Lecture: No. 3 Geothermometry, and fluid inclusion studies

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Lecture No. 3Geothermometry, and fluid
inclusion studies

• Geothermometry the branch of geology that
  measures temperatures deep below the surface of
  the earth
• Method for determining temperature of ore
  deposition
• A- Fluid inclusion
• Common daughter minerals include halite,
  sylvite, hematite, magnetite, anhydrite and
  chalcopyrite.

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• The genetic type of fluid inclusions may be
  primary, secondary
• or pseudo secondary.
• Primary inclusion
• Are those dispersed through a mineral with no
  clear relationship to
• any structure that would permit the escape or
  entry of either gas
• or liquid.
• Secondary inclusion
• Secondary inclusions are those inclusions that
  form by any
• process after the primary crystallization of the
  host is complete.
• Fluid will fill the cracks and dissolve and
  reprecipitate. Secondary
• inclusion give useful information about the
  genesis of ore but it
• does not established the pressure-temperature
  conditions at the
• time of crystal growth.
• Pseudo secondary
• Pseudo secondary could form in a fracture in a
  crystal while
• primary are going a millimeter away in a true
  growth ring.

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• Methods of study of fluid inclusion
• 1- Fluid inclusion can be study by a- heating or
  b- cooling.
• Boiling of fluid can be established if primary
  inclusion population
• includes two types,
• 1- Vapor-rich and homogenize to a vapor upon
  heating
• 2- Another that has small vapor bubble which
  dissolve by homogenizing to a liquid.
• Clearly two fluid were trapped, a vapor and
  liquid
• Most fluid inclusion investigation follows
  describing fluid inclusion
• in terms of five types (Fig. 1)
• 1- Liquid with small vapor bubble-No daughter
  minerals
• 2- Liquid with large vapor bubble- No daughter
  minerals
• 3- Poly phase essential inclusion with small
  vapor bubble
• 4- Two liquid with vapor and daughter minerals
• 5- Liquid CO2 with vapor

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• B- Synthesis of minerals
• C- Determination of melting points
• D- Determination of inversion point and stability
  range
• Examples Polymorphism (metallic mineral)
• 1- Chalcpyrite 525 C
  Chalcopyrite
• (cubic)
  (tetragonal)
• 2- Cu2S has three forms
• a- Cubic form above 430 10 C
• b- Hexagonal between 430 and 102 C
• c- Orthorhombic below 102 C

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• E- Determination of exsolution point
• Examples
• Cu-Fe Zn Sn- S system
• Chalcopyrite and stannite in sphalerite 550C
  
• Sphalerite in chalcopyrite
  400C
• Stannite in chalcopyrite
  475C
• Sphalerite in stannite
  325C
• Chalcopyrite in stannite
  400-475C

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• F- Study of mineral textures and habits
• G- Determination of electrical conductivity
• H- Isotope studies
• 1- Oxygen and hydrogen isotopes (fig.2)
• 2- Sulfur isotopes

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