LosAlamosNatlonat Laboralory Is operatedbythe Universityof Cdtomla for the Unled States DepaJlnmnlof Energy undercontractW-7405-ENG-36.

_,u05 " '

TITLE: EQUILIBRIUM MODELING OF THE FORMATION OF ZEOLITES IN FRACTURESAT YUCCA MOUNTAIN, NEVADA

AUTHOR(S): SteveJ. Chipera, David L. Bish,and BarbaraA. Carlos

SUBMITTED TO: Zeolite '93 ConferenceVolume

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United StatesGovernment. Neither the United States Government nor any agency thereof, nor any of their

employees, makes any warranty, express or implied, or assumes any legal liability or responsi-bility for the accuracy, completeness, or usefulness of any information, apparatus, product, orprocess disclosed, or represents that its use would not infringe privatcly owned rights. Refer-ence herein to any specific commercial prcduct, process, or service by trade name, trademark,manufacturer, or otherwise does not nccessarily constitute or imply its endorsement, recom-mendation, or favoring by the United States Government or any agency thereof. The viewsand opinions of authors expressed herein do not necessarily state or reflect those of theUnited States Government or any agency thereof.

By acceptanceof thisarticle,the publisherrecognizesthat the U.S. Govemmerdretains a nonexduslve,royalty-freelicense to publishor reproducethepublishedformof thiscordribuUon,or to allowothersto do so, for U.S. Governmentpurposes.

The LosAlamos NationalLaboratoryrequeststhat the publisherIdentifythis articleas workperformedunderthe auspioss ofthe U.S. Departmer,_of Energy.

_:_(__ _0_0___ Los Alamos National LaboratoryLos Alamos, New Mexico 87545

FORMNO.0361=,4

""="' MASTERjlLI,S_mtUTlOnOttHw_ilOCUMl_H?esU_LImtlt0

1,41tm_mlmt,_.ea.ab..,,.e,. • '_--

r

EQUILIBRIUM MODELING OF THE FORMATION OF ZEOLITES IN FRACTURES

AT YUCCA MOUNTAIN, NEVADA.

Steve J. Chipera, David L. Bish, and Barbara A. Carlos

Earth and Environmental Sciences, Los Alamos National Laboratory

Mail Stop D-469, Los Alamos, New Mexico, 87545

USA

Correspondence to:

Steve J. Chipera

Los Alamos National Laboratory, Mail Stop D-469

Los Alamos, New Mexico, 87545

i

ABSTRACT

Yucca Mountain, in southern Nevada, is currently being investigated to determine its suitability to

host the first U.S. high-level nuclear waste repository. One of the reasons that Yucca Mountain was chosen

for study is the presence of thick sequences of zeolite-rich horizons. Inasmuch as fractures may serve as

potential pathways for aqueous transport, the minerals that line fractures are of particular interest. Zeolites

are common in fractures at Yucca Mountain and consist mainly of clinoptilolite/heulandite and mordenite

although sporadic occurrences of chabazite, erionite, phillipsite, and stellerite have been identified using X-

ray powder diffraction. To understand better the conditions under which the observed zeolite species were

formed, thermodynamic data were estimated and calculations of log a((K')2/Ca _) versus log a(('Na.)2/Ca**)

were conducted at various temperatures and silica activities. Using present-day Yucca Mountain water

chemistries as a lower constraint on silica activity, clinoptilolite/heulandite and mordenite are still the zeolite

species that would form under present conditions. A slight reduction in silica activity or increase in Ca

content would account for the stellerite observed above the water table in drill holes USW G-1, G-2, and

UE-25a#1. The rare occurrences of erionite and phillipsite appear to have formed in localized environments

that were K enriched and probably at a lower silica activity than the rest of Yucca Mountain. Likewise, the

rare occurrences of chabazite appear to have formed in localized environments that were both Ca enriched

and at a reduced silica activity.

INTRODUCTION

Yucca Mountain, in southern Nevada, is currently being investigated to determine its suitability to

host the first U.S. high-level nuclear waste repository (Fig. I). One of the reasons that Yucca Mountain was

chosen as a potential site is the presence of thick sequences of zeolite-rich horizons formed by alteration of

the volcanic ash-flow tufts (12-15 My) that comprise the mountain. The zeolites that line fractures at Yucca

Mountain are of particular interest inasmuch as fractures may se_:e as transport pathways for radionuclides

that may leak from a potential repository.

!

The zeolite mineralogy of the bulk rock at Yucca Mountain consists mainly of

clinoptilolite/heulandite, mordenite, and analcime. The zeolite minerals found in fractures at Yucca

Mountain, however, can be somewhat more exotic. In addition to the above zeolites, which are common in

both the bulk rock and in fractures, we have identified chabazite, erionite, phillipsite, and stellerite using X-

ray powder diffraction. These additional zeolites are found sporadically in fractures generally above the

static water table and, except for stellerite, were identified only in close association with vitric zones.

