by Kathryn M. Goodenough, Michael A. W. Marks, Sam Broom-Fendley, John R. Spear

Alkaline-carbonatite igneous complexes host the world’s largest and highest grade rare earth element (REE) deposits and are critical for the global transition from fossil fuels towards a low-carbon society. Many aspects of these igneous complexes remain poorly understood, particularly relating to variation in composition and structure with depth. A significant question for this project is the spatial and temporal variability in fluids associated with alkaline-carbonatite complexes, and their influence on microbial deep life and on groundwater systems. We propose to undertake deep drilling of a carefully selected and well-characterised REE-rich complex in Malawi (Songwe Hill) to investigate, how fluid-rock interactions have evolved over time to control mineralisation geometry, groundwater hydrogeochemistry, and deep subsurface life. The new scientific drilling will be integrated with existing shallow cores and geophysical data provided by our industry partner, Mkango Resources. With this proposal, we aim to bring together an interdisciplinary team in an ICDP workshop to prepare a drilling proposal. This will be a unique research project, bringing together economic geologists and geochemists, hydrogeochemists and microbiologists to build up a holistic model of the subsurface environmental system in and around an alkali-carbonatite complex. This type of understanding is vital if such deposits are to be mined whilst ensuring minimal environmental impact. We plan to hold the 3-day workshop in Malawi (Blantyre) in May 2023. We anticipate around 35 attendees, largely from Europe, North America and East Africa, and we aim to reserve 5 spaces for an open call, which will prioritise Early Career and African researchers. The workshop will focus on refining the science questions; considering if any additional work is needed for site characterisation; developing the technical aspects; developing the details of the science plan; planning environmental impact assessments; and discussing plans for communication and outreach. The proposed project will work with the Malawi government, universities, and local school communities. Our PI/co-I team includes experts covering all science questions, and is drawn from 6 nations, of which 4 are current ICDP members.

• This project will aim to study three key science questions:
• (1) The relationship between carbonatites and associated alkaline rocks and how these evolve through magmatic-hydrothermal processes to form economic REE enrichment; in particular, how mineralising fluids vary with depth and over time, and how they are controlled by local structures and magmatic conduits.
• (2) The hydrogeological depth profile of these structural features associated with alkaline-carbonatite systems, and in particular the effect of this unique geology on groundwater hydrogeochemistry in near-surface groundwater, especially fluoride.
• (3) The nature of deep subsurface life in these unusual rock-types, and the relationship of the microbial community to both REE mineralisation and groundwater biogeochemistry.

Alkaline Rocks, Carbonatite, Deep Life, Groundwater, REE mineralization

Latitude: -15.70155, Longitude: 35.8215