R. I. 4421 MARCH 1949

- UNITED STATES

DEPARTMENT OF THE INTERIOR

J. A. KRUG, SECRETARY

BUREAU OF MINES

JAMES BOYD. DIRECTOR

LIBRARY COPY

* U. S. Bu.ecu hti-'ns

Boulder City, Nevada

REPORT OF INVESTIGATIONS

INVESTIGATION OF MUIR INLET OR NUNATAK MOLYBDENUM

DEPOSITS, GLACIER BAY, SOUTHEASTERN ALASKA

BY

R. S. SANFORD, G. A. APELL, AND F. A. RUTLEDGE
R. I. 4421,

March 1949.

REPORT OF INVESTIGATIONS

UNITED STATES DEPARTMENT OF TEE XNTERIOR - BUREAU OF MINES

INVESTIGATION OF MUIR INLET OR N.UNATAK MOLDENUM DEPOSITS,

GLACIER BAY, SOUTHEASTERN ALAS

By R. S. Sanford, G... A. Ape1l,. and F. A. Rutledge_/

CONTENTS

Page

Introduction and summary .. 1................

A cknowledgments . ........ .2

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

Physical features and climate .. . . 2

Property and ownership . . ........................... ' 3

Ore deposits .... .. .. ........ .3 . . .,..

Sampli g and analysis....... . ........ 5

Beneficiation tests.5

INTRPUCT ION AND 9UMMARY

The Muir Inlet or Niunatak molybdenum deposits are in the Glacier Bay

district, Muir Inlet, Alaska, 78 miles northwest of Juneau.

The deposits were examined by'Bureau of Minbs'engineers, and the area

was mapped by a. field party'of the Federal.Geological Survey during the

summer'of 1942'.2 '; -

The'following year the Bureau of Mines began developing the deposits.

A total of 215 channel samples were taken, and'2 diamond drill holes totaling 286 feet were drilled. The samples were sent to the Bureau's laboratories at Rolla, Mo. for'beneficiation.

Ai The Bureau of Mines will welcome reprinting of this paper, provided

the following footnote acknowledgment is use'd: "Reprinted from

Bureau of Mines Report of Investigations 4421."

SJ Senior mining engineer, College Park, Md.

3/ Mining engineer, Minneapolis, Minn.

gJ Mining engineer, Juneau, Alaska.

2/ Smith, Philip S., Occurrences of Molybdenum Minerals in Alaska: U. S.

Geol. Surv. Bull. 926-C, 1942, pp. 178-180.

Reed, J. C., Some Mineral Deposits of 'Glacier Bay and vicinity, Alaska:

Econ. Geol. vol. 33, No. 1, Jan.-Feb. 1938, pp. 56, 57.

2750
E. I. 4421

A discussion of the deposits, assay results, and drill logs are contained in this report.

ACKNOWLEDGMENTS

The authors acknowledge the assistance given by A. W. Tolonen and A.

W. Erickson, former Bureau of Mines engineers, and special acknowledgment is

made of the information and assistance given by W. S. Twenhofel of the

Geological Survey. -

LOCATION AND ACCESSIBILITY

The molybdenum deposits of the Muir Inlet or Nunatak Peak area are on

Muir Inlet, in the Glacier Bay district of southeastern Alaska (figs. 1 and

2). The area is 78 airline miles N. 530 W. of Juneau, Alaska, at 580 39' 30"

north latitude and 1360 06' 30." west longitude. Water distance from Juneau

is 129 nautical miles. Steamship lines pass the mouth of Glacier Bay at

37 nautical miles from the deposits, and, except for the hazard of icebergs,

the route is navigable for ocean steamships.

During the summer, Muir Glacier is very active, and the icebergs constitute a transportation problem. ,Under pormal. conditions the ice would

interfere with traisportation to a certain extent but would not constitute

a major hazard.'

PHYSICAL FEATURES AND CLIMATE

The physicai'features are characteristic of a recently glaciated region.

