PARAGENESIS, GEOCHEMISTRY, AND TEMPERATURES OF
FORMATION OF ALTERATION ASSEMBLAGES AT THE
SIERRITA DEPOSIT, PIMA COUNTY, ARIZONA
by
Richard Kellar Preece, III
A Thesis Submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In Partial Fulfillment of the Requirements
For the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
1 9
7 9
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library
to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable
without special permission, provided that accurate acknowlRequests for permission for exedgment of source is made.
tended quotation from or reproduction of this manuscript in
whole or in part may be granted by the head of the major
department or the Dean of the Graduate College when in his
judgment the proposed use of the material is in the interIn all other instances, however, perests of scholarship.
mission must be obtained from the author.
SIGNED:
X:.c .er
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
7/245/7 9
d E. Beane
Associate Professor
of Geosciences
Rich
Date
ACKNOWLEDGMENTS
I wish to thank Dr. R. E. Beane for selecting and
guiding the research phase of this project, for the many
discussions with him on the implications of the fluid inclusion data, and for his critical editing of this thesis.
I would also like to thank Drs. D. L. Norton and S.
R.
Titley for their suggestions that improved this manuscript.
Assistance with fluid inclusion and electron microprobe research was given by Robert Bodnar and Valerie
Walker, respectively, whom I gratefully acknowledge.
I am grateful for the financial aid received during
this project which came from The University of Arizona in
the form of a research assistantship, and from the Duval
corporation in the form of a scholarship.
Research was also
partially funded by National Science Foundation grant EAR77136 42
.
I am especially indebted to my wife, Eustolia, for
her incredible patience and support during what must have
seemed an interminable progression of days and nights that
I spent in the laboratory.
iii
TABLE OF CONTENTS
Page
vi
LIST OF ILLUSTRATIONS
viii
LIST OF TABLES
ix
ABSTRACT
1.
INTRODUCTION
1
2.
ALTERATION MINERALOGY AND PARAGENESIS
7
Alteration Paragenisis
Harris Ranch Quartz Monzonite
Biotite Quartz Diorite
Microprobe Data
Feldspars
Muscovite
Biotite
Chlorite
Epidote
Summary
.
3.
.
.
8
11
.
.
.
.
18
19
21
21
24
24
28
30
FLUID INCLUSION STUDIES
Temporal Classification of Fluid
Inclusions
Compositional Classification of Fluid
Inclusions
Moderate Salinity, Liquid -rich.
Type I:
Vapor -rich
Type II:
Type III: Halite -bearing
Fluid Inclusion Homogenization Data
Sample
Sample
Sample
Sample
15
HR -02
HR -01
BQD -03
BQD -01
30
32
32
32
33
35
35
39
41
Secondary Inclusions
Salinities
Composition of Halite- bearing
Inclusions
Na /K Mole Ratio of Moderate -Salinity
Fluids
Pressure Corrections
Discussion and Results
iv
42
44
44
50
55
57
60
V
TABLE OF CONTENTS -- Continued
Page
4.
SUMMARY AND CONCLUSIONS
APPENDIX A:
66
THIN AND POLISHED SECTION
DESCRIPTIONS
68
HR-01-01
HR-01-02
HR-01-03
HR-02-01
HR-02-02
HR-02-03
HR-02-04
BQD-01-01
BQD-01-02
BQD-01-02A
BQD-01-03
BQD-01-04
BQD-01-06
BQD-03
APPENDIX B:
APPENDIX C:
68
68
69
70
72
72
72
73
73
75
75
76
77
77
ELECTRON MICROPROBE PROCEDURES
AND ANALYSES
FLUID INCLUSION HOMOGENIZATION AND
FREEZING EQUIPMENT AND PROCEDURES
Optics
Sample Preparation
LIST OF REFERENCES
81
.
99
101
102
103
LIST OF ILLUSTRATIONS
Page
Figure
1.
2.
3.
Location Map of the Sierrita Porphyry
Copper Deposit
3
Generalized Geological Map of the Sierrita Open
Pit Showing Sample Location
4
Paragenesis and Relative Abundances of Minerals
12
in Sample HR -01
4.
5.
Schematic Diagram of Sample HR -02 Showing
Geometric Vein Relations and Mineralogy
.
8.
9.
10.
11.
Paragenesis and Relative Abundances of Minerals
17
Compositions of Alkali and Plagioclase
Feldspars
20
Portion of Compositional Triangle of Biotite
Octahedral Site Occupancy
23
Portion of Compositional Triangle of Chlorite
Octahedral Site Occupancy
25
Portion of Compositional Triangle of Octahedral
Site Occupancy of Coexisting Biotites and
Chlorites from Sample HR -02
26
Histogram of Fe3+ /Fe3 + +A1) Mole Ratios in
27
Epidotes
12.
Histograms of Primary Fluid Inclusion
Homogenization Temperatures (Th) from
36
Sample HR -02
13.
13
16
in Sample BQD -01
7.
.
Paragenesis and Relative Abundances of Minerals
in Sample BQD -03
6.
.
Distribution of Secondary Fluid Inclusion
Homogenization Temperatures in Quartz Grain
Cut by Vein in Sample HR -02
vi
38
vii
LIST OF ILLUSTRATIONS -- Continued
Figure
14.
15.
Page
Histogram of Primary Fluid Inclusion
Homogenization Temperatures (Th) from
Samples HR -01 and BQD-03
40
Histograms of Primary Fluid Inclusion
Homogenization Temperatures (Th) from
Sample BQD -01
16.
17.
18.
19.
20.
43
Comparison among Secondary Fluid Inclusion
Homogenization Temperatures (Th) from
Each Sample Studied
45
Relationship between Salinity and Homogenization Temperature of Fluid
Inclusions at Sierrita
47
Histogram of Measured Fluid Inclusion
Salinities at Sierrita
49
Temperature of Vapor Disappearance (Tv) vs.
Temperature of Halite Dissolution (TNaC1)
for Halite -bearing Inclusions from Sierrita.
.
52
Distribution of Daughter Products with Respect
to Salinity in Halite -bearing Inclusions
.
53
.
21.
22.
23.
.
Comparison between Homogenization Temperatures
and Pressure- corrected Trapping Temperatures
of Moderate -salinity Liquid -rich Fluid
Inclusions
59
Hypothetical Histograms of Fluid Inclusion Homogenization Temperatures from Three Crosscutting Veins
61.
Temporal Evolution of Temperature, Salinity, and
Vein Formation at Sierrita
64
LIST OF TABLES
Table
1.
Page
Modal Mineralogy of the Harris Ranch and
the Biotite Quartz Diorite
9
Daughter Products Observed in Fluid Inclusions
at Sierrita, with Optical and Physical
Properties
34
B.1.
Feldspar Microprobe Analyses
83
B.2.
Muscovite Microprobe Analyses
88
B.3.
Biotite Microprobe Analyses
89
B.4.
Chlorite Microprobe Analyses
93
B.5.
Epidote Microprobe Analyses
95
2.
viii
ABSTRACT
The Sierrita porphyry copper orebody is thought to
be contemporaneous with the emplacement of a Laramide -age
quartz monzonite porphyry into two older intrusives of distinctly different compositions:
biotite quartz diorite.
a quartz monzonite and
Wallrock chemistry appears to have
influenced the mineralogy of alteration and vein assem-
blages, in that minerals typical of potassic and propylitic
assemblages attend main -stage sulfide deposition in the
quartz monzonite and biotite quartz diorite, respectively.
In addition, late quartz + muscovite + sulfide veining was
observed to cut potassic veins only in the quartz monzonite.
Although the presence and relative abundances of hydrothermal minerals are governed by host rock lithology, electron
microprobe analyses of vein and alteration minerals indicate that compositional variations are independent of wallrock composition.
Fluid inclusion studies revealed that
early veining in both wallrocks occurred at temperatures of
300-430°C, from two chemically distinct fluids.
The earli-
est veining observed was associated with hypersaline brines
( - 12 molal NaCl equivalent) , which was followed by an ini-
tially hotter, locally boiling 2 molal NaCl equivalent solution.
The bulk of mineralization in both rocks was
ix
X
associated with the low salinity fluid at temperatures of
320- 370 °C, although sulfide deposition occurred at tempera-
tures as low as 190°C in the center of late phyllic veins.
CHAPTER 1
INTRODUCTION
Field and laboratory studies of porphyry copper -
type alteration and mineralization systematics have suggested that significant variations in temperature, pressure,
and hydrothermal fluid composition had occurred both temporally and spacially during ore - forming processes (i.e.,
Norton and Knight 1977, Gustafson and Hunt 1975, Bodnar
1978).
It has also been recognized that the nature of al-
teration assemblages may be greatly influenced by the chemical and mineralogical makeup of the host rock (Guilbert and
Lowell 1974, Beane 1979).
This study was designed to moni-
tor the temporal evolution of the thermal and chemical environment of hydrothermal mineral deposition, and the
effects of host rock composition on alteration assemblages
at the Sierrita porphyry copper deposit.
Relative temporal relationships among alteration and
vein assemblages were established by detailed examination of
crosscutting veins.
The scale of observation ranged from
hand lens inspection of rock slabs to detailed thin and polished section studies utilizing the petrographic microscope.
Standard fluid inclusion heating and freezing techniques
1
2
were used to determine the temperature and gross salinity of
hydrothermal fluids associated with the alteration assemblages.
The compositions of alteration and vein minerals
were established by electron microprobe analyses.
The Duval -Sierrita porphyry copper -molybdenum depos-
it, located 40 km south southwest of Tucson, Arizona (Fig.
1), was selected for study because supergene effects are
generally lacking, and because fracture -controlled hypogene
alteration and mineralization occurs in two chemically distinct wallrocks.
The deposit which is part of the Sierrita-
Esperanza porphyry copper system lies on the southeastern
flank of the Sierrita Mountain range.
The mining history
and geology of the complex has been previously described by
Lynch (1967), Cooper (1973), Smith (1975), and Aiken and
West (1978).
As such, only the general geology exposed in
the Sierrita pit will be discussed here.
The Sierrita deposit is localized in three intrusive bodies:
Jurassic -Triassic Harris Ranch quartz monzo-
nice,an early Paleocene biotite quartz diorite, and the
Laramide Ruby Star quartz monzonite porphyry (Fig. 2).
The
Harris Ranch quartz monzonite is medium grained equigranular to slightly porphyritic and outcrops in the southwestern part of the pit.
This rock unit has been dated at about
200 million years, making it the oldest intrusive in the pit
(Cooper 1973).
Laramide intrusive activity commenced with
3
ARIZONA
-*PHOENIX
TUCSON
0
150
X'SIERRITA
km
Figure 1.
Copper Deposit.
Location Map of the Sierrita Porphyry
4
E
Ó
rn
W
-J
4
c.
the emplacement of the biotite quartz diorite, dated at 67
million years ago (Cooper 1973).
The diorite, located in
the northwestern part of Sierrita, appears to be in intrusive contact with the Harris Ranch quartz monzonite.
It is
a fine to medium grained porphyritic rock, although it may
have a highly variable texture (Smith 1975).
The eastern
half of the Sierrita pit consists almost entirely of
Laramide -aged Ruby Star quartz'monzonite porphyry, which is
thought to be temporally related to mineralization (Smith
1975, Aiken and West 1978).
This quartz monzonite porphyry,
dated at around 57 million years ago, is a late -stage dif-
ferentiate of the 69 million year old Ruby Star granodiorite batholith which extends north of the Esperanza- Sierrita
complex, occupying most of the Sierrita Mountain range
(Cooper 1973).
The quartz monzonite porphyry enhibits sev-
eral textural variations which grade into one another, suggesting either a complex cooling history or multiple
intrusive events (Smith 1975).
An intrusive breccia (ap-
parently related to the emplacement of the quartz monzonite
porphyry), Triassic volcanics, and post- mineralization
quartz latite dikes also outcrop in the pit (Fig. 2).
Samples for petrographic and fluid inclusion studies
were collected along the contact between the Harris Ranch
quartz monzonite and the biotite quartz diorite, about 250 m
from the contact of the two with Ruby Star quartz monzonite
6
porphyry (Fig. 2).
Single and crosscutting veins were
studied from four samples collected within 50 m of each
other from the quartz monzonite and the biotite quartz diorite.
Because the samples were collected from a relatively
restricted area, the results should not be considered to
characterize the entire deposit.
However, the results of
this study are compatible with other studies at Sierrita
(Denis 1974,
Fellows 1976, Aiken and West 1978)
.
CHAPTER 2
ALTERATION MINERALOGY AND PARAGENESIS
Previous studies of hydrothermal alteration distribution and paragenesis at Sierrita -Esperanza have been car-
ried out by Smith (1975), Denis (1974), Fellows (1976), and
Aiken and West (1978).
These studies have shown that while
the spatial distribution of hydrothermal alteration assemblages at Sierrita is broadly comparable to other porphyry
copper deposits (Lowell and Guilbert 1970, Rose 1970), the
distribution and mineralogy of alteration assemblages are
strongly influenced by the composition of the host rock.
The most notable deviations from the generally accepted alteration model of Lowell and Guilbert (1970) are the absence of a pervasive quartz + sericite + pyrite assemblage,
and the abundance of epidote and chlorite associated with
mineralization in the center of the deposit.
The general
sequence of vein formation at Sierrita is (from early to
late):
biotite --quartz + K- feldspar
gypsum + zeolites.
quartz + sericite
Each of these stages of vein formation
consists of several generations of similar mineralogy and
relative abundances of phases, each of which may or may not
contain sulfides (Aiken and West 1978).
7
8
Slabbed surfaces of four rock samples of quartz monzonite (2) and biotite quartz diorite (2) were examined by
hand lens and stereomicroscope in order to determine the
relative ages of crosscutting veins.
Thin sections of se-
lected veins and intersections of veins were made for petrographic examination in order to establish the paragenesis
and mineralogy of vein and alteration assemblages.
Selected
thin sections were stained with sodium cobaltinitrite to
facilitate the identification of potassium feldspars.
When
necessary, polished sections were made so as to identify
sulfide and oxide minerals, utilizing vertically- incident
reflected microscopy.
Electron microprobe analyses were
used to obtain the compositions of biotite, feldspars, chlorite, muscovite, and epidote.
Alteration Paragenesis
Mineral abundances were visually estimated from thin
section examination, and modified from average estimates by
Denis (1974) and Smith (1975)
.
The approximate volume abun-
dance of the original rock -forming minerals of the quartz
monzonite and the biotite quartz diorite are presented in
Table 1, illustrating the difference between the two rock
types.
Tourmaline was not seen in this study, consistent
with the observation of Aiken and West (1978) that the
tourmaline content of the Harris Ranch quartz monzonite decreases as the contact with the Ruby Star quartz monzonite
Sphene
Amphibole (Tremolite ?)
