Geology of Part of the 

Craig C -2 Quadrangle 

and Adjoining Areas 

Prince of Wales Island 

Southeastern Alaska 

'ly C. L. SAINSBURY 

MINERAL RESOURCES OF ALASKA 

::iEOLOGICAL SURVEY BULLETIN 1058-H 

The gener.al and economic geology of an 

zrea 35 miles northwest of Ketchikan 

JNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961 
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington 25, D.C. 
CONTENTS 

Page 

Abstract _________________________________________________ ~ _ _ _ _ _ _ _ _ _ 299 

Introduction______________________________________________________ 300 

Previous investigations __________________________________ ~ _ _ _ _ _ 300 

Scope of the present investigation__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 302 

Acknowledgments_____________________________________________ 302 

(}eogra]JhY---------------------------------------------------- 303 

Loeation and accessibility___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 303 

Topography and drainage___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 304 

Climate and vegetation_________________________________________ 304 

The geologic map______________________________________________ 305 

(}eo logy_ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 307 

Bedded rocks_________________________________________________ 308 

Bedded rocks of Middle Ordovician to Early Silurian(?) age____ 310 

Volcanic graywacke, tuff, and conglomeratic volcanic 

graywacke__________________________________________ 311 

Feldspathic and lithic graywacke________________________ 312 

Fine-grained rocks_______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 313 

Argillite__________________________________________ 314 

Chert____________________________________________ 314 

Limestone________________________________________ 314 

Conglomerate_________________________________________ 315 

Andesite______________________________________________ 317 

Structure and thickness____________________________________ 318 

Metainorphism____________________________________________ 320 

Age and correlation________________________________________ 321 

Conditions of deposition____________________________________ 323 

Limestone of Middle Devonian age__________________________ 324 

Bedded rocks of Tertiary age_______________________________ 326 

Conglomerate, sandstone, and conglomeratic sandstone_____ 326 

Conglomerate_________________________________________ 327 

Conditions of deposition________________________________ 328 

Age__________________________________________________ 328 

Unconsolidated deposits________________________________________ 328 

(}lacial deposits_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 329 

Older moraines and till_________________________________ 329 

Younger moraines and tilL______________________________ 330 

Alluvium_________________________________________________ 332 

Beach graveL____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 332 

Intrusive rocks of pre-Tertiary age_______________________________ 332 

Plutonic rocks _____ -------------------------------------- 333 

Pyroxenite and gabbro_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 333 

Quartz diorite and related rocks_________________________ 335 

Plutons__________________________________________ 335 

Chemical composition_________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 338 

Age______________________________________________ 338 

III 
IV CONTENTS 

Geology-Continued 

Intrusive rocks of pre-Tertiary age--Continued PageDikerocks------------------------------------------------ 339 

Paleozoic dikes________________________________________ 339 

Dikes of Paleozoic and Mesozoic age_____________________ 341 

Diorite porphyry and related rocks__________________ 342 

Trachyte and related rocks------------------------- 344 

Sodic rhyolite porphyry, rhyolite, and sodic andesite 

porphyrY--------------------------------------- 34& 

Sodic granite, monzonite, and quartz pegmatite__ _ _ _ _ _ 346 

Crosscutting relations__________________________________ 347 

Intrusive rocks of Tertiary age__________________________________ 348 

Diabase-------------------------------------------------- 34S 

Pitchstone------------------------------------------------ 349 

Glacial history and postglacial uplift ___________ ----- __ --------___ 349 

~conomicgeologY--------------------------------------------- 351 

Pre-Tertiary copper-magnetite deposits not previously described------------------------------------------------- 352 

Magnetite south of Baker Point_________________________ 352 

Chalcopyrite near Kina Cove ____ ---------- _____ -----___ 352 

North contact of pluton west of Twelvemile Arm__________ 353 

Prospect on north branch of Paul Young Creek_ _ _ _ _ _ _ _ _ _ _ 354 

Prospects on North Pole HilL--------------------------- 354 

Other areas of interest--------------------------------- 355 

Tertiary deposits__________________________________________ 356 

Gold quartz veins near Granite Creek____________________ 356 

Tertiary pyrite-chalcopyrite veins near pluton east of Lava 

Creek______________________________________________ 356 

Conclusions----------------------------------------------- 357 

Regional distribution of ores____________________________ 357 

Periods of ore deposition_______________________________ 358 

Origin of magnetite-chalcopyrite ores_____________________ 358 

Suggestions for prospecting ____________________________ - 359 

References cited ___ ----- _____ -----_----____________________________ 360 

IndeX------------------------------------------------------------ 361 

ILLUSTRATIONS 

Page 

PLATE 33. Geologic map of most of the Craig C-2 quadrangle and parts of adjacent areas _________________________________ In pocket 

34. A, Photomicrograph of typical lithic graywacke in Thorne 

and Tolstoi Bays. B, Conglomeratic volcanic graywacke 

or tuff on the north shore of the entrance to Thorne Bay_ Facing 316 

35. A, Conglomeratic volcanic graywacke from the head of Karta 

Bay, with crude stratification of cobbles. B. Conglomeratic volcanic graywacke from the head of Karta Bay, with 

crude stratification of cobbles and fine-grained beds_ Following 316 

36. Folded limestone with intercalated tuff beds on east shore of 

Snug Anchorage _______________________________ }i'ollowing 316 
CONTENTS 

PLATE 37. A, Contorted fine-grained sedimentary rocks in slump conglomerate with limestone matrix on south shore of south 

entrance to Thorne Bay. B, Limestone-matrix slump conglomerate on north shore of island in entrance to Thorne 

v 

Page 

Bay _________________________________________ Following 316 

38. A, Photomicrograph of typical amygdaloidal lava flow fromarea west of Thorne Bay. B, Photomicrograph of trachytic 

lava flow with carbonate amygdules, Tolstoi Bay __ Following 316 

39. A, Tertiary conglomerate on a beach near the north end of 

Craig C-2 quadrangle. B, Photomicrograph of conglomerate from Berry Island, Kasaan Bay, showing magnetite 

pebble ___ ------ ____________ -------- _____________ Facing 317 

FIGURE 47 .. Index map of southeastern Alaska showing Craig C-2 quadrangle and adjoining areas, Prince of Wales Island________ 301 

MINERAL RESOURCES OF ALASKA 

GEOLOGY OF PART OF THE CRAIG C-2 QUADRANGLE 

AND ADJOINING AREAS, PRINCE OF WALES 

ISLAND, SOUTHEASTERN ALASKA 

By c. L. SAINSBURY 

ABSTRACT 

The area mapped is on the east coast of Prince of Wales Island, southeastern 

.Alaska, about 35 miles northwest of the town of Ketchikan. Deposits of magnetite and eopper in the mapped area and on Kasaan Peninsula, which adjoins 

it on the southeast, have been mined for copper and have produced more than 

600,000 tons of ore valued at more than $6 million. 

The bedded rocks of the area are composed of a great thickness of volcanic 

graywacke, tuff, conglomeratic volcanic graywacke, argillite, andesite, limestone, and conglomerate ranging in age from Middle Ordovician to Early 

Silurian ( ? ) . The age assignments of the bedded rocks, which previously were 

assigned to the Middle Devonian, are based upon six collections of graptolites. 

The thickness of the Middle Ordovician and Lower Silurian ( ? ) rocks is not 

apparent, but it must be at least several thousand feet and may be as much as 

17,000 feet. The structure of the bedded rocks undoubtedly is more complex 

than can be determined in the field . 

.An island in Kasaan Bay in the southern part of the mapped area is composed of limestone of Middle Devonian age. This limestone is in an anomalous 

position with respect to the older rocks and is thought to have been faulted 

into its present position sometime in the Tertiary, probably by thrust faulting 

on a major scale followed by block faulting. 

Small deposits of Tertiary conglomerate of local derivation, some of which 

have the form of old deltas, lie unconformably on the older rocks. These Tertiary rocks are restricted to the lowland areas. 

Surficial deposits of till, outwash gravel, and alluvium are widespread. 

Glacial features show that at one stage in the cycle of glaciation, ice flowed 

eastward from a center or centers west of the quadrangle. This is interpreted 

as evidence of valley glaciation that preceded and followed an ice sheet that 

completely buried mountains as much as 2,800 feet in altitude. Postglacial 

uplift amounts to at least 50 feet and may be more than 200 feet. 

The older rocks are intruded by many stocklike bodies of probable middle 

Cretaceous age ranging in composition from granite to olivine-bearing pyroxenite, and by innumerable dikes. The age of 1 stock was determined on the basis 

-of radiogenic lead to be 100 million years, or middle Cretaceous. 

The igneous rocks of intermediate composition in places contain large 

amounts of :alkali feldspar, and many dikes are converted to albite-rich rocks. 

299 
300 ~ERAL RESOURCES OF ALASKA 

The identification of anorthoclase phenocrysts in some of the sodic dikes raises 

the question as to which of the sodic rocks are primary and which are albitized. 

Three distinct periods of ore deposition are recognized, each with characteristic ore and gangue minerals. The oldest and most important is related to 

the intrusive activity of probable late Early to Late Cretaceous age; the second, of lesser importance, postdated the intrusion of diabase dikes, probably 

in the early Tertiary; and the youngest and least important either followed 

or was contemporaneous with the intrusion of pitchstone dikes that cut the 

Tertiary conglomerate. 

The association of magnetite ore with older bedded rocks rich in magnetite 

and with pyroxene that tends to be rich in iron suggests that the bedded rocks 

may be the source of at least part of the magnetite in the magnetite-chalcopyrite 

ores. 

INTRODUCTION 

The regional geology of a part of the Craig C-2 quadrangle and 

adjoining areas, Prince of Wales Island, Alaska, an area that is of 

economic interest because of the many deposits of copper and iron, 

is described in this report. The location of the area is shown on 

figure 4 7. Although some of the copper deposits in the coppermagnetite district, a part of which lies on the Kasaan Peninsula, 

were known to the Russians (Wright, 1915, p. 15), most of the 

mineral locations were made between the years 1895 and 1900, and 

the bulk of the copper ore shipped was produced before 1921. The 

district has produced more than 600,000 tons of copper ore valued 

at more than $6 million. No magnetite ore has been shipped, although substantial reserves of high-grade ore exist (Warner and 

others, 1960). Several of the old mines currently (1960) are being 

drilled by the Utah Construction and Mining Co. 

PREVIOUS INVESTIGATIONS 

Several geologists of the U.S. Geological Survey have reported 

on the geology and ore deposits of Kasaan Peninsula and vicinity, 

Prince of Wales Island, part of which is included in the area shown 

on plate 33. In 1901, A. H. Brooks visited the district briefly, and 

in 1904 and 1905, C. W. and F. E. Wright visited the area and 

reported upon mining developments. Their reports described the 

mines and prospects in some detail, but they did not describe the 

regional geology in detail. In 1907 and 1908, C. W. Wright prepared a geologic map of Kasaan Peninsula and the area immediately 

north and west. Between 1910 and 1941, several geologists of the 

Geological Survey visited the mines and prospects, and in 1941, 

J. C. Reed and George 0. Gates visited the district and recommended 

detailed geologic mapping of the mines and prospects. 

During the years 1942-44, detailed geologic maps, supplemented by 

dip-needle surveys, were made of all the larger mines and most of 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 301 

the prospects. This work was begun in 1942 under the direction of 

E. N. Goddard and continued in 1943 and 1944 under the direction 

o£ L. A. Warner. The results o£ these studies were made available 

in mimeographed reports. A comprehensive paper embodying the 

previous reports and additional data bearing upon the regional 

relations o£ structure, stratigraphy, and ore deposition has been 

prepared by Warner and others (1960). In 1943 and 1944, the U.S. 

Bureau o£ Mines trenched, sampled, or diamond drilled many of 

the mines and prospects (U.S. Bur. Mines, 1944; Wright and 

Tolonen, 194 7). 

