APES – Chapter 27: Minerals and the Environment

Tommy Hicks

APES – 6th period

· Case Study – Golden Colorado: Open-Pit Mine Becomes a Golf Course

· A gold course in Golden Colorado was once an open-pit mine excavated on limestone

· The mine produced mud for making bricks for prominent buildings

· (such as) the Governor’s mansion

· The mine had walls or limestone and a waste disposal area but it also had views of the Rocky mountains > desirable location for gold course

· The “Fossil Trace Golf Course” reflects its heritage > has pathways to fossil locations

· Also has channels, three lakes, and constructed wetlands that protect Golden from floods

· >MAIN IDEA: mining sites can be reclaimed and transformed into valuable property

· The Importance of Minerals to Society

· Many mineral products are found in a typical American home.

· Availability a measure of the wealth of a society.

· Those successful in locating and extracting or importing and using minerals have grown and prospered.

· W/o minerals, modern technological civilization not possible.

· To maintain our standard of living in the US, every person requires about 10 tons of nonfuel minerals/ year.

· The Importance of Minerals to Society

· Considered a nonrenewable resource

· New deposits forming but two slowly to be of use to us today.

· Increasingly difficulty to find deposits

· Recycling and conservation will help manage remaining supply.

· But eventually it will be exhausted.

· How Mineral Deposits are Formed

· Metals are concentrated in anomalously high amounts by geologic processes

· Ore deposits are formed.

· The discovery of natural ore deposits allowed early peoples to exploit copper, tin, gold, silver, and other metals.

· Distribution of Mineral Resources

· Earth’s crust, is silica rich

· Made up mostly of rock-forming minerals.

· Nine elements account for about 99% of the crust by weight

· Oxygen, 45.2%; silicon, 27.2%; aluminum, 8.0%; iron, 5.8%; calcium, 5.1%; magnesium, 2.8%; sodium, 2.3%; potassium, 1.7%; and titanium, 0.9%).

· Remaining elements are found in trace concentrations.

· Ocean water contains about 3.5% dissolved solids, mostly chlorine (55.1% by weight).

· Each cubic kilometer of ocean water contains

· ~2.0 metric tons of zinc, 2.0 metric tons of copper, 0.8 metric ton of tin, 0.3 metric ton of silver, and 0.01 metric ton of gold.

· These concentrations are low compared with those in the crust.

· Plate Boundaries

· Plate tectonics is responsible for the formation of some mineral deposits.

· Metallic ores deposited in the crust both at divergent and convergent plate boundaries.

· At divergent plate boundaries,

· Cold water comes in contact w/ hot molten rock.

· Heated water rises through fractured rocks and leaches metals from them.

· Metals are carried in solution and deposited as metal sulfides when the water cools.

· At convergent plate boundaries

· Rocks saturated w/ seawater are forced together, heated, and subjected to intense pressure, which causes partial melting.

· The combination mobilizes metals in the molten rocks.

· E.g. Most major mercury deposits

· Igneous Processes

· Related to molten rock material (magma).

· Ore deposits may form when magma cools.

· Heavier minerals that crystallize early may settle toward the bottom of the magma.

· Lighter minerals that crystallize later are left at the top.

· Hot waters source of most ore deposits.

· Circulating groundwater is heated and enriched with minerals

· This water then moves up or laterally to other, cooler rocks, where the cooled water deposits the dissolved minerals.

· Sedimentary Processes

· Relate to the transport of sediments by wind, water, and glaciers.

· Running water and wind help segregate the sediments by size, shape, and density.

· If the bedrock in a river basin contains heavy metals streams draining the basin may concentrate the metals.

· In areas where there is less water turbulence.

· Placer deposits

· Rivers and streams carry tremendous quantities of dissolved material.

· Marine basins and lakes that form will eventually dry up.

· As evaporation progresses, the dissolved materials precipitate (drop out of solution).

· Forms a wide variety of compounds, minerals, and rocks that have important commercial value.

· Most of these evaporates can be grouped into one of three types:

· Marine evaporates (solids)—potassium and sodium salts, gypsum, and anhydrite.

