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USGS Research on Mineral Resources-1985 

Program and Abstracts 

V.E. McKelvey Forum 

on Mineral and Energy 

Resources 

Public Inquiries Office 

u.s. Geological Survey 

504 custom House 

555 Battery Street . '-' ,~ay·~·i ...... ,. .. 0 C::;..l:i..for:~la uUn ......... n; ..... "'"'v ' 94111 

USGS Research on Mineral Resources-1985 

Program and Abstracts 

Edited by Kathleen Krafft 

V.E. McKelvey Forum 

on Mineral and Energy 

Resources 
Department of the Interior 

WILLIAM P. CLARK, Secretary 

U.S. Geological Survey 

Dallas L. Peck, Director 

Organizing Committee for the 1985 McKelvey Forum: 

Philip M. Bethke, Chairman 

Charles G. Cunningham 

Susan Hoffman 

Kathleen Krafft 

Gary P. Landis 

Bruce R. Lipin 

William R. Miller 

Free on application to Distribution Branch, Text Products Section, 

U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 

1985 
A society's wealth depends on the use it 

makes of raw materials, energy, and especially ingenuity 

-V. E. McKelvey 

Ill 
FOREWORD 

Dallas L. Peck, Director, U.S. Geological Survey 

The extended abstracts in this volume are summaries of the papers presented orally and as posters in the first V.E. McKelvey Forum on Mineral and 

Energy Resources, entitled "USGS Research on Mineral Resources-1985." 

The Forum has been established to improve communication between the USGS 

and the earth science community by presenting the results of current USGS 

research on nonrenewable resources in a timely fashion and by providing an opportunity for individuals from other organizations to meet informally with 

USGS scientists and managers. It is our hope that the McKelvey Forum will 

help to make USGS programs more responsive to the needs of the earth science 

community, particularly the mining and petroleum industries, and will foster 

closer cooperation between organizations and individuals. 

The Forum was named after former Director Vincent E. McKelvey in 

recognition of his lifelong contributions to research, development, and administration in mineral and energy resources, as a scientist, as Chief Geologist, 

and as Director of the U.S. Geological Survey. The Forum will be an annual 

event, and its subject matter will alternate between mineral and energy 

resources. We expect that the format will change somewhat from year to year as 

various approaches are tried, but its primary purpose will remain the same: to 

encourage direct communication between USGS scientists and the representatives of other earth-science related organizations. 

The topics selected for presentation at the first McKelvey Forum represent 

an overview of the scientific breadth of USGS research on mineral resources. 

They include the role of organic matter in forming and prospecting for ore 

deposits, the accumulation of metals in sedimentary basins, the evolution of oreforming hydrothermal fluids, and the concentration of sulfides and platinumgroup elements in ultramafic complexes. Research on methods of resource 

assessment using new geochemical and geophysical technology is described, 

along with studies devoted to the development and application of occurrence 

and genetic models of ore deposits. In addition to the technical sessions presenting the results of USGS research, each Congressionally. mandated USGS 

Mineral Resource Program has a display outlining plans and progress. 

We are all excited about this new opportunity to disseminate and discuss 

our research with our colleagues in industry and academia, and we welcome your 

suggestions on improving this new series of Forums. 

IV 
PROGRAM 

Wednesday, February 6, 1985 

8:15am. -Session I (Grand Ballroom) 

10:00 am. 

10:30 am. 

12:00 noon 

2:00p.m. 

3:30p.m. 

Thomas P. Miller and Charles H. Thorman 

presiding 

Opening remarks ...... Robert M Hamilton 

Introduction to Mineral Resource Studies 

. . . . . . . . . . . . . . . . . . . . . Glenn H. Allcott 

Metallogeny of Archean and Proterozoic ter· 

ranes in the Lake Superior region ....... . 

P.K. Sims 

Metallogenetic history of the Wrangellia ter· 

rane, eastern Alaska Range, Alaska ..... . 

WarrenJ. NoklebergandlanM Lange 

Mineral deposit models-Theory and prac· 

tice .... Steve Ludington and Paul Barton 

-Coffee break (Piccadilly Lane) 

-Session I continued (Grand Ballroom) 

Chemistry of ore-forming fluids . . ........ . 

Robert J. Bodnar, 1-Ming Chou, and 

Edwin Roedder 

Spectra of massive sulfide gossan and false 

gossan in the near infrared (800 nm to 

2500 nm) ....... Gary L. Raines, Linda G. 

McGee, and StevenJ. Sutley 

Preliminary results of an ALVIN dive program on active hydrothermal vents at the 

southern Juan de Fuca ridge ....... USGS 

Juan de Fuca Study Group 

-Luncheon honoring Vincent E. McKelvey 

(Grand Salon) 

Keynote speaker Dallas L. Peck 

"Mineral Resources Research: Opportuni· 

ties for Government-Industry Cooperation" 

-Session II (Grand Ballroom) 

Frank C. Frischknecht and Edwin H. 

McKee presiding 

Metal concentrations in marine black 

shales ............. Forrest G. Poole and 

George A. Des borough 

Sediment-hosted ore deposits: Genetic processes inferred from the mineralogic, 

chemical, and isotopic composition of clay 

minerals ........... H. Roy Northrop and 

Gene Whitney 

Stratigraphic and structural controls of 

Mississippi Valley-type ore deposits in 

Tennessee .......... . Joseph A. Briskey, 

Augustus K. Armstrong, Paul R. Dingess, 

Ray C. Gilbert, Walt B. Gaylord, and 

George P. Cole 

-Coffee break (Piccadilly Lane) 

v 

4:00p.m. -Session II continued (Grand Ballroom) 

Origin of sedimentary humic acids, potential 

carriers of ore-forming elements ........ . 

Patrick G. Hatcher 

Recent studies of the distribution of Bacillus 

cereus near subsurface gold deposits ..... 

Nancy L. Parduhn, John R. Watterson, 

and Miles L. Silberman 

A strategy in the exploration for sedimen· 

tary manganese ores .......... William F. 

Cannon and Eric R. Force 

5:30-6:30 p.m. -Mixer (Grand Salon) 

8:00-10:30 p.m. -Keg and poster session (Piccadilly Lane and 

Rotunda) 

Thursday, February 7, 1985 

8:30 am. -Session III (Grand Ballroom) 

10:00 am. 

10:30 am. 

Lawrence J. Drew and Bruce R. Lipin 

presiding 

Tin, molybdenum, and other metal elements 

in silicic magmas and their relation 

to fluorine and chlorine distribution ..... . 

Robert L. Smith 

Heat transfer and brine evolution in magmahydrothermal systems ........ . Robert 0. 

Fournier 

Multiple episodes of mineralization in the 

southern Toquima Range, Nye County, 

Nevada .............. . Daniel R. Shawe 

-Coffee break (Piccadilly Lane) 

-Session III continued 

Development of disseminated gold deposits 

of Cortez, Horse Canyon, and Gold Acres, 

Nevada, at the end stage of caldera-related 

volcanism ............ . James J. Rytuba 

Aeromagnetic and radiometric signatures of 

a possible porphyry system in the western 

Tushar Mountains, Utah ....... . David L. 

Campbel~ James A. Pitkin, Joseph S. 

Duv~ Thomas A. Steven, Charles G. 

Cunningham, and C. W. Naeser 

Fission-track dating applied to mineral ex· 

ploration ....... C. W. Naeser and Charles 

G. Cunningham 

Episodic metallization in the western San 

Juan caldera complex, Colorado ........ . 

R.I. Grouch, Ken Hon, R.L. Reynolds, D.J. 

Bove, and V.J.S. Grouch 

2:00-4:00 p.m. -Poster session (Rotunda) and 

Open house at U.S. Geological Survey laboratories, Branches of Analytical Chemistry and Exploration Geochemistry 
POSTER SESSIONS 

Mineral Resource Programs Booth 

Strategic and Critical Minerals program ........ Alfred H. 

Chidester 1 

The Development of Assessment Techniques program .. 

Charles G. Cunningham 2 

The Alaska Mineral Resources Assessment Program .. 

Gary R. Winkler 3 

The Conterminous United States Mineral Assessment Program . . Gary C. Curtin 4 

Mineral Resources of Public Lands ...... Gus H. Goudarzi 

and Susan M. Marcus 5 

Availability and application of NURE data sets in regional 

mineral survey programs of the U.S. Geological Survey .. 

Byron R. Berger, Thomas D. Fouch, Richard H. Godson, 

and Bruce F. Molnia 6 

The U.S. Geological Survey EEZ program. Terry W Offield 7 

Uranium and thorium investigations in the U.S. Geological 

Survey. . . Thomas D. Fouch and Jennie L. Ridgley 8 

Federal Mineral Land Information System. . . Richard 

L. Kleckner 9 

Geophysical Exploration Techniques 

Geophysical exploration for breccia pipes on the Colorado 

Plateau of northern Arizona . . . . . Vincent J. Flanigan and 

CarlL. Long 10 

A comparison of Landsat Thematic Mapper, Multispectral 

Scanner, and airborne sensors for mapping the distribution of alteration minerals: examples from the Southwestern United States ........ . MH. Podwysock~ MS. 

Power, O.D. Jones, MH. Koslow. and William E. Collins 11 

Processing of Landsat imagery to map surface mineral 

alteration on the Alaska Peninsula. Alaska ..... Frederic 

H. Wilson and James E. York 12 

Electrical geophysical studies of massive sulfide deposits 

and their host rocks, West Shasta copper-zinc district ... 

Robert Horton and Bruce D. Smith 13 

Aeromagnetic and gravity models of the pluton below the 

Lake City caldera, Colorado. . ..... V.J.S. Grauch 14 

Some geophysical guides to ore in southern and southwestem Alaska. . .................... . J.E. Case 15 

Other Exploration Methods 

Research on kimberlites and applications to diamond prospecting ....... B. Carter Hearn, Jr., and Elaine S. McGee 16 

Volatile elements and compounds in exploration geochemistry. . . . Margaret E. Hinkle and J. Howard McCarthy 17 

Partial chemical extractions-Their application to geochemical exploration for ore deposits in the tropical environment ............ Robert E. Learned, T T Chao, and 

Richard F. Sanzolone 18 

Metals in plants-Exploration of the Red Mountain goldbearing stockwork, Yellow Pine district, Idaho .... . B.F. 

Leonard, J.A. Erdman, andD.M. McKown 19 

Microbiology of soil derived from a copper deposit . . . . . . . 

John R. Watterson, Sarah S. Elliott, Nancy L. Parduhn, 

and David M Updegraff 20 

VI 

Minerals in the Oceans Booth 

Organic matter associated with metal ores of hydrothermal vent origin .... William H. Orem, Patrick G. Hatcher, 

and Elliott C. Spiker 21 

Geologic and hydrothermal characteristics of the Gorda 

Ridge ............ . David A. Clague and Mark Holmes 22 

Cobalt-rich ferromanganese crusts in the oceans . . . . . . . . . 

James R. Hein and Frank T Manheim 23 

Genesis of metalliferous sediment in the Atlantis II Deep, 

Red Sea. . . . . . . . . . . . . . ......... Robert A. Zierenberg 24 

Economic heavy minerals of the U.S. Atlantic Continental 

Shelf. . . ... . Andrew E. Grosz, Edward C. Escowitz, 

S. Jeffress Williams, Ricardo Lopez, John C. Hathaway, 

Joseph M Botbol, and LaurenceJ. Poppe 25 

Massive sulfide deposits from the southern Juan de Fuca 

Ridge. . .Randolph A. Kosk~ David A. Clague, 

James L. Bischoff, and Robert A. Zierenberg 26 

Regional Syntheses 

Early and middle Cenozoic volcanic syntheses .... . Robert 

G. Luedke 27 

Sediment dispersal pattern in the emerged Atlantic 

Coastal Plain (New Jersey-Georgia) from Early 

Cretaceous to Holocene: A guide to placer deposits . . . . .. 

James P. Owens 28 

Marine phosphorite deposits model for exploration, with 

emphasis on the deposits in the Atlantic Coastal Plain of 

the United States. . ............ . James B. Cathcart 29 

New silver resource map of the United States-Potential 

for increased domestic silver production . . ... Allen V. 

Heyl and Robert B. Hall 30 

Geology and geochemistry of wall rocks of Appalachian 

massive sulfide deposits ............... . Jacob E. Gair 31 

Sediment-Hosted Deposits 

Depositional model for sodium carbonate deposits in the 

Green River Formation. . .... . John R. Dyni 32 

Organic geochemistry of wall-rock alteration, ThompsonTemperly mine, southwest Wisconsin. . . . Joseph R. 

Hatch, Allen V. Heyl, and J. David King 33 

Mineral Deposit and Occurrence Models 

Base metals, precious metals, and molybdenum: New occurrence types in the Western United States ..... Wayne 

Hall, Steve Ludington, Ted G. Theodore, and Norman J 

Page 34 

Identification of regional mineral resource targets by using 

ore deposit models-Two examples from the Eastern 

U.S. early Mesozoic basins ...... Gilpin R. Robinson, Jr., 

and David Gottfried 35 

Some recent deposit modeling efforts ......... D.A. Singer 

and D.P. Cox 36 
Disseminated Gold Studies Booth 

Pathfinder elements in soils over the Dee disseminated 

gold deposit, Elko County, Nevada ........ W.C. Bagby, 

W.J. Pickthom, andR.J. Goldfarb 37 

Characteristics of lode-gold deposits in the Prince William 

Sound region, southern Alaska ............... Miles L. 

