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The Paleoproterozoic Thelon Basin is located in the Churchill Province of the Canadian Shield, Nunavut, Canada, and is host to economic unconformity-type uranium mineralization (the Kiggavik deposit) and has the potential to host other deposits. The Thelon Formation sandstones and conglomerates and the Pitz Formation sandstones from the Garry Lake area contain phosphates, illite, minor chlorite and quartz as cements. The matrix phosphates are fluorapatite with U concentrations up to 103.5 ppm in the Thelon Formation rocks and up to 991 ppm in the Pitz Formation rocks. Lead isotope ratios and associated trace element concentrations extracted from sandstones and conglomerates by partial leaching with 2% nitric acid show that rocks with phosphates in the matrix have radiogenic 206 Pb/ 204 Pb ratios as well as high U, Pb, Th, Ca and P concentrations. Some radiogenic Pb is interpreted to be produced in situ by breakdown of fluorapatites. However, a 206 Pb/ 204 Pb vs . 238 U/ 206 Pb diagram indicates that in some samples there is an excess of 206 Pb that could not have been produced by the amount of U in the sample and that must have been derived from an extraneous U-rich source and then introduced into the rock by later fluids. The Pb Pb model for leachates gives an age of ca. 1593 Ma, which is younger than the age of the detrital and early diagenetic phosphates and is close to the age of the phosphate cements from the Garry Lake area of 1558 Ma. This suggests that there was later remobilization and migration of uranium-bearing fluids when the aquifers were open to diagenetic fluids, which could have resulted in formation of a deposit in the north-eastern part of the Thelon Basin.

Both uranous and uranyl minerals are present in the Centennial unconformity-type U deposit situated in the SW Athabasca Basin, Canada. At least two generations of uraninite are present (disseminated and massive), often strongly altered to coffinite, followed by minor fibrous coffinite forming in veins. Uranyl minerals, mostly uranophane with minor haiweeite precipitating in veins and in hand sample-scaled breccias, are present in significant amounts ( ca . 5% of the ore) not observed elsewhere in the Athabasca Basin. The multi-stage evolution of the Centennial deposit is explained by the existence of high permeability conduits, promoting the recurrent circulation of P-rich fluids that remobilized U locally. Stable isotopes composition of uranophane (δD of ca . –130 ‰ and δ 18 O of ca . 6 ‰) suggests that recent oxidizing meteoric fluids penetrated to the unconformity (at a depth of ca . 800 m) via the major Dufferin lake fault.

Nous avons affine la structure cristalline de la senkevichite, de composition ideale Cs K Na Ca 2 T1 4+ O [Si 7 O 18 (OH)], triclinique, PI, a 10.4191(4), b 12.2408(5), c 7.0569(3) A, a 90.857(1), β 99.193(1). γ 91.895(1)°, V 887.8(1) A 3 , Z= 2. D calc 3.125 g/cm 3 , provenant du complexe de Dara-i-Pioz, dans les montagnes Tien-Shan. au Tajikistan, jusqu'a un residu R 1 de 4.5% en utilisant 4872 reflexions uniques (F o > 4σF) prelevees avec un diffractometre a monocristal Bruker P4 muni d'un detecteur CCD 4K et rayonnement MoKα. Les analyses effectuees avec une microsonde electronique ont donne SiO 2 51.08 TiO 2 8.94, FeO 0.50, MnO 2.59, CaO 10.98, K 2 O 6.13, Na 2 O 3.76, Nb 2 O 5 0.64, Cs 2 O 15.28, (H 2 O) calc 1.09, pour un total de 100.99% (poids), et la proportion de (H 2 O) a ete etablie par analyse de la structure. La senkevichite est isostructurale avec la tinaksite et la tokkoite. La structure contient sept sites Si a coordinence tetraedrique, avec une distance moyenne de 1.623 A. Six de ces sites sont coordonnes par des atomes d'oxygene, et le site Si(7) est coordonne par trois atomes d'oxygene et un groupe (OH). Il s'agit donc d'un groupe silicate acide. Il y a trois sites M a coordinence [6]. Le site M(1) contient surtout T1 4+ (et un peu de Nb), avec = 1.985 A. Le site M(2) contient uniquement Ca, avec = 2.382 A, et le site M(3) contient Ca (et des quantites mineures de Fe 2+ et Mn 2+ ). avec = 2.317 A. Il y a un site Na a coordinence [7], avec = 2.504 A. Il y a deux sites A, le site A(1) a coordinence [12], contenant surtout le cesium (et un peu de K), avec = 3.318 A. et le site A(2), a coordinence [10], contenant uniquement le K, avec = 2.987A. La senkevichite est l'analoque a Cs de la tinaksite, K 2 Na Ca 2 T1 4+ O [S1 7 O 18 (OH)], et l'oxyanalogue a Cs-Na-Ti 4+ de la tokkoite, K 2 Ca 4 F |Si 7 O 18 (OH)].

