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NICKEL-GOLD DEPOSIT NEAR

MOUNT VERNON, SKAGIT COUNTY

WASHINGTON

GEOLOGICAL SURVEY BULLETIN 93I-D

UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 931-D

NICKEL-GOLD DEPOSIT NEAR

MOUNT VERNON, SKAGIT COUNTY

WASHINGTON

BY

S. W. HOBBS AND W. T. PECORA

Strategic Minerals Investigations, 1941 

(Pages 57-78)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1941

For sale by the Superintendent of Documents, Washington, D. C. Price 15 cents

CONTENTS

Page

Abstract................................................. 57

Introduction............................................. 57

History............................................... 58

Previous Investigations.............................. 59

Field work and acknowledgments....................... 59

Topography........................................... 59

Geology.................................................. 60

Regional geology..................................... 60

Local geology........................................ 61

Pre-Tertiary sedimentary rocks................... 61

Serpentine........................................ 62

Eocene sandstone................................. 62

Latite (?)....................................... 63

Structure........................................ 63

Mineral depo sit.......................................... 64

Slllca-carbonat e ro ck................................ 64

Sulfide-bearing "breccia.............................. 65

Structural features.................................. 66

Mineralogy........................................... 67

Origin of the deposit................................ 68

Surficial alteration..,.............................. 70

Ore reserves............................................. 71

Size of mineral deposit.............................. 71

Sampling of the deposit.............................. 71

Trench sampling.................................. 73

Drill-core sampling........;..................... 73

"Character" sampling............................. 75

Significance of sampling.......................... 75

Quantity of sulflde ore.............................. 75

Experimental flotation tests......................... 76

Outlook...................................'........... 77

ILLUSTRATIONS

Page

Plate 11. Map showing location and geologic setting of

the Mount Vernon district................... 60

12. Geologic map and sections of Mount Vernon

nickel-gold deposit......................... 60

Figure 5. Generalized cross section of western end of

Mount Vernon district....................... 60

6. Vertical longitudinal section of the Mount

Vernon nickel-gold deposit.................. 72

III

NICKEL-GOLD DEPOSIT NEAR MOUNT VERNON, 

SKAGIT COUNTY, WASHINGTON

By S. W. Hobbs and W. T. Pecora

ABSTRACT

The Mount Vernon nickel-gold deposit is 4^ miles southeast 

of the city of Mount Vernon, Skagit County, Wash. It is a 

large, tabular, steeply dipping body of silica-carbonate rock 

which probably originated by hydrothermal alteration of serpentinized peridotite along a fault zone.

The serpentinized peridotite is intrusive into metamorphosed 

pre-Tertiary sedimentary rocks. These sediments and the serpentine are overlain unconformably by Eocene sandstone. The silicacarbonate rock lies along a normal fault on the south limb of a 

large anticlinal fold. The Eocene sandstone is everywhere the 

hanging wall and the serpentine the footwall of the deposit.

Locally the silica-carbonate rock is brecciated and has a 

cement of sulfides, quartz, and carbonates. Nickel is present 

in the sulfide-bearing breccia as bravoite and nickeliferous 

marcasite, in the main mass of silica-carbonate rock as nickeliferous ankerite and magnesite, and in the incompletely altered 

serpentine as nickeliferous serpentine or chlorite.

The approximate average tenor of the silica-carbonate rock, 

of which there are millions of tons, is 0.2-0.3 percent of 

nickel and about 0.02 ounce gold, to the ton. The sulfide-bearing breccia, of which probably 15,000 to 50,000 tons are available, may contain a slightly higher percentage of nickel and 

about the same amount of gold. The silica-carbonate rock is not 

amenable to effective concentration so cannot at present be considered ore. The sulfide-bearing breccia can be profitably concentrated by flotation so is regarded as possible ore.

The writers believe that the nickel was originally present 

in the serpentinized peridotite and that it was dissolved and 

redistributed by ascending hydrotherraal gold-bearing solutions 

while the serpentine was being altered into the silica-carbonate 

rock.

INTRODUCTION

The Mount Vernon nickel-gold deposit is a large body of 

mineralized rock exposed for a distance of more than 2 miles 

along the crest of Devils Mountain,.4^ miles southeast of the 

city of Mount Vernon, Skagit County, Wash. (pi. 11). Mount

57
58 STRATEGIC MINERALS INVESTIGATIONS, 1941 . , .

Vernon is a city of about 4,000 inhabitants, located. 65 miles 

north of Seattle. Two graded gravel roads give access to the 

property from Mount Vernon. One road approaches the ridge from 

the northeast and leads to the Devils Mountain Lookout Tower at 

the summit of the rldgej the other extends from U. S. Highway 99, 

a mile west of the property, to a point about halfway up the 

nose of the ridge, a mile west of the summit.

