GEOLOGICAL SURVEY CIRCULAR 824 

Thorium Resources of Selected Regions 

in the United States 

Prepared on behalf of the 

U.S. Department of Energy 

Thorium Resources of 

Selected Reg ions 

in the United States 

By M. H. Staatz, R. B. Hall, D. L. Macke, 

T. J. Armbrustmacher, and I. K. Brownfield 

GEOLOGICAL SURVEY CIRCULAR 824 

Prepared on behalf of the 

U.S. Department of Energy 

Thorium resources are reported on for the Pleistocene 

beach placers of northern Florida, stream placers of 

Idaho, veins and pipes in the Bokan Mountain district 

of Alaska, carbonatite dikes, and apatite-bearing iron 

deposits in the Mineville district of New York in the 

United States. 

1980 
United States Department of the Interior 

CECIL D. ANDRUS, Secretary 

Geological Survey 

H. William Menard, Director 

Free on application to Branch of Distribution, U.S. Geologica/Survey,1200 South Eods Street,Arlington, VA 22202 
Abstract ......................................... . 

Introduction ..................................... . 

Summary ........................................ . 

Florida Beach Placers ............................. . 

Idaho Stream Placers ............................. . 

General ...................................... . 

l.A>ng Valley .................................. . 

Bear Valley .................................. . 

Burgdorf-Warren Area ........................ . 

Boise Basin .................................. . 

Elk City-Newsome Area ....................... . 

Veins and Pipes in the Bokan Mountain District, 

Alaska ......................................... . 

CONTENTS 

Page 

1 

2 

2 

3 

9 

9 

15 

16 

17 

17 

18 

19 

Carbonatite Dikes ................................ . 

General ...................................... . 

Powderhorn District, Colorado ................. . 

Mountain Pass, California ..................... . 

Wet Mountains Area, Colorado ................ . 

Bearpaw Mountains, Montana ................. . 

Ravalli County, Montan81- Lemhi County, Idaho .. 

Magnet Cove and Potash Sulfur Springs, Ar· 

kansas ...................................... . 

Apatite-bearing iron deposits of Mineville, New York. 

References cited .................................. . 

ILLUSTRATIONS 

Page 

22 

22 

23 

24 

25 

26 

27 

27 

28 

30 

Page 

FIGURE 1. Map showing location of the principal stream placers in Idaho. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 

TABLES 

Page 

TABLE 1. Th02 reserves and probable potential resources in short tons, from selected districts in the United States.... 3 

2. Estimated volume of placer material dredged and amounts of monazite and other heavy minerals produced 

by three dredges in the Big Creek part of Long Valley . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

3. Mineral content, in percent, of heavy minerals from three Idaho placers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 

4. Th02 reserves and probable potential resources, in short tons, from various placer districts in Idaho. . . . . . . . . 15 

5. Th02 reserves and probable potential resources, in short tons, from placer areas in Long Valley . . . . . . . . . . . . . 16 

6. Th02 and U 30s reserves, in short tons, in placer areas of Bear Valley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 

7. Th02 reserves, irt short tons, from three placers in the Burgdorf-Warren area.............................. 18 

8. Th02 reserves and probable potential resources, in short tons, of carbonatite dikes in three districts . . . . . . . . . 23 

III 

Thorium Resources of Selected Regions 

in the United States 

By Mortimer H. Staatz, Robert B. Hall, David L. Macke, 

Theodore J. Armbrustmacher, and Isabelle K. Brownfield 

ABSTRACT 

Thorium resources have been assessed in a previous report 

entitled "Principal thorium resources in the United States" 

(Staatz and others, 1979) for (1) veins in the larger districts, 

(2) massive carbonatites, (3) disseminated deposits, and (4) 

stream placers of North and South Carolina. This report is a 

sequel to that report and assesses thorium resources in (1) 

Florida beach placers, (2) Idaho stream placers, (3) veins and 

pipes in the Bokan Mountain district, Alaska, (4) carbonatite 

dikes, and (5) apatite-bearing iron deposits near Mineville, 

New York. Thorium resources for each of these categories are 

divided into reserves and probable potential resources. When 

data are available, each of these is then divided into the 

following cost categories: (1) the amount of Th02 producible 

at a cost of less than $15/lb (per pound), (2) the amount producible at a cost of between $15 and $30/lb, and (3) the 

amount producible at a cost of between $30 and $50/lb. 

Beach placers of northern Florida have reserves of 16,200 

short tons of Th02 and probable potential resources of 5,120 

tons of Th02• These deposits are heavy-mineral placers that 

are mined for a variety of minerals-principally titanium 

minerals and zircon. The thorium-bearing mineral in these 

placers, monazite, makes up only a minor part of the heavy 

minerals. Therefore, production of Th02 from these placers is 

dependent on the markets for other heavy minerals. Assuming the market for other heavy minerals to be the same as 

in 1978, then 98 percent of the Th02 could be produced for 

less than $15/lb. If, however, no other coproducts were produced, then the cost of producing Th02 would be greater than 

$50/Ib. 

Stream placers containing thorium are found along many 

streams that drain the Idaho batholith, but most are too 

small to add significantly to the thorium resources. The 

resources of the five largest districts, each of which consists 

of at least several individual placers, have been tabulated. 

These districts are (1) Long Valley, (2) Bear Valley, (3) 

Burgdorf-Warren area, (4) Boise Basin, and (5) Elk CityNewsome area. These five areas have reserves of 10,100 short 

tons of Th02 and probable potential resources of 10,300 tons. 

Long Valley contains about half the reserves-5,680 tons of 

Th02-and all the probable potential resources. Monazite is 

the most important heavy mineral in all except the Bear 

1 

Valley deposit. Here euxenite, although not quite a~ abundant as monazite, is a more important mineral, becaus~ it contains approximately 14.5 percent U30 8 in addition tn 5 percent Th02• Reserves in this placer amount to 1,605 short tons 

of Th02 and 1,475 tons of U30s. Eighty-two percent of the 

reserves and all of the probable potential resources can be 

produced at less than $30/lb of Th02• The lower cost reserves 

are concentrated in the Long and Bear Valley areas. Here 64 

percent of the Th02 can be produced for less than $15/lb and 

another 29 percent of the Th02 at between $15 and f.'-JO/lb. 

Sixteen veins and pipelike bodies are evaluated in the 

Bokan Mountain area of southeastern Alaska. The district 

contains other deposits that are too poorly exposed to make 

meaningful resource estimates. Reserves estimated in this 

district are 1,440 short tons of Th02; probable potential 

resources amount to 2,320 tons of Th02• About 99 pel"cent of 

these resources are in deposits whose grade is at least 0.2 percent Th02• In addition, these deposits contain reserve~ of 420 

tons of U30 8 and probable potential resources of 820 tons of 

U30 8 • Eighty-two percent of the reserves and probable potential resources can be produced at less than $15rh. The 

average grade of this ore is 0.54 percent Th02 and 0 15 percent UaOs. 

Some carbonatite dikes, although generally not as high 

grade as the veins, contain resources of thorium. Car't~natite 

dikes in the following six districts were investigated: (1) Wet 

Mountains, Colo.; (2) Powderhorn district, ColorFdo; (3) 

Mountain Pass area, California; (4) Bearpaw Morntains, 

Mont.; (5) Ravalli County, Mont., and Lemhi County, Idaho; 

and (6) Magnet Cove-Potash Sulfur Springs, Ark. Sufficient 

resources are present in the first three districts to merit 

resource calculations. These three districts have reserves of 

978 tons of Th02 and probable potential resources C'f 5,480 

tons. The Powderhorn district contains 77 percent cf these 

resources. About one-third of the total reserves and p-obable 

potential resources could be produced at a cost of le~~ than 

$15/lb. Another half of the reserves and probable potential 

resources could be produced at a cost of between U5 and 

$30/lb. 

Thorium, together with rare earths and a little uranium, occurs in apatite that makes up approximately 8 per~ent of 
high-phosphorus iron ore tailings from the Mineville, N.Y~ 

area. Iron mines have been operated in this district for over 

150 years, and tailings piles contain millions of tons of 

material. Conservative estimates indicate that the dumps 

have reserves of 1,360 short tons of Th02, which could probably be produced at a cost of less than $30/lb. 

INTRODUCTION 

The U.S. Geological Survey, under a contract 

with the U.S. Department of Energy, began compiling data on thorium resources in the United 

States in May 1977. The Department of Energy 

wished to obtain data on most of the better 

known deposits within a year. A report covering 

thorium in many of the vein deposits, disseminated deposits, massive carbonatites, and stream 

placers in North and South Carolina was submitted to the Department of Energy a year later. 

This report, entitled ''Principal thorium 

resources in the United States" was subsequently published (Staatz and others, 1979). The 

data on resources that were used in this early 

report were mainly a byproduct of regional 

studies of thorium districts made by the U.S. 

Geological Survey over the past 20 years. 

The present report is a continuation of this 

assessment of thorium resources in the United 

States. It involves resources of districts that 

have been studied or compiled over the past 2 

years. Specifically it covers (l) beach placers 

of northern Florida, (2) stream placers of Idaho, 

(3) veins and pipes in the Bokan Mountain area of 

southeastern Alaska, (4) carbonatite dikes in 

Western United States, and (5) iron deposits in 

the Mineville area of New York. This progress 

report does not cover any of the deposits described in the previous report (Staatz and others, 

1979), and it covers only part of the other thorium 

deposits not previously covered. The material 

covered has been limited by data available in the 

literature and time necessary to obtain new data 

in the field. 

Research on and compilation of various parts 

of this report were done by the following people: 

Staatz wrote the sections on Bokan Mountain, 

Alaska, and Mineville, N.Y. either from his notes 

or from the literature. Armbrustmacher is 

responsible for the section on carbonatite dikes. 

Macke put together the section on beach placers 

of northern Florida. Hall collected the data 

on the Idaho placers. Brownfield calculated the 

2 

costs of producing ore from var.~~us properties. 

Much data on geologic backgr">und, geologic 

literature, past production, and size, and extent 

of the deposits were obtained ill conversations 

with people who have worked ir these various 

areas. We are indebted to many people for their 

shared knowledge and their hosp~tality while in 

the field. Among those who have aided us in this 

study are Thomas E. Garnar, Jr., John W. 

Sweeney, Allan Popp, J. K. Tho~as, James L. 

Hetherington, E. C. Pirkle, and C. W. Hendry, 

Jr., in the Florida area; Richard B. Porter, J. P. 

Jennet, Carleton N. Savage, and Miles Young in 

Idaho; Allan Bird, Robert L. anc Irene Dotson, 

and Kelly Adams at Bokan Mountain, Alaska; 

Drew F. Holbrook and Don R. O'"'ens on Arkansas carbonatites; and Harry Vlemic in the 

Mineville, N.Y. area. 

The present resource study on tl''lrium was also 

supported by the U.S. Departm~nt of Energy. 

The terms "reserves" and "prohable potential 

resources'' used in this report are those of the 

Department of Energy. These terms have been 

adopted so that the thorium rerources can be 

compared more directly with uranium resources. 

This comparison is important, c-~ both metals 

compete as fuel sources for nuclear reactors. 

''Reserves,'' as used by the Department of 

Energy, is equivalent, for the most part, to the 

terms "measured and indicated reserves," as 

used by the U.S. Geological Surv1~y and the U.S. 

Bureau of Mines. ''Probable potential resources'' 

is, likewise, in part equivalent to "inferred 

reserves'' and some ''hypotheti ~al resources.'' 

Resource figures for each depos~t are reported 

several ways. First, the reserves and the probable 

potential resources of each district are given. 

Then, these figures are divided into cost categories-the amount of Th02 that each could produce for less than $15/lb (per po11nd), for $15 to 

$30/lb, and for $30 to $50/lb. These cost boundaries were chosen so that they would be directly 

comparable to those used by the Department of 

Energy in reporting uranium resources. 

SUMMARY 

Resources of five types of thorium-bearing 

deposits are discussed in this paper. These 

resources are confined to those of a particular 

type in a specific area. For exam:"lle, the section 
TABLE 1.-Th02 reserves and probable potential resources, in short tons, from selected districts in the United States 

Total Total producible at Total producible at Total producible at Type of District Total probable less than ~15/lb between ~15 and $30/lb between ~30 and ~50/lb deposits or reserves potential Reserves area resources 

Beach •••••• Northern ••• 16,200 5,120 15,800 placers. Florida. 

Stream ••••• Idaho •••••• 10,100 10,300 4,640 placer. 

Veins and •• Bokan Moun- 1,440 2,320 1,180 pipes. tain, Alaska. 

Carbonatite United ••••• 978 5,480 332 

dikes. States. 

Iron ••••••• Mineville, 1,360 0 0 

deposits. N.Y. 

Total ••••••••••••••••• 30,078 23,220 21,952 

on stream placers is confined to those in Idaho. 

Resources of stream placers in North and South 

Carolina have been previously reported (Staatz 

and others, 1979). The five types of deposits 

studied in this report have 30,100 tons of reserves 

and 23,200 tons of probable potential resources, 

for a total of 53,300 tons of Th02. 

The largest amount of reserves (16,200 tons of 

Th02) occurs in the beach sands of Florida. These 

deposits are quite large, but the Th02 content is 

low. Such deposits in northern Florida and adjacent Georgia are mined principally for their 

titanium content. These deposits have been the 

only domestic source of thorium in the United 

States since at least 1960. The Th02 in these 

deposits is all byproduct and depends on the 

recovery of other heavy minerals. If these 

deposits were mined only for Th02, the cost per 

pound would exceed $50. The presence of a 

sizable market for Th02 would help put several 

marginal deposits into operation. Table 1 shows 

the cost of obtaining thorium from beach placers 

if they were operated under economic conditions 

existing in 1978. 

The resources of the Idaho stream placers 

(reserves plus probable potential resources) are 

almost as large as those of the Florida placers. 

The stream placers differ from the beach placers 

in that monazite is the principal heavy mineral 

and, with the exception of one placer area, other 

heavy minerals have little effect on the cost of 

production. The one exception is Bear Valley, 

which also has euxenite. In this placer almost as 

much U 308 would be recovered as Th02. 

3 

Probable Reserves Probable Reserves Probable 

potential potential potential resources resources resources 

5,120 190 0 168 0 

6,560 3J800 3,760 797 0 

1,890 0 0 80 290 

1,920 482 2,780 0 0 

0 1,360 0 0 0 

15,490 5,632 6,540 1,045 290 

Total reserves and probable potential resources 

of Th02 of the different types of deposits, as well 

as those resources producible within various cost 

ranges are given in Table 1. 

FLORIDA BEACH PLACERS 

Monazite-bearing beach placers in northern 

Florida and southern Georgia have been the only 

source of domestic thorium since at least 1960. 

Monazite, however, makes up only a small part of 

the total heavy minerals, and these deposits are 

mined principally for their titanium, which is 

used in the pigment industry. Other mineral 

byproducts that have been marketed from some 

of the deposits include zircon, kyanite, 

sillimanite, staurolite, and garnet. Monazite is 

present in very small quantities in many surficial 

sands in Florida (Carpenter and others, 1953, 

p. 789). It is most commonly concentrated in 

modern or raised beaches. During 1978 monazite 

was produced from two of the three operating 

heavy-mineral deposits in Florida: Titanium 

Enterprises at Green Cove Springs and Humphrey Mining Corporation at Boulogne recovered 

monazite as a byproduct. At the third deposit, 

E. I. du Pont de Nemours and Company's Trail 

Ridge deposit, only trace amounts of monazite 

are present. 

Heavy minerals have been mined at six places 

in Florida, and the details are summarized below. 

The first mining was started in 1916 along a 

modern beach near Mineral City by Buckman and 

Pitchard, Inc. (Martens, 1928, p. 125). This town, 

which is now known as Ponte Vedra, lies due east 
of Jacksonville. Ilmenite was the chief product, 

although some monazite was apparently recovered in 1916 or 1917 (Liddell, 1917, p. 153). 

The property was acquired in 1922 by National 

Lead Company, which is reported to have produced 1 short ton of monazite in 1925 (Santmyers, 1930, p. 11). Mining ceased in 1929. 