Silbennan and Dawn J. Madden 38 

Mahd adh Dhahab, a Proterozoic epithermal preciousmetal deposit, Kingdom of Saudi Arabia ......... . R.G. 

Worl andJ.L. Doebrich 39 

Igneous-Hosted Deposits 

Volcanic and hydrothermal systems: Early Proterozoic 

massive sulfide deposits, Bagdad, Arizona ........ Clay 

M. Conway, Thomas J. Connelly, and Lori C. Robison 40 

The setting and distribution of copper-nickel sulfides in the 

South Kawishiwi intrusion, Duluth Complex, Minnesota ............................ . Michael P. Foose 41 

Studies of ore deposits in the early magmatic environment: 

The Stillwater Complex, Montana ...... Nonnan J Page, 

W.J. Bawiec, R.J. Blakely, G.K. Czamanske, L.J. Drew, 

Michael P. Foose, R.L. Helz, MD. Kleinkopf, Bruce R. 

Lipin, Patricia J. Lofersk~ J.H. Schuenemeyer, and ML. 

Zientek 42 

High-alumina hydrothermal alteration systems and their 

role in mineral exploration, Southeastern United 

States .................. R. G. Schmidt and T.L. Klein 43 

Characteristics of and exploration for Sn-W granites in the 

Precambrian Arabian Shield ........ Edward A. du Bray 44 

VII 

Topical Studies: Field and Theoretical Booth 

Gas analysis of ore-forming fluids ............ G.P. Landis 45 

Precious and base metal mineralization in the Coeur 

d'Alene district, Idaho, during Proterozoic metamorphism of the Belt basin ............... David L. Leach, 

G.P. Landis, and Albert H. Hofstra 46 

Thermodynamic properties of minerals .......... Richard 

A. Robie, Bruce S. Hemingway, and John L. Haas, Jr. 47 

Resource Assessments: Techniques and Case Histories 

The role of regional subsurface geochemistry in resource 

assessment in the Central United States .......... . R.L. 

Erickson, E.L. Mosier, J. G. Viets, and MS. Erickson 48 

Mineral resource assessment of the San Isabel National 

Forest, Colorado: A prototype for 1:250,00Q-scale multidisciplinary assessments "from the literature" ........ . 

Richard B. TaylorandJohn S. Dersch 49 

Mineral resources of the Survey Pass quadrangle, Brooks 

Range, Alaska ......... . Donald J. Grybeck and Steven 

W. Nelson 50 

A multidisciplinary resource assessment of the Chugach 

National Forest, Alaska ............ . Steven W. Nelson 51 

Applications of the Mineral Resources Data System and 

the International Strategic Minerals Inventory in 

mineral-resource assessments by region and commodity .......... . Antoinette L. Medlin, David M Sutphin, 

and John H. De Young, Jr. 52 

Expert systems research in regional resource evaluation: 

Experiences in the application of microcomputer technologies .................... . Richard B. McCammon 53 
This Circular uses the following abbreviations: 

EEZ-Exclusive Economic Zone 

Ga-giga-annum (109 years ago) 

Ma-mega-annum (106 years ago) 

m.y.-106 years duration 

REE-rare-earth element 

The Deep Submergence Research Vehicle ALVIN is referred to 

throughout as ALVIN. 

VIII 
V.E. McKelvey Forum on Mineral and Energy Resources 

USGS Research on Mineral Resources-1985 

Program and Abstracts 

Edited by Kathleen Krafft 

PATHFINDER ELEMENTS IN SOILS 

OVER THE DEE DISSEMINATED GOLD DEPOSIT, 

ELKO COUNTY, NEVADA 

W.C. Bagby, W.J. Pickthorn, and R.J. Goldfarb 

The Dee disseminated gold deposit, owned 

and operated by Cordex Syndicate in Elko County, 

Nevada, is the northernmost mine in the Carlin 

gold belt. Soil samples were collected from undisturbed areas overlying the deposit to determine 

the usefulness of soil geochemistry in identifying 

separate ore zones. Samples were collected at random sites within a grid. The depth of sampling 

ranged from 30 to 35 centimeters, depending on 

soil depth. Each sample was double-bagged, in 

plastic and cloth, to prevent cross contamination, 

and was sieved in the laboratory. The -80 mesh 

fraction was analyzed by atomic absorption for 

Au, As, Sb, Hg, and Tl and by semiquantitative 

spectrographic analysis for Ag. Correlations on 

log-transformed data for the complete sample 

population are very low. Sub populations within 

the whole set, however, have improved correlations. These subpopulations were identified by 

plotting the samples on histograms and using the 

obvious histogram breaks to separate the elements 

into concentration ranges. As a first approximation, samples with values falling in the two highest 

histogram groups were considered to be anomalous for the sample population. 

The three anomalous areas thus identified 

were compared with the surface projections of ore 

zones already drilled and defined by Cordex: (1) a 

large area of multielement (Au, As, Sb, Hg, Tl, and 

Ag) anomalous samples covering parts of all 

known ore zones, (2) a small area defined by 

anomalous Hg, and (3) a small area defined by 

anomalous Tl. Samples containing anomalous Hg 

lie approximately 60 meters directly above ore, 

whereas samples containing anomalous Tl are offset approximately 15 meters to the side of known 

ore. 

High-potential targets within the multielement anomalous area were defined by outlining 

three or more anomalous samples that contain element concentrations in the uppermost histogram 

group for any given element and were spatially 

associated within an area of 5,806 m2 or less, as 

defined by a north-south grid. This resulted in four 

additional, more tightly defined, anomalous zones: 

an area defined by Au and Hg, another defined by 

Ag and Sb, and two areas defined only by As. The 

Au-Hg, the Ag-Sb, and one of the As anomalies all 

occur above known ore zones; the second highpotential As area is adjacent to ore. 

CHEMISTRY OF ORE-FORMING FLUIDS 

Robert J. Bodnar, 1 1-Ming Chou, and Edwin Roedder 

Highly saline brines of various compositions 

have been involved in the formation of many types 

of ore deposit and have been trapped in fluid inclusions in the minerals of these deposits. Study of 

the phase relations of such fluid inclusions, which 

may contain many daughter crystals formed during cooling, can provide semiquantitative and in 

part quantitative data on their composition. 

Knowledge of the chemistry of such fluids is essential to understanding the processes involved in ore 

transport and deposition. However, the interpretation of fluid-inclusion data is hindered by the lack 

of data on salt solubilities and on volumetric properties of brines at elevated P and T. 

'R.J. Bodnar, Chevron Oil Field Research Company, P.O. Box 446, 

La Habra, CA 90631. 
North wall of the Old Main and East pit, Carlin gold mine, Nevada 

Phase equilibria in the H20-NaCl system have 

been determined experimentally to 1000 o C and 

1500 bars by studying synthetic fluid inclusions in 

natural quartz. The results indicate a much larger 

immiscibility field for H20-NaCl than had been 

previously proposed. Solubility relations in the 

system NaCl-KCl-H20 have been determined by 

differential thermal analysis for compositions having more than 53 weight percent total salt, at pressures and temperatures up to 2 kbar and 820 o C. 

Volumetric (PVTX) properties of H20-NaCl 

compositions of 30, 50, and 70 weight percent 

NaCl have been determined experimentally over 

the range 20-900° C and 0.5-5 kbar. These results 

have been combined with other available volumetric data for H20-NaCl to generate a single 

equation for specific volume as a function of temperature, pressure, and composition. This equation, which has the form 

V=e 

3 

E 

i=O 

3 

E 

j=O 

a .. k(riphk) 3 l] 

E 

k=O 

2 

provides a reasonable approximation of specific 

volumes of H20-NaCl mixtures over the range 

100-900° C, 0.5-5 kbar, and 0-100 weight percent 

N aCl and is valid in both the one-phase (fluid) and 

two-phase (fluid+ solid) fields. Using a similar 

equation, with metastable liquid N aCl as the 

standard state, we have calculated partial molar 

volumes of both the H20 and NaCl components in 

H20-NaCl solutions over the same PTX range. 

Careful petrography permits recognition of 

some inclusions as samples of pre-ore or post-ore 

fluids responsible for wallrock alteration, whereas 

others can be shown to be samples of the actual 

ore-forming fluid. Studies now in progress include 

identifying and validating the criteria for determining inclusion origin and examining various 

procedures for obtaining compositional data on inclusions. A study of the brines present during the 

formation and later diagenesis of salt beds provides a low-temperature example. Compositional 

data on these bri~e inclusions have been obtained 

by two main procedures: (1) microscopy plus 

microthermometry of daughter crystal dissolution 

and (2) extraction and chemical analysis of single 
1-mm inclusions for Na, K, Ca, Mg, Cl, S04, and 

Br. Although the purpose is to evaluate the salt 

beds for possible nuclear waste repository sites, 

the work has helped in the study of similar highly 

saline brine inclusions from metallic ore deposits 

and has provided a possible tool for the search for 

potash ore deposits. 

STRATIGRAPHIC AND STRUCTURAL CONTROLS 

OF MISSISSIPPI VALLEY-TYPE ORE DEPOSITS 

IN TENNESSEE 

Joseph A. Briskey, Augustus K. Armstrong, 

Paul R. Dingess/ Ray C. Gilbert/ Walt B. Gaylord/ 

and George P. Cole5 

Mississippi Valley-type deposits of sphalerite 

(±galena, barite, and fluorite) in carbonate rocks 

of the Cambrian-Ordovician Knox Group in east 

and central Tennessee are the principal domestic 

sources of zinc, supplying 40 percent of U.S. production. Discovery of new ore bodies or districts, 

which now is dependent on nearly random drilling 

of large areas underlain at relatively shallow depth 

by favorable host rock, would be enhanced if the 

geologic controls of this type of deposit were better understood. Cooperative work recently begun 

by the USGS, the mining industry, and the Division of Geology of the Tennessee Department of 

Conservation is designed to improve understanding of the genesis and localization of these 

deposits. The principal goals include identifying 

and documenting (1) the geologic and geochemical 

controls of ore deposition, with which this abstract 

is chiefly concerned, (2) the channelways that 

guided mineralizing fluids to sites of ore deposition, and (3) the rocks that were the source of 

fluids, metals, sulfur, and hydrocarbons to form 

the deposits. 

Mineralization occurred principally by filling 

of caverns and of open spaces in dissolution collapse breccias, both of which formed in paleoaquifers related to paleokarst development on and 

below the regional unconformity at the top of the 

Knox Group. These breccias formed as a result of 

2

Paul R. Dingess, Asarco Exploration, P.O. Box 306, Salem, MO 

65560. 3

Ray C. Gilbert, Tennessee Department of Geology, 701 Broadway, 

Nashville, TN 37203. 

'Walt B. Gaylord, Jersey Miniere Zinc Company, P.O. Box 249, 

Gordonsville, TN 38563. 

'George P. Cole, Cominco American Inc., 831 East Glendale, Sparks, 

NV 89431. 

3 

dissolution of soluble limestone, followed by collapse of overlying, relatively insoluble dolostone 

beds. Consequently, the breccias are most common 

along limestone-dolostone facies contacts. 

In contrast to deposits in the paleokarst 

environment, some large zinc deposits in central 

Tennessee were localized by "primary" carbonate 

rock porosity. These deposits are in detrital carbonate rocks formed in tidal channels betweer 

stromatolites and stromatolite biostromes that 

also are locally mineralized. Stromatolites forming 

today in Shark Bay, Australia, appear to be modem analogues of those in the Knox Group in central Tennessee. 

Broad, gently dipping (2-5 o) structural highs 

control the distribution of ore within porous and 

permeable stratigraphic horizons in central Tennessee. Ore bodies are confined to the flanks and 

crests of these highs. This relationship may reflect 

the accumulation of hydrocarbons in the structural highs. Introduction of metalliferous brines 

containing sulfate from carbonate host rocks into 

the hydrocarbon-rich area would have resulted in 

the reduction of sulfate to sulfide and consequent 

precipitation of base-metal sulfides. 

The importance of stratigraphic and structural features in the localization of the Tennessee 

deposits emphasizes the need for detailed geologic 

analysis of potential host rocks, both before and 

during exploration drilling. Predicting the occurrence and distribution of porous and permeable 

zones, and of structural and stratigraphic traps, 

would provide specific drilling targets, thereby 

reducing the large number of holes now required 

by random exploratory drilling. Obvious benefits 

include both decreased drilling costs and increased 

rates of discovery of ore. 

AEROMAGNETIC AND RADIOMETRIC 

SIGNATURES OF A POSSIBLE PORPHYRY SYSTEM 

IN THE WESTERN TUSHAR MOUNTAINS, UTAH 

David L. Campbell, James A. Pitkin, Joseph S. Duval, 

Thomas A. Steven, Charles G. Cunningham, 

and C.W. Naeser 

Geologic mapping, petrologic analysis, isotopic dating, geochemical sampling, and geophysical studies have identified several areas in the 

western Tushar Mountains, Utah, that may be 

underlain by mineralized intrusive systems containing molybdenum, uranium, and other valuable 
Hard-rock uranium mining, Marysvale, Utah 

metals. One of these areas is near Indian Creek, 

18 km north of Beaver, Utah, where there may be 

a multiply intruded mineralized stock. Several 

lines of evidence were pulled together to make this 

interpretation, providing a good example of 

synergism in geological research. This report 

focuses on the geophysical component of these 

studies. 

