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Alluvial nodular monazite in Monfortinho (Idanha-a-Nova, Portugal): Regional distribution and genesis

2020Journal article Open access
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dc.contributor.authorSalgueiro, Rute
dc.contributor.authorInverno, Carlos
dc.contributor.authorde Oliveira, Daniel Pipa Soares
dc.contributor.authorGuimarães, Fernanda
dc.contributor.authorLencastre, José
dc.contributor.authorRosa, Diogo
dc.date.accessioned2021-01-15T16:42:19Z
dc.date.available2021-01-15T16:42:19Z
dc.date.issued2020
dc.description.abstractABSTRACT: This work constitutes a contribution to the knowledge on the occurrence of nodular monazite in the Monfortinho (Idanha-a-Nova) alluviums and its genesis. A new edition of the alluvial nodular monazite regional distribution map is presented, underlining its wide occurrence and preferential concentration in the north-western and central zones of this region. The assessment of the geological and environmental evolution during Neoproterozoic-Palaeozoic and Caenozoic times and alluvial nodular monazite accumulation seems to provide a direct association between the presence of the Ordovician rocks, in particular the radioactive (carrying radioactive heavy minerals) quartzite (one of the most probable original sources) and Caenozoic sedimentary rocks (most probably the secondary source). Nevertheless, the Slate-Greywacke Complex cannot be excluded as a host rock for nodular monazite as well. Alluvial heavy mineral concentrates include: iron oxide/hydroxide, ilmenite, tourmaline, nodular monazite, monazite, xenotime, zircon, rutile, anatase, brookite, apatite, andalusite, gold, cassiterite and topaz. There is a significant REE enrichment in these concentrates (up to> 32,000 mg/kg), mainly in LREE-MREE. The contents in Ce and Th, Th and REE and Ce and La showed good correlation (0.97, 0.96 and 0.99, respectively), reflecting mainly the striking presence of nodular monazite, as can be proved by the similarity among NASCN patterns of this mineral and concentrates. In Monfortinho there are two distinct alluvial nodular monazite populations: 1) distal pre-deformation nodules generation, from the central western area, mostly ellipsoidal to discoidal, with irregular not orientated probable detrital mineral inclusions; and 2) proximal generation, in the northern area near the Ordovician rocks, with smaller grains, with mostly irregular surfaces. Diagenetic/low metamorphic pre-deformation distal Monfortinho nodules population growth can be recognised and characterised by the encompassing of irregular unoriented mineral inclusions of the host matrix rock; preferential incorporation of MREE over other REE in the core nodules, consistent with diagenetic MREE-rich environmental/mineralized fluids supplied by the dehydration of Variscan sedimentary marine sequences with phosphatic rocks, at the start of nodule formation. The slight increase in Ca towards the nodule rims denotes a relative increase in fluid salinity during nodule growth, consistent with the ineffectiveness of metamorphic dewatering in dissolving the significant salt content of those marine sequence(s); Th increment in nodule rims points to the temperature increment at this stage; its moderately to pronouncedly negative Eu anomalies and the general involvement of the cheralitic substitution mechanism are characteristic of metamorphic monazites. Monfortinho and other published data suggest that in the beginning of nodular monazite formation the fractionation (La/Sm) N tended to be lower than that of the original source (detrital relic mineral/seawater), very similar to primary synsedimentary apatite or to monazite nodules interpreted to have precipitated directly from seawater. At the end the fractionation values can be substantially higher than those and may be dependent on the conditions established during the different geologic environments.pt_PT
dc.description.versioninfo:eu-repo/semantics/publishedVersionpt_PT
dc.identifier.citationSalgueiro, Rute... [et.al.] - Alluvial nodular monazite in Monfortinho (Idanha-a-Nova, Portugal): Regional distribution and genesis. In: Journal of Geochemical Exploration, 2020, Vol. 210, article nº 106444pt_PT
dc.identifier.doi10.1016/j.gexplo.2019.106444pt_PT
dc.identifier.issn0375-6742
dc.identifier.urihttp://hdl.handle.net/10400.9/3529
dc.language.isoengpt_PT
dc.peerreviewedyespt_PT
dc.publisherElsevierpt_PT
dc.relation.publisherversionhttps://doi.org/10.1016/j.gexplo.2019.106444pt_PT
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/pt_PT
dc.subjectMineraispt_PT
dc.subjectMonazitept_PT
dc.subjectAluviõespt_PT
dc.subjectTerras raraspt_PT
dc.subjectZona Centro Ibérica (Portugal)pt_PT
dc.subjectMonfortinho (concelho de Idanha-a-Nova, Portugal)pt_PT
dc.titleAlluvial nodular monazite in Monfortinho (Idanha-a-Nova, Portugal): Regional distribution and genesispt_PT
dc.typejournal article
dspace.entity.typePublication
oaire.citation.titleJournal of Geochemical Explorationpt_PT
oaire.citation.volume210pt_PT
person.familyNameSalgueiro
person.familyNameInverno
person.familyNamede Oliveira
person.familyNameGuimarães
person.familyNameRosa
person.givenNameRute
person.givenNameCarlos
person.givenNameDaniel Pipa Soares
person.givenNameFernanda
person.givenNameDiogo
person.identifier2216267
person.identifier.ciencia-idA11D-DDD7-29F2
person.identifier.ciencia-idCC15-B6CC-084A
person.identifier.orcid0000-0002-3740-2965
person.identifier.orcid0000-0002-0806-5330
person.identifier.orcid0000-0002-6338-8845
person.identifier.orcid0000-0001-6961-9256
person.identifier.orcid0000-0003-0160-5215
person.identifier.ridI-4511-2017
person.identifier.scopus-author-id7006112964
rcaap.rightsopenAccesspt_PT
rcaap.typearticlept_PT
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relation.isAuthorOfPublication.latestForDiscovery428698aa-a691-4084-8e51-9dcf2f8c735a

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