General geology and sulfide mineralization of Dry Canyon and vicinity, Gunnison Plateau, Sanpete Co., Utah

The area of investigation, which lies on the eastern front of the Gunnison Plateau between Coal Canyon and Maple Canyon (south), is formed of formations of Upper Mesozoic and Cenozoic ages. The formations of Upper Mesozoic age are represented by Twist Gulch-Upper Jurassic, Indianola undifferentiated-Upper Cretaceous, Price River-Upper Cretaceous, and the lower part of North Horn-Upper Cretaceous. The formations of Cenozoic Age are represented by the upper part of North Horn-Paleocene, Flagstaff-Paleocene, Colton-Eocene, and Green River-Eocene. Of all the formations, the Twist Gulch is the only marine formation present in the area. The other formations represent deposition under fluviatile, fluvio-lacustrine, and lacustrine environments. The clastic sedimentary rocks account for more than two third of the total thickness of the strata exposed in the area. The North Horn formation constitutes as much as 2000 feet of clastic sedimentary rocks. Igneous activity is indicated by the glass associated with the Flagstaff formation (limestone) and felsitic lava flows associated with the Green River formation. Some intrusions of quartz-monzonite porphyry occur west and north of the area of investigation. The area is traversed by EW and nearly NS striking high angle normal dip-slip faults. A few high angle reverse faults are also present. In the eastern part of the area of investigation, recent faulting has occurred. This faulting is mainly confined to recent alluvium and has given rise to prominent scarplets which strike NE-SW. North of Dry Canyon, the North Horn strata are mineralized. The mineralization of the strata is mainly limited to sedimentary units in the basal part of the North Horn formation where galena, pyrite, and chalcopyrite occur. A detail field work and laboratory studies revealed that galena, pyrite, and chalcopyrite associated with the North Horn strata are of epigenetic origin, and represent deposition at relatively low temperatures. The regional relationship of the area of investigation supports an epigenetic origin for these sulfide deposits associated with the North Horn strata. Evidence for the above conclusion consists of: 1. The localized occurrence of the sulfide deposits. 2. The occurrence of the quartz-monzonite porphyryintrusive bodies in adjacent localities. 3. Igneous activity during Green River time. 4. The typical replacement features present in the pyritized limestone and galena bearing sandstone and conglomerate.