DEPARTMENT OF THE INTERIOR

FRANKLIN K. LANE, Secretary

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, Director

Bulletin 699

THE PORCUPINE GOLD PLACER DISTRICT

ALASKA

BY

HENRY M. EAKTN

WASHINGTON

GOVERNMENT PRINTING OFFICE

«> 1919

CONTENTS.

Page.

Introduction___________________________________ _ 5

Geography___ ____ ____..___________ _ 5

Location and extent_________________________ 5

Topography_____,_________________________ '__ 6

Climate___________________________________ 7

Forests________________________________._,_- 7

Water supply _ ______ _ _ 8

Population __ _ __ __ __________________ 8

Communication ____________ __ _____________..__ 8

General geology __ ___ ___________ ____ _ 9

Character of the rocks___________________________ 9

Sedimentary rocks _ ___________ 9

Igneous rocks _ __ ___ 12

Igneous metamorphism_______ __________________ 13

Mineralization ___ ______ ______.______________ 13

Quaternary deposits ___ 15

Economic geology 18

Extent and character of the mineral deposits_____________ 18

Gold placers_ _ __________ 19

General features __ ___ _ _____ 19

Formation__________________ ____________ 20

Mining methods _ ___ _______ _ 21

History of development _ _ 23

Summary of mining in 1916_______________________ 25

Prospecting in adjacent districtsi_____________________ 26

Rainy Hollow district ______________.______._______ 26

Region east of Chilkat Valley__________________._. 26

 Geology- . 26

Veins and mineralization____________________ 26

Iron-ore deposits near Haines ______ _ 27

3
ILLUSTRATIONS.

Page. 

PLATE I. Geologic reconnaissance map, Porcupine district, Alaska____ 6

II. Map of part of southeastern Alaska showing location of Porcupine district_____________ _____________ 8

III. A, Glaciated mountains at the head of McKinley Creek, McKinley Creek canyon in middle ground; B, Spruce and hemlock 

forest near Pleasant Camp____ ________ _ _ 10

IV. CA, Klehini River at evening high water, a few miles above Pleasant Camp; B, Thin-bedded limestones and slates, Porcupine 

Creek __________ _______ _____ _ __ 11

V. A, Upper end of abondoned canyon of McKinley Creek; B, 

Lower end of same abandoned canyon showing glacial till 

exposed by placer workings_ _ _ __ 20

VI. A, Cable tramway formerly used in stacking boulders, Porcupine 

Creek; B, Crane hoist stacking boulders behind cribbing at 

sides of sluice box on McKinley Creek bench placer 21

VII. A, Diverting flume, Porcupine Creek; B, Worked-out section of

modern McKinley Creek canyon__________________ 22

VIII. A, Flume and spillway, Glacier Creek dam; B, Detail of

Glacier Creek flume, showing use of riffle blocks________ 23 

4
THE PORCUPINE GOLD PLACEE DISTRICT, ALASKA,

By HENRY M. EAKIN.

INTRODUCTION.

The Porcupine gold placer district includes the drainage basins 

of the westerly headwater tributaries of Chilkat River, which enters 

Chilkat Inlet, an arm of Lynn Canal, near Haines, a small town 

about 75 miles northwest of Juneau. Gold was first discovered inthis area in 1898. Productive mining was begun the following year 

and has been continued to the present time with such success that 

the district has ranked with the most important placer fields "of 

southeastern Alaska.

The region was first visited by a geologist of the United States 

Geological Survey in 1899, when an exploratory expedition on the 

way from Pyramid River to Eagle followed the old Dalton trail 

up Chilkat River and past the then newly discovered placers on 

Porcupine Creek.1 In 1903 C. W. Wright made a more extended 

study of the region and outlined the principal features of its geology 

and mineral deposits.2

The writer visited the district early in the summer of 1916, spending two weeks in the examination of properties then under development and in the study of bedrock and glacial geology related to 

the formation of the placer deposits.

The writer is indebted to the residents of the district, who extended 

generous hospitality during his stay and facilitated his work in 

every possible way. Acknowledgment is also due the earlier investigators, whose published papers have been drawn upon in assembling 

the data of this report.

GEOGRAPHY.

i

LOCATION AND EXTENT.

The general position of the Porcupine placer district in relation to 

the geographic features of southeastern Alaska is shown on Plate II.

1 Brooks, A. H., A reconnaissance from Pyramid Harbor to Eagle City, Alaska : U. S. 

Geol. Survey Twenty-first Ann. Kept., pt. 2, pp. 374-376, 1900.

2 Wright, C. W., The Porcupine placer district, Alaska: U. S. Geol. Survey Bull. 23G, 

1904.

5
6 . PORCUPINE GOLD PLACER DISTRICT, ALASKA.

The accompanying geologic reconnaissance map (PI. I) shows this 

district and some additional territory, covering an area about 25 

miles square which centers near latitude 59° 25' N. and longitude 

136° 10' W. The principal belt of mineralization that has produced 

placer deposits runs northwestward across the area shown on the 

map a little below its center. A secondary area of mineralization 

occurs in the vicinity of Bear Creek in the northeastern part of the 

region mapped.

TOPOGRAPHY.

The district is drained by four westerly headwater tributaries 

of Chilkat River, which flows into an arm of Lynn Canal, 40 

miles southeast of the main placer area. These streams, named 

iii order from north to south, are Bear Creek and Klehini, Salmon, 

and Takhin rivers. 'Of these the Klehini is much the largest, and 

its basin contains the most productive placers. All these streams 

flow through broad, glaciated valleys floored with thick deposits of 

gravel and boulders. Their grades are steep, and their swiftflowing waters are generally divided among numerous shallow shifting channels. These features are due to the presence of glaciers of 

considerable size on most of their headwaters. The topography of 

the district is typical of the coastal mountain province of southeastern Alaska in its strong relief and glacially developed features. 

(See PL III, A.) Summit elevations along the principal divides 

generally range between 3,000 and 5,000 feet, but individual peaks 

rise 6,000 to 7,500 feet above sea level. The topography has a 

smoothed aspect up to an altitude of about 3,000 feet, marking the 

level reached by ice during earlier periods of glaciation. Above 

this level more rugged forms abound, culminating in the serrate 

ridges and peaks of the high divides. The valley heads throughout 

the district have the form of glacial cirques. These occur at great 

elevations in the main divides, and the valleys leading from them 

do not descend with an even slope but in a series of steps, causing 

an alternation of falls or cascades and relatively sluggish reaches 

in the streams that drain them. The amount of glacial scour has 

varied with the size of the valleys, and the bottoms of main valleys 

are generally much below those of their tributaries. Streams draining these hanging valleys have generally intrenched themselves, producing an interesting series of canyons, and have built alluvial fans 

out into the valleys which they join.

Features formed directly by deposition from the ice are almost 

entirely absent except in the immediate vicinity of the present 

glaciers. There is a little morainic topography along the north side 

of the upper Klehini Valley, and there are some high terraces along 

the south side of the same valley that may in part be lateral moraines.
I 1 S. IDEOLOGICAL SURVEY BULLETIN 699 PLATE 1

Base from map by International 

Boundary Commission Scale I : 250,000

10 Miles

Geology by C. W. Wright, 1904 

and H. M. Eakin, 1916

EXPLANATION

Stream gravels

Including glacial deposits

Gold placers

Dlorlte

Shale and limestone 

{ Carboniferous)

Metalliferous prospect

GEOLOGIC RECONNAISSANCE MAP OF PORCUPINE DISTRICT, ALASKA
GEOGRAPHY. 7 

CLIMATE.

