Ar-40/Ar-39 age and chemistry of manganese mineralization in the Moab and Lisbon fault systems, southeastern Utah

Diagenetic iran and manganese mineralization is associated with the Moab an d Lisbon faults and is an important indicator of fluid how in Jurassic Nava jo Sandstone of southeastern Utah. Reducing brines originating from the Pen nsylvanian Paradox Formation (with or without hydrocarbons) mobilized disse minated iron and manganese in the Jurassic sandstones and mixed with shallo w, oxygenated groundwater to precipitate both iron and manganese mineraliza tion. Mineralization consists of colliform and concretionary hematite, pyro lusite, and cryptomelane-hollandite that contains 1.33-2.12 wt% K. The Ar-4 0/Ar-39 dating of vacuum-encapsulated cryptomelane yields age estimates of 25-20 Ma, indicating mineralization coincident with either a Colorado Plate au uplift episode or La Sal Mountains volcanism.