UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 936-G

CHROMITE DEPOSITS OF RED BLUFF BAY 

AND VICINITY, BARANOF ISLAND, ALASKA

BY

PHILIP W. GUILD AND JAMES R. BALSLEY, JR.

Strategic Minerals Investigations, 1942 

(Pages 171-187)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1942

For sale by the Superintendent of Documents, Washington, D. C. ....... Price 20 cents

CONTENTS

Page

Abstract................................................. 171

Introduction............................................. 171

Geology.................................................. 174

Metamorphic rocks.................................... 174

Igneous rocks........................................ 175

Ultramaf ic rocks.................................. 175

Dunlte....................................... 175

Pyroxenlte................................... 176

Other Igneous rocks.............................. 176

Structure............................................ 177

Chromite deposits........................................ 178

Mineralogy........................................... 179

Localization and origin of ore bodies................ 179

Ore bodies........................................... 180

No. 1.........................;.................. 181

No. 2............................................ 182

No. 3............................................ 182

No. 4............................................ 183

No. 5............................................ 184

No. 6............................................ 184

No. 7............................................ 184

No. 8............................................. 185

Reserves............................................. 185

ILLUSTRATIONS

Page

Plate 21. Geologic reconnaissance map of central Baranof

Island, southeastern Alaska................. 174

22. Geologic map of the Red Bluff Bay area,

Baranof Island, southeastern Alaska......... 178

Figure 15. Index map of southeastern Alaska showing location of the Red Bluff Bay area.............. 172

16. Geologic sketch map of deposit No. 2.......... 183

III

CHROMITE DEPOSITS OF RED BLUFF BAY AND VICINITY, 

BARANOF ISLAND, ALASKA

By Philip W. Guild and James R. Balsley, Jr.

ABSTRACT

Small deposits of chromite occur in serpentinized xiltramafic 

intrusive masses on Baranof Island, southeastern Alaska. The 

body of greatest importance as a possible source of chromite is 

at Red Bluff Bay, on the east coast of the island; seven others 

are known about 10 miles west-northwest, in the rugged interior. 

The ultramafic rocks are dunite and pyroxenite, largely altered 

to serpentine or talc. They are intruded into phyllite and 

greenstone schist of Triassic (?) age, and are cut by dikes that 

are probably related to the Coast Range batholith.

The ore deposits are lenticular concentrations of chromite 

((Mg,Fe)(Cr,Fe,Al)204), a norjnal accessory mineral of dunite. 

The chromite differs widely in composition in different deposits, 

or even in the same deposit, but in general it has a low ratio 

of chromium to iron, an undesirable feature in chromite ores.

Eight deposits at Red Bluff Bay are known, of which five 

contain ore of shipping grade and three contain material that 

may be of concentrating grade; but the estimated reserves amount 

to only 570 tons of ore containing 40 percent or more of chromic 

oxide (Cr203 ), and about 29,000 tons of low-grade material averaging 12 percent of chromic oxide. No deposits of economic 

importance are known to occur in the interior of the island.

INTRODUCTION

Chromite is present in a number of ultramafic Intrusive 

bodies on Baranof Island, southeastern Alaska, in latitude 

57° N., longitude 135° W. (fig. 15). Baranof Island is very 

rugged, with a relief of nearly 5,000 feet, and it bears abundant evidence of glacial action, such as U-shaped valleys, 

cirques, and deep gouges in rock surfaces, but only a few small 

glaciers remain at present.

Some of the ultramafic masses are high in the mountains in 

the central part of the island, but the one that offers the

171
172 STRATEGIC MINERALS INVESTIGATIONS, 1942

most hope as a source of chromite is at Red Bluff Bay, a deep 

fiord opening into Chatham Strait near the middle of the east 

coast of the-island. Red Bluff Bay takes its name from the bare,

Figure 15. Index map of southeastern Alaska showing location of the Red

Bluff Bay area.

reddish-brown, weathered surface of the ultramafic rocks.

Chromite-bearing rocks underlie an area of l£ square miles on a

long ridge north and east of the bay, and some crop out on
CHROMITE DEPOSITS, BARANOF ISLAND, ALASKA 173

several small islands In the mouth of the bay. Steep slopes 

rise from the shore to the crest of the ridge, which ranges in 

altitude from 500 to 1,200 feet.

