R. 1. 4356 OCTOBER 1948

UNITED STATES

DEPARTMENT OF THE INTERIOR

J. A. KRUG, SECRETARY

BUREAU OF MINES

JAMES BOYD, DIRECTOR

REPORT OF INVESTIGATIONS

INVESTIGATION OF KNIK VALLEY CHROMITE

DEPOSITS, PALMER, ALASKA

BY

STUART BJORKLUND AND W. S. WRIGHT
R. I. 4356,

October 1948.

REPORT OF INVESTIGATIONS

UNITED STATES DEPARTMENT OF THE INTERIOR - BUREAU OF MINES

INVESTIGATION OF KNIM VALLEY CHROMITE DEPOSITS, PAIMER, ALASK[AN/

By Stuart BjorklunM2/- and W. S. Wright2/

CONTENTS

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

Location and accessibility . . 2

Climate and vegetation . . 2

Ownership .......................... ....... 2

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

Occurrence of deposits ......... 3

Character of the ore . ........ 5

Sampling and analysis .. 5

Bibliography .......... .......... 5

INTODUCTION AND SUMMARY

This paper is one of many reporting various aspects of the Bureau of ---- Mines program initiated in August 1939 by passage of the Strategic Minerals

Act, the scope of which was greatly expanded by subsequent legislation. In

its program of investigation of mineral deposits, the Bureau of Mines has as

its primary objective the more effective utilization of our mineral resources

to the end that they make the greatest possible contribution to national

security and economy.

The occurrence of chromite in the Knik Valley near Palmer, Alaska, was

brought to the attention of the Bureau of Mines in September 1941 by George Johnson, of Ancho rage. At that time a preliminary investigation was made

by Robert, S. Sanford, an engineer of the Bureau of Mines.' The area was

investigated on June 4 and 5, 1943, by Henry R. Joesting and Leo E. Saarela2 engineers of the Territorial Department of Mines..

In August 1942, a second chromite occurrence, the Highway deposit, in

the Knik Valley, was reported to the Territorial Department of Mines by John E. Ryan of Anchorage.

I/ The Bureau of Mines will welcome reprinting of this paper, provided the

following footnote acknowledgment is used: "Reprinted from Bureau of

Mines Report' bf Investigations 4356."

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

2536
R. I. 4356

The United States Geological Survey had a field partyl/ in the region

during August and September 1942.

The results of these investigations proved that there was a small tonnage

of lov-grade chromite 'ore in the region,' Because of the large area of unexPlored dunite'and cl6se proximity of the Anchorage-Palmer highway and the

Alaska Railroad, the area was selected for further exploration. A Bureau of

Mines exploratory project begun on September 1 was completed November 20, 1942.

LOCATION AND ACCESSIBILITY

These two chromite occurrences are at latitude 610 27' N. and longitude

1490 ill W., at altitudes of 20 to 1,120 feet and on the south side of Knik

River Valley. Knik River drains into Knik Arm, at its head, which, in turn,

.tr .let' one of the major waterways of Southwestern

Alaska, as shown in figures 1 and 2. -

The Highway claim is located at mile 31.8 of the Anchorage-Palmer

Highway. The chromite outcrops in the south side of-a.highway cut.

The Pioneer Creek deposit is in Pioneer Gulch, about 3/4 mile south of

mile 32.8 of the same highway.

The Anchorage-Palmer Highway is a well-graded, graveled road connecting

the farming community of the Matanuska Valley and the city of Anchorage.

This highway, together with the Alaska Railroad, which passes within 2 miles

of the chromite deposits, affords ideal transportation facilities for any

development or production from the area under consideration.

CLIMATE AND VEGETATION

This area, because of its northern latitude, is characterized by long

winters and short summers. Climatic conditions are transitional between the

semi-aridness of the interior and the extreme humidity of the coast. Weather

Bureau records over a period of 5 years show temperatures ranging from 910

above to 300 below zero, or a mean annual temperature of 360. The average

annual rainfall over the same period was 18 inches, and snowfall was 44 inches.

The north and west slopes of the Chugach Mountains, on which the properties are situated, are covered with a dense growth of vegetation to an altitude of 1,250 feet. The principal timber of the area is spruce, although an

abundance of small birch grows in localized areas. The underbrush consists

mainly of alder and devil's club. Timber suitable for mine use can be found

in the immediate vicinity of the chromite prospects.

OWNERSHIP

The mining claims covering the Pioneer Creek chromite prospects were

staked July 9, 1940, by Gaylord R. Skinner, George Johnson, and 0. F. Ohlson.

3/ George 0. Gates, assistant geologist, and Jacob Freedman, junior

geologist.

