Pegmatites as Hosts of Critical Metals: From Petrogenesis to Mineral Exploration

Dear Colleagues,

The increasing demand for critical metals has recently renewed the interest of the scientific community in pegmatites, as their rising economic importance requires improved petrogenetic and exploration models. Pegmatites are crustal igneous rocks with unique textural and geochemical characteristics, such as extreme crystal sizes and pronounced mineral zoning. The origin of granitic pegmatites involves the advanced magmatic differentiation of a parent melt and/or direct anatexis of crustal rocks. Geochronology is often necessary to distinguish between these two scenarios. Current petrogenetic models propose that pegmatite crystallization involves undercooling below the equilibrium liquidus and suppressed nucleation rates coupled with enhanced growth rates, all of which promote the formation of megacrysts. The nature of pegmatite-forming melts, as well as the prevalent pressure and temperature conditions of crystallization in pegmatites, are still debated among researchers. Cooling rates are expected to be fast, approaching temporal scales in the order of days for thin pegmatitic dykes. The evolved, hydrous nature of pegmatite-forming melts leads to the accumulation of economically valuable minerals of Li, Cs, Be, Nb, Ta, Sn, and REEs, but the relation between rare-metal mineralization potential, undercooling and fluid exsolution remains poorly understood. Gem-quality crystals are also encountered in pegmatites, making these rocks a highly sought-after source of mineral specimens for museums and private collections alike.

This Special Issue aims to gather studies that examine the unique characteristics of pegmatites and address the conditions of their formation. We welcome studies that include, but are not limited to, the following topics:

• The origin of pegmatite-forming melts;
• The petrophysical and geophysical properties of pegmatites;
• Extreme crystal sizes and characteristic pegmatite textures;
• Rare-metal enrichment and depletion processes;
• Crystal nucleation and growth rates;
• Thermal modeling;
• Fluid and melt inclusions;
• Gemstones in pegmatites;
• Critical metals in pegmatites;
• Mineral chemistry;
• Geochemical diffusion halos;
• Pegmatite geochronology;
• New exploration methods.

We thank you and look forward to receiving your contributions.

Dr. Victoria Maneta
Dr. Mona-Liza C. Sirbescu
Dr. Julian Menuge
Guest Editors

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• pegmatites
• dyke propagation
• rare-element and critical-metal exploration
• lithium, cesium, tantalum
• megacrysts and gemstones
• fluid and melt inclusions
• nucleation and growth rates
• magmatic differentiation
• anatexis

1. Rainer Thomas. The role of supercritical fluids in pegmatite formation and critical-element redistribution

2. Teagan J. Cox, Mona-Liza C. Sirbescu, Luiza Maria Pereira-Pierangeli, Sérgio Henrique Godinho Silva, David C. Weindorf, Thomas R. Benson: Exploring for lithium pegmatites: Metasomatic and weathering dispersion aureoles assessed through soil geochemistry

3. Haili Li. Discussion on mineralization of the Liruo Beryllium-niobium-tantalum deposit in southern Jiangxi Province: evidence from major and trace geochemistry of granite pegmatite and zircon U-Pb chronology