Evolution of Fluid Phases Associated with Lithium Pegmatites from SE Ireland

Martin P. Whitworth and Andrew H. Rankin
Dept of Geology, Imperial College, London, SW72BP

Abstract: Fluid inclusions in quartz from internally zoned barren and spodumene-bearing pegmatites associated with the Leinster granite of SE Ireland represent a variety of early and late hydrothermal fluids responsible for the development of pegmatites. Microthermometry and optical examination reveal two main populations of inclusions. The first (Type 1) comprises low-moderate salinity brines which homogenized at temperatures up to about 400 °C. The second (Type 2) appear to postdate the first population and are characteristically more saline and homogenized at temperatures mostly below 250 °C. Isochores for model type 1 inclusion fluids indicate that a late-magmatic/early-hydrothermal fluid developed from the Leinster granite at 675 °C. and 2.5 kbar and cooled isobarically into the spodumene stability field where complete crystallization of the pegmatites took place. Later, more saline, type 2 fluids of unknown origin may have contributed to the alteration of spodumene to muscovite and albite with the accompanying release of lithium from the lattice of spodumene.

Keywords: fluid inclusions • pegmatite • lithium • Leinster • Ireland • isobaric cooling

Mineralogical Magazine; June 1989 v. 53; no. 371; p. 271-284; DOI: 10.1180/minmag.1989.053.371.01
© 1989, The Mineralogical Society
Mineralogical Society (www.minersoc.org)