The Toongi deposit is centred on a trachyte outcrop that forms one of several alkaline volcanic and intrusive bodies of Jurassic age in the region (formed approximately 205 to 140 million years ago). The elliptical-shaped body has approximate dimensions of 850m east–west by 550m north–south. The deposit forms a low irregular topographic rise and has a depth extent of 115m below surface.

The orebody is dominantly a massive, fine grained microporphyritic trachyte comprising more than 80% feldspar, albite and aegirine in roughly equal amounts. The remainder of the rock is made up of opaque minerals. Extensive mineralogical studies indicate that the ore minerals contained in the deposit are extremely fine-grained, being less than 100µm in size (and generally less than 10µm), and uniformly distributed throughout the rock mass. The bulk of the ore metals are hosted in complex Na–Ca Zr–Hf–HREE silicate phases (eudialyte like). The dominant Nb (and Ta) mineral is close to NaNbO3 (natroniobite) in composition. Separately bastnasite hosts the light rare earth metals.

The deposit contains elevated levels of the metals zirconium (Zr), hafnium (Hf), niobium (Nb), tantalum (Ta), yttrium (Y) and rare earth elements (REEs) – lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu). The orebody also contains uranium and thorium and is classified as a weakly radioactive ore.

Mining of the ore deposit will take place in a single open pit, using drill and blast methods to fragment material that will then be transported to the Run-of-Mine (ROM) Pad for crushing and grinding. Approximately 19Mt of ore will be extracted at a rate of 1Mt per year.

The open cut will be developed in two stages, each of approximately 10 years, commencing in the western half of the orebody (in accordance with project approvals received to date). The initial open cut will cover an area of approximately 20ha, excavated to a maximum depth of 32m (355m Australian Height Datum/AHD). During the second 10-year period, the eastern half of the orebody will be mined to approximately 360m AHD, with the depth below the natural land surface varying from 15m to 32m. At the end of 20 years, the open cut will cover approximately 40ha, with a long axis (east–west) of approximately 925m and a width (north–south) of approximately 550m. All mining during the 20-year operation will remain above the groundwater table.

Material that is excavated to enable access to the defined ore, or which contains insufficient grades of the targeted minerals, will be placed within a waste rock emplacement (WRE) located alongside the open cut to the southwest. The WRE has been designed with a capacity approximately 50% greater than the anticipated volume of waste rock to be generated from the open cut over 20 years. Waste rock will be used to back-fill a basalt quarry that will be commissioned to source construction materials.

The mined ore is delivered by road to the ROM pad, where it undergoes several stages of crushing and grinding in the comminution circuit. The crushed ore is then dry ground in a ball mill to the optimum particle size for good extraction of valuable elements.

At full capacity and once developed, the Dubbo Project mineral processing plant will be capable of receiving 1,000,000 tonnes per annum (1Mtpa) of crushed ore, which will be processed using sulphuric acid leach and solvent extraction recovery to recover zirconium, hafnium, niobium and rare earth products.

Sulphuric acid used for leaching will be produced on site using a sulphur burning acid plant that also generates electricity and steam for the process plant.

Dry ground ore is then mixed with concentrated sulphuric acid and roasted to form sulphated solids. These solids are cooled and mixed with chilled water in a leach tank, where the sulphate species formed during the sulphation process (including zirconium, hafnium, niobium and rare earths, along with impurities of iron, aluminium and zinc) are leached into solution.

After a nominal time of leaching, the leach slurry is passed through the counter current decantation (CCD) circuit to wash and separat ........