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Michigan State
University

 

 

 

This is to certify that the

thesis entitled

Mineral Weathering in the Lochvale Watershed,
Rocky Mountain National Park, Front Range, Colorado

presented by

Nadine Louise Romero

has been accepted towards fulfillment
of the requirements for

M.S. degree in 1989

,‘

Major professor

Date May 18, 1989

0-7639 MS U i: an Afirmau've Action/Equal Opportunity Institution

 

 

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MSU Is An Affirmative Action/Equal Opportunity Institution

 

 

___—___ . ___

MINERAL WEATHERING IN THE LOCHVALE WATERSHED,
ROCKY MOUNTAIN NATIONAL PARK, FRONT RANGE, COLORADO

BY

Nadine Louise Romero

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Geological Sciences

1989

L“.

DJ

T—

ABSTRACT

MINERAL WEATHERING IN THE LOCHVALE WATERSHED,

ROCKY MOUNTAIN NATIONAL PARK, FRONT RANGE, COLORADO

BY

Nadine Louise Romero

The origin of high calcium water compositions draining the
Precambrian crystalline rocks of the Rocky Mountains is
poorly understood. Petrographic observations and x-ray
diffraction results reveal mineral weathering of the
Lochvale drainage in Rocky Mountain National Park, consists
of four primary hydrolysis reactions: a) plagioclase-
anorthite 65 weathering to kaolinite; b) plagioclase-
anorthite 35 weathering to kaolinite; c) amphibole
weathering to kaolinite and d) biotite weathering to
vermiculite. Weathering rates of the four primary
silicates were computed using a geochemical mass balance
model: plagioclase (An65) weathers at a rate of 146-156
moles/ha/yr; plagioclase (An35) at a rate of 28-48
moles/ha/yr; ferrotremolite at a rate of 9-17 moles/ha/yr
and biotite at a rate of 17-25 moles/ha/yr. 70 percent of
the total cation releases may be due to the weathering of
amphibolite--a small mafic unit composing less than 5% of

drainage surface area.

Dedicated to the Memory of my brother,

Kenneth Eloy Romero

You and I we climbed
shoulder to shoulder
You decided to stay

I accept your peace

amidst these canyon walls--

our sacred land

and go you will with our Chiefs,

our grandmothers and grandfathers
across the backbone of the world.

--May 13, 1989

iii

ACKNOWLEDGEMENTS

A special thanks to my advisor, Dr. Michael Velbel for his
guidance and energy in keeping me inspired and "on track"
with this challenging research. This thesis could not be
completed without the quality research and hydrogeochemical
data collection by Jill Baron, her staff and the National
Park Service. A very special thanks to Carma San Juan, my
field assistant and fellow geologist for helping me
(prodding my newly acquired, low-elevation, graduate school
body) up the alpine slopes of Lochvale. Thanks to my
beloved friends for their love and encouragement: John and
Dana Nelson—Salvino, Mike and Beth Miller and Lois Caprio.
To my beloved, Charles F. San Juan, who held me and
encouraged my very soul to excel above and beyond. And to
my family and Charlotte San Juan, for their love and

endurance.

iv

TABLE OF CONTENTS

1. Introduction .... ..... .. ....... . ..................... 1
1.1 Statement of the Problem 1
1.2 Development of the Problem 2

1.2.1 Globally 2

1.2.2 Locally 5

1.3 Chemical and Mineralogical Weathering

Studies 6

1.3.1 Southern Rocky Mountains 6

2. Area of Study........... ............................ 9
2.1 Introduction 9
2.2 Regional Geology 11
2.3 Regional Geomorphology 15
2.4 Soil Types 17
2.5 Climate 18
2.6 Hydrology 18
3. Methods.......... ....... .................... ......... 20
3.1 Sample Collection and Thin Sections 20
3.2 X-Ray Diffraction and Clay Preparation 22
4. Mineralogy........ ..... ............................. 25
4.1 Schist Mineral Assemblages and Alteration
Features 25
4.2 Granitic Gneiss Mineral Assemblages and
Alteration 29
4.3 Amphibolite Mineral Assemblage and
Alteration 35
4.4 Granite Mineral Assemblages and Alteration 41
4.5 Soil Mineral Assemblages and Alteration 43
4.6 Summary of Mineralogical Findings 45
4.7 Literature Derived Mineral Compositions 47
4.8 Stoichiometric Weathering Reactions Summary 49
5. Rates of Mineral Weathering: Application of a
Geochemical Mass Balance Model.................. ..... 52
5.1 Introduction 52
5.2 Model Assumptions 52
5.3 Thermodynamic Stability of Lochvale Waters 54
5.4 Matrix Setup 54
5.5 Matrix Solution: Results and Discussion 57
5.6 Calculation of Tardy's Re 63
5.7 Comparison of Mineral Weathering Rates to
Other Research 65
5.7 Significance of Rock Types 67

6. conCIUSions...0.0.0.000...0.0.0.0....0.0.0.000000000070

Appendix A: X-Ray Diffraction Patterns
Appendix B: Hand Calculations of Clay structural Formulas

Appendix C: Hydrogeochemical Flux Data
Bibliography

vi

Table 1:
Table 2:
Table 3:
Table 4:
Table 5:
Table 6:

Table 7:

Table 8:

Table 9:

Table 10:

Table 11:

Table 12:

LIST OF TABLES

Clay Mineralogy Summary ............ .....28
Literature Derived Mineral Compositons..50

Mineral Weathering Reactions............51

Elemental Flux Numbers..................58
Mass Balance Equation Matrix... ...... ...58
Solution to Mass Balance Matrix.... ..... 58

Silica Release Rate Predictions vs.
Actual.OO.II.0.....OOOOOOOOOOOOOOOOOOO0.60

Annual Budgets for Major Cations and
Anions for 1984 and 1985 in Lochvale....62

Hydrologic Balance for Lochvale
Watershed for 1984 and 1985... .......... 62

Lochvale Drainage Tardy Re
Calculations ................. .......... 64

Plagioclase Weathering Rates from
watershed mass balance studies..........66

Characteristic X-ray Diffraction
Peaks ........................... ...... .67

vii

Figure

Figure

Figure
Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure

Figure
Figure
Figure
Figure

Figure

 

7:

8:

LIST OF FIGURES

Index Map of Rocky Mountain National

Park showing location of study area ...... 10
A geologic map of Precambrian rocks

in Northern Colorado.............. ....... 12
Topographic Map of Study Area ............ 16
Sample Location Map ......... . ............ 21

Vertical Distribution of Sampling
Points ................................... 22

Photomicrographs of altered sillimanitic
SChiSts... ...... ...OOOOOOOOOOOOOOOOO ..... 27

Photomicrographs of plagioclase
replacement textures.....................31

Photomicrographs of altered plagioclase
to clay mineral in surface of granite
gneiss ....... ............ ................ 32

Photomicrograph of altered biotites in
granite gneiss...........................33

Photograph of weathered amphibolite
lenses...................................37

Photomicrographs of altered amphibolite..38

SEM micrographs of weathered
amphimlite...0......00.000.000.00000000039

Stability diagram for the Na-Al-Si-HZO
systemeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeOOoess

Box Model........ ..... ...................56
Schist (ST-4).. ........... ..... .......... 79
Gneiss (ST-2).. ........... ...... ..... ....80
Gneiss (LV-lO).... ......... ..............81

Amphibolite (GN-14)......................82

viii

Figure

Figure

Figure
Figure
Figure
Figure

Figure

20: Granite (FR-64) I O O O O O O O O I O O ........ O O O O O .83

21: Hand Picked Micas from Granite
(HP-M)OOOOOOOOO OOOOOOOOOOOOOOOOOOOOOOOOOO 84

22: Soil Sample (LV-7) ..... ................. 85

23: Calcium Flux Diagram for Lochvale.......89

24: Sodium Flux Diagram for Lochvale ........ 90
25: Magnesium Flux Diagram for Lochvale ..... 91
26: Potassium Flux Diagram for Lochvale ..... 92

ix

CHAPTER 1

INTRODUCTION

1.1 STATEMENT OF THE PROBLEM

The role of mineral weathering in stream water chemistry
and landscape reduction. of the Colorado Front. Range is
poorly understood. However, mineral weathering may be
largely responsible for controlling the ionic character of
most streams draining the Front Range and shaping the
massive Precambrian crystalline terrains of the Southern
Rockies. Mineral or chemical weathering is poorly
understood because, in regions where severe climatic
conditions prevail, mechanical weathering (e.g. glacial and
periglacial processes) dominates (Birkeland, 1974; Ollier,
1984; Reynolds, 1971).

As long' as the role of ‘mineral weathering' remains
undefined in the Rocky Mountain Region, water quality
interpretations, predictive acid rainl models, denudation
estimates and forest ecosystem models will remain tenuous
at best.

In order to elucidate the role and implications of
mineral weathering in the Rocky Mountain Region, the

response of primary rock forming minerals to

2
hydrogeochemical attadk needs 1x3 be investigated.
Therefore, the objective of this research is to define: 1)
which minerals and rock types are weathering in present day
conditions: 2) the alteration products formed as a result
of mineral transformations; 3) the precise transformation-
reactions of primary rock forming minerals to clays and
oxides; 4) the rates of mineral weathering and 5) to
provide a mineral weathering framework for additional
research in landscape reduction rates for the Colorado

Front Range.

1.2 DEVELOPMENT OF THE PROBLEM

1.2.1 Globally

Chemical weathering of primary rock-forming minerals
occurs because these minerals are not at equilibrium with
surface waters, temperatures and pressures (Ollier, 1984;
Reiche, 1950: Birkeland, 1974). However, as the weathering
environment changes (e.g., by acidification) so too do
alteration products. Many approaches have been used to
qualitatively and quantitatively understand chemical
weathering of minerals in both laboratory and field
settings. Much of the earlier work in mineral weathering
was observational in approach, beginning with Goldich's
(1938) "weathering series", where more mafic-related
minerals appeared to weather more readily than felsic ones,

paralleling Bowen’s Reaction series. Other earlier work

3

focused on bulk chemistry comparisons of altered versus
unaltered rook (Wahlstrom, 1948) whidh produced elemental
mobility indices and initiated isovolumetric techniques for
the study of weathering profiles (Millot, 1970; Gardner,
Kheoruenromne and Chen, 1978). Laboratory research, on the
other hand, has been oriented towards understanding kinetic
behaviors and ultimately those mechanisms responsible for
controlling rate and morphology (Chou and Wollast, 1985;
Holdren and Speyer, 1986; Busenburg and Clemency, 1976;
Berner and Holdren, 1977; Velbel, 1984). Laboratory
mineral weathering rates are 1 to 3 orders of magnitude
greater than field weathering rates (Paces, 1983; Velbel,
1985a, 1986b; Drever, 1986). Such poor simulation of
natural weathering conditions by laboratory dissolution may
in part be attributed to differences in surface
characteristics of naturally versus artificially weathered
mineral surfaces (Velbel, 1986b). Field research on
mineral weathering rates and mechanisms have been

approached through: a) mass balance techniques (Cleaves,
Godfrey and Bricker, 1970: Paces, 1983; Velbel, 19853; Katz
at al, 1985: Garrels and. Mackenzie, 1967; Drever and
Hurcomb, 1986: Clayton, 1986): b) empirical and theoretical
mass-transfer techniques (Gardner, Kheoruenromne and Chen,
1978: 1981; Helgeson, Garrels and Mackenzie, 1969) and to
some degree, c)statistical techniques (Reeder, Hitchon and

Levinson, 1972).

