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A structural, geophysical, isotopic and geochemical appraisal of the CSA deposit, Cobar, Australia : implications for the deformation of the Cobar Basin and mineral potential.

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Jeffrey, S (1994) A structural, geophysical, isotopic and geochemical appraisal of the CSA deposit, Cobar, Australia : implications for the deformation of the Cobar Basin and mineral potential. Research Master thesis, University of Tasmania.

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Abstract

Since the discovery of base and precious metals in Cobar
during the latter part of last century much time and effort has
been spent researching the geological origins of and factors
influencing the Cobar style of deposit. Models have taken three
forms, epigenetic, syngenetic, and structural. Problems faced by
those working in the Cobar District include
1) relating structures to mineralisation and mineralising
events,
2) understanding the source of sulfides and quartz veining,
and the relationship between the two, and
3) using geophysics to enhance the knowledge of the basin.
The first of these problems has been clarified by the author
conducting detailed surface and underground mapping of the CSA
deposit and comparing the results with those of previous workers.
The structural mapping showed a pattern consistent with other
Cobar deposits and identified structural elements not
previously recorded. As a result the timing relationships of these
structures was redefined such that three deformation events were
identified, D1 being basin closure, D2 being sulfide injection
into pipe like fracture zones formed by sinistral deformation, and
D3 being simultaneous strike slip west block up movement and
quartz injection.
The problem of the significance of quartz veining has been
resolved by review of a range of isotopic and geochemical data.
Isotopic and geochemical data confirmed sulfide remobilisation by D3, a metamorphic origin for the quartz. but either a sedimentary
or igneous origin for the sulfides. Previous work had suggested
the sulfides to be of metamorphic origin based on their being
hosted by quartz filled structures. However the structural
reinterpretation clearly demonstrates that the quartz occupies
structures that displace and hence post date mineralisation.
Regional and local gravity models presented are based on the
recovery of an old gravity survey not previously compiled and
systematically interpreted. It is shown through the models that it
is possible for the mineralised systems to have a relief of more
than 2km given certain geological parameters, some of which are
based on assumption. Consequently, there is still a need to review
and refine the models and assumptions used as there is likely to
be more than one valid geological solution to the Cobar Basin
geometry. Future use of this data, coupled with some increase in
coverage may well change existing regional assumptions about the
Cobar Basin.

Item Type: Thesis (Research Master)
Additional Information:

Copyright 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).

Date Deposited: 03 Nov 2009 03:42
Last Modified: 11 Mar 2016 05:55
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