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At least 19 recordsLinked to original sources
USGS2001

Olivine-liquid relations of lava erupted by Kilauea volcano from 1994 to 1998: Implications for shallow magmatic processes associated with the ongoing east-rift-zone eruption

From 1994 through 1998, the eruption of Kîlauea, in Hawai’i, was dominated by steady-state effusion at Pu‘u ‘Ô‘ô that was briefly disrupted by an eruption 4 km uprift at Nāpau Crater on January 30, 1997. In this paper, I describe the systematic relations of whole-rock, glass, olivine, and olivine-inclusion compositions of lava samples collected throughout this interval. This suite comprises vent samples and tube-contained flows collected at variable distances from the vent. The glass composition of tube lava varies systematically with distance and allows for the “vent-correction” of glass thermometry and olivine–liquid K D as a function of tube-transport distance. Combined olivine–liquid data for vent samples and “vent-corrected” lava-tube samples are used to document pre-eruptive magmatic conditions. K D values determined for matrix glasses and forsterite cores define three types of olivine phenocrysts: type A (in equilibrium with host glass), type B (Mg-rich relative to host glass) and type C (Mg-poor relative to host glass). All three types of olivine have a cognate association with melts that are present within the shallow magmatic plumbing system during this interval. During steady-state eruptive activity, the compositions of whole-rock, glass and most olivine phenocrysts (type A) all vary sympathetically over time and as influenced by changes of magmatic pressure within the summit-rift-zone plumbing system. Type-A olivine is interpreted as having grown during passage from the summit magma-chamber along the east-rift-zone conduit. Type-B olivine (high Fo) is consistent with equilibrium crystallization from bulk-rock compositions and is likely to have grown within the summit magma-chamber. Lower-temperature, fractionated lava was erupted during non-steady-state activity of the Nāpau Crater eruption. Type-A and type-B olivine–liquid relations indicate that this lava is a mixture of rift-stored and summit-derived magmas. Post- Nāpau lava (at Pu‘u ‘Ô‘ô) gradually increases in temperature and MgO content, and contains type-C olivine with complex zoning, indicating magma hybridization associated with the flushing of rift-stored components through the eruption conduit.

Hawaii↗
USGS2001

The Gibbs free energy of nukundamite (Cu3.38Fe0.62S4): A correction and implications for phase equilibria

The Gibbs free energy of formation of nukundamite (Cu 3.38 Fe 0.62 S 4 ) was calculated from published experimental studies of the reaction 3.25 Cu 3.38 Fe 0.62 S 4 + S 2 = 11 CuS + 2 FeS 2 in order to correct an erroneous expression in the published record. The correct expression describing the Gibbs free energy of formation (kJ·mol −1 ) of nukundamite relative to the elements and ideal S 2 gas is Δ f G° nukundamite, T(K) = −549.75 + 0.23242 T + 3.1284 T 0.5 , with an uncertainty of 0.6%. An evaluation of the phase equilibria of nukundamite with associated phases in the system Cu–Fe–S as a function of temperature and sulfur fugacity indicates that nukundamite is stable from 224 to 501°C at high sulfidation states. At its greatest extent, at 434°C, the stability field of nukundamite is only 0.4 log f (S 2 ) units wide, which explains its rarity. Equilibria between nukundamite and bornite, which limit the stability of both phases, involve bornite compositions that deviate significantly from stoichiometric Cu 5 FeS 4 . Under equilibrium conditions in the system Cu–Fe–S, nukundamite + chalcopyrite is not a stable assemblage at any temperature.

Canadian Mineralogist↗
USGS2002

Ordonezite from the Theodoso Soto Mine, Sapioris, Durango, Mexico: New data and structure refinement

A new occurrence of the rare mineral species ordonezite has been found at the Theodoso Soto tin mine, near Sapioris, Durango, Mexico. The average composition of the samples is (Zn 0.98 Fe 0.02 ) Σ1.00 Sb 2.00 O 6 ; the core of the crystals is slightly richer in Fe than the rim. The mineral is uniaxial (+), with all n greater than 2.30 (n calc is 2.38 at 589 nm); D obs 6.66 g/cm 3 , D calc 6.67 g/cm 3 . It is isostructural with ferrotapiolite, with a 4.668(2), c 9.269(6) A (from powder-diffraction data), space group P4 2 /mnm, and is twinned on {103}. Its crystal structure, refined to R=4.1, wR=4.3% using 163 observed reflections, is fully cation-ordered.