In 1940 the Riz Mineral Co. began mining ilmenite, zircon, and rutile from monazite-bearing 

sands along the modern beach near Melbourne in 

the central part of Florida's eastern coast. A little 

later the company began to recover monazite, as 

well as ilmenite, rutile, and zircon, from dune 

sand near Vero Beach about 30 miles to the south 

(Overstreet, 1967, p. 125). This operation was 

more or less continuous until1946 and then intermittent until1948, when the company was reorganized under the name Florida Ore Processing 

Co., Inc., with a mineral separation plant at Palm 

Bay. This company ceased mining in early 1955 

but continued processing concentrates dredged 

by the Florida Minerals Co. until October 19, 

1955, when the plant burned. A new plant built 

near Winter Beach began operations in February 

1956 (Overstreet, 1967, p.125). The Winter Beach 

plant ceased operations in 1965 (Stamper, 1966, 

p. 940). 

In 1943 the Rutile Mining Co., a subsidiary of 

National Lead Co., began recovering ilmenite and 

rutile from monazite-bearing sand just east of 

Jacksonville. This sand was from older Pleistocene and Pliocene beaches approximately 15 

miles west of the Atlantic Coast. This plant 

recovered mainly ilmenite, rutile, and zircon, 

although a small amount of monazite was 

reported to have been produced annually 

(Overstreet 1967, p. 125; Gunter, 1955, p. 54). 

Production ceased in 1968 and the plant was 

dismantled. 

In 1949 E. I. duPont de Nemours and Company started producing heavy minerals from the 

large Trail Ridge ore body southwest of Jacksonville. This ore body, which has been traced for 

about 18 miles, lies along one of the higher beach 

lines in the state. Production started with the 

opening of a plant southeast of Starke. It was expanded with the opening of a second plant on 

another part of this deposit at Highland near 

Lawtey in 1955, (Overstreet, 1967, p. 125). Titanium minerals are the main product, but zircon, 

staurolite, kyanite, and sillimanite are also 

marketed (Garnar, 1972). Monazite is scarce in 

this sand body. 

4 

In 1972 Titanium Enterprises, Inc., a joint venture of Union Camp Corporation and American 

Cyanamid Co., began mining on a Pleistocene 

beach placer south of Jacksonville and west of the 

St. Johns River. The sand mined had an average 

of 3 percent heavy minerals; monazite made up 

approximately 0.3 percent of the heavy minerals. 

This plant had a designed capacity of 1,200 tons 

of sand per hour. Minerals recovered included ilmenite, leucoxene, rutile, zircon, and monazite. 

Mining ceased in June 1978 and the property was 

put up for sale. 

In 1974 Humphrey Minerals, presently a subsidiary of Buttes Gas and Oil Co., began mining a 

heavy-mineral deposit near Boulogne in northernmost Florida. This deposit is part of a Pleistocene 

shoreline that extends northward across the 

St. Marys River into Georgia. Previously, a 

heavy-mineral deposit along the same shoreline 

was mined near Folkston, Ga., by the same company. The Boulogne orebody underlies an area of 

about 1,000 acres and was mined to an average 

depth of about 15 feet. This orebody has about 4 

percent heavy minerals, of which monazite makes 

up 0.3 to 0.4 percent. Titanium minerals were the 

principal product here; byproduct zircon and 

monazite were also recovered. Active mining 

ceased late in 1978. 

The present report does not include all of 

Florida, but is confined to the Pleistocene and 

Pliocene placers of northeastern Florida. As 

noted previously, some of the early heavy-mineral 

operations occurred along the modern beaches on 

the east coast of Florida. Other resources occur 

along these beaches and on adjacent offshore 

islands. Since the late 1960's environmental 

restraints have made the mining here more costly. Also, the real estate values of beach-front 

property have skyrocketed. Even in the past the 

older inland beach deposits were preferred to 

deposits on modern beaches because the inland 

deposits are larger, have more uniform distribution of heavy minerals, and are not as vulnerable 

to severe storms (Overstreet, 1967, p. 125). Thus, 

it appears unlikely, despite any resources present, that any placers along the seashore will be 

mined in the future in Florida. Pleistocene and 

Pliocene beach placers, however, which occur inland along old shorelines, were available in 1978 

for development. These deposits are in general 

parallel to the present east coast and as much as 

50 miles inland. Most are concentrated in the 

northeastern part of the State. Hence, the present 
study is confined to an area from the east coast 

westward to about long. 81 o W., and from the 

Georgia border southward to the Green Cove 

deposit at about lat. 30 o N. 

Pleistocene and Pliocene beach placers are 

heavy-mineral concentrations in parts of relic 

shorelines, which occur in the outer coastal plain 

from Maryland to Florida. Relic shorelines are 

found at elevations ranging from about 10 to 110 

feet above sea level. The older, higher shorelines 

are farther inland, and the younger are towards 

the present coast. Shoreline scarps were recognized in the Atlantic coastal plain more than a 

century ago by Lyell (1845). These shorelines, 

which were called "marine terraces," were 

described by Shattuck (1906) in Maryland, Clark 

and Miller (1912) in North Carolina, Stephensen 

(1912) in North Carolina, and Veatch and 

Stephensen ( 1911) in Georgia. Relic shorelines 

have been mapped in Florida by Parker and 

Cooke (1944), MacNeil (1949), Vernon (1951), 

Doering (1960), Alt and Brooks (1965) and 

Winkler and Howard (1976, p. 124-125). Cooke 

(1931, 1932) attempted the first correlation of 

these so-called "marine terraces" between States 

based on the elevation of their tops. He developed 

a sequence of seven named terraces, whose elevations ranged from 25 to 270 feet. MacNeil (1949) 

limited the number of separate terraces to four. 

Vernon (1951) and Alt and Brooks (1965) described four and five terrace levels, respectively. 

Significant differences also occur between the terrace elevations and nomenclature proposed by 

these various investigators. These studies relied 

on an assumption of tectonic stability and absolute elevation of shoreline features (MacNeil, 

1949, p. 97; Doering, 1960, p. 185). 

A better understanding of these relic shorelines 

has come from recognizing that they closely 

resemble barrier-islands formed along modern 

coasts, rather than marine terraces, and that the 

coastal plain has been warped during Pleistocene 

time and the old strand lines may therefore vary 

considerably in elevation. Probably the best 

correlation of ancient shorelines is by Winkler 

and Howard (1976), who used basin and ridge patterns to trace Pleistocene coastal geomorphology. 

Forms used were (1) seaward-facing scarps, (2) 

beach and dune ridges, and (3) ridge and swale 

lineations that were commonly preserved as 

trellis drainage or alined karst features to outline 

the extent and form of the relic seashores. They 

discarded age correlations that used standard 

5 

elevations and based their age correlations on the 

pattern of net progradation, as seen in plan view, 

and the state of preservation of relic depositional 

surfaces. Using this system Winkler and Howard 

(1976) have divided relic shorelines on the Atlantic coastal plain from Florida north to Cape Fear 

River in North Carolina into three major and two 

minor sequences. Our work on Landsat satellite 

photography as well as on topographic maps supports this conclusion. Winkler and Howard (1976, 

p. 124-126) named their three major divisions 

from west to east the Trail Ridge, Effingham, and 

Chatham sequences. 

Each of these sequences consists of a major 

transgressive event marking the highest level of 

the sea stand, followed by a regressive sequence 

of shoreline features that is interrupted by minor 

fluctuations and pauses in sea-level retreat. 

The Trail Ridge sequence has been assigned an 

age of 3-5 m.y., and the Effingham sequence 

1.0-1.7 m.y.; the Chatham sequence has been 

dated near Cape Canaveral at approximately 

110,000 years old (Berggren and Van Couvering, 

1974; Osmond and others, 1970). 

All three sequences are regressive sequences, 

and their maximum elevation above sea level 

decreases from the Trail Ridge to the Chatham 

sequence. The maximum elevation of the Trail 

Ridge sequence is about 165 feet, the Effingham 

sequence about 95 feet, and the Chatham sequence about 50 feet. 

The sands in the Trail Ridge sequence are somewhat coarser than those in the other sequences, 

and its heavy minerals do not include monazite, 

garnet, and epidote (Gamar, 1972, p. 17). As this 

sequence does not have any thorium resources, it 

will not be discussed further. 

In Florida both the Effingham and the Chatham sequences consist of a series of shorelines 

that are parallel to and resemble the present 

coastline. Monazite-bearing heavy-mineral 

deposits have been found in both sequences. The 

Boulogne and Green Cove Springs heavy-mineral 

orebodies are related to relic shorelines in the 

Effingham sequence. The orebody mined at 

Jacksonville is within the Chatham sequence. 

Other unmined heavy-mineral orebodies are 

found within the Chatham sequence. 

Monazite and other heavy minerals found in the 

relic shorelines were originally derived from 

the crystalline rocks of the Piedmont province 

(Mertie, 1953, p. 13). These heavy minerals were 

carried seaward along various rivers and then 
southward by offshore currents. Some of these 

.heavy minerals were incorporated into Tertiary 

or Quaternary rocks along the coastal plain and 

later released by erosion of these rocks. Thus, the 

heavy minerals may have gone through several 

sedimentary cycles before they were finally 

deposited in the beach bars, where they are found 

today. Variations in the mineral content of beach 

placers are due not only to differences in the 

original rocks from which they were derived, but 

also to changes that took place during various 

sedimentary cycles. 

The concentration of heavy minerals in beach 

placers is a multistage process. It begins as the 

heavy minerals are transported by longshore 

drift. Particles are segregated by specific gravity 

and particle size and shape in the uppermost littoral zone during wave action. Wind action 

following the initial segregation acts to disperse 

the heavy minerals that are concentrated in the 

littoral zone. The result is to form coast-parallel 

dunes that have a heavy-mineral content intermediate between that of the littoral concentrates 

and the average beach sands (Neiheisel, 1962, 

p. 365). The process of heavy-mineral accumulation is accentuated by the progessive destruction 

of beach and barrier-island sediments along tidal 

inlets. When sediments are added to beach sequences, either by longshore drift or from fluvial 

action, the heaviest fraction of the sediment load 

is first deposited and the lighter fractions are 

moved on. As the beaches are being reworked, the 

heavy minerals are continuously being transported and sorted. This continuing process tends 

to eliminate all but the most stable heavy 

minerals. Lighter minerals may be intermixed 

from time to time with the heavier minerals as 

shoreline features change. Along the coastline, 

the overall effect through time will be to increase 

the concentration of heavy minerals, especially 

stable ones, as the coastline develops. 

Heavy-mineral placers generally make up only 

a part of a relic beach deposit. In other parts of 

the beach, light minerals are more plentiful. Concentrations of heavy minerals can be extremely 

local, and in many places the heavier mineral content of the sand may be sparse. The outline of a 

heavy sand deposit can be either sharp or gradational. Although some heavy-mineral deposits are 

only a few feet long, minable heavy-mineral 

deposits range in length from about 0.5 to 18 

miles and in width from about 0.1 to 2 miles. 

6 

These deposits extend to depths from about 5 to 

70 feet. The deposit at Boulogne is 2Yz to 3 miles 

long and Y2 to % mile wide. It varies in thickness 

from 5 to 25 feet (Pirkle and others, 1974, 

p. 1129). The heavy-mineral deposit at Green 

Cove Springs is 10 to 12 miles long, is % mile 

wide, and has an average thickness of about 20 

f~t (Pirkle and others, 1974, p. 1129). The largest 

known heavy-mineral deposit, at Trail Ridge, is 

approximately 18 miles long and 1 mile wide. It 

ranges in thickness from 25 to 70 feet (Garnar, 

1972, p. 17). Most deposits, however, are smaller 

than those in these operating properties. 

The heavy-mineral content of beach placers 

ranges from about 0.5 to 6 percent. Heavy 

minerals average from 3 to 4 percent of the sand 

deposits at Green Cove Springs and Boulogne 

(Pirkle and others, 1974, p. 1129) and 4 percent at 

Trail Ridge (Pirkle and Yoho, 1970, p. 17). 

Monazite makes up from almost nothing to about 

2 percent of the heavy-mineral concentrates. 

Titanium minerals make up the greater part of 

the heavy minerals. Most are called ilmenite and 

leucoxene. The principal titanium mineral is referred to as ilmenite; but during the long weathering 

process, transportation, and deposition, most of 

the FeO may be changed to Fe20 3, and then the 

iron may be partially leached out of the mineral. 

This process leaves a cryptocrystalline mineral 

with an above-average Ti02 content. If the titanium mineral has less than 65 percent Ti02, it is 

referred to in the trade as ilmenite; if it contains 

65 to 85 percent Ti02 , it is called leucoxene (Garnar, 1972, p. 18). Other heavy minerals commonly 

found are zircon, rutile, kyanite, staurolite, 

spinel, sillimanite, tourmaline, epidote, garnet, 

xenotime, corundum, and topaz. In all the 

deposits, more than 50 percent of the heavy 

minerals are titanium minerals. Zircon is ubiquitous and generally makes up 10-20 percent of the 

heavy minerals. Kyanite, staurolite, sillimanite, 

epidote, and garnet vary widely and may be 

relatively abundant in the heavy minerals in one 

placer and scant to absent in the next. The remaining minerals, including monazite, make up 

only a minor part of the total heavy minerals in 

any placer. An example of the mineral content of 

a heavy-mineral concentrate is reported on by 

Calver (1957, p. 18) from the property mined by 

the Rutile Mining Co., east of Jacksonville. This 

concentrate had an average composition of 40 

percent ilmenite, 4 percent leucoxene, 7 percent 
rutile, 11 percent zircon, 0.5 percent monazite, 

and 37.5 percent other minerals (mainly sillimanite, kyanite, and staurolite). 

Monazite is principally a rare-earth mineral, 

commonly containing 60-63 percent total rareearth oxides. The Th02 content can be highly 

variable, but the range is apparently small for the 

monazite found in beach placers in Florida. 

Kremers ( 1958, p. 2) reported that Florida beach 

placers contained 4.5 percent Th02. Calver (1957, 

p. 25) noted that the average of five analyses of 

monazite from heavy minerals on Amelia Island, 

St. George Inlet, Mayport, Ponte Vedra, and 

Anastasia Island was 4.96 percent Th02. 

Monazite concentrates from the mining operations at Boulogne and Green Cove Springs each 

had 4.44 percent Th02. The Th02 content of beach 

sands is quite low, and the amount found in raw 

sand from which recovery of monazite is likely is 

on the order of 0.0003-0.004 percent Th02. 

Monazite also contains small amounts of 

uranium, and the average U30 8 content of the five 

samples reported on above by Calver (1957, p. 25) 

is 0.55 percent. The monazite concentrate from 

Boulogne had 0.42 percent U30 8, and that from 

Green Cove Springs, 0.47 percent UsOs. 

The economic feasibility of any beach placer is 

determined primarily by its Ti02 content. In the 

1970's the minimum Ti02 content used as a cutoff 

in mining was 1 percent, and the Ti02 content of 

sands being mined was from 1 to 1.5 percent. The 

amount of various titanium minerals (ilmenite, 

leucoxene, or rutile) present and their Ti02 content are also important economic considerations. 

The Ti02 content is greater in the older beaches 

(those farther inland), primarily because of increased leaching of iron from ilmenite and the 

conversion of ilmenite to leucoxene (J. L. Hetherington, Humphrey Mining Corporation, oral commun., 1978). Thus, the Ti02 content may be as 

much as 15 percent greater in the placer beaches 

of the Effingham sequence than in those of the 

Chatham sequence. 

Th02 resources in Florida occur in many 

Pleistocene beach deposits. As noted previously, 

the amount of Th02 is quite small and its 

recovery is dependent on monazite being 

recovered as a byproduct during the mining of 

other heavy minerals. The total heavy-mineral 

content of the various placers commonly makes 

7 

up only 2-4 percent of the total sand in the 

deposits. Hence, beach-placer mining is a relatively large volume-low margin operation. In the 

1970's, to begin a mining operation on a large 

scale would take an estimated reserve of 

1,000,000 short tons of heavy minerals. A small, 

experienced company might be able, on a smaller 

scale, to develop a deposit that had half that 

amount of reserves. Thus, reserves of many small 

beach deposits add little to the minable resources 

of Th02. In this paper we have, therefore, included as reserves only those deposits containing 

500,000 tons or more of heavy minerals. Some of 

the beach placers are covered by from 1 to 40 feet 

of barren dune sand. Resources in these areas can 

only be ascertained by drilling. Further exploration will undoubtedly increase the Th02 resources 

in Florida. 

