The tectono-stratigraphy of the Emmie Bluff/Oak Dam IOCG deposits Exploring step-change ideas to expedite discovery

A tectono-stratigraphic model is proposed for the c.1588Ma Olympic Metallogenic Event (OME) that includes the iconic haematite iron oxide copper gold (HIOCG) deposits. The model has significant ramifications for research and copper exploration. A review of public data was undertaken for the well-preserved Emmie Bluff and Oak Dam HIOCG systems adjacent either side of a regional fault zone. The deposits formed near the palaeosurface on the shoulder of a mega 'Gawler' caldera where structural complexity facilitated pulsed compression and extension that injected hydrothermal metals into collapsed pipes of heterolithic breccia. A new c.1590Ma Emmie Formation is proposed to encompass a rift arkose and maar package of chlorite-magnetite and haematitic sediments previously considered to be unmetamorphosed c.1730Ma Wallaroo Group. The flat-lying Emmie sequence filled a half graben at the fault margin with the 1850Ma Donington granite. The granite hosts the Oak Dam West HIOCG pipe adjacent to the same fault zone. Rapid deposition of red shale then haematitic siltstone of the upper Emmie Formation preserved the tops of the deposits as a regional regolith and hydrothermal mound remnants above the Oak Dam West pipe, at Oak Dam East and over a potential undrilled pipe at Emmie Bluff. The Emmie Formation is correlated with the lower Pandurra Formation based on comparison with sedimentological facies, dating, geochemistry and spectral data from the distant type drillhole Vanguard 1. The tectono-stratigraphic model disrupts current targeting dogma, redefines the exploration space and will expedite further discoveries. In particular, 1) initial rifting and sedimentation of the Cariewerloo Basin was contemporaneous with the caldera collapse, OME and HIOCG formation; and 2) the Emmie Formation provides a regional datum and 4-D framework for advanced target vectoring, both locally at Emmie Bluff and regionally. Recommendations are made for further research and testing of the new concepts and target vectors.