Final report for Wellington Range 2015-2016 CORE Collaborations Funding

Abstract

Cameco Australia Pty Ltd (Cameco) and Rio Tinto Exploration Pty Ltd (RTX) have entered into a Joint Venture (JV) to explore for unconformity style uranium mineralisation in the Wellington Range (EL 5893), King River (EL 25064 and EL 25065), and Waidaboonar (EL 24017 and EL 27059) tenements in eastern Arnhem Land. As part of a tenement wide data review process the JV has identified several areas where there are significant knowledge gaps in the understanding of the distribution of prospective basement lithological units. The most significant knowledge gaps occur in the northern-most JV tenement, EL 5893, where there are significant thicknesses of Cretaceous sedimentary cover blanketing the area and where there has been limited historic drilling. The JV applied for CORE Geophysics and Drilling Collaborations Program funding to complete four diamond drillholes within EL 5893. Three of these holes were drilled in areas where in-house interpretations identified geological settings analogous to those observed in the Ranger area. The fourth hole targeted a high tenor, surficial uranium anomaly in an area that has seen limited, ineffective exploration. The total CORE Geophysics and Drilling Collaborations Program funding approved by the NTGS totalled $100,000. Three of the proposed holes were completed as proposed, the fourth hole (WRDD0129) failed prior to reaching the targeted depth due to difficult ground conditions. As a result of the reduced amount of core drilling completed, the CORE contribution to the overall program was $78,838 (inclusive of GST). The CORE collaborations drillholes completed have provided information that will assist in generating an improved geological framework for this part of Arnhemland. In addition this work has assisted in defining a new, previously unrecognised fertile corridor in the southwestern corner of EL 5893 at the Emu Prospect. The CORE funded diamond drillhole completed at the Emu prospect (WRDD0127) intersected three zones of weak uranium mineralisation in fractured, veined and altered Nimbuwah complex. The mineralisation occurs as 0.5 to 3 cm wide laminated quartzchlorite-carbonate-pitchblende veins surrounded by Mg-rich chlorite and phengite-illite alteration haloes. The alteration is coincident with Na and Ca depletion of the granite and Mg and K enrichment. Elevated V, Mo and Pb assays were observed in association with the mineralised intervals. This mineralisation occurs along an interpreted NNW trending lineament that extends to the south. The drillhole completed at Condor North (WRDD0129) intersected the Cretaceous/Proterozoic unconformity at a depth of 313.5 metres. The rocktypes intersected were consistent with the Cahill Formation. The drillhole completed at Condor South (WRDD0131) intersected a ~ 50 metre thick sequence of metasedimentary rocks similar in composition to the lower part of the Ranger Mine sequence. The sedimentary sequence comprised a 5 metre zone of interbedded psammitic and semipelitic units overlain by sillimanite-garnet bearing pelite in turn overlain by an 18 m thick, auto-brecciated marble. The metasedimentary sequence unconformably overlies interpreted Archean gneiss. The marble unit is bounded by shear zones which are intensely Mg-rich chlorite altered. Anomalous uranium results were returned (whole rock and WAL) from intervals flanking the marble unit. This discovery demonstrates that there is further potential for Ranger/Jabiluka style mineralisation along the northern strike extension of the Nanambu/Cahill unconformity. The drillhole completed at Kiwi (WRDD0132) confirmed the presence of Proterozoic metasedimentary rocks in the northeastern part of the Wellington Range tenement. The units intersected include semipelite, calc-silicate and amphibolite. A 20 m interval of anomalously low 207Pb/206Pb (WAL) ratios, associated with Na depletion and relative K2O enrichment was intersected within a semipelite and calc-silicate assemblage.