Petrology and Ore Deposits Course 10179

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Petrology and Ore DepositsCourse 10179

• Week 1
• Welcome!

2
Course Outline

• Week 1 - Revision and expansion of basic
  petrology concepts
• Week 2 - Petrology concepts continued, ore
  microscopy
• Week 3 - Igneous Rocks of the Oceanic Lithosphere
  
• Week 4 - Igneous rocks of Convergent Margins
• Week 5 - Igneous rocks of Continental Lithosphere
• Week 6 - Granites
• Mid-Semester Break Orange Field Trip
• Week 7 - Porphyry copper deposits
• Week 8 - Epithermal gold deposits
• Week 9 - Anorthositic plutons, Continental
  volcanism, Lamprophyres
• Week 10 - Volcanic rocks of extreme composition
• Week 11 - Iron-copper-gold association of
  continental settings
• Week 12 - Sedex deposits
• Week 13 - Revision

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What is Petrology and why study it?

• Simply - the study of rocks
• From the Greek Petra rock and Logos
  explanation
• The study of rocks is the source of virtually all
  our ideas about the history of the Earth
• Knowledge of the origin, ages and distribution of
  rocks is capable of contributing to the solution
  of a wide variety of problems that face
  geologists eg igneous rocks vary greatly in
  texture and composition (SiO2 45-75). Yet most
  ign rx consist of coarse-grained granitoids (SiO2
  65-75) or fine-grained basaltic rocks (SiO2
  45-75). What does this tell us about the
  formation and evolution of magmas and of crust
  forming processes?

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The Major Rock Types

• Igneous rock that solidified from a molten or
  parially molten material ie magma
• Sedimentary rock resulting from the
  consolidation of loose sediment that has
  accumulated in layers. Clastic rocks consist of
  mechanically eroded fragments of older rocks
  transported and deposited by water, air or ice.
  Chemical rocks formed by precipitation from
  solution. Organic rocks consist of the remains or
  secretions of plants and animals.
• Metamorphic Any rock derived from pre-existing
  rocks by mineralogical, chemical or structural
  changes, essentially in the solid state, in
  response to changes in T, P, shearing stress and
  chemical environment at depth ie below zones of
  weathering and cementation

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General Characteristics of igneous, sedimentary
and metamorphic rocks
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Ch1 Igneous Environments

• What is igneous petrology?
• Intrusive versus Extrusive

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Intrusive versus Extrusive
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Ch2 - Igneous Minerals and TexturesMinerals of
Igneous Rocks

• Intrusive v extrusive
• Silica minerals
• Feldspars
• Pyroxenes
• Olivine
• Feldspathoids
• Amphiboles
• Micas Sheet silicates
• Other silicates
• Oxides, sulfides and phosphates

Links Minerals http//sorrel.humboldt.edu/jdl1
/minerals.list.htmlanchor736357
http//www.science.ubc.ca/eoswr/cgi-bin/db_miner
als/search.cgi
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Igneous Textures and Structures

• Degree of crystallinity, grain size and shape
• Holocrystalline, holohyaline, hypocrystalline
• Aphanitic
• Phaneritic (fine-grained lt1mm medium 1-5mm
  coarse 5-30mm very coarse gt3cm)

Link - Textures http//sorrel.humboldt.edu/jdl1/
web.page.images/texture.name.html
Gabbro
Granite
Nepheline Basalt
Rhyolite
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Igneous Textures and Structures

• Ophitic
• Poikilitic
• Trachytic
• Coronas
• Vesicles, amygdules
• Orbicular
• Lineations
• Compositional layering
• Planar alignment of tabular minerals
• Mineral aggregates
• Flattened vesicles
• Link - Textures http//sorrel.humboldt.edu/jdl1/
  web.page.images/texture.name.html

• Fabrics
• Euhedral, subhedral, anhedral
• Granular (granitic texture)
• Porphyritic, glomeroporphyritic
• Graphic texture intergrowth of quartz and
  alkali feldspar
• Myrmekite
• Exsolution textures perthite

