Fault-hosted AU mineralization, Ester Dome, Alaska

Abstract

The Rhyolite gold prospect near Fairbanks, Alaska, appears to be different from most intrusion-related Au depositions within the Fairbanks area (e.g., Ryan Lode and Fort Knox), as it is located along a low-angle fault and is spatially associated with a quartz monozonite sill. A 1:60,000 scale geologic map was prepared using soil samples, airborne geophysical data, and mapping based on core and surface samples collected during 1998 and 1999. Mineralization does not appear to be temporally related to the quartz-monzodiorite sill, although mineralized fluids apparently used the sill as a pathway. ⁴⁰Ar/³⁹Ar dates of chloritized biotite from the intrusive (>75 Ma), sericite in mineralized gouge (9̃0 Ma), and white micas from metamorphic rocks (1̃00 Ma) correlate with dates from other plutonic-related deposits in the Fairbanks area ... Au-Ag, Au-Bi, and Au-As ratios suggest that the Rhyolite prospect is intrusion-related but distal to the causative body.