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.     

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 isotopic and chalcophile element compositions in the environment near a zinc smelting–secondary zinc recovery facility,Palmerton, Pennsylvania,USA

The environment surrounding Palmerton, Pennsylvania is contaminated with Pb arising from primary Zn smelting and a process involving Zn recovery from electric arc steel furnace dusts. Lead isotope systematics have been used to distinguish primary Zn smelting Pb (²⁰⁶Pb/²⁰⁴Pb∼18.4–18.5) from electric arc furnace dust lead (²⁰⁶Pb/²⁰⁴Pb∼19.0–19.1). Primary Zn smelting is the dominant source of Pb in O2 horizon soils from undisturbed near-Palmerton locations, which contain up to 3570 ppm Pb and 782 ppm Cd. Soils from undeveloped near-Palmerton locations also exhibit unusually elevated concentrations of other sphalerite-derived chalcophilic elements (Se, Ag, In, Sb, Te, Au, Hg, Tl and Bi); indium concentrations of up to 17.0 ppm are observed therein. Residential soils and dusts from Palmerton contain Pb which is largely explainable via mixing of Pb from primary Zn smelting and electric arc furnace dusts. Approximately 80% of the Pb in airborne particulate matter sampled at Palmerton in 1991 is derived from electric arc furnace dusts, and atmospheric enrichment factors for Cu, Sb, Pb, and Bi are observed which confirm this major source contribution. Residential samples from a control location contain Pb which is less radiogenic than is found in Palmerton, and exhibit no unusual elevation in sphalerite elements. Lead source discrimination in the Palmerton environment via Pb isotopic and elemental constituents approaches result in parallel conclusions.     

Lead in archaeological samples: an isotopic study by ICP-MS

Inductively coupled plasma mass spectrometry (ICP-MS) has been used to measure the concentration and isotopic composition of Pb in archaeological human and animal skeletal remains, soil from a village site of the Omaha tribe (U.S.A.) and cosmetic pigments.Lead concentrations in human bones from the Omaha tribe vary between 4.8 and 2570 μg/g, with younger people having the highest concentrations. Lead concentrations in animal bones from an Omaha village vary between 0.6 and 3.7 μg/g, and those of three soil samples range between 18 and 21 μg/g. Lead concentrations found in human bones from Anasazi (Utah, U.S.A.) and Alta (Peru) populations vary between 0.7 and 3.2 μg/g.Isotope ratios of a reagent grade Pb(NO₃)₂ solutions were measured by thermal ionization mass spectrometry (TIMS), as well as by ICP-MS to provide laboratory reference materials. The accuracy of the ICP-MS measurements relative to TIMS for the standard solution were found to be within 0.02–0.31% for²⁰⁶Pb/²⁰⁴Pb, 0.02–0.55% for²⁰⁷Pb/²⁰⁴Pb, and 0.16–0.56% for²⁰⁸Pb/²⁰⁴Pb. The precision of measurements on artifacts was 0.42–0.65% for²⁰⁶Pb/²⁰⁴Pb and 0.41–0.62% for²⁰⁷Pb/²⁰⁴Pb, whereas the precision for the same ratios for the bones was 0.85–1.8 and 0.82–1.67%, respectively. For the cosmetic lead-bearing pigments, a precision of 0.07–0.15% was found for both²⁰⁶Pb/²⁰⁴Pb and²⁰⁷Pb/²⁰⁴Pb ratios. Lead isotope ratios of artifacts give a radiogenic Pb signature, of which are close to signatures from PbZn mines of the central U.S. region. Lead isotope ratios of the pigments give non-radiogenic Pb signatures. Lead isotope ratios of the bones differ from those of the artifacts, and although similar in isotopic ratio to the pigments, they are more scattered, suggesting potential mixing of Pb from different regions.     

