Lead isotope systematics of vein-type antimony mineralization,Rheinisches Schiefergebirge,Germany: a case history of complex reaction and remobilization processes

Mesothermal vein-type Sb mineralization in the Rheinisches Schiefergebirge, Germany, is characterized by two different mineralization styles, which are (1) extensional quartz-stibnite vein systems, and (2) (Cu)-Pb-Sb sulphosalt assemblages in overprinted pre-existing Pb-Zn veins. A detailed Pb isotope study of 52 representative samples from both mineralization types indicates distinct compositional patterns. (Cu)-Pb-Sb sulphosalts (meneghinite, boulangerite, bournonite) formed by reaction/remobilization are characterized by Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb=18.179-18.223), which are identical to the precursor galena (²⁰⁶Pb/²⁰⁴Pb=18.168-18.223). The Pb isotope composition of sulphosalt minerals in these vein systems was controlled by lead inherited from pre-existing galena. Stibnite and Pb-sulphosalts (zinkenite, semseyite, plagionite) formed in quartz-stibnite vein systems display Pb isotope ratios (²⁰⁶Pb/²⁰⁴Pb=18.250-18.354), which are more radiogenic than galenas from Variscan Pb-Zn ore veins (²⁰⁶Pb/²⁰⁴Pb=18.162-18.303). Detailed small-scale investigation of thrust zones hosting Pb-Zn ores and crosscutting quartz-ankerite fissure veins (Ramsbeck deposit) indicates that the Pb isotope compositions of recrystallized (galena) and remobilized phases (boulangerite, semseyite, bournonite) are arranged along a linear trend. This is interpreted as mixing between primary galena with ²⁰⁶Pb/²⁰⁴Pb᜞.206 and overprinting hydrothermal fluids with a more radiogenic composition (²⁰⁶Pb/²⁰⁴Pb⁾.354), expressed by intermediate compositions (²⁰⁶Pb/²⁰⁴Pb=18.256-18.334) of newly-formed sulphosalts. The Pb isotope systematics of the vein-type Sb mineralization is in accordance with a model of Pb extraction from similar crustal sources (Palaeozoic sedimentary sequences) at different times.     

Lead sources in Mesozoic and Cenozoic Andean ore deposits,north-central Chile (30–34°S)

Mesozoic and Cenozoic ore deposits in the Chilean Andes between La Serena (~30°S) and Santiago (~34°S) include polymetallic vein, low- and high-sulfidation epithermal vein, skarn, porphyry copper-molybdenum and porphyry copper-gold. These deposits are associated with volcanic and plutonic complexes emplaced in eastward-migrating longitudinal arcs which formed during subduction along the continental margin of South America since the Middle Jurassic. Stratabound, but epigenetic, volcanic rock- and sedimentary rock-hosted manto deposits contain additional copper resources. Lead isotopic compositions in ore minerals from 29 deposits vary with age and geographic location, and hence with basement and host rocks. Lead in most ore deposits is derived from temporally related igneous rocks, except for the manto deposits whose lead is derived from host volcanic and sedimentary rock sequences. Lead in the ore deposits is dominated by two crustal sources. Low ²⁰⁷Pb/²⁰⁴Pb characterizes one source whereas high ²⁰⁷Pb/²⁰⁴Pb characterizes the second source. Lead isotopic compositions of Jurassic and Miocene ore minerals (²⁰⁶Pb/²⁰⁴Pb>18.50; ²⁰⁷Pb/²⁰⁴Pb>15.61) lie along the average crustal growth curve. By contrast, most Cretaceous deposits have ore minerals with lower ²⁰⁶Pb/²⁰⁴Pb (<18.39) and ²⁰⁷Pb/²⁰⁴Pb (<15.58) than Jurassic ore minerals. The shift in lead isotopic composition to lower lead isotopic values precludes derivation of lead from a source of similar composition to those in the Jurassic or Tertiary deposits. For Cretaceous deposits, polymetallic and low-sulfidation epithermal veins and a skarn have lower ²⁰⁶Pb/²⁰⁴Pb than a porphyry copper-gold system and peripheral gold veins at Andacollo (18.43-18.50). Late Cretaceous veins from the Bellavista deposit have the lowest ²⁰⁶Pb/²⁰⁴Pb (18.33) of all deposits. Ore minerals in Miocene and Pliocene porphyry copper-molybdenum deposits have higher ²⁰⁶Pb/²⁰⁴Pb (18.58-18.67) than Cretaceous deposits, consistent with their age being younger. The Miocene and Pliocene ore minerals also have higher ²⁰⁷Pb/²⁰⁴Pb (15.58-15.66) than Cretaceous ore minerals, thereby requiring an additional input from the high-²⁰⁷Pb/²⁰⁴Pb source into the younger deposits. Miocene auriferous deposits in the north have similar ²⁰⁶Pb/²⁰⁴Pb values as the Miocene and Pliocene porphyry copper-molybdenum deposits in the south, but they are distinguished by higher and variable ²⁰⁷Pb/²⁰⁴Pb (15.61-15.66) and ²⁰⁸Pb/²⁰⁴Pb (38.54-39.01), which are arrayed along steep mixing trends. These ore minerals have the largest input of high-²⁰⁷Pb/²⁰⁴Pb material in the deposits studied. By contrast, lead in the epigenetic manto deposits appears to be derived from the host volcanic or sedimentary rock-dominated sequences, and locally exhibits large-scale isotopic heterogeneity within a deposit. Overall, the lead isotopic compositions of ore minerals mimic the values and variations established in age-equivalent rock sequences. The low-²⁰⁷Pb/²⁰⁴Pb material in the deposits is derived from Cretaceous igneous rocks or their sources as they evolved with time; low ²⁰⁷Pb/²⁰⁴Pb characterizes these rocks. By contrast, high-²⁰⁷Pb/²⁰⁴Pb material is likely derived from Carboniferous to Triassic igneous rocks or their sources, as this lead isotopic characteristic dominates these rocks.     

