Transcript Earth Resources

Mineral Resources
Resource Use
• U.S. has 5% of World Population
• U.S. Consumes 1/4 of World Resources
BUT
• U.S. Produces 1/4 of Global GDP
BUT
• Much of our GNP is consumed internally
Mineral Resources
• Building
Stone, Sand, Gravel,
Limestone
• Non-metallic Minerals
Sulfur, Gypsum, Coal,
Barite, Salt, Clay, Feldspar,
Gem Minerals, Abrasives,
Borax, Lime, Magnesia,
Potash, Phosphates, Silica,
Fluorite, Asbestos, Mica
• Metallic Minerals
Ferrous: Iron and Steel,
Cobalt, Nickel
• Metallic Minerals
Non-ferrous: Copper, Zinc,
Tin, Lead, Aluminum,
Titanium, Manganese,
Magnesium, Mercury,
Vanadium, Molybdenum,
Tungsten, Silver, Gold,
Platinum
• Energy Resources
Fossil Fuels: Coal, Oil,
Natural Gas
Uranium
Geothermal Energy
Metal Prices: Nov. 9, 2011
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US Dollars/Lb.
Aluminum
Copper
Lead
Nickel
Tin
Zinc
Molybdenum
Cobalt
.9494
3.5473
.9051
8.4210
10.0698
.8859
14.1748
13.3810
• US Dollars/Troy Oz.(31.1
gm)
• Gold
1,798.40
• Silver
35.137
• Palladium 677.15
• Platinum 1,670.60
• Iron Ore (62% Fe)
• $130/ton
Types of Ore Deposits
Magmatic
• Pt, Cr, Fe, Ni, Ti, Diamond
Pegmatite
• Li, Be, U, Rare Earths,
Feldspar, Mica, Gems
Hydrothermal
• 600 C: W, Sn
• 400 C: Au, U, Ag, Co, Mo
• 200 C: Cu, Zn, Cd, Pb
• Cool: Hg, As
Sedimentary Rocks
• Fe, Cu, U, Mn, Mg
Weathering
• Secondary Enrichment:
– Cu, Ni
• Soils
– Al, Ni
Placer
• Pt, Au, Sn, Ti, W, Th, Rare
Earths U (Fossil), Gems
Magmatic Ore Deposits
• Usually as segregations in mafic or
ultramafic intrusions
• Settle because of high density and low
magma viscosity
• Chromite often in serpentine bodies
– Originally segregated in ultramafic rocks
– Possibly mechanically concentrated by
deformation
• Diamonds in kimberlites
Magmatic Ore Deposits
• Platinum
– Bushveld Complex
• Iron
– Kiruna, Sweden
• Carbonatite Ores
• Nickel
– Sudbury, Ontario
– Thompson, Manitoba
Pegmatite Ore Bodies
• The final water-rich residue of granitic
intrusions
• Enriched in “reject” elements
• Common or simple pegmatites contain
typical granite minerals plus black
tourmaline
• Lepidolite mica typical indicator of complex
pegmatites
• Sources of gems, mica, feldspar, lithium,
rare earths (including col-tan)
Hydrothermal Ore Bodies
• 600 C: W, Sn in granites
• 400 C: Au, U, Ag, Co, Mo, Cu
– Gold-Quartz deposits in metavolcanics
– Porphyry Copper
– Marginal ores around intrusions
• 200 C: Cu, Zn, Cd, Pb
– Outer contact zones
– Mississippi Valley ore deposits
• Cool: Hg, As
– Hot springs, fault zones
Hydrothermal Alteration
• Core area (High T): Potassic alteration with
potassium feldspar and biotite.
• Lower T: Sericitic or Phyllic with quartzsericite-pyrite.
• Outermost: Propylitic with quartz-chloriteepidote-carbonate-actinolite.
• Argillic: Low T near surface: Clay minerals
Metamorphic Minerals
• Apart from metasomatism, metamorphic
rocks are not major mineral resources
• Ornamental stone: marble, slate, migmatite
• Specific metamorphic minerals
– Kyanite, wollastonite for refractories
– Garnet for abrasives
• Lateral Secretion
– Metals liberated by metamorphic reactions
migrate to fault zones
Stratiform Ore Bodies
• Principal ore is copper; zinc and lead also
important
• Form in layered submarine volcanic deposits
• Volcanic emissions?