The Indian Creek area is characterized on the 

.aeromagnetic map by a horseshoe-shaped anomaly, a strong magnetic high with a reentrant central 

low. The high rim of this distinctive signature may 

be caused by the relatively magnetic 23-Ma Indian 

Creek granodiorite. The central low part of the 

anomaly lies over a number of 16-Ma rhyolite 

dikes, which probably are near-surface manifestations of a low-susceptibility pluton at depth. 

Alteration related to this hidden intrusion also 

may have destroyed earlier magnetic minerals and 

thus have contributed to the magnetic low. 

Horseshoe- or doughnut-shaped magnetic anomalies can be caused by a variety of geological circumstances, but where geological and geochemical 

4 

lines of evidence point to a porphyry system, such 

a signature shape can pinpoint the locus of most 

intense alteration and thus the core of the possible 

exploration target. 

Spectral radiometric surveys over the Indian 

Creek area showed relatively high concentrations 

of potassium (K), equivalent uranium (eU), and 

equivalent thorium (eTh). The K and U were probably introduced during hydrothermal alteration. 

The three spectral radiometric signatures were 

combined in a color radiometric composite (CRC) 

map, an image in which the abundance of K is 

represented by the intensity of blue, eU by red, 

and eTh by yellow. The changing tints on a CRC 

map thereby show K, eU, and eTh geochemical 

variations at a glance. Many of the tints on the 

CRC map were immediately correlatable with 

known geology, and the proposed porphyry system at Indian Creek was unmistakable. In addition, the CRC map highlighted other nearby areas 

showing high concentrations of radioelements and 

so may point to other possible porphyry systems. 

A STRATEGY IN THE EXPLORATION 

FOR SEDIMENTARY MANGANESE ORES 

William F. Cannon and Eric R. Force 

Sedimentary manganese ores consist of 

primary accumulations of manganese oxides, carbonates, and silicates deposited in relatively 

shallow marine water. Examples include giant 

deposits such as the Kalahari Field (lower Proterozoic) of South Africa, the Molango district 

(Jurassic) of Mexico, and the Nikopol and Chiatura 

districts (Oligocene) of the U.S.S.R. 

Exploration for such deposits should be restricted to areas containing rocks that (1) were 

deposited in extensive shelf or platform seas, (2) 

are time equivalents to rocks of euxinic facies 

elsewhere in the basin, (3) were deposited near 

paleoislands or paleoshoals, (4) were deposited in 

areas of upwelling, and (5) were deposited during 

high eustatic sea level when global climate was 

warm. Criteria 1-4 can be used to identify favorable parts of basins and favorable stratigraphic 

units for detailed exploration. Criterion 5 helps to 

define favorable time windows in any basin. 

The formation of manganese ore requires not 

only concentration of manganese to several hundred times its average crustal abundance but also 
fractionation of manganese from iron, with which 

it shares many geochemical properties. Ores best 

suited for metallurgical uses have Mn-Fe ratios of 

7 or greater whereas Mn:Fe of about 0.2 is typical 

of most rocks. Euxinic basins are capable of producing such fractionation on the scale required to 

form large manganese deposits. In water, iron 

sulfide is stable over a considerable range of low 

Eh conditions, hence most iron is fixed in this solid 

form resulting in very low dissolved iron. No comparable stability range exists for manganese sulfides, so dissolved Mn2

+ remains high. If such lowEh water is oxidized or raised to high pH, it will 

crystallize manganese minerals in greater abundance than iron minerals and thus may become the 

ore fluid to form manganese deposits. 

The identification of euxinic facies is, 

therefore, a key to searching for manganese. Rocks 

formed in truly euxinic conditions, as opposed to 

other organic-matter-rich environments, can be 

recognized by laminated organic-matter-rich 

pyritic shales with sulfur:organic carbon generally 

greater than 0.4. Because manganese is soluble in 

euxinic conditions, these black shales themselves 

are not likely host rocks and, in fact, should show 

manganese depletion relative to iron. Rather, 

manganese should accumulate in time-equivalent 

deposits in more oxygenated parts of the basin. 

There is growing evidence that certain time intervals are most favorable for the generation of 

euxinic conditions. These are times of very high 

eustatic sea level, generally warm global climates, 

and consequent subdued oceanic circulation, which 

promotes stratification of oceans and development 

of euxinic conditions. 

Another requirement to form ore is the transportation of dissolved manganese on a large scale 

from the euxinic into the oxidized part of the 

basin. Wind-driven currents and resultant upwelling are the likely mechanisms for this, so some 

understanding of paleoclimate and paleogeography is important. Known deposits worldwide 

show a tendency to occur near paleoislands or 

paleoshoals, probably because the shallow sea 

floor in these areas provided the required oxidized 

depositional and diagenetic setting without major 

clastic input. Comparably shallow conditions 

peripheral to larger land masses are likely to be 

dominated by clastic material delivered by major 

river systems. Also, shoals might provide physical 

barriers to lateral circulation and cause the upwelling and oxidation of deeper euxinic waters. 

5 

Finally, once favorable regions are identified 

using the above criteria, the search for deposits 

must depend on detailed chemical studies of 

lateral and stratigraphic distribution of manganese to identify enrichment trends that could lead 

to ore. 

SOME GEOPHYSICAL GUIDES TO ORE 

IN SOUTHERN AND SOUTHWESTERN ALASKA 

J.E. Case 

In southern Alaska, massive sulfide deposits 

are associated with Late Cretaceous-Paleogene 

pillow basalt, sheeted dikes, and overlying flysch 

deposits. Most such mafic assemblages in Prince 

William Sound are characterized by prominent 

positive gravity anomalies. Magnetic anomalies 

over the volcanic belts are positive, but their 

amplitudes range widely. Where massive sulfide 

deposits occur on Knight Island and the Ellamar 

Peninsula, magnetic anomalies are relatively flat 

or negative-a strong indication of hydrothermal 

alteration accompanying mineralization. To the 

north and west, a belt of late Mesozoic gabbros, 

diorites, and ultramafic rocks of the northern 

Chugach Range and western Kenai Peninsula is indicated by large positive gravity and magnetic 

anomalies. These rocks may contain chromite, 

massive sulfide, magnetite, and gold deposits. The 

gravity and magnetic anomalies show that the 

complex continues beneath glaciers, alluvial cover, 

and water-covered areas. 

On the Alaska Peninsula, ore deposits include 

porphyry copper-molybdenum types, some of 

which are accompanied by gold deposits. Few significant gravity anomalies have yet been identified, except that large granitoid plutons of Tertiary age commonly cause negative anomalies. 

Magnetic anomalies, however, have a twofold role 

in identifying granitoid plutons. First, most 

plutons cause prominent ovoid magnetic highs, 

which coincide with "centers of mineralization" as 

defined on the basis of geochemical anomalies and 

outcrop geology by D. Cox and D. Detra. Second, 

the most highly mineralized areas on or adjacent 

to the granitoid plutons are commonly expressed 

by subdued or relative negative anomalies, also indicating alteration associated with the ore-forming 

process. 

Elsewhere in southern and southwestern Alaska, gold deposits in the flysch terrane west of the 
Rugged topography, Chugach Mountains, southern Alaska 

6 
Alaska-Aleutian Range batholith are commonly 

associated directly or indirectly with granitoid 

plutons that cut the Mesozoic flysch. These 

plutons normally produce small-amplitude positive magnetic anomalies, or no anomaly at all, surrounded by negative anomalies caused by reversely magnetized pyrrhotite that resulted from 

metamorphism in contact aureoles. 

Major positive magnetic anomalies on the 

Alaska Peninsula are produced by magnetite-rich 

sandstones of the Naknek Formation of Jurassic 

age whose sedimentary provenance is the AlaskaAleutian Range batholith of Jurassic age. 

Whether fossil placer gold deposits might be 

associated with the Naknek Formation remains to 

be determined by geochemical sampling. 

MARINE PHOSPHORITE DEPOSITS MODEL FOR 

EXPLORA liON, WITH EMPHASIS ON DEPOSITS 

IN THE U.S. ATLANTIC COASTAL PLAIN 

James B. Cathcart 

Phosphorus is an essential element for growth 

in plants and animals; its principal source is 

deposits of phosphate rock. Onshore deposits of 

phosphorite, a marine sedimentary rock, constitute about 80 percent of the world's phosphate 

resources and are the source for about 80 percent 

of world production. Identified resources (reserve 

base) of phosphorite in the world are estimated to 

be about 69 billion metric tons containing at least 

25 percent P20 5, and resources in deposits that 

may become economic are thought to be about 

double the identified resources. Deposits on the 

sea floor form an additional, probably enormous, 

resource. 

The origin of marine phosphorites is complex. 

The phosphate originates in sea water, which is 

less saturated with P 20 5 at low temperature and 

high pressure. Therefore, warm surface water is 

saturated while cool, deep, or polar ocean water is 

undersaturated. Although some phosphate is being precipitated in sediments on the floor of the 

modem ocean, the large offshore deposits are 

either Miocene or Cretaceous in age. 

Major deposits differ in detail, but the following common factors can be used to formulate a 

model for exploration. 

7 

(1) Size: Resources are hundreds of billions of 

metric tons; reserves are billions or tens of billions of metric tons. 

(2) Periodicity: Major phosphogenic episodes are 

confined to four time periods: Late Proterozoic 

to Early Cambrian, Late Permian, Late Cretaceous to early Eocene, and Miocene. 

(3) Paleogeography: Phosphate was deposited at 

low paleolatitudes, either in shallow water on 

the continental shelf or in somewhat deeper 

water adjacent to the shelf (miogeosyncline). 

(4) Structure: Deposits are in tectonically very 

stable regions and in structural or topographic 

basins that were open to deep-sea circulation and where clastic deposition was at a 

minimum. 

(5) Form: Deposits are bedded and may cover 

thousands of square kilometers. The phosphate grains in the deposits characteristically 

are pelletal, and the phosphate mineral is 

always carbonate fluorapatite. 

The phosphate deposits of the Atlantic 

Coastal Plain of the United States exhibit all of 

these factors. They constitute a large phosphogenic province that extends from southern Florida 

into southern Virginia and includes the adjacent 

Continental Shelf of the Atlantic Ocean. The' 

deposits are in the marine, shallow-water Miocene 

Hawthorn and equivalent Pungo River Formations. They are on the stable platform in basins on 

the flanks of positive areas; their locations suggest 

that phosphorus could have been supplied by cool, 

southward-moving nearshore currents that were 

turbulently mixed with the warmer waters of the 

Gulf Stream. The deposits are unconsolidated, the 

phosphate is pelletal, and the phosphate mineral is 

carbonate fluorapatite. 

Identified resources in the onshore part of this 

phosphogenic province are about 8 billion metric 

tons of phosphate pellets that contain an average 

of about 30 percent P 20 5; identified resources offshore are about 6 billion tons of similar material. 

Total resources of potentially recoverable phosphate pellets must be scores to hundreds of billions of metric tons. Tonnage data are for phosphate concentrate-that is, pellets that can be 

recovered by metallurgical techniques. Phosphate 

mines in Florida and North Carolina account for 

about 85 percent of the U.S. production and for 

slightly more than one-fourth of the world's production of phosphate rock. 
GEOLOGIC AND HYDROTHERMAL 

CHARACTERISTICS OF THE GORDA RIDGE 

David A. Clague and Mark Holmes 

The Gorda Ridge, an oceanic spreading center 

with a full spreading rate of about 5.5 cm/yr, is 

within 200 nautical miles of the coast of northern 

California and southern Oregon. The ridge consists 

of three segments of ridgecrest offset by short 

transform fault zones or overlapping spreading 

centers. A short chain of seamounts trends northwesterly from a point on the ridge at about 42° N. 

The entire ridge is only 160 nautical miles long, 

and the southern 50 nautical miles is covered by 

turbidites. The ridge axis is unusually deep, ranging from 3,200 m to over 3,800 meters deep. The 

axial graben has from 800 to more than 1,400 m of 

vertical relief from the axis floor to the tops of 

inward-facing fault scarps. Single-channel seismic 

profiles show the irregular surface of the 5- to 

10-nautical mile-wide valley floor; in other crossings the central depression is a sharp notch. The 

depth to the valley floor varies systematically; the 

shallowest crossings are at about 42°45'N., 

42°17'N., and 41 °42'N. Multichannel seismic 

reflection profiles show that the surface sediments 

in the Escanaba Trough are cut by faults and 

demonstrate that the region is undergoing active 

extension. The discontinuous nature of the basement reflector may be due to sills intruded into the 

sediment. SeaMARC II side-scan imaging shows 

individual young lava flows, volcanic cones in the 

axial valley, and linear fractures on the inner 

valley walls. 

Mid-ocean ridge basalt was recovered in 15 

dredges along the northern two-thirds of the ridge. 

All recovered samples are pillow lavas; no lobate 

or sheet flow fragments were recovered. A number 

of the lavas have very fresh glass with little or no 

palagonite present. Most dredges recovered several lava types, which suggests that the lava flows 

along much of the Gorda Ridge are small in areal 

extent and therefore in volume. 

Many of the lava samples have thin coatings 

of hydrogenous Mn-oxides; other deposits and 

alteration products have a higher temperature 

hydrothermal origin. Alteration products include 

smectite, albite, quartz, and Mn- and Fe-oxides. 

Minerals of hydrothermal origin include chlorite, 

gypsum, barite, talc, boehmite, kaolinite, 

K-feldspar(?), and sulfide phases. The sulfide 

8 

phases occur as deposits along fractures and include pyrite and pyrrhotite with manganosiderite, 

and pyrite and sphalerite with barite. 