To understand better the conditions determining past and future alteration at Yucca Mountain, it is

desirable to evaluate the geochemical conditions under which different zeolite species were formed. Kerrisk

(1983), used the program EQ3/6 to model conditions under which zeolite formation at Yucca Mountain

could have occurred. His model showed that during the initial stages of dissolution of volcanic glass, high-

silica zeolites (clinoptilolite/mordenite) were formed along with smectite clay. Kerrisk found that he had to

suppress the formation of quartz in order to mimic the supersaturation of silica which is required to form the

high-silica zeolites. Kerrisk also found, however, that if cristobalite was also suppressed to allow the silica

activity to be held at amorphous silica concentrations, unrealistic results were obtained. If reactions were

allowed to continue, Kerrisk found that silica activity eventually dropped and the reactions progressed to

form a quartz-analcime-illite mixture, and then finally a quartz-albite-K-feldspar mixture with calcite

possibly present.

Bowers and Bums (1990) conducted a thorough study on the stability of clinoptilolite at Yucca

Mountain both with respect to the current conditions of temperature and water chemistry, and to potential

changes in water chemistry or increased temperature from emplacement of a high-level nuclear waste

repository. They found that clinoptilolite is stable under current conditions but could potentially react to

other phases under prolonged diagenetic reactions with groundwater depleted in A1 or enriched in Na or Ca,

and if subjected to increased temperature within the thermal envelope of a waste repository. Although

Bowers and Bums (1990) considered a wide assortment of phases in their calculations, they did not include

2

all of the zeolite species that are known to occur at Yucca Mountain _stellerite, erionite, and

laumontite).

Thermodynamic calculations have in the past been hindered by the lack of thermodynamic data for

zeolites. Although thermodynamic data have recently been measured on numerous zeolite minerals, data

have not yet been obtained for ali zeolite species of interest Furthermore, the chemistry of zeolites is highly

variable and the thermodynamic values obtained from one zeolite may not be perfectly representative of the

thermodynamic properties of that zeolite from other samples.

In the present work, a consistent set of thermodynamic data for ali of the zeolite phases that exist at

Yucca Mountain was estimated utilizing representative chemical formulas and the methods of Berman and

Brown (1985), Chermak and Rimstidt (1989), and Holland (1989). Appling the Ge0-Cale PTA program of

Brown et al. (1989), activity-activity diagrams were calculated at various temperatures and silica activities.

Since this work attempts to address the past conditit_ns which resulted in the formation of the zeolites that

are present in fractures today, the approach used was to include data for ali of the zeolite species that are

known to occur at Yucca Mountain, excluding minerals that are not known to occur.

METHODS

Fractures from drill holes J-13, UE-25a#1, UE-25b#1h, USW G-I, USW G-2, USW GU-3, USW G-

4, USW VH-1, and USW VH-2 (Fig 1) have been sampled for fracture-lining minerals. Summaries of

zeolite mine.als lining fractures can be found in Carlos (1985; 1987; 1989), Chipera and Bish (1989), and

Bish and Chipera (1991).

Various empirical routines have been formulated by which thermodynamic data for mineral phases

can be estimated. The more recent methods ali represent mineral phases as a set of elemental building

blocks composed of unique polyhedra _ Robinson and Hass, 1983; Berman and Brown, 1985; Hazen,

1985; Chermak and Rimstidt, 1989; and Holland, 1989). By summing the contributions from each

polyhedron, the thermodynamic properties are estimated for the complete mineral unit. In this study,

irl

thermodynamic data for the zeolites and for smectite were estimated using the method proposed by Berman

and Brown (1985) for heat capacity. The method of Chermak and Rimstidt (1989) was used to estimate

Gibbs free energies and enthalpies of formation at 298 K. Holland (1989) formulated a method to estimate

entropy from individual polyhedra which further improves on previous methods in that it takes into account

the volume of a phase. His method incorporates the fact that the entropy of a phase depends not only on the

individual polyhedra composing the phase, but also on how tightly the polyhedra are assembled. A slight

modification made to the Holland method was to incorporate an appropriate value for zeolitic water. In his

paper, Holland proposed two choices for entropy contributions of water in the polyhedrally-derived structure

(20.74 kJ/mol'K for structurally bonded and 30.03 kJ/mol'K for "loosely bonded" water). An average value

of 59.1 kJ/mol'K for zeolitic water was determined by comparing calculated entropies of anhydrous

analcime, mordenite, phillipsite, clinoptilolite, heulandite, and stilbite (phases representative of those at

Yucca Mountain) with the measured hydrous entropy values for these phases (Johnson et al., 1982; Johnson

et al., 1992; Hemingway and Robie, 1984; Hemingway and Robie, 1984; Johnson et al., 1985, and Howell et

fl__ 1990 respectively) and then determining the average difference on a per-mole-of-water basis. This value

(59.1 kJ/mol'K) compares well with the values measured by others for zeolitic water _ 55.0 for analcime,

Johnson et al., 1982; 57.0 kJ/mol'K for clinoptilolite, Hemingway and Robie, 1984; and 54.05 kJ/molK for

mordenite, Johnson et al., 1992).

Thermodynamic data for quartz, cristobalite, and tridymite were obtained from the B88.MIN

(Berman, 1988) thermodynamic database supplied with the Ge0-Calc software package. Thermodynamic

data for amorphous silica were obtained from the SUPCRT92 database (Johnson _ 1991). Values for

aqueous species _ water, aqueous SiO2, Ca", Na', K., H.) were from the HKF81 .AQU database

(Helgeson et al., 1981) also supplied with the Ge0-Calc software.

