Critical mineral deposits commonly form in magmatic-hydrothermal systems including carbonatites and/or alkaline syenites, and more evolved peralkaline granites where the rare earth element (REE) undergo a complex array of partitioning, transport and mineralization. Significant alteration and veining zones develop in these deposits and can be used to vector ore zones in the field [1]. The REE ore minerals typically reflect the characteristics of these systems, which are enriched in carbonate, fluoride, and phosphate or a combination thereof. The REE can also be incorporated into vein minerals such as calcite, fluorite and apatite where the REE3+ exchange for Ca2+ on the crystal lattice [2]. These minerals give us clues about the hydrothermal reaction paths of REE in critical mineral deposits. This study aims to: 1) present our recent findings from hydrothermal fluid-mineral REE partitioning experiments, 2) discuss thermodynamic models to simulate REE in critical mineral deposits, and 3) link the thermodynamic simulations to field observations.
Hydrothermal fluid-calcite partitioning experiments were conducted between 100 and 200 °C by hydrothermal fluid mixing and precipitation [2] at near neutral to mildly alkaline pH (6 – 9). The REE concentrations in synthetic calcite crystals and aqueous fluids sampled in situ were used to fit the data to the lattice strain model [3] and using the Dual Thermodynamic approach [4]. A second type of experiment consisted of reacting natural fluorite and apatite crystals with acidic to mildly acidic (pH of 2 – 4) aqueous fluids in batch-type reactors to study the behavior of REE and mineral dissolution-precipitation reactions near crystal surfaces. The GEMS code package [5] was used to implement these new data into a thermodynamic model and simulate possible REE reaction paths in hydrothermal fluids. Two REE mineral deposits in New Mexico (Lemitar and Gallinas Mountains) present ideal case studies to illustrate how these models can be linked to field observations from natural systems.
[1] Gysi et al. (2016), Econ. Geol. 111, 1241-1276; [2] Perry and Gysi (2020), Geochim. Cosmochim. Acta 286, 177-197; [3] Blundy and Wood (1994) Nature 372, 452-454; [4] Kulik (2006), Chem. Geol. 225, 189-212; [5] Kulik et al. (2013), Computat. Geosci. 17, 1-24.
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Simulation of REE mobility and evolution of F-NaCl-CO2-bearing fluids in hydrothermal calcite and fluorite ore-forming veins
Rare earth element (REE) deposits are commonly associated with carbonatites and (per)alkaline rocks where hydrothermal magmatic fluids can play a significant role in REE mobilization and deposition [1]. Thermodynamic modeling permits predicting the evolution of ore-forming fluids and can be used to test different controls on hydrothermal REE mobility including temperature, pressure, the solubility of REE minerals, aqueous REE speciation and pH evolution associated with fluid-rock interaction. Previous modeling studies either focused on REE fluoride/chloride complexation in acidic aqueous fluids [2] or near neutral/alkaline fluids associated with calcite vein formation [3]. Such models were also applied to interpret field observations in REE deposits Bayan Obo in China and Bear Lodge in Wyoming [3,4]. Recent hydrothermal calcite-fluid REE partitioning experiments provide new data to simulate the solubility of REE in calcite, REE carbonates/fluorocarbonates at high temperatures [5, 6].
We studied the competing effects controlling the mobility of REE in hydrothermal fluids between 100 and 400 °C at 500 bar. Speciation calculations were carried out in the Ca-F-CO2-Na-Cl-H2O system using the GEMS code package [7]. The properties of minerals and aqueous species were taken from the MINES thermodynamic database [3,5]. The Gallinas Mountains hydrothermal REE deposit in New Mexico was used as a field analogue to compare our models with the formation of calcite-fluorite veins hosting bastnäsite. Previous fluid inclusion studies hypothesized that the REE were transported as fluoride complexes [8] but more recent modeling studies have shown that fluoride essentially acts as a depositing ligand [2]. Here we show more detailed simulations predicting the stability of fluorite, calcite and REE minerals relevant to ore-forming processes in carbonatites and alkaline systems.
[1] Gysi et al. (2016), Econ. Geol. 111, 1241-1276; [2] Migdisov and Williams-Jones (2014), Mineral. Deposita 49, 987-997. [3] Perry and Gysi (2018), Geofluids; [4] Liu et al. (2020), Minerals 10, 495; [5] Perry and Gysi (2020), Geochim. Cosmochim. Acta 286, 177-197; [6] Gysi and Williams-Jones (2015) Chem. Geol. 392, 87-101;[7] Kulik et al. (2013), Computat. Geosci. 17, 1-24; [8] Williams-Jones et al. (2000), Econ. Geol. 95, 327-341
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- Award ID(s):
- 2039674
- PAR ID:
- 10321001
- Date Published:
- Journal Name:
- Goldschmidt
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Critical mineral deposits form through an interplay of magmatic-hydrothermal processes in carbonatites and (per)alkaline systems during their emplacement in the Earth’s crust. Hydrothermal aqueous fluids can lead to the mobilization, transport, and deposition of the rare earth elements (REE) coupled to development of alteration zones at the deposit scale [1]. However, unraveling the underlying processes that affect the solubility of REE in these geologic fluids is a challenge in high temperature and pressure fluids [2]. A holistic approach is key to understand the controls of fluid-rock interaction in mobilizing REE in critical mineral deposits. Through a joint effort, we formed a new U.S. geoscience critical minerals experimental–thermodynamic research hub between New Mexico Tech, Los Alamos National Laboratory and Indiana University. The goal of this project is to conduct frontiers research on the behavior of critical elements in supercritical aqueous fluids by integration of a wide array of high temperature solubility experiments complemented by spectroscopic measurements and molecular dynamic simulations. Here we present current advances to simulate a significant vein paragenesis of barite + fluorite +calcite +bastnäsite-(Ce) observed in many critical mineral deposits. A case study will be presented from the Gallinas Mountains REE-fluorite hydrothermal breccia deposit in New Mexico. Using the GEMS code package [3] and the MINES thermodynamic database (https://geoinfo.nmt.edu/mines-tdb), we highlight our current capabilities and limitations to simulate the behavior of REE in these hydrothermal fluids and minerals. A thermodynamic model is presented to simulate the partitioning of REE between calcite- and fluorite-fluid based on recent and ongoing experimental and thermodynamic work on the synthesis of REE doped minerals [4] and REE speciation in acidic and alkaline fluids. We further show how to integrate multiple experimental datasets and develop new thermodynamic models based on the new research efforts from the research hub and future directions to improve our prediction capabilities of REE complexation in supercritical fluids. [1] Gysi et al. (2016), Econ. Geol. 111, 1241-1276; [2] Migdisov et al. (2016), Chemical Geology 439, 13-42. [3] Kulik et al. (2013), Comput Geosci 17, 1–24. [4] Perry and Gysi (2020), Geochim. Cosmochim. Acta 286, 177-197.more » « less
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.7185/gold2021.6309
