Electron Probe Microanalysis Data Research Articles

When detection and quantification of mineral fibres in natural raw materials are at their limit – the case of a clay from the Gomsiqe–Puka mining area (Albania)

Abstract. In today's global market, the movement of raw materials and goods in the free global market can lead to unintended consequences. One significant concern is the potential presence of contaminants and carcinogens, particularly when products originate from regions with less strict regulations and enforcement. This issue is particularly pertinent in the natural raw materials utilized in the global building materials market, where contamination by asbestos minerals can occur. Therefore, the screening of natural raw materials for asbestos content is crucial to mitigate the risk of exposure to carcinogens for both workers and the general public. In this study, we examine a challenging case involving a smectite–kaolinite clay from Gomsiqe–Puka, Albania, possibly containing mineral fibres. Detection and quantification of asbestos in this material push the boundaries of current experimental methods. Using transmission electron microscopy (TEM), micro-Raman spectroscopy, and electron probe microanalysis (EPMA), we identified the presence of asbestos tremolite, along with a rare fibrous variety of diopside. EPMA data allowed the advancement of some speculations on the origin of the observed tremolites, showing that Al-rich tremolites are typical of oceanic settings and Al-poor tremolites are more similar to continental tremolites. We also investigated the impact of milling on the detection and quantification of mineral fibres, testing different milling times. This investigation is crucial as it can influence the classification of the raw material as asbestos-containing material or not. Our findings indicate that tremolite, cleavage fragments, and elongated particles break down into smaller World Health Organization (WHO) fibres with increasing milling times (1–5 min). However, prolonged milling (10 min) leads to overgrinding, resulting in a decrease in the number of counted WHO fibres with a length exceeding 5 µm.

The Study of Olivine Inclusions in Diamonds from Liaoning, China and the Evaluation of Related Thermometers

Olivine is the most abundant mineral in mantle peridotite and a typical inclusion in diamonds, providing essential evidence for the characterization of the diamondiferous lithospheric mantle. Three olivine inclusions in diamonds (OlDia) from Liaoning in the North China Craton (NCC) were exposed for in situ measurements, and the compositional data of 62 other OlDia from Liaoning were collected based on previous reports. The enrichment of TiO2 (>0.1 wt.%) with high Cr# (>50; Cr# = 100Cr/(Cr + Al) by atom) was revealed, despite the predominance of depleted TiO2 contents and high Mg# (92.8–93.2; Mg# =100Mg/(Mg + Fe) by atom) for OlDia. Silica fluid accompanying olivine still trapped in the host diamond was recognized using Raman spectroscopy. Three thermometers were applied to the OlDia, based on the data from Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Electron Probe Micro-Analysis (EPMA), and a temperature range (TLA and TEPMA) of 1080–1380 °C was yielded. With respect to the TLA, Al-in-olivine thermometers were preferred, although there was a smaller deviation between TEPMA and TLA when using the Cr-in-olivine thermometer. The results of these thermometers show a high correlation with TEPMA, enabling their application based on EPMA data. Projections onto 39–42 mW/m2 model geotherms underline a diamondiferous base of the lithospheric mantle beneath the NCC. The lithospheric mantle is characterized by refractory and depleted sections, where enrichment metasomatism may have occurred at the lower roots (161–178 km).

On the viability of detrital biotite Rb–Sr geochronology

Abstract. Re-examination of International Ocean Discovery Program (IODP) sediment samples collected from the Bay of Bengal via laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) Rb–Sr geochronology demonstrates the viability of the biotite Rb–Sr system for use as a detrital chronometer. The age population defined by the Rb–Sr dates essentially reproduces that previously published for detrital 40Ar/39Ar dates. The effect of unknown/assumed initial 87Sr/86Sr on the calculated population can be ameliorated by filtering for higher 87Rb/86Sr ratios. Such filtering, however, could introduce bias toward more radiogenic populations, especially in younger material that has not had time to accumulate radiogenic product (e.g. limiting the effect of initial 87Sr/86Sr to ∼ <5 % requires filtering of 87Rb/86Sr >500 at 250 Ma and 87Rb/86Sr >50 at 2500 Ma). Finally, Ti-in-biotite temperatures calculated based on element concentration data collected during LA-ICP-MS overlap with those calculated for the same material based on electron probe microanalyzer data, demonstrating the potential for in situ biotite petrochronology based on the Rb–Sr system.

