Environmental impacts

Question 1

Review the mining process

Answer 1

exploration
exploration drilling
mining
remediation

Question 2

Mining process at a gold mine

Answer 2

location drilling, blasting, mining, hauling, crushing, leaching, processing, pouring

Question 3

Bingham canyon - USA

Answer 3

Largest man-made excavation: 2.5 miles wide 0.5 deep

47.8 million tonnes of ore mined 2006

Question 4

Bingham landslide effects

Answer 4

Moved at 70mph and left deposit covering central park in 20 metres debris
Most visual impact from waste material from mining activity

Question 5

Aberfan 1966

Answer 5

Spoil heap failure, 144 dead

Spring added to already high pore pressures

Question 6

Spoil heap stability

Answer 6

• High pore pressures associated with fine grained materials with low permeability and high moisture content
• In soils with permeability < 510-9ms-1, there is no dissipation of pore water pressures. Perm > 510-7ms-1, there is complete dissipation.
• Coal discard typically 110-4 - 510-8ms-1

Question 7

Relationship between failure and rainfall

Answer 7

Increase of rapid failures

Question 8

Tailings

Answer 8

• Fine grained slurries
• Produced during crushing or ore or washing at collieries
• Mixed with water (ease of movement)
• Water may leach many chemicals from rock and may contain chemicals from extraction
• Commonly contain sulphide minerals – oxidise to form acid
• Tailings are major environmental hazard

Question 9

Tailings ponds

Answer 9

Usually deposited as a slurry (cheap_ and held within embankment dams
e.g Wheal Jane, Cornwall

Question 10

Tailings storage

Answer 10

-Quantity that can be stored depends on density
Tailings increase in density as they settle and compact with time
-Eventually tailings allowed to dry and environmental remediation started
-Any seepage from tailings ponds potentially damaging due to toxic nature. Ponds lined and maintained (should be)

Question 11

Tailing pond failure case study

Answer 11

• Aznalcollar mine, Spain 1998
• 600m section of tailings pond embankment suddenly slumped
• Surge of water- 7km downstream water level raised by 3.6m in 30 mins.
• 5.5million m3 acid water released
• 1.3-1.9M ton tailings released
• 4600ha land affected, 2600ha covered by tailings.
• Tailings up to 4m deep near mine
• Fault in marl bedrock, likely initiated by overburden of tailings and HP on interstitial water in clays

Question 12

Effects of Aznalcollar mine

Answer 12

• No loss of life or injury
• Severe depletion of biota
• Complete loss of agriculture in affected region
• Extensive clean-up involving stripping of all vegetation and soil in affected area (3000ha)
• .$200million price
• Mine now re-opened, tailings stored in abandoned open cast pit