define and explain carbonatite

1. Seminar on Carbonatites

2. Contents:
 Introduction
 Mineralogy
 Texture
 Classification
 Geochemistry
 Origin
 Carbonatites association
 Economic importance
 Occurence
 Conclusion
 Reference

3. e
Introduction
• Carbonatites are plutonic igneous rock and found either
in intrusive or extrusive igneous rocks more than
50% carbonate minerals are present .
• “Carbonatite” was introduced by the Norwegian
petrographer W. Brugger (1921).
• Carbonatites are primarily composed of calcite (or
dolomite) of igneous origin and silicate mineral are also
present.
• Importance:
Academic-Carbonatite are derived from mantle.
Economic- Carbonatites contain rare earth elements.

4. Ol Doinyo Lengai
volcano in
Tanzania.

5. Mineralogy:
Mineralogy:
•Carbonatites are composed of olivine, pyroxene, calcium
carbonate,apatite.
• They range from essentially monomineralic types consisting
nearly entirely of calcite or dolomite to varieties in which several
rhombohedra carbonates are accompanied by numerous light and
dark silicates and by phosphates, sulfates, iron oxide minerals, RE
carbonates, sulfides, fluorides and Nb oxide species.
•Carbonatites are classed as calcitic sovite and alvikite
varieties.The two are also distinguished by minor and trace
element .

6. Mineralogy:
•Natrocarbonatite is made up largely of two minerals, nyerereite and
gregoryite . These minerals are both carbonates in which sodium and
potassium are present in significant quantities.

7. Mineralogy:
Texture :
Carbonatites show coarse grain or fine grain texture in
hand specimens and hypidiomorphic texture in thin
section.
Fenite:
Fenite is the contact zone between carbonate and
country rock enriched in alkalis i.e. Na and K. This
fenite are the indicator zone that marks the presence
of a carbonatite.

8. Classification:
• Based on dominant mineral
– Calcite carbonatite
– Dolomite carbonatite
• Based on whole rock analysis
– Calciocarbonatite: >80% CaO
– Magnesiocarbonatites: MgO > FeO+Fe2O3+MnO
– Ferrocarbonatites: FeO+Fe2O3+MnO > MgO
– Natrocarbonatites: Alkali-rich – Na, K, Ca

9. Geochemistry:
• Carbonatite is composed predominatly of carbonate
minerals and extremely unusual in its major element
composition as compared to silicate igneous rocks
because it is composed primarily of Na2O and CaO plus
CO2.
• Geochemically, Carbonatites are dominated by
incompatible elements (Ba, Cs, Rb) and depletions
in compatible elements (Hf, Zr, Ti).
• This together with their silica-undersaturated
composition supports inferences that Carbonatites
are formed by low degrees of partial melting.

13. Origin of carbonatites:
• Direct generation by low degree partial melts in the
mantle and melt differentiation.
• Fractional crystallization of a carbonate alkaline
silicate melt.
• Liquid immiscibility between a carbonate melt and a
silicate melt.

14. ASSOCIATION OF CARBONATITES:
I. Associated with alkalic ring complexes:
1.Core Carbonatites: one or two small
plugs or stocks situated more or less
centrally in the ring complexes.
2. Dykes, ring-dykes, cone-sheets and
breccias zones of Carbonatites.

15. II. Associated with alkalic complexes not of the ring type
1.Large thick sheets or tabular to irregular masses.
2.Dykes, dike swarms, stock worth's or sill within or to alkalic
complexes of irregular structure.
III. Not directly associated with any alkalic complex.
1.Large sheets of composite structure.
2.Swarms of Carbonatite dikes or sills.
IV. Extrusive(volcanic) carbonatite.
1. Carbonatite lava flows.
2. Pyroclastic carbonatitic rocks.

16. World occurrences of
Carbonatites

17. United state:
• Magnet cove, Arkansas.
• Potash Sulphur springs, Arkansas.
• Southeastern Missouri.
• Westcliffe Colorado.
• Sulphide queen carbonatite body, mountain pass, san
Bernardino country, California.
Canada:
• Fort Rupert area, Quebec.
• Oak Rupert area, Quebec.
• Manitou Islands, Lake Nipissing, Ontario.

18. BRAZIL:
• Jacupiranga SAO Paulo
• Registo SAO Paulo
Green land, Europe and USSR:
Fen area, Telemark
• Alno island, Sweden
Africa:
Somalia, Uganda,
Suluku, Tororo,
Congo, Kenya

19. Indian occurrences of carbonatite:
• First Indian corbonatite has been discovered in
Amba Dongar area about 23miles south of Chota
Udaipur, Baroda district, Gujarat state.(Sukeshwala
and Udas in 1963).
• Kambam in Tamil Nadu.
• Some part of Niwania carbonatite in Rajasthan.
• North of Nagpur along Tapti rift valley.

20. Economic importance:
• Carbonatites may contain economic or anomalous
concentrations of rare
earth elements, phosphorus, niobium - tantalum, uranium, th
orium, copper, iron, titanium, vanadium, barium, fluorine,zi
rconium, and other rare or incompatible elements .
• Apatite, barite and vermiculite are among the industrially
important minerals associated with some carbonatites.
• Vein deposits of thorium, fluorite, or rare earth elements
may be associated with carbonatites, and may be hosted
internal to or within the metasomatized aureole of a
carbonatite.

21. Conclusion
• Carbonatites are plutonic igneous rock and found either in
intrusive or extrusive igneous rocks more
than50% carbonate minerals are present.
• Carbonatites are mostely medium grained carbonate but also
include very fine to coarse grained varieties and the colour
range from white to browish white.
• Carbonatites is never a batholiths or bosses but occur as
stocks, dykes etc.
• Carbonatites range in age from Precambrian to recent.

22. Reference:
 Donald W.Hyndman, Petrology of Igneous And
Metamorphic Rocks. Pp.359-368
 Walter T. Huang, Petrology.Pp.130
 Websites:
-www.google.com
-www.wikipedia.com
-www.the-conference.com/JConfAbs/5/904.pdf
www.jgeosci.org/content/jgeosci.025_2008_2_aichler.pdf

23. THANK YOU!!!