Uranium minerals brannerite

In most uranium ores the element is present in several, usually many diverse minerals. Some of these dissolve in sulfuric acid solutions under mild conditions, while others may require more aggressive conditions. Thus, while it may be comfortable to recover 90-95% of the uranium present, it may be tough or impractical to win the balance amount of a few percent economically. Some of the most difficult uranium minerals to leach are those of the multiple oxide variety, most commonly brannerite and davidite. These usually have U(IV) as well as U(VI), together with a number of other elements such as titanium, iron, vanadium, thorium, and rare earths. To extract uranium from these sources is not as easy as other relatively simpler commonly occurring sources. 

The major primary ore mineral is uraninite (basically UO2) or pitchblende (U2O5.UO3, better known as U3O8), though a range of other uranium minerals are found in particular deposits. These include camotite (uranium potassium vanadate), the davidite-brannerite-absite-type uranium titanates, and the euxenite-fergusonite-samarskite group (niobates of uranium and rare earths). 

Brannerite is the third most important reduced uranium mineral in that it occurs in many different types of deposits and is the chief uranium producer in the conglomerates of Blind River-Elliot Lake, Ontario, Canada. Although it has been found in pegmatites, hydrothermal and sedimentary deposits, it is always associated with uraninite and probably forms through reactions with uraninite and titanium phases that are also present. 

Mineral varieties of the brannerite series include lodochni-kite, absite and thorutite. Absite is a thorian-rich brannerite and does not warrant species status. Lodochnikite is a uranium-rich brannerite, possibly significantly oxidized. Heating produces a brannerite-like X-ray pattern, but with differing intensities. It probably does not warrant species status either. Thorutite is the thorium end member. 

Vein-like deposits in metamorphic rocks also occur in Pre-cambrian Shield areas, but they differ from unconformity-related uranium deposits in that they are not associated with major regional unconformities, the geometries of orebodies are different and they extend to greater depths. Vein-like deposits are closely associated with steeply dipping, brecciated major fault systems. Uranium minerals (pitchblende with some coffinite and brannerite) occur as open fracture fillings and as fine disseminations adjacent to the fractures in Proterozoic meta-igneous andmetasedimentary rocks. Common associated minerals are chlorite, hematite and pyrite. 

Minerals of the third group of Table 5.15 contain relatively small proportions of tetravalent uranium combined with a refractory oxide of titanium, niobium, or tantalum. To free the uranium from these minerals, they must be leached with hot, concentrated sulfuric acid. Davidite is one of the principal ores at Radium Hill in South Australia. Brannerite is found in the Blind River district of Ontario. Pyrochlore occurs in the Lake Nipissing district of Ontario and in Nigeria. 

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