Mineral Resources

1. 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