History of Rockhole Phosphate Prospect, Ammaroo Phosphate Project

Abstract

Attention was first drawn to the area because of a report of minor surface turquoise (Cu Al phosphate). This is not of gem-quality but has been visited sporadically by prospectors for decades. It was shown on published geological maps and is in the NTGS Mineral Occurrence database. Minor turquoise occurrences such as this are documented elsewhere in the Cambrian rocks of this part of the Georgina Basin. Such occurrences have been largely overlooked by previous mineral explorers. However, some, but not all, to the southwest have proved to be a vector to economic phosphate mineralisation and have contributed to Rum Jungle Resources' discovery of what is now the 40 km long, billion tonne Ammaroo Phosphate JORC resource. Hence, the company's continued interest in turquoise and other secondary phosphate minerals in the area. The same outcrops of turquoise/phosphate over about 1 km of strike have been described and rockchip sampled by three companies, dating back to at least 2006. There are numerous lithologies, textures and mineralogies, both primary and secondary, present within the same outcrop. These include pelloid/oolitic phosphorite; phosphatic siltstone; weathered stromatolitic, variably phosphatic, carbonate; turquoise; wavellite and crandallite. The highest grade phosphate appears to be stratigraphically just above a stromatolite marker interval near the base of the Cambrian Arthur Creek Formation and can be in almost any lithology. This strongly suggests that at least some of the phosphate is secondary. NuPower announced the results of selected rock chip samples collected in 2010 to ASX on 31 July 2012. The five assays quoted in the announcement ranged from 17.2% to 37.6% P2O5. Their announcement also alluded to a previously unreleased historical assay by Rio Tinto of 40.7% P2O5. Collectively, these rock chip results defined a phosphate prospect that NuPower then called Rockhole Bore. Of the 36 rock chip assays available to date, 17 are in excess of 20%P2O5 and ten of those are >27%P2O5. Admittedly, different analytical methods have been used, several of these samples came from very close together and the potential content of any deleterious elements has not been examined. Soil sampling by NuPower Resources/Central Australian Phosphate can be interpreted to suggest that such high-grade phosphate might extend several kilometres north in the shallow sub-surface from the sampled outcrop. This would indicate that an area of between 9 km2 and 15 km2 is worthy of drill testing. This area is referred to as the Rockhole Phosphate Prospect.