Chronology and origin of Au-Cu deposits related to paleozoic intracontinental rifting in West Tianshan Mountains,NW China

Located between the Tarim platform and Junggar massif, the West Tianshan intracontinental rift abuts against the China-Kazakhstan boundary in the west part, borders on the Yilianha-bierga late Paleozoic relic ocean basin and the South Tianshan late Paleozoic ocean basin respectively in the northeast separated by the Aibi Lake fault and in the southeast by the fault along the southern margin of the Yili massif. During the development and after the close of the West Tianshan intracontinental rifting in the Carboniferous-Permian period, a series of nonferrous and precious metal mineralizations occurred with the Au-Cu deposits being the most important. Isotopic chronologic study of representative deposits of different types shows that gold-copper mineralization in the West Tianshan intracontinental rift zone mainly happened during the middle-late Her-cynian Period, among which the Axi volcanic hydrothermal type gold deposit was formed during the Carboniferous with a fluid inclusion Rb-Sr isochron age of (339 ± 28) Ma; the Qiabukanzhuota quartzolite type gold deposit has a Rb-Sr isochron age of (312 ± 46) Ma; the Tawuerbieke porphyry type gold deposit has a Rb-Sr isochron age of (295 ± 16) Ma; the Jingbulak magmatic liquation Cu-Ni deposit and the Musizaote porphyry type Cu deposit have the forming ages of 300 Ma± and 250 Ma±, respectively. Analyses of crustal evolution and metallogenetic geological backgrounds of Au-Cu mineralizations in the studied area shows a close correlation with the rifting.

     

Chronology and origin of Au-Cu deposits related to Paleozoic intracontinental rifting in West Tianshan Mountains, NW China

Located between the Tarim platform and Junggar massif, the West Tianshan intraconti-nental rift abuts against the China-Kazakhstan boundary in the west part, borders on the Yilianha-bierga late Paleozoic relic ocean basin and the South Tianshan late Paleozoic ocean basin re-spectively in the northeast separated by the Aibi Lake fault and in the southeast by the fault alongthe southern margin of the Yili massif. During the development and after the close of the WestTianshan intracontinental rifting in the Carboniferous-Permian period, a series of nonferrous andprecious metal mineralizations occurred with the Au-Cu deposits being the most important. Isotopicchronologic study of representative deposits of different types shows that gold-copper mineraliza-tion in the West Tianshan intracontinental rift zone mainly happened during the middle-late Her-cynian Period, among which the Axi volcanic hydrothermal type gold deposit was formed duringthe Carboniferous with a fluid inclusion Rb-Sr isochron age of (339 ± 28) Ma; the Qiabukanzhuotaquartzolite type gold deposit has a Rb-Sr isochron age of (312 ± 46) Ma; the Tawuerbieke por-phyry type gold deposit has a Rb-Sr isochron age of (295 ± 16) Ma; the Jingbulak magmatic liqua-tion Cu-Ni deposit and the Musizaote porphyry type Cu deposit have the forming ages of 300 Ma ±and 250 Ma±, respectively. Analyses of crustal evolution and metallogenetic geological back-grounds of Au-Cu mineralizations in the studied area shows a close correlation with the rifting.     

Chronology and origin of VMS deposits in Xinjiang,NW China

VMS deposits in Xinjiang, NW China are widespread in the Altay, Tianshan and West Kunlun orogenic belt, mainly formed during the Proterozoic rifting and Phanerozoic post-orogenic extension and are related to the bimodal volcanism. The VMS deposits are middle and small in scale. According to assemblages of metallogenetic elements, they can be divided into four types (Cu-Zn, Cu-S, Pb-Zn-Cu and Pb-Zn types) with the Cu-Zn and Pb-Zn types being the most important ones. Research of isotopic chronology shows that the VMS deposits in Xinjiang were formed during the Proterozoic, Ordovician, Deovonian, Carboniferous and Permian periods and usually underwent multi-stage mineralization, especially the large-sized deposits usually have post-volcanic superimposed mineralization by tectonomagmatic or metamorphic hydrothermal metal-logenic fluids.

