Quantitative Mineral Resource:~ A!sse~s~ 

Selected Mineral Deposits· 1r • rn1P ·. 

. 

Challis Nation al Forest, I( 

IDAHO 
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Quantitative Mineral Resource Assessment of 

Selected Mineral Deposits in the 

Challis National Forest, Idaho 

By MARK W. BULTMAN 

U.S. GEOLOGICAL SURVEY BULLETIN 1987 
U.S. DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names 

in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Government 

Text and illustrations edited by Helen Gibbons 

Graphics prepared by Fred Garrido and Susan Mayfield 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1991 

For sale by the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

library of Congress Cataloging-in-Publication Data 

Bultman, Mark W. 

Quantitative mineral resource assessment of selected mineral 

deposits in the Challis National Forest, Idaho. 

p. em.- (U.S. Geological Survey bulletin: 1987) 

Includes bibliographical references. 

Supt. of Docs. no.: I 19.3: 1987 

1. Mines and mineral resources-Idaho-Challis National Forest. 

2. Geology, Economic-Idaho-Challis National Forest. I. Title. 

II. Series. 

QE75.89 no. 1987 

[TN24.12] 

55 7.3 s-dc20 

[553 1 .09796] 91-3768 

CIP 
CONTENTS 

Summary 1 

History of mineral production in Challis National Forest 1 

Methodology of the quantitative assessment 2 

Quantitative mineral resource assessment in Challis National Forest 3 

Quantitative assessment of selected mineral deposit models 4 

Polymetallic vein deposits 6 

Precious-metal vein deposits 6 

Stockwork molybdenum deposits (Cretaceous) 7 

Polymetallic skarn deposits (tungsten skarns and copper skarns) 9 

Irregular replacement deposits of base and precious metals 9 

Sediment-hosted, jasperoid-associated, precious-metal deposits 10 

Stratabound syngenetic deposits of precious and base metals 10 

Gold placer deposits 11 

Summary of quantitative assessment of Challis National Forest 11 

Selected references 11 

FIGURES 

1. Map showing location of Challis National Forest and principal mining 

districts 16 

2. Graph showing discoveries of mineral deposits in Challis National Forest 16 

3. Graph showing tonnages of ore in polymetallic vein deposits 17 

4. Map showing tracts permissive for occurrence of polymetallic vein deposits 18 

5. Graph showing tonnages of ore in precious-metal vein deposits 18 

6. Graph showing gold grades of ore in precious-metal vein deposits 19 

7. Graph showing silver grades of ore in precious-metal vein deposits 19 

8. Map showing tracts permissive for occurrence of precious-metal vein 

deposits 20 

9. Map showing tracts permissive for occurrence of Cretaceous stockwork 

molybdenum deposits 20 

10. Map showing tracts permissive for occurrence of tungsten skarns and copper 

skarns 21 

11-15. Graphs showing: 

11. Tonnages of ore in irregular replacement deposits of base and precious 

metals 21 

12. Lead grades of ore in irregular replacement deposits of base and 

precious metals 22 

13. Silver grades of ore in irregular replacement deposits of base and 

precious metals 22 

14. Copper grades of ore in irregular replacement deposits of base and 

precious metals 23 

15. Gold grades of ore in irregular replacement deposits of base and 

precious metals 23 

16-19. Maps showing: 

16. Tracts permissive for occurrence of irregular replacement deposits of 

base and precious metals 24 

17. Tracts permissive for occurrence of sediment-hosted, jasperoidassociated, precious-metal deposits 24 

18. Tracts permissive for occurrence of stratabound syngenetic deposits of 

precious and base metals 25 

19. Tracts permissive for occurrence of gold placer deposits 25 

Contents Ill 
IV Contents 

TABLES 

1. Mineral deposit models and grade and tonnage models used in this report S 

2. Probabilistic estimate of number of undiscovered deposits of selected mineral 

deposit models in Challis National Forest 7 

3. Probabilistic estimates of tonnages of metals and ore in undiscovered deposits of 

selected mineral deposit models in Challis National Forest 8 

4. Summation of probabilistic estimates of tonnages of metals and ore in undiscovered 

deposits in Challis National Forest 11 
Quantitative Mineral Resource Assessment of Selected 

Mineral Deposits in the Challis National Forest, Idaho 

By Mark W. Bultman 

Summary 

This quantitative assessment of selected mineral 

deposits in the Challis National Forest, Idaho, is provided 

to assist the U.S. Forest Service in complying with Title 36, 

Chapter 2, part 219.22, Code of Federal Regulations, 

which requires the Forest Service to provide information 

and interpretations so that mineral resources can be 

considered with other kinds of resources in land use 

planning. 

This report is a companion publication to Mineral 

Resource Potential and Geology of the Challis National 

Forest, Idaho, U.S. Geological Survey Bulletin 1873, by 

Worl and others (1989). Geologic, geophysical, 

geochemical, mineral resource, and mineral deposit data 

in Bulletin 1873 were used in this study to produce 

quantitative estimates of the potential resources available 

from selected mineral deposits in the Challis National 

Forest. 

The quantitative assessment involves three steps 

(W.O. Menzie, written commun., 1988) that are followed 

by a computer simulation. Known and possible mineral 

occurrences are identified and classified into appropriate 

mineral deposit models in the first step. The second step is 

the production of a mineral resource assessment map, 

which delineates tracts that are permissive for the 

occurrence of deposits described by the models defined in 

step one. The third step is the estimation of the number of 

undiscovered mineral deposits in each mineral deposit 

model. The computer simulation is carried out by a 

program informally referred to as MARK3. The output from 

the MARK3 program is a probabilistic estimate of the ore 

and metal contained in deposits of each mineral deposit 

model. 

Using available information and the MARK3 

program, it is estimated at a 50-percent confidence level 

that undiscovered mineral deposits in the Challis National 

Forest contain 35 tonnes of gold, 7,700 tonnes of silver, 

12,900 tonnes of copper, 4,790,000 tonnes of lead, 

7,880,000 tonnes of zinc, 52,700 tonnes of tungsten, and 

221,000 tonnes of molybdenum. 

Manuscript approved for publication, March 29, 1991. 

HISTORY OF MINERAL PRODUCTION IN 

CHALLIS NATIONAL FOREST 

The Challis National Forest (herein called "the 

Forest") contains 4,338 mi2 of mountainous terrain in 

three separate areas (fig. 1); elevations range from approximately 6,000 ft on the margin of the Snake River 

Plain to 12,662 ft on the summit of Bora Peak. The Forest includes the following physiographic features in central Idaho: the Lost River Range, the White Knob Mountains, the Boulder Mountains, the Pahsimeroi Mountains, 

the Stan ley and Copper basins, and parts of the Lemhi 

Range, the Pioneer Mountains, the Sawtooth Range, and 

the Salmon River Mountains. 

The Forest and the surrounding area have a long 

history of mineral exploration and mining, which have 

played a major role in the economy of central Idaho. 

Metals produced from mines in the Challis National Forest include gold, silver, lead, zinc, tungsten, and molybdenum. Small amounts of fluorspar, uranium, and rareearth-element minerals have also been produced. A 

number of other mineral commodities have been reported to be present in the Forest, but have never been produced. These include iron, barite, cobalt, mercury, sulfur, antimony, manganese, and arsenic. 

The discovery of mineral deposits in the Forest has 

been quite sporadic since 1860 (fig. 2). These sporadic 

discoveries are mostly a reflection of economic cycles in 

the minerals industry. Gold attracted the first prospectors 

to the area of the present-day Challis National Forest. 

From the early 1860's to 1869 most of the known gold 

placer deposits and a considerable share of the known 

gold lode deposits were found. Gold placer production 

died out by 1900, except for a limited reappearance from 

the 1930's through the 1950's, whereas production from 

gold lodes has been intermittent since their discovery. 

Exploration for silver-lead ores began around 1880 

and extended until about 1888. The discovery of numerous silver-lead mineral deposits in the 1880's resulted in 

the construction of a number of smelters in the region, 

the last of which closed in 1902. 

Most of the mines discovered in the early to middle part of the 20th century produced silver, lead, 

History of Mineral Production -in Challis National Forest 
copper, and zinc from multimetal veins, but tungsten 

production was also important during this time. There 

was considerable exploration for uranium in the 1950's 

and 1960's, resulting in some production of uranium in 

1959 and 1960. A number of porphyry molybdenum deposits were discovered in the 1960's, including the 

Thompson Creek deposit, which is still producing ore today. Another exploration program in the 1960's and 

1970's delineated a number of large stratabound deposits 

in the Bayhorse region, but no mineral production has 

yet (1989) resulted from the discovery of these deposits. 

METHODOLOGY OF THE QUANTITATIVE 

ASSESSMENT 

The quantitative assessment presented in this report 

is based on the concept of a mineral deposit model. A 

mineral deposit model can be defined as the systematically arranged information that describes the essential attributes of a particular group or class of mineral deposits 

(Cox and Singer, 1986). For the most part, these attributes are geologic, but they may also include characteristics affected by the utilization of a deposit, such as 

the grade of ore produced from it. For a deposit model 

to be of any use in a quantitative assessment, it must be 

combined with tonnage and grade models based on a 

large proportion of the deposits known to belong to the 

given deposit model. Such models are produced by plotting tonnage and grade against percentage of deposits. 

The resulting frequency distributions, which are most often approximated by the log normal distribution, show 

the percentage of deposits of a given model that have a 

particular tonnage or grade. 

The quantitative assessment involves three steps 

(W.D. Menzie, written commun., 1988) that are followed 

by a computer simulation. The first step is to identify 

known and possible mineral deposits in the region and to 

classify each into a mineral deposit model. This step 

may include an extensive literature search, a search of 

computerized data bases, and possibly field verification. 