The isotopic evolution of atmospheric Pb in central Ontario since AD 1800, and its impacts on the soils, waters, and sediments of a forested watershed, Kawagama Lake

A peat core from an ombrotrophic bog documents the isotopic evolution of atmospheric Pb in central Ontario since AD 1804 ± 53 (²¹⁰Pb dating). Despite the introduction of unleaded gasoline in the mid-1970’s, the ratio ²⁰⁶Pb/²⁰⁷Pb in atmospheric deposition has not increased as expected, but rather continues to decline. In fact, snowpack sampling (2005 and 2009) and rainwater samples (2008) show that the isotopic composition of atmospheric Pb today is often far less radiogenic than the gasoline lead that had been used in Canada in the past. The peat, snow, and rainwater data presented here are consistent with the Pb isotope data for aerosols collected in Dorset in 1984 and 1986 which were traced by Sturges and Barrie (1989) to emissions from the Noranda smelter in northern Quèbec, Canada’s largest single source of atmospheric Pb. Understanding atmospheric Pb deposition in central Ontario, therefore, requires not only consideration of natural sources and past contributions from leaded gasoline, but also emissions from metal smelting and refining.Lead in the streams which enter Kawagama Lake today (²⁰⁶Pb/²⁰⁷Pb = 1.16 − 1.19) represents a mixture between the natural values (1.191 − 1.201 estimated using pre-industrial lake sediments) and the values found in the humus layer of the surrounding forest soils (²⁰⁶Pb/²⁰⁷Pb = 1.15 − 1.19). In the lake itself, however, Pb is much less radiogenic (²⁰⁶Pb/²⁰⁷Pb as low as 1.09) than in the streams, with the dissolved fraction less radiogenic than particulate material. The evolution of Pb isotope ratios within the watershed apparently reflects preferential removal by sedimentation of comparatively dense, radiogenic, terrestrial particles (derived from the mineral fraction of soils) from the humus particles with lower ratios of ²⁰⁶Pb/²⁰⁷Pb (because of atmospheric Pb contamination). Despite the contemporary enrichments of Pb in rain and snow, concentrations of dissolved Pb in the lake are extremely low (sometimes below 10 ng/l), with Pb concentrations and Pb/Sc ratios approaching “natural” values because of efficient binding to particles, and their subsequent removal in the watershed.     

Concentration, isotopic composition, and sources of lead in Southern Ocean air during 1999/2000, measured at the Cape Grim Baseline Air Pollution Station, Tasmania

Southern Ocean aerosols were collected at the Cape Grim Baseline Air Pollution Station from onshore air under baseline conditions between February 1999 and April 2000. Thermal ionization techniques (TIMS) and isotope dilution mass spectrometry (IDMS) were used to measure the isotopic composition and concentration of lead in the air giving concentrations as low as 0.6 ± 0.1 pg · m⁻³. Air collected under baseline conditions for 12 months (May 1999-April 2000) yielded an overall lead concentration of 11.0 ± 0.2 pg · m⁻³ and isotopic composition of ²⁰⁶Pb/²⁰⁷Pb = 1.154, ²⁰⁸Pb/²⁰⁷Pb = 2.387 and ²⁰⁶Pb/²⁰⁴Pb = 17.93. The range in isotopic ratios was consistent with the mixing of lead from major population centers in the Southern Hemisphere in the mid to high latitudes, except for the presence of highly radiogenic lead in some samples. Contributions from radiogenic lead of up to ∼0.8% were observed. Three periods with the highest percentage contribution of radiogenic lead (>0.5%) were investigated in more detail, and 4-d back-trajectories and radon concentrations were used to help identify the sources. The sources are probably associated with the mining and processing of uranium rich ores in southern Africa and possibly South Australia.     

Lead-isotope inhomogeneity in Precambrian igneous K-feldspars

Stepwise Pb-removal experiments, using both vacuum volatilization and HF-leaching techniques, on acid-washed K-feldspar concentrates from Precambrian igneous rocks show that all contain some unsupported radiogenic Pb. Two types of radiogenic Pb were recognized. One has a “normal” isotopic composition, with relative abundances of ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb consistent with the age and U-Th contents of the rocks. The other type of unsupported radiogenic lead in the feldspars is apparently pure ²⁰⁶Pb, derived from long-term migration and accumulation of radioactive daughter(s) of ²³⁸U. This “pure ²⁰⁶pb” lead occupies different sites from the “normal” radiogenic lead, and tends to show a release maximum during vacuum volatilization at about 1150°C.The usefulness of stepwise vacuum volatilization may be limited by the tendency of a small amount of radiogenic lead to concentrate in the least volatile fraction. Stepwise partial HF attacks appear to give at least as good separation of radiogenic from original feldspar lead, and are recommended as a routine procedure for isotopic analyses of Precambrian feldspars. The fact that most of the five K-feldspars examined contained unsupported radiogenic lead implies that caution must be used in applying total-sample lead analyses of Precambrian feldspars to problems of lead-isotope evolution in crustal rocks.     

