White Mica Geochemistry of the Catheart Mountain 

Porphyry Copper Deposit, Maine 
--
White Mica Geochemistry of the Catheart Mountain 

Porphyry Copper Deposit, Maine 

By ROBERT A. AYUSO 

U.S. GEOLOGICAL SURVEY BULLETIN 1803 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

UNITED STATES GOVERNMENT PRINTING OFFICE: 1987 

For sale by the Books and Open-File Reports Section, U.S. Geological Survey 

Federal Center, Box 25425, Denver, CO 80225 

library of Congress Cataloging in Publication Data 

Ayuso, Robert A. 

White mica geochemistry of the Catheart Mountain porphyry copper deposit, 

Maine. 

(U.S. Geological Survey bulletin ; 1803) 

Bibliography: p. 

Supt. of Docs. no.: I 19.3:1803 

1. Mica-Maine-Somerset County. 2. Porphyry-Maine-Somerset 

County. 3. Geochemistry-Maine-Somerset County. I. Title. 

II. Title: Catheart Mountain porphyry copper deposit. Ill. Series. 

QE75.89 no. 1803 557.3 s 87~00317 

[QE391.M6] [549' .67] 
CONTENTS 

Abstract 1 

Introduction 1 

Analytical procedures 1 

Geology 2 

Summary of the petrography 3 

Summary of rock bulk composition 5 

Definition of white mica 7 

Composition of white micas at Catheart Mountain 7 

Regular variations in white mica composition 9 

Discussion 9 

Relation of white micas and bulk composition 9 

Aluminous white micas in mineralized rocks 11 

Summary 14 

Acknowledgments 14 

References cited 14 

FIGURES 

1. Location map and surface expression of hydrothermal alteration of the 

Catheart Mountain porphyry Cu-Mo deposit 2 

2-9. Graphs showing: 

2. Variation in Al2 03 and Cu, the wide range in Fe2 03 and Cu, and the 

variation in F and Cu in the mineralized bulk rocks at Catheart 

Mountain 5 

3. Wide range in S as a function of Cu, the variation in Mo and Cu, 

and the variation in Sn and Cu in the mineralized bulk rocks at 

Catheart Mountain 7 

4. Change in Fe+ Mg+ Mn as a function of 2-Alv1 in the white micas 

from Catheart Mountain 12 

5. Distribution of Na/(Na + K) and Si in the white micas from mineralized rocks and unmineralized rocks from Catheart Mountain 12 

6. Distribution of Al1v + Alv1 and Si+(Mg+ Fe) in the white micas 

from mineralized rocks and unmineralized rocks from Catheart 

Mountain 12 

7. Distribution of Si and Al1v + (Na + K) in the white micas from mineralized rocks and unmineralized rocks from Catheart Mountain 12 

8. Distribution of 2Alv1 and Mg+Ti in the white micas from mineralized rocks and unmineralized rocks from Catheart Mountain 13 

9. Change in Cu content of the bulk rock and the Al1v + Alv1 in the 

white micas coexisting with sulfides, and the distribution of S in the 

bulk rock and the Al1

v + Alv1 in the white micas coexisting with 

sulfides 13 

Contents Ill 
TABLES 

1. Summary of hydrothermal alteration, mineralogy, and sulfide occurrence in the 

Catheart Mountain Cu-Mo deposit, Maine 4 

2. Representative analyses of the mineralized and unmineralized rocks in the Catc-~a ~ !lllliH<tal l CCO'.:t~ 

3. Average compositions, standard deviations, and structural formulas of white mica 

in the potassic alteration zone at Catheart Mountain 8 

4. Average compositions, standard deviations, and structural formulas of white mica 

in the quartz sericite, sericitic, and propylitic alteration zones at Catheart 

Mountain 10 

IV Contents 
White Mica Geochemistry of the Catheart Mountain 

Porphyry Copper Deposit, Maine 

By Robert A. Ayuso 

Abstract 

White micas from hydrothermally altered and mineralized zones in the Catheart Mountain Cu-Mo porphyry 

deposit have regular compositional variations that are generally related to the contents of copper, total iron, and 

sulfur in the whole rock. Micas in unmineralized rocks 

exhibit no such relationship. White mica compositions 

reflect primarily the control imposed by the celadonitic substitution AIIV +Aiv1

=Si+ (Fe, Mg). 

The variation in white mica composition in the Catheart Mountain porphyry may be explained by superposition and overprinting of mineral assemblages by ore 

fluids during mineralization and during the waning stages 

of hydrothermal alteration. Local bulk compositional differences, changing PHao and fluid compositions during mineralization, and superposition of mineral assemblages along 

microzoned veins contributed to variation in white mica 

composition. However, the general relation between white 

mica composition and base-metal content in the mineralized rocks at Catheart Mountain suggests that identification 

of this white mica population might be useful as an indicator of mineralization gradients. 

INTRODUCTION 

Mineralized rocks from porphyry copper deposits 

represent a complex interaction of magmatic and hydrothermal processes. Titley (1982) and Beane and Titley 

(1981) recently summarized the geologic complexity of 

most porphyry copper deposits and noted the variation of 

the intensive parameters before, during, and after mineralization. Thus, the observed mineral assemblage depends 

on composition of the host rock, on position of the rock 

with respect to the ore fluid and heat sources, and on the 

intensity and efficiency of late hydrothermal alteration 

events. 

Mineralogic studies may be of great value in understanding the chemical environment during mineralization 

in porphyry copper systems. For example, white mica 

occurs in the potassic, phyllic, and mineralized zones of 

most porphyry copper systems (Creasey, 1959; Meyer and 

Remley, 1967; Lowell and Guilbert, 1970; Rose, 1970) 

and, thus, it is potentially a good monitor of the changing 

chemical environment. This paper discusses the composition of white mica from different hydrothermal alteration zones in the Catheart Mountain Cu-Mo deposit in 

Maine (fig. 1) as a function of the copper content of the 

whole rock. 

Recent investigations on the composition of white 

micas in porphyry copper deposits include studies by 

Guilbert and Schafer (1978), Beaufort and Meunier 

(1983), and Parry and others (1984). Guilbert and Schafer 

(1978) and Guilbert (1980) suggested that white mica in 

porphyry mineralized areas might be an aid in exploration. McDowell and Elders (1980) studied white micas 

from a geothermal field, and Hendry (1981) used white 

mica composition to study wall-rock alteration in volcanichosted copper mineralization. Gunow and others (1980) 

studied the fluorine content of sericite in the Henderson 

molybdenite deposit in Colorado. In addition, the possibility that white mica composition changes as a function of 

proximity to mineralization has been investigated in hydrothermally altered submarine exhalative ores (Plimer and 

de Carvalho, 1982), in stratiform sulfide deposits 

(McLeod and Stanton, 1984), and in stratabound Ba-Zn 

mineralization (Fortey and Beddoe-Stephens, 1982). 

ANALYTICAL PROCEDURES 

Twenty-two samples from the Catheart Mountain 

Cu-Mo deposit were obtained from representative drill 

cores traversing the regional hydrothermally altered and 

mineralized zones (fig. 1). Polished microprobe thin sections were obtained as close as possible to single veins in 

drill core splits analyzed for major and trace elements as 

well as for base metals (Mo, Cu, Sn, W, and so on). An 

effort was made to obtain the thin-section samples from 

areas in the drill core that clearly contained chalcopyrite 

and molybdenite in close proximity to white mica. 

Electron microprobe analyses of white mica were 

done at the U.S. Geological Survey, Reston, Va. Initially, 

the micas were analyzed with an automated, threechannel electron microprobe employing a combination of 

Analytical Procedures 
[] Quartz-sericitic 

rn Propylitic 

500 1000 METERS 

Figure 1. Location map and surface expression of hydrothermal alteration of the Catheart Mountain porphyry CuMo deposit. Also shown are the drill-hole sites. 

wave-length and energy-dispersive procedures. Approximately half of the analytical work was done using an 

automated ARL-SEMQ 1 nine-channel electron 

microprobe under similar operational conditions as in the 

first part of the study, including 15-kilovolt operating 

voltage, 0.1-microamp beam current, and data-acquisition 

(McGee, 1983) and correction procedures by the Bence 

and Albee (1968) and Albee and Ray (1970) methods. 

