Lecture 2 Ore Deposit Classification and Ore Reserves

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Field Mapping and Economic Geology EART 4002
(012999)

• Lecture 2 - Ore Deposit Classification and Ore
  Reserves
• Dr. Solomon BuckmanRm P1-39Email
  solomon.buckman_at_unisa.edu.au

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Mineral Resources and Ore Reserves
JORC Code

• Go to http//www.jorc.org/main.php?action4 to
  download a copy of the JORC Code and Guidelines
  for reporting Mineral Resources and Ore Reserves

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JORC Code

• Who has heard of the JORC Code?
• Why is the classification and public reporting of
  ore reserves so important?
• The main principles governing the operation and
  application of the JORC Code are transparency,
  materiality and competence.
• Transparency requires that the reader of a Public
  Report is provided with sufficient information,
  the presentation of which is clear and
  unambiguous, to understand the report and is not
  misled.
• Materiality requires that a Public Report
  contains all the relevant information which
  investors and their professional advisers would
  reasonably require, and reasonably expect to find
  in the report, for the purpose of making a
  reasoned and balanced judgement regarding the
  Exploration Results, Mineral Resources or Ore
  Reserves being reported.
• Competence requires that the Public Report be
  based on work that is the responsibility of
  suitably qualified and experienced persons who
  are subject to an enforceable professional code
  of ethics.
• As an exploration or mining geologist you must be
  familiar with this code for reporting purposes.
  It is also a good guide for writing geological
  reports in general.

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Joint Ore Reserves Committee(JORC) Code
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Reporting of Exploration Results
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Reporting of Exploration Results
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Misleading reporting
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Mineral Resources and Ore Reserves

• 20. A 'Mineral Resource' is a concentration or
  occurrence of material of intrinsic economic
  interest in or on the Earth's crust in such form
  and quantity that there are reasonable prospects
  for eventual economic extraction. The location,
  quantity, grade, geological characteristics and
  continuity of a Mineral Resource are known,
  estimated or interpreted from specific geological
  evidence and knowledge. Mineral Resources are
  sub-divided, in order of increasing geological
  confidence, into Inferred D21 , Indicated D22 and
  Measured D23 categories.
• 29. An 'Ore Reserve' is the economically mineable
  part of a Measured or Indicated Mineral Resource.
  It includes diluting materials and allowances for
  losses which may occur when the material is
  mined. Appropriate assessments, which may include
  feasibility studies, have been carried out, and
  include consideration of and modification by
  realistically assumed mining, metallurgical,
  economic, marketing, legal, environmental, social
  and governmental factors. These assessments
  demonstrate at the time of reporting that
  extraction could reasonably be justified. Ore
  Reserves are sub-divided in order of increasing
  confidence into Probable Ore Reserves D30 and
  Proved Ore Reserves D31 .
• 30. A 'Probable Ore Reserve' is the economically
  mineable part of an Indicated, and in some
  circumstances Measured Mineral Resource. It
  includes diluting materials and allowances for
  losses which may occur when the material is
  mined. Appropriate assessments, which may include
  feasibility studies, have been carried out, and
  include consideration of and modification by
  realistically assumed mining, metallurgical,
  economic, marketing, legal, environmental, social
  and governmental factors. These assessments
  demonstrate at the time of reporting that
  extraction could reasonably be justified.
• A Probable Ore Reserve has a lower level of
  confidence than a Proved Ore Reserve.
• 31. A 'Proved Ore Reserve' is the economically
  mineable part of a Measured Mineral Resource. It
  includes diluting materials and allowances for
  losses which may occur when the material is
  mined. Appropriate assessments, which may include
  feasibility studies, have been carried out, and
  include consideration of and modification by
  realistically assumed mining, metallurgical,
  economic, marketing, legal, environmental, social
  and governmental factors. These assessments
  demonstrate at the time of reporting that
  extraction could reasonably be justified.
• 32. The choice of the appropriate category of Ore
  Reserve is determined primarily by the
  classification of the corresponding Mineral
  Resource and must be made by the Competent Person
  or Persons.

