UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 849 H ^.AW/ ?

BY 

CLYDE P. ROSS

Investigations in Alaska Railroad belt, 1931 

(Pages 425-468)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1933

For sale by the Superintendent of Documents, Washington, D.C. ------ Price 15 cents

CONTENTS $j M

Foreword, by Philip S. Smith___ .___--_--__-___-_-__--_-----_------- v

Abstract--.-.... .----------------__--.-------_ ...-.__-.--.-._ 425

Introduction ...._______.____-__-____--_-__-____-_____-___-_-_.__.- 425-

Geography. _____._-_____-_______--__-_-__--__-- _ ___-____--_.____ 426'

History... .-..-..--.-------.._-_----_---- __ ____________________ 427

Stratigraphy and petrology _ _________-______________----_-_-----_- 42S

Greenstone.. ___.__.____..__________--__-____--__-----------_- 429

Limestone. . -________-_----__--_____-__-_-_-___-_-------_----- 430

Lenses between Clearwater Creek and the Susitna River... .... 430

Beds in the valley of Coal Creek. __.________________ _____-__ 431

Limestone mass north of Coal Creek.... _____________________ 431

Tuffaceous and related strata-_-________-______-_---_-__-_--.-.- 432

Rusty schist..... __ .. _ _ __ _ _____ _ ____.__..__..__._ 435

Argillite------ ---------- _ .. ___ ----- ______ -____........ 435

Schist near Valdez Creek __ ___________________________________ 437

Tertiary (Eocene ?) strata.... ___ . ___________ _.._....___ 438

Quaternary deposits. ..._______.____-_-__-_____-----_------...- 439

Intrusive rocks -_I_-___-__.___________^__-__________--------__ 440

Gneissic quartz diorite.. _ _______-_________________---_---_- 440

Other dioritic rocks----_-----------_--__-----_-----_------- 440

Dikes.. -----------_------------_..---------------------- 441

Age. .......... ...^.... ................................... 442

Structure ___-___________-___-_-_-___________-__-_____--_-------__ 442

Folding.. __...-.-___---.---.- _ -.-..___-._.-.-----.-_-_-.-.- 442

Faulting. -....-__---.-_--_-_----_----.-.---------------.---.- 443

Economic geology _.___._-_.________-.-____-__-_____-_____--.-..-__ 444

Placers ______________________________________________________ 444

Relation of placers to geomorphology ________________________ 444

Placer workingS--___--_-_____-____-__________--__-__--_-__ 449

Deposits at Denali. ___________________________________ 449

Bars of Valdez Creek. _____________________________ 449

Tammany Channel--_-___________-_______.________ 449

Bench gravel----_-__-_-___-_-__-______-_--_----__ 451

White Creek.. ....._.____._._________________.________ 453

Lucky Gulch. ________________________________________ 454

Other workings_-_______________________________._____ 455

Lodes ----_-.__-_____-__-______________________-__-__-__-__-__ 455

Veins with quartz as the essential gangue mineral. ____________ 455

Veins containing calcite--___-_________-______-_______--_-__ 457

Pyritic replacement deposits..--.--- __-____-___----__- -._.__ 458

Origin. _____________________ __ _ _ _ _ _________________ 458

'Suggestions for development._______________________________ 459

Prospects ________________________________________________ 461

Timberline-... -.-.------_-___".__ _ _____.-.___-_______ 461

Gold Hill____________________________________________ 463

Small prospects near Valdez Creek______________________ 463-

Rusty Hill___________________________________________ 464

Mineralization east of Clearwater Creek. ________________ 464

CoaL---------------_-.-____--__------ _ -______.__---.__.._ 465

Index. _ _ _______...-.______ _ _ __ _ ______ __ __________ __ ___ 467

in
ILLUSTRATIONS

Page 

PLATE 34. Geologic sketch map of the Valdez Creek mining district

and vicinity--________.__-_-__-___-_-----___-_____.__ 432

35. Placer claim map of the Valdez Creek mining district _______ 448

FIGURE 1. Index map showing areas investigated in Alaska Railroad belt,

1931_____________________._______________ vn

53. Probable location of buried channels near Denali with reference to present drainage.______________________________ 447

54. Contour map of the Tammany Channel..._______--__-___. 450

55. Contour map of hydraulic cut on the Folk claim_________ 452

56. Sketch map of the lodes on the Timberline prospects_____ 461

IT
INVESTIGATIONS IN ALASKA BAILKOAD BELT, 1931

FOREWORD

By PHILIP S. SMITH

To help the mining industry of Alaska and to assist in the development of the mineral resources of the Territory have been the prime 

motives of the Geological Survey's investigations in Alaska during 

the past 35 years, in which nearly one half of the Territory has been

covered by its reconnaissance and exploratory surveys. It was 

natural, therefore, that the Alaska Railroad, when it undertook intensive consideration of the problem of finding tonnage that would 

increase its revenues, should look to the Geological Survey to supply 

technical information as to the known mineral deposits along its 

route and to indicate what might be done to stimulate a larger 

production of minerals and induce further mining developments and 

prospecting that would utilize its service. Realization of the need for 

this information had long been felt by the officials responsible for the 

operation of the Alaska Railroad, and the need had been partly 

supplied by the Geological Survey, but funds to carry through an 

extensive, inquiry of this sort had not been available until 1930, 

when a special committee of the Senate, composed of Senators Howell, 

Kendrick, and Thomas, visited Alaska, studied some of the railroad's 

problems, and successfully urged Congress to grant it $250,000 for 

investigations of this kind.

On the invitation of the Alaska Railroad the Geological Survey 

prepared various plans and estimates for the investigations that 

appeared to be most likely to contribute the desired information as to 

the mineral resources. Selection of the problems to be attacked 

proved difficult, because the choice necessarily was hedged about with 

many practical restrictions. For instance, each project recommended 

must give promise of disclosing valuable deposits a requirement 

that was impossible to satisfy fully in advance, as it involved prophecy 

as to the unknown and undeveloped resources. Then, too, it was 

desirable that the search should be directed mainly toward disclosing 

deposits which if found would attract private enterprises to undertake their development in the near future. Finally, somo of the 

deposits that might be worked profitably did not appear likely to 

afford much tonnage to be hauled by the railroad. Under these
VI INVESTIGATIONS IN ALASKA RAILROAD BELT, 1931

limitations it should be evident that the projects that could be recommended as worth undertaking with the funds available by no means 

exhausted the mineral investigations that otherwise would be well 

justified. In a large sense, all of Alaska may properly be regarded as 

indirectly contributory to the welfare of the railroad, but even in 

that part of Alaska contiguous to its tracks there are large stretches 

of country that are entirely unexplored and large areas that have had 

only the most cursory examination. Although areas of this sort 

might well repay investigation, they were excluded from the list of 

projects recommended because they were not known to contain 

mineral deposits of value, and it therefore seemed better to make the 

selection from other areas that had been proved to hold promise. 

Furthermore, several areas within the railroad zone were excluded 

because their value was believed to lie mostly in their prospective 

placers, which would not yield much outgoing tonnage; others because 

their lodes carried mainly base metals, for which development and 

the recovery of their metallic content in a readily salable condition 

were relatively expensive; and still others because their resources 

consisted mainly of granite, building stone, or some other product 

for which at present there is only a small local demand.

After careful consideration ten projects were selected, and the 

funds required for undertaking them were made available. The 

projects that were selected involved the examination of two areas 

principally valuable for their coal (Anthracite Ridge and Moose 

Creek), five areas likely to be principally valuable for gold (Fairbanks, Willow Creek, Girdwood, Moose Pass, and Valdez Creek), 

and three areas whose lodes consisted mainly of mixed sulphides (the 

Eureka area in the Kantishna district, Mount Eielson, formerly 

known as Copper Mountain, and the head of West Fork of Chulitna 

River). The general position of these different areas is indicated on 

the accompanying diagram (fig. 1). A general study of the nonmetalliferous resources of the entire region traversed by the railroad 

was included in the projects to be undertaken, but the results obtained 

were not such as to permit adequate determination of their extent at 

this time.

Examinations were made in the field in each of the selected areas, 

all the known prospects and mines being critically examined and 

sampled so far as time and other conditions permitted. The records 

thus obtained, together with all other information bearing on the 

problems, were then subjected to further study in the laboratory and 

office, in the course of which other Geological Survey specialists whose 

knowledge and experience could be of assistance were freely consulted. 

The outcome of all these lines of analysis has been the reports which 

make up this volume. Although each chapter is presented as embodying the latest and most authoritative information available regarding 

the districts and properties described up to the time field work in them
FOREWOBD VII

so Miles

FIGURE 1. Index map showing areas investigated in Alaska Railroad belt, 1931j A, Anthracite Ridge 

B, Fairbanks; C, Willow Creek; D, Mount Eielson; E, West Fork of Chulitna River; F, Eureka and 

vicinity; G, Girdwood; H, Valdez Creek; I, Moose Pass and Hope
VUI INVESTIGATIONS IN ALASKA RAILROAD BELT, 1931

was finished, the authors make no claim that all the results they have 

presented are to be regarded as final nor as solving all the problems 

that have arisen. Actually none of the mines have been developed 

to such an extent as to furnish all of the evidence desired to solve the 

problems involved. At none of the properties is any considerable 

quantity of ore actually "blocked out" in the engineering sense of 

that term, so that instead of specific measurements as to the quantity 

and grade of ore the different camps will yield, the Survey geologists 

and engineers have necessarily had to make numerous assumptions 

and be content with estimates and generalizations as to the potential 

resources. Furthermore, the work was planned so as not to invade 

the proper field of the private mining engineer in the valuation of 

individual properties, but rather to occupy the open field of considering 

the districts as a whole.

In two of the districts, Anthracite Ridge and Moose Creek, whose 

value lay in their prospective coal resources, the examinations that 

could be made by ordinary geologic means were not adequate to arrive 

at a final judgment of the resources of the area but pointed to the 

desirability of further tests by drilling. As a consequence additional 

exploration of these districts by means of diamond "drilling was 

authorized, and this work was undertaken in the season of 1932. The 

results of these tests were not available at the time the manuscripts 

of the other reports were completed, and rather than delay their 

publication until the later reports could be finished and incorporated 

in the volume these reports have been omitted here and will be 

published later elsewhere.

This is not the place to summarize the detailed findings of the 

geologists as to the merits of the different districts, as those findings 

are explained in detail and summarized in the respective chapters. 

Suffice it to say here that on the whole the principal purpose of the 

investigations was carried through satisfactorily and that while the 

studies in some of the districts indicate that they hold little promise 

of extensive mineral development in the near future, others appear to 

encourage development under existing conditions, and still others 

seem to be worth development when some of the existing factors such 

as transportation or price of base metals are improved. That conditions which are now temporarily retarding the development of some 

of the deposits will become more favorable cannot be doubted. The 

entire region is becoming more accessible each year, and as a result 

costs are being lowered and experience is being gained as to the habit 

of the various types of deposits, so that the conclusions expressed in 

this volume as to the resources of the different districts should be 

reviewed from time to time in the light of the then current conditions.
THE VALDEZ CREEK MINING DISTRICT, ALASKA

By CLYDE P. Ross

ABSTRACT

The Valdez Creek mining district was one of those visited in 1931 in connection with the study of the mineral resources of the region tributary to the 

Alaska Railroad. It is underlain by argillite, schist, tuff, tuffaceous conglomerate, limestone, and greenstone, listed in approximate stratigraphic order beginning with the younge'st. These rocks are probably all of Upper Triassic 

age and form part of the north limb of a large fold that trends east to northeast but is locally broken by faults and minor flexures. There are a number 

of stocklike intrusions, mainly quartz diorite and similar rock, and small 

basic dikes, all of Upper Jurassic or later age. One small mass of Tertiary 

(Eocene?) coal-ben ring beds and considerable Quaternary alluvium and glacial 

deposits are present.

The district contains numerous auriferous quartz veins, which range in size 

from stringers along joints and similar openings to lodes more than 1,000 feet 

long and several feet wide. The larger masses lie in shear zones in which 

the altered country rock is itself mineralized, and such bodies are of possible 

commercial value, although apparently not of high grade. There is sufficient 

evidence suggesting the existence of high-grade pockets to justify " pocket 

hunting", wliich has not yet been systematically attempted in the district. 

Along the eastern border of the area examined during the present study limestone, schist, and greenstone have suffered igneous metamorphism, including 

the deposition of metallic minerals. This part of the area appears to justify 

more prospecting than it has yet received. Sufficient coal exists here to be of 

some local value if a metal mine were established.

The sole productive enterprise up to the present time has been placer mining, find this constitutes the best hope for future expansion. The geomorphology 

indicates that in addition to known deposits there may be large amounts of 

potentially valuable placer ground which cannot be economically handled under 

present methods of operation.

INTRODUCTION

The Valdez Creek mining district was one of the areas visited in 

connection with the study of the mineral resources of the region 

tributary to the Alaska Railroad. The party, consisting of Clyde P. 

Ross, geologist, and Marion Peel, packer and rodman, left Cantwell, 

the nearest point, on June 11, 1931, and returned there July 17. In 

this period geologic and topographic sketch maps of about 80 square 

miles of country were made (pi. 34), and the placers and lode prospects were examined. The work was extended eastward beyond the

425 

179229 33 2
426 INVESTIGATIONS IN ALASKA RAILROAD BELT, 1931

limits of the Valdez Creek district proper to include part of the 

drainage basin of Clearwater Creek. The location of the area 

mapped is shown in figure 1.

The work was greatly facilitated by the remarkably complete and 

accurate geologic data embodied in Moffit's reconnaissance report on 

this region.1 All correlations of geologic age given in the present 

report agree essentially with Moffit's assignments. The base for the 

topographic map (pi. 34) was obtained by photographic enlargement of the plane-table sheet for this area made by D. C. Witherspoon and C. E. Giffin for the map that accompanies Moffit's report. 

