GEOLOGICAL SURVEY CIRCULAR 783

The Alaskan Mineral Resource 

Assessrftent Prograrn; Background 

Information to Accompany Folio of 

Oeologic and Mineral Resource Maps 

of the Big Delta Quadrangle, Alaska
The Alaskan Mineral Resource 

Assessment Program: Background 

Information to Accompany Folio of 

Geologic and Mineral Resource Maps 

of the Big Delta Quadrangle, Alaska

By H. L. Foster, N. R. D. Albert, Andrew Griscom, T. D. Hessin, 

W. D. Menzie, D. L. Turner, and F. H. Wilson

GEOLOGICAL SURVEY CIRCULAR 783

1979
United States Department of the Interior

CECIL D. ANDRUS, Secretary

Geological Survey

H. William Menard, Director

Free on application to Branch of Distribution, U.S. Geological Survey, 1200 South Eads Street, Arlington, VA 22202
CONTENTS

Abstract _______________________________________________ 1

Introduction _____________________________________________ 1

Purpose and scope _______________________________________ 1

Geography and access _____________________________________ 3

Mineral production and exploration ______________________________ 4

Acknowledgments _______________________________________ 5

Geologic investigations _______________________________________ 5

Previous geologic and mineral resource investigations ____________________ 5

Present study __________________________________________ 5

Potassium-argon ages from the Big Delta quadrangle ____________________ 6

Description of component maps of the Big Delta quadrangle folio ________________ 11

Geology (78-529-A) _______________________________________ 11

Aeromagnetic map and interpretation (78-529-B) _______________________ 12

Interpretation of Landsat imagery (78-529-C)_ ________________________ 12

Mineral resources (78-529-D)_ _________________________________ 13

Reconnaissance geochemistry (78-529-E-N) __________________________ 13

References. _____________________________________________ 15

ILLUSTRATIONS

Page

FIGURE 1. Index map showing the location of the Big Delta quadrangle, Alaska ________________________ 3

2. Physiographic provinces of the Big Delta quadrangle and its location in relation to major faults _________ 4

3. Reference map of the Big Delta l:250,000-scale quadrangle showing the 24 larger scale (1:63,360)

quadrangles and the published maps. ________________________________________ 6

4. Map showing new potassium-argon ages of rocks of the Big Delta quadrangle ___________________ 8

TABLES

TABLE 1. Component maps of the Big Delta quadrangle mineral resource assessment ____________________ 2

2. New potassium-argon ages, Big Delta quadrangle, Alaska ______________________________ 9

III
The Alaskan Mineral Resource Assessment Program: 

Background information to accompany folio of geologic and 

mineral resource maps of the Big Delta quadrangle, Alaska

By H. L. Foster, N. R. D. Albert, Andrew Griscom, T. D. Hessin, W. D. Menzie, D. L.

Turner, and F. H. Wilson

ABSTRACT

The geology, geochemistry, geophysics, and Landsat imagery 

of the Big Delta quadrangle, 16,335 km2 in the Yukon-Tanana 

Upland of east-central Alaska, were investigated, and maps and 

reports were prepared by an interdisciplinary research team for 

the purpose of assessing the mineral potential. The quadrangle 

is dominantly a complex terrane of greenschist- to amphibolitefacies metamorphic rocks that have been intruded by Mesozoic 

and Tertiary dioritic to granitic rocks and are overlain by Tertiary sedimentary and volcanic rocks. Serpentinized peridotite 

and associated greenstone, graywacke, and chert crop out in 

some places.

The quadrangle is bisected by the northeastward-trending 

Shaw Creek fault, which, on the basis of aeromagnetic interpretation and geologic data, is postulated to have left-lateral offset 

of as much as 48 km. On the northwest side of the Shaw Creek 

fault, metamorphic rock units have a northwesterly regional 

trend, and the oldest rocks could be Precambrian in age. Gneiss 

and schist in the southwestern part of the quadrangle are derived from both igneous and sedimentary protoliths, some of 

which may be as old as Precambrian. Other rock units, which include calcareous schist and thin-layered marble, black quartzite, 

semischist, and cataclastic rocks, are considered to be of probable Paleozoic age, although no fossils have yet been found in 

these rocks. Radiolarians and conodonts in chert associated 

with greenstone and ultramafic rocks indicate that the chert is 

of Permian age.

Potassium-argon ages on igneous rocks of the Big Delta 

quadrangle fall into two groups: those with biotite, muscovite, 

hornblende, and sanidine ages between 50 to 69 m.y.; and those 

with biotite, hornblende, and sanidine ages between 88 to 105 

m.y. The younger of these two groups appears to indicate the 

time of a plutonic event marked by intrusion of mostly small, 

isolated plutons, including hypabyssal stocks, and the eruption 

of silicic volcanic rocks. Most of the plutons are quartz 

monzonite to granite.

The older group of ages (88 to 105 m.y.) on igneous rocks includes ages on the largest plutons of the Yukon-Tanana Upland. 

The rocks range from diorite to quartz monzonite in composition. The potassium-argon ages on the metamorphic rocks of the

Big Delta quadrangle, like those obtained elsewhere in the 

Yukon-Tanana Upland, appear to have been partly or completely reset by subsequent thermal events.

Vein and placer gold deposits have been mined in the Big 

Delta quadrangle, and although indications of mineralization 

are widespread, no other mineral deposits have yet been identified. The geologic, geochemical, and geophysical data are 

compatible with several types of deposits, including porphyry 

copper, massive sulfide, and skarn deposits. In certain aspects, 

the geology of the quadrangle is similar to areas in the eastern 

part of the Yukon-Tanana Upland and Canada where mineral 

deposits are known.

INTRODUCTION 

PURPOSE AND SCOPE

This circular, together with a separately 

available folio of open-file maps of the Big Delta 

quadrangle, is one of a series of U.S. Geological 

Survey reports intended to provide information for 

formulating a sound long-range national mineral 

policy to aid in Federal, State, and local land-use 

planning, to provide significant data for mineral 

explorations; and to increase the geologic understanding of the area. The work was carried out 

under the Alaskan Mineral Resource Assessment 

Program (AMRAP), authorized by Congress to begin on July 1, 1974.

The Big Delta mineral resource assessment consists of this Circular, geologic, geophysical, and 

geochemical maps, interpretation of Landsat imagery, and an analysis of the mineral endowment 

(table 1). Some of the geologic data were collected 

prior to July 1, 1974. Most of the field and laboratory studies were carried on from 1975 to 1977 by 

an interdisciplinary team of scientists.
Table 1 .--Component maps of the Big Delta mineral resource assessment

Map Subject

U.S. Geological Survey open-file

report 78-529 

78-529-A (Weber and others, 1978) Preliminary geology.

B (Griscom, 1979) -- - Aeromagnetic map and interpretation.

C (Albert and Steele, 1979) --- Interpretation of Landsat imagery.

D (Menzie and Foster, 19 7 °) - Mineral resources.

E (Hessin and others, 1978) -- --- Geochemical distribution and abundance of copper, lead, and zi

concentrate samples.

F (Hessin and others, 1978) -- - Geochemical distribution and abundance of bismuth, antimony, a

mineral concentrate samples.

s G (Hessin and others, 1978) ---- Geochemical distribution and abundance of tin, tungsten, and m

mineral concentrate samples.

H (Hessin and others, 1978) ---- -- Geochemical distribution and abundance of cobalt, chromium, an

mineral concentrate samples.

I (Hessin and others, 1978) ----- -- Geochemical distribution and abundance of copper, lead, and zi

sediment.

J (Hessin and others, 1978) -- -- Geochemical distribution and abundance of cobalt, chromium, an

sediment.