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.     

Genesis of the South Zhuguang Uranium Ore Field,South China: Pb Isotopic Compositions and Mineralization Ages

U–Pb isotopic analyses indicate that ores from the South Zhuguang uranium ore field, south China, have high common (non‐radiogenic) Pb contents, with variable and relatively radiogenic initial Pb contents. The U–Pb isochron method was used to date these ores, with plots of ²⁰⁸Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb being used to identify sample suites with similar initial Pb isotopic ratios and to normalize variable initial Pb isotopic ratios. The resulting U–Pb isochrons indicate two substages of uranium mineralization at ~57 and 52 Ma, with a later hydrothermal reformation at ~49 Ma, which homogenized Pb isotopic compositions. Initial Pb isotopic systematics indicate that the ore‐forming fluid was characterized by high ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb ratios and low ²⁰⁸Pb/²⁰⁴Pb ratios, suggesting that the ore‐forming fluid was sourced from Cretaceous–Paleogene red‐bed basins, rather than from magma or the mantle, with consideration of mineralization ages.     

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.     

Lead isotope data from the Sar-Cheshmeh porphyry copper deposit,Iran

Lead isotope compositions of nine sulfide concentrates from ore samples from the Sar-Cheshmeh deposit are reported. They range from virtually unaltered granodiorite through varying degrees of potassic alteration to ores showing strong phyllic alteration (sericite veins). The samples without strong phyllic alteration have fairly uniform lead isotope compositions around ²⁰⁶Pb/²⁰⁴Pb=18.6, ²⁰⁷Pb/²⁰⁴Pb=15.6, and ²⁰⁸Pb/²⁰⁴Pb=38.7. Two samples with sericite veins have markedly more radiogenic lead. It is concluded that the fluid responsible for the potassic alteration and the associated mineralization was essentially magmatic, whereas convecting meteoric water from the country rock acted as a mineralizing solution during phyllic alteration. In the context of the plumbotectonics model, the deposit has a typical orogen signature intermediate between primitive and mature island-arc settings.     

Nd,Sr and Pb isotopic and REE geochemical study of some Miocene submarine hydrothermal deposits (Kuroko deposits) in Japan

Neodymium, Sr and Pb isotopic compositions, along with rare earth element (REE) concentrations were determined for twelve black ores and one yellow ore from twelve localities of the Kuroko deposits, Japan. The ores were generated by submarine hydrothermal activity during the Miocene age. Neodymium isotopic compositions of the ores (_Nd: –4.9 to +6.5) mostly overlap with spatially associated igneous rocks. On a Nd versus Sr isotopic correlation diagram, however, ⁸⁷Sr/⁸⁶Sr ratios are shifted from the associated igneous rocks towards the higher contemporaneous seawater ratio. REE patterns are highly variable, ranging from light REE enriched to depleted, and show no Ce anomalies, as would be expected if they were derived from seawater. These results suggest that the REEs contained in ores were mainly derived from the associated igneous rocks, but that the ore Sr is a mixture derived from both seawater and the igneous rocks. Most Pb isotopic compositions fall within the range defined by the associated igneous rocks (²⁰⁶Pb/²⁰⁴Pb=18.35–18.84, ²⁰⁷Pb/²⁰⁴Pb=15.59–15.97 and ²⁰⁸Pb/²⁰⁴Pb=38.53–39.90), although several samples have very radiogenic compositions that were most likely derived from basement rocks. Our new Pb isotopic results display greater variation, and have a larger range of more radiogenic compositions than has been noted previously for these ores. In addition, the black ore with the most radiogenic Pb isotopic composition also has the least radiogenic Nd isotopic composition. This suggests that at least some of the Pb contained in the ores was derived mainly from older basement rocks. The large positive Eu anomalies for some black ores are consistent with a high-temperature origin for the parental fluids, irrespective of the source rock. The single yellow ore examined, however, has a small negative Eu anomaly, which may indicate derivation from a lower temperature fluid. Previous studies suggested that the Kuroko ores were formed in the presence of organic materials in an anoxic basin. Combined Nd, Sr, Pb and Os isotopic and REE abundance data indicate that multiple sources were involved in the genesis of Kuroko ores.     