A cannery in the bay burned down about 1935, and since that 

time there has been no Industrial activity in the area. The 

nearest settlement is Baranof, at Warm Springs Bay, 18 miles 

north. Red Bluff Bay is only 26 miles from Sitka, but as it 

lies across the Island from Sitka it can be reached from there 

only by plane or by boat, which must go some 100 miles around 

the island. A mail boat from Petersburg calls at Baranof once a 

week. The only practicable method of reaching the area is by 

chartering a plane or boat from Juneau, 140 miles north, from 

Petersburg, 80 miles east, or from Sitka.

At sea level, the climate is relatively mild, but the rainfall is probably between 100 and 200 inches a year. Over the 

higher parts of the island the snowfall is usually very heavy.

Chromite was recognized at Red Bluff Bay by Ray Race about 

1933. Twenty-eight claims, covering nearly the entire area of 

outcrop of the chromlte-bearing rocks, were then staked, but 

within a few years they were allowed to lapse, and no mining on 

them was ever attempted. About 1935, chromite was found in the 

serpentine masses in the central part of the Island by Joe Hill, 

and a number of claims were staked, but these also have been 

abandoned.

The Red Bluff Bay area was examined briefly for the Geological Survey by John C. Reed and others in 1939. During the summer of 1941 the writers, with R. E. L. Rutledge, mapped this 

area on a scale of 1:12,000 (see pi. 22), and examined the serpentine masses In the interior during the course of reconnaissance trips into the surrounding region (pi. 21).

The writers wish to express their appreciation to John C. 

Reed for his guidance both in the field and in the office, and 

also to George 0. Gates for his>many valuable suggestions.
174 STRATEGIC MINERALS INVESTIGATIONS, 1942

*:

GEOLOGY

The chromite of Baranof Island is present as small lenses, 

thin layers, and disseminated grains in ultramafic rocks, which 

intrude a sequence of phyllites and greenstone schists of Triassic (?) age. There is some evidence that the intrusion took 

place during the last stages of the deformation that metamorphosed the sediments. The most accessible and best known of the 

intrusive masses is at Red Bluff Bay. Seven others are known in 

the central part of the island, about 10 miles west-northwest of 

Red Bluff Bay, and there may well be more that have not been 

seen. The masses in the interior appear to be sills, but that 

at Red Bluff Bay, which is less well exposed, is more complex. 

Younger dikes cut both the metamorphic and the ultramafic rocks.

Metamorphic rocks

The invaded rocks comprise a thick sequence of phyllites 

and greenstone schists which have been tentatively correlated 

with rocks of similar appearance in the Chichagof district, 

Ghichagof Island, about 80 miles northwest of Red Bluff Bay. 

These rocks are regarded by Reed and Coats ^/as Upper Trlassic (?).

The rocks here designated phyllite were formed by the 

metamorphism of fine-grained detrital material. The phyllite 

includes dark, very fine grained graphitic shale, with or without megascopic biotite flakes; fine-grained quartz-biotite 

schist; thinly laminated siliceous rocks grading into chert; 

and some limestone in lenses a few feet thick. Interbedded and 

intermixed with these rocks are green chlorlte schists, probably derived from volcanic ash which was deposited in water contemporaneously with the associated detrital material. Some of

I/ Reed, J. C., and Coats, R. R., Geology and ore deposits of the 

Chichegof mining district, Alaska: U. S. Geol. Survey Bull. 929, pp. E4-30, 

1942.
GEOLOGICAL SURVEY 

20 135

BULLETIN 936 PLATE 21 | 3 4°40'

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20' 135° I34"4-0'

GEOLOGIC RECONNAISSANCE MAP OF CENTRAL BARANOF ISLAND, SOUTHEASTERN ALASKA

c o isMiles

j
CHROHITE DEPOSITS, BARANOP ISLAND, ALASKA 175

the green schist .is extremely fine grained, but it grades into 

coarser-grained rocks in which plagloclase and occasionally biotite or hornblende can easily be seen. The coarse-grained rock, 

mapped as amphlbolite, is believed to have been recrystallized 

by contact action of the diorite batholiths of the vicinity.