A New Type of White Nephrite from Limestone Replacement along the Kunlun–Altyn Tagh Mountains: A Case from the Mida Deposit, Qiemo County, Xinjiang, China

The recently discovered Mida nephrite deposit, located in the East Kunlun Mountains, Qiemo County, Xinjiang, Northwest China, contains new types of white and greenish white nephrite formed by limestone replacement, which shows microstructures, macroscopic features and country rocks typologies that are quite different from those of the other deposits along the Kunlun–Altyn Tagh Mountains. The gemological and mineralogical characteristics of Mida nephrite are presented here. These nephrites show an ivory white color and a porcelain-like appearance, with semitranslucent-to-opaque transparency and a porcelain-to-greasy luster. Petrographic study, electron probe microanalysis (EPMA) data and scanning electron microscopy (SEM) images have indicated that the nephrite is composed of tremolite, accompanied by minor quartz, calcite and diopside. Tremolite aggregates have shown different textures, like flaky, granular, fibrous–felted, bundle, radial and metasomatic relict textures. Quartz has appeared in granular or disseminated form, dispersed in the tremolite matrix. Calcite has shown a metasomatic relict texture in the white nephrite samples. Diopside has shown euhedral grains, with some distributed with a certain geometric appearance. Based on our observations, it is suggested that the quartz in the nephrite originated from Si-rich hydrothermal fluids. We propose that the substantial size difference of mineral grains, together with uncompacted grains with inter-particle pores, are the main reasons for the internal reflection and refraction under transmitted light, which allow less transmitted light to pass through the nephrite body and generate the appearance of a semitranslucent-to-opaque transparency, ivory white color and porcelain luster. Our study has unveiled that the Mida nephrite is not typical of the two known types (D-type: dolomite-related; S-type: serpentinite-related) and is overlapped by quartz grains dispersed throughout the less compact tremolite matrix. These observations would help set it apart from the majority of nephrite jades found in the Kunlun Mountains region and provide valuable insights for enhancing comprehension of the diversity of the nephrite deposits.

Mineralogical Characteristics of Baima Vanadium Titanomagnetite during Magnetic Separation Upgrading

The Baima vanadium titanomagnetite deposit, located in the Panzhihua-Xichang (Panxi) metallogenic belt in China, is one of the super-large deposits in the region. The titanomagnetite upgrading process involves grinding the raw ore followed by magnetic separation. To determine the processing characteristics of the ore and assess the upgrading process, this study employs various methods and techniques, including the X-ray fluorescence spectrometer (XRF), chemical element analysis, the electron probe microanalyzer (EPMA), and the advanced mineral identification and characterization system (AMICS). The results show that the Fe grades in the upgraded raw ore, upgraded concentrate, and upgraded tailings are 55.68%, 57.89%, and 15.62%, respectively. After upgrading, the titanomagnetite content increased from 77.41% to 82.10%, and the Fe distribution in titanomagnetite also increased from 91.05% to 93.14%. In the upgraded raw ore, titanomagnetite particles followed a normal distribution, with 50.44% in the 38–74 μm range. In the upgraded concentrate, titanomagnetite was concentrated in the 19–38 μm range. Based on EPMA data, the theoretical Fe grade in titanomagnetite was calculated to be 65.08%, indicating the potential for further improvement through the upgrading process. This study elucidates the mineralogical characteristics during the vanadium titanomagnetite upgrading, providing a theoretical basis to further enhance the Fe recovery rate.

Depth profile analyses by femtosecond laser ablation (multicollector) inductively coupled plasma mass spectrometry for resolving chemical and isotopic gradients in minerals

Abstract. Femtosecond laser ablation (fs-LA) coupled to a multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) instrument has been proven to be a powerful means to analyze isotope ratios of “non-traditional” stable isotope systems with high spatial resolution, precision, and accuracy. The technique has been successfully applied, e.g., to investigate diffusion-generated isotopic zoning of the elements Li, Mg, and Fe in magmatic crystals. Here, we present a novel sampling technique employing a fs-LA system that is equipped with a computer numerical control (CNC) laser stage, using the open-source software LinuxCNC. Combining this laser set up with ICP-MS or MC-ICP-MS allows us to perform depth profile analyses of major and trace elements, respectively, as well as metal stable isotope variations of Fe and Mg in olivine crystals and in experimental diffusion couples. Samples are ablated in circular patterns with profile diameters of 100–200 µm using a laser spot size of 25–30 µm. Depending on the scan speed and the repetition rate of the laser, each ablated sample layer is between 300 nm and 3.0 µm thick. The integrated signal of one ablated layer represents one data point of the depth profile. We have tested this technique by analyzing 5–50 µm deep depth profiles (consisting of 15–25 individual layers) of homogeneous and chemically zoned olivine crystal cuboids. The minor and trace element analyses of the zoned cuboids, conducted by fs-LA-ICP-MS, were compared with “horizontal” profiles analyzed in polished sections of the cuboids with electron probe microanalysis (EPMA). Furthermore, we analyzed Fe–Mg isotopic depth profiles of the same cuboids with fs-LA-MC-ICP-MS, of which the chemically zoned ones also showed isotopic zoning at identical scales. Isotopic depth profiles were also conducted on an unzoned olivine cuboid that was coated with a 26Mg- and 56Fe-enriched olivine thin film (of ∼ 800 nm) in order to investigate top-to-bottom contamination during depth profiling. Our results indicate that (i) concentration data acquired by fs-LA depth profiling match well with EPMA data, (ii) precise and accurate Fe and Mg isotopic data can be obtained (i.e., precision and accuracy are ≤ 0.12 ‰ and ≤ 0.15 ‰ for both δ26Mg and δ56Fe, respectively), and (iii) potential top-to-bottom contamination during depth profiling of isotope ratios can be avoided. The technique presented herein is particularly suitable for the investigation of minerals or glasses with chemical and/or isotopic gradients (e.g., diffusion zoning) vertical to planar surfaces. It can also be applied in materials sciences in order to analyze thin films, coatings, or surface contaminations on solids.

