Some comparative marine chemistries of rhenium, gold, silver and molybdenum

Four metals, Re, Au, Ag and Mo, whose dissolved forms in seawater can potentially be reduced to insoluble states, have been measured in a variety of solids depositing under anoxic conditions: hydrothermal sulfides; coastal sediments; and phosphorites. For comparative purposes these elements have also been determined in ferromanganese minerals and pelagic sediments which have accumulated under oxidizing conditions. Rhenium appears to be a unique sentinel for identifying reducing depositional environments, where enrichments of greater than three orders of magnitude above crustal concentrations are found. Molybdenum follows Re in these sediments but Mo is enriched also in those that accumulate under oxidizing conditions. The reported Mo crustal concentrations appear low in comparison to our measured sedimentary values. Gold and Ag are concentrated in hydrothermal deposits and sulfides appear to be involved in the precipitation of these elements. Coastal sediments adjacent to a domestic outfall of Los Angeles, California contain extraordinary high accumulations of anthropogenic Au, Ag and Pt. The study seeks an understanding of the mobilities and sinks of these metals in the marine environment during the major weathering cycle. Further, anthropogenic contributions to their sedimentary concentrations are identified.     

Comparative geochemistry of cadmium, rhenium, uranium, and molybdenum in continental margin sediments

The concentrations of authigenic phases of Cd, Re, U, and Mo increase with depth in four 45-cm-long sediment box cores collected along the axis of the Laurentian Trough, Gulf of St. Lawrence. Average authigenic accumulation rates, estimated from element inventories, are similar to rates in other continental margin environments. Strong regional variations in sediment accumulation rate and sulfide concentration have little influence on the accumulation rates of Cd and Re. This suggests that slow precipitation kinetics controls the accumulation of Cd and Re in these sediments. The accumulation rate of authigenic U is more variable; it may be tied to the kinetics of microbially mediated U reduction and be controlled by the availability of reactive organic matter. Authigenic Mo is distinguished by a sharp subsurface concentration minimum, above which Mo cycles with manganese. Mo released to pore water upon reduction of Mn oxides diffuses downward and enriches the subsurface sediment. Mo accumulates most rapidly in the sediment with the highest sulfide content. Slow conversion of molybdate to thiomolybdate may explain the much slower Mo accumulation rate in the less sulfidic sediments. A component of authigenic Mo accumulates with pyrite in an approximately constant Mo:Fe ratio. The accumulation rate of pyrite and associated Mo is insensitive to AVS abundance. Pyrite formation may be limited by the reactivity of iron oxide minerals.     

安徽泾县湛岭斑岩型钼矿床中铼的赋存状态研究

铼（Re）作为关键金属之一,是国家安全和军事战略必不可少的关键矿产,近年来受到世界各国的广泛关注。目前全球90%的Re产出于斑岩型矿床中,由于Re和Mo（钼）的元素性质相近,辉钼矿是Re的主要富集矿物。目前,前人的研究主要集中于含Re辉钼矿多型、辉钼矿中Re的含量、以及微米尺度上Re在辉钼矿中的赋存规律等方面,但纳米尺度上,Re在辉钼矿中的赋存状态研究仍十分薄弱。本次工作以安徽省泾县新发现的湛岭斑岩型钼矿床中的辉钼矿为研究对象,查明矿床中的辉钼矿主要有两种类型：粗粒叶片状辉钼矿（Ⅰ型）和细粒集合体辉钼矿（Ⅱ型）。通过电子探针（EPMA）和激光剥蚀电感耦合等离子质谱仪（LA-ICP-MS）确定了微米尺度上辉钼矿中的Re含量呈较大的不均一性。粗粒叶片状辉钼矿核部的Re含量（90.2×10^-6）高于边部（37.6×10^-6）,细粒集合体辉钼矿中的Re平均含量（89.4×10^-6）明显高于粗粒叶片状辉钼矿（50.0×10^-6）,其中可见多个无规律的局部Re富集区域。在此基础上,对细粒集合体辉钼矿中富Re区域进行聚焦离子束（FIB）原位取样,并运用透射电镜（TEM）分析发现,在纳米尺度上,辉钼矿Re含量也有较大不均一性。在ADF-TEM照片中识别出辉钼矿具有a、b两种不同的表征。表征a的辉钼矿Re含量较高,晶格受到明显干扰,除类质同象替换外,还存在以Re-S吸附的方式赋存的Re;而表征b中的辉钼矿Re含量较低,晶格并未受到明显的干扰,Re主要是以类质同象替换的形式存在。以上研究结果表明,湛岭斑岩型钼矿床中的Re除了类质同象替代Mo进入辉钼矿晶格外,还以Re-S的形式吸附在辉钼矿晶格表面,Re的两种赋存状态是辉钼矿中Re含量不均一性的主要原因。