0 

50 0 50 Miles 

~~~====================~~==~~~~=±=====r~~ 138° 134° no• FIGURE 47.-Index map of a part of southeastern Alaska showing Craig C-2 quadrangle 

and adjoining areas, Prince of Wales Island, Alaska. 

553362-61--2 
302 MITNERAL RESOURCES OF ALASKA 

SCOPE OF THE PRESENT INVESTI-GATION 

In 1954, a project was undertaken to map geologically that part 

of the Craig C-2 quadrangle not covered by geologic maps made 

by Wright (1915) and by Warner and others (1960) in an attempt 

to establish the details of the stratigraphy and structure of the area 

and to determine the geographic and geologic limits of the coppermagnetite district. The geologic rna pping of the mines and prospects by Warner and others was sufficiently detailed and little more 

could be done; hence, in the present investigation, no attempt was 

made to do more than visit some of the mines and prospects briefly. 

The pertinent information on ore deposits is only summarized here, 

and the reader is referred to the comprehensive paper by Warner 

and others for a detailed discussion of the economic geology of 

Kasaan Peninsula and the area between it and the Rush and Brown 

mine. A preliminary copy of the report by Warner and others was 

available during the fieldwork and was consulted freely during the 

writing of this report. 

The fieldwork for this report was begun in 1954, when the writer, 

assisted by William Hibberd, boatman, spent 30 days in the field 

mapping the southern part of the area. In 1955, assistants were 

Gordon W. Herreid, geologist, and Donald Forbes, boatman; 3 

months were spent in the field, during which time the remainder of 

the area covered by the geologic map was mapped. Herreid and 

the writer operated somewhat independently in the field, and much 

of the geologic data, especially in the area northeastward from the 

north arm of Thorne Bay, are Herreid's. 

In May 1955, the U.S. Geological Survey made an airborne-magnetometer survey of the area near Salt Chuck to supplement a 

reconnaissance magnetic map made in 1945. 

ACKNOWLEDGMENTS 

Many favors were received during the fieldwork, especially from 

Russell Simpson of Ketchikan, a bush pilot who delivered supplies 

and mail and flew the field party to small lakes, much of the time 

in unfavorable weather. Juan Munoz, a mining geologist engaged 

in work near North Pole Hill, accon1panied us to his prospects and 

:furnished geochemical and magnetic data. H. E. Anderson and 

other members of the U.S. Forest Service stationed at Hollis, and 

Clay Scudder of the U.S. Fish and Wildlife Service in Ketchikan 

provided storage for supplies. Officials of the l{etchikan Pulp Co. 

arranged mail delivery at their logging camp at Hollis during 1954. 

The help received is gratefully aclmowledged. 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 303 

GEOGRAPHY 

LOCATION .AND .A.CCESSIDILITY 

The area mapped is on the east shore of Prince of Wales Island~ 

Alaska, about 35 miles northwest of the town of Ketchikan, which 

is the southernmost city in Alaska (fig. 47). The area encompasses 

the north shore of Kasaan Peninsula, a long peninsula extending 

southeastward, and part of the main mass of Prince of Wales Island. 

It is bounded on the east by Clarence Strait, a narrow seaway 

about 120 miles long that is open at the south end to Dixon Entrance, 

a part of the Pacific Ocean. Three bays-Kasaan, Tolstoi, and 

Thorne-indent the coastline and give good bedrock exposures and 

accessibility at tide level. 

The area, which is accessible by boat and by plane, is served by 

scheduled and chartered airplanes and boats from Ketchikan. Before 1954, only a few people lived at Hollis, Kasaan, and Salt 

Chuck, but by 1954 several logging camps were being established 

to provide timber for the new pulp mill in Ketchikan. By 1955, 

logging camps were established at Hollis, Salt Chuck, Kina Cove, 

and on Thorne Bay; these logging operations require boat and plane 

service almost daily. 

Roads and trails are almost totally lacking in much of the mapped 

area. A foot trail leads from Salt Chuck to Kasaan and to the 

south arm of Thorne Bay, and another leads from the mouth of the 

!Carta River to the head of Sahnon Lake. A few short logging roads 

are being made at the established logging camps. A good logging 

road has been made from Hollis, just west of the southwest corner 

of the mapped area, up Maybeso Creek for several miles and gives 

improved access to the gold lodes on the west slope of Granite 

Mountain. A foot trail leads from Salt Chuck to claims on North 

Pole Hill, and an old wagon road leads from a small cove north of 

the mouth of Karla River to an old ferry terminal of the Flagstaff 

mine at the outlet of Little Salmon Lake. The wagon road coni 

tinues from the opposite shore up Granite Creek to the buildings 

at the Flagstaff mine, but it is thickly overgrown by heavy brush 

between the mine and the lake. Trails are nonexistent elsewher~ 

within the mapped area, especially north and west of Thorne Bay_: 

even game trails are lacking. Within most of the mapped area,: 

foot travel is slow, uncertain, and difficult, owing to the dense 

timber and brush and to the swamps and muskeg areas. The 

numerous magnetic anomalies that are present render a compass 

useless for long traverses, and it is often very difficult to determine 

exact localities in the field. · · 
304 ~ERAL RESOURCES OF ALASKA 

TOPOGRAPHY AND DRAINAGE 

-Relief within the area is moderate, except in the extreme southwestern part where the higher mountains within a few miles of the 

sea rise to an altitude of about 3,500 feet. The topography of most 

of Kasaan Peninsula south of the low pass from Tolstoi Bay to 

Kasaan Bay is rugged, even though the higher mountains rise only 

to an altitude of _about 2,800 feet. North of the head of Kasaan 

Bay the hills are low and rolling, and nowhere except locally in 

some of the steeper stream valleys are traverses prevented by steepness of the stream bed. 

A conspicuous broad depression extends northwestward from the 

head of Kasaan Bay and continues up the valley of the Thorne 

River beyond the mapped area. Another low pass extends from the 

head of Tolstoi Bay to Kasaan Bay. Innumerable small lakes, bogs, 

and muskeg areas have formed in all areas of low relief, and some 

occur even on the higher slopes and hills, especially where bedrock 

is thinly veneered by glacial deposits. 

The major drainage is controlled by the main preglacial valleys, 

except in the broad lowlands of the Thorne River valley, where 

glacial till and outwash gravel exert the primary control. The 

Thorne River, which is the largest stream of the area, flows mostly 

on alluvium or reworked outwash gravel, except for a short distance above the point where it curves southward to enter Thorne 

Bay. Here the river has cut a narrow, steep-walled canyon in bedrock. The small volume of alluvium in the present delta of the 

Thorne River, and the narrow, steep-walled canyon mentioned above, 

give evidence that the Thorne River altered its course in postglacial 

time. In preglacial time the Thorne River probably flowed southward past Angel Lake and emptied into the salt chuck at the head 

of Kasaan Bay. 

In upland areas, streams flow on bedrock or in stee.p, youthful 

valleys containing glacial deposits that are being eroded rapidly. 

Larger lakes in upland areas are tarns or cirque lakes in bedrock 

basins. Salmon, Little Salmon, and Wolf Lakes occupy bedrock 

basins scooped out by glaciers, and the lake levels are controlled by 

bedrock lips at the outlets. During yearly high tides, salt water 

flows into Lake Ellen north of the Salt Chuck mine. 

CLIMATE AND VEGETATION 

The climate of this part of Alaska is characterized by mild, wet 

winters and by cool, wet summers. At sea level, rain may fall at 

any time during the winter, but at higher altitudes snow accumulates to a considerable thickness and lies until late summer. In late· 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 305 

August 1955, heavy snowbanks were found on Granite Mountain, 

west of the Flagstaff mine. 

The mean annual precipitation at Ketchikan is about 151 inches, 

most of which falls as rain; the mean annual temperature is about 

45°F. and averages about 32°F. in the winter months and 56°F. in 

July and August. The monthly precipitation ranges from a low of 

6 or 7 inches in May, June, and July to a high of 20 to 24 inches 

in October and November (U.S. vVeather Bureau, 1901-53). Wide 

variations in monthly rainfall occur from year to year-for in;. 

stance, in 1954, the month of August was bright and sunny witn 

only a few days of light precipitation, but in 1955, 15 inches of rain 

fell between August 1 and August 20. During the field season in 

1955, the higher-than-average rainfall was a deterrent to fieldwork 

because storm clouds were so low for weeks at a time that no work 

could be done above an altitude of 800 feet. In addition, all streams 

were so high throughout the months of July and August that they 

were traversed only with difficulty, and many of the bedrock relations were obscured. Although camps were established at the base 

of Rush Peak on two occasions, the peak was shrouded in storm 

clouds for days at a time and could not be traversed to the summit 

even though it was the one mountain in the quadrangle composed of 

bedded rocks with excellent exposures. 

A thick forest of evergreen trees, berry bushes, and alder mantles 

the terrain to an altitude of about 1,500 feet. Between 1,500 feet 

and 2,500 feet, some stunted spruce and hemlock are found, but 

scrub cedar is more common. The timber lies within the holdings 

of the Ketchikan Pulp Co., and logging operations, where thorough, 

are rapidly stripping the timber from large areas. Peat bogs, muskeg areas, and grassy peat flats, with large numbers of beaver dams, 

are interspersed with dense evergreen growths in lowland areas. 

Alder is common at the tide line and along the streams. 

During summer months, from May to September, the insects, including whitesox, gnats, mosquitoes, and various types of black flies, 

are thick enough to be a constant irritation. The whitesox are particularly numerous and vicious. 

THE GEOLOGIC MAP 

The geologic map (pl. 33) is not an adequate portrayal of the 

regional geology of the area, except for the outlines of the larger 

intrusive bodies. The bedrock relations are largely obscured by a 

junglelike mat of evergreens and underbrush, by swamps and muskeg 

flats, and by the widespread glacial and alluvial deposits. In many 

areas, outcrops are limited to bare spots beneath overturned trees, 
306 MINERAL RESOURCES OF ALASKA 

where the roots have pulled up the thick mat of decaying vegetation, or to a few feet in creek bottoms where erosion has removed 

the glacial deposits and alluvium. In some areas, especially in the 

low land north westward from Lake Ellen to Angel Lake and the 

Thorne River, outcrops are so poor that an entire day's traverse 

might disclose but one outcrop beneath an overturned tree. On the 

geologic map, these outcrops are exaggerated to show the lithologic 

type. However, almost continuous outcrops are exposed along the 

shore, and relatively good exposures are found on slopes and creek 

bottoms in the higher mountains in the southwest part of the area. 

The geology of the area mapped in this study is shown on plate 

33. Although the geology of the l{asaan Peninsula was not plotted, 

the writer traversed enough of the peninsula to satisfy himself 

that the rocks in the area between Tolstoi and Thorne Bays are 

similar to those on the north end of l{asaan Peninsula, which are 

for the most part probably Early Silurian ( ~) in age; the geology 

of the peninsula is shown on the geologic maps of Wright (1915, 

pl. 15) and Warner and others ( 1960, pl. 1) . 

Some overlap exists between the geologic map (pl. 33) of this 

report and the geologic map of Wright, especially in a belt from 

the head of Tolstoi Bay to the area north of Karta Bay. The 

geologic interpretation of the areas between Tolstoi Bay and Karta 

Bay as shown on this map and the one made by Wright differs in 

many respects. Warner and others have also modified Wright's 

map in the areas near the principal mineral deposits of Kasaan 

Peninsula and at the Rush and Brown mine. The main differences 

in geologic interpretation, apart from minor variations in geologic 

contacts, that have resulted from these three studies can be summarized briefly as follows: 

1. Plate 15 of Wright's report shows the regional strike of the 

bedded rocks on the south shore of Tolstoi Bay, on the peninsula 

between Thorne and Tolstoi Bays, and west of Loon Lake to 

be northwestward. The present writers' map shows that in 

these areas the rocks generally strike northeastward. Detailed 

mapping by Warner and others (1960) in the area along the 

west contact of the pluton at Tolstoi Point shows that the sedimentary rocks here strike northe.astward. 

2. Wright, on the basis of the fossils found in limestone on Kasaan 

Island, assigns a Devonian age to his basic map unit, the 

Kasaan greenstone, which he interprets as consisting predominantly of clastic rocks with volcanic affinities. Warner and 

others feel that a large part of Wright's Kasaan greenstone consists of altered igneous material of Cretaceous age injected into 

an older series of clastic rocks, probably of Paleozoic age. 
1CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 307 

On the basis of five collections of graptolites from argillite beds 

intercalated within rocks shown on Wright's map as Kasaan greenstone, it is concluded that the Kasaan greenstone in the vicinity of 

Tolstoi and Thorne Bays is of Early Silurian ( ~) age. It appears 

also that the Kasaan greenstone consists predominantly of volcanic 

graywacke, conglomeratic volcanic graywacke, and associated andesite 

flows with lesser amounts of argillite, feldspathic graywacke, conglomerate, limestone, and chert; and that the entire sequence is of 

the same age. No evidence of large-scale injection of andesitic 

igneous material during the Cretaceous was found. The interpretation of Warner and others probably is based upon the fact that much 

of their mapping was done near plutonic igneous rocks where 

metasomatism has changed the Kasaan greenstone so much that its 

clastic origin is no longer apparent. Thus, the writer finds himself 

disagreeing with Wright and agreeing with Warner and others with 

respect to the age of the Kasaan greenstone, but agreeing with 

Wright and disagreeing with Warner and others on the origin of 

the Kasaan greenstone. 

The classification and distribution of the lithologic types shown 

on the geologic n1ap (pl. 33) are the responsibility of the writer, 

as are the petrographic descriptions, the interpretation of structure, 

and the age relations of the units, including dikes. 

GEOLOGY 

The general geology of the mapped area is shown on plate 33. 

The rocks comprise a great thickness of pyroclastic rock, lava, volcanic graywacke, and conglomerate with intercalated feldspathic 

graywacke, minor argillite, chert, and limestone or limy-matrix 

clastic rock. These rocks are intruded by igneous rocks ranging 

in size from dikelets a few inches thick to batholiths and ranging 

in composition from rhyolite and pitchstone to pyroxenite and 

olivine-bearing diabase. The bedded rocks were deposited in Ordovician, Silurian, Devonian, and Tertiary time, and the igneous rocks 

were intruded at various times from the Silurian to the Tertiary. 

Most of the bedded rocks are volcanic graywacke, tuff, conglomerate, 

and argillite or slaty argillite, all of Middle Ordovician to Early 

Silurian ( ~) age. These rocks are slightly to moderately deformed 

and but slightly metamorphosed regionally. The metamorphism in 

large part consists of albitization and the development of low-rank 

metamorphic minerals found in graywacke. Near the larger intrusive bodies they are thermally and hydrothermally altered. 

Highly fossiliferous and almost completely unmetamorphosed limestone of Middle Devonian age is found on l{asaan Island. It is in-
308 ~ERAL RESOURCES OF ALASKA 

truded by dikes and sills of rhyolite and andesite, probably also 

Middle Devonian in age. 

The Tertiary bedded rocks are conglomerate and conglomeratic 

sandstone that lie unconformably on older rocks in isolated patches 

at very low altitudes in the present stream valleys or lowlands. 

Quaternary glacial and glaciofluvial deposits are widespread throughout the entire quadrangle. 

The major structural feature of the rocks appears to be a great 

syncline whose axis strikes northwestward, about parallel to l(asaan 

Bay, although the syncline is complicated by faults of unknown 

displacement. The relation of the Middle Devonian rocks of Kasaan 

Island to the older rocks cannot be established, but their position 

can be accounted for only by large-scale faulting, probably after 

the injection of the stocks in Cretaceous time. Near some of the 

larger stocks the bedded rocks are folded and faulted, and they are 

so complex structurally and are metamorphosed so completely that 

no attempt has been made to differentiate the lithologic types. 

BEDDED ROCKS 

The bedded rocks of the area are extremely monotonous lithologically and in origin. The greater part is graywacke, tuff, and 

conglomeratic graywacke of somber gray-green color. The rocks 

contain large amounts of detrital pyroxene that could have been 

derived by erosion of older lava and tuff, or by simple reworking 

of unconsolidated ash or tuff. In this report, such rock is called 

volcanic graywacke or conglomeratic volcanic graywacke to emphasize the unmistakable volcanic affinity as well as the textural relations common in graywacke (Pettijohn, 1949, p. 243-246). An alternative tern1 might be "pyroxenitic graywacke" to parallel such 

accepted terms as "feldspathic graywacke" and "lithic graywacke." 

The usage, therefore, is similar to that of Williams, Turner, and 

Gilbert ( 1954, p. 303). Key beds are lacking entirely, and the 

only fossils are graptolites, which occur in some of the thin argillite beds that are intercalated in the generally unfossiliferous graywacke. These rocks have been deformed, and then intruded by many 

stocks, batholiths, and dikes. Near the larger intrusive bodies, 

thermal metamorphism has obliterated many of the earlier textures, 

and metasomatism has added large amounts of new material. These 

factors, combined with the generally poor exposures and the cursory 

nature of some of the early geologic work in the area, have led to 

confusion in defining the rocks lithologically and have led to some 

conflicting interpretations. 

The bedded rocks of Kasaan Peninsula were grouped by Brooks 

( 1902, p. 49-50) with other altered volcanic rocks east of Clarence 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 309 

Strait and named the ICasaan greenstone. Brooks assigned them a 

probable age of post-Triassic, probably Early Cretaceous, although 

he correlated the thin limestone beds within the unit with limestone 

units in the Vallenar series of Devonian age, a rather improbable 

correlation. 

In 1908 F. E. and C. W. Wright (1908, p. 110-111) described the 

rocks on l{asaan Peninsula, included by Brooks in the ICasaan 

greenstone, as altered sedimentary and pyroclastic rocks ranging 

from limestone to greenstone tuff, sandstone, and conglomerate 

composed largely of igneous material. They assigned no formation 

name and gave the age as Devonian, largely on the basis of the 

Middle Devonian fossils found on ICasaan Island. 

Later, Wright (1915, p. 67-73) described the volcanic rocks of 

ICasaan Peninsula in greater detail, and in his descriptions he 

stressed the similarity of the rocks on 1\::asaan Peninsula to rocks on 

Thorne Bay and at the Rush and Brown mine west of Suit Chuck 

at the head of Kasaan Bay. Wright discarded the term ICasaan 

greenstone and states (p. 68) : 

Nearly two-thirds of Kasaan Peninsula is occupied by clastic rocks, which 

in large part consist of a series of metamorphosed sediments, usually epidotized 

and containing crystals of amphibole or pyroxene. In texture these rocks .range 

from fine-grained compact rocks, such as quartzites and graywackes, to coarse 

conglomerates. As these sedimentary rocks are composed of igneous material, 

and as they have been greatly altered, they closely resemble massive igneous 

rocks, though in most places their clastic texture may be recognized, especially 

on weathered surfaces. 

Buddington and Chapin (1929, p. 77) collected fossil graptolites 

from the west side of the north arm of Thorne Bay that were 

referred to as being Ordovician in age. Buddington recognized 

the lithologic similarity of the volcanic rocks in Tolstoi and Thorne 

Bays to Silurian rocks exposed on the west coast of Prince of Wales 

Island, but he included the rocks of l{asaan Peninsula and the west 

part of the Craig C-2 quadrangle with his Devonian units. 

Warner and others (1960) discuss in some detail the bedded rocks 

of ICasaan Peninsula and conclude that the clastic rocks are older 

than the altered andesitic rocks, for which they retain the term 

"greenstone." They conclude that the greenstone in large part probably represents altered andesitic rock intruded as great siBs and 

sheets into the older clastic sedimentary rocks before intrusion of 

the dioritic stocks, but within the same general epoch of intrusion. 

This interpretation leads to the conclusion that much of the bedrock 

of l{asaan Peninsula and adjacent areas is intrusive and is much 

younger than the bedded rocks in which it is enclosed. 

In view of the foregoing interpretations, which in part are conflicting, the petrology of the rocks that heretofore have been called 

553362-61-3 
310 MrrNERAL RESOURCES OF ALASKA 

greenstone on Kasaan Peninsula, around Tolstoi and Thorne Bays 

and in the vicinity of the Rush and Brown mine, are discussed here 

in some detail. Quite similar rocks form most of the bedrock of 

the entire quadrangle and extend south, west, and north of it and 

have been assigned ages ranging from Ordovician to Devonian. The 

origin and extent of these rocks must be clearly understood in order 

to make a regional correlation of the various map units and correctly 

interpret the geologic history of the area. 

The writer concurs with Wright that most of the bedded rocks are 

clastic rocks composed of igneous material that underwent but little 

chemical alteration during its erosion and subsequent deposition. 

Most of the massive andesitic rocks within the sediments are volcanic in origin and belong to the same general volcanic epoch that 

produced the andesitic flows interbedded with the clastic rocks. A 

few irregular bodies of andesitic intrusive rocks could belong to the 

middle Cretaceous intrusive epoch, but these form a very minute 

percentage of the bedrock. No large-scale injection of andesitic sills 

preceded the intrusions of the granitoid rocks in the Cretaceous. 

BEDDED ROCKS OF MIDDLE ORDOVICIAN TO EARLY SILURIAN(?) AGE 

Bedded rocks predominantly of Early Silurian ( ~) age comprise 

a great thickness of somber volcanic graywacke, tuff, conglomerate, 

feldspathic graywacke, and andesitic flows that crop out continuously along the entire shore from Tolstoi Point, on l(asaan Peninsula, to Snug Anchorage, north of the entrance to Thorne Bay 

(pl. 33) . The age assignment of the rocks in this area is based 

upon several fossil collections made in Tolstoi and Thorne Bays, in 

the Thorne River south of the confluence of Lava Creek, and on 

the hill west of the north arm of Thorne Bay. Lithologically similar rocks crop out in a wide belt exposed on the south shore of 

Kasaan Bay from a point south of l(asaan Island westward to 

Twelvemile Arm, and on the west shore of Kasaan Bay from the 

entrance of Twelvemile Arm to l(arta Bay and thence northward 

to Salt Chuck. Similar rocks but undated by fossils, crop out along 

much of the shore from the village of l(asaan to a point south of 

the Rich Hill mine and on the shore east of the entrance to the 

salt chuck at the head of Kasaan Bay. These undated rocks, which 

are so similar to the Lower Silurian ( ~) rocks of Thorne and Tolstoi Bays, are almost certainly correlative with them, but in the 

absence of fossils they can only be included with a unit shown as 

Middle Ordovician to Lower Silurian ( ~) rocks west of Kasaan Bay 

and the strong linear that trends northwestward from l(arta Bay 

to the Thorne River. Within this unit of clastic, pyroclastic, and 

effusive rocks are thin beds of limestone, argillite, phyllitic argil-
CRAIG C-2 QUADRANGLE, PRINCE OF W ALE·S ISLAND 311 

lite, chert, and limy-matrix conglomerate, some of which may represent pyroclastic material. Where these different rock types are 

sufficiently diagnostic to be recognized in the field and where they 

are sufficiently large, they are shown separately on the geologic map 

as units within the predominant rock type, which is volcanic graywacke and conglomeratic volcanic graywacke that locally contains 

tuffaceous material admixed with mechanically eroded volcanic 

