DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, DIKECTOK

BULLETIN 539

SOME ORE DEPOSITS IN NORTHWESTERN 

OUSTER COUNTY, IDAHO

BY

JOSEPH B. UMPLEBY

WASHINGTON

GOVERNMENT FEINTING OFFICE

1913

CONTENTS.

Page.

Introduction.............................................................. 9

Scope of the report.................................................... 9

Field work and acknowledgments....................................... 9

Earlier work and literature............................................. 11

Geography .............................................................. 12

Situation and access................................................... 12

Settlements............................................................ 12

Lines of travel......................................................... 13

Climate and life........................................................ 13

History of the area.................................................... 14

Physiography.............................................................. 14

General relief......................................................... 14

Drainage............................................................ 14

Summit areas......................................................... 15

Valleys............................................................... 15

Relation to adjacent types............................................. 16

Physiographic history.................................................. 17

General geology.....................................'........'............... 17

Outline............................................................... 17

Algonkian rocks....................................................... 18

Distribution...................................................... 18

Characteristics..................................................... 18

Correlation....................................................... 18

Paleozoic rocks....................................................... 19

Distribution...................................................... 19

Structure........................................................... 19

Lithology.......................................................... 19

Correlation....................................................... 20

Late Cretaceous or early Eocene plutqnic rocks......................... j 21

Distribution................J................................ 1.... 21

Varieties......................................................... 21

Granite........................................................ 21

Quartz monzonite............................................. 22

Quartz diorite................................................. 22

Diorite........................................................ 22

Age and correlation............................................... 22

Early Eocene dikes................................................... 23

Distribution...................................................... 23

Varieties ...........................'............................... 23

Granite........................................................ 23

Granite porphyry.............................................. 24

Diorite porphyry.............................................. 24

Age of the dikes..........................i ......................... 24

Miocene volcanic rocks................................................. 24

Distribution and character.......................................... 24

Andesites and latites.............................................. . 25

Tuffs.............................................................. 28

Age of the lavas and tuffs........................................... 26

3
4 CONTENTS.

General geology Continued. Page.

Miocene lacustrine deposits............................................. 27

Distribution...................................................... 27

Character......................................................... 27

Age............................................................... 27

Pleistocene deposits................................................... 27

Morainic material................................................. 27

Outwash material.................................................. 28

Re'sume' of geologic history............................................. 28

Ore deposits.............................................................. 29

General features....................................................... 29

Character of the deposits............................................ 29

Periods of mineralization........................................... 29

Distribution...................................................... 30

Geologic relations................................................. 30

Pre-Oligocene ore deposits.............................................. 31

Classification...................................................... 31

Silver-copper deposits.............................................. 31

Distribution and history....................................... 31

Geologic relations............................................... 32

Form and structure of the deposits............................. 32

The ores...................................................... 32

Pay shoots................................................ 32

Minerals.................................................. 32

Relative abundance.................................... 32

Paragenesis of the vein materials........................ 33

Composition of the tetrahedrite......................... 34

Vertical distribution of minerals........................ 35

Age and genesis................................................ 35

Lead-silver deposits................................................ 38

Distribution and history....................................... 38

Geologic relations..........'................................... 39

Character of the deposits........................................ 39

The ores...................................................... 40

Ore shoots................................................. 40

Minerals of the ore......................................... 40

Tenor of the ore........................................... 41

Age and genesis................................................ 41

Gold-copper deposits.............................................. 42

Geologic relations............................................. 42

Character of the deposits........................................ 42

Ore shoots..................................................... 43

The ores...................................................... 43

General character......................................... 43

Mineralogy of the different shoots........................... 44

Tenor.................................................... 44

Age and genesis................................................ 44

Post-Oligocene ore deposits............................................. 45

Gold-silver veins................................................... 45

Geologic relations:............................................ 46

Metasomatic alteration of the wall rocks......................... 46

Character of the veins......................................... 46

Ore shoots..................................................... 47
CONTENTS. 5

Ore deposits Continued.

Post-Oligocene ore deposits Continued.

Gold-silver veins Continued. Page.

The ores...................................................... 47

Mineralogy................................................ 47

Tenor of the ores.......................................... 48

Age and genesis................................................ 49

Gold placers....................................................... 50

Distribution and history....................................... 50

Character of the deposits........................................ 50

Source of the placer gold....................................... 51

Age of the placers............................................. 51

Minerals of the deposits................................................. 51

Oxidation and ground-water level....................................... 53

Future of mining in northwestern Custer County......................... 54

Mining districts........................................................... 55

Bay Horse district..................................................... 55

Situation and extent............................................... 55

History............................................................ 56

Production........................................................ 56

Mining conditions. ................................................. 57

Topography....................................................... 57

Geology.......................................................... 58

Ore deposits...................................................... 59

Classification.................................................. 59

Lead-silver deposits............................................ 59

Distribution.............................................. 59

Geologic and structural relations............................. 60

Character of the deposits................................... 60

Silver-copper deposits.......................................... 61

Distribution ............................................. 61

Geologic and structural relations .......................... 61

Character of the deposits.................................. 62

The ore................................................... 62

Age and genesis................................................ 63

Mines and principal prospects...................................... 64

Ramshorn mine................................................ 64

Situation and development................................ 64

 History and production.................................... 64

Geologic relations......................................... 64

The veins.................................................. 64

The ore................................................... 65

Skylark mine................................................. 65

Situation and development................................ 65

History and production.................................... 66

Geologic relations......................................... 66

The vein................................................. 66

The ore................................................... 67

River View mine.............................................. 67

Excelsior mine................................................. 68

Beardsley mine................................................ 68

Pacific mine.................................................. 69

Hoosier group................................................. 70
6 CONTENTS.

Mining districts Continued.

Bay Horse district Continued.

Mines and principal prospects Continued. Page.

Silver Brick claim.............................................. 70

Cave mine.................................................... 70

Forest Rose mine............................................... 72

New Silver Bell mine.......................................... 72

Ella group...................................................... 73

Red Bird mine................................................ 73

Situation and history..............................."........ 73

Geologic relations......................................... 73

The ore bodies............................................ 74

Saturday group...........................................:.... 75

Cinnabar group................................................ 76

South Butte group............................................. 76

Dougherty group................................................. 76

Livingston mine................................................ 76

Yankee Fork district................................................... 76

Situation.......................................................... 76

History............................................................ 77

Production........................................................ 77

Topography....................................................... 78

Geology.......................................................... 78

Algonkian rocks .............................................. 78

Distribution.............................................. 78

Composition.............................................. 79

Late Cretaceous or early Eocene granite........................ 79

Tertiary volcanic rocks........................................ 79

Distribution.............................................. 79

Composition.............................................. 79

Quaternary deposits........................................... 80

Ore deposits...................................................... 80

General character............................................. 80

The veins.................................................... 81

Distribution.............................................. 81

Characteristics............................................. 81

Ore shoots................................................. 81

The ore....................................................... 81

Alteration of wall rock.................................:........ 82

Age and genesis................................................ 83

Mines and principal prospects...................................... 83

General Custer mine........................................... 83

Situation and history....................................... 83

Geologic relations ......................................... 83

The vein................................................. 84

The ore................................................... 84

Lucky Boy mine.............................................. 85

Badger mine.................................................. 86

Black mine.................................................... 86

Enterprise group...........................:.................. 86

Charles Dickens mine. ........................................ 86

Morrison group................................................ 87

Fairplay, Passover, Letha, and Julietta claims.................. 87
CONTENTS. 7

Mining districts Continued.

Yankee Fork district Continued.

Mines and principal prospects Continued. Page.

Golden Sunbeam mine......................................... 87

Situation and history....................................... 87

Character of the deposit..................................... 87

Montana mine.......................;......................... 88

McFadden group............................................... 88

Golden Gate group............................................. 89

Other properties on Estes Mountain............................ 89

Yankee Fork placers............................................... 89

Loon Creek district..................................................... 90

Situation........................................../................ 90

Mining conditions.................................................. 90

History and production............................................ 90

Geology.......................................................... 91

Physiography.................................................. 91

Sedimentary rocks............................................. 91

Igneous rocks................................................. 92

Glacial deposits............................................... 93

Ore deposits...................................................... 93

General character............................................. 93

Gold placer deposits........................................... 94

Gold-copper deposits.......................................... 94

The Lost Packer vein..................................... 94

Situation and development............................ 94

General character of the vein.......................... 94

The ore............................................... 96

Ore shoots............................................. 97

Undeveloped veins......................................... 98

Silver-lead deposits........................................... 99

Age and genesis................................................. 99
ILLUSTRATIONS.

Page. 

PLATE I. Topographic and geologic sketch map of a portion of northwestern

Ouster County, Idaho ......................................... 9

II. A, Salmon Canyon, with Clayton in the foreground; B, Bay Horse

Canyon as seen from a point near its head....................... 12

III. A, Spur on the north side of Poverty Flat; 5, Central portion of

Poverty Flat................................................. 14

IV. A, South wall of Kinnikinnick Canyon as seen from Poverty Flat;

B, Miocene lake beds northeast of Poverty Flat................. 15

V. A, Pleistocene gravel terraces along Salmon River below Robinson 

Bar; B, Slaty cleavage in Paleozoic (?) shales below Bay Horse 

Canyon....................................................... 20 ?

VI. A, Ramshorn and Skylark mines, Bay Horse district: B, Detail of

structure near the Ramshorn and Skylark mines................ 32 , VII. Specimens of ore from Ramshorn mine: A, Tetrahedrite replacing ; 

siderite and chalcopyrite along crack in former; B, Euhedral 

quartz crystals developed in siderite; G, Arsenopyrite replacing 

siderite....................................................... 33 

VIII. A, Chalcopyrite replacing siderite, Lost Packer vein; B, Sheared 

galena from Beardsley mine; (7, Fractured galena cemented with 

quartz, from Forest Rose mine................................. 44

I.. Lost Packer smelter and ore piles as seen from the south............ 90

X. Topographic and geologic map and sections of a portion of the Loon

Creek district, Idaho.......................................... 92

FIGURE 1. Index map of Idaho showing location of area investigated......... 10

2. Claim sheet of James McGregor group, Bay Horse district.......... 71

3. Claim sheet of Red Bird group, Bay Horse district............... 74

4. Plan and sections of Lost Packer mine, Loon Creek district, showing

the geology................................................... 95
LATE CRETACEOUS 

OR EARLY TERTIARY

TERTIARY (MIOCENE) ALGONKIAN PALEOZOIC
SOME ORE DEPOSITS IN NORTHWESTERN CUSTER 

COUNTY, IDAHO.

By JOSEPH B. UMPLEBY.

INTRODUCTION.

SCOPE OF THE BEPOBT.

This report sets forth the results of a short reconnaissance in the 

Loon Creek, Yankee Fork, and Bay Horse mining districts, situated 

in the northwestern part of Ouster County, Idaho. The area includes 

several promising ore deposits and a few mines where a considerable 

tonnage is blocked out, awaiting more advantageous transportation 

facilities.

The area is first treated as a unit in order to bring out the broader relations, and then the three districts are taken up separately. Although 

this arrangement involves some repetition, it is thought to be justified 

in order that the report may be equaUy valuable to the student of the 

general subject and to the person interested in a particular district.

FIELD WOBK AND ACKNOWLEDGMENTS.

Early in the fall of 1910 three days were spent in examining the 

Bay Horse district, it being the plan at that time to incorporate notes 

on the deposits there found in a report on Lemhi County. Later it 

was decided to make a reconnaissance of two other districts adjacent 

to Bay Horse and incorporate the results of the work in the three 

areas in a separate bulletin. Pursuant to this plan field work was 

begun August 27, 1911, and continued until September 20 of that 

year. The tune was divided about equally between the Loon Creek, 

Yankee Fork, and Bay Horse districts. A topographic and geologic 

sketch map was prepared showing most of the area (2,500 square 

miles) included in these districts. (See PL I.) On this map only 

the broader geologic divisions are recognized and except along the 

main line of traffic from Challis to Ivers and over small areas adjacent 

to the more important metalliferous deposits, the positions assigned 

tot their contacts are based largely on information derived from mining 

men and prospectors.

The base map is compiled from S. M. Ballard's map of Custer 

County, data furnished by the local office of the Forest Service, and

9
10 ORE DEPOSITS IN CUSTEE COUNTY, IDAHO.

FIGUBE 1. Index map of Idaho showing location of area investigated.
INTRODUCTION. 11

numerous compass triangulations by the writer. Vertical control 

along Salmon Jliver is taken from a location survey by the Gilinore 

& Pittsburgh Railroad; elsewhere it is taken form aneroid readings. 

Field work was greatly facilitated by generous courtesies and assistance given by mining men in the area, especially by the officials of 

the Lost Packer Mining Co.

EARLIER WORK AND LITERATURE.

The earlier work in the area is described principally in short articles. 

George H. Eldridge, during his reconnaissance from Boise to Salmon, 

passed through a part of the Loon Creek district and on his return 

touched the northeast corner of the Bay Horse district. His report, 

however, contains little specific -information concerning the area here 

considered. The Bay Horse district is the subject of a few notes by 

R. N. Bell, in which he describes the geologic features of the region

and the occurrence of silver ores. In another paper the same writer 

incorporates notes on the mines of the Yankee Fork and Bay Horse 

districts. The Lost Packer mine is described briefly by E. P. Jennings. 

The annual reports of the State Mine Inspector, many of which contain 

notes on the geology of the deposits, form another source of information regarding the ore deposits of the area. The more important 

reports and articles on this and nearby areas are listed below in 

chronologic order:

EMMONS, S. F., Livingston to the Snake Plains: Cong. ge'ol. internat., Compt. Rend. 

5th session, 1893, pp. 367-374.

Describes geology along route of travel and geologic history of the Snake Plains. 

STONE, GEOHGE H., An extinct glacier of the Salmon River Range: Am. Geologist, 

vol. 11, 1893, pp. 406-409.

Describes glacial geology of the Leesburg Basin and the mountains west of 

Salmon.

ELDRIDGE, GEORGE H., A geological reconnaissance across Idaho: Sixteenth Ann. 

Rept. U. S. Geol. Survey, pt. 2, 1895, pp. 211-276, Pis. XV-XVII. i 

Describes topography and geology along a route from Boise to Salmon and thence 

south to Hailey and west to Boise. Includes notes on the ore deposits at Yellow 

Jacket and the placers of Leesburg Basin and Kirtley Creek. i 

GOODE, R. U., BitteiToot Forest Reserve: Nat. Geog. Mag., vol. 9, 1898, pp. 387-400, 

and map. Contains general description of the reserve and definition of mountain systems. i 

BELL, R. N., The deepest mine in Idaho, the Ramshorn at Bay Horse: Mines and Minerals, vol. 21, 1900, pp. 174-176.

Describes geologic features of the region and occurrence of the silver ores. 

LINDGREN, WALDEMAR, The gold and silver veins of Silver City, De Lamar, and other 

mining districts of Idaho: Twentieth Ann. Rept. U. S. Geol. Survey, pt. 3, 1900, 

pp. 75-256, Pis. VII-XXXV.

Describes character and occurrence of the igneous and sedimentary rocks and 

occurrence and nature of the ore deposits of a large area lying south and west of 

Lemhi County.
12 ORE DEPOSITS IN CUSTER COUNTY, IDAHO.

BELL, ROBERT, An outline of Idaho geology and of the principal ore deposits of Lemhi 

and Ouster counties, Idaho: Proc. Internal Min. Cong., 4th sess., 1901, pp. 64-80. 

Describes briefly the principal mines of Lemhi and Ouster counties, stating 

amount of development, production, and something of their geologic relations. 

RUSSELL, I. 0., Geology and water resources of the Snake River Plains of Idaho: 

Bull. U. S. Geol. Survey No. 199, 1902, 192 pp. 25 pis.

Describes topography, basement series of rocks, recent eruptives, lacustrine 

deposits, and resources of the area.

LINDGREN, WALDEMAR, A geologic reconnaissance across the Bitterroot Range and 

Clearwater mountains in Montana and Idaho: Prof. Paper U. S. Geol. Survey 

No. 27, 1904, 123 pp., 15 pis.

Describes topography and character, occurrence, and geologic relations of the 

igneous and sedimentary rocks, the structure of the area, and character, occurrence and development of its mineral deposits. Gibbonsville and Mineral Hill 

districts, Lemhi County, are described briefly.

JENNINGS, E. P., The Lost Packer copper-gold lode (Idaho): Jour. Canadian Min. 

Inst., vol. 9, 1906, pp. 54-57. Min. and Sci. Press, vol. 92, June 30, 1906, pp. 

435-436.

Describes geologic relations and constitution of the Lost Packer vein. 

CARR, HENRY C., Vein structure in the Monument mine: Min. and Sci. Press, vol. 98, 

Apr. 17, 1909, pp. 557-558.

Includes notes on the geology and character and occurrence of the ores at Meyers 

Cove (Singiser), Lemhi County, Idaho.

UMPLEBY, J. B., Geology and ore deposits of Lemhi County, Idaho: Bull. U. S. Geol: 

Survey No. 528, 1913, pp. 182, pis. 23.

Describes physiography, general geology, and ore deposits of the county. In 

the final chapter the nineteen mining districts are treated separately.

GEOGRAPHY.

Situation and access. Northwestern Ouster County, in east-central 

Idaho, is most easily reached from Mackay, a terminus of a branch 

of the Oregon Short Line Railroad. Stages run daily except Sunday 

to Chains, 60 miles distant, and thence on to Bonanza and Custer, 

60 and 62 miles farther, respectively. These stage lines are official 

mail routes, but from Custer the mail is carried by private conveyance 28 miles westward to Ivers, thrice weekly when the smelter 

is running and twice monthly at other times. Challis may also be 

reached by stage three times a week from Salmon, 60 miles north, a 

terminus of the Gilmore & Pittsburgh Railroad.

Settlements. The region covered by this reconnaissance contains 

seven settlements, the chief of which is Challis, the county seat of 

Custer County, in the northeast corner of the area. Challis is an attractive little village of about 1,000 inhabitants and has a bank, two 

hotels, churches, a good school, and several stores. Adjacent to it 

are several valleys well adapted for agriculture, which have been 

settled largely within the last few years. Streams from the mountains 

afford abundant water for irrigation, and crops of the north temperate latitude flourish. At present the costs of transportation for
U. S. GEOLOGICAL SURVEY BULLETIN 539 PLATE II

A. SALMON CANYON WITH CLAYTON IN THE FOREGROUND. 

Looking north.

B. BAY HORSE CANYON AS SEEN FROM A POINT NEAR ITS HEAD 

Bay Horse 13 beyond the second bend.
GEOGRAPHY. 13

agricultural produce are prohibitive, so that agriculture in the region 

is only incidental to stock raising.

The other settlements are of about equal importance, and each 

depends on the mining industry for its existence. The old camp of 

Bay Horse, 14 miles south of Challis, once the site of an important 

smelting and mining industry, is now inhabited by only a few persons, 

representatives of the larger companies, lessees, and prospectors.

Clayton, 20 miles south of Challis, on the north bank of Salmon 

River (PI. II), is also the dwindling remainder of a once flourishing 

smelting and mining center. Being situated on the main stage route, 

however, and possessing a post office and large company store, it is 

still a center for prospectors and cattlemen.

Bonanza, half a mile below the junction of Jordan Creek and Yankee Fork, Custer, 1£ miles northeast of the same point, and Sunbeam, 

4 miles northwest of it, were each small settlements that are now 

abandoned except by a few prospectors and by persons held there 

by property interests.

Ivers was the only active camp in 1911. It is 28 miles northwest 

of Sunbeam and about 90 miles, by a circuitous route, west of Challis. 

Fifteen or twenty persons live at the camp throughout the year, but 

during the summer months the settlement has a population of 100 

to 200.

Lines of travel. A. good road follows Salmon River through the 

area and beyond and from it important branch roads extend up 

the valleys of Yankee Fork and East Fork, and numerous laterals 

follow tributary streams for a few miles. The East Fork branch 

leads to Mackay, and the Yankee Fork branch leads to Bonanza, 

whence it forks, one road leading to Custer and the other northwestward over Loon Creek summit, at an elevation of 8,800 feet, to Ivers.

The roads are good and as far as Sunbeam are open throughout 

the year; but thence westward traffic is impossible during the winter.

The great highland portions of the area are reached only by trails, 

which are few and little traveled. Perhaps the trail most used is 

that leading from Challis westward over the summit, 30 miles to 

Custer.

Climate and life. The range of climatic conditions is wide. From 

the highlands, which are deeply covered with snow throughout the 

whiter, the climatic transition is gradual to the lowlands, where sleighing is seldom possible. The open season for the region comprises 

May to October, inclusive. Frequent showers characterize May, and 

flurries of snow are common in October; but the intervening period 

is delightfully warm by day and cool at night.

The forests abound in wild game; hundreds of deer, and scores of 

bear, wolves, mountain sheep, goats, bobcats, and lynx are killed 

every year. Antelope and beaver are protected by State laws.
14 OEE DEPOSITS IN CUSTEE COUNTY, IDAHO.

Licenses are required of all huntsmen, and the charges are so fixed 

as to favor greatly the residents of the State. Heads and hides may 

be shipped from the State only by special permit.

History of the area. The history of northwestern Ouster County 

since its discovery by whites closely involves its mining development. 

Its early inhabitants were totally dependent upon the mining industry, but other sources of revenue, such as agriculture and grazing, 

were gradually developed until perhaps most of the present population is independent of the mining industry.

For about 30 years after the discovery of placer gold on Loon Creek, 

in 1868, mining was active and the population was much greater 

than at present. Custer, Bonanza, Clayton, and Bay Horse were 

flourishing settlements. More recently Sunbeam prospered, but at 

present Ivers alone is an active camp.

With the certain revival of mining in the future, agriculture will 

become much more important, by reason of increased local market 

and the probability of better transportation facilities.

PHYSIO GRAPHY.

GENERAL BELIEF.

Northwestern Custer County comprises a high mountainous area in 

which the summits stand about 9,600 feet and the beds of the major 

streams 5,000 to 6,000 feet above sea level. The mouth of Challis 

Creek, by railroad location elevations, is 4,830 feet and the mouth of 

Yankee Fork is 5,905 feet in elevation. The highest point visited in 

the area, as determined by aneroid, is Estes Mountain, which attains 

an altitude of 9,800 feet. The highlands form a network of connecting ridges, small areas, and flat-topped spurs. In extent they 

exceed the lowlands, though steep slopes connecting the two represent 

most of the surface.

DRAINAGE.

Salmon Kiver, the main artery of this part of Idaho, heads southwest of the area mapped, flows eastward along its southern border, 

and then abruptly turns to the north and continues along its eastern 

margin and beyond, finally by an abrupt turn flowing westward 

across the central part of the State. All the streams of the area are 

tributaries of Salmon River; most of them join the Salmon at headwaters, but those in the Loon Creek district reach it at a point in the 

central part of the State, well toward its mouth. Loon Creek Summit 

and its continuation to the southwest and northeast forms the local 

divide between northward and southward flowing drainage. Loon 

Creek and its tributaries have intricately dissected the country north 

of the divide, and numerous streams, most important among them 

Yankee Fork, have deeply carved the area south of it.
U. S. GEOLOGICAL SURVEY

A. SPUR ON THE NORTH SIDE OF POVERTY FLAT. 

Showing the highly inclined beds across which the flat has been developed, The flat is 9,600 feet above sea level.

./;. CENTRAL PORTION OF POVERTY FLAT. 

The low hills in the background are quartzite; in the foreground is steeply dipping slate.
U. S. GEOLOGICAL SURVEY

A. SOUTH WALL OF KINNIKINNICK CANYON AS SEEN FROM POVERTY FLAT.

'. MIOCENE LAKE BEDS NORTHEAST OF POVERTY FLAT. 

Note scarcity of vegetation in areas of lake beds.
PHYSIOGRAPHY. . 15

SUMMIT AREAS.

The uplands are characterized by small flat-topped areas, from 

which extend square-shouldered spurs, and by level-crested ridges. 

The striking character of these features has given rise to such local 

names as "Poverty Flat," applied to a tract 9,600 feet above sea level 

and about 25 square miles in extent, and "Railroad Ridge," which is 

more than 100 miles long and so even crested as to resemble, when 

viewed from a distance, a railroad grade. This ridge lies southeast 

of the area studied but may be clearly seen from Poverty Flat 

near Clayton. Equally striking in the evenness of their crests are 

Antelope Ridge, the Lost River Range, and Lemhi Range all blending to form the northeastern horizon as seen also from Poverty Flat. 

To the northwest there are no distinct ranges but instead a veritable 

labyrinth of small summit areas and short ridges, remarkable for their 

general accordance in elevation. Poverty Flat itself is a comparatively level tract (PI. Ill) bordered by canyons as much as 5,000 feet 

deep. It is reached with difficulty by trail from Clayton, 4 miles 

distant, but once on top a wagon could be driven over most of it. A 

few low quartzite hills rise from its general level and attain a height 

perhaps 100 feet greater. Along portions of the western and southern 

borders, notably on a spur west of the New Silver Bell mine, an almost 

horizontal bench, in places 50 to 100 feet wide but generally rather 

indistinct, follows along the side slope about 100 feet below the level 

of the flat. The level part of the flat is deeply mantled with soil, but 

the quartzite buttes are covered with angular blocks of the underlying 

material.

This striking summit surface extends across the rocks of the area 

irrespective of their attitude or composition. The intensely metamorphosed and crumpled schists of the Algonkian, the generally folded 

slates, quartzites, and dolomitic limestones of the Paleozoic, and the 

comparatively undisturbed granitic intrusions of the late Cretaceous 

or early Tertiary have all united to form the present high-level 

topography. (See PI. IV.)

The summits of the area, if combined, would determine an undulating plain, differing little in elevation from place to place though here 

truncating resistant beds and there cutting across shales and schists. 

The surface could have resulted only from erosion. The area was 

reduced nearly to base level for the region, where inequalities in rock 

resistance no longer found pronounced expression in the topography; 

then it was elevated and dissected by the streams which now drain it.

VALLEYS.

The valleys of the area are of two types those now occupied by 

lavas, tuffs, and lacustrine deposits, and those followed by the present 

streams,
16 OEE DEPOSITS IN CUSTEE COUNTY, IDAHO.

The present valleys of the area are for the most part deep and 

narrow, but a few have broad floors of gravels in which the streams 

are now intrenched to a depth of 10 to 50 feet. Valleys of this sort 

are locally typified by those of Loon Creek and Yankee Fork, but 

even along Salmon River remnants of deep gravel deposits occur in 

many places, Robinson Bar being a striking illustration.

The valley of Salmon River is narrow and canyon-like throughout 

most of its extent, but about Challis it widens, affording broad slopes 

admirably adapted for agriculture. Antelope Creek, a comparatively 

insignificant stream, occupies a valley vastly wider than that of Salmon River west of Big Birch Creek. These features are not to be 

accounted for by difference in rock formations or by structure. They 

may be interpreted only in the light of a complex drainage history 

a history which can be worked out only by physiographic studies 

broader than those yet undertaken.

Largest among the older valleys is the one crossed by the Ivers Road 

between points 7 miles south and 5 miles north of Loon Creek 

Summit. The bedrock of this old valley is exposed at Sunbeam at an 

elevation of 7,000 feet, but elsewhere it was not seen. If the Sunbeam 

exposure, which is almost halfway between its margins, is assumed to 

indicate the general elevation of its bed, the old valley is about 3,000 

feet deep and is now filled in most places by lavas and tuffs throughout 

its width of 12 miles.

About Challis the Miocene lake beds occupy a similar depression, 

but no exposures of its floor are known. Similarly situated 

topographically are the deposits east of Bay Horse.

RELATION TO ADJACENT TYPES.

The area herein described is a part of that great plateau-like expanse

known as the Salmon River Mountains, which is characterized 

throughout by even "summits and deep, narrow canyons carved from 

rock formations of diverse type and complex structure. Lemhi 

County, to the north, is continuous with this area and similar 

physiographically. There the history has been worked out in some 

detail and broad correlations have been made. 1 The discussion need 

not be repeated in this bulletin, though the general conclusions are 

incorporated below.

The old erosion surface represented by the summit levels of this 

area is known to have extended over much of Idaho and probably 

into adjoining parts of Montana, Washington, and British Columbia. 

It has been assigned to the Eocene, both because of the relation of 

Miocene lake deposits to it, and because of its relation to the Eocene 

deposits of the Northwest.

i Umpleby, J. B., Geology and ore deposits of Lemhi County, Idaho; Bull. U. S. Geol. Survey No. 528, 

1913, pp. 23-30; An old erosion surface in Idaho; its age and value as a datum plane: Jour. Geology, vol. 20, 

No. 2,1912, pp. 139-147.
GENERAL GEOLOGY. , 17 

PHYSIOGRAPHIC HISTORY.

The record of the physiographic history of the region is legible for 

only that comparatively small portion of geologic time sincfc the late 

Mesozoic. Near the close of the Cretaceous period extensive regional 

elevation, thought to have been accompanied by folding and great 

batholithic intrusions, rejuvenated the streams and inaugurated a 

period of rapid erosion which, by the close of Eocene time, had 

resulted in a far-reaching surface of gentle topographic forms. The 

amount of this early Eocene elevation is not definitely determinable, 

but it was doubtless a few thousands of feet, possibly comparable to 

that at the close of the same epoch.

Elevation at the close of the Eocene or early in the Oligocene once 

more rejuvenated the streams of the area. This uplift extended over 

essentially the same vast area as the former one. In northwestern 

Ouster County the elevation may be taken as about 8,000 feet, or 

somewhat less than the difference between the present high-level 

surface and base level for the region. During the Oligocene epoch 

the major streams developed broad, deep valleys, which in the 

Miocene and possibly also in part of the Pliocene were the sites of 

lava flows and lacustrine deposition.

The Pliocene again was a period of dominant erosion. Valleys as 

much as 4,000 or 4,500 feet deep were locally developed in the Miocene 

rocks and later shaped by glacial ice.

Ice fields covered the highlands during the Pleistocene, and 

glaciers extended down the valleys to elevations between 6,500 and 

7,500 feet. Below these elevations glacial waters deposited deep and 

extensive gravel beds, into which many of the present streams are 

cutting.

Erosion is now active within the region, and perhaps one-third of 

the task of reducing it once more to an area of. gentle topographic 

forms has been accomplished, this in spite of the far-reaching interruptions of the Miocene epoch.

GENERAL GEOLOGY.

OUTLINE.

The oldest rocks exposed in northwestern Custer County are 

schists, slates, and quartzites of Algonkian age. Unconformably on 

these rocks in the eastern and locally in the northwestern part of 

the area lies a great series, at least 9,000 feet thick, of Paleozoic 

quartzites, slates, and dolomitic limestones. These were not further 

subdivided, although there is some reason for thinking that they range 

in age from Cambrian to Devonian, inclusive. These rocks, and also 

the older rocks, are cut by large intrusive masses of granite, quartz 

98185° Bull. 539 13 2
18 OKE., DEPOSITS IN GUSTEE COUNTY, IDAHO.

diorite, and diorite, which are probably outliers of the great batholith 

that invaded central Idaho during the late Cretaceous or early 

Eocene ej>och.

