The purpose of this thesis is to investigate the isotopic composition of primary leads. The leads analysed were selected by R. L. Stanton in accordance with his geologic description for conformable deposits. It was anticipated that, of all available terrestrial leads, these were the least likely to have been modified isotopically by crustal processes. Detailed analyses and interpretations for fifty-six samples from nine different districts in Eastern Australia, Tasmania, Canada and New Zealand are presented. A precision of better than ±.05 per cent in the measurement of the Pb²⁰⁶/Pb²⁰⁴, Pb²⁰⁷/Pb²⁰⁴ and Pb²⁰⁸/Pb²⁰⁴ ratios was achieved for all samples by means of an intercomparison technique derived from that used by P. Kollar and R. D. Russell, and improved methods for reducing the data. As expected, the geologic criteria used by Stanton to identify conformable deposits have been found to be sufficient to identify deposits which are very uniform in isotopic composition. The findings of this research indicate that the criteria, although remarkably good, are not completely adequate for identifying primary leads. In particular, leads from two conformable deposits (Manitouwadge and Rosebery) were found to be anomalous, and those from two other deposits (Hall's Peak and Bathurst) may be anomalous. The single-stage lead model was found to be a very good approximation for isotopic development of the leads from the remainder of the conformable deposits studied by the writer, as well as for leads analysed by other workers at the University of British Columbia and assumed to be primary. These results suggest that primary leads have formed in a region for which there are very narrow limits of ±.6% and ± .8% to the variations in U²³⁸/Pb²⁰⁴ and Th/U ratios. They substantiate the hypotheses of Russell and Stanton that: (1) primary leads lie very closely to a unique single-stage growth curve in a plot of the ratios Pb²⁰⁷/Pb²⁰⁴ against Pb²⁰⁶/Pb²⁰⁴, and in a plot of Pb²⁰⁸/Pb²⁰⁴ against Pb²⁰⁶/Pb²⁰⁴; (2) leads away from this growth curve are anomalous. From the fit of the conformable leads to a single-stage growth curve, values of 4.52 ± .03 Gyr. and 4.54 ± .02 Gyr. have been calculated for the age of the earth. With the identification of a unique growth curve for primary leads, severe restrictions are placed on anomalous lead interpretations. These are illustrated in the interpretations of anomalous leads studied by the writer. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A new method has been proposed for determining the age of lead sulfide mineralization from anomalous lead Isotope abundances. The anomalous leads are most readily recognized by the linear relationship of the isotope ratios on any compositional diagram. The method assumes that the initial stage of lead isotope development occurred in a system having a uniform distribution of uranium, thorium and lead. This accords with experimental results obtained by the writer and other research workers at the University of British Columbia that single-stage isochrons as proposed by Houtermans are either very short or do not exist. Consider t₁ to be a time of tectonic activity during which ordinary leads were differentiated from a deep source and either concentrated to form a lead deposit at this time or disseminated throughout the upper crust. Contemporaneously uranium and thorium bearing solutions were incorporated into the same environment. At time t₂ tectonic activity recurred in the area. Some of the ordinary leads were remobilized and became contaminated with radiogenic lead to form anomalous lead deposits. Existing lead isotope analyses yield the following results. At Broken Hill, Australia, t₁ is 1600 million years, while t₂ is 510 ± 80 m.y. For Goldfields, Saskatchewan, t₁, is 2015 m.y. while t₂ is 560 ± 250 m.y. At Sudbury, Ontario, t₁ is 1730 m.y. and t₂ is 870 ± 280 m.y. For lead deposits around the Ozark Dome area, including Joplin and Bonne Terre, Missouri, t₁ is 1350 m.y. and t₂ is about 115 m.y. For leads in west-central New Mexico, t₁ is 1490 m.y. and t₂ is about 69 m.y. The errors in the estimates are generally quite large but the values quoted are consistent with available geological and chronological data. The simplest type of anomalous leads which can occur is a mixture of two ordinary leads. This has only been found to occur on the boundary between two geological provinces. Examples of this type have been identified in the Cobalt area, Ontario and in the Baltic Shield along the border between the Fenno-Karelides and Svecofennides. A large proportion of anomalous lead Isotope measurements may be interpreted on the basis of the two-stage models outlined above. Extension of this model to an n-stage system is considered. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Advances in mass spectrometry in the second half of this century allowed very accurate measurements of isotopic compositions of various elements. In turn it was discovered that due to the radiogenic origin of some of these isotopes their composition often reflects the geochemical history of minerals and rocks. Terrestrial lead is composed of four isotopes, of which three are radiogenic in origin as daughters of uranium and thorium. In geochronology the isotopic composition of minerals helps in dating the ore and rock formations. However, if there is enough diversity amongst the isotopic compositions of different deposits, then their lead isotope composition can be used as a simple and unique 'fingerprint', which can be scientifically measured. This feature can be used as a powerful tool in the identification of sources of ancient metals, because it passes unchanged through the smelting and refining processes. However, one of the most important requirements for such 'lead isotope provenance studies' is empirical investigation of the 'fingerprints' of ore deposits which are relevant to a given archaeological research. In this dissertation the scientific foundations of lead isotope provenance studies are described and examined in detail. All available evidence concerning the possibility of distinguishing isotopically between different European ore deposits is examined and methods of visual and numerical evaluation of the lead isotope data are suggested. Two examples of applications to specific archaeological problems are also given: the identification of sources of metals used for production of Bronze Age Cretan weapons and of non-ferrous metals in the Roman Period in Southern Poland. The interpretation of lead isotope data for archaeological objects is based on nearly 1500 isotopic analyses of ores.

Ratio recording methods in mass spectrometry have hitherto been successfully used in analyses involving only a few of the lighter elements. In all these cases a great improvement in precision has resulted. This thesis describes a means whereby grid ratio recording can be extended to the precise measurement of complex spectra in the high mass range. In particular, lead isotope studies in geophysics provide a great and continuing need for increased analytical precision. The project has involved the construction of a complete mass spectrometer which incorporates two main features which have not been used before in mass spectrometry. The first of these is a scanning mechanism which moves the collector across the stationary ion beams. It is this innovation which has made possible the development of grid ratio recording. Since the total ion beam is stationary, variations in its intensity during the scanning process can be monitored accurately. A servo-divider system is arranged to make the measuring system Insensitive to variations in the total ion beam by recording the individual ion beam currents as fraction of the total Ion beam. The ratio system will effectively reduce large variations in the total Ion beam due to changes in source conditions by a factor of fifteen. Smaller variations are reduced to below the noise level existing in the recording system itself. The second principle which is believed to be new to mass spectrometry is the method by which the results of an analysis are presented by the instrument. An expanded scale system of recording has been developed whereby the amplitude of an ion current is presented as a digit on a counting tube, with the remainder displayed as a peak on a chart recorder. It is demonstrated that the expanded scale arrangement will record a known signal with a standard deviation of less than 0.02%. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

On the basis of data published prior to 1960, two basic lead isotope models - the isochron model and the primary lead model - were postulated to fit those crustal leads that have had the simplest history. The present writer's analyses of samples from Southern Finland, and the results of other research workers, now indicate that the primary lead model more adequately describes these leads, and that primary "isochrons" are either very short, or else non-existent. Lead in conformable deposits and in ultrabasic sulfides were postulated by R.L. Stanton to be examples of primary lead. Analyses of samples from several massive lead-zinc conformable deposits have indicated that the leads of many of these deposits possess primary lead characteristics. The present thesis describes a technique devised to prepare tetramethyllead from the conformable chalcopyrite deposits and ultrabasic sulfides and describes some initial results. This is a free radical technique, involving the reaction of methyl radicals with a lead mirror evaporated out of a sulfide. It appears to be capable of preparing tetramethyllead from samples containing one to two orders of magnitude less lead than