Brazillian Rare Earth symposium – University of São Paulo
On 6 to 10 November 2017, the St Andrews team (Nicky Horsburgh, Adrian Finch and myself) attended the Brazilian SOS RARE symposium on Rare Earth Elements, held at the Institute of Geosciences, University of São Paulo. The symposium was organized by Prof. Daniel Atencio and Prof. Marcello Andrade (University of São Paulo) and comprised a series of invited talks followed by field excursions to famous Brazilian carbonatite and peralkaline localities.
Prof. Marcello Andrade kicked off the meeting with a presentation on Raman spectroscopy to fingerprint REE minerals. Dr Andrezza de Almeida Azzi (USP) introduced us to the fascinating geology and mineralogy of the Poços de Caldas alkaline complex. She catalogued many REE minerals from old sample collections of former Poços de Caldas mining sites, many of which are not properly documented to date. Prof. Daniel Atencio gave us a preview of the bewildering mineralogy of the Araxa and Jacupiranga carbonatites.
After lunch and an enjoyable visit to the local mineral museum, Prof. Hermi Felinto de Brito from the Institute of Chemistry (USP) talked about the luminescent properties of RE3+ compounds and the synthesis of persistent luminescent Eu, Tb and Tm materials which can luminesce up to 24 hours after being excited, offering many applications in for example traffic and emergency signalization. Prof. Brito also demonstrated how they synthesize RE3+compounds at high temperature using just a simple microwave oven.
Prof. Henrique Kahn of the Mining & Engineering department of the LCT-Polytechnic School (USP) presented work on metallurgical processing and mineralogical characterization of REE-rich lateritic soils from various Brazilian carbonatite localities. The last three talks were given by us from St Andrews. Prof. Adrian Finch spoke about REE and HFSE mineralisation in magmatic roof zones and applications of luminescence studies to understand hydrothermal alteration and mineralization processes. I presented on the pseudomorphic replacement of eudialyte in the Ilímaussaq complex, including new evidence for late-magmatic REE-HFSE remobilisation from trace element and Sm/Nd isotopic data of microdrilled pseudomorphs (work by my MSc student Mathijs vd Ven). Nicky Horsburgh gave the last talk, on luminescence studies of REE minerals. Nicky demonstrated that mineral luminescence is strongly provenance dependent, illustrating the need for site-specific luminescence studies if we are to apply luminescence as an automated sorting or core logging tool.
Keen to bring out our geological hammers, we ventured north of São Paulo on day two to see some rocks in the field. After a long bus journey, enjoying the luscious green scenery, we arrived at an amazing lujavrite outcrop in the northern part of the Poços de Caldas alkaline complex. This is one of the few places with good solid rock exposures, not obscured by the thick tropical weathering profile that covers much of the complex. The coarse grained lujavrite shows strong magmatic foliation fabrics defined by coarse feldspar laths wrapped in fine needles of aegirine (photo), which is a testament of the low viscosity melt and possibly subsolidus deformation and recrystallisation. The rock is peppered with large (5–6 cm) purple to pink eudialyte which overgrow the foliation fabric, resembling textures seen in the naujaite of the Ilímaussaq complex. We managed to collect a number of samples for further mineralogical studies and comparison to Greenland samples.