The climate of the Porcupine district is intermediate in general 

character between that of the excessively humid, equable climate 

of the coastal provinces, where the full influence of the Japan current 

is felt, and that of the interior of Alaska, where relative aridity and 

great seasonal variations in temperature prevail. The winters are 

long and fairly cold. Heavy snows may occur as early as October 

and as late as April, and its accumulation may reach a depth, of 10 

or 15 feet in the valleys and much more in the uplands. The line of 

perpetual snow is about 15,OQO feet above the sea, but snow banks in 

protected situations at much lower elevations may persist for the 

greater part of the summer. The summers are shorter than the 

winters, but they are for the most part warm and sunny. As the 

region is sheltered behind the great ice fields of the St. Elias Range 

the southerly and westerly winds that bring the summer rains to 

most of southeastern Alaska give fair weather in the Porcupine 

region. The weather in the valleys during the writer's visit in the 

later part of June was frequently uncomfortably hot. The season 

available for placer operations is much longer than in interior 

Alaska, as it extends from early May to late October.

The climate of the district" favors agriculture to an unusual degree 

in comparison with other sections of southeastern Alaska. Where 

the soil is favorable at low elevations practically all the common 

vegetables, small fruits, and cereals are grown successfully, and the 

gardens of Haines and the Chilkat Valley are justly celebrated for 

the abundance and fine quality of their strawberries.

FOBESTS.

The slopes of the region up to an altitude of 2,000 or 2,500 feet are 

generally covered with a dense forest, mainly of spruce and hemlock 

but with a few cedars and pines in places. The valley bottoms near 

the streams support an abundant growth of cottonwood which intermingles with the conifers toward the bordering slopes. The trees 

are generally of large size, suitable for lumber, and the supply 

far exceeds any possible demand of the local mining industry. (See 

PL III, B.) Large tracts of timber in the Klehini Valley in Canadian territory are held for future development for lumbering.

The hemlock is especially adapted for piles and also makes a good 

grade of lumber. The spruce meets with favor for flume and sluicebox lumber, and the cottonwood is preferred for riffle blocks owing 

to its tough fiber.

In most places the forests have a -dense undergrowth of alder, 

" devil's-club," blueberry, fern, and other plants, which, by concealing the bedrock and making walking difficult, hinders geologic study 

and bedrock prospecting. x
8 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

WATER SUPPLY.

The snow fields and glaciers of the high divides furnish an 

abundant water supply in all the streams throughout the summer. 

In fact, the chief difficulty encountered in mining has been that of 

handling the copious discharge of the glacial streams during the 

warm summer days, and the repeated failures of diverting flumes has 

detracted much from the profit of operations. The strong relief of 

the region and the steep grades of the streams permit water power 

and hydraulic systems to be developed at an unusually small outlay.

The streams are generally low during May and June, October and 

November, and the high-water season intervenes between these spring 

and fall periods. In winter the streams freeze over and are covered 

with snow, but flowage beneath the ice. is continuous. In summer 

there is a great daily variation in discharge in the glacial streams, 

with low water in the morning and high water in the evening. 

(See PL IV, A.)

POPULATION.

The population of the district is made up almost exclusively of the 

forces engaged in placer mining. Therefore it varies greatly in number with the seasons and from year to year. During the summer of 

1916 an average of about 60 persons were within the district. The 

principal settlement is Porcupine, near the mouth of Porcupine 

Creek. At the international boundary on Klehini River near the 

mouth of Jarvis Creek is the abandoned post of the Northwest 

Mounted Police, known as Pleasant Camp. In winter, when mining 

operations are at a standstill, almost everyone leaves: for the settlements on the lower Chilkat or elsewhere. The principal permanent 

settlements of the region are Klukwan, a native village near the 

mouth of Klehini River, and Haines, an important town at the base 

of Chilkat Peninsula. In addition there are a score or more of permanent homes on the ranches of Chilkat Valley between Haines and 

Klukwan.

COMMUNICATION.

Haines is on an arm of Lynn Canal and is a port of call for many 

of the boats plying the inside passage to and from Skagway. Mail 

service is thus maintained throughout the year. The service of the 

Government cable also is available at Haines. From Haines .to Klukwan and thence to Porcupine there is a Government wagon road that 

is generally open for traffic. In 1916 it was available for automobiles 

as far as Klukwan. Beyond this point jt runs partly over lowlands 

and along gravel bars of Klehini River that are subject to overflow 

at high stages of the river. However, horse-drawn vehicles use it
U. 8. GEOLOGICAL SURVEY BULLETIN 699 PLATE II

13630 20' 136 40'1 2O'

30

lOMHes

MAP OF PART OF SOUTHEASTERN ALASKA, SHOWING LOCATION OF PORCUPINE DISTRICT.
GENERAL GEOLOGY. 9

throughout the summer, regardless of the height of the water. The 

road has played an important part in the development of the district 

by permitting the haulage of the heavy equipment of the hydraulic 

plants and by lowering the cost of supplies.

^ GENERAL GEOLOGY.

CHARACTER OF THE ROCKS.

The solid rocks of the district consist mainly of altered sedimentary 

types and include limestones, slates, phyllites, and coarse clastic 

rocks. Silicification of the limestone has produced quartzitic rocks 

locally, and in a few places excessive alteration of the clastic rocks 

has given them the character of schists.

The general area of sedimentary rocks is bordered on the northeast by the great diorite belt of the Coast Kange, and outlying masses 

of diorite are intruded into the sedimentary rocks for some distance 

southwest of the principal contact. Small diabase dikes also intrude the bedded rocks locally. A narrow band of greenstone schist 

that is probably of igneous origin, associated with black slates, was 

noted by Wright 1 at a single locality on the north bank of Klehini 

River.

The general distribution of the sedimentary rocks and dioritic intrusives is shown on the accompanying geologic reconnaissance map 

(PI. I), which is reproduced with minor corrections from a map 

drawn by Wright.2

Unconsolidated deposits mantle much of the region below an altitude of 3,000 feet. They include gravels laid down by the streams 

in the present cycle of erosion, outwash gravels above the present 

stream levels, and morainic materials that are distributed in erratic 

fashion up to the highest levels reached by glaciers during their 

maximum development. Only the general distribution of present 

stream gravels and terrace deposits is indicated on the map (PL II).

SEDIMENTARY ROCKS.

The sedimentary rocks are mainly limestones and slates and "their 

metamorphic equivalents. Thin sandstone beds and fine conglomerates occur in the slates at one locality.

The limestones and slates, are in places clearly interbedded and of 

like age. Elsewhere limestone beds occupy considerable areas without associated slates, and some areas of slate are devoid of limestone 

beds. Massive limestone beds occur in a broad band along the south'

1 Wright, C. W., The Porcupine placer district, Alaska: U. S. Geol. Survey Bull. 236, 

p. 17, 1904.

2 Idem, pi. 5.

131077° 19 2
10 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

margin of the Klehini Valley, forming the walls of Porcupine and 

Glacier Creek canyons at their lower extremities. In line with this 

band a large area in the mountains north of Jarvis Glacier is occupied by similar beds. For several miles up the Klehini Valley above 

Jarvis Creek only limestone outcrops were found, although in places 

sections several hundred feet thick are exposed. These rocks, where 

least altered, are light gray in color, are locally fossiliferous, and 

show a fairly regular thick-bedded structure. In places, .as just 

east of Porcupine Creek and where the road going eastward from 

Porcupine leaves the Klehini bottom lands, silicification has occurred, producing quartzitic rocks that resemble the limestones in 

texture and color. On Glacier Creek and in the Klehini Valley the 

limestones are largely recrystallized, producing a light-colored compact marble.

Where limestone and slate are interbedded, as on Porcupine 

Creek above the marble canyon, the whole series is dark and both 

limestone and slate have a thin-bedded,'platy structure (PI. IV, B). 

A graduation in composition is evident, the limestones grading into 

calcareous slates and these into more purely siliceous beds. Graphitic 

material is present in all the beds, and in some of the slates it is very 

abundant, giving them a coal-black color and a soft, friable texture.

Thin beds of limestone and calcareous slates were noted also on the 

upper Porcupine, near the mouth of McKinley Creek, and in the road 

a few miles east of Porcupine. It would appear that there is among 

the sedimentary groups an important assemblage of slates distinguished by calcareous phases, among which are some nearly pure 

limestones.

