Oscar 1

Oscar 2

Oscar 3

Oscar West

LWM

West LWM

Little

Enchilada

Drumstick 3

Drumstick 2

Drumstick 1

Eva

Mitchell 186.2 ± 3.0 Ma

207.9

± 2.9 Ma

67.7±

0.7 Ma

Kr

Jgmv

Jt

m

Kqfp Jgmv

g g

qm qm

am

Jt

Kgu

Kgu

m

m

g q

q q

FEET

6000

4000

SEA LEVEL

2000

FEET

6000

4000

SEA LEVEL

2000

Selected Quaternary units omitted

KECHUMSTUK

FAULT ZONE

A A'

Jmig

Qa Qa Qc Qc Qa

T A

Location map in Alaska showing the approximate outline of the Fortymile mining district (light yellow), and the map area within

it (darker yellow polygon with solid black outline).

0 100 MILES

100 KILOMETERS

25 50 75

0 25 50 75

Basemap from Esri accessed Dec. 10, 2013 at http://www.arcgis.com/home/webmap/viewer.html.

Fortymile

River ileRiver

UNITED STATES

CANADA

ALASKA

YUKON TERRITORY

Fort Yukon

153° 150° 147° 144° 141° 138° 135°

Anchorage Anchorage nchorage

Eagle

Tok

64°

Chicken

65°

66°

67°

Cook Inlet

63°

62°

61°

60° Gulf of Alaska

PACIFIC OCEAN

Fortymile

mining district

Autolithic fragment of medium-grained quartz monzonite within 

megacrystic phase of Jurassic quartz monzonite of Mount Veta (Jgmv). 

Location: lat 64.1461°N., long 142.9544°W. Photograph taken 2010. 

Jgmv

Kgvc

Kgvc

Jgmv

Jgmv

Kgvc

Qc

Kqfp

Kggp

Jgmv

Kgvc

Mount Veta

View of Mount Veta looking from the southeast. Main peak of Mount Veta is made up of Late 

Cretaceous granite of Veta Creek (Kgvc) intruded into Jurassic quartz monzonite of Mount Veta 

(Jgmv). Thin white lines are contacts, thicker lines are faults. Fault line is dotted where obscured by 

hill. Photograph taken in 2010 from lat 64.1672°N., long 142.9432°W., looking towards Mount Veta.

John Rentfro, Yukon placer miner 

and cook. Eagle district, Yukon 

region, Alaska, July 1904. Plate 

5–A in U.S. Geological Survey 

Bulletin 263, 1905. ID Paige, S., 

365, pai00365, USGS.

http://libraryphoto.cr.usgs.gov/.

Up Wade Creek, Fortymile district, Yukon region, 

Alaska, 1903. Plate 6–B in U.S. Geological Survey 

Bulletin 251, 1905; Plate 1–B in U.S. Geological 

Survey Bulletin 375, 1909. ID Prindle, L.M., 63, 

plm00063, USGS. http://libraryphoto.cr.usgs.gov/.

Nonfoliated basaltic dike (Tb) intruded along a northeast-trending fault zone in 

Triassic hornblende-biotite granodiorite (g). Location: lat 64.0497°N., long 

134.0687°W. Photograph taken 2010.

Southeast-dipping metamorphosed

ultramafic (um) horizon.

Location: lat 64.1478°N., long 143.1582°W.

Photograph taken in 2009, looking northeast.

Paleozoic marble horizon (m) interlayered within siliciclastic metasedimentary

sequence (q, not shown) with internal isoclinal folding within the marble 

horizon. Location: lat 64.1643°N., long 43.1581°W. Photograph taken 2009.

Float rock showing ductile deformation within adjacent basal part of Jurassic 

Mount Veta intrusion (Jgmv). Location: lat 64.1520°N., long 143.1349°W. 

Photograph taken 2009. 

Megacrystic phase of quartz 

monzonite of Mount Veta 

(Jgmv).

Location: lat 64.1874°N.,

long 142.9216°W.

Photograph taken 2010.

Southeast-dipping marble horizon (m) intruded by foliated tonalitic sills (light 

gray bands) forming migmatite unit (mig) structurally beneath the quartz 

monzonite intrusion of Mount Veta. Photograph taken looking north. Location:

lat 64.1478°N., long 143.1582°W. Photograph taken 2010.

63°00'

141°00' 144°00' 147°00'

65°00'

64°00'

148°30'

66°00'

138°00’

TINTINA FAULT

MCKINLEY STRAND OF DENALI FAULT

HINES CREEK STRAND OF DENALI FAULT

DENALI

FAULT

Stewart River

Mosquito

Salcha River

Yukon River

Fortymile River

Fork

Mosquito

Tanana River

Delta River

Wood River

Birch Creek

Rive

C

r

hena

North Ladue River

Tanana River

Chatanika

River

White River

River

Yukon

Ladue River

Denison Fork

LIVENGOOD CIRCLE CHARLEY RIVER

DAWSON

TANACROSS

FAIRBANKS BIG DELTA

HEALY STEWART RIVER

MT. HAYES

SCF

BMTZ

MHL

KFZ

SML

Fairbanks

Big Delta

Tok

Dawson

Chicken

Eagle

Wickersham grit unit

Taylor

Mountain

YUKON (CANADA) ALASKA (UNITED STATES)

OCEANIC AND HIGH-P ASSEMBLAGES

Contact—Dashed where concealed or uncertain

High-angle fault—Arrows show direction of strike-slip movement;

dashed where inferred; dotted where concealed

Thrust fault—Sawteeth on upper plate; dashed where inferred

Low-angle normal fault—Sawteeth on upper plate; dotted where concealed

Lineament—Showing label

Quadrangle boundary—1:250,000 U.S. Geological Survey and Geological

Survey of Canada quadrangles

Cities and towns

CONTINENTAL MARGIN ASSEMBLAGES

(PARAUTOCHTHONOUS YUKON-TANANA ASSEMBLAGE)

Tertiary Rocks

Granitoid intrusions—Volcanic rocks

Terrestrial sedimentary rocks

Mesozoic Intrusive Rocks

Late Cretaceous intrusion

Late Cretaceous volcanic rocks

Mid-Cretaceous intrusion

Mid-Cretaceous volcanic rocks

Jurassic intrusion

Triassic intrusion

ARC AND BASINAL ASSEMBLAGES

(ALLOCHTHONOUS YUKON-TANANA TERRANE)

0 10 20 MILES

0 10 20 KILOMETERS

Klondike Schist—Permian felsic metaigneous rocks; minor metasedimentary and mafic rocks

Nasina assemblage—Schist, phyllite, marble; carbonaceous rocks; Permian and Mississippian felsic metavolcanic rocks

Chicken metamorphic complex—Intermediate-mafic metaigneous rocks, quartzite, Mississippian(?) marble

Fortymile River assemblage—Intermediate-mafic metaigneous gneiss, marble, quartzite; Mississippian

granodioritic gneiss (brown)

Ladue River unit quartz—Chlorite sericite schist and mafic and felsic metaigneous rocks (in part Devonian-Mississippian)

Butte assemblage, Alaska Range equivalents—Devonian-Mississippian metavolcanic rocks, phyllite, marble

Blackshell and Dan Creek units; Keevy Peak Fm.—Carbonaceous metasedimentary rocks, marble,

Devonian-Mississippian metarhyolite

Lake George and Fairbanks-Chena assemblages—Quartz-mica schist, amphibolite, quartzite;

Devonian-Mississippian augen gneiss (dark blue)

Seventymile terrane—Peridotite, greenstone; Mississippian to Triassic chert and limestone;

Chatinika assemblage (near Fairbanks), eclogite, marble, schist

EAGLE

EAGLE

Approximate outline

of map area

Figure 1. Regional geologic map of the Yukon-Tanana Upland area of east-central Alaska (modified after Dusel-Bacon and others, 2009) showing the approximate outline of the map

area and locations of known major northeast-trending fault, lineaments, and tectonic zones. SCF, Shaw Creek fault; BMTZ, Black Mountain tectonic zone; MHL, Mount Harper

lineament; KFZ, Kechumstuk fault zone; SML, Sixtymile lineament.