material. 

VOLCANIC GRAYWACKE, TUFF, AND CONGLOMERATIC VOLCANIC GRAYWACKE 

Volcanic graywacke, tuff, and conglomeratic volcanic graywacke 

are shown as Early Silurian in age in the northeast part of the map 

area where fossils of probably Early Silurian age were found, and 

as Middle Ordovician to Early Silurian in the southwest part of 

the map area where fossils of Middle Ordovician age were found in 

but one locality in a thick sequence of rock lithologically similar 

to the lower Silurian rocks. The dominant lithologic types of the 

Middle Ordovician to Lower Silurian ( ~) rocks are coarse-grained 

volcanic graywacke and tuff in beds ranging in thickness from a few 

feet to more than a hundred feet, and conglomeratic volcanic graywacke containing abundant rounded cobbles of coarsely porphyritic 

volcanic rocks and a few cobbles of other rock types, principally 

chert. The cobbles of the conglomeratic volcanic graywacke usually 

are not in contact, and individual beds may reach a thickness of a 

hundred feet or more without significant variation. Bedding within 

such rocks is extremely difficult to observe except on weathered 

surfaces or at the tide line, where the rocks are continuously exposed 

over long distances. Bedding is shown by local beds of finer grained 

graywacke and tuff in which graded bedding is visible (pl. 34A.), 

and by parallel alinement of cobbles (pl. 34B). The graded bedding shows that the beds are right side up. The volcanic graywacke, tuff, and conglomeratic volcanic graywacke are dark greenish gray to grayish green, are highly indurated, and locally are 

calcareous. The rocks fracture across the cobbles, pebbles, and lithic 

fragments. The mineral and lithic constituents of the volcanic graywacke, conglomeratic volcanic graywacke, and tuff vary considerably from place to place, and it is extremely difficult even in thin 

section to classify accurately any single specimen into 1 of the 3 

types listed. Their most striking feature is the large amount of 

euhedral to angular augite crystals that in places constitute at least 

40 percent of the rock. In small outcrops, these rocks appear to be 

igneous, and where they have been altered by thermal fluids, albitization, or metamorphism, the texture created by the alteration of the 

pyroxene crystals and groundmass certainly suggests an altered ig-
312 ~ERAL RESOURCES OF ALASKA 

neous rock. However, detailed search within any area usually discloses bedding and establishes the rock as being sedimentary. The 

clastic nature of the rock becomes accentuated by weathering, for 

cobbles and pebbles almost identical mineralogically to the groundmass are distinctly visible on weathered surfaces. The volcanic 

graywacke and conglomeratic volcanic graywacke contain some potassium feldspar where associated with lithic graywacke containing 

abundant fragments of porphyry that contains potassium feldspar. 

Elsewhere the content of potassium feldspar is low, generally less 

than 1 or 2 percent. 

The bedded fragmental and clastic rocks in the Thorne and Tolstoi Bay areas have been partly to completely albitized, but the 

degree of albitization varies from place to place. In general the 

groundmass of the volcanic graywacke has been more completely 

albitized than the individual clasts, indicating that grain size may 

have had some effect on the albitizing process. However, these roek~ 

are cut by dike rocks that are not albitized and that contain phenocrysts of albite or anorthoclase, indicating that some of the albitization may have been caused by albite-rich igneous emanations. This 

is discussed further on page 320. 

Four samples of the volcanic graywacke were analyzed chemically. 

The results are reported in the following table. Samples 1 an<l 2 

are from a thick sequence of volcanic graywacke in the entrance to 

Thorne Bay. Sample 3 is the matrix from the thick conglomeratic 

volcanic graywacke from the head of l{arta Bay and is shown in 

plate 35, and sample 4 is a composite chip sample from the numerous cobbles of pyroxene porphyry encased in the matrix of volcanic 

graywacke. These analyses show that the volcanic graywacke is but 

little changed chemically from the original volcanic rocks from 

which it formed, the chief change being the albitization of the 

rocks represented by samples 1 and 2. 

FELDSPATHIC AND LITHIC GRAYWACKE 

Beds of feldspathic graywacke and lithic graywacke are interbedded with the volcanic graywacke and tuff. The feldspnthic and 

lithic graywacke form isolated well-graded lenses in the tuff a11d 

volcanic graywacke. The feldspathic graywacke is a bluish-gray 

rock consisting of quartz and feldspar with minor lithic frng-nwnts 

and some magnetite. Locally it is highly calcareous. The lithi~"' 

graywacke commonly contains fragments of black argillite, nnm('rous volcanic rocks, and light-greenish-gray chert, although many 

other rock types are sparingly present. The matrix is recrystallized 

to epidote, zoisite, chlorite, and prehnite. Potassium feldspar is 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 313 

almost completely absent :from the rocks except where they are 

associated with :fragments of :feldspar porphyry containing orthoclase. 

Chemical composition in percent by weight, of conglomeratic volcanic graywacke, 

Craig C-2 quadrangle, Prince of Wales Island, Alaska 

[Analy!!tfl: PaulL. D. Elmore, Katrine E. White, and Samuel D. Botts] 

2 3 4 

Si02-------------------------- 50. 3 51. 3 44. 3 48. 4 A b03- ________________________ 18. 3 18. 8 18. 0 17. 2 

Fe203------------------------- 5. 0 5. 7 3. 5 3. 1 FeO __________________________ 3. 5 3. 0 8. 5 6. 4 ~gO _________________________ 4. 1 3. 4 6. 2 4. 3 CaO _________________________ 8. 3 7. 6 8. 7 10. 5 ~a20 _________________________ 4. 5 5. 2 1. 4 1. 8 1(20 __________________________ 1. 9 1. 0 1. 3 1. 2 Ti02 

_________________________ 53 74 . 85 74 

P20s------------------------- 24 28 37 43 ~lnO _________________________ 16 16 17 14 H2

0 __________________________ 2. 00 1. 80 4. 50 3. 40 COz __________________________ 48 34 1. 80 2. 20 

TotaL ________________ -- 99. 99. 100. 100. 

1. Chip sample of more than 100 feet of albitized conglomeratic volcanic graywacke or conglomeratic tuffaceous graywacke, north shore of entrance to Thorne Bay; sp gr, 2.967; laboratory No. 145070. 

2. Chip sample of slbitizPd conglomeratic volcanic !?raywacke or conglomeratic tuffaceous graywacke, so•1th shore of entrance to Thorn!' Bay near south arm of bay; sp gr, 2.900; laboratory No. 14.'1071. 3. M11trix or conglomeratic volc,mic g:raywarke from head of Karta Bay, 900 feet south of old wagon road 

t•l Flagstaff minP (see pl. 35R); sp gr, 2.975; laboratory No. 147327. 

4. Cobbles of pyroxene porphyry in sample 3; sp gr, 2.970; laboratory No. 147326. 

FINE-GRAINED ROCKS 

vVithin the volcanic graywacke, tuff, and conglomeratic graywacke that :form the bulk of the bedrock are beds of finer grained 

rocks whose lithologic characteristics are sufficiently different :from 

the enclosing rocks as to warrant their designation on the geologic 

map. In the field the rock types were classified as :feldspathic and 

lithic graywacke, argillite, chert, and limestone. Although these 

rocks occur sparingly throughout the entire map area, and usually 

grade imperceptibly into each other or into volcanic graywacke, they 

form the bulk of the bedrock in some areas, particularly in the 

northeastern and southwestern parts of the map area. The geologic 

boundaries of these areas of fine-grained rocks are not :formational 

boundaries, as is shown by the universal horizontal and vertical gradation into other rock types; but within the general areas shown 

as fine-grained rocks they :form the bulk of the bedrock. The lin1estone units in particular have rather sharp contacts, and a :few of 

the larger limestone beds are shown separately on the map. 

A thick sequence of deformed and slightly schistose argillite and 

slate with minor chert, conglomerate, and graywacke beds lies on 

the southwest contact of the pluton in the southwestern part of the 
314 MINERAL RESOURCES OF ALASKA 

quadrangle. It has been shown as a separate unit on the geologic 

map. Rocks :farther southwest, however, are volcanic graywacke, 

tuff, and conglmneratic volcanic graywacke, and it is not known i:f 

this very thick slate-argillite unit is local or whether it reflects a 

major change in sedimentation. 

ARGILLITE 

Beds o:f grayish-black argillite are intercalated within the :feldspathic and lithic graywacke. The beds range in thickness :from a 

dark film to as much as several inches and alternate with beds o:f 

:feldspathic graywacke normally o:f greater thickness. Interbedded 

argillite and :feldspathic graywacke in places reach a thickness o:f at 

least 100 :feet. 'Vhere intercalated with beds o:f massive volcanic 

graywacke, the argillite and :feldspathic graywacke are intensely 

deformed, presumably because they were relatively incompetent during deformation. The argillite is a hard rock that :fractures conchoidally, but in thin section it is seen to consist predominantly o:f 

small grains o:f quartz and :feldspar with graphitic argillaceous 

bands that create a slight tendency toward :fracturing parallel to the 

bedding. Even the most argillaceous and graphitic argillite contains 

more than 50 percent detrital mineral grains, chiefly quartz and 

feldspar. The more graphitic zones in the argillite have yielded 

graptolites that date the rocks in the area o:f Tolstoi and Thorne 

Bays as Early Silurian ( ~) in age. 

CHERT 

Within the volcanic graywacke, tuff, and conglomeratic graywacke are thin beds o:f pale-grayish-yellow to pale-greenish-yellow 

chert in beds ranging in thickness :from ljg o:f an inch to as much as 

6 inches, interstratified with dusky-yellow-green to dark-gray argillite with a chert matrix. The beds are lenticular and grade into 

volcanic graywacke. Beds o:f this type are especially common in 

the area :from Snug Anchorage to the north boundary o:f the rna pped 

area, but they occur sparingly throughout the bedded rocks over 

the entire rna pped area. They :form a large part o:f the area o:f 

fine-grained rocks north o:f the pluton in the southwestern part of 

the mapped area. Chert and argillite o:f this type are more common 

in the volcanic graywacke than in the :feldspathic graywacke. In 

thin section the chert is seen to contain abundant rounded :fragments 

o:f quartz and :feldspar encased in cryptocrystalline silica. 

LIMESTONE 

Thin beds of limestone or marble, limy-matrix graywacke, and 

limy-matrix tuff are contained within the thick series o:f volcanic 
:CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 315 

graywacke, tuff, and conglomeratic volcanic graywacke, especially in 

Thor~e and Tolstoi Bays. The purer marble is white to greenish 

whitel and contains isolated fragments of volcanic rocks and tuff. 

Loca~ly the limestone is very schistose, but at some places it is quite 

massirve. Dark aphanitic dikelets and tuff beds intercalat~d in the 

limestone have been disrupted during regional deformation to produce ! imestone in which angular fragments of dark rock lie isolated 

in a l~mestone or marble matrix. Locally the limestone is intricately 

folde~ (pl. 36) . Of special interest are the beds of limestone in 

KinaiCove, on the beach north of the pluton at the mouth of Twelvemile -¥\-rm, and in Thorne Bay that contain round porphyry cobbles, 

heavi~y pydtized, in crudely stratified beds. The limestone contains 

no sqlfide minerals; beds of this type probably were formed from 

volca~ic ejecta that had been previously pyritized, probably in the 

throaitl of a volcano, and that fell into limy mud. No fossils have 

been found in the limestone. 

I 

I 

CONGLOMERATE 

Th~ck lentoid beds of conglomerate are common within the finer· 

grai~ed rocks. Three distinct types of conglomerate are recognized. 

One ¢onsists of cobbles and pebbles of volcanic rocks in a matrix of 

volcahic graywacke. Conglomerate of this type grades laterally 

and iertically into conglomeratic volcanic graywacke which merely 

reflects less winnowing and sorting. This conglomerate grades so 

i~petceptibly into .conglomeratic volcanic graywacke that its separatiOn ~n the geologic map has not been attempted. 

Th~ second type of conglomerate contains well-rounded to subangu~ar fragments of diverse rock types, many of which are not 

recogtlized in place in the map area, and it is sufficiently different 

from I the conglomerate first described to be shown on the geologic 

map ~s a distinctive unit within the volcanic-graywacke unit. The 

congl~merate forms lentoid pods or piles, some of which are at 

least ~everal hundred feet thick, isolated within volcanic graywacke, 

tuff, ~r conglomeratic graywacke. Many of the lenses grade laterally ~nd vertically into conglomeratic graywacke, and some grade into lit~ic graywacke with intercalated argillite beds. Many of the 

steep I cliffs in the map area are developed in this type of conglomerate~ for it is resistant to erosion and glacial plucking has removed 

large I joint blocks. 

Th~ lithologic types most common in the conglomerate are rhyolite. ~orphyry, light-gray to light-bluish-gray chert or chalcedony, 

and ~uff-weathering limestone. The conglomerate also contains lesser aJ;nounts of banded chert, quartz-diorite, fine-grained light-colored ]andesite, rhyolite, argillite, vein quartz, slate, sandstone, and 
316 MINERAL RESOURCES OF ALASKA 

very minor amounts of other lithologic types. The cobbles in the 

conglomerate generally are in contact, either throughout the unit or 

within the thicker conglomerate beds that are separated by finer 

conglomerate or conglomeratic graywacke. · Stream channels and 

shingle pebbles and cobbles are common in the conglomerate, which 

was undoubtedly deposited by running water. Very thick conglomerate of this general type forms the north slope and east 

base of Rush Peak, and it is sufficiently different to warrant individual discussion. This conglomerate contains a larger amount of 

slate, argillite, and graywacke than the conglomerate in the Lower 

Silurian rocks of Thorne and Tolstoi Bays, and on the lower 

north slope of the mountain, certain beds several hundred feet thick 

consist almost entirely of very large cobbles of buff-weathering unfossiliferous limestone. Buff-weathering sandstone, a lithologic type 

not recognized in the conglomerate elsewhere in the map area, occurs 

sparingly, and locally the conglomerate grades to a fine-grained 

facies with a black argillaceous matrix. The conglomerate on the 

higher north slope of Rush Peak displays marked shingling, good 

grading, and abundant stream channels, suggesting subaerial deposition. However, within the conglomerate, and beneath it, are beds 

of black argillite interstratified with beds of lithic graywacke, which 

undoubtedly were deposited in water. 

The collection of Middle Ordovician fossils from argillite at the 

east base o-f Rush Peak shows that some of the rocks in this area 

are l\{iddle Ordovician in age, and it is entirely possible that the 

conglomerate of Rush Peak is also Ordovician, especially in view of 

the differences noted between this conglomerate and other conglomerate in the Thorne Bay-Tolstoi Bay areas. However, in spite of 

the differences noted, the similarities are more striking than the 

dissimilarities, for both types of conglomerate contain chert, graywacke, argillite, limestonB, vein quartz, chalcedony, quartz diorite, 

several types of light-colored felsitic rocks, some of which have flow 

lines, and porphyritic volcanic rocks similar to those forming the 

cobbles in the conglomeratic volcanic graywacke. Furthermore, the 

physical characteristics are quite similar; both types of conglomerate 

locally ai·e well sorted, contain cobbles in contact with each other, 

contain intercalated lithic graywacke beds, and vary rapidly lithologically and in physical properties. In short, their source rocks 

and their depositional environments were very similar, and without 

additional fossil evidence to indicate an age disparity the writer is 

reluctant to assign them a different age. 

Conglomerate of the type just described seems to have been deposited by streams whose transported load was derived from a 

geologic terrane containing diverse rock types, and much of the 
GEOLOGICAL SUJWEY "BULLETIN 1 0 3 8 PLATE 3 4 

A. Photomicrograph of typical lithic graywacke along the shore of Thorne 

and Tolstoi Bays. About X 6, crossed nicols. 

B. Conglomeratic volcanic graywacke or tuff on the north shore of the 

entrance to Thorne Bay. 
GEOLOGICAL SURVEY BULLETIN 1058 PLATE 35 

A. Co nglomeratic volcanic graywacke from the head of Karla Bay, with crude stratification of cobbl es. 

Dark specks In cobbles a nd matrix are pyroxene crystals. None of the cobbles arc amygdaloidal. 

B. Conglomeratic volca ni c graywacke from the head of Karta Bay, with crude stratification of cobbles anrl 

fine·grained beds (upper right). Small white spots are barnacles. 
GEOLOGICAL S"CR.VEY BULLETIN 1058 PLATE 36 

Folded limest·one with intercalated tuff beds on east shore of Snng Anchorage. 
GEOLO(JICAL SUHVEY BULLETIN 10;:;8 PLATE 37 

A. Contorted fine-grained sedimentary rocks in slump conglomerate with limestone matrix on south shore 

of ~outh entrance to Thorne Bay. 

B. Limestone-matrix slump conglomerate on north shore of island in entrance to Thorne Bay. 
GEOLOGICAL SURVEY BULLETIN 1058 PLATE 38 

A. Photomicrograph of typical amygdaloidal lava flow from the area 

west of Thorne Bay. About X 12, crossed nicols. 

B. Photomicrograph of trachytic lava flow with carbonate amygdules, 

Tolstoi Bay. About X 6. 
GEOLOGICAL SURVEY BULLETIN 1008 PLATE 39 

A. Tertiary conglomerate on a beach near the north end of Craig C-2 quadrangle. 

B. Photomicrograph of conglomerate from Beny Island, Kasaan Bay, showing 

magnetite pebble (black). About X 6. 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 317 

conglomerate was deposited where the streams entered salt water or 

flat areas near sea level. The preponderance of cobbles of rocks that 

in general are very resistant to erosion seems to be of particular significance, indicating that they were transported some distance from 

their source area. 

Limy-matrix conglomerate, which apparently represents submarine 

landsliding of coarse material into limy mud, is exposed only on 

the islands at the entrance to Thorne Bay, and along the shore of 

the south entrance to Thorne Bay. It represents the third distinctive type of conglomerate, but it does not occur in units large enough 

to be shown separately on the geologic rna p. The conglomerate 

contains boulders as much as several feet in diameter, which locally 

are in contact with each other. These cobbles generally are similar 

to the cobbles in the enclosing conglomeratic volcanic graywacke, 

but locally they are composed either of large fragments of contorted 

fine-grained sediment that was only partly lithified at the time of 

slumping (pl. 37) or of rounded pebbles of chert and argillite. 

ANDESITE 

Andesite flows are found throughout the sequence of volcanic 

graywacke and associated rocks, but most of the flows are too small 

or too poorly exposed to be shown individually on the geologic map. 

However, two areas in which flows form the bulk of the bedrock 

are shown, one of about 15 square miles in the north-central part of 

the quadrangle and a small one west of the south arm of Thorne 

Bay. The flows of the two areas are distinctly different. 

The flows west of Thorne Bay are dark-greenish-gray porphyritic 

and amygdaloidal andesite. The phenocrysts, which are composed 

entirely of plagioclase feldspar, are as much as 5 mm in length and 

constitute about 20 percent of the rock. The phenocrysts are imbedded in a pilotaxitic groundmass of microlites of albite, or of 

sodic oligoclase rimmed by albite. The amygdules consist entirely 

of calcite, of calcite cores rimmed with chlorite, or of plagioclase 

feldspar rimmed with chlorite. Most of the amygdules .contain 

chlorite (pl. 38A.). These andesite flows contain no phenocrysts of 

mafic minerals. 

The flows in the north-central part of the quadrangle are more 

varied and form a thin lower group of andesite flows somewhat 

similar to those west of Thorne Bay, and of amygdaloidal and nonamygdaloidal flows and flow-breccia that are characterized by a large 

proportion of phenocrysts of pyroxene and smaller amounts of plagioclase feldspar. Many of the pyroxene phenocrysts are broken 

euhedral crystals. Two types of pyroxene occur, one having an 

optic angle near 60° and a beta index of refraction of 1.705, and 

553362-61-4 
318 MINERAL RESOURCES OF ALASKA 

the other having an optic angle ranging between 22° and 30° and a 

beta index close to 1. 71. These optical properties indicate that the 

pyroxenes are calcic augite or augite, and pigeonitic augite. The 

plagioclase phenocrysts are andesine. In some of the flows the 

groundmass is composed principally of hornblende, pleochroic in 

blue green, and in others it consists of plagioclase laths, fragments 

of pyroxene, and epidote, prehnite, and cryptocrystalline quartz 

or feldspar. The amygdules consist either of feathery quartz that 

rims a core of calcite or wholly calcite, prehnite, or finely twinned 

albite. 

Thin lava beds occur elsewhe.re (pl. 38B), and a few exposures 

show that lava locally engulfed and deformed the underlying finegrained rocks prior to their lithification. No pillow structures were 

found in the flows despite the fact that they are interstratified with 

rocks that were deposited in a predominantly marine environment. 

It is possible that pillow lava would be found if exposures were 

more extensive. 

STRUCTURE AND THICKNESS 

The structure of the Middle Ordovician to Early Silurian bedded 

rocks is complex, owing to both folding and faulting, and much of 

it cannot be determined in the field. The apparent regional structure is a major synclinorium, the axis of which trends about N. 45° 

W., roughly parallel to Kasaan Bay. The southwest limb of the 

synclinorium contains smaller folds that cause great variations in 

strike and dip, but the rocks of the northeast limb are more constant 

in attitude, local disruptions of attitude being caused primarily by 

plutons. Impressed upon the broad synclinorium are numerous 

smaller folds whose axes trend both parallel to and at wide angles to 

the axis of the synclinorium. A system of northeastward-trending 

folds is apparent locally as shown by the axes of smaller folds and 

drag folds in the argillite and the slate-argillite band in the south'" 

west part of the mapped area, where the axes of small folds plunge 

rather consistently northeastward. Folds trending northeastward 

were noted by Warner and others ( 1960) on Kasaan Peninsula, and 

folds trending northeastward were noted to be the major structural 

features on the west side of Prince of Wales Island (Eberlein, G. D., 

written communication, and Buddington and Chapin, 1929, p. 290). 

The continuity of the rocks is interrupted by large and small 

faults, the displacement of which could not be determined because 

of the lithologic similarity of the rocks and the scarcity of outcrops. 

The faults actually detennined in the field are shown as solid lines 

on plate 33, and faults inferred from a study of aerial photographs 

are shown as questioned faults. The faults form three sets, one 

striking northwestward, one northeastward, and the third north-
·CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 319 

ward. Some of the faults are bordered by a zone of sheared rock of 

considerable width, indicating that the faults have appreciable displacement. The largest faults, which trend northwestward, and the 

northward-trending faults north of Thorne Bay, are bordered by 

several feet of sheared rocks and gouge. 

A second possible interpretation of the regional structure of the 

Middle Ordovician to Lower Silurian (?) rocks involves major movement on the fault that is assumed to be marked by the strong linear 

running from l(asaan Bay to the Thorne River valley and beyond. 

If this is a major fault with downthrown side to the east, the apparent regional structure could be caused by displacement that 

dropped the rocks east of the fault that strike northward or northeastward and dip westward or northwestward into contact with 

rocks west of the fault that strike northwestward and dip northeastward. Evidence supporting this conclusion is that the fault 

marks the rough boundary between rocks on the west from which 

was collected one group of fossils of Middle Ordovician age and 

rocks on the east that are believed to be virtually continuous with 

rocks of similar lithology and probable Early Silurian age west 

of the south arm of Thorne Bay. In general, the fault also separates rocks of known complex structure to the west from rocks of 

1nore simple structure to the east. This fault, if a major one, probably continues beneath Kasaan Bay and could help explain the 

anomalous position of Middle Devonian rocks on Kasaan Island, 

which is discussed later. 

The thickness of the Middle Ordovician and Lower Silurian ( ? ) 

