Prepared in cooperation with the

U.S. Department of Energy,

Office of Repository Development, under

Interagency Agreement DE-AI08-02RW12167

Secondary Mineral Deposits and Evidence of Past

Seismicity and Heating of the Proposed Repository

Horizon at Yucca Mountain, Nevada

Water-Resources Investigations Report 03–4321

U.S. Department of the Interior

U.S. Geological Survey

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Secondary Mineral Deposits and Evidence 

of Past Seismicity and Heating of the 

Proposed Repository Horizon at Yucca 

Mountain, Nevada

By Joseph F. Whelan

Prepared in cooperation with the

U.S. Department of Energy,

Office of Repository Development, under

Interagency Agreement DE-Al08-02RW12167

Water-Resources Investigations Report 03–4321

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

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Telephone: 1-888-ASK-USGS

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Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.
iii

Contents

Abstract .......................................................................................................................................................... 1

Introduction.................................................................................................................................................... 1

Site Geology................................................................................................................................................... 2

Secondary Mineral Deposits....................................................................................................................... 2

Vapor-Phase and Fumarolic Mineral Deposition............................................................................ 2

Low-Temperature Secondary Mineral Deposition..........................................................................3

Thermal History.............................................................................................................................................. 3

Evidence of Past Seismicity and Heating.................................................................................................. 4

Tuff Fragmentation................................................................................................................................5

Coating Displacement or Damage to Delicate Mineral Textures................................................. 6

Heating Effects and Alteration of Fracture Surfaces..................................................................... 6

Summary......................................................................................................................................................... 9

References Cited..........................................................................................................................................11

Figures

1. Map showing location of Yucca Mountain, Nevada, and the Exploratory Studies 

 Facility (ESF) and Enhanced Characterization of the Repository Block (ECRB)

 Cross Drift tunnels, with generalized surficial geology.............................................................2

 2–4. Graphs showing:

 2. Depositional temperatures and timing of secondary calcite 

 from deposits in the Exploratory Studies Facility (ESF) and Enhanced 

 Characterization of the Repository Block (ECRB) Cross Drift tunnels........................... 4

 3. Changes in calcite δ13C values with paragenetic stage for samples 

 from the Exploratory Studies Facility (ESF) and Enhanced 

 Characterization of the Repository Block (ECRB) Cross Drift tunnels........................... 5

 4. Values of δ13C and δ18O in calcite from locations in the Exploratory 

 Studies Facility (ESF) and Enhanced Characterization of the 

 Repository Block (ECRB) Cross Drift tunnels.......................................................................6

5. Photomicrograph of a petrographic section of tuff fragments in a secondary

 mineral deposit from a lithophysal cavity in the Enhanced Characterization of

 the Repository Block (ECRB) Cross Drift tunnel at about station 10+10................................ 7

6. Photograph of a sawn and polished surface of tuff fragments in a calcite-

 cemented breccia from the Exploratory Studies Facility (ESF) tunnel at about

 station 76+17.6................................................................................................................................. 8
iv

7. Photomicrograph of a petrographic section from a secondary mineral coating

 on a steeply dipping fracture in the Exploratory Studies Facility (ESF) tunnel at

 about station 52+43.........................................................................................................................9

8. Photomicrograph of a petrographic section of a coating of calcite, chalcedony, 

 and quartz showing early alteration of a near-vertical fracture in the 

 Exploratory Studies Facility (ESF) tunnel at about station 1+62............................................10

Conversion Factors, Standards, Acronyms, and 

Abbreviations

 

Multiply By To obtain

millimeter (mm) 0.03937 inch (in.)

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

 °F=(1.8×°C)+32

Stable isotope compositions are reported as delta (δ) values in units of parts per thousand 

(denoted as per mil or ‰) relative to a standard of known composition: Pee Dee Belemnite 

(PDB) for carbon (C), and Standard Mean Ocean Water (SMOW) for oxygen (O) (Craig, 1961).

DDA Drift Degradation Analysis

ECRB Enhanced Characterization of the Repository Block

ESF Exploratory Studies Facility

Ma million years ago

m.y. million years

Pb lead

U uranium

USGS U.S. Geological Survey

UZ unsaturated zone
Abstract

The Drift Degradation Analysis (DDA) (BSC, 2003) for 

the proposed high-level radioactive waste repository at Yucca 

Mountain, Nevada, describes model simulations of the effects 

of pre- and post-closure seismicity and waste-induced heating 

on emplacement drifts. Based on probabilistic seismic hazard 

analyses of the intensity and frequency of future seismic 

events in the region (CRWMS M&O, 1998), the DDA concludes that future seismicity will lead to substantial damage to 

emplacement drifts, particularly those in the lithophysal tuffs, 

where some simulations predict complete collapse of the drift 

walls. 

Secondary mineral studies conducted by the U.S. 

Geological Survey since 1995 indicate that secondary calcite 

and silica have been deposited in some fractures and lithophysal cavities in the unsaturated zone (UZ) at Yucca Mountain 

during at least the past 10 million years (m.y.), and probably 

since the tuffs cooled to less than 100°C. Tuff fragments, 

likely generated by past seismic activity, have commonly 

been incorporated into the secondary mineral depositional 

sequences.

