V019-0012
The economic potential of granitic pegmatites in Sri Lanka: preliminary findings

Thursday, 10 December 2020
Poster
Samadhi Disanayaka1, Prasanna P.L Dharmapriya2, Amarasooriya H.M.T.G.A Pitawala1, Sanjeewa P.K Malaviarachchi3, Robert R Martin4 and Deepal N.D Subasinghe5, (1)Department of Geology, Faculty of Science, University of Peradeniya, 20400, Sri Lanka and Postgraduate Institute of Science, University of Peradeniya, 20400, Sri Lanka,, Department of Geology, Peradeniya, Sri Lanka, (2)Department of Geology, Faculty of Science, University of Peradeniya, 20400, Sri Lanka, Department of Geology, Peradeniya, kandy, Sri Lanka, (3)Department of Geology, Faculty of Science, University of Peradeniya, 20400, Sri Lanka, Department of Geology, Peradeniya, Sri Lanka, (4)Department of Earth and Planetary Sciences, McGill University, 3450 University St., Montreal, Quebec H3A 0E8, Canada, Department of Earth and Planetary Sciences, Montreal, Canada, (5)National Institute of Fundamental Studies, Hantana Road, Kandy, Sri Lanka,, Earth Resource and renewable energy, Kandy, Sri Lanka
Abstract:
Abstract

Granitic pegmatites are not typical igneous rocks; they crystallize from magmas close to H2O saturation. Bubbles appear once the melt crystallizes, as the minerals are anhydrous. The proportion of aqueous fluid progressively increases as magma crystallizes. The industrial minerals quartz and the feldspars crystallize from the magma; the feldspars become modified by the aqueous fluid, and may be converted to clay minerals. Strategic metals are present in magmatic accessory minerals that become modified by the fluid medium. Pegmatites are repositories of coloured gemstones, which crystallized largely from the aqueous fluid enriched in elements rejected by the magmatic minerals. The magmatic fluid phase may mix with externally derived fluid, responsible for Ca, Al and Mg in cavity minerals. Diagnostic element enrichments reveal whether a pegmatite has formed in a context of crustal compression or crustal extension. We investigate large- to small-scale pegmatite bodies near Kaikawala, Owala and Kaudupelella and Randenigala in the central Highland Complex (HC), and near Indikolapelessa, Weligapola, Thanamawila, Wellawaya, and Balangoda, in southern Sri Lanka, close to the tectonic contact between the HC and Vijayan Complex (VC). In addition to quartz (milky, clear or smoky), sodic plagioclase and microcline (including amazonite) as major constituents, biotite and an amphibole are minor phases, and tourmaline, graphite, and allanite are accessories. Fluorite appears only the central HC. Further, yellow quartz, garnet, xenotime, and uraninite appear in pegmatites near the HC–VC contact. Granitic pegmatites in the HC and near the HC–VC contact belong to the NYF family, emplaced in a context of crustal relaxation after a series of collisions. Such pegmatites are generally enriched in Nb, Y, and F [along with Be, rare-earth elements, Sc, Ti, Zr, Th, and U]. Further work will determine whether the pegmatite bodies are related to a parental pluton or whether they are of anatectic origin.

Keywords: Granitic pegmatite, industrial minerals, NYF family, Sri Lanka

This project is funded by the National Research council (NRC), Sri Lanka ( Grant No.19-092)

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