One of the more reliable approaches to quantifying

4
present-day mineral weathering rates is to utilize small
scale, controlled field areas for geochemical mass balance
studies (Velbel, 1985a; Plummer and Back, 1980; Drever,
1986, 1982). The mass balance approach integrates both
quantitative and. qualitative chemical mineral weathering
information (chemical and hydrologic stream flux data,
weathering reactions) into a system of simultaneous
equations which are balanced and solved for elemental
transfer rates. Among a handful of geochemical mass
balance studies done on granitic and crystalline terrain
are Cleaves et; a1. (1970), Drever and Hurcomb (1986) and
Clayton (1986). These mass balance findings will be
discussed in more detail in the mass balance chapter of

this thesis (Chapter 5).

In R.C. Twidale’s book, ’Granite Landforms’ (1980),

Twidale comments,

" granites form the foundations of continents.
Many are of great antiquity and have, moreover
been either exposed or in the groundwater zone
for a long time."(p.186).

Twidale’s work profoundly elucidates the importance of
granites and hydrogeochemical attack on them in the
development of large, smooth erosional surfaces termed
'etchplains' or 'peneplains' exhibited worldwide. Yet
globally, few studies address the chemical and

mineralogical weathering of geomorphio features in terms of

5
kinetics and weathering mechanisms responsible for their

morphology and their significance to the geologic cycle.

1.2.2 Locally

Chemical weathering of primary rock-forming minerals
may be the only major long-term process of acid rain
neutralization (Drever, 1986). In light of increasing
acidity found in Colorado over the past decade (Lewis and
Grant, 1979 a, b; 1980; Grant and Lewis, 1982: Baron,
1983; 1984; and Kling and Grant, 1984), the sensitivity of
high-elevation crystalline terrains to acid charged waters
is a major research concern. There is considerable concern
regarding the Rocky Mountain region due to the vast
granitic bedrock, thin acidic soil veneers and sparse
vegetation that may lack the ability to buffer incoming
acidity (Baron, 1983). Kling and Grant (1984) suggest that
toxicity and adverse effects on biota. due to increased
acidity on crystalline bedrock may prevail within this
decade. Weekly NADP (National Atmospheric Deposition
Program) measurements reveal rainwater pH levels as low as
4.16 and sulfate/nitrate concentrations as high as 150
milli-equivalents per liter. Such results indicate that
sporadic polluted air masses have traveled over Rocky
Mountain National Park (Baron, 1986). Consequently, as a
result of anthropogenic impacts, there is a definitive need
to expediently understand the effects of acid deposition on
crystalline terrain. Measuring the effects of acidity can

only be accomplished by identifying key water rock

6

interactions and securing a mineralogical weathering data

base.

1.3 CHEMICAL AND MINERALOGICAL WEATHERING STUDIES

1.3.1 Southern Rocky Mountains

Hembree and Rainwater (1961) performed one of the
first denudation studies of the Southern Rockies.
Measuring hydrologic fluxes and analyzing water quality
from surface runoff of the Wind River Range, Hembree and
Rainwater derived chemical denudation rates of .364 cm/looo
years and .67 cm/1000 years for western and eastern slopes,
respectively. The western slope is composed of Precambrian
granites, whereas the eastern slope is composed of
Paleozoic and Mesozoic sandstones, shales and carbonates.
Hembree and Rainwater attributed differences in the
ciissolved stream loads due to lithology and postulated that
the rate of "chemical weathering" depended upon how fast
weathered mantle could be removed. Another early study
performed by Miller (1961) analyzed water quality from
Streams draining quartzites, granites and sandstones of the
Sangre de Cristo range, New Mexico. Gaging stations were
Placed at various altitudes along each stream. Each stream
was underlain by a single lithology. Miller calculated
Several chemical denudation rates, however, it is not clear

Precisely how these rates were derived. Although these

7
studies provide no qualitative information on mineralogical
weathering, they do address the importance of constraining
the study area and allude to the complexities of
ascertaining what controls stream water chemistry and rates
of mineral weathering. Caine (1979) also quantifies rock
weathering rates by placing crushed rhyodacite tablets in
porous bags above timberline in the San Juan Mountains,
Colorado. Caine derived weathering rates of .055 cm/ 1000
years and his research was essentially a laboratory
experiment taken 'outdoors’--unfortunately no qualitative

mineral weathering data were determined.

Detailed descriptive mineralogical weathering studies
are virtually non-existent in the Southern Rockies.
Isherwood and Street (1976) contend that grus formation in
the Precambrian Boulder Creek granodiorite is due to the
weathering and consequent expansion of biotite to
vermiculite. In the Cascade Mountains, Drever and Hurcomb
( 1986) applied one of the first geochemical mass balance
techniques to the Southern Rockies. The Cascade Mountain
drainages in Drever and Hurcomb’s study are underlain by
diorites and migmatites. They conclude weathering of
Plagioclase was negligible, biotite altered to vermiculite

and acid neutralization results from calcite dissolution.

The acquisition of mineral weathering data has been
linited in previous studies. However, mineral

transformations during weathering exert tremendous

8
influences on soils, ecosystems and ground and surface
waters. As we are inevitably charged with the task of
assessing anthropogenic impacts to highly sensitive
regions, it is vital that mineral weathering research be
applied to the crystalline terrains of the vast Southern

Rockies.

CHAPTER 2

AREA OF STUDY

2.1 Introduction

The Lochvale Watershed, latitude 40 16’, longitude,
105 41' is located in Rocky Mountain National Park in the
Colorado Front Range (Figure 1). Draining northeast from
the Continental Divide, watershed elevation ranges from
2987 meters to 4009 meters in elevation in less than 5
kilometers. The catchment basin occupies 660 hectares and
is composed of 3 shallow lakes: Loch (3100 m): Glass Lake
(3280 m) and Sky Pond (3291 m). The surface area of the
lakes total 7 hectares of the watershed: soils and
vegetation, 40 hectares and bedrock comprises 613 hectares

(Baron, 1987: Walthall, 1985).

To more closely study mineral transformations and
kinetics by hydrogeochemical attack, it wouLd be ideal to
find a catchment that can provide as much isolation as
possible from the effects of other weathering processes
(e.g. biochemical and human disturbance). Although the
Lochvale watershed is not 'ideal’, it was chosen as the
study site for the following reasons: 1) an extensive
amount of chemical, hydrologic and meteoric flux data has
been collected by several researchers (Baron and Bricker,
1984; 1987) providing data for kinetic/mass balance

calculations: 2) the catchment is composed of over 90%

10

 

 

 

 

 

 

 

0 A .. gpnfi

Figure 1. - Index Map of Rocky Mountain National Park,
showing location of study area.

11

crystalline bedrock with limited vegetational cover

affording a stricter focus on (inorganic) hydrogeochemical
weathering; 3) the high elevation catchment is not
hydraulically connected to more exotic waters as in the
case of springs: 4) an extensive body of regional
literature on petrology and chemical compositions of parent
and weathered mineral and rock types exists which helps
constrain stoichiometries of mineral weathering reactions;
5) the study area is considered environmentally sensitive
with respect to ’acid-rain' effects and 6) the author's

knowledge of the physical and geologic terrain of RMNP.

2.2 Regional Geology

An extensive body of literature exists on the
Precambrian geology of the Colorado Front Range (Tweto,
1980: Lovering and Goddard, 1950: Robinson, a a1, 1974:
Wahlstrom and Kim, 1959; Wells et al, 1964; Lovering, 1935;
Sims egg, 1963: Hutchinson, 1976; Barker etal, 1975).
Much of the regional literature grew out of the economic
and scientific significance of early mining activity.
Comprehensive public sources of literature have been USGS
Professional Papers. Tweto (1980) gives an excellent
summary of Colorado Precambrian geology.

Precambrian crystalline rocks constitute the core of

the Colorado Front Range (Figure 2). These rocks can be

12

5

0+,“ — /

I/l‘ ’I_:_—a

/

I

-, _.
/\I.I\/\ ___

Isuzu. ___

_5__=_
___—Es _
______._:

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I x _

/II\ 1.7,

"___:

_ _...

:_

.._______
___

_____:
_........;

r 4.:

 

STUDY AREA: ROCKY MOUNTAIN NATIONAL PARK

_

___: E...
a.\‘

1:
___:

___.

       

_.N,....,\

|/4\

                

MILES

     

Figure 2.- A geologic map of Precambrian rocks in Northern

Tweto, 1980). Lithologic

explanation on page 13.

Colorado (after

l3

 

- Metavolcanic gneisses agezl.800 m.y.

 

 

 

 

H

I"
I,’

Metasedimentary gneisses age H.800 m.y.

H
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_Granitic rocks age- L700 '11-)!-
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_, \ I \I " Granmc rocks age-L400 m.y.
+ + + + v - -

(Pikes Peak- bath l -
+_+ + + onth age LOOO m.y.

__ _ _ Contact

l4
classified into 6 major genetic classes: 1) a metamorphic
complex dated 1,800 m.y. in age, consisting of biotitic
gneisses an schists (known as series A) and hornblendic-
felsic gneisses (Series B): 2) a group of igneous rocks
about 1,700 m.y. in age: 3) a unit of moderately
metamorphosed sedimentary rocks between 1,400 and 1,700
m.y. in age: 4) a group of igneous rocks 1,400 m.y. in
age: 5) slightly metamorphosed sedimentary rock unit 950
to 1,400 m.y. in age and 6) igneous rocks 1,000 m.y. in
age. These units also compose the entire buried basement
of Colorado. Of these rock types, the complex and highly
deformed metasedimentary units serve as a host for the

igneous bodies.

