Petalite as determinant of maximum lithium content of Variscan pegmatites from NW Portugal – paragenetic and geochemical approach

Estudos petrológicos de aplito-pegmatitos Variscos, de tipo LCT, intrusivos em terrenos Silúricos do NW de Portugal, mostraram que o intercrescimento de espodumena + quartzo, em proporção modal 1:2, é persistente em dispositivos texturais circunscritos que podem ser interpretados como agregados miméticos, pseudomórficos após petalite em subsolvus, os quais depois evoluem sujeitos à deformação, metamorfismo e alteração. Cerca de 6 % dos corpos aplito-pegmatíticos que afloram naqueles terrenos, apresentam estes intercrescimentos, ou p etalite primária, a valores de Li2O situados no intervalo de 0,5 a 2,5 %. Uma sistemática químico - mineralógica das fácies analisadas sugere que o valor máximo de 2,5 % de Li2O em rocha total, pode ser considerado uma barreira geoquímica, imposta por um determinante petalítico primário cuja prevalência é balizada pelo equilíbrio com os feldspatos e pela magnitude da alteração argílica e correspondente lixiviação de LiPetrologica l studies of Variscan LCT aplite-pegmatites, hosted in Silurian metamorphic suites in Northwestern Portugal, revealed that the intergrowths of spodumene+quartz, in modal proportions 1:2, is ubiquitous in concealed pegmatite intergrowths, which can be interpreted as mimetic aggregates, pseudomorphic after petalite, that, afterwords, evolve, under changing conditions of metamorphism, deformation and alteration. 6% of the aplite –pegmatite bodies individualized in those Silurian host- rocks show this kind of intergrowths, or primary petalite, at a Li2O range between 0.5 % and 2.5 %. A chemical-mineralogical systematics of the composition data suggests that the maximum value of 2.5 % Li2O, in whole-rock analysis, should be considered a geochemical barrier imposed by a primary petalitic determinant and framed by the equilibrium with feldspars and by the magnitude of argillic alteration and corresponding lithium leaching(undefined)info:eu-repo/semantics/publishedVersio

Typology and evolution of the new mineralogy developed at the mine waste dump of Valdarcas (Vila Nova de Cerveira - N Portugal) - Environmental Implications

[Abstract] The abandoned waste dump of Valdarcas tungsten skarn deposit — Vila Nova de Cerveira, N Portugal, represents a key site, appropriate to study the environmental problems related to deactivated sulfide tails. The tungsten mineralization which occurs in coexistence with metallic sulfide minerals, calcium silicates and carbonates, confers to this deposit special characteristics. The water-mineral interactions at the waste dump surface, leads to the generation of acid mine waters (AMD) with high content of metals and sulfate (ASW), related to the sulfide minerals alteration. Consequently occurs the contamination of the Coura river system Simultaneously the alteration of calcium silicates and carbonates produces neutralization reactions, and the development of a new mineralogy - soluble salts, iron crusts and clay minerals. The new paragenesis reflects the occurrence of wet-dry cycles, related to the seasonal variations of rainfall. These geochemical trends and their role in the process evolution of the waste dump surface to the stabilization are the main subject of this work.The soluble salts, iron crusts and the clay minerals have different capacities and mechanisms to fixate the chemical potential associated to the AMD/ASW. The instability of the salt minerals leads only to a temporary fixation of the contaminant elements. On the other hand, the crusts are capable of fixate efficiently these elements, specially the iron oxides, furthermore, they isolate the reactive minerals from the weathering agents. Consequently they limit the aquatic contamination, the dispersion area of the environmental impact and contribute to the chemical stabilization of the waste dum