SML

Sample

number

Field

number

Latitude

(N.)

Longitude

(W.)

Map unit Mineral Analysis

location

Age (Ma)* Rock type

Late Cretaceous igneous rocks

1

2

3

4

5

6

08ADb03

08ADb19

129A5

81A5

140A5

118A5

64.2175°

64.2361°

64.1146°

64.2133°

64.0219°

64.0918°

142.9089°

143.0828°

143.0127°

143.0053°

143.0927°

143.0378°

Kgvc

Kgvc

Kgkc

Kgg

Kr

Kr

Zircon

Zircon

Zircon

Zircon

Zircon

Zircon

Core

Core

Core

Core

Core

Core

65.8 ± 1.4

65.8 ± 1.5

67.7 ± 0.7

67.9 ± 1.1

≤ ~ 65

68.1 ± 0.8

Nonfoliated medium-grained biotite granite 

Nonfoliated medium-grained hornblende-biotite granite

Nonfoliated fine-grained biotite granite

Nonfoliated biotite-hornblende granite with “smoky” quartz phenocrysts

Rhyolite porphyry dike

Rhyolite porphyry dike

Mid-Cretaceous igneous rocks

7

8

9

10

08AD–032A

09AD–343

08AD–052

08ADb20

64.0530°

64.0331°

64.0286°

64.0089°

143.1248°

143.2273°

143.2464°

143.3097°

Kqfp

Kqfp

Kgc

Kgc

Zircon

Zircon

Zircon

Zircon

Core

Core

Core

Core

93.9 ± 1.3

95.8 ± 1.5

108.8 ± 1.7

111.8 ± 1.5

Quartz feldspar porphyry intrusion

Quartz feldspar porphyry dike

Nonfoliated biotite granite

Nonfoliated leucogranite

Early Jurassic igneous rocks

11

12

13

14

15

16

10AD–368

8A5–4

08ADb22

08ADb08

08AD–100

09AD–240

64.2041°

64.0599°

64.0930°

64.2144°

64.1016°

64.1877°

142.8282°

143.1701°

143.1458°

142.8842°

143.1905°

143.1310°

Jgmv

Jgmv

Jgmv

Jgmv

Jt

Jt

Zircon

Zircon

Zircon

Zircon

Zircon

Zircon

Core

Core

Core

Core

Core

Core

Inherited Cores

183.4 ± 3.6

184.5 ± 3.0

186.2 ± 3.0

181.2 ± 2.6

184.8 ± 2.9

190.5 ± 4.8

~ 1–2 Ga

Nonfoliated K-feldspar megacrystic hornblende-biotite granite porphyry

Foliated coarse-grained hornblende-biotite megacrystic monzonite 

Foliated K-feldspar megacrystic hornblende quartz monzonite 

Foliated K-feldspar megacrystic hornblende quartz monzonite 

Foliated clinopyroxene-bearing tonalite dike

Foliated, medium-grained biotite granite

Late Triassic igneous rocks

17

18

19

09AD–338

08ADb24

09AD–319

64.1051°

64.0892°

64.1104°

143.1121°

143.0378°

143.1803°

g

g

g

Zircon

Zircon

Zircon

Core

Core

Core

Rim

207.9 ± 2.9

215.0 ± 3.5

215.5 ± 3.4

203 ± 4.0 

Foliated medium-grained hornblende leucotonalite

Hornblende-biotite granodiorite

Foliated medium-grained hornblende quartz diorite

Mississippian or older metamorphic rocks

20 09AD–264 64.2058° 142.8089° mv Zircon Core

Rim

332.6 ± 5.7

~ 70

Mylonitic tonalite gneiss interlayered within mafic metavolcanic

sequence (unit mv)

Table 1. New SHRIMP U-Pb zircon ages for samples from the western Fortymile mining district near Mount Veta, east-central Alaska. 

[In the analysis location column, the term ‘inherited cores’ represents a much older part of the analyzed zircon crystal that is xenocrystic, whereas the term ‘rim’ represents younger overgrowths along 

the margin of the zircon crystal. All samples were analyzed using the USGS/Stanford sensitive high resolution ion microprobe–reverse geometry (SHRIMP-RG) at Stanford University. The primary 

oxygen beam operated at about 6–8 nanoangstroms (nÅ) and excavated a pit about 25 micrometers (μm) in diameter and 1 μm deep. Elemental fractionation was corrected using zircon standard R33 

(419 Ma, Black and others, 2004). The age of each sample was determined by calculating the weighted average of selected 206Pb/238U ages. Raw data were reduced and plotted using the Squid 2 and 

Isoplot/Ex 3 programs of Ludwig (2003, 2009); age errors were calculated at the 95 percent confidence limit. Ma, million years.]

DESCRIPTION OF MAP UNITS

[Geological Society of America geologic time scale used to determine age boundaries (Geological Society of America, 2012)]

QUATERNARY SURFICIAL DEPOSITS

Alluvial and fluvial deposits (Holocene)—Clay, silt, sand, and pebble to cobble 

gravel deposited in narrow stream channels; locally includes minor colluvium 

(Qc). Maximum thickness unknown

Landslide deposits (Holocene)—Angular fragments of bedrock mixed with soil, or 

heterogeneous mixtures of boulders and finer grained material derived from 

adjacent steep hill slopes; characterized by irregularly shaped, hummocky 

topography. Estimated thickness less than 30 m

Solifluction deposits (Holocene)—Unsorted, water-saturated colluvial material 

restricted to higher mountain peaks; characterized by numerous elongate terraced 

or flattish areas that step down into adjacent active drainages. Estimated 

thickness less than 10 m 

Young alluvial fan deposits (Holocene)—Poorly sorted silty sand and gravel 

deposits that form small alluvial fans along margins of major stream drainages. 

