F.iiii~Jf~l~ U.S. Geological Survey Workshop on 

Nonfuel Mineral-Resource Appraisal 

of Wilderness and CUSMAP Areas 

U.S. Geological Survey Workshop on 

Nonfuel Mineral-Resource Appraisal 

of Wilderness and CUSMAP Areas 

Compiled by Daniel R. Shawe 

GEOLOGICAL SURVEY CIRCULAR 845 

A general approach to appraisal of mineral 

resources in CUSMAP 1 :250,000-scale 

quadrangles and in wilderness areas 

1981 
United States Department of the Interior 

JAMES G. WATT, Secretary 

Geological Survey 

Doyle G. Frederick, Acting Director 

Free on application to Branch of Distribution, U.S. Geological Survey, 1200 South fads Street, Arlington, VA 22202 
CONTENTS 

Page 

Introduction • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 1 

CUSMAP appraisals • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 1 

Compilation of data • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 2 

Ore-deposit modeling • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •.• • • 2 

First-stage analysis. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 

Field studies to acquire needed data • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 4 

Final-stage analysis • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 7 

Presentation of resource appraisals and supporting data • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 9 

Wilderness area appraisals. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 11 

Summary. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 13 

Recommendations • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 13 

Appendix A, Organizing committee • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 14 

Appendix B, Workshop participants • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 14 

Appendix C, Speakers • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 16 

ILLUSTRATIONS 

Page 

FIGURE 1. Interpretive maps showing favorableness of Bonneterre Formation in 

the Poplar Bluff quadrangle. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 10 

2. Diagram showing method of estimating amount of metal for a specific 

ore-depo~t type ••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 11 

3. Diagram comparing tonnages of known deposits and undiscovered deposits • • • • • • • • • 11 

4. Analytical steps to present mineral-resource ratings • • • • • • • • • • • • • • • • • • • • • • • • • • • • 12 

III 

U.S. Geological Survey Workshop on Nonfuel MineralResource Appraisal of Wilderness and CUSMAP Areas 

Compiled by Daniel R. Shawe 

INTRODUCTION 

The Organic Act that established the U.S. 

Geological Survey in 1879 charges the Survey with 

responsibility to classify the public lands and to examine the mineral resources of the national domain. 

Numerous subsequent laws have added specific impetus 

to that general mandate. The Wilderness Act of 1964 

directs._the U.S. Geological Survey and the U.S. Bureau 

of Mines to make mineral surveys of wilderness and 

primitive areas within the United States by 1984. The 

Mining and Minerals Policy Act of 1970 requires that 

the U.S. Geological Survey foster and encourage private enterprise by providing information that will aid 

the development of mineral resources. The Alaska 

Native Claims . Settlement Act of 1971 authorizes 

withdrawal and classification of large tracts of land in 

the State, called "National Interest Lands" or ·"d-2" 

lands, by 1978. As a result of the 1971 act, the U.S. 

Geological Survey initiated its Alaska Mineral 

Resource Assessment Program (AMRAP) to study 

1:250,000-scale topographic quadrangles in the State. 

The Conterminous United States Mineral Assessment 

Program (CUSMAP), patterned after AMRAP, has the 

objective of assessing the mineral-resource potential 

of the adjacent 48 States, and is responsive to the 

legal requirements of Congressional acts cited as well 

as of other acts. 

The U.S. Geological Survey has been conducting 

mineral-resource appraisals for different purposes and 

at different scales for ma.ny years, and its methods are 

constantly evolving. A workshop organized by the U.S. 

Geological Survey for the purpose of improving its 

appraisal of mineral resources in wilderness areas and 

CUSMAP quadrangles was held in Denver, Colo., 

December 10-12, 1979. Organizing committee members are listed in Appendix A. Participants, listed in 

Appendix B, included 34 members of the U.S. Geological Survey from Denver, Colo., Reston, Va., Menlo 

Park, Calif., and Salt Lake City, Utah; 11 representatives of the North American mining industry; six 

people from United States universities; four members 

of the Geological Survey of Canada; and one representative each from the U.S. Forest Service, the U.S. 

1 

Bureau of Land Management, the Colorado State Geological Survey, the Library of Congress, and the Colorado Mountain Club (an environmental group). 

The first day of the workshop consisted of talks 

by specialists on some of the most significant purposes 

and some of the essential mechanics of resource 

appraisal. Names of speakers and titles and brief 

summaries of talks are given in Appendix C. During 

the second day, six working groups met separately to 

plan the steps needed to appraise mineral resources in 

one CUSMAP quadrangle and one wilderness area in 

each of three major Hrologic provinces of the United 

States. The 1° X 2 (1:250,000) topographic quadrangles selected were: Tonopah, Nev., in the BasinRange province; Poplar Bluff, Missouri-Arkansas, in 

the mid-continent region; and Hibbing, Minn., in the 

upper Midwest. All have major resource potential, but 

they are not now CUSMAP projects. Two working 

groups independently planned appraisals of a 

quadrangle and a wilderness area (1:50,000) within that 

quadrangle. Names of the working-group leaders and 

participants are indicated in Appendix B. Group 

leaders presented oral summaries of the results of 

each working group on the morning of the third day. 

Those summaries, later submitted as written reports, 

are compiled in this report into a recommendation for 

a general approach to appraisal of mineral resources in 

CUSMAP quadrangles and wilderness areas. 

CUSMAP APPRAISALS 

CUSMAP projects, designed to assess mineralresource potential of 1:250,000-scale quadrangles, 

generally are planned for a duration of 3-5 years and 

may take as much as 20 man years of work to complete. The project leader should be an experienced 

economic geologist familiar with the geology of the 

region in and around the CUSMAP quadrangle. The 

multidisciplinary project team is composed of field and 

mineral resource geologists, geophysicists, geochemists, and geostatisticians and assistants and is 

aided, as needed, by specialists in isotope geology, 

remote sensing, and paleontology. Normal field 

'operations may be supplemented by extensive use of 
helicopters to facilitate geologic mapping and 

geochemical sampling. 

The mineral-resource appraisals to date primarily are of metallic mineral commodities, in~luding uranium and some high-unit-value nonmetallic commodities such as barite and fluorspar. Oil, gas, coal, and 

other nonmetallic resources are included in the 

appraisals, but were not discussed in this workshop. 

All the working groups established generally 

similar procedures for making mineral-resource 

appraisals of 1° X 2° (1:250,000) quadrangles, regardless of geologic province. The most complete and 

most systematic methods involved these steps: 

1. Compile data currently available. 

2. Model possible ore deposits: identify ·and define 

the geologic environments that might be present 

that are favorable for the occurrence of ore 

deposits. 

3. Prepare a first analysis of the available data. 

4. Gather data through field studies in parts of the 

quadrangle where information is inadequate for 

resource appraisal. 

5. Prepare a "final" analysis of the data. 

6. Present the data in the form of finished products 

such as maps, diagrams, and texts that convey 

conclusions as to the mineral-resource potential 

of the quadrangle. 

Because of time constraints, steps 1-4 may have 

to be carried out in part concurrently; the interplay of 

these operations carried out together, may in fact, 

offer some advantages. Of course, some planning and 

data compilation always will precede fieldwork when 

time permits. 

Compilation of Data 

Prior to fieldwork in the quadrangle, available 

factual data (from published literature and unpublished 

open sources), as well as subjective information obtained from knowledgeable individuals familiar with 

the quadrangle, are collected and compiled at scales of 

1:125,000 and 1:250,000, as appropriate. Data that can 

be advantageously so treated are prepared for computer storage for possible later manipulation. 

Classes of data that should be acquired are: 

Geologic data 

Geochronologic data 

Geochemical data 

Geophysical data, including magnetic data, gravity 

data, and radiometric data 

Rock-alteration data 

Landsat and other image data 

Water and oil well drill data 

Mines and mine production, prospects, and mining 

claims information 

Details regarding the kinds of data to be acquired in these classes are given later in this report in 

the section that describes field studies. 

Ore-Deposit Modeling 

After collection of available data, mineralresource appraisal requires preparation of models of 

ore deposits that are likely to occur in the CUSMAP 

quadrangle being evaluated. Ultimately, ore-deposit 

2 

modeling (description of ore deposits and definition of 

their geologic environments) should be a routine function of geologists in the Office of Mineral Resources 

of the U.S. Geological Survey, in which geologists 

other than those assigned to a CUSMAP project, particularly commodity geologists, should participate. 

Experience in the mining industry indicates that a useful ore-deposit model for exploration generally can be 

developed in 6 man months of literature search, mine 

visits, and interviews with experts, although some 

models are still only imperfectly developed, information on them is difficult to obtain, and probably years 

of work remain to be done on them. Models should be 

available at the onset of any CUSMAP project, and 

these models need only be "fine tuned" on the basis of 

data newly acquired in the CUSMAP quadrangle. 

Ore-deposit models are developed from information in published literature and from knowledge 

geologists have gained from experience in mines 

throughout the world. The models are descriptive of 

the three-dimensional setting (geology) of the deposits, 

and they may describe habitat and process of 

formation (genesis) of the deposits. This geneticgeologic concept of ore-deposit modeling permits a 

clear separation of factual data and inference. 

