SusChEM: Exploring Links Among U, Fe, and Hydrocarbon Movement in the Paradox Basin, Colorado Plateau

University Of Arizona, Tucson AZ

Investigators

Abstract

The Paradox basin and other sedimentary basins of the Colorado Plateau host many significant mineral and hydrocarbon resources, including iron, copper, cobalt, manganese, silver, and oil and gas, and are best known for hosting one of the world's great uranium-producing provinces. New reconnaissance geological studies in the Paradox basin revealed unexpected spatial and stratigraphic connections between uranium mineralization, hydrocarbon migration, and mobility of iron and other elements. These connections suggest that a new model for uranium deposition is required: one where oil, and possibly natural gas, leads to localized trapping of uranium perhaps in mixing zones, in contrast to the prevailing model where uranium is trapped by organic matter that is indigenous to the host rock. This new hypothesis does not preclude the alternatives, but it predicts that the larger deposits may have higher grades and have a distinct and more localized distribution. Evidence for concurrent redistribution of iron and other elements suggests that the same fluids move many elements; such element redistribution gives clues to fluid geochemistry and movement. This project will advance the fundamental geochemical understanding of metal movement and mass transport in the Paradox and other sedimentary basins and it may provide novel approaches to mineral discovery in a region with world-class mineral resources. Five focus sites along the 100+ km-long Lisbon Valley salt wall in the Paradox Basin have been selected for field mapping, core logging, petrographic, fluid inclusion, and elemental and isotopic analyses. The focus sites represent diverse stratigraphic and structural settings and range from the deep central part of the basin to the fringes, but all show uranium mineralization, iron mobility, and bleaching or other evidence of hydrocarbons. The mapping of alteration minerals, petrography, and whole-rock analyses will be used to document the distribution and paragenesis of iron, alkali, and base metal enrichment and depletion at scales from the single deposit to the sub-region. The investigators will correlate these observations with the distribution, evolution, and temporal sequence of uranium and related (vanadium, copper) mineralization and the loci of hydrocarbon reservoirs and migration paths. Coupled with fluid inclusion and isotopic analyses of alteration minerals and geochemical modeling to evaluate fluid characteristics and sources, these data will enable a systematic test of the interplay between metal-bearing basinal brines, hydrocarbons, and local structures and rock types - e.g. whether the movement and deposition of U, Fe, and hydrocarbons represent different facets of a single short-lived system, represent the evolution of a single system over a long time, or were produced by multiple unrelated superimposed events. This is a first step toward an integrated approach to studying linkages among mass transport phenomena in the Paradox Basin, which can be applied on the Colorado Plateau and worldwide both to understanding the geological and geochemical evolution of important resource provinces and to exploring and managing resource development therein.