The location of the principal peaks proved sufficiently accurate for 

use in triangulation, though for the larger scale here used the topographic sketching was completely revised. It was impracticable 

for the writer, working single-handed and with limited time, to 

maintain control of standard accuracy, but the map shows form 

with essential correctness. The datum for elevation above sea level 

was assumed from Witherspoon and Giffin's map and hence, as noted 

on that map, is about 200 feet higher than the datum in use along 

the Alaska Railroad. The geologic boundaries on plate 34 were 

sketched concomitantly with the topographic work.

GEOGRAPHY

The Valdez Creek mining district corresponds essentially to the 

drainage basin of the creek, which enters the Susitna River from 

the east about 25 miles south of the lower terminus of the Susitna 

Glacier in the Alaska Range. The principal development has been 

placer mining close to the mouth of Yaldez Creek, where the post 

office of Denali (formerly McKinley) has been established. This

point is now commonly reached by a trail from Cantwell, on the 

Alaska Railroad; the distance is somewhat more than 50 miles, and 

the trip as made with pack horses in summer generally occupies 

three days. Before the railroad was completed the district was 

reached from Valdez, Chitina, and other towns by way of the military road, now the Richardson Highway, and thence by one of 

several routes westward across the mountains or up the rivers.

Valdez Creek is in the southern foothills of the Alaska Range. 

Its mouth is somewhat more than 2,500 feet above sea level, and 

the highest summits in its vicinity are a little more than 6,000 feet. 

The hills are moderately steep, but only the highest summits are 

rugged. The main stream is intrenched to a maximum depth of 

about 150 feet for a distance of about 4 miles from its mouth. 

Between the upper end of the inner gorge and the mouth of RooseiMofflt, F. H., Headwater regions of the Gulkana and Susitna Rivers, Alaska, with 

accounts of the Valdez Creek and Chistochina placer districts: U.S. Geol. Survey Bull. 

498, 1912.
VALDEZ GREEK MINING DISTRICT 427

velt Creek, the principal tributary, it wanders over the floor of a 

U-shaped trough, as yet scarcely dissected. All but the smallest of 

the tributary gulches show evidence of the former presence of minor 

glaciers. On both sides of the incised channel of lower Valdez 

Creek the ground is hummocky and in part marshy, as a result of 

glacial dumping.

The Susitna River in this vicinity flows in shifting channels over 

a broad sandy flood plain. Channels more than 5 feet deep are 

rarely as much as 100 yards wide, but the total width of water, 

swamp, and quicksand in some places is 2,000 to 4,000 feet. This 

stream constitutes the greatest single obstacle to travel between the 

Alaska Railroad and Valdez Creek.

Farther east the drainage basin of Clearwater Creek, itself a tributary of the Susitna River, is reached through a low pass at the head 

oi Roosevelt Creek. The topography here differs materially from' 

that close to Valdez Creek. The mountains are steeper and more 

rugged, and the major streams meander in flood plains incised into 

broad gravel-floored benches. The ground is better drained, and 

travel is consequently easier than it is to the west. 

, Groves of rather small gnarled spruce trees grow on both sides 

of lower Valdez Creek and other tributaries of the Susitna River up 

to altitudes of 2,600 to 3,000 feet above sea level. Much of the lumber 

for buildings and for mining operations along Valdez Creek has 

been obtained from Butte Creek, about a mile south of Denali and on 

the opposite side of the Susitna. Most of the supply of suitable trees 

in more convenient locations was early exhausted. The lack of timber 

along upper Valdez Creek has been a serious obstacle to mining 

operations there. Except for willows, there is no timber in the part 

of the drainage basin of Clearwater Creek visited during the present 

investigation. Moffit's map of the distribution of spruce in the 

Broad Pass region 2 includes all of the timbered tracts in the district 

here considered.

HISTORY

Gold was discovered on Valdez Creek on August 15, 1903, by a 

party including Peter Monahan, J. S. Smith, J. M. Johnson, and 

J. C. Clarkson.3 Work started in earnest the following year, when 

these men returned in company with a number of others. Most of 

the claims shown in plate 35 were staked at this time, but nearly all 

the production in the early years came from the immediate vicinity 

of the present site of Denali. At the height of the boom probably 

about 150 miners were at work.

2 Mofflt, F. H., The Broad Pass region, Alaska : U.S;. Geol. Survey Bull. 608, fig. 2, 1915.

8 Mofflt, F. H., Headwater regions of the Gulkana and Susitna Rivers, Alaska, with 

accounts of the Valdez Creek and Chistochina placer districts: Bull. 498, pp. 53, 54, 

1912.
428 INVESTIGATIONS IN ALASKA KAILKOAD BELT, 1931

In 1912 most of the placer ground in the district was acquired 

by outside interests, although outlying claims continued to be worked 

by individuals. In 1913 to 1924 large quantities of mining supplies 

were brought in and hydraulic operations were undertaken by an 

organization known at first as the Valdez Creek Placer Mines and 

later as the McKinley Gold Placers and the McKinley Placer Mining 

Co. This company employed a maximum of about 50 men, but generally less. Most of its work was concentrated on a buried channel 

on the Tammany claim (see pp. 449-451), formerly worked by under r 

ground methods.4 Although considerable gold was produced during 

the period of the company's operations, it appears that the returns 

were not sufficient to counterbalance the heavy expenses incident to 

equipment and operation, and the company ceased work in 1924. 

Work in this district has always been hampered by the fact that 

hydraulic mining is obviously restricted to the open season, which 

rarely much exceeds 100 days.

For several years after company operation ceased little was done 

in the district except for the resumption of tunnel mining on a 

small scale in the Tammany channel. In 1928 hydraulic mining 

started on some rich gravel that had been found on the Folk claim, 

on the south side of Valdez Creek a short distance below the Tammany channel. Since then the principal production has come from 

this deposit, and the chief interest has centered in it. The total 

production to the end of 1930 is about $560,000.

In the summer of 1931 there were 15 placer miners and a small 

native settlement at Denali, 2 men were working in the Tammany 

tunnel, 2 placer miners were on White Creek, and 3 more on Lucky 

Gulch, and the placer deposits on Rusty Creek were receiving a little 

attention. Gold lodes are known on the ridge between Timberline

and Valdez Creeks, near Denali, and also close to Lucky Gulch, but 

little has ever been done on them.

STRATIGRAPHY AND PETROLOGY

The rocks of the region include metamorphosed lava and pyroclastic rocks, argillite, and schist, with subordinate amounts of limestone, sandstone, and conglomerate, locally intensely metamorphosed, 

and several intrusive rocks, mainly quartz diorite and similar rock, 

in part gneissic. Probably all the above-mentioned stratified rocks 

are Upper Triassic, and the intrusive rocks are Upper Jurassic or 

younger. Included also are a small mass of Tertiary (Eocene?) 

coal-bearing sedimentary rock and widespread, thick Quaternary 

clastic deposits, mainly the product of Pleistocene glaciation.

«Moffit, F. H., op. cit. (Bull. 498), pp. 60-62.
VALDEZ CREEK MINING DISTRICT 429

GREENSTONE

The somewhat metamorphosed volcanic rocks, which comprise 

basalt and andesite floAvs, breccias, and tuffs, with minor quantities 

of sedimentary material, may be conveniently included under the 

term " greenstone ", although they are on the whole somewhat less 

thoroughly altered than this name implies. They were examined 

during the present study only in the valley of Coal Creek, a tributary of Clearwater Creek, but are known 5 to crop out in a band 

roughly 15 miles wide, extending from a point east of the Richardson 

Highway near longitude 145°20' southwestward to the Susitna River 

near longitude 148°, a distance of fully 85 miles.

According to the descriptions given by Moffit and Chapin and the 

observations made during the present study, the greenstone is composed largely of black and dark-green basalt, in part amygdaloidal. 

Some of the basalt consists essentially of serpentinized olivine, 

augite, and calcic plagioclase, with considerable chlorite and other 

alteration products. Other flows consist of augite and labradorite, 

with epidote, chlorite, sericite, and ilmenite. Some purple, green, 

and red flows which were not studied petrographically are probably 

of andesitic composition. Several of the separate members consist 

largely of subangular fragments, mainly of lava, of a maximum 

diameter of about an inch. Some of these members have a clastic 

matrix, but others appear to be flow breccias, the matrix being composed of lava similar to the fragments. Moffit's descriptions indicate 

that slate, fine-grained tuff, and tuffaceous conglomerate are in places 

associated with the flows. Limestone lenses, locally fossiliferous, are 

interbedded with and overlie the flows.

The thickness of the volcanic rocks in the Valdez Creek region has 

nowhere been measured, but in and near the valley of Coal Creek it 

probably aggregates 1,500 feet. Moffit 0 calculates that the flows in 

the mountains south of Butte Creek, west of the Susitna River, have 

a thickness of 3,500 feet, and Chapin 7 notes that the maximum thickness in the mountains between Butte and Watana Creeks is evidently 

even greater.

Moffit 8 originally regarded the lava composing the greenstone in 

and bordering the Valdez Creek region as erupted either in late Carboniferous time or during early or Middle Triassic time, but in a later

0 Mofllt, F. H., Hendwater rppions of the Gulkana and Susirna llivprs, Alaska, with 

accounts of the Valdez Creek and Chistochina placer districts: U.S. Geol. Survey Bull. 498, 

pp. 29-30, pi. 2; The Broad Pass region, Alaska : U.S. Geol. Survey Bull. 608, pp. 35-38, 

pi. 2, 1915. Chapin. Theodore, The Nelchlna-Susitua region : U.S. Geol. Survey Bull. 668, 

pp. 26-27, pi. 2. 1918.

«Mofflt, P. H., op. cit. (Bull. 608), p. 27.

T Chnpln, Theodore, op. cit. (Bull. 668), p. 27.

* Moffit, F. H., op. cit. (Bull. 498), pp. 29-30.
430 INVESTIGATIONS IN ALASKA EAILEOAD BELT, 1931

paper 9 he assigned it to the Mesozoic rather than to the Carboniferous. Both Moffit and Martin 10 call attention to the resemblance in 

character and stratigraphies position between the strata here described and the Nikolai greenstone of the Chitina Valley and suggest approximate correlation with that formation. Observation during the present investigation shows that the greenstone of Coal Creek 

is interbeclded with limestone, which locally contains Upper Triassic 

fossils, and Moffit has shown that similar fossiliferous limestone 

overlies the greenstone to the southwest. (See below.) This evidence that part of the thick greenstone group is of Upper Triassic 

age strengthens Moffit's conclusion that none of it is as old as 

Carboniferous.

LIMESTONE

For convenience of description the limestones mapped in the Valdez Creek region may be divided into (1) the lenses near the upper 

contact of the greenstone in the area between Clearwater Creek and 

the Susitna River, (2) the beds in the valley of Coal Creek, a tributary of Clearwater Creek from the east, and (3) the large mass of 

rusty limestone north of Coal Creek. There are numerous minor 

lenses of limestone in the argillite, not distinguished on plate 34.

LENSES BETWEEN CLEARWATER CREEK AND THE SUSITNA RIVER

In the mountains south of Pass Creek several lenses of limestone 

are exposed. Moffit 11 has mapped 10 such lenses in the area between Clearwater Creek and the Susitna River. On the basis of his 

work several of these beyond the limits of the present study are included on plate 34, their contacts being drawn in dashed lines. Moffit collected Triassic fossils from a limestone lens overlying basalt 

a short distance south of the mouth of Pass Creek. Another of the 

limestone lenses is on the west side of the principal tributary that 

enters Pass Creek from the south, in the lower part of the tuffaceous 

unit. This limestone is crystalline and resembles some of the less 

altered parts of the large mass north of Coal Creek. On the margins 

of the lens it is interbedded with a small amount of rusty siliceous 

schist identical in appearance with that north of Coal Creek. No 

traces of fossils were observed. The absence of fossils and the crystalline character of the rock link it with the limestone farther southwest. Moffit suggests that either this crystalline limestone may differ 

in age from the fossiliferous beds elsewhere or that its greater local 

alteration and lack of recognizable organic remains may be due

9 Moffit, F. H., op. cit. (Bull. 608), pp. 26-28.

10 Martin, G. C., The Mesozoic stratigraphy of Alaska: U.S. Geol. Survey Bull. 776, 

pp. 38-39, 1926.

11 Moffit, F. H., op. cit. (Bull. 498), pp. 31-33, pi. 2.
VALDEZ CREEK MINING DISTRICT 431

to local igneous metamorphism caused by the presence of intrusive 

rocks close at hand. So far as present evidence goes, Moffit's second 

explanation appears the more probable. About 300 feet vertically 

above the limestone lens on the west side of Pass Creek there is an 

exposure of dioritic rock so intensely altered hydrothermally as to 

be scarcely recognizable.

BEDS IN THE VALLEY OF COAL CREEK

On the south flank of the valley of Coal Creek there are exposures 

of fossiliferous limestone in fault contact with greenstone. Beds 

2 to 6 inches thick of massive somewhat impure limestone are interleaved with platy calcareous strata. The rock is nearly black on 

fresh surfaces but weathers to a light rusty brown. Fossils are 

rather abundantly preserved on shaly partings. Disturbance, probably due to faulting, prevents accurate measurement, but these beds 

and similar limestone in the north bank, which is in part more 

sandy, probably have an aggregate thickness of fully 500 feet. Ma« 

terial from blocks in the creek bed collected by Moffit and regarded 

by him as derived from beds on the north slope, was assigned definitely to the Upper Triassic by Stanton because it contains Pseudomonotis stuibcircularis. The collection (U.S.Nat.Mus. No. 15953) made 

during the present study from the beds on the south slope contains 

this same fossil, according to J. B. Reeside, Jr. On the north side 

of the valley limestone corresponding in appearance to the fossiliferous beds was noted only close to creek level, mantled by talus, but 

farther up the slope rusty and locally brecciated and slickensided 

limestone projects in places through talus composed mainly of volcanic rocks. Unbroken masses of the volcanic rocks crop out here and 

there. In one exposure brecciated limestone lies against andesite, 

but neither has recognizable bedding. The general relations on this 

slope indicate with little probability of error that the limestone 

and greenstone are interbedded.

