L5 - Diamonds

Question 1

What are the primary applications of diamonds?

Answer 1

Jewelry.

Industrial applications: cutting and grinding.

Question 2

Where are diamonds typically found?

Answer 2

• Magmatic deposits: Volcanic pipes (kimberlites).
• Sedimentary deposits: Placers.

Question 3

How are diamond sizes measured?

Answer 3

In carats (1 carat = 200 mg)

Question 4

What factors determine the viability of a diamond deposit?

Answer 4

Grade and value/quality of individual stones

Question 5

What are typical grades of diamond deposits?

Answer 5

0.05 - 2 carats per ton (ct/t).

• Example: Canada (3.9 ct/t, $95/ct).
• Example: Lesotho (0.01 ct/t, $1000/ct).

Question 6

Which countries lead in diamond reserves by value?

Answer 6

Botswana.
Russia.
Angola.
Canada.

Question 7

What is the main producer of synthetic diamonds?

Answer 7

china

Question 8

What are the key lithologies of kimberlite pipes?

Answer 8

Kimberlite: Altered, K- and Mg-rich ultramafic rock with olivine, phlogopite, garnet, diamond xenocrysts, and mantle xenoliths.

Lamproite: Similar but saturated in SiO₂.

Question 9

What are diatremes?

Answer 9

• Pipe-like volcanic structures cutting through country rock.
• Formed by explosive eruptions due to volatile-rich magma.
• Often contain craters with volcanic material.

Question 10

How deep are kimberlite pipes?

Answer 10

1-2 km, with eruption craters at the surface.

Question 11

What conditions are necessary for diamond formation?

Answer 11

• Depth: 200-300 km in the mantle.
• Pressure: Found beneath old, thick, cold cratons (Archean crust).

Question 12

How are diamonds related to cratonic heels?

Answer 12

Diamonds form in the cold, stable regions at the base of cratons (heels)

Question 13

What mantle processes contribute to diamond formation?

Answer 13

• Subduction zones and mantle plumes deliver water to depths, driving partial melting.
• Conditions align with diamond stability fields.

Question 14

What global trends link kimberlite age and plate tectonics?

Answer 14

• Kimberlite volcanism correlates with plate reconfigurations, such as rifting and subduction.
• Examples include mountain-building events and mantle plume activities.

Question 15

What are placer diamond deposits?

Answer 15

• Secondary sedimentary deposits related to river and offshore processes.
• Concentrated in ancient river networks and coastal environments

Question 16

How do placer deposits concentrate diamonds?

Answer 16

• High-density diamonds accumulate in depressions, meander belts, and pockets in river basins.
• Diamonds resist abrasion and are transported by high-velocity currents.

Question 17

What is the role of Stokes’ law in placer deposits?

Answer 17

Density differences allow separation and concentration of diamonds in sediment.

Question 18

What are the main methods for diamond exploration?

Answer 18

• Structural context: Understanding fault lines and regional geology.
• Indicator mineral sampling: Analyzing heavy minerals associated with kimberlite.
• Geophysics: Airborne magnetics, resistivity contrasts, and density variations.

Question 19

How are pipe models built during exploration?

Answer 19

• Combine geophysical and drilling data to create 3D models.
• Determine deposit grade and mining potential.

Question 20

What are the main diamond production methods?

Answer 20

• Kimberlite pipes: Open-pit and underground mining.
• Alluvial and marine deposits: Sediment dredging and cleaning bedrock

Question 21

How are diamonds beneficiated after mining?

Answer 21

• Crushing and concentration using pans and cyclones.
• Fine material processed on grease tables.
• Coarser material separated via X-ray sorters and air jets

Question 22

Why are diamonds considered unique?

Answer 22

• Hardest material known (pure carbon).
• Used as abrasives and gemstones.

Question 23

What evidence supports diamonds forming in the mantle?

Answer 23

• Inclusions of mantle material.
• Density and structure of diamonds.

Question 24

What volcanic processes bring diamonds to the surface?

Answer 24

• Explosive kimberlite and lamproite eruptions.
• These eruptions serve as windows into mantle conditions.

Question 25

What is the link between kimberlite volcanism and tectonics?

Answer 25

Kimberlite volcanism is tied to plate tectonic events, such as rifting, subduction, and mantle plumes.