Variations In Pb Isotope Ratios Research Articles

Assessment of Zn pollution sources and apportionment in agricultural soils impacted by a Zn smelter in South Korea.

This study was conducted to assess the anthropogenic impact on the metal concentration in agricultural soils in the vicinity of a Zn smelter. We determined Pb isotope ratios to trace source of metals and calculate source apportionment. 19.7% of the agricultural soil samples had Zn concentrations exceeding the Korean worrisome level (WL). The isotopic variation in the contaminated agricultural soils reflected the input of contaminants derived from the Zn smelter. The spatial distribution of Zn concentrations and Pb isotopes suggested that the Zn smelter dust fallout was the major source of heavy metal pollution in the agricultural soils. Lead isotope compositions of soil horizon I was comparable to those of soil horizon II, indicating that smelter-origin Zn had migrated vertically. Binary mixing between Zn concentrates and background soils could explain the variations in Pb isotope ratios in the contaminated agricultural soils. Source apportionment calculations showed that for agricultural soils that were found to exceed the Korean countermeasure standard (CS), the average proportion of smelter-origin Zn was 45.8%-83.3% while for agricultural soils that exceeded the WL but were below the CS, the average proportion of smelter-origin Zn was 36.3%-68.1%. The remainder was derived from a geogenic source.

A study of radionuclides, metals and stable lead isotope ratios in sediments and soils in the vicinity of natural U-mineralisation areas in the Northern Territory

Australian guidelines recommend that tailings materials from uranium (U) mining and milling be contained without any detrimental impact on the environment for at least 1000 years. Natural analogue sites are being investigated to determine if they can provide data on the rates of natural erosion processes which occur over these timescales, for input into predictive geomorphic computer models. This paper presents radionuclide, metal and stable lead (Pb) isotope data from sediment cores and surface soils in the vicinity of two mineralised areas in the Alligator Rivers Region. Surface scrapes from the natural Anomaly #2, south of the Ranger mineral lease, exhibit radiogenic 206Pb/ 207Pb and 208Pb/ 207Pb ratios, and elevated U and metal concentrations typical for a near surface U anomaly. In contrast, samples taken from the Koongarra mineral lease (KML) show radionuclide activity and metal concentrations similar to natural areas elsewhere in the Alligator Rivers Region and Pb isotope ratios are closer to present day average crustal ratios (PDAC), as the orebodies at KML are covered by surficial sand. A sediment core collected from Anbangbang Billabong, downstream of KML, exhibits small variations in Pb isotope ratios that indicate that approximately 1% of the upper sediments in the sediment core may be derived from material originating from the U anomaly at Koongarra.

Compositions of dikes and lavas from the Pito Deep Rift: Implications for crustal accretion at superfast spreading centers

The northwest trending walls of the Pito Deep Rift (PDR), a tectonic window in the southeast Pacific, expose in situ oceanic crust generated ∼3 Ma at the superfast spreading southern East Pacific Rise (SEPR). Whole rock analyses were performed on over 200 samples of dikes and lavas recovered from two ∼8 km2 study areas. Most of the PDR samples are incompatible‐element‐depleted normal mid‐ocean ridge basalts (NMORB; (La/Sm)N < 1.0) that show typical tholeiitic fractionation trends. Correlated variations in Pb isotope ratios, rare earth element patterns, and ratios of incompatible elements (e.g., (Ce/Yb)N) are best explained by mixing curves between two enriched and one depleted mantle sources. Pb isotope compositions of most PDR NMORB are offset from SEPR data toward higher values of 207Pb/204Pb, suggesting that an enriched component of the mantle was present in this region in the past ∼3 Ma but is not evident today. Overall, the PDR crust is highly variable in composition over long and short spatial scales, demonstrating that chemically distinct lavas and dikes can be emplaced within the same segment over short timescales. However, the limited spatial distribution of high 206Pb/204Pb samples and the occurrence of relatively homogeneous MgO compositions (ranging <2.5 wt %) within a few of the individual dive transects (over distances of ∼1 km) suggests that the mantle source composition evolved and magmatic temperatures persisted over timescales of tens of thousands of years. The high degree of chemical variability between pairs of adjacent dikes is interpreted as evidence for along‐axis transport of magma from chemically distinct portions of the melt lens. Our findings suggest that lateral dike propagation occurs to a significant degree at superfast spreading centers.

Lead isotope zoning in galena; an ion microprobe study of a galena crystal from the Buick Mine, Southeast Missouri

Ion microprobe techniques have been used to determine the variations of Pb isotope ratios within a single octahedral crystal of galena from the Buick mine, southeast Missouri. The crystal shows uniform concentric zonation of Pb isotope ratios, with a total variation of approximately 3 percent in 208 Pb/ 206 Pb and approximately 4 percent in 207 Pb/ 206 Pb and with the crystal margin being less radiogenic (lower 206/204) than the core. The range in the observed 208 Pb/ 206 Pb ratio is larger than that observed previously for bulk galena analyses from throughout the mine and is almost as large as the total variation reported for the whole southeast Missouri ore district. The ion probe results are demonstrated to be accurate to 0.1-0.2 percent by comparison with conventional mass spectrometric analyses performed on microsamples of the same crystal. The ion probe technique holds promise for establishing a Pb isotope chronostratigraphy for the ore-bearing solutions, which will be useful in delineating temporal and spatial aspects of the fluid circulation patterns.