previously reported for such a technique. Unfortunately, the full extent of the method cannot be utilized with present gas source mass spectrometer facilities, and only fair precision (0.4%) is possible at 10 ppm. lead. Samples from the conformable chalcopyrite deposits of Mt. Isa were analysed. The lead isotope ratios were found to be significantly different from those of the massive lead-zinc deposits. The results, interpreted with other lead and sulfur isotope data, suggest that these deposits could be the result of metal-bearing solutions entering a partially enclosed bay. Initial results for two ultrabasic deposits suggest that the lead in the sulfides is not necessarily primary; for example, that in two Stillwater ultrabasic complex samples appears to be the result of three stages of development. Hence, both the present lead isotope analyses, and those reported earlier by Ostic (1963) indicate that Stanton's geological criteria, while good, are not completely adequate for identifying primary leads. It is here suggested that sulfur isotope analyses might indicate which of these samples have been contaminated by crustal leads. During the investigation of the gas source mass spectrometric analyses of small tetramethyllead samples, lead isotope fractionation was observed. This occured with molecular flow into the mass spectrometer. Lead isotope fractionation has not been reported previously, and has some interesting geophysical implications. A preliminary study suggests that such fractionation in nature is likely to be rare, except possibly in biological processes in the sea. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The isotopic constitution of lead became important in geophysics as the lead-uranium and lead-thorium methods of absolute geological age determination were established. Interest in the isotopic abundances of common lead in lead minerals was a natural development. The interpretations of observed variations in lead isotope ratios has been more simple than had been expected twenty years ago when the first measurements of this kind were made by A. 0. Nier, and results have been obtained that are of very great importance to geophysics. Consequently this field is now expanding very rapidly. Many interpretations now being made are limited by the available precision of the measurements, which is of the order of several tenths of a per cent. A mass spectrometer laboratory was set up in the Department of Physics at The University of British Columbia, and a mass spectrometer capable of measuring heavy elements with high precision was designed and constructed. It is a 90 degree sector, 12 inch radius, direction focusing instrument with a copper tube and using a modified Nier-type gas source. It is essentially of orthodox design, but special attention was given to try to eliminate small sources of error. To establish more stable source conditions, an exceptionally stable filament emission control was constructed and purified lead tetramethyl samples were used. The ion beam was measured with a servo-voltmeter of original design that is capable of a high precision. Readings can be made from a calibrated dial on the voltmeter eliminating sources of error in the usual chart recorder. Tests have shown that the improvement in precision warrants this step. This mass spectrometer is believed to be the first to use extensively transistorized circuits. Error was reduced further by comparing each sample measured with a standard within reasonably short intervals of time (about twenty minutes). Three comparisons were made to loop two samples with the standard, and the looping error was determined and distributed around the loop. The analyses obtained in this way were compared with existing analyses from other laboratories, and an improvement in precision between a factor of five and a factor of ten seems to have been obtained. To demonstrate the precision obtainable with this mass spectrometer and with the improvement in operating techniques, analyses were made on the isotopic composition of leads from Broken Hill and Mount Isa, Australia. It was previously known that the leads are very similar in composition at both localities. From these new measurements it was established that the Broken Hill and Mount Isa deposits contain lead of distinctly different isotopic composition. In both deposits the isotope ratios were found less variable than could be inferred from previous measurements. A fine structure was found in the isotope ratios in both localities. These small variations indicate contaminations due to radiogenic leads. Values of the thorium/uranium ratios of the source of contamination were estimated. The precision of analyses made it possible to determine an age difference between the Mount Isa and Broken Hill deposits of 40 million years. