Meta-sandstone, siltstone and phyllite, with marble and intermediate-to-felsic tuffaceous horizons, host the Munson (TBMB) and Mod zinc-lead occurrences, about 7 km southwest of the Dan and Crescent properties. These host rocks are part of the Late Devonian Dorsey assemblage. Complexities resulting from isoclinal folding and faulting inhibit direct correlation of strata from one ridge exposure to another.
The strata are overlain by dark meta-siltstone of the mid-Mississippian Swift River succession. Although faulted, the lack of a strong lithologic contrast between the units suggests only minor dislocation.
Pre-Jurassic and Cretaceous granites and a diorite sill intrude the Dorsey rocks. Chloritic tuffaceous layers host showings of pyrrhotite, chalcopyrite and sphalerite; carbonate pods contain sphalerite + galena ± pyrrhotite; and quartz-feldspar meta-tuff layers are pyritic.
U-Pb zircon age results for leucosome from a nearby exposure of lower Dorsey rocks indicate an approximate crystallization age of 373 Ma, and about 358 Ma for a granitic dyke in the upper Dorsey assemblage, bracketing the age of deposition of this Yukon-Tanana Terrane assemblage.