1 %
Trace
Tourmaline
4 %
Oligioclase
29 %
Biotite
Orthoclase
37 %
4 %
Quartz
25 %
.
Trace
5 %
5 %
20 %
25 %
45 %
Magnetite
Orthoclase
Quartz
Biotite
Hornblende
Andesine
Biotite Quartz Diorite
The estimated volume percentages are from this study, as modified from
Denis (1974) and Smith (1975)
Modal Mineralogy of the Harris Ranch and the Biotite Quartz Diorite
Harris Ranch Quartz Monzonite
Table 1.
10
porphyry is approached.
The total groundmass biotite con-
tent observed in altered quartz monzonite is close to the
combined igneous biotite, amphibole, and tourmaline content
reported by Denis (1974).
Although no compelling evidence
was seen, this is permissive evidence that the missing
tourmaline, as well as amphibole, may have been replaced by
hydrothermal biotite.
11
The following summary of vein and alteration assemblages in each of the four rock samples is derived from thin
and polished section petrographic descriptions in Appendix
A, as well as observations of textural relations made during
the fluid inclusion study.
Harris Ranch Quartz Monzonite
The two samples from the quartz monzonite are HR -01,
consisting of a single vein, and HR -02 which contains sev-
eral crosscutting veins, five of which were suitable for
fluid inclusion studies.
The paragentic sequences inter-
preted from the petrographic studies are shown in Figures 3
and 4.
The paragenesis and relative abundances of hydrothermal phases of Sample HR -01, a single mineralized vein,
are shown in Figure 3.
Early microcline and biotite altera-
tion of the wallrock was contemporaneous with cloudy quartz
and microcline deposition in the vein.
Pyrite was then de-
posited on the surfaces of the cloudy quartz, slightly overlapping deposition of the quartz.
Chalcopyrite and lesser
amounts of clear quartz, epidote, chlorite, K- feldspar, and
anhydrite fill open spaces, vein, and partially replace the
earlier assemblages.
Figure 4 is a schematic diagram of geometric relationships in Sample HR -02.
The earliest vein assemblage
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Paragenesis and Relative Abundances of Minerals in Sample HR -0l.
EARLY
Figure 3.
sericite
chlorite
epidote
anhydrite
chalcopyrite
pyrite
quartz
hematite
biotite
Kspar
13
VEIN D
VEIN A: qtz +
Kspar + blot
(
VEIN G: qtz+
Kspar + blot
VEIN E: qtz + musc+
Kspar+ py + cp + bn
Figure 4. Schematic Diagram of Sample HR -02 Showing
Geometric Vein Relations and Mineralogy.
14
documented in this sample is composed of quartz + micro cline + biotite (Vein A, Fig. 4).
This was followed by at
least two more generations of quartz + microcline + biotite
veining (Veins G and C, Fig. 4)
.
Vein filling in the potas-
sic veins was apparently uninterrupted except for Vein
C,
where evidence of reopening and deposition of quartz + Kfeldspar is present.
Flakes of hematite, tens of microns in
diameter, in quartz and K- feldspar are present in all potassic veins.
Quartz + muscovite veining (Veins D and E, Fig. 4)
cuts all potassic veins in Sample HR -02.
Filling of the two
veins initiated with an early assemblages of quartz + Kfeldspar + chlorite with minor muscovite, chalcopyrite, and
bornite.
Continued vein filling was dominated by muscovite
with minor amounts of quartz, chlorite, pyrite, chalcopyrite, and bornite.
Late stage deposition is primarily py-
rite and chalcopyrite, with minor bornite and quartz.
As no
reopening or brecciation textures were observed, filling of
Veins D and E is interpreted as having evolved continuously.
Alteration of Sample HR -02 may have commenced with
biotitization of amphibole and tourmaline ( ?) and the development of thin discontinuous stringers of biotite.
This is
taken from the observations of Aiken and West (1978), but
petrographic evidence on the scale of a single sample is
inconclusive.
15
Biotite Quartz Diorite
The paragenesis of Sample BQD -03, a single vein, is
very similar to that of HR -01.
The paragenesis of BQD -03
is shown in Figure 5, with the width of the bars proportional to the relative abundances of the respective mineral.
Early alteration and vein filling consisted of biotite, Kfeldspar, sodic plagioclase, and quartz.
Continued deposi-
tion of quartz was accompanied by anhydrite, and overlapped
with the development of bladed specular hematite.
Pyrite
was deposited on exposed surfaces of the previously formed
minerals, probably contemporaneously with the later stages
of hematite deposition and the subsequent replacement of
hematite by magnetite.
Chalcopyrite, epidote, and the other
associated phases (Fig. 5) filled open spaces, and veined
and replaced previous assemblages.
As biotite is confined
to a narrow selvage and to microfractures in the wallrock,
the time frame of biotitization relative to vein deposition
is incompletely known.
Sample BQD -01 contains five veins which crosscut
and offset each other.
As seen in Figure 6, each vein ex-
hibits much the same mineralogy and paragenesis as each
other and as BQD -03 (Fig. 5).
The major difference between
the five veins in BQD -01 and that of BQD -03 is the altera-
tion of wallrock plagioclase to sericite in Sample BQD -01.
Sericite is interpretated to be an intregal part of vein
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Figure 6.
sericite
magnetite
molybdenite
chalcopyrite
pyrite
chlorite
epidote
quartz
anhydrite
hematite
biotite
K spar
No -plag
®
VEIN C
a
VEIN D
Paragenesis and Relative Abundances of Minerals in Sample BQD -01.
NMI
INV -em
mom
VEIN A
LATE
18
formation, rather than as a later, separate event, for three
reasons.
1.
The abundance of sericitization decreases dramatically away from the veins.
2.
No veinlets or stringers of sericite alone were
seen.
3.
Only igneous plagioclase was replaced by sericite;
secondary feldspars were unaltered.
The timing of sericitization of walirock plagioclase with
respect to the evolution of vein mineralogy is unknown.
The paragenesis and relative abundance of vein and
alteration minerals for each vein in Sample BQD -01 are presented in Figure 6.
In each case, vein filling initiated
with an assemblage of quartz + biotite + K- feldspar, that
may or may not include sodic plagioclase and anhydrite.
This was followed by pyrite which commonly overlaps chalcopyrite + epidote + chlorite + quartz deposition.
Magne-
tite, molybdenite, and anhydrite are usually associated with
the later assemblage.
Microprobe Data
The compositions of alteration and vein minerals
capable of solid solution were determined by electron microprobe analyses.
Of particular interest in this study are
the variations of mineral compositions through time in a
19
particular sample, and correlations between walirock chemistry and alteration mineral composition.
Microprobe pro-
cedures and tabulated analyses are given in Appendix B, and
the resulting mineral compositions are summarized below.
Feldspars
As noted in the thin section studies, two solid
solution series of feldspars are present:
potassium -rich
alkali feldspar, and sodium -rich plagioclase.
Microprobe
analyses were made of 22 secondary K- feldspars and 7 plagio-
clases occurring in veins and in vein selvages.
In addi-
tion, two igneous feldspars in the diorite were analyzed.
The feldspar analyses are plotted in terms of end -member
component mole fractions on the orthoclase -albite- anorthite
compositional diagram in Figure 7A.
Plagioclase compositions generally fall near the
albite- anorthite tieline, but also include three theoretically impossible K- feldspar concentrations for low -
temperature feldspars (Deer, Howie, and Zussman 1966, p.
291).
These "impossible" compositions correspond to bulk
compositions of perthitic feldspars which are the result of
exsolution (Deer et al. 1966).
Plagioclase analyses from Samples BQD -01 and BQD -03
fall into three groups distinguishable by both composition
and mode of occurrence.
Plagioclase feldspars deposited in
Figure 7.
Feldspars.
Compositions of Alkali and Plagioclase
The symbols I, S, and V designate igneous, selvage, and vein
feldspars, respectively.
Compositional Triangle of Alkali and Plagioclase FeldA.
spars.
B.
Orthoclase Content of Alkali Feldspars.
20
A.
+ 8QD-03
BQD-01
X HR-02
O HR-01
Ab
FREQ.
8
B.
8QD-03
BQD-0I
6
HR-02
HR-01
4
2
xOry
0
96
92
88
84
82
Figure 7.
Compositions of Alkali and Plagioclase
Feldspars.
100
21
veins average Ab72An26Or2, the average of two igneous plagioclase feldspars in the diorite is Ab58An41Or1.
The two
alteration feldspars located on the vein- wallrock contact
average Ab67An31Or2, plotting between igneous and vein feldspar compositions.
K- feldspar compositions plot along the orthoclase -
albite tieline, ranging from Or99Ab1 to Or83Ab17 (Fig. 7A).
These compositions are plotted against frequency in Figure
7B.
The majority of microcline compositions fall between
Or100 and Or92' with four K- feldspars containing less than
90 mole percent orthoclase component.
The range of vein
and selvage K- feldspar compositions in both rock types are
similar, with no trend observed with respect to paragenetic
position.
The average composition is Or96Ab4.
Muscovite
Five muscovites from the quartz + muscovite + sulfide veins in HR -01 (Veins D and E) were analyzed.
The com-
positions are very similar to each other, with an average
of:
(K1.84'Na0. 16) 2.00 (A13.57'Ti0.03'Fe3+0.16'Mg0.21) 3.97
(Al1.
76' Si6.24) 8.00020 (OH) 4
Biotite
The results of microprobe analyses of 21 biotites
from the quartz monzonite and biotite quartz diorite are
22
portrayed in Figure 8.
The biotites may be broken into
three groups on the basis of octahedral site distribution
and mode of occurrence.
Biotites associated with early
potassic veins in HR -02 contain a significantly higher Mg/
(Mg + Fe) mole ratio than the rest of the analyzed biotites,
with an average mole ratio of 0.78.
Shreddy biotites and recrystallized igneous biotites
from Sample HR -02 contain only slightly more Mg than Fe,
with an average Mg /(Mg + Fe) mole ratio of 0.59.
The compo-
sitional shift between these and the more phlogopitic selvage biotites is shown in Figure 8.
All biotites in the biotite quartz diorite have very
similar compositions to each other.
In addition, the Mg/
(Mg + Fe) mole ratios are essentially identical to altera-
tion biotites in the quartz monzonite, with an average mole
ratio of 0.58.
One analyzed biotite in Sample HR -02 contains 4.50
wt. % TiO2, similar to the TiO
2
content of igneous biotites
at Bingham, Utah (Moore and Czmanske 1973).
As this bio-
tite was located on a polished section, the petrographic
difference between it and biotites identified as recrystallized igneous biotites was not established.
The composi-
tion is listed in Appendix B (Biotite HR- 02 -4I, Table B.3).
90
20
xQ
80
40
70
60
N
50
Mg/(Mg+Fe)
N
4%
40
30
HR-02 (igneous)
X HR - 02 (alteration)
HR - 02 (vein)
DioriM
20
\
10
in Sample HR -02.
Figure 8s
Portion of Compositional Triangle of Biotite Octahedral Site
Occupancy. --Arrow shows compositional shift between selvage and alteration biotites
Mg
10
:.i
x
`
\
X
,is:
,It
50
24
Chlorite
Analyzed chlorites include both vein chlorites and
alteration chlorites after biotite.
As seen in Figure 9,
the chlorites have a relatively constant octahedral (Al +
Ti), mole proportion, with variable Mg /(Mg + Fe) mole ratios.
Chlorites from the quartz + muscovite + sulfides veins have
an average Mg /(Mg + Fe) mole ratio of 0.46, and fall in the
ripodolite compositional field according to the classification of Hey (1954).
The remainder, occurring as both vein
and alteration chlorites, are classified as pycnochlores
(Hey 1954) , with an average Mg /(Mg + Fe) mole ratio of 0.63.
The compositions of alteration chlorites and parent
biotites from Sample HR -01 are shown in Figure 10.
The
limited data presented here suggest that the chlorite composition is relatively independent of parent biotite
composition.
Epidote
Twenty -two epidote analyses include both vein and
selvage epidotes from Samples HR -01, BQD -01, and BQD -03,
and are plotted in Figure 11.
The average Fe3 + /(Fe3+ + Al)
is 0.30, which compares favorably with the average value of
0.29 from 1382 analyses done by Fellows (1976).
90
Figure 9.
Occupancy.
Mg
70
60
Mg/(Mg+Fe)
50
40
30
20
10
Portion of Compositional Triangle of Chlorite Octahedral Site
80
HR-02 (vein)
HR-02 (alteration)
BQD-03
X HR-01
!
90
/
80
/
70
1
60
Mg /(Mg +Fe)
50
I
40
1
Chlorite
X Biotite
30
1
20
\
(AI+Ti)
10
\
Figure 10. Portion of Compositional Triangle of Octahedral Site Occupancy
of Coexisting Biotites and Chlorites from Sample HR -02. -- Coexisting phases are connected by tielines.
Mg
10
50
27
HARRIS RANCH
DIORITE
FREQ.
6543
2
I
0
0.20
0.30
0.40
XFe
Figure 11.
in Epidotes.
Histogram of Fea+/ Fe3 + +A11 Mole Ratios
28
Summary
Petrographic studies have shown that the presence
and relative abundances of alteration and vein minerals at
Sierrita bear a strong resemblance to the host rock mineralIn the quartz monzonite, alteration and vein assem-
ogy.
blages are dominated by microcline and muscovite.
Alteration of the biotite quartz diorite, on the other hand,
is dominated by calcium -, magnesium -, and iron -rich minerals:
biotite, chlorite, and epidote.
The paragenetic sequences that were developed from
this study demonstrate that vein filling typically involved
an
evolution of hydrothermal mineral assemblages.
In the
mineralized veins, sulfide deposition appeared late during
the development of vein assemblages, in most cases associated with an assemblage that altered earlier vein minerals.
The general sequence of vein and alteration mineralogy in
the quartz monzonite is an early quartz + K- feldspar assem-
blage which may or may not be associated with mineralization followed by the formation of quartz + muscovite
veining.
The biotite quartz diorite as seen in this study
is cut by a series of mineralized veins, all of which ex-
hibit an evolution from an early assemblage dominated by
quartz and biotite to a later epidote + chlorite + sulfide
assemblage.
29
Electron microprobe analyses indicate that the compositions of vein and alteration minerals were not affected
by distinctly different wallrock chemistries.
Composition-
al variations of plagioclase, biotite, and chlorite were
seen to be more a function of the mode of occurrence within
a particular rock type rather than the rock in which the
minerals appeared.
The compositions of K- feldspar and epi-
dote showed no systematic variation within a single sample
or between samples.
