TRENCHING AND SAMPLING

OF THE RHYOLITE MERCURY PROSPECT,

KUSKOKWIM RIVER BASIN, ALASKA

By Raymond P. Maloney

report of investigations 6141

,£

UNITED STATES DEPARTMENT OF THE INTERIOR

Stewart L. Udall, Secretary

BUREAU OF MINES

Marling J. Ankeny, Director
This publication has been cataloged as follows:

Maloney, Raymond P

Trenching and sampling of the rhyolite mercury prospect,

Kuskokwim River,Basin, Alaska. [Washington] U. S. Dept.

of the Interior, Bureau of Mines [19621

43 p. illus., maps, tables. 27 cm. (U. S. Bureau of Mines.

Report of investigations, 6141)

Bibliography: p. 27

1. Rhyolite. 2. Mercury. 1. Title. (Series)

TN23.U7 no. 6141 622.06173

U. S. Dept. of the Int. Library
CONTENTS

Page

Abstract ............................................................... 1

Introduction...............................1...........................

Acknowledgments................................................. 2

History........................................................ 2

Location and accessibility .................................. . 2

Physical features and climate . . ... 4

General geology................................................. 4

Description of the deposit ..................................... 5

Work by the Bureau of Mines ..... 15

Conclusions.................................................... 16

Bibliography................................................... 27

Appendix. - Log of trenches ................................. 28

ILLUSTRATIONS

Fig.

1. Index map of Alaska. . . 2

2. Location map, Rhyolite prospect. . . . 3

3. Geologic map of Rhyolite prospect area. . . . 6

4. Plan of trenches, Rhyolite prospect. . . . 7

5. Geologic map of trenches 1, 2, 8, and 9. . . . 9

6. Geologic map of trenches 3, 10, and 12 . . . . 10

7. Geologic map of trenches 4 to 8, 11, 13, and 14 .... 11

8. Geologic map of trenches 15 to 2... 12

9. Geologic map of trenches 22 to 25. . . 13

10. Plan of mineralized area in trench . . .. 14

11. Vertical sections of trench 1 .... 15

TABLES

1. Summary of trench sampling data .. 17

2. Petrographic analyses ...................................... 20

3. Spectrographic analyses...................................... 26
TRENCHING AND SAMPLING OF THE RHYOLITE MERCURY

PROSPECT, KUSKOKWIM RIVER BASIN, ALASKA

by

Raymond P. Maloney

ABSTRACT

The Rhyolite mercury prospect is on the south flank of Juninggulra

Mountain--a large rhyolite intrusive in the Kuskokwim River region about 36

airline miles northwest of Red Devil, Alaska. Bulldozer trenching by the

Bureau of Mines exposed bedrock at intervals in a 2,000- by 3,000-foot area

where previous prospecting by the owners had disclosed abundant float and

several in-place stringers containing cinnabar in widely varying amounts.

The additional trenching indicated that the mercury mineralization in the

limited area investigated was confined to erratically distributed short

stringers and to small lenses, occurring in discontinuous zones in numerous

silica-carbonate dikes and sills or along their altered contacts with sedimentary rocks. The geologic relationship of the mercury-bearing silica-carbonate

dikes and the nearby rhyolite intrusive is similar to that existing at several

other mercury mines and prospects in the Kuskokwim region. The depth of overburden and the presence of permafrost were serious obstacles to bulldozer

trenching, and only a comparatively small part of the mineralized area was thus

investigated.

INTRODUCTION

Reports by the Bureau of Mines and the Geological Survey (see bibliography

at the end of this report preceding the appendix) and records of gold-placer

operations indicate that mercury is widely distributed throughout the Kuskokwim

River Basin. Most early discoveries of mercury in the region were made in the

more accessible areas along the Kuskokwim River by prospectors searching for

placer gold. The Rhyolite prospect, however, was discovered as the result of

a deliberate search for mercury in an isolated area by prospectors familiar

with the geology of the mercury deposits. Preliminary work was limited to

shallow trenching. Further investigation was undertaken by the Bureau of

Mines to indicate the mercury resource potential of an undeveloped but geologically favorable area. This report describes the results of trenching and

sampling by the Bureau of Mines.

'Mine examination and exploration engineer, Alaska Office of Mineral Resources,

Region I, Juneau, Alaska.

Work on manuscript completed May 1962.
2

ACKNOWLEDGMENTS

Appreciation is expressed to Robert Lyman of Red Devil, Alaska, and to

Joe Struver of Moore Creek, Alaska, for information on the prospect.

HISTORY

In 1953, a few small stringers of cinnabar were found in rhyolite about

3 miles from Juninggulra Mountain. Robert Lyman and Joe Struver prospected

the area in 1956 and discovered the Rhyolite prospect; in 1957, they did some

bulldozer trenching and stream panning and dug numerous prospect pits with

hand tools. In 1958, the prospect was briefly examined by the Bureau, and

trenching operations were conducted during the summer and fall of 1959.

LOCATION AND ACCESSIBILITY

The Rhyolite prospect is on the south flank of Juninggulra Mountain in

the Kuskokwim River Basin at latitude 610 56' N. and longitude 1580 26' W.

It is 35 airline miles southwest of Flat and 36 airline miles northwest of

Red Devil (figs. 1 and 2).

0 200 400 600

0 / Scale, > Miles

FIGURE ACC 1. -

X~~~~~~~~~~~~ 

Index Map FAIRBANKS

X A N A D A

FIGURE 1. -Index Map of Alaska.
0 50 100 2 Nna

Scale, Miles

W 1580

W Modified from USGS map- N

FIGURE 2. - Location Map, Rhyolite Prospect. C~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~c-
4

There are no roads or trails in this uninhabited and isolated area.

Heavy equipment and supplies used on the project were tractor-freighted from

Flat before the spring breakup when the ground was frozen and snow covered.

An airstrip, suitable for the small, light planes used to bring in personnel

and small supplies was leveled by the Bureau.

Airfields suitable for large, multiengine planes are maintained at Flat

and at Red Devil; the Red Devil airfield serves the Red Devil mercury mine,

which, in 1962, was the largest lode mining operation in Alaska. Crooked Creek

and the DeCoursey Mountain mercury mine, 16 miles southeast and 9 miles north

of Juninggulra Mountain, respectively, have airstrips suitable for small,

single-engine planes.

River boats and large barges, operating on the Kuskokwim River from June

to about the last of September, bring heavy freight, fuel oil, and mining

equipment to a number of points along the river from Bethel, a port of ocean

freighters. Supplies and equipment could be tractor-freighted from Crooked

Creek during the summer months, but it is preferable that this be done before

the spring breakup when greater loads can be hauled on the frozen ground.

PHYSICAL FEATURES AND CLIMATE

The Kuskokwim Mountains in the vicinity of the Rhyolite prospect are low,

rolling hills and long, flat-topped ridges. Several isolated rhyolite intrusives have a distinctive dark color when seen from a distance because of a

cover of black lichen, which grows preferentially on the weathered rhyolite.

Juninggulra Mountain, the site of the Rhyolite prospect, is one of the larger

of these rhyolite intrusives; it has an altitude of about 1,200 feet. The

north flank of the Horn Mountains, an isolated group with a maximum altitude

of 3,600 feet, is a few miles to the south.

Frozen overburden (permafrost), from 5 to 16 feet or more in depth,

covers most of the area. Bedrock exposures are few, and they are generally

near the crest of the ridges and hills. The lower slopes are covered with

brush, dense growths of spruce, and some birch. Few trees reach 18 inches in

diameter, and most are less than 12 inches in diameter. Spruce trees, only 3

to 4 inches in diameter, have from 50 to 100 growth rings. Dense, almost

impenetrable alder thickets are found along the creekbeds.

Winters are long and cold, and the summers are short and comparatively

warm. Precipitation is probably less than 20 inches per year. Permafrost is

encountered in most of the area.

GENERAL GEOLOGY

The geology of the area has been mapped and described on a reconnaissance

basis by Cady and others (2).2 The following general description of the geology of the area is summarized from their reports.

2 Underlined numbers in parentheses refer to items in the bibliography at the

end of this report preceding the appendix. Page references refer to pages

in the items and not to pages in this report.
5

Most of the area is underlain by an extremely thick sequence (40,000 to

65,000 feet) of Cretaceous sedimentary rocks known as the Kuskokwim group.

They are primarily interbedded shales and graywackes, with some sandstone,

tuff, and conglomerate. Unconsolidated residual deposits and tuff, basalt

flows, and rhyolite lava of Tertiary age form the north slope of the Horn

Mountains and cover the contact between the Tertiary quartz monzonite stock of

these mountains and the sedimentary beds.

Both extrusive and intrusive Tertiary rhyolite occur in the area. The

rhyolite found on the north flank of the Horn Mountains is composed largely of

tuff with some lava and is classified as an extrusive. The albite rholite at

Juninggulra Mountain is classified as an intrusive and probably is hypabyssal;

it occurs in sheets, sills, and dikes.

The basalt, found along the periphery of the Horn Mountains, is classified as a flow rock and probably is younger than the rhyolites, whereas the

biotite basalt, of which dikes and sills are found at the Rhyolite prospect,

is classified as a hypabyssal intrusive and probably is older than the

rhyolites. This biotite basalt alters to a silica-carbonate, commonly associated with mercury mineralization.