rocks cannot be established with the present data. The rocks are 

moderately to strongly folded and faulted, and no distinctive beds 

have been found that enable one in the field to be certain of the 

stratigraphic position of any bed. However, some idea of the thickness may be obtained from areas where faulting and folding are 

moderate and where exposures are good along beaches. 

The rocks from Tolstoi Bay to the head of Thorne Bay and 

thence to Snug Anchorage strike northeastward, and they dip northwestward at angles that range from 20° to 50° and average 30° to 

40°. No faults have been recognized along the shores of the entrance 

to Thorne Bay, and only minor folds are known, none of which 

involve repetition of beds. A thickness of volcanic graywacke, tuff, 

conglomeratic volcanic graywacke, and argillite of at least 6,000 feet 

is indicated in this section. 

A line from Forss Cove, north of Snug Anchorage, to the mouth 

of Falls Creek on the Thorne River also roughly cuts across the 

strike of the beds, and although this area is faulted, no repetition 
320 MINERAL RESOURCES OF ALASKA 

of major units is recognized. The bedded rocks may be as much 

as 17,000 feet thick in this area. 

A thick section of conglomeratic volcanic graywacke, tuff, and 

argillite is exposed on the north shore of Twelvemile Arm between 

the quartz diorite (pl. 33) and l(arta Bay. These rocks are at least 

several thousand feet thick and probably are the equivalent of 

similar rocks exposed in Thorne and Tolstoi Bays. 

METAMORPHISM 

The Middle Ordovician to Lower Silurian ( ~) bedded rocks are 

regionally metamorphosed. The metamorphic rank is low and does 

not reach even the rank of the greenschist facies, except in the 

thennal metamorphic aureoles near the intrusive rocks. In the volcanic graywacke the regional !netamorphism produced mineral assemblages that are characteristic of indurated graywacke that has 

been deeply buried without being dynamically metamorphosed. The 

volcanic graywacke consists of discrete mineral and rock fragments 

that retain their original texture and in part their original composition. The groundmass is recrystallized to epidote, chlorite, calcite, prehnite, and other minerals characteristic of low-rank metamorphism. Reaction between matrix and grains is noticeable in 

some sections, but in others the grain boundaries are sharp and 

distinct. The grains in the fine-grained argillite have retained their 

form, and magnetite has not begun to clot. Bedding is everywhere 

preserved, and nowhere is regional fracture or flow cleavage developed. Limestone within the graywacke is recrystallized, and locally 

it is schistose, especially near faults. Some of the fine-grained argillite and slaty argillite is folded on a small scale, but even in these 

folds no fracture cleavage is developed. Fine-grained brittle cobbles in the conglomerate are not fractured. In short, all the regional 

metamorphic effects are those that might be expected from burial 

and Inoderate to slight folding at moderate depth and low temperature. The incompetent beds of argillite and shaly argillite, and the 

thin beds of limestone, were deformed complexly where interbedded 

with thick graywacke or conglomeratic graywacke, and some of the 

faulting that attended and followed the folding was in part localized 

by the less competent beds. The schistosity in the limestone at the 

head of Tolstoi Bay and on the south arm of Thorne Bay was 

produced by faulting. 

Near the plutons the rocks are changed considerably by thermal 

metamorphism and by metasomatic metamorphism involving chiefly 

the introduction of albite and orthoclase. However, these metamorphic changes are separate and distinct from the regional metamorphism, and in view of the low rank of the regional metamorphism 
·CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 321 

in the mapped area, the writer disagrees with the use of the term 

"greenstone" that has been applied to the bedded volcanic graywacke, conglomeratic volcanic graywacke, and associated rocks 

(Brooks, 1902, p. 49, 97; vVarner and others (1960) ). He agrees 

with and supports the conclusion by Wright (1915, p. 68) that the 

bedded rocks are largely clastic in origin with composition and 

texture still readily discernible. 

AGE AND CORRELATION 

The age of the thick sequence of volcanic graywacke, tuff, conglomerate graywacke, and minor beds of limestone, argillite, and 

chert is based upon six fossil collections made in the summer of 

1955. 

These collections were studied by J. T. Dutro, Jr., of the U.S. 

Geological Survey, who reports as follows: 

Coilection 55-AHd-330: Contains Dicranograptus sp. and Climacograptus aff. 

C. bicornus (Hall). The age is Middle Ordovician. Lat 53°38'14" N., long 

132°38' \V., about half a mile west of north end of Foot Lake. 

Collection 55-ASn-184: Contains Hallograptus?, CZimacograptus, AmpZea:ograptus?, several other types of diplograptids, and indeterminate fragments of 

inarticulate brachiopods. 'l'he faunule is possibly of Ordovician age. The predominance of diplograptid forms suggests a pre-Silurian age, whereas the absence of any leptograptids points to a post-Early Ordovician age. Lat 53°40' N., 

long 132°33'04" W., about 1.2 miles S. 70° W. of Davidson's logging camp, 

north arm of Thorne Bay. 

Collection 55-ASn-216: Contains Orthograptus?, Climacograptus?, and several undetermined diplograptids plus indeterminate inarticulate brachiopod 

fragments. This collection resembles 55-ASn-184 rather closely and may be of 

the same age. Lat 53°39'05" N., long 132°26'40" W., west shore of Tolstoi Bay, 

south of small cove near inlet. 

Collection 55-ASn-240: Contains only indeterminate diplograptid fragments. 

Sainsbury indicates that this collection is from about the same bed as 55-ASn216, and is, without doubt, the same age. Lat 53°37'55" N., long 132°27' W., 

west shore of Tolstoi Bay, 1 mile from head. 

Collection 55-ASn-125: Contains Rastrites?, Climacograptus?, Monograptus?, 

Lingula?, Orbiculoidea?, and indeterminate pelecypod fragments. The age is 

Early Silurian (?). Lat 53°39'56" N., long, 132°30'40" W., west shore of 

Thome Bay, opposite entrance. 

Collection 55-ASn-232: Contains Climacograptus? and diplograptids of uncertain generic affinities, monograpticls, and fragments of inarticulate brachiopods. The age is possibly Early Silurian (?), based on the comparison of this 

material with that of 55-ASn-125. Lat 53°42'20" N., long 132°36'30" W., east 

bank of Thorne River, 0.3 mile south of the mouth of Lava Creek. 

All collections are from argillite or slaty argillite beds. 

These collections indicate that the rocks in the general area of 

Thorne and Tolstoi Bays are Early Silurian ( ~) in age, and that 

some of the rocks west of Foot Lake are J\1idd1e Ordovician in age. 

The writer was unable to distinguish everywhere the Lower Silu-
322 MINERAL RESOURCES OF ALASKA 

rian ( ? ) rocks frmn the Middle Ordovician rocks, and west of the 

fault running north from Karta Bay both are included in the 

same map unit. This unit on the geologic map is noted as Middle 

Ordovician to Early Silurian ( ? ) in age. It is entirely possible that 

these rocks range in age from Middle Ordovician to Early Silurian. 

Buddington and Chapin (1929, p. 79-80) state that the lowermost 

formation of the Silurian system cannot be distinguished with certainty from the Middle Ordovician rocks, which is in accord with 

the findings of the present report. The fossils reported above show 

lnany similar forms, and Dutro, who identified these fossils, suggests 

that collections 55-ASn-184, -216, and -240 could be pre-Silurian in 

age. Collections 55-ASn-216 and -240 are from the lowest stratigraphic sequence on the north shore of Tolstoi Bay and may represent the lowermost Silurian rocks mapped, but collection 55-ASn184 comes from rocks that are believed to be stratigraphically higher 

than any possible Ordovician rocks in the Thorne Bay area. Thus, 

both lithologic and fossil evidence suggests that it is impossible at 

present to differentiate the Lower Silurian rocks from the Middle 

Ordovician rocks, but because a definite Early Silurian ( ? ) fauna 

is found in one area in Thorne Bay it seems preferable to assign 

an age of Early Silurian ( ? ) to those rocks and to similar rocks in 

the area north and west of Tolstoi and Thorne Bays. On the map 

explanation these Lower Silurian rocks are shown as a separate 

unit from the Middle Ordovician to Lower Silurian map unit. 

Because of the almost complete lack of detailed mapping on 

Prince of 'iV ales Island, it is difficult to correlate with reasonable 

confidence the Middle Ordovician and Lower Silurian ( ? ) rocks of 

the mapped area with other rocks on Prince of Wales Island. Buddington and Chapin (1929, p. 76) list Ordovician graptolites including Olimaeograptus bieornis var. tridentatus from rocks on Kla wak 

Lake about 14 miles west of the probable Middle Ordovician rocks 

at the base of Rush Peak, and on their n1ap they show a large area 

of Ordovician rocks north of Kla wak Inlet. These rocks are not 

lithologically silnilar to those of Rush Peak, but it is probable 

that Ordovician rocks, possibly with infolded or infaulted Lower 

Silurian(?) rocks, form a continuous belt from Klawak Inlet to 

Rush Peak. 

The Lower Silurian rocks exposed on Thorne and Tolstoi Bays 

are the equivalent, in part, of rocks mapped by Buddington and 

Chapin (1929, p. 75) and by Eberlein (written communication) on 

the south side of Heceta Island and vicinity, on the west side of 

Prince of Wales Island. These rocks are lithologically similar to 

the rocks on Thorne and Tolstoi Bays, and fossil collections establish them as Early Silurian ( ? ) in age. They represent the next to 
CRAIG C-2 QUADRANGLE, PRINCE OF WALE·S ISLAND 323 

the lowest formation within the Silurian system on Prince of Wales 

Island. 

If the undated beds of volcanic graywacke and conglomeratic graywacke exposed south of Karta Bay and along the south side of 

Kasaan Bay from Baker Point to Twelvemile Arm are Early 

Silurian ( n in age, as they appear to be, then the slate-argillite 

belt south of the pluton at the mouth of Twelvemile Arm may represent the lowest formation of the Silurian system as exposed elsewhere on Prince of Wales Island. Buddington and Chapin (1929, 

p. 81-82) state that the lowermost Silurian formation consists predominantly of dark to black graphitic slate with interbedded graywacke and some associated limy layers and sparse conglomerate. 

Rocks of this lithologic type lie beneath the volcanic graywacke and 

conglomeratic volcanic graywacke in the south part of the mapped 

area. These rocks locally are highly schistose, with bedding almost 

obliterated. The degree of defonnation and the dynamic metamorphism cannot be correlated entirely with nearness to intrusive 

rocks and may indicate that these rocks are appreciably older than 

the overlying beds. 

CONDITIONS OF DEPOSITION 

The Middle Ordovician and Lower Silurian ( ~) rocks of the 

mapped area appear to have been deposited for the most part in a 

marine environment in a region of active volcanism undergoing 

rapid marine erosion. The basin of deposition must have bordered 

either a volcanic archipelago or an older landmass containing predominantly volcanic rocks that furnished the lithic pebbles and the 

pyroxene fragments of the volcanic graywacke and conglomeratic 

volcanic graywacke. The bulk chemical composition of the volcanic 

graywacke closely approaches that of andesite, and the bulk chemical 

composition of the matrix of the conglomeratic volcanic graywacke is 

so close to that of the pyroxene porphyry cobbles that only the 

slightest chemical decay occurred between the erosion of the volcanic rocks and their subsequent deposition as marine volcanic 

graywacke. 

The basin of deposition also received volcanic material from contemporaneous volcanism, as evidenced by the tuffaceous beds in the 

volcanic graywacke, the interbedded flows, and the pyritized porphyry ejecta encased in limestone. The cleaner feldspathic graywacke is probably the distal equivalent of the coarser volcanic graywacke, and locally conditions were such that fine-grained argillite 

and chert were deposited. In deeper parts of the basin the finegrained rocks approached a shaly composition, and within these beds 

were buried the graptolites that date the rocks. Streams from the 
324 ~ERAL RESOURCES OF ALASKA 

eroding lands discharged into the margin of the basin, building 

up thick piles of conglomerate containing foreign rock types, and 

locally the conglomerate graded laterally and vertically into volcanic graywacke or conglomeratic graywacke of local derivation. 

In some areas submarine landsliding of angular and rounded cobbles 

and boulders into unconsolidated limy mud gave rise to the limestone-matrix conglomerate, and locally the recently buried rocks were 

reelevated and eroded to form local conglomerate composed of argillite, graywacke, and chert fragments. The general geologic environment may have resembled that of parts of the present Aleutian 

Islands, where older volcanic rocks are being rapidly eroded and 

the detrital sediments admixed with new volcanic material, stream 

conglomerate, chert and argillite, and limy-matrix clastic material. 

The source of the dioritic and rhyolitic cobbles of some of the 

conglomerate apparently lies outside the mapped area, for no Paleozoic rocks of dioritic composition are known in the map area, and 

only a few rhyolite dikes are known, their number within the 

mapped area being too small to account for the great predominance 

of rhyolite and rhyolite porphyry cobbles in some of the conglomerate. Buddington and Chapin (1929, p. 83) note Lower Silurian 

rhyolite flows and breccia at Sarheen Cove, El Capitan Passage, on 

the west coast of Prince of Wales Island, and this may be the source 

area of the rhyolite in the Lower Silurian ( ~) rocks near Thorne and 

Tolstoi Bays. 

LIMESTONE OF MIDDLE DEVONIAN AGE 

The Middle Devonian limestone of the mapped area is confined to 

Kasaan and Round Islands in Kasaan Bay. It consists of gray- to 

buff-weathering limestone, both thin bedded and massive, in beds 

ranging in thickness fron1 1 inch to 1nore than 100 feet. 

The limestone on both islands is highly fossiliferous, and some 

beds are composed almost entirely of fossils. Fossils in a collection 

made in 1905 by E. M. Kindle are reported by Wright (1915, p. 

70-71) to be of Middle Devonian or late Early Devonian age. On 

Kasaan Island the limestone is completely unmetamorphosed and is 

gently folded, but on Round Island it is strongly folded but unmetamorphosed, with folds plunging eastward at angles up to 70°. 

On Kasaan Island the limestone in general strikes northwestward 

and dips northeastward at angles ranging from 10° to 50°, although 

the strikes and dips change rapidly on numerous small folds that 

trend northwestward and northeastward. These folds are exposed 

particularly well on the shores of the small lagoon on the south side 

of the island. 
:CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND, 325 

The limestone on Kasaan Island is intruded by, and in part· interbedded with, platy rhyolite that was described by Wright (1915, 

p. 70) as sandstone, and by Buddington and Chapin (1929, p. 97) 

as Tertiary rhyolite. Detailed observations by the writer and G. D. 

Eberlein at the small cove on the south side of Kasaan Island show 

that the rhyolite is in part intrusive into, and in part contemporaneous with, the limestone and therefore is Middle or late Early Devonian in age. The limestone is intruded also by diabase dikes and 

contains one small area of contact rock composed of garnet and lime 

silicate minerals at the contact of a diabase dike. 

Warner and others ( 1960) feel that the Middle Devonian limestone of Kasaan and Round Islands is in an anomalous position with 

respect to the rocks of Kasaan Peninsula 2 miles to the east. They 

note that all the limestone observed by them on Kasaan Peninsula 

is highly metamorphosed and intricately folded, in great contrast 

to the fossiliferous and unmetamorphosed limestone on Kasaan 

Island. 

The writer agrees fully with their conclusions and feels that the 

Middle Devonian limestone of Kasaan and Round Islands must be 

part of a fault block moved into its present position in the Late 

Cretaceous or early Tertiary. A_dditional supporting evidence is as 

follows: 

1. Marmorized unfossiliferous limestone intruded by abundant dikes 

and sills of metamorphosed pyroxene porphyry forms the bulk 

of the bedrock on Berry Island, about 1500 feet north of 

Kasaan Island. The proximity of the two types of limestone, 

one highly metamorphosed and intruded by abundant pyroxene 

porphyry dikes and the other unaltered and intruded only by 

diabase dikes, is strong evidence of a structural disconformity 

between them. 

2. A small reef about 600 feet west of Kasaan Island is a hybrid 

rock composed of pink diorite and feldspathized volcanic graywacke, and the rocks on the shoreline west of Kasaan Island are 

so extensively metasomatized and contain so many dikes of diorite porphyry that it seems probable that a diorite pluton must 

underlie Kasaan Bay west of Kasaan Island. If the present 

position of Kasaan Island were its original position, this pluton 

almost certainly would have metamorphosed the limestone of the 

island. 

3. Kasaan Island is intruded only by rhyolite of Devonian age and 

diabase dikes believed to be Tertiary in age. It is unlikely that 

so large an area could be found anywhere else within the mapped 

area that does not contain other dikes related either to the vol553362-61--5 
326 MINERAL RESOURCES OF ALASKA 

canic rocks or to the plutons injected in the late Early to the 

Late Cretaceous. This also suggests that the limestone is not in 

its original position. 

4. Two of the diabase dikes, which are identical to those found 

throughout the mapped area and which intrude the rhyolite 

just east of the mouth of the lagoon on the southwest shore of 

Kasaan Island, are badly shattered and deformed. These are 

the only diabase dikes in the mapped area that were seen to be 

disturbed tectonically, which further suggests some tectonism of 

Kasaan Island in the Tertiary. 

Evidence that Kasaan and Round Islands are part of a fault block 

that moved into position after the intrusion of the plutons in Late 

Cretaceous time, and possibly in early Tertiary time, is extensive, and it seems best not to attach regional significance to the fossils of Kasaan Island or to use these rocks to date others in this area. 

BEDDED ROCKS OF TERTIARY AGE 

CONGLOMERATE, SANDSTONE, AND OONGLOM:ERATIO SANDSTONE 

Tertiary sedimentary rocks that lie with pronounced disconformity 

on older rocks are exposed at scattered places within the mapped 

area. The Tertiary rocks near Coal Bay and Little Coal Bay, on 

the south shore of Kasaan Bay, were described by Buddington and 

Chapin (1929, p. 263) as flat-lying sandstone unconformably overlying Devonian greenstone and sedimentary rocks. 

The Tertiary rocks of Coal Bay are exposed discontinuously in a 

creek bed for a short distance from the beach. They consist of 

light-gray to light-buff graywacke-sandstone containing carbonized 

logs with branches attached. The attitude of the sandstone cannot 

be determined, but it appears to dip gently, if at all. The underlying rocks are probably of Early Silurian age. 

In Little Coal Bay the Tertiary rocks are exposed in the creek 

bed for about three-quarters of a mile from the beach. Near the 

beach they consist of conglomeratic graywacke-sandstone in which 

the rounded cobbles reach a maximum diameter of 10 inches. The 

cobbles are not in contact with each other, and they consist predominantly of unweathered diorite; a few of the smaller cobbles are 

argillite. 

The stream rapidly erodes the graywacke-sandstone, leaving the 

diorite cobbles scattered along the stream channel. A few discontinuous flat-lying seams of lignitic coal that are a few inches thick 

and that contain marcasite crop out in the creek bottom. 

At an altitude of about 30 feet the rock is boulder conglomerate 

with a graywacke-sandstone matrix. The boulders and cobbles are 

composed predominantly of diorite and are in contact with each 
:CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 327 

other. The graywacke-sandstone matrix contains abundant slate 

fragments and is a very light gray on fresh fracture. No coal or carbonized wood is visible. 

The Tertiary strata at Coal and Little Coal Bays are for the 

most part covered by till and outwash gravel, and their extent cannot be determined. From the known relations of the Tertiary rocks 

elsewhere in the general area, it is probable that they are restricted 

to an area of not more than 1 or 2 square miles. The preponderance 

of cobbles of diorite and black argillite suggests that the source area 

may have been to the west where the bedrock contains a high percentage of these two rock types. 

CONGLOMERATE 

Friable and weathered Tertiary conglomerate is exposed at an altitude of about 100 feet for a few hundred yards along the logging 

road leading west from Davidson's logging camp on the north arm 

of Thorne Bay. The rock is grayish purple, and the pebbles consist predominantly of gray, white, and light-green chert, argillite, 

various types of andesitic lava and dike rocks, and a few pebbles of 

quartz in a matrix of the same material. The conglomerate contains terrigenous iron oxides, and in fresher part the matrix is seen 

to be lithified so that the rock fractures across some of the pebbles. 

These rocks are covered by glacial till, and their extent cannot be 

determined, but they probably do not extend more than a few hundred yards in any direction from the outcrops. 

Three small bodies of Tertiary conglomerate crop out in the valley 

of Lava Creek, in the north-central part of the quadrangle. The 

lowermost is about one-fourth of a mile from the Thorne River at 

an altitude of 80 feet and is well exposed in the bed and banks of 

Lava Creek, which has cut downward into it for at least 30 feet. 

The conglomerate is in the form of a delta, with foreset beds dipping 

about 60° downstream. It contains abundant pebbles and cobbles 

of 1netamorphosed argillite, gneiss, trachytic and amygdaloidallava, 

biotite granite, schist, and chert, and the lithified matrix contains 

rounded fragments of quartz, orthoclase, and microcline in addition 

to small fragments of the rocks listed. The detritus of all these 

rock types is derived locally. The conglomerate here is cut by pitchstone dikes that are somewhat fractured and deformed. The conglomerate is overlain by till and alluvium or glaciofluvial deposits. 

Bodies of conglomerate of similar lithologic and physical composition are exposed at altitudes of 220 feet and 240 feet in the bed 

of Lava Creek; each appears to be deltaic conglomerate, and they 

probably were deposited as isolated bodies rather than as a continuous conglomerate. 
328 MINERAL RESOURCES OF ALASKA 

Another very small body of Tertiary conglomerate crops out at 

the tide line near the head of the small cove at the extreme north 

part of the mapped area. It consists of rounded to angular pebbles, 

cobbles, and boulders as much as several feet across that consist of 

dioritic igneous rocks and metamorphic rocks, most of which were 

derived from the batholith or its metamorphic aureole that form the 

bedrock east of Lava Creek (pl. 39A.). The matrix of the conglomerate is fine and sandy in part· and weathers to dull light brown 

or moderate yellowish brown. In general appearance and color this 

conglomerate resembles superficially some of the Lower Silurian conglomerate in the south entrance to Thorne Bay. It lacks the distinct red color of the Tertiary conglomerate in Thorne Bay and 

Lava Creek. 

CONDITIONS OF DEPOSITION 

All the Tertiary rocks of the mapped area have certain characteristics in common: Most are poorly sorted; they consist of lithologic types that were derived locally; and they lie at low altitudes, 

the highest being about 220 feet above sea level. Some contain coal 

seams and carbonized logs. They seem to have been deposited by 

torrential streams which, debouching from an area of considerable 

relief, deposited the transported load as alluvial fans, deltas, or piedmont gravel in a brackish-water environment (Buddington and 

Chaplin, 1929, p. 267). 

AGE 

The Tertiary rocks in the mapped area are dated by their degree 

of lithification, by their complete lack of metamorphism, by the fact 

that they contain igneous and metamorphic rocks believed to be of 

middle Cretaceous age, and by the fact that in at least one place 

conglomerate is cut by pitchstone dikes that also are found cutting 

the batholith in the north-central part of the quadrangle. The Tertiary conglomerate resembles in detail other conglomerate in the 

Ketchikan areas described by Buddington and Chapin (1929, p. 

263) and assigned by them to the Eocene. North of Prince of Wales 

Island, on Zarembo, J{upreanof, and Kuiu Islands, the Eocene rocks 

