Lithologic Environments: The Controlling Factor for Green Mountain-Type Uranium Deposits: ABSTRACT

Abstract

Much has been written about Wyoming's roll-front uranium deposits, but little has been published about what is hereafter referred to as the Green Mountain-type uranium deposits. They occur in the Eocene Battle Spring Formation, a sequence of continental fluvial deposits over 5000 ft thick. This sequence consists of arkosic sandstones, conglomeratic sandstones, and siltstones. The Granite Mountains, an ancient crystalline high now partially buried in part by material eroded from it, supplied both the detritus and the uranium for the Battle Spring and the Wind River Formations, the latter being the host for uranium of the Gas Hills district. Both the similarities and dissimilarities of the Green Mountain-type vs. the roll-front-type uranium occurrences are discussed. Most of the Battle Spring Formation is a leaky aquifer devoid of consistent aquicludes, which explains the lack of high-grade uranium concentrations at the frontal or closure redox boundary. Instead, the high-grade mineralization occurs at the interface between carbonaceous debris-rich siltstone lenses and the permeable arkosic sandstone and conglomeratic sandstone. Economically significant deposits occur where mineralizing fluids penetrate a high frequency of these interfaces. Published minable reserves of Atlantic Richfield's Round Park deposit are 42 million lb U/sub 3/O/sub 8/ with an average grade ofmore » 0.23%. These and other deposits are examples of Green Mountain-type uranium deposits.« less