K (Hessin and others, 1978) -- -- Geochemical distribution and abundance of copper, lead, and zi

L (Hessin and others, 1978) --- Geochemical distribution and abundance of cobalt, chromium, an

M (Hessin and others, 1978) -- Geochemical distribution of copper, lead, and molybdenum in th

N (Hessin and others, 1978) -- - Geochemical distribution and abundance of zinc and cadmium in 
GEOGRAPHY AND ACCESS

The Big Delta quadrangle covers approximately 

16,335 km2 in east-central Alaska (fig. 1) between 

lat 64° and 65° N. and long 144° and 147° W. 

Three physiographic provinces are included in the 

quadrangle: the Yukon-Tanana Upland (Wahrhaftig, 1965), the Tanana Lowland, and the Northern 

Foothills of the Alaska Range (fig. 2). Most of the 

quadrangle is in the Yukon-Tanana Upland, a maturely dissected mountainous terrain, unglaciated 

except for a few valleys in the eastern part of the 

quadrangle, where elevations reach 1,788 m. The 

parts of the upland that border the valley of the 

Tanana River are extensively covered by loess and 

sand. Most of the upland is covered by brush and 

trees, although some high areas are tundra.

The Tanana River flows northwesterly in a broad 

braided channel across the southwestern part of

the quadrangle and is joined from the south by the 

Gerstle, Delta, and Little Delta Rivers, all glacial 

streams. Major tributaries from the northeast 

draining the Yukon-Tanana Upland are the Goodpaster and Salcha Rivers, both clear streams. A 

few small lakes occur at the margin of the upland 

and the Tanana valley, including Healy, Volkmar, 

Quartz, Birch, and Harding Lakes, named in order 

from southeast to northwest.

The Tanana Lowland is largely filled by Holocene alluvial deposits and Pleistocene and Holocene fan deposits and glacial deposits derived from 

alpine glaciers in the Alaska Range to the south. 

Much of the lowland is wooded; near Delta Junction, there are large open swampy areas and tracts 

that have been cleared for farmland.

Only a few square kilometers of intricately dissected Tertiary sedimentary rocks in the southwestern corner of the quadrangle make up the

BIG DELTA 

QUADRANGLE

' ^-J34° 

I ^\V \/^,^ \\JUNEAU

0 100 200 KILOMETERS

 

0 100 MILES

Fir.i'KE 1. Index map showing the location of the Big Delta quadrangle, Alaska.
0150 141

>> CHARLEY RIVER 

QUADRANGLE

50 MILES

Yukon-Tana nallpland

EXPLANATION

Tanana Lowland Northern Foothills

FIGURE 2. Physiographic provinces of the Big Delta quadrangle and its location in

relation to major faults.

Northern Foothills province. The Little Delta 

River flows northward from the Alaska Range 

through the province.

Most of the quadrangle is without roads, but the 

Richardson Highway cuts across the southwestern 

part of the quadrangle, and about 35 km of the 

Chena Hot Springs road traverses the northwestern corner.

Delta Junction is the only town; a small part of 

Fort Greeley, an Army installation for coldweather testing and training south of Delta Junction, extends into the quadrangle. Delta Junction 

has a paved airstrip and several small gravel 

strips. Other airstrips that can be used by light 

bush planes are at Caribou Creek and Tibbs Creek.

MINERAL PRODUCTION AND EXPLORATION

Mineral production from the Big Delta quadrangle, excluding sand and gravel, is limited to

gold from both lode and placer deposits and silver 

recovered from the gold ore. Placer gold was first 

discovered in the Big Delta quadrangle on Tenderfoot Creek in 1905 and soon thereafter on nearby 

creeks and on Caribou and Butte Creeks in the Salcha River drainage. Placer production from the 

Tenderfoot Creek area, commonly known as the 

Richardson district, is estimated at 95,000 troy oz 

gold and 24,000 troy oz silver (Bundtzen and Reger, 1977). A much smaller amount of gold was 

produced from Caribou Creek, where a dredge operated for a short time; other placer production 

from the Big Delta quadrangle has been very 

small. Lode gold was discovered in quartz veins in 

the early 1930's on Black Mountain near Tibbs 

Creek; several mines were explored, including the 

Blue Lead and Blue Lead extension, the Gray 

Lead, the Grizzly Bear, Hidden Treasure, and the 

Michigan Lead; some had minor production. Total 

production to about 1941, when work terminated, 

was about 32 troy oz gold and 25 troy oz silver
from an estimated 150 tons of ore (Thomas, 1970). 

In the mid-1970's there was minor renewed activity in this area and possibly minor production. 

Some old tailings were reworked.

Antimony occurs in this area but has not been 

found in sufficient quantity to mine.

Native bismuth has been reported from the placer concentrates of No Grub Creek in the Salcha 

drainage and is believed to occur in gold-bismuthbearing quartz veins that trend at 35°-45° angles 

across the creek. No effort has been made further 

to explore this occurrence or recover bismuth.

There has been some prospecting for molybdenum in the southeastern part of the quadrangle and 

for nickel in silica-carbonate rock associated with 

ultramafic rocks in the northern part of the quadrangle.

In general, prospecting for metalliferous deposits has not been particularly active in the Big Delta quadrangle in recent years and not as active as 

in some adjacent quadrangles. In part, the lack of 

recent geologic maps and the difficulty of access to 

much of the area without helicopter may have discouraged prospecting.

Little prospecting has been done for uranium 

minerals in the quadrangle.

Commercial deposits of oil, gas, and coal are not 

known in the Big Delta quadrangle. A Tertiary 

coal-bearing formation that has produced some 

coal near Nenana occurs in the southwestern corner of the quadrangle. It is unlikely that significant 

amounts of good quality coal will be found near the 

surface in this area.

ACKNOWLEDGMENTS

Many scientists have participated and contributed to the geologic mapping of the Big Delta 

quadrangle. Rachel M. Barker, who assisted in 

1964, and Alien Clark and his party, who contributed much data and field support in 1972, are particularly thanked. Much assistance was given by 

local Alaskans, by the U.S. Army, and by commercial fixed-wing and helicopter crews.

The able assistance in the office of Alice M. Cantelow, Diana J. Nelson, Steven T. Luthy, Barbara 

C. Thompson, and many others is much appreciated. Kathleen M. Johnson helped prepare the reference list. Gary C. Curtin assisted in preparing 

the geochemical data. Henry C. Berg, coordinator 

of AMRAP, has given continued assistance and 

guidance throughout the project.

GEOLOGIC INVESTIGATIONS

PREVIOUS GEOLOGIC AND MINERAL RESOURCE 

INVESTIGATIONS

The first recorded scientific observations in the 

Big Delta quadrangle were probably made by Lieutenant H. T. Alien on his remarkable traverse 

across the eastern Alaskan Range and down the 

Tanana River to the Yukon in 1885 for the U.S. 

War Department (Alien, 1887). Alien made the 

first reliable map of the Tanana River. The first 

geologic expedition that traversed part of the Big 

Delta quadrangle was that of A. H. Brooks and W. 

J. Peters in 1898, when they ascended the White 

River, portaged to the headwaters of the Tanana 

River, and descended the Tanana to its confluence 

with the Yukon (Brooks, 1900).

