Stratigraphy and 

General Geology of jke 

McCarthy C-5 Quadrangle; 

Alaska

By E. M. MAcKEVETT, JR.

Descriptions of the rocks 

of a quadrangle famous for 

its copper mines

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1971
UNITED STATES DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

William T. Pecora, Director

Library of Congress catalog-card No. 79-609946

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

Washington, D.C. 20402 - Price 30 cents (paper cover)
CONTENTS

	Page

Abstract . .....-.. . .... ........_.. . . . .. . .. . .. .. .. . .. 1

Introduction ...-. ..... . .... .... . .. .. . . . ... .. ._. 1

Geology -. . ... . _. __ .._____ _ . _ __.. . _ __. ____. . 4

General summary, regional setting, and structure......................... __...... 4

Stratigraphy and lithology . ... __. _ . 8

Hasen Creek Formation .. .. _ . ._.. 8

Nikolai Greenstone ..__ ......_ . . . _ 8

Chitistone Limestone ... .... ._ . __ _... . _ _ _ . 10

Nizina Limestone . .... _ .. . .._._ _..._ . _. 11

McCarthy Formation ._ . ... . 13

Lower member ...... . _...__. . __ _ . ._ . _ ._ 13

Upper member . _ .. . . . __. . _ .. 14

Lubbe Creek Formation _. . __ .. . 15

Nizina Mountain Formation .. _ . _-- . .. 16

Root Glacier Formation . __. ._.. ..__ . .. 17

Kennicott Formation .. .__. . _. ___ ___. _ ' ._ 19

Schulze Formation ..._... ___ __.. . . 20

Moonshine Creek Formation _.. ... . . _ 20

Frederika Formation .. _. .. _. . _. 21

Intrusive rocks . .. _. .._... .. . 23

Andesitic dikes and sills. ......................... ,.._ . .................. 23

Intermediate rocks ......................................-.......-..^.....................-.. 24

Felsic hypabyssal rocks .............. ................-...-. . . ...... .......... 24

Wrangell Lava ... ... ................ ........ ......... ............. ............. 25

Surficial deposits ...-. .......- ......-...-............. ..................... ......... .. 27

Alluvium and older alluvium...... . .... . ..... .! . . 27

Talus . .. ..... ....., . ..... . .... 27

Moraines ................ .... . .... .. ._ . . . 27

Landslides .......................................................... ......... .. ....... . 27

Rock glaciers .... ' . ; ... ...... .. ....... . 28

Fossil collections ......................................................... 28

Economic geology ................... _........ . ... . .............. ............... .. . 32

References ..............I............. ....... .!.... .. . 34

ILLUSTRATIONS

Page

FIGURE 1. Index map showing location of the McCarthy C-5 quadrangle.. 2

2. Panorama of part of the Wrangell Mountains showing the

McCarthy C-5 quadrangle and nearby geographic features.. 3

3. Isometric block diagram showing generalized geology of the

McCarthy C-5 quadrangle. . .. 6

TABLE

TABLE 1. Summary of rocks in the McCarthy C-5. quadrangle.... . . 4

in

STRATIGRAPHY AND GENERAL

GEOLOGY OF THE McCARTHY C-5

QUADRANGLE, ALASKA

By E. M. MACKEVETT, JR.

ABSTRACT

The McCarthy C-5 15-minute quadrangle includes a rugged area on the 

southern flank of the Wrangell Mountains having a relief of about 12,000 feet. 

The quadrangle contains a sequence of consolidated layered rocks, approximately 25,000 feet thick, local intrusive rocks, and widely distributed surficial 

deposits. The layered rocks are chiefly Mesozoic, but they range from Permian 

to Quaternary in age. They include two sequences of subaerial volcanic rocks, 

abundant shelf deposits, and continental sedimentary rocks. Some of the shelf 

deposits and the continental sedimentary rocks contain abundant fossils. The 

intrusive rocks are mainly Tertiary and include dikes and sills, largely of 

dacitic or andesitic composition, and a few small stocks of granodiorite. The 

diverse Quaternary surficial deposits are largely related to glacial processes.

The main faults and folds of the quadrangle formed during a major orogeny 

at or near the close of the Jurassic or in the pre-Albian Cretaceous. The quadrangle contains the main Kennecott mines of Alaska, for many years among 

the world's foremost copper producers, and a few lesser copper deposits and 

occurrences. The physiography of the quadrangle strongly reflects glacierrelated erosional and depositional processes.

INTRODUCTION

This report supplements the McCarthy C-5 15-minute geologic 

quadrangle map (MacKevett, 1970b) by providing data on the 

stratigraphy and lithology of the map units and on other geologic 

topics. The McCarthy C-5 quadrangle is in the eastern part of 

southern Alaska on the southern flank of the Wrangell Mountains 

(fig. 1), a scenic alpine range characterized by several snow-clad 

volcanic peaks (fig. 2). The relief in the quadrangle is about 12,000 

feet. The quadrangle is drained by McCarthy Creek and the Nizina 

River and their tributaries, parts of the Copper River system. The 

two largest of Kennecott's Alaskan copper mines, for many years 

among the major copper producers of the world, are near the southwestern corner of the quadrangle. The quadrangle is uninhabited 

and is accessible mainly to foot travel or helicopter.
GEOLOGY, MCCARTHY c-s QUADRANGLE, ALASKA

FIGURE 1. Location of the McCarthy C-5 quadrangle.

Extensive ice and snowfields cover bedrock throughout the high 

terrane in the northwest part of the quadrangle and sustain the 

large Regal and West Fork valley glaciers. The upper reaches of 

the valley glaciers are generally marked by icefalls. Parts of some 

glaciers are strongly crevassed or have extremely jagged surfaces; 

other glaciers, such as the West Fork Glacier, are relatively smooth 

and accessible throughout most of their extent. Smaller glaciers 

that are relicts of more widespread glaciation are widely scattered 

throughout the quadrangle. These and many patches of perennial 

snow in the higher terranes attest to the rigorous climate of the 

quadrangle.

The geologic mapping was done with helicopter support in 1961 

with minor additions and revisions in 1962, 1964, and 1965. A 

1:48,000 topographic base was used and to a lesser extent aerial 

photographs. Supplementary investigations consisted of thinsection studies, spectrographic, X-ray, and chemical analyses, feldspar and carbonate staining, and paleontologic studies. Grateful 

acknowledgment is made to D. L. Jones for his thorough studies of 

Cretaceous stratigraphy and paleontology; to M. C. Blake, Jr., who 

participated in the 1961 mapping; to N. J. Silberling, R. W. Imlay, 

and J. A. Wolfe, who respectively studied the Triassic, Jurassic,
INTRODUCTION

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4 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

and Tertiary fossils; to S. W. Muller, who studied specimens of the 

Jurassic Weyla, and to C. H. Schulze, Tom Gilmore, Howard 

Knutson, and Jack Wilson, who shared their knowledge of the local 

geography, logistic problems, and mining activity. Previous descriptions of the geology of the quadrangle are mainly in a report 

by Moffit (1938) and maps by MacKevett (1963 and 1970b). Fossils collected during the investigation are listed in the section 

following "Stratigraphy and lithology."

GEOLOGY

GENERAL SUMMARY, REGIONAL SETTING, AND STRUCTURE

The layered rocks in the quadrangle, which have a cumulative 

thickness of about 25,000 feet, are mainly Mesozoic but range from 

Permian to Quaternary in age (table 1). They comprise two sequences of continental volcanics, abundant shelf deposits, continental sedimentary rocks, and surficial deposits (fig. 3). The inTABLE 1. Summary of rocks in the McCarthy C-5 quadrangle

Formation 

or unit System Series

Estimated

maximum

thickness

(feet)

Dominant 

lithology

Surficial Quaternary.-, ._.... . ...- ............ .......... ...................

deposits. 

Wrangell Tertiary and .___ .... 5,000+ Andesite and

Lava. Quaternary. basaltic

andesite. 

Felsic Tertiary .. Dacite and

hypabyssal rhyodacite. 

rocks. 

Intermediate do. - Granodiorite.

intrusive 

rocks. 

Andesitic Tertiary .. .. Andesite.

dikes and and Quatsills. ernary.

Frederika Tertiary . Miocene .. 2,000 Sandstone, 

Formation. conglomerate, siltstone, and 

shale.

Moonshine Cretaceous Lower and 550 Sandstone 

Creek Upper Cre- and siltFormation, taceous. stone. 

Schulze . do. Lower(?) Siliceous 

Formation. and Upper 200 shale. 

 " ;« Cretaceous.
GENERAL SUMMARY, REGIONAL SETTING, STRUCTURE 

TABLE 1. Summary of rocks in the McCarthy C-5 quadrangle Continued

Formation 

or unit

Kennicott

Formation. 

Root Glacier

Formation.

Mountain 

Formation. 

Lubbe Creek

Formation. 

Upper member of 

McCarthy 

Formation. 

Lower member of 

McCarthy 

Formation.

Nizina

Limestone. 

Chitistone

Limestone. 

Nikolai

Greenstone. 

Hasen Creek

Formation.

System

..........do..........

Jurassic...........

..........do..........

..........do..........

Triassic(?) 

and 

Jurassic.

Triassic 

and Jurassic(?)

Triassic....-... .

........do..........

..........do..........

Permian...........

Series

Lower Cretaceous. 

....Upper

Jurassic.

Upper 

Jurassic.

Jurassic. 

Upper Triassic ( ?) 

and Lower 

Jurassic. 

Upper Triassic and 

Lower Jurassic ( ?).

...Upper Triassic. 

..........do..........

Middle and

(or) Upper 

Triassic. 

. Lower

Permian.

Estimated 

maximum 

thickness 

(feet)

700

' 3,000+

1,350

300

2,000+ 

950

1,250

2,100

3,000+

250

Dominant 

lithology

Conglomerate, sandstone, siltstone, and 

shale. 

Mudstone

and 

siltstone. 

Graywacke.

Impure

spiculite. 

Impure 

chert and 

spiculite.

Carbonaceous 

shale, impure limestone, and 

chert. 

Limestone.

Limestone

and 

dolomite. 

Basalt.

Bioclastic

limestone.

trusive rocks are mainly Tertiary and consist of diverse dikes and 

sills, chiefly andesitic and altered felsic types, and uncommon small 

stocks of granite rocks intermediate in composition. The widely 

distributed surficial deposits are mainly related to glacial processes.

