No description available.

No description available.

Amazonitic K-feldspar is characteristic of evolved granitic pegmatites of NYF (niobium-yttrium-fluorine) type, associated with A-type granite emplacement. In this work, I focus on four notable examples of such an association: (1) West Keivy, Kola Peninsula, Russia, (2) Saint-Ludger-de-Milot, Quebec, (3) Lac Sairs, Quebec, and (4) Morefield, Virginia. A fifth locality, the Broken Hill metamorphosed exhalative-type volcanogenic deposits in Australia, is an unusual type of amazonitic K-feldspar formed in an ore environment. A total of nineteen samples of amazonitic K-feldspar were characterized geochemically and mineralogically on the basis of X-ray diffraction, electron-microprobe and laser-ablation ICP-MS analyses. Lead, as an essential requirement for formation of the blue-green amazonitic color, has received particular attention. In every case, the analytical data show elevated amounts of Pb and rare alkalis, which strongly partition into the K-rich phase of the perthite intergrowth. Unusual micrometric grains, highly enriched in Pb, are found in cracks in the material from West Keivy. Some of the grains represent a new mineral species, a Pb-dominant feldspar. The presence of amazonitic K-feldspar in a granitic pegmatite is more than a curiosity. It can shed light on important petrogenetic issues such as metasomatic rejuvenation of crustal rocks prior to regional melting in a period of extension.

Thesis (Ph. D.)--McMaster University (Canada), 1990. / Source: Dissertation Abstracts International, Volume: 53-01, Section: B, page: 0310. Supervisor: J.E. Greedan.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 106-127). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2002. / Typescript. Vita. Includes bibliographical references (leaves 106-127). Also available on the Internet.

The gem pegmatites of Mt. Antero, Colorado occur in an Oligocene granitic stock containing aquamarine, smoky, clear and milky quartz, phenakite, muscovite, fluorite, garnet, pyrite, topaz and calcite. Aquamarine and smoky quartz contain abundant primary fluid inclusions outlining growth zones, as well as numerous trails of pseudosecondary and secondary inclusions. Salinities and homogenization temperatures (Th) of these inclusions define five distinct groups. The earliest primary fluid inclusions occur in outer growth zones of gem aquamarines. These inclusions have salinities of 2.6 - 3.9 wt.% and homogenize at 350°- 360°C. The earliest primary inclusions in smoky quartz have salinities of 5.0 - 5.6 wt. % and homogenize at the same temperature as the primaries in aquamarines. Paragenetically later primary and secondary C02-bearing inclusions in aquamarine, and secondary C02- bearing inclusions in smoky quartz homogenize at 350°-360°C. Later secondary inclusions in smoky quartz define two distinct groups based on salinity and Th (Group 1: Th = 285°-355°C, salinity = 6.1 - 7.9 wt.%; Group 2: Th = 215°-245°C, salinity = 3.0- 4.3 wt.%). Salinities and Th's of very latest primary inclusions in aquamarine overlap with those of group 1 in smoky quartz. Homogenization temperature of latest primary inclusions in smoky quartz is 194°-213°C and salinities range from 0.5 - 2.0 wt.%. Secondary inclusions in phenakite and fluorite crystals homogenize at about 270°C and 215°C, and have salinities of 1.3 and 0.5 wt. %, respectively. The fluid inclusion data, combined with constraints from mineral equilibria, suggest that gem aquamarines formed at approximately 500° to 600°C and - 1 kbar from low to moderate salinity aqueous fluids (2.6 - 6.2 wt. %). The salinity increased during the final stages of aquamarine growth and initial stages of smoky quartz formation, reaching a maximum of about 8 wt. %. During later stages of smoky quartz formation and subsequent fluorite and phenakite growth the salinity continuously decreased. Calcite and the latest quartz crystallized from -0.5 wt. % solutions. The beryl crystals from Mt. Antero vary in color from dark to pale blue aquamarines to the essentially colorless goshenite variety with some individual crystals showing color zoning. Quantitative electron microprobe analyses showed that iron, which imparts the blue color to the aquamarines, is enriched in the dark blue parts of a gem crystal and comparatively depleted in the paler blue terminated parts of the crystals. Most of the aquamarine crystals showed evidence of growth zoning. Quantitative analyses and X-ray maps generated with electron microprobe show that iron and cesium are depleted in the cores of the beryls and enriched in the rims of the crystals. An exact opposite trend is observed for sodium and magnesium, which are depleted in the rims but enriched in the cores of the beryls. / Master of Science

