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Lecture: No. 3 Geothermometry, and fluid inclusion studies

Lecture: No. 3 Geothermometry, 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

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Lecture: No. 3 Geothermometry, and fluid inclusion studies

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  1. 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.

  2. 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.

  3. 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

  4. 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˚

  5. 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˚

  6. 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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