Sediment samples recovered along the ridge 

axis contain a small amount of hydrothermal Mn. 

These samples also contain abundant benthic 

foraminifers and other larger fauna. A massive 

deposit of hydrothermal nontronite was sampled 

at 41 °31'N. This deposit is similar to other seabed 

hydrothermal deposits and probably formed from 

20-50 o C fluid. 

Hydrothermal activity is widespread along 

the axis of the northern two-thirds of the Gorda 

Ridge. Nearly all the evidence indicates rather low 

temperature activity with the possible exception 

of the sparse sulfides, sulfates, and talc deposits 

from 42°28'N. We have no data that suggest how 

long-lived these hydrothermal systems may be, if 

they are currently active, or if massive sulfide 

deposits are present. 

VOLCANIC AND HYDROTHERMAL SYSTEMS: 

EARLY PROTEROZOIC MASSIVE SULFIDE 

DEPOSITS, BAGDAD, ARIZONA 

Clay M. Conway, Thomas J. Connelly/ 

and Lori C. Robison 

A cluster of Zn-Cu massive sulfide deposits at 

Bagdad, Arizona, is hosted in an Early Proterozoic 

(about 17 40 Ma) 3-km-thick submarine volcanic 

succession. A lower basalt is overlain by rhyolite, 

which intertongues with and is overlain by mixed 

volcanic, volcaniclastic, and sedimentary rocks. 

This overturned stratified section constitutes a 

steeply dipping homocline with little internal 

folding and faulting. Metamorphism to lower amphibolite facies occurred before 1700 Ma 

The main ore bodies of the district (Old Dick, 

Bruce, Copper Queen) and cross-cutting faults and 

breccia zones are marginal to a central bulge in the 

exposure belt of rhyolite. Major alteration zones 

lie both within and next to the rhyolite bulge. 

Granophyre semiconformably intrudes the basalt 

close to the base of the rhyolite bulge. Offset apparently decreases upsection on one fault, and 

breccia zones are apparently fault controlled, 

evidence that faulting and brecciation were contemporaneous with volcanism. 

"Thomas J. Connelly, 912 W. 14th Street, Tempe, AZ 85281. 
Several types of alteration occur in the area. 

Epidote-quartz alteration (+Si, +Ca, -K, -Na, 

-Fe, - Mg, -base metals) is a widespread 

semiconformable alteration in the basalt. Chlorite 

alteration (+Fe, +Mg, -Si, -Ca, -K, -Na, 

+base metals), locally imposed on earlier epidotequartz alteration, has affected both basalt and 

rhyolite but is more common in basalt. Quartzsericite alteration (+Si, +K, -Fe, -Na, -Ca) is 

the most common alteration in rhyolite and is 

most intense in the upper parts of rhyolite lenses. 

The rhyolite bulge, faults, breccia zones, and 

granophyre suggest the presence of a felsic 

volcanic center. Heat from shallow magma may 

have driven hydrothermal systems, which altered 

stratified rocks and formed sea-floor sulfide 

deposits as volcanism progressed. The range of 

alteration types in the area may reflect variation in 

space and time of an evolving long-lived volcanohydrothermal system. 

Two different hydrothermal systems probably 

controlled ore formation at the Old Dick-Bruce and 

the Copper Queen deposits. The Old Dick-Bruce 

ore bodies lie at the basalt-rhyolite contact, above 

a series of stacked chlorite lenses in the basalt. 

Thin layers composed of varying amounts of 

sulfides, sericite, and chert are common at the tops 

of the chlorite lenses. These features are interpreted as resulting from continuous hydrothermal 

activity, including exhalation on the sea-floor, during repetitive deposition of basalt flows and 

volcaniclastic material. The system culminated in 

the formation of the Old Dick and Bruce ore bodies 

in a period of quiescence between basalt and 

rhyolite volcanism. The Copper Queen deposit, on 

the other hand, lies above highly silicified rhyolite 

and has little associated chlorite. Silicified upper 

parts of rhyolite layers may have been sealed caps 

of hydrothermal systems. Massive sulfides (such 

as the Copper Queen deposit) and spatially related 

breccia zones may have formed when these caps 

ruptured and allowed venting of hydrothermal 

fluids. 

CHARACTERISTICS OF AND EXPLORATION FOR 

Sn-W GRANITES IN THE 

PRECAMBRIAN ARABIAN SHIELD 

Edward A. du Bray 

Peraluminous granitoid plutons emplaced in 

the eastern part of the Precambrian Arabian 

9 

Shield between 580 and 570 Ma are similar in 

geology, geochemistry and petrology to metallogenically specialized granites. Most of the 

plutons are about 15 km2 in areal extent, but several are as large as 75 km2

• Geochemical data indicate that the plutons contain anomalous abundances of Sn, W, and other rare metals and may 

have associated ore deposits. The plutons were 

identified by integrated evaluation of geologic, 

geochemical, petrographic, and geophysical data 

The ten plutons studied are composed of allotriomorphic inequigranular subsolvus alkalifeldspar granite that contains an Fe-Li mica, 

fluorite, topaz, zircon, and ilmenite. Several contain traces of almandine-spessartine garnet. The 

major-element chemistry of the granites is like 

that of experimentally determined granite 

minimum-melt compositions: they contain more 

than 75 percent Si02; are low in total iron, CaO, 

Ti02, and MgO; and are peraluminous. These 

granites are significantly enriched in the incompatible trace elements Be, Ph, Sn, Li, F, Rb, Y, and 

Nb but, in comparison to average low-Ca granite, 

are depleted of the compatible elements Ba, Cu, 

and Sr. Pan concentrate samples from drainage 

areas underlain by these plutons contain highly 

anomalous abundances of Sn and unusual abundances of W, Mo, Ag, Ph, Zn, and Bi. 

Common-lead isotope data suggest that the 

granites include a component generated by partial 

melting of pre-existing continental crust. Majorelement chemical and petrographic data are consistent with crystallization of these plutons under 

conditions of PH2

o=2-4 kbar. Trace-element contents indicate that the granites evolved by fractional crystallization and must represent a very 

small percentage of the primary liquid. 

Most of the plutons have been eroded to a 

moderate level and, lacking evidence of mineralization other than scattered quartz-wolframite veins, 

it is assumed that cupola zones possibly bearing 

Sn or W have been removed. However, the most 

northerly pluton is in a less deeply eroded area and 

forms part of a subcaldera ring complex. Cupola 

zones in this granite are greisenized and contain 

notable concentrations of cassiterite. 

Exploration for possible Sn-W-bearing 

plutons commenced with stream-sediment and 

whole-rock sampling, which established the 

geochemical affinities of the plutons. Stream 

sediments were panned until samples had a color 

index of 50, most magnetite was removed with a 
hand magnet, and the samples were analyzed for 

30 elements by semiquantitative emission spectrography. Whole-rock samples were analyzed by 

semiquantitative emission spectrography, energydispersive X-ray fluorescence for several diagnostic elements, and wet-chemical methods for 

fluorine and lithium. Statistical analysis of the 

geochemical data enabled determination of background and anomalous abundances of each of the 

elements determined, for comparison with the 

chemical characteristics of known Sn-W mineralized plutons. Petrographic study of thin sections 

and modal analysis of stained slabs indicated the 

mineralogic and textural character of the plutons. 

Plutons determined by these analyses to be likely 

sites of mineralization are later explored for ore 

deposits. 

DE POSITIONAL MODEL FOR 

SODIUM CARBONATE DEPOSITS 

IN THE GREEN RIVER FORMATION 

John R. Dyni 

Five separate saline facies are recognized in 

kerogenous fine-grained lacustrine rocks of the 

Eocene Green River Formation that were deposited in four basins in Colorado, Wyoming, and 

Utah. Each facies consists of carbonate-bearing 

minerals of calcium, magnesium, and sodium, and, 

in three facies, halite. Differences in mineral 

solubilities and in composition, temperature, pH, 

and Pco2 of the lake waters resulted in spatial 

zonation and speciation of the saline minerals in 

each facies. The generalized sequence of minerals 

from the lake margin to the depocenter is (1) 

dolomite, ankeritic dolomite, (2) shortite, dawsonite, (3) trona or nahcolite, and (4) at the depocenter, 

halite mixed with trona or nahcolite, wegscheiderite, sparse searlesite, and rarely eitelite and 

northupite. 

Primary sulfate minerals are virtually absent 

in all five saline facies, even though probable 

source areas for Green River sediments suggest 

that sulfate was a common solute in stream waters 

emptying into the Green River lake system. Iron 

sulfide minerals are ubiquitous in the saline facies 

in amounts of about 1-2.5 weight percent. Smectite and illite, the chief clay minerals in profunda! 

sediments of the Green River Formation in Utah 

and Colorado, decrease in abundance toward the 

saline depocenters. This decrease may be due to 

hydrolysis of the clay minerals and neoformation 

of dawsonite and quartz or to nondeposition. 

Principal elements of a proposed depositional 

model for these saline deposits are (1) a closed 

basin containing a permanent body of water with 

anoxic bottom conditions, (2) abundant nutrients 

and relatively warm lake waters for high productivity of algae and bacteria, (3) a substantial but 

finite supply of sulfate, (4) a sustained high rate of 

bacterial reduction of sulfate with metabolic oxidation of organic matter, and (5) a relatively large 

Na/(Cl+Ca) ratio in the lake waters. 

Some predrilling guidelines for exploration of 

new deposits of sodium carbonate analogous to 

those of the Green River Formation include (1) 

evidence of water-soluble evaporite minerals in 

outcrops, such as vugs, crystal cavities, and solution breccias, (2) hydrologic evidence of dissolution 

of evaporite minerals at depth, (3) areal zonation of 

alkaline-earth to alkali-metal carbonate minerals 

that might point toward centers of evaporite deposition, (4) kerogen-rich sediments, and (5) seismic 

and gravity profiles across a basin to detect salt 

sequences, delineate basin structure, and locate 

basin depocenters. 

THE ROLE OF REGIONAL SUBSURFACE 

GEOCHEMISTRY IN RESOURCE ASSESSMENT 

IN THE CENTRAL UNITED STATES 

R.L. Erickson, E.L. Mosier, J.G. Viets, and 

M.S. Erickson 

Regional subsurface geochemical studies are 

an integral part of the U.S. Geological Survey program for assessing the mineral resource potential 

of platform carbonates in the Central United 

States. Much of this area is flat to gently rolling 

agricultural land, outcrops are few, and the known 

favorable host rocks are at depths ranging from a 

few hundred meters to more than a kilometer. 

Thus, traditional surface geochemical techniques 

are of little use in this area for evaluating the 

potential for the occurrence of concealed or undiscovered mineral deposits. 

Geochemical studies of subsurface Cambrian 

strata in the Rolla 1 o X 2" quadrangle, Missouri, 

completed in 1980, and current geochemical studies in the Springfield, Joplin, and Harrison 1 o X 2 o 

10 
quadrangles, which cover about 80,000 km2 in 

parts of Missouri, Kansas, and Arkansas, indicate 

that insoluble residues of carbonate rocks are a 

useful and informative geochemical sample 

medium in a carbonate environment. Commonly, 

the amounts of metals in carbonate rocks are very 

low, sometimes below spectrographic detection 

limits, and the rock appears geochemically "barren.'' However, traces of sulfide minerals present 

in the whole-rock samples are enhanced manyfold 

in the insoluble residue of those samples. The 

enhancement of the metal contents and the large 

suite of metals detectable in insoluble residues offer some hope of determining, on a regional basis, 

whether or not metal-bearing fluids have passed 

through the rocks in a given area and have left 

behind a faint trace of their passage. That faint 

trace, enhanced, may lead to the discovery of unsuspected subsurface mineral trends where metals 

such as Ph, Zn, Cu, and Co were precipitated in 

significant quantity from migrating fluids. 

The distribution of drill holes that have the 

largest amounts of Ph, Zn, Cu, Ni, Co, Mo, and Ag 

in insoluble-residue samples of otherwise apparently metal-barren carbonate rocks outlines the 

known mineralized trends in the Rolla quadrangle 

(for example, the Viburnum Trend). Use of this 

technique in the adjacent quadrangles has resulted 

in the detection of a new and untested belt of 

favorable ground for possible mineral discovery in 

southern Missouri and northern Arkansas. Regional distribution and abundance patterns of 

molybdenum for much of Missouri south of the 

Missouri River suggest that a broad molybdenumrich province in subsurface Cambrian rocks extends across southern Missouri and probably into 

northern Arkansas, an area of perhaps 25,000 km2

• 

The distribution and abundance patterns of 

metals in insoluble-residue samples also place 

some constraints on any model developed to explain the transport and deposition of metals in the 

carbonate-hosted lead-zinc deposits in this part of 

the midcontinent. Although basal sandstones are 

thought by many investigators to have been the 

principal aquifers for ore fluids before they were 

introduced into carbonate host rocks, our work indicates that regional fluid transport of metals occurred in porous, permeable zones in carbonate 

rocks as well as in basal sandstones. Further, we 

have demonstrated that fluids that brought 

metals to sites of deposition through the various 

flow channels were not of uniform composition. 

