The geology and mineralogy of the W. Wilson mine near Clancey, Jefferson County, Montana

The W. Wilson mine, near Clancey, Mont., explores a siliceous vein in quartz monzonite of the Boulder batholith. The vein is a composite structure that consists of several closely spaced veinlets of quartz and chalcedony separated by silicified quartz monzonite. The vein has been recurrently brecciated and silicified. Typically, the quartz monzonite has been hydrothermally altered in zones of decreasing intensity outward from the vein. Pitchblende was deposited in and along the vein during one stage of the silicification that is characterized by fine-grained disseminated pyrite in black chalcedony. Subsequently most of the pitchblende was oxidized and hydrated to form a series of brightly colored secondary uranium minerals that exhibit a zonal relationship. Most of the known uranium minerals are localized in two small elongate ore bodies.