CONSTRAINING THE TIMING OF HYDROTHERMAL FLUID FLOW AT THE MARIGOLD DEPOSIT, NEVADA USING (U-TH)/HE THERMOCHRONOLOGY

The Carlin-type deposits of northern Nevada contain disseminated gold ore with major economic importance but of uncertain origin. Although mineralization is generally accepted to be Eocene in age, the hydrothermal activity has been dated at relatively few individual deposits. The Marigold mine in the Battle Mountain mining district is currently operated by Silver Standard Resources and has recently been reclassified as a Carlin-style gold deposit. Gold mineralization at Marigold occurs in steeply dipping faults in the sedimentary host rock package, as well as spatially associated with the argillically altered margins of Cretaceous quartz monzonite dikes. To determine the age of the most recent hydrothermal fluid movement along these dikes, apatite aliquots from two dikes were dated using (U-Th)/He thermochronology. The ages for the two dikes are Eocene (39.9 ± 0.3 Ma and 41.9 ± 0.3 Ma), indicating that the most recent hydrothermal fluid activity corresponds to the accepted age of regional Carlin-type mineralization. Although Eocene intrusions have not been identified at Marigold, five intrusions at the Lone Tree deposit 8 km north of Marigold have recently been dated as Eocene, suggesting a possible connection with mineralizing hydrothermal activity at Marigold.

Jasperoids are commonly spatially associated with Carlin-style gold deposits although a direct connection between their formation and mineralization has not been established. An additional component of this research will be to analyze iron oxides within jasperoids from two mining districts (Battle Mountain and the Northern Carlin Trend) using (U-Th)/He thermochronology to determine the age relationship between jasperoid formation and gold mineralization. The petrographic and geochemical characterizations of the jasperoid samples prior to (U-Th)/He analysis are reported here. If mineralized jasperoids prove to be Eocene in age whereas barren jasperoids are of a different age, iron oxide (U-Th)/He thermochronology could serve as a valuable exploration vectoring technique for Carlin-type deposits in Nevada.