LIMESTONE MASS NORTH OF COAL CREEK

Immediately north of the valley of Coal Creek a large mass of 

limestone is exposed. Most of it is rather fine grained, crystalline, 

and light gray to pinkish buff, and in nearly all exposures it is surficially very rusty. It generally has well-defined thin banding, emphasized here and there by films of sandy material, and locally 

grades into calcareous shale so jointed as to break in long slivers. 

Both the limestone and the shaly beds in many exposures are intricately crenulated. Much of the limestone contains abundant chlorite 

and epidote. Some of the outcrops within the limestone mass are 

composed of rusty siliceous schist and others of chloritized rock,
432 INVESTIGATIONS IN ALASKA RAILROAD BELT, 1931

both apparently lenses intercalated in the limestone. One of the 

chloritic rocks studied microscopically is an altered basalt, probably 

of effusive origin. It contains plagioclase, augite, calcite, epidote, 

chlorite, secondary quartz, and leucoxene. A few of the more sericitized plagioclase grains have such high indices of refraction as to 

indicate a composition approximating that of labradorite, but most 

of them appear to be albite-oligoclase. The plagioclase is in ragged 

laths, most of which are 0.3 millimeter or less in length with a tendency to flow structure. Some of the plagioclase is in phenocrysts 

about 1 millimeter long, and the augite also tends to form phenocrysts. The limestone mass as a whole is inclined northward at 

high angles. In many exposures the beds stand nearly vertical. 

Contortion and faulting make measurement of the thickness of the 

limestone impracticable, but it doubtless exceeds 1,000 feet. There 

is evidence of faulting along its southern margin, but the displacement probably is not great, and the mass belongs stratigraphically 

above the greenstone on Coal Creek. It appears that the two groups 

of beds grade into each other as is suggested by the presence of rusty 

limestone within the greenstone and of lenses of igneous rock within 

the limestone mass. The limestone is interbedded with, and is evidently stratigraphically below the siliceous schist north of it. 

Though the evidence is inconclusive, it strongly suggests that this 

large mass of rusty limestone is of Upper Triassic age and corresponds in approximate stratigraphic relations to the smaller, locally 

fossiliferous limestone lenses mapped by Moffit farther southwest. 

These limestone lenses are not everywhere at the same horizon.

TUFEACEOUS AND RELATED STRATA

The mountains south of the pass at the heads of Koosevelt and

Pass Creeks are composed of tuffaceous conglomerate and somewhat 

altered tuff, with some basalt, slate, sandstone, and limestone. Observations along the east side of the South Fork of Pass Creek and 

Moffit's field notes for the area still farther east indicate that the 

strata in the mountains on the south side of lower Pass Creek are 

composed of slate, sandstone, and volcanic rocks, with some limestone lenses; hence the rocks in that area are tentatively correlated 

with the tuffaceous unit here described.

In most exposures of this unit visited during the present study 

conglomerate is abundant, and in the mountain faces immediately 

southeast of the pass leading to Roosevelt Lake it probably makes up 

more than three fourths of the beds. Here the major part of the 

conglomerate is composed of well-rounded elliptical pebbles half an 

inch to 6 inches in maximum diameter, with a few larger cobbles.
U. S. GEOLOGICAL SURVEY BULLETIN 849 PLATE 34

INTRUSIVE ROCKS <->

Alluvium of present 

flood plains

Older alluvial deposits.

Coal-bearing strata

Schist near Valdez Creek

Tuffaceous and related Rusty schist

strata with intercalated with intercalated

limestone (Is) chloritic beds (ch)

valley of Coal Creek

Section alon^ line A~A Sec."tion alon^ line C C

Limestone north of 

Coal Creek, with interLimestone in the calated bed8 of schist {sc)

Strike of vertical strata

Section o lon£ It n<? B - B'

GEOLOGIC' SKETCH MAP AND SECTIONS OF THE VALDEZ CREEK MINING DISTRICT AND VICINITY, ALASKA

Miles
VALDEZ CBEEK MINING DISTRICT 433

The pebbles are neither well sorted nor distinctly stratified. Most 

of them are black, red, purple, and green greenstone, but some are 

shale and sandstone. The matrix is a coarse green grit composed 

mainly of fragments of greenstone, quartz, and feldspar and colored 

by chlorite. Along the South Fork of Pass Creek the conglomerate 

is somewhat less abundant and the pebbles composing it are on the 

average smaller and more irregular in shape. The conglomerate 

farther east, south of Roosevelt Lake, is composed mainly of well" 

rounded pebbles less than an inch in maximum diameter, comparatively well sorted. Many of the pebbles are of fine-grained black 

rock. Conglomerate is widely distributed in this part of the area 

but probably makes up less than half of this unit. All the conglomerate observed, although composed mainly of igneous material, 

shows evidence of transportation of its constituents by water. The 

conglomerate is interstratified with coarse green and black chloritized feldspathic grit. These beds are too much altered for positive 

identification without extensive microscopic study but are doubtless 

mainly water-sorted tuff which has been somewhat altered hydrothermally.

Basaltic lava flows are rare and inconspicuous components of the 

tuffaceous unit. A specimen from one such flow exposed south of 

upper Pass Creek was found under the microscope to consist mainly 

of calcic plagioclase laths, with less than 10 percent of augite and 

hornblende and scattered grains of titaniferous magnetite. There 

is considerable sericite and chlorite and some epidote. The plagioclase laths and to a somewhat less extent the augite prisms have a 

rough parallelism indicating flowage. They vary in length from 

0.2 millimeter to well over 1 millimeter and are embedded in a finegrained matrix that was perhaps originally in part glassy. This 

characteristic lava texture coupled with the fact that the rock is 

interstratified with obviously clastic beds shows that the basaltic rock 

is of effusive rather than intrusive origin.

The thickness of the tuffaceous and conglomeratic strata here cannot be determined until the structure of the unit is better understood. 

Doubtless the structural disturbances indicated by marked variations 

in the attitude of the strata in different localities account in part for 

the great width of outcrop in these generally steeply dipping beds,, 

but with due allowance for this factor the indications are that the 

unit has a thickness of several thousand feet. (See pi. 34.)

M^ch of the conglomerate and grit, especially south of upper Pass 

Creek, appears to be partly silicified. Rather large lenses of limestone both east and west of the South Fork of Pass Creek have already been mentioned (pp. 430-431), and there are some smaller ones..

179229 33 3
434

Limestone is, however, nowhere an abundant constituent of the tuffaceous unit.

Argillaceous beds are sparsely distributed through the gritty strata 

west of the South Fork of Pass Creek and are somewhat more abundant east of this stream. They are plentifully interbedded with 

the conglomerate and tuffaceous grit bordering the most easterly of 

the tributaries of Koosevelt Creek from the south. Many are indistinguishable lithologically from the rock characteristic of the main 

argillite mass to the north and west, but most contain somewhat 

more chlorite and in other respects tend to resemble and grade into 

the feldspathic grits with which they are associated.

Final decision as to the stratigraphic relations of the unit must 

be postponed until additional structural and other data are available, but it seems clear that the time of deposition of these tuffaceous beds cannot differ greatly from that of the argillite, on the 

one hand, or the greenstone, on the other, and the unit is in consequence tentatively regarded as of Triassic age. The evidence 

obtained in approaching the area from the east strongly suggests that 

the tuffaceous beds immediately overlie the greenstone containing 

lenses of limestone. Some of the lenses at and near the base of the 

tuffaceous unit have yielded Upper Triassic fossils, indicating that 

the tuffaceous unit is of Upper Triassic age. The presence of basaltic 

flows intercalated in the tuffaceous rock links this unit with the 

underlying dominantly basaltic greenstone. The coarse gritty and 

conglomeratic beds of the tuffaceous unit are mainly water-laid but 

not well sorted and contain limestone lenses; they were probably laid 

down along a seacoast, partly in stream valleys, partly in the sea. 

They record rapid erosion of the greenstone beneath, accompanied

by some eruptions, probably in part explosive, in the final stages of 

the volcanism of which the greenstone was the principal product.

On the other hand, the tuffaceous beds south of Roosevelt Lake, 

which belong to the same stratigraphic unit, are undoubtedly interstratified with and conformably overlie argillite beds that evidently 

constitute an integral part of the argillite extensively exposed to the 

north and west. The most probable explanation of the relations here 

appears to be that argillite both underlies and overlies the tuffaceous 

unit, which thus constitutes a local, intercalated member in the thick 

argillite sequence. The interposition of wide detritus-floored valleys 

between the tuffaceous beds and the argillite to the north obscures the 

evidence and has resulted in failure to obtain proof of this hypothesis. 

Faults are known to exist in the vicinity, and the detritus may conceal faults of considerable displacement. The most probable explanation of the structure (outlined, on pp. 442-444) accords with the 

interpretation of the stratigraphy here offered.
VALDEZ CHEEK MINING DISTEICT 435

BUSTY SCHIST

There are two distinct kinds of schist in the area studied. One of 

these is a rusty, siliceous variety, of which the principal body lies 

east of Clearwater Creek .and north of Coal Creek and extends far 

beyond the limits of the area mapped. It has a light heliotrope 

color, but much of it is stained yellow by iron oxide. The rock is 

much crinkled, fairly hard, and locally calcareous. A few lenses 

of chloritic rock resembling the volcanic rocks in the adjoining limestone are interbedded with it. The portion of the schist mass within 

the area mapped probably has a thickness of nearly 1,000 feet.

This schist stands nearly vertical, but its contact with the large 

limestone mass just south of it appears to be inclined steeply north. 

As these two rocks are interbedded in the vicinity of the contact, it is 

probable that the schist overlies the limestone conformably. The 

limestone is of probable Upper Triassic age (see p. 432), and the 

schist may be tentatively regarded as of nearly the same age, although there is nothing to preclude its being as young as Jurassic. 

Under the interpretation of the structural and stratigraphic relations of the formations in this vicinity here given, the schist appears 

to be stratigraphically well over 1,000 feet above the Upper Triassic 

limestone on Coal Creek.

The presence of lithologically indistinguishable limestone and 

schist low in the sequence of tuffaceous beds on Pass Creek indicates 

that the contrast in metamorphism between the limestone and schist 

east of Clearwater Creek and the sedimentary rocks west of it are 

due to local modification of the rocks, probably through igneous 

agencies, rather than to difference in age.

ARGILLITE

The most abundant rock in the area is argillite. It is the principal rock on the south side of Valdez Creek and on the north side 

of Pass Creek throughout the length of these streams. Similar beds 

have been traced by Moffit 12 and Chapin 1S as far west as longitude 

148°25' near the Talkeetna River, and these may correspond approximately to the argillite of probable Triassic age which covers large 

areas still farther west and south.14

Within the Valdez Creek region the beds here included under the 

term argillite are for the most part black to dark-blue argillaceous 

rocks, largely slaty, with minor amounts of impure sandstone, lime12 Moffit, F. H., op. cit. (Bull. 608), pp. 29-31.

13 Chapin, Theodore, The Nelchina-Susitna region, Alaska : U.S. Geol. Survey Bull. 668, 

pp. 27-29, pi. 2, 1918.

14 Martin, G. C., The Mesozoic stratigraphy of Alaska: U.S. Geol. Survey Bull. 776, 

pp. 42-57, 1926.
436 INVESTIGATIONS IN ALASKA EAILROAD BELT, 1931

stone, and tuff, totaling thousands of feet in thickness. In much 

of the argillite the cleavage parallels the bedding or cuts it at 

an acute angle. Locally, however, the slaty cleavage is entirely 

independent of the bedding. In addition to the cleavage, there is 

jointing, generally pronounced and locally "closely spaced and forming a large angle with the cleavage. Most of the quartz veins in the 

argillite lie along either the slaty cleavage or the major joints. The 

few veins independent of these systems are generally small, and 

some of them are intricately crenulated.

Most of the argillite, both slaty and massive varieties, is composed 

mainly of quartz, sericite, chlorite, and biotite, with dark, probably 

carbonaceous coloring matter. Calcite is widely but in general 

sparsely distributed in the argillite. Locally, especially north of 

Pass Creek, there are small limestone lenses, and in the vicinity of 

some of these argillite is distinctly calcareous. In some places, 

mainly near intrusive bodies, the argillite, particularly the finer, 

more fissile varieties, glistens with sericite on cleavage faces and contains considerable chlorite. Some of the rock of this sort is essentially similar to much of the schist north of Valdez Creek.

Isolated lenses of tuff were noted on Gold Hill and north of Pass 

Creek close to its confluence with Clearwater Creek. Similar lenses 

probably exist in other places in the argillite but are nowhere abundant. Those seen consist of largely subangular fragments of several 

kinds of lava and broken crystals of quartz and sericitized feldspar, 

mainly plagioclase of intermediate composition. The matrix in 

which the fragments are embedded is largely fine-grained quartz 

of detrital origin. Biotite, chlorite, epidote, and leucoxene are also 

present.

No direct paleontologic evidence as to the age of the argillite in 

the region studied during the present investigation is available, although Moffit 15 found nondiagnostic fossils in a limestone lens 

exposed in a gulch tributary to Pass Creek from the north, a locality 

which would appear to be within the argillite area as here mapped. 

Moffit 16 grouped these beds, the tuffaceous and related strata south 

of Pass Creek, the rusty schist and neighboring limestone north of 

Coal Creek, and part of the greenstone in the valley of Coal Creek as 

one unit on his geologic map. As thus grouped, the limestone from 

which he collected Upper Triassic fossils is intercalated in the lower 

part of the unit, which, as a whole, was consequently referred to 

the Upper Triassic. As here delimited, the argillite unit would 

consequently be Upper Triassic or younger.