The most areally extensive metamorphic rock types to the
Rocky Mountain National Park vicinity are metasedimentary
gneisses and schists, principally biotite-silliminite
gneiss and schist (Nesse, 1977; Cole, 1977). Major mineral
composition is plagioclase, quartz and biotite with minor
sillimanite, microcline or muscovite. The metasediments
are migmatized throughout the region. It is believed that
the parent materials were graywackes and shales (Tweto,
1980). Interlayered lenses of calc-silicate rocks, uniform
textured microcline gneisses and amphibolites (metavolcanic
gneisses) are believed to be metamorphosed rhyodacitc tuffs
and basalts (Hutchinson, 1976; Tweto, 1980). These rock

types are not as interlayered as in other areas of the

15
state but exist as large discrete bodies. The igneous rock
types of the RMNP vicinity are primarily the result of two
major intrusions: Boulder Creek Orogeny (1,700 m.y.) and
the Silver Plume Disturbance Thermal Event (1,400 m.y.)
which includes the Sherman Quartz Monzonite (Hutchinson,

1976).

2.3 Regional Geomorphology

The Colorado Front Range possesses numerous and striking
erosional and depositional features (Figure 3) from
Holocene through Recent glaciation (e.g. cirques, valleys,
moraines etc.). Much of the geomorphic literature is
dominated by glacial studies. However, equally as striking
are massive flat to gently sloping surfaces, giving a
truncated appearance to the mountains of the Front Range.
These surfaces, which are beautifully exhibited in Rocky
Mountain National Park, were first described by Lee (1920)
as 'peneplains'. However, the term peneplain was first
coined by W.M. Davis in 1899 after reading the writings of
John Wesley Powell (Gerrard, 1981). Several more recent
discussions on these peneplains summarize evidence 'for a
late Eocene erosional surface. This surface is exhibited
in the Front Range and Rampart Range of Colorado and
extends to the Laramie Range of wyoming (Epis and Chapin,

1975: Eggler a: al. 1969).

16

-Y-

3 Far

‘KI‘L UP. \"11(
/;\‘ ' ' '
' - r

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’, /'/r 3709/ V
‘ ‘V '\\(\\c’1/

 

 

Figure 3.- Topographic Map of Study Area (40 16’lat; 105~
41' long).

17

The geomorphology of this erosional surface area,
consisting of more than 10,400 kmz, was characterized by
low relief and development of shallow, broad stream valleys
as seen below volcanic tuff deposits (Epis and Chapin,
1975). The erosional surface truncated Middle Eocene and
older rocks and deeply etched the Precambrian crystalline
rocks. Development of the peneplain began with the start
of the Laramide Orogeny, where erosion kept pace with
uplift and kept surrounding mountain elevations no higher
than the actual weathering front (Epis and Chapin, 1975).

The climate of the time was warm, temperate to subtropical.
2.4 Soil Types

Walthall (1985) characterized the Lochvale soils as
dominantly coarse textured, high in coarse fragments and
relatively young, with poorly developed horizons. Soil
temperatures were charactized as cryic with a mean annual
soil temperature between 0 degrees and 8 degrees Celsius
and a mean temperature difference of 5 degrees Celsius
between summer and winter soil readings. The soil
environment makes up aproximately 7 percent of the Lochvale
Watershed (Baron, 1987; Walthall, 1985). Walthall (1985)
characterized spruce and fir forest floor soils as
cryoboralfs and immature soils at the base of talus slopes
and alpine ridges were characterized as cryochrepts,

cryumbrepts and cryorthents. Walthall’s studies conclude

18
that given increases in acidic deposition, the Cryoboralfs
will promote surface water acidification. Cation exchange

capacities ranged from 4 to 76 cmol+/kg).

2.5 Climate

The present climate of the Loch Vale Watershed and
surrounding RMNP vicinity is temperate. The average annual
precipitation is 75 to 100 cm/year and the mean annual
temperature is 7 degrees Celsius. The drainage is
subalpine to alpine consisting of a spruce-fir forest at

the Loch elevation and alpine tundra above 3000 meters.

2.6 Hydrology

Annual hydrologic and chemical budgets of the Lochvale
watershed for 1984 and 1985 have been developed by Jill
Baron and others for the National Park Service (Baron and
Bricker, 1987). Results of Baron's studies show that 60 -
70% of the annual water input into Lochvale is snow. The
duration of snowmeIt is 2 months and controls the flow of
solutes out of the Lochvale system. For example, 70% of
the sulphate output occurs during snow melting. Winter is
also a time of increased concentrations of ions in lake
water. There is negligible storage of water in the

subsurface of mountain slopes due to near vertical to steep

19

elevation gradients. Hydrologic Balance inputs and outputs

are given in Appendix C.

j inilljify '1' ill-

 

 

Chapter 3

METHODS

3.1 Sample Collection and Thin Sections

Thirty-four thin-sections were prepared from all rock
types found in the Lochvale Drainage. Ninety percent of
the total outcrop area in Lochvale is a massive granitic
gneiss formed by the intrusion and cataclasis of Silver
Plume granite into metasedimentary rocks (Cole, 1977:
Robinson _e_t; a1, 1974). The remaining ten percent of the
total outcrop consists of discrete layers of schist (5-8%)
and small discrete lenses of amphibolite (3-5%). Outcrop
percentages were estimated visually during sample
collection. Fresh rock, weathered rock and soils were
taken wherever available in the drainage. However, due to
abundant near- vertical slopes most soils were restricted
to the valley bottom and in isolated pockets at the base of
seeps. Thus, most soil samples for this study were taken

in the vicinity of Glass Lake and Sky Pond, and in cracks

of wall rocks. Thoroughly weathered rock samples were
found in seeps and as rinds on granitic gneisses. See
Figure 4 for a sample location map. "Classic" thick

saprolite was not encountered in Lochvale; however the
peneplain region of the Continental Divide did exhibit

friable and decomposed rock similar to saprolite.

Caution was given to this sampling area as the peneplain

20

21

U T536

mb2

 

AnDREW
Lv-10 IGLACIEF'S .'

Aproximote Scale: 1" = 2500 feet

Figure 4. - Sample Location Map.

22

region may not be indicative of recent weathering, but of
Eocene weathering associated with the peneplain. Most
samples as shown in Figure 5 were taken 1000 to 2000 feet

below the peneplain or Eocene weathering front.

3.2 X-Ray Diffraction and Clay Preparation Techniques

Rock samples were crushed and ground with a mortar and
pestle. Aproximately 5 grams of sample was placed in a 500
ml beaker where 500 ml of deionized water was added. The
beaker was then placed in an ultrasonic bath where it was
agitated for a few minutes to help dissaggregate clay
clumps. The beaker was removed and stirred for several
seconds and then allowed to settle under gravity at 20
degrees celsius for approximately 3 hours and 50 minutes
using the Stokes equation for clay particle gravity
settling. Brindley and Brown (1980: p.306) show an example
of some of the settling times for various particle sizes

settling 5 cm:

Times for particles of density 2-65 3 cm", to settle 5 cm. in water at 20°C. Particle
sizes. e.s.d.. in put

 

Particle size 50 20 5 2
Time 22:13:: 2miu203e'e 37min30eee 3hr$0mie

 

In cases where good dispersion was not possible due to

flocculation of clays and organic matter, hydrogen peroxide

11l| Lui .IIle IIII I'll- I ‘II

 

 

 

 

23

A. Location at study lakes and Wentation

 

 

U

9

2

O

3

2

E

g TAYLOR cuczzn

u Lac“ sxy poND cuss out: VALE me LOCH
EXPLANATtON

NO? TO SCALE

A sonnet wart! SAMPLE Powers
0 WEAI’HEI STATDN .mo necmnrtou coutcroe

 

 

 

 
  
   
    

8. Omega in elevation V T36 LPQQ LP‘IO M 3 23 t
SOUTHWEST ‘ (L COLORADO
[ LOCATION um
LOOOm /
' .. | nonrnnsr
amass. '-V6 ' \ \gnan . / GN ._
sxv POND '+ — _ " "‘ I t " 4 -' -
“level-on 3322 more!“ 6153555 . u ...” 1
Itleveoen 3232 met-u " N ».
THE LOCH
not To sum temum 3040 mm»

 

 

Figure 5.- Vertical Distribution of Sampling Points
(after Baron and Bricker, 1987).

24

was added to induce oxidation and removal of organics.
After the 3 hour settling period, a pipette was used to
withdraw the upper 5 cm of the beaker which consisted of
the less than 2 micron clay fraction. This fraction was

then agitated in the ultrasonic bath for several seconds.

An oriented specimen mount was then made by placing clay
dispersion in. a clean cylinder attached by clamp to a
porous ceramic filter overlain by a cellulose ester <.45
micron filter. A vacuum pump was used to pull an oriented
film of clay on to the cellulose filter. The clay specimen
was then removed by rolling a glass rod over the filter on
to a glass slide. An untreated, a 1N potassium and 1N
magnesium treated sample were prepared as well as a 1N Mg-
glycerol and glycol solvated samples. Heat treatments were
done on potassium saturated samples at 300 and 600 degrees
celsius for 1 hour each. The x-ray diffraction radiation
used was CuK-alpha, run at 36kV and 25 mA. Scanning speeds
were 1 degree-2 theta, run at 2K (cps). The divergence
slit used was .3 degrees (2-theta); the receiving slit, .6
degrees (2—theta) and the antiscatter slit was 1 degree (2-
theta). The chart speed was 10 millimeters per minute and

the time constant used was 1 second.

A sample of Wyoming bentonite was treated and run on XRD
(see Appendix A) to test and ensure that treatment methods

used could differentiate smectite clays.

Chapter 4

MINERALOGY

4.1 Schist Mineral Assemblages and Alteration Features

The dominant schist-type of the Lochvale Drainage is a
coarse biotite-sillimanite schist, present in one-inch-to-
two-foot thick layers within the granitic gneisses, on the
faces of Otis Peak and Sharkstooth Mountain. Such schist
units are often seeps and conduits for water. Preferential
weathering of schist units appears to form ledges, cracks
and undercuts within the canyon walls. Most of the schist
layers are friable in hand sample and appear clay-rich.
In thin-section, schist samples are primarily composed of
coarse biotites, feldspars and sillimanite with very minor
amounts of chlorite. The texture of the biotite-
sillimanite schist is primarily grano-lepidoblastic
(recrystallized, uniform grain size, aligned). Some samples
exhibit cataclastic texture with angular clasts. Robinson
et al— (1974) state the Silver Plume intrusion was
contemporaneous with cataclastic deformation. Amphiboles
are not present in any of the biotite-sillimanite schists.
Blue-green pleochroic chlorite does not exhibit any
alteration texture and appears only as an accessory primary
mineral. Biotites of weathered schists display ’bird's eye
mottling', weaker pleochroism (clear to brown) and lower
birefringence than fresh biotite. sillimanite occurs as

'bundles’ (fibrolite) and as single slender, well-formed

25

26

euhedral crystals. Some metamorphic alteration of
sillimanite is seen in both fresh-rock interiors and
surface exposures of schists and gneisses. Such altered
sillimanite is cloudy (under plane light) with lower relief
and grades into muscovite under cross-polars (Figure 6).
Silliminite is a very common accessory mineral in the
majority of the gneisses and schists of the Colorado Front
Range, indicating moderate to high grade metamorphism

(Nesse, 1977).