Preliminary observations indicate that seismic activity has generated few, if any, tuff fragments during the last 

2 to 4 m.y., which may be inconsistent with the predictions 

of drift-wall collapse described in the DDA. Whether or not 

seismicity-induced tuff fragmentation occurring at centimeter 

to decimeter scales in the fracture and cavity openings relates 

directly to failure of tuff walls in the 5.5-m-diameter waste 

emplacement drifts, the deposits do provide a potential record 

of the spatial and temporal distribution of tuff fragments in the 

UZ. In addition, the preservation of weakly attached coatings 

and (or) delicate, upright blades of calcite in the secondary 

mineral deposits provides an upper limit for ground motion 

during the late stage of deposition that might be used as input 

to future DDA simulations. Finally, bleaching and alteration 

at a few of the secondary mineral sites indicate that they were 

subjected to heated gases at approximately the temperatures 

expected from waste emplacement. These deposits provide 

at least limited textural and mineralogic analogs for wasteinduced, high-humidity thermal alteration of emplacement 

drift wall rocks.

Introduction

Performance objectives for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, require 

waste containment for a minimum of 10,000 years (fig. 1). As 

a result, the long-term stability of emplacement drifts and the 

potential consequences of drift wall collapse on waste containment are central to assessments of site performance. The Drift 

Degradation Analysis (DDA) (BSC, 2003) describes model 

simulations of the effects of pre- and post-closure seismicity and waste-induced heating on (1) tuff fragmentation and 

the possible collapse of drift walls, (2) stress distribution in 

the drift wall rocks, and (3) possible alteration of fracture 

surfaces (weathering/rock joint degradation) produced by 

heating at high water-vapor pressures. Using probabilistic 

seismic hazard analyses of the intensity and frequency of 

future seismic events in the region (CRWMS M&O, 1998), 

the DDA concludes that post-closure seismicity will lead to 

substantial damage to emplacement drifts, particularly those in 

the lithophysal tuffs, where some simulations predict complete 

collapse of the drift walls.

Since 1995, the U.S. Geological Survey (USGS), in 

cooperation with the U.S. Department of Energy, has studied 

deposits of secondary calcite and silica in the tuffs. These 

deposits, located in centimeter to decimeter scale fractures and 

cavities in the unsaturated zone (UZ) rock at Yucca Mountain, 

contain evidence of past seismic and heating events. Whether 

or not seismicity-induced tuff fragmentation occurring in fracture and cavity openings relates directly to failure of tuff walls 

in the 5.5-m-diameter emplacement drifts, the deposits do provide a potential record of the spatial and temporal distribution 

of tuff fragmentation in the UZ and an upper limit for ground 

motion during the late stage of secondary mineral deposition. 

The existing archive of more than 400 samples of secondary 

mineral deposits collected by the USGS from underground 

Secondary Mineral Deposits and Evidence of Past 

Seismicity and Heating of the Proposed Repository 

Horizon at Yucca Mountain, Nevada

By Joseph F. Whelan
exposures in the Exploratory Studies Facility (ESF) and 

Enhanced Characterization of the Repository Block (ECRB) 

Cross Drift (fig. 1) would permit reconstruction of this record.

The DDA also addresses the alteration (rock joint 

degradation and loss of fracture surface contact cohesion) of 

tuff surfaces that could result from the moist and warm (140 

to 160°C) conditions following waste emplacement. Weak 

alteration observed on some fracture surfaces associated with 

a few of the secondary mineral deposits, possibly related to the 

waning stages of the initial cooling of the tuffs, may provide 

an analog for waste-induced thermal alteration.

This report describes observations made during the 

course of the USGS studies that relate to records of past seismicity and heating of the UZ. Site geology, secondary mineral 

deposits, and thermal history are summarized and evidence of 

past seismicity and heating is described.

Site Geology

The proposed high-level radioactive waste repository 

at Yucca Mountain would be constructed in the thick UZ in 

the Topopah Spring Tuff of the Paintbrush Group rhyolitic to 

quartz dacitic tuffs. The Miocene-age Paintbrush Group (12.8 

to 12.7 million years ago [Ma], Sawyer and others, 1994) consists of two 200- to 300-m-thick, largely welded tuffs, the Tiva 

Canyon Tuff (younger) and the Topopah Spring Tuff (older), 

which are separated by a thin (~50 m) sequence of nonwelded 

and weakly fractured bedded tuffs (Moyer and others, 1996).

The Topopah Spring Tuff has been divided into zones, 

primarily distinguished by the presence or absence of lithophysal cavities that formed from and were altered by gases 

that exsolved during the initial cooling of the tuffs (Buesch 

and others, 1996). Waste emplacement drifts would be located 

in the upper lithophysal (Tptpul), middle nonlithophysal 

(Tptpmnl), and lower lithophysal (Tptpll) zones.

