12

west are prominent examples (fig. 2). Potato Mountain is thought to be simi-
lar except that erosion has not exposed the granitic core. The apex of an
altered granitic (quartz porphyry) dike (fig. 3) is exposed near the northern
summits.

A number of large faults and a dense network of minor faults and joints
pervade the metasediments. It is not evident whether this breaking took place
before, during, or after the granitic intrusion. The major faults are charac-
terized by a filling of crushed wall rock fragments, or crushed zone, ranging
from 1 or 2 to 10 or 15 feet in width. Some of these faults were traced for
thousands of feet.

Tin-Bearing Deposits

Tin occurs as cassiterite (Sn0,) either associated with quartz in vein-
lets or veins, or as disseminated minute crystals in tourmaline schists.
Pyrite and arsenopyrite occur with most of the quartz-cassiterite deposits,
but both quartz-cassiterite and quartz-sulfide deposits also occur alone.
Plastic, white to yellow-brown to red earthy mixtures of clays and other min-
erals usually occur with both the cassiterite and the sulfide deposits. How-
ever, cassiterite and sulfide deposits are found where the earthy deposits are
absent, and earthy clays are found that contain neither sulfides nor cassiter-
ite. The segregation and identification of these clayey minerals requires
specialized techniques beyond the scope of this project.

Massive quartz veins and extensive systems of smaller quartz veins and
veinlets pervade the Potato Mountain area. Except in the relatively
restricted tin-bearing zones, these quartz veins and veinlets usually contain
only traces to minor amounts of pyrite or iron oxides. The most common type
of tin deposit is a cluster of cassiterite-bearing quartz veinlets in tourmal-
inized metasediments adjacent to a fault, joint, or similar opening filled
with crushed shale or earthy clay. Many of the smaller clay-filled openings
contain quartz and cassiterite, but none of the larger faults were found to
contain more than traces of tin.

Permafrost

The bedrock and the detrital cover, throughout the Potato Mountain area,
remain permanently frozen; only the top few feet thaw during the summer.
Zones that remain thawed throughout the year occur within permafrost areas,
but no such zones were recognized at Potato Mountain. No apparatus was avail-
able for measuring temperatures in the permafrost or for determining the
depths to which the permafrost may extend. Brine solutions were left over-
night in drill holes to prevent freezing. Temperatures of the solutions,
after flushing out of the hole, were 28° to 30° F. Since warming and mixing
took place while flushing the holes, ground temperatures probably were about
20° to 25° F.

The ground temperature at 30 to 50 feet below the surface remains almost
constant throughout the year and usually is about equal to the average annual
surface temperature. The average annual surface temperature probably is about


33

Diamond drilling supplemented trenching in the South Gulch area. The
drill was used to probe areas too deeply buried to be exposed by trenching and
areas where trenching was slow and difficult. In the latter case, the drill-
ing results indicated where trenches were needed. When drilling started, the
available evidence suggested that the principal tin deposits were alined with
the eastward-dipping bedrock. Several poor exposures also suggested the pres-
ence of a mineralized westward-trending fault. Drilling results indicated
that the tin occurs in an irregularly disseminated stockwork of discontinuous
fracture fillings and bedding plane deposits associated with tin-bearing tour-
maline schists. Earthy clays are common. The intense fracturing and the com-
bination of hard tourmaline schists and soft earthy material made core recov-
ery poor and sludge samples doubtful. Drilling was stopped when it became
evident that additional holes would add little to the information obtainable
on the surface.

A 3-inch hand-held power auger was used to probe the frozen overburden.
The auger could penetrate 10 to 20 feet into frozen detrital material derived
from the softer schists and shales, but it would not pierce the rubble of
broken quartz and tourmalinized schist that usually covered the tin deposits.
The auger was used principally when laying out trenches. The information
gained usually was negative and of transient value. A few auger holes that
penetrated faults or other features have been recorded with trench sampling
results.

West Side of South Gulch

Seven trenches were started on the west side of South Gulch. Sample
locations are shown on figure 11, and sample descriptions and analyses data
are in table 10. Discontinuous extensions added to trenches are indicated by
the letter A or B following the trench number. Trenches LL-7 and LL-6 were
abandoned because only occasional traces of tin were found. Sections of
trenches LL-2 through 5 were continued to bedrock to expose a zone of quartz
veinlets about 1,000 feet long and 7 feet in normal width alined with the
metasedimentary bedding. Clay minerals with some quartz and cassiterite
extend outward from this zone along a fracture intersected by trenches LL-4
(samples 59-123 through 59-127) and LL-2 (samples 61-128 through 61-131).

The Adit Fault was intersected by trenches LL-2A, LL-3, LL-4, and LL-5. Only
scant traces of tin were found in the crushed filling. This fault extends
into the Iron Creek drainage.

East Side of South Gulch

Trenching was started on the east side of South Gulch shortly after
starting on the west side. The trench numbers indicate the order in which the
trenches were excavated; otherwise, procedures were the same. Trenches and
sample locations are in figure 12; sample descriptions and analyses data are
in table 11.

The trenching revealed irregularly disseminated quartz-cassiterite veins
and veinlets with pyrite, arsenopyrite, and hydrothermal clays associated with
hard tin-bearing tourmaline schists. Tin is most abundant in a zone about 300
feet long and 10 to 30 feet wide extending from trench RL-3 to trench RL-5.
Within this zone grade ranges from less than 1 to almost 10 percent tin; the


29

No tin found in
these placer pits

’e
/
4

\
© Line

123
Bo5

LEGEND

RSS) Placer concentration
(see text and table 8)

©  Churn-drill hole

° 500 1000
ae a sa |
Scale, feet

FIGURE 9. - Tin Placer Deposits, West Fork.


84

14,

15.

16.

17.

18.

19.

20.

21.

22.

23.

24,

25.

26.

Brooks, A. H. Geologic Features of Alaskan Metalliferous Lodes. Ch. in
Mineral Resources of Alaska, Report on Progress of Investigations in
1910. U.S. Geol. Survey Bull. 480, 1911, pp. 88-90.

Hess, F. L. Tin Resources of Alaska. Ch. in Mineral Resources of
Alaska, Report on Progress of Investigations in 1911. U.S. Geol.
Survey Bull. 520, 1912, pp. 89-92.

Smith, P. S. Notes on Mining in Seward Peninsula. Ch. in Mineral
Resources of Alaska, Report on Progress of Investigations in 1911.
U.S. Geol. Survey Bull. 520, 1912, pp. 340-342.

Brooks, A. H. The Mining Industry in Alaska in 1912. Ch. in Mineral
Resources of Alaska, Report on Progress of Investigations in 1912.
U.S. Geol. Survey Bull. 542, 1913, p. 50.

Chapin, Theodore. Placer Mining on Seward Peninsula. Ch. in Mineral
Resources of Alaska. Report on Progress of Investigations in 1913.
U.S. Geol. Survey Bull. 592, 1914, p. 393.

Eakin, H. M. Tin Mining in Alaska. Ch. in Mineral Resources of Alaska,
Report on Progress of Investigations in 1914. U.S. Geol. Survey Bull.
622, 1915, pp. 81-94.

Brooks, A. H. The Alaskan Mining Industry in 1915. Ch. in Mineral
Resources of Alaska, Report on Progress of Investigations in 1915.
U.S. Geol. Survey Bull. 642, 1916, pp. 27-28.

Mertie, J. B., Jr. Lode Mining and Prospecting on Seward Peninsula;
Placer Mining on Seward Peninsula. Ch. in Mineral Resources of Alaska,
Report on Progress of Investigations in 1916. U.S. Geol. Survey Bull.
662, 1918, pp. 443-458.

Harrington, G. L. Tin Mining in Seward Peninsula. Ch. in Mineral
Resources of Alaska. Report on Progress of Investigations in 1917.
U.S. Geol. Survey Bull. 692, 1919, pp. 353-361.

Cathcart, S. H. Mining in Northwestern Alaska. Ch. in Mineral Resources
of Alaska, Report on Progress of Investigations in 1918. U.S. Geol.
Survey Bull. 712, 1920, p. 195.

Harrington, G. L. Mining on Seward Peninsula. Ch. in Mineral Resources
of Alaska, Report on Progress of Investigations in 1919. U.S. Geol.
Survey Bull. 714, 1921, p. 236.

Brooks, A. H. The Alaska Mining Industry in 1920. Ch. in Mineral
Resources of Alaska, Report on Progress of Investigations in 1920.
U.S. Geol. Survey Bull. 722, 1922, p. 22.

Steidtmann, E., and S. H. Cathcart. Geology of the York Tin Deposits,
Alaska. U.S. Geol. Survey Bull. 733, 1922, 130 pp.


38

Sholes with partly
developed sloty
cleavage

——s00

Western limit of a
Min deposition ° z
(see figure tt)

~ 00
0.5 ft of clay, quar

pyrite, and cass

on 0 bedding
is the eastern limit
of tin deposition
(see figure 12)

South Gulch

sholy _\

—100

LEGEND 2ing solutions apparently
ascended vertically along joints _
— ULe2 Bulldozer trench * : Gnd fractures ond ‘spread taterolly s00
60-197 Specimen , anolized e along bedding planes
petrographically Wao
__ DDH-5 Diomond-drill hole 213.0 500
+ West East

FIGURE 13. - Cross Section Through Diamond-Drill Holes 3, 4, and 5.

Trenches RL-1B, RL-13, and RL-9 exposed a major fault that also was penetrated
by a 15-foot auger hole between trenches RL-13 and RL-9. The fault contained a
filling of crushed shale and clay but no more than scant traces of tin. Clusters
of quartz veins and veinlets along the north wall of the fault (exposed in trenches
RL-1B and RL-13) contain up to 0.3 percent tin locally, but average about 0.1 per-
cent tin or less. No identifiable tin mineral was noted in trench RL-9, but analy-
ses indicated 0.01 percent tin.

A crushed zone similar to the major faults was exposed at the north end of
trench RL-1. An apparent extension of this zone was found by using an auger in
trench RL-2 (sample 59-74). Bedrock could not be exposed in this area because of
large hard blocks of schist and shale imbedded in frozen mud. Trench RL-16 was
excavated to expose this zone, but was only partially successful. Trench RL-4 could
not be excavated to bedrock along the projected strike because of large hard boul-
ders imbedded in frozen mud. No evidences of extensions of this crushed zone were
recognized in trenches RL-3 or RL-5.

TABLE 11. - Description and analyses of trench samples,
east side of South Gulch

Description Analyses
Sample Tin,
Number Length, Character of material per- |/Spec.1 |Petro.?
feet cent
Trench RL-1
59-81 12 Black shale with about 50 percent quartz 0.03) - -
veins.

59-82 2 dO.sseeeseee .07 - -
59-83 2 dows... 204) - -
59-84 2 Clay, crushed shale, and schist and quartz.. 13) - -
59-85 2 do.s..eee seceeeeeeeseee| 260] - -
59-86 2 dowssseee 3.00] - -
59-88 2 dossseseeee 3.40| - -

See footnotes at end of table.


LIVING CONDITIONS

Throughout northern Alaska the expansion of communication services and
air transport facilities has alleviated the disadvantages of isolation. Field
parties can communicate by radiotelephone. Repair parts and perishable food
can be delivered by bush plane as required. Food, clothing, and many hardware
items are stocked by stores in Nome or Teller; both Wales and Shishmaref have
small general stores. Supplies or parts not available locally can be ordered
by telephone or telegram and obtained by air in a few days from distributors
in the larger Alaskan cities or even from the factory.

Light uninsulated houses or tents are adequate and comfortable in summer.
A common practice is to mount light cabins or tents on skids so they can be
towed about with a tractor as needed. Heating is ordinarily by oil stoves.
Water is obtained from streams or ponds.

Sturdy well-insulated houses are essential in winter. Often water can be
obtained only by melting snow or ice as streams may be frozen. In the larger
communities, water is sold by distributors who make house-to-house deliveries
with a tank truck; other companies collect garbage and sewage which are
trucked to public dumps for disposal.

PHYSICAL FEATURES

Potato Mountain rises from the northern coastal plain of the Seward
Peninsula (fig. 3) to five rounded summits at 1,000 to 1,370 feet that form
the northern bastion of a low ridge extending south-southwest to York. The
northeast, north, and west sides of the mountain are drained by a number of
short streams that flow directly into Lopp Lagoon. The east and southeast
sides of the mountain are drained by the headwater tributaries of Buck Creek
which flows into Lopp Lagoon via Grouse. Creek and the Mint River. Lopp Lagoon
empties into the Chukchi Sea, an arm of the Arctic Ocean.

A thick growth of subarctic tundra vegetation extends from sea level to
about 800 feet and a gradually thinning growth extends to the mountaintops.
There are no trees; sparse groups of willow bushes, up to 4 or 5 feet high,
grow in some of the valleys. Underlying the tundra vegetation is a cover of
rock detritus, usually 3 to 5 feet thick but occasionally ranging in thickness
from a few inches to 20 feet or more. The tundra vegetation and detritus
blanket the entire area except for small scattered patches of bedrock exposed
on streambanks or near mountaintops.

CLIMATE

The Potato Mountain area is between the Chukchi Sea and the Bering Sea.
During the summer the normal temperature range at sea level is from 33° to
50° F. The wind blows persistently, and often is accompanied by fog and driz-
zling rain or occasionally snow, although the total annual precipitation is
low. During the winter persistent winds and consequent drifting snow prevail,
but temperatures are more moderate than at inland locations at the same lati-
tude. No weather records have been kept at Potato Mountain. Except that on


66

TABLE 24. - Description and analyses of trench samples,
Upper Buck Creek drainage basin

Description Analyses
Sample Tin,
Number Length Character of material per- |Spec.1 | Petro.?
feet cent
Trench BC-8
61-1 = Selected specimens, quartz veinlets... - xX
61-132 8 Crushed zone in fault, chip samples... - -
No sample 24 Iron-stained shale with few quartz - - -
veinlets, chip samples.
61-133 10 Quartz-pyrite veinlets in shale, 05 - -
chip samples.
61-134 10 Or eccccccccscccccccevcsscseceres -13 - -
No sample 21 Iron-stained gray shale, chip samples. - - -
61-135 7 Quartz lenses in gray shale, chip OL - -
samples.
61-136 7 GOcesccecccccvcncccsvcccssssevece 01} - -
Total or| 87 03) - -
average
Trench BC-5
61-3 - Selected specimens, quartz veinlets...| 0.03} - -
61-137 80 Occasional quartz-clay veinlets in -O1] - -
shale, chip samples.
61-138 5 (Pa Ol] - =
Trench BC-3
59-192 - Specimens of 1 to 3 inch quartz 0.04) - x
veinlets.
Other areas
59-193 - Specimens from prospect pit between 0.08] xX Xx
trenches BC-5 and BC-8.

1§See section entitled "Spectrographic Analyses."
2See section entitled "Petrography."

Miscellaneous Prospects

The various lode tin prospects in the Potato Mountain area were examined
during the investigation. Routine examinations included sampling the outcrop-
pings, if exposed, the dumps, and the detrital cover downhill from the pros-
pect. A description of the Daisy lode prospect is included with the data on
lode deposits in the Iron Creek area. An adit on the east slopes of Little
Potato Mountain is included in the area sampled at the head of West Fork. The
more prominent of the remaining prospects are described in the sections that
follow. Numerous other pits were examined, but no tin or only scant traces
were found.

Drusy Quartz Vein and Andesite Dike

A notable feature of the Buck Creek area is a prominent quartz vein aver-
aging about 12 feet wide, that was traced at least 8,000 feet from the Left


48

Locati

TABLE 13. - Diamond-drill-hole log and sample analyses, hole 2

on:

Elevation of collar:

Depth:
Dip:

Bearing:

114.

-35°

4 feet

N 80° W

See figure 11

778 feet

Date begun: July 27, 1961
Date finished: Aug. 4, 1961
Core sizes: BX to 8.3 feet

AX to 114.4 feet

Foota

e

Percent

From-

To-

Interval

Core
recovery

Tin in
sludge

Tin in
core

Tin
average

Formation

0.0

18.2

25.7

33.6

54.3

65.0

18.2

25.7

33.6

54.3

65.0

114.4

18.2

7.5

7.9

20.7

10.7

49.4

18

31

66

67

83

78

0.01

+03

<.01

0.04

0.03

Broken light-gray phyllite
with numerous dark spots
about 1/16 inch in diam-
eter composed of tourma-
line and ilmenite. Iron
stain on fractures.
Similar spotted phyllite
but more clay, iron stain,
and quartz and some
tourmaline.

Darker gray similar
spotted phyllite with
some quartz, tourmaline,
and iron-stained clay and
a trace of pyrite.

Medium-gray phyllite with
numerous 1/16 inch spots
of tourmaline and ilmen-
ite. Quartz-pyrite vein-
lets present but scarce.

Medium-gray tourmalinized
phyllite with veinlets
containing abundant mus-
covite and quartz and
less goethite, limonite,
pyrrhotite, and pyrite.
There is a contact with a
lower bed at 58.3 feet
but veinlets extend into
this bed.

Dark-gray to black rela-
tively unbroken phyllite
with minor amounts of
magnetite and ilmenite
and a small amount of
tourmaline. A few quartz-
pyrite veinlets extend to
84.0 feet.



46

relatively high-grade material encountered in the trenches resulted from resi-
dual concentration. The trenches therefore were dug several feet into bedrock
before sampling. Combined trenching and drilling results indicated a deposit
alined with metasedimentary bedding.

Diamond-Drill Hole 3. - DDH-3 (figs. 12 and 13 and table 14) was drilled
to determine the dip of the quartz-cassiterite deposit exposed in trench
RL-4. At the time the hole was started, evidence indicated that this was a
zone of veinlets alined with the metasedimentary bedding. Drilling results
indicated that this was not the case. The first 20 feet of hole penetrated a
zone containing abundant tin minerals. When this hole was completed, trenches
RL-17 and RL-18 were excavated and exposed an irregular high-grade concentra-
tion of tin minerals along a westward-trending vertical fracture.

Diamond-Drill Hole 4. - DDH-4 (figs. 12 and 13 and table 15) was drilled
to determine if the tin minerals in trenches RL-5 and RL-5A were parts of a
lode deposit alined with and underlying the eastward-dipping limy shales
exposed east of trench RL-5 (fig. 13). The hole was angled so that it would
also intersect the eastward extension of a line drawn through the tin-bearing
zone encountered in trench RL-4, DDH-3, and trench RL-5; results indicated
that this tin-bearing zone did not extend to the east of trench RL-5. No
definable lode deposit alined with bedding was found under the shaly limestone.
The hole intersected a generally low-grade stockwork of quartz-clay-cassiter-
ite minerals in tourmalinized tin-bearing rock.

Diamond-Drill Hole 5. - DDH-5 (figs. 12 and 13 and table 16) was drilled
to intersect the sedimentary beds that cropped out under deep overburden
between trenches LL-1 and RL-1. The object was to determine if these beds
contained tin deposits alined on bedding. The hole was continued until it
intersected magnetite-bearing beds previously intersected by DDH-2, and
exposed in the adjacent trenches (fig. 11). No definable lode deposit was
encountered. The hole penetrated a widespread low-grade zone of quartz veins
with clay, pyrite, and arsenopyrite in tourmalinized rock. The bottom of this
hole is about 380 feet below the tin outcroppings in trenches RL-4 and RL-5
(figs. 12 and 13). No evidence was noted that would indicate that the bottom
of the hole was close to a granitic intrusive.

Summary, Diamond-Drill Holes 1 Through 5. - The drilling results, coupled
with the trenching results, indicate that, in the South Gulch area, tin occurs
disseminated in an irregular stockwork of veins and veinlets of quartz, clay,
cassiterite, pyrite, and arsenopyrite associated with tin-bearing tourmaline
schists. The stockwork in this area appears to be independent of the major
faults. The northern and southern limits of deposition are vaguely defined.
The western limit of deposition generally coincides with a black phyllite con-
taining minor amounts of ilmenite, magnetite, and pyrrhotite that was cut by
diamond-drill holes 2 and 5 (figs. 11 and 13 and tables 13 and 16). The east-
ern limit of tin deposition (except for a small amount of tin in trenches RL-6
and RL-8) is a shaly limestone cut by diamond-drill hole 4 and trench RL-19
(figs. 12 and 13 and table 15). None of the drill holes encountered evidences
of granitic intrusives like those found in the Cape Mountain and Lost River
tin-bearing areas.



52

TABLE 16. - Diamond-drill-hole log and sample analyses, hole 5

Location: See figures 12 and 13 Date begun: Aug. 30, 1961
Elevation of collar: 724 feet Date finished: Sept. 13, 1961
Depth: 213.0 feet Core sizes: BX to 7.6 feet
Dip: Vertical AX to 75.0 feet
Bearing: --- EX to 213.0 feet
Footage Percent
From-} To- |Interval| Core |Tin in|Tin in] Tin Formation
recovery|sludge| core |average|
0.0} 35.0] 35.0 29 0.07 | 0.07 0.07 | Broken gray to dark-gray

tourmaline schist with
abundant quartz, minor
amounts of pyrite, goe-
thite, arsenopyrite, and
magnetite and a trace of
gypsum.

35.0] 68.0] 33.0 35 02 - - Hard black shale cut by an
occasional quartz veinlet
with a little pyrite or
by small clay-filled
fractures. A few beds
contain chlorite.
68.0/150.0} 82.0 26 +02 - - Hard, much jointed dark-
gray to black shales
(some might be called
schists) with much tour-
malinization cut by occa-
sional quartz-pyrite and
calcite veinlets.
150.0/163.8] 13.8 36 02 - - Gray shale to chlorite
schist with tourmaline
and quartz-pyrite-
arsenopyrite veinlets.
163.8 |169.0 5.2 46 204 - - Tourmaline schist with
quartz-pyrite-
arsenopyrite veins or
veinlets and calcite
veinlets and some frag-
ments of chlorite schist.