Maximum thickness unknown

Colluvium (Holocene)—Residual deposits of clay, silt, sand, pebbles, and cobbles 

that mantle gently to moderately dipping slopes. Estimated thickness ranges up 

to 15 m at the base of hill slopes 

TERTIARY IGNEOUS ROCK

Basaltic to andesitic dikes (Eocene?)—Dark-gray to black, non-foliated basalt dike 

containing small, randomly oriented plagioclase phenocrysts set in devitrified 

aphanitic groundmass. Age uncertain, but may be correlative with a 50‒54 Ma 

suite of bimodal volcanic rocks; basaltic dike swarms are commonly associated 

with these rocks throughout this part of the Yukon-Tanana Upland (Newberry 

and others, 1995, 1998). Non-foliated fabric indicates intrusions were emplaced 

after regional ductile deformation occurred (post-Early Jurassic, Dusel-Bacon 

and others, 2006)

CRETACEOUS IGNEOUS ROCK

Granite, undivided—Non-foliated granodiorite to granite forming isolated dikes and 

small intrusions. Age uncertain

LATE CRETACEOUS IGNEOUS ROCKS 

Granite of Veta Creek—Light-gray, homogeneous, medium-grained, non-foliated 

biotite-hornblende granite with minor alkali feldspar phenocrysts up to 1.5 cm 

diameter. Unit intrudes base of quartz monzonite of Mount Veta (Jgmv). 

SHRIMP U-Pb zircon crystallization ages ~ 65.8 Ma (table 1, samples 1 and 2).

Granite of Kechumstuk Creek—Light-gray, homogeneous, fine-grained, 

non-foliated biotite granite. Occurs as isolated intrusion east of the Kechumstuk 

fault zone. SHRIMP U-Pb zircon crystallization age of 67.7 ± 0.7 Ma (table 1, 

sample 3). Temporally and compositionally similar to granitic and rhyolitic units Kgvc, 

Kgg, and Kr, indicating unit was part of a broad Late Cretaceous intrusive event

Porphyritic granite of Gold Bottom Creek—Greenish-gray, non-foliated, porphyritic 

late-phase of granite of Gold Bottom Creek intrusion. Unit is porphyritic with 

distinctive dark gray “smoky” quartz phenocrysts in fine-grained gray silicified 

matrix. Unit is hydrothermally altered with distinctive network of quartz veins 

with minor disseminated pyrite and molybdenite

Granite of Gold Bottom Creek—Light-gray, non-foliated biotite-hornblende granitic 

hypabyssal intrusion with characteristic coarse-grained dark gray “smoky” quartz 

phenocrysts, which exhibit both rounded and euhedral morphology, set in a 

fine-grained granitic groundmass. Crystallization U-Pb SHRIMP age of 67.9 ± 

1.1 Ma (table 1, sample 4) is within analytical error of that of the granite of Veta 

Creek (Kgvc) and the granite of Kechumstuk Creek (Kgkc); thus all these late 

Cretaceous granitic units are thought to be coeval

Rhyolite dikes—Light-tan to light-gray felsic dikes of fine-grained quartz porphyry 

to quartz-feldspar porphyry rhyolite with biotite phenocrysts in an aphanitic 

groundmass. Locally pyrite bearing, causing rock to weather light brown. 

SHRIMP U-Pb zircon ages between ~ 65 Ma and 68.1 ± 0.8 Ma (table 1, samples 

5 and 6, respectively), making these dikes coeval, within analytical uncertainty, 

with the granite of Gold Bottom Creek (Kgg), the granite of Veta Creek (Kgvc), 

the granite of Kechumstuk Creek (Kgkc), and rhyolite tuff and granite porphyry 

of the Middle Fork caldera, which is approximately 10 km northwest of the map 

area (Bacon and Lanphere, 1996; Bacon and others, 2012)

Mafic dikes (Early? and Late? Cretaceous)—Dark gray, non-foliated dioritic to 

basaltic dikes and small plugs with 2‒4 mm diameter biotite ± hornblende 

phenocrysts in altered dark gray fine-grained matrix. Distinguished from unit Tb

due to high degree of alteration. Unit cuts Early Cretaceous granite of Corner 

(Kgc); absolute age uncertain

Quartz-feldspar porphyry—Non-foliated quartz-feldspar rhyolite porphyry 

characterized by distinctive medium-grained quartz “eyes” and sericitized 

plagioclase and biotite phenocrysts set in a fine-grained gray rhyolitic groundmass. 

These rock types yield SHRIMP U-Pb zircon ages of 93.9 ± 1.3 Ma and 95.8 ± 1.5 

Ma, respectively (table 1, samples 7 and 8). Interpreted to be hypabyssal bodies 

intruded into and adjacent to Kechumstuk fault zone

EARLY CRETACEOUS IGNEOUS ROCKS

Granite of Corner—Coarse-grained, medium-gray, non-foliated, porphyritic biotite 

granite with diagnostic 1.5-cm-diameter quartz and feldspar phenocrysts, and 

medium-grained leucogranite. U-Pb SHRIMP age of 108.8 ± 1.7 Ma on biotite 

granite (table 1, sample 9) and 111.8 ± 1.5 Ma on leucogranite (table 1, sample 

10); unit emplaced after regional Mesozoic ductile deformation. Type locality 

crops out in the SW1⁄4 SW1⁄4 sec. 20, T. 26 N., R. 11 E. at vertical angle 

benchmark (VABM) demarked as Corner on the Eagle (A–5) quadrangle 

EARLY JURASSIC IGNEOUS ROCKS 

Migmatite—Foliated migmatite with the paleosome a mixture of Paleozoic 

metasedimentary country rocks (ms), hornfels, amphibolite (am), laminated 

marble (m) invaded by neosome of foliated, medium-grained, 

biotite-hornblende quartz monzonite of Mount Veta (Jgmv). Neosome is foliated 

and forms sills within Paleozoic units parallel to strong penetrative ductile 

metamorphic fabric and compositional layering and is locally enfolded with the 

paleosome. Unit structurally underlies Jurassic quartz monzonite, forming 

migmatitic footwall zone of the Jurassic intrusion (Jgmv)

Quartz monzonite of Mount Veta—Coarse-grained porphyritic monzonite to quartz 

monzodiorite characterized by potassium feldspar megacrysts set in a coarse-grained 

hornblende-bearing groundmass. Grades locally into zones devoid of characteristic 

potassium feldspar megacrysts. Compositional variants also include granodiorite 

and granite. Locally cut by hornblendite dikes. Unit originally designated syenite 

of Mount Veta by Foster (1976). Ductile tectonic foliation forms near footwall 

and roof pendant zone of intrusion (approximately 4 km west of Mount Veta in 

northern part of map area) that is parallel to that of the dominant regional 

penetrative fabric in the country rock. Intrusion is interpreted to be a synkinematic 

tabular-shaped body intruded during waning stages of regional ductile deformation event, constraining the dominant metamorphic event to the Jurassic. 