This would seem to indicate that the
overriding factors dictating the most stable mineral composition are the prevailing temperature, pressure, and fluid
chemistry, rather than wallrock composition.
CHAPTER 3
FLUID INCLUSION STUDIES
Fluid inclusions from each vein discussed in the
previous chapter were examined utilizing standard fluid inclusion techniques.
Details of sample preparation and
heating and freezing methods used are in Appendix C.
The
purpose of this fluid inclusion study is to determine the
temperature and salinity of hydrothermal fluids associated
with particular mineral assemblages.
By correlating fluid
characteristics with the paragenetic positions of the respective alteration assemblages, the evolution of tempera-
ture and salinity of hydrothermal fluids through time can
be established for each sample.
In addition, as the samples
were selécted in order to minimize any difference in the
sourceregions of the hydrothermal fluids (Norton 1978), and
the thermal gradient between samples, it may be expected
that time equivalency can be established between alteration
assemblages of different samples on the basis of similar
temperatures and salinities of fluids.
Temporal Classification of
Fluid Inclusions
The relative time frame of a particular fluid inclusion depends on the position of the host crystal in a
30
31
paragenetic sequence, and on the relationship of the inclusion to the host.
A three -fold system, based on the timing
of the formation of the inclusion relative to the host, is
commonly used to classify fluid inclusions.
Primary fluid inclusions were trapped at the same
time as the enclosing minerals by irregularities in crystal
growth or fluid hetereogenity (Roedder 1967).
Pseudo -
secondary inclusions were formed during crystal growth by
the development of a fracture, which subsequently filled
with fluid and rehealed.
Further crystal growth resulted
in a plane of inclusions which abruptly ends within the
host crystal.
Primary and pseudosecondary inclusions rep-
resent conditions during crystal growth.
Secondary inclu-
sions were formed during a fracturing event at some time
after the growth of the host crystal.
Subsequent rehealing
of the fluid - filled fracture resulted in a train of fluid
inclusions that records the temperature of the fracturing
event (Roedder 1967).
Fluid inclusions of all three temporal types were
selected for heating and freezing studies, in order to determine the character of hydrothermal fluids, both during
and after vein formation.
Determination of the temporal
nature of fluid inclusions was based on the criteria given
by Roedder (1976).
32
Compositional Classification of
Fluid Inclusions
The classification used here was taken from Nash
(1976)
,
and is based on phase relationships observable at
room temperature.
Of the four general types listed by Nash
(19 76) as commonly found associated with porphyry copper -
type mineralization, three were observed at Sierrita.
Type I;
Moderate- Salinity, Liquid -rich
The most numerous type of inclusion observed in this
study consists of two phases:
bubble (10 to 40 vol %)
.
a liquid and a small vapor
Freezing tests indicate that the
liquid is a low to moderately saline NaC1 solution.
Rarely,
small daughter products of hematite or unknown opaques may
be present.
This type of inclusion homogenizes to the
liquid by contraction and disappearance of the vapor bubble
with increasing temperature.
Type II:
Vapor -rich
This type of inclusion, only present in one vein of
this study, contains a large vapor bubble (over 55 vol %)
and is a liquid phase.
Vapor -rich inclusions are commonly
believed to form by entrapment of low- salinity steam, or by
necking down of Type I inclusions (Roedder 1967).
Although
attempts at freezing the liquid in such inclusions were unsuccessful, the mode of occurrence, as discussed later, is
33
consistent with the former interpretation, rather than the
latter.
With increasing temperature, the vapor phase ex-
pands to completely fill the inclusion at the homogenization
point.
Type III:
Halite -bearing
These locally abundant inclusions contain a cube of
halite in addition to a salt- saturated solution and a small
vapor bubble.
This type of inclusion is the result of
trapping a fluid of a higher salinity than 6.1 molal NaC1,
which is halite saturation at room temperature.
At least
one other daughter product is regularly present, but as
many as three have been observed.
Those daughter products
observed in inclusions in this study are listed in Table 2..
Halite- bearing inclusions homogenized by contraction of the
vapor bubble and dissolution of the daughter minerals are
noted in Table 2.
The homogenization point is marked by the
disappearance of either halite or the vapor bubble, which-
ever temperature is higher, but other daughter minerals may
remain.
34
Table 2.
Daughter Products Observed in Fluid Inclusions at
Sierrita, with Optical and Physical Properties
Mineral
Properties
Halite (NaC1)
Colorless; high relief;
isotropic; cubic.
Sylvite (KC1)
Colorless; moderate relief;
isotropic; cubic, with
rounded corners; seen in
one inclusion only.
Hematite (Fe2O3)
Red to orange; high relief;
hexagonal to irregular;
does not dissolve upon
heating.
Anhydrite (CaSO4)
Colorless; high relief;
highly birefringent; rectanL
gular; occasionally corners
become rounded when heated.
Unknown opaque(s)
Opaque; doesn't respond to
magnet; too small to establish morphology; does not
dissolve upon heating.
Unknown A
Colorless; moderate relief;
low or no birefringence; no
distinctive morphology; seen
in one inclusion, only; dissolved at 309 °C.
35
Type IV inclusions of Nash (1976) contain a third
phase of liquid CO2.
No inclusions of this type were ob-
served during this study at Sierrita.
Fluid Inclusion Homogenization Data
Histograms summarizing primary fluid inclusion homogenization temperatures of each vein studied are shown in
Figures 12, 14 (p. 40), 15 (p. 43).
Inclusions are shown
in three categories according to the phase relationships as
discussed above.
Type I inclusion
homogenization temper -
atures are signified by the dotted pattern, vapor -rich inclusions by the V- pattern, and halite -bearing inclusion
homogenization temperatures are indicated by the line pattern.
In addition, a shaded pattern is used to distinguish
inclusions of different mineral assemblages, where evolution of alteration is observed in a single vein.
Sample HR -02
Histograms of primary fluid inclusion homogenization temperatures for quartz monzonite sample HR -02 are
shown in Figure 12, arranged in accordance with the crosscutting relations (earliest vein at top).
Both halite -
bearing and moderate- salinity, liquid -rich primary
inclusions were observed, indicating that both hypersaline
and moderately saline fluids were present during vein
filling.
Figure 12. Histograms of Primary Fluid Inclusion
Homogenization Temperatures (Th) from Sample HR -02.
The dotted pattern represents liquid -rich inclusions; the
lined pattern represents halite- bearing inclusions (total
homogenization); and the shaded pattern in the bottom histogram represents inclusions from selvage quartz (see text).
36
EARLY
FREQ.
VEIN A
5-
13
VEIN G
5
9
VEIN C
31
5
0
V
T
VEINS D & E
5
18
LATE
-
Th (°C)
wi
aaaa
Q
200
250
-
I
I
I
300
350
400
Figure 12. Histograms of Primary Fluid Inclusion
Homogenization Temperatures (Th) from Sample HR -02.
37
Halite- bearing inclusions occur in all three
potassic veins, and to a minor extent, in selvage quartz associated with the quartz + muscovite veining.
The homog-
enization temperatures of fluid inclusions from the
potassic veins exhibit considerable overlap, indicating that
early potassium feldspar- stable veining occurred at relatively constant temperature.
Moderate -salinity, liquid -rich primary inclusions
are present in Vein C and in both selvage and vein quartz in
the late phyllic veins.
In Vein C, two groups of homogeni-
zation temperatures of the Type I inclusions are present,
one from 290°C to 330°C, and the other from 350° to 380°C.
The bottom histogram in Figure 12 consists of primary fluid inclusion filling temperatures from Veins D and
E.
An important observation is that the range of primary
inclusion homogenization temperatures from 190° to 280 °C is
unique to the quartz + muscovite veining.
Primary inclu-
sions were observed in quartz grains in the selvage adjacent to the veins, and in quartz within the vein intergrown
with muscovite.
Inclusions in the selvage quartz (shaded
pattern, Fig. 12) homogenized between 240° and 280 °C, while
those in the veins homogenized between 190° and 240 °C.
An apparently pre -vein quartz crystal is cut by
healed and unhealed fractures paralleling Vein D (Fig. 13A).
The intense fracturing and the sulfide grains in the middle
Figure 13.
Distribution of Secondary Fluid Inclusion Homogenization Temperatures in Quartz Grain Cut by
Vein D in Sample HR-02.
Camera lucida of fractured quartz grain and sulfide
grains (shaded pattern) showing homogenization temperature ranges of inclusions found in the center and near the
edges of the quartz grain.
B.
Histogram of secondary inclusion homogenization temperatures (Th) from quartz grain.--The dotted pattern represents liquid-rich inclusions; and the lined pattern
represents halite-bearing inclusions.
A.
38
quartz grain
A.
Center of
Vein D
Center of
Vein D
1mm
B.
29 inclusions
Th (*C)150
200
250
Figure 13.
Distribution of Secondary Fluid Inclusion Homogenization Temperatures in Quartz Grain Cut by
Vein D in Sample HR -02.
39
of the quartz grain are coincident with the center of the
vein.
A fine- grained selvage of quartz + muscovite + pyrite
surrounds and partially embays the quartz grain.
Figure 13B
presents a histogram of homogenization temperatures of secondary inclusions found in the quartz crystal.
The higher
temperature group from 200° to 260 °C is from inclusions
located near the edge of the phenocryst, while the inclusions homogenizing around 140° to 150 °C are in the highly
fractured areas in the center of the quartz grain (Fig. 13A)
.
The distribution of secondary inclusions in the quartz
phenocryst is compatible with the interpretation that those
homogenizing between 140° and 150 °C represent the last
fluids flowing through Vein D, presumably responsible for
deposition of the sulfides observed filling the center of
the vein.
Sample HR -0l
As noted in the previous chapter, Vein HR -01 con-
sists of two vein assemblages (Fig.
3)
.
Primary inclusions
from cloudy quartz from the early assemblage and from later
clear quartz intergrown with sulfides were studied; the results of homogenization tests are summarized in Figure 14A.
All inclusions are moderate salinity, liquid -rich, and those
associated with the earlier assemblage are shaded.
vein filling occurred between 330° and 410 °C.
Early
Later sulfide
40
A.
HR -01
31 inclusions
300
400
350
FREQ.
10 -
B.
BQD -03
21 inclusions
5-
V.
..---
.;
:: :: :
,...
.:.
0
300
.. .
1
350
-
r:13
.`
400
V
V"
Th (°C)
450
Figure 14. Histogram of Primary Fluid Inclusion
Homogenization Temperatures (Th) from Samples HR -01 and
BQD -03.- -The dotted pattern represents liquid -rich inclusions; the V- pattern represents vapor -rich inclusions; and
the shaded pattern represents inclusions found in the
earlier assemblages (see text).
41
deposition persisted down to 290 °C, with a slight overlap in
temperatures between the early and late alteration assemblages.
Sample BQD -03
In a similar fashion to the paragenesis of Sample
HR -01, two mineral assemblages were observed in the petro-
graphic study of the single vein.
Primary fluid inclusions
from the early cloudy quartz and from clear quartz and epidote associated with later sulfide deposition are plotted in
Figure 14B.
Primary inclusions associated with the early
assemblage (shaded pattern, Fig. 14B) include both Type I
(dotted pattern, Fig. 14B) and vapor -rich (V- pattern, Fig.
14B) inclusions.
Vapor -rich inclusions were uncommon in Vein BQD -03,
appearing in groups of two or three randomly distributed inclusions, or in planes of secondary or pseudosecondary
inclusions.
Although, only four were suitable for homogeni-
zation, they appeared to be characteristic of those observed.
In one case, two vapor -rich and an adjacent
liquid -rich inclusion homogenized in the temperature range
of 418° to 427 °C.
These indicate that the vapor -rich in-
clusions are a manifestation of boiling of moderately saline
fluids during early quartz deposition.
Deposition of the
early assemblage continued with cooling to 350 °C, as
42
evidenced by four inclusions that homogenized at temperatures from 350 °C to 410 °C (Fig. 14B).
Homogenization temperatures of primary inclusions in
later clear quartz and epidote vary between 310° and 350 °C.
Only moderate -salinity, liquid -rich inclusions are associ-
ated with the later mineralizing event.
Sample BQD -01
The rather complex paragenesis of this sample (Fig.
6) may be generalized into an early and a late assemblage
for each of the five veins.
Figure 15 portrays histograms
of homogenization temperatures of primary fluid inclusions
from each of the veins, with the earliest vein at the top.
The inclusions associated with each of the early vein assemblages is in the shaded pattern.
With the exception of halite -bearing inclusions
present in the early assemblage of the earliest vein (Vein
E), fluid inclusions are moderate -salinity, liquid -rich.
Homogenization temperatures generally decrease with time
both within a particular vein, and from older to younger
veins.
Exceptions to this cooling trend are apparent in the
earliest vein (Vein E) , and in the transition from the late
assemblage of a particular vein to the early assemblage of
the subsequent vein.
43
FREQ.
VEIN E
7
5
EARLY
o
VEIN A
5-
16
0
VEIN C
::.
tj
0
e t
i. .
...
17
Si
.1 .T.
VEIN D
19
LATE
Th(°C)-
o
300
350
400
Histograms of Primary Fluid Inclusion
Figure 15.
Homogenization Temperatures (Tb) from Sample BQD -01.- -The
dotted pattern represents liquid -rich inclusion; the lined
pattern represents halite- bearing inclusion; and the shaded
pattern represents inclusions found in the early assemblage
of each vein (see text) .
44
Secondary Inclusions
Homogenization temperatures of secondary fluid inclusions from veins in the four samples are shown in Figure
16.
Each data point in the histograms consists of a repre-
sentative temperature of a plane of inclusions, determined
from the most common homogenization temperature of each
plane.
Locally, individual planes of secondary inclusions
could not be distinguished due to large amounts of inclusions.
In those cases, the reliability of the temperatures
obtained is not as good as those obtained from a recognizable plane, due to common -place necking -down of secondary
inclusions (Roedder 1967)
.
Three features are shown in Figure 16.
First, the
range of homogenization temperatures is similar in each sample, from
ti 130 °C to
ti 370°C.
appear in each histogram:
at 300 -310 °C.
Also three peaks consistently
at 190- 200 °C, at 270 -280 °C, and
Finally, only Sample HR -02 contains secondary
halite- bearing inclusions.
Salinities
Observations of fluid inclusions at room temperature
attest to the presence of at least two compositionally distinct fluids during vein formation at Sierrita.
Halite -
bearing inclusions are present only during early potassic
veining.
Lower salinity fluids, evidenced by Type I
45
20-
FREQ.
HR
10-
01
119
0
50-
40-
BQD -01
280
30-
2010 -
0
BQD-03
120
Th eC} -150
200
1
250
300
350
400
Figure 16.