169.0 |174.0 5.0 8 -03 - - Only tourmalinized black
shale fragments recovered.
174.0 |213.0] 39.0 18 02 - - Black, much broken phyl-

lite with abundant seri-
cite and biotite and a
few calcite veinlets.
Minor to trace amounts of
magnetite, ilmenite, and
pyrrhotite are present.



56

Sutter Creek, Iron Creek Drainage Basin

Placer Sampling, Iron Creek

The results of Bureau of Mines 1943 churn drilling on Sutter Creek and
Iron Creek (figs. 3 and 15 and table 18) indicated that a placer tin deposit
extended from the mining pit at the mouth of Sutter Creek upstream to the
mouth of Iron Creek, and up Iron Creek to the base of Big Potato Mountain.
On Sutter Creek, the grade is uniformly low (table 6). Examination of Sutter
Creek indicated that no tin occurs in the banks or in tributaries below Iron
Creek. Only traces of tin were found in Sutter Creek above Iron Creek. The
grade of the deposit on Iron Creek is greatest near the base of Big Potato
Mountain, and drops as it extends downstream.

TABLE 18. - Churn-drilling results, 1943, Iron Creek!

Line and hole Mining Tin Abundance
section, feet lb per cu yd factor?
Line 1:

2.0 0.83 166

3.0 +15 45

-0 Trace Trace

5.0 -40 200

0 Trace Trace

0 Trace Trace

0 Trace Trace

5.5 224 132

6.0 45 270

11.0 -06 66

0 Trace Trace

5.0 1.01 505

6.5 15 97

6.0 12 72

8.0 89 712

6.0 1.32 792

10.0 +09 90

7.0 ell 77

7.0 +30 210

10.0 86 860

0 Trace Trace

Cut 8..... 4.7 3.38 1,585

1Data from Bureau of Mines Report of Investigations 4418 (30)
except last column.

2(Mining section, feet) x (tin, 1b per cu yd) x 100 = abundance
factor. See section of this report entitled "Placer Sampling
and Evaluation."


44

TABLE 11. - Description and analyses of trench samples,

east side of South Gulch--continued

Description Analyses
Sample Tin,
Number = {Length,| Character of material per- |Spec.1 |Petro.?
feet cent
Trench RL-20 (East Fork, Trench RL-5A)
61-88 5 Altered shale, quartz, and clay.............|/<0.01| - -
61-89 5 <O1) - -
61-90 5 <-O1) - -
61-91 5 <-O1) - -
61-92 5 Ol} - -
61-93 5 .02{ - -
61-94 5 <.01] - -
61-95 5 <01}; - -
61-96 5 <01} - -
61-97 5 <-01| - -
61-98 5 <.01] - -
61-99 5 +01) - =
61-2 | _- | Specimen; veinlet 0.5 foot wide............-| - | - xX
Trench RL-6
60-140 - Specimen; hard fine-grained black shale.....|<0.01 - x
60-141 - Specimen; black fissile shale and quartz <.01 - xX
veins.
60-142 - Specimen; iron-stained shale, some clay, <-O1} - x
and quartz.
60-143 - Specimen; dark-gray slaty shale. <-O1] -
59-9 2 Crushed shale and quartz.. 202] - -
59-10 1 dowseseseee seeeeee see -02| - -
59-11 9 Limy shale with quartz veinlets. <.01] - -
59-12 8 (Cree <.01} - -
59-13 10 Iron-stained shale, clay, and quartz. 259 - ad
59-14 1 Crushed shale, quartz, and clay...... | <.01 - ~
Trench RL-7
59-2 2 Crushed shale, some clay....ssssseeereeeeees| 0.06] - -
59-3 1 dows seeeeeeeee 06) - 7
59-4 1 Iron-stained shale. . .02{ - =
Trench RL-8
59-5 2.5 | Iron-stained shale, clay, and quartz. «| 0.76) = -
59-6 2.5 Oss ee recsrevececceccececereneee 255) - -
Total or 5 266) - -
average
59-7 -5 | Clay and quartz veinlet......eesereesreeeere 02 - -
Trench RL-9
60-117 1 Specimen of 1-foot quartzite bed in shale.../<0.01] -
60-118 - Specimen of black shale.......+..++ . Ol} - -
60-119 12 Clay and crushed shale, little quartz....... 01] - =
Trench RL-10
60-137 [200 [Black shale with a few quartz lenses........[<0.01[ - | =
Trench RL-11
60-136 [100 Black shale with a few quartz lenses......../<0.01] - -

See footnotes at end of table.


FIGURE 15

1000, 2000 3000

Scale, feet

FIGURE 6. - Potato Mountain With Location of Figure Areas.


34

Medium groy Light gray,
phyllite spotted. phyllite

he

59-135—7/

»

Dork grays
to black

phyllite
3h
vw Minor amounts off
y fullide-minerats 6
> and. quartz clong ON
Contact aN
7 N
N
Section through DDH-2
LEGEND
<1 mpl
60-198 Sample ° 200 400
Bulldozer trench
LL-5 Scole, feet
© Churn-drill hole
<<-@ | Diomond-drill hole
ooR-2

FIGURE 11. - Lode Sampling, West Side of South Gulch.


65

ys

Q 100 200

Scale, feet

LEGEND
60-136 Sample

ies
$=— * Bulldozer trench

BC-7

Sample pit
x Trace of tin a
xx Moderate amount of tin gs
KX Abundant tin

ool

FIGURE 20. - Lode Sampling, Upper Buck Creek.

shale (fig. 20 and table 24). Although individual quartz veinlets were found
that contained 2 percent or more tin, the overall grade of the deposit does
not exceed 0.10 percent tin.


CONTENTS

ADStLACt sce eseccssceseaes
Introduction.....
Acknowledgments...
Location and accessibility
Labor...seeeecsccescecs
Living conditions...
Physical features...
Climate.....seeseeee
Water supply........
Property and ownership
HiStOry.ceccccccccsece
Placer mining.......
Lode prospecting.........-
General geology..........-
Bedrock. .eesessscscscecoee
Tin-bearing deposits......
PermafroSt..sessseveeeee
Detrital COVersssseeecesecccecsccceccsccee
Placer gravels..........
Work by the Bureau of Mines.
Nature and extent......
Definition of terms.........
Placer sampling and evaluation
Churn drilling..
Test pitting....
Detrital cover sampling and evaluation methods.
Augering and panning.........06.
Amount of tin detectable..
Lode sampling and evaluation methods
Bulldozer trenching.......... .
Diamond drilling...... seeccees

Summary of published data on relative abundance of tin in
Placer depoSitS..ccccccscccccvere
Old placer mining pits..
Buck Creek....seseeeeccecercvenes a eeee
Left Fork drainage basin......eseeeeeee oe
West Fork and Peluk Creek drainage basin..........
Placer sampling, West Fork..........
Detrital cover sampling, West Fork..
Lode sampling, West Fork.........
West side of South Gulch..
East side of South Gulch..
Diamond drilling results..
Peluk Creek area.
Sutter Creek, Iron Creek drainage basin...
Placer sampling, Iron Creek......s.e+eee
Detrital cover sampling, Iron Creek..........-
Lode sampling, Iron Creek area...eceeeececereces

i)
k
1

WCOMDDADUWWEH


68

c
3 LEGEND

+ Sample pit in detrital cover
x Trace of tin
3 Bulldozer pit

a Abundant quartz veins
in exposed bedrock. No
tin, but traces of
a ". | pyrite or limonite
In some veins

le} 500 1000
a a ce |
N Scale, feet
2
°
SE 20°

West Fork

FIGURE 21. - Intersection of Buck Creek and West Fork.

but no visible cassiterite. Two specimens were selected from what appeared to
be the highest grade material.

Sample descriptions and analyses data are in table 25.

TABLE 25. - Description and analyses of selected specimens, Red Fox prospect

Description Analyses
Sample Character of material Tin, |Spec.1|Petro.2
Number|Length, feet percent
60-12 - Selected specimens, western pit... 0.34 x -
60-13 - Selected specimens, shaft dump.... 07 xX -

1See section entitled "Spectrographic Analyses."
2See section entitled "Petrography."


67

Fork-Buck Creek intersection northward to the valley of Red Fox Creek (fig. 3).
Probably this vein extends farther on one or both ends. The vein pinches and
swells, and lesser veins and veinlets extend irregularly into the shale walls.
In some sections, the vein and the accompanying veinlets form an extensive
network up to 100 feet wide that encloses numerous shale horses and fragments.
The smaller shale fragments serve as nuclei for radiating clusters of quartz
crystals. Drusy cavities are common.

Northeast of the airfield (fig. 3) is an andesite dike (see sample 60-2,
in the section of this report entitled "Petrography") about 3 feet wide,
nearly vertical, and striking about N 25° W. The length was not determined.

Extensive panning along the outcrop of the drusy quartz vein and the
andesite dike indicated that no tin occurs in either. The only heavy metallic
mineral noted was an occasional trace of pyrite or limonite.

Mouth of West Fork

Placer miners who had mined on Buck Creek and West Fork reported that a
tin-bearing vein crossed the bed of West Fork about 300 feet from the mouth.
Abundant quartz veins and veinlets, some of which are iron stained, are
exposed in the streambed in this area and downstream to the West Fork-Buck
Creek intersection. Samples of these quartz veins contained occasional small
amounts of pyrite or limonite, but no tin. Samples 60-1 and 60-6 are typical
of the shale bedrock; sample 60-7 is a typical specimen of a vein cutting the
bedrock (see section of this report entitled "Petrography"). The detrital
cover on the banks of both Buck Creek and West Fork was sampled (fig. 21) with
negative results. While investigating Upper Buck Creek, occasional traces of
tin were found in the detrital cover 200 to 300 feet from the mouth of the
first right limit tributary above West Fork (fig. 21). The tin could not be
found in bedrock, but a crushed zone was found. By means of aerial photos,
this crushed zone was traced to the general locality of the reported tin vein
on West Fork. Trenches excavated on both sides of West Fork intersected.
crushed shaly material. No tin was found. It was concluded that, in the
streambed, the soft crushed zone had served as an efficient nugget trap and
hence resembled a lode outcropping.

Red Fox Prospect

The Red Fox prospect is at the head of Buck Creek on the summit of the
divide that separates the Buck Creek drainage basin from the Red Fox drainage
basin (figs. 3 and 22). The principal working is a 5- by 5-foot timbered and
lagged shaft. The size of the dump suggests that the shaft is about 30 feet
deep, if no drifts were driven. When examined, this shaft was filled with ice
to within 8 feet of the surface. The workings also include four hand-dug
trenches and a number of shallow pits. All workings are probably over 50
years old.

The detrital overburden and the dumps were sampled. The detrital over-
burden on both sides of the divide contained a scant trace of tin (fig. 22).
Examination of the dumps revealed a small amount of rock with visible pyrite,


70

(fig. 23) contained no
tin at all. Samples
taken from the headwater
tributaries of Peluk
Creek contained no tin.
The tin in Upper Buck
Creek was found to have
been derived from
another source (see
section on this drainage
basin). Therefore, it
seems apparent that
neither this quartz
porphyry dike nor the
adjacent rocks contain
significant deposits of
tin.

Alan Dale Prospect

The Alan Dale pros-
pect is thought to be
located as shown in fig-
ure 23. The dump was
examined and the detri-
tal cover downslope from
the pit was sampled. No
more than a scant trace
of tin was found.

LEGEND

+ Sample pit-no tin
x Trace of tin

© Old prospect pit
== Bulldozer trench

ro} 500 1900

Scale, feet

Eureka Prospect

The Eureka prospect
is on the northeast side
of the summit of Little
Potato Mountain 1,500 feet N 35° W of the Daisy lode (figs. 3 and 5). Work-
ings include a shaft about 6 feet deep, a hand-dug trench, a sample pit, and a
small rock-walled roofless shelter. The nature and distribution of quartz
float visible on the surface would suggest that quartz veins and veinlets
occur generally alined with bedding in shales that strike N 15° W and dip 20°
to the east. The quartz float occurs in an area about 40 feet wide and about
300 feet long.

FIGURE 23. - Quartz Porphyry Dike and Alan Dale Prospect.

Specimens, selected from the dumps of the workings, were analyzed. Speci-
men descriptions and analyses results are in table 26. No additional work was
done at this prospect.


27

TABLE 7. - Description of typical specimens of vein and dike
rocks found in the Buck Creek placers--continued

Specimen Petrographic description Tin,
percent?
243.....|The specimen is a highly altered acidic dike composed of 0.02

hydrothermal clay, tentatively identified as hydromus-
covite (hydromica or illite), and a small amount of clear
quartz. Dark, prismatic-shaped areas are filled with
tourmaline, probably an alteration product of earlier
ferromagnesian minerals.

245.....|The specimen is composed of quartz with small dark areas 2.78
of cassiterite and tourmaline.
246.....|The specimen is composed of quartz with small amounts of 04

pyrite, limonite, and tourmaline. Traces of tin and zinc
are present, but no tin or zinc mineral was detected.

247..... |The specimen, locally termed "greenstone," is a quartz <.01
basalt containing the calcic feldspar labradorite.
1Determined by chemical analyses. Dash indicates no chemical analysis made.

Left Fork Drainage Basin

Examination of Left Fork (fig. 8) revealed little tin above the mining
pits. However, reliable samples could not be taken because of a deep cover
of frozen muck. No tin was found in the banks. Test pits were dug in each
of the three headwater tributaries of Left Fork. Panned concentrates con-
tained chiefly phyllite fragments, quartz, and limonite pseudomorph after
pyrite. In the center headwater tributary a shallow and narrow tin-placer
deposit contained somewhat under 1 pound of tin per cubic yard near the mouth
and less towards the head. The northern headwater tributary contained little
more than traces of tin. The southern headwater tributary contained only the
usual trace of tin commonly found in placer gravels throughout the area.
Evidently the tin in the Left Fork placers was derived principally from the
area drained by the central headwaters tributary. Descriptions of lode
deposits in the area drained by this tributary are included with the data on
lode deposits in the West Fork drainage basin.

West Fork and Peluk Creek Drainage Basin

Placer Sampling, West Fork

The results of Bureau of Mines 1943 churn drilling on West Fork and Peluk
Creek (fig. 9 and table 8) indicated that a pay streak extended nearly to the
head of West Fork but that little tin occurred on Peluk Creek except near the
mouth. Test pits were dug in all the headwater tributaries of Peluk Creek,
including dry gullies. No tin was found. This and the configuration of the
West Fork placer deposit suggested that some placer tin may have been derived
from the area near the mouth of Peluk Creek but that most of the tin was
derived from the headwaters of West Fork.


13

equal to the average annual temperature at Wales (22° F). The geothermal gra-
dient varies substantially, but averages about 1° F rise in temperature per 70
feet in depth. Therefore, freezing temperatures may extend about 700 feet
below the surface. This estimate of the depth of permafrost could not be
verified.

Detrital Cover

The principal agent of erosion is frost breaking which can take place
only where thawing and freezing occur. The depth of summer thaw varies
greatly. The thaw penetrates to great depths where surface water percolates
through porous strata on hillsides; on relatively flat, well-drained but imper-
vious surfaces, the thaw may penetrate only 2 feet or less. A cover of vegeta-
tion insulates the surface from the sun's heat and tends to inhibit thawing.

Rock debris covers the entire surface, except for an occasional protrud-
ing outcrop of resistant rock or a streambank bared by water action. The
nature of the detrital material depends on the available openings in the
source rocks. Water enters the openings, freezes, expands, and breaks the
rock; the resultant rock debris may vary from coarse blocky fragments several
feet in diameter to individual crystals or fragments of crystals of the com-
ponent rock minerals. The debris derived from shales and schists generally
forms a soil that supports a vigorous growth of tundra plants and mosses.
Calcareous rock debris tends to inhibit the growth of tundra plants which
apparently thrive best in an acidic environment. Most igneous rocks and many
sedimentary or metasedimentary rocks break into coarse angular blocks and
fragments that can support little plant life. Where vegetation is abundant a
layer of peat, ranging in thickness from a few inches to a few feet, forms on
the surface.

The surface evidences of a rock outcropping depend on the nature of the
rock. The outcrop of a hard dense rock that resists frost breaking may pro-
trude through the overlying mantle or may be marked by an abundance of large
angular fragments on the surface overlying the outcrop. Rocks of medium
resistance to frost breaking ordinarily have no protruding outcroppings, but
the outcroppings may be indicated by fragments in the overburden. Relatively
soft rocks normally have no visible surface expression; the outcrop is eroded
slightly below the outcropping of the more resistant rocks. The material
derived from the softer outcrop usually breaks down into small fragments that
mix with fragments of more resistant rocks to form an indistinguishable cover.
Tin and other hydrothermal minerals commonly occur in deposits that are less
resistant to erosion than surrounding rocks; therefore, it is unusual for such
deposits to have any visible surface expression.

The frost-broken material is carried downhill as an earth flow that fol-
lows regular paths, or float lines, perpendicular to the elevation contour
lines. Practically all movement of material takes place in a near-surface
"Zone of movement" (fig. 5). This zone develops because the ground thaws
downward from the surface nearly to an equilibrium point early in the summer.
A narrow transitional zone, that thaws gradually as the summer advances, under-
lies the zone of movement. The transitional zone merges into an underlying


19

thawed gravels, and usually filled with water. Consequently, the evaluation
of samples from these pits was limited to noting the degree of roundness of
the cassiterite crystals, and to determining whether tin was absent, scarce,
or abundant. This was adequate for the purpose, and no attempt was made to
make more exact determinations of grade.

Detrital Cover Sampling and Evaluation Methods

The second stage of the investigation was to sample the detrital cover.

The general plan was to sample along the stream banks in areas from which the
placer deposits could have been derived. Sample pits were sunk to permafrost
on the sides of the valleys, 5 to 30 or more feet above the valley floor (high
enough on the hillside to make it reasonably certain that any material found
had been derived from the hill above rather than transported by stream action).
The line of sample pits roughly paralleled the stream at intervals of from 30
to 50 feet; most commonly, three samples were taken per 100 linear feet.

Augering and Panning

Sample pits in the detrital material were dug by hand, by bulldozer, and
by gasoline-powered posthole auger. Under most conditions, the power-driven
auger was the most economical and satisfactory sampling tool because it pro-
duced an adequate and reasonably uniform sample within a minute or two after
the hole was started (fig. 7). The usual practice was to drill down to perma-
frost, usually 2 to 3 feet, with a 6-inch posthole auger, stop the machine,
and pull up the auger. About one gold pan of material could be obtained from
the scroll; this was the sample. On steep rocky hillsides or where boulders
were abundant, samples could be obtained more rapidly from hand-dug pits.
Bulldozer trenching was slower than the other methods (in samples evaluated
per man-day).

Two men, using a tractor and sled to haul panning water and using the
gasoline-powered auger to obtain samples, could drill, sample, concentrate,
and evaluate 30 to 40 holes per 8-hour day. Cleaning and concentrating a sam-
ple usually required more time than obtaining the sample. The panning was
done with standard gold pans; the panning water was in two No. 3 washtubs.

The sample was washed and screened in a pan in which a close pattern of
3/8-inch round holes had been drilled. The washed oversize was inspected for
"nuggets" and discarded. Clay, soil, ice, and vegetable matter were washed
from the undersize and decanted off; then the heavy minerals were concentrated
by the usual panning techniques. Because of the relatively small size of the
individual samples and the great variation in the size range and condition of
the sampled material, mechanical concentration was considered impractical with
any presently available equipment.

The panned samples were graded visually. The results were recorded as:
O--no tin; 1 (or x)--trace of tin-bearing concentrate; 2 (or xx)--more than a
trace but less than an ounce of tin concentrate; 3 (or xxx)--an ounce or more
of tin concentrate. A more exact evaluation would have required additional
time and equipment and was considered unnecessary. Sample sites were marked
to indicate the amount of tin found. Occasionally the identification of


15

stream transport are about in equilibrium and have been so for a long time.
Buck Creek was mined from the mouth about 10,000 feet upstream to the lower
part of West Fork. The average gradient was 2 to 3 percent and the gravels
averaged about 200 feet wide and 4 to 6 feet deep. Other streams in the area
are proportionately similar.

WORK BY THE BUREAU OF MINES
Nature and Extent

The Potato Mountain lode tin outcroppings are buried under frost-broken
detritus and a mat of tundra and alpine-type vegetation. Therefore, the area
had to be investigated in three stages: First the placer gravels, then the
detrital cover, and finally the lode outcroppings. Each stage was designed to
eliminate large areas from further consideration, to indicate the general
extent of marginal areas, and to delimit the areas to be investigated during
the succeeding stage.

The various sampling procedures are described as they pertain to the suc-
ceeding steps in the investigation. Many of the placer samples and practi-
cally all detrital cover samples were roughly evaluated in the field. All
churn-drill placer samples and all lode samples having quantitative value were
analyzed in the Bureau of Mines laboratory at Juneau, Alaska. Numerous typi-
cal specimens and samples were checked for beryllium, radioactive minerals,
and fluorescent minerals. Selected specimens and samples were analyzed spec-
trographically and petrographically.

Descriptions of the principal placer and lode tin deposits are grouped
according to the drainage basin in which the deposits occur. These descrip-
tions are followed by descriptions of miscellaneous prospects. Tin analyses
data are included with the descriptions of the deposits. Petrographic descrip-
tions, spectrographic analyses, and analyses for metals other than tin are in
special sections following the descriptions of the deposits.

