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 MineralsSulfur, Gypsum, Coal, Barite, Salt, Clay, Feldspar, Gem Minerals, Abrasives, Borax, Lime, Magnesia, Potash, Phosphates, Silica, Fluorite, Asbestos, Mica

• Metallic MineralsFerrous: Iron and Steel, Cobalt, Nickel

• Metallic MineralsNon-ferrous: Copper, Zinc, Tin, Lead, Aluminum, Titanium, Manganese, Magnesium, Mercury, Vanadium, Molybdenum, Tungsten, Silver, Gold, Platinum

• Energy ResourcesFossil Fuels: Coal, Oil, Natural Gas Uranium Geothermal Energy

Metal Prices: Nov. 9, 2011

• US Dollars/Lb.• Aluminum .9494 • Copper 3.5473• Lead .9051 • Nickel 8.4210 • Tin 10.0698

• Zinc .8859 • Molybdenum 14.1748

• Cobalt 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 DepositsMagmatic• 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, MgWeathering• 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 quartz-sericite-pyrite.

• Outermost: Propylitic with quartz-chlorite-epidote-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• 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• 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 U-

235.– 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 ExplorationSatellite and Aerial

Photography Remote Sensing Geological MappingMagnetic 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

SatelliteImage of Wisconsin

Economic Factors in Mining

• 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