contain large amounts of rhyolite, and if the pitchstone dikes cutting the conglmnerate on Lava Creek are related to this period of 

extrusion of rhyolite, then the conglomerate must be at least as old 

as the Eocene. 

UNCONSOLIDATED DEPOSITS 

Unconsolidated deposits comprising till, glaciofluvial gravel, alluvium, and beach gravel are widespread throughout the mapped 

area; till and outwash gravel are by far the most abundant. The 

boundary of the till is not clear, for the till ranges in thickness 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 329 

from a few inches to at least 100 feet. In general, the thickness 

decreases with increasing altitude, except in upland valleys containing relatively young moraines. The till, moraines, glaciofluvial 

gravel, and partly reworked outwash gravel are classed as glacial 

deposits on the geologic map and are distinguished from alluvium 

and beach gravel. It is extremely difficult to separate glaciofluvial 

deposits, alluvium, and wave reworked till and outwash gravel, 

because much of the alluvium is composed of till with the rock-flour 

matrix removed, and almost all the present beaches are formed from 

till or glaciofluvial deposits that have been reworked by wave action 

and contain only small amounts of material eroded by waves from 

the underlying bedrock. Where till has been exposed to strong 

wave action, such as on the islands and shorelines at the head of 

Kasaan Bay, the fine matrix is removed entirely, and the striated 

and faceted cobbles are worn and rounded. As postglacial uplift 

has amounted to at least 50 feet, and possibly as much as 200 feet, 

all the till beneath this altitude has been exposed to the violent 

storms that sweep l{asaan Bay and has been reworked to varying 

degrees. 

To further complicate the matter the reworked till on the islands 

at the head of Kasaan Bay is exposed to tides with a current as 

swift as many low-gradient rivers, giving rise to deposits that cannot be classified correctly as till, alluvium, or beach deposits. 

In this report, unconsolidated deposits that obviously are reworked 

by water action not related to outwash streams are classed as alluvium or beach gravel, although it is recognized that much of the 

material is derived from till. 

The contact between the unconsolidated deposits and the bedrock 

is arbitrarily drawn on the map where bedrock becomes so obscured 

by surficial deposits that the numbers of outcrops is not sufficient to 

establish even the general lithology of the underlying rocks. 

GLACIAL DEPOSITS 

OLDER MORAINES AND TILL 

The oldest glacial deposits are represented by scattered glacial 

erratics and thin till that lie upon the highest mountains and the 

upland areas. Many of the erratics are quartz diorite and possibly 

were transported from the Coast Ranges to the east; however, many 

of the numerous plutons in the mapped area are quartz diorite, and 

these plutons could be the source of the quartz diorite erratics. One 

small area of older high-level till that is noticeably weathered is 

exposed in a small creek at an altitude of 750 feet, near the roof 

pendant in the pluton east of Lava Creek. It contains diorite cob-
330 MINERAL RESOURCES OF ALASKA 

hies that are badly weathered and chert and argillite cobbles that 

are weathered to a depth of one-quarter inch. 

A short distance above the point where Lava Creek turns abruptly 

northwestward and cuts a small gorge in bedrock, till with partly 

indurated matrix is exposed in the creek banks and in the streambeds. Similar till is also exposed at one point along the trail that 

follows the north shore of Salmon Lake. Thin till with noticeably 

weathered cobbles is exposed at scattered places in the gently sloping 

highlands in the extreme northwest part of the mapped area. The 

matrix of these older tills generally is weathered to very light gray 

to tan, whereas the matrix of the younger till is blue gray. The 

partly indurated and weathered tills are believed to be related to a 

period of continental glaciation that preceded a period of widespread valley glaciation after the retreat of the continental glaciers. 

YOUNGER MORAINES AND TILL 

Younger glacial deposits form a widespread mantle in the lowlands of the Thorne River valley and in the lowland area between 

l{ina Cove and Little Coal Bay. The deposits in the Thorne River 

valley comprise till, glaciofluvial gravel that is in part reworked by 

the Thorne River, and local areas of blue lake clay. These deposits 

are but slightly weathered, and they contain cobbles of most of the 

rock types known in the rna pped area. North of Angel Lake and 

in the Thorne River valley they contain a large amount of dioritic 

and aplitic igneous rocks and gneiss and a lesser amount of various 

types of volcanic rocks, graywacke, limestone, argillite, and chert. 

The drumlinoicls in and south of the Thorne River valley probably are bedrock knobs veneered to varying depths with till, for 

locally, at the extreme summit, bedrock can be found where glacial 

plucking has left a steep rock face. For the most part, however, 

these drumlinoids are completely mantled by till. They show that 

the major ice flow in the Thorne River valley was toward the southeast. Much of the ice belonged to a sheet extending far to the north 

and east, but some of it probably originated in the highlands west 

of the mapped area, for the long axes of the drumlinoids swing 

more to the west in the region adjacent to the northwest part of the 

rna pped area. 

At Coal Bay, stratified glaciofluvial gravel covers a marine till 

containing fragments of barnacles and small pelecypods. The top 

of the till is at an altitude of about 50 feet, and the stratified gravel 

above is at least 20 feet thick. The till contains a large amount of 

gray to black argillite cobbles, chert cobbles, and fewer cobbles of 

limestone, volcanic rocks, and diorite. The cobbles are faceted, striated, and grooved, and the rock types are those exposed along 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 331 

Twelvemile Arm. Similar till is exposed at an altitude of 380 feet 

on the hill to the southeast, but no thick till was found higher. A 

mile to the east, at an altitude of 380 feet, bedrock is moderately 

well exposed and is not mantled by glacial deposits, but strong glacial grooves strike S. 30° E., and plucking pits indicate that the ice 

flowed southeastward. 

Marine till containing shell fragments was observed in the lower 

valley of Maybeso Creek, which enters Hollis Anchorage from the 

north. A modified terminal moraine loops across the valley of 

Maybeso Creek about llh miles above Hollis. The moraine contains 

a high percentage of rock-flour matrix, and the poor drainage 

through the deposit has inhibited the growth of the evergreen forest in the valley. The poor stand of timber was recognized by foresters of the U.S. Forest Service and led them to seek the explanation, which was resolved when the terminal moraine was recognized. 

Small glacial moraines containing till of local derivation are present along the upper valley of Lava Creek and in upper Falls Creek. 

Locally the creeks have cut through the moraines, exposing the underlying bedrock. These moraines are at least 100 feet thick in 

places, and they contain cobbles derived from local rocks, among 

which is pyritized rhyolite dike rock not found elsewhere in the 

mapped area. These moraines are fresh and completely unindurated, and striated and faceted cobbles and pebbles are common. 

A small high-level moraine and gravel deposit of local derivation 

occurs at the head of Granite Creek. The moraine, which is relatively young as indicated by its position on a very steep slope, consists almost entirely of black argillite and diorite in a gray matrix 

of rock flour. Small creeks on the east side of Granite Creek have 

cut steep gulleys as much as 30 feet deep into the deposit without 

exposing bedrock. 

The thick surficial deposits that form the islands at the head of 

Kasaan Bay contain cobbles of diverse rock types. The cobbles are 

as much as several feet long and are rounded. Cobbles of quartz 

diorite from the pluton in the southwestern part of the mapped area 

occur with cobbles of lava breccia that is common in the northwestern part of the mapped area. These thick deposits are believed to 

represent a reworked intermediate moraine deposited where a glacier flowing southeastward from the Thorne River valley met a 

glacier or glaciers flowing eastward or northeastward from the valley of Big Salmon Lake and Twelvemile Arm, respectively. These 

deposits, which have been reworked by the intense wave action of 

violent storms that blow up Kasaan Bay and by moderately strong 

tidal currents, are shown on the geologic map as beach gravel. 
332 MINERAL RESOURCES OF ALASKA 

ALLUVIUM 

Alluvial deposits exist where stream erosion has reworked glacial 

till, removing the rock-flour matrix and smaller particles and depositing the transported material in flat low land areas and on tidal 

flats. Most of the material shown as alluvium on the geologic map 

is derived from glacial deposits; very little has been derived from 

stream-eroded bedrock, for most of the streams flow in courses covered with coarse cobbles left from eroded glacial deposits. The 

only important exception to this is the alluvium deposited by Granite Creek, which is building a delta into Little Salmon Lake. This 

alluvium is derived from an area of strong relief from which Granite 

Creek is actively removing talus, bedrock, and glacial deposits. 

BEACH GRAVEL 

Beach gravel in deposits large enough to be shown on the geologic 

map is restricted to the beaches at the head of Kasaan Bay and to a 

small island in the south entrance to Thorne Bay. These beach deposits consist for the most part of glacial and glaciofluvial deposits 

that have been reworked by wave action and locally by tidal currents. Their origin from glacial deposits is attested to by the lithologic similarity of the cobbles and boulders to those in nearby 

glacial deposits. The cobbles and pebbles, however, are rounded and 

unstriated, and the rock-flour matrix is removed, indicating considerable modification by wave action. It is probable that typical 

glacial deposits with rock-flour matrix could be found at shallow 

depth beneath many of the beaches, but their surficial shape and the 

shape of the boulders and cobbles is such that it seems best to show 

them on the geologic map as beach deposits. 

INTRUSIVE ROCKS OF PRE-TERTIARY AGE 

Intrusive rocks in the form of dikes, stocks, bosses, and batholiths 

intrude the bedded rocks of the mapped area and form a large part 

of the bedrock. They range in size from dikelets and small bosses 

less than a mile in diameter to batholiths that continue into adjacent areas, and they range in composition from olivine-bearing pyroxenite and gabbro to rhyolite and pitchstone. The igneous rocks 

exhibit considerable variation in structure and physical composition 

and in their effects upon the country rocks. 

The larger intrusive bodies probably are satellitic bodies of the 

Coast Range batholiths to the east, and their chemical composition 

approaches diorite or quartz diorite similar to the Coast Range 

batholiths. The dikes, however, form a bewilderingly complex 

group of rocks that differ markedly in texture, orientation, and 

composition, and their sequence of intrusion has been deciphered 

only in part. 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 333 

PLUTONIC ROCKS 

Under the term "plutonic rocks," the writer groups all the larger 

bodies of intrusive rocks that form bosses, stocks, and batholiths. 

In this report, these intrusive bodies are called plutons. The plutons conform to the regional structure in only a general way. The 

large pluton of quartz diorite in the southwestern part of the quadrangle conforms very well to the strike of the enclosing rocks, but 

the gabbro-pyroxene body near Salt Chuck crosscuts the regional 

strike at a large angle, as do many of the plutons. 

The plutons exhibit considerable variation with respect to their 

contacts, their effect upon the enclosing rocks, and their metamorphic 

aureoles. Considerable variation in texture and grain size also 

exists between plutons, yet each pluton is reasonably constant within 

itself. In view of the differences, each pluton more than one-half 

square mile in area is discussed separately below. Some of these 

plutons, notably the 2 at the head of l{asaan Bay and the 1 at the 

extreme southeast point of Tolstoi Bay, have been described previously by 1Vright (1915, p. 77) and Warner and others (1960) in the 

course of their investigations of the mineral deposits of l{asaan 

Bay and vicinity. In view of certain differences of opinion, these 

are discussed in more detail in this report. 

PYROXENITE AND GABBRO 

Pyroxenite and gabbro in large bodies are confined to the two 

plutons that crop out in the Salt Chuck ( Goodro) mine area and 

at the head of l{asaan Bay. 

Pluton in the Salt Chuck mine area.-The intrusive body in 

which the Salt Chuck mine lies ranges in composition from an olivinebearing pyroxenite rich in augite and labradorite feldspar to a rock 

type that could be called diorite containing as much as 30 or 40 percent 

orthoclase feldspar that is replacing labradorite. Magnetite ranges 

from as much as 10 percent of the rock to as little as 2 percent, 

and a peculiar type of mica, resembling prochlorite, at places reaches 

a maximum size of several inches. Locally, the rock contains as 

much as 60 or 65 percent phenocrysts of calcic augite that reach 

a maximum size of 1.5 em in an altered groundmass consisting of 

chlorite, epidote, zoisite, and prehnite. The distribution of the various phases is complex, and exposures within the body are not sufficient to establish their mutual relations and areal extent, although 

Gault ( 1945, p. 6) in his studies of the Salt Chuck mine came to 

the conclusion that the gabbro intrudes, and is younger than, the 

pyroxenite. 

In thin sections of the more leucocratic facies studied, the potassium feldspar rims and replaces labradorite, and the texture sug-
334 ruiTNERAL RESOURCES OF ALASKA 

gests that the diorite is formed from the pyroxenite by addition 

of potassium feldspar. It also seems significant that at the northwest end of the pluton, irregular areas of diorite contain pyrite and 

epidote, which also suggests an origin by metasomatic replacement 

of pyroxenite. Generally speaking, however, the pyroxenite is more 

common than the gabbro, which is more common than the diorite. 

This intrusive body is of economic interest, for confined within 

it are most of the prospects containing bornite and (or) palladium. 

One 1nine, the Salt Chuck, has produced more than 300,000 tons of 

ore containing copper and palladium. In addition to the prospects 

within the intrusive rock, one small vein containing bornite is found 

in altered conglomeratic volcanic graywacke, about 1 mile southwest 

of the Salt Chuck mine. 

Because this pluton crops out throughout most of its length in 

an area of low relief that is thickly covered by trees and brush, 

exposures of the contact are rare. However, the pluton cuts across 

the strike of the enclosing rocks, and north of Power Lake the 

contact is sharp. The contact also is exposed in a small creek that 

drains North Lake into Lake No. 3, but here the pluton is diorite 

containing epidote and pyrite and rocks along the contact are altered. 

The thennal metamorphic effects around the pluton are minor, for 

the clastic texture of the surrounding conglomeratic volcanic graywacke and volcanic graywacke is still discernible. In the vicinity 

of the Rush and Brown mine the pluton is diorite or gabbro and 

the two dikelike apophyses from it also are dioritic. No schist is 

developed near the contact of the pluton. 

The only dike known to cut this pluton is the dike noted by 

Gault (1945, p. 5) in the Salt Chuck mine. The dike is altered, 

contains ore minerals, and is undoubtedly older than the ore body 

at the Salt Chuck mine. 

Pluton at the head of Kasaan Bay.-The pluton that crops out at 

the head of Kasaan Bay is a complex rock of unusual texture. It 

ranges from very fine grained to coarse-grained gabbro cut by thin 

pegmatitic bands. The coarse-grained gabbro forms rounded masses 

isolated within, and cut by, the fine-grained gabbro. Locally, pegmatitic facies of plagioclase and pyroxene cut the rock and in 

places are cut by the fine-grained gabbro. Thin veinlets of quartz 

and plagioclase feldspar cut all the facies listed, and sma1ler dark 

veinlets. 1\fagnetite is present in small amount throughout the rock. 

In thin section both the coarse- and fine-grained facies of the 

rock are seen to consist of a mixture of plagioclase feldspar, some of 

which is sodic bytownite, and pyroxene that has an optic angle 

ranging from 32° to 48° and a beta index of refraction from 1.705 

to 1. 71. These optical properties determine the pyroxene to be 

augite, very close to ferroaugite in composition. 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 335 

The actual contact of this pluton was not observed. The metamorphic aureole about the pluton must be restricted to a zone not 

more than a few tens of feet wide, for the enclosing rocks near the 

north, the northwest, and the southwest sides are not visibly 

affected. 

Near its west margin the gabbro has been sheared and altered by 

solutions that deposited abundant pyrite and hematite. This alteration probably is related to the fault that follows the topographic 

linear that trends across the intrusive body into the valley of the 

Thorne River. No copper-bearing minerals were observed at any 

place in the gabbro. 

This intrusive body is cut by a diorite porphyry dike, by several 

pyroxene porphyry dikes, and by diabase dikes, all of which in 

general trend northwestward or northward. 

QUARTZ DIORITE AND RELATED ROCKS 

PLUTONS 

The other plutons shown on the geologic map range in composition 

from diorite to granite, but diorite or quartz diorite are the most 

common. The plutons of this composition not described by "\Varner 

and others ( 1960) are described in some detail in this report. 

Pluton east of Lava Oreek.-The pluton exposed east of Lava 

Creek is the south end of a batholith that extends northward for a 

distance of about 15 miles. Within the mapped area the pluton 

is notably complex in texture and cmnposition, in its metamorphic 

effect on the enclosing rocks, and in internal structure. The pluton 

includes large quantities of what is best described as diorite gneiss, 

and also a large roof pendant of metasomatized clastic rocks. Metasomatism of all the contacting rocks is widespread, and much of 

the intrusive mass contain abundant introduced pink feldspar as 

grains and veinlets. 

The pluton ranges in composition from diorite to sodic granite. 

The sodic granite occurs in small areas where the rocks have been 

modified by potassic metasomatism. The unaltered rock is hornblende diorite with faint gneissic banding and is best exposed in the 

beds of the creeks that flow northeastward toward Clarence Strait. 

In the higher hill that rises to an altitude of 1,400 feet to the west, 

the gneissic banding is much more noticeable. With increasing 

acidity the hornblende gives way in part to biotite, and in the most 

acid facies the dark minerals consist entirely of biotite and chlorite. 

The plagioclase feldspar of the diorite facies is calcic andesine, and 

the rock contains less than 5 percent alkalic feldspar. In the more 

alkalic facies the plagioclase is sodic oligoclase surrounded by large 

anhedral perthite crystals and a groundmass mozaic of albite and 
336 rurr.NERAL RESOURCES OF ALASKA 

quartz. A few crystals of microcline occur in the alkalic facies. 

Magnetite or ilmenite is a common accessory mineral, and locally 

apatite is very common. The texture of the rock is variable, but. 

normally the diorite is more gneissic and finer in grain size than 

the more acid facies in which the introduced potassium feldspar 

forms ragged porphyroblasts. 

The bedded rocks surrounding this pluton are metasomatized, and 

in places large porphyroblasts and veinlets of pink orthoclase and 

albite are found. The potassium feldspar clearly is introduced intosuch rocks. Owing to the widespread introduction of feldspar intothe surrounding rocks, and to the gneissic structure, the contact is 

gradational, at some places over a distance of several hundred feet. 

On the geologic map (pl. 33) the distribution of the contacting rocks 

affected by potassium n1etasomatism is shown by an overlay pattern. 

Along the southwest margin a little skarn is developed near the 

contact, and a zone of thermal metamorphism that has produced 

biotite schist from argillite, and hornblende gneiss from volcanic 

rocks, surrounds the body. \Vhere volcanic graywacke or other 

clastic rocks border the pluton, the metasomatic and thermal aureole 

is widest, and gradational contacts are commonest. The west contact is beneath the glacial deposits east of Lava Creek, but the 

creek bed exposes innumerable dikes or apophyses of the pluton, 

and a large apophysis intrudes the andesitic flows west of Lava 

Creek. Similar conditions are seen in the bed of the creek flowing 

eastward from the east contact, except that in this area the rocks 

contain a high percentage of argillite and other fine-grained rocks, 

and these rocks are schistose and thermally metamorphosed to 

biotite and hornblende schist much farther from the contact than 

are the rocks along the west contact. 

This pluton is cut by dikes of coarse-grained granite, trachytic 

rhyolite, and pitchstone, some of which are altered and contain 

abundant pyrite. A small magnetic anomaly lies near the skarn 

along the southwest margin, but only a very little magnetite was 

found at the surface in this area. 

Pluton north of Salt Ohuck.-The small pluton about a mile north 

of the pyroxenite at Salt Chuck is poorly exposed, but the most 

common facies is coarsely porphyritic quartz diorite with phenocysts 

of zoned plagioclase feldspar that reach a length of one-half inch. 

The phenocrysts form about 20 percent of the rock, and the groundmass consists of plagioclase, quartz, and minor orthoclase. Locally, 

especially along the southwest contact, the rock is alterPd and albitized and contains specks and minute veinlets of pyrite and chalcopyrite. A large dike identical in composition to this intrusive 

body crops out on the hill west of Thorne Bay. 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 337 

Pluton in the southwest part of the mapped area.-The large 

-pluton in the southwest part of the mapped area is remarkably 

hon1ogeneous quartz diorite containing free quartz in amounts as 

great as 30 percent. The plagioclase is sodic andesine or calcic 

oligoclase, and potassium feldspar is completely lacking. The mafic 

Jninerals are chlorite and locally a very little hornblend. The texture is granitoid and the grain size is medium. The rock is slightly 

gneissic near the contact, which is sharp in most places. 

The aureole of thermal metamorphism that surrounds the pluton 

is much more marked on the north margin, where the enclosing 

rocks dip gently northward, than on the south margin, where the 

.contacting rocks dip steeply. Biotite is developed in the bedded 

rocks on the north side, and locally the diorite near the contact and 

the metamorphic rocks adjacent are heavily charged with pyrite and 

pyrrhotite. The volcanic graywacke and conglomeratic graywacke 

()n the north contact near Twelvemile Arm are altered and metasomatized and locally resemble the diorite in texture. 

The slate-argillite beds on the southwest border of the pluton are 

intricately folded, and the fold axes trend parallel to the strike of 

the contact. Cliff exposures in the steep divide leading from Granite 

Creek to the valley of Maybeso Creek near Hollis Anchorage show 

that the slate-argillite beds are faulted. Many of the faults dip into 

the pluton at low angles, and one small fault is a low-angle thrust 

fault. This complex structure may reflect the. forceful intrusion 

of the pluton. 

The pluton is cut only by irregular diabase dikes and by quartz 

veins containing gold and sulfide minerals. 

Pluton on the east shore of Twelvemile .Ar1n.-The pluton that 

crops out on the east shore of Twelvemile Arm is lithologically 

similar to that on the west side, and probably is part of it. A few 

small areas of skarn are associated with this eastern part of the 

pluton, and pyrrhotite with minor specks of pyrite is common in 

the biotite schist near the contact. 

Pluton east of Baker Point.-The pluton exposed to the east at 

Baker Point is coarse-grained quartz diorite containing about 35 to 

40 percent quartz, 50 to 60 percent andesine feldspar, and about 5 

percent biotite. The rock is badly crushed, and locally it is albitized along joints and fractures. It is intruded by a great many 

diabasic dikes that in the vicinity of Baker Point are so numerous 

as to constitute a dike swarm. The pluton has sharp contacts, and 

on the south contact some magnetite in pods and thin beds replaces 