We have evaluated five large beach placers in 

the northern part of this State. These do not include the large Trail Ridge deposit, which does 

not contain more than traces of monazite, or the 

Boulogne or Jacksonville deposits, which are for 

the most part mined out. Data are mainly from 

drill holes. As this information is companyconfidential, we have consolidated the figures and 

give only the totals for all deposits. Total 

reserves are 16,200 short tons of Th02 in 364,000 

tons of monazite. This monazite also contains 

1,640 tons of U30 8 and 218,000 tons of total rareearth oxides. In addition, these deposits also contain 3,930,000 tons of ilmenite, 740,000 tons of 

rutile, and 590,000 tons of zircon. The heavy 

minerals from which this monazite is derived 

make up from 2. 7 to 4.1 percent of the beach 

placers. Reserves make up the greater part of the 

resources, as most of these deposits have been 

drilled out. The category of probable potential 

resources in a relatively undrilled extension has 

5,120 short tons of Th02 in 115,000 tons of 

monazite. This monazite also contains 520 tons of 

U30 8 and 69,000 tons of total rare-earth oxides. 

Other heavy minerals present include 890,000 

tons of ilmenite, 157,000 tons of rutile, and 

81,700 tons of zircon. These resources represent 

minimum resources, as several other known 

heavy-mineral Pleistocene placers exist for which 

the drilling data are not available. In addition, 

many Pleistocene strand lines, especially in central Florida, have yet to be carefully explored. 

Cost studies also were made on placer sands by 

Jim F. Lemons, Jr., Louis V. Coppa, and Ben-
jamin V. Clingan of the U.S. Bureau of Mines 

(Staatz and others, 1979). Cost calculations made 

by operators of monazite placers go only as far as 

the separation of the individual heavy minerals. 

We have carried this one step farther and have included the separation of the Th02 from the 

monazite in order to have a basis for comparing 

the cost of Th02 between different types of 

deposits. The cost calculation covers the mining 

of the sand and its processing through three 

separate mills. In the first mill, the heavy 

minerals are separated from the beach sands; in 

the second, monazite and various other heavy 

minerals are separated from each other; and in 

the third, thorium, uranium, and rare earths are 

recovered from the monazite. 

Although beach placers are an extremely lowgrade source of Th02, several factors aid in 

making this type of mining feasible. First, they 

are large in size; second, they have only a few feet 

of overburden and can be mined by open pit; 

third, they are loose, fairly well-sorted sand and 

need neither blasting during mining nor grinding 

and sorting during milling; and fourth, the water 

table is high enough in northern Florida so that 

they can be mined by a dredge floating on a pond. 

The first step is to make a pond into which to put 

the dredge. A hydraulic dredge having a rotating 

cutter head is used to loosen the alluvium, and 

the sediment is pumped to the surface. From 

there it is pumped through a pipeline floating on 

pontoons either to a floating heavy-mineral mill 

or to a mill on land. 

The mining costs are divided into capital and 

operating costs. Capital costs include mine 

development, mining plant, and equipment. 

These costs do not include those for exploration, 

acquisition of land, or obtaining working capital, 

because these costs have not been considered in 

comparative cost calculations for uranium. Most 

development costs include clearing trees and 

brush from the placer deposit, building roads, and 

digging the initial pond with a dragline. Miningplant costs include the dredge and any buildings 

needed for the operation. Equipment costs include all equipment and supplies necessary to 

bring the property into production. Operating 

costs are divided into direct, indirect, and fixed 

costs. Direct costs apply directly to the dredging 

operation and include labor, supervision, power 

and fuel consumption, cutter bits, and supplies. 

The indirect costs are for administrative and 

8 

clerical help, facility supplies, and general 

overhead. Fixed costs are for local taxes and insurance. These costs are a function of the capital 

costs and are estimated to be 3 percent of capital 

costs. 

Milling of placer sands is a fairly well-known 

process. In the first mill, which is attached to the 

dredge, the various heavy minerals are separated 

from the rest of the alluvium. This separation is 

made with spiral gravity separators, the common 

method used for separating heavy minerals from 

beach sands in Florida. The heavy sands go 

through three series of spirals-roughers, 

cleaners, and finishers-and the finished product 

is dewatered. The heavy concentrate makes up 

only about 2-4 percent of the alluvium mined. 

The rest of the alluvium is returned to the end of 

the pond through a moving pipe that spreads it 

evenly into the valley bottom so that it can quickly be returned to its original agricultural use. 

The concentrates are trucked to a dry mill, where 

the various heavy minerals are separated from 

each other using magnetic and electrostatic 

separators. 

Th02 is extracted from the monazite in a leachsolvent plant. This plant extracts not only the 

thorium from monazite, but also recovers 

uranium and rare earths. 

The milling costs for each mill are divided into 

capital and operating costs. Capital costs for each 

mill consist of the cost of building the mill and 

the cost of the equipment that is necessary to 

make it operational. The size of the mill is the 

principal factor that affects the original cost of 

the mill. The proposed gravity mills are designed 

to handle from 2,300 to 22,000 tons of sediments 

per day for an operating life of at least 15 years. 

The magnetic-electrostatic mills proposed for 

these deposits are designed to handle from 230 to 

615 tons of heavy concentrates per day. The life 

of this type of mill, assuming the most efficient 

use of all the equipment, would be at least 15 

years. The leach-solvent mill is a much smaller 

plant, and the proposed design can be used for a 

plant having an input of from 5 to 8 tons of 

monazite per day. This plant also is most efficient 

if it has a life of at least 15 years. 

The operating costs for milling can be divided 

into direct, indirect, and fixed costs. The direct 

costs include fuel and power consumption, 

reagents, labor, supervision, and supply maintenance. The indirect costs are those for ad-
ministration, technical and clerical help, facility 

maintenance, office supplies, and general 

overhead. Fixed costs are for local taxes and insurance on the milling facilities. The principal 

variable in a mill's operating cost is its capacity. 

Cost calculations were made on all five placer 

deposits. The reserves at three of these deposits 

can be produced for less than $15/lb of Th02• 

These deposits have reserves of 15,800 short tons 

of Th02 that are contained in 356,000 tons of 

monazite. This monazite also contains 1,600 

short tons of U30 8 and 214,000 tons of total rareearth oxides. A fourth deposit has reserves of 190 

short tons of Th02 that can be produced for between $15 and $30/lb. This Th02 is in 4,250 tons 

of monazite. The monazite also has 19 tons of 

U308 and 2,550 tons of total rare-earth oxides. 

The remaining placer has reserves of 168 short 

tons of Th02 that could be produced for between 

$30 and $50/lb. This Th02 is contained in 3, 770 

tons of monazite, which also contains 17 tons of 

U308 and 2,260 tons of total rare-earth oxides. 

The probable potential r~sources, found in only 

one deposit, could be produced for less than 

$15/lb. This tonnage is 5,120 short tons of Th02 , 

which occurs in 115,000 tons of monazite. The 

monazite also contains 520 tons of U 30 8 and 

69,000 tons of total rare-earth oxides. If only 

Th02 were recovered from these beach sands, 

then the cost of producing it would be considerably in excess of $50/lb. Thus, the recovery 

of Th02 in these deposits is dependent on recovering other heavy minerals, although a price for 

Th02 comparable with that for U 30 8 would undoubtedly permit some otherwise marginal 

heavy-mineral deposits to go into production. 

IDAHO STREAM PLACERS 

GENERAL 

Stream placers in Idaho are found principally 

along the west side of the Idaho batholith, north 

of Boise. Monazite is the principal thoriumbearing mineral in most of these placers. It was 

first identified in 1896 by Waldemar Lindgren 

11 (1897a, 1897b) in the heavy "yellow sand" that 

accumulated in the sluices of the placer gold 

mines in the Boise Basin around Idaho City, 

Centerville, and Placerville. Lindgren also 

recognized the economic potential of monazite 

and suggested that, if market conditions per9 

mitted, it might be profitably recovered as a 

byproduct of placer gold. In 1909 a mill was constructed to produce monazite by the Centerville 

Mining and Milling Co. Only token quantities of 

monazite concentrate were produced during the 

initial shakedown of the plant, and it was 

destroyed by a forest fire in 1910. Two placer 

areas were mined for radioactive minerals in the 

1950's: Long Valley and Bear Valley. 

In Long Valley, monazite was recovered by 

three dredges over a 5-year period. Dredging 

began in September 1950 in the Big Creek section 

of Long Valley by Baumhoff-Marshall, Inc. During the summer of 1951 two dredges-one of the 

Idaho-Canadian Dredging Co., the other of the 

Warren Dredging Co.-started operation. All 

three dredges were formerly used for recovering 

gold. They were refitted for monazite recovery 

with help from the U.S. Bureau of Mines under 

the sponsorship of the U.S. Atomic Energy Commission. The Warren dredging operation was 

relatively short-lived as this dredge capsized in 

1953 and was not put back into operation. Crude 

black-sand concentrates were recovered by jigs 

mounted on the dredges. These concentrates were 

dewatered and hauled to Boise to a magneticelectrostatic separation plant operated by 

Baumhoff-Marshall Inc. Part of the monazite was 

sold to the government stockpile and part to commercial monazite processors. Mining ceased in 

mid-1955 due to the filling of the government 

stockpile order (Eilertsen and Lamb, 1956, p. 25) 

and to increased foreign competition. An excellent summary of the Big Creek operations as of 

late 1953 is given by Argall (1954). 

The amount of heavy minerals produced by the 

three dredges has not been published. However, 

on the basis of known dredge capacities, time in 

operation, and estimates of the amount of placer 

material mined, the quantities of monazite and 

other heavy minerals recovered can be approximated (table 2). These figures suggest that the 

three dredges recovered 7,085 short tons of 

monazite containing 297 tons of Th02 • 

The other area in which thorium was produced 

is Bear Valley. This placer, although containing 

two principal radioactive minerals (euxenite and 

monazite), was operated principally for its 

niobium and tantalum content. Euxenite also 

contains thorium and uranium. The Porter 

Brothers Corp. obtained a contract to provide 

1,050,000 pounds of niobium-tantalum oxide for 
TABLE 2.-Estimated amount of placer material dredged and amounts of monazite and other heavy minerals produced by three 

dredges in the Big Creek part of Long Valley 

[B11sed in part on material derived from Argall, 1954] 

Dredge Period of Cubic yards Heavy minerals recovered 

operator operation dredged Monazite Ilmenite Zircon Garnet 

Th0 2 content 

of monazite in 

short tons 

Baumhoffrfarshall, Inc ••••• 9/50-8/5 5 6,380,000 

Idaho-Canadian 

Dredging Co ••••••• 8/51-8/55 5,400,000 

Warren Dredging 

Co •••••••••••••••• 9/51-5/53 1,100,000 

Total ••••••••••••• 9/50-8/55 12,880,000 

the General Services Administration stockpile. 

They began production with one dredge in 1955, 

and followed it with a second dredge in 1956. 

Black-sand concentrate was recovered by jigs 

mounted on the dredges. The crude concentrate 

was hauled 22 miles to Lowman, where relatively 

clean concentrates of euxenite, columbite, and 

monazite, and less clean concentrates of magnetite, ilmenite, garnet, and zircon were produced 

in an electromagnetic-electrostatic plant. Dredging ceased in October 1959 with the fulfilling of 

the General Services Administration contract. 

During the operation, approximately 6,500,000 

cubic yards of placer material was dredged 

(Richard B. Porter, written commun., 1958). 

From alluvium of Bear Valley, 2,049 short tons of 

euxenite, 83.5 tons of columbite, and 54,862 tons 

of ilmenite were recovered. Records are not 

available on the amount of monazite recovered. 

The greater part of the resource data on Idaho 

placers was obtained during a program to find 

new domestic monazite reserves by the U.S. 

Bureau of Mines using funds obtained from the 

U.S. Atomic Energy Commission. The program 

was a result of an embargo placed by Brazil and 

India on monazite, as these countries wished to 

save their thorium as an eventual atomic energy 

source (Eilertsen and Lamb, 1956, p. 4). The embargo effectively cut off the United States from 

their major sources of thorium ores. The program 

was carried out in Idaho, principally by the 

Bureau of Mines, between 1949 and 1954. During 

this period the Bureau explored 27 placers in 

Idaho, of which 9 were considered to have potential economic reserves (Storch and others, 1956, 

3,510 38,300 1,280 2,230 147 

2,970 32,400 1,080 1,890 125 

605 6,600 220 390 25 

7,085 77,300 2,580 4,510 297 

10 

p. 9). The Bureau of Mines has published data on 

most but not all of the placers they examined. 

They reported on a total of 12 placer areas, including the most important ones: (1) Bear Valley 

(Kline and others, 1953), (2) Beaver Creek (Storch 

and Robertson, 1954), (3) Big Creek (Kline and 

others, 1951a), (4) Boise Basin (Kline and others, 

1950), (5) Camp Creek (Robertson and Storch, 

1955a), (6) Corral Creek (Kline and others, 1955), 

(7) Deadwood (Storch, 1958b), (8) Gold Fork 

(Storch, 1958a), (9) Horsethief Basin (Kline and 

others, 1951b), (10) Pearsol Creek (Kline and 

Carlson 1954), (11) Rock Creek (Robertson and 

Storch, 1955b), and (12) Scott Valley (Kline and 

others, 1951b). Seven of these placers (Big Creek, 

Beaver Creek, Corral Creek, Gold Fork, Horsethief Basin, Pearsol Creek, and Scott Valley) are 

placers formed by streams flowing into Long 

Valley and are considered in this report as part of 

Long Valley district. The report on the Boise 

Basin, on the other hand, contains a description 

of six separate placers. These deposits were explored by a variety of methods, including churn 

drill holes, trenching, small shafts, and dredge 

sampling. Shaft sinking and trenching were important methods used to obtain bulk samples for 

analysis of average mineral contents. Drilling 

gave data on depth and extent of the placer. The 

Bureau of Mines in the above-reported projects 

drilled 542 holes from 5 to 140 feet deep, for a 

total of 22,072 feet of drilling, and collected over 

210 tons of samples. In addition, a few placers 

have been explored under Defense Minerals Exploration Administration contracts; and one such 

area, the Dismal Swamp placer in Elmore County, 
EXPLANATION 

I 3 Placer locality and number 

1 1 1 1 1 Approximate boundary of Idaho batholith 

MONAZITE PLACER DISTRICTS 

1. Long Valley 

2. Bear Valley 

3. Boise Basin 

4. Burgdorf-Warren area 

5. Elk City· Newsome area 

6. Dixie-Florence area 

7. Stanley Basin 

8. Clearwater River 

9. Salmon River 

10. Rock Creek-Camp Creek area 

11. Dismal Swamp 

FIGURE 1.-Map showing location of the principal stream placers in Idaho. 

is reported on by Armstrong (1955). 

The present study of Idaho placers included 

review of the literature, interviews with people 

connected with former dredging operations, and 

field reconnaissance of all major placer districts 

reported to have commercial possibilities as 

thorium sources. In addition, samples of placer 

alluvium, dredging tailings, and panned concentrates were taken for future mineralogic and 

economic studies. 

Thorium has been reported from many placer 

deposits in Idaho. The five most important 

districts are (1) Long Valley in Valley County, 

11 

(2) Bear Valley in Valley County, (3) BurgdorfWarren area in Idaho County, (4) Boise Basin in 

Boise County, and (5) Elk City-Newsome area in 

Idaho County (fig. 1). Six other less promising 

districts contain significant amounts of monazite 

or other thorium-bearing minerals. These 

districts, and their numbers as shown in figure 1, 

are (6) Dixie-Florence area, (7) Stanley Basin, (8) 

Clearwater River, (9) Salmon River, (10) Rock 

Creek-Camp Creek area, and (11) Dismal Swamp. 

Monazite has been reported in other parts of the 

State in and adjacent to the Idaho batholith, but 

the resource potential in these other areas ap-
pears low. Long Valley and Bear Valley are the 

two most important areas for mining thoriumbearing mine.rals. 

