A Discussion on natural strain and geological structure - Mt Isa — reconstruction of a faulted ore body

Abstract

A major geological problem in the Mount Isa District is the significance of the flat greenstone contact which underlies the copper ore bodies at the Isa Mine. Recent structural studies have shown this surface to be one of a set of curved normal faults which flatten in depth and are termed spoon faults. Displacement on the spoon faults ranges upward of 2 km and total extension for the spoon fault domain exceeds 80 km. The domain is bounded by tear faults of which the M ount Isa fault is an example. Reconstruction of the spoon fault domain gives insight to the sedimentary basin which originally included the Mount Isa ore bodies. The reconstruction indicates Isa and Hilton to be two faulted parts of the same ore basin and probably of the same ore body. It also strongly suggests a central concealed part to occur between Isa and Hilton. The extreme extension of the spoon fault domain coupled with the thick basic volcanic section suggests that the domain represents an ancient zone of crustal tension initiated by shear along a curved cratonic boundary.