Standards used in this study included natural and synthetic 

silicates and oxides. Typically, during standardization and 

analysis, 20 seconds were counted on the peak and 10 

seconds on the background for both the standards and the 

unknowns. The analytical procedure was monitored by 

repeated analysis of known sheet silicates, including muscovite and fluorphlogopite. 

Microprobe analyses of white mica in carboncoated thin sections were done on at least 10 grains per 

sample. At least three spot analyses per grain were 

performed, the number depending on the size of the white 

mica. Water determinations were not obtained independently of the microprobe analyses of white mica. 

Rock compositions were determined using the rapid 

rock technique (Shapiro, 1975) for the major elements; 

minor- and trace-element abundances were determined by 

1 Any use of trade names and trademarks in this publication is 

for descriptive use only and does not constitute endorsement by the 

U.S. Geological Survey. 

chemical, emission-spectrographic, and instrumental 

neutron-activation analyses. A complete presentation of 

the bulk-rock analyses and a discussion of the bulk 

chemistry are in preparation. 

GEOLOGY 

The Catheart Mountain Cu-Mo deposit is in a 

shallowly emplaced, fine- to medium-grained pluton that 

intruded the southeast flank of the Boundary Mountain 

anticlinorium (Albee and Baudette, 1972); this pluton 

belongs to a group of mineralized intrusives within the 

Appalachian porphyry province (Hollister, 1978). The 

two most important rock types at Catheart Mountain are 

quartz monzonite and quartz-feldspar porphyry, both of 

which contain mineralization. Nearby mineralized plutons 

in northern Maine include the newly reported Mo mineralization at Priestly Lake (Ayuso and Shank, 1983; Ayuso, 

1984) and the Cu-Mo mineralization at Deboullie (Boone, 

1962; Hollister, 1978). 

The Catheart Mountain quartz monzonite and 

quartz-feldspar porphyry occur within the Attean Quartz 

Monzonite of Ordovician age; this occurrence has led to 

the assumption that the Attean Quartz Monzonite and the 

rocks at Catheart Mountain are genetically related and 

may be of the same age. However, petrographic studies 

have indicated that rocks at Catheart Mountain are significantly different from those from the Attean Quartz 

Monzonite, and that they constitute a distinct mappable 

unit. 

The Attean Quartz Monzonite is coarsely 

porphyritic and intrudes volcanic and volcaniclastic rocks 

that unconformably overlie the Precambrian (Naylor and 

others, 1973) Chain Lakes Massif. No mineralization 

associated with intrusion of this pluton has been identified. Metasedimentary rocks of Silurian and Devonian age 

(Boone and others, 1970) are in the greenschist facies of 

regional metamorphism and unconformably overlie the 

Attean Quartz Monzonite. These metasedimentary rocks 

are also cut by plutons of Devonian age that were emplaced 

in the area during the closing stages of the Acadian 

orogeny. 

Boone and others (1970) reported ages of 433 m.y. 

by Rb-Sr dating of white mica and 465 m.y. by K-Ar 

dating of biotite in the Catheart Mountain area. On the 

basis of field relations, however, Schmidt (1974) suggested that the Catheart Mountain quartz monzonite was 

possibly intrusive into the 444-m.y.-old Attean Quartz 

Monzonite (Lyons and others, 1983 ), and that perhaps the 

main stage of plutonism and mineralization had not been 

properly dated. Schmidt's suggestion is supported by 

preliminary dating by the Rb-Sr whole-rock method of the 

least altered portions of the Catheart Mountain deposit, 

which indicates an age of about 425±6 m.y. (Ayuso, 

1986). 

2 White Mica Geochemistry of the Catheart Mountain Porphyry Copper Deposit, Maine 
This age probably does not represent the crystallization 

age but may be a result of the hydrothermal alteration. 

From the exploration standpoint, determining the true age 

of rocks associated with mineralization in this part of the 

New England Appalachians would be useful in order to 

identify other volcanoplutonic suites that may be mineralized. 

Schmidt (1974) recognized two centers of alteration 

(the main alteration system and a smaller peripheral 

system) on Catheart Mountain; samples used in this study 

were obtained from both centers. Petrographic study of 

rock alteration of the drill cores at Catheart Mountain 

allowed Schmidt (1974) to classify the regional alteration 

types and to emphasize their gradational nature. He 

distinguished five major gradational regional alteration 

zones in the Catheart Mountain area on the basis of the 

predominant alteration type found in the upper parts of 

the drill core (fig. 1 ). The regional zones ranged, from 

least altered to most intensely altered, in the sequence 

propylitic, outer phyllic, phyllic, quartz potassic, and 

potassic. The overall geometry of the hydrothermal system (fig. 1) resembles that of many other porphyry 

systems summarized by the Lowell and Guilbert (1970) 

model. 

SUMMARY OF THE PETROGRAPHY 

The predominant rock types in the Catheart Mountain deposit are fine- to medium-grained porphyritic 

quartz monzonite and quartz-feldspar porphyry. The least 

altered portions of these rocks consist of plagioclase and 

alkali feldspar, quartz, biotite, accessory minerals 

(sphene, zircon, apatite?), and secondary minerals 

(epidote, sericite, chlorite, and hematite). Most rocks in 

the area, however, exhibit the effects of hydrothermal 

alteration, so that alteration minerals (white mica, calcite, 

epidote, chlorite, and pyrite) commonly replace the original mineralogy (table 1 ). 

Quartz and white mica are the predominant alteration minerals, and all other phases, with the possible 

exception of calcite in some samples, are relatively minor 

in abundance. Hydrothermal alkali feldspar and biotite 

appear to be restricted to the most intensely altered 

portion of the hydrothermal system (potassic zone), 

whereas chlorite, calcite, and epidote are widely distributed across the hydrothermal zones. Most of the original 

silicate mineralogy and fabric of the granodiorite has 

been drastically modified. Traces of albite twinning in 

feldspar, and of granitic texture, are rarely seen except in 

portions of the quartz-sericite and propylitic zones. 

Quartz phenocrysts are one of the most persistent 

textural features retained from the original rock. They are 

generally subhedral to euhedral but may have significant 

embayments and indentations. Plagioclase forms fewer 

phenocrysts than quartz and occurs mostly in the matrix, 

where it is intensely replaced by hydrothermally produced 

minerals. Alkali feldspar occurs in the most strongly 

altered portions of the hydrothermal system. Biotite was 

the predominant primary mafic mineral at Catheart 

Mountain, but white mica, chlorite, and epidote replace 

magmatic biotite in all of the hydrothermal zones. 

The potassic zone has numerous veins of calcite, 

white mica, epidote, quartz, alkali feldspar, and sulfides 

(chalcopyrite, pyrite, and molybdenite). Most veins in the 

quartz-sericite alteration are mineralogically simple and 

consist of white mica, quartz, and sulfides. 

White mica is widely distributed in the hydrothermal system, varying in abundance and ranging in size from 

very fine grained selvages on the feldspars to coarse 

plates, rosettes, clusters, and vein-filling material (table 

1 ). Sericite ranges from trace to moderate amounts in the 

propylitic and argillic zones of the Catheart Mountain 

deposit. In many of the intensely fractured samples, the 

overall abundance of coarse white mica is much higher 

than that of the fine-grained mica, and intergrowths of 

white mica and sulfides are common. Coarse white mica 

in the fine-grained samples formed as a result of piecemeal and patchy replacement of biotite. 

