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

Mining archaeology sites at the Alto Minho region (Northern Portugal) - a management perspective

[Abstract] Archaeological mining sites in northern Portugal include a few roman gold mines in shear zones and the tin and tungsten mining of the first half of the XX century, widespread through the entire Alto Minho region, and related to residual-granite mineralization. Pre-roman vestiges of mineral resources disposal are restricted to Pleistocene industries, without known mining evidences. Better preserved sites represent the tin and tungsten period from which, some testimony of local peculiar technologies, are remaining. From a land use point of view, the preservation of old excavations and ruined plants may be in equilibrium with new mining projects for the mineral resources potential and new forms of tourism regional offe

Orbicular to framboidal textures in sulphide layers from Cerdeirinha Mine – Caminha, Northern Portugal – paragenesis and its relation with the tungsten mineralizations

A oeste de Caminha, rochas silúricas dobradas em antiforme, con- figuram uma megaestrutura denominada Domo de Covas (3a fase Varisca) onde o jazigo da Cerdeirinha ocupa uma posição de charneira. A mine- ralização tungstífera, típica deste jazigo ocorre em rochas calcossilicatadas e horizontes de sulfuretos de Fe, com predominância de pirrotite e pirite. Além das remobilizações metamórfico-metassomáticas, foi reconhecida uma poligénese primitiva vulcanossedimentar a sedimentar-exalativa (SEDEX) que terá produzido o stock metalífero inicial. Os surtos vulcanogénicos seriam bimodais e localmente verificar-se-iam condições para a cristalização de abundantes sulfuretos com tungstatos singenéticos associados. Na corta da Cerdeirinha foi identificado um horizonte estratigráfico onde se concentram nódulos de pirite framboidal, com evidências de sedimentação graduada e texturas orbiculares com mineralizações polimetálicas intersticiais, que são atribuídas a uma metalogenénese distal em contexto SEDEX, posterior- mente sujeita a remobilizações hidrotermais e metassomáticas.To the west of Caminha (Northern Portugal), silurian rocks define a mega antiform known as “Covas Dome” (3rd Variscan folding phase). Cerdeirinha orebody is located at the hinge zone of this structure. Its typical tungsten mineralization occurs in calc-silicate rocks and iron sulphide layers, with dominant pyrrhotite and pyrite. Besides the metamorphic-metasomatic processes, a primitive volcano-sedimentary to sedimentary-exhalative polygenesis would have produced the primitive, syngenetic, metal stock. Related volcanism seems to be bimodal and locally, metallogenic conditions (SEDEX affiliated) where favourable to the precipitation of iron sulphides and syngenetic tungsten minerals. In the Cerdeirinha’s open pit, it was identified a stratigraphic horizon where framboidal pyrite nodules are accumulated evidences of graded bedding, generating some orbicular textures with interstitial polymetallic mineralizations, which are attributed to a distal SEDEX deposition, lately affected by hydrothermal to metassomatic remobilization.(undefined

Anatomia de algumas ocorrências de gemas e seu enquadramento em protocolos de ordenamento territorial – contributo para uma reflexão sobre o estatuto dos depósitos gemíferos portugueses

[Abstract] Anatomy and Classification of Portuguese Gemstone Deposits and their inclusion in Territorial Management Protocols - The concept of gemstone resources includes the consideration of aspects such as the genetic type of deposits, geographical location and geological characterization of the ores. Based on archeological evidences and assuming the geological potentiality it is possible to consider the existence of resources base with gem quality, in Portugal. The main deposits are related to residual granite systems. In order to ensure a sustainable use, economical or patrimonial, it is necessary to classify these occurrences in a context of land management. This paper presents the typology of the most interesting occurrences considering its economical and patrimonial potentiality

Pegmatite productive terrains in the Variscan Granite hosts from Northern and Central Portugal

The detection of suboutcropping pegmatite deposits in regions recognizably fertile regarding the occurrence of pegmatites depends upon the optimization of conceptual models which support the interpretation of the regional distribution of pegmatites and the structure of their assemblies. In intra-granitic context is at concern the more conventional cartographic expression of pegmatites in connection with the structuring of granitic cupolas. The establishment of occurrence situations linked to certain lithological units or structural alignments is a pathway for the delimitation of productive research areas. Some productivity situations deduced from geological mapping include: accommodation in preferred structural directions, proximity to mixing-mingling corridors, certain petrographic structuring units that reflect irregularities in terms of flow and fractionation processes, and trends of hydrothermal and supergene alteration of host granitic masses. The detection of these aspects, to regard as exploration guides, can avail itself of remote sensing, as they represent contrasting chromatic lithotypes with sufficient surface continuity.(undefined

Contributions to pegmatite exploration within granitic plutons in Central and Northern Portugal

Exploration programs for granitic pegmatites face the lack of detectable contrasts, either geophysical or geochemical, between pegmatites and their granitic host-rocks. The known productive sectors bearing pegmatites located inside granitic plutons, with economic interest for quartz and feldspar provide adequate field testing for alternative research, dealing with the peculiarities of lithological diversity and the arrangement of structural elements, around pegmatite swarms at suitable granite cupolas. The most efficient assessment for pegmatite positioning in tactical stages of exploration is the use of geological factors analyzed through raw or specifically treated remote imagery, enhancing the favorable lineaments and the most productive granite-host matrixes. The identification of targets using this approach led to a reasonable success tested by experimental drilling in some selected sites

Geological mapping of the Cabeço de Vide basic-ultrabasic complex: essay on geometry and metalogenesis potential

A área detém as características mínimas necessárias ao desenvolvimento da prospecção de sulfuretos magmáticos primários e mineralizações de platinóides: litologias básicas e ultrabásicas e teores de Ni, Cu, Pt e Pd, anómalos. Na cartografia à escala 1:10 000 individualizam-se quatro domínios geológicos: litologias ultrabásicas, gabróicas, o domínio metassomático, e calcários do Câmbrico. O complexo básico e ultrabásico terá resultado de dois episódios de instalação ígnea, sendo o impulso ultrabásico anterior ao que originou os gabros.The area holds minimal characteristics that are needed to develop Magmatic sulphide deposits and PGE mineralization: basic and ultrabasic lithologies and anomalous Ni, Cu, Pt, Pd grades. It is possible to discriminate four geological domains based on 1: 10 000 mapping of the area: ultrabasic lithologies, gabbroic lithologies, metasomatic rocks and Cambrian limestones. The basic-ultrabasic complex might have resulted from two different magmatic pulses (the ultrabasic event preceding the gabroic pulse)

Utilização do fosfato de tapira em dietas de frangos de corte.

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