The mode.ls are thus descriptive dimensioned 

generalizations of the ore-deposit types that are likely 

to occur in any CUSMAP quadrangle. They include 

information on grade, tonnage, chemistry, and mineralogy of the ore deposits, as well as chemistry, 

physical properties, lithologies, and alteration haloes 

of the rocks that surround the ore deposits. The 

models include descriptions of geologic, geochemical, 

and geophysical signatures associated with ore-deposit 

types, and they emphasize the regional environment of 

the typical deposit. The most useful characteristics of 

ore-deposit models are those that are general and not 

dependent upon detailed investigations and, hence, are 

more readily determined during regional mineralresource appraisals. Genetic concepts can be built 

into the models when lack of facts prevents the 

construction- of a complete picture of the geologic 

environment of the modeled ore deposits. 

Consideration should be given to all possible oredeposit types that occur in the United States and 

throughout the world. With this broad view in mind, 

the first and largest effort should go into establishing 

models of ore-deposit types known to occur within and 

near the quadrangle. These deposit types, because 

they are known, likely have been searched for in the 

quadrangle; other possible ore-deposit types also 

should be evaluated carefully. The tables of oredeposit types for the three quadrangles considered in 

this study, presented below, are not exhaustive, but 

they serve to show the variety, and variations from 

region to region, of deposits to be modeled. 

Ore-Deposit Types, Tonopah Quadrangle 

Major 

Porphyry molybdenum-copper (Hall deposit) 

Arsenical gold 

Stockwork (in Tertiary rhyolite, Round Mountain; 

in Cambrian argillite-quartzite, Manhattan) 

Disseminated (Northumberland) 

"Epithermal" silver-gold (Tonopah) 
Magnesium (Gabbs) 

Bedded sedimentary barite (East Northumberland 

Canyon) 

Minor 

Gold-silver placers 

Tungsten skarns 

Tungsten veins 

Magnetite skarns 

Mercury veins 

In granite 

In volcanics 

Antimony veins 

Lithium-boron brines and associated hectorite clay 

Lead-zinc replacements in carbonate 

Base-metal sulfides with gold and silver in veins 

Fluorspar veins and breccia pipes 

Metal-bearing organic shales (Devonian) 

Volcanogenic massive sulfide (Devonian) 

Nickel-chromium-cabal t serpentini tes 

Tertiary lacustrine uranium (Siebert Tuff) 

Uranium deposits associated with igneous rocks 

Tin-titanium-vanadium placers 

Some of the deposit types listed as minor, such 

as volcanogenic massive sulfide deposits and metalbearing organic shales of Devonian age, and lithiumboron brines and associated hectorite clays, may with 

further development become of major importance. 

Ore-Deposit Types, Poplar Bluff Quadrangle 

Major 

Lead deposits that also contain zinc, copper, 

cobalt, nickel, and silver in the Cambrian Bonneterre Formation 

Iron-copper deposits in Precambrian rocks 

Minor 

Zinc-lead deposits in Ordovician rocks 

Barite vein and replacement deposits in Paleozoic 

formations 

Manganese deposits in Precambrian rocks 

Tin deposits in Precambrian granites 

Copper-lead-zinc massive sulfide deposits in Precambrian rocks 

Bauxite or nickel-laterite deposits associated with 

buried weathered intrusives 

Fluorspar and carbonatite deposits associated with 

buried syenite intrusives or cryptovolcanic 

centers, including fluorspar veins and mantas of 

Kentucky-Illinois type 

Manganese and iron deposits in weathered surface 

rocks 

Texas coastal-plain type uranium deposits in 

Tertiary sedimentary rocks of the Mississippi 

embayment 

Copper-cobalt-nickel deposits associated with 

Precambrian ultramafic rocks 

Ore-Deposit Types, Hibbing Quadrangle 

Major 

Volcanogenic massive sulfide deposits in greenstone 

belts 

Magmatic copper-nickel deposits that also contain 

platinum, palladium, and cobalt in Duluth 

Complex 

3 

Archean gold deposits 

Biwabik Iron-formation 

Cretaceous unconformity-related uranium deposits 

Cretaceous unconformity-related iron deposits 

Sandstone-type uranium-gold deposits in Pokegama 

Quartzite 

Sandstone-type lead-copper deposits in Pokegama 

Quartzite 

Shale-hosted stratiform lead-zinc deposits in Virginia Argillite 

Sedimentary manganese deposits 

Minor 

Carbonatites-kimberlites 

Porphyry copper-molybdenum deposits 

Accessory platinum, vanadium, and titanium in 

fossil placers 

Archean nickel- and copper-bearing serpentinites 

Silver veins (for example, Silver Islet type) 

Ore-deposit models in the Tonopah quadrangle.-

The geologic settings of the Hall porphyry molybdenum-copper deposit and the Tonopah "epithermal" 

silver-gold district in the Tonopah quadrangle are described to show some aspects of ore-deposit modeling. 

The descriptions are by no means complete and are not 

adequate for mineral-resource appraisal. 

Hall porphyry molybdenum-copper deposit: 

1. The deposit is at and near the contact of a Cretaceous quartz monzonite-alaskite stock intruded 

into metamorphosed Permian clastic strata. 

2. A large volume of Tertiary volcanic rocks lies east 

of the Hall deposit. 

3. The deposit lies in a large zone of hydrothermally 

altered rocks. 

4. Within a mile north and south of the deposit are 

small quartz veins that have produced minor 

silver and gold. 

5. The deposit lies on the northwest flank of a large 

positive magnetic anomaly. 

6. The deposit has not been dated but it may be no 

older than middle Tertiary. 

7. The deposit is a large stockwork that contains on 

the order of 150,000,000 tons of rock grading 

0.125 MoS2; 40,000,000 tons of rock grading 0.4 

percent Cu also is present. 

Deposits of the Tonopah district: 

1. Ore deposits of the district are dominantly in hydrothermally altered andesites and dacites of the 

Miocene Mizpah Trachyte. 

2. The deposits are surrounded by a large zoned halo 

of hydrothermally altered rocks. 

3. The ore deposits are quartz veins that contain adularia, albite, barite, sericite, and other gangue 

minerals, and abundant chalcopyrite, galena, and 

sphalerite, together with silver minerals argentite, polybasite, pyrargyrite, and electrum, and 

minor native gold. Supergene ore minerals also 

are present. 

4. The productive zone is a broad, concave-downward, 

saucerlike form, nearly 3 mi (5 km) across, 

centered on the core of the district. 

5. Light-stable isotope studies suggest deposition of 

ore and gangue minerals from moderate-
temperature ground waters circulated by heat 

from a buried stock beneath the core of the 

district. 

6. Mineralization took place about 18-19 m.y. ago. 

7. The district lies on the southeast flank of a large 

positive magnetic anomaly. 

8. The district, now essentially inactive, has produced 

about 175,000,000 ounces of silver and 2,000,000 

ounces of gold, together with minor lead and 

copper. 

The geologic environment of the Tonopah district 

suggests that the large hydrothermally mineralized 

system of quartz veins and altered rocks may be a halo 

above a buried stock beneath the core of the district. 

The stock may be surrounded by a large porphyry (molybdenum-copper?) deposit. 

The Hall deposit, prior to erosion of volcanic 

rock mantle, may have been capped by a system of 

silver- and gold-bearing quartz veins similar to that at 

Tonopah, assuming that the deposit is as young as Miocene. 

Ore-deposit models in the Poplar Bluff quadrangle.-A skeletonized summary of the significant 

features of lead deposits of the southeast-Missouri 

type that likely are the major resource potential in the 

Poplar Bluff quadrangle provides a framework for 

deposit modeling. 

Major or requisite criteria: 

1. The deposits are in the Cambrian Bonneterre 

Formation. 

2. The ore tends to be associated with Precambrian 

highs that were islands in the Late Cambrian sea. 

3. The ore occurs within certain facies of the carbonate formation: 

a. Near the limestone-dolomite interface and 

always on the dolomite side of the interface. 

b. Generally in a belt of "brown rock" that surrounds the St. Francois Mountains (Precambrian high) like a collar. 

4. The ore deposits are large (as much as 100 ft or 30 

m thick, 500 ft or 150 m wide, and 5,000 ft or 

1500 m long--one is as long as 5 mi or 8 km); 

individual deposits may contain as much as 

50,000,000 tons of ore, grading about 3-10 

percent Pb, 0.2-3.5 percent Zn, and a few tenths 

percent Cu; they contain also cobalt, nickel, and 

silver. 

Minor or permissive criteria: 

1. Pinchout of the underlying Lamotte Sandstone 

suggesting proximity to a buried Precambrian 

high. 

2. Presence of major faults, known mineralization, 

favorable trace-element geochemistry, Davis 

Formation overlying the Bonneterre, algal reefs, 

solution collapse structures. 