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 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     

Caledonian upgrading of Proterozoic low-grade base-metal deposits in Northern Sweden

Summary Proterozoic sulfide deposits within the basement of northern Sweden have lead isotopic compositions that fall on a mixing line in the²⁰⁶Pb/²⁰⁴Pb-²⁰⁷Pb/²⁰⁴Pb diagram. These deposits contain a highly radiogenic Phanerozoic lead component that was leached from the Proterozoic basement at around 0.4 Ga during the Caledonian orogeny. Within the Proterozoic deposits, the less radiogenic lead isotopic compositions occur in undeformed and little deformed sections, while the more radiogenic lead isotopic compositions are observed along fault, fracture, and shear zones. These zones with radiogenic Phanerozoic lead also have higher contents of lead, zinc, and gold, respectively, than the other parts of the deposits, which suggests that these metals were introduced together with the radiogenic lead at a much later event than the metals in the unaltered Proterozoic deposit. The Proterozoic deposits acted as traps for metal additions along Caledonian reactivated fault and shear zones in the Proterozoic basement.

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Kaledonische Metallanreicherung in niedrighaltigen proterozoischen Buntmetallerzen in Nordschweden

Zusammenfassung Proterozoische Sulfidvererzungen im proterozoischen Grundgebirge weisen Bleiisotopenzusammensetzungen auf, die auf eine Mischungslinie im²⁰⁶Pb/²⁰⁴Pb-²⁰⁷Pb/²⁰⁴Pb Diagramm fallen. Die proterozoischen Vererzungen enthalten eine Komponente radiogenen Bleis, welches im Verlaufe der kaledonischen Orogenese aus dem proterozoischen Grundgebirge ausgelaugt wurde. Wenig oder nicht deformierte Abschnitte in den proterozoischen Sulfidvererzungen weisen weniger radiogene Bleiisotopenzusammensetzungen auf, als Bruch- und Scherzonen in denselben Vererzungen. Diese Zonen mit radiogenem, kaledonischem Blei weisen auch höhere Blei-, Zink- und Gold-Gehalte auf als die übrigen Teile der Vererzung, was andeutet, daß diese Metalle zusammen mit dem radiogenen Blei zu einem viel späteren Zeitpunkt in die Vererzung eingebracht worden sind. Die proterozoischen Vererzungen bewirkten die Metallausfällung aus Fluiden, die entlang von kaledonisch mobilisierten Verwerfungen und Scherzonen flossen.

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With 3 Figures     

Geology and Lead-Isotope Study of the Baiyinnuoer Zn-Pb-Ag Deposit, South Segment of the Da Hinggan Mountains, Northeastern China

The Baiyinnuoer deposit (32.74 Mt ore with grades of 5.44% Zn, 2.02% Pb and 31.36 g t^?1 Ag), the largest Zn‐Pb‐Ag deposit in northern China, is hosted by crystalline limestone and slate of the Early Permian Huanggangliang Formation. Detailed cross‐section mapping indicates stratigraphic and fold structural controls on the mineralization. The Zn‐Pb‐Ag mineralization is hosted predominantly by skarn, which occurs as bedding‐parallel lens that pinch out at the margins of the main economic zone. Three skarn stages are identified at the deposit: (i) garnet‐clinopyroxene; (ii) sulfides; and (iii) carbonate‐epidote. Lead isotopic compositions were determined for galena and sphalerite of the ores, whole rock samples of the Yanshanian granite and granodiorite, Permian marble and tuff, and Jurassic volcanic and subvolcanic rocks in and around the Baiyinnuoer area in order to discuss the sources of ore‐forming materials and the relationship between the ore formation and these whole rocks. Galena and sphalerite of the Baiyinnuoer ore have uniform isotopic ratios (²⁰⁶Pb/²⁰⁴Pb, 18.267–18.369; ²⁰⁷Pb/²⁰⁴Pb, 15.506–15.624; ²⁰⁸Pb/²⁰⁴Pb, 38.078–38.394) consistent with the granite and granodiorite (²⁰⁶Pb/²⁰⁴Pb, 18.252–18.346; ²⁰⁷Pb/²⁰⁴Pb, 15.504–15.560; ²⁰⁸Pb/²⁰⁴Pb, 38.141–38.320), whereas the ratios for Jurassic volcanic and subvolcanic rocks are variable and radiogenic (²⁰⁶Pb/²⁰⁴Pb, 18.468–18.614; ²⁰⁷Pb/²⁰⁴Pb, 15.521–15.557; ²⁰⁸Pb/²⁰⁴Pb, 38.304–38.375). These results indicate that the mineralization was not related to the Jurassic volcanism, but to the Yanshanian magmatism. The Permian strata may have a slight contribution to the mineralization. All features show that the Baiyinnuoer deposit is related to the Yanshanian granitic magmatism, and can be classified as a zinc‐lead‐silver skarn deposit.     