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Common Plutonic Rocks

• Granite and alkali granite
• Syenite and alkali syenite
• Nepheline syenite
• Monzonite
• Diorite
• Gabbro
• Ultramafic rocks
• Link Rock types
• http//sorrel.humboldt.edu/jdl1/web.page.images/r
  ocks.html

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Common Volcanic Rocks

• Rhyolite, dacite, obsidian, vitrophyre, pumice,
  scoria
• Trachyte
• Phonolite
• Latite
• Andesite
• Basalt

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Ch3 Chemistry and Classification of Igneous Rocks

• Physical properties of magma
• Density
• Melting point
• Viscosity

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Chemical Constituents of Igneous Rocks

• The 2 most important elements in Earths crust
  are the 2 most abundant Si O
• The chemical constituents of rocks fall into 3
  categories
• Major elements (gt2 wt) reported in the form of
  their simple oxides SiO2, TiO2, Al2O3, FeO
• Minor elements (0.1-2 wt)
• Trace elements (lt0.1 wt) ppm, ppb eg Nb, Zr

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Chemical Constituents of Igneous Rocks

• Weight percents of oxides is the most commonly
  used format for rock analyses but molar amounts
  are also used for many petrological purpose
  including calculation of normative minerals
  CIPW-norm

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Methods of Chemical Analysis

• Wet chemical analysis
• Atomic Absorption Spectrophotometry AAS
• X-ray Fluorescence Spectroscopy XRF
• Electron microprobe EMP Proton Induced X-ray
  Emission PIXE
• Induced Coupled Plasma ICP Spectroscopy
• Instrumental Neutron Activation Analysis INAA
• Mass Spectrometry MS methods

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Chemical Composition of Igneous Rocks

• Chemical analyses have identified several
  fundamental patterns eg mafic rocks are richer in
  Ca, Fe, Mg and poorer in Na, K, Si relative to
  felsic rocks

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Measuring and Estimating Mineralogy

• Weight and volume modes
• The CIPW norm
• Hydrous versus Anhydrous
• KMg3AlSiO10(OH)2 KAlSi3O8 3 MgSiO3 3 SiO2
  H2O
• Biotite K-feldspar enstatite quartz
• Ca2Mg5Si8O22 2 CaMgSi2O6 3 MgSiO3 SiO2
  H2O
• Actinolite diopside enstatite
  quartz

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Mineralogical Classification

• For 200 years petrologists have been attempting
  to classify igneous rocks on the basis of
  mineralogy, chemistry, locality, texture etc etc.
  Thus a huge historical nomenclature exists
• The IUGS Classification System
• To classify a rock on the basis of mineral
  composition, the of 5 minerals must be
  determined quartz, plagioclase (anorthite
  content gt5), alkali feldspar (including albite),
  ferromagnesian minerals and feldspathoids
• IUGS classification scheme distinguishes rocks
  firstly on the basis of grain size phaneritic
  (plutonic) and aphanitic (volcanic)
• Triangular diagrams - QAP

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Mineralogical Classification Diagrams
Phaneritic igneous rocks
Aphanitic igneous rocks

• Fig 3-2 A B

Q quartz A alkali feldspar P plagioclase F
feldspathoids
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Mineralogical Classification Diagramsfor
Gabbroic rocks
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Mineralogical Classification Diagrams for
Ultramafic rocks
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Other Aspects of Classification

• The IUGS classification does not include a
  textural input apart from phaneritic v aphanitic
• A few igneous rocks are classified on the basis
  of textural criteria, with mineral content a
  secondary consideration. Eg. Pegmatite, obsidian,
  tuff, breccia, aplite, porphyry
• Other igneous rocks are defined on the basis of
  highly unusual bulk chemistry or characteristic
  post-magmatic alteration. Eg Carbonatite,
  spilite, serpentinite, lamprophyres

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Chemical Classification

• Silica saturation
• Alumina content of granites

Source http//geollab.jmu.edu/Fichter/RockMin/Roc
kMin.html
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Chemical Trends