The pre-Cretaceous rocks occupy part of an extensive northwesttrending belt along the southern flank of the Wrangell Mountains. 

This belt is overlapped from the north by the voluminous Wrangell 

Lava and continental sedimentry rocks of,the Frederika Formation 

and from the south by marine Cretaceous sedimentary rocks and 

widespread fluvioglacial deposits.

Most structural features in the quadrangle probably formed during the major orogeny near the close of the Jurassic or in the
GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

EXPLANATION

Glaciers and perennial snowfields

Surficial deposits

Include moraines, rock glaciers, alluvium, 

talus, and landslides

Wrangell Lava and Frederika Formation 

QTw, chiefly andesitic flows of Wrangell Lava

overlying continental sedimentary rocks of the

Frederika Formation 

Ti, granodiorite and altered felsic intrusive rocks

Marine sedimentary rocks

Mainly sandstone, siltstone, shale, and conglomerate. Include Kennicott, Schulze, and Moonshine Creek Formations

UJO

Marine sedimentary rocks

Mainly mudstone, siltstone, sandstone, spiculite, 

and coguina. Include Lubbe Creek, Nizina 

Mountain, and Root Glacier Formations

McCarthy Formation

Upper member; chiefly chert and spiculite 

Lower member; carbonaceous shale, chert, and 

subordinate limestone '

FIGURE 3. Isometric block diagram showing
GENERAL SUMMARY, REGIONAL SETTING, STRUCTURE 7

Regal Mountain

13,845

Chitistone and Nizina Limestones 

Nikolai Greenstone

Contact approximate

High-angle fault

Thrust fault

-10,000 FEET

- 5000 s~ 10,000 FEET 

5000

generalized geology of the McCarthy C-5 quadrangle.
8 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

pre-Albian Cretaceous. They are largely represented by a conspicuous northwest-striking thrust fault in the southern part of the 

quadrangle (fig. 3) and by a series of northwest-trending, generally 

moderately open folds. Younger structures are chiefly manifested 

by steep north-striking faults that include one east of McCarty 

Creek having right-lateral displacement of more than a mile (fig. 

3). A pronounced angular unconformity separates Cretaceous and 

older rocks, and a slight angular unconformity separates Cretaceous and Tertiary rocks. Disconformities separate several of the 

Mesozoic formations.

STRATIGRAPHY AND LITHOLOGY

HASEN CREEK FORMATION

A small outcrop of coarse bioclastic limestone near the extreme 

northeast corner of the quadrangle (not shown in fig. 3) represents 

a northwestward extension of the Golden Horn Limestone Lentil 

of the Hasen Creek Formation (Smith and MacKevett, 1970, p. 

Q20-Q25) which is well developed in the adjacent McCarthy C-4 

quadrangle. The exposed thickness is about 250 feet, but neither 

its base nor its top is visible. The lentil forms bold outcrops that 

are light gray with variegated red or yellow stained surfaces. Its 

strata are less than 10 feet thick and locally slabby or flaggy. Following Dunham's classification (1962, p. 117), the lentil consists 

largely of bioclastic grainstone and packstone. These rocks are 

composed mainly of coarse disarticulated crinoid fragments with 

or without matrices of lime mud. A few beds of black shale and 

chert are associated with the limestone lentil. More detailed descriptions of the Golden Horn Limestone Lentil and other rocks 

within the Skolai Group are given by Smith and MacKevett (1970). 

Fossils collected from the limestone lentil in the C-4 quadrangle 

are indicative of an Early Permian age.

NIKOLAI GREENSTONE

The Nikolai Greenstone, named by Rohn (1900, p. 425), is an 

extensive sequence of subaerial basaltic lavas. It probably underlies 

a large part of the quadrangle, but its exposures are confined to 

the southern part of the quadrangle and to its northeastern part 

near Regal Glacier. The base is not exposed in the C-5 quadrangle. 

Contacts between the Nikolai Greenstone and the overlying Chitistone Limestone are disconformities marked by an apparent concordance of subjacent Nikolai flows with overlying Chitistone 

strata. Where the Chitistone Limestone is absent, Nikolai Greenstone unconformably underlies younger rocks. Accuracy of thickness estimates of the Nikolai is limited by faults. The incomplete
STRATIGRAPHY AND LITHOLOGY y

greenstone section probably is 3,000 to 4,000 feet thick in the quadrangle. Most Nikolai flows are 2 to 15 feet thick; exceptionally, they 

are as much as 30 feet thick. The greenstone forms moderately 

rugged slopes that are locally cliffy and craggy.

The Nikolai Greenstone consists of altered basalts characterized 

by diverse secondary minerals, chiefly chlorite, and by several textural variations. Its fresh surfaces are greenish gray or dark 

greenish gray and less commonly dark or medium gray. Its weathered surfaces are medium brown and subordinately greenish, yellowish, or reddish brown. Veinlets, composed mainly of quartz and 

epidote or of calcite. and chlorite, cut some of the greenstones. 

Amygdules of a variety of secondary minerals are distributed 

rather uniformly throughout most Nikolai flows. They form 

spheroidal, ellipsoidal, and dumbbell-shaped pods 0.5 to 10 mm 

(millimeters) long.

Most Nikolai Greenstones are fine-grained porphyritic rocks 

with intergranular groundmasses composed chiefly of plagioclase 

and augite. Generally, they contain labradorite phenocrysts 1 to 4 

mm long in groundmasses whose major constituents are less than 

0.5 mm long. Uncommon textural variants in the greenstones are 

intersertal, felty, subophitic, and pilotaxitic. Sparsely distributed 

corroded phenocrysts of augite and relict olivine occur in some of 

the greenstones. Primary minerals in the greenstone, in general 

order of decreasing abundance, are plagioclase (chiefly labradorite), augite, relict olivine, opaque minerals, sphene, and apatite. 

Secondary minerals are abundant chlorite, less abundant iron oxides, epidote, clay minerals, calcite, sericite, prehnite, ferruginous 

serpentine minerals, pumpellyite, quartz, and rare zeolites. Opaque 

minerals, chiefly magnetite, subordinately ilmenite, constitute as 

much as 10 percent of some greenstones. Several varieties of chlorite, the dominant secondary mineral, are particularly well developed in the amygdules, forming spherulites, radial lamellar bundles, 

and scaly aggregates. Most of the amygdules are composed of 

chlorite with or without calcite; the rest are rich in quartz and 

epidote, and a few contain small amounts of native copper and 

associated secondary copper minerals.

The abundance of amygdaloidal minerals and alteration products 

makes the Nikolai Greenstone difficult to classify lithologically. The 

Nikolai Greenstone is a voluminous sequence of altered flood basalts that probably covered large areas in the Wrangell Mountain 

region and nearby Yukon Territory in the late Middle and (or) 

early Late Triassic time. Its age limits are imposed by the greenstone conformably overlying fossiliferous Middle Triassic strata
10 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

in the McCarthy C-4 quadrangle (MacKevett, 1970a) and by its 

stratigraphic position beneath the Late Triassic Chitistone Limestone.

CHITISTONE LIMESTONE

The Chitistone Limestone, named by Rohn (1900, p. 425), underlies topographically rugged areas in the southeastern and southwestern parts of the quadrangle. This formation is the best cliff 

former in the quadrangle. A few of its outcrops are marked by 

caverns and smaller solution cavities. Thickness of, the Chitistone 

Limestone within the quadrangle ranges from 1,250 to 2,100 feet; 

its constituent strata are 2 to 20 feet thick. The Chitistone disconformably overlies the Nikolai Greenstone and gradationally underlies the Nizina Limestone.

The Chitistone Limestone consists of limestone, subordinate 

dolomite, and minor amounts of chert. Following Dunham's classification (1962, p. 117), the Chitistone carbonates comprise lime 

mudstone and wackestone, subordinate packstone and grainstone, 

and some crystalline dolomite, dolomitic limestone, and limestone. 

Most Chitistone rocks are cut by calcite veinlets, and a few contain 

stylolites. Some Chitistone and Nizina limestones, particularly 

mudstones and wackestones, emit fetid odors when broken. The 

carbonate petrography and depositional environments of the Chitistone and Nizina Limestones have been investigated in some detail 

in the southern Wrangell Mountains, including the C-5 quadrangle 

(Armstrong and others, 1970). Much of the petrographic information concerning these formations and many of the inferences about 

their depositional environments are results of this investigation.

The mudstones and wackestones are dark greenish gray, dark 

gray, or dark medium gray and weather to various shades of gray 

and 'brown. These rocks contain matrices of lime mud, generally 

partly recrystallized, and sparse to abundant very fine-grained 

clastic components, chiefly clots of lime mud, fragments of echinoids and mollusks, and calcite grains. Some of the lime mudstones 

and wackestones contain widely dispersed opaque minerals, including pyrite, and small quantities of carbonaceous detritus, secondary 

iron oxides, quartz, chalcedony, and clay minerals. Dolomitic lime 

mudstones and less abundant argillaceous lime mudstones occur 

near the base of the formation.

The packstones and grainstones form several zones, each about 

100 feet thick, throughout the formation. Typically these rocks are 

medium gray or medium dark gray. They contain well-sorted 

clasts, generally about 0.1 mm in diameter, that consist of rounded 

pellets of lime mud, ooids, and sparse bioclastic fragments. The
STRATIGRAPHY AND LITHOLOGY 11

packstones contain interstitial lime mud; the grainstones are 

cemented by sparry calcite.

The crystalline carbonates are lighter colored than most other 

Chitistone rocks. They are mainly light or medium gray and 

weather to light brownish gray. They consist of interlocking mosaics of carbonate crystals, generally between 0.1 and 1.0 mm long, 

and uncommon scattered opaque and clay minerals. The crystalline 

dolomites have been recognized only from the stratigraphic interval between 100 and 300 feet above the base of the formation near 

the copper mines in the southwestern part of the quadrangle. The 

crystalline limestones, though not abundant, have a wider stratigraphic range, but generally are best developed in the lower part 

of the formation. Some of the crystalline limestones are dolomitic. 

Carbonate veinlets generally are abundant in the crystalline carbonates, particularly in the dolomites.

The chert which is usually associated with lime mudstone or 

wackestone forms irregular grayish-black nodules less than 6 

inches long and a few small lenses.

Armstrong, MacKevett, and Silberling (1970, p. 055) imply that 

the Chitistone reflects an early intertidal and supratidal depositional environment and subsequent low-energy, restricted shallowwater marine deposition alternating with high-enegry shoalingwater deposition. The transition from Chitistone to Nizina 

deposition accompanied a rise in sea level and the drowning of the 

Chitistone carbonate platform. Several lesser fluctuations in sea 

level are indicated during the period of Chitistone and Nizina 

deposition.

