Mining Textbook pages 226 – 230

Minerals, Rocks, and the rock cycle The earth’s crust consists of solid inorganic elements and compounds called minerals that can be utilized Mineral resource: a concentration of naturally occurring material in or on the earth’s crust that can be extracted and processed into useful materials at an affordable cost.

What is a mineral? What is rock? Naturally occurring, inorganic, solid element or compound with a definite chemical composition and a regular internal crystal structure What is rock? solid, cohesive, aggregate of one or more minerals Each rock type has a characteristic mixture of minerals

Geologic processes Deposits of nonrenewable mineral resources in the earth’s crust vary in their abundance and distribution Very slow cycle recycles three types of rocks (and subsequently minerals) found in the earth’s crust Sedimentary rock (ex: sandstone, limestone) Metamorphic rock (ex: slate, marble, quartzite) Igneous rock (ex: granite, pumice, basalt)

Mining for Ore An ore is an economically exploitable deposit What is an economic geological resource? A mineral that is heavily used in some human endeavor (e.g., metal ores) and therefore is an important part of domestic/international commerce.

General classification of nonrenewable mineral resources The U.S. Geological Survey classifies mineral resources into three major categories: Identified: known location, quantity, and quality or existence known based on direct evidence and measurements. Undiscovered: potential supplies that are assumed to exist. Reserves: identified resources that can be extracted profitably.

Environmental effects of using mineral resources Minerals are removed through a variety of methods that vary widely in their costs, safety factors, and levels of environmental harm The methods are used based on mineral depth Surface mining Subsurface mining Shallow deposits are removed Deep deposits are removed

Open-pit mining (surface) Machines dig holes and remove ores, sand, gravel and stone. Toxic groundwater can accumulate at the bottom.

Area strip mining (surface) Earth movers strips away overburden, and giant shovels removes mineral deposit Often leaves highly erodible hills of rubble called spoil banks.

Contour strip mining (surface) Used on hilly or mountainous terrain Unless the land is restored, a wall of dirt is left in front of a highly erodible bank called a highwall.

Mountaintop removal (surface) Machinery removes the tops of mountains to expose coal The resulting waste rock and dirt are dumped into the streams and valleys below.

PLAcer Mining (surface) Looking for mineral resources in river/stream beds by sifting through river sediments. Use the flow of water to help separate heavier minerals from lighter sand/mud. Gold Mining is an example.

Underground (“hard rock”) Mining Underground excavation of hard materials Accomplished using a variety of equipment and technologies

Gangue - Mine Tailings Worthless minerals that are associated with the valuable minerals in an ore Concentrating and smelting removes as much of this gangue as possible “Leftover waste” Concentrating and smelting removes as much of this gangue as possible Where can we safely leave the gangue? Does it represent a potential environmental hazard? Example: Acid Mine Drainage (AMD) from sulfide ores and coal

Mine Reclamation Re-contouring land back to its original topography Improve soil quality by adding topsoil / nutrients Replanting with native, fast growing, early successional species Monitor the site for 5 – 10 years More difficult in arid areas b/c difficult to grow vegetation

Supplies of mineral resources The future supply of a resource depends on its affordable supply and how rapidly that supply is used A rising price for a scarce mineral resource can increase supplies and encourage more efficient use. Rising prices can also place undue pressures on developing nations in which large stores of mineral reserves are located

Environmental effects of using mineral resources The extraction, processing, and use of mineral resources has a large environmental impact.

Environmental Damage 4FeS2 + 14H2O = 4Fe(OH)3 + 8H2SO4 Gaping holes in ground (old open pit mines). Particulate air pollution Piles of mine tailings (non-ore removed from mines) = Gaunge Accidental draining of rivers and lakes. Disruption of ground water flow patterns. Loss of topsoil in strip-mined regions (350 to 2,700 km2 in US alone). Contamination from sulfuric acid (H2SO4) produced through weathering of iron sulfide (FeS2, pyrite) in tailings. 4FeS2 + 14H2O = 4Fe(OH)3 + 8H2SO4 Contamination from heavy metals (e.g. arsenic, mercury) in mine tailings. Acid Mine Drainage

Mining impacts Metal ores are smelted or treated with (often toxic) chemicals to extract the desired metal Example: cyanide for extraction of low grade gold ores