11 

GEOPHYSICAL EXPLORA liON FOR BRECCIA PIPES 

ON THE COLORADO PLATEAU OF 

NORTHERN ARIZONA 

Vincent J. Flanigan and Carl L. Long 

Exploration for hidden breccia pipes in the 

sedimentary rocks on the Colorado Plateau of 

northern Arizona has proven to be an interesting 

and difficult geophysical problem. The breccia 

pipes are believed to have formed as a result of 

solution collapse within the Redwall Limestone 

and stoping of the overlying strata. Copper, 

uranium, lead, zinc, and silver are the metals found 

in mineralized breccia pipes, although an extensive 

suite of other elements is more abundant at the 

pipes than in the Paleozoic and lower Mesozoic 

host formations. Numerous pipes have been 

mapped along canyon walls where they are partially exposed, but they are much more difficult to 

recognize on the plateau itself. Several geophysical 

methods have been tested over known breccia 

pipes in order to characterize the geophysical properties associated with breccia pipes and to 

evaluate the methods as exploration tools for hidden pipes. The most diagnostic methods are 

magnetic measurements, telluric profiling, and 

time-domain electromagnetic (TDEM) profiles and 

soundings. Audio-magnetotelluric soundings give 

a good picture of the electric section but are less 

diagnostic for pipe location than the methods mentioned above, most probably because of low horizontal resolution of the method. Shallow-sounding 

electromagnetic methods, such as VLF (very low 

frequency communication signals) and slingram, 

and gravity methods were less effective at the 

sites tested. 

One site, generally considered a stratabound 

copper prospect, was chosen to illustrate the 

results that are to be expected from a breccia pipe 

of about 200m diameter. This site is characterized 

by a small magnetic low (5-10 nT) surrounded by 

short-wavelength highs and lows. Telluric data using 50-m E-lines (grounded electric lines) operating 

at 7.5-27 Hz suggests a conductive zone coinciding with the short-wavelength magnetic anomalies. A TDEM profile across the pipe reveals a 

response that compares favorably with modelled 

TDEM responses over a conductive cylinder. The 

data are interpreted to be the geophysical response 

of a central core or plug of Kaibab Limestone surrounded by a 50-m-wide fracture zone. The circular 
fracture zone surrounding the breccia pipe is more 

conductive than unfractured rocks. Magnetic minerals, most likely magnetite, deposited in the fracture zone are the source of the short-wavelength 

magnetic anomalies. Ground magnetic data mathematically continued upward to aircraft flight 

height (100m) indicate that a 10-nT magnetic low 

at ground level would appear in an airborne survey 

as a magnetic low of somewhat less than half the 

ground level value, and the character of the shortwavelength anomalies would be altered accordingly. To detect such magnetic anomalies from the 

air, however, would require the use of a highsensitivity magnetometer and closely spaced 

(50-100 m) flight lines. A high-precision magnetometer airborne survey could locate exploration 

targets, which could then be followed up by reconnaissance telluric profiles and detailed magnetic 

and TDEM measurements. 

Regional airborne magnetic data provide 

several clues that may be used as exploration 

criteria in locating breccia pipes in tree-covered 

areas on the Colorado Plateau. Predominant basement magnetic trends in the study area are northeast, and secondary trends are north-south and 

northwest. These magnetic anomalies are thought 

to be due to intrusion of basic rocks along basement fault zones; these faults were probably important for the karst development in the Redwall 

Limestone. Exploration should be concentrated 

along basement magnetic trends, especially at intersections of northeast and northwest basement 

structures inferred from the magnetic data. 

THE SETTING AND DISTRIBUTION OF 

COPPER-NICKEL SULFIDES IN THE 

SOUTH KAWISHIWIINTRUSION, 

DULUTH COMPLEX, MINNESOTA 

Michael P. Foose 

The Duluth Complex in northeastern Minnesota is a composite mafic intrusion that contains 

large amounts of low-grade copper-nickel sulfides. 

These magmatic sulfides differ from most others 

by being relatively young (1.1 Ga) and by having 

formed within a rift setting. Study of one part of 

this complex, the South Kawishiwi intrusion, 

shows that the sulfides form a discrete zone underlying sulfide-free rocks. The sulfide-free zone, 

which exceeds 3,500 m in thickness, is mostly troctolite containing laterally persistent anorthosite 

12 

layers. These layers are parts of cyclic units 

formed by repeated crystallization of plagioclase 

followed by plagioclase plus olivine. Chemical 

variations associated with the cycles show trends 

both normal and reversed to those typical of fractional crystallization. These trends and the absence of systematic chemical evolution within the 

sulfide-free zone are consistent with crystallization 

of this zone in an open magmatic system such as 

would be expected in an active rift environment in 

which the magma chamber was virtually continuously replenished by liquids of slightly different 

compositions. 

In contrast, the lower (70- to 200-m-thick) 

sulfide-bearing zone is a heterogeneous mixture of 

troctolite, picrite, dunite, anorthosite, oxide 

cumulates, and hornfels in which sulfides are ubiquitously disseminated. The sulfide-bearing zone is 

internally chaotic, and its contact with the sulfidefree zone is sharp. Unlike the overlying rocks, the 

sulfide-bearing zone was emplaced in a physically 

restricted environment in which repeated surges of 

magma associated with the initial stages of intrusion caused complete disruption of the internal 

stratigraphy. 

The sulfides are predominantly pyrrhotite, 

chalcopyrite with cubanite, and pentlandite. Most 

sulfides occur interstitially between euhedral 

olivine or plagioclase or are included in rims of silicates. These relations show that sulfide formed 

after most silicates had accumulated. The close 

association of sulfides with hydrous phases or with 

grains that show reverse compositional zoning further indicates that volatiles were important in 

their formation. The few available isotopic analyses confirm a nonmagmatic source for at least 

some of the sulfur. Footwall rocks in this intrusion 

are granite, but abundant metasedimentary inclusions are present throughout the lower zone and 

show either that sulfide- and volatile-bearing 

sedimentary rocks once formed the footwall or 

that large amounts of these rocks were entrained 

in the initial magma injections. Dispersion of these 

xenoliths during emplacement of the basal zone 

largely controlled the appearance of disseminated 

and sporadically distributed sulfides. 

Faulting was active from the onset of intrusive activity and continued to be active during 

and after magma consolidation. Offsets are mostly 

small and show variable directions of displacement, but the overall sense of movement is 

downwards to the southeast, a pattern that is consistent with the area's setting on the northwest 
flank of a regional rift system. The early faulting 

controlled the form of the basal contact and made 

troughs in which thicker sequences of sulfidebearing rocks accumulated. Offsets associated 

with later faulting disrupted layers and juxtaposed diverse groups of rocks. These later offsets 

may also affect the lateral continuity of the sulfide 

mineralization. 

HEAT TRANSFER AND BRINE EVOLUTION 

IN MAGMA-HYDROTHERMAL SYSTEMS 

Robert 0. Fournier 

There are many uncertainties in the mechanism (or mechanisms) by which heat is transferred from magma to a surrounding hydrothermal system. Mechanisms that have been proposed 

include (a) conduction, (b) transfer of heat by movement of water and volatiles out of the magma, and 

(c) circulation of meteoric water into a thin zone of 

thermal cracking that migrates inward towards 

the magma with time as the rocks cool. Several recent investigations have focussed upon the likely 

significance of this last mechanism, but major 

aspects are poorly understood. Among these are 

the thickness of the cracking zone, the temperature gradient across it, the temperatures at which 

it occurs (perhaps 350-450 o C), and the chemical 

consequences of water-rock interaction in that 

zone. More than one convection cell may be present at a given time within an active hydrothermal 

system, with fluids of varying composition 

associated with different types of mineralization in 

the various cells. Convecting hydrothermal systems at hydrostatic pressure may partly surround 

hydrothermal systems in which fluid pressures are 

greater than hydrostatic but less than or equal to 

the least principal stress in the rock. Fluid 

pressures greater than hydrostatic are particularly 

likely to develop where the flow of fluid away from 

a heat source is impeded by a barrier of relatively 

impermeable rock, perhaps a layer of very ductile 

material such as shale in otherwise brittle rock, or 

a zone where mineral deposition has filled all or 

most of the pre-existing fractures and pore spaces. 

Our present knowledge of hydrothermal mineral deposits and active geothermal systems 

demonstrates the importance of interaction between shallow dilute meteoric water and deeper 

brines. The highly concentrated brines thus far encountered in active hydrothermal systems are all 

13 

Castle Geyser, Yellowstone National Park, Wyoming 

in environments in which the waters may have interacted with evaporites. Experimental data, 

however, indicate that highly saline as well as 

moderately concentrated brines may evolve from a 

crystallizing magma, depending on the initial 

water and chloride contents and the depth of 

crystallization. Brines may also develop from 

dilute meteoric water as a result of boiling, which 

disproportionates the fluid into a more concentrated liquid (brine) and a gas. As a result of boiling or gas disproportionation, highly saline brines 

are likely to evolve in and around shallow magmatic intrusions, particularly at depths less than 6 

to 8 km. Because of density contrasts, hot brines 

will remain below hot, dilute, hydrothermal waters 

or to the side of cold, dilute waters. These hot 

brines will scavenge metals from the surrounding 

rock, and the base metals in tum will react with 

much of the sulfur that is liberated from crystallizing magma. Thus, a base-metal ore deposit may 

form in the brine part of the hydrothermal system 

while the dilute part remains relatively unmineralized with respect to base metals. 
GEOLOGY AND GEOCHEMISTRY OF WALL ROCKS 

OF APPALACHIAN MASSIVE SULFIDE DEPOSITS 

jacob E. Gair 

During the past few years, distinctive mineral 

and chemical compositions have been noted in wall 

rocks of a number of Appalachian massive sulfide 

deposits. Such compositions also appear to be 

associated with many massive sulfides in other 

areas. 

Wall rocks of sediment-hosted massive sulfides in the Gossan Lead district, Virginia, and at 

Ducktown, Tennessee, are parts of thick flyschoid 

metagraywacke-schist sequences deposited in 

craton-margin rifts with or without substantial 

mid-ocean-ridge-type basalt (MORB). Adjacent to 

the sulfide bodies, lenses of the wall rock commonly are of unusual composition, containing a high 

proportion of a single mineral (sodic plagioclase, 

Mn-garnet, biotite, or muscovite); in places, some 

lenses are virtually monomineralic. Other lenses 

contain a large amount of two minerals such as 

sodic plagioclase and biotite, Mn-garnet and 

quartz, or Mn-garnet and biotite. In the Gossan 

Lead district, the Mn-garnet near sulfide bodies 

contrasts with Mn-poor (almanditic) garnets in the 

more distant country rocks. Dravitic tourmaline is 

an important constituent of wall rocks and (or) 

gangue in a few such sediment-hosted deposits 

elsewhere in the Appalachians. These minerals 

reflect metasomatic additions of Na, Mn, K, and 

(or) B to the normal flyschoid sediments. The 

association of these added materials and sulfide 

deposits is attributed to deposition from the same 

or closely related hydrothermal fluids. Rifts were 

the sites both of the flyschoid sedimentation and 

of hydrothermal circulation and mineralization. 

Volcanic-hosted massive sulfide deposits in 

the Appalachians, as in many other places in the 

world, are preferentially associated with felsic to 

intermediate calc-alkalic island-arc volcanic rocks. 

In the Mineral district, Virginia, such volcanic 

rocks in the walls of the deposits are enriched in 

the light rare-earth elements (with La!Yb > 5 and 

commonly > 8) and have Nb > 7 ppm; some of 

these rocks were residually enriched in Al by 

hydrothermal volcanic activity as they formed or 

shortly thereafter, so that subsequently the 

aluminous metamorphic minerals, chloritoid and 

(or) staurolite, formed in them. Kyanite-rich rock 

at Graves Mountain, Georgia, in the southwestern 

part of the Carolina slate belt, also has been at14 

Wall-rock fragments in massive sulfide ore, Gossan Lead 

district, Virginia 

tributed to residual enrichment in Al by hydrothermal leaching during volcanism, and nearby 

massive sulfide deposits are considered to be a 

product of the same hydrothermal activity. Garnet 

in the wall rocks at Mineral is rich in Mn, but 

whether this contrasts with garnet compositions 

in country rock distant from the deposits, as in the 

Gossan Lead district, has not yet been determined. 

In appropriate (meta)volcanic or (meta)sedimentary terranes, the discovery of rocks, mineral 

concentrations, or geochemical anomalies consistent with the features described here can aid in 

targeting massive sulfide exploration. 

EPISODIC METALLIZATION IN THE WESTERN 

SAN JUAN CALDERA COMPLEX, COLORADO 

R.I. Grauch, Ken Hon, R.l. Reynolds, D.J. Bove, 

and V.j.S. Grauch 

Base- and precious-metal (BPM), Mo, U, Al, 

and Sn concentrations in volcanic and intrusive 
host rocks are spatially and temporally related to 

the evolution of the Lake City and Uncompahgre 

calderas of the western San Juan volcanic field, 

Colorado. The Uncompahgre caldera forms the 

eastern half of the Uncompahgre-San JuanSilverton caldera complex, which collapsed and 

resurged between 27 and 29 Ma to create the 

northeast-oriented Eureka graben along the crest 

of the resurgent dome. Nested within the Uncompahgre caldera is the younger Lake City (LC) 

caldera, which collapsed following the eruption 

of the Sunshine Peak Tuff, a 23.1-Ma, compositionally zoned intracaldera ash-flow sheet 

(

87Sr/86Sr = 0.7061-0.7068 and 206Pb/205Pb = 

18.55-18.62). Emplacement of cogenetic quartz 

syenite magma caused asymmetric resurgence of 

the LC caldera and uplift of at least 1,500 m along 

the northern ring fault. Aeromagnetic and gravity 

data show that exposed quartz syenites represent 

a single large resurgent intrusion. Paleomagnetic 

and radiometric data indicate that the time required for caldera development, from eruption of 

the ash-flow tuffs to emplacement of resurgent intrusions, was less than 300,000 years. During the 

same interval, post-collapse lavas and a composite 

dome, the Red Mountain center, were emplaced 

along the east side of the caldera and were hydrothermally altered. The youngest intrusions in the 

area are 19-Ma rhyolite porphyry plugs north of 

the caldera and 17±0.5-Ma rhyolite porphyry 

dikes southwest of the caldera. 