Estimated thermodynamic data for the zeolites that occur at Yucca Mountain, utilizing representative

chemical formulas, are given in Table 2. Actual analyses of Yucca Mountain zeolites were used whenever

possible. If analyses were unavailable for a phase found at Yucca Mountain _ chabazite, erionite,

4

I

laumontite), an approximate formula was estimated from sedimentary zeolite analyses published in Gottardi

and Galli (1985). Since wide variations in chemical composition occur for zeolites at Yucca Mountain

(Broxton _ 1987) some constraints on "representative" chemical formulas were made. Since the largest

variety of zeolite species occurs in the unsaturated diagenetic Zone I (where much glass remains unaltered),

chemical analyses for clinoptilolite and heulandite were used that are representative for these phases in

diagenetic Zone I (Broxton et al., 1987). Additional chemical constraints were formulated noting that

coexisting mordenite/clinoptilolite show mordenite containing more Na and K and less Ca than clinoptilolite

(Caporuscio _ 1982 and Carlos, 1987), and heulandite is more Ca-rich than clinoptilolite in coexisting

clinoptilolite/heulandite (Broxton _ 1987). Chemical analyses were normalized to form proper

structural formulas when the individual atom abundances were rounded off to the first decimal piace.

Formulas using more significant digits were not used due to problems in balancing reactions. To simplify

the calculations, the chemical system was constrained to Na-K-Ca-AI-Si-O-H.

Zeolites also exhibit wide variations in water contents, readily responding to environmental

, conditions such as temperature and humidity. For ali calculations, the zeolites were assumed to be in a fully

hydrated state as would be typical of conditions below the water table or above the water table at elevated

humidity. The absolute quantity of water in the zeolites, however, is not critical since reactions involving

the exchange of water are somewhat balanced by free water in the system (AG zeolite water (55.1) - AG free

water (-70) = -15 kJ/mol'K difference).

Ali thermodynamic calculations were conducted using the Ge0-Cale PTA-System software program

(Brown _ 1989). Temperatures for the calculations were constrained to paleogeotherms for drill holes

USW G-I, G-2, and G-3 at Yucca Mountain as determined by Bish (1989) using fluid inclusion data and the

degree of transformation from smectite to illite. In ali three drill holes, temperatures were -25-60°C at the

surface, and -30-70°C at the elevation of the present water level (572 to 750 m [1876 to 2462 feet]). At a

depth of 1219 m (4000 feet), Bish estimated the paleotemperatures at --110°C in USW G-I, -175°C in G2,

and -50°C in G3. At a depth of 1524 m (5000 feet), the temperatures were estimated at -160°C, -240°C,

5

and -60°C and at a depth of 1829 m (6000 feet), the temperatures were estimated at -210°C, -280°C, and

-65°C for drill holes USW G-l, G-2, and G-3 respectively. The variable temperatures are due to the

location of each drill hole with respect to the Timber Mountain Caldera Complex, with USW G-2 being

closest, and USW G-3 being the most distant. Pressures were constrained such that ali calculations were

conducted on the liquid side of the water liquid-vapor curve. This is readily accommodated below the water

table by hydrostatic pressure. For a temperature of 150°C, pressure must be >4.7 bars or equal to a

hydrostatic pressure from an approximately 47-m tall column of water. For a temperature of 200°C,

pressure must be >16.5 bars or equal to an approximately 165-m tall column of water, pH values used for

the calculations were constrained to -8, a value that is representative of present-day waters at Yucca

Mountain (Kerrisk, 1987).

For the calculations, only zeolite phases known to exist at Yucca Mountain were used. Although

other mineral phases may be in true equilibrium with respect to zeolites, zeolites often form metastably due

to the kinetic limitations on the formation of more stable species (Moncure _ 1981). Consequently,

phases which may potentially be more stable for the given conditions _ feldspars, mica, etc.) were not

included in the calculations.

RESULTS AND DISCUSSION

Figures 2-5 show the results of modeling log a((K')Z/Ca.*) versus log a((Na')2/Ca '-') at various

temperatures and silica activities. The figures demonstrate the importance of cation composition on the

formation of individual zeolite species. The exact stability fields for phases which exhibit a wide variation

in cation ratios, however, can change drastically in response to the cation ratios used for the calculations.

Although attempts were made to use "representative" chemical analyses, chemical compositions have been

shown to vary considerably depending on drill hole locations and depth (Broxton _ 1987). Therefore,

several calculations were conducted to determine sensitivity of the stability fields with variable input cation

ratios for the phases. These calculations showed that those zeolites which exhibit a large variation in cation

6

¢

composition _ clinoptilolite/heulandite, mordenite, and erionite) were most sensitive to changes in input

cation ratios. For example, although mordenite retains its central position on the activity-activity di-grams

with changes in exchangeable cation composition, its stability field is strongly anti-correlated with that of

clinoptilolite. The mordenite stability field grows larger as that for clinoptilolite grows smaller, and vice

vers_.__aa.A similar, less-dramatic effect was noted with clinoptilolite/mordenite and erionite.

