Origin of mineralizing fluids of the sediment-hosted Navachab gold mine, Namibia: Constraints from stable (O, H, C, S) isotopes

The Navachab gold mine in the Damara belt of central Namibia is characterized by a polymetallic Au-Bi-As-Cu-Ag ore assemblage, including pyrrhotite, chalcopyrite, sphalerite, arsenopyrite, bismuth, gold, bismuthinite, and bismuth tellurides. Gold is hosted by quartz sulfide veins and semimassive sulfide lenses that are developed in a near-vertical sequence of shelf-type metasedimentary rocks, including marble, calcsilicate rock, and biotite schist. The sequence has been intruded by abundant syntectonic lamprophyre, aplite, and pegmatite dikes, documenting widespread igneous activity coeval with mineralization. The majority of quartz from the veins has delta(18)O values of 14 to 15 per mil (V-SMOW). The total variations in delta(18)O values of the biotite schist and calcsilicate rock are relatively small (12-14 parts per thousand), whereas the marble records steep gradients in delta(18)O values (17-21 parts per thousand), the lowest values being recorded at the vein margins. Despite this, there is no correlation between delta(18)O and delta(13)C values and the carbonate content of the rocks, indicating that fluid-rock interaction alone cannot explain the isotopic gradients. In addition, the marble records increased delta(13)C values at the contact to the veins, possibly related to a change in the physicochemical conditions during fluid-rock interaction. Gold is interpreted to have precipitated in equilibrium with metamorphic find (delta(18)O 12-14 parts per thousand; delta D = -40 to -60 parts per thousand) at peak metamorphic conditions of ca. 550 degrees C and 2 kbars, consistent with isotopic fractionations between coexisting calcite, garnet, and clinopyroxene in the alteration halos. The most likely source of the mineralizing fluid was a midcrustal fluid in equilibrium with the Damaran metapelites that underwent prograde metamorphism at amphibolite- to granulite-facies grades. Although there is no isotopic evidence for the contribution of magmatic fluids, they may have been important in contributing to the overall hydraulic regime and high apparent geothermal gradients (ca. 80 degrees C/km(-1)) in the mine area.

Mineralization of the Bonanza Mine

The Bonanza mine of the Emery mining district in Powell County is on the largest veins in the area, and is developed to a depth of 680 feet by an incline shaft following the dip of the structure. Sulfide ores carrying gold and silver values are mined throughout the area which is easily accessible by road from Deerlodge, Montana, ten miles west of the district.

40ar/39ar Dating of alunite from the Pueblo Viejo Gold-Silver District, Dominican Republic

New 40Ar/39Ar ages for alunite from the Moore and Monte Negro deposits in the Pueblo Viejo district, as well as from a newly discovered alunite-bearing zone on Loma la Cuaba west of the known deposits, are reported here. The ages range from about 80 to 40 Ma, with closely adjacent samples exhibiting very different ages. Interpretation of these results in the context of estimated closure temperatures for alunite and the geologic and tectonic evolution of Hispaniola does not lead to a simple conclusion about the age of mineralization. The simplest interpretation, that mineralization was caused by a buried Late Cretaceous (~80 Ma) intrusion, is complicated by lack of intrusions of this age in the area and absence of alteration in overlying limestone. The alternative interpretation, that mineralization was formed during Early Cretaceous (~110 Ma) magmatism and that the 40Ar/39Ar ages were completely reset by Late Cretaceous thrusting, is complicated by a lack of information on the timing and thermal effects of thrusting in central Hispaniola. Alunite studies have yielded similar unclear results in other pre-Cenozoic ore systems, notably those of the Lachlan fold belt in Australia

ELA-ICP-MS U-Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu-Au deposit: implications for porphyry-related mineralization

