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

An automated sample preparation line has been developed to equilibrate water samples for determination of their oxygen isotope ratio. Preliminary estimates put the repeatability of the sample preparation methods at approximately 0.04°/oof a figure that compares very favourably with the present state of the art. A noteworthy feature of our sample line, is that temperature control is unnecessary during sample equilibration. Errors arising from non-constant temperature conditions are prevented by simultaneously saving all of the equilibrated gas samples in separate reservoirs when the equilibration reaction is complete. Several other innovations in sample rack design are also described. These are: a circular rack geometry; an improved, inexpensive, magnetic stirrer design to agitate water samples; a Peltier cooling device to trap water vapour; and the use of standard Pyrex test tubes as equilibration flasks. The preparation line is highly modular. Up to sixteen racks, each capable of preparing sixteen samples, can be included in the system. Racks may be removed, repaired or modified, and replaced, without disturbing the operation of any other racks in the system. The current configuration is a minimum system with only one rack. The programming concepts used to control operation of the system are new to this application, and hence are a significant contribution. A multi-tasking executive allocates resources amongst the racks on a priority basis. By using linked list structures, the operating system maximises resource and processor utilisation, but does not compromise flexibility and modularity. The operator can submit any rack for preparation at any time, and the system could, with sixteen racks, prepare a full load of 256 samples in a day. A simple handshaking interface has been provided to control the release of samples for analysis. This should make it possible to connect the sample line to any mass spectrometer capable of the automated analysis of carbon dioxide. The user controls sample line operation by commands entered on a teletype keyboard. The command language is deliberately unstructured, and users can type in "natural" English sentences if they wish. All system operations and user sentences are printed on the teletype to provide a permanent record for later scrutiny. Finally a manual command repertoire has been provided. It allows the operator complete control over any rack. All solenoids, registers, and control lines, can be manipulated on an individual basis from the teletype keyboard. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

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Natural calcium carbonates, such as foraminifera and speleothems, are ubiquitous on the Earth’s surface and are essential subjects of study to the field of paleoclimatology. In particular, climate proxies using stable isotope and/or trace element concentrations of marine or continental carbonates largely rely on laboratory calibration studies in which carbonates are synthesized and their geochemical properties are carefully quantified. The boron isotope compositions of marine carbonates are a potentially powerful tool for the reconstruction of ancient seawater pH. If proven reliable, this tracer will allow systematic recording of paleooceanographic conditions, greatly assisting climatologists identifying historical fluctuations in atmospheric carbon dioxide concentrations. The boron isotope-pH proxy relies on the hypothesis that only the charged borate ion, possessing a distinct boron isotope composition as a function of pH, is incorporated into the carbonate crystal lattice. In this study, abiotic calcite was synthesized in high ionic strength solutions (0.7 mol/kg) across a range of controlled pH conditions (low pH ~ 7.15, mid pH ~ 8.35 and high pH ~ 9.15). The magnitude of boron isotope fractionation (δ11B) was determined to quantify the pH-dependence of δ11Bcalcite between the carbonate and the precipitating solution. The observed increase in boron isotope composition of calcite with pH is consistent with preferential incorporation of borate ion into the crystal lattice, however the sensitivity of the acid dissociation and isotope equilibrium constants render it difficult to ascertain its exclusive contribution to the boron isotope composition of calcite. Observed non-equilibrium effects further mask the interpretation of the underlying mechanisms, which must be understood precisely to validate the proxy. Ultimately, the relationship between the boron isotope composition of marine carbonates and ocean pH may provide objective evidence for ocean-CO2 system alterations possibly stemming from human-induced climate change. This research also evaluated the temperature- and pH-dependence of oxygen isotope fractionation (between calcite and water) in high ionic strength systems at 10, 25 and 40 °C over a pH range of 7.46-9.43. Our study is the first to assess oxygen isotope effects and fractionation behaviour under these varied conditions while employing the constant addition method. Preliminary results support several working hypotheses in the field and have proven consistent with previously untested theoretical predictions. / Thesis / Master of Science (MSc)

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