40Ar/39Ar, K/Ar, and fission track geochronology of sediment-hosted dessiminated gold deposits at Post-Betza, Carlin Trend, Northeastern Nevada - a discussion

Arehart et al. (1993) set out to date hydrothermal Au mineralization at the Post-Betze deposit in an attempt to place the formation of this deposit into a metallogenetic setting. Toward this end they have used many modern dating techniques including 40Ar/39Ar, K/Ar, and fission track geochronology. Based on the 39 measurements presented, they conclude that "based upon what we consider to be the most reliable" data this deposit formed at 117 Ma. This date is said to be consistent with similar ages for other intrusions in northeastern Nevada, and although one is not seen at the deposit, it is implied that a major nearby pluton is responsible for the formation of Post-Betze. By extrapolation, it is then suggested that Carlin-type Au systems are all of similar age, and thus, are the result of compressional tectonics operating prior to development of the current extensional environment. Because of the inescapable importance of the inferences and conclusions generated by the assignment of a 117 Ma age to the formation of the Post-Betze deposit, I would like to discuss the data and conclusions presented by Arehart et al. (1993).