First-Stage Analysis 

Fallowing collection of available data and development of ore-deposit models, the next step in 

resource appraisal is to make a first-stage evaluation 

of mineral-resource potential in those parts of the 

CUSMAP quadrangle for which data are more or less 

4 

complete and of high quality (admittedly subjective 

evaluations). No attempt should be made to estimate 

potential of areas in the quadrangle for which data are 

incomplete or of poor quality. The purpose of the 

initial analysis is to identify deposit types and 

mineralizing episodes likely in the quadrangle and to 

form working hypotheses that will be tested and modified by subsequently acquired data for application to 

the "final" resource appraisal. Study areas and topical 

problems specific to the quadrangle will be identified 

for which additional data are needed to complete the 

evaluation. The general deposit models already established can at this stage be modified to better fit local 

conditions on the basis of data from mines and prospects in and adjacent to the quadrangle. 

Several preliminary interpretive maps should be 

prepared prior to the field-data collection phase. The 

types of maps compiled depend partly upon the geologic province being dealt with; some of the maps are 

described as follows. 

1. Maps showing post-mineral cover for each 

period of mineralization and deposit type believed to 

occur in the quadrangle. As familiarity is gained with 

the quadrangle, areas of shallow post-mineral cover 

should be distinguished. This set of maps will ultimately show those areas that are permissive for 

deposits of a specific type within a few thousand feet 

(say, 5,000 ft or 1500 m) of the surface. 

2. Tectonic-lithologic terrane maps that show 

those parts of the quadrangle that have behaved as. a 

unit--perhaps even as a metallogenetic unit or 

"metallotect"--through geologic time. In the Tonopah 

quadrangle, such metallogenetic units might include 

the eugeosynclinal lithofacies of the Roberts Mountains allochthon, major strands of the Walker Lane 

strike-slip fault system, and Tertiary calderas. In the 

Poplar Bluff quadrangle, the most useful maps would 

be subsurface maps, and they might include topography 

of the buried Precambrian surface, isopach of the 

Lamotte Sandstone, and lithofacies of the ore-hosting 

Bonneterre Formation. In the Hibbing quadrangle, 

such metallogenetic units might include the Archean 

Ely Greenstone and the Lake Vermilion Formation, the 

Proterozoic X Biwabik Iron-formation, and the Proterozoic Y Duluth Complex. 

3. Map showing ages, compositions, and tectonic types of intrusive rocks. 

Field Studies to Acquire Needed Data 

Using the working hypotheses developed in the 

first-stage analysis, together with the ore-deposit 

models developed for the quadrangle, the CUSMAP 

team identifies the kinds of data needed to solve specific problems and develops the strategy to acquire the 

data. Discussion of each of the major data categories, 

with variations dictated by the geologic settings of the 

CUSMAP quadrangles, follows. 

GEOLOGIC DATA presented in the form of a 

geologic map generally provide the most fundamental 

information used in resource appraisal. Significance of 

surface data varies substantially among geologic 

provinces, however. In extremely complex geologic 

terranes such as the Basin-Range province, exemplified by the Tonopah quadrangle, elements of virtually 
all lithologic units known to be ore bearing are ~xposed 

in places at the surface and a geologic map is essential 

to define both the surface and subsurface distribution 

of ore-bearing units. In the Hibbing quadrangle in the 

upper Midwest, known ore-bearing units lie near the 

surface but are widely covered by thin glacial drift and 

outwash. Geologic mapping at the surface is not adequate to define the distribution of the ore-bearing 

units, and geophysical and geochemical surveys (as 

described later) can be applied to construct an 

adequate geologic map. In the Poplar Bluff quadrangle 

in the United State~ midcontinent region, rock units 

that are ore bearing to the north in the Rolla 

quadrangle are present in the deep subsurface. Their 

character, position, and mineral potential must be 

determined not by geologic mapping but by geophysical 

surveys, drilling, and regional stratigraphic and 

geochemical study of subsurface materials. 

Geologic mapping, generally at a scale no larger 

than 1:50,000, should be designed to look for and to 

identify "geological metallotects" or regional geological structures or lithofacies supposed or known to be 

favorable for the occurrence of ore deposits. The 

mapping thus is guided by the ore-deposit models 

already established (both in fact and in concept). In 

the Tonopah quadrangle, examples of such metallotects are the Walker Lane zone of northwest-trending 

strike-slip faults (structurally controlled epigenetic 

metal deposits), the eugeosynclinal facies of marine 

Paleozoic rocks in the upper plate of the Roberts 

Mountains thrust system (gold, mercury, and barite 

deposits of "source-bed" origin), and certain Tertiary 

volcanic assemblages ("epithermal" gold and silver deposits). In the Poplar Bluff quadrangle, examples are 

Tertiary sedimentary deposits of the Mississippi embayment (Texas coastal-plain type uranium deposits), 

and southwest-striking faults of the New Madrid fault 

zone (Illinois-Kentucky type fluorspar deposits). Although much of the Poplar Bluff quadrangle has not 

been mapped at large scales, the surficial deposits are 

generally so thick and so widespread that additional 

mapping at the surface would provide little or no insight into the subsurface character and structure of 

the base-metal ore-bearing units. In the Hibbing quadrangle, examples are the Ely Greenstone and Lake 

Vermilion Formation (volcanic massive sulfide 

deposits), Biwabik Iron-formation (Proterozoic banded 

iron-formation deposits), and the Duluth Complex 

(magmatic copper-nickel deposits). 

GEOCHRONOLOGIC DATA on the ages of rocks 

and minerals in CUSMAP quadrangles may be essential 

to the construction of ore-deposit models and to 

mineral-resource appraisal. Where the ages of sedimentary rocks are inadequately known, paleontologic 

information should be sought. Dating of some 

sedimentary units may be possible by determining 

isotopic ages of interlayered . volcanic materials. 

Determinations of ages of metamorphic minerals may 

provide valuable data for interpretation of geologic 

(thermal) history and of the settings of mineral 

deposits. Isotopic age data on igneous rocks, which are 

commonly genetically related to ore deposits, and on 

minerals of the deposits themselves, are invaluable for 

constructing many ore-deposit models. 

5 

GEOCHEMICAL DATA are an essential part of 

the ore-deposit model and of the resource appraisal. 

The distribution and abundance patterns of suites of 

elements in relation to aeoloaic parameters commonly 

are diagnostic for different types of ore deposits, their 

zonation, and their associated alteration halos. The 

presence of anomalously high amounts of metals in 

rocks may signal the proximity of a mineral deposit, or 

it may indicate "leakage" up through a hydrothermal 

system that contains mineral deposits at depth, or it 

may be unrelated to a mineral deposit. The geochemical "signature" of lithologic units may provide clues to 

geologic environments that are favorable for the occurrence of mineral deposits. Accurate geochemical 

data obtained from geologic formations which, because 

of their unusual character (for example, high organicmatter content), have not been characterized 

adequately geochemically in the past may reveal a 

resource previously overlooked. 

Geochemical studies are planned in such a way as 

to provide data that are not already available, so that 

anticipated ore-deposit models for the quadrangle can 

be evaluated. Samples commonly are collected of 

stream sediments and of the B soil horizon in glaciated 

terranes throughout an area to provide geochemical 

data used to identify zones of metal concentrations. 

Metal concentrations thus found may indicate a favorable environment for ore deposits that otherwise may 

have been overlooked. But such surveys should not be 

carried out as though they were designed to identify 

ore-deposit targets. Further, the failure of streamsediment geochemistry to reveal metal anomalies at 

the surface cannot be used in a negative way to rule 

out the presence of favorable environments or of ore 

deposits. Samples of rocks provide geochemical data 

valuable for characterizing the geologic environment 

in which the rocks formed and hence can be used in 

ore-deposit modeling. Samples of hydrothermally 

altered rocks provide geochemical data that can be 

used to determine favorableness or unfavorableness of 

some geologic environments. Furthermore, bedrock 

geochemistry may reveal whether or not the rocks 

have been altered, as some altered rocks are not 

obvious to the naked eye. 

Three types of geochemical surveys are appropriate for the Tonopah quadrangle. The first is a 

regional geochem~cal sur~ey with a density of one 

sample per 2 mi (7 km ) in areas not covered by 

Quaternary valley fill. Heavy-media splits and minusSO-mesh fractions of stream-sediment samples should 

be analyzed by the six-step (33 elements) spectrographic method. The second type of survey is tailored 

to specific deposit types within areas favorable for 

those deposits. Sample density, element suite 

analyzed for, and method of collection and treatment 

of samples would be tailored to the deposit type, 

considering factors such as dimensions and form of the 

deposit and its possible alteration halo. 

Spectrographic analysis of these samples may not be 

desirable if secondary dispersion of elements in 

geochemical haloes is suspected. The third type of 

geochemical survey is for the purpose of determining 

the chemical character of lithologic units throughout 

the quadrangle. Depending upon the physical variation 

within lithologic units and the extent of their 
distribution, perhaps 5 to 25 samples would be required 

to characterize each unit. Six-step spectrographic 

analyses should provide adequate chemical data for the 

characterizations, and only in special cases should 

additional methods be required (for example, specific 

ion electrode to determine fluorine content). 

Geochemical sampling of surficial materials 

(rock, stream sediment, soil) in the Poplar Bluff quadrangle would not be useful in the search for Viburnumtype lead deposits because the ore-hosting Bonneterre 

Formation is deeply buried. On the other hand, if 

drill-hole samples of the buried formations become 

available, geochemical studies would be of great value 

in characterizing possible favorable geologic environments for ore deposits. The inadequacy of any surface 

methods, geologic or geochemical, in characterizing 

geologic environments of the buried rocks emphasizes 

the necessity of acquiring drill-hole samples for study. 

