MC-ICP-MS高精度测定Pb同位素比值

多接收器等离子体质谱是近年发展起来的高精度同位素分析手段之一，通过用等离子体质谱测量Pb国际标准物质NBS981和NBS982,显示出多接收器等离子体质谱分析Pb同位素的优势。利用205Tl/203Tl进行作为内标，可以实现Pb同位素的质量分馏校正，极大地提高了Pb同位素分析的重现性。相比较热电离质谱，该方法精度更高，样品的用量更少，测试时间更短，多接收器等离子体质谱测定Pb同位素技术有良好的应用前景。     

High-precision Pb isotope analysis by multicollector-ICP-mass-spectrometry using 205Tl/203Tl normalization: Optimization and calibration of the method for the studies of Pb isotope variations

The development of the MC-ICP-MS method, which was launched about one decade ago and was largely stimulated by the need to solve geological problems, has opened a new avenue in isotope mass spectrometry. One of the advantages of this method is the possibility of applying a newly developed approach to the correction of analytical results for the effect of mass discrimination by normalizing the measured isotope ratios of an element to a reference (standard) isotope ratio of another element. This makes it possible to overcome the main disadvantage of conventional thermal ionization mass spectrometry (TIMS), in which the effect of mass discrimination cannot be fully taken into account during isotope analysis, and thus to implement a highly accurate method for the analysis of Pb-isotope composition. In application to the capability of the NEPTUNE MC-ICP mass spectrometer, we optimized and calibrated a method for high-accuracy Pb isotope analysis in solutions spiked with Tl, with all currently measured Pb-isotope ratios normalized to the standard ²⁰⁵Tl/²⁰³Tl ratio (TLN-MC-ICP-MS). The factors affecting the random and systematic analytical errors were examined, and the optimal operating regime and analytical conditions were determined. Much attention was paid to the correlation of the measurement results and the mass discrimination effect determined from the ²⁰⁵Tl/²⁰³Tl ratio. The value of the ²⁰⁵Tl/²⁰³Tl normalizing ratio was analytically determined through isotope analyses of the NIST SRM 981, and SRM 982 standard samples of Pb-isotope composition. The data obtained for two mixtures Tl + Pb (SRM 982) and Tl + Pb (SRM 981) in ten replicate analyses were 2.38898 ± 12 and 2.38883 ± 20, respectively. These results are in good mutual agreement, and their general mean ²⁰⁵Tl/²⁰³Tl = 2.3889 ± 1 coincides (within the error) with the recently published values of 2.3887 ± 7 [Collerson et al., 2002] and 2.3889 ± 1 [Thirlwall, 2002]. The precision of the method (±2SD), which was assayed by the long-term reproducibility of the results of replicate analyses of SRM 981 and seven galena samples (90 analyses) was 0.016–0.018% for the ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios and 0.005 and 0.009% for the ²⁰⁷Pb/²⁰⁶Pb and ²⁰⁸Pb/²⁰⁶Pb ratios, respectively. The precision of the isotope analysis of common Pb was significantly improved (by factors of 6–10 for various isotope ratios) compared with the precision of TIMS techniques acceptable in isotope studies during three decades. The described method was applied to examine the Pb-isotope composition of approximately 250 samples of galena, scheelite, and pyrite from a number of well known (including large) gold, sulfied, and base-metal deposits. The precision of the method (0.01–0.02%) makes it possible to study small inter-and intra-phase differences in Pb-isotope ratios in hydrothermal and magmatic rocks, to assay the scale of regional and variations in the isotope composition of ore Pb, and to correlate the Pb-isotope composition of rocks and ores and reveal its evolutionary trends.     