     

分光光度法测定钼矿石中钼不确定度评定

对分光光度法测定钼矿石中钼质量分数的不确定度进行评估,建立了数学模型,评定测量过程中不确定度主要来源于曲线拟合,以及重复实验产生的不确定度。当矿石中钼质量分数为0.054%时,评定其扩展不确定度为0.003 0%（k=2）。     

世界铼资源供需现状及展望

铼在地壳中的丰度低且分散,多伴生于钨钼矿中,现有方法常采用碱熔富集,流程长且繁琐,亟需开发一种简便快捷的检测方法。本文建立了逆王水微波消解钨钼矿石样品,8-羟基喹啉沉淀分离钨钼元素,与电感耦合等离子体质谱联用的检测方法。结果表明：0.0500g样品,2.80mL逆王水即可实现铼元素的全部溶出,0.20mL有机沉淀剂8-羟基喹啉（3%）在乙酸-乙酸铵缓冲体系（pH 4.5）中可选择性沉淀钼、钨元素,有效消除基体元素钼、钨（沉淀率>95%）对Re定量干扰,同时不引入新干扰元素。相比现有分离富集前处理流程更加简便快捷,前处理时间缩短为现有方法的1/4;该方法对Re的检出限为6.9ng/g,采用国家一级标准物质钼矿石（GBW07238）、钼矿石（GBW07285）、铼钼矿石（GBW07373）和钨锡铋矿石（GBW07369）对方法的准确度进行了验证,测定值与推荐值吻合,相对误差为0.71%～6.07%,RSD＜5%。本方法建立的“消解-分离富集”处理流程所需时间从常规的8～12h缩短至2h左右,在准确定量矿石样品中Re的同时简化了样品前处理流程,快速的样品处理及低廉的测试成本有助于关键稀有金属矿产的开发利用。

     

豫西钼矿集区地表水重金属时空分布特征及健康风险评价

豫西钼矿集区内长期的矿产资源开发向周围环境释放大量的重金属,区内地表水环境质量现状尚不明晰。于2019年丰水期（8月）和枯水期（12月）对矿集区内5条河流进行地表水采集,调查地表水重金属（Mo、Cd、Hg、As、Cr、Cu、Pb、Zn）的时空分布特征,并用健康风险模型评价地表水重金属人体健康风险。结果表明,丰水期地表水主要污染元素为Mo、Zn和Cd,而枯水期地表水主要污染元素为Mo、Hg和Cd,大多数点位地表水符合II类标准。地表水中的Mo主要来源于钼矿;Pb和Zn主要来源于钼矿和铅锌矿;Cd主要源于金矿和铅锌矿;Hg主要源于金矿。健康风险评价结果表明,地表水重金属通过饮用水途径所致的总个人年健康风险均低于美国环保署（US EPA）推荐的最大可接受风险水平。除丰水期成人总个人年健康风险低于国际辐射防护委员会（ICRP）推荐的最大可接受风险水平外,丰水期儿童、枯水期成人和儿童高于ICRP推荐的最大可接受风险水平。研究的结果可为钼矿集区地表水污染防治和风险管控提供科学依据。     

Formation of the world's largest molybdenum metallogenic belt: a plate-tectonic perspective on the Qinling molybdenum deposits

