Granitic Pegmatite hosted Deposits

1. Granitic Pegmatite hosted
Deposits
By:

2. Objectives
• To describe in 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

3. Introduction
• Felsic pegmatites are 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.

5. Distribution
• Pegmatites occur in 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.

6. Distribution cont…
• Notable pegmatites 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)