The second step is to produce a mineral resource 

assessment map. This map delineates all of the geologic 

terranes (based on rock type) that are permissive for the 

occurrence of deposits in each of the mineral deposit 

models identified in step one. These terranes, or tracts, 

are delineated using the most recent and comprehensive 

geologic information about the region along with as 

much geochemical, geophysical, and mineral-occurrence 

data as possible. If enough data are present, it may be 

possible to define smaller areas that have a higher potential than other areas in the same tract for the occurrence 

of a deposit. 

The third step in a quantitative mineral resource 

assessment is to estimate the number of undiscovered 

deposits in the tracts delineated in step two for each 

mineral deposit model. This is perhaps the most difficult 

step in assessing undiscovered mineral resources, and no 

definitive statements can be made at this time on how to 

make such estimates (W.D. Menzie, written commun., 

1988). In general, the estimates are made subjectively 

and are based on geologic know ledge of the region in 

question and knowledge of the deposit model being considered. Often the estimate of the number of undiscovered mineral deposits is made in the form of a probability distribution, and estimates are given for the 10-, 50-, 

and 90-percent levels of confidence. 

The estimates of the number of undiscovered mineral deposits in this report are subjective and are based 

on the information available to the author at the time the 

assessment was made. All of the estimates are based on 

geological analogy. Such estimates begin with an inspection of all of the available geological, geochemical, geophysical, and mineral-occurrence data of the region and 

the postulation that areas with similar geologic attributes 

may contain similar densities of mineral deposits. 

Estimation of the number of undiscovered deposits 

was done in two parts. First, estimates were made within 

known mineral districts and in areas that have geologic 

attributes favorable for the existence of mineral deposits. 

In the latter group, deposit densities were assumed to be 

similar to those in the mineral districts. Included in the 

latter group are areas of high resource potential delineated by Worland others (1989), some of which lie outside 

known mineral districts. The delineation of an area of 

high resource potential requires, among other things, data 

that indicate a high degree of likelihood for resource accumulation and evidence of mineral-forming processes in 

at least part of the area (Worland others, 1989). 

Second, estimates were made in areas that are outside known mineral districts and lack favorable geologic 

attributes. These areas have the proper host-rock lithology for deposits described by a given mineral deposit 

model, but they lack a known combination of geological 

attributes that make it highly probable that such deposits 

are present. The two types of estimates were then combined in a final estimate of the number of undiscovered 

deposits of a given mineral deposit model. 

Finally, the probability distribution of the number 

of undiscovered deposits estimated for a given deposit 

model was combined with the frequency distributions of 

tonnage and grade for the same deposit model in a simulation procedure. The purpose of the simulation is to estimate the metal contained in deposits of the given deposit model in the region being assessed. A computer 

program, informally known as MARK3, does the simulation (Drew and others, 1986). 

Simulation allows an assessor to create a number 

of scenarios by submitting probability distributions of 

the number of undiscovered deposits to MARK3 and ex2 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
ammmg the results. For each deposit model, MARK3 

randomly selects a number of deposits from the probability distribution of deposit occurrence provided by the 

assessor. It then selects a tonnage and grade for each deposit from tonnage and grade models that are provided 

by the assessor or are already in the MARK3 program as 

a result of previous studies (most of the tonnage and 

grade models used in this study fall into the latter category). The simulator calculates the types and amounts of 

metals in each of the deposits. The process is repeated 

many times and produces frequency distributions of metals contained in deposits of the given deposit model. 

MARK3 assumes that the frequency distribution of 

the logs of tonnages and grades for a given deposit model can be modelled as individually normal and jointly bivariate normal. The parameters of the distributions are 

chosen in such a way that the median and mean of the 

individual normal distributions are equal to the median 

and mean of the tonnage and grade data. For the bivariate normal distribution, the correlation is chosen so that 

the mean of the product of the tonnage and grade distributions for a given deposit model is equal to the mean 

metal content of deposits in the model (Root and Scott, 

1988). 

Different deposits in the same deposit model may 

contain different suites of metals. In such a case, the 

MARK3 program divides the deposit model into subtypes such that the deposits of each subtype all contain 

the same suite of metals. Distributions of tonnage and 

grade are calculated separately for each subtype. For example, if MARK3 is working with deposit model A, 

which has some deposits containing Cu and Au (subtype 

A1) and some deposits containing only Cu (subtype A2), 

it will calculate distributions of tonnage, Cu grade, and 

Au grade for subtype Ah and distributions of tonnage 

and Cu grade for subtype A2• When MARK3 is asked to 

simulate the tonnage and grade of a metal in deposit 

model A, it will select a subtype at random. Then it will 

randomly select tonnage and grade values from the tonnage and grade distributions it has constructed for that 

subtype. The likelihood that MARK3 will select a certain subtype is set equal to the fraction of deposits in the 

given deposit model that belong to that subtype. After 

many random selections, MARK3 will have combined 

tonnage and grade data from the various subtypes of a 

deposit model. Thus, MARK3 can estimate how much of 

a certain metal is likely to be contained in deposits of a 

given deposit model even if that metal is missing in 

some of the deposits. 

MARK3 also allows an estimate of the number of 

deposits of a given deposit model to be conditioned on 

the probability that at least one such deposit is present. 

This is useful when estimates are made of the number of 

undiscovered deposits of a deposit model not known to 

be represented in a region. The number of undiscovered 

deposits can be estimated as if at least one is present in 

the region and then conditioned according to what the 

prospects are for that one occurence. The conditional 

probability for the existence of at least one undiscovered 

deposit of a given deposit model is subjectively determined by the assessor. 

Steps one and two of the three-step quantitative assessment method described above were accomplished by 

Worl and others (1989) and will be modified slightly for 

the purposes of this report. Worl and others (1989) presented mineral deposit models (referred to by them as 

"deposit types") for the mineral deposits that are found 

in the Forest, and they delineated areas of moderate and 

high resource potential for each of the deposit models. 

Modifications have been made to some of their deposit 

models in order to use existing grade and tonnage models. Also, in place of their areas of high and moderate 

mineral resource potential, this report presents tracts that 

are simply permissive for the occurrence of deposits of a 

given mineral deposit model. Areas of high mineral resource potential, discussed above, are more restrictive 

than permissive tracts. Areas delineated as having a 

moderate mineral resource potential include areas where, 

among other things, "geologic, geochemical, and geophysical characteristics indicate a geologic environment 

favorable for resource occurrence, where interpretations 

of data indicate a reasonable likelihood of resource accumulation, and (or) where an application of mineral-deposit models indicates favorable ground for the specified 

type(s) of deposits" (Worl and others, 1989); these areas 

have the possibility of being more restrictive than permissive tracts. 

This study focuses on the third step of the quantitative assessment method described above, the estimation of the number of undiscovered deposits, and presents the results of a simulation conducted using 

MARK3. 

QUANTITATIVE Ml NERAL RESOURCE 

ASSESSMENT IN CHALLIS NATIONAL FOREST 

The Challis National Forest has a complex geologic and metallogenic history. A complete discussion of 

the geology of the Forest can be found in reports by 

Worland others (1989) and Fisher and Johnson (1987). 

Several geologic terranes in the Forest are important to the mineral resource assessment. These terranes, 

defined by Worl and others (1989), are the Proterozoic 

terrane, the carbonate terrane (Paleozoic), the quartzite 

terrane (Paleozoic), the flysch terrane (Paleozoic), the 

black-shale terrane (Paleozoic), the Cretaceous intrusive 

rock terrane, the Tertiary extrusive rock terrane (the 

Challis Volcanics), the Tertiary intrusive rock terrane, 

and the post-Challis cover rock terrane. The occurrence 

Quantitative Mineral Resource Assessment in Challis National Forest 3 
of mineral deposits within a terrane depends on many 

factors including regional and local structures, facies 

changes within units, and juxtaposition of terranes. 

A quantitative assessment of the mineral resources 

in a region is based on the availability of tonnage and 

grade models for each of the mineral deposit models 

considered. Worl and others (1989) presented a number 

of mineral deposit models that describe the deposits 

present, or suspected to be present, in the Challis National Forest. Many of these deposit models are based on 

local deposits with little or no record of production, and 

therefore they have no associated grade or tonnage model. Others are identical to or directly related to deposit 

models in the report by Cox and Singer (1986). Many of 

the deposit models of Cox and Singer (1986) are accompanied by tonnage and grade models and can be immediately incorporated into the quantitative assessment. 

Where the tonnage and grade models of Cox and Singer 

(1986) are used, the name of the mineral deposit model 

in this report is the same as that of W orl and others 

(1989; see table 1). 

Two strategies have been used in this report to 

deal with models presented by Worl and others (1989) 

for which no tonnage and grade information exists. First, 

an extensive literature search was done in an attempt to 

create tonnage and grade models for any local deposits 

with adequate data. Because most mining has long since 

ceased in this area, records with both grades and tonnages of any deposits were extremely hard to find. Only two 

deposit models had enough data to allow the creation of 

tonnage and grade models. These models, to be discussed later, are the precious-metal veins model and the 

irregular replacement deposits of base and precious metals model. 

The second strategy used to deal with mineral deposit models of Worl and others (1989) that lack grade 

and tonnage information was to aggregate or disaggregate those models until they matched one of the models 

of Cox and Singer (1986). The four polymetallic vein 

deposit models presented by Worl and others (1989) are 

classified on the basis of the terranes in which they occur, one each for the black-shale terrane, the carbonate 

terrane, the quartzite terrane, and the Tertiary extrusive 

terrane. The polymetallic vein deposit model of Bliss 

and Cox (1986) in the report by Cox and Singer (1986) 

includes all of the above-mentioned terranes as possible 

host rocks. 

