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Societal demand for critical metals used in the high-tech and green industries has led to an increased interest in REEs associated with ore deposits. Hydrothermal mineralization of monazite (CePO4) in various REE deposits can display significant variations in REE mineralogy and rock chemistry. Monazite displays textural and REE compositional variations, such as those observed in the giant Bayan Obo REE deposit in China and in the Pea Ridge iron-oxide-apatite (IOA) deposit in Missouri. The coupling of compositional variations of monazite with thermodynamic modeling of fluid-rock interaction processes may provide a useful vectoring tool in these ore deposits. However, interpreting these geochemical fingerprints requires building an internally consistent thermodynamic dataset for REE minerals and their relevant aqueous complexes. In this study, a series of hydrothermal solubility experiments were carried out using synthetic monazite crystals (i.e., LaPO4, PrPO4, NdPO4, and EuPO4) to assess the consistency of reported mineral calorimetric data and the thermodynamic data of the aqueous REE complexes. The solubility experiments were conducted in aqueous HClO4-H3PO4–bearing solutions at temperatures between 100° and 250°C and at saturated water vapor pressure. Equilibrium constants (Ks0) for the dissolution reaction of monazite end members were retrieved as a function of temperature and extrapolated to standard conditions of 25°C and 1 bar. Results indicate significant differences between the new solubility data and those reported in the literature. We demonstrate the impact of these new thermodynamic data in a series of fluid-rock interaction models using the GEMS code package (http://gems.web.psi.ch) and the MINES thermodynamic database (http://tdb.mines.edu). The simulated monazite stability can be correlated to field observations and allows for the prediction of the behavior of REE in hydrothermal fluids and their association to alteration observed in ore deposits.
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Numerical Modeling of Hydrothermal Ore-Forming Processes and the Link to Lithogeochemical Vectors for Exploration
Hydrothermal ore deposits involve complex fluid-rock interactions, where alteration zones yield information on physicochemical conditions of ore-forming processes and fluid pathways. Lithogeochemical vectors can be used to delineate alteration zones and potentially yield information for targeting ore zones for the exploration of mineral deposits. To be able to recognize these geochemical and mineralogical signatures, it is imperative to understand the underlying ore-forming processes and link them to geochemical vectors. Numerical modeling permits tracking changes in rock chemistry and metal precipitation mechanisms by simulating various alteration and fluid evolution scenarios such as boiling, fluid mixing, fluid-rock interaction, and changes in redox, pH, and temperature. The open-access MINES thermodynamic database (http://tdb.mines.edu) has been recently launched for modeling fluid-rock interaction and the chemical changes related to ore-forming processes, using the program GEM-Selektor (http://gems.web.psi.ch). The philosophy behind the MINES database is to focus on testing a series of numerical modeling projects used to simulate various ore deposits. We present a number of case studies where GEM-Selektor has been successfully applied to simulate ore-forming processes. These include Cu transport and mineralization at the Kansanshi Cu-Au deposit hosted in metasedimentary rocks, and the metasomatism of pegmatites and mobilization of rare earth elements (REEs) in the Strange Lake REE-Zr-Nb mineral deposit. We also use this method to demonstrate the coupling of complex chemical equilibria with reactive mass transport along a fluid flow path for simulating the deposition of Pb and Zn in a Mississippi Valley-type (MVT) deposit and the alteration associated with volcanogenic massive sulfide (VMS) deposits. The long-term goal of this project is the generation of a geochemical vectors database for interpreting field data, using knowledge gained from numerical simulations combined with field observations. This link between fundamental and applied research is expected to significantly advance ore vectoring for the exploration industry.