Differences in lead isotope composition in the stratiform McArthur zinc-lead-silver deposit

Lead isotopic composition and uranium and lead concentrations have been determined for galena, sphalerite, pyrite and acetic acid soluble material from the McArthur area in order to test the hypothesis of a dual sulphur source suggested by the sulphur isotope data of Smith and Croxford (Sulphur isotope ratios in the McArthur lead-zinc-silver deposit, Nature Phys. Sci. 245, 10–12 (1973)). Galena, sphalerite and the acetic acid washes from the McArthur deposit have uniform isotopic ratios (²⁰⁶Pb/²⁰⁴Pb, 16.07–16.15; ²⁰⁷Pb/²⁰⁴Pb, 15.37–15.47; ²⁰⁸Pb/²⁰⁴Pb, 35.57–35.89) consistent with other conformable ore deposits, whereas the ratios for pyrite are variable and quite radiogenic (²⁰⁶Pb/²⁰⁴Pb, 16.24–16.49; ²⁰⁷Pb/²⁰⁴Pb, 15.42–15.58; ²⁰⁸Pb/²⁰⁴Pb, 35.82–36.98). Acid washes where dolomite is a major dissolved phase are also radiogenic. The lead in the pyrite appears to have been derived from at least two sources: the less radiogenic lead coming from an exhalative source as for galena and sphalerite and the more radiogenic lead probably being leached from the country rocks. It is proposed that analysis of pyrite for isotopic composition and concentration of lead could be used as an indicator for similar types of deposits in this area.     

Lead isotopes of the carbonate-hosted Kabwe, Tsumeb, and Kipushi Pb-Zn-Cu sulphide deposits in relation to Pan African orogenesis in the Damaran-Lufilian Fold Belt of Central Africa

Lead isotope ratios of galena from the carbonate-hosted massive sulphide deposits of Kabwe (Pb-Zn) and Tsumeb (Pb-Zn-Cu) in Zambia and Namibia, respectively, have been measured and found to be homogeneous and characteristic of upper crustal source rocks. Kabwe galena has average isotope ratios of ^206/204Pb = 17.997 ± 0.007, ^207/204Pb = 15.713 ± 0.010 and ^208/204Pb = 38.410 ± 0.033. Tsumeb galena has slightly higher ^206/204Pb (18.112 ± 0.035) and slightly lower ^207/204Pb (15.674 ± 0.016) and ^208/204Pb (38.276 ± 0.073) ratios than Kabwe galena. The isotopic differences are attributed to local differences in the age and composition of the respective source rocks for Kabwe and Tsumeb. The homogeneity of the ore lead in the two epigenetic deposits suggests lead sources of uniform isotopic composition or, alternatively, thorough mixing of lead derived from sources with relatively similar isotopic compositions. Both deposits have relatively high ²³⁸U/²⁰⁴Pb ratios of 10.31 and 10.09 for Kabwe and Tsumeb galenas, respectively. These isotope ratios are considered to be typical of the upper continental crust in the Damaran-Lufilian orogenic belt, as also indicated by basement rocks and Cu-Co sulphides in stratiform Katangan metasediments which have a mean μ-value of 10.25 ± 0.12 in the Copperbelt region of Zambia and the Democratic Republic of Congo (formerly Zaire). The ²³²Th/²⁰⁴Pb isotope ratios of 43.08 and 40.42 for Kabwe and Tsumeb suggest Th-enriched source regions with ²³²Th/²³⁵U (κ-values) of 4.18 and 4.01, respectively. Model isotopic ages determined for the Kabwe (680 Ma) and Tsumeb (530 Ma) deposits indicate that the timing of the mineralisation was probably related to phases of orogenic activity associated with the Pan-African Lufilian and Damaran orogenies, respectively. Galena from the carbonate-hosted Kipushi Cu-Pb-Zn massive sulphide deposit in the Congo also has homogeneous lead isotope ratios, but its isotopic composition is comparable to that of the average global lead evolution curve for conformable massive sulphide deposits. The μ (9.84) and κ (3.69) values indicate a significant mantle component, and the isotopic age of the Kipushi deposit (456 Ma) suggests that the emplacement of the mineralisation was related to a post-tectonic phase of igneous activity in the Lufilian belt. The isotope ratios (^206/204Pb, ^207/204Pb, ^208/204Pb) of the three deposits are markedly different from the heterogeneous lead ratios of the Katangan Cu-Co stratiform mineralisation of the Copperbelt as well as those of the volcanogenic Nampundwe massive pyrite deposit in the Zambezi belt which typically define radiogenic linear trends on lead-lead plots. The host-rock dolomite of the Kabwe deposit also has homogeneous lead isotope ratios identical to the ore galena. This observation indicates contamination of the Kabwe Dolomite Formation with ore lead during mineralisation. Received: 8 September 1997 / Accepted: 21 August 1998     