The major source of thorium-bearing minerals 

in the placer deposits is the Idaho batholith. 

Monazite is by far the most common thoriumbearing mineral and has been found in many 

parts of the batholith (Mackin and Schmidt, 

1957, p. 2). The monazite is disseminated in the 

igneous rock as tiny grains, most of which are less 

than 0.5 mm across. Other thorium-bearing 

minerals, such as euxenite and uranothorite, tend 

to be local in their distribution and occur mainly 

in veins or pegmatite bodies rather than dispersed within the batholith like monazite. The 

distribution of the monazite in the granitic rock 

of the Idaho batholith is .erratic. Samples collected from the granitic rock in the drainage 

basins adjacent to Long Valley varied in 

monazite content from 1 to 0.3 pound per cubic 

yard (Mackin and Schmidt, 1957, p. 2). Heavy 

minerals weather out of the granitic rocks of the 

Idaho batholith and are washed downslope into 

the stream bottoms, where the heavy minerals 

tend to form placers fairly near their sources. 

Most of the placers that form along stream bottoms are narrow, fairly shallow, and not of sufficient size to support a large-scale dredging operation. To be economically minable, a thorium 

placer deposit must contain a large volume of 

alluvial fill that can sustain large-scale dredging 

operations over a period of years. Such largevolume deposits occur not as narrow, shallow 

veneers of sand and gravel on creek bottoms, but 

rather in broad basins (such as Long Valley and 

Bear Valley). In Idaho, such basins have been 

formed by (1) block faulting (2) damming of 

streams by glacial deposits, and (3) damming of 

streams by basalt flows of Pleistocene age 

(Mackin and Schmidt, 1957, p. 2). Block faulting 

during Pleistocene time deranged the drainage 

and developed Long Valley. A glacial moraine 

dammed a creek, forming a basin at Bear Creek 

Valley and leading to the subsequent development of a large placer in Big Meadows. A basalt 

flow cutting across the drainage lines near Hailey 

helped form the Rock Creek-Camp Creek uranothorite placers in that area. 

Placers in Idaho range widely in size. The 

largest volume of minable placer ground is found 

in Long Valley, where alluvium fill underlies an 

area of more than 5 mi2

• Another large placer, 

12 

that in Bear Valley, has a length of 14 mi and a 

width varying from 650 to 6,000 ft. The Grimes 

Creek and Mores Creek placers in the Boise Basin 

are 10 miles long by 600 ft wide and 7% mi long 

by 700 ft wide, respectively. Other placers are 

considerably narrower and contain less placer 

material. A fairly typical example is near Elk 

City, where a placer along a 10-mile stretch of the 

American River only locally exceeds 200 ft in 

width. 

Depth of deposits also shows a large range, 

from those in deep down-faulted valleys to those 

in shallow rock-carved stream basins. In Long 

Valley, where faulting continued during the 

Pleistocene, a thick wedge of monazite-bearing 

sediments has a maximum depth of several thousand feet (Mackin, 1952, p 19). The deepest drill 

hole in this valley is 123 feet at Corral Creek 

(Kline and others, 1955, p. 14). Depth of the 

placer in upper Bear Valley is from less than 10 to 

over 100 feet, with an average of about 40 feet. In 

the Boise Basin, the Grimes Creek placer has an 

estimated average depth of about 28 feet, and the 

Mores Creek placer has an average depth of about 

25 feet. Other dredgable placers commonly have 

average depths of from 10 to 15 feet. 

The average heavy-mineral content of various 

Idaho placers sampled by the U.S. Bureau of 

Mines ranges from 0.10 to 1.06 percent of the 

placer sediments and averages about 0.5 percent. 

Rock Creek placer in Blaine County (Robertson 

and Storch, 1955b, p. 18-19) and Bear Valley 

placer in Valley County (Kline and others, 1953, 

p. 14-16), with 1.06 and 1.01 percent heavy 

minerals respectively, have the greatest known 

amounts of heavy minerals. Five placers that occur in Long Valley have a heavy-mineral content 

of from 0.23 to 0. 70 percent (Kline and others, 

195la, p. 17; 1951b, p. 17; Kline and Carlson, 

1954, p. 18-19; and Kline and others, 1955, p. 17). 

Heavy-mineral content commonly varies between 

individual samples, and samples from 65 drill 

holes at the Pearsol Creek placer in Long Valley 

had from 0.072 to 2.55 percent heavy mineral, 

with an average of 0.54 percent (Kline and 

Carlson, 1954, p. 11, 18, 19). The average 

monazite content makes up from a trace to 16 percent of the heavy minerals in the various placers. 

Monazite is most abundant in the Corral Creek 

placer in Long Valley (Kline and others, 1955, 

p. 17). Camp Creek and Rock Creek in Blaine and 

Camas Counties, which have only traces of 
TABLE 3.-Mineral content, in percent, of heavy minerals from three placers 

m.neral Pear sol Creek Bear Valley Camp Creek 

Monazite •••••••••• 8.4 

Euxenite •••••••••• Trace 

Uranothorite •••••• 0 

Ilmenite •••••••••• 80.5 

Zircon •••••••••••• .1 

Garnet •••••••••••• 1.6 

Magnetite ••••••••• .7 

Sphene •••••••••••• 0 

monazite, contain thorium in uranothorite. 

Uranothorite makes up about 1.2 percent of the 

heavy minerals in the Camp Creek placer (Robertson and Storch, 1955a, p. 24) and 0.45 percent in 

the Rock Creek placer (Robertson and Storch, 

1955b, p. 22). The placer in Bear Valley contains 

thorium and uranium in euxenite. Euxenite 

makes up approximately 0.5 percent of the heavy 

minerals in upper Bear Valley (Kline and others, 

1953, p. 17-19). Ilmenite may be the most common heavy mineral, and in individual placers its 

average abundance ranges from about 14 to 95 

percent of the heavy minerals. Zircon is a common constituent of the heavy minerals, but varies 

greatly in amount in different placers. It makes 

up only 0.11 percent of the heavy minerals in 

Bear Valley (Kline and others, 1953, p. 17-19) but 

makes up 23 percent of the Wolf Creek placer in 

Boise Basin (Kline and others, 1950, p. 17). 

Garnet, another possible economic mineral, 

ranges from a trace to 54 percent of the heavy 

minerals in different placers. The variation in 

some of the more common heavy minerals was 

compiled by Storch and others, (1956, p. 14) (table 

3). In addition to the above-mentioned minerals, 

other heavy minerals occurring in various placers 

in generally minor amounts are hematite, pyrite, 

biotite, amphibole, pyroxene, epidote, rutile, 

anatase, cassiterite, allanite, columbite, samarskite, topaz, xenotime, and gold. Gold has been 

recovered from placers in the Boise Basin, 

Burgdorf-Warren, and Elk City districts and 

from other placers; it is a potential byproduct of 

monazite in these placers. Gold, however, is 

sparse to absent in the most promising thoriumbearing placers of Long Valley and Bear Valley. 

13 

3.6 0.1 

.14-.3 0 

0 1.2 

58.6 26 -30 

.07 .5- .8 

20 .2 

10.3 29 -33 

1. 0 10 -12 

The Th02 content of monazite in the Idaho 

placers varies from 2.2 (Staley, 1952, p. 308) to 

6.24 percent (Kauffman and Baker, 1956, p. 6). 

The amount of Th02 in the monazite, in g~neral, 

seems to increase southward in Idaho (Overstreet, 1967, p. 142). The Th02 content of 

monazite in the larger placers (Long V alhy and 

Bear Valley) varies from about 4.1 to 4. 7 percent 

(Kline and others, 1955, p. 18; Kline and others, 

1951, p. 19; Kline and Carlson, 1954, p. 21-22; 

Kline and others, 1953, p. 20; Kline, and others, 

1951a, p. 21-22). Average Th02 content of 

monazite from the Boise Basin is 3.2 percent 

(Kline, and others, 1950, p. 32). Only a few 

analyses are available on the total rare-earthoxide content of monazite from Idaho. These 

analyses indicate that monazite from this area 

has approximately 63 percent total rare-earth oxides (Overstreet, 1967, p. 146-159). 

Monazite also contains small amounts of 

uranium, and the U 30 8 content of monazite from 

Idaho varies from 0.10 to 0.36 percent.. The 

monazite in most of the larger placers in Long 

Valley contains only 0.1 to 0.15 percent U30 8• 

As euxenite is an important mineral in the Bear 

Valley placer, its chemical composition is c-lso important. Two samples of euxenite had an rverage 

Th02 content of 4.97 percent (Kline and others, 

1953, p. 20). They also contained 14.40 percent 

U30 8 , 25.0 percent Nb20 5, and 3.0 percent Ta205. 

In the past, placers in Idaho were mined mainly 

for the gold. A few placers were dred~ed for 

monazite or euxenite. Although most of tl'a. highgrade gold deposits have been exhausted, only a 

minor part of the thorium resources he~ been 

recovered. Much of the thorium resource~ occur 
in a few large placers in unmined areas, but some 

are found in old tailings piles left by early 

operators dredging for gold. Virtually all placers 

in the central part of Idaho are composed of sediment which originated from the Idaho batholith, 

and this sediment contains some monazite. 

Although monazite may be recognized in 

sediments of more than a hundred streams, only a 

few have large enough resources to be mined by 

dredges. Over 90 percent of all the resources 

estimated is in the three largest deposits. The 

principal placer-thorium resources of Idaho are in 

five districts, named in order of relative importance: (1) Long Valley, (2) Bear Valley, (3) WarrenBurgdorf, (4) Boise Basin, and (5) Elk CityNewsome. Most of these areas consist of several 

adjacent placers in the same drainage or valley. 

The largest, Long Valley, is a large downfaulted 

valley filled with sediments from several streams 

that flow into it. 

The U.S. Bureau of Mines explored a number of 

heavy-mineral placer deposits in Idaho during the 

early 1950's (Eilertsen and Lamb, 1956; Storch 

and Holt, 1963). Although the Bureau's published reports give useful data on areas covered, depths of drill holes, and mineral tenors, they do not 

give information on volumes of the deposits. We 

have estimated volumes by measuring areas on 

topographic maps with a polar planimeter and 

multiplying the area figure by an average-depth 

figure obtained by averaging drill-hole depths 

given in the Bureau's reports. For those districts 

where published drilling reports by the Bureau 

are not available, as for the Warren-Burgdorf and 

Elk City-Newsome districts, the average depths 

have been estimated conservatively from older 

published reports by Idaho Bureau of Mines and 

Geology, that mention dredging depths or give 

other information on which to base estimates of 

probable average depths (Capps, 1940; Reed, 

1937; and Reid, 1960). The Bureau's drilling patterns for the larger areas were laid out in rectangular form on lines spaced 800-1,600 feet 

apart. The holes were spaced 600-800 feet apart 

on the lines. Drilling on smaller, irregularly 

shaped areas was done at selected points ranging 

from 400 to 1,000 feet apart (Eilertsen and Lamb, 

1956, p. 18). 

Reserves are distinguished from probable 

potential resources by depth of drilling. Reserves 

are that part of the resources that have been 

drilled out. Many holes were bottomed at the base 

of the placer in country rock. In these cases there 

are no probable potential resources. Elsewhere, 

those sediments lying below the depth of drilling 

but no deeper than 130 feet were co'lsidered probable potential resources. The dep'lsits in Long 

Valley may extend to a depth of seY~ral thousand 

feet (Mackin, 1952, p. 19), which is c. much greater 

depth than can be mined by the largest dredge. 

As these deposits are both long and wide, a large 

dredge could operate in this valley. Daily (1968, 

p. 507) reported dredging to depthr of 158 feet in 

Malaysia. We have chosen 130 feet as the lower 

limit of our probable potential resources. This 

figure, which is only used in Long Valley, is a 

compromise figure between the d ~pth obtained 

by local dredges and that which has been obtained by dredges in other parts of t.he world. Two 

of the placer areas, Bear and Long Valleys, have 

been in part dredged previously. T1''1 dredged-out 

areas are not included in the resource calculations. In Bear Valley, perhaps 10 percent of the 

total reserves have been mined; the: percentage in 

Long Valley is even less. Total reserves are 

10,062 short tons of Th02 (table 4). This Th02 is 

in 227,000 tons of monazite and 9, 760 tons of euxenite. The monazite also contains 386 tons of 

U30 8 ; the euxenite contains approyimately 1,410 

tons of U 30 8 • The reserves of many small placers 

are not included in our total reserve figure, but 

they would not greatly increase this figure. 

However, some areas in Long Vclley have not 

been explored, and additional reserves might be 

found in this area. 

14 

Total probable potential resources, all from 

Long Valley, are 10,320 short tons of Th02 (table 

4). This Th02 is in 237,000 tons of monazite. The 

monazite also contains 404 tons of U aOs. 

Cost studies were made on fluviatile placer 

deposits by Jim F. Lemons, Jr., Lnuis V. Coppa, 

and Benjamin V. Clingan of the U.S. Bureau of 

Mines (Staatz and others, 1979). Mining of these 

deposits would be done using a dredge floating on 

a pond, as has been done in the ar<:"!~ in the past. 

The dredge would deliver sand to a floating mill, 

either on the same or a separate barge. The heavy 

minerals would be separated here and the light 

minerals returned to the far end of the pond. A 

hydraulic dredge with a rotary cutting head 

would be used to loosen the alluvium, which then 

would be pumped to the surface. The heavy 

minerals would be trucked to a nef'.rby magneticelectrostatic mill, in which the various heavy 
TABLE 4.-Th02 reserves and probable potential resources, in short tons, from various placer districts in ldah-:~ 

Total Total producible at Total producible at Total producible at 

Placer Total probable less than $15/lb between $15 and $30/lb between $30 and $50/lb 

district reserves potential Reserves Probable Reserves Probable Reserves Probable reserves potential potential potential 

resources ['esources resources 

Long Valley ••••••• 5,680 10,320 3,500 

Bear Valley ••••••• 1,605 0 1,140 

Bu['gdorfWarren area ••••• 1,940 0 0 

Boise Basin ••••••••• 660 0 0 

Elk CityNewsome area •••••• 177 0 0 

Total •••••••••• 10,062 10,320 4,640 

minerals would be separated from one another. In 

this plant, not only monazite and (or) euxenite 

would be separated from the other heavy 

minerals, but several byproducts, such as ilmenite, zircon, and garnet, could be obtained as 

well. Although these minerals would be the final 

product sold by the operator from these placers, 

we have added the cost of a separate leaching mill 

from which Th02 and U30 8 would be extracted 

from the radioactive minerals. This added step 

was necessary so that the cost of producing Th02 

from a placer could be compared directly with 

that of producing it from a vein. The type of 

mining and milling costs used in these calculations are the same as those described in the section on Florida beach placers. 

Cost calculations were made on the placers of 

all five principal areas (table 4). Two of the areas 

(Long and Bear Valleys) have reserves producible 

at less than $15/lb. These deposits have reserves 

of 4,640 short tons of Th02 and 1,380 tons of U 30 8 

that are contained in 96,500 tons of monazite and 

8,360 tons of euxenite. Three areas (Long and 

Bear Valleys and the Burgdorf-Warren area) have 

reserves producible at between $15 and $30/lb. 

These placers have reserves of 3,800 short tons of 

Th02 and 335 tons of U 30 8 that are contained in 

82,900 tons of monazite and 1,400 tons of euxenite. Two areas (Long Valley and the BurgdorfWarren area) have reserves producible at between 

$30 and $50/lb. These deposits have reserves of 

797 short tons of Th02 and 25 tons of U 30 8 that 

are contained in 19,800 tons of monazite. None of 

the reserves in any of the placers in the Boise 

Basin or the Elk City-Newsome area are producible at less than $50/lb. Probable potential 

6,560 1,670 3,760 513 0 

0 465 0 0 0 

0 1,660 0 284 0 

0 0 0 0 0 

0 0 0 0 0 

6,560 3,795 3,760 797 0 

15 

resources are only found in the Long Valley 

placers. Here the tonnage that may be proiucible 

at less than $15/lb is 6,560 short tons of ':':"h02 in 

152,000 tons of monazite. In addition, 3, 760 tons 

of Th02 may be producible at between $15 and 

$30/lb. This amount of Th02 occurs in 85,700 tons 

of monazite. 

