Transport Of Gold Research Articles

Comparison of forward and reverse single-file reciprocation for root canal instrumentation in curved mandibular molar canals - a Micro-CT analysis

ABSTRACT To compare (i) canal centering ability and transportation of Primary WaveOne Gold in combination with WaveOne Gold Glider with ProTaper Next X2 in combination with ProGlider using Micro-CT, and (ii) difference in final preparation times between these two preparation groups. Mesiobuccal canals of 50 mandibular first molars were used. Teeth were randomly divided into two preparation groups. Results were analysed using a one-way analysis of variance (ANOVA). Apically, ProGlider/ProTaper Next X2 demonstrated better centering ratio values and lower transportation values compared to WaveOne Gold Glider/Primary WaveOne Gold (p<.05). No differences were found in the mean combined centering ratios and transportation values between groups (p>.05). No statistically significant differences between the canal preparation times were found (p<.06). The combination of ProGlider /ProTaper Next X2 yields better results for transportation and centering ability apically compared to WaveOne Gold Glider in combination with Primary Wave-One Gold. Keywords: Centering ability, ProTaper Next, reciprocation, transportation, WaveOne Gold.

Comparative evaluation of canal transportation, centering ability, and dentin removal between ProTaper Gold, One Curve, and Profit S3: An in vitro study.

Aim:The aim of the study was to compare the canal transportation, centering ability, and dentin removal of Profit S3 (PS3), One Curve (OC), and ProTaper Gold (PTG) systems using cone-beam computed tomography (CBCT).Materials and Methods:Thirty extracted human single-rooted premolars were used in the present study. Preinstrumentation scanning of all the teeth in arch form was taken using CBCT. To increase standardization, crowns were removed and only teeth measuring 16 mm were included in the study. The samples were randomly divided into three groups, with ten samples in each group; Group I was instrumented with PS3, Group II was instrumented with OC, and Group III – PTG. Postinstrumentation scans were performed, and the two scans were compared to determine canal transportation, centering ability, and dentin removal at 3, 6, and 9 mm, from the apex.Statistical Analysis:One-way-ANOVA and the independent t-test were done for the pairwise comparison. The significance level was set at P = 0.05; statistical analysis was performed with SPSS statistics version 20.0 (SPSS Inc., Chicago, IL, USA).Results:The mean canal centering ratio and canal apical transportation for PS3, OC and PTG show no statistical difference (P > 0.05). The mean value of dentin removal showed a statistically significant difference between the three groups (P < 0.05). PS3 and OC rotary file showed less removal of dentin compared to PTG (P < 0.00).Conclusion:It was evident that PS3, OC, and PTG had no statistically significant difference when analyzed based on canal transportation and canal centering ratio. However, there was a significant difference among the three groups comparing the removal of dentin. PS3 and OC rotary file showed less removal of dentin compared to PTG.

Formation of Au-Bearing Antigorite Serpentinites and Magnetite Ores at the Massif of Ophiolite Ultramafic Rocks: Thermodynamic Modeling

We constructed thermodynamic models of the formation of two types of gold-ore mineralization at the Kagan ultramafic massif in the Southern Urals (Russia). The first type of gold-mineralization is widely spread at the massif in the tectonic zones of schistose serpentinites containing typically ≤ 0.1 ppm Au. The second type of gold-ore mineralization is represented by veined massive, streaky and impregnated magnetite ores in contact with serpentinites. It contains to 5 vol.% sulfides and 0.2–1.2 ppm Au. Our thermodynamic calculations explain the formation of two types of gold-ore mineralization in the bedrocks of ultramafic massifs. Metamorphic water, which is the result of the dehydration of early serpentinites (middle Riphean) during high-temperature regional metamorphism (700 °C, 10 kbar) (late Precambrian), is considered as the source of ore-bearing fluid in the models. The metasomatic interaction of metamorphic fluid with serpentinites is responsible for the gold-poor mineralization of the 1st type at T = 450–250 °C and P = 2.5–0.5 kbar. The hydrothermal gold-rich mineralization of the 2nd type was formed during mixing of metamorphic and meteoric fluids at T = 500–400 °C and P = 2–3 kbar and discharge of mixed fluid in the open space of cracks in serpentinites. The model calculations showed that the dominant forms of gold transport in fluids with pH = 3–5 are AuCl2− complexes (≥450 °C) and, as the temperature decreases, AuHS0, or AuOH0. Mineral associations obtained in model calculations are in general similar to the observed natural types of gold mineralization.