 

Products.

X-ray diffraction data of the < 2 micron fraction of the
biotite-sillimanite schists (ST-4; Appendix A) reveal sharp
and intense mica/illite peaks (10.0, 4.988 angstroms) with
less intense kaolinite (7.18 angstrom) peaks and minor
chlorite (14.2 angstroms). vermiculite is not present in
any of the schist rock samples (Table 1). One phenomenon
noted in the biotite-sillimanite schist is a very slight
collapse of the 14.24 angstrom peak at 600 celsius
(Appendix A). This may be attributed to some
dehydroxylation of an iron-chlorite structure. Dorothy
Carroll (1964) notes ‘that. Fe-chlorite jpeaks Ibecome less
intense and may broaden above 500 degrees Celsius versus
Mg-chlorite whose peaks intensify at 650 degrees Celsius.
The chlorite group itself shows gradual weight loss without
structural change from 600-800 degrees Celsius. It is also

possible oven temperatures may have slightly exceeded 600

 

Figure 6.- Photomicrographs of altered sillimanitic schists

(sample taken from seeps in Lochvale). Top: plane
polarized light; high relief sillimanitic fibrolites and
biotites in dark cloudy matrix; 80X. Bottom: biotite

altered to a clay mineral; 80X.

28

Table l
CLAY IIIXHHLOGI SUMMARY

 

 

SAHPLH Hica/ Hydroxy Interlayer
I Slectite Iaolinite Verliculito Chlorite Illite VI SI

LV-l X X X X HIV or HIS
LV-9 X X HIV

SOILS LV-6 X X X HIV or HIS
LV-I X X X HIV or HIS
LV-ll X X X X HIV or HIS
LV-B X X
LV-I X X X X

GIIISS/ 0P-10 X X

SCHIST OP-ll X X
81-2 X X X
31-16 X X X
Hl-22 X X
0P-8 X X
0P-9 X

saprolitic LV-lo IR X X HIV or HIS
HH-23 X X
LP-29 X X
81-4 X X X

AHPHIHOLIIH Gl—li X X (10.5 A) X G! t

alphibole pk

GRAIIIH 0-5? X X HIV or HIS
0-61 I X HIV or HIS
IH-BZ X X
FH-il X (10.5) X X HIV or HIS

alphibolo pk

00-71 I X X
HP-H X X X RIC
l-HP-l X I
01-30 I X X HIV or HIS
AP-CI X X

013 = aoethite peak around 4.10 angstroes
H10 = randolly Interstratifiod clay

29

degrees Celsius.

Summary of Schist Weathering

Petrography of the biotite-sillimanite schist shows the
only primary mineral component presently weathering is

biotite.

X-ray diffraction reveals kaolinite as the dominant clay—
type, followed by' minor amounts of chlorite (which ‘was
determined petrographically to be a primary accessory
mineral component). No relationship was inferred from
these findings that biotite was weathering directly to

kaolinite.

Because most schist samples were also from seeps, it may be
possible kaolinite was transported by waters from other

bulk rock sources such as the granite-gneisses.

4.2 Granitic Gneiss Mineral Assemblages and Alteration

Silver Plume-related granitic gneisses are the most
dominant rock type of the Lochvale drainage. The gneisses
are massive and well indurated (a hammer will rebound very
easily upon striking the canyon-wall rocks). sillimanite
is also distinctly present throughout the gneisses.
Several thin-sections show some of the gneisses have

abundant microcline and plagioclase. Unweathered specimens

30
of gneiss exhibit foliation and idiomorphic or grano-
lepidoblastic texture. Several specimens show ndgmatitic
textures with biotite aligned in microfolds or ’fish bone’

patterns.

Thin-sections of weathered samples reveal clay-rich and
altered plagioclases and biotites. Alteration features
include pseudomorph textures of plagioclase where clay
material has replaced and mimicked parent plagioclase
textures such as twinning, cleavage and grain morphology.
Pseudomorph textures are seen at the weathering surfaces of
gneiss samples (Figure 7)-- interiors of rock samples
appear ’fresh’ and non-weathered (Figure 8). The biotites
of the weathered gneisses also show alteration products and
textures (Figure 9). Many of the weathered biotites show a
mottled texture with interdigitations of fresh and
weathered lamellae. Such weathered biotite
interdigitations remain dull low order browns under both
crossed and uncrossed nicols when the stage is turned a
full 360 degrees. Some specimens show a high birefringence
clay appending to scalloped edges of the biotites. Minor
amounts (<5%) of blue-green pleochroic chlorite was also
seen and did not appear altered, but as a euhedral primary
mineral. Although fresh microcline is prominent in many of
the gneisses it also did not appear altered in any of the

weathered specimens, unlike plagioclase (Figure 8).

31

 

replacement

plagioclase

of
80X.

1c gneiss;

Photomicrographs
t

in grani

0

Figure 7.-
textures

32

 

Figure 8.- Photomicrographs of altered and fresh
plagioclase. Top: incipient plagioclase alteration to clay
Bottom:

mineral taken from surface of granite gneiss; 80X.
fresh interior; clean feldspars; 80X.

33

 

Figure 9.- Photomicrographs of altered biotites from
granite-gneiss. Top: plane light; 80X. Bottom: polarized
light; low order interference colors and mottled texture on
biotites; alteration to a high birefringence clay mineral;
80X.

34

z-Ray Diffraction of Gneiss Weathering Products

Much like the < 2 micron fraction of the biotite-
silliminite schist, the < 2 micron fraction of the granitic
gneisses contained kaolinite, illite and minor amounts of
chlorite (Table l; ST-2). One gneiss sample taken on the
Continental Divide or peneplain surface contained hydroxy-
interlayered clays which can be interpreted as either a
vermiculite or smectite (LV-10; Appendix A).
Unfortunately, as discussed by R. Barnhisel (1977; p. 535)
there is no definitive means to identify hydroxy
interlayered clays as either vermiculites or smectites, as
their mineralogic properties overlap. The peneplain sample
was similar to the XRD patterns of the Lochvale soils,
which are discussed later in this chapter. Hand picked
feldspars from. *weathered. gneiss samples contained. a
dominant kaolinite peak (HP-4 of Table 1: ST-2 of Appendix

A).

The bulk of the granite gneiss samples show plagioclase and
biotite as the main weathering minerals. Textural evidence
shows that plagioclase feldspars are replaced by a clay,
preserving parent cleavage and twin planes along with

original grain shape. Such pseudomorph textures were found

only in the outer, surface exposed layer of the gneisses.
The interior of the gneisses were unaltered. X—ray

diffraction shows a prominence of kaolinite and a

35

mica/illite peak shown petrographically to be dominantly
biotite. X—ray diffraction of hand picked feldspars shown
a dominant kaolinite peak. Chlorite, as also found in two
of the samples in minor amounts, appears petrographcally to
be a primary accessory mineral. One sample taken on the
peneplain also has an unknown hydroxy-layered mineral and
vermiculite. In summary it can be inferred from all
petrographic and x-ray diffraction work of the granite-
gneisses that plagioclase is weathering to kaolinite. The
peneplain gneiss sample (which may be indicative of more
prolonged weathering) shows plagioclase weathers to
kaolinite and biotite weathers to vermiculite. In
addition, the possibility exists that vermiculite may

eventually weather to a hydroxy interlayered clay.

4.3 Amphibolite Mineral Assemblages and Alteration
Features

Lenses of amphibolite are widely scattered in isolated
pockets throughout the gneisses of the Lochvale drainage
and the entire Front Range (Cole, 1977: Nesse, 1977;
Robinson _e_t_ a1, 1974; Wahlstrom and Kim, 1969; Wells _e_t_
a1, 1964; Lovering, 1935: Sims, Drake and Tooker, 1963:
Tooker, 1963). Dramatic hollows and depressions are left
where the amphibolite appears to have preferentially
weathered out with respect to the enclosing gneiss (Figure
10). The preferential weathering of these amphibolites is
seen throughout the Front Range and has been described in

many studies as a rock-type with such a "tendency to

36

weather more heavily, that it is seldom seen in outcrop",
(Cole, 1977; p. 41). In the Lochvale drainage, the
amphibolite comprises an estimated 5% of all rock types
found in the drainage. Hand samples of amphibolite show
that it is a dark green to black, almost ’mafic’ appearing
rock, which contrasts sharply with the surrounding gray-
pink granitic gneisses (Figure 10). Thin-sections (Figure
10) show abundant blue-green pleochroic amphibole and some
brown to dark brown pleochroic biotite, with varied amounts
of iron-staining along cracks throughout samples,
suggesting iron-enriched amphiboles or biotites may be
weathering. Thin-section evidence for amphibole and
biotite weathering was not conclusive (Figure 11) as there
was great difficulty in obtaining a weathered specimen such
as weathering rind. Unlike the granites and gneisses, the
finely crystalline (.2mm) amphibolites appeared to have
just dissolved and disappeared, leaving no soil traces or
other solid residues, but rather fresh to slightly iron
stained, smooth round surfaces and weathered out hollows.
One reason for the observed 'dissappearance' of the
amphibolite is the small amounts of resistant quartz (less
than 20%) composing the amphibolite rock matrix. The
quartz may serve as a skeletal framework retaining
weathered minerals and. clays in other’ quartz rich. rock
types. SEM work was done on amphibolites to discern any
other textural evidence for weathering such as etch-pits,

dissolution voids and fractures and/or the characteristic

37

 

Figure 10.- Photograph of weathered amphibolite. Bottom:
photomicrograph of amphibolite; polarized light; 80X.

38

 

Figure 11.— Photomicrographs of altered amphibolite. Top:
incipient alteration of hornblende to clay mineral; plane

light; dark Fe—Mg staining; 200x. Bottom: polarized light;
200x.

39

’sawtooth’ or denticulated terminations associated with
amphibole weathering (Berner g a_1, 1980; Velbel, 1984).
Figure 12 shows. an. extensively' weathered. amphibole 'with
similar ’saw tooth-like’ terminations from a Lochvale
amphibolite. Likewise the ‘microcrystalline feldspars,
mostly plagioclase, did not have conclusive thin-section
evidence for weathering. SEM micrographs show feldspar

etch pits.

