Quicksilver Deposits Near 

Weiser, Washington 

County, Idaho

GEOLOGICAL SURVEY BULLETIN 1042-D

Prepared in cooperation with the 

Idaho Bureau of Mines and Geology

CONTRIBUTIONS TO ECONOMIC GEOLOGY

QUICKSILVER DEPOSITS NEAR WEISER, 

WASHINGTON COUNTY, IDAHO

By CLYDE P. Eoss

ABSTRACT

The quicksilver deposits in the general vicinity of Weiser, Washington County, 

Idaho, were first recognized about 1936. They are in an agricultural community with almost no previously known evidence of the presence of metallic 

lodes. A deposit opened in 1939 became by the following year one of the 

leading quicksilver producers in the United States. The mine was operated by 

the Idaho Almaden Mines Co. through December 1942. As yet none of the 

other quicksilver deposits in the district has become productive and there 

has been little mining activity since 1943.

All of the deposits are of the opalitic type, and are in sedimentary rocks 

of Tertiary age, which have been altered along fractures and in zones of tension 

by hydrotherrnal solutions. The principal shoots, which have been mined, 

are under a cover of relatively impermeable rock. Silica and clay minerals 

were formed in several pulses of mineralization, during which the grains 

composing the sedimentary rocks were dissolved and contributed their constituents to the minerals of the opalite. The opalite is finely brecciated, apparently in part because of swelling and contraction of colloidal.gels. Cinnabar 

was introduced during each of the pulses of mineralization, but principally 

in the last one.

The district has promise for the future, as the mining and prospecting already 

done have not exhausted the possibilities. When economic conditions warrant, 

it will be worthwhile to search for cinnabar in areas of sedimentary rock that 

show evidence of opalitization. In 1942 at the close of productive activity 

much low-grade material was known to have been left unmined, but there may 

remain ore as rich as that already mined.

INTRODUCTION

The quicksilver deposits near Weiser, Washington County, Idaho, 

(fig. 7) appear to have been first discovered about 1936. Soon thereafter one mine became, for a few years, one of the country's leading 

quicksilver producers; it still has possibilities of future production. 

The delay in recognizing the quicksilver lodes resulted largely from 

the fact that the mineralized outcrops are inconspicuous and have few 

features commonly regarded as characteristic of metallic .mineral deposits. The deposits occur in an agricultural community, but metalmining districts are close by. Experienced mining men would not

79
80 CONTRIBUTIONS TO ECONOMIC GEOLOGY

116° . _ 114" .___ _.__ . 112"

 ' 42°

FIGURE 7. Index map showing location of the principal quicksilver deposits near Weiser,

-L... . .' . .. . Washington County, Idaho. - " . ;
81

have expected to find ore deposits in the lava flows and soft sedimentary beds of the area.

LOCATION

- The principal quicksilver deposits are immediately east of the 

Weiser River, which here flows south near the common boundary of 

T. 11 .N., R. 3 and 4 W. (pi. 4). This area is served by the New 

Meadows branch of the Oregon Short Line (Union Pacific System), 

which joins the main line at Weiser. County roads near Weiser have 

recently been paved, others are gravel-surfaced with many dirt roads 

leading from them. The Idaho Almaden mine, the only significantly 

productive mine in the district, is at the south end of this area and 

15 miles by road from Weiser.

Plate 4 shows the topography of this area and the position of the 

principal mines and prospects. This map is compiled from the map 

of Weiser Cove quadrangle published by the U. S. Geological Survey 

in 1952 and from manuscript copies of parts of adjacent maps. The 

township lines shown on plate 4 are projected from data on the map 

of the Weiser Cove quadrangle.

Cinnabar has been reported also from prospects (fig. 9) in the 

southeastern part of T. 12 N., R. 5 W. along U. S. Highway 95 about 

8 miles north of Weiser (fig. 7). Some of these prospects were originally opened in search for gold. Quicksilver has also been found 

in a prospect in T. 15 N., R. 6 W. near the Snake River (fig. 7).

' ' SCOPE OP THE REPORT

The studies here summarized were carried out mainly in 1941 as a 

part of the strategic minerals investigations of the U. S. Geological 

Survey. The data were used in exploration made by the U. S. Bureau 

of Mines and are of interest in connection with any future explorations for the metal in southwestern Idaho. Quicksilver lodes somewhat similar to those near Weiser are widespread in northern Nevada 

and southeastern Oregon, and some, without present known commercial value, have been noted by the writer also in parts of Owyhee 

County, Idaho.

During the summer of 1941 an area that includes the principal 

quicksilver deposits east of Weiser was studied by C. H. Dane, Jr., 

assisted by R. P. Full; they also visited the prospects in T. 12 N., 

R. 5 W. and T. 15 N., R. 6 W. At the same time the writer mapped 

and studied the properties then held by the Idaho Almaden Mines 

Co. and the Consolidated Quicksilver Mining Corporation, and 

visited nearby prospects. The writer was assisted by R. P. Full in 

the planetable surveying; Full also participated in the underground 

work.'
82 CONTRIBUTIONS TO ECONOMIC GEOLOGY : Since .1941 the area has been revisited several times. In June 1943,. 

the writer, assisted by N. W. Balcom, mapped the then-existing 

workings at and near the Idaho Almaden mine. At that time work 

was in progress at the Zucker group, northwest of the main workings 

of the Idaho Almaden mine;* therefore the planetable map was extended to include that part of the Zucker group in which there was 

activity. In June 1954, the writer, assisted by Jack Terry, visited 

other parts of the district and further extended the map.

ACKNOWLEDGMENTS

Cooperation was received throughout the investigations from the 

Idaho Almaden Mines Co., represented by its president, L. K. Requa, 

and superintendent, Reginald Lee. Dr. J. C. Bartlett, who represented the owners of the Idaho Almaden property, was most cooperative. Dr. F. L. Richardson, president of the Consolidated 

Quicksilver Mining Corporation, and those interested in the other 

properties visited were likewise cordial and helpful. Data on production and assay values given in the present report are based on the 

records of the Idaho Almaden Mines Co., released through the 

courtesy of the present owners.

Clarence S. Ross of the Geological Survey identified the constituent 

minerals of the clay aggregates and aided in evaluating their significance. K. E. Lohman, F. S. MacNeil, R. W. Brown and D. W. Taylor 

furnished paleontologic information. C. A. Ecklund made the compilation of plate 4 possible by furnishing data in advance of 

publication.

PREVIOUS WORK

Several valuable geologic reconnaissances have been made in this 

part of Idaho, notably that by Lindgren in 189T (Lindgren, 1900, 

1901) and those by Washburne (1911) and Buwalda (1923). Kirkham's work on water supply at Weiser (Kirkham, 1928) added details.

Kirkham (1930; 1931a, b, c; 1935) later mapped and described a large

area that includes all the cinnabar deposits here described. His 

work constituted a distinct advance in the study odH the Tertiary ftftd 

Quaternary history of the region. However, the present studies, 

which are more detailed and cover a much smaller area, differ from

Kirkham's in enough respects tO emphasize the need for further 

structural and stratigraphic work.