Mechanistic investigation of facilitated transport of gold(III) from HCl media using ionic liquid Cyphos IL102 as carrier across a supported liquid membrane

The transport of gold(III) across a supported liquid membrane containing the ionic liquid Cyphos IL102 (trihexyl(tetradecyl)phosphonium bromide) in Solvesso 100 has been investigated. The investigation was carried out under various experimental variables affecting to the transport process: stirring speed in the aqueous feed solution, HCl and gold(III) concentrations in this same phase, and carrier concentration in the membrane phase. The transport of gold(III) was compared against the transport of Fe(III), Cu(II), and Ni(II) from aqueous solutions containing the four elements, whereas the performance of Cyphos IL102 was compared, with respect to the gold transport, against other potential carriers for gold(III) from this acidic medium. Gold can be recovered in the strip solution as zero valent gold nanoparticles.

Improved transport of gold(I) from aurocyanide solution using a green ionic liquid-based polymer inclusion membrane with in-situ electrodeposition

Ionic liquid-based polymer inclusion membranes (PIMs) are an environmentally benign separation technology. PIMs are especially suitable for separation of dilute substances, but their application is hindered by their relatively low permeability rate. In this paper, a novel ionic liquid-based PIM system integrated with an electroplating unit was developed to improve the permeability of gold from aurocyanide solutions. Under the optimal conditions, 98.6% of gold(I) was transported, and more than 96.4% of gold was simultaneously deposited on the copper cathode. The gold(I) transport rate was considerably enhanced with in-situ electrodeposition of gold in the stripping phase. With a constant voltage of 1.50V applied to the stripping solution, the permeability coefficient increased from 9.25×10−6m/s (with no voltage) to 21.5×10−6m/s (with voltage). SEM and EDX analysis show metallic state gold was coated evenly on the surface of the electrode. Results of a stability evaluation experiment show that the PIM can be operated stably for 10 cycles on a continuous run mode. The method of simultaneous transport and in-situ electrodeposition expands the application of the PIM technology for separation, which shows good prospects for the removal and recovery metal ions.

An essential role for sulfur in sulfide-silicate melt partitioning of gold and magmatic gold transport at subduction settings

Sulfide-silicate melt partitioning controls the behavior of gold in magmas, which is critical for understanding the Earth's deep gold cycle and formation of gold deposits. However, the mechanisms that control the sulfide-silicate melt partitioning of gold remain largely unknown. Here we present constraints from laboratory experiments on the partition coefficient of gold between monosulfide-solid-solution (MSS) and silicate melt (DAuMSS/SM) under conditions relevant for magmatism at subduction settings. Thirty-five experiments were performed in Au capsules to determine DAuMSS/SM at 950-1050°C, 0.5-3 GPa, oxygen fugacity (fO2) of ∼FMQ-1.7 to FMQ+2.7 (FMQ refers to the fayalite-magnetite-quartz buffer), and sulfur fugacity (fS2) of −2.2 to 2.1, using a piston cylinder apparatus. The silicate melt composition changes from dry to hydrous andesite to rhyolite. The results obtained from electron microprobe and laser-ablation ICP-MS analyses show that the gold solubility in silicate melts ranges from 0.01 to 55.3 ppm and is strongly correlated with the melt sulfur content [S]melt at fO2 of ∼FMQ-1.7 to FMQ+1.6, which can be explained by the formation of complex Au-S species in the silicate melts. The gold solubility in MSS ranges from 130 to 2800 ppm, which is mainly controlled by fS2. DAuMSS/SM ranges from 10 to 14000 at fO2 of ∼FMQ-1.7 to FMQ+1.6, the large variation of which can be fully explained by combined [S]melt and fS2. Therefore, all of the parameters that can directly affect [S]melt and fS2, such as alkali metals, water, FeO, and fO2, can indirectly affect DAuMSS/SM. The mechanisms that control the sulfide-silicate melt partitioning of gold and the other chalcophile elements, such as Ni, Re, and Mo, differ significantly. This is because gold is dissolved mainly as Au-S species in the silicate melts, while the other chalcophile elements are dissolved mainly as metal oxides in the silicate melts. Applying the correlation between DAuMSS/SM and [S]melt to slab melting and arc magmatic differentiation under different redox conditions, we find that ancient to modern slab melts carry negligible to less than 25% of the slab gold to the subarc mantle; however, gold-enrichment can occur in MSS-saturated arc magmas that have differentiated under moderately oxidized conditions with fO2 between FMQ and FMQ+1.6, in particular if the magmatic crystallization follows a fractional crystallization model. We conclude that moderately oxidized magmas with high contents of alkali metals, sulfur, and water, owing to their low DAuMSS/SM and efficient magma-to-fluid transfer of gold and sulfur, have a high potential to form gold deposits.