DESCRIPTION OF THE DEPOSIT

Mercury occurrences in this section of the Kuskokwim River Basin have a

similar geologic relationship. Cinnabar usually is associated with basalt

dikes and sills, hydrothermally altered to silica-carbonate rock; only minor

amounts have been found in the numerous albite-rhyolite intrusives of the

basin. Cady and others (2), Webber and others (9), Rutledge (7), and Smith

and Madden (8) describe in detail other known occurrences of mercury in the

Kuskokwim River Basin.

From 5 to 16 feet of frozen overburden, composed mainly of clastic material, conceals most of the bedrock at the Rhyolite prospect; the crest and

steeper slopes of Juninggulra Mountain are partially covered by a loose,

barren mantle of broken and weathered rhyolite. Interbedded shale, sandstone,

graywacke, and tuff, intruded by basalt, silica-carbonate (altered basalt),

and rhyolite, occur in the immediate area (fig.3);(2, pp. 50-54, 69, 78-80).

Bedrock observation at the prospect was limited to that exposed in

trenches excavated within a 2,000- by 3,000-foot area (fig. 4). Here a number of silica-carbonate dikes and sills intrude sedimentary beds, which dip

about 800 N. and strike about N. 70° E. Only minor faulting of the dikes and

sills was evident, and intrusion probably occured after the uplift of the

sedimentary beds; offsets and abrupt endings of these intrusives were common,

resulting in disconnected and erratically placed segments. Dike widths varied

from a few inches to over 50 feet, but the thickness of the sills was not

determined except in trench 1, where one sill was found to be about 10

feet thick. Alteration to silica-carbonate was generally complete; many of

the dikes and sills were weathered to a yellow-brown color, whereas others had

the fresh light-gray color of unweathered material. Both weathered and

unweathered silica-carbonate were found in all parts of the trenched area.
LEGEND

X = Shale or overburden

, a' mBasalt EV 

I Tuft

\~~~~~~~~~~ ~ ~ ~ ~ ~ \7'_ ~~~~~~~~~~~~~~~~~~ i-3 Tuf f

FIGURE 3. - Geologic Map of Rhyolite Prospect Area.
0~~~~~~~~~~~~~~~~~~~~~

0 8°X°

0~~~~~~~~~~~~~~~~~~~~

'4-N 5i500

N 5,0O0

260 N 4,500

- [5 t < < 07 ~~~~~~~~~~~~~~N 4,000

N 3,500

5________________ N 3.000

LEGEND

43 Trench

_ _ _ _ _ _N 2,500

0 200 400 600 800 000

Scale in Feet Pln of___________Pos e t

FIGURE 4. -Plan of Trenches, Rhyolite Prospect.
8

Mercury mineralization was introduced as cinnabar in the silica-carbonate

dikes and sills and in much lesser amounts in the adjacent, altered sedimentary rocks; the degree of weathering of the silica-carbonate had no connection with the amount of mineralization. Neither altered nor unaltered basalt

intruded the rhyolite in the exposed areas.

Cinnabar was found in 15 places in the bedrock exposed by trenching

(figs. 5 through 9). Occurrences were small and erratic--generally as small

lenses or as 1/4- to 1/2-inch wide, high-grade stringers, several feet or

less in length. All were associated with silica-carbonate dikes and sills,

occurring within them or at the contact with the sedimentary beds.

Occasionally, a few feet of the adjoining sedimentary rocks, if altered,

were mineralized; where this occurred, cinnabar was in small erratic lenses

and blebs. Sometimes there was very little alteration of the adjoining sedimentary beds by the silica-carbonate; if there was no alteration, there usually

was no cinnabar in the silica-carbonate nor in the sedimentary rock. Mercury

mineralization was not found in unaltered sedimentary beds, and only trace

amounts were found in the rhyolite. A white, puttylike kaolin mineral (probably dickite) was often present in small amounts where cinnabar occurred,

although it was not a positive indication of cinnabar as it sometimes occurred

alone in the silica-carbonate. Only trace amounts of antimony and arsenic

occur with the cinnabar; the only antimony found on the prospect was one small

piece of float stibnite near the top of Juninggulra Mountain.

The strongest and topographically highest occurrence of mercury mineralization was found in trench 1 (figs. 4, 5, 10, and 11) at an altitude of

approximately 670 feet. The lowest occurrence was at an altitude of 430 feet,

in trench 17, in the southern end of the area investigated. In trench 1,

cinnabar occurs in small lenses and stringers in a silica-carbonate sill

8 to 10 feet thick, dipping about 150 N., and lying on top of the upturned

shale. This sill is near the shale-rhyolite contact and dips toward the

rhyolite; it may contact the rhyolite. Minor amounts of cinnabar occurred in

the adjoining shale but were confined to an altered zone only several feet

wide. No mineralization was found at the contact between the bottom of the

sill and the shale. The mineralized area exposed by trenching is about 140

by 20 feet, but its exact size is not known owing to excessive overburden on

the steep hillside. An attempt to further outline the area with 2-inch

auger holes (fig. 5) was not successful. Only a trace of cinnabar was found

in one other silica-carbonate exposure in trench 1. An estimate made from

channel samples taken in this 140- by 20-foot zone indicates a mercury content of about 2 pounds per ton.

A high-grade vein of cinnabar, 2 to 4 inches wide and 10 feet long,

occurs in trench 7 (fig. 7) at the contact between a silica-carbonate sheet

(or dike) and shale. The shale side of the contact was slickensided, showing

postmineral movement. The strike of the vein was N. 70° W., and the dip was

vertical; excavation indicated that it ended at the bottom of the silicacarbonate sill or at the shale contact, thus limiting the vertical depth of

the vein to 6 to 7 feet.
o 0 0 0

10 ID 0rq(

AH-2 w w ~~~~~~~~~~LEGEND

0 N 46001 _ AH-6 _H-12 A = Silica -carbonate 12 N 4,600 AAHI26A-11

oAA-5 70 92 88 AH-9 E Sandstone 0A- 17 OAH-10 0 8

AH-4 16 0 89 Shale 0

14 V6 (Hgs) 26 Sample number

AH-1 15 10 AH-7 ~~~~~~~~~~~~~~~(HgS) Visible trace of cinnabar,

19 tAR-I g Xno sample

20 AH-6

+~~~~ ~ ~ ~~~~~ ~ 2 Auge hole odsapl N 4,400- (HgS) ~ ~ ~~~~~~~~~~~~17 number

TO~~~~~~~~~~.

C ~~~~~~~~~~~~~~~~~~~~

N 4,200- -____

0 50 00 200 300

Scole in Feet

FIGURE 5.- Geologic Map of Trenches 1, 2, 8, and 9.
o o 0 o 0 0

LEGEND Z i

Rhyolite

Silica -carbonate _ A .; N 4,000

3iii Sandstone

m Shale i

81 Sample I

5-T Strikeond dip of c bedding

XN 3,800

0 50 100 20030

Scale In Feet

FIGURE 6. - Geologic Map of Trenches 3, 10, and 12.
LEGEND

Rhyolite \\

#+I- Silica - carbonate

mui: Sandstone A z Shale OD

77 Sample N4,00

8(HgS) Sample with visible cinnabar m

C9D- Strike and dip of bedding

- Strike of vertical bed

N 4,000

0p°

N SoO 600-ga

0 0 ~~~~~~~~~~~~~0

AC~~ 0 e~ It ~ ~ ~~~~~~~~~~~~~~~~~~~~~~~~~

76 0 50 100 200 300

Scale in Feet

FIGURE 7. -Geologic Map of Trenches 4 to 8, 11, 13, and 14.
o 0 0 o 0 0

^ ~~~~~~~~~~~~Trench 20' ,,/

N 2,400 l | _ N 2,000

690C)~~~~~~~~~~~~

Scale~ ~ ~~~~~~~~~~~~~~- ~ ~ an)ee N 2,200 Silica-carbonate LEGEND A

~J Sandstone

Shale

70 Sample

69(HgS) Sample with visible cinnabar

0 100 200 300N200

Scale in Feet

FIGURE 8. - Geologic Map of Trenches 15 to 21.
o 0 o 0 0

LEGEND l- le

A Rhyolite _ _ = 21

Silica-carbonate i o

3Sandstone (~_~__v/~

3 Shale <1 ~ O ~ _ \ \ Alp rJ

82 Sample l

\ \ N 5,200

Tre8

N 5,000

w1~ 5- / 0 50 00 ISO 200 250

// / SScale in Feet

FIGURE 9. - Geologic Map of Trenches 22 to 25.
tt/t//t t~~ 74 +j/////%

(} go 2 ~~~~~~~~~~~~~~~~Shale

m Altered shale

"±+ Altered shale S silica carbonate

tE Silica carbonate

0 5 10 20 30 } 47 Channel sample

Scale in Feet _4 46 Channel sample on vertical wall

x5 Grab sample

NOTE: Samples 26 to 32 (not shown) are specimen samples

FIGURE 10. - Plan of Mineralized Area in Trench 1. 34 + + + 56+ + 8 ++ -f +t
15

0 5 10 20 30

Scale in Feet

_ ~~~~~~Surface

SECTION A-A

LEGEND 0

Overburden+ t

3Silica carbonate +

m Shale t + + -F , + * 14/41 ~ ~ ~ ~ ~ ~ 4

Altered shale a silica carbonate X /t-

)40 Channel sample on trench wall -V////t//A//

SECTION B-B

FIGURE 11. - Vertical Sections of Trench 1.