Surface Silvering and Silver Enrichment of the Surface Layer of AD 253/4 Bosporan Staters: Electron Probe Microanalysis Data

Surface Silvering and Silver Enrichment of the Surface Layer of AD 253/4 Bosporan Staters: Electron Probe Microanalysis Data

Can lithium contents in mica be correctly calculated? Tischendorf́s proposal (Mineralogical Magazine 61/1997) 25 years after

AbstractMicas are the most common hosts of lithium in granitoid igneous rocks. Unfortunately, their Li contents cannot be determined by electron-probe microanalysis (EPMA) which is the most common method of mineral analysis. In an effort to avoid the use of other, technically more complex and expensive methods, several empirical schemes for the estimation of Li-contents from EPMA data have been developed. The methods proposed by Tischendorf (Mineralogical Magazine, 1997) have found the widest application. After 25 years of common usage, we have evaluated these methods by direct Li determination using laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS). Approximately 3000 spot analyses of Li in micas from eight areas worldwide obtained by LA–ICP–MS were compared with the values yielded by the methods of Tischendorf. We conclude that none of the lithium estimation methods can compensate fully for a real local analysis by LA–ICP–MS or secondary-ion mass spectrometry (SIMS). Generally, SiO2-based estimation for trioctahedral micas provides a better match to the analysed values than F-based estimation for dioctahedral micas. The Rb-based estimation for dioctahedral micas does not provide acceptable results. The usage of averaged Si- and F-based estimations can be accepted in common petrological studies for a general characterisation of mica species. Large errors of individual spot estimations preclude their usage in detailed mineralogical studies.

Trace Element Composition of Pyrite from Selected Black Shale and Chert Exposures in the Central Belt of Peninsular Malaysia: Implications for Mineral Exploration

Sedimentary and hydrothermal pyrites contained in selected Malaysian black shale and cherts have been analysed using laser ablation inductively coupled plasma (LA ICP-MS) and electron probe microanalysis (EPMA) at the University of Tasmania, Australia. This study shows that gold is concentrated in sedimentary and hydrothermal pyrite in the Middle Permian to Late Triassic black shales and Devonian cherts. According to LA ICP-MS analysis, gold contents in pyrite varied from 0.5 to 0.8 ppm Au in the Permo-Triassic black shale and between 0.2 and 0.8 ppm Au in the Devonian cherts. The lowest level of gold (0.3 ppm Au) was observed in the Permo-Triassic black shale that crops out at the Selinsing gold mine. In the Permo-Triassic period, the selenium contents display one peak (average range: 63.4–103.4 ppm Se) that is far from any gold deposit and one lowest point (average: 5.3 ppm Se) at the Selinsing gold deposit. In the Devonian period, the selenium content in sedimentary pyrite shows a peak (72.6–243.8 ppm Se) in the cherts. EPMA and LA ICP-MS data show consistent Se content variation in the Devonian and Permo-Triassic periods. Using selenium as a proxy for atmospheric oxygenation, the lowest level of Se content in the Permo-Triassic period is believed to decrease atmospheric oxygenation, as recorded in sedimentary pyrite found in black shale from the Selinsing gold deposit. The two peaks of selenium contents are interpreted as periods of increased atmospheric oxygenation. From an exploration perspective, the concentration of gold in sedimentary pyrites makes them sources for gold in the central sedimentary basin of Peninsular Malaysia. Therefore, the two maximum levels of Se and gold content during Permo-Triassic and Devonian times correspond to two stratigraphic levels of potential for orogenic gold mineralisation in the district. The EPMA data show significant values of Co over Ni in pyrite from the Gua Musang, Semantan, and Karak formation black shales, indicating a volcanic contribution of Co during the formation of sedimentary pyrite. Based on the current study’s findings, gold exploration should not be restricted to areas in and around the Selinsing gold mine, Buffalo Reef, Penjom mine, Tersang mine, and Bukit Koman mine but can be extended to BRSZ Units 1 and 2, Gua Musang, and Karak formations in the central belt of Peninsular Malaysia.

