The Mt Thirsty Cobalt Deposit is hosted in a strongly weathered ultramafic peridotite rock located between a sediment-ultramafic-basalt sequence to the west and a thick gabbro-pyroxenite unit to the east. Weathering and supergene enrichment processes have produced the oxide deposit which is enriched in cobalt, nickel and manganese. The manganese and cobalt contents are particularly high compared to most nickel oxide deposits located in Western Australia.
The oxide mineralisation typically starts from near surface to around 12 meters below the surface where limonitic clays are present with an iron composition of around 30%. Deeper down the colour of the limonitic clays darken as the asbolane (manganese oxide mineral) content increases. This darkening marks the start of the cobalt enriched, high-grade portion of the deposit. Further down, the dark colouring due to the asbolane diminishes with greenish nontronite and serpentine minerals becoming dominant (lower saprolite). Near the bottom of the lower saprolite zone chalcedonic banding is common. High-grade cobalt is almost always associated with dark asbolane (Figure 2). A typical cross section through the mineralisation is shown in Figure 3.
The moisture content of the deposit is low, with an average free moisture content of 4%. The water table is located below the mineralised zone, so no de‐watering is expected during mining. Preliminary mining assessment also shows the deposit should be free digging. The low moisture content also results in a high in‐situ bulk density of the ore with an average specific gravity of 1.8 observed for the deposit. The high bulk density in combination with the relatively large ore thickness results in a relatively large tonnage density per unit area for the project.
Geological development work was carried out by Barra Resources in 2007 and 2008, which resulted in a substantial increase in the resource base. In mid-2008 Conico Ltd purchased a 100% interest in Meteore Metals Ltd, the holder of the other 50% of the Mt Thirsty Cobalt Project. The MTJV carried out further infill drilling in 2009 & 2010 and in February 2011 the following updated JORC (2004) reported resource was announced for the Mt Thirsty Cobalt Deposit (Table 1):
The following resource was estimated by independent mining and geological consulting firm Golder Associates Pty Ltd using a cut‐off grade of 0.06% Co.
Table 1: Mt Thirsty Cobalt Deposit Resource
(This resource information was prepared and first disclosed under the JORC Code 2004. It has not been updated since to comply with the JORC Code 2012 on the basis that the information has not materially changed since it was last reported, refer ASX Announcement 8th March 2011: “Resource Upgrade”.)
The Total Resource contains approximately 40,000 tonnes of cobalt 177,000 tonnes of nickel, and 274,000 tonnes of manganese over a strike length of approximately 1.8km and a width up to 1km.