In addition to the general papers just cited, three that summarize

the early work at the Idaho Almaden mine are available. TllGSB 9T6 

a news note written soon after production started (Mining World, 

1939), followed soon by an account of operations written by the 

president of the company (Eequa, 1940), and somewhat later a geo1 Mining at the Idaho Almaden mines Is reported to have been resumed in 1955 and 

1956 by the Rare Metals Corporation of America.
QUICKSILVER DEPOSITS, WEISER, WASHINGTON COUNTY, IDAHO 83

logic -study made for the Idaho Bureau of Mines and Geology 

(Anderson, 1941). Eeference should also be made to notations in 

the annual reports of the Idaho Inspector of Mines for 1939 through 

1943 (Campbell, 1942 and 1944).

GEOGRAPHY

The quicksilver deposits here described are in the low hills north 

of the west end of the Snake River plain. These hills are drained by 

the Weiser River and its tributaries. The Weiser River enters the 

Snake River near the city of Weiser at an altitude of about 2,110 feet 

above sea level. Some of the hills are flat topped and steep sided but 

many have gentle slopes. On the whole, the topography is far more 

subdued than that of most areas in central Idaho. Nutmeg Mountain 

(altitude 3,735 feet) is one of the highest hills in the vicinity of the 

quicksilver deposits. Farther east and north, mostly beyond the limits 

of the area shown in plate 4, some summits rise over 4,000 feet above 

sea level. The upper reaches of the Weiser River flow through 

canyons but within the area (pi. 4) the river valley broadens sufficiently to permit some f arming.and west of that area, toward Weiser, 

the valley is even wider and more intensively cultivated.

As the mean annual precipitation is little more than 11 inches, 

uncultivated land has a somewhat scanty cover of grasses and sagebrush, with trees only in favored spots. However, the soil of the 

large valleys responds so readily to cultivation under irrigation that 

favorably situated parts of Washington County contain many 

ranches, dairy farms, and orchards. The county, with an area of 

1,479 square miles, had a population of 8,853 according to the 1940 

census and 8,576 according to the 1950 census. Weiser, the county 

seat, had a population of 3,663 people in 1940 and 3,961 in 1950, and 

is a center of trade for a wide area that stretches beyond the county 

limits.

GEOLOGY

STRATIGRAPHY AND LITHOLOGY

Tlier most abundant rocks near Weiser are moderately consolidated 

sandstone and siltstone or shale with subordinate conglomerate. 

Basalt flows are intercalated in these, and a few small dark dikes have 

been noted. The bedrock is masked by alluvium in the valleys and 

by landslide debris on some slopes.

The sedimentary rocks are largely arkosic, but locally include 

some tuffaceous material and a few diatomaceous beds. They are 

stream, fan, and pediment deposits broadly similar to those forming 

in modern valleys. Beds of lignitic coal crop out along Crane Creek

388401 56 2
84 r -: ' -CONTRIBUTIONS TO ECONOMIC. '.GEOLOGY -Tt:. .-:.?;.;<::,

several Smiles* to the ea'sfc (.fig. 7). -The coal beds have -little: #.conQmi<i 

value .under present conditions.' They .'indicate. tha.t .the Tertiary ;v/aLley; fill included some swamps. Ponds or lakes may also ; have j been 

present locally. The arkosic material was probably derived) from 

the Idaho batholith, whose west border is exposed along the North 

Fork of the Payette River about 35 miles east of Weiser (fig. 7) .

Plant fossils were collected by Dane in 1941 in sec. 31, T. 11 N., R. 

3 W. and were reported by R. W. Brown to include Zelkova ofegoniana 

(Knowlton) Brown, Quercus colwribiana Chaney, and Saliss.'inquirenda Knowlton. Brown noted that "These species are common 

Miocene elements in Idaho and Washington," probably middle or 

upper Miocene in age. Paleobotanists are inclined to believe that the 

flora to which these plants belong indicates a climate more humid than 

the present one in the region (Axelrod, 1950) .

Fossil shells collected by Dane were examined by F. S. MacNeil. He 

found that a collection from near the Idaho Almaden mine on Nutmeg 

Mountain contained

Gonioftasis sp. aft'. G. taylori (Gabb) and Goniabasis sp.?, a' gigantic form of 

nearly four inches in length and lacking the axial structure characterizing 

G. taylori with which the smaller specimens are compared.

The second collection came from about 4 miles north of the Idaho 

Almaden mine, south of Crane Creek and at an altitude of roughly 

2,500 feet ; in it MacNeil found Campeloma sp., Vorticifex cf . binneyi 

(Meek) and Sphaerium cf . idahoense Meek. MacNeil, whose communication was dated January 12, 1942, was not then in a position to 

assign an age to the fossils he listed. D. W. Taylor had recently made 

studies pertinent to the problem so the lis.t was sent to him for comment. 

His reply, dated October 8, 1954, suggested a Pliocene age. ..

Dane collected diatomaceous material close to the spot where he got 

the second collection of fossil leaves referred to above. K. $. Lolinian 

(written communication, February 1955) stated that he recognized 64 

kinds of diatoms. He commented, that the assemblage of fresh- water 

diatoms he identified is characteristic of a large, cool, and fairly deep

lake. The diatoms are mixed" with -Volcanic ash in abOUt GQUal PPOportions, which suggests light but continuous ash fall during the time

interval represented by the collection. Many of the larger diatoms

are broken. With sharp, jagged edges. -Lohman suggested that they

might have been broken during compaction of the material into rock 

Or that the broken diatoms might have been derived froni some older

diatomaceous sediment. ..,.'*

With reference to the age of the deposit Lohman commuted as

This assemblage is unusually diverse in character, as it contains a. few. species 

which in other localities are restricted to fairly short periods of geologic time,
QUICKSILVER- DEPOSITS; WEISER, WASHINGTON COUNTY, IDAHO $5}

coupled with many long ranging species that range from-Miocene to Recent: The 

most diagnostic, extinct species, and also the most abundant in this assemblage is 

M-elosira, solida, which reached its heyday in early to middle Pliocene time and 

has never been found in Pleistocene rocks. Gomphonema grovei is another species 

with a similar history and which occurs frequently in this assemblage. Several 

of the un-named species are ones which I have found in rocks of Pliocene age in 

other localities. The unusual preponderance of long ranging species makes an 

age assignment of this collection dependent upon the-small proportion of species 

considered to be definitive and reduces the certainty with which such an assignment may be made. With these uncertainties expressed, the most -probable age 

assignment is early to middle Pliocene. _ ' '!'

Kirkham. (1930) assembled data on the Tertiary strata in this 

part of Idaho. He said the Payette formation (Miocene of Kirkham)' 

is interbedded with the Columbia River basalt and in most places it 

underlies the upper flows of the Columbia River basalt. On this basis 

his generalized map shows the sedimentary rocks east of that part of; 

the Weiser River shown in plate 4 of this report as belonging to the, 

Payette formation, whereas it shows those to the west of the river 

as belonging to the Idaho formation which he regarded as Pliocene (?). 

In this report the sedimentary rocks are assigned simply to the Ter-; 

tiary, leaving more precise subdivision and age assignment to future 

work.;

; The only other pre-Quaternary rock extensively exposed is the. 

basaltic lava. Kirkham's map shows this as part of the Columbia; 

River basalt. The lava generally resembles that formation and Kirkham's assignment is assumed to be broadly correct for. the region 

he mapped. However, the correlation of the flows within the area 

(pi. 4) is subject to the same uncertainties as the enclosing sedimentary beds. Like the enclosing rocks, the flows are, of course, .Tertiary; 

in; age; -A few dark fine-grained dikes have -been noted.

Large areas are covered by alluvium and hill wash. Landslidedebris is fairly plentiful. '... . .