The Chemical Composition of Helvine-Group Minerals and Implications for Ore Genesis: Case Studies from the Dawan, Qidushan, and Taoxikeng Deposits

Abstract Helvine-group minerals have characteristic chemical compositions and textures and occur in different environments within magmatic–hydrothermal deposits. However, their origin is still unclear. There are several quartz-vein beryllium deposits with different element assemblages existing in southeastern China; these include the Dawan Be-Mo, Qidushan Be-Zn-Sn, and Taoxikeng Be-W deposits. We present the chemical composition of helvine-group minerals analyzed by electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry, in addition to zircon sensitive high-mass-resolution ion microprobe U-Pb and cassiterite laser ablation inductively coupled plasma mass spectrometry U-Pb ages. The zircon and cassiterite U-Pb data indicate that the Qidushan deposit formed during the Late Cretaceous (127–132 Ma). The electron probe microanalysis data show that the helvine-group minerals from the three deposits are helvine and/or danalite. A wide variety of different trace elements display high concentrations in the different deposits [e.g., helvine-group minerals from the Dawan deposit are rich in Li, B, Sc, V, Ga, Y, Sn, Cs, Th, and U; those from the Qidushan deposit are rich in Sc, Cd, and Sn; whereas those from the Taoxikeng deposit are rich in Y, Cd, Sn, Ta, and total rare-earth elements (ΣREE). The material analyzed from the Dawan deposit has the highest concentrations of Li (28.03–134.96 ppm), Sn (126.01–709.24 ppm), Sc (108.10–287.64 ppm), Cs (0–37.24 ppm), Th (4.78–112.63 ppm), and U (0.79–4.13 ppm). The material analyzed from the Taoxikeng deposit has the highest concentrations of Y (594.95–899.95 ppm), Cd (22.63–25.21 ppm), Ta (0.41–0.86 ppm), and ΣREE (281.69–451.79 ppm). However, those from the Qidushan deposit have the lowest concentrations of Y (10.21–37.70 ppm), Sn (0–26.88 ppm), U (0–19.06 ppm), Eu (0–0.14 ppm), and Cs (being below the detection limit). All of them are rich in heavy REEs but poor in light REEs, with distinctive REE patterns. Our results reveal that both crystallographic substitution and fluid composition control the enrichment of trace elements in helvine-group minerals. The textures and trace element compositions of helvine-group minerals can represent various parageneses and ore-forming fluid compositions. We propose that the δEu values and (La/Yb)N ratios can be used as markers to discriminate the genesis of helvine-group mineral precipitated from different environments based on the chemical compositions and the origin of ore-forming fluids.

Micro‐Raman spectroscopy and complementary techniques applied for the study of copper and iron wastes from Motya (Italy)

AbstractThis work is the first archaeometric investigation on copper and iron wastes from the Phoenician site of Motya (Sicily, Italy), dating back to the 8th to the 4th century BC. The samples were analyzed through micro‐Raman Spectroscopy (μ‐RS), Optical Microscopy (OM), Scanning Electron Microscope‐Energy‐Dispersive X‐ray Spectroscopy (SEM‐EDS), High‐Resolution Field Emission Scanning Electron Microscopy (HR‐FESEM), and Electron Micro‐Probe Analysis (EMPA). Micro‐Raman techinique permitted to identify both primary phases, for example, calchopyrite, and secondary products such as cuprite and copper thrihydroxychlorides in the Cu‐slags and goethite in the Fe‐slags. SEM and HR‐FESEM imaging showed the occurrence of inhomogeneous microstructures in the Cu‐ and Fe‐slags due to elements segregation, solidification, and corrosion. EMPA data revealed that the archaeometallurgical wastes from Motya can be differentiated on the basis of their chemical compositions. These preliminary results showed different typologies of by‐products, such as base metals speiss, copper slags from smelting sulfide ore with matte, and iron smelting and smithing slags, suggesting different stages of copper and iron productions.

Textural and chemical characteristics of beryl from the Baishawo Be-Li-Nb-Ta pegmatite deposit, Jiangnan Orogen: Implication for rare metal pegmatite genesis

