GEOLOGICAL SURVEY CIRCULAR 479

BERYLLIUM DEPOSITS OF THE WESTERN

SEWARD PENINSULA, ALASKA
BERYLLIUM DEPOSITS OF THE WESTERN 

SEWARD PENINSULA, ALASKA

By C. L. Sainsbury

Washington 1963
United States Department of the Interior

STEWART L. UDALL, SECRETARY

Geological Survey

THOMAS B. NOLAN, DIRECTOR

Free on application to the U.S. Geological Survey, Washington 25, O. C.
CONTENTS

Page Page

Abstract___________..___.._._.___.._ 1 Areas favorable for prospecting.------ 13

Introduction _________________________ 1 Lost River -Brooks Mountain area .. _ 13

Location and accessibility __-__-.___-_ 1 King River _______________________ 14

Geologic setting _____________________ 2 Area east of Tin Creek.---.-------- 14

Beryllium deposits __________________ 3 Ear Mountain _______________--_--- 14

Known lodes ______-____-__-_-__--___ 4 Cape Mountain _________----_-_--__ 15

Camp Creek-Lost River mine _______ 4 Potato Mountain ________--___----_- 15

Lost River Valley ____---_-__-_--_- 8 Black Mountain..------------------ 16

Rapid River __-____._....___.__..__ 9 Suggestions for prospecting ----------- 16

Tin Creek ________________________ 9 Selected bibliography _._.__-__--.--.- 17

ILLUSTRATIONS

Page 

Figure 1. Map of the western Seward Peninsula, Alaska, showing areas of known and

potential beryllium deposits_______________________________-___--_----_--- IV

2. Geologic map of the Lost River-Tin Creek area, Seward Peninsula, Alaska..---- 6

3. Geologic map of the Rapid River area, Seward Peninsula, Alaska-..--.----..... 10

4. Geologic map of the Tin Creek area, Seward Peninsula, Alaska ___...___._.._._ 12

5. Map showing location and beryllium content of sediment samples, Lost River

area, Seward Peninsula, Alaska _______________._._._._.._..__.-_...------ 13

6. Geologic map of Ear Mountain, Seward Peninsula, Alaska _____________________ 14

7. Geologic map of Cape Mountain, Seward Peninsula, Alaska ____________________ 15

8. Geologic map of Black Mountain area, Seward Peninsula, Alaska ___--___--__-_- 16

TABLES

Page 

Table 1. Beryllium minerals in ores from the Lost River area._____-___-__--___--_--_-_ 4

2. Beryllium content of nonberyllium minerals, Lost River area, Alaska ___________ 4

3. Quantitative spectrographic analyses of bulk samples of beryllium ores, Lost

River area, Alaska._____________________________________________________ 5

4. Beryllium and fluorine content of ores from Camp Creek-_-_-----------__-----_ 7

5. Beryllium and fluorine content of ores from Lost River Valley.---.------------- 8

6. Beryllium and fluorine content of ores from Rapid River _______________________ 11

7. Beryllium content of ores from Tin Creek ____________________________________ 13

III
INDEX MAP OF ALASKA

Figure 8

Area covpred by deti 

known lode deposit 

geochemieal anom; 

fluorine, or beryll

Area containing lode 

'fluorine associa

Area containing sulfid 

associated with sm 

near beryllium de;

V

Lost River mint

168°00' 167° 00'

Figure 1. Map of the western Seward Peninsula, Alaska, showing areas of known and potential beryllium d
Beryllium Deposits of the Western Seward Peninsula, Alaska

By C. L. Sainsbury

ABSTRACT

Deposits of beryllium ore in the Lost River area of the 

western Seward Peninsula, Alaska, consist of replacement 

veins, pipes, and stringer lodes in limestone in a zone 

about 7 miles long and 2 to 3 miles wide which is faulted 

and intruded by dikes and stocks.

The ores are remarkably alike and typically consist of 

the following minerals, in percent! fluorite, 45 65; diaspore, 

5 10; tourmaline, 0 10; chrysoberyl, 3 10; white mica, 

0 5; small amounts of hematite, sulfide minerals, manganese oxide, other beryllium minerals; and traces of minerals 

not yet identified. The ores generally are cut by late veinlets which are of the same mineralogy as the groundmass 

ore, or which consist of fluorite, white mica, and euclase. 

The ores are fine grained, and many of the individual mineral grains, except fluorite, are less than 1 mm in size. The 

beryllium content of bulk samples of ore ranges from 0.11 

to 0.54 percent (0.31 to 1.50 percent BeO). High-grade 

nodules, composed principally of chrysoberyl, diaspore, 

fluorite, and mica, contain as much as 6 percent BeO.

Geochemical reconnaissance has disclosed other areas 

of anomalous beryllium in stream sediments elsewhere on 

the Seward Peninsula, generally around biotite granites that 

have them associated with tin deposits; additional exploration probably will disclose other deposits.

INTRODUCTION

Nonpegmatitic beryllium deposits of a type 

not previously known in North America were 

found in several localities in the western part 

of the Seward Peninsula, Alaska, during geologic mapping by the U.S. Geological Survey 

in 1961 and 1962, and anomalous geochemical 

concentrations elsewhere suggest that other 

comparable deposits may be found. The area 

under discussion is shown in figure 1.

Tin deposits have long been known in the 

western Seward Peninsual (see "Selected bibliography"), and beryllium minerals and beryllium-bearing skarns have been known in the 

Lost River area since 1942. In 1960, W. R. 

Griffitts of the U.S. Geological Survey noted 

that reports published by the U.S. Bureau of 

Mines indicated that beryllium was present

in anomalous amounts in placer concentrates 

elsewhere on the Seward Peninsula, and this 

observation led to the geochemical reconnaissance which resulted in the discovery of the 

deposits described below.

The writer gratefully acknowledges support 

received from many sources. A beryllium 

detector built by John Ohm of the Geological 

Survey, under the guidance of W. W. Vaughn, 

aided mapping of the Rapid River deposits and 

the estimation of grade of ores. Donald Grybeck and T. E. Smith assisted in the field investigations, and G. D. Eberlein helped in 

sample collection. Many Alaskan residents 

and organizations freely provided material 

support and aided the author in many ways.

LOCATION AND ACCESSIBILITY

Nome is the nearest large town, Teller, 

Teller Mission, and Wales are villages within 

the area (fig. 1). Gasoline, foodstuffs, and 

common supplies are available at Nome and 

Teller, although the selection is limited prior 

to the arrival of the first ship in Nome in 

June or July. Three established airlines 

serve the western Seward Peninsula from 

Nome and Teller, and supplies can be landed 

at numerous small unmarked airstrips as 

well as at larger airfields. Heavy supplies 

and equipment must be lightered ashore or 

landed from barges which serve the coastal 

areas from Nome and from Teller, which is 

the nearest deepwater harbor. A mining access road is under construction from Teller 

to Lost River, and a gravelled road is under 

construction between Nome and Teller. A 

good gravel road leads from the beach at the 

mouth of Lost River to an airstrip which can 

accomodate C-46 cargo aircraft, and thence 

to the mine.
BERYLLIUM DEPOSITS OF THE WESTERN SEWARD PENINSULA. ALASKA

The various reports listed in the bibliography, especially Lorain and others (1958), 

provide more detailed information on access, 

climate, and operating problems.