The greenstone schist and phyllite sequence is overlain on 

the west by graywacke, believed to be identical with the graywacke of probable Lower Cretaceous age which occupies the same 

stratigraphic position in the Chichagof district.=/

Igneous rocks 

Ultramafic rocks

Ultramaflc intrusive rocks are rich in magnesia and iron and 

deficient in alkalies and silica; their characteristic minerals 

are olivine and pyroxene, and they commonly carry chromite as an 

accessory mineral. The ultramafic rocks at Red Bluff Bay are 

predominantly dunite, which is rich in olivine., and pyroxenite, 

which is rich in pyroxene. In places these two materials are 

finely interlayered and form a rock that has the bulk composition of a peridotite, composed of both olivine and pyroxene.

Dunite. The fresh dunite is hard and granular, with a gray, 

glassy appearance on unweathered surfaces. Accessory chromite 

grains, many with crystal faces, are commonly present. Optical 

tests indicate that the olivine ((Mg,Fe)2Si04) has an Mg:Fe 

ratio of about 95:5. The dunite at Red Bluff Bay, except in a 

small area near the center of the mass, has been more or less 

altered to serpentine,- a rock in which the olivine has been 

replaced by antigorite (H4Mg3Si209 ). The serpentine is a compact, tough rock, dark green on fresh surfaces but weathering to 

the characteristic reddish-brown color. It also contains

2/ Reed, J. C., and Coats, R. R., op. cit., pp. 30-35. 

471316 O- 42-2
176 STRATEGIC MINERALS INVESTIGATIONS, 1942

varying proportions of ankerite (Ca(Mg,Fe)(CO,) 0 ), with magne-

<J Ct

slum present in larger amounts than iron.

Masses of schistose talc (HgMg-Si^O..^) have been developed 

by the alteration of serpentine, and perhaps also directly from 

the original silicates, ollvine and pyroxene. Many of the talc 

masses lie along shear zones, but a few, of irregular shape, are 

not related to any known faults. Serpentine, ankerite, and talc 

are found here and there in narrow veins as well as in the 

altered rock.

Pyroxenite. The fresh pyroxenite is composed of a green 

monoclinic pyroxene of the variety diopslde (Ca(Mg,Pe)(Si03 )g). 

It is in general a medium-grained rock, with the grain size 

ranging from a few millimeters to several centimeters. It is 

easily distinguished from dunite by its gray weathered surfaces, 

and by the prominent pyroxene cleavage faces on fresh surfaces. 

Accessory chromlte is much less common than in the dunite, and 

ordinarily can be seen only under the microscope. Although the 

pyroxenite usually forms layers, lenses, or larger irregular 

bodies, dikelets of fresh pyroxenite cut the dunite in a few 

places.

The pyroxenite has commonly been altered to a fibrous amphibole which in turn is more or less replaced by carbonate, talc, 

and antigorite. The altered rock surface weathers to a soft, 

dirty gray which contrasts sharply with that of the dunite.

Other igneous rocks

Biotite-bearing and hornblende-bearing quartz diorlte also 

intrude the metamorphosed sedimentary rocks in the area around 

Red Bluff Bay (pi. 21). These batholithic rocks are light-colored and granular and are made up of roughly 60 percent of feldspar, which is largely andesine but includes a little orthoclase; 

30 percent of quartz; and 10 percent of biotite or hornblende 

and accessories. These batholiths are considered to be off-
CHROMITE DEPOSITS, BARANOF ISLAND, ALASKA 177

shoots from the Coast Range batholith, which is probably of 

Lower Cretaceous age.

The nearest batholithic rocks are 4 or 5 miles from the

ultramafic mass at Red Bluff Bay, but numerous dikes believed to

/

be genetically related to them cut across both the sedimentary 

and intrusive rocks in the Red Bluff Bay area. The dikes are 

porphyritic hornblende andesites, ranging in color from white to 

dark gray, and in width from a few inches to 15 feet or more. 

Diabase dikes, consisting of andesine laths and augite in 

approximately equal proportions together with minor quantities 

of biotite and magnetite, cut the serpentine and the metamorphic 

rocks. They are probably younger than the hornblende andesite 

dikes and unrelated to them, although the evidence is not conclusive.

Structure

The structure of most of the western side of Baranof Island 

appears to be relatively simple. The beds are overturned, with 

the younger graywacke and underlying older phyllite and greenstone schist striking N. 30°-50° W. and dipping steeply northeast. (See pi. 21). The ultramafic masses of the interior of 

the island are also simple in form, being concordant, sill-like 

bodies which strike about N. 50° W. and dip steeply northeast, 

parallel with the overturned bedding in the phyllite.