calated between the M–Al–OH sheets are layers of (SO4) tetrahedra and (H2O) groups. All H atoms of (OH) and (H2O) groups were located, and details of hydrogen bonding are discussed. The structure of “nickelalumite” is similar to those of alvanite, ZnAl4(VO3)2(OH)12(H2O)2, and ankinovichite, NiAl4(VO3)2(OH)12(H2O)2, and stoichiometry and cell dimensions suggest that mbobomkulite and hydrombobomkulite also are related to “nickelalumite”. All structures are based on a positively charged sheets of octahedra of the form [ M 2+ M 3+ 4 (OH)12] 2+ that are intercalated with interstitial complexes of oxyanions and (H2O) groups. The Lewis acidity of the structural unit is 0.167 vu, and the character of the interstitial complexes is constrained by the valencesum rule of bond-valence theory. Possible interstitial oxyanions are (SO4) 2– , (NO3) 1– 2 and [VO3] 1– 2, whereas (SiO4) 4– , (BO3) 3– 2, (PO4) 3– and (BO4) 5– have Lewis basicities that are too high and hence cannot form “nickelalumite”-type structures.

Oxykinoshitalite, ideally Ba (Mg 2 Ti 4+ ) (Si 2 Al 2 ) O 10 O 2 , is a new species of mica from Fernando de Noronha Island, Pernambuco, Brazil; it is found in an olivine nephelinite with olivine, clinopyroxene, Fe–Ti oxide, nepheline, calcite, apatite and K-rich feldspar. Oxykinoshitalite forms corroded irregularly shaped grains 0.03 to 0.05 mm across, and its color varies from bright orange to brown. It is brittle, H = 2½, D obs = 3.3(1), D calc = 3.45 g/cm 3 , has a brown streak, vitreous luster and does not fluoresce in ultraviolet light; it has a perfect cleavage on {001} and a splintery fracture. In transmitted plane-polarized light, oxykinoshitalite is strongly pleochroic, X pale brown, Y ≈ Z deep red-brown; X ∧ c = 2° (in β obtuse), Y = b , Z ∧ a = 8° (in β obtuse), with absorption X Y ≈ Z. It is biaxial positive, α 1.708 ± 0.001, β 1.710 ± 0.001, γ 1.719 ± 0.001, 2 V obs = 56 ± 2°, 2 V calc = 51°. Oxykinoshitalite is monoclinic, space group C 2/ m , a 5.3516(7), b 9.2817(11), c 10.0475(13) A, β100.337(3)°, V 490.98(18) A 3 , Z = 2. The strongest ten X-ray-diffraction lines in the powder pattern [ d in A( I )( hkl )] are: 2.637(10)(131), 2.172(9)(133), 3.646(7)(112), 3.130(7)(112), 3.383(6)(002), 2.902(5)(113), 2.435(5)(201), 1.988(5)(133), 1.661(5)(135), 1.547(5)(312), and 1.526(5)(206). Analysis by a combination of electron microprobe, SIMS and crystal-structure refinement gives SiO 2 28.92, Al 2 O 3 15.26, TiO 2 11.94, Cr 2 O 3 0.03, Fe 2 O 3 9.07, FeO 3.84, MnO 0.14, MgO 10.74, CaO 0.03, BaO 15.49, Na 2 O 0.39, K 2 O 4.05, F 0.91, H 2 O 0.55, sum 100.97 wt.%; V, Ni, Zn, Sr, Cl were not detected. The formula unit, calculated on the basis of 12(O,OH,F) is (Ba 0.50 K 0.43 Na 0.07 ) ∑ 1.00 (Mg 1.33 Fe 2+ 0.27 Mn 2+ 0.01 Fe 3+ 0.57 Ti 4+ 0.74 ) ∑2.92 (Si 2.40 Al 1.49 ) ∑3.89 O 10 [O 1.46 (OH) 0.30 F 0.24 ] ∑2.00 . Refinement of the crystal structure shows it to be the 1 M polytype. The refinement converged to R 1 = 4.3% for 585 unique ( F o > 4σ F o ) reflections, collected on a Bruker single-crystal P 4 diffractometer with a CCD detector and Mo K α X-radiation. Electron-microprobe and SIMS analysis of the crystal used to collect the data on X-ray intensities gave the empirical formula (Ba 0.47 K 0.42 Na 0.06 Ca 0.01 ) ∑0.96 (Mg 1.35 Fe 2+ 0.28 Fe 3+ 0.59 Ti 4+ 0.75 Mn 0.01 ) ∑2.98 [Si 2.31 Al 1.56 ] ∑3.97 O 10 (O 1.44 OH 0.31 F 0.25 ) ∑2.00 . The oxygenian Ti-dominant analogue of kinoshitalite occurs in olivine nephelinite and is associated with olivine, clinopyroxene, Fe–Ti oxide, nepheline, calcite, apatite and K-rich feldspar. There is one tetrahedrally coordinated T site, T –O> = 1.671 A, occupied by (Si 2.31 Al 1.56 ). There are two octahedrally coordinated sites, M (1) occupied by (Mg 0.52 Fe 2+ 0.13 Fe 3+ 0.27 Ti 4+ 0.08 ) with M (1)–O> = 2.110 A, and M (2) occupied by (Mg 0.84 Fe 2+ 0.15 Fe 3+ 0.33 Mn 0.01 Ti 4+ 0.67 ) with M (2)–O> = 2.065 A. The interstitial [12]-coordinated I site is occupied by (Ba 0.47 K 0.42 Na 0.06 Ca 0.01 ), with I –O> = 3.107 A. There are two main coupled substitutions in this structure: (1) Ti 4+ for Mg, primarily at the M (2) site, and O 2− for (OH) − and F − at the O(4) site, and (2) K for Ba at the I site, and Si for Al at the T site.

