The Whirling Dervish deposit is located 1km to the North of the Carosue Dam processing plant. The ore zone is of considerable width (25-30m) with grades of approximately 3g/t. The open pit provides a low cost mill feed source in close proximity to the processing facilities.
Whirling Dervish is hosted by volcaniclastic sandstones, intermediate tuffs and porphyry units. Gold mineralisation is strongly associated with hematite-silica-sericite alteration. The deposit is dominated by the north-west striking footwall domain, which is up to 30m wide. Mineralised structures in the hanging wall are less continuous and typically narrower in width.
The mineralization is terminated to the south by the regionally extensive Osman Fault.
Whirling Dervish is a technically advanced and permitted underground mining opportunity, with a current Ore Reserve of 90koz @ 3.0g/t. The deposit is located less than 500m from the Carosue Dam mill. Whirling Dervish forms part of the same mineralisation package as Karari and has been offset some 1.5km to the north by the Osman Fault.
The proposed underground development is a depth extension of the highly successful Whirling Dervish open pit which was completed in June 2015. Total open pit production totalled 7.38Mt @ 1.49g/t for 352,800oz and performed very well relative to the estimated Mineral Resource and Ore Reserves.
Whirling Dervish underground can be brought into production when required in the five-year plan. The pit is being maintained in a dewatered state, with high voltage power lines and electric pumps already established. Minimal infrastructure is required to commence underground mining.
It is proposed that an underground drill platform will be established during the March quarter 2017 to enable the commencement of underground diamond drilling in the June quarter 2017. This drill platform will allow the full definition of the current underground Resource and also provide a position to cost effectively test below the base of the current drilling. The Resource remains open with the deepest hole returning 7m @ 5.7g/t.
The first phase of underground development will primarily be focused on establishing the hangingwall drill drive. The drill drive consists of 525m of lateral development and will take 4 months to complete. A total of 8,900 drill meters are planned before the end of the FY17. The position of the drill drive is proximal to the southern end of the hangingwall lodes and will provide an opportunity to access early revenue when the decision to commence full scale mining is made.