Sandstone-hosted uranium deposits amenable for exploitation byin situleaching technologies

Abstract

Sandstone uranium deposits represent uranium concentrations formed by low-temperature hydrothermal processes, usually of diagenetic to epigenetic origin. The deposits are commonly hosted in arkosic sandstone and are therefore referred to as sandstone-type uranium. Globally, this is the most abundant type of uranium mineralisation, containing approximately 28% of the world's uranium resources and including several giant deposits with resources exceeding 100 kt of uranium. The main uranium minerals are pitchblende and coffinite, and uranium is recovered from host rocks by conventional hydrometallurgical technologies using sulphuric acid or alkaline leach. Host sediments were deposited in many different geological environments including continental intracratonic basins, intermontane depressions, coastal-plains and palaeo-river channels. Mineralisation is mostly stratabound and localised in the permeable sandstone at the redox interfaces where oxidised uranium-rich fluids have intersected with relatively reduced basin lithologies. Sandstone-type uranium mineralisation can also be distributed along permeable fault zones cutting sedimentary sequences. Deposits are subdivided into four groups: roll front (rolltype), tabular, basal channel and tectonic-lithologic types. Many sandstone uranium deposits cannot be exploited by conventional mining technologies because of low grade and difficult geotechnical conditions created by the presence of poorly consolidated wallrocks and the location of ore bodies below the water table. However, because of high permeability of the host sediments and the favourable uranium mineralogy, these deposits are well-suited to exploitation by in situ leach (ISL) technique. ISL mining is defined as the process of uranium extraction from the host sandstone in situ by injecting the chemical leach solutions directly into the ore zone. The pregnant solutions containing leached uranium are transported to the surface through production wells. Uranium is recovered from the solutions to produce yellowcake.

Selenium and Other Trace Element Mobility in Waste Products and Weathered Sediments at Parys Mountain Copper Mine, Anglesey, UK

“…A well-known concern to former and operational mining sites worldwide is contamination of soils and groundwaters from Se, particularly in U mining sites [11,81,82]. The release of Se during extraction can have environmental ramifications, affecting livestock [3,4,7,10,[83][84][85].…”

Paleovalley-related uranium: exploration criteria and case-studies from Australia and China

“…Due to diagenetic and epigenetic modifications, the idealised structure of uranium mineralisation concentrated along a distinct boundary at or near the contact with obvious reduced materials, as shown in Figure 4, may not always be present, such as Beverley deposits of South Australia. The features controlling uranium deposition can be made complex, or completely destroyed, by multiple groundwater and/or hydro-thermal pulses, in particular, when uranium mineralisation is modified and remobilised by post-ore, reduced/oxidised and saline solutions (Abzalov, 2012).…”

“…These models have been applied in Australia and China at local scale with some success and there is broad consensus that considerable scope exists for ongoing discovery of paleovalley-related uranium mineralisation on a scale comparable to that discovered in Kazakhstan and USA. Variations to the models reflect local conditions and include the source of uranium, nature of the groundwater and transportation mechanisms, and type and distribution of reducing agents which affect precipitation of uranium minerals (Abzalov, 2012).…”

Sandstone-Hosted Uranium Deposits as a Possible Source for Critical Elements: The Eureka Mine Case, Castell-Estaó, Catalonia

“…Major uranium sandstone hosted deposits are also being mined in Australia, China, and Kazakhstan [12,13]. Sandstone deposits represent~35% of the uranium deposits and~28% of the world uranium resources [14]. In these deposits, reducing agents in the sediments (i.e., sulphides, coal seams, hydrocarbons, or organic matter) trigger the precipitation of metals with high valence states, typically U 6+ and V 5+ [15].…”