Qinling ore belt is the largest known molybdenum belt in the world with a total reserve of >5 Mt of Mo metal. Based on the geochemical behaviour of Mo, the structural settings of the Qinling orogenic belt, and geological events in eastern China, we propose that tectonic settings are of critical importance to the formation of these ore deposits. Molybdenum is very rare in the earth with an abundance of ～0.8 ppm in the continental crust. Both surface- and magmatic-hydrothermal enrichment processes are required for Mo mineralization. It can be easily oxidized to form water-soluble MoO₄ ^– in the surface environment, especially in the Phanaerozoic, and then precipitated under anoxic conditions. Therefore, closed or semi-closed water bodies with large catchment areas and high chemical erosion rates are the most favourable locations for Mo-enriched sediments. The Qinling orogenic belt was located in the tropics during crustal collisions, such that the chemical erosion was presumably intense, whereas the Erlangping back-arc basin was probably a closed or semi-closed water body as a result of plate convergence. More than 90% of the Mo reserves so far discovered in the Qinling molybdenum belt are associated with the Palaeozoic Erlangping back-arc basin. Compiled Re–Os isotopic ages for porphyry deposits (including several carbonate vein deposits) that have been dated show peaks during 220 million years (>0.32 Mt), 145 million years (>?3.5 Mt), and 115 million years (>?0.84 Mt), which correlate well with the three major episodes of granitoid magmatism since the Triassic. The ～220 million year episode of mineralization, represented by the Huanglongpu carbonate vein-type deposit and the Wenquan porphyry deposit, coincided with the formation of the South Qinling syn-orogenic granites as well as the Dabie ultrahigh-pressure metamorphic rocks, suggests a genetic relationship with the collision between South and North China Blocks. The ～145 Ma porphyry Mo deposits, representing the main mineralization, are attributed to reactivation by ridge subduction along the lower Yangtze River belt to the east of the Qinling orogen ～150–140 Ma. The ～115 Ma Mo deposits likely reflect slab rollback of the northwestwards subducting Pacific plate ～125–110 Ma.     

Mega-monsoon variability during the late Triassic: Re-assessing the role of orbital forcing in the deposition of playa sediments in the Germanic Basin

The formation of the supercontinent Pangaea during the Permo–Triassic gave rise to an extreme monsoonal climate (often termed ‘mega-monsoon’) that has been documented by numerous palaeo-records. However, considerable debate exists about the role of orbital forcing in causing humid intervals in an otherwise arid climate. To shed new light on the forcing of monsoonal variability in subtropical Pangaea, this study focuses on sediment facies and colour variability of playa and alluvial fan deposits in an outcrop from the late Carnian (ca 225 Ma) in the southern Germanic Basin, south-western Germany. The sediments were deposited against a background of increasingly arid conditions following the humid Carnian Pluvial Event (ca 234 to 232 Ma). The ca 2·4 Myr long sedimentary succession studied shows a tripartite long-term evolution, starting with a distal mud-flat facies deposited under arid conditions. This phase was followed by a highly variable playa-lake environment that documents more humid conditions and finally a regression of the playa-lake due to a return of arid conditions. The red–green (a*) and lightness (L*) records show that this long-term variability was overprinted by alternating wet/dry cycles driven by orbital precession and ca 405 kyr eccentricity, without significant influence of obliquity. The absence of obliquity in this record indicates that high-latitude forcing played only a minor role in the southern Germanic Basin during the late Carnian. This is different from the subsequent Norian when high-latitude signals became more pronounced, potentially related to the northward drift of the Germanic Basin. The recurring pattern of pluvial events during the late Triassic demonstrates that orbital forcing, in particular eccentricity, stimulated the occurrence and intensity of wet phases. It also highlights the possibility that the Carnian Pluvial Event, although most likely triggered by enhanced volcanic activity, may also have been modified by an orbital stimulus.     

Determination of rhenium and osmium by ICP-MS for galena and sphalerite

Digestion with aqua regia in a Carius tube and separation of Re with anion exchange resin is commonly employed for Re–Os dating of molybdenite and pyrite. However, the recovery of Re is extremely low when this routine anion exchange method is applied to galena, causing difficulty in Re–Os dating of galena. In this study, we investigated the mechanism of Re loss during sample preparation and tested a revised procedure for Re–Os dating of galena and sphalerite.     

钼精矿中铀的测定

酸法溶矿,加入氨水,钼形成（NH4）2MoO4、铜形成络离子：[Cu（NH4）4]2＋留在溶液里,过滤除去钼、铜。滤渣经2%盐酸溶解,铅与残渣留在滤纸上,铁等金属元素与铀以离子形式存在滤液中。在滤液中加入EDTA,用氨水调节溶液的酸度,控制溶液的pH=7±0.5,铀以（NH4）2U2O7形式沉淀,铁形成Fe（OH）Y络离子,过滤分离。该方法的加入标准回收率为98.8%～101.4%。     

A spectrophotometric method for the determination of rhenium in geologic materials

Existing methods for the chemical determination of rhenium have been modified and adapted for the analysis of rock, sediment, water, brine, and mineral concentrates.Little restriction is placed on sample size, but usually between 0.1 g and 100 g of solid sample is used which contains between 1 and 200 μg of rhenium giving a detection limit of 10 p.p.b. in the sample. Several liters of water sample may be used giving a detection limit of less than 1 p.p.b.The spectrophotometric method concentrates and isolates the rhenium from the sample by using carbon adsorption and solvent extraction.     