Comparison among Secondary Fluid Inclusion Homogenization Temperatures (Th) from Each Sample
Studied. - -The dotted pattern represents liquid -rich inclusions; and the lined pattern represents halite- bearing
inclusions.
46
inclusions, were also present, although at a later time.
Figure 17 presents measured salinities of 234 primary and
secondary inclusions plotted against homogenization temperature.
Salinity is given in moles NaC1 equivalent per 1000
grams H2O (molality).
As sylvite was seen as a daughter
product in only one inclusion, the total salinity of the remainder of the halite -bearing inclusions may only be approx-
imated from halite solubility, due to an unknown KC1
content.
The salinities of these inclusions are more
closely approximated by expressing the salinity in terms of
molality rather than weight percent salt.
In addition, the
freezing point depression of NaC1 + KCI aqueous solutions
are nearly identical to those of NaC1 solutions of equiva -.
lent total molality.
The procedure used to determine the salinity of an
inclusion depends on the phases present.
Salinities of
halite- bearing inclusions were determined by heating the in-
clusion and noting the temperature at which the salt dissolved.
The salinity was approximated by comparing this
temperature with the NaCl solubility data compiled by Potter,
Babcock, and Brown (1977)
.
Freezing point depression determina-
tions were carried out on selected Type I inclusions, employing
the procedure outlined in Appendix C.
The salinities were
calculated from equations regressed on experimentally
47
I
I
1
X XX
X
X
X
X
X
X
X
X
00
o °o
O
o
00
O
N
o
Ir)
N
80
°
0$0
do
0 o
4
o
Sao
4o
oo
I
I
II
lfl
co
o
oo
o
00
00
o
v
Z
O
°°
DI C"
Z.3
.
o
o
°o° 0
° o0
I-
d"
O
ß0
% ocaso
pp,, o
o0°0 °0000G
á
Z
O
N
0
O
v
Ó
O
.
I
I
tt
N
(ninbe DDNw) JIlINI1dS
O
48
derived freezing point depression curves for aqueous NaC1
solutions (Potter, Clynne, and Brown 1978)
.
The linear distribution of most halite- bearing in-
clusions in Figure 17 is the result of the salt dissolving
at a higher temperature than the vapor bubble.
As a result
of defining the homogenization temperature as the temperature of the disappearance of the higher- temperature phase,
and of defining the salinity by the dissolution temperature
of halite, the inclusions must plot along the NaCl -H2O saturation curve.
As experimental solubility data in the NaC1-
H2O system is limited to vapor- saturated determinations
(Potter and Brown 1975)
,
the salinities defined in this man-
ner are approximate values only.
Unknown pressure depend-
ency, if any, on NaC1 solubility cannot be taken into
account.
Liquid -rich inclusions undersaturated with respect
to NaC1 at room temperature vary considerably in salinity,
from 0.25 to 4.7 molal NaC1 equivalent.
The great majority
of inclusions, however, cluster between 1 to 3 molal NaC1
equivalent, irregardless of the homogenization temperature.
As seen in Figure 18, two basis populations of
fluid salinities are obvious.
The pronounced bimodal nature
of the salinity distribution is best explained by a discrete
change, rather than a continuous evolution, of fluid salinity.
0
2
4
8
SALINITY (m NacI equiv)
6
IO
12
275 inclusions
14
Figure 18. Histogram of Measured Fluid Inclusion Salinities at Sierrita. -The dark pattern represents primary inclusion; and the lined pattern represents
secondary inclusions.
0
10
20
30
40
FREQ.
50
Composition of Halite- bearing Inclusions
As indicated above, halite (with rare exceptions)
dissolved at a higher temperature than the disappearance of
the vapor bubble.
The persistence of daughter products at
temperatures higher than the liquid -vapor homogenization
point has been ascribed to four mechanisms by Roedder
(1972)
.
1.
Equilibrium was not attained during the heating run.
2.
The mineral was a solid inclusion, trapped accidently by the inclusion.
3.
The inclusion has necked down, trapping the daughter
product in a smaller inclusion, thus increasing the
salt - liquid ratio.
4.
The dissolution temperature is the actual temperature of halite saturation.
The first three explanations can be dismissed for the inclusions included as data points.
In the first case, halite
equilibrates with the solution rapidly (Roedder 1972), and
several inclusions were heated several times at different
rates with no change in the salt -dissolution temperature.
In the case of the second and third explanations, trapped
solid inclusions and necked -down inclusions would exhibit
diverse phase ratios and resultant homogenization temperatures.
The consistency of both temperatures of vapor
51
disappearance and halite dissolution, as seen in Figure 19,
argue against these explanations.
Conversely, hematite probably does occur as an accidently trapped mineral in a number of the halite- bearing inclusions.
A diversity in the volume proportion of hematite
compared to the vapor bubble and salt crystal was observed.
In a few cases, the hematite was seen to apparently cross
the inclusion walls.
Hematite flakes appear as precipitated
phases within quartz, and some may have trapped fluid inclusions as the host quartz grew around the hematite (Roedder
1967; 1972).
Not all hematite was trapped, however, as
trains of secondary inclusions in quartz phenocrysts were
seen to contain hematite flakes in consistent phase proportions.
This is diagnostic of a true daughter mineral
(Roedder 1972).
Although the gross salinity of halite -bearing fluid
inclusions exhibit a relatively continous range from 8 to
13 molal NaCl equivalent, the distribution of additional
daughter products (Table 2) varies with respect both salinity and time.
Figure 20 presents the occurrence of daugh-
ter products as a function of salinity.
Inclusions with
halite only, halite + hematite, and halite + opaque(s) in
the salinity range of 10.5 to 13 molal NaCl equivalent are
found as primary inclusions in Veins A, G, and C in Sample
HR -02, and in Vein E, Sample BQD -01.
Those in the range of
Figure 19. Temperature of Vapor Disappearance (Tv)
vs. Temperature of Halite Dissolution (TNaC1) for Halite bearing Inclusions from Sierrita.
The "x" symbols represent primary inclusion; and the "o"
symbols represent secondary inclusions. Also shown are
TNaC1 -Tv values of 200 °C, 100 °C, and 0 °C (Tv TNaC1).
Ty (°C)
250
300
350
Figure 19. Temperature of Vapor Disappearance (Tv) vs. Temperature of
Halite- bearing Inclusions from Sierrita.
200
53
I) Halite only.
2} Sylvite + opaque
3) Unknown A + opaque
4) Hematite
5) Hematite + opaque
5
4
0
1
5
7) Anhydrite + hematite
or opaque
7
o
8
10
12
14
SALINITY Cm Nocl equiv)
Figure 20.
Distribution of Daughter Products with
Respect to Salinity in Halite- bearing Inclusions.
54
8 to 10 molal NaC1 equivalent are present as primary inclu-
sions in Vein C, and as secondary inclusions in Veins A and
G of Sample HR -02.
Halite -bearing inclusions with anhydrite
are restricted to a narrow range of salinities (9.5 to 11
molal) and are found as primary inclusions only in Vein C,
and as secondary inclusions in the two earliest veins in
Sample HR -02.
This seems to suggest that the appearance of
anhydrite as a daughter product may signify a fluctuation in
solution composition.
One primary inclusion from Vein G (Sample HR -02)
contained both halite and sylvite.
Although only one such
inclusion was seen in fluid inclusion polished sections,
others with similar phase proportions were seen in thin section.
The inclusion homogenized by the disappearance of
halite at a temperature of 269 °C, with a total salt content
of 9.2 molal (compare Figs. 12 and 20).
The composition
determined from the H2O -NaCl -KC1 phase diagram compiled by
Roedder (19 71)
is 5.2 molal NaC1, 4.0 molal KC1, with an
Na /K mole ratio of 1.3.
Halite -bearing inclusion may contain up to 2.3 moles
KC1 /1000 gm H2O at room temperature without precipitating
sylvite (Roedder 1971)
.
The maximum solubility of sylvite
in the presence of halite may be used to arrive at the minimum Na /K mole ratios of the halite- bearing inclusions.
The
ratios range from 3.3 for the lower salinity halite- bearing
55
inclusions to 5.7 for the higher salinity inclusions.
Pri-
mary halite -bearing inclusions associated with early potas-
sic veining cluster around 11.5 molal NaCl equivalent; the
minimum Na /K mole ratio for these inclusions is 5.0.
Na/K Mole Ratio of Moderate -Salinity Fluids
Although the absence of both halite and sylvite as
daughter products in Type I inclusions prohibits the direct
measurement of the Na /K mole ratio of the low salinity
fluids, the ratio may be calculated from a reaction between
coexisting albite and K- feldspar:
NaA1Si3O8 + K+ = KA1S í3O8 + Na+
(1)
The Na /K mole ratio of a fluid in equilibrium with an alkali
feldspar may be calculated from:
log (aNa + /aK +) = log K1 - log aOrpar + log
aAKbspar
(1a /mK) _ (aNa +aK +) (YK + /YNa +)
(2)
(3)
here a is the activity of the subscripted component in the
superscripted phases, y is the stoichiometric activity coefficient of the subscripted component, and K1 is the activity
product of Reaction (1)
.
Fluid inclusion evidence indicates alkali feldspar
deposition occurred between the temperature range of approximately 410° to 320°C (Figs. 12, 14, and 15)
.
An average
temperature of 350 °C will be used in the following calculations.
Alkali feldspars in both the quartz monzonite and
56
biotite quartz diorite have an average composition of
Or96Ab4 (Fig. 7b)
.
The activity coefficients of the orthoclase and albite components in alkali feldspar were calculated utilizing
the excess molar free energy of mixing equation given by
Waldbaum and Thompson (1969) :
ex
(P,T)
=
(6326.7 + 0.0925P - 4.6321T) (XAb) (XOr)2 +
(7671.8 + 0.1121P - 3.8565T) (XOr) (X
2
Ab
(4)
)
here the subscripts Ab and Or refer to the albite and orthoclase components, respectively, GeX is the molar excess
free energy of mixing, Xi is the mole fraction of component
i,
P is pressure in bars, and T is the temperature in de-
grees Kelvin.
The activity coefficients of orthoclase and
albite are then used to calculate activity of each of the
components in the alkali feldspar solid solution.
The ac-
tivies calculated in this manner at 350°C and 330 bars pressure are 0.96 and 0.71 for the orthoclase and albite
components, respectively.
At 350°C, the activity product of Reaction (1) is
100'77 (Helgeson et al. 1978), while the stoichiometric ac-
tivity coefficients of Na+ and K+ are 10 -1'00
and 10
respectively (extrapolated from Helgeson 1969)
.
-1.07
The Na /K
mole ratio thus calculated from Equations (2) and (3)
3.75.
is
57
Pressure Corrections
The homogenization temperature of a fluid inclusions
corresponds to the trapping temperature only when the vapor
pressure of the trapped brine equals total pressure on the
system (Nash 1976).
If the composition and temperature of
the boiling fluid can be ascertained, the pressure is
uniquely determined.
Inclusions that are trapped at some
pressure above the vapor-saturation curve homogenize at a
lower temperature than the true trapping temperature.
Coexisting vapor-rich and moderate-salinity, liquidrich inclusions homogenizing in the same temperature range
were found in the early quartz of Vein BQD-03.
An average
temperature of 425°C is indicated for boiling (Fig. 14b).
Although freezing tests on inclusions coexisting with vaporrich inclusions were unsuccessful, salinities of inclusion
with slightly lower homogenization temperatures are about 2
molal NaC1 equivalent (Fig. 17).
According to the data of
Sourirajan and Kennedy (1962), a 425°C, 2 molal NaCl solution boils at a pressure of 330 bars.
density of 0.82 gm/cm
3
,
Assuming an average
this pressure corresponds to a maxi-
mum hydrostatic column of about 4.4 km (Haas 1971).
Pressure corrections on 175 moderate-salinity,
liquid-rich inclusions that have had both heating and freezing tests done were calculated from the data of Potter
58
(19 77) and assuming a constant pressure of 330 bars.
Histo-
grams comparing homogenization temperatures are shown in
Figure 21.
The result of pressure corrections seems to justify
the assumption of constant pressure.
The peaks of homog-
enization temperatures (Fig. 21A) are strengthened by application of pressure corrections (Fig. 21B).
Pressure
corrections range from 60° at 140 °C to 10 °C at 400 °C.
The difference between vapor- liquid homogenization
temperatures and the higher temperatures of halite dissolution of up to 200 °C (Fig. 19) have been used as indications
of high trapping pressures (Denis 1974; Bodnar 1978; Kamilli
1978; Erwood, Kesler, and Cloke 1979; and others) .
As ex-
perimental data on the solubility of halite and densities
of hypersaline brines at pressure greater than the vapor -
saturated surface is not available, the variations in temperature, pressure, and composition of the fluid in
halite- bearing inclusions is unknown at temperatures higher
than the disappearance of the vapor bubble.
Pressure cor-
rections on homogenization temperatures of halite- bearing
inclusions are not possible owing to the lack of knowledge
of both homogenization pressures. and isochores for high
salinity brines.
Comparison between Homogenization TemFigure 21.
peratures and Pressure- corrected Trapping Temperatures of
Moderate -salinity Liquid -rich Fluid Inclusions.
The lined pattern represents primary fluid inclusion homogenization and trapping temperatures; and the shaded pattern
represents secondary fluid inclusion homogenization and
trapping temperatures.
A.
Homogenization Temperatures.
B.
Pressure- corrected Trapping Temperatures.
59
FREQ.
A.
15 -
10 -
5
Th (°C)
150
200
250
300
350
400
Comparison between Homogenization TemFigure 21.
peratures and Pressure -corrected Trapping Temperatures of
Moderate- salinity Liquid -rich Fluid Inclusions.
60
Discussion and Results
For a given vein, a group of secondary inclusion
homogenization temperatures represents the prevailing temperature at some time after the formation of that vein.
It
may be expected that, if another vein is filling at that
later time, primary inclusions in those later veins would
homogenize in the same temperature range as secondary inclusions in the earlier vein.
Shown in Figure 22 are hypothet-
ical histograms of filling temperatures of primary inclusions
(lined pattern) and secondary inclusions from three crosscutting veins.
Each vein exhibits a group of primary inclu-
sions filling temperatures characteristic of that vein.
In
the oldest vein, two groups of secondary filling temperatures are also present:
the lowest temperature peak being
correlative to the primary inclusion temperatures of the
youngest vein; the
higher peak of secondary inclusions
present in the intermediate vein stems from the filling
event related to the youngest vein.
This general relationship between primary and secondary inclusions has two ramifications.
First, the para-
genesis of veins not observed to crosscut each other can be
established; secondly, thermal events not responsible for
alteration or veining in a particular sample can be tracked
through secondary inclusions.
61
FREQ.