The source of lead in Archaean lode gold deposits of the Menzies-Kalgoorlie-Kambalda region,Yilgarn Block,Western Australia

The Archaean greenstone terrane between Menzies and Kambalda exhibits a coherent, although deformed, stratigraphic sequence intruded by granitoids and bounded by major NNW-trending shear and/or fault zones. The greenstone terrane hosts a large number of lode gold prospects and deposits, including the giant Kalgoorlie deposits. The initial Pb isotope compositions of lode gold deposits, as determined from ore related galena and pyrite, vary systematically in a linear trend on a²⁰⁷Pb/²⁰⁴Pb versus²⁰⁶Pb/²⁰⁴Pb diagram which reflects crustal heterogeneity at the time of mineralisation. Deposits hosted within a 90 km section of the Menzies-Boorara Shear Zone have a uniform, radiogenic initial Pb isotope composition irrespective of temperature of mineralisation and proximity to granitoid-gneiss in plan view. The Pb in these deposits is considered to be derived largely from older felsic crust underlying the greenstone belt and was accessed via this major shear-zone system. Deposits in a transect unrelated to a major shear zone show a systematic correlation between initial Pb isotope compositions and proximity to granitoid-gneiss and/or to mineralisation temperature. These compositions are less radiogenic than those within the Menzies-Boorara Shear Zone, but trend on a²⁰⁷Pb/²⁰⁴Pb versus⁶⁰⁶Pb/²⁰⁴Pb diagram between this isotope signature and the uniform Pb isotope signature which characterises the >100 km greenstone transect from the Mt Pleasant area through Kalgoorlie to Kambalda. These data are interpreted to reflect Pb derivation from discrete crustal segments within and below the greenstones, and require that mineralisation was related to crustal-scale hydrothermal systems that accessed both sialic mid- to lower-crust and the greenstone succession.     

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.     

大兴安岭南段多金属成矿带硫、铅同位素组成及其地质意义

大兴安岭南段是我国北方重要的多金属矿床成矿带,对其成矿物质来源的分析研究有利于区域成矿规律的总结。在前人的工作基础上,对典型矿床的矿石矿物进行了硫、铅同位素研究。结果表明:闪锌矿、方铅矿、毒砂、黄铜矿、辉钼矿等硫化物的δ34S值主要变化范围为-6‰～4‰,平均值为0‰,峰值出现在0‰～2‰,呈塔式分布;无明显的重硫、轻硫富集,说明硫源较单一;矿石矿物及岩石的206 Pb/204 Pb、207Pb/204Pb、208Pb/204Pb值的变化范围主要集中在18.13～18.74、15.38～15.68和37.1～38.93,其平均值分别为18.38、15.54和38.09。同时,数据结果显示:成矿带的东部与西部存在较为明显的铅同位素差异,西部矿床中铅的分布主要集中在造山带演化线附近,而东部矿床中铅主要集中分布在上地幔和造山带演化曲线附近。     

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     

Lead isotope signatures of epithermal and porphyry-type ore deposits from the Romanian Carpathian Mountains