STRUCTURE ..-...- .

Kirkham (1931a, b, c) concluded that Tertiary rocks near Weiser 

are flexed into subparallel irregular folds that trend northwestward. 

He mapped four anticlines, with their corresponding synclines, from 

Weiser past the east border of the area (pi. 4), but showed no faults. 

In an earlier paper Kirkham (1928) reported more than 10 nearly 

parallel folds in the vicinity of Weiser. He said these strike N. 45° 

W. and plunge southeast. In contrast, Dane believed that normal 

faulting dominates the structure. He believed faults trending north-- 

westward are closely spaced in the area (pi. % 4). These faults are 

Variable but most strike N. 20°-30° W.; some are inferred to dipi 

northeast,' others southwest. The rather ill-defined folds on Nutmeg' 

Mountain strike northeast, presumably a local feature.- Buwaldai
86

(1923) referred to folds near Weiser and in other localities in the 

general region but emphasized that they are irregular and discontinuous, commonly with low dips. Washburne (1911) similarly 

suggested that the folds are poorly defined and agreed with the results 

obtained on Futmeg Mountain during the present investigation.-

QUICKSILVER DEPOSITS

Cinnabar was apparently first recognized in this area in 1936 on 

Nutmeg Mountain, although the mineral is reported to have b,een 

noted by placer prospectors in the surrounding region much earlier. 

The Idaho Almaden Mines Co. at Nutmeg Mountain was among 

the leading quicksilver producers in the United States from 1939 

through 1942; it had a total output of nearly 4,000 flasks of quicksilver derived from nearly 53,000 tons of ore. This company closed 

down at the end of 1942 and no other has yet produced. From 1943 

through 1954 mining was confined to sporadic prospecting, mostly 

on and near Nutmeg Mountain, where in 1954 the only work was 

being done.

Most of the quicksilver lodes are in zones in the sedimentary rocks 

that, through introduction of silica and clay minerals, have been 

converted into the material commonly called opalite, which is an 

aggregate formed by replacement; it consists largely of chalcedony 

and other silica minerals, and is so fine grained as to have an opaline 

appearance. The distribution of these zones is indicated in plate 4. 

Within the opalitized rocks relatively small portions, mostly roughly 

accordant with the bedding, contain cinnabar. In and near these 

are a few irregulaT steep fracture zones that contain high-grade; cinnabar veinlets. These fractures have not yet yielded any large quantities of-ore:

MINERALOGY

The deposits contain cinnabar, pyrite, opal, chalcedony, and clay 

minerals, mingled with unreplaced constituents of the original sedimentary rock. Locally, a little limonite is present.

The cinnabar is everywhere fine grained, and is exceptionally so

in some of the high-grade stringers; but it is still coarse enough so that

individual grains, some with crystal faces, can be discerned with a

hand lens. Throughout the district most of the cinnabar has rounded

grains and dendritic, incipient crystals with maximum dimensions

of o.i to o.ooi millimeter. Although the microscope shows that many,

if not all, of these tiny grains line cracks and coat different kinds of

surfaces, the grains are so fine and SO scattered that much of the 

opalite has a faint vermilion tint that results from cinnabar particles 

not visible at low magnifications.
QUICKSILVER DEPOSITS, WEISER, WASHINGTON COUNTY, IDAHO 87

, Eyrite as the only other metallic mineral detected. It occurs in 

minute grains that are generally partly altered, and is visible in only 

a few places, mainly in the more veinlike lodes. Assays show that 

much of the cinnabar ore contains about 0.01 ounce of gold to the 

ton; one small sample assayed 0.16 ounce to the ton. These small 

quantities of gold, too small to be of commercial interest, may be 

associated with the pyrite. North of Weiser are quicksilver prospects 

.that .were -.originally .opened for gold, which may ..have occurKed likewise .in pyrite. The local limonite stains in the opalite are derived 

in:.p;a.rt Jram altered pyrite.

Opal in. rounded to irregular aggregates, locally with colloform 

banding, is fairly abundant. Probably much of the clay contains 

opal so finely dispersed that it cannot be recognized with certainty. 

Most of the clear opaline aggregates, comparatively free from other 

minerals, show dessication cracks. It is doubtful if any of the opalitized rock now contains as much as 50 percent opal. However, much 

of the silica may have been originally deposited as opal, followed by 

partial crystallization later.

Chalcedony is widespread and locally may be the most abundant 

constituent of the opalite. The walls of cavities are coated with 

chalcedony, which forms small irregular commonly radiate masses 

that appear to invade and replace the mixtures of opal and clay. 

Possibly the chalcedony was formed in part by recrystallization of 

preexisting opal. Chalcedony is the principal gangue mineral in the 

steep stringers in fracture zones.

The part of the opalitized rock that contains cinnabar also contains 

clay minerals, locally well over 50 percent. Close to the surface the 

altered rock is so dried and hardened that its clay content is not 

perceptible on casual inspection. Perhaps this accounts for the apparent paucity of clay minerals in opalite not exposed in prospect cuts. 

In underground workings, such as the main workings of the Idaho 

Almaden, the abundance of soft moist clay is obvious.

The most abundant clay mineral is beidellite. This mineral when 

pure has the formula Al2 03'3Si02 t nH2O, but here, as in many other 

places, that molecule is isomorphously mixed with variable proportions of the nontronite molecule, Fe2 03 -SSiCVnH^O. Some of the 

beidellite contains enough ferric iron to make it a distinct greenishyellow. Kaolinite (Al2 03 -2Si02 -2H2 0) is present in some of the 

opalitic rock, particularly that which is soft, nearly white, and obviously claylike. Halloysite, which is similar in composition to kaolinite but is isotropic, has been noted in a few places.

The minerals above enumerated probably include all those formed 

in significant quantities during mineralization. Quartz, feldspar, and 

mica remain in varying amounts in the opalitized sandstones. Small
§S . ......,-,. CONTRIBUTIONS TO ECONOMIC GEOLOGY ' ; '

sparse grains of-zircon and tourmaline in the opalite are probably also 

residual from the original-sandstone. Similarly, tuffaceous and shaly 

rocks that are now opalitized retain some of their original constituents.

" I.-.....' :: OPALITE

CHARACTER

. The cinnabar deposits are all within parts of the sedimentary rocks 

that have been more or less completely altered to opalite. The altered 

rock in this area (pi. 4) contains, at least locally, more clay than most 

pf those deposits called opalite in other quicksilver districts. Opalite 

<is a more appropriate name for the rocks of this area than it is for 

rocks of many other areas, including those of the type locality (Yates, 

1942, p. 323-339), the Opalite district in Oregon. Near Weiser much 

cf the opal remains unaltered, whereas, in the Opalite district the 

silica is mainly chalcedony, perhaps originally deposited as opal.

. The opalitized masses are irregular, both in form and in degree of ; 

alteration. Most are thought to be near faults but they are rarely 

bounded by fracture planes or other definite limiting features. The 

larger and more intensely altered masses are mostly in flat or gently 

inclined beds. They constitute blanketlike bodies that conform 

roughly with the bedding of the host rock and pass gradually into 

unaltered material at-the borders. Where the beds are steeply inclined, 

however, the opalitic material tends to remain nearly horizontal rather 

than to reach out far down the dip of the beds. (See plate 5.) On. v 

the other hand, where the" rocks have not been extensively opalitized, 

small masses of intensely opalitized rock are steep and accord with 

fractures rather'than-with bedding planes. This is illustrated at the > 

principal prospect in T.° 12 N., E. 5 W:, where a fracture zone in 

slightly opalized shale is followed by opalite that widens upward. 

