News Registration Abstract submission Deadlines Excursions Accommodation Organizing committee
First circular Second circular Abstracts Seminar History Program Travel Contact us
Первый циркуляр
Второй циркуляр
Оформление тезисов
Важные даты
Обратная связь

Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Origin of the mantle xenoliths with green garnets in kimberlites

(Newlands dyke, South Africa and Nyurbinskaya pipe, Yakutia)

Sablukov S.M. * , Sablukova L.I. * , Stegnitsky Yu.B. ** , Karpenko M.A. ***

     *“RUSGEO” Limited, Moscow, Russia;

  ** NIGP ALROSA Co. Ltd., Mirny, Russia;

*** Nyurbinskaya Mine, ALROSA Co. Ltd., Mirny, Russia.



Green garnets occur in concentrates of diamondiferous kimberlite bodies in Yakutia (Udachnaya, Zimnaya, Mir, etc.), South Africa (Newlands, Bellsbank), Venezuela (Guaniamo sills), and Canada (Mud Lake field) (Clarke and Carswell, 1977). Mantle xenoliths of rocks containing such garnets are very rare (Kharkiv, 1978).

We found peridotite xenoliths with green garnet in situ in kimberlites of the Newlands dike.  Xenoliths are irregular in form, 4.5*1.9 cm, 1.5*0.8 cm  (sample NL-11), and 1.0*0.5 cm in size  (sample NL-21), and have similar modal compositions: gar(70)+ol(28)+sp(2), gar(9)+ol(90)+sp(1) and gar(50)+ol(30)+sp(20). Rock texture is medium-crystalline, while structure is massive. We also identified a garnet macrocryst of 0.5*0.4 cm in size with a pale green kelyphytic rim  (sample NL-31) and 1.7*1.5 cm in size intergrowth: green garnet (14) + altered olivine (75) + chrome spinel small inclusions (1) (sample NL-41).

Garnet composition in the studied samples is quite constant and is characterized by the high Cr2O3 content (10.94-11.99%) and CaO content (19.52-24.94%) at the reduced contents of TiO2 (0.24-0.52%).  The chrome spinel is high Cr2O3 (55%) content and the low TiO2 (0.5-0.6%) content.  Olivine is high-Mg (Fo95), but elevated CaO content (0.09%).

Isotopic composition of oxygen in garnet (d18O = 4.05-4.25 pm) and olivine (d 18O = 4.91 pm) differs drastically from the mantle values  (d 18О = 5,5+/-0,4 о/оо  after Mattey et al., 1994).

Rb-Sr and Sm-Nd isotopic composition  (sample NL-11) show the relatively "young" model age of the sample relative to the depleted mantle (1.78 billion years), the age of formation of this rocks is also relatively "young" – probable mezoproterozoic.

In kimberlites and placers of the Nyurbinskaya pipe (Nakyn field, Yakutia) there are 4 green garnet grains of 0.5-2.0 mm in size, including one intergrowth gar+sp.   Most garnets are characterized by the higher CaO (18.06-22.87%) and TiO2 (1.46, 1.65, 1.75%) contents not noted before for similar garnets.

Studied green garnets have the similar "sine wave" type of REE distribution for low-Ti garnets and a "raised" type of REE distribution with enrichment in medium and light REE for high-Ti garnet.

All green garnets are characterized by an increased content of light REE and Sc. High-Ti garnets are characterized by an increased content of light and middle REE, as well as titanium, and a particularly sharply increased content of Zr (up to 1042 ppm!).

Paragenesis ol+sp is formed at 805o and 23.4 kbar, and paragenesis ol+gar is formed at 1080o and 23.8 kbar.   The rocks are characterized by nonequilibrium paragenesis ol+sp+gar and formation at moderate depths (80-90 km) under conditions of high heat flow (52-55 mW/m2).

Judging from variations modal composition of studied xenoliths, absence of clinopyroxene, variations in chemical compositions and trace element compositions, relatively "young" model age and non-mantle isotopy of oxygen in garnets, these rocks are not “wehrlites” and likely represent metasomatic rocks such as uvarovite-chromite veins or schlierens at the moderate depths of upper mantle – it is similar to uvarovite-chromite veins of the metasomatic or a hydrothermal origin in the crustal serpentinites.


Clarke D.B. and Carswell D.A. (1977) Green garnets from the Newlands kimberlite, Cape Province, South Africa. Earth and Planetary Science Letters 34 . p. 30- 38.

Kharkiv A.D. (1978) A find of the ore wehrlite xenoliths in “Zimnaya” kimberlite pipe (Verhne-Munsky diamondiferous region, Yakutia) Dokl. Akad. Nauk SSSR. 252(3), 707-711 (in Russian).

Mattey, D., Lowry, D., Macpherson, C. (1994). Oxygen isotope composition of mantle peridotite. Earth Planet. Sci. Lett. 128, P. 231-241.