2536 -2-
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Figure 2. -Geologic SKetch map, Turnagain-Knik region.
Knik River Flood P/ane

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LEGENI/D

1 D1s5seminafed and Bonded Chromite

ng Pyroxeni fe

Blureau of Mines Samples

A/ote All analyses by 7erritory of

Alaska Assay Office, Anchorage

Alaska, unless ofherwlse noted

TooogropI0y by GeologicalSurvey

Geology of frenches by /SBM.

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Figure 3. - Topographic map, Highway claim property.
5ample Len/77h , 7_ NO. f_ C6rz03 -Fe

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Figure 4. - Trench sampling, Highway claim.
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LEGEND

U1 5Banded and dlssen- - 0 20

/ na/ed C/?rompite _ ___ __ 0

EIJ Dunite. Scale in Fee/-

Figure 5. - Trench sampling, Highway claim.
R. I. 4356

Information obtained in the field indicated that the property comprises three

unpatented claims - the Pioneer No. 1, Pioneer No. 2, and the Big Mogul.

The Highway claim chromite prospect was filed upon by John E. Ryan and

associates. During the summer'of 1942, Ryan and associates filed on two

additional claims adjoining the Highway No. 1 claim. All of the chromite

showings occur on the Highway Claim No. 1.

Both groups of claims are within the area tentatively designated as the

Eklutna Indian Reserve.

ORE DEPOSITS

The ultra-basic rocks of Knik Valley area are intrusive into a complex

of volcanic and sedimentary rocks and have been altered to greenstone. The

predominant intrusive is a dunite associated with bands of pyroxenite and

scome peridotite and olivine gabbro. The dunite occupies much of the approximately 4 by 10 mile area between the Knik River and Eklutna Creek.

The ultra-basic rocks are characterized by their high content of magnesia

and iron, low silica and alumina, and almost complete lack of alkalies.

Chromite is associated with rock of this type.

The dunite consists almost entirely of oLivine (Mg, Fe)2SiO4, with

accessory chromite grains. The outcrops weather to a reddish or terra-cotta

color. On fresh dunite surfaces the rock shows a dense texture and a

greenish-gray color. Chromite is seldom seen in hand specimens.

The greenish pyroxenite consists mostly of augite. It is-distinguished

from the dunite by a greenish-gray color on weathered surfaces. No ore

bodies are known to occur in the pyroxenite.

OCCURRENCE OF DEPOSITS

Highway Claim Deposit

The chromite occurs as nearly vertical stringers and poorly defined

bands within dunite. At an altitude of approximately 20 feet, one band

measuring 0.7 foot and containing 25.8 percent Cr2OR is present with several

smaller stringers varying from 1/4 to 1 inch in width. The chromite-bearing

zone at this point is 7.8 feet wide, strikes N. 170 E., and dips about 850

to the northwest. A plan of the deposit is shown on figure 3. Details of

trench sampling and analyses are shown on figures 4 and 5.

The deposit has been cut by two minor fault systems. The first system strikes northwest and dips southwest. Displacements along parallel planes

have resulted in "step faults." The second fault system strikes northerly.'

A maximum displacement of 5 feet was noted in trench 4. The majority of the

displacements are only about 1 foot.

2536 -3-
R. I. 4356

The most striking features of the deposit are the pinching and swelling

of the mineralizedzone and a decrease in grade at higher altitudes. In

trench 3, at 85 feet, one of the faults was intersected. The main chromite

bandi Bas consistent in width and grade for about 1 foot beyond this fault.

At this point a vertical outcrop clearly showed the band fingering into

several narrow chromite stringers separated by nearly barren dunite. The

mineralized zone increases to a width of about 20 feet in trench 7, with a

corresponding decrease in the grade of the ore. A decided decrease in the

width of the zone between trench 7 and trench 8 was noted. This deposit

could have economic significance only in the event of an appreciable increase

in grade or size at depth.

One hole was diamond-drilled to test this possibility. The hole was

drilled 160 feet N. 70° W. of trench 7 at an angle of minus 450., The hole

cut tho projected-dip of the chromite stringers appearing in trench 7 at

25 feet below sea level. Only dunite having the usual chromite content was

encountered, and the hole was terminated in barren pyroxenite. Considerable

difficulty was encountered in drilling because of "blocky" anid caving ground.

A section through the drill hole and analyses are shown on figure 6.

The deposit may extend beyond trench Iand even north of the AnchoragePalmer Highway, and it is not improbable that the grade also increases in

this direction, The existence of ore on the north side of the highway,

however, is only of academic interest, as the possibility of finding ore

that would warrant development beneath the Knik River flood plane is remote.