Chalcopyrite, pyrite, and molybdenite are the predominant sulfides at Catheart Mountain. The area near 

the interface between the potassic and the quartz sericite 

alteration zone contains the highest abundance of ore 

minerals (Schmidt, 1974), and this feature is also in 

agreement with the general concepts of porphyry copper 

mineralization (Lowell and Guilbert, 1970). Stannite was 

reported to occur erratically in veins within the phyllic 

zone, and sphalerite in the propylitic zone (Hollister, 

1978). There is, however, no clear evidence of zoning of 

these minerals as a function of the intensity of hydrothermal alteration. The sulfides occur in siliceous veinlets and 

as disseminated grains. The total amount of sulfides is 

probably less than 5 percent in the samples studied. Pyrite 

accounts for the bulk of the sulfides, attaining a ratio of 

10:1 with chalcopyrite in samples of the quartz-sericite 

zone. Molybdenite occurs as fine-grained disseminations, 

large rosettes, and molybdenite "stain," and as clusters in 

quartz sulfide veins. Many of the veins carrying white 

mica and quartz in the potassic zone also contain large 

plates of molybdenite. A good correlation exists between 

the type of alteration, the intensity of veining, and the 

intensity of mineralization, so that the highest amounts of 

Cu and Mo, as well as the lowest Cu/Mo ratio, are found 

in potassically altered rocks closely associated with the 

quartz-feldspar porphyry. In-the potassic zone the grade is 

about 0.2 percent Cu plus minor Mo (Hollister, 1978). 

Some of the veinlets in the propylitically altered parts of 

the system, according to Schmidt (1974), consist of an 

inner zone containing the ore minerals and quartz 

Summary of the Petrography 3 
ol:lo 

:E 

=r 

i 

s:: 

r;· 

I» 

G) 

CD 

0 

() 

=r 

CD 

3 

~ 

-< 

2. 

.. 

=r 

CD 

0 

I» 

.. 

=r 

CD 

I» 

::a. 

s:: 

0 

r::: 

::J 

S' s· 

"tJ 

0 

-a 

=r 

'< 

... 

'< 

0 

0 

, 

, 

~ 

c 

CD , 

0 

w~ 

s:: 

I» s· 

CD 

Table 1. Summary of hydrothermal alteration, mineralogy, and sulfide occurrence in the Catheart Mountain Cu-Mo deposit, Maine 

[Sample identification numbers refer to drill core number and depth, in feet; regional hydrothermal alteration zones based on core descriptions by Schmidt (1974, and personal commun., 

1981) and this study. Abbreviations: q, quartz; af, alkali feldspar; s, sericite; ep, epidote; cc, calcite; b, biotite; z, zircon; ch, chlorite; l, large plates of sericite; s, small plates of sericite; M, 

mineralized; U, unmineralized] 

Sample 

5-680 

8-288 

36-1142 

86-240 

28-159 

28-214 

28-263 

4-250 

4-280 

4-300 

4-350 

5-740 

12-370 

15-124 

42-289 

88-452 

96-110 

96-310 

6-200 

32-642 

86-186 

31-160 

39-463 

Alteration 

potassic 

potassic 

potassic 

potassic 

potassic 

potassic 

potassic 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

quartz-sericite 

sericitic 

sericitic 

sericitic 

propyl it ic 

propylitic 

Alteration Minerals 

q, a f, s, ep, cc, b?, z 

q, af, s, ep, cc, b? 

q, af, s, cc 

q, af, s, ch 

q, af, s, cc 

q, af, s, cc 

q, af, s, cc 

q, s 

q, s' cc 

q, s, cc 

q, s 

q, s, cc, ch 

q, s, ep, ch 

q, s, cc, ch 

q, s' cc 

q, s 

q, s, ep, cc, ch 

q, s, ep, cc 

q, s, ep 

q' s' cc 

q, s, ep, ch 

q' s: cc 

q, s 

Sericite 

Occurrence 

1 >s 

s»l 

1 »s 

s»l 

l»s 

1 »s 

1 >s 

s>l 

s> 1 

s>l 

l»s 

s>l 

s»l 

s»l 

l»s 

s>l 

s>l 

s»l 

S> 1 

s»l 

s»l 

1 »s 

s»l 

Sulfide(%) 

<1 

3 

2 

2 

3 

2 

4 

no data 

2 

2 

2 

5 

<1 

<1 

% Pyrite/ 01 Cha 1 copyri te 

10 

3 

3 

5 

5 

8 

8 

10 

10 

10 

10 

10 

5 

5 

3 

no data 

5 

5 

3 

3 

3 

5 

10 

Molybdenite Occurrence 

Concentrated in quartz veins 

Very fine grained 

Concentrated in quartz veins 

Few concentrations 

Disseminated, sparse 

Disseminated, sparse 

Di s s emi nat ed , spa rs e 

None seen 

None seen 

Concentrated in fractures 

Concentrated in quartz veins 

Concentrated in quartz veins 

None seen 

Very fine grained 

Disseminated 

No data 

None seen 

None seen 

None seen 

Disseminated, sparse 

Disseminated 

No data 

Concentrated in quartz veins 

Remarks 

M 

M 

r~ 

t1 

t1 

r1 

M 

u 

u 

u 

M 

u 

u 

u 

M 

M 

M 

u 

u 

t1 

M 

u 

u 
sericite (phyllic) alteration, enveloped by a potassiumfeldspar-enriched alteration zone (potassic). 

Samples used in this study are subdivided into a 

mineralized or unmineralized group according to degree 

of alteration, and sulfide abundance determined on the 

basis of core descriptions and thin-section analyses (table 

1). Samples from the mineralized group have higher 

contents of Cu and Mo than samples from the unmineralized group (table 2). Unmineralized samples are also 

easily distinguishable by a lack of disseminated sulfides 

and by their generally lower density of fractures. 

SUMMARY OF ROCK BULK COMPOSITION 

A brief summary of the major features of the major 

oxide composition of the rocks at Catheart Mountain is 

presented in this section (table 2). The Catheart Mountain 

rocks are characterized by a narrow silica range and by a 

lack of well-defined variations of the major elements as a 

function of silica. The major oxides CaO, MgO, Ti02 , and 

P 2 0 5 are broadly and inversely correlated with Si02 , as 

are F and H 20+. Compared with the average highcalcium calc-alkaline granite of Nockolds (1954), the 

unmineralized rocks at Catheart Mountain are generally 

lower in Si02 , Ti02 , Al2 0 3 , FeO, Na2 0, and P20 5 (table 

2). Also, rocks from the unmineralized group are slightly 

higher in Fe2 0 3 , CaO, and MgO than the average calcalkaline granite and show a broadly calc-alkaline trend on 

the AFM diagram. 

Comparison of the mineralized and unmineralized 

rock groups shows that higher contents of K20, Fe2 0 3, S, 

Cu, and Mo are generally characteristic of the mineralized rocks. The unmineralized rocks are generally higher 

in FeO than the mineralized rocks. Values for F as high as 

0.14 weight percent were found at Catheart Mountain, 

suggesting only a moderate enrichment in fluorine in these 

rocks. In contrast to F, the content of 0 is low, generally 

about 0.01 weight percent. Although high values for S (up 

to 4.0 weight percent) are characteristic of the mineralized rocks at Catheart Mountain, many of the rocks from 

the unmineralized group also have abnormally high values of S compared with unaltered calc-alkaline rocks. The 

range in values for C02 and H20+ in these rocks is 

generally great and clearly indicates the effects of hydrothermal alteration; this is further supported by the presence of calcite, hydrous alteration minerals, pyrite, and 

other sulfides. In general, both groups of rocks also show 

higher Cu and Mo contents than do rocks from typical 

calc-alkaline suites (table 2). 

For the most part, Cu in rocks of the mineralized 

group is not directly correlated with other elements. For 

example, there is no clear trend between Al2 0 3 content 

and Cu (fig. 2A), although there is probably a trend 

toward higher Cu in rocks containing the highest Fe2 0 3 

16 

• • I .. ,.. ('I) 14 • I .. 0 • • N 

< 12 • 

10 

0 2 3 4 

Cu 

6 

B 1 I I I I I 

• - -

4- • • - •• • ('I) 

0 

N - - Q) 

•• u. • • 

• • • • • 2 - • -

• • ~ • -

0 I I I I Ill I I 

0 1 2 3 4 

Cu 

1.2 

c 

1.0 

4 

Figure 2. Composition of mineralized bulk rocks at Catheart Mountain: A, Variation in Al20 3 and Cu; B, Wide range 

in Fe2 0 3 and Cu; and C. Variation in F and Cu. All values 

are in weight percent. Graphs show all available data on 

mineralized bulk samples from Catheart Mountain and 

include samples used in this study. 

