Petrology Lunch - The Genesis of Lithium-rich Granites and Pegmatites by the Partial Melting of Metasediments - Bence Horanyi

We are pleased to announce a Petrology Lunch with Bence Horanyi on the topic of: The Genesis of Lithium-rich Granites and Pegmatites by the Partial Melting of Metasediments.

Abstract:

Rare-metal granites and pegmatites (RMGPs) are characterised by their enrichment in incompatible elements such as Li, Cs, Ta, Sn, W, Nb, and Rb. RMGPs account for approximately half of the world’s Li production [1], therefore it is important to understand the mechanism of their formation and evolution through the crust to improve the exploration prospects of rare-metal deposits. The genesis of RMGPs is often associated with the protracted fractional crystallization of peraluminous melts; however, this mechanism fails to explain the strong enrichment of Li (over 1000 ppm) observed in some RMGPs [2]. Alternatively, rare-metal enrichment during the partial melting of metasediments has been postulated to be a mechanism of RMGP genesis; however, there is a lack of experimental data to support this. In order to test this hypothesis, partial melting experiments were performed on Li-rich mica-schists and metabauxites in a piston-cylinder apparatus (at 750-800^oC and 700 MPa) to explore the composition of the melts produced. The experiments produced peraluminous granitic melts with strong Li-enrichment (up to 2000 ppm), which is consistent with RMGPs. However, in order to produce the most enriched RMGPs (up to 10,000 ppm of Li), the partial melt must undergo further fractional crystallization. In order to interpret Li-enrichment during fractionation, crystallization experiments were performed on peraluminous rhyolitic samples in an internally-heated pressure vessel (at 600-675^oC and 300 MPa) to acquire mineral-melt partition coefficients of rare-metals in quartz, plagioclase, k-feldspar, biotite, and muscovite. Trace element modelling using mineral proportions in RMGPs and bulk partition coefficients from the crystallization experiments (bulk D_Li of 0.26) shows that further enrichment by fractionation of >80% can produce RMGPs with Li contents of 5000-9000 ppm.

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Meeting ID: 955 0416 0063

Passcode: 249311