A bimodal volcanic suite of rhyolite intrusions and flows and columnar olivine basalt, basaltic tuff and tuff breccia occurs along and immediately north of the Tintina Fault from near Faro to Tuchitua in east-central Yukon. The results of recent fieldwork and geochronometry over the northern part of this belt expands the known areal distribution of rhyolitic volcanics and confirms their age as late Paleocene to Eocene. Basalt formerly thought Quaternary is also of Eocene age. The concordance of dates between the mafic and felsic volcanics indicates a single Paleogene bimodal volcanic province. Such bimodal suites are commonly linked to crustal extension and normal faulting, which in this case are presumably related to transcurrent slip along Tintina Fault.
The connection between Paleogene volcanism and the geographical extent of placer gold in this area is more than circumstantial. The recent lode gold discovery at Grew Creek appears to be intimately associated with Paleogene felsic volcanism. Hydrothermal systems associated with similar felsic volcanic centres elsewhere in the region, perhaps unmapped or buried by drift, may be the ultimate source of the placer gold.