(fig. 2B), because of the presence of chalcopyrite. Many 

of the rocks containing high Cu also have high F values 

(fig. 2C). 

Mineralized rocks from the Catheart Mountain 

Cu-Mo deposit show a general, positive correlation 

between S and Cu (fig. 3A ), a tendency for higher Mo in 

Summary of Rock Bulk Composition 5 
CJ) 

~ 

i 

3: 

c;· 

I» 

C) 

CD 

0 

() 

:::r 

CD 

3 

[ 

-< 

2. 

.. 

::::r 

CD 

0 

I» 

:T 

CD 

I» 

::t 

3: 

0 

c 

:I 

; 

:;· 

, 

0 

., 

.. 

::::r 

'< 

-< 

0 

0 

., 

., 

CD 

.. 

c 

CD ., 

0 

tn 

;:.: 

s: 

I» 

:;· 

CD 

Table 2. Representative analyses of the mineralized and unmineralized rocks in the Catheart Mountain deposit 

Sample 

Si Oz 

A1 2o3 

Fe2D3 

FeD 

r1go 

CaD 

NazO 

K20 

Ti02 

P2o5 

MnO 

SrO 

BaO 

Zr02 

Cr2D3 

Ni 0 

C0 2 

Cl 

88-452 

64.50 

15.30 

2.60 

• 52 

1.30 

2. 50 

1.50 

4. 60 

• 38 

.18 

.04 

.04 

.07 

.02 

.00 

.oo 

2.00 

1. 50 

.oo 

0.08 

H2o+ 2.10 

H2o- .16 

Subtotal 99.39 

Less 0 .78 

Total 98.61 

Cu 2300 

Mo 20 

39-463 

65.40 

15.10 

2.60 

• 20 

1.30 

3. DO 

.47 

5. 70 

• 33 

.14 

• 07 

.01 

.07 

.01 

.oo 

.oo 

2.20 

1.40 

.00 

.14 

2 .oo 

• 07 

100.22 

o. 76 

99.46 

780 

• 3 

32-642 

67.40 

14.80 

2.10 

.12 

1.00 

3. 00 

1. 70 

4. 30 

• 31 

.14 

.06 

.01 

.06 

.02 

.00 

.00 

2. 30 

1.40 

.oo 

.10 

1.80 

.04 

100.66 

• 74 

99.92 

1800 

31 

28-263 

67.40 

14.50 

2.80 

• 20 

• 94 

1. 90 

.87 

5. 20 

• 32 

.18 

.02 

.01 

.07 

.02 

.00 

.00 

1.50 

2. 20 

.00 

.10 

1.80 

.06 

100.10 

1.14 

98.96 

3500 

210 

MINERALIZED 

28-159 

66.90 

13.80 

3. 90 

• 20 

.77 

1. 60 

.14 

6.00 

• 29 

,17 

.04 

.01 

.10 

.02 

.00 

.oo 

1.24 

3.10 

0.00 

0.10 

1. 70 

,06 

100.10 

1.59 

98.51 

2700 

160 

36-1142 

67.10 

14.10 

2. 20 

.32 

• 74 

1. 70 

.60 

6. 90 

• 31 

.15 

.03 

• 02 

.12 

.01 

• 00 

.oo 

1.40 

1. 70 

.01 

.09 

1.40 

o. 04 

98.94 

.89 

98. OS 

2600 

420 

96-110 86-240 42-289 4-350 86-186 

Major and minor element composition in weight percent 

69.30 

14.70 

2. 70 

.28 

1.10 

1. 40 

2.00 

4. 70 

• 37 

.15 

.06 

.03 

.10 

.02 

.00 

.00 

.48 

1. 60 

.01 

.08 

1.60 

0.08 

100.76 

.83 

99.92 

2200 

65 

69.40 

14.70 

1.40 

.44 

1.00 

1.60 

2. 30 

5. 50 

.18 

.15 

.05 

.03 

.09 

.02 

.oo 

.oo 

1.30 

• 73 

.01 

• 06 

1.30 

.06 

101.93 

• 39 

99.92 

70.30 

13.10 

4. 20 

• 20 

.58 

.90 

.13 

5. 60 

• 32 

.15 

.03 

.01 

.11 

.01 

.oo 

.oo 

.62 

3. 30 

. oo 

• 10 

1.60 

.13 

101.39 

1.69 

99.70 

70.70 

12.50 

5.40 

• 20 

.so 

• 46 

.15 

4.10 

.27 

.14 

.01 

.01 

• 06 

.02 

.00 

• 00 

• 27 

4.00 

.00 

.08 

1. 70 

.04 

100.60 

2.03 

98.57 

Elements in parts per million 

620 3700 3300 

120 510 84 

71.10 

14.60 

1.60 

.20 

• 93 

2.10 

2. 70 

4. 70 

• 31 

.15 

.04 

.05 

.09 

.01 

.00 

.oo 

.18 

.56 

.01 

.05 

1.20 

.04 

100.63 

.30 

100.32 

940 

120 

I Average composition of granodiorite (Nockolds, 1954; Turekian and Wedepohl, 1961); n.d.: not determined. 

96-310 

66. 10 

15.90 

2. 90 

1.00 

1.40 

2.40 

2. 70 

3.50 

.38 

.16 

• 06 

.04 

.07 

.02 

.00 

.on 

• 54 

1. 70 

.01 

.10 

1.80 

.07 

100.85 

0.89 

99.96 

520 

18 

4-250 

67.40 

15.30 

1. 50 

• 28 

.63 

3.00 

2. 90 

3.40 

. 24 

.09 

.02 

.02 

.08 

.02 

.oo 

.oo 

2. 30 

.so 

.01 

.10 

1. 50 

.08 

99.66 

.44 

99.22 

180 

Ul'tH NERAL !ZED 

15-124 

67.70 

14.40 

2. 20 

1.10 

1. 30 

2.10 

2. 30 

4.50 

• 39 

.14 

.04 

.03 

.08 

.02 

.00 

.00 

1.10 

1.10 

.01 

.08 

1.80 

.15 

100.55 

.58 

99.96 

420 

11 

31-160 

68.70 

14.80 

1. 50 

.92 

1.10 

2.40 

2. 70 

4.50 

• 31 

.14 

.04 

.04 

.10 

.01 

.oo 

.DO 

.91 

.84 

.01 

.07 

1.20 

0.08 

100.37 

.45 

99.92 

450 

.4 

4-300 

69.30 

14.10 

1.80 

.28 

• 70 

2. 70 

2.10 

3. 90 

• 25 

.11 

• 05 

,01 

,09 

,01 

.oo 

.oo 

2.00 

.87 

.00 

,07 

1.40 

.08 

99.79 

.45 

99.34 

280 

30 

4-280 Granodiorite! 

69. 70 66.88 

14.30 15.66 

1. 90 1. 33 

.32 2.59 

.66 1.57 

2.80 3.56 

2.50 3.84 

3.50 3.07 

• 24 • 57 

.10 .21 

.05 .07 

.02 n.d • 

• 07 n .d • 

.01 n .d. 

• 00 n.d • 

.00 

2.12 

1.10 

.00 

.07 

1.40 

.08 

100.92 

.58 

100.34 

250 

18 

n .d • 

n.d. 

n.d. 

n.d • 

n.d • 

• 65 

n.d. 

n.d. 

n .d. 

30 
en 

0 

~ 

4 ,---,~----~~----~~---~~--~~----~1~.~~1~ 

A 

'--

3r2 -

- • -

• r-1 • 

• • 

..... 