Diagnostic fossils are sparsely distributed in the Chitistone 

Limestone; none were found in the C-5 quadrangle. Chitistone 

fossils from nearby quadrangles studied by N. J. Silberling contain 

a fauna characterized by the ammonite genus Tropites and are 

indicative of the late Karnian Stage of the Late Triassic.

NIZINA LIMESTONE

Martin (1916, p. 693) applied the names Nizina Limestone to the 

predominantly thin-bedded limestone that previously was considered to constitute the upper part of the Chitistone Limestone. The 

Nizina is widely distributed in the southern part of the quadrangle, 

where it generally forms bold, cliffy outcrops. Its approximate 

thicknesses range from 350 to 1,250''feet in the C-5 quadrangle. 

Most strata in the formation are between 1/2 and 3 feet thick, but 

a few are as much as 10 feet thick. The Nizina Limestone gradationally overlies the Chitistone Limestone and conformably underlies the lower member of the McCarthy Formation.
12 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

The Nizina Limestone consists of very fine grained limestone and 

subordinate chert. According to Dunham's classification (1962, p. 

117), the limestone includes grainstone, mudstone, and wackestone. 

Many of these rocks are micropelletoidal and some are bioclastic. 

Most Nizina Limestone is dark greenish gray and weathers to various shades of brown; its uncommon phases are light or medium 

gray and weather brownish gray. Calcite veinlets are fairly abundant in many of the limestones. The grainstones are composed of 

pellets of lime mud, fragments of fossils, and uncommon ooids less 

than 1 mm in diameter. Their grains are generally well sorted, 

rounded, and cemented by sparry calcite.

The lime mudstones and wackestones are characterized by matrices of lime mud. Clasts are sparsely distributed in the lime mudstone and abundant in the wackestone. They include subrounded 

pellets from 0.05-0.2 mm long of lime mudstone, calcareous fossil 

fragments, minor quartz, plagioclase, and widely scattered opaque 

minerals, chiefly pyrite. The matrices of the pellets contain small 

amounts of carbonaceous material and silica and clay minerals.

The chert forms irregular nodules and lenses throughout much 

of the formation. Commonly the nodules are less than 6 inches in 

diameter. The lenses are as much as 30 feet long and 6 inches thick. 

Locally the chert forms interlacing networks. It is dark gray or 

grayish black and generally is flecked with rhombohedrons of calcite or dolomite as much as 0.02 mm across. Most of the chert contains a few grains of opaque minerals and is cut by calcite veinlets.

Regional mapping augmented by biostratigraphic studies by N. 

J. Silberling indicates some contemporaneity between older parts 

of the Nizina Limestone and younger parts of the Chitistone Limestone and a similar partial contemporaneity between the uppermost 

Nizina strata and basal strata of the McCarty Formation. The 

Nizina Limestone is interpreted as having formed in a gently 

sloping basinal apron fronting a carbonate platform of Chitistone 

Limestone and in part on a contiguous shallow marine shelf. Generally limestones of the Nizina reflect a deeper water environment 

than the Chitistone carbonates and a shallower environment than 

the McCarthy Formation.

Fossils useful for age determinations are not found widely distributed in the formation. They consist mainly of pelecypods of 

the genus Halobia. Paleontologic studies by N. J. Silberling (written commun., 1962) indicate that the Nizina Limestone is Late 

'triassic and ranges in age from late Karnian or early Norian to 

early middle Norian.
STRATIGRAPHY AND LITHOLOGY 13

MCCARTHY FORMATION

The McCarthy Formation, originally named the McCarthy Creek 

Shales (Rohn, 1900, p. 426), was divided into two informal members by MacKevett (1963).

LOWER MEMBER

The lower member of the McCarthy Formation crops out in the 

southern part of the quadrangle, where it conformably overlies the 

Nizina Limestone and gradationally underlies the upper member. 

Maximum thickness is about 950 feet, but reliable thickness estimates are precluded by numerous folds and plications in the incompetent rocks. Discrete strata range from less than an inch to 

about 4 feet in thickness. The member consists of calcareous carbonaceous shale, impure limestone, and impure chert. Its outcrop 

pattern strongly reflects lithology; the shale forms subdued outcrops, and the chert and limestone generally form bold outcrops. 

Most of the rocks are conspicuously dark colored which is attributed to their carbonaceous content. Characteristically they are 

dark gray, dark greenish gray, or grayish black and weather dark 

brown, but some of the limestones are paler shades of gray.

The lower member is crudely tripartite in lithology. Its lowermost 300 fet consists of interbedded shale and chert; its middle 

300 feet are dominated by impure limestone; and its stratigraphically higher parts are composed of intercalated shale and chert 

with subordinate limestone. Calcite veins and veinlets, including 

gash veins that are well developed along crests and troughs of folds, 

are widely distributed in parts of the member. Discoidal calcareous 

concretions less than 2 inches in diameter occur locally near the 

top, and similar but larger concretions occur sparsely near the base.

The calcareous and carbonaceous shales are finely laminated and 

contain calcite, partly of bioclastic derivation, along with carbonaceous material, illite, clay minerals, and chlorite and subordinate quartz, chalcedony, dolomite, pyrite, and secondary iron 

minerals.

The impure cherts have fine wispy laminations and are chalcedony-rich rocks containing subordinate clastic and carbonaceous 

material and siliceous fragments of Radiolaria and sponge spicules. 

Their clasts include calcite and minor amounts of quartz, plagioclase, dolomite, pyrite and other opaque minerals, apatite, and 

biotite. Most of the cherts also contain minor quantities of illite, 

clay minerals, and secondary iron oxides.

The impure limestones range from varieties with dominant calcite grains in chalcedony-rich matrices to those whose matrices are 

partly recrystallized lime mud. Most of the impure limestones are
14 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

partly recrystallized bioclastic wackestone (terminology of Dunham, 1962). These rocks are composed of abundant clastic grains, 

chiefly calcite of bioclastic origin, embedded in partly crystallized 

lime mud. They contain minor amounts of other clasts similar to 

those in. the impure cherts and varying amounts of carbonaceous 

material aud clay minerals. Most of the clasts are subrounded or 

subangular and less than 0.1 mm long.

Most rocks of the lower member probably formed in a fairly deep 

sea, partly in a starved basin. The lower member is Late Triassic 

and Early Jurassic (?) in age. Pelecypods of the genus Monotis are 

abundant and widespread through a stratigraphic interval from 

200 to 400 feet above the base and indicate the late Norian Stage 

of the Late Triassic. Middle and early Norian fossils have been 

collected from the member in nearby quadrangles and studied by 

N. J. Silberling. A conformable stratigraphic succession about 800 

feet thick and apparently barren of diagnostic fossils intervenes 

between the highest documented Triassic beds of the lower member 

and beds of the upper member that have yielded Hettangian fossils in the McCarthy B-4 quadrangle. Parts of this succession may 

represent the Rhaetian or Hettangian Stages. The lower part of 

the lower member probably is a deeper water temporal equivalent 

of the upper part of the Nizina Limestone.

UPPER MEMBER

The upper member of the McCarthy Formation is well developed 

in the southern part of the C-5 quadrangle, where it attains a 

maximum thickness of more than 2,000 feet. It is separated from 

the overlying Lubbe Creek Formation and the subjacent lower 

member by gradational contacts. Where the Lubbe Creek Formation is absent, the upper member disconformably underlies the 

Nizina Mountain Formation. Strata of the upper member are between 1/2 and 3 feet thick and form rugged, ribby, or, less commonly, subdued outcrops.

Rocks of the upper member include impure calcareous organic 

chert and spiculite and subordinate shale and impure limestone. 

Most of the shale is near the top of the member. The rocks of the 

member are shades of dark gray and weather dark yellowish brown 

or medium brown. Limy concretions, generally less than 6 inches 

in diameter, are sparsely distributed in the upper part.

The abundant impure cherts and spiculites commonly are finely 

laminated, are chalcedony rich, and contain diverse amounts of 

detrital grains, chiefly calcite less than 0.2 mm across. Most of 

these rocks contain abundant chalcedonic or calcareous spicules and 

siliceous Radiolaria. As calcite content increases, the cherts and
STRATIGRAPHY AND LITHOLOGY 15

spiculites grade into impure limestones characterized by abundant 

calcite grains and subordinate chalcedonic matrix material. There 

are wide lithologic gradations between the dominant chalcedonyrich cherts and spiculites and the less common calcite-rich impure 

limestones. Subordinate clasts in most of these rocks are quartz, 

plagioclase, dolomite, apatite, and cherty fragments. Some of the 

cherts, spiculites, and impure limestones also contain minor 

amounts of carbonaceous material, pyrite, hematite, potassiumfeldspar, albite, ilmenite, leucoxene, chlorite, biotite, and clay minerals. Some of these minerals probably formed authigenically. 

Many of the carbonate grains have overgrowths and are partly 

recrystallized.

The shales typically are fissile, calcareous, and carbonaceous and 

are composed of clay minerals, quartz, chalcedony, calcite, carbonaceous debris and minor plagioclase, dolomite, opaque minerals, 

and carbonate fluorapatite.

The upper member probably formed mainly in a rather quiet 

sea where siliceous organisms flourished. Its dominant rocks probably reflect the fixation of biogenic silica and the admixture of 

small to large quantities of clastic components. This member is 

largely or entirely Early Jurassic in age, although its oldest strata 

possibly range into the latest Triassic. Fossils that provide critical 

age data were found only near the top of the member within the 

quadrangle and are indicative of the Sinemurian and probably 

Pliensbachian Stages. Unequivocal Pliensbachian fossils were collected from near the top of the member in the adjacent McCarthy 

C-4 quadrangle (MacKevett, 1970a) and Hettangian fossils were 

collected from near the base of the member in the nearby McCarthy 

B-4 quadrangle.

LUBBE CREEK FORMATION

The Lubbe Creek Formation, named by MacKevett (1969, p. 

A37) from excellent exposures along Lubbe Creek in the C-5 quadrangle, extends nearly across the southern part of the quadrangle, 

where it conformably overlies the upper member of the McCarthy 

Formation and disconformably underlies the Nizina Mountain and 

Root Glacier Formations. It constitutes an excellent marker horizon, being less than 300 feet thick, lithologically distinctive, and 

exposed in bold outcrops that contain diagnostic fossils. Strata in 

the formation are commonly y% to 3 feet thick, exceptionally as 

much as 8 feet thick.