Slates without interbedded limestones are exposed on McKinley 

and Cahoon creeks, in the upper part of Glacier Creek valley, and in 

Jarvis Creek valley below the glaciers. In each locality the rocks 

are thin-bedded, dark, clastic sediments. The most obvious distinction between different beds is in their graphitic content. In this 

respect they grade from a soft, richly graphitic type to hard, relatively pure quartzose slates.

A group of coarse-grained sedimentary rocks, including thinbedded sandstones and slates, and a fine-grained conglomerate bed 

are exposed on the south slope of Jarvis Valley near the international 

boundary at an altitude of about 2,000 feet. Lower down on the 

same slope limestones of the massive type crop out. The clastic 

beds of this locality were not encountered elsewhere in the district, 

and their relation to the other terranes is not definitely known. The 

massive limestones there, locally at least, dip southwest. If this 

indicates a general structure the conglomerate and associated rocks 

overlie them.
IT. S. GEOLOGICAL SURVKY BULLETIN 699 PLATE III

A. GLACIATED MOUNTAINS AT THE HEAD OF McKINLEY CREEK 

McKinley Creek Canyon ia middle ground.

jB. SPRUCE AND HEMLOCK FOREST NEAR PLEASANT CAMP.
U. S. GEOLOGICAL SURVEY BULLETIN 689 PLATE IV

A. KLEHINI RIVER AT EVENING HIGH WATER A FEW MILES ABOVE PLEASANT ']

CAMP j

- . . The stream was fordable here earlier in the day. : : ' " ^ i

S. THIN-BEDDED LIMESTONES AND SLATES, PORCUPINE CREEK.
GENERAL GEOLOGY. 11 

The structure of the sedimentary rocks is apparently much more 

complex and irregular than it is generally in southeastern Alaska. 

The beds are -steeply tilted wherever observed, dips of 75° to 90° 

being common. The apparent trend of the great limestone band 

that crosses the lower courses of Porcupine and Glacier creeks is 

northwesterly. The limestones of Klehini Valley above Jarvis 

Creek also strike northwest, and this is the direction of elongation 

of the larger igneous bodies of the region. However, in many places 

in Klehini and Jarvis valleys where observations on the structure of 

the slates were taken the strike is northeast. The apparent differences in structure of the slate and massive limestone series adjacent 

to Klehini River suggest that the limestone may be a younger formation that overlies the slates unconformably. This interpretation is 

supported by the fact that the slates have strong compressional 

structures, whereas near-by limestone beds are massive and unsheared. However, the stratigraphy and structure of the whole assemblage are so complex and obscure that much additional work 

must be done before the relations and sequence of the various terranes will be revealed.

The general age of the bedded rocks of the region is indicated by 

fossils found in the limestones on lower Porcupine Creek.

A small collection made by Wright1 in 1903 was doubtfully identified as lower Carboniferous (Mississippian) by G. H. Girty, an 

identification which was corrected the following year when larger 

collections were made at Pybus and Herring bays. 2 The first collection, which was obtained on Porcupine Creek, contains the following species with revised identifications:

Oinoicl fragments.

Procluctus aif P. mammatus.

Procluctns af£. P. grtienwaldti.

Spidfer aff. S. marcoui and S. musakheylensis.

Camarophoria aff. C. margaritovi.

The same fauna is more completely shown in collections from 

Saginaw Bay, Kuiu Island, and the facies appears to be that of the 

Spirifer arcticus zone, believed to correlate with the Russian Artinskian (of late Pennsylvanian or early Permian age).

As already stated, there are structural grounds for considering the 

limestones on lower Porcupine Creek to be the youngest of the stratified rocks of the region, except, perhaps, the conglomerate and associated finer clastic beds noted at the locality south of Klehini River, 

near the international boundary. Though the limestone and asso-

> Wright, C. W., op. cit., p. 16.

2 Wright, C. W., A reconnaissance of Admiralty Island: U. S. Gcol. Survey Bull. 287 p. 

143, 1906.
12 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

elated beds may represent the upper Carboniferous and earlier Paleozoic, the coarser elastic series may correspond with the Mesozoic beds 

of Admiralty Island, which they resemble in a general way.

The correlation of the rocks of the Porcupine district with terranes 

that occur on Admiralty Island emphasizes a feature of the Coast 

Range intrusions noted by Spencer 1 namely, the edging over of the 

igneous mass toward the north, whereby one after another of the formations present in the Juneau gold belt is terminated.

The last of these formations to be cut out by the diagonal boundary of the diorite is a group of basic volcanic rocks that make up 

the Chilkat Peninsula and extend up the east side of Chilkat Valley 

halfway to Klukwan. They have the general characteristics of the 

group of metabasalts that lie next to the diorite rocks in the Berners 

Bay region, which Knopf 2 assigns to the Jurassic or Lower Cretaceous.

The contact between these rocks and the sedimentary rocks that 

extend into the Porcupine district is covered by the alluvium of the 

Chilkat Valley. Their difference in physical alteration points to an 

unconformable relation and is entirely compatible with the age assignments that have been indicated.

The rocks of the Porcupine district are therefore not to be correlated with those of the Juneau gold belt. The only point of similarity in the two regions is their proximity to the intrusive rocks of 

the Coast Range. It seems clearly apparent that the mineralization 

in both regions is due to the influence of the intrusive rocks and not 

to any inherent qualities in the bedded rocks which were invaded.

IGNEOUS BOCKS.

The igneous rocks of the district are apparently all intrusive. The 

bodies large enough to be represented on the geologic map are 

diorites connected with the deep-seated intrusive complex of the 

Coast Range. In addition there are a few small diabase dikes whose 

age and relation to the other intrusive rocks have not been determined.

The diorite of the northeastern part of the area is part of the 

main Coast Range belt, which extends uninterruptedly from lower 

British Columbia northwestward past this region and across the 

Alsek drainage basin. A small outlying band of diorite forms the 

crest of the range north of Jarvis Glacier; a larger one extends 

northwestward from upper Salmon River, across the heads of Porcupine and Glacier creeks and beyond the international boundary.

1 Spencer, A. C., The Juneau gold belt: U. S. Geol. Survey Bull. 287, p. 12, 1906.

2 Knopf, Adolph, Geology of the Berners Bay region, Alaska: U. S. Geol. Survey Bull. 

446, p. 19, 1911.
GENEEAL GEOLOGY. 13

The diorites of the district vary considerably in texture and composition, but the most prevalent types are moderately coarse, equigranular light-gray rocks composed dominantly of plagioclase feldspar and hornblende with smaller amounts of biotite and quartz and 

with accessory apatite, titanite, and magnetite. The rocks of the 

main Coast Eange belt are chiefly of this character, but local facies 

show either quartz or mica or both in unusual abundance, giving 

them the character of quartz diorites and quartz-mica diorites.

The narrow band at the head of Porcupine Creek is described by 

Wright,1 as follows:

The narrow belt at the head of Porcupine Creek contains more biotite, 

and segregations of hornblende and mica are often prominent, causing large 

dark spots, which are locally characteristic. The continuation of this belt to 

the east at Cotton wood Creek is characterized by a microcline feldspar and 

a larger amount of quartz. Under the microscope some of the minerals are seen 

to have been crushed, indicating that since the intrusion of the diorite they 

have been subjected to pressure and movement. This diorite rock is locally 

termed granite, which it resembles very closely and from which it can be 

distinguished only by careful examination.

IGNEOUS METAMORPHISM.

The metamorphic effect of the diorites upon the inclosing rocks 

is generally limited to a zone only a few hundred feet wide along 

the contact. As pointed out by Wright, the slates have been " baked 

and altered to a flinty hornstone" in such metamorphic zones, and 

the limestones have been recrystallized, forming white, compact 

marble. A more widespread phenomenon, also due to the influence 

of the invading magmas, is evident in the mineralization of the 

district and adjacent areas.

