Lithium in carbonatites — consequence of an enriched mantle source?

Abstract

The rare Li-mica taeniolite is described from the Dicker Willem carbonatite complex, Namibia, and from the Alpine carbonatitic lamprophyre dyke swarm at Haast River, New Zealand. At Haast River, taeniolite occurs in sodic and ultrasodic fenites derived from quartzo-feldspathic schists and rarely in metabasites, adjacent to dykes of tinguaite, trachyte and a spectrum of carbonatites ranging from Ca-to Fe-rich types. In Namibia, taeniolite is present in potassic fenites derived from quartz-feldspathic gneisses and granitoids at the margin of an early s6vite phase of the complex and in a radial s6vite dyke emanating from this centre.The occurrence of taeniolite in these totally disparate carbonatite complexes, together with examples of lithian mica from other carbonatite complexes worldwide, raises the question of the status of Li as a 'carbonatitic element'. We argue that lithium is not a consequence of crustal assimilation or interaction, but reflects the geochemical character of the magmatic source. Li, an overlooked and little-analysed element, may be an integral part of metasomatic enrichment in the mantle, and of magmas derived by partial melting of such a source.

Nb-rich baotite in carbonatites and fenites at Haast River, New Zealand

“…Halogens, in particular fluorine, have long been known as an essential ingredient of carbonatites, manifest generally in the ubiquitous appearance of fluorite, fluormicas (e.g. Cooper et al, 1995), pyrochlore (Hogarth, 1989) and fluor-carbonates of the bastnaesite group. Fluorite, in particular, attains the status of an essential rock-forming mineral, subordinate only to nyerereite and gregoryite, in the 1988 natrocarbonatites of Oldoinyo Lengai (Keller and Krafft, 1989).…”

Internal distribution of Li and B in serpentinites from the Feather River Ophiolite, California, based on laser ablation inductively coupled plasma mass spectrometry

“…In addition to serpentinization, there are many other ways to get secondary Li enrichments. For example, mesomatism by carbonatite melts and subduction‐related fluids can give rise to Li enrichments [ Cooper et al , 1995; Brenan et al , 1998a; Brenan et al , 1998b; Ottolini et al , 2004; Halama et al , 2007].…”

Mineralogical evolution and REE mobility during crystallisation of ancylite-bearing ferrocarbonatite, Haast River, New Zealand

“…The anomalous REE profiles at Pivot Creek could arise during the late-stage hydrothermal or carbothermal stages of carbonatite evolution rather than during earlier crystal fractionation or liquid immiscibility. The ubiquitous presence of a fenite aureole around carbonatite intrusions and the abundance of fluid inclusions in carbonatite minerals testify to the importance of a fluid phase (see also Buhn, 2008 , and OH − as potential ligands, while the presence of taeniolite and baotite (Cooper, 1996;Cooper et al, 1995) in other Haast carbonatites indicates that, at least locally, F − and Cl − play important roles.…”