REVISED 40AR/39AR AGES OF THE WHITE CLOUD MOLYBDENUM DEPOSIT, CUSTER COUNTY, IDAHO
Three replicate analyses on sericite from Mo-bearing quartz veins, hosted in the Little Boulder Creek satellite pluton, yield indistinguishable plateau ages within the limits of precision and provide a mean age of 84.65 Ma. We also report a plateau age of 84.80 ± 0.30 Ma on sericite from a similarly mineralized quartz vein in hornfelsed Paleozoic sediments adjacent to the Little Boulder Creek stock. These ages clearly date the Mo-mineralization event at 84 m.y., which is at odds with prior conventional K-Ar estimates of 61.5 m.y. (Armstrong et al., 1978). This new data suggest that the Little Boulder Creek stock and the associated White Cloud Mo deposit are older and perhaps more closely related to the proximal ~83 Ma White Cloud quartz monzonite of the Idaho batholith than previously thought.