Secondary Mineral Deposits

Vapor-Phase and Fumarolic Mineral Deposition

The earliest secondary mineralization in the tuffs was 

from hot gases that exsolved during initial cooling of the tuffs. 

Fracture and lithophysal cavity walls were altered by these 

gases, which also deposited vapor-phase minerals consisting largely of tridymite or cristobalite, sanidine, and minor 

amounts of hematite, biotite, and garnet (Vaniman and others, 

1984). Fumaroles occurred near the tops of the Tiva Canyon 

and Topopah Spring Tuffs, with clay, zeolitic, and (or) silicic 

alteration and deposition of minor amounts of drusy quartz 

Figure 1. Location of Yucca Mountain, Nevada, and the 

Exploratory Studies Facility (ESF) and Enhanced Characterization 

of the Repository Block (ECRB) Cross Drift tunnels, with surficial 

geology generalized from Day and others (1998). The distribution 

of Quaternary valley fill (white) and bedrock (shaded) are shown 

in the upper map.

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EXPLANATION

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2 Secondary Mineral Deposits and Evidence of Past Seismicity at Yucca Mountain, Nevada
and fluorite on some fractures (Levy and others, 1996). As 

the tuffs cooled, weak or waning fumarolic systems may have 

deposited calcite and silica at near-boiling temperatures on the 

surfaces of some fractures in the Tiva Canyon Tuff (Whelan 

and others, 2003).

Low-Temperature Secondary Mineral 

Deposition

Calcite and silica (quartz, chalcedony, and opal) with 

minor amounts of fluorite, zeolites, and manganese oxides are 

found in some open fractures and lithophysal cavities in the 

Topopah Spring and Tiva Canyon Tuffs in the UZ (Whelan 

and others, 1994; Paces and others, 2001; Whelan and others, 

2002). Reconnaissance studies of these deposits from drill 

core samples indicate that the secondary minerals formed in 

the UZ from meteoric waters percolating along fractures to 

the water table (Szabo and Kyser, 1990). This interpretation is 

supported by textural and geochemical studies of pedogenic 

calcrete in soils and fault-infillings at the surface (Quade and 

Cerling, 1990; Stuckless and others, 1991; U.S. Department 

of Energy, 1993; Vaniman and others, 1994; and Vaniman and 

Whelan, 1994) that demonstrate a clear link between pedogenic deposition in the overlying soils, infiltration of meteoric 

water, and secondary mineral deposition in the UZ (Whelan 

and others, 1994; Paces and others, 2001). 

Further evidence that secondary mineral deposition in the 

UZ occurred under vadose conditions is provided by underground exposures in the ESF and ECRB Cross Drift. These 

exposures show the deposits are sparsely and heterogeneously 

distributed on less than 10 percent of potential fracture and 

cavity depositional sites, and are generally restricted to the 

floors of lithophysal cavities and the footwalls of fractures in 

the welded tuffs (Paces and others, 2001; Whelan and others, 

2002).

The secondary mineral deposits range in thickness from 

a fraction of a millimeter to as much as 5 cm. Typical coatings are 5 to 10 mm thick in cavities and 1 to 5 mm thick on 

fractures. Secondary mineral deposits on fracture footwalls 

tend to form coatings of relatively uniform thickness or masses 

of calcite-cemented fracture (or fault) breccia. On the floors of 

lithophysal cavities, the deposits are coarser grained and commonly contain elongate, thin blades of calcite.

Based on visual examination of samples, the generalized 

paragenetic sequence of secondary mineral deposition in the 

UZ is divided into early, intermediate, and late stages (Whelan 

and others, 2002). The early stage consists of calcite, followed 

by calcite that is locally admixed with fluorite and commonly 

capped by deposition of thick (up to about 1 cm) layers of botryoidal chalcedony and (or) drusy quartz. Where present, this 

layer of silica minerals marks the end of the early stage. The 

intermediate and late stages are mineralogically similar, but 

the textures are different. Both consist mainly of calcite and 

opal (although minor amounts of chalcedony may be found 

in the basal part of the intermediate stage). Intermediatestage calcite typically displays an elongate, thin-bladed habit, 

whereas late-stage calcite typically forms overgrowths on 

older calcite, often as distinctive knobby or corniced masses 

on the tips of intermediate-stage blades. Intermediate- and 

late-stage opal forms botryoidal masses and laminar sheets on 

or interlayered with calcite (Whelan and others, 2002).

