Thesis (M.S.)--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 79-85).

Twenty-five muscovites have been systematically studied chemically, optically, and structurally. Multiple linear regressions were performed on these data to determine the correlations of the compositional components with both the optical properties and the unit cell parameters. The results of this study indicate refractive indices increase to the extent Fe and Ti constitute the octahedral cations, and to the extent OH rather than F coordinates to these cations. The optic angle 2VX decreases nearly linearly with the Ti content. The b cell edge follows a near-linear trend with ∑(Mg + Fe(total)), similar to that found by Guidotti (1984). / Master of Science / incomplete_metadata

Veins and pervasive wall-rock alteration composed of coarse muscovite +/- quartz +/- pyrite are documented for the first time in a porphyritic granite at Luhr Hill in the Yerington District, Nevada. Coarse muscovite at Luhr Hill occurs at paleodepths of similar to 6-7 km in the roots of a porphyry copper system and crops out on the scale of tens to hundreds of meters, surrounded by rock that is unaltered or variably altered to sodic-calcic assemblages. Coarse muscovite veins exhibit a consistent orientation, subvertical and N-S striking, which structurally restores to subhorizontal at the time of formation. Along strike, coarse muscovite veins swell from distal, millimeter-thick muscovite-only veinlets to proximal, centimeter-thick quartz-sulfide-bearing muscovite veins. Crosscutting relationships between coarse muscovite veins, pegmatite dikes, and sodic-calcic veins indicate that muscovite veins are late-stage magmatic-hydrothermal features predating final solidification of the Luhr Hill porphyritic granite. Fluid inclusions in the muscovite-quartz veins are high-density aqueous inclusions of similar to 3-9 wt% NaCl eq. and < 1 mol% CO2 that homogenize between similar to 150 and 200 A degrees C, similar to fluid inclusions from greisen veins in Sn-W-Mo vein systems. Our results indicate that muscovite-forming fluids at Luhr Hill were mildly acidic, of low to moderate salinity and sulfur content and low CO2 content, and that muscovite in deep veins and alteration differs in texture, composition, and process of formation from sericite at shallower levels of the hydrothermal system. Although the definition of greisen is controversial, we suggest that coarse muscovite alteration is more similar to alteration in greisen-type Sn-W-Mo districts worldwide than to sericitic alteration at higher levels of porphyry copper systems. The fluids that form coarse muscovite veins and alteration in the roots of porphyry copper systems are distinct from fluids that formed copper ore or widespread, shallower, acidic alteration. We propose that this style of veins and alteration at Luhr Hill represents degassing of moderate volumes of overpressured hydrothermal fluid during late crystallization of deep levels of the Yerington batholith.

TThe disruption of the aluminosilioate crystal lattice by aqueous fluoride solutions has been studied, The effect of reaction time, fluoride concentration, pH, and temperature on the reaction have been investigated« The stoichiometric exchange of hydroxyls by fluoride ions in kaolinite and muscovite at pH 7 below? was extremely doubtful., Disruption of the aluminosil ate crystallattice was thought t o be the predominant reaction over the acid pH range• Fluoride ions were found t react preferentially with the aluminium in the cry s tallattice to form AlP especially at the high e r temperature w

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Mineral textures, preserved in the metamorphosed sedimentary sequences that are exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. In this thesis the textural record of anatexis and melt transfer in the Himalayan metamorphic core is decoded and the controls that these processes exert on the tectonic evolution of the Himalaya are explored. The problem is divided into two parts, corresponding to variations in protolith lithostratigraphy: melt source - the pelitic region where melt was first generated, and melt sink - the psammitic region where melt accumulated and crystallised. Dehydration melting of muscovite has long been recognized as a critical reaction for the generation of anatectic melt in the Himalaya, but a textural understanding of how this reaction progresses is limited by the inherent difficulties in identifying specific reaction products. Using samples collected from the Langtang area in central Nepal, a mechanistic model for muscovite dehydration melting was constructed, and a set of textural criteria were developed, which were used to distinguish peritectic K-feldspar from K-feldspar grains formed during melt crystallisation. Melt is transferred from the source to the sink in two stages: firstly along a pervasive network of mineral grain boundaries, and secondly via a channelised network of sills and dykes in the melt sink where it solidified as leucogranite. Variation in the primary mineral assemblage and appearance of leucogranite bodies reflect the degree of interaction that occurred between the melt and metasedimentary country rock, rather than a change in primary melt composition. The modal proportion of K-feldspar in the melt source requires vapour-absent conditions during muscovite dehydration melting and leucogranite formation, indicating that the generation of large volumes of granitic melts in orogenic belts is not necessarily contingent on an external source of fluids. The crystallisation of hydrous minerals in leucogranite consumes &LT;15.5 % of water released by the breakdown of muscovite. These results indicate that anatexis efficiently dehydrates the middle crust and suggests that the continents have limited potential to store water over geological time.

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In order to assess the importance of particle size on elemental composition, structure, morphology, and charge characteristics of 2:1 micas, mechanically produced clay separates were analyzed by; electron probe microanalysis (EPMA), transmission electron microscopy (TEM), thermogravimetry, specific surface area analysis, and ion exchange. Books of biotite and muscovite were reduced to clay size « 2.0 μm) particles by mechanical comminution, then further fractionated into coarse (0.2-2.0 μm), medium (0.08-0.2 μm), and fine (< 0.08 μm) clay sizes. Composition of the clay size micas was particle size dependent, compositional changes being smaller for the medium and coarse clays. Grinding produced significant losses of interlayer K, decreased crystallinity, but increased water content as particle size decreased. The medium and coarse clays maintained coherent basal diffractions, whereas, significant peak broadening of x-ray diffraction maxima was observed for the fine clays. Diffracted peak broadening was due to the reduced crystallite size and the semirandom orientation of lath shaped particles. Specific surface area, adsorbed water. and structurally coordinated water increased as particle size decreased. Specific surface areas were determined by adsorption of molecular nitrogen, at liquid nitrogen temperatures. The increased water contents were measured by thermogravimetric analysis. An increase in CEC of the muscovite clays was detected with decreasing particle size, increasing solution pH, and increasing ionic strength. Assignment of specific exchange capacities for the three clays was confounded by AI hydrolysis and depressed solution pH. / Master of Science

Mount Mica is a poorly zoned sodic LCT-type pegmatite consisting dominantly of quartz, albite and muscovite in the outer portions. Potassium feldspar and lepidolite are restricted to the core zone. Micas in the wall zone are chemically homogeneous, but abruptly evolve into higher Cs + Rb bearing lithian muscovites and lepidolites in the core zone. The abrupt increase of the Cs, Rb in K-feldspar, and Cs, Rb and F in muscovite, and lepidolite combined with the occurrence of highly evolved species lepidolite, pollucite, elbaite, beryl and spodumene in the core zone suggests that incompatible elements were retained in residual fluid until their concentration was high enough to initiate crystallization of incompatible-rich mineral phases. The relatively low abundance of incompatible elements in the hanging wall suggest that the fractionation process was efficient in sweeping incompatibles into the core-zone, producing proportionally small volumes inside the pegmatite with very high enrichment in incompatible elements.