Lead Isotope composition and origin of the quaternary lavas of Elbrus Volcano, the Greater Caucasus: High-precision MC-ICP-MS data

A systematic study of Pb isotope composition was carried out for Elbrus Volcano, one of the Europe’s largest volcanoes, using high-precision method of multi-collector inductively coupled plasma mass spectrometry. The measurement error of Pb isotope ratios was estimated from the results of replicate analyses of international BCR-1 and AGV-1 standards as ±0.03% (±2SD). The study of a representative collection showed that dacites of all three phases of the Elbrus eruptive activity are characterized by relatively small-scale variations of Pb isotope composition: ²⁰⁶Pb/²⁰⁴Pb 18.621–18.670, ²⁰⁷Pb/²⁰⁴Pb 15.636–15.659, and ²⁰⁸Pb/²⁰⁴Pb 38.762–38.845. New Pb isotope geochemical characteristics in combination with existing Sr-Nd data indicate that the parental magmas of Elbrus are of mixed mantle-crust origin. They were formed by interaction of mantle-derived melts with continental crust of the Greater Caucasus during continental collision between the Eurasian, Arabian, Turkish, and Iranian plates.     

Lead Isotopic Composition and Lead Source in the Bainiuchang Ag-polymetallic Deposit, Yunnan Province, China

The Bainiuchang deposit in Yunnan Province, China, is located geographically between the Gejiu ore field and the Dulong ore field. In addition to the 〉7000 t Ag reserves, the deposit also boasts of large-scale Pb, Zn and Sn reserves with a lot of dispersed elements （In, Cd, Ge, Ga, etc.）. We have determined systematically the Pb isotope composition of the deposit. The Pb isotope ratios of the ores that are of sea-floor exhalative sedimentary origin in the northwest of the mining district, are 206pb/204pb = 17.758-18.537, 207pb/204pb = 15.175-15.862 and 206pb/204pb = 37.289-39.424, while those of ores that are of magmatic hydrothermal superimposition origin in the southeast of the mining district, are 206pb/204pb = 17.264-18.359, 207pb/204pb = 14.843-15.683 and 208pb/204pb = 36.481-38.838, respectively. In terms of the Pb isotope composition of feldspar in magmatic rocks or magmatic whole- rock samples from the mining district, we have determined the Pb isotope composition and acquired the Pb isotope ratios as： 206pb/204pb -- 18.224-18.700, 207pb/204pb -- 15.595-15.797 and 208pb/204pb -- 38.193-39.608. Then, in the light of the Pb isotope composition of metamorphic rock samples from the Proterozoic basement exposed in the Dulong ore field, we have determined the Pb isotope composition and obtained the isotope ratios as： 206pb/204pb -- 18.434-19.119, 207pb/204pb -- 15.644-15.693, and 208pb/204pb = 38.514-38.832. And the Pb isotope ratios of Cambrian sedimentary rocks, which are exposed in the Bainiuchang mining district, are 206pb/204pb = 18.307-19.206, 207pb/204pb = 15.622-15.809, and 208pb/204pb = 38.436-39.932. By comparing the two types of ores with respect to their Pb isotope compositions, it is indicated that lead in the Bainiuchang deposit was derived largely from the lower-crust granulite which is earlier than Neoproterozoic in age, but the Yanshanian magmatic hydrothermal fluids probably provided a part of ore-forming elements such as Sn for the ore blocks in the south of the mining district.     

Lead Isotopic Composition and Lead Source in the Bainiuchang Ag-polymetailic Deposit,Yunnan Province,China