Durango↗
USGS2003

Bobjonesite, V4+ O (SO4) (H2O)3, a new mineral species from Temple Mountain, Emery County, Utah, U.S.A

Bobjonesite, V 4+ O (SO 4 ) (H 2 O) 3 , is a new mineral species from Temple Mountain, Emery County, Utah, U.S.A. It occurs as blue-green crusts and efflorescences in fractures in a fossil (Triassic) tree; individual crystals are <<1 mm and are intimately intergrown. Bobjonesite hydrates very easily, and is unstable in all but the driest atmosphere. Its structure was determined on a crystal of bobjonesite; however, the physical properties, optical properties and X-ray powder-diffraction pattern were recorded on the synthetic equivalent, and an electron-microprobe analysis was not possible. Bobjonesite has a pale blue streak, a vitreous luster and no observable fluorescence under ultraviolet light. It has no cleavage or parting. The Mohs hardness is ~1, and the calculated density is 2.28 g/cm 3 . Bobjonesite is biaxial positive, with α 1.555(2), β 1.561(1), γ 1.574(2), 2 V (obs.) = 72(1)°, 2 V (calc.) = 69°; it is non-pleochroic, X = b , Y ≈ a , Z ∧ c ≈ 19° (in β obtuse). Bobjonesite is monoclinic, space group P 2 1 / n , cell dimensions from single-crystal data: a 7.3940(5), b 7.4111(3), c 12.0597(9) Å, β 106.55(1)°, V 633.5(1) Å 3 , Z = 4. The strongest seven lines in the X-ray powder-diffraction pattern [ d in Å( I )( hkl )] are as follows: 5.795(100)(002), 3.498(90)(112), 3.881(48)(1̅03), 5.408(37) (101), 4.571(20)(012), 6.962(11)(1̅01) and 6.254(11)(011). The chemical formula was derived from crystal-structure analysis; the end-member formula is V O (SO 4 ) (H 2 O) 3 . The crystal structure of bobjonesite was refined to an R index of 3.6% for 1105 observed (| F o | > 5> F ) reflections measured with an automated four-circle X-ray diffractometer using Mo K α X-radiation. There is one V site occupied by V 4+ and surrounded by three O atoms and three (H 2 O) groups in an octahedral arrangement, with one short vanadyl bond (1.577 Å), four similar equatorial bonds (<2.022 Å>), and one longer V–O bond (2.278 Å) trans to the vanadyl bond. The structure consists of isolated [V 4+ 2 O 2 (H 2 O) 6 (SO 4 ) 2 ] clusters linked by hydrogen bonds.

Utah↗
USGS2004

Nevadaite, (Cu2+, Al, V3+)6 [Al8 (PO4)8 F8] (OH 2 (H2O)22, a new phosphate mineral species from the Gold Quarry mine, Carlin, Eureka County, Nevada: Description and crystal structure