SHRIMP U-Pb zircon data indicate the primary crystallization ages range from 

183.4 ± 3.6 Ma for a small intrusion on the east side of the Kechumstuk fault 

zone (table 1, sample 11) to a range from 181.2 ± 2.6 to 186.2 ± 3.0 Ma recorded 

in samples taken from the main intrusion west of the Kechumstuk fault zone 

(table 1, samples 12‒14)

Tonalite—Foliated, fine- to medium-grained, leucocratic, biotite granite, hornblende 

tonalite, and clinopyroxene tonalite dikes and small intrusions. Locally, unit is 

intensely deformed, as evidenced by the mineral foliation as well as polygonal, 

strained quartz grains (table 1, samples 15 and 16). Unit occurs structurally 

beneath the main quartz monzonite of Mount Veta intrusion (Jgmv). Although 

U-Pb SHRIMP ages for unit Jt (184.8 ± 2.9 Ma and 190.5 ± 4.8 Ma; table 1, 

samples 15 and 16, respectively) are within error of those of unit Jgmv, relative 

age is inferred to be slightly older

EARLY JURASSIC AND OLDER METAMORPHIC ROCK

Metahornblendite dike (pre-Early? Cretaceous)—Black, coarse-grained, foliated 

metahornblendite dike. Age uncertain, but presence of tectonic foliation indicates 

unit present during regional pre-Early Cretaceous deformation

LATE TRIASSIC IGNEOUS ROCK

Hornblende granodiorite—Dark-gray, weakly foliated, medium-grained hornblendebiotite granodiorite, hornblende quartz monzodiorite, and hornblende 

leucotonalite. Unit forms batholithic intrusion in southeastern part of map and 

smaller intrusions to the west of the Kechumstuk fault. U-Pb zircon ages range 

from 207.9 ± 2.9 Ma to 215.5 ± 3.4 Ma (table 1, samples 17‒19) 

PALEOZOIC AND OLDER METAMORPHIC ROCKS

Metavolcanic and lesser metasedimentary rocks (Middle Mississippian or older)—

Dark green to black, fine-grained, weakly to moderately foliated metabasalt and 

meta-andesite volcanics interlayered with metasedimentary rocks of the Chicken 

metamorphic complex of Werdon and others (2001). Thin interlayers of mylonite 

made up of recrystallized quartz and feldspar locally lie between foliation 

surfaces, presumably developed during regional tectonism, which thrust unit over 

supracrustal Paleozoic metamorphic rocks (ms). Unit metamorphosed to upper 

greenschist facies, with chlorite-epidote-calcite alteration assemblage. Primary 

age of unit uncertain, but an interlayered mylonitic felsic horizon (approximately 

2 m thick), whose protolith was a dacitic volcanic rock or tonalite sill within the 

mafic metavolcanic rocks was dated at Middle Mississippian (table 1, sample 

20). Mafic metavolcanic rocks have island-arc tholeiite trace-element signatures 

(Dusel-Bacon and others, 2013). U-Pb SHRIMP analyses of zoned zircons from 

the mylonite have cores dated at 332.6 ± 5.7 Ma (table 1, sample 20), which 

represent the age of volcanism (or intrusion?) of the protolith, and rims dated at 

~70 Ma, interpreted to be the youngest possible age of tectonism undergone by 

the mylonite. At a locality within the Chicken metamorphic complex in the 

southeastern Eagle quadrangle, marble interlayered with metabasalt yielded 

poorly preserved conodonts of late Paleozoic, possibly Mississippian, age 

(Dusel-Bacon and Harris, 2003)

Augen gneiss (Early Mississippian to Late Devonian)—Inhomogeneous orthogneiss

dominated by light-gray, medium- to coarse-grained, strongly foliated 

biotite-muscovite augen gneiss with zones of relatively augen-free biotite gneiss 

of granodioritic to granitic bulk composition. Unit is characterized by lenticular 

augen made up of alkali feldspar porphyroclasts (as much as 5 cm in diameter) 

and quartz, feldspar, mica, and garnet mineral aggregates (amphibolite-grade) set 

in a medium-grained, foliated to granoblastic matrix of granodioritic composition. 

Anastomosing mica-rich shear bands separate zones of both equigranular matrix 

and augen into sigmoid-shaped zones (mesolithons). Dusel-Bacon and Aleinikoff 

(1985) described the regional geologic context for the unit and documented a 

porphyritic granitoid protolith. Dusel-Bacon and others (2006, and references 

therein; see their table 1) and Dusel-Bacon and Williams (2009) reported U-Pb 

zircon ages that range from 347 ± 5 Ma to 371 ± 3 Ma for compositionally and 

texturally similar bodies of augen gneiss in the USGS Big Delta and Tanacross 

1:250,000 quadrangles. Day and others (2003) reported a U-Pb zircon SHRIMP 

age of 365 ± 4 Ma (Late Devonian) for unit in the Big Delta (B–2) quadrangle, 

which lies approximately 80 km to the west of this study area. Aleinikoff and 

others (1981; their sample AG–5) reported K-Ar dates on muscovite of 113 ± 4 

Ma and on biotite of 110 ±4 Ma from Devonian augen gneiss in the Big Delta 

quadrangle, reflecting postmetamorphic cooling during the Early Cretaceous

Biotite orthogneiss (Late Devonian)—Predominantly light to medium gray, 

medium-grained, layered trondhjemitic to granodioritic orthogneiss with lesser 

amounts of biotite schist, quartzite, and paragneiss. Undated in the map area, but 

similar rocks in the Big Delta quadrangle yielded Late Devonian (367 ± 7 Ma) 

U-Pb SHRIMP dates on zircon cores (Day and others, 2007). That study also 

showed that U-Pb SHRIMP ages on zircon rims showed two populations: (1) an 

older group at 114 ± 2 Ma and (2), a younger group at 109 ± 2 Ma. The U-Pb 

SHRIMP data on zircons from the sample indicate that the protolith intrusion (or 

intrusive complex?) inherited zircons from a crustal source that was in part 

Precambrian, was emplaced during the Devonian, and was recrystallized twice 

during pulses of regional Cretaceous tectonism at ~114 Ma and at ~109 Ma. The 

younger age is coeval with the Early Cretaceous intrusions in the western 

Fortymile district mapped in this study (Kgc) 

Quartzite-rich metasediments, undivided (middle Paleozoic or older)— 

Predominantly light gray, fine-grained, laminated micaceous quartzite with lesser 

amounts of dark green micaceous layers of metamorphosed shale, amphibolite, 

micaceous schist, metagraywacke, and minor metapelite. Interlayered with white 

to light-gray marble (m). Section exposed on western part of map area 

progresses up structural section (west to east) and seemingly forms an upward 

coarsening sequence from micaceous schist and metagraywacke up through dark 

green phyllite, argillite, light gray to white, medium-grained platy, and laminated 

quartzite; to light gray cherty marble, laminated, white to light gray fine-grained 

quartzite; to light gray thinly bedded marble; to tan to light brown fine-grained, 

platy micaceous quartzite interlayered with massive marble. Metamorphic grade 

is uppermost greenschist facies to lower amphibolite facies. Protolith was 

sequence of sandstone with variable clay content, mudstone, graywacke, locally 

mafic (tuff?) interlayers, and limestone horizons in a relatively shallow, 

near-shore environment

Marble (Paleozoic)—Light gray marble with thin (cm-thick) metachert lenses. Unit 

forms discontinuous beds in a predominantly siliciclastic sequence (q) and 

undivided metasedimentary rocks (ms). Unit is more massive in the northern 

part of the map area, whereas marble layers become more interlayered with 

micaceous units farther south. Age is unknown. Fossils in the region are extremely 

rare and include only the possible Mississippian conodont occurrence described 

above for unit mv and Late Mississippian to Early Permian conodonts from 

marble in the Fortymile River assemblage in the southeastern Eagle quadrangle 

(Dusel-Bacon and Harris, 2003). Alternatively, the unit may predate Early 

Mississippian orthogneiss that intrudes a similar marble-bearing sequence 

(Fortymile River assemblage) in the eastern Eagle quadrangle (Day and others, 

2002; Dusel-Bacon and others, 2006), and (or) the Late Devonian to Early 

Mississippian age of the augen gneiss and orthogneiss in the southwestern edge 

of the map area

Quartzite and mafic volcaniclastic metasediment, undivided (pre-Late Devonian)—

Light gray fine-grained micaceous quartzite intermixed with dark green layers of 

mafic metavolcanic to volcaniclastic metasedimentary rocks and biotite schist. 

