Fault-related bleaching and sedimentary rock-hosted copper mineralization around the Paradox Valley, Montrose County, Colorado

The Cashin mine in western Montrose County, Colorado is
a sandstone-hosted copper deposit in the Jurassic Wingate Sandstone
on the southwest side of the Paradox Valley salt anticline
(Figure 1a), with a measured and indicated resource of 6.5 million
tons at 0.52% copper (Hahn, 2004). The Wingate Sandstone
is typically red/orange fine-grained eolian sandstone (Figure 1b).
However, in the study area the Wingate Sandstone and other
eolian sandstones are bleached white/tan (Figure 1c). Bleaching
also extends into less permeable siltstones and shales where they
are in contact with bleached sandstones or faults (Figure 1d).
Reduced fluids responsible for the bleaching appear to have
traveled up along steeply dipping, northeast-trending normal
faults before moving laterally into gently dipping high permeability
sandstones. Bleaching in the Wingate Sandstone extends
southeast of the Cashin fault approximately 1400 meters, southwest
at least 1300 meters, and northwest more than 8 kilometers
(Figure 2). Around the Paradox Valley many of the same faults
that provided pathways for bleaching fluids also host copper
mineralization, as at the Cashin, Cliffdweller, and Sunrise mines
(Figure 1a). Copper mineralization, like bleaching, extends laterally
in favorable zones (Figure 2). Narrow bands of finely disseminated
copper mineralization have been traced