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The geochemistry of mercury at Ngawha Springs, New Zealand.

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posted on 2023-05-27, 00:11 authored by Davey, Herbert Andrew
Currently cinnabar is depositing at Ngawha Springs from mercury transported as the element. Much of the deposition is weather dependent and all ore occurs in the uppermost few metres of the ground. Field conditions and laboratory experiments demonstrate that deposition requires oxygen and that the presence of chloride enhances the oxidation of mercury. The deposition of the cinnabar proceeds according to the reaction: ... The mercury 11 thus formed rapidly reacts with reduced-sulphur species from geothermal and biogenic sources to produce cinnabar. Biogenic replacement of organic material by metal sulphides is an important deposition mechanism, for it is responsible for the bulk of the richest cinnabar occurrences via the marcasite pseudomorphing of vegetation debris adjacent to the geothermal emanations. The oxidative destruction of the pseudomorphs yields the high concentrations of cinnabar by removing all but the resistant mercury sulphide. Investigation of the mercury species and their concentrations in gases, waters, soils, biota and rocks showed that mercury 11 compounds generally dominate in the solid materials, where as elemental mercury dominates in the subterranean fluids and mercury adsorbed onto particulate matter dominates most surface-waters. Organo-mercurials and cold, dilute-acid-extractable mercury did not dominate anywhere. The source of the anomalous mercury is two sedimentary facies which underlie the Ngawha Basin: the basement and the subordinate olistostrome known as the Northland Chaos Breccia. Radiocarbon fourteen dating, mass-balance analyses and flux calculations reveal that the ore deposits are nearly 6900 years old, and that ca. 520 kg of mercury enter the Ngawha Basin and environs each year. About 44% of the mercury diffuses into the air and ca. 5% is carried off by fumarole gases; of the remaining mercury only about 4.5% occurs in ore-grade concentrations. The deposition and attrition mechanisms for the Ngawha deposits (which are closely compatable with many other mercury deposits) yield explanations for the traits of mercury deposits. Nearly all the traits are inherent in the mechanisms developed for Ngawha. Similarly means for more efficient mercury exploration result, as well as applications for pollution abatement and geothermal anomaly detection.

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Copyright 1979 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 1979. Bibliography: l. 197-209

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