Helium transfer from water into quartz crystals: A new approach for porewater dating

Several important fundamental and applied problems require a quantification of slow rates of groundwater flow. To resolve these problems helium appears to be a promising tracer. In this contribution we discuss a new approach, which gives the helium inventory in a rock – pore water system by using the relevant mineral record, i.e., without extraction and investigation of the porewater samples. Some U- and Th-poor minerals such as quartz (quartz separates from Permo-Carboniferous Formation, sandstone–shale interlayering, Molasses Basin, Northern Switzerland, hereafter PCF, are used in this study) contain excessive helium having migrated into their internal helium-accessible volume (HAV) from the surrounding porewater [I.N. Tolstikhin, B.E. Lehmann, H.H. Loosli, A. Gautschi, Helium and argon isotopes in rocks, minerals and related groundwaters: a case study in Northern Switzerland, Geochim. Cosmochim. Acta 60 (1996) 1497–1514]. These volumes are estimated by using helium as a nano-size penetrating tool, i.e., by saturation of the minerals with helium under controlled pressure–temperature conditions and subsequent measurements of the helium-saturated concentrations. In the quartz separates HAV/total volume ratios vary from 0.017% to 0.16%; along with the measured initial (unsaturated) He concentration the HAV gives the internal helium pressure, the mean value obtained for 7 samples (25 sample aliquots) is P=0.45F0.15 atm (1 r). The product of helium pressure and solubility (7.35_10_3 cc STP He/cc H2O for the temperature and salinity of PCF aquifers reported in [F.J. Pearson, W. Balderer, H.H. Loosli, B.E. Lehmann, A. Matter, T. Peters, H. Schmassmann, A. Gautschi, Applied Isotope Hydrogeology–A Case Study in Northern Switzerland, Elsevier Amsterdam, 1991, 439 pp.]) is the mineral-derived He concentration in the respective porewater, CPW=0.0035F0.0017 cc He/cc H2O. This value is in full accord with measured He concentrations in PCF aquifers, CPCF, varying from 0.0045 to 0.0016 cc He/cc H2O. This agreement validates the proposed approach and also shows that the mineral–porewater helium–concentration equilibrium has been established. Indeed, estimates of the He-migration rates through our quartz samples show that in ~6000 years the internal pressure should equilibrate with He-concentration in related porewater of PCF, and this time interval is short compared to independent estimates [I.N. Tolstikhin, B.E. Lehmann, H.H. Loosli, A. Gautschi, Helium and argon isotopes in rocks, minerals and related groundwaters: a case study in Northern Switzerland, Geochim. Cosmochim. Acta 60 (1996) 1497–1514]. The helium inventory in the rock–porewater assemblage shows that helium abundance in pore waters is indeed important. In shale samples (with ~15% porosity) porewaters contain more helium than the host minerals altogether. Porewater heliumconcentration profiles, available from the mineral record, along with helium production rates are input parameters allowing model(s) of helium migration through a hydrological structure to be developed. Quite high helium concentrations in PCF porewaters imply slow removal mechanisms, which will be discussed elsewhere.

Morphological ripening of fluid inclusions and coupled zone-refining in quartz crystals revealed by cathodoluminescence imaging: Implications for CL-petrography, fluid inclusion analysis and trace-element geothermometry

Cathodoluminescence (CL) studies have previously shown that some secondary fluid inclusions in luminescent quartz are surrounded by dark, non-luminescent patches, resulting from fracture-sealing by late, trace-element-poor quartz. This finding has led to the tacit generalization that all dark CL patches indicate influx of low temperature, late-stage fluids. In this study we have examined natural and synthetic hydrothermal quartz crystals using CL imaging supplemented by in-situ elemental analysis. The results lead us to propose that all natural, liquid-water-bearing inclusions in quartz, whether trapped on former crystal growth surfaces (i.e., of primary origin) or in healed fractures (i.e., of pseudosecondary or secondary origin), are surrounded by three-dimensional, non-luminescent patches. Cross-cutting relations show that the patches form after entrapment of the fluid inclusions and therefore they are not diagnostic of the timing of fluid entrapment. Instead, the dark patches reveal the mechanism by which fluid inclusions spontaneously approach morphological equilibrium and purify their host quartz over geological time. Fluid inclusions that contain solvent water perpetually dissolve and reprecipitate their walls, gradually adopting low-energy euhedral and equant shapes. Defects in the host quartz constitute solubility gradients that drive physical migration of the inclusions over distances of tens of μm (commonly) up to several mm (rarely). Inclusions thus sequester from their walls any trace elements (e.g., Li, Al, Na, Ti) present in excess of equilibrium concentrations, thereby chemically purifying their host crystals in a process analogous to industrial zone refining. Non-luminescent patches of quartz are left in their wake. Fluid inclusions that contain no liquid water as solvent (e.g., inclusions of low-density H2O vapor or other non-aqueous volatiles) do not undergo this process and therefore do not migrate, do not modify their shapes with time, and are not associated with dark-CL zone-refined patches. This new understanding has implications for the interpretation of solids within fluid inclusions (e.g., Ti- and Al-minerals) and for the elemental analysis of hydrothermal and metamorphic quartz and its fluid inclusions by microbeam methods such as LA-ICPMS and SIMS. As Ti is a common trace element in quartz, its sequestration by fluid inclusions and its depletion in zone-refined patches impacts on applications of the Ti-in-quartz geothermometer.

