Surrender report for EL 30221 and ELA 30661 Area 13 Phosphate Project

Abstract

The Area 13 Phosphate Project comprised EL 30221 and ELA 30661 which straddled the Central Australian Railway and was targeting Cambrian rock phosphate. The project was midway between Tennant Creek and Katherine and covered the junction between the Cambrian Wiso Basin, Daly Basin and the northwestern edge of the Georgina Basin. The titles are overlain by the Mesozoic Carpentaria Basin and Cenozoic cover. There is no Cambrian outcrop. Vale held the ground previously for phosphate exploration but did not drill any holes. Area 13 was initially thought to be prospective based on the geophysical interpretation of small basement highs and the presence of putative Cambrian phosphate detected in separate NTGS and CSIRO/Vale waterbore studies. Both studies were purely geochemical; there was little or no geological control on the samples. The CSIRO/Vale study rated bores in EL 30221 and ELA 30661 as highly prospective with up to 10%P (greater than 20% P2O5) but at depths greater than 100 m which were considered excessive for open-cut mining. The NTGS study covered a different area and identified much lower grades, below 60 m, to the east. Rum Jungle Resources undertook a comprehensive study of the full transcripts of 56 waterbores including the driller's logs, hydrological and water production data and gamma logs (where available) to add geological validation. Particular emphasis was placed on whether the phosphate was likely to be below the watertable and to identify any areas where prospective Cambrian stratigraphy might be shallower. Unfortunately, any shallow P reported was found to be in the Cretaceous and to be relatively low grade and discontinuous. The relatively higher-grade Cambrian intercepts were found to be in both the Jinduckin Formation and the Tindall Limestone equivalent. Both of these have erosional tops, meaning that prospective section is commonly missing. Furthermore, and most importantly, all the significant phosphate intercepts were found to be in the main Cambrian aquifer or below the watertable and, in many cases, tens of metres below the standing water level. There was little prospect for finding shallower occurrences within the study area. EL 30221 is being surrendered and ELA 30661 dropped. ELA 30661 is on Aboriginal Land and was immediately previously in moratorium. This also contributed to the decision to drop it.