Protolith thought to be mixture of siliciclastic sedimentary units interspersed with 

volcaniclastic sediments predominantly of mafic composition. Age uncertain but 

a pre-Late Devonian age is based on the interpretation that this unit is intruded by 

unit Dog of assumed Late Devonian age

Ultramafic (late to middle Paleozoic)—Light brown to dark green, coarse-grained, 

massive, non-foliated, weakly serpentinized metaharzburgite that forms approximately 200-m-wide body located within the metamorphosed mafic sequence 

(am). Uncertain if protolith of ultramafic unit was coeval with protoliths of 

adjacent metamorphosed mafic rocks (am) or, as proposed in Dusel-Bacon and 

others (2013), is a tectonic sliver emplaced during late Paleozoic or Mesozoic 

tectonism. Metaharzburgite is identical in composition and texture to partially 

serpentinized harzburgite in other parts of the Eagle quadrangle that are interpreted

as alpine-type peridotites derived from the mantle and part of the Seventymile 

terrane (Group II of Foster and Keith, 1974; Foster and others, 1994)

Amphibolite and metagabbro, undivided (middle Paleozoic or older)—Dark 

green, fine- to medium-grained strongly foliated to gneissic amphibolite and 

metagabbro commonly interlayered with biotite schist, dark gray siliciclastic 

metasedimentary rocks and foliated, medium-grained leucogranite, granite and 

tonalite (Jt). Textures indicating primary depositional environment have been 

obliterated during regional Mesozoic ductile deformation; pillow structures not 

observed. Protolith was basalt and gabbro interlayered with argillaceous 

siliciclastic sediments. Unit occurs west of the main Mount Veta ridge and 

becomes more common in southwestern part of map area. Northeastward along 

structural trend, the unit is interlayered with the metasedimentary sequence 

suggesting paleoenvironment was dominated by an emergent mafic volcanic 

sequence in the south that graded into a near-shore sedimentary sequence (q) to 

the north of exposed area

Metasediments, undivided—(middle Paleozoic or older)—Predominantly 

metapelite and argillite with lesser amounts of quartzite, graywacke, greenstone 

and sand-rich marble horizons intermixed with volcaniclastic metasedimentary 

rocks. Interlayered with white to light-gray marble (m). Differs from map unit 

q exposed to the west of the Kechumstuk fault in that unit contains less 

quartzite. Metamorphic grade is uppermost greenschist. Protolith was sequence 

of mudstone, shale, and graywacke with interlayers of sandstone and volcaniclastic

sediments. Regional relations suggest unit was deposited on the continental 

margin of North America during the early Paleozoic (Dusel-Bacon and others, 

2006)

Qa

Qls

Qs

Qc

Qf

Kgu

Kgkc

Kr

Kgvc

Kggp

Kgg

Kdm

Jmig

Jgmv

Jt

Kgc

Kqfp

mh

g

mv

MDag

Dog

q

m

qm

um

am

ms

Tb

CORRELATION OF MAP UNITS

Intrusive contact

Intrusive contact

Faulted contact 

PALEOZOIC AND OLDER

METAMORPHIC ROCKS

LATE TRIASSIC IGNEOUS ROCK

EARLY JURASSIC IGNEOUS ROCKS

LATE CRETACEOUS IGNEOUS ROCKS

TERTIARY IGNEOUS ROCK

QUATERNARY SURFICIAL DEPOSITS

Intrusive contact

Intrusive contact

Intrusive contact

EARLY CRETACEOUS

IGNEOUS ROCKS

Intrusive contact

Late Triassic

Early

Cretaceous

Late Cretaceous

Holocene

MISSISSIPPIAN

AND OLDER

TRIASSIC

CRETACEOUS

TERTIARY

QUATERNARY

Early Jurassic JURASSIC

Early Mississippian

to Late Devonian

Middle Mississippian

(or older)

Alluvial

and fluvial

deposits

Landslide

deposits

Solifluction

deposits Young alluvial fan

deposits

Colluvium

CRETACEOUS 

IGNEOUS

ROCK

Qa Qls Qs Qf Qc

Tb

Kgkc Kggp

Kgg

Kr Kgvc

Jmig Jgmv

Kgc

Kqfp

Kgu

Kdm

Jt

mh

Dog

MDag

qm

g

m

mv

q

m

ms

am

um

m

EARLY JURASSIC

AND OLDER

METAMORPHIC

ROCK 

?

?

?

?

EXPLANATION

Alteration zone—Silicification and iron oxide staining due to alteration of

mafic, iron oxide, and sulfide minerals producing red to ochre staining

Shear zone—Broad zone of interleaved faulting, fracturing, and brittle

cataclastic deformation of adjacent geologic units

Contact—Dashed where inferred, dotted where concealed

Fault—Dashed where inferred, dotted where concealed

Normal fault—Dashed where inferred, dotted where concealed; bar and ball on 

downthrown block

Thrust fault—Dashed where inferred; sawteeth on upthrown block

Strike-slip fault—Dashed where inferred, dotted where concealed; arrows show 

direction of apparent lateral displacment (left-lateral offset). In cross section, A

indicates movement away from observer; T indicates movement toward observer

Antiform—Showing trace of axial surface; dotted where concealed

Synform—Showing trace of axial surface; dotted where concealed

Foliation

Inclined—Showing strike and dip. May also be combined with lineation symbol,

showing bearing and plunge

Vertical—Showing strike

Sample location—Location with sample number and new SHRIMP U-Pb zircon 

ages. See table 1

Prospect—With name. Some prospects may also have drill holes. Little

Enchilada

22 15

108.8

±1.7 Ma 9

REFERENCES CITED

Aleinikoff, J.N., Dusel-Bacon, Cynthia, Foster, H.L., and Futa, Kiyoto, 1981, Proterozoic zircon 

from augen gneiss, Yukon-Tanana Upland, east-central Alaska: Geology, v. 9, p. 469–473.

Bacon, C.R., Dusel-Bacon, Cynthia, Aleinikoff, J.N., and Slack, J.F., 2012, Late Cretaceous Middle 

Fork caldera and its resurgent intrusion, east-central Alaska [abs.]: Geological Association of Canada, 

Mineralogical Association of Canada Joint Annual Meeting, St. John's, Newfoundland, v. 35, p. 6, 

http://www.stjohns2012.ca/gac/wp-content/uploads/2012/05/StJohns2012_GAC-MAC_Abstracts.pdf.

Bacon, C.R., and Lanphere, M.A., 1996, Late Cretaceous age of the Middle Fork caldera, Eagle 

quadrangle, east-central Alaska, in Moore, T.E., and Dumoulin, J.A., eds., Geologic studies in 

Alaska by the U.S. Geological Survey, 1994: U.S. Geological Survey Bulletin 2152, p. 143–147.

Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, J.N., Valley, J.W., Mundil, R.M., 

Campbell, I.H., Korsuch, R.J., Williams, I.S., and Foudoulis, Chris, 2004, Improved 206Pb/238U 

microprobe geochronology by the monitoring of a trace-element-related matrix 

effect—SHRIMP, ID–TIMS, ELA–ICP–MS and oxygen isotope documentation for a series of 

zircon standards: Chemical Geology, v. 205, p. 115–140.

Day, W.C., Aleinikoff, J.N., and Gamble, B.M., 2002, Geochemistry and age constraints on 

metamorphism and deformation in the Fortymile River area, eastern Yukon-Tanana Upland, 

Alaska, in Wilson, F.H., and Galloway, J.P., eds., Studies by the U.S. Geological Survey in 

Alaska, 2000: U.S. Geological Survey Professional Paper 1662, p. 5–18.

Day, W.C., Aleinikoff, J.N., Roberts, Paul, Smith, Moira, Gamble, B.M., Henning, M.W., Gough, 

L.P., and Morath, L.C., 2003, Geologic map of the Big Delta B–2 quadrangle, east-central 

Alaska: U.S. Geological Survey Geologic Investigations Series I‒2788, scale 1:63,360.

Day, W.C., O’Neill, J.M., Aleinikoff, J.N., Green, G.N., Saltus, R.W., and Gough, L.P, 2007, 

Geologic map of the Big Delta B–1 quadrangle, east-central Alaska: U.S. Geological Survey 

Scientific Investigations Map 2975, scale 1:63,360. 

Day, W.C., O’Neill, J.M., Dusel-Bacon, Cynthia, Aleinikoff, J.N., and Saltus, R.W., 2010, Influence 

of geologic structures on mineral resources in the Yukon-Tanana Upland, Alaska [abs.], in

Geological Society of America Annual Meeting, Denver, Colo., Oct. 31–Nov. 3, 2010: 

Geological Society of America Abstracts with Programs , v. 42, p. 674.

Day, W.C., O’Neill, J.M., Dusel-Bacon, Cynthia, Aleinikoff, J.N., Saltus, R.W., McLeod, Rob, 

Lester, Cullan, and Siron, Christopher, 2009, Structural corridors in the Yukon-Tanana Upland, 

Alaska—A tool for understanding regional metallogeny in a concealed terrane [abs.], in

Northwest Mining Association 115th Annual Meeting, Exposition, and Short Courses, Sparks 

Nev., Nov. 30–Dec. 4, 2009: Northwest Mining Association, Nevada, Technical Session 

Abstract Book, p. 45‒46, C.

Dusel-Bacon, Cynthia, and Aleinikoff, J.N., 1985, Petrology and tectonic significance of augen 

gneiss from a belt of Mississippian granitoids in the Yukon-Tanana terrane, east-central 

Alaska: Geological Society of America Bulletin, v. 96, p. 411–425.

Dusel-Bacon, Cynthia, Aleinikoff, J.N., Day, W.C., O'Neill, J. M., Slack, J.F., and Wintzer, N.E., 

2009, Implications of new SHRIMP U-Pb zircon crystallization ages for the origin of 

carbonate replacement and skarn mineralization in the western Fortymile mining district, 

east-central Alaska [abs.]: Geological Society of America Abstracts with Programs, v. 41, no. 

7, p. 417.

Dusel-Bacon, Cynthia, Day, W.C., and Aleinikoff, J.N., 2013, Geochemistry, petrography, and 

zircon U-Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of 

east-central Alaska—Implications for the evolution of the westernmost part of the 

Yukon-Tanana terrane: Canadian Journal of Earth Sciences, v. 50, no. 8, p. 826–846.

Dusel-Bacon, Cynthia, and Harris, A.G., 2003, New occurrences of late Paleozoic and Triassic 

fossils from the Seventymile and Yukon-Tanana terranes, east-central Alaska, with comments 

on previously published occurrences in the same area, in Galloway, J.P., ed., Studies by the 

U.S. Geological Survey in Alaska, 2001: U.S. Geological Survey Professional Paper 1678, 

chap. 2, p. 6–25, 1 pl.

Dusel-Bacon, Cynthia, Hopkins, M.J., Mortensen, J.K., Dashevsky, S.S., Bressler, J.R., and Day, 

W.C., 2006, Paleozoic tectonic and metallogenic evolution of the pericratonic rocks of 

east-central Alaska and adjacent Yukon Territory, in Colpron, Maurice, and Nelson, J.L., eds., 

Paleozoic Evolution and Metallogeny of Pericratonic Terranes at the Ancient Pacific Margin of 

North America, Canadian and Alaskan Cordillera: Geological Association of Canada, Special 

Paper 45, p. 25–74.

Dusel-Bacon, Cynthia, Slack, J.F., Aleinikoff, J.N., and Mortensen, J.K., 2009, Mesozoic 

magmatism and base-metal mineralization in the Fortymile mining district, eastern 

Alaska—Initial results of petrographic, geochemical, and isotopic studies in the Mount Veta 

area, in Haeussler, P.J., and Galloway, J.P., eds., Studies by the U.S. Geological Survey in 

Alaska, 2007: U.S. Geological Survey Professional Paper 1760‒A, 42 p., 

http://pubs.usgs.gov/pp/1760/a/.

Dusel-Bacon, Cynthia, and Williams, I.S., 2009, Evidence for prolonged mid-Paleozoic plutonism 

and ages of crustal sources in east-central Alaska from SHRIMP U–Pb dating of 

syn-magmatic, inherited, and detrital zircon: Canadian Journal of Earth Sciences, v. 46, p. 21–39.

Foster, H.L., 1967, Geology of the Mount Fairplay area, Alaska—Contributions to General 

Geology: U.S. Geological Survey Bulletin 1241‒B, p. B1‒B18.

Foster, H.L., 1976, Geologic map of the Eagle quadrangle, Alaska: U.S. Geological Survey 

Miscellaneous Investigations Map I‒922, scale 1:250,000.

Foster, H.L., and Keith, T.E.C., 1974, Ultramafic rocks of the Eagle quadrangle, east-central 

Alaska: Journal of Research of the U.S. Geological Survey, v. 2, no. 6, p. 657‒669, 

http://pubs.usgs.gov/journal/1974/vol2issue6/report.pdf.

Foster, H.L., Keith, T.E.C., and Menzie, W.D., 1994, Geology of the Yukon-Tanana area of 

east-central Alaska, in Plafker, George, and Berg, H.C., eds., The geology of Alaska, v. G‒1, 

of The geology of North America: Boulder, Colo., Geological Society of America, p. 205‒240.

Geological Society of America, 2012, GSA Geologic time scale, ver. 4.0: Boulder, Colo., The 

Geological Society of America, Inc.

Ludwig, K.R., 2003, User’s manual for Isoplot/Ex version 2.00, a geochronological toolkit for 

Microsoft Excel: Berkeley, Calif., Berkeley Geochronology Center, Special Publication no. 1, 46 p.

Ludwig, K.R., 2009, Squid 2, version 2.50, A user's manual: Berkeley Geochronology Center, 

Special Publication, no. 5, 110 p.