EARLY
LATE
TEMPERATURE !Figure 22. Hypothetical Histograms of Fluid Inclusion Homogenization Temperatures from Three Crosscutting
Veins.- -The lined pattern represents primary inclusions,
and the dark pattern represents secondary inclusions.
62
Inspection of the distribution of secondary inclusion homogenization temperatures (Fig. 16) reveals that each
of the samples exhibits the same thermal peaks as noted previously
( q,190 °C,
ti270 °C,
',300°C).
Primary inclusion
homogenization temperatures for all veins are typically in
the 300° to 400 °C range.
The only exception is in Sample
HR -02, where fluid inclusion homogenization temperatures of
140° to 280°C are associated with late quartz + muscovite
vein filling.
The secondary inclusion homogenization tem-
peratures in the range of 140° to 280°C in Sample HR -02 are
undoubtedly a reflection of this late veining event.
As
quartz + sericite veinlets are seen to cut Vein HR -01, secondary inclusion temperatures in HR -01 would be expected to
be in this same range of 140° to 280°C if the veinlets (and
therefore the secondary inclusions) in HR -01 formed at the
same time as the late phyllic veins in HR -02.
The lowest temperature peaks of secondary inclusion
homogenization temperatures in the diorite are identical to
those associated with late quartz + sericite veining in the
Harris Ranch quartz monzonite.
No veining was seen in the
biotite quartz diorite to correspond with these temperatures.
The repetition of homogenization temperatures of
primary and secondary inclusions across the veins in all
four samples, presumably resulting from the same fracturing
events in all samples, suggests that no thermal gradient
63
existed between the samples.
Thus, the temporal correla-
tion of different alteration and vein -filling assemblages
associated with primary inclusions of similar temperatures
and salinities in different samples appears to be justified.
The temporal evolution of the temperature and salinity of hydrothermal fluids are shown in relation to vein
formation in each of the samples in Figure 23A and 23B, respectively,
Paragenetic relations between veins are seen in
Figure 23C.
Sulfide deposition in each of the mineralized
veins is indicated by the double bar.
The temperature range
of hydrothermal-deposition was derived from pressure -
corrected homogenization temperatures.
The evolution of alteration mineralogy and associated fluid characteristics of alteration and mineralization in
the Harris Ranch quartz monzonite and the biotite quartz
diorite are as follows:
1.
Early veining in both rocks consisted of barren
quartz + K- feldspar + biotite, deposited from hyper -
saline brines at temperature of approximately 300°
to 370°C.
2.
Subsequent low -salinity fluids
(
ti2 molal NaC1
equivalent) at higher temperatures of 390° to 430°C
and locally boiling
were associated with quartz +
K- feldspar alteration in the quartz monzonite,
while albitic plagioclase, and locally, epidote +
chlorite + sulfides were deposited in the diorite.
Figure 23.
Temporal Evolution of Temperature,
Salinity, and Vein Formation at Sierrita.
Fluid Temperature vs. Time.
Fluid Salinity vs. Time.
Vein Formation vs. Time.- -The double bar represents the
interval of sulfide deposition.
A.
B.
C.
64
TIME -SALIN ITY
B.
(m NaCI)
®
10
a
1
5
.
0
1
TIME -C.
VEIN
HR-01
jA
HR-02
D
BQD-OI
A
'"'"'""""=I=
D
BQD-03
TIME -Figure 23. Temporal Evolution of Temperature,
Salinity, and Vein Formation at Sierrita.
65
3.
The bulk of mineralization in both rocks was associated with 2 molal NaC1 equivalent solutions at
temperatures of 320° to 370 °C, with lesser amounts
up to 390°C.
In the diorite, the sequence of quartz
+ K- feldspar + albitic plagioclase + biotite fol-
lowed by the epidote + chlorite + sulfides assem-
blage occurred repeatedly, accompanied by
fluctuations in temperature, where fracturing was
continuous.
Reopening and repeated deposition of
quartz + K- feldspar may have occurred during this
interval in the quartz monzonite (Vein C, Sample
HR -02)
4.
.
As solutions cooled to below 300°C, alteration in
the quartz monzonite evolved to quartz + K- feldspar
+ chlorite with lesser amounts of muscovite, chalcopyrite, and bornite.
Some local fluctuations of
fluid salinity between 2 molal and 9 molal NaC1
equivalent may have occurred during this time.
Muscovite replaced K- feldspar as the stable
potassium -bearing mineral as solutions cooled to below 270°C.
Late sulfides found in the center of
muscovite veins were deposited to temperatures as
low as 190 °C.
Veining corresponding to this late
quartz + muscovite veining was not observed in the
diorite, but may be present in other samples.
CHAPTER 4
SUMMARY AND CONCLUSIONS
This study at the Sierrita porphyry copper deposit
has shown that a combination of fluid inclusion and petrographic techniques is a powerful tool that may be brought
to bear on problems related to ore deposition.
Of particu-
lar importance to this study is the application of second-
ary inclusions to establish a relative time frame among
veins in different samples.
Within each sample, standard
petrographic studies form a basis on which the evolution of
hydrothermal fluid characteristics was established.
The
major outcomes of this study are:
1.
Hydrothermal alteration was seen to occur over a
wide range of temperature range; between temperatures greater than 400 °C and less than 200 °C.
2.
At least two chemically distinct fluids were present during the hydrothermal process.
A hypersaline
brine of 8 to 13 molal NaCl equivalent with minimum
Na /K mole ratios ranging from 3.3 to 5.7 was associated with early quartz + K- feldspar + biotite
veining in both the Harris Ranch quartz monzonite
and biotite quartz diorite.
66
Mineralization was
67
associated with fluids of much lower salinity, about
2 molal with a Na /K mole ratio of
3.
ti 3.8.
The bulk of mineralization took place between temperatures of 320° to 370 °C, although late sulfide
deposition associated with quartz + muscovite veining continued to temperatures as low as 190°C in the
quartz monzonite.
4.
In the Harris Ranch quartz monzonite, alteration and
vein filling associated with early sulfide deposition consists of minerals typical of the potassic
alteration zone of porphyry copper deposits (Lowell
and Guilbert 1970).
Simultaneously, in the biotite
quartz diorite the same fluids produced minerals
generally considered to be diagnostic of a peripheral propylitic zone.
5.
Alteration in the quartz monzonite progressed from a
microcline- stable assemblage to a muscovite -stable
assemblage with a significant temperature or fluid
salinity discontinuity.
Although no veining of the
biotite quartz diorite was seen contemporaneous with
the late phyllic alteration in the quartz monzonite,
the event was recorded in the former by the development of secondary fluid inclusions.
APPENDIX A
THIN AND POLISHED SECTION DESCRIPTIONS
HR -01 -01
This thin section contains vein HR -01,
and extends about 1 cm into the wallrock.
3 cm wide,
The vein is com-
prised of interlocking anhedral quartz grains up to 6 mm in
diameter.
Veinlets and stringer, 0.3 to i mm wide, of
quartz + K- feldspar, quartz + sulfides, quartz + K- feldspar
+ epidote + chlorite + sulfides, and quartz + sericite cut
the veins and adjacent wallrock.
The quartz + sericite
veining was the only one seen to exhibit crosscutting relations with any other veinlet, and was later than those
that it cut.
The wallrock appears to be completely altered
to microcline, biotite, epidote, chlorite, quartz, and sulfides.
The microcline has been lightly dusted by sericite,
and the biotite has been partially to completely be replaced by chlorite and rutile, with or without epidote and
sulfides.
HR -0l -02
This polished section of the vein is dominated by
quartz and chalcopyrite, with lesser amounts of pyrite and
minor to trace amounts of epidote, chlorite, K- feldspar,
68
69
and anhydrite.
Pink K- feldspar and chloritized biotite are
localized in the walirock, and are cut by epidote + chalcopyrite veining.
X -ray analyses on K- feldspar give the
clear separation of the 131 and 11 peaks that is indicated
of microcline (Deer et al. 1966)
.
Denis (1974) and Smith
(1975) also report the occurrence of microcline as vein K-
As cloudy quartz in the vein is intergrown with
feldspar.
selvage K- feldspar, the vein -walirock contact is diffuse.
Euhedral to subhedral 0.5 to 3 mm pyrite grains are localized along the surfaces of the quartz, most of which are
intergrown with the outer few tenths of a millimeter of the
quartz.
Massive chalcopyrite and minor amounts of anhedral
.clear quartz, epidote, chlorite, and anhydrite occupy the
center of the vein, and fill fractures in the cloudy quartz
and pyrite.
Minor replacement of pyrite by chalcopyrite is
evident along some of the fractures.
Irregular blebs,
0.05 to 0.3 mm in diameter, of silicates and anhydrite are
present in chalcopyrite.
HR-01-03
This thin section is of both vein and walirock in
equal amounts.
The vein is dominated by quartz as de-
scribed previously, with lesser amounts of sulfides inter -
grown with epidote, chlorite, and anhydrite.
Secondary
K- feldspar comprises about 60 vol. % of the walirock, some
70
exhibiting the crosshatch twinning diagnostic of microcline.
Albite- twinned plagioclase remnants occur in the center of
a few microcline grains.
Randomly oriented biotite grains,
0.1 to 0.5 mm in diameter occur in irregular masses and in
discontinuous veinlets.
Biotite is partially to completely
replaced by epidote, or by chlorite and rutile, with or
without sulfides.
The degree of chloritization of the
biotite decreases away from the vein.
Veinlets of quartz
+ K- feldspar + epidote + chlorite + sulfides cut alteration
microcline.
Sericite and minor epidote dusts the micro -
cline, occupying 5 to 25 vol. % of the grains.
HR -02 -01
This thin section is comprised of two 2.5 to 3 mm
wide quartz + K- feldspar veins and a single quartz + musco-
vite vein 2 mm wide, with a 2 to 3 mm wide selvage.
Veins
A and G, the potassic veins, are very similar to each
other, both consisting of sub -equal amounts of interlocking
1 to 3 mm grains of quartz and K- feldspar.
A finer -grained
selvage of quartz + K- feldspar + biotite is irregularly
distributed, usually replacing plagioclase.
From cross-
cutting relationships, Vein A is older than Vein G,
and
both are older than Vein E, the quartz + muscovite vein.
Interfingering radiating fans and rosettes of
bladed muscovite 0.5 to 1 mm long constitutes about 70 vol.
71
% of Vein E.
Although colorless in thin section, the musThe color and
covite appears tan - colored in hand sample.
a relatively high birefringence indicates a predominance of
ferric over ferrous iron (Deer et al. 1966)
.
Minor amounts
of K- feldspar, quartz, chlorite, chalcopyrite, and bornite
are present along the edge of the vein.
Trace amounts of
quartz and sulfides are intergrown with the muscovite, and
larger amounts of pyrite, chalcopyrite, bornite and quartz
occupy spaces between muscovite fans.
The selvage is dom-
inated by quartz with lesser amounts of K- feldspar and
muscovite.
Biotite is replaced by chlorite, muscovite, and
sulfides with rutile as a by- product.
The wallrock is a porphyritic quartz monzonite composed of 2 to 3 mm phenocrysts of subhedral to anhedral
quartz, perthitic orthoclase, and oligioclase.
The ground -
mass consists of the same minerals, plus accessory zircon.
The groundmass averages about 0.5 mm in diameter.
appears in three textural modes:
Biotite
as 1 to 2 mm anhedral
reddish -brown crystals with corroded edges, often con-
taining randomly oriented needles of rutile; as shreddy
flakes 1 to 0.4 mm in diameter, appearing to be in irregular, discontinuous veinlets; and as psuedomorphs after
amphibole.
Nearly all biotites are altered to chlorite +
rutile, with or without sulfides.
Plagioclase, and to a
72
lesser extent orthoclase, are dusted and veined by sericite.
HR -02 -02
This thin section contains the two crosscutting
quartz + K- feldspar veins described above:
Veins A and G.
The veins and groundmass are as described in HR- 02 -01.
HR -02 -03
This thin section contains Vein A and Vein D, a
quartz + muscovite vein similar to Vein E.
Vein A, ap-
pearing as described above, is cut by the 2 mm wide Vein D.
Vein D contains over 90 vol. % 1 mm -long bladed muscovite
radiating from the walls of the vein and interfingering
with each other in the center of the vein.
Minor amounts
of quartz and sulfides occur in the center of the vein between muscovite fans.
A quartz + K- feldspar + muscovite
selvage similar to that of Vein E is present.
All other
.aspects of Sample HR-02-03 are as described in HR- 02 -01.
HR -02 -04
Sample HR -02 -04 is a thin section containing two
quartz + K- feldspar veins:
Vein G and Vein C.
Vein D, the
quartz + muscovite vein discussed above, is also present in
this sample.
Vein C, 2 mm wide, is similar to Veins A and
G, although it apparently contains more K- feldspar than the
73
other two veins, and no replacement textures adjacent to
the vein were seen.
A discontinuous 0.1 to 0.5 mm wide
veinlet of quartz + K- feldspar cuts the coarser grained
vein material of Vein C.
Vein D.
Vein C cuts Vein G and is cut by
The latter two veins are similar to the previous
descriptions.
A grain of colorless amphibole (tremolite ?)
partially replaced by chloritized biotite was observed in
this sample.
BQD -01 -01
This thin section consists of the biotite quartz
diorite near Vein A (described below) .
The rock has a
slightly porphyritic texture, with subhedral phenocrysts of
green to blue -green hornblende and andesine.
The ground -
mass is composed of 1.5 to 0.4 mm long laths of subparallel
andesine, anhedral orthoclase, and quartz.
Flakes of bio-
tite, 0.5 to 0.1 mm in diameter, are interstitial to the
groundmass plagioclase.
The plagioclase is 10 to 20 vol. %
altered to sericite and epidote, while the hornblende is
replaced by biotite and magnetite or pyrite.
BQD -01 -02
This thin section consists of Vein A cutting altered biotite quartz diorite.
Vein A, 2.5 to 3 mm wide, is
comprised of quartz, sulfides, epidote, chlorite, anhydrite, K- feldspar, sodic plagioclase, and biotite.
The
74
vein is bounded by a i to 1.5 mm wide selvage, where alteration of the wallrock is about 90 vol. % complete.
Con-
sistent intergrowth and replacement textures suggest that
the vein and alteration minerals are in two assemblages.
Quartz, K- feldspar, plagioclase, and biotite are found near
the edges of the vein, with quartz, sulfides, epidote,
chlorite, and anhydrite filling around the grains of the
previous assemblage.
The average grain size is about 0.5
mm, ranging up to 1 mm.
Quartz in this and subsequent
veins are characteristically, but not invariably, slightly
biaxial which indicates that they have undergone strain
(Deer et al. 1966) .
