Please do not destroy or throw away this publication. If you have no further use 

for it write to the Geological Survey at Washington and ask for a frank to return it

UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 847 D ''"ED.

PHOSPHATE ROCK NEAR MAXVILLE 

PHILIPSBURG, AND AVON

MONTANA

BY

J. T. PARDEE

Contributions to economic geology, 1934-36 

(Pages 175-188)

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1936

For sale by the Superintendent of Documents, Washington, D. C. ------ Price 20 cents
CONTENTS

Page

Abstract. _----___--_--__-----_--_--_-____________________________ 175

Introduction__ __________________________________________________ 175

Production- _-_-_-----^______-___--_____--_______-________________ 176

Markets._________________---_--____---__-__-__-_-_--__--___.__ 177

Surface features_____________^-___________________________________ 177

Rocks. __----_---_-----_.__-___--_--___-_-_---_-_---_-________._ 177

Structure. _____________________________-._._.______ 180

F-)lds__-__---____--_-_-------------------___--______-_-_____- 180

Faults. _______-_.___-------_-___._______________ 182

Phosphate rock___________________________________________________ 183

Occurrence.----__--____--_-_----_-_-__---___-------_--_______ 183

Composition. ___________-----___---____----___-____.___-_____. 184

Beneficiation _________________________________________________ 185

Reserves.___--__________--_____----___--______-_____---______ 186

Development workings___--_____-__-___-._____________.___.__ 187

ILLUSTRATIONS

Page 

PLATE 28. Geologic map of Maxville phosphate area, Montana__ _ In pocket

29. Geologic map of Philipsburg phosphate area, Montana. __ In pocket

30. Structure sections and profiles, Maxville area._-___----- In pocket

31. Structure sections and profile, Philipsburg area___-___-__ In pocket

32. Geologic map and structure sections of area near Avon,

Mont_____-____-__---_-__-_-_-__-____-.__-_-_ In pocket

33. Plan and section along tunnel of Washington Phosphate

& Silver Co., Maxville, Mont_-_______________ 188

34. Columnar sections of phosphate and associated beds near

Maxville, Philipsburg, and Avon, Mont___________.. 188

FIGURE 56. Index map showing location of phosphate areas near

Maxville, Philipsburg, and Avon, Mont__________ 176

n
PHOSPHATE ROCK NEAR MAXVILLE, PHILIPSBURG, AND

AVON, MONTANA

Bv J. T. PABDEB ' * *- hi.

ABSTRACT

This paper gives the results of a resurvey of certain areas in Montana to which 

renewed interest has been directed by the development recently of a market for 

crude phosphate rock in British Columbia, nearby.

The phosphate rock occurs in these areas as layers distributed through a 

stratum 12 to 16 feet thick in the lower part of the Permian Phosphoria formation. 

The neighboring sedimentary rocks are chiefly shale, sandstone, and limestone 

that range in age from pre-Cambrian to Cretaceous. The formations are involved 

in a series of tightly squeezed folds and are displaced by an overthrust and by 

faults of normal type. The folding has caused the phosphate bed to be steeply 

inclined and to rise to the surface along the sides of several anticlines.

In most places a closely spaced group of the phosphate layers form a workable 

bed 3 feet or more thick that averages about 70 percent of tricalcium phosphate, 

or "bone phosphate of lime." In general the phosphate rock contains a small 

amount of organic matter, and in one place a residue of 2 percent of carbon dust 

and traces of vanadium, tin, and boron are present.

The topography is favorable to mining through adits, and parts of the 3-foot 

phosphate bed thus accessible are calculated from profiles and cross sections to 

contain 18,650,000 tons near Maxville, 8,000,000 tons near Philipsburg, and 

,600,000 tons near Avon.

INTRODUCTION

This paper is based chiefly upon a resurvey of areas near Maxville 

and Philipsburg, Mont., described in previous reports. 1 In addition 

it covers a small area northwest of Avon adjoining the Garrison area. 

(See fig. 56.)

Since the reports cited were published additional exposures of the 

phosphate bed have been made by mine workings, and interest in the 

phosphate deposits of the general region has been greatly increased 

by the shipment, in 1930-32, of large amounts of the phosphate rock 

from a point near Garrison to the smelter of the Consolidated Mining 

& Smelting Co. of Canada at Trail, British Columbia, for use in the 

manufacture of fertilizer.

i Pardee, J. T., The Garrison and Philipsburg phosphate fields, Mont.: U. S. Oeol. Survey Bull. 640, 

pp. 195-228, 1917; Phosphate rock near Maxville, Granite County, Mont.: U. S. Geol. Survey Bull. 715, 

pp. 141-145, 1921.

175
176 PHOSPHATE ROCK IN MONTANA

The area near Maxville was resurveyed during parts of the summers 

of 1932 and 1933. In this work the writer received much valuable 

assistance from the Northwest Development Co. in setting triangulation monuments and from Omer Edgar and Glenn C. Reed as rodmen. The areas near Philipsburg and Avon were examined respectively in 1924 and 1931, chiefly to obtain information needed in the 

administration of the public lands.

FIGURE 56. Index map showing location of phosphate areas near Maxville, Philipsburg, and Avon, Mont.