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Classification of Ore Deposits

• No two ore deposits are the same! However, they
  can be divided into broad classes eg syngenetic
  (BIF) vs epigenetic (vein)

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Discordant Orebodies

• Regularly shaped bodies
• Tabular veins, faults. Divides footwall and
  hanging wall
• Tubular pipes or chimneys (vertical) and mantos
  (horizontal)
• Irregularly shaped bodies
• Disseminated deposits eg diamonds in kimberlites,
  closely spaced veins called a stockwork
• Irregular replacement deposits eg magnesite
  replacement of limestone, skarn

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Concordant Orebodies

• Sedimentary host rocks
• particularly important for base metals and iron.
• Parallel to bedding and limited development
  perpendicular to it, thus strataform. Not to be
  confused with stratabound, which refers to type
  of orebody, concordant or discordant, which is
  restricted to a particular part of the
  stratigraphic colomn

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Stratiform Deposits
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Sedimentary host rocks

• Limestone hosts
• Very common host for base metal sulfide deposits
• Due to their solubility and reactivity they
  become favourable horizons for mineralisation
• Argillaceous hosts
• Shale, mudstone, argillites and slates
• Eg Kupferschiefer copper bearing shale, 1m thick
  over 136 km2.
• Arenaceous hosts next slide
• Rudaceous hosts
• Alluvial gravels and conglomerates often host
  placer deposits of gold, PGEs and Uranium
• Chemical sediments
• Iron, manganese, evaporite and phosphorite
  formations

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Arenaceous Hosts

• Heavy minerals in beach sands eg Crowdy Head, NSW
• Unconsolidated, easy to process using gravity
  settling techniques
• Formed by marine regressions and transgressions

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Igneous Host Rocks

• Volcanic hosts
• Volcanic-associated massive sulfide (VMS)
  deposits. Important source of base metals.
  Consist of gt90 pyrite and generally stratiform
  bodies.

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Igneous Host Rocks

• Plutonic hosts
• Layered mafic intrusions
• Rythmic layering in the form of alternating bands
  of mafic and felsic minerals
• Host to chromite, magnetite, ilmenite and PGEs
• Stratiform, great lateral extent eg Bushveld
• Komatiites
• Nickel-copper sulfide ores formed by the sinking
  of an immiscible sulfide liquid to the bottom of
  a magma chamber or lava flow. Liquation deposits.
• Sulfides usually accumulate in hollows at the
  base of the magma forming conformable sheets or
  lenses

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Residual Deposits

• Formed by the removal of non-ore material from
  proto-ore.
• Eg leaching of silica and alkalis from a
  nepheline syenite may leave behind a surface
  capping of hydrous aluminum oxides, called
  bauxite.
• Eg weathering granite kaolinite
• Eg laterite can enrich nickel from peridotites

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Supergene Enrichment

• Groundwater circulation can lead to
  redistribution of metals above the water table

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Textures and Structures of Ore and Gangue Minerals
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Terminology Ore Deposits

• Ore
• Gangue
• Waste
• Grade
• Cut-off
• Reserves
• Host rock
• Country rock
• Hydrothermal

• Alteration
• Metamorphism
• Vein
• Replacement
• Massive sulphide
• Skarn
• Epigenetic
• Syngenetic
• Gossan

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Terminology - Deposit Scale Structure

• Concordant
• Discordant
• Stratiform
• Stratabound
• Footwall
• Hangingwall

• Fault
• Shear zone
• Lode, shoot
• Breccia
• Stockwork
• Chimney
• Manto

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Terminology - Hand specimen scale structure