Património mineiro da Serra de Arga - Minho

O A Região da Serra d’Arga apresenta grande diversidade litológica, de depósitos minerais e mineralizações metálicas (Au, Ag, Sn, Nb-Ta, W, Zn, Li), razão pela qual tem sido palco de vários ciclos de aproveitamento extractivo. Destes subsistem diversos vestígios mineiros na paisagem, na organização do território e na memória colectiva das comunidades. O funcionamento mineiro passado revelou ainda um importante património natural - geológico e, bem assim, se expressa num conjunto diversificado de vestígios classificáveis como património cultural e industrial mineiro. Muito embora nesta região as evidências associadas ao aproveitamento de recursos minerais se reconheçam desde o Paleolítico, e ainda com grande incidência na época romana, este trabalho analisa vestígios relativos ao séc. XX, dos quais persistam referências documentais e testemunhos da vivência mineira. No estudo usaram-se métodos multidisciplinares de análise, obtendo: 1) a discriminação de indícios de depósitos filonianos explorados e da implantação das áreas intervencionadas e/ou do edificado; 2) a dispersão espacial de vestígios da actividade extractiva, segundo os principais períodos de intervenção (pela análise documental de arquivos e por inquérito sociológico). A sistemática efectuada e a organização segundo divisões geomineiras regionais permitiu deduzir, respectivamente, faixas e campos mineiros que sustentam uma adequada fundamentação para a avaliação do interesse patrimonial mineiro e geológico associado.The Serra d‘Arga Region is characterized by a great diversity of ore and industrial minerals deposits. The overall set of metallizations includes Au, Ag, Sn, Nb-Ta, W, Zn and Li. Owing to this metalliferous diversity and potentiality the region has been the target for several exploration cycles and mining activities since pre-historical times, which remnants are still very present not only in the traditions and cultural heritage of the local resident people, but also in a lot of material remarks, natural and antropic, and ancient sites where industrial mining heritage and some of its most peculiar remains and assets, are preserved. Evidences of mining activities date from Paleolithic times. Afterwards they were strongly diversified, in what concerns the remarks of Roman activities and some post Medieval-Age thecnologies. However, the main goal of the present study is the mine exploitation occurred during de XX century. The approach follows an analytical perspective dedicated to documental references of technical and administrative nature, which are remaining in state and private-companies archives and museums. The local people collective memoir was accessible through opinion survey, planned interviews and inquiries to ancient miners and some known old, still-living, members of the ancient mining population. The material assets remaining in site or preserved in museological context were also considered and studied using analytical geology and mining archaeology procedures. This multidisciplinary approach allowed: 1) the discrimination of the technological remains and geological exposures of the affected ore deposits as well as the systematics of the mining areas and its remaining edification remarks; 2) the description of space dispersion of the mining activities according to the main mining cycles (recognized in field after documental analysis and sociologic inquiries). This systematics, and the study of the regional geological and mining organization, allowed the definition of geological corridors favorable to mineral exploitation and related mining fields, which sustain an adequate background for the evaluation of mining potentialities and the regional value of natural and industrial-archaeological heritage

Amphibolites and associated rocks of Monteiro and Verdes – rift correlation hypothesis for some Silurian terranes of Serra de Arga (Minho)

"VIII Congresso Nacional de Geologia"Nas áreas do Monteiro e Verdes (Serra de Arga) a sucessão metamórfica aflorante compreende anfibolitos e um conjunto de rochas invulgares turmalínicas, fosfáticas e proto-vulcânicas félsicas e máficas. O estudo geoquímico indica assinaturas que se ajustam às tendências alcalinas típicas de ambientes de rift. A proto-alteração sobreposta que se verifica em fácies perianfibólicas relaciona-se com processos de fosfatização, fenitização e dessilicificação. O enriquecimento em Au nestas fácies é compatível com o modelo petrogenético proposto.In the areas of Verdes e Monteiro (Serra de Arga) the outcropping metamorphic succession comprises amphibolites and a set of unusual rocks quite enriched in tourmaline and phosphate, besides felsic and mafic proto-vulcanogenic rocks. The geochemical study indicates alkaline signatures typical of rift environments. The Au-enrichment recorded by altered facies is consistent with the petrogenetic model proposed

