Garnet as Indicator of Pegmatite Evolution: The Case Study of Pegmatites from the Oxford Pegmatite Field (Maine, USA)

Almandine-spessartine garnets, from the Oxford County pegmatites and the Palermo No. 1 pegmatite, record significant compositional variations according to the degree of evolution of their hosting rock. Garnets from the most fractionated pegmatites (Mt. Mica, Berry-Havey, and Emmons) show the highest Mn, Nb, Ta, Zr, and Hf values, followed by those from the intermediate grade pegmatites (Palermo No. 1) and, finally, garnets from the barren pegmatites show the lowest values (Perham and Stop-35). Iron, Ca, and Mg contents follow an inverse order, with the highest contents in the latter pegmatites. Major element zoning shows increasing Mn values from core to rim in most garnet samples, while trace element zoning is not systematic except for some crystals which show a core to rim depletion for most of these elements. Chondrite normalized HREE (Heavy Rare Earth Elements) spectra show positive slopes for garnets from barren pegmatites, both positive and negative slopes for those associated with the intermediate pegmatite, and negative or flat slopes in garnets from the highly fractionated pegmatites. Ion exchange mechanisms, including Fe2+−1Mn2+1, (Fe2+, Mn2+)−1Si−1Li1P1; and, (Y, Ho3+)2(vac)1(Fe2+, Mn2+)−3, could explain most of the compositional variations observed in these garnets. These compositional variations are the reflection of the composition of the pegmatitic magma (barren pegmatites originate from a more ferromagnesian magma than fractionated pegmatites); and of the coexisting mineral phases competing with garnets to host certain chemical elements, such as biotite, schorl, plagioclase, apatite, Fe-Mn phosphates, Nb-Ta oxides, zircon, xenotime, and monazite.This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness (project no. RTI2018‐094097‐B‐100, with ERDF funds), the University of the Basque Country UPV/EHU (grant no. GIU18/084) and the European Union’s Horizon 2020 Innovation Programme (grant agreement no. 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green‐Tech Resources). Maine Mineral and Gem Museum (USA) also contributed economically

Semi-Automatization of Support Vector Machines to Map Lithium (Li) Bearing Pegmatites

Machine learning (ML) algorithms have shown great performance in geological remote sensing applications. The study area of this work was the Fregeneda–Almendra region (Spain–Portugal) where the support vector machine (SVM) was employed. Lithium (Li)-pegmatite exploration using satellite data presents some challenges since pegmatites are, by nature, small, narrow bodies. Consequently, the following objectives were defined: (i) train several SVM’s on Sentinel-2 images with different parameters to find the optimal model; (ii) assess the impact of imbalanced data; (iii) develop a successful methodological approach to delineate target areas for Li-exploration. Parameter optimization and model evaluation was accomplished by a two-staged grid-search with cross-validation. Several new methodological advances were proposed, including a region of interest (ROI)-based splitting strategy to create the training and test subsets, a semi-automatization of the classification process, and the application of a more innovative and adequate metric score to choose the best model. The proposed methodology obtained good results, identifying known Li-pegmatite occurrences as well as other target areas for Li-exploration. Also, the results showed that the class imbalance had a negative impact on the SVM performance since known Li-pegmatite occurrences were not identified. The potentials and limitations of the methodology proposed are highlighted and its applicability to other case studies is discussed.The authors would like to thank the financial support provided by FCT—Fundação para a Ciência e a Tecnologia, I.P., with the ERA-MIN/0001/2017—LIGHTS project. The work was also supported by National Funds through the FCT project UIDB/04683/2020—ICT (Institute of Earth Sciences). Joana Cardoso-Fernandes is financially supported within the compass of a Ph.D. Thesis, ref. SFRH/BD/136108/2018, by national funds from MCTES through FCT, and co-financed by the European Social Fund (ESF) through POCH—Programa Operacional Capital Humano. The Spanish Ministerio de Ciencia, Innovacion y Universidades (Project RTI2018-094097-B-100, with ERDF funds) and the University of the Basque Country (UPV/EHU) (grant GIU18/084) also contributed economically

