Trace element catalyses mineral replacement reactions and facilitates ore formation

Abstract

Reaction-induced porosity is a key factor enabling protracted fluid-rock interactions in the Earth’s crust, promoting large-scale mineralogical changes during diagenesis, metamorphism, and ore formation. Here, we show experimentally that the presence of trace amounts of dissolved cerium increases the porosity of hematite (Fe2O3) formed via fluid-induced, redox-independent replacement of magnetite (Fe3O4), thereby increasing the efficiency of coupled magnetite replacement, fluid flow, and element mass transfer. Cerium acts as a catalyst affecting the nucleation and growth of hematite by modifying the Fe2+(aq)/Fe3+(aq) ratio at the reaction interface. Our results demonstrate that trace elements can enhance fluid-mediated mineral replacement reactions, ultimately controlling the kinetics, texture, and composition of fluid-mineral systems. Applied to some of the world’s most valuable orebodies, these results provide new insights into how early formation of extensive magnetite alteration may have preconditioned these ore systems for later enhanced metal accumulation, contributing to their sizes and metal endowment.

Rapid Marcasite to Pyrite Transformation in Acidic Low-Temperature Hydrothermal Fluids and Saturation Index Control on FeS2 Precipitation Dynamics and Phase Selection

“…While the catalytic role of hydrothermal fluids in the marcasite to pyrite transformation requires further detailed studies, it is likely that the rapid transformation is due to CDR mineral replacement reactions rather than solid-state transformation. This is because at low temperatures, CDR is much faster than solid-state reactions, as has been demonstrated in numerous hydrothermal mineral phase transformations in sulfides, ,− tellurides, , phosphates, , carbonates, − oxides, , and silicates. , …”

Stratiform Host-Rock Replacement via Self-Sustaining Reactions in a Clastic-Dominated (CD-type) Zn Deposit

“…2C, 6A), is consistent with the preservation of external shape and dimensions during pseudomorphic replacement (Putnis, 2009). At temperatures below 300°C (the upper temperature limit for CD-type deposits, e.g., Wilkinson, 2013), mineral replacement occurs via coupled dissolution-reprecipitation reactions (CDR), which can result in positive feedbacks that are integral for ore formation (e.g., Xing et al, 2021). In the following discussion, we evaluate the reactions involved in hydrothermal fluid flow through the host rock and use mineralogical constraints to determine the local evolution of pH and fO 2 during fluid-rock interaction.…”

The role of nanocerianite (CeO2) in the stability of Ce carbonates at low-hydrothermal conditions

“…, monazite). 31–36 It is identified as a late-stage secondary mineral. 2,31,37,38 For example, A. Mahmoud and Williams-Jones 31 suggested that cerianite is the product of the weathering of minerals containing light REEs such as monazite and bastnasite in their studied granitic batches from Egypt.…”