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Тезисы международной конференции

Рудный потенциал щелочного, кимберлитового

 и карбонатитового магматизма

Abstracts of International conference

Ore potential of alkaline, kimberlite

and carbonatite magmatism

Petrological problems of Badmer nephelinite-phonolite association, Rajasthan, India

Viladkar S.G.

Carbonatite Research Centre, Amba Dongar, India


Nephelinite-phonolite rocks are exposed in the northwestern part of India around Barmer at Sarnu, Dandali and Kamthai (Rajasthan).  The occurrence of alkaline rocks at Sarnu-Dandali were first reported by Udas et al. (1974) and later described by Narayan Das et al. (1978).  Study of the area was followed by Chandrasekaran et al. (1990) and   

Occurrences of nephelinite and phonolite from Rajasthan are situated within the Luni Graben. In general, nephelinite outcrops as small plugs without sharp contacts with the country rock.  Felsic and melanocratic phonolite (melaphonolite) occur mainly in the form of dikes that contain xenoliths of metamorphic basement.  Thin veins consisting mainly of feldspar invade the felsic phonolites.  The contact between melaphonolite and felsic phonolite is usually sharp; the latter intrude the former in the form of thin dikes.  Compared to the carbonatite occurrences from the Sarnu-Dandali area, carbonatite dikes from the Kamthai area are more numerous and larger in size.

Unpublished work of Viladkar suggest that Mg numbers (63 to 70), Cr (146 to 484 ppm) and Ni (54 to 123 ppm) ) contents for melanephelinites from Barmer are similar to those from olivine-bearing nephelinites from Napak (Simonetti and Bell, 1994a).  Such low abundances of Ni and Cr may be attributed to olivine fractionation, and are not indicative of primitive magmas.  The composition of melanephelinite is also similar to the average composition of olivine-poor nephelinite as determined by Le Bas (1987).  Compared to the major element composition from melanephelinite, analyses for felsic phonolites show higher Si, Al, Na and K contents, and lower Ca, Fe, Mg, P and Ti abundances.

Among all of the silicate rocks analyzed from Barmer, melanephelinite contains the lowest abundance of REEs, and their chondrite-normalized patterns are steeply-sloping, LREE-enriched.  Two melaphonolites contain an extremely high content of total REEs.  Among the felsic phonolites, sample 20BAR shows both the highest abundance of total REEs and LREEs indicating that it is likely to be the most differentiated from the series.  In addition, two samples (one melaphonolite and felsic phonolite) show a prominent, negative Eu anomaly, which may be attributed to the fractionation of alkali feldspar.



Udas, G.R., 1974.  Geochemistry of Pre-cambrian carbonatite complexes of India: Present status of and gaps in our knowledge.  Journal Geological Society of India 7, 457-462.

Narayan Das, G.R., Bagchi, A.K., Chaube, D.N., Sharma, C.V. & Navaneetham, K.V., 1978.  Rare metal content, geology and tectonic setting of the alkaline complexes across the Trans Aravalli region, Rajasthan.  Recent Researches in Geology 7, 201-217.

Le Bas, M.J. 1987. Nephelinites and carbonatites. In Fitton J.G. and Upton, B.G.J (eds) Alkaline Igneous Rocks. Geol. Soc. London.Spec. Publ. 30, 53-83

Simonetti, A and Bell, K., (1994) Nd, Pb and Sr isotopic data from the Napak carbonatite-nephelinite centre eastern Uganda: an example of open system crystal fractionation. Contri. Mineral. Petrol. 115, 356-366.

Chandrasekaran, V., Srivastava, R.K. and Chawade, M.P. (1990) Geochemistry of the alkaline rocks of Sarnu-Dandali Area, District Barmer, Rajasthan, India. J. Geol. Soc. India. 36, 365-382.

Viladkar S.G., Zaitsev V.A.Preliminary data about alkaline rocks occurrences from Barmer region, Rajasthan, India//Abstracts of International conference Ore potential of alkaline, kimberlite and carbonatite magmatism, Minsk 2011 pp 45-47.