Garnet as Indicator of Pegmatite Evolution: The Case Study of Pegmatites from the Oxford Pegmatite Field (Maine, USA)

Almandine-spessartine garnets, from the Oxford County pegmatites and the Palermo No. 1 pegmatite, record significant compositional variations according to the degree of evolution of their hosting rock. Garnets from the most fractionated pegmatites (Mt. Mica, Berry-Havey, and Emmons) show the highest Mn, Nb, Ta, Zr, and Hf values, followed by those from the intermediate grade pegmatites (Palermo No. 1) and, finally, garnets from the barren pegmatites show the lowest values (Perham and Stop-35). Iron, Ca, and Mg contents follow an inverse order, with the highest contents in the latter pegmatites. Major element zoning shows increasing Mn values from core to rim in most garnet samples, while trace element zoning is not systematic except for some crystals which show a core to rim depletion for most of these elements. Chondrite normalized HREE (Heavy Rare Earth Elements) spectra show positive slopes for garnets from barren pegmatites, both positive and negative slopes for those associated with the intermediate pegmatite, and negative or flat slopes in garnets from the highly fractionated pegmatites. Ion exchange mechanisms, including Fe2+−1Mn2+1, (Fe2+, Mn2+)−1Si−1Li1P1; and, (Y, Ho3+)2(vac)1(Fe2+, Mn2+)−3, could explain most of the compositional variations observed in these garnets. These compositional variations are the reflection of the composition of the pegmatitic magma (barren pegmatites originate from a more ferromagnesian magma than fractionated pegmatites); and of the coexisting mineral phases competing with garnets to host certain chemical elements, such as biotite, schorl, plagioclase, apatite, Fe-Mn phosphates, Nb-Ta oxides, zircon, xenotime, and monazite.This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness (project no. RTI2018-094097-B-100, with ERDF funds), the University of the Basque Country UPV/EHU (grant no. GIU18/084) and the European Union’s Horizon 2020 Innovation Programme (grant agreement no. 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources). Maine Mineral and Gem Museum (USA) also contributed economically

Calibrating a Handheld LIBS for Li Exploration in the Barroso–Alvão Aplite-Pegmatite Field, Northern Portugal: Textural Precautions and Procedures When Analyzing Spodumene and Petalite

In pegmatites containing abundant petalite and spodumene, such as those from the Barroso–Alvão (BA) aplite-pegmatite field, calibrating a portable laser-induced breakdown spectroscopy (pLIBS) equipment to identify and analyze these minerals may be challenging. Forty-nine samples of spodumene, petalite and spodumene + quartz were collected from 22 aplite-pegmatites from the BA field and sent for inductively coupled plasma-mass spectroscopy analysis. One calibration for both spodumene and petalite has been proven to be impossible since almost all the LIBS intensity ratios, including for Li, overlapped on both minerals. Thus, three calibrations were developed: one qualitative to distinguish both minerals and two more quantitative, specifically made for each mineral. The first LIBS calibration only has Fe since it is the sole element with intensity ratios different enough to distinguish both minerals. Eleven calibration lines were created: Li, Al, Si, Be, Na, P, K, Mn, Fe, Rb and Cs; however, only the Li, Al, and Si have consistent errors below 20%. Thin sections were produced and observed with optical microscopy and cathodoluminescence (CL) to control the purity and mineral paragenesis of the samples. The petalite pellets were also controlled with cold CL since petalite crystals often present fine spodumene and quartz inclusions.This work was funded by the European Commission’s Horizon 2020 innovation programme under grant agreement no. 869274 by the project GREENPEG New Exploration Tools for European Pegmatite Green-Tech Resources. This work was co-funded through the project CAVALI—Cadeia de Valor do Lítio, reference POCI-01-0247-FEDER-047728, cofinanced by FEDER—Fundo Europeu de Desenvolvimento Regional, in the scope of the Programa Portugal 2020, through COMPETE 2020—Programa Operacional. This work was co-funded through the project INOVMINERAL 4.0—Tecnologias Avançadas e Software para os recursos Minerais, reference POCI-01-0247-FEDER-046083, cofinanced by FEDER—Fundo Europeu de Desenvolvimento Regional, in the scope of the Programa Portugal 2020, through COMPETE 2020—Programa Operacional. The work is co-funded by national funds through FCT—Fundação para a Ciência e Tecnologia, I.P., in the framework of the ICT project with the references UIDB/04683/2020 and UIDP/04683/2020. Filipa Dias and Ricardo Ribeiro are financially supported within the compass of their respective Ph.D. theses, ref. 2020.05534.BD and ref. SFRH/BD/140266/2018, by national funds from MCTES through FCT, and co-financed by the European Social Fund (ESF) through POCH—Programa Operacional Capital Humano—and the NORTE 2020 regional program

