The formation of lithium-rich melts during early crustal evolution - a case study from the Acrhean Zimbabwe Craton

Thesis

The exponential increase in demand for electric vehicles as part of the renewable energy transition is driving a surge in production of the critical metal lithium. Several forecasts have predicted a deficit in supply owing to declining rates of new economic discoveries at a time where over 50 new mines are needed to come online by 2030 to meet demand. The primary source of lithium is hard rock (pegmatite) deposits, which account for 70% of current reserves. Given their critical importance in securing sufficient lithium supply, a better understanding of how these deposits form is of vital importance to aid new discoveries. This thesis aims to contribute towards a mineral system model for lithium-rich pegmatites, by integrating new petrological modelling to detailed field-based, geochemical, and geochronological studies of the Zimbabwe craton – a relatively understudied Archean craton which supplied 9% of global lithium production in 2024. In this thesis, I propose that the Zimbabwe craton grew through episodic felsic magmatism between 3.8 and 2.5 Ga, and that major siliciclastic supracrustal successions formed through erosion as a result of continental emergence which was driven by a major orogenic episode c. 2.68 Ga. Through petrologic modelling, I show that whilst conventional pegmatite formation models are feasible, they do not sufficiently account for the necessary enrichment required to generate economic hard rock lithium deposits. Importantly, the absence of potential metasedimentary sources in source regions for lithium-rich pegmatites in Zimbabwe suggests an alternative process may have occurred. I show that the formation of intermediate, K-rich, granitoids through melt-driven crustal recycling can sufficiently enrich the source region to form the geochemical signatures found in lithium-rich pegmatites. Finally, transcurrent shear zones are proposed as fundamental components of the lithium mineral system, and future exploration should focus on delineating these structures to identify new targets.

Authors: Koopmans, L

• DOI: 10.5287/ora-qzoqkrb4y
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: pegmatite; lithium; economic geology; petrology; Zimbabwe
• Subjects: Geology, Economic; Geology