Lead isotope analyses have been performed on the two major Miocene mining districts of Romania, Baia Mare and Apuseni Mountains. These two districts have different non-overlapping ²⁰⁶Pb/²⁰⁴Pb isotopic signatures ranging from 18.752 to 18.876 and 18.497 to 18.740. In the Baia Mare district, epithermal deposits are overall homogeneous in their lead isotopic compositions and have values similar to the average of the calc-alkaline volcanic rocks. These results suggest a magmatic signature for the Pb (and possibly other metals) in the hydrothermal fluids. However, magmas in this district show isotopic evidence of crustal assimilation. In the southern Apuseni Mountains, the lead isotope compositions of sulfide minerals in porphyry copper deposits are clustered, confirming that Pb, and probably other metals, were derived principally from associated porphyry stocks. On the other hand, lead isotope data on sulfides in epithermal ore deposits are much more scattered, indicating a notable contribution of Pb from local country rocks. In the Apuseni Mountains, 'fertile' volcanics are few and appear to come from a more primitive mantle-derived source. Most of the analysed volcanic rocks seem 'barren'. Differences in lead isotopic compositions between the Baia Mare district and the Apuseni Mountains are due to a different basement, and probably to variations in crustal assimilation superimposed on variations in the mantle source composition. In the Apuseni Mountains, Pb may be partly inherited from the previous Mesozoic magmatic-hydrothermal stage. From a geodynamic point of view, it seems that the nature and the source of volcanic rocks and their position related to the collision area of the Carpathian arc are not the only factors controlling the 'fertility' of a volcanic district.     

Pb isotopic constraints on the formation of the Dikulushi Cu–Pb–Zn–Ag mineralisation, Kundelungu Plateau (Democratic Republic of Congo)

Base metal–Ag mineralisation at Dikulushi and in other deposits on the Kundelungu Plateau (Democratic Republic of Congo) developed during two episodes. Subeconomic Cu–Pb–Zn–Fe polysulphide ores were generated during the Lufilian Orogeny (c. 520 Ma ago) in a set of E–W- and NE–SW-oriented faults. Their lead has a relatively unradiogenic and internally inhomogeneous isotopic composition (²⁰⁶Pb/²⁰⁴Pb = 18.07–18.49), most likely generated by mixing of Pb from isotopically heterogeneous clastic sources. These sulphides were remobilised and enriched after the Lufilian Orogeny, along reactivated and newly formed NE–SW-oriented faults into a chalcocite-dominated Cu–Ag mineralisation of high economic interest. The chalcocite samples contain only trace amounts of lead and show mostly radiogenic Pb isotope signatures that fall along a linear trend in the ²⁰⁷Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁴Pb diagram (²⁰⁶Pb/²⁰⁴Pb = 18.66–23.65; ²⁰⁷Pb/²⁰⁴Pb = 15.72–16.02). These anomalous characteristics reflect a two-stage evolution involving admixture of both radiogenic lead and uranium during a young fluid event possibly c. 100 Ma ago. The Pb isotope systematics of local host rocks to mineralisation also indicate some comparable young disturbance of their U–Th–Pb systems, related to the same event. They could have provided Pb with sufficiently radiogenic compositions that was added to less radiogenic Pb remobilised from precursor Cu–Pb–Zn–Fe polysulphides, whereas the U most likely originated from external sources. Local metal sources are also suggested by the ²⁰⁸Pb/²⁰⁴Pb–²⁰⁶Pb/²⁰⁴Pb systematics of combined ore and rock lead, which indicate a pronounced and diversified lithological control of the immediate host rocks on the chalcocite-dominated Cu–Ag ores. The Pb isotope systematics of polysulphide mineralisation on the Kundelungu Plateau clearly record a diachronous evolution.     

云南格咱岛弧岩浆成矿带铅同位素特征及成矿物质来源示踪

云南格咱岛弧成矿带是西南三江构造岩浆岩带的重要组成部分,是我国近年来新发现的铜多金属矿集区,产出有普朗超大型斑岩型铜矿、雪鸡坪中型斑岩型铜矿、红山大型矽卡岩-斑岩型铜矿等。测试结果表明,典型成矿斑岩体的矿石矿物铅同位素组成:206Pb/204Pb为17.680～19.165,207Pb/204Pb为15.453～15.773,208Pb/204Pb为37.730～39.654,铅同位素组成较为稳定,具有贫铀铅、富钍铅的特征。铅同位素组成与特征参数(Δβ与Δγ、V1与V2)之间具有明显的正相关性,依据铅构造模式判别和成因分类的综合分析,格咱岛弧成矿带的铅主要来源于地幔和下地壳,具壳幔混合来源的特征,其成矿作用与岩浆岩活动存在较为密切的关系。     