The Li-Bearing Pegmatites from the Pampean Pegmatite Province, Argentina: Metallogenesis and Resources

The Li-bearing pegmatites of the Pampean Pegmatite Province (PPP) occur in a rare-element pegmatite belt developed mainly in the Lower Paleozoic age on the southwestern margin of Gondwana. The pegmatites show Li, Rb, Nb ≤ Ta, Be, P, B, Bi enrichment, and belong to the Li-Cs-Ta (LCT) petrogenetic family, Rare-Element-Li (REL-Li) subclass; most of them are of complex type and spodumene subtype, some are of albite-spodumene type, and a few of petalite subtype. The origin of the pegmatites is attributed predominantly to fractionation of fertile S-type granitic melts produced by either fluid-absent or fluid-assisted anatexis of a thick pile of Gondwana-derived turbiditic sediments. Most of the pegmatites are orogenic (530–440 Ma) and developed during two overlapped collisional orogenies (Pampean and Famatinian); a few are postorogenic (~370 Ma), related to crustal contaminated A-type granites. The pegmatites were likely intruded in the hinterland, preferably in medium-grade metamorphic rocks with PT conditions ~200–500 MPa and 400–650 °C, where they are concentrated in districts and groups. Known combined resources add up 200,000 t of spodumene, with variable grades between 5 and 8 wt.% Li2O. The potential for future findings and enlargement of the resources is high, since no systematic exploration program has yet been developed.This research was funded by CONICET grants during several periods and lastly by PIP 1489 from CONICET to M.F.M.-Z. The Spanish Ministry of Economy, Industry and Competitiveness (project no. RTI2018-094097-B-100, with ERDF funds), and the European Union’s Horizon 2020 Innovation Programme (grant agreement no. 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources) granted E.R.-R

The metasomatic enrichment of Li in psammopelitic units at San Jose-Valdeflorez, Central Iberian Zone, Spain: a new type of lithium deposit

A new type of Li mineralisation in hard rock has been found to occur in the Valdefórez area (Cáceres, Spain), where there is 111.3 Mt of resources and a mean value of 0.61 wt% of Li2O. Lithium is mainly held by very fne-grained micas, important constituents of Ordovician psammopelitic rocks belonging to the Palaeozoic metasedimentary sequence of the Cáceres syncline. The mineralised zone has an elliptical surface shape with a dimension of~ 700 × 500 m. Lithium-bearing rocks show a characteristic layered appearance, in which light grey quartz-micaceous laminae< 1 mm to some centimetres in thickness, with a variable ratio of quartz to mica, alternate with fne to very fne-grained, dark grey to black tourmalinite laminae parallel to the regional foliation. Subvertical quartz+ (montebrasite)-veins that cut the regional foliation at an extremely high angle are also common in this area. Mineralisation and the associated veins are likely to be linked to the intrusion of the nearby Cabeza de Araya pluton. The infltration of granite-derived Li-, F-, B- and P-rich aqueous fuids into the host rocks through fractures related to shearing processes is considered to be the cause of the formation of Li-rich micas and intense tourmalinisation at the expense of pre-existing phyllosilicates.Spanish Ministerio de Ciencia, Innovacion y Universidades RTI2018-094097-B-100Spanish Ministerio de Ciencia, Innovacion y Universidades (ERDF funds)University of Basque Country GIU18/08

