Some Pegmatite 

Deposits in 

Southeastern Alaska

GEOLOGICAL SURVEY BULLETIN 1024-G

Some Pegmatite 

Deposits in 

Southeastern Alaska

By C. L. SAINSBURY

MINERAL RESOURCES OF ALASKA

GEOLOGICAL SURVEY BULLETIN 1024-G

A description of the geology of two areas 

that contain pegmatite bodies of possible 

commercial significance

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1957
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 25 cents (paper cover)
CONTENTS

Page

Abstract__ _____________________________________________________ 141

Introduction._ ____________________________________________________ 142

Pegmatite deposits near Redfish Bay, Baranof Island-_________________ 144

Areal geology-_________________________________________ 144

Geology of the pegmatite-bearing rocks at Redfish Bay_________ 144

Intrusive rocks________________________________________ 144

Metamorphic rocks_ ___________________________________ 147

Faults____________________________________________ 147

Pegmatite deposits___________________________________________ 148

Structure of the pegmatite..-_______-______________.__--__-- 148

Zoning of the pegmatite.___________________________________ 148

Minor constituents.________________________________________ 150

Inferred pegmatite areas______________________________________ 151

Economic aspects of pegmatite deposits, Baranof Island-___________ 151

Pegmatite deposits near Sitklan Passage, southeastern Alaska.__________ 152

Geology_______________________________________ 152

Bedded rocks____________..________________________________ 152

Folding of the bedded rocks___________________________ 154

Intrusive rocks.___________________________________________ 154

Pegmatite- ___________________________________________ 154

Basalt dikes-_-__-__-_____________-____-___--___-----_ 155

Faults______________________________________ 155

Individual prospects.______________________________________ 156

Last Chance prospect-_________________________________ 156

Hyder Mica No. 1 prospect-____________________________ 156

Zoning of the pegmatite____________---_---___-__----_------ 159

Genesis of pegmatite.__________________________________________ 159

Economic aspects of pegmatite deposits, Sitklan Island.____________ 160

Literature cited-_________________ _____________________-___-____-- 161

ILLUSTRATIONS

PLATE 19. Photograph of larger mica book from prospect on Sitklan

Island_________________________________________ Faces 158

FIGURE 16. Index map of southeastern Alaska showing location of two

pegmatite areas-.____-_____________-___--__--___-_-__- 142

17. Geologic sketch map of area near pegmatite deposits, Baranof

Island, Alaska-______________________________________ 145

18. Geologic sketches of several pegmatite deposits, Baranof

Island, Alaska_______________________________________ 149

19. Generalized geologic map of pegmatite area near Sitklan

Passage, southeastern Alaska_________________________ 153

20. Geologic sketch map of pegmatite deposits at Hyder Mica

No. 1 prospect, Sitklan Island, Alaska__________________ 157

in
IV CONTENTS

TABLES

Page 

TABLE 1. Mineralogic composition of granite at pegmatite deposit at

Redfish Bay______________._____...__... 146 

2. Mineralogic and spectrographic composition of stream concentrates, Redfish Bay, Baranof Island...__-.___._.____._ 151
MINERAL RESOURCES OF ALASKA

SOME PEGMATITE DEPOSITS IN SOUTHEASTERN

ALASKA

By C. L. SAINSBURY

ABSTRACT

A pegmatite deposit about 600 feet in diameter crops out on a high bluff less 

than half a mile east of a small unnamed cove between Redflsh and Byron Bays, 

on the west coast of Baranof Island, southeastern Alaska. The deposit, which 

comprises several pegmatite bodies, consists of quartz, albite-oligoclase, microcline, and mica, listed in the order of abundance. Feldspar and quartz crystals 

in some places attain a length of more than 1 foot. Muscovite mica as much as 

2 inches in diameter occurs, but the major part of the mica is concentrated 

in deposits, many of which are as large as 10 feet across, that contain mica 

flakes half an inch in diameter. Ruby mica of commercial grade has been 

obtained from float from this deposit.

Pegmatite bodies containing large books of mica locally are found in a belt of 

intensely feldspathized granulite and gneiss along the west margin of intrusive 

rocks of the Coast Range complex in the vicinity of Sitklan Passage near the 

mouth of the Portland Canal in southeastern Alaska. These deposits occur 

along two distinct zones in which sill-like bodies of gneissic pegmatitic rock several 

hundred feet wide can be traced along the regional strike for several miles. 

Locally, smaller dikes of pegmatite crosscut the structure of the granulite. The 

deposits consist almost entirely of albite-oligoclase feldspar, granular quartz, and 

subordinate mica. The structural characteristics of the deposits indicate that 

the pegmatite is probably in part synkinematic with the late stages of the Coast 

Range orogeny in the Ketchikan area.

Mica of commercial size and grade has been obtained from several pegmatite 

deposits in the Sitklan Passage area, and two prospect pits in a large pegmatite 

deposit on Sitklan Island have disclosed relatively large books of mica. The 

tectonic history of many of these pegmatite deposits indicates that they were 

emplaced under a stressed environment and probably do not contain mica of 

commercial size and grade, but the abundance and areal distribution of the 

pegmatite bodies are such that detailed prospecting of the area is warranted. 

Pegmatite deposits discordant with the structure of the enclosing gneiss and 

granulite are the only ones in the area thus far known to contain mica of commercial grade.

The preliminary examination of the Sitklan Passage and Baranof Island pegmatite deposits disclosed none of the rarer minerals, such as beryl, columbitetantalite, or cassiterite, that often occur in pegmatite veins. One small concentrate sample obtained by panning stream sands from the Baranof Island area 

contained a few grains of cassiterite. No radioactivity anomalies were detected 

in the stream concentrates or in any of the pegmatite in either area.