Mount Vernon.is on the Great Northern Railway, which passes 

within 2.miles of the west end of the property; a branch of the 

Northern Pacific Railway runs within 2 miles of the east end of 

the deposit.' Salt-water shipping facilities are available at 

the Puget Sound ports of Mount Vernon, Anacortes, and Everett.

History

The property was first prospected for gold more than 20 

years ago, when an adit was driven 50 feet into the lowermost 

outcrop of the deposit on the west end of the ridge but was 

abandoned until 1935. In-that year scattered areas of green 

coloration on the surface rocks aroused the interest of local 

prospectors, and analyses of the material proved the presence of 

nickel. The Pacific Nickel Co., organized in 1938, principally 

by local residents, controls about 2,100 acres which includes 

most of the deposit. Since 1938 tunnels aggregating about 300 

feet have been driven, and in 1939-40 the deposit was tested by 

27 diamond-drill holes totalling 6,375 feet.

No ore has been shipped from the property, but large samples have been collected for experimental flotation tests. In 

1940 mining operations were being planned by the company, which 

expected to start with a 250-ton pilot mill and hoped later to 

operate on a much larger scale.
59

Previous investigations

No previous geologic report of the Mount Vernon deposit has 

"been published. C. E. Weaver has described the general geology of a region that includes the mineral deposit, and R. D.

2/ 

McLellan has described the pre-Tertiary rocks of the areas

directly to the northwest. A report on the coal fields of west3/

ern Skagit County by Jenklns ' briefly describes the lithology

and structure of the Eocene rocks near Mount Vernon but does not 

mention the occurrence of nickel.

Field work and acknowledgments

The writers were engaged in field work In the Mount Vernon 

district from July 15, 1940, to August 29, 1940. They are 

greatly indebted to the officers of the Pacific Nickel Co. for 

their cordial cooperation and assistance in making available the 

company's maps, assays, and experimental results. Especial 

thanks are due to Mr. R. J. Cole, the company engineer, for much 

information and assistance both in the office and in the field. 

Mr. Thomas B. Hill, of the Washington State Department of Conservation and Development, Division of Mines and Mining, also 

placed much information at the disposal of the writers. Mr. 

John W- King assisted in the topographic mapping. The authors 

are indebted to F. C. Calkins, of the Geological Survey, for 

many helpful suggestions in the preparation of this report. '

Topography

The topography of the area reflects the bedrock structure. 

The rocks strike about N. 70° W., as does the sharp ridge of

I/ Weaver, C. E., Tertiary stratigraphy of western Washington and northwestern Oregon: Washington Univ. /^Seattle/ Pub. in Geology, vol. U, 266 pp.,

2/ McLellan, R. D., The geology of the San Juan Islands: Washington 

Univ. /Seattle/ Pub. in Geology, vol. 2, 185pp., 1927.

2/Jenkins, 0. P., Geologic investigations of the coal fields of Skagit 

County, Wash.: Washington Geol. Survey Bull. 29, 60 pp.,
60

Devils Mountain, which is carved from the resistant rock of the 

mineral deposit. Prom its highest point, at an altitude of 

1,750 feet, the crest of the ridge slopes gradually to the west 

for about a mile and then plunges more steeply toward the Skagit 

River-flood plain. - The nose of the ridge is mantled with glacial debris to an altitude of 300 feet.

The valley on the south side of the ridge is deeply cut into 

the Eocene sandstones and is occupied by a small stream for most 

of the year. In the valley 800 feet north of the central part 

of the ridge is Lake Ten, which is about a 'third of a mile long 

'and lies at an altitude of 1,240 feet. It was probably formed 

by the damming of the valley with glacial debris. The lake has 

.a very small drainage area, and its inflow and outflow are intermittent. : The lake water is available for mining purposes.

GEOLOGY 

Regional 'geology

The rocks exposed in northwestern Washington may be divided 

into two main groups: (1) pre-Tertiary sedimentary and Intrusive rocks ranging in age from Devonian to Cretaceous, and (2) 

a thick sequence of Eocene sandstones, shales, and conglomerates 

which overlie the older rocks with marked unconformity (fig. 5).

A

N- . Devils Mountain 

Little Mountain

Geology modified 

from C.E.Weaver

Figure 5. Generalized cross section of western end of Mount Vernon district. 

Cretaceous rocks are known on Vancouver Island and in the San 

Juan Islands of northern Puget Sound but are not found in the 

vicinity of Mount Vernon.
GEOLOGICAL SURVEY

122° 20' R.4E.

BULLETIN 981 PLATE 11 

R.5E.