A silica-carbonate dike containing cinnabar was exposed in trench 17

(fig. 8), where, in an area about 4 to 6 feet, the mineral was erratically

disseminated in small lenses and blebs. Mineralization was localized in this

small area and had a depth of only a few feet.

The other occurrences were in small stringers and lenses; the best were

in trench 16 (fig. 8); however, none were large, and most were only a single,

short stringer of erratic mineralization.

The walls of the trenches were panned, and many show small to trace

amounts of very fine cinnabar in particles one-sixteenth of an inch or less

in diameter. A 12- by 12-inch piece of silica-carbonate float, containing

considerable cinnabar, was found in trench 11; such float is very hard to

detect during bulldozing operations and can be easily overlooked.

WORK BY THE BUREAU OF MINES

Twenty-six bulldozer trenches, 12.5 feet wide and totaling 7,326 linear

feet, were excavated to bedrock Ninety-two samples, mostly channel, were
16

taken, and twelve 2-inch auger holes, averaging about 12 feet in depth, were

hand-drilled to bedrock. Two airstrips, necessary because of crosswinds, were

leveled with the bulldozer; one was 1,000 feet long, and the other, 800 feet

long.

Permafrost was encountered in all trenches, and in some places, continued to bedrock. The maximum depth of overburden and permafrost encountered

was 16 feet; the average depth of both was about 10 feet. The trenches at the

south end of the project averaged about 8 feet, and the permafrost, about 4 to

5 feet. Large ice lenses were often encountered a few feet below the surface,

which added to the difficulties in trenching and particularly in moving the

bulldozer.

Chemical, petrographic, and spectrographic analyses are in tables 1, 2,

and 3, and the log of the trenches is in the appendix at the end of this

report.

CONCLUSIONS

The geology of this virtually unprospected area is that usually associated with mercury mineralization in other parts of the Kuskokwim River Basin.

Numerous dikes and sills, associated with a rhyolite intrusive and largely

altered to silica-carbonate, were exposed by the bulldozer trenches. Some of

the highly altered dikes and sills were mercury bearing; few, if any, had

recognizable surface expression. The Rhyolite prospect occupies only a small

segment on the periphery of the large Juninggulra Mountain intrusive, which,

in turn, is only one of the several rhyolite intrusives in the area.

Permafrost makes trenching difficult and costly, because several trenches

have to be started at the same time to facilitate thawing; hence, considerable

work is done before any bedrock is exposed, and this often results in poor

location of trenches. The use of portable augers, drills, or some other

method of rapid subsurface reconnaissance would be desirable as an aid in

placing bulldozer trenches in the most favorable locations.
17

TABLE 1. - Summary of trench sampling data

Interval

Sample Trench or Description Analyses. percent

location, Hg Sb As

__ _feet

1 3 17 to 25 Type specimen of silica- <0.02 - _

carbonate sill.

4 4 97 to 123 Type specimen of silica- .05 - _

carbonate intrusive.

5 4 140 to 147 Type specimen of small basalt < .02 - -

inclusions in sandstone.

8 5 2 to 17 Silica-carbonate with trace .34 <0.05 0.01

of cinnabar; sample is

picked specimen of best

mineralization.

99 6 18 to 57 Small inclusions of rhyolite <.02 - -

in shale.

11 1 Hole 1 Auger hole in sandstone <.02 - -

near west end trench 1.

12 1 Hole 2 Auger hole in shale near <.02 - -

west end trench 1.

13 1 Hole 3 Auger hole in rhyolite <.02 - -

near west end trench 1.

14 1 Hole 4 Auger hole in shale near <.02 - -

west end trench 1.

16 1 Hole 5 Auger hole in sandstone near <.02 - -

west end trench 1.

17 1 Hole 6 Auger hole in graywacke near <.02 - -

west end trench 1.

19 1 Hole 7 Auger hole in sandstone near <.02 - -

west end trench 1.

20 1 Hole 8 Auger hole in shale near west <.02 - -

end trench 1.

21 Stibnite float near airstrip. .08 66.3 <.05

22 11 520 Silica-carbonate with small .04 - -

amount of cinnabar.

23 13 100 to 126 do. <.02 - -

24 11 522 to 552 Type specimen of silica- <.02 - -

carbonate.

25 11 615 to 630 Type specimen of silica- <.02 - -

carbonate dike.

26 1 60 Specimen of silica-carbonate 1.70 <.05 .06

sill and cinnabar.

27 1 50 do. .68 <.05 <.01

28 1 60 Specimen of altered shale .23 <.05 <.01

and cinnabar.

29 1 60 do. .43 <.05 <.-01

30 1 65 Specimen of silica-carbonate 2.13 <.05 .01

sill and cinnabar.
18

TABLE 1. - Summary of trench sampling data (Con.)

Interval

Sample Trench or Description Analyses, percent

location, Hg Sb As

feet _

31 1 70 Specimen of silica-carbonate 0.10 - -

sill and cinnabar.

32 1 70 do. 1.25 <0.05 0.02

33 1 37 Wall of silica-carbonate sill, .09 - -

2 feet high.

34 1 37 Wall of silica-carbonate sill, .09 - -

4 feet high.

35 1 47 Trench wall, 7 feet of silica- .08 - -

carbonate sill.

36 1 47 4 feet of silica-carbonate .10 - -

sill.

37 1 47 5-foot cross section of .18 - -

silica-carbonate sill.

38 1 47 6 feet of sill and altered .14 - -

shale.

39 1 47 5 feet of shale. .10 - -

40 1 57 Trench wall, 8 feet of silica- .21 - -

carbonate sill.

41 1 57 8 feet of silica-carbonate .41 <.05 .01

sill.

42 1 57 4-foot cross section of .40 <.05 .01

silica-carbonate sill.

43 1 57 10 feet of sill and altered .45 <.05 .02

shale.

44 1 67 Trench wall, 7 feet of silica- .02 <.05 <.01

carbonate.

45 1 67 8 feet of silica-carbonate .05 - _

sill.

46 1 67 7-foot cross section of .21 - -

silica-carbonate sill.

47 1 67 4 feet of altered shale, minor .09 - -

amount of sill.

48 1 77 Trench wall, 7 feet of silica- .03 - -

carbonate.

49 1 77 5 feet of silica-carbonate < .02 - -

sill.

50 1 77 8 feet of shale. .07 - -

51 1 77 10 feet of shale. .04 - -

52 1 67 to 77 Shale, grab sample. .04 - -

53 1 57 to 67 Shale, silica-carbonate, grab .13 - -

sample.

54 1 87 Trench wall, 6 feet of silica- <.02 - -

carbonate.
19

TABLE 1. - Summary of trench sampling data (Con.)

Interval

Sample Trench or Description Analyses. Percent

location, Hg Sb As

feet

55 1 97 Trench wall, 5 feet of <0.02 - -

silica-carbonate.

56 1 87 10 feet of silica-carbonate < .02 - -

sill.

57 1 87 8 feet altered shale. .02 - -

58 1 97 10 feet of silica-carbonate .05 - -

sill.

59 1 107 Trench wall, 4.5-foot .10 - -

silica-carbonate.

60 1 97 6 feet, shale and .15 - -

silica-carbonate.

60T 7 (See High-grade vein cinnabar, 54.0 <0.05 <0.01

fig. 7) 4 inches wide in trench 7.

61 1 107 10 feet silica-carbonate. .02 - -

62 1 117 4 feet silica-carbonate. .06 -_

63 17 52 to 76 Small piece of cinnabar in 1.49 <.05 <.01

silica-carbonate dike.

64 17 52 to 76 Type specimen of above dike. <.02 <.05 <.02

65 17 255 to 269 Type specimen of fault gouge. .02 - -

66 17 271 to 276 18-inch-wide zone of erratic 2.99 <.05 <.01

cinnabar in silica-carbonate

dike.

67 17 297 to 371 Type specimen of fault gouge < .02 - -

in section containing gouge,

shale, and silica-carbonate

fragments.

69 15 350 to 357 Sample of 1/4-inch or less 3.75 <.05 <.01

stringers of cinnabar,

exposed in silica-carbonate

sill.

70 15 356 to 357 Rusty-red, altered shale. .27 - _

71 16 71 to 73 Type specimen of best cinna- 3.98 <.05 <.01

bar in silica-carbonate

dike.

72 16 71 to 73 Weathered brown portion of .82 <.05 <.01

silica-carbonate dike.

73 16 71 to 73 Light-gray, unaltered portion .71 <.05 <.01

portion of above dike.

74 16 134 Mineralized section, 4 to 6 1.03 <.05 < .01

inches wide and 2 feet long

of silica-carbonate dike.

75 16 134 to 220 Type specimen of pink silica- .03 <.05 <.01

carbonate.

76 18 11 to 36 Type specimen of dolomite in .02 - _

silica-carbonate.
20

TABLE 1. - Summary of trench sampling data (Con.)