141
142 MINERAL RESOURCES OF ALASKA

INTRODUCTION

This report describes the geology of two areas in southeastern Alaska 

that contain pegmatite deposits large enough to be of economic interest. The deposits discussed in the first part of the report are near 

a small bay between Redfish and Byron Bays (fig. 17) on the west 

coast of Baranof Island, southeastern Alaska (fig. 16). The deposits 

are about 60 miles by air southeast of Sitka, the nearest established 

port. William Hanlon, Sr., and Glenn Morgan of Sitka, who own 

the pegmatite claims, called the deposits to the attention of the writer 

in 1952. These claims were staked as possible gold lodes about 1906 

by Hanlon and Edward and Thomas C. Haley of Sitka, but no exploratory work on the lodes has been done since.

1340 132° 130°

FIGURE 16. Index map of southeastern Alaska showing location of two pegmatite areas.
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 143

No reference to these deposits appears in the literature concerning 

the mineral resources of Alaska, and, according to Hanlon, the deposits 

had not been examined by a geologist before the writer's visit. This 

report briefly discusses the general geology of the deposits and of the 

adjacent area, concerning which little additional information is available at present.

The writer spent September 13-16,1953, in the general area of Redfish Bay and a part of that time at the pegmatite deposits. The deposits were revisited in August 1954 to obtain additional information 

on the internal structure of the pegmatite and to examine the west face 

of the outcrops.

The writer wishes to acknowledge the able field assistance of Glenn 

Morgan and to thank especially the pilot, Dick Pherson of Sitka, for 

transporting the party by air in unusually bad weather.

The deposits discussed in the second part of this report are in the 

vicinity of Sitklan Passage at the mouth of Portland Canal.

The field work in the area near Sitklan Passage was done May 28-31,

1953. and September 1-3, 1954. During the first examination the 

writer, accompanied by R. L. Thorne of the U. S. Bureau of Mines, 

completed a rapid ground reconnaissance of parts of Sitklan Island, 

Kanagunut Island, and the mainland north of Sitklan Passage. The 

prospects near Sitklan Passage were mapped bjy the writer at this 

time. In September 1954 the writer was accompanied by Fred Barker 

and R. S. Velikanje of the U. S. Geological Survey; the newest workings on the pegmatite deposits were examined ajid mapped, and the 

south end of Sitklan Island was examined. During the second examination B. W. W. McDougall, consulting engineer and geologist for a 

Canadian mining concern, accompanied the party on Sitklan Island. 

The geologic data and conclusions expressed in this report are based 

entirely upon the writer's observations.

At the time of field work in 1953 the prospects were being actively 

explored by a partnership consisting of Frank Blasher, Paul J. Ater, 

Louis Pearson, and J. H. O'Leary, all of Seattle or vicinity. All 

except Ater were on the property during the examination; they were 

accompanied by Robert O'Conrior of Seattle. In late 1953 or early

1954. their claims were sold to B. C. Mica Mines, Ltd., a Canadian 

company, and much additional prospecting of some pegmatite deposits 

had been accomplished by the time of the writer's visit in September 

1954. Ovela Cote, agent for the company, was on the property during 

the second examination. The writer wishes to acknowledge the assistance of all these men and to express his appreciation for the many 

favors extended by them.
144 MINERAL RESOURCES OF ALASKA

PEGMATITE DEPOSITS NEAR REDFISH BAY, 

BARANOF ISLAND

ABEAL GEOLOGY

Very few geologic data pertaining to the regional geology of the 

southern part of Baranof Island are available. Knopf (1912, pi. 1) 

shows an intrusive batholith or stock in the general area of Big Branch 

Bay, and Buddingtoti and Chapin (1929, pi. 2) also show a batholith 

that intrudes sedimentary and volcanic rocks of Paleozoic age in this 

region. Keed and Gates (1942, p. 323-324) discuss a basic nickeliferous intrusive body at Snipe Bay, about 20 miles north of Redfish 

Bay, and state:

The principal country rocks in the vicinity of Snipe Bay are biotitic quartzite 

and biotitic-quartz schist. These rocks are part of a graywacke formation, believed to be of Lower Cretaceous age, which is widespread on Chichagof and 

Baranof Islands. The graywacke formation, and the predominantly volcanic 

formations that underlie it, are cut by a variety of intrusive igneous rocks, which 

are thought to be mainly of Cretaceous but possibly in part of Tertiary age.

The quartzite and quartz-schist strike northwestward and dip northeast.

Guild and Balsley (1942, p. 174-178) discuss the geology of the 

chromite deposits at Red Bluff Bay, on the east coast of Baranof Island 

about 30 miles north of Redfish Bay. The schist of this region includes 

folded and faulted phyllite and greenstone schist of Triassic(?) age. 

The schist strikes northwestward and dips northeastward, and the 

beds are overturned. Fold axes trend about IS". 30° W. and plunge 

10°-50° SE., and a prominent set of joints cuts the rocks almost 

perpendicularly to the axes of folding. Shear zones are abundant in 

the ultramafic rocks, and follow two general directions: one striking 

about north, and the other striking northeastward.

GEOLOGY OF THE PEGMATITE-BEARING BOCKS AT REDFISH BAY

INTRUSIVE ROCKS

Quartz diorite and related types. The bedrock along the eastern 

shore of the small unnamed cove near the pegmatite deposits consists 

of a massive, unf oliated intrusive rock. The composition of the rock 

ranges from muscovite-granite through biotite-quartz monzonite to a 

biotite-quartz diorite (fig. 17) which at places contains xenoliths of 

paragneiss consisting predominantly of felsic minerals. Locally the 

gneiss comprises as much as 30-40 percent of the bedrock, but these 

areas of gneissic rocks are restricted in extent, except near the borders 

of the intrusive mass.

At the west contact of the pegmatite body, the rock is a granite of 

the mineralogic composition shown in table 1.

The intrusive rock on the north tip of the small cove northwest 

of the pegmatite deposits is a granodiorite or quartz diorite containing
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 145

Location of panned 

concentrate sample

Base compiled from aerial photographs Geology by C. L. Sainsbury, 1953-54

FIGURE 17. Geologic sketch map of area near pegmatite deposits, Baranof Island, Alaska.

abundant quartz, many zoned crystals of plagioclase, and some microcline, biotite, and muscovite. Apatite, chlorite, bleached biotite, 

garnet, sphene and an opaque mineral (magnetite or ilmenite) are 

the minor constituents.