EXPLANATION

N.FVe-Tertiary sedimentary

Silica-carbonate rock 

containing ore

Fault

3 Miles

i i i Geology modified from Cf .Weaver

Contour interval 250 feet 

MAP SHOWING LOCATION AND GEOLOGIC SETTING OF THE MOUNT VERNON DISTRICT
UNITED STATES DEPARTMENT OF THE INTERIOR 

GEOLOGICAL SURVEY R.4- E. BULLETIN 931 PLATE 12

Contour interval 50 feet

GEOLOGIC MAP AND SECTIONS OF MOUNT VERNON NICKEL-GOLD DEPOSIT
NICKEL-QOLD DEPOSIT NEAR MOTJNT VEKNON, WASHINGTON 61

Most of the Paleozoic and early Mesozoic sedimentary rocks 

have been metamorphosed to arglllites, quartzites, schists, and 

phyllltes. The Cretaceous Nariaimo formation of Vancouver Island 

and the Eocene Chuckanut formation of Washington, both of which 

contain coal seams, are unaffected by such me tamo rphl am.

The pre-Tertlary sedimentary rocks have been intruded by a 

series of igneous rocks that range in composition from dunite to 

granite. Most of the intrusive activity in Washington occurred 

in late Jurassic or early Cretaceous time. Most of the perldotltes in the San Juan Islands, however, are assigned to the TrlV assic by McLellan, although some small masses of very fresh

dunite are considered by him to be post-Jurassic. Post-Eocene 

ultrabasic rocks have" not been reported in this region.

Local geology

In the area that includes Devils Mountain (pi. 12) the 11- 

thologic units exposed are pre-Tertiary sedimentary rocks> ser-» 

pentine derived from peridotite, Eocene sandstone, latitic 

rocks, and silica-carbonate rock formed by alteration of the 

serpentine. As this last unit comprises the mineral deposit, it 

will be discussed in detail under that heading. It occupies the 

crest of Devils Mountain, lying, between the serpentinized peridotite of the north slopes and the Eocene sandstone of the south 

slopes. Pre-Tertiary sediments> Intruded by serpentine, occur 

north of Lake Ten. The contact between the Eocene sandstone and 

the silica-carbonate rock is a fault wherever it has been observed.

Pre-Tertlary sedimentary rocks.--The sedimentary rocks that 

underlie the Eocene sandstone are far from uniform in composition. They consist mainly of quartzitic sandstones and highly 

deformed argillite, but they include some phyllite. The individual beds are variable in thickness, but they are rarely more

U/ Mdellan, R. D., op. clt., pp. lU2-lU6. 

416229 0-41-2
62 STRATEGIC MINERALS INVESTIGATIONS, 1941 .

than a few inches thick. Their dips, where observed, are steep, 

and in places they are vertical. These rocks are probably the

same'age as the pre-Cretaceous formations in the San Juan Is5/ 

lands that are described by McLellan. They have the same

northwest trend as most of the sedimentary rocks in northwestern 

Washington.

Serpentine.-"The serpentine forms irregular masses intruded 

:into the pre-Tertlary sedimentary complex and is in places 

faulted against it. Serpentine forms the footwall of the silicacarbonate rock, which encloses irregular lenses and wedges of 

serpentine.

The typical serpentine is dark green, coarse-grained, commonly slickensided, and veined by carbonates and chrysotile. It 

was originally a peridotite composed essentially of olivlne and 

pyroxene, but these minerals have been almost entirely replaced 

by serpentine minerals. A black, fine-grained variety is the 

principal departure from the more typical green, granular rock, 

and is the result of alteration so complete as to have completely destroyed the original minerals and texture of the peridotite* Small chromlte grains are scattered through the serpentine, and chlorite, carbonates, and quartz are present in some 

places.

On the south slope of Little Mountain, email bodies of serpentinlzed peridotite are intrusive into the metamorphosed sediments, which unconformably underlie the Eocene sandstone.

Eocene sandstone* The Eocene sandstone unit, Identified by

6/ Weaver 'as the Chuckanut formation, Is brownish gray and masalve, cross-bedded, or coarsely stratified. Subordinate amounts 

of light-gray sandy shale, associated with some very black carbonaceous shale and thin seams of coal, are locally present.

Lenses of conglomerate from a few Inches to more than a hundred

McLellan, B. D.. op. cit., pp. 91-112. 

Weaver, C. B., op. cit., pp. 76-77.
NICKEL-GOLD DEPOSIT NEAR MOUNT VERNON, WASHINGTON 63

feet In thickness occur near the base of the formation and are 

Interbedded with the sandstone above the base. The llthology of 

the formation is extremely variable from base to top as well as 

along the strike.

Fossil leaves and leaf Imprints occur throughout the formation and are especially characteristic of its lower part. The

stratigraphy of this formation has been discussed in detail by

7/

Weaver. .

Latlte (?). Northeast of the Lookout Tower and about 400 

feet below the crest of the ridge is a conspicuous cliff of 

buff-colored fine-grained rock, which contains veinlets of carbonate. The rock has the general appearance of an altered sandstone, but microscopic study shows it to be composed of alkali 

feldspar and sodic plagioclase in a matrix of carbonate, sericite, and iron oxides. The feldspar constitutes 50 to 60 percent of the rock, and the feldspar laths, which are very elongate and partly distorted, have a very crude orientation suggestive of flow structure. The outcrops examined are nonporphyritic, although phenocrysts elsewhere have been reported. 

