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Mineral and Rock Resources
Mineral Resources
• Backbone of modern societies
• Availability of mineral resources as a measure of the wealth of a
society
• Important in people’s daily life as well as in overall economy
• Processed materials from minerals accounting for 5 percent of the U.S.
GDP
– Value of domestic minerals ~454 billion
– Value of domestic reclaimed minerals ~9.3 billion
– Value added by major industries (including manufacture of durable
goods)that use processed mineral materials ~1.9 trillion
• Mineral resources are nonrenewable
• Mineral resources: Usable economic
commodity (profitable) extracted from
naturally formed material (elements,
compounds, minerals, or rocks)
• Reserve: Portion of a resource that is
identified and currently available to be
extracted legally
Types of Mineral Resources
• Based on how we use them
– Materials for metal production and technology
– Construction materials
– Agricultural industry (fertilizers)
– Mineral resources for chemical industry
– Others (precious gem stones, cosmetics, food,
etc.)
– Energy mineral resources
Mineral Resource Problems
• Nonrenewable resources
• Finite amount of mineral resources and growing
demands of the resources
• Supply shortage due to the growing global
industrialization, with more developed countries
consuming disproportionate share of mineral resources
• The erratic distribution of the resources and uneven
consumption of the resources
– Highly developed countries use the most of the resources
Responses to Limited Availability
•
•
•
•
Find more sources
Find a substitute
Recycle
Use less and make more efficient use of what
is available
• Do without
Classification of Mineral Resources
• Based on geologic process of formation
– Igneous
– Metamorphic
– Sedimentary
– Biologic
– Weathering
Igneous Processes
• Crystal Settling
– As magma cools, heavy minerals that crystallize early may settle
to bottom of magma chamber
– Example: Chromite (ore of chromium)
• Late Magmatic Process
– Occur toward the end of crystallization
– Heavy metals in water solution is squeezed into fractures
• Hydrothermal replacement
– Originate from late stage magmatic processes
– Mineralizing fluids that migrate through a host rock, crystallizing
as veins
– Sources for gold, silver, copper, mercury, lead and other
resources
Metamorphic Processes
• Contact
– Metamorphism in response to the heat provided
by a nearby magma body
• Regional
– Large areas subjected to intense pressure
Metamorphic Processes
• Contact
– Ore deposits are often found along the contact
between the igneous rock and the rocks they
intrude upon
– The width of the metamorphosed zone depends
on the nature of the host rock
Contact Metamorphism
Metamorphic Processes
• Regional
– Possible source of some hydrothermal fluids
– May form in high temperature, high pressure
zones, where fluids may be produced and forced
into nearby cavities
Igneous and Metamorphic Processes
• In addition to producing ore deposits, these processes also
produce stone that has economic viability
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Granite
Basalt
Marble
Slate
Quartzite
• In total value, with the exception of iron and steel, the stone
industry is the largest nonfuel mineral industries
Sedimentary Processes
• Sand and Gravel
– Wind and running water help segregate sediments by size,
shape, and density
– Best deposits are those in which finer sediments have been
removed by water or wind
– US sand and gravel industry amounted to approximately $7
billion
– Most sand and gravel are obtained from river and glacial
deposits
– Shortages expected with restrictions on land zoning and
extraction
– Environmental degradation can occur and objections are
becoming common
Sedimentary Processes
• Placer Deposits
– If the bedrock in a river
basin contains heavy
metals (including gold),
streams draining the
basin may concentrate
these heavy metals to
form placer deposits
– Helped stimulate
settlement in the
western US
Sedimentary Processes
• Evaporite Deposits
– Widely used in industry and agriculture
– Can be grouped into three types
• Marine
• Nonmarine
• Brines
– Some beds are compressed by overlying rock
layers to form salt domes
• Good source for nearly pure salt
• Oil deposits can be found on their flanks
Salt Dome
Evaporite Deposits
Biologic Processes
• Organisms can produce many types of valuable
minerals
• Phosphate deposits consist of phosphorous-rich
rocks which include bones and teeth (the mineral
apatite)
– Large phosphate deposits are found in “Bone Valley” in
western Florida
– Consists largely of fossils of marine organisms
– Have supplied up to 1/3 of the world’s phosphorous
production
Bone Valley
Weathering Processes
• Residual Ore Deposits
– Intensive weathering of rocks can produce
deposits of less soluble materials
– Laterites – a residual soil derived from Al-rich and
Fe-rich igneous rocks