South and southeast of the pegmatite deposits, in the area near 

the large lake at altitude 280 feet, the intrusive body is a massive 

quartz diorite containing about 20-25 percent of the mafic minerals 

biotite and hornblende, about 50 percent of plagioclase feldspar,
146 MINERAL RESOURCES OF ALASKA

TABLE 1. Mineralogic composition of granite at pegmatite deposit at Redfish Bay 

[Based on Rosiwal analysis of two thin sections]

Mineral

Quartz. ____ ___. . _ ______

Albite 1 _ _

Oligoclase L ____ _ ___-__-__.__

Mierocline

Muscovite _______ _ _ _ _ _

Chlorite __

Other 2 __

Total. ______________________________________

Volume 

percent

21.9

17.6

18.4

34.0

2. 5

4. 6

1. 1

100. 1

Weight 

percent

22.0

17.4

18.5

32.0

2.6

4.7

1.8

99.0

i The relative proportions of albite and oligoclase may differ slightly from these figures, owing to the 

albite contained in perthitic intergrowth in the microcline. 

*Includes garnet, apatite, sphene, ilmenite or magnetite.

25 percent of quartz, 1 percent of hornblende pleochroic to blue green, 

and minor accessory minerals including apatite, sphene, magnetite, 

or ilmenite, and a few needles of sillimanite. The quartz is fractured 

and strained and contains abundant trains of inclusions; the biotite 

commonly is grouped about remnants of hornblende; and the opaque 

minerals are associated with the biotite or hornblende. The zoned 

plagioclase crystals contain as much as 60 percent anorthite in the 

cores and as much as 40 percent in the rims. Apatite commonly is 

included in the calcic cores of the zoned plagioclase crystals.

The rock types listed above represent related facies of the quartz 

diorite, but it is not known whether the rock types are gradational 

or whether they are distinct intrusive bodies with sharp boundaries. 

The microscopic examination of thin sections of each rock type shows 

a distinctive progressive mineralogic change from quartz diorite to 

granite. These changes are: a progressive increase of microcline and 

albite; a progressive bleaching of biotite and a conversion of all 

biotite to muscovite or chlorite; destruction of apatite; subtraction 

of calcium from the plagioclase, leading to the destruction of zoned 

crystals and the conversion of andesine to oligoclase or albite; and 

removal of iron by the destruction of biotite, magnetite, or ilmenite, 

hornblende, and pyrite, although some iron probably was incorporated 

in the few very small red garnets.

The volume percentage of free quartz in the microcline granite is 

no greater than the volume percentage in the quartz diorite. The solutions that converted large amounts of plagioclase to microcline or 

albite apparently were in equilibrium in relation to the free quartz 

in the quartz diorite. The changes outlined indicate a magmatic
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 147

alteration, probably deuteric stage, rather than hydrothermal alteration.

Alaskite dikes. Small alasfcite dikes cut the major intrusive rocks 

and the schist and gneiss to the east. These dikes of coarse-grained 

pegmatite normally are less than 2 feet thick and locally contain muscovite flakes as much as 1 inch in diameter. The dikes appear to be 

more abundant in the quartz diorite south and southeast of the main 

pegmatite area than in the schist and gneiss east of the intrusive 

body. This may be more apparent than real because the alaskite 

dikes are light colored in contrast to the darker quartz diorite and 

gneiss. Many alaskite dikes were tested with the Geiger counter, 

but none was noticeably radioactive. The alaskite dikes are not 

favorable zones for commercially valuable mica or feldspar, unless 

dikes much thicker than those observed can be found.

Granite dike. One granite dike about 200 feet thick was observed 

where it intrudes hornblende-biotite gneiss at the head of Redfish 

Bay. In hand specimen it consists of felsic minerals, including 

much muscovite, and appears to be identical with the granite near 

the pegmatite body. The dike has sharp boundaries and it crosscuts 

the foliation of the enclosing gneiss at a small angle. This dike is 

important because it indicates that the area was invaded by a magma 

chemically similar to that which produced the granite near the 

pegmatite body.

METAMORPHIC ROCKS

Schist and paragneiss. The metamorphic rocks immediately north 

and east of Kedfish Bay (fig. 17) comprise hornblende-biotite paragneiss, quartz-mica paragneiss, quartzite, slate, and feldspathic graywacke. Paragneiss is most abundant in the small peninsula on the 

northwestern shore of Eedfish Bay. The gneiss grades abruptly to 

the east into metamorphosed sedimentary rocks whose original composition is still readily discernible. The schist strikes northwestward 

(N". 10°-50° W.) and generally dips northeastward at high angles, 

although reversals in dip are common. Fold axes in the schist and 

gneiss generally plunge southeastward from 10° to 70° but local 

variations are common.

FAULTS

The faults observed in the field are shown in figure 17 as solid lines 

and those plotted from aerial photographs, as dotted lines. In general, the faults belong to two systems: one striking northward, and 

one striking northeastward. This arrangement of faults apparently 

has controlled erosion in this part of Baranof Island because most of 

the larger bays, indentations, and lakes trend either northeastward or 

northward.

One fault, too small to be shown on the map, cuts the north boundary 

of the massive pegmatite body. The shattering of some of the larger
148 MINERAL RESOURCES OF ALASKA

clear quartz crystals in the pegmatite possibly was contemporaneous 

with the faulting.

PEGMATITE DEPOSITS

The massive pegmatite deposit about 600 feet in diameter crops out 

less than half a mile southeast of the eastern shore of the unnamed 

cove (fig. 17). It can be reached most easily from the northeast arm of 

the bay by the trail along the south bank of the small creek. The 

deposit has been glaciated, as seen from roches moutonnees and glacial 

striations preserved on the surface of the pegmatites, but only slight 

weathering has taken place. The complete lack of soil cover would 

allow easy prospecting of the pegmatite bodies.