Systematic geologic study of the Yukon-Tanana 

Upland was undertaken in 1903 by L. M. Prindle 

with other U.S. Geological Survey geologists, but 

he made few or no observations in the Big Delta 

quadrangle that year. A topographic party led by 

T. G. Gerdine covered the northern and eastern 

parts of the Goodpaster River drainage and part of 

the area between the Goodpaster and Salcha River 

drainages with reconnaissance topographic mapping reported in Prindle (1905, p. 14). The Big Delta quadrangle seems to have been largely excluded 

in many of the early geologic studies of the YukonTanana Upland in favor of the more important 

gold-producing areas of Eagle, the Fortymile, Circle, and Fairbanks. Prindle included the geology of 

the eastern two-thirds of the quadrangle in his 

"Description of Circle quadrangle" (1906a) and 

discussed the gold placer mining of the Salcha 

region. In 1937, Mertie published his compilation 

of the available data on the Yukon-Tanana region, 

including the Big Delta quadrangle, and this report 

has served as the basis for all further geologic 

work and is still the principal reference on parts of 

the area.

PRESENT STUDY

Reconnaissance geologic mapping and geochemical sampling under AMRAP was carried on 

principally in the field seasons of 1975 and 1977; 

limited geologic mapping was done in 1974 and 

1976. Preliminary geologic maps at a scale of 

1:63,360 have been published for the A-l, A-2, A-3, 

B-l, and C-4 quadrangles (Weber and others, 1975,
1977a; Foster and others, 1977; fig. 3). Some 

geologic and geochemical data used in this study 

were collected in 1972 by a field party led by Alien 

Clark making a reconnaissance study of the large 

ultramafic masses in the northern part of the 

quadrangle. Some reconnaissance data were collected by the U.S. Geological Survey in cooperation with the Office of the Engineer, U.S. Army, 

Defense Intelligence Agency in 1964.

Samples for potassium-argon age determinations were mostly collected in 1975, and some of 

the data have already been made available (Wilson, 

1976).

The aeromagnetic map of the Big Delta quadrangle used for aeromagnetic interpretation in this 

study was compiled from a survey flown in 1973 for 

the State of Alaska, Division of Geological and 

Geophysical Surveys (1975).

POTASSIUM-ARGON AGES FROM THE BIG DELTA 

QUADRANGLE

Thirty-two potassium-argon age determinations 

on 26 different rocks are reported here. Eighteen, 

on 14 different rocks, were made as a part of AMRAP, and some of these ages are included in an 

open-file report (Wilson, 1976). The rest were determined at the Geochronology Laboratory of the 

Geophysical Institute, University of Alaska, Fairbanks.

The potassium-argon ages on igneous rocks of 

the Big Delta quadrangle fall into two groups: 

those with biotite, muscovite, hornblende, and 

sanidine ages between 50 to 69 m.y and those with 

biotite, hornblende, and sanidine ages between 

about 88 to 105 m.y. The younger of these two 

groups appears to indicate the time of a plutonic

65

J47" CIRCLE 144°0

FAIRBANKS

64°

D-6

C-6

B-6

A-6

D-5

C-5

B-5

A-5

D-4

C-4

Foster 

and 

others, 

1977

B-4

A-4

D-3

C-3

B-3

A-3 

Weber

and

others.

1977b

D-2

C-2

B-2

A-2 

Weber

and

others.

1977b

D-1

C-1

B-1

Weber

end

others.

1975

A-1 

Weber

and

others.

1975

EAGLE

MT. HAYES ^

FIGURE 3. Reference map of the Big Delta 1:250,000-scale quadrangle showing the 24 larger scale (1:63,360) quadrangles and

the published maps.
event marked by intrusion of mostly small, isolated 

plutons, including hypabyssal stocks, and the eruption of silicic volcanic rocks. The plutons are mostly quartz monzonite to granite and range from medium grained equigranular, through coarse grained equigranular to porphyritic.

One of the largest plutons of this intrusive event 

is the Tors pluton in the northwestern part of the 

quadrangle. A biotite age from a quartz monzonite 

in the southeastern part of this pluton (locality 

75AFr 2000b, fig. 4; and table 2) is 49.8 ± 1.5 m.y., 

the youngest age yet obtained for a plutonic rock in 

the Yukon-Tanana Upland. A pair of mineral ages 

from another quartz monzonite (75AFr2001, fig. 4; 

table 2) in the same pluton, 2.2 km northeast, are 

67.7±2 on biotite and 62.7±2 on muscovite. The 

muscovite age may be younger than the biotite age 

because the rock contains both disseminated muscovite and muscovite in veinlets. The differences in 

the ages of rocks from the Tors pluton at these two 

localities, suggest that the Tors pluton may be 

composite.

The Eielson pluton, about 20 km southeast of the 

Tors pluton, has a biotite age of 67 ±2 m.y. (Forbes 

and Weber, 1975, p. 656). Dated volcanic rocks include a porphyritic rhyolite with a sanidine age of 

61.6 ±2 m.y. (75ASJ528, fig. 4; table 2) in the 

eastern part of the Big Delta quadrangle and two 

welded tuffs in the Tanacross quadrangle to the 

southeast, one with a sanidine age of 56.4 ±2 m.y. 

(Foster and others, 1976) and the other a sanidine 

age of 57.8 ±2 m.y. (J. G. Smith, written commun., 

1976). l Also, the porphyritic syenite of Mount 

Fairplay in the east-central part of Tanacross 

quadrangle has a biotite age of 67.2 ±2 m.y. 2 and 

an amphibole age of 59.5 ±3 m.y. (J. G. Smith, 

written commun., 1976). The occurrence of several 

plutons in the Big Delta quadrangle with biotite 

and muscovite ages of 50 to 68 m.y., small plutons 

in the Tanacross quadrangle with biotite ages in 

this age range, and the association of dated volcanism of similar age to these plutons suggest that 

most of the Tertiary plutonic ages represent times 

of emplacement and cooling. The Nisling Range 

alaskite of Tempelman-Kluit and Wanless (1975), a

'Sample 74ASJ111, Tanacross B-l quadrangle, 63°28'44" N., 141°1815" W. 

Sanidine: percent K20, 8.59; 4°Arrad 7.263 X 10-10 moles/g; percent 4°Arrad 67; 

calculated age 57.8 ± 2 m.y.

suite that occurs as high-level batholiths in the 

southern parts of the continuation of the YukonTanana Upland in the Yukon Territory, Canada, 

has biotite ages determined by them to be 50 to 60 

m.y. and may represent the same event; if it does, 

this event was fairly widespread in east-central 

Alaska and parts of Canada.

The older group of ages (88 to 105 m.y.) on igneous rocks includes ages on the largest plutons of 

the quadrangle and of the Yukon-Tanana Uplands. 

These plutonic rocks are abundant and widely distributed throughout the quadrangle and intrude a 

previously regionally metamorphosed gneiss, 

schist, and quartzite terrane. The rocks range from 

diorite to quartz monzonite in composition, and 

potassium-argon age determinations have been 

made on pyroxene diorite, granodiorite, and quartz 

monzonite. The rocks are mostly medium grained 

and equigranular; a few are porphyritic. Generally, 

they are without planar fabric or microfabric. Concordant biotite and hornblende ages on two mineral pairs from plutons of this group have been determined in the Big Delta quadrangle (75AFr2175 

and 75AFr2184, fig. 4; table 2), and a concordant 

biotite hornblende mineral pair in the same age 

range occurs in a pluton to the south in the Mount 

Hayes quadrangle (biotite, 88.8 ±2.7 m.y. and 

hornblende, 92.9 + 2.8 m.y., recalculated ages from 

Wilson, 1976). Biotite ages from plutonic rocks in 

the range of this older group occur in the Tanacross quadrangle to the southeast (Foster and 

others, 1976), and a concordant mineral pair with 

biotite yielding an age of 92.8 m.y. and a hornblende giving an age of 89 m.y. were determined in 

the Eagle quadrangle to the east from a granodiorite pluton (Foster, 1976). In the southwestern Big 

Delta quadrangle on Democrat Creek, an age of 

86.9 ±2.6 m.y. on potassium feldspar from a 

quartz-feldspar porphyry with an aphanitic to finegrained quartz-sercite groundmass was determined by Bundtzen and Reger (1977), although 

these workers consider this to be a minimum age 

that may date hydrothermal alteration and mineralization. Sanidine ages of 93.9 m.y. and 93.5 m.y. 

