Abstract The Section 23 mine is one of about 18 large uranium mines opened in sandstones of the fluvial Westwater Canyon Member of the Jurassic Morrison Formation, in the Ambrosia Lake uranium district, during the early 1960s. Two distinct types of unoxidized ore occur in the mine. One type consists of uranium-rich authigenic organic matter that impregnates parts of the reduced sandstone host rocks. This type of ore occurs as peneconcordant layers which are typically elongate east-southeast, subparallel both to the sedimentary trends and to the regional strike of the host rock. A second type of ore is essentially devoid of organic matter and occurs in thick zones which conform to interfaces that separate oxidized from reduced parts of the host rocks. Genesis of the second type of ore is similar to that of roll-type deposits in Tertiary rocks of Wyoming and Texas. Organic matter in the primary ores was probably introduced into the host rock as humic acids that precipitated in the pores of the sandstone. This material is inferred first to have fixed uranium as urano-organic compounds but, with further diagenesis, to have released some of the uranium to form coffinite. Vanadium, molybdenum, and selenium are associated with primary ore and may also have been fixed by the organic matter. The secondary or roll-type ores contain uranium mostly in the form of coffinite and only rarely as uraninite. They also contain vanadium and selenium but are virtually devoid of molybdenum.

Abstract Statistical treatment of the chemical data for samples from the Church Rock, Smith Lake, Ambrosia Lake, and Laguna districts, all in the Grants uranium region, San Juan basin, indicates that primary ore-forming processes concentrated copper, iron, manganese, molybdenum, selenium, vanadium, yttrium, arsenic, organic carbon, and sulfur, along with uranium. The initial uranium and vanadium mineralization occurred before compaction of the host rocks. A barium halo associated with all of these deposits formed as a result of secondary processes. Calcium and strontium were also enriched in the ores by secondary processes. Comparison of the chemical characteristics of redistributed deposits in the Church Rock district with those of primary deposits in the Grants uranium region indicates that calcium, manganese, strontium, yttrium, copper, iron, molybdenum, lead, selenium, and vanadium are chemically separated from uranium during redistribution of the deposits in the Church Rock district. Comparisons of the chemical characteristics of the Church Rock deposits with those of the secondary deposits in the Ambrosia Lake district suggest some differences in the processes that were involved in the genesis of the redistributed deposits in these two areas.

Sediments, soils, and fossils are used to interpret paleoenvironmental conditions during the last interglacial-glacial transition in Illinois. The sediments include the classic Sangamonian-Wisconsinan and Wisconsinan/Farmdalian-Woodfordian successions; both consist of loess overlying pedogenically modified or generally colluviated sediment. Although the contacts between the loess and soil are defined as isochronous, they are diachronous. The age of basal Wisconsinan deposits spans from at least 50 to 22 ka, and the age of basal Woodfordian sediments spans from 25 to 20 ka. Recognition of the last interglacial episode, the Sangamonian Age, is based on Mollisols, Alfisols, and Ultisols that formed in Illinoian glacigenic deposits. Sangamonian flora and fauna, although sparsely preserved, include pollen well represented by deciduous trees, grasses, and Ambrosia. Sangamonian vertebrates included giant tortoise, mastodon, giant beaver, snapping turtle, and short-nosed gar. The Wisconsinan Age (Altonian Subage) began as Roxana Silt (loess) was deposited under periglacial conditions. The vegetation was characterized by coniferous trees that grew in weakly developed, often organic-rich, cryoturbated soils. Periglacial conditions persisted during the Altonian and Farmdalian Subages, from before 50 ka to about 25 ka, after which loess, outwash, and till were deposited under glacial conditions during the Woodfordian Subage and much of the remainder of the Wisconsinan Age. The vegetation that grew during the last glacial episode includes plants that are now found at and north of the treeline in Canada.