The discovery hole was drilled close to the margin of the palaeochannel. Most of the interpreted 1000-2000 meter width of the palaeochannel at this point remains to be tested
The following characteristics of the palaeochannel in the discovery hole are considered favourable for sandstone-hosted uranium mineralisation, and have been found in the discovery drill hole.
Increasing depth of palaeochannel into the basement.
Increasing proportion of reduced carbonaceous sands and gravels in the palaeochannel in relation to clays.
Zones of oxidation in the basal sands and gravels.
The discovery hole has the geological and mineralisation characteristics of the margins of the Double 8 deposit, for which Manhattan has recently released a maiden resource of 11 Mlb.
The closest drill lines in this programme crossing the whole palaeochannel are 7 kilometers up channel and 30 kilometers down channel.
Aura Energy is developing a programme and budget to systematically test the palaeochannel in the vicinity of the discovery.
The palaeochannel is about 220 kilometers in length, is entirely held by Aura Energy and forms part of the Gunbarrel Basin joint venture with Mega Uranium Ltd (Mega Uranium). Mega Uranium is funding the programme to earn an initial 50% interest and has the option to increase its interest to 70%.
The Gunbarrel Basin contains uranium mineralisation at Energy and Minerals Australia Ltd’s Mulga Rock deposits and Manhattan’s Double 8 deposit. Despite the amount of uranium present, the Basin is significantly less explored than the other major uranium provinces of Australia. EMA recently announced a JORC compliant inferred resource of 24,500 t U3O8 at a cut off grade of 200 ppm U3O8 for the Mulga Rock deposits.
The drill programme was designed to test the prospectivity of the Junction Palaeochannel based on its similarity with the palaeochannels hosting Mulga Rock and Double 8, and also on the presence of the Thatcher Soak calcrete deposit up-drainage in the channel. Thatcher Soak, held by Uraneex NL and Eleckra Mines Ltd, contains almost 20 million pounds of U3O8 in JORC compliant resources.
The programme comprised 30 holes of about 2225 meters of drilling.
The programme comprised 30 drill holes on six lines. The eastern three lines contain favourable reduced carbonaceous sediments but there was no evidence of uranium mineralisation from downhole gamma logging.
Line 4 contained a well developed palaeochannel in the underlying Proterozoic basement. However, the palaeochannel was relatively broad, 1800 meters in width, and was only incised to depths of about 40 meters into the palaeosurface. Furthermore, most of the palaeochannel sediments were clays, which restrict the entry of mineralising waters, and hence are poor host rocks.
The most northerly hole of Line 5, JUAC020, intersected 14 meters of uranium anomalism, including 3 individual meter intercepts containing values of greater than 100ppm eU3O8. The best intersection was 2 meters at 147ppm eU3O8 from 99 to 101m. The equilibrium state of the uranium is unknown.
Samples from the anomalous intervals have been submitted for chemical assay. The remaining three holes drilled on the section were not in the palaeochannel, and consequently the palaeochannel’s edge must be between hole JUAC020 and hole JUAC023, only 200 meters to the south. The bulk of the palaeochannel, estimated to be at least 1000 meters wide at this point, lies to the north of JUAC020.
The position of the palaeochannel had been interpreted from the topography and the airborne electromagnetic survey completed in 2007. However, the area is relatively flat-lying, and the palaeochannel is now interpreted to be about two kilometers north-east of the original interpretation. Unfortunately Aura Energy had not cleared access lines for the drill rig any further north than JUAC020, so was unable to test the remainder of the palaeochannel at this point in the programme just completed.
Discussion
This reconnaissance drilling programme has achieved its purpose – to identify sandstonetype uranium mineralisation within the Junction palaeochannel. Because of the very considerable length of the palaeochannel (220 kilometers), and the issue of specifically locating the actual channel within the interpreted five kilometers width where it may occur, Aura Energy designed a drill programme at a wide line spacing and distance between drill holes on lines such that one hole would intersect a typical uranium deposit in the Gunbarrel province should one be present. This strategy has proved to be successful, as indicated by the results.
The implementation of this programme requires the drilling of at least 160 holes along the length of the palaeochannel. Aura Energy has discovered what it believes to be significant mineralisation in hole 20 of the programme.
Aura Energy sees analogues between the geology and mineralisation intersected in hole JUAC020 and the discovery of Manhattan’s Double 8 deposit in 1986. In particular the presence of uranium over a 14 meter thickness at the edge of a channel is seen as being particularly encouraging. Anomalous uranium values do occur in palaeochannels that are not related to significant mineralisation, but these are commonly limited in thickness.
Western Australia government co-funding
The Aura Energy / Mega Uranium, Junction palaeochannel aircore drilling program in the Gunbarrel Basin Joint Venture was one of 35 drill programs out of some 168 submissions to receive W.A Department of Mines and Petroleum Exploration Incentive Scheme support.
The criteria by which the programmes were assessed included the following:
Innovation in exploration.
The exploration model and targeting criteria.
The data to be produced.
The more remote geographic locations were regarded more favourably.
Aura Energy’s proposal was one of only two successful uranium drill programme applications.