• Banding Banding may represent small scale
  sedimentary layering in a syngenetic deposit such
  as a massive sulphide or repeated pulses of
  mineralization in a vein.
• Crustiform bandingWhen minerals grow within a
  vein, they often grow inwards from the vein wall.
  Several layers of different types of minerals,
  representing different pulses of hydrothermal
  fluids passing through the structure, may be
  observed in a single vein. These bands are often
  aligned symmetrically away from the center of the
  vein.
• Comb structureWhen minerals crystallize inwards
  from opposite walls of a vein, they often meet in
  the center to form an interdigitating pattern of
  crystals, usually quartz, which has an appearance
  similar to a rooster's comb.
• VugThis is an open space or cavity, usually
  within a vein.
• CockscombThis is a crustiform banding when it
  surrounds breccia fragments.

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Crustiform banding
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Fluid Inclusions

• Formed during crystal growth and provide us with
  a sample of the ore forming fluid
• Yield crucial geothermometric data and tell us
  about the physical state of the fluid eg boiling
• Most fluid inclusion work carried out on
  transparent minerals such as quartz, fluorite and
  sphalerite
• Principle matter is water and carbon dioxide.
• 4 groups of inclusions
• Type 1 two phase, principally water with some
  vapour
• Type 2 two phase, principally vapour with some
  water
• Type 3 three phase, water-vapour-halite,
  contain daughter mineral that have crystallised
  from solution
• Type 4 CO2-rich inclusions, CO2 liquid.

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Fluid inclusions

• Fluids trapped in small crystal imperfections
• Can reveal information about the nature of ore
  forming fluids ie exceedingly strong brines form
  at depth indicating chloride in hydrothermal
  solutions is a potent solvent of metals through
  the formation of metal-chloride complex ions
  (ligands)

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Wall Rock Alteration

• Argillic clay minerals (dickite, kaolinite,
  pyrophylite, montmorillonite)
• (Na,Ca) 0.33(Al,Mg) 2Si4O10(OH)2nH2O
• Sericitization
• 3KAlSi3O8 2H ? KAl3Si3O10 (OH)2 6SiO2
  2K
• K-feldspar Sericite Silica
•  
• Ca, NaAlSi3O8 K 2H ? KAl3Si3O10 (OH)2
  6SiO2 3Na, Ca
• Plagioclase and Albite Sericite Silica
• Propylitic - Characterized by chlorite, calcite
  and minor epidote. Mafic minerals highly altered
  and plagioclase less so
• Chloritisation
• 4H 2K(Mg,Fe)3(Si3Al)O10(OH)2 ?
  Al(Mg,Fe)5(Si3Al)O10(OH)8 (Mg,Fe)2 K
  3SiO2
• Biotite Chlorite Quartz
• Carbonatisation pptn of carbonates (calcite,
  dolomite, magnesite, siderite)
• Potassic secondary biotite, orthoclase,
  chlorite
• Silicification addition of silica (Quartz,
  chalcedony)

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Figure 3-3 Photograph of thin section 17 showing
chloritisation and associated opaques in this
case most likely Fe oxides (f.o.v 1mm / PPL).
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Theories of Ore Genesis

• Internal Processes
• Magmatic crystallisation
• Diamonds in kimberlites, feldspar in pegmatites
• Magmatic segregation
• Fractional crystallisation
• Liquation
• Hydrothermal processes
• Sources of the solutions and their contents
• Meteoric water
• Sea water
• Deeply penetrating ground water
• Metamorphic water
• Magmatic water
• Means of transport (ligands)
• Lateral secretion
• Metamorphic processes

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Fluid Sources
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Geothermal Systems
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Lateral Secretion
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Metamorphic Processes
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Origin Due to Surface Processes

• Exhalative processes (volcanic and sedimentary) -
  exhalites

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VMS Formation
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VMS Fluid Circulation
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Stages of VMS Develop-ment Zoning
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Hydraulic Fracturing

• Fracturing of rock by water under high pressure
• Increases permeability
• Transport and deposition of ores

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Fracturing