西藏雄村斑岩型铜金矿集区I号矿体的硫、铅同位素特征及其对成矿物质来源的指示

西藏雄村斑岩型铜金矿集区是近年来西藏冈底斯斑岩铜矿带内发现的一处超大型铜金矿集区,其形成于与新特提斯洋向北的洋内俯冲作用有关的岛弧环境,成矿时代为中侏罗世。该矿集区位于冈底斯火山-岩浆弧的中段南缘,其南侧紧邻日喀则弧前盆地,目前探明Ⅰ(原命名为雄村铜矿床)、Ⅱ、Ⅲ号铜金矿体规模达大型-超大型,同时还存在多个矿化异常带。本文以雄村Ⅰ号矿体为研究对象,对雄村Ⅰ号矿体含矿斑岩、赋矿凝灰岩和主要硫化物的硫、铅同位素开展研究,结果表明:①含矿斑岩、赋矿凝灰岩和主要硫化物具有较为一致的硫同位素组成,δ34SCDT变化范围为-3.5‰～2.7‰,平均-1.07‰,十分接近于零,塔式分布效应显著,硫可能主要来自地幔;②含矿斑岩、赋矿凝灰岩和主要硫化物具有相对一致的铅同位素组成,均以放射性成因铅含量低为特征,206Pb/204Pb、207Pb/204Pb和208Pb/204Pb变化范围分别为18.369～18.752、15.473～15.589和38.389～39.1531,位于地幔与造山带铅演化线之间,并且相对靠近地幔铅演化线,显示出铅主要来源于地幔,可能有少量地壳物质的混染。通过西藏冈底斯斑岩铜矿带碰撞造山环境和岛弧环境(以雄村Ⅰ号矿体为代表)斑岩型铜矿床的硫、铅同位素组成特征对比,认为两者的成矿物质来源是相似的,碰撞造山环境的地壳物质混染较强烈,而岛弧环境的地壳物质混染较弱。     

Pb Isotopic Composition and Metal Sources of Au and Ag Deposits of the South Verkhoyansk Region (Yakutia,Russia) According to High-Precision MC-ICP-MS Data

The paper considers the results of high-precision Pb–Pb isotopic analysis of 120 galena samples from 27 Au and Ag deposits of the South Verkhoyansk Synclinorium (SVS) including large Nezhdaninsky deposit (628.8 t Au). The Pb isotopic composition is analyzed on a MC-ICP-MS NEPTUNE mass-spectrometer from solutions with an error of no more than ±0.02% (2σ). Four types of deposits are studied: (i) stratified vein gold–quartz deposits (type 1) hosted in metamorphosed Upper Carboniferous–Lower Permian terrigenous rocks and formed during accretion of the Okhotsk Block to the North Asian Craton synchronously with dislocation metamorphism and related granitic magmatism; (ii) vein gold–quartz (Nezhdaninsky type) deposits also hosted in Lower Permian metasedimentary rocks; (iii) Au–Bi deposits localized at the contact zones of the Late Cretaceous granitic plutons; and (iv) Sn–Ag polymetallic deposits related to granitic and subvolcanic rocks of the Okhotsk Zone of the SVS. The deposits of types 2, 3, and 4 are postaccretionary. The general range of ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios is 18.1516–18.5903 (2.4%), 15.5175–15.6155 (0.63%), and 38.3010–39.0481 (2.0%), respectively. In ²⁰⁶Pb/²⁰⁴Pb–²⁰⁷Pb/²⁰⁴Pb and ²⁰⁶Pb/²⁰⁴Pb–²⁰⁸Pb/²⁰⁴Pb diagrams, the data points of Pb isotopic compositions of all deposits occupy restricted, partly overlapping areas along a general elongated trend. The various SVS Au–Ag deposits can be classified according to the Pb isotopic composition in accordance with all three Pb ratios. Deposits of the same type show distinct Pb isotopic compositions that strongly exceed the scale of analytical error (±0.02%). The differences in Pb isotopic composition within specific deposits are low and subordinate and have little effect on variations in the Pb isotopic composition of the SVS deposits. The μ₂ values (Stacey–Kramers model), which characterize the ²³⁸U/²⁰⁴Pb ratios of ore lead sources of the SVS deposits, widely vary from 9.7 to 9.38. The ω₂ values (²³²Th/²⁰⁴Pb) are 39.82–36.61, whereas the Th/U ratios are 4.04–3.86. The content of all three radiogenic Pb isotopes and μ₂ values of feldspars from SVS intrusive rocks are strongly distinct from those of galena of stratified gold–quartz and vein gold–quartz deposits and are identical to Pb of galena from Au–Bi and Sn–Ag polymetallic deposits, indicating a mostly magmatic origin for the Pb of these deposits. Detailed isotopic study of the Nezhdaninsky deposit shows different Pb isotopic composition of two consecutive mineral assemblages (gold–sulfide and Ag polymetallic): ~0.30, ~0.07, and ~0.22% for ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios, respectively. These differences are interpreted as a result of involvement of at least two metal sources during the evolution of an ore-forming system: (i) host Lower Permian terrigenous rocks and (ii) a magmatic source similar in Pb isotopic composition to that of Sn–Ag polymetallic deposits. The Pb isotopic composition and μ₂ and Th/U values show that lead of stratified gold–quartz deposits combines isotopic tracers of lower and upper crustal sources (Upper Carboniferous–Lower Permian terrigenous rocks), lead of which was mobilized by ore-bearing fluids. The high ²⁰⁸Pb/²⁰⁶Pb ratios and Th/U evolutionary parameter are common to all Pb isotopic composition of all studied Au–Ag deposits and SVS Cretaceous intrusive rocks and indicate that Pb sources were depleted in U relative to Th. Taking into account the structure of the region and conceptions on its evolution, we can suggest that the magma source was related to lower crustal subducted rocks of the Archean (~2.6 Ga) North Asian Craton and the Okhotsk terrane.     

