The Charley Creek project area is dominated by the MacDonnell Ranges which trend east-west to the immediate south of the project tenements. The MacDonnell Ranges are an uplifted, tilted and dissected plateau of basement Proterozoic rocks comprising metasediments, mafic and felsic granulites, gneisses, migmatites and granites. To the south, Devonian sediments form the northern rim of the Amadeus Basin. The northern boundary of the MacDonnell Ranges is marked by a major fault zone, the Redbank Thrust Zone. North of the Redbank Thrust Zone the basement rocks of the Arunta Block are largely buried beneath flat lying plains, with occasional hills of basement rocks protruding through the younger sediments. The buried basement rocks commonly show a zone of saprolitic weathering, overlain by Tertiary sediments and calcrete, overlain in turn by Quaternary colluvial and alluvial gravels and sands, representing outwash fans from the weathering of the older basement rocks. The basement rocks contain elevated values of uranium and thorium and are also the source of the rare earth minerals found in the Charley Creek alluvials. Drilling elsewhere has intersected up to 80m of Quaternary alluvial sands, gravels and calcrete, but the average resource thickness over the Western Dam and Cattle Creek resource areas is 15m.
The rare earths in the alluvials are contained in the rare earth phosphate minerals, monazite ([Ce, La, Y, Th]PO4) and xenotime (YPO4). The term ‘Rare Earths’ refers to a group of 15 chemical elements, with similar properties and with atomic numbers ranging from 57-71. Rare earths are also termed ‘lanthanides’, deriving from the transition element Lanthanum. Yttrium is commonly included with the RE elements because it tends to occur in association with them due to its similar chemical properties. The first four lanthanide elements, from Lanthanum to Neodymium are referred to as the ‘light’ RE elements (“LREE”), Samarium to Gadolinium are referred to as the ‘mid’ RE elements (“MREE”), while the remaining elements, Terbium to Lutetium plus Yttrium, comprise the Yttrium subgroup or ‘heavy’ RE elements (“HREE”). The occurrence of xenotime at Charley Creek is significant in that xenotime is enriched in the heavy (and more valuable) rare earths, with approximately 17% of the Charley Creek total rare earth oxides, as currently defined, classified as heavy rare earth oxides. The grade of the rare earths in the Charley Creek alluvials is relatively low, averaging only 300ppm (0.03%)TREO in the previously defined Indicated Mineral Resource, compared with levels of 5-15.0% TREO in some hard rock carbonatite deposits. However, the Charley Creek alluvials are only loosely consolidated and the mineralisation is amenable to standard and relatively low cost mineral sands processing techniques and upgrading. Process testwork has shown a heavy minerals concentrate can be produced using simple methods yielding TREOs grading 8-12%.
Charley Creek Project - view of project area showing extent of alluvial fans