Main characteristics and genesis of the Vale de Pães skarn (Cuba-Vidigueira, Ossa Morena Zone, Portugal)

The Vale de Pães (Cuba-Vidigueira) mineralisation is composed of magnetite ± sulphides and hosted in a Pre-Variscan metamorphic sequence intruded by igneous rocks belonging to the Beja Igneous Complex. Its mineral and chemical features are compatible with a zoned Fe-skarn: Mg-rich (Fo + Di90, oxidised) and Ca-rich (Grs + Di81-39, oxidised or relatively reduced). In the Fe-Mg skarn, magnetite deposition occurred along with the anhydrous mineral assemblage at ≈ 600 °C; sulphides precipitated from the retrograde stage onset (≤ 550 °C) and during the hydrated and carbonate phases formation period (< 420 °C). In the Fe-Ca skarn, magnetite precipitated during the retrograde stage (< 550 °C) together with the hydrated mineral association, and was followed by sulphides at ≈ 400°C. The mineralising process involved moderate-high salinity fluids and was controlled by variations in redox potential and pH.info:eu-repo/semantics/publishedVersio

Principales características y génesis del skarn de Vale de Pães (Cuba-Vidigueira, Ossa Morena Zone, Portugal)

The Vale de Pães (Cuba-Vidigueira) mineralisation is composed of magnetite ± sulphides and hosted in a Pre-Variscan metamorphic sequence intruded by igneous rocks belonging to the Beja Igneous Complex. Its mineral and chemical features are compatible with a zoned Fe-skarn: Mg-rich (Fo + Di90, oxidised) and Ca-rich (Grs + Di81-39, oxidised or relatively reduced). In the Fe-Mg skarn, magnetite deposition occurred along with the anhydrous mineral assemblage at ≈ 600 °C; sulphides precipitated from the retrograde stage onset (≤ 550 °C) and during the hydrated and carbonate phases formation period (< 420 °C). In the Fe-Ca skarn, magnetite precipitated during the retrograde stage (< 550 °C) together with the hydrated mineral association, and was followed by sulphides at ≈ 400°C. The mineralising process involved moderate-high salinity fluids and was controlled by variations in redox potential and pH.La mineralización del Vale de Pães (Cuba-Vidigueira), compuesta de magnetita ± sulfuros, se produce dentro de una secuencia metamórfica ante-Varisca intruida por el Complejo Ígneo de Beja (Beja Igneous Complex). Sus características químicas y mineralógicas son consistentes con un skarn de Fe zonificado: rico en Mg (Fo + Di≈90, oxidado) y rico en Ca (Grs + Di81-39, oxidado o relativamente reducido). En el skarn de Fe-Mg, la deposición de magnetita acompaña a la paragénesis mineral anhidra (≈ 600 °C); la precipitación de sulfuros se produce desde el comienzo de la etapa retrógrada (≤ 550 °C) y continuó durante la formación de fases hidratadas y carbonatadas (< 420 °C). En el skarn de Fe-Ca, la magnetita se genera en la fase de retroceso (< 550 °C), en relación con la asociación de minerales hidratados, seguido de sulfuro (≈ 400 °C). El proceso de mineralización de los fluidos de salinidad moderada-alta era controlado por los cambios en el potencial redox y el pH

Matching characteristic codes: exploiting two directions

Combining incoming and outgoing characteristic formulations can provide numerical relativists with a natural implementation of Einstein's equations that better exploits the causal properties of the spacetime and gives access to both null infinity and the interior region simultaneously (assuming the foliation is free of caustics and crossovers). We discuss how this combination can be performed and illustrate its behavior in the Einstein-Klein-Gordon field in 1D.Comment: 10 pages, 9 postscript figures. To appear in Int. Journ. of Mod. Phys.