Interval

Sample Trench or Description Analyves. prcent

location, Hg Sb As

feet

77 11 0 to 43 Type specimen of shale and 0.02 - -

sandstone.

80 12 121 to 132 Silica-carbonate. .04 - -

82 22 0 to 208 Type specimen of rhyolite. .03 - -

83 22 316 to 319 Altered rhyolite. .02 - -

85 14 120 to 125 Erratic 1/4-inch stringers .07 - -

of cinnabar in silicacarbonate,

88 1 Hole 11 Auger hole in sandstone near < .05 - -

east end trench 1.

89 1 Hole 9 do. .10 - -

90 20 24 to 34 Silica-carbonate dike, small .69 <.05 < .01

lenses cinnabar.

91 1 Hole 10 Auger hole in sandstone near < .05 _ _

east end trench 1.

92 1 Hole 12 do. < .05 _ _

TABLE 2. - Petrographic analyses

Sample Trench Interval, Description

feet

1 3 29 to 34 An epithermally altered rock, now composed of

quartz with some hydromuscovite clay, and limonite. Some shale, composed of illite and chlorite with a trace of limonite, was present.

2 3 57 to 133 Altered tuffaceous sandstones, composed of illite

and chlorite with small amounts of montmorillonite, limonite, quartz, and kaolin. The spectroscope indicates lithium.

3 3 57 to 133 Altered tuffaceous sandstone, composed of calcite,

illite, chlorite, muscovite, traces of quartz,

and limonite, The spectroscope indicates lithium.

4 4 97 to 123 Epithermally altered rock, now composed of hydromuscovite (illite clay of hydrothermal origin),

chlorite, dolomite, and some fine quartz. Traces

of magnetite, pyrite, and limonite stain are

present.

5 4 123 to 150 Partly weathered basalt, containing some euhedral

phenocrysts of augite. The groundmass has much

limonite stain due to weathering. A trace of

quartz is present.

7 4 162 to 173 Highly weathered felsite or tuff, containing

euhedral biotite phenocrysts. The groundmass

is albite,
21

TABLE 2. - Petrographic analyses (Con.)

Sample Trench Interval, Description

_ feet

8 5 2 to 17 Epithermally altered rock similar to a gossan by

mineral composition. Composed of quartz, kaolin,

limonite, chlorite, and a small amount of cinnabar. The white mineral coating is one of the

kaolin minerals.

9 6 18 to 57 Altered porphyritic rhyolite, composed of hydromuscovite, quartz, and some biotite. Moderately

small amounts of lithium.

10 6 107 to 141 Altered tuffaceous sandstone, composed of kaolin,

illite, quartz, biotite-chlorite, and limonite

stain. The spectroscope indicates lithium.

lOa 6 107 to 141 Altered soda rhyolite, composed of quartz, albite,

hydromuscovite, traces of muscovite, and limonite

stain. Moderately small amounts of lithium.

11 1 Hole 1 Auger hole, 7 feet deepnear west end of trench 1.

Altered tuffaceous sandstone containing some

altered rhyolite and a small amount of shale; now

composed of chlorite-biotite, illite, some quartz,

kaolin, and limonite stain. Only a trace of

montmorillonite may be present. The spectroscope

indicates lithium.

12 1 Hole 2 Auger hole, 7 feet deep, near west end of trench 1.

Phyllite with a trace of altered rhyolite, composed of hydrobiotite, hydromuscovite, chlorite,

and some quartz. Kaolin and some montmorillonite

is associated with sample.

13 1 Hole 3 Auger hole, 9 feet deep, near west end of trench 1l

Altered porphyritic rhyolite, containing euhedral

quartz phenocrysts, hydromuscovite, and chlorite

but with less muscovite and albite; traces of

epidote, hornblende, and kaolin are present.

14 1 Hole 4 Auger hole, 9 feet deep, near west end of trench 1.

Shale composed of illite and chlorite.

16 1 Hole 5 Auger hole, 8.5 feet deep, near north side of

trench 1. Altered, tuffaceous sandstone containing some altered rhyolite; composed of hydromuscovite, chlorite, and traces of quartz, limonite

stain, and muscovite.

17 1 Hole 6 Auger hole, 8.5 feet deep, near north side of

trench 1. Altered graywacke and altered rhyolite

composed of hydromuscovite (illite), chlorite,

quartz, and traces of muscovite.

19 1 Hole 7 Auger hole, 8.5 feet deep, near west end of trench

1. Altered, tuffaceous sandstone with some

altered rhyolite and a small amount of shale.

The chief minerals present are hydromuscovite

(illite), chlorite, quartz, with less muscovite,

montmorillonite, and a trace of limonite.
22

TABLE 2. - Petrographic analyses (Con.)

Sample Trench Interval, Description

feet

20 1 Hole 8 Auger hole, 8.5 feet deep, near west end of trench

1. Shale composed of illite and chlorite.

21 Float, 50 feet from top of ridge near airstrip.

Composed of stibnite with cryptocrystalline

quartz and stibiconite (hydrous antimony oxide).

Quartz and limonite stain are present.

22 11 520 Epithermally altered rock or gossan, composed of

quartz, cryptocrystalline quartz, kaolin, chlorite, and a small amount of oligoclase and limonite stain. Lithium is present in trace amounts.

23 13 100 to 126 Epithermally altered rock or gossan, composed of

cryptocrystalline quartz with some kaolin, hydromuscovite, limonite, and a trace of quartz, The

white veins are mixtures of kaolin, cryptocrystalline quartz, and quartz. Cinnabar is present.

30 1 37 to 107 Epithermally altered igneous rock, now composed of

cryptocrystalline quartz, quartz, kaolin, and

limonite. Cinnabar and a trace of chromite in

octahedral form are present. The soft white

areas are kaolin. The presence of octahedrons of

chromite indicate that the rock may have been

derived from an ultrabasic,

36 1 37 to 107 Epithermally altered igneous rock, composed of

cryptocrystalline quartz, kaolin, limonite, and

quartz. Traces of chlorite, chromite, and cinnabar are present. As noted in log of trench 1,

part of bedrock was shale. Part of sample 36 is

an epithermally altered shale, now composed of

illite (hydromuscovite) cryptocrystalline to fine

quartz, kaolin, limonite, and ankerite. Traces

of cinnabar are present. There is a trace of a

green claylike material; the color is due to the

presence of chromium oxide.

39 1 37 to 107 Altered shale, composed of hydromuscovite and

hydrobiotite with limonite, quartz, kaolin, and

a minor amount of chlorite. A trace of cinnabar

associated with kaolin is present.

52 1 37 to 107 Altered sandy shale and shale, composed of hydromuscovite, kaolin, quartz, some limonite, and

chlorite. A trace of hornblende and muscovite

are present.

53 1 37 to 107 Epithermally altered rock, now composed of quartz,

kaolin, limonite, and traces of hydromuscovite

and cinnabar. Inclusions of argillite composed

of illite (hydromuscovite) with some chlorite and

limonite. No carbonaceous material.
23

TABLE 2. - Petrographic analyses (Con.)

Sample Trench Interval, Description

feet

60 1 37 to 107 Epithermally altered rock, now composed of quartz,

kaolin, limonite, and traces of hydromuscovite

and cinnabar. Inclusions of argillite composed

of illite (hydromuscovite) with some chlorite

and limonite. No carbonaceous material.

63 17 52 to 76 Epithermally altered rock, now composed of quartz,

kaolin, some limonite and cinnabar, and traces

of chlorite, oligoclase, and chromite.

64 17 52 to 76 Epithermally altered rock, now composed of quartz

with kaolin, hydromuscovite, limonite stain, and

a small amount of chromite. Quartz phenocrysts

are present.

65 17 255 to 269 Shale, composed of illite and hydrobiotite with

some chlorite, and a trace of cryptocrystalline

quartz.

66 17 269 to 277 Epithermally altered rock, now composed of quartz,

kaolin, limonite, cinnabar, and traces of chlorite and biotite.

67 17 297 to 371 Chiefly a carbonaceous shale, composed of illite,

chlorite, and carbonaceous material. The darkgray to black color is not due to manganese. A

small amount of epithermally altered rock, now

composed of quartz, kaolin, and limonite, is

present.

68 17 297 to 371 Epithermally altered rock, now composed of kaolin,

ankerite, quartz, some dolomite, limonite stain,

and a trace of cinnabar,

69 15 350 to 356 Epithermally altered rock, now composed of kaolin,

small amounts of quartz, limonite, chlorite,

cinnabar, and a trace of chromite.

70 15 356 to 357 Epithermally altered rock, now composed of cryptocrystalline quartz with kaolin, small amount of

chlorite, limonite, and a trace of cinnabar and

chromite.

71 16 12 to 26 Epithermally altered rock, now composed of kaolin,

cryptocrystalline quartz, some limonite, chlorite, cinnabar, and traces of quartz, biotite,

illite, and chromite. Phenocrysts of quartz,

altered in part to cryptocrystalline quartz are

present.

72 16 12 to 36 Epithermally altered rock, now composed of kaolin,

cryptocrystalline quartz, quartz, limonite, small

amount of chromite, and traces of cinnabar and

chlorite.

73 16 12 to 26 Epithermally altered rock, now composed of cryptocrystalline quartz, kaolin, chlorite with quartz,

chromite, and a trace of cinnabar and limonite.