– The weathering process concentrates insoluble Al
and Fe oxides
– If sufficiently concentrated, bauxite can form
Weathering Processes
• Secondary Enrichment
– Near the surface, primary
ores (iron, copper, silver) is in
contact with slightly acidic
soil water
– As they ores are dissolved,
they migrate downward
toward the water table
– Below the water table, the
solutions may be deposited
as sulfides (which are much
higher in concentration than
near the surface)
Minerals from the Sea
• Sulfide deposits
– Massive sulfide deposits containing zinc, copper, iron, and
trace amounts of silver are produced at the black smokers
along the oceanic ridges, from which the hot, darkcolored, mineral-rich water emerges as hot springs
• Manganese nodules
– cover vast areas of the deep-ocean floor (up to 50 percent
in certain area), containing manganese (24 percent) and
iron (14 percent), with secondary copper (1 percent),
nickel (1 percent), and cobalt (0.25 percent). Most
abundant in where sediment is at a minimum, generally at
depths of 5 to 7 km
Environmental Impact from Mineral
Development
• The impact depends upon many factors
– Mining procedures
– Hydrologic conditions
– Climate factors
– Types of rocks and soils
– Topography
Environmental Impact from Mineral
Development
• Mineral exploration and testing
– Surface mapping, geochemical, geophysical, and
remote-sensing data collection
– Test drilling
• Impact
– Generally minimal impact
– More planning and care needed for sensitive areas
(arid, wetlands, and permafrost areas
Environmental Impact from Mineral
Development
• Mineral Extraction and Processing
– Direct impact on the land, water bodies, air
quality
– Indirect impact on topography of the landscape,
transportation of materials
– Social impact by creating a need for increased
housing and services
Environmental Impact from Mineral
Development
• Minimizing environmental degradation canbe
difficult because as the demand for more minerals
increases, exploitable deposits are decreasing
• Thus, mining operations have to increase to meet
demand
• Environmental degradation can extend beyond the
borders of the mine; the impact of a single mine can
have far reaching consequences
Mine Wastes
• Approximately 60% of land dedicated to
mining is used for extraction
• The remaining 40% is used for waste disposal
• Most waste is overburden – rock removed to
get to the ore
• Represents 40% of all solid waste generated in
the US
Types of Mining
• Surface mining is more economical but has a
greater environmental impact
Surface Mining
• More common
• Less expensive
• Overburden must be removed
– Soil and vegetation
• There are two kinds of surface mining
– Open-pit surface mining
• A giant hole is dug to extract minerals
– Strip mining
• A trench is dug to extract the minerals
Subsurface Mining
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•
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Disturbs the land less than surface mining
More expensive
More hazardous for miners.
Subsurface mining may be done
– Underground shaft mines
• Direct vertical shaft to the ore
• Hoisted to the surface with buckets
– Slope mines
• Has a slanting passage
• Ore hauled out by mine car
Water Pollution
• Runoff from mines may infiltrate
waste material leaching
(dissolving) trace elements and
minerals
• These leached minerals may be
toxic, creating diseases in plants,
animals, and people
• May include Cadmium, Cobalt,
Copper, Lead, Molybdenum, and
Zinc
• Specially constructed ponds may
help contain some runoff but
cannot eliminate the problem
Water Pollution
• Groundwater may also be impacted by mining
operations
• Impacted water infiltrating into the subsurface may
collect as the groundwater
• Groundwater can flow into other areas or seep into
rivers and impact surface water bodies
• Groundwater reclamation and remediation is very
difficult and expensive
Air Pollution
• Smelting releases enormous amounts of
pollutants into the atmosphere
• Dust may also be released, affecting air quality
• Scrubbers may be emplaced to limit air impact
but these are expensive
Biologic Impact
• Direct impact includes the deaths of plants,
animals, and people caused by mining activity
• Indirect impacts include
– Changes in nutrient cycling
– Changes in species diversity
– Changes in ecosystem stability
Social Impact
• Rapid influx of workers into an area
unprepared for growth
• Stress placed on local services
• Land use changes from rural to urban
– Affects water drainage (increased hardtop)
– Increased air pollution
– Disrupts ecological balance
Minimizing Impact
• Requires examination of the entire cycle
• Environmental regulation that addresses problems
such as water, air and sediment pollution resulting
from all aspects of the mining operation
• Onsite and offsite treatment of waste
• Practicing the three R’s of waste management
– Reduce the amount of waste produced
– Reuse materials as much as possible
– Maximize recycling