• Submarine hydrothermal activity?
• Ancient rift hot springs?
Iron Ore
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Rarely magmatic as magnetite (Kiruna)
Pyrite common but rarely an ore
Archean sedimentary deposits
Proterozoic banded iron formations
– Probably due to cyanobacteria
– Cutoff after 1.8 Ga
– Rare later deposits due to local conditions?
– Snowball Earth?
• Oolitic iron ores
Residual Deposits
• Bauxite is an oxisol
• Nickel laterites in tropical countries
– Ni substitutes for Mg
– Very enriched in ultramafic rocks
– Concentrates at water table
• Supergene enrichment
– Cu leached out of surface zone
– Concentrates at water table
– Raises ore to minable grade
Detrital (Placer) Ores
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Concentrated by density
Mechanical separation
Gold (Sierra Nevada, Piedmont)
Platinum (Russia)
Tin(Malaysia)
Diamonds (Namibia, West Africa)
Heavy Beach Sands (Australia, Africa)
– Zircon, Ilmenite, Monazite, Tungsten
Detrital Ores
• Fossil Uranium Placer Deposits
– Uranium is the reverse of iron: highly oxidized
state is soluble
– Uraninite (UO2) weathers easily today
– Detrital uranium limited to Precambrian
– Detrital pyrite common
– Evidence of reducing atmosphere
Oklo, Gabon
• Wild fluctuations in isotopic ratios
• Strong depletion of U-235
• Natural Fission Reactor!
– Now, U-235 is 0.7% of natural uranium
– 2 Ga = ½ half-life of U-238 but 3 half-lives of U235.
– U-238 was 50% more abundant, U-235 8 times
– At 2 Ga, U-235 was 4% of total U
– A sufficiently large mass of U was naturally
critical.
Oklo, Gabon
• Reactor probably ran for 100,000 to
1,000,000 years
• Moderated by interstitial water
– Water needed to slow down neutrons
– Excessive heat would generate steam
– Steam would be less capable of slowing
neutrons
– Reaction would slow down
• No other cases discovered
• Mines now exhausted
Concentration Factors and Economics
• Natural Abundance
• Geologic Processes to Concentrate Element
– Most involve water
• Intrinsic Value of Material
• Cost of Extraction from Earth
– Gold versus Gravel
Prospecting
• Looking for small targets
• Don’t show up in gross geology
• Mineralization causes are subtle
– But-• Knowing types of ore deposits can help
identify likely places to explore
• 1% of sites sampled are worth a closer look
– 1% of those are worth detailed
exploration
• 1% of those are commercially viable
Prospecting and Exploration
Satellite and Aerial
Photography
Remote Sensing
Geological Mapping
Magnetic Mapping
Gravity Mapping
Radioactivity Mapping
Geochemical Sampling
Electrical Sounding
Ground-Penetrating
Radar
Seismic Methods
– Reflection - Detailed
but Expensive
– Refraction - Cheap but
Not Detailed
Core Sampling and Well
Logging
Drill Core
Geologic
Map of
Wisconsin
Gravity
Map of
Wisconsin
Magnetic
Map of
Wisconsin
Satellite
Image of
Wisconsin
Economic Factors in Mining
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Richness of Ore
Quantity of Ore
Cost of Initial Development
Equipment, Excavation, Purchase of Rights
Operating Costs: Wages, Taxes, Maintenance,
Utilities, Regulation
• Price of the Product
• Will Price Go up or down?
Life Cycle of a Mine
• Exploration
• Development
• Active Mining
– Excavation
– Crushing, Milling, Flotation, Chemical
Separation
– Smelting and Refining
– Disposal of Waste (Tailings)
• Shut-down
Sulfur
• Present in sulfide ores, pyrite or organic
sulfur in coal, organic sulfur in petroleum
• Smelting or burning create SO2
• 2SO2 + O2  2SO3
• H2 O + SO3  H2 SO4
Sulfuric Acid
• Contributor to Acid Rain
– Neutralized by carbonates and mafic igneous
rocks
– Worst in granitic bedrock
• Weakens tailings piles, slopes, dams
• Acidifies surface water
• Contributes to dissolved metals