The.rock is probably an altered latite. Its relation to the 

sedimentary rocks is obscure, but it may be a member of the preTertlary complex.

Structure . The local structure conforms to the general 

structural pattern of western Washington. Movement which has 

occurred at intervals since early Mesozoic time has produced a 

series of northwest-trending anticlines, synclines, and faults, 

so that now the strikes of the various rock formations are approximately parallel. The only angular unconformity observed is 

the marked one between the Eocene sandstone and the underlying 

pre-Tertiary complex.

The Eocene sandstone has been folded into an east-west anticline, the axis of which lies north of Devils Mountain and

2/ Weaver, C. B., op. clt., pp. 77-?8.
parallel to It) and the mineral deposit occupies a later strikefault zone on the south limb of the anticline but near Its 

crest. This fault may appropriately be called'the Devils Mountain fault. Figure 5 Is a generalized cross section of'these 

structural features.

The Devils Mountain fault first produced a shear zone in the 

serpentine, along which alteration took place to produce the 

silica-carbonate rock, here considered the mineral deposit. Renewed movements, with an appreciable horizontal component, 

dropped the Eocene sandstone into its present position and also 

caused displacements within the silica-carbonate rock itself 

Other faults, of less displacement, have been observed on 

the north side of Devils Mountain. They may be related in age 

and origin to the Devils Mountain fault.

MINERAL DEPOSIT

The mineral deposit consists essentially of two kinds of 

rock: (1) silica-carbonate rock, and (2) sulfide-bearing breccia. The first, formed by nearly complete replacement of serpentine by quartz and carbonates, constitutes the bulk of the 

mineral deposit. The silica-carbonate rock was locally brecci~ 

ated, and quartz, carbonate, and sulfides were introduced to 

form the sulfide-bearing breccia, a part of which represents the 

only potential ore in the deposit.

Silica-carbonate rock

The silica-carbonate rock, the most resistant to erosion of 

any rock on Devils Mountain, crops out continuously along its 

crest for a distance of 2 miles. In many places the erosion and 

sliding of material from the hanging walls and footwalls has 

left long steep-sided reefs of the silica-carbonate rock projecting as much as 50 feet above the enclosing country rock. 

Surface outcrops are characteristically buff to brown in oolor.
NICKEL-GOLD DEPOSIT NEAR MOUNT VERNON, WASHINGTON 65

The resistant .character, of the rock is .caused by the abundance 

of quartz, which forms a .ramifying network of veins and irregular small masses. ' ' :

The silica-carbonate rock consists principally of a mixture 

of quartz, chalcedony, and carbonates, with small amounts of 

iron oxides and scattered grains of chromite, which are probably 

remnants of the grains in the original peridotite. Near the 

Lookout Tower and east of Lake Ten, wedge- or lens-shaped bodies 

of serpentine are Included in the silica-carbonate rock, and 

complete gradations between the two can be observed.

Three varieties of silica-carbonate rock can be recognized. 

The most abundant variety is hard, predominantly buff-colored, 

and very fine-grained; it is cut by many irregular stringers of 

coarse-grained carbonate and quartz. Local brecciation and irregular fracturing are evident in many places. Incompletely altered residuals of a green silicate mineral probably a chlorite- are present in the rock. :This variety is most abundant in 

the western half of the mineral deposit.

The dominant variety grades into a soft, earthy, very limonitlc one that makes up a rather small.part of the mass. This 

variety commonly appears at the surface as irregular bands in 

the dominant rock and in the partly altered small serpentine 

bodies within the mineral deposit. 'Layers of it as much as 10 

or 12 feet thick have been observed in drill cores from depths 

of 600 to 700 feet below the crest of the hill.

A third variety, making up only a very small percentage of 

the deposit, is porous, flaky, and rich In a green chloritic 

mineral, quartz, and carbonates. This .represents a less ad-? 

vanced stage of alteration than the first two varieties and is 

found most'commonly in the partly altered serpentine bodies.

Sulflde-bearing breccia

The sulfide-bearing breccia is exposed at many places in the 

central part of the deposit. The fault contact between this

416289 O - 41 - 3
66 STRATEGIC MINERALS INVESTIGATIONS, 1941

rock and the sandstone of the hanging wall is best shown in the 

small crosscut adit; it is visible also in several trenches 

farther east. The rock is typically a hard, compact breccia. 