The effect of silica activity is clearly illustrated by the calculations conducted at amorphous silica

saturation (Fig. 2), at cristobalite saturation (Fig. 3), and at quartz saturation (Fig. 4). The stability fields for

the more siliceous zeolites _ mordenite and clinoptilolite) dominate the figures at the high silica activity

(amorphous silica saturation), then decrease in size at cristobalite saturation, and then disappear almost

entirely at quartz saturation. Silica activity can be constrained by the SiOz polymorphs which coexist with

the zeolites. Opal-CT is generally found intergrown with mordenite and clinoptilolite/heulandite at Yucca

Mountain (Bish and Chipera, 1989). Preliminary analysis of fracture mineralogy in UZ-16 suggests

stellerite is intergrown with tridymite and heulandite is intergrown with cristobalite. Present-day water

chemistries (Kerrisk, 1987, Table 3) can also provide some constraints as to past conditions that resulted in

the zeolites that are present at Yucca Mountain today. A region representing the present-day water

chemistry has been superimposed on the activity/activity diagrams (Figs, 2-5). Conducting the calculation at

a representative present-day silica activity [log a(SiOz) = -3.1 ] and at a representative present-day water

temperature (-35°C) shows clinoptilolite/mordenite as the stable zeolite assemblage that would occur at

Yucca Mountain today (Fig. 5). Only a small reduction in silica activity or increase in Ca content, however,

is required to cross into the stellerite stability field and may explain the stellerite found in fractures above the

static water level in drill holes USW G-l, USW G-2, and UE-25a#1.

Increasing temperature has several effects. With increased temperature for a given silica-polymorph

saturation (silica activity also increases with increasing temperature), the stability fields for mordenite and

clinoptilolite decrease as the surrounding stability fields increase. Also, increasing temperature produces an

increased stability field for chabazite (Fig. 3) and at significantly increased temperature (>300°C), a stability

field for laumontite appears.

Subtle differences in geochemical conditions must have occurred locally in fractures over short ranges

of distance to give rise to the variety of zeolites observed. For example, drill hole UE-25a#1 contains a

sequence where clinoptilolite and mordenite coexist, then only clinoptilolite, then erionite-clinoptilolite, then

phillipsite-clinoptilolite, and then back to coexisting clinoptilolite-mordenite, ali within a depth range of

approximately 21.6 m (71 feet) (Table 4, Fig. 6). Likewise, the same sequence is observed in drill hole

USW GU-3 (Table 4). Interestingly, although erionite has a prominent stability field, a stability field for

phillipsitc was obtained only when silica activity was reduced _ to cristobalite saturation) and when the

formation of erionite was suppressed (Fig. 7). The suppression of erionite is consistent with the two

observed occurrences of phillipsite at Yucca Mountain that both occurr in close proximity to erionite (Table

4). It is possible that a stability field could be created such that phiUipsite coexists with erionite by slightly

varying the cation compositions of the two phases. These occurrences suggest that environments that were

considerably more potassic and possibly at a lower silica activity existed locally at Yucca Mountain.

Heulandite, which is isostruetural with clinoptilolite and relatively common at Yucca Mountain, had a

stability field only when silica activity was reduced to cristobalite saturation and only when stellerite was

suppressed (Fig. 7). This contrasts with the common occurrence of heulandite in fractures in devitrified tufts

at Yucca Mountain. The stability field for heulandite can be increased by varying the exchangeable-cation

compositions for heulandite, clinoptilolite, and mordenite, suggesting that our "representative" chemical

formulas could be modified to represent heulandite better. In addition, Yucca Mountain zeolites often

contain significant Mg and Sr which were not included in the calculations. Including Mg and Sr in the

calculations may increase the stability of heulandite with respect to analcime and stellerite.

Chabazite had a stability field in both reduced-Na and reduced-silica activity environments. Increased

temperature also facilitated the formation of a stability field for chabazite. At Yucca Mountain, chabazite

has been identified in only 3 fracture samples (Table 1), ali of which are located below the static water level.

Laumontite, which has been found in deep rocks at Yucca Mountain (at the bottom of drill hole UE-

25p#1 and suspected at the bottom of USW G-l), has not yet been observed in any fractures, lt would not

have formed in any of the shallow fractures due to the elevated temperature, calcic water conditions, and

reduced silica activity required to provide a laumontite stability field. Although laumontite has not been

encountered in fractures at Yucca Mountain, deep fractures are not routinely sampled and it may not have

been encountered simply due to insufficient sampling. Likewise, analcime which is a common phase found

deep in Yucca Mountain, may not be routinely encountered since fractures at the depths where analcime is

known to occur in the bulk rock are rarely sampled.

CONCLUSIONS

Using estimated thermodynamic data and representative chemical formulas for the zeolites that occur

at Yucca Mountain, Nevada, log a((K')2/Ca _) versus log a_((Na')2/Ca._) stability diagrams were calculated to

model the conditions under which the various zeolite species were formed, lt appears that at Yucca

Mountain, the relative cation abundances and silica activity are the most important factors in determining

which zeolite species formed, although temperature was also shown to have a minor effect. The pH,

although not found to influence directly which zeolite species would form, is important in determining if

zeolites would form at the expense of other potentially stable assemblages.