The principal product of the Idaho stream 

placers, unlike the situation in the Floridr beach 

placers, would be the thorium- and W'aniumbearing minerals, monazite and (or) euxenite. 

Other minerals, such as ilmenite, ziro'>n, or 

garnet, would only be of secondary intere~t.. The 

euxenite in Bear Valley, which contains roproximately three times as much uranium as tl''lrium, 

also contains niobium. Niobium, although not 

taken into account in our cost calculations., would 

be a significant source of income in Bear Valley. 

LONG VALLEY 

Long Valley resources have been divided into 

areas adjacent to the individual streams thqt flow 

across Long Valley. The greater part of these 

resources is adjacent to Big Creek (whnre the 

dredging in the 1950's was done) (Kline and 

others, 1951a), Pearsol Creek (Kline and Carlson, 

1954), Corral Creek (Kline and others, 19f'5) and 

Scott Valley (Kline, and others, 1951b). Another 

promising placer was explored in Horq~thief 

Basin (Kline and others, 1951b), but as this placer 

is now covered by a reservoir, its resour~es are 

not included. Other parts of Long Valley li~ adjacent to the areas of exploration. Although data 

are not available on these parts, the sed~ments 

here probably contain monazite. We have not in-
TABLE S.-Th02 reserves and probable potential resources, in short tons, from placer areas in Long Valley 

Total producible at Total producible at Total producible at 

Total less than $15/lb between $15 and $30/lb betwe~n $30 and $50/lb 

Placer Total probable Reserves Probable Reserves Probable Reser'res Probable 

deposits resources potential potential potential potential 

reserves resources resources resources 

Big Creek •••••••• 1,350 2,690 1,350 2,690 0 0 0 0 

Pearsol Creek •••• 2,150 3,870 2,150 3,870 0 0 0 0 

Corral Creek ••••• 1,670 3,760 0 0 1,670 3,760 0 0 

Scott Valley ••••••• 513 0 0 0 0 0 513 0 

Total •••••••••• 5,683 10,320 3,500 6,560 1,670 3,760 513 0 

eluded these unexplored areas in our calculations, 

but parts of these areas could conceivably add 

significantly to the overall thorium resources in 

Long Valley. 

The reserves and probable potential resources 

of Th02 for four principal placer areas in Long 

Valley and amounts that can be produced in 

several cost categories are given in table 5. The 

5,683 short tons of Th02 reserves would be 

recovered from 132,000 tons of monazite; the 

10,320 tons of Th02 in probable potential 

resources is contained in 237,000 tons of 

monazite. In addition, the monazite in the 

reserves would also contain 180 tons of U30 8 and 

82,800 tons of total rare-earth oxides. The 

monazite in the probable potential resources 

would contain 344 tons of U30 8 and 150,000 tons 

of total rare-earth oxides. Other heavy minerals 

that could be recovered from the reserves include 

1,040,000 short tons of ilmenite, 23,700 tons of 

zircon, and 61,200 tons of garnet. The amounts of 

other heavy minerals in the probable potential 

resources are 2,450,000 tons of ilmenite, 4 7, 700 

tons of zircon, and 145,000 tons of garnet. 

Monazite is the principal economic mineral in 

these deposits. If a market were readily available 

for all heavy minerals and Th02 were marketed 

for $15/lb, then the value of monazite would make 

up 65-90 percent of the total value of the Long 

Valley deposits. If the price for Th02 were 

greater, then the value of monazite would make 

up an even larger percentage of the total value of 

the economic minerals. 

BEAR VALLEY 

Bear Valley Creek is a headwaters stream and 

an important tributary of the Middle Fork of the 

16 

Salmon River. Placer deposits occ·1r in three contiguous areas along at least 20 mH~s of this creek. 

These areas are called the Upper (Big Meadows 

area), Middle, and Lower Bear Valley areas. Bear 

Valley is unique among Idaho placers because, in 

addition to monazite, it also ha~ economically 

significant amounts of euxenite. This mineral is 

derived locally from a 6-squarr~-mile area of 

quartz diorite in the Idaho batholith (Mackin and 

Schmidt, 1957, p. 3). Euxenite is a hard, brittle 

mineral that breaks up fairly easily during 

downstream transportation. Mackin and Schmidt 

(1957, p. 6) noted that the larger euxenite grains 

decrease in size by three to four times within the 

first mile of movement downstrE'.fim. Thus, the 

euxenite is principally concentrated in the Big 

Meadows area close to its source. Drilling by the 

U.S. Bureau of Mines (Kline and others, 1953) in 

the three areas indicates that th~ upper or Big 

Meadows area has the best tenor of heavy 

minerals. In the Middle Bear Cr~ek placer, the 

grade of the monazite and euxenite is about half 

that found in Upper Bear Valley. In the Lower 

Bear Creek placer, only negligiHe amounts of 

thorium-bearing minerals occur in the alluvial 

sediments. Because of the low grf'de of thoriumbearing minerals, Lower Bear Valley is not considered further in this report. Mor~t drill holes in 

Bear Valley went entirely through the placer, so 

we do not have any underlying prCJ hable potential 

resources. Resources of the Bear Valley placers 

differ from those in other Idaho placers in that 

they contain as much U 30 8 as Th02. In addition 

to the small amount of U 30 8 four1 in monazite, 

significant amounts of this oxide occur in euxenite. Kline and others (1953, p. 21) reported the 

average U 30 8 content of two euxenites from Bear 

Valley to be 14.4 percent. The re~~rves of Th02 
TABLE 6.-Th02 and U30 8 reserves, in short tons, in placer areas of Bear Valley 

Placer Th02 reserves u3o8 Total Th02 producible Total Th02 producible 

at between 

Th0 2 producible 

at between 

$30 and $50/lb 

reserves at less than 

$15/lb 

Upper Bear 

Valley •••••••••• 1,140 1,250 1,140 

Middle Bear 

Valley •••••••••• 465 225 0 

Total •••••••••• 1,605 1,475 1,140 

and U30 8 for Upper and Middle Bear Valley 

placers and the amounts that can be produced in 

several cost categories are given in table 6. Total 

reserves of these two placers is 1, 605 short tons 

of Th02 and 1,475 tons of U30 8, which are contained in 24,200 tons of monazite and 9,760 tons 

of euxenite. The two minerals also contain about 

17,800 tons of total rare-earth oxides. In addition, 

the euxenite has about 2,440 tons of Nb20 5 • Other 

heavy minerals that could be recovered from the 

reserves include 1,510 short tons of columbite, 

391,000 tons of ilmenite, 940 tons of zircon, and 

87,600 tons of garnet. Euxenite, monazite, and 

columbite are the principal economic minerals in 

these deposits. 

BURGDORF-WARREN AREA 

The Burgdorf-Warren area (fig. 1) is known for 

many gold placers, which have not been worked 

on a large scale since the early 1950's. The placers 

occur in stream valleys near the small communities of Burgdorf and Warren, which formerly 

were important gold-mining camps 10-12 miles 

south of the Salmon River. Significant quantities 

of monazite and other black-sand minerals occur 

in alluvium and old gold-dredge tailings in three 

areas: (1) Warren Meadows, (2) Secesh Meadows, 

and (3) Ruby Meadows. These broad meadows are 

thought to have been formed by block faulting 

(Savage, 1961, p. 112). In any reworking of these 

placers monazite would be the principal product, 

although a little gold missed during the previous 

operations also would be recovered. The largest of 

the three placer areas is at Warren Meadows, 

which contains approximately 39,000,000 cubic 

yards of alluvial material. The average monazite 

content of the three placers is between 0.033 and 

0.044 percent. Monazite is reported to be the prin-

$15 and $30/lb 

0 0 

465 0 

465 0 

cipal heavy mineral (Reed, 1937, p. 31-33; Capps, 

1940, p. 34, 37). Garnet is also common. All the 

resources in these three placers are well enough 

defined to be included in reserves. Reserves in the 

three placer areas and amounts that can be produced in two cost groups are given in tr-1' ble 7. 

Total reserves for this area is calculated to be 

1,940 short tons of Th02, contained in 43,500 tons 

of monazite. The monazite also contains f f5 tons 

of U 30 8 and 27,400 tons of total rare-earth oxides. 

At a January 1980 price of $650 per troy ounce, 

the Warren Meadows placer tailings contain approximately $1.59 cents worth of gold pe~ cubic 

yard. The value of the gold was not taken into account in calculating the cost of producing a pound 

of Th02. 

BOISE BASIN 

The Boise Basin is a depression 15 mil,~s long 

and 12 miles wide surrounded by ~ll mountains. 

This area is traversed by several branching 

streams which are separated by flat-topped, gently sloping ridges that rise a few hundr~d feet 

above the stream levels. Six placers sc~ttered 

along these creeks have been described by the 

U.S. Bureau of Mines (Kline and others, 1950, 

p. 10). These placers are called (1) Grassy Flats, 

(2) Wolf Creek, (3) Fall Creek, (4) Granite Creek, 

(5) Grimes Creek, and (6) Elk and Mores Creeks. 

The greater part of the monazite-bearin~ sediments is in tailings left from early gold mining 

operations. Some areas of unworked placer 

ground remain on Wolf, Mores, and Fall Creeks 

and on Grassy Flats. The six placers have 

reserves totaling 660 short tons of Th02 ir 20,700 

tons of monazite. Reserves range in size from 49 

tons of Th02 in the Wolf Creek placer to 240 tons 

of Th02 in the Grimes Creek placer. In addition to 

17 
TABLE 1.-Th02 reserves, in short tons, from three placers in the Burgdorf-Warren area 

Placer Total 

reserves 

Warren Meadows •••••••••• 935 

Secesh Meadows •••••••••• 725 

Ruby Meadows •••••••••••• 284 

Total ••••••••••••••• 1,944 

monazite, these placers contain 69,200 short tons 

of ilmenite, 27,300 tons of zircon, and 27,200 tons 

of garnet. 

A maximum depth of 58 feet was obtained in 

one hole in the Wolf Creek placer (Kline and 

others, 1950, p. 31). The thickness of most placers 

is about 30 feet. The Bureau of Mines drilling in 

1949 (Kline and others, 1950) reached bedrock in 

virtually all parts of the Boise Basin; therefore, 

there are no underlying probable potential 

resources. 

The cost of producing Th02 from any of the six 

placers, even with the aid of byproducts, would be 

greater than $50/lb. High cost is due in part to 

the rather low heavy-mineral content of the placer 

alluvium, in part to the low Th02 content of the 

monazite, and in part to the relatively small size 

of these placers. Heavy minerals of these six 

placers make up only 0.10 to 0.33 percent of the 

placer material, and the average Th02 content of 

four analyses made on monazite from the Boise 

Basin is 3.2 percent (Kline and others, 1950, 

p. 32). 

ELK CITY-NEWSOME AREA 

The placers of the Elk City-Newsome area lie 

along the drainage of the upper South Fork of the 

Clearwater River in Idaho County (Reid, 1960); 

for the most part they occur along the tributaries 

emptying into this river. Placers in this area that 

have been evaluated for their monazite content 

are (1) Big and Little Elk Creeks, (2) American 

River, (3) Red Horse Creek, (4) Red River, (5) 

Crooked River, and (6) Newsome Creek. Most lie 

within 5 miles of Elk City, although Newsome 

Creek is about 10 miles from this town. The depth 

18 

Total reserves 

producible at 

between $15 

and $30/lb 

935 

725 

0 

1,660 

Total reserves 

producible at 

between $30 

and $50/lb 

0 

0 

284 

284 

of the alluvium that makes up tt~se placers is 

generally about 6-10 feet. The upp~r part of it is 

generally silt and the lower part, gravel. The latter contains some boulders over 10 inches across 

(Reid, 1960, p. 6-7). Dredging for gold has occurred along these streams. The average heavymineral content of the above-noted six placers 

ranges from about 0.4 to 1.3 percert of the placer 

sediments (Reid, 1960, p. 14-15; Storch and Holt, 

1963, p. 63). Although the amount of heavy minerals compares favorably with that of placers in 

Long Valley, monazite makes up a much smaller 

percentage of the heavy minerals, ranging from 

about 0.35 to 1.8 percent. The principal heavy 

minerals in these placers are magnetite and ilmenite. Together they make up mo"':'e than 90 percent of the heavy minerals in each of the placers. 

Garnet and zircon are also found ill these placers. 

Zircon is about as abundant as monazite, and 

garnet about twice as common. The Th02 content 

of the monazite is low, about. 2.7 percent 

(Overstreet, 1967, p. 149). 

The six placers evaluated have reserves totaling 177 short tons of Th02 in 6,540 tons of 

monazite. Reserves range in size from 1.4 tons cf 

Th02 on Red Horse Creek to 79 tons on Red 

River. In addition to monazite, the~~ placers contain 124,000 tons of ilmenite, 7,180 tons of zircon, 

and 14,100 tons of garnet. The plac~~rs are shallow 

and do not have any underlying p"':'obable potential resources. 

The cost of producing Th02 from any of the six 

placers, even with the aid of byproducts, would be 

greater than $50/lb. High cost is due to low 

monazite content of the heavy minerals and low 

Th02 content of the monazite. 
VEINS AND PIPES IN THE 

BOKAN MOUNTAIN DISTRICT, ALASKA 

The Bokan Mountain district surrounds the 

mountain of this name in the southern part of 

Prince of Wales Island in the southern part of the 

Alaskan panhandle. Bokan Mountain is about 40 

miles southwest of Ketchikan, the nearest town. 

The district lies between the head of the West 

Arm of Kendrick Bay on the east and the South 

Arm of Moira Sound on the northeast. These two 

waterways afford access by boat within a few 

miles of most prospects. Thorium is associated 

with uranium and rare earths in veins, pegmatites, and a few irregular pipelike bodies. These 

deposits occur in and adjacent to the Bokan 

Mountain Granite, which underlies Bokan Mountain in a crudely circular area of a little over 3 

square miles. This granite is a sodium-rich, 

riebeckite- and acmite-bearing rock with accessory zircon, fluorite, and thorite. It was intruded in Late Triassic or Early Jurassic time 

(Lanphere and others, 1964, p. 707), principally 

into quartz monzonite and quartz diorite of Ordovician age (Lanphere and others, 1964, p. 707). 

In addition, older metavolcanic rocks lie to the 

northwest of Bokan Mountain, and black slate interlayered with some phyllite, metasiltite, and 

impure quartzite forms a semicircular band 

around part of the Bokan Mountain Granite 

(MacKevett, 1963, pl. 1). 

MacKevett (1963, pl. 1) showed 26 prospects 

containing uranium that lie within the Bokan 

Mountain Granite and another 14 in the surrounding rocks within 1.5 miles of this body. 

Since this early work several other prospects 

have been found. Short, irregular, granitic 

pegmatite lenses and dikes occur within the 

Bokan Mountain Granite (MacKevett, 1963, pl. 

1). Some of these bodies contain thorium and 

uranium minerals, which are commonly concentrated in small pockets. Other parts of these 

pegmatites, as well as some entire pegmatites, 

are not abnormally radioactive. Because of the 

small size and erratic distribution of thorium and 

uranium values within these bodies, they are not 

considered a potential resource of either of these 

two metals. 

The greater part of the thorium and uranium 

occurs in veins and pipes. A pipe on the Cub 

claims (Ross-Adams mine) was the source of the 

only uranium produced in Alaska. Approximately 

19 

94,000 short tons of high-grade uranium ore, containing about 1 percent U30 8 as well as substantial amounts of Th02, was produced from this 

orebody during three separate periods of production (Stephens, 1971, p. 152, 158). Known 

pipes are confined to the vicinity of the old RossAdams mine on the Cub property. The :rfpe that 

was mined here had an irregular plung~ to the 

south. Its upper part had a shallow dip and was 

first mined from a broad trench some 300 feet 

long (Eakins, 1970, p. 14). At the south end of this 

trench the pipe plunged steeply and waq traced 

another 670 feet during mining (Eakins, 1970, 

p. 13; Stephens, 1971, p. 157). Its crosf' section 

in this trench was reported by MacKeve+t (1963, 

p. 63-64) to be about 40 by 50 feet. The <Jre in the 

upper trench contained more than 0.5 percent 

U 30 8 , and a large part of the high-grade. ore had 

about 1 percent U30 8 (MacKevett, 1963, p. 67). 