The surface of the pegmatite slopes northward and (or) eastward. 

It is bounded on the west by a vertical cliff at least 60-75 feet high 

and on the north by a steep gulch eroded along a small fault.

STRUCTURE OP THE PEGMATITE

The outcrop suggests that the pegmatite is a large, almost circular 

body, in which pegmatite minerals are distributed at random. Exposures on the west cliff reveal, however, that the pegmatite is a compound body consisting of two or more dikelike pegmatite deposits 

striking northward and dipping eastward. The largest pegmatite is 

at least 30-40 feet thick, and several smaller bodies lie above and 

below it. It appears to pinch out near the center of the cliff, and 

another thick pegmatite having about the same attitude, but stratigraphically lower, appears to continue northward. The major peg-, 

matite bodies are underlain by quartz monzonite containing a band 

of paragneiss about 20 feet thick, and both rock types are cut by irregular patches and dikelets of granite and pegmatite. The paragneiss 

band strikes about K 30° W. and dips 25° NE.

Another pegmatite about 15 feet thick, not continuous with either 

pegmatite exposed in the west cliff, crops out in the steep bluff on the 

north side of the pegmatite area. It too strikes northward, and dips 

about30°E.

ZONING OF TH33 PEGMATITE

Each of the pegmatite deposits examined has marked zoning. In 

the large deposit the zones are distinct, but less so in the smaller ones. 

Each pegmatite contains a core of quartz or of quartz and microcline. 

Succeeding zones differ in different pegmatite bodies (fig. 18). The 

quartz core may be succeeded by a core-margin zone of perthite, 

quartz, graphic granite, and granular mica; of pure microclineperthite; or of perthite, granular mica, and quartz. Succeeding zones 

are not easily recognized, but the wall zone generally is quartz and 

graphic granite. No distinct border zone was recognized in any 

deposit.
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 149

A. SKETCH OF PEGMATITE DEPOSITS EXPOSED ON WEST CLIFF FACE

EXPLANATION

Altered monzonite

B. SKETCH OF PEGMATITE EXPOSURE ON CREEK

Pert te and quartz

Complex mixture of quartz veins, 

perthite, muscovite, and graphic 

granite in a poorly defined zone

Contact 

Dashed where approximate or inferred

' Geology by C.- L Samsbury, 1954 C. SKETCH OF MICA-RICH PEGMATITE 

FIGURE 18. Geologic sketches of several pegmatite deposits, Baranof Island, Alaska.

The mineral of chief economic interest in the pegmatite is microclineperthite, occurring in each of the larger pegmatite veins as a coremargin zone ranging from 4 feet to 10 feet in thickness (fig. ISA, B). 

In two of the larger pegmatite veins the perthite is almost pure, and 

in one it is admixed with minor amounts of granular mica and small 

pods of quartz. The most continuous zone of perthite is at least 120 

feet long and averages from 6 to 8 feet in thickness (fig. ISA). 

Another zone of perthite containing only minor amounts of quartz 

and granular mica is at least 60 feet long and 8 to 10 feet thick. In 

a third deposit of pegmatite exposed across the strike, the pure 

microcline-perthite forms a solid zone ranging from. 4 to 6 feet in 

thickness (fig. 185).

Petrographic studies indicate that albite occurs along twin planes 

and cleavages in the perthitic microcline in such thin bands that 

coarse grinding in the mortar frees only a few fragments of albite. 

Thin sections show that the albite is segregated along cleavages, 

fractures, and twin planes in the microcline, and may aggregate as 

much as 15 percent of the total volume. N"o chemical analysis of the 

microcline was made, but the writer believes that the massive perthite 

zones can produce substantial tonnages of ceramic-grade potash 

feldspar.

406162 57 2
150 MINERAL RESOURCES OP ALASKA

Two varieties of mica occur. In one small pegmatite deposit 

(fig. 186") "rum mica" occurs as wedge-shaped books as much as 

2 inches long. These books are intergrown in such a manner as to 

suggest the three common faces of a tetrahedron. This mica occupies 

a distinct zone, possibly a core-margin zone, around a core of quartz 

and perthite. In mica-bearing zones of other pegmatite deposits, 

the mica generally occurs as thin, rounded green flakes as much as 

half an inch in diameter, and locally it may aggregate 50 percent 

of the rock in a zone of several feet across. No mica deposit of sufficient 

size to furnish even the smallest "punch mica" was observed, although 

Hanlon obtained strategic mica from float in this area that trimmed 

to sheets 3 inches by 4 inches.

Large euhedral quartz crystals were observed at several places 

in the pegmatite. They usually were oriented with the c axis perpendicular to the dip of the deposit. The largest crystal measures 

27 inches in length and is found in the quartz core of the pegmatite 

exposed on the west cliff. Other crystals as much as 5 inches in diameter were observed. These crystals of quartz are remarkably clear. 

All this clear quartz is shattered, but fragments as much as threeeighths inch thick may be found that are so clear that typewritten 

words may easily be read through them. Some quartz of optical 

grade might be obtained during exploitation of the deposits for 

feldspar.

MINOR CONSTITUENTS

The only minor constituent of the pegmatite deposits that can be 

identified in hand specimen is red garnet. It usually occurs in the 

quartz zones as small euhedral crystals that attain a maximum size 

of one-eighth inch.

Small amounts of heavy-mineral concentrates were obtained from 

three areas: a stream that heads in the pegmatite area, a stream that 

drains an area of quartz-monzonite, and the outlet of the large lake 

southeast of the pegmatite deposits. The mineralogic and spectrographic composition of these concentrates is summarized in table 2.