The formation consists of impure spiculite with lesser amounts 

of coquina in its stratigraphically higher parts. Its rocks are medium gray and mainly weather medium brown. A few chert lenses,
16 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

as much as 10 feet long and 6 inches thick, occur in some of the 

spiculite. The spiculites are dense fine-grained silica-rich rocks that 

contain organic and inorganic clasts in chalcedony-rich matrices. 

Their clasts include spicules, Radiolaria, fragments of pelecypods, 

echinoderms, belemnites, and the minerals calcite, quartz, dolomite, 

and plagioclase. Calcite is the principal constituent of both the 

clastic grains and the fossil fragments. Most of the clasts are 

ragged or subangular to subrounded particles less than 0.2 mm 

across. The abundant spicules are less than 0.2 mm long and composed of chalcedony, or, less commonly, of calcite. A few have 

chloritic cores. Minor constituents of the spiculite are chlorite, 

hematite, pyrite, carbonaceous material, ilmenite, and rare biotite 

and apatite.

The coquina consists of poorly sorted bioclastic material, chiefly 

whole and comminuted shells of megafossils, in a chalcedony-rich 

matrix that forms a small part of the rock. It also contains minor 

quantities of detrital grains similar to those of the impure spiculite.

The Lubbe Creek Formation is of nearshore marine genesis, and 

its depositional site was subjected to local wave action. Its fauna, 

chiefly diagnostic pelecypods of the genus Weyla, are indicative of 

the Toarcian and probably Pliensbachian Stages of the Lower 

Jurassic Series.

NIZINA MOUNTAIN FORMATION

The name Nizina Mountain Formation was applied by MacKevett (1969, p. A42) to a sequence of reddish-brown-weathering 

graywacke exposed in the central part of the C-5 quadrangle. Both 

the upper and the lower stratigraphic boundaries are disconformities marked by irregular erosion surfaces without apparent discordance of the juxtaposed strata. Thickness of the formation 

ranges from a few feet to about 1,350 feet. The Nizina Mountain is 

characterized by well-bedded strata, commonly 1/2 to 2 feet thick, 

that form slopes of moderate relief.

The formation consists of fine and very fine grained feldspathic 

graywacke with sparsely distributed yellowish shaly partings, limy 

lenses, and limy concretions as much as 2 feet in diameter. The 

graywacke is dark greenish gray and locally finely laminated. It is 

composed of poorly sorted subangular to subrounded clasts 0.05 to 

0.5 mm in maximum dimensions in a microcrystalline matrix. The 

clasts consist of plagioclase, chiefly sodic labradorsite, and quartz 

along with less abundant cherty lithic fragments, calcite, opaque 

minerals, and rare biotite and apatite. The dominant matrix constituents, chalcedony, chlorite, and clay minerals locally are associated with epidote, leonhardite, calcite, and prehnite. Opaque
17

minerals in the formation include pyrite, hematite, ilmenite, and 

magnetite. Fractures in a few of the graywackes are coated with 

gypsum. Sparsely distributed small spheres of chalcedony or calcite 

in a few of the rocks may be microfossil remains.

The Nizina Mountain Formation probably formed in a moderately deep sea. It contains fairly abundant fossils, including ammonites indicative of the Bathonian and Callovian Stages of the 

Middle and Upper Jurassic Series.

ROOT GLACIER FORMATION

The Root Glacier Formation named by MacKevett (1969, p. A45) 

is widely distributed throughout the central part of the C-5 quadrangle, where it disconformably overlies the Nizina Mountain Formation or the Lubbe Creek Formation. Its contacts with younger 

rocks are unconformities. Maximum thickness is probably between 

3,000 and 4,000 feet, but accurate thickness estimates are precluded by its unconformable upper contact. Numerous andesitic 

dikes and sills and a few sandstone dikes cut the formation. The 

Root Glacier Formation consists of mudstone and siltstone with 

lesser amounts of shale, sandstone, and conglomerate. It contains 

a few thin beds and lenses of impure limestone and uncommon 

small limy concretions. The dominant mudstones are thick bedded 

to massive; other strata range widely in thickness. The conglomerate is maily confined to a lentil about 200 feet thick that grades 

vertically and laterally into sandstone. Rocks of the formation 

characteristically weather to moderately smooth slopes that are 

locally breached by resistant conglomeratic or limy beds. Parts of 

the formation are strongly jointed. Some Root Glacier rocks show 

small-scale cut-and-fill relations, and a few have graded bedding. 

Many of the siltstones and shales are finely laminated. Most rocks 

of the formation are dark greenish gray or dark gray and weather 

to various shades of brown.

The mudstones, siltstones, and shales contain mineralogically 

similar, poorly to moderately well sorted, subangular to subrounded 

clasts, chiefly quartz, calcite, and plagioclase, in microcrystalline 

matrices. These pelitic rocks are differentiated by the sizes of their 

clasts, by the proportions of microcrystalline matrix relative to 

clasts, and the shales, by the development of fissility. Clastic constituents predominate in the siltstone and matrix material in the 

mudstone and shale. The matrix material consists of calcite, chlorite, clay minerals, and lesser .quantities of chalcedony, sericite, 

illite, secondary iron oxides, leucoxene, carbonaceous trash, and 

rarely leonhardite. Uncommon grains in the mudstone, siltstone, 

and shale include pyrite, biotite, magnetite, and ilmenite and rare
18 GEOLOGY, MCCARTHY c-s QUADRANGLE, ALASKA

epidote, apatite, and zircon. Some of. the pelitic rocks contain reworked shaly fragments, scattered fossil wood, minute calcite 

spheres with concentric structures, and calcite veinlets.

Sandstones in the-Root Glacier Formation, following the terminology of Williams, Turner, and Gilbert (1954, p. 289-301), which 

is used throughout this report except where otherwise noted, 

include graywacke, wacke, and arenite. Characteristically, these 

rocks are fine to medium grained, but they include a few coarser 

grained types. The graywackes and wackes are poorly sorted and 

composed of subangular clasts in microcrystalline matrices that 

constitute between 10 and 30 percent of their volumes. The graywackes differ from the wackes by being extremely well indurated 

and darker. Most of the graywackes and wackes are feldspathic 

and contain clasts of quartz, plagioclase, and less abundant clinopyroxene; lithic fragments, chiefly chert; biotite, potassium-feldspar, 

hornblende, calcite, and opaque minerals, chiefly magnetite, pyrite, 

and hematite. Their matrices consist of calcite-chlorite-clay assemblages with subordinate chalcedony and sericite.

The arenites contain less matrix material than the other sandstones and generally have moderately well sorted subrounded 

clasts. They comprise fine or very fine grained feldspathic, lithic, 

or calcareous arenite with grains of quartz, calcite, and plagioclase 

that are either calcite cemented or embedded in microcrystalline 

matrices composed of chlorite, clay minerals, chalcedony, calcite, 

and sericite. Less abundant clasts in the arenites include biotite, 

opaque minerals and their alteration products, and rare apatite, 

epidote, and potassium-feldspar.

The impure limestones are mainly calcite-cemented detrital rocks 

that contain clasts of calcite and rarer quartz and plagioclase.

The conglomerate consists of well-indurated cobble and pebble 

conglomerate. Generally it grades into very coarse and coarsegrained sandstone that locally contains wood fragments. Its constituent pebbles commonly are well rounded and embedded in a 

sandstone matrix. The dominant lithic clasts are limestone, probably derived from the Nizina and Chitistone Limestones. Its rarer 

cobbles and pebbles include mudstone and siltstone derived from 

the Root Glacier Formation, pink granite rich in potassium 

feldspar, Nikolai Greenstone, chert, and quartz.

The Root Glacier Formation probably was deposited in a moderately shallow sea. Paleontologic studies by R. W. Imlay, of the 

U.S. Geological Survey, indicate that the formation is Late Jurassic, more specifically, late Oxfordian and Kimmeridgian. Its diagnostic fauna are mainly pelecypods of the genus Buchia (Aucella) 

and less abundant ammonites.
STRATIGRAPHY AND LITHOLOGY 19 

KENNICOTT FORMATION

The Kennicott Formation was redefined by Jones and MacKevett 

(1969, p. K7) to correct disparities in previous use of the name. 

It is exposed south of Regal Glacier near the eastern border of the 

quadrangle and in a small outlier near Green Butte. Maximum 

thickness in the quadrangle is approximately 700 feet; its constituent beds are mainly 1 to about 30 feet thick. Outcrops range 

from bold, for some of the conglomerate, to subdued, for most of 

the shale.

The Kennicott Formation is the basal Cretaceous unit in the 

quadrangle and overlies older rocks with a strong angular unconformity. It is disconformably overlain by the Moonshine Creek 

Formation and unconformably overlain by the Frederika Formation. The formation consists of a basal conglomerate, as much as 

100 feet thick and overlying sandstone, siltstone, and shale. Calcareous concretions are locally abundant. Most of the conglomerates and sandstones are dark greenish gray and weather dark 

greenish brown. The constituent cobbles, pebbles, and boulders of 

the conglomerates reflect local provenances and consist chiefly of 

Nikolai Greenstone. They commonly are subrounded or subangular. 

Matrices of the conglomerates are mainly coarse-grained sandstone.

The sandstones include feldspathic wacke and arenite and less 

abundant arkosic wacke. They generally are fine-grained, fairly 

well-sorted rocks that contain diverse subangular clasts embedded 

in a microcrystalline matrix that constitutes between 5 and 25 

percent of the rock. Their clasts include quartz and plagioclase, 

smaller quantities of glauconite, chert, opaque minerals, chlorite, 

biotite, calcite, and rare epidote and garnet. The matrices consist 

of chlorite, chalcedony, sericite, calcite, secondary iron minerals, 

montmorillonite, and kaolinite. Some of the sandstones are partly 

zeolitized and contain heulandite or analcite.

The siltstones are mineralogically and texturally similar to the 

sandstones. Their clasts are finer grained and generally better 

sorted than those of the sandstones. Most shales in the formation 

are medium gray and weather to dark brown. They consist of clay 

minerals and scattered detrital grains, chiefly quartz.

