Non-metallic Resources:
Diamonds
Rock cycle and plate boundaries
• One or more minerals held together by a matrix
Rock types: Igneous
• Form from the solidification and crystallization of
-magma (molten rock below ground)
-lava (molten rock above ground)
• Most common examples
-Basalt
-Granite
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
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Rock types: Igneous
• Four types of igneous rocks
Mafic minerals
Felsic minerals
Contain iron and magnesium
No iron and magnesium
Bowen’s
reaction
series:
arranged by
temperature
of formation
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Igneous
• Classified by texture and color/composition
“slow” = thousands to millions of years
“fast” = days to weeks
Texture
Cooling History
Examples
Glassy
Very fast (hours) cooling; noncrystalline.
Obisdian
Vesicular
Very fast cooling with rapid
gas escape forming bubbles in
the non-crystalline rock.
Pumice, scoria
Aphanitic (fine grained)
Slow cooling; microscopic
crystal growth.
Rhyolite, andesite, basalt
Phaneritic (coarse grained)
Very slow cooling; crystals
grow to visible size.
Granite, diorite, gabbro
Porphyritic (two grain sizes)
Two stage cooling; one slow
underground creating visible
phenocrysts, the second fast at
the earth's surface producing a
fine grained groundmass.
Any aphanitic rock with the
word “porphyry”
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
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Pegmatite
4
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Rock types: Igneous rock distribution
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
Rock types: Igneous rock distribution
http://csmres.jmu.edu/geollab/fichter/IgnRx/Introigrx.html
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Diamond
Graphite
Composition: Carbon
Hardness: Hardest known, 10
Electrically: Insulator
Luster:
High, dispersion of light
Uses:
Gemstone, cutting
Carbon
1.0
Conductor
Dull, metallic
Pencils, lubricant
Carbon allotropes
http://www.chem.ufl.edu/~itl/2041_u01/lectures/lec_h.html
Diamond formation: Primary deposits
Kimberlite rock
- Volatile rich (CO2 & H2O) ultramafic rock
- [Rarely] contains xenoliths (solid rocks incorporated into
magma) of diamond
http://www.diamond-all.com/Diamond.html
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Diamond formation
• Originate in Earth’s mantle, 150 km deep (~90 miles)
http://dao.mit.edu/8.231/carbon_phase_diagram.jpg
Diamond formation: Primary deposits
Diatreme
- Explosive volcanic pathway
to Earth’s mantle
- 50 m high tuff ring
- Youngest event ~50 million
years ago
- 1 in 200 contain diamonds
http://www.diamond-all.com/Diamond.html
Diamond formation: Primary deposits
Kimberlite pipe
(Older than 2.5 Byr)
Lamproite pipe
(Youngest 50,000 years)
http://www.brc-diamondcore.com/s/Technical.asp?ReportID=282496
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Diamond formation: Primary deposits
• Kimberley mine
-Dug without any machinery, 1871-1908
-460 m diameter by 1100 m deep
-3 tons of diamonds were extracted
South Africa
Diamond formation: Primary deposits
• Open pit mine
-Used when material is too loose for underground tunnels
-Explosives break up layers of “overburden”
-Rocks removed and inspected
-Overburden replaced or made into a landfill
Canada
Diamond formation: Primary deposits
• Open pit mine
Siberia
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Diamond formation: Primary deposits
• Open pit mine
South Africa
Diamond formation: Primary deposits
• Open pit mine
Australia (Lamproite pipe, broader cone)
Diamond formation: Primary deposits
• Open pit mine
Canada
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Diamond formation: Primary deposits
• Hydraulic mining
-Jets of water loosen gem material
-Sluices catch gravel slurry for inspection
-Ended in 1960’s
Diamond formation: Primary deposits
• Strip mining
-Similar to open pit mines but done in long strips
-Strip one material is removed
-Strip two material fills strip one . . .
Bucket wheel
excavator: moves
material 100 m by 25
m deep per day
http://apod.nasa.gov/apod/ap061122.html
Diamond formation: Primary deposits
• Underground mining
Diavik open pit mine,
Northwest Territories Canada
55 million year old pipe
Planned 2012 transition to an
underground mine
Red: three kimberlite pipes
Green/blue: planned mine
network
http://www.diavik.ca/ENG/ouroperations/1624_underground_mining_equipment.asp
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Diamond formation: Primary deposits
• Underground mining
L: Block cave 250 m deep
C: Underground entrance
R: Haul trucks
http://www.argylediamonds.com.au
Diamond formation: Primary deposits
• Diamond recovery
-Millions of tons removed per year
-Diamonds represent 1 part per million of host rock!
1,000,000 tons rock = 999,999 tons waste + 1 ton diamonds
-Processing:
1. Gravity separation
2. X-ray detection
-Waste
1. Piled
2. Covered and sealed “forever”
http://www.diavik.ca/ENG/ouroperations/1624_underground_mining_equipment.asp
Diamond formation: Secondary deposits
• Alluvial (placer) deposits or “artisanal diamond mining”
• Weathering of diamond-bearing pipes into water
• Simple mining techniques
Zimbabwe
http://www.galdu.org/web/index.php?odas=5116&giella1=eng
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Diamond formation: Secondary deposits
• International concerns:
-no regulatory framework
-lack of safety measures
-child labor
-environmental degradation
-prostitution in mining camps
-spread of HIV/AIDS
Conflict diamonds, or
Blood diamonds
-“...diamonds that originate from areas controlled by forces or
factions opposed to legitimate and internationally recognized
governments, and are used to fund military action in opposition
to those governments, or in contravention of the decisions of the
Security Council”. UN
http://www.galdu.org/web/index.php?odas=5116&giella1=eng
Diamond formation: Secondary deposits
Conflict diamonds, or
Blood diamonds
• Regulations, 2003
-Kimberley Process
Certification Scheme
-US Clean Diamond Act
• 1% of diamonds sold today are conflict diamonds according
to the World Diamond Council
http://en.wikipedia.org/wiki/File:Kimberly_Process_Map.svg
• International concerns:
-no regulatory framework
-lack of safety measures
-child labor
-environmental degradation
-prostitution in mining camps
-spread of HIV/AIDS
Diamond formation: Secondary deposits
• Marine deposits
http://www.amnh.org/exhibitions/diamonds/marine.html
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US diamond mines
• Murfreesboro, Arkansas discovery in 1906
-1 lamproite pipe
-100,000 stones between 1907-1933
• Kelsey Lake, 1996-2002
-8 kimberlite pipes
-2 open pit mines
http://www.amnh.org/exhibitions/diamonds/marine.html
Diamonds and the environment
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