Newberry, R.J., Layer, P.W., Burleigh, R.E., and Solie, D.N., 1998, New 40Ar/39Ar dates for 

intrusions and mineral prospects in the eastern Yukon-Tanana terrane, Alaska—Regional 

patterns and significance, in Gray, J.E., and Riehle, J.R., eds., Geologic studies in Alaska by 

the United States Geological Survey, 1996: U.S. Geological Survey Professional Paper 1595, 

p. 131–159.

Newberry, R.J., Layer, P.W., Solie, D.N., and Burleigh, R.E., 1995, Mesozoic-Tertiary igneous 

rocks of the eastern interior Alaska: Ages, compositions, and tectonic settings [abs.]: 

Geological Society of America Abstracts with Programs, v. 27, no. 5, p. 68.

Saltus, R.W., and Day, W.C., 2006, Gravity and aeromagnetic gradients within the Yukon-Tanana 

Upland, Black Mountain Tectonic Zone, Big Delta quadrangle, east-central Alaska: U.S. 

Geological Survey Open-File Report 2006‒1391, http://pubs.usgs.gov/of/2006/1391/.

Saunders, R.H., 1962, Report on the examination of the Mitchell copper prospect, Eagle Quadrangle: 

Alaska Division of Mines and Minerals Prospect Evaluation 60‒11. 4 p., 2 pl., scale 1 in. = 200 ft.

Siron, C.R., Hitzman, M.W., McLeod, Robert, Goldfarb, R.J., and Marsh, E.E., 2010, Geology of 

the Little Whiteman carbonate-hosted replacement Zn-Pb-Ag-(Cu) prospect, western Fortymile 

District, Alaska, in Goldfarb, R.J., Marsh, E.E., and Monecke, Thomas, eds., The challenge of 

finding new mineral resources—Global metallogeny, innovative exploration, and new discoveries: 

Society of Economic Geology Special Publication 15, v. II, p. 421‒436.

Werdon, M.B., Newberry, R.J., and Szumigala, D.J., 2001, Bedrock geologic map of the Eagle A–2 

quadrangle, Fortymile mining district, Alaska: Alaska Division of Geological and Geophysical 

Surveys Preliminary Interpretive Report 2001‒3B, scale: 1:63,360.

Wilson, F.H., Smith, J.G., and Shew, Nora, 1985, Review of radiometric data from the Yukon 

crystalline terrane, Alaska and Yukon territory: Canadian Journal of Earth Science, v. 22, p. 

525–537.

Yeend, W.E., 1996, Gold placers of the historical Fortymile River region, Alaska: U.S. Geological 

Survey Bulletin 2125, 75 p.

INTRODUCTION

The Kechumstuk fault zone is a northeast-trending zone of faults that transects the crystalline 

basement rocks of the Yukon-Tanana Upland located in the western part of the Fortymile mining 

district of east-central Alaska. The Kechumstuk zone, which is mapped in detail for the first time in 

this report, is one of numerous major northeast-trending zones of deformation that formed between 

the Denali fault on the south and the Tintina fault on the north (fig. 1). The Denali and Tintina are 

major right-lateral strike slip faults that form a regional dextral wrench zone that has deformed the 

intervening terrane. The northeast-trending systems of faults and lineaments (for example, the 

Shaw Creek fault, Black Mountain tectonic zone, Mount Harper lineament, and Kechumstuk fault 

zone) bound structural blocks tens of kilometers wide and hundreds of kilometers long that are 

displaced by left-lateral high-angle faults (Wilson and others, 1985; Saltus and Day, 2006; Day and 

others, 2007, 2009, 2010). Our new mapping and accompanying age dates demonstrate that the 

Kechumstuk fault zone was active at least since the earliest Late Cretaceous (Cenomanian), during 

which a series of about 96–94 Ma quartz-feldspar porphyry intrusions (Kqfp) were emplaced in the 

zone (Kqf). Subsequent brittle deformation has brecciated the mid-Cretaceous intrusions along the 

through-going fault. In the Black Mountain tectonic zone, approximately 50 km to the west in the 

U.S. Geological Survey (USGS) Big Delta (B–1) 1:63,360 quadrangle, Early and Late Cretaceous 

(about 109–95 Ma) igneous intrusions and associated gold mineralization were also localized along 

the northeast-trending structures. Locally, the fault scarps are seen in Quaternary deposits as well 

(Day and others, 2007) indicating Holocene displacment on some northeast-trending faults. As 

such, these major northeast-trending structural zones have a prolonged history that started in the 

mid-Cretaceous and lasted, at least locally, into the Holocene.

The map area lies in the Fortymile mining district in the Mount Veta area. The Fortymile 

mining district was one of the earliest placer-mining districts discovered in Alaska during the 

1896–1898 gold rush and has a long history of metals exploration, from placer gold (Yeend, 1996), 

to precious and base-metal load deposits (Saunders, 1962). Placer gold mining is still active in the 

region, especially near the town site of Chicken, Alaska. The study area is in the western part of 

the Fortymile mining district and hosts several epigenetic base- and precious-metal lode prospects 

(Dusel-Bacon, Aleinikoff, and others, 2009; Dusel-Bacon, Slack, and others, 2009). The prospects 

are spatially associated with Mesozoic intrusions and are hosted in Paleozoic carbonate horizons 

(m) and are of both replacement and skarn origin. The Little Whiteman prospect (LWM, 

northeast part of map area), one of the more important prospects that has received a lot of exploration attention (Siron and others, 2010), lies within the Kechumstuk fault zone. The age of mineralization is either coeval with the Early Jurassic quartz monzonite of Mount Veta or related to the 

Late Cretaceous igneous activity ubiquitous in the adjacent terrane. A comparison of lead isotope 

data using feldspars from dated Mesozoic intrusions and sulfides from mineral prospects suggests a 

Cretaceous age for mineralization (Dusel-Bacon, Aleinikoff, and others, 2009; Dusel-Bacon, Slack, 

and others, 2009).

Economic geology, geochronological, and petrologic studies associated with this mapping 

effort are focusing on the characterization of the mineral occurrences, their origin, and the regional 

evolution of the Mesozoic igneous intrusions and associated volcanism (Dusel-Bacon, Aleinikoff, 

and others, 2009; Dusel-Bacon, Slack, and others, 2009; Dusel-Bacon and others, 2013).

ACKNOWLEDGMENTS

This study was greatly aided by the field and logistical support provided by Full Metal 

Minerals, Ltd., Vancouver, B.C., Canada, and is gratefully acknowledged. The project was made 

possible through funding by the U.S. Geological Survey Mineral Resources Program under the 

Assessment Techniques for Concealed Mineral Resources Project. Donald S. Sweetkind and James 

Channing Cole (both of the USGS) provided critical and thorough reviews of the map and their 

insights and comments are greatly appreciated. The authors would also like to thank Carma San 

Juan (USGS) for preparing the geographic information system digital files.