Lead isotopic composition from data of high-precession MC-ICP-MS and sources of matter in the large-scale Sukhoi Log noble metal deposit,Russia

The lead isotopic composition of 33 sulfide samples from orebodies of the Sukhoi Log deposit was studied by high-precession MC-ICP-MS with a precision of ±0.02% (±2SD from 120 analyses of the SRM 981 standard sample). The deposit is located in the Bodaibo gold mining district in the northern Baikal-Patom Highland. Gold mineralization is hosted in Neoproterosoic black slates. Variations of lead isotope ratios of the Sukhoi Log sulfides are generally typical of Phanerozoic deposits and ore fields. They are significant for ²⁰⁶Pb/²⁰⁴Pb (17.903–18.674), moderate for ²⁰⁸Pb/²⁰⁴Pb (37.822–38.457), and relatively narrow for ²⁰⁷Pb/²⁰⁴Pb (15.555–15.679). In the Pb-Pb isotope diagrams, the data points of pyrite and galena constitute a linear trend. The points corresponding to pyrite from metasomatic ore occupy the left lower part of the trend. Galena from late gold-quartz veins shows more radiogenic Pb, and corresponding data points are located in the upper part of the trend. According to the Stacey-Kramers model, the end points of the trend, which is regarded as a mixing line, have μ₂ = 9.6 and μ₂ = 13.2 and model Pb-Pb ages 455 and 130 Ma, respectively. The isotope characteristics of ore lead, their relationships in pyrite and galena, and the mixing trend of Pb isotopic compositions are clearly tied to two Paleozoic stages in the formation of the Sukhoi Log deposit (447 ± 6 and 321 ± 14Ma) and testify to the leading role of crustal sources, which are suggested as being the Neoproterozoic black-shale terrigenous-carbonate rocks.     

深穿透地球化学异常源同位素识别研究:以新疆金窝子金矿床、内蒙古拜仁达坝—维拉斯托多金属矿床为例

通过研究两个已知隐伏矿床(新疆金窝子金矿床、内蒙古拜仁达坝—维拉斯托多金属矿床)不同介质(地气、细粒级土壤、围岩、矿石)中的铅、硫同位素特征,探讨铅、硫同位素对地气、土壤中异常物质来源的示踪,得到以下结论:(1)两矿床的介质从地气、矿石、围岩到土壤,铅同位素比值(208Pb/204Pb、207Pb/204Pb、206Pb/204Pb)一般依次增加;土壤异常区相对土壤背景区,δ34S偏高。但对两个矿床背景区、异常区地气中的铅同位素组成、土壤中的铅、硫同位素组成进行方差分析后发现,数据均没有明显的差异,从统计学的角度初步证明研究区不适宜用铅、硫同位素示踪地气、土壤中异常物质的来源。(2)两个矿床的矿石、围岩中铅同位素组成均有明显差异,即围岩中明显有放射成因铅的积累。但这种差异没有显著地反映到背景区、异常区的地气中,原因有待进一步查证。仅从捕获剂的角度初步探讨了其原因。用土壤全量中铅、硫同位素组成特征来示踪土壤异常源,并没有成功,建议采用偏提取的方法测量其中活动态中的铅、硫同位素组成,在深穿透地球化学研究中更合理。     

Petrogenesis of Quebrada de la Mina and Altar North porphyries (Cordillera of San Juan,Argentina): Crustal assimilation and metallogenic implications