The Tres Arroyos Granitic Aplite-Pegmatite Field (Central Iberian Zone, Spain): Petrogenetic Constraints from Evolution of Nb-Ta-Sn Oxides, Whole-Rock Geochemistry and U-Pb Geochronology

Abundant Li-Cs-Ta aplite-pegmatite dykes were emplaced in the western Central Iberian Zone of the Iberian Massif during the Variscan Orogeny. Their origin and petrogenetic relationships with the widespread granitoids have led to a currently rekindled discussion about anatectic vs. granitic origin for the pegmatitic melts. To deal with these issues, the aplite-pegmatite dykes from the Tres Arroyos area, which constitute a zoned pegmatitic field related to the Nisa-Alburquerque granitic batholith, have been studied. This work comprises a complete study of Nb-Ta-Sn oxides’ mineralogy, whole-rock geochemistry, and U-Pb geochronology of the aplite-pegmatites that have been grouped as barren, intermediate, and Li-rich. The most abundant Nb-Ta-Sn oxides from Tres Arroyos correspond to columbite-(Fe), columbite-(Mn) and cassiterite. Niobium-Ta oxides show a marked increase in the Mn/(Mn+Fe) ratio from the barren aplite-pegmatites up to the Li-rich bodies, whereas variations in the Ta/(Ta+Nb) ratio are not continuous. The probable factors controlling fractionation of Mn/Fe and Ta/Nb reflected in Nb-Ta oxides may be attributed to the crystallization of tourmaline, phosphates and micas. The lack of a progressive Ta/Nb increase with the fractionation may be also influenced by the high F and P availability in the parental pegmatitic melts. Most of the primary Nb-Ta oxides would have crystallized by punctual chemical variations in the boundary layer, whereas cassiterite formation would be related to an undercooling of the system. Whole-rock composition of the distinguished lithotypes reflects similar tendencies to those observed in mineral chemistry, supporting a single path of fractional crystallization from the parental Nisa-Alburquerque monzogranite up to the most evolved Li-rich aplite-pegmatites. The age of 305 ± 9 Ma, determined by LA-ICP-MS U-Pb dating of columbite-tantalite oxides, reinforces the linkage of the studied aplite-pegmatites and the cited parental monzogranite.This research was funded by the Spanish Ministry of Economy, Industry and Competitiveness (Project RTI2018-094097-B-100, with ERDF funds), the University of the Basque Country UPV/ EHU (grant GIU18/084) and the European Union’s Horizon 2020 Innovation Programme (grant agreement No 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources). Work of Idoia Garate-Olave has been supported also by the UPV/EHU by means of the “Convocatoria de contratación para la especialización de personal investigador doctor en la UPV/EHU 2019”

Metasomatic effect of Li-bearing aplite-pegmatites on psammitic and pelitic metasediments: Geochemical constraints on critical raw material exploration at the Fregeneda-Almendra Pegmatite Field (Spain and Portugal)