In order to use the existing tonnage and grade 

models for polymetallic veins, it is necessary to assume 

that the tonnages and grades from all four polymetallic 

vein models presented by Worl and others (1989) belong 

to one frequency distribution. To test this hypothesis, 

data were gathered for the polymetallic vein deposits in 

the Forest. Unfortunately only seven deposits had 

enough data to create a tonnage figure, and no good 

grade data were available. The data from the seven deposits, which include at least one deposit from each terrane, were combined and plotted. The resultant distribution of tonnage (fig. 3B) was nearly identical to the 

tonnage distribution (fig. 3A) presented for the polymetallic vein model of Bliss and Cox (1986). Therefore, the 

four polymetallic vein deposits in the Forest are described by a single deposit model in this report. 

Worl and others (1989) described a polymetallic 

skarn deposit model that contains both copper and tungsten skams. Their model differentiates copper and tungsten skams as subtypes of a single deposit model. The 

report by Cox and Singer (1986) presents separate deposit models for copper and tungsten skams. In this report, copper and tungsten skarns are assessed separately 

in order to take advantage of the models of Cox and 

Singer (1986). 

Worland others (1989) also define two subtypes in 

their stockwork molybdenum deposit model, namely 

Cretaceous and Tertiary stockwork molybdenum deposits. In this study these are treated as separate models, the 

Cretaceous model after Hall (1987) and the Tertiary 

model after Kiilsgaard and Bennett (1987). The Cretaceous model corresponds to a model presented by Theodore (1986) in the report by Cox and Singer (1986). 

There is no analog to the Tertiary stockwork molybdenum deposit model in the report by Cox and Singer 

(1986). Thus, grade and tonnage models are available 

only for the Cretaceous stockwork molybdenum deposit 

model, and only the Cretaceous deposits are assessed in 

this report. 

QUANTIT AliVE ASSESSMENT OF SELECTED 

MINERAL DEPOSIT MODELS 

A complete list comparing the deposit models used 

by Worl and others (1989) and the associated tonnage 

and grade models used in this report is given in table 1. 

The report by Cox and Singer (1986) is a compilation of 

mineral deposit models and associated grade and tonnage 

models produced by many authors. The individual authors of this volume will be referenced from this point. 

Due to the lack of tonnage and grade information, 

only 9 deposit models were used for simulation in this 

study, but these 9 represent 11 of the 20 deposit models 

presented by Worl and others (1989). In this section, a 

summary of each deposit model used in this report is 

presented along with the median estimate of the number 

of undiscovered deposits and the mean estimated tonnage of ore and metals in the deposits. For a more thorough discussion of the mineral deposit models used here, 

see Worl and others (1989), Fisher and Johnson (1986), 

or Cox and Singer (1986). Those reports are the main 

sources of the summaries presented below. 

4 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
Table 1. Mineral deposit models and grade and tonnage models used in this report 

Mineral deposit models of 

Worl and others (1989) 

A. Fluorspar veins --------------------------------

B. Polymetallic veins in blackshale terrane. 

C. Polymetallic veins in quartzite 

terrane. 

D. Polymetallic veins in carbonate 

terrane. 

E. Polymetallic veins in Tertiary 

extrusive terrane. 

F. Precious-metal veins 

G. Base-metal veins ------------------------------

H. Vein uranium deposits -----------------------

I. Tungsten stockwork and vein deposits ------

J. Stockwork molybdenum deposits: 

Cretaceous----------------------------

Tertiary--------------------------------

K. High-level, rhyolite-hosted, 

precious-metal deposits. 

L. Polymetallic skarn deposits ------·------{ 

M. Irregular replacements of base and 

precious metals. 

N. Fluorspar breccia manto deposits -----------

0. Sediment-hosted, jasperoid-associated, 

precious-metal deposits. 

P. Precious-metal deposits in volcanic tuffs ---

Q. Stratabound syngenetic deposits of 

precious and base metals. 

R. Stratiform vanadium deposits 

Corresponding mineral deposit models 

(first cilation) and grade and tonnage models 

(second citation) of Cox and Singer (1986) 

None ------------------------------------------------

Polymetallic veins (Cox, 1986a; Bliss and 

Cox, 1986). 

None ------------------------------------------------

None ------------------------------------------------

None ------------------------------------------------

None ------------------------------------------------

Porphyry Mo, low-F (Theodore, 1986; 

Menzie and Theodore, 1986). 

None ------------------------------------------------

None ------------------------------------------------

W skarn deposits (Cox, 1986b; 

Menzie and Jones, 1986). 

Cu skarn deposits (Cox and Theodore, 

1986; Jones and Menzie, 1986). 

} 

None ------------------------------------------------

None ------------------------------------------------

Carbonate-hosted Au-Ag (Berger, 1986; 

Bagby and others, 1986). 

None ------------------------------------------------

Sedimentary exhalative Zn-Pb (Briskey, 

1986; Menzie and Mosier, 1986). 

None ------------------------------------------------

None. 

Mineral deposit 

model names used 

in this report 

Polymetallic vein deposits. 

Precious-metal vein deposits. 

(Grade and tonnage model 

presented in this report.) 

None. 

None. 

None. 

Stockwork molybdenum deposits 

(Cretaceous). 

None. 

None. 

Polymetallic skarn deposits (tungsten 

skarns and copper skarns). 

Irregular replacement deposits of base 

and precious metals. (Grade and tonnage model presented in this report.) 

None. 

Sediment-hosted, jasperoid-associated, 

precious-metal deposits. 

None. 

Stratabound syngenetic deposits of 

precious and base metals. 

None. 

S. Gold placer deposits -------------------------- Placer Au-PGE (Yeend,1986; Orris and Gold placer deposits. 

Bliss, 1986). 

T. Radioactive black-sand placer deposits ---- None ------------------------------------------------ None. 

Quantitative Assessment of Selected Mineral Deposit Models 5 
Polymetallic Vein Deposits 

As explained earlier, the polymetallic vein models 

were aggregated into one polymetallic vein model (Cox, 

1986) in order to use the tonnage and grade models presented by Bliss and Cox (1986). 

The polymetallic vein deposits of the Forest produced mainly silver and lead and lesser amounts of zinc, 

gold, and copper. Some production of tin, antimony, and 

bromine has been reported. The deposits are found near 

high-angle faults and flat to steeply dipping shear zones 

beneath major thrust faults or near regional unconformities, and they are associated with nearby plutonic or hypabyssal rocks (Worl and others, 1989). The host rocks 

and the alteration associated with the ore bodies are different in each of the terranes and will be discussed on a 

terrane-by-terrane basis. 

Within the black-shale terrane the host rocks are 

generally black argillite or carbonaceous micritic limestone, but may also include siltite, siltstone, shale, finegrained quartzite, and gray limestone. Veins are found 

mainly in contact metamorphic zones close to felsic intrusive bodies where the country rocks have been altered 

to hornfels, tremolite-bearing limestone, calc-hornfels, 

and locally skarn. Known polymetallic vein deposits 

within this terrane all lie within 3.5 mi of a felsic intru-· 

sive body (Worl and others, 1989). 

Polymetallic vein deposits found within the quartzite terrane are generally hosted by quartzite or dolomitic 

quartzite. Sandy dolomite, shaly limestone, and black 

shale are often found near the deposits. Where dolomite 

is the host, it commonly has been altered to jasperoid. 

The quartzite host rocks display carbonate replacement 

and a halo of manganese and iron oxides. The altered 

and mineralized zones are concentrated in north- to 

northwest-striking high-angle faults and near northtrending folds and associated thrust faults. The major 

mineralized zones are found in the dolomitic members of 

the quartzite, in carbonatized quartzite, or along highly 

fractured zones in the quartzite (Worl and others, 1989). 

Polymetallic veins found within the carbonate terrane are hosted by white to blue, massive to thick-bedded limestone. The deposits occur as replacements of 

limestone along both fractures and bedding planes. The 

deposits are closely related to high-angle faults and felsic dikes, both of which tend to have a north-northeast 

strike. The host rocks are not altered and have only a 

narrow zone of contact metamorphism (containing calcite and some calc-silicate minerals) along some of the 

veins that are related to the deposits (Worl and others, 

1989). 

The polymetallic vein deposits of the Tertiary extrusive terrane are hosted by a number of highly altered 

calc-alkaline, peraluminous volcanic rocks that formed 

between 51 and 45 million years ago (Fisher and 

Johnson, 1987) and include flows, pyroclastic deposits, 

and hypabyssal intrusions. The host rocks have been 

bleached light gray and display cubes of secondary pyrite; they are silicified, sericitized, and pyritized in the 

vicinity of the ore bodies. Sericitization is the most extensive form of alteration, extending tens of feet from 

the lodes, and wall-rock texture is completely obliterated 

near the lodes (Worland others, 1989). The polymetallic 

veins in the Tertiary extrusive terrane are associated with 

the intersections of northwest-striking and northeaststriking high-angle faults, and they tend to be located in 

minor fissures and zones of fracturing at the intersections (Worland others, 1989). 

Tracts delineated as permissive for the occurrence 

of polymetallic vein deposits in the Forest include large 

portions of the black-shale, carbonate, quartzite, and 

Tertiary extrusive terranes (fig. 4). Several areas of high 

resource potential were identified by Worl and others 

(1989) on the basis of the presence of high-angle faults, 

evidence of alteration zones, proximity to plutons and 

hypabyssal bodies, and anomalous concentrations of lead 

and zinc; these areas were considered in the estimate of 

the number of undiscovered deposits. 

On the basis of available information, it is estimated at a 50-percent confidence level that 12 polymetallic 

vein deposits remain to be discovered in the Forest. Calculations made using MARK3 indicate that these undiscovered deposits contain 102,000 tonnes of lead, 1,200 

tonnes of silver, and 71,000 tonnes of zinc. The total 

mean tonnage of ore from undiscovered polymetallic vein 

deposits is estimated at 1,400,000 tonnes. A breakdown 

of the number of undiscovered deposits and the predicted 

amount of contained metal in polymetallic veins in the 

Forest is presented in tables 2 and 3, respectively. 