• • • 

• 

• 

-

• -

• -

-

-

-

0 ~--~~----~l ____ L_l __ ~I ____ ~I ____ L_I __ ~I--~ 

0 1 2 3 4 

Cu 800,---,----,----,---,----,----~--,---~ 

400 

200 

B 

2 

Cu 

• 

3 4 

a~c--~~----~~----~~--~~----~~--~1----~l--~ 

- • 

6 '--

4 rr2 r • • 

• I I 

• 

• 

I 

• • 

• • • 

• • 

• 

I 

2 

Cu 

• 

-

-

• • • 

-

-

• 

• -

-

-

I I • I 

3 4 

Figure 3. Composition of mineralized bulk rocks at Catheart Mountain: A, Wide range in S as a function of Cu; 8, 

Variation in Mo and Cu; and G, Variation in Sn and Cu. All 

values are in weight percent. Graphs show all available 

data on mineralized bulk samples from Catheart Mountain 

and include samples used in this study. 

rocks containing high Cu (fig. 3B), and a positive correlation between Sn and Cu (fig. 3C). 

DEFINITION OF WHITE MICA 

The field term "sericite" has previously been used 

to refer to any white mica and illite, regardless of 

composition (for example, Meyer and Remley, 1967). The 

term "white mica," as used in this paper, includes sericite, 

illite clay minerals, hydromuscovite, and micas having 

compositions in the solid solutions between muscovite and 

paragonite, muscovite and phengite, muscovite and ferrimuscovite, and phengite and ferriphengite. Illites are 

more silica-rich than muscovite and contain fewer 

interlayered cations . 

Dioctahedral white micas have two-thirds of the 

octahedral sites filled and have the general formula 

XY2 (T4 0 10 )(0H) 2 , where X=K, Na, Ca, Rb, Cs, and Ba 

and is the inter layer cation; Y =AI, Mg, Fe2+, Mn, Li, Cr, 

Ti, and V and comprises the octhaderal cations; and 

T= Si, AI, and Fe3 + (?) and fills the tetrahedral sites (Deer 

and others, 1962). The most important substitutions in 

naturally occurring muscovite are Fe2 + and Mg for AI in 

theY-site and Na forK in the X-site (Guidotti and Sassi, 

1976). However, other substitutions involving vacancies, 

other alkali elements, orCa in the X-site and Ti and Fe3+ 

for AI in the Y -site are also indicated. Solid solution 

between K and Na gives rise to the well-known muscovite 

KA1 2 (A1Si3 010 )(OH2 )-paragonite NaA1 2 (AlSi 3 0 10 ) 

(OH2 ) series (Eugster and Yoder, 1955; Eugster and 

others, 1972). 

Muscovite (KA12 (A1Si3 )010 (0H) 2 ), ferrimuscovite 

(KFe1" 3(A1Si3 )010 (0H)z), and celadonite (K(Fe+3,Al) 

(Mg,Fe)Si4 0 10 (0H)2 ) have complete solid soultion and 

result from the substitution in the octahedral sites of Mg 

and Fe+2 for AI in the X- andY-sites (Guidotti and Sassi, 

1976). Phengite (Ernst, 1963) refers to Fe- and Mg-rich 

white micas (Velde, 1965) that obey the substitution 

Al1

v +Alv1=(Mg,Fe+2 )v1+Si, but Guidotti and Sassi 

(1976) suggest that the term "celadonitic muscovite" be 

used instead of phengite. 

COMPOSITION OF WHITE MICAS AT 

CATHEART MOUNTAIN 

Results of white mica analyses obtained using the 

electron microprobe are summarized in tables 3 and 4. 

The lowest sum of the oxides is 90.22 and the highest is 

96.88. Many white micas have lower sums than typical 

muscovites (Deer and others, 1962) and probably represent more hydrated white mica varieties (for example, 

hydromuscovite and illite). White micas having low total 

sums tend to have low K in the X-site (all calculations 

herein were for 11 oxygens), and thus these micas agree 

with the compositions of hydromuscovite and illite. 

White micas from the Catheart Mountain deposit 

have substantial contents of trioctahedral components and 

are similar to plutonic muscovites (Anderson and Rowley, 

Composition of White Micas at Catheart Mountain 7 
Table 3. Average compositions, standard deviations, and structural formulas of white mica in the potassic alteration zone 

at Cat heart Mountain 1 

5-680 8-288 36-1142 86-240 

Weight percent 

Si02 ------ 47.63! .17 45.98 + .62 49.84 + 1.70 50.50 + .88 

Al203 ----- 33.58! 1.22 32.04 + 1.05 31.76 + 1.90 27.17 + .85 

Ti02 ------ 0.45 + .49 0.64 + .15 0.74 + 0.38 0.04 + .05 

FeD ------- 2.28 + .87 2.54 + .28 1.86 + .46 2.08 + .28 

MnO ------- 0.04 + .01 0.03 + .01 0.05 + .01 

MgO ------- 0.97 + .10 1.71 + .32 1.51 + .51 3.14 + .37 

CaO ------- 0 0 0.02 + .02 0 

Na20 ------ 0.29 + .05 0.26 + .04 0.26 + .05 0.01 + .01 

K2D ------- 8.46 + .30 9.87 + .27 9.75 + .31 8.03 + .34 

Cl -------- 0 0.06 + .02 0.01 + .02 0.02 + .02 

F --------- 0.09 + .02 0.18 + .07 0.24 + .07 0.21 ! .04 

Subtotal 

O=Cl ,F 

Total 

Si --------

AJIV ------

AJVI ------

Ti --------

Fe --------

Mn --------

Mg --------

Ca --------

Na --------

K ---------

Fe/(Fe+Mg) 

93.79 

.04 

93.75 

3.19 

0.81 

1. 84 

0.02 

0.13 

0 

0.10 

0.04 

o. 72 

0.57 

1 Total iron as FeD 

93.28 

.09 

93.19 

3.15 

0.85 

1. 72 

0.03 

0.14 

0 

0.17 

0.04 

0.86 

0.45 

96.02 

.10 

95.92 

91.25 

.09 

91.16 

Number of ions per 11 oxygens 

3. 26 

o. 74 

1. 74 

0.04 

0.10 

0.17 

0 

0.03 

0.82 

0.37 

3.46 

0.54 

1. 65 

0 

0.12 

0 

0.32 

0 

0 

0.70 

o. 27 

28-159 

48.36 + .16 

30.50 + .02 

0.59 + .06 

1.67 + .45 

0 

1.95 + .04 

0.03 + .02 

0.18 + .05 

9.00 + .08 

0.03 + .01 

0.32 + .01 

92.63 

.14 

92.49 

3.29 

o. 71 

1. 73 

0.03 

0.09 

0 

0.20 

0.02 

o. 78 

o. 32 

28-214 

47.18 + 1.30 

31.51 + 1.50 

0.51 + .27 

1.89 + .61 

0.04 + .01 

2.68! 1.40 

0 

0.24 + .11 

9.31 + .14 

0.02 + .02 

0.30 + .12 

93.68 

.13 

93.55 

3. 21 

0.79 

1. 70 

0.03 

0.11 

0 

0.27 

0.03 

0.81 

0.29 

28-263 

48.66 + 1.99 

33.60 + 1.30 

0.74+ .32 

2. 26 + .17 

0 

1.29 + .35 

0 

o. 29 + .14 

6.63 + .09 

0.01 + .02 

0.28 + .20 

93.76 

.12 

93.64 

3. 22 

o. 78 

1.84 

0.04 

0.13 

0.13 

0 

0.04 

0.56 

o. 50 

1981; Miller and others, 1981) because of their high total 

Fe+ Mg, high Ti, and excess Si. Thus, the micas contain an 

excess of octahedral cations (Fe, Mg, Mn) compared with 

the complement of AI in octahedral positions (AI octahedral deficiency: 2-Alv1

). Micas from the unmineralized 

and mineralized rock groups show substantial compositional overlap (fig. 4) despite significant bulk chemical 

differences. Plutonic muscovites also show significant 

variation in composition which Miller and others (1981) 

could not relate directly to the coexisting phase assemblage. They attributed this variation to the latest stage at 

which the mica reached equilibrium. 

