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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. Such deposits form where uranium-bearing oxidised 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).

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

This paper outlines the geology of the world-class sandstone uranium deposits in the Chu- Sarysu and Syrdarya basins in the south-central portion of Kazakhstan, which are hosted by sandstones relatively poor in organic matter. We 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.


 


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