ALBERT

Description: Interface coupled dissolution-reprecipitation reactions (ICDR) are a common feature of fluid-rock interaction during crustal fluid flow. We tested the hypothesis that ICDR reactions can play a key role in scavenging minor elements by exploring the fate of U during the experimental sulfidation of hematite to chalcopyrite under hydrothermal conditions (220–300 °C). The experiments where U was added, either as solid UO 2+x (s) or as a soluble uranyl complex, differed from the U-free experiments in that pyrite precipitated initially, before the onset of chalcopyrite precipitation. In addition, in UO 2+x (s)-bearing experiments, enhanced hematite dissolution led to increased porosity and precipitation of pyrite+magnetite within the hematite core, whereas in uranyl nitrate-bearing experiments, abundant pyrite formed initially, before being replaced by chalcopyrite. Uranium scavenging was mainly associated with the early reaction stage (pyrite precipitation), resulting in a thin U-rich line marking the original hematite grain surface. This "line" consists of nanocrystals of UO 2+x (s), based on chemical mapping and XANES spectroscopy. This study shows that the presence of minor components can affect the pathway of ICDR reactions. Reactions between U- and Cu-bearing fluids and hematite can explain the Cu-U association prominent in some iron oxide-copper-gold (IOCG) deposits.

Description: The Olympic Dam IOCG-U-Ag deposit, South Australia, the world’s largest known uranium (U) resource, contains three main U-minerals: uraninite, coffinite, and brannerite. Four main classes of uraninite have been identified. Uraninite occurring as single grains is characterized by high-Pb and REE+Y (REY) but based on textures can be classified into three of these classes, typically present in the same sample. Primary uraninite (Class 1) is smallest (10–50 μm), displays a cubic-euhedral habit, and both oscillatory and sectorial zoning. "Zoned" uraninite (Class 2) is coarser, sub-euhedral, and combines different styles of zonation in the same grain. "Cobweb" uraninite (Class 3) is coarser still, up to several hundred micrometers, has variable hexagonal-octagonal morphologies, varying degrees of rounding, and features rhythmic intergrowths with sulfide minerals. In contrast, the highest-grade U in the deposit is found as micrometer-sized grains to aphanitic varieties of uraninite that form larger aggregates (up to millimeter) and vein-fillings (massive, Class 4) and have lower Pb and REY, but higher Ca. Nanoscale characterization of primary and cobweb uraninite shows these have defect-free fluorite structure. Both contain lattice-bound Pb+REY, which for primary uraninite is concentrated within zones, and for cobweb uraninite is within high-Pb+REY domains. Micro-fractured low-Pb+REY domains, sometimes with different crystal orientation to the high-Pb+REY domains in the same cobweb grain, contain nanoscale inclusions of galena, Cu-Fe-sulfides, and REY-minerals. The observed Pb zonation and presence of inclusions indicates solid-state trace-element mobility during the healing of radiogenic damage, and subsequent inclusion-nucleation + recrystallization during $${f}_{{\mathrm{s}}_{2}}$$ -driven percolation of Cu-bearing fluid. Tetravalent, lattice-bound radiogenic Pb is proposed based on analogous evidence for U-bearing zircon. Calculating the crystal chemical formula to UO 2 stoichiometry, the sum of cations (M*) is ~1 for most classes, but the presence of mono-, di-, and trivalent elements (REY, Ca, etc.) drive stoichiometry toward hypostoichiometric M*O 2–x . In the absence of measured O and constraints of hypostoichiometric fluorite-structure, charge-balance calculations showing O deficit in the range 0.15–0.36 apfu is compensated by assumption of mixed U oxidation states. Crystal structural formulas show up to 0.20 apfu Pb and 0.25 apfu REY in Classes 1–3, while for Class 4, these are an order of magnitude less. Low-Pb and REY subcategories of Classes 2 and 3 are similar to massive uraninite with ~0.2 apfu Ca. Other elements (Si, Na, Mn, As, Nb, etc.), show two distinct geochemical trends: (1) across Classes 1–3; and (2) Class 4, whereby low-Pb+REY sub-populations of Classes 2 and 3 are part of trend 2 for certain elements. Plots of alteration factor (CaO+SiO 2 +Fe 2 O 3 ) vs. Pb/U suggest two uraninite generations: early (high-Pb+REY, Classes 1–3); and late (massive, Class 4). There is evidence of Pb loss from diffusion, leaching and/or recrystallization for Classes 2–3 (low-Pb+REY domains). Micro-analytical data and petrographic observations reported here, including nanoscale characterization of individual uraninite grains, support the hypothesis for at least two main uraninite mineralizing events at Olympic Dam and multiple stages of U dissolution and reprecipitation. Early crystalline uraninite is only sparsely preserved, with the majority of uraninite represented by the massive-aphanitic products of post-1590 Ma dissolution, reprecipitation, and possibly addition of uranium into the system. Coupled dissolution-reprecipitation reactions are suggested for early uraninite evolution across Classes 1 to 3. The calculated oxidation state [U 6+ /(U 4+ +U 6+ )] of the "early" and "late" populations point to different conditions at the time of formation (charge compensation for REY-rich early fluids) rather than auto-oxidation of uraninite. Late uraninites may have formed hydrothermally at lower temperatures ( T 〈 250 °C).