The Baishawo pegmatite deposit is a newly discovered large Be-Li-Nb-Ta deposit, with estimated reserves of 16,160 t BeO @ 0.084 %, 11,280 t Li2O @ 0.85 %, and 3,450 t (Ta2O5 + Nb2O5) @ 0.201 %. The 3# pegmatite is internally zoned into border (contact against two-mica granite), wall, intermediate, and core zones. Beryl, the dominant economic mineral, occurs mainly in the intermediate and wall zones. In the intermediate zone, beryl coexists with feldspar and quartz, and in the wall zone, with quartz, tourmaline, garnet, and feldspar. Geological and petrographic observation, Electron-probe Microanalysis (EPMA), TESCAN Integrated Mineral Analyzer (TIMA), X-ray mapping, and Laser Ablation Inductive Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis were conducted to study the textural and compositional features of the beryl. The EPMA data show the concentrations of Al2O3, SiO2 and BeO in beryl are 17.61–18.32 wt.%, 64.01–65.23 wt.%, and 13.09–13.89 wt.% from the intermediate zone, respectively, and 17.57–18.52 wt.%, 64.33–65.15 wt.%, and 13.20–14.10 wt.% from the wall zone, respectively. Beryl from the intermediate zone contains higher concentrations of Ti (4.29–34.5 ppm), Mn (33.9–277 ppm), Rb (86.2–230 ppm), Cs (3333–4522 ppm) and Sn (0.571–28.7 ppm) than beryl from the wall zone (Ti 2.65–5.70 ppm, Mn 19.0–54.2 ppm, Rb 104–114 ppm, Cs 747–1242 ppm and Sn 0.085–1.26 ppm). Substitutions in beryl of the intermediate and wall zones are Li for Be, and Fe for Al. The distributions of alkali metals, Mg and Fe in beryl suggest that the pegmatite in the two beryl-bearing zones is the product of magmatic-hydrothermal interaction. Decreasing Mg content and Mg/Fe ratio with increasing Cs content and Cs/Na ratio suggest that beryl compositions reflect evolution of a highly differentiated two-mica granite magma, of which there is a residual fraction.

Mica Types as Indication of Magma Nature, Central Anatolia, Turkey

AbstractThis study focuses on the nature of giant micas occurring at the contact between the Özvatan (foid‐bearing) syenites and the metamorphic basement in Central Anatolia. The studied micas are dark greenish‐black in color and crystallized within vein shape like bodies as a narrow lens. The origin and processes responsible for the formation of these independent crystals of the giant micas were investigated by mineralogical, petrographical and geochemical analyses with the use of Confocal Raman Spectroscopy (CRS), Fourier Transform Infrared (FTIR) Spectroscopy, X‐Ray Diffraction (XRD), Polarized Energy Dispersive X‐Ray Fluorescence Spectrometer (PED‐XRF) and Electron Probe Micro Analysis (EPMA). According to XRD, CRS, FTIR and EPMA data, the giant micas are phlogopite. EPMA results reveal that studied mica minerals represent the products of re‐equilibrated primary mica characterized by high MgO and FeO and low Al2O3 and TiO2 contents. The trace element concentrations of the giant micas display similar patterns with the upper crust. The giant micas are crystallized within small cubicles from an alkaline magma and their composition is possibly modified by a mixing event between the crust‐ and mantle‐derived magmas and contaminated at varying extent by the basement metamorphic rocks.

Discrimination of Mineralization Types of Skarn Deposits by Magnetite Chemistry

There are different mineralization types for skarn deposits with various origins and ore-forming conditions. Magnetite is one of the main ore minerals in skarn deposits, but whether chemical compositions of magnetite can be used to discriminate different mineralization types remains unknown. This paper collects the published magnetite electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) data of skarn deposits and investigates the relationship between magnetite geochemistry and mineralization types of skarn deposits using the partial least squares-discriminant analysis (PLS-DA). For EPMA data, magnetite from Fe-Zn skarn deposits can be roughly separated from that of Cu-Fe-Pb-Zn, Fe, Fe-Co-Bi-Ag, Fe-Cu, and Fe-Zn-Pb skarn deposits due to the relative enrichment of Al and Mn for the former. For LA-ICP-MS data, magnetite from Fe-Sn, Fe-Zn, and W-Mo-Pb-Zn-Fe-Cu skarn deposits can be roughly separated from that of other skarn deposits due to positive correlation with Mn, Zn, and Sn and the negative correlation with V for the former. The relative depletion of V for these mineralization types likely reflects higher oxygen fugacity than the other types of skarn deposits. Magnetite from Fe-Au skarn deposits is separated due to the relatively high Cr and Ga contents, whereas magnetite from Fe-Cu skarn deposits can be discriminated because of the relative enrichment of Mg and Co. The discrimination between different types of skarn deposits in the plot of Mg + Mn vs. (Si + Al)/(Mg + Mn) indicates that the chemical composition of magnetite is significantly affected by the fluid–rock interaction, where magnetite from Fe-Au skarn deposit shows the lowest fluid–rock ratios. The PLS-DA discrimination based on LA-ICP-MS data is better than that of EPMA data, and the main discriminant elements for the different mineralization types are Mg, Al, Ti, V, Mn, Co, Zn, Ga, and Sn. Based on the discriminant elements, we propose a plot of Mg+Mn vs. Ga+Sn to discriminate different mineralization types of skarn deposits.