MINERALIZATION.

The very general mineralized condition of the sedimentary rocks 

of the region is well described by Wright,2 who says:.

The sedimentary rocks have all been more or less mineralized by stringers 

and veins of quartz and calcite, but an especially noteworthy impregnation 

of iron sulphides forms an interrupted zone of mineralization in the southern 

portion of the sedimentary series. The sulphides in the slates occur as films 

or frequently as lenticular masses a few. inches in width, parallel with the 

bedding. Two samples of the mineralized slates one an average across several 

feet and the other from a rich seam gave, respectively, $0.41 and $2.48 per ton 

in gold. Samples from near the mouth of the Porcupine, where the slates are 

apparently unmineralized, taken by Mr. Brooks during his short visit to this 

region in 1899, gave traces of both gold and silver.

1 Wright, C. W., The Porcupine placer district, Alaska : U. S. Geol. Survey Bull. 236, 

p. 17,1904.

2 Idem, pp. 17-18.
14 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

The quartz veins are not very abundant, and as a rule are short and small, 

often merely stringers parallel with the structure of the slates. A few which 

cut directly across the formation carry galena and sphalerite, with a small 

amount of chalcopyrite, and, though quite narrow, often persist for considerable distances. Calcite veins, which are more numerous than those of quartz, 

are usually a foot or more in width and are often weathered to a light-brown 

color on the surface, while of a bluish color and fine granular structure when 

freshly broken. They often carry cubes of pyrite, which occasionally measure 

an inch across. From veins of this nature up McKinley Creek some native 

gold has been reported.

Besides the small veins a quartz ledge 100 feet wide outcrops at an elevation 

of 2,000 feet on the ridge south of Porcupine. Although apparently quite barren, a small sample from this gave an assay value of $5.28 in gold. A similar 

ledge occiys across the Klehini at 1,500 feet elevation, on the ridge west of 

Boulder Creek. About 2 miles below Porcupine is a third mineralized deposit 

rich in sulphides, with calcite as gangue' mineral, but a sample taken here gave 

an assay value of only 41 cents.

The general zone of mineralization from which the placers of 

Klehini and Salmon river basins have been derived appears to be 

elongated in a northwesterly direction, extending from a point south 

of Salmon Kiver across the basins of Porcupine, Glacier, and Jarvis 

creeks and into the mountain mass north of Jarvis Glacier. The richness of mineralization varies from place to place, and there are 

large areas of lean or barren rock in this zone. But there are also 

remarkably large areas in which sulphide minerals are generally 

abundant and which are reported to yield substantial returns in 

gold on assay. A band of this sort that cuts across Cahoon Creek 

near its mouth in the slate formation shows abundant quartz veining and sulphide mineralization for a width of nearly 1,200 feet. 

Random samples taken across this belt are reported to assay from a 

trace up to several dollars a tori in gold, a large number of assays 

going between $1 and $2 a ton. v

The point farthest northwest along the general zone of mineralization at which gold has been found is in the mountains north of the 

lower end of .Jarvis Glacier, west of the international boundary. 

Here, at an elevation of about 4,500 feet are several gold quartz 

ledges in granitic country rock about 300 feet above its contact with 

limestones. The lowest and apparently the richest of the ledges is 

traceable for over 2,000 feet along the strike. It ranges from 1 to 4: 

feet in width. Assays of numerous samples taken across the full 

width of the vein are. reported to give from a few dollars to $70 a 

ton; the higher tenor is generally found where the vein is relatively 

narrow. A silver content of a few ounces to the ton is indicated 

in most samples. ' Picked specimens give much higher assay values.

Southeast of the main placer area, on the slope north of Salmon 

River, are a number of narrow silver-lead veins that represent still 

another type of mineralization in the district. So far as known the
GENERAL GEOLOGY. 15

largest are less than a foot in width. The maximum metal content 

of the veins is said to be about $3 a ton in gold, about 60 ounces a 

ton in silver, and about 35 per cent of lead. One sample shows a 

copper content of nearly 3 per cent. v

The mineralization that has furnished the placer gold in the 

vicinity of Bear Creek has not been studied geologically. Prospectors report that a zone along the ridge west of Bear Creek is heavily 

mineralized and that in places it contains commercial grades of copper ore. A specimen from this deposit, taken apparently from a 

vein a few inches wide, contains pyrite, pyrrhotite, chalcopyrite, and 

sphalerite, together with a little quartz gangue. The zinc sulphide 

occurs as a marginal band, and the main mass of the vein is dominantly chalcopyrite and pyrrhotite. This type of mineralization 

seems to be allied with that of the Rainy Hollow district, at the head 

of Klehini River, in Canadian territory, which is briefly described 

elsewhere (p. 26).

QUATERNARY DEPOSITS.

The Quaternary deposits of the region include both glacial and 

fluviatile types. Deposits made directly by ice are of surprisingly 

rare occurrence in a region that has been so extensively glaciated. 

Moraines are found about the ends of the present glaciers but are 

almost wholly lacking elsewhere. Glacial till is more widespread, 

and small deposits of this character occur here and there wherever 

conditions favored lodgment and protection from subsequent erosion. 

On some of the glaciated slopes till deposits form a thin veneer; on 

others only a few scattered erratic boulders are to be found. Till is 

more abundant in or near the bottoms of the valleys. It enters 

largely into the composition of terraces along the upper Klehini 

River, which have a broad extent near the international boundary. 

A considerable area at the north side of the valley opposite Glacier 

Creek behind an outlying bedrock ridge is underlain by till, the surface of which in places is marked by kettles and other morainic features. Abandoned canyons in the valleys of Glacier and Porcupine 

creeks are filled with till.

The fluviatile deposits include the gravels of the present valley 

bottoms, alluvial fans of tributary streams, and older gravels that 

form extensive terraces along the lower courses of the larger streams. 

The trunk streams are at present aggrading their valleys. Their 

load, which is derived mainly from glacial sources, includes heavy 

boulders, gravels, sands, and silts. The coarse part is deposited 

mainly along a broad zone in each valley, which is traversed and reworked by the numerous shifting channels of the anastomosing 

streams. Such zones are clear of vegetation and at low stages expose 

a great expanse of gravel and boulder bars, shaped into fantastic
16 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

forms by the transitory channels of the last flood and varying in 

texture from place to place according to strength of the currents 

that brought their materials into place.

The higher floods are not confined to the channels of the barren 

zones of the valleys but overflow the timbered tracts of bottom lands 

along the valley sides. The overflow waters carry only the finer 

grades of detritus, so that though the main flood way is built up with 

boulders and gravels other areas of the bottom lands are occupied 

only by sands and silts. The barren flood ways shift their positions 

from side to side, so that boulder deposits may come to rest on top 

of silt beds and vice versa.

The heaviest boulders find permanent lodgment near their glacial 

sources. The smaller boulders and gravels and much of the sands 

and silts are carried farther downstream, the distance depending 

upon their fineness. Thus there is a gradation from coarse to fine 

materials in contemporaneous deposits along the main flood way 

from source to mouth. The delta of the Chilkat is being built up 

entirely of very fine gravels, sands, and silts.- N

Much of the valley of Chilkat River and perhaps of its main 

tributaries was scoured by ice to a considerable depth below sea 

level. As the glaciers retreated, so long as they continued to end 

in the sea their detritus must have been deposited with little or no 

assortment on the estuary floors. When their retreat brought their 

ends up to sea level fluviatile deposition and delta building began. 

Further retreat of the glaciers and the extension of deltas brought 

the processes of assortment into play. As the texture of the debris 

deposited at any point along the stream is a function of the distance 

to its glacial source the vertical section of the deposits, where considerable aggradation has occurred during the ice retreat, shows 

progressively finer materials toward the surface.