(J. G. Smith, written commun., 1976)3 from a 

welded tuff in the Tanacross quadrangle appear to 

indicate volcanism associated with intrusive activity. The wide distribution of potassium-argon ages

2 Sample 74ASJ144, Tanacross C-3 quadrangle,63°39'15" N., 142°14'42" W. 3 Sample 74ASJ143, Tanacross B-6 quadrangle, 63°24'08" N., 143°55'02" W. SaniBiotite: percent K20, 8.64; 4°Arrad 8.513 X 10->° moles/ g; percent 4°Arrad 81; dine: percent K20, 12.485; 4°Arrad 17.29 X 10'10 moles/g; percent 4°Arrad 92;

calculated age 67.2 ±2 m.y. Amphibule: percent KZ0, 0.503; 4°Arrad 0.4398 X 10'10 calculated age 93.9±3 m.y. Sanidine: percent K20, 12.85; 4°Arrad 17.23 X 10'10

moles/g; percent 4°Arrad 58.0; calculated age 59.5 ± 3 m.y. moles/g; percent 4°Arrad 87; calculated age 93.5 + 3 m.y.
J47

00

75AFr2001

67.712.1 B 

@ 62.7±2M

©75AFr2000 

49.8+1.58

75AFr217B 

93.2±2.8B

75AFr2179 

91.912.7B

72AWr85

106.5±3.2 B 

111.813.4M

75AFr21

®98.9±

101 

72AWrB3b 

® 107.4i3.2B

109.8±3.3H 

72AWr83c

106.9+3.2B

107.4±3.2B 

123.6+6.1H

72AFr143c 

115.6+5.6H

72AFr143e

75AF

18

EXPLANATION

®75AFr631 

Locality and number

©107.612B 

Age in m.y. and

mineral dated 

(B, biotite; H, hornblende; 

M, muscovite;S, sanidine)

20 KILOMETERS

0 10 MILES

FIGURE 4. New potassium-argon ages of rocks of the Big Delta quadrangle.
on hornblende and biotite from plutonic rocks in 

the 88- to 105-m.y. range in the Big Delta quadrangle and other parts of the Yukon-Tanana 

Upland, the occurrence of concordant mineral 

pairs, and the associated volcanism suggest that 

the ages are emplacement and cooling ages indicative of a major thermal event about 88 to 105- 

m.y. ago. This event is recognized in the Yukon 

Territory, Canada, where biotite ages determined 

by Tempelman-Kluit and Wanless (1975) range

from 91.5 to 99.6 m.y. in their Coffee Creek quartz 

monzonite.

The potassium-argon ages on the metamorphic 

rocks of the Big Delta quadrangle, like those obtained elsewhere in the Yukon-Tanana Upland, appear to have been partly or completely reset by 

subsequent thermal events and are therefore difficult to interpret. At this time, these ages can only 

be considered as minimum ages for the dated 

rocks. Further study and application of other

Table 2.--New pot irgon ages. Big Delta quadrangle, Alaska

[Ages were determined using standard isotope dilution techniques for extraction and measurement of argon and flame photometry for potassium (Dalrymple and 

Lanphere, 1969). The plus-or-minus value assigned to each is an estimate of the standard deviation of analytical precision (Cox and Dalrymple, 1967), 

together with an estimate of accuracy based on evaluation of the uncertainties in concentration of the 38Ar tracer and potassium measurements.]

Sample No.

Location 

quadrangle 

and latitude 

longitude Rock type

Mineral dated 

mesh size

Age in 

i40Ar million years 

rad 1,0^ plus or minus 

(moles/gm rad analytical 

Percent K20 XIO" 10) (percent) uncertainty Dated by

Igneous rocks

1.

2. 

3. 

4. 

5. 

6. 

7.

8. 

9. 

10.

12.

13.

14. 

15.

75AFr2001

75AFr2000b 

75AFr2178 

75AFr2179 

75ASJ539 

75ASj537a 

75AFr2175

75ASJ530 

75ASJ528 

75AFr2174 

75AFr2181 

75AFr2182 

75AFr2184

74AFr61 3 

DT75-13

Big Delta C-5 Quartz monzonite 64°52'09"N, 

146°12'07"W.

Big Delta D-5 Biotite quartz 

64°5T10"N, monzonite 146°13'59"W.

Big Delta D-4 Pyroxene diorite 64°48'18"N, 

145°45'26"W.

64°46'33"N, 

145°41'02"W.

Big Delta D-l Granodiorite 64°58'18"N, 

144°23'36"W.

Big Delta D-l Quartz monzonite 

64°49'N, 144°08'18"W.

Big Delta C-2 Granodiorite 64°40'50"N, 

144°45'50"W.

Big Delta C-l Granite 64°37'48"N, 

144°12'W.

Big Delta C-l Rhyolite 64 0 33'18"N, 

144°10'24"W.

Big Delta B-2 Pyroxene quartz 

64 0 26'23"N, diorite 144°50'51"W.

Big Delta B-3 Pyroxene diorite 64°17'06"N, 

145°21'09"W.

64°24'25"N, 

146°58'10"W.

Big Delta B-6 Hornblende 

64°19'02N, granodiorite 146 0 33'06"W.

Big Delta B-1 Quartz monzonite 64°20'37"N, 

144°I5'T?"W.

Big Delta B-1 do 

64°30'N, 

144°28'W.

60-100 

Hornblende - 

100-200 

60-100 -

Hornblende 

Hornblende - -

8.06 7.938 73 67.7+2.1

8.065 

10.33 9.417 61 62.7+2.0

10.32

8.72 6.36 68.6 49.8+1.5 

8.78 

8.75

8.24 11.37 87.5 93.2+2.8 

8.28 

8.26

8.87 12.02 91.1 91.9+2.7 

8.85 

8.86

9.10 12.19 92.7 90.4+3 

9.17 

9.135

8.98 8.42 75.5 64.1+1.9 

8.96 

8797

9.12 13.30 68.0 98.9+3 

9.07 

^7095 

1.057, 1.063 1.59 75.5 101.4+3 

1.058, 1.047

1.056 

9.00 7.206 68.8 55.2+1.7

8

07

8.935

12.31 11.07 23 61.6+2 

12.24 

12.28

8.38 11.40 88.8 92+2.8 

8.38 

8.38

9.03 11.94 83.1 89.9+2.7

9

AQ

9.055

9.47 12.73 83.1 91.2+2.7 

9.42 

9.445

8.77 11.53 88.4 89.3+2.7 

8.75 

8.76 + 

1.129, 1.124 1.461 74.3 87.8-2.7 

1.140, 1.117

8.895 14.28 94.5 107.6+3.2 

9.010

8.752

0.740 10.05 65.2 96.0+2.9 

0.740 

0.740

F. H. Wilson 

 -Do.- 

 Do. 

 Do. 

 Do. 

 Do. 

 Do.-- 

J. G. Smith 

F. H. Wilson 

 Do. 

 Do. 

 Do.- 

D. L. Turner 

 Do. 
Table 2. New potassium-argon ages. Big Delta quadrangle, Alaska--Cont.

Sample no.