^Mofflt, F. H., op. cit. (Bull. 498), p. 31. 

18 Idem, pp. 31-33, pi. 2.
VALDEZ CREEK MINING DISTRICT 437 

SCHIST NEAR VALDEZ CREEK

In addition to the rusty schist north of Coal Creek, schist that is 

somewhat less siliceous occupies large areas north of Valdez and 

Eoosevelt Creeks. It is black to dark brown, generally with a distinct silvery sheen resulting from the abundance of mica. The 

extent of metamorphism varies markedly in different places. Locally the rock is a fissile glistening sericite schist. Most of this 

variety is crowded with crystals of metamorphic silicates, of which 

garnet is by far the most conspicuous. Elsewhere it is green with 

abundant chlorite and distinctly less fissile. In some outcrops the 

rock differs little in appearance from much of the argillite farther 

south and is distinctly less metamorphosed than the more intensely 

schistose varieties of the argillite. It is exceptional for the rock to 

be so schistose that original bedding cannot be discerned. Coarse,

sandy, and massive beds are less common within the schist than 

within the argillite, but the character and appearance of such beds 

in the two areas are almost identical. In some places, notably in the 

vicinity of Kusty Hill, massive beds are intercalated in decidedly 

schistose rocks, and their comparatively unmetamorphosed appearance is striking. Crenulation and contortion render any attempt to 

measure the thickness of the schistose strata unreliable, but plate 34 

shows that the thickness is great, probably several thousand feet.

The schist has not been studied petrographically, but heavy sand 

concentrates from placer operations near Denali, examined by 

Charles Milton, of the Uniteol States Geological Survey, were found 

to contain abundant garnet (mostly pink, rarely yellow), green and 

brown hornblende, magnetite, and pyrite, slightly less abundant 

zircon and apatite, some staurolite, sillimanite, cyanite, and biotite, 

and rare epidote, hypersthene, titanite, and probably monazite. 

Most of these minerals probably came from the schist, and they thus 

serve to indicate the character of the metamorphic silicates in that 

rock. Some of the minerals in the sand doubtless came from the 

 dioritic intrusive rocks, and some from the more metamorphosed 

varieties of the argillite.

In a very general way metamorphism is greatest close to the main 

body of quartz diorite, but there is much local variation. Some of 

the most intensely metamorphosed schist occurs in small exposures 

surrounded by comparatively little-metamorphosed rock. The schist 

in the area between the outlying dioritic stock near Fox Creek and 

the main mass along the ridge crest is more thoroughly metamorphosed 'than most of that seen elsewhere, but the schist south of the 

outlying mass, close to Valdez Creek, is slaty and differs little from 

much of the argillite. Some of the argillite close to the small stock 

on Gold Hill, immediately to the south, is about as schistose as any
438 INVESTIGATIONS IN ALASKA BAILKOAD BELT, 1931

within the area mapped. Both the tendency to greater metamorphism near igneous masses and the irregularity in degree of metamorphism suggest genetic relation between the metamorphism of 

this schist and the intrusion of the dioritic rocks. Though the 

known mineral assemblage in the schist is not incompatible with 

this idea it includes a number of silicates, such as staurolite and 

cyanite, commonly found in crystalline schists of deep-seated origin 

rather than in zones of igneous metamorphism. The intrusive rocks 

are themselves somewhat altered (pp. 440-441). The most probable 

conclusion from the available evidence is that intrusion took place 

under considerable pressure and that the metamorphism of the schist 

occurred during and subsequent to the intrusion. If, as appears probable, the intrusion took place during Jurassic time or later, the 

associated metamorphism is too recent to give any clue to the relative age of the schist and argillite. The resemblances noted above 

between the argillite and schist accord with the apparent structure 

(pi. 34) and indicate that they are concordant components of the 

same sedimentary sequence, the schist being stratigraphically the 

higher. The greater metamorphism of the schist would then be 

explained by its being both nearer the main intrusive mass and, on 

the whole, originally more fissile than the argillite. On this assumption the schist is of Upper Triassic or possibly Jurassic age. This 

conclusion accords with that formed by Moffit 17 in the field. He 

points out that the possibility of faulting casts doubt on the observed stratigraphic relations. Nevertheless, the lithologic resemblances between the schist and argillite appear to require close 

stratigraphic relations, and the origin of the metamorphism here 

suggested adequately accounts for the apparent anomaly of schistose 

rocks stratigraphically above less metamorphosed rocks.

TERTIARY (EOCENE?) STRATA

The small mass of rather poorly consolidated sandstone, shale, and 

conglomerate, with some coal, which underlies much of the upper 

valley of Coal Creek, is strikingly different from and obviously 

younger than the other preglacial sedimentary rocks of the region. 

As most of the similar deposits elsewhere in Alaska are commonly 

regarded as of Eocene (?) age, these beds are so designated to distinguish them from the Mesozoic strata previously described. Moffit 18 and Mendenhall 19 describe a number of isolated localities of 

similar rocks farther east, but the occurrence on Coal Creek is the 

only one known in or near the Valdez Creek region.

"Mofflt, F. H., op. cit. (Bull. 498), pp. 32-33. 

18 Idem, pp. 35-38.

19 Mendenhall, W. C., Geology of the central Copper River region, Alaska: U.S. Geol. 

Survey Prof. Paper 41, pp. 52-54, 1905.
VALDEZ CEEEK MINING DISTEICT 439

The Eocene (?) beds at this locality occupy an irregular area about 

5,000 feet long and 1,500 feet wide and extend up the valley slopes 

to a maximum of about 500 feet above their downstream margin in 

the channel of Coal Creek. The bedding is nearly flat, except that 

along the southwestern border it is contorted and broken and locally 

stands vertical. The strata are everywhere discordant in attitude 

with the older rocks on which they lie.

The pebbles in the conglomerate are poorly rounded and range 

from 1 to 5 inches in maximum dimension, with scattered larger 

cobbles. Most of the pebbles are similar in composition to the neighboring volcanic rocks. Some of the sandstone is brown, coarsegrained, firmly cemented, and feldspathic and contains a few carbonized rootlets. Other beds are chalky white and composed of 

thoroughly kaolinized grains with sparse less-altered feldspars. Shaly 

beds are in the minority; they are yellow and light brown in color,

and many are so soft as to be scarcely more than indurated clay. 

The principal exposure of coal is in the south bank of Coal Creek, 

close to the downstream margin of the Eocene (?) beds, but float 

indicates the presence of a number of other coal seams.

The marked discordance with neighboring rocks and the comparative lack of induration fully justify the assignment of these beds to 

the Tertiary, but no specific evidence permitting close dating is 

available within the area studied. Mendenhall 20 found plant remains of so-called "Arctic Miocene " that is, Eocene age in somewhat similar strata roughly 55 miles farther east, which he called the 

Gakona formation, and the fossil plants collected from most of the 

numerous similar occurrences in the broad region south and east of 

the Alaska Range are identified as Eocene. Hence the beds on Coal 

Creek may be tentatively so assigned.

QUATERNARY DEPOSITS

Deposits of unconsolidated gravel, sand, and silt are abundant in 

all the valleys of the region. They range in thickness from a few 

inches to well over 200 feet. Most of the material, especially in the 

benches into which the present streams are incised, is clearly older 

than the present erosion cycle. Both the topography and the character of the material show that much of it is related to glaciation. It 

is doubtless of Pleistocene age.

Except along the silt-laden Susitna River, which is still fed by 

glaciers, the modern flood plains are narrow and the recent deposits 

in them are shallow.

2° Mendenhall, W. C., op. cit, p. 53.
440 INVESTIGATIONS IN ALASKA BAILBOAD BELT, 1931

INTRUSIVE BOCKS 

GNEISSIC QUARTZ DIORITE

The ridge crest north of Valdez Creek is composed of quartz 

diorite that forms the southern border of a large body extending 

far beyond the area studied. Moffit's mapping indicates that this 

mass has an areal extent of well over 250 square miles, although it is 

in part covered by Quaternary deposits. The border portion of the 

mass, the only part examined during the present investigation, has a 

distinctly gneissic texture that results mainly from the parallel 

arrangement of the ferromagnesian minerals but also in part from 

banding due to variation in the average size of grain in the rock. 

Locally, in the immediate vicinity of the contact, there are dark 

bands probably resulting from the presence of schist slivers permeated with igneous material; here the dioritic rock breaks in thin 

slabs. With due allowance for its coarser texture, some of this rock 

is almost as schistose as the schist it intrudes. The gneissic foliation 

in the quartz diorite approximately parallels the contact between the 

diorite and schist, which, in turn, is essentially parallel with the 

cleavage in the schist, both in strike and in dip. Locally, apophyses 

of the quartz diorite somewhat finer and more silicic than the main 

mass have been injected parallel to the foliation of the schist at intervals for a distance of nearly half a mile south of the contact. 

These are rarely more than a few feet wide. One of the larger ones 

is shown on plate 34 (somewhat exaggerated in width).

There is local variation in composition as well as texture, but 

much of the quartz diorite is a coarse-grained mottled gray rock, 

distinctly fresher than the rocks that compose the subsidiary stocks 

farther south. Typical material has an average grain somewhat 

more than 2 millimeters in diameter and contains about 45 percent 

of oligoclase-andesine, 30 percent of quartz, 20 percent of biotite, 

4 percent, of hornblende (commonly somewhat altered), and nearly 

1 percent of epidote. Locally the rock contains a somewhat higher 

proportion of hornblende. Some of the finer-grained gneissic bands 

contain distinctly smaller amounts of ferromagnesian minerals 

than the average rock and resemble aplite in appearance. Lenses 

of vein quartz are locally numerous near the contact with the schist.

OTHER DIORITIC ROCKS

In addition to the batholithic mass above described numerous 

bodies of similar but generally more altered rock occur within the 

area mapped, both as stocks and as minor masses having only a few 

square feet of surface exposure. One of the stocks is on the ridge 

between Timber line and Valdez Creeks, another on Gold Hill between Lucky Gulch and White Creek, another on the north side of
VALDEZ CREEK MINING DISTBICT 441

Valdez Creek between Fox and Craig Creeks, and another just north 

of the pass at the head of Roosevelt Creek. The small mass in the 

extreme northeast corner of the area mapped is part of a body 

of considerable size that extends well beyond this area. Southwest 

of it there are a number of very small masses of similar rock; the 

larger ones are mapped on plate 34 (somewhat exaggerated in 

scale): The small stock south of Pass Creek (shown with dashedline boundary on pi. 34) was mapped by Moffit 21 but was not 

reached during the present study. A number of the gulches, particularly on the north side of Pass Creek, contain chips of similar 

rock in the talus, suggesting the presence of other small bodies.

The rock of the stocks and minor bodies resembles that of the 

batholith except that it is much more hydrothermally altered and is 

less gneissic in texture. It is generally colored green by the abundant chlorite. Much of it has a moderately coarse granitic texture, 

but some, such as that near Timberline Creek, has prevailingly lathshaped feldspars as much as 2 millimeters long, with interstitial 

quartz, and thus has a texture resembling that of a coarse-grained 

dike rock. Alteration is so prevalent that exact determination of 

the constituents is difficult, but it is evident that the rock in the different localities ranges in composition from quartz diorite to quartz 

monzonite, the average being intermediate between these extremes 

and approximating granodiorite. The principal original constituents are plagioclase of intermediate to sodic composition (generally 

50 percent or more), microcline (none up to nearly 40 percent), 

quartz (generally 5 to 10 percent), biotite, and hornblende (variable 

up to about 15 percent). The plagioclase is intensely sericitized and 

in many places is rimmed with secondary albite. The biotite is generally bleached and chloritized. In most of the rock the hornblende 

is so altered and broken up as to be difficultly recognizable and is itself in large part the product of uralitic alteration of pyroxene. 

Epidote is abundant, and calcite, titanite, and leucoxene are locally 

plentiful.

DIKES

Small black dikes are scattered sparsely throughout the area. One 

exposed in the present hydraulic cut at Denali is a lamprophyre that 

consists principally of laths of sericitized plagioclase of the approximate composition of andesine, hornblende, and thoroughly chloritized biotite with abundant grains of titaniferous magnetite and local 

aggregates of secondary calcite and epidote. The other similar dikes 

in the area were not studied microscopically but probably have about 

the same composition. Moffit 22 records the presence of numerous 

hornblende porphyries in the surrounding region.

21 Moffit, F. H., op. cit. (Bull. 498), pi. 2. 

23 Idem, p. 34.

179229 33 4
442 INVESTIGATIONS IN ALASKA EAILROAD BELT, 1931

AGE

All the intrusive rocks above described are doubtless of essentially 

the same age. The principal alteration in most of them is hydrothermal. Both the alteration and the local tendency to gneissic texture appear to be closely related to the intrusive activity, and the 

differences in composition that exist within the area examined are 

such as are to be expected in offshoots of a single magmatic mass. 

Hence within the Valdez Creek district there appears to be no evidence in support of Moffit's suggestion 23 that the dioritic intrusions 

in the upper Susitna region as a whole may have extended over a 

considerable length of time. The principal difference in metamorphism within the area near Valdez Creek is between the rock of the 

principal batholith on the one hand and that of the outlying smaller 

masses on the other, and the difference in structural relations may be 

quite sufficient to account for this. The direct evidence available does 

not permit dating the diorite rocks more closely than that they are 

later than Triassic and were consolidated long before the Quaternary 

glaciation and probably before the deposition of Eocene (?) beds. 

The character of the metamorphism suggests that intrusion took 

place at considerable depth and, consequently, that prolonged erosion 

has been required to expose the rocks at the surface as they are today. 

In accordance with Moffit's conclusion they may be tentatively 

regarded as of Upper Jurassic or later age.

STRUCTURE

The Valdez Creek district is underlain by part of the north flank of 

a large fold which trends somewhat north of east. There are minor 

folds and local contortions. The stratified rocks are cut by a number of stocks and dikes and are offset by several faults. Dynamic 

and igneous metamorphism are prevalent and, with local exceptions, 

increase northward.

