Fe Au Research Articles

Porphyry Cu–Au and associated polymetallic Fe–Cu–Au deposits in the Beiya Area, western Yunnan Province, south China

The Alkaline porphyries in the Beiya area are located east of the Jinshajiang suture, as part of a Cenozoic alkali-rich porphyry belt in western Yunnan. The main rock types include quartz-albite porphyry, quartz-K-feldspar porphyry and biotite–K-feldspar porphyry. These porphyries are characterised by high alkalinity [(K 2O + Na 2O)% > 10%], high silica (SiO 2% > 65%), high Sr (> 400 ppm) and 87Sr/ 86Sr (> 0.706)] ratio and were intruded at 65.5 Ma, between 25.5 to 32.5 Ma, and about 3.8 Ma, respectively. There are five main types of mineral deposits in the Beiya area: (1) porphyry Cu–Au deposits, (2) magmatic Fe–Au deposits, (3) sedimentary polymetallic deposits, (4) polymetallic skarn deposits, and (5) palaeoplacers associated with karsts. The porphyry Cu–Au and polymetallic skarn deposits are associated with quartz–albite porphyry bodies. The Fe–Au and polymetallic sedimentary deposits are part of an ore-forming system that produced considerable Au in the Beiya area, and are characterised by low concentrations of La, Ti, and Co, and high concentrations of Y, Yb, and Sc. The Cenozoic porphyries in western Yunnan display increased alkalinity away from the Triassic Jinshajiang suture. Distribution of both the porphyries and sedimentary deposits in the Beiya area are interpreted to be related to partial melting in a disjointed region between upper mantle lithosphere of the Yangtze Plate and Gondwana continent, and lie within a shear zone between buried Palaeo-Tethyan oceanic lithosphere and upper mantle lithosphere, caused by the subduction and collision of India and Asia.

Laser-Assisted Synthesis of Superparamagnetic Fe@Au Core−Shell Nanoparticles

A novel method combining wet chemistry for synthesis of an Fe core, 532 nm laser irradiation of Fe nanoparticles and Au powder in liquid medium for deposition of an Au shell, and sequential magnetic extraction/acid washing for purification has been developed to fabricate oxidation-resistant Fe@Au magnetic core-shell nanoparticles. The nanoparticles have been extensively characterized at various stages during and up to several months after completion of the synthesis by a suite of electron microscopy techniques (HRTEM, HAADF STEM, EDX), X-ray diffraction (XRD), UV-vis spectroscopy, inductively coupled plasma atomic emission spectroscopy, and magnetometry. The surface plasmon resonance of the Fe@Au nanoparticles is red shifted and much broadened as compared with that of pure colloidal nano-gold, which is explained to be predominantly a shell-thickness effect. The Au shell consists of partially fused approximately 3-nm-diameter fcc Au nanoparticles (lattice interplanar distance, d = 2.36 A). The 18-nm-diameter magnetic core is bcc Fe single domain (d = 2.03 A). The nanoparticles are superparamagnetic at room temperature (300 K) with a blocking temperature, T(b), of approximately 170 K. After 4 months of shelf storage in normal laboratory conditions, their mass magnetization per Fe content was measured to be 210 emu/g, approximately 96% of the Fe bulk value.

Spin-Polarized Scanning Tunnelling Microscopy of Ultrathin Films

Using low temperature spin-polarized scanning tunneling microscopy we have studied the morphology and magnetic properties of ultrathin Fe(0.5 ML)Au(0.5 ML) nanowires prepared on a Mo(110) single crystal. The Fe nanostripes grown by step flow on a Mo(110) at 700 K were covered by Au at RT, and subsequently annealed at 700 K. Differences in the morphology of Au on Fe(110)/Mo(110) and clean Mo(110) surfaces are observed and discussed. After annealing, the Mo is covered by a homogeneous FeAu ML alloy with several iron enriched islands which reveal an out-of-plane magnetic contrast. Direct lateral exchange coupling has been observed for these islands.