The majority of the zeolites present in fractures at Yucca Mountain (clinoptilolite and mordenite)

formed under conditions of elevated silica activity that are consistent with the frequency with which they

coexist with opal-CT. Only a small reduction in silica activity or increase in Ca content would be required

to form stellerite, which is also present in fractures at Yucca Mountain. Preliminary studies of fracture-

lining stellerite from drill hole UZ-16 show it to coexist with tridymite which is indicative of a lower silica

activity relative to opal-CT. The formation of erionite and phillipsite, both of which are extremely rare at

Yucca Mountain, are indicative of environments that are more potassic and at a lower silica activity.

Likewise, the rare occurrences of chabazite are indicative of environments with reduced silica activity and

'11 '

i

increased Ca (and possibly K) with respect to Na, although increased temperature also favors chabazite

formation.

Comparison of the fracture-lining zeolites and their coexisting silica polymorphs with present

groundwater chemi._tries suggests that the past water compositions from which zeolites formed at Yucca

Mountain are not sil_nificantly different than what is observed today. The occurrences of erionite, phillipsite,

and chabazite suggest, however, that geochemical environments existed locally that were significantly

different than the rest of Yucca Mountain.

ACKNOWLEDGMENTS

We wish to extend our thanks to D. Vaniman for his thorough review and to R. Raymond for

providing microprobe analyses of Yucca Mountain stellerite. This work was supported by the Yucca

Mountain Site Characterization Project Office as part of the Civilian Radioactive Waste Management

Program. This Project is managed by the U.S. Department of Energy, Yucca Mountain Site Characterization

Project. The Yucca Mountain Project Technical Data Catalog Data Tracking Number for this paper is LA-

000000000055.001.

REFERENCES

Berman, R.G. (1988) lntemaily consistent thermodynamic data for minerals in the system Na20-K20-CaO-

MgO-FeO-Fe_O3-A1203-SiO2-TiO2-H20-C02: J. Petrol. 29, 445-522.

Berman, R.G. and Brown, T.H. (1985) Heat capacity of minerals in the system Na,O-K20-CaO-MgO-FeO-

Fe203-A1203-SiO2-TiO2-H20-CO2: representation, estimation, and high temperature extrapolation:

Contr. Mineral. & Petrol. 89, 168-183.

Bish, D.L. (1989) Evaluation of past and future alterations in tuff at Yucca Mountain, Nevada, based on the

clay mineralogy of drill cores USW G-I, G-2, and G-3: Los Alamos National Laborator?

LA- 10667-MS, 40p.

10

6

Bish, D.L. and Chipera, S.J. (1991) Detcction of trace amounts of erionite using X-ray powder diffraction:

Erionite in ruffs of Yucca Mountain, Nevada, and central Turkey: Clays& Clay Minerals 39, 437-

445.

Bish, D.L. and Chipera, S.J. (1989) Revised Mineralogic Summary of Yucca Mountain, Nevada: Lo.._.ss 4

Alamos National Laboratory Report, LA-11497-MS, 68p.

Bish, D.L., Ogard, A.E., Vaniman, D.T., and Benson, L. (1984) Mineralogy-petrology and groundwater

geochemistry of Yucca Mountain tufts: in Scientific Basis fo_.£rNuclear Waste Management VI__[I,

Materials Research Society Symposia Proceedings_ Boston, Mass.1 (G.L. McVay, Ed.), 283-291.

Bowers, T.S. and Burns, R.G. (1990) Activity diagrams for clinoptilolite: Susceptibility of this ,.eolite to

further diagenetic reactions: Amer. Mineral. 75, 601-619.

Brown, T.H., Berman, R.G., and Perkins, E.H. (1989) PTA-SYSTEM: A Ge0-Calc software package for

the calculation and display of activity-temperature-pressure phase diagrams: Amer. Mineral. 74, 485-

487.

Broxton, D.E., Bish, D.L., and Warren, R.G. (1987) Distribution and chemistry of diagenetic minerals at

Yucca Mountain, Nye County, Nevada: _Cla_y_s_.&Clay Minerals 35, 89-110.

Carlos, B.P,. (1987) Minerals in fractures of the saturated zone from drill core USW G-4, Yucca Mountain,

Nye County, Nevada: Lo_.._sAlamos National Laboratory Report, LA-10927-MS, 32p.

Carlos, B.A. (1985) Minerals in fractures of the unsaturated zone from drill core USW G-4, Yucca

Mountain, Nye County, Nevada: Lo_.._ssAlamo.........._sNational Laboratory Report, LA-10415-MS, 55p.

Carlos, B.A. (1989) Fracture-coating minerals in the Topopah Spring Member and upper Tuff of Calico

Hills from drill hole J-13: Lo_._.ssAlamo__......_sNational Laboratu_ Report, LA-11504-MS, 2013.