X-Ray Diffraction of Amphibglite Weathering

X-ray diffraction of the < 2 micron fraction of the
amphibolite (GN‘14; Appendix: A) reveals an intense 8.41
angstrom peak which correlates to the amphibole (001).
Kaolinite, mica/biotite, a mixed layered clay of 7 and 10
angstroms, goethite and a hydroxy interlayered vermiculite

or smectite are also present in lesser amounts.

Summary of Amphibolite Weathering

Textural evidence based on SEM was found for the weathering
of plagioclase and amphibole in the amphibolites.

x-ray diffraction data of the amphibolite shows kaolinite,
a hydroxy interlayered vermiculite or smectite and a mixed

layer clay.

As supported by previous textural evidence, plagioclase is

 

Figure 12.- SEM micrographs of weathered amphibole with
characteristic 'sawtooth’ terminations from a Lochvale
amphibolite; 200x; 1000X.

41

weathering to Ikaolinite; amphibole is ‘weathering ‘to

kaolinite and biotite is weathering to vermiculite.

4.4 Granite Mineral Assemblages and Alteration

Discrete non-foliated granites are not as areally extensive
as the granitic gneisses of the Lochvale drainage and are
harder to discern from weakly foliated gneiss. Near the
junction of Icy Brook and Andrews Creek, a large noteable
outcrop of gray-pink, medium-grained Silver Plume granite
can be seen. Thin sections of the Silver Plume granite
show typical granular igneous textures with random
subjunctions (idiomorphic) to annealing textures, with some
triple junctions. Granites contain abundant microcline,
quartz and biotites and minor amounts of plagioclase.
Weathered biotites exhibit brown to dull, low order
birefringence, with mottled texture. Some weathered
biotites have altered rims and clay—appendages on
terminations. No other weathering or alteration features

were observed.

-Ra ' actio of mi d Weat er' duct
The <2 micron fraction of the granite (FR-64) consists of
vermiculite, mica/illite (biotite), hydroxy-interlayered.
vermiculite or smectite and minor amounts of kaolinite. On

several diffraction patterns, hydroxy-interlayered clays

42

show a characteristic peak at 14.1 angstroms ’bridged’ to a
10.0 angstrom mica/illite peak. After potassium treatment,
part of this peak collapses towards 10.0 angstroms; the
peak shifts even further towards the 10.0 angstrom peak
upon heat treatment to 300 degrees Celsius. The peak then
almost entirely collapses to 10.0 A at 600 degrees Celsius.
Such patterns may indicate a hydroxy-interlayered
vermiculite or smectite, where pillared smectite or
vermiculite is propped open by an aluminum or magnesium
hydroxide (gibbsite or brucite) sheet (R. Barnhisel, 1977;
p. 535). Successive heat treatments can dehydroxylate
these interlayer materials. Similarily, the soils also
exhibit the same hydroxy-interlayered patterns. Unlike the
gneisses or schists, kaolinite is not consistently found in
the granites. X-ray diffraction of hand-picked micas was
also done for the granites (HP-M; Appendix A). Vermiculite
and some kaolinite was found, however it was difficult to
remove micas without disturbing other minerals such as
feldspars and clays. Therefore, the kaolinite peak on the
biotite sample pattern may not be from the weathering of
biotite, but may be a product of the feldspar. Sample HP-M
also contained a broad 8.0 angstrom peak which may
represent a randomly interstratified clay of
vermiculite/kaolinite; smectite/kaolinite ; chlorite
vermiculite or other (Sawhney, 1977; p. 413-431). One XRD
pattern (FR-64) also contained a moderate amphibole peak at

8.41 angstroms.

43

Summary of Granite Weathering

Based on petrographic and x-ray diffraction work it appears
biotite weathers to vermiculite and possibly a hydroxy-
interlayered vermiculite or smectite. This weathering
scheme has also been well documented in the Front Range
literature by other researchers (Isherwood and Street,
1976; Blair, 1976). Minor amounts of plagioclase also
appear to be weathering to kaolinite, where present in the
granites. The sporadic and minor amounts of kaolinite in
the granites may indicate biotites are not weathering to

kaolinite but are transformed directly to vermiculite.

4.5 Soil Mineral Assemblages and Alteration Products

Soils of the Lochvale drainage were mostly taken from below
the massive gneiss wall rocks near Sky Pond, Glass Lake and
above the Loch. Such soils were not very thick
(approximately 6 inches to 1 foot) and were sampled below
an aproximately 1 inch thick black organic surface layer.
Several soil samples were also taken from granites at the
entrance of the Lochvale drainage (Figure 4) . Like the
granites, the soils also show a variety of clay mineral
assemblages. x-ray diffraction of the <2 micron soil
fraction reveals large quantities of kaolinite,
vermiculite, and some chlorite (LV-7; Appendix A A). In

addition, virtually all samples show the same hydroxy-

44

interlayered clay patterns as observed in the granite

diffraction patterns.

Summary of Soil Weathering

The Lochvale soil environment occupies less than 6% of the
total watershed surface area. Even though the soil areal
extent is small in contrast to the exposed bedrock
surfaces, it is not precluded from supplying, exchanging or
storing significant sources of cations or anions from the
Lochvale drainage. Lochvale soils may represent ongoing,
dynamic weathering unit, composed of older and possibly
more advanced stages of weathering. The predominance of
hydroxy-intelayered clays and vermiculites may suggest
additional soil—biotite weathering to vermiculite and
pedogenic chlorite, vermiculite weathering to a hydroxy-
intelayered clay and lithic fragments of pflagioclase
weathering to kaolinite. The Lochvale soil samples
collected for this thesis, however, revealed no additional
clay types outside those weathering products observed for
the various lithologies. Walthall (1985) did find smectite
in his soil samples from Lochvale, however, many of his
soil samples were taken in poorly drained areas, such as
the forest floor. Furthermore, most of his soils had
generally low CEC capacities indicating a pmedominance of
relatively non-exchangeable clay types such as kaolinite

and vermiculite.

45

4.6 Summary of Mineralogical Findings

A summary chart of X-ray diffraction data is given for
Lochvale gneisses, schists, amphibolites, granites and
soils in Table 1. The most prominent clay mineral is
kaolinite, occuring in all rock types and soils of the
Lochvale drainage, with the exception of some granite
samples. All samples have biotite with the exception of 1
soil sample, which was composed entirely of kaolinite,
vermiculite and a hydroxy-interlayered clay. Virtually all
of the soils, (as well as the granites) have a hydroxy-

interlayered vermiculite or smectite clay present.

X-ray diffraction of hand-picked plagioclase and biotite
reveal strong' evidence that. plagioclase 'weathers ‘to

kaolinite and biotite weathers to vermiculite.

The amphibolites contained large amounts of relict primary
amphibole, followed by biotite, kaolinite and minor
vermiculite and goethite.

Granite rock samples contained hydroxy-interlayered clays,
vermiculite, mica/biotite, amphibole and several granite

samples lacked kaolinite.

In order to validate mineral transformation reactions, it
is necessary to link petrographic evidence with the clay

mineralogy findings summarized above.

46

Textural evidence from thin-sections and SEM show only
plagioclase, biotite, and amphibole as primary minerals
presently weathering. Plagioclases were observed to
weather into pseudomorphs on surface rinds of granite
gneisses and were observed to contain etch-pits in
amphibolites. Weathered biotites displayed mottled, dull
birefringent colors with interdigitations of more highly
birefringent (fresh) biotite. Amphibolites consisting
predominantly of amphibole were observed to extensively
weather only on a field scale forming holes and vugs once
occupied by amphibolite. SEM work done on amphiboles also
showed characteristic ’sawtooth-like’ or denticulated
terminations on amphiboles, indicating pronounced

weathering.

In summary, the following key mineral transformations are

defined for the Lochvale drainage:

Plagioclase -------- >Kaolinite
Biotite -------- >Vermiculite
Amphibole -------- >Kaolinite + Goethite

Based on the petrographic and x-ray diffraction findings,
the weathering of the amphibolites, gneisses, granites and
schists are considered as the key reactions controlling the
cation budgets of the watershed. Complete stoichiometric

weathering reactions are based on literature-derived

47

mineral compositions for the various Lochvale lithologies.

4.7 Literature Derived Mineral Compositions

A thorough search of the literature on the granitic,
gneissic and amphibolite lithologies of the Colorado Front
Range was done: a) to establish the rock types of the
Lochvale drainage; and b) to secure mineralogical data,
especially mineral compositions, for use in mineral
weathering reactions. Several local dissertations were
studied (Nesse, 1977 and Cole, 1977) as well as an
extensive body of literature describing the rocks of the
Front Range (Robinson et al, 1974; Wahlstrom and Kim, 1969;
Wells et a1, 1964; Lovering, 1935; Simms, Drake and Tooker,

1963; Tooker, 1963).

In addition, several local ’weathering’ papers and
dissertations (Isherwood and Street, 1976; Blair, 1976;
Nesse, 1977) supplied microprobe analyses for biotite,
vermiculite/hydrobiotite and plagioclase of the Silver
Plume and Boulder Creek granites which were calculated into
full cell mineral formulas (hand calculations in Appendix
B; formulas on Table 2). Granite and gneiss plagioclase

compositions ranged from anorthite 15 to 35.

A thorough search of the literature was also done on the
Front Range amphibolites, however, chemical compositions

for amphiboles were virtually non-existent. Front Range

48

amphibolites have not been considered as an important or
significant rock type because of their ’non-mappable’ or
small areal extent (Cole, 1977; Robinson et ai, 1974). It
is theorized that the amphibolites are metamorphosed
basalts (Tweto, 1980; Cole, 1977). Barker at EL (1975)
studied the chemical composition and origin of the Pikes
Peak batholith and its relationship to the older Boulder
Creek (calc-alkalic 'magma source), the Silver' Plume
(peraluminous magma source) and the once overlying 15,000
meters of basaltic volcanics“ They concluded. that 'the
formation of the Pikes Peak batholith was due to reaction
melting of overlying and surrounding rocks and a parent

basaltic magma.

Although Barker EL al_ (1975) microprobed only quartz
syenite amphiboles, their model suggests amphibolite-
amphiboles are extremely calcic and iron-enriched:
ferrotremolites (actinolite) solid solution series. Other
literature also suggests tremolite and a generic hornblende
based solely on optical properties (Robinson a a_1, 1974;
Wells et a1, 1964).