Similarly, the elongate opalite 'bodies (pi. 8) may be controlled by < 

fractures or joints. ;Their shapes do not appear to correspond to 

the bedding. '''/.

. In other places, notably in and near the upper quarry and the 

eastern part of the' underground workings of the Idaho Almaden

mine, all sides of joint blocks are altered, leaving the rock in the core

of the blocks comparatively unaffected. The alteration here simulates ^'

the effects of weathering in producing curved exfoliation shells.

Where the effects of this process are conspicuous the rock superficially

resembles a conglomerate with boulders of arkoSe embedded ill altered 

material. : The character and degree of opalitization change from place to j

place. In slightly altered rock, generally outside the ore zones, the *
QUICKSILVER. DEPOSITS, WEISER, WASHINGTON COUNTY, IDAHO 89

cement of the sandstone has been'replaced by opalitic matefial'| which 

in some places is mainly opal, and in other places is mainly chalcedony. 

Glay minerals where present are not'conspicuous. - The material added 

is more voluminous than the original cement so that the detrital-grains 

are moved and broken. In moderately altered rock the original 

constituents, other than quartz,-have begun to be destroyed. <:Even 

the quartz grains are rounded and embayed, and many are broken into 

sharply .angular .fragments. In. more highly altered rock .the'feldspar and most of the mica are gone and the formerly abundant quartz 

grains are reduced to tiny splinters scattered through a medley of opal, 

chalcedony, and clay minerals. This aggregate was irregularly 

broken and converted into a complex breccia.

Apparently, as Anderson (1941, p. 6) had suggested, some opal 

consolidated early and is now represented by comparatively clear 

rounded to irregular bodies 1 to 2 millimeters in maximum dimensions; 

these are embedded in a mixture of opal, clay, and chalcedony and 

have highly irregular textures that are in part distinctly colloform. 

This mixture is also brecciated and the component fragments of different shapes and sizes are embedded in and tend to merge into surrounding material of similar composition. In the fragments of sup-

 posedly early opal other minerals are comparatively rare; thereby 

tljey differ from other fragments. Dessication cracks are more conspicuous in the clear, early opal than in the surrounding mixtures.

 3S|uch of the chalcedony in the opalitized rock coats the walls of 

openings; This mineral is a major constituent of the filling of many 

:of the mineralized fractures that are at a distance from the opalitic 

.ore bodies.

. Cinnabar is distributed unevenly through the opalitized rock. In 

most of this rock it is far too sparse to be visible; and only those portions of the opalite that contain visible cinnabar have proved, rich 

enough to be mined.. Opalite with less readily detectable cinnabar 

may be mineable under different economic conditions. In the ore 

booties cinnabar is present in the fragments of supposedly early opal, 

.though in such minute and sparsely distributed grains as to be difficult 

to find even under the miscroscope. It is somewhat more abundant 

in the embedding mixtures mainly on grain boundaries, the surfaces 

.between eolloform bands, and as linings of other openings. A large 

part, probably more than half, of the cinnabar in the ore fills cracks

 that formed during and following the consolidation of the opalitic 

gangue minerals. Anderson (1941, p. 7, pi. 3) noted that the cinnabar 

appears to have entered the cracks by replacement. In some localities

 the spaces between exfoliation shells surrounding residual joint blocks 

are filled with cinnabar. In veins in the fracture zones outside the 

.opalitic ore bodies cinnabar forms layers several millimeters wide.
90 CONTRIBUTIONS TO ECONOMIC GEOLOGY

Many of these are approximately parallel to the vein walls and.tend - 

to be more abundant close to the walls than in the-center of individual 

veinlets. Some of these cinnabar layers have pronounced colloform 

texture.

DISTRIBUTION

The principal masses of opalitized material in the area that contains most of the lodes are indicated in plate 4. In addition small 

areas in the sedimentary rocks in T. 12 N., R. 5 W. and in other localities in the region around Weiser are partially opalitize.d. So far 

as known, however, these are neither as large nor as thoroughly altered 

as those within this area (pi. 4). Within the mapped area the 

opalitized masses are so distributed as to suggest that faults served 

as channels along which the mineralizing solutions rose, a suggestion 

that is in harmony with Dane's work. Support for this concept is 

furnished by the fact that tests by means of the ultraviolet lamp and 

willemite screen show that traces of quicksilver are present along 

fault fractures and breccias, which were noted by Dane; although, 

similar rocks remote from faults react negatively to this exceedingly 

delicate test for quicksilver. A number of the rocks that re.a.ct positively to this test are not visibly opalitized. Exceptionally, fault 

breccias at a distance from known ore bodies contain enough cinnabar 

to be visible; of these some are in basalt, although no ore is known 

in basalt anywhere in the region.

The known opalitic masses that contain enough cinnabar to be of 

commercial interest contain fractured, sheeted, and brecciated zones. 

The impression that they are more broken than lower grade masses 

may be deceptive; perhaps it is only that mine openings give better 

exposures. Further, and more significantly, part of the fracturing 

in the more intensely opalitized areas results from structural instability there. Changes related to conversion of opal into chalcedony 

and volume changes in the clays would produce late-stage fractures. 

Both would be more plentiful in and near ore bodies than elsewhere. 

SllCh Changes began long before mineralization ceased and relatively 

abundant fractures, irrespective of origin, Contributed tO the Concentration of Cinnabar in the fractured areas. On the other hand, none

of the known ore bodies is on a major fault as is evidenced by the

absence Of large failltS, (See plates 5 and 8 and figure 9.) The walls 

of such faults may have been tightly pressed together and ftHy OpeillllgS that remained Were filled with gangue so as to be comparatively

impermeable before the cinnabar solutions cirCUlcltfid.

The only quicksilver Ore bodies SO far profitably mined in the region are along the crest of the transverse uplift that underlies Nutmeg 

Mountain. Plate 5 shows the uplift to be poorly defined. Several 

-short synclines are plotted but in large parts of the uplifted areas
GEOLOGICAL SURVEY 

Quarry in o'palite or^ei^r-^Sr*:'^

MAIN QUARRY OF THE IDAHO ALMADE

View taken from the ore l»iil on west border of quarry. Man is tramming toward portal of drift 

on lower level leads into slope A. Some of the fractures (f) above slope A are visible, which illuat the top of the quarry wall, in the middle distance, is the cap rock. Above cap rock is sandsto
QUICKSILVER DEPOSITS, WEISER, WASHINGTON COUNTY, IDAHO 91

b,etwe§na.the,i§y^cliiies the bfids, remain flat .or nearly so. Nevertheless, 

the,..rocks of the crest of,.Nutmeg Mountain were put under tension 

by the uplift so that whatever fractures existed tended to be open, 

facilitating passage of solutions through them. The mountain has a 

complex fracture system whose components are clearly visible only 

in fresh mine openings. (See plates 5 and 6.) Most of the faults 

(pi. 5) have no apparent relation to the large northwestward-trending faults that Dane regarded as dominant in the regional structure. 

From the eastern part of Sly Park No. 5 claim to about the center 

of Weiser Cove No. 1 claim, exposures of sheeted and slickensided 

sandstone are thought to mark the positions of faults (pi. 5). Attention was first called to these by a series of nearly straight bluffs a 

few feet high, too small to be reflected in the contours on the map. 