PRODUCTION

The reported production of phosphate rock in Montana in 1929-321 

amounted to 94,028 long tons, worth at the mine more than $400,000,, 

as follows:

Production of phosphate rock in Montana, 1929-32 l

Year

1929-.. ......... -.. .......... .-_-.-.........-..._-...

1930. _ ............ _ ..-.. _-..-.-._-...._._._..___....

1931........... ................ ...... .... ...........-...

1932.. ......... ......... -. -.. .-.-.- .-....-_____.

Long tons

40 

6,005 

67,893 

20,090

Value at mine

Total

$400 

27,457 

301, 511 

79, 271

Per long ton

$10.00* 

4.57 

4.44 

3.9&

i U. 8. Bur. Mines, Minerals Yearbook, 1932-33, statistical appendix, p. 26,1933.

The great bulk of this production came from the mine operated by 

the Montana Phosphate Products Co. and its successor, William 

Anderson, on East Brock Creek near Garrison, in an area described 

in Bulletin 640. Shipments from the particular areas covered by 

this paper include 2 cars from the mine of C. A. Graveley, near Avon; 

10 cars from the Northwestern Improvement Co.'s mine, on Douglas.
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36 177

Creek, near Maxville; and several cars from the mines of Omer Edgar 

and the'Washington Phosphate & Silver Co., near Maxville, and of 

Dissett Bros., at Philipsburg.

MARKETS ^^V-V/ r ' 'Ji 'Rft

Most of the crude phosphate rock mined in this region to date 

has been shipped to the smelter at Trail, British Columbia. Some 

comparatively small lots have gone to the Anaconda Copper Co.'s 

fertilizer plant at Anaconda, Mont., and to dealers or agents at Seattle 

or other shipping points who were seeking to establish markets in 

Australia and Japan.

Sample lots of finely ground "raw rock" produced at the Washington & Montana Phosphate Co.'s mill at Maxville and the fine 

concentrate from a test run on rock from Dissett Bros.' mine at 

Philipsburg have been sent to points in the agricultural areas of 

eastern Washington for trial as fertilizer. What measure of success 

has attended these attempts to develop new markets was not learned.

During 1933 mining and development work practically ceased. 

The return of activity on an increasing scale is expected with general 

industrial recovery.

SURFACE FEATURES

-The areas here considered are characterized by rather marked 

relief, a condition that is favorable to the development and mining of 

the phosphate bed through adit levels. In the Maxville area Boulder, 

 Gird, and Douglas Creeks and at Philipsburg the stream in Stewart 

Gulch have cut deep valleys that cross repeated outcrops of the 

phosphate bed. Intervening ridges carry the phosphate outcrops 

from 500 to 1,500 feet above the drainage levels of these streams.

The same valleys afford down-grade roadways from the deposits 

to the Drummond and Philipsburg branch of the Northern Pacific 

Railway. From the mine-entry sites the distance to the railroad 

along these valleys ranges from 2 to 8 or 9 miles, but from most of

them it is less than 6 miles.

ROCKS

The rocks that underlie the areas described include shale, sandstone, limestone, and related sedimentary beds that range in age from 

pre-Cambrian to Cretaceous, and sedimentary and igneous rocks of 

later ag6 that rest upon or intrude them. (See pis. 28, 29, 32.) 

Summary descriptions of these rocks are given in the reports cited, 

and most of them are described in detail by Calkins,2 from whose 

report the following tabular description is condensed.

' Emmons, W. H., and Calkins, F. C., Geology and ore deposits of the Philipsburg quadrangle, Mont.: 

U. S. Qeol. Survey Prof. Paper 78, pp. 35-81,1913. Calkins, F. C., and Emmons, W. H. U. S. Qeol. Survey Qeol. Atlas, Philipsburg folio (no. 196), 1914.
178 PHOSPHATE ROCK IN MONTANA

Generalized section of pre-Tertiary sedimentary rocks in the Flint Creek Range, Mont.

Geologic 

age

Upper Cretaceous

&3 cs OT

£ 8 o

3oS

Jurassic

Carboniferous -

6 a

t§Qfl

pJ3 .

o3

Cambrian

Algonkian

Colorado

Permian?

Pennsylvanian?

Missis- sippian

<D

l|gs« s

'S

«

Formation

Kootenai formation

Ellis formation

Phosphoria formation

Quadrant quartzite

Madison limestone

JeflEerson lime stone

l§gl S*£~

|| ^M^+J ii

J§ii «e$*

Mg S w .|s

.i'C.S

£SS3 **&

Character

Chiefly gray to olive sandstone; some beds of dark-gray to green shale. 

Top removed by erosion.

Fissile black shale.

Red and green shales and flaggy sandstones. Pebbly bed at bottom. 

Several thin bands of limestone. Those in lower portion weather 

buff. The uppermost is crowded with small fresh-water gastropods.

Chiefly gray to green shale and sandstone. Bufl or yellow on weathered 

surface. Thin beds of limestone in lower part contain marine Jurassic fossils.

Gray, somewhat cherty quartzite; weathers rusty brown. A little 

shale interbedded.

\

Chiefly gray cherty limestone. Marine Pennsylvanian or Permian 

fossils. A bed of rock phosphate in lower part. ' '

Massive fine-grained quartzite, white to pale drab, stained yellowish 

brown.

Maroon shale, commonly mottled, and gray to pink magnesian limestone.

