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Laser-ablation high-resolution inductively coupled plasma mass spectrometry (LA-HR-ICP-MS) is a rapid, accurate, and inexpensive technique for making in situ U-Pb isotopic measurements of uraninite and davidite. The advantages of this method include: (1) mineral separation and chemical digestion are not required; (2) measurements on complex samples are feasible because significant isobaric interferences can be resolved; and (3) accurate U-Pb and 207Pb/206Pb dates on 10-25 µm spots can be obtained rapidly. The LA-HR-ICP-MS method is applied to U oxide minerals from four deposits and prospects from northern Australia, and the new dates are compared to previously published conventional thermal ionization mass spectroscopy (TIMS) dates, and to known ages of geologically important events. These comparisons permit us to assess elemental fractionation of U and Pb for uraninite and davidite of the new method, relative to zircon, as well as its geochronological accuracy and precision. U-Pb apparent ages measured previously agree well with our measurements for El Sherena, Palette, and Mt. Isa. Additionally, the upper-intercept 207Pb/206Pb dates for Adelaide River (701 ± 190 Ma, 1σ) and Palette (841 ± 94 Ma, 1σ) uraninite, measured here, are similar to those previously obtained for Palette (730 Ma), Nabarlek (920 Ma), and Koongarra (870 Ma), and the upper-intercept date for El Sherena uraninite (1573 ± 160 Ma) is within error of that previously determined for Ranger (1550 ± 15 and 1472 ± 40 Ma). Such apparent-age agreement for uraninite (and similarly for davidite) indicates that U and Pb fractionations are within error of that for zircon, whereas the inherent imprecision of our dates and their associated MSWD values greater than 2.5 probably indicate that multiple resetting events affected our samples. Analytically, these results demonstrate that the LA-HR-ICP-MS technique provides excellent spatial resolution while also removing argide, phosphide, sulfide, and halide interferences that can otherwise lead to erroneous data when using quadrupole-ICP-MS. Geologically, the individual 207Pb/206Pb and upper-intercept U-Pb dates of uraninite from Adelaide River and Palette are ca. 800 Ma, possibly reflecting recrystallization of uraninite during the break-up of Rodinia. [ABSTRACT FROM AUTHOR]

The Bigrlyi deposit is a tabular, sandstone-hosted, uranium–vanadium deposit of Carboniferous age located in the Ngalia Basin of central Australia. The deposit is similar to the continental, fluvial Saltwash-type of sandstone-hosted U-V deposits which are well known from the Colorado Plateau, USA. Most mineralization at Bigrlyi occurs as thin, multiple-stacked, stratiform lenses at the base of fluvial channels near the contact between a grey sandstone succession and a hematitic, purple–red sandstone succession. A larger halo of lower grade vanadium mineralization extends beyond the main U-V-mineralized zone. The host is an immature, feldspathic sandstone, grading into arkose and lithic-rich variants. Lithic 'rip-up' clasts of clay-rich sediments are common in the basal parts of fluvial channels, and are frequently the focus of, and have acted as sites for, U-V mineralization. Coffinite and uraninite are the main uranium minerals, with the former dominant. Vanadium is mainly hosted by Fe-V-bearing clays and chlorite, including roscoelite, grading into vanadian illite, the interlayer mineral corrensite, and altered detrital biotite. The V-Fe–oxyhydroxide minerals montroseite, haggite and doloresite, and altered detrital Fe-Ti oxides, are minor V-hosts. Mineralized zones correlate with enrichments in Se, Li, Ba, Be, Mo, Mg and Fe, and elevated Se/S ratios are characteristic of U-mineralized zones. Petrographic studies show that a heterogeneous mixture of variably mineralized lithic clasts is present; in the same rock, some clasts are Fe-rich and only weakly U-V-mineralized, while other clasts are strongly V- and/or U-mineralized. These observations point to mineralization processes that did not take place in-situ in the host sandstone at the site of deposition as required by conventional groundwater models. Lead isotope results provide evidence of the open-system mobility of radiogenic elements in parts of the deposit. In V-bearing zones, radiogenic Pb contents were found to be unsupported by current U levels, suggesting that over time U has been mobilized from these zones and redistributed, resulting in U-enrichment in other parts of the deposit. Mobility pathways were likely open over time from early in the history of the Bigrlyi deposit. A hybrid mineralization model, involving an interplay between solution-precipitation processes, detrital transport and post-depositional U remobilization, is proposed for Bigrlyi. Ferrous-ion-bearing clay minerals and pyrite are considered to be the most likely primary reductants/adsorbents, while the deposit is lacking carbonaceous matter. [ABSTRACT FROM AUTHOR]

The article provides information on the fluoropatite crystals from Lake Boga, Victoria, one of the classic Australian mineral localities. The large granite quarry in Lake Boga is the type locality for two new minerals, ulrichite and bleasdaleite, with potentially another three. However, they are so rare that collectors hardly ever see them. Instead, another mineral, fluorapatite, may be more familiar, forming beautiful crystals in late-stage hydrothermal cavities in the granite.