In the vicinity of Red Bluff Bay the phyllite and greenstone 

schist lie in somewhat open folds, with axes trending about 

N. 30° W. and plunging 10°-50° SE. (see pi. 22). A strong.lineation and much minor tight crumpling have developed in the 

weaker beds, and a prominent set of joints cuts the rocks at 

about right angles to the axes of folding. Most of the contact 

of the intrusive ultramafic mass is below sea level, but at the 

north end. of the mass the contact seems to indicate that the 

mass is concordant and spoon-shaped, plunging to the south.
178 STRATEGIC MINERALS INVESTIGATIONS, 1942

The Intrusion appears to have taken place during the later 

stages of the period of deformation in which the surrounding 

sediments were folded and metamorphosed.

The internal structure of the mass is complex (see pi. 22). 

Pyroxenite predominates in the northwestern half of the area and 

crops out In large irregular lenses. Throughout most of the 

exposed area the dunite shows a more or less regular banding 

caused by pyroxene-rich layers in thfi rock. In the southeastern 

half this feature is well developed the strike of the layers 

there deviates only slightly from north, and the dip is everywhere very steep. Chromite-rich layers .or lenses in dunite lie 

parallel to the pyroxene-rich layers, but in general they are 

narrow and discontinuous.

These structures are believed to be due to a flow banding of 

inhomogeneous material partially differentiated in depth, In 

which the massive pyroxenite bodies were localized for the most 

part near the bottom the periphery and northwestern half, In 

particular, of the mass now exposed while the individual grains 

of pyroxene and chromite.were being swept along in the currents 

and formed the well-banded type of rock.

Shear zones are abundant and prominent in the ultramafic 

rocks. They fall in general into two sets, those of one striking about north and those of the other northeast. The northeasterly-trending set usually displaces the other, but in a few 

places the reverse is true. The shear zones are younger than 

the hornblende andesite dikes, but older than the diabase dike, 

which follows one of them. Talc has developed along them in 

many places.

CHROMITE DEPOSITS

Small tabular or lenticular masses of chromite occur at a 

number of places In the ultramafic rocks. A few may be of some
UNITED STATES DEPARTMENT OF THE INTERIOR 

0 , GEOLOGICAL SURVEY !34°42' BULLETIN 936 PLATE 22

EXPLANATION

Hornblende andesite dikes

Shear zone with talc

Chromite

(Deposits numbered 

as in text)

Dunite

(Largely altered 

to serpentine)

Phyllite with some interbedded

Amphibolite 

Shearzone

Contact definitely located 

Contact inferred

v 70

Strike and dip of layering 

in igneous rocks

Strike of vertical layers

©

Horizontal layers

Strike and dip of bedding 

in metamorphic rocks

Axis of fold in metamorphic rocks, 

showing direction and amount of 

pitch. Direction of stretching in 

serpentine

I34°44' !34°42'

GEOLOGIC MAP OF THE RED BLUFF BAY AREA, BARANOF ISLAND, SOUTHEASTERN ALASKA

1000 o 3000 FEET

. . i_______i________i i
CHROMITE DEPOSITS, BARANOF ISLAND, ALASKA 179

slight economic importance, but the outlook is not encouraging

i

for a substantial production from this area.

Mineralogy

Chromite is a black, hard, heavy mineral with a submetallic 

luster and a brown streak* It may occur in octahedrons, but it

s

more commonly forms irregular grains or irregular aggregates of 

grains. It is not uniform in composition, but contains varying 

proportions of chromium, iron, magnesium and aluminum oxides.

The formula is usually written as (Mg,Fe)(Cr,Pe,Al) 00.. The *& 4

important considerations from an economic standpoint are the 

percentage of chromic oxide (Cr20,), and the ratio of chromium 

to iron. Analyses of ore from Red Bluff Bay show a wide range 

in these factors, but all the samples were too rich in iron to 

be ore of metallurgical grade, which should contain 48 percent

or more of Cr00, and have a Cr:Pe ratio of 3:1 or better. A d, o

rough estimate of the Cr:Pe ratio may be made on the basis of 

the magnetism of the mineral and the color of its streak, the 

magnetism increasing and the streak becoming darker brown with 

increasing iron content.