The individual angular fragments in the breccia, some of which 

are as much as 3 Inches in diameter, are composed of highly 

silicified to typical.silica-carbonate rock. The sulfides are 

fine-grained and are restricted to the interstices between fragments, although minute sulfide veinlets are present in some 

fragments. In places the. breccia is barren of sulfides. Commonly, the sulfides in the breccia are partly or completely oxidized. The sulfides in breccia are very well exposed in a deep 

surface trench about 800 feet east of the crosscut adit, where 

the breccia is y in contact with an irregular vein of shattered, 

glassy, bull quartz whose maximum thickness is 4 feet. Chemical 

tests and petrographic observations indicate that the nickel 

content of the sulfide-bearing breccia is not a direct function 

of the sulfide cont ent. ' i

Structural features

The silica-carbonate rock occupies a fault zone between 

sandstone and serpentinized peridotite. The form, thickness, 

and general attitude of the deposit in the central part of 

Devils Mountain, a typical cross section of which is shown on 

plate 12, was established by 16 drill holes in 12 localities. 

The silica-carbonate rock has a sharp fault contact with the 

hanging-wall sandstone and commonly also a well-defined contact 

with the serpentinized peridotite of the footwall. Where faulted the contact with the- serpentine is very sharp. Evidence of 

brecclation and renewed movement is abundant 

Small cross faults are common and are best o'/served in the 

adits. The deposit is cut throughout its length by a steeply 

dipping set of fractures oblique to its trend. These fractures, 

together with nearly horizontal slickensides on the longitudinal
TTECKEL-GOLD DEPOSIT HEAR MOtJNT VERNON, WASHINGTON ' 67

fault fissures, suggest a strong horizontal component of movement along the main fault, at least during the last stages of 

faulting. Although the greatest movement occurred along the 

break between the serpentine and the sandstone, numerous other 

slippage planes are distributed through the silica-carbonate 

zone.

Mineralogy

The minerals identified in the deposit are the silica minerals quartz, opal, and chalcedony; the carbonates ankerite, magnesite, dolomite, and calcltej marcasite and pyrlte; bravoite 

((Fe, Nl) Sg); chromite (FeCrgO^); and serpentine minerals, 

which are hydyous magnesium silicates. Much of the rock exposed 

at the surface is stained with oxides of manganese and iron. 

The chromite and the serpentine are'residual from the original 

serpentinized peridotlte.

Marcasite is by far the most abundant of the three sulfides. 

A small crushed sample of unaltered marcasite, recovered from 

the gangue minerals by use of heavy liquids, was analyzed by 

Michael Plelscher, of the Geological Survey, and found to contain a trace of nickel. Bravoite is scarce and unevenly distributed, but It is so intimately associated with marcasite that 

both minerals probably originated under the same conditions. 

Bravoite cannot be detected in hand specimen, but it can easily 

be identified under the microscope by its lavender color. The 

pyrite, which occurs in small quantity, is cciarser-grained than 

marcasite. It was formed earlier than either marcasite or bravoite. Where the sulfides have been completely oxidized a porous breccia weakly cemented with iron oxide remains.

Quartz is the most abundant gangue mineral and forms veinlets, geodes, clusters, or boxworks. Carbonates are locally 

abundant in the partly altered serpentinized peridotite and form 

veinlets or disseminated masses in the silica-carbonate rook.
68

In surface outcrops, silica tends to replace the carbonate minerals and to form a rock very rich in silica; carbonates, on the 

:other hand, are abundant in the cores from deep drill holes. A 

sample of greenish ankerite tested by. Fleischer showed an appreciable quantity of nickel, thus indicating that some of the 

carbonates are to a small extent nickeliferous.

Native gold has not been seen in either the silica-carbonate 

rock or the sulfide-bearing breccia, although it is distributed 

in small quantity throughout the mineral deposit. The gold is 

probably in the free state and although it is very fine grained, 

it is reported to be effectively concentrated from sulfide-bearing breccia by means of flotation of the sulfides (see p. 77).

 

Origin of the deposit

The unaltered wedges of serpentinized peridotite in the 

silica-carbonate rock, the gradations between unaltered and altered serpentine, the residual chromite grains, the association 

of nickel and gold, and the abundant evidence of shearing and 

faulting all indicate that the silica-carbonate was formed by 

intense alteration of serpent in,ized peridotite along a shear 

zone* The abundant carbonates and quartz and the auriferous 

iron-nickel sulfides were probably introduced by hydrothermal 

solutions.

The serpentine contains about 0.25 percent of nickel, which 

is about the average nickel content of serpentines elsewhere in 

the Coast Range province. The nickel was probably contained 

originally in the primary silicates, the chief of which is oilvine, and was retained in the serpentine minerals to which the 

olivine was altered.

Much or all of the nickel, magnesia, and iron in the silicacarbonate rock could have been taken into solution by the hydrathermal attack on the serpentine, transported to new sites by 

the solutions, and there deposited in the form ef secondary
NICKEL-GOLD DEPOSIT NEAR MOUNT VERNON, WASHINGTON 69

minerals. A large part of the silica itself could have resulted 

from a "break-down of the original silicates and "been transported 

to new sites for redeposition as quartz and chalcedony. Calcium 

also may have originated in the serpentine, and likewise the 

gold. Assay reports of the Pacific Nickel Co. indicate that the 

maximum gold content of the serpentine is 25 cents to the ton.