The geochemistry of Au–Ag minerals and base‐metal sulphides as indicators for gold precipitation: Case study of the Shihu gold deposit, central North China Craton

The Shihu quartz vein‐type gold deposit, the largest gold deposit in the central North China Craton, occurs within wall rocks of Neoarchean TTG (tonalite–trondhjemite–granodiorite) gneiss and shows a close relationship with the early Cretaceous Mapeng granitoid pluton and various intermediate–mafic dykes. The occurrence, morphology, composition, and precipitation mechanism of the Au–Ag minerals are short of research, which is the purpose of this study. The primary mineral assemblage of orebody contains quartz, calcite, and base‐metal sulphides including pyrite, galena, sphalerite, chalcopyrite, and minor pyrrhotite and enargite. The Au–Ag minerals can be classified into three distinct types, namely, (a) quartz‐hosted, (b) pyrite‐hosted, and (c) base‐metal sulphidehosted, corresponding to formation sequence. Electron microprobe analysis indicates that these Au–Ag minerals show fineness (=Au/[Au + Ag] × 1,000) ranging from 976 to 366 with an average of 667 and are rich in Bi, Te, and Hg while deficient of Cu, As, and Se. Bismuth and tellurium in the Au–Ag minerals show a linear relationship with Au, whereas in the coexisted sulphides are almost below detection limits. We suggest that Bi and Te fundamentally influenced the transportation, enrichment, and precipitation of gold as scavengers to concentrate and deposit gold at the location with an “appropriate distance” from magma. Phase analyses of native bismuth and Bi–Te minerals included in pyrite, reported for the first time in Shihu Gold deposit, imply that the gold precipitation witnessed the ore‐forming fluid evolution with log fTe2 decreasing from approximately −11 to approximately −15 and log fS2 increasing from approximately −13 to more than −11. Mineralogical mapping with the fineness of Au–Ag minerals (fineness contours) suggest that the ore‐forming fluids came from the deep earth beneath the north of the mining area with excellent gold potential, which has been verified by later drilling.

Vapor transport of silver and gold in basaltic lava flows

Abstract We documented occurrences of native copper (Cu), silver (Ag), and gold (Au) in a pāhoehoe flow from Kīlauea volcano (Hawaii, USA), an a‘ā flow from Mauna Loa volcano (Hawaii), and a mid-oceanic-ridge basalt (MORB) from the Chile Ridge (southeastern Pacific Ocean). Native Ag in Kīlauea and MORB samples consistently contained minor Cl (&lt;1 wt%). Native Ag in Hawaiian basalts can occur at the center of nearly circular patches of relatively evolved minerals, which presumably formed after late-stage silicate liquid infilled pipe vesicles. Sulfur loss and oxidation of a Cu-sulfide phase can explain the native Cu, but not Au and Ag deposition. The rare occurrence of native Cu-Au-Ag alloys and the large native Au and Ag grain size suggest separate metal precipitation mechanisms. A fractional crystallization and degassing model envisions initial Au and Ag enrichment in crystallizing interstitial liquid and further enrichment in a separating vapor phase. From the flow interior, the metals ascend through ephemeral pipe vesicles as bisulfide (Au) or chloride (Ag) vapor complexes and precipitate in the transition zone below the upper vesicular zone, owing to temperature and oxidation state changes. Our results support igneous vapor transport of ore elements in mafic plutonic systems and imply preconcentration of gold during lava solidification before later hydrothermal remobilization.