Dikes of granite, granite porphyry, and diorite porphyry, closely 

related in. age to the granitic rocks, are locally abundant in the 

western part of the area. In the central portion and along the 

eastern margin occur, vast accumulations of Miocene lava and tuff, 

which occupy old erosion valleys. Morainic material covers much of 

the highland area and extends down the larger valley to elevations 

of 6,500 or 7,000 feet. Locally it coalesces with outwash gravels 

deposited along the major streams. (For distribution, see map, PL I.)

ALGONKIAN BOCKS.

Distribution. Algonkian rocks are widely distributed in the northwestern and south central parts of the area included in the reconnaissance. Perhaps the best exposures of these rocks are along 

Salmon River, between Thompson and Cold Spring creeks, where for 

a distance of about 6 miles outcrops are almost continuous. For 

about 4 miles along Yankee Fork, south from Sawmill Creek, and 

about the junction of Canyon Creek with Loon Creek, there are also 

numerous exposures.

Characteristics. The Algonkian rocks comprise an intensely metamorphosed series of sedimentary deposits, in which schistosity is well 

developed, in many places to the concealment of bedding structure. 

Where the attitude of the beds is determinable, however, steep dips, 

usually away from north-south axes, prevail.

The stratigraphic sequence of the series could not be carefully 

worked out in the short time available. Along Yankee Fork perhaps 

2,000 feet of beds dipping steeply southwestward are exposed between, 

the lavas on the north and the granite on the south. The lower part 

is dark-gray medium-grained quartzite, and the upper part is composed of thin-bedded blue-black micaceous slates. About Ivers the 

series comprises sericitic and chloritic schists with interbedded siliceous bands. The three f acies of the series schists, slates, and quartzites butcrop in the Salmon River section. In the western portion 

of this exposure bluish-gray fine-grained quartzites are cut off by 

granite. Below the quartzites are dull black, slightly crumpled slates, 

which dip 80° W. and outcrop along the road for about 4,000 feet. 

East of these slates micaceous schists continue to the area about the 

mouth of Thompson Creek, beyond which Paleozoic formations come 

in. The relation of the schists to the slates was not observed, although 

it is believed that they occur lower in the stratigraphic column.

Correlation. Close correlation of these old metamorphic rocks is 

not possible from the incidental attention given them during these 

studies. From their lithologic character and degree of metamor-
GENERAL GEOLOGY. 19

phism, however, there is no doubt that they are part of the same 

general series which is widely exposed to the north in Lemhi County. 

The rocks there found fall into divisions which accord roughly with 

the Cceur d'Alene Algonkian section,1 and it is believed that careful 

study would reveal approximately the same sequence here.

PALEOZOIC BOCKS.

Distribution. Beds of Paleozoic age are widely exposed in the 

eastern half of the area mapped and also occur in a small area south of 

Ivers in the northwestern portion. The best exposures are along 

Salmon River, from Thompson Creek to East Fork, and in the walls 

of Bay Horse Canyon.

Structure. The eastern area only was studied even in moderate 

detail. Here three large anticlines and two synclines characterize 

the structure. The west anticline, later referred to as the Clayton 

anticline, forms a broad arch between Clayton and Squaw Creek. 

On the eastern limb the dips are about 80°, and on the western about 

45°. Beds which reach the river level at points 2 miles apart are 

approximately 2,000 feet above it along the axis of the anticline. A 

similar structural feature about 4 miles wide but with maximum dips 

to the west and east of 30° and 40° respectively spreads between 

Clayton and East Fork. It is across this anticline that the erosion 

surface of Poverty Flat extends. The third and most important 

anticline, because of its relation to the ore deposits, extends in a northsouth direction through the Bay Horse district, and is designated the 

Bay Horse anticline. On its east limb the beds dip about 40° and 

on its west about 80°. Northward within 2 miles the arch flattens, 

and at the same distance beyond the beds are almost horizontal.

Lithology. The Paleozoic section is perhaps best exposed in the 

north wall of Bay Horse Canyon. At Bay Horse the beds are almost 

horizontal, and in a single cliff at the mouth of Beardsley Creek about 

1,000 feet of the section is exposed as follows: At the base lies 300 

feet of thinly laminated dark bluish-gray slate, minutely crumpled 

but without slaty cleavage. . Above this is 500 feet of rather massive 

beds of dolomitic limestone of diverse purity, in some places a dolomite, in other places limestone, and in still others either argillaceous 

or siliceous. This grades into a thin-bedded slate, about 200 feet of 

which is here exposed. Westward from Bay Horse the beds are 

nearly horizontal for about a mile and in the southeast face of Democrat Hill the .section may be continued. Here the slate, which is 

200 feet thick in the other exposure, is 600 feet thick, and is overlain 

by dolomitic limestone 1,300 to 1,500 feet thick. About 2 miles 

above Bay Horse the beds assume a steep westerly dip and this

i Ransome, F. L., and Calkins, F. C., The geology and ore deposits of the Cceur d'Alene district, Idaho; 

Prof. Paper U. S. Geol. Survey No. 62,1908, p. 27.
20 ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

limestone in a short distance descends to the creek level. Beyond 

is a monotonous succession of thin-bedded slates in which slaty 

cleavage is in many places more conspicuous than the bedding planes. 

These slates continue for 1| miles and are cut off by granite. Their 

average dip is possibly 35°, which if duplication by faulting be negligible, as is thought to be the case, indicates a thickness of more than 

4,000 feet. Thus the Paleozoic section as exposed in Bay Horse 

Canyon is thought to be about 7,000 feet thick.

In the walls of Salmon Canyon, above Clayton, are massive flatlying quartzites, which extend from the water line upward possibly 

2,000 feet and underlie 200 or 300 feet of massive blue dolomitic 

limestone. These beds do not appear hi the Bay Horse section. 

Thus the total thickness of the Paleozoic section as exposed in this 

area is more than 9,000 feet, including neither top nor bottom, and 

with an unspanned break between the two sections studied.

It is possible that the 4,000 feet of slates which outcrop above 

Bay Horse may prove to be Algonkian, separated from the Paleozoic 

rocks east of them by a fault, but this is thought improbable, the 

only suggestion of the relation being their greater metamorphism, a 

metamorphism more likely resulting from the granite intrusion than 

from the diastrophism which preceded the Paleozoic era. A fault 

does cross the canyon a short distance above Bay Horse, but the 

meager evidence secured favors a downthrow on the west. (See PL 

V,£.)

Correlation. Lithologically the rocks here found agree closely with 

the Paleozoic formations of the Gilmore section, Lemhi County.1 

There the section comprises between 5,000 and 6,000 feet of beds, 

including 2,000 feet or more of fine-grained Cambrian quartzite, 500 

feet of massive Ordovician dolomitic limestone, 300 feet of massive 

Silurian (?) dolomitic limestone, 2,000 feet of thin-bedded Devonian 

dolomitic limestone, and at least 300 feet of massive blue limestone 

of Mississippian age. Comparing the two sections, it seems probable 

that the quartzite exposed above Clayton agrees with the Cambrian 

quartzite at Gilmore. The 200 to 300 feet of massive blue dolomitic 

limestone above it may thus be tentatively correlated with the 

Ordovician at Gilmore, with which it corresponds lithologically. 

That portion of the section at Bay Horse does not agree closely with 

any part of the Gilmore section. In the Bay Horse section there is no 

group of limestone beds free from dolomite, which affords some basis 

for thinking that the Mississippian, which constitutes the top of the 

Gilmore section, is absent. Thus it seems most probable that the 

Bay Horse section falls between the Ordovician and Mississippian 

that is, that the beds probably represent the Silurian and Devonian.

i Umpleby, J. B., Geology and ore deposits of Lemhl County, Idaho: Bull. U. Si Geol. Survey No. 528, 

1913, pp. 32-35.
A. PLEISTOCENE GRAVEL TERRACES ALONG SALMON RIVER BELOW ROBINSON BAR.

SLATY CLEAVAGE IN PALEOZOIC (?) SHALES AT ROADSIDE 2 MILES BELOW BAY HORSE 

- CANYON. .-- ;:.

^ :,'
GENERAL GEOLOGY. 21

If this is true, however, these systems are vastly thicker than at 

Gilmore. In later work it might be well to entertain as a field hypothesis the possibility that the slates west of Bay Horse are Pennsylvanian and that the Mississippian is there faulted down by the displacement believed to extend northwest across the canyon above 

Bay Horse.

Fossils were not found, but as only incidental search for them was 

made, it is not unlikely that the problem may be ultimately solved 

on fossil evidence. For the present the beds are simply assigned 

to the Paleozoic, the closer correlations being merely suggestions.

LATE CRETACEOUS OB EARLY EOCENE PLUTONIC ROCKS. 

DISTRIBUTION.

Plutonic rocks appear at the surface in the northwestern and 

south-central parts of the area mapped, also at three localities in 

the eastern part. In the Loon Creek district a great batholith of 

quartz diorite extends into the district from the west and again 

outcrops as quartz monzonite in a belt about 6 miles wide along its 

eastern border. The largest area of plutonic rock is perhaps that 

near the junction of Yankee Fork and Salmon River. The main 

stream in this locality flows between rugged walls of granite for 14 

miles below this junction. Northward the area continues for 2£ 

miles, but to the south and west its extent was not determined. In 

the Bay Horse district there are three small areas of plutonic rocks. 

The largest is granite, which comprises a north-south belt about a 

mile wide that crosses the upper end of Bay Horse Canyon. The 

other two are diorite, and each is about three-fourths of a mile wide; 

one crosses Kinnikinnick Canyon 4 miles above Clayton, and the 

other traverses Salmon Canyon 3 miles below Clayton.

VARIETIES .

The several areas of granitoid rocks differ markedly in composition 

and in the following paragraphs will be described separately. The 

rocks were studied hastily in the field and the specimens secured 

may not be altogether typical. Granite, quartz monzonite, quartz 

diorite0, and diorite are represented.

Granite. Granite occurs about the mouth of Yankee Fork and near 

the head of Bay Horse Canyon. Specimens from the former locality 

are light gray to pink in color, medium grained, and about equigranular, but locally, as near Robinson Bar, there is a marked 

phenocrystic development of orthoclase, individual crystals attaining 

an inch or more in length. Megascopically the rock is characterized 

by its light color and the small amount of biotite compared with the 

other granitoid rocks of the area. Microscopically examined, it is
22 ORE DEPOSITS IN CTJSTEB COUNTY, IDAHO.

seen to contain the following minerals, named in order of decreasing 

amount: Orthoclase, quartz, microcline, biotite, albite, oligoclase, 

micropegmatite, muscovite, apatite, magnetite, and rutile. Some of 

the feldspars show zonal growth from albite, possibly also oligoclase, 

at the center to orthoclase on the margins. The granite from .Bay 

Horse Canyon is coarse textured and contains much more biotite. 

It is dark gray in color. Although orthoclase is by far the most 

abundant feldspar in this rock, albite and oligoclase are both prese.nt 

in amounts about equal to the quartz and biotite. Hornblende, 

micropegmatite, magnetite, and apatite, may be considered accessory.

Quartz monzonite. A rock intermediate in composition between the 

granite and quartz diorite comprises a large area west of Loon Creek 

Summit. It is commonly medium gray in color, though locally, 

as near the mouth of East Mayfield Creek, it is dark gray. The 

darker shades are due to excessive amounts of biotite. In places 

gneissoid structure is well developed, but this appears only along 

local zones of shearing. In the thin sections studied orthoclase and 

plagioclase (oligoclase and less albite) are about equally abundant. 

Quartz is almost constant in amount and biotite may be either much 

less or much more abundant than the quartz. Apatite, titanite, and 

magnetite are the more important accessory minerals.

Quartz diorite. Quartz diorite is widely exposed south and west of 

Ivers. It is a dark bluish-gray equigranular rock, rich in biotite. It 

contains abundant plagioclase (oligoclase and andesine), much 

quartz, about an equal amount of biotite, and a little orthoclase. 

Hornblende, apatite, and titanite are accessory constituents.

Diorite. The diorite in Kinnikinnick Canyon was only seen as float 

along the east wall, where it is continuous for about three-fourths of a 

mile. The rock is fine grained, equigranular, and of dark greenishgray color. The feldspars' have approximately the composition of 

andesine and occur as interlocking lath-shaped crystals. Hornblende 

is abundant and olivine and augite are almost equal to it in amount.

The other area of diorite occurs east of Clayton. Here the rock is 

extensively sheared and so highly altered that microscopic study 

adds little to the field diagnosis. Its texture is equigranular and it 

consists of andesine and ferromagnesian minerals, the latter completely changed to chlorite and calcite. Its gneissoid structure 

suggests that it is older than the other intrusive masses, but as older 

igneous rocks were not found in the area it is grouped with the late 

Cretaceous or early Eocene plutonic rocks.

AGE AND CORRELATION.

The plutonic rocks of northwest Custer County extend up to the 

level of the Eocene erosion surface and hence must have invaded 

the area before the close of the Eocene. On the other hand the
GENERAL GEOLOGY. 23

youngest rocks which they cut are the Paleozoic sediments, so that 

their local geologic relations show only that they are later Paleozoic, 

Mesozoic, or very early Cenozoic. Broader considerations, however, permit their age to be rather definitely fixed.

Batholithic intrusions are widespread in Idaho. In the central 

part of the State is a granitic mass more than 20,000 square miles 

in extent. Numerous smaller areas have been considered outliers 

from it. Some of these granites are of the same composition, others 

are more basic, and in one locality granite and diorite have been 

found to grade into each other.1 For these reasons, and because 

nowhere in the State have batholithic intrusions of widely different 

age been recognized, it is believed that these several types of rock 

date from the same general period of intrusion and are of the same 

age as the great Idaho batholith. This batholith has been assigned 

on what are believed to be sound deductions to the late Cretaceous 

or very early Eocene,2 and it is therefore concluded that the batholithic intrusions of Ouster County are also of that age.

EARLY EOCENE DIKES.

o 

DISTRIBUTION.

Dikes are abundant only in the northwestern part of the area, in 

the immediate vicinity of Ivers, where 10, averaging perhaps 30 

feet in width, have been encountered in the workings of the Lost 

Packer min«e. Most of these dikes are approximately paraUel and dip 

northwest at about 40°. In the Yankee Fork district dikes of this 

age were not recognized, and in the Bay Horse district but one 

was noted. This is a narrow intrusion which appears in the lowest 

tunnel of the Ramshorn mine.

VARIETIES.

The dikes fall into three general groups granite, granite porphyry, and diorite porphyry. Included in the last is the peculiar 

rock which occurs in the Ramshorn mine and which is designated 

an augite melaphyre. The several groups will be briefly described.

Granite. Granite dikes, in places 30 feet wide but generally about 

10 feet across, parallel the ore body on the hanging-wall or footwall 

side in parts of the Lost Packer mine. The rock has been greatly 

crushed, but the constituent minerals are readily determinable. It 

is light gray, inequigranular due to a phenocrystic development of 

the feldspars and consists of microcline, orthoclase, quartz, and

1 Lindgren, Waldemar, The gold and silver veins of Silver City, De Lamar, and other mining districts 

of Idaho: Twentieth Ann. Kept. U. S. Geol. Survey, pt. 3, 1900, p. 195.

* Umpleby, J. B., An old erosion surface in Idaho; its age and value as a datum plane: Jour. Geology, vol. 

20, No. 2,1912, pp. 139-147.
24 ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

muscovite, decreasingly abundant in the order named. Ferromagnesian constituents are rare.

Granite porphyry. Granite porphyry, younger than the granite 

dikes (fig. 4, p. 95), occur in the Lost Packer mine as flat-lying 

bodies 20 to 40 feet wide. It is a medium-gray rock with phenocrysts and groundmass about equal. The degree of alteration of the 

specimens studied leaves some doubt as to whether the rock might 

not better be called a quartz monzonite. Most of the feldspars 

seem to have an index lower than Canada balsam, but a few are 

certainly higher. Quartz exceeds biotite and hornblende is rare.

Diorite porphyry. Several flat-lying dikes of diorite porphyry 

about 20 feet wide occur in the Lost Packer mine. They are intermediate in age between the granite and granite porphyry. The 

rock is dark gray, rather mottled by the lighter-gray feldspar crystals. 

The feldspars are predominantly andesine, though in some of the 

thin sections labradorite appears and in others oligoclase. Biotite 

is abundant, though in few specimens conspicuous. Quartz and 

apatite are the principal accessory minerals. Locally, as in No. 3 

tunnel, marginal phases of the rock contain a large amount of augite.

The smalPdike that is cut about 200 feet from the face of the lowest 

Ramshorn tunnel differs from the others in that augite, its only 

recognized mineral, studs a groundmass itself containing much augite. 

A few other phenocrysts, now completely altered largely to calcite 

were probably feldspars.

AGE OF THE DIKES.

All the dikes above described are cut by the Eocene erosion surface. On the other hand the granite dikes are probably almost 

contemporaneous with the granitic batholiths; if there is any difference in age, they are a little younger. The other dikes are still younger 

than these. As the granitic rocks are assigned to the late Cretaceous 

or early Eocene the dikes are thus believed to have entered during 

the early part of the Eocene epoch. It further follows that they 

entered in fairly rapid succession, the sequence being granite, diorite 

porphyry, granite porphyry.

MIOCENE VOLCANIC BOCKS. 

DISTRIBUTION AND CHARACTER;

Lavas and tuffs extend as a broad belt northeast through the 

central part of the area covered by this reconnaissance. They fill 

completely an Oligocene erosion .valley which, where traversed by 

the road to Ivers, is 12 miles wide and about 3,000 feet deep. Lavas 

and tuffs also form broad areas in the northeastern and eastern parts 

of the Bay Horse district. Here also they occupy erosion valleys,
GENEBAL GEOLOGY. 25

but in no place were they seen to reach the level of the Eocene 

surface.

The general sequence of volcanic rocks seems to be andesites and 

latites, followed by andesitic and rhyolitic tuffs, and these in turn 

followed by basalts. In the western part of the Yankee Fork district the series is chiefly tuff, but east of Ouster lava flows appear 

in the canyon sides through a vertical range of several hundred feet. 

The extrusive rock above the Lost Packer mine is quartz latite, and 

that near the lower end of the Loon Creek placers is andesite. About 

Challis and east of Bay Horse both lavas and tuffs are abundant, 

and in them the major sequence is from lavas, presumably, andesites, 

to tuffs. East of Bay Horse, however, basalt dikes cut the tuffa'ceous 

material and locally spread out as flows on its upper surface.

The dearth of rhyolites in this area is in striking contrast to the 

great amount- of this rock which appears about Parker Mountain, 

in Lemhi County. 1 The two areas are said to be continuous, yet 

the prevailing type of rock is very different. In each locality 2,000 

feet or more of the series is exposed. About Salmon, still farther 

north, however, andesites are abundant, 1 and this area also is believed to be continuous with that at Parker Mountain. The several 

rocks will be described briefly.

ANDESITES AND LATITES.

Latite was not recognized from microscopic examination, but one 

specimen, thought from the thin section to be a dacite, proved on 

partial analysis to contain 3.26 per cent of potassium oxide, and 

another, which appeared to be a normal andesite, was found to 

contain 3.86 per cent of potassium oxide. (See p. 26.) In these 

specimens, the only ones analyzed, the potash is evidently in the 

groundmass, which leads to the belief that many of the rocks herein 

described as andesites will prove, on chemical analysis, to be latites. 

Thus the two groups are described jointly.

The rocks range in color from dark gray through various shades 

of purple to bluish black, perhaps a brownish-gray variety being 

most abundant. Phenocrysts and groundmass comprise about equal 

areas. The minerals of the groundmass are determinable in but few 

specimens. Among the phenocrysts feldspar predominates, though 

some ferromagnesian mineral is generally conspicuous. The feldspars 

are commonly oligoclase and andesine, but a few crystals of labradorite are present. In a specimen taken near Jensen's bridge, in the 

Bay Horse district, hypersthene, biotite, and augite occur with andesine. A rock from the mouth of Jordan Creek contains much pyroxene and a little olivine. In another specimen, obtained near the

i Umpleby, J. B., Geology and ore deposits of Lemhi County, Idaho: Bull. U. S. Geol. Survey No. 528, 

1913, p. 47.
26 OEE DEPOSITS IN CUSTEK COUNTY, IDAHO.

Badger mine, augite is abundant. A dark-gray rock at the head of 

Bay Horse Canyon contains conspicuous amounts of biotite and hornblende. Partial analyses of two of the rocks included in this group 

appear below:

Partial analyses of volcanic rocks from northwestern Ouster County, Idaho. 

[R. C. Wells, analyst.]

Si02 . . ..........................................................................

CaO.. ..........................................................................

NajO. .......................................................................... KjO. ..........:................................................................

1

60.58

4.31

3.86

3.86

2

64.20

3.99

i 4n

3.26

3

80.47

.14

.16

3.80

1. Latite. taken from roadside 1 mile below Sunbeam. Phenocrysts><microcrystalline groundmass. 

Feldspar AbTsAnjs. A little augite as small anhedral crystals. Biotite and magnetite accessory. Calcite 

and iron oxide secondary.

2. Quartz latite, taken above Lost Packer mine. Phenocrysts<cryptocrystalline. groundmass. Feldspar about AbToAnao. Scattered grains of quartz and less biotite. Chlorite, calcite, and iron oxide secondary.

3. Rhyolitic tufi, taken on west slope, 200 feet below Loon Creek Summit, at roadside. Very fine grained, 

Iragmental, mostly glass. A few feldspar grains, all with higher index of refraction than Canada balsam.

TUFFS.

The tuffs of the area are fine-grained rocks of dull-white to reddish 

color and generally form steep chalky white slopes. The}' are well 

exposed on the west face of Estes Mountain, where for several hundred feet below its summit vegetation is meager. In the Yankee Fork 

district the tuffs are commonly massive, but about Challis they are 

thin bedded and interstratified with seams of clay that are again 

referred to in connection with the lacustrine,deposits.

The tuffs are commonly fine grained and composed of angular 

fragments of glass, quartz, and feldspar, together with a few needles 

of hornblende and scales of biotite. The feldspar grains are commonly striated and have an index of refraction higher than Canada 

balsam, but the only specimen submitted for partial analysis contains 3.80 per cent of potash and less than 1 per cent each of soda 

and lime. It is clearly a rhyolitic tuff. That some of the tuff, 

however, is andesitic^or at least latitic is shown by the abundance of 

the striated feldspar fragments. The tuffs near Challis have been 

described petrographically by A. A. Julien. 1

AGE OF THE LAVAS AND TUFFS.

The lavas and tuffs of northwest Custer County are assigned to the 

Miocene for the following reasons: They occupy valleys- developed 

after the elevation of 'the Eocene erosion surface. If the Oligocene 

be allowed for the development of these valleys the lavas and tuffs 

are post-Oligocene. On the other hand, glacial ice occupied the

i Volcanic tuffs of Challis, Idaho: Trans. New York Acad. Sci., vol. 1,1882, pp. 49-53.
GENERAL GEOLOGY. 27

upper parts of the valleys carved in the volcanic rocks. Some of these 

preglacial valleys, as Yankee Fork and Jordan Creek, are 3,000 feet 

or more deep. It therefore seems probable that much of Pliocene 

time was consumed in their development.

MIOCENE LACUSTRINE DEPOSITS.

Distribution. Lacustrine deposits occur in the northeastern and 

eastern portions of the area studied. The northern area comprises an 

irregular belt about 10 miles across, with tongues reaching up the 

several valleys tributary to the basin in which Challis is situated: 

To the south, west, and north the lake beds give way to lava flows, 

but to the southeast they connect across a low divide at the head of 

Antelope Valley, with similar deposits in the valley of Big Lost River. 

The area east of Bay Horse is of peculiar shape, but seems to have an 

outward continuation south of Antelope Ridge.

Character. Perhaps the best exposures of these beds are along the 

east bank of Salmon River below Challis. Here the bluffs are about 

200 feet high, and as seen from across the river are made up of light 

gray sandstones, probably tuffaceous, and dove-colored shales. 

Conglomeratic members are sparsely and irregularly distributed 

through the section. The beds vary in thickness from less than an 

inch to several feet. In bluffs north of Challis tuffaceous material, 

generally very fine grained and of green, gray, and white color, predominates. It is nicely bedded, in places thinly laminated.

The hurried observations afforded little idea of the thickness of the 

deposits, although it must unquestionably be hundreds of feet.

Age. Fossils were not found in this area, but the topographic relation of these beds is similar to those at Salmon, which were assigned 

to the Miocene on floral evidence. 1

PLEISTOCENE DEPOSITS.

Morainic material. The highland parts of the area in most places 

are covered by loose unsorted rocko material, locally overlying distinctly striated rock surfaces. The innumerable valleys and canyons 

which head at elevations greater than 7,500 or 8,000 feet are terminated by cirques, widely different in size and many of them occupied 

by small lakes. Below these the canyons are U-shaped, strewn 

unequally witn detrital material, and in many places followed by low 

hummocky ridges roughly parallel to the base of the. walls. Deposits 

of this sort extend down the larger valleys to elevations of about 

7,000 feet, rarely to 6,500 feet, as in Bay Horse Canyon.

These several features clearly indicate glacial action. The ice 

probably covered all the areas above 8,000 feet and attained the lower 

levels only in the form of alpine glaciers.

1 Umpleby, J. B., Geology and ore deposits of Lemhl County, Idaho: Bull. U. S. Geol. Survey No. 528, 

1913, pp. 38-39.
28 ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

Outwasli material. The valleys of Yankee 'Fork from Custer to 

Salmon River and of Loon Creek, at least from Cottonwood Creek 

headward for 10 or 12 miles, are filled to a maximum known, depth of 

90 feet (see p. 80) with roughly sorted rounded to subangular material 

derived from the adjacent highlands. These deposits indicate a 

change from conditions of erosion, as shown by the existence of the 

valleys which they occupy, to conditions of deposition; there was a 

transition from degradation to aggradation. Such a change may take 

place conceivably in many ways, but the essential factor must be 

either a decrease in stream velocity or an excess of available material. 

The presence of the deposits in great valleys developed within areas 

of Miocene lavas shows that the deposits are Pliocene or later.

Erosion preceded the formation of the deposits and erosion is now 

removing them, hence it is reasonable to look to the Pleistocene, a period of special climatic conditions, for an explanation of their presence. 

At this time glacial ice operating on the highlands and within the upper parts of the valleys was loosening and grinding up vast quantities 

of material, some of which has not yet been removed. During the 

general period of ice advance much of this was covered by the ice and 

protected, although even then vast amounts of material were doubtless available for transportation. Not, however, until the general 

period of ice recession commenced did the supply of available material 

reach its maximum, and at this time, also, the run-off from the glacier 

areas was greatest, and the streams fully loaded in their upper, swifter 

portions, must have deposited their load farther downstream, where 

the gradient was less. It is therefore believed that the great gravel 

deposits of Loon Creek and Yankee Fork valleys are of late Pleistocene 

age.

RESUME OF GEOLOGIC HISTORY.

The earlier geologic history of northwestern Custer County, Idaho, 

comprises a record of long-continued sedimentation, followed by 

strong regional metamorphism and erosion in the pre-Cambrian. In 

the Paleozoic, again, sedimentation was the dominant feature, and 

some time after its close great dynamic movements developed folds 

whose limbs now commonly dip about 45° away from general northsouth axes. In so far as the record is legible, erosion was the dominant 

feature during the Mesozoic, but near its close great batholithic intrusions entered beneath the area. Their invasion is believed to have 

been expressed at the surface by a pronounced elevation, which during 

the Eocene was planed well toward the base-level of erosion.

The Eocene surface of gentle topographic forms was soon elevated 

7,000 or 8,000 feet, and deep valleys developed by the close of the 

Oligocene. During the Miocene, volcanic activity was rife; vast 

quantities of lavas and tuffs filled the larger valleys, some of them 

more than 3,000 feet deep. Incident to the lava eruptions many of
GENERAL FEATURES. 29

the streams were impounded, and lakes corresponding in shape to 

former valleys ramified among the mountains. In these lakes muds-, 

sands, and volcanic ash accumulated to great depths during Miocene 

time. During the Pliocene epoch erosion once more became dominant, 

but accompanying it were the dying stages of the volcanic activity 

which characterized the Miocene. The Pleistocene was an epoch 

when destruction of the highlands exceeded erosion along the main 

arteries. Glacial ice covered the summits and occupied the heads of 

canyons. More material was supplied than could be carried onward 

By the larger streams, which along their lower courses deposited 

vast beds of gravels, ready for removal when conditions of erosion 

once more became normal.

The deposition of metallic ores followed both the late Cretaceous or 

early Eocene and the Miocene igneous activity. The former resulted 

in gold-copper, silver-copper, and lead-silver deposits; the latter in 

gold-silver veins.

ORE DEPOSITS.

GENERAL FEATURES.

Character of the deposits. The ore deposits of northwest Ouster 

County comprise gold placers and lodes carrying gold-silver, goldcopper, silver-copper, and lead-silver ores. The first, second, and 

third types of lodes are typically fissure fillings, but the fourth might 

equally well be considered of replacement origin, the solutions, however, directed largely by fissures. Thus they are all characteristically 

of tabular outline.

In most of the deposits the ore is of excellent grade, little of that 

which has been mined affording a return of less than $30 to the ton 

and some of it $500 or $600. Perhaps most of the production of the 

area has come from ores worth $50 to $100 to the ton.

The gold-silver deposits are characterized by a highly siliceous 

gangue; the others by a siderite gangue. The former also present 

much more intense metasomatic alteration of the wall rock than the 

others.

Periods of mineralization. Two distinct periods of mineralization 

are recognized. These periods were separated by a long interval in 

which the area was reduced to gentle topographic forms, elevated 

several thousand feet, further dissected, and many of the valleys 

filled or partly filled with volcanic material. The deposits of the two 

periods are distinct in character and their age relations so clearly 

determinable that in the following sections age is taken as the basis of 

major classification, and the deposits are grouped as pre-Oligocene 

and post-Oligocene. Great difference in age with profound erosion 

intervening shows that the older deposits must have been formed at 

vastly greater depth than the younger, a fact thought to account for
30 QBE DEPOSITS IN OUSTER COUNTY, IDAHO.

conspicuous differences in the structure of the ores and probably 

also in the mineralogy of the two groups of deposits.

Distribution. Ore deposits are widely distributed in the northwestern .part of Ouster County. In the Loon Creek district they are 

largely grouped around Ivers, near which town gold placers, goldcopper veins, and lead-silver veins are recognized. In the Yankee 

Fork district the old mining towns of Ouster, Bonanza, and Sunbeam 

are each centrally situated with respect to gold-silver veins. Near 

Bonanza gold placers occur. In the Bay Horse district the deposits 

are more widely distributed, but here Bay Horse, Clayton, Squaw 

Creek, and Slate Creek may be taken as centrally situated with reference either to silver-copper or lead-silver deposits.