The dominant plagioclase of the amphibolite is labradorite
--Anorthite 60-65, determined through microprobe analysis
done by Nesse (1977) and Cole (1977). Other researchers
prior to Nesse (1977) and Cole (1977) optically determined

the plagioclase composition of the amphibolite to be less

49

calcic--Anorthite 35-45 (Robinson et a1, 1974), but still
more calcic than the plagioclase of the granites or

gneisses.

Table 2 summarizes literature derived compositions and

respective references.

4.8 Stoichiometric Weathering Reactions Summary

Based on the x-ray diffraction data, the literature derived
mineral compositions and the textural and mineralogical
evidence, the following mineral transformations (Table 3)
are proposed as the key weathering reactions supplying the
vast majority of base cations out of the Lochvale

watershed.

50

Table 2

Front Range Literature-Plagioclase Compositions

Biotite
Gneisses and Sohists An 20—35 (Robinson a; ai, 1974)

Granitic Gneisses and
Sohists (Migmatites) An 15—35 (Robinson et 51, 1974)

Sillimanite Gneisses

and Schists (calc-

silicate rocks) An 20-35 (Robinson at al, 1974)
Amphibolites An 60-65 (Cole,1977; Nesse,1977)
Silver Plume Granites An 15-25 (Robinson, et a1, 1977)

and Monzonites An 20-25 (Nesse, 1977)
An 24—30 (Nesse, 1977)

Front Range Biotite Compositions

Fresh Biotite (Isherwood and Street, 1976)

K+1.994(Fes+.4asFe2+1.772Mg2+s.iisTi4+.242)(Al.0128ie.ess)

020(OH)4

Weathered Biotite (Isherwood and Street, 1976)

K+1.094 Ca2+.226(Fe3+1.ess FeZ+.1vs M82+2.2eo Ti4+.2os
A13+.2zo)(A13*1.seesi4+e.146)020(0H)4

Amphibole Compositions
Ferrotremolite—Aotinolite Intermediate (Barker et a1, 1975;

Deer et a1, 1980)

Ca2(MgiFez+4)[AliSieJOzz(0H)2

51

Table 3

Balanced.Mineral Weathering Reactions

Anorthite ee<N."°v 1977) ------------- >Kaolinite

Na.se Ca.se Ali.ss 812.35 Os + 3.885 H20 + 1.65C02 ‘
------------ > .82 A1281205(OH)4 + .35Na+ + .65Ca++
+ 1.85HCOs—+.71 H45104

Anorthitestrflchoimicm °P a1- 1974) ------- >Kaolinite

Na.ee Ca.se Ali.se 812.85 Os + 4.625 H20 + 1.35C02 -
-------------- >.675 A1281205(OH)4 + .85Na+ +.35Ca++
+1.35 HCOs‘ + 1.30 H48104

Biotite< Isherwood 0t .1. . 1978) ..... >
Vermiculite(I-horwood at n1..1976)

K+1.994(Fea+.4esFez+1.772Mg2+s.iisTi4+.242)(Al.01281
5.933) 020(0H)4 + .2260a2+ + 1.0502 (s) + 3.20 C02 +
.71 H20 ----------------------- > .970 K+1.094
Ca2+.22s(Fe3+1.ess Fe2+.1vs Mg2+2.2eo Ti4+.2oe
A13+.220)(A13+1.seasi4+e.146)02o(0H)4 + .933K+
+.119Fe(0H)2(aq) + .936Mg2+ + .042Ti4+ + 3.20HCOs- +
.026H45104

(Deer at 31. 1980)
Ferrotremolite(Actinolite)(Berk-r at :1. 1976) ......

——————— > Kaolinite + Goethite

C32(M31Fez+4)[AliSis]022(0H)2 + 12H20 + 6C02
+1.2502(3)---> .5A12SizOe(0H)4 + ZCa++ + 1M3++
+ 18HCOs‘ +5H48104 + 4Fe0(OH)

52

CHAPTER 5

RATES OF MINERAL WEATHERING: APPLICATION OF A GEOCHEMICAL
MASS BALANCE MODEL

5.1 Introduction

Watershed geochemical mass balance studies of mineral
weathering rates are believed to provide the most reliable
estimates of field mineral weathering rates (Cleaves,
Godfrey and Bricker, 1970; Paces, 1983; Velbel, 1985a; Katz
et ai, 1985; Garrels and Mackenzie, 1967; Drever and
Hurcomb, 1986; Clayton, 1986). For this research a
watershed mass balance study of mineral weathering rates
was performed using the mineralogical findings of Chapter 4
and hydrogeochemical flux data (Appendix C) for the

Lochvale Drainage, Rocky Mountain National Park.

5.2 Model Assumptions

The geochemical mass balance technique assumes that all
water leaving the catchment originated as precipitation
that fell directly within the catchment boundaries. As
discussed in Chapter 2, there are no known springs in the
Lochvale drainage due to the very high basin elevation.
Hydrologic budgets computed by Baron and Bricker (1987) in
1984 and 1985 did show conservative ion chloride with a 35%
discrepancy. However, it was concluded precipitation
measurement errors were made due to high winter winds

altering gauges and underestimating catch efficiencies and

53

not to unlikely, exotic water sources. Input cation

budgets were normalized to chloride.

Mass balance techniques also assume steady-state
conditions, where net cation exports equal the sum of
precipitation inputs and weathering rates, and that
exhangeable base pools such as biomass and soils are
negligible and static with respect to growth and time. The
Lochvale drainage, as discussed in chapter 2, is
predominantly an alpine-subalpine catchment, where only 6
percent of the drainage surface area is covered by soil and
vegetation and 94 percent is exposed bedrock. Severe
climatic conditions of the alpine form little or no soil,
readily removing regolith and weaker friable material.
Consequently, fresh bedrock surface areas are continually
renewed, promoting a greater potential for primary mineral
hydrolysis. A. small biomass and soil areal extent. may
influence cation export budgets, but primary mineral
hydrolysis may outrank exchangeable base pool processes in
alpine-subalpine scenarios. Baron and Bricker (1987) state
that the hydrology of the Lochvale watershed exerts the
most influence on the water chemistry, as sulfate budgets
suggest solutes have little opportunity to interract with
the ecosystem before they are flushed out during snowmelt.
They further contend net exports of major cations 2.5 to
4.0 greater than inputs is the direct result of

mineralogical weathering.

54

5.3 Thermodynamic Stability Relations of Lochvale Waters

Figure 14 shows that the waters draining the Lochvale
watershed (average, high and low concentrations plotted)

are in equilibrium with the kaolinite.

5.4 Matrix Setup

The geochemical mass balance used for this study is
illustrated as a box model which quantitatively maps inputs

and ouputs of base cations (Figure 15).

In many watershed field settings, as many as 6 major
sources and sinks are responsible for net cation imports
and exports. In the Lochvale box model, uptake into
forest or other biomass, and storage in ground water, are
considered negligible as discussed earlier. The most
significant cation inputs are mineral weathering and
precipitation. Plummer and Back (1980) summarize the
following mass balance relationship with the following

equations :
¢
2 an
:1=1~1

= A
ch me

The delta 1110 term is the net flux of element c, determined

by subtracting precipitation input from stream output

fluxes, and is expressed in moles/ha/yr (Table 4). The

55

 

  
      

1C 1 r l I
l I ‘
a! '
em I
.._ Ci 1 _
\I I t
31 I
d I
“ 1
:' 1
0- I “
Alblte :
I r
1
_ 1 -
I
I
I
:
B I" ' -
Glbbelte 1
I
+; 1
z — 1 -
I: tt-otIntte
2 I
" I
ll 9 ' : ‘
O
J I
I
I
_ I -
I
I
1
I
a "' : b -‘
I
I
I
_ 1 -
I 8
1
1
I
I l L I
O

 

 

 

 

 

-3 —4 -3 -2
Leo (H43IO4I

Figure 14.-Stability diagram for the Na-Al-Si-HZO system
at equilibrium for 25 Celsius and 1 bar pressure

--circles represent Lochvale water analyses (from
Feth 3.11 ll- 3 1984).

 

56

        
 

 

 

 

 

 

 

 

 

 

 

 

 

'te-z' % ,. .
Atmospheric Forest
Precipitation Biomass
A
Addition vio > K Wafershed \
Weatherm/q C0 . DISSO/VEd Removal
4. . '
Remove! vio Mg Mineral Sire-dams
cr'r‘i’rmgiifnm Na Nu frienfs 7
‘ 7
Storéqe lo
Groundwater

Figure 15.-Box Model (from Velbel, 1985a)

57

beta term (Hg) is the stoichiometric coefficient of element
c in reaction j which is expressed in moles of c per mole
of weathering reaction j. The alpha term is the number of
moles of weathering reaction j and is expressed in
moles/ha/yr. If alpha is a negative value then the
reaction is not forward as written, but reverse. In order
to solve the Plummer and Back mass balance equations, the
stoichiometric coefficients of the mineral weathering
reactions are found from the clay mineralogy and
petrographic studies. As shown in Chapter 4, the primary
mineral transformations observed consist. of 4 different
weathering reactions and the stoichiometric coefficients
listed in Table 5.

Thus, the Lochvale ‘model consists of four' mass Jbalance
equations (n34) for calcium, sodium, potassium and
magnesium and four unknown alpha values (a =4) or four
different mineral weathering rates in terms of moles/ha/yr.
These components comprise a 4 by 4 linear algebraic matrix
which is solved by computer and checked with hand

calculations (Table 5 and Appendix B).
5.5 Matrix Solution: Results and Discussion

The most significant weathering processes in the Lochvale
drainage are the transformation of plagioclase composition-

An (amphibolite) and An (granitic gneisses) to

65 35
kaolinite. Releasing 3.3 to 3.8 metric tons of dissolved

1904
1005

58

Table 4

Ilenental Flux Inshore
(Lochvale Vaterahed)

 

Inputs ninue Outputs/Holecnlar it. Holes per hectare per year
g/ha / g/nol / yr 1904 1905
Ca 4950/40.00 = 123.50 02 04
lg BOO/24.31 = 32.90 10.11
in 1690/22.99 = 73.51 33.73
I 940/39.10 = 24.04 143.40
Table 5
Hana Balance Equation Hatrix
-l -1

Holes ha yr Coefficient Hatrix

----------- (in X roles of nineral weathered per hectare per year)

1904 1905 Biotite hnorthite 05 Inorthite 35 Ictinolite
= 73.51 02.04 = 0 + .35 + .05 + 0
= 24.04 10.11 = 0.933 + 0 + 0 + 0
= 32.9 33.73 = 0.930 + 0 + 0 + l
= 123.5 143.40 = -.226 + .05 + .35 + 2

Table 0
Solution to Hana Balance Matrix
(Holes per hectare per year)
Ierrotrenolite-
Biotite Inorthite 05 Inorthite 35 Actlnolite
25.7003 150.30 20.0070 0.7027

17.2009 140.743 40.1231 17.5002

59
calcium per year and 1.1 to 1.25 metric tons of dissolved
sodium, the weathering of An 65 occurs at a rate of 146.7
to 156.4 moles/ha/year and An at a rate of 28.9 to 48.12

35
moles/ha/year. Weathering of the ferrotremolite-actinolite
amphibole and biotite have lesser effects on solute budgets
in the Lochvale drainage. Producing a half-metric ton of
both magnesium and potassium per year, the transformation
of biotite to vermiculite occurs at a rate of 17-25

moles/ha/year and ferrotremolite to kaolinite at a rate of

8.7 to 17.6 moles/ha year (Table 6).