Limestone, massive, white to pale gray in upper part; lower part thinbedded, flaggy, black, weathering light blue; fossiliferous.

Light-gray to black magnosian limestone; fossiliferous.

Magnesian reddish, gray, and whitish limestone and gray and green 

shale.

Laminated siliceous white to drab and purple limestone and black to 

olive-green calcareous shale.

Magnesian white to blue-gray limestone and calcareous shale.

Brown, white, and green banded calcareous shale, siliceous laminated 

limestone, and dark-green shale.

Vitreous gray to drab quartzite.

Shale and sandstone, chiefly red.

Thin-bedded siliceous and ferruginous limestone and shale, generally 

buff on weathered surface. (The underlying formations exposed in 

other parts of the Philipsburg quadrangle are not present in the Flint 

Creek Range.)

Thickness 

(feet)

1,000+

500 

1,500

430 .

120

90

220-350 -

100-300

1,200-1,500 '

1,000 .

200-300

300

1,000

330db

150

5,000

4,000=t
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36 179

,The phosphate rock occurs within the older group, where it is 

associated with beds of shale, sandstone, arid other sediments composing the Phosphoria formation.

Several layers of phosphate rock and phosphatic clay or shale 

together make up a phosphatic stratum which is .generally from .12 .to 

15 feet thick. This stratum is comparatively soft and nonresistant 

to weathering, and its outcrop is therefore .generally concealed by a 

surface mantle. As a rule, however, its position can be determined 

within a few feet by reference to certain neighboring beds that crop 

out prominently. Of these=the nearest and most useful is the quartz-, 

ite member of the Quadrant formation, a bed 100 feet or more thick 

of hard fine-grained dense rock that appears light gray on fresh fracture and light reddish brown on weathered surfaces. Its outcrops 

are cliffy or wall-like and generally prominent enough to be seen from 

a distance. In most places the phosphatic stratum lies less than 100 

feet stratigraphically above the quartzite. Northwest of Avon the 

two are separated by only about 20 feet of cherty-appearing rock. At 

an open cut on the south side of Douglas Mountain 40 feet of hard 

gray limestone containing thin bands of chert separates them. North 

of Gird Creek in sec. 7, T. 8 N., R. 12 W. (pi. 28), the phosphate is 

nearly 100 feet above a prominently outcropping bed of the quartzite, 

and the intervening space is occupied by about 30 feet of cherty limestone and 70 feet of limy sandstone, named in descending order. On 

Flagstaff Hill, at Philipsburg (pi. 29), the phosphatic stratum is about 

30 feet thick and about 100 feet above the main quartzite bed, and 

part of the intervening space is occupied by cherty limestone. On the 

upper side of the phosphatic stratum are three beds that generally crop 

out prominently enough to form useful reference planes. The nearest 

of these is a bed of extremely fine grained cherty-appearing light- to 

dark-gray quartzite or sandstone, without the slight reddish tint 

generally shown by the quartzite of the Quadrant formation. In 

places its outcrop shows small cavities due apparently to the solution 

of lime. This bed probably the equivalent of the Rex chert member 

of the Phosphoria formation ranges from 150 to 200 feet in thickness. 

In the Maxville area (pi. 28) the more prominently exposed part is 40 

or 50 feet above, the phosphatic stratum, and on Flagstaff Hill from 

30 to 40 feet above. In both areas soft shaly beds intervene.

The next higher prominent stratum is a thick bed of sandstone 

belonging to the Ellis formation, which in the Maxville area crops 

out from 360 to 400 feet above the phosphate. It is light gray and 

speckled with grains of black chert.

About 2,000 feet above the phosphate a bed of limestone in the 

Kootenai formation is crowded with small snail-like fossil shells 

(gastropods). It forms very persistent light-colored reefs.
180 PHOSPHATE ROCK IN MONTANA

The Tertiary "lake beds" and later alluvial deposits bear no 

relation to the phosphatic stratum and its related rocks except to 

conceal their outcrops in places. At Philipsburg they form a thick 

cover over the phosphate outcrop between Red Hill and Flagstaif 

Hill (p. 29). In the Maxville area and near Avon they do not 

overlap the outcrops sufficiently to make the position of the phosphatic beds uncertain.

The intrusive granitic bodies came to place later than the phosphatic stratum and its enclosing rocks and evidently have displaced 

or engulfed large parts of them east of Philipsburg and southeast of 

the Maxville area. The diorite sills east of the Maxville area are, so 

far as exposed, not in contact with the phosphate.

STRUCTURE

In the Maxville and Philipsburg areas the phosphatic stratum and 

its enclosing rocks are involved in a series of rather tightly squeezed 

folds and are broken and displaced by a great overthrust and by large 

faults of normal type. The folds and normal faults trend northward, 

and the axes of the folds persistently descend in the same direction.. 

The beds have been overthrust eastward. A group of small faults 

superimposed on the structural- features mentioned strike northwest. 

The folding has caused the beds to be steeply inclined and the phosphatic layer to rise to the surface on the sides of several anticlines. 

The overthrusting has buried the phosphate in places along the west.

FOLDS

Four of the larger folds in the Maxville area are described in a former 

report 3 the Dunkleberg Ridge, Royal, Douglas Mountain, and 

Princeton anticlines, named from east to west. Of these no further 

information is available for the Dunkleberg Ridge and Royal anticlines or for the other two south of Princeton Gulch.

