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 uraniu ........