Description: Nordgauite, MnAl2(PO4)2(F,OH)2{middle dot}5H2O, is a new secondary phosphate from the Hagendorf-Sud pegmatite, Bavaria, Germany. It occurs as white to off-white compact waxy nodules and soft fibrous aggregates a few millimetres across in altered zwieselite-triplite. Individual crystals are tabular prismatic, up to 200 {micro}m long and 10 {micro}m wide. Associated minerals include fluorapatite, sphalerite, uraninite, a columbite-tantalite phase, metastrengite, several unnamed members of the whiteite-jahnsite family, and a new analogue of kingsmountite. The fine-grained nature of nordgauite meant that only limited physical and optical properties could be obtained; streak is white; fracture, cleavage and twinning cannot be discerned. Dmeas. and Dcalc. are 2.35 and 2.46 g cm-3, respectively; the average RI is n = 1.57; the Gladstone-Dale compatibility is -0.050 (good). Electron microprobe analysis gives (wt.%): CaO 0.96, MgO 0.12, MnO 14.29, FeO 0.60, ZnO 0.24, Al2O3 22.84, P2O5 31.62, F 5.13 and H2O 22.86 (by CHN), less F=O 2.16, total 96.50. The corresponding empirical formula is (Mn0.90Ca0.08Fe0.04Zn0.01Mg0.01)-{Sigma}1.04Al2.01(PO4)2[F1.21,(OH)0.90]{Sigma}2.11{middle dot}5.25H2O. Nordgauite is triclinic, space group P[IMG]f1.gif" ALT="Formula" BORDER="0"〉, with the unit-cell parameters: a = 9.920(4), b = 9.933(3), c = 6.087(2) A, = 92.19(3), {beta} = 100.04(3), {gamma} = 97.61(3){degrees}, V = 584.2(9) A3 and Z = 2. The strongest lines in the XRD powder pattern are [d in A (I) (hkl)] 9.806 (100)(010), 7.432 (40)(1[IMG]f1.gif" ALT="Formula" BORDER="0"〉0), 4.119 (20)(210), 2.951 (16)(0[IMG]f2.gif" ALT="Formula" BORDER="0"〉1), 4.596 (12)(2[IMG]f1.gif" ALT="Formula" BORDER="0"〉0), 3.225 (12)(220) and 3.215 (12)(121). The structure of nordgauite was solved using synchrotron XRD data collected on a 60 {micro}m x3 {micro}m x4 {micro}m needle and refined to R1 = 0.0427 for 2374 observed reflections with F 〉 4{sigma}(F). Although nordgauite shows stoichiometric similarities to mangangordonite and kastningite, its structure is more closely related to those of vauxite and montgomeryite in containing zig-zag strings of corner-connected Al-centred octahedra along [011], where the shared corners are alternately in cis and trans configuration. These chains link through corner-sharing with PO4 tetrahedra along [001] to form (100) slabs that are interconnected via edge-shared dimers of MnO6 polyhedra and other PO4 tetrahedra.