The Bainiuchang deposit in Yunnan Province,China,is located geographically between the Gejiu ore field and the Dulong ore field.In addition to the>7000 t Ag reserves,the deposit also boasts of large-scale Pb,Zn and Sn reserves with a lot of dispersed elements(In,Cd,Ge,Ga,etc.).We have determined systematically the Pb isotope composition of the deposit.The Pb isotope ratios of the ores that are of sea-floor exhalative sedimentary origin in the northwest of the mining district,are ~(206)Pb/~(204)Pb=17.758-18.537,~(207)pb/~(204)pb=15.175-15.862 and ~(208)pb/~(204)pb=37.289-39.424,while those of ores that are of magmatic hydrothermal superimposition origin in the southeast of the mining district, are ~(206)Pb/~(204)Pb=17.264-18.359,~(207)Pb/~(204)Pb=14.843-15.683 and ~(208)Pb/~(204)Pb=36.481-38.838, respectively.In terms of the Pb isotope composition of feldspar in magmatic rocks or magmatic whole- rock samples from the mining district,we have determined the Pb isotope composition and acquired the Pb isotope ratios as:~(206)Pb/~(204)Pb=18.224-18.700,~(207)Tpb/~(204)Pb=15.595-15.797 and ~(208)Pb/~(204)Pb= 38.193-39.608.Then,in the light of the Pb isotope composition of metamorphic rock samples from the Proterozoic basement exposed in the Dulong ore field,we have determined the Pb isotope composition and obtained the isotope ratios as:~(206)Pb/~(204)Pb=18.434-19.119,~(207)Pb/~(204)Pb=15.644-15.693,and ~(208)Pb/~(204)Pb=38.514-38.832.And the Pb isotope ratios of Cambrian sedimentary rocks,which are exposed in the Bainiuchang mining district,are ~(206)Pb/~(204)Pb=18.307-19.206,~(207)Pb/~(204)Pb= 15.622-15.809,and ~(206)Pb/~(204)Pb=38.436-39.932.By comparing the two types of ores with respect to their Pb isotope compositions,it is indicated that lead in the Bainiuchang deposit was derived largely from the lower-crust granulite which is earlier than Neoproterozoic in age,but the Yanshanian magmatic hydrothermal fluids probably provided a part of ore-forming elements such as Sn for the ore blocks in the south of the mining district.     

Large thallium isotopic variations in iron meteorites and evidence for lead-205 in the early solar system

Lead-205 decays to ²⁰⁵Tl with a half-life of 15 Myr and should have been present in the early solar system according to astrophysical models. However, despite numerous attempts, Tl isotopic measurements of meteorites have been unable to demonstrate convincingly its former presence. Here, we report large (∼5‰) variations in Tl isotope composition in metal and troilite fragments from a range of iron meteorites that were determined at high precision using multiple collector inductively coupled plasma mass spectrometry. The Tl isotopic compositions of seven metal samples of the IAB iron meteorites Toluca and Canyon Diablo define a correlation with ²⁰⁴Pb/²⁰³Tl. When interpreted as an isochron, this corresponds to an initial ²⁰⁵Pb/²⁰⁴Pb ratio of (7.4 ± 1.0) × 10⁻⁵. Alternative explanations for the correlation, such as mixing of variably mass-fractionated meteorite components or terrestrial contamination are harder to reconcile with independent constraints. However, troilite nodules from Toluca and Canyon Diablo contain Tl that is significantly less radiogenic than co-existing metal with isotope compositions that are variable and decoupled from ²⁰⁴Pb/²⁰³Tl. These effects are similar to those recently reported by others for Fe and Ni isotopes in iron meteorite sulfides and appear to be the result of kinetic stable isotope fractionation during diffusion. Though it cannot conclusively be shown that the metal fragments are unaffected by the secondary processes that disturbed the troilites, mass balance modeling indicates that the alteration of the troilites is unlikely to have significantly affected the Tl isotope compositions of the co-existing metals. It is therefore reasonable to conclude that the IAB metal isochron is a product of the in situ decay of ²⁰⁵Pb. If the I-Xe ages of IAB silicate inclusions record the same event as the ²⁰⁵Pb-²⁰⁵Tl chronometer then crystallization of the IAB metal was probably completed between 10 and 20 Myr after the condensation of the first solids. This implies an initial solar system ²⁰⁵Pb/²⁰⁴Pb of (1.0-2.1) × 10⁻⁴, which is in excellent agreement with recently published astrophysical predictions. Similar calculations yield an initial solar system Tl isotope composition of ε²⁰⁵Tl = −2.8 ± 1.7. The Tl isotopic composition and concentration of the silicate Earth depends critically on the timing and mechanism of core formation and Earth’s volatile element depletion history. Modeling of the Earth’s accretion and core formation using the calculated initial solar system Tl isotope composition and ²⁰⁵Pb/²⁰⁴Pb, however, does not yield reasonable results for the silicate Earth unless either the Earth lost Tl and Pb late in its accretion history or the core contains much higher concentrations of Pb and Tl than are found in iron meteorites.     