The Kennicott Formation probably formed in a shallow marine 

environment. Only the younger of its two well-defined early Albian 

faunal zones is represented in the quadrangle. Age of the Kennicott is best documented by the ammonite Breivericeras hulenense 

(Anderson), which along with other megafossils is abundant in 

some of the concretions. Fossil wood and plant debris are found
20 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

locally in the formation, mainly near its base. Some of the finergrained rocks of the formation contain spherical or rodlike remains 

of microfossils.

SCHULZE FORMATION

The Schulze Formation, named by Jones and MacKevett (1969, 

p. K13), underlies a small area near the southwestern corner of 

the quadrangle, where it is about 200 feet in maximum thickness. 

It is in fault contact with the Nikolai Greenstone and locally cut 

by felsic hypabyssal rocks. Rocks of the formation are characteristically thin bedded and weather to aggregates of small chips that 

partly mask their outcrops.

The Schulze Formation consists of siliceous shale or porcellanite 

and smaller amounts of siltstone and very fine grained sandstone. 

Rocks of the formation are light or medium gray when fresh and 

light or yellowish brown when weathered. The siliceous shale consists of extremely fine-grained quartz and minor amounts of calcite; clay minerals, chiefly kaolinite; plagioclase, sericite, and 

secondary iron oxides. The siltstone and very fine grained sandstone consist of small clasts, mainly quartz, in silica- or carbonaterich matrices that contain scattered clay minerals, chlorite, sericite, 

and secondary iron minerals. The siliceous shales and a few of 

the other rocks contain abundant Radiolaria or less abundant 

Foraminifera.

The megafossil fauna of the formation is meager in the C-5 

quadrangle, but paleontologic studies of megafossils from the B-5 

quadrangle indicate that the Schulze Formation is contemporaneous with part of the Moonshine Creek Formation and that it has 

an age span from late Albian(?) (Early? Cretaceous) to Cenomanian (Late Cretaceous) (Jones and MacKevett, 1969, p. K14, 

15).

MOONSHINE CREEK FORMATION

The Moonshine Creek Formation, named by Jones and MacKevett (1969, p. Kll), crops out near the eastern boundary of the 

quadrangle between Regal Glacier and "the amphitheatre," where 

it attains a maximum thickness of about 550 feet. Its exposure in 

the C-5 quadrangle constitute the western margins of an extensive 

and much thicker Moonshine Creek sequence that underlies nearby 

parts of the McCarthy C-4 quadrangle (MacKevett, 1970a). The 

Moonshine Creek Formation unconformably underlies the Frederika Formation and disconformably overlies the Kennicott Formation. It apparently unconformably overlies pre-Cretaceous rocks 

near its poorly exposed southernmost exposures. Strata in the for-
STRATIGRAPHY AND LITHOLOGY 21

mation are as much as 10 feet thick and form moderate to subdued 

outcrops.

The Moonshine Creek Formation consists of diverse sandstone, 

siltstone, and less common shale and conglomerate and locally contains calcareous concretions from 1/2 to 3 feet in diameter, mainly 

in the siltstones. The sandstones are greenish gray or medium gray 

and weather to various shades of brown. Most of them are fine 

grained, but they range from very fine to very coarse varieties. 

Generally they are moderately well indurated, moderately well 

sorted, and contain subrounded to subangular clasts. The sandstones consist of feldspathic or lithic wacke and arenite. Their 

clasts include quartz, plagioclase, K-feldspar, lithic fragments, and 

subordinate glauconite, opaque minerals, calcite, and biotite; generally quartz and plagioclase are dominant. The wackes contain 

more than 10 percent microcrystalline matrix composed of chlorite, 

chalcedony, sericite, secondary iron minerals, clay minerals, and 

rare zeolite. The arenites differ from the wackes in containing less 

than 10 percent microcrystalline matrix, or more commonly by 

being calcite cemented. A few of the coarse sandstones grade into 

granule conglomerates that generally contain lithic clasts.

The siltstones are moderately well sorted gray or olive-gray 

rocks that contain fine clasts, mainly of quartz and plagioclase, in 

microcrystalline matrices. The matrices are clay rich and also contain subordinate chlorite, calcite, sericite, and rare epidote and 

heulandite.

Shales in the formation are medium gray and weather dark 

yellowish brown. They consist of abundant clay minerals, including montmorillonite and kaolinite, and less abundant fine quartz, 

plagioclase, sericite, and heulandite. The shales and some of the 

other rocks contain calcareous or siliceous remains of microfossils.

The Moonshine Creek Formation probably was deposited in a 

shallow, restricted marine basin. Its megafossils are mainly preserved in concretions and include diagnostic ammonites indicating 

an age span from probable middle Albian (Early Cretaceous) to 

late Cenomanian (Late Cretaceous).

FREDER1KA FORMATION

The Frederika Formation, named by MacKevett (1970a), consists of diverse continental sedimentary rocks that are widely 

distributed in the northern part of the quadrangle. The formation 

is intercalated with older flows of Wrangell Lava and gradationally 

underlies the Wrangell Lava. Its basal contacts are unconformities: 

those with the Moonshine Creek Formation are slightly angular; 

those with older rocks generally are moderately angular. Locally
22 GEOLOGY, MCCARTHY c-s QUADRANGLE, ALASKA

abundant andesitic sills and a few andesitic dikes cut the formation, which is from 1,000 to 2,000 feet thick. Thicknesses of its 

strata range from a few millimeters for fissile shales to about 100 

feet for massive conglomerates. Outcrop patterns reflect the varied 

lithology and include gentle subdued slopes underlain by shale or 

some siltstone and sandstone as well as bold cliffy exposure characteristic of the conglomerate.

The Frederika Formation contains several varieties of conglomerate and sandstone along with siltstone, shale, and some lignite. 

The conglomerates are mainly pebble or cobble conglomerate but 

include subordinant boulder conglomerate. They range from wellindurated rocks to poorly indurated crumbly masses. The conglomerates are variegated with multicolored clasts in light-gray, lightbrown, or yellowish-brown matrices. Generally their cobbles and 

pebbles are well rounded and their boulders subrounded or subangular. Matrices of most of the conglomerates consist of poorly 

sorted coarse-grained calcite-cemented sandstone that is rich in 

quartz and plagioclase. The conglomerates are polymict, and their 

clasts generally consist of Wrangell Lava, some Nikolai Greenstone, and rare chert, quartz, granitic rocks, quartzite, shale, and 

limestone.

The sandstones are mainly feldspathic and arkosic wackes that 

typically are coarse grained and less commonly fine or medium 

grained. Some of the sandstones are tuffaceous. Most of them are 

well cemented and light brown, buff, light greenish brown, or pale 

olive. They consist largely of poorly sorted angular to subrounded 

grains of quartz and plagioclase with interstitial chlorite, illite, 

and clay minerals, chiefly montmorillonite, and minor amounts of 

calcite, quartz, or chalcedony cement. Common detrital components 

of the wackes are lithic clasts, potassium-feldspar, biotite, magnetite, ilmenite, and apatite. Pyrite and hematite are sparse constituents of a few of the wackes. Some of the wackes are cut by 

calcite veinlets.

Siltstones of the formation are light gray and weather mottled 

brown. Some have crude graded bedding. They are essentially finer 

grained replicas of the wackes and are characterized by poorly 

sorted subangular clasts of quartz and plagioclase, including some 

albite, associated with chlorite, illite, and montmorillonite and cemented by chalcedony or calcite. They contain sparse magnetite, 

ilmenite, leucoxene, and secondary iron oxides and are cut by a 

few veinlets of calcite and secondary iron minerals.

Other rocks in the formation are extremely fine grained and include shale, carbonaceous shale, and lignite. The shale is light to
STRATIGRAPHY AND LITHOLOGY 23

dark gray and weathers to shades of brown. Where baked and 

welded near contacts with some flows and sills, the shale is red or 

reddish brown. The shales are finely laminated and composed of 

quartz and clay minerals with rare biotite, muscovite, and opaque 

dust. The carbonaceous shale is fissile and grayish black. It contains detrital quartz and feldspar along with authigenic minerals 

and organic matter, including abundant plant remains. The lignite 

is finely laminated and dark gray to black, in alternating dull and 

glistening layers. It is composed chiefly of organic remains and, 

with the addition of detrital and authigenic components, grades 

into carbonaceous shale.

The Frederika Formation contains abundant plant debris, including leaves that according to J. A. Wolfe (written commun., 

1961, 1964), indicate a Miocene age.

INTRUSIVE ROCKS

Intrusive rocks, which are mainly Tertiary in age, in the C-5 

quadrangle include varied andesitic dikes and sills, felsic hypabyssal plutons, and granodiorite. Some of the andesitic rocks and 

possibly a few felsic dikes are Quaternary, and some andesitic 

dikes and sills may be late Mesozoic.

ANDESITIC DIKES AND SILLS

The andesitic dikes and sills (not shown in figure 3) are mainly 

related to Wrangell Lava volcanism, but they cut most of the bedrock units and are particularly abundant in the Frederika and 

Root Glacier Formations. Most of these dikes and sills, which commonly form bold outcrops, are between 1 to 10 feet thick, but a 

few are as much as 50 feet thick. They include andesite and rare 

dacite, basalt, diabase, .and lamprophyre. These rocks are greenish 

gray and weather to medium or dark brown. They are predominantly fine-grained altered intergranular or intersertal rocks that 

locally have thin very fine grained chilled borders. Many of the 

andesitic dikes and sills are porphyritic; a few are amygdaloidal. 

Most of the porphyritic varieties contain plagioclase or clinopyroxene phenocrysts 1 to 4 mm long.

The andesites consist mainly of plagioclase and clinopyroxene. 

The plagioclase forms oscillatorily-zoned phenocrysts of labradorite and andesine and abundant small elongate crystals of andesine. 

The clinopyroxene consists of augite and less common pigeonite 

that forms a few partly resorbed phenocrysts and more abundant 

small crystals scattered throughout the bulk of the rock. Rare primary constituents in the andesite are quartz, brown biotite, potassium feldspar, sphene, and opaque minerals. Secondary minerals in
24 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

the andesite include calcite, clay minerals, sericite, chlofite, and 

hydrous iron oxides. The amygdules consist of calcite and chlorite 

with uncommon chalcedony in their cores, and rare botryoidal 

masses of hematite and limonite.

