Relações de contato entre as rochas sieníticas do stock de Serraria e as rochas máficas plutônicas e hipoabissais do setor norte da suíte alcalina da Ilha de São Sebastião (Ilhabela) são descritas pela primeira vez, permitindo a indicação de relações temporais entre diferentes pulsos magmáticos. Os afloramentos apresentam variedade sienítica hololeucocrática hospedando mega-, macro- e microxenólitos de diferentes rochas, formando agmatitos. Cinco unidades principais são descritas: álcali feldspato sienitos, melassienitos, diabásios, cumulatos máficos (melagabros/clinopiroxenitos) e gabros heterogêneos. Geoquimicamente,o magmatismo alcalino bimodal encontrado na ilha é bem representado pelas rochas dos afloramentos estudados. A sequência de eventos magmáticos consiste em: colocação e cristalização de pulsos de magmas básicos alcalinos, em ambiente de câmara magmática, gerando as variedades gabroicas cumuláticas, principalmente melagabros e clinopiroxenitos com olivina, e brechas de matriz gábrica com evidências de reequilíbrio textural por ação de temperatura; intrusão de novos pulsos de magma básico alcalino, representados pelos fragmentos de diabásios, que apresentam também, reequilíbrio textural (textura granoblástica predominante); intrusão de pulso sienítico na câmara máfica que fragmentou o gabro já parcial ou totalmente cristalizado, transportando ampla proporção de xenocristais e xenólitos, o que gerou rochas classificadas como melassienitos; nova intrusão de pulso sienítico, que fragmenta todo o sistema formando um agmatito com megaxenólitos e microxenólitos de gabro cumuláticos, diabásios, agmatitos de matriz gabroica (gabros heterogêneos) e melassienitos; veios e diques de pegmatito e aplito de sienitos com quartzo cortam todos os litotipos. Todos os tipos amostrados como xenólitos apresentam algum grau de recristalização e de reação química com o magma sienítico final que os hospeda.
Brazil has 95 million tons of Li reserves in the form of pegmatites but produces less than 1% of the global output. Historically Li production in Brazil has been low due to governmental restrictions aimed at controlling the exploitation and trade of Li in Brazil. However, as of 2022, these restrictions were revoked. The abundance of untapped pegmatite ores in Brazil complements the soaring demand for Li in energy-storage applications. This study performs process mineralogy studies on 10 samples collected from a Li pegmatite deposit in the southeastern region of Minas Gerais in Brazil. The samples were characterized by combining density separation and SEM-based automated mineralogy processing system allied with XRF, ICP OES, XRD, and LA–ICPMS. The latter was used to determine Li content in micas which allowed determining the Li deportment between Li-bearing minerals. The results show that the samples contain such Li-bearing minerals as muscovite (0.5 wt% Li2O) and lepidolite (3.1 wt% Li2O), in addition to spodumene (8.0 wt% Li2O). According to the characterization of the spodumene concentrate (d = 3.11) by density separation (at d = 2.95), two main trends were observed: (a) low Li deportment in the sink product (approximately 44% wt%) and higher Li2O grade (approximately 6.5 wt%), and (b) higher Li deportment in the sink product (58%) and lower Li2O content (approximately 4.9 wt%). The first trend is associated with higher modal content of mica since it carries Li to the light product. Lower Li grade is related to the presence of Fe-bearing minerals (e.g., epidote and amphibole) as they report to the dense product and do not contain Li. Spodumene has a high degree of liberation in all samples; therefore, it did not influence the deportment results. The findings highlight the benefit of combining scanning electron microscopy-based automated mineralogy with LA–ICPMS and other techniques from process mineralogy studies in mineral processing. In addition to the mineralogy and liberation characteristics, identifying Li-bearing minerals and determining Li deportment is crucial.
Brines located in Chile and Argentina are the main lithium reserve, however over 50% of lithium production comes from pegmatites distributed around the world. With the increase in lithium demand driven by its applications in energy storage technologies, pegmatite deposits become increasingly economically viable. Lithium's reserve in Brazil is found exclusively in pegmatites and accounts for less than 1% of global reserves, but a recent study indicates that Brazil can reach up to 8% of global reserves. This paper reports process mineralogy studies performed in 10 samples from a lithium pegmatite deposit from southeastern of Minas Gerais state in Brazil. Samples characterization were carried out combining heavy liquid separation and X-ray based automated mineralogy using Mineral Liberation Analyzer system (MLA) allied to XRF, ICP-OES, XRD and LA-ICPMS. Results showed that besides spodumene (8.0 wt% Li2O), there are other lithium-bearing minerals, as muscovite (0.5 wt% Li2O) and lepidolite (3.1 wt% Li2O). The characterization of the spodumene (d=3.11) concentrate obtained by heavy liquid separation (d=2.95) revealed that samples present two main trends a) -samples with low lithium distribution in the sink product (~44%) with higher Li2O grade (~6.5 wt%) and b) -samples with higher lithium distribution in the sink product (58%) with lower Li2O content (~4.9 wt%). Lower lithium distribution in sink product is associated with higher modal content of micas since they carry lithium to the floated product. Lower lithium grade is related to the presence of iron-bearing minerals (e.g., epidote and amphibole), since they report to the sink product and do not contain Li. The liberation degree of spodumene is high and similar in all samples, therefore it did not influence distribution results. This work highlights the use of scanning electron microscopy (SEM) based automated mineralogy combined with other techniques in process mineralogy studies to guide mineral processing. Besides mineralogy and liberation characteristic, especially important was identifying lithium-bearing minerals and determining lithium's deportment.
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