Correlation between thermoluminescence sensitivity and crystallization temperatures of quartz: Potential application in geothermometry

The thermoluminescence (TL) characteristics of quartz are highly dependent of its thermal history. Based on the enhancement of quartz luminescence occurred after heating, some authors proposed to use quartz TL to recover thermal events that affected quartz crystals. However, little is know about the influence of the temperature of quartz crystallization on its TL characteristics. In the present study, we evaluate the TL sensitivity and dose response curves of hydrothermal and metamorphic quartz with crystallization temperatures from 209 +/- 15 to 633 +/- 27 degrees C determined through fluid inclusion and mineral chemistry analysis. The studied crystals present a cooling thermal history, which allow the acquiring of their natural TL without influence of heating after crystallization. The TL curves of the studied samples present two main components formed by different peaks overlapped around 110 C and 200-400 degrees C. The TL sensitivity in the 200-400 degrees C region increases linearly with the temperature of quartz crystallization. No relationship was observed between temperatures of quartz crystallization and saturation doses (<100 Gy). The elevated TL sensitivity of the high temperature quartz is attributed to the control exerted by the temperature of crystallization on the substitution of Si(4+) by ions such as Al(3+) and Ti(4+), which produce defects responsible for luminescence phenomena. The linear relationship observed between TL in the 200-400 degrees C region and crystallization temperature has potential use as a quartz geothermometer. The relative abundance of quartz in the earth crust and the easiness to measure TL are advantageous in relation to geothermometry methods based on chemistry of other minerals. (C) 2010 Elsevier Ltd. All rights reserved.

Helium in solubility equilibrium with quartz and porefluids in rocks - a new approach in hydrology

Quartz crystals in sandstones at depths of 1200 m–1400 m below the surface appear to reach a solubility equilibrium with the 4He-concentration in the surrounding pore- or groundwater after some time. A rather high 4Heconcentration of 4.5x10E-3 cc STP 4He/cm3 of water measured in a groundwater sample would for instance maintain a He pressure of 0.47 atm in a related volume. This value is equal within analytical error to the pressure deduced from the measured helium content of the quartz and its internal helium-accessible volume. To determine this volume, quartz crystals of 0.1 to 1 mm were separated from sandstones and exposed to a helium gas pressure of 32 atm at a temperature of 290°C for up to 2 months. By crushing, melting or isothermal heating the helium was then extracted from the helium saturated samples. Avolume on the order of 0.1% of the crystal volume is only accessible to helium atoms but not to argon atoms or water molecules. By monitoring the diffusive loss of He from the crystals at 350°C an effective diffusion constant on the order of 10E-9 cm2/s is estimated. Extrapolation to the temperature of 70°C in the sediments at a depth of 1400 m gives a typical time of about 100 000 years to reach equilibrium between helium in porewaters and the internal He-accessible volume of quartz crystals. In a geologic situation with stagnant pore- or groundwaters in sediments it therefore appears to be possible with this new method to deduce a 4He depth profile for porewaters in impermeable rocks based on their mineral record.

