Mount Isa Projects

Rod Holcombe

Dept of Earth Sciences
The University of Queensland

The Mount Isa Inlier is an Early to Middle Proterozoic intracratonic fold belt in northwestern Queensland, Australia. Since 1975 I have been involved in a number of projects in the Inlier, principally in the higher grade belt around the old uranium-rare earth mine at Mary Kathleen, and in the Sybella/Mica Creek area south and west of Mount Isa mine. Most of these projects involved many Honours students, and a small amount of ARC funding.

From 1981-1986 I was involved in the MIRTH project, a multi-institutional project, under the auspices of the (then) BMR, to construct a regional tectonic transect across the Inlier. Together with two PhD students, Paul Pearson and Nick Oliver (Monash), and a number of Honours students we were responsible for the Mary Kathleen Fold Belt section. The major conclusions from this work were:

• the Mary Kathleen Fold Belt is an anticlinorial structure with the foliated Wonga Granite (a composite batholithic-sized body) exposed in the core;
• the Wonga Granite is a syntectonic body intruded as sills into an active, subhorizontal, mid-crustal detachment shear zone at ~1740 Ma (i.e. it is a core-complex-like structure);
• the adjacent, undeformed, "anorogenic" Burstall Granite is coeval and its undeformed aspect is due to intrusion into the brittle upper plate of this extensional detachment system;
• the Wonga belt is the mid-crustal expression of an extensional basin forming episode and there have been several such episodes in the evolution of the Inlier. Another such, is the Sybella Granite formed during the initial extension producing the Mount Isa Group sediments.

1998-2004 Mount Isa - Mica Creek - Sybella Granite. A series of projects (with Honours students and 1 PhD student) focussed principally on the relationship between low grade and high grade rocks across the Mount Isa Fault system, and the structure and kinematics of the syntectonic Sybella Granite. The connection between this project and the earlier Wonga Belt project is the similarity in fabrics (and interpretation) of the Sybella Granite. Again L-tectonite fabrics dominate.

2000-2004 Rick Gordon, PhD project "Isan deformation, magmatism and extensional kinematics in the Western Fold Belt of the Mount Isa Inlier". This project really brought to a satisfying conclusion all of the ideas and hypotheses we had developed over the previous 7-8 years. See here for the Abstract and contents of Rick's thesis.

Phone: +61 7 3365 2375 (Dept Office)
FAX: +61 7 3365 1277

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