Minerals and the

Environment

The Rock Cycle

Definitions

• Mineral– a solid homogenous (crystalline) chemical

element or compound; naturally occurring

• Ore– rock substance containing a valuable mineral

which is mined for that substance– ores are concentrated around the world in ore

deposits

Some minerals and their sources• Plate boundaries

– melting allows settling by density – mercury• Igneous processes

– Magma cools and crystallizes - diamonds• Sedimentary processes

– Settling by size – sand– Settling by density - gold– Evaporation – salt

• Biological processes– CaCO3

• Weathering– Water (and acid) carries minerals down and concentrates them -

copper• Minerals from the sea

– Sulfur (vents) and manganese nodules

Impact of Mining on the Environment

Methods of Mining

• Subsurface mining– coal mining

– disturbs less than 1/10 as much land

– produces less waste

– more dangerous

Methods of Mining• Surface mining

– open-pit mining• copper, iron, sand, gravel, limestone

– dredging• buckets and draglines scrape underwater deposits

Strip mining• overburden (and all vegetation) is removed in strips• resource is removed• spoil is replaced in rows• spoil is susceptible to erosion (sediment pollution)• rainwater leaches chemicals into ground water (acid

drainage)

Mine tailings• Mine tailings often include sulfide

compounds• When these react with water, sulfuric acid

and toxic minerals can be washed into local water

Processing Materials

• Minerals are extracted from ores by heating or chemical reactions– smelting - roasting the ore - produces huge

amount of air pollution (SOx)

Heap-leach Extraction

• heap-leach extraction - separating gold from low grade ores - spraying rock with a cyanide solution which dissolves the gold - mining sites are often left unaltered with high toxin levels

Placer Mining• placer mining

– Destroys riverbanks– Increases sediment in rivers– Uses heavy metals like Mercury that contaminate

waters• in the Amazon, gold miners are using mercury and have

dumped 100 tons of mercury into the Amazon river

Are there enough mineral resources for our needs?

Classification of resources and reservesA reserve is is that portion of a resource that is identified and from which usable materials can be legally and economically extracted at the time of evaluation

Resources are not reserves

Depletion Time

Strategies for improved mineral use

• Conserve the resources we have

• Find substitutes (ceramics)

• Recycle minerals• Use lower quality ores