AGE AND ORIGIN OF A GOLD-BEARING BRECCIA FROM THE HILLTOP GOLD DEPOSIT, LANDER COUNTY, NEVADA
Analysis of primary fluid inclusions (n=4) within the quartz yield salinity (2.7-4.0 equiv wt % NaCl) and Th (180.6-192.4oC) data. The calculated δ18OVSMOWsignature of the quartz matrix source fluid (-7.5 to -6.5‰) suggests the breccia formed from a mixture of meteoric and magmatic components.
Argon/argon age determination of a three-phase, K-bearing clay (65% illite, 22% quartz, 13% scorodite) within the quartz matrix yields a plateau age of 46.1±0.4 Ma, indicating a breccia age ~10 Ma older than a previously-reported age of 35.9±0.4 for the same breccia (illite/smectite; Kelson, 2008) and ~6 Ma older than ages of igneous rocks and molybdenites proximal to the breccia studied here (Kelson, 2008).
Fluid inclusion and stable isotope data support an epithermal origin for the breccia.