Dr. Alexander Gysi

Ore Deposits and Critical Minerals (ODCM) research group and experimental laboratory

The Ore Deposits and Critical Minerals experimental laboratory (ODCM Lab) and research group was established at the bureau in Fall 2020. We use a holistic approach to study critical mineral deposits including field observations, numerical modeling and laboratory experiments. The ODCM Lab is currently supported by NSF and DOE grants and equipped to conduct hydrothermal fluid-rock experiments to study the stability of minerals and speciation of metals relevant to ore-forming processes at high temperatures. The current focus of our research is on the properties of rare earth elements (REE) in hydrothermal aqueous fluids with MS/PhD students and Postdocs conducting research and we also include undergraduate student research over Summer/Fall semesters. Here is a list of current funded projects conducted in the ODCM research group:

• An internally consistent thermodynamic database for the rare earth elements (REE) at hydrothermal conditions
• Partitioning of Rare Earth Elements (REE) between minerals and aqueous fluids in ore deposits
• The thermodynamic properties of rare earth element (REE) minerals: a solid solution model for xenotime-(Y) and monazite-(Ce)
• Molecular complexation of Rare Earth Elements (REE) in high temperature and pressure supercritical geologic fluids
• The geochemistry and mineral paragenesis of REE-fluorite bearing veins in the Gallinas Mountains hydrothermal breccia deposit, NM.

Thermodynamic modeling and database development

Thermodynamic modeling permits simulating the behavior of fluids in the crust and test hypotheses to understand field observations and the geochemistry of ore deposits. The MINES Thermodynamic Database is an initiative to provide for free a thermodynamic database for the geochemistry community to model fluid-rock interaction and ore-forming processes. All the data and models generated by our ODCM Lab are provided in this database, and we are one of the few experimental laboratory worldwide that study the critical metals in minerals and aqueous fluids. Currently we contribute with tutorials and the MINES thermodynamic database to the GEMS code package, which is a geochemical modeling program developed by our collaborators at the Paul Scherrer Institute in Switzerland. We are also working on a new experimental database and are planning on contributing code to link thermodynamic and experimental databases in the near future. Stay tuned!

We also work on many collaborative projects to try solving many different geochemical and mineralogical problems related to hydrothermal fluid-rock interaction and ore-forming processes. We organize annually online and on-site workshops and also provide modeling tutorials that can be found on the MINES thermodynamic database webpage.

Hydrothermal fluid-rock interaction experiments in the ODCM lab

The Ore Deposits and Critical Minerals experimental lab is equipped with an unique array of experimental equipment to study the properties of REE in minerals and aqueous fluids (ODCM Lab). Hydrothermal experiments provide us with a window into the Earth's crust and essentially the link to understand ore-forming processes and field observation in geologic systems.

We currently synthesize/equilibrate calcite, fluorite and apatite with REE-doped solutions to study the partitioning of these elements between fluid-minerals in high pressure-temperature reactors. We also measure the thermodynamic properties of REE aqueous species by combining calorimetric (heat) measurements and in situ UV-vis spectroscopy to determine equilibrium constants, mineral solubility, and the nature of aqueous complexes in high temperature fluids between 100 - 350 ºC at saturated water vapor pressure. We also develop new types of experiments to measure in situ pH at high temperature, and are currently building a new Raman facility combined with a hydrothermal diamond anvil cell that permits studying supercritical fluids in the 400 - 600 ºC temperature range at pressures of 0.5 to 5 kbar.

The data generated from the experiments are implemented in the MINES thermodynamic database and used to develop new models to predict REE transport, fractionation and deposition in critical mineral deposits. We also value education and learning and have researchers form different career stages working in the lab including undergraduate students, MS and PhD students, as well as Postdoctoral Fellows.

Field projects critical mineral deposits

All the experimental and modeling work we do is inspired from natural geologic systems. Field projects are also an excellent experience for students to gain knowledge in mapping, sampling, and geochemical/mineralogical data interpretation. The current focus of our research is on the formation of calcite, fluorite and apatite bearing veins in alkaline and carbonatite mineral deposits.

Gallinas Mountains in New Mexico is a hydrothermal-magmatic REE-fluorite vein/breccia deposit and an ideal laboratory to study the controls of hydrothermal processes on REE mobility and enrichment in this type of system. This field work is also done in collaboration with our colleague Dr. Virginia McLemore at the bureau. We are currently determining the mineral paragenesis of the different vein types, studying microtextural relationships, and the geochemistry of barite, fluorite, calcite and basntäsite-(Ce). We are also working on fluid inclusions in collaboration with Dr. Nicole Hurtig in the EES department in the new fluid inclusion laboratory.