Mineralization at the Win prospect consists of polymetallic-sulfide and quartz-cassiterite mineralized vein and breccia vein systems within a quartz-tourmaline (dravite)-altered hornfels aureole that appears to be related to a small felsic stock and related dikes. Host rocks for the veins and vein breccias are lithic sandstone and siltstone of the Upper Cretaceous Kuskokwim Group (Bundtzen and Miller, 1997); age of mineralization is inferred to be Late Cretaceous based on 70.0 Ma age of nearby Cloudy Mt. intrusion (Moll and others, 1981). The intrusions are calc-alkalic, high Ca, low K, biotite rich, magnetite-bearing, oxidized garnet bearing dacite and granite porphyry (Burleigh, 1992). Mineralization in the hornfels covers a diffuse 1.25 square mile (3.2 square km) area, mainly south of the intrusive center. Mineralized veins and breccia zones exhibit a pronounced N 65 to 75 W trend, coincident with several regional faults in the immediate area (Patton and others, 1980). Virtually all significant mineralization occurs in hornfels and not in intrusives.