Melt inclusions and crystal-liquid separation in rhyolitic magma of the Bishop Tuff

Article Abstract:

Crystals and liquids in silicic magma separate during the crystallization of plinian phenocrysts. The uranium, barium, strontium and europium concentrations support the separation process that occured in the rhyolitic magma. The uranium concentration in the melt inclusions must have a minimum amount of 33% by weight for fractional crystallization but only 17% is detected in the plinian pumice sample. In addition, uranium concentration in matrix glass must be higher than in melt inclusions but the opposite is observed in the phenocrysts.

Rocks, Igneous, Xenoliths

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Time scales of large volume silicic magma systems: Sr isotopic systematics of phenocrysts and glass from the Bishop Tuff, Long Valley, California

Article Abstract:

An analysis of the time scales of magmatic processes is presented. The analysis tests initial Sr isotopic compositions of glass and mineral separates taken from the Bishop Tuff in Long Valley, CA. It is shown that a substantial isotopic heterogeneity exists. The heterogenous characteristic is exhibited between eruptive units and between glass and phenocryst stages of each unit. Variations were generated by magmatic processes.

Research, Silica, Magma, Silicon dioxide, Radioactive tracers

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Pre-ore hydrothermal alteration in an unconformity-type uranium deposit

Article Abstract:

The changes in the hydrothermal conditions causing unconformity-type uranium deposit are due to substitution of intense chlorite with metamorphic mineral assemblages. The stages of pre-ore alteration include the changing of muscovite to mica having high octahedral occupancy and small interlayer content, substitution of the altered muscovite by Mg-rich serpentine and clinochlore and further substitution by Fe-rich chlorite.

Observations, Muscovite, Hydrothermal deposits

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