Diamond Geology

DIAMOND GEOLOGY & EXPLORATION

Form on cratons, old parts of the crust which plunge deep into the mantle.
Vertical volcanic intrusions called pipes which carry diamonds and indicator minerals up from the deep mantle (150-200 km down).
Result of explosive vent volcanism from very deep mantle-derived sources.
Within 1.5-2 km (0.93-1.24 mi) of the surface, highly pressured magma explodes upwards and expands to form a conical to cylindrical volcanic pipe – erupts on the surface.
Kimberlite dykes and sills-thin (1-4 m).
Pipes range in diameter from about 50 m to 1.5 km.
Two distinct varieties of kimberlite volcanics, commonly called Group 1 and 2 types.
Diamonds also sourced by lamproites, which are related to kimberlites.

Kimberlites are peculiar igneous/volcanic rocks that formed under high pressure and temperature within the mantle.
Similar conditions for the formation of diamond.
KIMs: Pyrope garnets rich in chromium and ilmenite and chromium diopside, chromium spinels.
KIMs are absent from most other igneous/volcanic rocks – indicators for kimberlites.
KIMs are sought and found in stream sediments (alluvium) and in modern soils as part of the diamond exploration process.
KIMs may indicate the presence of a kimberlite within the erosional watershed that produced the alluvium.

Typical Kimberlite Product Mix

World ave. diamond size: 0.30 carats (30 points)

Alluvial Deposits