Precious-Metal Vein Deposits 

The precious-metal vein deposits found in the Forest are hosted by Cretaceous and Tertiary hypabyssal intrusive rocks that include dikes, stocks, and plugs. Most 

of these deposits are in the trans-Challis fault system, a 

series of northeast-striking high-angle fractures, or along 

other northeast- or northwest-striking high-angle fracture 

zones. The deposits are epithermal in nature, as indicated 

by their mineralogy, and are associated with moderate to 

intense hydrothermal alteration including silicification 

and argillization near the veins. The alteration is zoned, 

and propylitization and sericitization occur farther from 

the vein. Ore was deposited as fissure and breccia fillings and is highest in grade near the premineralization 

land surface (Worl and others, 1989; Fisher and others, 

1987). The commodities produced from these deposits 

include gold and silver and trace to by-product amounts 

of lead, copper, and zinc. 

6 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
Table 2. Probabilistic estimate of number of undiscovered deposits of selected mineral deposit models in Challis National Forest 

[A tOO-percent probability that one or more deposits are present (see third column) indicates that at least one deposit of the given model has already been 

discovered in the Forest] 

Probability that one 

Mineral deposit model (names modified Tonnage and grade model or more deposits Estimated number of undiscovered 

from Worl and others, 1989; see table 1) are present deposits at given probabilities 

(percent) 90 percent 50 percent 10 percent 

Polymetallic vein deposits ----------------- Polymetallic veins (Bliss and 100 5 12 21 

Cox, 1986). 

Precious-metal vein deposits -------------- Precious-metal vein deposits 100 4 9 17 

(this report). 

Stockwork molybdenum deposits Porphyry Mo, low-F (Menzie 100 1 1 2 

(Cretaceous). and Theodore, 1986). 

Polymetallic skarn deposits: 

Tungsten skarns ------------------ W skarn deposits 100 0 1 2 

(Menzie and Jones, 1986). 

Copper skarns -------------------- Cu skarn deposits 100 1 2 3 

(Jones and Menzie, 1986). 

Irregular replacement deposits Irregular replacement deposits 100 3 8 15 

of base and precious metals. of base and precious metals 

(this report). 

Sediment-hosted, jasperoid-associated, Carbonate-hosted Au-Ag 20 3 7 

precious-metal deposits. (Bagby and others,1986). 

Stratabound syngenetic deposits of Sedimentary exhalative Zn-Pb 100 1 2 4 

precious and base metals. (Menzie and Mosier, 1986). 

Gold placer deposits ------------------------ Placer Au-PGE (Orris and 

Bliss, 1986). 

An extensive literature search was conducted in an 

attempt to create tonnage and grade estimates for these 

deposits, which have no real analog in the report by Cox 

and Singer (1986). Although data on contained metal are 

abundant, only eight deposits have enough tonnage and 

grade data to allow an accurate estimate. The resulting 

tonnage and grade models for the precious-metal vein 

deposits are presented in figures 5, 6, and 7. 

The tracts delineated as permissive for the occurrence of precious-metal vein deposits are shown in figure 8. These tracts contain most of the Challis Volcanics 

(the Tertiary extrusive terrane) along with Tertiary intrusive rocks. A number of recognized areas of high resource potential were considered in making the estimates 

of undiscovered deposits (Worland others, 1989). These 

areas show evidence of precious-metal mineralization, 

high-angle faults and fractures, Tertiary hypabyssal 

rocks (including dikes, stocks, and plugs), proximity to 

the trans-Challis fault system, alteration, and anomalous 

100 5 8 13 

levels of copper, lead, and zinc in stream sediment 

samples. 

On the basis of available information, it is estimated at a 50-percent confidence level that nine preciousmetal vein deposits remain to be discovered in the Forest 

(table 2). Calculations made using MARK3 indicate that 

these undiscovered deposits contain 643,000 tonnes qf 

ore containing 5.7 tonnes of gold and 67 tonnes of silver. 

A breakdown of the estimated number of undiscovered 

deposits and the contained metal in precious-metal veins 

in the Forest is presented in tables 2 and 3, respectively. 

Stockwork Molybdenum Deposits (Cretaceous) 

The Cretaceous stockwork molybdenum deposits 

in the Challis National Forest are in or associated with 

granitic plutons and hypabyssal bodies of rhyolite. 

The plutons are differentiated, low-fluorine, !-type, 

Quantitative Assessment of Selected Mineral Deposit Models 7 
Table 3. Probabilistic estimates of tonnages of metals and ore in undiscovered deposits of selected mineral 

deposit models in Challis National Forest 

Mineral deposit model Metal 

Polymetallic vein deposits --------- Copper 

Gold 

Zinc 

Silver 

Lead 

Ore 

Precious-metal vein deposits ------- Gold 

Silver 

Ore 

Stockwork molybdenum Molybdenum 

deposits (Cretaceous). Ore 

Polymetallic skarn deposits: 

Tungsten skams ------------ Tungsten 

Ore 

Copper skams--------------- Copper 

Gold 

Silver 

Ore 

Irregular replacement deposits of Copper 

base and precious metals. Gold 

Silver 

Lead 

Ore 

Sediment-hosted, jasperoid- Gold 

associated, precious-metal Silver 

deposits. Ore 

Stratabound syngenetic deposits Zinc 

of precious and base metals. Silver 

Lead 

Ore 

Gold placer deposits ----------------- Gold 

Ore 

compositionally zoned bodies with high strontiumrubidium ratios and low niobium concentrations compared to average granites (Worl and others, 1989). The 

composition of these bodies ranges from quartz diorite to 

granite. The deposits can be found entirely within the 

intrusive rocks, entirely within the adjacent country 

rocks, or partially within both. Where located in the 

country rocks, the deposits are usually found directly 

above the intrusive rocks. The deposits are often found 

on the margins of positive magnetic anomalies that probably reflect associated buried granitic plutons (Hall, 

1987a). This deposit model corresponds to the deposit 

model called "porphyry Mo, low F" by Theodore (1986) 

in the report by Cox and Singer (1986). An associated 

Estimated tonnages (in tonnes) at given probabilities 

90 percent 50 percent 10 percent 

1.3X102 1.5X103 3.1X103 

4.oxw-2 3.4X10° 9.8X10° 

3.3X103 7.1X104 1.9X105 

7.2X101 1.2X103 3.6X103 

9.5X103 l.OX105 2.3X105 

1.3X105 1.4X106 3.1X106 

?.oxto-1 5.7X10° 1.2X101 

3.8X10° 6.7X101 1.5X102 

9.9X104 6.4X105 1.3X106 

1.8X104 2.2X105 6.0X105 

2.0X107 2.8X108 8.6X108 

4.7X102 5.3X104 1.5X105 

8.4X104 7.1X106 2.5X107 

2.5X103 1.1X105 3.0X105 

O.OX10° 1.7X10° 3.6X10° 

O.OX10° 1.7X101 4.4X101 

1.6X105 8.5X106 2.7X107 

3.6X101 6.5X102 1.4X103 

O.OX10° 4.oxto-1 ?.oxw-1 

9.0X10° 1.4X102 3.7X102 

3.2X103 4.9X104 1.2X105 

2.8X104 7.4X105 1.9X106 

O.OX10° 2.3X101 7.1X101 

O.OX10° 3.9X101 O.OX10° 

O.OX10° 9.0X106 2.7X107 

2.6X105 7.8X106 2.0X107 

4.1X101 6.2X103 1.7X104 

1.2X105 4.6X106 1.2X107 

5.7X106 1.1X108 2.6X108 

2.7Xto-1 1.2X10° 2.4X10° 

3.6X105 1.7X106 3.4X106 

tonnage and grade model by Menzie and Theodore 

(1986) is presented in the same report. 

The ore is associated with intensely silicified and 

pyritized rock surrounded by envelopes of potassic alteration grading outward to phyllic alteration. Some of the 

deposits are associated with hypabyssal rhyolitic bodies 

that are aligned with major high-angle fault systems 

within the Forest (Worl and others, 1989). The major 

commodity produced from these deposits is molybdenum; also present are trace to by-product amounts of 

copper and silver. 

Tracts that are permissive for the occurrence of 

Cretaceous stockwork molybdenum deposits in the Forest (fig. 9) include all areas that have evidence of 

8 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
Cretaceous plutons or hypabyssal bodies. Several areas 

of high resource potential were identified by Worl and 

others (1989) on the basis of alteration and geochemistry. These areas were considered in making the estimates 

of the number of undiscovered deposits. 

On the basis of available information, it is estimated at a 50-percent confidence level that one Cretaceous 

stockwork molybdenum deposit remains to be discovered 

in the Forest (table 2). Calculations made using MARKJ 

indicate that undiscovered deposits contain 285 million 

tonnes of ore and 221,000 tonnes of molybdenum. A 

breakdown of the estimated number of undiscovered 

deposits and the predicted contained metal in Cretaceous 

stockwork molybdenum deposits in the Forest is presented in tables 2 and 3, respectively. 

Polymetallic Skarn Deposits (Tungsten Skarns and 

Copper Skarns) 

The host rocks for the polymetallic skarn deposits 

are carbonate or carbonate-bearing rocks-mainly clean 

to impure limestone, carbonaceous micritic limestone, 

and limy sandstone-that are in contact with felsic intrusive rocks. The carbonate rocks within the contact zone 

have been altered to Fe-Mg-Mn-silicate mineral assemblages. Skarns occur where conditions were right for 

carbonate minerals to be replaced by silicate and ore 

minerals. This location is controlled by the ability of 

ore-forming solutions to penetrate the rocks, which is 

itself controlled by the relationship between bedding 

planes, faults, and breccia zones at the contact between 

the intrusive body and the carbonate host rock (W orl and 

others, 1989; Cookro and others, 1987). The commodities produced from these deposits vary according to the 

type of skarn. Tungsten skarns produce mainly tungsten, 

whereas copper skarns produce copper, silver, and gold. 