This outline of the processes that have operated in the aggradation 

of main valleys of the region indicates the probable complexity of 

the valley fillings generally, below the present flood levels. The 

logs of drill holes in the Klehini Valley show that this probable complexity is fully developed in some places at least.

The alluvial fans of tributary streams lie at higher elevations than 

the adjacent deposits of the trunk streams, and therefore they have 

been interpreted by some as terrace deposits laid down in adjustment, to a higher base-level of erosion than the present. They are 

not level topped, as terrace deposits should be, but slope uniformly 

away from the points where the tributaries leave the confines of their 

own hanging valleys and debouch upon the graded plains of trunk 

streams.

The fans are marked by numerous shallow channels leading from 

summit to margin, one or more of which convey the present drain-
GENEKAL GEOLOGY. 17

age. The fans have been built up by the present streams out of 

materials such as they now carry and in adjustment to the main 

streams in the present cycle of erosion.

The appearance of a level terrace has been developed between the 

alluvial fans of Glacier and Porcupine creeks where the town of 

Porcupine stands. These creeks are so near each other that their 

fans come together some distance out from the edge of Klehini 

Valley. The rudely triangular area bordered by the two fans and 

the south slope of the main valley have been filled level with silt and 

peaty material.

Alluvial deposits that are unrelated to the present cycle of erosion 

form terraces at several places in the district and the adjacent regions. The east side of the Klehini Valley for several miles above 

Jarvis Creek has broad terraces, from 100 to 300 feet above the present stream. At the apex of the .alluvial fan of Porcupine Creek 

there are high gravels that appear to be the remnants of an old 

fluviatile terrace, and a similar feature occurs at the mouth of Boulder 

Creek. The broad plateau that lies between Klehini and Little Salmon rivers is apparently underlain by alluvium.

The origin of these features has not been fully determined. They 

may have been built as the result of retreat of tributary glaciers before the trunk glacier had receded past their junctions. According 

to this hypothesis the tributary streams filled in the lower ends of 

their valleys against the side of the main glacier, and when the ice 

had retreated sufficiently they intrenched themselves in the deposits 

which they-had just made and which have persisted as terraces up to 

the present time. In some places the glacial evidence seems to accord 

with this hypothesis, but it is possible that the region has been uplifted in late Quaternary time and that these deposits were laid 

down nearer sea level than their present altitude would suggest. 

Some recent elevation of the land about Lynn Canal and Chilkat 

Inlet is clearly indicated by marine terraces, but the extent of uplift 

directly evident is far short of that required by this hypothesis. 

Farther south, in the vicinity of Juneau, sea shells and old beach 

deposits occur up to elevations of 600 feet or more above the present 

sea level.1 More extensive uplift is noted along the coast southwest 

of the district where, near Yakataga, Pleistocene marine deposits 

occur up to a known elevation of over 5,000 feet above sea level.2

More complete data regarding the structure of the high terrace 

deposits and the extent of recent uplift in the Porcupine region itself 

will be required before the origin of these deposits can be definitely 

stated.

Spencer, A. C., field notes, 1916.

3 Maddren, A. G., Mineral deposits of the Yakataga district, Alaska: U. S. Geol. Survey 

Bull. 592, pp. 131-132, 1914.
18 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

ECONOMIC GEOLOGY. 

EXTENT AND CHARACTER OF THE MINERAL DEPOSITS.

Gold is widely distributed in bedrock in the Porcupine district, 

for it occurs in placer form in the gravels of Bear Creek and Klehini, 

Salmon, and Takhin rivers, as indicated on the map (PI. II). 

Workable placers, however, have been found only in the Klehini 

and Salmon river basins, on tributary streams that have had a 

peculiar erosional history, as described elsewhere (p. 19).

The commercial possibilities of gold deposits in bedrock have 

been investigated only to a very slight extent. Erratic prospecting 

in the vicinity of the richer placers has shown that considerable 

bodies of rock are gold bearing, and samples have been assayed 

which show a gold content of $1 to several dollars a ton. Although 

the existence of ore bodies of such size and richness as to be at 

present available for development has not yet been demonstrated, 

the showing that has been made should encourage further search for 

commercial lode deposits. The type of deposit to be looked for is 

that of large low-grade stockworks and mineralized zones in the 

slates. Quartz veins and abundant pyrite in the rocks should prove 

a rude indication of the presence of gold.

Gold quartz lodes of more compact form than the type suggested 

above have been found just west of the international boundary in 

the mountains north of Jarvis Glacier, at an altitude of about 4,500 

feet. One of these lodes consists of a quartz vein that is 1 to 4 feet 

wide and is traceable for about 2,000 feet. The compactness of the 

vein is due to the fact that it cuts a diorite country rock which, on 

being deformed, develops a few large widely spaced fissures rather 

than numerous smaller ones, as do the slates. The location of the 

lode that is best developed is indicated on the map, although it is 

in Canadian territory. It is mentioned in this report because of 

its evident relationship to the deposits on the American side of the 

boundary.

. Silver, lead, and copper occur in the district, but as yet they show 

little promise of commercial importance. Silver and lead occur 

together in some narrow veins that have been slightly developed on 

the north side of the Salmon River valley near Summit Creek. A 

little copper also is found at this locality. These veins are rich in 

the metals but are too small for profitable exploitation.

Copper deposits are reported to occur in the area between Bear and 

Clear creeks in the northeastern section of the district. Specimens 

from this locality show iron, copper, and zinc sulphides in vein form. 

The extent and richness of the deposits have not been determined.
ECONOMIC GEOLOGYo 19

GOLD PLACERS. 

GENERAL FEATURES.

The distribution of auriferous gravels and gold placers is indicated 

on the map (PI. II). The bedrock source of the gold is discussed 

under "Mineralization" (pp. 13-15), and the history of its concentration in placers is discussed on pages 20 and 21. Peculiarities of 

form, distribution, and topographic relations of the placers are here 

described and explained.

The only placers regarded as workable at present are those of the 

Glacier and Porcupine drainage basins. The placers of Nugget 

Creek were formerly worked in a small way, but this ground is now 

abandoned. Extensive tracts of auriferous gravels were formerly 

held on Bear Creek, on the Kletiini bottoms near Porcupine, and in 

the Salmon River valley near Nugget Creek. Extensive prospecting 

in these areas, by manual methods on Bear Creek and in the Salmon 

River valley and by drilling on the Klehini bottoms, failed to develop workable deposits, and the claims were abandoned.

The gold of the placers is generally well worn, of a bright color, 

and of medium fineness, assaying on the average about $17 an ounce. 

The texture of the gold dust shows a lack of assortment, the particles 

ranging in size from flour gold to nuggets weighing several ounces. 

Flour gold is present in unusual amount along with the coarser particles, and it occurs also in deposits of glacial mud or rock .flour associated with the placers. This distribution is believed to be due to 

glacial abrasion during certain epochs in the erosion of the valleys 

and concentration of the placers. Great quantities of mineralized 

rock have been scoured out by the action of the ice. The rock removed by this process was largely in the form of rock flour; the gold 

which it contained must likewise have been largely reduced to a flourlike powder. The load of the streams that concentrated the placers 

has at all times been composed dominantly of glacial detritus. 

Though perhaps the most of the flour gold has been carried beyond 

the limits of the placers, much has found lodgment with the coarse 

gold and in the fine sediments that have been deposited here and 

there in the placer-bearing valleys.

A sample of glacial mud taken at random on Porcupine Creek near 

the lower end of its canyon gave an assay of 1.10 ounces of gold a ton.1 

Other assays of sediments reported by local operators show that considerable gold is commonly present in them.

The flour gold is practically all lost in the present mining operations. As the placers are all of similar genesis, great importance 

should be attached to further investigation of the distribution of

1 Wright, C. W., op. clt., p. 20.
20 PORCUPINE GOLD PLACEE DISTRICT, ALASKA.

flour gold and to the adaptation of methods to its recovery, if possible, along with the product now saved.

FORMATION.

