EOSC 118 - Lesson 10

Diamond: Geology and Geography

Which of these techniques are commonly used to explore for diamond in arctic regions?

* a) aeromagnetic surveys
* b) panning rivers
* c) glacial till sampling
* d) offshore drilling platforms

A and C

What is unique about the Argyle mine in Australia?

they are the only mine producing lamproite-hosting diamonds commercially

Describe the geological conditions necessary for diamond formation

* high pressure
* depth: 140km or more
* ‘cool’ temperature region: a region between 950 and 1400 C

how diamonds are brought from the mantle to the surface?

Kimberlite magma generates at the base of the craton, at 200-300km depth, and ascends through 140km of crust, picking up diamonds along the way, and brings them to the Earth’s surface through eruptions in special volcanoes

Explain why diamonds are rare.

They are rare because they form so deep underground and need special environmental conditions in order for them to be brought to the surface

Describe the global distribution of diamond deposits, geographically and geologically.

the main producer is Africa, followed by Russia, Australia and Canada

Briefly summarize the change in diamond production by country through history

* historically produced in India and Brazil, but these were alluvial secondary deposits
* late 19th century, discovered diamond-bearing kimberlite in South Africa
* 1957: First significant non-African mine opens in Russia
* 1983: Australian Argyle mine opens, producing diamond-bearing lamproite
* 1998: Canada joins trade with the Ekati mine

What rock type are most primary diamond deposits hosted in?

kimberlite

Why are diamonds only found in regions of very old continental crust?

Because the conditions at the base of the Archean cratons is a favourable environment for diamond growth (high pressures + relatively ‘cool’ temperatures)

Why do you think kimberlites form “carrot-shaped” deposits?

Because as the magma ascends upwards through the crust it moves into regions with less and less confining pressure, which allows for faster and faster propagation of the magma

Kimberlite magma

sourced from upper mantle, Fe- and Mg- rich (aka ultramafic) as well as K rich

lamproite

another host rock for diamonds, a lot less common, can exist outside Archean cratons