Granitic Pegmatite hosted Deposits.pptx

Granitic Pegmatite hosted Deposits.pptx

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  Granitic Pegmatite hosted Deposits By:
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  Objectives • To describein detail granitic pegmatites in mesothermal deposits. • Discuss the importance of pegmatite deposits in an economy like Zimbabwe. • Describe size and grade of deposits in relation to pegmatite deposits. • Describe the geological features; geological setting, age of host rocks and mineralization, structure of pegmatite deposits, ore mineral and textures. • State exploration guides for granitic pegmatite deposits
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  Introduction • Felsic pegmatitesare volatile rich post magmatic fluids which are similar in composition with granites, that is feldspar rich, exceptional coarse grained and zoned. • Most of the rare earth elements are associated with post magmatic crystallisation as they are highly incompatible to the mantle so they crystallise in the residual melt. • They are rich in the rare earth metals such as rubidium, lanthanium, cadium, niobium, tantalum, yttrium and tin. • They are useful in the electronic industry and metallurgical industry.
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  Distribution • Pegmatites occurin rocks of all ages from Archean to the Cenozoic, but Phanerozoic occurrences are far less numerous. • Pegmatites can occur in a variety of tectonic settings, but those of Precambrian age are associated with amphibolite grade metamorphism, while younger pegmatites occur within roof pendants and the associated intrusives along tectonic belts. • Within the United States important pegmatite districts occur in New England, throughout the southern Piedmont from Virginia to Alabama, and in association within generally Precambrian age intrusives in the western Cordillera.
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  Distribution cont… • Notablepegmatites are within major cratons and within green schist facies metamorphic belts • Archean pegmatites intruded during 2 main phases which coincide with the 2 major episodes of granite-greenstone terraine formation. • From 3900-3300Ma (most of which are barren as they lie within the predominantly tonalitic gneisses which are too basic. • From 2800-2600Ma (extensive and mineralized)