thin-bedded argillite. 

Elsewhere within the quadrangle are small bodies of quartz diorite 

that attain a maximum width of a few hundred feet. Some are 

shown on the geologic rna p but are not discussed here. 
338 ~ERAL RESOURCES OF ALASKA 

CHEMICAL COMPOSITION 

Three samples of typical quartz diorite and related rocks were 

analyzed chemically. The results and the norms calculated from 

these analyses according to the CIPW system are shown in the 

following table. 

Chemical composition of quartz diorite, Craig C-2 quadrangle and vicinity 

[Analysts: Samples 1-3, PaulL. D. Elmore, Katrine E. White, and Samuel D. Botts, U.S. Geological Survey; sample 4, F. E. and C. W. Wright (1908)] 

2 3 4 

CIPW norm 

Quartz___________________________ 3. 60 7. 980 24.186 Orthoclase_______________________ 6.12 18.348 6.672 Albite____________________________ 26.20 40.348 35.632 Anorthite________________________ 26.69 15.969 19.792 Diopside__ _ _ ____ ___ _ _ _ ____ _ ____ __ 11. 26 ______________________ ----------------- ____________ _ 

Hypersthene _________ ------------ 18.31 6. 684 4. 453 Ilmenite _________ -----------_____ 1. 82 . 912 . 730 

Magnetite __ --------------------- 3. 48 5.104 4.176 Hematite_----------------------- ·------------------ _______ _______________ . 800 Calcite___________________________ . 20 1. 600 . 600 

Apatite_------------------------- . 99 . 654 . 592 Corundum _______________________ ------------------ . 673 .228 

TotaL ___ -________________ _ 100.07 99.672 99.261 

CIPW classification 

Class_____________________________ II 1. 74 Dosalic 

Order____________________________ 5 .06 Perfelic 

Rang____________________________ 4 .45 Docalcic 

Subrang_________________________ 4 .32 Dosodic 

II 5. 5 Dosalic I 7. 50 Persalic 3 1. 07 Quarfelic 4 . 39 Quardofelic 2 1. 74 Domalkalic 3 1. 23 Alkali calcic 4 . 428 Dosodic 5 . 183 Persodic 

Chemical composition 

8102----------------------------- 52.8 58.4 64.2 AhOa---------------------------- 15.9 17.7 17.4 Fe20a- --------------------------- 2. 4 3. 5 2. 9 FeO ____________________ ._________ 7.5 2.4 1.9 

MgO_____________________________ 5.5 2.3 1.5 

CaO--------------"-------------- 8. 9 4. 5 4. 7 Na20____________________________ 3.1 4.8 4.2 

K20"---------------------------- 1.0 3.1 1.1 Ti02---------------------·-------- . 98 . 52 . 38 P20s----------------------------- .44 .34 .26 MnO_ -----------~---------- _____ . 21 . 12 .13 

H20-- --------------------------- 1. 40 1. 40 1.40 C02------------------------------ .10 . 70 .28 

61.0 

17.5 

1.6 

2. 7 2.4 

6.9 

3.3 

2.3 

1.0 

.30 

.1(} 

.00 ____________ , _______________ , _______________ , ____ __ Total_------------------____ 100.23 99.78 100.35 100.00 

1. Stock at Tolstoi Mountain at east end of the south shore of Tolstoi Bay; collected from island off Tolstoi 

Point, and along shore in small cove half a mile south; sp gr, 2.915; laboratory No. 147328. 2. Stock that forms south end of Kasaan Peninsula (not shown on geologic map); collected along half a mile of beach south of steep cliffdue east of south tip of Kasaan Island; sp gr, 2.765; laboratory No. 177330. 3. Large stock in Twelvemile Arm; collected along beach from north end of small cove in center of stock to point north of cove at south end of stock, northwest shoreline; sp gr, 2.763, laboratory No. 147329. 4. The average chemical composition computed for seven specimens of quartz diorite from Ketchikan area, Alaska, by F. E. and C. W. Wright (1908). 

In chemical composition and in modal and normative mineral 

composition these rocks belong to the quartz diorite family. Sample 1 is diorite and sample 3 is leucodiorite. 

AGE 

The three rocks analyzed were submitted for age determination 

by means of radiogenic-lead content. Only sample 1, from Tolstoi 
CRAIG C-2 4~UADRANGLE, PRINCE OF WALE'S ISLAND 339 

Point, contained enough of the required accessory minerals for age 

determination in a sample of 100 pounds. Its age was determined 

as 100 million years, or roughly in the middle of the Cretaceous. 

The plutonic rocks probably were intruded throughout most of the 

middle of the Cretaceous, if it is assumed that all the plutons of 

the quadrangle were intruded in the same general cycle of intrusive 

activity and that the most basic ones were intruded first, as the 

pluton at Tolstoi Point is one of the more basic of the plutons of 

intermediate composition. In addition, most of the plutons are 

cut by diabase dik1es believed to be of Tertiary age; the gabbro 

pluton south of Salt Chuck is cut by at least two diorite porphyry 

dikes of the type that is believed by Warner and others ( 1960) to be 

related on Kasaan Peninsula to the stocks of intermediate composition, and the composite pluton in the north-central part of the quadrangle is cut by trachytic rhyolite dikes as well as by pitchstone dikes 

equivalent to those that cut the Tertiary conglomerate on Lava Creek. 

DIKE ROCKS 

PALEOZOIC DIKES 

Owing to the extreme diversity of the dikes of the quadrangle, 

both mineralogically and texturally, and to the few exposures that 

reveal intrusive relations between various types of dikes, the writer 

has recognized only one type that he believes is definitely of Paleozoic age. 

This Paleozoic intrusive rock is rhyolite that crops out over a.· 

large part of Kasaan Island and that intrudes, and in part is interbedded with, highly :fossiliferous lin1estone of Middle Devonian age. 

Wright (1915, p. 70) describes these rocks as sandstone and conglomeratic sandstone interbedded with limestone. Buddington and 

Chapin (1929, p. 2613) call these rocks platy rhyolite and include 

then1 with their Tertiary rocks. In 1955, the writer and G. D. 

Eberlein found good evidence that some of the rhyolite is contemporaneous with the limestone, for rhyolite fragments are very common in the limestone immediately above some of the larger rhyolite flows. No fossils are present in the limestone immediately 

above the flows, but the fossils gradually become more abundant 

higher up in the lin1estone, and within a foot may amount to 50 

percent of the limestone, ·suggesting that the marine life was killed 

by the rhyolite, but was soon reestablished. This evidence is almost 

conclusive thnt the rhyolite is of Middle Devonian age. 

The rhyolite is extremely platy because it has marked flow foliation. On the northe:ast side of Kasaan Island the platy structure 

bends around two plug like masses· of coarse-grained rhyolite that hns 

no flow foliation, suggesting that these were centers of extrusion. 
340 MINERAL RESOURCES OF ALASKA 

The microscope reveals several distinct textures ranging from 

extremely fine-grained to porphyritic. In some sections the rock 

contains corroded quartz phenocrysts with euhedral albite phenocrysts surrounded by albite and orthoclase microlites with trachytic 

texture; in others the phenocrysts are oligoclase feldspar or minor 

quartz in a nontrachytic groundmass of albite and orthoclase; and 

on the east side of the island, corroded garnets are the phenocrysts .. 

In coarser grained parts the groundmass contains a little hornblende. 

Thin diabase dikes cut the rhyolite, and locally they are faulted 

and folded into complex folds. 

Two samples of the rhyolite were analyzed chemically, and theresults are shown in the following table. 

Chemical and normative composition of rhyolite, Kasaan Island 

[Analysts: Paul L. D. Elmore, Katrine E. White, and Samuel D. Botts] 

2 

CIPWnorm 

Quartz_------------------------------------------------- 34.02 25.50 ()rthoclase_______________________________________________ 21.24 16.68 

Albite_ ·------------------------------------------------ 38.152 44.54 Anorthite ____________________________________________________________ --------- ______ --- __ ---- __ -- ____ ---

Diopside ______ ------------------------------------------ ___ --------------------- ______ ------ _ ----------- Hypersthene_------------------------------------------- . 50 1. 50 

Dmenite _________ --------------------------------- _______ -------------------- _ __ _ . 061 

M agnPtite __ ------------------------------------------ ___ . 464 1. 972 Hematite________________________________________________ . 40 • ro·. 

Calcite_------------------------------------------_______ . 40 2. 70 Apatite ___________________________________________ ------- . 448 • 616 

Corundum ____________________________________ ---------- 3. 06 4. 48 

TotaL ______ ------------------- __ ------ ___ --------- 99.76 99.45 

CIPW classification 

Class ___________________ ----------------------- __ -------- I 52.7 Persalic I 20.3 Persalic 

Order. __ -----------------------------------------------_ 4 .575 Quardofelic 4 .42 Quardofelic 

Rang ___ -----------------------------_------------------_ 1 Infinity Peralkalic 1 Infinity Peralkalic 

Subrang _____________________________ -------------------- 4 .548 Dosodic 4 .358 Dosodic 

Chemical composition 

SlOs----------------------------------------------------- 75. 2 68.0 

Alt03---------------------------------------------------- 14.6 16.2 

Fet03---------------------------------------------------- . 8 1. 8 Feo ______________________________________ -------------- .16 .96 

MgQ __ -------------------------------------------------- .18 • 59 cao ____________________________________ ----------------- . 22 1. 8 

NatO _______ -------------------------------------------- 4. 5 5. 3 

K20------------------------ ---------------------------- 4. 0 2. 9 

TiOt. _ -------------------------------------------------- . 01 • 3 

P20s----------------------------------------------------- .14 . 32 

MnO _________ ------------------------------------------ _ . 02 . 08 

HtO- . -------------------------------------------------- 1.00 1.00 

C02--- _ ------------------------------------------------ .16 1. 2 1---------------1-------------- Totall____________________________________________ 100.99 100.45 

1 Includ~ water. 1. From platy rhyolite from southwest side of Kasaan Island, west of entrance to small cove; sp gr, 2.420; 

laboratory No. 147802. 

2. Composite of several samples from east side of Kasaan Island; sp gr, 2.445; laboratory No. 147803. 
CRAIG C-2 <~UADRANGLE, PRINCE OF "WALES ISLAND 341 

DIKES: OF PALEOZOIC AND MESOZOW AGE 

Dikes that probably were injected during the epoch of the intrusion of the plutons are widespread in the 1napped area. They 

range in thickness from a few inches to as much as 200 feet and 

in composition fron1 gabbro to granite. They generally are more 

common near the plutons of felsic and intermediate composition, 

where their mineralogic composition is varied and in part controlled 

by metasomatic introduction of albite and orthoclase. Many are 

coarsely porphyritic, others are fine-grained, and all gradations exist 

between the two types. They range in color from brownish black 

and grayish olive green to pale or moderate red and grayish orange 

pink. ~1any exhibit n1arked flow foliation and chilled borders; 

others are unfoliated and have only slight marginal chilling. Some 

are deformed, and near the plutons most types are deformed or 

metasomatized at ono place or another. At places they constitute 

dike swarms, which n1ay form a large part of the bedrock. The 

dikes constitute a bewilderingly complex assemblage, and the relations among them can be deciphered only in part. 

The grouping of these dikes in this report, which in part follows 

and in part differs widely from the grouping by Warner and others 

(1960) or vVright (1915, p. 77-84) is given below. This classification is based upon the mineralogic and textural relations that made 

possible in the field the grouping of certain of the dikes. Although 

in· subsequent microscopic studies it was seen that the mineralogic 

and chemical compositions vary considerably within any one group, 

it seems advantageous, because there are so few chemical analyses, 

to retain this classification, for it permits a reasonable grouping 

which fits the field relations. Because the dikes are metasomatized 

to varying degrees near some of the plutons, a chemical classification of such dikes would be misleading. 

Most of the dikes are not shown on the geologic map, for the following reasons : 

1. The dikes are exposed best along steep shorelines, and a plot 

based on these exposures would give an unrealistic picture of the 

distributional density of the dikes. 

2. The dikes seldom are traceable under the vegetal and surficial 

cover, and the attitude observed at any one place may not reflect the true attitude. 

3. At places the dikes are so numerous as to constitute a high percentage of the bedrock, and even if these dikes were traceable, 

the scale of the: map is such that it would be impossible to plot 

them. 

In view of the above, it seems advisable to discuss the general 

distribution of the dikes rather than to attmnpt to plot them on 
342 ~ERAL RESOURCES OF ALASKA 

the map. A few of the largest dikes are plotted where their size 

and extent are known and are commensurate with the map scale. 

DIORITE PORPHYRY .AND RELATED ROCKS 

Feldspar porphyry.-Dikes of feldspar porphyry correspond in 

general to those described by Warner and others ( 1960) as diorite 

porphyry dikes. Their common feature is a coarsely porphyritic 

texture caused by plagioclase feldspar phenocrysts that may reach 

a length of one-half inch; flow foliation is distinct, and in some dikes 

it is very well marked. The dikes vary in thickness from a few 

inches to more than 200 feet. Most have sharp contacts and chilled 

borders. A few of the more irregular dikes near the margins of 

plutons have been altered and metasomatized, the contacting rocks 

resemble diorite, and the boundary between original dike rock and 

~ountry rock is transitional. The strike is variable and seems to 

depend in part upon the association with certain plutons. In the 

vicinity of Tolstoi and Thorne Bays the dikes strike northeastward, 

on the shoreline of Kasaan Bay west of J(asaan Island many strike 

southward, and in the area south of Coal and Little Coal Bays the 

strike is varied but many strike northwestward. 

The dikes are variable in length ; the longest seen in good exposure 

.are two that strike northeastward for about three-quarters of a n1ile 

along the shoreline from the east contact of the small quartz diorite 

pluton at the cove at the northeast end of Tolstoi Bay. Others in the 

mapped area probably are as continuous. 

The dikes are most common in the area near Tolstoi and Thorne 

Bays and on the south shore of Kasaan Bay between Kasaan Island 

:and Kina Cove, and Warner and others (1960) indicate that they 

are common on Kasaan Peninsula. Similar dikes have been found 

on the hill north of Rush Peak. 

The microscope discloses that the composition of the dikes is 

complex. The feldspar of the phenocrysts normally is andesine but 

may range down to sodic oligoclase, particularly in those dikes in 

which the feldspar phenocrysts are small. Some contain minor 

quartz phenocrysts, and some contain corroded augite phenocrysts. 

The groundmass usually consists of quartz, orthoclase, hornblende, 

and plagioclase, all in various stages of alteration to chlorite, epidote, calcite, and sericite. Magnetite, often in amounts as much 

as 2 percent, js always an accessory mineral, and abundant leucoxene 

in the altered dikes suggests that the magnetite contained ilmenite. 

Hornblende porphyry.-Dikes of hornblende porphyry are distinguishable from the other porphyry dikes because the phenocrysts 

usually are basaltic hornblende. Hornblende is a common constituent 

of the feldspar porphyry dike rocks, but in such dikes it always is 
CRAIG C-2 QUADRANGLE, PRINCE OF WALE.S ISLAND 343 

pleochroic in shades of blue and green. The hornblende porphyry 

dikes in general are relatively dark and fine grained, and the prismatic hornblende phenocrysts 1nay reach 7 mm in length. The dikes 

vary in thickness frmn a few inches to a maximum of about 6 feet, 

.and the average thickness probably is about 4 feet. The dikes have 

-chilled borders, and a faint lineation is seen in all hand specimens. 

The dikes vary considerably in strike and appea,r to have no region-

,ally constant attitude. These dikes are most numerous in the 

area from Thorne Bay northward, but a few are found cutting the 

.gabbro pluton south o:f Salt Chuck, where they are somewhat irregular in outline but strike northeastward and slightly west of north. 

None of these dikes have been traced, and their average length is 

not known. 

The microscope discloses that the dikes are variable in composition 

.and texture, but not as varied as the feldspar porphyry dikes. The 

groundmass may contain abundant orthoclase, in which case the hornblende is pleochroic in dark olive green and greenish brown; but 

normally it consists of intergrown oligoclase ranging into albite, 

quartz, and orthoclase, all in part altered to epidote, chlorite, calcite, 

and quartz. Some of these dikes contain a small proportion of 

augite phenocrysts. In composition the dikes probably range from 

diorite to monzonite. Magnetite is a ubiquitous accessory mineral 

and at some places it is very abundant. 

Pyrowene porphyry.-Pyroxene porphyry dikes that closely resemble in color and texture some of the cobbles that are common in the 

conglomeratic volcanie graywacke are very numerous in the northeast part of the mapped area but are found .sp2~ringly elsewhere. 

All the pyroxene porphyry dikes have certain features in common-all contain numerous stubby pyroxene phenocrysts, have chilled 

borders and are unfoliated, and are a somber gray-green color. 

Few of the dikes exc:eed a thickness of 7 feet, and most are less 

than 3 feet thick. The dikes are extremely erratic in orientation, 

both regionally and locally. They are most common in the area 

between Thorne and Tolstoi Bays, north of the entrance to Thorne 

Bay, on Berry Island, and on the shoreline south of the pluton at 

Baker Point. A few are albitized in areas far removed from the 

plutons, and some are metamorphosed to hornblende porphyry, especially in the area north of Forss Cove. The albitization and metamorphism suggest that these dikes are older than most of the other 

types of dikes, and their relative abundance in the tuff, volcanic 

graywacke, and conglomeratic volcanic graywacke that in the same 

area are almost free of other dikes suggests a genetic relationship 

to the volcanic rocks. No dikes of this type are known to cut any 

of the plutons. On weathered surfaces these dikes are almost in-
344 ~ERAL RESOURCES OF ALASKA 

distinguishable from the volcanic graywacke that contains euhedral 

augite crystals, and in the field there was little doubt that they 

were related to the Early Silurian volcanism. However, at two 

places these dikes were found cutting alkalic dikes and diorite 

porphyry, and therefore it appears doubtful that they should be 

assigned a Paleozoic age with certainty. 

The microscope discloses that in some of these dikes pyroxene and 

hornblende phenocrysts are equally abundant, and that a few dikes 

contain a few plagioclase feldspar phenocrysts of smaller size. The 

pyroxene phenocrysts are augite that is close to ferroaugite in composition, having an optic angle near 53° and a beta index of refraction of 1.710. The groundmass consists of epidote, albite, chlorite,. 

zoisite, calcite, and prehnite and resembles the matrix of the volcanic 

graywacke. 

TRACHYTE AND RELATED ROCKS 

Dikes of trachyte and related rocks are characterized by fine grain,. 

marked trachytic texture, light-tan to reddish color, and a high 

content of albite in addition to the orthoclase. These dikes and 

irregular dikelike bodies probably are equivalent in part to similarrocks on l{asaan Peninsula, which are classed by Warner and others 

(1960) as alkalic granodiorite and alkalic dacite. The dikes and 

bodies are as much as several hundred feet in width. In color the 

dikes range from pale orange to light pale red. A marked flow 

structure is developed locally, and such foliated rocks are similar in 

texture and composition to the Middle Devonian rhyolite on l{asaan 

Island. A few are tabular and have sharp contacts, but some, such 

as those in the area west of Lava Creek near the two small lakes at 

the north end of the mapped area, crop out in irregular outline and 

include altered andesite and tuff. Two irregular bodies are exposed 

in the bed of Lava Creek below the apophysis from the pluton to 

the east. One forms the bedrock where exposed discontinuously 

in the creek for several hundred feet, but the shape of the mass is 

not determinable, for most of it is covered by gravel and till. Several tabular dikes as much as 12 feet thick occur in the southwestern 

part of the pluton east of Lava Creek. One is shattered and cut off 

by the fault on the west side of the room pendant in this pluton. 

The trachyte dikes are the most numerous in the area north of 

the north arm of Thorne Bay, and they are the most numerous dikes 

in the pluton east of Lava Creek. None were found west of l{asaan 

Bay or in the Salt Chuck area. Their occurrence near Tertiary 

pitchstone dikes suggests that some of thmn may be of Tertiary age. 

The microscope discloses that the phenocrysts, which are scattered 

and many of which are too small to discern megascopically, normally 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 345 

are albite or orthoclase, but quartz forms phenocrysts in subordinate 

.amounts. 

The length of the crystals of the groundmass ranges from 0.1 

to 1.0 mm; in some, orthoclase forms the bulk of the groundmass, 

and albite is subordinate, and in others, albite is dominant over 

orthoclase. In a few, hornblende in small needles that are pleochroic to brilliant blue and blue green, suggesting a sodic amphibole, 

forms part of the groundmass. 

SODIC RHYOLITE PORP'HYRY, RHYOLITE, AND SODIC ANDESITE PORPHYRY 

The dikes of sodic rhyolite porphyry, rhyolite, and sodic andesite 

porphyry are distinguished from the preceding group by the general 

absence of trachytic texture and the greater size and nmnber of 

phenocrysts. Their chemical similarity and association with dikes 

of the previous group indicate that the two groups are closely 

allied. The dikes are thin, many have very gradation contacts with 

the enclosing rocks, and they range in color from light brownish 

gray to medium light gray. They are well exposed on the shoreline 

of Tolstoi and Thorne Bays and are very numerous in the metasomatized country rock on the shoreline west of the pluton at Tolstoi Point. Dikes of this composition are found at other places in 

the mapped area and are more abundant near the borders of the 

plutons. The southwest shore of J(asaan Bay opposite Kasaan 

Island has a great many pale-red dikes and irregular masses within 

the metasomatized zone shown on the geologic map (pl. 33), and 

similar effects are noted in the metasomatized zone on the north 

border of the pluton on Twelvemile Arm. Similar dikes and metasomatized rocks are common along the southwest shore of Kasaan 

Bay opposite 1\::asaan Island. 

The microscope diseloses that the groundmass of the dikes generally is so fine grained that the rock looks almost glassy. The 

phenocrysts have a maximum length of 5 mm and may be quartz, 

albite, microline, or anorthoclase. The groundmass generally consists of minute laths of orthoclase and albite, the proportion of the 

two differing in different rocks. The dikes containing microcline 

phenocrysts are confined to the area east of IGna Cove; these dikes 

are a light olive green, and their color, microcline phenocrysts, and 

spatial distribution indicate that they probably are not genetically 

related to those in the northeast part of the quadrangle. 

The feldspar phenoerysts in some of the sodic andesite porphyry 

dikes are of special interest. The feldspar is pink and on first 

examination was thought to be orthoclase. However, it was found 

that these phenocrysts would not take a potassium cobalt nitrite 

stain. Subsequent examination with the universal stage showed that 
346 rurr.NERAL RESOURCES OF ALASKA 

the optic angle (-) of the phenocrysts consistently averaged between 52° and 58°. A sample of the phenocrysts gave an X-ray 

powder defraction curve corresponding to albite that seems to be a 

mixture of low- and high-temperature albite (Tuttle and Bowen,. 

1950, p. 57 4). The optic angle is reasonably consistent with data 

of Tuttle and Bowen (1950, p. 574) for high-temperature albite. 

However, the feldspar could be anorthoclase insofar as the optical 

data are concerned. The spatial relation of the dikes with areas of 

alkalic metasomatism of the enclosing rocks seems significant, but 

it is not possible to state whether the sodic dikes are responsible 

for the abundance of alkalic feldspar, or whether the dikes are sodic 

because they have been subjected to alkalic metasomatism connected 

with the plutons. Both processes seem necessary to explain the 

field relations between dikes and the irregularly metasomatized rocks 

near the plutons. 

SODIC GRANITE, MONZONITE, AND QUARTZ PEGMATITE 

Coarse-grained dikes of sodic granite and monzonite are restricted 