Alteration of the wallrock is clearly related to
the vein, as the intensity of alteration decreases dramatically away from the vein.
Groundmass plagioclase and
hornblende are completely replaced within 1 to 1.5 mm of
the vein by quartz, feldspars, biotite, epidote, chlorite,
and opaques.
Plagioclase phenocrysts are 80 to 90 vol. %
replaced by sericite and lesser amounts of epidote, biotite, and K- feldspar.
Alteration decreases to 10 -30 vol.
% of the rock 2 mm away from the vein.
A veinlet of gypsum was observed to meet Vein A at
an angle, become deflected and run down the center of the
vein, and leaves the vein at the original angle.
Anhydrite
75
is almost completely altered to gypsum where the veinlet
cuts an anhydrite grain.
BQD- 01 -02A
Sample BQD- 01 -02A is a polished section of Vein A.
The dominate non -silicate mineral is massive chalcopyrite,
with lesser amounts of pyrite, magnetite, molybdenite, and
Magnetite is present as psuedo-
remnant specular hematite.
morphs after 1.5 to 2 mm long blades of specular hematite
and as irregular masses intergrown with chalcopyrite.
netite also replaces pyrite.
Mag-
The bases of the specularite
blades are imbedded in the outer few tenths of a millimeter
of the pyrite.
Pyrite bounds euhedral quartz, contains
blebs of quartz and euhedral pyrite faces bound quartz.
Chalcopyrite is intergrown with quartz and epidote, veins
and replaces pyrite and occurs as massive chalcopyrite
filling open spaces between previously formed minerals.
Minor amounts of molybdenite are present as 0.1 to 0.5 mm
long sheath -like aggregates intergrown with magnetite,
chalcopyrite, and epidote.
Molybdenite was observed in
discontinuous microfractures cutting chalcopyrite.
BQD -01 -0 3
This thin section contains Veins E and C, with Vein
C cutting Vein E.
each other.
Both veins are similar to Vein A and to
Vein E, 1.5 mm wide, is composed mainly of 0.5
76
to 1 mm quartz with lesser amounts of K- feldspar, biotite,
epidote, chlorite, and sulfides.
Minor amounts of seri-
cite alter wallrock plagioclase, but epidote, biotite and
K- feldspar are volumetrically more important.
Minor
amounts of pyrite and chalcopyrite, intergrown with each
other, epidote, chlorite, and quartz are later than the
quartz + K- feldspar assemblage.
Wallrock alteration is
relatively weak, even adjacent to the vein.
Late gypsum
is also present altering anhydrite grains intergrown with
quartz and K- feldspar.
Vein C, 3 mm wide, is very similar to Vein A, ex-
cept specular hematite was not observed, only massive magnetite.
Anhydrite is present with both the early quartz +
feldspar + biotite and with the later quartz + epidote +
chlorite + sulfides.
Average grain size of vein minerals
in Vein C is about 1 mm.
BQD -01 -0 4
This thin section contains the intersection of
Veins C and D.
tion.
Vein C is similar to the previous descrip-
Vein D, which cuts and offsets Vein C contains two
texturally distinct assemblages.
An early assemblages of
0.5 mm quartz, K- feldspar, plagioclase, biotite, and anhy-
drite is located along the edges of the vein and is cut by
an assemblage of 0.05 to 0.2 mm epidote, chlorite,
77
anhydrite, chalcopyrite, pyrite, magnetite, and molybdenite.
Pyrite was deposited with and slightly before chal-
copyrite.
Alteration of the adjacent wallrock is dominated
by biotite and epidote, but minor amounts of sericite, Kfeldspar, chlorite, and anhydrite is also present.
BQD -01 -06
Sample BQD -01 -06 is a thin section of 1 to 1.5 mm
wide Vein B.
A mosaic of 0.5 to 0.2 mm quartz, K- feldspar
sodic plagioclase, with lesser amounts of anhydrite and
biotite compose about half of the vein.
Masses and single
crystals of epidote 0.5 to 1 mm in diameter, along with
quartz, pyrite, chalcopyrite, magnetite, and trace amounts
of chlorite and hematite surround and fill fractures
through the earlier quartz and feldspars.
Most of the
pyrite in the vein appears earlier than epidote and chalcopyrite, and is slightly replaced by magnetite.
is usually slightly chloritized.
Biotite
Wallrock alteration is
similar to those described above, with biotite and epidote
the dominate alteration phases.
Sericite, K- feldspar, and
sodic plagioclase are also present in smaller amounts.
BQD -0 3
Sample BQD -03 contains a single 2 cm vein cutting
the biotite quartz diorite.
The volumetrically important
minerals are quartz, chalcopyrite, pyrite, and epidote,
78
with lesser amounts of biotite, anhydrite, molybdenite, Kfeldspar, sodic plagioclase, chlorite, magnetite, and remnant specular hematite.
The following description of Vein
BQD -03 is based on observations of five polished sections
and two thin sections.
The two types of quartz were observed:
cloudy quartz and finer grained clear quartz.
massive
Cloudy
quartz is volumetrically the dominate mineral, locally as
much as 90 vol. % of the vein.
The quartz is subhedral to
anhedral crystals, 3 to 10 mm in diameter, growing away
from the vein walls.
The quartz has interlocking grain
boundaries when in contact with other quartz crystals and
the feldspars.
Conversely, interfaces with the sulfides
and epidote are governed by euhedral to subhedral quartz
surfaces.
The clear quartz is present as 1 to 3 mm anhed-
ral grains intergrown with epidote and sulfides.
The
cloudy quartz exhibits undulatory extinction and biaxial
character, indicating that the quartz has undergone strain
(Deer et al. 1966)
.
The clear quartz shows no sign of
having been strained.
K- feldspar and sodic plagioclase are usually 0.5 to
0.3 mm-sized anhedral crystals intergrown with the cloudy
quartz and biotite along the vein- wallrock contact.
feldspars are replaced by epidote.
A few
79
Pyrite is present as subhedral to anhedral masses
0.5 to 2 mm across, and as 1 mm anhedral grains surrounding
cloudy quartz and anhydrite crystals.
Cubic faces are
present only in contact with epidote and chalcopyrite.
Chalcopyrite is slightly more volumentrically abundant than pyrite.
Massive chalcopyrite fills in open
spaces, veins and replaces pyrite, and occurs in chalcopyrite + magnetite + pyrite + clear quartz veinlets cutting
cloudy quartz.
Chalcopyrite is intergrown with epidote,
chlorite, molybdenite, and magnetite.
Chalcopyrite con-
tains 0.1 to 0.3 mm blebs of anhydrite, quartz, and epidote.
Magnetite occurs as pseudomorphs after 3 to 9 mm
blades of specular hematite; as anhedral to euhedral grains
intergrown with epidote, chalcopyrite, and molybdenite; and
replacing pyrite.
The psuedomorphs, a few containing rem-
nant hematite, are either imbedded in the outer few tenths
of a millimeter of the cloudy quartz or are entirely within pyrite.
In places, broken psuedomorphs are cemented by
chalcopyrite or epidote.
Epidote and chlorite are intimately intergrown with
clear quartz, anhydrite, chalcopyrite, molybdenite, and magnetite.
Epidote occurs as 3 to 5 mm long bladed crystals
and in veinlets with chalcopyrite and quartz cutting pyrite
80
and cloudy quartz.
A few broken epidote blades were ob-
served, cemented by chalcopyrite.
The contact between epi-
dote and both pyrite and magnetite psuedomorphs are
governed by the euhedral pyrite and specularite crystal
faces, respectively.
Wallrock alteration is dominated by biotite, epidote, and chlorite.
Complete biotite flooding 1 to 2 nun
from the vein grades out to biotite microfractures 2 to 0.5
mm apart perpendicular to the vein as much as 5 cm from the
vein.
Much of the early alteration is indiscipherable due
to wallrock flooding by epidote + chlorite + sulfides up to
1 cm from the vein.
APPENDIX B
ELECTRON MICROPROBE PROCEDURES
AND ANALYSES
The electron microprobe was used in this study to
determine compositional variations of feldspars, muscovite,
biotite, chlorite, and epidote between samples and with a
sample.
In each case, minerals with and adjacent to a
vein was analyzed, as well as occasional analyses on minerals with no clear relationship to any vein.
Elements
analyzed include Si, Al, Fe, Mg, Ca, K, Na, and either Ti
or Mn, with analyses given terms of weight percent oxides.
As the microprobe cannot distinguish between valence
states, either ferric or ferrous iron must be specified.
Biotite and chlorite were analyzed in terms of FeO, while
the feldspars, muscovite, and epidote were analyzed in
terms of Fe203.
The weight percent elemental compositions were recalculated into mineral compositions on the basis of oxygen equivalents.
Biotite and muscovite were recalulated
on the basis of 22 oxygen equivalents, the feldspars, epidote, and chlorite on the basis of 24, 25, and 14 oxygen
equivalents, respectively.
As the concentration of ferric
81
82
iron is unknown, the resultant biotite compositions are
approximate, only.
The analytical standards used to calibrate the
respective elements are:
Element
Standard
Si, Mg
Diopside Glass
Al, Ca
Anorthite
Fe
Ch romi te
K
Microcline
Na
Albite
Ti
Sphene
Mn
Rhodochrosite
0.44
0.19
16.58
99.84
CaO
Na20
K20
Total
99.04
16.53
0.17
0.00
0.08
18.42
0.01
65.37
8.95
0.00
2.97
0.04
0.07
0.05
2.98
Si
Ti
Al
Fe (III)
Ca
Na
K
2.91
0.05
0.00
0.01
2.99
0.00
9.01
Molecular formula based on 24 oxygens.
0.41
Fe203
0.00
63.51
17.90
2
2
A1203
TiO
SiO
HR-01-2S
2.89
0.06
0.01
0.00
3.04
0.00
8.97
99.84
16.25
0.24
0.08
0.05
18.49
0.00
64.38
HR-01-3S
Feldspar Microprobe Analyses
HR-01-1S
Oxide analyses.
Table B.l.
2.91
0.05
0.00
0.00
3.01
0.00
9.00
99.04
16.41
0.18
0.01
0.00
18.37
0.01
64.81
HR-01-3S
2.94
0.07
0.00
0.02
2.96
0.01
9.00
99.69
16.44
0.27
0.02
0.16
17.89
0.09
64.16
HR-01-3S
2.95
0.09
0.00
0.00
2.90
0.00
9.06
97.51
16.24
0.34
0.00
0.00
17.30
0.00
63.62
HR-02G-4V
2.97
0.11
0.00
0.01
3.03
0.00
8.95
99.40
16.60
0.41
0.00
0.07
18.37
0.00
63.95
HR-02A-5S
0.03
TiO
0.01
0.00
0.34
15.64
96.61
CaO
Na20
K20
Total
0.02
2.95
0.00
0.00
0.00
3.04
0.01
0.00
0.09
2.86
Ti
Al
Fe (III)
Ca
Na
K
2.86
0.18
9.01
8.97
Si
Molecular formula based on 24 oxYgens.
98.68
15.93
0.65
0.03
0.08
Fe203
17.80
17.96
0.16
64.09
A1203
2
62.55
SiO 2
2.89
0.15
0.00
0.00
3.00
0.00
8.99
100.35
16.36
0.55
0.00
0.00
18.38
0.00
65.05
HR-02A-7V
2.49
0.52
0.01
0.00
3.03
0.01
8.96
99.98
14.17
1.94
0.06
0.01
18.68
0.08
65.02
HR-02A-8V
Feldspar Microprobe Analyses
HR-02A-6V
Continued.
HR-02A-5S
Oxide analyses.
Table B.l,
2.83
0.19
0.00
0.01
3.03
0.00
8.97
99.57
15.93
0.72
0.00
0.08
18.43
0.00
64.40
HR-02A-9S
2.91
0.13
0.00
0.00
3.03
0.00
8.97
98.88
16.25
0.47
0.00
0.00
18.33
0.00
63.83
HR-02A-10S
2.82
0.12
0.00
0.01
3.00
0.00
9.01
97.26
15.54
0.44
0.01
0.13
17.86
0.00
63.27
HR-02A-11S
2
2
100.34
14.51
16.47
100.18
1.66
0.26
0.01
0.00
0,15
18.54
18.21
0.02
0.02
65.45
0.08
65.14
HR-02C-13S
9.02
0.01
2.97
0.00
0.00
0.07
2.91
Si
Ti
Al
Fe (III)
Ca
Na
R
2.54
0.44
0.02
0.00
3.00
0.00
8.99
2.84
0.19
0.00
0.01
3.02
0.00
8.97
99.97
16.05
0.70
0.03
0.12
18.45
0.00
64.61
HR-02C-14V
2.68
0.33
0.01
0.00
2.92
0.01
9.04
100.39
15.29
1.23
0.04.
0.05
18.02
0.08
65.67
HR-02C-15V
Feldspar Microprobe Analyses
Molecular formula based on 24 oxygens.
Total
K20
Na20
Ca0
Fe203
A1203
TiO
SiO
Oxide analyses.
HR-02C-12V
Table B.l, Continued.
2.85
0.17
0.00
0.00
2.98
0.01
8.99
100.74
16.25
0.63
0.00
0.05
18.39
0.08
65.34
HR-02C-16S
2.63
0.22
0.00
0.01
3.21
0.00
8.86
98.81
14,79
0.82
0.00
0.09
19.53
0.05
63.51
BQD-01A-17V
0.06
1.99
0.86
0.02
4.01
0.01
8.02
100.84
0.35
7.77
6.03
0.23
25.72
0.09
60.61
BQD-01A-18S
2
101..66
0.22
7.05
98.87
6.05
5.36
0.29
0.23
8.63
28.42
20.20
1.92
0.10
57.95
0.00
64.10
BQD-01B-20I
8.74
0.00
3.25
0.02
0.28
1.42
1.23
Si
Ti
Al
Fe (III)
Ca
Na
K
0.04
1.55
1.22
0.03
4.42
0.01
7.65
0.05
2.00
0.71
0.07
3.81
0.01
8.23
101.18
0.30
7.87
5.02
0.70
24.63
0.06
62.60
BQD-01B-21V
0.04
2.02
0.96
0.03
3.74
0.00
8.17
99.85
0.22
7.77
6.67
0.30
23.74
0,05
61.09
BQD-01B-22S
0.03
1.76
1.11
0.02
4.23
0.00
7.81
99.36
0.20
6.75
7.71
0.18
26.55
0.00
57.96
BQD-01C-23I
Feldspar Microprobe Analyses
Molecular formula based on 24 oxygens.
Total
K20
Na20
Ca0
Fe203
A1203
TiO 2
SiO
Oxide analyses.
BQD-01B-19V
Table B.l, Continued.