Metal sources of the large Nezhdaninsky orogenic gold deposit, Yakutia, Russia: Results of high-precision MC-ICP-MS analysis of lead isotopic composition supplemented by data on strontium isotopes

A collection of galena from the Nezhdaninsky gold deposit (62 samples), as well as galena from the Menkeche silver-base-metal deposit and the Sentyabr occurrence and K-feldspar from intrusive rocks of the Tyry-Dyby ore cluster have been studied using the high-precision (±0.02%) MC-ICP-MS method. Particular ore zones are characterized by relatively narrow variations of isotope ratios (no wider than σ_6/4 = 0.26%). Vertical zoning of Pb isotopic composition is not detected. Variation in Pb isotope ratios mainly depends on the type of mineral assemblage. Galena of the gold-sulfide assemblage dominating at the Nezhdaninsky deposit is characterized by the following average isotope ratios: ²⁰⁶Pb/²⁰⁴Pb = 18.472, ²⁰⁷Pb/²⁰⁴Pb = 15.586, and ²⁰⁸Pb/²⁰⁴Pb = 38.605. Galena from the regenerated silver-base-metal assemblage is distinguished by less radiogenic lead isotope ratios: 18.420, 15.575, and 38.518, respectively. In lead from the Nezhdaninsky deposit, the component, whose source is identified as Permian host terrigenous rocks, is predominant. The data points of isotopic composition of lode lead make up a linear trend within the range of μ₂ = 9.5-9.6. K-feldspar of granitic rocks has less radiogenic and widely varying lead isotopic composition compared to that of galena. The isotopic data on Pb and Sr constrain the contribution of Late Cretaceous granitic rocks as a source of gold mineralization at the Nezhdaninsky deposit. The matter from the Early Cretaceous fluid-generating magma chamber participated in the ore-forming system of the Nezhdaninsky deposit. The existence of such a chamber is confirmed by the occurrence of Early Cretaceous granitoid intrusions on the flanks of the Nezhdaninsky ore field. The greatest contribution of magmatic lead (～30%) is noted in galena from the silver-base-metal mineral assemblage. This component has isotopic marks characteristic of lower crustal lead: the elevated ²⁰⁸Pb/²⁰⁶Pb ratio relative to the mean crustal value and the lower ²⁰⁷Pb/²⁰⁴Pb ratio. Taken together, they determine a high Th/U ～ 4.0 in the source and μ₂ = 9.37–9.50. This conclusion is consistent with the contemporary tectonic model describing evolution of the South Verkhoyansk sector of the Verkhoyansk Foldbelt and the Okhotsk Terrane.     

Application of lead stable isotopes to the Guadiamar Aquifer study after the mine tailings spill in Aznalcóllar (SW Spain)

On 25 April 1998 the tailings dam of the Aznalcóllar mine burst, a great quantity of pyrite waste sludge and acid water was spilled reaching the vicinity of the Doñana National Park. In surface and ground water samples taken a week after dam breaking, metals, trace elements and Pb isotopic ratios (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) were analysed. In September 1998 a second sampling survey was carried out. The surface waters have a similar isotopic composition as the lead contained in the pyrite from the Aznalcóllar mine. The polluted groundwater of the Guadiamar aquifer also shows the influence of the mining origin of the lead. Lead isotope ratios (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) in the groundwater of the Almonte-Marismas are very low and they differ clearly from the rest of groundwater samples. A further group of wells has a lead isotope composition intermediate between the Aznalcóllar mine and the atmospheric aerosols of the Iberian Peninsula.     