GEOLOGIC SETTING

The principal rocks of the western Seward 

Peninsula are the slate of the York region, a 

thick unit of highly deformed and slightly 

metamorphosed shale, graVwacke, and schist - 

ose argillaceous limestone of pre-Early 

Ordovician age (Steidtmann and Cathcart, 

1922), and the Port Clarence Limestone, a 

thick sequence of limestone, argillaceous 

limestone, and dolomitic limestone which 

overlies the slate unconformably. The Port 

Clarence Lime stone has yielded fossils ranging in age from lowest Early Ordovician to 

Late Silurian. Recent geologies mapping has 

disclosed that in the York Mountains a shaly 

limestone, generally schistose and cut by 

numerous quartz-calcite veins, lies between 

the slate of the York region and rocks generally referred to the Port Clarence Limestone; it too is probably pre-Early Ordovician 

in age. Numerous small bodies of basic rocks 

were intruded into the slate in pre-Early Ordovician time, and one sheared gabbroic dike 

has intruded the schistose limestone. The 

Port Clarence Limestone and older rocks 

have been intruded by granites, rhyolites, and 

quartz diabase dikes. A long period of erosion 

and deformation probably intervened between 

deposition of the slate of the York region and 

the Port Clarence Limestone.

Within the area containing the known beryllium deposits, the Port Clarence Limestone 

is predominantly Early Ordovician in age, although some Middle Ordovician rocks are 

known.

Sections of the limestone 3,0001feet thick 

have been measured, and it is probably much 

thicker in places.

In Late Cretaceous time, plutons and dikes 

of medium- to coarse-grained biotite granite 

and rhyolite porphyry intruded the slate of 

the York region and Port Clarence Limestone. 

Subsequently, quartz diabase dikes were injected along some of the fractures of the 

same systems occupied by earlier dikes. The 

granite forms bosses which are exposed at 

Cape Mountain, Ear Mountain, Brooks Mountain, Tin Creek, and Black Mountain (figs. 1, 

4, 7, and 8), and which underlie the Lost River

mine area, and probably the Potato Mountain 

area, at shallow depth. The youngest igneous 

rocks, of Quaternary and Recent ages, are 

dikes and flows of olivine basalt, in part 

scoriaceous.

Coarse cobble and pebble conglomerates 

occur on the York Terrace, which appears to 

be an elevated marine platform along the 

southern part of the York Mountains (Steidtmann and Cathcart, 1922, p. 16). The conglomerates are probably not more than 150 

feet thick, and crop out in isolated patches 

having areas of generally less than a square 

mile.

Because the slate of the York region generally surrounds the younger Port Clarence 

Limestone in the western and northern Seward 

Peninsula, earlier workers interpreted the 

structure as a great north-trending faulted 

syncline (Steidtmann and Cathcart, 1922, p. 

32). Recent detailed geologic mapping has 

shown that in the York Mountains numerous 

low-angle thrust faults cut the limestone and 

locally cut the slate. Over an area about 30 

miles in an east-west direction and 20 miles 

in a north-south direction, the Port Clarence 

Limestone dips generally north at angles 

from a few degrees to almost vertical. This 

attitude prevails to the west end of the York 

Mountains where the contact with the slate 

strikes almost north. This is believed to be 

strong evidence that the Port Clarence is in 

thrust contact with the slate. The constant 

northward dips of the limestone beds, even 

where thrust sheets of different facies of 

limestone of approximately equivalent age 

overlie each other, constitute the most notable 

structural feature in the York Mountains and 

probably explain the fact that thrusting was 

not previously recognized.

Following the thrusting, normal faults of 

three distinct systems occurred in the limestones. The strongest and most persistent 

system strikes generally N. 70 85°E. and is 

characterized by faults which are downthrown 

to the south, the second set strikes N. 30 50° 

W., and the third set strikes a few degrees 

west of north. These fractures guided the 

emplacement of the dikes and provided the 

main channels for ore deposition. Most of 

the known beryllium deposits are alined along 

a zone about 7 miles long and 2 to 3 miles 

wide which trends N. 80-85° E. from Rapid 

River on the west to east of Tin Creek (fig. 1) 

and which contains numerous dikes and faults
BERYLLIUM DEPOSITS

as well as several plutons. This zone is a 

large-scale feature which is evident only on 

geologic maps covering areas larger than 

those that accompany this report, although 

individual maps (figs. 2, 3,4) depict fractures 

and dikes which are part of the large zone. 

A few beryllium deposits occur as veins along 

fractures formed radially around the granite 

on Tin Creek (fig. 4), and in innumerable 

small fractures near or above buried plutons.

BERYLLIUM DEPOSITS

The beryllium-bearing deposits found to 

date lie along a zone about 7 miles long by 2 

to 3 miles wide that extends N. 80°E. across 

the drainage basin of Lost River. Within this 

zone are four distinct mineralized areas, each 

about 4,000 feet long by 1,000 feet wide; however, only a small part of the bedrock in 

these areas is ore.

Except for minor amounts of beryllium in 

tactite (skarn) near granite contacts, the 

beryllium deposits are replacement lodes in 

limestone and consist of veins, pipes, and irregular stringer lodes. Veins range from a 

few hundred to 2,000 feet in length and from 

less than 2 to 12 feet in thickness. Some 

stringer lodes cover areas of several thousand square feet. In any one area, veins, 

pipes, and stringer lodes generally occur 

together.

The beryllium ores are nondescript rocks 

which differ but slightly in appearance from 

the argillaceous limestones in which they 

commonly occur. In hand specimen, the ores 

are noticeably heavy, for their specific gravity ranges from 2.98 to 3.5, substantially 

above that of the limestone (2.60 2.65). On 

weathered surfaces, the ores often have a 

distinct purplish or faint greenish caste, and 

the purplish coloration especially contrasts 

with most of the surrounding limestone. 

Faint bands, generally a few millimeters 

wide, are oriented subparallel to the veins. 

Late veinlets as much as a few millimeters 

thick, generally white, cut the ores and stand 

out on weathered surfaces. These veinlets 

both parallel and cut across the faint banding. 

A gray-white lichen grows preferentially on 

some ores and aids in their recognition. 

Where found in argillaceous limestone, the 

ore customarily weathers into blocks substantially larger than the limestone because 

of its greater coherence and its resistance to 

frost action and to solution.