The carbon dioxide in the carbonates Is much harder to explain, but its source is a significant question because of its 

great quantity. The problem of the origin of sulfur in the sulfide-bearing breccia, which, it will be remembered, was formed 

later than the silica-carbonate rock, is likewise significant. 

However, no conclusive evidence has been found bearing on the 

origin of either the carbon dioxide or the sulfur. Although the 

character of the quartz and chalcedony in surface outcrops suggests deposition from low-temperature supergene solutions, some 

of the glassy quartz which forms thick veins or boxworks in the 

silica-carbonate rock resembles the quartz that is characteristic of mesothermal deposits. The alteration of the serpentine, 

redistribution of the nickel, and introduction, from unknown 

sources, of at least the carbon dioxide and sulfur and possibly 

also a considerable part of-the gold and silica are therefore 

attributed to hydrothermal solutions.

The sequence of geologic events that the writers believe to 

have caused this deposit is summarized below. Both the silicacarbonate rock and sulfide-bearing breccia are here assigned to 

the same post-Eocene metallogenetic epoch.

1. Serpentinization of peridotite.

2. Erosion of serpentine. Deposition of Eocene sandstone unconformably above serpentine.

3. Folding of Eocene sandstone into an anticline, and

faulting to produce the Devils Mountain fault zone 

near the crest of the fold.

4. Formation of silica-carbonate rock along the fault

zone.

a. Alteration and replacement of tlie serpentine by 

quartz and carbonates through action of hydrothermal solutions.

b. Renewal of fault movement, causing local brecciation of the silica-carbonate rock.
70 STRATEGIC MINERALS INVESTIGATIONS, 1941

c. Introduction of quartz, carbonates, and sulfides, which cemented and replaced the brecciated1 fragments to form a hard rock, 

d. Renewed movement and small-scale fracturing, 

followed by introduction of light-green to 

colorless carbonate, glassy quartz, and opal- 

, ine quartz.

e. Renewed movement with a strong easterly compon- 

. ent, producing gouged, grooved, and slickensided surfaces, and localized cross-fracturing 

in the deposit and in the adjacent Eocene 

sandstone. Introduction of coarse-grained 

calcite along the fractures. 

5. General surface oxidation and leaching, the end

product of which was rich in silica, and oxidation 

of the sulfide-bearing breccia, producing a porous 

llmonitlc residue nearly devoid of sulfides near 

the surface.

Surficial alteration

Weathering of the deposit has had two principal effects. 

Through leaching of carbonates the surface outcrops are left 

richer in silica (including quartz, chalcedony, and opal), and 

through oxidation of the sulfides much limonite has been formed, 

especially in the sulfide-bearlng breccia. The drill cores also 

contain much limonite. Furthermore, drill-core recoveries ranged 

from 15 to 70 percent, which indicates that some parts of the 

deposit are either porous or friable at the depths drilled, perhaps as the result of deep weathering. It is probable that oxidation and leaching extend below the drilled part of the deposit, for the climate is humid, the water table low, and the 

fractured parts of the rocks permeable.

Sulfides and silicified breccia are rare in drill cores,, 

even In those obtained directly beneath surface showings of sulfide-bearing breccia. The fact that some sulfides are present 

at the surface la evidence that the unfractured rock Is almost 

Impervious. The absence of sulfide-bearing breccia in the drill 

cores cannot readily be explained.

There is. not enough evidence in hand to show whether or not 

a zone enriched in nickel lies below the drilled part of the deposit. This is one of the problems that should be considered In 

planning future exploratory work.
NICKEL-GOLD DEPOSIT NEAR MOUNT VERNON, WASHINGTON 71

ORE RESERVES

i i i

Size of mineral deposit

The nickel-gold deposit near Mount Vernon is exposed for 

about 2 miles between altitudes of 300 and 1,750 feet. Drilling 

records and geologic evidence both show that the deposit is a 

steeply dipping tabular body ranging in thickness between 100 

and 300 feet and probably extending below sea level. The bulk 

of the deposit is composed of hard silica-carbonate rock that 

cannot properly be called ore because of its low tenor and the 

difficulties of concentrating and extracting the little nickel 

that it contains. According to reports, however, the sulfldebearing breccia can be effectively concentrated by flotation.

A vertical, longitudinal section along the strike of the 1 deposit is shown in figure 6. Block A, estimated from the results 

of exploration and drilling to contain more than 15,000,000 

tons, is the most favorable ground in the deposit. Only a part 

of block A is sulfide-bearing breccia. Block B, so far as examination of surface outcrops and of the drift adit at the west 

end indicates, contains no sulfide-bearing breccia. In block C 

partly replaced wedges and bodies of serpentine are common and 

outcrops of sulfide-bearing breccia are rare. The deposit as a 

whole must contain more than 50,000,000 tons of silica-carbonate 

rock.