AG-MP-1M阴离子交换树脂分离-表面热电质谱法测定沉积物中的铅同位素组成

利用新型阴离子交换树脂分离沉积物中的重金属Pb,采用表面热电离质谱法(TIMS)测定了沉积物样品中的Pb同位素组成。新型树脂为大孔径阴离子树脂AG-MP-1M,淋洗液采用低浓度的盐酸,避免了使用难以纯化的氢溴酸,可有效地降低试剂空白。通过对铅同位素标准物质NIST NBS-981的重复测试,方法的精密度(<0.5%,2s)和准确度均达到了应用研究的要求。对5个实际沉积物样品中的铅同位素组成进行测定,获得了理想的分析效果。     

Parental Sources of High–Alumina Alkaline Melts: Nd,Sr, Pb,and O Isotopic Evidence from the Devonian Kiya–Shaltyr Gabbro–Urtite Intrusion,South Siberia

Doklady Earth Sciences - The isotope geochemistry (εNd(t) 4.8–5.4, 206Pb/204Pb in 18.05–18.36, 207Pb/204Pbin 15.53–15.57, 208Pb/204Pb in 37.59–37.83, 87Sr/86Sr(t)...     

浙江安吉港口多金属矿床铅物质来源初探——铅同位素证据

位于浙西北安吉港口的铅锌银(钼)多金属矿床,是新近在钦杭成矿带东北缘发现的一个产于大陆环境且具较好前景的矿床.文章通过对矿区坞山关杂岩体三套岩性单元、细粒花岗岩和方铅矿铅同位素的全面对比研究,探讨了矿床的铅物源岩浆岩.矿区中的方铅矿为含较高放射性成因铅的J-型铅,在铅同位素的V1-V2和△γ-Δβ图解中,本次研究的样品分别落入华南和岩浆作用上地壳混合地幔铅范围,显示出方铅矿与华南地球化学省壳幔混合岩浆作用的密切关系.矿区铅锌矿体的方铅矿铅同位素比值显示其具有共同的物质来源,并基本保持了细粒花岗岩206Pb/204Pb值的特征,而207Pb/204Pb值具有坞山关杂岩体和细粒花岗岩混合的特征,208Pb/204Pb和208Pb/206Pb值则仅显示出与细粒花岗岩最相近.方铅矿铅同位素比值特征和比值等值线分布形式显示,铅主要来源于细粒花岗岩,杂岩体对铅成矿贡献了少量的206Pb和207Pb,矿区地层对铅成矿贡献了一定的208Pb.安吉矿区进一步针对铅的找矿工作围绕细粒花岗岩展开,取得成果的可能性更大.     

Long-Term Observations of Isotope Ratio Accuracy and Reproducibility Using Quadrupole ICP-MS

High precision isotope ratio and trace element determination can be achieved with modern quadrupole ICP-MS provided that short and long-term instrument performance is accurately monitored. Here we present results for the isotope ratios ⁶Li/⁷Li, ¹⁴⁷Sm/¹⁴⁹Sm, ¹⁶⁰Dy/¹⁶¹Dy, ²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb, ²⁰⁶Pb/²⁰⁴Pb and ²³⁵U/²³⁸U with which we determined long-term isotope ratio stability of relevance to both trace element and isotope determination. With respect to trace element determination, we first present long-term observations regarding oxide formation rates of Ba and Nd on light REE and heavy REE, as well as Zr on Ag. These showed good correlations and could be used to correct effectively the interference. The efficacy of this correction was demonstrated with analyses of the rock reference material BHVO-2 at both low and high oxide formation rates. Next, we studied the long-term reproducibility of a Dy isotope ratio that was measured to correct for the isobaric interference on Gd. It was found that, regardless of tuning condition, the ratio reproduced very well (0.58% RSD, 1s) and that the estimate of the Gd concentration did not suffer from the large correction (> 10%) caused by the Dy isobar. Long-term reproducibilities of Li, Sm and U isotope ratios, required for accurate mass bias correction when isotopically enriched internal standards of these elements are employed, were measured in the rock reference materials AGV-2 and JA-3 over a time period of up to 3 years. As expected, the Li isotope ratio showed the largest variability (RSD = 7%), but the other two ratios had relative external reproducibilities of only 1.01% (1s, U) and 0.67% (Sm). The mass bias-induced scatter in measurements for Sm and U was so small that the internal standard correction was effective, even for samples with high concentrations of these elements. With regard to Pb-isotope ratio determination, we also present long-term reproducibility for NIST SRM 982, run as an unknown and two accuracy tests for Pb separated from granitoids and from meteorites. It is demonstrated that the obtained ratios, including those involving ²⁰⁴Pb, are accurate relative to MC-ICP-MS determinations and of comparable precision to conventional TIMS analysis. The excellent agreement between all data sets shows the potential of modern quadrupole ICP-MS instrumentation for Pb-isotope determination, particularly for samples with very low Pb content.     

