BUILDING A FRAMEWORK FOR INTERPRETING THE MO ISOTOPIC COMPOSITION OF ORE

Molybdenum (Mo) is an element that we come across daily in our lives, which plays an integral role in industrialized society. It is primarily used as an alloying agent in steel, enhancing its strength and increasing its resistance to heat and corrosion. In nature, Mo is a redox-sensitive element with seven stable isotopes that can be leveraged to better understand Mo’s behavior in Earth’s crust. Primarily, Mo is used as a redox tracer for low-temperature (T) geologic systems, including paleo-oceanic environments. However, there are still many uncertainties regarding the geochemical behavior of Mo at higher temperatures in the crust and, specifically, within Mo-bearing ore deposits. Outstanding questions include: What is the source of Mo in magmatic-hydrothermal ore deposits? And how is Mo transported in high-T geologic fluids? Previous studies on Mo solubility and isotope fractionation at high-T show that Mo isotopes fractionate due to a number of processes and that Mo solubility increases with increasing T, salinity, oxygen fugacity, and decreasing sulfur fugacity. This work aims to analyze and compare the Mo and sulfur (S) isotope compositions of molybdenite (MoS₂) from a suite of high-T ore deposits to investigate the effect of a variety of ore forming processes on molybdenite geochemistry. Pairing a relatively new technique applied to ore deposits (Mo isotope geochemistry) with an isotope system that is well-studied in ore-forming environments (S isotopes) can help us better understand how Mo moves through and becomes concentrated within the crust. Because both Mo and S are redox sensitive, these results have the potential to reveal the redox evolution and conditions within different ore deposits. These new data will determine if Mo isotopes and/or Mo-S isotope pairs are a useful geochemical tool for understanding geological origin of an ore sample and the processes that formed it. When considering Mo as an important resource, molybdenite geochemistry may hold the key to understanding the redox evolution of geologic fluids and finding more resources.