• Harker diagrams
• AFM (or FMA) diagrams
• Differentiation index
• Alkali-lime index
• Larsen index
• Spider diagrams
• Assimilation and Fractional Crystallization (AFC)

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Basalt Classification
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Ch4 - Crystallization of Magmas

• Equilibrium
• Phases
• Components
• Phase rule -
• http//www.brocku.ca/earthsciences/people/gfinn/pe
  trology/phase.htm

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Study Exercises

• Shart answer questions. Taken directly from Blatt
  and Tracey Petrology Igneous, sedimentary
  and metamorphic see library special reserve.
• Chapter 1
• 1. What is igneous petrology, and why is it an
  important part of an undergraduate geology
  curriculum?
• 2. As a field geologist, what criteria would you
  use to determine whether an outcrop of igneous
  rock represented an old lava flow or an igneous
  intrusion?
• 3. Briefly describe the different forms of
  volcanic vents, and explain what genetic factors
  determine the external forms.
• 4. What petrologic or structural factors might be
  important in determining whether a batch of magma
  in the crust was finally emplaced as a dike, as a
  sill, or as a bulbous, stock-sized pluton?
• 5. What chemical or physical factors are
  important in causing a magma to erupt explosively
  and create a pyroclastic deposit?
• Chapter 2
• 1. What is the distinction between texture and
  fabric? which texture elements are directly
  related to cooling rates and which are
  independent of cooling?
• 2. Lineations are parallel linear textural
  elements that are important because they commonly
  reveal direction of magma flow. List the number
  of different textures and structures of igneous
  rocks that might produce lineations.
• 3. What is the most ubiquitous mineral of igneous
  rocks? why is itso abundant?
• 4. Based on mineral chemistry, why are sodic and
  potassic feldspars typical of lower-T magmas,
  such as granites, and calcic feldspars typical of
  highenT magmas, such as basalt?
• Chapter 3
• 1. Viscosity is one of the most important
  physical propem ties of maginas. what physical
  and chemical factors are most important in
  controlling viscosity?
• 2. How do trace elements differ from mor
  elements in magmatic rocks? How do stable
  isotopes differ from radioactive or radiogenic
  isotopes? Are the same analytical techniques
  used to measure the content of each of these in a
  rock?
• 3. Volume modes are easily calculated from
  measurements made in thin sections. How is this
  done? For some petrologic purposes, weight modes
  are required. They are messy to measure directly
  because the rock must be broken up into
  individual grains and each distinct mmeral
  fraclion weighed. A weight mode can be calculated
  from the more easily measured volume mode. How is
  this done?
• 4. what is the purpose for calculating a
  normative mmeralogy such as the CIPW norm?
• 5. Using the rules presented in Appendix 1,
  calculate by hand a CIPW norm for any one of the
  average igneous rock compositions given in Table
  3-4. If a computer program is available, use it
  to calculate CIPW norms for all the compositions
  given in Table 3-4.
• Optional Questions

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Recommended Reading/Links

• Blatt Tracey. 1996. Petrology Igneous
  Sedimentary and Metamorphic 2nd Edition. W. H.
  Freeman and Company, New York.
• Athena Mineralogy http//un2sg4.unige.ch/athena/mi
  neral/mineral.html Good!
• Bowens Reaction Series http//www.geog.ouc.bc.ca/p
  hysgeog/contents/10e.html
• Geology Web Links http//www.earthsci.org/geologyl
  inks.htmigneous EXCELLENT SITE!!
• Igneous Rocks http//www.science.ubc.ca/geol202/i
  gneous/igneous.html
• Petrology http//www.brocku.ca/earthsciences/peopl
  e/gfinn/petrology/321lect.htm Good summaries!
• Petrographic concepts http//plymouth.ces.state.nc
  .us/programs/drees2.html
• Geokem http//www.geokem.com/ A truly excellent
  site !! Comprehensive and detailed
• The lava hunters ABC Tuesdays at 9.30pm
  http//www.abc.net.au/tvpub/highlite/h0210theb.htm