Source of the detrital components of uraniferous conglomerates, Quirke ore zone, Elliot Lake, Ontario, Canada
Large volumes of pyritic quartz-pebble conglomerate in the Elliot Lake district of Ontario contain at least 300,000 tonnes U3O8 recoverable at a grade of 0.1% (ref. 1), with much greater tonnages available at lower recovery grades. The Quirke zone alone contains in excess of 224,000 tonnes U3O8 at ∼0.1% (refs 2–4) and is, accordingly, one of the world's largest known uranium deposits. Situated 40 km north of the North Channel of Lake Huron, 400 km north-west of Toronto, ore conglomerates occur in the Matinenda Formation, locally the basal unit of the Huronian Supergroup, and, although their age is not well constrained, they are probably close to 2,350 Myr old.5 Uraninite, the most important primary ore mineral, occurs as poorly rounded to euhedral grains 0.05–0.2 mm across within the matrix between quartz pebbles. While its chemical and morphological characteristics have led most workers to consider that the uraninite is detrital5–7, there has hitherto been no attempt to characterize its source lithology, a matter of considerable significance as regards mineral exploration. This was the aim of the present study. We have examined the mineral and fluid inclusions observed in the quartz pebbles in the conglomerate and conclude that they were derived from a pegmatitic, potassic (alaskitic) granite. We have also demonstrated that in this source lithology, pebble-sized quartz was spatially associated with radioactive minerals, by inference, uraninite. The postulated characteristics of such a source are remarkably similar in several respects to the uraniferous alaskites of the Rössing deposit in Namibia.
Uranium in South Africa and South West Africa (Namibia)
A number of genetically different uranium deposits occur in South Africa and South West Africa in rocks of widely differing ages. Early Proterozoic clastic rocks contain sedimentary uraninite, whose deposition in auriferous quartz-pebble conglomerates and carbon seams can be related to fluvial fans and algal mats. Recently discovered deposits of uranium in the Phanerozoic Karoo Supergroup occur as widespread but small bodies in channel sandstones of fluvial association. Carnotite deposits are developed in Cainozoic calcretes in the western, more arid, regions of southern Africa in which the uranium has been precipitated epigenetically from circulating groundwater. Uranium mineralization in magmatic rocks is present to a small extent in phoscorite and carbonatite of the middle Proterozoic Phalaborwa Igneous Complex, and is associated with alkaline lavas and intrusive rocks in the Pilanesberg alkaline complex of middle-late Proterozoic age. Multicyclic processes of ore formation have produced extensive deposits of uraninite-bearing alaskitic pegmatitic granites, of Phanerozoic age, in the Pan-African Damara metamorphic belt.
Pioneer 10 Observations of the Ultraviolet Glow in the Vicinity of Jupiter
A two-channel ultraviolet photometer aboard Pioneer 10 has made several observations of the ultraviolet glow in the wavelength range from 170 to 1400 angstroms in the vicinity of Jupiter. Preliminary results indicate a Jovian hydrogen (1216 angstrom) glow with a brightness of about 1000 rayleighs and a helium (584 angstrom) glow with a brightness of about 10 to 20 rayleighs. In addition, Jupiter appears to have an extensive hydrogen torus surrounding it in the orbital plane of Io. The mean diameter of the torus is about equal to the diameter of the orbit of Io. Several observations of the Galilean satellites have also occurred but only a rather striking Io observation has been analyzed to date. If the observed Io glow is predominantly that of Lyman-α, the surface brightness is about 10,000 rayleighs.