Thermal History

The post-eruptive thermal history of the UZ tuffs has 

been determined by combined oxygen isotope, fluid inclusion, 

and uranium-lead (U-Pb) dating studies of secondary minerals from deposits found in the ESF and ECRB Cross Drift 

(Whelan and others, 2001; Whelan and others, 2002; Neymark 

and others, 2003; Wilson and others, 2003). Although the UZ 

calcite is not amenable to U-Pb dating, chalcedony and opal 

provide reliable 207Pb/235U ages and, where closely associated with calcite whose depositional temperature could be 

estimated from fluid inclusions or δ18O values, provide the 

age framework for the thermal history of the UZ. Figure 2 

shows depositional temperatures of calcite in deposits from the 

ESF and ECRB Cross Drift, determined from fluid-inclusion 

homogenization temperatures (triangles or diamonds) or estimated from δ18O values (circles) and the 207Pb/235U ages (±2 

sigma) of chalcedony or opal associated with the calcite. For 

determinations that are a minimum age of calcite deposition 

(triangles and some circles), the true age of the calcite deposition lies somewhere along the tie lines (dotted) connecting 

the measured age to the eruptive age of the Paintbrush Group 

tuffs. Diamonds and most circles represent calcite whose 

depositional age is tightly constrained by opal or chalcedony 

age determinations. Temperatures were calculated from the 

δ18O value of calcite (circles) assuming a δ18O value of –11 

per mil (‰) for the depositing water. Best-fit curves are shown 

for depositional waters having δ18O values of –13, –11, and 

–9‰. This thermal history indicates that the early stage ended 

about 8 Ma with depositional temperatures of 50 to 90°C. 

Depositional temperatures then slowly decreased during the 

intermediate stage to present-day ambient temperatures of 20 

to 25°C, which have prevailed for the past 2 to 4 million years 

(m.y.), through deposition of the late-stage minerals (Whelan 

and others, 2001, 2003; Wilson and others, 2003).

The δ13C values of calcite constrained by 207Pb/235U 

ages of chalcedony or opal are shown in figure 3. Where the 

associated chalcedony or opal provides only a minimum or 

maximum estimate of the age of the calcite, an arrow points in 

the direction of the true age of the calcite. Approximate time 

boundaries separating the early, intermediate, and late stages 

of deposition are shown. Calcite δ13C values decrease steadily 

from the early stage, where values commonly exceed +4‰, 

through the intermediate stage to the late stage, where they are 

generally less than –4‰. This time-dependent decrease allows 

Secondary Mineral Deposits 3
Figure 2. Depositional temperatures and timing of secondary calcite from 

deposits in the Exploratory Studies Facility (ESF) and Enhanced 

Characterization of the Repository Block (ECRB) Cross Drift tunnels. Temperature estimated from fluid inclusions or calcite δ18O values and timing 

estimated from the 207Pb/235U ages of chalcedony or opal associated with 

the calcite (modified from Whelan and others, 2003).

general inferences of the timing of deposition from the δ13C 

values of calcite. Figure 4 shows the δ13C values of calcite 

decreasing and the δ18O values increasing from the early to 

the late stages. Basal, intermediate, and outer positions were 

determined by petrographic examination and generally correspond to the early, intermediate, and late paragenetic stages. 

The δ13C and δ18O values, combined with the textural and mineralogical characteristics of the different stages and age- δ13C 

relations shown in figure 3, permit δ13C and δ18O studies of 

individual samples to be correlated with the age framework of 

calcite deposition.

Evidence of Past Seismicity and 

Heating

The secondary mineral deposits record not only the thermal history of the UZ but also, by their textures, local records 

of tuff fragmentation (breccia deposits) in faults, fractures, 

and lithophysal cavities. In addition, the survival of weakly 

attached coatings and (or) delicate mineral textures may 

provide an estimate of past peak ground motions in the rocks 

in the proposed repository. Finally, alteration and bleaching 

of the fracture walls of some deposits may present an analog 

for the weathering effects of hot, water-saturated air on tuff 

surfaces.

4 Secondary Mineral Deposits and Evidence of Past Seismicity at Yucca Mountain, Nevada

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Tuff Fragmentation

As secondary mineral coatings formed, some incorporated tuff fragments. In faults and fractures, these fragments 

generally came from higher in the rock mass and they record 

the availability of loose tuff fragments and (or) past seismic 

activity that may have generated or dislodged loose material. Secondary mineral deposits may incorporate such tuff 

fragments (fig. 5) or cement them in fault or fracture breccias (fig. 6). Figure 5 shows a secondary mineral coating 

with included tuff fragments from a lithophysal cavity at 

ECRB Cross Drift station 10+10. The paragenetic boundaries 

between the early, intermediate, and late stages of deposition 

are delineated in red. Calcite δ13C and δ18O values range from 

–6.4 to 4.8‰ and from 14.6 to 16.2‰, respectively, and are 

consistent with the paragenetically constrained ranges shown 

in figure 4. Angular fragments of tuff ranging in size from less 

than a millimeter to more than a centimeter, as shown in the 

sample from ECRB Cross Drift station 10+10, are common in 

early-stage calcite and rare in intermediate- and late-stage calcite. Impregnation with blue-dyed epoxy distinguishes primary 

porosity. Figure 6 shows calcite cementation of a fault breccia 

at ESF station 76+17.6. This cemented breccia fills a nearvertical fault opening that is about 10 cm wide. Paragenetic 

relations in cemented breccias are generally ambiguous, even 

at the small scale of a petrographic section. Calcite δ13C and 

δ18O values range from –6.4 to 2.5‰ and from 14.0 to 18.3‰, 

respectively, and are consistent with the calcite δ13C and δ18O 

variations shown in figure 4.

