- Title
- Nature of occurrence and economic potential of granitic pegmatites of Mzimba district in Northern Malawi
- Creator
- Salima, Jalf William Joseph
- Date Issued
- 2014
- Date
- 2014
- Type
- Thesis
- Type
- Masters
- Type
- MSc (Geology)
- Identifier
- vital:11527
- Identifier
- http://hdl.handle.net/10353/d1016192
- Description
- A swarm of granitic pegmatites occurs in Mzimba district from northern Kasungu to Kafukure near the western international border with Zambia. The granitic pegmatites are hosted by a mobile belt, within the Mozambiquan orogenic belt (c. 900 - 1800 Ma). They have been dated as 485 Ma. They intruded metasediments of high to medium grade metamorphic rocks of a Precambrian Basement Complex. The dominant trend of the pegmatites is NW - SE, exhibiting a cross-cutting relationship with the country rocks and their contacts with the latter are usually sharp. The six pegmatites investigated in this study are inhomogeneous, composed of a massive quartz core, an intermediate zone composed of a blocky pink K-feldspar rich sub-zone and muscovite rich sub-zone and a wall zone composed of quartz - pink K-feldspar - muscovite mineral assemblage. The Mzimba pegmatites are classified as lithium-caesium-tantalum (LCT) family of rare element granitic pegmatites as described by Černý and Ercit (2005). They belong to the beryl-columbite subtype and beryl-columbite-phosphate subtype of the rare element pegmatites. It is suggested that the pegmatites are the product of magmatic differentiation and that they form roofs of granite plutons lying deep below the current level of erosion. The six pegmatites were sampled and minerals analysed using standard analytical methods such as petrographic microscopy, X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis. Mineralogy of the granitic pegmatites indicates that they are predominantly composed of perthitic K-feldspar (perthite), Na-plagioclase (albite), quartz and muscovite as main mineral phases and accessory minerals including beryl, tantalite-columbite (ferrotantalite), iron-titanium oxides (ilmeno-rutile and ilmenite), tourmaline (schorl), garnet (almandine-spessartine) and triplite. Triplite is a very rare mineral found in a few pegmatites around the world, and this is the first reported account of this mineral in the Mzimba pegmatites and probably in Malawi. These minerals are being exploited by artisanal and small scale miners. Trace elements in K-feldspar and muscovite are significant indicators for the evaluation of economic potential of pegmatites as well as for the differentiation degree and origin of the magma. The K/Rb ratio for K-feldspars ranges between 12.72 and 109.38, while for muscovites it is between 16.66 and 82.36 indicating that the pegmatites are moderately evolved. The Ta versus Cs and the Ta versus K/Cs discrimination diagram indicates that all the investigated pegmatites plot above the 20 ppm threshold suggesting that the pegmatites have potential for Ta and Nb mineralization.
- Format
- 184 leaves; 30 cm
- Format
- Publisher
- University of Fort Hare
- Publisher
- Faculty of Science & Agriculture
- Language
- English
- Rights
- University of Fort Hare
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