Dacites associated with the andesitic rocks are darker than dacites of the felsic hypabyssal rocks. They resemble andesite in texture and color but contain more quartz than andesite. The few 

diabase and basalt dikes in the quadrangle are richer in labradorite 

than the andesites; the diabases are medium grained and have 

subophitic textures. The lamprophyres are fine-grained porphyritic 

rocks whose groundmasses have been largely obliterated by alteration. They contain phenocrysts of brown biotite or clinopyroxene 

in altered groundmasses rich in calcite and chlorite. Their minor 

constituents include magnetite, apatite, plagioclase, potassiumfeldspar, quartz, and secondary iron minerals.

INTERMEDIATE ROCKS

Granite rocks of intermediate composition, chiefly granodiorite, 

are exposed in a few rugged nunataks between the heads of Regal 

and West Fork Glaciers. These rocks cut the lower part of the 

Wrangell Lava and are cut by a few andesitic dikes. They are fineto medium-grained speckled rocks that locally contain fine-grained 

mafic inclusions as much as 10 cm long. The intermediate intrusive 

rocks are hypidiomorphic granular and mainly of plagioclase and 

slightly less abundant quartz and potassium-feldspar. The plagioclase is normally zoned sodic andesine, commonly with altered borders. Less abundant primary minerals include brown hornblende, 

reddish-brown biotite, and rare apatite, magnetite, and ilmenite. 

Sparsely distributed alteration products in the granodiorite and 

related rocks include epidote, chlorite, clay minerals, calcite, and 

hematite.

FELSIC HYPABYSSAL ROCKS

The felsic hypabyssal rocks are exposed chiefly in the southwestern part of the quadrangle, where they mainly cut the Schulze 

Formation. They represent apophyses of shallow felsic plutons that 

are well exposed in nearby parts of the adjoining McCarthy B-5 

quadrangle (MacKevett, 1965). The felsic dikes and sills, which 

form bold outcrops, typically are 2 to 10 feet thick, rarely as much 

as 200 feet thick. The felsic plutons, many of which are extensively 

altered, are light gray or pinkish gray and weather light brown to 

yellowish brown; Uncommonly they are vesicular or amygdaloidal, 

and locally they are cut by calcite veinlets.

The felsic hypabyssal rocks consist of dacite and rhyodacite and
STRATIGRAPHY AND LITHOLOGY 25

variants of these rocks. They are porphyritic or, less commonly, 

seriate with very fine grained felty or, uncommonly, pilotaxitic or 

intersertal groundmasses. Phenocrysts, 0.5 to 2.5 mm in maximum 

dimensions, constitute as much as 30 percent of the felsic rocks. 

They consist of normally zoned andesine and less abundant quartz, 

biotite, and relicts of clinopyroxene and amphibole. The groundmass minerals consist of andesine, quartz, and potassium-feldspar, 

generally with copious secondary minerals and less common to rare 

biotite, magnetite, ilmenite, zircon, and apatite. The secondary 

minerals include clay minerals, chlorite, calcite, and iron minerals, 

chiefly hematite. A few of the felsic hypabyssal rocks contain 

sparsely disseminated pyrite. Probably components of some of 

their groundmasses represent devitrified glass.

WRANGELL LAVA

The Wrangell Lava (Mendenhall, 1905, p. 54) constitutes the 

youngest bedrock in the quadrangle. It underlies most high parts 

of the Wrangell Mountains throughout their extent and is widespread in the northern part of the C-5 quadrangle. Some older 

Wrangell Lava flows are intercalated with Miocene strata of the 

Frederika Formation, but most of the Wrangell Lava conformably 

overlies the Frederika. Locally, the Wrangell Lava unconformably 

overlies the Nikolai Greenstone or the Golden Horn Limestone 

Lentil of the Hasen Creek Formation. Many exposures are nunataks. Wrangell Lava volcanism probably extended intermittently 

from the Miocene into the Holocene, but the age of its younger 

flows is not well documented in the quadrangle.

The Wrangell Lava forms a sequence of subaerial lava flows, 

less common pyroclastic rocks, vitrophyre, and conglomerate more 

than 5,000 feet thick. Thickness of its constituent flows range from 

1 to 25 feet but commonly are 2 to 10 feet. Generally the Wrangell 

Lava forms rugged outcrops. Columnar joints are well developed 

in a few of the flows. Flows of Wrangell Lava are predominantly 

andesite and basaltic andesite, but a few flows consist of dacite, 

rhyodacite, or basalt. The andesites and basaltic andesites commonly are medium dark gray or greenish gray when fresh and 

medium brown when weathered. They generally are porphyritic 

and contain about 10 percent phenocrysts, chiefly plagioclase crystals less than 2 mm long. Many of the andesitic rocks contain 

amygdules or vesicles between 0.1 and 0.5 mm in diameter. Textures of the andesites and basaltic andesites are fine-grained intersertal or, less commonly, pilotaxitic and hyaloptilitic. Plagioclase, 

the dominant mineral, forms oscillatorily zoned phenocrysts of 

sodic labradorite and calcic andesine and abundant andesine mi-
26 GEOLOGY, MCCARTHY c-s QUADRANGLE, ALASKA

crolites. Pyroxene in the andesitic rocks forms numerous small 

anhedral crystals and scarce phenocrysts of augite, hypersthene, 

and rare pigeonite. A few of the andesitic rocks contain scattered 

phenocrysts of relict olivine. Sparse primary constituents in the 

andesites and basaltic andesites are opaque minerals, chiefly magnetite, and glass, hornblende, biotite, and quartz. Secondary minerals that generally occur as alteration products in these rocks 

include uralitic hornblende, biotite, chlorite, calcite, goethite, hematite, limonite, sericite, clay minerals, chalcedony, and epidote. 

The secondary minerals of the amygdules and vesicles are generally 

calcite, chlorite, and silica minerals, and uncommonly, siderite, 

ankerite, and zeolites.

The dacites and rhyodacites are light gray or buff and weather 

light brown. They are porphyritic with fairly abundant phenocrysts between 0.5 and 2.5 mm long in very fine grained groundmasses commonly hyalopilitic or pilotaxitic in texture. A few of 

the dacitic rocks are. amygdaloidal and contain amygdules compositionally similar to those of the andesitic rocks. Flow structure 

manifested by alined microlites is well developed in some of the 

dacitic rocks. Andesine is the most abundant mineral in the dacites and rhyodacites and constitutes nearly all of the phenocrysts 

and most of the groundmass microlites. Quartz forms rare phenocrysts in some of the dacite. Potassium feldspar is abundant in 

groundmasses of the rhyodacite. Less abundant groundmass constituents of the dacitic rocks include quartz, biotite, glass, magnetite, ilmenite, and trace amounts of zircon and sphene. Secondary 

minerals in these rocks consist of chlorite, calcite, clay minerals, 

illite, leucoxene, sericite, chalcedony, and hydrous iron oxides.

The basalt flows are dark gray and porphyritic with plagioclase 

and (or) less common relict olivine phenocrysts in a fine-grained 

intergranular groundmass. Most of the basalts are amygdaloidal. 

They are mineralogically similar to the andesitic rocks but contain 

more labradorite and relict olivine.

Vitrophyre forms a few small lava domes in the Wrangell Lava 

sequence. It commonly is greenish black and is characterized by 

scattered quartz and (or) plagioclase phenocrysts in a glassy 

groundmass. Most of the vitrophyre has good flow structure and 

numerous microfractures perpendicular to the flow structure or, 

uncommonly, reticulate or concentric.

Pyroclastic rocks, which are rare in the quadrangle, consist of 

tuffs that generally are light gray and well indurated and of 

variegated reddish-brown and gray volcanic breccias.

Conglomerate forms a few small lentils within the Wrangell
STRATIGRAPHY AND LITHOLOGY 27

Lava. It consists of light-gray well-indurated boulder conglomerate 

containing subangular boulders of Wrangell Lava in a coarsegrained sandstone matrix.

SURFICIAL DEPOSITS

The Quaternary surficial deposits include alluvium and older 

alluvium, talus, moraines, landslides, rock glaciers, and minor 

unmapped colluvium, slope wash, soil, and mudflows. The surficial 

deposits are poorly consolidated, and precise ages and age relations 

have not been ascertained, because many of the deposits represent 

products of recurrent deposition or are partly contemporaneous.

ALLUVIUM AND OLDER ALLUVIUM

Alluvium and older alluvium occupy flood plains along the Nizina 

River and McCarthy Creek, with other small deposits of alluvium 

being localized along most other streams. The alluvial deposits 

consist of detritus, chiefly poorly sorted, sometimes imbricated, 

sand and gravel, largely outwash from overloaded glacial streams. 

The older alluvium forms terraces that support vegetation and 

succesively are 1 to 6 feet higher than the modern flood plains or 

contiguous streamward terraces. Many alluvial deposits are 

ephemeral and subject to destruction by the shifting channels of 

modern flood plains. Maximum thicknesses are not known.

TALUS

Only a few talus masses were mapped, but smaller exposures 

of talus are numerous, particularly along oversteeped vall'ey walls 

of the Nizina River and McCarthy Creek and near bases of cirque 

walls. The talus forms elongate or crudely lobate thin veneers 

whose lower extremities have locally coalesced to form aprons. It 

is largely composed of monolithologic angular boulders of various 

sizes.

MORAINES

Moraines are abundant in the quadrangle. They include several 

types that are associated with, and in places overlie, modern 

glaciers and scattered ground moraines that are mainly relicts of 

older more extensive glaciation. The moraines consist .largely of 

angular and subangular boulders that have a great range in size 

and a diverse lithology, although parts of some moraines are 

virtually monolithologic. The moraines have rough, hummocky 

surfaces. Probably none exceed 100 feet in thickness.

LANDSLIDES

The only mapped landslides are near the western boundary of the 

quadrangle adjacent to Root Glacier. They consist of hummocky,
28 GEOLOGY, MCCARTHY c-s QUADRANGLE, ALASKA

jumbled masses of boulders and probably are less than 100 feet 

thick. Their upper extremities are partly bounded by escarpments.

ROCK GLACIERS

Rock glaciers are well developed in the southern part of the 

quadrangle. They consist of crudely lobate, spatulate, or sinuous 

masses that attain lengths of more than a mile. Throughout most 

of their extent they are typically narrow and constricted, but 

commonly their lower margins have steep-fronted lobate configurations. Characteristically, the rock glaciers occupy subjacent valleys 

emanating from cirques occupied by small glaciers. Hummocky on 

their surfaces, they are composed of angular, slabby, and locally 

blocky rocks a few inches to 10 or 12 feet across, partly cemented 

by ice and in a few places stabilized enough to support scanty 

vegetation. Lithologically they are related to the rocks of the 

cirques from which they are derived. Maximum thicknesses are 

not known but probably are less than 200 feet.