Detection of Gold Nanoparticles in Hydrothermal Fluids

The transport and deposition of gold from colloidal suspensions in hydrothermal fluids has been a persistent theme in ore deposits research. Studies of active geothermal systems show that a complete model of gold transport must include both dissolved and particulate forms. However, samples of the hydrothermal fluids are commonly spiked with aqua regia after collection in order to put any solids back into solution, thus preventing a quantitative assessment of the particle load. Although attempts have been made to filter the solids, gold nanoparticles (Au NPs) will mostly pass the 0.2-µm filters that are in common use, and a simple technique for analyzing suspended particles in the liquids has been lacking. In this study, we demonstrate how time-resolved acquisition of mass 197 in a conventional inductively coupled plasma-mass spectrometer (ICP-MS) can be used to detect and measure Au NPs in the filtered liquids, with an example of well-characterized fluids from the Reykjanes geothermal field on Iceland. The technique allows for precise monitoring of the solution as it is introduced into the plasma with the capability of identifying individual particles carried in suspension. Results show that Au particles passing the 0.2-µm filters are abundant in the studied samples, and measurements of the individual particles can be used to determine their size. The experiment highlights the potential of emerging ICP-MS techniques, including very fast data acquisition and multielement analysis of single particles in timeof-flight mode, for characterization of NPs in hydrothermal fluids.

Colloidal and Deposited Products of the Interaction of Tetrachloroauric Acid with Hydrogen Selenide and Hydrogen Sulfide in Aqueous Solutions

The reactions of aqueous gold complexes with H2Se and H2S are important for transportation and deposition of gold in nature and for synthesis of AuSe-based nanomaterials but are scantily understood. Here, we explored species formed at different proportions of HAuCl4, H2Se and H2S at room temperature using in situ UV-vis spectroscopy, dynamic light scattering (DLS), zeta-potential measurement and ex situ Transmission electron microscopy (TEM), electron diffraction, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Metal gold colloids arose at the molar ratios H2Se(H2S)/HAuCl4 less than 2. At higher ratios, pre-nucleation “dense liquid” species having the hydrodynamic diameter of 20–40 nm, zeta potential −40 mV to −50 mV, and the indirect band gap less than 1 eV derived from the UV-vis spectra grow into submicrometer droplets over several hours, followed by fractional nucleation in the interior and coagulation of disordered gold chalcogenide. XPS found only one Au+ site (Au 4f7/2 at 85.4 eV) in deposited AuSe, surface layers of which partially decomposed yielding Au0 nanoparticles capped with elemental selenium. The liquid species became less dense, the gap approached 2 eV, and gold chalcogenide destabilized towards the decomposition with increasing H2S content. Therefore, the reactions proceed via the non-classical mechanism involving “dense droplets” of supersaturated solution and produce AuSe1−xSx/Au nanocomposites.

Crude oils as ore fluids: An experimental in-situ XAS study of gold partitioning between brine and organic fluid from 25 to 250 °C

Organic matter can be associated with mineralization in hydrothermal ore deposits. One hypothesis is that this organic matter represents remnants of organic fluids (crude oils) that were competing with aqueous fluids for metal transport and contributed to metal endowment. We investigated the transport of gold (Au) in model oil compounds (S-free n-dodecane, CH3(CH2)10CH3, DD; and S-bearing 1-dodecanethiol, CH3(CH2)10CH2SH; DDT) from 25 °C to 250 °C using in-situ synchrotron X-ray absorption spectroscopy (XAS) experiments to determine the speciation and the structural properties of gold complexes in the aqueous- and oil-based fluids. For most experiments, DD or DDT were in contact with Au-bearing acidified water, or acidified water plus 10wt% NaCl (pH25°C = 1.85 in both cases). Gold rapidly partitioned from the aqueous phase into DD and DDT. Below 125 °C, Au(III)Cl is dominant in the DD and the adjacent water with a refined coordination number (CN) of chloride of 4.0(3) and an AuCl bond length of 2.28 Å, consistent with the tetrachloroaurate complex (AuCl4−) being stable in both the aqueous and organic phases. In contrast, Au(III) is rapidly reduced in the presence of DDT and an Au(I) complex dominates in both water and adjacent DDT with a CN of sulfur ∼2.0, suggesting a [RS-Au-SR]− (RS = DDT with deprotonated thiol group) complex with AuS bond lengths ranging from 2.29(1)Å to 2.31(3)Å. In an open system of DDT in contact with water, of which the water and DDT were analyzed separately, AuCl4− was dominant in the water phase, and Au(RS)2− dominant in DDT, possibly due to different equilibration kinetics in the beaker and glassy carbon tube.Since sulfur and organothiol compounds are ubiquitous and abundant components in natural oils, this study demonstrates the potential of natural oils to scavenge and enrich gold from co-existing gold-bearing brines. In particular, Au(I) organothiol complexes may contribute to transport in low-temperature (<125 °C) ore fluids such as those in basinal environments – in both hydrothermal fluids and oils. At temperatures ≥125 °C, gold was reduced to metallic gold in all experiments, suggesting that organo-stabilized nanoparticles may be the major form of gold to be scavenged, concentrated or transported in crude oils at these conditions. The results imply that brine-oil interactions may enrich Au in oils, and that oils may be an effective ore fluid in sedimentary environments.