In contrast to the sericites studied by Guilbert 

(1980) and Guilbert and Schaefer (1978) in porphyry 

copper deposits from Arizona, the compositions of white 

micas at Catheart Mountain do not show consistent 

variations in Mg!(Mg+ Fe) across the regional hydrothermal zonation, probably because the white mica composition depends on the composition of the precursor mineral 

(Ayuso, 1983). In the porphyries from Arizona, Guilbert 

(1980) demonstrated that aluminum diminished outward 

from the phyllic to phyllic-argillic zones, but at Catheart 

Mountain this variation is more random and inconsistent. 

Similarly, the Si/Al1

v ratio does not show a progressive 

8 White Mica Geochemistry of the Catheart Mountain Porphyry Copper Deposit, Maine 
variation compared with micas from the Arizona porphyry 

copper deposits. In both the Arizona deposits and the 

white micas at Catheart Mountain, however, the changes 

in Fe, Mg, and Ti in the octahedral site are the most 

informative and suggest the control of coupled substitutions with AI. 

White micas containing high Ti in the Catheart 

Mountain hydrothermal system might have crystallized at 

higher temperatures than micas containing low Ti. This 

suggestion agrees with Guidotti's (1978a) demonstration 

of Ti enrichment in muscovites at high metamorphic 

grades, and with the general high Ti content of primary, 

igneous muscovite, as suggested by Anderson and Rowley 

(1981) and by Miller and others (1981). Other possible 

but qualitative indicators of temperature in micas from a 

hydrothermal system include the Fe/(Fe+ Mg) ratio and 

the Na/(Na + K) ratio (paragonite substitution). The range 

in Na/(Na + K) ratio in the Catheart Mountain white micas 

is from 0 to 0.67, with the change inK being the dominant 

factor (table 3). The Na/(Na+ K) ratio is inversely correlated with the calculated Si content in the formula (a 

measure of the celadonite substitution) for white micas 

from Catheart Mountain (fig. 5). 

In the Catheart Mountain deposit, the most aluminous micas are also the most enriched in magnesium. In 

most of these micas, the octahedral substitution of Mg for 

AlY1 is regular and contrasts with the more dispersed 

variation of Fe. Variation in intrazonal mica composition 

is significant, however, and the composition does not 

change systematically from the weakest regional alteration 

zone to the strongest regional alteration zone. 

Regular Variations in White Mica 

Composition 

The composition of white mica in the Catheart 

Mountain deposit changes regularly, progressively, and 

consistently according to the control imposed by crystal 

chemical substitutions. Among the major substitution 

schemes for ideal muscovite are (1) the solid-solution 

series with celadonite (Velde, 1967, 1972) according to 

Al1Y +AlY1=Si+(Fe,Mg),(2) the substitution Si+vacancy 

(XII)= Al1Y + (K + Na), which represents a solid solution 

between pyrophyllite and muscovite (McDowell and 

Elders, 1980), and (3) the reaction 2-AlY1=Mg+Ti, 

which has been suggested as a possible control for Ti 

enrichment in white micas (see, for example, Guidotti 

1973, 1978a,b; Anderson and Rowley, 1981). 

White micas from individual hydrothermal alteration zones in the Catheart Mountain deposit have variable compositions that lack a direct correlation with their 

position within the regional alteration zonation (figs. 4-8). 

This diversity of composition conforms to the substitutional schemes but results in a wide compositional range 

for micas within individual regional hydrothermal zones, 

as exemplified by the variation in celadonite content (fig. 

5) of white micas in the regional potassic zone. Similarly, 

white micas from the sericitic alteration zone show a wide 

range in aluminum content, and they generally overlap the 

range of white micas in the potassic zone. Thus, despite 

the overall regional systematic change in aluminum content, white micas from individual regional alteration zones 

are not systematically grouped. This probably reflects 

that hydrothermal alteration events produce superimposed mineral assemblages, and that in Catheart Mountain there are veins containing quartz-sericite alteration 

within the regional zone designated as part of the potassic 

alteration. 

Beaufort and Meunier (1983) found that around 

phyllic veins (sericitic alteration) of the Sibert prophyry, 

the compositions of white micas were mainly restricted to 

the muscovite-illite-phengite solid solution. They suggested that white micas that are poorer in Fe, Mg, and Ti 

occurred in the alteration zone that attained the highest 

temperature, and that more celadonitic micas were in 

areas that might have crystallized at lower temperatures. 

This concept of celadonitic mica stability was initially 

suggested by Velde (1965) and agrees with McDowell and 

Elders (1980), who demonstrated a change in white mica 

composition from celadonite-rich micas toward more 

ideal muscovite with increasing temperature. Results for 

the Catheart Mountain white micas are consistent with 

these studies, and the speculation is that the more aluminous white micas may indicate higher temperatures than 

the more celadonitic white micas. 

The solid solution between muscovite and pyrophyllite as expressed by Si +vacancy XII= Al1

Y + (Na + K) also 

may have contributed to the compositional variation of the 

white micas of the Catheart Mountain deposit (fig. 7). 

This substitution, however, is not clearly demonstrated 

here because of the wide variation of Al1Y and interlayer 

cations. As in the celadonitic substitution, the composition 

of white micas in each alteration zone varies in the same 

way the entire hydrothermal system varies. 

The variation of Ti in the white mica of the Catheart 

Mountain deposit might reflect the control imposed by a 

substitution of the type 2AlY1=Mg+Ti (fig. 8). According 

to Guidotti (1978b ), this reaction is probably the most 

important control of Ti in muscovite, and for the Catheart 

Mountain white micas, no reasonable alternative exists. 

Substitutions of the type Si + AlY 1 =Ti + Al1Y and 

Ti = 2(Mg,Fe) do not appear to be significant. 

DISCUSSION 

Relation of White Micas and Bulk 

Composition 

The compositions of white micas in the mineralized 

rocks of the Catheart Mountain deposit show a broad, 

Discussion 9 
Table 4. Average compositions, standard deviations, and structural formulas of white mica 

QUARTZ 

Sample 4-250 4-280 4-300 4-350 5-740 12-370 15-124 

Weight 

Si 02 ---- 48.87 + 1.02 49.70 + .58 48.47 2:. .09 46.61 + 1.14 46.03 + .18 49.96 + 1.10 49.00 + .65 

Al 2o3 --- 31. 20 + .47 31.25 + .69 30.472:_1.11 35.74 + 2.58 30.96 + 2.70 31.64 + .82 30.77 + • 90 

Ti 02 ---- o. 25 + .11 o. 28 + .12 o. 51 2:. .18 0.59 + 1.20 0.41 + .22 o. 30 + • 21 0.15 + • 95 

FeD ----- 2. 26 + .16 2. 68 2:. .49 2. 23 2:. • 51 2.13 + .22 3.86 + 1.20 1. 31 + • 27 2.41 + .11 

t~nO ----- 0.04 + .01 0.04 + .02 0.04 + .02 o. 01 + .01 

MgO ----- o. 48 + .19 2. 29 + • 74 2.49 2:. .48 0 1.68 + .66 1. 91 + .37 1. 91 + .32 

CaD ----- 0.01 + .01 0.04 + .03 

Na 2o ---- 0. 10 + .03 0.16 + .02 0.17 + .15 0.29 + .03 0.15 + .08 0.22 + .07 0.34 + .05 

K20 ----- 6. 61 + .15 9.80 + .33 9. 31 2:. .22 7.09 .:!:. • 29 8. 29 + .33 8. 91 + • 95 10.04 + • 34 -

Cl ------ 0.01 + .02 0.01 + .02 0.02 + .02 0.01 + .02 0.01 + .01 0.01 + .01 -

F ------- 0. 76 + .17 0.33 + .03 0.27.:!:. .10 0.25.:!:. .08 0.11 + .06 0.17 + 

- .02 o. 11 + .04 

90.54 96.50 93.98 92.71 91.53 94.48 94.79 

O=Cl, F .32 .13 .11 .11 .05 .07 .05 

Total 90.22 96. 37 93.87 92.60 91.48 94.41 94.74 

Nur1ber of ions 

Si ------- 3. 35 3. 27 3. 27 3.13 3.19 3.31 3. 28 

Al IV ----- o. 65 o. 73 o. 73 0.87 0.81 0.69 0. 72 

Al VI ----- 1.88 1. 69 1.68 1.96 1.72 1. 78 1.71 

Ti ------- 0.01 0. 01 0. 03 0.03 0.02 0.02 o. 01 

Fe ------- 0.13 0.15 0.13 0.12 0. 23 0.07 0.12 

Mn ------- 0 

Mg ------- 0.05 0. 22 0.25 o. 17 0.19 0.19 

Ca ------- 0 0 

Na ------- 0.01 0.02 0.02 0.04 0.02 0.03 0.04 

K -------- 0.58 o. 82 0.80 0. 61 o. 74 0. 75 0.86 

Fe/ ( Fe+Mg) o. 72 0. 41 

1 Tot a 1 iron as FeD 

positive correlation with the copper (fig. 9A) and sulfur 

(fig. 9B) content of the whole rock, so that the most 

celadonitic micas are found in rocks containing lower 

amounts of base metals. With the exception of Si02 of the 

whole rock, the major oxides are not clearly correlated 

with white mica composition. The trace elements, including the rare-earth elements, are also uncorrelated. 