Nevadaite, (Cu 2+ , □, Al, V 3+ ) 6 (PO 4 ) 8 F 8 (OH) 2 (H 2 O) 22 , is a new supergene mineral species from the Gold Quarry mine, near Carlin, Eureka County, Nevada, U.S.A. Nevadaite forms radiating clusters to 1 mm of prismatic crystals, locally covering surfaces more that 2 cm across; individual crystals are elongate on [001] with a length:width ratio of > 10:1 and a maximum diameter of ~30 μm . It also occurs as spherules and druses associated with colorless to purple-black fluellite, colorless wavellite, strengitevariscite, acicular maroon-to-red hewettite, and rare anatase, kazakhstanite, tinticite, leucophosphite, torbernite and tyuyamunite. Nevadaite is pale green to turquoise blue with a pale powder-blue streak and a vitreous luster; it does not fluoresce under ultra-violet light. It has no cleavage, a Mohs hardness of ~3, is brittle with a conchoidal fracture, and has measured and calculated densities of 2.54 and 2.55 g/cm 3 , respectively. Nevadaite is biaxial negative, with 1.540, β 1.548, γ 1.553, 2 V (obs.) = 76°, 2 V (calc.) = 76° , pleochroic with X pale greenish blue, Y very pale greenish blue, Z blue, and with absorption Z ≫ X > Y and orientation X = c, Y = a, Z = b. Nevadaite is orthorhombic, space group P 2 1 mn , a 12.123(2), b 18.999(2), c 4.961(1) Å, V 1142.8(2) Å 3 , Z = 1, a:b:c = 0.6391:1:0.2611 . The strongest seven lines in the X-ray powder-diffraction pattern [ d in Å(I)( hkl )] are: 6.077(10)(200), 5.618(9)(130), 9.535(8)(020), 2.983(6)(241), 3.430(4)(041), 2.661(4)(061), and 1.844(4)(352). A chemical analysis with an electron microprobe gave P 2 O 5 32.54, Al 2 O 3 27.07, V 2 O 3 4.24, Fe 2 O 3 0.07, CuO 9.24, ZnO 0.11, F 9.22, H 2 O (calc.) 23.48, OH ≡ F–3.88, sum 102.09 wt.% ; the valence states of V and Fe, and the amount of H 2 O , were determined by crystal-structure analysis. The resulting empirical formula on the basis of 63.65 anions ( including 21.65 H 2 O pfu ) is ( (Cu 2.00 2+ Zn 0.02 V 0.98 3+ Fe 0.01 3+ Al 1.15 ) ∑ 4.16 Al 8 P 7.90 O 32 [F 8.37 (OH) 1.63 ] ∑10 (H 2 O) 21.65 . The crystal structure of nevadaite was solved by direct methods and refined to an R index of 4.0% based on 1307 observed reflections collected on a four-circle diffractometer with Mo K α X-radiation . The structure consists of ordered layers of vertex-sharing octahedra and tetrahedra alternating with layers of disordered vertex-sharing and face-sharing octahedra in the b direction. [Alϕ 5 ] chains of octahedra are decorated by (PO 4 ) tetrahedra that share vertices with octahedra adjacent in the chain . These chains link in the c direction by sharing vertices between octahedra and tetrahedra to form an ordered layer of the form [Al 8 (PO 4 ) 8 F 8 (H 2 O) 8 ] . In the disordered layer, octahedra containing positionally disordered Cu 2+ , V 3+ , Al and □ (vacancy) share trans faces to form columns that link by sharing octahedron vertices to form ribbons extending in the c direction; the resulting layer has the form {(Cu 2 2+ □ 2 V 3+ ,Al) ∑6 (H 2 O) 12 (OH) 2 (H 2 O) x }, x ≈ 2 . The layers link in the b direction by sharing vertices between octahedra and tetrahedra. Although decorated chains topologically equivalent to that in nevadaite are common in many oxysalt minerals, its chain is geometrically distinct from those topologically equivalent chains. The M – M linkage along the [ M ϕ 5 ] chains in most minerals take place through trans vertices of the octahedra, with one example of linkage through cis vertices; in nevadaite, the M – M linkage involves both trans and cis vertices, as does the chain in slavíkite . In most of these decorated chains, alternate tetrahedra along the chain occur either in a trans or a cis arrangement. In nevadaite and slavíkite, the tetrahedra are arranged in both trans and cis arrangements; the arrangements in these two minerals are geometrically distinct, however.

Nevada↗
USGS2005

Foliation development and reaction softening by dissolution and precipitation in the transformation of granodiorite to orthogneiss, Glastonbury Complex, Connecticut, U.S.A

Textures, microstructures, and patterns of chemical zoning in minerals in a granodioritic orthogneiss in the Glastonbury Complex, Connecticut, lead to the interpretation that foliation development was facilitated by retrograde hydration reactions in the presence of an aqueous fluid. Incomplete replacement of the metastable magmatic minerals K-feldspar + hastingsite + magnetite produced foliation-defining biotite + epidote + quartz. These reaction products did not replace K-feldspar – hastingsite interfaces; rather, either biotite or epidote replaced the amphibole, and plagioclase replaced K-feldspar. Biotite and epidote precipitated syntectonically in discrete layers that define the foliation in the orthogneiss, whereas quartz precipitated primarily in ribbons, further enhancing the fabric. Metastable REE-rich igneous titanite also dissolved, and was incompletely replaced by REE-poor, Al-bearing metamorphic titanite. The similar concentrations of the REE in epidote and titanite show that the REE released by titanite dissolution were precipitated locally as the allanite component in adjacent grains of epidote. The entire process was syntectonic, with most grains showing multiple overgrowths in the direction of extension as defined by stretched xenoliths. Sufficient U was present in the titanite overgrowths to allow SHRIMP dating of cores, mantles, and rims. These results suggest at least three retrograde Alleghanian events of growth in a span of ~30 m.y. Thus the dissolution – transportation –precipitation process not only describes the reaction mechanism but also leads to the redistribution of reaction products into nearly monomineralic layers, thus contributing to metamorphic differentiation and to the development of the foliation. The resulting orthogneiss was much weaker that the granodiorite protolith, owing to this reaction and textural softening.

