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Important Economic Minerals

Important Economic Minerals. Elements: Gold, Copper, Zinc… Sulfur Diamond, Graphite, Iron Oxides: Hematite (Fe 2 O 3 ), Magnetite (Fe 3 O 4 ) Elements and Ores Usually concentrated by biological or hydrothermal processes Associated with volcanism (plutonics) or metamorphism.

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Important Economic Minerals

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  1. Important Economic Minerals • Elements: • Gold, Copper, Zinc… • Sulfur • Diamond, Graphite, • Iron Oxides: • Hematite (Fe2O3), • Magnetite (Fe3O4) • Elements and Ores • Usually concentrated by biological or hydrothermal processes • Associated with volcanism (plutonics) or metamorphism

  2. Rock-Forming Minerals • Sediments and Sedimentary Rocks • Oxides (e.g., Iron oxides) • Fe2O3, Fe3O4 • Halides (e.g., with Cl- or S-2) • NaCl, FeS2 • Sulfates (SO4)-2 and Carbonates (CO3)-2 • FeSO4, CaSO4, CaSO4,·(2H2O) • CaCO3, CaMg(CO3)2,

  3. % of Tot. # of atoms Fe/Mg:Silicon: Systematic SilicateMineralogy 29% 14% <20% 20% <3% 23% <2% 25% (0) 33% (0) 23% (0) 15%* Olivine Pyroxene Group • Fig. 2.9 • From bottom to top • Increasing Fe/Mg/Ca • Decreasing silica • Increasing density • Darker minerals Amphibole Group Mica Group Decreasing Silica Increasing Fe/Mg/Ca Quartz K and Na Feldspar Ca Feldspar Increasing Density

  4. Systematic Silicate Mineralogy and Engineering Properties Olivine Mantle Pyroxene Group • Fig. 2.9 • From bottom to top • Increasing Fe/Mg/Ca • Decreasing silica • Increasing density • Darker minerals Oceanic Crust# Increasing • Melting and crystallizing Temperature~ • Fe/Mg/Ca Content • Density • Susceptibility to Weathering* Amphibole Group Mica Group Decreasing Cont. Crust *All of these silicates weather to form Clay Minerals Except quartz Quartz K and Na Feldspar Ca Feldspar# ~Quartz melts first

  5. Minerals in sedimentSandy and clayey soils Rocks (at surface)SedimentWeathered to form Sediments of: Quartz Feldspar Clay Calcite Hematite Biotite Quartz Na Plagioclase

  6. Minerals in Rocks Clastic sedimentary rocks • E.g., Sandstone • Primary minerals: Quartz and Feldspar • Secondary mineral from weathering: Clay and Oxides • Lithified (Compacted and cemented together) • From Sand deposited by a river or beach

  7. Minerals in RocksBiochemical and bioclastic sedimentary Shells, Coral, Calcite and Dolomite in Limestone • Lithified lime mud and • Shell fragments • Crystalline or Bioclastic

  8. Minerals in Rocks Clastic sedimentary rocks • E.g., Shale • Primary mineral: Clay • Minor mineral Quartz and Feldspar and Oxides From mud deposited in a deep lake, sea or ocean

  9. Minerals in RocksMetamorphic E.g. Schist • Mica, Quartz and Feldspars • Interlocking crystals (i.e., crystalline) Shale metamorphosed Minerals Changed in the solid state by heat and pressure

  10. Minerals in RocksIntrusive igneous rocks • E.g., granite • Quartz, Feldspar and a few Ferromagnesian minerals • Tightly interlocking crystals (crystalline) Minerals formed from crystallizing magma

  11. IV. Igneous Rocks A. Igneous Rocks and the Rock Cycle B. Basaltic Volcanism and Volcanic Rocks (extrusive igneous rocks) C. Silicic Volcanism and Volcanic Rocks D. Intrusive Igneous Rocks and E. Igneous Rock Classification

  12. Igneous Rocks and The Rock Cycle • Geological Materials Transformation Processes • Igneous Rock Solidification • Magma Partial Melting • Mantle Rock Fig 3.1 See Kehew, Fig 2.53

  13. % of Tot. # of atoms Fe/Mg:Silicon: Melting Points ofSilicate Minerals 29% 14% <20% 20% <3% 23% <2% 25% (0) 33% (0) 23% (0) 15%* Olivine Pyroxene Group > 1,100oC • Fig. 2.9 • From bottom to top • Increasing Fe/Mg/Ca • Decreasing silica • Increasing density • Darker minerals Amphibole Group Mica Group Increasing Melting Temperature Quartz K and Na Feldspar Ca Feldspar <700oC