The descriptions of the lode and placer deposits and prospects include
maps. An index map of Potato Mountain (fig. 6) shows the location and orien-
tation of the various maps. Sketches, cross sections, and a photograph
supplement the descriptions and maps.

Definition of Terms

Geological and related terms in general have been used in accordance with
definitions in the 1960 edition of the Glossary of Geology and Related
Sciences? or in Webster's Third New International Dictionary. The following
terms are defined for the reader's convenience:

Clay. - An earthy and usually plastic mixture of fine-grained mineral
and rock fragments and crystals found in or along fractures, joints, bedding

S8Howel, J. V. (Coordinating Chairman). Glossary of Geology and Related
Sciences. American Geological Institute, Washington, D.C., 1960, 397 pp.


28

_— = Seventeen churn-drill

TM~ 180-5, 700 65° holes were drilled at the head
ee: ; of West Fork to delineate the
_ a fo. upstream limits of placer
a Soy = deposition (fig. 9 and table
9). The placer deposits were
found to extend into the
extreme headwater tributaries.
A considerable placer deposit
extended to the extreme head-
waters of South Gulch, but
only a minor amount of tin
°o occurred in West Gulch. This
suggested that the tin in the
West Fork placers was derived
principally from South Gulch.

The cassiterite in the
West Fork placers generally
et etoid prospect pit was angular indicating that it
o NU? had not been transported great

distances. Placer sampling
results indicated that much of
the tin was derived from South
Gulch but some tin was derived
from Peluk Creek and West
Gulch. Therefore, it seemed
probable that tin also was
derived from other places in
the valley.

LEGEND

Bulldozer trench

Auger hole

x Trace of tin

xx Moderate amount of tin

% a ore Detrital Cover Sampling,

West Fork

Scale, feet

FIGURE 8.- Placer and Detrital Cover Sampling, Left Fork. The detrital cover was

sampled on both banks of West
Fork, South Gulch, West Gulch, and the lower third of Peluk Creek (fig. 10).
Results indicated that practically all the tin in the West Fork placer gravels
was derived from an area drained by South Gulch and extending a few hundred
feet down West Fork. A comparatively minor amount of tin was derived from the
Peluk Creek-West Fork divide on the south side of Peluk Creek. Further work
in the West Fork drainage basin was confined to these areas.

Additional samples were taken in lines generally parallel to the stream-
banks to outline the tin-bearing areas. The higher-than-normal grade zones
within these areas were defined by rough grids of more closely spaced samples.
A roughly circular tin-bearing area about 1,500 feet in diameter was outlined
in the South Gulch drainage basin. Within this area numerous higher grade
zones formed an irregular pattern on both sides of South Gulch. In the Peluk
Creek-West Fork area scattered traces of tin formed a poorly defined zone that
included one relatively small, well defined zone of higher-than-normal grade.


10

A gradual rise in tin
prices during the late
1930's led to renewed activ-
ity in the Potato Mountain
area. Prospecting was the
principal activity, although
about 6 tons of tin were
produced in 1937. The
threat to the national tin
supply caused by the Japa-
nese seizure of Southeast
Asia resulted in exploration
of the placer reserves by
the Bureau of Mines and the
U.S. Geological Survey dur-
ing World War II (30). No
production was attempted at
that time.

Tin-marketing condi-
tions remained favorable
after World War II, and
prices tended to increase;
placer tin mining was
resumed in 1948. The opera-
tor used a skid-mounted
recovery plant equipped with
a trommel screen, jigs, and
a tailings stacker belt.
Water was pumped to the
plant. The gravel was mined
d with a tractor-dozer and

ushed to a dragline that
FIGURE 4, - Placer Claims in the Potato Mountain Area. pod the recovery apparatus.
The entire plant was moved
from place to place as needed. A drop in tin prices, and the uncertain market-
ing conditions brought about by the closing of the Texas City tin smelter,
resulted in a shutdown at the close of the 1953 season. The operation has not
been resumed.

Approx seal:

Lode Prospecting

Prospectors repeatedly searched the Potato Mountain area for lode tin
deposits. Prospect pits and trenches are evident on almost every exposure of
quartz. All workings have either sloughed in or filled with ice, and all
appear to have been dug prior to 1920. The principal workings are a timbered
shaft (Red Fox prospect) near the head of Buck Creek (fig. 3); a timbered
shaft on the summit of Little Potato Mountain (Daisy prospect); and a par-
tially timbered adit on the east face of Little Potato Mountain. The various
prospects were examined during this investigation, and the results are
included in this report. Usually no more than traces or minor amounts of tin


82

Cassiterite occurs in three environments: (1) In fissure veins as aggre-
gates (10-mm maximum diameter) of coarse cassiterite (1 mm); (2) in replace-
ment veins as discontinuous border zones in the metasomatic quartz adjacent to
tourmaline schist; (3) intimately associated with fine-grained tourmaline
schist as minus 200-mesh grains with an average grain size of less than 5
microns (3,200-mesh).

Diamond-Drill Hole 1, 38.0 Feet. - Veinlike material in tourmaline schist
at 38.0 feet in diamond-drill hole 1 (table 12) is high in quartz and pyrite
as compared to the surrounding tourmaline schist. The quartz-pyrite rich
areas could represent (1) areas of the original shale that were higher in
silica, iron, and sulfur; (2) areas into which silica, iron, and sulfur have
been introduced by boron solutions; or (3) regions of lesser pressure (in the
shale being tourmalinized) into which iron sulfide and silica have migrated
from adjacent areas. The quartz-pyrite areas are coarser grained than the
tourmaline schists and are cut by indistinct bands of tourmaline parallel to
the general schistosity.

Diamond-Drill Hole 4, 13.5 Feet. - The core sample at 13.5 feet, DDH-4
(table 15) is a shale replaced to a great extent by fine-grained hydrothermal
quartz (not cryptocrystalline). Calcite veinlets cut the hydrothermal quartz
and are cut in turn by recent limonite-stained gypsum veinlets.

Diamond-Drill Hole 4, 126.9 Feet. - The core sample at 126.9 feet DDH-4
(table 15) is an altered tourmaline schist with pyrite and cassiterite. Much
of the pyrite has altered to limonite or goethite. The cassiterite has an
average grain size of 800-mesh with 95 percent of the cassiterite less than
200-mesh. Estimates of amounts and grain size of cassiterite may include some
goethite after pyrite because of the similarity of the two minerals in
reflected light.

Diamond-Drill Hole 4, 131.0 Feet. - The core sample at 131.0 feet DDH-4
(table 15) is a tourmaline schist cut by calcite-filled fractures cut in turn
by gypsum-filled fractures. Pyrite masses are cut by both calcite and gypsum
veinlets.

Diamond-Drill Hole 4, 136.0 Feet. - The core sample at 136.0 feet DDH-4
(table 15) is a fine-grained tourmaline schist. Pyrite is distributed at ran-
dom within the tourmaline schist. Calcite-filled fractures cut the tourmaline
schist and are in turn cut by gypsum veinlets.

Diamond-Drill Hole 4, 138.0 Feet. - The core sample at 138.0 feet DDH-4
(table 15) is a fine-grained tourmaline schist containing irregular stringers
of pyrite, up to 1 cm in length, distributed at random. Gypsum fills a multi-
tude of fracture fissures. There is a banding in the tourmaline schist based
on the amount of quartz present.

The Clays. - Fourteen earthy clay specimens from both the tin-rich areas
and from the major faults were examined. The specimens usually contained
shale or phyllite fragments, quartz, calcite, and gypsum. Gyrolite, one of
the zeolite group, was identified in a few specimens from the tin-rich zones.
A kaolin-type clay was identified in one sample from a major fault. In all
other samples, the clay minerals could not be segregated or identified with
the equipment available.


69

Quartz Porphyry Dike

A quartz porphyry dike on
the divide between the west
branch of Red Fox Creek and
the first right limit tribu-
tary of Upper Buck Creek
(figs. 3 and 23) had been
prospected by several pits.
The apex of the dike is
exposed in a pit on the north-
east side of the knoll that
forms the south side of the
divide; the shale can be seen
arching over the apex. From
this pit, the dike outcrop,
or frost-broken fragments of
the outcrop, can be traced to
the northeast for almost 2,000
feet (fig. 23).

)

ST 700
S80 —*-12—

eS 800 2

850
S05

&
('s

LEGEN

60-12 Sample
Bs Shaft
A Old hand-dug
pits ond trenches

The following petro-

. Sample pit graphic report describes a
* Trace of tin
° 500 1000 typical specimen of the hard,

light-gray dike material:

Scale, feet

FIGURE 22. - Red Fox Prospect, Potato Mountain Area. 244) qhe specimen (No.

rock hydrothermally
derived from an acidic igneous rock. Only euhedral Beta-quartz forms
of quartz phenocrysts remain intact from changes produced by metaso-
matism. Pseudomorphs of original feldspars can be seen readily, but
the feldspars and the groundmass have both been altered to hydromusco-
vite. An introduction of a myrmekitic-like intergrowth of pyrite
probably accompanied the hydration of the feldspathic minerals. The
pyrite does not replace the euhedral quartz grains but does penetrate
the groundmass and large pseudomorphs without respect to chemical
environment. Like myrmekitic quartz intergrowth, the numerous and
fine penetrations are all one pyrite crystal; this is revealed by the
presence of exactly parallel pyrite faces with parallel pyrite stria-
tions. No tin mineral was recognized. Chemical analyses indicated
0.04 percent of tin.

Frost-broken material on the outcrop of this dike was panned. No tin was
found. Most of the area in which the dike occurs is drained by the western
branch of Red Fox Creek. A panned sample of placer gravels from near the
extreme head of this stream contained little more than traces of tin. A
series of detrital cover samples taken from the hill slopes below the outcrop

5Previously unpublished report by Walter Gnagy, petrographer, Area VIII
Mineral Resource Office, Bureau of Mines, Juneau, Alaska.


54

100 200
Scale, feet

10}
LEGEND
60-215 Sample
fo) Churn-drill hole
. Sample pit
x Trace of tin
x Moderate amount of tin
xxx Abundant tin

FIGURE 14. - Lode Sampling, Peluk Creek Area.


KOTZEBUE

NORTON

FIGURE 1. - Seward Peninsula, Alaska.

‘¢ hex WH y)
ISS
SS

WSS
‘\

Nig

—

Sy

Yf

©

FIGURE 2 AREA



25

Qld Placer Mining Pits

A single continuous placer mining pit extends from near the mouth of East
Fork on Grouse Creek upstream to the mouth of Buck Creek, then up Buck Creek
to the mouth of West Fork, and up West Fork about 1,000 feet (figs. 3 and 4).
Branches of this pit extend over 1,000 feet up Sutter Creek and about 2,500
feet up Left Fork. The only other recognizable placer working in the Potato
Mountain area is a narrow, hand-dug placer pit that extends about 1,500 feet
down Iron Creek from the base of Big Potato Mountain.

Buck Creek

Buck Creek was examined to determine if the placer tin was derived from
the headwaters or from many places along the banks. Starting at Grouse Creek
(figs. 3 and 4) and continuing upstream, samples from pits in the placer grav-
els of Buck Creek were panned and examined. It was found that the tin
occurred as cassiterite crystals that showed progressively less wear as the
headwater tributaries were approached. Concurrently, samples were panned from
shallow pits sunk on the banks where quartz float appeared and in tributary
gullies and streams. No tin was found on the banks of Buck Creek or in the
gullies entering Buck Creek, but traces of tin were found in several of the
tributary streams. The only tributaries that contained more than traces of
tin were Sutter Creek, Left Fork, West Fork, and Upper Buck Creek (above West
Fork).

Typical specimens of vein and dike material, that might have been the
source of placer deposits, were collected (table 7). Tin was found to occur
as cassiterite in fragments of vein quartz; however, most quartz fragments con-
tained no cassiterite. Tourmaline, pyrite, and arsenopyrite were associated
with the cassiterite in some specimens. A few specimens of quartz-porphyry
dike were found but little or no tin occurred in this material. The relative
scarcity of quartz-porphyry fragments and the general scarcity of tin in the
fragments suggested that little cassiterite was derived from this source.

TABLE 7. - Description of typical specimens of vein and dike
rocks found in the Buck Creek placers

Specimen Petrographic description Tin,
percent?
5-1-1... |The specimen is a segment of a vein 3 to 6 cm in width, com- -
posed predominantly of cassiterite, abundant quartz, and
minor limonite and tourmaline. The vein is bordered by
tourmaline schist on both walls. An irregular subdued
foliation in the cassiterite vein perpendicular to the
tourmaline schist walls is indicated by limonitic rows of
holes, irregular quartz lenses, and irregular cassiterite
bands. The limonite-stained holes in the cassiterite vein
may be remnants of earlier iron sulfide. Almost pure
quartz veins penetrate both the cassiterite vein and the
tourmaline schist and have more limonite stain or color
than the quartz lenses associated only with the cassiterite
vein.

See footnote at end of table.



61

TABLE 20, - Description and analyses of trench samples, Daisy Fault
Iron Creek drainage basin--continued

Description Analyses
Sample Tin,
Number |Length,| Character of material per- |Spec.1|Petro.?
feet cent
60-66 4 Quartz veinlets and lenses with clay in 0.12] - -
shale.
60-67 4 do -16 -
60-68 4 do.. .07| - -
Total or} 32 12) - -
average
58-4 2 Clay-filled fault or joint.....--.se+e-eeeee 08 = -
Trench LL-12
59-167 1 Quartz veinlet...ecesseesesecceeeece <0.02]) - x
59-187 2 Crushed-shale fault filling.. 03] - -
59-188 2 -10| - -
59-189 2 02 - -
59-190 2 Clay, quartz, and altered shale. <.01] - =
Trench LL-12A
59-159 [1 [quartz and clay veinlet....sssseessseeseeeee] ONL] - [xX
Other areas
60-45 - Prospect pit 670 feet N 60° W of Daisy shaft] 0.03] - -
60-59 - Specimens from Daisy prospect pit.......see- 03 -
59-186 - Dump of prospect pit near Daisy shaft....... 03 = =

1See section entitled "Spectrographic Analyses."
2See section entitled "Petrography."
30ccasional large crystals of cassiterite were noted that appeared to have been
derived from these veinlets, but sample 241 was composed of very fine vein
quartz, pyrite, and limonite with no visible cassiterite.
4Equivalent uranium by Geiger counter = 0.003 percent.

TABLE 21. - Description and analyses of trench samples,

Adit Fault, Iron Creek drainage basin
Description Analyses
Sample Tin,
Number Length , Character of material per- |Spec.1|Petro.?
feet cent
Trench IC-5
61-4 [ 13.5 [Clay and crushed-shale fault filling......../<0.01] -  [ -
Trench IC-3
60-71 12 Clay and crushed-shale fault filling........| 0.02] - -
60-82 = Pan concentrate from west side Adit Fault... 02] -
Trench LL-3
231 2 Quartz and Clayscssccscsccscccccccscceces <0.03| xX -
232 2 Clay and clayey-shale fragments? . oe 06] X -
233 3 Clay and shale.........++sesseeeee eeeseee -06| - -
Other areas
60-78 T= TAdit dump... esse esses eee e eee eeeeee eee e ees] O01] = T=

1See section entitled "Spectrographic Analyses."

2See section entitled "Petrography."

3Note that the Adit Fault samples also are included in analyses data from trenches
on the west side of South Gulch (fig. 11 and table 10).


Detrital cover sample pits
were continued across the
head of Upper Buck Creek.
\_ Only one sample, taken
directly below Red Fox
prospect, contained a trace
of tin.

LEGEND

[aese) Placer concentration
(see text and table 23)
© — Churn-drill hole

==$ Bulldozer pit

x Trace of tin

xx Moderate amount of tin
xxx Abundant tin

.  Detrital cover sample pit <°

°

60°

° 500

Scale, feet

FIGURE 19. - Placer and Detrital Cover Sampling, Upper Buck Creek.

63


64

TABLE 23. - Churn-drilling and trench-sampling results,
1943, Upper Buck Creek1

Line and hole Mining Tin, Abundance

section, feet lb per cu yd factor?
Line 34:

3 (LL)........ 3.0 0.26 78

2 (LL).. 3.5 -69 241

1 (LL)..... 3.5 1.65 578

1 (RL) a 4.0 2.92 1,168

2 (RL)o eee secon 3.0 +05 15
Line 35:

2 (LL). see e ee eeee 3.5 +63 221

1 (LL).. 4.5 1.89 850

1 (RL).. . 3.5 1.00 350

2 (RL) . 2.0 +20 40
Line 36:

3 (LL).. 5.0 +21 105

2 (LL) 7.5 41 308

1 (LL) 2.0 +63 126

1 (RL).. 1.5 +28 42
Line 37:

6.0 +36 216

7.0 1.79 1,253

5.0 1.67 835

4.0 1.46 584

3.0 1.30 390

4.0 1.64 656

5.0 19 95

0 0 0

1.7 1.46 248

2.5 6.21 1,553

3.6 37 133

1Summary of data from Bureau of Mines Report of Investigations

4418 (30).

2(Mining section, feet) x (tin, lb per cu yd) x 100 = abundance
factor. See section of this report entitled "Placer Sampling
and Evaluation."

Lode Sampling, Upper Buck Creek

Nine bulldozer trenches were started where detrital cover sampling indi-
cated the presence of tin (fig. 20). Three were continued to bedrock;
trenches BC-3, BC-5, and BC-8. The others were abandoned when panning indi-
cated that little or no tin was present. Panning results are indicated in
figure 20. The three trenches continued to bedrock exposed a cluster of
quartz veinlets in shales adjacent to a fault filled with clay and crushed


22

Lode Sampling and Evaluation Methods

Bulldozer Trenching

The final stage of the investigation was to expose and sample the lode
outcroppings. Trenches were started where detrital cover sampling indicated
the presence of outcroppings. When exposed by bulldozer trenching, the frozen
detrital material would thaw from an inch to a foot or more per day. A sample
of the newly exposed material in the trench bottom was panned. If no tin was
found, the trench or section of trench was abandoned. If tin was found, the
thawed material was removed and the process repeated until tin minerals were
traced downward to the lode outcropping.

Heavy minerals tend to form a residual concentrate on and near the frost-
broken outcroppings. In every case that could be checked, the material on or
directly over the outcrop was higher in grade than the lode source. The ratio
of concentration varied widely; the broken material overlying the outcrop
might contain up to 10 times as much tin as the lode. The weathered material
exposed in the bottom of a bulldozer cut could not always be distinguished
from bedrock, particularly where clay alteration was extensive. Therefore,
the maximum depth to which surface concentration might extend never was deter-
mined satisfactorily. Samples taken 1 or 2 feet below the apparent bedrock
surface often contained several times as much tin as those taken 3 to 6 feet
deeper.

The outcrop was cleaned and sampled after it had thawed. In some cases,
trenches 1 to 3 feet deep were excavated by pick and shovel in the bottom of
the bulldozer trenches prior to sampling. Uniform channels were cut in the
clay-quartz and soft shaly deposits with a prospector's pick and an iron
spoon. Zones containing harder rocks required the use of a hammer and moil.
Chip samples were taken across some of the obviously lower grade deposits.
Many outcroppings had to be resampled when it became evident that residual
concentration extended into the apparent bedrock. Because of the inherent
difficulties of digging frozen bedrock of varying hardnesses, it is not cer-
tain that all samples were taken below the zone of residual concentration.

Diamond Drilling

Five diamond-drill holes, ranging in depth from 114 to 213 feet for a
total of 764 feet, were drilled with a conventional gasoline-powered drill.
Normal core drilling procedures were followed. Drilling water was pumped from
the extreme headwaters of West Fork. The broken nature of the rock made core
recovery poor; sludge samples were saved at all times. Water and sludge
recovery usually were good but the clay-filled openings in the rock may have
affected the grade of the sludge samples. The cracks in the rocks could have
acted as riffles to hold heavy minerals or the water action could have washed
extra material from the cracks into the holes. The diamond drilling data can
be considered only as generally indicative of the grade of material
encountered.


A Over 10 percent
B 5 to 10 percent
* Sn interference

TABLE 28. - Spectrographic analyses

Letters indicate estimates from qualitative analyses:

c 1 to 5 percent
D 0.1 to 1 percent

E 0.01 to 0.1 percent
F 0.001 to 0.01 percent

G Under 0.001 percent
- Not detected

A724

Sample.

Composite
59-137-139

Trench, location®.. | TR-LL-5

Table

Composite
59-124-126

TR-LL-4
10

Composite
61-128-131

TR-LL-2
10

59-94
TR-RL-1

Composite
59-71-72

TR-RL-2
il

Composite
60-150-155,
61-110-116
TR-RL-2A
1

Composite
60-165-170

TR-RL-2B
11

Composite
59-45-51

TR-RL-3
iL

61-49

TR-RL-14
il

Composite
59-26-29

TR-RL-4
11

Aluminun.
Arsenic.......
Barium. .
Beryllium...
Bismuth..

Manganese.
Molybdenum.
Nickel...
Phosphorus.
Scandium.
Silicon.
Silver
Sodium.
Tinesseeeeee
Titanium.
Vanadium.
Yttriun.

Zinct...seeeeeeee

Zirconium, .

TSample numbers are inclusive; that is, 59-137-139 covers 59-137, 59-138, and 59-139, and so on.

TEU OMOM

tmaaaars

F

A

(HHO EP iat moOmoOmal

tHaAAauUmb

F

2Trench, drill hole, or other sample site.
8Table in which sample is described.

Cadmium occurring in the absence of zinc was considered anomalous.

scopically.

THM OWN OP ad mon AOMataD

tHaAAVaAr!