In lithophysal cavities, tuff infall from the walls or 

ceilings into secondary mineral deposits provides a record 

of caving or scaling from the cavity walls that could have 

been in response to seismic shaking. In faults, fractures, and 

lithophysal cavities, these fragments generally range from less 

than a millimeter to several centimeters. In a few lithophysal cavities, larger fragments of the walls or ceilings fell and 

became cemented into deposits on the cavity floors. Although 

the distribution and frequency of fragment incorporation into 

the coatings has not been documented, general observations 

made during previous studies of samples from the ESF and 

Figure 3. Changes in calcite δ13C values with paragenetic stage for samples 

from the Exploratory Studies Facility (ESF) and Enhanced Characterization of the 

Repository Block (ECRB) Cross Drift tunnels (modified from Whelan and Moscati, 

1998).

Thermal History 5

Paintbrush Group Eruptions

Late

Intermediate

Early

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ECRB Cross Drift indicate that inclusion of tuff fragments was 

common during the early stage but became increasingly rare 

during the intermediate and late stages of secondary mineral 

deposition (fig. 5). These preliminary observations could be 

verified by systematic examination of the existing collection 

of samples and petrographic sections from the ESF and ECRB 

Cross Drift. Such data, combined with geochronologic, isotopic, and textural constraints, could be used to generate a map 

and history of tuff fragmentation in the UZ at Yucca Mountain.

Coating Displacement or Damage to Delicate 

Mineral Textures

Fracture coatings that are or were weakly attached to 

the fracture walls locally provide an additional, anecdotal 

indication of peak ground motions. Some fracture coatings 

observed in the ESF and ECRB Cross Drift were so weakly 

attached that they could be pried easily from the fracture wall 

with a knife or even removed by hand. Such in-place coatings 

provide a measure of the maximum intensity of past ground 

motions in the UZ.

Some secondary mineral deposits contain fragments of 

fracture coatings that apparently have been dislodged from 

higher in the fracture, accumulated at a restriction, and then 

cemented together by later calcite deposition. Figure 7 shows 

a secondary mineral deposit at ESF station 52+43, from a 

steeply dipping fracture in the Topopah Spring Tuff, containing identifiable fragments of vapor-phase and calcite coatings. 

Although the high δ13C values indicate that coating deposition began in the early stage, the δ13C and δ18O values of 

–6.7‰ and 18.4‰, respectively, are consistent with late-stage 

deposition and indicate that some of the coating displacement 

probably postdates 2 to 4 Ma. The paragenetic position of the 

calcite with δ13C of 5.7‰ and δ18O of 14.5‰ is uncertain but 

consistent with either the early or intermediate stage. Impregnation with blue-dyed epoxy distinguishes primary porosity. 

Combined isotopic and geochronological study of the secondary minerals could provide estimates of the timing of infall in 

such deposits.

Delicate, upright calcite blades with heights and widths 

of as much as 2 to 3 cm, but thicknesses less than a millimeter, 

are common. These delicate blades began forming during the 

intermediate stage and typically have top-heavy overgrowths 

of late-stage calcite and (or) opal that should increase their 

susceptibility to breaking during seismic shaking. Although 

the ground motion accelerations required to break such blades 

are unknown, broken crystals have not been observed in the 

deposits that have been studied. The preservation of these 

blades, therefore, provides an upper limit for ground motion 

during the late stage.

Surface maps of fault displacements at Yucca Mountain 

show that 12 seismic events producing displacements greater 

than 20 cm (with estimated magnitudes of 5.6 to 6.9) occurred 

during the last 500,000 years (CRWMS M&O, 2000, sec. 

12.3.7.6). The average recurrence interval for these events is 

44,000 years. However, late-stage secondary mineralization 

records little tuff fragment input or damage to the coatings 

that would be evidence for large-magnitude earthquakes. 

Although the open-space dimensions of UZ fractures and 

cavities are considerably smaller than the design dimensions 

of the emplacement drifts modeled in the DDA, the degree of 

tuff fragmentation and collapse predicted by the DDA from 

pre- and post-closure seismic and heating effects appears to 

be much greater than that recorded by the secondary mineral 

deposits.

Heating Effects and Alteration of Fracture 

Surfaces

The DDA (BSC, 2003) predicts maximum drift wall 

temperatures of 140 to 160°C within 100 years of waste 

emplacement, with concomitant thermal expansion stresses 

to the rocks and increased rates of weathering (alteration) of 

fracture walls. Secondary mineral fluid-inclusion studies show 

that the UZ was heated to temperatures of at least 50 to 70°C, 

Figure 4. Values of δ13C and δ18O in calcite from locations in the 

Exploratory Studies Facility (ESF) and Enhanced Characterization 

of the Repository Block (ECRB) Cross Drift tunnels (modified from 

Whelan and others, 2002). Stable isotope standards are Pee Dee 

Belemnite (PDB) for carbon and Standard Mean Ocean Water 

(SMOW) for oxygen.

