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 reserves A 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