The petrogenetic meaning of schorl-dravite transition and apatite association in periamphibolitic tourmalinites – Northern Portugal

Publicado em "Acta Mineralogica-Petrographica. Abstract series

Study of the volcano-sedimentary nature of the Serro formations – Silurian terranes of Serra de Arga – Minho (Northern Portugal)

Petrography and paragenetic analysis of some phyllitic Silurian formations from the North of Serra de Arga (Minho – Northern Portugal) revealed an abnormal modal percentage of iron sulfides in a complex set of lithologies that include amphibolic members and tourmaline-garnet rich horizons as well. Excluding the geochemical influence and expression of superposed metamorphism and metasomatism, whole rock analysis shows conspicuous high Fe and Al percentages and low contents of incompatible elements in some facies. Significant Zn, Mn, Sc, Ba and Sr may be related to the presence of accessory minerals suggesting an exhalitic affinity. Pyrrotite and pyrite are the main sulfides but sphalerite, galena and molybdenite are also present in low quantities. These petrographic and geochemical characteristics and the presence of textural aspects such as clastic and/or porphyric relict geometries support the establishment of some correspondences between the observed rock types and few possible volcanosedimentary or exhalitic ancestors. Whole rock geochemistry also suggests the manifestation of a protolithic polimodal volcanism with a main expression in the felsitic domain with several complex primordial textures indicating that the primitive rock types could be tuffaceous/volcanoclastic to porphyric

Paragenetic diversity in contaminated granite pegmatites – Serra de Arga (Minho)

"VIII Congresso Nacional de Geologia"No Domo de Covas (Serra de Arga), a contaminação de magmas pegmatíticos por reacção com rochas calcossilicatadas, metacarbonatadas e metaexalíticas originam paragéneses dessilicificadas com mineralogia anómala que inclui além da plagioclase, escapolite, fosfatos de Li e minerais de epídoto. A evolução paragenética manifesta-se para uma modificação da atitude dos veios e pode resultar de processos de fraccionação e/ou evolução térmica que culminam na formação de venulações ricas em prenite e associações com oligoclase+escapolite.In Domo de Covas (Serra de Arga), the contamination of pegmatitic magmas by reactions with calcsilicate, metacarbonate and metaexalitic rocks, originate desilicated paragenesis with anomalous mineralogy, that includes in addition to plagioclase, scapolite, Li- phosphates, and epidote minerals. The paragenetic evolution is concomitant to the modification of veins direction and can result from fractionation processes and or thermal changes that culminate in the formation of prehnite veins and oligoclase + scapolite associations

Epidote populations in contaminated granitic pegmatites from Northern Portugal

Publicado em "Acta Mineralogica-Petrographica. Abstract series 6

Petrogenetic repositioning of W-Mo from Silurian to late-D3 Variscan remobilization – Serra de Arga (Minho)

"VIII Congresso Nacional de Geologia"A mineralização tungstífera principal detectada na região da Serra de Arga inclui scheelite e volframite e também raramente tungstenomolibdenite. Esta encontra-se hospedada em suportes litológicos diversos: rochas calcossilicatadas, anfibolitos, segregações de leucossoma e veios de quartzo em cisalhamentos tardi-D3. A mineralização tungstífera primária, possivelmente singenética e ortomagmática e as remobilizações posteriores foram estudadas em microscopia óptica e microssonda, reconhecendo-se tendências de sucessão paragenética e química relacionadas com variações na fO2 dos meios de deposição.The main W mineralization detected in Serra de Arga includes scheelite and wolframite and also rarely W-molybdenite. It is hosted in various lithologies: calcsilicate rocks, amphibolites, leucosomes and quartz veins in late-D3 shear zones. Primary W mineralization, possibly syngenetic to orthomagmatic, and later remobilizations were studied in optical microscope and microprobe, allowing the recognition of trends of paragenetic succession and chemical variation, related to fO2 changes