R. I. 4323 AUGUST 1948

UNITED STATES

DEPARTMENT OF THE INTERIOR

J. A. KRUG, SECRETARY

BUREAU OF MINES

JAMES BOYD, DIRECTOR

LIBRARY COPY

U. S. Bureau Minos

Boulder City, Nevada

REPORT OF INVESTIGATIONS

INVESTIGATION OF THE TOZIMORAN CREEK TIN PLACER

DEPOSITS, FORT GIBBON DISTRICT, ALASKA

BY.

BRUCE I. THOMAS AND W. S. WRIGHT
R.I. 4323,

August 1948.

REPORT OF INVESTIGATIONS

UNITED STATES DEPARTMENT'OF THE INTERIOR - BURFAU-OF MINES

INVESTIGATION OF THE TOZIMORAN CREEK TIN PLACER DEPOSITS

FORT GIBBON DISTRICT, ALASKA1

By Bruce I. ThomasjP and W. S. Wrighti/

CONTENTS '

Page

Introduction and summary . . 1

Acknowledgments. . 2

Location and accessibility . . 2

Physical features and climate 2

History and production ....................... 3

Property and ownership. . . 3

Water supply ... 3

Occurrence of deposits . . 4

Character of deposits. . 4

Sampling.. 5

Channel sampling ................ '., 5

Shaft sampling. .................... 7

Channel-sample summary ............... 10

ILLUSTRAi.TIONS

Following

Figure page

1. Index..map showing location of

Tozimoran Creek ................. 2

2. Tozimoran Creek area, Alaska...... 2

3. Shaft holes Tozimoran Creek,

Alaska .............................. ' 2

4. Old open-cut workings, Tozimoran

Creek, Alaska................. 4

INTRODUCTION AND SUMMARY

The occurrence of tin-bearing gravels along Tozimoran Creek in

e central Alaska has been known for a number of years.,

1/ The Bureau o.f Mines will welcome reprinting of this paper,'provided the

following footnote acknowledgment is used: "Reprinted from Bureau of

Mines Report of Investigation 4323."'

2/ Mining engineer, Bureau of Mines, Fairbanks, Alaska.

/ Mining engineer, Bureau of Mines, Juneau, Alaska.

2445
R.I. 4323

In September 1944 the Bureau of Mines investigated an area approximately 1,000 feet long and 200 feet wide along Tozimoran Creek to determine the cassiterite content. of the stream gravels, which are about 4

feet deep and covered by 3 feet of overburden. Nine trenches and two

shafts were excavated, from which samples of the underlying gravels were

taken.

This report contains a discussion of sampling methods and tables

giving the results of analyses.

ACKNOWLEDGMENTS

Special acknowledgment is extended to Martin Webories and I. W.

Purkeypile, the owners, who contributed their services and furnished

housing and various small tools to expedite the exploratory work.

LOCATION. AND ACCESSIBILITY

Tozimoran Creek is in central Alaska at approximately 650 20' north

latitude and 1530 west longitude.. (Seefig. 1.) The headwaters of

Tozimoran Creek are accessible from the mouth of GrantCreek, a tributary

on the north side of the Yukon River 30 miles downstream from Tanana. A

tractor trail extends 4 miles up Grant Creek to the Fisher and Fisher

mine; from there, a pack trail about 12 miles long follows a ridge into

the headwaters of Tozimoran Creek, as. shown in figure 2. With some

relocation and a considerable amount of work, this trail could be made

into a passable tractor road.

The closest settlement is Tanana, which is approximately 40 airline

miles southeast of Tozimoran. Tanana has a population of about 150

people - 50 whites and 100 Indians. It has two general stores, a roadhouse, an airfield capable of accommodating large airplanes, a Territorial

school, a goverrment-operated hospital, and a church.

Freight is brought in from the Coast by railroad to Nenana, thence

by river boat to Tanana, and thence to Grant Creek. In winter travel is

dog team or airplane. Planes land on the ice on Yukon River at the mouth

of Grant Creek. In summer pontoon-equipped airplanes land on the river,

or wheel-equipped planes land on a gravel bar in the center of the river

3 miles below the mouth of Grant Creek.

PHYSICAL FEATURES AND CLIMATE

Tozimoran Creek is a northeast-flowing tributary of the Tozitna

River-about 12 miles long, and in its upper bed flows in a narrow

alluvium-filled valley. The region is one of considerable relief; most

of the ridges attain an altitude of more than 2,000 feet, whereas the

domes rise to more than 3,000 feet. The tin deposit lies near the headwaters of the creek at an altitude of approximately 800 feet.