Quartz phenocrysts are present.
24

TABLE 2. - Petrographic analyses (Con.)

Sample Trench Interval, Description

___ __ feet

74 16 130 to 132 Epithermally altered rock, now composed of quartz,

kaolin, cryptocrystalline quartz, limonite, a

small amount of a yellow titanium mineral, which

may be anatase, and traces of cinnabar, hornblende,

pyrite, and chlorite.

75 16 130 to 220 Epithermally altered rock, now composed of cryptocrystalline quartz, kaolin, ankerite, quartz,

dolomite, and traces of chromite, chlorite, and

limonite. No cinnabar. Quartz phenocrysts are

present. This rock has a pink color.

76 18 11 to 36 Weathered, brown silica-carbonate limonite.

77 11 85 to 163 Two different materials. Altered tuffaceous

sandstone composed of hydrobiotite, chlorite, and

hydromuscovite with quartz, albite, oligoclase,

muscovite, kaolin, and limonite stain. Silicacarbonate, composed of ankerite, cryptocrystalline

quartz, kaolin, and quartz with limonite, chlorite, and hydromuscovite.

78 11 0 to 43 Altered tuffaceous sandstone, composed of kaolin,

fine quartz with less chlorite, hydromuscovite,

limonite, and a trace of biotite.

79 12 0 to 121 Altered tuffaceous sandstone, composed of quartz,

chlorite, some hydromuscovite, and traces of

albite and limonite.

80 12 121 to 132 Silica-carbonate, composed of oligoclase with some

cryptocrystalline quartz and limonite stain, and

traces of biotite, chromite, and chlorite.

81 12 206 to 218 Altered tuffaceous sandstone, composed of chlorite,

hydromuscovite, some kaolin and muscovite, and a

trace of quartz.

82 22 0 to 208 Sample was intended as a type specimen of rhyolite;

however, some material from a clay slip in this

interval may have gotten into sample. Two different types of material: (1) A greisen, composed

chiefly of a lithium mica, tentatively identified

as lepidolite (some quartz and kaolin); (2) an

altered rhyolite, composed of hydromuscovite

(illite) and quartz. Some green muscovite,

kaolin, chlorite, and limonite stain. Trace

(normal) of lithium.

83 22 316 to 319 Two different materials in sample: (1) An altered

rhyolite composed of quartz, albite, hydromuscovite with green muscovite, traces of kaolin,

chlorite, and cinnabar (spectroscope indicates

lithium); (2) an altered felsite composed of

hydromuscovite, quartz, kaolin, and traces of

chlorite and cinnabar.
25

TABLE 2. - Petrographic analyses (Con.)

Sample Trench Interval, Description

feet

84 23 119 to 125 Epithermally altered rock, composed of quartz,

kaolin, and limonite.

85 14 120 to 125 Epithermally altered rock, composed of cryptocrystalline quartz, limonite, kaolin, and a trace of

cinnabar.

88 1 Hole 11 Auger hole, 6 feet deep, near east end of trench

1. Altered rhyolite, composed of hydromuscovite

(illite), chlorite, quartz, traces of limonite

stain and montmorillonite clay. Spectroscope

indicates lithium.

89 1 Hole 9 Auger hole, 5.5 feet deep, near east end of trench

1. Altered rhyolite and tuffaceous sandstone,

composed of hydromuscovite, chlorite, quartz with

traces of muscovite, limonite stain, montmorillonite, potash feldspar, hornblende, and a trace

of lithium.

90 20 24 to 34 Epithermally altered rock, composed of quartz

kaolin, limonite, and cinnabar.

91 1 Hole 10 Auger hole, 6.3 feet deep, near east end of trench

1. Tuffaceous sandstone containing a trace of

rhyolite, composed of hydromuscovite, chlorite,

quartz, small amount of kaolin, and traces of

limonite stain and montmorillonite.

92 1 Hole 12 Auger hole, 4.3 feet deep, near east end of trench

1. Altered rhyolite composed of hydromuscovite,

chlorite, and quartz with traces of muscovite,

kaolin, hornblende, limonite stain, calcite,

montmorillonite, and lithium.
26

TABLE 3. - Spectrographic analyses

Legend

A over 10 percent. E 0001 to 0.1 percent.

B 5 to 10 percent. F 0.001 to 0.01 percent.

C 1 to 5 percent. G under 0.001 percent.

D 0.1 to 1 percent. - not detected.

Type s ecimen, trench 1

Sample Silica- SilicaElement 3 82 carbonate carbonate, Altered

and cinnabar shale, and shale

cinnabar

Al ................ , A A C C C

B..... ........... E D F E E

Ba a. ......... E D D D D

Be .................. G G G G

Ca... . ........... A E E F D

Co .......... - - F F F

Cr. ............ F F E E E

Cu . ........... F F F F F

Fe ...... A A C C C

Ga ............. G G _

Hg........... - - D A E

Mg ............. C D D E D

Mn .. . D E E F E

Mo ... ....- -... F E E

Na . E C _ E

Ni........... . F F E E D

Pb.... .... .... E E _

Sb... . . E

Si. . o A A A A A

Sr.- - E D D

Ti................. C D D D D

V.O. E _ E E E

Zr ....... ..... F F F

y... F _

Note: Checking took place for elements Ag, As, Au, Bi, Cd, Ge, Hf, In, Li,

Nb, P., Pd, Pt, Rh, Sn, Ta, Te, T1, W, and Zn; however, these elements

were not detected.
27

BIBLIOGRAPHY

1. Brooks, Alfred H. Antimony Deposits of Alaska. Geol. Survey Bull. 649,

1916, pp. 12, 43-47.

2, Cady, W. M., R. E. Wallace, J. H. Hoare, and E. J. Webber. The Central

Kuskokwim Region, Alaska. Geol. Survey Professional Paper 268, 1955,

132 pp.

3. Maddren, A. G. Gold Placers of the Lower Kuskokwim, With a Note on

Copper in the Russian Mountains. Ch. in Mineral Resources of Alaska,

Report on Progress of Investigations in 1914 by A. H. Brooks and

others. Geol. Survey Bull. 622, 1915, pp. 295-298.

4, Mertie, J. B., Jr., and G. L. Harrington. The Ruby-Kuskokwim Region,

Alaska. Geol. Survey Bull. 754, 1924, pp. 35, 83, 108-109, 116-117.

5. Mertie, J. B., Jr. Mineral Deposits of the Ruby-Kuskokwim Region,

Alaska. Ch. in Mineral Resources of Alaska Report on Progress of

Investigations in 1933 by P. S. Smith and others. Geol, Survey Bull.

864, 1936, pp. 118, 143, 197-198, 223-226, 243-244.

6. Pennington, James W. Mercury--A Materials Survey. BuMines Inf. Circe

7941, 1959, pp. 12, 52.

7. Rutledge, F. A. Investigation of Mercury Deposits, Cinnabar Creek Area,

Georgetown and Akiak Districts, Kuskokwim Region, Southwestern Alaska.

BuMines Rept. of Inv. 4719, 1950, 9 pp.

8. Smith, Philip S., and A. G. Maddren. Quicksilver Deposits of the

Kuskokwim Region. Ch. in Mineral Resources of Alaska, Report on

Progress of Investigations in 1914 by A. H. Brooks and others. Geol.

Survey Bull. 622, 1915, pp. 272-291.

9. Webber, B. S., Stuart C. Bjorklund, Franklin A. Rutledge, B. I. Thomas,

and Wilford S. Wright. Mercury Deposits of Southwestern Alaska.

BuMines Rept. of Inv. 4065, 1947, 57 pp.
28

APPENDIX. - LOGS OF TRENCHES

Trench 1

Length: 455 feet. Average depth: 10 feet.

Bearing: 0 to 89 feet, N. 720 E. Maximum depth: 16 feet.

89 to 300 feet, N. 84° E. "0" is west end.

300 to 455 feet, N. 810 E. This trench is probably within 100

feet of rhyolite-shale contact.

Interval, Sample Description

feet Petrographic Chemical

0 to 37 _ _ Shattered shale.

37 to 107 30, 36 26, 62 The largest area of cinnabar mineralization

39, 52, found. When first exposed, the bedrock

53, 60 was silica-carbonate with erratic dissemination of cinnabar. Additional excavation

removed the silica-carbonate and exposed

the unmineralized slate bedrock underneath.

Apparently the silica-carbonate is a flatlying 8- to 9-foot-thick sill. Contacts

at 37 and 107 feet are N. 300 E.

107 to 189 - - Shattered silicified shale and light-gray

silicified sandstone.

189 to 205 - - Shattered shale and compact sandstone.

Limonite stain on fractures. Small amount

of white kaolin.

205 to 209 - - 18 inches of very soft, black shale or

fault gouge; strike N. 600 E.

209 to 260 - - Dark-gray shale and poorly cemented sandstone. At 254 feet, beds strike N. 700

E. and dip 800 N.

260 to 273 - - Weathered, brown silica-carbonate sill with

100 dip S. Considerable silica-carbonate

float in lower 4 feet of north wall of the

trench. Minor alteration of shale at contact. Trace of cinnabar in silicacarbonate.

273 to 315 _ _ Thin-bedded shales and sandstone. Excellent

exposure of attitude of beds at 280 to 300

feet; strike is N. 75° E. and dip 800 N.