Dog

Jt

Jt

Jt

Jt

Jt

Jt

Jt

Jt

Jt Jt

Jt Tb

Jt

g

Jt

Jt

Jt

Jt

Jt

Jt

Jt

Jgmv Jgmv Jgmv

Jgmv

Jgmv

Jgmv

Jmig

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jgmv

Jmig

Jmig

Jmig

Jmig

Jmig

Jmig

Jmig

Kdm

Kdm

Kdm

Kdm

Tb Kgc

Kgc

Kgc

Kgc

Kgc

Kgg

Kggp

Kgg

Kgg

Kgg

Kgg

Kggp

Kgkc

Kgu

Kgu

Kgu

Kgu

Kgu

Kgu

Kgu

Kgu

Kgu

Tb

Kgu

Kdm

Kgu

Kgu

Kgu

Kgu

Kgu

Kgu

Kgu

Kgu

Kgvc

Kgvc

Kgvc

Kgvc

Kqfp

Kr

Kqfp

Kqfp

Kqfp

Kqfp

Kqfp

Kqfp

Kqfp

Kqfp

Kqfp Kqfp

Kr

Kr

Kr

MDag

MDag

am

am

am

am

am

am

am

am

am

um

m

q q

q

q

q

q

q

m

m

m

m

m

m

m

m

mv

ms

ms

ms

ms

mv

mv

mv

mv

mv

mv

m

m

m

ms

mh

q

q

q

q

q

q

q

q

q

q q

q

qm

qm

qm

q

q

q

q

Qa

Qa Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Qc

Qc

Qc

Qc

Qc

Qs

Qs

Qc

Qc

Qc

Qc

Qls

Qls

Qc

Qc

Qc Qc

Qc

Qc

g

g

g

g g

g

g

g

g

g

g

g

g

g

g

g

Qc

Qc

Qc

Qc

Qf

Qf

Qf

Qf

Qc

Qc

Qc

Qc

Qc

Qc

Qc

Qc

Qc

Qc

Qc

Qc

Tb

Tb

Qf

Qf

Qf

Qf

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Qs

Kr

Kr

Kr

mh

1 .5 0 1 2 3 4 5 6 7 KILOMETERS

SCALE 1: 63 360

1 1/ 2 0 234 1 5 MILES

3000 0 3000 6000 9000 12000 15000 18000 21000 24000 27000 FEET

EAGLE

A–6 A–1 A–3 A–2

B–6 B–1 B–5 B–3 B–4 B–2

C–6 C–1 C–5 C–3 C–4 C–2

D–6 D–1 D–5 D–3 D–4 D–2

64°00’

64°30’

64°45’

65°00’

144°00’ 143°30’ 143°00’ 142°30’ 142°00’ 141°30’ 141°00’

64°15’

QUADRANGLE LOCATION

A–5 A–4

Base from U.S. Geological Survey Eagle (A–4) and Eagle (A–5), Alaska, 1956, scale 1:63,360

Universal Transverse Mercator projection, 1927 North American Datum (NAD 27)

10,000-foot grid based on Alaska coordinate system, zone 2

1000-meter Universal Transverse Mercator grid ticks, zone 7

Geologic mapping was carried out during the summers of 

2008–2010 by W.C. Day and J.M. O’Neill (USGS). Geologic 

mapping by C.R. Siron and others (Full Metal Minerals, Ltd., 

written commun., 2009) was incorporated for the area east of 

the Kechumstuk fault zone and north of Kechumstuk Creek.

Photographs by W.C. Day, unless otherwise noted.

ALASKA

CONTOUR INTERVAL 100 FEET MAP LOCATION

DOTTED LINES REPRESENT 50 FOOT CONTOURS

NATIONAL GEODETIC VERTICAL DATUM OF 1929 (EAGLE A–5 QUADRANGLE)

DATUM IS MEAN SEA LEVEL (EAGLE A–4 QUADRANGLE)

APPROXIMATE MEAN

DECLINATION, 2010 TRUE NORTH

MAGNETIC NORTH

22°

34

20

2

20

30

45

12

25

21

35

38

35

36

15

42

44

58

32

20

22

42 30

25

22

42

20

20

20

20

36

33

32

42

24 43

24

53

38

42 18

46

8

52

28 15

48 35

30 42

12

22

22 15

18

38

32

34

25

40

44

25

25

28 30

32 0

28

12 15

40

22 15

15

28

28 13

33

30

16

49

65

25

27

28

20

49

43

42

60

55

68

46

42

A

A'

Any use of trade, firm, or product names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this information product, for the most part, is in the public domain, it also contains 

copyrighted materials as noted in the text. Permission to reproduce copyrighted items must 

be secured from the copyright owner.

This database, identified as SIM 3291, has been approved for release and publication by the 

U.S. Geological Survey (USGS). Although this database has been subjected to rigorous 

review and is substantially complete, the USGS reserves the right to revise the data 

pursuant to further analysis and review. Furthermore, it is released on condition that neither 

the USGS nor the U.S. Government may be held liable for any damages resulting from its 

authorized or unauthorized use.

For more information concerning this publication, contact:

Center Director, USGS Central Mineral and Environmental Resources Science Center

Box 25046, Mail Stop 973

Denver, CO 80225

(303) 236-1562

Or visit the Central Mineral and Environmental Resources

Science Center Web site at:

http://minerals.cr.usgs.gov/

Publishing support provided by: 

Denver Publishing Service Center

Edit and digital layout by L.J. Binder

Manuscript approved for publication Feb. 20, 2014

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This report is available at:

http://pubs.usgs.gov/sim/3291

Suggested citation: Day, W.C., O’Neill, J.M., Dusel-Bacon, Cynthia, Aleinikoff, J.N., 

and Siron, C.R., 2014, Geologic map of the Kechumstuk fault zone in the Mount 

Veta area, Fortymile mining district, east-central Alaska (ver. 1.1, March 12, 2014): 

U.S. Geological Survey Scientific Investigations Map 3291, scale 1:63,360,

http://dx.doi.org/10.3133/sim3291. 

ISSN 2329-132X (online)

http://dx.doi.10.3133/sim3291

65.8

± 1.5 Ma

67.9 ±1.1 Ma

65.8

± 1.4 Ma

181.2

± 2.6 Ma

183.4

± 3.6 Ma

332.6

± 5.7 Ma

190.5 ± 4.8 Ma

215.5 ± 3.4 Ma

184.8

± 2.9 Ma

68.1

± 0.8 Ma

215.0

± 3.5 Ma

93.9±

1.3 Ma

184.5

±3.0 Ma

95.8

108.8 ± 1.5 Ma

± 1.7 Ma

111.8 ± 1.5 Ma

−

<~65 Ma

Geologic Map of the Kechumstuk Fault Zone in the Mount Veta Area, Fortymile Mining District, East-Central Alaska

By

Warren C. Day,1

 J. Michael O’Neill,1 Cynthia Dusel-Bacon,1 John N. Aleinikoff,1 and Christopher R. Siron2

2014 1

U.S. Geological Survey

2

Full Metal Minerals, Ltd., Vancouver B.C., Canada

CONVERSION FACTORS

Multiply By To obtain

inches (in.)

inches (in.)

0.3937

0.03937

3.281 feet (ft)

0.6214 mile (mi)

millimeters (mm)

centimeters (cm)

meters (m)

kilometers (km)

KECHUMSTUK

FAULT

FAULT

ZONE

ZONE

KECHUMSTUK

16

17

13

19

15

2

4

1

14

11

20

3

10

5

7

12

8

9

6

18

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3291

Version 1.1, March 12, 2014