Smoothing of Fe/Au and Fe/Ag multilayers by swift heavy ion bombardment

We have investigated the influence of swift heavy ion (SHI) irradiation as well as thermal annealing on the interface roughness in thermally immiscible Fe/Au and Fe/Ag multilayers. The 5-fold multilayers consisted of 20–25nm Fe-, 10nm Ag- and 7–21nm Au-layers and were partly irradiated at liquid nitrogen temperature with 80–350MeV Ar, Ni, Kr, Xe ions at fluences between 1012cm−2 and 1015cm−2. The irradiated as well as the unirradiated parts of the samples were analyzed by means of Rutherford backscattering spectrometry (RBS) using 1MeV He+ ions. In the case of Fe/Ag, no change in the RBS spectra due to the ion irradiation could be detected, while in the case of Fe/Au, a clear increase of the steepness of the high energy edge of the Au signal was observed. A detailed analysis of the RBS Au profiles in comparison with RBS simulations for different shapes of the Au-layers allowed us to conclude that SHI irradiation results in smoothing of the Fe–Au interfaces, which can be understood in terms of a local minimization of the interface energy. In the Fe/Ag case, the symmetry of the RBS profiles of the Ag layers indicated that the interfaces became already smooth during the layer deposition. Heating of the Fe/Au multilayers resulted in broadening of the Au profiles and finally a complete destruction of the multilayer structure was observed. Here the whole sample is at high temperature and therefore interface energy minimization now occurs by the formation of spherical Au particles, which destroys the layered structure.

Evidence of a high-spin ferromagnetic state in fcc-structured Fe–Ag (Au) alloys synthesizedby ion beam manipulation

Based on the design of interfacial free energy in Fe–Ag (Au) multilayered films, metastableFe40Ag60 and Fe40Au60 alloys were synthesized by ion beam manipulation in the Fe–Ag and Fe–Au systems. Thesynthesized alloys were identified to crystallize in a large fcc structure with a lattice constant of0.38–0.39 nm and the associated magnetic moments per Fe atom were measured to be around2.10–2.30 μB. The above experimental observations, together with some theoretical analysis, confirm theexistence of a high-spin ferromagnetic state in the fcc-structured Fe-containing alloys.

Magnetic properties of new glassy Fe–Au(Cu)–B alloys

The evolution of the microstructure and soft magnetic properties of Fe 76Au 4− x Cu x B 20 and Fe 87Au 2− x Cu x B 11 melt spun ribbons prepared at different cooling rates were investigated. The samples are stable above room temperature and display saturation induction up to 1.79 T and magnetic permeabilities of over 2×10 4 at 300 K. The structure is not fully amorphous, as proved by DSC and HRTEM investigations, but consists of very small grains of about 10 nm, randomly dispersed in the amorphous residual matrix. The grains composition strongly depends on the B content.

Observation of the domain structure in Fe?Au superlattices with perpendicular anisotropy

Polar Kerr Microscopy was used to visualize characteristic transitions and external magnetic field driven domain structure evolution in a perpendicularly magnetized Fe–Au AF/FM double multilayer structure. Real time imaging performed in the external magnetic field allowed for identification of all sublayers magnetization reversal in accordance with measured PMOKE magnetization curve, showing strong dependence of transition character on the interlayer coupling type and adjacent sublayers magnetization orientation.

Observation of the domain structure in Fe–Au superlattices with perpendicular anisotropy

Polar Kerr Microscopy was used to visualize characteristic transitions and external magnetic field driven domain structure evolution in a perpendicularly magnetized Fe–Au AF/FM double multilayer structure. Real time imaging performed in the external magnetic field allowed for identification of all sublayers magnetization reversal in accordance with measured PMOKE magnetization curve, showing strong dependence of transition character on the interlayer coupling type and adjacent sublayers magnetization orientation.