From Princeton Gulch north the Douglas Mountain anticline is 

exposed for a distance of 10 miles, beyond which it is concealed by 

Tertiary and later sediments. Along the axis of this fold Madison 

limestone is exposed as far as Douglas Mountain. Beyond, as a 

result of the northward dip of the axis, the Madison is succeeded in 

order by younger beds. The phosphate bed crops out on both sides 

of this fold as far as the northern part of sec. 30, T. 9 N., R. 12 W. 

(pis. 28, 30), the western outcrop being a repetition due to one of the 

larger normal faults.

The Princeton anticline can be traced from Princeton Gulch northward 6 or 7 miles to Douglas Creek, where it likewise disappears 

beneath the Tertiary deposits. At the extreme south end this fold 

brings Jefferson limestone to the surface. The northward dip of its

»Pardee. J. T.. op. cit. (Bull. 715), pp. 142-143.
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36 181

axis, somewhat steeper than that of the Douglas Mountain anticline, 

limits the northward exposure of the phosphate bed at a point in sec. 

36, T. 9 N., R. 13 W., on the ridge between Gird Creek and Douglas 

Creek (pis. 28, 30). The west branch of the Princeton anticline 

joins that fold at the south. Part of its east side is exposed east of 

Gird Creek in sees. 2 and 11, T. 8.N., R. 13 W., and a ledge of Quadrant quartzite west of that stream marks its west side. To the north 

it is buried by overthrust masses and areas of Tertiary and later 

sediments.

East of the Douglas Mountain anticline a broad syncline carries 

the phosphate bed to a depth of several thousand feet. Between 

the Douglas Mountain and Princeton anticlines is a relatively narrow 

and tightly squeezed syncline, and between the branches of the 

Princeton anticline a more open one. All the synclines deepen toward 

the north and become shallower toward the south. The two last 

mentioned terminate at Princeton Gulch and Gird Creek respectively.

In the Philipsburg area (pis. 29, 31) the principal fold is a rather 

broad, flat arch called the "Philipsburg anticline" by Calkins.4 

Southeast of Philipsburg it is cut off by intrusive granite. From that 

point it extends to Wyman Gulch, a distance of 5 or 6 miles, along a 

course that curves from northwest to northeast. Its axis dips 20° 

or more northward, and rocks ranging from Belt (pre-Cambrian) to 

Kootenai (Cretaceous) are exposed in order along its crest. The 

phosphate crops out on the west side of this fold for 2 miles or more, 

beginning at a point about a mile north of Philipsburg. Thence, on 

the north side of Stewart Mountain, it curves around the plunging 

arch and returns southward a short distance.

West of the Philipsburg anticline another fold, the Red Hill anticline, begins in Red Hill, and extends north 2 miles to a fault. It is 

tightly squeezed, broken with faults, and overturned eastward. In 

places at least the phosphate bed appears on both sides of it.

Between these two anticlines is the Wyman Gulch syncline. This 

fold begins in the southern part of Red Hill and extends northward 

and northeastward. Beyond Stewart Gulch it deepens rapidly and 

widens to surround the north end of the Philipsburg anticline. A few 

miles farther north it is buried by overthrust masses from the west. 

The west side is overturned eastward and broken by the Bungalow 

thrust (p. 182). It carries the phosphate outcrop, at least in places.

In the area northwest of Avon the phosphate and its enclosing 

rocks are deformed by the northeast limb of the Garrison anticline 5 

and by an adjoining syncline and the succeeding limb of an anticline 

(pi. 32). In addition a small fold in the western part of the area 

rises across the axis of the Garrison anticline. The phosphate bed

< Calkins, F. C., op. cit. (Prof. Paper 78), p. 143. 

 Pardee, J. T., op. cit. (Bull. 640), p. 213.

34643 36 2
182 PHOSPHATE KOCK IN MONTANA

is carried to a considerable depth by the syncline mentioned and raised 

to the surface by both of the adjoining anticlines.

FAULTS

The most impressive structural .feature of the region that 'includes 

the Maxville and Philipsburg areas is a fault on which the overlying 

mass has moved eastward for a distance of several miles. This fault, 

which may be referred to as the Philipsburg overthrust, is .mapped 

within the Philipsburg quadrangle and described by Calkins.6 After 

the overthrust mass had come to place it was further deformed by 

folding and faulting, partly engulfed or displaced by intrusive granite, 

and largely removed by erosion. As a result the thrust plane shows 

variations in dip, dislocations, and interruptions, and its trace or 

intersection with the present surface is a correspondingly irregular 

and broken line (pis. 28, 29).

The overthrust mass is composed chiefly of Belt sandstone and shale 

but includes younger rocks along its eastern border (pis. 28, 30). 

It was deformed along an axis extending from Philipsburg northnortheastward to Maxville by arching and by the Bungalow upthrust. 

To the east, along South Boulder Creek, it was also depressed by a 

downfold and a normal fault. The elevated portion has been largely 

removed by erosion, and the underlying rocks are thus exposed as 

through a window. In the depressed area .the overthrust rocks still 

remain.

Outlying bodies detached from the main overthrust mass by faulting and erosion occur on the slope northeast of Gird Creek in sec. 