Little is known of the country intermediate between these widely 

separated localities. In the early days much of it was run over by the 

prospector, but there is little evidence in the way of prospect pits 

to show that it was seriously examined. Many outlying deposits 

may yet be discovered.

Geologic relations. The oldest rocks known to be exposed in the 

area are Algonkian schists, slates, and quartzites, widely distributed 

in the south-central and northwestern portions. These rocks are 

overlain unconformably by a great series, more than. 9,000 feet thick, 

of quartzites, dolomitic limestones, and slates, of Paleozoic age. 

These are most widely exposed in the Bay Horse district, but are also 

present south of Ivers in the Loon Creek district. The next younger 

rocks are the batholithic intrusions which are assigned to the late Cretaceous or early Eocene. These appear atthesurface as an area of quartz 

diorite near Ivers; an area of quartz monzonite between Ivers and Sunbeam; a broad expanse of granite about the mouth of Yankee Fork 

and a smaller mass near the head of Bay Horse Canyon; and two 

small areas of diorite, both near Clayton. The boundaries of the 

several intrusions are not indicated completely on the map, but in 

general terms these types may be considered to form the surface rock 

over about 10 per cent of the area.

Closely related to the batholithic intrusions are the granite, granite 

porphyry, and diorite porphyry dikes, which are numerous only in 

the vicinity of Ivers.

The youngest rocks in the area, exclusive of glacial debris, are 

tuffs, lavas, and lacustrine deposits of Miocene and possibly in part 

Pliocene age. The largest area of these extends northeast-southwest 

through Yankee Fork district. Here an old valley, some 10 miles 

wide and 3,000 feet deep, is filled with latites, andesites, and tuffs, 

the latter locally nicely stratified. In the east-central and northeastern parts of the area are other widespread deposits of this age, 

but in these localities clastic material is of equal abundance with the 

tuffs and lavas.
PRE-OLIGOCENE DEPOSITS. 31

Deposits of ore occur in all the groups of rocks above mentioned. 

The late Tertiary eruptives inclose the gold-silver veins of the Yankee 

Fork district. Granite is the inclosing rock of part of the leadsilver deposits south of Ivers. Formations of Paleozoic age inclose 

the lead-silver and silver-copper deposits near Clayton and Bay 

Horse. Algonkian schists constitute the country rock for the goldcopper deposits and may also inclose the lead-silver veins of the 

Livingston group.

PRE-OLIGOCENE ORE DEPOSITS. 

CLASSIFICATION.

The pre-Oligocene metalliferous deposits of northwestern Ouster 

County may most advantageously be classified, according to the 

principal metals which they contain, as silver-copper, lead-silver, 

and gold-copper deposits. The three types1 have much in common 

and mineralogic gradations between them occur locally, but as groups 

they are exceptionally well characterized by their leading metals. 

The features which they have in common are (1) a siderite gangue; 

(2) similar paragenesis, the general order being iron carbonate followed by quartz, the metallic sulphides, and sulphantimonites; (3) 

subordinate metasomatic alteration of the wall rock when cjmpared with the post-Oligocene deposits; and (4) a close accordance 

with one another in age.

The kind of inclosing rock may also be taken as the basis for classification, but this only separates, and that incompletely, the leadsilver deposits from the others. Such a classification comprises (1) 

deposits inclosed in calcareous and dolomitic rocks, and (2) those 

inclosed in slates and schists. The first includes the lead-silver 

deposits, the second those carrying silver-copper and gold-copper 

ores. The classification according to metals contained is followed in 

the later discussion.

SILVER-COPPER DEPOSITS. 

DISTRIBUTION AND HISTORY.

Deposits of silver-copper ore have been found only in the Bay 

Horse district, where the two most important mines the Kamshorn 

and Skylark produce ores of this kind. In addition to these mines 

the lodes of the New Silver Bell mine, one of the Hoosder veins, and 

some small deposits near the head of Garden Creek are of this type.

The Ramshorn vein, located in August, 1877, was the first deposit 

of this type recognized in Custer County. A short time thereafter 

the Skylark and Silver Bell were staked and for 20 years following 

these and the Ramshorn were active producers. Although during recent years but little ore of this type has been mined, there is
32 - ORE DEPOSITS IN CUSTEK COUNTY, IDAHO.

more of it blocked out in the area than of any other type. In all 

about $6,250,000 has been derived from this ore; approximately 

$625,000 from copper, the balance from silver.

GEOLOGIC RELATIONS.

All tne silver-copper deposits are inclosed in slates, probably of 

Paleozoic age, whose cleavage, forming high angles with the bedding 

planes, is commonly well developed and locally is more conspicuous 

than the bedding structure.

Granite outcrops a few hundred feet west of the Skylark and 

Ramshorn veins, but no igneous rock was noted in the immediate 

vicinity of the Silver Bell deposits.

FORM AND STRUCTURE OF THE DEPOSITS.

The silver-copper ores occur in tabular deposits which range in 

width from a few inches to 4 feet, averaging perhaps 20 inches. 

They are bounded by well-defined walls and the few offshoots follow 

bedding or joint planes. Their general strike is north-south and the 

dip either to the east or to the west. The dip of the veins is largely 

determined by lines of parting which antedate the period of fissuring. 

The Ramshorn vein follows the slaty cleavage of the inclosing rocks; 

the Skylark occurs along a bedding plane; but the New Silver Bell is 

independent of either cleavage or bedding planes, the fissuring here 

cutting across the flat-lying beds at a low angle in the upper part and 

a considerable angle in the lower part. (See PL VI.)

THE ORES.

PAY SHOOTS.

Within the veins the ore occurs in shoots of irregular shape which 

range in length from 15 or 20 to 200 or 300 feet, and in width from a 

few inches to 4 feet, averaging perhaps 20 inches. The vertical 

extent of the shoots generally exceeds the horizontal and in many 

places, as in the Skylark mine, the shoots are distributed one above 

the other along roughly parallel lines. The portion of the fissures 

intermediate between the shoots is locally filled with gangue or 

gouge, equal in width to the ore, but in most such places the walls 

are close together and only a narrow selvage marks the fissure.

MINERALS.

Relative abundance. The ore is characterized by tetrahedrite in a 

siderite gangue. Associated with these minerals, but in very subordinate amounts, are quartz, chalcopyrite, galena, arsenopyrite, 

pyrite, and sphalerite. Withiti'the deposits as now worked secondary 

minerals are negligible, although in the upper levels cerargyrite was 

present in large amounts. It is said that there, too, lead was much 

more abundant than in the present ore.
U. S. GEOLOGICAL SURVFY

 *., Wm^ '#wMw<-

A. RAMSHORN AND SKYLARK MINES, BAY HORSE DISTRICT.

The strike of the Ramshorn vein is shown by the series of dumps on the right. 

The Skylark dumps are shown at the left, in the upper part of the view.

P>, DETAIL OF STRUCTURE NEAR THE RAMSHORN AND SKYLARK MINES. 

Showing slaty cleavage followed by the Ramshorn vein and bedding planes followed by the Skylark vein.
U. S. GEOLOGICAL SURVEY BULLETIN 539 PLATE VII

. SPECIMENS OF ORE FROM UTAH BOY NO. 5 TUNNEL, RAMSHORN MINE.

A, Tetrahedrite (dark areas) and siderite (light areas). Films and veinlets of chalcopyrite occur along the

crack in the siderite. Natural size.

11, Euhedral crystals of auartz in nicely crystallized siderite. Natural size. 

C\ Along The fracture (a) is a veinlet of arsenopyrite with columnar crystals replacingthe inclosing siderite.

Near the top is quartz intergrown with the siderite. Natural size.
PKE-OLIGOCENE DEPOSITS. 33

In, addition to the minerals which are confined to the fissures, the 

vein solutions have developed certain others in the inclosing rock. 

Among the minerals here formed sericite alone is abundant, but as it 

characterizes the slates well removed from the fissures, the extent to 

which it is due to the ore-bearing solutions is difficult to determine. 

Perhaps the best basis for comparison is the state of preservation of 

minerals other than sericite which were developed by the earlier 

metamorphism. Of these an andalusite-like mineral 1 is excellently 

preserved in the slates well removed from the fissures, but near them 

this mineral is completely altered to sericite and calcite. Thus in 

thin sections taken near the vein sericite of two generations is thought 

to be present; the earlier resulted from regional metamorphism, the 

later represents metasomatic alteration by vein solutions. Accompanying the sericite. are numerous small opaque specks which in, 

reflected light are dull gray. They were not identified.

Paragenesis of the vein minerals. The sequence of formation of the 

more abundant vein minerals, is rather definite, but among the 

accessory minerals the order is recurrent. Siderite is clearly the 

earliest mineral formed. It was closely followed by tetrahedrite, 

which occurs along fractures in the siderite and occupies embayments 

in it, but in a few places the two are so intergrown as to suggest contemporaneous deposition. Arsenopyrite bears the same relation to 

siderite as does tetrahedrite, but their relation to each other is not 

known. Quartz occurs both as massive intergrowths with the siderite 

and tetrahedrite and as doubly terminated prisms either occupying 

small cavities in the tetrahedrite or embedded in the siderite. Chalcopyrite occurs principally as narrow films along fractures and as tetrahedrons lining cavities in the tetrahedrite, but locally seems to be intergrown with that mineral. In many places a narrow band of chalcopyrite separates the tetrahedrite from the siderite. Galena is found 

as isolated grains in the tetrahedrite but most commonly occurs as 

bunches partly filling cavities an inch or more across. Pyrite is 

extremely rare, but a few crystals were noted embedded in the 

siderite. In such places it was formed later than the tetrahedrite, 

but before the chalcopyrite, the latter mineral in some specimens 

coating it. Upon some of the free faces of the galena are small crystals of sphalerite so thickly spaced as to form a drusy surface. They 

appear to be entirely superficial, for in no place were they seen to 

extend into the galena. Also "among the last minerals to form are 

small lamellar crystals of siderite, which protrude from the sides -of 

small cavities along the margins of siderite areas. (See PI. VII.)

Thus the general sequence of deposition was from carbonate to 

sulphantimonite to sulphides, the order of formation of the sulphides

1 The index of refraction is 1.62±, whereas andalusite (mean) is 1.638. A few sections also give an inclined extinction up to 11°.

98185° Bull. 539 13 3
34 ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

being iron-copper, lead, and zinc. It is noteworthy that pyrite is 

rare in the deposits, but arsenopyrite is very generally present, 

though nowhere abundant.

Composition of the tetrahedrite. Tetrahedrite, commonly known as 

gray copper ore, is a sulphantimonite of copper in which the copper 

is commonly replaced in part by iron, zinc, lead, mercury, silver, 

manganese, nickel, and the antimony by arsenic and bismuth. It is 

widely distributed in metalliferous deposits but is usually an accessory 

constituent. Perhaps the largest deposits in the United States heretofore described are those of the Sheba and De Soto mines in Humboldt County, Nev. Here, however, the principal ore mineral was 

j amesonite. 1 Tetrahedrite is also found at many localities in Colorado, 

Mexico, Bolivia, and Chile, and in numerous deposits in Europe.2 

So far as the writer has been able to ascertain, however, no locality has 

been described which has produced an amount even comparable to 

the $6,250,000 derived from the three deposits of this mineral in the 

Bay Horse district. Of this amount $3,000,000 came from the Ramshorn mine, in which a large tonnage yet remains.

The tetrahedrite here found is dark gray with splendent luster on 

fresh fracture and metallic luster after moderate exposure.' It is massive in its occurrence; in no specimen was a crystal face seen. Numerous fairly smooth planes appear on the specimens, but the arrangement of these is such as to indicate fracturing instead of cleavage. 

Locally such faces are doubtless due to juxtaposition with siderite.

A complete analysis of the tetrahedrite from Utah Boy No. 5 level, 

Ramshorn mine, was made in the Survey laboratory by R. C. Wells. 

The material was carefully selected to preclude chalcopyrite, the only 

mineral likely to be intermixed with it. The analysis follows:

Analysis of Letrahedrite from Ramshorn mine, CiLster County, Idaho.

[R. C. Wells, analyst.] 

Gangue. ..................................................... 0.08

Sulphur....................................................... 25.74

Silver......................................................... 4.86

Bismuth. .................................................... .34

Arsenic...................................................... 1.46

Antimony.................................................... 25. 22

Copper........................................................ 33.39

Iron......................................................... 4. 64

Zinc......................................................... 3.53

Manganese................................................... .01

Nickel....................................................... tr.

99.27

i Ransome, F. L., Notes on some mining districts in Humboldt County, Nev.: Bull. U. S. Geol. Survey 

No. 414, 1909, p. 43.

3 For a list of localities and numerous analyses, see Hintze, Carl, Handbuch der Mineralogie, vol. 1,1902, 

pp. 1082-1120.
PKE-OLIGOCENE DEPOSITS. 35

If the analysis is calculated in molecular quantities the following 

proportions result: Sb(Bi,As), 1; Cu (all other metals), 3.03; S, 3.48. 

The theoretical proportions for tetrahedrite are 1.3.3, but a study of 

available analyses 1 shows that sulphur is commonly in excess. In 

this tetrahedrite, however, the excess is greater than in any of the 

analyses which have been examined. Chalcopyrite is the only mineral which, from metallographic studies, can reasonably be assumed 

to be present as an impurity, but to calculate the excess sulphur as 

that mineral uses up all the iron in addition to an equal number of 

copper molecules, and thus reduces, beyond reason, the molecular 

value of the copper component. From these calculations it is concluded that the analysis was of essentially pure tetrahedrite and that 

the excess of sulphur, if significant, may be in solid solution or possibly 

combined as a higher sulphide of one or more of the metals.

Vertical distribution of minerals. Throughout the workings now 

safely accessible there is no appreciable difference in the mineralogic 

association with depth from the surface. The lowest level of the 

Rarnshorn mine is 1,650 feet vertically below the apex of the vein. 

From the lowest tunnel up to the Utah Boy No. 3, a vertical distance 

of about 900"feet, the tunnels were explored; above are abandoned 

stopes. In this lower half of the mine the relative amount of the 

several minerals, so far as observed, is constant. Of the mineralogic 

make-up of the ore from the old workings there is no available record. 

A brief note on the Ramshorn deposit when only two tunnels had been 

driven 2 states that the better grade of ore ran 500 ounces in silver per 

ton and 16 per cent of lead, no mention being made of copper. This 

probably means an abundance of cerargyrite and sand carbonate near 

the outcrop, but whether that part of the vein once contained copper 

as well as lead can not be determined from such a statement, for the 

copper, if formerly present, would readily have been leached during 

the formation of cerargyrite and sand carbonate. A zone of secondary 

chalcocite below the oxidized ore would support the opinion of the 

writer that tetrahedrite once extended up to and beyond the level of 

the present surface. No information was procured concerning the 

mineralogy of the zone between the oxidized ore and the primary 

ore now exposed. It is said, however, that most of the production has 

come from ores similar to those now developed.

AGE AND GENESIS.

The three principal silver-copper deposits are truncated by the' 

Eocene erosion surface and hence were formed at least before the close 

of the Eocene. On the other hand, they have much in common with

1 Kretschmer, A., Analyse und chemische Zusammensetzung der Fahlerze: Zeitschr. Kryst. Min., vol. 48, 

No. 5, 1910, pp. 484-513.

2 News note, Min. and Sci. Press, Oct. 2,1880, p. 220.
36 OKE DEPOSITS IN OUSTER COUNTY, IDAHO.

the lead-silver deposits and are thought to have been deposited during 

the same period of mineralization. As in the Loon Creek district 

some of the lead-silver veins are inclosed in granite, it is probably 

safe to assume that the silver-copper deposits are postgranitic even 

though the youngest rock-inclosing them is of Paleozoic age. The 

granite is pretty surely of late Cretaceous or early Eocene age, hence 

these deposits are believed to date from the late Cretaceous or early 

Eocene. This assignment is compatible with the age of deposits in 

Idaho of similar type though somewhat different mineralogicalry, 

which have been described elsewhere.

The depth at which the deposits were formed can not be definitely 

determined, but it is certain that a vast amount of erosion has taken 

place since their deposition. In the development of the Eocene 

erosion surface several thousand feet of beds must have been removed; 

a conclusion which follows from a study of the anticlinal structures 

truncated. Another line of suggestion is based on the belief (p. 24) 

that the granitic intrusions accompanied the profound elevation of 

the surface which inaugurated the rapid erosion of the Eocene epoch. 

The cover was entirely removed from the batholiths over broad 

areas and the igneous rock itself deeply planated. StiH another line 

of attack is based on the accumulation of great fluviatile deposits in 

adjacent areas during the Eocene. The region must at that tune 

have been sufficiently elevated for the efficiency of the streams in 

transporting sediments to be far greater within the area than beyond 

it. From these several lines of evidence it is believed that 5,000 feet 

may be taken as a safe minimum estimate of the amount of Eocene 

erosion. Thus the highest deposits are thought to have been formed 

at a depth of at least 5,000 feet, probably much deeper, and the 

lowest ones at a depth 3,000 feet greater. These figures correspond 

closely to those thought by Ransome l to be applicable at Coeur 

d'Alene.

The temperature at which the deposits formed can not be known 

even approximately, although the normal temperature gradient for 

increasing depth below the earth's surface places a minimum of about 

100° C. for a depth of 8,000 feet. The proximity of the cooling 

granitic mass which now outcrops within 600.feet of the deposits 

must have raised this temperature greatly. Therefore, in any consideration of genesis high temperature and, because of 'the depth, 

high pressure must be assumed.

There is abundant reason for believing that the deposits were formed 

from solution. The two other possibilities, namely, volatilization 

and a melt, are ruled out by the mineral compounds of the deposits. 

The carbonate gangue is incompatible with the conception of a melt,

1 Eansome, F. L., and Calkins, P. C., The geology and ore deposits of the Coeur d'Alene district, Idaho: 

Prof. Paper XJ. S. Geol. Survey No. 62,1908, pp. 139-140,
PRE-OLIGOCENE DEPOSITS. 37

and the difficulty of volatilization of the metals in the right proportions, even when combined, eliminates the other hypothesis.

The most striking feature of the deposits is the great quantity of 

tetrahedrite, a mineral remarkable for the complexity of its composition. It is thought that this must have a marked significance with 

respect to the genesis of the deposits. K. C. Wells, who made the 

analysis (p. 34) of this mineral, has supplied the following comment 

on the conditions of formation of tetrahedrite from aqueous solutions.

The conception that tetrahedrite forms from simple aqueous solutions is unsatisfactory for several reasons. In the first place, the sulphides are among the most 

insoluble compounds known in chemistry and tetrahedrite commonly contains lead 

and silver, whose suplhides are among the most insoluble of sulphides. 1 Secondly, it 

would be remarkable if such a process did not result in greater differentiation into 

single sulphides; for if the solutions were acid the precipitation of zinc and iron would 

be retarded, whereas if they were alkaline the deposition of antimony and arsenic 

would be prevented. In neutral solutions fractionation should still occur.2 These 

are the behaviors under ordinary conditions, and it seems reasonable to suppose that 

they would persist to some extent even under high pressure, although by a mass effect 

of much hydrogen sulphide under pressure all the sulphides could probably be produced under any condition of acidity or alkalinity.

As a sulphide dissolving into pure water would be hydrolyzed into metallic hydroxide 

and hydrogen sulphide, it is obvious that a large excess of hydrogen sulphide would 

be required to prevent this hydrolysis and maintain a suitable .concentration of sulphide in the solution to reprecipitate the sulphide at another point. Similarly, 

with the concentrations of metallic ions. It is conceivable that a particular concentration of copper and antimony, and of all the other bases as well as the sulphide, 

might be in equilibrium with tetrahedrite and by cooling deposit it from solution. 

For this to occur I should hazard the guess that the metals in solution would be in the 

following order, beginning with that of the highest concentration: Iron, zinc, arsenic, 

antimony, copper, silver. This guess is made upon the principle that the concentrations should be in inverse order to the solubilities. However, our knowledge of 

these matters, particularly about the conditions of the precipitation of compound 

sulphides, is so scant that further speculation might not even be suggestive.

The solvent usually assumed for carrying these sulphides is sodium or potassium 

sulphide. Becker 3 showed that mercuric sulphide, pyrite, cupric sulphide, and 

zinc sulphide are soluble in differing degrees in sodium sulphide solution. He concluded, however, that "the sulphides of lead and silver seem to be entirely insoluble in 

sodic sulphide, sodic sulphydrate, or in solutions of sodic carbonate partially saturated 

with sulphydric acid." He obtained no evidence of solution with these sulphides 

even when heated above 100° with reagents in closed tubes. As silver is an important 

constituent of the Bay Horse tetrahedrite, this would indicate that it was not carried 

in sodium sulphide solutions unless antimony, copper, or some soluble salts affect the 

solubility of the silver. I have been unable to find any marked solubility of silver 

sulphide in sodium sulphantimonite. Ditte 4 has shown that silver sulphide in 

contact .with potassium sulphide solution forms a very slightly soluble compound of 

red color, possibly of the composition 4Ag2S.K2S.2H20. This compound is decomposed by excess of water. A double salt with sodium sulphide was obtained by Ditte

1 Weigel, O., Zeitschr. physikal. Chemie, vol. 58, 1907, p. 293.

2 Wells, R. C., Econ. Geology, vol. 3,1910, p. 6.

8 Becker, G. F., Geology of the quicksilver deposits of the Pacific slope: Mon. U. S. Geol. Survey, vol. 

13,1888, p. 430. 

< Ditte, A., Chem. Rev., vol. 120,1895, p. 91.
38 OEE DEPOSITS IN OUSTER COUNTY, IDAHO.

only at a high temperature from a saturated solution of sodium sulphide which at 

110° contains about 800 grams of Na2S. Its 'formula is given as 3Ag2S.Na2S.2H20. 

It is decomposed by excess of water.

Hence silver sulphide is soluble in concentrated potassium or sodium sulphide 

solutions but practically insoluble in dihite solutions of the alkalies.

In view of these facts it appears that the transfer of tetrahedrite could not be accomplished by dilute solutions of alkaline sulphides much more advantageously than by 

solutions of any other salts, although if the solutions were concentrated it might be 

carried.

Two factors which seem to have a bearing on the nature of the 

mineral-bearing solutions are,'first, the development of sericite, a 

potash-rich mineral, in the walls, and second, the presence of an 

excess of sulphur in the tetrahedrite. This would seem to justify an 

opinion that potassium sulphide was a constituent of the mineralizing 

solutions, and from Wells's discussion of the chemistry involved that 

it was very possibly the solvent of the tetrahedrite.

The source of the solutions is even more difficult of determination 

than their nature. If potassium sulphide was the solvent it could 

have been efficient only at high temperatures, as indicated by Ditte's 

experiments J temperatures probably greater than are normal at a 

depth of 8,000 feet. It has already been shown from geologic and 

physiographic evidence that the granite intrusions and the veins are 

closely related in age, and as special conditions of deposition are 

necessary to account for the deposits it seems altogether reasonable 

to assume a genetic relation between the two. Elsewhere in Idaho, 

notably in the Wood Kiver district 2 and in Lemhi County, 3 a genetic 

relation to an igneous mass of the same age is indicated by geographic 

distribution. Thus it is concluded that the silver-copper deposits 

are genetically related to an outlier of the great granitic batholith of 

Idaho. The nature of this relation, however, is not susceptible of 

demonstration. The magma may be thought (1) to have supplied 

the solutions or (2) to have stimulated the circulation of meteoric 

waters. The first view is favored by most economic geologists, but 

to distinguish between the alternatives is a problem on which individual deposits of this type throw but meager light.

LEAD-SILVER DEPOSITS. 

DISTRIBUTION AND HISTORY.

Lead-silver deposits have been recognized in the Bay Horse and 

Loon Creek districts. In the Loon Creek district only two prospects 

have been opened on this type of ore and neither is extensive, but 

about Bay Horse and Clayton there are several mines noteworthy

1 Op. cit.

2 Lindgren, Waldemar, The gold and silver veins of Silver City, De Lamar, and other mining districts 

of Idaho: Twentieth Ann. Kept. U. S. Geol. Survey, pt. 3,1900, p. 217.

3 Umpleby, J. B., Geology and ore deposits of Lemhi County, Idaho: Bull. U. S. Geol. Survey No. 528, 

1913, p. 51.
PBE-OLIGOCENE DEPOSITS. 39

for their lead-silver production, important among which are the 

Red Bird, Excelsior, Beardsley, River View, Pacific, and Cinnabar 

properties.

The total production from deposits of this type within the area is 

about $4,000,000, three-fifths of which has been derived from lead 

and the balance from silver. Since the general slump in local mining, 

which took place about 1900, the annual production has averaged 

perhaps $15,000, derived largely from small shipments made by leasers 

operating on inadequately developed claims.

GEOLOGIC RELATIONS.

The deposits near Bay Horse are inclosed, without exception, in 

dolomitic limestone and dolomite, but the Red Bird deposit is in 

part inclosed in dolomitic limestone and in part in calcareous shales. 

One of the deposits near Ivers is within granite and the other within 

Algonkian schist, but both are in close proximity to areas of dolomitic 

limestone. Schist also is said to be the country rock at the Livingston 

property, near the head of Slate Creek. It is most striking, however, 

that the lead-silver deposits which have been important producers 

are all situated within or near areas of dolomitic limestone or dolomite.

Igneous rocks do not occur in their immediate vicinity, although 

both diorite and granite outcrop within a few miles of the principal 

mines.

CHARACTER OF THE DEPOSITS.

The lead-silver deposits are commonly tabular in general outline, 

but in their formation replacement processes have played an important though not a dominant part. Preexisting lines of parting have 

determined the general shape of the deposits. Thus they follow 

either fissures, as the Red Bird vein, or bedding planes, as the Pacific 

deposit, extensions from each being determined by fissures, joints, or 

bedding planes. In detail, however, some of the deposits are most 

irregular. In the Beardsley mine, for instance, bunches of ore isolated 

in the walls, save for narrow stringers connecting them with the main 

deposit, are common. These bunches of ore range from pieces the size 

of baseballs to masses 10 or 25 feet across. Also in old stopes, where 

the walls have been carefully stripped of ore, the surface is in many 

places exceedingly ragged and characterized by angular protuberances 

from a few inches to 3 or 4 feet in length, corresponding to which were 

embayments of ore into the country rock. In contrast to the deposits 

where such irregularities are common, the Red Bird vein is bounded 

by rather even walls.

Although all development has been well above the ground-water 

level of the region, yet in but few of the deposits is oxidation complete 

or even well advanced. The Red Bird ore is largely oxidized, but 

elsewhere the primary minerals predominate, most important among
40 ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

them being argentiferous galena and siderite. This is true of all the 

deposits at Bay Horse, with the possible exception of the Beardsley 

and Excelsior, in which oxidation, though well advanced, is by no 

means complete.

THE ORES.

Ore shoots. Pay shoots, in the strict sense of that term, are not 

common in the lead-silver deposits. The relative amount of ore and 

gangue is almost constant from place to place, so that when one gives 

out the other also is absent. Certain of the ore bodies have proved 

especially remunerative because of their persistence, and these have 

commonly been called shoots, important among them being the 

Potato Patch shoot of the Red Bird mine, and the main BeardsleyExcelsior ore body. The latter ranged from 100 to 200 feet in length 

and 1 to 20 feet in width; the former was 60 to 80 feet long and 20 to 

30 feet wide.

Minerals of the ore. Mineralogically, the lead-silver ores, are sunpie, the essential primary minerals being argentiferous galena in 

a quartz-siderite gangue. Associated with the galena is a little tetrahedrite, sphalerite, pyrite, and chalcopyrite. Near the surface in all 

the deposits, and in the Red Bird mine throughout its known vertical 

extent of perhaps 900 feet, the ore consists of the oxidation products 

of these minerals.

The secondary ore is predominantly composed of sand carbonate 

heavily stained with the oxides of iron and manganese. The sulphate 

of lead, anglesite, is an intermediate product in the transformation 

of galena to cerusite, but, though very common, is abundant only 

locally in the Red Bird mine. Its usual occurrence is as a narrow and 

poorly defined band between the sulphide and carbonate, easily recognized by its dark color and adamantine luster, thus contrasting with 

the metallic luster of galena on the one side and with the lighter color 

of cerusite on the other. Smithsonite occurs as botryoidal surfaces 

of drusy appearance, lining cavities in the secondary ore. In many 

places columnar crystals of calamine protrude from such surfaces. 

Fluorite occurs locally in the Red Bird mine as small bluish-white 

cubes set on drusy surfaces of smithsonite. Manganese oxide is 

conspicuous in much of the secondary ore, but its primary equivalent 

was not recognized. Copper carbonates, though not abundant, are 

rather uniformly distributed. Iron oxide, derived largely from 

siderite and subordinately from pyrite and chalcopyrite, is everywhere 

present in the sand carbonate ores. Of the several elements found 

in the oxidized ores the mineralogic form of silver alone is doubtful. 

Minute grains of cerargyrite have been identified, but it can not be 

said that all the silver is in this form. Minium, the red oxide of lead, 

was recognized in specimens from the Beardsley ore bins.
PRE-OLIGOCENE DEPOSITS. 41

A general and probably fairly accurate idea of the composition of 

these ores may be had from the following smelter returns. The shipments represent roughly hand-sorted material, which, from the range 

in sulphur, evidently includes both primary and secondary minerals.

Average analyses of IS shipments of ore from the McGregor group, Bay Horse, Ouster

County, Idaho,

Au.

Ounces. 

0.041

.016

.075

Ag.

Ounces. 

69.90

92.5

44.7

Pb.

Per ct. 

57.34

63.30

47.85

Cu.

Per ct. 

1.76

3.06

1.80

Fe.

Per ct. 

1.29

3.16

.58

Zn.

Per ct. 

2.59

3.4

1.86

S.

Per ct. 

4.92

7.4

.91

Si02 .

Per ct. 

21.17

29.5

15

Total 

shipped.

Tons. 

553

Tenor of the ore. The lead-silver ores are of excellent grade, perhaps 40 to 60 per cent of lead and 60 to 80 ounces of silver to the 

ton being the tenor of those most commonly mined in this area. So 

generally and uniformly is the galena argentiferous that where it is 

present somewhat more than 1 ounce of silver for every per cent of 

lead may be assumed with fair safety.

The many problems connected with the alteration of this type of 

ore the relative amounts of lead, silver, and zinc near the outcrop 

compared with the relative amounts 'below, and the value of the 

oxidized ore relative to the primary ore can be elucidated but little 

as a result of these studies. When the district becomes active, however, it will be an excellent field for special studies on these problems.

AGE AND GENESIS.

The discussion of the age of the silver-copper veins (pp. 35-38) 

applies equally well to the lead-silver deposits. They are thought to 

have formed during the late Cretaceous or the early Eocene.

The genesis of the lead-silver deposits also is thought to be similar 

to that of the silver-copper veins. The two types have many important features in common. In each the formation of siderite characterized the earliest stage of mineralization. This was followed by 

quartz and the metallic sulphides and sulphantimonites. Both types 

are rich in silver; both contain lead and copper, although the vastly 

different amounts of these metals afford the basis for a fairly definite 

distinction. The Hoosier mine contains two parallel flat-lying veins 

60 feet apart, which have the same geologic relations; both are followed by a thick vein of barren quartz, and indeed there is every 

geologic reason for thinking that they are absolutely contemporaneous in origin, yet one furnishes a distinct lead-silver ore and the 

other a distinct silver-copper ore.