Simulation and implementation of a tunable C-band dielectric resonator oscillator

Microwave sources used in present day applications are either multiplied source derived from basic quartz crystals, or frequency synthesizers. The frequency multiplication method increases FM noise power considerably, and has very low efficiency in addition to being very complex and expensive. The complexity and cost involved demands a simple, compact and tunable microwave source. A tunable dielectric resonator oscillator(DRO) is an ideal choice for such applications. In this paper, the simulation, design and realization of a tunable DRO with a center frequency of 6250 MHz is presented. Simulation has been carried out on HP-Ees of CAD software. Mechanical and electronic tuning features are provided. The DRO operates over a frequency range of 6235 MHz to 6375 MHz. The output power is +5.33 dBm at centre frequency. The performance of the DRO is as per design with respect to phase noise, harmonic levels and tunability. and hence, can conveniently be used for the intended applications.

利用石英晶体平凸透镜实现激光束的空间整形

基于石英晶体的旋光特性，我们提出利用石英晶体平凸透镜和偏振片来实现线偏振光的空间强度整形，通过控制入射光的偏振方向可以方便地改变输出激光的空间强度分布。

Brumadoite, a new copper tellurate hydrate, from Brumado, Bahia, Brazil

Brumadoite, ideally Cu(2)Te(6+)O(4)(OH)(4)center dot 5H(2)O, is a new mineral from Pedra Preta mine, Serra das Eguas, Brumado, Bahia, Brazil. It occurs as microcrystalline aggregates both on and, rarely, pseudomorphous after coarse-grained magnesite, associated with mottramite and quartz. Crystals are platy, subhedral, 1-2 mu m in size. Brumadoite is blue (near RHS 114B), has a pale blue streak and a vitreous lustre. It is transparent to translucent and does not fluoresce. The empirical formula is (Cu(2.90)Pb(0.04)Ca(0.01))(Sigma 2.95) (Te(0.93)(6+)Si(0.05))(Sigma 0.98)O(3.92)(OH)(3.84)center dot 5.24H(2)O. Infrared spectra clearly show both (OH) and H(2)O. Microchemical spot tests using a KI Solution show that brumadoite has tellurium in the 6(+) state. The mineral is monoclinic, P2(1)/m or P2(1). Unit-cell parameters refined from X-ray powder data are a 8.629(2) angstrom, b 5.805(2) angstrom, c 7.654(2) angstrom, beta 103.17(2)degrees, V 373.3(2) angstrom(3), Z = 2. The eight strongest X-ray powder-diffraction lines [d in angstrom, (l),(hkl)] are: 8.432,(100),(100); 3.162,(66),((2) over bar 02); 2.385,(27),(220); 2.291,((1) over bar 12),(22); 1.916,(11),(312); 1.666,(14),((4) over bar 22,114); 1.452,(10), (323, 040); 1.450,(10),(422,403). The name is for the type locality, Brumado, Bahia, Brazil. The new mineral species has been approved by the CNMNC (IMA 2008-028).

Automatic devices for monitoring environmentally induced auto-oxidative degradation of artistic materials in conservation sites

This paper describes an automatic device for in situ and continuous monitoring of the ageing process occurring in natural and synthetic resins widely used in art and in the conservation and restoration of cultural artefacts. The results of tests carried out under accelerated ageing conditions are also presented. This easy-to-assemble palm-top device, essentially consists of oscillators based on quartz crystal resonators coated with films of the organic materials whose response to environmental stress is to be addressed. The device contains a microcontroller which selects at pre-defined time intervals the oscillators and records and stores their oscillation frequency. The ageing of the coatings, caused by the environmental stress and resulting in a shift in the oscillation frequency of the modified crystals, can be straightforwardly monitored in this way. The kinetics of this process reflects the level of risk damage associated with a specific microenvironment. In this case, natural and artificial resins, broadly employed in art and restoration of artistic and archaeological artefacts (dammar and Paraloid B72), were applied onto the crystals. The environmental stress was represented by visible and UV radiation, since the chosen materials are known to be photochemically active, to different extents. In the case of dammar, the results obtained are consistent with previous data obtained using a bench-top equipment by impedance analysis through discrete measurements and confirm that the ageing of this material is reflected in the gravimetric response of the modified quartz crystals. As for Paraloid B72, the outcome of the assays indicates that the resin is resistant to visible light, but is very sensitive to UV irradiation. The use of a continuous monitoring system, apart from being obviously more practical, is essential to identify short-term (i.e. reversible) events, like water vapour adsorption/desorption processes, and to highlight ageing trends or sudden changes of such trends. (C) 2007 Elsevier B.V. All rights reserved.