This ore generally contains slightly more thorium 

than uranium, but in a few places the thorium-touranium ratio is as much as seven to c~e. Texturally this ore resembles the granitic h'lst rock, 

and most of the uranium and thorium minerals 

are scattered through the granitic hc'i't rock, 

although some mineralization is found along veinlets in the rock. Thorian uraninite and tr0rite are 

the principal primary uranium and thorium 

minerals. A little brannerite occurs locally. Th& 

principal gangue minerals are albite, quartz, and 

acmite. Accessory minerals include l'~matite, 

pyrite, galena, fluorite, zircon, sphalerite, and 

magnetite. 

Veins are more widely scattered over an area of 

at least 18 miles and are found on all sides of 

Bokan Mountain. The larger and better explored 

veins lie along the mountain's southeast flank. 

The best known group, which consists of a 

number of parallel and subparallel veins that can 

be traced for 1.6 miles, belong to the I and L 

system (Staatz, 1978). Exposures are generally 

poor, and heavy soil cover and thick vr~getation 

make tracing individual veins difficult. Veins in 

this area tend to be thin and commonly pinch out 

in short distances. Exposed vein lengths range 

from about 6 to 2,100 feet. The longef't vein is 

part of the I and L vein system and oc~-::urs near 

the southwest end of this system. Veinf' range in 

thickness from about a quarter of an inch to 10 

feet; most, however, are less than 1 foot thick. 

Numerous fractures cut the Bokan I fountain 

Granite and adjacent rocks. These fractures 
strike in several directions, but the most common 

and the longest fractures have a northwest strike. 

Veins are intruded along these fractures, and 

although they strike in several directions, most of 

them have a northwest strike. Dips are generally 

steep. 

Mineral content may be highly variable even 

along the same vein. Quartz and albite are the 

principal gangue minerals. The principal thorium 

mineral is thorite, and the principal uranium 

mineral is thorian uraninite. These two elements 

also occur locally in allanite and brannerite. Rare 

earths are fairly abundant and occur principally 

in bastnaesite and xenotime. Less commonly they 

are found in synchisite, monazite, and allanite. 

Iron oxides are plentiful in some parts of the 

veins. They consist chiefly of goethite and 

hematite; minor amounts of magnetite are also 

present in many veins. Zircon, pyrite, and fluorite 

are found in many samples. In addition, some 

veins locally contain a little sphalerite, galena, 

rutile, phenacite, pyrochlore, and columbite. 

Uranium-rich areas can be identified in some 

places by the presence of thin coatings of secondary yellow uranium minerals, such as sklodowskite or kasolite, along fractures. Some veins are 

crudely zoned. In the I and L vein system, 

uraninite and xenotime occur mostly in the northwest part of the system and allanite in the 

southeastern part (Staatz, 1978, p. 518-519). 

The Th02 content of the veins in the Bokan 

Mountain area is known from 44 samples. The 

values range from 0.0038 to greater than 11 

percent. Individual analyses have been previously published on about two-thirds of these 

samples (MacKevett, 1963, p. 77; Staatz, 1978, 

p. 518-519). Some veins vary considerably in 

Th02 content from place to place, and nine 

samples from the longest vein in the I and L 

system ranged from 0.11 to greater than 11 percent Th02 (Staatz, 1978, p. 518-519). Although 

the Th02 content of individual parts of different 

veins may vary widely, particular veins, .. as a 

whole, tend to contain either small or large 

amounts of Th02. 

The U 30 8 content of 48 samples varies from 

0.0033 to 3.3 percent and the thorium-to-uranium 

ratios of these samples range from 0.046 to 276. 

The thorium-to-uranium ratios of most samples 

fall in the range from 0.10 to 24. Some veins, such 

as the Wennie on the west side of Bokan Mountain, are characterized by high thorium-to20 

uranium ratios; others, like a grour of small veins 

lying adjacent to the I and L vein system on the 

Atom Marietta claims, have lo .. v thorium-touranium ratios. These veins have some of the 

highest U30 8 content of all the veir~ analyzed. In 

some veins, however, the thorium-to-uranium 

ratio varies from place to place. This ratio ranged 

from 0.20 to 80 in the nine sampl~s collected on 

the longest vein in the I and L syr+--em. 

The total rare-earth-oxide contE'~t of 23 analyzed vein samples ranged from (].05 to 13 percent. Individual analyses from eight different 

veins contain more than 1 percent total rare-earth 

oxides. Overall the total rare-earth oxides are 

about 2.5 times more abundant than the Th02. No 

apparent relationship exists, how'1ver, between 

the amount of one in a particular sqmple and the 

amount of the other, and the total ratio of rareearth oxides to Th02 varies frorr 0.21 to 570. 

Veins on the west side of Bokan Mountain and in 

the southeast part of the I and L system tend to 

be proportionally rich in rare earth~ compared to 

thorium. 

The relative amounts of lanthanFies vary from 

sample to sample. In most other, districts the 

amount of lighter rare earths (atomic numbers 57 

to 64) greatly exceeds the amount of heavier rare 

earths. In the Bokan Mountain district, however, 

some samples are principally heavy rare earths, 

some have similar amounts of he.~vy and light 

rare earths, and some are principally light rare 

earths. This erratic rare-earth distr~bution occurs 

not only between veins but also within veins. The 

Bokan Mountain veins contain mere heavy rare 

earths than most other rare-~arth-bearing 

deposits. 

Many veins and pipelike bodies were too poorly 

exposed or sampled to use in 1978 in making 

meaningful resource calculations. These calculations were made on veins as thin a~ 0.2 of a foot 

and include 16 veins and pipes. The resources are 

divided into reserves and probable potential 

resources. The reserves of a vein are calculated in 

the following manner: known length times 

average thickness times a depth equal to onethird the known length. The reserve:~ of a pipe are 

the average cross-sectional area times the known 

length measured along its plunge. Probable 

potential resources are extensions c.-: the reserves 

both laterally and at depth. For pr,obable potential resources, the vein or pipe we~ extended a 

quarter of the known length in each direction. 
This distance was shortened when rock exposures 

indicated that the vein had either pinched out or 

been faulted off. In veins the thickness used is the 

same as that used in calculating reserves, and the 

depth is one and a half times the trace of the vein, 

or half again as deep as the depth used for 

calculating the reserves. In pipes the length was 

multiplied by the average cross-sectional area 

used in calculating reserves. A tonnage factor of 

12 cubic feet per short ton was used in converting 

volume to weight. 

The total reserves and probable potential 

resources of Th02 in the 16 veins and pipes vary 

widely and range from less than 0.1 to about 

1,600 tons of Th02. Total known reserves for this 

district are 1,440 short tons of Th02; total probable potential resources are 2,320 tons of Th02. 

Together they add up to 3,760 short tons ofTh02. 

The average grade of Th02 in these deposits 

ranges from 0.012 to 1.44 percent, but 99 percent 

of these resources come from deposits whose 

grade is at least 0.2 percent Th02. 

These veins and pipes also have reserves of 

U30 8 of 420 short tons; the probable potential 

resources for this U 30 8 are 820 tons. Together 

they add up to 1,240 short tons of U30 8 • The 

average grade of U 30 8 in these deposits ranges 

from 0.016 to 1.3 percent; most of these resources 

come from deposits whose grade ranges from 0.06 

to 0.55 percent U 30 8 • 

The Bokan Mountain district also has 

resources of rare earths. Some of the smaller 

deposits have not been analyzed for rare earths. 

Grade data are available on 10 deposits, which 

contain 98 percent of the total rock that makes up 

all the resources. These deposits contain 9,320 

short tons of total rare-earth oxides in reserves 

and 9,370 tons of total rare-earth oxides in probable potential resources. The average grade of 

these 10 deposits ranges from 0.16 to 8.9 percent 

total rare-earth oxides, but 90 percent of these 

resources comes from deposits whose grade is at 

least 2.0 percent total rare-earth oxides. Heavy 

rare earths are much more abundant in these 

deposits than in most deposits in other areas. 

Yttria (Y20 3) makes up 24 percent of the total 

rare-earth oxides in our samples. Reserves of 

yttria in these veins and pipes total 3,130 short 

tons and probable potential resources, 2,350 tons. 

In addition to calculating total thorium 

resources, as above, the reserves and probable 

potential resources are divided into those that 

can be produced at three sets of costs: (1) those 

that can be produced at less than $15/lb of Th02, 

(2) those that can be produced at between $15 and 

$30/lb, and (3) those that can be produced at between $30 and $50/lb. To obtain a basis f,r calculating these costs, J. F. Lemons, Jr., L. V. Coppa, 

and B. V. Clingan of the U.S. Bureau of Mines 

made cost analyses for both mine and mill models 

(Staatz and others, 1979; Lemons and Coppa, 

1979, p. 3-25). The mine model used for making 

cost calculations is the cut-and-fill mining 

system, which was chosen because of its advantages of flexibility, grade control, and ground 

support. This method is designed to use mill tailings as backfill. Mine recovery of th q ore is 

assumed to be 90 percent. Although the resources 

of all veins or pipes over a certain rrinimum 

thickness are included in the total reserve and 

resource calculations, some deposits do not contain enough ore to be economically mined. For 

purposes of the present calculations, deposits 

containing less than 35,000 short tons of minable 

ore are considered uneconomic and are not included in the resources producible at various 

costs. The type of mill visualized for re:~overing 

thorium in the Bokan Mountain district is one 

using acid-leach solvent-extraction techniques. 

The calculations assume that one hyp~thetical 

mill would be located by a stream near the head of 

the West Arm of Kendrick Bay. The c<J ~t of the 

mill would vary, depending on whether or not it 

also has circuits for recovering uranium and rare 

earths. To simplify procedures the cost divisions 

are calculated assuming that only thorium will be 

recovered. A description of the mining ahd milling method, as well as a discussion o~ various 

costs is given in Staatz and others (1979). 

21 

Cost calculations were made on the seven veins 

or pipes that were large enough to support an 

operating mine. Three of these deposits c'>uld produce Th02 at less than $15/lb, one at bet,.veen $30 

and $50/lb, and the rest at more than $50/lb. A 

total of 3,070 short tons of Th02 is procucible at 

less than $15/lb. This total can be divided into 

1,180 tons of Th02 in reserves and 1,890 tons in 

probable potential resources. In additior to Th02, 

the ore contains 300 short tons of U aOs in 

reserves and 575 tons of U30 8 in probal~ ~ potential resources. This product would be obtained 

from 571,000 tons of ore having an average grade 

of 0.54 percent Th02 and 0.15 percE'nt UaOs. 

Another 370 short tons of Th02 is producible at 
between $30 and $50/lb. This total can be divided 

into 80 tons of Th02 in reserves and 290 tons in 

probable potential resources. This ore also has 

reserves of 35 tons of U 30 8 and probable potential 

resources of 125 tons of U30 8• This product is 

obtained from 49,000 tons of ore having an 

average grade of 0. 76 percent Th02 and 0.33 percent U 30 8• If the value of the U 30 8 is taken into 

account in the deposit that could produce Th02 at 

between $30 and $50/lb, then the Th02 would be 

producible at between $15 and $30/lb. 

CARBONATITE DIKES 

GENERAL 

Carbonatite dikes in the United States, like carbonatites around the world, typically contain a 

suite of rather exotic minerals and elements. 

They have been investigated at various times as 

potential sources of thorium, uranium, rare-earth 

elements, niobium, phosphate, and agricultural 

lime. Carbonatite dikes have been reported from 

many areas, but in most only one or two small 

dikes are known. This report covers six of the better known districts in which a number of carbonatite dikes have been reported. They are (1) 

the Powderhorn district, Colorado; (2) Mountain 

Pass, Calif.; (3) the Wet Mountains, Colo.; (4) 

Bearpaw Mountains, Mont.; (5) Ravalli County, 

Mont.-Lemhi County, Idaho; and (6) Magnet 

Cove and Potash Sulfur Springs, Ark. Carbonatite dikes are mainly tabular bodies, 

although small, irregular bodies in Arkansas 

have been included in this paper. Carbonatite 

dikes are from a few to several thousand feet in 

length and from a fraction of an inch to 150 feet 

thick. Individual dikes commonly vary in 

thickness along their strike. The principal 

mineral is a carbonate, generally calcite, although 

dolomite and siderite predominate in a few dikes. 

Over 50 different minerals have been identified in 

the carbonatite dikes described. Minerals common, although not necessarily plentiful, in many 

of those carbonatite districts include biotite, 

pyrite, potassium feldspar, quartz, fluorite, 

apatite, pyrrhotite, barite, pyrochlore, galena, 

and sphalerite. Thorium and (or) rare-earth 

minerals include thorite, monazite, bastnaesite, 

allanite, synchisite, ancylite, xenotime, parisite, 

and thorianite. Rarely do more than two of the 

thorium or rare-earth minerals occur in a single 

carbonatite. Carbonatites invariably contain 

considerably greater amounts of rare earths than 

they do thorium. They also may contain 

economically interesting amounts of Nb20 5 in 

pyrochlore or columbite. 

The thorium resources for each district are 

reported in two ways: (1) total res'lurces of all the 

carbonatites, and (2) resources that can be produced at three sets of costs. The first category is 

divided into reserves and pro"lable potential 

resources. Reserves are those ref"lurces that are 

in part directly measured and sa1npled. Reserves 

of the carbonatite dikes are calculated in the 

following manner: known length C'f the dike times 

average thickness times a depth equal to onethird the length. Probable potentjal resources are 

extensions of the reserves both laterally and at 

depth, and they form a block of ore that surrounds the reserves. To estimate the probable 

potential resources, the carbonqtite dike was 

assumed to extend on the surfac1~ one-quarter of 

the known length in each directio"'l. This distance 

was shortened when rock expo~nres indicated 

that the dike either pinched out or ended by 

faulting. The same average dik€ thickness was 

used as in calculating the reserves. The depth of 

the probable-potential-resources t·Jock is assumed 

to be one-half times the trace of the dike. The 

resources of the shorter carbonathe dikes are not 

included in the overall resou~ce calculation 

because the total amount of res ~urces of dikes 

having a length of less than 100 feet is insignificant when compared to the total resources of all 

carbonatite dikes. A tonnage fact.or of 11.4 cubic 

feet per short ton (cu ft/short ton) is used in converting dike volume to dike weigrt. 

22 

Although six well-known dirtricts are discussed, resources of three dist.ricts-Bearpaw 

Mountains, Mont.; Magnet Cove-Potash Sulphur 

Springs, Ark.; and Ravalli County, Mont.-Lemhi 

County, Idaho-are not evaluate('. The Th02 content of the carbonatites in these three districts is 

so low that no significant reso':trces would be 

found, nor could the Th02 be recovered at a cost 

of $50/lb. Total reserves and probable potential 

resources of Th02 in carbonatite cUkes in the Wet 

Mountains, Colo.; Mountain Pass district, 

California, and Powderhorn district, Colorado, 

total6,450 short tons (table 8). ThQ,se are divisible 

into 978 tons of reserves and 5,480 tons of probable potential resources. The aY~rage grade of 

these carbonatites ranges from 0.0015 to 1.07 per-
TABLE 8.-Th02 reserves and probable potential resources, in short tons, of carbonatite dikes in three distri'Jts 

District Reserves 

Powderhorn, 

Colo •••••••••••••• 763 

Mountain Pass, 

Calif •••••••••••••• 84 

Wet Mountains, 

Colo ••••••••••••••• 131 

Total ••••••••••••• 978 

Probable 

potential 

resources 

4,240 

486 

753 

5,479 

cent Th02• The highest grade carbonatites occur 

in the Mountain Pass district. 

The resources of Th02 are also divided into 

those reserves and probable potential resources 

that can be produced at less than $15/lb of Th02 , 

those that can be produced at between $15 and 

$30/lb, and those that can be produced at between 

$30 and $50/lb. To obtain a basis for calculating 

these costs, J. F. Lemons, Jr., L. V. Coppa, and 

B. V. Clingan of the U.S. Bureau of Mines made 

cost analyses for both mine and mill models 

(Staatz and others, 1979). The mine model used 

for making cost calculations is the cut-and-fill 

mining system; it is similar to that described in 

the section on Bokan Mountain veins and pipes. 