Les pegmatites à éléments rares de type LCT sont depuis longtemps étudiées et exploitées pour leurs gemmes et les métaux rares qu’elles contiennent. Malgré de nombreuses études réalisées sur les processus d’enrichissement en éléments rares, ou les mécanismes à l’origine de leurs textures, très peu d’études ont été dédiées aux mécanismes de mise en place des pegmatites et à leur répartition spatiale à l’échelle du champ. Afin de déterminer les mécanismes moteurs à l’origine de l’ascension de ces magmas, une étude multidisciplinaire a été menée sur 3 champs de pegmatites à éléments rares, répartis à l’échelle de la chaîne Varisque. Les résultats démontrent la proximité entre la localisation des pegmatites minéralisées et l’intensité de la déformation encaissante. De plus, la mise en place de ces magmas semble facilitée par un certain mode de fracturation. La modélisation numérique de la mise en place des magmas dans ces zones crustales fragilisées indique que l’ascension est facilitée par leurs faibles viscosité et densité, mais aussi par des perméabilités crustales très élevées (> 10⁻¹² m²), à des profondeurs de l’ordre de 10 km. Enfin, d’après les signatures isotopiques du Li mesurées sur des micas pegmatitiques, le lithium ne fractionne pas depuis le granite voisin, jusqu’aux pegmatites les plus différenciées, puisque les valeurs δ⁷Li (‰) sont toutes comprises dans une gamme de - 2 à + 2 ‰, similaire à celle rencontrée dans les granites orogéniques. Nous suggérons donc que la genèse des magmas pegmatitiques est commune à celle des granites hyperalumineux. Les mécanismes de fracturation et d’attraction (« magma-pumping ») sont envisagés pour avoir favorisé l’ascension de ces magmas résiduels, enrichis en éléments rares, de faibles volumes, au cours de transitions brutales et de courtes durées (~ 10³ ans), de la perméabilité. L’ensemble de ces résultats permet de remettre en question le modèle du granite parent classiquement utilisé pour la prospection de ces gisements, et de proposer un modèle revisité couplant la genèse et la mise en place de ces magmas. / LCT-type rare-element pegmatites have long been studied and exploited for their gems and rare metals they contain. Despite many studies about the rare-element enrichment, or about the mechanisms leading their exotic textures, very few studies have been dedicated to the mechanisms controlling their emplacement and their spatial distribution at the scale of the pegmatite field. To better investigate the origin of ascent-driving mechanisms of these magmas, a multidisciplinary study was conducted on 3 rare-element pegmatite fields across the Variscan belt. The results demonstrate the spatial proximity of the rare-metals-rich pegmatites with the intensity of deformation of the hosting rocks. In addition, spatial statistical analyses suggest that the emplacement of such magmas has been facilitated by fracture-controlled model. According to numerical models, the rise of these pegmatite-forming melts along weakened crustal zones would be facilitated by their peculiar physico-chemical properties (low viscosity and density), but also by very high crustal permeability (> 10⁻¹² m²) at depths around 10 km. Finally, accordingly to Li isotope signatures measured on pegmatitic micas, lithium does not fractionate from neighbouring granite up to the more differentiated pegmatites, since all δ⁷Li (‰) fall within a range of - 2 to + 2 ‰, as for orogenic granites. Therefore, we suggest that the genesis these pegmatite-forming melts is common to that of peraluminous granites. Mechanisms of fracturation and magma-pumping may have favoured the rise of these low volumes of residual melts, enriched in rare-elements, during short periods (~ 10³ yrs) of strong permeability increase. These results question the granitic model commonly used for the exploration of this type of mineral deposits. We suggest a revisited model accounting for both genesis and emplacement controlling mechanisms of the pegmatite-forming melts.

