How do you identify komatiite?
Komatiite can be classified according to the following geochemical criteria;
- SiO2; typically 40–45%
- MgO greater than 18%
- Low K2O (<0.5%)
- Low CaO and Na2O (<2% combined)
- Low Ba, Cs, Rb (incompatible element) enrichment; ΣLILE <1,000 ppm.
- High Ni (>400 ppm), Cr (>800 ppm), Co (>150 ppm)
What type of mineral composition is komatiite?
Komatiite lavas are famous for their unique olivine spinifex and cumulate crystal textures and internal textural zonation. In komatiitic basalts, such textures can also involve pyroxene. In a typical komatiite lava, the textural profile of the lava from top to bottom (Fig.
Is komatiite intrusive?
Komatiites are very rare igneous rocks. They are one variety of extrusive ultramafic igneous rock (although a komatiite in Canada has been interpreted to be an intrusive sill). They are named after the Komati River in South Africa, the type locality. Komatiite is an exceedingly rare type of lava.
Is komatiite fine grained?
After Arndt et al. (1977). A1—This uppermost layer is aphyric or extremely fine grained and only a few mm to a few cm thick.
Where is komatiite found?
Komatiites are fairly rare rocks, but they are found throughout the world in places such as Canada and South Africa. Most komatiites were formed billions of years ago in the Archean (approximately 2.5 to 3.8 billion years ago).
What color is komatiite?
This should discriminate some picrites without the corresponding texture to be classified as komatiites. Colour Black, grey, locally grey-green. Structure Pillow-like, porphyric, spinifex. Texture Porphyric – spinifex.
What is the cooling rate of komatiite?
Donaldson (1982) estimated that cooling rates in the A3 layer of a typical 5–10 m thick komatiite flow were <1 C/h. In contrast, to reproduce the dendritic mor- phology of platy spinifex olivine crystals in normal dynamic cooling laboratory experiments requires cooling rates >50 C/h (Donaldson, 1982).
Why do komatiites not form anymore?
The interior of the Earth might not be hot enough to produce many (if any) komatiites, and definitely not at the rate it was back when the Earth was only 1 or 2 billion years old.
Where do komatiitic deposits occur?
These deposits typically occur at the contact surface between the underlying rock and the flowing lava of the molten komatiite. Hotter komatiitic magma melts S-rich underlying rocks (sedimentary and volcanic) to produce sulfide melt enriched in Ni-Cu-PGE which is accumulated at the depressions of the footwall rocks.
What is the type locality of the komatiites?
The type locality of the komatiites is at the same time the oldest one – Barberton greenstone belt, South Africa, where these rocks occupy nearly 25% of the lowest stratigraphic unit called Komati Formation. (Note: a “type locality” is the specific defining occurrence of a geologic formation, deposit or rock type.)
Is komatiite a juvenile-magmatic model of stratiform nickel-sulfide ore deposits?
A juvenile-magmatic model of the formation of stratiform nickel-sulfide ore deposits in komatiite host rocks. G eologiya a Geofizika, 25, p. 84-91.
What is the mineralogy of komatiite-associated Ni-Cu-(PGE) (Kambalda) ore concentrates?
Mineralogy of komatiite-associated Ni-Cu- (PGE) miner- § showing common substitutions for some minerals. Abundance: major +++, minor ++, trace +. Other minerals in Kambalda ore concentrates, most likely derived from