Elemental distribution patterns (K, Th, Be, U, 

Mo) show distinct anomalies related to the LC 

caldera and are generally associated with the Sunshine Peak Tuff. However, more localized and intense geochemical anomalies, combined with 

variations in spectral reflectivities and in wholerock isotope ratios, clay, and metal contents, 

define distinct hydrothermal cells within the 

caldera complex. Major fracture zones, resurgent 

intrusions, and post-caldera intrusions apparently 

controlled the distribution of hydrothermal cells 

and metal concentrations. BPM- and Te-bearing 

veins associated with U occur west of the LC 

caldera at Gravel Ridge in structures of the 

Eureka graben and east of the caldera at the 

Golden Fleece mine, where the vein yielded a U-Pb 

isochron age of 27.5±0.5 Ma. Highly radiogenic 

initial Ph-isotope ratios of ore samples from 

the Golden Fleece (206Pb/2°4

Pb = 19.078-19.58; 208Pb/2°4

Pb = 38.533-38.84) suggest that a significant amount of common lead, and possibly of other 

metals, was derived from upper crustal Precam15 

brian rocks by deeply circulating hydrothermal 

fluids. A near-surface, low-temperature Au-Te 

deposit at the nearby Golden Wonder mine has 

much less radiogenic common lead and is thought 

to have formed as part of a contemporaneous but 

separate hydrothermal cell. Minor concentrations 

of BPM, U, and Sn are spatially associated with 

the resurgent intrusion in the northwest portion of 

the LC caldera The Red Mountain alunite deposit, 

one of the largest in the United States, formed 

during the same time interval and involved the 

shallow circulation of large quantities of meteoric 

fluids in and around the Red Mountain composite 

dome. Radiometric data suggest that the major 

BPM deposits of the Lake City District, northeast 

of the LC caldera, formed at the same time as the 

Red Mountain deposit. Anomalous concentrations 

of Be, Mo, U, and Fare associated with 19-Ma intrusions north and west of the caldera and with 

17-Ma dikes southwest of the caldera. These occurrences and deposits document episodic metallization, over a period of about 10 m.y., related to 

the evolution of the western San Juan caldera 

complex. 

AEROMAGNETIC AND GRAVITY MODELS 

OF THE PLUTON BELOW THE 

LAKE CITY CALDERA, COLORADO 

V.j.S. Grauch 

Aeromagnetic and gravity data collected over 

the Lake City caldera, San Juan Mountains, Colorado, were used to calculate models of the pluton 

below the caldera. Magnetic data are from a 

draped airborne survey and are in digital form. 

Gravity data were assembled from the Department of Defense files and were combined with 

more recent data collected across the caldera Both 

data sets were gridded and contoured in map form 

and also examined in profile form. Regional trends 

were removed where necessary and data were continued upward mathematically, to enhance the effect of the subsurface pluton over the effects of 

shallow sources. 

Geologic mapping by P. Lipman and more recently by K. Hon, both of the USGS, revealed isolated outcrops of quartz syenite inside the caldera. 

These workers inferred that these rocks were intruded at the time of resurgence of the caldera. 

Aeromagnetic and gravity data strongly suggest 
View of Lake City caldera, looking west from Slumgullion Pass. Red Mountain (3 ,900 m) visible at far left 

that the individual quartz syenite outcrops are 

part of a larger body at depth-the resurgent intrusion. Many of the gold, silver, and uranium occurrences are related to hydrothermal cells inside 

the caldera, which in tum were controlled by the 

emplacement of the resurgent intrusion. A model 

of the top of the intrusion, then, is important to 

understanding the origin of mineralization. 

Models calculated by inverting intersecting 

magnetic and gravity profiles show a pluton whose 

top surface is asymmetric; it is shallower in the 

northwestern part of the caldera and deeper in the 

southeast. The pluton model extends further east 

than expected from the geologic evidence. It is 

more magnetic on the eastern side and also more 

deeply buried, which might explain the absence of 

surface geologic evidence for an intrusion on the 

east. Thus, modelling aeromagnetic and gravity 

data in caldera areas provides information on subsurface structure that is valuable in determining 

the evolution and mineralization of the caldera 

system. 

16 

ECONOMIC HEAVY MINERALS OF THE 

U.S. ATLANTIC CONTINENTAL SHELF 

Andrew E. Grosz, Edward C. Escowitz, 

S. Jeffress Williams, Ricardo Lopez, 

john C. Hathaway, Joseph M. Botbol, and 

Laurence J. Poppe 

The Nation's demand for heavy minerals, 

including many strategic and critical minerals, exceeds the domestic supply. For example, in 1982 

the United States imported 60 percent of the ilmenite and nearly 100 percent of the rutile it 

required. 

In the United States, heavy minerals, such as 

ilmenite, leucoxene, rutile, zircon, monazite, and 

other minerals resistant to weathering, have concentrated along fossil beaches, alluvial floodplains, 

and recent shorelines. Major onshore deposits are 

located in Coastal Plain sediments of New Jersey, 

the Carolinas, Georgia, and Florida. Economic concentrations of heavy minerals may also be associ-
ated with former shoreline and fluvial deposits 

now submerged on the Continental Shelf. 

The Atlantic Continental Shelf (ACS) has an 

area of about 3.91 X 105 km2 and probably contains 3-7 X 1011 m3 of sand and gravel, at an 

average grade of approximately 1 percent heavy 

minerals. This preliminary result is in contrast to 

previous estimates of 0.16 percent heavy minerals 

in the ACS sand and gravel. Therefore, estimates 

by others of 1.3 X 109 m3 of sand bearing heavy 

minerals are almost certainly low. The USGS is 

now systematically assessing placer heavymineral resources within the U.S. Exclusive 

Economic Zone; initial efforts are concentrated on 

the ACS. The primary goal is to locate heavymineral deposits offshore and to understand the 

geologic and geochemical factors governing their 

distribution. 

Heavy minerals in 71 grab samples from offshore of well-studied Coastal Plain marine sediments in Virginia, South Carolina, and northeastem Florida were studied. Results indicate that surface grab samples from an extensive area offshore 

of Virginia, where onshore deposits contain the 

lowest concentrations measured, have the highest 

concentrations of heavy minerals, comparable to 

the richest onshore control area (South Carolina) 

and even some commercial deposits in Florida and 

New Jersey. These results are at variance with 

previously published hypotheses, which state that 

the best target areas for accumulation of heavy 

minerals should be situated offshore of known 

concentrations in onshore sediments. 

Other research focused on the ACS includes 

analyses of more than 500 grab samples (from the 

USGS-Woods Hole Oceanographic Institution 

ACS collection) and over 1,200 sediment cores and 

associated 18,000 line km of high-resolution 

seismic reflection profiles (from the U.S. Army 

Corps of Engineers) to determine the areal and vertical distribution and economic potential of the 

identified offshore heavy-mineral accumulations. 

Quantitative analyses of sediment characteristics, 

bathymetry, and other variables show distinct 

patterns in areas of the ACS where high heavymineral concentrations are present. These patterns 

are evident on many parts of the central ACS 

(Long Island to Cape Hatteras). On parts of the 

southern ACS (Cape Hatteras to Miami), high 

heavy-mineral concentrations appear to be limited 

to the Inner Shelf. Potential economic value of the 

heavy-mineral concentrations in these areas is be17 

ing assessed by quantifying the individual mineral 

species relative to the absolute concentrations and 

dimensions of deposits. A variable called ECON, 

which is the sum of weight percent ilmenite, 

leucoxene, rutile, sillimanite, and monazite in a 

sample, is used to indicate potential economic 

value. The mean ECON value for offshore Virginia, for example, is 1.13 percent. However, the 

ECON reaches values of 4.58 percent in some 

samples. For comparison, the average ECON 

value for working deposits in northeastern Florida 

is about 2 percent. 

MINERAL RESOURCES OF THE SURVEY PASS 

QUADRANGLE, BROOKS RANGE, ALASKA 

Donald j. Grybeck and Steven W. Nelson 

The mineral resources of the Survey Pass 

quadrangle (mapped at 1:250,000) in the central 

Brooks Range were evaluated under the Alaska 

Mineral Resource Assessment Program (AMRAP) 

beginning in 1977. Like all AMRAP studies, the 

Survey Pass effort is not a literature search but is 

based on a comprehensive field program specifically tailored to collect and integrate geological, 

geochemical, geophysical, and mineral deposit 

data to achieve a modem (reconnaissance) assessment of the quadrangle's mineral resources. 

The essential framework for producing the 

mineral resource assessment is the geologic map; 

more than half the effort in the study and considerable scientific talent in several disciplines was 

devoted to understanding the geology of the quadrangle. The geologic map was then used as the 

foundation for interpreting and integrating the 

geochemical, geophysical, and mineral deposit 

data with ore deposit models to define areas of 

mineral resource potential. The areas varied greatly in their apparent mineral potential, not only 

because of differences in their inherent mineral endowment but because of the considerable variation 

in the amount and the implications of the data 

that were available. 

Seven terranes, bounded mainly by known or 

suspected north-dipping thrust faults, can be 

distinguished by stratigraphy, metamorphic 

grade, structural fabric, and magnetic signature. 

Almost all the rocks in the quadrangle are known 

or presumed to be Late Devonian or Early Mississippian in age, although they differ widely in 
Geologists examining stratiform Zn-Pb sulfide deposit at Drenchwater Creek, northwestern Brooks Range, Alaska 

18 
lithology. The northernmost terrane consists 

mainly of a thick, unmetamorphosed red-bed sequence deposited in a delta that covered much of 

what is now the Brooks Range in Late Devonian 

time. South of the red-bed sequence, four terranes 

consist of unmetamorphosed to low-grade rocks, 

mainly phyllites, and carbonates. South of them, 

the central portion of the quadrangle consists of 

low- to medium-grade calcareous to pelitic schist, 

gneiss, marble, and quartzite that surround two 

Devonian gneissic granite batholiths. The southernmost terrane, the " schist belt" , consists of lowgrade pelitic schists with scattered occurrences of 

blueschist. The schist belt also contains a distinctive sequence of felsic and calcareous schist, rhyolite, and mafic igneous rocks, which hosts large 

volcanogenic massive sulfide Cu-Zn-Pb(-Ag-Au) 

deposits. 

Only two classes of deposits appear to be of 

major importance in the quadrangle: the volcanogenic massive sulfide deposits and several types of 

deposit associated with felsic plutonic rocks. 

Numerous lines of evidence indicate that additional massive sulfide deposits may exist in the 

schist belt, but only in its western half in the quadrangle. This study identified many skarn and other 

contact metamorphic deposits and veins containing various combinations of Ph, Zn, Cu, Ag, Au, 

Mo, Sn, W, and other elements around the Devonian granite batholiths, and the geochemical data 

indicate additional undiscovered deposits of this 

type. However, all the known deposits associated 

with the granites are small; most are little more 

than mineralogical occurrences. While the known 

granite plutons are an attractive environment for 

mineral deposits of several types, their roof zones, 

which were the most likely sites of mineralization, 

are largely eroded away. However, the geochemical, remote-sensing, and mineral deposit data 

strongly suggest that at least two large buried and 

previously unsuspected granitic plutons are present in the northern part of the quadrangle, and 

several more are suspected elsewhere. 

BASE METALS, PRECIOUS METALS, AND 

MOLYBDENUM: NEW OCCURRENCE TYPES 

IN THE WESTERN UNITED STATES 

Wayne Hall, Steve Ludington, Ted G. Theodore, 

and Norman J Page 

Central Idaho Black Shale Mineral Belt 

(Hall)-A highly mineralized black shale belt 60 mi 

(95 km) long and 8-30 mi (13-48 km) wide of Ordovician to Permian age crops out on the east side 

of the Atlanta lobe of the Idaho batholith in central Idaho. These black shales occur in imbricated 

tectonostratigraphic plates separated by regional 

thrust faults. Mineralized resources include (1) 

Open-pit molybdenite mine at Questa, New Mexico 

19 
small to moderate-sized high-grade Pb-Ag-Zn vein 

deposits that account for most past production, (2) 

two large Mo deposits associated with granodiorite stocks intruded into Mississippian black 

argillites, and (3) stratabound deposits of Zn-PbAg, barite, and V, mostly in highly carbonaceous 

shale and limestone of the Devonian Milligan Formation and Mississippian Salmon River sequence. 

Geologic, stable-isotope, and fluid-inclusion data 

indicate that the sources of metals and sulfur for 

the vein deposits are the host black shales near intrusive bodies. These vein deposits may be used as 

guides to possible nearby syngenetic deposits. 