0.36
1.98
0.55
0.01
3.57
0.00
8.46
100.44
2.11
7.70
3.90
0.05
22.84
0.04
63.79
BQD-01C-24V
2.84
0.12
0.00
0.00
2.97
0.00
9.03
100.98
16.24
0.46
0.00
0.00
18.41
0.00
65.87
BQD-01C-25V
2
2
98.51
15.36
13.99
98.22
0.62
1.37
0.00
0.00
0.02
18.90
19.12
0.02
0.00
63.60
0.03
63.66
BQD-01D-27V
8.91
0.00
3.15
0.00
0.00
0.37
2.50
Si
Ti
Al
Fe (III)
Ca
Na
K
2.75
0.17
0.00
0.00
3.13
0.00
8.92
2.95
0.04
0.00
0.04
3.09
0.00
8.90
101.80
16.90
0.16
0.01
0.36
19.20
0.01
65.16
BQD-01E-28V
0.04
2.17
0.78
0.00
3.94
0.00
8.10
96.92
0.23
2.17
5.30
0.05
24.30
0.00
58.91
BQD-03-29V
2.66
0.18
0.01
0.02
3.32
0.00
8.77
91.71
13.85
0.61
0.07
0.16
18.72
0.04
58.25
BQD-03-30V
Feldspar Microprobe Analyses
Molecular formula based on 24 oxygens.
Total
1(20
Na20
CaO
Fe203
A1203
TiO
SiO
Oxide analyses.
BQD-01D-26V
Table B.l, Continued.
0.65
1.98
0.30
0.01
3.56
0.00
8.51
96.42
3.65
7.38
2.00
0.12
21.83
0.00
61.44
BQD-03-31V
HR-02D-1V
0.01
0.53
10.91
0.00
0.61
10.71
CaO
0.00
0.16
1.85
Ca
K
X
3.52
0.05
0.12
0.26
Al
Ti
Y
Fe (III)
Mg
Na
6.36
1.64
Al
Si
Molecular formula:
Total
K20
Na20
0.00
0.14
1.90
3.53
0.04
0.14
0.22
6.34
1.66
X2Y4Z8020(OH)4
92.82
1.08
1.27
Mg0
93.70
1.35
1.16
Fe203
A1203
32.19
46.32
32.40
47.05
0.43
2
2
0.51
TiO
SiO
HR-02D-2S
0.00
0.15
1.85
3.66
0.02
0.17
0.15
6.12
1.88
94.29
10.75
0.56
0.00
0.75
1.69
34.87
0.22
45.44
HR-02E-3V
Muscovite Microprobe Analyses
Oxide analyses.
Table B.2.
0.01
0.12
1.82
3.62
0.02
0.17
0.18
6.20
1.80
94.56
10.67
0.47
0.04
0.89
1.68
34.32
0.23
46.25
HR-02E-4V
0.01
0.21
1.78
3.54
0.04
0.18
0.24
6.16
1.84
93.29
10.24
0.78
0.08
1.17
1.78
33.54
0.44
45.26
HR-02E-5V
8.64
17.51
0.00
0.30
9.99
9.62
17.71
0.00
0.23
10.14
Mg0
CaO
1.93
0.00
0.07
Ca
Na
K
X
0.50
0.34
1.21
3.96
Al
Ti
Y
Fe (III)
Mg
Al
Z
0.00
0.09
1.90
0.74
0.30
1.08
-3.88
5.82
2.18
X2Y6Z8020(OH)4
5.79
2.21
Si
Molecular formula:
Total
K20
Na20
94.70
16.57
15.45
A1203
Fe0
94.91
2.66
3.03
TiO
2
38.74
SiO 2
39.09
HR-02G-2S
1.75
0.00
0.20
0.68
0.34
2.05
2.93
5.86
2.14
93.59
8.78
0.66
0.01
12.59
15.65
15.36
2.92
37.62
HR-02-3A
Biotite Microprobe Analyses
HR-02A-1S
Oxide analyses.
Table B.3.
0.00
0.23
1.75
0.71
0.37
2.05
2.87
5.82
2.18
93.62
8.75
0.73
0.03
12.30
15.76
15.67
3.12
37.26
HR-02-3A
1.83
0.00
0.16
0.65
0.37
2.12
2.86
5.82
2.18
95.81
9.37
0.56
0.03
12.49
16.54
15.61
3.29
37.93
HR-02-3A
0.02
0.12
1.68
0.67
0.54
2.12
2.67
5.75
2.25
92.47
8.28
0.42
0.11
11.28
16.00
15.63
4.50
36.25
HR-02-4I
0.00
0.07
1.85
2.87
0.74
0.36
2.03
5.80
2.20
94.63
9.38
0.25
0.00
12.44
15.68
16.16
3.17
37.53
HR-02-5A
2
2
0.34
9.14
0.21
9.71
Y
X
Ca
Na
K
Z
Al
Ti
Fe (II)
Mg
Al
Si
0.53
0.35
2.11
3.01
0.01
0.10
1.81
0.56
0.35
1.87
3.22
0.00
0.06
1.88
5.78
2.22
X2Y6Z8020(OH)4
5.73
2.27
Molecular formula:
Total
K20
93.99
0.07
0.00
CaO
95.48
13.00
14.21
Mg0
Na20
16.30
15.00
15.80
14.71
2.94
37.21
3.11
37.73
HR-02-7A
0.00
0.05
1.87
0.68
0.27
1.87
3.18
5.80
2.20
94.59
9.58
0.17
0.01
13.93
14.59
15.98
2.41
37.93
HR-02-8A
0.10
0.19
1.30
0.26
0.30
2.17
3.27
5.61
2.39
92.31
6.63
0.62
0.64
14.19
16.79
14.53
2.57
36.35
BQD-03-9S
Biotite Microprobe Analyses
FeO
A1203
TiO
SiO
Oxide analyses.
HR-02-6A
Table B.3, Continued.
0.00
0.40
1.38
0.23
0.27
2.33
3.17
5.62
2.38
94.02
7.08
1.35
0.01
13.89
18.20
14.44
2.32
36.74
BQD-01A-10S
0.04
0.05
1.72
0.34
0.26
2.16
3.24
5.55
2.45
93.45
8.72
0.16
0.27
14.08
16.73
15.25
2.26
35.99
BQD-01B-11S
0.00
0.08
1.90
0.35
0.35
2.07
3.23
5.66
2.34
96.90
9.89
0.29
0.03
14.41
16.46
15.19
3.05
37.60
BQD-01B-12S
2
8.75
8.93
3.38
0.25
2.23
3.14
Y
X
Al
Al
Ti
Fe (II)
Mg
Ca
Na
K
0.03
0.09
1.71
5.52
2.48
Si
Molecular formula:
Total
1(20
0.01
0.12
1.70
0.42
0.21
2.33
3.03
5.65
2.35
X2Y6Z8020(OH)4
94.81
9.76
0.42
0.29
96.53
0.13
0.05
0.21
CaO
Na20
12.85
13.30
14.06
Mg0
0.00
0.04
1.90
0.50
0.33
2.25
2.92
5.76
2.24
96.21
0.03
17.66
15.23
18.19
15.35
16.23
2.86
37.70
BQD-01C-155
17.79
1.86
36.91
2.26
36.75
BQD-01B-14S
0.02
0.05
1.75
0.28
0.28
2.11
3.33
5.65
2.35
96.55
9.19
0.17
0.12
14.96
16.83
14.92
2.55
37.83
BQD-01C-16S
Biotite Microprobe Analyses
FeO
A1203
TiO 2
SiO
Oxide analyses.
BQD-01B-13S
Table B.3, Continued.
0.01
0.21
1.60
0.22
0.34
2.23
3.21
5.69
2.31
98.18
8.54
0.73
0.03
14.61
18.10
14.49
3.06
38.62
BQD-01D-175
0.00
0.07
1.91
0.48
0.34
2.15
3.03
5.85
2.15
95.37
9.75
0.23
0.00
13.23
16.75
14.47
2.88
38.05
BQD-01E-18V
1.86
0.00
0.09
0.37
0.30
2.35
2.98
5.62
2.38
97.23
9.68
0.30
0.00
13.22
18.61
15.50
2.65
37.29
BQD-01-19A
2
0.00
9.38
0.14
9.45
0.00
0.04
1.79
0.14
0.32
2.42
3.12
0.02
0.00
1.87
0.5/
0.26
2.24
2.93
5.90
2.10
X2Y6Z8020(OH)4
5.51
2.49
1Pseudomorph after hornblende
K
X
Y
Al
Ti
Fe (I1)
Mg
Ca
Na
Z
Si
Al
Molecular Formula:
Total
K20
93.76
0.15
0.02
CaO
98.13
12.58
14.10
Mg0
Na20
17.21
14.53
15.00
19.46
2.16
37.75
2.85
37.12
BQD-01-21A1
Biotite Microprobe Analyses
Fe0
A1203
TiO
SiO2
Oxide analyses.
BQD-01-20A
Table B.3, Continued.
0.04
0.02
0.03
0.07
2.83
0.01
0.00
0.00
?Altering Biotite HR -02 -4I
Altering Biotite HR -02 -7A
K
Ca
Na
Y
--1.72
Fe (II)
Mn
Mg
1.30
2.85
1.15
Ti
Z
86.30
---
3.00
0.01
0.01
0.01
2.78
0.01
0.01
0.00
1.29
0.00
1.58
2.92
1.08
89.55
0.05
0.04
0.14
20.32
19.14
20.31
0.04
29.52
HR-01-3V
---
1.45
0.01
1.54
2.96
1.04
Y674010(OH)8
Al
Al
Si
Molecular formula:
Total
K20
88.58
0.05
0.07
Ca0
Na20
0.10
18.71
Mg0
18.27
0.77
Mn0
18.07
20.68
0.08
29.00
20.30
20.54
28.14
Fe0
A1203
TiO 2
SiO 2
HR-01-2S
Chlorite Microprobe Analyses
HR-01-1V
Oxide analyses.
Table B.4.
0.00
0.09
0.01
---
--2.01
2.20
0.00
0.03
0.01
1.31
0.00
2.43
2.76
1.24
87.04
0.05
0.13
0.00
13.79
27.09
20.18
0.00
25.79
HR-02D-5V
1.34
0.00
2.59
2.65
1.35
86.03
0.07
0.44
0.04
12.31
28.20
20.80
0.00
24.17
HR-02D-4V
2.26
0.05
0.02
0.33
---
---
2.60
0.01
0.02
0.01
1.48
0.07
1.54
3.23
0.77
87.68
2.56
0.09
0.43
14.90
18.16
18.80
0.89
31.84
HR-02-7A2
1.34
0.00
1.92
2.88
1.12
85.02
0.06
0.08
0.09
16.41
21.61
19.63
0.01
27.13
HR-02-6A1
0.07
0.19
3.10
0.02
0.03
0.01
2.88
0.00
0.00
0.03
3Altering Biotite HR -02 -3A
K
Ca
Na
---
---
Mn
Mg
Y
1.22
0.00
1.61
2.83
1.17
Y6Z4010(OH)8
1.23
0.01
1.83
Z
2.82
1.18
86.57
AI
Ti
Fe (II)
Si
Al
Molecular formula:
Total
K20
85.33
0.16
0.00
Na20
0.15
0.04
CaO
1.23
--1.67
0.06
2.98
0.01
0.00
0.00
2.84
1.16
84.86
0.02
0.01
0.12
18.97
18.28
Mg0
20.21
0.62
- --
Mn0
18.89
20.70
19.25
26.96
BQD-03-10S
FeO
18.68
19.76
19.35
A1203
0.00
0.10
TiO 2
27.55
26.67
SiO 2
Oxide analyses.
BQD-03-9S
Continued.
HR-02-8A3
Table B.4.
1.53
0.05
2.97
0.02
0.09
0.02
---
1.30
2.83
1.17
83.12
0.16
0.41
0.14
18.63
0.58
17.11
19.61
26.48
BOO-03-11S
1.30
--1.69
0.05
2.85
0.01
0.01
0.00
2.86
1.14
85.33
0.03
0.06
0.11
18.21
0.58
19.31
19.72
27.30
BOO-03-12S
2
0.00
0.08
0.02
0.09
0.07
0.03
3.79
0.01
0.02
Mn
Mg
Ca
Na
K
Ti
X
4.51
1.56
Al
Y
Fe (III)
Al
z
0.06
0.04
3.79
0.00
0.02
4.49
1.58
5.99
0.01
X4Y6Z6024(OH)2
5.99
0.01
Si
Molecular formula:
Total
K20
99.73
22.68
22.65
Ca0
99.69
0.15
0.13
Mg0
Na20
0.48
13.44
13.31
0.55
24.50
38.40
24.56
38.38
Mn0
Fe203
A1203
TiO
Si02
HR-01-2V
0.00
3.81
0.00
0.01
- --
0.01
3.94
1.96
6.08
0.00
95.96
0.04
0.01
22.55
0.02
15.89
20.35
0.08
37.02
HR-01-3V
Epidote Microprobe Analyses
HR-01-1V
Oxide analyses.
Table B.5.
0.03
0.04
3.59
0.10
0.02
4.42
1.78
5.96
0.04
99.31
0.08
0.33
21.32
0.16
0.25
15.04
24.13
38.00
BQD-01A-4V
0.02
0.01
3.80
0.02
0.01
4.57
1.56
5.90
0.10
100.34
0.04
0.07
22.96
0.03
0.18
13.45
25.66
38.16
BQD-01B-5V
0.05
0.04
3.83
0.01
0.02
4.21
1.85
5.95
0.05
99.83
0.08
0.04
22.74
0.17
0.34
15.61
23.01
37.85
BQD-01B-6V
4.02
0.01
0.01
0.01
0.00
3.97
2.01
0.04
5.96
99.86
0.03
0.05
23.68
0.01
0.08
16.89
21.49
37.63
BQD-01C-7V
2
2
0.90
0.06
0.05
0.04
K
X
0.01
0.00
3.92
0.02
0.01
0.04
0.01
3.55
0.27
0.01
- --
- --
Ti
Fe (III)
Mn
Mg
Ca
Na
6.20
0.00
4.16
1.76
Y
z
X4Y6Z6024(OH)2
5.87
0.13
4.19
1.89
Al
Al
Si
Molecular formula:
Total
K20
99.79
21.22
23.45
CaO
100.96
0.03
0.00
Mg0
Na20
0.25
14.98
16.12
0.10
22.61
39.74
23.53
-
37.66
BQD-01D-9V
- --
0.04
0.01
3.86
0.03
0.02
---
0.02
0.01
3.86
0.00
0.01
4.02
2.05
5.95
0.05
100.79
0.08
0.10
22.96
0.04
0.27
17.35
22.04
37.95
BQD-01E-11V
4.11
1.99
5.90
0.10
101.42
0.04
0.00
23.17
0.04
0.12
17.05
23.02
37.99
BQD-01D-10V
Epidote Microprobe Analyses
Mn0
Fe203
A1203
TiO
SiO
Oxide analyses.