Selective separation of gold from iron ore samples using ion exchange resin

Gold in iron ore samples is separated from iron (major matrix cation), antimony and vanadium using anion exchange resin in (0.2 M) HBr, potassium peroxodisulfate and acetone:water:nitric acid media. The exchangeable anion Cl − of the ion exchanger Dowex 1X 4 is replaced by Br − using (6 M) HBr solution. Certified reference material DGP-M1, spiked ferric magnetic oxide, gold radioactive tracer 198Au and gold standard solutions are used to study the adsorption efficiency and the yield recovery of tetrabromoaurate AuBr 4 − from the resin. Ten eluents have been tried to elute gold from the column, and it has been found that a 10 ml potassium peroxodisulfate and 240 ml acetone:water:nitric acid [125:5:5] solution fulfills the objective. The set up of the separation procedure allows quantitative adsorption of gold by the resin, while the major matrix cation (Fe) and others (Cd, Ag, Cu, V, Sb, Ti) have been passed through the column with the feeding solution (0.2 M) HBr. The resin selectivity coefficient ( K) of separating Au from Fe has been found to be K Fe Au≈6.4×10 11. The eluted Au is treated with K 2S 2O 8 and H 2O 2 for spectrophotometric determination as rhodamine-B complex at 555.6 nm. The linearity, detection limit, precision, and accuracy of the determination method have been found to be up to 2.0 μg g −1, 0.018 μg g −1, 0.009 μg g −1 and 3%, respectively.

Major and trace element geochemistry and 40Ar/ 39Ar geochronology of Laramide plutonic rocks associated with gold-bearing Fe skarn deposits in Guerrero state, southern Mexico

Fe–Au skarn deposits related to intrusive centers, mostly of granodioritic composition, are widespread in southern Mexico's Guerrero state. These intrusive rocks are largely associated with the NW–SE-oriented Laramide magmatic belt that extends across most of western Mexico. The geochemical composition and ages of representative rocks from the Mezcala mining district in central Guerrero are studied to evaluate the petrogenetic aspects of the ore-related magmas. Some major and trace elements display nearly linear silica variation trends, which suggest a possible comagmatic origin. However, other elements have scattered distributions, possibly due to irregular mantle-to-crust magma mixing ratios, heterogeneities in the composition of the assimilated crustal material, or modifications during the emplacement or postemplacement processes. Major element chemistry indicates calc-alkalic metaluminous compositions, whereas trace element data suggest a volcanic arc tectonic setting, confirming that these rocks evolved from magmas generated above a subduction zone. Compared with the Laramide granites from the northern part of the belt in northwestern Mexico, which intruded a crust underlain by Proterozoic North American rocks, the studied samples are similar but relatively low in Nb and high in Sr, the middle rare earth elements (REE), P, and Zr. They also display minor Ti enrichments and a moderate depletion in the heavy REE. These characteristics may indicate a source of basaltic composition. New 40Ar/ 39Ar dating of granodiorites and dacite porphyries shows a north-to-south age progression from 66.2±0.8 Ma in the northern part of the belt to 62.2±0.7 Ma in the south. Moreover, the argon dates identify a younger postorogenic igneous event 35–30 Ma ago. This event is poorly documented and may have occurred after the extinction of the Laramide arc and prior to the mid-Tertiary Sierra Madre Occidental ignimbrite flare-up. On the basis of limited geochemical data, these rocks appear to be depleted in P 2O 5 and Sr and enriched in U relative to the studied Laramide granites. A Fe skarn deposit located in Buena Vista de Cuéllar, in the north central part of Guerrero, suggests that this magmatic pulse took place after the ore development of the Mezcala district.

Peculiar magneto-optical and magnetic properties of Au–Fe alloy films and Au/Fe multilayered films

In this study, peculiar magneto-optical (MO) and magnetic properties of Fe–Au alloy films and Au/Fe multilayered films (MLF) were investigated. It was elucidated that alloy-like regions are spontaneously formed near the interfaces between Au and Fe sublayers during the Au/Fe MLF fabrication. The measured magnetic-circular-dichroism characteristics reveal that the orbital magnetic moment of the constituent Fe atoms in the bcc Fe–Au alloy film is about twice larger than that of pure Fe. This implies a hybridization between Fe and Au atoms. It is thought that a prominent feature observed in the UV range of the MO response of Au/Fe MLF results not from the quantum confinement, but probably from an enhanced magnetic moment of Fe (and/or an induced magnetic moment of Au).