Canal Transportation and Centering Ability of WaveOne Gold in Combination with and without Different Glide Path Techniques

IntroductionThe aim of this study was to compare centering ability and transportation values of the Primary WaveOne Gold (PWOG; Dentsply Sirona, Ballaigues, Switzerland) instrument with or without different glide path techniques. Centering ability and transportation were also compared between the 3 different glide path preparation groups. MethodsThe mesiobuccal canals of 60 extracted human mandibular molars (curvature angles between 25° and 35° and radii ≤10 mm) were selected and randomly divided into 4 groups with 15 canals each. Canals were negotiated to patency with a #8 K-file. Canal preparations were performed by a single operator using precurved #10, 15, and 20 stainless steel manual K-files (group KF); a #10 stainless steel manual K-file followed by PathFiles #1–3 (Dentsply Sirona) (group PF); a #10 stainless steel manual K-file followed by the WaveOne Gold Glider (Dentsply Sirona) (group WOGG); and no further glide path preparation (group NG). Micro–computed tomographic imaging was used to scan teeth before and after glide path preparation. The final canal preparation was performed with PWOG; after which, all 60 specimens were scanned again using micro–computed tomographic imaging. Canal transportation and centering ratio values were determined over levels 3 mm, 5 mm, and 7 mm from the root apex after glide path preparation and again after final preparation with PWOG. One-way analysis of variance was used to statistically compare groups. The significance level was set at P < .05. ResultsNo statistically significant difference in the mean centering ratios was found after glide path preparation when the KF, PF, and WOGG groups were compared (P > .05). The mean combined transportation values after glide path preparation were statistically significantly higher in the KF group compared with the PF and WOGG groups (P > .05). There was no statistically significant difference in the mean combined centering ratios or transportation values of the NG and 3 glide path groups in combination with PWOG over the 3 levels (P > .05). ConclusionKF group showed the highest mean transportation values during glide path preparation. However, the PWOG instrument's performance regarding centering ability and transportation was not influenced by the different glide path/no glide path preparation groups.

Age and petrogenesis of the Andagul granodiorite and its implications on gold mineralization of the Kassan region, western Kyrgyzstan Tian Shan

