41373

R. 1. 4373 DEcEMUER 1948

UNITED STATES

DEPARTMENT OF THE INTERIOR

J. A. KRUG, SECRETARY

BUREAU OF MINES

JAMES Boyo, DIRECTOR

REPORT OF- INVESTIGATIONS

INVESTIGATION OF TOLSTOI MOUNTAIN IRON DEPOSITS

KASAAN PENINSULA, PRINCE OF WALES ISLAND

SOUTHEASTERN ALASKA

ANE;W EIC3Y

AMER W. ERICKSON
R. I. 4373,

December 1948.

.REPORT OF INVESTIGATIONS

UNITED STATES DEPABTM T OF THE INTERIOR - M LREAU OF MINES

INVESTIGATION OF TOLSTOI MOUNTAIN IRON DEPOSITS, KASAAN INSULA,

PRINCE OF WALES ISLAND, SOUTHEASTERN ALASKA2./

By Aner W. Erickson_'/

CONTENTS

Page

Introduction.., 1

Acknowledgments ....... 2

Location.and-accessibility .............. 2

Physical features and climate . 2

History .... .... ,.,.. , 3

Property and ownership ....... 3

Geology . .......... 3

Occurrence of the deposits .. 44.. 

Character of mineralization . 5

Sampling and analysis. .. 5

Bibliography .. 5

ILLUSTRATIONS

Following

Fig. page

1.. Index map of Alaska showing'location of Prince of Wales

Island ..... .. .... ...... ... ......... 2

2. Vicinity map - Prince of Wales Island ............. 2

3. Vicinity map - Kasaan Peninsula . .. .. , 2

4. Index map of area investigated on Tolstoi Mountain ... 4

5. Magnetic surveying, sampling - deposit 1 . ............... 4

6. Magnetic surveying, sampling - deposit 2 ........ 4

7. Magnetic surveying, sampling - deposit 3 4

INTRODUCTION

Magnetite iron deposits on Tolstoi Mountain were examined as part of the

investigations by the Bureau of Mines of iron-abd copper ores on Prince of

Wales Island. The Tolstoi Mountain project was a part of a program for investigating mineral deposits in Alaska, under the general supervision of R. S.

Sanford, acting branch chief.

Sj The Bureau of Mines will .welcome reprinting of this paper, provided the

following footnote acknowledgment is used, "Reprinted :from Bureau of

Mines Report of Investigations 4373." / Assistant mining engineer, Bureau of Mines, Juneau, Alaska.

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n.I. 4373

A preliminary examination-was made by S., P. Bolt, mining engineer of the

Bureau of Mines, in company with John Reedj -L., -A ... Warner, and W. S. Twenhofel

of the Federal Geological Survey, on July 14, 1943. Three samples were taken, rough estimates were made, and it was proposed that the area be.ma'pped, topo- graphically and.geologically.. DJ-p-needle .work-was added to the program, and

it was decided that., should results warrant, the deposits would be diamonddrilled.

From March 26 to May 28, 1944e, the deposits were examined thoroughly by Bureau of Mines personnel under the directioa.of the author. Thirty-two acres

were mapped with contour intervals of 10 feet, grids were established covering the principal outcrops, over.1,500 dip-needle readings were secured, and the

magnetite bodies were outlined. Additional information was gathered by trenchinch and channel-sampling, 600 linear feet of trench being dug and 32 channel

samples being cut. Fiinally,..the.m~pped area was checked for nonoutcropping

deposits by taking dip-needle'readings at 10-foot intervals along the traverse

lines, creeks, trails,'aad.all'outstanding topographical features. This reconnaissance work gave sufficient coverage of-the 32 acres to eliminate the

possibility of further.magnetite.bodies of any consequence remaining undiscovered.

ACKNOWLEDGMNTT

Acknowledgment is made to Nils Johannsen, assayer, Territorial Department

of Mines, Ketchikan,.Alaslk, for. det~rmination of ,samples.

LOCATION. AND ACCESSIBILITY

.The deposits are on Prince of Wales Island in Southeastern Alaska near

Tolstoi Bay, a deep-water indentation at the northwest end of Kasaan Peninsula.

The physical features are shown on figures 1 and 2 and the location of- the

deposit on, figure3.- Oldd workihgs were-found on the vest side bf Tolstoi

Mountain, between elevations of 650 and 1,150 feet, at distances of 3/4 to

1-1/4 miles f.rom the' east shore 'of Tolstoi Bay.

Access to the ar'ea is over a brushed foot trail built by the Bureau-of

Mines. TopographY would permit construction of either surface or aerial tramways at moderate cost but would make road building expensive. Deep-water navigation, permitting inexpensive water transportation, is possible the year around.

PHYSICAL FEATURES AND CLIMATE

Kasaan Peninsula is an area of moderate relief, being considerably less

rugged than the mainland to the east. Most of the mountains and ridges are

less than 2,500 feet in height and show evidence of having been covered by the ice cap of the Pleistocene age.. -..Rock exposures .. below- elevations of 2,000 feet are limited, as extensive'overburden 2 to 20'feet deep covers the greater

part of the peninsula.