Ocorrência de xenótimo em amostras aluvionares da região centro-leste de Portugal, Zona Centro Ibérica-Zona de Ossa Morena

Foi identificado, possivelmente pela primeira vez em Portugal, xenótimo aluvionar em concentrados de bateia colhidos numa campanha de prospecção de terras raras desenvolvida pelo ex-IGM no centro-leste deste país. O xenótimo ocorre em grãos sub-rolados de dimensão média =250um, em concentrações mais significativas em Nisa, Stº António das Areias e Marvão. A geologia regional e o cortejo mineral das amostras sugerem proveniência do xenótimo dos maciços graníticos de Penamacor e Nisa e ainda das Arcoses da Beira Baixa e níveis de cascalheiras plio-plistocénicas com intercalações argilo-arenosas

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

ABSTRACT: 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.info:eu-repo/semantics/publishedVersio

Time and Observables in Unimodular General Relativity

A cosmological time variable is emerged from the hamiltonian formulation of unimodular theory of gravity to measure the evolution of dynamical observables in the theory. A set of constants of motion has been identified for the theory on the null hypersurfaces that its evolution is with respect to the volume clock introduced by the cosmological time variable.Comment: 16 page

Alluvial xenotime and heavy minerals assemblage from the northern edge of Nisa-Albuquerque Batholith, eastern Portugal : provenance and geochemical implications

Alluvial xenotime and heavy minerals assemblage from the northern edge of Nisa-Albuquerque Batholith, eastern Portugal : provenance and geochemical implications / Rute Salgueiro... [et al.]. - Amsterdam : Elsevier, 2014. - [18] p. : il., 13 figuras e 8 tabelas ; 30 cm The xenotime-bearing heavy mineral assemblages present in the alluvial samples from Vila Velha de Ródão, Nisa, Póvoa e Meadas and Sto. António das Areias, localized in the northern edge of Nisa-Albuquerque Batholith, Eastern Portugal, were studied in detail. The insights for mineral provenance came from the analysis of the drainage network and from the composition of the regional alluvial samples and outcropping lithologies. Since xenotime is a mineral with economic interest, the motivation of the current work is its contribution for exploration studies, considering the potential information contained in the alluvial samples. In the study region, the alluvial heavy minerals and their morphology reflect clearly the mineralogy and relative distance to their source, respectively. In alluvial samples with direct provenance from the Nisa granite (late Carboniferous), the increase in xenotime concentration and decrease in monazite, apatite, zircon, ilmenite and iron oxide concentration, from W (Nisa) to E (Sto. António das Areias), matches the increase in P2O5 and decrease in REE, CaO, Zr, TiO2, and Fe2O3 contents in granite rocks. The geochemical signature of xenotime studied reveals an igneous source, characterized by the characteristic strong Eu negative anomaly in REE patterns. Their YPO4 values (72–78 mol%) are similar to xenotime from Erzgebirge (Germany) granites. The high values of Y/Ho (50–71) and, in some cases, downward kinks at Ho in REE plots, suggest generation in late stages of crystallization and association with a siliceous evolved magmatic system. The slight decrease in HREE contents in xenotime, from W to E, and Ho anomalies in the normalized REE pattern are similar to those identified in the Nisa granite, which supports the sourcing of xenotime from these granitic rocks. The genetic development of the batholith chemical zonation (more evolved to E) seems to have favoured the generation of xenotime instead of apatite, monazite and zircon, in the eastern end area (Sto. António das Areias). Supporting the geochemical signature, the alluvial zircons also display morphological typologies that are compatible with provenance from peraluminous granites formed at temperatures of 600–700 °C, possibly from the Nisa granite. Since all xenotime grains show the same magmatic affinity, this leads to the hypothesis that the xenotime from the Vila Velha de Ródão sample, with provenance from Cenozoic sedimentary rocks, has been transported to this northern area, after been disaggregated from Nisa batholith granites, most probably by braided anastomosing and erratically sandy channels, that explains its actual position in the opposite bank of the Tagus river. This phosphate has been deposited with other sediments in tectonic depressions and subsequently included in the formation of sedimentary rocks. The greater development of Ca, Th and U phosphate inclusions/substitutions in these xenotime grains can be explained by the chemical mobility provided during all the geological processes