Textures of gold-bearing sulfides and gold precipitation mechanism, Wangu gold deposit, Jiangnan Orogen

万古金矿床位于江南造山带中部，赋存于新元古界冷家溪群浅变质岩系中，受NNE-NE向长沙-平江断裂带和近EW向九岭-清水韧性剪切带联合控制，金资源量约85t。其主要矿石类型为毒砂-黄铁绢英岩型和石英-硫化物脉型，其次为构造角砾岩型。毒砂和黄铁矿为该矿床主要的载金矿物，分布广泛。金成矿作用可分为四个阶段，I为乳白色石英-绢云母-白钨矿阶段；Ⅱ为烟灰色石英-绢云母-毒砂-黄铁矿-金阶段；Ⅲ为烟灰色石英-绢云母-黄铁矿-毒砂-多金属硫化物-金阶段；Ⅳ为乳白色石英-方解石阶段。其中，Ⅱ、Ⅲ为成矿主阶段。根据成矿主阶段毒砂电子探针分析结果，Ⅱ阶段毒砂中As的含量在42.19%~44.84%之间，均值为43.42%（n=56），Ⅲ阶段毒砂中As的含量在40.08%~43.36%之间，均值为42.08%（n=19）。通过毒砂温度计相图估算出Ⅱ、Ⅲ阶段的形成温度和硫逸度分别为364±21℃、319±22℃和10^-9.7~10^-7、10^-11.5~10^-8.6。电子探针数据揭示的载金毒砂和黄铁矿中不可见金含量分别为0.01%~0.66%和0.01%~0.11%。黄铁矿Au-As元素投点分布于金溶解度曲线两侧，说明其内金主要以纳米级颗粒和固溶体金或晶格金的形式赋存；其中Ⅱ阶段黄铁矿纳米级金颗粒占比为73.33%，多于Ⅲ阶段黄铁矿（67.80%）。以上数据说明在水岩反应过程中，围岩中的含铁矿物与成矿流体中的H₂S发生反应，生成毒砂和黄铁矿。伴随着强烈的水岩反应，成矿温度和硫逸度降低，成矿Ⅱ阶段至Ⅲ阶段主要载金硫化物由毒砂转变为黄铁矿，强烈的硫化作用导致金-硫络合物失稳并释放金，金以置换的方式进入硫化物晶格或以显微-超显微金颗粒的形式沉淀，形成含金硫化物；即硫化作用是导致万古矿床不可见金沉淀的主导机制。;The Wangu gold deposit, with a proven gold resource of~85t, is located in the middle section of the Jiangnan Orogen and occurs in metamorphic rock series of the Neoproterozoic Lengjiaxi Group. It formed under the control of the NNE-NE-trending Changsha-Pingjiang fault zone and the EW-trending Jiuling-Qingshui ductile shear zone. The main ore types of the deposit include arsenopyrite-, pyrite-, sericite-, and quartz-altered slate and quartz-sulfide veins, followed by slate breccia within hydrothermal quartz. Arsenopyrite and pyrite are the main gold bearing minerals in the deposit, which are widely distributed in the deposit. Gold mineralization can be divided into four stages:I, the milky quartz-muscovite-scheelite; Ⅱ, the smoky gray quartz-muscovite-arsenopyrite-pyrite-gold; Ⅲ, the smoky gray quartz-muscovite-pyrite-arsenopyrite-polymetallic sulfide-gold; and Ⅳ, the milky quartz-calcite. Among them, the Ⅱ and Ⅲ are the main mineralization stages. Based on the results of Electron Probe Micro Analysis (EPMA) of arsenopyrite from the main mineralization stages, the contents of As in arsenopyrite at stage Ⅱ range from 42.19% to 44.84%, with an average of 43.42% (n=56). The contents of As in arsenopyrite at stage Ⅲ range from 40.08% to 43.36%, with an average of 42.08% (n=19). According to the phase diagram of arsenopyrite thermometer, the formation temperature of Apy-1 in the stage Ⅱ is estimated to be 364±21℃ with a sulfur fugacity varying within 10^-9.7~10^-7. The formation temperature of Apy-2 in the stage Ⅲ is 319±22℃, and its sulfur fugacity is 10^-11.5~10^-8.6. The contents of invisible gold in gold-bearing arsenopyrite and pyrite were 0.01%~0.66% and 0.01%~0.11%, respectively, revealed by EPMA data. The Au-As data of pyrite are plotted on both sides of the gold solubility curve, indicating that gold in pyrite mainly exists in the form of nano-scale particles and solid solution or lattice gold. The proportion of nanometer gold particles in Py-1 pyrite is 73.33%, more than that in Py-2 (67.80%). The above data indicate that in the process of water-rock reaction, the iron-bearing minerals in surrounding rocks react with H₂S in ore-forming fluid to form arsenopyrite and pyrite. Accompanied by a strong water-rock reaction, the main gold-bearing sulfides changed from arsenopyrite to pyrite during mineralization from stage Ⅱ to Ⅲ with the decrease of mineralization temperature and sulfur fugacity, i.e., strong sulfurization results in instability of the gold-sulfur complex and the release of gold. As a result, gold is deposited into the sulfide lattice by substitution or in the form of microscopic-ultra microscopic gold particles to form gold-bearing sulfide. Therefore, sulfidation is the main mechanism of the precipitation of invisible gold in sulfides at the Wangu gold deposit.