Highly oxidised gold skarn fluids evolution in the Mezcala deposit, Guerrero, Mexico

Intrusives associated with the Mezcala oxidised Fe Au skarns present a prograde and retrograde alteration process. The early mineralized fluids are strongly oxidised and saturated in salts. These fluids evolve rapidly to cold and diluted fluids, probably under the influence of meteoritic waters, during the mineralized precipitation event.

Magnetic relaxations in metallic multilayers

The intrinsic damping mechanism in metals caused by incoherent scattering of itinerant electron-hole pair excitations by phonons and magnons will be reviewed. The unique features of magnetic relaxations in multilayers were studied by ferromagnetic resonance (FMR) using magnetic single, Au–Fe–GaAs(001), and double layer Au–Fe–Au–Fe–GaAs(001) structures prepared by molecular beam epitaxy. The magnetic relaxation in single-layer films is described by the Gilbert damping with no extrinsic contributions to the FMR linewidth. These films provided an excellent opportunity to investigate nonlocal damping. The main result of these studies is that ultrathin Fe films in magnetic double layers acquire an additional interface Gilbert damping. This is in agreement with recent predictions of nonlocal interface damping which is based on the transport of spin angular momentum between the ferromagnetic layers. Measurements of the nonlocal Gilbert damping offer a possibility to carry out quantitative studies of the relaxation torques caused by nonlocal spin momentum transfer. Numerical simulations of magnetization reversal and stationary precession for an applied perpendicular current in Au–Fe–Au–Fe–GaAs(001) multilayers will be shown.

Direct observation of surface alloying and interface roughening: growth of Au on Fe(001).

Scanning tunneling microscopy studies on the growth of Au on Fe(001) are reported. A surface alloy is observed for submonolayer deposition ( <0.5 monolayer) at temperatures higher than 370 K. This surface-confined alloy demixes when it is covered with Au and in combination with imperfect layer-by-layer growth a rough interface consisting of Au islands in and Fe islands on the original Fe(001) substrate is created. A real-space high resolution study of this buried interface is possible because of the large difference in interlayer spacing between bcc Fe(001) and fcc Au(001).

Spin engineering with Fe–Au monolayers

FeAu superlattices were grown using MBE by alternative deposition of Fe(0 0 1) and Au(0 0 1) atomic layers. Polar MOKE loops taken at the room temperature showed that all superlattices with single Fe monolayers (MLs) were magnetized along the film normal but the character of the hysteresis loop depended strongly on the repetition number N in a (Fe 1Au 1) N stack, where Fe 1Au 1 denotes a single sequence of the Fe(0 0 1) and Au(0 0 1) MLs. The loop character changed from a low remanence one for N=20 to a narrow ( H C=50 Oe) rectangular one for N=3. (Fe 1Au 1) 3 stacks, denoted as (FeAu) 3, were used to construct multilayers, in which they were spaced by K Au(0 0 1) atomic layers (AL). In the tri-layer, (Fe 1Au 1) 3/Au( d Au)/(Fe 1Au 1) 3, antiferromagnetic exchange coupling was clearly observed around the Au(0 0 1) spacer thickness d Au=10 AL (about 2 nm). For [(Fe 1Au 1) 3/Au ( d Au)]× M ( M=4,6) the magnetization process becomes more complicated revealing a sharp multistage spin-flip transition including well-distinguished surface spin flip.

The Xinqiao Cu–S–Fe–Au deposit in the Tongling mineral district, China: synorogenic remobilization of a stratiform sulfide deposit

