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Titanium (Ti) typically exhibits low mobility in geologic fluids due to the low aqueous solubility of common (Fe-)Ti oxide minerals. Consequently, Ti isotope variations (δ49/47Ti, given as δ49Ti) in geologic systems are primarily attributed to magmatic differentiation. Thus, the potential for fluid-mineral fractionation has received less attention. However, ligand-rich fluids are capable of mobilizing Ti as observed in natural systems and laboratory studies. As hydrothermal ore mineralization is commonly associated with ligand-rich brines capable of transporting significant quantities of metals, Ti isotopes may aid in understanding mineralization and alteration in complex hydrothermal systems. Here we present data from computational modeling of various Ti coordination complexes theorized to exist in geologic systems and/or under relevant experimental conditions as well as computed fractionation factors for various Ti-bearing crystalline phases to investigate the basic mechanics of equilibrium fluid-mineral Ti isotope fractionation. These results indicate that equilibrium fluid-mineral Ti isotope exchange between our modeled Ti complexes and phases with 6-coordinated Ti is predicted to generally lead to enrichment of heavy Ti isotopes in the fluid. Because minerals with 6-coordinated Ti (such as magnetite and ilmenite) are the most important reservoirs of Ti in the solid Earth, Ti isotope equilibration between terrestrial rocks and fluids can be generalized to enrich the fluid in heavy Ti isotopes. We also performed magnetite-ülvospinel leaching experiments to investigate fluid-mineral Ti isotope fractionation in this phase. Mineral leaching experiments varying acid strength, leaching temperature, and reaction time with HCl and HF qualitatively support the prediction that the fluid phase will become enriched in heavy Ti isotopes during fluid-mineral interactions that approach equilibrium with Ti-rich magnetite. Additionally, the leaching data also suggest that the fluid becomes slightly enriched in lighter Ti isotopes when Ti exchange is limited—potentially due to kinetic effects. Therefore, magnetite from natural systems may be depleted in heavy Ti isotopes during regenerative mineral replacement involving equilibration with fluids or may possibly become depleted in light Ti isotopes under a kinetic fractionation regime—leading to mineral δ49Ti values that are insufficiently explained by magmatic differentiation or inter-mineral fractionation. These results are a first look at fluid-mineral interactions that may affect Ti isotope fractionation in hydrothermal mineral systems, and Ti isotopes should be further studied as a potential method of understanding aqueous metal transport and tracing alteration in mineral deposits.
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Predicting new mineral occurrences and planetary analog environments via mineral association analysis
Abstract The locations of minerals and mineral-forming environments, despite being of great scientific importance and economic interest, are often difficult to predict due to the complex nature of natural systems. In this work, we embrace the complexity and inherent “messiness” of our planet's intertwined geological, chemical, and biological systems by employing machine learning to characterize patterns embedded in the multidimensionality of mineral occurrence and associations. These patterns are a product of, and therefore offer insight into, the Earth's dynamic evolutionary history. Mineral association analysis quantifies high-dimensional multicorrelations in mineral localities across the globe, enabling the identification of previously unknown mineral occurrences, as well as mineral assemblages and their associated paragenetic modes. In this study, we have predicted (i) the previously unknown mineral inventory of the Mars analogue site, Tecopa Basin, (ii) new locations of uranium minerals, particularly those important to understanding the oxidation–hydration history of uraninite, (iii) new deposits of critical minerals, specifically rare earth element (REE)- and Li-bearing phases, and (iv) changes in mineralization and mineral associations through deep time, including a discussion of possible biases in mineralogical data and sampling; furthermore, we have (v) tested and confirmed several of these mineral occurrence predictions in nature, thereby providing ground truth of the predictive method. Mineral association analysis is a predictive method that will enhance our understanding of mineralization and mineralizing environments on Earth, across our solar system, and through deep time.
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- Award ID(s):
- 2126315
- PAR ID:
- 10423646
- Editor(s):
- McSween, Harry
- Date Published:
- Journal Name:
- PNAS Nexus
- Volume:
- 2
- Issue:
- 5
- ISSN:
- 2752-6542
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/pnasnexus/pgad110