Location

quadrangle 

and latitude

longitude Rock type

"°Ar

rad 

Mineral dated (moles/gm

mesh size Percent K2 0 X10- ic )

itOflr flrrad

(percent)

Age in

million years

plus or minus 

analytical

uncertainty Dated by

Metamorphic rocks

16

17

18

19

20

21

22

23

24

25

26

. 75AFr2100

. 72AFrl31c

. 72AFrl43b

72AFrl43c

72AFrl43e

. 72AWr83b

72AWr83c

72AWr85

. 72AWr79a

. 72AWr79b

. 72AWr78

Big Delta B-2 Garnet

64°17'53"N, amphibolite

144°38'20"W.

Big Delta C-3 Amphibolite 64°36'51"N, 

144°23'45"W.

Big Delta C-3 Biotite 

64°36'18"N, amphibolite 145°18'23"W.

Big Delta C-3 Hornblendite

64°36'18"N, 

145°18'23"W.

Big Delta C-3 do - - 

64°36'18"N, 

145°18'23"W.

B1g Delta C-2 Augen gneiss

64°35'09"N, 

144°55'35"W.

Big Delta C-2 do 64°35'09"N, 

144°55'35"W.

Big Delta C-3 do 

64°40'35"N, 

149°25'55"W.

Big Delta C-3 Amphibole

64°30'OVI N, gneiss 145°29'10"W.

Big Delta C-3 do -

64°30'01"N,

145°29'10"W.

Big Delta B-4 Biotite gneiss 64°26'50"N,

145 n 45'30"W.

Amphibole 0.242 0.696 

100-120 0.245

0.2435 

Hornblende 0.307 .49

0.308 

0.310

0.308 

Biotite 7.950 12.73

8.045 

7.997 

Hornblende -- 0.539 .98

0.522

0.530 

-.-do--- - 0.353 .61

0.360 

0.360

0.342

0.354 

 do 0.368 .68

0.382

0.375 

Biotite 8.540 13.59

8.530 

8.535 

Hornblende 1.549 2.53

1.552

1.554

T7552 

Biotite - 8.760 13.88

8.740 

8.750

 do 8.474 13.39

8.478 

8.476 

Muscovite - 10.235 17.01

10.253

10.244

Hornblende - 0.243 1.13

0.253

0.248

 do 0.256 .94

0.253

0.254

Biotite 8.640 13.99

8.610

8.625

68. 2

58.2

90.9

84.1

73.5

68. 7

0-5 n

OJ. U

88. 3

79.6

90.0

07 n o / . U

83.0

79.9

89.1

188^5.6 F. H. Wilson

107.8+3.2 D. L. Turner

107.4+3.2 Do. 

123.6+6.1 Do. 

115.6+5.6 Do.- 

121.3+5.9 Do. 

107.4+3.2 - Do. 

109.8+3.3 Do. 

106.9+3.2 Do. 

106.5+3.2 Do. 

111. 8+3. 4 Do. 

291.4+14.6 -Do. --

239.1+7.1 -Do. ------

109.3+3.3 Do. 

U'= 8.78-10' 

K /'* n K (total) = 1. 167- lO" 1* (mole/mole)

10
dating techniques are needed in order to determine 

the age of the metamorphic rocks and the history 

of metamorphic events in the Yukon-Tanana 

Upland.

DESCRIPTION OF COMPONENT MAPS OF 

THE BIG DELTA QUADRANGLE FOLIO

GEOLOGY (78-529-A)

The Big Delta quadrangle is dominantly a complex terrane of greenschist- to amphibolite-facies 

metamorphic rocks that have been intruded by 

Mesozoic and Tertiary dioritic to granitic rocks and 

are locally overlain by Tertiary sedimentary and 

volcanic rocks. Ultramafic rocks and associated 

greenstone and chert crop out in some places. This 

terrane lies sandwiched between two major faults, 

the Tintina to the north and the Denali to the 

south, both outside the Big Delta quadrangle. It 

has been postulated that much of this fault-bounded terrane is allochthonous (Tempelman-Kluit, 

1976) or that it is a continental fragment that 

moved in over oceanic crust along an ancient continental margin that lay along what is now the Tintina fault line (Foster and Keith, 1974).

The part of the Big Delta quadrangle south of the 

Tanana River is mostly Tertiary nonmarine sedimentary rocks, extensive Pleistocene glacial deposits derived from alpine glaciers in the Alaska 

Range to the south, and Pleistocene and Holocene 

alluvial and windblown deposits.

On the north side of the Tanana River particularly in the western part of the quadrangle for distances of as much as 50 km northward from the 

river, the bedrock is largely obscured by extensive 

deposits of windblown sand and loess, locally as 

much as 50 m thick. The Big Delta quadrangle is in 

an area of discontinuous permafrost, and much of 

the ground in the large swampy areas along the 

Tanana River, in the lower Shaw Creek valley, the 

Chena, the lower Salcha and Goodpaster River valleys, is permanently frozen.

During the Pleistocene a few small alpine glaciers developed in some of the highest mountains in 

the eastern and northeastern parts of the quadrangle, resulting in the formation of cirques, Ushaped valleys, and small morainal and outwash 

deposits.

Along the lower reaches of Shaw Creek and 

extending northeastward, the quadrangle is bisected by a major fault, the Shaw Creek fault,

postulated on the basis of aeromagnetic interpretation and geologic data to have left-lateral strikeslip movement of as much as 48 km.

A band of partly serpentinized ultramafic rocks 

with associated greenstone, chert, quartzite, and 

graywacke occurs on the northwest side of this 

fault in the northern part of the quadrangle. These 

rocks are believed to be in thrust relation with the 

underlying semischists, greenschists, quartzite, 

and marble. Radiolarians and conodonts found in, 

the chert associated with the ultramafic rocks indicate a Permian age for the chert (D. L. Jones, oral 

commun., 1978). Although many of the other metamorphic rocks of the quadrangle, including those 

beneath the thrust, are postulated to be of Paleozoic age, no fossils have been found in them.

Some of the highest grade metamorphic rocks of 

the quadrangle occur in a gneiss dome south of the 

Salcha River in the central part of the quadrangle. 

The central part of the dome is composed of greatly deformed sillimanite gneiss. Other possible 

gneiss domes are in the West Point area, in the C-l 

quadrangle in the vicinity of bench mark "Edge," 

and in an area of augen gneiss in the southwestern 

part of the quadrangle. More gneiss and schist occur in the southwestern part of the quadrangle. 

Protoliths were both igneous and sedimentary 

rocks, and some may have been as old as Precambrian.

On the northwest side of the Shaw Creek fault, 

metamorphic rock units have a generally northeasterly regional strike, and an apparent stratigraphic sequence is recognized, with the oldest 

rocks postulated to be on the north and west. The 

oldest rocks, mostly quartz-mica schist, quartzite, 

and some amphibiolite, could be as old as Precambrian.

Unfossiliferous thin-layered marbles, calcareous 

phyllite, and calcareous schist appear to overlie the 

quartz-mica schist but may be in fault relation. A 

metasedimentary sequence characterized by black 

quartzite and black siliceous slaty rock overlies the 

calcareous rocks in apparent stratigraphic succession and crops out in the center of a synform in the 

northwestern part of the quadrangle. These rocks 

are overlain either unconformably or in thrust contact by a greenschist facies metamorphic unit that 

includes semischist, greenschist, marble, quartzite, 

and greenstone. A widespread rock type of this 

unit is light-green or gray semischist characterized 

by rounded to angular, glassy clear gray or bluishgray quartz grains that range in size from less than

11
1 to 5 mm in diameter. Some of the semischists are 

feldspathic. Locally, this unit is in contact with, or 

perhaps grades into, a unit composed predominantly of quartzitic and feldspathic cataclastic 

rocks. The cataclasized rocks may be in a large 

part cataclasized equivalents of the semischist 

unit, but rocks with widely ranging degrees of 

cataclasis are common throughout the quadrangle 

in many different rock units. Although no fossils 

have yet been found, greenschist-facies rocks of 

this sequence, comprising the calcareous unit, 

black quartzite unit, semischist, and cataclastic 

unit, are considered to be of probable Paleozoic 

age, largely on the basis of lithologic similarities to 

Paleozoic sequences elsewhere in Alaska and in the 

Yukon Territory of Canada.

