Subhash Jaireth, Aden McKay and Ian Lambert report that sandstone uranium deposits account for approximately 30% of annual global production, largely through in situ leach (ISL) mining. Most of this production has come from deposits in the western United States, Niger and Kazakhstan. In Australia, sandstone-hosted uranium is being produced from the Beverley deposit in the Frome Embayment of South Australia, and a second ISL mine is under development at Honeymoon in the same region. Also in Texas as well.
Such deposits form where uranium-bearing oxidized groundwater moving through sandstone aquifers react with reducing materials. The locations of ore zones and the sizes of mineral deposits depend, among other factors, on the abundance and reactive nature of the reductant. Hence, the nature and abundance of organic material in the ore-bearing sedimentary sequence may be of critical importance for the formation of sandstone uranium deposits. In sandstones rich in organic material (containing debris of fossil plants or layers of authigenic, or in situ generated, organic material) the organic matter either reduces uranium directly with bacteria as a catalyst, or through the production of biogenic hydrogen sulfide (H2S: Spirakis 1996). In sandstones relatively poor in organic material, it has been proposed that the reduction is caused either by H2S (biogenic as well as nonbiogenic) produced from the interaction of oxidized groundwater with pyrite in the sandstone aquifer (thiosulfate produced initially by oxidation of pyrite breaks down to form reduced sulfur), or from the introduction of reduced fluids/gases (H2S, hydrocarbons or both) along favorable structures
(Spirakis 1996).
This paper outlines the geology of the world-class sandstone uranium deposits in the ChuSarysu and Syrdarya basins in the south-central portion of Kazakhstan, which are hosted by sandstones relatively poor in organic matter. They highlight the crucial role that hydrocarbons appear to have played in the formation of these and other large sandstone type uranium deposits. Based on the model developed, we conclude that there is considerable potential in Australia for the discovery of large sandstone-hosted uranium mineralisation, including in little explored regions underlain by basins with known or potential hydrocarbons.
Aubakirov (1998) suggested that the uranium mineralisation formed at a geochemical trap created by an influx of reduced fluids/gases (hydrocarbons and H2S) along relatively deeply penetrating structures. Chemical analyses of drill core samples through the ore zones show that hydrocarbon gases have accumulated along the redox front. Some authors consider that this accumulation of hydrocarbon gases facilitated large-scale ore formation over extensive redox boundaries (Fyodorov 1999), although the detailed geochemical (including sulfur and carbon isotopic) studies required to define more precisely the role of hydrocarbons and/or H2S in the Chu-Sarysu and Syrdarya basins have not been conducted.
The close spatial association between sandstone uranium deposits and hydrocarbon-bearing basins observed in the Chu-Sarysu Basin is not unique. In recent years, sandstone uranium deposits closely associated with hydrocarbon-bearing basins have been identified in the Ordos and Songlio basins in China (for example, Huang Xian-fang et al 2005). Further afield, in the Texas Uranium Region (Texas Coastal Plain), uranium mineralization in organic-poor sandstones has been attributed by several researchers to the influx of H2S along faults from hydrocarbon reservoirs at depth (Reynolds and Goldhaber 1978).
Managed & Built by I2M Consulting, LLC | © 2010-