In 1926, the&United States Navy made the first aerial photographs of Muir

Inlet. At that time the mineralized area shown as No. 1 on figure 3 was

partly covered to a depth of over 300 feet by ice of the Muir Glacier.

Since that date this glacier has retreated 3-1/2 miles. The mineralized

area is at present surrounded on three sides by active and stagnant glaciers.

Stumps and broken tree trunks of an ancient, pre-glacial forest can be seen

in places.

The large ice fields have a marked influence upon the climate. During

the summer the temperature drops to almost freezing each night. There are

more rain and lower temperatures in the Muir Inlet area than at Juneau,

where the weather has been recorded for a number of years. The Juneau average annual'precipitation is 80 inches and the mean temperature 420 F. The

temperature at Juneau is very rarely lower than -7° F.

The region has almost no vegetation. Natural carriers must transport

seeds for a considerable distance before vegetation can secure a foothold.

Only an occasional small bush and s6me'moss cin be seen.

?750 2
SIBERIA

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Morame and 7alu,5 := Rock bearlaqgconsplcuou5 molybdenfte. _ Grnodolorlte 17infr15ve ond Rockbearling/nconspicuolsrnolybdenite, ou>ter s111ceous5 eavelope - -V1OI Ge/gC017.Aact Uppelr cherf.K ---- . -

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EfO Lowecr cerf - ~Ou~fcr liit of y uariz veinlefs.

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Figure 3. - Generalized geologic map, Nunatak area.
R. I. 4421'

PROPERTY AND OWNERSHIP

Lode claims covering the mineralized areas were staked in 1941 and

1942 by three groups. The original discoverers, John Johnson, Hoonah,

Alaska, and Tom Smith, Juneau, Alaska, located four claims. Later, S. H.

Pi Vevelstad and George Comstock, of Juneau, Alaska, located two claims.

The largest number of claims., 8_,.was .located by.Cari.t vejestad, Petersburg, Alaska. A list of unsurveyed claims with ownership follows: John Johnson and Tom Smith,O. K. Nos. ', 2, 3, and 4;: S. *H...P. Vevel4tad, and George

Comstock, Triton hanid Tri't6n No: '-;< Carl Ve-vqlstad,, triton.Nos. :2-to 20.

*' ORE DEPOSITS'"

Field studies of the NunatakY.Muir-Inlet area, were made by the United

States Geological Survey during the summer of 1942. The f0lloi4in- description of the deposi f-'is'q4uoted in part from'Twenhofe2',s. Keport 64

The be rotks of the Nuhatak;'trea include a metamorhosed

sedimentary sequente2 of tightly:f'olded&Paleozoip :(possibly

Devonian) hornfels with some shale and limestone. **. The

earliest intr-sio'n'sr'into 'the'stfratified.'rc-bks ar.e a group Q odark altered'd-ikes ar sills '***'. :;The hbrnfels was intruded

by a small bodyonf' z onltb porphyry, probably early in

Cretaceous time 'afte-the- foIding of bhe bedded. rocks.

Around the' intfiusive',' and developed.by it;, is a contact..

aureole charnclierizecd by abundant diopside' in the hornf.el]s.

The diopside imparts'a dr. 'col'or to the.normally light-colored

hornfels. The contact sureole and- the three recognized-hornfels..

units *** are cut by myriad quartz veinlets. The quartz veinlets

are increasingly .andan {owad'the'intrusive-mass. r -Weqrits,

periphery th'ey colescn and'lea'Veaonly faint remnants of the

original rbock. 'In p1aces the6o'tet part 'of the intrusive is

almost completely gilicified.' " ''

The general trehd `of -the -b-hded rocks is about N.;.° wm,.

but at most places,' because of minor plicationb, the:;rocksstrike about 9'. 300 .E. Near tle -stoek the bedding 11as.been

obscured. Steeply dipping, closely spaced Joints cross' al

the bedrocks. The majority Df these strike about N. 650 W:''

The numerous quartz veinlets for th most part ares.in these

joints. Many faults strike northeastward and dip:.step y"

southeastward. 'A few of'the faults are zones as uch 'as&75

feet wide. 'The most.-recent dikes are Approximately vertical

and trend northeastward..,.F-4;t. movements both preceded and

followed the formation of the quartz veinlets and the intriusion

of the dikes. ' - '.;':.

