Fathoming SEquestration and Enrichment of metals in DEEP marine deposits with novel micro-X-ray emission spectroscopy

Introduction

Rare earth elements (REE) and transition and post-transition metals (TM) are essential to modern life, yet we know little about how they concentrate at Earth's surface, especially on the seafloor, which holds vast reserves. The DEEP-SEE project will shift paradigms on marine metal deposits from chemical composition and resource inventories to a holistic view based on atomic-scale observations and modeling.

Objectives

This research will determine geochemical processes that give rise to some of the highest metal partitionings in supergene ores. The main objectives include:

1. Crystal Chemistry of REE:

   • Investigating the crystal chemistry of 3+ REE in biogenic vs. authigenic sedimentary apatite as a new proxy for the paleoceanographic enrichment setting, with the potential to become an indicator for future exploration sites.

2. Scavenging History of Fe-Mn Crusts:

   • Elucidating the scavenging history of Fe-Mn crusts and the corresponding evolution of seawater REE as recorded in growth layers over millions of years.

3. Redox Chemistry and Mineralogy:

   • Investigating the redox chemistry and mineralogy of Fe-Mn crusts and nodules to explain how the redox-sensitive metals Co, Ce, Tl, and Pt are enriched from 10^9 to 10^6 times relative to seawater.

Challenges

To date, these processes have been impossible to interrogate because of analytical challenges posed by the multi-elemental composition and mineralogical heterogeneity of seafloor deposits.

Methodology

A promising approach for tackling these challenges is new micro-X-ray emission spectroscopy using a unique high-luminosity compact XES spectrometer at the European Synchrotron Radiation Facility.

• The installation of the spectrometer on a microfocus beamline under construction on the new 4th generation ESRF X-ray source will provide a momentous gain of at least 100 in detection limit and unprecedented sensitivity and precision in the analysis of REE and TM.

Broader Impact

More broadly, the research will show how new knowledge about Earth processes can be obtained with a fresh look at individual trace elements previously inaccessible by crystal chemical study.