Pioneer Greek Deposit

The occurrence of chromite on Pioneer Creek can be grouped into two

poorly defined-mineralized zones. The two-zones are approximately 400 feet

apart and are separated by Pioneer Creek. A plan of the Pioneer Creek

deposit is shown on figure 7.

The northernmost of the two zones is on a steep hillside at an altitude

of 900 feet. Normal faulting, with very little horizontal displacement, is

present. The dunito is badly shatterdd,-a!nd slump has developed crevices.

Strikes and dips are erratic. The general trend of the stringers and

disseminated zone is N. 500 W., with dips ranging from 520.to 78° in a

northeastern direction.

Trenching exposed the zone for a length of 50,feet. Few samples were

taken on this zone because of the irregularity of the ore occurrence. At

the southeastern limit the analysis of 5-foot sample was 13.2 percent Cr2O3.

The zone terminated a few feet beyond the point sampled. Trenching and

stripping were continued for 150 feet along the strike in an unsuccessful

attempt to pick up a continuation of this zone.

The-southern chromitc-bearing-zone of the Pioneer Creek deposit is

situated on a steep hillside at an altitude of 1,150 feet. This zone is

composed of a number of small pods and elliptical segregations of disseminated chromite. The general trend of the zone is due north; it extends

for 82 feet and has a width of about 30 feet.

2536 -4-
Beor-/ng of Hole, 5 70 E f,

E/e/vf 1.04 Dip 02'Chlromil'e

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LEGEND 0 '

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Figure 6. - Profile diamond-drill hole, Highway claim.
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Figure 7. - Topographic map, Pioneer Creek deposit.
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Figure 8. - Trench sampling, southern chromite-bearing zone,

Pioneer Creek deposit.
Channel

;en ch5./4 2 1 

1⁄2 re,7chC MOa/3 K 1 3 1.35 lel I6 

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LEGEAD IA

EZ Banded and disse N Aole A// ano/yses by 7rr--r -

inc7fed Chromife. /fory of A/asoa Assay

z Dun/fe. Office., Aachoralue,q/ess ,

n2 Bel7ch Co07/omerafe o/herwise ind7c7ted 7 77-enchA/ /7

Topoqr-aphy by Geo/og/ca/ Survey

° 10 20 X 40 50

Scale in Feef

Figure 9. - Trench sampling, northern chromite-bearing zone, Pioneer Creek deposit.
R. I. 4356

The zone is bounded on the north, east, and south by outcrops of barren

dunite and on the west by a thick mantle of soil and overburden. An attempt

was made to determine the western limit by trenching, but after a depth of

16 feet was reached in trenches 25 and 26 excavation had to be abandoned.

No chromite-bearing float was observed in the overburden. Analyses and

location of trench samples on the north and south zones are shown on figures

8 and 9.

CHARACTER OF THE ORE

The term "ore," as used in this report, refers to material that, although

it cannot be handled profitably at present, might be of economic importance

in the future.

No massive high-grade chromite was discovered on either the Highway

claim or the Pioneer Creek prospects. The highest analysis showed a Cr2O3

content of 31.1 percent and an iron content of 11.1 percent.

The grain size of the chromite ranges from 1 to 2.5 millimeters.

Metallurgical tests on a similar ore indicate that concentration of the ore

into a marketable product would not involve any difficulty.

SAMPLING AND ANALYSIS

The Highway claim deposit was trenched at intervals of approximately

25 feet along its strike. All samples taken from these trenches consisted

of 2- by 4-inch grooves cut perpendicular to the strike of the ore occurrence.

Whenever possible, a standard sample length of 5 feet was taken. However,

when changes in grade of formation occurred along any one section, the sample

lengths conformed to such changes.

It was difficult to follow a systematic trenching pattern on the Pioneer

Creek deposit, and the work consisted mostly of stripping wherever the depth

of the bedrock was not excessive and wherever chromite mineralization could

be found. On the northern zone of the Pioneer Creek deposit, samples were

taken wherever chromite occurred. In sampling the southern zone an attempt

was made to obtain a cross section of the zone at three intervals. It will

be noted in figures 7, 8, and 9 that the samples are not cut parallel to one

another, nor are all of them cut perpendicular to the apparent strike of the

zone. Considering the irregularity of the ore in this zone, this diversion

from standard sampling procedures will not affect the resultant grade of the

zone appreciably.

The calculated grade of the Highway-claim deposit, based upon weighted

average analysis from each trench, is 5.7 percent Cr2O3. The weighted

average of samples taken from the northern zone of the Pioneer Creek deposit

shows a chromic trioxide content of 658 percent; the southern zone contains

6.9 percent Cr203.

BIBLIOGRAPHY

Capps, Stephen R., The Turnagain-Knik Region: Geol. Surv. Bull. 642, 1916.

2536 - 5