2445 -2-
/74v /5' 3e

~~~~~~O

Fiur ndxma . hoig oato o ozmra rek
0-4

0

MORAN

Do E

/ C~~L GRANT-,

J'.

z

-- _e~2

SCALE OF MILES

MODIFIED FROM USGS MAP

Figure 2. - Tozimoran Creek area, Alaska.
Line NA 24

/ \\i Hole N /

*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

\ C~~~~reekI

H .. Na /ole \Scale

v~ ~ ~ ~ ~Hl Nai M//e//al/ llco s( / /Hale N /ol\ a 

HoleNa

Enlarged fromh rap by uss.S

Figure 3. - Shaft holes, Tozimoran Creek, Alaska.

Cut a

^ 9 ~~~~~~~cuilo

= = ~~~~ ~~ ~ < ~~~~~~Dltch C

Cu 7 Cutl

i, ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~Ci ' /060 

Figure u.. - Old openscoC

modified fromfw map p u LS

Figure 4. - Old open cut workings on bench, Tozimoran Creek, Alaska.
R.I. 4323

The climate of the region is typical of central Alaska; winters are

long and cold and summers short and relatively warm. The temperature

ranges from minus 700 F. in winter to 900 F. or higher in summer, and

the annual mean is about 230 F. A large portion of the alluvial deposits

is permanently frozen, as the surface thaws only a few feet during the

summer. However, in places on Tozimoran Creek circulating ground water

has thawed the ground for a considerable distance from the present stream

banks.

The valley floor is covered by brush and an occasional stand of

small spruce suitable for mine and camp use. The ridges rise well above

timber line and are barren except for scattered Patches of scrubby brush.

HISTORY AND PRODUCTION

Placer gold was discovered on Tozinoran Creek in 1902; many prospectors and miners visited the district since the discovery of gold, but not

enough of this metal was found to warrant mechanized mining. Up until

1938, prospecting in the area was intermittent. Claims were staked,

allowed to lapse, and were then restaked by others. During this period

a small amount of hand mining was dore on a left-limit bench of Tozimoran

Creek 2,000 feet downstream from Ash Creek, R headwater tributary (see

fig. 3).

Since 1938, the upper tin-bearing portion of Tozimoran Creek has

been held by two partners, who have carried on intermittent handmining

on the bench and at various times prospected on various parts of the

creek.

The total production for the creek has probably been not more than

a few ounces of gold and a few hundred pounds of tin.

PROPERTY AND OWNERSHIP

Eighteen 40-acre association placer claims covering the tin-bearing

area are held by partners I. 'v. Purkeypile, of Fairbanks, Alaska, and

Martin Webories, of Tanana, Alaska. All these claims are recorded at

the Fort Gibbon recording office at Tanana, Alaska.

WATER SUPLY

Tozimoran Creek contains enough water for a small placer mining

operation. During low stages it is estimated that approximately 400

miner's inches of water flows through the tin-bearing area. lWater

measurements made by the Bureau of Mines during a high stage show a

flow of 4,200 miner's inches in the vicinity of the tin deposit.

One small ditch excavated several years ago supplies water for handmining on the bench. This ditch is too small to furnish water for a

mechanized operation.

2445 -3-
R.I. 4323

OCCURRENCE OF DEPOSITS

The principal tin-bearing area on Tozimoran Creek is a bench 1,000

feet long and 200 feet wide on the north side of Tozimoran Valley down--

stream from the mouth of Ash Creek (see fig. 3). Tin, in the form of

cassiterite, and gold are found in the gravels on this bench. Small

amounts of tin and gold occur in the gravels of the valley floor downstream from the bench.

The hills on the south side of the valley rise steeply, but to the

north they slope more gently, indicating the presence of a higher bench.

This latter bench begins near the confluence of Ash and Tozimoran creeks

and extends 3 miles down Tozimoran Valley.

The bedrock in the tin-bearing area of the bench and in the valley

floor consists of quartz mice. schist and appears to have a fairly even

surface.

There are no known tin lode deposits in the district, and the exact

source of the placer tin has not been determined.

CHAhACTER OF DEPOSITS