36, T. 9 N., R. 13 W., and on top of Eyebrow Hill, in sec. 25, south 

of Douglas Creek. In .most places there is rather close agreement in 

strike and dip between the rocks above, and below the thrust plane,

but in Eyebrow Hill an anticline formed of Madison and Quadrant 

beds is superimposed on a syncline in Cretaceous formations.

A fault shown in the tunnel of the Washington Phosphate & Silver 

CQ. just east of Maxville (pis. 28, 30, 33) forms the boundary of the 

"window" previously mentioned. This fault dips 50°-60° W., and 

the movement on it was an upthrust of the hanging wall, causing 

the rocks that had been overridden to lie once more above those overthrust. To the north across Boulder Creek a tunnel of the Fields 

mine, which was accessible in 1916, penetrates the same fault. A 

house nearby called "The Bungalow" stands above the fault line and 

affords a convenient name for it.

North of the Fields tunnel the Bungalow fault is concealed by later 

sediments, but the dissimilar strikes of two neighboring rock outcrops beyond Gird Creek suggest that it passes between them. 

Southward the fault has not been definitely traced, but a reverse

o. Calkins, V. C., U. S. Oeol. Survey Prof. Paper 78, pp. 146-148,1913; Folio 196,1915.
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36 183

fault mapped near the head of Wyman Gulch (pi. 29) is suggestively 

in line with it. That intense compression attended the faulting 

is shown by a breccia iOO feet thick (pi. 33).

In the Maxville area several strike faults of normal type cut both 

the overthrust mass and the underlying rocks. Some of them are 

10 miles or more long and cause displacements of 3,000 feet or more. 

One along the west side of the Douglas Mountain anticline repeats 

the outcrop of the phosphate bed for several miles. At a few places 

in the Maxville and Philipsburg areas small faults that strike northwest cut/across those described.

At the Graveley mine, northwest of Avon, a fault that strikes northwest separates the phosphate bed and its enclosing rocks from an 

area of extrusive rocks on the northeast that forms the downthrown 

block (pi. 32). To the southwest across Gimlet Creek the phosphate 

outcrop is jogged by several normal faults transverse to the axis of the 

Garrison anticline.

PHOSPHATE ROCK

OCCURRENCE

The phosphate rock is a sedimentary deposit that occurs like coal, as 

beds enclosed between layers of other sediments. In this region 

the known phosphate beds are found only in the lower part of the 

Phosphoria formation, where together with several layers of phosphatic clay or shale they form a phosphatic stratum that ranges in 

thickness from 9 to 12 feet near Maxville and is 15 or 16 feet 

thick at Princeton Gulch and, Philipsburg (pi. 34, sections A to L).

Individual layers of the phosphate rock range from an inch to a 

foot or two in thickness and number 5 to 7 or more. Near Maxville 

their aggregate thickness is about 4 feet, at Philipsburg 5 feet, and at 

Princeton Gulch 6 feet. They are distributed throughout the phosphatic stratum but occur mostly at the top, where they form a closely 

spaced group that is generally 3 feet or a little more in thickness. 

This upper group is therefore the most valuable part of the:phosphatic 

stratum, and its members are referred to collectively as the "main 

phosphate bed."

The deformation described above has caused the phosphate bed in 

most places to be steeply inclined (pis. 30, 32). It is carried to the 

surface by several of the anticlines and lowered to considerable depths 

in some of the synclines. The overthrust masses doubtless bury parts 

of it west of the Maxville and Philipsburg areas. The phosphate 

outcrop is repeated by faulting along the west side of the Douglas 

Mountain anticline, but most of the other strike faults displace the 

deposit underground (pi. 30). In addition, slight displacements by 

the northwest faults may be observed at several places. At the Fields 

tunnel and the mine of the Washington Phosphate & Silver Co. the
184 PHOSPHATE ROCK IN MONTANA

Bungalow fault has crushed the phosphatic stratum and its adjoining 

bed to a formless breccia (pi. 33).

Since the deformation described was accomplished, much of the 

elevated part of the phosphate bed has been cut away by erosion. 

The bulk of the remainder is therefore present in the synclines and 

sides of the anticlines.

COMPOSITION

The amount of phosphatic material in the phosphate rock as determined by analysis is usually reported as tricalcium phosphate 

(Ca3 (P04 ) 2 ), commonly known as "bone phosphate of lime" or 

"b. p. 1." In the Maxville area, as shown in sections A to G, plate 

34, samples of the phosphate rock range in b. p. 1. content from 67.05 

to 73.27 percent and average slightly more than 70 percent. In 

collecting these samples certain narrow clay or shale seams were 

rejected, as indicated in plate 34. Inclusion of them may give a 

result 10 percent lower, as shown by samples from the Edgar tunnel 

(pi. 34, F). Samples of the beds designated "phosphatic clay" 

(pi. 34, A, B, I, L) contain somewhat less than half as much b. p. 1. as 

the phosphate rock. Layers of the material called "phosphatic 

chert" are visibly high in silica and low in phosphate. No analyses 

of them are available. In the Philipsburg area the samples indicate 

a somewhat lower average. In addition to those given in plate 34 a 

sample from a 3-foot layer 100 feet west of the New Hope shaft showed 

69.68 percent of b. p. 1. and one from a 3-foot layer at the face of the 

100-foot tunnel on Flagstaff Hill 63.35 percent.