F

MCORP OOP IM MOIR Om Oma) Obl

(OAD OP MM On OD

tmaaambt

F

IMI OOMOtAN MO ONO

toumoIb

mB

(HIM OMMOtssMATAttMoA

tyomuIbt

E

A

IPma timer areal

trot

ImaqAaPt

Less than 0.001 percent cadmium was indicated and occasional traces of zinc were found.

i)

tPigamorarant

ImaAAgAat rat amt

1

ee ee en eS

ImMADUaArm:

'

(Pimmmatgiat

'mOUU hry i mmmot

Therefore cadmium-bearing samples were reanalyzed spectro-


Fig.

17.
18.
19.
20.
21.
22.
23.

2.
3.
4,

6.

8.
10.
11.

12.
13.
14,

16.
17.
18.
19.
20.

21.
22.
23.
24.

25.
26.

27.

28.
29.

ILLUSTRATIONS (Con.)

Section through Daisy Fault, trench IC-1, looking south.........
Daisy Fault and Daisy prospect, summit of Little Potato Mountain...
Placer and detrital cover sampling, Upper Buck Creek...........-..4.
Lode sampling, Upper Buck Creek... ..ccccccccccc ccc ccrceccccscccseceee
Intersection of Buck Creek and West FOrk.......sseececesescececcees
Red Fox prospect, Potato Mountain area......
Quartz porphyry dike and Alan Dale prospect........s.seeeeeee

TABLES

Population of the western part of the Seward Peninsula............ .
Weather statisticS...cccsccccccccccccccccrsssscssccssscsrsseee
Placer-mining claims in the Potato Mountain area.
Production of Potato Mountain area placers.. eeeccceee
Amount of cassiterite in detrital material detected by panning.....
Summary of published data on tin placer deposits, Potato

Mountain area... see recceeee
Description of typical specimens of vein and dike rocks found

in the Buck Creek placersS....cscecccesccccrccccccccssceccccescees
Churn-drilling results, 1943, West Fork and Peluk Creeks...........
Churn-drilling results, West Gulch and South Gulch.......seeeseoeee
Description and analyses of trench samples, west side of

South Gulch....eeseseseeseoes be eeeeeeceeeee
Description and analyses of trench samples, east side of

South Gulch. ..ccsccscccsccccecccecscersesessssesccecevecccccccees
Diamond-drill-hole log and sample analyses, hole 1
Diamond-drill-hole log and sample analyses, hole 2
Diamond-drill-hole log and sample analyses, hole 3
Diamond-drill-hole log and sample analyses, hole 4
Diamond-drill-hole log and sample analyses, hole 5..
Description and analyses of trench samples, Peluk Creek area.......
Churn-drilling results, 1943, Iron Creek...
Churn-drilling results, headwaters of Iron Creek..
Description and analyses of trench samples, Daisy Fault, Iron

Creek drainage basin.......eese0e Peeereeerrey
Description and analyses of trench samples, Adit Fault, Iron

Creek drainage basin... ecececceccccccccrcccerccceeseccecencsees
Miscellaneous trench samples, Iron Creek drainage basin..........--
Churn-drilling and trench-sampling results, 1943, Upper Buck Creek.
Description and analyses of trench samples, Upper Buck Creek

drainage DaSin....cccccccccccccccccccecceseccessceesseceeeeseeees
Description and analyses of selected specimens, Red Fox prospect...
Description and analyses of specimens, Eureka prospect, Little

Potato Mountain. .....-eereecececeeeeee sence cece e eee ee reves ceece
Description and analyses of specimens, Oakland Creek-West Fork

GIiVide. cece sec c cree cecccccccsccccsvvvees
Spectrographic analyses....
Petrographic identifications...

iii


ii

Bibliography. .ccsccccccccccccccccccccccccseccccseesscesess

CONTENTS (Con. )

Upper Buck Creek drainage basin..
Placer sampling, Upper Buck Creek...
Detrital cover sampling, Upper Buck Creek.
Lode sampling, Upper Buck Creek.

Miscellaneous prosSpectS....eseeeeees
Drusy quartz vein and andesite dike.
Mouth of West Fork..
Red Fox prospect...
Quartz porphyry dike
Alan Dale prospect.
Eureka prospect...-eecsecseeeee
Oakland Creek-West Fork divide.
Iron Creek-Oakland Creek divide
Summit of Big Potato Mountain.

Associated minerals..........
Copper, lead, and zinc
Radioactive minerals.
Fluorite...
Beryllium.
Gold.......

Spectrographic analyses.

Petrography........
Identification..
Supplemental notes on selected specimens

ILLUSTRATIONS

Seward Peninsula, Alaska... ..ecscccceccccceccecceccerecceceereeete
Location and general geology, western Seward Peninsula tin belt.
Potato Mountain areds.sseeeeseseccecceccsssereres
Placer claims in the Potato Mountain area........
Frost breaking and transport of material from a typical outcrop,
Potato Mountain area........ .
Potato Mountain with location of figure areas....
Sampling the detrital cover with a gasoline-powered posthole auger.
Placer and detrital cover sampling, Left Fork....
Tin placer deposits, West Fork.......... beveee
Detrital cover sampling, West Fork......eceeceeeee
Lode sampling, west side of South Gulch.....
Lode sampling, east side of South Gulch.....
Cross section through diamond-drill holes 3, 4, and 5.
Lode sampling, Peluk Creek area.....+.s-eseeeee
Placer and detrital cover sampling, Sutter Creek and Iron Creek.
Lode sampling, Iron Creek area... .cececccececccecenceeseeerreceres .



1

were found in the prospect dumps. An exception was two small heaps near the
Daisy shaft containing about one-half ton of finely broken tin-bearing quartz
that appeared to have been hand sorted from quartz veinlets in shale. No lode
tin production has been reported.

TABLE 4. - Production of Potato Mountain area placers?

Year Tin, Value Year Tin, Value
short tons short tons

1902........46 15.0 $8,000 1916....... 97.0 84,600
1903.. oe 25.0 14,000 1917. 85.0 104,553
1904..... 14.0 8,000 1918. 48.0 83,560
1905.. 6.0 4,000 1919. 36.0 47,182
1906. 28.0 31,821 1920. 10.5 10,574
1907.. 22.0 16,752 1937. 5.95 6,426
1908. 25.0 15,180 1948. 4.07 7,975
1909. 11.0 7,638 1949, 32.82 64,984
1910.. 10.0 8,335 1950. 42.00 80,640
1911. 61.0 52,798 1951. 52.50 134,400
1912.. 130.0 119 ,600 1952.... 63.70 152,880
1913.... 48.5 42,780 19537 ce eeeeee 55.30 106,176
1914..... 74.0 47,321

1915. ..eeeeeee 100.0 77,300 Total.... | 1,102.34 | 1,337,475

1This record may be revised slightly as a result of a continuing reexamination
of old production records, but is substantially correct.
2No production recorded after 1953.

GENERAL GEOLOGY
Bedrock

The predominant rocks in the Potato Mountain area are a series of shales,
phyllites, slates, schists, and occasional shaly limestones (fig. 2). In
local usage and in previous reports, this series has been referred to collec-
tively as "black-slates."" Use of the term will be continued in this report.
The black-slates are believed to be of early Paleozoic or pre-Paleozoic age.
A series of generally gray limestones overlay the black-slates south and east
of the Potato Mountain area, but none were recognized on Potato Mountain. The
gray limestones are believed to be principally of Ordovician or Silurian age,
although the upper beds may be Mississippian.

Two distinct periods of igneous activity are evident. The first period
is represented by mafic stocks, sills, and dikes, locally called greenstones,
which intrude the black-slates, but apparently antedate the limestones. Mafic
intrusives are an abundant and pervasive feature of the black-slate areas, but
only a few prominent outcrops have been mapped. The second period of igneous
activity followed the deposition of the limestones; granitic stocks and dikes
intruded both the slates and the limestones. The stocks and their associated
halo of dikes, veins, and metamorphosed sedimentary rocks are more resistant
to erosion than the surrounding sediments and tend to form mountains with an
exposed granitic core. Brooks Mountain to the east and Cape Mountain to the


TIN-LODE INVESTIGATIONS, POTATO MOUNTAIN AREA,
SEWARD PENINSULA, ALASKA

by
John J. Mulligan!

With Section on Petrography by Walter L. Gnagy

ABSTRACT

The Bureau of Mines investigated lode tin deposits on Potato Mountain,
Seward Peninsula, Alaska. Tin was found to occur as cassiterite associated
with quartz, tourmaline, pyrite, arsenopyrite, and earthy clays, but the
deposits lack the varied accessory minerals commonly found in tin districts.
The tin-bearing deposits are in metasediments along minor breaks and bedding
planes but not in the crushed earthy filling of major faults. Cassiterite and
sulfides occur with quartz in veins, both with and without earthy clays, and
disseminated through tourmalinized wall rocks. The deposits are characterized
by irregular segregations containing 1 to 10 percent tin within zones averag-
ing not over 0.25 percent tin. The largest segregation exposed is on the
summit of a low hill on the east-central slopes of Little Potato Mountain;
most of the outcroppings are in an area trending east to west, roughly 10 to
30 feet wide and 300 feet long. Sample values ranged as high as 12 percent
tin, but the average grade may be about 1 percent tin. The extreme irregular-
ity of both grade and composition precludes a more exact determination. Simi-
lar concentrations are scattered for over 1,000 feet to the west and north,
but these are smaller and lower in grade. Elsewhere on Potato Mountain, gen-
erally similar deposits occur as clusters of veinlets at widely separated
points in the metasedimentary walls of major faults.

INTRODUCTION

The Bureau of Mines has been investigating lode and placer tin deposits
in the western Seward Peninsula, Alaska (fig. 1) intermittently since 1941.
The Cape Mountain, Brooks Mountain (Lost River), Ear Mountain, Potato Mountain,
and York areas have been investigated, and the results have been presented in
Bureau of Mines publications (27-34).?

iMine examination and exploration engineer, Area VIII Mineral Resource Office,
Bureau of Mines, Juneau, Alaska.

2Underlined numbers in parentheses refer to items in the bibliography at the
end of this report.

Work on manuscript completed February 1964.


10.

11.

12.

13.

83

BIBLIOGRAPHY

Schrader, F. C., and A. H. Brooks. Preliminary Report on the Cape Nome
Gold Region, Alaska. U.S. Geol. Survey Spec. Pub., 1900, pp. 25-26.

Brooks, A. H. An Occurrence of Stream Tin in the York Region, Alaska.
Ch. in Mineral Resources of the United States, Calendar Year 1900.
U.S. Geol. Survey, 1901, p. 270.

Collier, A. J. A Reconnaissance of the Northwestern Portion of Seward
Peninsula, Alaska. U.S. Geol. Survey Prof. Paper 2, 1902, pp. 48-49.

. Tin Deposits of the York Region, Alaska. Ch. in Contributions
to Economic Geology. U.S. Geol. Survey Bull. 225, 1903, pp. 154-167.

. Tin Deposits of the York Region, Alaska. U.S. Geol. Survey Bull.
229, 1904, 61 pp.

. Recent Development of Alaskan Tin Deposits. Ch. in Report on
Progress of Investigations of Mineral Resources of Alaska in 1904.
U.S. Geol. Survey Bull. 259, 1905, pp. 120-127.

Hess, F. L., and L. C. Graton. The Occurrence and Distribution of Tin.
Ch. in Contributions to Economic Geology, 1904. U.S. Geol. Survey Bull.
260, 1905, pp. 161-187.

Hess, F. L. The York Tin Region. Ch. in Report on Progress of Investi-
gations of Mineral Resources of Alaska in 1905. U.S. Geol. Survey Bull.
284, 1906, pp. 145-157.

Brooks, A. H. The Mining Industry in 1906. Ch. in Report on Progress of
Investigations of Mineral Resources of Alaska in 1906. U.S. Geol.
Survey Bull. 314, 1907, pp. 28-29.

Collier, A. J., F. L. Hess, P. S. Smith, and A. H. Brooks. The Gold
Placers of Parts of Seward Peninsula, Alaska, Including the Nome,
Council, Kougarok, Port Clarence, and Goodhope Precincts, U.S. Geol,
Survey Bull. 328, 1908, pp. 268-282.

Knopf, Adolph. The Seward Peninsula Tin Deposits. Ch. in Mineral
Resources of Alaska, Report on Progress of Investigations in 1907.
U.S. Geol. Survey Bull. 345, 1908, pp. 251-267.

. Geology of the Seward Peninsula Tin Deposits, Alaska, U.S. Geol.

Survey Bull. 358, 1908, 71 pp.

Brooks, A. H. The Mining Industry in 1909. Ch. in Mineral Resources of
Alaska, Report on Progress of Investigations in 1909. U.S. Geol.
Survey Bull. 442, 1910, p. 39.


76

Petrography
by
Walter L. Gnagy®
Identifications

Identifications of rocks and component minerals are in table 29. Sample
descriptions and other analytical data are in the tables listed at the head of
each column below the sample number and location. The relatively limited
assemblage of minerals present in the Potato Mountain area contrasts markedly
with the varied assemblage of minerals associated with the tin deposits in the
nearby Brooks Mountain-Lost River area.

Supplemental Notes on Selected Specimens

Sample 61-75. - Sample 61-75 (table 11, trench RL-18) is a fine-grained
tourmaline schist that includes thin lenticular veins and has been cut by
fissure veins and replacement veins. The lenticular veins are up to 1 mm in
width and 20 mm in length; they contain arsenopyrite and have been subjected
to irregular differential deformation along with the tourmaline schist. The
fissure veins range in width from 0.2 mm to 20 mm and contain cassiterite
associated with arsenopyrite, pyrite, and quartz. The replacement veins have
replaced much of the tourmaline schist through solution; they are irregular in
shape and composed primarily of quartz with rotated tourmaline schist frag-
ments, calcite, and coarse crystals and aggregates of pyrite. The individual
replacement veins have a maximum width of 50 mm but occur in a brecciated zone
that exceeds 10 cm in width.

Arsenopyrite occurs in four environments: (1) In small veinlets of
arsenopyrite, cassiterite, and quartz; (2) in larger fissure veins as coarse
aggregates adjacent to the tourmaline schist; (3) in replacement (metasomatic)
veins with coarse cassiterite crystals that make up discontinuous coarse
aggregates along tourmaline schist borders; and (4) in thin veinlike lenses
in tourmaline schist that have been subjected to irregular differential defor-
mation along with the tourmaline schist.

Pyrite occurs in four environments: (1) In thin (0.1-mm) veins filling
fractures; (2) in thin borders on some fissure cassiterite veins; (3) along
some borders between tourmaline schist and replacement (metasomatic) quartz
veins; and (4) as large (20-mm) pyrite aggregates in metasomatic quartz veins.

Quartz occurs in two environments: (1) With cassiterite in fissure-type
veins; and (2) with coarse pyrite in replacement (metasomatic) quartz veins.

6Petrographer, Area VIII Mineral Resource Office, Bureau of Mines, Juneau,
Alaska.


TABLE 29. - Petrographic identifications--continued

Predominant...
- Abundant...
Subordinate
Minor......
Few. sees

HARP
1

0.

5-

. Over 50 percent
- 10 - 50 percent
2 - 10 percent
2 percent
«- 0.1 - 0.5 percent
Trace...... Less than 0.1 percent

X - Detected in sample
N - Sought but not dete
C - Rock classification

79

cted

Samplel...eeccccccceee
Trench, location.
Tablel........-

59-162

60-59
Daisy
20

60-59A
Daisy
20

60-59B
Daisy
20

60-59C
Daisy
20

60-59D
Daisy
20

59-163
LL-9
20

59-167

LL-12
20

Rocks:
Andesite.......
Breccia...
Clay...
Gossan...
Phyllite..
Quartzite......
Schist....
Shale..........
VEIN. cssccescceseees

Minerals:
AlDite...ceceeeeeeee
Andesine.... .
Ankerite..
Arsenopyrite
Biotite.....
Biotite-chlorite
Calcite........
Cassiterite..
Chlorite....
Chlorite clay
Dolomite.
Epidote..
Fluorite.
Graphite.
Gypsum....
Hydrobiotite.
Hydromuscovite..

Sericite.
Tourmaline
Zircon.....+.ss+-

See footnotes at end of table.

teats

tebe

tiotmas
trttimtAnme

tee
CHP
i)

i

i)
tne

n



7

planes, etc. Both clay minerals and various other minerals may be present in
such mixtures.

Daisy Fault, Adit Fault. - Two prominent parallel crush zones, presumably
faults, that cut across Iron Creek valley and Little Potato Mountain. The ~*
Daisy Fault crosses the summit of Little Potato Mountain a few feet east of
the Daisy prospect shaft. The Adit Fault cuts across the eastern slopes of
Little Potato Mountain a few feet east of an old adit.

Detrital Cover Sampling. - A term used to indicate that the material
sampled is the rock debris that results from frost breaking and other erosive
processes, The term is used in preference to the term "soil sampling" for two
reasons: First, in the usual sense of the word, soils were scarce or absent;
second, the samples were evaluated by placer sampling techniques rather than
by the usual soil sediment evaluation procedures.

Float Line. - A generally linear grouping of detached rock fragments
extending from the outcrop source downhill to the stream placer deposits.

Left Limit (LL). - The left hand side of a stream gravel deposit when the
observer faces downstream.

Right Limit (RL). - The right hand side. Placer miners also commonly
refer to the left or right limit bank, tributary, etc., to indicate that the
observer faces downstream.

South Gulch, West Gulch. - Two small headwater tributaries of West Fork.
The usage is for convenience in this report, but the names have not been
passed on by the Board on Geographic Names.

Upper Buck Creek. - As used in this report, the section of Buck Creek
that is above the mouth of West Fork. The branch that extends towards the Red
Fox prospect is considered to be the main stream.

West Gulch. - See South Gulch.
Placer Sampling and Evaluation

The first stage of the investigation was to collect published data on the
placer tin deposits in the Potato Mountain area, principally churn-drill
sampling results (30). Gaps were filled by churn-drill sampling, test pitting,
or other appropriate means. The objective was to determine the areas from
which the placer deposits could have been derived. Therefore, a departure was
made from conventional placer evaluation procedures. The pertinent informa-
tion required was the relative amount of tin that had been deposited and the
degree of wear evident on the cassiterite crystals. The value of a placer
sample normally is expressed as a given number of pounds per cubic yard con-
tained in a pay horizon of a given depth. For this project, the depth of the
pay horizon in feet was multiplied by the pounds of tin per cubic yard and the
result was multiplied by 100 (to eliminate decimals). This gave a readily com-
parable figure (abundance factor) proportional to the amount of tin present


CRS Copy

bi f mi
p | esa he ecains 6587

TIN-LODE INVESTIGATIONS,
POTATO MOUNTAIN AREA,
SEWARD PENINSULA, ALASKA

By John J. Mulligan

UNITED STATES DEPARTMENT OF THE INTERIOR
BUREAU OF MINES

1965


80

TABLE 29. - Petrographic identifications--continued

eee 005 -
ose. O.1 - 0.5 percent

P

A

S - Subordinate......
M - Minor..

F - Few..

T

~ Predominant...... Over 50 percent
- Abundant......... 10 - 50 percent

2 - 10 percent
2 percent

X - Detected in sample
N - Sought but not detected
C - Rock classification

- Trace.. . Less than 0.1 percent
Samplel.......+4+.|59-168 | 59-169 | 60-82 | 61-1 59-192 |59-193| 60-2} 60-1) 60-6] 60-7
Trench, location..|LL-10 |LL-10 |IC-3 |BC-8| BC-8 | BC-8 |(*) |(&) |(&) | (8)
Tablet...........-| 20 20 21 24 24 24 = = : =
Rocks:
Andesite........| - - - - - - - - -
Minerals:
Albite.......... - - - - - - - - - -
Andesine. - - - - - - - - -
Ankerite........ - - - - - - - - - -
Arsenopyrite.... - - - - - - - - - -
Biotite.......0. - - - - - - - -
Biotite-chlorite| - - - - - - - - - -
Calcite......... - - - - - - - - - -
Cassiterite..... - - T s T N N N N N
Chlorite........ s - M - - s - -
Chlorite clay... - - - - - - - - - -
Dolomite.. - - - - - - - - - -
Epidote.. - - - - T - - - - -
Fluorite. . - - - - - - - -
Graphite. . - - - - - - - - M -
Gypsum.... - - - - - - - - - -
Hydrobiotite. - - - - - - - - s -
Hydromuscovite.. P P Pp - - Pp P -
Limonite........| T F s s M - - - s
Magnetite. - - - F - - - - - -
Muscovite. - - - - - - - - - -
Pyrite... - - - - N N - - - -
Quartz... s M A P s - = P
Scorodite... - - - - - - - - - -
Sericite.... - - - - - - - - - -
Tourmaline... T M F - - - -
Zircon. .....+s-+ - - - - - - - - - -
See footnotes at end of table.