  14. Melting ofGranite (Quartz, Na Plagioclase, Biotite) ~600oC ~700o ~800o Quartz Melts Na-Feldspar First Begins to melt ~900o ~1000o Biotite begins Magma is enriched Magma is separated from solid to melt in Si, Na, Al (K) and melts upward in crust Silicic Melt

  15. Fig 3.13 Partial Melting and Magma E.g., Silicic mineral melt first Resulting in Silicic Magma Enriched: O, Si, Al, Na, K, Depleted: Ca, Fe, Mg Gasseous: (H2O, CO2) Poor in: O, Si, Al, Na, K, (<50%) Magma Partial MeltingRich in: Ca, Fe, Mg (>50% wght)

  16. Solidification of Melts • Magma, Intruded or Extruded, • Solidifies (crystallizes) to form • Intrusive or Extrusive • Igneous Rocks Fig 3.12, 3.13 See Kehew, Fig 4.48

  17. E.g., Granite (Silicic, Intrusive Igneous Rock): Crystallized (Solidified) Silicic Melt Poor in: Fe, Mg, Ca, (<20%) Rich in: Silica (>70%) Biotite Quartz Na Plagioclase Igneous Rock

  18. Formation ofMagma • How are rocks melted? • 1. Heating ■ 2. Depressurization • 3. Increase water content • 4. Increased silica content • Where do rocks melt? • Subduction zones (Silicic andIntermediate magma) • Divergent Plate Boundaries • Mantle Plumes(“Hot Spots”) Mafic Magma See Fig. 4.1 Hot and Low Pressure Hot and High Pressure

  19. Intrusive vs.Extrusive • Silicic Magmas (& Lavas) • Cool(<700oC) • Viscous • Gaseous(steam of H2O and C02) • Silicic Rocks • Usuallyintrusive, course-grained, Silicic (Granite) to Intermediate (Diorite) rock forms plutons • If extrusive, fine-grained rocks are formed by explosive volcanoes Rhyolite or Andesite Volcanoes • Also injects surrounding rocks with silica laden steam Batholith made of Plutons Fig 4.17 Composite Volcano

  20. Dikes: Intruded near a pluton • Silica rich fluids and rare elements are injected into cracks in all directions • Discordant: cutting across layers • Forming deposits of • Precious minerals • Ores • Precious metals

  21. Extrusive vs. Intrusive • Mafic Magmas (& Lavas) • Hot(>1000oC) • Non-Viscous(runny, flows easily) • “Dry”(no H2O or C02) • Mafic Rocks • UsuallyExtrusive, Fine-grained, Mafic (Basalt) rock forms oceanic crust, Shield Volcanoes and Basalt Floods • If Intrusive, course-grained mafic rocks are formed Gabbro. • If intrusive, Dikes and Sills more common. (Plutons don’t form) Fig 3.10

  22. Mafic Sill: Intruded between layers • Mafic magma is less viscous and hotter so • Does not form plutons but • Cuts along layers (Sills) or even across layers (Dikes) • Also Baked Zones of adjacent country rock and Chill Zones within the intrusion

  23. B. Basaltic Volcanism • 1. Types of Rocks are controlled by  Fig. 3.7  • 2. Characteristics of volcanism which are contr. by  • 3. Types of eruptions which are controlled by  • 4. Type of lava which is contr. by  • 5. Source of lava which is contr. by  • 6. Plate tectonics  Fig. 3.22

  24. Types of RocksComposition and Texture • Basalt Figs. 4.9, 4.11, 4.17, 4.18 • ‘A’a • Pahoehoe • Vesicular Basalt • Pillow Basalt • Columnar Jointing • Obsidian (Glass)

  25. 2. Characteristics of Volcanism Fissures Through Crust Fig. 4.1 • Fissures Fig. 3.22 • Shield volcanoes Fig. 4.16 • Cinder cones Fig. 4.20 Calderas atop of Kilauea Shield Hawaii Cinder Cone

  26. 3. Types of Eruptions • Non-explosive • Lava flows, streams, ponds, floods • Fountains • Spatter cones • Pyroclastic eruptions

  27. 4. Types of Lava • Types of lava Basaltic • Hot • Non-viscous • Dry • Partial melting of mantle • Directly from mantle • Mantle plumes • Divergent plate boundaries 5 . Source of Lava

