The Magmatic–Hydrothermal Transition in Lithium Pegmatites: Petrographic and Geochemical Characteristics of Pegmatites from the Kamativi Area, Zimbabwe

Richard A Shaw,Jeremy C Rushton,Brian Ruzvidzo,Ian Mounteney,Paul Nex,Kathryn M Goodenough,Eimear Deady

doi:10.3749/canmin.2100032

Richard A Shaw, Jeremy C Rushton + Show 5 more

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https://doi.org/10.3749/canmin.2100032

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Abstract

ABSTRACTLithium is a critical metal, vital for electrification of transport. Currently, around half the world's lithium is extracted from rare-metal pegmatites and understanding the genesis and evolution of these igneous rocks is therefore essential. This paper focuses on the pegmatites in the Kamativi region of Zimbabwe. A group of early pegmatites is distinguished from a late pegmatite suite which includes the ca. 1030 Ma Main Kamativi Pegmatite. Previously mined for tin, the mine tailings are now being investigated for lithium. Mineral-scale investigation of samples from the Main Kamativi Pegmatite has allowed recognition of a four-stage paragenesis: (1) an early magmatic assemblage dominated by quartz, alkali feldspar, spodumene (LiAlSi2O6) and montebrasite [LiAl(PO4)(OH, F)]; (2) partial alteration by widespread albitization, associated with growth of cassiterite and columbite group minerals; (3) irregular development of a quartz, muscovite, columbite group mineral assemblage; and (4) widespread low-temperature fluid-induced alteration of earlier phases to cookeite, sericite, analcime, and apatite. Whole-rock geochemistry indicates that the late pegmatites are enriched in Li, Cs, Ta, Sn, and Rb but depleted in Nb, Zr, Ba, Sr, and the rare earth elements relative to early pegmatites and country rock granitoids. A combination of field relationships and published dating indicates that the granitoids, and probably the early pegmatites, were emplaced toward the end of the ca. 2000 Ma Magondi Orogeny, whereas the late pegmatites are almost 1000 million years younger. The late pegmatites thus cannot be genetically related to the granitoids and are instead likely to have formed by partial melting of metasedimentary source rocks. The drivers for this melting may be related to crustal thickening along the northern margin of the Kalahari Craton during the assembly of Rodinia.

Highlights

As the world moves toward a low-carbon future, there is increasing demand for a range of raw materials used in electric vehicles and other green energy technologies
The late pegmatite group includes the Main Kamativi Pegmatite, which has been mined for tin and remains prospective for lithium
The temporal disparity between the late pegmatites and the country rock granitoids (Melcher et al 2017, Glynn et al 2020) clearly indicates that these granitoids cannot be parental to the late pegmatites

Summary

Introduction

As the world moves toward a low-carbon future, there is increasing demand for a range of raw materials used in electric vehicles and other green energy technologies. Lithium, used in batteries, is an example of a raw material for which demand is likely to rapidly increase (Pehlken et al 2017). Some economically important lithium pegmatites, for example those in the TinSpodumene Belt, USA (Swanson 2012); the Central Iberian Zone of Spain and Portugal (Roda-Robles et al 2016); Mt. Cattlin, Australia (Sweetapple et al 2019); Jiajika, China (Dai et al 2019); and Goulamina, Mali (Wilde et al 2021), lack the classic concentric internal zonation described by Cameron et al (1949), Norton (1983), and London (2014). There has been an increasing research focus on such pegmatites because of their importance for Li-Cs-Ta-Sn mineralization (Martins et al 2011, 2012, London 2018, Dai et al 2019, Ballouard et al 2020, Barros et al 2020, Simmons et al 2020)

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