Elements in the history of erosion have already been presented 

(p. 19) that show the main valley fillings and high terraces to 

have been built up by processes that did not favor the concentration 

of placer gold. The placers all lie in the smaller tributary valleys. 

The history of this erosion includes the origin of the placers and 

explains their character and distribution.

During the periods of more extensive gllaciation of the region, 

both trunk and tributary valleys were deeply scoured by the action 

of the ice, but the main valleys were generally lowered below the 

level of their tributaries, giving to the tributary valleys the character of hanging valleys. When the ice had retreated the streams 

from the hanging valleys found abrupt declivities in their courses at 

the margins of the main valleys, which brought about the erosion of 

canyons in tributary valleys and the deposition of detritus in the 

form of alluvial fans along the margins of the main valleys.

In places in the Porcupine Valley at the side of the present canyon 

there are so-called bench deposits, which consist of stream gravels 

overlain by glacial detritus. It is evident that these deposits occupy 

sections of a canyon, older than the present but of similar origin, 

which was in some places followed and in others missed by the course 

of the stream when the last intrenchment began. (See PI. V, A 

and B.} Two distinct ice advances are thus indicated, each of which 

was followed by intrenchment of the hanging-valley streams.

The modern canyon has been eroded to a lower level than the 

earlier throughout the middle and upper sections of Porcupine Valley. 

Near the lower end of the valley the conditions are not so simple, and 

it seems likely that the stream accomplished considerable intrenchment along more than two courses. The identity and relations of 

the different bedrock canyons at this place could not be fully de~ 

ciphered from the available exposures. It is clear, however, that the 

Porcupine was controlled by a lower base-level than that afforded 

by the present position of Klehini River at the time of maximum 

intrenchment in each position.

In the Glacier Creek valley also there is evidence of two "distinct 

ice advances with a period of stream erosion intervening. An extremely deep and narrow bedrock gorge filled with glacial detritus 

has been traced for some distance along the lower part of the 

valley beneath the modern stream gravels. A-base-level of erosion 

much lower than the present is indicated the same as in the lower 

Porcupine Valley. The upstream extension of this older canyon
U. S. GEOLOGICAL SURVEY

A. UPPER END OF ABANDONED CANYON OF 

McKINLEY CREEK.

The glacial filling has been sluiced out for a short distance. The water of the falls comes from a hydraulic plant and spills over the rim of the modern canyon into McKinley Creek. (See also PI. VII, B.)

BULLETIN 699 PLATE V

B. LOWER END OF SAME ABANDONED CANYON 

SHOWING GLACIAL TILL EXPOSED BY PLACER WORKINGS.
TJ. S. GEOLOGICAL SURVEY BULLETIN 699 PLATE VI

A. CABLE TRAMWAY FORMERLY USED IN STACKING BOULDERS, PORCUPINE

CREEK.

B. CRANE HOIST STACKING BOULDERS BEHIND CRIBBING AT SIDES OF SLUICE 

BOX ON McKINLEY CHEEK BENCH PLACER.
ECONOMIC GEOLOGY. 21

is not now evident. It may have been destroyed by later ic© erosion 

in the Glacier Creek valley, or it may have been followed by the 

stream in its last intrenchment. The narrowness of the valley favors 

the latter interpretation.

The concentration of placer gold took place in conjunction with 

the intrenchment of the streams in the hanging valleys wherever 

their courses traversed zones of mineralized bedrock. The placers 

are therefore of two distinct ages, corresponding with the separate 

periods of stream erosion.

The concentrations are generally found in a thin stratum of stream 

gravels lying on the bedrock bottoms of the canyons. Locally, as 

below the falls on McKinley Creek, gold has been found on bare 

bedrock practically without associated gravels. The gold-bearing 

stratum is generally overlain by barren or very low grade gravels 

that are progressively deeper downstream. Their deposition is due 

to the rising base-level afforded by the aggrading Klehini River.

The stream gravels in the bottoms of the older canyons, which are 

gold bearing in places, are overlain by glacial detritus the depth of 

which is generally equal to the height of the canyon walls. In the 

lower section of Glacier Creek modern gravels overlie the glacial 

fill of the older canyon, which extends to a great depth below the 

present stream and has a much steeper grade.

At the lower ends of the modern canyons, where the alluvial fans 

begin, there are certain concentrations that extend out into the gravel 

deposits somewhat above bedrock. They are less regular in form and 

of lower grade than the gravels within the confines of the canyons 

and extend but a short distance out into the Klehini Valley. Apparently the alluvial fans are devoid of notable placer concentrations, except possibly at their very heads.

MINING METHODS.

The strong relief and abundant water supply of the region afford 

splendid facilities for hydraulic mining. Ample hydraulic head can 

be developed with an unusually short length of flume, owing to the 

steep grades of the streams. The abundant local supply of timber 

makes the cost of flume construction low. It is therefore natural 

that equipment for hydraulic mining has replaced all the various 

devices that were tried out in the course of the earlier operations.

The chief obstacles to mining the creek gravels are presented by 

the great, discharge of the streams during the mining season and 

the presence in the placers of boulders that are too large for sluicing. 

(See PI. VI, A and B.) The bench deposits also contain large 

boulders, but there is no problem of water control connected with 

working them.
22 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

The streams are diverted from the placer ground by means of 

wooden flumes. The flume on Porcupine Creek is 24 to 30 feet wide 

and 6 feet deep and was originally over a mile long (PI. VII, A}. 

A section 2,000 feet long at the downstream end is now out of repair 

and not in use. The slope is about 5 inches in 100 feet. The water 

develops very high velocities in the flume during floods, so that the 

entire discharge of Porcupine Creek is generally handled successfully. At high stages a large amount of debris, including gravels 

and fairly large boulders, passes through the flume, which causes 

considerable wear and makes replanking necessary every year or two.

Similar diverting flumes were used in mining the placers of McKinley and Cahoon creeks. The available ground is now worked out. 

and the flumes are largely destroyed. (See PL VII, B.)

The diverting flume-on Glacier Creek is only 8 feet wide and 5 

feet high, but the grade is 6 to 10 inches in 12 feet, so that the discharge of the creek, about 1,000 second-feet at the maximum, is 

ordinarily handled successfully. (See PL VIII, A.) The flume is 

floored with 6-inch riffle blocks cut across the grain, which makes 

reflooring necessary only at long intervals. (See PL VIII, B.) The 

flume is 1,950 feet in length. It carries the water from the dam at 

the upper end of the placer ground to the head of an old channel on 

the alluvial fan east of the one normally followed by Glacier Creek.

Successful mining of the creek gravels depends primarily upon 

keeping the diverting flumes in full commission at all times. Temporary failure, even for a few hours, in time of flood may result in 

complete refilling of working pits with coarse wash. This has happened on both Glacier and Porcupine creeks in the past. The filling 

in the workings on Porcupine Creek during the flood of 1915 is 

estimated to have had an average depth of. 12 feet for a distance of 

over half a mile. Much valuable time and labor is sacrificed in 

dead work in restoring workings to proper shape after each failure 

of the flumes. The operators are now paying special attention to 

maintenance of the flumes, and it is hoped that improved construction may eliminate this precarious feature entirely.

The large boulders in the placers, which are handled by crane 

hoists, are lifted in cable slings either whole or after being blasted; 

those small enough to be handled are thrown on tables which are 

hoisted and dumped mechanically. Hydroelectric power is used 

on Glacier Creek, steam power is used at the Porcupine plant, and 

power is delivered directly from a Pelton wheel to the winch on 

McKinley Creek.