若尔盖高原土壤和近地表大气气溶胶铅同位素组成测试及示踪研究

若尔盖高原牧场处于中国偏远洁净高海拔地区,大气沉降是污染物主要来源途径之一。由于季风的影响,污染源的辨析较为困难。本文通过多点大气气溶胶不同季节同时采样方式,利用热电离固体同位素质谱仪可有效校正质谱分析中同位素分馏效应的优点,对若尔盖地区土壤和大气气溶胶的铅同位素比值进行精确分析,并结合季风特征对该地区污染物的来源进行解析。结果表明:土壤的208Pb/204Pb比值变化范围为38.79059±0.00194~38.94461±0.00135,206Pb/207Pb为1.18551±0.00002~1.19362±0.00002;大气气溶胶的208Pb/204Pb比值变化范围为37.49571±0.00117~38.48980±0.00105,206Pb/207Pb为1.12894±0.00001~1.16734±0.00001。该地区土壤铅同位素的特征是放射成因铅高,来自于自身天然存在的岩石矿物,与大气污染关系不大;大气气溶胶的铅同位素组成与土壤差异较大,显示为多元混合模式,受到了天然物质和人类活动来源的混合影响,机动车尾气及来自北部(兰州)和西北部(青海、新疆、哈萨克斯坦、俄罗斯)的大气远程运移是若尔盖大气气溶胶及污染物质的主要来源。     

白云鄂博陆缘裂谷系沉积物源与超大型稀土矿床含矿白云岩的成因探讨

白云鄂博群尖山组H4岩性段石英砂岩中的碎屑锆石年龄纪录了华北克拉通北缘两期重要的构造岩浆事件,一组年龄集中在新太古代—古元古代初期(2379～2596Ma),另一组年龄集中在古元古代晚期(1761～1946Ma),该结果与白云鄂博地区基底岩石的锆石年龄相吻合。白云鄂博群沉积碳酸盐岩的全岩207Pb-206Pb等时线年龄1649±45Ma,代表了白云鄂博群的沉积时代。白云鄂博地区沉积灰岩、白云岩与含矿白云岩的Pb同位素组成存在非常大的差异,在Pb同位素组成和构造图解中,含矿白云岩都集中在地幔演化线附近,靠近亏损地幔端元[(206Pb/204Pb)i=15.04～16.49,(207Pb/204Pb)i=15.17～15.28,(208Pb/204Pb)i=31.20～36.40],而白云鄂博群中的灰岩、白云岩则位于造山带演化线附近,靠近深海沉积物端元[(206Pb/204Pb)i=17.28～19.35,(207Pb/204Pb)i=15.47～15.69,(208Pb/204Pb)i=36.62～37.12]。     