FOLDING

The fact that the area lies on the north flank of a major fold is 

clearly reflected in the generally uniform easterly strike and the 

northerly dip of the strata, especially in the western part of the 

area, where faulting is at a minimum. The trend is east to N. 50° E., 

and the average within the area mapped is about N. 70° E. All the 

larger rock masses are alined in conformity with this trend. Moffit 24 

shows that throughout most of the surrounding region similar trends 

are maintained, and successively older rocks are exposed from Valdez 

Creek southward.

23 Mofflt, F. H., op. cit. (Bull. 498), p. 35. 

24 Idem, pi. 2.
VALDEZ CREEK MINING DISTRICT 443

The departure from the general trend in the vicinity of the confluence of Valdez and Roosevelt Creeks results in part from a flexure, 

probably augmented by a fault along upper Valdez Creek.

A small 'subsidiary anticline is exposed in the gorge of Valdez 

Creek above the present main hydraulic workings, and there are 

minor folds and crenulations elsewhere, in part related to the intrusion of igneous rocks. For example, the westernmost of the tributaries that enter Pass Creek from the north exposes highly contorted strata whose deformation is related to the nearby stock. 

The large mass of conglomerate, tuff, and related rocks south of this 

locality is inclined steeply to the south but with marked variation in 

attitude. The probable structure here is indicated in the structure 

section on plate 34.

The limestone and schist east of Clearwater Creek are contorted 

and in large part intricately crenulated, doubtless as a result of 

combined intrusion and faulting. The rocks show evidence of having been permeated and metamorphosed by heated solutions of igneous origin, and this may have aided in rendering them incompetent. 

They are cut by numerous small masses of gneissic diorite, of which 

only a few could be mapped. These are probably offshoots of a large 

mass whose intrusion may have been a dominant cause of the contortion of the limestone and schist.

FAULTING

The rocks in the eastern half of the area mapped are broken by 

normal faults with an average trend of N. 65° E. and steep northwesterly dips. Though such faults have been actually traced only 

for short distances, both the general relations of the rocks and the 

topography suggest that they persist for miles, buried under the 

alluvium of the valleys. Moffit 25 has mapped one such fault with a 

length of 8 miles. If, as seems probable, the fault near Coal Creek 

continues along Pass Creek it would be as long. The shape of the 

body of gneissic diorite mapped by Moffit along upper Valdez Creek, 

just beyond the limit of the present study, and the offset in the schist 

mass suggest that a similar long fault exists here. Such a fault 

would trend slightly more to the north than the others mentioned 

above.

There is some evidence suggestive of faults trending N. 70° W. 

The departure from the average structural trend along the valleys 

of Clearwater and Eldorado Creeks is only partly explained by the 

known faults of northeast trend but would be adequately accounted 

for by conjugate faults of northwest trend underlying the gravel of 

these creeks. Unless the volcanic rocks near Coal Creek are strati-

=5 Mofflt, F. II., op. cit. (Bull. 498), pi. 2.
444 INVESTIGATIONS IN" ALASKA EAILBOAD BELT, 1931

graphically equivalent to the conglomerate and associated rocks south 

of Pass Creek, it would seem that such a fault must be present along 

Clearwater Creek. Along upper Pass Creek the relations between 

the tuffaceous beds on the south and the argillite on the north indicate the probable presence of a fault of about this trend buried under 

the alluvium, as is shown on plate 34. East of the igneous stock in 

this vicinity there is much crenulation and variation in attitude and 

the rocks are locally sheared and broken. It is inferred that there 

is a fault trending about N. 10° W. with downthrow to the east. 

The combined effect of these two faults would be to elevate relatively 

the block of argillite which is intruded by the stock. This argillite, 

consequently, doubtless belongs stratigraphically low in the sequence 

and is to be correlated approximately with the argillite that underlies 

the tuffaceous unit south of Eoosevelt Creek.

ECONOMIC GEOLOGY

PLACERS

The Valdez Creek mining district is primarily a placer area, 

essentially all its production to date being from this source. The 

development so far accomplished has proved the presence of extensive deposits in the immediate vicinity of Denali, and there are 

widely distributed and locally rich auriferous gravels elsewhere. 

The deposits near Denali have been profitably worked on a small 

scale. The one attempt so far made to operate with comparatively 

abundant capital was confined to hydraulicking the gravel in part 

of a deep filled gorge, known as the Tammany Channel. Gravel 

along the old channel had previously been worked by underground 

methods. Auriferous gravel is known to be widely distributed over 

the area but has been worked only in the few localities where bedrock could be reached by a few men working with primitive 

equipment.

RELATION OF PLACERS TO GEOMORPHOLOGY

The oldest drainage ways of which remnants persist are the buried 

channels near Denali. The Tammany Channel, because of the extensive placer mining in it, is the best known of these, but there are 

a number of others. Tammany Channel and probably others were 

relatively narrow, approximately V-shaped rock-cut gorges that 

appear to have been incised in a moderately mature topography 

without the aid of glaciation. So far as can be judged from evidence at the surface, these gorges do not continue up the present 

Valdez Creek Valley as much as 5 miles from its mouth. They 

probably record an incipient rejuvenation which was halted by the
. VALDEZ CKEEK MINING DISTRICT 445

raising of local baselevel, probably by the filling of the neighboring 

part of the valley of the Susitna Kiver either by glacial debris or

 by ice. In consequence the gorges were filled with alluvium. 

Glaciers are abundant today on and near the headwaters of the 

.Susitna. Extension of their limits during the Pleistocene so as to 

fulfill the conditions here suggested would be in accord with the 

known history of the general region.

According to operators the richest and most extensive placer 

ground in the vicinity of Denali is close to the old buried bedrock 

surface. Concentration of this material took place mainly in the 

streams flowing in the rock-cut channels prior to and at the start of 

the interference that caused the filling. Pay gravel has also been 

found at two or more higher horizons in the filled channels, showing 

that at intervals the streams maintained themselves long enough to 

permit concentration of the gold.

The original discovery of placer ground was made on bars in the 

recent channel of Valdez Creek, which derived their gold largely from 

reconcentration of that in the old alluvium. Above the Tammany 

Channel Valdez Creek flows mainly in a rock gorge, and its bars 

have yielded notably less gold than those below, doubtless because 

much less of the old material was available for reconcentration. The

 deposits now filling the old channels on lower Valdez Creek, as exposed in natural and artificial cuts, are characteristically well bedded. 

Locally boulders are numerous and heterogeneously distributed, but it 

is clear that the greater part of the material Avas laid down in water. 

The scarcity of cross-bedding indicates that currents were not swift, 

.and the thorough sorting and almost perfectly regular horizontal 

bedding in some places suggest ponding. A good example is found 

in a cut on the north side of Valdez Creek just above the mouth of 

Timberline Creek. Isolated boulders in the sandy beds and nearby

 cobble deposits record less tranquil conditions. All cuts of any considerable size expose so -many cobbles and boulders that it is clear 

that vigorous erosion, doubtless related to glaciation, was taking 

place in the vicinity throughout the period of accumulation, but 

the largest and least-rounded boulders are almost entirely confined 

to the immediate vicinity of the surface of the present hummocky 

benches; hence it appears that the last incident of glaciation here 

recorded was the dumping of morainal material over the surface 

of the water-laid strata.

In postglacial time retreat of the Susitna Glacier and removal and 

spreading out of its deposits have again lowered the baselevel of 

Valdez Creek and permitted it to trench a new, steep-sided channel, 

without any direct relation to preglacial channels. This new cut
446 INVESTIGATIONS IN ALASKA EAILEOAD BELT, 1931

has penetrated the detritus and become incised into rock for a distance of about 4 miles and is still in process of being extended headward. The rock walls are highest at the upper end of the trench. 

About three quarters of a mile above the mouth of Timberline Creek 

the rock walls extend more than 150 feet above Valdez Creek. For 

some distance below the Tammany Channel rock bluffs extend generally to heights of 30 feet or more above Valdez Creek on its south 

side and of 5 to 15 feet on its north side.

The trend of the Tammany Channel and the reported results of 

drilling by the company suggest that its head ward continuation lieswithin the confines of the valley of Valdez Creek but north of the 

present stream. There are extensive gravel deposits between Denali 

and Kusty Hill, flanked by rock on both sides. Clark Duff drilled 

some holes here in the summer of 1931 in search of a channel. The 

results obtained, though incomplete at the time of the present study, 

suggest that an ancient drainage way exists here, but that bedrock 

is so close to the surface that the existence of a channel as large as the 

Tammany is unlikely.

Gravel is exposed in the flank of the Valdez Creek gorge immediately opposite the Tammany Channel and may mark the southern 

continuation of this channel east of the present stream. The gravel 

in the present main hydraulic working lies nearly flat and is locally 

inclined about 2° E. The small amount of original bedrock surface 

now accessible is inclined westward toward Valdez Creek at an angle 

of more than 5°. The gravel deposits here, therefore, bear no known 

relation to any channel, present or buried. The lack of accord between dip of gravel beds and inclination of underlying bedrock 

suggests dumping of the gravel on a rolling surface, presumably as a 

delta or alluvial fan.

The swampy ground at the base of the hills east of the hydraulic 

cut appears to be underlain by deep alluvial deposits. The hummocky, poorly drained character of the surface and the numerouserratic boulders result from glacial dumping, but exposures (in part 

artificial) on the south side of Timberline Creek near its mouth show 

clearly that gravel extends considerably below the morainal material 

at the surface. Similar evidence indicates that the benches on both 

sides of Valdez Creek for fully half a mile back from the bluffs 

bordering the present flood plain of the Susitna River are composed 

of alluvium mantled by morainal deposits.

The most probable location of the buried channels, as deduced 

from the available data summarized above, is that indicated in 

figure 53. According to this, ancestral Valdez Creek reached the 

flood plain of the Susitna River, a plain wider than the present
VALDEZ CREEK MINING DISTRICT 447

one, at a point 1 or possibly 2 miles south of its present mouth, and 

the largest buried channel should be at the foot of the mountains 

some distance south of the hydraulic pit now in operation. Because 

of the difficulty of working ground on the higher benches, relatively 

remote from the existing gorge, little attention has yet been paid 

to the gravel south of the hydraulic pit in what should be, according to the above explanation, the principal buried channel. Drilling 

or other exploration would be required in order to fix the limits of 

the channel more definitely. Except that prospecting in the highlevel gravel north of Timberline Creek is reported to have shown 

rich ground in places, nothing is known as to the gold content of the 

postulated main channel. 

The results of operations 

in the Tammany Channel and the hydraulic pit 

and the presence of auriferous lodes on the northeast side of Timberline 

Creek all suggest that a 

channel in the position 

indicated should be auriferous. At all events, 

this ground is worthy of 

careful test by anyone 

contemplating expansion 

of placer activities in the 

district.

The gravel along Valdez Creek above the 

point reached by the 

recent inner gorge is 

known to contain gold, but because of practical difficulties it has 

nowhere been adequately tested. Should the ancient narrow gorges 

uncovered near Denali not extend upstream it may well be that 

the concentration of the gold has been less, but on the other hand 

the depth of gravel would not be great probably less than 100 feet 

and possibly little over 20 feet close to the present stream. The 

benches, especially that between White and Roosevelt Creeks, may 

locally have gravel deposits more than 200 feet deep. Only testing 

at depth can settle this point. There is ample evidence of wide 

distribution of auriferous quartz lodes, most of them small, in the 

headwater basin of Valdez Creek. The gold of Lucky Gulch and 

at least some of the gold of White Creek and its tributaries have

2. Miles

FIGURE' 53. Probable location of buried channels near 

Denali with reference to present drainage.
448 INVESTIGATIONS IN ALASKA EAILEOAD BELT, 1931

been derived mainly from the erosion of lodes in the immediate 

vicinity. This fact is abundantly demonstrated by the lack of 

rounding and sorting in the detritus, the coarseness and angularity of the gold, and the fact that gold is not confined as closely 

to the vicinity of bedrock or of definite channels as is commonly the 

case. Several of the lodes are known and have been prospected to 

some extent. Placer deposits of such origin, though they may be 

locally very rich, are likely to be comparatively spotty and of small 

oxtent. Small-scale operations may occasionally be richly rewarded, 

but the hope for large production in this part of the district rests 

on the possibility that the relatively undissected gravel deposits of 

Valdez Creek from the head of the youthful trench near its mouth 

to its confluence with Roosevelt Creek may prove valuable.

Roosevelt Creek and the other headwater branch of Valdez Creek 

have comparatively steep and narrow valleys. Gravel is abundant, 

but the relatively steep grades and short distances from the source 

of the material render these valleys somewhat less favorable sites for 

the accumulation of placer deposits. In Roosevelt Creek, particularly, the gravel is scarcely channeled. The creek water is divided 

among numerous shallow and anastomosing rivulets. This lack 

of adjustment suggests that there has been little opportunity for the 

long process of sorting and concentration required for placer deposits. Such prospecting as has been done in this part of the region, 

mainly on Surprise Creek and other tributaries of Roosevelt Creek, 

was unsuccessful.

