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Magnetic characteristics of Broken Hill type deposits and their host provinces

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Kerr, TL (1994) Magnetic characteristics of Broken Hill type deposits and their host provinces. Coursework Master thesis, University of Tasmania.

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Abstract

In technical geological publications it has been demonstrated that Broken Hill Type
deposits and their host provinces are characterised by similarities in their geological
settings and ore deposit mineralogy at both local and regional scales. The purpose of
this thesis was to examine magnetic characteristics of the globally most significant
BHT deposits, and their host provinces, in order to develop a magnetic exploration
model for BHT deposits. This involved detailed aeromagnetic interpretation of
available datasets with reference to mapped geology.
Four significant BHT provinces were studied:
Broken Hill Block - Australia
Eastern Succession, Mt Isa Block - Australia
Bergslagen District - Sweden
Aggenys -Gamsberg District - South Africa
The study showed that host provinces to BHT deposits share common magnetic
characteristics which reflect common geological characteristics. However, significant
differences in the aeromagnetic character occur which are related to differences in
volume of BHT host stratigraphy, basement stratigraphy and structural style of the
host province.
BHT deposits naturally divide into two classes, based on the presence or absence of
magnetic minerals within the ore. This may result from differing ore-forming
environments and/or fluid chemistry. Deposits which contain magnetic minerals within
the ore are commonly associated with magnetic anomalies which are amongst the
strongest within the host meiasedimentary /metavolcanic sequence. Deposits which do
not contain magnetic minerals within the ore itself are associated with a locally
anomalous signature when the immediate environs of the ore deposit are considered.
The most economically signifcant deposit, Broken Hill (Australia), is of this type,
although both types include large tonnage deposits.
Thermodynamic modelling was undertaken to test whether the variations of magnetic
deposit signatures could be explained by variations in the environment of exhalation.
The roles of boiling, cooling and seawater mixing (oxidised and reduced) as
precipitation mechanisms were examined. The modelling showed that a single fluid can
give rise to a spectrum of iron oxide distribution, depending on whether the dominant
precipitation mechanism was boiling, cooling, mixing with oxidised sea water or
mixing with reduced sea water. Precursors to metamorphosed BHT ore and gangue
minerals were produced by several of these thermodynamic models.
It is concluded that the interpreter, when defining the likely spectrum of magnetic
responses of a BHT deposit, must consider the likely range of environments of
deposition consistent with known geology.

Item Type: Thesis (Coursework Master)
Keywords: Ore deposits
Copyright Holders: The Author
Copyright Information:

Copyright 1995 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 (M.Econ.Geol.)--University of Tasmania, 1995. Includes bibliographical references

Date Deposited: 19 Dec 2014 02:27
Last Modified: 11 Mar 2016 05:55
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