BQD-01C-8V
Table B.5, Continued.
- --
0.03
4.03
0.01
0.01
0.01
4.07
0.01
0.01
0.02
4.27
1.68
5.92
0.08
100.47
0.03
0.02
24.15
0.12
14.34
23.66
0.16
38.00
BQD-03-13S
- --
0.01
4.24
1.70
0.02
5.9-8
100.40
0.05
0.02
24.33
0.03
14.50
23.12
0.05
38.30
BQD-03-12S
0.00
4.05
0.00
0.01
- --
0.00
4.43
1.53
6.00
0.00
99.06
0.04
0.01
24.04
0.00
12.95
23.91
0.00
38.11
BQD-03-14V
2
0.07
0.04
K
---
0.01
3.87
0.01
0.01
0.00
---
0.03
0.00
4.05
0.01
0.01
Ti
Mn
Mg
Ca
Na
X
4.20
1.84
4.16
1.80
Al
Y
Fe (III)
6.02
-0.00
5.94
0.06
X4Y6Z6024(OH)2
97.68
Si
Al
Molecular formula:
Total
K20
99.08
0.02
0.01
Na20
22.53
23.78
CaO
0.04
0.02
3.81
0.00
0.01
---
4.29
1.80
5.99
0.01
99.72
0.04
0.01
22.68
0.09
0.06
0.02
Mg0
15.21
0.30
15.21
15.10
23.23
-
38.15
BQD-03-17V
0.24
22.23
0.01
37.54
22.53
37.36
BQD-03-16V
0.03
0.03
3.77
0.01
0.01
---
4,31
1.81
5.96
0.04
98.62
0.05
0.03
22.18
0.13
0.22
15.17
23.25
37.59
BQD-03-18V
Epidote Microprobe Analyses
Fe203
Mn0
A1203
TiO 2
SiO
Oxide analyses.
BQD-03-15V
Table B.5, Continued.
0.04
0.22
3.73
0.02
0,02
---
4.18
1.84
5.94
0.06
97.12
0.08
0.05
21.55
0.90
0.26
15.16
22.29
36.83
BQD-03-19S
0.03
3.85
0.00
0.01
0.03
---
4.40
1.66
6.00
0.00
99.35
0.05
0.00
22.90
0.11
0.20
14.06
23.78
38.26
BQD-03-20S
0.03
0.00
3.91
0.01
0.01
---
4.33
1.70
5.99
0.01
99.02
0.04
0.03
23.12
0.00
0.24
14.32
23.32
37.94
BQD-03-21S
22.84
CaO
Mn
Mg
Ca
Na
K
Ti
0.01
0.01
3. 89
0.03
0.00
Al
Y
Fe (III)
X
3.88
2.19
Z
Al
5.91
0.09
Si
Epidote Microprobe Analyses
X4Y6Z6024(OH)2
99.97
0.03
Molecular formula:
Total
K20
0.04
0.01
Mg0
Na20
0.26
18.36
Mn0
Fe203
A1203
21.23
- --
TiO
2
37.19
SiO 2
Oxide analyses.
BQD-03-22S
Table B.5, Continued.
APPENDIX C
FLUID INCLUSION HOMOGENIZATION AND
FREEZING EQUIPMENT AND PROCEDURES
A dual -purpose heating and freezing stage was used
for homogenization and freezing tests on fluid inclusions.
The stage was modified from designs formulated by Dr. Gary
Landis of the University of New Mexico, Albuquerque by Dr.
Richard E. Beane through the Creative Laboratory in the
Physics Department at the University of Arizona.
The body
of the stage was constructed from Transite, an asbestos based insulating material.
Invar, a nickel -steel alloy, was
used for the sample chamber and gas inlets.
The heating
element consisted of a nichrome induction coil wrapped
around the sample chamber insulted by an asbestos -based
cement.
Current was supplied to the coil through a Variac
variable transformer.
The temperature inside the sample
chamber was measured by a chromel -alumel thermocouple con-
nected to a Doric Model 410 Digital Trendicator.
The ther-
mocouple and Trendicator were calibrated using a D.C.
power source as per the method suggested by the manufactor.
Commercially available eutectic mixtures of organic compounds with known melting points were used to verify the
calibrations within the stage.
99
In addition, the freezing
100
point of distilled water sealed in capillary tubes was measured.
The accuracy of temperatures measured is within 5 °C
for homogenization tests, and within 0.1 °C at 0 °C.
Bodnar
(1978) found that a positive thermal gradient of 10 °C exists
between the center to the wall of the sample chamber at
400 °C.
Organic compounds used to calibrate the stage be-
gan melting at the bases of the grains, before the tops of
the grains, indicating a negative thermal gradient of unknown magnitude upward from the base of the sample chamber.
These thermal gradients were minimized by placing the sample
in the middle of the chamber.
The tip of the thermocouple
was positioned near the fluid inclusion of interest, making
sure the tip of the thermocouple was touching the sample.
Freezing runs incorporated cooling of the stage by
passing highly purified nitrogen gas through a liquid nitrogen bath and into the stage.
Due to the difficulty of
nucleating ice (Roedder 1962), it was usually necessary to
cool the inclusions to temperature of -100 °C or less.
This
was accomplished by pouring a small amount of liquid nitrogen directly in the sample chamber.
After the inclusion was
frozen, the temperature was allowed to rise by decreasing
the flow of nitrogen gas and applying a small amount of current to the heating coil.
Two temperatures were recorded
during each freezing run:
the temperature at which liquid
was first observed (first melting temperature), and the
101
temperature at which the last crystal of ice melted (final
melting temperature).
The first melting temperature may
provide some insight to the gross composition of the fluid
(Roedder 1962), while the difference between the final
melting temperature of the fluid and that of pure water
(the freezing point depression) allows the salinity of the
fluid to be approximated.
At the first melting temperature,
the gas flow was increased and the current turned off in
order to control the rate of temperature increase.
Just
before the last ice crystal melted, the gas flow was increased to assure that the inclusion was melting under reversible equilibrium.
Reversibility was indicated by an
increase of the size of the ice with a slight drop in temperature (Roedder 1962).
Optics
Both a Leitz Ortholux binocular microscope and a
Leitz Simplex binocular microscope were used for fluid inclusion studies.
A long focal length 50X objective was
used for heating and freezing runs on both microscopes,
while 5.6X, 16X, 20X, and 30X objectives were utilized to
search for suitable inclusions, and to establish the temporal relationships between inclusions and host crystal.
Oculars of 10X, 16X, or 25X were used for both searching
for inclusions and the subsequent heating and freezing runs.
102
Illumination was provided by a Leitz high intensity Xenon
burner XBO 150 and a Leitz fiber optics light source for the
Ortholux and Simplex, respectively.
Sample Preparation
Samples for fluid inclusion studies were selected
from pit bench faces and talus slopes.
Thin -section sized
blocks were cut out of samples and ground on one side using
400, 600, and 1000 mesh grinding grit.
It was then polished
on rotating laps using 0.3 micron powder.
The polished side
was mounted on a slide with Lakeside Cement and cut to a
thickness of several millimeters.
The unpolished side was
ground to a thickness of 0.5 to 1.0 millimeters and polished
as described above.
During the latter stages of the study,
the polishing was done on a Westinghouse Mazur automatic
polishing machine.
After polishing was completed, the
doubly- polished sample was removed from the slide and placed
in a boiling 10 wt. % aqueous solution of sodium borate for
1 -2 minutes in order to dissolve the Lakeside.
The polished sections were examined under a stereo -
microscope in order to establish the paragenetic relationships in the vein.
The samples were broken into chips 3 to
5 mm in diameter and were ready for heating and freezing
runs.
This step was greatly aided by Xeroxing the polished
section and noting the position of the selected quartz and
epidote crystals.
LIST OF REFERENCES
Aiken, D. M., and West, R. J., 1978, Some geologic aspects
of the Sierrita -Esperanza copper -molybdenite deposit, Pima County, Arizona: Arizona Geol. Soc.
Digest', vol. 11, p. 117-128.
Beane, R. E., 19 79 , Studies of mineralization and alteration at the Sierrita porphyry copper deposit, Arizona:
II.
wallrock influence on alteration and
mineral deposition [abs.]: AIME Abstracts with
Programs, p. 76.
Bodnar, R. J., 1978, Fluid inclusion study of the porphyry
copper prospect at Red Mountain, Arizona; Unpublished M.S. Thesis, University of Arizona, 70 p.
Cooper, J. R., 1973, Geologic map of the Twin Buttes quadrangle, southwest of Tucson, Pima County, Arizona:
U. S. Geol. Survey Misc. Geol. Inv. Map I -745.
Deer, W. A., Howie, R. A., and Zussman, J., 1966, An Introduction to the Rock - forming Minerals:
John Wiley
and Sons, Inc., New York, 528 p.
Denis, M., 1974, Alterations et fluides associes dans le
porphyre cuprifere de Sierrits: Unpublished Dissertation 3° Cycle, University of Nancy, France,
146 p.
Erwood, R. J., Kesler, S. E., and Cloke, P. L., 1979, Compositionally distinct, saline hydrothermal solutions, Naica Mine, Chihuahua, Mexico: Econ. Geol.,
vol. 74, p. 95 -108.
Fellows, M. L., 1976, Composition of epidote from porphyry
copper deposits:
Unpublished M.S. Thesis, University of Arizona, 190 p.
Guilbert, J. M., and Lowell, J. D., 1974, Variations in
zoning patterns in porphyry ore deposits:
Canadian
Inst. Mining Metall. Bull., vol. 67, p. 99 -109.
Gustafson, L. B., and Hunt, J. P., 1975, The porphyry copper
deposit at El Salvador, Chile: Econ. Geol., vol.
70, p. 857-912.
103
104
Haas, J. L., 1971, The effect of salinity on the maximum
geothermal gradient of a hydrothermal system at
hydrostatic pressure: Econ. Geol., vol. 66, p. 9409 46 .
Helgeson, H. C., 1969, Thermodynamics of hydrothermal systems at elevated temperatures and pressures: Am.
Jour. Sci., vol. 267, p. 729 -804.
,
Delany, J. M., Nesbitt, H. W., and Bird, D. K.,
1978, Summary and critique of the thermodynamic
properties of rock- forming minerals:
Am. Jour.
vol. 278 -A, p.
1 -229.
Hey, M. H., 1954, A new review of the chlorites:
vol. 30, p. 277.
Min. Mag.,
Kamilli, R. J., 1978, The genesis of stockwork molybdenite
deposits:
implication from fluid inclusion studies
at the Henderson mine tabs.]: Econ. Geol., vol. 73,
p. 1392.
Lowell, J. D., and Guilbert, J. M., 1970, Lateral and vertical alteration -mineralization zoning in porphyry ore
deposits: Econ. Geol., vol. 65, p. 373 -408.
Lynch, D. W., 1967, The geology of the Esperanza mine and
vicinity, Pima County, Arizona: Unpublished M.S.
Thesis, University of Arizona, 70 p.
Moore, W. J., and Czamanske, G. K., 1973, Compositions of
biotites from unaltered and altered monzonite rocks
in the Bingham Mining District, Utah: Econ. Geol.,
vol. 68, p. 269 -274.
Nash, J. T., 1976, Fluid inclusion petrology - data from
porphyry copper deposits and applications to exploration:
U. S. Geol. Survey Prof. Paper 907 -D, 16 p.
Norton, D., 1978, Sourcelines, sourceregions, and pathlines
for fluids in hydrothermal systems related to cooli
cooling plutons: Econ. Geol., vol. 73, p. 21-28.
and Knight, J., 1977, Transport phenomena in
hydrothermal systems: cooling plutons: Am. Jour.
Sci., vol. 277, p. 937 -981.
,
105
Potter, R. W., Jr., 1977, Pressure corrections for fluid inclusion homogenization temperatures based on the
volumetric properties of the system NaCl-H20: U. S.
Geol. Survey Jour. Res., vol. 5, no. 5, p. 603 -607.
Babcock, R. S., and Brown, D. L., 1977, A new
method for determining the solubility of salts in
aqueous solutions at elevated temperatures: U. S.
Geol. Survey Jour. Res., vol. 5, no. 3, p. 389 -395.
,
Potter, R. W., Jr., and Brown, D. L., 1975, The volumetric
properties of aqueous sodium chloride solutions from
0 to 500 °C at pressures up to 2000 bars based on a
regression of available literature data: U. S.
Geol. Survey Open -file Rept. 75 -636, 29 p.
Potter, R. W., Jr., Clynne, M. A., and Brown, D. L., 1978,
Freezing point depression of aqueous sodium chloride
solutions: Econ. Geol., vol. 73, p. 284 -285.
Roedder, E., 1962, Studies of fluid inclusions:
I.
low temperature application of a dual purpose freezing
and heating stage:
Econ. Geol., vol. 57, p. 10451061.
1967, Fluid inclusions as samples of ore fluids,
in Geochemistry of Hydrothermal Ore Deposits,
Barnes, H. S. (ed.), Holt, Rinehart, and Winston,
Inc., New York, p. 515 -574.
,
1971, Fluid inclusion studies on the porphyry type deposits at Bingham, Utah, Butte, Montana, and
Climax, Colorado: Econ. Geol., vol. 66, p. 98 -120.
,
1972, Composition of fluid inclusions, in Data
of Geochemistry, Fleisher, M. (tech. ed.), 6th ed.:
U. S. Geol. Survey Prof. Paper 440 -JJ, 164 p.
,
1976, Fluid inclusion evidence on the genesis of
ores in sedimentary and volcanic rocks, in Handbook
of Strata -bound and Stratiform Ore Deposits, Wolfe,
K. H. (ed.), Elsevier Sci. Pub. Co., Smdyrtfsm, vol.
2, p. 67 -110.
Rose, A. W., 1970, Zonal relations of wallrock alteration
and sulfide distribution at porphyry copper deposits:
Econ. Geol., vol. 65, p. 920 -936.
106
Sourirajan, S., and Kennedy, G. C., 1962, The system H20NaC1 at elevated temperatures and pressures: Am.
Jour. Sci., vol. 260, p. 115 -141.
Smith, V. L., 1975, Hypogene alteration at the Esperanza
Mine, Pima County, Arizona:
Unpublished M.S.
Thesis, University of Arizona, 161 p.
Waldbaum, D. R., and Thompson, J. B., Jr., 1969, Mixing
properties of sanadine crystalline solutions: IV.
phase diagrams from equations of state: Am. Mineralogist, vol. 54, p. 1274-1298.