Connecticut↗
USGS2005

Terlinguacreekite, Hg2+3O2 Cl2, a new mineral species from the Perry pit, Mariposa mine, Terlingua mining district, Brewster County, Texas, U.S.A

Terlinguacreekite, ideally Hg 2+ 3 O 2 Cl 2 , has a very pronounced subcell that is orthorhombic, space-group choices Imam , Imcm , Ima 2 and I 2 cm , with unit-cell parameters refined from powder data: a 6.737(3), b 25.528(10), c 5.533(2) Å, V 951.6(6) Å 3 , a:b:c 0.2639:1:0.2167, Z = 8. The true symmetry, supercell unit-cell parameters, and details regarding the crystal structure are unknown. The strongest nine lines of the X-ray powder-diffraction pattern [ d in Å ( I )(subcell hkl )] are: 5.413(30)(011), 4.063(80)(121), 3.201(50)(080), 3.023(50)(161), 2.983(60)(240), 2.858(30)(211), 2.765(50)(002), 2.518(100b)(091, 251) and 2.026(30)(242). The mineral is found in an isolated area measuring approximately 1 × 0.5 m in the lower level of the Perry pit, Mariposa mine, Terlingua mining district, Brewster County, Texas (type locality), as mm-sized anhedral dark orange to reddish orange crusts of variable thickness on calcite, and rarely as 0.5 mm-sized aggregates of crystals of the same color. It has also been identified at the McDermitt mine, Humboldt County, Nevada, U.S.A., where it occurs with kleinite and calomel in silicified volcanic rocks and sediments. Terlinguacreekite is a secondary phase, most probably formed from the alteration of primary cinnabar or native mercury. At Terlingua, most crusts are thin, almost cryptocrystalline, with no discernable forms, and are resinous and translucent to opaque. Crystals are up to 0.2 mm in length, subhedral, acicular to prismatic, elongation [001], with a maximum length-to-width ratio of 4:1. They are vitreous, transparent, and some crystals have brightly reflecting faces, which may be {010} and {110}. The streak is yellow, and the mineral is brittle with an uneven fracture, no observable cleavage, and is soft, nonfluorescent under both long- and short-wave ultraviolet light. D (calc.) is 9.899 g/cm 3 (empirical formula). Material from the McDermitt mine is reversibly photosensitive, and turns from vivid orange to black in strong light. In reflected plane-polarized light, it is bluish grey, with very weak (in air) to distinct (in oil) bireflectance, nonpleochroic, and distinctly anisotropic, with colors masked by ubiquitous yellowish orange to orange internal reflections. Measured values of reflectance obtained in air and in oil are tabulated. Averaged results of electron-microprobe analysis give HgO 92.03, Cl 9.54, Br 1.22, sum 102.79, less O = Cl + Br 2.28, total 100.51 wt.%. The empirical formula is Hg 2+ 3.00 O 2.00 (Cl 1.90 Br 0.11 ) ∑2.01 , based on O + Cl + Br = 4 atoms per formula unit. The mineral name recalls the creek that flows through the Terlingua mining district and into the Rio Grande River.

Texas↗
USGS2005

Mineralogy and provenance of clays in miarolitic cavities of the Pikes Peak batholith, Colorado

Clay samples from 105 cavities within miarolitic granitic pegmatites throughout the Pikes Peak batholith, in Colorado, were analyzed by powder X-ray diffraction (XRD). Smectite (beidellite), illite, and kaolinite were found within the cavities. Calculation of crystallite-thickness distribution (CTD), mean thickness of the crystallites, and variance in crystallite thickness, as deduced from XRD patterns, allowed a determination of provenance and mode of formation for illite and smectite. Authigenic miarolitic-cavity illite and smectite show lognormal CTDs and larger mean thicknesses of crystallites than do their soil-derived counterparts; non-lognormal illite in a cavity results from mixing of cavity and soil illite. Analysis of mean thickness and thickness variance shows that crystal growth of illite is initiated by a nucleation event of short duration, followed by surface-controlled kinetics. Crystallization of the miarolitic cavity clays is presumed to occur by neoformation from hydrothermal fluids. The assessment of provenance allows a determination of regional and local distributions of clay minerals in miarolitic cavities within the Pikes Peak batholith.

