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Abstract

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.

Item Type:	Thesis - PhD
Authors/Creators:	Davey, Herbert Andrew
Keywords:	Mercury
Copyright Holders:	The Author
Copyright Information:	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).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1979. Bibliography: l. 197-209
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