Caporuscio, F., Vaniman, D., Bish, D., Broxton, D., Aroey, B., Heiken, G., Byers, F., Gooley, R., and

Semarge, E. (1982) Petrologic studies of drill cores USW-G2 and UE25b-IH, Yuc_.a Mountain,

Nevada: Los Alamos National Laboratory Report, LA-9255-MS, 111p.

11

Chermak, J.A. and Rimstidt, J.D. (1989) Estimating the thermodynamic properties (AG_ and AH_) of

silicate minerals at 298 K from the sum of polyhedral contributions: Amer. Mineral. 74, 1023-1031.

Chipera, S.I. and Bish, D.L. (1989) The occurrence and distribution of erionite at Yucca Mountain, Nevada:

Lo_._.ssAlamos National Laboratory Report, LA-11663-MS, 20p.

Gottardi, G. and Galli, E. (1985) Natural Zeolites: Mineral and Rocks Series, Vol. 18, Springer-Verlag,

New York, 409pp.

Hazen, R.M. (1985) Comparative crystal chemistry and the polyhedral approach: In Microscopic to

macroscopic: Atomic environments to mineral thermodynamics, S.W. Kieffer and A. Navrotsky,

Eds., Mineralogical Society of America Review in Mineralogy, 14, 317-345.

Helgeson, H.C., Kirkham, D.H., and Flowers, G.C. (1981) Theoretical prediction of the thermodynamic

behavior of aqueous electrolytes at high pressures and temperatures: IV. Calculation of activity

coefficients, osmotic coefficients, and apparent molal and standard and relative partial molal

properties to 600°C and 5kb: Amer. J. Sci. 281, 1249-1516.

Hemingway, B.S. and Robie, R.A. (1984) Thermodynamic properties of zeolites: Low-temperature heat

capacities of thermodynamic functions for phillipsite and clinoptilolite. Estimates of the

thermochemical properties of zeolitic water at low temperature: Amer. Mineral. 69, 692-700.

Holland, T.J.B. (1989) Dependenceof entropyon volume for silicate and oxide minerals: A review and a

predictive model: Amer. Mineral. 74, 5-13.

Howell, D.A., Johnson, G.K., Tasker, I.R., and O'Hare, P.A.G. (1990) Thermodynamic properties of the

zeolite stilbite: Zeolites 10, 525-531.

Johnson, G.K., Tasker, I.R., Flotow, H.E., and O'Hare, P.A.G (1992) Thermodynamic studies of mordenite,

dehydrated mordenite, and gibbsite: Amer. Mineral. 77, 85-93.

Johnson, G.K., Flotow, H.E., and O'Hare, P.A.G (1985) Thermodynamic studies of zeolites: Heulandite:

Amer. Mineral. 70, 1065-1071.

i2

I

Johnson,G.K., Flotow, H.E., and O'Hare, P.A.G (1982) Thermodynamic studies of zeolites: Analcime and

dehydration analcime: Amer. Mineral. 67, 736-748.

Johnson, J.W., Oelkers, E.H., and Helgeson, H.C. (1991) SUPCRT92: A software package for calculating

the standard molal thermodynamic properties of minerals, gases, aqueous species, and reaction from 1

to 5000 bars and 0° to 10(DoC: Earth Sciences Dept., L-219, Lawrence Livermore National

Laboratory, Livermore, CA 94550.

Kerrisk, J.F. (1987) Groundwater chemistry at Yucca Mountain, Nevada, and vicinity: Los Alamos

National Laboratory Report LA-10929-MS.

Kerrisk, J.F. (1983) Reaction-path calculations of groundwater chemistry and mineral formation at Rainier

Mesa, Nevada: Los Alamos National Laboratory Report, LA-9912-MS. 41pp.

Levy, S.S. (1984) Petrology of samples from drill holes USW H-3, H-4, and H-5, Yucca Mountain, Nevada:

Lo____sAlamos National Laboratory Report, LA-9706-MS. 77 pp.

Moncure, G.K., Surdam, R.C., and McKaque, H.L. (1981) Zeolite diagenesis below Pahute Mesa, Nevada

Test Site: Clays & Clay Minerals 29, 385-396.

Robinson, G.R., Jr., and Haas, J.L. Jr. (1983) Heat capacity, relative enthalpy, and calorimetric entropy of

silicate minerals: An empirical method of prediction: Amer. Mineral. 68, 541-553.

Sheppard, R.A., Gude, A.J., T d,and Fitzpatrick, J.J. (1988) Distribution, characterization, and genesis of

mordenite in Miocene silicic tufts at Yucca Mountain, Nye County, Nevada: U.S.G.S. Bulletin 1777,

22pp.

Smyth, J.R. and Bish, D.L. (1988) Crystal Structures an__ddCation Sites of the Rock-Forming Minerals: Allen

& Unwin, London, 332p.

FIGURE CAPTIONS

Figure 1: Location map of Yucca Mountain, Nevada, showing the outline of the exploration block and the

locations of drill holes mentioned in the text and tables. Drill hole J-12 is located outside of this

figure to the southeast. Drill holes USW VH-1 and VH-2, also outside of this figure, are located to

the west-southwest. Locations for J-12 and VH-1 can be found on the location map published in Bish

et al. (1984).