The Cu–S–Fe–Au deposit at Xinqiao is located in the Tongling mineral district, Anhui Province, People's Republic of China. It is a large-scale polymetallic deposit with drilling indicated reserves of 0.5 million tonnes of Cu averaging 0.71%, 75.5 million tonnes of S averaging 29.3% and 24.9 million tonnes of Fe averaging 46%, as well as 11.2 tonnes of Au averaging at 4.7 g/tonne plus 248.4 tonnes of Ag averaging at 248.4 g/tonne. There are two major mineralization types in the Xinqiao deposit: one is the economically significant stratiform orebody hosted in the Lower Carboniferous Gaolishan siltstone (C 1g) and overlying Middle Carboniferous Huanglong limestone (C 2h), while the other is the less important skarn-type mineralization restricted to the contact between the Yanshanian diorite (110–168 Ma) and the Lower Permian Qixia marble (P 1q). The ore in the Xinqiao deposit is dominated by massive pyrite with minor amount of chalcopyrite, magnetite, pyrrhotite, galena, sphalerite, quartz and dolomite. Four stages of deformation have been recognized to affect the sedimentary rocks in the Xinqiao area. The first two (D 1 and D 2) produced mainly NE–SW and NNE–SSW trending open folds, whereas D 3 is characterized by normal faults striking NNE–SSW and D 4 is dominated by post-mineralization strike-slip faults segmenting the orebody. The structural information obtained by this study not only revealed the transgressive nature of the stratiform orebody, but also identified a strong structural control on the formation of the deposit. It is concluded that the Xinqiao polymetallic deposit was formed through remobilization of a Carboniferous sulfide source bed by hydrothermal solutions related to late Yanshanian plutonism (110 Ma), during which D 3 normal faulting played an important role in localization of the mineralization. Such a two-stage ore-forming model is consistent with the most recent genetic interpretations of the deposit.

The temperature-dependent growth of Fe submonolayer film on Au(001) studied by barrier height imaging using scanning tunneling microscopy

The growth of Fe submonolayer films on Au(001) at various substrate temperatures (300–500 K) was investigated by scanning tunneling microscopy (STM). STM topographic and barrier height images show that the growth mode and morphology of the films markedly depend on growth temperature. Fe islands with a monolayer height nucleate and grow on flat terraces of Au(001) at 300 K. However, Fe islands with double-layer height and small pinholes were observed on terraces at 353 and 393 K, and step edges were decorated by Fe dendrites. A clear element-specific contrast between Fe islands and Au substrate was observed below 400 K. At elevated growth temperature, above 400 K, a segregated Au layer was observed. The mechanism of the surface segregation of Au is also discussed in terms of the surface diffusion through the pinholes.

Low-temperature thermoelectrical power measurements using analogue subtraction

A simple, inexpensive analogue subtraction method for measuring thermoelectrical power from 4 to 300 K using two chromel (KP)/Au-7 at% Fe (Au:Fe) thermocouples is described. The average sample temperature is varied by lowering a small insert probe into a liquid-He-storage container or raising the probe. Details concerning the interface of the experiment to a personal computer are presented. Data collected on constantan, Bi2Sr2CaCu2O7+ and carbon-nanotube samples show the utility of the method.

The Lower Changjiang (Yangzi/Yangtze River) metallogenic belt, east central China: intrusion- and wall rock-hosted Cu–Fe–Au, Mo, Zn, Pb, Ag deposits