FOSSIL COLLECTIONS

Fossils collected from the McCarthy C-5 quadrangle are given 

in the following list. Locations of the fossil collections are keyed 

numerically to the geologic quadrangle map, U.S. Geological Survey 

GQ-series (MacKevett, 1970b). Credit for the fossil identifications 

is as follows: Triassic invertebrates, N. J. Silberling, Stanford 

University and U.S. Geological Survey. Jurassic invertebrates 

(except Weyla from the Lubbe Creek Formation), R. W. Imlay, 

U.S. Geological Survey. Weyla from the Lubbe Creek Formation, 

S. W. Muller, Stanford University. Cretaceous invertebrates, D. L. 

Jones, U.S. Geological Survey. Tertiary flora, J. A. Wolfe, U.S. 

Geological Survey.

USGS Mesozoic 

Map No. locality No. Fauna

Nizina Limestone

1 ........ Gryphaeal

2 ........ Halobia cf. H. brooksi Smith

3 1792 Halobia "austriaca Mojsisovics" of Smith

4 1793 Halobia "austriaca Mojsisovics" of Smith 

Discophyllites cf. D. ebneri (Mojsisovics) 

Juvavites sp. indet.

5 1794 Halobia "austriaca Mojsisovics" of Smith 

Indet. ammonite

6 1695 Pterotoceras cf. P. helminae Diener

Lower member of the McCarthy Formation

7 ........ Monotis subcircularis Gabb

8 ........ Carditoid pelecypod

Monotis sp. indet.

9 ........ Monotis cf. M. subcircularis Gabb

10 ........ Monotis subcircularis Gabb
FOSSIL COLLECTIONS 29

Map No.

USGS Meaozoic 

locality No.

23

24

25

26

27

28

29

Fauna 

Lower member of the McCarthy Formation Continued

11 ........ Monotis cf. M. subcircularis Gabb

12 ........ Monotis salinaria ssp.

13 (float) ........ Monotis subcircularis Gabb

14 2207 Impressions of small, evolute, ribbed ammonite 

Indet. pelecypods, including Halobial

15 ........ Indet. impressions of haloritid ammonites

Upper member of the McCarthy Formation

16 28534 Crucilobiceras sp.

Aeg aster ocerast or Arctoasteroceras Frebold, 1962

17 ........ "Entolium" semiplicatum (Hyatt)

18 28536 Crucilobicerast sp.

19 (float) ........ Arniceras sp.

20 ........ Megarietitesl

21 ........ Arnioceras sp.

22 28537 Lima sp.

Camptonectes'! sp. 

Crucilobiceras sp. 

........ "Entolium" semiplicatum (Hyatt)

28540 Crucilobiceras sp. 

Crucilobicerasl sp.

28684 Oxytomat sp.

28685 Pelecypod fragment, undet.

28686 "Entolium" semiplicatum (Hyatt)

28687 cf. Paracoroniceras 

Belemnite, undet. 

Oxytoma sp.

28688 Arnioceras cf. A. semicostatum (Young and Bird).

cf. Arctoasteroceras.

Belemnite fragment

Weyla sp.

Gastropod, undet.

Oxytoma sp.

Myophorella sp.

Cardinia sp. 

28690 Crucilobicerast sp.

"Entolium" semiplicatum (Hyatt)

28694 Uptoniat sp. 

Chlamyst

28695 Crucilobicerast sp.

28704 Crucilobiceras'! sp.

28705 Ammonite fragment, urdet.

28706 cf. Paracoroniceras

Lubbe Creek Formation

28678 Peronocerasl sp. 

Ammonite, undet. 

Gryphaea sp. 

Ostrea sp. 

Weyla sp. 

Camptonectes sp.

28679 Weyla sp. 

........ Weyla dufreynoyi d'Orbigny

Gryphaea sp.

Camptonectes sp.

Chlamys sp. 

........ Weyla dufreynoyi d'Orbigny

........ Weyla dufreynoyi d'Orbigny

Chlamys sp.

Camptonectes sp.

Gryphaea sp.

30

31

32

33

34

35

36

37

38

39

40
30 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

Mop 

41

42

43

44

45

46

C/SGS Mesozoic 

locality No.

28524

28525

47

48

28256

28257

49 28681

50 28682

Fauna 

Lubbe Creek Formation Continued

Liostrea sp.

Camptonectes sp.

Chlamysl sp.

Weyla dufreynoyi d'Orbigny

Liostrea sp.

Weyla dufreynoyi d'Orbigny

Camptonectes sp.

Nizina Mountain Formation

Parareineckeia cf. P. hickersonensis Imlay

Parareineckeia cf. P. shelikofana (Imlay)

Belemnites, undet.

Entolium sp.

Thracia sp.

Cobbanites cf. C. talkeetnanus Imlay

Parareineckeia! sp.

Cranocephalites cf. C. costidensus Imlay

Cranocephalites! sp.

Arctocephalites! sp.

Belemnites, undet.

Inoceramus cf. /. ambiguus Eichwald

Entolium sp.

Parareineckeia sp.

Belemnites, undet.

Parareineckeia cf. shelikofana (Imlay)

Parareineckeia cf, P. hickersonensis Imlay

Cranocephalites! cf. C. pompeckji (Madsen)

Cranocephalitesl sp.

Cobbanites? sp.

Belemnites, undet.

Aptychus, undet.

Coelastarte sp.

Pleuromyal sp.

Parareineckeia cf. P. shelikofana (Imlay)

Parareineckeia cf. P. hickersonensis Imlay

Cranocephalites cf. C. costidensus Imlay

Cranocephalites cf. C. pompeckji (Madsen)

Belemnites, undet.

Liostrea sp.

Entolium sp.

Camptonectes sp.

Pleuromyal sp.

Coelastarte sp.

Reineckeial sp.

Parareineckeia hickersonensis Imlay

Parareineckeia cf. P. skelikofana (Imlay)

Cobbanites cf. C. talkeetnanus Imlay

Cobbanites sp.

Cranocephalitesl cf. C. pompeckji (Madsen)

Cranocephalitesl cf. C. costidensus Imlay

Cranocephalitesl sp.

Belemnites, undet.

Inoceramus cf. /. ambiguus Eichwald

Oxytoma sp.

Entolium sp.

Camptonectes sp.

Pleuromya sp.

Thracial sp.

Quenstedtial sp.

Coelastarte sp.

Fish scales

Crustacean appendage
FOSSIL COLLECTIONS 31

USGS Mesozoic 

Map No. locality No. Fauna

Nizina Mountain Formation Continued

51 28683 Parareineckeia cf. P. shelikofana (Imlay)

52 28691 Cranocephalitest sp.

53 28692 Parareineckeiat sp.

Inoceramus cf. /. ambiguus Eichwald

54 28696 Parareineckeia cf. P. shelikofana (Imlay) 

Cranocephalitesl sp. 

Belemnites, undet.

55 28697 Pleuromyal sp.

56 28698 Parareineckeia cf. P. hickersonensis Imlay 

Parareineckeia cf. P. shelikofana (Imlay) 

Cranocephalitest sp. 

Belemnites, undet.

Inoceramus cf. /. ambiguus Eichwald 

Oxytoma sp. 

Entolium sp. 

Thracia sp. 

Coelastarte sp.

57 28699 Parareineckeia sp.

Cobbanites cf. C. talkeetnanus Imlay 

Cranocephalites"! sp. 

Belemnites, undet. 

Oxytoma sp.

58 28701 Parareineckeia cf. P. hickersonensis Imlay 

Belemnites, undet.

Root Glacier Formation

59 ........ Partschiceras sp.

Buchia rugosa (Fischer)

60 ........ Partschiceras sp.

Buchia rugosa (Fischer)

61 ........ Buchia rugosa (Fischer)

62 ........ Buchia cf. B. rugosa (Fischer)

Lima sp.

63 ........ Buchia rugosa (Fischer)

Camptonectes sp. 

Belemnite fragments

64 ........ Ctenostreon sp.

Belemnite fragments

65 ........ Buchia rugosa (Fischer)

66 ........ Buchia cf. B. rugosa (Fischer)

67 ........ Buchia concentrica (Spwerby)

68 ........ Buchia cf. B. concentrica (Sowerby)

69 ........ Buchia rugosa (Fischer)

Buchia mosquensis (von Buch) 

Belemnites, undet.

70 ........ Buchia concentrica (Sowerby)

71 ........ Buchia rugosa (Fischer)

Belemnite fragments

72 ....... Buchia rugosa (Fischer)

73 ........ Buchia cf. B. rugosa (Fischer)

74 ........ Buchia concentrica (Sowerby)

75 ........ Buchia rugosa (Fischer)

76 ........ Buchia sp.

77 ........ Buchia cf. B. rugosa (Fischer)

. 78 ........ Partschiceras sp.

79 ........ Buchia cf. B. concentrica (Sowerby)

80 ........ Amoeboceras (Prionodoceras) sp.

81 ........ Buchia cf. B. rugosa (Fischer)

"Turbo" sp.

82 ........ Amoeboceras (Prionodoceras) sp.

83 ........ Buchia cf. B. concentrica (Sowerby)
32 GEOLOGY, MCCARTHY c-s QUADRANGLE, ALASKA

Map No.

84

85

86

87

88

89

90

91

92

93

USGS Mesozoic 

locality No. Fauna

94

95

96

97

98

99

100

28680 Buchia mosquensis (von Buch)

Cylindroteuthis sp. 

28700 Buchia mosquensis (von Buch)

Amoeboceras (Prionodoceras) sp.

28702 Buchia concentrica (Sowerby)

28703 Lwnasp.

Kennicott Formation

1376 Brewericeras hulenense (Anderson) 

Arcthoplites belli (McLearn)

1377 Brewericeras hulenense (Anderson)

1378 Grantzicerasl sp.

1471 Arcthoplites belli (McLearn)

1467 Brewericeras hulenense (Anderson)

1380 Brewericeras hulenense (Anderson)

Fauna and flora 

Moonshine Creek Formation

1381 Desmoceras (Pseudouhligella) dawsoni Whiteaves

1469 Pseudohelicoceras sp.

1468 Seed pods

1470 Desmoceras (Pseudouhligella) dawsoni Whiteaves

1357 Desmoceras dawsoni Whiteaves

1358 Desmoceras (Pseudouhligella) dawsoni Whiteaves 

1361 Anioceras sp.

Desmoceras (Pseudouhligella) dawsoni Whiteaves 

1359 Desmoceras dawsoni Whiteaves 

1362 Marshallites cumshewaensis (Whiteaves)

Desmoceras (Pseudouhligella) dawsoni Whiteaves

Fragments of Desmoceras (Pseudouhligella) 

dawsoni Whiteaves

Desmoceras (Pseudouhligella) dawsoni Whiteaves

Fauna 

Schulze Formation

Inoceramus scraps

Flora 

Frederika .Formation

........ Carpinus sp.