to the area in and near the pluton east of Lava Creek, where they 

are exposed best in the bed of Lava Creek along the west margin of 

the pluton. Many cut the pluton. The dikes attain a maximum 

thickness of 150 feet, and many have gradational contacts with the 

bordering gneiss and schist. The trend of the dikes is variable. 

They range from grayish pink to very light gray. The texture 

also is variable, ranging from coarse-grained, granitoid to porphyritic in which the phenocrysts are orthoclase, albite, antiperthite, or 

oligoclase, the orthoclase and albite enclosing and rimming other 

grains. The groundmass consists of interlocking quartz, albite, oliglocase, and orthoclase. Myrmekitic intergrowths of quartz and 

feldspar are common. Magnetite is a constant accessory mineral, 

and in some of the dikes amounts to more than 1 percent of the 

rock. In some specimens apatite is relatively abundant. The orthoclase content ranges from about 30 to 50 percent, and albite ranges 

from about 10 to 30 percent. The mafic constitutents are hornblende 

and biotite, which seldom exceed 10 percent of the rock. 

The texture of the alkalic granite and monzonite dikes, and their 

occurrence in rocks containing an abundance of introduced pink 

feldspar, lead to the conclusion that many of these dikes were modi.: 

fled by metasomatic replacement by orthoclase and albite of the 

plagioclase feldspar in older dikes of dioritic composition. As noted 

before, much of the diorite of the pluton in this area has been 

metasomatized and converted to monzonite and granite. 

The quartz pegmatite dikes are confined entirely to the vicinity 

of the pluton in the southwestern part of the quadrangle. The 
CRAIG C-2 QUADRANGLE, PRINCE OF WALE.S ISLAND 34 7 

biggest occur on the Bast side of Twelvemile Arm in the vicinity of 

the quartz diorite pluton. They range in thickness from a few 

inches to 8 feet, and the longest one has been traced for about 900 

feet. Their texture is coarse grained and pegmatitic, and they consist almost entirely of quartz and oligoclase feldspar with a little 

biotite. Micrographic intergrowths of quartz and oligoclase are 

common. Some contain pyrite and magnetite, and such dikes probably are transitional between quartz pegmatite and the quartz veins 

found in the same area. One quartz pegmatite dike is intensely 

folded, suggesting that it is older than the pluton in the southwestern part of the quadrangle. 

CROSSCUTTING RELATIONS 

In order to illustrate the complexity of the age relations of the 

dikes, a few of the observed crosscutting relations are listed below. 

The station numbers are those on the original field map, which is 

in the collection of the Geological Survey. 

1. Station 273, in diorite pluton at a point about one-half mile west 

of Tolstoi Point, south shore of Tolstoi Bay: Diorite is cut 

by a dike, 2 feet thick, of pink fine-grained sodic rhyolite. .A. 

dark diorite porphyry dike cuts the pink dikelets associated with 

the pink dike. Near by a diorite porphyry dike with feldspar 

phenocrysts cuts pink dikelets. The pink dike is much jointed, 

the other dikes are not. 

2. Station 291, near center of north shore of Tolstoi Bay : A thick 

coarse-grained diabase dike is cut by a smaller diabase dike 

almost identical :in hand specimen, except for its finer grain. 

3. Station 305, about midway on south shore in south entrance to 

Thorne Bay : A gray diorite porphyry dike is cut by a darkgreen diorite porphyry dike, and to the west a light-gray diorite 

dike. The dark-green diorite dikes display chilled borders 

against the light--gray dikes. 

4. Station 309, southeast tip of large island in entrance to Thorne 

Bay: A diorite porphyry dike with feldspar phenocrysts is cut 

by a pink fine-grained sodic rhyolite dike. Both dikes are cut 

by a dark pyroxene porphyry dike. A fine-grained gray andesite dike nearby euts none of these dikes, but it contains xenoliths of the diorite porphyry. 

On the east shore of the same island, a dark-green pyroxene 

porphyry dike is cut by a diorite porphyry dike with feldspar 

phenocrysts. 

On the northeast shore of the island a light-colored andesite 

porphyry dike with feldspar phenocrysts is cut by a dark-green 

pyroxene porphyry dike. Several diabase dikes cut the diorite 

porphyry. 
348 ~ERAL RESOURCES OF ALASKA 

5. Station 385, small island close by shore near northwest head o:f 

Thorne Bay: A diorite porphyry dike with large feldspar 

phenocrysts is cut by a hornblende porphyry dike, and both are 

cut by a dike of fine-grained basalt which probably is diabase. 

Tlwse dikes are not altered or deformed, but nearby a fine-

~rained red sodic rhyolite porphyry dike is badly mashed, 

broken, anrl erusherl. and it obviously is older. 

6. Station D I, west ~hor(> of Kasaan Bay opposite south end o:f 

l(asan n Island: Coarse-grained quartz diorite locally cuts and 

loca Jl ~· is cut by dark fine-grained basalt dikes. 

The :foregoing descriptions are sufficient to show that the sodic 

rhyolite is cut hv many types of dikes and that complex crosscutting 

relations are common among all dikes except the diabase, which 

cuts all types listed. It is inferred that dikes of sin1ilar texture and 

composition probably were injected at different times :from separate 

magma chambers, and that the more felsic dikes cannot be considered as end members in a regional dike sequence in which basic 

dikes were intruder first, fol1owed by the sodic rhyolite and andesite. 

INTRUSIVE ROCKS OF TERTIARY AGE 

The intrusive rocks considered to be of Tertiary age consist only 

of dikes of diabase and pitchstone, but possibly some of the sodic 

dikes cutting the rocks in and west of the pluton east of Lava 

Creek may be Tertiary in age. The diabase dikes are widespread 

throughout the quadrangle, but the pitchstone dikes are confined to 

the north-central part. The relatives ages of the two types of dikes 

have not been established, but the pitchstone dikes cut the Tertiary 

conglomerate on Lava Creek, indicating that they may be the 

younger. 

DIABASE 

The diabase dikes range in width from a few :feet to as much 

as 100 feet, but the average width is probably about 10 feet. The 

dikes are relatively fresh and were intruded in large part along the 

direction of the strong joints, which trend northeastward in the 

bedded rocks. They are very common in the joints in the pluton 

near Twelvemile Arm, where on the high slopes bare of vegetation 

the dark diabase stands out in sharp contrast to the light-colored 

quartz diorite. Several very large diabase dikes are exposed on the 

north shore of Tolstoi Bay and on the islands at the entrance to 

Thorne Bay. They seem to be particularly abundant in the area 

between Loon Lake and Power Lake. A very large body of diabase 

midway along the north shore of Tolstoi Bay strikes northward and 

is shown on the geologic map (pl. 33). Another very large dike of 

irregular form crops out on the steep north slope of Granite ~Ioun-
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 349 

tain and is also shown on the geologic map. Many of the gold lode 

deposits in this pluton lie along the contacts of diabase dikes. 

The diabase is a fine- to medium-grained dark rock that is distinctly 

heavy in hand specirnen, owing to the high content of magnetite. 

The texture is ophitic in dikes containing a high percentage of 

pyroxene, but it approaches trachytic in fine-grained dikes showing 

flow structure. The dikes invariably have chilled borders. 

The microscope disdoses that the mineral composition of the diabase is somewhat variable, the most abundant type consists of 

augite, ferroaugite or titaniferous augite, and labradorite :feldspar 

in highly zoned crystals. In one dike, olivine constitutes about 12 

percent of the rock, and in some, hornblende constitutes several 

percent. Biotite is rare, and the common accessory minerals are 

magnetite, apatite, and pyrite. Alteration products consist only o:f 

chlorite :formed at the expense o:f hornblende or pyroxene. 

PITCHSTONE 

The pitchstone dikes are rare, and :few o:f those seen exceed a 

thickness o:f 10 feet. They are confined entirely to the extreme 

north end o:f the mapped area. Some are associated with faults and 

some form pitchstone-cemented breccia along :faults. At one place, 

pitchstone and sodic rhyolite dikes are intimately associated in a 

small fault, suggesting that the two are of the same age. 

The pitchstone dikes are so completely glassy that only a few 

minute crystals, of plagioclase :feldspar, are seen in thin section. 

Minute needlelike crystallites show up under crossed nicols and 

show that the pitchstone has flow structure. The index o:f refraction o:f the glass is about 1.48, suggesting that the pitchstone is 

rhyolite. The pitchstone dikes are important because they have been 

brecciated in places by :faults that contain abundant pyrite and a 

little chalcopyrite, which proves some Tertiary metallization in this 

area. 

GLACIAL HISTORY AND POSTGLACIAL UPLIFT 

The major geomorphic features of the quadrangle probably 

existed before Pleistocene glaciation, which merely modified the 

shape of the mountains and disrupted the drainage to some degree. 

As noted in the discussion of unconsolidated deposits two distinct 

types of glacial deposits are recognized and are referred to as older 

and younger deposits. The time relation of these deposits to major 

glacial advances cannot be asserted definitely, but at least two distinct glacial advances are indicated. At the height of glaciation, 

the entire mountain 1nass of Kasaan Peninsula was overridden by 

ice (Wright, 1915, p. 66; Warner and others (1960) ). At this stage 

of glaciation, the highest mountains in the mapped area, with the 
350 MINERAL RESOURCES OF ALASKA 

possible exception of Granite Mountain, were buried beneath the 

ice, but some of the mountain to the west, which exceed 3,300 feet 

in height, may have stood as nunataks above the ice level. It is not 

known if ice ever flowed southward over the island from continental 

glaciers originating in the Coast Ranges to the east or whether it 

flowed radially outward from an ice center in the highlands west 

of the mapped area, but the general southeastward trend of ridges, 

valleys, roches moutonnees, and lakes suggests that most of the 

existing glacial sculpture was accomplished by ice moving eastward 

and southeastward from the highlands west of the mapped area 

and outward in all directions from cirques on the higher peaks on 

Kasaan Peninsula. As the maximum height of these highlands to 

the west is about 4,000 feet, and the highest glaciated mountains on 

Kasaan Peninsula are 2,800 feet high, it seems unlikely that ice 

flowed eastward and completely buried l{asaan Peninsula unless the 

highlands were buried deeply under the ice. However, if the ice 

was sufficiently thick, it is possible that at such a time the continental glaciers from the Coast Ranges would have advanced westward in such thickness as to force a general movement of ice westward over much of the low land areas of Prince of Wales Island. 

An alternate hypothesis is that even at the height of Pleistocene 

glaciation a separate ice center coincided with the highlands west of 

the mapped area, and that ice flowed outward and met the ice from 

the Coast Ranges east of the mapped area. Probably the latter 

interpretation is the more likely of the two. 

Following (and undoubtedly also preceding) the widespread glaciation discussed above was a period in which valley glaciers flowed 

radially outward from the highlands west of the mapped area, 

continuing the formation of horns, serrate ridges, and U-shaped 

valleys heading in cirques now occupied by tarns. Roches moutonnees, glacial striations, and plucking pits well preserved even at tide 

level show beyond any doubt that during this glaciation ice moved 

generally eastward until it reached and partly filled the existing 

valleys now occupied by salt water. Roches moutonnees related 

to this stage of glaciation are found at an altitude of 380 feet southwest of Baker Point, which indicates that ice probably filled Kasaan 

Bay. Moraines that are believed to represent time intervals within 

this general glacial stage are found at Kina Cove and in the Thorne 

River valley, and the extensive deposits on the islands at the head of 

Kasaan Bay are reworked moraines of this same stage. As noted before, the course of the Thorne River probably was changed by 

moraines related to this glacial stage. During this time, cirques 

in mountains that in places did not exceed 2,600 feet in height were 

occupied by ice in the area north and west of the quadrangle. Jacobs 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND, 351 

Mountain on Kasaan :Peninsula, which reaches an altitude of 2,370 

feet, is a broad horn between 3 large cirques, 2 of which are occupied by cirque lakes. The large moraine in the valley of the 

'Thorne River was formed by coalescing glaciers from highlands to 

the west and by smaller glaciers heading in lower hills north and 

west of the mapped area. 

No glaciers exist today on Prince of Wales Island, but perennial 

snowbanks exist in the highlands. The last glaciers probably disappeared not rnore than a few hundred years ago ; the presence of 

high-level till of local derivation on the steep slope at the head of 

Granite Creek supports this conclusion. The ridge at an altitude 

of 3,200 feet between the 2 peaks of Granite Mountain is an arete 

with large joint blocks of granite sapped apart and sitting one atop 

the other. If the Thorne River was forced into a new channel by 

glacial deposits formed in the period of valley glaciation, as postulated here, the time since this glacial stage was sufficient to enable 

the Thorne River to cut a narrow canyon at least 80 to 100 feet deep 

in bedrock west of the mouth of Falls Creek. 

Marine till with shell fragments was found at an altitude of about 

50 feet above high-tide level in the stream at Little Coal Bay, and 

very similar till, but without shells, was found at an altitude of 

almost 200 feet in the valley of Maybeso Creek, just west of the 

south end of the mapped area. Marine till with shell fragments is 

found above high-tide: level at the mouth of the small stream that 

flows northeastward into Clarence Strait from Salamander Lake. 

The islands at the head of l(asaan Bay reach a height of at least 

100 feet and are made entirely of reworked till or outwash. Wright 

(1915, p. 66) recognized various levels of erosion on l(asaan Peninsula, at altitudes between 100 and 150 feet, between 250 and 300 

feet, at 500 feet, between 1,100 and 1,300 feet, and at 1,850 feet. 

In the present investigation not all of these levels were recognized 

elsewhere in the quadrangle, but postglacial uplift is proved by 

the raised marine till and by the fact that near their mouths most 

of the streams flow on, or expose, bedrock, whereas at altitudes 

ranging roughly fron1 50 to 100 feet they flow on alluvium and 

till or reworked till. Thus, postglacial uplift amounts to at least 

50 feet and may amount to 200 feet or more. 

ECONONITC GEOLOGY 

The regional distribution, mineralogy, mineral paragenesis, classification, and origin of the ore deposits on Kasaan Peninsula and 

northwestward to the Rush and Brown mine are discussed in detail 

by Wright (1915, p. 85-108) and by Warner and others (1960). 

Individual deposits are discussed in detail by these writers, and the 
352 ~ERAL RESOURCES OF ALASKA 

Salt Chuck (Goodro) mine is discussed by Gault (1945). No useful purpose would be served by repeating here their lengthy descriptions. The purpose of the present investigation was to attempt to 

apply the factual data developed by previous work in a search for 

additional areas where copper or magnetite ore might be expected, 

to establish the regional geologic relations among lithologic units, 

to interpret the geologic structure, and to gain additional data on 

the genesis of the different types of ore within the quadrangle. 

These objectives were achieved with varying degrees of success, 

as illustrated in part in the foregoing pages. 

Only those prospects or areas of possible economic interest not 

discussed by previous writers are described in this paper. Conclusions and contributions that support or go beyond those expressed 

by earlier writers are also presented. 

PRE-TERTIARY COPPER-MAGNETITE DEPOSITS NOT PREVIOUSLY 

DESCRIBED 

A few previously undescribed prospects and areas that contain 

ore minerals were found in the mapped area, but surface exposures 

do not indicate that any are large enough or rich enough to be 

of immediate economic interest. 

MAGNETITE SOUTH OF BAKER POINT 

Bande.d magnetite ore is found on the south side of the small cove 

on the south contact of the pluton at Baker Point. The magnetite 

forms thin pods and lenses as much as several inches thick in banded 

chert and argillite intercalated in an altered pyroxene-bearing 

rock that could be a dike or a flow. To the south is deformed limestone, and the banded chert and argillite are in part calcareous. The 

absence of either skarn rock or massive hornblende, which generally 

are associated with the larger deposits elsewhere, indicates that this 

deposit is small and of little economic interest. 

At an altitude of 120 feet, near the south contact of the same 

pluton, a prospect tunnel, now partly caved, was driven at least 

50 feet S. 20° W. along a joint in altered volcanic graywacke. The 

dump discloses pyritized greenstone, with specks of magnetite, that 

is cut by epidote veinlets. No copper minerals were observed. The 

absence of skarn and hornblende rock indicates that the prospect is 

of little economic significance. 

CHALCOPYRITE NEAR KINA COVE 

Chalcopyrite disseminated in a recrystallized limestone bed is exposed in the creek bottom on the west side of Kina Creek at an 

altitude of 40 feet. The chalcopyrite is the only ore mineral, and 

it forms about· 2 percent of the bed, which ranges from 4 to 6 feet 
·CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 353 

in thickness. Beds above and below the limestone contain no chalcopyrite, and the length of the metallized bed is unknown, for its 

westward extension is buried under creek gravel. No chalcopyrite 

was found in the bed on the east cutbank of the creek, where bedrock is well exposed. 

In 1954, workmen from the logging camp at Kina Cove blasted 

a bedrock knob uncovered in the process of bulldozing for a logging 

road just above the beach. The blast unearthed recrystallized 

limestone containing as much as 5 percent chalcopyrite in selected 

specimens. The extent of the metallized limestone could not be 

determined, owing to the glacial deposits and thick vegetation. 

On the west side of the small peninsula between Kina Cove and 

Twelvemile Arm, the rocks on the south contact of the quartz 

diorite contain pyrite and pyrrhotite and locally consist of skarn 

composed of garnet and diopside. Chalcopyrite is disseminated in a 

quartz vein 6 inches wide that cuts the skarn. Elsewhere in this 

general area are small quartz veins and veinlets containing pyrrhotite and pyrite and occasional specks of chacopyrite. Locally, the 

country rock, which here is metamorphosed to quartz-mica schist, 

contains as much as 5 percent pyrrhotite. No magnetite was observed. 

NORTH CONTACT OF PLUTON WEST OF TWELVEMILE ARM 

Sulfide minerals are disseminated irregularly in the bedded rocks 

along the entire north contact of the quartz diorite of the pluton 

west of Twelvemile Arm. Locally the sulfide minerals constitute 

several percent of the rock, and at many places they form small 

lenticular pods and veinlets. The minerals include pyrrhotite, pyrite, 

and at places a little chalcopyrite. At the east end of Salmon Lake, 

the quartz diorite and the contacting schist contain more than the 

usual amount of disseminated sulfide minerals. The sulfide minerals 

in places constitute as much as 5 percent, by volume, of the rock 

along the contact in a zone several hundred feet wide that includes 

at least 150 feet of the intrusive mass. Small veinlets of quartz, 

containing pyrite, pyrrhotite, and occasional specks of chalcopyrite, 

a.nd pyrite veinlets are common in the schist exposed in the bed of 

the small creek flowing into Salmon Lake at the outlet, and along the 

trail to the west. A :few of these small veinlets contain some galena 

and marmatite, and a sample from 1 quartz veinlet 2 inches wide 

contains 2 grains of scheelite. 

A chip sample was taken a.cross 300 feet of sulfide-bearing quartz. 

diorite and schist, at right angles to the contact, at the outlet on 

the south shore of Salmon Lake. The sample was analyzed quantitatively for gold, silver, and copper, and part of the panned concentrate was analyzed qualitatively spectroscopically to detect minor 
354 MIT.NERAL RESOURCES OF ALASKA 

amounts of other elements of economic interest. The analysis showed 

no gold or silver and only 0.02 percent copper. The spectrographic· 

analysis disclosed no elements of economic interest in more than 

trace amounts. 

PROSPECT ON NORTH BRANCH OF PAUL YOUNG CREEK 

Several pits and opencuts mark an old prospect on the slopes of 

the small creek that flows southward into Paul Young Creek. Although the prospect is in the general area of one previously described 

as the Venus prospect (Wright, 1945, p. 100) , it is described briefly 

here because the geologic occurrence is unlike that of the Venus 

prospect. The location of the pits is shown on the geologic map 

(pl. 33). 

The prospect is at an altitude of about 170 feet and consists of· 

several trenches, over a distance of about 350 feet, aligned along 

the creek and the fault followed by the creek. The southernmost 

pit, sunk in pyritized argillite heavily stained with iron, discloses 

pyrite and chalcopyrite in seams and replacement quartz veins, the 

most continuous of which strike N. 40° E. and dip 85° NW. along a 

joint in the argillite. Pyrite and chalcopyrite form solid layers 

ranging from lj8 to 1~ inch in thickness. One fault plane observed 

strikes N. 50° W. and dips 75° SW. 

About 40 feet upstream, an opencut 75 feet long and trending 

N. 55° E. discloses black argillite containing disseminated pyrite 

and chalcopyrite and small sulfide veinlets striking along the cut. 

The dump contains fragments of calcite containing sulfide minerals. 

The third cut, 200 feet upstream, discloses pyritiferous calcite 

veins that reach a maximum thickness of 6 inches and follow joints 

in black argillite. In the face of the opencut is a small fault that 

strikes N. 20° E. and dips vertically. Both walls of the fault are 

argillite of similar appearance, which indicates that displacement 

on the fault is minor. 

The wallrocks along the great fault that continues northwestward 

and northeastward from the prospect pits are broken and pyritized,. 

indicating that the ore minerals at this prospect may be part of a 

larger zone of sulfide-bearing rock related to hydrothermal solutions 

that rose along the fault. 

PROSPECTS ON NORTH POLE HILL 

During the summers of 1954 and 1955 Juan Muiioz, a mining 

geologist prospecting near Salt Chuck, completed magnetic and 

geochemical exploration at several points on North Pole Hill. Small 

pits were sunk to bedrock in two areas where the concentration of 

copper in soil samples was encouraging. In each pit bornite was 

found in the bedrock, which is pyroxenite or gabbro of the large 
CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 355 

pluton containing the ore body of the Salt Chuck ( Goodro) mine 

about 2 miles east. East of the pits exposing bornite, Mr. Muiioz 

has made a shallow opencut that exposes several veins ranging from 

6 to 18 inches in width and containing pyrite and quartz. The veins 

are said by Mr. ~{ufioz to assay about $7 in gold per ton. No copper 

minerals are associated with the pyrite. These veins are near a fault 

locally known as Murphy's Slip that can be traced from the Rush 

and Brown mine. 

Elsewhere on North Pole Hill, Mr. Munoz found bornite in gabbro 

or pyroxenite. He also found magnetic and geochemical anomalies, 

many of which are associated with intersections of smalllinears that 

are assumed to be faults. 

The prospects on North Pole Hill are of interest because they are 

similar in mineralogy and geologic setting to the Salt Chuck 

(Goodro) mine, which produced more than 300,000 tons of ore containing copper and palladium. 

OTHER AREAS OF INTEREST 

The diorite porphyry that forms a complex pluton about 1 mile 

northeast of Lake No. 3, near Salt Chuck, is altered and pyritized 

near many parts of the contact, especially along the south margin. 

In some hand specimens chalcopyrite is visible, but it does not exceed 1 percent of the rock. As vegetation is thick in this area, discovery of deposits of economic interest would require detailed prospecting, supplemented by digging of shallow pits to test the 

1netallized areas. 

The bedrock at many places is bleached, pyritized, and silicified 

along the fault zone that extends northwestward from l{asaan Bay 

to the Thorne River. Most of this area is very low and is covered 