S/ Twenhofel, W. S., Molybdenite Deposi.ts of the Nunatak Aiea, Muir Inlet,

Glacier Bay, Alaska: U. S. Geol.' Sury. Bull. 947-B, 1946, pp. 12-16.

2750 -3-
R. 'I. 4421

The molybdenite deposits of the Nunatak area are of two

types - a stockwork type and a fault type.

The stockwork is by far the largest deposit. It embiaces

all the diopside-rich contact aureole described *** and extends

outward beyond its limits but not inward into the intrusive

core or its silicified outer parts. The stockwork as herein

defined is that part of the zone of qusrtz'veinlets already

mentioned in which molybdanite is prevalent.''

Where the zone of quartz veinlets projects conspicuously

northwestward to Muir Inlet it contains most of the richer

parts of the stockwork. In this part of the zone the bedrock has been folded into a well-defined anticline.

Several faults within the zone of quartz veinlets contain conspicuously more molybdenite than their-wall rocks.

The fault deposits are similar to the stockwork, in that

molybdenite is present generally'along the margins of the

quartz veinlets, but.-they differ from it principally in

containing many open. fractures, in containing molybdenite

in thicker masses, and in being locally almost completely

epidotized. The deposit along the Nunatak fault is particularly large and well-mineralized.,,

The Nunatak fault deposit crops out for a length of

2,000 feet. It disappears to the north beneath talus and

moraine and to the south beneath moraine and a small lake.'

The known vertical range of the deposit is from about 380

feet to about 910 feet above-sea level. Its width ranges

from about 5 feet to as much as 20 feet and averages about'

9 feet. The fault strikes about N. 50 E., and its dip steepens

from 600 E. in its southern part to 750 E. at its northernmost

exposure.

The quartz veinlets that cross the fault zones are similar

in most respects to the quartz veinlets elsewhere. The veinlets are better mineralized in the fault zones and seem to

indicate that earlier fault movements formed places particularly favorable for molybdenite deposition.

Molybdenite is the most conspicuous metallic mineral in the deposits,.

because much of it occurs as films and thin plates along the margin of thequartz veinlets. This'mode of occurrence makes a visual grading of the, ore

difficult and is probablyrthe reason the importance of the deposits has been

overestimated in the past.

.750

2750 '- 4-
I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~A/

of do/.(""oReoc COWlero) / /I J

_Foigue II.. Assa y p'n ae I.

Figure 4. - Assay plan, area 1
CHANNz/ EL./ CHANiNEL A 2 CIA'ANvEL #3 CHANAEL qO4 C/IA NVEL -/O

5ome/v ZMo Sompl/e- 7%A/o M o ,7peIw Z/ilo Vp| %fo

I aos 7 005 006 301 006 8 0.o4

2 .07 8 .03 4S 08 3/ .06 9 .03

3' .09 9 .06 46 o-ST cHANNvELw5 /0 04 4 -U9 C/AA _EL 43 7 _ .04 Sar)/C oMo / / 04