Geochemical surface sampling would be useful to test 

the potential for coastal-plain-type uranium deposits 

and Kentucky-Illinois-type fluorspar deposits in the 

southeast part of the quadrangle. Elsewhere in the 

quadrangle, surface sampling would probably reveal 

zinc anomalies in Ordovician rocks, but the known zinc 

deposits of northern Arkansas are small and uneconomic. Also, the possibility that unrecognized types 

of deposits miqht occur close to the surface suggests 

that some surface geochemical surveys may be 

warranted. 

In the Hibbing quadrangle, geochemical surveys 

of surface materials should be carried out in areas that 

may contain mineral deposits but where favorable 

environments were not recognized in the past. The 

entire quadrangle thus need not be covered. Sample 

stations should be about 2 mi (3 km) apart, and soil 

sampling of the B horizon is recommended. In 

addition, geochemical surveys of some bedrock lithologic units should be made, as for example the Archean 

iron-formations, to locate zones of anomalously high 

gold content that may indicate the presence of gold 

ore deposits. Auger drilling through glacial debris may 

be required to collect samples in some areas. 

GEOPHYSICAL DATA, incluaing magnetic, 

gravity, and radiometric, are needed for mineralresource appraisal in almost all areas. Other geophysical data such as rock magnetization and density, 

seismic, electromagnetic, electrical resistivity, and 

audio-magnetotelluric are valuable in special areas, 

but will not be discussed further here. 

MAGENTIC DATA, commonly obtained by airborne surveys, are useful to infer subsurface distribution of lithologic units as well as to pinpoint certain 

anomalies related to mineral deposits. The data also 

may provide ·insight into regional structural framework. 

An airborne magnetic survey in the Tonopah 

quadrangle should be flown at a line spacing of 1,500 ft 

(0.5 km) and at a terrain clearance of 500-1,000 ft 

(150-300 m). The aeromagnetic data can be used to 

detect possible unidentified or shallow, buried 

intrusive bodies, zones of sulfide-mineralized rocks, 

and highly magnetic rocks possibly related to mineral 

deposits. The magnetic map also may be used to 

project exposed geology into covered areas, and it may 

reveal discontinuities related to important structural 

6 

zones. Aeromagnetic mapping of the Poplar Bluff 

quadrangle is important, as the data indicate depth to 

magnetic basement and thus could indicate highs on 

the buried Precambrian surface. Stratigraphic pinchouts against the Precambrian "highs" may have 

localized mineralized zones in buried Paleozoic formations. Aeromagnetic data (3,000-ft or 1-km line 

spacing, 1,000-ft or 300-m terrain clearance) that is 

available for the Hibbing quadrangle is necessary to 

aid identification of lithologic units where they are 

buried beneath glacial debris. These data also may 

provide information valuable for the definition of 

zones favorable for the occurrence of certain types of 

ore deposits. Some favorable areas in the Hibbing 

quadrangle may require further testing by aeromagnetic surveys at a line spacing of about 1,500 ft (0.5 km) 

and terrain clearance of 500 ft (150 m), and by ground 

electromagnetics, to improve understanding of the 

geologic environments in which ore might have been 

deposited. 

GRAVIMETRIC DATA, obtained from ground 

stations, may aid interpretation of the subsurface 

distribution of rock units and may provide insight into 

regional structural framework. 

In the Tonopah quadrangle, gravity profiles 

should be established using roughly half-mile (1-km) 

spacing on lines about 10 mi (15 km) apart, partly to 

define intermontane basins and pediment geometries, 

partly to define subsurface distribution of major rock 

units, and partly to refine interpretation of regional 

gravity data bearing on regional structures. Gravity 

data are considered less important for evaluation of 

mineral potential in the Poplar Bluff quadrangle. 

However, both gravity and aeromagnetic data are 

essential to an understanding of the New Madrid rift 

zone that extends across the southeast part of the 

quadrangle. Postulated buried basic to ultrabasic plutons along the margins of the rift may have played a 

role in genesis of mineral deposits in this and adjacent 

quadrangles. In the Hibbing quadrangle, gravity 

stations should be established throughout in a grid of 

2-mi (3-km) spacing to provide data useful for interpreting the distribution of rock units beneath glacial 

debris. In addition, specific environments can be 

further evaluated; for example, the known gravity low 

in the Virginia Argillite should be evaluated further to 

establish presence or absence of a second-order 

sedimentary basin that has possible strati form leadzinc potential. 

RADIOMETRIC DATA, obtained by airborne surveys, generally are used to search for radioactivity 

anomalies related to deposits of radioactive minerals. 

The data should be applied more widely to define distribution of rock units of differing radioactivities 

(distinguished as to amounts of potassium, thorium, 

and uranium). These data then can be used to help 

establish the geologic occurrence of these rock units, 

and can be applied to ore-deposit modeling. 

The distribution of hydrothermally altered rocks 

in any geologic terrane outlines zones through which 

mineralizing fluids have passed; mineral deposits may 

occur within these zones wherever favorable lithologic 

and structural environments existed for precipitation 

of ore minerals. In the arid West, as exemplified by 
the Tonopah quadrangle, the generally excellent 

exposure of bedrock allows ground mapping of hydrothermally altered rocks. Also, as will be discussed, 

certain aerial or satellite photography when used in 

this region may provide images from which zones of 

hydrothermally altered rocks can be interpreted. 

LANDSAT images can be used to help determine 

regional structural elements that have influenced 

mineral distribution, such as lineaments, and that are 

not evident on available geologic maps or on largescale aerial photographs. Certain multispectral 

images obtained from satellite or aerial photography 

may reveal zones of altered rock (specifically, distribution of hydrated iron oxides) spatially associated 

with deposits in the Basin-Range province. 

Even where surface geology is well known and 

where geophysical data aid projection of surface geology into the subsurface, geologic information obtained 

from water, oil, gas, and other drill holes can be of 

great value. Where surface units are flat and widespread, drill data may be indispensable to determine 

subsurface geology. 

In the Tonopah quadrangle, almost no data are 

available from water, oil, or gas test wells. Some 

information can be obtained from test holes drilled in 

a few places by the U.S. Geological Survey during 

studies in the central Nevada Test Site in the 1960's. 

In general, information from mining industry drilling in 

the quadrangle is impossible to obtain because of company policy. However, drilling by the U.S. Geological 

Survey to test hypotheses of hitherto-unknown deposit 

types envisioned within the quadrangle, or to obtain 

geological information essential to ore-deposit modeling, is feasible and appropriate to reach the objectives 

of CUSMAP projects. Of course such drilling would be 

used to test for ore-deposit environments and to 

develop models for ore types and not to define or to 

test actual ore-deposit targets. In the Poplar Bluff 

quadrangle, some subsurface information may be 

available from water, oil, and gas drill holes; in 

general, mining industry drill-hole data are not available because of company policy. The U.S. Geological 

Survey should drill some deep holes to reach· favorable 

ore-deposit horizons, particularly the Bonneterre 

Formation, host of the great lead deposits of the 

Viburnum trend farther north in Missouri, in order to 

acquire the geologic information necessary to make an 

adequate mineral-resource appraisal. Locally, in the 

Hibbing quadrangle, shallow drilling of overburden in 

order to sample bedrock for petrographic and geochemical studies, and·to determine thickness of glacial 

drift, may be required. Some water well-log data on 

the character of the shallow subsurface are available 

for the Hibbing quadrangle. 

Information on mines and mine production, 

prospects, and mineral occurrences is highly desirable, 

if not necessary, for any mineral-resource appraisal as 

such data form a factual basis for judging resource potential in favorable geologic environments where 

mineral deposits are not known. Data needed include 

details of the geologic setting of mined ore deposits 

and mineral deposits exposed in prospect workings, 

such as petrography, physical properties, and chemistry of host rocks, character of alteration haloes, 

structural controls, and grade, tonnage, chemistry, and 

7 

mineralogy of the ore. Information on mining claims--

their type and location--facilitates their later study 

and aids determination of the legal status of land in 

areas being evaluated for the possible use of natural 

resources. 

Data on mines and mine production, prospects, 

and mining claims should be obtained throughout the 

CUSMAP quadrangle; where data from mines and 

prospects in the vicinity of the quadrangle can be 

useful in developing ore-deposit models for application 

in the quadrangle, these, too, should be collected. 

Final-Stage Analysis 

After newly acquired field and other data have 

been added to the previously compiled data on base 

maps at a scale of 1:125,000 or 1:250,000, then interpretation takes place in three steps. 

1. Each map depicting a parameter (such as geologic 

or aeromagnetic) is examined for anomalies and other 

indications of environments favorable for ore deposits. 

For example, large magnetic anomalies are looked for 

on the aeromagnetic map, metal anomalies are determined on the geochemical maps, and lithologic and 

structural peculiarities are noted, or favorable geologic relations are outlined, on the geologic map. 

2. An integrated interpretation is made of all the data 

bases wherein converging lines of evidence are used to 

define environments favorable for mineral deposits. 

