The Bundarra Project is DEX’s flagship project that includes the Bundarra tenement (EPM 26499), plus the nearby Duania (EPMA 27474) and Waitara (EPMA 27609) tenements, are located approximately 130 km southwest of Mackay and 50 km east of Moranbah, in the Central Queensland coal fields.
The Bundarra tenement occurs in the Lower Permian to Triassic Bowen Basin, west of South Connors Arch. Copper mineralisation in the Flora and Kerlong Ranges occurs on and around the margins of the Bundarra Pluton, an Early Cretaceous composite pluton that intrudes Lower Permian Back Creek Group carbonaceous shale, sandstone and marl. The pluton crops out poorly, forming an area of low relief surrounded by a ring of hills of contact metamorphosed sediments.
Regional geology of the Bundarra tenement in relation to main historic mines and development prospects
Historic small-scale mining activities started in in the late 1800s targeting copper, silver and gold veins around the contact of the Bundarra Pluton. Historic drilling results confirm that the metamorphic contact zone around the pluton to be associated with significant copper mineralisation at the Mt Flora mine, Isens mine, Rogers prospect and Quorn prospect, respectively. Historic data from these mines and prospects were used in the Independent Geological Report (IGR) for the prospectus to define an Exploration Target, which is detailed in the Independent Geological Report Pg 28 Table 2.
More recently Duke Exploration has successfully defined a Maiden Inferred Mineral Resource Estimate at Mt Flora comprising 16 Mt at an average grade of 0.5% Cu and 6.9 ppm Ag. The resource is reported at a 0.2% Cu cut-off grade as classified and reported in accordance with the JORC Code (2012). The cut-off grade of 0.2% Cu used to report the Mt Flora Mineral Resource estimate was confirmed by the mining study and is in line with cut-off grades for other similar open pit copper projects. The Mt Flora Mineral Resource estimate is based on a total of 87 RC holes (15,834 m) and does not include a additional 22 holes (7,659m) to the north, including 4 holes with significant intersections 300m north of the resource area.
Bundarra drill core highlighting massive sulphides with sericite rich alternation halo
Geophysical surveys are an instrumental exploration technique which help identify and define mineralised zones around the Bundarra Pluton. Conductivity was measured in all of the resource holes with a downhole probe. The downhole data confirmed that copper mineralisation is statistically correlated with increasing conductivity values.
Bundarra drill results
With this information, Duke ran a 3D IP survey and Fixed loop EM survey over Mt Flora in 2020 and reprocessed a pluton scale VTEM survey in 2021. The result of the surveys successfully mapped the known historic mineralisation around the pluton and mapped many new anomalous areas. Duke developed a targeting system using the collected geophysical datasets and pXRF copper in soil results to define the location and likely size of mineralisation targets around the Bundarra pluton. The below image demonstrates the utility of the processed VTEM data at Mount Flora, where the modelled higher conductivity response is correlated with mineralisation in fresh rock at a depth of approximately 70 m below surface.
Section 7572270mN of the most northern line of resource drilling of the Quarry Lode relative to pXRF soil and electrical geophysical anomaly profiles
The new processing allows both the horizontal and vertical extent of conductors to be defined by manually examining successive depth slices (at 100 m, 170 m and 240 m) through the 3D conductivity model. A set of linear trends were digitised on each depth slice to define conductive zones, which were then correlated with surface copper in soil anomalies. A total of 39 km of linear conductive trends were identified through this targeting analysis from which 19 km were associated with anomalous copper in soil (below picture). The majority of conductive trends associated with copper in soil anomalies are untested by drilling. The large scale of the combined geophysical and geochemical anomalism provides excellent exploration potential. The most prospective areas for follow up future drill programmes are areas with extensive geophysical responses, anomalous copper in the soils and historic drilling if available, historic workings and mapped mineralisation at the surface.
Interpreted linear trends form pXRF copper soil and conductivity profile targets from survey areas
The ability to directly detect the sulphides that host the copper, silver and gold in the Bundarra mineral system using geophysics will not only speed up the exploration process and significantly reduce costs but also add value to the project more quickly than would happen in projects that require drilling to establish project valuations.
For more information follow this link to the Duke Exploration IGR