A number of significant gold deposits in the Kassan region in west Kyrgyzstan are associated with the Andagul granitic intrusion. These gold deposits share similarities with the class of “intrusion-related gold deposits”, implying that the gold mineralization may be genetically related to the intrusion. In order to evaluate this potential relationship, it is important to study the petrogenesis of the intrusion. This paper examines the sources and physiochemical conditions of magma generation and crystallization of the Andagul intrusion and their implications for gold mineralization, through an integrated study involving zircon geochronology, mineral chemistry, whole-rock chemistry and isotopic geochemistry. The Andagul intrusion consists mainly of granodiorite, which is characterized by metaluminous and median-K calc-alkaline compositions, high LREE and LILE, low HFSE, right-inclined REE pattern with a flat HREE pattern, and insignificant Eu anomalies ((Eu/Eu∗)N = 0.79–0.85). These geochemical characteristics, together with relatively low positive εNd(t) values (+2.1–+4.3), moderately low (87Sr/86Sr)i ratios (0.7049–0.7059), relatively low initial Pb isotopic ratios ((206Pb/204Pb)t = 17.76–18.51, (207Pb/204Pb)t = 15.56–15.62, and (208Pb/204Pb)t = 37.89–38.33), juvenile εHf(t) (+2.29–+4.80) but relatively old model ages (T2DM(Hf) = 1026–1175 Ma, T2DM(Nd) = 728–907 Ma) indicate that the magma was mainly sourced from partial melting of juvenile basaltic lower crust with the involvement of a small proportion (ca. 5%–10%) of Precambrian basement rocks. The high Zr saturation temperatures (807 °C to 825 °C), relatively high Mg# values (43–52) and presence of mafic enclaves, and development of acicular apatite and oscillatory plagioclase and titanite, suggest that the magmatism was related to injection of hot mantle material. The magma generation and intrusion took place during 299–310 Ma based on LA-ICPMS zircon U-Pb dating, suggesting a post-collisional setting. Remelting of sulfide accumulate residual with high Au/Cu ratios in the juvenile lower crust, formed in the pre-collisional plate subduction-related magmatic arc stage, is proposed to account for the Au mineralization in the Kassan region. The high water contents (4.0–5.2 wt% H2O) and weakly oxidized or slightly reduced redox state (ΔFMQ = −0.33 ∼ +0.49) deduced from mineral composition and zircon Ce anomaly are favorable for the transport and enrichment of gold in the magmatic fluids. These geochemical characteristics suggest that the Andagul granodiorite and related granitic rocks in the Kassan region have the potential to provide ore-forming materials and fluids for gold mineralization.

Hydrothermal evolution of granitoid-hosted gold mineralization in gidami area: An example for orogenic-gold deposits in Egypt

The Gidami gold ore is a unique form for the orogenic-gold deposits in Egypt. The gold lode is found in the form of auriferous quartz veins and aplitic dikes, cut through hosting granitic rocks and probably extend into the neighbor metavolcanic rocks. The geochemical data revealed that the granitic rocks are of tonalite-granodiorite composition, show calc-alkaline nature and related to active continental margin (syn-orogenic). The ore body is controlled by NNW trending shear/fault zones, occupying fracture zones and fissures and dipping generally to East direction. Microscopic examination accompanied with Electron Microprobe Analyses revealed that, the existed sulfide minerals are (pyrite, sphalerite, chalcopyrite, molybdenite, pyrrhotite, covellite, Galena, and pentlandite). Ilmenite and goethite are the main oxide minerals. Native gold commonly occurs as small inclusions within pyrite and goethite, and also detected as tiny grains scattered within quartz vein (near the sulfides). Well-developed alteration zones occur associated with auriferous quartz veins; two types of wallrock alteration are distinguished: a) Inner (phyllic) alteration zone, and b) Outer (carbonatized) alteration zone. The outer alteration zone always exhibits higher gold content than the inner zone.Three types of fluid inclusions are recognized at the core and rim of the auriferous quartz vein as follows: 1) Two phases aqueous (H2O-NaCl ± KCl), 2) Two phases aqueous (H2ONaCl ± MgCl2), and 3) Three phases aqueous-carbonic (H2O–NaCl-CO2±CH4) fluid inclusions. Isochores intersection from fluid inclusions data outlines that, the Gidami gold deposits are of the mesothermal type formed at temperatures range between (270–300 °C), and pressure (750–850 bar) corresponds to a depth around 3 km (assuming pure lithostatic pressure). The ore-bearing fluids are supposed to be sourced mainly by fluids of metamorphic and meteoric origin. However, criteria of partial mixing with water of magmatic signatures has been proposed during fluid evolution. The transportation of gold was in form of bisulphide compounds in moderately reduced, neutral to weakly alkaline environment and then the precipitation occurred as a result of changing in Eh and pH conditions.

