Lithium, used as cathode in lithium-ion batteries, is in high demand. Currently, about 40 percent of lithium comes from lake brine and 60 percent from pegmatites and other igneous rocks. Geological and geochemical understanding of lithium enrichment in igneous rocks has drawn much attention. In this edition, we will look at two recent studies from Africa and China.
Rasoul Sorkhabi
Editor, Core Elements
Lithium Pegmatites in Africa
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An article in Economic Geology reviews the geology of lithium pegmatites in Africa.
Lithium minerals: The researchers list 23 lithium-bearing minerals from pegmatites, including spodumene, petalite, and lepidolite present in African rocks.
African cratons: African cratons are Archean to Paleoproterozoic continental cores dominated by tonalite-trondhjemite-granodiorite gneisses with greenstone belts comprising mafic igneous and metasedimentary supracrustal rocks.
Five cratons in Africa with abundant pegmatite rocks are the:
West African craton, which includes the Leo-Mab shield in the south and the Reguibat shield in the north
Saharan metacraton in north Africa
Congo craton in central Africa
Tanzanian craton in southeast Africa
Kalahari craton in south Africa, which includes the Kaapvaal craton in the southeast and the Zimbabwe craton in the northwest. These cratons contain Africa’s oldest rocks (older than 3.5 billion years old).
Pegmatite mines:
The researchers list 12 known pegmatite deposits of commercial interest that were examined from 2018–2024. These deposits contain mainly petalite and spodumene minerals.
Of these, five are in Zimbabwe, two in Namibia, two in the Democratic Republic of Congo, two in Mali, and one in Ghana.
Several other countries, including Rwanda, Niger, and South Africa have great potential for pegmatite mining.
Africa’s best-known pegmatite mine is Bikita in the Masvingo province in Zimbabwe. It was discovered in 1910 and has been commercially mined since the 1940s.
The Bikita deposit formed at 2.6 billion years old and contains 113 million tons with a commercial grade of 1.03 percent of lithium oxide.
The largest lithium deposit studied last year is the Manono-Kitotolo deposit in the Democratic Republic of Congo with tonnage of 842 million tons and a commercial grade of 1.61 percent of lithium oxide.
Pegmatite formation: The researchers suggest four main stages in lithium pegmatite formation. These stages, with decreasing temperatures, are:
Crystallization from magma
Albitization: Alteration by potassium-rich fluids and formation of albite in the rock
Greisenization: Post-magmatic process involving greisen fluids at crustal depths shallower than five kilometers that enriches the rock with high silica leucocratic (whitish) minerals, especially quartz and muscovite
Low-temperature alteration of the igneous intrusion within the host rock
Tectonic events: The researchers suggest five main tectonic events that have produced lithium pegmatites in Africa:
Archean pegmatites, which consist mainly of petalite deposited at relatively shallow crustal depths with high geothermal gradients
Paleoproterozoic pegmatites such as the Birimian spodumene deposits of West Africa
Mesoproterozoic pegmatites, which include very large igneous intrusions such as Manono-Kitotolo pegmatite
Neoproterozoic to Paleozoic, which are typically zoned pegmatites, including various lithium-bearing minerals but less enriched in lithium
The bottom line:
Lithium from pegmatites is currently produced in Australia, China, Canada, Portugal, and Brazil.
Zimbabwe is Africa’s only producer. However, many African countries possess large volumes of lithium pegmatites that deserve further investigations.
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An interesting study by Chinese scientists reported in Nature Communications describes how lithium may be lost from pegmatites to country rocks at low temperatures.
Background:
Pegmatites are very coarse-grained, intrusive igneous rocks containing various commercial minerals and elements.
Their formation starts deep in the crust, undergo various alteration processes and take a final shape at shallow levels.
They often occur as swarms of dikes that arise from the underlying pluton into the surrounding rocks.
Pegmatites are the main hard rocks from which lithium is extracted, but not all pegmatites are enriched in lithium.
Lithium isotopes:
Lithium is the smallest, lightest, and fastest diffusive metallic element.
Lithium has two stable isotopes: The diffusion rate of lithium-6 is about three percent faster than that of lithium-7.
The new study:
Researchers collected samples from three Jiajika pegmatite deposits as well as samples from the surrounding country rocks in the eastern Tibetan plateau.
They analyzed lithium and rubidium concentrations and lithium isotope ratios of samples from both pegmatite bodies and country rocks.
The study also included coupled thermal and chemical diffusion modeling.
Jiajika pegmatite:
Jiajika deposit formed at 220 to 210 Ma based on zircon U-Pb ages.
Jiajika Pegmatite occurs in more than 1000 dikes, of which about 30 pegmatite bodies contain high lithium, and each body has an area of more than 20 square meters.
It is the world’s largest lithium pegmatite deposit with about 1.3 million tons.
What they found:
The study showed that during the final emplacement of pegmatite, higher temperatures in the host country rock will cause lithium loss and transfer to the country rock.
Low-temperature country rock provides a better environment for lithium enrichment in pegmatite rocks.
These findings are consistent with the observations that those Jiajika pegmatites emplaced far from the main plutonic body contain more lithium concentrations.
Why it matters: Many studies of how lithium-rich pegmatite form have focused on crystallization processes of lithium-rich melts. This study shows that the original lithium-rich melt may lose lithium at low temperatures to the country rock, and that the temperature of host country rock at shallow depths has an important impact on lithium pegmatites.
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