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i74 /f2/50

.. / , SEWARo i i> \ F I C 7,e--- D r I i

Figure 1. - Index map of Alaska showing location of Prince of Wales Island.
SCL IN MILE

MODIFIED FROM U.S. FOREST e vw

Figure 2. - Vicinity map - Prince of Wales Island.
CONTOUR INTERVAL- 200F0

SCALE IN FEET d

MODIFIED FROM U.S. FOREST SERVICE MAP l{

Figure 3. - Vicinity map - Kasaan Peninsula.
R.I.4373

Timber anzd vegetation are abundant throughout the lower flanks of the

area, and hinder exploration 6f prospects. Ample mine timber is available,

mostly western and black hemlock and.Sitka spruce. The underbrush consists

mainly of huckleberry, salmonberry, and cranberry bushes, intermingled with

considerable devil's-club, a shrubicovered with sharp thorns.

The climate is characterized by moderate temperatures throughout the

year. Precipitation is heavy and, although disagreeable, is an asset in that

it makes, available many potential sources of water power.

Snowfall is moderate at the lower elevation, there seldom being more than

a foot or'two on the ground at any time. Apprec-iable snowfall rarely occurs

before December. and usually all snow has melted by April.-

Weather records kept for 14 years at Ketchikan, 40 miles southeast of

the prospect, show an average annual precipitation of 156.51 inches and an

average annual temperature of .43.80. F.

HISTORY

It is reported_3/ that -this area was prospected to a considerable extent

by. trenching and diamond drilling in 1901 and that some work was done each

year up to 1908. No records'have been found of work done since that time.

There.is no history of production of ore from Tolstoi Mountain, and the appearanceof cuts and dumps and the absence-of docks or tramways indicate that

no ore has been shipped from the prospect.

PROPERTY AND OWNERSHIP

The deposits investigated appear to be part of what was known as the

Iron Cap'group. A few old claim posts were locatea but the writing on then

was illegible. No signs of recent assessment or location work were noted

nor do records show any patented claims in the vicinity; therefore it is assumed that the claims examined have reverted to the public domain.

GEOLOGYd/

Tolstoi Mountain is composed largely of diorite intrusive masses, probably

of.Jurassic age, which'have invaded Devonian sediments and associated volcanics. The contact zone, with the diorite occupying the northerly side, strikes

about N. 600 W..and dips southwest,

. ..

Rocks comprising the sedimentary group are graywackesy conglomerates,

slates, and limestones; the volcanics consist of andesitic-lavas, breccias,

* . ~/ Wright, Charles Will, Geology and Ore Deposits of the Copper Mountain,

and Kasaan Penlisula, -Alaska: Geological Survey-Prof. T'aper 87, 1915,

p. 101. .

g/ Buddington, A. F., and 'Chapin, Theodote, Geology kind Mineral Deposits of

Southeastern Alaska: Geol. Survey Bull. 800, 1929, pp'. 94-96, 242.

2617 -3-
R.I. 4373

and tuff1s. Of these rocks, only the tuffs were noted in the immediate

vicinity of the deposit,

The ore bodies, like most of the contact replacement deposits on Kasaan

Peninsula, occur in and along a wide. zone of alteration. .No.. sharp line of

demarcation was -noted between the tuffs and diorite, the .tuffs gradually. giving way to the ldiorite in both physical and chemical characteristics.

- OCCUR1ENCE CF DEPOSITS

The deposits occur as pods, kidneys,. and lenses.scattered through a zone

striking about N. 600 W., 2,000 feet long and 200 to 500 feet wide. These

are shown on figure 4. F4fteen separate magnetite bodies are shown on the

map, all-of which, when surveyed by cip-needle methods,2 1 gave corrected

vertical magnetic anomalies of plus 300 or higher. Of these, deposits l, 2, and 3 showed the greatest intensities and were further examined by trenching, sampling, and-detailed mapping.. These are shown on figures. 5,.6, and 7

respectively.'

Deposit 1 is a flat-lying body, about 4 feet thick where exposed. Replacement appears to have taken place along a more clastic member of a series

of greenstone tuffs. The magnetite mineralization'is poorly developed.

Topography indicates the body to bQ cut off by-erosion on the north.and west

sides. The south and east sides are delimited by the magnetic survey, from

whichlit is inferred that replacement processes diminished gradually in those

directions.

Deposit 2 is thought to be a yesterly dipping continuation.of the flatlying bed described as deposit 1, erosion dividing into-two bodies'a domelike

strata of mineralization. Replacement-is more intense in this body, giving a

deposition of higher iron content. Several of the more clastic members of

the greenstone tufts have been affected, as is shown in trenches,2-1, 2-4,

2-5, and 2-6, where beds of impure magnetite are stratigraphically separated by unaltered country rock.

The adit under the north end of the deposit cuts, near the-face, a few

thin bands of partly replaced tuff, none of which are thicker than 6 inches.