Investigação das propriedades ópticas, elétricas e estruturais em ametista

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Opalas gemológicas do Piauí: gênese revelada por microtermometria e minerais associados

As opalas de Pedro II e Buriti dos Montes, no estado do Piauí, constituem as mais importantes ocorrências brasileiras dessa gema, tanto em termos de volume quanto pela qualidade gemológica, que é comparável à das famosas opalas australianas. No entanto, a informalidade na extração e comercialização destas opalas, assim como a falta de informações quanto à gênese destes depósitos não permitem a prospecção por novas jazidas e o estabelecimento de um certificado de procedência para as opalas do Piauí que permitisse sua inserção formal no mercado gemológico internacional. Alguns autores têm se dedicado ao estudo dessas opalas, revelando fortes evidências de sua origem hidrotermal, mas até então, nenhum trabalho abordou as características físico-químicas dos fluidos que teriam originado esses depósitos de opalas. Diante disso, o principal objetivo deste trabalho foi entender o sistema hidrotermal responsável pela gênese das opalas do Piauí, ou seja, caracterizar os fluidos que originaram a mineralização e mostrar sua relação com o contexto geológico da região. Os municípios de Pedro II e Buriti dos Montes se localizam na porção nordeste do estado do Piauí, a aproximadamente 230 km a leste da capital Teresina, e as ocorrências de opala se encontram na porção basal da Bacia do Parnaíba, constituindo veios e vênulas nos arenitos dos grupos Serra Grande (Buriti dos Montes) e Canindé (Pedro II), os quais são seccionados por soleiras e diques de diabásio da Formação Sardinha. Elas também ocorrem cimentando brechas e como depósitos coluvionares e de paleocanal. Associados às opalas, localmente encontram-se veios de quartzo, calcedônia, barita e hematita (ou goethita). De maneira geral, as opalas de Pedro II apresentam jogo de cores, são predominantemente brancas ou azuladas com aspecto leitoso, semitranslúcidas a opacas e com inclusões sólidas pouco aparentes. Em contrapartida, as opalas de Buriti dos Montes não apresentam jogo de cores, a cor varia entre amarelo claro e vermelho amarronzado, são semitransparentes a translúcidas e contêm grande variedade de inclusões sólidas. Os dados obtidos revelam que as opalas de Pedro II são tipicamente do tipo amorfo (opala-A), enquanto as opalas de Buriti dos Montes variam entre amorfas e cristobalita-tridimita (opala-CT). Na opala preciosa, o típico jogo de cores é causado pelo arranjo regular das esferas de sílica que as constituem. A ausência de cimento opalino entre as esferas reforça a beleza desse efeito. Em contrapartida, as opalas laranja não apresentam jogo de cores, mas têm maior transparência devido ao diminuto tamanho das esferas. As inclusões sólidas também produzem belos efeitos nas opalas estudadas, principalmente na variedade laranja, que é mais transparente. Além disso, o conjunto de inclusões sólidas revela características intrínsecas aos processos hidrotermais que originaram as opalas estudadas. Agregados botrioidais, dendríticos e nodulares são exemplos de inclusões formadas por fragmentos dos arenitos hospedeiros carreados pelos fluidos hidrotermais que geraram as opalas. As inclusões sólidas também têm relação direta com a cor das opalas. Nas opalas de Buriti dos Montes, os tons de vermelho, laranja e amarelo são produzidos pela dissolução parcial das inclusões constituídas por oxihidróxidos de Fe. De maneira semelhante, a cor verde nas opalas preciosas está relacionada aos microcristais de Co-pentlandita inclusos nas mesmas. O conjunto de minerais associados às opalas conduz a uma assinatura mineralógicogeoquímica marcada pelos elevados teores de Fe e Al nas opalas com inclusões de hematita/goethita e caulinita, e assim também com aumento considerável dos teores de elementos terras raras nas opalas em que se concentram as inclusões de caulinita e apatita. Entre os elementos-traço, Ba é o mais abundante, e provavelmente foi incorporado pelo fluido hidrotermal, tendo em vista que veios de barita são encontrados com frequência nessa região da Bacia do Parnaíba. Várias feições como estruturas de fluxo nas opalas, corrosão e dissolução parcial dos cristais de quartzo hialino e de inclusões mineralógicas, vênulas de quartzo hidrotermal sobrecrescidas aos grãos detríticos, e zoneamento dos cristais de quartzo confirmam que essas opalas têm origem hidrotermal. A ruptura do Gondwana teria provocado um vasto magmatismo básico fissural, que por sua vez foi responsável pelo aporte de calor que gerou as primeiras células convectivas de fluidos quentes. A água contida nos arenitos certamente alimentou o sistema e se enriqueceu em sílica através da dissolução parcial ou total dos próprios grãos de quartzo dos arenitos. Este fluido hidrotermal foi posteriormente aprisionado em sistemas de fraturas e nelas se resfriou, precipitando a opala e minerais associados.

