Electromagnetic response of MVT sulfide deposits on the Lennard Shelf, Canning Basin

The Canning Basin hosts Mississippi valley-type (MVT) lead-zinc sulfide occurrences, including the shallow (<500 m) Pillara, Kapok and Cadjebut deposits hosted in the Devonian reef complexes on the Lennard Shelf, as well as deeper examples within Ordovician carbonates along the Admiral Bay Fault Zone. The basin is covered by a regional airborne electromagnetic (AEM) survey with a nominal spacing of 20 km, funded by the Commonwealth Government's Exploring for the Future (EFTF) program. Some of the flight lines were slightly deviated to fly directly over the shallow MVT sulfide deposits on the Lennard Shelf. The resulting conductivity profiles help resolve the geometry of these mineralization occurrences and structural configurations. Based on existing drillholes at the Kapok West deposits, sulfide mineralization correlates with a thick zone of high conductivity, which stands out from the background of more resistive carbonate platform in the Devonian reef complexes. The sulfide mineralization zone is interpreted to have been displaced by a set of antithetic north-dipping faults, which postdate the south-dipping Cadjebut Fault. Multiple phases of faulting might explain the topography of the Emanuel Range, and facilitated the movement of basinal brines leading to the MVT deposit in the brecciated zone. Sulfide occurrences at Pillara are not as prominent as Kapok West, but they are still resolvable as a weakly conductive feature against the more resistive platform. The AEM data over the Pillara deposits show a more accurate depth-extent of the subsurface Devonian carbonates than gravity modelling. An east-southeast dipping fault interpreted in the AEM data is likely associated with a thin interval of moderate grade zinc mineralization as intersected by drillholes. The observations and interpretations illustrated above highlight the value of AEM data for predicting the structural geometry and exploration for sulfide deposits, particularly those hosted by resistive Devonian reef complexes on the Lennard Shelf.