The chief impurities in the phosphate rock are clay and silica. 

The silica occurs mostly in the form of fine-grained cherty-appearing quartz. Determinations of iron and alumina have not been made 

in the Maxville area, but samples from Philipsburg (pi. 34) show from 

3 to 5 percent of those substances together, the clay-free samples 

containing the smallest amount.

In general when struck with a hammer the phosphate rock emits a 

fetid odor due to the presence of a little organic matter.

In the mine of the Washington Phosphate & Silver Co., east of 

Maxville, sheared and crushed phosphate rock occurring in the 

Bungalow fault breccia is coal-black. A sample of pulp made from 

it in the company's mill contained 34.03 percent of b. p. 1. Examination of specimens in the laboratory of the United States Geological 

Survey shows that the black color is due to the presence of 2 percent 

or more of carbon dust. Some of the specimens are cut by veinlets 

of calcite and very thin seams of a white mineral that is probably 

gypsum. Some contain seams of a soft black vitreous mineral that, 

when.heated in a test tube, yields no evidence of volatile organic 

matter except a faint odor but burns slowly in the presence of oxygen, 

leaving a small amount of ash. Apparentlv no hydrocarbons are
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36 185

'now present as such, but the fixed carbon and the black vitreous 

mineral were probably derived from such compounds or from other 

organic matter by the heat generated during the folding and faulting. 

In places the cleavage planes in the sheared rock are coated with 

thin greenish films that contain vanadium. Several tests of the same 

material failed to show any uranium. A spectroscopic test by 

George Steiger, however, detected traces (0.02 percent or more), of 

tin and boron but no gold, tungsten, tantalum, cadmium, germanium, 

or beryllium.

In the Philipsburg area the b. p. 1. content of samples ranges from 

45 to 64 percent and averages about 55 percent (pi. 34, I, K, L). A 

sample of material in the ore bin at the Dissett mine from which most 

of the clay had separated during handling contained 64.05 percent 

of b. p. 1. and 3.01 percent of iron and alumina.

The highest grade of the phosphate rock so far reported from the 

areas here considered occurs in the mine of C. A. Graveley, northwest 

of Avon. A recent shipment of 100 tons from this mine averaged 

76.4 percent of b. p. L, and a sample of a 3%-foot layer in the face of 

the tunnel contained 79.06 percent.

In neighboring areas phosphate rock containing 80 percent or 

more of b. p. 1. is reported at the mine of the Northwestern Improvement Co. near Elliston, and more than 67,000 tons shipped from the 

Anderson mine, northwest of Garrison, in 1931 averaged 69.8 percent.

BENEFICIATION

The analyses of mine and ore bin samples from the Dissett mine 

(pi. 34, I) show that the mere handling of the phosphate rock tends 

to enrich it by shaking out some of the clay not separated in mining. 

At the Edgar mine a sample from which the clay seams were excluded 

was 10 percent richer than one which included them. These facts 

suggest that the "run of mine" product might be materially improved 

either by coarse-crushing and dry screening or by washing.

A wet gravity-concentration test was made by the operators of the 

Dissett mine in 1931 on the material classified as phosphatic clay 

(pi. 34, I). After fine grinding the material was washed in a crude 

launder that had been originally designed to concentrate sulphides 

and gold from quartzose ores. The result reported was a concentration of 2 into 1, the crude material containing about 40 percent of 

b. p. 1. and the concentrate 65 percent. The results obtained by 

investigators of the United States Bureau of Mines 7 by wet-concentration methods on Florida phosphatic sands were somewhat better. 

Recently a still higher concentration was obtained by flotation.8 These

7 Lawrence, H. M., and O'Meara, R. G., Gravity concentration on certain Florida phosphatic sands: 

U. S. Bur. Mines Kept. Inv. 3018,1930.

8 Lawrence, H. M., and Roca, E., Flotation of low-grade phosphate ores II: U. S. Bur. Mines Kept. 

Inv. 3105, 1931.
186 PHOSPHATE ROCK IN MONTANA

results are mentioned to show that much of the material in the phosphatic stratum outside the main phosphate bed may, when the market 

demands, prove to be workable.

RESERVES

The most1 easily workable and consequently the most valuable 

parts of the phosphate bed are those that lie above existing drainage 

levels. The topography in many places permits the deposit to be 

opened by adit levels or crosscuts projected from easily accessible 

locations. In general, the bed is inclined sufficiently to be mined by 

overhead or gravity stoping.

Within the areas here considered the phosphate bed, where not 

badly disturbed by faulting, shows no great variations in thickness. 

It is believed that an average of at least 3 feet can be safely counted 

on. With that figure and the aid of the accompanying cross sections 

and profiles (pis. 30-32), which are drawn to scale, the amounts 

available in any particular block can be calculated approximately. 