The metamorphic history of the Big Delta quadrangle is still in doubt, as the time or times of metamorphism is uncertain. The youngest regional 

metamorphism occurred before Late Triassic or 

Early Jurassic time, for metamorphic rock fragments are caught up in granitic rock along the 

margin of a Jurassic pluton in the adjacent Eagle 

quadrangle.

Intrusive history before the Mesozoic is difficult 

to determine, although some small dioritic bodies 

apparently were emplaced in the Paleozoic. The 

Permian age of the chert, which is associated with 

a peridotite mass, documents a late Paleozoic or 

younger period of major tectonic activity during 

which oceanic rocks were emplaced on a substratum that is largely continentally derived. The main 

period of felsic intrusive activity was in middle 

Cretaceous time and was followed by felsic intrusive and volcanic activity in the Paleocene, possible 

extending into Eocene time. Local thermal metamorphism occurred adjacent to some of the granitic intrusions. The Big Delta quadrangle seems to 

have been subject to erosion during most of Mesozoic and Cenozoic time; locally subaerial deposits 

were laid down in the early Tertiary and glacial, 

windblown, and alluvial deposits in the Pleistocene 

and Holocene.

AEROMAGNETIC MAP AND INTERPRETATION

(78-529-B)

The aeromagnetic map (sheet 1) of the Big Delta 

quadrangle was made in 1974 and released by the 

State of Alaska as an open-file map (Alaska Div. 

Geol. Geophys. Surveys, 1975). The variations in 

the magnetic field as depicted on maps such as

these provide valuable information concerning the 

lateral and vertical extent of rock units containing 

varying amounts of magnetic minerals, generally 

magnetite. Aeromagnetic maps are a most useful 

support for a geologic mapping program as well as 

for mineral resource assessment. An interpretative map (sheet 2) identifies various rock units in 

the Big Delta quadrangle that have characteristic 

magnetic anomalies, thereby enabling the interpreter to extrapolate geologic information from 

known areas into covered or inaccessible regions. 

In particular, this aeromagnetic map makes it possible to locate the contact-metamorphosed rocks 

bordering various plutons, some of which are concealed. In addition, the map indicates the position 

of several masses of ultramafic rocks.

INTERPRETATION OF LANDSAT IMAGERY (78-529-C)

An abridged interpretation of Landsat imagery 

of the Big Delta quadrangle, Alaska, is given on a 

black and white Landsat mosaic (band 7) of the 

State of Alaska assembled by the U.S. Department 

of Agriculture and on computer-enhanced black 

and white and color Landsat imagery processed by 

the U.S. Geological Survey in Flagstaff, Ariz. 

Landsat scenes selected for computer enhancement are 1768-20342 and 1768-20345, taken August 30, 1974, and 1029-20383, taken August 21, 

1972. Parts of these three scenes have been 

mosaicked by computer so as to cover the entire 

quadrangle by one image.

Color computer-enhanced products used in the 

interpretation include linearly "stretched" standard false-color, sinusoidally "stretched" falsecolor, and simulated natural color images. A black 

and white diagonal first-derivative image also was 

used. Copies of these products are available at 

nominal cost from the EROS Data Center, Sioux 

Falls, S.D. (Albert and Steele, 1978, sheet 1, table

1). 

Information obtained from the various Landsat

products includes lineaments, circular and arcuate 

features, and telegeologic units identified as unique color and "textural" patterns on the color 

computer-enhanced imagery.

A number of lineaments correspond to mapped 

faults; some of these indicate that these faults may 

extend beyond their mapped limits.

Several circular and arcuate features are spatially associated with intrusive bodies; others may

12
reflect intrusive bodies that have not reached the 

surface.

Telegeologic units identified on the computerenhanced imagery show a fair to good correlation 

with mapped geologic units (Weber and others, 

1978). This correlation is best for unconsolidated 

deposits and sedimentary rocks. Correlations with 

igneous and metamorphic rocks, though fair, are 

not as good, perhaps because of similarities between actual rock types from one geologic unit to 

another. Some geologic units can be seen in more 

than one telegeologic unit, this suggests that some 

lithologic differences within these geologic units 

may be distinguishable by telegeology.

MINERAL RESOURCES (78-529-D)

The mineral resources map of the Big Delta 

quadrangle delineates areas that, on the basis of 

geologic, geochemical, and geophysical data, are 

considered to have the greatest potential for new 

mineral resources, and known mineral prospects 

and mines are shown. The kinds of deposits that 

may be present in these areas are described, and 

estimates of grades and tonnages of ore that might 

be expected are given.

Vein and placer gold deposits are known in the 

quadrangle, and, although indications of mineralization are widespread, no other mineral deposits 

have yet been identified. The geologic, geochemical, and geophysical data are compatible with several different types of deposits, and in certain 

aspects of the geology, the quadrangle is similar to 

areas in the eastern part of the Yukon-Tanana Upland and Canada where mineral deposits are 

known.

Kinds and ages of intrusions, geochemical anomalies, and aeromagnetic interpretation suggest 

that porphyry copper deposits may be present in 

the eastern and northern parts of the quadrangle. 

Porphyry molybdenum may also occur. Massive 

sulfide deposits associated with both mafic and 

felsic metavolcanic rocks could occur in association 

with basaltic greenstones and greenschists in the 

northeastern part of the quadrangle. The possibility of skarn deposits as a source of copper and 

tungsten should be investigated.

Most of the gold from the Big Delta quadrangle 

has come from placer deposits in two areas, the 

Richardson district (Banner and Tenderfoot 

Creeks and tributaries) and, in lesser amount,

Caribou Creek and nearby tributaries to the Salcha 

River. Although minor prospecting continues in 

both areas, large future production is not expected. Most of the creeks in the Big Delta 

quadrangle have been fairly thoroughly prospected, and the possibility of new discoveries of 

major gold placer deposits is not especially promising. In some areas, however, glacial deposits and 

thick deposits of windblown silt and sand could 

cover deep placers.

Some additional gold-bearing quartz and antimony-bearing quartz veins can be expected to be 

found in the area of previous lode gold mining near 

Tibbs Creek, but it seems unlikely that large nearsurface occurrences have been missed.

Although ultramafic rocks occur in the Big Delta 

quadrangle, evidence for large deposits of chromite, nickel, platinum, or asbestos has not been 

found.

Some areas that appear geologically favorable 

for mineral deposits, such as the extensively altered zones in the east-central part of the quadrangle, do not have favorable geochemical anomalies.

RECONNAISSANCE GEOCHEMISTRY (78-529-E-N)

A geochemical reconnaissance study was made 

of the Big Delta quadrangle during the summer 

field seasons of 1975 and 1977 to aid in identifying 

areas of possible mineral occurrences. The data delineate areas that contain anomalous concentrations of certain metallic and nonmetallic elements 

sought.

