Petrogenetic Implications of Garnets Associated with Lithium Pegmatites from SE Ireland

Martin P. Whitworth*
Department of Geology, Imperial College, London SW7 2BP, U.K.
*Present address: Primary Processes Department, Process Development Group, British Steel Technical, Teesside Laboratories, Middlesbrough TS6 6UB, UK

Abstract: Spodumene pegmatites, aplites and schists from the Aclare Li prospect of SE Ireland host sporadically developed, small, red, euhedral garnets. Chemical data indicate that the pegmatite- and aplite-hosted garnets are rich in spessartine and are similar to garnets in many African Li-rich pegmatites. Partial melting as a source of the garnets is unlikely due to the large spessartine component, the abundance of inclusions within the garnets and the general P-T-X evolution of the pegmatite body. It is suggested that an aqueous fluid was exsolved during pegmatite crystallisation and complexed available Mn. Movement of this fluid to the intermediate zone of the pegmatite body produced areas of high Mn concentrations which permitted the crystallisation of spessartine-rich garnets at low pressures (<3 kbar).

Keywords: garnets • lithium pegmatites • manganese • Aclare • Ireland

Mineralogical Magazine; March 1992 v. 56; no. 382; p. 75-83; DOI: 10.1180/minmag.1992.056.382.09
© 1992, The Mineralogical Society
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