Examples of types of useful evidence are magnetic 

features that are incompatible with the known rock 

units, weak geochemical anomalies that correlate with 

specific rock units, and certain geologic units that 

signal a specific mineral environment, such as 

fluorine-rich rhyolites with which might be associated 

uranium, fluorspar, or beryllium deposits. 

3. The data base maps are given an integrated interpretation for each deposit type, as established in the 

ore-deposit modeling stage, to determine characteristics that may indicate that an area is permissive for 

that deposit type. Where indicators of geologic 

favorableness do not fit in the context of known oredeposit types, clues may be provided to previously 

unrecognized deposit types. 

This subjective analysis is performed jointly by 

the data gatherers that form the CUSMAP team and 

the ore-deposit-model builders both on the CUSMAP 

project and throughout the Office of Mineral 

Resources of the U.S. Geological Survey, especially 

commodity geologists. The assessing team must spell 

out the reasoning behind its analysis so that users can 

understand the rationale of the evaluation. As shown 

later, the manner of presentation of the data in maps, 

tables, and texts can demonstrate rationality of 

analysis. 

The subjective analyses of possible occurrences 

of certain ore-deposit types within a CUSMAP quadrangle can be refined beyond the assessment that an 

area is favorable for the occurrence of a particular 

deposit type. Such refinements permit fixing degrees 

of favorableness that can be presented in qualitative 

or possibly semiquantitative terms. The majority of 

participants in the Mineral-Resource Appraisal workshop, however, believed that quantitative estimates of 
mineral-resource potential are impossible and consequently are generally inadvisable to attempt. Nevertheless, among the participants there was a strongly 

held minority view of the validity of geostatistical 

evaluation of resources to produce quantitative values 

that have probability limits. But also there was a 

generally held belief, even among the statisticians, 

that adequate, accurate data of the right kind (objective data) are not available to permit rigorous statistical appraisals of potential resources. Furthermore, 

statistical estimates of mineral resources have never 

been adequately tested by production. 

Favorableness can be described using three 

criteria: (1) likelihood (or degree of favorableness) 

that a deposit type is present; (2) size of the deposit or 

deposits (amount of commodity that may be available) 

if present; and (3) adequacy of the data on which the 

assessments are made. A simple numerical scale can 

be used to grade these categories. Thus, likelihood can 

be graded as a (1) high probability of containing 

deposits of the type, (2) probability of containing 

deposits of the type, and (3) low probability of containing deposits of the type. Some of the working 

groups believed that a fourth category indicating no 

probability is warranted. Size (or amount) can be 

graded as (1) large, (2) moderate, and (3) small. Known 

size and grade ranges of particular ore-deposit types 

should be used in making the significance classifications so that users will have a basis for judging the 

meaning of the size classifications indicated. Whether 

or not estimates of favorableness and amount of 

resources present are valid depends upon the quality of 

the data available for the assessments; hence, some 

indication of adequacy of the data should be given. 

Deposit category ••••••••••• Productive1 

Because of differences in judgment, not everyone will 

agree that the available data are sufficient for 

mineral- resource appraisals at the 1:250,000 scale of 

the CUSMAP quadrangles. But a twofold classification, (1) adequate data, and (2) inadequate data, will at 

least inform the users of the appraisers' opinion of the 

sufficiency of the data. 

Other factors that have a bearing on the importance of mineral-resource data generated by the U.S. 

Government are current accessibility of mineral 

deposits, their present and future economic certainty 

of production, their time lag to production, the desirability of the commodities for National strategic 

purposes, and the desirability of the commodities for 

National economic leverage. Assessments by the U.S. 

Government of these factors may not be meaningful to 

the private mining industry for exploration for and 

development of economic supplies of mineral commodities, but they are meaningful in respect to planning 

and decisions that the Government itself must make in 

the interests of National security and welfare. 

In order to systematize the final-stage analysis 

of resource potential in the Tonopah quadrangle, the 

working group under D. R. Shawe set up a review procedure that could permit a certain quantification, 

albeit subjective, of the importance of assessed 

resources. The following table outlines the main elements of the review, using as an example the porphyry 

molybdenum-copper-deposit type. In this example the 

information supplied is in part imaginary and is 

furnished merely for demonstration purposes; classification numbers, where used (in parentheses), are those 

previously defined. 

Subeconomic •••••• Projected 

Number of deposits ••••••••••• 

Favorableness ••••••••••••••• 

Size •••••••••••••••••••••••• 

1 (Hall deposit) •••••••• 

Known deposit ••••••••• 2 ••••••••••••••••••• 4 

Known deposit • • • • • • High probability (1). 

Certainty (data adequacy) ••••• 

Co-products ••••••••••••••••• 

Current accessibility ••••••••• 

Present-future economic 

certainty ••••••••••••••••• 

Time lag to production •••••••• 

Desirability for National 

strategic purposes ••••••••• 

Desirability for National 

economic leverage ••••••••• 

Large (1) •••••••••••••• 

Known deposit ••••••••• 

Mo, Cu, Sn, Au, Ag ••••• 

Easy •••••••••••••••••• 

High •••••••••••••••••• 

Slight ••••••••••••••••• 

Moderate ••••••••••••• 

Minor ••••••••••••••••• 

Large (1). • • • • • • • • • • Large (1). 

Known deposit • • • • • • Inadequate data (2). 

Mo, Cu, Au, Ag • • • • • Mo, Cu, Sn, Au, Ag. 

Difficult • • • • • • • • • • • Unknown. 

Moderate •••••••••• 

Major •••••••••••••• 

Moderate •••••••••• 

Minor •••••••••••••• 

Moderate. 

Major. 

Moderate. 

Minor. 

1Past or present production, or capability of current production. 

The various classifications shown in the table can be weighted as to relative significance in order to 

arrive at a general value (importance) of the assessed resources. 

8 
The majority of participants in the working 

groups concluded that statistical quantification of 

resource appraisals on the basis of available data 

generally is not warranted. However, the statistical 

treatment proposed by the Hibbing quadrangle working 

group under D. F. Sangster may be useful for certain 

geologic environments if properly qualified.! For 

example, existing frequency-distribution curves of ore 

tonnages and copper grades in massive sulfide deposits 

could be combined with subjectively derived estimates 

of number of deposits in areas determined to be favorable for the occurrence of massive sulfide deposits. 

These probability curves could be combined by the 

Monte Carlo technique to produce a probability curve 

for tons of contained copper in deposits of the massive 

sulfide type. Other deposit types in specific 

lithologic-structural domains, or in favorable geologic 

environments (metallotects), might be treated similarly if available data seem adequate. 

Presentation of Resource Appraisals and 

Supporting Data 

Two distinct products for two completely 

different audiences should result from the CUSMAP 

studies. One should be a succinct summary that 

presents in as simple language as possible the major 

results of the resource analysis. The other is a technical product that presents as fully as possible the 

detailed data resulting from the field and office 

studies. 

The first and more important product from the 

standpoint of National welfare should be an "executive 

summary" that is a succinct statement of the major 

results of the mineral-resource appraisal. Such a 

summary is already a part of the reports of wilderness 

investigations. This product is prepared for the use of 

nongeologists who are generally specialists in other 

government agencies, in the U.S. Congress, and in 

organizations outside the government that have 

mineral-resource interests. Because such users must 

understand clearly the message of this product, the 

report should be proofread by a college-trained 

nongeologist before it is presented to its users. The 

report should be short and should contain a simple 

message based on the needs of the ultimate users of 

the mineral-resource analysis. It must contain maps 

that clearly show areas of mineral potential and tables 

that describe what that mineral potential is. Maps 

used in the report should be simple and understandable 

to the public. The summary should list the commodities likely to occur and their amounts in as quantita1To properly qualify any resource estimate, 

which is a quantification of the unknown, it must be 

emphasized that a resource estimate cannot be used as 

an indication of amount of resources that ultimately 

will be pPoduced. 

9 

ti ve terms as is reasonable. Absolute numbers for a 

specific deposit type are not possible, but "order of 

magnitude" can be implied by comparisons to known 

typical sizes and grades of deposits of that type. The 

value of commodities relative to National requirements is an appropriate subject to be ~ddressed in the 

executive summary. Reference can be made in the 

summary to strategic minerals as classified by the U.S. 

Bureau of Mines. The date of the mineral-resource 

appraisal should appear in the title of the executive 

summary report, to emphasize the fact that mineralresource appraisals are only interim assessments that 

should be updated periodically. 

The second or technical product consists of text, 

tables, and all the data maps and interpretive maps, at 

a scale of 1:250,000, that have been produced in a 

CUSMAP study. Data maps needed for the CUSMAP 

technical report are of considerable number and 

variety. Most important are geologic maps, especially 

a primary colored geologic map of the quadrangle at a 

scale of 1:250,000. Additional geologic maps at the 

same scale might be appropriate, such as structural or 

tectonic maps, and "breakout" maps showing separate 

important geologic units. Geologic maps at a regional 

scale (perhaps 1:1,000,000 or even smaller scale) may 

be useful to show the relation of major metallotects to 

the CUSMAP quadrangle. Geophysical maps, where 

needed, show gravity, aeromagnetic, airborne radioactivity, and other types of geophysical data. 