Questa Molybdenite Deposits (Ludington)-A 

number of molybdenite deposits near Questa, New 

Mexico, share many characteristics with models 

developed for "Climax-type" or "high-fluorine" 

stockwork molybdenite deposits. To the explorationist, all these deposits belong to the same class; 

they can be discovered using the same recognition 

criteria and exploration strategies. However, at 

Questa, local structural and petrologic criteria 

suggest a petrotectonic setting and emplacement 

history different from those of the classic Climax 

and Henderson deposits. The rhyolite magmas 

that were the source of the Questa deposits were 

closely associated with, and may have been derived from, large bodies of calc-alkaline quartz 

monzonite. Rhyolites at Questa show substantially less enrichment in lithophile elements such as F, 

Rb, and Nb that are characteristic of Climax-type 

deposits; ore bodies at Questa are less regular in 

shape and are not so clearly related to individual 

plutons. 

Though much field evidence suggests that the 

Questa deposits formed late in the history of the 

peralkaline Questa caldera, other evidence (detailed trace-element, isotopic, and geochronologic 

studies) is compatible with the view that the oreforming events were subsequent to and independent of the caldera cycle. 

Gold in two-mica granites (Theodore and 

Page)-Mesothermal gold mineralization in the 

Gold Basin district, Arizona, occurs in intensely 

brecciated veins and in small, high-grade, feldspathic, funnel-shaped alteration zones of episyenite-all associated genetically with Upper Cretaceous two-mica, peraluminous granites. Some 

veins, such as the one at the Cyclopic mine, probably reflect several stages of brecciation. Initially, 

flat-lying cap-rock breccias developed in zones of 

silica deposition above episyenite that formed 

20 

deep within two-mica granite. Subsequent faulting 

along low-angle, Miocene detachment surfaces further brecciated the veins. Similar relations between mineralization and tectonics may occur 

elsewhere in the belt of two-mica granites along 

the eastern margin of the Basin and Range. 

ORGANIC GEOCHEMISTRY OF WALL-ROCK 

ALTERATION, THOMPSON-TEMPERLY MINE, 

SOUTHWEST WISCONSIN 

Joseph R. Hatch, Allen V. Heyl, and J. David King 

Previous studies of the Thompson and Temperly zinc-lead ore bodies, southwest Wisconsin, 

show alteration aureoles in the Middle Ordovician 

host-rock limestones, dolomites, and shales 

extending laterally as much as 60 m from the ore. 

Texture, clay mineralogy, and major-, minor-, and 

trace-element and o13C and o180 compositions of 

the host rocks have all been significantly affected 

by mineralization processes. Fluid-inclusion studies indicate that maximum temperatures of ore 

deposition were about 120-130° C. 

We performed organic geochemical analyses 

on samples of the basal 3-inch-thick (8-cm-thick) 

carbonaceous shale and the immediately overlying 

limestone bed of the Quimbys Mill Member of the 

Platteville Formation. The samples were collected 

from the ore body, the alteration aureole, and 

unaltered rock. Results and conclusions include 

the following: 

(1) Total organic carbon (TOC) contents in the 

basal carbonaceous shale are relatively 

high but range widely, from 1.7 to 6.7 percent. TOC is higher in shale samples from 

the ore and alteration aureole (mean = 4.2 

± 1.3 percent, 12 samples) than in 

unaltered shale (mean= 2.5 ± 0.7 percent, 

5 samples). In the overlying limestone, 

TOC is much higher in samples from the 

ore (mean = 1.5 ± 1.2 percent, 5 samples) 

than in samples from the alteration 

aureole or unaltered country rock (0.2 ± 

0.06 percent, 11 samples). The higher TOC 

of samples of limestone within the ore and 

in the alteration aureole are a result of 

solution of carbonates and residual concentration of organic matter. 

(2) Organic carbon o13C is -31.2 ± 0.3 per mil for 

the carbonaceous shale (18 samples) and 
-30.6 ± 0.3 per mil for the limestone (8 

samples). Organic carbon o13C does not 

change systematically with distance from 

the ore body in either shale or limestone. 

(3) Results from Rock-Eval pyrolysis show that 

carbon-normalized volatile hydrocarbon 

(HC) contents (81/TOC) decrease toward 

the ore body in both shale and limestone 

(from about 0.3 to about 0.1 mg HC/g 

TOC) and that carbon-normalized pyrolytic HC contents (hydrogen index, HI, 

82/TOC) are much lower in the shale near 

the ore body (HI = 50-250 mg HC/g TOC) 

than in the outer part of the aureole or 

unaltered rock (HI = 350-580 mg HC/g 

TOC). In contrast, limestone samples from 

within the ore body have much higher HI 

(HI = 390-460 mg HC/g TOC) than limestone from the aureole or unaltered rock 

(HI = 80-260 mg HC/g TOC). The temperature at which the 82 peak reaches a maximum (Tmax) ranges from 423 to 432° C for 

all samples, indicating immature to marginally mature organic matter. T max• however, shows no systematic changes with 

distance from the ore. The decrease in 

81/TOC towards the ore indicates loss of 

lower molecular weight organic compounds during mineralization. The decrease in hydrogen index for the shale indicates alteration of organic matter. The 

higher hydrogen index of the limestone 

within the ore may be an artifact caused 

by concentration of organic matter. The 

lack of change in T max is a probable result 

of a relatively short time of hydrothermal 

activity. 

(4) Distributions of saturated hydrocarbons extracted from both shale and limestone 

samples show relative decreases in 

amounts of lower molecular weight compounds ( < n-C25) in and near the ore. This 

supports the loss of volatile hydrocarbons 

indicated by 81/TOC. Biological-marker 

distributions for all samples are remarkably similar regardless of lithology or 

proximity to the ore body. Biologicalmarker maturity indicators, c29 sterane 

5a(H), 14a(H), 17a(H), 208 to 5a(H), 

14a(H), 17a(H), 20R ratios and 228/22R 

c31 hopane ratios, are 0.6 ± 0.1 and 1.4 ± 

0.1, respectively, and indicate marginally 

21 

mature organic matter. The lack of effect 

on the biological marker maturity indicators by the alteration and mineralization suggests a relative short interval of 

hydrothermal activity; biomarker equilibration apparently requires more time 

than the duration of Upper Mississippi 

Valley-type mineralization. 

ORIGIN OF SEDIMENTARY HUMIC ACIDS, 

POTENTIAL CARRIERS OF 

ORE-FORMING ELEMENTS 

Patrick G. Hatcher 

Humic acids are complex, macromolecular 

organic components of sediments and are defined 

by their solubility in dilute alkali and insolubility 

in dilute acid. Because of their general structural 

characteristics (for example, their high proportion 

of oxygen functional groups), humic acids can 

complex with inorganic cations and may be important in forming ore deposits. In some instances 

(such as uranium ores), ore bodies are believed to 

have originated by mobilization of an ore-forming 

element complexed with humic acids and subsequent precipitation. 

Little is known about the mechanisms by 

which humic acids evolve from sedimentary 

organic matter. Humic acids were generally 

thought to be molecular polymerization products 

of smaller molecules produced by microbial decomposition of plant remains. However, studies of 

humic acids by nuclear magnetic resonance (NMR) 

techniques show that they are derived by degradation of macromolecules formed in plants. When 

compared to these insoluble macromolecules, 

humic acids in aerobic sediments show many 

similar structural features, invariably a greater 

proportion of carboxyl groups, and a tendency to 

be more aromatic. Carboxyl groups are thought to 

be introduced during oxidative decomposition of 

the plant macromolecules. The oxidation products 

become more soluble in aqueous alkali, resulting in 

the formation of substances that are operationally 

classed as humic acids. Very little structural 

alteration would occur by such oxidation. This proposed pathway is consistent with the observed 

structural similarity between humic acids and the 

plant macromolecules as determined by NMR. The 

increased aromaticity probably results from the 
higher susceptibility of aromatic structures to 

degradation under oxidizing conditions. 

In anaerobic sediments, the production of humic acids is suppressed by the lack of oxidation. In 

such sediments, materials extracted as humic acids, 

usually in low yields, bear little structural resemblance to preformed macromolecules. Rather, these 

humic acids appear to be mostly fermentation products of decomposing plant litter or simply fragments of the soluble plant macromolecules. 

Knowing the mechanism by which humic 

acids originate is fundamental to our understanding of the role of organic matter in ore deposition. 

We can begin to understand transport of oreforming elements by humic acids only when we 

know how humic acids originate. The chemical 

structural composition of humic acids affects their 

ability to complex with certain elements. The 

chemical structure of humic acids responsible for 

formation of a particular ore body must be defined 

so that we can use this information in predictive 

models. 

Knowledge of the mechanism for the formation of humic acids is being applied to two major 

ore deposits. Studies of organic matter associated 

with tabular uranium ores of the San Juan basin 

and disseminated, Carlin-type gold ores from 

Nevada show that humic acids may have been precursors. This suggests that the humic acids could 

have played a major role in the transport and 

accumulation of the ore. For example, oxygenated 

ground waters or hydrothermal fluids passing 

through organic-matter-rich rocks could have oxidized the indigenous organic matter to produce 

soluble humic acids that subsequently complexed 

gold or uranium ions. The humic acids carrying 

these elements could have precipitated in host 

rocks. During maturation, the humic acids may 

have lost their oxygen functionality, become insoluble, and lost their complexing ability for 

metals. These metals released from the organic 

matter could then become incorporated in mineral 

phases. 

RESEARCH ON KIMBERLITES AND APPLICATIONS 

TO DIAMOND PROSPECTING 

B. Carter Hearn, Jr., and Elaine S. McGee 

Research on kimberlites in Montana and 

northern Michigan has concentrated on field mapping, mineralogy of xenocrysts and megacrysts, 

22 

Kyanite-garnet-pyroxene inclusion (kyanite eclogite) from the 

Lake Ellen kimberlite, northern Michigan; derived from 

a calculated depth of 115 km (940° C) in the upper mantle 

mineralogy of upper-mantle peridotite and eclogite 

xenoliths, and bulk chemical composition. The 

Montana kimberlites contain no diamonds. 

Whether the Lake Ellen, Michigan, kimberlite contains diamond is unknown. The Lake Ellen kimberlite is particularly important because primary 

kimberlite sources for the diamonds found in 

glacial deposits in the Midwest may lie within the 

United States rather than in southern Canada. 

Because kimberlites typically have poor exposures, mapping commonly involves panning, 

pitting, soil auguring, and geophysical surveying. 

Ground magnetometer surveys clearly distinguish 

the boundaries of the kimberlite pipes as zones of 

high magnetic gradient around a central irregular 

magnetic high. The magnetically defined borders 

correspond to geologically determined contacts 

where exposures give sufficient control. 

Xenocrysts (size < 1 em) and megacrysts 

( > 1 em), particularly of the indicator minerals 

Cr-rich pyrope, Cr-rich diopside, and Mg-rich ilmenite, provide information about both the presence of kimberlite pipes and their diamond potential. Pyrope megacrysts are conspicuous because 

of their large size and their red-orange color. Crpyrope xenocrysts, because of their purple to red 

color, are the most conspicuous of the durable indicator minerals and are typically 0.5-5 mm in 

size. These garnets are chemically similar to 

garnets in garnet peridotite xenoliths in Montana 

kimberlites and thus are from disaggregated 

peridotites, indicating that the kimberlite has 

sampled depths in the upper mantle where diamond might be present. Most of the Cr-rich, Mg-
rich garnets from alluvium show a positive correlation of CaO and Cr20 3 that matches the band of 

CaO-Cr 20 3 compositions of garnets from lherzolites. Cr-rich, Ca-poor pyropes that are derived 

from Ca-poor garnet harzburgites are favorable indicators of diamond presence in kimberlites elsewhere in the world. We have not found garnets of 

markedly low CaO content in Montana or Michigan kimberlites, but we have found a few garnets 

that contain slightly less CaO than the lherzolite 

garnets and thus may be significant. Mg-rich 

ilmenites in both the Michigan and Montana 

kimberlites are in the compositional range favorable for diamond presence (high MgO, moderate 

CrzOa. and low Fez03). 

Calculated temperatures and pressures for 

garnet peridotite xenoliths from Montana kimberlites and for eclogite xenoliths and composite 

peridotitic xenocrysts (Cr-rich pyrope plus Crdiopside) from the Michigan kimberlite range from 

the graphite stability field into the diamond stability field. Thus kimberlites of both areas have 

originated from or ascended through regions of the 

upper mantle where, if carbon were present and 

oxygen fugacity were low, diamond would be a 

stable phase. 

Comparison of bulk chemical compositions of 

U.S. kimberlites using the discriminant function 

of Zhong Ruyuan (1983, Geochemistry, v. 2, 

p. 233-242) shows that Kentucky (diamondbarren) and Colorado (diamond-bearing) kimberlites are in the diamond-bearing range, Michigan 

kimberlite (diamond content unknown) and Arkansas lamproite (diamond-bearing) are in the overlap 

zone of diamond-bearing and diamond-barren 

kimberlites, and Montana kimberlite (diamondbarren) is in the diamond-barren range. 

COBALT-RICH FERROMANGANESE CRUSTS 

IN THE OCEANS 

James R. Hein and Frank T. Manheim 

Ferromanganese crusts form on hard substrates in three general geotectonic environments: 

flanks of midplate seamounts, ridges, and plateaus 

(chiefly hydrogenous crusts); active oceanic 

spreading ridges (hydrothermal crusts); and convergent margins such as island arcs (combinations 

of hydrothermal and hydrogenous processes). 