     

Chronology and origin of VMS deposits in Xinjiang,NW China

VMS deposits in Xinjiang, NW China are widespread in the Altay, Tianshan and West Kunlun orogenic belt, mainly formed during the Proterozoic rifting and Phanerozoic post-orogenic extension and are related to the bimodal volcanism. The VMS deposits are middle and small in scale. According to assemblages of metallogenetic elements, they can be divided into four types (Cu-Zn, Cu-S, Pb-Zn-Cu and Pb-Zn types) with the Cu-Zn and Pb-Zn types being the most important ones. Research of isotopic chronology shows that the VMS deposits in Xinjiang were formed during the Proterozoic, Ordovician, Deovonian, Carboniferous and Permian periods and usually underwent multi-stage mineralization, especially the large-sized deposits usually have post-volcanic superimposed mineralization by tectonomagmatic or metamorphic hydrothermal metal-logenic fluids.     

Chronology and origin of VMS deposits in Xinjiang, NW CHINA

VMS deposits in Xinjiang, NW China are widespread in the Altay, Tianshan and WestKunlun orogenic belt, mainly formed during the Proterozoic rifting and Phanerozoic post-orogenicextension and are related to the bimodal volcanism. The VMS deposits are middle and small inscale. According to assemblages of metallogenetic elements, they can be divided into four types(Cu-Zn, Cu-S, Pb-Zn-Cu and Pb-Zn types) with the Cu-Zn and Pb-Zn types being the most impor-tant ones. Research of isotopic chronology shows that the VMS deposits in Xinjiang were formedduring the Proterozoic, Ordovician, Deovonian, Carboniferous and Permian periods and usuallyunderwent multi-stage mineralization, especially the large-sized deposits usually have post-volcanic superimposed mineralization by tectonomagmatic or metamorphic hydrothermal metal-logenic fluids.     

土壤地球化学在广南斗月金矿中的应用

对现已发现的超大型金矿和国内金矿资源进行统计,结果表明,大型、超大型矿床中与微细浸染型金矿相对应的金矿成因类型(如渗滤热液型金矿、含碳浅变质碎屑岩型金矿等)占有很大比例。因此开展对微细浸染型金矿的研究和找矿具有重要的实际意义。在广南斗月金矿开展1∶10000土壤地球化学测量(简称化探),了解测区以Au为主的As、Sb、Hg、Ag土壤地球化学背景,确定化探异常下限,圈定Au、As、Sb、Hg、Ag化探(次生晕)异常,根据各异常面积的大小、浓度的高低以及五个元素异常套合(组合)情况等综合因素,对化探综合异常进行评序和分级,结合地质简测等地质资料的综合研究分析,判别具有潜在找矿价值的异常区,为进一步地质勘探工作提供靶区。     

11th International Conference on Methods and Applications of Radioanalytical Chemistry (MARC XI) introduction

Nuclear terrorism has led to newer investigative methods for building national nuclear forensic libraries. The objective of this work was to resolve these signatures by applying the ICP-MS for isotope ratio (IR) analysis on uranium containing samples. Lead (Pb) isotope ratios for the studied gold mine has ²⁰⁷Pb/²⁰⁴Pb values between 13–20 and ²⁰⁶Pb/²⁰⁴Pb values ranging from 16–25, which confirm that the Carletonville gold fields are of uraninite detrital pyrite deposits. Trace elemental concentrations indicated a pyrite type of uranium deposit. Uranium in the deposit exhibits geochemical signatures of the radiogenic formations of the ore enhanced in ²⁰⁶Pb.     

The use of sector field ICP-mass spectrometry for Rb-Sr geochronological dating

Rb-Sr dating, one of the most important tools in geochronology, requires determination of the Rb/Sr concentration ratios and the 87Sr/86Sr isotope ratios in co-genetic minerals or rocks and is traditionally performed by thermal ionization mass spectrometry (TIMS). In this work we investigated whether sector field inductively coupled plasma mass spectrometry (ICP-MS), which is characterized by a high sample throughput and straight-forward sample introduction, could be used as an alternative to TIMS. To avoid spectral overlap of the ion signals of the isobaric nuclides 87Sr and 87Rb, Sr was separated from Rb by cation-exchange chromatography. A mathematical correction was applied to take into account the small amount of Rb that can be present in the Sr fraction. The isotope ratio accuracy and precision attainable with ICP-MS were evaluated by analysis of several reference materials from the US Geological Survey. The results of this evaluation show that excellent accuracy could be achieved; the internal precision (repeatability) of the isotope ratio (expressed as the relative standard deviation for 10 successive 1-min measurements) was 0.04-0.12%. An attempt was made to calculate the total or combined uncertainty on the isotope ratio results, by also taking into account other possible error sources (corrections for mass discrimination, detector dead time, blank signal and Rb fraction). Finally, the same procedure was used for dating two rock formations that were 2,500 Ma and 350 Ma old, according to age determinations previously performed by the Rb-Sr laboratory of the University of München (Germany) using TIMS. The ICP-MS results (2,520 +/- 150 Ma and 379 +/- 48 Ma) obtained for these formations compare well with the corresponding TIMS data (2,509 +/- 120 Ma and 357 +/- 25 Ma).     