Although the ores vary somewhat from deposit to deposit, they all consist basically of 

fluorite, diaspore, chrysoberyl, white mica, 

and tourmaline, together with minor amounts 

of other beryllium minerals, sulfide minerals, hematite, manganese minerals, and other 

minerals as yet unidentified.

The modal composition of typical ore, as 

determined by a study of thin sections, is, in 

percent: fluorite, 45 65; diaspore, 5 15; tourmaline, 0 10; chrysoberyl, 3 10; white mica, 

0 5; small amounts of hematite, arsenopyrite, 

euclase, phenakite(?), milarite(?), bertrandite(?), and pyrite; and minute amounts of 

other minerals. The fluorite occurs as clear 

ovoid grains as much as 2 mm in diameter 

and as intimate inter growths with other minerals as small as a few microns in diameter. 

The space between the larger fluorite grains 

is filled with a very fine grained intergrowth 

consisting of fluorite, diaspore, and chrysoberyl, and, less commonly, tourmaline and 

mica. The chrysoberyl is commonly on the 

borders of the fluorite. Some chrysoberyl 

occurs as festoonlike bands composed of 

grains a few microns across. Other festoonlike bands are composed of fluorite and almost cryptocrystalline mica(?). Occasionally grains of chrysoberyl, phenakite(?), bertrandite(?), and milarite(?), generally less 

than O.lmm in size, occur in fractures in the 

larger fluorite grains. Younger veins cutting 

the ores may be similar in mineralogy to the 

groundmass but of noticeably coarser texture, 

or they may consist of mica, fluorite, euclase, 

bertrandite(?), milarite(?), and hematite. 

Where mica predominates over fluorite in 

the late veinlets, cassiterite and hematite 

occur, as well as an unidentified sulfide mineral resembling tetrahedrite. The euclase in 

the late veinlets forms lustrous pearly-white 

flakes as much as a centimeter in diameter. 

Locally, as in the Lost River valley, late 

veinlets of purplish fluorite and white mica 

as much as 2 inches thick cut the ores. Some 

specimens of ore from Tin Creek are encrusted with white mica in tabular growths. 

Unusual nodules as much as a foot in diameter occur in the Camp Creek ores; a typical 

nodule consists of a central core of very fine 

grained chrysoberyl, diaspore, and minor 

white mica surrounded by a rim as much as 

an inch thick of gray to faintly purplish fluorite. Abundant white mica and diaspore occur 

between the rim and core, and a black manganese oxide coats fractures in the nodules. 

These nodules contain as much as 6 percent
BERYLLIUM DEPOSITS OF THE WESTERN SEWARD PENINSULA, ALASKA

Table 1. Beryllium minerals in ores from the Lost River area

Material

Chrysoberyl 2 _ _ _ _ 

Euc lase_ _ _______

Bertrandite _____

Beryl. __________

Phenakite _______

Milarite ________

Formula

BeAl2O4 _________________

BeAlSiO4 (OH) ____________

Be 4 Si2O7(OH)2 ___________

Be 3 Al 2 (SiO3 )6___ _________

Be 2 SiO 4 _________ ________

K 2 Ca4Be4Al2 Si24Ogo-H2O__

BeO 1 

(percent)

16.9-19.7 

16.9

39.6-42.6 

10.0-14.0

44.0-45.6 

5.0

Occurrence

Common in almost all samples. 

In late veinlets; associated with white 

mica; common. 

In late veinlets; associated with mica; 

uncommon. 

In quartz-muscovite veins at Lost River 

mine; absent or rare in fluorite ores. 

In altered granite at Lost River mine; 

rare or absent in fluorite ores. 

Enclosed in fluorite in some ores from 

Rapid River; rare.

1 Usual BeO content of similar minerals as reported by Warner and others, (1959).

2 Pure chrysoberyl separated from ore from Rapid River and analyzed spectrographically by 

John Hamilton of the U.S. Geological Survey contains 7 percent Be (19.4 percent BeO).

BeO. Hematite and a black manganese mineral provisionally identified as todorokite 

are conspicuous in some ores from Camp 

Creek and Tin Creek. A summary of information on the beryllium minerals identified 

to date is given in table 1. All except milarite are confirmed by X-ray diffraction.

The beryllium in the ores is believed to be 

present principally in definite beryllium minerals, although small amounts are in minerals that normally do not contain beryllium, 

especially in tourmaline. Preliminary spectrographic analyses of virtually pure fractions of other minerals separated from the 

ores gave the results reported in table 2.

Because many specimens of ore containing 

as much as 6 percent BeO contain no tourmaline, it is assumed that the beryllium in

Table 2. Beryllium content in percent of nonberylliuni 

minerals, Lost River area, Alaska

[Analysts: Fred Waring and John Hamilton, 

U.S. Geological Survey]

Mineral Be BeO

Mica_____________ 0.01 0.03

Fluorite__________ .01 .03

Tourmaline_______ .30;!.0 .8;2.8

Diaspore 1 ________ .02 .06 (estimated)

1 Identified by Fred H. Hildebrand, U.S. 

Geological Survey, by use of the powder

camera.

tourmaline constitutes only a minor percentage of the total beryllium in bulk ore samples. In one specimen tested, about 85 percent of the contained beryllium was recovered as chrysoberyl.

Spectrographic analyses of bulk ores from 

several of the deposits show small amounts 

of other common elements, as shown in table 

3. No attempt has yet been made to account 

for the distribution of these elements, but 

their presence may influence the choice of 

recovery processes and metallurgy of the 

ores.

KNOWN LODES

The four areas where deposits have been 

found are described below in the order of 

their assumed potential.

CAMP rKF.tk-i.OSr KIVFK MINIThe largest known veins, as well as the 

largest potential reserves of beryllium, are 

near the Lost River mine (fig. 2). The deposits consist of (1) a discontinuous vein or 

stringer lode- trending eastward for about 

5,000 feet along the south slope of Camp 

Creek from a point near the junction of Camp 

Creek and Cassiterite Creek and (2) of innumerable smaller bodies in and near the 

Lost River mine. Neither (1) nor (2) has yet 

been studied in detail by the Geological 

Survey.

The ore in Camp Creek trends approximately east-west in the western 1,000 feet
Table 3. Quantitative spectroQraphic analyses in percent of bulk samples of beryllium ores, Lost River 

[Analysts: Harry Bastron, U.S. Geological Survey; Be,beryllium determined fluorimetrically by Ardeth B

overall accuracy of ± 15 percent except near limits of detection where only one digit is reported. Look

An, Hg, Ru, Rh, Pd, Ir, Pt, Mo, W, Re, Ge, As, Sb, Bi, Te, Zn, Cd, Tl, In, Co, Ni, Ga, Sc, Y, Yb, La, Zr

Field No.

Rapid River !__________

Rapid River 2 _________

Bessie -Mable __________

East Lost River 1 ______

East Lost River 2 ______

East Lost River 3 ______

Camp Creek 1 _________

Camp Creek 2 _________

Camp Creek 3A-1 ______

Camp Creek 3A-2 ______

Camp Creek 3B-2 ______

Camp Creek 3B-1 ______

62-ASn-791____________

62 -ASn-792 ____________

Lab. No.