Several tracts in the Forest have been delineated as 

permissive for the occurrence of polymetallic skarns (fig. 

10). The tracts are divided into those that are permissive 

for tungsten skarns, those that are permissive for copper 

skams, and those that are permissive for both. In general, the tungsten skarn tracts include roof pendants in the 

Idaho batholith, the eastern margin of the Idaho batholith, and areas where Cretaceous plutons are in contact 

with calcareous rocks. The copper skarn tracts include 

areas where plutons are found in the black-shale and 

carbonate terranes. A number of areas of high resource 

potential were defined by Worl and others (1989) using 

evidence of ore mineralization, skarn mineral assemblages, and geochemical anomalies. These areas were considered in making estimates of the number of undiscovered deposits. 

Separate assessments were made of the tungsten 

and copper skams, using the grade and tonnage model of 

Menzie and Jones (1986) for tungsten skams and the 

grade and tonnage model of Jones and Menzie (1986) 

for copper skarns. These models (especially the tungsten 

skarn model) are for the most part district based rather 

than deposit based. This means that production data from 

individual deposits have been combined and reported by 

district, and only the district totals were available for 

construction of grade and tonnage models. The estimates 

of undiscovered deposits were converted to estimates of 

undiscovered districts to make them compatible with the 

grade and tonnage models. The conversion was made by 

dividing the estimate of undiscovered deposits by the 

number of deposits generally found in a district. Theresulting estimates of undiscovered districts were combined with the district-based grade and tonnage models 

in the MARK3 program to produce estimates of copper 

and tungsten contained in undiscovered deposits in the 

Forest. 

It is estimated at a 50-percent confidence level that 

there is one tungsten skarn remaining to be discovered in 

the Forest. Also, it is estimated at a 50-percent confidence level that there are two copper skarns remaining to 

be discovered in the Forest. Calculations made using 

MARK3 indicate that undiscovered tungsten skarns contain 53,000 tonnes of tungsten and 7,100,000 tonnes of 

tungsten ore. Undiscovered copper skarns are estimated 

to contain 109,000 tonnes of copper and 8,600,000 

tonnes of copper ore. A breakdown of the estimated 

number of undiscovered deposits and the predicted contained metal in tungsten and copper skarns in the Forest 

is presented in tables 2 and 3, respectively. 

Irregular Replacement Deposits of Base and 

Precious Metals 

The irregular replacement deposits of base and precious metals in the Forest are hosted by calcareous rocks 

or dolomitic rocks with varying amounts of impurities. 

The movement of ore-forming solutions was controlled 

by high-angle faults and shear and brecciated zones. 

These solutions were trapped in some areas by overlying 

impervious shale and siltstone strata that had been emplaced by thrusting. Anticlines also formed large solution traps. In the Forest, the ores are found in the Bayhorse Dolomite, the Ella Dolomite, and the Saturday 

Mountain Formation, and generally occur as selectively 

replaced strata. In general, local dolomitization is present 

near the ore bodies, but pervasive hydrothermal alteration is missing (Worland others, 1989; Hobbs and others, 1987). The commodities that have been produced 

from these deposits include silver, lead, and zinc; copper 

and gold are by-products. 

There is no good analog of this deposit model in 

Cox and Singer (1986) and therefore no associated tonQuantitative Assessment of Selected Mineral Deposit Models 9 
nage and grade models. Enough data were available to 

allow the creation of tonnage and grade models from deposits within the Forest. Data from 22 deposits were 

used, including data from the Pittsburgh-Idaho, Ramshorn, Clayton, and Latest Out mines, and the models are 

shown in figures 11 through 15. The deposits in the Forest may be similar to those described in the polymetallic 

replacement deposit model of Morris (1986); however, 

that model's associated grade and tonnage model is 

based not on deposits but on districts with over 100,000 

tonnes of production (Mosier and others, 1986), and it is 

quite different from the deposit-based model used here. 

The tracts delineated as permissive for the occurrence of irregular replacement deposits in the Forest are 

shown in figure 16. The tracts outline the rocks of the 

black-shale terrane and part of the flysch terrane. Areas 

of high resource potential, identified by Worl and others 

(1989), are defined by north-striking high-angle faults, 

nearby intrusive rocks, the presence of gossans, and evidence of base- and precious-metal mineralization. These 

areas were considered in making estimates of the number of undiscovered deposits. 

The tonnage and grade model presented here was 

used for the quantitative assessment of irregular replacement deposits. On the basis of available information, it 

is estimated at a 50-percent confidence level that eight 

irregular replacement deposits of base and precious metals remain to be discovered in the Forest. Calculations 

made using MARK3 indicate that these undiscovered deposits contain 49,000 tonnes of lead, 650 tonnes of copper, and 140 tonnes of silver in 740,000 tonnes of ore. A 

breakdown of the estimated number of undiscovered deposits and the predicted contained metal in these deposits is presented in tables 2 and 3, respectively. 

Sediment-Hosted, Jasperoid-Associated, PreciousMetal Deposits 

The sediment-hosted, jasperoid-associated, precious-metal deposits are found in carbonaceous limestone and dolomite, calcareous carbonaceous shale and 

siltstone, and bioclastic limestone. This deposit model is 

here considered identical to the carbonate-hosted Au-Ag 

model of Berger (1986), for which an associated grade 

and tonnage model was constructed by Bagby and others 

(1986). The host rocks are commonly thinly bedded and 

sufficiently silicified to be termed jasperoids. High-angle 

faults are present near all deposits and controlled the 

flow of solutions that formed the ore. Intermediate to 

silicic plutonic or hypabyssal intrusions are generally 

present near deposits, although the relationship of the intrusions to the precious-metal mineralization is unknown 

(Worland others, 1989). Most known deposits are Cretaceous to middle Tertiary in age, and the· typical commodities are gold and silver; arsenic, antimony, thallium, 

and mercury are present in trace amounts. 

Currently, no sediment-hosted, jasperoid-associated, precious-metal deposits have been recognized in the 

Challis National Forest or the surrounding area. There 

are, however, several areas with the appropriate geology 

for the occurrence of these deposits in the Forest. These 

areas, shown as tracts in figure 17, were delineated on 

the basis of carbonaceous sedimentary rocks that could 

serve as host rocks for these deposits; they include the 

black-shale terrane and parts of the flysch terrane. 

Since no sediment-hosted, jasperoid-associated, 

precious-metal deposits exist in the Forest, the estimate 

of undiscovered deposits was conditioned on the premise 

that there is a 20-percent chance that at least one such 

deposit exists in the Forest. On the basis of available information, it is estimated at a 50-percent confidence level that there are three undiscovered sediment-hosted, jasperoid-associated, precious-metal deposits in the Challis 

National Forest. Calculations made using MARK3 indicate that these undiscovered deposits contain 23 tonnes 

of gold, 39 tonnes of silver, and 9,000,000 tonnes of ore. 

A breakdown of the number of estimated undiscovered 

deposits and the predicted contained metal in these deposits is presented in tables 2 and 3, respectively. 

Stratabound Syngenetic Deposits of Precious and 

Base Metals 

The host rocks of the stratabound syngenetic deposits of precious and base metals are generally euxinic 

marine sedimentary rocks. They include black siliceousfacies carbonaceous argillite and fine- to mediumgrained gray limestone or micritic carbonaceous limestone. The deposits are stratiform masses and lenses rich 

in sphalerite and galena; also present are pyrite, pyrrhotite, barite, arsenopyrite, quartz, calcite, clay minerals, 

and tremolite. The deposits formed in restricted depositional environments where metal-bearing geothermal 

brines were localized (Worl and others, 1989; Hall, 

1987b ). The commodities produced from these deposits 

include zinc, lead, silver, and gold; vanadium and molybdenum are present in trace to by-product amounts. 

This deposit model is considered to be identical to the 

sedimentary exhalative Zn-Pb deposit model of Briskey 

(1986). 

The tracts that are permissive for the occurrence of 

stratabound syngenetic deposits of base and precious 

metals are shown in figure 18. These tracts include the 

black-shale terrane and the part of the flysch terrane (the 

Copper Basin and McGowan Creek Formations) that 

shows evidence of a marine basinal black-shale setting. 

Areas of high resource potential were delineated by 

Worl and others (1989) on the basis of anomalous con10 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
Table 4. Summation of probabilistic estimates of tonnages 

of metals and ore in undiscovered deposits in Challis 

National Forest 

Metal 

Gold-----------------

Silver ---------------

Copper --------------

Lead-----------------

Zinc -----------------

Tungsten -----------

Molybdenum ------

Estimated tonnages (in tonnes) 

at given probabilities 

90 percent SO percent 10 percent 

1.1X10° 3.5X101 l.OX102 

1.2X102 7.7X103 2.1X104 

2.7X103 1.3X104 3.1X105 

1.3X105 4.8X106 1.3X107 

2.6X105 7.9X106 2.0X107 

4.7X102 5.3X104 1.5X105 

1.8X104 2.2X105 6.0X105 

centrations of zinc and (or) lead, and these areas were 

considered in the estimate of the number of undiscovered deposits. 

The tonnage and grade model used for these 

deposits is by Menzie and Mosier (1986). On the basis 

of available information, it is estimated at a 50-percent 

confidence level that there are two undiscovered stratabound syngenetic deposits of base and precious metals in 

the Forest. Calculations made using MARK3 indicate 

that these undiscovered deposits contain 7,800,000 

tonnes of zinc, 6,200 tonnes of silver, 4,600,000 tonnes 

of lead, and 10,700,000 tonnes of ore. A breakdown of 

the number of undiscovered deposits and the contained 

metal in these deposits is presented in tables 2 and 3, 

respectively. 

