Thunderbox is a mesothermal lode gold deposit located at the southern end of the Yandal greenstone belt in an area where several major shear zones converge and join with the Perseverance Fault. The shear zone dips at 30° to 60° WSW, with the exception in the vicinity of the mineralisation, where the shear is vertical to steeply dipping. Mineralisation is hosted by strongly deformed, silicified and carbonate altered albite-quartz porphyry in the hangingwall of the shear zone. The shear juxtaposes foliated basalts and intrusive porphyries in the hangingwall against sedimentary rocks in the footwall. The zone of shearing is over 200m wide. An ultramafic unit occurs within the shear, in the footwall of the deposit and is attenuated along the shear. The main gold related hydrothermal alteration assemblage comprises quartz-ankerite arsenopyritepyrrhotite-galena and gold. This assemblage has been overprinted by a retrograde chlorite-epidote-white mica-biotite-quartz and pyrite assemblage. Syn-mineralisation veins have a continuum of vein textures ranging from laminated to pseudo-breccias.

Thunderbox mineralisation extends from 6879000mN to 6881000mN, 304000mE to 304400mE and 500 meters below surface. The Thunderbox shear generally strike NNW and dips 60° towards the WSW. In the vicinity of the strongest gold mineralisation the shear is vertical to steeply west dipping. The shear and mineralisation is offset across a series of dextral, NE trending faults.

The Thunderbox gold deposit consists of free milling gold which occurs as inclusions within, and at the rims of arsenopyrite crystals, and as free gold clusters within quartz-carbonate veins.

The Thunderbox deposit is amenable to mining by both open pit and underground methods. The deposit has successfully been mined by open pit in the past between 2002 and 2007. Saracen is currently mining the C-Zone pit using Open pit methods and the A-Zone using underground methods. Beneath the mined C Zone pit is a portion of the mineral resource that has potential to be extracted by a bulk underground method. It has been discussed that in the thicker potions of the resource that an underground caving approach may be an efficient means of economic extraction. With supplementary traditional long hole stoping in areas with narrower widths.

The Kailis deposit is amenable to mining using the open pit mining method. The deposit has successfully been mined by open pit in the past. There are reasonable grounds to assume that in the future this deposit will again be mined by conventional open pit load and haul operations.

The Bannockburn deposit is amenable to mining by both open pit and underground methods. The deposit has been mined by open pit and underground methods historically. There are reasonable grounds to assume that in the future this deposit will again be mined by conventional open pit load and haul operations.

The Thunderbox processing facility incorporates a single-stage crusher, a SAG mill and a ball mill as well as conventional CIL cyanide leach, gravity circuit and elution circuits. Nameplate capacity of the TBO processing plant is 2.5Mtpa.