During the two field seasons, samples of stream 

sediments, heavy-mineral concentrates of stream 

sediments, and willow leaves and twigs were collected at approximately 600 sites within the quadrangle at an average density of one site per 20 

km2 . Wherever possible, a composite sample of 

stream-sediment and heavy-mineral concentrate 

was collected across the width of the stream.

The minus-80-mesh stream-sediment and heavymineral concentrates are composed mainly of detrital material that has been mechanically introduced into a stream from bedrock and colluvium 

within a particular drainage basin. Data from 

stream sediments and heavy-mineral concentrates 

are most useful, therefore, for outlining occurrences of outcropping mineralized rock.

The secondary iron and manganese oxides coat13
ing stream-sediment grains (oxide residue) are considered scavenging agents that concentrate elements that have been leached from bedrock and 

colluvium and are migrating as ions in solution. 

The hydromorphic anomalies produced by the 

scavenging processes form patterns that outline 

both known and possible areas of concealed mineralized rock. Willows take up ions moving in soil 

and ground water and concentrate them in the 

leaves and twigs. The hydromorphic anomalies 

produced by this process are similar to those produced by the scavenging action of the iron and 

manganese oxides. In this way, the data from the 

ash of willow leaves and twigs supplement information of the other sample media.

North of the Tanana River for distances of 5 to 

50 km, there is an extensive cover of windblown 

silt and sand that ranges from 0.1 m to more than 

50 m thick. The windblown mateial is largely derived from glacial and alluvial material from the 

Alaska Range and contaminates the stream sediment of this area. It contains comparatively few 

heavy metals.

In the higher eastern parts of the quadrangle, 

small alpine glaciers formed during the Pleistocene. Most of these glaciers, however, were confined to single valleys, and the glacial deposits are 

derived from the same drainage area as the more 

recent stream sediments and probably have a 

minor effect on the analytical results.

Sample preparation began at the collecting site, 

where the stream-sediment samples were sieved 

through a 2-mm screen and the minus-2-mm fraction collected. The sediment mateiral for heavymineral concentrate was sieved through a 2-mm 

screen after a preliminary separation of heavy 

minerals from the bulk of the stream sediment by 

panning.

The samples were air dried in the field and the 

stream sediments then sent to the Geological 

Survey laboratory in Anchorage, Alaska. In the 

laboratory, the dried stream sediment was sieved 

through a minus-80-mesh screen and the minus80-mesh fraction was analyzed for silver, arsenic, 

beryllium, cadmium, cobalt, chromium, copper, 

iron, magnesium, manganese, molybdenum, nickel, lead, antimony, tin, titanium, tungsten, and zinc 

by a semiquantitiative emmission spectrographic 

method for geologic materials (Grimes and Marranzino, 1968). These samples were analyzed for 

copper, lead, zinc, mercury, and gold by atomic absorption (Ward and others, 1969).

The other sample media were prepared and analyzed in the U.S. Geological Survey laboratories in 

Denver, Colo. The amorphous iron-manganese oxides were leached from the stream sediment using 

oxalic acid as described by Alminas and Hosier 

(1976). The oxide residue of the oxalic acid leachate 

was analyzed by the semiquantitative spectrographic method of Grimes and Marranzino (1968).

The heavy-mineral concentrates were sieved 

through a 20-mesh (0.8 mm) screen and the minus20-mesh fraction processed in bromoform (density 

= 2.86) to remove the remaining light-mineral 

grains. The heavy minerals were further separated 

according to magnetic susceptibility by use of a 

hand magnet and a Frantz Isodyamic Separator. 4 

A nonmagnetic fraction was obtained at a setting 

of 0.6 amperes and split. One split was pulverized 

and analyzed by the spectrographic method of 

Grimes and Marranzino (1968). The remaining split 

of the nonmagnetic fraction was saved for mineralogical examination.

The willow leaves were air dried, separated from 

the twigs, and shredded using a commercial 

blender. This material was then ashed in a furnace 

at 500° C and the resulting ash samples analyzed 

by a semiquantitative spectrographic method for 

plant materials (Hosier, 1972).

The distribution and abundance of copper, lead, 

zinc, cadmium, molybdenum, tin, tungsten, 

bismuth, antimony, cobalt, chromium, and nickel 

are shown in this folio (78-529-E through N). Complete analytical data for minus-80-mesh stream 

sediment, nonmagnetic heavy-mineral concentrates of stream sediment, oxide residue (the oxalic 

acid leachable fraction) of stream sediment, and 

the ash of willow leaves and twigs are available in 

an open-file report (O'Leary and others, 1978). 

Analytical data for rock samples are available in 

another open-file report (Foster and others, 1978).

The results indicate that all four sample media 

are useful in this terrane for outlining areas of both 

known and possible mineral occurrences. The results further suggest that mineral occurrences are 

more completely defined by data from a combination of sample media than by data from any one of 

the sample media alone.

iinstitute en14
REFERENCES

(The asterisks (») denote references cited in this report. 

Plus signs (+) indicate references that mainly or entirely 

pertain to the Big Delta quadrangle or are especially 

significant for regional relations of the Big Delta 

quadrangle. Unmarked references are general, regional, or 

topical in scope but contain material relevant to the Big 

Delta quadrangle.)

+ Ager, T. A., 1975, Late Quaternary pollen record from 

Birch Lake, Tanana Valley, Alaska: Geological 

Society of America Abstracts with Programs, v. 7, no. 

3, p. 289.

Alaska Department of Mines, 1948, Report of the

Commissioner of Mines for the biennium ended December 

31, 1948: Juneau, Alaska, 50 p.

_1950, Report of the Commissioner of Mines for the 

biennium ended December 31, 1950: Juneau, Alaska, 57 

P.

_1952, Report of the Commissioner of Mines for the 

biennium ended December 31, 1952: Juneau, Alaska, 66 

P-

_1957, Report of the Commissioner of Mines for the 

biennium ended December 31, 1956: Juneau, Alaska, 103

P-

* Alaska Division of Geological and Geophysical Surveys,

1975, Aeromagnetic map. Big Delta quadrangle, Alaska: 

Alaska Division of Geological and Geophysical Surveys 

open-file map AOF-73, 2 p., 1 sheet, scale 1:250,000.

Alaska Division of Mines and Minerals, 1963, Report for 

the year 1963: Juneau, Alaska, 87 p.

 Albert, N. R. D., and Steele, W. C., 1979, Interpretation 

of Landsat imagery of the Big Delta quadrangle, 

Alaska: U.S. Geological Survey Open-File Report 

78-529-C, scale 1:250,000.

* Alien, H. T., 1887, Report of an expedition to the Copper, 

Tanana, and Koyukuk Rivers, in the Territory of 

Alaska, in the year 1885: Washington, U.S. Government 

Printing Office, 172 p.

 Alminas, H. V., and Hosier, E. M., 1976, Oxalic acid

leaching of rock, soil, and stream sediment samples 

as an anomaly accentuation technique: U.S. Geological 

Survey Open-File Report, 25 p.

Anderson, G. S., 1970, Hydrologic reconnaissance of the 

Tanana basin, central Alaska: U.S. Geological Survey 

Hydrologic Investigations Atlas HA-319, 4 sheets.

Barnes, D. F., 1967, Four preliminary gravity maps of 

parts of Alaska: U.S. Geological Survey Open-File 

Report, 5 p.

1976, Bouger gravity map of Alaska: U.S. Geological 

"Survey Open-File Report 76-70, scale 1:2,500,000.

Barnes, D. F., and MacCarthy, G. R., 1964, Preliminary 

report on tests of the application of geophysical 

methods to Arctic ground-water problem: U.S. 

Geological Survey Open-File Report, 32 p.

