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Geology Today Chapter 16 Barbara W. Murck and Brian J. Skinner

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1 Geology Today Chapter 16 Barbara W. Murck and Brian J. Skinner
Earth Resources Geology Today Chapter 16 Barbara W. Murck and Brian J. Skinner Petroleum, solar energy, and biomass - California N. Lindsley-Griffin, 1999

2 Mineral Deposits Reserve - known resource that can be extracted profitably at current market conditions and levels of technology Source: U.S. Geological Survey

3 Mineral Deposits Mineral deposit - a naturally occurring accumulation of mineral material of potential economic value Banded Iron Deposit, Lake Superior Ore - the naturally occurring material from which a mineral can be profitably extracted N. Lindsley-Griffin, Dolgoff, 1998

4 The plate tectonic setting controls which mineral deposits form
Fig , p. 493 j N. Lindsley-Griffin, 1999

5 Mineral deposits form by natural Earth processes:
At depth, from internal heat and pressure Near the surface, from rock interactions with atmosphere and hydrosphere N. Lindsley-Griffin, 1998

6 Types of deposits: Magmatic Hydrothermal Metamorphic
Mineral Deposits Deep mineralizing processes at: Divergent margins Convergent margins Hot spots Mt. Hood, Oregon Types of deposits: Magmatic Hydrothermal Metamorphic Migmatite, Wyoming N. Lindsley-Griffin, 1999

7 Magmatic Deposits Form as molten magmas crystallize
Mineral Deposits Layered gabbro, Smartville ophiolite, CA Magmatic Deposits Form as molten magmas crystallize Metallic minerals settle to form layers in the magma chamber Chromium Platinum N. Lindsley-Griffin, 1999

8 Model for magmatic deposit formation
Mineral Deposits Model for magmatic deposit formation Fig , p.497 Chromite and plagioclase layers, Bushveld complex,South Africa N. Lindsley-Griffin, 1999

9 Hydrothermal Deposits
Mineral Deposits Hot water and sulfide particles issuing from a black smoker, East Pacific Rise Hydrothermal Deposits Hot water and gases circulate through fractures in crust Metal ions leached from rock at depth are concentrated and redeposited Gold, zinc, lead, copper Sulfide minerals deposited here Woods Hole Oceanographic Institution N. Lindsley-Griffin, 1998

10 Mineral Deposits Hydrothermal deposits in ophiolites (on-land fragments of ocean lithosphere) Veins are deposited along fractures in basalts of oceanic crust - Divergent margins, oceanic rift valleys Ores are transported by subduction and plate movement, emplaced on land by terrane accretion in ophiolites - Convergent margins, active continental margins Houghton Mifflin, Dolgoff, 1998; N. Lindsley-Griffin, 1999

11 Mineral Deposits Hydrothermal deposits associated with convergent margins form beneath stratovolcanoes. Hydrothermal solutions deposit copper-iron sulfides in porphyritic andesites - porphyry copper deposits Metallogenic province of rich porphyry-copper deposits along the western edge of the Americas Skinner et al., 1999; N. Lindsley-Griffin, 1999

12 Hydrothermal veins may form at depth beneath any volcano
Mineral Deposits Hydrothermal veins may form at depth beneath any volcano Geologist inspects a hydrothermal gold vein being mined at Cripple Creek, Colorado (Fig , p. 496) N. Lindsley-Griffin, 1999

13 Mineral Deposits Hydrothermal ore deposits are forming today in the Imperial Valley of California - a graben formed by rifting along the northern end of the East Pacific Rise which runs up Gulf of CA. Metallic ions are leached from the sediments under the graben by hot fluids resulting from volcanism. Hot brines deposit siliceous scale containing 20% copper and 8% silver on the insides of pipes in drilled wells. Fig. B16.1, p. 494 N. Lindsley-Griffin, 1999

14 Hydrothermal deposits forming today in the Red Sea:
Mineral Deposits Hot, dense brines rise up along normal faults that bound the graben. Heated by deep magmas along the oceanic rift, they precipitate chalcopyrite, galena, and sphalerite as they cool. Fig. B16.2, p. 495 N. Lindsley-Griffin, 1999

15 Hydrothermal deposits forming today in the Red Sea:
Mineral Deposits Brines remain pooled in the deep graben because they are denser than sea water. This hydrothermal deposit is called a stratabound deposit, because the minerals are precipitated as layers interbedded with sediments. Fig. B16.2, p. 495 N. Lindsley-Griffin, 1999