Les roches affleurant dans le Massif Chapédony appartiennent à la Formation de Chapédony défInie par HAGHlPOUR er PEUSSlER (1968) c'est-à-dire à la formartion la plus ancienne et la plus métamorphisée parmi les roches précambriennes de la région Sâghand - Posht-e-Bâdâm, et probablement de l'Iran tout entier . Le massif se compose d'une alternance de gneiss, marbres, roches scapolitiques. amphibolites. roches volcaniques et intrusions. Les faciès de migmatitisation, les petites masses de granite anatectique, les pegmatites et les fîlonnets d'aplite y sont nombreux et caractérisent ce massif. Grâce au climat sec, désertique, leurs affleurements sont aussi beaux que ceux des régions côtières et glaciaires dénudées de Fennoscandinavie, Groenland, Canada et Sibérie, où les pétrographes ont souvent pris leurs types de roches migmatitiques. Ces roches, à première vue, toutes semblables et indifférenciables, montrent en fait de nombreuses variations dans la taille, les grains, la couleur, l'épaisseur et la finesse de la foliation et du litage, dans leurs associations mutuelles, la présence ou l'absence de pegmatites, la présence de différentes associations de minéraux leucocrates, leur mode d'adaptation aux efforts tectoniques, etc .. En se basant sur ces caractères, on peut distinguer sept grands ensembles que nous étudierons successivement en partant de l'Est vers l'Ouest et depuis le bas vers le haut . Il faut mentionner que, bien que nos ensembles puissent correspondre à des événements géologiques ou être mis en corrélation avec des formations. des séries ou groupes stratigraphiques, ils n'ont pas pour nous d'autre signification qu'une classification purement pétrographique. Nous décrirons les diverses roches volcaniques et intrusives qui ont influencé la région pendant différentes phases tectoniques et métamorphiques. Enfin nous nous occuperons du sujet principal de ce travail: l'étude des faciès de granitisation, des migmatites, des pegmatites et des aplites. La direction générale des plans de litage et de foliation est NE-SW,

Os pegmatitos estudados estão associados à fácies albita granito do granito Madeira, a qual corresponde ao depósito de Sn-Nb-Ta (F, ETR, U, Th) Madeira, na mina Pitinga (AM) e estão associados a falhas de orientação N320/60SW. Estas rochas contêm minerais poucos comuns como gagarinita (NaCaYF6), genthelvita (Zn4Be3(SiO4)3S) e polilitionita (KLi2AlSi4O10(F, OH)2), além de grandes quantidades de criolita (Na3AlF6). Com base na composição química e mineralógica, estes pegmatitos foram classificados em três tipos: PEG ANF (teores médios de K e Na, com alta concentração de anfibólios), PEG POL (rico em K e com alta concentração de polilitionita) e PEG CRIO (rico em Na e com alta concentração de criolita). Estes pegmatitos contêm altos teores de ETR (especialmente ETRP) e Y, que estão concentrados principalmente na xenotima e na gagarinita. Estes elementos também ocorrem em elevados teores na grande parte dos demais minerais analisados. Também se destacam as concentrações anômalas de F, muito superiores às detectadas nos pegmatitos de outras localidades, e que promoveram o enriquecimento em Li, Na, K, Rb e Cs. A similaridade na composição química do AGN com os pegmatitos indica que eles possuem a mesma fonte. / The pegmatites studied are associated with the albite granite facies of the Madeira granite, which corresponds to the Sn-Nb-Ta (F, ETR, U, Th) Madeira deposit at the Pitinga mine (AM). They are associated with N320/60SW orientation faults. These rocks contain few common minerals such as gagarinite (NaCaYF6), genthelvite (Zn4Be3(SiO4)3S) and polylithionite (KLi2AlSi4O10(F,OH)2), as well as large amounts of cryolite (Na3AlF6). Based on the chemical and mineralogical composition, these pegmatites were classified into three groups: PEG ANF (medium K and Na, with high concentration of amphiboles), PEG POL (K rich and with high polylithionite concentration) and PEG CRIO (rich in Na and with high concentration of cryolite). These pegmatites contain high levels of REE (especially HREE) and Y, which are mainly concentrated in xenotime and gagarinite. These elements also occur at high levels in most of the other minerals analyzed. Anomalous concentrations of F, much higher than those detected in pegmatites from other localities, were also highlighted, and promoted enrichment in Li, Na, K, Rb and Cs. The similarity in the chemical composition of AGN with pegmatites indicates that they have the same source.