Gold-Quartz deposits in metavolcanics. Porphyry Copper

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Mineral Resources
2
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

3
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

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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

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Types of Ore Deposits

• 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
• 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

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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

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Magmatic Ore Deposits

• Platinum
• Bushveld Complex
• Iron
• Kiruna, Sweden
• Carbonatite Ores
• Nickel
• Sudbury, Ontario
• Thompson, Manitoba

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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)

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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

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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

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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

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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?

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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

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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

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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

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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

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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.

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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

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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

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Prospecting

• Looking for small targets
• Dont 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

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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

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Drill Core
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Geologic Map of Wisconsin
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Gravity Map of Wisconsin
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Magnetic Map of Wisconsin
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SatelliteImage of Wisconsin
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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?

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Life Cycle of a Mine

• Exploration
• Development
• Active Mining
• Excavation
• Crushing, Milling, Flotation, Chemical Separation
  
• Smelting and Refining
• Disposal of Waste (Tailings)
• Shut-down

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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

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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