龙首山中段芨岭花岗岩体Sr-Nd-Pb同位素特征及意义

龙首山中段芨岭早古生代花岗岩体与碱交代型铀矿化关系密切,是龙首山花岗质岩浆活动带重要组成部分,但人们对芨岭岩体的成因、岩浆源区性质以及与铀成矿之间的关系还了解得不多.花岗岩体Sr-Nd-Pb同位素研究结果表明,不同期次花岗岩(早古生代第一次灰白色二长花岗岩、第二次肉红色二长花岗岩、晚古生代肉红色细粒(钾长)花岗岩)的(87Sr/86Sr)_i值均介于大陆地壳范围内(0.706~0.718),同时有(87Sr/86Sr)_i均值先升后降(0.707 12→0.710 00→0.707 89)、ε_Nd(t)均值先降后增(-7.00→-8.09→-4.65) 的特征.不同期次花岗岩体t_DM2均值分别为1 735.50 Ma、1 814.66 Ma、1 737.50 Ma,接近残留地壳年龄,表明岩体的主要物质来源为古元古代龙首山群地层,并有部分幔源组分或年轻地壳物质的加入.岩体的Pb同位素比值较高,灰白色二长花岗岩的206Pb/204Pb=18.328~19.240,207Pb/204Pb=15.549~15.619,208Pb/204Pb=38.390~39.075,μ=9.37~9.43(平均为9.40);肉红色二长花岗岩的206Pb/204Pb=30.209~43.529,207Pb/204Pb=16.097~25.076,208Pb/204Pb=39.107~39.420,μ=18.47~30.24(平均为24.355);肉红色细粒(钾长)花岗岩的206Pb/204Pb=19.071~19.767,207Pb/204Pb=15.577~25.438,208Pb/204Pb=38.682~42.593,μ=9.36~9.49(平均为9.41),显示为高放射性成因铅同位素特征,表明岩体的铅为混合来源但以壳源为主.Sr-Nd-Pb同位素对比研究表明,钠交代岩(矿石)的(87Sr/86Sr)_i、ε_Nd(t)与早古生代第二次侵入的肉红色斑状二长花岗岩极为相似,在(87Sr/86Sr)_i-ε_Nd(t)图解投影点也吻合,表明研究区碱交代型铀成矿主要与早古生代第二次侵入有关.其他期次花岗岩体同样具有高铀背景值,表明其可能也提供了一定的铀源.      

Molybdenum Concentrations Measured in Eleven USGS Geochemical Reference Materials by Isotope Dilution Thermal Ionisation Mass Spectrometry

Molybdenum concentrations in eleven USGS geochemical reference materials AGV-1, BCR-1, BHVO-1, BIR-1, DNC-1, DTS-1, G-2, GSP-1, MAG-1, PCC-1 and W-2 were measured by isotope dilution thermal ionisation mass spectrometry (ID-TIMS). In every case but one, the concentrations determined in this study were significantly lower than the current consensus values. Molybdenum concentrations determined by ID-TIMS are inherently more accurate and precisions may be up to an order of magnitude higher than those measured by other analytical techniques.     

Lead isotopes as tracers of anthropogenic pollution in urban topsoils of Mexico City

A survey was performed to trace the main source of anthropogenic Pb pollution in Mexico City through Pb isotopic signatures (²⁰⁸Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁷Pb, and ²⁰⁸Pb/²⁰⁷Pb) from 103 urban topsoil (0–5 cm) samples. Those were collected in the metropolitan area of Mexico City and compared with isotopic compositions of leaded gasoline (LG), domestic Pb ores (DLO) and parent rock (PR). The isotope ratios (IRs) of Pb were determined by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) and total Pb concentration analyzed by wavelength dispersive X-ray fluorescence (WDXRF). The range of Pb concentrations levels in urban topsoil samples was 15–473 mg/kg. The IR values obtained for these samples were 37.965–39.718 (²⁰⁸Pb/²⁰⁴Pb), 18.375–19.204 (²⁰⁶Pb/²⁰⁴Pb), 1.177–1.218 (²⁰⁶Pb/²⁰⁷Pb) and 2.443–2.496 (²⁰⁸Pb/²⁰⁷Pb). Analyzed topsoil samples with low Pb content (<50 mg/kg) displayed high dispersion in ²⁰⁸Pb/²⁰⁴Pb values, which are determined by different natural sources. Samples with 51–200 mg/kg Pb content, shown low dispersion that revealed the mixing between the natural Pb and anthropogenic Pb. The assessment of the IR values shown that, as Pb concentration increases, a trend toward gasoline IR data has been observed. The results obtained by this research suggest that although the use of leaded petrol had been banned in Mexico since 1997, the Pb pollution in the urban topsoils due to the historical use of Pb in petrol is still significant.     