Colorado↗
USGS2005

The composition of coexisting jarosite-group minerals and water from the Richmond mine, Iron Mountain, California

Jarosite-group minerals accumulate in the form of stalactites and fine-grained mud on massive pyrite in the D drift of the Richmond mine, Iron Mountain, California. Water samples were collected by placing beakers under the dripping stalactites and by extracting pore water from the mud using a centrifuge. The water is rich in Fe 3+ and SO 4 2− , with a pH of approximately 2.1, which is significantly higher than the extremely acidic waters found elsewhere in the mine. Electron-microprobe analysis and X-ray mapping indicate that the small crystals (<10 μm in diameter) are compositionally zoned with respect to Na and K, and include hydronium jarosite corresponding to the formula (H 3 O) 0.6 K 0.3 Na 0.1 Fe 3 3+ (SO 4 ) 2 (OH) 6 . The proton-microprobe analyses indicate that the jarosite-group minerals contain significant amounts of As, Pb and Zn, and minor levels of Bi, Rb, Sb, Se, Sn and Sr. Speciation modeling indicates that the drip waters are supersaturated with respect to jarosite-group minerals. The expected range in composition of jarosite-group solid-solution in equilibrium with the pore water extracted from the mud was found to be consistent with the observed range in composition.

California↗
USGS2008

Mineral chemistry and shrimp U-Pb Geochronology of mesoproterozoic polycrase-titanite veins in the sullivan Pb-Zn-Ag Deposit, British Columbia

Small polycrase-titanite veins 0.1-2 mm thick cut the tourmalinite feeder zone in the deep footwall of the Sullivan Pb-Zn-Ag deposit, southeastern British Columbia. Unaltered, euhedral crystals of polycrase and titanite 50-100 ??m in diameter are variably replaced by a finer-grained alteration-induced assemblage composed of anhedral polycrase and titanite with local calcite, albite, epidote, allanite, and thorite or uranothorite (or both). Average compositions of the unaltered and altered polycrase, as determined by electron-microprobe analysis, are (Y0.38 REE0.49 Th0.10 Ca0.04 Pb0.03 Fe0.01U0.01) (Ti1.48 Nb0.54 W0.04 Ta0.02)O6 and (Y0.42 REE0.32 Th0.15 U0.06 Ca0.04 Pb0.01 Fe0.01) (Ti1.57 Nb0.44 W0.04 Ta0.02)O6, respectively. The unaltered titanite has, in some areas, appreciable F (to 0.15 apfu), Y (to 0.40 apfu), and Nb (to 0.13 apfu). SHRIMP U-Pb geochronology of eight grains of unaltered polycrase yields a weighted 207Pb/206Pb age of 1413 ?? 4 Ma (2??) that is interpreted to be the age of vein formation. This age is 50-60 m.y. younger than the ca. 1470 Ma age of synsedimentary Pb-Zn-Ag mineralization in the Sullivan deposit, which is based on combined geological and geochronological data. SHRIMP ages for altered polycrase and titanite suggest later growth of minerals during the ???1370-1320 Ma East Kootenay and ???1150-1050 Ma Grenvillian orogenies. The 1413 ?? 4 Ma age for the unaltered polycrase in the veins records a previously unrecognized post-ore (<1470 Ma) and premetamorphic (>1370 Ma) mineralizing event in the Sullivan deposit and vicinity. The SHRIMP U-Pb age of the polycrase and high concentrations of REE, Y, Ti, Nb, and Th in the veins, together with elevated F in titanite and the absence of associated sulfides, suggest transport of these high-field-strength elements (HFSE) by F-rich and S-poor hydrothermal fluids unrelated to the fluids that formed the older Fe-Pb-Zn-Ag sulfide ores of the Sullivan deposit. Fluids containing abundant REE, HFSE, and F may have been derived from a geochemically specialized magma such as those that form alkaline granites, pegmatites, or carbonatites. In an alternative model. preferred here, these fluids were associated with a rift-related, crustal metasomatic event in the region. Determination of a Mesoproterozoic age for the polycrase-titanite veins establishes the first known occurrence of pre-Grenvillian REE-rich mineralization in the Belt-Purcell basin.