Fluid-assisted mass transfer and re-equilibration of mineral phases are common consequences of metasomatism associated with igneous intrusions. The addition and/or removal of chemical components in these environments may result in the generation of metasomatic aureoles, which can be recognized by their mineralogy and geochemistry. Due to an increasing demand for critical raw materials used in green energy technologies, rare-element granitic pegmatites have seen renewed interest in the mineral exploration industry. Granitic pegma-tites represent potential sources of critical commodities and geochemical studies of their related aureoles help to advance techniques in exploration targeting. Moreover, the role and timing of fluid exsolution during magma-tic-hydrothermal evolution in granitic-pegmatitic systems and concomitant element mobility remain highly debated.We present a prospect-scale systematic study of geochemical haloes generated by LCT (Li-Cs-Ta) family pegmatite dykes from the Fregeneda-Almendra Pegmatite Field, in the Central Iberian Zone of the Iberian Massif (Spain and Portugal). To understand the magnitude of metasomatic processes linked to these intrusions, we performed whole-rock mass-balance calculation of element gains and losses in variably metasomatized psam-mitic and pelitic host metasediments. The results show that F, B, Li, Rb, Cs, Sn, Be, Tl, As, W and S (+/- Mo, Ta) were carried by early exsolved and expelled aqueous fluids. The first evidence of element enrichment is recorded at distances of 4-5 times the thickness of the dykes, with exponentially increasing gains of those fluid-mobile elements proximal to the pegmatite margin. Enrichments that were detected farthest from the pegmatite mar-gins were those of Li and Cs, followed by Rb and, to a lesser extent, Sn, F, B, Be, and Tl. The most evolved (fractionated) aplite-pegmatites generated the broadest haloes, with concentrations higher than 200 ppm Li, 30 ppm Cs, 300 ppm Rb, and 15 ppm Sn in the metasediments indicating proximity to a mineralized dyke. In addition, absolute gains of up to-4000 ppm Li,-1300 ppm Cs,-1300 ppm Rb, and 170 ppm Sn in the host rocks could point to the presence of superimposed haloes from multiple evolved dykes.Financial support was provided by the European Commission's Horizon 2020 Innovation Programme [grant agreement No 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources]; grant RTI2018-094097-B-100 funded by MCIN/AEI/10.13039/501100011033 and, by "ERDF A way of making Europe"; and the University of the Basque Country UPV/EHU [grant GIU18/084]. The authors are grateful to Kathryn M. Goodenough, an anonymous reviewer, and Tania Martins for their constructive comments, which have improved considerably the quality of the manuscript. Editorial handling and helpful suggestions by Franco Pirajno and Allen K. Andersen are also acknowledged. The. Work of I. Garate-Olave has been supported also by the UPV/EHU by means of the "Convocatoria de contratacion para la especializacion de personal investigador doctor en la UPV/EHU 2019". Financial support provided by FCT- Fundacao para a Ciencia e a Tecnologia, I.P., with the ERA-MIN/0001/2017 - LIGHTS project and through the FCT project UIDB/04683/2020 and UIDP/04683/2020 - ICT (Institute of Earth Sciences) is recognized. J. Cardoso - Fernandes has been financially supported within the compass of a Ph.D. Thesis, ref. SFRH/BD/136108/2018, by Portuguese national funds from MCTES through FCT, and co-financed by the European Social Fund (ESF) through POCH - Programa Operacional Capital Humano - and NORTE 2020 regional program

Quartz chemistry of granitic pegmatites: Implications for classification, genesis and exploration

Quartz from 254 pegmatites representing eight pegmatite fields and provinces worldwide was investigated by laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) to determine concentrations of trace elements Al, Ti, Li, Ge, B, Be, Rb, Na, K, Ca, P, Ga, Sb, Zn and U. A total of 271 new analyses combined with 535 published LA-ICP-MS quartz chemistry data were evaluated with binary and ternary trace element discrimination plots and principal component analysis (PCA). The classifications applied for discrimination of pegmatite types include the widely applied NYF(Nb-Y-F) - LCT(Li-Cs-Ta) classification and the new RMG (pegmatites derived from residual melts of granite magmatism) - DPA (pegmatites as direct products of anatexis) grouping. Pegmatites of both classifications can be well distinguished via Al-Ti, Al-Li and Al/Ti-Ge/Ti binary trace element plots and the Ti - Al/10 - 10*Ge ternary diagram. PCA applied to Al, Li, Ti, Be, B, Ge and Rb contents in quartz allowed to further distinguish between anatectic DPA-1 (Li-enriched DPA) and granite-pluton-derived RMG-1 (Li-enriched RMG) pegmatites. Some pegmatite fields and provinces (Hagendorf-Pleystein, Oxford County) are distinguishable by region-specific Li, Ge and Al contents. The results imply that the chemistry of pegmatite quartz is mainly controlled by the origin (source rock chemistry) of pegmatite melts and, to a much lesser extent, by the geodynamic setting of the pegmatite fields and provinces. Chemically primitive NYF and DPA-2 type pegmatites contain quartz with the lowest total trace-element contents and lowest internal-pegmatite trace-element variation, making it potentially suitable for high-tech application. Pegmatite quartz containing >30 μgg-1 Li and >100 μgg-1 Al is strongly indicative of economic spodumene/montebrasite mineralization and, thus, serves as a strong Li-mineralization pathfinder mineral. Quartz with >5 μgg-1 B may be a potential indicator for gem-quality tourmaline mineralization.Fil: Müller, Axel. University of Oslo; Noruega. Natural History Museum; Reino UnidoFil: Keyser, William. University of Oslo; NoruegaFil: Simmons, William B.. Maine Mineral And Gem Museum; Estados UnidosFil: Webber, Karen. Maine Mineral And Gem Museum; Estados UnidosFil: Wise, Michael. Smithsonian Institution; Estados UnidosFil: Beurlen, Hartmut. Universidade Federal de Pernambuco; BrasilFil: Garate Olave, Idoia. Universidad del País Vasco; EspañaFil: Roda Robles, Encarnación. Universidad del País Vasco; EspañaFil: Galliski, Miguel Angel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentin

Compositional Variations in Apatite and Petrogenetic Significance: Examples from Peraluminous Granites and Related Pegmatites and Hydrothermal Veins from the Central Iberian Zone (Spain and Portugal)

Apatite can be used as an archive of processes occurring during the evolution of granitic magmas and as a pegmatite exploration tool. With this aim, a detailed compositional study of apatite was performed on different Variscan granites, pegmatites and quartz veins from the Central Iberian Zone. Manganese in granitic apatite increases with increasing evolution degree. Such Mn increase would not be related to changes in the fO2 during evolution but rather to a higher proportion of Mn in residual melts, joined to an increase in SiO2 content and peraluminosity. In the case of pegmatitic apatite, the fO2 and the polymerization degree of the melts seem not to have influenced the Mn and Fe contents but the higher availability of these transition elements and/or the lack of minerals competing for them. The subrounded Fe-Mn phosphate nodules, where apatite often occurs in P-rich pegmatites and P-rich quartz dykes, probably crystallized from a P-rich melt exsolved from the pegmatitic melt and where Fe, Mn and Cl would partition. The low Mn and Fe contents in the apatite from the quartz veins may be attributed either to the low availability of these elements in the late hydrothermal fluids derived from the granitic and pegmatitic melts, or to a high fO2. The Rare Earth Elements, Sr and Y are the main trace elements of the studied apatites. The REE contents of apatite decrease with the evolution of their hosting rocks. The REE patterns show in general strong tetrad effects that are probably not related to the fluids’ activity in the system. On the contrary, the fluids likely drive the non-CHARAC behavior of apatite from the most evolved granitic and pegmatitic units. Low fO2 conditions seem to be related to strong Eu anomalies observed for most of the apatites associated with different granitic units, barren and P-rich pegmatites. The positive Eu anomalies in some apatites from leucogranites and Li-rich pegmatites could reflect their early character, prior to the crystallization of feldspars. The increase in the Sr content in apatite from Li-rich pegmatites and B-P±F-rich leucogranites could be related to problems in accommodating this element in the albite structure, favoring its incorporation into apatite. The triangular plots ΣREE-Sr-Y and U–Th–Pb of apatites, as well as the Eu anomaly versus the TE1,3 diagram, seem to be potentially good as petrogenetic indicators, mainly for pegmatites and, to a lesser extent, for granites from the CIZFinancial support was provided by the European Commission’s Horizon 2020 Innovation Programme (grant agreement No 869274, project GREENPEG: New Exploration Tools for European Pegmatite Green-Tech Resources); by Ministerio de Ciencia e Innovación and Agencia Estatal de Investigación (Project RTI2018-094097-B-100, with ERDF funds, A way of making Europe); and by the University of the Basque Country UPV/EHU (grant GIU18/084). The work was also supported by Portuguese National Funds through the FCT–Fundação para a Ciência e a Tecnologia, I.P., with projects UIDB/04683/2020 and UIDP/04683/2020-ICT (Institute of Earth Sciences)