Komatiites
Omer M. Ahmed
University of Kerala, India
2015

o Named after the Komati River in South Africa.
o first described by Morris and Richard (twins) for
ultramafic units in the Barberton Greenstone belt of South
Africa.
Komatiites

o Mostly of komatiite are Archean age
o distributed in the Archaean shield areas.
o Also a few are Proterozoic and Phanerozoic.
o In all ages komatiites are highly magnesium.
o Mostly a volcanic rock; occasionally intrusive.
o Mafic rocks were identified as extrusive because of their volcanic
textures and structures, and they seem to have been accepted as a
normal component of Archean volcanic successions, Abitibi in
Canada.
o The ultramafic rocks were interpreted as intrusive which are founded
as sills and dykes, Barberton in South Africa.
Komatiites

Spinifex texture-typical of Komatiites
 The name Spinifex refer to a spiky grass in Australian.
 Restricted in komatiite and most distinctive feature in
the field .
 Formed due to rapid cooling of rich magnesium lavas.
 The olivine grains are less closely packed, randomly
distributed and poorly sorted.
 Pyroxene shows zoning.
 Recognized in well preserved Archaean greenstone
belts.

(a) Spinifex grass
(b) Weathered surface of Komatiite
shows Spinifex texture.
(Nicholas Arndt, 2008).
(a)

Spinifex texture in PPL.
shows partial
Serpentinization and iron
oxide.
(Source-Robin Gill, 2010).
In XPL

Spinifex texture with large zoned Pyroxene (Kambalda, Nicholas Arndt, 2008).

 Abundance of olivine, pyroxene rich in chromite and glassy
material.
 Some silicates confined in matrix between olivine grains like
augite, plagioclase or Ni–Fe sulfides and in some case quartz.
 Most komatiites are altered- olivine to chlorite or serpentine;
Pyroxene is partially replaced by tremolite and chlorite; and
glass to secondary hydrous minerals.
Mineralogy

Elements Percentage
SiO2 46
TiO2 0.53
Al2O3 11.1
Cr2O3 0
Σ FeO 11.3
MnO 0
MgO 20.6
NiO 0
CaO 9.3
Na2O 0.84
K2O 0.03
Total 99.7
Robin Gill, 2010
Geochemistry
 ultramafic mantle-derived
volcanic rocks.
 chemically distinctive in being
highly magnesium
(18% < MgO < 32% ).
 low SiO2, low K2O, low Al2O3.

Association
Komatiites occur with other mafic and ultramafic high-
magnesium rocks such as:
• Pillow basalts.
• Peridotite.
• Picrites
• Calc–alkaline felsic volcanics rocks in subduction zone.

Komatiites have been recognized in many areas
around the world such as:
 The Greenstone Belt of Barberton South Africa.
 The Pilbara Block and the Yilgarn Craton, Western
Australia.
 Munro Township, Ontario.
 Abitibi Greenstone Belt in Canada.
 Lion Hills Vetreny belt, Russia.
 The Belingwe belt in Zimbabwe.
Occurrence of Komatiite in the world

Komatiite in India
The Archaean Greenstone Belt of Kolar Schist, Karnataka.
 Komatiite reported from Dharwar craton - shows spinifex
texture.
 Associated with metamorphosed Pyroxenite, Norite gabbro,
anorthosite, altered dunite, harzburgite, Chromite and schist.
 In east Dharwar craton it surrounded and intruded by
granodioritic to quartzo monozonitic gneisses.
 Dharwar Craton has metabasaltic rocks from both high and low
grade schist belt (Drury ,1984).

Mineral deposits associated with Komatiite
Komatiites contain valuable primary and secondary ore
deposits such as:
 primary magmatic Sulfide deposits which mined for
their nickel (about 18%of global sulfide nickel ) content
with minor product of Cu and PGEs mineralization.
 secondary laterite deposits enriched in nickel and
cobalt, developed over thick olivine cumulate units.
 At Dachine in French , komatiites (ultramafic) are the
host rocks of a large deposit of micro diamonds.

Conclusion
• komatiite is mafic / ultramafic
• Shows that lavas of ultramafic composition have erupted on the
Earth’s surface, at early times of history.
• Spinifex texture is a product of extremely rapid crystallization
of high MgO minerals.
• Many komatiites are host for massive sulphide deposits.
• Komatiites associated with high magnesium rocks

References
 Gill, R (2010), Igneous Rocks and Processes A Practical Guide, John Wiley &
Sons Ltd, 428 P.
 Gupta A K.Alok (1998) ,Igneous rocks, Allied Publishers Limited 690 P.
 Srivastava R K (2011), Dyke Swarms: Keys for Geodynamic Interpretation,
Springer-Verlag Berlin Heidelberg, 605 P.

Thanks So Much