The first finds of rhenium minerals in Karelia

Rhenium is one of the rarest elements of the earth crust (abundance ratio 0.7 mg/t). In the Karelian region, Re and accompanying Os were discovered in a copper-molybdenum-porphyry ore formation, represented by the Lobash deposit, the Jalonvaara occurrences etc., and in a noble-metal-Cu-U-vanadium ore formation (Padma Group occurrences). Molybdenites from the above deposits are enriched in Re and Os (Lobash: 13–187 g/t Re, 0.4–6 g/t Os). So far, however, no rhenium minerals proper have been revealed in the Karelian deposits and occurrences of the above formations or elsewhere. As a result of the microprobe study of mineral assemblages of cupreous sandstones from the Voronov Bor deposit (bornite ore) and sulphide-copper-nickel ore from the Rybozero deposit, osmium-cupreous rheniite (Re, Cu, Os, Fe)₁S₂ that contains 56.53–60.25% Re, 4.61–10.99% Cu, 1.52–3.77% Os and up to 4.75% Fe was revealed and studied for the first time.     

An atomic level study of rhenium and radiogenic osmium in molybdenite

Local atomic structures of Re and radiogenic Os in molybdenite from the Onganja mine, Namibia, were examined using X-ray absorption fine structure (XAFS). Rhenium L_III-edge X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) show that the oxidation state of Re, the interatomic distances between Re and the neighboring atoms, and the coordination number of Re to S are very similar to those of Mo in molybdenite. The results confirm that Re is present as Re(IV) in the Mo site in molybdenite.Measurement of L_III-edge XANES and EXAFS of a minor concentration (8.55 ppm) of radiogenic Os was accomplished in fluorescence mode by removing the interfering X-rays from Re and other elements using a crystal analyzer system. The data indicate that the oxidation state of radiogenic Os is Os(III) and Os(IV) and clearly different from Os(II) in natural sulfide minerals, such as OsS₂ (erlichmanite). XANES data also suggest that radiogenic Os does not form a secondary Os phase, such as OsS₂ or Os metal, in molybdenite.EXAFS of radiogenic Os was successfully simulated assuming that Os is present in the Mo site in molybdenite. The data are consistent with the XANES data; Os does not form Os phases in molybdenite. The EXAFS simulation showed that the interatomic distance between Os and S is 2.27 Å, which is 0.12 Å smaller than the distances of Re-S and Mo-S (2.39 Å) in molybdenite. Similar valences and ionic sizes of Re and Mo in molybdenite support the fact that large amounts of Re can be incorporated into the Mo site as has been observed in previous studies, whereas the different properties of Os compared to Mo and Re suggested here support much lower abundance of common Os in molybdenite. This makes molybdenite an ideal mineral for the Re-Os geochronometer as shown in many studies. However, the shorter distance between radiogenic Os and S compared to those of Re-S and Mo-S in molybdenite suggests that the radiogenic Os has a smaller ionic size than Re(IV) and Mo(IV). Furthermore, Os may be partly present as Os(III). Smaller and lower charge Os can diffuse faster than larger and higher charge Re in molybdenite at a given set of conditions. Hence, our study provides an atomic-level explanation for the high mobility of Os compared to Re, which has been suggested by earlier workers using laser ablation ICP-MS.     

煤中黄铁矿的铼-锇同位素含量及其地质意义

采用Carius管溶样方法,通过热电离质谱对淮北煤田煤中黄铁矿样品的Re、Os含量及其同位素进行了测定,得出黄铁矿样品中Re和Os含量分别为1·22~1·29ng/g和0·0046~0·0054ng/g。对两个样品同位素定年测定得出,其年龄值分别为(73·9±3·2)Ma和(33±9)Ma,两个样品的年龄相差约258~286Ma。含量和同位素年龄差值表明两个样品是不同时代形成的黄铁矿。Re-Os同位素体系比值揭示黄铁矿所赋存的地质体受到来自地壳物质的显著混染。另外,γOTs参数也证实了这一点。该参数分别为+17和+18,表明了有富含Re母体的地壳物质的加入,这为煤中Re-Os含量及地质理论研究提供了参考资料。     

Geological and geochemical characteristics and metallogenic model of the Wenquan molybdenum deposit