The drainage basin of Clearwater Creek differs from that of Valdez 

Creek in the details of its geomorphic history. The Clearwater is 

much the longer stream. Its gravel deposits are broader and have a 

flatter surface. The inner trench has been widened much more, relatively, than that of Valdez Creek and has been carried much farther 

upstream. This trench is distinct in all the major tributaries as far 

up as they were examined. All these features point to longer and 

more tranquil stream erosion in the Clearwater drainage basin than 

in that of Valdez Creek. The greater opportunity for gravitational 

sorting thus afforded would seem to favor the accumulation of placer 

deposits, provided suitably situated and abundant gold-bearing lodes 

were available. No placer mining has been done here, so far as can 

be learned. It is reported that panning of creek gravel has yielded 

.some gold, but not enough to encourage development under existing 

conditions. As shown on pages 464r-465, some mineralization has 

occurred in the neighboring mountains, but the available information is inadequate to form any basis for estimate as to whether it 

could have yielded sufficient gold for commercial placer deposits.
U.S. GEOLOGICAL SURVEY BULLETIN 849 PLATE 35

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PLACER CLAIM MAP OF THE VALDEZ CREEK MINING DISTRICT.
VALDEZ CREEK MINING DISTRICT ' . 449

PLACER WORKINGS

DEPOSITS AT DENALI 

BARS OF VALDEZ CREEK

The original discovery of placer gold in the district was made in 

the gravel bars bordering Valdez Creek, in the bend of the stream 

immediately above the post-office building at Denali. Claims were 

staked covering the present flood-plain gravel of the creek and its 

tributaries almost to their heads. Plate 35 is a fairly recent revision 

(date unknown) of the claim map of the district, but nearly all the 

ground indicated on it was staked in the early days. Most of the 

creek claims never received any development. The creek claims near 

Denali that have been worked to any extent are Discovery, no. 1 

below, no. 2 below, no. 2 above, and no. 3 above. Of these, Discovery, 

no. 1 below, and the lower half of no. 2 below were the richest,26 A

little more than one third of the total gold produced on Valdez 

Creek from 1903 to 1910 came from the creek claims, but by 1910 

much of the richer ground had been worked and production from 

these claims declined. Except for a little hydraulic work on no. 2 

below, the mining on the creek claims was done by pick and shovel. 

A few years later hydraulic mining in the Tammany Channel filled 

the creek below it with debris and brought operations there to an end. 

The deposits of creek gravel on the three most productive claims 

ranged originally from 3 to 8 feet in thickness and consisted of 

fragments of slate, schist, and diorite, with small amounts of other 

igneous rocks. They ranged in coarseness from fine sand to boulders 

as much as 6 feet in diameter. The boulders, mainly diorite, were 

abundant and added much to the difficulty of mining. The gold 

from the creek claims was of variable appearance. Some was flat 

and well worn, but some was rough, showing little evidence of wear. 

That found above the Tammany Channel was finer and less worn 

than that below, but included a small proportion of smooth flat gold. 

As the decrease in coarseness is more marked downstream from the 

Tammany Channel than upstream, there seems to be no doubt that 

the richness of Valdez Creek downstream from claim no. 2 above 

is due to the old canyon gravel.

TAMMANY CHANNEL

On Valdez Creek immediately above the present main part of the 

settlement of Denali, a large excavation marks the place where the 

gravel fill has been removed from a section of a buried rock-cut

a»Moffit, F. H., op. clt. (Bull. 498), pp. 58-60. Most of the historical data and 

descriptions given in this report of workings now inaccessible are taken from Mofflt's 

paper. Production figures are based mainly on the records of the United States Geological 

Survey.
450 INVESTIGATIONS IN ALASKA RAILKOAD BELT, 1931

gorge generally referred to as the Tammany Channel, from the 

name of the placer claim covering it. Early in the history of the 

district a tunnel was driven along the bottom of this old gorge. The 

work was done under the leadership of Peter Monahan, and in consequence the channel is sometimes referred to by his name. This 

tunnel is reported to have been almost as long as the bottom of the 

present excavation that is, nearly 1,000 feet. There were at least 

two crosscuts, and stoping was generally carried to widths of 25 to 

35 feet and reached a maximum of 70 feet. The available data do 

not permit accurate determination of the production from the tunnel 

prior to company operation, but it was probably nearly $200,000.

Approximate lower 

edge of gravel

FIGURE 54. Contour map of the Tammany Channel. By C. P. Ross and Fred Buck.

The gravel in the filled gorge is similar, in general, to that in the 

bars along Valdez Creek. The lower 500 feet of gravel in the old 

gorge contains flat diorite boulders with rounded edges, rounded 

slate and schist fragments, and fine black clay. Much of it is indistinctly stratified and clearly of fluvial origin. The bedrock in the 

bottom of the gorge, exposed by. the hydraulic work, is carved and 

smoothed by the action of rapidly moving water, but shows no evidence of glacial polishing or scratching. The fill at higher levels 

presents a greater appearance of disorder and contains a large proportion of diorite boulders, which are round rather than flat. It thus 

resembles glacial detritus. The chief accumulation of gold is in the 

lower 5 feet of the gravel, although fine gold occurs throughout the 

fill. Most of it is found in the hard black clay and the fine gravel 

composed of rounded fragments of slate. Some of this finer material 

is sufficiently compacted to require blasting. Most of the gold is
VALDEZ CREEK MINING DISTRICT 451

 coarse, flattened, and smooth, though rough pieces are present. 

Nuggets worth several dollars are common.

The principal accomplishment under company operation in the 

district (see also p. 428) was the removal of about 500,000 cubic yards

-of fill from the Tammany Channel, as shown in figure 54, and the 

total production from the cut during this period is estimated at 

$135,000. If the production previously obtained from the tunnel on 

bedrock in the same part of the channel is added, it appears that the 

.average value of the gravel removed was roughly 65 cents a cubic 

yard. As much of this gravel was almost barren, the pay streaks 

must have been rich.

Since the cessation of company activity tunneling in the fill at the 

bottom of the gorge has been resumed. A winding tunnel 350 feet 

long had been driven at the time of survey, June 26, 1931. (See

fig. 54.) Stopes, not shown because largely filled, have been opened 

along this tunnel, and gold has been obtained from them. The 

production in 1928 and 1930 amounted to $4,168.

In addition to the work in the Tammany Channel, above described, 

there have been several attempts to work the gravel in the high 

benches on both sides of Valdez Creek close to Denali. The only 

place where much has been accomplished is in the hydraulic cut 

being operated at present on the Folk claim. Kich ground here was 

discovered by natives about 1927. Since then it has been worked with 

hydraulic equipment salvaged from that left by the company and 

has yielded by far the greater part of the gold recovered in recent 

years. About 100,000 cubic yar^s of gravel had been removed up to 

July 13, 1931. (See fig. 55.) The total production in 1928 to 1930 

was about $57,000. With due allowance for gold in the sluice boxes 

at the time the survey was made this indicates an average value of 

about 70 cents a cubic yard. This value agrees reasonably well with 

the estimate of 65 cents a cubic yard for the Tammany Channel and 

suggests that the high-level gravel deposits near Denali are quite 

ri«h enough to warrant consideration of the feasibility of working 

them on a large scale. The benches on both sides of Valdez Creek 

here probably contain well over 2,000,000 cubic yards of gravel, as yet 

practically untested.

The gravel on the Folk claim is not confined to a gorge as restricted 

as the Tammany Channel, although doubtless deposited at about the 

same time. Most of the deposit, however, is distinctly bedded, well 

rounded, and fairly well sorted, being quite evidently water-laid 

rather than of glacial origin. On top there is a soil cover several 

feet deep containing scattered boulders. Most of the gravel is com-
452 INVESTIGATIONS IN ALASKA EAILBOAD BELT, 1931

posed of cobbles less than 1 foot in maximum diameter, but boulders, 

as much as 4 feet in diameter are common, and a few are as much 

as 10 feet. The large amount of blasting needed to break up theJoi'5-

«0 CD 

'

fc I

boulders is one of the principal items of expense in working this cut. 

Hard beds of fine material such as occur in the lower part of the 

Tammany Channel are rare. Here, as elsewhere, diorite and slate 

are the principal rocks present in the gravel. There are some cobbles
VALDEZ CREEK MINING DISTRICT ' 453

of aplite. The small amount of original bedrock surface visible shows 

irregular channeling by flowing water. The gold is most abundant 

close to bedrock, but most of the gravel contains some gold, and there 

are reported to be several higher beds that contain notable quantities.

Shallow ditches have been dug to carry water to work the bench 

gravel on the north side of Valdez Creek opposite the cut just 

described, but as yet little has been accomplished. This area is not 

especially hummocky and may not have as many large boulders as 

the bench on the south side of the stream. On the other hand, there 

is little definite evidence of the existence of any channels that would 

tend to confine and hence concentrate the gold-bearing material.

Some ground sluicing has been done on the benches on both sides 

of the mouth of Timberline Creek, especially on the northeast side. 

Although the amount of ground moved has been small, the work

has proved the presence of gold, and one very rich pocket with 

numerous nuggets is reported to have been found. J. M. Olsen has 

driven a tunnel 150 feet through the slate in the south rim of the 

canyon of Valdez Creek, intending to prospect the gravel at depth. 

This tunnel is roughly 40 feet below the top of the rim and at its 

face has penetrated the gravel nearly 10 feet, apparently close to the 

bottom of the buried channel. It is to be further extended so as to 

test this material.

WHITE CREEK

"White Creek is the principal tributary to the middle portion of 

Valdez Creek, which it enters from the south 4% miles above Denali. 

Placer operations on a small scale have been carried on intermittently 

since about 1908 on White Creek and its tributaries Big Kusty, Little 

Rusty, and Rusty Creeks. In recent years almost the sole activity 

has been the work done by the two Wickersham brothers on White 

Creek ll/£ miles above its mouth. The total production from this 

creek and its tributaries is estimated by the Wickershams at $10.000. 

There are several small hydraulic cuts in this vicinity. That at 

which work was in progress in the summer of 1931 is roughly 15 feet 

deep and over 150 feet long. It traverses part of a fan composed of 

gravel overlain by and mingled with talus from the adjacent slope 

of Gold Hill. The cut exposes slate which strikes nearly east and 

dips 15° N.; its major joints are spaced 5 to 6 inches apart, strike 

N. 50° W., and dip 80° S. There is an irregular basic dike a few 

feet wide-which strikes N. 50°-70° W. and dips north at high 

angles.

At points where the dike bulges the slate is bent around it. The 

hanging wall is bordered by gouge with quartz lenses at intervals. 

This and similar lodes farther upstream are evidently among the 

principal sources of the placer gold being mined. Samples of placer
454 INVESTIGATIONS IN ALASKA BAILROAD BELT, 1931

concentrates kindly furnished by the Wickersham brothers contain 

bright coarse gold, in part intimately intermingled with quartz. The 

gold is rough, and much of it shows so little evidence of attrition or 

flattening that it cannot have been carried far from its source. A 

few of the bits of gold, much paler in color than the rest, are distinctly water-worn. In addition to the gold, the concentrate contains quartz and rock fragments, hessite (determined chemically by 

W. T. Schaller), pyrite, galena, arsenopyrite, magnetite, pyrrhotite, 

realgar, orpiment, and native copper, listed in order of decreasing 

abundance. The metallic minerals, especially the hessite, have calcite associated with them. The presence of hessite in placer concentrate from this locality was recognized several years ago by Paul 

Hopkins, United States Bureau of Mines, Fairbanks, Alaska, in a 

specimen collected by Norman L. Wimmler, also of the Bureau of 

Mines.

LTTCKY GULCH

Lucky Gulch is a small depression at the east end of Gold Hill 

about 6 miles up Valdez Creek from Denali. Gold was found here 

early in the history of the district, and during most summers since 

then from 1 to 3 men have been engaged in mining here, principally 

by use of the boomer, a device which dams and automatically releases 

the creek water at intervals. It is rarely possible to operate here 

much over 2 months each summer. Data on production are incomplete, but the total probably does not greatly exceed $20,000.

The gulch is carved by a little stream fed by snow banks, and in 

the autumn it contains little or no water. The gulch is distinct only 

on the steep hill slope; below, several branching channels, in part 

natural and in part resulting from the placer operations, lead from

it across the bench bordering Valdez Creek. The unconsolidated

material in the gulch is made up largely of slate fragments, scarcely 

water-worn and indistinguishable from the slide rock on both sides. 

It includes some pieces of vein quartz and of pegmatite. Near the 

lower end of the gulch the slate slabs are mingled with subangular 

cobbles of diorite, diabase, conglomerate, chlorite schist, and other 

rocks. These are part of the bench deposits of glacial origin. The 

loose material in the steep gulch reaches a maximum depth of about 

25 feet at the lower end. A short distance below the surface it is 

locally cemented by ice throughout the year, which hampers booming 

operations.

In such a gulch snowslides and the movement of the talus have 

probably caused numerous shifts in the course of the stream, with 

resultant wide distribution of the gold content. Hence the entire 

fan-shaped mass of detritus and not merely a narrow channel in 

it is potential placer ground. A relatively small amount of this fan 

has yet been trenched by booming.
VALDEZ CREEK MINING DISTRICT 455

Moffit 2T describes the gold from Lucky Gulch as follows:

Lucky Gulch gold is coarser than that from any other part of the Valdez 

Creek district. In general it is rough, and many pieces contain fragments 

of granular quartz, although some of the gold is flattened and well worn. This 

difference in surface character probably indicates nothing more than a variation in the manner of rubbing and pounding the pieces have undergone in 

traveling down the gulch, for there is little doubt that the gold is derived from 

a small area and has not moved far from its source. Large nuggets form an 

important part of the gold product of this stream. One found in 1910 weighed 

32 ounces, and a larger one weighing 52 ounces was taken from the gulch 2 

or 3 years previously.

OTHER WORKINGS

The workings described above include all from which there has 

been any considerable production. The tributaries of Timberline 

Creek have been prospected and one or more boomers installed on 

them at different times, but the results were evidently disappointing, 

as the projects were promptly abandoned.

Pits have been sunk in the benches bordering the middle portion 

of Valdez Creek in several places, and above the mouth of White 

Creek the bench on the south side has been cut into by booming. It 

is reported that gold was generally found in this prospecting, but 

bedrock was not reached, and the difficulties of operation resulted in 

early discouragement.

Surprise Creek, Eldorado Creek, and the other unnamed tributary 

to Roosevelt Creek have yielded some gold to prospectors, but the 

amount is reported to have been small. No work has been done on 

any of them for many years.

