The Mineralogy,petrology,ore Genesis And Resources Of The R?ssing South-West U Deposit(ML 121)

The southern Central Zone(sCZ)of the Neoproterozoic to early Palaeozoic Damara orogenic belt hosts significant uranium deposits in Namibia,but Rossing,a world class deposit which accounted for the majority of uranium produced in Namibia is close to depletion.In order to increase Namibia's uranium mining efficiency,production and boost its economy,this paper analyzes the Rossing-South West(SW)deposit which is located in the sCZ to the southwest of the Rossing Dome.It investigates the geology,mineralogy,petrology,geochemistry and resources of this deposit,aimed at determining whether these attributes resemble those of the Rossing and Husab deposits,and whether ore from Rossing-SW's ML 121 area can be processed at the Rossing or Husab sulphuric acid plants.U mineralization at ML 121 is hosted in mainly type-D and type-E post-tectonic leucogranites intruded into the metapelites of the Karibib Formation around �500 Ma and bounded by the Karibib marble to the north and thin Arandis marble to the south in this area.Uraninite is the chief primary U-bearing mineral which mainly exists as independent grains and Th isomorphs while the major secondary U mineral betauranophane coats surfaces and structural dislocations in the host and country rocks.Uraninite in this area is associated with xenotime,uranothorite,coffinite,thorogummite,accessory zircon and possibly carnotiteThe mineralogy,major and trace element geochemistry of the uraniferous leucogranites in ML 121 suggest they are S-type granites produced by the partial melting of metapelites,however Pb anomalies suggest there was crustal input while the Nb-Ta and Zr-Hf anomalies indicate that mantle sourced mafic melts may have played a role in leucogranite formation.This study assumes that the same mechanisms responsible for leucogranite emplacement at Rossing and Husab were also responsible for the ML 121 leucogranite emplacement although,geological differences in local emplacement environments may have resulted in minor variations in the morphology and mineralization of the respective oresOre genesis processes at ML 121 included accumulation of uranium along with other incompatible elements in residual magmas during magmatic differentiation where it crystallized in late stage minerals such as uraninite.Altered uraninite grains and pitchblende veinlets in the host rocks suggest there was further post-magmatic hydrothermal overprint.Supergene enrichment at ML 121 area is evidenced by the increase in grade with depth and the presence of secondary mineralization(mostly betauranophane)in the structural dislocations of the host and country rocks.U mineralization at ML 121 is a result of magmatic differentiation,hydrothermal alteration and supergene enrichment congeneric to that of the Rossing and Husab deposits.The resource at Rossing-SW was calculated using the inverse distance weighting method producing an inferred resource of 16660t U3O8 using an average grade of 233ppm and cut-off grade of 120ppm.Consequently,ore from Rossing-SW's ML 121 area can be processed at the Rossing or Husab sulphuric plants to extend the life of mine and decrease unemployment while boosting the Namibian economy.