40

TABLE 11. - Description and analyses of trench samples,

east side of South Gulch--continued

Description Analyses
Sample Tin,
Number [Length, | Character of material per- |Spec.1] Petro.?
feet cent
Trench RL-2A--continued

60-152 5 Altered shale, clay, and quartz.... 0.07] xX -
60-153 5 bee e cece eee eeeeeceecees +05} X -
60-154 5 eeee +05] X -
60-155 5 eee neenecensene 01} X -

Total or| 64 203] - -

average
Trench RL-2B

60-165 5 Altered shale, clay, and quartz. 0.01} xX -
60-166 5 do. x -
60-167 5 do. x -
60-168 5 do. x -
60-169 5 do.. xX -
60-170 5 dowsseee +01} X -

Total or | 30 O01) - -

average
60-171 3 Varicolored clay and crushed altered shale.. Ol] - -
60-172 2 Broken shale with some clay...... «| .01] - :
Trench RL-24 (Between Trenches RL-1 and RL-2
61-123 4 Tourmaline schist, clay, and quartz.. 0.08; - -
61-124 4 do.. . sence eeeeee see] 607] - -
61-125 4 do.. eee . seeee . 06 - -
61-126 1 Fault filling, dark-green clay.. . O01] - =
Trench RL-23 (South Fork, Trench RL-2)
61-119 19 Tourmaline schist, shale contact zone.......| 0.12 - -
61-120 11 Altered shale, clay, and quartz.... 01] - -
61-121 5 . Ol} - -
61-122 7 +43] - =
61-55 2.5 | Shaly fragments and dark-green clay.........| 0.03] - -
61-56 4 Black broken tourmaline schist and quartz... 704) - -
61-57 3.5 | Yellow clay, shaly clay, and quartz.........|  .14| - =
Trench RL-22 (Southeast Fork, Trench RL-3)
61-108 16 Iron-stained shale, clay, and quartz......../<0.01| - -
61-109 9 do...sssee, ses eeeeeeee weee| <-01] - -
ench RL-3

61-105 5 Clay, altered shale, and quartz. 0.06 - -
61-106 5 see c eens 16 -
61-107 5 bo veee 03 - -
59-43 2 Iron-stained shale and quartz. _<.01]_ - =
59-44 2 Clay, altered shale, and quartz. weee| <eOL] ~
59-45 2 wee] <O1l] X -
59-46 2 o- -08; X -
59-47 2 Oss seeeeeecceseeeeeee veoe] 231] X -
59-48 2 White to yellow clay and quartz. eeeeee| 1.80] X -
59-49 2 Clay, altered shale, and quartz. seeeee| 2.70] X -
59-50 2 1.90} X -
59-51 2 +50; X -

See footnotes at end of table.



LEGEND

Granite
yon Limestone
Basalt and gabbro

Slates and schists 4

65°45"
Covered by recent
sediments and tundra
=== Tractor trail
Lode mine
Airfield or landing strip
ive,
Wale: Se Ze
fF 65°30"
° 4 8 12
Scale, miles
BERING SEA

168°00' 167°00'

FIGURE 2. - Location and General Geology, Western Seward Peninsula Tin Belt. (Modified from Geological Survey maps.)


This report of an investigation of lode tin deposits in the Potato Moun-
tain area includes an account of the work done, a description of the deposits,
chemical and petrographic analyses made at the Bureau of Mines, Area VIII
Mineral Resource Office, Juneau, Alaska, and spectrographic analyses made at
the Bureau of Mines, Albany Metallurgy Research Center, Albany, Oreg. The
lode outcroppings were delineated by systematically sampling the placer grav-
els and the frost-broken detritus that blanket the area. Therefore, this
report also summarizes the distribution of placer tin deposits and includes a
description of the detrital overburden and the methods used to delineate the
lode outcroppings.

ACKNOWLEDGMENTS

Historical notes and general geological data were compiled principally
from the Bureau of Mines and Geological Survey publications listed in the
bibliography. Figure 1, in this report, is based on the Army Map Service
1:1,000,000 series map entitled Nome. Figure 2 is based on plate 1 of Geolog-
ical Survey Bulletin 733. Figures 3 and 6 are based on the Teller (C-6)
Alaska topographic map made by the Army Map Service but published and distrib-
uted by the Geological Survey. The chief modifications were adding or identi-
fying features, trails, and prospects mentioned in the text and omitting data
not pertinent to this report.

The personnel of the Nome station of the Alaska Communications System and
Mrs. Helen Blodgett, who operated a cooperating radio station at Teller, main-
tained daily radio schedules with the field party that saved much time in the
transmission of reports and orders, and provided a means of summoning assist-
ance in case of emergency.

LOCATION AND ACCESSIBILITY

Potato Mountain is about 60 miles south of the Arctic Circle and 100
miles N 38° W of Nome at latitude 65°39' N and longitude 167°33' W (fig. 1).
The Potato Mountain area is uninhabited; the nearest inhabited villages are
Wales, about 15 miles to the west-southwest; Teller Mission and Teller, about
40 miles to the southeast; and Shishmaref, about 60 miles to the northeast.
Tin City, 13 miles to the southwest (fig. 2), is the site of a small military
installation; York, about 12 miles to the south-southwest, has been uninhab-
ited for many years; Lost River, about 20 miles to the southeast, is the site
of a lode tin mine. A couple of small dilapidated cabins at York and a half
dozen light frame cabins on the bank of Buck Creek about a mile east of Potato
Mountain are the only structures in the area between Tin City and Lost River.

The Potato Mountain area is readily accessible by plane from Nome, the
center of air traffic for the Seward Peninsula. The principal airfield near
the Potato Mountain area is at Tin City; this field has been used by commer-
cial planes such as the DC-3 and military planes such as the C-46. An air-
field suitable for bush planes carrying payloads of 1,000 pounds or less is on
the northeast flank of Potato Mountain (fig. 2). Another airfield about 3
miles southeast of Potato Mountain at the intersection of Buck Creek and
Grouse Creek was used occasionally, but floods eroded the runway making it
unsafe for any except the lightest planes.


53

Peluk Creek Area

Detrital cover sampling (fig. 10) indicated that scattered traces of tin
were derived from the left limit banks at the mouth of Peluk Creek and that
some tin was derived from the divide between Peluk Creek and West Fork. The
placer tin deposits at the mouth of Peluk Creek probably derived from these
areas because no tin minerals were found at any other place in the Peluk Creek
drainage basin.

The tin found in the detrital cover on the left limit bank at the mouth
of Peluk Creek occurred as cassiterite attached to or associated with a few
scattered quartz veinlets having a maximum width of about 2 inches. Similar
veinlets were exposed in the bed of Peluk Creek (samples 60-3 and 60-4, table
17). No additional work was done on the left limit of Peluk Creek.

TABLE 17. - Description and analyses of trench samples,
Peluk Creek area

Description Analyses
Sample Tin,
Number Length, Character of material per- |Spec.1 |Petro.?
feet cent
Trench Peluk 5

60-215 9 Hard, blocky shale....sssccccseseeeeee| O.OL] - -

60-216 6 Medium-soft iron-stained shale with -O1] - -
secondary cleavage. —

60-217 2 Very soft gray shale...........0ee2e0s -O1l} - -

60-218 6 Clay, quartz, pyrite, cassiterite. -| 3.13 - -

60-219 20 Medium-hard iron-stained shale... «| <.O1] - -
60-220 8 Medium-hard iron-stained shale wit -l7| - -
quartz veinlets.
Total or | 36 56] - -
average?
60-221 6 Crushed zone (fault).....sesecccesecee -02] - -
60-222 4 Soft iron-stained shale........ oo -O1} - -
60-30 = Pan concentrate. ...+++++.+++++e-eeeees 137-90
Other areas
60-3 - Specimen shale bedrock in Peluk Creek - - x
50 feet upstream from mouth.
60-4 - Quartz veinlets cutting the shale - - x

bedrock (60-3),

1See section entitled "Spectrographic Analyses."

2See section entitled "Petrography."

8This series of samples was taken across the highest grade zone indicated by
detrital cover sampling. Lesser amounts of tin occur along the fault for
about 100 feet to the northwest, and traces extend about 200 feet farther.
Only a trace of tin was found in trench Peluk 6 which crosses the fault 100
feet to the southeast. Sample 60-218 represents a roughly lenticular zone
of enrichment within the tin-bearing area. The long dimension of the lens
is about 25 or 30 feet. Detrital cover sampling results indicate that this
is the only such zone of enrichment in this area.



36

TABLE 10. - Description and analyses of trench samples,

west side of South Gulch--continued

Description Analyses
Sample Tin,
Number [Length, Character of material per- |Spec.1| Petro.”
feet cent
Trench LL-4--continued
59-122 3 Crushed shale eee eeeeee <0.01) - -
59-123 2 Shale and quartz.. 05) - -
59-124 2 | Quartz...cceeeee .04] x -
59-125 2 Clay and quartz. eee sees 40] X -
59-126 2 (ee see. 30) X -
59-127 1 Shale, clay, and quartz...... -17|_ - =
Trench LL-3
59-132 2.5 | Crushed shale with some clay.... +{<0.01] - -
59-133 2 Yellow clay and some quartz..... o- 03] - -
59-134 2 Gray clay, shale fragments, and quartz. <O1|) - -
59-135 2 [CP ee <-01|] - =
Trench LL-2A
60-188A 7 | Shale with some quartz and clay......+++s«++ 0.01] - =
60-189 5 do... seeeeeececeseeeee| 602] = -
60-190 5 do. . Ol} - -
60-191 5 do. . Ol} - -
60-192 4 do. . 03] - -
60-193 4 do. 03} - -
60-194 5 do... see eeecnee 214] - -
Total or} 35 +03) - -
average
60-188 23 Shale. seeeeee eens . 0.01} - -
61-35 5 | Shale with quartz veinlets and clay -16| - -
61-36 5 dOssseceseeee see eeeeeeeee . +02] - -
61-37 5 dowsseee beeeceecccececceseeee! 1.19] - -
61-38 5 do... +04] - -
61-39 5 do. 14) - -
61-40 5 do. +39] - -
61-41 7 do. oe 224) - -
61-42 5 dOsssseeeeee 07} - -
Total or| 42 +28) - -
average
Trench LL-2
61-128 6 Crushed altered shale, iron-stained clay, <0.01] xX -
and quartz.
61-129 5 do.... sevens] 006] X -
61-130 5 dowsseee 24) X -
61-131 5 dowsseseoee 2.02] xX -
Total or| 21 55
average
Trench LL-1
59-97 1 Tron-stained gray shale......++.seeereeeeeee 0.04) - -
59-98 3 Crushed altered shale, iron-stained clay, 08) - -
and quartz.
59-99 2 Iron-stained gray shale.......... eecccccccee 03 - -
60-197 - Specimen; shale from same place as samples - -
59-97 and 59-99.
Trench LL-1B
207 [1 | Clay-quartz vein...........+ ste ceceseceeees [0.067 - =

TSee section entitled "Spectrographic Analyses."
2See section entitled '"Petrography."


77

TABLE 29. - Petrographic identifications

- Predominant
- Abundant...
- Subordinate

- Over 50 percent X - Detected in sample

- 10 - 50 percent N - Sought but not detected
« 2 - 10 percent C - Rock classification
Minor... 0.5 - 2 percent

- Few.... eooee O11 - 0.5 percent

- Trace...... Less than 0.1 percent

Aa Robs
'

Samplel......2eeeee0+ | 60-197/ 61-75] 60-135 |60-134|61-2 |60-140/60-141A] 60-141B
Trench, location. . LL-1 |RL-18} RL-5 | RL-5 |RL-19] RL-6 | RL-6 RL-6
Tablel....-+.ssseseee 10 11 11 11 11 11 11 1
Rocks :
Andesite......s.00. - - - - - - - -
Breccias.ssssecseees - - - - - - - -
Clay...
Gossan... sees
Phyllite........... c - Cc Cc - c - -
Quartzite
Schist....scseseeee - Cc - - - - - -
Shale........
Vein. wee ee eeeee
Minerals:
Albite.

1
1
1
1
'

a

rp
ee
op
ee
va
va
va
a
a
iPIin

tro Dp

Arsenopyrite....... - M -
Biotite....sssseeee - -
Biotite-chlorite...
Calcite......
Cassiterite.
Chlorite....
Chlorite clay
Dolomite.....
Epidote......
Fluorite.....
Graphite...
Gypsum......-
Hydrobiotite....
Hydromuscovite..
Limonite....sessee.
Magnetite........06 -
Muscovite....eseeee -
Pyrite.....eeeee
Quartz.....6.
Scorodite....sseeee
Sericite.....seeeee
Tourmaline
Zircon....+sssereee =
See footnotes at end of table.

'

rnine
ian

Laepe
fan
fan

1

retire

rare
'

(PH!
'
n
'

Pine
'
'
'
'
'
'
'

'
'
'
'
'
1
'



24

TABLE 6. - Summary of published data on tin placer deposits, Potato Mountain areal
Tin, Churn
Creek 1b per | drill Location of deposit Remarks
cu yd® | holes
averaged

Peluk Creek..... 0.5 2 Near mouth, No mining.

Upper Buck Creek -0 7 Below mouth of first About 0.2 1b tin per
right limit tributary cubic yard found above
above West Fork. the first right limit

tributary.

West Fork.......] 1.1 18 From mouth to headwaters.|Mined for about 1,000
feet? above the mouth.

Buck Creek......| 2.9 - Mined from West Fork Estimate based on
15,000 feet downstream mining records.
to Grouse Creek.

Grouse Creek.... 2.9 - From the mouth of Buck Reports (23) indicate
Creek downstream about that the tin occurred
5,000 feet to the mouth | as much rounded cassit-
of East Fork, erite and that no tin

was found above the
mouth of Buck Creek.

Tron Creek...... 6 11 Downstream from base of |Hand mined about 1,500
Big Potato Mountain. feet along stream bed

prior to drilling.

Sutter Creek.... +2 30 Downstream from mouth of |Mined from mouth
Iron Creek. upstream about 1,000

feet.3

Left Fork.. -|Unknown| None |Unknown. Mined from the mouth
upstream about 2,500
feet.3 Only traces of
tin reported above the
workings.

Potato Creek.... 2 15 Downstream from a small |No mining.

left limit tributary
that enters Potato Creek
about 2 miles west-
northwest of Big Potato
Mountain.

Oakland Creek... al 15 Extends about 1 mile This stream also called
along creek channel Diomede Creek and Lynx
near western base of Creek.

Potato Mountain.

Red Fox Creek... |Unknown| None [None known. Occasional traces to
minor amounts of tin
can be panned. No
mining.

lIncludes mined-out tin and is not indicative of recoverable tin.

Data from Bureau

of Mines Report of Investigations 4418 (30) unless otherwise stated.
2Average grade of samples from the pay streak.
8Data from conversation with George Ramstad who mined this stream after publication
of Report of Investigations 4418 (30).


TABLE 11. - Description and analyses of trench samples,
east side of South Gulch--continued

41

Description Analyses
Sample Tin,
Number |Length,| Character of material per- |Spec.1| Petro.”
feet cent
Trench RL-3--continued
59-52 2 Shale, clay, and quartz. seeeecceceececeee| 0.32] - -
59-53 2 Oss ecccecccccccecscseccccseccccecceee| SOL] - -
Total or} 20 - -
average >=}
59-54 4 Iron-stained shale with some quartz......... - -
59-55 4 do..... - -
59-56 4 do.. - -
59-57 4 do.. - -
Total or| 16 - -
average =
59-58 2 «| 05] - -
59-59 1.5 +{ 602] - -
59-60 2 «| <-O1] - -
59-61 2 «| 602} - -
59-62 2 . -06 - -
59-63 2 «| .05] - -
59-64 2 +] .30]) - -
59-65 2 . 09 - -
59-66 2 «| 202} - -
Total or} 17.5 07] - -
average —
59-67 3.5 | Clay, altered shale, and quartz.. -| 0.03] - -
59-68 3.5 Oss cesecccrccccceervccsecee «| 630] - -
59-69 8 Clay-quartz veinlets in altered shale. . -05] - -
Total or| 15 -10} - -
average
Trench RL-3A
59-210 10 Iron-stained clayey schist and quartz -{ 0.28] - -
59-211 10 «| 616] - -
59-212 10 -| 613] - -
59-213 10 +] 11] - -
59-214 10 +} 453] - -
Total or} 50 224) - -
average
Trench RL-14 (East Fork, Trench RL-3A)
61-47 5 Altered shale, clay, and quartz.. «| 0.31 - -
61-48 5 «| 1.36] - -
61-49 5 «| 1.65 -
61-50 5 +{ 637] = -
61-51 5 . 204) - -
Total or| 25 75] - -
average
61-52 7 Crushed green shale and black schist, strike| <.01] - -
N 15°, dip 60° W.
61-53 6 COs se eceeercceceeseese| <eOL} - -
61-54 9 Altered shale, clay, and quartz...........+. 06} - -

See footnotes at end of table.


23

Permafrost was encountered in all holes at all depths. This presented no
particular difficulty except that water in the drill hole would freeze if the
drilling water was too cold, or if circulation stopped. When the temperature
of the water entering the drill pump dropped below 37° F, drilling was stopped
because, at lower temperatures, ice formed in the return water and there was
danger of a "flash freeze." As a matter of routine, whenever circulation was
stopped for more than 30 minutes, about 10 or 15 pounds of calcium chloride or
rock salt were poured down the hole. This eliminated loss of time drilling
out ice, but care was required when flushing out the brine solution. After
standing overnight, the temperature of the brine solution in the hole was
estimated to be about 20° to 25° F. Fresh water would freeze in the rods as
they were lowered into the brine unless circulation was maintained.

Cement was used instead of casing, whenever practical, because the broken,
highly abrasive, quartz- and tourmaline-bearing metasediments caused excessive
wear on casing and casing bits. Portland cement and "quick-setting mixes'*
were tried. Portland cement would not set in the drill hole even if left for
2 days; apparently the permafrost inhibited the setting action. The usual
"quick setting mixes" of portland and lummite cement behaved freakishly; they
set while being mixed and poured or never set at all. However, it was found
that a mixture containing 80 percent lumnite cement and 20 percent portland
cement would produce a hard durable concrete if left in the hole overnight.

Summary of Published Data on the Relative Abundance
of Tin in the Placer Deposits

The relative abundance of cassiterite in the placer gravels of the
streams draining Potato Mountain was estimated from published data (table 6
and fig. 3). These rough estimates are in no way indicative of the recovera-
ble tin because mined-out tin has been included and sample spacing has been
disregarded. The estimates, however, do indicate where the principal placer
tin concentrations formed, and thus indicate where the principal sources must
have been.

Buck Creek and some of its tributaries contained many times more placer
tin than any of the other streams in the Potato Mountain area. The configura-
tion of the Buck Creek placers and the distribution of tin in its various trib-
utaries indicated that the principal lode sources of the placer tin were in
the Buck Creek drainage basin and probably in the area drained by Upper Buck
Creek, West Fork, Iron Creek, and Left Fork on the eastern slopes of Potato
Mountain (fig. 3). Although erosional conditions were similar, only rela-
tively small amounts of placer tin were found in the other drainage basins in
the Potato Mountain area. This indicates relatively minor lode sources.
Therefore, except for brief examinations, the investigations were confined to
the Buck Creek drainage basin.

4The most common "quick-setting mixes" used in diamond drilling are mixtures
of portland and lumnite cement that take an initial set in 10 to 30 minutes
and a final set in 1 hour or less. Normally the proportions, by weight,
range from 15 to 25 percent lumnite cement, with the balance portland
cement. The exact mix to be used must be determined by experiment; varia-
tions in the temperature, the water, or even the batch of cement used will
cause variations in setting time.


60

pits on Iron Creek to trench LL-5 on the west side of South Gulch (fig. 11). Figure
17 is a cross section through the Daisy Fault where it crosses Iron Creek; it is
typical of a number of similar occurrences in the Potato Mountain area. The Daisy
Fault was traced to the summit of Little Potato Mountain where a cluster of low-
grade quartz-clay-cassiterite veinlets (Daisy prospect) was found along the western
side of the fault (fig. 3). Sample locations in trenches LL-7 through LL-12 at the
Daisy prospect are on figure 18. Analyses data are in tables 20, 21, and 22.

TABLE 20. - Description and analyses of trench samples, Daisy Fault,
Iron Creek drainage basin

Description Analyses
Sample Tin,
Number —_|Length,| Character of material per- |Spec.1 |Petro.?
feet cent
Trench IC-1
225 4 Clay and shale (fig. 17)........ 0.06) - -
226 4 do.sseee seeeee seen e ee eceeee +06} X -
227 4 Clay and clayey shale (fig. 17). «| 09] X -
228 +2 | White clay (fig. 17).. aeeel 06] X -
229 +8 | Quartz vein (fig. 17). . see eeee -06] X -
230 20 Quartz veinlets in shale (fig. 17).......... 06} X -
241 - Specimens; quartz-arsenopyrite-pyrite 43] - -
veinlets in shale.’
CD-59 - Bedrock churn-drill hole 59 (table 19 and <-03|} X -
fig. 16).4
Trench LL-3A
221 10 Shale with quartz veinlets. . . - -
222 18 Iron-stained shale with quartz veinlets.....| <.05 - -
223 20 Iron-stained shale with clay and quartz <-05) - -
veinlets.
224 16 Clay and crushed shale.. aoe - -
Trench LL-7B
60-228 [0.5 | Quartz veinlet........seeseeeeeeeeeee eeeeeee L0.04[ - -
Trench LL-8
58-1 6 Crushed-shale fault filling... eee{ 0.05] - -
58-2 4 do... see eeceeeeersereceeeeeee| <A05] = -
58-3 6 do... tee sees <.05] - -
59-156 1 Crushed shale and clay veinlet +02] - =
Trench LL-9
59-161 1 Clay, pyrite, and quartz...... eee 0.07} xX x
59-162 1 Clay and quartz.... eee seeeee 02] xX x
59-163 3 do. aoe «| 08] X x
59-165 -1| Quartz-pyrite veinlet «| 03) - -
59-166 1 Clay and quartz....... necsee -06| - -
Trench LL-10
63-1 15 Crushed-shale fault filling..... +[<0.05}  - -
59-168 30 Specimen; east wall of crushed zone «| <.O1] - x
59-169 63__| Specimen; west wall of crushed zone.........|_<.01] - x
60-61 4 | Quartz veinlets and lenses with clay in 204|  - -
shale.
60-62 4 do... 44) - -
60-63 4 do. sO7}  - -
60-64 4 dow... «| 04] - -
60-65, 4 dosessee 03 - -

See footnotes at end of table.