Figure 2: Log a((K.)2/Ca..) versus log a((Na*)2/Ca*.) at amorphous-silica saturation and 75°C (solid lines)

and 175°C (dashed lines). Present-day Yucca Mountain water chemistries (Kerrisk, 1987) fall within

the clinoptilolite stability field.

Figure 3: Log a((K.)2/Ca..) versus log a((Na.)2/Ca..) at cristobalite saturation and 750C (solid lines) and

1750C (dashed lines). Present-day Yucca Mountain water chemistries (Kerrisk, 1987) fall within the

steIlerite stability field. Chabazite now possesses a stability field at the elevated temperature.

Figure 4: Log a((K.)2/Ca_) versus log a((Na.)2/Ca **)at quartz saturation and 75°C (solid lines) and 175°C

(dashed lines). The stability fields for mordenite and clinoptilolite are restricted at 75°C and

disappear completely at 175°C.

Figure 5: Log _a((K.)2/Ca..) versus log a((Na*)2/Ca..) using a representative present-day water temperature of

-35"C and silica activity of log a(SiOz) = -3.1. Present-day Yucca Mountain water chemistries

(Kerrisk, 1987) fall within the clinoptilolite stability field although a slight decrease in silica activity

or increase in Ca content would result in crossiag into the stellerite stability field.

Figure 6: Relative zeolite abundances for a short interval in drill hole UE-25a#1 from 381 to 418 m (1250-

1370 feet). The left ordinate uses units of feet so that it can be directly correlated to the sample labels

listed on the right ordinate of the diagram. Smectite and clinoptilolite occur throughout the interval;

however, erionite, phillipsite, and mordenite appear mutually exclusive with respect to each other.

Figure 7: Log a((K.)2/Ca ++)versus log a((Na.)2/Ca'0 at 75°C and cristobalite saturation for ali zeolite phases

(solid lines) and with the formation of erionite and steUerite suppressed (dashed lines). Suppression

of erionite results in the appearance of phillipsite and chabazite stability fields, and the extension of

mordenite and clinoptilolite to regions of greater K concentrations. Suppression of stellerite results in

the expansion of clinoptilolite stability and the formation of a heulandite stability field under

extremely calcic conditions.

2() i i i i i i i

Amorphous-Silica Saturated15-

10 Analcime

_ 5 t_ - M rde item -- -_---___ o n ,

Present ErioniteL'_ YM Water

t_'5o Stellerite-J -10

Clinoptilolite-15 75°C

175oc ....

-2O-20-15-10-5 0 5 10 15 20

Log a((K2)/Ca)

I Fig. 2

20 i i i i i i I

Cristobalite Saturated15- -

10Analcime

O 5

_= r-':-. _, Erionite

YM Water

"5o_ Stellerite ',O ,,

=J-10 __ __,_

-15 75°C - Clinoptilol175oc ..... _ _"

-20-20 -15 -10 -5 0 5 10 15 20

Log a((K2)/Ca)

I Fig. 3

20 I l I ' I l I I

Quartz Saturated15- -

10_" Analcime

5 Mordenite (75°C)o4

_ .......... , ErioniteZ 0 0 "PresentV

YM Water

-5 _c_ Stellerite

-10 %Clinoptilol

(75°c) Chabaz-15 75°c

175oc ....

-20-20 -15 -10 -5 0 5 10 15 20

Log a((K2)/Ca)

Fig. 4

2O35°C, Present YM Water Silica Activity

15-

10 AnalcimeO

5Mordenite

Z 0_ Present Erionite

YM Water

-5o Stellerite

-lO linoptiloli

-20-20 -15 -10 -5 0 5 10 15 20

Log a((K2)/Ca)

" Fig "

! '°II1'

Smect. Clinopt. Mord. Erion. Phillip.1250

1270 I .

l/ 1274.5i _76_

1282.6tl

1290 /

1296.214,,-

1301.5

1310 . 1309.0

_ 1318.4

1322.9

1330

Abundance 1339.5

- Trace1350 -

•---" Minor

L_ Major 1361.8

1370

, Fig. 6!

ii

Oft IIII I III

r.V l I I I l I l

Cristobalite Saturated at 75°C15 - , Withali Phases

.... Erionite and Stellerite Suppressed

_10

o Analcime ----5 rdenite

_= - r - i Mord.

0 ' ---- - i Present0 .F_,rjor_ite"Heui. -. Phillip.I YM Water _ _

0_-5 i "o ' tilo 'Chab,

--I-10 S_ellerite ',Clinoptilol

-15 iI

I

-20-20 -15 -10 -5 0 5 10 15 20

Log a((K2)/Ca)

Fig. 7III"

Table 1

Fracture Lining Zeolites Which Occur at Yucca Mountain t

Abundance

Sample 2 in Fracture Coexisting Zeolite/Clay Minerals

Analcime

USW G-2 3137.0/3137.3 Major Mordenite

Chabazite

J- 13 1345 Major Clinoptilolite, SmectiteVH- 1 1690.8/1691.0 Trace Clinoptilolite, SmectiteUE-25b#1h 2164.7/5.0 Trace Clinoptilolite, Mordenite, Smectite

