The “Exceptionally Fresh” Udachnaya-East Kimberlite: Evidence for Brine and Evaporite Contamination

Ultrafresh salty kimberlite of the Udachnaya–East pipe (Yakutia, Russia): A petrological oddity or fortuitous discovery?

“…Two areas appear particularly contentious: our interpretation of these compositions as "fresh" or "least altered" (Kjarsgaard et al, 2009) and our assertion that they represent mantle-derived melt (Kostrovitsky et al, 2012). Critics cite the C-O stable isotope compositions of our rocks (Table 1 and Fig.…”

Was Crustal Contamination Involved in the Formation of the Serpentine-Free Udachnaya-East Kimberlite? New Insights into Parental Melts, Liquidus Assemblage and Effects of Alteration

“…In general, all units of kimberlite at the 410 -500 m depth interval have been referred to as 'Serpentine Free Udachnaya-East' (SFUE) kimberlite by Kopylova et al (2013) and Kostrovitskiy et al (2013). Note that kimberlitic units 9 and 10 are partially serpentinised at depths of 370 -410 and 500 -640 m (Fig.…”

“…Six partially serpentinised samples (K16/05, K20-05, K28/05, K17/04, K25/04, K-U) were derived from depth intervals of 480 -520 m (below the SFUE) and 400 -420 m (roof of the SFUE) and five unserpentinised samples (UV-K1-15, K2-03, K24/04A, K24/04B, UV-K1-05) were sourced from a depth interval of 440 -500 m (within the SFUE; Table 1). The petrography of both serpentinised and unserpentinised varieties of the UE kimberlites have been extensively described in the literature (e.g., Marshintsev, 1986;Egorov et al,1991;Kharkiv et al, 1991;Kamenetsky et al, 2004Kamenetsky et al, , 2008Kamenetsky et al, , 2012Kamenetsky et al, , 2014Kopylova et al, 2013Kopylova et al, , 2016Kostrovitskiy et al, 2013;d'Eyrames et al, 2017;Kitayama et al, 2017).…”

“…This has motivated a group of authors to assert that the parental magma was no different to other kimberlites worldwide (i.e. H 2 O-rich, ultramafic), but was contaminated by crustal xenoliths (e.g., evaporites) and, or, altered by post-emplacement sedimentary Na-Ca-Cl brines (Kopylova et al, 2013(Kopylova et al, , 2016Kostrovitskiy et al, 2013). These authors have presented numerous accounts of the preservation of olivine, the low H 2 O contents and origin of high alkalis, chlorine and sulphur in unserpentinised UE kimberlite rocks.…”

“…These studies have consistently produced similar results, advocating the Si-poor and alkali-Cl-S (and to a lesser extent P-F)-bearing carbonaterich nature of kimberlite melts entrapped within inclusions. This alternative model for kimberlite petrogenesis has been heavily criticised in recent studies by Kopylova et al (2013Kopylova et al ( , 2016 and Kostrovitskiy et al (2013). These authors emphasise that the unique Na-Cl-S-enriched groundmass mineralogy of the Udachnaya-East pipe is not exceptional or representative of pristine kimberlite, but can be explained by:(i) contamination of the kimberlite magma by crustal material, and (ii) interaction with external Na-Ca-Cl brines that precipitate salts and carbonates.…”