5 .04 5Lmple %Mo 46 .02 / 05 /2 .06

6 T0? / .05 49 06 Z 03 /3 04

7 .08 2 07 50 .04 3 .08 /4 cs 8 .08 3 .03 5/ .06 4 .05 /5 04

9 09 4 .04 52 o0 5 .04 /6 .04

/ 08 5 .08 53 .05 6 .05 /7 007 1/ 7 /0 6 . 54 .06 7 .5 /8 .05

12 .17 7 .08 55 .04 8 .06 /9 .07

/3 0E 8 0 56 .0 //1 20 07

74./Z 9 /0 57 08 CWAN 06L 2/ .05

5 o~ 70 T7V 58 5 .3 OS SO0D/e Zo Z2 ./0

/6 .07 / /I .03 59 .06 / .05 23 08

/7 .07 /2 008 60 .07 Z 1 .04 24 .07

/8 .05 /3 .06 C"4 C/HANNVEL 25 2 ./ 

/9 .05 /4 .06 5omp le Mo Ionpk o 2 6 .1/0O 20 09 /S ./0 / .08 / .02 27 .09

2/ .07 ? /6 .05 2 .08 Z .0W 28 .08

22 .06 / 7 04 3 07 C/AI/A '2 8 29 .13 23 .06 18 .02 4 03 5o'7w/e-I %Afo 30 .20

24 05 /9 03 5 .06 / .05 3/ .09

25 .05 20 .04 6 0 7 2 04 32 2/

26 704 2/ 02 7 .09 3 .04 .7 .09

2 7 .05 22 .03 B .09 41.07 34 /1/ 06_ 23 .03 9 /2 C7T7/ 7EL 9S 35 ./0

29 09 24 .03 /O .09 5omple ZMo 36 .07 30 T3 Z'S .03 //7 .06 / .05

3/ .07 Z6 OZ 12 .07 2 05

3Z .05 27 .05 /3 7 3 .06

33 .09 28 03 /4 5 4/ .09

34 .06 29 .03 /5 .05 S .08

35 .07 30 .0 /6 .73 6 . // C#A.MEL AM1

36 .08 3/ 03 /7 .08 7 .08 / .07

37 .0 32 .04 / C9/ -8 ./ / .05 38 .04 ./ .9 .07 9 .08 3 .05

39 05 34 .03 20 .07 /0 .0 7 4 .07

40 06 35 .06 2/ 06 CAI/ 5L .// . C/IANEL w Z 36 .07 ?2 /O SOnrZ/0 ZMO t 6 .05

O7r"A o 37 .04 Z3 05 / .06 t 7 .03

/ 03 3 °8 Z4 08 2 ./O f S 70

2 .05 39 .04 .05 _0 3 .05 _07 3 03 -40 .0 26 .06 4 .05 /0 .07

4 °02.07 1 02 2I7 3 0 7

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t -2 omolp/es 7o;reporese/7fo/Ive.

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Figure 5. - Assay data, area 1.
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.~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Z ._98s iS ~ ~ ~ .&*Iws~~I 0/0 /0

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PRO JEC7-EC PROFI/ Of I-ANsG/No/ WALL

PLA NV

Figure 6. - Plan and profile, area 2.
Pitch 71'

Of 41 ~* Elev. 918 -4'

/Ya 5 1 r,.. 1 PPitt 4 755 Pitch " 49e

Iva// A~z,, 8 Elev. 899 4<%i. P?, 4i

-91NoG. Elev 893

Sh,~ ~ ~~~~~~ 4 S ~ed $

8.I' ~'~dQu0 ,.z ef~Id 

5ECTION SECTION SECTION

CHANNEL NO.ZO LOOKING SOUTH CHANNEL NO. 21 LOOKING SOUTH CHANNEL NO. 22 LOOKING SOUTH

PFtcgh 7. -ic S o r

Elev- 871 No Hanging Wall l~ey. 828 'pDike

No Han#n u all ValIues .. Elev. 815'

Values~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~au

SECTION SECTION SECTION~~~~~~~

CHANNEL 23 LOOKIN NO SOUTH CHANEL NO.s2 LOKN OT HNE N.2 OKN OT

67o .- ecios "Q;%Fgue are 2
le \ Pitch 55' o~~~~~~~~~r ~~~~~~~~Elev. 738'

'~~ 49 ~~Pitchi 55' Hanging Wall

TrcRe Ptch Elev. 50° ofV~lus ,'X 'e >zz EEIev. 766 Mineralized ; I 790'u

Trace of Valus -/

in Hanging Woll ., \

T~~~~~us ~~~~~~Talus?