Canadian Mineralogist↗
USGS2009

The weathering of a sulfide orebody: Speciation and fate of some potential contaminants

Various potentially toxic trace elements such as As, Cu, Pb and Zn have been remobilized by the weathering of a sulfide orebody that was only partially mined at Leona Heights, California. As a result, this body has both natural and anthropogeni- cally modified weathering profiles only 500 m apart. The orebody is located in a heavily urbanized area in suburban Oakland, and directly affects water quality in at least one stream by producing acidic conditions and relatively high concentrations of dissolved elements (e.g., ??500 ??g/L Cu, ??3700 ??g/L Zn). Micrometric-scale mineralogical investigations were performed on the authigenic metal-bearing phases (less than 10 ??m in size) using electron-probe micro-analysis (EPMA), micro-Raman, micro X-ray absorption spectroscopy (??XAS), scanning X-ray diffraction ((??SXRD) and scanning X-ray fluorescence (??-SXRF) mapping techniques. Those measurements were coupled with classical mineralogical laboratory techniques, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Authigenic metal-bearing phases identified are mainly sulfates (jarosite, epsomite, schwertmannite), Fe (oxy-)hydroxides (goethite, hematite and poorly crystalline Fe products) and poorly crystalline Mn (hydr-)oxides. Sulfates and Fe (oxy-)hydroxides are the two main secondary products at both sites, whereas Mn (hydr-) oxides were only observed in the samples from the non-mining site. In these samples, the various trace elements show different affinities for Fe or Mn compounds. Lead is preferentially associated with Mn (hydr-)oxides and As with Fe (oxy-)hydroxides or sulfates. Copper association with Mn and Fe phases is questionable, and the results obtained rather indicate that Cu is present as individual Cu-rich grains (Cu hydroxides). Some ochreous precipitates were found at both sites and correspond to a mixture of schwertmannite, goethite and jarosite containing some potentially toxic trace elements such as Cu, Pb and Zn. According to the trace element distribution and relative abundance of the unweathered sulfides, this orebody still represents a significant reservoir of potential contaminants for the watershed, especially at the non-mining site, as a much greater proportion of sulfides is left to react and because of the lower porosity at this site.

Canadian Mineralogist↗
USGS2009

Characterization of flux-grown Trace-element-doped titanite using the high-mass-resolution ion microprobe (SHRIMP-RG)

Crystals of titanite can be readily grown under ambient pressure from a mixture of CaO, TiO 2 and SiO 2 in the presence of molten sodium tetraborate. The crystals produced are euhedral and prismatic, lustrous and transparent, and up to 5 mm in length. Titanite obtained by this method contains approximately 4300 ppm Na and 220 ppm B contributed from the flux. In addition to dopant-free material, titanite containing trace alkali and alkaline earth metals (K, Sr, Ba), transition metals (Sc, Cr, Ni, Y, Zr, Nb, Hf and Ta), rare-earth elements (REE), actinides (Th, U) and p-block elements (F, S, Cl, Ge, Sn and Pb) have been prepared using the same procedure. Back-scattered electron (BSE) imaging accompanied by ion-microprobe (SHRIMP-RG) analysis confirms significant incorporation of selected trace-elements at structural sites. Regardless of some zonation, the large size of the crystals and broad regions of chemical homogeneity make these crystals useful as experimental starting material, and as matrix-matched trace-element standards for a variety of microbeam analytical techniques where amorphous titanite glass, heterogeneous natural titanite or a non-titanite standard may be less than satisfactory. Trace-element-doped synthetic crystals can also provide a convenient proxy for a better understanding of trace-element incorporation in natural titanite. Comparisons with igneous, authigenic and high-temperature metasomatic titanite are examined. The use of high-mass-resolution SIMS also demonstrates the analytical challenges inherent to any in situ mass-spectrometry-based analysis of titanite, owing to the production of difficult-to-resolve molecular interferences. These interferences are dominated by Ca-Ca, Ca-Ti and Ti-Ti dimers that are significant in the mass range of 80-100, affecting all isotopes of Sr and Zr, as well as 89 Y and 93 Nb. Methods do exist for the evaluation of interferences by these dimers and of polyatomic interferences on the LREE.