The displacements along the faults were not large enough to bring 

unlike units against each other or to produce major shear or breccia 

zones. As the structure sections show, they are thought to be similar 

in magnitude to the fractures exposed underground, most of which 

have small, almost undetectable, offsets. The bluffs result from especially intensive silicification along the faults; this has made the sandstone along the faults more resistant to erosion than the sandstone, 

at a distance from faults, even though the latter is also altered. Such 

features may well be independent of amount of displacement.

In the area occupied by the main mine workings, fractures or faults 

that trend about N. 60° W. and have vertical displacements of a few 

inches to a few feet are plentiful though apparently discontinuous. 

Those visible in the summer of 1941 are shown in plate 6 and in a 

much more generalized fashion in plate 5. A fault, or possibly several closely associated fractures, of this group bounds the main Idaho 

Almaden ore body on the north. On and near the Missouri and Ibex 

claims farther north, discontinuous fractures of similar trend are 

exposed."

A less prominent and abundant group of faults has a trend of 

about N. 15° W. These are clearly recognizable only in mine workings (pi. 6) and only a few have been mapped even there. The topographic break that passes east of the upper quarry and west of the 

high ridge that begins in the northeast corner of the Eimrock claim 

may mark the presence of a fault of this group. Such a fault (pi. 5) 

would help to account for the fact that an isolated body of cap rock 

is exposed at the site of the water tank nearly 50 feet higher than 

the nearest exposure of the large cap rock body near the main workings. On the other hand, no evidence of such a fault has been found 

in the exposures along the steep flanks of Nutmeg Mountain. The 

faults of N. 60° W. trend and those of N. 15° W. trend contain cinnabar in enough places to show clearly that they are of premineral
92 :.-'.' , - CONTRIBUTIONS TO. ECONOMIC: GEOLOGY; . -::::..X;.

origin although they also show abundant evidence of. postmineral 

movements. : . 

. Minor fractures of other trends, most of which are so small that they 

are not mapped, cut the opalite. These include the cinnabar-lined 

cracks in the ore bodies. In the underground workings of the Idaho 

Almaden the more systematic of these trend northeasterly; almost 

normal to the long axes of the ill-defined masses that make' up the ore 

body. ...

 In addition to the fractures, the thin somewhat opalitized shale 

bed, called cap rock by the operators, that overlies the main Idaho 

Almaden ore body (pis. 5 and 7) may have been a potent factor in 

localizing the cinnabar. This bed forms a sharp upper limit of the 

ore body, whereas the lower limit is determined solely by decreases in 

the cinnabar content of the opalite (Requa, 1940, p. 8). . Thus, the 

local conditions correspond closely to the "structural traps" which

 Schuette (1931, p. 406) regarded as essential to the formation of commercially valuable quicksilver ore shoots. While the shale cap rock 

probably did aid in concentration of the cinnabar in the only ore body 

so far successfully mined in the area, it should be emphasized that this 

does not imply that prospecting in the general area should be confined 

to places where a cap rock is thought to exist. So far, the main Idaho 

Almaden ore body is the only one known to have a cap rock above it, 

yet cinnabar in significant quantities is known in other parts of Nutmeg 

Mountain and in several other places in the district. In general, 

cinnabar ore shoots may form under many conditions. The one condition that seems essential is that at the time of mineralization ready 

passage of solutions into the rock being mineralized was possible (Ross, 

1942, p. 454-459).

ORIGIN

The opalite and its contained ore bodies result from the effects of 

mineralizing solutions on the sedimentary rocks. The solutions rose 

along faults and fractures and the attack on the rocks was at an unknown but probably shallow depth. There were several pulses of the 

mineralizing solutions in which differences in composition arid in the

conditions governing precipitation were such that silica minerals,

mainly opal, may have predominated in a poorly defined early stage,

mixtures of silica and clay minerals in intermediate stages, and Cinnabar .with or without silica in the final stages, Some cinnabar accompanied each pulse of mineralization; and in each stage it tended to

consolidate after the gangue minerals. Variations in the different

factors involved produced diversity in details. Special structural COnditions, such as zones of tension and traps produced by impermeable 

beds, appear to have resulted in especially thorough alteration in a few 

places. Presumably ore shoots were formed wherever openings suit-
QUICKSILVER DEPOSITS, WEISER; WASHINGTON COUNTY, IDAHO 93

able for the free passage of solutions were available during the late 

stages in.the sequence of mineralization, during which cinnabar could 

be deposited in relative abundance. As only a single mine has been 

opened, and even there most of the exploration was very shallow, the 

factors that may have influenced the formation of ore shoots cannot be 

satisfactorily evaluated. Any body of opalitized sedimentary rock 

that shows evidence of fracturing would be worthy of prospecting.

The prevalence of opal and of clay minerals among the products and 

the abundance of collof orm textures indicate that colloidal conditions 

prevailed during mineralization. These conditions may account in 

part' for the repeated brecciation that has occurred in blanket or 

mantolibe. deposits which do not appear to have suffered major deformation during mineralization. Colloid gels may swell by imbibition 

of water and exert marked pressure in doing so (Ware, 1930, p. 250- 

255). Apparently, opal would not contribute markedly to volume 

changes related to imbibition as silica gel is reported to hold only 

one H2O to one Si02 and to be one of the "rigid" gels that swell only 

slightly when immersed in liquid (McBain, 1950, p. 168-170). Clays, 

however, would be expected to swell markedly in water (McBain, 1950, 

p. 394.; Marshall 1949, p. 162-164).

It seems probable that volume changes in the colloids may have 

occurred several times and in different ways in the course of the intermittent mineralization. The water taken up by the gels may have 

come in part from rising hydrothermal solutions and in part from 

surficial sources. Changes in chemical and physical conditions that 

result from variations in composition, quantities, temperatures, and 

othe"r factors which affect the water from different sources contributed 

to thXcpmplexities.

Although imbibition produces gel swelling the net result" is a 

decrease in the total volume of the mixture of 'gels, liquid, and 

crystalline matter. Consequently movements of adjustment along 

fractures and subsidence in weakened areas took place. Later, when 

the water drained off, the gels dried and shrunk. Silica.gel shrinks 

markedly when water is removed from it (Herman, 1949, p. 529-536). 

It appears from Herman's discussion that sorption and swelling 

effects in gels are complex and imperfectly understood. Under the 

conditions connected with the process of opalization they may well 

have been adequate to cause or contribute to the origin of shallow 

structural basins like those at the Idaho Almaden mine. This concept implies that a basin within an area of opalitization may be caused 

by particularly intense mineralization and hence, deserves prospecting.

The beidellite in the opalite may have formed concomitantly with 

the silica minerals and the cinnabar, but the locally conspicuous 

kaolinite probably formed in a more acid environment. Most de-
94 CONTRIBUTIONS TO ECONOMIC GEOLOGY

posits of- kaollnite are thought to-result,, from weathering, rather 

than hydrothermal agencies. The opalitic lodes, like many other 

quicksilver lodes, were formed at such shallow depths that acid vadose 

water may have mingled with the hydrothermal solutions in the 

course of the original mineralizations; therefore sharp distinctions 

between hypogene«and supergene effects cannot be drawn.