Dendrite structure of electrolytic gold deposited from molten chlorides

The structure of gold deposits produced by electrolysis of molten eutectic NaCl-KCl-CsCl at 500–700°C in an inert atmosphere is studied. The initial process on the gold cathode is the epitaxial growth of a layer up to 3 μm thick with a smoothed surface and a considerably later growth of grain boundaries. Gradually, on the protruding parts of deposit, the growth of dendrites starts. The dendrites are the major form of gold deposits. Typical gold dendrites are two-dimensional 2D〈112〉 and 2D〈112〉–〈110〉 and three-dimensional 3D〈100〉. Upon supplying air into the atmosphere above the melt at high current densities at the initial period there appears a powder comprising particles of a rounded twisted shape. Probable mechanisms leading to the formation of the “rounded” powder are discussed.     

Optimization of gamma activation autoradiography for searching noble methods in samples of ultrabasic rocks

The conditions for the gamma activation autoradiography of some noble metals are optimized by selecting electron energy upon irradiation with bremsstrahlung from a U-17 linear electron accelerator (Moscow Engineering Physics Institute). Two ultrabasic rocks are taken as examples. It is shown that the reduction of electron energy from 25 to 15 MeV lowers the detection limits for some platinum-group metals and gold in such samples to the level attained at an electron energy of 25 MeV in the absence of background radiation. In one of the samples (Gal’mano-Enansk massif, Kamchatka), we detected an inclusion that can be due to the presence of (0.18 ± 0.03) ng Au or (8.4 ± 1.4) ng Pt. The detection limits (ng) are as follows: Au, 0.03; Pt, 0.16; Pd, 0.42, and Rh, 3.4.     

Disperse Electrolytic Platinum and Palladium Deposits of Submicron Thickness on Polycrystalline Supports: An X-ray Diffractometry and Microscopy Study

The structure of model electrode materials broadly used in electrocatalysis (platinized platinum, palladized platinum, platinized gold) is studied by x-ray diffractometry, scanning electron microscopy, and transmission electron microscopy. Disperse platinum and palladium coatings less than 1 m thick are obtained by potentiostatic or galvanostatic deposition from solutions of complex chloride salts. Lattice parameters of disperse metals are shown to be considerably smaller than those of bulky crystals. Some new tendencies of variations in structural parameters with the deposition potential are revealed. Special attention is paid to a reliable determination of the size of regions of coherent scattering (ROCS) and microdistortion; in connection with this, results of approximation of reflections by various functions and a harmonic analysis of reflections are compared. The latter are used for constructing ROCS distributions by size. Good agreement is found with the STM data for platinum deposits obtained earlier. Conversely, in the case of palladium deposits, ROCS are smaller than the particle size in an outer layer of the deposit by the STM data. This result is interpreted in terms of strong concrescence of palladium nanoparticles. To determine the true surface areas of deposits and estimate continuousness of covering the support by the deposit and regularities of platinum aging on gold in conditions of potential cycling, a voltammetry method is applied.     

Effects of retrograde-zoning of garnet on Sm-Nd isotopic dating of eclogite and oxygen isotopic disequilibrium between eclogitic minerals

The compositional zoning of the garnet in a strongly deformed eclogite from Raobazhai foliated peridotite has been recognized. The CaO concentrations of the garnet are decreased from the core to the rim, while its MnO concentrations are increased, suggesting the retrograde origin of such CaO—MnO zoning. The tie line of garnet + omphacite from this eclogite gives a Sm-Nd age of (187 ± 5) Ma, which is less significant than the Sm-Nd ages of (221±5)—(228 ± 3) Ma and (210 ± 6)—(214 ± 6) Ma for ultrahigh-pressure eclogites in the southern Dabie zone and in the northern Dabie zone, respectively. This younger Sm-Nd age could result from the¹⁴³Nd/¹⁴⁴ Nd ratio decrease of the retrograde zone in the garnet. The δ¹⁸O values of the garnet and omphacite show that their fractionation values are less than the equilibrium fractionation value between the garnet and omphacite at 500—900°C, which suggests an oxygen isotopic disequilibrium between them.     