The arrangement of sluice boxes and the methods of delivering 

the pay dirt to them and of disposing of tailings differ according 

to the situation of the placers and the general equipment of the 

plants. On Glacier Creek the gravels average between 45 and 50
IT. S. GEOLOGICAL SUKVEY BULLETIN 699 PLATE VH

A. DIVERTING FLUME, PORCUPINE CREEK.

S. WORKED-OUT SECTION OF MODERN McKINLEY CREEK CANYON. 

Note position of abandoned canyon at head of waterfalls, same locality as shown in Plate V, B.
U. S. GEOLOGICAL SURVEY BULLETIN 699 PLATE VIII

A. FLUME AND SPILLWAY, GLACIER CREEK DAM.

£. DETAIL OF GLACIER CREEK FLUME, SHOWING USE OF RIFFLE HLOCKS.
ECONOMIC GEOLOGY. 23

feet in depth. The upper gravels to a depth of 20 feet are piped off 

and stacked at one side by a 3-inch giant working under a hydraulic 

head of about 400 feet. The rest of the deposit is piped over a grizzly, which passes materials less than 1 foot in diameter to a hydraulic 

elevator. The elevator has a 12-inch throat and 20-inch tube and 

elevates the materials 45 feet to the sluice box. The box is 4 feet 

wide, 3 feet deep, and 128 feet long and is floored throughout with 

60-pound steel rails set crosswise for riffles. Tailings are stacked 

with a 3-inch giant.

On Porcupine Creek the pay gravel is hydraulicked directly into 

sluice boxes set in bedrock, and the tailings are carried through a 

flume set with block riffles for about 2,000 feet, where they are delivered to the creek bed at the lower end of the diverting flume.

The bench placers of McKinley Creek are about 200 feet above the 

level of the stream, so that there is abundant room for tailings. The 

face of the cut is about 60 feet high and 50 to 70 feet wide between 

bedrock walls. The gravels and glacial overburden are caved by 

giants, the heavy boulders are stacked behind cribbing at one side 

(PL VI, B), and all the finer material is hydraulicked directly into 

sluice boxes set in bedrock, which discharge over the rim of the 

modern canyon of McKinley Creek.

HISTORY OF DEVELOPMENT.

, Gold was first discovered in the Porcupine district in 1898. The 

following year mining operations were begun on Porcupine Creek, 

and the great number of prospectors who assembled staked claims on 

other creeks of the district. Though gold-bearing gravels were 

= found on Bear Creek, on .several tributaries of the Salmon, and on 

the head of Takhin River, productive operations up to the present 

time have been almost entirely limited to Porcupine Creek and its 

tributaries. A little mining was done on Nugget Creek from 1902 

to 1911. The ground was then abandoned, and no further work has 

been done. It is estimated by local operators that about $6,000 worth 

of gold was produced.

The gold production of Porcupine Creek and its tributaries from 

1898 to 1903 is given in the following table by Wright i1

Gold produced in the Porcupine region, 1898-1908.

1898________________ $1,000 

1899________________ 9,000 

1900___________..___ 50, 000

1901___________*______ 110, 000

1902_______________ $140, 000 

1903_______________ 150, 000

460, 000

1 Wright, C. W., The Porcupine placer district, Alaska: U. S. Geol. Survey Bull. 256, 

p. 13, 1904.
24 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

The production from these creeks is said to have continued at the 

rate of about $150,000 a year until 1906, when the principal works 

were destroyed by an unusual flood. From 1907 to 1909 large operations were discontinued, and the only production was made by a few 

laymen, 'who worked small lots of ground by manual methods. Production on a large scale was resumed in 1910, and it is estimated 

that an average yearly production of $50,000 was maintained until 

1915, when another disastrous flood occurred. The total output for 

the district from 1898 to 1916, inclusive, estimated on the basis of 

these very incomplete data, is about $1,200,000.

In 1908 the Porcupine Mining Co. was organized to exploit the 

placers of the main Porcupine on a large scale. It was financed in 

the Eastern States, and in view of the equipment installed in the next 

few years it must have had a large investment fund. The first move 

of the new company was to construct a flume a mile long, 24 feet 

wide, and 6 feet deep, supported on piles, to carry the waters of Porcupine Creek past the placer ground to be worked. This piece of 

construction, which required nearly a millon feet of lumber and several thousand piles, was completed late in the summer of 1909, and 

mining was begun at the lower end of the canyon. This company 

operated until August, 1915, when the lower part of the flume was 

demolished and the pits were filled in by a flood. During the last 

few years of operation the work was done under a receivership but 

with the same local management.

After the disastrous flood of 1915 the property and holdings of the 

company were taken over by the Alaska Corporation. This concern in 1916 repaired the upper section of the old flume, constructed 

a new high-line flume to deliver water to the giants, and began the 

reexcavation of the buried workings.

But little mining was done on the tributaries of Porcupine Creek 

before 1908, when the Cahoon Creek Gold Mining Co. began work on 

McKinley and Cahoon creeks. The operations of this company have 

continued to the present time, working out the placers on Cahoon 

Creek near its mouth and for about 2,000 feet down McKinley Creek 

below Cahoon. The plan followed in the operations on McKinley 

Creek was essentially similar to that employed on Porcupine Creek 

the stream was diverted into a wooden flume, making the stream bed 

available for hydraulic mining. Below the workings on McKinley 

Creek the stream runs through a narrow box canyon. The difficulty 

of diverting the stream in this reach has thus far prevented the exploitation of the gravels of its bed. In 1916 the company was engaged in working the placers of a high glacially filled channel on 

the right side<of McKinley Creek, opposite the reach of the modern 

channel that had been worked out.
ECONOMIC GEOLOGY. 25

A little mining was done on the head of Cahoon Creek in the early 

days of the camp, but these operations are said to have met with little 

success, and the hope of working this ground on any large scale has 

long since been abandoned. However, a little prospecting and 

" sniping " has been done from time to time by laymen.

The most notable development in the district in the last few years 

has been the investigation of the Glacier Creek placers by drilling 

and the installation of a large hydraulic plant to work this ground. 

The Glacier Creek placers were staked in the early days of the district, and repeated attempts to prospect and mine the ground by ordinary methods failed, owing to the depth of the gravels and the 

abundance of ground water. In 1911 the claims, which had been 

abandoned by the previous holders, were restaked and systematic 

drilling was begun. Drill sections across the valley bottom were 

made at close intervals for over a mile upstream from the margin of 

the Klehini Valley. On the basis of the results of this investigation 

extensive preparations were made to work the lower section of the 

valley, 4,200 feet long, by hydraulic methods. The installation of 

a very complete plant, including dams, flumes, pipe lines, giants, 

hydraulic elevator and other machinery, was finished in the midsummer of 1915, but operation was prevented for the rest of the season by the unusual floods of that year. In 1916 work was started 

early in the spring, but owing to damage done the workings by a 

flood in the later part of June the season netted but little productive 

operation.

SUMMARY OF MINING IN 1916.

Mining in the Porcupine district in 1916 was confined to Porcupine 

Creek and its main east tributary, McKinley Creek, and Glacier 

Creek. A single plant using hydraulic methods worked on each 

stream throughout the summer. The principal work done on Porcupine and Glacier creeks consisted of the installation of hydraulic 

equipment and the repairing of damage done to workings and equipment by floods, so that little productive mining was accomplished. 

Two small plants, using manual methods, worked on the lower Porcupine part of the summer. The plant on McKinley Creek opened 

up a new pit in an old elevated channel and worked out a considerable area,' although the operations were hampered somewhat by the 

presence of an overburden of glacial till 60 feet thick, in which there 

are numerous large boulders.

About 50 men on an average were employed during the summer in 

the whole district, divided about equally among the three active 

creeks. Though the production for 1916 was small, it is reported that 

the plants had all been put in good repair and were ready for more 

extensive operations.
26 PORCUPINE GOLD PLACER DISTRICT, ALASKA. 

PROSPECTING IN ADJACENT DISTRICTS. 

KAINT HOLLOW DISTRICT.

The Rainy Hollow district is in Canadian territory on the headwaters of Klehini River about 12 miles northwest of the mouth of 

Jarvis Creek. 1 About 40 lode claims are held on several more or less 

parallel ledges that trend in a northerly direction. The most valuable deposits have been formed by the replacement of limestone. The 

mineralization of the district is markedly different from that of the 

main Porcupine placer area and is more nearly allied with that of 

Bear Creek. The metals are chiefly copper, silver, zinc, and lead. 

