Annual report for EL 23774 'Rodinga', for the year ending 22 November 2005

Abstract

Exploration Licence 23774 'Rodinga' is located in the southeastern sector of the Amadeus Basin in the Northern Territory. The Amadeus Basin contains two sequences prospective for potash mineralisation; the Neoproterozoic Bitter Springs Formation and the Early Cambrian Chandler Formation. Both of these formations occur within the basin at exploitable depths.The Chandler Formation is the primary target for potash mineralisation. In the eastern part of the Amadeus Basin, the Chandler Formation contains thick sequences of evaporitic rocks. Halite beds range in thickness from less than 50 m to over 1,000 m and average 470 m thick in the Rodinga area. These thickness variations are accentuated in areas of structural thickening due to salt tectonics. Within the Rodinga project area the Mt Charlotte No1 well intersected a 225 m thick section of Chandler Formation halite from 710 metres depth to the bottom of the hole and the Bluebush No1 well intersected 690m of halite from 786 metres depth. These intersections occurred between depths of 700 and 1,500 m, within the depth range of economic exploitation. The Chandler salt has high bromine levels that suggest precipitation from late stage brines which is a positive indicator for the presence of potash salts. The main Chandler Formation target interpreted from seismic surveys in the Rodinga Project is a basinal depression target at Camel Flats, just north of Bluebush No1. Other targets are areas of thickening of the Formation in localised basinal depressions adjacent to salt diapirs and salt walls derived from the underlying Bitter Springs Formation. Potential exists for large flat-lying Canadian-type potash deposits as well as diapir related European-style potash deposits.Within the Bitter Springs Formation, the evaporitic Gillen Member is the target horizon for potash mineralisation. It was deposited in the Neoproterozoic and comprises interbedded carbonates, sulphates and halite beds typical of a marine evaporitic sequence. It is widely distributed throughout the Amadeus Basin covering an area significantly greater than the Chandler Salt. The thickness of the Gillen Member averages 800 m but varies from 100 m to more than 2,000 m with the thickening of the beds mainly due to salt tectonism. Halite units are common within the Gillen Member but have been poorly tested by drilling, with a number of holes terminating in halite units at considerable depths. In the Rodinga project area, two drill holes ended in the Gillen Member, Mt Charlotte No1 after intersecting 556 m and Bluebush No1 after intersecting 85 m of this formation. Halite beds up to 60 m thick were intersected in the Gillen Member in the Mt Charlotte hole. Bromine levels in the Gillen Member vary from 130-190 ppm indicating precipitation of salts occurred from late stage brines. Potential exists for both large, flat-lying, Canadian style as well as diapir related potash mineralisation within the Bitter Springs Formation. Further work is required to establish the best target areas for potash mineralisation. Bore hole location and analytical data was purchased from the Conservation and Natural Resources Group to cover the whole of the Rodinga 1:250,000 sheet. Unfortunately no assays for K and TDS corresponding to the bore holes were taken. During this reporting year, a review of all previous work and investigations was completed with a view to selecting targets for potash exploration, based largely on petroleum data.Site visits were made both by vehicle and helicopter to determine site suitability, access and logistic support. Further seismic profiling and interpretation is needed in the area where salt doming has occurred in the vicinity of the western part of the Chandler syncline.