Two eccentric occurrences which may have considerable genetic 

significance are related to this type of deposits, and although no
42 OEE DEPOSITS IN OUSTER COUNTY, IDAHO.

attempt is made to interpret them the facts are recorded in this connection. The peculiar veins of massive clear-white quartz, one 10 to 

12 feet thick and the other 40 feet thick, which overlie both of the 

Hoosier veins, form one of these features. They are slightly later 

than the vein, and, as is suggested (p. 70), it is believed that they followed closely the opening of the spaces which they occupy, or perhaps caused them. The other special feature is the sharp transition 

of the Red Bird lead-silver ore body into an underlying mass of 

vuggy pyrite 50 or more feet across, at a point between the seventh 

and eighth levels of the mine, the only place where it has been crosscut. (See p. 75.)

GOLD-COPPER DEPOSITS.

Deposits characterized by gold-copper ores are recognized only in 

the Loon Creek district, in the northwestern part of the area studied. 

Here but one mine, the Lost Packer, has been an important producer 

of this type of ore, although two or three similar veins are situated 

in its immediate vicinity.

GEOLOGIC RELATIONS.

The deposits are situated in a mountainous area in which elevations range from 5,000 to more than 9,500 feet. The topographic 

features are carved from rocks of Algonkian, Paleozoic, late Cretaceous, and early Tertiary ages. The Algonkian comprises mica 

schists and quartzites which outcrop over an irregular area of about 

2 square miles, in the northern part of which the deposits are situated. West of the Algonkian area a vast extent of quartz diorite 

appears at the surface, and southwest of it outcrop the Paleozoic 

beds, which consist of quartzites, slates, and dolomitic limestones. 

A great number of granite, granite porphyry, and diorite porphyry 

dikes traverse the Algonkian rocks, and extrusions of quartz latite 

cap the Algonkian in its northern part.

In age the veins are intermediate between the granite and the 

numerous granite porphyry and diorite porphyry dikes.

CHARACTER OF THE DEPOSITS.

The gold-copper deposits occupy fissures which strike a few degrees 

east of north and dip about 75° NW. The Lost Packer fissure has 

been traced from Canyon Creek, at Ivers, north about 3,000 feet, to 

the quartz latite above the mine. South of Canyon Creek it has 

not been definitely recognized, but several small outcrops may 

represent its continuation. This fissure has been explored for about 

2,000 feet along its strike and 1,000 feet on its dip. It is bounded 

by well-defined walls which commonly stand 3 to 5 feet apart, the 

interim being filled with gouge, sheeted wall rock, or ore. The
PBE-OLIGOCENE DEPOSITS. 43

walls present numerous slickensides, but distinct grooves having 

even an approximately uniform direction do not appear. The gouge 

also evidences much shearing and gliding between contiguous parts. 

Important displacement along this fissure, however, is not recorded. 

Most of the movement clearly antedates the ore and probably determined the channels along which the ore-bearing solutions traveled. 

In general, the vein material is confined to the fissure, though in a 

few places bunches of chalcopyrite have been found as far as 20 feet 

from the main ore bodies. Within the fissure, in most places the 

ore occurs as a definite band, ranging in width from a few inches to 

3 or 4 feet and averaging perhaps 20 or 24 inches. It follows either 

the footwall or the hanging wall, perhaps being more commonly 

next to the former.

ORE SHOOTS.

The deposits are further characterized by ore shoots, which lie in 

the plane of the vein at irregular intervals along its strike. In the 

Lost Packer mine three are recognized. Intermediate between the 

shoots the walls are much closer together than elsewhere, although 

the position of the fissure is always indicated by a band of gouge 

from 1 inch to 3 or 4 feet thick. The shoots are unequally spaced, 

but all pitch to the south, thus presenting a decided parallelism 

(fig. 4, p. 95). The position of these shoots is thought to have been 

determined by relative movement of the walls sufficient to bring 

reversed curves opposite each other. This opinion is based on two 

observations: First, although in any cross section in a shoot both 

ore and gouge are commonly present, it seems to be true that where 

the walls are farthest apart the ore is widest, and also that the walls 

are farther apart within the shoots than at points intermediate 

between them. Second, the general parallelism of the shoots suggests this origin.

THE ORES.

General character. The gold-copper ore is essentially auriferous 

chalcopyrite in a siderite-quartz gangue, the relative importance of 

the three minerals varying markedly from place to place in the same 

shoot and especially in the different shoots. The amount of gold 

associated with the chalcopyrite is exceptionally large, assays of this 

mineral commonly showing 2 to 3 ounces of gold to the ton. Intergrown with the siderite of the gangue is a little calcite. Pyrite is 

exceedingly rare, but locally occurs as small grains and cubes within 

the chalcopyrite. Similar in its occurrence is pyrrhotite, but it is 

even less abundant. A little barite has been reported by Jennings, 1 

but careful search during the present studies failed to reveal this 

mineral.

1 leanings, E. P., The Lost Packer copper-gold lode [Idaho]: Jour. Canadian Min. Inst., vol. 9,1906, p. 55.
44 OEE DEPOSITS IN OUSTER COUNTY, IDAHO.

Oxidation products are not quantitatively important in the deposits 

and disappear entirely within 50 or 75 feet from the surface. Most 

important among them are oxides of iron and carbonates of copper. 

Films of bornite and a few of native copper occur locally a few feet 

beneath the surface.

Mineralogy of the different shoots. The three shoots of the Lost 

Packer mine, the only developed deposit of this type, contain ores 

rather distinct from each other in mineralogic composition. The 

shoots are locally designated the north, south, and middle. Ore 

from the north shoot consists of coarse-textured milky to bluish 

white quartz with much chalcopyrite and a little pyrrhotite irregularly scattered through it. On most levels siderite is rare, but on 

No. 4 it is equally abundant with chalcopyrite and presents the 

same irregular distribution. The middle shoot, the most productive 

in the mine, contains ore which consists essentially of chalcopyrite and 

distributed as bunches, small patches, irregular grains, and interstitial 

fillings in a gangue of coarse white quartz. Here chalcopyrite constitutes about one-third of the total material mined. Siderite is 

present but is never an important constituent. The south shoot 

contrasts with the other two in that siderite is its most abundant 

mineral. Chalcopyrite is associated with the siderite in such proportions that the ore runs 26 per cent iron and 4£ per cent copper. 

(See PI. VIII, A.)

Gold is included about equally in the quartz and the chalcopyrite, 

each containing 2 to 3 ounces to the ton, but less is present in the 

siderite, assays of this mineral commonly showing about half an 

ounce to the ton.

Tenor of the ore. The ore which has supplied the total production 

of about half a million dollars, has averaged between $80 and $90 to 

the ton, but for every ton of this grade which has been encountered 

in the deposit there is estimated to be 2^ tons which will average $25.

AGE AND GENESIS.

The gold-copper veins outcrop through a vertical range of about 

1,600 feet, the highest exposure being but little below the level of the 

Eocene erosion surface. Within this distance there is no mineralogic 

change which seems in any way related to depth of deposition. In 

the deposit, however, are appreciable quantities of pyrrhotite, a mineral believed to indicate deposition at considerable depth a depth 

probably exceeding 3,000 or 4,000 feet. It is believed, therefore, that 

the veins were formed well before the close of the Eocene. On the 

other hand, the Lost Packer vein cuts across granite dikes which are 

evidently a phase of the quartz diorite intrusion. Thus the veins 

are post-quartz diorite. It has been shown (p. 23) that this igneous 

mass was very probably intruded at about the close of the Cretaceous.
U. 8. GEOLOGICAL SURVEY BULLETIN 539 PLATE VIII

SPECIMENS OF ORE,

A, Chalcopyrite (dark) which has replaced siderite. Note the veinlets of chalcopyrite along the fractures

in the siderite. Dark mottled area on right middle margin is a fragment of schist. Lost Packer mine.

No. 7 level. Natural size. 

1$, Sheared galena (main mass). The large area at the bottom is siderite. The structure in the galena

was brought out by etching for 24 hours in warm dilute acetic acid. From dump of Beardsley mine.

Natural size. 

C, Fractured galena cemented by quartz. From Forest Rose mine. Natural size-
POST-OLIGOCENE DEPOSITS. 45

These veins are therefore believed to have formed during -the early 

part of the great period of erosion which resulted in an Eocene surface of gentle topographic forms (p. 28). Further evidence that they 

were formed during the early part of this period is afforded by their 

relation to the granite and granite porphyry dikes. These dike rocks 

are probably very closely related hi age, yet the veins are older than 

the one and younger than the other.

The genesis of the deposits is not apparent from local evidence, 

although their close accordance in age with the quartz diorite batholith 

strongly suggests a genetic relation between the two. Considered 

broadly, the most significant fact relative to the genesis of ore deposits 

in general is the almost universal presence of igneous rocks near them. 

The metallic constituents of some types, such as contact-metamorphic replacement deposits and segregated ores, have been unquestionably derived from the inclosing or near-by igneous rock. Gradations exist between these types and veins, and hence in studies of 

small areas it is not inappropriate to revert to broad correlations for 

evidence on genesis.

Granitic rock, one phase of which is represented by the quartz 

diorite near Ivers, outcrops continuously over more than 20,000 

square miles in central Idaho. Surrounding this area are numerous 

batholiths, reasonably supposed to be outliers. Igneous intrusions, 

therefore, which must have created very exceptional physical and 

chemical conditions at about the time the ores were deposited, are 

present. In places in adjoining regions comparable deposits are 

definitely distributed along the margins of such intrusions. Thus 

the deposits at Wood River occur along the borders of a central 

granitic mass,1 and those in the Mackinaw district, Lemhi County, 

are similarly situated.2

From the above considerations it is concluded that the quartz 

diorite intrusion is the direct cause of the formation of the gold-copper 

veins, and it is believed that it supplied most of their constituents.

POST-OLIGOCENE ORE DEPOSITS. 

GOLD-SILVER VEINS.

Veins characterized by gold-silver ores have been found only in the 

Yankee Fork district, but here they are rather widely distributed. 

Custer, Bonanza, and Sunbeam have each in the past been centers 

of important mining operations. The total production of the goldsilver veins is estimated at $12,000,000, about 40 per cent of which 

has been in gold and the remainder in silver.

1 Lindgren, Waldemar, The gold and silver veins of Silver City, De Lamar, and other mining districts 

in Idaho: Twentieth Ann. Kept. U. S. Geol. Survey, pt. 3, 1900, pp. 190-230.

 2 Umpleby, J. B., Geology and ore deposits of Lemhi County, Idaho: Bull. V. S. Geol. Survey No. 528, 

1913, p. 152.
46 OKB DEPOSITS IN OUSTER COUNTY, IDAHO.

GEOLOGIC RELATIONS.

The rock formations in the vicinity of the gold-silver veins include 

Algonkian schists and quartzites, and Miocene tuffs, latites, andesites, 

basalts, and rhyolites. The Miocene rocks occupy a great erosion 

valley about 10 miles wide and 3,000 feet deep, which was developed 

after the elevation of. the Eocene erosion surface. The gold-silver 

veins are wholly inclosed in these rocks.

METASOMATIC ALTERATION OF THE WALL ROCKS.

Intense metasomatic alteration of the wall rocks adjacent to the 

fissures is a conspicuous feature of the gold-silver veins. Silicification 

or sericitization, or both, characterize the rocks for 50 or 100 feet, 

and in many places for 1,000 feet or more from the deposits. The 

silicification is most intense next to the veins and gradually gives way 

to sericitization at a distance of 50 or 100 feet. Well removed from 

the veins, say beyond 200 feet, chlorite is locally an abundant metasomatic mineral. So intense is this alteration that in many of the 

thin sections it is impossible to determine whether the original rock 

was a tuff, andesite, or rhyolite. Where better preserved the rhyolites show phenocrysts of quartz and partly altered orthoclase in a 

highly sericitized or silicified groundmass. In the andesites and latites 

the phenocrysts and groundmass seem to have altered with about 

equal facility. Small cubes and patches of pyrite are abundant in 

most of the wall rock near the veins. For more detailed descriptions 

see page 83.

CHARACTER OF THE VEINS.

The ore bodies commonly occur as veins about 4 feet wide, but in 

the Golden Sunbeam mine the principal body was a great irregular 

mass of mineralized tuff, which on No. 2 level was 130 feet long by 

75 feet wide and extended upward 85 feet and downward 115 feet. 

The Montana shoot also was of exceptional shape, being 20 to 25 feet 

in length by 5 to 17 feet in width and 530 feet in depth. In general, 

the contact of the vein material with the inclosing rock is sharp and 

the numerous included fragments of wall rock are angular. A pronounced banding is conspicuous in the veins; the bands broadly parallel the walls, but in detail concentric arrangement is common.

The vein filling is predominantly fine-grained quartz, and associated with it are small amounts of chalcedony and opal. Calcite is 

conspicuous in some of the deposits, as in the Lucky Boy, where it 

constitutes perhaps 20 per cent of the vein. The calcite occurs both 

as equidimensional rhombohedral crystals and as lamellar crystals, 

the latter commonly replaced by quartz. Indeed, much of the quartz 

has this lamellar form, showing it to be pseudomorphous after calcite. 

Adularia is locally either intergrown with or embedded in the quartz.
. POST-OLIGOCENE DEPOSITS. 47

The metallic minerals are irregularly distributed through the quartz 

and, to a less extent, through the calcite. Dark-gray bands of submetallic luster parallel the crustification of the vein material in many 

places. Within these bands individual minerals are too small for 

identification even with a microscope. Along the strike of the veins 

the ore minerals are largely confined to definite sections, thus forming 

the ore shoots, which alone have been mined at a profit.

ORE SHOOTS.

The ore shoots of these deposits comprise (1) segments of otherwise 

comparatively barren quartz-calcite veins, (2) disseminations of 

stock-like form not related to fissure fillings, and (3) chimneys of ore 

apparently independent of fissure veins. The most important deposits are of the first type, which represents all the mines except the 

Golden Sunbeam and the Montana. The Golden Sunbeam was a 

great stock-like body of mineralized tuff, and the Montana was a 

chimney of ore about 10 by 20 feet in cross section.

THE ORES.

Mineralogy. The unaltered ore is a fine-grained quartz, locally 

accompanied by large amounts of calcite and a little chalcedony, 

opal, and adularia. Of the metallic sulphides pyrite alone is abundant and uniformly present. Tetrahedrite is not uncommon, and 

chalcopyrite, galena, and rarely enargite occur in some of the deposits. Widespread and important, as they have been found to 

characterize the richer ores, are blue-black submetallic bands and 

blotches, in which pyrite and gray copper and rarely chalcopyrite 

may be recognized with the aid of the microscope, but the predominant material shows as blue-black specks too small to be identified. Partial analyses of two specimens of this material were made 

by R. C. Wells. A specimen from the Montana mine showed gold, 

selenium, lead, a little bismuth, and a trace of copper. Tellurium 

was not present. A specimen from the Lucky Boy dump contained 

gold, selenium, lead, some copper, and a trace of bismuth. Here also 

tellurium was not detected. The definite amount of selenium in 

both of these ores, the only ones analyzed for it, suggests the presence 

of some selenide.
48 ORE DEPOSITS IN. OUSTER COUNTY, IDAHO.

An analysis of Lucky Boy ore taken at a depth of about 400 feet 

from the surface was furnished by Mr. Nicholas Treweek, manager 

of the Lucky Boy Gold Mining Co., i£nd is as follows:

Partial analysis of ore from Lucky Soy mine, Ouster County, Idaho. 

[Analysis by Union Assay Office. Gold and silver in ounces per ton; other Items in percentages.]

Gold......................................................... 1. 34

Silver......................................................... 25. 90

Lead ......................................................... .00

Copper........................................................ .00

Insoluble...................................................... 67. 30

Zinc......................................................... .00

Sulphur........................:.............................. .50

Iron......................................................... 1. 40

Lime. ...............................^........................ 15.40

By calculating the calcium oxide as calcite, and adding to this the 

amounts of other constituents shown in the analysis, it is readily seen 

that about 3 per cent of material is not accounted for. Some of this 

material is doubtless moisture, but it probably also represents the 

several constituents identified by Mr. Wells (cited above).

The oxidized ore is firm quartz, heavily stained with iron, manganese, and locally with copper. Calcite is rare in the outcrops, but 

numerous lamellar and rhombohedral forms of quartz indicate its 

former presence. Kaolin of creamy white color, unless stained by 

iron oxide, occurs in cavities and along crevices in the oxidized ore. 

It is probably in part due to the weathering of adularia, and in part 

is infiltrated from the sericite and feldspar of the wall rocks. Cerargyrite and wire silver are both present, but only locally do they 

occur in noteworthy quantities. Much of the gold even in the 

primary ore is free, though so minutely divided as to be invisible even 

microscopically. Coarse gold occurs near the surface in some of the 

deposits, notably the Morrison vein. Some of the gold may be associated with the selenium as a selenide, though the relation, if it 

exists, has not proved susceptible of demonstration with the material 

at hand.

Tenor of the ores. Gold and silver are present in quantities which 

vary from place to place. Thus the Montana shoot furnished predominantly gold ores, whereas the General Custer contained only 1 

ounce of gold to 80 or 90 ounces of .silver. In general, the ores 

mined have been high grade, common assays ranging from $50 to 

$100 per ton, some of them much more.

It has been generally found in the area that the tenor of the ores 

decreases markedly with.depth. The Montana shoot was worked at 

big profit for the first 500 feet, but a tunnel driven to tap it at greater 

depth tailed to reveal ore in commercial quantities. The General 

Custer ore body was not worked below the level of Yankee Fork.
POST-OLIGOCENE DEPOSITS. 49

The Golden Sunbeam was disappointing on the lower levels. The 

Charles Dickens was abandoned at a depth of 250 feet, as was also the 

Morrison. The Lucky Boy, the deepest mine in the district, was 

worked to the 900-foot level, but most of the production came from 

much nearer the surface.

An analysis of the problem, however, indicates that for the veins 

as a whole this impoverishment may be more apparent than real. 

In the first place, the ores below a depth of 50 to 100 feet are primary; 

second, they were formed before erosion had carved most of the 

present topographic features; and, third, they occur at various 

elevations between 6,500 and 9,500 feet. Otherwise stated, primary 

ore plays out at a moderate depth below an accidental surface of 

erosion which is far from parallel to the surface prevailing at the time 

of ore deposition. Thus it can not be assumed that depth below 

the original surface determined the lower limit of the deposits as now 

known. From this line of evidence it would seem that though the 

shoots now known have given out at moderate depth, others like 

ijhem in shape may be present well below the now existing accidental 

surface. Opposed to such a conclusion, however, is the fact that 

with a few exceptions veins of this type and age have not been 

worked at a profit belo'w 1,000 feet, and the greater part of their 

aggregate production has come from a depth less than 500 feet.

, AGE AND GENESIS.

The gold-silver veins are inclosed in lavas of Miocene age. After 

their formation great valleys were carved and a's these valleys are 

partly filled with outwash from the ice they evidently existed at the 

beginning of the Pleistocene. Some of them, as that of Yankee 

Fork, are more than 3,000 feet deep, and because they occur near the 

headwaters of the stream which drains the area it does not seem 

unreasonable to assign most of the Pliocene .epoch to their development. As the veins existed before the valleys were formed, and as 

they are inclosed in Miocene rocks, the ore deposits are believed to be 

of late Miocene or early Pliocene age.

In a study of the genesis of these deposits three principal features 

stand out (1) the intense and far-reaching alterations of the wall 

rock, (2) the angular form of wall-rock fragments inclosed in the 

veins, and (3) the general crustified arrangement of the vein material. 

The composition of the veins themselves is important but seems to 

have less bearing on the problem of genesis. Intense alteration of 

the wall rock appears in .every specimen studied near the veins 

silicification, farther removed sericitization, and locally also chloritization. Solutions thus capable of working out into the walls were 

.probably highly heated and impelled by considerable pressure, 

98185° Bull. 539 13 4
50 ORE DEPOSITS IN CUSTER COUNTY, IDAHO.

They did not, however, possess corroding properties to any marked 

degree, for included fragments of wall rock are notably angular. 

Further, the solutions operated in open channels, as shown by the 

general crustification of the vein material and the numerous cavities 

lined with druses of quartz crystals.

It has been shown above that the veins are closely related in age to 

the lavas, and tuffs which inclose them. They also present the type 

of wall-rock alteration which in many districts where detailed studies 

have been made has been attributed to hot ascending solutions 

genetically related to some igneous activity. It is believed, therefore, that the gold-silver veins of Yankee Fork district are genetically 

related to ..the same igneous activity which earlier found expression 

in the great beds of tuffs and lavas.

GOLD PLACERS.

Distribution and history. Gold placers are recognized in the Loon 

Creek and Yankee Fork districts. The first discovery was made 

near the mouth of Canyon Creek, a tributary of Loon Creek, in 

1869 and during the decade following the placers were actively worked, 

producing upward of $1,000,000. During the period of placer 

activity on Loon Creek gold was discovered in the gravels along 

Jordan Creek in the Yankee Fork district. Here the production 

was not large, probably not more than $50,000.

Character of the deposits. Placer locations along Yankee Fork 

cover the valley flat from Salmon River to Jordan Creek, and thence 

extend up the latter stream for about 2 miles. Extensive exploration 

by drilling has been accomplished, but with what success is not generally known. The early production came from the area near the 

mouth of Jordan Creek, where the gold occurred as fine flakes and a 

few large nuggets that were found near bedrock. Here the gravel 

bed was thin, but south of this place it is known to be as much as 90 

feet thick.

On Loon Creek 470 acres are held as placer ground by the Loon 

Creek Hydraulic Placer Co. The area is 4£ miles long and about 1,000 

feet in average width. A strip 75 feet wide and about 1 mile long, 

situated along the upper part of the main channel, afforded the early 

production. Here the gravel bed is 2 to 6 feet thick, but back of it 

are terraces 10 to 30 feet high, which the present owners have prospected during two seasons and are now planning to hydraulic. The 

average return from the numerous prospect pits in these terraces 

was about 25 cents a cubic yard.

The Loon Creek placers comprise loosely cemented auriferous 

gravels which rest upon a rather even floor of schist. The pebbles 

average perhaps 3 inches in diameter, though locally bowlders as
MINERALS. 51

much as 3 feet and a few 6 feet across are eilcpuntered. Sand is the 

cementing material. The gold occurs in the lower 2 or 3 feet of the 

deposits and in joints and shallow depressions in bedrock. Coarse 

gold prevails, nuggets weighing an ounce or more being not uncommon, and perhaps 50 per cent of the product averaging, 25 cents a 

color or more. Its market value is $18 per ounce. '

Source of the placer gold. The gold of the Yankee Fork placers is 

obviously derived from the late Tertiary veins, above which it does 

not extend. Most of the production came from that portion of Jordan Creek immediately below its intersection with, the MorrisonCharles Dickens vein a relation which points to that vein as the 

source of. most of the gold heretofore mined.

The Loon Creek Placer gold is thought to have come from the late 

Cretaceous or early Eocene veins which cross Canyon Creek, for the 

following reasons: First, placers have not been found above the 

mouth of Canyon Creek, and, second, the amount of gold diminishes 

abruptly with increasing distance below its junction with Loon Creek.

It is noteworthy that, although the older veins themselves have 

not been nearly as productive as the younger ones, the * placers 

derived from them have been vastly more productive a relation in 

keeping with the widely made observation that the late Tertiary 

Veins do not yield extensive placers even though they are not uncommonly bonanza deposits.

Age of ike placers. The placers are believed to have formed late 

in the Pleistocene epoch. The great gravel beds, which in part are 

auriferous, occupy post-Miocene erosion valleys. Their accumulation in such Valleys indicates a change from conditions of erosion to 

those of deposition. This may most reasonably be thought to have 

occurred during the general period of ice recession. ' At this time there 

was an abundant supply of running water and a proportionately 

greater supply of rock rubble loosened and in part ground up by the 

glaciers. As the ice front retreated up the precipitous tributary 

canyons, vast amounts of material would continually be made available for transportation, and the 'streams, if fully loaded in their upper, 

swifter parts, would necessarily deposit below, where the grade was 

lower.

It is therefore believed that the auriferous gravels were deposited 

late in Pleistocene time a belief which is supported by the small 

amount of erosion which they ha.ve undergone.

MINERALS OF THE DEPOSITS.

At least 32 mineral species occur in the deposits of the three districts herein described. These include 7 gangue minerals and 8 primary and 1.7 secondary metallic minerals. Of the several species
52 OEE DEPOSITS IF CI7STEE COUNTY, IDAHO.

chalcopyrite, galena, tetfahedrite, and quartz (auriferous) are individually important as ores. The minerals are listed in alphabetical 

order below, together with brief notes on their occurrence.

Adularia. Vein feldspar is common though not abundant in the 

late Tertiary veins of the Yankee Fork district. It is usually of 

microscopic size 'and occurs either intergrown with the quartz or 

included in it.

.Anglesite. Lead sulphate occurs in all the lead-silver deposits of 

the area. It represents an intermediate stage in the alteration of lead 

sulphide to lead carbonate.

Argentite. Silver glance is rather abundant in many of the silverrich oxidized ores of the late Tertiary veins.

Arsenopyrite. The iron sulpharsenide is a primary mineral of minor 

importance in the silver-copper deposits of the Bay Horse district.

Azurite. This carbonate of copper appears in many of the vein 

outcrops of the area but is nowhere sufficiently abundant to constitute 

an ore.

Barite. Barite has been reported from the Lost Packer vein, but 

none was seen during the present investigation.

Calcimine. Zinc silicate occurs as bundles of clear white columnar 

crystals protrudmg from the walls of small cavities in the oxidized 

lead-silver ores.

Calcite. Calcite is a common gangue mineral in the late Tertiary 

veins, in one of them, the Lucky Boy, constituting about 20 per cent 

of the ore.

Cerargyrite. Silver chloride, though little of it is susceptible of 

identification, is probably the most abundant silver mineral in the 

oxidized lead-silver ores.

Cerusite. Sand carbonate is the most important ore of lead that 

has been mined in the area. It occurs as granular masses, as a rule 

heavily stained with oxides of iron and manganese.

CJialcocite. Copper glance is found locally as films along cracks in 

the upper level of the Lost Packer mine. It is probable that it was 

also present in the upper levels of the silver-copper deposits.

CJialcopyrite. Chalcopyrite is the principal ore mineral at the Lost 

Packer mine, where it carries 2£ to 3 ounces of gold per ton. It occurs 

in small amounts in most of the other deposits of the area.

Dolomite. Dolomite occurs rarely as a gangue mineral in the leadsilver deposits.

Enargite. Enargite was found in a few specimens of ore from 

Dickens Hill, Yankee Fork district. 

Fluorite. Small cubes of fluorite occur in cavities in the oxidized 

ore of the Red Bird mine, Bay Horse district.
MINEBALS. 53

Galena. Argentiferous galena constitutes the chief primary ore 

mineral in the lead-silver deposits. It also occurs sparingly in the 

silver-copper deposits.

Gold. Native gold is found in placers in the Yankee Fork and Loon 

Creek districts. It also occurs in the oxidized gold-copper ores, and 

in both the primary and secondary gold-silver ores.

Hematite. Ferric oxide is widespread in the deposits of the area as 

an oxidation product.

Limonite. Ferric hydroxide is similar in distribution to hematite.

Malachite. Green copper carbonate is common as a stain in the 

outcrops of the gold-copper and silver-copper deposits.

Minium. Lead oxide was seen in one specimen of ore from the 

"Beardsley ore bins.

Pyrite. Pyrite is a persistent mineral in the area, occurring in all 

the deposits. In the wall rock of the late Tertiary veins abundant 

small cubes of it accompany the metasomatic alteration.

Pyrolusite. Dendritic manganese oxide is not uncommon along 

fractures in the lead-silver deposits.

Pyrrhotite. This sulphide of iron was seen only in the ores of the 

Lost Packer mine, where it occurs sparsely as small crystals inclosed 

either in chalcopyrite or in quartz.

Quartz. Quartz is a common gangue mineral in aU the deposits, 

but is the predominant constituent only in the late Tertiary veins.

Siderite. Iron carbonate is the characteristic gangue mineral in the 

pre-Oligocene deposits.

Silver. Native silver occurs sparingly as twisted wirelike filaments 

in cavities in the late Tertiary oxidized ore.

Smifhsonite.^-Zmc carbonate occurs as botryoidal forms with drusy 

crystal surfaces lining cavities in the oxidized lead-silver ores.

Sphalerite. Sphalerite is common in the primary lead-silver ore 

and occurs sparingly in the silver-copper ores. A few crystals also 

appear in the late Tertiary veins.

Tetrahedrite. Tetrahedrite is the characteristic ore mineral in the 

silver-copper veins.

Wad. An earthy mixture of metallic oxides in which manganese 

oxide is the dominant constituent is abundant in the upper portions 

of the lead-silver deposits. It may best be classed as wad.

OXIDATION AND GROUND-WATER LEVEL.

The extent to which oxidation has affected the ore deposits of northwestern Ouster County varies markedly in different parts of the area and 

in different deposits in the same district. In general, the gold-silver 

deposits are comparatively little .oxidized below a depth of 40 or 50 

feet. In the gold-copper veins oxidation is even less extensive, but
54 OKE DEPOSITS IN CUSTEtt COUNTY, IDAHO.

in the lead-silver and silver-copper deposits probably most of the ore 

which has been mined has been largely oxidized.

The difference in extent of oxidation is due to a number of factors, 

most important among them the amount of postmineral fracturing. 

The gold-copper veins are not only comparatively unfractured but are 

crossed by flat-lying, unjointed dikes, which protect the underlying 

portions of the ore body. Lack of fracturing 'also is the dominant 

factor in preserving the primary minerals of the late Tertiary veins. 

The deposits of Bay Horse district, on the other hand, are rather 

extensively fractured, but even here the extent of oxidation is erratic. 

In the Red Bird mine sand carbonate is conspicuous in the ore of the 

lowest workings, about 900 feet below the surface, although galenao 

also is abundant. In the Pacific mine, however, with less than 200 

feet of cover, galena predominates. The River View ore, as seen on 

the dump, is largely galena, though the mine is situated well up on a 

cliff of intricately jointed limestone. The silver-copper deposits, 

with the exception of the New Silver Bell, present primary ore throughout those portions of the workings now safely accessible.

If permanent ground-water level for the region be assumed to accord 

approximately with the bottoms of the numerous canyons, nearly all 

the mining development has been well above ground-water level. 

As in this area, where the beds are in general steeply inclined and 

joints and slaty cleavage are abundant, there seems no reason to 

doubt the above assumption, it is concluded that in the general 

erosion of the region oxidation has not kept pace with the general 

lowering of the water table.

FUTURE OF MINING IN NORTHWESTERN OUSTER COUNTY.