Milling of carbonatite ore in various districts 

might vary somewhat depending on possible 

byproduct or coproducts recovered. Total rareearth-oxide content in many samples is greatly in 

excess of the Th02 content, and in the carbonatite 

dikes evaluated, the average total rare-earthoxide content is from 4 to 270 times more abundant than the Th02 content. Rare-earth recovery 

is taken into account in evaluating these rocks. In 

the Mountain Pass district, a mill for recovery of 

the rare earths from the massive carbonatite 

already exists. The separation of thorium from 

carbonatite dikes would only require an added circuit. These carbonatite dikes are primarily rareearth deposits. If the value of rare is considered 

at 1978 prices, then the reserves of 332 short tons 

of Th02 could be produced at less than $15/lb, and 

482 tons of Th02 could be produced at between 

$15 and $30/lb; the cost of producing the reTotal producible at 

less than $15/lb 

Total produc]ble at 

between $15 an1 $30/lb 

Reserves Probable 

potential 

resources 

Reserves Probable 

potential 

resources 

248 1,430 390 2,250 

84 486 0 0 

0 0 92 531 

332 1,916 482 2,781 

I 

I 

I 

mainder of the Tll-02 would be greater than $50/lb 

(table 7). The amounts of probable r0tential 

resources in the same price range would be 1,920 

tons of Th02 at a cost of less than $15/lb and 

2,780 tons of Th02 at a cost of between $15 and 

$30/lb. Although the production of muc't of the 

Th02 is dependent on having a sizable rare-earth 

byproduct, some of the Th02 could be produced 

without a rare-earth byproduct. If Th02 ~"(rere the 

only product, then reserves of 296 tons of Th02 

could be produced at less than $15/lb, 174 tons of 

Th02 could be produced at between $'15 and 

$30/lb, and 333 tons could be produced at between $30 and $50/lb. The amounts of probable 

potential resources in the same price rang~ would 

be 1, 700 tons at a cost of less than $15/lb, 1,000 

tons of Th02 at a cost of between $15 anrl $30/lb, 

and 1,920 tons at a cost of between $30 and 

$50/lb. Over 80 percent of the reserves and probable potential resources could be produced at less 

than $50/lb without considering the Yalue of 

byproduct rare earths. 

23 

POWDERHORN DISTRICT, COLORADO 

Carbonatite dikes are associated with alkalic 

rocks, including a large massive carbonatite at 

Iron Hill and thorium veins in the Povrderhorn 

district, Gunnison County. Thorium resources in 

thorium veins, the massive carbonatite, and 

disseminated deposits in nearby granite bodies in 

this district have previously been c~~scribed 

(Staatz and others, 1979). 
The Powderhorn area is underlain largely by 

metasedimentary and metavolcanic rocks intruded by Precambrian granite and other igneous 

rocks. In late Precambrian or Early Cambrian 

time, about 570 million years ago, the Precambrian rocks were intruded by alkalic igneous 

rocks and carbonatite of the complex at Iron Hill 

and by slightly younger diabase dikes (Olson and 

others, 1977). The complex consists chiefly of 

pyroxenite, magneti te-ilmeni te-perovski te 

segregations, uncompahgrite, ijolite, hybrid 

pyroxenite-syenite rocks, nepheline syenite, and 

carbonatite, listed oldest to youngest (Hedlund 

and Olson, 1961). The central part of the complex 

is made up of massive carbonatite. Rocks of the 

complex and surrounding area have been mapped 

in detail by Hedlund and Olson (1968, 1975) and 

Olson (197 4). 

Several hundred carbonatite dikes intruding 

mainly pyroxenite of the complex at Iron Hill and 

the adjoining Precambrian rocks have been mapped by Olson (1974) and Hedlund and Olson 

(1975). They radiate outward from the carbonatite stock at Iron Hill, but do not appear to 

intrude it. The carbonatite dikes are typically 3-5 

feet thick but a maximum thickness of 150 feet 

has been noted. Some dikes can be traced discontinuously for 300-600 feet along strike. All carbonatite dikes recognized to date are found 

within 1 mile of the alkalic complex at Iron Hill. 

The distribution of minerals and their grain sizes 

tend to be fairly homogeneous, although breccia 

and mineral layering have been observed. The 

near-surface and surface exposures are various 

shades of brown, reddish brown, and yellowish 

brown because of the oxidation and hydration of 

iron-bearing minerals. According to J. C. Olson 

and D. C. Hedlund (written commun., 1978), the 

following minerals, in decreasing order of frequency of occurrence, are found in the carbonatite 

dikes: dolomite, calcite, siderite, biotite, 

phlogopite, pyrite (including goethite pseudomorphs after pyrite), barite, apatite, potassium 

feldspar, pyrochlore, monazite, chalcopyrite, 

sphalerite, galena, fluorite, synchisite, and 

parisite. Siderite occurs as distinct segregations 

in a few dikes, and these siderite-rich zones contain ralatively abundant pyrite and tend to be 

more radioactive than the portions of carbonatite 

that lack siderite. The pyrite may be partly or entirely replaced by geothite. The other sulfide 

minerals are sparse. No minerals that contain 

24 

thorium as a major constituent have been found, 

although thorium most likely occurs in pyrochlore and monazite and perh~os in the other 

minerals that contain abundant rare-earth 

elements. The Th02 content of various carbonatite dikes ranges from about 0.0035 to 0.361 

percent. 

Resources were calculated fo:":" 13 carbonatite 

dikes that have an exposed lengt.h of from 150 to 

1,200 feet. Reserves of these dnposits total 763 

short tons of Th02 and probable potential 

resources are estimated to be 4,240 tons. The 

total reserves and probable potential resources of 

individual carbonatite dikes range from 14 to 

1,670 tons of Th02. In addition, these carbonatites also contain reserves of 21,000 tons of 

total rare-earth oxides, 1,330 to'"ls of Nb205, and 

57 tons of U30 8• Other probable potential 

resources in these carbonatites include 106,000 

tons of total rare-earth oxider, 6,590 tons of 

Nb20 5, and 287 tons of U 30 8• Truelve of the thirteen dikes were large enough to be considered in 

opening a mine. The cost of producing a pound of 

Th02 in one of these dikes was less then $15/lb. 

This carbonatite had reserves of 248 tons of Th02 

and probable potential resourcns of 1,430 tons. 

The cost of producing a pound of Th02 in four 

other dikes was between $15 and $30/lb. These 

carbonatites had reserves of 390 tons of Th02 and 

probable potential resources of 2,250 tons. The 

cost of producing a pound of T'102 from all the 

other carbonatites is greater the-n $50/lb. 

MOUNTAIN PASS, CALIFORNIA 

Three types of thorium depo"its occur in the 

Mountain Pass district, San Bernardino County, 

Calif.: carbonatite dikes, a mar'3ive carbonatite 

body (the Sulphide Queen body), and thorium 

veins. A mine on the Sulphide Q 'Ieen carbonatite 

is the largest producer of rar~ earths in the 

United States. Both the masqive carbonatite 

body and the thorium veins have been discussed 

previously (Staatz and others, 1979, p. 19-20 and 

31-33). Carbonatite dikes at Mountain Pass are 

found chiefly in the Birthday area north and 

northwest of the Sulphide Queen massive carbonatite, just south of the tran~verse fault that 

defines the northern boundary of the area. Carbonatite dikes are also found at several other 

localities, such as the Simon-Ray prospect about 

600 feet southeast of the Sulphide Queen stock. 
The carbonatite dikes are associated with 

potassic igneous intrusive rocks. These rocks 

intrude a belt of Precambrian metamorphic and 

igneous rocks. The area including these carbonatites is bounded on the east and south by 

alluvium of I vanpah Valley and on the west by 

the Clark Mountain fault. The north boundary is 

formed by a transverse fault that cuts the Clark 

Mountain fault (Olson and others, 1954, p. 4-8). 

The carbonatite dikes range in thickness from 

less than 1 to about 20 feet and can be traced 

along strike for a maximum of about 400 feet. 

They characteristically contain abundant calcite 

and barite with or without abundant bastnaesite. 

Other minerals include siderite, quartz, fluorite, 

galena, pyrite, apatite, crocidolite, wulfenite, 

biotite, thorite, hematite, magnetite, goethite, 

and potassium feldspar. Calcite may form as 

much as 90 percent of some dikes and occurs as 

grains several tenths of an inch in diameter. 

Barite is usually pink or tan and may form as 

much as 30 percent of some dikes. Thorite, the 

principal source of thorium, is found in tiny 

reddish-brown crystals, commonly along fractures. Bastnaesite, which is the chief rare-earth 

mineral, occurs as tabular crystals as long as 

4 inches and may form as much as 30 percent of 

the rock. The Th02 content of the carbonatite 

dikes varies from 0.024 to 2.39 percent (Olson and 

others, 1954, p. 68-69). These same dikes range in 

total rare-earth-oxide content from 2.03 to 18.64 

percent. Some carbonatites are narrow and some 

are exposed in only one working. We have limited 

our resource calculations to carbonatites at least 

3 feet in average thickness and at least 100 feet 

long for which analytical data are available. Five 

carbonatites fall in this category. Average 

thickness among these ranges from 3 to 10 feet. 

The combined figures for reserves plus probable potential resources for each of these five carbonatites ranges from 65 to 220 short tons of 

Th02, and the total for all five deposits is 570 

tons. Of this amount reserves make up 84 short 

tons and probable potential resources 486 tons. 

In addition, the reserves and probable potential 

resources would yield approximately 40 times as 

much total rare-earth oxides as Th02• Thorium 

would normally be produced here as a byproduct 

of the recovery of rare earths. All the reserves and 

probable potential resources could be produced at 

less than $15/lb. Although our calculations incorporate the cost of building a new mill, all that 

25 

needs to be done to recover thorium in this area 

is to add a thorium circuit to the mill used in 

recovering rare earths. 

WET MOUNTAINS AREA, COLORADO 

Carbonatite dikes in the Wet Mountains area, 

Fremont and Custer Counties, can be diviqed into 

primary magmatic and replacement carb ~natites 

(Armbrustmacher, 1979). Only the primc.ry magmatic carbonatites have sufficiently high concentrations of thorium to be considered as a resource. 

Carbonatite dikes in the Wet Mountains are 

spatially and genetically related to thre':'l alkalic 

intrusive complexes of Cambrian age (Olson and 

others, 1977): the Gem Park Complex (Parker 

and Sharp, 1970; Roden and Cullers, 1 f76), the 

McClure Mountain Complex (Shawe and Parker, 

1967), and the complex at Democrat CreE'~ (Heinrich and Dahlem, 1966). Precambrian h(J~t rocks 

of the alkalic complexes and carbonatites consist 

of Proterozoic X metamorphic rocks-primarily 

layered granitic gneisses, hornblende gneisses, 

and amphibolites-and Proterozoic X andY intrusive granitic rocks of Boulder Cr:lek age 

(1. 72 b.y.) and Silver Plume age (1.45 b.y.) (Taylor 

and others, 1975a, b). The mafic-ultramafic parts 

of the McClure Mountain and Gem Park Complexes are similar to each other in near1

y every 

respect. They consist chiefly of layered gabbro 

and pyroxenite, although rocks at Iron Mountain 

(McClure Mountain Complex) also include minor 

anorthosite, dunite, peridotite, and troctolite. In 

addition, the McClure Mountain Complex contains abundant biotite-hornblende syenite, 

nepheline syenite, and mafic nepheline.~bearing 

rocks, whereas the Gem Park Complex contains 

leucocratic rocks-pegmatitic nephe1ine-and 

sodalite-bearing syenite-at only one locality. 

Mafic-ultramafic rocks also occur with the 

predominantly leucocratic complex at D ~mocrat 

Creek. Carbonatite dikes intrude the alkalic complexes and their Precambrian host rocks. 

Thorium veins also occur in the vicinit:v of the 

alkalic intrusions and are probably ge:-tetically 

related to them (Armbrustmacher, 1976: Christman and others, 1959). The resourcer of the 

thorium viens have been reported (Stc.~tz and 

others, 1979, p. 12-13). 

Carbonatites in the Wet Mountains area form 

dikes that range in thickness from about 1 inch to 

9 feet-a typical thickness is 3 feet. 'They are 
discontinuous along strike and are rarely traced 

along strike for a distance of more than several 

hundred feet, although one carbonatite has been 

traced for 1,400 feet. They tend to be quite coarse 

grained; carbonate grains as much as 2 inches 

across are common. Most carbonatite outcrops 

are brown, greenish brown, or, rarely, bluish gray 

on fresh surfaces. Unoxidized carbonatite from 

below the zone of oxidation is nearly white. All of 

the primary magmatic carbonatites thus far examined occur within 4 miles of one of the alkalic 

intrusive complexes. They are quite numerous 

west of the McClure Mountain Complex, east of 

the McClure Mountain complex along Bear 

Creek, and at Gem Park. Carbonatites west of the 

McClure Mountain Complex in the Road Gulch 

area have been discussed by Staatz and Conklin 

(1967), and the Goldie carbonatite has been 

described by Heinrich (1977). A total of 41 

mineral species have been identified in the carbonatites, and they are listed in Armbrustmacher 

and Brownfield (1978). Calcite is ubiquitous, 

dolomite is very common, and strontianite and 

ankerite are sparse. Bastnaesite is a fairly 

common constituent and has been identified in 

nearly 50 percent of the samples studied. Quite 

commonly the bastnaesite is associated with synchisite and, rarely, with ancylite and strontianite. 

Other rare-earth-bearing minerals include 

monazite, xenotime, and fluorapatite. Quartz, 

hematite, and barite are common and are present 

in variable amounts; microcline is also quite common. Pyrite is more common than sphalerite or 

galena and its alteration product cerussite. 

Thorite, fluorite, and pyrochlore have also been 

identified in a few samples. A unique 

aluminofluoride mineral assemblage occurs in the 

Goldie carbonatite (Heinrich and Anderson, 1965; 

Heinrich and Quon, 1963; and Heinrich, 1977). 

The carbonatite dikes at Gem Park contain 

minerals that have not been identified in carbonatites elsewhere in the Wet Mountains area 

and inclurle columbite, natrolite, pyrrhotite, and 

thorianite (Parker and Sharp, 1970). 

Primary magmatic carbonatites in the Wet 

Mountains area contain an average of 0.17 percent Th02, 0.0097 percent Nb20 5 , 0.0031 percent 

UsOs, and 2.15 percent total rare-earth oxides. 

Many of the carbonatites tend to be elongated, 

lens-shaped bodies that have a limited strike 

length. Resources were calculated on the seven 

largest carbonatite dikes, including the Klondike, 

26 

Cabin, Dreamer's Hope, and Goldie. Total 

reserves in these deposits are 131 tons of Th02; 

total probable potential resources are 7 53 tons. 

The total reserves and prob ~ble potential 

resources of individual deposits range from 14 to 

288 tons of Th02• In addition to Th02 the total 

reserves contain 2,500 tons of total rare-earth oxides, 17 tons of U30 8, and 40 ton<;~ of Nb20E. The 

probable potential resources also contain 14,300 

tons of total rare-earth oxides, 1 (' ~ tons of U 30 8, 

and 228 tons of Nb20 5• The cost of producing a 

pound of Th02 was less than $50/lb from only 

three of these dikes. These tl'ree dikes had 

reserves of 92 tons of Th02 and probable potential resources of 531 tons of Th02• Th02 could be 

recovered from these three dikes at between $15 

and $30/lb. 

BEARPAW MOUNTAINS, MOti'TANA 

The Bearpaw Mountains repref~nt an isolated 

mountain range of volcanic orig~n rising about 

4,000 feet above the surrounding plains in northcentral Montana. Carbonatites and other alkalic 

rocks, including the Rocky Boy stock, are found 

in the west end of these mountaiiJ s. Carbonatites 

in the Bearpaw Mountains are Pssociated with 

alkalic magmas that were intrude~. and extruded 

to form the Bearpaw volcanic fie ~ in early Tertiary time (Schmidt and others, 19~4). The largest 

and most complex alkalic body is the Rocky Boy 

stock, which is composed of forr general rock 

groups, oldest to youngest: (1) bio+.ite pyroxenite, 

(2) shonkinite, (3) monzonite, and (4) porphyritic 

potassic syenite (Pecora, 1962). SHicocarbonatite 

dikes and stockworks occupy fr,ctures in this 

plug and the adjacent shonkinite and monzonite. 