16 Stratabound ore of lead and zinc; Kimberley, British Columbia.
Mineral Deposits Stratabound ore of lead and zinc; Kimberley, British Columbia. Layers of pyrite (yellow), sphalerite (brown), and galena (gray) are parallel to the layering of the sedimentary host rock. Skinner et al., 1999; N. Lindsley-Griffin, 1999

17 Iron ores, marble, serpentine
Mineral Deposits Metamorphic deposits form by the heat, pressure, liquids associated with metamorphism Iron ores, marble, serpentine N. Lindsley-Griffin, 1998

18 Metamorphic deposits form by two main processes:
Mineral Deposits Metamorphic deposits form by two main processes: 1) recrystallization during regional metamorphism along convergent margins 2) contact metamorphism by hot solutions (hydrothermal solutions) near magma Houghton-Mifflin, Dolgoff, 1998; N. Lindsley-Griffin, 1999

19 Metamorphism - ores of tungsten, zinc and iron
Mineral Deposits Scheelite (CaWO4) Pyrite (FeS) Calcite (CaCO3) Fluorite (CaF) Ore, Tem-Piute Mine, NV (Fig , p. 496) N. Lindsley-Griffin, 1999

20 Shallow mineral deposits form by:
Surface water Mechanical concentration Evaporation Groundwater Leaching Secondary enrichment Biochemical reactions in seawater Types of deposits: Sedimentary Placer Residual N. Lindsley-Griffin, 1998

21 Sedimentary deposits form by evaporation and precipitation
Mineral Deposits Anhydrite, gypsum, halite Evaporite Deposits at Bonneville Salt Flats, Utah N. Lindsley-Griffin, 1998

22 Sedimentary deposits form by biochemical reactions in seawater
Mineral Deposits Sedimentary deposits form by biochemical reactions in seawater Banded iron formations were precipitated by biochemical reactions in a low-oxygen atmosphere during the Precambrian Banded Iron Deposit, Lake Superior N. Lindsley-Griffin, 1998

23 Manganese Nodules form by direct precipitation from seawater
Concentric rings enriched in: Copper, Cobalt, Nickel, Manganese Metallic ions from mid-ocean ridge hydrothermal vents Cold water lowers solubility Found in thin marine oozes (young crust or slow sedimentation) Best commercial potential: central Pacific Ocean N. Lindsley-Griffin, 1998; Dolgoff, 1998

24 Mechanical Concentration
Mineral Deposits Mechanical Concentration Placer deposits: Heavy grains sorted by currents Deposited in rivers or beaches Previously weathered from bedrock source Gold, platinum, diamonds, chromite, Zirconium and Titanium minerals Olivine beach placers, South Point, Hawaii N. Lindsley-Griffin, 1998

25 Placers are deposited:
Mineral Deposits Placers are deposited: Behind rock bars In rock holes Below waterfalls In point bars inside meander loops Downstream from a tributary Along beaches and behind undulations on the ocean floor. N. Lindsley-Griffin, 1999

26 Residual mineral deposits form by chemical weathering
Soluble minerals are leached - dissolved by rain water and carried downward by infiltration, leaving behind less soluble minerals. Laterites are mined for iron and sometimes nickel. Iron ore, Australia N. Lindsley-Griffin, 1999

27 Residual mineral deposits
Bauxite is the main source of aluminum ore - found in laterites formed in tropical climates. Fig , p. 499 Bauxite (aluminum ore) Weipa, Australia N. Lindsley-Griffin, 1999

28 Phelps-Dodge-Morenci open pit copper mine, Clifton, Arizona
Secondary Enrichment - metals leached from the surface are precipitated below the water table Upper zone: insoluble iron oxides left behind Leaching Precipitation Enriched zone: soluble metal sulfides of Zn, Pb, Cu, Au, Ag, Hg, Fe Phelps-Dodge-Morenci open pit copper mine, Clifton, Arizona N. Lindsley-Griffin; Dolgoff, 1998

29 Mining Mining can harm the environment if not done properly - that’s one reason why recycling is beneficial Sound mining practices include: Reclamation of mined areas Proper disposal of tailings and waste water Subsurface mine shaft Surface mine Spoil Banks Acid spill in stream Houghton Mifflin, Dolgoff, 1998; N. Lindsley-Griffin, 1999

30 REVIEW: plate tectonic setting controls which mineral deposits form
Fig , p. 493 j N. Lindsley-Griffin, 1999

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