1. Economic and environmental considerations
Mineral Resources
Economic and environmental considerations

2. Eight chemical elements make up 98.3% of Earth’s crust.
O – 46.6% Si – 27.78%
Al – 8.1% Fe – 5.0%
Ca – 3.6% Na – 2.8%
K – 2.6% Mg – 2.1%

3. 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.

4. 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.

5. 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.

6. 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

7. 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

8. How do ores become concentrated?
Ores may become concentrated by processes that are:
Chemical
Physical
Biological

9. 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

10. 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.

11. 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.

12. 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

13. “Black Smokers”

14. Sulfide Mine in Exhalite Deposit

15. Ore Concentration by Sedimentary Processes
Placers
Concentration by density and current action
Residuum
Enrichment by chemical weathering
Other minerals are removed leaving ore

16. 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

17. 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

18. 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

19. 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

20. 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