LAUR-80-1663, 'Zeolites in Silicic Tuffs of The Nevada ...

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LAi'Ro80-1 663

97-3

TITLE: ZEOLITES IN SILICIC TUFFS OF THE NEVADA TEST SITE

AUTHOR(S): M L Sykes. G. H. Heiken, J. R. Smyth, and

P. Knauth, Dept. of Geology, Arizona State University, Tempe, AZ

SUBMITTED TO: Geological Society of America

1980 Ann. Meeting Novenber 17-20, 1980

Form No. S3 R3 St. Nc. 2629

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(ONLY ONE PLEASEA D archaeological geoloY

.V C

a0

0 coal geology 0 economic geology

< ZEOLITES IN SILICIC TUFFS OF THE NEVADA TEST SITE

0 engineering geology

.E SYKES, M. L., HEIKEN, G. H., SMYTH, J. R., Los Alamos Scientific ?environmentalgeology

Laboratory, Los Alamos, New Mexico 87545 and KNAUTH, P., Dept. 0 xtraterrestrial geology

of Geology, Arizona State University, Tempe, Arizona 85281 Zeolites in the Tertiary age Paintbrush and Crater Flat Tuffs of the Nevada Test Site, Nye Co., Nevada, have been studied as part of the characterization of tuff as a potential radioactive waste repository

0 general geology [M eochemistry 0 geology education

D geomorphology

host rock. Samples from two drill holes about 6 km apart drilled to"' 0 geophysics 760 and 1060 m depth display the authigenic phase zonation with depth'; 0 geoscienie information

of montmorillonite opal * clinoptilolite (CPT) analcime. Both 13 historyofeology

sections contain two stratigraphically-equivalent zeolitized horizons" 0 hydrogeology in nonwelded ashflow and air fall tuff bounded by welded tuff. In the"' 0 marine geology

shallower hole the dominant zeolite is CPT with Si/Al+Fe of 4 to 5.5 D m hematcageology e and Ca>K>Na. In the upper horizon K and Na increase 7- and 4-fold' micropaleonology

respectively with depth. The ratio (Ca+Ba+Mg)/(Na+K) is proportional 0 mineralogy/rynallography

to Ca-content of plagioclase phenocrysts indicating control by initial - 0 paleontology!paleobotany

tuff composition. CPT in the lower horizon is similar but composi-

petrology

E 3tional variations are less consistent. In the deeper drill hole, the 0 experimental

]dominant zeolite in the upper horizon is CPT, nearly identical to that 0 IgneoUs

in the shallower hole. Analcime is dominant in the lower horizon and 0 mraorphlo

replaces some precursor zeolite; Si/unit cell varies from 33.9 to 34.9. 0 Pecmbriangeology

X

Isotopic studies of a bulk sample of zeolitized tuff from the upper D useternteology

horizon suggest water exists in at least three different types. About . : dimnt pelg

77% occurs as H 0 which exchanges readily with D-enriched water at, D srtigraphy 25C. Most of Ais is released below 3500C. About 8% occurs as hy- O tructuralgeology droxyl which resists isotopic exchange and is released above 3000C. At,

least 15% of the water is loosely bound H 0, removable at 25?C.

0 tectonics

This tuff sequence contains abundant eolites which can effectively' Ololrgy

sorb radionuclides migrating from a waste repository, but the effect of 0

temperature on zeolitic water needs further evaluation.

SDIOral :0 Poster 30 Either '0 Symposium

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