62M-64

62M-65

62M-66

62M-67

62M-68

62M-69

62M-70

62M-71

62M-72

62M-73

62M-74

62M-75

62M-76

62M-77

Cu

0.0014

.0011

.0008

.0008

.0022

.0012

.0006

.0011

.0010

.0012

.0007

.0009

.0008

.0011

Sn

0.012

.016

.010

.014

.033

.014

.009

.010

.015

.014

.012

.016

.017

.016

Pb

0.012

.048

.023

.006

.004

.007

.007

.037

.008

.008

.006

.006

.005

.015

Mn

0.22

.25

.16

.14

.12

.18

.20

.16

.11

.25

.18

.14

.22

.32

Fe

0.50

.48

.26

.18

.80

.28

.25

.41

Q7

.38

.34

.40

.41

.18

Cr

0.0018

.0027

.0002

.0006

.0018

.0013

.0008

.0007

.0014

.0010

.0010

.0012

.0010

.0004

V

0.0024

.0020

.0008

.0020

.0024

.0012

.0012

.0009

0094

009 ^

.0019

.0021

.0020

.0014

Ti

0.029

.030

.010

ni q

.060

O9 1

.022

.016

09 ^

094

.025

09Q

01 Q

.014

Mg

0.80

.90

.47

.38

.75

1 90

.50

qn

.55

.85

.41

.40

.10

4Q
APPROXIMATE MEAN 

DECLINATION, 1963

E

wh

Mafic int

Geology by C. L. Sainsbury, 1960-62

]Limestone, 

[_ and dolo

Contact, das

loc

Fault, d

Thrust fau

Saw

Strik

Vein or string

Abundant float 

x 

Prospect 

© 

Locatio

ber

Figure 2. Geologic map of the Lost River-Tin Creek area, Seward Peninsula, Alaska.
KNOWN LODES

where outcrops are discontinuous and about 

S. 85° E. for 2,000 feet, where it is traceable 

as a practically continuous run of heavy float 

which is within a few feet of its bedrock 

source. A continuation, or a noticeably narrower en echelon vein, crosses Camp Creek 

east of its main north tributary and has been 

traced by Mr. Grothe (one of the owners of 

the Lost River mine) for at least another 

2,000 feet, almost to the ridgetop between 

Camp Creek and Tin Creek. The weathered 

beryllium ore is dark purplish and stands 

out as a heavy float run containing thousands 

of tons. Ore occurs locally along cross fractures perpendicular to the main lode. Where 

exposed in the bed of a small gully near the 

eastern end of the zone of continuous float, 

the vein zone consists of three - parallel clayfilled fractures that dip steeply south. The 

limestone between the fractures is partly 

replaced by the usual fluorite-beryllium ore. 

A chip sample taken across 40 feet of bedrock perpendicular to the veins contained 

detectable beryllium. Bulk samples of float 

ore and individual specimens of ore from

Camp Creek were analyzed (table 4). Most 

of the selected specimens contain more than 

the usual number of late white veinlets, which 

explains the fact that they contain more beryllium than the bulk samples.

The occurrence and distribution of beryllium within the immediate area of the Lost 

River mine are not yet well known. Numerous veinlets of fluorite, tourmaline, chrysoberyl, and diaspore, ranging in thickness 

from a hairline to several inches, cut the 

marmorized limestone. Banded fluoritetourmaline rock forms local selvages along 

the walls of the Cassiterite dike and also 

small veins parallel to the dike; samples 

from the selvages contain beryllium in the 

range 0.0015 to 0.15 percent (0.004 to 0.42 

percent BeO) (McKelvey, 1960, p. A5>. Zones 

of iron-stained, altered, and fluoritized limestone which occur underground along the 

walls of the Cassiterite dike on the main-adit 

level contain beryllium in amounts estimated 

on the basis of preliminary examination with

Table 4. Beryllium and fluorine content, in percent, of ores from Camp Creefe

[Analysts: Ardith Bartel and C. L. Sainsbury, beryllium; L. F. Rader, fluorine; all of U.S. Geological Survey. Beryllium and fluorine in bulk samples determined by wet analyses by Bartel 

and Rader, respectively; beryllium in selected specimens determined by neutron activation by 

Sainsbury using laboratory instrument built by W. W. Vaughn and others. Sample type: A, bulk 

grab of float; B, selected specimen. For approximate location of samples see corresponding 

circled letters on fig. 2]

Field No.

Camp Creek !__________

Camp Creek 2_ _________

Camp Creek 3A-1 ______

Camp Creek 3A-2 ______

Camp Creek 3B-2 ______

Camp Creek 3B-1 ______

62-ASn-791_____. ______

62-ASn-792 ___________

62-ASn-795 ____________

Assav 1 _______________

Assay 2 _______________

Assay 3 _______________

Assay 4 _______________

Camp Creek select 2____

Camp Creek select 3-2__

Camp Creek select 4____

Camp Creek select 5____

Camp Creek select 6____

Camp Creek select ?____

Lab. No.

303153

303154

303155

303156

303157

303158

303159

303160

Type

A

A

A

A

A

A

A

A

B

B

B

B

B

B

B

B

B

B

B

Location

(A) Extreme west end____________

( T^ TNT.^ Q T* \TJ £* Q + o Y\ H

(C) West end continuous float _____

(D) West end continuous float _____

(E) Center continuous float _______

(F) Center continuous float _______

(G) Distinct ore shoot. __ _________

(H) East of ore shoot ____________

Nodule, west end continuous ore __

Near (A)________ ________________

_________do ____________________

From (G) _______________________

_________do ____________________

_________do ____________________

_________do ____________________

_________do ____ __ _____ __ _____

Near (H)________________________

Near (B)________ __ _________ __

Near (A) ________________________

Be

0.25

.11

.20

04

.26

.26

.54

.23

2.16

.26

.25

.75

.61

.83

1.15

.76

.65

.35

.36

BeO

0.69

.31

.56

.67

.72

.72

1.50

.64

6.00

.73

.70

2.10

1.70

2.30

3.20

2.10

1.80

.97

1.02

F

28.9

27.6

29.5

27.7

28.4

29.0

31.2

27.3

F as 

CaF2

57.8

55.2

59.0

55.4

56.8

58.0

62.4

54.6
BERYLLIUM DEPOSITS OF THE WESTERN SEWARD PENINSULA, ALASKA

the beryllium detector at as much as 0.5 

percent BeO. In contrast to the fluorite-beryllium veins elsewhere in the district, this 

banded fluorite-tourmaline rock locally contains as much as 3.35 percent tin, most of 

which is in cassiterite. The distribution of 

these fluoritized rocks within the mine is 

shown on detailed geologic maps prepared in 

1953 55 (Sainsbury, in press).