For an example may be taken the block that lies above an adit level 

supposed to be driven 5,000 feet north from Douglas Creek, the site 

of the Northwest Improvement Co.'s tunnel 3, on the bed that crops 

out on the east side of the Douglas Mountain anticline. From sections B-B' and C-C' and profile V-V, plate 30, it appears that the 

slope height of the bed above the adit ranges from 0 to 850 feet and 

averages 450 feet. Therefore the area of this block is 2,250,000 

square feet, and its content of phosphate, if the bed is 3 feet thick, 

is 6,750,000 cubic feet. As 13 cubic feet of phosphate in place is 

equivalent to 1 ton of 2,240 pounds, the amount is, in round figures, 

500,000 tons. In a similar manner the following amounts may be 

calculated:

Estimates of phosphate rock above possible entries driven at natural drainage levels

Maxville area

Long tons

East limb of Douglas Mountain anticline from sec. 30, 

T. 9 N., R. 12 W., south to Princeton Gulch, in sec. 

20, T. 8 N., R. 12 W. Outcrop 3 (pi. 30, profile 

V-V, cross sections A-A' to F-F')-~ -------- 4,350,000

West limb of Douglas Mountain anticline from sec. 30,. 

T. 9 N., R. 12 W., south to Princeton Gulch, in sec. 

19, T. 8 N., R. 12 W. Outcrop 2 (pi. 30, profile 

W-W, cross sections A-A' to F-F')__. _ . ___ 4, 000, 000

West limb of Douglas Mountain anticline from sec. 31, 

T. 9 N., R. 12 W., south to Princeton Gulch, in sec. 

19, T. 8 N., R. 12 W. Outcrop 1 (pi. 30, profile 

X-X', cross sections B-B' to F-F')______________ 3, 850, 000

East limb of Princeton anticline from sec. 36, T. 9 N., 

R. 13 W., south to slope north of Princeton Gulch 

(pi. 30, profile Y-Y', cross sections B-B' to F-F')- 3, 350, 000
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1934-36 187

Estimates of phosphate rock above possible entries driven at natural drainage levels 

Continued

Maxville area Continued

Long tons

West limb of Princeton anticline from sec. 36, T. 9 N., 

R. 13 W., south to slope above Gird Creek in sec. 11, 

T. 8 N., R. 13 W. (pi. 30, profile Z-Z', cross sections.B-B', C-C', D-D')-.--------------------- 1,600,000

East limb of west branch of Princeton anticlin.e in 

sees. 2 and 11, T. 8 N., R. 13 W., east of Gird Creek.. 1, 500, 000

18,650,000 '

Philipsburg area

Around Philipsburg anticline from Red Hill, in sec. 24, 

T. 7 N., R. 14 W., north and east to South Boulder 

Creek, in sec. 3, T. 7 N., R. 13 W. (pi. 31).-. .'. 8, 000, 000

Northwest of Avon

From Graveley mine northwest 2 miles in sees. 2 and 3, 

T. 10 N., R. 9 W. (pl.,32).... .. .. 600, 000

Large additional amounts of phosphate are probably to be found 

above natural drainage levels on the sides of the Ked Hill anticline, 

near Philipsburg, and on the west side of the Wyman Gulch syncline, 

between Stewart Gulch and Maxville, but information on which to 

base a trustworthy estimate is not available. There is also a small 

quantity in Flagstaff Hill.

Below natural drainage levels there is a large amount of phosphate 

that may be regarded as a reserve for the distant future. For the 

purposes of classification, lands that are underlain by phosphate of 

the quality and thickness here described down to a depth of about 

2,200 feet are considered phosphate-bearing. The total amount of 

phosphate within such a depth is indicated to be 30,000,000 tons in 

the Philipsburg area and 90,000,000 tons in the MaxvilJe area.

DEVELOPMENT WORKINGS

In the last few years development workings have been made on the 

phosphate bed along Douglas Creek and at other places near Maxville, 

on Red Hill near Philipsburg, and on the property of C. A. Graveley, 

near Avon.

Along Douglas Creek in sec. 31, T. 9 N., R. 12 W., the Northwestern Improvement Co. has driven adit levels on three segments of the 

phosphate beds that extend to the surface on the flanks of the Douglas 

Mountain anticline (pi. 28). From west to east these segments are 

known respectively as beds 1, 2, and 3, and their adit levels by the 

same names. Adit 1 is 50 feet long; adit 2, 160 feet; and adit 3, 500 

feet. Depths below the surface to which they expose the phosphate 

range from about 30 feet at adit 1 to about 250 feet at adit 3. Ore 

bins are built at adits 2 and 3, and adit 3 is equipped with chutes for
188 PHOSPHATE ROCK IN MONTANA

overhead stoping. In other places nearby, mostly on Douglas Mountain in sees. 30 and 31, the phosphate bed is exposed by open cuts and 

pits.

Between Douglas and Gird Creeks, in sec. 36, T. 9 N., R. 13 W., two 

adits of Omer fidgar, each about 50 feet long and equipped with oreloading platforms, are made on the phosphate outcrop that rounds the 

north end of the Princeton anticline.

In sec. 12, T. 8, N., R. 13 W., about 2 miles south of the Edgar 

mine, a tunnel at the Blue Bell mine of Eplin & Horton penetrates 

the phosphate bed on the east flank of the Princeton anticline at a 

depth of about 80 feet. On Gird Creek about three-quarters of a 

mile southeast of the Blue Bell mine the continuation of phosphate 

bed 1 on the west flank of the Douglas Mountain anticline is partly 

exposed near the portal of a tunnel pf the Barnes mine.