Although these concentrates were obtained in relatively small 

amounts without digging deeply into the stream channels, the writer 

believes that the results are diagnostic enough to indicate that few 

of the minor constituents of pegmatite veins, such as beryl, columbitetantalite, or cassiterite, occur in detectable quantities in the major pegmatite body. The samples containing tourmaline and the grains 

provisionally determined as cassiterite were from the areas of granite 

or altered quartz diorite relatively near the main pegmatite body. No 

radioactivity anomalies were detected in any of the samples.
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 151

TABLE 2. Mineralogic and spectrographic composition of stream concentrates, 

Redfish B'ay, Baranof Island

[Analyst, J. J. Matzko]

Sample No.i

1

2

3

Mineralogic composition

Garnet, hornblende,

quartz, tourmaline,

zircon, muscovite

epidote, sphene, magnetite, cassiterite(?).

Garnet, hornblende,

quartz, ilmenite(?),

tourmaline, zircon,

hematite.

Garnet (limonite-stained) ,

hornblende, quartz,

biotite, ilmenite.

Spectrographic composition

Greater than 

5 percent

Fe, Al, Ti,

Mn

Fe, Al, Ti,

Mg, Na

Fe, Al, Mg,

Mn, Ca

Less than 

5 percent

Na, Mg

Mn, Ca

Na, Ti

Not detected

Sn, Pb, Cu,

Zn, Ni, Go,

F .

Sn, Pb, Cu,

Zn, Ni, Co

Sn, Pb, Cu,

Zn

> Samples (locations shown on fig. 17):

1. From a small creek that drains the pegmatite area.

2. From a small stream flowing into north arm of cove.

3. From outlet of large lake southeast of pegmatite zone.

INFERRED PEGMATITE AREAS

Two other areas that possibly contain pegmatite were selected from 

aerial photographs and are shown in figure 17.

Several large pegmatite (?) dikes were seen from the air along the 

beach cliffs between Redfish Bay and Byron Bay. This area was not 

traversed on foot by the writer, and the size, extent, and mineralogy 

of these dikes are unknown. The writer recommends detailed prospecting throughout the outcrop area of the quartz-diorite stock and 

the schist and gneiss zones.

ECONOMIC ASPECTS OF PEGMATITE DEPOSITS, BARANOF ISLAND

The following factors indicate that the major pegmatite deposits 

of Baranof Island constitute a commercially valuable body of feldspar, 

and possibly of mica and optical quartz:

1. Large tonnages of pegmatite are available and could be mined 

by open-pit methods, or perthite zones could be mined by shallow 

underground openings in an easterly direction, sloping at about 

25°-30°.

2. The principal deposit is less than half a mile from tidewater in 

a relatively sheltered cove, the entrance of which is protected by several 

small, rocky islands. An aerial tram could be built at low cost, and 

loading facilities for large barges could easily be constructed, although
152 MINERAL RESOURCES OF ALASKA

in stormy weather the exposed coastline of Baranof Island is battered 

by large waves and entrance to the small cove is impossible.

3. The deposit is near the regularly traveled sealanes, permitting 

shipment to markets in the United States at low freight rates.

4. Abundant timber is available on the wooded slopes of the cove 

for mine and mill use.

5. The deposits, although probably containing few of the rarer and 

more valuable minerals that often occur in pegmatite deposits, are 

free from deleterious constituents, such as iron, high calcic plagioclase, 

and manganese. The mica could easily be tabled or floated from a 

ground millfeed.

PEGMATITE DEPOSITS NEAR SITKL.AN PASSAGE, 

SOUTHEASTERN ALASKA

GEOLOGY 

BEDDED ROCKS

The bedded rocks of Sitklan Island, Kanagunut Island, and the 

adjacent mainland to the north comprise high-rank metamorphic 

rocks, provisionally of Mesozoic and Paleozoic age or older, derived 

from a sequence of predominantly clastic beds possibly of marine 

origin. This origin is favored because of the thin, continuous units, 

the lack of conglomerate beds, and the few thin but persistent limestone 

beds in the sequence.

The beds have been tilted steeply eastward and regionally metamorphosed to garnet-biotite-hornblende-quartz-plagioclase granulite. 

Ked garnet as much as 1 inch across is conspicuous in a wide belt of 

garnetiferous schist and granulite on the western part of Kanagunut 

Island and Port Tongass (fig. 19). The garnets commonly are 

euhedral, but fractured.

A smaller dark-red to black garnet is associated with the red garnet. 

These garnet beds are estimated to contain as much as 30-40 percent 

garnet locally. The garnet sands along the west coast of Kanagunut 

Island are beach placers derived from the schist. Thin, persistent 

beds of coarsely crystalline and pure limestone or marble occur in 

the garnet granulite on Kanagunut Island, and a few beds of quartzite 

are found opposite Tongass Island.

To the east, and overlying the garnet granulite, is a belt of hornblende-biotite-garnet granulite in which green hornblende is much 

more conspicuous and garnet is much smaller and less conspicuous 

than in the underlying rocks. This belt appears to be generally less 

schistose than the underlying rocks.

The hornblende-biotite-garnet granulite grades eastward into a belt 

of rocks that was mapped as a "zone of feldspathization" because it 

appears to be a greatly f eldspathized f acies of granulite and paragneiss
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 153

containing rocks that originally were similar to 

blende-biotite-garnet granulite. In places, the 

intense that a coarse-grained rock consisting of 

is produced. This rock is so similar in minera

the underlying hornfe Idspathization is so 

quartz and feldspar 

to the pegmatite

EXPLANATION 

Hornblende or pyn

Observed pegma

Pegmatite

Inferred from aeria.