........ Metasequoia glyptostroboides Hu and Cheng

"Betula" confusa lata Hollick

Betula sp. 

........ Corylus cf. C. kenaiana Hollick

Acer sp. 

9935 Glyptostrobus sp.

Picea sp.

Pinus sp. (five needled)

Populus kenaiana Wolf e

Alnus largei (Knowltpn) Wolfe

Betula sublutea Tansi and Suzuki

Symphoricarpos n. sp.

ECONOMIC GEOLOGY

The two largest of the Kennecott mines in Alaska, the Bonanza 

and Jumbo, and a third Kennecott mine, the Mother Lode, are in 

the southwestern part of the quadrangle. These mines and another 

Kennecott mine, the Erie in the C-6 quadrangle, are interconnected 

by extensive underground workings. Between 1911 and 1938

103

104

105

106

107

108

109

1473

USGS Paleobotany 

locality No.
ECONOMIC GEOLOGY 33

Kennecott's Alaskan mines ranked among the world's major copper 

producers, producing about 1.2 billion pounds of. copper and 

significant quantities of byproduct silver (Bateman, 1942, p. 501). 

The only recent production from the mines consisted of several 

hundred tons of copper ore derived from surficial operations 

during the 1960's.

The Kennecott mines contain the only important known mineral 

deposits in the quadrangle and have been well described by 

Bateman and McLaughlin (1920). Stratigraphically the Kennecott 

deposits are mainly confined to the lowermost few hundred feet 

of the Chitistone Limestone; they are best developed near the 

troughs of minor northeast-plunging synclines. Most of the deposits 

are in crystalline dolomite that is locally brecciated, but a few 

occur in limestone. The Kennecott lodes formed largely as replacement masses and subsidiary veins, disseminations, and stockworks 

and are renowned for the size and tenor of their chalcocite-rich 

ore. Sulfide minerals constitute about 75 percent of the Kennecott 

ore and oxidized minerals about 25 percent. Chalcocite and related 

cuprous sulfides form more than 90 percent of the typical sulfide 

ore. Other sulfide minerals in the ore include covellite and enargite 

and minor to rare bornite, chalcopyrite, luzonite, tennantite, pyrite, 

sphalerite, and galena. The oxidized ore consists chiefly of malachite and azurite. Silver is probably incorporated in the lattices 

of some of the sulfides, as no discrete silver minerals are found in 

the deposits. Some of the limestone near the Kennecott deposits 

contains disseminated pyrite. Small potassium-rich hydrothermally 

altered zones are locally developed along the Chitistone-Nikolai 

contact near the Kennecott mines (MacKevett and Radtke, 1966).

Armstrong, MacKevett, and Silberling (1970, p. D61, note that 

the lower part of the Chitistone Limestone at the Kennecott mines 

differs from typical Chitistone Limestone by containing a section 

of crystalline dolomite approximately 200 feet thick near its base, 

and that this dolomite is the host rock for most of the Kennecott 

ore. Armstrong and his associates also believe that much of the 

lower Chitistone strata formed in intertidal and supratidal depositional environments.

An attractive speculation is that thermal brines may have been 

important in the genesis of the Kennecott lodes. The efficacy of 

thermal brines as metal solvents and carriers has been stressed in 

recent years (White, 1967, p. 575-631; 1968, p. 301-335; Davidson, 

1965, p. 942-954). Conceivably brines developed in an early 

Chitistone intertidal-supratidal depositional environment were 

heated and mobilized during a later thermal event, such as the
34 GEOLOGY, MCCARTHY c-5 QUADRANGLE, ALASKA

Tertiary plutonism manifested by the presence of felsic plutons 

near the mines mainly in the McCarthy B-5 quadrangle (MacKevett, 1965), or the early stages of Wrangell Lava volcanism. The 

mobilized thermal brines could have migrated through parts of 

the subjacent Nikolai Greenstone, acquired their copper, and 

subsequently recycled to sites of the Kennecott deposits, where 

structure favored ore formation. Probably hydrothermal dolomitization and the recrystallization of primary dolomite preceded 

the initial stages of ore deposition. Additional evidence for the 

presence of Chitistone brines is from the thorough investigations 

of dolomite by Friedman and Sanders (1967, p. 331), who conclude 

that probably all dolomites were deposited from hypersaline brines. 

The brines may have acquired sulfur by dissolving intertidalsupratidal evaporites or by subsequent dissolving sulfides during 

their migration. Although this speculation provides a plausible 

mechanism for the genesis of the Kennecott lodes, much additional 

data is needed before it can be confirmed.

Probably some of the mining claims on Kennecott-type lodes 

east of McCarthy Creek extend into the southern part of the C-5 

quadrangle, but the known lodes and workings on these claims are 

confined to the B-5 quadrangle (MacKevett, 1965). A few small 

copper-bearing veins cut Nikolai Greenstone at the Independence 

mine and elsewhere in the vicinity of the Kennecott mines. Most 

of these veins have been explored by small pits and trenches, but 

none of them is large enough or rich enough to encourage exploitation. In contrast to the Kennecott lodes, the veins generally 

contain chalcopyrite, bornite, and pyrite in a quartz-rich gangue. 

Scattered copper-bearing veinlets cut parts of the McCarthy 

Formation and the Nizina and Chitistone Limestones at a few 

places in the southwestern part of the quadrangle, generally near 

the Kennecott mines. The only other known copper mineralization 

away from the mines is in Nikolai Greenstone amygdules which in 

places contain small pods of native copper and associated secondary 

copper minerals.

No potentially minable deposits of commodities other than 

copper are known in the quadrangle. The lignite seams in the 

Frederika Formation are too small and of too low rank for 

exploitation.

REFERENCES

Armstrong, A. K., MacKevett, E. M., Jr., and Silberling, N. J., 1970, The 

Chitistone and Nizina Limestones of part of the southern Wrangell Mountains, Alaska a preliminary report stressing carbonate petrography and 

depositional environment in Geol. Survey Research 1969: U.S. Geol. Survey Prof. Paper. 650-D, p. D49-D62.
REFERENCES 35

Bateman, A. M., 1942, Economic mineral deposits: New York, John Wiley and 

Sons, 898 p.

Bateman, A. M., and McLaughlin, D. H., 1920, Geology of the ore deposits of 

Kennecott, Alaska: Econ. Geology, v. 15, no. 1, p. 1-80.

Davidson, C. F., 1965, A possible mode of origin of strata-bound copper ores: 

Econ. Geology, v. ,60, no. 5, p. 942-954.

Dunham, R. J., 1962, Classification of carbonate rocks according to depositional 

texture, in Ham, W. E., ed., Classification of carbonate rocks, a symposium: Am. Assoc. Petroleum Geologists Mem. 1, p. 108-121.

Friedman, G. M., and Sanders, J. E., 1967, Origin and occurrence of dolostones, 

in Chilinger, G. V., Bissell, H. J., and Fairbridge, R. W., eds., Carbonate 

rocks: Amsterdam and New York, Elsevier Publishing Co., p. 267-348.

Jones, D. L., and MacKevett, E. M., Jr., 1969, Summary of Cretaceous stratigraphy in part of the McCarthy quadrangle, Alaska: U.S. Geol. Survey 

Bull. 1274-K, p. K1-K19.

MacKevett, E. M., Jr., 1963, Preliminary geologic map of the McCarthy C-5 

quadrangle, Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map 1-406, scale 

1:63,360.

 1965, Preliminary geologic map of the McCarthy B-5 quadrangle, 

Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map 1-438, scale 1:63,360.

 1969, Three newly named Jurassic formations in the McCarthy C-5 

guadrangle, Alaska, in changes in stratigraphic nomenclature by the U.S. 

Geological Survey 1967: U.S. Geol, Survey Bull. 1274-A, p. A35-A49.

 1970a, Geologic map of the McCarthy C-4 quadrangle, Alaska: U.S. 

Geol. Survey Geol. Quad. Map GQ-844, scale 1:63,360.

1970b, Geologic map of the McCarthy C-5 quadrangle, Alaska: U.S.

Geol. Survey Geol. Quad. Map GQ-899, scale 1:63,360.

MacKevett, E. M., Jr., and Radtke, A. S., 1966, Hydrothermal alteration near 

the Kennecott copper mines, Wrangell Mountains area, Alaska a preliminary report: U.S. Geol. Survey Prof. Paper 550-B, p. B165-B168.

Martin, G. C., 1916, Triassic rocks of Alaska: Geol. Soc. America Bull., v. 27, p. 

685-718.

Mendenhall, W. C., 1905, Geology of the central Copper River region, Alaska: 

U.S. Geol. Survey Prof. Paper 41, 133 p.

Moffit, F. H., 1938, Geology of the Chitina Valley and adjacent area, Alaska: 

U.S. Geol. Survey Bull. 894,137 p.

Rohn, Oscar, 1900, A reconnaissance of the Chitina River and the Skolai Mountains, Alaska: U.S. Geol. Survey 21st Ann. Rept., pt. 2, p. 399-440.

Smith, J. G., and MacKevett, E. M., Jr., 1970, The Skolai Group in the McCarthy B-4, C-4, ,and C-5 quadrangles, Wrangell Mountains, Alaska: 

U.S. Survey Bull. 1274-Q, p. Q1-Q26..

White, D. E., 1967, Mercury and base metal deposits with associated thermal 

and mineral waters, in Barnes, H. L., ed., Geochemistry of hydrothermal 

ore deposits: New York, Holt, Rinehart, and Winston, p. 575-631.

 1968, Environments of generation of some base-metal ore deposits: 

Econ. Geology, v. 63, no. 4, p. 301-335.

Williams, Howel, Turner, F. J., and Gilbert, C. M., 1954, Petrography an 

introduction to the study of rocks in thin section: San Francisco, Calif., 

W. H. Freeman and Co., 406 p.

 &U.S. GOVERNMENT PRINTING OFFICE: 1971 O 4OS-123