Geochemical maps show stream-sediment sample 

geochemistry, rock geochemistry, and distribution of 

minor commodities, based on data such as that from 

spectrographic analyses of mineralized rocks from 

prospects and mines. Depending upon complexity, 

each geochemical map .can show the distribution of one 

to several elements. In general, elements shown are 

metals; some nonmetals such as fluorine that may be 

useful "pathfinder" or guide elements should be shown. 

A map indicating distribution of hydrothermally 

altered rocks is of great value in some regions. A spot 

map gives distribution, size, and type of the known 

mineral deposits in the CUSMAP quadrangle. The 

known deposits should be distinguished as to those 

currently in production, those that are subeconomic, or 

those that are being prepared for but are not yet in 

production. 

The data maps are used to produce interpretive 

maps that show the quadrangle divided into units of 

specific geologic environment and mineral potential. 

These units are then further defined into permissive 

areas in which rock assemblages of appropriate age 

that are favorable for specific ore deposit types occur 

within a reasonable distance (say, 5,000 ft or 1500 m) 

of the surface. The permissive areas are then subdivided and classified into those prospective areas that 

contain positive indications of a mineral deposit or 

district of the type considered. Statements such as 
"there is an X-percent probability that Y number of 

deposits (of a certain type) may occur in Z area" are 

appropriate, if adequately supported. The prospective 

areas also may be classified as to high, medium, or low 

potential for specific deposit types, using the subjective-probability classification already described. 

Reasons for the classification should be stated clearly. 

Areas for which data are insufficient to indicate 

mineral-resource potential should be labeled clearly. 

A statistical (or even subjective) extrapolation of 

mineral-resource. potential into areas of shallow cover 

in which the quality of the available data is greatly 

reduced should be attempted, but the tentative nature 

of the data should be emphasized. 

Interpretive maps accompanying the technical 

report are primarily to show distribution of areas 

favorable for the occurrence of mineral deposits. The 

favorableness maps show distribution of geologic 

environments of each of the important ore-deposit 

types in the quadrangle; the maps should indicate also 

the metal co-products, ranked by significance, because 

the commodities present have a bearing on favorableness classification. In some areas a spot map of known 

deposits can be inc6rporated with a favorableness map 

in order to ifidicate more cle::!rly the reasons for the 

favorableness classification. Degrees of favorableness 

shown on the map are based on the three-criteria 

classification already described. 

Some possible derivative maps, proposed by the 

working group under E. L. Ohle for the Poplar Bluff 

quadrangle and based both on available data and on 

interpretation, might show the subsurface distribution 

EXPLANATION 

1 1 1 1 Bonneterre Formation (dolomite) is present 

northwest of this line 

Criteria for mineral deposits 

Bonneterre Formation 

Dolomite 

Buried Precambrian knobs 

Major faults 

Base metals 

DISTRIBUTION OF 

FAVORABLE CRITERIA 

~ Major faults 

~ Bonneterre is limestone 

• Buried Precambrian knobs (from aeromagnetic map) 

Zones of abnormally high content of base metals 

in drill samples 

N No subsurface information available 

Areas numbered on map 

1 2 3 4 5 6 

+ + + + + + 

+ + + + + + 

+ - - + - -

+ + - - + -

+ + + - - -

7 8 9 

- + + 

- - 0 

- - -

+ - 0 

'+ + 0 

+ 

0 

EXPLANATION 

Listed criterion is present 

Listed criterion is absent 

Insufficient data to infer presence 

or absence 

EXPLANATION 

-Highest 

~High 

DLow 

~Insufficient 

~data 

FIGURE I.--Interpretive maps showing favorableness of the Bonneterre Formation for ore deposits of the 

Viburnum type in the Poplar Bluff quadrangle. 

10 
Number of deposits 

>-

() 

r:::::: 

Q) 

::I 

C" 

Q) 

"- u. 

Monte 

Tonnage 

II Ca~ simulation 

Determined by 

subjective judgment 

of "experts" 

Tonnage-grade 

model determined 

from known deposits 

Tons of contained metal 

FIGURE 2.--Diagram showing method of estimating 

amount of metal for a specific ore-deposit type 

within an area defined as geologically favorable. 

of the Bonneterre Formation, topographic highs on the 

Precambrian surface, distribution of brown rock, and 

distribution of hydrothermally altered and mineralized 

rock. Using some of these same parameters, the 

working group under A. V. Heyl prepared an example 

of a set of partly imaginary interpretive maps showing 

favorableness of the Bonneterre Formation for ore 

deposits of the Viburnum type in the Poplar Bluff 

quadrangle, as shown in the accompanying illustration 

(fig. 1). 

The Hibbing quadrangle working group under 

D. F. Sangster was the only one to propose in detail 

how favorable areas might be rated by subjective 

probability. This group suggested a summary display 

of information for nontechnical users. The 

accompanying diagram (fig. 2) shows the method of 

estimating amount of metal for a specific ore-deposit 

type within an area defined as geologically favorable. 

Tonnage of known deposits and estimated tonnage of 

Known Undiscovered 

Probability level 

10 percent 

90 percent 

Tonnage proportional to area 

FIGURE 3.--Diagram comparing tonnage of known 

deposits and estimated tonnage of undiscovered 

deposits. 

undiscovered deposits (shown at the 10-percent and 90-

percent probability levels) are compared in a diagram 

(fig. 3). These diagrams then are included on the map 

showing favorableness for the deposit type(s) (fig. 4). 

To complete the presentation of data, appropriate texts and tables, fitted to the function of the 

maps, should accompany both the data maps and the 

interpretive maps. 

The technical product should include recommendations for further work to (1) improve the mineralresource appraisal, and (2) advance the science of 

geology based on additional geologic and other geescientific observations within the quadrangle. An 

important final step of each CUSMAP project is to 

review critically the method used for mineral-resource 

analysis and to prepare a modified version for other 

CUSMAP studies that will follow. And again, the date 

of the mineral-resource appraisal should appear in the 

title of the technical report. 

11 

WILDERNESS AREA APPRAISALS 

Wilderness area stuodies generally are planned for 

a duration of 1-3 years and may take more than 10 

man years of work to complete. Project personnel 

require the same qualifications as do those of the 

CUSMAP projects. Wilderness mineral-resource 
INFORMATION ANALYSIS - PRESENTATION -

Known Undiscovered 

Litho-tectonic domain 

Known Undiscovered 

+ Deposit-type A--metal x 

X Deposit-type 8--metals y and z 

Deposit-type A lJilh 

Number of deposits 

Grade 

~ x Simulation Contained ~ x 

Tonnage 

~ 

Deposit-type B lrillh 

Number of deposits 

Grade ~ y ~ - Simulation - Contained y 

Grade 

~ z 

- - Containedz ~ 

L6 

Tonnage 

FIGURE 4.--Maps and diagrams showing analytical steps to present mineral-resource favorableness ratings. 

12 
appraisals are simi~r to the CUSMAP appraisals and 

differ only in scale. 

The two working groups that evaluated the 

Tonopah quadrangle also considered procedures for 

mineral-resource appraisal of an area arbitrarily 

designated as the "North Reveille Wilderness" (not a 

real wilderness) in the northern Reveille Range. The 

area covers about 65,000 acres and is adjacent to the 

Reveille mining district to the southeast. Minor 

mineral occurrences and areas of hydrothermally 

altered rocks lie within the boundaries of the wilderness area. Adequate appraisal of the mineral-resource 

potential of the wilderness requires, in addition to, 

study of the area itself, study of some of the area 

surrounding it, particularly the Reveille mining 

district. 

The two working groups that evaluated the 

Poplar Bluff quadrangle also considered procedures for 

mineral-resource appraisal in an area designated by 

the U.S. F crest Service as the Irish Wilderness. The 

Irish Wilderness, in the central part of the Poplar Bluff 

quadrangle, covers about 23,000 acres and has no 

known mineral deposits in or near it. The wilderness 

nevertheless is underlain by the Bonneterre Formation 

in an area that may be favorable for the occurrence of 

ore deposits of the Viburnum type. In order to 

appraise this possibility adequately, two m~thods of 

investigation seem necessary--an aeromagnetic survey 

to evaluate the possibility of a buried Precambrian 

high in the vicinity, and drilling several deep holes, 

perhaps as many as six, to determine the character of 

the Bonneterre Formation. 

The two working groups that evaluated the 

Hibbing quadrangle also considered procedu~es for 

mineral-resource appraisal in an area hypothesized to 

represent a wilderness area. The "Chippewa 

Wilderness" (not a real wilderness) in the northwest 

cor11er of the Hibbing quadrangle covers about 110,000 

ac1·es and has no known mineral deposits in or near it, 

although similar geologic terranes elsewhere in the 

world may be richly mineralized. The wilderness area 

is almost wholly covered by glacial debris and the 

bedrock geology is poorly known. The almost total 

lack of geologic information prompted the working 

group under D. F. Sanqster to propose the following 

steps that would help to complete a mineral-resource 

appraisal of the Chippewa Wilderness. 

1. Obtain airborne total-field magnetic, airborne 

gradiometer, and airborne electromagnetic data 

at a line spacing of 1,500 ft (0.5 km) or 0.5 mi 

(800 m). -

2. Make a geological examination of whatever 

outcrops (probably few) can be found within the 

area. 