The carbonatite dikes are fairly abl1ndant in holes 

drilled by Texas Instruments C(]. to assess the 

distribution of rare earths. Almort 20 percent of 

the core consisted of silicocarbonatite and sovitic 

carbonatite in intersect segments ranging from a 

few tenths of an inch to 50 feet thick (Pecora, 

1962). The largest carbonatite dikes exposed on 

the surface exceed 40 feet in width. Much of the 

anomalous radioactivity in the core, however, 

does not occur in the carbonatites but is localized 

in altered potassic syenite and associated 

pegmatites. 

The silicocarbonatites and sovitic carbonatites 

consist chiefly of calcite, orthoclase, biotite, 

pyrite, and pyrrhotite. Accessory minerals in-
elude aegirine, siderite, apatite, quartz, uranoan 

pyrochlore, barite, ilmenite, sphalerite, galena, 

zircon, burbankite, ancylite, calkinsite, strontianite, celestite, and lanthanite. The rare-earth 

carbonates burbankite and calkinsite were first 

described from this area (Pecora and Kerr, 1953). 

A wide variation in the distribution of essential 

and accessory minerals occurs between carbonatites. Thorium minerals have not been identified. Surface exposures of carbonatites, 

although not particularly abundant, are not 

especially radioactive. Analyses of five carbonatites, including the most radioactive one 

noted, contain from 4 to 60 ppm Th02. These 

rocks have an average of about 17 ppm Th02. The 

Th02 content of the carbonatite dikes, from the 

limited analytical information available, does not 

indicate either economic or near-economic 

amounts. 

RAVALLI COUNTY, MONT ANA-LEMHI COUNTY, IDAHO 

A variety of carbonatite dikes is found in an 

area nearly 18 miles long by 4 miles wide that 

straddles the Montana-Idaho border across the 

Bitterroot Mountains. The southern part of this 

area is in the Mineral Hill mining district. 

The carbonatite dikes are intruded chiefly into 

Precambrian metamorphic rocks. The dikes are 

tabular to lens-shaped and tend to either lie 

parallel to the foliation of their gneissic host rock 

or at a small angle to the foliation. The dikes are a 

few inches to about 10 feet thick. One of the more 

fully explored carbonatites can be traced for more 

than 300 feet; it ranges from 1 1/2 to 6 feet thick. 

Another carbonatite, as evidenced from scattered 

exposures, may be more than 1,000 feet long 

(Anderson, 1960, p. 1183). Byron Sharp and 

Donald Hetland, then of the U.S. Atomic Energy 

Commission, reported on another carbonatite 

that can be traced for 2,200 feet (written commun., 1968). Texturally the carbonatites range 

from fine to coarse grained. Their major constituents are calcite and dolomite; biotite, chlorite, 

actinolite, allanite, quartz, barite, apatite, 

monazite, pyrite, magnetite, ancylite, and columbite may be present in significant amounts locally. Additional minerals usually present in 

accessory amounts include pyrrhotite, chalcopyrite, molybdenite, hematite, rutile, crocidolite, 

niobium, rutile, ilmenite, fersmite, eschynite, 

fluorite, malachite, garnet, albite, muscovite, 

glaucophane, and wollastonite (Anderson, 

27 

1960, p. 1184; Heinrich and Levinsoll, 1961, 

p. 1429-1438). 

Although several thorium-bearing minE.rals are 

fairly common in these carbonatites, their Th02 

content tends to be low. Monazite from a carbonatite dike in the northern part of the area 

is reported by Heinrich and Levinson (1961, 

p. 1434) to contain 0.7 percent Th02, and allanite 

from the same dike, only a trace Th02. 

Analytical data on the carbonatite dikes are 

sparse. Two samples cut across carbonatite dikes 

in the southern part of this area containE'd 0.089 

and 0.0054 percent Th02. Sufficient data on size 

of the various carbonatite dikes are not available 

to make reliable estimates of their volume.. As the 

average thickness of most of these dike:~ is between 1 and 2 feet and as their Th02 co'"ltent is 

apparently low, the carbonatite dikes in this area 

do not appear favorable for significart Th02 

resources. 

MAGNET COVE AND POTASH SULFUR SPRINGS,ArllfANSAS 

Magnet Cove is in Hot Springs Count:?, Ark., 

and Potash Sulfur Springs area is nearly 6 miles 

west of there in Garland County. Car1''lnatite 

dikes and small bodies form parts of alkalic 

igneous complexes at these two places. Economically significant deposits of rare-earth el ~ments, 

barite, niobium, titanium, uranium, phosphate, 

agricultural lime, and vanadium have r~Ipplied 

the incentive for detailed studies of the geology 

(Erickson and Blade, 1963; Howard and Steele, 

1975). Carbonatite bodies at Magnet Cove are 

part of a complex of alkalic rocks that forn a welldifferentiated ring-dike sequence (J ohnPon and 

Baker, 1976). These igneous rocks are intruded into complexly folded sedimentary rocks ranging 

from Silurian to Mississippian in ag~~. Carbonatite dikes at Potash Sulfur Springs intrude 

alkalic rocks that have also been descril'a.d as a 

ring-dike sequence (Howard and Steele, 1975). 

The alkalic complex at Potash Sulfur S:rrings is 

the site of the only mine operated for vznadium 

alone in the United States. Carbonatite dikes and 

irregularly shaped masses that occur in this area 

consist of coarse-grained sovitic carbonatite 

covered in part at Magnet Cove by residual 

phosphate-rich saprolite. Natural exposures are 

rare, and the best exposures occur at the Kimzey 

calcite quarry at Magnet Cove and at th~ Union 

Carbide Corp. open-pit vanadium mine at Potash 

Sulfur Springs. The carbonatite at Magnet Cove 
consists chiefly of seven primary minerals in the 

following order of decreasing abundance: calcite, 

apatite, monticellite, magnesium-rich magnetite, 

perovskite, phlogopite, and pyrite (Nesbitt and 

Kelly, 1977). The mineral kimzeyite, a zirconium 

garnet, was first described from carbonatite at 

the Kimzey calcite quarry (Milton and Blade, 

1958). Other minerals include anatase, idocrase, 

anhydrite, humite, dolomite, molybdenite, 

biotite, and pyrrhotite. Minerals found in the carbonatite at Potash Sulfur Springs include calcite, 

aegirine-augite, andradite, pyrite, zircon, 

analcite, and biotite. The thorium, uranium, and 

rare-earth contents of carbonatites from Magnet 

Cove and Potash Sulfur Springs are low relative 

to carbonatites from other areas. At the outcrop 

the Arkansas carbonatites are not anomalously 

radioactive. According to Erickson and Blade 

(1963), thorium does not exceed about 34 ppm in 

all the rocks of the Magnet Cove Complex. Six 

samples of unweathered carbonatite taken from 

the two areas by us range from 0.65 to 24 ppm 

Th02• All except one sample, however, had less 

than 5 ppm Th02• The analyses available, as well 

as their low overall radioactivity, suggest that 

the amount of Th02 in the carbonatites is too 

small to represent even a subeconomic resource. 

APATITE-BEARING IRON DEPOSITS OF 

MINEVILLE, NEW YORK 

Thorium, rare earths, and a little uranium were 

found in 1952 in apatite from iron ores in the 

Mineville, N.Y., area (McKeown and Klemic, 

1956, p. 9). The Mineville iron district is located 

in the northeastern part of the Adirondack Mountains along the west side of Lake Champlain. 

Most of the iron mines here are near the towns of 

Mineville and Port Henry in Essex County. There 

are several iron deposits in an area of approximately 30 square miles in this district. The main 

apatite-rich deposits are the Old Bed, Cheever, 

and Smith orebodies. The Cheever and Smith 

orebodies are mined out. 

Iron-ore mining started at the Cheever mine in 

1804 (Birkinbine, 1890, p. 7 4 7). In 1824 other 

mines were opened (J. R. Linney, 1943, p. 481). 

The district did well during the period between 

1860 and 1890. Mining was severely curtailed in 

the next 10 years owing to the depressed state of 

28 

the iron industry and expansion of mines in the 

Lake Superior district. The vari ~us holdings in 

the district were incorporated by Witherbee, 

Sherman, and Co., who developed the district into 

one of the more successful enterprises of its day 

(J. R. Linney, 1943, p. 481). This C">mpany bought 

land, did exploration, and openec new orebodies, 

such as Old Bed, Harmony, New P~d, Fisher Hill, 

and Sherman. During World War I this company 

was an important contributor to this country's 

supply of iron. Changes in the industry following 

this war caused the company to have financial 

setbacks, and in 1938 the company's holdings 

were leased to Republic Steel Corp. Republic 

Steel replaced worn-out equipmert and increased 

the amount of ore shipped to thn blast furnaces 

from 500,000 to 1,000,000 long tons per year by 

1942 (R. J. Linney, 1943, p. 488). f:nce then, some 

of the deposits have been wcrked out, and 

Republic Steel Corp. closed their operation in 

1970. 

The iron deposits are divided ac ~ording to their 

phosphorus content into high- and low-phosphorus deposits, or into Bessemer and nonBessemer grades (R. J. Linney, 1943, p. 488). 

Separate mills were set up to sepqrate iron from 

each of these types of deposits. High-phosphorus 

ores are those containing more than 0.5 percent 

phosphorus in the ore. The Olcl Bed orebody, 

which averaged 1-1.25 percent p~osphorus, furnished the greater part of the Bessemer-type ore 

(R. J. Linney, 1943, p. 489). This amount of 

phosphorus would be equivalent to about 6-7.2 

percent apatite. As the thorium i~ principally in 

the apatite, the principal phos-nhorus-bearing 

mineral in the ore, the low-phosp."'torus ores contain little thorium. 

The rocks in the area of the maptetite deposits 

form a complex suite of metamorp"'tic and igneous 

rocks of Precambrian age (Ken'll and Ruedemann, 1910; Newland, 1908). G~anite, gabbro, 

syenite, gneiss, and diorite are thn principal rock 

types and, in most places, the host rocks for the 

iron deposits. Extensive foldin!7 and faulting 

have resulted in a complex structure. The iron 

deposits are made up principally of magnetite, 

martite, and apatite. Gangue minerals include 

augite, hornblende, albite, quartz, pyrite, and 

tourmaline (McKeown and Klemic, 1956, p. 14). 

Except in ore that is almost entirely magnetite, 

no obvious relationship exists between the 

amount of magnetite and the amc~Int of apatite; 
apatite is generally present in the Old Bed ore. 

Apatite occurs in slightly distorted rice-shaped 

grains about 1-3 mm long. The apatites vary in 

color and may be reddish brown, green, white, or 

transparent. The reddish-brown apatite is by far 

the most common variety. The rare-earth content 

of the apatites, and presumably the thorium content, varies considerably. The reddish-brown 

apatite contains between 5.8 and 20.6 percent 

total rare earths, the green variety between 0.5 

and 2.0 percent, and the white and transparent 

varieties only trace amounts. Microscopic examination of the reddish-brown apatite indicated 

that the color is due to mineral inclusions and 

coatings (McKeown and Klemic, 1956, p. 12). 

X-ray diffraction patterns of reddish-brown 

material left after the apatite was leached away 

by acid showed it to be monazite, bastnaesite, 

and hematite. In addition to rare earths, the 

apatite contains thorium and uranium. Analyses 

made on 14 samples of apatites separated from 

the Old Bed, Joker, and Smith orebodies had an 

average Th02 content of 0.17 percent and an 

average U30 8 content of 0.038 percent (McKeown 

and Klemic, 1956, p. 15). 

Apatite occurs in 1978 both in large tailings 

dumps from previous operations and in \}nmined 

portions of various magnetite orebodies. The 

amount of ore in unmined bodies is not known. As 

sufficient data are not presently available to 

assess possible resources in unworked parts of 

various mines, the rest or this paper is confined to 

the more readily available thorium and uranium 

resources in the tailings dumps. Furthermore, the 

cost of recovering apatite from the dumps is 

much less, as it is already mined, ground, and partially sorted. 

Tailings piles include material derived from 

both the high- and low-phosphorus deposits (or 

apatite-rich and apatite-poor deposits). Some 

piles are mixtures of both types of ore. The lowand high-phosphorus ores were partly divided 

from the early 1900's, when separate mills were 

set up to handle the different types of ores. Tailings piles made up primarily of low-phosphorus 

iron ore are not important as sources of thorium. 

The Old Bed deposit was the largest and most extensively worked apatite-rich deposit in the 

district. In addition, the Old Bed mill also handled ore from adjacent apatite-poor deposits. 

Other tailings piles that have received some 

apatite-rich ore are adjacent to the no. 6, no. 7, 

29 

and Cheever mills. The old no. o mill was at Port 

Henry on Lake Champlain. This mill r.q_ndled 

some low-grade apatite ores, although the greater 

part of the operation involved apatite-rich ores. 

This tailings pile extends out into Lake 

Champlain. The no. 7 mill tailings pile, cbout a 

mile east of Moriah Center, is the largest: in the 

district. Although this mill has treated both 

apatite-rich and apatite-poor iron ores, N>proximately two-thirds of the tailings pile cairo. from 

apatite-rich orebodies. The Cheever mine and tailings dump is about 21 miles north of Port Henry 

on the west side of Lake Champlain. In aidition 

to these tailings piles, there is a small dunp containing partially concentrated apatite, which lies 

approximately 500 feet northwest of the C1

i Bed 

tailings pile. This concentrate was made at the 

no. 5 mill, which was built to recover apatite for 

fertilizer before it burned down. 

Dumps in the Mineville district are estimated 

to have about 18,000,000 short tons of tR.ilings. 

Approximately two-thirds, or at least 10,[10,000 

tons, of these tailings was derived from roatiterich iron ores. The amount of apatite in the tailings from the apatite-rich dumps was calculated 

from data given by McKeown and Klemic (1956, 

p. 21-22). These figures indicated that 8 percent 

of the tailings is apatite, or that approximately 

800,000 short tons of apatite occurs in the dumps. 

The average apatite contains about 0.17 percent 

Th02 and 0.038 percent U30 8 (McKeown and 

Klemic, 1956, p. 15). The amount of apatitP- in the 

dumps would contain 1,360 short tons of Th02 

and 304 tons of U 30 8 • In addition, the ap<:~.tite is 

rich in rare earths, and McKeown and Klemic 

(1956, p. 15) reported that 12 specimens had an 

average rare-earth-oxide content of 13 Jl~rcent. 

Thus, the dumps would also contain 1 04,000 

short tons of total rare-earth oxides. S·1ectrographic analyses given by McKeown and Klemic 

(1956, p. 12) indicated that yttrium is one of the 

principal rare earths. Hence, these tailir~s are 

also a potential source for the yttrium-gro·1p rare 

earths. 

The cost of milling the tailing piles has n'lt been 

calculated. The possible economic products of the 

apatite from the Mineville area are tl''lrium, 

uranium, total rare-earth oxides, yttrium oxide, 

and phosphoric acid. The cost of milling the tailings under various conditions can be calculated. 

If only thorium and uranium were recover~d and 

they could be sold for $30/lb, then the value of the 
thorium and uranium per ton of tailings would be 

about $10. Rare earths and phosphorus, however, 

would undoubtedly play an important part in any 

economic recovery of thorium and uranium. In 

1978 total rare-earth oxides were selling for about 

$0.60/lb and Y203, about $7/lb. The value of the 

total rare-earth oxides would be equivalent to 

$12.48/ton of tailings, if a market could be found 

for this amount of rare earths at 1978 prices. If 

Y20s made up 10 percent or more of the total rare 

earths, then the added value due to the Y 20 3 

would more than double the value due to rare 

earths in a ton of tailings. Because the apatite 

would be taken into solution to recover the 

thorium, coproducts of uranium, rare earths, and 

phosphorus could be cheaply produced. 

The above figures suggest that thorium and 

uranium could be recovered at a cost between $15 

and $30/lb without the aid of any other product; 

with the development of a rare-earth market they 

could probably be produced at less than $15/lb. 

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