by thick brush, muskeg, and glacial deposits. It is possible that 

detailed prospecting of this zone might reveal deposits of economic 

interest, but prospecting would require geophysical methods supplemented by pits and trenches. 

A 1nagnetic anomaly is associated with skarn on the southwest 

contact of the pluton east of Lava Creek. The anomaly lies on the 

east shore ofthe small lake on the fault zone that strikes northward 

from the head of Thorne Bay. The area of skarn is small, and the 

country rock consists of altered flows and volcanic graywacke; elsewhere in the area this is not a good host rock for copper-magnetite 

deposits. The location of the skarn and the anomaly in a strong 

fault zone near an igneous contact is of interest. Bedrock in this 

area is covered with peat, muskeg, and till, and prospecting would be 

difficult. Dip-needle readings taken jn a line trending about N. 20° 

E. from the southwest end of the lake to the contact of the pluton 
356 ~ERAL RESOURCES OF ALASKA 

indicate that the vertical magnetic intensity is greatest for a distance 

of 600 feet from a point about 30 feet northeast of the lake. The 

vertical magnetic intensity lessens appreciably over the pluton and 

southwest of the lake. 

At many places in the mapped area are small areas of bedrock that 

are bleached and pyritized; many of them contain disseminated 

magnetite and chalcopyrite. Many of these areas are along shear 

zones or faults, but none has proved to be of economic interest. In 

the aggregate, however, they show that deposition of copper and 

iron minerals has been widespread in large parts of the quadrangle. 

TERTIARY DEPOSITS 

GOLD QUARTZ VEINS NEAR GRANITE CREEK 

The gold quartz veins in the southeast part of the rna pped area 

have been described by F. E. and C. W. Wright (1908, p. 164). 

Several small mines on similar lodes were developed in the area 

north and west of Hollis Anchorage, but the Flagstaff mine is the 

only one established on lodes within the mapped area. This mine 

is described by Twenhofel, Reed, and Gates (1949, p. 10-13); and 

their descriptions of these deposits are not repeated here. The location of the other old prospects :found in the mapped area by the 

writer are shown on the geologic rna p (pl. 33) . All the prospects 

are located on quartz veins ranging in strike from N. 20° W. toN. 

50° W., and all dip northeastward. The veins range from 2 to 5 feet 

in thickness, and many are along the contacts of diabase dikes believed to be of Tertiary age. The ore minerals are pyrite, subordinate chalcopyrite and galena, and gold. On the southeast side of 

the divide between Granite Creek and the valley of Maybeso Creek, 

the veins are in black slate and argillite. The mineralogy is similar 

to that of the veins in the quartz diorite. 

The average gold content of the gold quartz veins has not been 

determined. The Flagstaff vein is discussed by Twenhofel, Reed, 

and Gates who say, "The value of the ore is reported by the operators 

to average about $12 per ton, but recovery as indicated by production returns is considerably less." 

The vein near the contact on the south slope of Granite Mountain 

has a zone about 4 inches thick on the hanging wall that contains 

visible grains of gold. Two chip samples of the vein east of the 

divide between Granite and Maybeso Creeks contained only a trace 

of silver and 0.03 ounce of gold per ton. 

flERTIARY PYRITE-CHALCOPYRITE VEINS NEAR PLUTON EAST Ol!' LAVA CREEK 

Tertiary veins believed to be younger than those near Granite 

Mountain were found at several places in the north-central part of 
:cRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 357 

the quadrangle and in the area immediately north. The veins, or 

lodes, are variable in physical structure, but all are characterized by 

pyrite as the dominant sulfide. Chalcopyrite is associated with 

pyrite in some, especially where carbonate minerals form part of the 

gangue. The lodes consist of altered, bleached, and pyritized fault 

zones, along some of which are intruded trachyte and pitchstone 

dikes, or of pyritized breccia cemented by pitchstone. Near some 

of the lodes, introduced fine-grained silica has formed a chertlike 

rock that transgresses other rock types. Beca.use no metallic minerals 

other than pyrite and occasional specks of chalcopyrite were observed 

in any of the lodes, they are assumed to be of little economic value, at 

least in the area rna pped, although they were not studied in detail. 

CONCLUSIONS 

REGIONAL DISTRIBUTION OF ORES 

The present study supports the conclusion that most of the coppermagnetite bodies of economic interest in the mapped area appear to 

be limited to the area near and in the pyroxenite intrusive body 

near Salt Chuck, and to the area along the south shore of Kasaan 

Bay from Twelvemile Arm to a point south of Baker Point. The 

peninsula between Thorne and Tolstoi Bays and the large area north 

of Thorne Bay are singularly lacking in metallized areas, except for 

the Tertiary pyrite metallization noted previously. Rush Peak also 

appears to be barren of deposits. 

The structural localization of ore deposits throughout the mapped 

area is in general conformity with the ideas expressed by Warner 

and others (1960). The deposits containin,g a high percentage of 

magnetite show close spatial relationship to igneous rocks, and many 

sulfide-rich deposits with little magnetite are localized along igneous 

rocks. Calcareous sedimentary rocks were replaced in preference 

to pure limestone, and most of the ore deposits containing magnetite are associated with skarn. However, disseminated ore minerals 

are found in fault zones without associated skarn or magnetite. 

Pyrite and pyrrhotite are common near plutons where dark argillaceous and cherty rocks are thermally metamorphosed. The scarcity 

of chalcopyrite in such rocks, and the absence of hydrothermal 

alteration, suggests that the sulfide minerals were formed by the 

addition of sulfur to iron-bearing minerals that were already in 

these rocks before their metamorphism. 

Quartz veins are relatively rare except in and near the pluton in 

the southwestern part of the quadrangle, but these gold-bearing 

quartz veins, which have been described by F. E. and C. W. Wright 

(1908, p. 158-168), are of Tertiary age and are not allied with the 

copper-magnetite deposits. The pyritized Tertiary dikes in the 
358 MINERAL RESOURCES OF ALASKA 

north-central part of the quadrangle also represent a distinct type 

of metallization. 

PERIODS OF ORE DEPOSITION 

Three distinct periods of metallization were recognized in the 

present study, each with characteristic ore and gangue minerals. 

The oldest is that which produced the copper-magnetite deposits, 

and deposition of which probably was confined to the Late Cretaceous 

epoch. The Salt Chuck mine, which contains bornite as the principal 

ore mineral and platinum-group metals in small amounts, seems to 

represent a unique type of ore within the district. It is highly unlikely that bodies of similar mineralogy will be found beyond the 

borders of the pyroxenite-gabbro pluton. 

The next oldest period of ore deposition produced the gold quartz 

veins, of which those in the southwest part of the mapped area are a 

small part. These veins are younger than the diabase dikes of 

probable early Tertiary age. 

The most recent period of ore deposition is that which produced 

the pyrite-bearing :fault zones in the north-central part o:f the 

mapped area. These deposits contain only a little chalcopyrite. 

This period o:f ore deposition definitely is later than the pitchstone 

Jikes with which the deposits are closely related. The pitchstone 

dikes are younger than the Tertiary conglomerate on Lava Creek. 

This last period of ore deposition has not been recognized previously, 

and its areal distribution and economic potential are unknown. 

The question o:f the relative ages of the two periods of ore deposits 

of Tertiary age cannot be resolved with certainty. A younger age 

is assigned to those associated with the pitchstone dikes only on the 

-evidence that diabase dikes are not known to cut the bedded rocks 

assigned to the Tertiary, whereas the pitchstone dikes do. 

ORIGIN OF MAGNETITE-CHALCOPYRITE ORES 

The genetic relation o:f the deposits of magnetite-chalcopyrite ore 

to the plutons was pointed out by Wright ( 1915, p. 67). Warner 

and others ( 1960) suggest that the ores show a rough zonal arrangement with respect to the late granodiorite intrusive bodies, such as 

that at Tolstoi Mountain, and that the ore bodies lie in a belt trending northwestward from the Mount Andrew mine to the Salt Chuck 

mine, parallel to the topographic depression that extends into the 

Thorne River valley. The present writer :found by chemical analysis 

that the intrusive rock at Tolstoi Mountain is the most mafic o:f the 

three plutons sampled and believes that the high content of orthoclase 

and albite of the rocks from this pluton described by Warner and 

others (1960) is a result o:f alkalic metasomatism, such as is very 

common about the pluton east o:f Lava Creek. 
·CRAIG C-2 QUADRANGLE, PRINCE OF WALES ISLAND 359 

The pluton west of Twelvemile Arm is the most silicic of those 

analyzed chemically, and it is intruded into a thick sequence of rocks 

containing a high percentage of argillite, chert, and slate. However, 

no deposits of copper or magnetite of economic interest are found 

near this pluton. This apparently conflicts with the explanation 

given by Warner and others (1960) and is!, therefore, further explained below. 

Petrologically, the rocks of the Craig C-2 quadrangle are characterized by the ubiquitous occurrence of abundant free magnetite and 

of pyroxenes that tend to lie in the augite :field described by Hess 

( 1941), near the ferroaugite field. Almost every thin section of the 

bedded or dioritic intrusive rocks studied by the writer contained 

abundant magnetite, and in some sections of the cleaner graywacke, 

magnetite is seen to be concentrated as if it represents sedimentary 

enrichment. The conglomerate on Berry Island contains some 

rounded pebbles of volcanic graywacke in which magnetite forms 

the bulk of the pebbles (pl. 39B). Similar pebbles have been obtained from Thorne Bay, showing that magnetite was clotting into 

large grains before the intrusion of the plutons. It seems probable 

that the source of part of the magnetite in the ore bodies is the 

magnetite of the volcanic rocks, which may, in fact, be the ultimate 

source of most of the magnetite by having contributed iron to the 

igneous rocks which assimilated large amounts of volcanic rock. 

The apparent scarcity of magnetite deposits about the stock in the 

southwest part of the quadrangle possibly is due to its low initial 

iron content and to the fact that it was emplaced into rocks with a 

generally low iron content. 

SUGGESTIONS FOR PROSPECTING 

The search for additional ore deposits of possible economic interest 

will require exploration techniques involving detailed mapping on 

a large scale, supplemented with magnetic surveys as pointed out by 

Warner and others (1960). In the search for copper deposits, primary exploration might be aided by geochernical techniques, such as 

water and soil sampling. Large parts of the quadrangle, such as the 

area north and east of Thorne Bay, appear on the basis of the 

present study to offer little promise of economic deposits; and other 

areas, such as the area adjacent to the fault trending northwestward 

from the head of Kasaan Bay, seem to contain more than the average 

amount of disseminated sulfide minerals. The small sulfide-bearing 

pluton north of Lake No. 3 should be prospected in detail in the 

interest of outlining a large tonnage of low--grade ore. 

In the search for copper deposits it would seem desirable to test 

with the diamond drill some of the new bornite prospects in the 
360 ~ERAL RESOURCES OF ALASKA 

pyroxenite body at the salt chuck at the head of Kasaan Bay. The 

magnetic anomaly near the pluton north of Thorne Bay should be 

investigated. 

REFERENCES CITED 

Brooks, A. H., 1902, Preliminary report on the Ketchikan mining district, 

Alaska: U.S. Geol. Survey Prof. Paper 1. 

Buddington, A. F., and Chapin, Theodore, 1929, Geology and mineral deposits 

of southeastern Alaska: U.S. Geol. Survey Bull. 800. 

Gault, H. R., 1945, The Salt Chuck copper-palladium mine, Prince of Wales 

Island, southeastern Alaska: U.S. Geol. Survey open-file report. 

Hess, H. H., 1941, Pyroxenes of common mafic magmas : Am. Mineralogist, 

v. 26, p. 515-535, 573-594. 

Pettijohn, F . .J., 1948, Sedimentary rocks: New York, Harper and Brothers. 

Tuttle, 0. F., and Bowen, N. L., 1950, High temperature albite and contiguous 

feldspars: .Jour. Geology, v. 58, p. 572-583. 

Twenhofel, W. S., Reed, .J. C., and Gates, G. 0., 1949, Some mineral investigations in southeastern Alaska: U.S. Geol. Survey Bull. 963--A, p, 10-13. 

U.S. Bureau of Mines, 1944, Poor Man iron deposit, Kasaan Peninsula, Prince 

of Wales Island, southeastern Alaska: War Minerals Rept. 227. 

U.S. Weather Bureau, 1901-55, Climatological data of Alaska: Washington, 

U.S. Govt. Printing Office. 

Warner, L.A., and others, 1960, Iron and copper deposits of Kasaan Peninsula, 

Prince of Wales Island, southeastern Alaska: U.S. Geol. Survey Bull. 1090 

(in press). 

Williams, Bowel, Turner, T. .J., and Gilbert, C. M., 1954, Petrography: San 

Francisco, Calif., W. H. Freeman and Co. 

Wright, C. W., 1915, Geology and ore deposits of Copper Mountain and Kasaan 

Peninsula, Alaska: U.S. Geol. Survey Prof. Paper 87. 

Wright, F. E., and Wright, C. W., 1908, The Ketchikan and Wrangell mining 

districts, Alaska: U.S. Geol. Survey Bull. 347. 

Wright, W. S., and Tolonen, A. W., 1947, Mount Andrew iron deposit, Kasaan 

Peninsula, Prince of Wales Island, southeastern Alaska : U.S. Bur. Mines 

Rept. Inv. 4129. 
INDEX 

Page 

Albitization __ -------------------------------- 312 

Alluvium, deposition------------------------- 332 

Amphibole--------------------------------- 309,345 Andesite, lithologic character _______________ 317-318 

Antiperthite---------------------------------- 346 

Apatite------------------------- 336,338, 340, 346,349 

Argillite, lithologic character _____ ------------ 314 

Augite ______________ 3ll, 333, 334, 342,343, 344,349, 359 

:Baker Point, glaciation----------------------- 350 

magnetite._------------------------------ 352 

pluton------------------------------------ 337 

:Barnacles------------------------------------- 330 :Batholiths ______________________ 307,308,328, 332,335 

:Beach gravel, description_____________________ 332 

:Bedded rocks, age------------------ 307,308-300,328 

deposition ____________________ ------ 323-324, 328 

fine-grained----------------------------- 313-315 

limestone, Devonian. ___ --------------- 324--326 

lithologic character----------------------- 307 

Ordovician----------------------------- 31D-311 

origin _______ ------------------------------ 310 

Silurian __ -------------------------------- 310 

Tertiary-------------------------------- 326-328 :Berry Island, conglomerate _____________ 359, pl. 39 

dikes.----- ___ ------_-----________________ 343 

limestone ___ --------------- ______ --------- 325 

Biotite •• ----------------------- 335, 336,337,347, 34,9 

Bornite----------------------------- 334,354,355,358 

Calcite------------- 317,320,338,340,342,343,344,354 

Chalcopyrite ___ 336, 349, 352, 353, 354, 355, 356,357, 358 

Chert, lithologic character____________________ 314 

Chlorite ________ 312,317,320,333,335,342,343,344,349 

Clarence Strait, description___________________ 303 

Climate._---------------------------------- 304-305 

Coal Bay, glaciofluvial deposits--------------- 330 

sandstone. ___ ---------------------------- 320 Coast Ranges, batholiths_____________________ 332 

erratics source---------------------------- 329 

glaciation_________________________________ 350 

Conglomerate, lithologic character __ 315-317,327-328 

Copper·------------------------------------ 354,358 

Copper deposits, production history ____ 300,334, 355 Corundum _________________________________ 338,340 

Davidson's logging camp, conglomerate near. 327 

Dikelets-------------------------------- 307,315,347 

Dikes, andesite porphyry, sodic ________ 345-346,347 

crosscutting relations ___________________ 347-348 

diabase _____ 325,326,339,340,347,348-349,356,358 

diorite porphyry __ ------------- 339,342,347,348 

feldspar porphyry________________________ 342 

granite, sodic_____________________________ 346 

hornblende porphyry--------------------- 34:& 

monzonite________________________________ 346 

pitchstone ______________ 327,328,339,348,349,358 

pyroxene porphyry----------------- 343-344,347 

quartz pegmatite _______________________ 346-347 

rhyolite, chemical analyses_______________ 310 

Middle Devonian ______________ 308,339-340 

pyritized ___ -------------------------- 331 

Page 

Dikes-Continued 

rhyolite porphyry, sodic ________________ 345-346 

trachyte ____________________________ 339,344-345 

Diopside __ ----------------------------- 338, 340, 353 

Drainage·---------------------·-------------- 304 

Economic geology_--------------------- 334, 351-360 Epidote ____________ 312,318,320,333,334,342,343,344 

Erratics __ ------------------------------------ 329 

Faults __ 308,318-319, 320, 326, 335, 337, 349, 354, 355, 356 

Ferroaugite----------------------------- 344,349, 359 

Folds------------------------------- 318,319,320,324 

Foot Lake, fossils_____________________________ 321 

Fossiliferous limestone __________________ 307,324--326 

Fossils.----------·------------------ 306,308,309,310, 

311, 314,316,321-322,323, 324,330, 339 

Gabbro, in plutons------------------------- 333-335 

Galena_------------------------------------ 353,356 

GameL-------------------------------- 325,340, 353 

Geography--------------------------------- 303-304 

Glacial deposits ... _------------- 304,308,329-331,355 

Glacial history ___ -------------------------- 349-351 

Glaciofluvial deposits ___________ 308,327,328,329, 33J) 

Gold __ ------------------------- 303,355,356,357,358 

Granite Creek, glacial deposits near __ -------- 331 

gold-bearing quartz veins ___________ 356,357,358 

Granite Mountain, dikes ___________________ 348-349 

gold lodes ___ ·----------------------- 303, 349,356 

Graywacke, conglomeratic volcanic___________ 307, 

308,311-312,313, pis. 34,35 

feldspathic and lithiC------------------- 312-313 

Heceta Island __ ----------------------------__ 322 

Hematite ________ ----------------------- 335, 338, 340 

Hornblende __ -------------------------------- 318, 

:336, 340, 342-343, 344, 345, 346, 348, 349 Hypersthene _______________________________ 338,340 

Ilmenite .• -------------------------- 336,338,340,342 

Jacobs Mountain.---·---------------------- 35o-351 

Karta Bay, graywacke, conglomeratic volcanic _____________________ 312,323, pl. 35 

Kasaan Bay, beach graveL------------------- 332 

dikes.---------------------------------- 345, 348 

pluton-------------------------- 325,333,334-335 

Kasaan greenstone, age----------------------- 307 

lithologic character--------------------- 306-307 

Kasaan Island, d:ikes----------------------- 326,344 

fossils _______ ----------------------------- 309 

limestone.-------------------------- 307,324--325 

reeL _________ ----------------------------- 325 

rhyolite, platY---------------------------- 339 

Kasaan Peninsula, copper deposits___________ 300 

dikes------- __ ------------------------_____ 342 

geology------ __ --------------------- 306, 308-309 

glaciation.---·--- _____________ ----------- 349-350 

location _____ ----------------------------- 303 

postglacial uplift__________________________ 351 

topography--·----------------------------- 304 

361 
362 INDEX 

Page Page 

Kina Cove, chalcopyrite ____________________ 352-353 Quartz-diorite, age __________________________ 338-339 

glacial deposits___________________________ 350 chemical analyses_________________________ 338 

limestone ___ ------------------------------ 315 in plutons.----------------------------- 335-339 

Klawak Inlet, Ordovician rocks______________ 322 

Klawak Lake, fossils------------------------- 322 ReeL---------------------------------------- 3

3

2

50

5 

Roches moutonnees ___ -----------------------

Lava.---------------------------------- 317-318,327 

Lava Creek valley, conglomerate _______ 327,328,339 

dikes------------------------------- ____ 346,348 

pluton __________________ 329,335,355,356--357, 3b8 

pyrite-chalcopyrite veins _______________ 356--357 

tilL __ ---------------------------------- 330, 331 

Round Island, limestone ___________________ 324,225 

Rhyolite, platy----------------------------___ 33~ 

Rush and Brown mine _________________ 309,310,351 

Rush Peak, conglomerate_____________________ 316-

dikes.------------------------------------ 342 

fossils _____________ -------·---------------- 322 

Limestone, Devonian •.. --------------- 307,324-326 Salmon lake, till near------------------------- 330 

lithologic character--------------------- 314-315 Salt Chuck mine area, plutons-_ 333-334,336,339,343 

Little Coal Bay, sandstone___________________ 326 Sandstone, lithologic character ______________ 326--327 

till_______________________________________ 351 s h rt 353 

Little Salmon Lake, alluvium________________ 332 S~ri~~t~~--~=~~::~::::~~::::::::::::::~::~~~~~: 342 

Magnetic anomalies._-------------- 303, 336, 355, 360 Sills ________________________________________ 308• 309 

Magnetite ______________ 312, 320, 333, 334, 336, 338, 340, Silver---------------------------------------- 356-· 

Skarn __ -------------------------------- 337, 353, 357 342, 343, 346, 347, 349, 352, 357, 358, 359 s A h r t Magnetite ore re.serves________________________ 300 nug nc orage, Imes one ___________________ P 1 36 · 

Marble------------------------------------- 314_315 Stocks __________________________________ 308,309, 359· 

Marcasite._---------------------------------- 326 Submarine landslides _______________________ 317,324 

Marmatite ____ ------------------------------- 353 Syncline ________________________________ 30!, 308, 318 

Maybeso Creek valley, till _________________ 331,351 Tectonism---------------------------------- 326,351 

Metamorphic rocks, age and correlation ____ 321-323 Thome Bay, andesite flows near______________ 317 

lithologic character--------------------- 320-321 conglomerate exposed near________________ 317 

Mica _______________________ 333,336,337,342,347,349 dikes _______________________ 343,314,345,347,348. 

Moraines, lithologic character_ ______________ 329-331 graywacke, volcanic ____________ 312,315, pl. 34 

North Pole Hill, prospects ___________________ _ 354 

Olivine ___________________________ ---------- 333, 349 

Palladium __________________________________ 334,355 

Paul Young Creek, prospect near_____________ 354 

Perthite .. ------------------------------------ 335 

Platinum ____ --- _____ ------------------- ___ --- 358 

Pluton, southwestern part of area ___________ 313,337 

Plutons, erratics source _____________________ 329,331 

See also Gabbro, Quartz diorite, and particular area and structure. 

Postglacial uplift.-------------------------- 329, 351 

Precipitation. ______ --_----------- ____ ------ 304-305 

Prehnite ________________________ 312,318,320,333,344 

Production, history--------------------------- 300 

Prospecting, suggestions ____________________ 359-360 

limestone near ___ -·----------------------- 320· 

Thome River, course, ancestraL ____________ 350,351 

course, present. __ ------------------------ 304 

Thorne River valley, glacial deposits_________ 330 

glaciation_________________________________ 350 

Till, lithologic character---------------------- 330, 

thickness ________________ ----------_----__ 329 

Tolstoi Bay, dikes ______________________ 345,347, 34S. 

graywacke, volcanic_----------- 312,315, pl. 34 

limestone near---------------------------- 320 

Tolstoi Point, pluton ________ ---------~------ 339· 

Topography---------------------------------- 304 

Tuff _______________________ ~------------ 308,309,311 

Twelvemile Arm, contact of pluton _________ 353-354 

dikes_---------------------------- __ 346--347, 348. 

graywacke, volcanic______________________ 320• 

pluton __________________ 315,323,337,338,347,359 

sulfide minerals___________________________ 353. 

tilL __ ------------------------------------ 331 

Pyrite ______________________________ 315, 331,334,335, Unconsolidated deposits ____________________ 328-332 · 

336, 337, 347, 349,353, 354, 355, 356, 357,358 

Pryoxene__________ __ __________ _______ ________ 309, Venus prospect. ______________________ -------- 354 

311,317-318,325,334,343,344,347,319,359 Volcanism ______________________________ 310,323,344 

Pyroxene, in plutons _______________________ 333-335 Wright, c. w., quoted.·--------------------- 309· 

See also particular pyroxene mineral. 

Pyrrhotite------------------------------ 337,353,357 Zoisite·--------------------------------- 312,333,344. 

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