14

zone of broken but normally

frozen material that remains

Heavy minerals tend to form a essentially in place except

concentrate over the outcrop for some downhill creep
resembling glacial flow.

Practically all movement of This broken zone in turn

material occurs within upper i

zone. Mixing and lateral dis- "er 8eS gradually into

persal gradually lower grade unbroken permanently frozen

of bedrock.

Tundra vegetation and peat 0 to! foot thick

The heavier fragments
broken from an outcrop tend
to sink into the transi-
tional and broken zones on
top of the outcrop thus
forming a residual concen-
tration. The lighter mate-
vial is carried off in the
zone of movement. Ulti-
mately, however, much of the
heavy material also is

FIGURE 5. - Frost Breaking and Transport of Material From removed. In the zone of

. . movement, heavy minerals are
a Typical Outcrop, Potato Mountain Area. carried along with the

lighter frost-broken mate-
rial; there appears to be a churning or mixing action that prevents heavy mate-
rial from sinking but results in some lateral dispersal. The mass ultimately
enters the streams. Water carries off the finer particles and lighter mate-
rials, and a placer concentration develops.

SKETCH SECTION
Not to scale

Placer Gravels

A long period of uplift and erosion followed the tin mineralizing epoch.
Possibly one or more advance and retreat of the sea dispersed placer accumula-
tions. A relatively recent elevated beach deposit (34), that may be contempo-
rary with the intermediate beach at Nome (letter from Dave Hopkins, Federal
Geological Survey geologist), has been identified 12 miles west of Potato
Mountain on Boulder Creek in the Cape Mountain area at an altitude of about
90 feet. No similar beach has been found in the Potato Mountain area, but
valuable tin placer concentrations are not known below 150 to 175 feet alti-
tude. During the Illinois glacial stage extensive glaciers evidently formed
in the mountains 10 to 15 miles south of Potato Mountain (35). Contemporary
glaciers may have formed on Potato Mountain but, if so, subsequent erosion has
obscured the usual evidences.

The tin-bearing alluvial concentrations in the Potato Mountain area
appear to be typical stream placer deposits that formed under present-day
conditions. Any deposits that have formed during previous erosive cycles
probably have been eroded and redeposited in the streams. The placer gravels
are shallower and less extensive than the broad open nature of the valleys and
the gentle gradients of the streams would suggest. Evidently erosion and


78

TABLE 29. - Petrographic identifications--continued

- Abundant......

- Few..
- Trace..

HAR AP
'

- Subordinate......
Minor.......00+. 0.5 -
eeeee O11 - 0.5 percent
.-.- Less than 0.1 percent

- Predominant...... Over 50 percent

- 10 - 50 percent
2 - 10 percent
2 percent

X - Detected in sample
N - Sought but not detected
C - Rock classification

Samplel.....ceeeee
Trench, location..
Tablel......+++++-

60-141¢
RL-6

60-142
RL-6
1

60.

- 143

RL-6

11

60-117
RL-9
11

60-3

17

60-4

17

59-161
Daisy
20

Rocks¢
Andesite........

Quartzite.
Schist.
Shale.......000.
Veinsssscssecoee
Minerals:
Albite....seeeee
Andesine........
Ankerite..
Arsenopyrite.
Biotite.....sse.
Biotite-chlorite
Calcite.........
Cassiterite.....
Chlorite........
Chlorite clay...
Dolomite........
Epidote.....
Fluorite........
Graphite..
Gypsum.....e-
Hydrobiotite....
Hydromuscovite..
Limonite........
Magnetite....
Muscovite.

Scorodite.
Sericite........
Tourmaline...
Zircon.......+-+

\
a

See footnotes at end of

table.

lHIb>b> ribs

toe

HrPiprani pr

nme 1

tmm '

twat

temo Rme

tiebat


51

TABLE 15. - Diamond-drill-hole log and sample analyses, hole 4--continued

Location: See figures 12 and 13
894 feet

Elevation of collar:
Depth: 172 feet
Dip: -37°

Bearing: N 49° W

Date begun: Aug. 16, 1961
Date finished: Aug. 29, 1961
Core sizes: BX to 2.0 feet

AX to 41.6 feet
EX to 172.0 feet

Footage

Percent.

From- | To- |Interval

Core
recovery

Tin in|Tin in
sludge| core

Tin
average

Formation

95.9 |108.1] 12.2

108.1 116.2 8.1

116.2 |140.1] 23.9

140.1/172.0| 31.9

64

95

74

45

<0.01) -

205} 0.04

+34] «26

+03) .03

0.04

231

+03

Soft gray shale with clay,
calcite, and gypsum in
fractures with a few
small quartz veinlets.
Gray medium-hard shale
with a few clay veinlets
and quartz veinlets.
Broken tourmaline schist
with numerous quartz
veins and veinlets, cal-
cite veinlets, and frac-
tures filled with iron-
stained clay and some
gypsum. Pyrite is common
in both clay and harder
rock and some limonite is
present. Cassiterite
occurs as random, very
fine grains within the
tourmaline schist. In 3
fragments of core
examined (131.0 feet,
136.0 feet, 138.0 feet)
over 95 percent of the
cassiterite grains were
smaller than 600-mesh.
Some chlorite fragments
also noted.

Shale grading from
intensely altered,
broken, and stained at
140 feet to hard gray
shale at 172 feet. Clay
and limonite abundant
from 140 to 150 feet.
Calcite, gypsum, epidote,
and chlorite also occur
at 140 to 150 feet. A
few quartz veins and
veinlets with some pyrite
noted to about 168 feet.



TABLE 28. - Spectrographic analyses--continued

Letters indicate estimates from qualitative analyses:

A Over 10 percent C 1 to 5 percent E 0.01 to 0.1 percent G Under 0.001 percent
B 5 to 10 percent D 0.1 to 1 percent F 0,001 to 0.01 percent - Not detected
* $n interference
Sample. <] 61-81 | 59-203 | 60-30 |Composite] cD-59 | 60-67 Composite | Composite [Composite] 59-195 |Composite| 59-191
226-230 59-161-163| 231-232 |60-10-11 60-12-13
Trench, location? |TR-RL-5|TR-RL-5A|TR-Peluk-5| TR-IC-1 |TR-IC-1)/TR-LL-10| TR-LL-9 TR-LL-3 TR-IC-4 | TR-BC-5| Red Fox |OC-WF Div.
Table? 1L 1L 7 20 20 20 20 21 22 24 25 27
A c Cc A A Cc A A B c Cc c
Cc - B D D D - D D D
- - - E - E - E - E - -
G G G F G G G G G G G G
F F - - - - - - - -
- c * D Cc c Cc c Cc c Cc Cc
- - - - - - E - - - E -
D D E Cc B D Cc D c E c D
E E E E E E E E F E F E
F F E E E F F F E F E F
F F E F F F F F F F F F
- - - - - - - - E - E -
B A A A A A A A A A A A
E - E E E - - - - E E E
c c c c c c B c c c c c
Manganese... E E E D D E D D E E E E
Molybdenum..... F F - F E F E F - E - E
Nickel...eeseeeee E E E E E E E E E E E E
Phosphorus - - - - - - - - - - - -
Scandium. . - F - - - F - - F F - F
Silicon... A A A A A A A A A A A
Silver... - - G - - - G - G - F -
Sodium... . D Cc E - D Cc c Cc Cc D D D
Tine sececseeeee A Cc A E - D D E E D D D
Titanium... Cc Cc E Cc c c Cc Cc D c D Cc
E E E E D E E D E E E E
- - - - - - - - F - - -
- - E - - - - - - - - -
F E E E E F E E

Sample numbers are inclusive; that is, 59-137-139 covers 59-137, 59-138, and 59-139, and so on.
2Trench, drill hole, or other sample site.
2Table in which sample is described.

4Cadmium occurring in the absence of zinc was considered anomalous.

spectroscopically. Less than 0.001 percent cadmium was indicated and occasional traces of zinc were found.

Therefore cadmium-bearing samples were reanalyzed

SL


HAR aAPry

81

TABLE 29. - Petrographic identifications--continued

Predominant... sees Over 50 percent
Abundant... «++ 10 - 50 percent
Subordinate. .» 2 - 10 percent
Minor. 0.5 - 2 percent
Few.. . 0.1 - 0.5 percent

Tracessoe

. Less than 0.1 percent

X - Detected in sample
N - Sought but not detected
C - Rock classification

Samplel.........
Trench, location
Tablel......

60-58 |60-58A | 60-58B
cw) | ©) ce)
27 27 27

60-58C
cs)
27

60-58D
(8)
27

60-58E
(6)
27

60-58F
cs)
27

61-8
\)

Rocks:

Andesite...
Breccia.
Clay...
Gossan..

Vein.

Minerals:

Albite........
Andesine......
Ankerite..
Arsenopyrite.
Biotite......
Biotite-chlorite
Calcite......
Cassiterite.

Ch

Chlorite clay

Do
Ep:
Fh

Graphite..
Gypsum.......
Hydrobiotite.
Hydromuscovite

Lit

Magnetite.

Mu
Py:

QuartZ..seeee

Sei
Se:
Tor

Zircon.....--.+-

lorite...

lomite..
idote.
uorite...

monite..

scovite.
rite....

orodite.
ricite
urma Line.

'
' atars

tame
romyme

nt

rope

A

1See the listed table for sample description. Letters A,
sample number designate lithological variations in the

ap -
3p -
4See
5 See
6See
7See

Peluk.
Bed of P
section
section
section
section

eluk Creek.

B, C, etc. following the
sample or specimen.

entitled "Drusy Quartz Vein and Andesite Dike."

entitled "Mouth of West Fork."

entitled "Oakland Creek-West Fork Divide."

entitled "Summit of Big Potato Mountain."




58

\ setae,
\ Daisy Fault

231,232,233

Details of trenchs
in this area are

> WN
226 10 230.\
see figure 17 \\

Shovel pi
\\ ound
\\
o\\
Z\\
o

LEGEND
60-11 Sample

= Bulldozer trench
ic-6
Sample pit
+ Trace of tin

x Moderate amount of tin

FIGURE 16. - Lode Sampling, Iron Creek Area.

in figure 1 ips

No tin
in bedrock:


TABLE 9. - Churn-drilling results, West Gulch and South Gulchl

31

Drill-hole depth, feet Concentrate Mining section

Hole | Total|Over- |Gravel|Bed-|Cased | Weight,| Tin, |Depth,| Vol,2| Tin, Abun-
burden rock 1b per-| feet |cu yd|/1b per| dance

cent. cu _yd |factor>
41 | 25.5 | 3.0 17.0 | 5.5] 23.0 | 2.75 |0.75} 18 |0.154] 0.13 234
42 23.5 - 20.5 3.0] 21.5 1.67 225 21 179 +02 42
43 | 17.0 - 14.0 | 3.0] 6.6 | 2.61 +96) 15 -070| .36 540
44 | 15.5 35 12.0 | 3.0} 5.0 | 1.40 +20} 13 061) .05 65
45 | 16.5 - 13.5 | 3.0] 15.0 | 1.11 |1.50) 14 120} «14 196
46 | 21.5 - 9.0 |12.5] 5.0] 2.82 +21) 10 +047 13 130
47 | 25.9 - 22.0 | 3.9] 3.0 | 2.30 05} 23 +108} 01 23
48 | 26.7 - 22.0 | 4.7] 3.0] 2.41 |3.16} 23 +108} .70 1,610
49 | 13.0 - 11.0 | 2.0} 11.2 -89  |1.22) 12 -102} «11 132
50 | 32.0 | 4.0 24.0 | 4.0] 4.0 | 2.21 |5.39] 25 +117) 1.02 |2,550
51 | 18.8 - 16.5 | 2.3} 3.0 | 1.83 |2.46] 17 080} .56 952
52 | 19.5 - 18.0 | 1.5] 3.0 |] 1.40 +87] 19 +089} .14 266
53 | 31.2 - 29.0 | 2.2} 10.0 | 3.28 {1.76} 30 +140] .41 [1,230
54 | 24.8 - 22.0 | 2.8] 4.0 | 2.43 +66] 23 -108} .15 345
61 | 31.2 - 26.0 | 5.2] 3.0 | 4.50 +30] 27 +126) «11 297
62 | 28.2 - 20.0 | 8.2] 3.0 | 3.33 -53] 21 +098! .18 378
63 | 10.0 - 7.5 | 2.5] 3.0] 1.07 +23 8 +037} .07 56

Table based on

data obtained during this project.

2Average volume of drill hole is 0.00854 cubic yard per linear foot of cased
drill hole, and 0.00468 cubic yard per linear foot of uncased drill hole.

3(Mining section, feet) x (tin, lb per cu yd) x 100 = abundance factor.

section of this report entitled "Placer Sampling and Evaluation."

See


71

TABLE 26. - Description and analyses of specimens, Eureka
Prospect, Little Potato Mountain

Description Tin, analyses
amp le Character of material percent
Number | Length, feet
6-17-1 - Specimens of quartz float....... <0.01
6-17-2 - Dump specimens, hand-dug trench. 04
6-17-3 - Dump specimens, shaft..........+ -23

Oakland Creek-West Fork Divide

A body of frost broken massive dominantly quartz rock and a large number
of quartz veins occur in the Oakland Creek-West Fork divide. These have been
explored by several very old prospect pits including a hand-dug trench about
40 feet long and a sample pit (figs. 3 and 5) dug in the mass of quartz rock
near the center of the divide. A number of smaller pits explore less promi-
nent quartz outcroppings on the north side of the divide.

The detrital cover was sampled on both the Oakland Creek side and the
West Fork side of the divide (fig. 10). No recognizable tin mineral was
recovered. Samples also were taken from the gravels at the head of Oakland
Creek and West Gulch, the headwater tributary of West Fork. Only barely recog-
nizable traces of cassiterite were found. Selected specimens for laboratory
analyses were taken from the dump of the trench and the sample pit because of
the relatively large amount of massive quartz present. Specimen descriptions
and analyses are in table 27. No tin mineral was recognized, either in the
field or in the laboratory, but chemical analyses indicated the presence of
somewhat less than 0.1 percent of tin, apparently associated with tourmaline
and quartz.

TABLE 27. - Description and analyses of specimens,
Oakland Creek-West Fork divide

Description Analyses
Sample Tin
Number | Length, Character of material per- | Spec.} | Petro.2
feet cent
60-58 - Assorted specimens of the trench dump..| - - x
219 - Goes cececcccccrcccccccscccevsceces | 0209 - -
59-191 - Assorted specimens of the prospect dump| .03 4 -

1See section entitled "Spectrographic Analyses."
2See section entitled "Petrography."

Iron Creek-Oakland Creek Divide

The only evidence of lode prospecting in the Iron Creek-Oakland Creek
divide is a small pit on a quartz outcropping about 200 feet east of the cen-
ter of the divide (figs. 3 and 15). Selected specimens from this dump were
analyzed chemically and found to contain 0.05 percent tin; but the tin min-
eral could not be identified. Detrital cover samples across the head of Iron


32

LEGEND

* Sample pit
x Trace of tin

xx Moderate amount
of tin
xxx Abundant tin

° 500 1000

Scale, feet

Lode Sampling, West Fork

The lode deposits were exposed by bulldozer trenching. The west side of
South Gulch was started first, then the east side, and later the Peluk Creek
area. Trenches were excavated where detrital cover sampling indicated higher-
than-normal concentrations of cassiterite. The irregular concentrations in
the South Gulch drainage basin were difficult to interpret. Therefore,
trenches also were put down to intersect apparently favorable structural
features, particularly large faults.


47

TABLE 12. - Diamond-drill-hole log and sample analyses, hole 1

Location: See figure 12 Date begun: July 1, 1961
Elevation of collar: 729 feet Date finished: July 26, 1961
Depth: 141.2 feet Core sizes: AX to 74.0 feet
Dip: -36° EX to 141.2 feet
Bearing: S 28°00' W
Footage Percent
From- | To- |Interval} Core |Tin in|Tin in] Tin Formation
recovery|sludge| core |average|
0.0} 9.0 9.0 - - - - Overburden.
9.0] 20.0} 11.0 74 0.03 | 0.01 0.02 | Fractured, thin-bedded

black iron-stained shale
with a clay-quartz vein
from 18 to 19 feet and
clay in other fractures.
20.0 | 30.0 10.0 14 -03 | <.01 02 | Clay, black shale, and
schist with some quartz.
Some tourmaline in the
shale.

30.0] 47.0} 17.0 72 02 - - Fine-grained blocky black
tourmaline schist with
thin quartz-pyrite vein-
lets and thin veinlets of
calcite along some
fractures.

47.0| 57.6] 10.6 33 .07 04 -06 | Fine-grained, hard, blocky
black tourmaline schist
with quartz-pyrite vein-
lets up to 1 inch wide
and a few thin calcite
veinlets in fractures.
57.6] 74.0} 16.4 64 05 04 -05 | Fine-grained, hard, blocky
black tourmaline schist
with few quartz-pyrite or
calcite veinlets and no
visible bedding.

74.0| 90.0) 16.0 67 02 - - Hard black shale with lit-
tle quartz or pyrite and
no visible bedding.

90.0 |116.2| 26.2 29 ell 01 -10 | Broken black tourmaline
schist with clay, quartz-
pyrite veins, and calcite
veins.

116.2 /141.2} 25.0 48 03 - - Broken black tourmaline
schist with some gray
clay and a few very thin
veinlets of quartz,
pyrite, and calcite.



20

FIGURE 7. - Sampling Detrital Cover With a Gasoline-Powered Posthole Auger. The hole
has been drilled, the auger is standing in a gold pan, and the kneeling man
is scraping the sample from the scroll into the pan.

cassiterite was verified by placing crystals in hydrochloric acid in the
presence of zinc--a tin plate formed on the cassiterite crystals.

Sampling was continued on both sides of a valley to the headwaters; or
as far upstream as the stream placers contained tin. The sampling results
indicated where the cassiterite-bearing float lines were entering the placers.
Normally, an area of interest along a streambank would be indicated by tin
minerals in practically every sample for at least several hundred feet.
Nothing more was done in areas that contained no tin or only an occasional
trace.

The sampling process was repeated a couple of hundred feet up the slope
from any areas of interest encountered. The second row of holes roughly


50

TABLE 15. - Diamond-drill-hole log and sample analyses, hole 4

Location: See figures 12 and 13 Date begun: Aug. 16, 1961
Elevation of collar: 894 feet Date finished: Aug. 29, 1961
Depth: 172 feet Core sizes: BX to 2.0 feet
Dip: -37° AX to 41.6 feet
Bearing: N 49° W EX to 172.0 feet
Footage Percent
From- | To- {Interval} Core |Tin in|Tin in} Tin Formation
recovery|sludge| core |average|
0.0) 23.9] 23.9 39 <0.01| - - Intensely broken black

medium-hard shaly lime-
stone and some tourmalin-
ized shale with a few
quartz and calcite vein-
lets. Well-crystallized
gypsum occurs with clay
and limonite along frac-
tures. Some chlorite is
present.

23.9 | 47.9] 24.0 48 <Ol} - - Black, slightly graphitic
limy shale with small cal-
cite veinlets and some
iron stain on fractures.
A few quartz veinlets
also are present and
fractures contained a
clay filling. Calcareous
material most abundant in
lenticles up to % inch
thick alined with bedding.

47.9 | 69.0] 21.1 68 <O1] - - Black, slightly graphitic
shale with tiny calcite
veinlets.

69.0 | 82.0 13.0 74 02 - - Gray altered shale with

gypsum in iron-stained,
clay-filled fractures and
a few quartz-pyrite vein-
lets. Biotite is abun-
dant and part of the
shale has been altered to
a hornfels.

82.0 | 89.2 7.2 46 -02} 0.03 0.02 | Broken shale, shaley clay,
clay, quartz, calcite,
and gypsum.

89.2 | 95.9 6.7 96 Ol] - - Gray shale with iron-

stained joints and frac-
tures and some quartz
veinlets.



59

Light grey to white clay

Quartz vein with pyrite ond
orsenopyrite

FIGURE 17. - Section Through Daisy Fault,
Trench IC-1, Looking South.

22:
Churn rill hole 59
(Grilled into outerop)

59-190

LEGEND
59-166 Sample

—— __ Bulldozer trench wee

LL-7 bors
x Trace of tin +>
Xx Moderate amount of tin

FIGURE 18. - Daisy Fault and Daisy Prospect, Summit of Little Potato Mountain.


This publication has been cataloged as follows :

Mulligan, John J
Tin-lode investigations, Potato Mountain area, Seward Pe-
ninsula, Alaska; with section on petrography by Walter L.

Gnagy. [Washington] U. S. Dept. of the Interior, Bureau of
Mines [1965]

85 p. illus., tables. (U. S. Bureau of Mines. Report of investiga-
tions 6587)
Includes bibliography.