Northwestern Ouster County is certain to produce important 

amounts of silver, lead, copper, and gold in the future, if only from 

deposits now developed. The deposits of the Bay Horse district are 

by no means exhausted, and in some a considerable tonnage is actually blocked out. Many others are inadequately developed and much 

of the intermediate territory is comparatively unprospected. In the 

Yankee Fork district little ore is in sight, and any important future 

production from the shoots now recognized is problematic, but in a 

heavily timbered area where such bonanza deposits have been found 

there is ever the probability of new discoveries. The Loon Creek district contains°gold placers which will probably be worked in the near 

future. In addition to these are gold-copper veins, one of which has 

been explored to a depth of 1,000 feet and throughout the ore has 

varied in value from $25 to $90 to the ton with no evidence of impoverishment with depth. The area of dolomitic limestone near the head 

of Deer Creek is also thought to be a promising field in which to prospect for lead-silver deposits.
BAY HORSE DISTRICT. 55

It is highly probable that in a rough country like northwestern 

Ouster County new deposits will be found when mining again becomes 

active. Whether such activity will precede the advent of a railroad 

is doubtful, for the larger properties are held by companies which for 

many years have shown no inclination to rob the known deposits. 

The advent of a railroad, however, would doubtless inaugurate a mining activity of considerable importance.

The area is one far more worthy the attention of the prospector 

than many which are being more adequately explored. Few silverlead deposits show prominently at the surface not only because they 

are slightly less resistant than the inclosing rocks but because the 

oxidation products, cejargyrite and sand carbonate, are earthy in 

appearan.ee and commonly break up into small fragments. The 

absence of a quartz gangue implies the absence of the iron-stained 

quartz float, which has led the prospector to most deposits of ore. 

The silver-copper and gold-copper deposits, hi that copper stains 

accompany their outcrops, are more readily recognized, and it is probable that fewer of them have been overlooked. The gold-silver veins 

outcrop fairly distinctly at the surface and their iron-stained float 

lessens the.probabilities of new discoveries. New discoveries of any 

of the types of deposits, however, are to be expected, for most of the 

area is well timbered and many of the upper slopes are covered by a 

mantle of drift.

MINING DISTRICTS.

BAY HOUSE DISTRICT. 

SITUATION AND EXTENT.

The Bay Horse district, situated in the west-central part of Custer 

County, Idaho, comprises the area about that great bend in Salmon 

River where it changes from an easterly to a northerly course. 

Challis, the county seat of Custer County, is near its northern border, 

and the old mining town of Clayton is centrally situated within it. 

About midway between Challis and Clayton is Bay Horse, once a 

flourishing settlement of several hundred inhabitants, which now 

has dwindled to 7 or 8 persons, as most of the properties are held 

by three companies.

Excellent roads connect the principal settlements, and a daily 

(except Sunday) stage runs both up Salmon River to Yankee Fork 

district and down the Salmon to Challis. Mackay, reached from 

Clayton by way of East Fork and from Bay Horse and Challis by a 

more northerly route, is about 60 miles southeast and is the principal 

supply point. 

The district is unorganized and of very indefinite extent. From 

the Livingston group in the southern part to the Dougherty claims 

in the northern is a distance of about 30 miles. Its average width 

is perhaps 15 miles.
56 OEE DEPOSITS IN OUSTER COUNTY, IDAHO.

HISTORY.

The first location in the Bay Horse district was made in March, 

1877, when the River View deposit was staked. In August of 

the same year the Ramshorn, Beardsley, and Excelsior were located. Active development began in 1880, and from then until 

1898 the district supported an important mining industry. Two 

smelters, each of 60 tons daily capacity, are situated in the district, 

one at Bay Horse the other at Clayton. Both commenced operations 

in 1880 and operated four to five months each year until 1897, when 

the Bay Horse plant was permanently closed and later dismantled. 

Operation of the other plant continued until 1902, when it also was 

closed. In 1896 a mill was built at Bay Horse for concentrating 

the low-grade lead-silver ores encountered in the deeper workings of 

the Beardsley mine but was operated only a short time.

Since the smelters and mill were closed some of the mines have 

continued to produce a small amount each year., the ore at first 

being hauled 165 miles to Blackfoot, and after the fall of 1901 60 

miles to Mackay. This annual output, larger at first, has averaged 

about two cars of ore, derived largely from development work.

During the period of. activity three principal companies operated 

in the district the Ramshorn Mining Co., the Clayton Mining & 

Smelting Co., and the Beardsley Mining Co. The Beardsley mines, 

however, early passed into the possession of the Ramshorn Co. 

Recently a large group, known as the James McGregor group, has 

been formed and now includes most of the smaller properties. The 

properties of the Clayton Co. are situated on Squaw Creek, near 

Clayton, and in Bay Horse Canyon (Skylark and Hood mines); the 

holdings of the other companies are near Bay Horse.

PRODUCTION.

Only a rough estimate of the total production of the district is 

possible. Much ore has been shipped in small lots and the early 

production is not definitely known. The total of the estimates 

given by local residents and the State mine inspector for the several 

properties indicates a production for the district of approximately 

$10,000,000. This has been derived from three metals about as 

follows: $6,900,000 from silver, $2,700,000 from lead, and $650,000 

from copper. The silver was associated with the lead as argentiferous galena and its oxidation products, and with the copper as tetrahedrite and minerals derived from it. Of the productive mines the 

Ramshorn, Skylark, and Silver Bell, producing silver-copper ores, and 

the Red Bird, Beardsley-Excelsior, and River View, producing leadsilver ores, have been by far the most important. ,
BAY HORSE DISTRICT. 57 

MINING CONDITIONS.

The Bay Horse district is a well-timbered, well-watered area of bold 

topographic forms. It is a region of widely diverse climatic conditions 

due to its great ranges in elevation, but the principal.roads are open to 

traffic throughout the year, and communicatio.n with outside supply 

pointsQs easily carried on, even during the winter months. Salmon 

River and its tributaries present water-power sites suitable for the 

development of far more power than will ever be needed by local 

industries. The bold topographic forms encourage mining by tunnels in many places to depths of 2,000 feet, or more.

Exclusive of- transportation, facilities, conditions affecting mining 

are far better than in most western camps. Under existing conditions a freight and treatment charge of $20 to $25 must be met by 

every ton of ore which is hauled the 60 miles to Mackay and thence 

shipped to the smelters at Salt Lake; the local treatment rate, including the consequent haulage of coke and bullion, was but little less. 

Much of the ore in the district could meet this charge and allow a 

good margin of profit, but to rob the deposits of their better ores has 

not been the policy of the companies which own the larger mines. 

As the district is traversed by the valley of Salmon River, a 

natural railroad route, and separated from Mackay by an exceptionally low divide, it would seem that the companies are justified in 

awaiting and expecting better transportation facilities.

At the time of the writer's visit the district was inactive., but in 

the spring of 1912 the properties of the Clayton Mining & Smelting 

Co. were purchased by the Idaho Smelting & Mining Co., and early 

in the fall the smelter at Clayton was blown in.

TOPOGRAPHY.

The Bay Horse district is a portion of an old plateau now deeply 

dissected by the streams which drain it. The largest of these is 

Salmon River, which flows in a deep, narrow canyon whose walls rise 

abruptly from its'water line at an elevation of 5,000 to 5,500 feet by 

precipitous slopes to 9,000 or 9,800 feet above the sea and there open 

out into summit tracts remarkable for their accordance in elevation. 

The best-preserved remnant of the old plateau surface which these 

summits record is Poverty Flat, an area of about 25 square miles near 

Clayton. It stands 9,600 "feet above sea and clearly bespeaks a 

former erosion surface which once stood near the base level of erosion 

for the region. This old erosion surface was developed during the 

Eocene epoch (see p. 17) and constitutes the most valuable local 

datum plane for that part of geologic time between the Paleozoic 

and the late Tertiary.
58 OBE DEPOSITS IN CUSTER 'COUNTY, IDAHO.

Salmon River is a rapidly flowing stream which heads about 50 

miles West of the district. Within the district East Fork'constitutes 

its principal tributary, although Slate, French, and Spudd creeks 

from the southeast, and Thompson, Squaw, Kinnikinnick, and Bay 

Horse creeks from the northwest add greatly to its volume.

GEOLOGY. O '

The most widespread rocks in the Bay Horse district are dolomites, 

dolomitic limestones, slates, and quartzites of Paleozoic age. In the 

southwestern part Algonkian metamorphic rocks are present, and in 

the eastern and northeastern parts are Miocene lacustrine deposits. 

Andesites and tuffs are intimately associated with the lake beds, and 

locally intruded into the older rocks are masses of late Cretaceous or 

early Eocene granite and diorite.

The Algonkian rocks, composed of slates, schists, and quartzites, 

outcrop along Salmon River from a point near the mouth of Thompson Creek westward for about 6 miles. The Livingston deposits are 

possibly inclosed in rocks of this age, but all the others are within 

Paleozoic beds. The Paleozoic section is perhaps best exposed in 

the north wall of Bay Horse Canyon, and in the sides of Salmon Canyon near Clayton. It comprises about 9,000 feet of beds, consisting 

of massive quartzite overlain by dolomite, dolomitic limestones, and 

shales, and these followed by a great thickness of shales and slates. 

The section is discussed in some detail in another part of the report 

(p. 19) and need not be further described here.

Igneous rocks of late Cretaceous or early Eocene age comprise 

three areas; 'two of diorite and one of granite. One diorite mass 

outcrops for three-fourths of & mile in Kinnikinnick Canyon 1\ miles 

north of Clayton; the other is of comparable size and is cut across 

by Salmon River 2 miles east of Clayton. The granite crosses the 

upper end of Bay Horse Canyon as a belt about a mile wide. Contact metamorphism due to the diorite was not noted, but adjacent 

to the granite the slates present an abundant development of andalusite (?) and muscovite, together with a few crystals of zoisite, 

actinolite, garnet, and tourmaline.

The lake beds and associated eruptive rocks and tuffs have no 

direct bearing on the ore deposits and will not be discussed here. A 

description of them appears on pages 26-27.

Structurally the dominant features of the district are north-south 

anticlines, one of which, traversed by Bay Horse Canyon, is about 3 

miles across and on its limbs the beds dip 30° to 60°. From Bay 

Horse it plunges northward, and within 2 -miles the flat-lying beds 

constituting its crest descend to the bottom ci Beardsley Gulch on a 

dip of about 25°. The structure of this anticline south of Bay Horse 

is not known. Between East Fork and Squaw Creek are two anti-
BAY HOttSE DISTRICT. 59

clines separated by a syncline which is followed by Kinnikinnick 

Canyon. Common dips on the limbs of these are 40° and 50°.

Faults are not conspicuous in. the district, although the hurried 

nature of the examination makes it possible that important dislocations were overlooked. Probably the largest fault noted passes 

northwest-southeast a short distance above Bay Horse. It has a 

throw sufficient to bring the overlying (?) shales against the limestone 

which outcrops near the-bottom of the canyon above Bay Horse a 

throw which is probably hundreds of feet. In the Ramshorn mine 

two north-south faults with downthrow of 20 to 30. feet on the east 

were noted, and in the Skylark mine an .east-west fault displaces the 

vein about 50 feet to the east on the north side.

ORE DEPOSITS. 

CLASSIFICATION.

The ore deposits of the Bay Horse district fall into two fairly well 

defined group^ according to the principal metals contained. Thus 

they may be classified as lead-silver and silver-copper deposits, the 

two differing somewhat in form and geologic occurrence. The leadsilver deposits, though broadly tabular, are very irregular in detailed 

outline, in most places clearly showing the action of replacement 

processes or at least the filling of solution cavities. The silvercopper ores, on the other hand, occupy fissures of comparatively 

definite outline, which probably stood open at the time of mineralization. Closely related to this difference in the two groups is the 

unexplained fact that the lead-silver deposits are by far more commonly inclosed in dolomitic limestones and dolomites and the silvercopper deposits in slates and shales.

The silver-copper deposits have been more extensively explored 

than the others and have afforded about two-thirds of the total 

production of the district. Among the more important mines the 

Ramshorn, Skylark, and Silver Bell have produced this kind of ore, 

and the Red Bird, Beardsley, Excelsior, and River View have produced the other.

Both types of deposits afford high-grade ores, 60 to 80 ounces of 

silver being commonly associated with 40 to 50 per cent of lead, and 

80 to 100 ounces of silver with 8 to 10 per cent of copper.

LEAD-SILVER DEPOSITS.

Distribution. Lead-silver ores have been mined at widely scattered 

localities in the Bay Horse district. Between the Livingston group 

on the south and the Daugherty claims on the north, a distance of 30 

miles, similar ores have been found on Squaw Creek, near Clayton, 

and in the east half of the area adjacent to Bay Horse.
60. ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

The deposits occur at widely different elevations, the Ella mine, 

5,500 feet above sea, being the lowest, and the mines on Democrat 

Hill, at an elevation of about 8,500 feet, the highest. Thus they 

range vertically about 3,000 feet.

Geologic and structural relations. The lead-silver deposits are principally inclosed in dolomitic limestones and dolomites. The more 

important exceptions are the Livingston ore bodies, said to be 

inclosed in slate, and part of the Red Bird deposit, which is also in 

slate.

The general strike of the deposits is north-south, .but the dip is 

variable, some being blanket veins, as the Pacific, and others dipping 

steeply, as the Red Bird. In the flat-lying veins, bedding planes 

determine the general altitude of the ore bodies, though locally 

joints have had a controlling influence. The steeply dipping deposits 

in general follow fissures, which in many places have been greatly 

widened by solution and metasomatic replacement of the wall rock.

Many of the deposits are definitely related to anticlines. Thus the 

Red Bird and South Butte properties are on the west) limb and the 

Ella group is distributed along the east limb of what may be termed 

the Clay ton anticline. The River View mine is on the east limb of 

the Bay Horse anticline, and the Pacific, Democrat, Cave, Forest 

Rose, and other properties are situated near the point where the 

anticline plunges north at an angle of about 30°. The Excelsior and 

Beardsley properties are near the axis of this structural feature, but 

not far removed from its north end.

Character of the deposits. In shape the lead-silver deposits are 

broadly tabular, but in detailed outline they are exceedingly irregular. 

Bunches of ore varying in size from that of a baseball to a mass 10 to 

15 feet across occur in places out in the walls several feet from the 

main ore body, with which they are usually connected by narrow 

stringers. Elsewhere ore extends out along joint planes or expands 

from the main mass. In general the flat-lying deposits are more 

irregular in outline than those that dip steeply, but in both types 

bodies of regular outline may merge into those of most erratic shape.

The Beardsley-Excelsior vein, which produced about $2,500,000, 

and the^Red Bird veins, which produced more than $1,000,000, were 

the largest and most regular deposits recognized in the district. The 

principal ore body in the former varied from 100 to 200 feet in length 

and from 1 to 20 feet in width; that in the latter was 60 to 80 feet 

long and 20 to 30 feet wide. The Beardsley-Excelsior shoot was 

worked to a depth of 500 feet, where it expanded into a mass of 

low-grade ores; the Red Bird shoot was worked for somewhat more 

than 400 feet below the surface, although below this and to the side 

other shoots were found, at least five now being recognized.
BAY HORSE DISTRICT. 61

Mineralogically the lead-silver deposits are rather simple. The 

primary ores consist predominantly of argentiferous galena, with 

which quartz and siderite are associated as gangue minerals. Tetrahedrite, sphalerite, pyrite, and chalcopyrite occur in unimportant 

amounts. As.mined, however, the ores are mostly earthy sand 

carbonate stained with iron and manganese. Anglesite, the lead 

sulphate, occurs as a transition stage in the alteration of galena to 

cerusite but is local in its occurrence and abundant only in parts of 

the Ked Bird mine. Minium, the oxide of lead, was noted in one 

specimen from the Beardsley ore bins. The alteration products 'of 

the sphalerite are smithsoriite and calamine, the former occurring as 

druses and the latter as sheaf-like bundles of crystals extending from 

the walls of cavities otherwise lined with smithsonite. Fluorite 

occurs in places in the oxidized ore of the Ked Bird mine as small 

bluish-white cubes set on druses of smithsonite. In many of the 

deposits a large amount of manganese oxide colors the secondary 

ore, but the primary mineral from which it is the alteration product 

was not recognized. The iron oxide, abundant hi the altered ores, 

results principally from siderite and subordinately.from chalcopyrite 

and pyrite.

Analyses of ores from most of the mines were not available, but 

the compilation which appears on page 41 is probably fairly typical 

of the composition of roughly hand-sorted material.

SILVER-COPPER DEPOSITS.

Distribution. Silver-copper veins, though less widely distributed 

hi the district than the lead-silver deposits, have played an even more 

important part in its economic history. Three properties have produced considerable amounts of this type of ore :the Silver Bell mine, 

on Poverty Flat, and the Ramshorn and Skylark mines, at Bay Horse. 

The first is about 8 miles south of the other two. Some 6 miles north 

of*Bay Horse a little gray copper also occurs in the ores of the 

Dougherty property at the head of Garden Creek. Thus this type of 

deposit is recognized at intervals along a north-south belt about 15 

miles in length.

Geologic and- structural relations. All of the silver-copper deposits 

are inclosed in slates, presumably of Paleozoic age. The slates generally present a marked slaty cleavage at a high angle to the bedding, 

a structure locally so pronounced that the bedding planes are not discernible. The two principal deposits bear a definite relation to these 

structures; the Skylark vein follows the bedding and the Ramshorn 

the lines of slaty.cleavage. The Silver Bell, however, occupies a fissure 

independent of either type of parting. All the deposits are fissure 

fillings, the fissures having opened along preexisting planes of parting
62 ORE DEPOSITS IN CUSTER COUNTY, IDAHO.

in the two larger deposits and in the other one along a zone independent of any such planes.

About 600 feet west of the Skylark mine and possibly 1,000 feet from 

the Ramshorn is a granite mass about a mile across. The slates adjacent to this mass present an appreciable metamorphism, characterized 

by the development of andalusite (?) and muscovite and to .a minor 

extent of zoisite, actinolite, garnet, and rarely tourmaline. No igneous 

rock was seen in the immediate vicinity of the New Silver Bell mine.

Character of the deposits. The silver-copper deposits are tabular in 

outline and conform closely to the walls of the fissures which they 

occupy. Bunches of ore isolated in the walls, such as are common in 

the lead-silver deposits of the district, are rare in the silver-copper 

deposits. Where offshoots from the main body occur they follow distinct lines of parting, as joints or bedding planes, and then are mere 

stringers, some of them little more than films of ore.

The' ore occurs in shoots of irregular shape, which range in length 

from a few feet to 200 or 300 feet and in width from a few inches to 4 

feet, the most common dimensions being possibly 100 feet by 20 inches. 

Their vertical extent is commonly two or three times greater than 

their horizontal extent. Within the veins shoots are distributed without apparent regularity, although they commonly show a tendency 

to occur one above the other and in the same deposits to pitch in the 

same'direction. Along then\>margins the shoots wedge out or merge 

into comparatively barren gangue and gouge.

The ore. The silver-copper ore as mined consists of two quantitatively important minerals and several others which, though persistent, 

are accessory. Siderite constitutes possibly three-fourths of the vein 

material and tetrahedrite one-third of the remainder. Among the 

accessory minerals quartz is by far the most abundant, but chalcopyrite is more evenly distributed. Galena, arsenopyrite, pyrite, and 

rarely sphalerite' occur hi small amounts. Secondary minerals are 

negligible in the'deposits as now worked. . 

The siderite is coarsely crystallized and most commonly occurs in 

rhombic forms, as in Plate VII, B (p. 33), but locally in elongated 

forms (PI. VII, (7) and as lamellar crystals lining small cavities. 

Tetrahedrite occurs in bunches, which cut across the siderite crystals 

or follow their cleavage planes. A complete analysis of the tetrahedrite appears on page 34. The quartz is intergrown with the siderite in most places, but locally occurs as beautiful doubly terminated 

hexagonal crystals, either embedded in the siderite or perched against 

-the sides of small cavities in the tetrahedrite. Chalcopyrite occurs 

as netlike films along numerous minute fractures in the ore and as linings of. small cavities in the tetrahedrite. Galena occurs as small 

grains and crystals intergrown with the tetrahedrite or clustered 

in cavities in it. Less abundant than the chalcopyrite, though
BAY HORSE DISTRICT. 63

probably formed before most of it, is arsenopyrite, which occurs as 

grains and columnar crystals, generally related to fractures in the 

siderite (PI. VII, O). The only sphalerite seen in the deposits occurs 

as minute crystals set upon free faces of galena in cavities in the Ramshor-n ore.

The tenor of the ore varies according to the amount of tetrahedrite 

it contains. Specimens of this mineral from the large ore shoot in the 

Ramshorn mine contained 33.39 per cent copper and 4.86 per cent 

silver (or 1,417 fine ounces to the ton). The average tenor of the ore 

in this shoot is said to be 3 per cent copper and about 125 ounces in 

silver to the ton. By roughly hand sorting, however, this grade may 

be greatly raised. The Skylark ore, on broad averages, is said to have 

contained 8 per cent copper and 80 to 100 ounces silver to the ton, 

although some of it ran 12 per cent copper and 600 to 700 ounces in 

silver.

Little information is available concerning the nature and tenor of 

the ore from the old Silver Bell workings, but it occurred so near to 

the surface that oxidation was probably well advanced, the tetrahedrite being altered to carbonates of copper and chloride of silver. 

It is said that chalcocite was rare.

AGE AND GENESIS.

The two types of deposits recognized in the Bay Horse district are 

closely related in age and as phases mineralogically intermediate 

between the two occur, they are thought to have had practically the 

same origin. They have a wide vertical range, the difference in elevation between the Ella mine, at Clayton, and the Silver Bell mine, 

on Poverty Flat, being about 3,000 feet. No single ore- body has 

been traced throughout this extent, but the Ramshorn vein has 

been explored to more than half that depth and ore found on all the 

levels.

The higher deposits, such as those on Democrat Hill, the Ramshorn and Skylark veins, and the Silver Bell, are truncated by the 

Eocene erosion surface and hence are older than late Eocene. On 

the other hand, they ar<3 inclosed in Paleozoic sedimentary rocks, 

which probably range from Cambrian to Devonian, perhaps younger. 

Closer than this the age of the. deposits can not be determined from 

local evidence, but from the broad considerations outlined on pages 

35-36 it is concluded that they were formed shortly after the 

intrusion of the granitic rocks, which are considered to be late 

Cretaceous or early Eocene.

Their genesis is more difficult of determination. The conclusion 

that they were formed 'at great depth follows from the similarity in 

the mineralogy of the ore found at different elevations in the mines, 

for if conditions of deposition were the same throughout the range of 

2,000 to 3,000 feet, the upper part must have been sufficiently below
64 OBE DEPOSITS IN CUSTEK COUNTY, IDA^O.

the then existing surface to exclude the influence of oxidizing surface 

agencies. Aside from this, however, there are physiographic reasons 

(see p. 36) for believing that a vast amount of erosion took place 

after the deposits formed and before the elevation of the Eocene 

erosion surface probably more than 5,000 feet of beds were removed. 

The deposits are thought to be genetically related to the intrusive 

masses of granitic rocks a relation discussed in the general section, 

pages 35-38, 41-42.

.MINES AND PRINCIPAL PROSPECTS. 

RAMSHORN MINE.

Situation and development. The Kamshorn mine comprises seven 

patented claims situated on the north side of Bay Horse Canyon 

about 2 miles above Bay Horse. Development consists of 15 tunnels 

which enter along the strike of the vein at unequal intervals through 

a vertical range of about 1,650 feet. From highest to lowest the 

tunnels are designated Ramshorn Nos. 1 to 7, Utah Boy Nos. 1 to 5, 

and Post Boy Nos. 3 to 1. Above the Utah Boy No. 3 most of the 

tunnels are inaccessible, but those below are open. Raises connect the 

several levels and above the Utah Boy No. 2 are large stopes from 

which the early production was derived. In all there is perhaps 

6 or 7 miles of development on the property. 

History and production. The Ramshorn ° mine was located in 

August, 1877. Development began soon thereafter and was pursued actively most of the time until the fall of 1897. Since then a 

watchman has been kept at the mine, and a small amount of tunnel 

work accomplished each year. During the period of activity the ore 

was conveyed by aerial tram from the upper tunnels to the bottom of 

the canyon and thence by wagon to the smelter at Bay Horse. The 

total production of the property is said to have been about $3,000,000.

Geologic relations. The Ramshorn mine is situated well within the 

area of slates that forms the western limb of the anticline which 

centers near Bay Horse. The slates are all fine grained and characterized by an abundant development of c sericite. In some of the 

slates which outcrop on the lower slopes of the canyon side at the 

mine small elongated crystals, possibly andalusite but now completely altered to calcite, stud rather evenly the otherwise fine-grained 

mass. In color the slates vary from dull to light gray, though locally 

they present a greenish cast. Slaty cleavage is well developed and in 

places completely obliterates the bedding structure, across which it 

cuts at an angle of about 50°. The ore bodies follow fissures which 

parallel the slaty cleavage, though locally stringers extend out along 

the bedding planes.

The veins. The vein fissures strike N. 15°-30° W., and dip 57°-85° 

SW., the average strike being about N. 15° W. and the most common.
BAY HOESE DISTRICT. ' * 65

dip about 80° SW. Above the lower three levels two parallel veins 

30 to 50 feet apart are recognized, but below them only one has been 

encountered. In each a zone of crushed wall rock, 3 to 6 feet wide, 

follows the fissure and is generally present even where mineralization 

is lacking. In these parallel fissures the ore bodies occur in shoots, 

which alternate from one fissure to the other. Thus in many places 

where the ore body pinches out in one fissure a crosscut to the other 

one has revealed another shoot.

The veins are bordered by well-defined walls, though locally 

stringers extend into the country rock. In general, the fissures 

parallel the cleavage of the inclosing slate, but in a few places ore 

follows the bedding planes, which dip westward at a much lower 

angle. This is thought to explain the difference in dip .between the 

ore body in the Post Boy tunnels and that in the Utah Boy tunnels. 

Nos. 3, 4, and 5.

Faults are not numerous in the mine, only two being seen during 

the hasty examination, both of which occur in the Utah Boy section 

of the vein, to which they are parallel in strike but opposite in dip. 

In each of these faults the hanging wall has moved down about 25 feet 

relative to the footwall.

The ore. The ore is essentially 'gray copper in a siderite gangue. 

Associated with the tetrahedrite are unimportant amounts of pyrite, 

galena, chalcopyrite, arsenopyrite, and sphalerite. Quartz occurs as 

isolated euhedral crystals, which stud sparsely the siderite gangue, 

and as irregular patches intefgrown with the metallic minerals. A 

complete analysis of the tetrahedrite, which contains 4.86 per cent 

silver (equivalent to 1,417 fine ounces per ton) and 33.39 per cent 

copper, appears on page 34. This mineral is present on all levels 

of the mine, but the largest body found lies between the Utah Boy 

tunnels Nos. 3 and 4. Here occurs a shoot of ore, which on No. 4 

level is between 350 and 400 feet long and continues upward to No. 3 

level, 140 feet higher, although there the north end draws southward, 

shortening it many feet. The ore averages about 2 feet in width 

and is made up principally of tetrahedrite and siderite in such proportions that the average ore contains 3 per cent copper and 100 

ounces of silver per ton. The tetrahedrite occurs in bunches both 

along cleavage planes of the massive siderite and as tabular bodies 

cutting across them. In general the tetrahedrite attains its maximum development on the footwall side of the vein.

The paragenesis of the ore minerals is discussed on page 33.

SKYLARK MINE.

Situation and development. The Skylark mine is situated immediately west of the Ramshorn on the same side of Bay Horse 

Canyon. The property comprises 9 or 10 claims, two of which

98185°-+Bull. 53&-13 5
66 ' ,OKE DEPOSITS IN OUSTER COUNTY, IDAHO.

are patented. Development consists of 16 principal tunnels, which 

enter at unequal intervals along 2,000 feet of the outcrop of the vein 

and represent in all perhaps 25,000 feet of work. The tunnels are 

divided into east and west groups with the old boarding house as 

datum. Thus they are known as Nos. 1 to 7 east and Nos. 1 to 10 

west. All the ore is said to have been removed above No. 7 west.

History and production. The property was located in 1877 and 

in 1880 was purchased by the Omaha Smelting & Mining Co., which 

recently sold it to the Idaho Smelting & Mining Co. In 1883 the 

Kamshorn Mining Co. had the property bonded for $35,000, but owing 

to the poor showing of ore they allowed the option to lapse. A short 

time thereafter the ore bodies which afforded the principal production 

were encountered and for several years the mine was an important 

producer of silver and copper. A great deal of the ore was smelted 

at Bay Horse, but far more was sent by pack trains over the summit, 

12 miles to Clay ton. After the Clay ton smelter was closed in 1902 

considerable ore was shipped by leasers to Salt Lake and Denver at 

a cost of about $30 per ton for freight and treatment. The charge 

for treatment by the local smelters was. $18 and $20 per ton, the lower 

charge applying when the amount of lead exceeded a stated percentage.

The total production of the property is said to be $2,700,000, 

derived from ore which averaged about 8 per cent copper and 80 

ounces of silver per ton.

Geologic relations. The vein is inclosed in greenish-gray thinbedded sericitic slates, which strike N. 8° W. and have a general dip 

of 22° SW., although locally as steep as 60°. These extremes of dip 

were recorded in tunnel No. 9 west, where for 250 feet from the portal 

the beds dip about 60° and then abruptly dip 22°. The plane of 

transition is an east-west fault, which displaces the north-lying beds 

50 or 60 feet east. Westward from the mine the thin-bedded slates 

grade into micaceous quartzites, which occur in beds 5 to 10 feet in 

thickness. These quartzites continue as the predominant type of 

rock to a point possibly 500 feet west of tunnel No. 9 west, where 

granite comes to the surface as a mass about a mile across. At the 

border of the granite an andalusite-like mineral (p. 33) is abundantly 

developed in the sedimentary rocks, as well as muscovite and biotite. 

This metamorphic effect contrasts rather sharply with that which 

accompanies the ore bodies; where calcite and sericite are the important alteration products.

The vein. The vein follows the bedding of the inclosing formation. 

In most places there is an appreciable brecciation along the particular 

bedding plane which the ore follows, but this is in few places more 

than 3 feet wide and is bordered by firm walls. Within this general 

crushed layer the ore occurs in irregular lenslike shoots, which are
BAY HORSE DISTRICT. 67

usually elongated parallel to the dip, but few of which have proved 

continuous for more than 200 or 300 feet, most of them having given 

out within 100 feet. The old workings were not safely accessible at 

the time of visit, but an inspection of an old mine map showed more 

than 40 such lenses of ore to have been worked. The tenor of the 

ground between the old stopes is not known to the writer, although 

it should be borne in mind that at the time this portion of the vein 

was worked the cost of mining and treatment was about $25 to the 

ton of ore. Thus it is thought to be highly probable that a considerable tonnage of medium-grade ore remains in the abandoned workings. Another possible source of ore may be vertical veins which 

follow the slaty cleavage, as in the Ramshorn mine. Apparently all 

of the development has been along the bedding planes, yet there 

seems to be no particular reason why the ore-bearing solutions should 

have followed one set of major partings to the total exclusion of the 

other.