Localization and origin of ore bodies 

The chromite is found in thin tabular bodies which lie parallel to the pyroxenite layers. The ore bodies are restricted 

to the dunite areas. If the large pyroxenite masses are localized near the bottom of the intrusive, as some evidence- seems 

to indicate, it is probable that the lower parts of the ultramafic body will be practically free of chromite, for no appreciable concentration of that mineral has been discovered in the 

pyroxenite.

The similarity in shape and mode of occurrence between the 

chromite-rich and pyroxene-rich layers or lenses indicates that 

there was no essential difference in the method of origin of the
180 . STRATEGIC MINERALS INVESTIGATIONS, 1942

two. Chromite grains were probably concentrated into irregular 

masses before the ultramafic rocks were intruded into their 

present position, the tabular shapes of the deposits being produced by the flow of the magma. The chromite began to crystallize out of the magma somewhat earlier than the silicate minerals, but the periods of crystallization overlap. Late dikelets of olivine and pyroxene cut the chromite and early formed 

silicate grains, indicating that some movement and fracturing 

occurred before the final consolidation of the magma.

Ore bodies

Several small chromite bodies are known in the serpentines 

of the interior of Baranof Island, but none of them appear to 

offer any hope for production, particularly in view of their 

inaccessibility. They may contain a few dozen or a hundred 

tons in all. The lack of high-grade chromite float in the interior Indicates that there are few or no large deposits.

The chromite deposits at Red Bluff Bay are for the most part 

either too small or of too low grade to be of economic importance, but five bodies containing from a few tons to a few hundred tons apiece may be of sufficiently high grade to be mined 

and shipped without concentration. These deposits range from a 

few feet to a few tens of feet in length and are all narrow; in 

only a few places is there a width of more than 1 foot of solid 

ore. Layers of barren dunlte commonly separate the high-grade 

chromite layers, and will make careful hand-sorting necessary if 

even a very small production is to be obtained.

Three deposits of larger dimensions but of lower grade are 

known. These are from 100 to 300 feet long and 1 foot to about 

30 feet wide, and are estimated to have depths of one-half their 

lengths. These low-grade bodies are chromite-rich masses of 

dunite in which the chromite is disseminated as small pods and 

lenses of solid ore. Most of these pods and lenses, even though
CHROMITE DEPOSITS, BARANOP ISLAND, ALASKA 181

they are of shipping grade, are much too small to be mined separately; the grade of the chromite-rich masses may be high 

enough, however, to make the deposits concentrating ore.

In the table of analyses below, the concentrates represent 

the pure chromite mineral, separated from the silicate minerals 

by laboratory methods. The percent-chromite column gives the 

percentage of chromite by weight in the sample.

Partial analyses of chromite samples from Red Bluff Bay, Alaska 

[R. E. Stevens, analysis]

Sample

number

AG41-87

AG41-88

AG41-86

AB41-12

AG41-48

AB41-25

AG41-49

AG41-69

AB41-19

AB4L-18

AG41^46

AG4lU?

Concentrate

Or 

(percent)

33.40

35.70

35.96

39.30

36.48

36.00

38.27

37.02

33.05

36.97

23.50

33.47

Pe 

(percent)

23.17

18.48

16.66

18o05

20.87

20.28

18.88

22.12

23.51

18.67

33.58

28.51

Cr:Pe

1.44

1.93

2.16

2.18

1.75

1.78

2.03

1.67

1.41

1.98

.70

1.17

Cr2°3 

(percent.)

48.80

52.19

52.55

57.44

53.30

52.59

55.91

54.12

48.29

54.01

34.32

48.90

Crude ore

Cr203 

(percent)

25.48

29.09

40.13

50o56

34.80

47.66

46.38

18.65

43.10

46.30

20.08

24.45

Chromite 

(percent)

52

56

76

88

65

91

83

34

89

86

59

52

AG41-87. From south end of deposit No. 1.

AG41-68. From north end of deposit No. 1.

AG41-86. From north lens of deposit No. £.

AB41-12. From deposit No. 3.

AG41-48". From deposit No. 4.

AB41-25. From deposit No. 5.

AG41-49. From south end of deposit No. 6.

AG41-69. From north end of deposit No. 6.

AB41-19. From deposit No. 7.

AB41-18. From high-grade lens, deposit No. 8.

AG41-46. From narrow layers 1,000 feet west-northwest of deposit No. 3.

AG41-47. From chroraite lens 500 feet northwest of deposit No. 3.

