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

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: 30 March 2025 | Viewed by 3990

Special Issue Editors


E-Mail Website
Guest Editor
Geological Survey of Canada—Central Division, Natural Resources Canada, 601 Booth Street, Ottawa, ON K1A 0E8, Canada
Interests: igneous petrology; mineralogy; geochemistry; granite origin and evolution; pegmatites

E-Mail Website
Guest Editor
Department of Earth and Atmospheric Sciences, Central Michigan University, 314 Brooks Hall, Mount Pleasant, MI 48859, USA
Interests: mineralogy; igneous petrology; high-temperature geochemistry; economic geology; pegmatites

Special Issue Information

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
Guest Editors

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Keywords

  • 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

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Published Papers (2 papers)

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Research

20 pages, 2190 KiB  
Article
Quantification of Feldspar and Quartz Nucleation Delay in a Hydrous Peraluminous Granitic Melt
by Maude Bilodeau and Don R. Baker
Minerals 2024, 14(6), 611; https://doi.org/10.3390/min14060611 - 15 Jun 2024
Viewed by 716
Abstract
A modified model based on classical nucleation theory was applied to a natural hydrous peraluminous pegmatite composition and tested against crystallization experiments in order to further investigate the quantification of nucleation delay in felsic melts. Crystallization experiments were performed in a piston-cylinder apparatus [...] Read more.
A modified model based on classical nucleation theory was applied to a natural hydrous peraluminous pegmatite composition and tested against crystallization experiments in order to further investigate the quantification of nucleation delay in felsic melts. Crystallization experiments were performed in a piston-cylinder apparatus at 630 MPa and temperatures between 650 and 1000 °C for durations ranging from 0.3 to 211 h. Experimental run products were investigated by scanning electron microscopy paired with energy dispersive spectroscopy analyses of both crystalline and quenched liquid phases, the results of which were compared to an established theoretical nucleation delay model from the literature. The experiments showed good agreement (within a factor of 5) with the model for quartz, while it showed moderate agreement (within a factor of 10) with the model for sodic feldspar. Other crystals also nucleated, demonstrating abundant features of disequilibrium. Our research further demonstrates the potential of the model to predict nucleation delay, showing promising results for the quantification of the nucleation delay of quartz and feldspar in natural felsic melts, thus adding to previously published studies on hydrous, metaluminous, felsic melts and dry basaltic melts. Full article
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21 pages, 1537 KiB  
Article
Reevaluation of the K/Rb-Li Systematics in Muscovite as a Potential Exploration Tool for Identifying Li Mineralization in Granitic Pegmatites
by Michael A. Wise, Adam C. Curry and Russell S. Harmon
Minerals 2024, 14(1), 117; https://doi.org/10.3390/min14010117 - 22 Jan 2024
Cited by 3 | Viewed by 2276
Abstract
A dataset of >1190 published compositional analyses of muscovite from granitic pegmatites of varying mineralogical types was compiled to reevaluate the usefulness of K-Rb-Li systematics of muscovite as a tool for distinguishing mineralogically simple pegmatites from pegmatites with potential Li mineralization. Muscovite from [...] Read more.
A dataset of >1190 published compositional analyses of muscovite from granitic pegmatites of varying mineralogical types was compiled to reevaluate the usefulness of K-Rb-Li systematics of muscovite as a tool for distinguishing mineralogically simple pegmatites from pegmatites with potential Li mineralization. Muscovite from (i) common, (ii) (Be-Nb-Ta-P)-enriched, (iii) Li-enriched, and (iv) REE- to F-enriched pegmatites contain Li contents that vary between 10 and 20,000 ppm depending on the degree of pegmatite fractionation. Common pegmatites are characterized by low degrees of fractionation as exhibited by K/Rb ratios ranging from 618 and 25 and Li contents generally being <200 ppm but infrequently as high as 743 ppm in muscovite. Moderately fractionated pegmatites with Be, Nb, Ta, and P enrichment contain muscovite having K/Rb ratios mostly between 45 and 7 plus Li contents between 5 to >1700 ppm. Muscovite from moderately to highly fractionated Li-rich pegmatites exhibit a wide range of K/Rb ratios and Li values: (i) K/Rb = 84 to 1.4 and Li = 35 to >18,100 ppm for spodumene pegmatites, (ii) K/Rb = 139 to 2 and Li = 139 to >18,500 ppm for petalite pegmatites, and (iii) K/Rb = 55 to 1.5 and Li = 743 to >17,800 ppm for lepidolite pegmatites. Pegmatites that host substantial REE- and F-rich minerals may carry muscovite with K/Rb ratios between 691 to 4 that has Li contents between 19 to 15,690 ppm. The K/Rb-Li behavior of muscovite can be useful in assessing the potential for Li mineralization in certain granitic pegmatite types. The proposed limits of K/Rb values and Li concentrations for identifying spodumene- or petalite-bearing pegmatites as part of an exploration program is reliable for Group 1 (LCT) pegmatite populations derived from S-type parental granites or anatectic melting of peraluminous metasedimentary rocks. However, it is not recommended for application to Group 2 (NYF) pegmatites affiliated with anorogenic to post-orogenic granitoids with A-type geochemical signatures or that derived by the anatexis of mafic rocks that generated REE- and F-rich melts. Full article
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

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

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