OUTLOOK

Quicksilver mining in the general vicinity of .WeiseivhaM ,come 

to an end by the summer of 1943, except for'minor p]?ospectingi<n*part 

by bulldozing. The latter has continued intermittently but late in 

1954 had not yet resulted in new production of record. In the sole 

productive mine, the Idaho Almaden, known ore bodies of a tenor 

regarded by the operators as profitable have been exhausted and all 

equipment removed. Small but rich veinlets on and near the Sly 

Park No. 5 claim have been mined. Other broadly similar veins on 

and near Nutmeg Mountain probably remain unmined and some of 

these might repay operation by a few men, using retorts. The ground 

bordering the main Idaho Almaden excavations on the southeast is 

known to contain cinnabar. On the Basis of drill holes, shafts, and 

trenches, the Idaho Almaden Mines Co. estimated that this ground 

contains about 100,000 tons of opalite with a content of between 2 

and 3 pounds of quicksilver to the ton. A test run of 200 tons of this 

material through the furnace yielded 2 to 6 pounds to the ton. An 

area west of the main workings has so many geologic features similar 

to those of the ore body mined by the Idaho Almaden Mines Co. 

as to warrant more investigation than it has yet received. The characteristics on which this suggestion are founded are outlined in the 

description of the mine.

Exploration by bulldozer cuts and shalloAv drill holes on.JSJLy;Park 

Nos. 2, 3, 4, and 5 claims on'the northern part of 'Nutmeg rMmntam 

was Carried out from 1952 through 19-54 by Dr. J. C. Bartlett and 

associates with results reported by him to be encouraging (Bartlett,

written communication, October 1954). Thus, there is enough cinnabar in that area to warrant consideration.

Other localities are known to contain cinnabar and the possibility 

of new discoveries remains. Prospecting in the district has been by 

no means exhaustive. Many of the cinnabar-bearing masses that 

remain are low grade but resumption of quicksilver mining in the 

district might well result in significant production. Quicksilver

mining in general is subject to fluctuations in price and demand but

should the high prices obtained in the fall of 1954 persist this district 

may well have a revival.
95

MINES AND PROSPECTS 

IDAHO ALMADEN (OSA ANNA) MINE

The property known as the Idaho Almaden mine is on Nutmeg 

Mountain*about -13' miles?east: of Weiser. The common corner of sees. 

4 and^T: 10 N., E. 3 W., and sees. 32 and 33, T. 11 N., E. 3 W., 

is near,;tKe' center of the property. Its approximate position is indicated on plate 5 but the corner was not found during the surveying 

on which that map is based.

.The* first definitely established discovery of cinnabar in place in 

this part of Idaho was made on Nutmeg Mountain in the summer of 

1936 by Harry Brown. During 1937 and 1938 claims were staked 

;and the propery came under the control of Ethel Bartlett and Osa 

Anna Brown of Ontario, Oreg. They named it the Osa Anna. The 

property was leased in 1938 by L. K. Eequa, and later the Idaho 

Almaden Mines Co., with Mr. Eequa as president and general man- 

.ager, was organized. The original group of 17 claims was gradually 

.added to so that in 1941 the property included 30 claims, one of which 

was patented, and a little deeded land. Plate 5 shows only that part

 of. the group on which mining has been done. The claim boundaries 

on this map should be regarded as approximate as not all corners were 

found.

A 50-ton Gould rotary furnace and other necessary equipment were 

installed. Production began May 18, 1939 and was essentially continuous until the mine shut down in December 1942. Development 

was so rapid that by the end of 1939 the mine was the seventh largest 

producer in the United States and in 1940 it was one of a group of 

29 leading producers: that together yielded 85 percent of the total

 quicksilver produced in the United States (Meyer and Mitchell, 

1940, p. 669, and 1941, p. 656).

The total production obtained throughout the operation by the 

Idaho Almaden Mines Co. is given in the table below and is publishedv with permission of Dr. J. C. Bartlett, who represents the 

owners. ;>

Production of the Idaho Almaden mine 

[Data from records of the U. S. Bureau of Mines, 1943)

Year

1939 

1940-... 

1941 .. .. 

1942 ...... ............... . . 

Tons treated

8,457

14, 491

15, 748

14,154

52,850

Flasks of 

quicksilver

1,040

1,097

991

830

3,958

Pounds recovered per 

ton

9.36

5.75

4.78

4.45

6.27
- CONTRIBUTIONS.-TO,- ECONOMIC

The steady decline in .the average ;ienQr;pf;the ore mined,, coupled 

with the fact that extensive exploration by drill holes and su:af£is-had 

failed to disclose much ore of satisfactory grade beyond the limits 

already:mined induced the company to suspend operations'atrthe: end 

of 1942 and return the property tp.;the original owners. In June 1943 

the furnace and .most of-the ; buildings had been, removed andnthe 

workings had begun to cave.: At.that time representatives of.the 

owners were prospecting by means, of-shallow pits,, mainly along the 

northern part of the crest of Nutmeg Mountain, where small veins 

conspicuously banded with cinnabar had been exposed. Veinlets'on 

Sly Park No. 3 claim are reported to have yielded 20 pounds to the 

ton of quicksilver on assay. For.some years after this little appears 

to have been done. A little work may have been carried on at the 

main workings as a map.prepared about 1952 by Edgar Bailey of the. 

U. S. Geological Survey shows .some excavations not shown on previous 

maps. ..According to Dr.; J. C. Bartlett (written communication, 

October 1954) he and G. N. Brown had a bulldozer working on Sly 

Park Nos. 2, 3,4, and 5. claims from 1952 through 1954. The.trenches 

on these'claims (pi. 5) represent such of this work as had been:acconv 

plished prior to June 1954. The presence of cinnabar in several spots 

in these trenches is shown in plate 5.. . . . ;:';..>

When the mine was originally opened, the ore that cropped .outiat 

the surface was mined in a quarry or open cut which finally: attained 

a length of about 270 feet with a maximum breadth of about. il$5j|eet 

and a maximum depth of 30 feet (pi. 7), In addition, therenwjas:a 

scraped and trenched area south of the quarry from which, no.;ore 

was mined except for a sample lot of 204 tons which yielded 2.6 po.tmds 

of quicksilver to the ton. Prospecting was mainly by shafts and drill 

holes which served satisfactorily to indicate tlie material of mineable 

grade. Most of the shafts and holes were stopped less : than .30, feet 

from the surface. One shaft was sunk 165 feet in the crushed rock 

of the fault zjone near the west end of the northern margin of the 

quarry but disclosed only one slab of ore, 6 feet long, at a depth of

100 feet. A sample from this slab yielded 27 pounds to the ton on .assay.

It was soon found desirable to undertake underground mining both

because the overburden east of the quarry was too deep to remove 

economically and because of the protection from the weather thus 

given the miners.. As the ore body was irregular, defined by assay 

limits, and had its: greatest dimensions in the horizontal .plane, .the 

workings were necessarily unsystematic. In some of the underground, 

work done the ore mined was two sets or more high. Where this: was 

required (stope A, pi. 6) square sets were used. Elsewhere only such1 

stulls and other, timbers as were essential for safety were employed. 