Deposit 3 does not appear to be directly connected to the previously described bodies. Bedding of .the. greenstone tuffs dips. 200 to 3.00 in a

westerly direction as in deposit 2. Replacement, however, has been localized

along a series of westerly trending joint planes occurring in a zone striking N. 450 E. Several members of the tuffs show partial replacement.

It is inferred that the mineralizing solutions ascended along the joint- ing planes, replacing the more clastic beds a few feet outward from these

cracks. The extent of replacement in the zone making up deposit 3 was not"'

determined, as heavy overburden makes it' imjptactibable. It-. is estimated from

available data that not over 35 percent of the greenstone tuff has been

affected.

21 As described by A. A. Brant, Interpretation of Dip Needle Surveys: Trans.,

Canadian Inst. 'Min. and Met., vol. 41, -1938, pP. 501-516.

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1200 N N AEAS H N ~ HGH ~ MsGNEIC 

~ NK)^FLI0X 0 ~

Figure 4. - Index map of area investigated on Tolstoi Mountain.
I id: 1 VX J

0

! \ t-- TRENCI 1-3

900 N

13] GREENSTONE TUFF B MAGNETITE |SIMIFL+Ž1%2 i

0 SCALE IN FEET 10 12231 .42871 0.04

0 ~~~~~~Figure 5. - Magnetic surveying, sampling - deposit 1.
30N

0

p.~~~~~~~~p F9S~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

S MPLE 22 I % F A.- /1 < ISA~MPLE 262tlo\ I~ \ \ ~~ 2 TFINH - 1

IEI GREENSTONE TUFT 2114T7F0 241 54.8 0.41 1200 ~ ~ ~ 22 270082266002 E MAGNETITE 213 38. 6 0. 09 22432 567.9 0.2510

214 37.2 0.02 251 21.6 0.22 _____________ 221 39.7 0.09 252 42.8 0.22 . 222 29 8 0.02 253 64.3 018 0 50 23; 26.7 1.05 254 61.0 0 31

SCALE IN FEET 233 57.2 C.13 262 42.0 0.09

Figure 6. Magnetic surveying, sampingI depost 2.
GREENSTONE TUFF TFRE C%4- !\"

MAGNETITE

- - - 100*4 -/1600

0 SCALE IN FEET / /

421 39.0 .04 /.nLE'4.,r64 i

422 38.6 0.06 SAMPLE 431 , PE 4 423 41.6 0.04/ / / _/ 424 29.0 0.02 SAMPLE 4 I 425 21.7 0.02 -. 426 22.8 0.04

427 34.1 0.02 /

432 441 44.1 34.2 0.02 0 09 an2,SAMPLE 441

44

Figure 7. - Magnetic surveying, sampling - deposit 3.
P.1. 4373

A number of other scattered deposits giving high magnetic anomalies are

shown on figure 4. As intensities were lower and areas were smaller than

deposits 1, 2, and 3, they were not investigated in detail.

CHARACTER OF MINERALIZATION

Mineralization is typical of the contact iron deposits of Kasaan Peninsula. The ore mineral is magnetite, carrying small quantities of chalcopyrite

and pyrite. Gangue minerals noted were garnet, epidote, calcite, and quartz.

SAMPLING AND ANALYSIS

Thirty-two channel samples were cut from deposits 1, 2, and 3. Grooves

were 4 inches wide by 2 inches deep. Locations and analyses are shown on

figures 5, 6, and 7.

All analysis work was performed by the Territorial Department of Mines S

at Ketchikan. Samples were tested for iron and copper only, the sulfur and

phosphorus having been determined to be within allowable limits on the

preliminary samples as follows:

- - Assay

Sample Location and length 'Au,' Ag, Percent

No. of sample cut ioz. oz. Cu Fe S P

T-1 14' chip sample along east I

wall of open-cut, 200' SE. !

of and 50' above tunnel. Tr. 0.60 0.24 i63.9 *2.32 0.02

T-2 ..... 17' chip sample along north i

wall of open-cut in creek

bed, 25' above and 100' SE. i

of tunnel. ' Nil I o.60 1.88 161.6 !2.39 0.02

T-3 ..... 15' chip sample along east | i

wall of tunnel, to face. !

Includes some altered '

greenstone and pyrite. Tr. 10.40 I 0.87 '39.9 0.63 0.02

BIBLIOGRAPHY

BRANT, A. A. Interpretation of Dip-Needle Surveys. Trans., Canadian Inst.

Min. and Met., vol. 41, 1938, pp. 501-516.

BUDDINGTON, A. F., and CHAPIN, THEODORE. Geology and Mineral Deposits of

Southeastern Alaska. Gol. Survey Bull. 800, 1929, pp. 94-96, 242.

WRIGHT, CHARLES WILL. Geology and Ore Deposits of the Copper Mountain and

Kasaan Peninsula, Alaska. Geol. Survey Prof. Paper 87, 1915, p. 101.

Pi Nils Johannsen, assayer.

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