Rock samples classified as mineralized because of 

their numerous fractures and high Cu content contain a 

population of white micas having progressively higher 

total aluminum contents (fig. 9A). This relation may be a 

useful indicator of compositional gradients in the Catheart Mountain hydrothermal system and suggests that the 

events responsible for mineralization may also control the 

composition of the coexisting white micas in the rocks 

0. 34 1.0 0.58 0.27 0.39 

containing high Cu. Unmineralized rocks containing fewer 

fractures and lower abundance of sulfides show no correlation between Cu in the whole rocks and total AI in the 

white micas. White mica compositions exhibit no consistent correlation with molybdenum content of the whole 

rock because of the erratic distribution of molybdenite in 

the drill core. 

Sulfur content of the whole rock is positively correlated with white mica composition (fig. 9B). This relation 

gives strong evidence for reconstitution of white micas 

during the massive increase in sulfur during alteration of 

the whole rock. Although the geometric position of quartzsericite rocks in porphyry copper systems is intermediate 

to potassic and propylitic rocks (Lowell and Guilbert, 

1970; Rose, 1970; Guilbert and Lowell, 1974), there is 

10 White Mica Geochemistry of the Catheart Mountain Porphyry Copper Deposit, Maine 
in the quartz sericite, sericitic, and propylitic alteration zones at Cat heart Mountain 1 

SERICITE - 5ERJrJTIC - --- PROPYL !TIC 

42-289 88-452 96-110 96-310 6-200 32-642 86-186 31-160 39-463 

percent 

4 7. 37 + • 56 47.50 + 1.00 46.67 + .06 45.67 + 1.21 46.70 + .58 50.40 + • 70 50. 21 + 1. 30 46.91 + • 73 51.00 + • 29 

33.78 + .82 32.67 + .31 32.56 + 1.30 32.95 + 1.30 34.10 + .11 30.16 + 1.30 29.04 + 1.10 32.78 + .86 29.90 + .40 

0.51 + .09 0.31 + .05 0.55 + .09 0.80 + .58 o.13 + .nz o. 20 + .10 o. 24 + • 10 0.31 + .23 0. 11 + • 04 

1.71 + .51 1.44 + .02 2. 36 + • 93 1.59 + .48 2.66 + .16 1.49 + .44 2.10 + .23 1.76 + .70 0.83 + .09 

0.04 + .01 0.01 + .01 0.04 + .01 1.02 + .06 0.05 + .01 0.03 + .03 0.04 + .01 0.09 + .02 

1.16 + .06 1.40 + .14 1.64+1.10 1.29 + .31 1.35 + .52 3.15 + .65 2.59 + .10 1.56 + .37 3. 3 5 + • 38 

o. 01 + .01 0 0.02 + .02 

0.03 + .03 0.44 + .04 0.38 + .12 0.29 + .04 0.43 + .06 0.06 + .01 0.01 + .07 0.29 + .06 0.08 + .02 

8.57 + .03 9. 75 + 1.40 8.60 + .21 9.23 + .53 10.39 + .49 9.55 + .17 8. 96 + • 34 9. 76 + • 30 8. 74 + • 05 

0.02 + .01 0.02 + .02 0. 01 + . 01 0.01 + .01 0.02 + .01 0.01 + .01 0.02 + .01 

0. 17 + • 02 0.16 + .04 0.20 + .09 0.06 + .02 0.16 + .08 0.46 + .02 0.37 + .06 0.15 + .04 0.57 + .06 

93.34 

• 07 

93.27 

per 11 oxygens 

3. 17 

0.83 

1.84 

o. 02 

0.10 

0.11 

0.04 

o. 73 

0. 48 

93.69 92.99 

.07 .08 

93.62 92.91 

3. 20 

0.81 

1.80 

0. 02 

0.08 

0.14 

0.06 

0. 84 

0.36 

3. 17 

0.83 

1.77 

o. 03 

0.14 

o. 17 

0.05 

0. 74 

0.45 

91.93 96.95 

.03 • 07 

91.90 96.88 

3.14 

o. 59 

1.80 

o. 04 

0.09 

0.13 

0.04 

0.81 

0.41 

much evidence suggesting that alteration zones did not 

form contemporaneously (Meyer and Hemley, 1967; Gustafson, 1978; Titley and Beane, 1981; Titley, 1982) and 

that quartz-sericite alteration is a relatively late, feldspardestructive event in which a large amount of pyrite is 

deposited. Thus, the broad correlation between white 

mica composition and the sulfur content of the whole rock 

suggests that the white micas were probably reequilibrated late in the evolution of the Cathcart Mountain 

deposit. 

Aluminous White Micas in Mineralized Rocks 

White micas are potential monitors of the physiochemical parameters during crystallization, as reflected by 

3.12 

0.88 

1. 80 

0.01 

0. 15 

o. 10 

o. l}f, 

0.89 

0.60 

95.52 93.58 93.57 94.71 

.19 .16 .06 .24 

95.33 93.42 93.51 94.47 

3. 33 

0.67 

1. 68 

0.01 

0. 08 

0. 31 

o. 01 

o. 81 

o. 21 

3. 37 

o. 63 

1. 68 

0.06 

0.12 

o. 26 

o. 01 

0.77 

o. 32 

3. 17 

0.83 

1. 79 

0.02 

0.10 

0.16 

0. 04 

. 0.84 

o. 38 

3. 37 

0.63 

1. 70 

0.01 

o. 05 

0.01 

o. 33 

0.01 

0. 74 

0.13 

extensive solid solution in the tetrahedral and octahedral 

sites. In the Cathcart Mountain deposit, the fact that 

white micas change compositions but are not grouped in 

the regional hydrothermal alteration zones might be 

explained as follows: (1) consistent and progressive variations in mica composition within the system were undetected by microprobe analysis; (2) compositional variations were removed by subsequent regional metamorphic 

effects; and (3) mica compositions reflect the changing 

conditions during mineralization, including the strong 

overprint and superposition of mineral assemblages during the waning stages of hydrothermal activity, possibly 

involving massive fluid influx as suggested in other porphyry copper systems. 

Additional components in the mica structure such 

as Li, Rb, Ba, Fe+3 , and H2 0 were not analyzed in this 

Discussion 11 
r:::: 0.4 

~ 

+ 

C) 

~ 

+ 

Q) 

LL 0.2 

OL-----~-----L----~------L-----~----~ 

0 0.2 0.4 0.6 

Figure 4. Change in Fe+ Mg+ Mn as a function of 2-Aiv1 in 

the white micas from Catheart Mountain. Samples plot 

between the 1:1 and 3:1 lines, suggesting an excess of 

octahedral cations (Fe+ Mg+ Mn) compared with octahedral aluminum in the formula. Solid squares are white 

micas from mineralized rocks, and open squares are white 

micas from unmineralized rocks. Values are number of 

ions per 11 oxygens. 

. 08.--------------------------------------

10% 20% I I 

- I I 

•• 

a- . 06- • 

•o 

D. D 

Q -

+ 

~ .04-

co • 

z rD 

.02 t3?% 

D 

• 

o• 

D 

I 

• 

• 

40% I ... I - CELADONITE 

-

-

-

-

-

o. 