Geology and Mineral Chemistry of Gold Mineralization in Mirge‐Naqshineh Occurrence (Saqez, NW Iran): Implications for Transportation and Precipitation of Gold

AbstractThe Mirge‐Naqshineh gold district is situated at northwest of Iran with a NW‐trending brittle‐ductile shear zone. It is hosted by Precambrian meta‐sedimentary and meta‐volcanic units traversed by mineralized quartz veins. In terms of cross‐cutting relationships and sulfide content three types of quartz veins are identified in the region. Among those, parallel to bedding quartz vein (type I) is the main host for gold mineralization. Gold is found in three different forms: 1) submicrometer‐size inclusions of gold in arsenian pyrite, 2) as electrum and 3) in the crystal lattice of sulfides (pyrite, galena and chalcopyrite). Six types of pyrite (Py1‐Py6) were identified in this ore reserve. Py3 coexists with arsenopyrite and contains the greatest As‐Au concentrations. There is a negative correlation between the As and S contents in Py2 and Py3, implying the substitution of sulfur by arsenic. Pyrites and mineralized quartz veins were formed via metamorphic‐hydrothermal fluid and reflect the gold‐transportation as Au(HS)−2 under reducing and acidic conditions. The gold precipitation mainly controlled by crystallization of arsenian pyrite during fluid/rock interactions and variation of fO2. The volcanic host rock has played an important role in gold concentration, as Py3 in this rock contains inclusion of gold particles, but gold is within the lattice of pyrite in phyllite or other units.

Canal Transportation and Centering Ability of Reciproc Blue, WaveOne Gold and ProTaper Next in Simulated Curved Canals.

The aim of this study was to evaluate the canal transportation and centering ability of ProTaper Next (PTN), WaveOne Gold (WOG) and Reciproc Blue (RCB) in simulated curved resin canals. A total of 43 blocks of simulated resin canals with 40° of curvature were prepared to an apical size of 0.02. Flexofile #15 instruments were used along the root canal to reach patency. The blocks were randomly assessed and sequence instruments were used according to each system: PTN, RCB and WOG. The imposition of pre and post instrumentation images were composited and analyzed. The canal transportation and apical centralization were measured using the software GIMP (2.8.4, Creative Commons - Share Alike 4.0 International License, 2013). Data were statistically analyzed using the Shapiro-Wilk test, ANOVA test and Tukey's test. The level of significance was set at 0.05. There were no statistical differences in canal transportation between three systems. The general assessment of three systems presented the RCB group with higher values of centralization and more numbers of centralized points with significant differences between the PTN and RCB groups (P<0.05). In this in vitro study, there were no statistical differences in canal transportation between the RCB, WOG and PTN systems. The lowest transportation was observed in the apical region at 3 mm performed with RCB system, followed by WOG and PTN systems. The RCB demonstrated higher values of centralization and more centralized points when assessed by regions.

Uatú Júpú: a history of the indigenous Rio Doce

This essay examines the long history of resistance by Jê speaking indigenous peoples who have inhabited the basins of the Doce River and its many tributaries. It provides an overview from the colonial era to the present, examining the disparate perceptions and uses that Portuguese and Jê-speaking indigenous peoples have applied to river systems in Brazil. For native communities, the Doce is a source of both spiritual and material sustenance. Portuguese explorers, settlers, and miners viewed rivers as potential transportation and sources of gold and gems. This mutually conflictive history contributes to our understanding of why and how access to rivers has mattered historically and continues to matter in the wake of the Fundão Dam breach in Mariana, Minas Gerais, in 2015.

Nature and source of the ore-forming fluids associated with orogenic gold deposits in the Dharwar Craton