Quartzo e zircão como marcadores da evolução magmático-hidrotermal do Granito Antônio Vicente, Suíte Intrusiva Velho Guilherme, Província Carajás

Quatro tipos morfológico-texturais de quartzo, informalmente denominados Qz1, Qz2, Qz3 e Qz4, foram identificados nas diferentes fácies do Granito Antônio Vicente, Província Carajás, por meio de imagens de microscopia eletrônica de varredura-catodoluminescência (MEV-CL). Nas rochas menos evoluídas, contendo anfibólio e biotita, dominam cristais anédricos a subédricos bem desenvolvidos, luminescentes e intensamente fraturados (Qz1). Fluidos hidrotermais que percolaram o granito transformaram o quartzo magmático (Qz1) em Qz2 e Qz3 por meio de processos de alteração, dissolução e recristalização, sendo essas transformações muito mais evidentes nas rochas sienograníticas intensamente alteradas. O Qz4 forma cristais médios a grossos, geralmente luminescentes e comparativamente pouco fraturados. Sua ocorrência é restrita às rochas sienograníticas fortemente hidrotermalizadas e aos corpos de greisens, sugerindo o início do processo de greisenização. Nos greisens, dominam cristais de quartzo euédricos médios a grossos, zonados concentricamente e com feições típicas de origem hidrotermal (Qz5). Finos cristais de cassiterita zonada (≤ 100 µm) são comuns e preenchem cavidades nos tipos Qz4 e Qz5. Zircões dominantemente anédricos, corroídos, com os mais elevados conteúdos de Hf e as mais baixas razões Zr/Hf, pertencem às rochas mais evoluídas e alteradas hidrotermalmente e aos corpos de greisens associados, ambos portadores de mineralizações de Sn. Tal fato sugere que a assinatura geoquímica do zircão, em especial a razão Zr/Hf, pode ser utilizada na avaliação preliminar do potencial metalogenético de granitos estaníferos.

A cor do citrino: efeito de irradiação e tratamento térmico

Quartz crystals under natural or artificial irradiation can acquire dark shades and variations btween smoky, black and brown but when submitted at heat-treatment they can become greenish, yellowish or brownish, called citrine at gem shops. In this work a lot of samples was collected from different places in Brazil (Corinto - MG, Diamantina - MG, Sento Sé - BA and Santana do Araguaia – PA) and at first they were submitted at artificial irradiation resulting in dark colours. After that they were submitted at heat-treatment in differents temperatures and time of exposure to record when color change happened to light colours. It variated according to each origin, temperature, time of expousure and different aluminiun and other chemical elements content. Its was possible to define the ideal conditions to results better colours and related it with geology and chemical quartz composition.

Orange opals from Buriti dos Montes, Piauí: solid inclusions as genetic guides

As opalas laranjas de Buriti dos Montes (Piauí, nordeste do Brasil) têm propriedades gemológicas que favorecem seu uso como jóias; essas características incluem as cores, transparência, dureza e estabilidade relativamente elevadas. O exótico conteúdo de inclusões sólidas proporciona maior beleza às opalas da região. Essas opalas foram originadas por processos hidrotermais e são encontradas, principalmente, em vênulas e veios nos arenitos do Grupo Serra Grande, seccionados por soleiras e diques de diabásio da Formação Sardinha. Inclusões sólidas, tais como bolhas, agregados botrioidais, dendritos e nódulos, entre outras, consistem, principalmente, de caulinita, hematita/goethita e quartzo e influenciam a composição química das opalas. O zoneamento intenso dos cristais de quartzo e os elevados valores de Ba e Fe sugerem que os depósitos de opala foram formados em ambiente hidrotermal. Os diques de diabásio teriam sido responsáveis pelo aquecimento dos fluidos hidrotermais. Os arenitos, ricos em soluções aquosas, também teriam contribuído com a sílica disponível para a saturação dessas soluções e as fraturas permitiram a migração e aprisionamento dos fluidos hidrotermais, resultando nos veios mineralizados.