Miocene gold mineralization and exhumation of the southern Shoshone Range, north-central Nevada

Apatite fission-track thermochronology was used to constrain the age of the
Cedars prospect, an epithermal gold-bearing hydrothermal system on the western
flank of the southern Shoshone Range, and the regional uplift-related cooling history
of the southern Shoshone Range. The hydrothermal system at the Cedars prospect
was developed in coarse-grained clastic rocks of the Pennsylvanian Battle Formation
of the Antler overlap assemblage and the unconformably overlying late Eocene
Caetano Tuff and is associated with a breccia pipe that intrudes both units. Apatite
fission-track dating of the hydrothermal alteration zone and the breccia pipe indicate
that both cooled at ~19 Ma. The similarity of age, coupled with alteration assemblages,
and elevated concentrations of gold and silver in both, suggest a model
whereby heat and fluids from the breccia pipe invaded a local groundwater aquifer
developed in permeable strata in the Battle Formation, setting up a convective thermal
system that transferred precious metals from the intrusion to subsurface
hydrothermal deposits.
The regional uplift-related cooling was determined by apatite fission-track dating
of the top and bottom of the steep eastern escarpment of the southern Shoshone Range.
The results suggest that cooling occurred at ~60 Ma and 45 Ma and was followed by
another episode of cooling at ~19 Ma. The early Tertiary episodes of cooling are interpreted
to have been caused by uplift in the hinterland of the Laramide orogenic belt,
whereas the Miocene cooling marks the onset of Basin and Range extensional faulting
in this part of the Great Basin. The concordant ages of the onset of Basin and Range
faulting, intrusion of the breccia pipe, and epithermal mineralization suggest that
onset of Basin and Range faulting allowed fluid-rich magma to transfer precious
metals into the uppermost crust by exploiting newly formed extensional faults.