The tin-bearing gravels on the bench are about 4 feet deep and are

covered with muck to an average depth of 3 feet. Along the margins of

the bench the muck and gravels are thawed, but back from the margins

both are permanently frozen. The muck, consisting of organic matter,

some fine sand, and clay is overlain by a thin mantle of moss. The

gravel is fairly coarse and contains many boulders over 2 feet in diameter. Very little clay is found in the upper portions of the gravel, but

near bedrock a considerable quantity is found.

The gravel in the valley floor is also overlain with moss and muck.

The muck is frozen, but the underlying gravels are thawed. Along the

outer rim-of the valley some of the gravel is frozen, but this condition

seems to exist only along the margins of the alluvium. Unlike the bench

gravel, considerable clay is foimd in the upper portions as well as near

bedrock. The size of material is comparable to that found on the bench.

On the bench cassiterite, associated with gold and the heavy

minerals magnetite and limonite, is concentrated in the 'ravels 2 feet

above bedrock, but in the valley floor these minerals are sparsely disseminated in the upper gravels and concentrated in the last 5 feet above

bedrock. In no case do these minerals appear to penetrate the bedrock

for more than 6 inches.

The cassiterite is 1/16 to 1-1/2 inches in diameter; however, the

largest percentage is found in the smaller sizes.

2445 4
R.I. 4323

SAMPLING

During the preliminary examination, two methods of sampling were

used. Channel samples were cut through exposed pay sections of gravel

in open cuts on the bench, and shaft holes were sunk in the grarel of

the valley floor.

Channel Sampling

4~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Nine channel samples were cut at convenient locations along the banks

of the open cuts on the bench (see fig. 4). Prior to cutting samples all

sloughed material was cleaned away from the face of the banks to expose

virgin gravel. Small samples were panned'from v.riius depths in the

gravel to determine the pay horizon. When the pay horizon had been

established, the barren upper gravel was excavated and a channel was cut

through the pay horizon only.

Each channel was measured after it was cut. All material cut from

the channel was weighed, and a loose volume measurement was made. The

entire sample was run through a rocker, from which a concentrate was recovered. Gold was extracted from the concentrate and weighed, and the

remaining concentrate was weighed and analvzed for its tin content.

Table 1 is a summary of tin-concentrate analyses, and table 2 is a

compilation of channel sampling data.

TABLE 1. - Summary of tin concentrate analysis from channel samples

Sample Percent tin Sample, Percent tin

C.S. 1 45.37 C.S. 5 27.82

2 57.13 6 51.83

3 62.26 7 60.11

4 32.29 8 15.40

23.85

2445 -C5-
R.!. 4323

TABLE 2. - Calculated tin and gold content

Depth pay Measured Calculated Weight of Weight of tin Weight

Depth, feet horizon, volume loose, volume, sample, concentrate, of gold,

Sample Muck Gravel Bedrock feet cubic feet cubic feet pounds grams mg.

1 1.0 4.5 0.5 3.0 4.8 4.32 529 156.2 143.18

2 3.0 4.0 .5 2.5 1.4 1.60 149 59.9 122.03

3 3.0 4.5 .5 3.1 2.2 1.86 207 196.5 214.40

4 1.0 3.5 .5 3.0 1.9 1.68 213 22.8 32.51

5 3.0 4.5 .5 3.9 3.0 2.81 348 36.9 4.68

6 4.0 5.0 .5 3.1 2.0 1.54 231 37.5 126.30

7 2.0 2.5 .5 2.0 1.3 .96 126 51.6 19.02

8 3.5 1.5 .6 2.1 2.4 1.26 265 13.0 7.55

9 1.5 1.0 .8 1.3 1.0 .78 115 16.1 2.27

2445 -6-
R.I. 4323

Shaft Sampling

Two shaft holes 50 feet apart on line 24, 1-1/2 miles below the

bench, were sunk in a narrow portion of the valley floor. A small section of the valley floor was frozen sufficiently to permit sinking open

shaft holes at this location. An attempt was made to sink two more holes

in order to crosscut the valley at this point, but ground water prevented

attaining a depth over 4 feet, so they were abandoned.

A small prospect boiler was used during thawing of frozen muck and

