L5 - Diamonds Flashcards
What are the primary applications of diamonds?
Jewelry.
Industrial applications: cutting and grinding.
Where are diamonds typically found?
- Magmatic deposits: Volcanic pipes (kimberlites).
- Sedimentary deposits: Placers.
How are diamond sizes measured?
In carats (1 carat = 200 mg)
What factors determine the viability of a diamond deposit?
Grade and value/quality of individual stones
What are typical grades of diamond deposits?
0.05 - 2 carats per ton (ct/t).
- Example: Canada (3.9 ct/t, $95/ct).
- Example: Lesotho (0.01 ct/t, $1000/ct).
Which countries lead in diamond reserves by value?
Botswana.
Russia.
Angola.
Canada.
What is the main producer of synthetic diamonds?
china
What are the key lithologies of kimberlite pipes?
Kimberlite: Altered, K- and Mg-rich ultramafic rock with olivine, phlogopite, garnet, diamond xenocrysts, and mantle xenoliths.
Lamproite: Similar but saturated in SiO₂.
What are diatremes?
- Pipe-like volcanic structures cutting through country rock.
- Formed by explosive eruptions due to volatile-rich magma.
- Often contain craters with volcanic material.
How deep are kimberlite pipes?
1-2 km, with eruption craters at the surface.
What conditions are necessary for diamond formation?
- Depth: 200-300 km in the mantle.
- Pressure: Found beneath old, thick, cold cratons (Archean crust).
How are diamonds related to cratonic heels?
Diamonds form in the cold, stable regions at the base of cratons (heels)
What mantle processes contribute to diamond formation?
- Subduction zones and mantle plumes deliver water to depths, driving partial melting.
- Conditions align with diamond stability fields.
What global trends link kimberlite age and plate tectonics?
- Kimberlite volcanism correlates with plate reconfigurations, such as rifting and subduction.
- Examples include mountain-building events and mantle plume activities.
What are placer diamond deposits?
- Secondary sedimentary deposits related to river and offshore processes.
- Concentrated in ancient river networks and coastal environments
How do placer deposits concentrate diamonds?
- High-density diamonds accumulate in depressions, meander belts, and pockets in river basins.
- Diamonds resist abrasion and are transported by high-velocity currents.
What is the role of Stokes’ law in placer deposits?
Density differences allow separation and concentration of diamonds in sediment.
What are the main methods for diamond exploration?
- 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.
How are pipe models built during exploration?
- Combine geophysical and drilling data to create 3D models.
- Determine deposit grade and mining potential.
What are the main diamond production methods?
- Kimberlite pipes: Open-pit and underground mining.
- Alluvial and marine deposits: Sediment dredging and cleaning bedrock
How are diamonds beneficiated after mining?
- Crushing and concentration using pans and cyclones.
- Fine material processed on grease tables.
- Coarser material separated via X-ray sorters and air jets
Why are diamonds considered unique?
- Hardest material known (pure carbon).
- Used as abrasives and gemstones.
What evidence supports diamonds forming in the mantle?
- Inclusions of mantle material.
- Density and structure of diamonds.
What volcanic processes bring diamonds to the surface?
- Explosive kimberlite and lamproite eruptions.
- These eruptions serve as windows into mantle conditions.