吉黑东部花岗岩类的稳定同位素组成

吉黑东部花岗岩类分布广泛，形成历史漫长，岩石类型齐全。按成因类型划分，以I型为主，A型次之，S型很少，M型极少。其稳定同位素组成独特，大多数岩体锶初始值低，氧同位素正常或低，铅同位素以低^204Pb和高^206Pb/^204Pb、^207Pb/^204Pb、^208Pb/^204Pb为主，钕初始值高，说明其基底岩石成熟度低，地幔物质混入量较多。这些特点明显区别于华北和华南的花岗岩。     

Neodymium and Strontium Isotope Data for USGS Reference Materials BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, GSP-1, GSP-2 and Eight MPI-DING Reference Glasses

We have measured ⁸⁷Sr/⁸⁶Sr and ¹⁴³ Nd/¹⁴⁴ Nd isotope ratios in different batches and aliquots of the new US Geological Survey (USGS) reference materials (RMs) BCR-2, BHVO-2, AGV-2 and GSP-2 and the original USGS RMs BCR-1, BHVO-1, AGV-1 and GSP-1 by thermal ionisation mass spectrometry. In addition, we also analysed the eight Max-Planck-Institut-Dingwell (MPI-DING) reference glasses. Nearly all isotope ratios obtained in the different aliquots and batches agree within uncertainty limits indicating excellent homogeneity of the USGS powders and the MPI-DING glasses. With the exception of GSP-2, the new USGS RMs are also indistinguishable from the ratios found in the original USGS RMs (⁸⁷Sr/⁸⁶Sr: 0.704960, 0.704958 (BCR-1, -2), 0.703436, 0.703435 (BHVO-1, -2), 0.703931, 0.703931 (AGV-1, -2); ¹⁴³ Nd/¹⁴⁴ Nd: 0.512629, 0.512633 (BCR-1, -2), 0.512957, 0.512957 (BHVO-1, -2); 0.512758, 0.512755 (AGV-1, -2)). This means that for normalisation purposes in Sr and Nd isotope geochemistry BCR-2, BHVO-2 and AGV-2 can well replace BCR-1, BHVO-1 and AGV-1 respectively.     

Isotope characterization of lead in galena from ore deposits of the Aysén Region, southern Chile