Canadian Mineralogist↗
USGS2011

Fluid sources and metallogenesis in the Blackbird Co-Cu-Au-Bi-Y-REE district, Idaho, U.S.A.: Insights from major-element and boron isotopic compositions of tourmaline

Tourmaline is a widespread mineral in the Mesoproterozoic Blackbird Co–Cu–Au–Bi–Y–REE district, Idaho, where it occurs in both mineralized zones and wallrocks. We report here major-element and B-isotope compositions of tourmaline from stratabound sulfide deposits and their metasedimentary wallrocks, from mineralized and barren pipes of tourmaline breccia, from late barren quartz veins, and from Mesoproterozoic granite. The tourmalines are aluminous, intermediate in the schorl–dravite series, with Fe/(Fe + Mg) values of 0.30 to 0.85, and 10 to 50% X -site vacancies. Compositional zoning is prominent only in tourmaline from breccias and quartz veins; crystal rims are enriched in Mg, Ca and Ti, and depleted in Fe and Al relative to cores. The chemical composition of tourmaline does not correlate with the presence or absence of mineralization. The δ 11 B values fall into two groups. Isotopically light tourmaline (−21.7 to −7.6‰) occurs in unmineralized samples from wallrocks, late quartz veins and Mesoproterozoic granite, whereas heavy tourmaline (−6.9 to +3.2‰) is spatially associated with mineralization (stratabound and breccia-hosted), and is also found in barren breccia. At an inferred temperature of 300°C, boron in the hydrothermal fluid associated with mineralization had δ 11 B values of −3 to +7‰. The high end of this range indicates a marine source of the boron. A likely scenario involves leaching of boron principally from marine carbonate beds or B-bearing evaporites in Mesoproterozoic strata of the region. The δ 11 B values of the isotopically light tourmaline in the sulfide deposits are attributed to recrystallization during Cretaceous metamorphism, superimposed on a light boron component derived from footwall siliciclastic sediments ( e.g. , marine clays) during Mesoproterozoic mineralization, and possibly a minor component of light boron from a magmatic–hydrothermal fluid. The metal association of Bi–Be–Y–REE in the Blackbird ores suggests some magmatic input, but involvement of granite-derived fluids cannot be conclusively established from the present database.

Canadian Mineralogist↗
USGS2014

The global age distribution of granitic pegmatites

An updated global compilation of 377 new and previously published ages indicates that granitic pegmatites range in age from Mesoarchean to Neogene and have a semi-periodic age distribution. Undivided granitic pegmatites show twelve age maxima: 2913, 2687, 2501, 1853, 1379, 1174, 988, 525, 483, 391, 319, and 72 Ma. These peaks correspond broadly with various proxy records of supercontinent assembly, including the age distributions of granites, detrital zircon grains, and passive margins. Lithium-cesium-tantalum (LCT) pegmatites have a similar age distribution to the undivided granitic pegmatites, with maxima at 2638, 1800, 962, 529, 485, 371, 309, and 274 Ma. Lithium and Ta resources in LCT pegmatites are concentrated in the Archean and Phanerozoic. While there are some Li resources from the Proterozoic, the dominantly bimodal distribution of resources is particularly evident for Ta. This distribution is similar to that of orogenic gold deposits, and has been interpreted to reflect the preservation potential of the orogenic belts where these deposits are formed. Niobium-yttrium-fluorine (NYF) pegmatites show similar age distributions to LCT pegmatites, but with a strong maximum at ca. 1000 Ma.

Canadian Mineralogist↗
USGS1982

Palladium, platinum, rhodium, iridium and ruthenium in chromite- rich rocks from the Samail ophiolite, Oman.

30 samples of chromitite and chromite-rich rocks from two stratigraphic sections, 250 km apart, through the basal ultramafic member of the Samail ophiolite were spectrographically analysed for platinum-group elements (PGE) and for Co, Cu, Ni and V. These data are reported as are Cr/(Cr + Al), Mg/(Mg + Fe) and wt.% TiO2 for most samples. The chromitite occurs as pods or lenses in rocks of mantle origin or as discontinuous layers at the base of the overlying cumulus sequence. PGE abundances in both sections are similar, with average contents in chromite-rich rocks: Pd 8 ppb, Pt 14 ppb, Rh 6 ppb, Ir 48 ppb and Ru 135 ppb. The PGE data, combined with major-element and petrographic data on the chromitite, suggest: 1) relatively larger Ir and Ru contents and highest total PGE in the middle part of each section; 2) PGE concentrations and ratios do not correlate with coexisting silicate and chromite abundances or chromite compositions; 3) Pd/PGE, on average, increases upward in each section; 4) Samail PGE concentrations, particularly Rh, Pt and Pd, are lower than the average values for chromite-rich rocks in stratiform intrusions. 2) suggests that PGEs occur in discrete alloy or sulphide phases rather than in the major oxides or silicates, and 4) suggests that chromite-rich rocks from the oceanic upper mantle are depleted in PGE with respect to chondrites. L.C.C.