Sampling of the deposit

The silica-carbonate rock was sampled by three different 

methods, which give closely similar results. The results of two 

programs of systematic sampling, one a State-supervised Works 

Progress Administration project and another by the Pacific 

Nickel Co. have been made available for this report. The writers themselves employed a method of "character sampling" to gain 

additional information concerning the general distribution of
72 STRATEGIC MINERALS INVESTIGATIONS, 1941

5 c 5 5.3 33

§ 5
73

nickel and gold In the various rock types. A comparison of the 

results obtained by these three methods Is shown In tables 1 

and 2.

Trench sampling

In 1937 the Works Progress Administration of the State of 

Washington, sponsored by the State Department of Conservation 

and Development, and the State Commissioner of Public Lands, 

sampled the outcrop of the Mount Vernon deposit. Under the 

supervision of Mr. P. E. Crane, trenches were cut across the deposit at Intervals of about 400,feet and channel samples were 

taken from the bottom of each trench. Nickel assays were made 

by I. A. Pearl, but no gold assays were made. Assays representing 74 samples and 600 feet of channeling (see table 1) show a 

weighted average, as computed by the writers, of 0.293 percent 

of nickel.

Drill-core sampling .

In the spring of-1940, the Pacific Nickel Co. drilled 16 

holes in the area shown on plate 12. Of the 6,375 feet of 

drilling, 2,598 feet, in 10 holes, traversed the silica-carbonate rock, and the cores from these were split into 157 samples 

for assays by well-known assay companies. Core recoveries 

ranged from 15 to 70 percent. The average of the 157 samples, 

weighted according to the length of core.represented by each 

sample and disregarding percentage of core recovery, is 0.251 

percent of nickel. The unweighted average for gold is 0.0195 

ounces to the ton. It is possible that part of the sulfides enclosed in porous rock may have been lost during extraction of 

the drill cores. The results from both trench and core samples 

are shown in table 1.
74 STRATEGIC HINERALS INVESTIGATIONS, 1941

Table 1. Assays of trench and drill-core samples from the nickel-gold deposit

near Mount Vernon

Nickel 

(percent)

0.10-0.20

.20- .30

.30- .40

.40- .50

.50- .60

.60- .70

.70- .80

.80- .90

.90-1.00

No. 

of 

Assays

16

31

16

8

2

0

1

0

0

74

Length 

of 

sample 

(feet)

125

225

150

70

20

0

10

0

0

600

Weighted 

average

(percent)

0.155

.245

.343

.456

.555

_ _

.70

 

 

.293

Drill-core samples

Nickel

Nickel 

(percent)

0.10-0.20

.20- .30

«30- .40

.40- .50

.50- .60

.60- .70

.70- .80

.80- .90

.90-1.00

No. 

of 

Assays

22

105

22

3

2

0

1

1

1

157

Length 

of 

core 

(feet)

316

1,829

334

61

24

0

19

10

5

2,598

Weighted 

average 

(percent)

0.184

.225

.340

.466

.528

 

.78

.81

.96

.251

Gold

Gold 

(ounces 

per ton)

0.01-0.02

.02- .03

.03- .04

.04- .05

.05- .06

_ . _

No. 

of 

Assays

67

65

. 15

8

1

156

Average 

(ounces 

. per ,/ 

ton)^

0.012

.020

.030

.040

.06

.0195

I/ Unweighted.

Table 2. Analyses of representative nickel-bearing rocks

Description

Porous, flaky, buff -colored rock, in varioua stages 

of transition to silica-carbonate rock.

Sillcified breccia with sulfides. Marcasite is 

predominant, but some bravoite is present in 

No. 4.

Nickel i/ 

(percent)

/ 0.24

f .21 

.24 

1 .26

.19 

.18 

.22 

.47 

.20

Gold 

(ounces o/ 

per ton)-'

Not det.

...do... 

.01 

.01

f)T

.016 

Not det. 

.022 

Not det. 

.07

Value^

$2.00 

2.00

2.20 

2.75 

3.80

I/ Assays ty Michael Fleischer.

Z] Assays by Ledonz and Co., New Tork.

3_/ Hlckel calculated at 35 cents a pound and gold at $35 an ounce.
NICKEL-GOLD DEPOSIT NEAR MOUNT VERNON, WASHINGTON 75 

- " "Character" sampling

During the course of the field work, the writers collected 

.samples representing typical serpentinized peridotite, the several varieties of silica-carbonate rock, and the sulfide-bearing 

breccia. Some of these samples were assayed by Michael Fleischer, of the Geological Survey, for nickel and by Ledoux & Co. for 

gold. The results' are shown in table 2, which also shows the 

approximate value at present prices of 35 cents a pound for 

nickel and $35 an ounce for gold. Mr. R. J. Cole reported that 

a composite sample of sulfide-bearing breccia ore, collected by 

him for metallurgical tests, contained 1.07 percent of nickel 

and 0.015 ounces of gold to the ton and that the sulfide' concentrate from this sample contained about 6 percent of nickel and 

0.16 ounces of gold to the ton.