The relationship between dental metal allergy, periodontitis, and palmoplantar pustulosis: An observational study.

This study aimed to investigate the relationship between dental metal allergy, periodontitis, and palmoplantar pustulosis among patients from a dental metal allergy clinic over a period of 8 years. This study included 436 patients who visited our dental metal allergy clinic between April 1, 2009 and March 31, 2016. Diagnoses of skin diseases, periodontal records, dental metal series patch test results, and electron probe microanalysis (EPMA) data were obtained from medical records. Relative risk (RR) values were estimated from these data. Of the 359 patients who underwent the patch test, 241 showed a positive reaction. Of the 187 patients who underwent EPMA, 113 had allergenic metals in their dental prostheses. These patients were suspected to have a dental metal allergy. Furthermore, 150 of the 436 patients were diagnosed with palmoplantar pustulosis (PPP). The RR of metal allergy between patients with PPP and healthy subjects was 3.88. The RR of periodontal disease between patients with PPP and PPP-negative patients in the national average was 2.54. In this study, both dental metal allergy and periodontitis showed a high RR for PPP.

Microchemical signatures of placer gold grains from the Gamba district, northern Cameroon: Implications for possible bedrock sources

The Central African Fold Belt (CAFB) in Cameroon hosts numerous alluvial gold deposits derived from known deposit types in the eastern and southern part of the country. In contrast, in northern Cameroon, primary source of gold remains enigmatic. Based on the morphological and geochemical signature of alluvial gold grains from northern Cameroon, this study discusses the distance-to-source and the style of gold mineralization of the Gamba district. Three hundred and fifty gold grains collected from the four locations were primarily analyzed by scanning electron microscopy (SEM) to investigate their morphological characteristics, and subsequently the composition was examined through the SEM and electron microprobe analysis (EMPA). The gold grains from the four locations have irregular to rounded morphology, with a microtextures indicating a proximal source at less than 5 km. Most of the gold grains display evidence for mechanical hammering and abrasion. EMPA results show mainly Au-Ag alloys, dominated by high Ag values in the cores from different location. Thus, Djaba is characterized by a range of 1.1–22.1 wt% Ag with 77.2–99.3 wt% Au; Bigbal includes a range of 10.3–32.9 wt% Ag with 66.1–88.7 wt% Au; Bougma is distinguished by a range of 7.3–18.3 wt% Ag with 80.8–91.9 wt% Au; and Mayo Salah is characterized by a range of 2.8–22.8 wt% Ag with 77.3–96.8 wt% Au. These range in compositions suggest multiple deposits of the same type in different locations. Gold grains from the four locations show the Te (0.1–0.3 wt%) content, Bi (0.1–0.7 wt%) content, and Cu (0–0.05 wt%) content, suggesting a source of orogenic gold mineralization. Most of the gold grains are Ag-depleted from both the cores and rims and show lack of Au-rich rims indicate no evidence of supergene precipitation, which suggests that the grains were transferred directly from hypogene source to surficial and fluvial system. EMPA data on the gold grains, plotted in the ternary diagram of Au-Ag-Cu, suggest that gold from the Gamba district is hydrothermal-orogenic in origin. Mineral inclusions include silicates (zircon, titanite, quartz, muscovites, biotite, actinolite, titanite, albite and almandine), oxides (magnetite, ilmenite and hematite), and phosphates (apatites), which suggest the magmatic and metamorphic conditions of formation for the hypogene source. This indicates the granitoids and metasediment of schists which bear multiple quartz veins as the potential bedrock sources. The microchemical signature of placer gold used in this study is a useful tool to explore the hypogene environment of an unknown primary source that can greatly help in mineral exploration in northern Cameroon.

Characteristics of fluid inclusions in the sandstone‐hosted Qianjiadian uranium deposit, southwest Songliao Basin, northeastern China: Implications for the nature and evolution of ore‐forming fluids