Gold Placer Deposits 

The gold placer deposits in the Forest are fluvial 

accumulations of elemental gold with sand, gravel, and 

boulders. Gold, silver, and other heavy minerals were 

concentrated by streams where turbulent and irregular 

flow patterns separated the light and heavy mineral fractions being transported downstream. Ilmenite, magnetite, 

euxenite, brannerite, zircon, monazite, cinnabar, stibnite, 

and garnet are some of the other mineral components of 

gold placer deposits in the Forest. These deposits are 

commonly found in terraces a few to several hundred 

feet above the present stream levels and downstream 

from lode deposits (Worl and others, 1989). They are 

young, ranging from Pleistocene to Holocene (presentday) in age. 

Tracts delineated as permissive for the occurrence 

of gold placer deposits are shown in figure 19. These 

tracts include mapped fluvial accumulations or possible 

fluvial accumulations. Worl and others (1989) identified 

areas of high resource potential, defined by the occurrence of precious metals in stream sediments and locations within 5 mi (downstream) of a known gold lode 

deposit. These areas were considered in making estimates of the number of undiscovered deposits. 

The tonnage and grade model used for these deposits is by Orris and Bliss (1986). It is estimated at a 

50-percent confidence level that there are eight undiscovered gold placer deposits in the Challis National Forest. Calculations made using MARK3 indicate that these 

undiscovered deposits contain 1.2 tonnes of gold and 

1,730,000 tonnes of ore. A breakdown of the number of 

estimated undiscovered deposits and the predicted contained metal in these deposits is presented in tables 2 

and 3, respectively. 

SUMMARY OF QUANTITATIVE ASSESSMENT 

OF CHALLIS NATIONAL FOREST 

The summary of the quantitative analysis is presented in tables 2, 3, and 4. The models used in thereport and the probability distributions of undiscovered deposits (used as input to the MARK3 program) are 

presented in table 2. The distributions of metal endowment for each deposit (the results of the MARK3 procedure) are given in table 3. The results of table 3 are 

summed for each metal and shown in table 4, which thus 

presents a distribution of the total contained metal (in 

deposits of the mineral deposit models used in this report) in the Challis National Forest. 

Note that although this information is presented in 

a quantitative, probabilistic format, the analysis is based 

on subjective estimates of the number of undiscovered 

mineral deposits for each specific mineral deposit model 

considered. These estimates are based solely upon the 

author's knowledge at the time of the assessment (1989) 

and are not probabilistic in a statistical sense. 

SELECTED REFERENCES 

Anderson, A.L., 1929, Geology and ore deposits of the Lava 

Creek district, Idaho: Idaho Bureau of Mines and Geology 

Pamphlet P-32, 70 p. 

--1949, Silver-gold deposits of the Yankee Fork district, 

Custer County, Idaho: Idaho Bureau of Mines and Geology Pamphlet 94, 41 p. 

--1953, Gold-copper-lead deposits of the Yellowjacket 

district, Lemhi County, Idaho: Idaho Bureau of Mines and 

Geology Pamphlet 94, 41 p. 

--1961, Geology and mineral resources of the Lemhi 

quadrangle, Lemhi County, Idaho: Idaho Bureau of Mines 

and Geology Pamphlet P-124, 111 p. 

Selected References 11 
Anderson, R.A., 1948, Reconnaissance survey of the geology 

and ore deposits of the southwestern portion of the Lemhi 

Range, Idaho: Idaho Bureau of Mines and Geology Pamphlet P-80, 18 p. 

Bagby, W.C., Menzie, W.D., Mosier, D.L. and Singer, D.A., 

1986, Grade and tonnage model of carbonate-hosted AuAg, in Cox, D.P., and Singer, D.A., eds., Mineral deposit 

models: U.S. Geological Survey Bulletin 1693, p. 175-

177. 

Bennett, E.H., 1980, Granitic rocks of Tertiary age in the Idaho 

batholith and their relation to mineralization: Economic 

Geology, v. 75, no. 2, p. 278-288. 

Berger, B.R., 1986, Descriptive model of carbonate-hosted AuAg, in Cox, D.P., and Singer, D.A., eds., Mineral deposit 

models: U.S. Geological Survey Bulletin 1693, p. 175. 

Bliss, J.D., and Cox, D.P., 1986, Grade and tonnage model of 

polymetallic veins, in Cox, D.P., and Singer, D.A., eds., 

Mineral deposit models: U.S. Geological Survey Bulletin 

1693, p. 125-129. 

Bond, J.C., 1978, Geologic map of Idaho: Idaho Bureau of 

Mines and Geology Miscellaneous Map Series, scale 

1:500,000. 

Briskey, J.A., 1986, Descriptive model of sedimentary 

exhalative Zn-Pb, in Cox, D.P., and Singer, D.A., eds., 

Mineral deposit models: U.S. Geological Survey Bulletin 

1693, p. 211-212. 

Callaghan, Eugene, and Lemmon, D.M., 1941, Tungsten resources of the Blue Wing district, Lemhi County, Idaho: 

U.S. Geological Survey Bulletin 931-A, 21 p. 

Cater, F.W., and others, 1973, Mineral Resources of the Idaho 

Primitive Area and vicinity, Idaho: U.S. Geological Survey Bulletin 1304, 431 p. 

Chambers, A.E., 1966, Geology and mineral resources of the 

Bayhorse Mining district, Custer County, Idaho: Tucson, 

University of Arizona, Ph.D. dissertation, 271 p. 

Cook, E.E., 1956, Tungsten deposits of south-central Idaho: 

Idaho Bureau of Mines and Geology Pamphlet P-108, 40 

p. 

Cookro, T.M., Hall, W.E., and Hobbs, S.W., 1987, Polymetallic skarn deposits, in Fisher, F.S., and Johnson, K.M., 

eds., Preliminary manuscript for "Mineral-resource potential and geology of the Challis 1 °><2° quadrangle, Idaho": 

U.S. Geological Survey Open File Report 87-480, p.172-

175. 

Cox, D.P., 1986a, Descriptive model of polymetallic veins, in 

Cox, D.P., and Singer, D.A., eds., Mineral deposit models: 

U.S. Geological Survey Bulletin 1693, p. 125. 

Cox, D.P., 1986b, Descriptive model of W skarn deposits, in 

Cox, D.P., and Singer, D.A., eds., Mineral deposit models: 

U.S. Geological Survey Bulletin 1693, p. 55. 

Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, 379 p. 

Drew, L.J., and others, 1986, Quantitative estimation of undiscovered mineral resources-A case study of U.S. Forest 

Service Wilderness tracts in the Pacific mountain system: 

Economic Geology, v. 81, p. 80-88. 

Fisher, F.S., and Johnson, K.M., eds., 1987, Preliminary manuscript for "Mineral-resource potential and geology of the 

Challis 1 °X2° quadrangle, Idaho": U.S. Geological Survey 

Open-File Report 87-480, 251 p. 

Fisher, F.S., Kiilsgaard, T.H., Johnson, K.M., and Bennett, 

E.H., 1987, Precious-metal veins, in Fisher, F.S., and 

Johnson, K.M., eds., Preliminary manuscript for "Mineralresource potential and geology of the Challis 1 OX2° quadrangle, Idaho": U.S. Geological Survey Open File Report 

87-480,p. 117-125. 

Fisher, F.S., and May, G.D., 1983, Geochemical characteristics 

of metalliferous Salmon River sequence, central Idaho: 

U.S. Geological Survey Open-File Report 83-670,28 p. 

Fisher, F.S., May, G.D., Mcintyre, D.H., and Johnson, F.L., 

1983, Mineral resource potential, geologic, and geochemical maps of part of the White Cloud-Boulder Roadless 

Area, Custer County, Idaho: U.S. Geological Survey Miscellaneous Field Studies Map MF-1580, scale 1:62,500. 

Fisher, F.S., Mcintyre, D.H., and Johnson, K.M., 1983, Geologic map of the Challis 1° by 2° quadrangle, Idaho: U.S. 

Geological Survey Open-File Report 83-523, 41 p., scale 

1:250,000. 

Hall, W.E., 1985, Stratigraphy of and mineral deposits in 

middle and upper Paleozoic rocks of the black-shale mineral belt, central Idaho, Chap. J in Mcintyre, D.H., ed., 

Symposium on the geology and mineral deposits of the 

Challis 1 °X2° quadrangle, Idaho: U.S. Geological Survey 

Bulletin 1658, p. 117-132. 

---1987a, Cretaceous molybdenum stockworks, in Fisher, 

F.S., and Johnson, K.M., eds., Preliminary manuscript for 

"Mineral-resource potential and geology of the Challis 

1 °><2° quadrangle, Idaho": U.S. Geological Survey Open 

File Report 87-480, p. 152-158. 

---1987b, Stratabound syngenetic deposits of precious and 

base metals in argillic rocks and micritic limestones, in 

Fisher, F.S., and Johnson, K.M., eds., Preliminary manuscript for "Mineral-resource potential and geology of the 

Challis 1 °><2° quadrangle, Idaho": U.S. Geological Survey 

Open File Report 87-480, p. 205-208. 

Hobbs, S.W., 1985, Precambrian and Paleozoic sedimentary 

terranes in the Bayhorse area of the Challis quadrangle, 

Chap. Din Mcintyre, D.H., ed., Symposium on the geology and mineral deposits of the Challis 1 °><2° Quadrangle, 

Idaho: U.S. Geological Survey Bulletin 1658, p. 59-68. 

