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

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posted on 2023-05-26, 19:12 authored by Law, Steve R
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.


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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). Thesis (M.Sc.Exp.Geosc.)--University of Tasmania, 1999. Includes bibliographical references

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