We investigate the geology of Altar North (Cu–Au) and Quebrada de la Mina (Au) porphyry deposits located in San Juan Province (Argentina), close to the large Altar porphyry copper deposit (995 Mt, 0.35% Cu, 0.083 g/t Au), to present constraints on the magmatic processes that occurred in the parental magma chambers of these magmatic-hydrothermal systems. Altar North deposit comprises a plagioclase-amphibole-phyric dacite intrusion (Altar North barren porphyry) and a plagioclase-amphibole-biotite-phyric dacite stock (Altar North mineralized porphyry, 11.98 ± 0.19 Ma). In Quebrada de la Mina, a plagioclase-amphibole-biotite-quartz-phyric dacite stock (QDM porphyry, 11.91 ± 0.33 Ma) crops out. High Sr/Y ratios (92–142) and amphibole compositions of Altar North barren and QDM porphyries reflect high magmatic oxidation states (fO₂ = NNO +1.1 to +1.6) and high fH₂O conditions in their magmas. Zones and rims enriched in anorthite (An_37–48), SrO (0.22–0.33 wt.%) and FeO (0.21–0.37 wt.%) in plagioclase phenocrysts are evidences of magmatic recharge processes in the magma chambers. Altar North and Quebrada de la Mina intrusions have relatively homogeneous isotopic compositions (⁸⁷Sr/⁸⁶Sr_(t) = 0.70450–0.70466, ε_Nd(t) = +0.2 to +1.2) consistent with mixed mantle and crust contributions in their magmas. Higher Pb isotopes ratios (²⁰⁷Pb/²⁰⁴Pb = 15.6276–15.6294) of these intrusions compared to other porphyries of the district, reflect an increase in the assimilation of high radiogenic Pb components in the magmas. Ages of zircon xenocrysts (297, 210, 204, 69 Ma) revealed that the magmas have experienced assimilation of Miocene, Cretaceous, Triassic and Carboniferous crustal rocks.Fluids that precipitated sulfides in the Altar deposit may have remobilized Pb from the host rocks, as indicated by the ore minerals being more radiogenic (²⁰⁷Pb/²⁰⁴Pb = 15.6243–15.6269) than their host intrusions. Au/Cu ratio in Altar porphyries (average Au/Cu ratio of 0.14 × 10^?4 by weight in Altar Central) is higher than in the giant Miocene porphyry deposits located to the south: Los Pelambres, Río Blanco and Los Bronces (Chile) and Pachón (Argentina). We suggest that the increase in Au content in the porphyries of this region could be linked to the assimilation of high radiogenic Pb components in the magmas within these long-lived maturation systems.     

Metallogeny and lead isotopic composition of base metal sulfide deposits in the Rappen area,northern Sweden

Early Proterozoic volcanic and sedimentary rocks of the Rappen district in northern Sweden were deposited at a destructive plate margin to the south of the Archaean craton of the western Baltic Shield. The volcano-sedimentary suite was intruded by two generations of early Proterozoic granites at ca. 1.89–1.85 Ga and ca.1.82–1.78 Ga, respectively, and metamorphosed at upper amphibolite facies conditions. Small stratabound iron, copper, and zinc deposits occur in felsic to mafic tuffs and arkosic sediments. Small deposits of molybdenum, tungsten, and uranium formed during the emplacement of the younger granites. The lead isotopic compositions of sulfide trace lead from the various deposits are highly heterogeneous. In the ²⁰⁶Pb/²⁰⁴Pb–²⁰⁷Pb/²⁰⁴Pb diagram they fall on mixing arrays between little evolved early Proterozoic lead and highly radiogenic Caledonian lead. The least radiogenic lead isotopic compositions from the various deposits have a wide range of ²⁰⁷Pb/²⁰⁴Pb ratios and thus indicate variable involvement of Archaean crustal lead in the Proterozoic deposits. Deposits hosted by siliciclastic rocks have higher ²⁰⁷Pb/²⁰⁴Pb ratios than deposits hosted in mafic to felsic tuffites. The lead isotopic heterogeneity suggests that the lead in the various deposits was locally derived and, furthermore, that the sedimentary rocks in part originated from the Archaean craton to the north. Lead mixing arrays in the ²⁰⁶Pb/²⁰⁴Pb–²⁰⁷Pb/²⁰⁴Pb diagram demonstrate that in Paleozoic time radiogenic lead was mobilized and transported in the basement. Source ages calculated from the mixing arrays (ca.1.9 Ga and ca.1.8 Ga) correspond to the age of the Early Proterozoic volcanism and metamorphism respectively. One group of deposits includes lead from at least three sources and illustrates that radiogenic lead was multiply mobilized and transported in the Proterozoic basement. It occurs in deposits that occur in zones that became permeable during the reactivations of the basement.     

Lead isotope geochemical characteristics of Pb-Zn-Cu deposits on the southwestern margin of Tarim, and their significance