Regional organic geochemistry of host sediments of Palaeoproterozoic McArthur River Ore deposit, Australia

The 1,640 Ma HYC (Here’s Your Chance) deposit at McArthur River, Northern Territory, Australia, is one of the largest and least metamorphosed Proterozoic stratiform lead-zinc-silver deposits in the world. The thermal history of the deposit is a currently not well understood, both low and high temperature mechanisms have been proposed. From our study we were able to estimate (from both kerogen and bitumen thermal maturity indices which concur) the thermal maturity to be equivalent to Ro 1.1–2.0%, corresponding to the wet gas generation zone, with a maximum relatively low burial temperature range of 120–180 °C in the ore samples. Regionally, temperatures were not further constrained due to the complex and dynamic nature of the sedimentary environment. Contribution to the 65th Birthday Festschrift Issue.     

Spontaneous oscillations in gold electrodeposition

We report the appearance of spontaneous oscillations during the electrodeposition of gold along the surface of aqueous hydrogen tetrachloroaurate solutions coated by a positively charged dimethyldioctadecylammonium monolayer, when a current ramp with a rate comprised between 1 and 1.5 nA s⁻¹ is applied to the working electrode. Alternating sequences of two-dimensional (2D) growth and three-dimensional (3D) thickening of the deposits leading to gold films with a well-defined terraced structure are observed. Such a phenomenon appears to be produced by the competition between two mechanisms controlling the current density J₁: one is the current ramp which tends to increase J₁ and the other one is the growing of the gold deposit which induces a decrease of J₁.     

Texture of Electrolytic Platinum Deposited on Polycrystalline Gold

Platinum deposits of submicron thicknesses on polycrystalline gold substrates subjected to different thermal treatments and characterized by texture 200, 311, and 220 are characterized by methods of x-ray diffractometry and scanning electron microscopy. No deposits prepared in a potentiostatic mode exhibit a pronounced texture or a reliable correlation between a weak texture of a deposit and the substrate texture. Established is the difference of predominant directions of secondary nucleation–growth of deposit on neighboring grains of the substrate. The assumption that the deposit includes fragments the size of a few tens of micrometers with pronounced texture of different directions is substantiated.     

Preparation and certification of high-grade gold geochemical reference material

One high-grade gold geochemical reference material-BND 3401.01 has been prepared by the National Geophysical Research Institute (NGRI), Hyderabad in collaboration with the Hutti Gold Mines Company Limited (HGML), Hutti and National Physical Laboratory (NPL), New Delhi, in India. The sample is a sheared gold-sulphide-bearing quartz vein emplaced in a sheared acid volcanic rock that was collected at the 2400-foot level from the middle reef of Hutti deposit located in the north-western periphery of the late-Archaean Hutti-Maski greenstone belt, Karnataka, India. Fifteen institutions in India, Canada, China and Tanzania having experience in geochemical analysis had participated in this collaborative analysis programme. The sample was extensively characterized for its major, minor, trace and ultra-trace element composition by using a variety of analytical techniques. Usable values were provided for major, minor and several trace elements including all rare earth elements (REE). The certified value for the gold concentration in BND 3401.01 gold ore is 12.1±0.7 mg/kg.     

FT-IR microscopic imaging of calcified deposit of rotator cuff tendonitis: A pilot study and a randomised identification of the compositional components after extrusion from tendon to muscle

Fourier transform infrared (FT-IR) microspectroscopy with mapping system was applied to identify and evaluate what difference in the distribution and compositional components of the calcified deposit of rotator cuff tendonitis after dislocation from tendon to muscle. A 49 year-old female patient suffered from severe shoulder pain was enrolled in this study. Diagnostic high-resolution ultrasonography (HRUS) was initially carried out to verify the calcific tendonitis. The calcified deposits were then examined by histopathologic assessment and FT-IR microspectroscopy. Diagnostic HRUS reveals that the calcified deposits were observed in the subscapularis tendon and infraspinatus muscle of the shoulder for this patient. FT-IR microspectroscopic imaging results clearly indicate that both IR spectra of the calcified deposits in tendon and muscle were almost the same as that of the IR spectrum of hydroxyapatite except the peak at 873 cm⁻¹. It is also found that the peak intensity at 1030 cm⁻¹ for tendon sample was somewhat more intense than that of the peak at 1031 cm⁻¹ for muscle sample, implying that the calcified sample in the tendon seems to be mature than that in the muscle. The second-derivative IR spectra of two calcified samples exhibit two specific sharp peaks at 880 and 872 cm⁻¹, indicating that the type A and type B carbonated apatites were markedly co-existed in both calcified deposits of tendon and muscle even the calcified deposit was dislocated from tendon to muscle. These carbonated apatites presented in the calcified deposits of either tendon or muscle of the shoulder were also consistent with the nodular or nodular nodular-cystic morphology of calcified plaque of the shoulder after HRUS examination.     

