Economic Geolog•j

The Wenatchee district, site of the Cannon mine, is located on the east flank of the Cascade Range in central Washington. Epithermal gold mineralization of Eocene age (44 Ma) is hosted by the Eocene Chumstick Formation, a sequence of interbedded arkosic sandstone, conglom-erate, and mudstone. This study focuses on the structure and hydrothermal alteration and mineralization south of the Cannon mine. Hydrothermal alteration and mineralization is hosted by Chumstick arkose, minor Eocene dacite, and andesite dikes, and locally, Eocene felsic volcanic rocks (flows, ash flows, eruption breccia) and extends for at least 4 km southeast of the Cannon mine. The district-scale structure is dominated by a postmineralization, ortheast-verging fold and thrust belt which consists of three major southwest-dipping reverse faults and associated folds produced by the propagation of the faults. Arkose-hosted alteration consists of zones of silicification which grade symmetrically outward to argillization and a widely dispersed, district-scale propylitic alteration. Alteration is strata bound within units of arkosic sandstone and conglomerate bound or capped by mudstone-ric