In June 2021, the Company secured a prospective ground position, close to Coda Minerals, Emmie Bluff Deeps Prospect Iron-Oxide Copper-Gold (IOCG) discovery (Refer to Coda Minerals (ASX: COD 09/06/21 ASX release) near Woomera in South Australia (Figure 1). The Licence Application (ELA 2021/00066), Woomera Project, covers a 209 km2 area. Open file historical company reporting has additionally recorded significant historical copper drill intersections from three drill holes just north of the new tenement area (Figure2). The Company has initiated Native Title proceedings concurrently with the licence application process to ensure ground exploration works can begin quickly after the grant of the licence which is expected early in the 2022 calendar year.
The Winjabbie IOCG Prospect occurs just north of the new tenement area and is situated along an extension of the high gravity zone (Figures 1 & 2). Three historical vertical drill holes have been drilled at Winjabbie and all intersected broad zones of significant Iron-Oxide Copper-Gold (IOCG) style alteration with intervals of copper mineralisation. A summary of significant drill results from Winjabbie Prospect are presented below (refer to PTR ASX release 01/07/2021).
Drill hole WJD1 (WMC, 1980) – testing a magnetic anomaly returned:
62m @ 0.33% Cu from 864m.
Drill hole SAE11 (MIM,1990) – evaluating a second magnetic feature returned:
94 metres @ 0.21% Cu (interval 1005-1099 m.)
– Including 7m @ 0.48% Cu from 1006 m.
– Including 9m @ 0.52% Cu from 1086 m.
42 metres @ 0.28% Cu (Interval 1123 – 1165 m.)
– Including 5m @ 1.1% Cu from 1160 m.
Drill hole 07WJ01 (Uranium Exploration Australia, 2008) – evaluating a residual gravity anomaly just north of the WJD1 and SAE11 returned:
42 metres @ 0.34% Cu (Interval 824 – 866 m.)
– Including 9m @ 0.8% Cu from 824 m.
These holes are widely spaced (ranging between 1.8 to 3 km apart, Figure 2) indicating IOCG style mineralisation occurs over a large area.
The Company has completed initial processing and gridding of historical open-file gravity data. The gravity data coverage over the Woomera Project Area is good, with several modern close spaced surveys (200 metre to 400 metre station spacing) completed by previous explorers. A prominent northwest trending zone of high gravity anomalism is evident and shown to extend over 10 kilometres in length across the tenement area (Figures 1 & 2). IOCG mineralisation, being iron rich, is associated with areas of high gravity anomalism and is one of the main direct targeting tools used by explorers. Whilst earlier exploration work by other explorers identified the prominent high gravity zone, no historical drilling has been undertaken over the tenement area.
Woomera IOCG Gravity Targets
Gravity modelling work performed during the period has identified a robust gravity target (herein termed the Rocky Well Gravity Anomaly) in the south-eastern corner of the tenement area. The gravity model suggests that a dense body comparable in size and density to Oz Minerals’, world-class Carrapateena Orebody, fits the observed data (Figure 3). The target is a high priority for the Company moving forward.
In addition to this “classical” IOCG gravity target, the Company’s evaluation work highlights the presence of what has been interpreted as “Stratabound Replacement Style IOCG Mineralisation” (Stratabound IOCGs) which produce flat lying sheet-like IOCG mineralised occurrences. The recent Emmie Bluff Deep IOCG discovery by Coda Minerals, 17 kilometres east of the project area, has reported high-grade copper and gold intercepts which to date appear to occur as stratabound bodies and similarly the Winjabbie IOCG mineralisation along the northern edge of the Woomera Project Area appears to be of the same general form. Importantly, high cobalt grades are also a feature of this style of IOCG mineralisation.
These mineralised bodies appear to be fault controlled, with better mineralised zones spatially associated with major faults which have acted as the principal conduit for mineralising fluids. The replacement style of ore occurs as a result of ore precipitating along reactive host rock sequence and/or where also ore fluid mixing may be occurring, triggering precipitation of ore nearer to the ancient palaeosurface. Stratabound IOCGs appear to surround or occur close to the magmatic rupture style pipes/maars which typify the classic IOCG breccia ore setting.
Petratherm postulates that “Stratabound IOCG’s” offer a new style of exploration target with large tonnage and high-grade potential. Whilst the source of the mineralising fluids are of magmatic hydrothermal origin, the Stratabound IOCGs share some key similarities to the giant stratabound copper deposits of the Central African Copper Belt and therefore require a different targeting approach. One of the key issues is that whilst they occupy a large area, they have thinner vertical extent (nominally less than 100 metres of vertical thickness) and therefore produce a more subtle gravity anomaly response. Gravity modelling undertaken during the period highlights large areas where potential stratabound IOCG mineralisation may be occurring on the Woomera Project Tenement as shown in Figure 2.
The Company is very pleased to be able to secure a significant holding in the Woomera region, which is proving fertile for significant IOCG style mineralisation, with not only the new Emmie Bluff Deeps Discovery, but also includes BHP’s recent Oak Dam West Discovery and OZ Minerals’ newly operating world-class Carrapateena Cu-Au deposit (Figure 1). At this stage, the exploration licence is expected to be granted early in the 2022 calendar period which will allow ground exploration activities to get underway.