During 1960 and 1961, the U.S. Bureau of 

Mines drilled several dozen percussion drill 

holes in marmorized limestone along Cassiterite Creek to test the overall tenor of the 

limestone, and a report on this work is being 

prepared (J. A. Herdlick, oral communication, 1962). Complete evaluation of the beryllium potential of the Lost River mine will 

require additional detailed work.

LOST RIVER VALLEY

The known beryllium lodes in what is here 

termed "Lost River valley" form an eastwardtrending belt of en echelon replacement veins 

which cross Lost River about lj miles below 

the Lost River mine (fig. 2). The deposits 

were discovered in late August 1962 and have 

not yet been mapped in detail. The ore is the 

usual banded fluorite-diaspore-chrysoberyl 

variety. Vein material has been found in 

place and as float in a zone approximately

1,000 feet wide and 4,200 feet long. The 

known mineralized area starts near an old 

airstrip on the low hill between Lost River 

and Tin Creek and continues west at least as 

far as the Bessie and Mabel prospect, which 

lies on the ridge between Lost River and 

Curve Creek. The geology in the vicinity of 

this prospect was shown first by Steidtmann 

and Cathcart (1922, p. 78). East of the alluvium in Lost River, several replacement 

veins as much as several hundred feet long 

are marked by continuous runs of float in the 

thin mantle of frost-riven limestone and tundra which covers bedrock. These veins are 

parallel to discontinuous mafic dikes which 

weather dark brown. Locally, replacement 

veins lie along dike walls, but most of the 

veins are along fractures unoccupied by dikes. 

A single bulldozer trench dug by Mr. Grothe 

across one of the float zones exposed banded 

fluorite rock about 3 feet thick.

Ore fragments as much as a foot across 

have been brought to the surface in frost 

boils in the alluvium of Lost River, and float 

ore occurs in distinct linear runs across the 

wide tundra-covered bench west of the river 

to the point where bedrock appears. Here 

banded and veined fluorite-beryllium rock 

crops out as lenticular masses up to 12 feet 

wide and 100 feet long, and a combined replacement vein and stringer lode continues

Table 5. Beryllium and fluorine content, in percent, of ores from Lost River valley

[Analysts: Ardith Bartel and C. L. Sainsbury, beryllium; L. F. Rader, fluorine, U.S. Geological 

Survey. Beryllium and fluorine in bulk samples determined by wet analyses by Bartel and 

Rader, respectively; beryllium in selected specimens determined by neutron activation by 

Sainsbury using laboratory instrument built by W. W. Vaughn and others. Sample type: A, 

random bulk sample of float fluorite rock from one particular vein or outcrop; B, single specimen float from base of outcrop or in alluvium]

Field No.

Bessie- Mabel______

East Lost River 1 __

East Lost River 2__ 

East Lost River 3 __ 

B. M. 1 _ ____ ____

LRV 01 _____ __ _

LRV 03 _____ ____

LRV 04 __ _ __ ____

Lab. No.

303149

303150

303151 

303152

Tvne

A

A

A 

A 

B

B

B

B

Circled

fig. 2

1

2

3

4 

5

6

7

8

Location

Description

South of east dump, Bessie and

Mabel. 

East of road on bench- _ ______ _

East of road on bench, 2ndvein__ 

East of road on bench, 3rd vein. _ 

Outcrop south of Bessie and

Mabel. 

Frost boils along road ______ __

Frost boil 100 feet east of

road. 

From float run, bench, east of

road.

Be

0.4

.25

.15 

.17 

.23

.35

.70

.27

BeO

0.389

.694

.416 

.472 

.64

.97

1.95

.76

F

28.6

24.4

23.0 

27.1

F as

CaF2

58.8

50.1

47.3 

55.7
KNOWN LODES

for several hundred feet along a fracture zone 

trending about west. Several brown-weathering dikes follow some of these fractures. The 

western continuation of ore has not been delimited.

The ore near the Bessie and Mabel prospect in in thin-bedded medium-gray to darkgray dolomitic limestone, probably of latest 

Early Ordovician age, which is overlain to 

the west and north by argillaceous limestone 

believed to be of early Early Ordovician age. 

These relations suggest that the dolomitic 

limestone is part of a thrust sheet (fig. 2). A 

small mafic pluton intrudes the dark dolomitic limestone about 100 yards south of the 

ore outcrops.

Analyses o*f bulk samples of ore and of selected specimens of ore from outcrops near 

the Bessie and Mabel prospect and from 

linear float runs east of Lost River are given 

in table 5.

BAPID RIVER

The beryllium deposits in Rapid River lie 

4| miles by air S. 65°W. from Lost River 

mine (fig. 1). They consist of veins and pipes 

of fluorite-beryllium ore and of stringer 

lodes or stockworks in fractured argillaceous 

limestone. The general geology is shown in 

figure 3. The deposits are alined in a zone 

about 4,400 feet long and 1,000 feet wide 

trending N. 85° E. across Rapid River, a tributary of Lost River. The ores are similar to 

those previously described, although tourmaline is more common in the Rapid River ores 

than elsewhere.

The best deposits exposed lie east of Rapid 

River on a wide bench covered by a thin 

veneer of frost-riven limestone and tundra. 

Within this area, which is about 1,200 feet 

long and 800 feet wide, ore occurs as replacement veins as much as 300 feet long and 

as elliptical pipes as much as 30 feet long. 

These lie within areas containing abundant 

float fragments of ore that show the underlying limestone contains veins and veinlets 

as much as 1 foot thick. The more continuous 

veins, which can be traced by surface float, 

strike parallel to the main fault. Numerous 

preore lenticular dikes of quartz diabase intruded fractures nearly parallel to the veins. 

Near the dikes and veins, the argillaceous 

limestone has been completely brecciated and 

dolomitized. About 1,300 feet south of the

best ore, a swarm of larger and more continuous dikes, including quartz diabase and 

rhyolite porphyry, strikes subparallel to the 

ore-bearing fault and cuts a thrust plate exposed on the hill to the east. Only small 

amounts of fluorite -beryllium ore have been 

found along these dikes.

Both the fluorite-beryllium veinlets and the 

quartz diabase dikes continue west of Rapid 

River into an area covered more deeply by 

tundra and alluvium where only a little ore 

crops out, commonly as selvages along dike 

walls. This area lies just north of a thick 

dolomite breccia, which may mark the continuation of a major fault to the west that dips 

south at a low angle, outside the area of 

figure 3. Dikes of quartz diabase cut the 

dolomite breccia, but no fluorite-beryllium 

ore is known to be associated with them. A 

sample of stream sediments from a tributary 

entering Rapid River from the west, just south 

of the area shown in figure 3, contains 15 ppm 

(parts per million) beryllium.