The Wenquan molybdenum deposit is a kind of large-sized porphyry molybdenum deposit found in re-cent years.In this paper,on the basis of deposit geology,geochemistry and isotope geochronology data,the metal-logenic model of this deposit was established.The Wenquan granitic batholith belongs to the K-rich(alkali-rich) calc-alkaline rock series,which is the mineralization parent rock.The rock massif shows the characteristics of both crust-remelting granite and mantle-source granite.At the same time,the data of REE contents,hydrogen and oxygen isotopes and inclusion temperatures showed that the metallogenic hydrothermal solution is a mixed mesothermal solution of magmato-hydrothermal fluid and meteoric water.Mineralization was dated at 214±7.1 Ma,basically identical with the parent rock’s age(207-226 Ma).This reflects that molybdenum mineralization has a close relation to tectonic magmatism evoked by orogenic processes,and molybdenum mineralization occurred mainly at the petrogenesis stage at the late stage of magma emplacement.Mixing with meteoric water led to a decrease in the sa-linity of magmato-hydrothermal solution and changes in other physical and chemical properties.During the tectonic process,ore-bearing hydrothermal solution ascended along favorable fault structure channels.With physicochemical changes,it filled in the surrounding rock joints on both sides of faults,forming ore deposits.     

Sources of unique rhenium enrichment in fumaroles and sulphides at Kudryavy volcano

Rhenium (Re) is one of the least abundant elements in Earth, averaging 0.28 ppb in the primitive mantle. The unique occurrence of rheniite ReS₂ (74.5 wt% of Re) in Kudryavy volcano precipitates raises questions about recycling of Re-rich reservoirs within the Kurile-Kamchatka volcanic Island arc setting. The sources of this unique Re enrichment have been inferred from studies of Re-Os isotope systematic and trace elements in volcanic gases, sulphide precipitates and host volcanic rocks. The fumarolic gas condensates are enriched in hydrophile trace elements relative to fluid-immobile elements and exhibit high Ba/Nb (133-204), Rb/Y (16-406) and Th/Zr (0.01-0.25) ratios. They are characterised by high Re (7-210 ppb) and Os abundances (0.4-0.9 ppb), with ¹⁸⁷Os/¹⁸⁸Os ratios in a range 0.122-0.152. This Os isotopic compositional range is similar to that of the peridotite xenoliths from the metasomatised mantle wedge above the subducted Pacific plate, the radiogenic isotopic signature of which is probably due to radiogenic addition from a slab-derived fluid.Re- and Os-rich sulphide and oxide minerals precipitate from volcanic gases within fumarolic fields. Molybdenite (MoS₂), powellite (CaMoO₄) and cannizzarite (Pb₄Bi₆S₁₃) contain 1.5-1.7 wt%, 10 ppm, and 65-252 ppb of Re, respectively. Both molybdenite and rheniite contain normal Os concentrations, with total Os abundances in a range from 0.6 to 3.1 ppm for molybdenite, and 2.3-24.3 ppb for the rheniite samples. Repeated analyses of osmium isotope ratios for two rheniite samples form a best-fit line with an initial ¹⁸⁷Os/¹⁸⁸Os ratio of 0.32 ± 0.15 and an age of 79 ± 11 yr, which is the youngest age ever measured in natural samples. The high Re contents in molybdenite and rheniite led to high radiogenic ¹⁸⁷Os values, even in the limited period of time, with ¹⁸⁷Os/¹⁸⁸Os ratios up to 3.3 for molybdenite and up to 4.4 for rheniite.The Os isotopic compositions of andesite-basaltic rocks from the Kudryavy volcano (¹⁸⁷Os/¹⁸⁸Os up to 0.326) are more radiogenic than those of residual peridotites and fumarolic gas condensates that are mainly constituted from magmatic vapor. Such radiogenic values can be attributed either to the addition of a radiogenic Os-rich subduction component to the depleted mantle, or to the assimilation of older dacitic caldera walls (¹⁸⁷Os/¹⁸⁸Os = 0.6) during arc magma ascent and emplacement. The latter hypothesis is supported by the correlation between ¹⁸⁷Os/¹⁸⁸Os ratio and indicators of fractionation such as MgO or Ni, and by low contents of potentially hydrophile trace elements such as Ba, Rb and Th relative to fluid-immobile elements such as Nb, Zr and Y. The high Re flux in the Kudryavy volcano (estimated at ∼46 kg/yr) can be explained by remobilisation of Re by Cl-rich water from an underplated mantle wedge and subducted organic-rich sediments of the Pacific plate.