Beikman, H. M., 1974, Preliminary geologic map of the

southeast quadrant of Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-612, 2 sheets, 

scale 1:1,000,000.

Berg, H. C., and Cobb, E. H., 1967, Metalliferous lode 

deposits of Alaska: U.S. Geological Survey Bulletin 

1246, 254 p.

Blean, K. M., ed., 1977, The United States Geological

Survey in Alaska Organization and Status of Programs 

in 1977: U.S. Geological Survey Circular 751-A, p. 

A33-A34.

Bottge, R. G., 1975, Impact of a natural gas pipeline on 

mineral and energy development in Alaska: U.S. Bureau 

of Mines open-file report 20-75, 177 p., 101 maps. 

(Also available as Natl. Tech. Inf. Service PB 240 

638/AS.)

Brabb, E. E., and Hamachi, B. R., 1977, Chemical

composition of Precambrian, Paleozoic, Mesozoic, and 

Tertiary rocks from east-central Alaska: U.S. 

Geological Survey Open-File Report 77-631, 166 p.

Brice, James, 1971, Measurement of lateral erosion at

proposed river crossing sites of the Alaska pipeline: 

U.S. Geological Survey Open-File Report, 39 p.

 Brooks, A. H., 1900, A reconnaissance in the White and

Tanana river basins, Alaska, in 1898: U.S. Geological 

Survey 20th Annual Report, pt. 7, p. 425-494.

J906, The mining industry in 1905: U.S. Geological 

Survey Bulletin 284, p. 4-9.

_1907, The mining industry in 1906: U.S. Geological 

"Survey Bulletin 314, p. 19-39.

_1908, The mining industry in 1907: U.S. Geological 

"Survey Bulletin 345, p. 30-53-

_1909, The mining industry in 1908: U.S. Geological 

Survey Bulletin 379, p. 21-62.

_1914, The Alaskan mining industry in 1913: U.S. 

Geological Survey Bulletin 592, p. 45-74.

J915, The Alaskan mining industry in 1914: U.S. 

Geological Survey Bulletin 622, p. 15-68.

_1916, The Alaska mining industry in 1915: U.S. 

Geological Survey Bulletin 642, p. 16-71.

J918. The Alaska mining industry in 1916: U.S. 

Geological Survey Bulletin 662, p. 11-62.

_1922, The Alaska mining industry in 1920: U.S. 

Geological Survey Bulletin 722, p. 7-67.

_1923, The Alaskan mining industry in 1921: U.S. 

Geological Survey Bulletin 739, p. 1-44.

Brooks, A. H., and Capps, S. R., 1924, The Alaskan mining 

industry in 1922: U.S. Geological Survey Bulletin 

755, p. 3-49.

Brooks, A. H., and Martin, G. C., 1921, The Alaskan mining 

industry in 1919: U.S. Geological Survey Bulletin 

714, p. 59-95.

Brosgf*. W. P., Brabb, E. E., and King, E. R., 1970, 

Geologic interpretation of reconnaissance 

aeromagnetic survey of northeastern Alaska: U.S. 

Geological Survey Bulletin 1271-F, p. F1-F14.

 Bundtzen, T. K., and Reger, R. D., 1977, The Richardson

lineament A structural control for gold deposits in 

the Richardson mining district, interior Alaska, in 

Short notes on Alaskan Geology, 1977: Alaska Division 

of Geologic and Geophysical Surveys Geologic Report 

55. p. 29-34.

Bunker, C. M., Bush, C. A., and Forbes, R. B., 1973,

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15
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 Foster, H. L., Dusel-Bacon, Cynthia, Weber, F. R., 1977, 

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« Foster, H. L., and Keith, T. E. C., 1974, Ultramafic rocks 

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« Foster, H. L., O'Leary, R. M., McDanal, S. K., and Clark, 

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+ Foster, H. L., Weber, F. R., and Dusel-Bacon, Cynthia,

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Gedney, L., Shapiro, L., Van Wormer, D., and Weber, F. R., 

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 Grimes, D. J., and Marranzino, A. P., 1968, Direct-current 

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16
* Griscom, Andrew, 1979, Aeromagnetic map and interpretation 

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» Hessin, T. D., Cooley, E. F., and Dusel-Bacon, Cynthia, 

1978, Geochemical map showing the distribution and 

abundance of bismuth, antimony, and silver in 

non-magnetic heavy-mineral concentrate samples in the 

Big Delta quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 78-529-F. scale 1:250,000.

» Hessin, T. D., Cooley, E. F., Hopkins, R. T., McDougal, C. 

M., and Detra, D. E., 1978, Geochemical map showing 

the distribution and abundance of cobalt, chromium, 

and nickel in the oxide residue of stream sediment 

samples from the Big Delta quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 78-529-L, scale 

1:250,000.

» Hessin, T. D., Cooley, E. F., and Siems, D. F., 1978, 

Geochemical map showing the distribution and 

abundance of copper, lead, and molybdenum in the ash 

of willow leaves from the Big Delta quadrangle, 

Alaska: U.S. Geological Survey Open-File Report 

78-529-M, scale 1:250,000.

» Hessin, T. D. , Cooley, E. F., Siems, D. F., and McDanal, 

S. K., 1978, Geochemical map showing the 

distribution of tin, tungsten, and molybdenum in 

non-magnetic heavy-mineral concentrate samples in the 

Big Delta quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 78-529-G, scale 1:250,000.

» Hessin, T. D., Day, G. W., Crim, W. D., and Donate, M. M., 

1978, Geochemical map showing the distribution and 

abundance of zinc and cadmium in the ash of willow 

leaves from the Big Delta quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 78-529-N, scale 

1:250.000.

« Hessin, T. D., O'Leary, R. M., Hoffman, J. D., and Detra, 

D. E., 1978, Geochemical map showing the 

distribution and abundance of copper, lead, and zinc 

in minus-80 mesh stream sediment from the Big Delta 

quadrangle, Alaska: U.S. Geological Survey Open-File 

Report 78-529-1, scale 1:250,000.

» Hessin, T. D., Taufen, P. M., Cooley, E. F., and McDougal, 

C. M., 1978, Geochemical map showing the distribution 

and abundance of copper, lead, and zinc in 

non-magnetic heavy-mineral concentrate samples in the 

Big Delta quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 78-529-E, scale 1:250,000.

» Hessin, T. D., Taufen, P. M., Cooley, E. F., Siems, D. F., 

and McDanal, S. K., 1978, Geochemical map showing the 

distribution and abundance of cobalt, chromium, and 

nickel in non-magnetic heavy-mineral concentrate 

samples in the Big Delta quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 78-529-H, scale 

1:250,000.

« Hessin, T. D., Taufen, P. M., Day, G. W., and Karlson, M. 

E., 1978, Geochemical map showing the distribution 

and abundance of copper, lead, and zinc in the oxide 

residue of stream sediment samples from the Big Delta 

quadrangle, Alaska: U.S. Geological Survey Open-File 

Report 78-529-K. scale 1:250,000.

» Hessin, T. D., Siems, D. F., and Day, G. W., 1978. 

Geochemical map showing the distribution and 

abundance of cobalt, chromium, and nickel in minus-80 

mesh stream sediment from the Big Delta quadrangle, 

Alaska: U.S. Geological Survey Open-File Report 

78-529-J, scale 1:250,000.

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mounds observed from the ground, from aerial 

reconnaissance, and on aerial photographs in interior 

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PHolmes, G. W., Hopkins, D. M., and Foster, H. L., 1968, 

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Hopkins. D. M., Karlstrom, T. N. V., and others, 1955, 

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17
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18
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19