AbstractThe Qianjiadian deposit is a typical sandstone‐hosted uranium deposit that is hosted mainly in sandstone and siltstone of the Lower Cretaceous Yaojia Formation, located within the transition between the Kailu Depression and Jiamatu Uplift in the Songliao Basin, northeastern China. We studied the geological characteristics of this deposit, and analysed the mineralized sandstone by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) to identify the host minerals of fluid inclusions associated with uranium mineralization and describe their petrographic characteristics. In addition, this research investigated the origin of ore‐forming fluids and the relationship between petroleum fluids and uranium mineralization, based on the following findings. (1) EPMA and SEM data show that uranium minerals are hosted mainly in hydrothermal quartz (HQ) within sandstone cement, which indicates that uranium minerals co‐precipitated with HQ. (2) The fluid inclusions in the HQ show low homogenization temperatures (102.5–169.5°C) and low salinities (1.7–6.1 wt%). In contrast, aqueous inclusions in quartz overgrowths show lower temperatures (60.5–117°C) and higher salinities (4.2–8.7 wt%). (3) Petroleum fluids trapped in HQ homogenize fluid and those along healed microfractures in quartz overgrowth or plagioclase overgrowths at ~70–80°C, those trapped in present‐day organic inclusions at ~85–95°C, and at the boundary of detrital mineral grains show higher homogenization temperatures (~135–145°C). These results indicate that the hydrothermal quartz cement is associated with uranium mineralization, and the ore‐forming fluid of Qianjiadian sandstone‐hosted uranium deposit are characterized by low‐temperature, low‐salinity hydrothermal fluids, and the changes of temperature and salinity of hydrothermal fluids may not be intimately associated with uranium mineralization.

Trace precious metals in major sulfide minerals from the Federova Tundra platinum group element deposit in the Fedorova-Pana layered intrusion, central Kola Peninsula, Russia

ABSTRACTDrill-core samples from the basal Cu-Ni-platinum-group element mineralization of the Early Proterozoic Fedorova Tundra intrusion in the Fedorova-Pana layered intrusion, central Kola Peninsula, Russia, were studied in two separate projects in Canada and Russia. In Canada, trace precious metal analyses by laser ablation inductively coupled mass spectrometry of 323 base metal sulfide particles [pentlandite (101), pyrrhotite (98), chalcopyrite (25), and pyrite (99)] show that Pd is highly concentrated in pentlandite. Most of the analyses (71%) were done using two master composite samples of comminuted drill core representative of the West Pit and East Pit mineralization, FWMC and FEMC, respectively. Fewer analyses were made of three other comminuted drill core samples from the West Pit referred to as “lithology” samples: OLFW (olivine-bearing rocks), ANFW (leucocratic rocks), and GNFW (gabbronorite). In Russia, 120 polished sections sliced from drill core from the West and East Pits and from four other Fedorova Tundra intrusion deposits (Kievey, Northern Kamennik, Eastern Chuarvy, and Southern Kievey) were studied mineralogically. Platinum group mineral characterization and trace Pd electron probe microanalyses of pentlandite were done using polished sections from all six locations (n = 95). The trace electron probe microanalysis data for Pd in pentlandite from the West (n = 35) and East (n = 19) Pit samples, though at much higher detection levels, are considered to be comparable to the laser ablation inductively coupled mass spectrometry data. The Eastern Chuarvy samples show particularly high Pd concentrations averaging 0.49 wt.% Pd (n = 11) and as high as 1.64 wt.% Pd. The combined data from these studies guides our estimate that pentlandite accounts for 30 to 50% of the Pd in these ores and that Rh solid solution in sulfides may account for >98% of the total Rh.

Vertical Zoning in Hydrothermal U-Ag-Bi-Co-Ni-As Systems: A Case Study from the Annaberg-Buchholz District, Erzgebirge (Germany)

AbstractThe Annaberg-Buchholz district is a classic occurrence of hydrothermal five-element (U-Ag-Bi-Co-Ni-As) veins in the Erzgebirge (Germany) with an historic production of ~8,700 metric tons (t) Co ore, 496 t U ore, and 26.9 t Ag. Multiple mineralization stages are recognized in polyphase veins hosted by Proterozoic paragneiss. Fluorite-barite-Pb-Zn mineralization occurs across the entire vertical profile of the district, whereas U and five-element stages are restricted to the upper 400 m below surface, coinciding with a graphite-rich gneiss lithology.Here, we present field and petrographic observations, electron probe microanalysis and fluid inclusion data, as well as thermodynamic calculations to characterize five-element and fluorite-barite-Pb-Zn associations, and to constrain the origin of the vertical zoning in the Annaberg-Buchholz district. Microthermometric analyses of fluid inclusions related to the fluorite-barite-Pb-Zn stage yield homogenization temperatures between 78° and 140°C and salinities between 21.9 and 27.7 equiv wt % (NaCl-CaCl2). A correlation of fluid inclusion Na/ (Na + Ca) ratios with salinity suggests fluid mixing as a likely precipitation mechanism and relates ore formation tentatively to regional tectonics of the Mesozoic opening of the Atlantic.Thermodynamic calculations indicate that U is more sensitive to reduction than As, predicting that arsenide minerals are precipitated more distally relative to uraninite upon reduction along the fluid-flow path. This implies that the observed vertical zoning is not a primary feature but is the result of hydrothermal remobilization. The observations made in the Annaberg-Buchholz district have general importance to the understanding of U-rich five-element mineralization and may be relevant for exploration targeting in unconformity-related U deposits.