Lepidolite

About: Lepidolite is a research topic. Over the lifetime, 483 publications have been published within this topic receiving 6689 citations. The topic is also known as: lepidolite mica series.

Extreme fractionation in rare-element granitic pegmatites; selected examples of data and mechanisms

Abstract: Granitic pegmatites of the rare_element (and miarolitic) class display extreme fractionation and accumulation.of rare lithophile elements, beyond the limits observed in other igneous and postmagmatic assemblages. Enrichment in Li and -Cs leads to precipitation of rock-forming spodumene, petalite, Li-phosphates or lepidolite, and pollucite. These gqeoes-can be interpreted as crystallochemically conditioned Li- and-Csbased feldspathoids, crystallizing along with (and after) the last generations of primary K- and Nalfeldspars. Extreme fractionation is encountered in K-feldspar gi,znb !,9.rK/Qs 22.4, K/Tt 236, Rb,zCs 6.5, Rb,/Tt 130 io 35, K,/Ba 18,0@, BalRb <0.002); muscovite and lepidolite q/R! !.4, K,/Cs 4.0, K/Tl3ZO, Rb,/Cs 4.4, nb,ril SO ro 3.6, N/Ga239): pollucite (KAl 10, Rb/Tl 60io l3); microute, srmpsonite and other late oxide minerals of Ta (Nb/Ta < 0.001); manganoranialire (Fe,/Mn 0.@3): spes_ sartine @e,/Mn < 0.@3); lithiophilite (FeZVn < O.oii: iraf_ yoy (ZrlHf 0.014), and hawteyite and dernjite (in/Cd, 0.067)- Classic crystallochemical concepts of Goldichmictr and Ringwood alone are not adequate tb explain the above values. Selective extraction and transport in a volatile phase (by diffusion or in an exsolved hydrous fluid), complex_ ing stable to relatively low late- to postmagmaiic temieratures, and crystallochemical for specific mineral structures operate in conjunction with crystal,/melt fractionation; the environment evolves from that of a volatile_ saturated residual granitic melt, through that ofa melt coex_ isting with exsolved supercritical fluid, to that of an aque_ ous solution and possibly a gas phase, in a closed oirestricted system.

The Beauvoir topaz-lepidolite albite granite (Massif Central, France); the disseminated magmatic Sn-Li-Ta-Nb-Be mineralization

Abstract: The Beauvoir topaz lepidolite albite granite (French Massif Central) is the latest intrusion in a Variscan peraluminous granitic complex composed of three units successively emplaced: the concealed La Bosse granite, the Colettes two-mica granite, and the Beauvoir granite. The 900-m-deep drill hole of the Geologie Profonde de la France deep drilling program of the continental crust has provided a continuously cored section of the Beauvoir granite. The exposed section of the Beauvoir granite is presently mined for kaolin in the upper 200 m. It also represents a huge subeconomic disseminated Li, Sn, Ta, Be deposit sharing many characteristics with rare metal-bearing pegmatites. Compared to similar Li-F-rich igneous bodies, the Beauvoir granite is strongly enriched in Sn (200-1,400 ppm), Ta (20-400 ppm), and Be (20-300 ppm). Li is located in lepidolite and amblygonite, Ta and Nb mainly in columbo-tantalite and uranium-rich microlite, and Sn in cassiterite. Be is located in lepidolite crystals and in unidentified mineral(s). The major element composition of the Beauvoir granite is similar to that of Macusani volcanic glasses of Peru and ongonite subvolcanic rocks of Mongolia. The main structural, textural, mineralogical, and geochemical characteristics of the Beauvoir granite can be explained by extreme fractionation of F- and Li-rich magmas and associated fluid phases. Most trace elements show a strong upward enrichment. The high f (sub O 2 ) , low solidus temperature, and high fluorine content of the Beauvoir magma have considerably reduced Sn and W fractionation in the expelled magmatic fluid despite its high chlorine content (25-30 wt % NaCl equiv). However, F- and Li-enriched geochemical halos have developed in the enclosing mica schist in response to the boiling of the magmatic fluid. The relatively deep emplacement of the granite (3 km) has limited the development of hydraulic fracturing and subsequent hydrothermal circulation and mineralization. Thus, despite the very high specialization of the Beauvoir granite, no significant vein-type mineralization is directly related to it. The La Bosse quartz-ferberite stockwork was developed before the emplacement of the Colettes and Beauvoir granites and is related to the earlier concealed La Bosse granite.