gravel. The pay gravels were washed in a rocker, and the gold was extracted from the recovered concentrate. The remaining concentrate was

weighed and then analyzed for tin content. Table 3 is a sumnmary of tin

concentrate analyses.

TABLE 3. - Summary of tin concentrate

analyses from shaft-hole samples

Percent

Hole tin

3 52.16

4 49.02

The pay gravel Was extracted in sections approximately 2 feet deep.

The.material from each section was measured in a volume bucket., and the

size of the hole at each section was measured with a tape. In order to

recover all the cassiterite, the pay gravel was washed through the

rocker twice.

The logs of each shaft hole are shown in tables 4 and 5.

2445 -7-
R.I. 4323

TABLE 4. - Log of shaft holes, Tozimoran Creek, Alaska

Hole 3, line 24

Measured Calculated Weight of tin Weight

Depth, volume loose, volume, concentrate, of gold,

feet cubic feet cubic feet ramsmg. Remarks

1 0 Moss

3 0 0 Frozen muck; some sand top of bravel 5.0 ft.

6 0 0 Frozen fine gravel and sand.

10 0 0 Frozen coarse gravel; some clay schist and

quartz.

.11 0 0 Frozen, coarse gravel, sand, and some clay.

12 21.24 12.4 120 91.29 Frozen, coarse gravel, much clay, some sand.

13 22.42 10.8 69 46.32 Frozen, coarse gravel, much clay many small

boulders.

16.2 35.40 27.0 431 323.30 Top bedrock 16.0 ft; bedrock decomposed

schist.

16.5 0 0 Decomposed schist (gray color).

79.06 50.2 620 460.91

Depth: Moss ....... . 1.0

Muck ........ 4.0

Gravel ...... 11.0

Bedrock ..... 0.5

Total 16.5

2445 -8-
R.I. 4323

- TABLE'5. - Log of shaft holes, Tozimoran Creek, Alaska

Hole 4, line 24

Measured Calculated Weight of tin Weight

Depth, vol~Lme loos-e, volume, concentrate, of gold,

feet cubic feet cubic feet gramsg. Remarks

1 Moss.

5.5 Frozen muck; top gravel 5.5 ft.

11.2 0O 0 Frozen medium gravel and sand.

13.2 30.68 25.1 163 160.04 Frozen, coarse gravel; some sand and clay.

15.2 23.60 13.9 57 24.55 Frozen, coarse gravel, and much clay.

17.0 21.24 15.8 310 237.00 Frozen, coarse gravel; many boulders and

much clay.

17.6 24.78 15.6 204 34.25 Frozen, coarse gravel; many boulders and

much clay; top bedrock 17?.7 ft.

18.2 _ _._ . ._ . _- _ _ ;0 0

.~~~~~~~0 .. 3.

100.3 70.4 734 455.84

Depth: Moss ........ 1.0

Muck ........ 4.5

Gravel ..... 12.1

Bedrock ..... 0.6

Total 18.2

2445 - 9
R.I. 4323

Attempts were made to sink shaft holes at eight other loeations on

upper Tozimoran Creek and its upper tributar ies, but excessive ground

water prevented reaching bedrock (see fig. 3). One of these shaft holes,

near the mouth of Ash Creek, was sunk 12 feet before it was abandoned.

Table 6 lists each shaft hole and shows the depths attained.

TABLE 6. - Depths of abandoned shafts

Depth abanHole doned, feet

1 4.5

2 4.0

5 4.0

6 5.0

7 6.0

8 6.5

9 4.5

10 3.5

11 3.0 -

12 12.0

Channel-Sample Summary

The examination indicated a tin-bearing area approximately 650 feet

long and 80 feet wide, which constitutes a portion of the bench below Ash

Creek. The sampled block averages 0.731 pound tin and 0.0228 ounce gold

per cubic yard. Table 7 is a summary of channel-sample results.

TABLE 7. - Summary channel-sample results

Depth Pounds tin Ounces gold Depth

mining section, per per muck section,

Sample feet cubic yard cubic yard feet

C.S. 1 5.5 0.536 0.01390 1.0

2 5.0 .630 .02950 3.0

3 5.5 2.190 .05030 3.0

4 4.5 .170 .0(950 1.0

5 5.5 .150 .00090 3.0

6 6.0 .400 .03300 4.0

7 3.5 1.100 .00860 2.0

8 2.5 .079 .00390 3.5

9 2.0 .190 .00140 1.5

The tin content of gravel in the valley floor below the bench was

not estimated. The two shaft holes (numbers 3 and 4, at line 24) were

in a narrow portion of the valley.. The results of the sampling from

these two holes do not indicate the presence of a paystreak. Table 8 is a

summary of shaft-hole sampling results.

2445 -10-
R.I. 4323

TABLE 8. - Summary of shaft hole sampling results

Depth 1 Pounds tin Ounces gold Depth

mining section, per per muck section,

Hole feet cubic yard cubic yard feet

3 12.0 0.197 0.0031 5.0

4 13.1 .146 .0029 5.5

2445 -11-