The deposits described below include all the ore bodies from 

which any appreciable amount of chromite could be obtained that 

are known to occur at Red Bluff Bay, and the good exposures in 

most of the area near the bay make it unlikely that any large 

bodies there have escaped notice. No description of deposits in 

the interior of Baranof Island is given because too little is 

known about them.

No. 1. A northward-trending zone, about 600 feet long, 

carrying chromite stringers and blebs, lies at an altitude of
182 STRATEGIC MINERALS INVESTIGATIONS, 1942

about 350 feet on the east slope of the main ridge, near the 

northern end. In the northern part of this zone, rich layers of 

chromlte in dunite striking N. 20°-35° E. and dipping 85° W. 

extend for about 300 feet through a width of from 1 to 5 feet. 

Two samples, AG41-87 and AG41-88, containing respectively 25.5 

percent and 29.1 percent of chromic oxide, Indicate that about 

half the material Is chromlte. (See p. 181.) The ore Is well 

exposed on a sloping surface for most of Its length, and at the 

north end a cliff exposes It for 70 feet vertically. The total 

relief on the outcrop Is some 130 feet. This deposit affords 

the best hope for a relatively large tonnage of concentrating 

ore.

No. 2,--Deposit No. 2, the best In the area, Is at the 

southern end of the chromite-rich zone In which No 0 1 is found. 

It consists of two masses of high-grade ore (sample AG41-86 

shows 40.1 percent chromic oxide), apparently segments of one 

vertical, northward-trending body that is out by a fault striking east and dipping 30° S. This southern segment is 50 feet 

long and 1 to 2^ feet wide but is cut off at the bottom by the 

fault. The northern segment is exposed for 40 feet horizontally 

and 42 feet vertically and is from 1.6 to 3,9 feet wide; It lies 

beneath the fault plane, so that the possibility of a southerly 

continuation and of a greater depth is Increased.

No. 5. Deposit No. 3 is at an altitude of more than 700 

feet on the crest of the ridge in the center of the exposed 

dunite mass. It comprises three small pods of high-grade ore, 

a sample of which (AB41-12, p. 181) contains 50.6 percent of 

chromic oxide. The largest and most southerly of these pods is 

a mass of chromite 4 feet high and 4 feet long, exposed in a low 

cliff. It pinches out at the top, but is 2 feet wide at the 

base of the exposure. About 50 feet north of this a small semispherical body of chromite 3 feet in diameter crops out, and a 

still smaller body occurs 30 feet farther north.
183

AT. . . . :. V

EXPLANATION

Chro'mite ore

30

Fault,showing" dip 

Probable trace of fault 

Strike of vertical layer

50 Feet

Figure 16. Geologic sketch map of deposit No. 2.

No. 4. A low-grade body of chromite crops out on the crest 

of the ridge 600 feet south of deposit No. 3. It consists of
184 STRATEGIC MINERALS INVESTIGATIONS, 1942

several thin layers of chromite in a zone about 2 feet thick 

which strikes N. 60° E. and dips 30° SE. Sample AG41-48 

(p. 181), containing 34.8 percent of chromic oxide, represents 

one of the better layers. The zone is about 10 feet long; at 

the southwest end It is cut off by a fault, at the northeast end 

the ore pinches out.

No. 5. Deposit No. 5 is at an altitude of 280 feet on the 

east slope of the main ridge. A zone 1 foot thick of thin lenticular chromite masses strikes north and dips 75* W. A fault 

cuts it off at the south end; 10 feet to the north it is exposed 

in a vertical cliff, which is its northernmost outcrop. It 

apparently has a depth of 10 feet, for it pinches toward the top 

and bottom. The analysis of sample AB41-25 (p. 181), indicates 

that this ore contains 47.7 percent of chromic oxide.

No. 6. Deposit No. 6 crops out on a high bench at the top 

of the large cirque south of No. 5. A long narrow body of chromite extends nearly 300 feet, striking N. 10° E. and dipping 

80° W. The southernmost 100 feet is a single layer of good 

chromite (sample AG41-49, 46.4 percent of chromic oxide) ranging 

from 1 to 18 inches in thickness. To the north the ore breaks 

up into many 1- to 2-inch chromite-rich layers separated by barren dunite. Sample AG41-69 (18.7 percent of chromic oxide) was 

cut across this lower-grade part of the deposit. The thickness 

of the zone increases to about 5 feet at the north end. The 

body has been faulted and offset 'slightly at many places, and at 

the north end it is cut off by a major shear zone. It pinches 

out to the south.