A short distance southeast of Maxville the tunnel of the Washington Phosphate & Silver Co. (pi. 33) penetrates, at a depth of about 

300 feet, broken masses of the phosphate bed that he within the 

.breccia zone accompanying the Bungalow fault. At this working 

ore bins and a mill for fine grinding of the phosphate rock have been 

erected.

On Red Hill, near Philipsburg, the workings of the Dissett mine 

consist of a crosscut adit 300 feet long from which a north drift 

connects with an inclined shaft. They expose the phosphate bed to 

a depth.of 100 feet at the south end of the Wyman Gulch syncline. 

Incomplete exposures are made on the same fold by a trench at the 

New Hope mine, a mile to the north, and on Stewart Mountain, 

about 3 miles to the northeast. In 1924 the phosphate .bed on Flagstaff Hill had been developed by a tunnel 100 feet long and by several 

trenches on ground that is now occupied by the manganese milling 

plant of the Trout Mining Co.

In the tunnel of C. A. Graveley, near Avon, the phosphate bed is 

exposed at a depth of 80 feet.

Outside the areas covered by the present report, much development work was done several years ago by the Anaconda Copper 

Mining Co. at Warm Spring Creek, north of Garrison, on segments 

of the phosphate bed, elevated along the west limb of the Garrison 

anticline. 9 More recently extensive mining was done at East Brock 

Creek farther northwest on the same fold by William Anderson, who 

produced and shipped a large amount of phosphate rock (p. 185).

Near Elliston considerable development work has been done recently by the Northwestern Improvement Co. along outcrops described in a former report. 10

» Pardee, J. T., U. S. Qeol. Survey Bull. 640, p. 219,1917.

i" Stone, R. W., and Bonine, C. A., The Elliston phosphate field, Mont.: U. S. Geol. Survey Bull. 580, 

pp. 373-383, 1915.

O
U. S. GEOLOGICAL SURVEY BULLETIN 847 PLATE 33

 Zone of the Bungalowthrust

EXPLANATION

Breccia Phosphate rock p b,shale of Belt Talus

series 

(pre- Cambrian)

Quadrant

formation

(Pennsylvania!!)

Fault plane 

with gouge

Minor fault 

or slip

PLAN AND SECTION ALONG TUNNEL OF WASHINGTON PHOSPHATE & SILVER CO.
EXPLANATION OF PLATE 34, BULLETIN 847-D

A. Trench across outcrop 3 on north slope of Douglas Mountain in sec. 30, T.

9 N., R. 12 W. 

B. Face of Northwest Development Co.'s tunnel 3 at Douglas Creek in sec. 31,

T. 9.N., R. 12 W. 

O. Trench across outcrop 2 on south slope of Douglas Mountain near top, in

sec. 31, T. 9 N., R. 12 W. 

D. Face of Northwest Development Co.'s tunnel 2 at Douglas Creek in sec. 31,

T. 9 N., R. 12 W.. 

E. Face of Northwest Development Co.'s tunnel l.at Douglas Creek in sec. 31,

T. 9 N., R. 12 W.

F. Face of Edgar tunnel 1 in N% sec. 36, T. 9 N., R. 13 W. 

G. Face of tunnel at Blue Bell mine near center of sec. 2, T. 8 N., R. 13 W. 

H. Slope north of Princeton Gulch in sec. 18, T. 8 N., R. 12 W. (U. S. Geol.

Survey Bull. 715, p. 144, 1921.)

I. Shaft of Dissett mine in sec. 24, T. 7 N., R. 14 W. 

K. Trench on Stewart Mountain in sec. 8, T. 7 N., R. 13 W. 

L. Trench on south slope of Flagstaff Hill, Philipsburg.' (U. S. Geol. Survey

Bull. 640, p. 224, 1917.) 

M. Face of tunnel at Graveley mine in sec. 2, T. 10 N., R. 9 W., near Avon.

82754 36

U. S. GOVERNMENT PRINTING OFFICE: 1936
U. S. GEOLOGICAL SURVEY

ABC

P205 Ca3(POjz P2 05 Ca3 (P04)2

B.P.L. B.P.L. '

3137 69.32

11,87 25.32

23.43 64.23

30.70 67.05

 IS.7O 34.29

D 

P2 05 Ca3 (P<X,)2 

E 

P2 05 Ca3 (P04)2 

F 

P2 05 Ca3 (P04)2 

GH

P2 05 Ca,(POj2

B.P.L. B.P.L. ...... B.P.L. B.P.L.

EXPLANATION

Phosphate rock Phosphatic shale Phosphatic sandStone and chert

Vertical scale

I O 1 23456

2S.29 57.42

29.O4 S3.42 '33.55°- 73.27° >3t.9l G9.S9

B.PL.

 31.53 GS.3 i'

*

K L

P2 05 Ca 3 (P04)2 P2 05 Ca3(POj2 P20S Ca3 (P04)2

B.P.L. B.P.L. B.RL.

BULLETIN 84? PLAfE 34 

M

29.3 65.02

Shale Sandstone and limestone

 22.93 50.O8

/O.9O S3.SI

a,, Ciqy seams excluded.

6, Average. ofccv£oad. shipments

29.50 64.42

223O 43.7O

COLUMNAR SECTIONS OF PHOSPHATE AND ASSOCIATED BEDS NEAR MAXVILLE, PHILIPSBURG, AND AVON, MONT.