6 Secondary Mineral Deposits and Evidence of Past Seismicity at Yucca Mountain, Nevada

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Figure 5. Photomicrograph of a petrographic section of tuff fragments in a secondary 

mineral deposit from a lithophysal cavity in the Enhanced Characterization of the 

Repository Block (ECRB) Cross Drift tunnel at about station 10+10 showing: A, the 

secondary mineral paragenetic stages in transmitted plane light; and B, the same image 

showing the δ13C and δ18O values of calcite subsamples. Black square is approximately 

2.3 millimeters wide.

and locally to at least 90°C, during the early stage (Whelan 

and others, 2003). 

A few of the higher temperature (80 to 90°C) secondary 

mineral coatings, such as those observed at ESF station 1+62, 

have bleached and altered fracture and clast surfaces. This 

bleaching and alteration is not accompanied by deposition of 

vapor-phase minerals, such as tridymite or hematite, indicating that it postdates the highest temperature vapor-phase 

Evidence of Past Seismicity and Heating 7

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δ

18O of calcite in per mil, SMOW (Standard Mean Ocean Water)

Approximate paragenetic stage boundary

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Figure 6. Photograph of a sawn and polished surface of tuff fragments in a calcitecemented breccia from the Exploratory Studies Facility (ESF) tunnel at about station 

76+17.6 showing: A, the breccia texture; and B, the δ13C and δ18O values of calcite 

subsamples. Scale bar is 3 centimeters.

alteration. Figure 8 shows early-stage calcite, chalcedony, and 

quartz, followed by intermediate- and late-stage calcite coatings on a tuff fragment from a near-vertical fracture at ESF 

station 1+62. In other sections from this site, calcite paragenetically equivalent to that calcite marked with a red “+” has fluid 

inclusion temperatures of 80 to 90°C and low δ18O values of 

3 to 5‰ that are consistent with elevated temperatures. The 

tuff fragment has thin rinds of bleaching and alteration beneath 

the secondary minerals. At higher magnification (50X), the 

rind shown in the inset photomicrograph (a) is finer grained 

and less recrystallized than that in inset photomicrograph (b), 

indicating alteration at somewhat lower temperatures. This 

sample site is less than 50 m below the present-day land surface. Paleostratigraphic reconstruction indicates the maximum 

8 Secondary Mineral Deposits and Evidence of Past Seismicity at Yucca Mountain, Nevada

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δ

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Figure 7. Photomicrograph of a petrographic section from a secondary mineral coating 

on a steeply dipping fracture in the Exploratory Studies Facility (ESF) tunnel at about station 52+43. Black square is approximately 2.3 millimeters wide.

burial depth was never more than 125 m (D.C. Buesch, U.S. 

Geological Survey, oral commun., 2002). Impregnation with 

blue-dyed epoxy distinguishes primary porosity. In typical 

hydrothermal systems, such bleaching is commonly accompanied by a change in the whole-rock δ18O values due to O 

isotopic exchange between the rock and the altering solution 

(for example, Criss and Taylor, 1986; and Holt, 2002). The 

bleached wall rock at ESF station 1+62, however, shows no 

shift from the δ18O values of the unaltered wall rock (J.F. 

Whelan, U.S. Geological Survey, unpub. data, 2003). This 

indicates that the alteration did not result from interaction 

with hot, liquid water, but from reaction with water vapor. 

The O mass balance and, therefore, the capacity for fluid-rock 

interactions to shift the δ18O value of the altered rock, is much 

lower for vapor-rock exchange than for water-rock exchange. 

The bleached tuff surfaces at locations such as ESF station 

1+62 are, therefore, consistent with formation from weak 

or waning fumarolic systems during the latter stages of tuff 

cooling and may provide textural and mineralogic analogs for 

the post-emplacement effects of heated, moist weathering on 

fracture surfaces in the drift walls.

Examination of the bleached zone at higher magnification (fig. 8 a, b) indicates that this heating coarsened mineral 

textures and increased porosity. Whether the bleaching also 

was accompanied by significant changes in tuff chemistry or 

mineralogy, such as the formation of more easily deformed 

clay minerals that could facilitate movement along fractures 

and (or) tuff fragmentation, is not known. Such changes 

could be determined by X-ray diffractometry or inductively 

coupled plasma mass spectrometry techniques. Studies of the 

deposits at ESF station 1+62 could provide useful analogs for 

the effects of post-waste-emplacement fracture-wall weathering processes on the mineralogy and mechanical strength of 

fracture surfaces. 

Summary

The DDA (BSC, 2003) for the proposed high-level radioactive waste repository at Yucca Mountain, Nevada, describes 

model simulations of the effects of pre- and post-closure seismicity and waste-induced heating on the emplacement drifts. 

Based on probabilistic seismic hazard analyses of the intensity 

and frequency of future seismic events in the region, the DDA 

concludes that future seismicity will lead to substantial damage to emplacement drifts, particularly those in the lithophysal 

tuffs, where some simulations predict complete collapse of the 

drift walls. 