· Nonmarine evaporates (solids)—sodium and calcium carbonate, sulfate, borate, nitrate, and limited iodine and strontium compounds.

· Brines (liquids derived from wells, thermal springs, inland salt lakes, and seawaters)—bromine, iodine, calcium chloride, and magnesium.

· Biological Processes

· Some mineral deposits are formed by biological processes.

· Phosphates

· Others formed under conditions of the biosphere that have been greatly altered by life.

· Iron ore deposits formed more than 2 billion years ago.

· There are several types of iron deposits.

· Gray beds contain unoxidized iron.

· Formed when little oxygen in the atmosphere

· Red beds contain oxidized iron.

· Formed when there was relatively more oxygen

· Major deposits of iron stopped forming when the atmospheric concentration of oxygen reached its present level.

· Organisms are able to form many kinds of minerals

· Calcium minerals in shells and bones.

· Cannot be formed inorganically in the biosphere.

· Thirty-one different biologically produced minerals have been identified.

· Weathering Processes

· Weathering

· Chemical and mechanical decomposition of rock

· Concentrates some minerals in the soil

· Accumulation occurs most readily when the parent rock is relatively soluble.

· The more soluble elements, such as silica, calcium, and sodium, are selectively removed by soil and biological processes.

· Produces sulfide ore deposits from lowgrade primary ore through secondary enrichment processes.

· Sulfides are oxidized, they dissolve, forming solutions rich in sulfuric acid as well as silver and copper sulfate

· Solutions migrate downward, producing a leached zone

· Below the water table, if oxygen is no longer available, the solutions are deposited as sulfides

· Enriching the metal content of the primary ore by as much as 10 times.

· Resources and Reserves

· We can classify minerals as resources or reserves.

· Mineral resources are broadly defined as elements, chemical compounds, minerals, or rocks concentrated in a form that can be extracted to obtain a usable commodity.

· A reserve 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.

· Estimating future resources requires continual reassessment of all components of a total resource through consideration of

· New technology

· Probability of geologic discovery

· Shifts in economic and political conditions.

· The problem with all mineral resources, is not total abundance but w/ concentration and relative ease of extraction.

· Classification, Availability, and Use of Mineral Resources

· Earth’s mineral resources can be divided into several broad categories:

· Elements for metal production and technology

· Building materials

· Minerals for the chemical industry

· Minerals for agriculture

· Metallic minerals can be further classified according to their abundance.

· Abundant metals include iron, aluminum, chromium, manganese, titanium, and magnesium.

· Scarce metals include copper, lead, zinc, tin, gold, silver, platinum, uranium, mercury, and molybdenum.

· Some mineral resources, such as salt, are necessary for life.

· With the exception of iron, the nonmetallic minerals are consumed at much greater rates than are elements used for their metallic properties.

· Availability of Mineral Resources

· Exhaustion or extinction of mineral resources not the problem but the cost of maintaining an adequate stock.

· At some point mining cost exceed the worth of material

· When the availability becomes a limitation, there are four possible solutions:

· 1. Find more sources.

· 2. Recycle and reuse what has already been obtained.

· 3. Reduce consumption.

· 4. Find a substitute.

· Mineral Consumption

· We can use a particular mineral resource in several ways:

· Rapid consumption

· Consumption with conservation

· Consumption and conservation with recycling

· Which option is selected depends in part on economic, political, and social criteria.

· Limits on minerals threaten affluence.

· Developed countries consume a disproportionate amount of the mineral resources extracted.

· As the world population and the desire for a higher standard of living increase, the demand for mineral resources expands at a faster rate.

· Increase in supply unlikely

· Affluent countries will thus have to find substitutes for some minerals or use a smaller proportion.

· US Supply of Mineral Resources

· Domestic supplies of many mineral are insufficient for current use and must be supplemented by imports from other nations.

· Does not mean they don’t exist in the US

· Suggests that there are economic, political, or environmental reasons that make it easier, more practical, or more desirable to import the material.