315 to 365 _ _ Altered shale, shale, soft to medium hard

sandstone, considerable weathered silicacarbonate, and chert. Trace of cinnabar

in silica-carbonate. This appears to be

the south edge of a sill that extends

northward.

365 to 455 _ _ Shale and soft sandstone. At 400 feet,

excellent exposure of strike (N. 650 E.)

and dip (800 N.) of beds. At 405 to 455

feet, no permafrost after 12-foot depth.

In rest of trench permafrost was still

present at 16-foot maximum depth.
29

Trench 2

Length: 150 feet. Average depth: 8.5 feet.

Bearing: S. 200 E. Maximum depth: 13 feet.

"0" is north end.

Interval, Description

feet

0 to 33 Altered shale and minor amount of cinnabar, which is very erratic.

33 to 150 Shale, sandy shale, soft sandstone, strike of bedding N. 50' E.,

vertical dip. Walls of trench panned no cinnabar.

Trench 3

Length: 417 feet. Average depth: 10.5 feet.

Bearing: S. 110 W. Maximum depth: 14.0 feet.

"0" is north end.

Interval, Sample Description

feet Petrographic Chemical

0 to 17 _ _ Shale.

17 to 25 _ _ Light-brown, weathered silica-carbonate,

fractured with thin coating of light

cream-colored kaolin on fractures. Minor

amount of limonite stain and a few 1/4-

inch calcite stringers. Contact at 25

feet strikes N. 480 E. This appears to

be a 2- to 3-foot sill with a 100 dip SW.

25 to 29 - - Chill zone of altered shale and some weathered silica-carbonate.

29 to 34 1 1 Mostly weathered silica-carbonate and some

shale.

34 to 57 - - Dark-gray broken shale and occasional thin

layers of sandstone.

57 to 133 2, 3 _ Broken, shattered dark-gray shale with

numerous thin layers of light-brown to

light-gray sandstone, probably derived

from weathered graywacke. Bedding strikes

N. 500 E. and dips 800 SE. Samples 2 and

3 are of sandstone.

133 to 152 _ _ Dark-gray shale, sandy shale, and sandstone

with a 2-foot-wide lens of weathered

silica-carbonate down center of trench. A

1-foot-wide halo of altered shale surrounds

this lens.

152 to 163 _ _ Shale.

163 to 174 _ _ Shale with a 2-foot, irregular-shaped lens

of silica-carbonate which strikes N.

100 E.
30

Trench 3 (Con.)

Interval, Sampl Description

feet Petrographic Chemical

174 to 209 _ - Shale and occasional bands of sandstone.

209 to 226 _ - Light-green, altered rhyolite.

226 to 318 _ - Altered shale, sandstone, and weathered

silica-carbonate. Kaolin on fractures

of silica-carbonate which appears to be

part of a sill, dipping 100 E.

318 to 417 - Shale, sandstone, and small stringers of

I silica-carbonate.

Trench 4

Length: 394 feet. Average depth: 7.5 feet.

Bearing: 0 to 200 feet, N. 660 E. Maximum depth: 11.5 feet.

200 to 394 feet, N. 710 E. "O" is southwest end.

Interval, Sample

feet Petrographic Chemical Description

0 to 67.5 - Dark-gray shale, sandy shale, and small

lens of sandstone,

67.5 to 78 - Altered shale.

78 to 97 - Weathered, brown silica-carbonate; bearing of contact at 78 feet is N. 470 W.;

no faulting. On north wall of trench

silica-carbonate extends 4 feet up wall

of trench. At base of south wall the

bedrock is shale. The contact between

shale and silica-carbonate is approximately in center of trench.

97 to 123 4 - Weathered, brown silica-carbonate, which

is light-gray where not weathered. Not

as weathered as 78- to 97-foot secti6n.

123 to 150 5 5 Very hard shale, sandstone which is

almost a quartzite, and occasional small

inclusions of silica-carbonate; from 140

to 147 feet, weathered silica-carbonate

protrudes out 4 feet from south wall of

trench (sample 5).

150 to 162 - - Hard, altered shale; considerable limonite stain.

162 to 173 7 - Either a soft sandstone, derived directly

from an igneous material, or a tuff.

173 to 200 - - Hard, altered shale; considerable limonite stain. From 178 to 191 feet, a

lens of weathered silica-carbonate

extends 5 feet in an irregular line

toward the center of the trench from the

north wall. It is not present in the
31

Trench 4 (Con.)

Interval, Sample Description

feet Petrographic Chemical

173 to 200 south wall. The lens starts at the bottom

(Con.) of the trench at 178 feet on the north

wall and is 3 feet high on the wall at

191 feet.

200 to 360 _ _ Black shale and minor amount of sandstone.

360 to 365 Irregular lens of weathered silicacarbonate, striking about normal to trench

and not exposed in south wall.

365 to 394 I Shale and soft sandstone.

Trench 5

Length: 29 feet. Average depth: 7.0 feet.

Bearing: N. 640 E. Maximum depth: 11.0 feet.

"0" is south end.

Interval, Sample Description

feet Petrographic Chemical

0 to 2 Altered, black shale.

2 to 17 8 8 Weathered, brown silica-carbonate and trace

of cinnabar which is usually associated

with cream-colored kaolin. Strike of contact N. 250 W.

17 to 29 1 _ Altered shale.

Trench 6

Length: 149 feet Average depth: 7.0 feet.

Bearing: N. 26° E. Maximum depth: 11.0 feet.

"0" is south end.

Interval, Sample Description

feet Petrographic Chemical

0 to 12 _ - Shale.

12 to 18 _ _ Weathered, brown silica-carbonate; strike

normal to trench. Walls of trench from 6

to 14 feet panned minor amount of coarse

cinnabar.

18 to 57 9 9 Shale and occasional 12-inch inclusions of

rhyolite. Sample 9 is of rhyolite.

57 to 107 Shale and sandy shale.

107 to 141 10, lOa 75 percent medium-grained, thin-bedded sandstone and shale. Strike of beds is normal

to trench and dip 800 S. 25 percent

altered rhyolite. Sample 10 is of sandstone, and sample lOa is of rhyolite.

141 to 149 -__ Soft sandstone; considerable folding of beds.
32

Trench 7

Length: 200 by 200 feet. Average depth: 8 feet.

Maximum depth: 14 feet.

Interval, Description

feet

This is where an area about 200 by 200 feet was excavated to bedrock (fig. 7). A high-grade vein of cinnabar, about 2 to 6

inches wide, had been exposed by previous trenching. A fairly

flat silica-carbonate sill, about 10 feet thick, intrudes the

shale. The cinnabar vein could only be followed for a few feet

and was on the contact between the sill and shale. There is

evidence of post mineral movement.

Trench 8

Length: 287 feet. Average depth: 8.0 feet.

Bearing: N. and S. Maximum depth: 11.0 feet.

"O" is south end of trench and is

the junction of trench 4 and

trench 8. Overburden is fine

silt and rhyolite fragments,

found to within 3 feet of the

trench bottom.

Interval, Description

feet

0 to 157 Dark-gray, shattered shale.

157 to 197 Weathered, brown silica-carbonate; strike of contacts N. 40° E.

197 to 233 Black, altered shale and very hard brown sandstone; some limonite

stain.

233 to 235 Irregular-shaped lens of weathered silica-carbonate strike

N. 500 W.

235 to 257 Shale.

257 to 276 Brown, weathered silica-carbonate, extending 8.5 feet from the

east side of the trench. The remaining 4.5 feet of the 13-footwide trench is highly altered shale.

276 to 287 Shale and sandstone; the walls in this section of the trench pan

minor amounts of fairly coarse cinnabar from bedrock to the

surface.
33

Trench 9

Length: 155 feet. Average depth: 9.0 feet.

Bearing: 0 to 100 feet, N. 610 E. Maximum depth: 11.0 feet.

100 to 155 feet, N. 700 E. "O" is southwest end.

Permafrost to bottom of entire

trench.

Interval, Description

feet

0 to 41 Black, fractured shale and lighter colored soft sandstone.

General character of overburden of trench is fine sandy silt.

41 to 46 Weathered, brown silica-carbonate, about 3 feet wide and striking

S. 60' E. On northwest side of trench it is exposed only in the

bottom of trench, whereas on northeast side it is exposed for 2

feet in the wall. Minor chill zone at contacts.

46 to 64 Broken shale and sandstone.

64 to 90 Silica-carbonate; contacts N. 400 W.; alteration at contact is

minor. Upper 4 feet of overburden pans minor amount of fairly

coarse cinnabar,

90 to 155 Shale and sandstone; bedding strikes N. 700 E. and dip is vertical.

Trench 10

Length: 480 feet. Average depth: 9.0 feet.

Bearing: S. 680 W. Maximum depth: 11.5 feet.

"O" is northeast end. Overburden

of trench fairly coarse material

mostly shale and sandstone.

Permafrost to bottom of entire

trench.

Interval, Description

feet

O to 8 Weathered, brown sandstone and silica-carbonate. Considerable

alteration of sandstone.

8 to 59 Shattered, black shale, extending 7 feet from north wall, and

weathered, brown sandstone in remaining part along south wall.