Gold is present only in negligible amounts. The dominant gangue 

minerals are quartz, garnet, and tremolite. '

REGION EAST OF CHILKAT VALLEY.

Local interest has attached for several years to prospecting for 

gold and copper in the mountain range between Chilkat and Chilkoot valleys, northwest of Haines. Fine specimens of gold-bearing 

quartz and bornite copper ore, said to represent large deposits in this 

range, are frequently brought into Haines. If the current reports 

of the size and richness of these deposits are correct this locality 

should quickly assume a high rank among those producing these 

metals.

GEOLOGY.

The salient geologic features of this group of mountains is the contact between the diorites of the Coast Range, which make up their 

main mass, and the group of altered volcanic rocks that form their 

western base and extend southeastward into Chilkat Peninsula and 

the Berners Bay region. Several bodies of schist and limestones are 

included in the diorite near its main contact with the bedded rocks. 

Considerable alteration is generally evident in the bedded rocks near 

the contact with the diorite. The limeistones are thoroughly recrystallized, and other types of bedded rocks are converted into 

biotite schists. Quartz veins and aplite dikes are locally abundant 

near the diorite, and in places quartz veins extend far out into the 

invaded rocks.

VEINS AND MINERALIZATION.

The metamorphism of the volcanic rocks near Haines apparently 

comprises their complete recrystallization with partial segregation 

of iron in the form of magnetite. Farther from the intrusive conBrewer, W. M., British Columbia Minister of Mines Ann. Kept. 1914, pp. 94-99, 1915.
ECONOMIC GEOLOGY. 27

 ¥,

^ tacts the volcanic 'rocks have largely preserved their original character but generally show more or less mineralization. Thin veinlets 

of bornite are very prevalent throughout the volcanic area. Quartz 

veins and reticulating quartz stringers carrying copper and iron 

sulphides occur in places. Some of the quartz veins contain gold,

 according to local reports.

^ The most promising gold and copper prospects are said to be 

located near the top of the range, about 10 miles from Haines. Both 

gold and copper ores purporting to come-from extensive ledges at 

this locality were examined by the writer. The gold ore consisted

v of vein quartz which contained fine specks of native gold and a little

>, pyrite. The copper specimens were chiefly bornite, broken from a 

vein apparently several inches across. The bornite is said to have 

a notable content of gold, as shown by assay.

The gold quartz is said to occur in a broad ledge along a dioritelimestone contact, and the copper ore in a vein several feet wide 

which cuts diagonally across.it. The deposit occurs at an altitude

^ of about 4,500 feet, in a small basin that is free from snow for only

^ a short time each year.

In view of the widespread evidences of mineralization in this area

~ it is a matter of great interest that prospectors are actively investigating it and that the results thus far achieved have stimulated 

hopeful expectations.

IRON-ORE DEPOSITS NEAR HAINES.

 Rocks which are probably related in origin to both the volcanic 

group and the diorites of the Coast Range and which contain so 

much magnetite that they have been regarded as a possible source 

of iron ore crop out along the shore of Chilkoot Inlet and in 'the 

^ adjacent mountains near Haines. Their lithology has been well 

described by Knopf/ who studied them in 1908, as follows:

The rock mass exposed along the shore north of Haines is a remarkable 

occurrence geologically. Specimens collected from the finest-textu red portions 

show a rock composed of a coarsely crystalline aggregate of feldspar, hornblende, and pyroxene, throughout which are scattered some visible grains of 

magnetite. The dark minerals (the hornblende and pyroxene) make up half 

the bulk of the rock. When examined microscopically the rock is found to consist of an allotriomorphie granular assemblage of plagioclase feldspar (bytow- 

* nite), hornblende, and augite. Magnetite and apatite are present as accessory 

constituents in unusually large amounts. From this normal type of rock, 

which would be termed a gabbro, abrupt variations in texture and mineral 

composition are encountered. In places the cliffs for hundreds of feet are com- 

^v posed solidly of formless hornblende individuals 6 inches long by 3 inches 

j 

1 Knopf, Adolph, The occurrence of Iron ore near Haines: U. S. Geol. Survey Bull. 442, 

£- pp. 144-145,1909.
28 PORCUPINE GOLD PLACER DISTRICT, ALASKA.

 broad. Commonly this hornblende rock contains more or less grayish-green 

augite admixed with it and is ramified by coarse white feldspathic dikelets or 

blotched by masses of gabbro. In places it even forms a breccia cemented by 

such' material. Locally the hornblendite contains numerous lumps and particles of magnetite, which can easily be recognized by the characteristic bluish 

tarnish that they assume upon weathered surfaces. At no point along the 

shore, however, has the segregation of magnetite proceeded far enough to yield 

a solid body of iron ore, or even a body of ore of commercial grade.

The structure of these rocks shows that they are not of simple 

magmatic origin. The hornblende rock is everywhere traversed in 

many directions by light-colored feldspathic dikelets and by feldspathic zones with less distinct outlines. In the greater part of the 

area the dikes and feldspathic zones are closely spaced and by intersection divide the hornblende rock into a multitude of separate 

blocks: The dikes are plainly intrusive in the basic rock. The 

feldspathic zones likewise have been developed subsequent to its 

original consolidation, probably by magmatic solutions. The disposition of the younger rocks in the general mass seems patterned 

after a rather definite joint system. Clearly the hornblendic portions 

of the mass represent the original rock of the area and the dominantly feldspathic portions a later development related to the diorite 

intrusion.

The origin of the magnetite-bearing hornblende rocks is somewhat 

problematic. Knopf 1 holds that they "represent various modifications of a single intrusive mass of deep-seated origin." On the 

other hand, it seems possible that they have been produced by the 

recrystallization of basalts of the volcanic group that partly surrounds the area. Basaltic and coarse-textured hornblendic rocks 

alternate in the exposures along the shore northwest of Battery 

Point, and in places there is an apparent textural gradation from one 

type into the other. In this area the constant association of feldspathic dikelets with the hornblende rock is strikingly exemplified. 

Some of the feldspathic zones and dikes merge with the hornblende 

rock in a way that suggests contemporaneous crystallization of the 

ferromagnesian and feldspathic minerals. There is nothing to indicate that the ferromagnesian minerals of the hornblende rock differ in age from those of the feldspathic zones. Thus it might well 

be inferred that the texture and mineralogic character of the hornblende rocks were developed pyrogenetically Tit the time of the intrusion of the feldspathic dikes presumably during some epoch 

in the general period of intrusion of the diorites of the Coast Kange.

The economic possibilities of the deposits have been summed up 

by Knopf,2 as follows:

*Op. cit., p. 144. "Op. cit., p. 146.
ECONOMIC GEOLOGY. 29

The iron ore occurring near Haines consists of primary magnetite sparsely 

disseminated in a basic igneous rock composed of pyroxene and hornblende. 

An ore of this character would require fine crushing and concentration. A 

study of producing iron-ore properties where the adoption of such processes 

was necessary will therefore furnish valuable data for an analysis of the commercial possibilities of the Alaskan iron-ore deposits. Many factors enter into 

the problem but hardly need discussion at this time. At Lyon Mountain, N. Y., 

where crushing, drying, and electromagnetic concentration are necessary, the 

lowest-grade iron ore treated contains 34 per cent of metallic iron.1 This is far 

above that of the highest-grade rock so far found at Haines. Geologically it is 

possible that richer bodies of magnetite may occur as segregations in the basic 

granular rocks that form the ridge extending northwestward from Haines. A 

magnetic survey of the area underlain by these rocks would undoubtedly prove 

a quicker and more economical way to test this possibility than the driving of 

expensive prospect tunnels.

1 Eng. and Mln. Jour., vol. 82, p. 916, 1906.

o