Lead isotope analyses of galena from five ore deposits and six prospects in the Aysén region of southern Chile are reported. Most of the deposits are either low sulfidation epithermal gold–silver veins or skarn and manto deposits; the majority are either suspected to be, or dated as, Late Jurassic to mid-Cretaceous. Galena lead isotope data for most of the deposits from southern Chile cluster near the “orogene” within a “plumbotectonic” model framework. Average values (²⁰⁶Pb/²⁰⁴Pb=18.53, ²⁰⁷Pb/²⁰⁴Pb=15.63, and ²⁰⁸Pb/²⁰⁴Pb=38.50) are near Jurassic to Cretaceous model ages on the “orogene” curve of Zartman and Doe (1981) and the second-stage curve of Stacey and Kramers (1975) on a ²⁰⁶Pb/²⁰⁴Pb versus ²⁰⁷Pb/²⁰⁴Pb plot. These model ages are compatible with absolute ages as currently known. The elongate trends in the general cluster indicate mainly an orogenic model fit, suggesting variable mixing of lead from different sources, mainly model upper crust and lesser model mantle and lower crust reservoirs. Galena lead associated with one deposit (El Faldeo) is relatively radiogenic, and lies near a Jurassic age on the “upper crustal” curve of Zartman and Doe (1981), which is compatible with the Ar/Ar age of the deposit. Galena lead isotope clusters define three main groups of deposits. These three groups appear to be related to three mineralizing events, dated by K–Ar and Ar/Ar, in the Late Jurassic (group 3), and in the Early and mid-Cretaceous (groups 1 and 2 respectively). Averages for group 1, the northern group including El Toqui and Katerfeld, are ²⁰⁶Pb/²⁰⁴Pb=18.51, ²⁰⁷Pb/²⁰⁴Pb=15.62, ²⁰⁸Pb/²⁰⁴Pb=38.48. Averages for group 2, the southern group with Fachinal and Mina Silva, are ²⁰⁶Pb/²⁰⁴Pb = 18.56, ²⁰⁷Pb/²⁰⁴Pb=15.63, ²⁰⁸Pb/²⁰⁴Pb=38.52. Averages for group 3, the southernmost group with the El Faldeo, Lago Chacabuco and Lago Cochrane prospects, are ²⁰⁶Pb/²⁰⁴Pb=18.83, ²⁰⁷Pb/²⁰⁴Pb=15.65, ²⁰⁸Pb/²⁰⁴Pb=38.63. The Cretaceous deposits (groups 1 and 2) contain orogene-type lead that becomes increasingly radiogenic southward. Lead from the Late Jurassic deposits (group 3) appears to reflect mixing of orogene lead with highly radiogenic lead. The observed linear array of lead in group 3 probably reflects mixing of orogene lead with highly radiogenic lead, which was likely extracted by selective leaching of mineralizing hydrothermal solutions from the metamorphic basement. Received: 10 July 1999 / Accepted: 15 July 2000     

大别山北缘中生代火山—侵入岩铅同位素组成特征及其地质意义

大别山北缘中生代火山－侵入岩的１４个夺铅同位素组成表现为高的非放射性成因＾２０４Ｐｂ,较低的＾２０６Ｐｂ／＾２０４Ｐｂ比值和低且相对一致的＾２０７Ｐｂ／＾２０４Ｐｂ比值,属于明显的低Ｕ／Ｐｂ体系,并暗示它们由具低μ值的源岩衍生的。     

东昆仑东段那更康切尔银矿硫-铅同位素特征与找矿模型

那更康切尔银矿是东昆仑造山带的大型热液脉型独立银矿床,有望达到超大型规模。以矿区地质特征为研究基础,开展硫化物硫-铅同位素、二长花岗岩和花岗闪长岩铅同位素研究,探讨成矿物质来源及两类岩体与成矿的关系。矿区硫化物样品(黄铁矿、方铅矿和闪锌矿)的δ34S值介于-6.1‰~3.9‰之间,主体δ34 S值介于-4‰~2.1‰之间,数值集中,指示成矿物质硫源具有深源岩浆硫的特征。矿石铅同位素组成中206 Pb/204 Pb、207 Pb/204 Pb、208 Pb/204 Pb的变化范围分别为18.28~18.62、15.6~15.73、38.38~39.1,矿石铅具有壳幔混合源的特点。矿区内二长花岗岩LA-ICP-MS锆石U-Pb年龄为239±1 Ma,(206Pb/204Pb)i、(207Pb/204Pb)i、(208Pb/204Pb)i值分别为18.389~18.585、15.638~15.648、38.288~38.558;花岗闪长岩LA-ICP-MS锆石U-Pb年龄为252±1 Ma,(206Pb/204Pb)i、(207Pb/204Pb)i、(208Pb/204Pb)i值分别为18.348~18.447、15.625~15.629、38.394~38.412,铅同位素组成投图显示成矿与2类岩浆岩关系较弱,与区域上鄂拉山组火山岩呈较明显的线性相关。那更康切尔银矿与邻区哈日扎铅锌银矿床具有相似的成矿物质来源,硫源具有同一性,且矿石铅同位素组成表现出很明显的线性关系,表明2个矿床的成矿物质具有相近或相似的源区或演化过程。成矿地质条件、成矿物质来源及成矿流体特征均表明两者属中-低温热液脉型矿床。综合本文及前人对那更康切尔银矿床的研究,构建了成矿模式和找矿模型,为区域内同类型银矿床的找矿工作提供了指导作用。