ISSUE 89 Mar 2008 Association of large sandstone uranium deposits with hydrocarbons Canning The geology of uranium deposits in Kazakhstan Basin Bigrlyi Walbiri points to similar deposits in Australia Ngalia Basin Western Angela Subhash Jaireth, Aden McKay and Ian Lambert Sandstone uranium deposits account for approximately 30% of or through the production of annual global production, largely through in situ leach (ISL) mining. biogenic hydrogen sulfide (H2S: Most of this production has come from deposits in the western Spirakis 1996). In sandstones United States, Niger and Kazakhstan. In Australia, sandstone-hosted relatively poor in organic material, uranium is being produced from the Beverley deposit in the Frome it has been proposed that the Embayment of South Australia, and a second ISL mine is under reduction is caused either by H2S development at Honeymoon in the same region. (biogenic as well as nonbiogenic) Such deposits form where uranium-bearing oxidised groundwaters produced from the interaction moving through sandstone aquifers react with reducing materials. of oxidised groundwater with The locations of ore zones and the sizes of mineral deposits depend, pyrite in the sandstone aquifer among other factors, on the abundance and reactive nature of the (thiosulfate produced initially by reductant. Hence, the nature and abundance of organic material in oxidation of pyrite breaks down the ore-bearing sedimentary sequence may be of critical importance to form reduced sulfur), or from for the formation of sandstone uranium deposits. the introduction of reduced fluids/ gases (H S, hydrocarbons or In sandstones rich in organic material (containing debris of fossil 2 plants or layers of authigenic, or in situ generated, organic material) the both) along favourable structures organic matter either reduces uranium directly with bacteria as a catalyst, (Spirakis 1996). This paper outlines the geology of the world-class sandstone Turgai Hydrocarbon 65° E70°E Region uranium deposits in the Chu- 0 200 km Sarysu and Syrdarya basins in the south-central portion of Kazakhstan, which are hosted Chu-Sarysu Lake by sandstones relatively poor Inkai Hydrocarbon Aral Region Sea Chu-Sarysu Basin 45° N in organic matter (figure 1, Kyzl-Orda table 1). We highlight the Kara Moinkum Syrdarya BasinKaramurun tau Mo unta crucial role that hydrocarbons ins appear to have played in the Zarechnoye formation of these and other ? Chimkent ? large sandstone type uranium deposits. Based on the model 07-2553-1 Cenozoic Sedimentary basins Redox front in Uranium mine developed, we conclude that underlain by Palaeozoic Palaeogene sands Mesozoic Oil/gas field sediments Redox front in Upper there is considerable potential Archaean, Proterozoic Cretaceous Gas field and Palaeozoic - upper sands in Australia for the discovery of metasediments Redox front in Upper Outline of and granitoids Cretaceous hydrocarbon - middle sands region large sandstone-hosted uranium mineralisation, including in little Figure 1. Regional geology of Chu-Sarysu and Syrdarya basins, southern Kazakhstan. Geological data plotted from the Generalized Geological Map of the World (1995), Geological Survey of explored regions underlain by Canada Open File 2915d. Boundary of the hydrocarbon basins and location of oil and gas fields basins with known or potential in the underlying Permian rocks from a map produced by Blackbourn Geoconsulting (http://www.blackbourn.co.uk/databases/hydrocarbon/chusarysu.html). hydrocarbons. Association of large sandstone uranium deposits with hydrocarbons 1 ISSUE 89 Mar 2008 Table 1 Uranium resources, organic carbon and sulfides in basins hosting The ore zones extend for major resources of sandstone uranium deposits 20 to 30 kilometres along the Basin/sub-basin Resources Organic Iron sulfide redox front; in plan, they form (‘000 tonnes carbon (wt%) ribbons 50 to 800 metres wide U3O8) (wt%) (rarely, 1.7 kilometres). In cross- Chu-Sarysu and 1340a < ~ 0.03–0.05b 0.1c section, the zones are asymmetric Syrdarya roll-fronts, tabular bodies and Callabonna (Frome 41.2d < 0.05 to 0.5e Tracese lenses. Thickness varies from five Embayment) metres to more than 25 metres. Wyoming 320f 0.5c 1 to 4c Uranium mineralisation occurs as South Texas 45 to 80g <0.16h 0.5 to 4h coffinite and pitchblende, which a Fyodorov (1999); b Petrov (1998); c Fyodorov (1996); d Ozmin database, Geoscience are finely dispersed in the clay Australia (2007); e Heathgate Resources (1998); f after de Voto (1978); g Dhalkamp (1993); matrix and also infill cavities in h Goldhaber et al (1978) sandstone (Petrov 1998). The depth of uranium ore varies from 100 metres to more than 800 The geological setting in Kazakhstan metres (Fyodorov 1996). The Chu-Sarysu and Syrdarya basins of Kazakhstan