No. 7. Small stringers of chromite are found in a northward-trending zone about 600 feet long that is exposed on the 

cres't of the main ridge at its southern end. The largest of 

these bodies, known as deposit No. 7, is at the north end of 

this zone. It consists of narrow layers of good ore, striking 

N. 10° E. and dipping 65° E. A sample of this ore (AB41-19,
CHROMITE DEPOSITS, BARANOF ISLAND, ALASKA 185

p. 181), contains 43.1 percent of chromic oxide. The individual 

layers are from 1 to 6 inches thick, two of them being 4 and 6 

inches thick, respectively, and the zone has a total width of 

some 2 feet. It is exposed at the south end in a steep outcrop, 

from which it can be traced continuously for 20 feet north and 

intermittently for 30 feet more. Several small faults offset 

the zone 1 to 6 inches.

No. 8. Deposit No. 8 is at the southern end of the zone in 

which No. 7 occurs. An area about 30 feet wide and 100 feet 

long contains many layers of disseminated chromite, together 

with irregular lenses, up to a foot long, of much higher-grade 

material. -Sample AB41-18 (p. 181), is from one of these small 

lenses. The high-grade lenses are too small to mine individually and would have to be included with the low-grade material. 

Even with these lenses the deposit is of very low grade, probably averaging about 5 percent chromic oxide, which is too little to be considered economic.

Reserves

In the table of reserves given on the following page the 

deposit numbers correspond to those given on the map (pi. 22). 

Figures are long tons. The grade of the ore is taken from the 

table on page 181, except that of deposit No. 8, which is estimated. It should be remembered that the ore is so variable in 

dimensions and grade that these figures are only a rough approximation, and also that they are based only on outcrops.

The method of origin of these deposits leads to the belief 

that they were probably about as long in the vertical as in the 

horizontal dimension before erosion exposed them. Some have 

undoubtedly been entirely removed, and others almost certainly 

exist that do not crop out. The average depth of those known at 

present has been assumed for the purposes of this report to be 

about half the length.
186 STRATEGIC MINERALS INVESTIGATIONS, 1942

Chromite is unaffected by chemical processes of weathering; 

therefore the ore has been neither leached nor enriched near the 

surface. ~ J

number

1......

2......

4......

5......

6......

7......

8......

Total

Possible

Long 

tons

p-Zf)

10

5

OKO

rtc

570

» shipping ore

/ Cr2°34., 

(percent)

40.1

Cf\ c

ATI Tf

46.4

43.1

* * 

POS£

Long 

tons

9,000

10

5,000

15,000

29,010

jible concentral

CrgO-j 

(percent)

r>r> -z

M O

no e

/ 0\ G.

Weighted 

average 12

ting ore

Cnromite 

( long tons )

4,860

7

1,700

(?) 1,500

8,067

The high-grade deposits are very small, but several factors 

make them attractive for development. The area is easily accessible by water, and the ore bodies are not over one-fourth of a 

mile from the beach; No. 2, the best deposit, is only 500 feet 

from the low-lying valley of the creek flowing from the northern 

cirque. Little mining equipment would be necessary a compressor could be set on the beach, and air taken to the deposits by 

pipe-line and mining costs therefore would probably be low. A 

small outfit could mine out the known deposits quickly, perhaps 

with men and equipment from some intermittently active mine during a period of slack. The ore could be transported readily to 

the beach, and to a shipping point such as Petersburg by a small 

boat. Shipping costs from Petersburg to Seattle would be about 

$4 per ton.

The situation with regard to the low-grade bodies is very 

different. Although the table shows some 29,000 tons of concentrating ore, this figure is based on surface exposures only. In 

order to produce possibly 8,000 tons of concentrates, extensive 

development work and milling tests would have to be made and a
CHROMITE DEPOSITS, BARANOP ISLAND, ALASKA 187

mill would have to be built, all of which would require a large 

investment with little prospect of an adequate return.

The high iron content of the chromite of these deposits 

makes them less desirable than they would otherwise be, and more 

extensive deposits of such ore are available elsewhere.

The few high-grade bodies may afford a small, readily available source of a few hundred tons of chromite, but there is little prospect that future reserves of any consequence can be , 

developed in this area.

O