Transcript Mineral Resources

Mineral Resources
Economic and environmental
considerations
Eight chemical elements make
up 98.3% of Earth’s crust.
 O – 46.6%
 Al – 8.1%
 Ca – 3.6%
 K – 2.6%
Si – 27.78%
Fe – 5.0%
Na – 2.8%
Mg – 2.1%
Other elements comprise 1.7% of
Earth’s Crust
 Many of these are important to industry
 Examples:
 Ni, Ti, Cr, Cu, Pb, Zn, U, Pt, Au, Ag, etc.
Distribution of these elements in
not uniform across the Earth.
 Many rocks contain none of these elements or
only trace quantities.
 Other areas may have one or more of these
elements in abundance.
Ore
 If one or more chemical elements occur in
sufficient abundance that they may be mined for
a profit, then the rock is termed an ORE.
Ore today, not tomorrow.
 Designation as an ore depends on
The degree of concentration of the mineral
The current market price of the mineral
The cost of production
Why do ore deposits occur
where they do?
 Why are they not found everywhere?
 The location of an ore deposit depends on
The geologic history of an area
The specific process by which the minerals became
concentrated
How do ores become
concentrated?
 Ores may become concentrated by processes
that are:
Chemical
Physical
Biological
Processes of ore concentration
are related to formation of rocks.
 Rocks are grouped in three major families,
based upon their processes of formation.
 Igneous Rocks
 Sedimentary Rocks
 Metamorphic Rocks
Three Families of Rock
 Igneous Rocks – form by the cooling and
crystallization of magma (melted rock).
 Sedimentary Rocks – form by deposition and
consolidation of sediments (e.g., sand, mud,
etc.) or by evaporation of water and
crystallization of dissolved materials.
 Metamorphic Rocks – form by the action of
heat and pressure on some other rock.
Ore Concentration by Igneous
Processes
 Magmatic segregation – crystals sink in magma
and concentrate near bottom of magma chamber
 Hydrothermal enrichment – water, superheated
by magma, dissolves minerals
 Dissolved minerals move with water to a new
location and are then precipitated to form ore.
Hydrothermal Enrichment
 Pegmatites – “veins” in continental rocks
Common form of gold enrichment
 Exhalites – Submarine vents of hot, mineral-rich
water
“Black Smoker Chimneys”
Associated with mid-ocean ridges
“Black Smokers”
Sulfide Mine in Exhalite Deposit
Ore Concentration by
Sedimentary Processes
 Placers
Concentration by density and current action
 Residuum
Enrichment by chemical weathering
– Other minerals are removed leaving ore
Ore Concentration by
Metamorphic Processes
 During metamorphism, heat and pressure alter
pre-existing rock
 If water is present, process is more efficient and
related to hydrothermal processes
 Metamorphism occurs deep within mountain
systems as they form
Plate Tectonic Connections
 Hydrothermal enrichment associated with
volcanic activity at convergent and divergent
margins
 Placer and Residuum enrichments occur on
stable continental platforms (plate interior)
 Metamorphic enrichment occurs at convergent
margins in mountain systems
Economic Implications
 Ores are not found everywhere
 Some ores are richer than others
 Ore distribution is a function of geology
 Ore distribution is not equal across the world
 Some nations are rich in mineral resources
 Other nations have few mineral resources
 No nation is self sufficient in mineral resources
Environmental Considerations
 Mining leaves holes in the ground
 Mining adds unusual quantities of sediment to
rivers and streams
 Mining exposes minerals to interaction with
surface and groundwater, which may
contaminate them
 Mine waste may be unstable - landslides
 Smelting may pollute air and water
We all make choices.
 Industrialized societies depend on mineral
resources
 Environmental problems must be considered in
extracting wealth from the Earth
 Its not Good (environment) vs. Evil (industry)
 It’s a compromise, of which, we must make the
best