The Federation deposit is located on the eastern margin of the Palaeozoic Cobar Basin, an intracratonic basin within the Lachlan Orogen. Mineralisation at Federation is epigenetic and structurally controlled with several steeply dipping vein breccia/massive sulphide lenses developed in the centre of a broad northeast-southwest striking corridor of quartz–sulphide vein stockwork mineralisation. The mineralisation is hosted by fine-grained sedimentary rocks and is best developed within open upright anticline closures in areas of strong rheology contrast imposed by early stratiform alteration.

Massive sulphide and sulphide breccia base metal mineralisation is typically zinc-rich and associated with intense cross-cutting black chlorite alteration in the lower parts of the known deposit, with silica-sulphide dominant infill in the upper parts. Late bedding-parallel faults have been identified that may have caused some brittle offset within the system. These structures possibly started as extensional faults and could have focused hydrothermal fluids during alteration and mineralisation.

The mining evaluation of the Federation Mine considered the technical and economic aspects of a new underground mine using information available at February 2022.

The selected mining method is longitudinal retreat longhole stoping where the deposit is narrow, and transverse longhole stoping where the deposit is wider. Stope voids will be backfilled to maximise ore recovery and maintain excavation stability, primarily using pastefill in longitudinal stopes, primary transverse stopes, and in areas of poorer ground conditions. Unconsolidated rockfill (URF) and cemented rockfill (CRF) will be used as backfill material prior to the pastefill plant being available. The preferred timing for pastefill plant operation is July 2024.

Haul trucks will transport ore from the underground mine to a surface ROM ore pad adjacent to the boxcut. Ore will be crushed on surface at the Federation site and transported to the Hera and Peak process plants using onhighway trucks. Filtered tailings will be backhauled by on-highway trucks from the Hera site for use in pastefill. Stockpiled surface waste rock will be back-loaded into underground dump trucks for haulage and placement into stope voids when waste generation from development mining cannot satisfy URF and CRF backfill placement demand.

Various level spacings and stope strike lengths were adopted to account for variable ground conditions and dominant geological structures. The typical stope height is 30m floor ........

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