The ore. The Skylark ore, like that of the Ramshorn mine, is essentially gray copper in a siderite gangue. Accompanying the tetrahedrite in very subordinate amounts are chalcopyrite, arsenopyrite, 

galena, and less pyrite and sphalerite. In the oxidized ore cerargyrite and the carbonates of copper were common, and argentite, leafy 

native silver, wire silver, pyrargyrite, and native copper were occasionally found. The average width of the ore bodies is said to have 

been about 20 inches, the ore in general running 8 per cent copper 

and 80 ounces in silver to the ton. Some of it, however, ran several 

hundred ounces in silver and up to 20 per cent copper.

RIVER VIEW MINE.

The River View mine is situated 1^ miles southeast of Bay Horse, 

well up on the cliff which faces Salmon River. This claim was staked 

in March, 1877, and was the earliest location in the district. Development consists of several tunnels and a 100-foot shaft, in all perhaps 

5,000 or 6,000 feet of work. The total production of the mine is said 

to be $500,000, derived principally from silver-lead ores.

The deposit is situated within the area of dolomitic limestone on 

the east limb of the Bay Horse anticline. The limestones occur in 

massive beds, which vary in color from sky-blue to bluish gray. 

Joints traverse them in various directions; the most conspicuous, 

perhaps, strike N. 60° W. and dip 80° NE. Eastward the dolomitic 

limestones are covered within a short distance by lacustrine deposits 

and lavas of Tertiary age.

The ore occurs in irregular lenses and bunches, and as parallel 

stringers alternating with quartz and limestone, and represents .about 

one-fourth of a zone 5 feet wide. The larger lenses conform to the 

bedding planes, and most of the stringers and bunches are related to
68 OKE DEPOSITS IF CUSTEB COUNTY, IDAHO.

joints. Those parts of the workings which were visited have been 

stoped, But good ore is said to occur in drifts from the bottom of a 

shaft, now inaccessible. Near its collar, however, is a pile of ore, 

containing perhaps 400 tons. This ore is for the most part argentiferous galena accompanied by a little sphalerite and is associated with 

a porous manganese-stained quartz. Much of it is oxidized, the secondary minerals being cerusite, a little argentite and native silver, 

malachite and azurite, and small amounts of smithsonite.

EXCELSIOR MINE.

The Excelsior mine comprises one claim situated at an elevation of 

6,600 feet, on the east side of Beardsley Gulch, about 1,500 feet northeast of Bay Horse. Development consists of a principal tunnel and 

a winze which attains a depth of 500 feet. The production of the 

property is not known, although the total output of the ore body 

which is common to this and the Beardsley mine is stated as 1,500,000 

ounces of silver and 15,000 tons of lead.1

The mine is situated near the axis of the Bay Horse anticline and 

is well within the area of dolomitic limestone. The surface workings 

(the only part accessible) are inclosed in this type of rock, but it is 

probable that the lower levels extend into the calcareous and dolomitic slates which outcrop at the base of the cliff a short distance 

south.

The chief ore body was a large lenticular mass which varied from 

100 to 200 feet in length and from 1 to 20 feet in width. The ore was 

sand carbonate heavily stained with iron and manganese, and ran 

from 40 to 60 per cent of lead and 50 to 60 ounces of silver to the ton. 

At a depth of about 500 feet the rich ore is said to have given way to 

disseminated material of much lower grade.

BEARDSLEY MUTE.

The Beardsley group comprises four patented claims in Beardsley 

Gulch, the principal workings being situated about midway of the 

group and half a mile above Bay Horse. The mine has not been 

worked for 20 years and at the time of visit was extensively caved. 

The development consists of several tunnels and a winze on the ore; 

the latter attained a depth of 500 feet.

The inclosing rock is gray dolomitic limestone, which is intricately 

jointed in various directions and fissured along north-south courses. 

The fissuring parallels the crest of the anticline near the longitudinal 

axis of which the deposit occurs.

The principal ore body followed a north-south fissure and varied in 

width from 1 to 20 feet or more. The shoot, which was from 100 to 

200 feet long, extended south into the Excelsior ground, and is said

1 Bell, Robert, An outline of Idaho geology and of the principal ore deposits of Lemhi and Ouster 

counties, Idaho: Proc. Internat. Min. Cong., 1901, p. 73.
BAY HORSE DISTRICT. 69

to have yielded about 1,500,000 ounces in silver and 15,000 tons of 

lead from a sand carbonate ore. Of the several tunnels only the 

northernmost one was accessible at the time of visit. In this tunnel 

300 or 400 feet of work has been done on a ledge which strikes northsouth and dips 30° E. The deposit, which consists of innumerable 

veinlets of ore along fractures and bunches in the solid limestone, is 

extremely irregular. The bunches range from lumps the size of baseballs to masses 14 or 15 feet across, yet all distributed along a zone 

perhaps 40 feet wide which dips 30° E. The minerals are ironstained sand> carbonate and cerargyrite, the latter in minute grains 

identifiable with difficulty. Stains of copper carbonate and druses of 

smithsonite are common; sheaf-like aggregates of calamine crystals 

are less numerous. It is said that the purer grades of ore ran 40 to 60 

per cent lead, 2 to 3 per cent copper, and 50 to 60 ounces in silver to 

the ton.

PACIFIC MINE.

The Pacific claim is now one of the McGregor group, but as it has 

commonly been considered a separate mine it will be described 

separately here. It is situated at an elevation of 7,800 feet on the 

northeast slope of Democrat Hill, about 1£ miles northeast of Bay 

Horse. The property has produced $65,000 from the two short 

tunnels, which total perhaps 1,000 feet in length and comprise its 

only development.

The deposit, which follows the flat-lying beds of the massive 

dolomite that forms the summit area of Democrat Hill, varies in 

width from narrow stringers to 5 or 6 feet. The ore is locally clean 

sand carbonate, though in most places quartz is the predominant 

mineral. Commonly the ore extends as irregular bunches into the 

adjacent wall rock or leads off along joints and narrow fissures. 

The ore minerals are sand carbonate, cerargyrite, smithsonite, and a 

little argentiferous galena, so proportioned in a quartz gangue that 

average shipments of hand-picked material run 50 to 60 per cent of 

lead, 60 to 80 ounces of silver, 2 to 3 per cent of zinc, 4 to 6 per cent of 

sulphur, and 20 to 25 per cent of silica. Two partial analyses of the 

inclosing dolomite, which were supplied by Mr. James McGregor, of 

Salt Lake City, owner of the property, are as follows:

Partial analyses of country rock at Pacific mine, Ouster County, Idaho.

1

7.00

35.00

14.63

2

5.1

30.60

20.18
70 OBE DEPOSITS IN CUSTEE COUNTY, IDAHO.

HOOSE2R GROUP.

The Hoosier group, recently consolidated with the McGregor group, 

consists of four claims situated on the lower slopes of Bay Horse 

Canyon, a few hundred feet above the Beardsley mill. (See fig. 2.) 

The development consists of several short tunnels on either side of 

the creek, in all perhaps 2,500 feet of work.

The principal deposits are two parallel veins about 60 feet apart. 

They strike north-south, dip 22° W., and are inclosed in the shales 

and slates which at this place extend well up the valley sides. The 

upper or west vein ranges from 1 inch to 4 feet in width, averaging 

about 2 feet. Pyrite associated with coarsely-crystallized quartz is 

the most common metallic mineral, though tetrahedrite, which occurs 

only locally, is the mineral sought. Hand-picked shipments from 

this ledge contained 20 to 25 per cent copper and 200 to 400 ounces in 

silver to the ton. To such ore a production of about $50,000 is 

credited. The lower vein differs from the upper in that little tetrahedrite is present, the dominant ore mineral being argentiferous galena. 

This vein averages about 15 inches in width, but the valuable constituents occur only in small irregular patches in its general plane. It 

has produced about $20,000 in silver and lead.

A remarkable feature of both veins is a mass of clear-white, coarsely 

crystallized barren quartz which overlies them. The quartz above 

the upper vein is 10 to 12 feet thick; that above the lower, 40 feet 

thick. This quartz is almost if not altogether devoid of metallic 

inclusions. Locally a thin clayey seam separates it from the veins, 

but elsewhere the quartz cuts the ore. The country rock is a slate so 

fissile that the footwall of an open, flat-lying fissure in it would have 

been covered before long with fragments from the roof. No such 

rubble is present on the upper surface of the ore, which suggests 

that the incoming quartz material followed quickly the opening of 

the cavity or perhaps caused it.

SILVER BRICK CLAIM.

The Silver Brick claim, also one of the McGregor group, joins the 

Pacific on the west. The development consists of two tunnels 100 

feet apart vertically, the lower 700 feet and the upper 150 feet in 

length. The ore occurs irregularly along a fissure which strikes N. 

10° W. and dips 40° NE. A small production has resulted from 

stopes between the two levels.

The inclosing rock is a dolomite similar to that at the Pacific mine.

CAVE MINE.

The Cave mine, owned by Christopher Peterson, a local resident, 

comprises a single unpatented claim situated about a mile northwest 

of Bay Horse, at an elevation of 8,100 feet on the south slope of Democrat Hill. Development consists of a shaft and an 840-foot tunnel in
BAY HORSE DISTRICT. 71

_ 8 inch vein of spar betwee 

porphyry hanging wall and 

shale footwan

FIGURE 2. Claim sheet of James McGregor group, Bay Horse district.
72 OEE DEPOSITS IN CUSTEB COUNTY, IDAHO.

addition to various drifts and crosscuts, in all perhaps 1,500 feet of 

work. Two veins which strike N. 20° W. and dip 70° NE. are recognized, but only one has proved productive. This vein is a band of ore 

about 18 inches in average width, which is accompanied by a variable 

amount of gouge, the usual distance between the fairly well defined 

walls being about 4 feet. The ore contains lead and silver and is 

similar to that found in the Beardsley and Pacific mines. In the outer 

part of the tunnel thin-bedded slates dipping 10° S. pass in a short 

distance through more massive varieties into the underlying dolomite 

which incloses the veins.

FOREST ROSE MINE.

The Forest Rose group, consisting of three patented claims, lies 

immediately south of the Cave property on Democrat Hill. It is 

situated on the same ledge which is worked in the Cave mine, but the 

snoots here found have been less productive. Development consists 

of a tunnel 600 feet long and two raises on the ore. The ore occurs in 

shoots, which range in width from a few inches to 5 or 6 feet. These 

appear to strike north-south and to dip approximately 60° E., 

although development is not sufficient to determine their attitude 

definitely. The ore is partially oxidized argentiferous galena. At 

present the property is being worked by lessees.

NEW SILVER BELL MINE.

The New Silver Bell mine (formerly known as the Silver Bell) is 

situated on the east margin of Poverty Flat at an elevation of 9,500 

feet. The mine is reached by trail from Clay ton, 4 miles on a direct 

line south-southeast. The deposits were discovered in 1879 and were 

worked for the 18 years following, having produced in all about 

$600,000 from silver-copper ores. The property comprises five unpatented claims and is developed to a maximum depth of 100 feet by some 

10,000 feet of tunnels.

Poverty Flat is a remnant, several miles in extent, of an Eocene 

erosion surface developed at this locality across steeply tilted slates 

and quartzites of Paleozoic age. The quartzites are fine-grained and 

massive; the slates thin bedded and fissile, in many places with 

marked slaty cleavage. The ore deposits are found within the slates.

The vein strikes N. 60° W. and dips 30° NE. It follows the inclosing formation in strike but is independent of it in dip, cutting across 

both the primary and secondary structures. The vein is said to have 

steepened with increasing depth. Within a general zone of fissuring, 

perhaps 100 feet wide, ore occurred as narrow lenses of irregular shape 

and unequal extent. The ore consisted of gray copper in a siderite 

gangue and is similar to that of the Ramshorn and Skylark mines, 

although the shoots here were much less continuous. In many places
BAY HOKSE DISTBICT.

along the vein ore was mined within 5 or 10 feet of the surface, where 

the copper occurred principally as malachite and azurite and the silver 

as cerargyrite and argentite. The claims have recently been relocated 

and are now being prospected at greater depth.

ELLA GROUP.

The Ella group comprises four claims situated on the south slope of 

Kinnikinnick Canyon near its junction with that of Salmon River. 

Development consists of several tunnels, the longest of which starts 

near Clayton and continues 1,600 feet on a course N. 15° W. This 

tunnel follows the general strike of the Paleozoic formations which 

constitute the country rock. The ore. occurs along bedding planes 

between a general hanging wall of dolomitic limestone and a f ootwall 

of fine-grained quartzite. Very little ore appears in this tunnel, but 

a considerable amount of argentiferous galena in a quartz-siderite 

gangue lies on the dump. Pyrite and tetrahedrite are intermixed 

with the galena but in subordinate amounts.

The group produced a considerable tonnage during the early days 

of mining in the district, but most of it was derived from openings 

which are farther up the canyon and are now inaccessible. The ore 

was desired because of its high content of siderite, which served as a 

flux in smelting other ores of the district.

RED BIRD MINE.

Situation and history. The Red Bird mine is situated on the east 

side of Squaw Creek, 5 miles above its confluence with Salmon River 

and by wagon road 9 miles northwest of Clayton. The deposit, 

situated near the north end of a group of 10 claims (fig. 3), was 

located in 1878, and the active work, which continued until 1902, 

was begun in 1880. During this period from 1,000 to 1,500 tons of 

ore which ran 30 to 40 per cent of lead and 40 to 60 ounces of silver 

to the ton were delivered to the Clayton smelter annually.1

The mine is opened on eight levels by five tunnels, the upper four 

of which enter the canyon side at intervals of about 100 feet. All 

the tunnels are connected by raises and between Nos. 4 and 8 are 

three blind levels, the total development aggregating 10,000 to 

15,000 feet. Most of the production came from the upper four 

levels, which represent a depth on the ore shoots of 600 to 700 feet. 

Below this depth little ore had been mined at the time of the writer's 

examination, but since then this portion of the deposit has been 

extensively worked.

Geologic relations. The Red Bird mine is well within the area of 

Paleozoic rocks. The sharp anticline cut across by Salmon River

i The mine was reopened in 1912 by the Idaho Smelting & Mining Co. and has been actively worked since, 

supplying most of the ore for the Clayton smelter.
74 OEE DEPOSITS IN OUSTER COUNTY, IDAHO.

between Squaw Creek and Clayton continues northward, and these 

deposits occur on its western limb. The rocks inclosing the ores are

predominantly dolomitic 

slates; but locally dolomitic 

limestone and clayey 

quartzite occur. The lower 

tunnel crosscuts the beds 

for 1,600 feet and affords a 

fair idea of the formations 

and their attitudes. Thinbedded calcareous slates, 

dipping 70° W., prevail for 

the first 80 feet of this tunnel, but from this point 

they grade rapidly into 

I more massive varieties and 

\ the dip flattens to the horil zontal. About 600 feet 

,, from the portal the beds 

1 are steeply inclined east1 ward and the thin-bedded 

a* slates seen near the portal 

* again appear, but within a 

I short distance give way to 

! massive dolomitic Ume0

I stone, which continues to a 

| point 1,400 feet from the 

f entrance. From this point 

I on to the face at 1,600 feet 

\ the beds are nearly horizon- 

^ tal and argillaceous quartzite predominates.

The ore bodies. At least 

five ore bodies have been 

encountered in the mine, 

but two have proved of paramount importance. One 

of these bodies, known as 

the Potato Patch shoot, 

was 60 to 80 feet long by 

20 to 30 feet wide and was 

worked to a depth of more 

than 400 feet. Its strike 

was N. 65° W., and its dip 45° SW. The ore throughout was an 

earthy mass of sand carbonate which ran 30 to 40 per cent of lead
BAY HOESE DISTBICT. 75

and 40 to 60 ounces in silver to the ton. Although of broadly regular outline, the old stopes show the ore body to have been irregular 

in detail. Here and there it extended) out along joint cracks; elsewhere great swells protruded into the inclosing rock.

Parallel to this shoot and about 150 feet east of it is another, 

which on No. 2 level corresponds to it in strike and dip but on the 

lower levels changes to a strike of N. 20° W. and dips 40° NE. A 

considerable tonnage of ore is blocked out on this shoot between No. 

2 and No. 8 levels. Within it the ore occurs in bunches of irregular 

shape and extent which, however, usually have a roughly tabular 

form parallel to the general plane of the fissure. In places the 

bunches give way to a veinlike mass 50 to 75 feet in length and as 

much as 12 feet in width, as near No. 2 level. The ore is similar in 

general character to that in the west shoot and is fairly continuous 

to a point within 65 feet of No. 8 level, where it gives way to a mass 

of pyrite 55 feet wide at the only point where it has been crosscut. 

This pyrite carries traces of gold and an unimportant amount of 

copper. It is exceptionally vuggy throughout the mass. The vugs 

are lined by pyritohedrons of pyrite and here and there a little 

manganese oxide. Among the minerals which occur in the productive part of this shoot, sand carbonate heavily stained with iron 

and manganese is most common. Minute grains of cerargyrite occur 

with it and vugs in the ore are commonly lined with crusts of smithsonite. Set upon these smithsonite druses are needlelike crystals 

of calamine and bluish-white cubes of fluorite. In protected spots 

only do the primary minerals, argentiferous galena, pyrite, and 

sphalerite, occur. Anglesite occurs in places as the principal ore 

mineral in this shoot. It contains 2 to 3 ounces of silver to the unit 

of lead, whereas in the carbonate ore there is only 1 ounce of silver 

for each 1 per cent of lead, the latter ratio being about the same as in 

the argentiferous galena, in which 0.5 to 1 ounce of silver accompanies each unit of lead.

Since the writer's examination a large ore shoot has been found on 

No. 7 level and penetrated for 60 feet, although its dimensions have 

not been determined.

SATURDAY GROUP.

The Saturday group consists of two patented claims situated on 

the west side of the canyon near the mouth of Squaw Creek. The 

development consists of a shallow shaft and one or two tunnels, all 

of which date from the early days of mining in the district. The 

property is said to have produced a few thousand tons of argentiferous 

galena ore but has not been worked for 20 years or more.
76 QBE DEPOSITS IN CUSTEB COUNTY, IDAHO.

CINNABAR GROUP.

The Cinnabar group comprises two patented claims situated 5 

miles up Bruno Creek, a northwest tributary of Squaw Creek, which 

it joins at a point 2 miles below the Red Bird mine. The property 

was not visited but is said to have produced about $100,000 from 

lead-silver ore. At a later date it was sold as a gold mine to certain 

eastern speculators, but as such it proved a total disappointment.

SOUTH BTJTTE GROUP

C. L. Tratht owns a small group of claims immediately east of the 

Red Bird mine, which produced about 1,000 tons of argentiferous 

galena ore in the early days and have been worked intermittently 

by leasers during the past few years. They were not visited.

DOUGHERTY GROUP.

The Dougherty group, consisting of seven claims, is situated on 

Garden Creek, 9 miles west-southwest from Challis, at an elevation 

of 7,700 feet. The development consists of six tunnels on the north 

side of the gulch and two on the south side in all, perhaps, 2,000 

feet of work. The deposits are irregular lenses inclosed in dolomitic 

limestone and thin-bedded slates. Two types of ore ore recognized 

argentiferous galena and tetrahedrite accompanied by pyrite and 

chalcopyrite. In general the strike is N. 50° W. and the dip 30° SW., 

but in no place has a sufficiently continuous deposit been exposed to 

determine any persistent attitude.

LIVINGSTON MINE.

The Livingston group, consisting of five or six patented claims, 

is situated near the head of Slate Creek, about 9 miles from Salmon 

River and 20 miles southeast of Clayton. This property was not 

visited during the reconnaissance, but its promise is such that it 

deserves special mention.

The development consists of about 600 feet of tunnels and several 

open cuts on a ledge said to be remarkable for its continuity. The 

production amounts to $40,000 or $50,000, which has resulted from 

ores removed during development. The property has been sampled 

several times and would probably have been worked before this were 

it not for its comparative inaccessibility. It is said that a large 

tonnage of silver-lead ore is partially blocked out.

YANKEE FORK DISTRICT. 

SITUATION.

The Yankee Fork district comprises an unorganized area of possibly 

150 square miles situated in the northwestern part of Custer County. 

It lies south-southeast of the Loon Creek district, northeast of Stanley
YANKEE FOKK DISTKICT. 77

Basin, and west of the Bay Horse district about 20 miles from 

each. There are three settlements in the area Bonanza, Ouster, 

and Sunbeam all grouped within a radius of 5 miles from the 

junction of Jordan Creek with Yankee Fork. The settlements have 

regular stage communication with Challis, 60 miles distant by a route 

which follows Yankee Fork and Salmon River. Mackay, the nearest 

railroad point, is 85 miles southeast by a route which leaves the 

Challis stage road near the confluence of East Fork with Salmon 

River. Roads also connect north-northwest with Loon Creek district and southwest with Stanley Basin. A trail which is used a 

great deal leads over the mountains to Challis, 30 miles northeast.

HISTOKY.

Prospectors spreading from the placer excitement on Loon Creek 

discovered placer gold on Jordan Creek near its confluence with 

Yankee Fork hi the middle seventies of the last century. Soon 

thereafter the lodes on Dickens Hill and those about Custer were 

located and quickly drew attention from the placers. The General 

Custer vein was especially attractive to those seeking lode deposits, 

for it lay against the canyon side as a great slab several thousand 

square feet in extent and promised strength and persistence together 

with exceptional amounts of the precious metals. In many respects, 

however, it was misleading. Developments have failed to add more 

than 20 per cent to its productive area as exposed by erosion and 

none of the other veins have even approached it in total production.

The district experienced its greatest activity prior to 1900, though 

the General Custer mill operated most of the tune until 1905. After 

that mining operations were unimportant until 1907, When the Golden 

Sunbeam was opened on a large scale, a mill built, and a hydroelectric 

plant installed on Salmon River. In 1911, however, this enterprise 

also was temporarily abandoned, leaving the entire district inactive.

PRODUCTION.

The total production of the Yankee Fork district is estimated at 

$12,000,000, two->thirds of which is credited to the General Custer 

vein. Of the remainder about one-third was derived from the Lucky 

Boy and the rest principally from the Charles Dickens, Golden 

Sunbeam, Montana, Morrison, and McFadden properties.

The relative importance of gold and silver in making up the total 

production can only be roughly approximated. During the twentyodd years that the camp was active the price of silver varied greatly, 

as did also the amount of bullion produced each year. The latter 

factor is not known, hence the only means of estimating the separate 

amounts of gold and silver produced is a survey of their relative 

importance in the ores of individual mines. The General Custer,
78 OKE DEPOSITS IN OUSTER COUNTY, IDAHO.

Lucky Boy, and Charles Dickens veins contained about 85 ounces of 

silver to 1 of gold. These properties produced three-fourths of the 

total amount derived from the district. The Montana and Golden 

Sunbeam contained much more gold than silver, but their combined 

production was less than a million dollars. In the other veins in the 

camp silver exceeded gold in amount. Thus considered, it is estimated that about 40 per cent of the total production of Yankee 

Fork district has been from gold and the remainder from silver.

TOPOGRAPHY.

The Yankee Fork district is a high, mountainous area which varies 

in elevation from 6,000 to 9,500 feet. Yankee Fork, a stream which 

flows south-southwest through the district, occupies the principal 

valley. Tributary to it from the west are Cabin, Jordan, and Eightmile creeks, and from the east a number of small streams of minor 

importance.

The dominant feature of the higher areas is the general accordance 

of summit levels, a feature conspicuous from any point of vantage. 

This is somewhat remarkable, for most of the rocks in the district 

are Miocene tuffs, and the plateau surface of this part of Idaho is of 

Eocene age. The key to the explanation, however, is afforded by 

the water-laid tuff, which appears at elevations of 9,000 feet on Estes 

Mountain and is well exposed at 8,800 feet along the road over Loon 

Creek Summit. This tuff clearly bespeaks a Miocene water surface, 

which stood at about the level of the Eocene erosion surface, at least 

locally, and probably over a considerable area. The present valleys 

of the district are in large part cut in these volcanic rocks and hence 

are obviously jtost-Miocene in age.

Among the minor features of topographic interest is the valley of 

Yankee Fork below the mouth of Jordan Creek. Above this point it 

is comparatively narrow, but below it broad terraces follow the stream 

to its junction with Salmon River. These terraces in many places 

extend back 500 or 1,000 feet from the present channel. Locally the 

gravels composing them are more than 90 feet deep, though usually 

their thickness is less than 25 feet.

GEOLOGY. 

ALGONKIAN ROCKS.

Distribution. Rocks of Algonkian age* are exposed locally in the 

district. They outcrop along the sides of Yankee Fork valley for a 

distance of about 3$ miles, beginning at a point 2 miles below Bonanza 

and continuing southward. They are said to continue a short distance to the west, but to the northeast they open out into a broad

1 For age determination see pp. 18-19.
YANKEE FOEK DISTRICT. 79

area along the eastern border of the district. A small isolated area 

of the same system of rocks is exposed in the bottom of Jordan Creek 

valley near Sunbeam.

Composition.-i-Witiwi this district the Algonkian system is represented by dark-gray massive quartzites, mica schists, massive black 

slates, and thin-bedded gray slates. Their sequence was not determined. Metamorphism is well advanced throughout, slaty cleavage 

and schistosity in most places concealing the original bedding structure. Sufficient^ primary structure remains, however, to indicate 

unmistakably their sedimentary derivation.

LATE CRETACEOUS OR EARLY EOCENE GRANITE.

The late Cretaceous or early Eocene granite, which is widely exposed 

in Idaho, is found only in the south part of this district, where it forms 

the walls of Salmon Canyon near the mouth of Yankee Fork. Northward from this point granite outcrops for about 2| miles, but to the 

east, west, and south its extent is much greater. A description of the 

rock constituting this area appears on pages 21-22.

TERTIARY VOLCANIC ROCKS.

Distribution. Tertiary volcanic rocks are widely exposed in the 

Yankee Fork district, extending through it as a broad belt in a northeast-southwest direction. Their maximum thickness is not definitely 

known, although near Sunbeam they are-exposed in uninterrupted 

succession through a vertical range of 3,000 feet, the lowest member 

resting on Algonkian beds. They occupy a post-Eocene erosion valley, and as the Sunbeam exposure is -near the center of this old valley, 

it may be safely assumed that the exposure there presents approximately the maximum thickness.

Composition. In general the volcanic rocks of this area are andes^ 

ites and latites below and andesitic and rhyolitic tuffs, with interbedded andesite or latite flows, above. In the western part of the 

district the series is chiefly tuff, but east of Custer lavas, principally 

andesites, predominate. Northeast from the Enterprise mine 

numerous low hills, which attain perhaps 8,000 feet elevation, present 

excellent sections of parts of the lava series. These were not visited, 

but as seen from a distance of a mile or so eight or ten distinct flows 

of lava, each 10 to 25 or 30 feet in thickness, were recognized. About 

the Enterprise mine and over the summit to the Lucky Boy andesites 

are predominant, but toward Custer, at an elevation of 1,500 feet 

lower than the summit, tuffs are present in thick beds. Below these 

beds andesites are again exposed in the valley sides near Custer. 

Northwest of Sunbeam, along the road to Loon Creek, the Tertiary 

rocks are predominantly of different type, tuffs being very abundant 

and, together with a few lava flows, outcropping through a vertical
80 OEE DEPOSITS IN CTJSTER COUNTY, IDAHO.

range of possibly 2,000 feet. In places the tuffs are massive, but 

elsewhere they are thin-bedded, even finely laminated, and were 

clearly deposited in standing water. An exposure of this variety 

forms Loon Creek Summit, but here siliceous shales "are interbedded 

with the tuffs. The west face of Estes Mountain, as seen from Loon 

Creek Summit, presents the chalky white slopes typical of the areas 

of tuff.

Petrographic descriptions of these volcanic rocks appear on 

pages 25-26.

QUATERNARY DEPOSITS.

Evidences of glaciation appear on all those parts of the Yankee 

Fork district which exceed 7,500 feet in elevation and in places 

morainal de*bris and U-shaped valleys extend to elevations 500 or 

1,000 feet lower. Jordan Creek valley is glaciated as far as Sunbeam. 

Glaciers radiated from Estes Mountain and left topography especially typical of their action on the north slope and down the valley 

of Eightmile Creek. About the Lucky Boy and Enterprise mines 

also glacial deposits are widespread.

The thick gravel deposits along Yankee Fork are thought to date 

from the period of general ice retreat which closed the Pleistocene. 

These gravels indicate the overloading of' a stream which earlier in 

its history actively eroded its channel, and it seems that only during 

the period of ice recession were conditions favorable for this excess 

of material. At this time'there was an abundant supply of running 

water, and a proportionately greater supply of rock rubble was 

loosened and in part ground up by the glaciers. As the ice front 

retreated this material was continually available for transportation, 

and the streams, if fully loaded in their upper swifter parts, must 

necessarily deposit nearer to their mouths, where the grade was lower. 

This was the condition along the valley of Yankee Fork.

ORE DEPOSITS. 

GENERAL CHARACTER.

The ore deposits of the Yankee Fork district are exclusively goldsilver veins inclosed in volcanic rocks of middle Tertiary age. In 

some of the deposits gold is present almost to the exclusion of silver 

and in others silver is greatly in excess. Copper and lead, are much 

more abundant in these veins than is common in the late Tertiary 

deposits, though in none of them are these metals in sufficient quantities to constitute an ore.

The veins were worked for'a number of years at a large profit, but 

in general have not proved remunerative below a depth of a few 

hundred feet. The General Custer vein is a feature of especial interest, 

and within the knowledge of the writer is unique in that erosion had 

exposed most of its ore body.
YANKEE FORK DISTRICT. 81 

THE VEINS.

Distribution. The veins of the district may be considered as two 

parallel systems about 4 miles apart. In each system four or five 

veins are recognized, most of which strike in a general northeastsouthwest direction and dip westerly. The eastern system attains 

its maximum development on Ouster Mountain, where it comprises 

the Badger, Lucky Boy, Enterprise, Summit, and General Ouster 

veins. Southward it is represented on Dickens Hill by the Charles 

Dickens, Letha, and Julietta veins, and southwestward across Jordan Creek, by the Morrison, Fairplay, and Passover veins. The 

western system is best developed on Estes Mountain, where the 

Montana and McFadden veins are the most important representatives. Southwestward the deposits at Sunbeam should be considered 

in the same general group, although here much of the ore occurs as 

disseminations of irregular shape instead of in veins.

Characteristics. The veins range from stringers to 18 feet or more 

in width, averaging perhaps 4 feet. In general their contact with 

the inclosing rock is sharp and the numerous included fragments are 

angular. Crustification is conspicuous throughout; the bands broadly 

parallel the walls, but in detail concentric arrangement is common. 

