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Mineralogy and Petrography of Rare Earth Element (REE) mineralisation, Browns Ranges, W.A. Daniel O'Rielly A1176590

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Mineralogy and Petrography of Rare Earth Element (REE) mineralisation, Browns Ranges, W.A. Daniel O'Rielly A1176590
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  Page | 1 Mineralogy and Petrography of Rare Earth Element (REE) mineralisation, Browns Ranges, W.A. Daniel O’Rielly A1176590 Supervisor Nigel J. Cook Co-supervisor Cristiana L. Ciobanu Centre for Tectonics, Resources and Exploration   Department of Geology and Geophysics   School of Earth and Environmental sciences   University of Adelaide, South Australia   daniel.orielly@alumni.adelaide.edu.au   Page | 2 ABSTRACT Northern Minerals’ current Browns Range exploration project is situated within the Gordon Downs Region, W.A. This area is remote and relatively unstudied, with only a few regional mapping studies and old exploration reports available. The area is currently being explored for REE mineralisation. Identified REE-prospects contain xenotime-dominant mineralisation hosted within Lower Proterozoic Arkoses and Archean metasediments (Browns Range Metamorphics) .  Detailed ore mineralogical, petrographic and mineral-chemical investigation of samples from the six currently-known prospects within the exploration area give insights into the mineralogical distribution of REE and provide evidence for the genetic evolution of the Browns Range REE mineralisation via a succession of hydrothermal processes. Two main REE-bearing minerals are identified: xenotime [(Y,REE)PO 4 ], HREE selective; and florencite [(REEAl 3 (PO 4 ) 2 (OH) 6 ], LREE selective. Two distinct generations of xenotime are recognised. EPMA and LA-ICP-MS analysis provide a large chemical data set for both xenotime and florencite allowing comparison with other localities worldwide. Xenotime contains Dy (up to 6.5 wt%), Er (up to 4.35 wt%), Gd (up to 7.56 wt%), Yb (up to 4.65 wt%) and Y (up to 43.3 wt%). Xenotime composition is shown to be consistent across all prospects and xenotime generations. Florencite is commonly zoned and contains Ce (up to 11.54 wt%), Nd (up to 10.05 wt%) and La (up to 5.40 wt%) and is also notably enriched in Sr (up to 11.63 wt%) and Ca.   Subordinate zircon is also enriched in REE (up to 13 wt% Σ REE) and is the principal host of Sc (up to 0.8 wt%). Early xenotime occurs as coarse euhedral grains which underwent surface etching, fracturing, partial breakdown and replacement by florencite. Second generation xenotime occurs as abundant small blades commonly associated with needles of hematite. Florencite occurs as replacement of xenotime and as overgrowths on detrital feldspar in the arkose, giving a  Page | 3 characteristic skeletal replacement texture. The preliminary genetic model involves percolation of a   reduced, acidic, volatile-rich, granite-derived   hydrothermal fluid   through porous arkose units.   The presence of late hematite suggests that mixing with meteoric water and subsequent oxidation may have played a role in the later stages of deposit evolution. Field observations suggest that faults acted as fluid conduits and that brecciation, possibly associated with release of volatiles from the fluid, occurred along these faults. As well as providing a characterisation of the Browns Range deposits, the data generated provided valuable data, largely unavailable elsewhere, on chemical compositional trends in hydrothermal xenotime and coexisting minerals. Given the current surge in REE exploration, this data will assist in the development of exploration models for comparable terranes. Keywords: Xenotime; florencite; hydrothermal; Browns Range; replacement; REE geochemistry  Page | 4 INTRODUCTION Northern Mineral’s Rare Earth Element (REE) exploration project at Browns Ranges, Gordon Downs Region, northeastern W.A., is one of a number of new projects generating attention due to a rapid upsurge in the search for exploitable REE resources in Australia. The present focus of Northern Minerals Ltd. within their exploration licenses is the elevated Heavy Rare Earth Element (HREE)/ Light Rare Earth Element (LREE) ratio at a number of previously-known and newly-discovered prospects. Such exceptional HREE/LREE enrichment is unusual and of major economic significance. RC drilling began on the license area in late June 2011. The geology of the area is poorly constrained and the style of mineralisation containing the REE concentrations is largely unknown at the present time. This situation is exacerbated by the lack of comparable hydrothermal xenotime-dominant deposits elsewhere which might serve as the basis for an exploration model. REEs are used for many purposes (Long  et al.  2010; Hoatson  et al.  2011) but are critical for the sustained development of new technologies. The current green energy drive is part of the reason for the sudden increase in demand for REE’s due to their importance in the development of these green technologies. REE’s are also imp ortant in a wide range of commercial and scientific applications for which demand continues to increase. D emand for REE’s is expected to increase dramatically over the next 5-10 years (Hoatson  et al.  2011), with no expected major increase in current REE reserves, thus highlighting the need for more REE deposits to be located. At present China produces around 95% of global REE production and no less than 99.8% of Global HREE’s (Gleason  et al.  2000; Long  et al.  2010; Hoatson  et al.  2011). Recently China has begun reducing its export quota which has been causing some panic in the stock market as prices  Page | 5 of all REE have risen dramatically due to supply shortages. Many governments around the world are beginning to realise that a supply interruption could occur if China were to cease trading or further reduce their REE export quota. This would expose our reliance on China as rest of world (ROW) production would be almost zero and would take many years to even partially cover ROW demand. A developed country would struggle to manage without available REE’s. As Australia further pursues a Green energy future and further improvements to current technologies and cutting edge scientific research our demand for R EE’s will increase, hence the desire for domestic production that will reduce our reliance on China. The current Northern Minerals Ltd. tenements lie along the North Western area of the Browns Ranges Dome. This consists of Lower Proterozoic Arkoses and Archean metasediments (Blake  et al.  1979; Page  et al.  1995; Hendrickx  et al.  2000; Cross & Crispe 2007; Tunks & Cooke 2007). Throughout the exploration area, these metamorphic units contain abundant quartz veining in areas with dominant 260 o  and 320 o  structures (PNC Exploration 1989). The quartz veining appears to be somewhat controlled by these structures with the REE mineralisation being found within and surrounding the quartz veins particularly where veins intersect. During 1987-1991 a Japanese exploration company (PNC Exploration) carried out detailed field work in the Browns Range area searching for unconformity-style uranium mineralisation. They carried out geophysical surveys, geological mapping, rock chip assays, petrological analysis and drilling identifying REE elevations within the area however relinquished the area after receiving “uninspiring results”. Their work is noted in a series of exploration reports (PNC 1987-1991, 1988). The present project aims to characterise potential REE-ore from the 6 prospects defined in June 2011. This is done using a combination of field observations along with an array of microanalytical methods. The main goals to achieve were:
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