The polymetallic(Pb,Zn,Cu,etc) ore belt on the southwestern margin of Tarim is one of the major regions with the greatest prospecting potential in Xinjiang.Reported in this paper are the lead isotope data for 66 sulfide samples(including 50 galena samples,15 chalcopyrite samples and 1 pyrite sample) collected from such representative deposits as Tamu,Tiekelike,Kalangu,Abalieke,etc.in this ore belt.The Pb isotopic ratios of 206 Pb/204 Pb,207 Pb/204 Pb and 208 Pb/204 Pb in the galena samples range from 17.931 to 18.176,15.609 to 15.818 and 38.197 to 38.944,with the average values of 18.017,15.684 and 38.462,respectively.Those in the chalcopyrite samples range from 17.926 to 18.144,15.598 to 15.628 and 38.171 to 38.583,with the average values of 18.020,15.606 and 38.262,respectively.The pyrite sample has the Pb isotopic ratios of 206 Pb/204 Pb,207 Pb/204 Pb and 208 Pb/204 Pb to be 17.980,15.604 and 38.145,respectively.In combination with the previous Pb isotope data for sulfides,it is found that there is only a slight variation in the Pb isotopic composition of galena,chalcopyrite,sphalerite and pyrite in the ore belt.However,there is some difference in Pb isotopic characteristics between galena and chalcopyrite,especially the Pb isotopic composition of galena shows an obvious linear correlation with some other relevant parameters(e.g.β and γ).The comprehensive analysis suggested that lead in galena(maybe including sphalerite and pyrite) was derived principally from wall rocks and underlying basement,and that in chalcopyrite only originated from the basement.The single-stage model ages of these sulfides couldn’t indicate the time limit of metallogenesis(Pb,Zn,Cu,etc.),and the positive linear correlations for the Pb isotopic composition of galena are of no single-stage and two-stage Pb-Pb isochron significance.Furthermore,there are significant differences in Pb isotopic composition characteristics between the genetic type of deposits in this polymetallic ore belt and the Mississippi Valley type(MVT).In addition,the authors also pointed out that there is a phenomenon of differentiation(not paragenesis) for lead and copper elements during the process of metallogenesis in this ore belt.     

西藏甲玛铜多金属矿床S、Pb、H、O同位素特征及其指示意义

西藏甲玛铜多金属矿床是中国近年来发现的特大型铜铅锌多金属矿床之一,其产出的环境和形成机理为国内外矿床学家所关注。对甲玛铜多金属矿床中代表性岩（矿）石样品进行了S、Pb、H和O同位素分析,并从成矿系统中“源”的角度对其变化规律和成因意义进行了探讨。研究结果表明,甲玛铜多金属矿床的围岩和矿石中δ34S值变化于-4.9‰～0.5‰,在硫同位素直方图上呈塔式分布,成矿热液δ34SΣS在0值附近,与矿区内斑岩体的δ34S组成（-0.2‰～-0.7‰）十分接近。表明了矿石中硫的来源单一,主要来源于岩浆。矿石铅同位素变化范围较大,明显分为两组：第一组样品富放射性成因铅,其206Pb/204Pb变化范围为18.603～18.752,207Pb/204Pb变化范围为15.610～15.686,208Pb/204Pb变化范围为38.910～39.135;第二组样品具有低放射性成因铅特征,其206Pb/204Pb变化范围为18.130～18.270,207Pb/204Pb变化范围为15.470～15.480,208Pb/204Pb变化范围为38.140～38.850。各同位素比值相对稳定,变化范围较小。将含矿斑岩的岩石铅与矿石铅进行综合投图,两种类型的铅并非单阶段正常铅,而是混合铅,有放射性成因铅的加入。可能存在不同的源区或在演化过程中有不同源区物质的混入。氢氧同位素研究结果显示,氢同位素的来源主要为深部的花岗岩体,而氧同位素由于后期大气降水增多、水/岩比值升高,导致含矿石英脉中δ18OH2O降低。因此推断甲玛铜多金属矿床成矿流体早期以深源流体为主,随着成矿过程的演化,大气降水所占的比例也越来越大。     

Lead isotope heterogeneity in sulfides from different assemblages at the Verninskoe gold deposit (Baikal-Patom Highland,Russia)

Using the high-precision technique of MC-ICP mass spectrometry, the isotope composition of lead was studied for the first time in sulfides of different mineral associations at the Verninskoe deposit that belong to large gold deposits of the Lena Province. In 23 monofractions of sulfides (pyrite, arsenopyrite, galena, and sphalerite), the Pb-Pb data showed a pronounced heterogeneity of the isotope composition of ore lead (²⁰⁶Pb/²⁰⁴Pb = 18.21–18.69, ²⁰⁷Pb/²⁰⁴Pb = 15.59–15.67, and ²⁰⁸Pb/²⁰⁴Pb = 37.98–38.63) for the deposit as a whole. This heterogeneity is also seen to a lesser degree within individual samples. In this case, a correlation takes place between the isotope composition of ore Pb and the type of mineral association: the sulfides in earlier associations are characterized by lower contents of the ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb radiogenic isotopes compared to the minerals of later parageneses. The comparison of Pb-Pb isotope characteristics of ore mineralization of the Verninskoe deposit to those of the Sukhoi Log deposit (the greatest in the Lena Province) testifies to the geochemical similarity of the sources of ore Pb involved in the formation of these deposits. The sources as such were terrigenous rocks of the Bodaibo synclinorium formed mainly as a result of the disintegration of Precambrian rocks of the Siberian craton.