One way to check whether the mineral weathering
reactions and rates accurately describe the system being
modelled, is to compare ‘measured silica outputs to 'the
silica release rates predicted by the stoichiometric mass
balance equations. As shown in Table 7, the predicted
silica releases described by the fOur stoichiometric
weathering reactions from Chapter 4 was within 2% of the

actual silica measurement for 1984 and within 37% for 1985.

In 1984 the mineral weathering reactions and mass balance
derived mineral weathering rates clearly account for the
observed water chemistry, however, in 1985 the accuracy
drops. Few studies successfully' match predicted silica
release rates with measured flux rates. Clayton (1988)
computes mass balance weathering rates for three forested

watersheds in the Idaho batholith. His predicted silica

60

Table 7

Silica Release Rate Predictions vs. Actual

Measured Si02
(moles/ha/yr)

Predicted from
stoichiometric
reactions

1984

197.3

161.0

Predicted vs.
actual accuracy

98%

(+/- 2%)

63%

(+/-37%)

61

release rates were also within 94% of the measured silica
flux, suggesting that primary mineral hydrolysis accounts
for the net loss of cations from the watersheds. Clayton
(1988), Velbel (1985a), Drever and Hurcomb (1987) suggest
the reason that few predictions of silica release rates are
successful in watershed mass balance studies may be due to
complex lithologies and incorrect characterization of
weathering products and reactants. In this thesis it is
not clear why a discrepancy exists between the 1984 and
1985 predicted versus the actual silica release rates.
Mineral weathering rates increased in different proportions
from 10 to 20 moles of mineral per hectare per year, yet
there were no significant differences in pH (in fact, pH
rose by .05 units; Table 8) and precipitation and measured

water outflow decreased in 1985 (Table 9).

A study of Baron and Bricker (1987) cation and anion data
shows an aproximate 6 to 12% increase in their measured
outputs, yet an 8% decrease in the measured inputs was

found (Table 8).

Another interesting trend found was sulfate had a 12%
increase in output from 1984 to 1985, yet a 24% decrease in
inputs. Such trends may indeed indicate a non-steady
state source or sink exists within the Lochvale drainage.
Baron and Bricker (1987) cite soil and biomass as the long
term sink in the Lochvale watershed, producing the observed

cation and anion trends. However, Baron and Bricker (1987)

Table 8

62

1985 in Loch Vale Watershed.

\

Annual Budgets for Major Cations and Anions for 1984 and
Values (kg/ha) have been

 

 

 

 

Normalized to the Balanced Chloride Budget. In 1984
This Caused a 35% Increase in Input Values. In 1985
This Caused a 6% Increase in Output Values.
1984 1985
In Out 935 In Out 935
Species kg/ha kg/ha In kg/ha kg/ha In
Caz’ 2.61 7.55 2 90 2.46 8.21 3.34
Mg2+ 0.57 1.36 2.40 0.42. 1.24 2.95
Na’ 1.07 2.76 2.59 0.79 2.69 3.41
K’ 0.31 1.25 4.02 0.40 1.03 2.58
NH.+ 1 88 0.37 0.20 1.21 0.11 0.09
‘5042' 10.68 8.25 0.77 8.18 9.30 1.14
N03" 10.23 7.14 0.70 8.25 6.49 0.79
CI' 1.39 1.39 l 00 1.21 1.21 1.00
Si02 - 11.84 - - 9.68 -
pH 5.01 6.33 5.06 6.27 -

 

Table 9 Hydrologic Balance for Loch Vale Watershed for 1984 and

 

 

 

 

 

 

1985. Values are in Million Cubic Meters.
1984 1985
Water Adjusted by Adjusted by
parameter Value Cl-balance Value Cl-balance
Deposition (0) 7.337 9.905 7.162 7.162
(measured)
Evaporation (E) 5.165 5.165 4.078 4.078
(calculated)
Outflow (0) 5.996 5.996 4.152 4.401
(measured)
0 - (6+0) -3.824 -l.256 -1.068 -l.3l7
Percent deposition
as snow ' 64% 68%
(from Baron and Bricker, 1987)

63
also note (as discussed earlier) problems with the
deposition and. chloride imbalance--where more deposition
and chloride inputs should have been measured. Their
explanation for this problem was error in nmasurement due

to wind, snow and/or the evaporation model used.

In summary, the mass balance findings suggest the cation
budgets can be explained by the weathering of four primary
minerals. 1985 mass balance findings suggest a possible
sink as silica’s release rate predictions become less

accurate.

5.6 Calculation of Tardy’s Re

Mineral weathering findings of this thesis are consistent
with the plot of Lochvale waters in the kaolinite stability
relation diagram of section 5.3. Because mass balance
findings may suggest a component of non-steady state
release in the Lochvale system another useful and simple
semiquantitative mass balance tool was used to confirm
kaolinite. Tardy’s Re consists of a formula for estimating
the silica to alumina ratio retained in the solid
weathering products from dissolved cations and silica of

stream waters (Tardy, 1971; Velbel, 1985b).

64

Re =( 81 O2/A1203)residue

= 2 (3K+ -+ 3Na+ -+ 2Ca

2Ca2+

2+ + +

-Si02/ K + Na +

)streams

Several assumptions are built into Tardy’s Re: a) quartz
and muscovite are unweatherable and weatherable minerals
have feldspar and biotite stoichiometries and b) all
minerals dissolve stoichiometrically. When the Re=0 the
predicted weathering residues are aluminous (e.g.
gibbsite); when Re=2, a 1:1 atom ratio of silica to
aluminum is attained which corresponds to a 1:1 clay
mineral (e.g. kaolinite) and when Re=3, silica is withheld
by the weathering profile to form 2:1 clays (e.g.
smectite). The following Re's were calculated for the

Lochvale drainage:

Table 10

Lochvale Drainage
Tardy Re Calculations

1.090
0.910
1.263
The results of the Lochvale Tardy Re's show Lochvale

weathering products should be more kaolinitic to aluminous

as opposed to 2:1 clay type residues. Such results support

65
the observed kaolinite mineralogy of the Lochvale watershed
but do not support the formation of a smectite dominated
weathering profile. As stated previously, however, Tardy’s
Re is used only as a semiquantitative tool and the results

are looked at more qualitatively.

5.7 Comparison of Mineral Weathering Rates to other

Research

The following Table 11 modified after Velbel (1985a) shows
plagioclase weathering rates from various watershed mass
balance studies which are normalized to modal abundance of
plagioclase. As shown, the results of this thesis combines
both plagioclases ( An35 and An65) weathering rates into a
combined weathering rate of 194.86 moles/ha/year. Although
An65 is known to occur only in amphibolite rocks, which
occupy roughly 5% of the total lithologies in Lochvale, the
modal percentage (43%) was normalized to the entire
drainage area, to a new modal value (2.15%). Likewise,
using an average modal percent for An35 (15%), which
composes granitic gneisses representing 95% to the total
rock types, a surface area normalization was done to the

entire drainage giving a new modal value of (14.2%).

66

 

 

Table 11
Plagioclase weathering rates from watershed mass balance
studies
Rate Modal % Normalized Rt.
Watershed (moles/ha/yr) Feldspar (rate/%fe1ds)
Coweeta 2 Velbel, 1985a 613
18 453
34 497
36 732
14 274
27 305 8.3 36.7
32 308
Pond Cleaves 148 10.6 14.0
Branch 9: Q1, 1970
Trnavka X-O Paces, 1983 210 (19) 11.1
X-9 550 14 39.4
Filson Creek Siegel, 1984 235
Silver Creek Clayton, 1988 448
Lochvale This study 194.86 16.35 11.9
Ratemax Normalized ratemax
Ratio ------- = 4.95 Ratio -------------------- = 3.54
Ratemin Normalized rate min

(after Velbel,

1985b)

67

Adding both the new An35 and An65 modal values together
gives a net surface area normalized value of 16.35%. Thus,
the normalized rate of plagioclase for Lochvale becomes
11.9, within the range of other normalized values. Taking
only one of plagioclases, however, and normalizing to
surface area and modal abundance brings the normalized
plagioclase weathering rate to less than 4, far slower than

other findings.

5.8 Significance of Rock Types

As shown in the mass balance modeling, the Lochvale
watershed cation chemistry may be largely controlled by
four key hydrolysis reactions. Two of the minerals, An 65
plagioclase and ferrotremolite, are predominant minerals of
amphibolite units arranged in lenses and pods throughout
the granitic gneisses of the Front Range. The striking
dark green to black amphibolites have been described to
profusely weather throughout the Front Range as well as
Rocky Mountain National Park forming holes and hollows in
the sturdier and more massive granite-gneiss complex (Cole,
1977: Nesse, 1977; Robinson gal, 1974). A visually
estimated 5% of the Lochvale drainage contains small 3 to 5
foot amphibolite lenses within the gneisses, larger lenses
and layers (10-30 feet) are seen at the entrance of

Lochvale and Mills Lake as well as the Bear Lake area.

68

Along the Ute trail, northwest of Lochvale, even larger
lenses of dark green to black amphibolite can be seen.
Amphibolite weathering in the Colorado Front Range may be a
significant source of base cations, contributing a
significant fraction of acid neutralization. Furthermore,
a winter visit to Lochvale, reveals that the holes and vugs
once or partially occupied by dark green to black
amphibolite serve as hydrologic conduits and preferential
pathways for water. Frozen seeps emanated from all of the
amphibolite units. Thus, the reasons for preferential
weathering of amphibolites can be considered two fold: 1)
as observed by previous researchers (Goldich, 1938: Reiche,
1950) more mafic minerals, following Bowens Reaction
series, tend to weather more rapidly-- more calcic
plagioclases for example, are observed to weather more
rapidly than sodic ones (Goldich, 1938) and 2) as a
consequence of their rapid weathering hydraulic pathways
are formed where precipitation can collect and continually
keep in contact with fresh amphibolite mineral surfaces.
Consequently, disproportionately high ionic contributions
are made per unit mass or surface area. Thus, small
amounts of highly reactive rock types can account for the
bulk cation chemistry of waters. Even though amphibolites
represent only 5% of the total lithologies of the Lochvale
drainage, it is evident from the mass balance model, the
accuracy of the silica release rate check, field evidence
and previous research that preferential weathering of this

unit supplies roughly 70 percent (refer to Table 6) of the

69

total cation flux of Lochvale.