1, Tin mines and mining—Alaska. 2, Petrology—Alaska. I. Gnagy,
Walter L. Il. Title. (Series)

TN23.U7 no. 6587 622.06173

U. S. Dept. of the Int. Library



TABLE 11. - Description and analyses of trench samples,
east side of South Gulch--continued

39

Description Analyses
Sample Tin,
Number ‘Length ,| Character of material per- |Spec.1| Petro.
feet cent
Trench RL-1--continued
59-89 2 Clay, crushed shale, and schist and quartz..] 2.50 - -
59-90 2 12 - -
59-91 2 19 - -
Total or] 14 1.42] - -
average
59-92 2 Broken iron-stained black shale.... 07) - -
59-93 4 DOs se ceccccccccccceccccrcercersccseceee| 202] - -
59-94 14 Panned concentrate same place as samples - -
59-84 to 59-91.
Trench RL-1A
59-95 [2 [Quartz vein in black shale..........--+-----] 0-03] ~ | =
Trench RL-1B
60-223 5 Black shale with quartz veinlets. 0.31) - -
60-224 4 do. se eeeeee «| <O1] - -
200 3 do... 06] - -
201 -5 | Quartz veinlet..... -06{ - -
202 1.5 | Iron-stained black shale with quartz 209] - -
veinlets.
Total or| 14 14] - -
average —
203 2 Clay, crushed shale, and some quartz 709) - -
204 5 Or sce ccececceresccccccccceeecees 06] - -
Total or 7 07] - -
average
205 8 Slightly iron-stained schist. <.01| - -
206 7 Oss sesecccrrccssrsccoee -O1| - =
Trench RL-2
59-70 2 Brown to yellow clay with quartz and partly | 0.02] - -
59-71 2 altered shale at contact between medium 02) X -
59-72 2 soft gray shale (upper bed) and black 02) X -
59-73 2 blocky tourmaline schist (lower bed). 02] - -
59-74 2+ | Drilled into crushed zone with a 3-inch <O1) - -
auger.
3033 } 5 Crushed schist and shale.........eeeeeeeeeee | <eOl] - -
Trench RL-2A
61-110 4 Altered shale, clay, and quartz....... 0.02] xX -
61-111 4 see 02) xX -
61-112 4 <O1] X -
61-114 4 <.01] X -
61-115 4 -03] X -
61-116 4 04) X -
61-117 5 204] - -
61-118 5 204] - -
60-150 5 Ol} X -
60-151 5 -O1| X -

See footnotes at end of table.



37

LEGEND “ x
~
LEGEND we G4
59-74 Sample 60-223, 60-224
200, 201,202 aM
=<  Bullaozer trench S 203,204 eT RL 138A 40°
REA EG 205
206
owes Diomond- drill hole \— No tin in bedrock
62 S N
é Churn-drill hole = °
° N\A ye 4
2 6I-
. NN greg Inrouge ks
\ pentouon] 61-5)" 39, °
Kas oiSh35!
—— WW ae
6I-2,
——, 6
OM
N ° 61-33 °
Ny 48 3

Noir Auger hole into crushed shale
and clay (only trace of tin found)

J-— Crushed

Aire tin)
\

AU96,
59

hole
vealed

*o bedrocy

Ws NOTE: Bedrock, except where sompled is o series
6 ft crush zone of much’ broken shale, phyllite, and fine
(no tin) We Qrained schists. Dips of bedding indicated.
wee | Becouse of breaking and general similarity ,
individual beds could not be traced from trench
. to trench. Tin minerals appear to have been
60-141 5 emplaced 8 0 generally vertical stockwork
v with some tendency to spreod loterally olong
2, ag bedding plones.
0
Wes
~~
°s 60-136
<

100 200 300 No tin minerals found on the
southern slopes of this hill

Scole,feet

FIGURE 12. - Lode Sampling, East Side of South Gulch.


62

TABLE 22. - Miscellaneous trench samples, Iron Creek drainage basin

Description Analyses
Sample Tin,
Number |Length, Character of material per-|Spec.1| Petro.?
feet cent
Trench IC-2
60-40 - Pan concentrate from right limit bank 5.89 - -

Iron Creek.

Trench IC-4
60-10 0.5 Quartz vein, strike N 80° E, dip vertical, |0.03] xX -
width 0.3 feet.
60-11 05 Quartz vein, strike N 80° E, dip vertical, 02 x -
width 0.5 feet.

1See section entitled "Spectrographic Analyses."
2See section entitled "Petrography."

Upper Buck Creek Drainage Basin

Placer Sampling, Upper Buck Creek

The results of the Bureau of Mines 1943 churn drilling on Upper Buck
Creek indicated that a pay streak extended from the mouth of West Fork
upstream to the mouth of the first right limit tributary above West Fork (fig.
19 and table 23). Only minor amounts of tin were found in drill-hole line 38
above the mouth of this tributary. The configuration of the placer deposit
suggested a deltalike deposit at the mouth of this right limit tributary
(drill-hole line 37, fig. 19).

Five sample pits were excavated by bulldozer in the placer gravels of the
first right limit tributary above West Fork. Substantial quantities of tin
were found in pits A, B, and C. Only traces of tin were found in pits D and E.
The relatively uniform amounts of tin in pits A, B, and C, and the abrupt
decrease in grade between trenches C and D suggested that the principal source
of tin was near pit C or between pits C and D.

Detrital Cover Sampling, Upper Buck Creek

Results of detrital cover sampling (fig. 19) tended to confirm deductions
that the principal lode source was between placer pits C and D on the first
right limit tributary above West Fork although some tin was derived from the
headwaters of this tributary. A second row of sample pits on the right limit
indicated a decrease in the grade. A few pans taken further uphill indicated
that decreasingly small traces of tin extended a few hundred feet above the
second row of pits. The amount of cassiterite above the second row of pits
appeared to be too small to warrant additional sampling. Traces of cassiter-
ite also were found in a few pits on the right limit bank near pit A.

Detrital cover sampling was continued to the headwaters of Upper Buck
Creek because of the old prospects in this area. Results were negative except
for a scant trace of tin found below the Red Fox prospect at the extreme head
of the valley.


LOPP LAGOON

}
oe
4

00d
ae

Ly,
si?
Le”

Xe cle a a
o 3)e 8
2, of§ a
7 oy a
* He 7 *o e
e o sie S e
a Gs OF
rN
lo 2
3 2
‘quartz
Porphyry
Give
Rea Fox
Eureka B= prospect
prospect,
Daisy ar ¥
3 Little Potato xs
prospect aig ge
Plocer miners’ camp
Seore, miles

FIGURE 3. - Potato Mountain Area. (Modified from Geological Survey map.)


Locati

49

TABLE 14. - Diamond-drill-hole log and sample analyses, hole 3

on:

Elevation of collar:

Depth:
Dip:

123.

-35°

Bearing: N

5 feet

73°30' W

See figures 12 and 13

888 feet

Date begun: Aug. 5, 1961
Date finished: Aug. 15, 1961
Core sizes: AX to 76.2 feet

EX to 123.5 feet

Foota;

e

Percent.

From-

To-

Interval

Core
recovery

Tin in
sludge

Tin in
core

Tin
average

Formation

0.0
5.0

10.0

19.9

27.4

41.6

83.5

5.0
10.0

19.9

27.4
41.6
71.0
83.5

123.5

5.0
5.0

9.9

7.5
14.2
29.4
12.5

40.0

12

14

37

56

83

73

61

0.38

<.01

<.01

<.01

<O1

0.90

71

0.40

Overburden.

Broken tourmalinized shale,
with clay, quartz, cal-
cite, pyrite, arsenopy-
rite, and cassiterite.
Cassiterite may have been
upgraded by residual con-
centration on the frost-
broken outcropping. No
sludge recovered.

Yellow to white clay,
tourmaline schist, and
quartz with aluminite and
chlorite abundant and
some limonite, hematite,
cassiterite, hydromusco-
vite, and magnetite.

Broken black to iron-
stained shale with gray
clay, brown clay, chlo-
rite, quartz, gypsum, and
limonite.

Black shale with some
quartz and pyrite from
39.0 to 41.6 feet.

Black biotite phyllite
with some included magne-
tite cut by a few quartz-
pyrite veinlets.

Black shale with some clay
and small amounts of
chlorite, limonite, and
calcite.

Dark-gray shale with a few
small quartz-pyrite vein-
lets and a trace of cas-
siterite with quartz at
113.5 to 114.0 feet



LEGEND

I Placer concentration
(see text and table 18)

© Churn-drill hole

+ Sample pit

x Trace of tin

xx Moderate amount of tin

xxx Abundant tin

===" Bulldozer pit

fo} 500 1000

Scale, fee

FIGURE 15. - Placer and Detrital Cover Sampling, Sutter Creek and

Iron Creek.

)

<
e
of

Cr, Sey

55

Detrital
cover sampling was
continued on the
right limit of
Peluk Creek and
the left limit of
West Fork. A tin
occurrence was out-
lined almost on
the summit of the
Peluk Creek-West
Fork divide.
Trench Peluk 5
(fig. 14 and table
17) exposed the
deposit where
detrital cover
sampling indicated
the highest grade.
The cassiterite
occurred associ-
ated with quartz,
sulfide minerals,
and clay, in an
irregular zone or
cluster of vein-
lets and lenses in
the metasediments
along a northwest-
ward-trending fault.
Only a trace of
tin was found in
trench Peluk 6
that crosses the
fault 100 feet to
the southeast.
Detrital cover
sampling indicated
that minor to
trace amounts of
tin occur along
the fault for 300
feet to the north-
west. No other
work was done in
the area.


TABLE 3. - Placer-mining claims in the Potato Mountain area

Claims Number of Acres
claims (approx.)

No. 1 Association on Iron Creek...... 2 40
No. 2 Association on Iron Creek... 2 40
Sutter Association on Sutter Creek..... oe 8 160
Billy Claim on Sutter Creek.......... 1 20
Discovery Claim on Left Fork Creek... eee 1 20
No. 1 Above Discovery Claim on Left Fork Creek. see 1 20
Elma Claim on Left Fork Creek......... . 1 20
Upper Buck Association on Buck Creek. . 2 40
Cub Claim on Buck Creek..........4. . 1 20
Stuart Claim on Buck Creek... . 1 20
Marvin Claim on Buck Creek. . 1 20
Whibby Claim on Buck Creek.. . 1 20
Ptarmigan Claim on Buck Creek... 1 20
Wild Goose Claim on Buck Creek.. see 1 20
No. 1 Discovery Association on Buck Creek... seeeeee 2 40
No. 2 Association on Buck Creek......... 2 40
No. 3 Association on Buck Creek.......+ 2 40
No. 4 Association on Buck Creek and Grouse Creek. 2 40
No. 5 Association on Grouse Creek. 2 40
No. 6 Association on Grouse Creek..... 2 40
Fox Claim on Grouse Creek.....seseeececeseeees 1 20
No. 1 West Fork Association on West Fork Creek. 2 40
No. 2 West Fork Association on West Fork Creek. 2 40
Junction Association on Grouse Creek............ 2 40

HISTORY

Placer Mining

Tin was found in the placer gravels of Buck Creek in the Potato Mountain
area in 1901 (figs. 2, 3, and 4). Placer tin production started in 1902
(table 4). Between 1902 and 1911, about 300 tons of concentrate containing
about 50 percent tin were produced by manual and small-scale mechanical meth-
ods from open placer pits on Buck Creek. In 1911, a double-flume, open-
connected bucket-line dredge with a capacity of about 800 cubic yards per day
was erected. Starting near the mouth of Sutter Creek, the gravels of Buck
Creek were mined upstream reportedly about 6,500 feet and downstream to the
mouth of Buck Creek, then down Grouse Creek to the mouth of Left Fork. The
gravels mined averaged about 5 or 6 feet deep. Further upstream, the gravels
averaged only about 4 feet deep which was too shallow for the dredge. A sec-
ond dredge, similar except designed for the shallower gravels, was erected in
1915. Using this dredge, Buck Creek was mined upstream almost to the mouth of
West Fork. Intermittent small-scale hand-mining operations on Buck Creek and
on Iron Creek (a headwater tributary of Sutter Creek) added a few tons to the
total production during this period. Tin prices dropped in 1920 and 1921, and
all activity stopped; ruins of the dredges remain where they were abandoned.


TIN-LODE INVESTIGATIONS,
POTATO MOUNTAIN AREA,
SEWARD PENINSULA, ALASKA

By John J. Mulligan

With Section on Petrography by Walter L. Gnagy

so 4 * * © » * 4% & » »% report of investigations 6587

UNITED STATES DEPARTMENT OF THE INTERIOR
BUREAU OF MINES


30

TABLE 8. - Churn-drilling results, 1943, West Fork and Peluk Creeks?

Creek and Line Hole Mining Tin, Abundance
section, feet lb per cu yd factor?
4 4.0 0.77 308
. 3 3.5 +22 77
Peluk Creek: 1.. 2 5.0 “04 20
1 2.0 01 2

West Fork:

2 2 4.0 +10 40
errr rrr errr rr rrr ee 1 3.0 “34 102
Becececceecsenseeeeees {i 4.0 +04 16
1 3.5 +35 122
5 5.0 75 375
4 3.0 97 291
evsccccceccccccccvcces 3 2.0 «49 98
2 2.0 1.68 336
1 5.0 07 35
4 3.0 +85 255
5 3 2.0 5.98 1,196
eee eeeereeeeecereecees 2 4.0 “20 80
1 0 0 (0)
Gocececccesccccvcsscecs 2 2.0 +31 62
cree 1 4.0 +05 20
1 4.0 +59 236
Tocesccceccccccccescoes 2 4.0 2.06 824
3 3.0 +61 183
1 (LL) 7.0 31 217
Bi ccccevescccccvscsvecs 1 (RL) 7.0 2.86 2,002
2 4.5 +31 140
2 5.0 14 70
Dieccccccccccccccesccees 1 (LL) 6.0 1.44 864
1 (RL) 8.0 07 56

1Table based on data abstracted from Bureau of Mines Report of Investigations

4418 (30).

2(Mining section, feet) x (tin, 1b per cu yd) x 100 = abundance factor. See

section of this report entitled "Placer Sampling and Evaluation."


72

Creek (fig. 15) indicated that the only tin in the area was a scant trace of
cassiterite derived from the vicinity of this prospect pit. Panned stream
concentrates taken from the extreme headwaters of both Iron Creek and Oakland
Creek indicated only traces of cassiterite in the gravels.

Summit of Big Potato Mountain

A series of small shovel pits and trenches at intervals of 200 to 400
feet in a line roughly N 10° W extend across the summit of Big Potato Mountain
(fig. 3) and about 1,000 feet down the southern slope. The pits explore a
thin line of quartz-pyrite and limonite fragments in soft earthy to shaly
debris. The quartz and associated minerals appear to be the surface expres-
sion of a deposit alined along the contact between an overlying hard blocky
schist and a softer shale. Examination of the material on the surface failed
to yield any recognizable tin minerals. A suite of selected specimens from
the pit dumps were analyzed chemically and found to contain 0.05 percent tin.
A typical specimen (sample 61-8) was analyzed petrographically (see the sec-
tion entitled "Petrography"). The placer examinations and detrital cover
sampling along Iron Creek (fig. 15) indicated that only traces of tin were
derived from the upper slopes of Big Potato Mountain.

Associated Minerals
Copper, Lead, and Zinc

Widespread traces of copper and lead that can be detected by spectro-
graphic or chemical analyses occur in the Potato Mountain area but no deposits
were recognized in the field. The widespread occurrence would suggest that
copper and lead sulfides may be minor components of the widespread pyrite and
arsenopyrite deposits. Zinc was detected in a few samples by spectrographic
or spectroscopic analyses but apparently it is less abundant than copper or
lead.

Radioactive Minerals

No radioactive minerals were identified in the Potato Mountain area.
Routine checks were made with a laboratory Geiger counter on several hundred
samples and specimens of the various rocks in the area. Results generally
were negative although in a few cases traces were indicated. The samples
checked included the churn-drill concentrates from West Fork and Iron Creek;
most were negative but a few indicated an equivalent uranium content of 0.001
percent. In bedrock samples traces of radioactivity occasionally were found
in zones containing quartz-pyrite veins and clay minerals. The greatest
amount of radioactivity observed in such zones indicated 0.003 percent equiva-
lent uranium; the radioactive mineral or rock could not be isolated. No radio-
activity was detected in specimens of the various igneous dikes. Because the
results were negative except as mentioned above, data on the analyses for
radioactive minerals have not been tabulated.


18

regardless of the depth of gravel in which it occurred. When the abundance
factors were plotted on a map, areas of comparable abundance could be outlined
in a manner similar to drawing contour lines. The minimum grade of the placer
deposits mined on Buck Creek is believed to have been at least one pound of
tin per cubic yard in a pay horizon averaging about 5 feet deep. Areas of
comparable abundance were outlined in the headwater tributaries. The location
of these placer concentrations, combined with information on the degree of
wear evident on the cassiterite crystals, indicated limited areas from which
the placer deposits must have been derived.

Churn Drilling

A churn drill was used to sample the extreme headwaters of West Fork and
Iron Creek. No published data were available, and the depth of the placer
deposits on these streams made test pitting impractical. Standard placer
evaluation procedures were followed, except that reliable water measurements
of uncased holes could not be made in the loose unsorted detrital material
found near the headwaters of these streams. No clear distinction could be
made between overburden and gravel; therefore, the pay horizon was assumed to
extend from the surface to bedrock and to include from % to 1 foot of bedrock.

The drilling was done with a Fairbanks-type skid-mounted churn drill
equipped with bits designed for use inside 5-inch casing. Holes were drilled
open where possible, but casing had to be used in many holes. The casing shoe
had a diameter of 6% inches. Theoretical volumes were used in evaluating the
sampling results; 0.00568 cubic yard per foot of depth uncased, and 0.00854
cubic yard per foot of depth cased. The depth of the pay horizon in feet (ph)
multiplied by the theoretical volume in cubic yards per foot (v) gave the vol-
ume of the pay horizon in cubic yards (V). Dividing this volume into the
weight of concentrate in pounds (C) gave the pounds of concentrate per cubic
yard (c) in the pay horizon. This figure multiplied by the percent of tin in
the concentrate (t) gave the value of the pay horizon in pounds of tin per
cubic yard (T). For this project an abundance factor (AF) was determined by
multiplying the value of the pay horizon by the depth and multiplying this by
100 to eliminate decimals. Computations are summarized as follows:

phxv=V
Cue
Vv
ext=T
T x ph x 100 = AF

Test Pitting

Test pits were sunk in the placer gravels either to determine the amount
of wear evident on the cassiterite or to determine the upstream limits of
deposition; both supplemented churn-drilling and other placer evaluation data
as a guide for lode exploration. The test pits were dug in or near the stream
channels, usually with a bulldozer but occasionally by hand. The pits were in






42

TABLE 11. - Description and analyses of trench samples,
east side of South Gulch--continued
Description Analyses
Sample Tin,
Number |Length,| Character of material per- |Spec.1 |Petro.2
feet cent
Trench RL-15 (East Fork, Trench RL-3A)
61-44 2.5 | Iron-stained altered shale and clay.. «| 0.02 - -
61-45 3 Altered shale, clay, and qWATEZ ees eee «| -1L] - -
61-46 5 dO. sssssesscsessscesseerces nee <.01}] - =
Trench RL~21 (Between Trenches RL-3 and Rie 4
61-100 10 Iron-stained shale, clay, and quartz........| 0.07] - -
61-101 10 dOsssssscseceee deere rerceecccees -10} - -
Total or| 20 08} - -
average —=——=== =
61-102 4 Iron-stained altered shale, clay, and quartz| .08| - -
61-103 5 do. eee see . +02) - -
61-104 4 Os eccccccscvesccsccocees «| 207] - -
Total or| 13 06] - -
average
Trench RL-4
59-26 2 Iron-stained schist, clay, and quartz... 0.62) X -
59-27 4 -10} xX -
59-28 1.3 02} X -
59-29 1.7 +03) X -
59-30 4 <-01} - -
59-31 47 <01} - -
59-32 4.3 <.01] - -
59-33 5 <.01| - -
59-34 5 <.O1]} - -
59-35 2 02) - -
59-36 2.8 06) - -
59-37 2.5 +99} - -
59-38 2.5 31) - -
59-39 4.4 <.O1} - -
59-40 2.9 -14] - -
59-41 2 3.00] - -
59-42 3 1.42) - -
Total 54.1 40
average
Trench RL-17 (Between Trenches RL-4 and RL-5.
61-58 4 Altered shale, iron-stained clay, and quartz|<0.01| - -
61-59 4 dowsseeee eee tee e er eewevene Ol) - -
61-60 4 dowsseeee . tee e eee eeeeene 16] - -
61-61 4 Gray to red-brown clay, altered shale, “and 4.96) - -
quartz.
61-62 4.5 | White, yellow, and pale-green clay... weee| 3.37 ~ -
61-63 4.5 | Gray altered shale, clay, and quartz. on 1.68) - -
61-64 2 White to yellow clay, altered shale, and” 18} - -
shale, and quartz.
61-65 3 . . 12 - -
61-66 4 . 253] - -
Total or| 34 1.36) - -
average
61-67 4 Iron-stained, dark-gray shale. Ol; - -
61-68 2 Shale, quartz, and clay......- Ol] - -

See footnotes at end of table.



26

TABLE 7. - Description of typical specimens of vein and dike
rocks found in the Buck Creek placers--continued

Specimen

Petrographic description

Tin,
percent?

5-1-lA..

5-1-2...

101.....

239...6.

240.....

242.....

The specimen is a fragment of a quartz vein which is adja-
cent to some cassiterite and includes other small cassit-
erite crystals. Running through the quartz in parallel
rows are limonite-stained holes up to 1 mm in diameter.
Also present are 2 sets of crosscutting fractures stained
with limonite. A few grains of tourmaline are associated
with cassiterite aggregates. The parallel rows of
limonite-stained holes in this sample are analogous to
those in sample 5-1-1. These two fragments probably are
of related origin.

The specimen is a "breccia" of angular shale fragments in a
matrix of pure white quartz. Parallel rows of quartz
prisms are oriented perpendicular to and adjacent to the
embedded shale fragments. Cavities within the quartz
matrix are also lined with parallel growths of quartz
prisms. The average width of these prisms is 0.5 mn.

The specimen is composed predominantly of cassiterite with
abundant biotite-chlorite and lesser amounts of limonite
and arsenopyrite.

The specimen is composed predominantly of massive vein
quartz with yellow limonite stains. Small amounts of radi-
ating fibrous iron silicate, present in cavities of the
vein quartz, are tentatively identified as cummingtonite.
A trace of light-green tourmaline is present. Cassiterite
occurs as partly euhedral crystals filling a cavity in the
vein quartz.

