The Ore and Gangue Mineralogy of the Newly-Discovered Federation Deposit, Central NSW, Australia

The newly discovered Federation deposit, with a resource estimate of 2.6 Mt @ 7.7% Pb, 13.5% Zn, 0.8 g/t Au, and 9 g/t Ag, lies 10 km south of the Hera deposit within the Cobar Basin of the Lachlan Orogen. Located just north of the Erimeran Granite contact and between the Lower Amphitheatre Group and underlying shallow marine Mouramba Group Roset Sandstone, the host siltstones and sandstones have been brecciated, intensely silicified, and chloritized close to mineralization. Oriented in an overall east-northeast strike and with a steep south-southeast dip, the siltstones mainly comprise quartz, clinochlore, biotite, and muscovite. Federation also has highly fragmented zones with breccia and vein-fill of calcite. The main ore mineralization includes sphalerite and galena, with lesser chalcopyrite, pyrrhotite, pyrite, gold, and very rare meneghinite. Mineralization occurs within silicified veins and breccias of Zn-Pb sulfides, which generally grade to moderate veining of sulfides with Pb and Cu dominant sulfides, as well as minor veining of base metals associated with visible gold. Mineralization throughout the deposit is fairly simple, with a low diversity of minerals. Iron concentration varies throughout the deposit, decreasing towards the center. Observations of massive sphalerite with gradations of red to honeycomb yellow indicate the transition from high Fe (7–10%) to low Fe (2–5%) within the coarse sulfide assemblages over a very short distance. Within the main mineralized corridor, fibrous amphibole inclusions within galena/sphalerite assemblages are observed at 251 m, as well as epidote associated with sulfides at 573 m. Other ore-associated gangue minerals include ilmenite, siderite, scheelite, magnetite, apatite, and rutile.