Contact 

Dashed where approxtm,

Fault 

Inferred from aerial photographs

Strike and dip of beds

x 

Mica prospect

Base from aerial photograph Geology by C. l_ Sainsbury, 1953-54

FIGDRB 19. Generalized geologic map of pegmatite area near Sitklan Passage, southeastern Alaska.
154 MINERAL RESOURCES OF ALASKA

veins that it has been called "pegmatite" by some of those people interested in the mica prospects. In this report, rock of this type is called 

"pegmatitic rock." At places the pegmatitic rock grades into coarsergrained bodies of quartz, feldspar, and mica that retain features suggesting relict bedding. These coarser-grained bodies are referred to 

in this report as replacement pegmatite bodies. The feldspathization 

is probably caused in part by higher-rank metamorphism that locally 

produced a gneissic texture and in part by the introduction of soda 

feldspar. Without exception, the true pegmatite bodies are confined 

to this belt of feldspathized rocks. The claims staked on Sitklan Island, on the mainland north of Sitklan Island, and on Nakat Bay are 

in this zone of pegmatite-bearing, feldspathized rock. This is important in considering the genesis of the pegmatite bodies. The feldpathized rocks locally contain recrystallized limestone beds as much 

as 20 feet thick.

Many pegmatite bodies that apparently represent replaced gneiss 

or schist were observed. Such deposits show relict planar structures 

of the same thickness as the contacting granulite or gneiss, are concordant, and consist of albite or albite-oligoclase intergrown with 

granular vitreous quartz and minor amounts of muscovite mica in 

small flakes. These deposits are well exposed on the northern shore of 

Sitklan Passage and on the southeastern part of Sitklan Island.

Coarser grained, poorly foliated pegmatite bodies of similar mineralogy that contain muscovite flakes as large as V/2 inches in diameter 

possibly are the next stage in the formation of replacement pegmatite. 

Such deposits are common, and they too are roughly concordant with 

the contacting schist, gneiss, or granulite. None of these pegmatite 

bodies was proved to be formed by replacement, however,-and the proof 

of their origin must await additional detailed mapping.

FOLDING OF THE BEDDED ROCKS

No major folds were seen in the metamorphic rocks, although the 

strike of the beds ranges from N. 5° W. to N. 60° W. An abrupt change 

in strike from N. 30° W. to N. 5° W. was probably caused by the 

eastward-trending fault on the east side of Sitklan Island. Drag folds 

are abundant in the limestone and commonly plunge steeply down 

the dip of the beds.

INTRUSIVE BOCKS

PEGMATITE

Intrusive pegmatite bodies as much as 30-40 feet thick, and from 

a few to several hundred feet long, occur in two distinct belts in the 

zone of feldspathization on Sitklan Island and on the mainland to the 

north (fig. 19). An aerial reconnaissance showed that pegmatitic rocks 

west of Nakat Harbor were a continuation of one or more of these 

belts. Exposures in the mountains north of Sitklan Passage show
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 155

two distinct zones of pegmatitic rocks that possibly are continuations 

of those exposed on Sitklan Passage and Sitklan Island.

Discordant pegmatite bodies within the pegmatitic rock are composed essentially of pearly-white albite or oligoclase intergrown with 

vitreous massive or granular quartz. Locally, muscovite mica forms 

books that reach a maximum diameter of 8 inches, but most of the 

pegmatite contains little or no mica. Minor amounts of biotite, 

chlorite, and muddy-green epidote crystals, attaining a maximum 

length of several inches, occur in some of the pegmatite deposits. 

These crystals have reaction rims composed of muscovite, chlorite, 

and a little magnetite. A rusty fracture in one sample of pegmatite 

contained specks of free gold.

The pegmatite veins classed as intrusive are generally discordant; 

they tend, however, to be elongate in the direction of the foliation of 

the enclosing rocks. No zoning was observed in any of the pegmatite 

veins. Twenty samples of feldspar selected at random from the pegmatite veins were examined in the laboratory by crushing and immersion 

in oil. In 19 samples the indices of refraction were bracketed by oils 

of index 1.53 to 1.545, indicating that all the feldspar was albiteoligoclase. Each sample contained intergrown glassy quartz. One 

sample consisted of microcline. None of the rarer minerals commonly 

associated with pegmatite was found, and no anomalous radioactivity 

was detected by the Geiger counter.

BASALT DIKES

Basalt dikes intrude the metamorphic rocks and the pegmatite 

bodies. They were injected generally along the well-defined joint 

system, which strikes about N. 30°-50° E. The basalt dikes have 

chilled borders and the enclosing rocks are altered. In one exposure 

basalt dikelets filled fractures in a large pegmatite body. The flow 

lineation and displaced pegmatite xenoliths in this dike indicate that

magma had perhaps flowed from

dikes have phenocrysts of plagioclaso feldspar 1 centimeter long, and

one dike contains smaller phenocryste

magnetite, and pyrrhotite are common accessory minerals. The dikes

are not metamorphosed or deformed,

took place after regional deformation. The relationship also indicates that the pegmatite bodies are o

FAULTS

The dotted lines in figure 19 designate 

photographs. Only one major fault 

faults occur near the pegmatite deposits 

prospect on Sitklan Island. Pyrite 

into the enclosing rocks along the faults, 

pegmatite and massive hornblendite

st to east. Some of the basalt

of basaltic hornblende. Pyrite,

indicating that igneous activity

der than the basalt dikes.

faults inferred from aerial 

was seen in the field. Small 

at the Hyder Mica No. 1 

and pyrrhotite were introduced 

One fault contact of the 

or hornblende-granulite was
156 MINERAL RESOURCES OF ALASKA

observed, indicating that some faulting occurred after the emplacement of the pegmatite rock. It is not known whether the basalt dikes 

are faulted.

INDIVIDUAL PBOSPKCTS

In this report, the term "prospect" applies only to mica-bearing 

pegmatite bodies that have been explored by trenching or drilling and 

that show mica books of commercial size.

LAST CHANCE PROSPECT

The Last Chance prospect is on the mainland about 1,500 feet from 

the beach camp in a north-northwesterly direction (fig. 19). It consists of a small trench about 4 feet long on a pegmatite deposit about 

2-3 feet thick. The pegmatite contains silvery mica in thin books as 

much as l1/^ inches in diameter that surround albite crystals. The 

mica books have a crude foliation, and their resemblance to many 

similar exposures elsewhere leads the writer to conclude that the mica 

deposit is not of commercial grade or is not large enough to yield any 

but the smallest of punch mica. The estimated mica content of the 

pegmatite is less than 10 percent; the mica is distributed at random, 

and the pegmatite is so thin that it probably could not be mined economically. The enclosing country rock is a quartz-biotite paragneiss.

