Date of Award


Degree Name

Master of Science




Gail L. Arnold

Second Advisor

Benjamin . Brunner


More than 95% of the world's molybdenum (Mo) is mined from porphyry deposits (Sinclair, 2007). Molybdenum is an important component for the metal industry, as a key ingredient in stainless steel alloys and high-speed heat resistant tools. Despite the importance of porphyry deposits for the supply of this industrially important metal, major questions about Mo mineral precipitation remain unresolved and the process of ore body emplacement and formation remains poorly investigated (Cooke et al., 2014a).

Recent observations have revealed a wide range of Mo isotope compositions in porphyry deposits, both globally and locally (Greber et al., 2014a; Shafiei et al., 2014; Li et al., 2019), demonstrating that Mo isotope signatures may represent an excellent record of processes during formation of molybdenite (MoS2) ores. It has been hypothesized that Rayleigh isotope fractionation accounts for the large variation in MoS2 ore isotope compositions (Hannah et al., 2007). Also agreed upon is that sulfide (H2S, HS-, S2-) is key in the formation of MoS2 deposits and that sulfide availability is a driver for ore mineral precipitation. A Rayleigh isotope fractionation process not only places a major control on the Mo isotope variability, it should also exert a similar control on sulfur (S) isotopes. To date, it has not been tested if there is a systematic relationship between Mo and S isotope compositions, despite the fact that the combined Mo and S isotope compositions of MoS2 offers a window into the reconstructing ore formation processes.

I present Mo and S isotope data obtained from drill-core samples from the Santa Rita / Chino Mine. The coupled Mo-S isotope systematics of MoS2 mineralization in this deposit demonstrate that Rayleigh isotope fractionation processes may not always be the sole "answer", and that different mineralization events and processes can be identified and characterized through a combination of petrography, chemical inventory and coupled isotope studies.




Received from ProQuest

File Size

120 pages

File Format


Rights Holder

Joshua Roger Peterson

Included in

Geochemistry Commons