3. Drill overburden by drills mounted on tracked 

vehicles to obtain samples of till. This work 

would be contingent upon obtaining permission 

from the U.S. Fa rest Service for access by 

tracked vehicles; if the work were done in winter 

2Wilderness projects, by legislative mandate, are 

carried out in cooperation with the U.S. Bureau of 

Mines. The USBM examines records for claim and 

mine locations, tabulates reserves and past production, 

studies metallic and nonmetallic ores, and participates 

in determination of resource potential. 

when the ground and bodies of water are frozen 

and covered by snow, little if any damage to the 

terrain would occur. Drilling should begin along 

the existing roads that rim the area and the one 

road cutting through the middle of the area. 

Drilling to a depth of 200 ft (60 m) may be 

required in places. 

4. Analyze till samples for standard elements; 

examine suboutcrop rock chips and heavymineral concentrates under the microscope. 

Failure to detect anomalously high amounts of 

valuable metals or minerals as a result of 

sampling and geochemical analysis cannot be 

construed as an indication of unfavorableness for 

mineral potential. 

5. Compile data from studies 1-4 to produce geologic 

and geochemical maps; more detailed drilling and 

ground geophysical surveys to complete geologic, 

geochemical, and geophysical coverage might be 

required the following year. 

13 

6. Delineate on maps any favorable areas found. 

SUMMARY 

The U.S. Geological Survey workshop concluded 

that mineral-resource appraisals of CUSMAP quadrangles and wilderness areas should be undertaken in 

the following steps: (1) compile available data; (2) 

model possible ore-deposit types; (3) prepare a firststage analysis of the available data; (4) gather additional needed data through field studies; (5) prepare a 

final-stage analysis; and (6) present the data in the 

form of two products, the first an executive summary 

that is a simple and succinct statement of the results 

of the mineral-resource appraisal for the use of nongeologists in other government agencies, in the U.S. 

Congress, and in organizations outside the government 

who have need of such information, and the second a 

technical product consisting of data maps and interpretive maps supported by appropriate texts and 

tables. Because of logistical constraints (primarily 

time limitations), steps 1-4 may have to be carried out 

more or less concurrently. Step 1 (compilation of 

available data), except under extreme circumstances, 

should largely precede step 4 (field studies). In some 

instances, simultaneous operation of the first four 

steps provides a beneficial feedback and interplay of 

effort. 

RECOMMENDATIONS 

Use by the U.S. Geological Survey of the sugges- , 

tions just outlined for mineral-resource appraisals 

should provide the advantages of a consistent and 

systematic process. However, as noted in previous 

pages, the variations and exceptions in the application 

of the procedures to CUSMAP quadrangles and wilderness areas in different geologic provinces emphasize 

the need for flexibility. 

The workshop participants recognized that their 

efforts culminating in this report did not encompass all 

aspects of resource appraisal at the map scales 

considered, and they recognized also that many 

aspects of the procedures proposed can be improved 

with further knowledge of and experience with mineral 
deposits and mineral-resource appraisals. They 

recommended that joint studies by government, 

industry, and academic specialists, such as the 

December 1979 workshop held in Denver, be continued, 

and that the U.S. Geological Survey continue to 

reexamine its methods of mineral-resource appraisal. 

by mineral-resource appraisal projects could come 

from other sources. Thus, research toward better 

understanding of geologic environments and processes, 

and ultimately better success at mineral-resource 

appraisal, can be fostered and strengthened. 

The U.S. Geological Survey invites comments 

from readers regarding its methods of mineralresource appraisal. Please send comments to the 

author, Daniel R. Shawe, Mail Stop 905, U.S. 

Geological Survey, Box 25046, Federal Center, Denver, 

co 80225. 

The workshop participants also recommended 

that studies of CUSMAP quadrangles and wilderness 

areas should provide latitude for scientific 

investigations beyond the objective of mineralresource appraisals. Funding for research instigated 

Name 

Allen F. Agnew 

Frederik P. Agterberg 

Joseph R. Anzman 

Roger P. Ashley 

Paul A. Bailly 

Paul B. Barton, Jr. 

Helen M. Beikman 

Henry C. Berg 

Byron R. Berger 

Arthur A. Brant 

Donald A. Brobst 

Calvin S. Bromfield 

Frank C. Canney 

William R. Cannon 

Douglas R. Cook 

Duncan R. Derry 

John H. De Young, Jr. 

Lawrence J. Drew 

Gordon P. Eaton 

Ralph L. Erickson 

Frank C. Frischknecht 

Gus H. Goudarzi 

William R. Greenwood 

John M. Guilbert 

APPENDIX A 

Organizing Committee 

Paul A. Bailly, Occidental Minerals Corp., Denver, 

Colo. 

Henry C. Berg, U.S. Geological Survey, Menlo Park, 

Calif. 

Ralph L. Erickson, U.S. Geological Survey, Denver, 

Colo. 

Richard F. Meyer, U.S. Geological Survey, Reston, Va. 

Daniel R. Shawe, chairman, U.S. Geological Survey, 

Denver, Colo. 

Donald A. Singer, U.S. Geological Survey, Menlo Park, 

Calif. 

APPENDIXB 

Workshop Participants 

Affiliation 

Library of Congress, Washington, D.C. 

GSC, Ottawa, Canada 

Houston Oil & Minerals, Denver 

USGS, Menlo Park 

Occidental Minerals, Denver 

USGS, Reston 

USGS, Reston 

USGS, Menlo Park 

USGS, Denver 

Consultant, Tucson 

USGS, ReSton 

USGS, Denver 

USGS, Denver 

USGS, Reston 

Freeport Exploration, Reno 

Derry, Michener & Booth, Toronto 

USGS, Reston 

USGS, Reston 

USGS, Reston 

USGS, Denver 

USGS, Denver 

USGS, Reston 

USGS, Denver 

University of 1Arizona, Tucson 

14 

Participation 

Poplar Bluff 2 (geology) 

Hibbing 1 (geostatistics) 

Poplar Bluff 2 (geophysics) 

Tonopah 1 (geochemistry) 

Hibbing 1 (geology) 

Hibbing 2 (geology) 

Observer 

Speaker; Tonopah 1 (geology) 

Tonopah 2 (geochemistry) 

Speaker; Hibbing 1 (geophysics) 

Poplar Bluff 2 (geology) 

Tonopah 2 (geology) 

Hibbing 1 (geochemistry) 

Hibbing 2 (geology) 

Tonopah 2 (geology) 

Hibbing 2 (geology) 

Hibbing 2 (geostatistics) 

Speaker; Tonopah 1 (geostatistics) 

Tonopah 1 (geophysics) 

Speaker; Poplar Bluff 1 (geochemistry) 

Hibbing 2 (geophysics) 

Observer 

Hibbing 1 (geology) 

Tonopah 2 (geology) 
Stanley K. Hamilton 

William F. Hanna 

J. Julian Hemley 

Allen V. Heyl 

Jean Juilland 

William R. Keefer 

Stephen E. Kesler 

Rodney V. Kirkham 

Geoffrey B. Leech 

Don R. Mabey 

David Menzie 

Richard F. Meyer 

Leo J. Miller 

Ernest L. Ohle 

Pierce D. Parker 

Jack Phillips 

F arrest G. Poole 

Walden P. Pratt 

William C. Prinz 

John W. Rold 

Arthur W. Rose 

Donald H. Richter 

James Rytuba 

Donald F. Sangster 

Daniel R. Shawe 

PaulK. Sims 

Donald A. Singer 

Norman Stark 

Thomas A. Steven 

Richard B. Taylor 

Ted G. Theodore 

William C. J. 

van Rensburg 

Anne Vickery 

Stewart R. Wallace 

Stanley H. Ward 

John C. Wilson 

Amax Exploration, Chesterfield, Mo. 

USGS, Denver 

USGS, Reston 

USGS, Denver 

USBLM, Denver 

USGS, Denver 

University of Michigan, Ann Arbor 

GSC, Ottawa, Canada 

GSC, Ottawa, Canada 

USGS, Salt Lake City 

USGS, Menlo Park 

USGS, Reston 

Texasgulf, Golden, Colo. 