Significance of sampling

The accumulated assay figures for the entire deposit indicate that in general the serpentinized peridotite contains more 

nickel than the silica-carbonate rock. The nickel content is 

greatest in some of the sulfide-bearing breccia, probably because that rock contains unevenly distributed bravoite and nlckeliferous marcasite. The silica-carbonate rock cannot be considered nickel ore, first because the nickel content is low and 

se.cond because the nickel is divided between carbonate, sulfide, 

and silicate rather than concentrated in a single mineral. This 

rock, however, may possibly be regarded as submarglnal gold ore, 

and some of the sulfide-bearing breccia may be regarded as potential ore by virtue of the combined nickel and gold content.

Quantity of sulfide ore

Exposures indicate that the deposit contains at least 15,000 

tons, and possibly as much as 50,000 tons, of sulfide-bearing 

breccia. As to tenor, all that can be said with any assurance
76 - STRATEGIC MINERALS INVESTIGATIONS, 1941

is that the breccia averages more' than 0.20 percent of nickel 

and about 0.02 ounces of gold to the ton. Its silver content is 

negligible. At the present market prices of 35 cents a pound 

for nickel and $35 an ounce for gold, the gross value of this 

material-would thus be--at least $2.00 a short ton.

In a large trench immediately east of the crosscut adit, a 

shoot of hard, brown, sulfide-bearing breccia a foot thick, with 

a few auxiliary shoots, is exposed in the buff silica-carbonate 

rock. It strikes obliquely to the mineral deposit and dips 

northwest. The breccia here is of the same character as that 

in the crosscut adit. The sulfide-bearing breccia is dlscontinuously exposed along the crest of the ridge for about 1,500 

feet east of this trench. The largest exposure, about 800 feet 

1 east of the crosscut adit, has been proved by trenching to be 

30 feet wide and appears from surface observations to be more 

than 60 feet long. No drilling has been done below this large 

exposure. None of the shoots of sulfide-bearing breccia exposed 

east of the drilled area are more than a few feet wide.

The most favorable localities for other shoots of sulfidebearing breccia may be immediately beneath surface outcrops of 

sulfldes. Such localities have not been investigated thoroughly. 

Future exploration may also reveal other sulfide-bearing breccia 

ore shoots within the silica-carbonate rock. The known exposures of sulfides would indicate.that a surface mining method 

would be most advantageous.

Experimental flotation tests

Experimental flotation tests on a selected sample of sulfidebearing breccia, made by Mr. W. H. Marquette, of Seattle, Wash., 

for the Pacific Nickel Co., Indicate a high concentration ratio. 

The results of tests on a sample : of several hundred pounds of 

ore collected by Mr. R. J. Cole are shown in table 3. The assays were made by private companies.
NICKEL-GOLD DEPOSIT NEAR MOUNT VERNON, WASHINGTON ' 77

Table 3. Results of flotation tests on sulfide-bearlng breccia

TToo A a

Rough concentrates

rp«4 1 a

Weight 

(percent)

100.0

2 Q

 8

96.3

Gold 

(evinces 

per ton)

0.015

i a

.08

.0025

Silver 

(ounces 

per ton)

O oe

1.46

1.04

.06

Nickel 

(percent)

1.07

6 OR

2.84

.08

Value 

per ton

(fto on

50.39

23.42

.1Q

The most encouraging results of tests made by Mr. Marquette 

on a large sample of silica-carbonate rock selected by Mr. Cole 

are shown in table 4. It is not known whether this sample contained sulfides. The presence of 0.68 percent of nickel suggests the presence of sulfides or nickeliferous carbonates.

Table 4. Results of flotation tests on silica-carbonate rock

Heads .............

To1 1 q .............

Weight 

(percent)

100

1.4

QO A.

Gold 

(ounces 

per ton)

0.015

.PO

.005

Nickel 

(percent)

0.68

8.21

.45

Value 

.per ton

$5.29

64.48

3 ^0

Outlook

The silica-carbonate rock on Devils Mountain cannot properly 

be considered a large potential nickel reserve. At best, if 

selective large scale low-cost mining methods and favorable 

means of concentration are employed, it might be considered a 

marginal to submarginal gold deposit, whose value would be 

slightly enhanced by the small amount of nickel recoverable from 

the sulfide minerals of the concentrates.

The sulfide-bearing breccia, because of its uneven tenor and 

small tonnage, cannot be depended upon to sustain any long mining operation. Some of it, however, 1 might be mined .at a profit 

under present economic conditions. This sulfide ore could best
78 ' STRATEGIC MINERALS INVESTIGATIONS, 1941

"be mined selectively, on a small scale, and concentrated by flotation, to which the ore Is well adapted.

O
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