· Impacts of Mineral Development

· The impact of mineral exploitation on the environment depends on such factors as;

· Ore quality, mining procedures, local hydrologic conditions, climate, rock types, size of operation, topography, and many more interrelated factors.

· The impact varies with the stage of development of the resource.

· Environmental Impacts

· Exploration activities vary

· Collection and analysis of remote-sensing data

· Fieldwork involving surface mapping

· Drilling.

· Generally, exploration has a minimal impact on the environment.

· Provided that care is taken in sensitive areas

· Arid lands, marshes, and areas underlain by permafrost.

· The mining and processing of mineral resources have a considerable impact on land, water, air, and biological resources.

· As we use ores of lower and lower grades, negative effects on the environment tend to become greater problems.

· Several differences between surface (open-pit) and subsurface mining:

· Subsurface mines are much smaller than open-pit mines.

· Mining activities at subsurface mines are less visible because less land at the surface is disturbed.

· Subsurface mining produces relatively little waste rock compared to open-pit mining.

· Surface mining is cheaper but has more direct environmental effects.

· The trend in recent years has been away from subsurface mining and toward large, open-pit mines.

· Causes aesthetic degradation, dust pollution, topographic changes and potential water pollution.

· Another problem is release of harmful trace elements

· Water resources are particularly vulnerable to such degradation

· When leached from mining wastes and concentrated in water, soil, or plants, may be toxic or may cause diseases.

· Direct and indirect affect on biological environment:

· Direct impacts- Plants and animals killed by mining activity or contact with toxic soil or water.

· Indirect impacts- Changes in nutrient cycling, total biomass, species diversity, and ecosystem stability

· Social Impacts

· Social impacts result from rapid influx of workers into areas unprepared for growth.

· Stress is placed on local services.

· Land use shifts to urban patterns.

· Air quality is reduced as a result of more vehicles, dust from construction, and generation of power.

· Adverse social impacts also occur when mines are closed.

· Towns surrounding large mines come to depend on the income of employed miners.

· Closures produced ghost towns

· Minimizing Environmental Impact of Mineral Development

· Requires consideration of the entire cycle of minerals

· Many components of this cycle are related to generation of waste material.

· Waste produces pollution that may be toxic to humans, may harm natural ecosystems and the biosphere, and may be aesthetically undesirable.

· Waste also depletes nonrenewable mineral resources and provides no offsetting benefits for human society.

· Environmental regulation at the federal, state, and local levels address:

· Sediment, air and water pollution

· May also address reclamation

· Minimization of environmental impacts:

· Reclaiming areas where physical, hydrological, and biological disturbance has occurred.

· Stabilizing soils that contain metals to minimize their release into the environment.

· Controlling air emissions of metals and other materials from mining areas.

· Preventing contaminated water from leaving a mining site.

· Treating waste on-site and off-site.

· Practicing the three R’s of waste management.

· Wastes may themselves be referred to as ores, because they contain materials that might be recycled.

· Iron and steel are recycled in large volumes for three reasons:

· 1.Market is huge, and there is a large scrap collection and processing industry.

· 2. Enormous economic burden would result from failure to recycle.

· 3. Significant environmental impacts related to disposal of over 50 million tons of iron and steel.

· In addition, only 1/3 the energy is required to produce steel from recycled scrap as from native ore.

· Other metals that are recycled in large quantities include

· lead (63%)

· Aluminum (38%)

· Copper (36%).

· Minerals and Sustainability

· Simultaneously considering sustainable development and mineral exploitation and use is problematic.

· Sustainability is a long-term concept and minerals are a finite resource

· Human ingenuity will be important because often it is not the mineral we need so much as what we use the mineral for.

· A measure of the time available for finding the solutions to depletion of nonrenewable reserves is the R-to-C ratio

· R is the known reserves

· C is the rate of consumption

· The ratio is a present analysis of a dynamic system in which both the amount of reserves and consumption may change over time.

· The ratio provides a view of how scarce a particular mineral resource may be.

· Those metals with relatively small ratios can be viewed as being in short supply.

· Those resources for which we should find substitutes through technological innovation.