59 to 66 Weathered, brown sandstone and shale.

66 to 115 Altered shale, soft sandstone, and minor amount of sandstone that

is almost a quartzite.

115 to 200 Much shattered shale and sandstone extends 3 to 4 feet up the

northwest wall and is in place. The entire southeast wall is

silt. The bottom of the trench is bedrock.

200 to 391 Shale, sandstone, and sandy shale.

391 to 442 Weathered, brown silica-carbonate with 2 feet of shale at 412 to

414 feet.

442 to 480 Shale and sandstone.
34

Trench 11

Length: 630 feet. Average depth: 7.0 feet.

Bearing: 0 to 182 feet, N. 810 E. Maximum depth: 8.5 feet.

182 to 332 feet, N. 310 E. "O" is west end.

332 to 460 feet, N. 40- E.

460 to 510 feet, N. 270 E.

510 to 568 feet, N. 640 E.

568 to 630 feet, N. 660 E.

Interval, Sample Description

feet Petrographic Chemical

0 to 43 78 78 Hard, gray sandstone and blocky and shattered shale. Strike of bedding is N.

310 E.

43 to 63 - - Weathered, brown silica-carbonate sill;

strike S. 600 W., and dip is steep to the

south.

63 to 85 - - Shale, hard sandstone; bedding strikes

S. 600 W., and dips 700 S.

85 to 163 77 - Shale, very hard, thin bands of sandstone,

and minor amounts of silica-carbonate.

163 to 182 - - Shale and sandstone; strike of bedding

S. 450 W. and dip 800 S. Considerable

deformation.

182 to 196 - North half of trench is black, thin-bedded

shales and sandstones; strike of bedding

is N. 680 E. and dip is vertical. South

half of trench is partially weathered

silica-carbonate, which is light gray when

not weathered. At 196 feet, silicacarbonate curves into south wall. Contact

between sediments and silica-carbonate is

along bedding plane of shale.

196 to 247 - _ Thin-bedded, black shales and sandstone;

much of sandstone is very hard. Strike

of bedding N. 650 E. and dip is vertical

or slightly to the south.

247 to 272 _ _ Lens of brown, weathered silica-carbonate,

about 3 feet wide in center of trench;

from 65 to 74 feet, it extends into north

wall of trench; 18- to 24-inch silicified

zone of hard shale on both sides.

272 to 276 - - Altered shale and sandstone.

276 to 295 - - Weathered, brown silica-carbonate.

295 to 299 - - Highly altered shale; silicified zone.

299 to 311 - - Black shale.

311 to 522 22 22 Weathered, broken, brown silica-carbonate;

center of rock fragments often are unweathered and light gray. Considerable creamcolored kaolin present. One 1- by 4-inch
35

Trench 11 (Con.)

Interval, Sample Description

feet Petrographic Chemical

311 to 522 piece of very high-grade, well-worn cinna-

(Con.) bar float. Small amount of cinnabar at

520 feet. Several prospect holes a few

feet north of this section carried fairly

good cinnabar float. From 347 to 382 feet,

walls of trench panned fair amount of

cinnabar.

522 to 552 _ 24 Same as 311 to 522 feet but not as much

weathered; some is light gray and some is

limonite stained. Walls pan appreciable

amount of coarse cinnabar.

552 to 582 _ _ Predominately shale and minor silicacarbonate. Most of south side of trench

is shale.

582 to 614 _ - Shale.

614 to 630 _ 25 Shale with 4-foot-wide zone of weathered,

brown silica-carbonate down center of

________________ _trench. Sample 25 is of silica-carbonate.

Trench 12

Length: 633 feet. Average depth: 8.0 feet.

Bearing: 0 to 200 feet, N. 510 W. Maximum depth: 12.0 feet.

200 to 235 feet, N. 440 W. "0" is south end and at junction

235 to 382 feet, N. 220 W. with trench 10. Permafrost to

382 to 633 feet, S. 790 W. bottom and large ice lens in

overburden.

Interval, Sample Description

feet Petrographic Chemical

0 to 121 79 - Hard sandstone and some shale.

121 to 132 80 80 Weathered, brown silica-carbonate; contact

strikes S. 640 W.; no chill zone.

132 to 143 - - Shale and sandstone.

143 to 147 - - Irregular lens of silica-carbonate, partially surrounded by clay.

147 to 179 - - Dark-gray shale and sandstone; small 1-inch

wide irregular lens of silica-carbonate at

164 feet.

179 to 197 - - Weathered, brown silica-carbonate; irregular

contact at 179 feet and minor chill zone;

contact at 197 feet is sharp with a 6-inch

clay seam; strike is S. 650 W.

197 to 206 - _ Shale.

206 to 218 81 _ Tuffaceous sandstone.

218 to 260 - _ Thin-bedded shale, sandstone, and clay;

strike of bedding S. 600 W.
36

Trench 12 (Con.)

Interval, Sample Description

feet Petrographic Chemical

260 to 382 _ _ Shale, sandstone, and silica-carbonate partially exposed; some frozen muck and large

ice lenses. Silica-carbonate between 260

to 268 feet and 310 to 335 feet.

382 to 633 _ _ Shale, sandstone, and sandy shale. General

I________ __________ _ ___strike of bedding N. 700 to 750 E.

Trench 13

Length: 126 feet. Average depth: 9.0 feet.

Bearing: 0 to 27 feet, S. 43° E. Maximum depth: 10.0 feet.

27 to 60 feet, S. 33° E. "0" is northwest end,

60 to 126 feet, S. 680 E.

Interval, Sample Description

feet Petrographic Chemical

0 to 32 _ _ Mostly shale and some sandstone.

32 to 46 _ _ Light-brown, medium-grained sandstone.

46 to 100 - - Shale, some sandstone, and clay.

100 to 126 23 23 Weathered, brown silica-carbonate and small

amount of cinnabar. Contact at 100 feet

is irregular.

Trench 14

Length: 123 feet. Average depth: 9.0 feet.

Bearing: 0 to 52 feet, S. 43° E. Maximum depth: 10.0 feet.

52 to 123 feet, S. 320 E. "0" is northwest end or at junction with trench 4.

Interval, Sample Description

feet Petrographic Chemical

0 to 106 - - Shale, hard sandstone, and no bedding; from

90 to 106 feet, a few small irregularshaped lenses of silica-carbonate.

106 to 123 85 85 Weathered, brown silica-carbonate with

minor amounts of cinnabar from 120 to

125 feet. Cinnabar occurs in high-grade,

1/4-inch short stringers, which are very

erratic. Sample 85 is best of

mineralization.
37

Trench 15

Length: 600 feet. Average depth: 8.0 feet.

Bearing: 0 to 325 feet, N. 580 E. Maximum depth: 9.0 feet.

325 to 600 feet, N. 650 E. "O" is northeast end. Dry

permafrost (no ice lens) to

bottom. 4 feet of overburden

is fine silt.

Interval, Sample Description

feet Petrographic Chemical

0 to 84 _ _ Thin-bedded shale, soft sandstone, and sandy

shale; strike of bedding is S. 700 E., and

dip is vertical at 19 feet. At 75 feet,

strike of bedding is E. and W., and dip is

vertical. Small fragments of silicacarbonate at 54 feet, apparently dragged

in by small fault.

84 to 350 _ _ 85 percent soft sandstone; rest shale and

numerous small faults. At 86 feet, a

fault dipping 20° NE. and going under vertical shale beds. At 155 feet, a 2-footwide zone of thin-bedded shales striking

N. 25° E., dipping 800 E.

350 to 357 69, 70 69, 70 Weathered, brown silica-carbonate sill;

strike S. 450 E. and 700 to 900 dip S.

Small shale lens at 355 to 357 feet.

Other small inclusions of shale throughout. At 356 to 357 feet, rusty red

silica-carbonate. Few 1/4-inch stringers

of cinnabar with vertical dip. None over

2 to 3 feet long. Mineralization apparent

in north wall only; none, in south wall,

Sample 69 is best of cinnabar stringers;

sample 70 is from 356 to 357 feet. The

entire 7-foot face, exposed in the north

wall, will assay less than 0.2 percent

cinnabar.

357 to 394 _ - Shale and sandstone.

394 to 410 - - Weathered, shattered, brown silicacarbonate; strike S. 750 E. and vertical

dip.

410 to 421 _ _ Fault gouge; strike S. 70° to 750 E.

421 to 434 - - Shale.

434 to 437 - - Silica-carbonate dike; strike S. 15° W. and

vertical dip.

437 to 600 - - Shale, sandy shale, sandstone, and numerous

small faults. Bedding indefinite but

appears to strike S. 750 W. At 533 feet,

2-foot vertical silica-carbonate dike

striking S. 200 E. with vertical dip. At

552 feet, 1-foot vertical silica-carbonate

dike striking S. 300 W.
38

Trench 16

Length: 220 feet. Average depth: 6.0 feet.

Bearing: S. 600 W. Maximum depth: 7.0 feet.

"O" is northeast end. General

overburden is very fine silt.

Very little rhyolite float.

Interval, Sampl Description

feet Petrographic Chemical

0 to 14 _ _ Shale, with irregular lens of silicacarbonate.