Canadian Mineralogist↗
USGS1985

Abhurite, a new tin hydroxychloride mineral, and a comparative study with a synthetic basic tin chloride.

Abhurite is a new mineral species found in blister-like protuberances on the surface of tin ingots submerged at a depth of 35 m in the Red Sea. It forms 1.5 mm diameter hexagonal plates bounded by the negative rhombohedron (0115); is colourless, transparent with opalescent lustre, white streak, hackly fracture, with no cleavage, and H.approx 2; D(calc) 4.34, D(meas) 4.29 g/cm3; epsilon approx 2.11, omega 2.06. Chemical analysis gave 73.4 wt.% Sn, 15.7 Cl, 11.0 0 and 0.4 H. leading to the formula Sn3O(OH)2Cl2. DTA shows release of H2O at 235oC and SnCl2 at 525oC. Indexed XRD powder data are tabulated; prominent lines 2.5313(100), 2.8915(70), 4.139(50), 3.404(50), 2.8175(50) A; a 10.0175(3), c 44.014(2) A; space group R3m, R3m or R32; Z = 21. Comparison is made with a hexagonal synthetic dimorph. The name refers to the geographical origin, an arm of the Red Sea known as Sharm Abhur.-L.T.T.

Canadian Mineralogist↗
USGS1985

Durangite from the Black Range, New Mexico, and new data on durangite from Durango and Cornwall.

Durangite, associated with cassiterite, hematite, quartz, tridymite, cristobalite and clinopyroxene, occurs in small veinlets within flows, ash-flow tuffs and lithic tuffs in a tin mine near Boiler Peak, New Mexico. It is clear to semi-translucent, pale yellow-orange to medium orange-red with a vitreous lustre, pale yellow streak; H. 5-5.5%; irregular to conchoidal fracture and a good (110) cleavage; elongate along c with (110), (010), (021) and (111) the prominent forms; Dmeas 3.90, Dcalc 3.92 g/cm3; alpha medium yellow orange 1.634(3), beta pale yellow orange 1.663(3), gamma colourless 1.685(3); weak to moderate dispersion r < v. The structural formula is: (Na0.93Li0.07)SIGMA 1.00(Al0.89Fe0.07Mn0.06)SIGMA 1.02As0.99O4(F0.90(OH)0.07)SIGMA 0.97. Indexed XRD powder data are tabulated; a 6.574(1), b 8.505(2), c 7.019(1) A, beta 115.34o; space group C2/c; Z = 4. Additional X-ray and chemical data on durangite from Durango and Cornwall are also included.-L.T.T.

Canadian Mineralogist↗
USGS1984

PALLADIUM, PLATINUM, RHODIUM, RUTHENIUM AND IRIDIUM IN PERIDOTITES AND CHROMITITES FROM OPHIOLITE COMPLEXES IN NEWFOUNDLAND.

Samples of spinel lherzolite, harzburgite, dunite, and chromitite from the Bay of Islands, Lewis Hills, Table Mountain, Advocate, North Arm Mountain, White Hills Periodite Point Rousse, Great Bend and Betts Cove ophiolite complexes in Newfoundland were analyzed for the platinum-group elements (PGE) Pd, Pt, Rh, Ru and Ir. The ranges of concentration (in ppb) observed for all rocks are: less than 0. 5 to 77 (Pd), less than 1 to 120 (Pt), less than 0. 5 to 20 (Rh), less than 100 to 250 (Ru) and less than 20 to 83 (Ir). Chondrite-normalized PGE ratios suggest differences between rock types and between complexes. Samples of chromitite and dunite show relative enrichment in Ru and Ir and relative depletion in Pt and Pd.

Canadian Mineralogist↗