Small veins and fragments of fine-grained 

gray quartz containing minor fluorite and 

calcite are common in the argillaceous limestone north of the beryllium-bear ing veins, 

and the fault east of the main ore zone is 

filled with quartz. No quartz occurs in the 

fluorite ores.

Samples from the Rapid River area gave 

the results shown in table 6.

TIN CREEK

The beryllium deposits in Tin Creek are 

about 1-3/4 miles southeast of the Lost River 

mine. Figure 1 shows the location, and figures 

2 and 4 show the geology of the area. Two 

distinct types of deposits are present, veins 

and veinlets of the usual fluorite-diasporechrysoberyl-mica type common elsewhere, 

and beryllium-bear ing skarn (tactite) at the 

margins of a medium-grained biotite granite 

that intrudes limestone. The fluorite-beryllium ores at Tin Creek locally contain considerable manganese and in general more 

mica and sulfide minerals than they do elsewhere. Weathering of the sulfide minerals in 

some of the veins has produced a porous ore 

stained heavily with limonite. Samples of this 

type of ore are referred to as "oxidized ore" 

in table 7. The skarn ores have been described by Knopf (1906) and, inasmuch as they 

are of relatively low beryllium content, they
Alluvium and stream gravel

Terrace gravel

Dikes, include quartz-diabase and 

rhyolite porphyry

NXXVwXXW1^ 

Heavy float runs of dike rock

EXPLANATION

\£>^ xxxxl

Dolomite breccia and dolomitized limestone 

along faults or dikes

Massive to thick-bedded dark limestone, 

locally dolomitized

Thin-bedded argillaceous limestone, 

locally dolomitized

Contact, dashed where gradational or inferred 

Fault, dashed where inferred

Thrust fault, sawteeth on upper plate 

Veins containing beryllium

Areas containing pipes and stockworks 

with beryllium

Areas having isolated veinlets, or float of 

veinlets, that contain beryllium

Float quartz veinlets

Claim line, and claim post in place, 1962

Scarp in terrace gravel, line at top

dX

Location of sample analyzed for beryllium (see text)

.«2

Stream sediment sample showing beryllium content 

in parts per million

Figure 3. Geologic map of the Rapid River area, Seward Peninsula, Alaska.
KNOWN LODES 11

Toble 6. Beryllium and fluorine conterct.in percent, of ores frorc Rapid Riuer

[Analysts: Ardith Bartel and C. L. Sainsbury, beryllium; L. F. Rader, fluorine, U.S. Geological 

Survey. Beryllium and fluorine in RR-1 and RR-2 determined by wet analyses by Bartel and 

Rader, respectively; beryllium in remaining samples determined by neutron activation by 

Sainsbury, using laboratory instrument built by W. W. Vaughn and others. Sample type: A, 

random bulk of float fluorite rock; B, single specimen of float or outcrop of single vein; C, bulk 

of alluvium in main ore zone]

Field No.

RR-1_ __________

RR-2______ _____

62-ASn-B_ ______

62-ASn-C________

62-ASn-E________

62-ASn-F________

62-ASn-G____-___

62-ASn-RR8 _____

62-ASn-RR9 _____

62-ASn-RR12 ____

62-ASn-RRl3A___

62-ASn-RR15 -___

Lab. No.

303147

303148

Type

A

A

C

A

c

A

A

B

A

A

A

B

Circled

no., 

fig. 3

1

o

3

4

5

6 .

7

8

9

Location

Description

________do__________ ________

________do ___________________

end.

end.

ore area. 

Dike walls, west end ore zone __

wall, east tributary of Rapid 

River.

Bulk of float along dike wall,

west of Rapid River. 

Veinlets, south edge of creek

bed of east tributary of Rapid 

River. 

Pinkish fluorite veinlet 4 -in.

wide, south edge of creek bed 

of east tributary of Rapid 

River.

Be

0.24

.24

.05

.14

.09

.38

.30

.05

.26

.18

.12

.18

BeO

0.666

.666

.15

.38

.26

1.05

.82

.15

.72

.50

.32

.50

27.6

27.5

F as

CaF2

56.7

56.5

are not here considered as a potential ore of 

beryllium. The better deposits are replacement veins which formed in fractures which 

occur radially around the south margin of the 

granite. Rhyolite porphyry and porphyry 

dikes containing conspicuous feldspar phenocrysts intruded the granite and country rock 

along some of the radial fractures prior to 

the formation of the fluorite-beryllium veins. 

Dikes were injected also along numerous 

faults of the regional systems striking N. 85° 

E. and N. 40-50° W. Very little fluorite -beryllium ore has been found along these dikes, 

whereas many of the veins are localized at 

margins of the dikes which intruded the radial fractures on the south margin of the 

granite (fig. 4).

The most promising vein can be traced for 

about 700 feet and reaches a maximum thickness of 8 feet. Other veins, most of which 

are recognized only by linear runs of float in 

frost-riven bedrock, can be traced for several 

hundred feet but are of unknown thickness. 

Smaller veinlets as much as 6 inches thick 

ramify in the limestone on the south margin 

of the granite, where they give rise to abundant float. A few of the larger veins continue 

into the granite for short distances.

Base-metal veins near the granite have 

been described by Knopf (1906) and by Steidtmann and Cathcart (1922), as were in the tin 

deposits, and are not discussed here. With 

respect to exploration in other areas, it is 

important to point out that most of the fluorite-beryllium veins at Tin Creek lie well 

away from the granite beyond the berylliumbearing skarns and do not coincide with the 

tin deposits. This physical separationbetween
EXPLANATION

Alluvium, stream gravel, and till 

Dike, dashed wheri approximately located

Heavy float run of dike rock

Granite

Argillaceous limestone and massive 

brownish limestone

Thick-bedded dark limestone, and marble

Argillaceous limestone and 

massive gray limestone

Thin-bedded argillaceous limestone

Massive tactites, and tactile' veins with 

sulfide minerals and fluorite

Vein containing beryllium

Areas with veinlets or float containing beryllium

Quartz or clay alteration 

Contact, dashed where approximately located or inferred

Fault, bordered by dolomitized breccia

A JP x

Adit Strike and dip of beds Prospect pit

Location of sample analyzed for 

beryllium (see text)

.18

Sample of stream sediment or alluvium showing 

beryllium content in parts per million

Figure 4. Geologic map of the Tin Creek area, Seward Peninsula, Alaska.
AREAS FAVORABLE FOR PROSPECTING 13

Table 7. Beryllium content of ores, in percent, from Tin Creek

[Analyst: C. L. Sainsbury, U.S. Geological Survey. Beryllium determined by neutron activation 

using laboratory instrument built by W. W. Vaughn and others. Sample type: A, bulk grab of 

float or outcrop; B, single specimen of vein float]

Field No.

62-ASn-TC 29_____

62-Asn-TC 33____.