14 to 26 71 to 73 71 to 73 Partially weathered, brown silica-carbonate

dike; strike N. 100 E., and dip is probably vertical. Contacts with shale very

irregular. Unweathered parts of dike are

light gray. Some cinnabar in irregularshaped areas not over 1 foot in diameter.

Where cinnabar is in weathered part of

dike, post mineral movement is often evident. Dike will assay less than 0,1

percent Hg. Sample 71 is best of mineralization; 72 is of weathered portion with

cinnabar; 73 is of light-gray dike material with cinnabar.

26 to 134 _ _ Shale, soft sandstone, no bedding planes,

and numerous small faults. At 53 feet,

1-inch vertical silica-carbonate stringer,

striking S. 350 W. From 125 to 134 feet,

harder sandstone--probably a silicified

zone.

134 to 220 74, 75 74, 75 Weathered, brown silica-carbonate, pink,

fresh-appearing silica-carbonate,and shale.

Contact at 120 feet strikes east-west; dip

vertical. At 134 feet, cinnabar occurs in

a zone, 2 feet long and 4 to 6 inches wide.

Well mineralized. Sample 74 is the best

of this zone; sample 75 (200 feet) is of

pink silica-carbonate.
39

Trench 17

Length: 371 feet. Average depth: 5.5 feet.

Bearing: 0-161 feet, N. 670 E. Maximum depth: 7.0 feet.

161-371 feet, N. 63° E. "O" is southwest end. Dry

permafrost. Overburden consists

of about 4 feet of silt, shale,

and small amount of rhyolite.

Permafrost to bottom of trench.

Top 2 feet of bedrock is so

badly decomposed that it is hard

to distinguish it from overburden.

Interval, Sample Description

feet Petrographic Chemical

0 to 28 - Fine-grained, soft sandstone, and some

shale.

28 to 52 - - Black, fractured shale; could be fault

gouge.

52 to 76 63, 64 63, 64 Weathered, brown silica-carbonate dike;

strike S. 5° W. and vertical dip. Badly

fractured, soft silt or mud on fractures. One small piece of cinnabar

found (sample 63). Sample 64 is type

specimen of dike.

76 to 78.5 _ - Black, fractured shale.

78.5 to 81.5 - - Same as 52 to 76 feet, except no cinnabar.

81.5 to 100 - - Shale and sandy shale.

100 to 101 - - Silica-carbonate dike; strike north and

south.

101 to 142.7 - - Shale, sandy shale, and no bedding.

142.7 to 144 - - Weathered, brown silica-carbonate and

shale.

144 to 156 - - Weathered, brown, shattered silicacarbonate dike; strike S. 5° W.

156 to 160 - - Hard sandstone, shale, and some limonite

stain; appears to be chill zone.

160 to 236 - - Sbale, soft sandstone, and sandy shale.

Strike of bedding about S. 65° E.; dip

is vertical or steeply to southwest.

236 to 238 - - Irregular lens of silica-carbonate normal

to trench.

238 to 245 - - Black shale and black fine mudlike fault

gouge.

245 to 255 - - Shattered, weathered, brown silicacarbonate sill; dips vertical and strike

S. 550 E.

255 to 269 65 65 Black to dark-gray fault gouge.

269 to 277 - - Silica-carbonate dike. 4 feet of depth

exposed in trench.
40

Trench 17 (Con.)

Interval, Sample Description

feet Petrographic Chemical

_ 66 66 Good but erratic cinnabar in south wall,

2 feet from top of dike to bottom of

trench. Nothing in north wall. Mineralization is about 18 inches wide and

very erratic from 271 to 276 feet. Dike

ends abruptly. Sample 66 is most of the

deposit. Attempt to follow mineralization with trench 17A failed, Apparently

this is a small isolated pocket.

277 to 297 _ - Shale, black fault gouge and fragments or

pockets of silica-carbonate, which are

mostly embedded in fault gouge.

297 to 371 67, 68 67 Black fault gouge and shale with isolated

fragments or boulders of silica-carbonate

embedded in gouge. Sample 67 is type

specimen of gouge; sample 68, of silicacarbonate fragments.

Trench 17A

Length: 55 feet. Average depth: 6.0 feet.

Bearing: S. 250 W. Maximum depth: 8.0 feet.

"O" is center line of 295-foot

point in trench 17. This trench

was an attempt to follow mineralization in trench 17.

Interval, Description

feet

0 to 10 Fault gouge.

10 to 19 Shattered, brown silica-carbonate; fault gouge.

19 to 55 Shale, sandstone, and sandy shale.
41

Trench 18

Length: 243 feet. Average depth: 6.0 feet.

Bearing: N. 680 E. Maximum depth: 8.0 feet.

"0" is southwest end; overburden

is fine silt; no rhyolite float.

Interval, Sample Description

feet Petrographic Chemical

0 to 11 _ _ Shattered shale and an irregular-shaped

inclusion of silica-carbonate, about 7

by 5 feet in size, in south side.

11 to 36 76 76 Weathered, brown silica-carbonate and

unaltered, very hard, light-gray silicacarbonate. Sample 76 is of altered

material. Contact at 36 feet is irregular, but strike is approximately

S. 700 E.

36 to 68 - Shale with an irregular-shaped 4- by 6-

foot lens of silica-carbonate. Could

be a fault zone.

68 to 180 - Shale and sandstone. At 129 feet, a 4-

inch-wide silica-carbonate dike

(S. 600 E.).

180 to 183.5 _ - 2-foot-wide silica-carbonate dike

(S. 650 E.), bedding of sediments striking S. 600 to 70° E., as do small fault

planes.

183.5 to 214 _ - Shale and sandstone.

214 to 229 _ - Weathered, brown silica-carbonate; strike

S. 65° E. and vertical dip.

229 to 243 _ - Shale and sandstone; strike of bedding

S. 65° E. and dip 80° S.

Trench 19

Length: 243 feet. Average depth: 8.0 feet.

Bearing: 0 to 90 feet, N. 90 W. Maximum depth: 10.0 feet.

90 to 243 feet, N. 30 W. "0" is south end.

Interval, |Description

feet
42

Trench 20

Length: 60 feet. Average depth: 6.0 feet.

Bearing: N. 850 W. Maximum depth: 7.0 feet.

"0" is east end.

Interval, Sampl Description

feet Petrographic Chemical

0 to 16 Shale and sandstone.

16 to 24 - - Silica-carbonate and shale.

24 to 34 90 90 Silica-carbonate dike; strike S. 250 W.;

minor amount of cinnabar (less than 0.1

percent), which occurs in small slips

and partings.

34 to 38 _ _ Shale.

38 to 44 _ _ Silica-carbonate dike; strike S. 42° W.

44 to 60 - _ Shale and sandstone.

Trench 21

Length: 324 feet. Average depth: 7.0 feet.

Bearing: S. 60° W. Maximum depth: 8.0 feet.

"0" is northeast end.

Interval, Description

feet

0 to 324 Interbedded shale and sandstone.

Trench 22

Length: 453 feet. Average depth: 6.0 feet.

Bearing: 0 to 375 feet, N. 800 W. Maximum depth: 8.0 feet.

374 to 453 feet, S. 850 W. "0" is southeast end, Near top

of rhyolite ridge, no frost.

Overburden is broken rhyolite.

Interval, Sample Description

feet Petrographic Chemical

0 to 208 82 82 Rhyolite, light gray, not weathered; at

121 feet, clay slip (fault) that strikes

S. 200 E. and dips 280 W.

Sample 82 is type specimen of rhyolite.

208 to 240 _ _ Hard, altered shale and sandstone; strike

about normal to trench.

240 to 316 - - Unaltered, light-gray rhyolite.

316 to 319 83 83 Altered, rhyolite dike; strike is normal

to trench; vertical dip. Considerable

quartz along contact.

319 to 453 - - Same as 240 to 316 feet.
43

Trench 23

Length: 326 feet. Average depth: 6.0 feet.

Bearing: S. 640 E. Maximum depth: 8.0 feet.

"0" is west end.

Interval, Sample Description

feet Petrographic Chemical

0 to 109 - Unaltered, light-gray rhyolite.

109 to 119 - - Hard, silicified shale.

119 to 125 84 - Silica-carbonate dike; strike normal to

trench and dip vertical.

125 to 196 - - Shale and hard sandstone; no bedding and

irregular contacts approximately normal

to trench,

196 to 326 _ - Rhyolite, much bending on flow lines.

Trench 24

Length: 136 feet. Average depth: 5.0 feet.

Bearing: N. 350 E. Maximum depth: 7.0 feet,

"0" is southwest end.

Interval, Description

feet _

0 to 136 Unaltered, light-gray rhvolite.

Trench 25

Length: 47 feet. Average depth: 6.0 feet.

Bearing: N. 350 E. Maximum depth: 8.0 feet.

"0" is southwest end,

Interval, Description

feet

0 to 47 Shale and fault gouge.

Trench 26

Length: 74 feet, Average depth: 7.0 feet.

Bearing: 0 to 40 feet, due west. Maximum depth: 10.0 feet.

40 to 74 feet, due south. "0" is west end.

Interval, Description

feet

0 to 23 Shattered shale.

23 to 56 Weathered, brown silica-carbonate; a few very small lenses of

cinnabar.

56 to 74 Shattered shale.

INT.. BU .OF MINES.PGH. PA. 4681