A Territorial Department of Mines engineer collected a powder 

box of commercial-grade mica from a pegmatite body in this area, but 

the collection has not been duplicated since and the location of the 

pegmatite is unknown.

HYDER MICA NO. 1 PROSPECT

Hyder Mica No. 1 prospect is on the northeast corner of Sitklan 

Island about 300 feet from the beach at an altitude of about 140 feet 

(fig. 20). Opencuts 30-40 feet long were made on two massive pegmatite bodies that intrude unfoliated hornblende rock. Four of the 

five larger trenches expose pegmatite containing mica plates as much 

as 8 inches across (pi. 19). Small pits on other outcrops of pegmatite 

disclose no mica.

Broken and bent books of mica predominate over those from which 

sheets could be cut, although Frank Blasher has cut many perfect 

sheets measuring 3 by 4^ inches from some of the better books. Most 

of the deformed books are ruled. In many places an intersecting 

cleavage forms "J." mica. The mica is dark grayish green to muddy 

green, and some samples from this prospect submitted by the Territorial Department of Mines and by Blasher to the General Services 

Administration were classed as "strategic grade muscovite mica." 

Other samples of the mica tested partly by the General Services Administration, by the Varlacoid Chemical Co. of New York, and by 

Associated Laboratories of Portland, Oreg., have been described, 

respectively, as "surface samples not suitable for grading," "mine-run
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 157

EXPLANATION

Hornblendite or hornblende-granulite 

Inferred where questioned

Sho

Open pit on pegmatite 

Containing mica where indicated

Geology and topography by 

C. L. Sainsbury, 1953-54 

ZOO Feet

_____I

Contour interval 25 feet 

Datum is approximately mean high tide

FIGDEE 20. Geologic sketch map of pegmatite deposits at Hyder Mica No. 1 prospect,

Sitklau Island, Alaska.

ruby muscovite mica," and "muscovite mica, non-ruby, stained A 

quality, A. S. T. M. size grade 6y2 and 6, heating loss 0.17 percent." 

All the characteristics of the mica from this deposit have not been 

determined.

Other pegmatite bodies crop out in the area near the prospect pits. 

Many outcrops were examined, and a few smaller mica books were 

found, but the mica content is generally very small. In some, the 

alinement of the mica books makes a foliated pegmatite. The pegmatite bodies are similar to those exposed on the beach and consist of 

albite or albite-oligoclase and quartz, including minor muscovite and 

epidote, except near contacts where some pegmatite contained horn-
158 MINERAL RESOURCES OF ALASKA

blende xenoliths altered to biotite. J. C. Roehm * of the Territorial 

Department of Mines ascribed the formation and localization of mica 

to amphibolite-pegmatite contacts where amphibolite had been ingested. For the following reasons this genesis is not accepted by the 

writer who examined the contacts in detail: mica was not observed 

near any of the contacts, nor was it found abundant near any of the 

hornblende xenoliths; a chemical reaction between iron-bearing hornblende and pegmatite to produce iron-free muscovite mica, without 

evidence of associated alteration minerals, would seem improbable; and 

mica occurs sporadically in many of the pegmatite veins with apparently no close relationship to hornblende rock-pegmatite contacts.

It seems most likely that the mica is merely a local concentration, 

common in all mica-bearing pegmatite deposits.

Prospect pits that expose pegmatite have been dug at scattered 

points in a line striking southwestward from the larger trenches. The 

present owners of the property believe these pits are on one continuous 

pegmatite body several thousand feet long striking southwestward 

(Ovela Cote, oral communication). The writer found many outcrops 

of hornblende rock and hornblende granulite in the creek bed that 

parallels the line of pits, and concludes that the pits were located upon 

outcrops of many pegmatite bodies rather than a continuous one. The 

dense cover of timber, brush, and rotting vegetation prohibits the 

tracing of contacts, and care is urged in extrapolating individual pegmatite bodies without close bedrock control. Mica reserves in such 

pegmatite deposits should not be computed until sufficient trenching 

has been done to give reliable data.

Two fault zones, both of which strike northeastward and are hydrothermally altered, were mapped near the open pits. Pyrite was introduced into the wall rocks near the faults, and some of the massive 

hornblende rock was altered to biotite or vermiculite. Hydrothermal 

solutions from one of these faults or from the pegmatite probably 

formed the biotite or vermiculite in the hornblende rock on the f ootwall 

of the pegmatite body exposed near the northwestern opencut. One 

probable fault contact between pegmatite and hornblende rock was 

observed near the intersection of the faults (fig. 20).

The massive hornblende rock could be a f acies of the normal hornblende granulite recrystallized under the influence of heat from the 

pegmatite deposits, and not an altered intrusive body, for the following reasons: the contacts of the pegmatite and the hornblende rock 

at many places strike and dip parallel or almost parallel to the regional 

bedding, thus maintaining the sill-like attitude of the pegmatite; 

gradations from the massive rock showing decussate structure into 

a foliated hornblende-garnet granulite were observed; and a similar

1 Roehm, J. C., Preliminary report of investigations and itinerary of J. C. Roehm in the 

Ketchikan and Hyder mining precincts July 14 to August 18, 1945. Manuscript report in 

flies of Territorial Department of Mines.
GEOLOGICAL STJKVEY BULLETIN 1024 PLATE 19

PHOTOGRAPH OF LARGER MICA BOOK FROM PROSPECT ON SITK LAN ISLAND. SILVER DOLLAR

INDICATES SCALE

SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 159

massive hornblende rock at one other locality was found to be a contact 

phase between hornblende-garnet granulite and pegmatite.