Description: Byrudite (IMA 2013-045, Raade et al ., 2013 ), with simplified formula (Be,)(V 3+ ,Ti) 3 O 6 , occurs in emerald-bearing syenitic pegmatites of Permian age at Byrud farm, Eidsvoll, Akershus, South Norway. It has a norbergite-type structure, Pnma , with a = 9.982(1), b = 8.502(1), c = 4.5480(6) Å, V = 385.97(9) Å 3 , Z = 4. The structure was refined to R 1 = 0.045 for 1413 unique reflections. Twinning occurs on {210}. The occupancy of the tetrahedral Be site refined to 0.84(1). The presence of Be was verified by secondary ion mass spectrometry but could not be quantified. Electron-microprobe analyses of the crystal used for structure determination gave the empirical formula (Be 0.84 0.16 )( $${\mathrm{V}}_{1.32}^{3+}$$ Ti 1.25 Cr 0.29 Fe 0.09 Al 0.07 ) 3.02 O 6 . There is a strong inverse correlation between V and Cr. The ideal endmember formula is Be $${\mathrm{V}}_{2}^{3+}$$ TiO 6 . The mineral is black and opaque with a metallic lustre. Reflectance data in air are reported from 400 to 700 nm. The Commission on Ore Mineralogy required wavelengths are [ R 1 , R 2 ( in nm)]:16.6,17.5(470), 16.7,17.9(546), 16.8,18.3(589) and 16.8,18.6(650). The Mohs hardness is ~7, based on indentation measurements. The mineral is brittle with an uneven fracture; cleavage is not present. D (calc.) = 4.35 g cm –3 for the empirical formula with 0.84 Be a.p.f.u. The strongest reflections of the calculated powder X-ray diffraction pattern are [ d in Å( I rel)( hkl )]: 3.721(72)(111), 2.965(100)(121), 2.561(50)(311), 2.464(41)(230), 2.167(24)(231), 1.681(34)(402), 1.671(66)(232), 1.435(23)(630).

Description: A new mineral chrysothallite K 6 Cu 6 Tl 3+ Cl 17 (OH) 4 ·H 2 O was found in two active fumaroles, Glavnaya Tenoritovaya and Pyatno, at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption, Tolbachik volcano, Kamchatka, Russia. Chrysothallite seems to be a product of the interactions involving high-temperature sublimate minerals, fumarolic gas and atmospheric water vapour at temperatures not higher than 150°C. It is associated with belloite, avdoninite, chlorothionite, sanguite, eriochalcite, mitscherlichite, sylvite, carnallite and kainite at Glavnaya Tenoritovaya and with belloite, avdoninite, chlorothionite, eriochalcite, atacamite, halite, kröhnkite, natrochalcite, gypsum and antlerite at Pyatno. The mineral forms equant-to-thick tabular crystals up to 0.05 mm, typically combined in clusters or crusts up to 1 mm across. Crystal forms are: {001}, {100}, {110}, {101} and {102}. Chrysothallite is transparent, bright golden-yellow to light yellow in finely crystalline aggregates. The lustre is vitreous. The mineral is brittle. Cleavage was not observed, the fracture is uneven. D meas = 2.95(2), D calc = 2.97 g cm –3 . Chrysothallite is optically uniaxial (+), = 1.720(5), = 1.732(5). The Raman spectrum is given. The chemical composition (wt.%, electron-microprobe data, H 2 O calculated based on the crystal structure data) is: K 15.92, Cu 24.56, Zn 1.38, Tl 13.28, Cl 40.32, H 2 O(calc.) 3.49, total 98.95. The empirical formula, calculated on the basis of 17 Cl + 5 O a.p.f.u., is: K 6.09 (Cu 5.78 Zn 0.32 ) 6.10 Tl 0.97 Cl 17 [(OH) 3.80 O 0.20 ]·H 2 O. Chrysothallite is tetragonal, I 4/ mmm, a = 11.3689(7), c = 26.207(2) Å, V = 3387.3(4) Å 3 , Z = 4. The strongest reflections of the powder X-ray pattern [ d , Å( I )( hkl )] are: 13.20(44)(002); 6.88(100)(112); 5.16(30)(202, 114); 4.027(25)(220); 3.471(28)(206), 3.153(30)(314), 3.075(47)(305), 2.771(38)(316). The crystal structure (solved from single-crystal X-ray diffraction data, R = 0.0898) is unique. Its basic structural unit is a (001) layer of edge-sharing distorted CuCl 4 (OH) 2 octahedra. Two Tl 3+ cations occupy the centre of isolated TlCl 6 and TlCl 4 (H 2 O) 2 octahedra connected to each other and to the Cu polyhedral layers via KCl 6 and KCl 9 polyhedra. The name reflects the bright golden-yellow colour of the mineral (from the Greek ó, gold) and the presence of thallium. Chrysothallite is the second known mineral with species-defining trivalent thallium.