Hobbs, S.W., Fisher, F.S., and Johnson, K.M., 1987, Irregular 

replacement deposits of base and precious metals, in 

Fisher, F.S., and Johnson, K.M., eds., Preliminary manuscript for "Mineral-resource potential and geology of the 

Challis 1 °X2° quadrangle, Idaho": U.S. Geological Survey 

Open File Report 87-480, p. 175-178. 

Hustedde, G.S., Copeland, J.A., Stroud, W.B., Mitchell, V.E., 

and Bennett, E.H., 1981, Mines and prospects of the 

Hailey quadrangle, Idaho: Idaho Bureau of Mines and Geology, Mines and Prospects Map Series, 41 p., scale 

1:250,000. 

Hyndman, D.W., 1983, The Idaho batholith and associated plutons, Idaho and western Montana, in Roddick, J.A., ed., 

Circum-Pacific plutonic terranes: Geological Society of 

America Memoir 159, p. 213-240. 

Jones, G.M., and Menzie, W.D., 1986, Grade and tonnage 

model of Cu skarn deposits, in Cox, D.P., and Singer, 

D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 86-89. 

Kiilsgaard, T.H., 1949, The geology and ore deposits of the 

12 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
Boulder Creek mining district, Custer County, Idaho: 

Idaho Bureau of Mines and Geology Pamphlet 89, 27 p. 

Kiilsgaard, T.H., and Bennett, E.H., 1985, Mineral deposits in 

the southern part of the Atlanta lobe of the Idaho batholith 

and their genetic relation to Tertiary intrusive rocks and 

faults, Chap. Min Mcintyre, D.H., ed., Symposium on the 

geology and mineral deposits of the Challis 1 °x2° quadrangle, Idaho: U.S. Geological Survey Bulletin 1658, p. 

153-165. 

---1987, Tertiary molybdenum stockworks, in Fisher, F.S., 

and Johnson, K.M., eds., Preliminary manuscript for 

"Mineral-resource potential and geology of the Challis 

1 °x2° quadrangle, Idaho": U.S. Geological Survey Open 

File Report 87-480, p.158-162. 

Kiilsgaard, T.H., and Lewis, R.S., 1985, Plutonic rocks of Cretaceous age and faults in the Atlanta lobe of the Idaho 

batholith, Challis quadrangle, Chap. B in Mcintyre, D.H., 

ed., Symposium on the geology and mineral deposits of 

the Challis 1 °X2° quadrangle, Idaho: U.S. Geological Survey Bulletin 1658, p. 29-42. 

Kiilsgaard, T.H., and VanNoy, R.M., 1984, Eastern part of the 

Sawtooth National Recreation Area, Idaho, in Marsh, S.P., 

Kropschot, S.T., and Dickerson, R.G., eds., Wilderness 

mineral potential-Assessment of mineral resource potential in U.S. Forest Service lands studied 1964-1984: U.S. 

Geological Survey Professional Paper 1300, p. 573-576. 

Mabey, D.R., and Webring, M.W., 1985, Regional geophysical 

studies in the Challis quadrangle, Chap. E in Mcintyre, 

D.H., ed., Symposium on the geology and mineral deposits of the Challis 1 °X2° quadrangle, Idaho: U.S. Geological Survey Bulletin 1658, p. 69-79. 

Menzie, W.D., and Jones, G.M., 1986, Grade and tonnage 

model of W skarn deposits, in Cox, D.P., and Singer, 

D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 55-57. 

Menzie, W.D., and Mosier, D.L., 1986, Grade and tonnage 

model of sedimentary exhalative Zn-Pb, in Cox, D.P., and 

Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 212-215. 

Menzie, W.D., and Theodore, T.G., 1986, Grade and tonnage 

model of porphyry Mo, low-F, in Cox, D.P., and Singer, 

D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 120-122. 

Mitchell, V.E., Stroud, W.B., Hustedde, G.S., and Bennett, 

E.H., 1981a, Mines and prospects of the Challis quadrangle, Idaho: Idaho Bureau of Mines and Geology, Mines 

and Prospects Map Series, 47 p., scale 1:250,000. 

---1981 b, Mines and prospects of the Dubois quadrangle, 

Idaho: Idaho Bureau of Mines and Geology, Mines and 

Prospects Map Series, 22 p., scale 1:250,000. 

---1986, Mines and prospects of the Challis quadrangle, 

Idaho (2d ed.): Idaho Bureau of Mines and Geology, 

Mines and Prospects .Map Series, 56 p., scale 1:250,000. 

Morris, H.T., 1986, Descriptive model of polymetallic replacement deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 

1693, p. 99-100. 

Mosier, D.L., Morris, H.T., and Singer, D.A., 1986, Grade and 

tonnage model of polymetallic replacement deposits, in 

Cox, D.P., and Singer, D.A., eds., Mineral deposit models: 

U.S. Geological Survey Bulletin 1693, p. 101-104. 

Orris, G.J., and Bliss, J.D., 1986, Grade and tonnage model of 

placer Au~PGE, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 

1693, p. 261-264. 

Root, D.H., and Scott, W.A., 1988, User manual for mineral 

simulation program: U.S. Geological Survey Open File 

Report 88-15, 64 p. 

Ross, C.P., 1930, The Thunder Mountain mining district, 

Custer and Camas Counties, Idaho: Idaho Bureau of 

Mines and Geology Pamphlet 33, 26 p. 

---1937, Geology and ore deposits of the Bayhorse region, 

Custer County, Idaho: U.S. Geological Survey Bulletin 

877, 171 p. 

---1963, Mining history of south-central Idaho: Idaho Bureau of Mines and Geology Pamphlet 131, 29 p. 

Stroud, W.B., Mitchell, V.E., Hustedde, G.S., and Bennett, 

E.H., 1981, Mines and prospects of the Idaho Falls quadrangle, Idaho: Idaho Bureau of Mines and Geology, Mines 

and Prospects Map Series, 10 p., scale 1:250,000. 

Theodore, T.G., 1986, Descriptive model of porphyry Mo, lowF, in Cox, D.P., and Singer, D.A., eds., Mineral deposit 

models: U.S. Geological Survey Bulletin 1693, p. 120. 

Treves, S.B., and Melear, J.D., 1952, The geology and ore deposits of the Seafoarn mining district, Custer County, 

Idaho: Idaho Bureau of Mines and Geology Pamphlet 96, 

19 p. 

Umpleby, J.B., 1912, The lead-silver deposits of the Dome 

district, Idaho: U.S. Geological Survey Bulletin 540, p. 

212-222. 

U.S. Geological Survey, 1988, Mineral Resource Data System 

(MRDS) (active computer file): Reston, Va., U.S. Geological Survey. [Available from U.S. Geological Survey, 

Branch of Resource Analysis, MS-920, Reston, VA, 

22092.] 

Wells, M.W., 1983, Gold camps and silver cities in Idaho: 

Idaho Bureau of Mines and Geology Bulletin 22, 165 p. 

Worl, R.G., Wilson, A.B., Smith, C.L., and Kleinkopf, M.D., 

1989, Mineral resource potential and geology of the 

Challis National Forest, Idaho: U.S. Geological Survey 

Bulletin 1873, 101 p., 4 pls. 

Y eend, W.E., Descriptive model of placer Au-PGE, in Cox, 

D.P., and Singer, D.A., eds., Mineral deposit models: U.S. 

Geological Survey Bulletin 1693, p. 261. 

Selected References 13 

FIGURES 1-19 
115°30' 115°00' 

45°00' r-------.---~.----------.--..,-------r----r--------r-----, 

0 

I I 

I I 

0 

~ 

5 ~<v 

.4 ~' 6 

0~ 

~ 

c,~ " 

25 MILES 

I 

25 KILOMETERS 

MONTANA 

A.,.e;, 

~ 

7 

I 

I "' 

9 '-"J 

Figure 1. Location of Challis National Forest and principal mining districts within or partially within its 

boundaries (Worl and others, 1989). Mining districts: 1, Yellow Pine; 2, Thunder Mountain; 3, Gravel 

Range; 4, Sea Foam; 5, Sheep Mountain; 6, Loon Creek; 7, Parker Mountain; 8, Stanley; 9, Yankee Fork; 

10, Robinson Bar; 11, Bayhorse; 12, Boulder Creek; 13, East Fork; 14, Warm Springs; 15, Alto; 16, 

Copper Basin; 17, Alder Creek; 18, Little Wood River; 19, Lava Creek; 20, McDevitt; 21, Blue Wing; 22, 

Junction; 23, Texas; 24, Spring Mountain; 25, Hamilton; 26, Dome. 

Cl 12 

w 

a: 

w iJ 10 

(.) 

(/) 

i5 

(/) 8 

!:: 

~ fb 6 

Cl 

~ a: 4 w 

~ 

~ 2 

1880 1900 1920 1940 1960 1980 

YEAR OF DISCOVERY 

Figure 2. Discoveries of mineral deposits in Challis National Forest 

(compiled from data available in Mineral Resources Database System, 

U.S. Geological Survey, 1988). 

16 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
1.0 

n=75 

0.9 

0.8 

0.7 en 

tCi5 

0 

a. 0.6 w 

0 

~ 0.5 

t5 

i= 

a: 

0 0.4 Q. 

0 

a: 

a. 0.3 

0.2 

ORE, IN MILLION TONNES 

1.0 

n=7 

0.9 

0.8 

0.7 en 

tCi5 

0 

Q. 0.6 w 

0 

LL 

0 0.5 z 

0 

i= 

a: 

0 0.4 Q. 

0 

a: 

a. 0.3 

0.2 

0.1 

0.0002 0.0067 0.2 

B 0.0 

0.00002 0.0001 0.0004 0.0016 0.0063 0.025 0.1 0.4 1.6 6.3 25 

ORE, IN MILLION TONNES 

Figure 3. Tonnages of ore in polymetallic vein deposits. A, Bliss and 

Cox (1986); B, this report. n, number of deposits used to construct 

graph. Tonnages for 90 percent, 50 percent, and 10 percent of deposits 

are written from left to right above horizontal axis. 

