Chapter 26: Minerals and the Environment. The Importance of Minerals to Society Many mineral products are found in a typical American home. Availability

Chapter 26: Minerals and the Environment

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.

Distribution of Mineral Resources

• 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.

Plate Boundaries

• 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.

Weathering 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 and Reserves

• 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.

Mineral Consumption

• 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.

Social Impacts

• 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.

Gold mining Copper smelter Sheets of cooper

Use of metals Tailings pond


• 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.

Documents

Chapter 26: Minerals and the Environment. The Importance of Minerals to Society Many mineral products are found in a typical American home. Availability