Secondary mineral deposits, consisting largely of calcite 

and silica minerals, are found in some fractures and lithophysal cavities in the UZ, where they have been forming during 

Summary 9

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Figure 8. Photomicrograph of a petrographic section of a coating of calcite, chalcedony, 

and quartz showing early alteration of a near-vertical fracture in the Exploratory Studies 

Facility (ESF) tunnel at about station 1+62. Alteration texture of inset photomicrograph (a) is 

finer grained and less recrystallized than that of inset photomicrograph (b). Scale bar is 1 

centimeter.

at least the past 10 m.y., and probably since the tuffs cooled to 

less than 100°C. Depositional temperatures of the secondary 

minerals ranged to as high as 90°C but were generally from 

35 to 60°C during the early stage and parts of the intermediate 

stage. Late-stage deposition during the past 2 to 4 m.y. appears 

to have been at or near present-day ambient temperatures of 

20 to 25°C. Tuff fragments, likely generated by past seismic 

activity, are commonly part of the secondary mineral depositional sequences. The secondary mineral deposits, therefore, 

provide a physical record of the effects of past heating and 

seismicity on open spaces in the tuffs. Although the secondary 

mineral coatings have not been systematically examined for 

evidence of tuff fragmentation, the petrographic thin sections 

and hand specimens from more than 400 samples collected 

by the USGS from the ESF and ECRB Cross Drift since 1995 

could be used to construct a time-dependent record and spatial 

distribution map of tuff fragmentation. Preliminary observations indicate that few, if any, tuff fragments were incorporated 

into mineral coatings during the last 2 to 4 m.y., and there 

has been little, if any, disturbance of weakly attached coatings and (or) delicate, upright blades of secondary calcite 

contained in the deposits. Whether or not seismicity-induced 

tuff fragmentation occurring at centimeter to decimeter scales 

in the fracture and cavity openings relates directly to failure 

of tuff walls in the 5.5-m-diameter waste emplacement drifts, 

the deposits do provide a potential record of the spatial and 

temporal distribution of tuff fragments in the UZ and an upper 

limit for ground motion during the late stage of secondary 

mineral deposition.

The DDA also addresses the alteration of fracture surfaces that will accompany heating to 140 to 160°C in a highhumidity atmosphere and whether it will compromise the contact cohesion between fracture walls (BSC, 2003). Bleaching 

and alteration at a few of the secondary mineral sites indicate 

that they were subjected to heated gases at temperatures of at 

least 90°C. These deposits, therefore, may provide textural and 

10 Secondary Mineral Deposits and Evidence of Past Seismicity at Yucca Mountain, Nevada

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mineralogic analogs for the effects of waste-induced heating 

on the drift wall rock.

References Cited

BSC (Bechtel SAIC Company), 2003, Drift degradation 

analysis: Las Vegas, Nevada, Bechtel SAIC Company, 

ANL-EBS-MD-000027 REV 02, 316 p.

Buesch, D.C., Spengler, R.W., Moyer, T.C., and Geslin, J.K., 

1996, Proposed stratigraphic nomenclature and macroscopic 

identification of lithostratigraphic units of the Paintbrush 

Group exposed at Yucca Mountain, Nevada: U.S. Geological Survey Open-File Report 94–469, 45 p.

Craig, H., 1961, Isotopic variations in meteoric waters: 

Science, v. 133, p. 1702–1703.

Criss, R.E., and Taylor, Jr., H.P., 1986, Meteoric-hydrothermal systems, in Valley, J.W., Taylor, Jr., H.P., and O’Neil, 

J.R., eds., Stable isotopes in high temperature geological 

processes: Reviews in Mineralogy, v. 16, p. 373–424.

CRWMS M&O (Civilian Radioactive Waste Management 

System Management and Operating Contractor), 1998, 

Probabilistic seismic hazard analyses for fault displacement 

and vibratory ground motion at Yucca Mountain, Nevada: 

Las Vegas, Nevada, CRWMS M&O, Milestone SP32IM3, 

September 23, 1998, v. 1–3.

CRWMS M&O, 2000, Yucca Mountain site description: Las 

Vegas, Nevada, CRWMS M&O, TDR-CRW-GS-000001 

REV 01 ICN 01, sec. 12.3.7.6.

Day, W.C., Potter, C.J., Sweetkind, D.S., Dickerson, R.P., and 

San Juan, C.A., 1998, Bedrock geologic map of the central 

block area, Yucca Mountain, Nye County, Nevada: U.S. 

Geological Survey Miscellaneous Investigations Series Map 

I–2601, 15 p., 2 sheets.

Holt, E.A., 2002, 18O/16O evidence for an early, short-lived 

(~10 yr), fumarolic event in the Topopah Spring Tuff near 

the proposed high-level nuclear waste repository within 

Yucca Mountain, Nevada, USA: Earth and Planetary 

Science Letters, v. 201, p. 559–573.

Levy, S.S., Norman, D.I., and Chipera, S.J., 1996, Alteration 

history studies in the Exploratory Studies Facility, Yucca 

Mountain, Nevada, USA, in Murphy, W.M. and Knecht, 

D.A., eds., Scientific Basis for Nuclear Waste Management 

XIX: Warrendale, Pennsylvania, Proceedings of the Materials Research Society, v. 412, p. 783–790.