D -

o~----~~------~~-------L-~----~~----~--~ 

3 3.2 3.4 

Si 

Figure 5. Distribution of Na/(Na+ K) and Si in the white 

micas from mineralized rocks (solid squares) and unmineralized rocks (open squares) from Catheart Mountain: Arrow 

shows increasing percentages of celadonitic component. 

Values are number of ions per 11 oxygens. 

study, and they might show strong variations correlated 

with their position in the regional hydrothermal system. 

For example, barian muscovite is a major constitutent in 

the Alberfeldy Ba-Zn mineralization (Fortey and BeddoeStephens, 1982), and variations in Ba might be useful 

indicators of the mineralized area in porphyry systems. 

White mica compositions in the Catheart Mountain 

deposit probably do not reflect intense reequilibrium 

2.8 

> 2.6 

<{ 

+ 

~ 

<{ 2.4 

2.2 

2.0 l__ __ L_ __ ...J..__ __ __J__ __ ---'-------'-----<'----....___ __ ~--~ 

3.1 3.3 3.5 3.7 3.9 

Si+(Mg+Fe) 

Figure 6. Distribution of Al 1v + Alv1 and Si+ (Mg+ Fe) in the 

white micas from mineralized rocks (solid squares) and 

unmineralized rocks (open squares) from Catheart Mountain. Trend shown connects ideal muscovite to celadonite. 

Values are number of ions per 11 oxygens. 

I I I I I 

• 

3.4 t- -

D • D 

D • ren 

• DO. • -

3.2 t- • D • • -

•• 0 

• D • -

3.0 1 '--------'---- l ____ __._l ______ .___l ____ _.____ ! ____ ___,___ ____ ____. 

1.2 1.4 1.6 1.8 

Al'v + (Na + K) 

Figure 7. Distribution of Si and Al1v+(Na+K) in the white 

micas from mineralized rocks (solid squares) and unmineralized rocks (open squares) from Catheart Mountain. Values are number of ions per 11 oxygens. 

resulting from Acadian metamorphism. Although mica 

compositions might have been affected by Acadian events, 

the general correlation between mineralized rocks and 

their white mica compositions probably would not have 

been spared during massive, regional metamorphic equilibration. If a strong overprint existed, white mica compositions probably would reflect the subsequent metamorphic event and their compositions should not be correlated 

with the Cu contents of the rocks. 

Catheart Mountain rocks near the interface between 

the potassic and quartz-sericite regional alteration zones 

12 White Mica Geochemistry of the Catheart Mountain Porphyry Copper Deposit, Maine 
4.0 I I I I I I I 

- • -

3.8- -

0 

- - o• • > 

<( 3.6 t-- 0 •oo - N 

.o - -

• • 

3.4 - 0~ 

• 0 -

0 

- 0 

- • -

3.2 I I I I I I I 

0.0 0.1 0.2 0.3 0.4 

Mg+Ti 

Figure 8. Distribution of 2Aiv1 and Mg+ Ti in the white 

micas from mineralized rocks (solid squares) and unmineralized rocks (open squares) from Catheart Mountain. Values are number of ions per 11 oxygens. 

contain the highest Cu and Mo contents, but the white 

micas in these rocks are not systematically distinct in 

composition from the white micas in rocks from milder 

regional alteration zones and having lower contents of Cu 

and Mo. The preferred explanation for this is that mica 

compositions in the different veins and fractures were 

locally controlled by changes in PH~o and by the composition of the evolving fluid phase as a result of thermal 

collapse of the hydrothermal system. Thus, regional determinations of metal content and intensity of alteration on a 

zonal basis are not directly equivalent to the chemical 

changes in the small chemical domains represented by 

single veins from drill cores used in this study. 

White mica composition and bulk-metal content at 

the Catheart Mountain deposit might best be related 

because the micas formed from mineralizing hydrothermal fluids of predominantly magmatic origin which carried the base-metal complexes. In contrast, white micas 

from the unmineralized rock group are generally unrelated to the Cu content of the rock because these micas 

perhaps formed after the main period of mineralization, 

and from different fluids than those that produced the 

influx of metals and white micas associated with the main 

stage of mineralization. These fluids might have been 

predominant} y of meteoric origin, reflecting the progressive thermal collapse during the waning stages of the 

hydrothermal system. Such temporal evolution of fluids 

during the mineralizing process would be in accord with 

studies by Sheppard and others (1969, 1971 ). Thus, 

significant differences in mica composition might be a 

result of subsequent reequilibration of previously formed 

white micas, followed by and modified as a result of the 

formation of newly crystallized white micas during the 

waning stages of the hydrothermal system. 

A 

3 

8 2 

0 ~_______j_______v_______L____.._~~ 2.0 2.2 2.4 2.6 2.8 3.0 

APV +AIVI 

B 

4 

(/') 

2 

OL-~--~--~---L---L--~--~--~--~~ 

2.0 2.2 2.4 2.6 2.8 3.0 

Figure 9. A, Change in Cu content (in weight percent) of 

the bulk rock and the Al1

v + Alv1 (ions per 11 oxygens) in 

the white micas coexisting with sulfides. B, Distribution of S 

(in weight percent) in the bulk rock and the Al 1v + Alv1 (ions 

per 11 oxygens) in the white micas coexisting with sulfides. 

Mineralized samples are shown as solid squares, and 

unmineralized samples as open squares. 

The most likely explanation of the variability in 

mica composition within each of the regional alteration 

zones is that white micas reflect local bulk-compositional 

differences retained in the host rock. In fact, overprinting 

of younger mineral assemblages on older assemblages has 

been documented in many hydrothermal systems, including the Bingham (Utah) (Peters and others, 1966), the 

Silver Bell (Arizona) (Graybeal, 1982), and the Sierrita 

(Arizona) (West and Aiken, 1982). Because of the complex superposition of fracturing and vein mineral assemblages in many porphyry systems, including Catheart 

Mountain, during the waning stages of alteration, the host 

rock is composed of microdomains exhibiting a range in 

bulk composition. Thus, because of the variation in minDiscussion 13 
eralogy, subsequent hydrothermal reactions also must 

show strong local control over the occurrence, stability, 

and composition of the resulting minerals. 

The broad correlation between white mica composition and base metal content of the rocks at Catheart 

Mountain suggests that white micas can be used as 

general indicators of mineralization gradients. Although 

rocks that are not intensely fractured and do not contain 

abundant disseminated sulfides also contain white micas 

and have compositions broadly similar to those in the 

mineralized rocks, the white micas remain uncorrelated 

with the metal content ofthe rocks. The comparison of 

compositional trends in the white micas and the bulk 

rocks at Catheart Mountain readily distinguishes the 

positive trend between the population of white micas in 

mineralized rocks from white micas in rocks containing 

lower amounts of Cu and Mo. By applying this distinction, 

highly mineralized zones may be found in systems that 

exhibit less obvious petrographic features associated with 

mineralization. 

SUMMARY 

1. White micas from intensely fractured and hydrothermally altered rocks containing abundant disseminated sulfides show a broad positive correlation between 

their aluminum content and the Cu content of the whole 

rock. 

2. The compositional gradients in the white micas 

are not clearly related to their position in the regional 

hydrothermal zonation. 

3. Compositional variability of the white micas is 

best explained by superposition and overprinting of fluids 

during mineralization and during the last stages of hydrothermal alteration. 

4. The general correlation between white mica 

composition and base metal content in the mineralized 

rocks at Catheart Mountain suggests that white mica 

composition could be a useful indicator of the mineralization gradient. 

ACKNOWLEDGMENTS 

Scott Paper Company granted access to the property at Catheart Mountain and to core samples necessary 

to carry out this study. I am particularly indebted to my 

colleague Robert G. Schmidt for his advice throughout 

this study, and for his reviews of earlier versions of the 

manuscript. I am also grateful to N.K. Foley, S.D. Ludington, and G.R. Robinson for their informative discussions 

and reviews. 

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16 White Mica Geochemistry of the Catheart Mountain Porphyry Copper Deposit, Maine