ELA-ICP-MS U-Pb zircon geochronology has been used to show that the porphyritic intrusions related to the formation of the Bajo de la Alumbrera porphyry Cu-Au deposit, NW Argentina, are cogenetic with stratigraphically well-constrained volcanic and volcaniclastic rocks of the Late Miocene Farallon Negro Volcanic Complex. Zircon geochronology for intrusions in this deposit and the host volcanic sequence show that multiple mineralized porphyries were emplaced in a volcanic complex that developed over 1.5 million years. Volcanism occurred in a multivent volcanic complex in a siliciclastic intermontane basin. The complex evolved from early mafic-intermediate effusive phases to a later silicic explosive phase associated with mafic intrusions. Zircons from the basal mafic-intermediate lavas have ages that range from 8.46 +/- 0.14 to 7.94 +/- 0.27 Ma. Regionally extensive silicic explosive volcanism occurred at similar to8.0 Ma (8.05 +/- 0.13 and 7.96 +/- 0.11 Ma), which is co-temporal with intrusion of the earliest mineralized porphyries at Bajo de la Alumbrera (8.02 +/- 0.14 and 7.98 +/- 0.14 Ma). Regional uplift and erosion followed during which the magmatic-hydrothermal system was probably unroofed. Shortly thereafter, dacitic lava domes were extruded (7.95 +/- 0.17 Ma) and rhyolitic diatremes (7.79 +/- 0.13 Ma) deposited thick tuff blankets, across the region. Emplacement of large intermediate composition stocks occurred at 7.37 +/- 0.22 Ma, shortly before renewed magmatism occurred at Bajo de la Alumbrera (7.10 +/- 0.07 Ma). The latest porphyry intrusive event is temporally associated with new ore-bearing magmatic-hydrothermal fluids. Other dacitic intrusions are associated with subeconomic deposits that formed synchronously with the mineralized porphyries at Bajo de la Alumbrera. However, their emplacement continued (from 7.10 +/- 0.06 to 6.93 +/- 0.07 Ma) after the final intrusion at Bajo de al Alumbrera. Regional volcanism had ceased by 6.8 Ma (6.92 +/- 0.07 Ma). The brief history of the volcanic complex hosting the Bajo de la Alumbrera Cu-Au deposit differs from that of other Andean provinces hosting porphyry deposits. For example, at the El Salvador porphyry copper district in Chile, magmatism related to Cu mineralization was episodic in regional igneous activity that occurred over tens of millions of years. Bajo de la Alumbrera resulted from the superposition of multiple porphyry-related hydrothermal systems, temporally separated by a million years. It appears that the metal budget in porphyry ore deposits is not simply a function of their longevity and/or the superposition of multiple porphyry systems. Nor is it a function of the duration of the associated cycle of magmatism. Instead, the timing of processes operating in the parental magma body is the controlling factor in the formation of a fertile porphyry-related ore system.

Bajo de la Alumbrera copper-gold deposit: Stable isotope evidence for a porphyry-related hydrothermal system dominated by magmatic aqueous fluids

Alteration zones at the gold-rich Bajo de la Alumbrera porphyry copper deposit in northwestern Argentina are centered on several porphyritic intrusions. They are zoned from a central copper-iron sulfide and gold-mineralized potassic (biotite-K-feldspar +/- quartz) core outward to propylitic (chlorite-illite-epidote-calcite) assemblages. A mineralized intermediate argillic alteration assemblage (chlorite-illite +/- pyrite) has overprinted the potassic alteration zone across the top and sides of the deposit and is itself zoned outward into phyllic (quartzinuscovite-illite +/- pyrite) alteration. This study contributes new data to previously reported delta(18)O and delta D compositions of fluids responsible for the alteration at Bajo de la Alumbrera, and the data are used to infer likely ore-forming processes. Measured and calculated delta(18)O and delta D values of fluids (+8.3 to +10.2 and -33 to -81 parts per thousand, respectively) confirm a primary magmatic origin for the earliest potassic alteration phase. Lower temperature potassic alteration formed from magmatic fluids with lower delta D values (down to -123 parts per thousand). These depleted compositions are distinct from meteoric water and consistent with degassing and volatile exsolution of magmatic fluids derived from an underlying magma. Variability in the calculated composition of fluid associated with potassic alteration is explained in terms of phase separation (or boiling). if copper-iron sulfide deposition occurred during cooling (as proposed elsewhere), this cooling was largely a result of phase separation. Magmatic water was directly involved in the formation of overprinting intermediate argillic alteration assemblages at Bajo de la Alumbrera. Calculated delta(18)O and delta D values of fluids associated with this alteration range from +4.8 to +8.1 and -31 to -71 per mil, respectively Compositions determined for fluids associated with phyllic alteration (-0.8 to +10.2 and -31 to -119 parts per thousand) overlap with the values determined for the intermediate argillic alteration. We infer that phyllic alteration assemblages developed during two stages; the first was a high-temperature (400 degrees-300 degrees C) stage with D-depleted water (delta D = -66 to -119 parts per thousand). This compositional range may have resulted from magma degassing and/or the injection of new magmatic water into a compositionally evolved hydrothermal system. The isotopic variations also can be explained by increased fluid-rock interaction. The second stage of phyllic alteration occurred at a lower temperature (similar to 200 degrees C), and variations in the modeled isotopic compositions imply mixing of magmatic and meteoric waters. Ore deposition that occurred late in the evolution of the hydrothermal system was probably associated with further cooling of the magmatic fluid, in part caused by fluid-rock interaction and phase separation. Changing pH and/or oxygen fuoracity may have caused additional ore deposition. The ingress of meteoric water appears to postdate the bulk of mineralization and occurred as the system at Bajo de la Alumbrera waned.