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Data of good quality is necessary to further the study of rock lead isotopic interpretations. An internal standard (double-spike) was employed to correct for fractionation accompanying the single filament analyses, and lead isotope ratios with a standard deviation of 0.15% were obtained. Lead sulphide mounted on tantalum was employed for the lead analyses. Discrimination in the analyses using tantalum filaments was consistent with the theoretical fractionation laws. This was not found to be the case for rhenium. Lead and uranium analyses from the Vogt-Hobbs area near Lake Timagami, Ontario and from the Rice Lake-Beresford Lake Area, Manitoba revealed variations from a simple two stage model that could not be accounted for by experimental error. Interpretation of the data yields a three stage history for both of these regions, marked by major events at approximately 3400 and 2600 my ago. This earlier crustal history is supported by ore lead data from the vicinity. Both of the suites have a lower average value of (U238/Pb204) for the second stage, of their three stage history, than is characteristic of the source of single stage leads. Variations from closed system behaviour for the Ontario samples is attributed to lead remobilization at the time of the Grenville event. Remobilization of the lead tends to mask the 2600 my old event. The Vogt-Hobbs area is characterized by more acidic igneous rocks and more radiogenic lead than the Rice Lake-Beresford Lake area. These differences are thought to represent the environment 2600 my ago or earlier. The Manitouwadge lead analysed by Ostic resembles the lead - 2600 my ago in the Rice Lake-Beresford Lake rock samples. The Rice Lake-Beresford Lake rock samples are shown according to the interpretation presented, to have had a crustal history prior to 2600 my ago. This lends weight to arguments that exclude Manitouwadge from the class of single stage leads used in calculations of the age of the earth. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Lead has a more than three-millennia-long pollution history in Europe. Metal production, burning of coal and use of leaded petrol resulted in a significant pollution of the atmosphere. As a consequence of atmospheric fallout, the Swedish boreal forest is strongly contaminated by airborne lead pollution. High levels of lead in the soil and soil pore water are of concern because the soil fauna, plants and aquatic biota may respond negatively to this toxic element. The fate of the accumulated pool of pollution in the soil is not well known. In this thesis, I determine four variables of importance for increasing our knowledge about the past, present and future lead levels in the boreal forest soil: 1) the pre-pollution atmospheric deposition rate of lead; 2) the upward flux of lead from deeper soil layers to near-surface horizons as a result of plant uptake; 3) the mean residence time of lead in the mor layer (the organic horizon at the surface of forest soils); and 4) the vertical and lateral transport of pollution lead within the mineral soil and to streams. Lead concentration measurements and stable lead isotope analyses were used for distinguishing pollution lead from natural lead in cores from ombrotrophic bogs, forest soil profiles, forest mosses, soil-water and stream-water samples. The results clearly stress that the boreal forest ecosystem is totally dominated by pollution lead. This is proved by low 206Pb/207Pb ratios (mainly between 1.14 and 1.20) in the mor layer, forest plants and stream water, while the local geogenic lead of the mineral soil (C-horizon) has high ratios (> 1.30). The dominance of pollution in the mor layer is caused by high deposition rates of airborne lead pollution, minute transport rates of lead from the mineral soil by forest plants (about 0.02 mg lead m-2 year-1) and a long mean residence time of the deposited lead (~250 years for mature forest). In the pristine pre-pollution environment, lead was a rare element due to low atmospheric deposition rates (0.001 to 0.01 mg m-2 year-1). It is estimated that the present lead inventory in the mor layer is up to 100 times higher than in the pristine environment where ≤ 8 mg m-2 was present in the mor. The levels in this biologically important horizon will decrease at a very slow rate and it will take centuries for the deeper part of the mor layer to fully respond to decreasing atmospheric inputs. In a hypothetic scenario with a ceased atmospheric lead deposition, the pool of pollution lead will ultimately be redistributed to deeper water-saturated soil layers from where a lateral transport to surface waters occurs. In the studied catchment, the export of pollution lead from the soil to the stream is estimated to peak slightly about one thousand years from now.

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