A recent theory implicated redox-gradients in vertical transport of elements from buried mineral deposits to surface soils and predicted the formation of 'reduced chimneys' in intervening overburden. This thesis tests that theory through surface and/or subsurface investigations at six sites; two host electronically conductive sulphide mineralization and four host non-conductive chemically reduced features including three kimberlites and an H2S-sourced 'forest ring.' Redox and spontaneous potential (SP) measurement techniques were developed and surveys carried out on surface and down-hole. Methods included: oxidation-reduction potential on groundwater and soil slurries; determination of H2S(aq)/SO42-(aq) in groundwater and O2(g) and CH4(g) in the headspace of wells; and a hybrid redox-SP method using both Pt and non-polarizable electrodes.
The predicted 'reduced chimneys' were observed in overburden above mineralization. SP measurements demonstrate the presence of negative electrical anomalies over buried electronic conductors but positive responses over the non-conductors. It is proposed that strong redox gradients induce an electrical field, which results in mass transport of ions. Redox-active chemical species in a redox gradient are influenced by neighbouring species that are more electronegative on one side than the other. Redox-active polar ions and molecules should therefore exhibit a preferred orientation with their negative poles pointing in the positive redox direction, i.e. toward the neighbours with the strongest affinity for electrons. Alignment of constituent dipoles would result in a macroscopic polarity within the redox gradient and electrical anomalies that are negative at its oxidizing end. Since resistivity is finite, this electrical field should induce current in the form of an ion flux.
The theory accounts for geochemical and electrical anomalies over buried mineralization in a variety of environments. It suggests that a negative SP response should develop above a buried, reduced feature if a redox gradient above it is positive-upward. However, where a reduced chimney extends to surface, the predominant redox gradient is horizontal and oxidizing-outward, which would induce a positive-inward electrical polarity and a positive SP response on surface above the feature. Buried electronic conductors are a special case in which the whole conductor polarizes in the positive-upward redox gradient of the shallow Earth's crust.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/29652 |
| Date | January 2007 |
| Creators | Hamilton, Stewart MacNaughton |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 176 p. |
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