The predominant gangue mineral is cryptocrystalline quartz associated with which are small quantities of chalcedony, opal, and adularia. Calcite is important in some of the deposits, as in the Lucky 

Boy, where it comprises perhaps 20 per cent of the vein. The calcite 

occurs both as equidimensional rhombohedrons and as lamellar 

crystals, some of which have been replaced by quartz that retains 

perfectly the crystal form of the calcite.

Metallic minerals are irregularly distributed through the quartz 

and to a less extent through the calcite. In many places they are 

arranged as broken layers parallel to the banding of the gangue. 

Along the strike of the fissures the metallic minerals are largely confined to definite sections of the veins, thus forming the ore shoots, 

which have proved to be the only parts worth mining.

Ore shoots. The ore bodies of the Yankee Fork district comprise

(1) segments of otherwise comparatively barren quartz-calcite veins,

(2) disseminations of stocklike form not related to fissure fillings, and

(3) chimneys of ore apparently independent of fissure veins. The 

most important deposits belong to the first type, which is illustrated 

by all the deposits except the Golden Sunbeam and the Montana, 

the former being a great stocklike body and the latter a chimney 

of ore.

THE ORE.

The unaltered ore of the district is a fine-grained quartz, locally 

accompanied by considerable quantities of calcite and a little chalcedony, opal, and adularia. Scattered irregularly through the gangue, 

98185° Bull. 539 13 6
82 OEE DEPOSITS 1ST CUSTEE COUNTY, IDAHO.

yet conforming roughly to the crustification which characterizes it, are 

metallic sulphides, of which pyrite is most abundant and is present 

in all the deposits. In some of the veins, as the McFadden and 

Julietta, chalcopyrite and galena are also present, and in some of those 

about Ouster enargite, probably also primary, was recognized. Tetrahedrite is not uncommon in the ores, although nowhere an abundant 

constituent. Most important, however, as they have been found to 

inclose the gold and silver, are blue-black submetallic bands and 

blotches which are present in all the better grades of ore. In these 

bands and blotches pyrite and gray copper and in a few specimens 

chalcopyrite are recognizable, but the predominant mineral occurs as 

minute blue-black specks too small to be identified. Partial chemical 

analyses of these bands show a definite trace of selenium, suggesting 

the presence of some selenide.

The oxidized ore is very different in appearance, being a firm quartz 

heavily stained with iron and manganese oxides and locally with 

malachite. Calcite appears in the immediate outcrop in but few 

places, but its former presence is indicated by lamellar and rhombohedral forms of quartz pseudomorphic after it. Kaolin of creamy 

white color, unless stained by iron, is common along crevices in 

the oxidized ore and is probably partly derived from the adularia of 

the gangue and partly infiltrated from the sericite and feldspar of the 

wall rock. The silver of the oxidized ore occurs as cerargyrite, 

argentite, and wire silver, and locally is found in conspicuous quantities. Gold is free but is generally so minutely divided that it is not 

visible to the unaided eye, although coarse gold has been reported from 

some of the deposits, notably the Morrison vein.

The ores of the district have been mined exclusively for gold and 

silver. In the western system of veins gold is commonly equal to or 

in excess of the silver, but in the eastern system silver greatly predominates. Extremes are possibly recorded in the General Ouster 

vein, where there was 1 ounce of gold to 80 or 90 ounces of silver, and 

in the Montana shoot, where only traces of silver accompanied the 

gold.

ALTERATION OF WALL ROCK.

Metasomatic alteration of the wall rock is a conspicuous feature of 

the Yankee Fork gold-silver veins. It is impossible to take a specimen 

within 50 feet of the vein, and in many places within 1,000 feet or more, 

that is not intensely silicified or sericitized. The silicification is most 

intense next to the deposits and gradually dies out with increasing 

distance from them until at 100 feet or so secondary silica is scarce, if 

present at all. Well beyond this distance, however, sericitization is a 

conspicuous feature of the wall rock. This relation is well illustrated 

in the Golden Sunbeam mine. A specimen taken from the lower 

tunnel of this property at a distance of possibly 400 feet from the
YANKEE FORK DISTRICT. 83

main ore body is a chalky-white rhyolitic tuff, sparsely specked with 

iron stains. When microscopically examined it is seen to be made 

up of fragments of altered quartz and orthoclase scattered sparsely 

through a mass of highly sericitized material. A specimen taken from 

the similar rock next the ore body contains much secondary quartz, 

commonly as bunches of small anhedral crystals, accompanied bypyrite 

and a little sericite. The same relation exists in two specimens from 

the General Ouster mine, one taken next the vein and the other 1,000 

feet or so distant. The more remote specimen, however, is also 

chloritized. Similar pairs of specimens from the Lucky Boy and 

Charles Dickens properties show the same relation, seeming to indicate that in the deposits of the district as a whole the wall rock has 

been silicified near the veins and sericitized farther away.

AGE AND GENESIS.

The age of the Yankee Fork deposits is rather definitely limited 

by the age of the inclosing rocks on the one hand and the amount of 

preglacial erosion which has affected them on the other. Thus they 

are assigned to the late Miocene. (See pp. 49-50.)

Their genesis is less definite, but, as discussed on pages 49-50, several lines of evidence lead to the belief that they are genetically 

related to the igneous activity which earlier found expression in the 

great accumulation of tuffs and lavas that incloses them.

MINES AND PRINCIPAL PROSPECTS. 

GENERAL OUSTER MINE.

Situation and history. The General Ouster mine is situated on the 

east wall of Yankee Fork Canyon near the town of Ouster. The 

property comprises several claims located along the vein from a point 

near the valley flat at an elevation of 6,600 feet up the rugged mountain slope to an altitude of 8,500 feet. The vein was discovered in the 

late seventies and was worked actively most of the time from then 

until 1905, when it was closed.

The total production of the mine is said to be about $8,000,000, 

most of which was extracted by a mill situated at Ouster and connected with the workings by aerial tram. Prior to the construction 

of the mill, however, a considerable amount of ore was hand picked 

and shipped to Salt Lake, the returns averaging about $600 per ton. 

The local mill is equipped with 30 stamps, several Wilfley tables, a 

roaster, and cyanide tanks.

Geologic relations. The wall rock of the General Ouster vein is a 

bluish-gray lava, probably andesite, which is now intensely altered. 

The phenocrysts of feldspar ai'e completely changed to quartz, sericite, and calcite, and those of ferromagnesian minerals to quartz, 

sericite, and chlorite. A little sericite also appears in the groundmass,
84 QBE DEPOSITS IN OUSTER COUNTY, IDAHO.

which is studded with small grains of quartz and a few cubes of pyrite, 

both apparently secondary. This rock inclosed the upper 500 feet of 

the vein, now exposed, but below that portion a formation of different 

composition is said to have been encountered. The latter is probably 

one of the tuffaceous beds common in the district. A specimen 

secured at 7,300 feet from the next gulch north of the one occupied 

by the General Custer vein, and which is probably from the same bed 

of tuff, is a greenish-gray rock composed of fragments of unstriated 

feldspar in part altered to calcite and sericite. The ferromagnesian 

constituents are altered to chlorite and commonly arranged in beautiful spherulitic patches. This rock is probably a trachytic tuff. 

Beneath it andesite crops out again, as shown in the valley walls 

near Custer.

The vein. The General Custer vein is a fissure filling which strikes 

N. 60° W. and dips 35° NE. It varies in width from a few inches up 

to 12 feet and in a few places to 18 feet, averaging perhaps 6 feet. 

The topographic relations of the vein are unique in that erosion has 

completely stripped the hanging wall from perhaps 80 per cent of its 

known extent, so that the ore lay as a great slab against the side of a 

narrow gulch tributary to the main canyon at Custer. Now that the 

vein has been worked off, the footwall resembles a dip slope pitching 

toward the bottom of the gulch and clearly records the structural disturbances which affected the vein after its formation. The wall is 

remarkably smooth and regular but is offset by several faults both 

along the strike and along the dip. The former throw the west side 

5 feet to 20 feet to the south and the latter present drops of equal 

extent on the lower side.

Drifts to the east from the margin of the exposed portion showed 

that the vein split into two parts, neither of which was sufficiently 

metalized to constitute an ore; westward the vein has been removed 

by the erosion of Yankee Fork. Down the pitch of the ore shoot, 

which corresponded closely with the grade of the gulch, the ore 

changed on entering the tuffaceous beds, widening to 30 feet and 

becoming too low grade for profitable extraction.

East of the General Custer vein, on the same property, is a vein 

which crops out on the Summit claim at an elevation of 8,500 feet. 

It strikes N. 45° W. and dips 80° SE., thus according in general course 

with the other vein. The opinion held by some who are acquainted 

with the deposits that the lower vein is a portion of the upper which 

has "broken over," is not supported by geologic evidence; both are 

clearly in place.

The ore. That portion of the vein which constitutes an ore is 

characterized by dark-colored blotches and bands which grade into 

the general gangue. The metallic minerals which give the dark color 

to these portions are in most places too minute for identification, but
YANKEE FORK DISTRICT. 85

locally gray copper, pyrite, and in a few specimens chalcopyrite can 

be identified in them.1 The ore in that part of the shoot which has 

been developed is highly oxidized, and in many places is minutely 

fractured. Of the oxidation products which have formed, iron oxide 

alone is conspicuous, but manganese oxide and malachite occur 

locally.

The ore removed was of excellent grade, several of the earlier mill 

runs averaging from $150 to $300 to the ton in silver and gold. During the later stages of mining, however, the tenor fell to $30 and lower. 

The gold was largely free, and the silver occurred as wire silver, argentite, and cerargyrite. The proportion of the metals was 1 ounce of 

gold to 80 or 90 ounces of silver.

LUCKY BOY MINE.

The Lucky Boy property, said to have produced about $1,750,000, 

comprises several claims, two of which are patented. It is situated 

east-southeast of the General Ouster group, at an elevation of 8,400 

feet above sea level. The deposit was discovered about 1878, but not 

until the General Ouster ore body began to show signs of exhaustion 

in the late nineties was it extensively opened. It was worked actively 

from then until 1904, the ore being carried by aerial tram to the General Ouster mill. Development consists of two incline shafts, ftne of 

which attains a vertical depth of 900 feet, with drifts at 100-foot 

intervals.

The rock inclosing the Lucky Boy vein is a bluish-gray lava, probably andesite, which has been so completely altered in proximity to 

the vein that its identification is uncertain. Within this rock sericite 

is extensively developed, both in the groundmass and after the feldspar phenocrysts. Chlorite is present in small scattered patches and 

quartz is abundant as small grains and -veinlets. Small cubes of 

pyrite stud the altered rock in many places, numbers of them being 

inclosed in the quartz veinlets.

The Lucky Boy deposit is a quartz-calcite vein which averages 

about 5 feet in width, though in places it narrows to a stringer and 

elsewhere widens to 15 or 18 feet. It strikes N. 85° E. and dips 64° 

NW. At the time of the investigation most of the workings were 

inaccessible, but from material on the dump it appears that the 

deposit contains 15 or 20 per cent calcite, much more than is present 

in any other known vein in the district. The calcite occurs both as 

lamellar crystals and as irregular areas; in many places it has been 

partially replaced by quartz. The predominant gangue mineral is 

cryptocrystalline quartz, which is generally arranged in bands parallel 

to the vein walls. Included in the gangue are numerous angular

1 For other minerals, which a more thorough study would probably reveal in this ore, see the general 

discussion, p. 47.
86 OEE DEPOSITS IN CUSTEE COUNTY, IDAHO.

fragments of wall rock which are intensely silicified and studded 

thickly with minute cubes of pyrite. Chalcedony and opal both 

appear locally in this deposit, but adularia was not recognized. .

The precious metals accompany the darker bands of quartz. These 

bands owe their color to very minute metallic particles, which, though 

rather abundant, it was not possible to identify. Associated with 

them are small cubes of pyrite and a little gray copper. The ore is 

said to have contained gold and silver in about the same proportions 

as that of the General Ouster, but was of lower grade.

BADGER MINE.

The Badger claim adjoins the Lucky Boy property on the east. 

The mine was worked intermittently for.several seasons, the ore 

being treated at the General Ouster mill, but for the past 12 years 

the property has been idle. The vein parallels the Lucky Boy, with 

which it corresponds in general characteristics.

BLACK MINE.

This property joins the Badger on the south, but has not produced 

as much ore. A 20-stamp mill situated on the property was operated 

intermittently for two or three years.

° ENTERPRISE GROUP.

The Enterprise group comprises six unpatented claims situated a 

few hundred yards northeast of the Lucky Boy mine. Development 

consists of a tunnel 850 feet long and a few open cuts. Three ledges 

have been recognized on this property, two of which are possibly 

offshoots from the southern or largest ledge, which is known as the 

"back vein." This vein strikes N. 75° E. and dips 65° NW. It 

consists of a brecciated zone 25 or 30 feet wide which has been 

impregnated and cemented by vein quartz, in amount constituting 

perhaps one-half of the whole. Metallization is most intense near 

the hanging wall, where a cross section of 10 feet gave returns of $10 

to the ton in gold, together with traces of silver. The gold is probably contained in the ill-defined blue-black bands which traverse the 

quartz. In these bands pyrite is the only recognizable mineral, and 

it is not abundant. Laterally or vertically the lode has not been 

explored more than a few feet from the tunnel.

CHARLES DICKENS MINE.

The Charles Dickens mine is situated at an elevation of 7,200 feet 

on the south slope of Dickens Hill, a bold topographic feature bounded 

on the east by Yankee Fork and on the south by Jordan Creek. The 

property produced about $600,000 in gold and silver bullion during 

the period from 1888 or 1889 to 1902. Development consists principally of a tunnel and a winze from it, the total depth attained being 

about 250 feet.
YANKEE FORK DISTRICT. 87

The vein, which strikes N. 70° E. and dips 70° to 75° NW., is a 

fissure filling ranging in width from 2 to 6 feet. It is inclosed in tuff 

in its upper portion and probably in andesite in the lower workings. 

The gangue is the fine-grained quartz common in the deposits of the 

district. Associated with it, however, there seems to be less calcite 

and more of the base metals than is common elsewhere. Small cubes 

of galena, irregular specks and bunches of chalcopyrite, and small 

areas of gray copper are common in the better grades of the primary 

ore. Gold is not visible. In the oxidized ore the valuable minerals 

are free gold, wire silver, cerargyrite, and argeritite.

MORRISON GROUP.

The Morrison property is situated across Jordan Creek westsouthwest from the Charles Dickens. The property produced about 

$100,000 during the early days of the camp. It was not visited during the reconnaissance but is thought to be a continuation of the 

Charles Dickens, with which it corresponds in strike and dip.

FAIRPLAY, PASSOVER, LETHA, AND JULIETTA CLAIMS.

South of the Morrison mine are the Fairplay and Passover claims, 

each of which has produced $20,000 to $25,000. North of these, across 

Jordan Creek, are the Julietta and Letha claims; the former has 

produced a few thousand dollars and the latter $60,000.

GOLDEN SUNBEAM MINE.

Situation and history. The Golden Sunbeam group, comprising 

nine claims and three fractional claims, is situated on the south side 

of Jordan Creek, 4 miles above its confluence with Yankee Fork. 

The property was worked for several years prior to 1906, but not until 

then was extensive development begun. About this time a large 

irregular body of ore was encountered, which encouraged the operators to construct a 450-ton mill and install a hydroelectric plant on 

Salmon River, 10 miles distant. The mill is arranged for six Monadnock mills, four of which are installed. Two of the mills were operated for a time with indifferent success, and in June, 1911, the plant 

was closed. It is said that on broad averages the deposit was of too 

low grade to be worked at a profit. The property is said, however, 

to have produced about $400,000 from gold and silver.

Development consists of three tunnels and two intermediate levels 

in the main mine, the Bismarck tunnel a short distance south of it, 

and the Matilda to the north, in all perhaps 8,000 feet of tunnel work. 

The maximum depth on the deposit is 440 feet.

Character of the deposit. The Golden Sunbeam ore bodies comprise 

mineralized zones and chimneys of ore in bedded tuffs. Locally, as 

in the Bismarck tunnel, the ore follows fairly well defined brecciated 

zones and thus resembles the veins found elsewhere in the district, 

but in general there is little evidence of fissure filling. The most
88 OEE DEPOSITS IN OUSTER COUNTY, IDAHO.

important ore body, locally known as the "big stope," was an irregular mass which on No. 2 level was 130 feet long by 75 feet wide. 

From this level it extended upward 85 feet and downward 115 feet. 

Most of the production came from this stope, the ore running $2 to 

$4 to the ton. The shoot had a general strike N. 30° E. and stood 

nearly vertical.

The ore, as seen on the margin of the " big stope," is a soft grayishyellow rhyolitic tuff studded sparsely with small specks of iron oxide, 

doubtless due to the alteration of pyrite crystals. In a few places 

copper stains also are present. The tuff is intensely silicified near 

this stope, minute bunches and scattered grains of secondary quartz 

being abundant. A specimen taken about 200 feet from the same 

stope is not silicified but is extensively sericitized.

Both in the " big stope " and elsewhere on the property vertical fractures are followed by narrow stringers of ore, in places high in grade. 

These stringers, however, are so small that as a rule it has not paid 

to mine them. The gold is pale yellow, owing to the high percentage 

of silver, in some specimens more than one-half, which is associated 

with it. Near the surface native silver is said to have been found, and 

with it a purer grade of gold, which suggests a separation of the two 

metals during oxidation.

MONTANA MINE.

The Montana mine is situated on the south slope of Estes Mountain, 

a few hundred feet below its summit. The property was worked many 

years ago and was reopened in 1905 to 1907. It has produced 

$337,000, most cwf which was recovered from a shoot 20 to 25 feet 

in length by 5 to 17 feet in width, which extended to a depth of 530 

feet. In the upper 250 feet the shoot dipped 80° W., flattening 

below to 45°. The inclosing rock is a fine-grained tuff rather intensely 

silicified near the ore shoot. The ore differed from that found elsewhere in the district in the small quantity of silver associated with 

the gold, less than 1 ounce to the ton being common.

McFADDEN GROUP.

The McFadden group of two patented claims lies on the northeast 

slope of Estes Mountain at an elevation of 8,600 feet. The property 

was located in 1878 and has been worked at intervals since, producing 

in all about $200,000. Development consists of about 2,000 feet of 

tunnels and a shaft 500 feet deep. A 10-stamp mill is situated on 

Eightmile Creek, 3 miles below the mine.

The vein, which strikes N. 20° E. and dips 37° NW., lies between 

a hanging wall of light-gray fine-grained tuff and a f ootwall of greenishgray porphyritic rock, possibly aridesite. Both are intensely silicified, and in the f ootwall rock zoisite and chlorite are also abundantly
YANKEE FORK DISTRICT. 89

developed. The vein averages about 3 feet in width and is composed 

principally of coarse quartz roughly crustified parallel to the walls or 

concentrically banded about included fragments of wall rock. Both 

intergrown with the quartz and included in it are a few crystals of 

adularia. The metallic minerals are distributed erratically through 

the quartz and consist chiefly of chalcopyrite, pyrite, tetrahedrite, 

and galena, decreasingly abundant in the order named. The gold 

and silver are associated with these minerals in the ratio to each other 

of about 1 to 100. The ore occurs in two shoots which are poorly 

defined but range in length up to possibly 100 feet. In the upper 

workings oxidation is well advanced, but about 200 feet below primary 

minerals predominate. The oxidized ore is stained with iron and 

copper and contains seams and small isolated specks of kaolin, the last 

probably derived from the alteration of adularia.

GOLDEN GATE GROUP.

The Golden Gate group, joins the McFadden on the north. The 

two mines are on the same vein and as the geology is similar in both 

it will not be necessary to repeat the description. One ore shoot is 

recognized in the 1,000-foot tunnel which comprises the development 

on this property. From it some ore has been taken, but the production is much less than from the McFadden mine.

OTHER PROPERTIES ON ESTES MOUNTAIN.

Several other veins are recognized on Estes Mountain, but they are 

little developed and have produced only small amounts of bullion.

YANKEE FORK PLACERS.

Placers, said to have produced $50,000 in gold, were discovered in 

the middle seventies on Jordan Creek, near its junction with Yankee 

Fork. About the same time gold was found in the high bars below 

Bonanza, but these have never proved profitable. During the past 

few years the valley flat along Yankee Fork from Salmon River to 

Jordan Creek and thence along that stream for about 2 miles has been 

located, and extensive exploration carried on by drilling, but with 

what success is not known to the writer.

The gravels form broad terraces, said to be 90 feet deep in places 

although averaging possibly less than 30 feet. Little is popularly 

known of the distribution of gold in the gravels except on Jordan 

Creek, where the placers have been largely worked out. Here the 

gold was next to bedrock, and although commonly fine some large 

nuggets were obtained, one weighing 32 ounces being said to have 

been found near the outcrop of the Morrison vein. Several others 

from the same vicinity weighed 8 or 10 ounces, and many exceeded 1 

ounce in weight.
90 ORE DEPOSITS IN OUSTER COUNTY, IDAHO. 

LOON CHEEK DISTRICT. 

SITUATION.

The Loon Creek mining district comprises an unorganized area of 

perhaps 75 square miles situated in the northwestern part of Ouster 

County. It lies immediately west of Sheep Mountain district and 

about 15 miles northwest of Yankee Fork district. Mackay, 11-0 

miles southeast of Ivers, the principal local settlement, is the most 

accessible supply point. To reach Ivers from Mackay, however, it is 

necessary to cross two high summits in addition to a 3-mile climb 

from the mouth of Canyon Creek to the settlement. The roads are 

better than in most mountainous regions, but owing to snow on the 

summits are impassable for teams during the whiter months.

MINING CONDITIONS.

The Loon Creek district is a well-timbered and well-watered region 

of bold topographic forms. Owing to the range in elevation from 

5,000 to 9,500 feet, the district experiences a great variety of climatic 

conditions. Snow covers the higher areas to a depth of several feet 

throughout the winter months, but in the lowlands the weather is 

seldom severe.

The area is well adapted to mining operations. The abrupt transitions from lowlands to highlands make it feasible to explore most of 

the known deposits to a depth of 1,000 to 2,000 feet by means of tunnels. Local smelting is facilitated by an abundance of suitable fluxes 

within the area. Indeed the only handicap to successful and economical mining is the expense of freighting supplies, especially coke, from 

the Oregon Short Line terminus at Mackay, 110 miles distant. The 

cost of this haulage is 2£ cents a pound for the round trip. When 

loaded both ways this is spilt into 1^ cents in and 1 cent out. 

The cost of coke, therefore, is the prime problem in local smelting, 

its average price laid down at Ivers being $46 per ton.

The various expenses charged against a ton of ore delivered as 

matte free on board at Mackay aggregate $20 to $22. It is this 

high cost which retards mining activity in the Loon Creek and adjoining districts; the need of the region is railroad transportation. Only 

ore running $70 to $90 a ton has been smelted, but for every ton of 

this grade which has been developed there are estimated to be 2$ 

tons which will average $25.

HISTORY AND PEODUCTION.

Placers which produced a large amount of gold were worked 

actively on Loon Creek during the decade closing with 1879. Most 

of the production, however, dates from the first half of this period, 

the excitement gradually dying out until only 30 or 40 Chinese
U. 8. GEOLOGICAL SURVEY 

LOST PACKER SMELTER AND ORE PILES AS SEEN FROM 
LOON CREEK DISTEICT. 91

remained, who were massacred in the winter of 1879 by a band of 

men supposed at that time to be Indians but now commonly believed to have been whites. Since that time comparatively little 

mining has been done on the creek, although all the promising ground 

is now held as placer claims.

The principal lode mine in the district at present is the Lost 

Packer, located by Clarence E. Eddie in July, 1902. Soon thereafter it was purchased by Ivers & Finlan, of Salt Lake, who instituted development in the spring of 1904. A 100-ton smelter (PI. IX) 

was completed in 1905, and although it has been necessary to haul 

coke 110 miles consistent development has been carried on with the 

returns from three short smelter runs one in 1907, one in 1908, and 

another in 1911. 

Numerous other properties have been located in the district, but 

they are little developed and most of them have changed, hands several 

tunes, successive holders becoming discouraged because of the 

difficulties of transportation.

The total production of Loon Creek district is variously estimated 

from $1,000,000 to $2,500,000, $500,000 of which is credited to the 

Lost Packer lode and the remainder to the gold placers during the 

decade of their activity which closed with 1879. In recent years 

the placers have produced a small amount, the recovery each year 

being sufficient to pay assessment costs. The lode production 

includes both gold and copper, about $150,000 having been derived 

from the latter. A good grade of lead-silver ore occurs in the district, but little or none has been marketed.

GEOLOGY.

Physiography. The Loon Creek district is a high mountainous 

region ranging in elevation from 5,000 to more than 9,500 feet. 

Loon Creek, a rapid stream, averaging perhaps 30 feet in width, 

flows north through the area. Its more important tributaries are 

Mayfield and Cottonwood creeks from the east and Trail Canyon 

and Grouse creeks from the west. The area is a part of the broad 

region known as the Salmon River Mountains and preserves on its 

highest parts the Eocene erosion surface fronio which those mountains were carved. This feature constitutes the most valuable 

geologic datum plane in the area. The topography and geology of 

a part of the district are shown on Plate X.

Sedimentary .rocks. The oldest rocks in the area are mica schists 

and quartzites of Algonkian age. They outcrop over an irregular 

area of about 2 square miles in the central part of the district. In 

most directions they are cut off by quartz diorite which invaded 

the region in late Cretaceous or early Eocene tune, but northward 

they disappear beneath a capping of quartz latite. These ancient
92 ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

sediments are intensely metamorphosed, a strong schistosity, which 

strikes west of north and dips southwest, obliterating the bedding 

structure in most exposures.

Beds of Paleozoic age overlie the Algonkian deposits and are 

separated from them by a marked structural unconformity. These 

beds are confined to the south-central portion of the district. They 

are steeply inclined to the east, south, or southeast, the direction 

varying from place to place. Within them schistosity occurs only 

along special zones of shearing; thus they are readily distinguishable 

from the underlying Algonkian, from which they differ also in 

composition.

The Paleozoic beds consist of fine-grained quartzites and massive 

blue dolomitic limestones, neither of which yielded fossils on a 

cursory examination. Nevertheless the lithologic similarity of the 

beds to those at Gilmore, Lemhi County, suggests that the quartzite 

is of Cambrian age and that the massive blue dolomitic limestone 

is Ordovician. This assignment is apparently refuted by the juxtaposition of the Algonkian schist with the dolomitic limestone near 

Lost Eagle mine, but it is thought that this contact records faulting, 

although, owing to a thick mantle of soil, the relation was not 

determined with certainty. The thicknesses of 'the quartzite and 

dolomite were not determined. Higher horizons of the Paleozoic 

probably outcrop hi the extreme south-central part of the district, 

but this area was not visited.

Igneous rocks. Igneous rocks of diversified types and widely 

different ages are present in the district. The oldest and most 

important of these rocks is a great batholith of quartz diorite which 

extends into the area from the west and again crops out along its 

eastern border. It is a dark-gray rock, composed of oligoclase, 

quartz, conspicuous amounts of biotite, and subordinate hornblende. Orthoclase, titanite, and apatite are accessory. This 

batholith is thought to be a phase of the great granitic magma 

which invaded central Idaho in late Cretaceous or early Eocene 

time and which now crops out over a continuous area more than 

20,000 square miles in extent.

Soon after the quartz diorite invasion came the intrusion of numerous, medium-grained granite dikes, peculiar because of their small 

content of ferromagnesian minerals. These dikes are from 2 or 3 to 

more than 30 feet in width; yet the texture in all is about the same. 

In general they follow the schistosity of the Algonkian rocks, but 

locally they cut across it.

Subsequent to the intrusion of the granite dikes there entered 

dikes and sills of granite porphyry and diorite porphyry. These 

dikes are excellently exposed in the Lost Packer mine, where they 

traverse the ore body in several places (fig. 4, p. 95). On No. 3 level 

they intersect, but in this place the fine grain and extremely altered
U. S. GEOLOGICAL SURVEY 

GEORGE OTIS SMITH. DIRECTOR IN 539 PLATE X

LEGEND

SEDIMENTARY ROCKS

Magnesian limestones, \ -J 

slates, and quartzites I J

Schists and quartzites 3

IGNEOUS ROCKS

Tql

Quartz latite

Dikes

>p, granite porphyry 

ip, diorite porphyry 

(dikes numerous but not , 

ippedexcept in section A-A

qd

Control by stadia and planetable triangulation 

Elevation in Elevations refer to superintendent's residence, 

'&* assumed from aneroid readings to be 7,200 feet 

9,000 -i

8,000 -

7.000

Elevation in 

feet

r 9,000

- 8,000

SECTION B-B (Dikes not shown)

7,000

7,000

Elevation in 

feet

- 9,000

- 8,000

SECTION A-A (Dikes as shown in workings of Lost Packer mine) SECTION C-C (Dikes not shown)

TOPOGRAPHIC AND GEOLOGIC MAP AND SECTIONS OF A PORTION OF THE 

LOON CREEK DISTRICT, IDAHO

By Joseph B. Umpleby

7,000

Scale 24,000

iMfle

Contour interval 200 feet 

Itatumismean -tea level 

1913
LOON GREEK DISTRICT. 93

condition of the specimens collected from the older dike make it impossible to classify it definitely. The younger dike also is altered, but 

numerous quartz phenocrysts indicate that it is a granite porphyry. 

Near the portal of No. 6 tunnel the diorite porphyry presents a marginal facies similar in appearance to the older dike in No. 3 tunnel, 

and this is thought to further indicate that the granite porphyry is 

the younger intrusion. In the larger dikes a phenocrystic development of quartz characterizes the granite porphyry, but this is lacking 

in the narrower dikes. The age of these intrusions is not definitely 

known, although they are thought to antedate the Eocene erosion 

surface.

Quartz latite flows, still younger than the granite and diorite 

porphyries, cap the summit above the Lost Packer mine. They rest 

on an uneven erosion surface of post-Eocene age, but further thasi this 

the period of their extravasation is not fixed. They are gray in color 

and made up of phenocrysts of oligoclase, quartz, and biotite set in a 

fine-grained groundmass, which constitutes over one-half of the rock 

and which from partial chemical analysis is known to contain considerable potash. (See p. 26.)

Glacial deposits. During the Pleistocene epoch glacial ice covered 

those parts of the area above 8,000 or 8,500 feet and sent tongues 

down the larger valleys to points about 7,000 feet above the sea, 

locally perhaps to 6,500 or even 6,000 feet. Evidence of such glaciation is presented by all the larger valleys. At their heads are invariably steep-sided cirques, many of them occupied by small lakes. 

Below these cirques the canyons are broad and U-shaped for a distance, with morainic material along their sides and bottom, but 

finally they become narrow and V-shaped. This transition in most 

places marks the lower limit of glaciation.

ORE DEPOSITS. 

GENERAL CHARACTER. o

The Loon Creek district comprises an area noteworthy at present 

because of its gold deposits, including lodes in which chalcopyrite, 

quartz, and siderite carry the gold, and placers along the streams in 

favorable places below them. In addition to the gold-bearing lodes, 

lead-silver deposits are found in the district. These lead-silver deposits have been inadequately prospected, but the ore is of excellent 

grade, being in many places clean galena that carries from 60 to 100 

ounces of silver to the ton.