Lead and uranium isotopic behavior in diagenetic and epigenetic manganese nodules, Timna Basin, Israel, determined by MC-ICP-MS

Isotope ratios of U and Pb were measured in two types of Mn nodules from the Cambrian Timna Formation, Israel. Type A nodules are mainly composed of pyrolusite and hollandite, with Mn, Ba, Pb and U concentrations of 30–60%, 0.2–2.5%, 0.2–1.0% and 500–3500 ppm, respectively, whereas type B nodules were formed by alteration of the former, and contain mainly coronadite, with Mn, Ba, Pb and U concentrations of 7–48%, 0.2–7%, 0.6–5% and 10–160 ppm, respectively. The isotopic composition of U and Pb was measured by MC-ICP-MS on Mn-rich solutions (up to 100 mg/L) without and with chromatographic separation. The values for the 207/206 and 208/206 ratios have been determined with precisions of up to 50 ppm and those of 206/204, 207/204 and 208/204 – up to 200 ppm. The values for the 234/238 ratios have been determined with precisions of 0.4–1%. The results of the separated and unseparated solutions were shown to be equal within the error. Thus there is no significant matrix effect while measuring U and Pb in Mn rich solution using the MC-ICP-MS.The isotopic composition of Pb and U support the distinction between the two types of Mn nodules. Type A nodules have a wide range of ²⁰⁶Pb/²⁰⁴Pb ratios (18.278–19.776), and an almost constant ratio of ²⁰⁸Pb/²⁰⁴Pb. In contrast, type B nodules have almost constant ²⁰⁶Pb/²⁰⁴Pb ratios and a wide range of ²⁰⁸Pb/²⁰⁴Pb ratios (37.986–38.079). Type A nodules form a linear array on a ²⁰⁷Pb/²⁰⁴Pb vs ²⁰⁶Pb/²⁰⁴Pb diagram, while type B nodules form a tight group characterized by lower Pb isotope ratios that slightly deviate from the type A array. The ²³⁴U/²³⁸U ratio differs between the two types of nodules; type A nodules exhibit a uniform and close to equilibrium ²³⁴U/²³⁸U ratio while type B nodules show a wide range of ²³⁴U/²³⁸U ratios above and below the equilibrium value. The isotopic composition of Pb in type A nodules might reflect Pb contributions from plutonic rock weathering, exposed at the time of deposition or later, to the Cambrian sea. These nodules have remained unaffected by processes that occurred since the Cambrian. The higher ²⁰⁸Pb/²⁰⁴Pb values of type B indicate that these nodules were formed from a Th-enriched solution probably during epigenetic processes which occurred also during the last 1 Ma.Thus the two isotopic systems of U and Pb can record formation, leaching and redeposition of Mn ores.     

Sulphur and Lead Isotope Compositions of the Dajiangp—ing Deposit in Western Guangdong Province1

Abstract The Dajiangping pyrite deposit located in the middle sector of the Yunkai uplift in western Guangdong is a stratiform sulphide deposit occurring in Sinian marine clastic and fine clastic rocks. The formation of the deposit was related to submarine exhalation and hot brine deposition. A part of it was reformed by late-stage hydro thermal solution. The δ³⁴S values of pyrite vary from — 25.55‰ to + 21.07‰, which are inversely proportional to the content of organic carbon in ore and pyrite. Passing from striped fine-grained pyrite ore to massive coarse-grained pyrite ore, i.e. from south to north, the sulphur isotopic composition changes from the light sulphur-enriched one to the heavy sulphur-enriched one. The lead isotopic composition of striped ore is consistent with that of the country locks of orebodies and the lead is radiogenic lead derived from the upper crust. The lead isotopic composition of massive ore is relatively homogeneous and its ²⁰⁶/Pb²⁰⁴Pb, ²⁰⁷/Pb²⁰⁴Pb and ²⁰⁸/Pb²⁰⁴Pb ratios are a bit lower than those of striped ore; the lead result from mixing of synsedimentary ore lead with that derived from basement migmatite brought by late-stage hydrothermal solutions.