Figures 1-19 17 
115°30' 45•oo·.-------------.-------.---------------------~~-------r-----.------------~----~ 

0 

0 

25 MILES 

I 

25 KILOMETERS 

Figure 4. Tracts (shaded) permissive for occurrence of polymetallic vein deposits. 

Figure 5. Tonnages of ore in preciousmetal vein deposits. n, number of deposits used to construct graph. Tonnages 

for 90 percent, SO percent, and 1 0 percent of deposits are written from left to 

right above horizontal axis. 

en 

t::: 

en 

0 

Q. 

UJ 

0 

u. 

0 

z 

0 

i= 

a: 

0 

Q. 

0 

a: 

Q. 

1.0 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0.0 

0.0016 

1.5 16 

0.0063 0.025 0.1 0.4 1.6 6.3 25 

ORE, IN THOUSAND TONNES 

.. \._ MONT ANA I 

\ I 

\ 

) 

' 

~ I 

\ 

" 

180 

100 

... 

I 

,_""'\ \ 

, ... 

n-8 

400 

18 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 

1600 
0.9 

0.8 

0.7 

~ en 

~ 0.6 

~ u. 

0 z 0.5 

0 

~ 0 0.4 a. 

0 

c: 

a. 0.3 

0.2 

0.1 

2.1 

0.4 1.0 2.5 

n-8 

7.4 26 

6.3 16 40 100 250 630 1600 4000 

GOLD GRADE, IN GRAMS PER TONNE 

1.0 r-----r---,---e-.,..------,,----r-----r---.-----..,.---.-----. 

en 

!::: 

0.9 

0.8 

0.7 

~ a. 0.6 w 

0 

u. 

0 0.5 z 

0 

~ 0 0.4 a. 

0 

c: 

a. 0.3 

0.2 

0.1 

0.4 1.0 

3.5 27 210 

2.5 6.3 16 40 100 250 630 1600 4000 

SILVER GRADE, IN GRAMS PER TONNE 

Figure 6. Gold grades of ore in precious-metal vein deposits. n, number 

of deposits used to construct graph. 

Grades for 90 percent, 50 percent, 

and 1 0 percent of deposits are written 

from left to right above horizontal 

axis. 

Figure 7. Silver grades of ore in precious-metal vein deposits. n, number 

of deposits used to construct graph. 

Grades for 90 percent, 50 percent, 

and 1 0 percent of deposits are written 

from left to right above horizontal 

axis. 

Figures 1-19 19 
115"30' 115°00' 114~0' 113°00' 45~o·.-------------.-------.---------------------,~------.-----r------------.------, 

44~0' 

25 MILES 

I 

25 KILOMETERS 

MONTANA 

Figure 8. Tracts (shaded) permissive for occurrence of precious-metal vein deposits. 

115°30' 115°00' 114°00' 113°00' 45~o·.-------------.-------.---------------------~~------.-----.------------.------, 

44°00' 

25MILES 

I 

25 KILOMETERS 

'\.. MONTANA I 

\ I 

~ 

" ~ 

\.. ,' '-'"'\J 

Figure 9. Tracts (shaded) permissive for occurrence of Cretaceous stockwork molybdenum 

deposits. 

20 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
C/) 

!:::: 

C/) 

0 

a. 

UJ 

0 

u.. 

0 

z 

0 

~ 0 

a. 

0 

c: 

a. 

115°30' 

45°00'.---------------.-------.-----------------------.-r--------.-----.--------------.-------, 

44ooo· 

EXPLANATION 

I I] T~~;~::;~s::~ for 

ITIIJ] Tracts permissive for 

copper skarns 

.. Tracts permissive for tungsten and copper skarns 

0 

0 

25 MILES 

I 

25 KILOMETERS 

'\... MONTANA I 

\ I 

I 

( 

\ , 

' '-, /' 

-'"'\ \ , ... 

Figure 10. Tracts permissive for occurrence of tungsten skarns and copper skarns. 

1.0 .----.-----.----~-----.----.-----,-----.----.-----.-----, 

0 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0.0 

0.0016 0.0063 0.025 0.1 0.4 1.6 6.3 25 100 400 1600 

ORE, IN THOUSAND TONNES 

Figure 11. Tonnages of ore in i rregular replacement deposits of base and 

precious metals. n, number of deposits used to construct graph. Tonnages 

for 90 percent, 50 percent, and 1 0 

percent of deposits are written from 

left to right above horizontal axis. 

Figures 1-19 21 
Figure 12. Lead grades of ore in irregular replacement deposits of base and precious metals. n, number of deposits used to construct 

graph. Grades for 90 percent, 50 percent, and 

1 0 percent of deposits are written from left to 

right above horizontal axis. 

Figure 13. Silver grades of ore in irregular replacement deposits of base and precious metals. n, number of deposits used to construct 

graph. Grades for 90 percent, 50 percent, and 

1 0 percent of deposits are written from left to 

right above horizontal axis. 

(/) 

!::: 

(/) 

0 

a. 

w 

0 

u.. 

0 

~ 

b: 

0 

a. 

0 

a: 

a. 

(/) 

!::: 

(/) 

1.0 

0.9 

0.8 

0.7 

0.6 

0.5 

0.4 

0.3 

0.2 

0.1 

0.0 

0.9 

0.8 

0.7 

2 0.6 w 

0 

u.. 

0 0.5 

~ 

~ 0 0.4 a. 

~ 

a. 0.3 

0.2 

0.1 

0 

4.8 16 

0.4 1.0 2.5 6.3 16 40 100 250 

LEAD GRADE, IN PERCENT 

0.4 1.0 2.5 6.3 16 40 100 250 

SILVER GRADE, IN GRAMS PER TONNE 

22 Quantitative Mineral Resource ASsessment of Selected Mineral Deposits in the Challis National Forest, Idaho 

n-18 

630 1600 4000 

630 1600 4000 
(/) 

!::: 

(/) 

0 

c.. 

UJ 

0 

L.L. 

0 

z 

0 

~ 

1.0 

0.9 

0.8 

0.7 

0.6 

0.5 

2 0.4 

0 

a: 

c.. 0.3 

0.2 

0.1 

0 

0.02 

0.013 0.032 0.056 

(/) 

!::: 

(/) 

2 

UJ 

0 

L.L. 

0 

z 

0 

1.0 

0.9 

0.8 

0.7 

0.6 

0.5 

~ 0 0.4 c.. 

~ 

c.. 0.3 

0.2 

0.1 

0 

0.03 

n-17 

0 

0.14 0.94 

0.1 0.18 0.32 0.56 1.0 1.8 3.2 5.6 10.0 

COPPER GRADE, IN PERCENT 

n-19 

0 

0.38 4.4 0.0 I....----L...--..I..-.----L--__l_-----1 __ -L... __ l-._-L. __ .i...._ _ _J 

0.01 0.025 0.063 0.16 0.4 1.0 2.5 6.3 16 40 100 

GOLD GRADE, IN GRAMS PER TONNE 

Figure 14. Copper grades of ore in irregular replacement deposits of base and precious metals. n, number of deposits used to construct 

graph. Grades for 90 percent, 50 percent, and 

1 0 percent of deposits are written from left to 

right above horizontal axis. 

Figure 15. Gold grades of ore in irregular replacement deposits of base and precious metals. n, number of deposits used to construct 

graph. Grades for 90 percent, 50 percent, and 

1 0 percent of deposits are written from left to 

right above horizontal axis. 

Figures 1-19 23 
44•oo· 

115•oo· 

25 MILES 

I 

25 KILOMETERS 

114°00' 113000' 

'\.... MONTANA I 

\, 

~ 

\ 

~ " : '-'-"J 

Figure 16. Tracts (shaded) permissive for occurrence of irregular replacement deposits of base 

and precious metals. 

44•oo· 

11s•oo· 

25MILES 

h,--L,' 1---r"--r-'r-'----JI 

25 KILOMETERS 

114°00' 113000' 

MONTANA 

/ 

I -'-"J 

Figure 17. Tracts (shaded) permissive for occurrence of sediment-hosted, jasperoid-associated, precious-metal deposits. 

24 Quantitative Mineral Resource Assessment of Selected Mineral Deposits in the Challis National Forest, Idaho 
115°30' 115•oo· 114•oo· 113°00' 45•oo·.-------------~------~--------------------~~--------~----~------------~------, 

44000' 

25 MILES 

I 

25 KILOMETERS 

MONTANA 

,./ 

Figure 18. Tracts (shaded) permissive for occurrence of stratabound syngenetic deposits of 

precious and base metals. 

115°30' 115000' 114•oo· 113°00' 45•oo·.-------------~-------,----------------------.. --------.-----~------------~------. 

'\ ', 

~~/-''\_ MONTANA 

44•oo· 

'• 

25 MILES 

I 

25 KILOMETERS 

Figure 19. Tracts (shaded) permissive for occurrence of gold placer deposits. 

I 

\, 

~ 

\ I 

\ 

\ I '-'"'\J 

Figures 1-19 25 



SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS 

Periodicals 

Earthquakes & Volcanoes (issued bimonthly). 

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volumes, publications listing and index) and as a set of microfiche. 

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent 

years since the last permanent catalog may be purchased by mail and 

over the counter in paperback book form. 

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by mail 

and over the counter in paperback booklet form only. 

"Price and A vailablllty List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet form only. 

Selected copies of a monthly catalog "New Publications of the U.S. 

Geological Survey" available free of charge by mail or may be obtained 

over the counter in paperback booklet form only. Those wishing a free 

subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 

National Center, Reston, VA 22092. 

Note.--Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the 

prices charged may differ from the prices in catalogs, announcements, 

and publications.