Micro-PIXE Analysis of Monazite from the Dora Maira Massif, Western Italian Alps

Quantitative micro-PIXE and electron microprobe analyses, as well as micro-PIXE compositional mapping of trace elements were performed on monazite [(Ce, La, Nd, Th)PO₄] inclusions in pyrope megablasts from Dora Maira Massif, Western Italian Alps for petrological and geochronological purposes. Monazite was studied by SEM-BSE imaging and by X-ray qualitative compositional maps of major elements; further WDS electron microprobe analyses were carried out in areas showing different BSE intensity in order to quantify chemical zoning. Finally, micro-PIXE compositional maps and quantitative analyses were performed on selected spots and areas. EPMA data indicate that the Dora Maira monazite is Ce- and Th-rich with homogeneous concentrations of LREE, but with a significantly heterogeneous distribution of Th, as well as of Y, Sr, U and Pb as displayed by micro-PIXE compositional mapping. HREE mostly occur in concentrations below the detection limit for standard quantitative EPMA. Th–U–Pb zoning suggests two monazite growth events, dated at 35 (±7 Ma) and 60 Ma (±10 Ma), respectively. While the younger age of 35 Ma found in high-Th monazite areas corresponds to the thermal and baric peak of the UHP metamorphism in the Dora Maira Massif, in agreement with previous literature data, the older ages of 60 Ma found in low-Th areas have to be confirmed by U–Th–Pb isotopic data.     

n型半导体硅电极表面Au的电化学成核机理

在成功实现半导体硅表面电沉积致密金膜的柠檬酸盐镀金实际应用体系中,运用循环伏安和电位阶跃法研究了Au在n型Si(111)电极表面的电沉积过程和成核机理.结果表明,在该体系中, Au在Si表面呈现不可逆电极过程,成核过电位达到250 mV;根据Cottrell方程求得扩散系数D = (1.81 ± 0.14) × 10^-4 cm₂·s^-1;运用Scharifker-Hills (SH)理论模型对比分析拟合实验结果,表明Au在n型Si表面遵循扩散控制下的三维连续成核机理;通过扫描电子显微镜观察Au初期成核、生长形貌,进一步证实了Au的三维连续成核机制,并讨论了阶跃电位和阶跃时间对Au核形貌和密度的影响.     

Application of Inductively Coupled Plasma-Atomic Emission Spectrometry/Mass Spectrometry to Phase Analysis of Gold in Gold Ores

Inductively coupled plasma-atomic emission spectrometry/mass spectrometry (ICP-AES/MS) is a potentially powerful tool in chemical phase analysis of gold in batch mode, especially applicable to the low-grade gold ores with gold content of far below detection limit of the other methods, but it has not been used in gold phase analysis of gold ores. In this work, three types of typical gold deposits (altered rock type, quartz vein type, and microscopic disseminated type) and national standard reference materials of gold ores were used to establish and validate a method for gold phase analysis of gold ores using ICP-AES/MS. The optimum conditions of phase analysis were determined, including the sample granularity and preparation procedures, separation absorbent, pretreatment procedures of various phases of gold and optimized instrument parameters. Evaluation of the optimized method showed that this method had acceptable precision (RSD: 1.1%–10.6%) and accuracy (relative error, RE: 0.5%–6.3%), and the detection results of gold in ores were comparable with those obtained using the hydroquinone volumetric method-extraction flame atomic absorption spectrometry (VOL-AAS) and graphite furnace atomic absorption spectrometry (GFAAS) methods. The sum content of gold of the 4 phases (free gold, F_Au; linked gold, L_Au; sulphide-bearing gold, S_Au; and other mineral-bearing gold, A_Au) conformed to the total gold content and was consistent with the results of rock-mineral identification. The proposed method had a low detection limit (0.30 ng g^–1) and wide linear range (5.0 ng mL^–1–20.00 μg mL^–1). It is a simple, rapid, and efficient method for gold phase analysis in batch form.