LODES

Up to the present time there has been little prospecting for lode 

deposits in this area and almost no development. The known types 

of lode deposits may be divided for purposes of description into 

veins in which quartz is almost the only gangue mineral, veins in 

which the gangue contains ferruginous calcite, and pyritic replacement deposits in lava, limestone, and schist. The first two lands 

have been prospected locally by shallow pits and cuts. Decomposed 

material derived mainly from veins of the second kind has yielded 

a small amount of gold by panning and rocking. The third kind has 

received little attention from prospectors.

VEINS WITH QUARTZ AS THE ESSENTIAL GANGUE MINERAL,

All the pre-Tertiary rocks contain quartz lenses and stringers. So 

far as can be judged from the distribution of float quartz and the 

frequency with which veins in place were noted during the geologic 

work, mineralization of this kind is so general that no particular

P. H., op. cit. (Bull. 498), p. 03.
456 INVESTIGATIONS IK ALASKA EAILEOAD BELT, 1931

part of the area nor kind of rock can be regarded as especially favorable to it. Most of the veins are composed of coarse-grained glistening white quartz with locally a little mica and small amounts of 

fine-grained pyrite. Many are slightly rusty, especially on fracture 

surfaces. Some of these veins follow bedding or schistosity, others 

follow the major cross joints, and still others are irregular and follow fractures belonging to no apparent system. Veins of this kind 

are common in many regions and generally contain little of value. 

They are related more or less closely to regional metamorphism in 

which igneous intrusion has played a part. A sample from one such 

veinlet on a joint crack in argillite close to the bridge on Valdez. 

Creek yielded on assay 0.01 ounce of gold and 0.30 ounce of silver 

to the ton, which suggests that these widespread veinlets, though too 

low in grade to be mined themselves, contain sufficient gold to be 

included among the sources of the metal in the placer deposits.

Quartz veins differing from those already referred to mainly in 

their much greater persistence and in the presence of notable 

amounts of shearing and hydrothermal alteration in the wall rocks 

have been prospected in the vicinity of Denali and are known to be 

auriferous. As far as can be judged from present development, 

bodies of this type offer greater promise of profit than any others in 

the area. Most of the prospects are on the hill between Timberline and 

Valdez Creeks and are collectively referred to as the Timberline prospects. (See pp. 461-463.) Another, near the head of Fourth of July 

Creek, not visited during this investigation, was worked in the early 

days of the camp. These veins originally contained pyrite, arsenopyrite, pyrrhotite, and a little chalcopyrite, which are now largely 

oxidized in surface exposures but only partly altered at depths of 

5 or 6 feet. Kernels of metallic £old are visible on fracture faces of

several pieces of quartz on the dumps of the Timberline prospects. 

Locally the massive lenses of glistening white coarse-grained quartz 

contain a little calcite in tiny grains, which tends to link these veins 

with those of Gold Hill and other localities that contain abundant 

calcite.

The writer's assays listed on page 463, together with statements by 

the operators, indicate that there is little relation between abundance 

of sulphides and gold content. The first sample listed contains considerable sulphide but only traces of precious metals; the richest of 

the writer's samples, on the other hand, is massive quartz without 

visible sulphide. The coarse, visible gold in these veins is largely 

if not exclusively related to joints and hence doubtless of late origin. 

Some of the assays show disproportionately abundant silver with reference to the gold, suggesting the presence of some unidentified sil-
VALDEZ GREEK MINING DISTRICT 457

ver-bearing mineral. The sheared rock in and closely associated 

with the lodes is a dark-colored chlorite schist that microscopic study 

proves to be altered igneous rock differing only in degree of alteration from the country rock, which here is a stock with the composition of granodiorite and which shows hydrothermal alteration in all 

outcrops, even at a distance from known veins. The sheared rock 

adjacent to the quartz veins contains sulphides and gold. Locally 

lenses of quartz and bands and irregular bunches of massive sulphides 

occur in the sheared material, thus adding considerably to the width 

of possible ore bodies. The individual quartz veins are rarely much 

over a foot wide, but mineralized shear zones are locally 5 to 10 

feet wide.

VEINS CONTAINING CAL.CITE

Some of the quartz veins differ from the rest in that they contain 

abundant calcite. Most of the known lodes of this type are on Gold 

Hill between Lucky Gulch and White Creek. (See p. 463.) At the 

time of the writer's visit little work had been done on the lode prospects for a long time; most of the cuts were so slumped as to conceal 

bedrock, and the only good exposure noted was at the Wickersham 

placer mine, on White Creek (pp. 453-454). Similar veins have been 

staked along Surprise Creek near Eoosevelt Lake but are undeveloped. The calcite-bearing veins are in part, like those of the Timberline prospects, enclosed in somewhat altered dioritic ro k, but 

they also occur in the somewhat schistose argillaceous strata adjacent to the intrusions. Shearing in the country rock is not as conspicuous as in the Timberline prospects. Development is so scanty 

that data regarding the mineralogy of the lodes must be gleaned in 

part from the constituents of placer concentrates from White Creek 

and Lucky Gulch, undoubtedly derived from nearby lodes. The 

proportion of calcite varies widely. Locally, it makes up more than 

half the vein matter. It is, in part at least, of earlier origin than 

the quartz. Most of the carbonate is colored yellow by a content 

of iron, but its indices of refraction are but little higher than those 

of pure calcite. Some of it approaches ankerite in composition. 

The vein walls and fractures in the wall rocks are lined with brilliant green chlorite. The hypogene metallic minerals that have 

been recognized either in the lodes or in related placers included 

native gold, arsenopyrite, pyrite, galena, sphalerite, pyrrhotite, and 

hessite. Of these arsenopyrite is by far the most abundant. Pyrite 

is generally present, but the other minerals listed are of sporadic 

occurrence. The coarseness and crystalline character of much of 

the gold from both White Creek and Lucky Gulch suggest that 

rich pockets may exist in the lodes. Possibly the fact that hessite,
458 INVESTIGATIONS IN ALASKA RAILBOAD BELT, 1931

which is abundant in pannings from White Creek, has not been 

recognized in bedrock exposures is in part due to its concentration in small pockets or kidneys. Such local concentration of tellurides and native gold is common in numerous mining districts.

PYBITIC REPLACEMENT DEPOSITS

Much of the hydrothermally altered rock in the area contains 

small amounts of disseminated pyrite. East of Clearwater Creek 

and also at Kusty Hill, north of Denali, such material is so abundant 

as to give a rusty color to large masses of rock through oxidation. 

In these areas most of the more thoroughly rusty rock is nearly 

white on fresh fractures because of the bleaching of the original 

dark constituents. It contains much introduced quartz, both in 

distinct veins along fractures and permeating trie rock. Some of the 

material thus altered is greenstone, some is limestone, and some is 

schist. In a few places individual quartz veins are as much as a 

foot wide, but most are veinlets that are characteristically irregular^ 

except where locally controlled by foliation in the schist. Both the 

vein quartz and the associated altered rock contain disseminated 

pyrite with local pyrrhotite and chalcopyrite. Small amounts of 

gold and silver are present. Mineralization of this character has 

affected large masses of rock in this region, but, so far as present 

information goes, it does not appear to have been intense enough 

anywhere within the area mapped to produce commercial ore. 

Rusty outcrops are widespread over many square miles, extending 

far to the northeast beyond the limits of the present study, and 

may somewhere include a mass of more thoroughly mineralized 

material.

ORIGIN

Among the mineral deposits of the area the resemblances are morestriking than the differences. It is clear that all are related and arethe results of dominantly hydrothermal processes that followed 

closely the intrusion of the dioritic rocks. The major effects of theseprocesses were confined to the dioritic masses and their immediate' 

vicinity. The smallest of the dioritic masses as now exposed show,, 

in general, the greatest hydrothermal alteration, suggesting concentration of the solutions in.the apophyses of the stocks. In the Timberline prospects, at least, the lodes occur in zones of relatively 

intense metamorphism; it may be, therefore, that some of the veins, 

close to these small, inconspicuous dioritic bodies may prove valuable.

Although deposition of the metallic ores is thus related to theintrusion and metamorphism that have affected the region as a*. 

whole, it must be realized that the process was complicated, being-
VALDEZ CREEK MINING DISTRICT 459

made up of many steps, and required much time. Gold is probably 

present to some degree even in the small quartz lenses so widely 

distributed as a result of regional metamorphism. The region owes 

its valuable placer deposits largely to this fact, but additional steps 

in the general process were required to effect any considerable concentration of the metals. One such step was the production of shear 

zones subsequent to the consolidation of the outer portions of the 

stocks but while the hydrothermal solutions were still in circulation. 

These are doubtless later and of far more restricted distribution 

than the joints in which the minor lenses consolidated. Individually, 

however, they are much larger and provide room for ore bodies of 

commercial size. Deposition, even in a single fissure, was by no 

means instantaneous. Much of the sulphide material consolidated 

prior to part of the quartz and calcite, and much of the native gold 

is later than any of these. Possibly some of the gold is of supergene

origin, but most of it is clearly hypogene and doubtless was formed 

here, as in a number of other districts, in one of the last stages of 

the original mineralization. The meager amount of unoxidized vein 

matter available renders it impossible to determine the history of 

mineral formation with any completeness. 

\ SUGGESTIONS FOR DEVELOPMENT

The development work accomplished has shown conclusively that 

auriferous gravel exists in large quantities along Valdez Creek and 

that under favorable conditions it can be worked at a profit. The 

termination of company operation, however, suggests that care must 

be exercised to avoid too costly methods. A great deal of gravel 

remains untouched, and there is proof that parts of it contain considerable gold. Auriferous quartz veins are so widely distributed, 

even though many are individually small, that probably all the gravel 

deposits contain auriferous portions. Though it would require an 

extensive and costly campaign of testing to determine whether the 

distribution and grade of such auriferous material would justify 

large-scale operation, shafts could be sunk to bedrock at selected 

places, thus furnishing information at relatively small cost on which 

to base judgment as to the wisdom of more comprehensive tests. It 

is suggested that a few such shafts on the benches near Denali, on 

upper Valdez Creek, and perhaps also along Clearwater Creek might 

lend sufficient encouragement to interest capital.

The placer deposits of Lucky Gulch and similar places are too 

small and irregular to be of value for extensive operation, although 

locally such deposits may prove profitable to a few men. Deposits 

of this kind show, however, that auriferous lodes exist in the imme-'
460 INVESTIGATIONS IN ALASKA RAILROAD BELT, 1931

diate vicinity. Furthermore, the nuggets that have been occasionally found along Lucky Gulch and the hessite in the gravel of White 

Creek indicate the probability that rich pockets are present in some 

of these lodes. Possibly systematic " pocket hunting" would be 

rewarded.

Most of the many quartz veins in the area are of no commercial 

interest. Those which have been shown to contain notable amounts 

of gold are quartz lenses in sheared country rock, commonly altered 

quartz diorite or argillite adjacent to such a dioritic body. It is probable that in this region movement sufficient to produce such shear 

zones is a necessary factor in the complicated process of forming 

valuable lodes. Hence it would be well for prospectors to watch 

for such shearing. Some of the lodes contain ferruginous calcite, 

which weathers rather easily, forming soft ocherous masses in which 

the characteristic carbonate cleavage can generally be discerned 

in places where the weathering is incomplete. Probably all such 

lodes contain some gold and are worthy of attention from prospectors. Though the precious-metal content is not proportionate 

to the amount of sulphide, rusty outcrops and other evidence of the 

presence of sulphides at depth are to be regarded as favorable indications. So far as present data go, none of the quartz lodes contain 

sufficient of any of the base metals to be of commercial value, though 

some may contain enough arsenic to be valuable as a byproduct 

under favorable market conditions. The present scanty development prohibits anything but rough quantitative estimates of tonnage 

and grade of ore, but it seems probable that the area contains 

several hundred thousand tons of mineralized material whose 

precious-metal content may be between $5 and $20 to the ton, with 

some relatively small high-grade bodies, Operation of the lodes

will probably be deferred until better transportation facilities are 

available, though possibly the construction of those facilities will 

receive the greatest impetus through further development of the 

placer deposits.

There is abundant evidence of mineralization in the rusty schist 

and limestone along Clearwater Creek, but in the small part of the 

area visited its effects are spread so widely through the rocks as to be 

worthless. The possibility that local conditions may have permitted 

concentration into workable ore bodies is sufficiently strong to justify 

careful prospecting in this part of the area. The principal bodies 

will presumably be those formed by pyritic impregnation and containing copper and gold. Such ore is likely to be of low grade but 

to occur in large masses. There are also quartz veins in this locality, some of which may prove to contain valuable shoots of gold ore.
VALDEZ CEEEK MINING DISTRICT

PROSPECTS

TIMBEBLINE

461

On the hill between Timberline and Valdez Creeks there is a group 

of lode claims held by Lawrence Coffield, Clark Duff, and J. M. Olsen 

and called the Timberline prospects. They are developed by several 

pits, a few of which are more than 10 feet deep. This development 

constitutes the greatest amount of underground work on lode deposits 

anywhere in the area.

The principal lodes are marked on the surface by long natural 

hollows resembling shallow trenches, which aided the prospectors in

FIGURE -06. Sketch, map of the lodes on the Timberline prospects. By C. P. Ross and

J. M. Olsen.

their search. The vein system, as indicated in figure 56, includes 

2 long, roughly parallel veins known as the Big Caribou and Little 

Caribou veins and 3 short segments which may be individual veins 

or else parts of a single vein that was originally parallel to the first 

two but is now displaced by faults.

The Big Caribou vein has been traced for fully 1,000 feet and 

doubtless extends farther. Its trend is somewhat curved but averages about N. 80° W., and its dip is steep to the north. The westernmost of the cuts on this vein shown in figure 56 is the largest and the 

only one recently cleared out. It is the one in which the samples 

listed on page 463 were obtained. This cut exposes a lode 8 feet wide 

consisting of sheared and chloritized diorite with disseminated pyrite
462 INVESTIGATIONS IN ALASKA BAILROAD BELT, 1931

and other sulphides and with quartz kidneys and lenses containing 

arsenopyrite, pyrite, pyrrhotite, and a little chalcopyrite. A solid 

band of white vein quartz 2 feet wide occupies the footwall side of 

the lode. On the basis of its known extent and on the assumption 

that it persists downward at least 100 feet this lode is estimated to 

contain fully 100,000 tons.

