 Lamprophyre!
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LAMPROPHYRE
it is a greek word Lampros meaning "bright", Prophyre meaning "rocks". they are uncommon, small volume ultrapotassic igneous rocks primarily occuring as dikes, lopoliths, laccoliths, stocks & small instrusions. they are alkaline silica-undersaturated , ultramafic rocks with high magnesium oxide, >3% potassium, high sodium oxide & high nickle & chromium. they occur in all geologic eras.
ESSENTIAL COMPONENTS OF LAMPROPHYRE :
- high depth of melting which yields more mafic magmas.
- low degrees of partial melting, which yields magmar rich in the alkalies (potassium mainly)
- lithophile element (K, Ba, Cs, Rb) enrichment , high Ni & Cr.
- high potassium & sodium concentrations.
- some form of volatile enrichment, to provide the biolite (phlogopite) & amphilobole (pargasite) mineralogy.
- lack of fractional crystallisation
- high Mg# (NgO// FeO+Fe2O3).
Lamprophyre are usually associated with voluminous granodiorile intrustive episodes ^. Lamprophyre are also known to be spatially & temporarily associated with gold mineralisation.
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Linear Mode
