博茨瓦纳杰姆斯博克盆地砂岩型铀成矿条件与找矿远景预测OA

Gemsbok Basin lies in southwestern Kalahari Karoo Basin of Botswana and extends southwestward into Aranos Basin of Namibia.Because the two basins share similar tectonic settings,Karoo Supergroup stratigraphic frameworks,and sedimentary histories,the Wings sandstone-hosted uranium deposit in Aranos Basin provides a useful analogue for assessing uranium potential in Gemsbok Basin.This study evaluates the prospectivity of sandstone hosted uranium in Gemsbok Basin through integrated analysis of regional geology,stratigraphic correlation,palaeoflow patterns,representative boreholes,and fence sections.Wings deposit is hosted in Early Permian Auob Formation of Ecca Group and is controlled by a redox front.Mineralization is concentrated in Auob 3 sandstone aquifer,which is bounded above and below by coal-bearing strata and forms a characteristic mudstone-sandstone-mudstone configuration.In the Gemsbok Basin,the upper part of Otshe Formation is the closest equivalent to the ore-hosting interval of Auob Formation in terms of stratigraphic position,lithological association,and depositional facies,and is therefore considered the principal target horizon.Borehole data further indicate that Otshe Formation is best preserved in the northern part of the basin,suggesting that this area is the most favorable for uranium exploration.Interpretation of 12 boreholes from the northern part of the study area allows recognition of eight facies associations,of which Facies Associations 4 and 5 are the most favorable for sandstone-type uranium mineralization.Facies Association 4 represents delta-front sand bodies that likely acted as permeable aquifers and pathways for fluid migration,whereas Facies Association 5 comprises coal-bearing intervals that could have served as effective reducing barriers.Together,these units define the most prospective stratigraphic interval in the basin.Favorable conditions for uranium mineralization in Gemsbok Basin include:potential uranium sources in Precambrian basement and Damara Belt to the north and northwest;a gently inclined slope-belt structural setting along the northwestern basin margin further promoted the development of a groundwater recharge-runoff-discharge system;basinward transport of clastic material during Ecca deposition;the close spatial association between permeable sand bodies and coal-bearing reducing strata in the upper Otshe Formation.On this basis,a prospective mineralization area was preliminarily defined in the central-eastern part of the northern drill-controlled area,from ACP19—ACP13 area to the vicinity of MP1,with W3 forming the northern boundary.