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Leaching of quartz from precambrian hypabyssal rhyolite porphyry, Llano County, Texas

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Abstract

A Precambrian hypabyssal rhyolite porphyry in central Texas has retained its original texture, although alkali feldspar phenocrysts have inverted and unmixed from zoned, single-phase high-temperature feldspar to zoned microperthite with an intermediate microcline host.

Blue quartz phenocrysts owe their color to dispersion by zircon inclusions. Neutron activation analysis reveals substitution of tetravalent cations for silicon in the quartz.

In two outcrops, quartz and albite have been completely leached from the rock and K-feldspar added, leaving the texture intact. The leaching was most likely accomplished by residual brine from an overlying Lower Cretaceous evaporite deposit subsequently removed by erosion.

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Authors and Affiliations

  1. Department of Geological Sciences, The University of Texas at Austin, 78712, Austin, Texas

    Daniel S. Barker

  2. Department of Geological and Geophysical Sciences, Princeton University, 08540, Princeton, New Jersey

    Russell F. Burmester

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  1. Daniel S. Barker
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  2. Russell F. Burmester
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Barker, D.S., Burmester, R.F. Leaching of quartz from precambrian hypabyssal rhyolite porphyry, Llano County, Texas. Contr. Mineral. and Petrol. 28, 1–8 (1970). https://doi.org/10.1007/BF00389222

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