The specimen is composed of quartz and cassiterite inti-
mately mixed in vein quartz. Essentially all the mineral
grains of both quartz and cassiterite are coarser than 2 m
in diameter. A few small cavities in the vein quartz are
partly filled with light-colored limonite.

The specimen is a highly altered acidic dike composed of a
hydrothermal clay, tentatively identified as hydromus-
covite (hydromica or illite), and a small amount of clear
quartz. Dark, prismatic-shaped areas are filled with tour-
maline, probably an alteration product from an earlier
ferromagnesian phenocryst.

The specimen is composed of cassiterite with quartz,
limonite, and tourmaline.

The specimen is composed of quartz, very fine-grained vein
quartz, and limonite; dark areas contain fine-grained

tourmaline. No tin mineral was detected.

See footnote at end of table.

0.02

63.1


35

average may be about 1 percent tin, but the extreme irregularity makes any determina-
tion of average grade doubtful. Outside this zone are numerous similar, but smaller
and lower grade zones. Trench RL-1 exposed 14 feet of clay and quartz with an aver-
age grade of 1.42 percent tin. Attempts to find an extension of this deposit were
unsuccessful. Other similar concentrations ranged in grade from 0.75 percent tin
downward to less than 0.1 percent tin. No tin was found east of the shaly limestone
exposed in trench RL-19 (fig. 13), except for a narrow zone of clay and quartz vein-
lets alined with the sedimentary bedding and exposed in trench RL-8 and trench RL-6
(sample 59-13).

TABLE 10. - Description and analyses of trench samples,
west side of South Gulch

Description Analyses
Sample Tin,
Number = _|Length,} Character of material per- |Spec.1|Petro.2
feet cent
Trench LL-5
59-136 5 Altered shale, iron-stained clay, and quartz| 0.90] - -
59-137 5 .- «| 24) x -
59-138 4 | 1.60} xX -
59-139 1 «| 29] X -
59-140 5 eeee | <O1l] - -
59-141 5 «| <.O1] - -
59-142 5 -| 46] - -
59-143 5 eeee | 602] - -
59-144 5 «| 02] - -
59-146 5 | -67] - -
59-147 5 «| 683] - -
59-148 5 «[<.O1] - -
59-149 5 +| 36] - -
59-150 5 +f .1L] - -
59-151 5 «| 05] - -
59-152 5 «| 03] - -
59-153 5 «| 602] - -
59-154 5 «| 263} - -
Total or| 85 +33) - -
average
59-155 5 Gray to brown shale.........+ssssseesereeees Ol} - =
Trench LL-4

60-202 5 Iron-stained shale with quartz veinlets. 0.06; - -
60-203 10 do... . . o 08] - -
60-204 5 dows... te eceeees 09) - -
60-205 3 Altered shale, clay, and quartz. 25) - -
60-206 3 +23] - -
60-207 3 «15} - -
60-208 4 {| .10} - -
60-209 5 . -03) - -
60-210 5 Clay with some quartz <.O1] - -
60-211 5 Oss eseeceeeeceeee seeee . «| -40] - -
60-212 5 Altered shale, quartz, and some clay.. . 262] - -
60-213 5 Altered shale and quartz..... -Ol} - -
60-214 5 Soft altered shale.....ssssseeeeeesoee . O01} - -

Total or 63 215

average

See footnotes at end of table.


27.

28.

29.

30.

31.

32.

33.

34.

35.

36.

85

Heide, H. E. Investigation of the Lost River Tin Deposit, Seward
Peninsula, Alaska. BuMines Rept. of Inv. 3902, 1946, 57 pp.

Heide, H. E., Wilford S. Wright, and Robert S. Sanford. Exploration of
Cape Mountain Lode-Tin Deposits, Seward Peninsula, Alaska. BuMines
Rept. of Inv. 3978, 1946, 16 pp.

Heide, H. E., and Robert S. Sanford. Churn Drilling at Cape Mountain
Tin Placer Deposits, Seward Peninsula, Alaska. BuMines Rept. of Inv.
4345, 1948, 14 pp.

Heide, H. E., and F. A. Rutledge. Investigation of Potato Mountain Tin
Placer Deposits, Seward Peninsula, Northwestern Alaska. BuMines Rept.
of Inv. 4418, 1949, 21 pp.

Lorain, S. H., R. R. Wells, Miro Mihelich, J. J. Mulligan, R. L. Thorne,
and J. A. Herdlick, Lode-Tin Mining at Lost River, Seward Peninsula,
Alaska, BuMines Inf. Circ. 7871, 1958, 76 pp.

Mulligan, John J. Tin Placer and Lode Investigations, Ear Mountain Area,
Seward Peninsula, Alaska, BuMines Rept. of Inv. 5493, 1959, 53 pp.

. Sampling Stream Gravels for Tin, Near York, Seward Peninsula,
Alaska. BuMines Rept. of Inv. 5520, 1959, 25 pp.

Mulligan, John J., and Robert L. Thorne. Tin-Placer Sampling Methods
and Results, Cape Mountain District, Seward Peninsula, Alaska.
BuMines Inf. Circ. 7878, 1959, 69 pp.

Hopkins, David M. Cenozoic History of the Bering Land Bridge. Science,
v. 129, No. 3362, June 5, 1959, pp. 1519-1528.

Sainsbury, C. L. Beryllium Deposits of the Western Seward Peninsula,
Alaska. U.S. Geol. Survey Circ. 479, 1963, 18 pp.

INT. eBULOF MINES.PGH..PAL 7766


21

paralleled the first and was continued until no cassiterite was found at
either end. Additional similar lines of holes were put in at successively
higher elevations until no more tin minerals were found or the summit was
reached. This procedure outlined an area in which the detrital material con-
tained tin. The uppermost lode source usually would be obvious, but minerals
derived from the uppermost deposits tended to obscure lode outcroppings lower
on the hillside. Therefore, additional samples were taken to form a rough
grid pattern. Zones of higher-than-normal concentrations within this grid
usually occurred in a pattern that indicated the general location of outcrops.

Amount of Tin Detectable

Twenty samples of the detrital cover were analyzed to determine the mini-
mum amount of tin that a skilled panner could detect in the field by routine
panning and visual inspection. Samples were taken at sites where panning
indicated either traces of cassiterite or no cassiterite. As a matter of
interest, one sample was taken where panning indicated an abundance of tin.

Two samples were taken at each sample site; each sample filled one
16-inch gold pan. Both samples were washed and screened with a pan in which a
pattern of 3/8-inch round holes had been drilled. Oversize was discarded and
slimes were decanted off. One sample was panned on the spot, and the tin con-
tent was estimated. The duplicate sample was analyzed in the laboratory at
Juneau. Results of the test are in table 5.

The tests showed that 0.05 percent tin can be detected in the field by
routine panning if the tin occurs as visible cassiterite crystals. Cassiter-
ite crystals that occur attached to lighter minerals might be lost during the
panning process. For this reason, tourmaline schists with disseminated fine-
grained cassiterite may be more widespread than indicated by the sampling.
Minor amounts of tin occurring as a component of stannite or some other tin
mineral probably would not be recognized in the field; therefore, selected
panned samples from the various areas sampled were submitted for petrographic
analyses.

TABLE 5. - Amount of cassiterite in detrital material detected by panning

Sample Panner's Sample, Sample Panner's Sample,
estimate! | percent tin? estimatel| percent tin®

1.. x 0.05 ll... ooee X 0.05
x 05 Oo None
ie} Trace oO Trace
Oo Trace ie} Trace
ie) Trace 0 Trace
ie) Trace Oo None
oO Trace oO Trace
ie) Trace O Trace
x -05 XXX 60
x 205 noes xX +05

1X Trace of cassiterite. XXX Abundant cassiterite.
2Chemical analyses.




Freight too heavy or bulky for air transport is shipped by barge from
Nome or lightered ashore from steamships. Nome is the principal port of call
for ships that service the Seward Peninsula. Three steamships per year bring
cargo to Nome and the Bering Sea ports; the first normally arrives in late
June; the last departs in late October. There are no ports on the Seward
Peninsula where ships discharge directly. The ships anchor offshore and dis-
charge into lighters. Barges of 50 to 150 tons burden, towed by small tugs,
are used both for lightering and for coastwise shipping. Oil shipments are
handled by dealers in Nome and distributed either in bulk or by the barrel.

A sandy beach at York is the most convenient landing place to the Potato Moun-
tain area. No freight handling facilities of any sort are available; barges
or other landing craft are beached and unloaded on the sand. Obviously, such
operations require favorable weather.

There are few roads or trails in the Potato Mountain area. An access
road extends from Teller to Lost River. A trail from Lost River to Potato
Mountain, York, and Tin City (fig. 2) has been used by horse and wagon and by
tractors, but would require substantial preparation to be practical for use by
trucks. During most of the summer, except during occasional brief floods,
off-highway-type trucks can travel along many of the streambeds with little or
no preliminary road work. Such vehicles usually require prepared trails over
the tundra-covered countryside. Heavily loaded standard six-wheel-drive
military-type trucks have been driven over the trail from York to the head of
Buck Creek.

Crawler-type tractors towing sleds or trailers are the most commonly used
overland transportation. Heavy freight normally is hauled in late winter and
early spring, but summer travel is practical throughout the area because of
the rounded topography, the lack of trees, and the general absence of unforda-
ble streams. In late summer and fall only light loads can be hauled, and
skill and local knowledge are required because of the soft marshy conditions
resulting from thawing of the detrital cover.

LABOR

Unskilled, semi-skilled, and many types of skilled labor can be obtained
from the native Eskimo and resident white population of the Seward Peninsula.
Supervisory personnel and some specialized technicians usually must be brought
from other localities. Table 1 lists the population of the western part of
the Seward Peninsula (fig. 1) as recorded in 1950 and 1960. A very high per-
centage of the population is available for employment because of the decrease
in gold mining and the lack of other industrial development.

TABLE 1. - Population of the western part of the Seward Peninsula

Settlements 1950 | 1960 Settlements 1950 | 1960
Diomede......seeeeeeeee 103 88 Teller....sscsescvccece 160 217
Igloo.... eee 64} (1) Teller Mission. eee 109 109
Nome...seseeeeeceeeeeee | 1,876 12,316 Wales........- eee 141 128
Shishmaref........+.0e- 194 217 Total.... --- (2,647 | 3,075

1Settlement abandoned.


57

Obviously, the tin in the Sutter Creek-Iron Creek drainage was derived
from the area drained by Iron Creek. Six churn-drill holes (fig. 15 and table
19) were put down on Iron Creek upstream from the previous Bureau drill holes.
Bulldozer trenches and shovel pits were dug in the extreme headwaters of Iron
Creek and in its right limit tributary. Little more than traces of tin were
found. This placer sampling program indicated that the tin must have been
derived from the area where Iron Creek rounds the eastern slope of Big Potato
Mountain.

TABLE 19. - Churn-drilling results, headwaters of Iron Creek

Drill-hole depth, feet Concentrate Mining section?
Hole | Total] Over-|Gravel|Bed- |Cased | Weight,|Tin,|Depth,| Vol, | Tin, |Abun-
No. burden rock 1b per-| feet |cu yd|lb per|dance
cent cu _yd |factor?

55 | 21.4 - 18.5 | 2.9] 4.0 4.17 |0.05| 19.0 |0.089| 0.02 38
56 | 15.7 - 12.5 | 3.2] 6.0 1.64 |2.01] 13.0 | .061} .54 702
57 | 16.0 - 13.0 | 3.0] 5.0 2.19 | .26) 14.0 | .066} .09 126
58 | 30.0 - 24.0 | 6.0} 5.0 7.15 | .14) 25.0] .117| .09 225
59 | 26.8 - - {26.8} 3.0] 31.79 | - - 2125] - -

60 | 23.0 - 15.0 | 8.0] 15.0 3.80 | .03| 16.0 | .137] .01 16

lAverage volume of drill hole is 0.00854 cubic yard per linear foot of cased
drill hole, and 0.00468 cubic yard per linear foot of uncased drill hole.
2(Mining section, feet) x (tin, lb per cu yd) x 100 = abundance factor.
See section of this report entitled "Placer Sampling and Evaluation."

Detrital Cover Sampling, Iron Creek

The detrital cover on both banks of Iron Creek was sampled as indicated
in figure 15. The only significant occurrence of tin was found near the
eastern base of Big Potato Mountain. A relatively dense grid of detrital
cover samples failed to indicate the presence of strong concentrations at any
point.

Lode Sampling, Iron Creek Area

Examination of the tin-bearing area on the eastern base of Big Potato
Mountain revealed that the tin minerals occur associated with quartz, pyrite,
and arsenopyrite in veinlets in the metasediments both adjacent to and between
two major faults (fig. 16). No concentrations were found that would indicate
the presence of a large lode outcropping; few trenches were excavated. The
two major faults, the Adit Fault and the Daisy Fault, were exposed at several
points. Sample locations in trenches IC-1 through IC-5 and trench LL-2 through
LL-5 are on figure 16. The Adit Fault was traced from the head of the placer


73

Fluorite

No fluorite was recognized in the field but a small amount was found during the
petrographic analyses of a sample (sample 60-59, table 20) from the Daisy prospect
on the summit of Little Potato Mountain, Fluorite is a common accessory mineral in
the Seward Peninsula tin deposits; therefore, the scarcity of fluorite and fluorine
minerals in the Potato Mountain area was considered remarkable, As a partial check,
semiconcentrates from churn-drill holes 41 through 63 (tables 9 and 19) were ana-
lyzed spectroscopically, The method used would detect as little as 0.2 percent CaFp,
but none was found, As an additional check, a number of samples were mixed to form
a composite sample typical of the quartz-clay-pyrite-cassiterite deposits, Analyses
of the composite sample indicated 0.2 percent CaF,. Apparently minor amounts of
fluorite or other fluorine minerals occur associated with the quartz-clay-
cassiterite deposits,

Beryllium

The investigation did not include a geochemical or other specific reconnais-
sance for beryllium minerals, The sampling program was designed to delimit tin
deposits, As a matter of routine, 23 representative specimens and samples were
analyzed spectrographically (see the section entitled "Spectrographic Analyses").
Every sample contained beryllium but the amounts ranged downward from 0,01 percent
(100 parts per million) to the minimum detectable, The beryllium mineral could not
be isolated or identified, Forty-five additional specimens and samples represent-
ing the placer gravels and the principal rock types on the eastern slopes of Potato
Mountain were scanned with a berylometer. Results were negative, However, the
minimum amount of beryllium detectable with this instrument certainly was over 100
parts per million and probably was about 200 parts per million, well above the
maximum amount indicated by spectrographic analyses,

Obviously the scarcity or lack of beryllium in these samples does not eliminate
the possibility that valuable beryllium concentrations may occur in the area. How-
ever, deposits of beryllium that were found in the nearby Lost River area occur
associated with fluorite in a thick series of metalimestones. At Potato Mountain
calcereous shales and shaly limestones occur in the black-slate series but neither
massive metalimestones nor abundant fluorite are known.

Gold

Only an occasional flake of gold was found while sampling the tin placers, and
no gold at all was found during the detrital cover and lode sampling programs. How-
ever, the placer tin mining operations on Buck Creek consistently recovered some
gold. There is no exact data on the amount of gravel mined, the efficiency of the
gold recovery equipment, or the total amount of gold recovered. During one 4-year
period of operation about 200 tons of tin and 270 ounces of gold were recovered from
an estimated 300,000 cubic yards of gravel. At $35.00 per troy ounce gold recovered
from the gravel had an average value of 3 cents per cubic yard. The occurrence of
placer gold appears to have no relationship to the occurrence of placer tin.

Roughly similar amounts of gold have been found in many streams draining the
black-slate areas.

Spectrographic Analyses

Semiquantitative spectrographic analyses data are in table 28. The sample num-
ber, the sample location, and the number of the table in which the sample is
described appear in the boxheads above analyses data.


TABLE 11. - Description and analyses of trench samples,
east side of South Gulch--continued

43

Description

Analyses

Character of material

Tin,
per-
cent

Spec.1

Petro.?

Trench RL-18 (Between Trenches RL-4 and RL-5

61-69
61-70
61-71
61-72
61-73
Total or
average
61-74
61-76
Total or
average
61-75

Altered shale, iron-stained clay, and quartz

Tourmaline schist and quartz-pyrite veins...
doweeeeeee

Tourmaline schist and quartz-pyrite vein,
selected specimens from the same place
as 61-74.

0.11

Trench RL-5

60-131
60-132
60-133
Total or
average
61-78
61-79
61-80

61-81
61-82
61-83
61-84
Total or
average
60-134
60-135
59-195

(oF

Www
wu

e
Cilywnnr

Iron-stained altered shale, clay, and quartz
do
do..

Black shale with some clay and quartz

Ose cveccscccsscccccccscccsscces oe
White, gray, and iron-stained clay, altered
shale, and quartz.

Quartz veinlet in shale..

Trench RL-5A

60-120
60-121
60-122
60-123
60-124
60-125
60-126
60-127
60-128
Total or
average
60-129
60-130
59-203

Gluuuuuuuy ul

a

tu
w&

Altered shale, quartz, and iron-stained clay

Quartz veinlet..
Quartz lens in shale.
Panned concentrate from same place as
samples 60-120 through 60-128.

See footnotes at end of table.



TABLE 11. - Description and analyses of trench samples,

east side of South Gulch--continued

45

Description Analyses
Sample Tin,
Number |Length,| Character of material per- |Spec.1 | Petro.?
feet cent
Trench RL-13
61-9 4 Crushed altered shale, iron-stained clay, <0.01) - -
and quartz.

61-10 5 <.01| - -
61-11 8 02 - -
61-12 5 <.01) - -
61-13 3 +02} - -
61-14 5 05) - -
61-15 5 +03) - -
61-16 5 <.01] - -
61-17 5 <-01| - -
61-18 4 <O1l} - -
61-19 6 <.01] - -
61-20 5 <-O1] - -
61-21 5 <-01|] - -
61-22 5 -1ll] - -
61-23 5 03) - -
61-24 5 02) - -
61-25 5 212] - -

Total or| 85 202] - -

average

61-26 9 Shale with clay and quartz veinlets.........| <.01| - -
61-27 6 pee e cece eeee ee eecseeees - -
61-28 4 shale with clay and quartz. - -
61-29 4 .- sees seeeeees - -
61-30 4 sees see eeeee - -

Total or| 12 - -

average

61-31 6 Shale with quartz and clay veinlets... <-O1] - -
61-32 6 do. eeeee . <-O1} - -
61-33 10 Shale with some clay and quartz...... 01 - -

1See section entitled "Spectrographic Analyses."
2See section entitled "Petrography."

Diamond Drilling Results

Diamond-Drill Hole 1. - DDH-1 was drilled directly under a clay-quartz-cassit-

erite outcrop exposed in trench RL-1 (fig. 12 and table 12).

It was not possible to

trace the outcropping under the deep overburden in South Gulch, but it was thought
that the deposit was alined with a westward-trending vertical fracture encountered in
trenches LL-1 and LL-2. The hole did not intersect a downward extension of the
deposit in trench RL-1. The deposit apparently is a pod or lens of limited linear
extent. Core recovery was poor, but sludge was collected at all times.

Diamond-Drill Hole 2. - DDH-2 was drilled to intersect a quartz-cassiterite
deposit which, at the time the hole was drilled, was partly exposed in trenches
LL-2A through LL-5 (figs. 11 and 13 and table 13).
the dip of the metasediments and of the tin deposit and to obtain a sample below the

zone of surface concentration. Little tin was detected.

The objective was to determine

This suggested that the


the mountain rain, wind, and fog may be more prevalent, the climate is similar
to that of Wales and Shishmaref for which weather statistics (table 2) were
furnished by the Federal Weather Bureau, Anchorage, Alaska.

TABLE 2. - Weather statistics?

Shishmaref | Wales
Average annual temperature....... errr ere) 20.2 21.8
Period when average temperature is above 32° F...... 4 4
Average annual precipitation... . eoee 8.02 11.98
Average annual snowfall.... 32.6 51.7
Prevailing wind direction... North North
Highest recorded temperature 78 75
Lowest recorded temperature... -48 -41

lAverage breakup:
Bering Strait....... June 7
Port Clarence....... June 12
Arctic Ocean... . June 18
Shishmaref Inlet.... June 20

Average freezeup:
Arctic Ocean.
Port Clarence
Shishmaref Inlet
Bering Strait...

November 6
November 7
November 9
November 29

WATER SUPPLY

The water supply at Potato Mountain during the summer is greater than the
low annual rainfall would indicate. Buck Creek and Sutter Creek (fig. 3) did
not dry up at any time during the investigation; however, the dredges that
operated on Buck Creek (1911 to 1920) were occasionally short of water. Iron
Creek and West Fork always carried some water, but at times, only a trickle.
Streamflow was not observed during the winter. Because this is a permafrost
area, it is probable that all the smaller streams dry up shortly after the
ground surface freezes.

Lode mine operators in this area may find it more economical to mine and
stockpile ore during the winter and mill it during the summer when water is
available. This requires a larger mill, but eliminates the need for weather-
proof mill structures and cold weather pumping installations, assuming that
water could be found. It also reduces the number of winter employees, thus
reducing the housing, transportation, and community services that must be
provided.

PROPERTY AND OWNERSHIP

The placer claims listed in table 3 were held by Northern Tin Mining Co.
at the time of the investigation and are described in notices of location and
grouping on file in the Nome Recorder's Office, Nome, Alaska. The approximate
area included in the claims is shown on figure 4. Claim names are not on the
map, because no attempt was made to verify either the location or the title.
No other placer or lode claims are known in the area.