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- PAR ID:
- 10076701
- Date Published:
- Journal Name:
- SEG Meeting
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The rare earth elements (REE) are essential for the high-tech and green technology industries, and used, for example, in computers, smartphones, and wind turbines. The REE are considered critical minerals and can be highly enriched in certain magmatic-hydrothermal systems including alkaline complexes and carbonatites. Almost all of the critical mineral deposits show a complex overprint by hydrothermal processes during their genesis. However, our understanding of the mobility in these ore- forming systems and our knowledge about the stability of REE minerals is still very limited. The MINES thermodynamic database is an open-access database and continuously updated with the most up to date thermodynamic data for REE aqueous species and minerals. This database also includes rock-forming minerals and permits simulating the mineralogy and alteration geochemistry that relates to the formation of these critical mineral deposits. This study gives a short overview of the MINES thermodynamic database and the GEMS code package for simulating the formation of hydrothermal calcite, fluorite and bastnäsite-(Ce) veins relevant to interpreting critical mineral deposits.more » « less
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The growing applications of the rare earth elements (REE) to the high-tech and green technology industry has led to an increased interest in the thermodynamic behavior of REE minerals and their aqueous complexes within the geochemical community. The REE minerology and rock chemistry of REE deposits can display significant variations during hydrothermal overprint 1,2 . Monazite (CePO 4 ) is a common mineral in these deposits and, in several cases, can be attributed to hydrothermal mineralization processes. The giant REE deposit in the Bayan Obo carbonatite 3 and the IOA deposit in Pea Ridge 4,5 contain monazite displaying significant compositional and textural variations that may provide useful vectors of fluid-rock interaction and ore deposition processes. To quantify the meaning of these variations using thermodynamic modelling will require a robust thermodynamic dataset for REE minerals and their aqueous complexes 6 . In this study, a series of hydrothermal batch solubility experiments have been conducted using LaPO 4 , PrPO 4 , NdPO 4 and EuPO 4 to assess the compatibility of available calorimetric data of these minerals and the thermodynamic data of the aqueous REE species. Additional calorimetric and XRD measurements were carried out to determine the thermodynamic properties of a series of monazite solid solutions. Solubility experiments were carried out in aqueous HClO 4 -H 3 PO 4 -bearing solutions at temperatures between 100 and 250 °C at saturated water vapor pressure. The equilibrium constants (K s0 ) determined for each endmember was then evaluated as a function of temperature and extrapolated to standard conditions of 25 °C and 1 bar. The results indicate significant differences in retrieved solubilities in comparison to the available literature data. We will demonstrate the impact of this new thermodynamic data by analyzing the results of several batch system equilibrium simulations using the GEMS code package (http://gems.web.psi.ch) and the MINES thermodynamic database (http://tdb.mines.edu). Our current and future thermodynamic data will be implemented in this thermodynamic framework and allow for the more accurate prediction of the hydrothermal behavior of REE in mineral deposits.more » « less
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(Per)alkaline complexes and carbonatites evolve through a complex sequence of magmatic-hydrothermal processes. Most of them are overprinted by late auto-metasomatic processes which involves the mobilization, fractionation and/or enrichment of critical elements, such as the rare earth elements (REE) [1]. However, our current ability to predict the behavior of REE in high temperature aqueous fluids and interpret these natural systems using geochemical modeling depends on the availability of thermodynamic data for the REE minerals and aqueous species. Previous experimental work on REE solubility has focused on acidic aqueous fluids up to ~300 °C and considered chloride, fluoride and sulfate as important ligands for their transport [2]. However, magmatic-hydrothermal systems that form these critical mineral deposits may cover a wider range of fluid chemistries spanning acidic to alkaline pH as well as temperatures and pressures at which the fluids are supercritical. A few recently published studies have shown that other ligands (e.g., REE carbonates and/or combined fluoride species) could become important in near-neutral to alkaline fluids [3,4], and that REE mobility can also be increased in saline alkaline fluids reacted with fluorite [5]. Here we present new hydrothermal REE hydroxyl/chloride speciation data and REE phosphate/hydroxide minerals [6,7], calcite and fluorite solubility experiments as a function of pH, salinity and temperature. We use an integrated approach to link a wide array of experimental techniques (solubility, calorimetry, and spectroscopy) with thermodynamic optimizations using GEMSFITS [8], and present the development of a new experimental database for REE and its integration into the MINES thermodynamic database (https://geoinfo.nmt.edu/mines-tdb). The latter permits simulating hydrothermal fluid-rock interaction and ore-forming processes in critical mineral deposits to better understand the behavior of REE during metasomatism.more » « less
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