Erionite

UE-25a#1 1296.2 Major Clinoptilolite, SmectiteUSW GU-3 1189.3/1189.6 Minor Clinoptilolite, Smectite

PhiUipsite

UE-25a#1 1301.5/1302.0 Major Clinoptilolite, Smectite

USW GU-3 1290.1/1200.6 Major Clinoptilolite, Smectite

Stellerite

UE-25a#1 1243 Minor Clinoptilolite, Mordenite

USW G-1 -- Sporadic from 209-391 m (686-1282 feet)

Abundance varies from Trace to MajorOccurs with Clinoptilolite and Smectite

USW G-2 -- Sporadic from 441-504 m (1447-1653 feet)

Abundance varies from Trace to MajorOccurs with Clinoptilolite, Mordenite, and Smectite

_Clinoptilolite/heulandite and mordenite are not included in this table since they are common throughoutYucca Mountain.

'Sample label is equal to the sample depth in feet.

Table 3

Representative Yucca Mountain Water Analyses

From Kerrisk (1987)

SampledDrill Depth Temp Log Log LogHole (meters) °(2 Ca I M_ I Na_ K__...___ _ p__H_.K21Ca Na21Ca SiO.Q_

J- 12 In_gral 2 27 0.3493 0.0864 1.6529 0.1304 0.8987 7.1 -4.31 -2.11 -3.05

J-13 Integral 2 31 0.2994 0.0864 1.8269 0.1279 0.9487 7.2 -4.26 -1.95 -3.02

UE-25blh Integral 2 36 0.4242 0.0243 2.0009 0.0895 0.8655 7.5 -4.72 -2.03 -3.06

UE-25blh 863-875 37.2 0.4491 0.0296 2.0009 0.0716 0.8488 7.1 -4.94 -2.05 -3.07

UE-25p#1 381-1197 44.3 0.9232 0.4114 4.0018 0.1432 0.8155 6.8 -4.65 -1.76 -3.09

UE-25p#1 1297-1805 56 2.4950 1.6046 6.5246 0.3069 0.6828 6.6 -4.42 -1.77 -3.17

USWG-4 Integral z 35.6 0.3244 0.0082 2.4794 0.0537 0,7490 7.7 -5.05 -1.72 -3.13

USW H-1 572-687 33 0.1123 0.0041 2.2184 0.0614 0.7822 7.7 -4.47 -1.36 -3.11

USW H-1 687-1829 34.7 0.1547 0.0041 2.2184 0.0409 0.6657 7.5 -4.97 -1.50 -3.18

USWH-3 822-1220 26.5 0.0200 0.0008 5.2197 0.0281 0.7157 9.2 -4.40 0.13 -3.15

USW H-4 Integral 2 34.8 0.4242 0.0119 3.1753 0.0665 0.7656 7.4 -4.98 -1.62 -3.12

USWH-5 Integral 2 35.3 0.0499 0.0004 2.6099 0.0537 0.7989 7.9 -4.24 -0.86 -3.10

USW H-6 Integral 2 37.8 0.1023 0.0037 3.7408 0.0333 0.7989 8.1 -4.96 -0.86 -3.10

USWH-6 753-835 41.6 0.0349 0.0008 3.8278 0.0333 0.7822 8.3 -4.50 -0.38 -3.11

USWH-6 608-646 37.2 0.1173 0.0029 3.8278 0.0358 0.8155 8.3 -4.96 -0.90 -3.09

USW VH-I Integral 2 35.5 0.2470 0.0617 3.3928 0.0460 0.8155 7.5 -5.07 -1.33 -3.09

mmoles/liter.

2 Integral well sample in which the entire well bore was pumped.

Table 4

Unique Zeolite Sequences Occurring in Fractures in

Drill Holes UE-25a#1 and USW GU-3

Depth Smec- Ciinopt- Mord- Erion- Phillip-

Sample I meters tite ilolite enite ite site

UE-25a#1

1252.3 381.6 Trace Minor Major ......

1274.5 388.4 Major Major Trace .....

1276.0/76.2 388.9 Major Minor Minor ......

1282.6 390.9 Major Major Trace ......

1296.2 395.1 Minor Major --- Major ---

1301.5/2.0 396.6 Minor Major ...... Major

1309.0/9.2 399.0 Minor Major .........

1318.4/19.5 402.0 Trace Major Minor ......

1322.9/23.2 403.2 Minor Major Minor .......

1339.5/9.7 408.3 Minor Major Major ......

1361.8/62.0 415.1 Minor Major Minor ......

USW GU-3

1162.7/63.0 354.5 Major --- Minor ......

1189.3/89.6 362.4 Minor Major ..... Minor ---

1200.1/.6 365.7 Minor Minor ...... Major

1210.2/10.6 368.8 Major --- Trace ......

1232.0/32.1 375.5 Major ............

'Sample label is equiv',dent to the sample depth in feet.

'1II _v, If

Additional QA Documentatiom

DATA Sources:

Data used in this report can be found in the notebook TWS-EES-l-1-92-3,

pages 25 to 31.

Software Used:

Ge0-Calc - PTA System

YMP Release Label = GE0-CALC PTA/PTX-01-00-00

ECD # = 29

Approval Date = 08/22/91

''/ I