2-2.3 wt%), but high CaO
(8.4-18.2 wt%) and CO 2 (4-14 wt%) contents. Trace element compositions are similar to those
of other kimberlites, having incompatible element enrichment and depletion in heavy rare-
earth elements and Y (Fig. 4). The radiogenic isotope data ( 87 Sr/ 86 Sr t ≈ 0.7047, ￿Nd ≈ +4,
206 Pb/ 204 Pb t ≈ 18.7, 207 Pb/ 204 Pb t = 15.53, 208 Pb/ 204 Pb t = 35.5-38.9, t = 367 Ma; Maas et al., 2005)
fall within the field defined by most group-I kimberlites (Fraser et al., 1985; Smith, 1983;
Weis & Demaiffe, 1985). The overall petrographic, mineralogical and chemical
characteristics of the Udachnaya-East kimberlites suggest that they are common type-I
(Mitchell, 1989) or group-I (Clement & Skinner, 1985; Smith, 1983) kimberlite.
However, the studied Udachnaya-East samples are distinctly different from other
kimberlites in that they have high abundances of alkali elements (up to 6 wt% Na 2 O), strong
enrichment in chlorine (up to 6 wt%), and extraordinary depletion in H 2 O (< 0.5 wt%)
correlated with absence of primary or secondary serpentine. Thus unusual for kimberlites
low H 2 O abundances coupled with extraordinary enrichment in Na 2 O and Cl (Fig. 5) may