Combined annual report on the East Arnhem Land Project for the period 20 April 2009 to 19 April 2010 EL 10182, EL 24524, EL 27216, EL 27217 and EL 27249

Abstract

This report describes the work which BHPB has undertaken to explore for Mn on this project during the current reporting period 20 April 2009 to 19 April 2010. The Cretaceous package of rocks in east Arnhem Land area is stratigraphically similar to that of Groote Eylandt which hosts one of the largest Mn deposits in the world. Historical prospecting undertaken during 1960's by BHPB (then BHP Ltd) had identified a number of Mn occurrences in the region including Peter John River, Caledon Bay and Lake Evella. The Peter John River prospect extends over a large area straddling EL 24524 and EL 4171. Most of the exploration work during the reporting period focused on this prospect and surrounding areas and hence work completed in EL 4171 is also included for completeness. In addition, some ground traversing was undertaken in EL 10182, located near the Caledon Bay prospect, in preparation for a planned drilling programme in 2010. The Mn mineralisation at Groote Eylandt is known to be conductive. In view of this a small airborne geophysical survey was planned for orientation and target generation purposes. Fugro's 25Hz TEPMEST system was used and the EM-cum-magnetic survey covered an area of 200 sq km (115 sq km in EL 4171 and 85 sq km in EL 24524). A total of 1145 line km of data was collected, of which approximately 490 line km is attributable to EL 24524. The survey was flown at 250m line spacing and the flight height was 120m above the ground level. Flat lying conductive layers at shallow depths were identified from conductivity depth slices of EM data, some of which were drill tested. A total of 27 reverse circulation (RC) drill holes (totalling 1333 m) were drilled at 1 to 2 km spacing to test the geological and EM targets in EL 24524. All were vertical holes with lengths ranging from 28 m to 82 m. Wherever it was possible drilling continued through the entire Cretaceous rock package into basement. Drill chips were collected at 0.5 m intervals for geological logging. Samples for assaying were predominantly taken as composites over lithological units. Only the intervals with visible Mn mineralisation were sampled at 0.5 m. A total of 414 samples were collected which represent drilling intervals ranging from 0.5 m to 15 m. Drilling results indicated the presence of thin and discontinuous intervals of low-grade sandy Mn mineralisation in only three holes in EL 24524. The best interval contained 12.7% Mn over 1.5 m starting from a depth of 1.5 m in EARC48. Further it was found that the conductive layers corresponded with greyish to black-coloured clays within the Cretaceous rocks.