The primary objective of the subject successful Accelerated Discovery Initiative (ADI) project proposal has been to determine the nature, extent and economic potential of rare earth elements (REE) mineralisation in the Benagerie Ridge portion of...
The primary objective of the subject successful Accelerated Discovery Initiative (ADI) project proposal has been to determine the nature, extent and economic potential of rare earth elements (REE) mineralisation in the Benagerie Ridge portion of the Curnamona Craton. Initially its focus was to be on the West Kalkaroo copper-gold deposit located on EL 5800/6659 Kalkaroo, and the Croziers copper prospect located on EL 5873 Benagerie, where limited assays done to date had indicated potentially economic levels of the higher value heavy REE associated with the copper mineralisation. Previously, during 2013 regional exploration drilling on the Benagerie Dome, significant REE were discovered by Havilah's former joint venture partner MMG in Proterozoic metasedimentary rocks in the drill core from diamond drillhole BNG13DD001 put in at the Croziers Dam prospect, which followed up earlier shallow aircore drilling done by both Pasminco and MMG. Havilah has subsequently drilled four RC holes up dip of the BNG13DD001 copper and REE intercept, which confirmed the presence of this mineralisation at shallower depth. An evaluation of available geochemical results made early in 2020 by distinguished expert, Dr Ken Collerson, had confirmed the prospectivity of the Curnamona Craton for REE (his report is provided herein as Appendix 1). This prompted an expanded effort by Havilah to investigate the distribution and grade of REE at West Kalkaroo and Croziers Dam, and whether it was feasible to produce a REE mineral concentrate. During the period March to July 2020, an aircore drilling programme consisting of 90 shallow, east to south-southeastwards angled drillholes for a total penetration of 8394.5 m was performed at West Kalkaroo in order to determine the subsurface distribution there of REE mineralisation. Samples of saprolite recovered from these drillholes were assayed for gold and a range of other elements, including contents of the REE La, Ce, Nd, Pr and Y, by using a hand-held Niton portable XRF spectrometric analyser. Good geochemical correlations were observed between concentrations of the REE themselves, as well as moderate correlations to those of Cu, Co, Ni, Pb and P. The spatial distribution of REE contents within the saprolite gold ore zone was subsequently defined using 3D mine mapping and visualisation software. Drillhole samples were selected for undergoing detailed laboratory studies of the West Kalkaroo REE mineral species characterisation, abundance and deportment, which were made during September-October 2020 in collaboration with the University of South Australia’s Future Industries Institute. This work determined that the primary REE-containing mineral present in the samples is bastnasite, a REE-carbonate-fluoride mineral that is intergrown with silicate minerals. It has crystallised mostly within the minus 38 microns to plus 8 microns particle size range, and hence is amenable to separation via flotation; initially, tests were done using this method, and proved to be moderately successful in concentrating REE from de-slimed material. However, magnetic mineral separation using a wet high intensity magnetic separator produced better yields and higher REE concentrate grades than did flotation, and therefore this method of processing will be the subject of future study and refinement using new magnetic separation equipment. During December 2020, only two angled RC holes totalling 351 m could be drilled at the Croziers Dam prospect located on the Benagerie Dome, due to an inability to undertake native title cultural heritage protection clearance surveys since the outbreak of COVID. Laboratory assaying of drill samples obtained from there returned only moderate lanthanum values, the tenor of which is indicative of only moderate overall REE contents. Accordingly, no samples were taken from these drillholes to send for REE laboratory studies. The findings of this study have confirmed that potentially economic levels of REE exist in saprolite gold ore material from West Kalkaroo. It has been shown that the predominant REE mineral is bastnasite, and that a significant proportion of it can be recovered from deslimed material by utilising flotation and/or magnetic separation. Havilah has concluded that these research results are extremely positive for the ultimate recovery of material quantities of REE minerals from the West Kalkaroo saprolite gold ore, and potentially likewise from deposits that the company has discovered at other locations in the region. Gaining this knowledge now could lead to the early commencement of the first commercial production of REE from South Australia, as by-products of copper and gold mining operations.
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