are components The source of uranium in the of a large artesian basin that was split into two main components deposits is not clear. It could have following the Pliocene uplift of the Karatau Mountain Range (figure been derived from Ordovician 1). The basins are filled with thick sandstone aquifers capped by and Silurian metasediments impermeable shaly beds. Mineralisation, often as roll fronts, is hosted and granites exposed in the by sands of Upper Cretaceous and Palaeocene–Eocene age. Tyan-Shan Ranges along the The Chu-Sarysu Basin is more mineralised than the Syrdarya Basin southeastern flanks of the basin, and contains larger uranium deposits, which are hosted by a Late which also provided the detrital Cretaceous – Palaeogene age multicoloured clay–gravel–sandstone material for the sedimentary sequence deposited in a continental environment. The large deposits sequence hosting mineralisation. include Inkai, Moinkum, Karamurun and Zarechnoye. In the Uranium-bearing hydrothermal Syrdarya Basin, the host is a grey clay – sandstone sequence formed in vein deposits hosted in pre- coastal-marine and continental conditions (Petrov 1998). Mesozoic metasediments along The roll fronts display mineral and geochemical zoning typical of the northeastern flanks of the oxidation–reduction fronts associated with sandstone uranium deposits Chu-Sarysu Basin could also elsewhere. Hydroxides of iron dominate the oxidation zone, whereas have been a source (Petrov 1998). the reduced zones are dominated by iron sulfides (pyrite and marcasite). Further uranium could have been The uranium zone is enriched in rhenium, zinc, copper, silver, cobalt, contributed from devitrification molybdenum, nickel and vanadium. Significant enrichments of of volcanic tuff interbedded with selenium occur towards the contact with the zone of reduction. Palaeocene/Eocene sands. Lead–lead isotope model ages suggest that mineralisation “Based on the model developed, we occurred in three more or less continuous stages starting conclude that there is considerable potential from Late Oligocene – Middle Miocene and continuing into in Australia for the discovery of large Late Pliocene to Quaternary time (Mikhailov and Petrov 1998). sandstone-hosted uranium mineralisation.” Tectonic reactivation during Association of large sandstone uranium deposits with hydrocarbons 2 ISSUE 89 Mar 2008 the Late Oligocene – Middle Miocene created palaeogeographic thick containing oil and gas conditions favourable for large-scale groundwater flow from the (figure 2; Bykadorov et al 2003). palaeo Tyan-Shan region in the southeastern flanks of the basin. The Chu-Sarysu hydrocarbon The regional extent and general distribution of the redox fronts in basin is made up of two the basins suggests that the palaeo-groundwater flow direction was sequences: lagoonal to marginal- predominantly from the southeast to the northwest. Groundwaters marine salt-bearing strata of probably entered permeable aquifers adjacent to the Tyan-Shan Famenian – Early Carboniferous uplands (Petrov 1998) and flowed towards discharge zones in the age; and alluvial-lacustrine red- general region of the Aral Sea. beds of Middle Carboniferous Late Pliocene – Quaternary ages of mineralisation coincide with – Permian age. The latter include intensive tectonic activity associated with orogenic movements in the Tyan-Shan and the uplift of the Karatau Mountains, along a 500 metres of Permian evaporites. pre-existing regional fault, which created the present-day Visean and Early (pre-salt) hydrodynamic regime. Groundwater flows associated with the Permian sandstones host minor Karatau uplift only caused minor changes in the configuration of volumes of gas. The southeastern the mineralised regional redox fronts created in the Late Oligocene – part of the basin contains Middle Miocene (Petrov 1998). hydrocarbon source rocks and Although organic material in the ore-bearing grey sandstones is also hosts the principal oil and quite low (generally <0.03–0.05%; table 1), Petrov (1998) believes gas fields. Famenian – Early that it was enough (with a minor contribution from iron sulfides) to Carboniferous marls and black produce large sandstone uranium deposits. Petrov ascribes the lack of shales and Permian bituminous direct correlation between uranium and the concentration of organic marls with high total organic material to coalification of organic material, which caused loss of carbon may be an additional active organic reductants such as waxy bitumen and humic acids. source, with Permian salts acting as a regional cap (Bykadorov Chu-Sarysu oil and gas basins et al 2003). The Late Cretaceous to Palaeogene continental and marine Aubakirov (1998) suggested sedimentary sequence that hosts world-class sandstone uranium that the