Abstract Our understanding of the formation of mineral deposits and fluid circulation has increased greatly over the last few decades, through the use of increasingly sophisticated hydrogeochemical and hydrothermal fluid circulation models. However, for these models to be valid, accurate knowledge of the age of a deposit, the lifetime of the hydrothermal system(s) and an understanding of the tectonic, emplacement and/or cooling history of possible sources of heat, metals, and fluids is necessary. Some of these most basic questions concerning ore deposits remain poorly constrained despite long and intense scrutiny. The inability to tie down the timing of ore deposition and multiple episodes of hydrothermal circulation has led to a number of conflicting theories for fluid movement, fluid origin, and metal sources (e.g., Slack, 1976; Skinner, 1979; Sangster, 1986). In part, some of the conflicting theories are due to the lack of a regional framework that establishes the timing and duration of the circulation of mineralizing fluids, and to the lack of dating techniques to apply to well-documented paragenesis within an ore deposit or district. Recent advances in analytical methods and new geochronometers now allow, not only accurate dating of a mineral deposit, but in some cases potential resolution in time between different paragenetic sequences of mineralization within a single deposit (Snee et al., 1988; Chesley et al., 1993; Brannon et al., 1996b). This chapter is an attempt to demonstrate that through the application of multiple geochronologic techniques, the temporal relationship between igneous intrusions and associated hydrothermal mineralization or timing of largescale crustal fluid flow can be refined. This chapter is divided into two parts. The first part is a discussion of different geochronologic methods.

Abstract Four molybdenite samples from veins in the Bingham Canyon porphyry copper deposit yield a weighted average Re-Os age of 37.0 ± 0.27 Ma. The molybdenite ages all overlap at the 2σ level. Previous investigations have suggested that mineralization at Bingham Canyon is coincident with and genetically related to the emplacement of the Bingham stock within the Bingham intrusive complex. However, the molybdenite ages are younger than all reported ages for magmatism in the Bingham porphyry deposit (~39.8 to 37.6 Ma). This suggests either that all the reported ages of the Bingham intrusions are disturbed and the actual ages of the intrusive rocks are younger or that molybdenite mineralization is not directly related to emplacement and cooling of any dated intrusion exposed at Bingham. The latter scenario would suggest the Bingham stock is just the focal point for the superposition of exsolved fluids from deeper in the system.