Description: The crystal structure of the manganese phosphate mineral gatehouseite, ideally , space group P212121, a = 17.9733(18), b = 5.6916(11), c = 9.130(4) Å, V = 933.9(4) Å3, Z = 4, has been solved by direct methods and refined from single-crystal X-ray diffraction data (T = 293 K) to an R index of 3.76%. Gatehouseite is isostructural with arsenoclasite and with synthetic . The structure contains five octahedrally coordinated Mn sites, occupied by Mn plus very minor Mg with observed distances from 2.163 to 2.239 Å. Two tetrahedrally coordinated P sites, occupied by P, Si and As, have distances of 1.559 and 1.558 Å. The structure comprises two types of building unit. A strip of edge-sharing Mn(O,OH)6 octahedra, alternately one and two octahedra wide, extends along [010]. Chains of edge- and corner-shared Mn(O,OH)6 octahedra coupled by PO4 tetrahedra extend along [010]. By sharing octahedron and tetrahedron corners, these two units form a dense three-dimensional framework, which is further strengthened by weak hydrogen bonding. Chemical analyses by electron microprobe gave a unit formula of (Mn4.99Mg0.02)S5.01(P1.76Si0.20As0.07)S2.03O8(OH)3.97.

Description: Shimazakiite occurs as greyish white aggregates up to 3 mm in diameter. Two polytypes, shimazakiite-4 M and shimazakiite-4 O , have been identified, the former in nanometre-sized twin lamellae and the latter in micrometre-sized lamellae. Shimazakiite was discovered in an irregular vein in crystalline limestone near gehlenite-spurrite skarns at Fuka mine, Okayama Prefecture, Japan. Associated minerals include takedaite, sibirskite, olshanskyite, parasibirskite, nifontovite, calcite and an uncharacterized hydrous calcium borate. The mineral is biaxial (–), with the following refractive indices (at 589 nm): α = 1.586(2), β = 1.650(2), = 1.667(2) and 2V calc = 53° [shimazakiite-4 M ]; and α = 1.584(2), β = 1.648(2), = 1.670(2) and 2V calc = 54.88° [shimazakiite-4 O ]. Quantitative electron-microprobe analyses (means of 28 and 25 determinations) gave the empirical formulae Ca 2 B 1.92 O 4.76 (OH) 0.24 and Ca 2 B 1.92 O 4.76 (OH) 0.24 for shimazakiite-4 M and shimazakiite-4 O , respectively. The crystal structure refinements: P 2 1 / c , a = 3.5485(12), b = 6.352(2), c = 19.254(6) Å, β = 92.393(13)°, V = 433.6(3) Å 3 [for shimazakiite-4 M ]; and P 2 1 2 1 2 1 , a = 3.55645(8), b = 6.35194(15), c = 19.2534(5) Å, V = 434.941(18) Å 3 [for shimazakiite-4 O ], converged into R 1 indices of 0.1273 and 0.0142, respectively. The crystal structure of shimazakiite consists of a layer containing B 2 O 5 units (two near-coplanar triangular corner-sharing BO 3 groups) and 6- and 7-coordinate Ca atoms. Different sequences in the c direction of four layers are observed in the polytypes. The five strongest lines in the powder-diffraction pattern [listed as d in Å( I )( hkl )] are: 3.02(84)(022); 2.92(100)(104I) 2.81(56)(104); 2.76(32)(113); 1.880(32)(118I,126I,126,118) [for shimazakiite-4 M ]; and 3.84(33)(014); 3.02(42)(022); 2.86(100)(104); 2.79(29)(113); 1.903(44)(126,118) [for shimazakiite-4 O ].