The crystal structure of arapovite, ideally U4+ (Ca,Na)2 (K1– x □ x ) [Si8 O20], x ≈ 0.5, tetragonal, a 7.5505(4), c 14.7104(9) A, V 838.6(1) A3, space group P 4 /mcc , Z = 2, D calc. 3.365 g/cm3, was refined to an R 1 index of 2.9% based on 528 observed [ F o > 4σ F ] unique reflections measured with Mo K α radiation on a Bruker P 4 diffractometer with a 1K CCD area detector. In the crystal structure of arapovite, there is one tetrahedrally coordinated site solely occupied by Si, with = 1.617 A. There are two [8]-coordinated sites, A and B , occupied by (U0.594+ Th0.26 Ca0.10 REE0.04) and (Ca1.23 Na0.68 REE0.08 Ba0.01), with = 2.403 and = 2.490 A. There is one [12]-coordinated site, C , partly occupied by K (K0.52 □0.48), with = 3.103 A. In the crystal structure of arapovite, (SiO4) tetrahedra form a double four-membered ring: [Si8O20]. Eight-coordinated A and B polyhedra share common edges to form a (001) sheet. The sheets are connected through [Si8O20] groups to form a framework; C atoms are situated in large cages within the framework. The topology of the arapovite structure is identical to that of turkestanite, Th (Ca,Na)2(K1– x □ x ) Si8 O20 (H2O) n , and steacyite, Th (Na,Ca)2 (K1– x □ x ) Si8 O20, x ≈ 0.5. The topology of silicate minerals with [Si8O20]8–units, including ekanite, Th Ca2 Si8O20, and litidionite, Na2 K2 Cu2 Si8O20, is discussed.

The crystal structure of shcherbakovite from Mount Rasvumchorr, Khibina massif, Kola Peninsula, Russia, ideally K2 Na Ti 4+ 2 O (OH) (Si4O12), a 8.1538(4), b 10.5569(5), c 13.9882(6) A, V 1204.1(2) A 3 , space group Imma, Z = 4, Dcalc 3.194 g/cm 3 , has been refined to R1 = 3.2% for 960 unique (Fo > 4� F) reflections collected on a Bruker single-crystal P4 diffractometer equipped with a CCD detector and MoKX-radiation. Shcherbakovite occurs in late (hydrothermal) shallowly dipping veins of natrolite and is associated with natrolite, aegirine, K-feldspar, strontian apatite, titanite, spherulitic baryllite and rare pyrrhotite and chalcopyrite. Electron-microprobe analysis gave SiO2 40.57, TiO2 18.87, Fe2O3 1.05, MnO 0.06, BaO 6.7, CaO 0.20, K2O 13.22, Na2O 5.59, Nb2O5 10.49, SrO 0.08, ZrO2 0.84, Ta2O5 0.06, (H2O)calc 0.73, sum 97.83 wt.%. The amount of H2O was determined from crystal-structure analysis. There is one tetrahedrally coordinated T site, 1.607 A, occupied by Si. There are two octahedrally coordinated sites, M(1), occupied by (Ti0.68 Nb0.32 1.00), with = 2.016 A, and M(2), occupied by (Ti0.72 Nb0.15 Fe 3+ 0.08 Zr0.04 1.01), with = 1.999 A. The M(1) and M(2) sites are separated by 0.477 A, and hence cannot be occupied simultaneously at a local level. There are three interstitial A sites: the A(1) site is (9)-coordinated and is occupied by (K0.66 Ba0.23 Na0.07 Ca0.02), with = 2.952 A; the A(2) site is (8)-coordinated and is occupied by K, with = 2.861 A, and the A(3) site is (6)-coordinated and is occupied by Na, with = 2.493 A. Shcherbakovite is a K-analogue of batisite, ideally Ba Na2 Ti 4+ 2 O2 (Si4O12). Shcherbakovite is related to batisite by substitution of K for Ba and K for Na. "Noonkanbahite", ideally Ba K Na Ti 4+ 2 O2 (Si4O12), has never been approved by the IMA as a new mineral species. Based on the crystal chemistry of this structure type, the general formula of these minerals may be written as A B C M2 � 2 (Si4O12), with the following end-member compositions: batisite A = Ba, B = Na, C = Na; shcherbakovite, A = K, B = K, C = Na; "noonkanbahite", A = Ba, B = K, C = Na; unnamed, A = K, B = Na, C = Na.