Sonophotocatalytic mineralization of Norflurazon in aqueous environment

Norflurazon (4-chloro-5-(methylamino)-2-[3- trifluoromethyl)phenyl]pyridazin-3(2H)-one; C12H9ClF3N3O) is an excellent weed controlling agent being practiced in the agricultural lands. The excessive addition or the undissolved Norflurazon (maximum solubility 28 mg/L at 25 C) enters into the aquatic environment and causes the adverse effects associated with its high concentration. To avoid the perilous effects, visible light assisted photocatalysis set-up coupled with the 42 kHz ultrasound producing bath type sonicator is used to completely mineralize the Norflurazon. TiO2, ZnO and gold loaded zinc oxide nanocatalysts were utilized to study the mineralization of Norflurazon. AueZnO shows the greater efficiency for the sonophotocatalytic removal of Norflurazon among the various nanocatalysts employed to study the mineralization. The order of Norflurazon mineralization was sonophotocatalysis > sonocatalysis > photocatalysis. The additive effect was achieved for the sonophotocatalytic degradation. The high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometric (LCMS) analyses were employed to identify the various intermediates produced during the mineralization. The identification of four pseudo molecular ions and various intermediates using the LCMS analysis evidently suggests the sonophotocatalytic degradation was preceded in various decay pathways. A suitable mechanism has been proposed for the sonophotocatalytic mineralization of Norflurazon

Photoluminescence enhancement by gold nanoparticles in Eu(3+) doped GeO(2)-Bi(2)O(3) glasses

We report large photoluminescence (PL) enhancement in Eu(3+)-doped GeO(2)-Bi(2)O(3) glasses containing gold nanoparticles (NPs). Growth of approximate to 1000% in the PL intensity corresponding to the Eu(3+) transition (5)D(0)->(7)F(2), at 614 nm, was observed in comparison with a reference sample that does not contain gold NPs. Other PL bands from 580 to 700 nm are also enhanced. The enhancement of the PL intensity is attributed to the increased local field in the Eu(3+) locations due to the presence of the NPs and the energy transfer from the excited NPs to the Eu(3+) ions.

Structure of disordered gold-polymer thin films using small angle x-ray scattering

We have investigated the structure of disordered gold-polymer thin films using small angle x-ray scattering and compared the results with the predictions of a theoretical model based on two approaches-a structure form factor approach and the generalized Porod law. The films are formed of polymer-embedded gold nanoclusters and were fabricated by very low energy gold ion implantation into polymethylmethacrylate (PMMA). The composite films span (with dose variation) the transition from electrically insulating to electrically conducting regimes, a range of interest fundamentally and technologically. We find excellent agreement with theory and show that the PMMA-Au films have monodispersive or polydispersive characteristics depending on the implanted ion dose. (C) 2010 American Institute of Physics. [doi:10.1063/1.3493241]

Surface plasmon resonance of gold nanoparticles formed by cathodic arc plasma ion implantation into polymer

Shallow subsurface layers of gold nanoclusters were formed in polymethylmethacrylate (PMMA) polymer by very low energy (49 eV) gold ion implantation. The ion implantation process was modeled by computer simulation and accurately predicted the layer depth and width. Transmission electron microscopy (TEM) was used to image the buried layer and individual nanoclusters; the layer width was similar to 6-8 nm and the cluster diameter was similar to 5-6 nm. Surface plasmon resonance (SPR) absorption effects were observed by UV-visible spectroscopy. The TEM and SPR results were related to prior measurements of electrical conductivity of Au-doped PMMA, and excellent consistency was found with a model of electrical conductivity in which either at low implantation dose the individual nanoclusters are separated and do not physically touch each other, or at higher implantation dose the nanoclusters touch each other to form a random resistor network (percolation model). (C) 2009 American Vacuum Society. [DOI: 10.1116/1.3231449]

Structural properties of buried conducting layers formed by very low energy ion implantation of gold into polymer

We have investigated the fundamental structural properties of conducting thin films formed by implanting gold ions into polymethylmethacrylate (PMMA) polymer at 49 eV using a repetitively pulsed cathodic arc plasma gun. Transmission electron microscopy images of these composites show that the implanted ions form gold clusters of diameter similar to 2-12 nm distributed throughout a shallow, buried layer of average thickness 7 nm, and small angle x-ray scattering (SAXS) reveals the structural properties of the PMMA-gold buried layer. The SAXS data have been interpreted using a theoretical model that accounts for peculiarities of disordered systems.