The lower valley of Changjiang, from Wuhan of the Hubei Province in the west to Zhenjiang of the Jiangsu Province in the east, contains more than 200 polymetallic (Cu–Fe–Au, Mo, Zn, Pb, Ag) deposits and is one of the most important metallogenic belts in China. This metallogenic belt, situated at the northern margin of the Yangzi craton and bordered by the Dabieshan ultrahigh pressure metamorphic belt to the north, consists mainly of Cambrian–Triassic marine clastic sedimentary rocks and carbonate and evaporite rocks, which overlay a Precambrian basement and are intruded by Yanshanian (205 to 64 Ma) granitoid intrusions and subvolcanic complexes. Repeated tectonism from Late Proterozoic to Triassic resulted in extensively developed networks of faults and folds involving the Cambrian–Triassic sedimentary strata and the Precambrian basement. The Yanshanian granitoid intrusions and subvolcanic complexes in the Lower Changjiang metallogenic belt are characterized by whole-rock δ 18 O of +8‰ to +10‰, initial 87 Sr/ 86 Sr of 0.704 to 0.708, and ϵNd t from −10 to −17 and have been interpreted to have originated from mixing between juvenile mantle and old crustal materials. Also, the Yanshanian granitoids exhibit eastward younging and increase in alkalinity (i.e., from older calc–alkaline in the west to younger subalkaline–alkaline in the east), which are related to oblique collision between the Yangzi and Sino-Korean cratons and tectonic evolution from early compressional to late extensional or rifting regimes. Most polymetallic deposits in the Lower Changjiang metallogenic belt are clustered in seven districts where the Yanshanian magmatism is particularly extensive: from west to east, Edong, Jiurui, Anqing–Guichi, Luzhong, Tongling, Ningwu and Ningzhen. Mineralization is characterized by the occurrence of three distinct types of orebodies in individual deposits: orebodies in Yanshanian granitoid intrusions, skarn orebodies at the contact zones between the Yanshanian intrusions and Late Paleozoic–Early Mesozoic sedimentary rocks, and stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata. The most important host sedimentary strata are the Middle Carboniferous Huanglong Formation, Lower Permian and Lower–Middle Triassic carbonate and evaporite rocks. The intrusion-hosted and skarn orebodies exhibit well-developed zonation in alteration assemblages, metal contents, and isotopic compositions within individual deposits, and apparently formed from hydrothermal activities related to the Yanshanian magmatism. The stratabound massive sulfide orebodies in the Late Paleozoic–Early Mesozoic sedimentary strata have long been suggested to have formed from sedimentary or volcano-sedimentary exhalative processes in shallow marine environments. However, extensive research over the last 40 years failed to produce unequivocal evidence for syngenetic mineralization. On the basis of geological relationships and isotope geochemical characteristics, we propose a carbonate-hosted replacement deposit model for the genesis of these stratabound massive sulfide orebodies and associated skarn orebodies. This model suggests that epigenetic mineralization resulted from interactions between magmatic fluids evolved from the Yanshanian intrusions with carbonate and evaporite wall rocks. Mineralization was an integral but distal part of the larger hydrothermal systems that formed the proximal skarn orebodies at the contact zones and the intrusion-hosted orebodies. The stratabound massive sulfide deposits of the Lower Changjiang metallogenic belt share many features with the well-studied, high-temperature, carbonate-hosted replacement deposits of northern Mexico and western United States, particularly with respect to association with small, shallow granitoid complexes, structural and stratigraphic controls on mineralization, alteration assemblages, geometry of orebodies, metal association, metal zonation and isotopic systematics.

Metal-residence sites in lavas and tuffs from Volc�n Popocat�petl, Mexico: implications for metal mobility in the environment

Volcan Popocatepetl is a Quaternary stratovolcano located 60 km southeast of Mexico City. The summit crater is the site of recent ash eruptions, excess degassing, and dacite dome growth. The modern cone comprises mainly pyroclastic flow deposits, airfall tephras, debris flows, and reworked deposits of andesitic composition; it is flanked by more mafic monogenetic vents. In least-degassed fallout tuffs and mafic scoria, transition metals are concentrated in phases formed before eruption, during eruption, and after eruption. Preeruptive minerals occur in both lavas and tephra, and include oxides and sulfides in glass and phenocrysts. The magmatic oxides consist of magnetite, ilmenite, and chromite; the sulfides consist of both (Fe,Ni)1-xS (MSS) and Cu–Fe sulfide (ISS). Syn- and posteruptive phases occur in vesicles in both lavas and tephra, and on surfaces of ash and along fractures. The mineral assemblages in lavas include Cu–Fe sulfide and Fe–Ti oxide in vesicles, and Fe sulfide and Cu–Fe sulfide in segregation vesicles. Assemblages in vesicles in scoria include Fe–Ti oxide and rare Fe–Cu–Sn sulfide. Vesicle fillings of Fe–Ti oxide, Ni-rich chromite, Fe sulfide, Cu sulfide, and barite are common to two pumice samples. The most coarse-grained of the vesicle fillings are Cu–Fe sulfide and Cu sulfide, which are as large as 50 μ in diameter. The youngest Plinian pumice also contains Zn(Fe) sulfide, as well as rare Ag–Cu sulfide, Ag–Fe sulfide, Ag bromide, Ag chloride, and Au–Cu telluride. The assemblage is similar to those typically observed in high-sulfidation epithermal mineralization. The fine-grained nature and abundance of syn- and/or posteruptive phases in porous rocks makes metals susceptible to mobilization by percolating fluids. The abundance of metal compounds in vesicles indicates that volatile exsolution prior to and/or during eruption played an important role in releasing metals to the atmosphere.