Neoarchean orogenic gold deposits, associated with the greenstone-granite milieus in the Dharwar Craton include (1) the famous Kolar mine and the world class Hutti deposit; (2) small mines at Hira-Buddini, Uti, Ajjanahalli, and Guddadarangavanahalli; (3) prospects at Jonnagiri; and (4) old mining camps in the Gadag and Ramagiri-Penakacherla belts. The existing diametric views on the source of ore fluid for formation of these deposits include fluids exsolved from granitic melts and extracted by metamorphic devolatilization of the greenstone sequences. Lode gold mineralization occurs in structurally controlled higher order splays in variety of host rocks such as mafic/felsic greenstones, banded iron formations, volcaniclastic rocks and granitoids. Estimated metamorphic conditions of the greenstones vary from lower greenschist facies to mid-amphibolite facies and mineralizations in all the camps are associated with distinct hydrothermal alterations. Fluid inclusion microthermometric and Raman spectroscopic studies document low salinity aqueous-gaseous (H2O + CO2 ± CH4 + NaCl) ore fluids, which precipitated gold and altered the host rocks in a narrow P–T window of 0.7–2.5 kbar and 215–320 °C. While the calculated fluid O- and C-isotopic values are ambiguous, S-isotopic compositions of pyrite-precipitating fluid show distinct craton-scale uniformity in terms of its reduced nature and a suggested crustal sulfur source.Available ages on greenstone metamorphism, granitoid plutonism and mineralization in the Hutti Belt are tantamount, making a geochronology-based resolution of the existing debate on the metamorphic vs. magmatic fluid source impossible. In contrast, tourmaline geochemistry suggests involvement of single fluid in formation of gold mineralization, primarily derived by metamorphic devolatilization of mafic greenstones and interlayered sedimentary rocks, with minor magmatic contributions. Similarly, compositions of scheelite, pyrite and arsenopyrite point toward operation of fault-valves that caused pressure fluctuation-induced fluid phase separation, which acted as the dominant process of gold precipitation, apart from fluid-rock sulfidation reactions. Therefore, results from geochemistry of hydrothermal minerals and those from fluid inclusion microthermometry corroborate in constraining source of ore fluid, nature of gold transport (by Au-bisulfide complex) and mechanism of gold ore formation in the Dharwar Craton.

Synergistic extraction of gold(I) from aurocyanide solution with the mixture of primary amine N1923 and bis(2-ethylhexyl) sulfoxide in supported liquid membrane

Utilization of supported liquid membrane (SLM) for the extraction of Au(I) from alkaline cyanide solution was investigated. The SLM consisted of a synergistic mixture of primary amine N1923 and bis(2-ethylhexyl) sulfoxide (BESO) in kerosene as carrier and a hydrophobic microporous polyvinylidene fluoride (PVDF) membrane as the solid support. The presence of both BESO and N1923 extractants in the liquid membrane induces an evident synergistic effect, allowing the latter to transfer Au(I) from the highly alkaline solution (pH>9.21). The fundamental parameters influencing the gold transport, such as stirring speed, composition of the liquid membrane, feed pH, NaOH concentration in stripping solution, and initial gold concentration in the feed solution were explored. The gold transport is almost quantitative after 7h under the optimum process conditions: a mixture of (0.50mol/L N1923 + 0.75mol/L BESO) in kerosene as membrane phase, stirring rate of 1000rpm in both phases, 5.0mg/L gold in 0.20mol/L NaCl solution with a pH of 9.60, and 0.10mol/L NaOH as stripping agent. The parameters defining the mass transfer model of Au(I) through the SLM are experimentally determined as: maximum permeability coefficient, P = 31.45 × 10−6m/s, the diffusion coefficient for [Au(CN)2−·RNH3+ ·2BESO] complex across the liquid membrane, Dorg = 1.42 × 10–12m2/s, and the thickness of the aqueous diffusion layer, daq = 2.07 × 10−5 m. Selectivity of this SLM system was evaluated by performing the permeation test of Au(CN)2- with other metal cyanide species in aqueous solution and it was found that the gold ions were preferred over other impurity ones. Finally, stability of this SLM system has also been examined on a continuous run mode and satisfactory stability was observed for five runs.

Non-dispersive extraction of gold(III) with ionic liquid Cyphos IL101

The permeation of gold(III), through a supported liquid membrane (SLM), in flat-sheet operational mode, impregnated with Cyphos IL101 (ionic liquid with a quaternary phosphonium salt as active substance) in Solvesso 100 has been investigated. The transport of gold(III) has been studied under various experimental conditions: stirring speed of the aqueous phases, initial metal and carrier concentrations, HCl concentration in the source phase, etc. The overall mass transfer coefficient was calculated as 0.19 cm/min and the thickness of the aqueous boundary layer was of 3.2 × 10−3 cm. The performance of Cyphos IL101 has been studied with respect to other carriers and also the selectivity of the membrane-carrier system on various metal-bearing aqueous solutions. Gold is recovered in the strip phase as nanogold.