Consultant, Salt Lake City 

Amax Exploration, Denver 

Chevron Resources, Denver 

USGS, Denver 

USGS, Denver 

USGS, Reston , 

Colorado State Geologist, Denver 

Pennsylvania State, University Park 

USGS, Denver 

USGS, Menlo Park 

GSC, Ottawa, Canada 

USGS, Denver 

USGS, Denver 

USGS, Menlo Park 

USFS, Ogden, Utah 

USGS, Denver 

USGS, Denver 

USGS, Menlo Park 

University of Texas, Austin 

Colorado Mountain Club, Boulder 

Consultant, Denver 

University of Utah, Salt Lake City 

Anaconda, Denver 

GSC 

USBLM 

USFS 

USGS 

Geological Survey of Canada 

U.S. Bureau of Land Management 

U.S. F crest Service 

U.S. Geological Survey 

15 

Poplar Bluff 2 (geology) 

Poplar Bluff 1 (geophysics) 

Poplar Bluff 2 (geology) 

Poplar Bluff 2 (leader) 

Observer 

Observer 

Poplar Bluff 2 (geology) 

Hibbing 2 (geology) 

Hibbing 1 (geology) 

Tonopah 2 (geophysics) 

Poplar Bluff 2 (geostatistics) 

Observer 

Speaker; Hibbing 1 (geology) 

Poplar Bluff 1 (leader) 

Poplar Bluff 1 (geology) 

Poplar Bluff 1 (geology) 

Tonopah 2 (geology) 

Poplar Bluff 2 (geology) 

Hibbing 2 (geology) 

Speaker 

Poplar Bluff 2 (geochemistry) 

Tonopah 1 (geology) 

1onopah 1 (geology) 

Speaker; Hibbing 2 (leader) 

Speaker; Tonopah 2 (leader) 

Hibbing 1 (leader) 

Speaker; Tonopah 2 (geostatistics) 

Speaker 

Tonopah 2 (geology) 

Speaker 

Tonopah 1 (geology) 

Speaker; Hibbing 1 (geology) 

Speaker 

Tonopah 1 (geology) 

Poplar Bluff 1 (geology) 

T a nopah 1 (leader) 
APPENDIXC 

Workshop Speakers 

December 10, 1979 

Daniel R. Shawe 

Introduction 

The objective of the workshop is to determine the format and the substance of 

mineral-resource appraisals of CUSMAP quadrangles and wilderness areas. Format 

considers what steps need to be taken in collecting data, analyzing data, and finally in 

generating the resource appraisal. Substance considers how the resource information should 

be presented: statements of qualitative value; semiquantitative assessments such as small, 

moderate, large, low-grade, high-grade; or as subjective statistical probabilities. 

Norman Stark 

The U.S. Forest Service's view of mineral-resource appraisals 

The Forest Service, in order to make its determinations on land use for wilderness and 

RARE II lands, requires easily understandable information presented in simple maps, tables, 

and texts. Mineral potential should be rated as specifically as possible, giving numerical 

data. Data presented should include areas of favorable geology, locations of mines and 

deposits, what minerals are present, their critical nature, their economic value, when and 

how they are to be mined, and what area is needed to mine them. 

Ame Vickery 

The environmentalists' view of mineral-resource appraisals 

The primary point of view of environmentalists is that, in wilderness areas, there 

should be no exploration for mineral resources, although surface geologic mapping and map 

interpretations are appropriate. In lands reserved for wilderness, the most important 

resource values are untouched or natural ecological and biological systems, water and air 

sheds, and recreational use. Improved communication between environmentalists and 

mineral-resource appraisers is desirable. 

John W. Rold 

Requirements of mineral-resource appraisal presentations 

Simple maps are the most effective way to show evaluations. The appraisals must be 

geologically and technically accurate, they should be conducted with a mineral-exploration 

approach, the results must be defensible, the data must be presented in an understandable 

manner, and the data must be timely. 

Leo J. Miller 

The mining industry's outlook on mineral-resource appraisals 

Previously published U.S. Geological Survey reports on mineral-resource appraisals are 

difficult for bureaucrats to understand. In general, appraisals of areas have not been 

enhanced by the use of geochemical and geophysical data. The most important factors to 

consider in future reports are these: (1) An understanding of the total geologic environment 

is fundamental to mineral-resource appraisals, and (2) geologic environments favorable for 

the occurrence of mineral deposits are essential to our society and civilization. 

William C. J. van Rensberg 

A review of the philosophy of mineral resources 

The two basic sources of wealth are agriculture and mining. There are two types of 

mineral commodities in the United States, those that are not adequate (manganese, nickel, 

16 
chromium, and so forth), and those that could be adequate (copper, molybdenum, and so 

forth). Many commodities are becoming more difficult to obtain overseas and stockpiles in 

some strategic commodities are inadequate. Distinction should be made between the 

strategic and economic value of resources, such as resources of chromium in the Stillwater 

Complex. 

Resources are made; they don't simply exist; and they are made through progressive 

steps of exploration. Because of the uncertainty of resources, we can hardly pass up any 

opportunity to obtain them. Evaluations of resources need to take into consideration lead 

times and delays resulting from exploration, regulations, and other factors. 

The definition of "resources" to include "undiscovered resources" (for example, the 

McKelvey diagram) is a recent development. Great care must be applied in attaching 

numbers to unknown resources defined as "hypothetical" and "speculative." 

Richard B. Taylor 

The realm of the possible in U.S. Geological Survey mineral-resource appraisal 

Funding and staffing levels for the mineral appraisal programs of the U.S. Geological 

Survey require that most of the project activities be regional in scope. Under the CUSMAP 

program, 1:250,000-scale geologic compilations, aeromagnetic and gravity surveys, and 

stream-sediment geochemical surveys form the core of the program. Similar activities at 

about 1:50,000 scale are characteristic of appraisal projects' of wilderness areas. Detailed 

studies to characterize deposit types and topical studies to solve geologic problems, 

including isotopic studies, and more detailed geophysical and geochemical surveys can and 

will be undertaken, but the level of support for detailed work is limited. As interpretation 

of the regional data depends upon detailed data synthesized into occurrence models, a 

limited number of these detailed studies in the economic geology of ore deposits will be a 

regular part of the appraisal programs. 

Artrur A. Brant 

Factors in mineral-resource appraisal 

The U.S. Geological Survey should make mineral appraisals, not resource appraisals. 

A committee composed of U.S. Geological Survey and mining industry representatives to 

consult on the problems of mineral appraisals would be valuable. 

Ralph L. Erickson 

Role of geochemistry in mineral-resource appraisal 

The role of geochemistry in mineral-resource appraisal depends upon the existing 

geologic knowledge of the area being assessed. Geochemistry can and should be used to 

help (1) recognize and define broad geochemical provinces, (2) estabUsh zoning patterns of 

mineralizing systems and mineral districts, and (3) outline favorable ground for mineral 

discovery within the broad system or district. In this framework, concepts can then be 

tested about recognition and understanding of mineralizing systems, potential areas for 

concealed mineral deposits, and new and conventional environments of ore deposition. 

Successful use of geochemistry in mineral-resource appraisal requires a knowledge of 

the geochemical cycle of elements, normal crustal abundances and distribution in relation 

to rock type, diagnostic suites of elements that characterize certain types of deposits, 

metal endowment ·and enrichment, and attributes of different geochemical sample media 

and different analytical methods. 

Lawrence J. Drew 

Subjective-experience judgment in mineral-resource appraisal 

A group of experienced mineral-resource specialists can, on the basis of their 

knowledge of the environments of ore deposits, make individual subjective assessments of 

possible resources within specific areas. The range of the individual assessments considered 

together provides a basis for establishing probability for the occurrence of the resources. 

17 
Donald F. Sangster 

Metallogeny in mineral-resource appraisal 

Metallogeny is similar in definition to ecology: the interrelationships of mineral 

deposits and their environments. Recognition of favorable environments provides the key to 

resource appraisal. Evaluations must be made by experts using subjective judgment rather 

than by machines that have been fed data. Estimates of resources can be presented as 

ranges of tonnages and grades. 

Donald A. Singer 

Review of geostatistical methodology of mineral-resource appraisal with emphasis on the 

U.S. Geological Survey's Alaska program 

Many statistical methods are used for mineral-resource assessment either by extrapolation or by analogy. Extrapolation uses such methods as time-rate, crustal-abundance, and 

cumulative tonnage-versus-grade. Analogy uses such methods as simple subjective, complex 

subjective, Bayesian, frequency, trend, geometric probability, multiple regression, discriminant, modified component, multivariate logistic, cluster analysis, "pattern recognition," 

and simulation. The type of appraisal product needed influences selection of method of 

assessment. 

Henry C. Berg 

The U.S. Geological Survey's Alaska mineral-resource appraisal program 

The Alaska Mineral Resource Assessment Program (AMRAP) is a statewide 

investigation of mineral potential whose objective is to show on a map areas that have 

metallic mineral potential and areas that do not. Metals that might be found and types of 

deposits in which they might occur are identified where possible. If enough data are available, a quantitative-probabilistic estimate of undiscovered resources contained in those 

mineral deposits is presented. 

AMRAP is a long-term, systematic program in which the basic land unit studied is the 

1:250,000-scale quadrangle (there are 153 in Alaska). Much field and laboratory work is 

involved, and the results are published as a folio of maps that usually includes the following: 

(1) a geologic map, (2) a suite of geochemical maps and a computer printout of all analyses, 

(3) an aeromagnetic map based on flightlines at 1-mi (1.6-km) spacing, (4) a map of known 

deposits and occurrences, (5) a map based on interpretations of satellite images, and (6) a 

resource-assessment map. A pamphlet describing the salient results of the investigations 

accompanies the maps. 

Such a study of a quadrangle requires approximately 3 years to complete the field and 

laboratory work and another year to publish the results. Each quadrangle involves at least 

30 man years of work. Since the program began in 1974, resource assessments have been 

completed in 22 quadrangles. Field and laboratory investigations currently are underway in 

five quadrangles. 

fl U.S. GOVERNMENT PRINTING OFFICE: 198o-777·034j31 

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