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The Mount Isa deep copper orebodies : characteristics and structural controls on mineralisation


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Law, Steve R 1999 , 'The Mount Isa deep copper orebodies : characteristics and structural controls on mineralisation', Research Master thesis, University of Tasmania.

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The 3000 and 3500 orebodies form part of the world class copper deposit at
Mount Isa. The Deep Copper Mine (now renamed Enterprise Mine) came into
production in 1993 and provided the opportunity to study the characteristics of
these orebodies and the structural controls on copper and cobalt mineralisation.
In the Enterprise Mine orebodies, chalcopyrite and silica rich breccia cores are
surrounded by a halo of recrystallised dolomitic shales and siliceous shales with
lesser dolomite breccias. A distinctive talc+pyrrhotite alteration zone occcurs on
the footwall of the 3500 Orebody adjacent to a band of sub-economic Ag-Pb-Zn
mineralisation, which has associated phyllosilicate alteration. The Ag-Pb-Zn
mineralisation is unrelated to the chalcopyrite and silica-dolomite alteration. The two orebodies are situated on the west dipping limb of the Mount Isa Fold,
which formed during the third period of regional deformation (D3). There are two
main structural controls that localised the copper bearing hydrothermal fluids:
(1) The basement contact fault is a large scale regional fault that has been affected
by all three regional deformation periods. It separates the Urquhart Shale (orebody
host sequence) from the older Eastern Creek Volcanics. The position of D3 related
flexures in the basement contact fault are a major control on the localisation of
copper mineralisation and possibly of cobalt mineralisation.
(2) Bedding parallel shear zones and associated splay shear zones form an
anastomosing network within the orebodies. The orientation of bedding and faults,
and indicators that bedding plane slip was an important process, suggest that the
shear zones formed towards the latter stages of development of the Mount Isa Fold
and that the shear zone geometry strongly influenced the position of the orebodies.
The bedding parallel shear zones were pathways for the hydrothermal fluids,
especially in the up-dip direction. They have a strong influence on local variations
in copper distribution. The shear zones flatten in dip towards the basement contact
fault and propagate from D3 flexures. The shear zone networks are most
extensively developed in the more laminated sections of the.original stratigraphy,
and occur as contacts between different layers variously affected by the carbonate
and silica bearing hydrothermal fluids.

Item Type: Thesis - Research Master
Authors/Creators:Law, Steve R
Keywords: Copper ores
Copyright Holders: The Author
Copyright Information:

Copyright 1999 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.Sc.Exp.Geosc.)--University of Tasmania, 1999. Includes bibliographical references

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