Gold-implanted shallow conducting layers in polymethylmethacrylate

PMMA (polymethylmethacrylate) was ion implanted with gold at very low energy and over a range of different doses using a filtered cathodic arc metal plasma system. A nanometer scale conducting layer was formed, fully buried below the polymer surface at low implantation dose, and evolving to include a gold surface layer as the dose was increased. Depth profiles of the implanted material were calculated using the Dynamic TRIM computer simulation program. The electrical conductivity of the gold-implanted PMMA was measured in situ as a function of dose. Samples formed at a number of different doses were subsequently characterized by Rutherford backscattering spectrometry, and test patterns were formed on the polymer by electron beam lithography. Lithographic patterns were imaged by atomic force microscopy and demonstrated that the contrast properties of the lithography were well maintained in the surface-modified PMMA.

Conducting polymer formed by low energy gold ion implantation

A buried conducting layer of metal/polymer nanocomposite was formed by very low energy gold ion implantation into polymethylmethacrylate. The conducting layer is similar to 3 nm deep and of width similar to 1 nm. In situ resistivity measurements were performed as the implantation proceeded, and the conductivity thus obtained as a function of buried gold concentration. The measured conductivity obeys the behavior well established for composites in the percolation regime. The critical concentration, below which the polymer remains an insulator, is attained at a dose similar to 1.0 x 10(16) atoms/cm(2) of implanted gold ions. (C) 2008 American Institute of Physics.

High performance magnetic separation of gold nanoparticles for catalytic oxidation of alcohols

We present the magnetic separation approach to facilitate the recovery of gold nanoparticle (AuNP) catalysts. The use of magnetically recoverable supports for the immobilization of AuNPs instead of traditional oxides, polymers or carbon based solids guarantees facile, clean, fast and efficient separation of the catalyst at the end of the reaction cycle. Magnetic separation can be considered an environmentally benign separation approach, since it minimizes the use of auxiliary substances and energy for achieving catalyst recovery. The catalyst preparation is based on the immobilization of Au(3+) on the surface of core-shell silica-coated magnetite nanoparticles, followed by metal reduction using two different methods. AuNPs were prepared by thermal reduction in air and by hydrogen reduction at mild temperature. Interestingly, the mean particle size of the supported AuNPs was similar (ca. 5.9 nm), but the polydispersity of the samples is quite different. The catalytic activity of both catalysts in the aerobic oxidation of alcohols was investigated and a distinct selectivity for benzyl alcohol oxidation was observed.

Clean preparation of methyl esters in one-step oxidative esterification of primary alcohols catalyzed by supported gold nanoparticles

Methyl esters were prepared by the clean, one-step catalytic esterification of primary alcohols using molecular oxygen as a green oxidant and a newly developed SiO(2)-supported gold nanoparticle catalyst. The catalyst was highly active and selective in a broad range of pressure and temperature. At 3 atm O(2) and 130 degrees C benzyl alcohol was converted to methyl benzoate with 100% conversion and 100% selectivity in 4 h of reaction. This catalytic process is much ""greener"" than the conventional reaction routes because it avoids the use of stoichiometric environmentally unfriendly oxidants, usually required for alcohol oxidation, and the use of strong acids or excess of reactants or constant removal of products required to shift the equilibrium to the desired esterification product.

Cold nuclear matter effects on J/psi production as constrained by deuteron-gold measurements at root S(NN)=200 GeV

We present a new analysis of J/psi production yields in deuteron-gold collisions at root s(NN) =200 GeV using data taken from the PHENIX experiment in 2003 and previously published in S. S. Adler [Phys. Rev. Lett 96, 012304 (2006)]. The high statistics proton-proton J/psi data taken in 2005 are used to improve the baseline measurement and thus construct updated cold nuclear matter modification factors (R(dAu)). A suppression of J/psi in cold nuclear matter is observed as one goes forward in rapidity (in the deuteron-going direction), corresponding to a region more sensitive to initial-state low-x gluons in the gold nucleus. The measured nuclear modification factors are compared to theoretical calculations of nuclear shadowing to which a J/psi (or precursor) breakup cross section is added. Breakup cross sections of sigma(breakup)=2.8(-1.4)(+1.7) (2.2(-1.5)(+1.6)) mb are obtained by fitting these calculations to the data using two different models of nuclear shadowing. These breakup cross-section values are consistent within large uncertainties with the 4.2 +/- 0.5 mb determined at lower collision energies. Projecting this range of cold nuclear matter effects to copper-copper and gold-gold collisions reveals that the current constraints are not sufficient to firmly quantify the additional hot nuclear matter effect.