Pillars were left in early stages and removed as mining progressed.
QUICKSILVER DEPOSITS', WEISER, WASHINGTON COUNTY, IDAHO 97;

flu ;;

Elev. 365Q.V 

: .EXPLANATION

.55

N" Coarse imperfectly silicified. 

sandstone with clay layers

Clay shale 

Chert

Fracture, showing dip

,90

Vertical fracture

_i£s 

Strike and dip of beds

Down 10 feet vertically, 

then 10 feet on bedding

55

^

Limonite on fractures

7O

40 Clay on fracture 

40 surfaces

Black opalite

Chalky white opalite

Opalite with residual joint blocks

FIGURE 8. Geologic map of the tunnels on the Sly Park No. 5 claim, Idaho Almaden mine. i'

In so far as possible mining was selective but eventually so large a 

portion of the material was removed that the ground above the entire 

area of underground workings collapsed. Caving is now so complete 

that any cinnabar that may remain would be difficult or impossible 

to obtain. , ,

In addition to the main quarry and workings leading therefrom, 

some ore was taken from an excavation on the Rimrock. claim known 

as the upper quarry, and from two short tunnels on the Sly Park No. 5 

claim (fig. 8). The upper tunnel has now been converted into a narrow caved open cut perhaps in part by collapse of stopes above it. A 

shallow quarry has been excavated south of this cut, but no data as 

to the recovery from it, if any, are available.

;Late in the summer of 1941 a shaft, called the North Shaft, was 

started in the hanging wall of the fault that bounds the main workings. 

During 1942 ore was mined at a depth of 75 feet below the collar of 

this shaft, about 40 feet below the bottom of the main quarry. A winze
98 CONTRIBUTIONS TO ECONOMIC GEOLOGY

was sunk 67 feet below this level but apparently failed to reveal 

enough ore to encourage further exploration. In 1943 trenches on 

Sly Park Nos. 3 and 4 claims revealed rich cinnabar veinlets in a few 

spots. More recently this area has been explored by bulldozer cuts 

(pi. 5) and by drilling. It is reported that assays from the bulldozer 

cuts run as high as 20 and 34 pounds to the ton. Here, as in the main 

workings, the richest samples doubtless include cinnabar from narrow 

veinlets. So far as could be seen in June 1954 much of the rock exposed 

in the cuts is not markedly opalitized. Much of the cinnabar noted 

at that time was in the western parts of the cuts. (See pi. 5.)

Plates 5 and 6 are composite. Together they record all available 

data on the geology of Nutmeg Mountain and the workings accessible 

to the present writer. The geologic observations incorporated in both 

maps are those of the writer but the mine workings shown in them 

and also in figure 8 are based largely on maps furnished by the Idaho 

Almaden Mines Co., and represent conditions existing in 1941 and 

1943 rather than those of the present. As plate 5 represents three 

separate planetable surveys without sufficient control points tp tie the 

three together with a high degree of precision minor errors of adjustment between the three parts presumably exist.

All of the cinnabar in the Idaho Almaden is in shoots within masses 

of opalitized sandstone, the opalite being far more extensive than the 

mineable ore. The principal ore body is the irregular, roughly horizontal mass, or assemblage of interconnected ore shoots, mined in 

the main quarry and workings connected thereto. This body is in a 

shallow structural and topographic depression on the crest of the 

poorly defined anticline of northeasterly trend that occupies the 

southern part of Nutmeg Mountain. The ore is beneath an opalitized 

shale bed, which is termed caprock by the operators. The anticline is 

cut by fractures or faults of slight displacement that are difficult to 

trace except in mine workings. For example, plate 7 shows several 

eXDOSed faults in the wall of the quarry above the entrance to a stope 

but the displacements are so small that most cannot D£ identified &S

such in the photograph. The principal ones are indicated by arrows.

The faults or fractures are mainly premineral and haV6 inftueHCed 

the Shape Of the Ore ShoOtS, They do not, however, delimit the ore.

In the main workings work stopped on the north against fairly 

Well defined fault Walls, but the workings from the North Shaft later

found ore north of this fault ZOne. The limits of StOpillg In tltt mill

workings were set solely by the tenor Of the material found. The

mined material had an average content of close to 6 pounds of QUlcksilver per ton and few of the closely Spaced Samples taken during the 

operation of the main workings yielded more than 20 pounds to the 

ton on assay. Mining was stopped when the samples on the periphery 

of the workings showed an average grade close to 3 pounds to the ton.
QUICKSILVER DEPOSITS, WEISER, WASHINGTON COUNTY, IDAHO 99

On the east and south, particularly, the only limits to the ore body 

are those imposed by d6crease in the cinnabar content. Beyond these 

limits the tenor decreases, but not uniformly. Plate 6 has a dashed 

line corresponding to the limit of the low-grade zone as estimated by 

the Idaho Almaden Mines Co. but some cinnabar is known to extend 

into the opalite far beyond this line. The upper quarry, where some 

material rich enough to mine was found, is 300 feet southeast of the 

border of the low-grade zone mentioned above. Thus, that border 

by no means sets a limit on prospecting.

Within the area of the main workings fractures lined with cinnabar 

locally raised the average grade. Similar rich veinlets have been 

mined in other parts of the property.

All the opalitized rock on Nutmeg Mountain not already mined 

is worthy of exploration. Attention is directed to the southern part 

of the Ked Rose and northern part of the Sandstone claim. This area 

appears to have been little prospected but has features in common 

with the area that contains the main workings. The cap rock so prominent in the main workings is present in much and probably most of 

this area. Hence, it could Im7 e had much the same effect in checking 

the ascent of solutions there as it is supposed to have had at the site 

of the main workings. Likewise in both localities there appear to be 

structural sags, which are reflected in the topography. Around the 

periphery of the main workings the opalitized sandstone beds dip 

inward toward the quarry at angles of 5° to 35°. In the area under 

discussion the dips are so slight that most of the beds are represented 

(pi. 5) as flat. However, from the gentle ridge (crest at about 3,540 

feet) within the 3,525-foot contour to the low point near the southeast corner of the Red Rose claim (altitude about 3,528 feet) the beds 

are thought to dip in approximate conformity to the topographic 

surface, as is indicated in section A-A' plate 5. If this sag and that 

at the main working are, as suggested above, genetically related to 

changes in the colloids introduced during opalitization, their presence 

implies thorough and presumably relatively deep opalitization, a 

favorable feature. The dips bordering the unmined area are much 

less than those on the borders of the mined ground. In so far as this 

may reflect less intense or deep opalitization in the unmined area it 

agrees with the fact that such test holes as have been put down there 

have not had results sufficiently encouraging to have led to mining. 

Even so, it is felt that exploration so far done is not adequate to rule 

out the area as a possible source of ore.

ZUCKER PROPERTY (PARKER GROUP)

The property formerly held by Zucker Mines, Inc., of Spokane, 

Wash., adjoins the Idaho Almaden mine on the northwest. It is reported to center around the northwest corner of sec. 32, T. 11 N.,
100 CONTRIBUTIONS TO ECONOMIC GEOLOGY

R. 3 W., and in 1943 according to the State Mine Inspector' (Campbell, 1944, p. 228) consisted of 6 unpatented claims. This property was 

originally known as the Parker group. Work began here in August 

1941 and continued into the spring of 1942, with a little additional 

activity in 1943. Several pits, shallow shafts, and short tunnels were 

driven. A bulldozer was used to drain a stagnant pool oh the top 

of a hillock and to clean small surface areas. The principal workings 

visible in 1943 are shown on plate 5. At that time a special kind of 

retort designed to permit agitation of the ore during Toasting had 

been installed but apparently little used. When the property was 

revisited in 1954 the retort and all buildings had been removed and 

there appeared to have been no activity for years.

