Geochemical Weathering Processes in Mineral Deposits

Geochemical weathering in mineral deposits encompasses the breakdown of primary rock‐forming minerals, the mobilisation and fixation of liberated elements, and the development of secondary mineral assemblages within surficial and near‐surface environments. This transformation begins with the chemical dissolution of silicates, oxides and sulphides under the influence of water, acidity, redox conditions and biological activity. Elements released during dissolution may be transported in solution, adsorbed to mineral surfaces or precipitated as new phases, leading to the enrichment of critical metals such as rare earth elements, aluminium and iron. Profiles of weathering span from slightly altered bedrock through saprolite to soil horizons, each governed by distinct hydrological regimes and reactive fluid compositions. The interplay of climate, fluid flow, organic ligands and mineral structure controls both the rate of weathering and the distribution of residual and secondary phases. Such processes underpin the formation of economic bauxites, ion-adsorption clay deposits and weathering crusts of granitic terrains that supply strategic metals. Understanding these pathways is essential for resource exploration, environmental assessment and sustainable management of critical raw materials.

Research from Nature Portfolio

Recent studies have elucidated the atomic‐scale mechanisms by which rare earth elements (REEs) become weakly held by clay minerals in ion-adsorption profiles. Synchrotron X-ray absorption spectroscopy has demonstrated that heavy and light REEs form easily leachable outer-sphere hydrated complexes dominantly on kaolinite surfaces, confirming the genuine analogue of Malagasy clays to major Chinese deposits.

Investigations into heavy REE enrichment in weathered granites have revealed that highly oxidised, REE-rich fluids metasomatise granitic host rocks. This fluid-driven alteration depletes cerium through Ce4+ mobilisation and preferentially concentrates remaining REEs, especially heavy species, within weathering crusts of southern Chinese granites.

Microscopic and spectrometric analyses of REE-bearing particles in weathered granite have identified kaolinitic aggregates—comprising kaolinite, illite and hematite—as primary hosts for light and heavy REEs. In-situ desorption experiments indicate that inner-sphere complexation on these particles limits extraction efficiency, shedding light on constrained recoveries in ammonium-based leaching processes.

Geochemical Weathering Processes in Mineral Deposits publication trend

The graph below shows the total number of articles in geochemical weathering processes in mineral deposits across all publications each year (not limited to Nature Index journals).

Technical terms

Regolith-hosted deposit: A surficial accumulation of weathered material in which metals are retained by adsorption onto clays and oxides.

Saprolite: Deeply weathered bedrock retaining original fabric but with extensive mineral alteration and porosity.

Outer-sphere complex: A metal ion sorbed to a mineral surface via intervening water molecules without direct coordination to surface functional groups.

Inner-sphere complex: A metal ion directly coordinated to specific surface sites of a mineral, often requiring ligand exchange.

Metasomatism: Chemical alteration of a rock by fluid transport that introduces or removes elements, changing its mineralogy.

Ion-adsorption deposit: A type of clay-rich ore where metal ions are weakly held by exchangeable sites on clay minerals.

References

1. Adsorption of rare earth elements in regolith-hosted clay deposits. Nature Communications (2020).
2. Origin of heavy rare earth mineralization in South China. Nature Communications (2017).
3. Microscopic analyses of weathered granite in ion-adsorption rare earth deposit of Jianxi Province, China. Scientific Reports (2020).
4. Weathering of the primary rock-forming minerals: processes, products and rates. Clay Minerals (2004).
5. Geochemistry and Mineralogy of Rare Earth Elements (REE) in Bauxitic Ores of the Catalan Coastal Range, NE Spain. Minerals (2018).
6. Provenance and ore-forming process of Permian lithium-rich bauxite in central Yunnan, SW China. Ore Geology Reviews (2022).