Description: Geologic samples are extremely diverse and share a tendency for both heterogeneity and complexity. This is especially true for ores, which commonly result from a complex interplay of processes in highly dynamic environments. In recent years, a number of tools allowing the chemical mapping of major (e.g., mineral liberation analysis, MLA), minor (e.g., electron microprobe, EPMA), and trace (e.g., laser ablation-inductively coupled plasma-mass spectrometry, LA-ICP-MS) elements in geologic samples at ~1- to 50- μ m resolution and over mm2 areas have seen rapid development and have become readily available. To date, the application of synchrotron-based X-ray fluorescence (SXRF) mapping has been limited to addressing key questions because of low availability and high cost. This paper demonstrates how recent advances in X-ray fluorescence detector technology are bringing new possibilities to ore petrology. Millisecond dwell times allow collection of thin section size maps at resolutions of a few μ m in hours, while improvements in data analysis software simplify the production of quantitative elemental maps. Based on the imaging of six samples representative of different commodities (Pt, U, Cu, Ge) and different geologic contexts (PGE deposit; sandstone-hosted U deposit; vein-type polymetallic hydrothermal deposit; iron oxide-copper-gold (IOCG) deposit), we demonstrate that megapixel SXRF (MSXRF) can efficiently provide the information necessary to understand metal speciation in the context of thin section-scale textural complexity. Image analysis revealed a number of new results for the studied deposits, for example, (1) the distribution of micrometer-sized Pt-rich grains and Ti mobility during the formation of schistosity at the Fifield Point prospect (New South Wales, Australia); (2) the presence of Ge contained in organic matter and of Hg minerals associated within quartzite clasts in the Lake Frome U ores (South Australia); (3) confirmation of the two-stage Ge enrichment in the Barrigão deposit, with demonstration of the presence of Ge in solid solution in the early chalcopyrite (Portuguese Iberian pyrite belt); and (4) the enrichment of U during late dissolution-reprecipitation reactions in the bornite ores of the Moonta and Wallaroo IOCG deposits (South Australia). These results illustrate that MSXRF is a powerful technique for locating nano- to microparticles of precious metals (Pt) and trace contaminants (e.g., Hg) that form distinct (micro) minerals. In addition, it is a powerful tool for understanding commodities with relatively low ore grades and complex distribution (100–1,000 ppm; e.g., U, Ge).

Description: Chalcopyrite (CuFeS 2 ) and bornite (Cu 5 FeS 4 ) are the most abundant Cu-bearing minerals in hydrothermal Cu deposits, forming under a wide range of conditions from moderate-temperature sedimentary exhalative deposits to high-temperature porphyry Cu and skarn deposits. We report the hydrothermal synthesis of both chalcopyrite and bornite at 200–300 °C under hydrothermal conditions. Both minerals formed via the sulfidation of hematite in solutions containing Cu(I) (as a chloride complex) and hydrosulfide, at pH near the pK a of H 2 S(aq) over the whole temperature range. Polycrystalline chalcopyrite formed first, followed by bornite. Assuming that Fe behaves conservatively, the transformation of hematite to chalcopyrite involves a large increase in volume (~290%). The reaction proceeds both via direct replacement of the existing hematite and via overgrowth around the grain. Chemical exchanges between bulk solution and hematite are enabled by a network of micrometer-size pores. However, in some cases the chalcopyrite overgrowth develops large grain sizes with few apparent pores and in these cases fluid transport may have been via a network of fractures. Similarly to the replacement of hematite by chalcopyrite, bornite forms via the replacement of chalcopyrite. The reaction has a large positive volume (~230%), and proceeds both via chalcopyrite replacement and via overgrowth. This study shows that replacement reactions can proceed via coupled dissolution-reprecipitation even where there is a large volume increase between parent and product mineral. This study also provides further evidence about the controls of reaction pathways onto the final mineral assemblage. In this case, the host initial fluid was undersaturated with respect to Fe-bearing minerals. Upon slow release of Fe at the surface of hematite, a mineral assemblage of chalcocite, bornite, and finally chalcopyrite is expected. However, in practice chalcocite did not nucleate on the surface of hematite. Rather relatively slow nucleation of bornite enabled high concentrations of Fe to build up near the dissolving hematite, so that chalcopyrite (high-sulfidation experiments) or chalcopyrite+pyrite (low sulfidation) crystallized first.