Much of the surface of the property is mantled with landslide material and hill wash, derived from Nutmeg Mountain and spread rather 

thinly through solifluction and related processes. Some of this, particularly the larger blocks of landslide debris, consists of-opalitized 

sandstone which here and there contains visible cinnabar. As the 

landslides came from the west and northwest flanks of Nutmeg Mountain, they did not involve rock close to that which the Idaho Almaden 

Mines Co. found rich enough to be profitably mined. Small amounts 

of sandstone, in place, are exposed at the surface and in the shallow 

workings on the Zucker property. None of the sandstone1 seen shows 

much evidence of mineralization although some is cut by minor faults.

PROSPECTS NEAR NUTMEG MOUNTAIN

Claims have been staked by several different prospectors on the lower 

slopes of Nutmeg Mountain and in nearby areas. The shallow shaft 

(pi. 5) south of the Rose claim was started in 1941 on a group of 13 

claims then held by Peter and Robert March. Cinnabar was found 

in shale at a depth of 12 feet in this shaft. Other claim groups south 

of the Idaho Almaden property are reported to have been located by 

C. W. and R. M. Curl and by H. Midland. In addition, prospect

holes east of Nutmeg Mountain were noted during the study in

1941. Some of these showed cinnabar in fractures. No activity was

seen at any of the prospects here referred to during the visits in

1943 and later. .

CONSOLIDATED QUICKSILVER MINING CORPORATION

The Consolidated Quicksilver Mining Corp., formerly the Hoover

Consolidated Quicksilver Mining Corp., held 69 unpatented claims in

1941 (Campbell, 1942, p. 245). The property is in and south of sec. 

36, T. 12 N., R. 4 W. In 1940 and 1941 the company explored its

claims by means of trenches, shafts, a tunnel, and drill holes, but since 

August. 1941, the company appears to have been inactive. .. '
QUICKSILVER DEPOSITS, WEISER, WASHINGTON COUNTY, IDAHO 101

The part of the Consolidated property where most of the exploration has been done is shown in plate 8, which is based on a planetable 

survey by C. P. Ross and R. P. Full. In this area arkosic sandstone 

with some conglomerate beds and a little shale is interbedded with 

basalt. The shale is not shown separately in plate 8. The rocks are 

inclined to the northeast and east at angles that range from horizontal 

on the hilltop up to 30° at the south edge of the area mapped. The 

sandstone is somewhat opalitized but most of it is much less intensely 

so than at Nutmeg Mountain. Only the more thoroughly opalitized 

bodies are distinguished in plate 8. There are conspicuous joints of 

nprthwesterly trend and some of the more intensely opalitized material follows these. Fracture zones in the tunnel are lined with clay. 

They range in strike from N. 60° W. to N. 15° W., and dip both northeast and southwest. The only quicksilver seen by the writer was in 

the patch of marked opalitization in the southern part of the area 

; (pi. 8) but jointed and opalitized rock in several places on the property 

jis reported to yield cinnebar when panned. 

i...

i PROSPECTS IN T. 12 N., K. 5 W.

In 1941 prospects close to U. S. Highway 95 about 8 miles northeast of Weiser and almost as far due west of the property of the Consolidated Quicksilver Mining Corp. were being explored for quicksilver. These were visited by C. H. Dane and R. P. Full. Cinnabar 

was discovered here early in June 1941 by Frank Coats, mainly on 

land southeast of the highway in sec. 25, T. 12 N., R. 5 W., then owned 

by John Coats. The land was leased to Chester Lackey, Ontario, 

Oreg., for exploration. This was done by means of shallow pits and 

bulldozer cuts starting 1,800 feet southeast of the John Coats house 

and extending 500 feet farther southeast. The largest pit, in 1941, 

was 20 feet long and 20 feet deep, and was at the south end of the 

explored area.

Other small workings on land that in 1954 was being ranched by 

Line Brothers \vere dug about a mile to the southwest and immediately north of the highway. One of these, when seen in 1954, was 

a trench about 90 feet long. Farther north there is a small quarry 

in sandstone, which is used for construction. Much earlier prospecting for gold is reported to have been carried on at this place, evidently without sufficient success to induce exploration at depth. Apparently almost no prospecting for quicksilver has been done since 

1941. When the locality was revisited in 1954 no evidence of more 

recent mining was noted and the ground was being used as a ranch 

by Line Brothers. However, at the more southerly of the two localities just mentioned a notice was found indicating that Glenn and 

'Grary Efharde had claimed the ground as the "Tip Top Mine," under
102

EXPLANATION

Opalitized rock

Poorly consolidated shale, sandy 

shale and sandstone, Tsh; with 

lenses of coarse crossbedded 

arkosic sandstone, Ts

Basalt

A finely banded 

nearly black rock

Biotite andesite

A finely weathered dark

gray rock

Quarry, for rocV for 

construction uses

Pit, sunk in prospecting 

for metals

Contact, dashed where 

approximately located

Fault, showing direction 

of dip

Strike and dip of beds

Base from air photograph, 

U. S. Bureau of Reclamation

Geology by C. H. Dane and ft P. Full. 1941

FIGURE 9. Geologic map of prospects in T. 12 N., R. 5 W.

date of February 10, 1954. Varley (Varley, and others, 1919, p. 51) 

mentions a gold mining district, called the Monroe Creek or Weiser 

district, about 10 miles north of Weiser. The prospects here described 

would be within that district. Monroe Creek, not shown on maps 

in the present report, passes just west of the prospects and enters the 

Snake River at Weiser.

The geology of the area that includes the two groups of prospect 

holes is shown in figure 9. This figure shows that each group is in 

an area where the shaly and sandy country rock has been opalitized,

within the vicinity of small mafic intrusive bodies. Near tlie John 

Coats house the opalitized rock trends roughly N, 20° E, but Small,

more thoroughly silicified shoots within it trend N. 10°-55° W. These

latter (not shown on fig. 9) are rudely tabular and dip steeply eastward. They are not conformable with the bedding where that can

be determined, Figure 9 shows that most beds nearby dip westward.

The silicified rock has been crumpled and broken. In 1941 in the

largest pit near the house cinnabar was visible in irregular day-filled 

fractures between the small angular fragments of the brecciated. 

opalite. At the openings a mile farther south mineralization effects 

are even more scanty. The trench mentioned above exposes a fault 

that strikes west of north and dips east, between sandstone and shale.
QUICKSILVER DEPOSITS, WEISER, WASHINGTON COUNTY, IDAHO 103

The offset is probably small. A poorly exposed dike of biotite andesite lies west of the fault. The igneous rock north of the John Coats 

house is a finely banded basaltic rock, whose presence is shown by 

abundant fragments but no actual exposures.

LITERATURE CITED

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Buwalda, J. P., 1923, A preliminary reconnaissance of the-gas and oil possibilities

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Campbell, Arthur, 1942, Forty-third annual report of the mining industry of

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p. 569-591.

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Yearbook 1940, p. 659-676.

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Mining^orld, 1939/ Idaho Almaden Gem State's first quicksilver mine: Min. 

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United States: Econ. Geology, v. 37, no. 6, p. 439-465.

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Varley, Thomas, and others, 1919, A preliminary report on the mining districts 

of Idaho : U. S. Bur. Mines Bull. 166, p. 1-89.
104 CONTRIBUTIONS TO ECONOMIC GEOLOGY

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and Sons. _; 

Washburne, C. W., 1911, Gas and oil prospects near Vale, Oregon, and Payette,

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