< * .W t 4 4

SECTION SECTION SECTION s

CHANNEL NO. 26 LOOKING SOUTH CHANNEL NO. 27 LOOKING SOUTH CHANNEL NO. 28 LOOKING SOUTH

'a'- Pitch 60. Pitch 60

4Q~'f Elev. 629' Fair Values in PEtcvi 614 Fair Values inl Elev. 568' 9Iai, H'%. *. EX v 614' Hanging Wall

Hanging Wall

le ~ ~ ~ ~ -

SECTION SECTION

CHANNEL NO. 19 LOOKING SOUTH CHANNEL NO. 30 LOOKING SOUTH CHANNEL NO. 31 LOOKING SOUTH

Figure 8. - Sections, area 2.
R. I. 442i

SAMPLIXG AND;ANALT.YI$

'Stockwork deposits. - The stockwork molybdenite deposits-outcrop over

an area-of about two million square feet and are partly covered by glacial

moraines The more noticeable mineralization is confined to an area of

550,000 square feet. This is designated as Area No. 1 and was selected for

systematic exploration. (See fig. 3.)

A total of 203 channel samples were cutover a length of 1,44o feet.

These samples averaged ,0.07 percdnt molybdenum. 'The highest analysis from

this-group-of samples.1vas;:0.52 percent-;molybdenum, and only four samples

assayed 0.15 percent molybdenum or higher. -The location of samples takenis shown on ;figure 4, and the -analyses aire shown on .figure 5.

Two core drill holes were put down in this area. Hole 1 was drilled

at an inclination of -300 and completed to a depth of 46,7 feet. Hole 2

was drilled at an inclination of -45° and completed to a depth of 238.1

feet. This hole reached a vertical depth of 169 feet below the surface

or 158 feet below sea level. The location of the holes is shown on figure 4.

The grease ordinarily used to lubricate the drill rods could easily

float the molybdenite when core drilling in this type of deposit. The

possibility was anticipated, and provisions were made to recover all of

the sludge for analysis.

The following tabulation gives the total weighted core and sludge

analyses and the adjusted average analyses:

Percent Holybdenum

Hole Core Sludge Adjisted .Average

1 . ... 0.043 0.041 0.042

2 .. 0.063 0.073 0.072

The same uniformly low-grade mineralization as found on the surface continued

to the bottom of the holes. Only two samples obtained in the drilling contained more than 0.15 percent molybdenum.

Fault 'deposits. - There are four faults that contain more molybdenite

than is found in the wall rock. The Nunatak fault, the largest, is wellmineralized. This deposit was selected for exploration and is designated

Area 2. The samples were cut in 12 channels spaced over a length of 1,100

feet. These samples contained an average of 0.10 percent molybdenum. The

average width of fault samples was 10.3 feet. Only three of the samples

obtained from this deposit contained more than 0.15 percent molybdenum. The

analysis of individual samples and a plan and profile of Area 2 are shown on

figure 6. Sections through the fault at points sampled are shown on figures

7 and 8.

2750 5
R. I. 4421

BENEFICIATION TESTS

Two representative samples were shipped to the Bureau of Mines Laboratory in Rolla, Mo., for metallurgical testing. One sample was taken near

the first drill site in Area 1. The other sample was obtained from the

shear zone in Area 2.

On the sample from Area l, a concentrate containing 88.04 percent

molybdenumn sulfide was recovered, whereas on the one from Area 2 (shear

zone) the recovered concentrate contained 94.49 percent molybdenum sulfide.

As molybdenum concentrates are usually quoted on the basis of 90 percent

minimum molybdenum sulfide content, the product made from the Area 1

sample was slightly below specification; the other concentrate, however,

was considerably above the minimum.

2750 6-