The Cloncurry Lineament: Geophysical and geological evidence for a deep crustal structure in the Eastern Succession of the Mount Isa Inlier

The Cloncurry Lineament is a major feature evident from wavelet processed magnetic and gravity potential field data over the Mount Isa Inlier Eastern Succession. It is laterally continuous over 200 km of strike length and is inferred from the gravity data to extend to at least 30 km depth. It delineates the contact between two major Paleoproterozoic sedimentary sequences, and is spatially associated with a number of mineral deposits including Cannington Ag–Pb–Zn, Ernest Henry Cu–Au and many smaller Cu ± Au deposits.Mapping and magnetic forward modelling along several profiles perpendicular to the Cloncurry Lineament suggests that it corresponds to the eastern margin of a 5–10 km wide deformation zone within the calc-silicate dominated Doherty Formation. The western boundary of this deformation zone is a distinct narrow fault zone (the Cloncurry Fault). The deformation zone consists of multiple generations of shearing and faulting accompanied by metasomatic alteration. Large variations in the magnetic response within the deformation zone can be modelled as sub-vertical brecciation zones. Breccia types range from highly magnetic actinolite–albite–magnetite breccias through to late stage, non-magnetic, quartz–K-feldspar ± hematite breccias. The long-lived history of multiple reactivation, strike continuity, width and vertical extent of the deformation zone suggest that it is a major crustal structure. The structure may have originated during basin formation and later acted as a fluid pathway for alteration and base metal mineralization.