62-Asn-TC 35_____

62-ASn-TC 36_____

62-ASn-TC 38_____

62-ASn-TC 40 __ __

62-ASn-TC 41_ __ _

62-ASn-TC 42 __ __

62-ASn-TC 01_____

62-ASn-TC 02_____

Type

A

A

A

A

A

A

A

A

B

B

Circled 

no.,

fig. 4

1

o

3

4

5

6

7

8

q

10

Location

Description

Oxidized ore _________________________________

Veinlets in limestone _________________________

Oxidized ore ______________________--__------_

__ __ __ ____do _______________ __ __ __

Fluorit e - be ryllium ve in_ ______________________

Fluorite- beryllium vein, southwest side of

granite. 

Leached, porous ore from vein near south

margin, of granite. 

Northwest end of most continuous vein, southeast

side of granite. 

4 -in. vein, near south margin of granite ________

6-in. vein, south .margin of granite ___________ __

Be

0.17

.14

,20

.05

.27

.35

.31

.21

.40

.31

BeO

0.47

.40

.56

.13

.76

.98

.85

.58

1.11

.85

the ores of tin and tungsten, and of beryllium, 

is also noted at Camp Creek and in Lost 

River valley.

Analyses of fluorite-beryllium ore from 

Tin Creek are reported in table 7.

AREAS FAVORABLE FOR PROSPECTING

Other areas on the western Seward Peninsula that are considered favorable ground for 

prospecting are shown on figure 1 and discussed below. Geochemical reconnaissance 

has already been done in some of these, and 

results have been encouraging. In other 

areas where geologic conditions are considered favorable, no geochemical reconnaissance has yet been carried out.

LOST RIVER-BROOKS MOUNTAIN AREA

The results of sampling stream sediments 

and slope wash from the drainage basin of 

Lost River are shown on figure 5. Beryllium 

in amounts as high or higher than that found 

in Tin Creek occurs in slope wash from the 

south margin of the granite of Brooks Mountain. This may be contained in disintegrating 

idocrase which often contains a high percentage of beryllium (Warner and others, 1959, 

p. 17) and which is widespread in the contact 

rocks around the granite. However, the beryllium may have been derived from deposits, 

partly exposed in several prospects at the

"^^^y>:

41"

Sediment sample 

showing Be content 

in ppm

Figure 5. Map showing location and beryllium content of sediment samples, Lost River area, Seward Peninsula, Alaska.
14 BERYLLIUM DEPOSITS OF THE WESTERN SEWARD PENINSULA, ALASKA

margin of the granite, that contain abundant 

fluorite as well as sulfide minerals. Several 

northwest-striking veins cut the limestone on 

the ridge northwest of these prospects. The 

lodes near the south margin of the granite of 

Brooks Mountain have been described in some 

detail by West and White (1952). The similarity to the Tin Creek area is striking.

Where the Ida Bell dike of the Lost River 

mine crosses the south headwaters of Cassiterite Creek (fig. 2), T. E. Smith obtained float 

pieces of fluorite-beryllium ore that contain 

0.58 percent BeO. This area should be examined in detail.

KING RIVER

In the second small tributary entering King 

River (fig. 1) from the east, a small pluton 

similar to that south of the Bessie and Mabel 

prospect intrudes argillaceous limestone. 

Brown-weathering dikes extend westward and 

eastward from this pluton. The area has not

been prospected for beryllium deposits, but 

the similarity to the area herein called Lost 

River valley suggests that it should be prospected.

AREA EAST OF TIN CREEK

Faults of the persistent system striking 

eastward from Rapid River to Tin Creek 

continue at least into the headwaters of the 

next streams about 2 miles east of Tin Creek. 

Brown-weathering dikes also continue east of 

Tin Creek, and the area should be prospected.

EAR MOUNTAIN

At Ear Mountain, 41 miles N. 40° E. of the 

Lost River mine (fig. l),a porphyritic biotite 

granite that intrudes schistose limestone of 

the Port Clarence is accompanied by tin, fluorite, and sulfides. The general geology, taken 

from a map prepared by P. L. Killeen (1945), 

is shown on figure 6. The beryllium content 

of stream sediments and alluvium collected

Landing area

Qta

Tundra and alluvium

si

Dike, dashed where 

approximately located

Porphyritic granite

: ;j|s: ,::

Slate, shale, and quartzite

Schistose argillaceous limestone, 

and calc-silicate rock

Contact, dashed where approximately 

located or inferred

jo 

Strike and dip of beds

»JO 

Sample of stream sediment or alluvium

showing beryllium content in parts 

per million

1MILE

Geology by P. L. Killeen and 

R. J. Ordway, 19^5; modified 

slightly by C. L. Sainsbury, 

I960

Figure 6. Geologic map of Ear Mountain, Seward Peninsula, Alaska.
AREAS FAVORABLE FOR PROSPECTING 15

 ---'"

ontact, dashed where approximately 

located or inferred

Fault, dashed where inferred

Strike and dip of beds

 3 

Sample of stream sediment or

alluvium showing beryllium content 

in parts per million Geology by C. L. Sainsbury. I960

Figure 7. -Geologic map of Cape Mountain, Seward Peninsula. Alaska.

by the writer in 1960 are also plotted: they 

show a distinct geochemical anomaly around 

the granite. Mafic dikes similar to those 

associated with beryllium deposits in Lost 

River valley cut the granite and surrounding 

limestone as at Tin Creek. Rock samples 

randomly collected from metasomatized 

limestone near the Winfield shaft contain as 

much as 380 ppm of beryllium. The limestone 

surrounding Ear Mountain should be prospected in detail, even though good exposures 

are limited to a zone about half a mile wide 

around the granite. Beyond this, tundra 

covers most of the bedrock, and geochemical 

methods would be required.

CAPE MOUNTAIN

Aporphyritic biotite granite intrudes limestone at Cape Mountain at the western tip of 

the Seward Peninsula (figs. 1 and 7). Lode 

and placer tin deposits are associated with

the intrusions. The granite and surrounding 

limestone are cut by fractures, many of 

which are intruded by dikes (Steidtmann and 

Cathcart, 1922). Geochemical reconnaissance 

shows anomalous amounts of beryllium, which 

are not, however, as great as those at Ear 

Mountain and Lost River. Prospecting will 

be hampered by the tundra which covers most 

of the area surrounding Cape Mountain on the 

east and north. The geochemical data are 

insufficient to prove or disprove the existence 

of beryllium deposits, but additional prospecting is warranted.