Iron and lime fluxes are abundant along the contact between the 

Paleozoic dolomitic limestone and the quartz diorite south of Ivers. 

They are especially valuable as they contain about 60 cents in gold 

and 1 ounce in silver to the ton almost sufficient to pay for handling 

them.
94 OEE DEPOSITS IN CUSTEB COUNTY, IDAHO.

GOLD PLACER DEPOSITS.

The Loon Creek Hydraulic Placer Co. owns six claims, in all 470 

acres, which extend from a point near the mouth of Canyon Creek to 

the Loon Creek Narrows, 4£ miles north. Their average width is 

approximately 1,000 feet. A strip about 75 feet wide and 1 mile 

long, comprising the upper part of the central channel, was worked 

during the sixties and is variously estimated to have produced from 

$500,000 to $2,000,000, an occasional pan having yielded as much as 

$300. These gravels were 2 to 6 feet thick, but back of them are 

gravel terraces which were not explored during the early days. The 

present owners prospected these terraces during two seasons and 

obtained an average yield of 25 cents a cubic yard. A flume capable 

of delivering 80 second-feet of water to any part of the ground is 

partly completed, and will probably be in operation in a short time. 

Heretofore water has been derived from two small streams Grouse 

Creek and White Creek but the present plans include the diversion 

of Loon Creek at a point well above the placer grounds.

The auriferous gravels rest on a floor of schist, which as now exposed 

presents a comparatively even surface. The inclosing gravels are 

usually less than 6 niches in diameter, although in places at various 

distances from the base of the deposits bowlders as much as 3 feet and 

a few up to 6 feet in diameter are encountered. As the gravels are 

loosely cemented they fall apart readily when undermined by the 

hydraulic giant. The beds are in few places more than 15 or 20 feet 

thick, although locally they attain a depth of 30 to 40 feet. The gold 

is near bedrock and in joints and shallow depressions in it. As a rule 

the gold is coarse, nuggets weighing more than an ounce being not 

uncommon, and perhaps 50 per cent of the product averages 25 cents 

or more to the color. The market value is $18 an ounce.

GOLD-COPPER DEPOSITS.

THE LOST PACKER VEIN.

Situation and development. The Lost Packer vein, the principal 

lode deposit in the Loon Creek district, crops put here and there along 

a course extending north from the town of Ivers. It follows roughly 

a steep, narrow gulch, which within 4,000 feet attains an elevation 

2,000 feet greater than that at Ivers. The development comprises 

eight tunnels which enter along the strike of the vein, the lowest, or 

No. 10, attaining a depth of 1,000 feet below the quartz latite flow that 

caps the vein at an elevation of 8,700 feet. The levels are numbered 

from No. 1, driven 100 feet below the apex of the vein, to No. 10, the 

lowest, and all except Nos. 5 and 9 connect directly with the surface. 

(See fig. 4.)

General character of the vein. The fissure followed by the Lost Packer 

vein strikes N. 5° E. and dips 75° NW. It has been traced from
Ci

to

Longitudinal section of vein,showing outline 

of ore shoote and geologic relations

FIGTJBE 4. Plan and sections of Lost Packer mine, Loon Creek distric
96 OEE DEPOSITS IN OUSTER COUNTY, IDAHO.

Canyon Creek, at Ivers, north about 3,000 feet to the dacite cap above 

the mine. South of Canyon Creek it has not been definitely recognized, although a few small-prospects have been opened on its general, 

course. Northward, where the fissure has been explored by tunnels 

throughout about 2,000 feet of its extent, it presents well-defined 

walls, which commonly stand 3 to 5 feet apart, with gouge, sheeted 

wall rock, and ore between them. The walls present numerous slickensides, but distinct grooves having even an approximately uniform 

direction were not noted. Within the gouge also there is abundant 

evidence of shearing and gliding of contiguous parts, all bespeaking 

important movements along the vein fissure. Most of the movement, 

however, antedates the ore and determined the channels along which 

the ore-bearing solutions entered. Evidence of extensive displacement along this plane is apparently lacking; the dislocation probably 

did not exceed a few score of feet at most.

The fissure traverses the schists and granite dikes but is itself 

crossed by the granite porphyry and diorite porphyry. In general 

it cuts the structure planes of the schists, which commonly strike a 

little west of north at a low angle.

The vein material follows the fissure closely, although in a few 

places as far as 20 feet from it small lenses of chalcopyrite occur in the 

schist. Within the fissure the ore is distinct from the gouge and 

sheeted schist and usually comprises a single band, either next the 

hanging wall or footwall, more often next to the latter. The ore 

varies in width from a narrow stringer to 4 or 5 feet, averaging perhaps 

20 inches. Along the strike of the fissure mineralization is so localized 

that three distinct shoots of ore are recognized. Where not vertical 

each shoot pitches south at a high angle. The shoots are connected 

on most levels by narrow bands of ore.

Even though ore and gouge are commonly present in the same cross 

section, it seems that where the walls are farthest apart the ore is 

widest. This relation suggests that the shoots are determined by a 

relative movement of the fissure walls sufficient to bring reverse curves 

opposite each other; a suggestion further supported by the parallel 

arrangement of the shoots.

The ore. The ore consists of auriferous chalcopyrite in a sideritequartz gangue, the relative importance of the three minerals varying 

markedly from place to place in the same shoot and especially in the 

different shoots. Thus in the south shoot siderite predominates and 

in the two others quartz is most important. The relative amount 

of chalcopyrite is greatest in the middle shoot, where it represents 

about one-third of the total vein material. The Lost Packer ores are 

exceptional in the amount of gold associated with the chalcopyrite; 

assays of this mineral usually show 2£ to 3 ounces of gold to the ton. 

Equally important with the chalcopyrite as a carrier of gold is the
LOON CREEK DISTRICT. 97

quartz, especially that of the middle shoot, but the siderite as a rule 

does not contain more than half an ounce of gold to the ton. In both 

the chalcopyrite and the quartz silver runs about 2£ ounces to the 

ounce of gold. The total production of the property, about one-half 

million dollars, has been derived from ore averaging between $80 and 

$90 to the ton. However, for every ton of this grade which has been 

encountered in the mine there is estimated to be 2£ tons which average $25.

Mineralogically the ore is comparatively simple; chalcopyrite, 

siderite, and quartz only are common. A little calcite is prosent. 

Pyrite is exceedingly rare, occurring as small grains and cubes, 

usually included in the chalcopyrite. Pyrrhotite has a similar distribution but is even less abundant. Jennings * reports barite as a 

primary constituent, but careful search during the present studies 

failed to reveal this mineral. The oxidation products are principally 

iron oxides and the carbonates of copper. Immediately beneath the 

surface films of bornite and native copper are locally present, but 

here also the chief alteration products are malachite, a little azurite, 

and much limonite and hematite.

Ore shoots. The three ore shoots recognized in the Lost Packer 

vein present important differences in constitution ancl form and hence 

will be discussed separately. Each stands vertical or pitches south 

at a high angle.

The north shoot is reached only by No. 4 and No. 3 tunnels. On 

the former level it is 120 and on the latter 250 feet in length, the average width on each being about 2 feet. The ore consists of coarse-textured milky to bluish-white quartz with chalcopyrite and a little 

pyrite irregularly scattered through it, the chalcopyrite frequently 

inclosing small cubes and grains of the pyrite. On No. 3 level siderite 

is rare, but on the next level below it is equally abundant with chalcopyrite and has a similarly irregular distribution. This ore body 

is comparatively lean, roughly sorted material running about $20 

to the ton one-half ounce of gold, 2 ounces of silver, and 3£ per cent 

of copper.

The middle shoot is by far the most important in the mine. It lies 

200 feet south of the north shoot and is developed from the seventh 

level to the quartz latite cap 700 feet above. The southern limit of the 

ore is a fairly regular line, but the north boundary is not parallel to it. 

Thus the shoot is about 500 feet long on No. 2 level, narrowing both 

above and below, its average length being about 300 feet. Locally 

the shoot appears at the surface as a honeycombed quartz heavily 

stained by iron together with a little manganese oxide and copper 

carbonate, but in most places it has little or no surface expression.

' Jennings, E. P., The Lost Packer copper-gold lode [Idaho]: Jour. Canadian Min. Inst., vol. 9,1906, p. 56. 

98185° Bull. 539 13 7
98 ORE DEPOSITS IF OUSTER COUNTY, IDAHO.

The ore ranges in width from a few inches to 4 or 5 feet, averaging 

about 20 inches, and wedges out on the ends of the shoot. This 

wedging out of the shoot seems to bear a definite relation to the tenor 

of the ore, for it has been commonly found that as the ore body narrows its assay value diminishes. Thus the ends of stopes temporarily 

abandoned are generally in ore running about $25 to the ton, whereas 

the portion removed averaged between $70 and $90 to the ton. On 

No. 4 level the shoot is shorter than elsewhere in the mine and here 

also it contains a minimum amount of gold to the ton. Ore from 

levels both above and below contained 2 to 3 ounces to the ton, but 

here less than 1 ounce was present.

The ore consists essentially of chalcopyrite distributed as bunches, 

small patches, irregular grains, and interstitial fillings in a gangue of 

coarse white quartz. The chalcopyrite constitutes about one-third 

of the total material mined. Siderite is present in small quantities, 

but is nowhere an important constituent. The chalcopyrite and 

quartz each carries about 3 ounces in gold to the ton, but less than 

half an ounce is present in the siderite.

The south shoot of ore differs markedly from the other two in its 

high content of siderite. It lies 500 feet south of the middle shoot, 

and is developed' from No. 10 level to its outcrop near the portal of 

No. 6 tunnel. This ore body ranges in length from 75 to 150 feetf 

and is about 20 inches wide. It consists of siderite and chalcopyrite 

intergrown with coarsely crystallized quartz in such proportions that 

the ore runs 26 per cent of iron and 4£ per cent of copper. Gold and 

silver averaging half an ounce and 3 ounces respectively are present. 

This ore body is a valuable asset to the mine because it combines a 

f air amount of the precious metals and copper with an excess of iron, 

an element which must be added in the smelting of ores from the other 

shoots.

Considerable ore was blocked out in the mine at the time of visit; 

and this was materially increased during the last year. Returns from 

the last smelter run were used to extend No. 7 tunnel beneath the 

north shoot and No. 10 tunnel beneath the middle shoot (fig. 4, p. 95).

UNDEVELOPED VEINS.

A description of the Lost Packer vein constitutes essentially a 

description of the known gold-copper deposits of the district. Other 

veins are recognized, but they are little developed and have produced 

only returns from test samples. Among these, the Effa ledge, which 

outcrops a few hundred feet west of the Lost Packer vein, is promising. 

The Sunset and South Packer groups also present some encouragement to the operators, although the small amount of development on 

them has not revealed commercial deposits.
LOON CREEK DISTRICT. 99

SILVER-LEAD DEPOSITS.

Silver-lead deposits have been found near the dolomite area south 

of Ivers. The Lost Eagle claim and the Metcalf group are the 

principal properties, but neither is sufficiently developed to afford 

a satisfactory idea of the nature or extent of this ore body. Their 

occurrence, however, is thought to be of special significance, and. 

therefore they will be described briefly. The Lost Eagle claim is 

situated on the divide between Canyon and Deer Creek cirques, at 

an elevation of 8,800 feet above sea. It is inclosed in Algonkian 

schist, though removed but a few hundred feet from an area of 

Paleozoic dolomitic limestones. Development consists of a shaft 

50 feet deep and a short drift from it. The vein, which strikes 

N. 5° W. and dips 85° SW., is about 6 feet wide and bordered by 

well-defined walls. Between them is crushed wall rock with bands 

and interstitial areas of argentiferous galena, pyrite, and a little 

chalcopyrite in a quartz-siderite gangue. (See PL VIII, A, p. 44.)

The Metcalf property, situated about 1,000 feet northeast of the 

Lost Eagle shaft, contains an irregular vein partly developed for 

about 100 feet along its outcrop. The deposit is a fissure filling 

inclosed in granite near its contact with Paleozoic dolomitic limestone. The ore consists of argentiferous galena, which fills the 

fissure almost exclusively and ranges in width from a narrow stringer 

inmost places to 3| feet in other places. The galena contains about 

1 ounce of silver to the unit of lead.

In each of the deposits just described the amount of ore actually 

found is not of so much significance as its geologic occurrence. Both 

deposits as now known are inclosed in rocks which are not nearly as 

favorable to the deposition of lead ore as is limestone, even when 

impure; hence, in the opinion of the writer, the area of dolomitic 

limestone adjacent to these deposits should be encouraging territory 

for the prospector. In the few places where time permitted an 

examination of the limestone area it was found to be rather intensely 

mineralized, as illustrated by the three iron mines which supply 

flux to the Ivers smelter, each of which is in a deposit of pyrite, 

now oxidized, which has replaced the dolomitic limestone.

AGE AND GENESIS.

The Loon Creek deposits crop out at elevations ranging from 

7,200 to more than 9,000 feet; the greatest elevation is essentially 

that of the present Eocene erosion surface. As the mineralogy of 

the deposits clearly indicates deposition at great depth, a depth 

probably exceeding 3,000 or 4,000 feet for the Lost Packer vein, 

where pyrrhotite occurs, it is evident that the veins were formed 

before the close of the Eocene epoch. On the other hand, the
100 ORE DEPOSITS IN OUSTER COUNTY, IDAHO.

v Metcalf deposit is inclosed in granite and the Lost Packer cuts across ( 

granite dikes; thus the deposits are postgranitic. If the granite 

caused or accompanied the elevation which resulted in the Eocene 

erosion surface, as brought out in another paper,1 it follows that the 

age of these ore deposits is limited to the late Cretaceous or early 

Eocene.

The genesis of the deposits is not susceptible of as satisfactory 

analysis. From broad considerations discussed on page 45, it is 

concluded that these deposits are genetically related to the quartz 

diorite intrusion. Just what part that intrusion played, however, 

is not clear. It is certain that two distinct types of ores were 

deposited, namely, gold-copper ores and silver-lead ores. Both 

occupy fissures, but the former are in schist and the latter not far 

removed from thick beds of dolomitic limestone, thus suggesting 

the possibility that the beds traversed by the solutions exercised 

some control on the nature of the deposits. But to accept this 

view it seems necessary to suppose that the metals either were 

derived in large part from the stratified rocks or that the different 

rocks precipitated different metals from the same magmatic solutions. 

The latter view seems more tenable, as if the intrusion served only to 

stimulate meteoric circulation, ore deposits should occur in connection with the later intrusions also. It is thought, therefore, that the 

Loon Creek ore deposits owe their origin to solutions given off from 

the quartz diorite magma during the later stages of its consolidation.

A study of the sequence in which the minerals were formed brings 

out some interesting facts in the deposition of the ores. In both the 

gold-copper and the silver-lead deposits siderite was the earliest 

mineral to form, followed by chalcopyrite and quartz in the former, 

and galena and quartz in the latter. Chalcopyrite, galena, and 

quartz replace the siderite, as shown by their protuberances and 

the thin films of them which follow fractures and cleavage planes 

in the siderite. This seems to indicate that in their early stages 

the solutions were highly charged with carbon dioxide, and that 

later the copper and lead-bearing compounds, possibly chlorides of 

these metals plus hydrogen sulphide, became of paramount importance in the solutions.

i Umpleby, J. B., An old erosion surface in eastern Idaho; its age and value in time determinations: 

Jour. Geology, vol. 20,1912, pp. 139-147.
INDEX.

A.

Page.

Access, means of................... 12,13,55,77,90

Acknowledgments to those aiding........... 11

Adularia, occurrence and character of........ 52

Algonkian rocks, correlation of.............. 18-19

distribution and character of............ 17-18,

30,58,78-79,91-92 

Andesites, analyses of....................... 26

distribution and character of............ 25-26

Animal life, nature of........................ 13-14

Antelope Creole, valley of.................... 16

Argentite, occurrence and character......... 52

Arsenopyrite, occurrence and character of... 52

view of.................................. 33

Azurite, occurrence and character of.......... 52

B.

Badger mine, description of.................. 86

Ballard, S. M., map of........................ 9

Barite, occurrence and character of........... 52

Batholiths, age of............................ 23,28

distribution and character of....... 17-18,21-22

Bay Horse, description of.................... 13

mines near............... 56,61,64,67,68,69,70

smelter at............................... 56

Bay Horse anticline, description of........... 19

Bay Horse Canyon, geology of................ 58

mines in........................... 56,64,65,70

views in and near........................ 12,20

Bay Horse district, access to................. 55

geology of............. 16,19-27,30,31,39,58-59

. historyof................................ 56

location of............................... 55

mines of................................. 64-77

mining conditions in.................... 57

ore deposits of......... 30,31,38,39,41,54,59-64

age and genesis of.................... 63-64

classification of...................... 59

description of........................ 59-63

See also Lead-silver; Silver-copper, 

production from......................... 56

topography of........................... 67-58

Beardsley mine, description of............... 68-69

discovery of............................. 56

geology near............................. 68

ores of....................... 39,40,59,61,68-69

view of............................. 44

production from......................... 60-69

Bell, R. N., work of.......................... 11

Bibliography of region....................... 11-12

Black mine, description of................... 86

Bonanza, description of...................... 13

gold placers near......................... 30

C.

Calamlne, occurrence and character of........ 52

Calcite, occurrence and character of........... 52

Cave mine, description of.................... 70,72

location of............................... 60,70

Cerargyrite, occurrence and character of...... 52

Page. 

Cerusite, occurrence and character of......... 52

Chalcocite, occurrence and character of....... 52

Chalcopyrite, occurrence of.................. 43,52

view of.................................. 44

Challis, description of........................ 12-13

geology near.......................... 16,26,27

Charles Dickens mine, description of......... 86-87

oresof.......................... 49,78,83,86-87

Cinnabar group, description of............... 76

ores of................................... 39

Clayton, description of....................... 13

geology near................. 20,21,22,30,31,58

mines near.............................. 39,56

smelter at............................... 56,57

Clayton anticline, description of............. 19

Cleavage, slaty, views of..................... 20,32

Climate, character of........................ 13

Copper-gold. See Gold-copper. 

Copper-silver. See Silver-copper. 

Cretaceous rocks, distribution and character

of............................ 21-23,79

Custer, geology near......................... 79,84

mines near............'............ 77,83,85,86

Custer Mountain, mines on.................. 81

D.

Daugherty mine, description of............. 76

ores of................................... 61,76

Deer Creek, deposits on..................... 54

Democrat Hill, mines on.............. 60,69,70,72

Democrat mine, location of.................. 60

Dickens Hill, mines on...................... 77,86

Dikes, age of................................ 24

distribution and character of......... 18,23-24

Diorite, distribution and character of........ 22

Diorite porphyry, dikes of................... 24

Dolomite, occurrence and character of....... 52

Drainage, description of..................... 14

E.

Effa vein, location of........................ 98

Eldridge, G. H., work of.................... 11

Ella group, description of................... 73

location of............................... 60,73

Enargite, occurrence and character of........ 52

Enterprise mine, description of.............. 86

geology near............................. 79,86

Eocene rocks, deposition of.................. 28

distribution and character of......... 21-24,79

Erosion, progress of......................... 28-29

Estes Mountain, geology at and near........ 80

mines on............................. 81,88,89

Excelsior mine, description of............... 68

discovery of............................. 56

geology near............................. 68

location of............................... 68

ores of............................. 39, 40,59,68

production from......................... 60,68

101
102 INDEX.

F.

Fairplay mine, description of................ 87

Field work, extent of........................ 9,11

Fluorite, occurrence and character of........ 52

Forest Rose mine, description of............ 72

location of............................... 60,72

ore of, view of........................... 44

G. 

Galena,- occurrence of........................ 40,53

views of................................. 44

Garden Creek, mines on..................... 76

General Custer mine, description of.......... 83-85

development of.......................... 77

geology near............................. 83-84

ore deposits and ores of... 48,77-78,82,83,84-85 

production from......................... 83

Geography, description of.................... 12-14

Geologic history, account of............... 17,28-29

Geology, account of......................... 17-29

outline of................................ 17-18

Gilmore, section at.......................... 20-21

Glacial deposits. See Pleistocene deposits.

Gold, occurrence and character of........... 53

Gold-copper deposits, age of................. 44-45

character of.................... 42-43,55,94-96

distribution of........................... 42

genesis of................................ 45

geologic relations of...................... 42

location of............................... 94

ores of...............'.............. 43-44,96-98

oxidation of.......................... 44,53-54

Golden Gate group, description of........... 89

Golden Sunbeam mine, description of....... 87-88

development of.......................... 77,87

ores of.................... 46,49,78,82-83,87-88

production from.....i................... 87

Gold placers, age of.......................... 51

character of........................ 50-51,89,94

distribution of........................ 50,89,94

gold of, source of......................... 51

production from...................... 50,89,94

Gold-silver veins, age of..................... 49

character of........................... 46-47,55

distribution of........................... 45

genesis of................................ 49-50

geologic relations of...................... 46

ores of................................... 47-48

oxidation of............................. 53

production from......................... 45

wall rocks of............................. 46,49

Granite, dikes of............................. 23-24

distribution and character of......... 21-22,45

Granite porphyry, dikes of.................. 24

Ground-water level, position of.............. 54

H.

Hematite, occurrence and character of....... 53

Historical geology, outline of................ 28-29

History, outline of........................... 14

History, geologic, outline of.................. 17

Hood mine, location of...................... 56

Hoosier group, description of................ 70

ores of................................ 41-42,70

I.

Intrusive rocks, age and correlation of....... 22-23

distribution and character of....... 17-18,21-22

Investigations, early, reports on............. 11

Ivers, description of.

Page. 

.................. 13

......... 23,24,30,31,45

ores near............................. 42,94,99

smelting at.............................. 90

J. 

Jennings, E. P., work of..................... 11

Jordan Creek, description of................. 27

geology on............................... 25

mines on................................ 87-89

placers of............................. 50,77,89

Julietta claim, description of................. 87

ores of................................... 82

K.

Kinnikinnick Canyon, geology in...... 21,22,58-59

mines in................................. 73

view of.................................. 15

L. 

Lake beds, age of............................ 27

distribution and character of............ 27

view of.................................. 15

Latites, analyses of.......................... 26

distribution and character of............ 25-26

Lavas, age of................................ 26-27

distribution and character of......... 18,24-26

Lead-silver deposits, age of........... 41,63,99-100

Character of........................... 39,60,99

distribution of.................. 38-39,59-60,99

genesis of...................... 41-42,62-63,100

geologic relations of................... 39,60,99

minerals of.............................. 40,61

ores of............................ 40-41,99-100

oxidation of.......................... 39-40,54

production from......................... 39, CO

Letha claim, description of.................. 87

Limonite, occurrence and character of....... 53

Literature,list of............................ 11-12

Livingston mine, description of.............. 76

geology at............................ 39,58,60

Location of area, map showing.............. 9,10

Loon Creek, character of..................... 14

placers of................................ 50-51

Loon Creek district, access to................ 90

geologic map of.......................... 92

geology of................ 21-22,25,28,30,91-93

history of................................ 90-91

location of ....................I........... 90

map of.................................. 90

mining conditions in.................... 90

ore deposits of........... 30,36,38,42,54,93-100

age and genesis of.................. 99-100

character of.......................... 93

See also Gold placers; Gold-copper;

Silver-lead, 

production from......................... 90-91

Loon Creek Summit, geology of.............. 80

Lost Eagle mine, description of.............. 99

geology at............................... 92,99

Lost Packer mine, development of........... 94

geology at and near................ 23-25,92-93

history of................................ 91

location of............................... 94

ore deposits and ores of............ 42-45,94-98

view of.............................. 44

plan and sections of...................... 95

smelter at............................... 91

view of.............................. 90
INDEX. 103

Page.

Lost Packer Mining Co., acknowledgments to 11 

Lucky Bay mine, description of............. 85-86

geology at............................... 85

ores of....................... 46,49,78,83,85-86

analysis of........................... 48

M.

McFadden group, description of............. 88-89

ores of................................ 82,88-89

McGregor group, claim sheet of.............. 71

mines of................................. 56

ores of, analyses of....................... 41

See also Hoosier group; Silver Brick

claim; Paci"c mine. 

Malachite, occurrence and character of....... 53

Map, index, showing location of area......... 10

Map, topographic and geologic, of area....... 9

of Loon Creek district................... 92

Metcalf mine, description of................. 99

Mineralization, period of..................... 29-30

Minerals, distribution of.................. 35,43,47

list and description of.................... 51^53

paragenesis of............................ 33-34

relative abundance of.............. 32-33,40,47

Mining, future of............................ 54-55

Mining districts, description of.............. 55-100

Minium, occurrence and character of......... 53

Miocene rocks, deposition of................. 28-29

distribution and character of.... 24-27,46,79-80

view of.................................. 15

Montana mine, description of................ 88

ores of............................. 48,78,82,88

Morainic material, distribution and character

of............................... 18,27

Morrison group, description of............... 87

N.

New Silver Bell mine, description of......... 72-73

geology near............................. 62,72

ore deposits and ores of.................. 72-73

See also Silver Bell.

O.

Ore deposits, age of.......... 29-30,63-64,83,99-100

character of...... 29,39-40,46-47,59,60-62,94-96

description of............................ 29-51

distribution of..................... 30,59-60,61

genesis of................... 33-34,63-64,83,100

geologic relations of. 30-31,32,39,42,46,60,61-62 

mineralization of, period of.............. 29-30

minerals of....................... 32-35,40-41,

44,47-48,51-53,61,62-63,96-97 

ores of, tenor of.......................... 29

oxidation of....................... 44,48,53-54

wall rock of........................ 46,49,82-83

See also Pre-Oligocene deposits; PostOligocene deposits. 

Ores, deposition of........................... 29

views of................................. 33,44

Ore shoots, occurrence of...... 32,40,43,47,81,97-98

Outwash, distribution and character of...... 28

Oxidation, extent of................... 44,48,53-54

P.

Pacific mine, description of.................. 69

dolomite at, analyses of.................. 69

location of............................... 60,69

ores of............................. 39,54,60,69

Paleozoic rocks, correlation of............... 20-21

distribution and character of............ 19

lithology of.............................. 19-20

slaty cleavage in, view of................ 20

structure of............................. 19

Passover mine, description of................ 87

Pay shoots, description of.... 32,40,43,47,81,97-98

Physiography, account of................... 14-16

development of.......................... 16-17

Placers. See Gold placers." 

Pleistocene deposits, distribution and character of................. 18,27-28,80,93

erosion of............................. 28,29,80

Pliocene time, events in..................... 29

Plutonic rocks, age and correlation of..... 22-23,28

distribution and character of............ 21-22

Post-Oligocene ore deposits. See Gold-silver

veins; Gold placers.

Poverty Flat, location and character of... 15,57,72 

mines on................................ 72

spur near, view of....................... 14

views on................................ 14

Pre-Oligocene deposits, classification of...... 31

See also Silver-copper; Lead-silver; Goldcopper. 

Prospecting, data for........................ 55

Pyrite, occurrence and character of.......... 53

Pyrolusite, occurrence and character of...... 53

Pyrrhotite, occurrence and character of...... 53

Quartz, occurrence and character of ......... 53

Quartz diorite, distribution and character of. 22 

Quartz monzonite, distribution and character

of............................... 22

Railroad Ridge, location and character of. ... 15

Ramshorn mine, description of .............. 64

discovery of .......................... 31, 56, 64

geology near. ...................... 32, 59, 62, 64

location of ............................... 61, 64

ore deposits and ores of. ........ 35, 59, 61, 64-65

analysis of. .......................... 34

view of .............................. 33

production from. ........................ 64

structure near, view of .................. 32

view of .................................. 32

Red Bird mine, claim sheet of ............... 74

description of ........................... 73-75

' geology at. ........................ 39, 60, 73-74

location of ...............................

ores of ................. 39, 40, 54, 59, 60, 61, 74-75

production from. ........................ 60, 73

Relief, data on ............................... 14

River View mine, description of ............. 67-68

discovery of ............................. 56, 67

geology near. ............................ 67

location of ............................... 60

ores of ............................. 39, 54, 59, 67

Roads, courses of ......................... 13, 55, 77

S. 

Salmon, geology near. ....................... 25

Salmon River, canyon of, view in ........... 12

description of ........................... 14, 58

geology on ........................... 18-22, 27

terraces on, view of ...................... 20

valley of ................................ 16
104 INDEX.

Saturday group, description of.............. 75

Scope of report.............................. 9

Settlements, description of.................. 12-13

Siderite, occurrence and character of......... 53,62

view of.................................. 33

Silver, occurrence and character of........... 53

Silver Bell mine, discovery of............... 31

geology near............................. 32

location of............................... 61

ores of................................ 54,59,61

Silver Brick claim, description of............ 70

Silver-copper deposits, age of............. 35-38,63

character of........................ 32,55,62-63

distribution of........................ 31-32,61

genesis of.......................... 37-38,62-63

geologic relations of................... 32,61-62

mines on................................ 31

ores of............................. 32-38,62-63

oxidation of............................. 54

production from......................... 32

Silver-lead. See Lead-silver.

Skylark mine, description of................. '65-67

discovery of.............. 1.............. 31,65

geology near.......................... 32,62,66

location of......................... 56,61,64-65

ore deposits and ores of......... 32,59,61,66-67

production from......................... 66

structure near, view of.................. 32

view of.................................. 32

Slate Creek, mines on....................... 76

Smithsonite, occurrence and character of..... 53

South Butte mine, description of............ 76

location of...........'.................... 60,76

South Packer group, location of............. 98

Sphalerite, occurrence and character of...... 53

Squaw Creek, mines on................ 56,73,75,76

Stage routes, account of..................... 12

Summit areas, description of................ 15

rocks of................................. 15

Page. 

Sunbeam, geology near...................... 30,79

ore deposits at........................... 81

Sunset group, location of.................... 98

T.

Tetrahedrite, analyses of.................... 34

composition of........................... 34-35

occurrence of................ 32,34,3 7,53,62-63

view of.................................. 33

Tuffs, age of................................. 26-27

distribution and character of............. 24-26

V. 

Valleys, character of......................... 15-16

Volcanic rocks, age of.................. 26-27,28-29

analyses of.............................. 26

distribution and character of...... 24-26,79-80

W.

Wad, occurrence and character of............ 53

Wall rocks, alteration of............... 46,49,82-83

Wells, R. C., on formation of tetrahedrite.... 37-38

Y.

Yankee Fork, description of................. 27,78

gravels on............................... 80

places on.......................... 50-51,77,89

production of........................ 89

ore deposits of..................... 30,54,.80-83

age and genesis of................... 83

Yankee Fork district, access to.............. 77

geology of.......... 18,21,23,25,28,30-31,78-80

history of................................ 77

location of............................... 76-77

mines and prospects of.................. 83-89

ores of................................... 81-82

production from......................... 77-78

topography of........................... 78

wall rocks of............................. 82-83

o