Experimental authigenesis of phyllosilicates from feldspathic sands

Authors

  • ALLAN F. DIVIS,

    1. Geological Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92037, U.S.A.
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  • JUDITH ANNE McKENZIE

    1. Geological Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92037, U.S.A.
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    • *

      Swiss Federal Institute of Technology, Zurich, Switzerland.


ABSTRACT

Hydrothermal experiments with primary detrital components of feldspathic sands (orthoclase, albite, quartz, and calcite) were conducted to simulate possible diagenetic changes in geosynclinal sedimentary accumulations and the geothermal reservoir of the Imperial Valley area, California. Phyllosilicate and zeolite mineralization was produced at 200°C and 1 Kb Ph2o and at 300°C and 1 and 3 Kb Ph2o. Scanning electron microscope examination of the detrital grains shows the development of authigenic minerals and solution features. Phyllosilicate development occurred as dense surface coatings on orthoclase crystals in concentrated brines and as scattered grain clusters in dilute brines. Cation concentration is considered to be a controlling factor in phyllosilicate formation and growth.

During formation the phyllosilicate crystals appear to utilize the surficial feldspar lattice structure as a preferred growth site. Electron diffraction studies indicate the crystals are a 1 Md mica similar to illite. Initial phyllosilicate formation occurs principally on orthoclase in systems containing this mineral, but is disseminated on other mineral surfaces in systems without orthoclase.

This experimental development of authigenetic illite via the destruction of potassium feldspar may offer a potential mechanism to help explain the resulting mineralogy of diagenetic processes occurring in natural sediments such as in feldspathic sands and argillaceous sediments.

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