A small outcrop of pyroxenite on the northern shore of Sitklan 

Passage clearly has an intrusive form, thus confirming the occurrence 

of ultrabasic intrusive rocks in the area. Possibly the hornblende rock 

observed near the main prospects is a facies of the pyroxenite, but 

determination of the origin must await further field mapping.

ZONING OF THE PEGMATITE

No zoned pegmatite bodies were found in the area examined. 

Because of the economic implications, special attention was given to 

this matter during the second field examination. Although none of 

the pegmatite bodies is completely exposed, enough exposures were 

examined to establish firmly the fact that the deposits generally are 

not zoned. If the pegmatite bodies are zoned, the mineralogic and 

physical variations between zones are so slight as to be undetectable 

in the field. The mica exposed in the prospect pits bears no relation 

to its position in the pegmatite, and the pegmatite does not vary 

perceptibly in composition.

The feldspar of the pegmatite deposits is almost entirely albiteoligoclase, with only minor amounts of microcline. Granular, vitreous 

quartz is intergrown with all feldspar observed, and no concentrations 

of quartz were found that indicated quartz cores. The texture may 

vary among pegmatite deposits and within the same ore; such variations, however, are not consistent and are not accompanied by 

mineralogic changes.

GENESIS OP PEGMATITE

Pertinent observations regarding the genesis of the pegmatite 

deposits are summarized below.

1. The deposits are generally sill-like bodies lying in the plane 

of the bedding of metamorpliic granulite along a zone of f eldspathization. No pegmatite deposits were seen outside of this zone. Some 

have crosscutting contacts and some have gradational contacts, but 

their long axes are always parallel or subparallel to the regional strike 

of the rocks.

2. The deposits altered some of the host rock.

3. The deposits contain only quartz, feldspar, epidote, and mica 

associated with muscovite in composition.

4. In many places the flakes of muscovite create a foliation almost 

parallel to that of the enclosing rocks. The mica is bent around 

augenlike albite crystals.

5. The quartz of the pegmatite is broken and fractured to such 

an extent that it breaks down into a mass of fine grains upon 

weathering.
160 MINERAL RESOURCES OF ALASKA

6. The pegmatite is intruded by basalt dikes injected in a northeasterly direction along a well-defined joint system.

7. Most of the larger mica observed was cleaved and ruled. Some 

fairly large unruled sheets can be obtained although they are a very 

small part of the total mica observed at any of the pits. Some mica 

of commercial size and grade can be obtained.

The above observations suggest that the pegmatite was intruded as 

heated bodies of soda-rich fluids into the enclosing rocks during the 

late stages of the Coast Range orogeny. The pegmatite bodies probably were derived, in part at least, from syngenetic fluids created 

from the rocks in the zone of feldspathization under the influence of 

the heat of regional metamorphism at depths well below the present 

position of the pegmatite. No genetic relationship to the exposed 

intrusive rocks of granitoid composition can be shown.

The pegmatite bodies were injected before the formation of the 

strong northeastward-trending joints when the bedding or foliation 

of the granulite was the easiest channel of entrance. Widespread 

feldspathization probably was contemporaneous with the formation 

of the pegmatite deposits so that some gradational contacts resulted.

The foliation of the pegmatite and the granulation of the quartz 

indicate that the pegmatite bodies were subjected to some dynamic 

metamorphism after their formation. No evidence has been found of 

deformation after the injection of the basalt dikes and the later 

faulting.

ECONOMIC ASPECTS OF PEGMATITE DEPOSITS, SITKLAN ISLAND

From the preliminary field work it is concluded that pegmatite 

bodies and intensely feldspathized metamorphic rocks are common 

throughout a zone at least 1 mile wide that occupies the east part of 

Sitklan Island and continues northward on the mainland for several 

miles. The pegmatite deposits locally contain mica books of commercial size and grade, but the events of the tectonic history of the 

rocks caused many pegmatite bodies to be crushed or become foliated. 

The writer does not believe the geologic environment favors the occurrence of the large, slowly cooled, unstressed pegmatite bodies that 

are the usual hosts of minable deposits of commercial-grade mica. 

Not enough prospecting has been done to determine the content of 

minor constituents of the pegmatite bodies.

The pegmatite consists predominantly of albite or albite-oligoclase 

and quartz in fine intergrowths. Although a large tonnage of material 

is available, the separation of quartz and feldspar would require special 

beneficiation and the resulting feldspar would not be usable in the 

many industries that consume potassic feldspar. The deposits are 

located near tidewater on or near regular sealanes so that transportation to market would be relatively cheap.
SOME PEGMATITE DEPOSITS IN SOUTHEASTERN ALASKA 161

Additional field work is recommended, especially on Sitklan Island 

where the larger, discordant pegmatite deposits appear to be more 

abundant. Prospecting to the north among the f eldspathic and pegmatitic rocks in the zone of f eldspathization should be directed toward 

outlining unfoliated, mica-bearing pegmatite bodies. A few surface 

trenches should show the type, grade, and amount of mica present.

The pegmatite deposits in which mica is oriented so as to give a 

crude foliation are not considered to be a favorable host rock for mica 

of commercial size and grade and do not warrant extensive exploration.

.Some prospecting for economic deposits of vermiculite is recommended along the contacts between pegmatite and hornblendite or 

pyroxenite.

LITERATURE CITED

Buddington, A. F., and Chapin, Theodore, 1929, Geology and mineral deposits

of southeastern Alaska: U. S. Geol. Survey Bull. 800. 

Guild, P. W., and Balsley, J. R., Jr., 1942, Chromite deposits of Red Bluff Bay

and vicinity, Baranof Island, Alaska: U. S. Geol. Survey Bull. 936-G. 

Knopf, Adolf, 1912, The Sitka mining district, Alaska: U. S. Geol. Survey Bull.

504. 

Reed, J. C., and Gates, G. O., 1942, Nickel-copper deposits at Snipe Bay, Baranof

Island, Alaska: U. S. Geol. Survey Bull. 936-M.

O