POTATO MOUNTAIN

At Potato Mountain (fig. 1), the slate is cut 

by numerous quartz veins containing cassiterite and by several types of dikes (Steidtmann and Cathcart, 1922). More than 2,000 

tons of placer tin has been recovered from 

creeks draining Potato Mountain, and recent
16 BERYLLIUM DEPOSITS OF THE WESTERN SEWARD PENINSULA, ALASKA

EXPLANATION

Slate

Contact dashed 

where inferred

Fault, dashed where 

inferred 

_i_/0

Strike and dip 

of beds

Geology by Edward Steidtman 

and S. H. Cathcart, 1922

Figure 8. Geologic map of Black Mountain area, Seward Peninsula, Alaska.

diamond drilling by the U.S. Bureau of Mines 

has disclosed kaolinized veins containing 

tourmaline andcassiterite (J. J. Mulligan, oral 

communication, 1961). Although beryllium 

may be associated with the tin lodes, the bedrock is slate. The presence of the slate bedrock is considered an unfavorable factor because fluorine-bearing solutions would not 

react so readily with slate as with limestone, 

and beryllium lodes, if they exist, would likely 

be narrow. Prospecting would be difficult because of the almost continuous tundra which 

mantles the entire area. However, the area 

may warrant geochemical exploration.

BLACK MOUNTAIN

At Black Mountain, some 14 miles due east 

of Lost River (fig. 1), a biotite granite pluton 

intrudes slate and the Port Clarence Limestone. The general geology of the area is 

described in some detail by Steidtmann and 

Cathcart (1922), whose geologic map is reproduced in this report as figure 8. Although 

no tin, boron, or fluorine minerals are known

around the granite, skarn and veins containing 

pyrite and arsenopyrite do occur. Several 

sets of faults cut the limestone, and some 

are intruded by dikes. Beryllium could be 

present.

SUGGESTIONS FOR PROSPECTING

These beryllium ores are not of a common, 

well-known type and can easily be overlooked. 

It seems worthwhile, therefore, to make available to future searchers experience gained by 

the writer over several seasons.

It should be emphasized that the fluoriteberyllium rock can be recognized visually, 

although some practice is needed if it is in 

dolomite. All the deposits discussed in this 

report were discovered in this manner. The 

chief value of the beryllium detector is to 

confirm the beryllium content of the ores and 

to trace ore zones through areas covered by 

tundra. The detector proves valuable in 

tracing ore into dolomitized limestone but 

is no substitute for careful prospecting. A
SELECTED BIBLIOGRAPHY 17

prospector who has examined any of the lodes 

discussed herein to familiarize himself with 

the ore has a good chance of recognizing 

other lodes that may crop out elsewhere.

Geochemical reconnaissance by use of 

stream sediments is of value for outlining 

broad areas that contain beryllium lodes and 

is considered to be the best method available 

for prospecting in areas not covered already 

by such reconnaissance. In our work, we took 

a bulk sample of the fine-grained sediment 

found in the lee of boulders in most streams. 

Most of this sediment passed a 40-mesh 

screen. If it proved impractical to secure 

such sediment, larger amounts of coarser 

material were screened to obtain sufficient 

material. On hillslopes without streams, 

sediments in rivulets or water-sorted alluvium were sampled. A dependable method 

using an ultraviolet light and common chemicals to determine trace amounts of beryllium 

has been developed by the Geological Survey 

(Patten and Ward, 1962) and can be applied in 

the field.

The background content of beryllium in 

sediments from the limestone areas was determined to be less than 2 ppm. Values between 3 and 10 ppm are definitely anomalous, 

and experience shows that where values are 

consistently greater than 15 ppm, megascopic 

amounts of fluorite-beryllium vein material 

are present either in the stream bed or in 

bedrock nearby. If values reach 30 ppm in 

areas without noticeable skarn in bedrock or 

in the stream bed, veins as large as those in 

Tin Creek or Rapid River probably exist 

within a few hundred feet; if values are found 

in excess of 100 ppm, large quantities of ore 

should be found within a few dozen feet either 

in place or as numerous boulders in the 

creek bed, as is true in Camp Creek.

In prospecting new areas,particular attention should be paid to the limestone surrounding granites and to limestone areas qontaining dikes that weather dark brown. Present 

experience indicates that areas having numerous short dikes alined along theN. 70 85° 

E. fault system are more likely to contain 

fluorite-beryllium deposits than areas containing large and continuous dikes of rhyolite. 

The vicinity of dark dikes is considered more 

favorable than that of rhyolite and rhyolite 

porphyry, which are usually more closely related to tin deposits.

In areas containing tin lodes, as at Ear 

Mountain and Cape Mountain, attention should 

be focused on surrounding areas, particularly 

if dikes or fractures can be found nearby. 

Above all, any distinctly dark colored area in 

the usually gray or white limestone should be 

examined, especially if the dark area has a 

tinge of purple. Faint linear trends in thin 

alluvium on upland areas should be examined 

in detail.

Most of the ore is noticeably heavy because 

of its high fluorite content. It is more resistant to frost breaking than most of the argillaceous limestone, and blocks as much as 6 

inches in diameter can be found in float runs 

on gentle slopes where the associated limestone fragments seldom exceed an inch or 

two. In places the late fluorite veins cutting 

some of the ore have an unmistakable light 

bluish to purple coloration. Most of the fluorite in the ores, however, is fine-grained 

and white to grayish, and cannot be recognized easily.

Because all the promising lodes found to 

date are in limestone areas, the broad expanses of limestone in the York Mountains 

and to the east and north of Black Mountain 

should be prospected before attention is paid 

to the slate outside those areas specifically 

discussed in this report.

The fact that all the known lodes discussed 

herein consist of the usual fluorite-diasporechrysoberyl type does not preclude the possibility that other types may also exist.

SELECTED BIBLIOGRAPHY

Brooks, A. H., 1902, Placer gold mining in 

Alaska in 1902^ Contributions to economic 

geology: U.S. Geol. Survey Bull. 213, p. 

41-48.

Collier, A. J., 1902, A reconnaissance of the 

northwestern portion of Seward Peninsula, 

Alaska: U.S. Geol. Survey Prof. Paper 2, 

70 p.

Heide, H. E., 1946, Investigation of the Lost 

River tin deposit, Seward Peninsula, Alaska. 

U.S. Bur. Mines Rept. Inv. 3902, 57 p.

Heide, H.E.,and Rutledge, F.A., 1949,Investigation of Potato Mountain tin placer deposits, Seward Peninsula, Northwestern 

Alaska: U.S. Bur. Mines Rept. Inv. 4418, 

21 p.
18 BERYLLIUM DEPOSITS OF THE WESTERN SEWARD PENINSULA, ALASKA

Heide, H. E., Wright, Wilford, S., and Sanford, 

Robert S., 1946, Exploration of Cape Mountain lode tin deposits, Seward Peninsula, 

Alaska: U.S. Bur. Mines Kept. Inv. 3978, 

16 p.

Killeen, P. L., and Ordway, R. J., 1945, Radioactivity investigations at Ear Mountain, 

Seward Peninsula, Alaska: U.S. Geol. Survey Bull.l024-C, p. 59-94.

Knopf, Adolph, 1908, Geology of the Seward 

Peninsula tin deposits: U.S. Geol. Survey 

Bull. 358, 71 p.

Lorain, S. H. and others, 1958, Lode tin .mining 

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