2. 218462 : Gemstone Deposits

3. Introduction - About the course - Teaching and learning - Assignments - Exam and grading

4. General mode of gemstone occurrences Distribution of world gemstone deposits Origin and occurrences of gemstones Geological processes of gemstone deposits - subsurface processes - surficial processes

5. Distribution of Principal Diamond Deposits 

6. Distribution of Principal Beryl Deposits  Tectonic - hydrothermal type Granitic pegmatite - hydrothermal type

7. Distribution of Principal Corundum Deposits  RubySapphire

8. Distribution of Principal Opal Deposits  Precious opal Common opal

9. Distribution of Principal Peridot Deposits 

10. Distribution of Principal Jade Deposits  Jadeite Nephrite

11. Distribution of Principal Turquoise Deposits 

12. Gems, when present at all, tend to be scattered sparsely throughout a large body of rock or to have crystallized as small aggregates or fill veins and small cavities. The average grade of the richest diamond kimberlite pipes in Africa is about 1 part diamond in 40 million parts "ore.” Gemstones occur in most major geologic environments. Most gemstones are found in igneous rocks and alluvial gravels, but sedimentaryand metamorphic rocks may also contain gem materials.

13. Origin and Occurrences of Gemstones Igneous Origin e.g. - diamond - bearing kimberlites / lamproites - corundum-bearing basalts Metamorphic Origin e.g. - garnet-bearing mica schists - jadeite and nephrite Hydrothermal Origin e.g. - emerald-bearing calcite veins of Colombia Pegmatitic Origin e.g. - gem-bearing pegmatites of Brazil Etc.

14. Geological Processes of Gemstone Deposits A. Subsurface processes magmatic metamorphic and metasomatic pneumatolytic and hydrothermal B. Surficial processes weathering sedimentation