The Little Caribou vein is developed only by small cuts, all so 

badly slumped that no sampling could be done at the time of the 

writer's visit. It trends about N. 65 E., has a width of several feet, 

and is surely 200 feet long and probably much longer.

The Big Water Hole or Valdez Creek no. 5 vein is definitely exposed only in two pits close together, but float suggests that it 

extends some distance to the east. It strikes east and dips steeply 

north. The pits show sheared and much altered diorite with quartz 

lenses. Both the altered rock and the quartz contain sulphides. 

The more easterly of the two pits was cleaned out by Lawrence 

Coffield and sampled by the writer. The sheared material of the lode 

here is 1 feet wide.

Shallow cuts near the crest of the ridge expose two vein segments. 

One known as the Freda G strikes about N. 75° E., dips 83°-90° SE., 

and consists of a little more than 1 foot of massive white quartz 

enclosed in somewhat sheared diorite. The lower of the two cuts 

shown on plate 56 was sampled here. The other vein segment, 

known as Valdez Creek no. 6, strikes about east, dips 70° N., and 

consists of 2 feet of quartz. The lower cut was sampled 'here also.

The table below gives the results of assay of samples taken recently 

by Lawrence Coffield, one of the owners, and those obtained from 

samples taken by the writer. ' Samples taken at different times by 

the owners are reported to vary widely, and it is evident that here,

as in many other gold lodes, numerous samples systematically taken 

are needed in order to arrive at a reliable approximation to the 

average content of precious metal. There is visible gold in a number of the pieces of quartz on the dumps of the prospect pits, but 

evidently such material did not happen to get into the writer's 

samples.

Assays from Timberlvrve prospects 

[By Paul Hopkins, U.S. Bureau of Mines, Fairbanks, Alaska]

Source

Samples taken by Lawrence Coffield:

Freda G... __ ................ ___ . __ . __ . __ ... __ ..

Valdez Creek no. 6 _________ . __ 

Gold 

(ounces to 

the ton)

0.58

3.96

.68

.40

.24

Silver 

(ounces to 

the ton)

0.10

.80

.20

.10

.10

Value «

$11. 63

79.44

13.66

8.03

4.83

Gold at $20 an ounce, silver at 30 cents an ounce.
VALDEZ CKEEK MINING DISTEICT 

Assays from Timberline prospects Continued

463

Source

 Samples taken by C. P. Ross:

Big Caribou:

Freda G... ....... ..............................................

Valdez Creek no. 5:

Gold

(ounces to

the ton)

Trace

0.33

.06

na

Trace

Silver

(ounces to

the ton)

Trace

0.20

.20

.20

Trace

Value

$6.66

1.26

1.66

None

GOLD HILL

There has been desultory prospecting for lodes on Gold Hill, but 

 development has not progressed beyond the digging of shallow 

pits, many of which never penetrated the talus cover and all 

of which were slumped at the time of visit. The Wickersham 

brothers and Lawrence Coffield have been the principal prospectors 

on this hill in recent years. The fragments of lode matter and a few 

bedrock exposures in the pits indicate the presence of several veins 

but give little information as to their size or trend. Presumably the 

exposure in the Wickersham placer cut described on pages 453-454 is 

more or less typical of occurrences here, although some of the quartz 

.lenses are wider and some contain more carbonate and sulphides than 

.are visible at this place. This is the only locality where a dark, 

presumably lamprophyric dike is exposed in juxtaposition with 

a lode.

Some gold has been produced by panning and rocking detritus 

from a pit on the Yellowhorn claim, near the center of the northern 

slope of Gold Hill. Bedrock has not been reached here, but con- 

.siderable rusty quartz is mixed with the slate fragments. Moffit 28 

notes that at the time of his visit bedrock was exposed in the Accident claim on the same slope as the Yellowhorn and somewhat east 

of it. The country rock here contained considerable pyrite, and 

some rusty vein quartz containing sphalerite and galena was also 

exposed. Fine gold was found in the decomposed vein matter. 

.About 300 or 400 feet above the Accident ledge and in the same steep 

gulch a little stream of water was running down over angular wash 

made up of slate and rusty quartz. A rocker had been set up at this 

point, and good prospects were obtained from the gravel.

SMALL PROSPECTS NEAR VALDEZ CREEK

Shallow holes have been dug on quartz leads in schist at several 

places on the north side of Valdez Creek, especially near the mouth

28 Mofflt, P. H., op. cit. (Bull. 498), p. 57.
464 INVESTIGATIONS IN ALASKA RAILEOAD BELT, 1931

of White Creek. Some gold is reported to have been found, but the 

quantity was insufficient to encourage further work. Quartz lodes 

in both schist and slate on Surprise Creek have been similarly prospected and promptly abandoned. One of the veins in slate was 

sampled by the writer, but this sample yielded only traces of gold 

and silver.

The granodiorite mass at the head of Pass Creek contains some 

small quartz veins in sheared and mineralized rock. A sample from 

one of these veins yielded on assay 0.06 ounce of gold and 0.20 ounce 

of silver to the ton. Iron stains and other evidence of mineralization are so common in the granodiorite here that further prospecting 

might well be rewarded.

RUSTY HILL

At one place in the schist on the north side of Valdez Creek about 

2 miles from Denali oxidized iron sulphide is so plentiful as to give 

the rock a decidedly rusty appearance. This material forms the 

small eminence which has been named Kusty Hill. The rock here 

was originally lithologically identical with the main mass of schist 

to the east, although discordance in altitude indicates structural disturbance. It contains numerous quartz veinlets injected along the 

schistosity and merging into the adjacent rock. Both the vein quartz 

and the schist contain small amounts of disseminated pyrite and 

pyrrhotite. A sample of the more thoroughly mineralized rock from 

this locality yielded on assay 0.01 ounce of gold and a like amount 

of silver to the ton. Clark Duff and Lawrence Coffield, who have 

prospected here, report similar results. As Rusty Hill is about 2,000 

feet in diameter and 250 feet high, the rock containing disseminated 

pyrite must exceed 250,000 tons, but the grade appears to be much, 

too low for profitable mining.

MINERALIZATION EAST OF CLEARWATER CREEK

The limestone and schist north of Coal Creek are everywherestained with iron. In several places there are spring deposits composed of limonitic and calcareous tufa cementing angular rock fragments. Along the main gulch in the limestone belt several small 

springs stain the rock at their orifices a bright, rusty red. In a few 

places here and also in the metamorphosed lava on the north side of 

Coal Creek finely disseminated pyrite is visible in the rock, and this 

mineral is probably the source of much of the limonitic material. In 

several places, especially in the lava, small amounts of malachite 

and chrysocolla impregnate the rock and coat seams. In some of these 

places pyrite and quartz have replaced the rock. The oxidized cop-
VALDEZ CREEK MINING DISTRICT 465

per minerals show that the pyritic replacement deposits have copper 

minerals associated with them, but at no place seen during the 

present study was copper present in commercial quantity. The lava, 

limestone, and schist on the north of Coal Creek have unquestionably 

been subjected to the action of mineralizing solutions doubtless related to the dioritic intrusions of the vicinity. These solutions have 

altered the rocks over so wide an area that it seems quite possible that 

somewhere in this vicinity mineralization has been sufficiently intense 

to deposit enough copper, gold, or other metals to be of commercial 

interest. Rusty outcrops extend for many miles on the east side of 

Clearwater Creek, far to the north of the area reached during the 

present study. The area of rusty rocks is recommended to prospectors interested in the discovery of metallic lodes.

COAL

The coal in the valley of Coal Creek, east of Clearwater Creek, 

would be of commercial interest only if mining or some other industry requiring power were started in the immediate vicinity, as it 

obviously cannot compete with the large quantities of similar coal 

more favorably situated with respect to transportation. Coal is at 

present exposed at only one point in the south bank of the creek, but 

chips on the hillside above prove the presence of other beds. The 

outcrop shows a nearly vertical but contorted and broken bed 10 to 

12 feet thick, with several small lenses of bone in it. The bed narrows upward, and at the top of the 50-foot bank it is only about 3 

feet wide.

The coal was picked away to a depth of nearly 3 feet, and a sample 

was taken across a band about 3 feet wide representative of the better 

and less crushed coal. The analysis of this sample is given below. 

Small quantities of the coal from this place have been taken at 

various times to placer mines along Valdez Creek for use in blacksmith forges. That in use at Denali in the summer of 1931 had lain 

exposed to the weather for several years but was reported to give 

satisfactory service. Though all the coal obtainable from the present exposure is much fractured, it does not appear to crumble or 

discolor greatly on weathering. As originally obtained it is shiny 

black and breaks into sharply angular, nonplaty fragments. These 

facts coupled with the results of the analysis suggest that fresh 

material from a short distance below the surface would be found to 

be low-rank bituminous coal.29

20 Campbell, M. R., The coal fields of the United States: U.S. Geol. Survey Prof. 

Paper 100, pp. 3-7, 1922.
466 INVESTIGATIONS IN ALASKA BAILEOAD BELT, 1931

Analysis of coal from Coal Greek, a tributary of Clearwater Creek, in the

Susitna Basin, Alaska

[Sample taken July 2,1931, by Clyde P. Ross and Marion Peel. Analysis Oct. 17,1931, by H. M. Cooper, 

U.S. Bureau of Mines. Air-drying loss 6.7 percent]

Ash................................................................

Sulphur.... _ ... ___________________________

Calorific value:

As received

14.1

40.3

37.1

8.5

100.0 

.3

5,556

10, 000

Moisture 

free

46.9

43.2

9.9

100.0 

.3

6,467

11, 640

Moisture 

and ash 

free

52.0

48.0

100.0 

.3

7,183

12, 930

Softening temperature of ash, 2,600° F.
INDEX

Page

Abstract of report--_ __ _ 425 

Accessibility of the district_____ 426 

Argillite, age of_____________ 436 

occurrence and character of_435-436 

Assays of ores__________ 462-463, 464

Big Caribou vein ________ 461-462 

Big Rusty Creek, placer workings on_ 453 

Big Water Hole vein__ _____ 462

Calcite-bearing veins, occurrence and

character of____ 457-458 

Clearwater Creek, features of drainage basin of____ 448 

limestone lenses between, and

Susitna River____ 430-431

mineralization east of____ 464-465

Coal, analysis of__________ 466

occurrence of, on Coal Creek. 465-466

Coal Creek, limestone beds in valley

of____________ 431 

limestone mass north of___ 431-432 

Conglomerate, tuffaceous, occurrence

and character of__ 432-433 

Cooper, H. M., analysis of coal by 466

Denali, buried channels near___ 446-447 

placer deposits at_______ 449-453 

Dikes, occurrence and character of 441 

Diorite and dioritic rocks, occurrence

and character of_ 440-441

Eldorado Creek, prospecting on 455

Faulting____ ________ 443-444 

Field work________________ 425-426 

Folding__________ ______ 442-443 

Folk claim, placer workings on__ 451 453 

Foreword, by Philip S. Smith__ v-viii 

Freda G vein_____________ 462

Geologic map of the district__ pi. 84

Gold Hill, prospecting for lodes on 463

Greenstone, age of--____ _ 429-430

occurrence and character of 429

Hessite, occurrence of_______ 454 

Hopkins, Paul, assays by ____ 462-463

Intrusive rocks, age of--_ ___ 442 

occurrence and character of 440-441

Page 

Lava flows, basaltic, occurrence and

character of- 433

Limestone, age of________ _ 431, 432

occurrence and character of 430-432

Little Caribou vein_________ 461, 462

Little Rusty Creek, placer workings

on ____________ 453

Location of the district__ 426

Lode deposits, classification of 455

origin of _____ 458-459

suggestions for development

of ___________ 459-460 

Lucky Gulch, placer workings on__ 454-455

Mining, history of_________ 427-428 

Mofflt, F. H., quoted______ 455 

Monahan Channel. See Tammany 

Channel.

Petrology__ ___ 428-442 

Placers, relation of, to geomorphology________ 444-448 

Placer claims, map showing_ _ pi. 35

Quartz diorite, gneissic, occurrence

and character of 440

Quartz veins, occurrence and character of____ __ 455-457

Quaternary deposits, occurrence and

character of-____ 439

Replacement deposits, pyritic, occurrence and character of_ 458 

Roosevelt, features of valley of^__ 448 

prospecting on 455 

Rusty Creek, placer workings on__ 453 

Rusty Hill, prospecting on__ __ 464

Schist near Valdez Creek, age of___ 438 

occurrence and character of- 437 438 

Schist, rusty, age, occurrence, and

character of __ 435 

Stratigraphy_______________ 428-442 

Structure________________ 442-444 

Surprise Creek, prospecting on __ 455 

Susitna River, limestone lenses between Clearwater Creek 

and _______ 430-431

Tammany Channel, placer workings

in ____________ 449-451 

trend of - _ _ __ _ 446

467
468 1^ UKX

Page

Tertiary (Eocene?) etrata, occurrence and character 

of_______ ______ 438-439

Timber. __ _ 427 

Tlmberline Creek, ground sluicing at

mouth of________ 455

placer prospects on tributaries

of____ __________ 453

Timberline prospects, assays of ore

from_________ 462-463 

development of 461-462

Page

Topography. _ ___ _ 426-427

Tuffaceous strata, age of _ 434

occurrence and character of 432 434

Valde,z Creek, bars of, at Denali 449 

prospecting on middle portion

of __ 455 

small lode prospects near 463-464

Valdez Creek nos. 5 and 6 veins 462

White Creek, placer workings on_ 453 454

o