  28. Fig. 3.7 C. Silicic Volcanism • 1. Types of Rocks Fig. 3.7  • 2. Characteristics of volcanism  • 3. Types of eruptions  • 4. Type of lava  • 5. Source of lava  • 6. Plate tectonics  Fig. 3.24 Fig. 3.24

  29. 1mm Types of RocksComposition and Texture • Andesite (and Rhyolite) • Pumice (quenched glass froth) • Porphyritic Texture (partial crystallization and extrusion) • Welded Tuffs (welded pyroclastics) • Breccias (welded, coarse, angular pyroclatics) Fig. 4.12 Fig. 4.10

  30. 2. Characteristics of Volcanism • Lava Domes Composite Volcanoes • Layers of Pyroclastics (or tephra), ash and • Lava flows Fig. 4.26 Fig. 4.21 Pyroclastic Layers

  31. 3. Types of Eruptions Fig. 4.1 Box. 4.19 Mt. St. Helen’s Cascade Range • Explosive • Pyroclastic Flows and surges • Lahars (saturated pyroclastics) Fig. 4.20

  32. Mt. St. Helen’s Before and After 1 mile

  33. 4. Types of Lava • Silicic • Cool • Viscous • Gaseous

  34. 5. Source of Lava • Partial melting at Subduction Zone • Partial melting of continental crust • Convergent plate boundaries Fig. 3.24

  35. Igneous Rock Classification Intrusive(Plutonic) Extrusive(Volcanic) • E.g., Basalt and Gabbro have two minerals • Pyroxene • Ca-Feldspar Kehew Figure 4.58 Lab Manual Fig. 3.8 Volume Percent of Minerals Continental CrustOceanicMantle Crust

  36. Frame- Double Single Iso. work Sheet Chain Chain Igneous Rocks and Silicates Fig. 2.9 The Igneous Rock Classification parallels the systematic Silicate Mineral Classification Volume Percent of Minerals

  37. Igneous Rock Classification SilicicIntermediateMafic Granite Diorite Gabbro Rhyolite Andesite Basalt Fig. 3.7 (Porphyritic) Intrusive Extrusive

  38. Bowen’s Reaction Series Temperature of Crystallization Low Silica Magma Two series of minerals formed during crystallization of magma Intrus. Extrus. Gabbro Basalt Diorite Andesite Granite Rhyolite 1200oC 1000o Frame- Double Single Isolated work Sheet Chain Chain 750o High Silica Magma Kehew, Figure 4.53 (upside down)

  39. Crystallization ofGabbroandBasalt ~1,450oC ~1,400o ~1,350oThe remaining melt is enriched in silica (Int-Felsic) Ca-Feldspar Olivine Olivine converts Forms Forms to Pyroxene ~1,300o ~1,250o GabbroBasalt Remaining silica crystallizes into Ca-Feldspar. Intrusive Extrusive Cooling: Slowly Quickly Mafic Melt If melt is extracted Ultramafic Rock will be formed

  40. Crystallization ofDioriteandAndesite If cooled slowly in the magma chamber then extruded, Andesite Porphyry will be formed ~1,400oC ~1,300o ~1,200o Ca Feldspar Olivine converts Ca Feldspar Forms to Pyroxene absorbs Na ~1,100o ~1,000o DioriteAndesite Pyroxene converts Remaining silica Intrusive Extrusive to Amphibole forms Na-Ca Fldspr. Slowly Cooled Quickly Cooled Intermediate Melt

  41. Crystallization ofGraniteandRhyolite ~1,200oC ~1,100o ~1,000o Na-Feldspar Pyroxene Pyroxene dissolves forms and grows forms to form Amphibole ~900o ~750o GraniteRhyolite Amph. dissolves Remaining silica Intrusive Extrusive to form Biotite forms Quartz Slowly Cooled Quickly Cooled Silicic Melt

  42. Physiographic Map of the World Reading the features • Dark Blue (to black) lines are Oceanic Trenches • Light blue long light blue regions within the darker blue ocean basins are Mid-Ocean Ridges • Red linear regions on continents are mountain ranges

  43. Vocanic Hazards • Volcanic Earthquakes • Directed Blast • Tephra • Volcanic Gases • Lava Flows • Pyroclastic Flows and Surges • Lahars • Debris Avalanches, Landslides, and Tsunamis

  44. Hawaii Hazards

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