Moyer, T.C., Geslin, J.K., and Flint, L.E., 1996, Stratigraphic 

relations and hydrologic properties of the Paintbrush Tuff 

nonwelded (PTn) hydrologic unit, Yucca Mountain, Nevada: 

U.S. Geological Survey Open-File Report 95–397, 151 p.

Neymark, L.A., Paces, J.B., and Amelin,Y.V., 2003, Reliability 

of U-Th-Pb dating of secondary silica at Yucca Mountain, 

Nevada, in High-Level Radioactive Waste Management, 

Proceedings of the Tenth International Conference, Las 

Vegas, Nevada, March 30–April 2, 2003: La Grange Park, 

Illinois, American Nuclear Society, p. 1–12.

Paces, J.B., Neymark, L.A., Marshall, B.D., Whelan, J.F., and 

Peterman, Z.E., 2001, Ages and origins of calcite and opal 

in the Exploratory Studies Facility tunnel, Yucca Mountain, Nevada: U.S. Geological Survey Water-Resources 

Investigations Report 01–4049, 95 p.

Quade, J., and Cerling, T.E., 1990, Stable isotopic evidence for 

a pedogenic origin of carbonates in Trench 14 near Yucca 

Mountain, Nevada: Science, v. 250, p. 1549–1552.

Sawyer, D.A., Fleck, R.J., Lanphere, M.A., Warren, R.G., 

Broxton, D.E., and Hudson, M.R., 1994, Episodic caldera 

volcanism in the Miocene southwestern Nevada volcanic 

field – Revised stratigraphic framework, 40Ar/39Ar geochronology, and implications for magmatism and extension: 

Geological Society of America Bulletin, v. 106, no. 10, p. 

1304–1318.

Stuckless, J.S., Peterman, Z.E., and Muhs, D.R., 1991, U and 

Sr isotopes in ground water and calcite, Yucca Mountain, 

Nevada—Evidence against upwelling water: Science, v. 

254, p. 551–554.

Szabo, B.J., and Kyser, T.K., 1990, Ages and stable isotope 

compositions of secondary calcite and opal in drill cores 

from Tertiary volcanic rocks of the Yucca Mountain area, 

Nevada: Geological Society of America Bulletin, v. 102, 

no. 12, p. 1714–1719.

U.S. Department of Energy, 1993, Report on the origin of 

calcite-silica deposits at Trench 14 and Busted Butte and 

methodologies used to determine their origin: U.S. Department of Energy, Yucca Mountain Site Characterization 

Report YMP/93–11–R, 64 p.

Vaniman, D.T., Bish, D.L., Broxton, D.E., Byers, 

F.M. Jr., Heiken, G.H., Carlos, B.A., Semarge, R.E., 

Caporuscio, F.A., and Gooley, R.C., 1984, Variations in 

authigenic mineralogy and sorptive zeolite abundance at 

Yucca Mountain, Nevada, based on studies of drill cores 

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References 11
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studies of calcretes and fracture calcites, in High-Level 

Radioactive Waste Management, Proceedings of the Fifth 

Annual International Conference, Las Vegas, Nevada, May 

22–26, 1994: La Grange Park, Illinois, American Nuclear 

Society, p. 2730–2737.

Whelan, J.F., and Moscati, R.J., 1998, Nine million year 

record of southern Nevada climate from Yucca Mountain 

secondary minerals, in High-Level Radioactive Waste Management, Proceedings of the Eighth Annual International 

Conference, Las Vegas, Nevada, May 11–14, 1998: La 

Grange Park, Illinois, American Nuclear Society, p. 12–15.

Whelan, J.F., Neymark, L.A., Roedder, E., and Moscati, R.J., 

2003, Thermochronology of secondary minerals from the 

Yucca Mountain unsaturated zone, in High-Level Radioactive Waste Management, Proceedings of the Tenth International Conference, Las Vegas, Nevada, March 30–April 2, 

2003: La Grange Park, Illinois, American Nuclear Society, 

p. 357–366.

Whelan, J.F., Paces, J.B., and Peterman, Z.E., 2002, Physical and stable-isotope evidence for formation of secondary 

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Whelan, J.F., Roedder, E., and Paces, J.B., 2001, Evidence for 

an unsaturated-zone origin of secondary minerals in Yucca 

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Whelan, J.F., Vaniman, D.T., Stuckless, J.S., and Moscati, 

R.J., 1994, Paleoclimatic and paleohydrologic records from 

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Fifth Annual International Conference, Las Vegas, Nevada, 

May 22–26, 1994: La Grange Park, Illinois, American 

Nuclear Society, p. 2738–2745.

Wilson, N.S.F., Cline, J.S., and Amelin, Y.V., 2003, Origin, 

timing, and temperature of secondary calcite-silica mineral formation at Yucca Mountain, Nevada: Geochimica et 

Cosmochimica Acta, v. 67, p. 1145–1176.

12 Secondary Mineral Deposits and Evidence of Past Seismicity at Yucca Mountain, Nevada