The less calcic An35 granitic gneisses are also very
important suppliers of sodium and calcium. Although
gneisses represent 95% of drainage rock types, their
weathering appears less pronounced than the amphibolites.
One reason for this is the short 'water-mineral surface
contact time due to steep terrain and lack of hydraulic
conduits. Petrographic and mass balance results do suggest
granite-gneisses also help neutralize proton inputs on a

long term scale due their extensive nature.

Finally, the weathering of the biotite fraction of
schists soils and granitic gneisses of the Lochvale
drainage to vermiculite appears to supply the potassium to

the drainage.

70

Chapter 6

CONCLUSIONS

Mineral weathering in the Lochvale drainage consists of 4
key hydrolysis reactions: 1) plagioclase (An65) to
kaolinite; 2) plagioclase (An35) to kaolinite; 3) amphibole
(ferrotremolite) to kaolinite and 4) bdotite to

vermiculite.

Mass balance calculations using the 4 stoichiometric
weathering reactions as stated above and the net cation
fluxes for Lochvale shows plagioclase (An65) weathers at a
rate of 146-156 moles/ha/year. Plagioclase (An35) weathers
at a rate of 28-48 moles/ha/year. Ferrotremolite weathers
at a rate of 9-17 moles/ha/year and biotite at a rate of

17-25 moles/ha/year.

The mass balance model accuracy was checked by comparing
the model predicted silica release rates to actual measured
silica fluxes. Few studies have been able to accurately
predict silica. release rates (Clayton, 1988). iLochvale
mass balance reactions and rates accurately predict 1984
silica fluxes within 2% and 1985 silica fluxes within 36%.
The decreased accuracy in 1985 and the 8% increase in
cation fluxes suggests a component of non-steady state
release may exist in the Lochvale watershed.

Following Goldichs weathering observations (1938) where

71

more mafic minerals were observed to weather more readily
than felsic ones, the mafic Lochvale amphibolites were
observed to weather more extensively than the more felsic
granite gneisses. Volumetrically, the amphibolite
represents less than 5% of all rock types found in the
Lochvale drainage (in contrast to the granite gneisses
which represent 95%). Yet, disproportionately large
amounts (70%) of the cation releases out of Lochvale are
from the weathering of this highly reactive rock type. The
weathering of amphibolite units throughout the Colorado
Front Range may be largely responsible for calcium
dominated stream waters and neutralizing hydrogen ion

inputs.

BIBLIOGRAPHY

72

BIBLIOGRAPHY

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in Rocky Mountain National Park. Water Resources Bulletin,
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Baron, J. and Owen Bricker, 1987. Hydrologic and Chemical
Flux in Lochvale Watershed, Rocky Mountain National Park:
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Robert C. Averett and Diane McKnight, Lewis Publishers,
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Barnhisel, R., 1977. Chlorites and hydroxy interlayered
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Berner, R., Sjoberg, E., Velbel, M. and M. Krom, 1980.
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Blair, R.W., Jr. 1976. Weathering and Geomorphology of the
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Caine, N., 1979. Rock Weathering rates at the soil surface
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Carroll, Dorothy, 1970. Clay Minerals: a guide to their x-
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73
Society of America. Boulder, Colorado, 80 pp.

Clayton, L.C., 1986. An Estimate of Plagioclase Weathering
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Clayton, L.C., 1988. Some Observations on the
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Cleaves, E.T., Godfrey, A.E. and Bricker, O.P. 1970.
Geochemical mass balance of a small watershed and its
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Cole, J .C. 1977. Geology of East-central Rocky Mountain
National Park and vicinity, with emphasis on the
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Longs Peak-St Vrain Batholith. Ph.D. Disseration,
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Drever, J. I. and D.F. Grigal, 1986. Report of
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Knoxville, TN , 8 pp.

Drever, J. and D. Hurcomb, 1986. Neutralization of
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Epis, R.C. and Chapin, 1975. Geomorphic implications of
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Gerrard, A.J., 1981. Soils and Landforms: An Integration of
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Gardner, 1“ R., Kheoruenromne, I. and H.S. Chen, 1978.
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Helgeson, M.C., Garrels, R.Mg and. F.T. .Mackenzie, 1969.
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Isherwood and Street. 1976. Biotite-induced
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Geological Society of America Bulletin, v. 87: 366-370.

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11-17.

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75

1243, 31 pp.

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76

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77

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APPENDIX A

X-ray Diffraction Patterns

78

Table 12

Characteristic X-Ray Diffraction Peaks

CuK-alpha
2 theta Peak

Angstroms - ----- ----
Amphibole 8.40 - 8.41 10.5 001
Kaolinite 7.15 12.35 001
Kaolinite 3.57 24.9 002
Kaolinite 2.35 38 2 003
Oriented mounts 4.48 19.8 _
Oriented mounts 4.35 20.4 110
Oriented mounts 4.17 21.3 111
*1
Nacrite 7.18 12.3 002
(type of Kaolinite 3.58 24.8 004
Vermiculite 14.2 6.22 001
*2 4.8 19.22 003
Smectite 15 5.8 001
Chlorite 14.1-14.2 6.27-6.22 001
Mica 10 8.8 001
Muscovite 5 17.7 002
Biotite 10.1 8.77 002
Mica 2M 9.29 8.85 002

10.4 8.8

Calcite 3.03 29.47 104
Dolomite 2.88-2.87 30.05 104

1: Disorder in Kaolinite results in broadening of 001, 002
deflections.

2: By heating to 500 C interlayer water is expelled but quickly
rehydrates on heating to 700 Cvariance will collapse to 4.3 A
for the (001).

79

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Odp

APPENDIX B

Hand Calculations of Clay Structural Formulas

APPENDIX C

Hydrogeochemioal Flux Data

86
HALF CELL FOFMVIQ':

[Mi] [Al+3 4. F *3, N\ ‘1 +3 .+4
" “v 94 ”Elli-Joni“).

FVQSH Bin-OWE (From “microprobe, Dwia- Isucrwaod direct)
/6 Fauna fifl°fllmli Si" Bu.L VALENCE

 

 

Si02. 344.0 (,0 .coo i 4
TiOL 1“} 79'? .0106 4
Alto3 \l.7.o SI .2394 A 3
F20 (4.04 71.8 .l‘iSS B 2;
FL. 03 3.45 go .0444 B 3
CaO irace, S'lp X 2
m3 0 \345 40 . 34 38 D 2,
NaLO 3| )
K2. 0 \o.35 47.] ,2lQ8 N 1

H10 3.48 6~O .9300

K: prop Co nsian‘i‘
= 22..

46 660) +4(.o:u,g) + 362144) +204“) +3604“) r-
2034”) + l(.zms) = 4.5344

.. 4 _ ..
1;. ”13341 -“0 = 4/K E
7:. .222. A\ {n 41%an lea,”

A'Y: .2196 " .ZZZ -‘- ‘. 0015 Alumnium I»; dd‘fd/Iednt/
““3 .-.. ['4' Y) K ‘5 (‘.OOZ$)(15377)=O M7“

lo -- BK = (.Iixs)(4.53<14)=.9% Le":- -ZZ4
oL , D K = (.843:)(4.5341)= £559

‘1 = y K =- (.2.22) (4.5344): we

h = MK = c.219&)(4.5374)= .9947

 

weaning) BiofiT-E

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87

Eoporn'ans; 51mg“ VAlmce.

.0194
.0118
.1196
.0198
.2492
.0150
.2488

JZJO
L606

K: zz/Mu. = 4.5::

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2' ‘l
A 3
3 z
B 3
X z
I) 2.
TV” 1'

’ I

A-Y= .2198 - .205! = .0145
“-3)“ HO 0L: /./7_s
lo = .089 3: .42;
, X: .ll3
bfim‘ qqq h = 54?-

 

88

CALQ- FRESH BloriTE
(ISHERWOOD + smear, um)

HALF CELL'

4+
MQQQLF‘ 890 5.3224 m7”!- $71.12!][4‘3WW $239747
[cu] o
2. lo

CAL. Nausea) 8.3“}?
(IsumwOoo i-S‘mem" 19%)

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cam: K5411}; as E 974 Mat/ZSTIJOJA.” ”a

[AW .92?- 5:}:137 Ola [0 H]!-

 

 

 

APPENDIX C

Hydrogeochemical Flux Data

89

C8: kQ/Yl‘ [kg/ha]

  

PRECIP-
ITATICN

 
   

 

 

 

93%.

 

 

 

 

EEDECCK . L sows

1120 KG CA/HA

 

 

 

 

 

1984

Figure 23.- Calcium Flux Diagram for Lochvale
(from Baron, personal communication)

      

PRECIP-
ITATICN

 

—--—-—----‘

 

 

 

 

 

’I‘
93% I 6%
EEC-ROCK SOlLS
41 kg Na/ha

 

 

 

 

 

 

 

 

1984

Figure 24.- Sodium Flux Diagram for Lochvale
(from Baron, personal communication)

91

Mg, kg/yr (kg/ha)

 
   
   

PRECIP-
ITATION

 

 

 

 

 

 

 

 

 

 

 

 

 

 

350.1 | A
(0.53) y I
93% | 6%
EEDROCK , m >‘ SOILS
[196 kg Mg/ha
3.8
(0.01)
836.6 59.2
(1.26) , (0.09)
1%
.\
SURFACE WATER
—--'""""l 899.6
. ' " l
r“"---1 ————-L_E.'3'_’.l.l ”'36)
:SEDIMENTS/ ' '
L..-__---_
- . \

1984

Figure 25.- Magnesium Flux Diagram for Lochvale
(from Baron, personal communication)

92

K, kg/yr (ks/ha).

   
 

PRECIP-
ITATION

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

l
93: A 6%
EEDROCK SOILS
2 1 ' 110 kg K/ha
(0.01)
769.9
(1.16) 55.9
1‘» (0.08)
* ' I.
SURFACE WATER
,_ _______ 827.9
—-- - 1.25)
' i BIOTA: ( .
(- ---------- 1 -—-—o '
I ' _..-—_-..
ESEDIMENTS, ‘
- -------- x
1984 I

Figure 26.- Potassium Flux Diagram for Lochvale
(from Baron, personal communication)

 

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