Crusts commonly have botryoidal surfaces and 

laminar internal development on a continuous 

substrate or around isolated nuclei. Since the West 

German Midpac cruise of 1981, hydrogenous 

crusts have been recognized as potential offshore 

mineral resources owing to their valuable metal 

content. They are of special interest to the United 

States since many crust areas lie within the U.S. 

EEZ (Exclusive Economic Zone). The principal exploratory cruises devoted to crust investigations 

are listed in table 1. 

Be10 and uranium-series radiometrically dated 

hydrogenous crusts have been shown to grow at 

TABLE I.-Principal exploratory cruises devoted to crust investigations 

Date Vessel Sponsor Area 

July '81 ---- Sonne --------- Univ. Clausthal/Ministry of Technology/------ Midpacific Mountains, Line Islands. 

German National Science Foundation 

Sep. '82 ---- Gyre ---------- U.S. Geological Survey-------------------- Blake Plateau. 

(Atlantic Branch) 

Oct. '83 ---- S.P. Lee ------- U.S. Geological Survey-------------------- Midpacific Mountains, Line Islands. 

(Pacific Branch) 

July '84 ---- Kana Keoki ---- Hawaii Institute of Geophysics ------------- Hawaiian Archipelago. 

Aug. '84 ---- S.P. Lee ------- U.S. Geological Survey-------------------- Marshall Islands. 

(Pacific Branch) 

Aug. '84 ---- Sonne --------- Univ. Clausthal/Ministry of Technology/------ Southeastern Hawaiian Archipelago, MidGerman National Science Foundation pacific Mountains, Line Islands. 

23 
rates of about 1-3 mm/m.y., and their thickness 

commonly corresponds to the age of the substrate. 

Consequently, old oceanic features, like the Cretaceous Line Islands and Midpacific Mountains in 

the Pacific and New England Seamounts in the 

Atlantic, have the thickest crusts (as much as 

11 em). Economically significant thicknesses of 

crusts (thicker than 2 em) have been found in many 

ocean areas, but the highest content of valuable 

metals has been found in the north equatorial 

parts of the Line Islands trend (Co~ 1.2 percent, 

Mn = 25-34 percent, Ni = 0.4-0.6 percent, Pt = 

0.2-0.8 ppm); metal content varies inversely with 

water depth. Slightly lower values have been 

found in the Midpacific Mountains area, the northwestern Hawaiian Archipelago seamounts, and 

the Marshall Islands. Where iron contents are high 

(Mg/Fe < 1.0), as in the Tonga Ridge, cobalt and 

other valuable metals are lower (Co = 0.36 

percent). 

The Blake Plateau, off North and South Carolina, has large tonnages of low-grade ferromanganese oxides in water depths of 700-1,000 m, 

within the U.S. EEZ. The oxides form nodules, 

slabs, and hard pavements mixed with phosphorite and cover as much as 14,000 km2

• Other 

documented or inferred crust provinces on the 

Atlantic margin are the easternmost part of the 

New England Seamounts, the Bahamas slope region, and old, exposed ridges in the Caribbean Sea 

(Aves Ridge and Beata Ridge). 

NEW SILVER RESOURCE MAP OF THE 

UNITED STATES-POTENTIAL FOR INCREASED 

DOMESTIC SILVER PRODUCTION 

Allen V. Heyl and Robert B. Hall 

A new silver resource map of the United 

States was compiled in 1984 to replace the out-ofprint U.S. Geological Survey Map MR-34 published in 1962. Estimated past production (in troy 

ounces) plus estimated resources of each district 

are indicated on the new map by the size of the dot 

representing the district. The text includes brief 

summaries of mining history, geologic setting, and 

character of the ores for each district, an improvement over the one-line descriptions of districts 

that accompanied the 1962 map. Many locations 

have been added, especially in the Eastern United 

States. 

24 

Information gained during compilation of the 

new map suggests that domestic silver resources 

may be considerably greater than previously 

believed. The Eastern United States, particularly 

the Appalachian province from northern New 

England to Alabama, is a more promising source 

of silver and associated metals than generally is 

realized. Deposits mined during the 19th century 

and even earlier, before the American Revolution, 

merit further investigation in areas where urban 

encroachment does not yet inhibit mining. The 

Western United States will continue to be the Nation's principal source of newly mined silver, with 

the Coeur d'Alene region in Idaho likely to remain 

preeminent for the foreseeable future. Newly 

developed silver mines, such as the Escalante in 

Utah, the Troy in Montana, and others in Nevada, 

Idaho, and California, are expected to make an 

increasingly important contribution. 

Silver and gold-silver mines are now the main 

sources of the country's silver. In the Southwest, 

output of byproduct silver from low-grade porphyry copper deposits has been reduced sharply in 

recent years because of production cutbacks 

resulting from low copper prices. Part of this lost 

silver production is being made up by revived 

operations in old Western mining districts. Some 

of these have been abandoned for nearly a century, 

but they contain veins and replacement deposits, 

which, although much smaller than the porphyry 

deposits, contain a much higher tenor of precious 

and base metals. Heap leaching of old dumps and 

tailings represents a temporary revival at some 

districts, but ultimately new ore must be mined if 

production is to be sustained. Some districts probably contain large resources of primary sulfide 

ores, which, although lower grade than the oxidized ores mined during the 19th and early 20th 

centuries, are amenable to modern processing 

techniques. 

Numerous once-productive districts of the 

Western United States are located on the new map 

and described in the accompanying text. Most of 

the districts in the Eastern United States produced little silver, but several are believed to have 

significant potential. The revised silver resource 

map and text will be useful to industry in selecting 

new exploration targets for silver and associated 

metals. Factors that will influence future exploration and mining are (1) favorable metal prices, (2) 

funds available to finance exploration and establish mine plants and concentrators, (3) convenient-
The famous Matchless silver mine, Leadville, Colorado 

ly located smelters and refineries so that cost of 

shipping ores and concentrates is not prohibitive, 

and (4) favorable Federal and State policies. 

VOLATILE ELEMENTS AND COMPOUNDS 

IN EXPLORATION GEOCHEMISTRY 

Margaret E. Hinkle and J. Howard McCarthy 

The use of gases in geochemical exploration is 

receiving increased attention as an exploration 

technique in the search for concealed mineral 

deposits. Volatile components of soil gases such as 

carbon dioxide, oxygen, sulfur compounds, hydrocarbons, and helium have delineated known ore 

deposits. The goal of volatile-element research in 

the Branch of Exploration Geochemistry is to 

develop the use of these constituents of soil gas in 

the search for concealed deposits. 

Two methods are used to collect soil gas in the 

25 

field. The first method consists of pounding a 

hollow probe into the ground and collecting a soil 

gas sample in a syringe by inserting the syringe 

needle through a cap in the probe and withdrawing 

the gas sample. This gas sample is analyzed without further treatment. The second method uses the 

soil itself as a collector of gases rising from below. 

Soils are placed in vials, which are sealed and then 

heated to drive off the gases. The gas in the vial 

(headspace gas) is analyzed. 

Soil gas samples are analyzed in the field for 

constituents such as carbon dioxide, oxygen, and 

hydrocarbons by a truck-mounted quadrupole 

mass spectrometer. Analyses of soil gas samples 

collected by hollow probe and gas samples liberated from heated soil samples are performed in the 

laboratory. Analyses of gases such as carbon dioxide, oxygen, hydrocarbons, and sulfur compounds 

are performed by gas chromatography; helium is 

analyzed by a modified mass-spectrometer helium 

detector. 
Recent Research Results 

Massive sulfide deposit, Wisconsin. -Soil gas 

anomalies were found over a massive sulfide 

deposit in northern Wisconsin through as much as 

60 m of glacial deposits. Anomalous carbon dioxide contents were as high as 6 percent of the soil 

gas sample, and coincident but negative anomalous oxygen contents were as low as 9 percent of 

the soil gas sample. Hydrocarbon gases (alkanes) 

also coincided with the mineralization. 

North Silver Bell porphyry copper deposit, 

Arizona.-Volatile elements and compounds were 

measured in gases derived from soil samples. 

Anomalous concentrations of helium ( > 10 ppm), 

carbon disulfide ( > 100 ppb), and sulfur dioxide 

(>300 ppb). were found adsorbed on soil samples 

taken over the ore body. Higher than normal concentrations of carbon dioxide ( > 0.25 percent) and 

carbonyl sulfide ( > 300 ppb) were found adsorbed 

on soil samples taken over the alteration zones 

around the ore body. 

Johnson Camp copper-zinc deposit, Arizona.-

Sulfide ore bodies occur at depths ranging from 10 

to 225 m at Johnson Camp. Above-average concentrations of carbon dioxide ( > 1.5 percent) and 

helium ( > 5.5 ppm) were present in soil samples 

taken·· over all the ore bodies; high carbonyl sulfide 

(>600 ppb) and carbon disulfide (>60 ppb) contents were found in soil samples taken over ore 

bodies as deep as 150 m. The occurrence of volatile 

elements and compounds related to ore bodies at 

these depths below the ground surface indicates 

that these volatiles could be valuable aids to 

geochemical exploration. 

ELECTRICAL GEOPHYSICAL STUDIES OF 

MASSIVE SULFIDE DE POSITS 

AND THEIR HOST ROCKS, 

WEST SHASTA COPPER-ZINC DISTRICT 

Robert Horton and Bruce D. Smith 

The West Shasta copper-zinc district, Shasta 

County, California, contains many volcanogenic 

sulfide deposits within Middle Devonian rhyolite 

volcanic rocks that have not been highly metamorphosed. The district was selected for intensive 

geological, geochemical, and geophysical study by 

the U.S. Geological Survey because good exposures have been created both by erosion and by 

mining. This report describes the galvanic and inductive electrical methods applied to characterize 

the large- and small-scale electrical geophysical 

properties of selected massive sulfide deposits and 

their host rocks. Electrical geophysical methods 

have long been used in exploration for massive 

sulfide deposits of Precambrian age, but little has 

been reported on electrical geophysical applications to younger, less metamorphosed deposits. 

The electrical geophysical techniques used included galvanic (electrical currents introduced 

directly into the earth) and inductive methods (currents indirectly introduced). Inductive methods 

can locate the following conductive features: fault 

zones, hydrothermally altered bedrock, conductive 

shales, and massive sulfide deposits. Combined 

use of methods that have different depths of 

penetration can provide useful information about 

the geometry and depths of a conductor. A profile 

using very low frequency (VLF), slingram, and 

time-domain electromagnetic induction methods 

over a known tabular sulfide body at the Hornet 

Mine showed that all three can detect the shallow 

sulfide deposit. Part of a profile measured in the 

Keystone mine area is over a small block of shale 

that has been downfaulted into volcanic rock. 

Anomalies from the VLF survey in this area define 

the conductive nature of the fault zone, while 

deeper penetrating frequency and time-domain 

methods indicate that a separate conductor is also 

present. 

Though inductive electromagnetic methods 

can define conductive features, they cannot identify the source, whether massive sulfide bodies, 

conductive formations or structures. In situ spectral induced polarization (SIP) measurements were 

carried out to electrically characterize massive 

sulfide bodies exposed at the Iron Mountain and 

Balaklala mines. In addition, in situ measurements were used to evaluate whether SIP measurements could provide additional information for 

classifying the source of electromagnetic anomalies. These in situ measurements defined the 

resistivity of these massive sulfide bodies to 

range from 5 to 0.05 ohm-meters. This range is 

similar to resistivities observed in Archean 

massive sulfide deposits. In situ SIP phase spectra 

(the IP effect as a function of frequency) have 

much less character and lack the distinctive shape 

reported for Canadian massive sulfide deposits. 

Additionally, the magnitude of the IP response is 

about 50 percent less than reported values of older 

26 
massive sulfide deposits. We attribute the more 

nondescript spectral signature and lower IP 

response to the lack of development of polarization 

processes and a high percentage of nonpolarizable 

gangue minerals. However, a SIP profile over the 

Hornet massive sulfide body shows much better 

development of the spectral response. Interestingly, most of the Hornet ore body has been mined, 

leaving only a 2- to 3-m shell. The observed 

polarization response is therefore dominated by 

polarization of the ground water-sulfide contact, a 

polarization mechanism different from that observed during in situ measurements. The Hornet 

survey demonstrates that the electrical signature 

of a massive sulfide body differs from that of its 

host rock. The SIP survey on the Keystone profile 

suggests that part of the electromagnetic response 

is due to massive sulfides. Thus the source of electrical geophysical anomalies can be determined 

from their polarization signatures. 

MASSIVE SULFIDE DEPOSITS FROM THE 

SOUTHERN JUAN DE FUCA RIDGE 

Randolph A. Koski, David A. Clague, 

James L. Bischoff, and Robert A. Zierenberg 

Six hydrothermal vent sites and associated 

benthic communities were located in the axial 

valley of the southern Juan de Fuca Ridge in 1981, 

by means of transponder-navigated bottom 

photography. The hydrothermal deposits form 

chimneys, spires, and mounds within a central 

zone characterized by a linear bathymetric depression and numerous collapse features. The flat 

valley floor adjacent to the central zone consists of 

ferrobasalt lobate sheetflows; sediment cover is 

minimal. Vent sites are characterized by concentrations of tube worms, clams, limpets, gastropods, and several unidentified fauna. 

Two types of massive sulfide were dredged 

from one of the vent sites. Type A samples are 

angular slabs of dark-gray Zn-rich sulfide with interlayers and a thin, partly oxidized crust of Fe 

sulfide. The outer sulfide wall is composed mainly 

of colloform Fe sulfide and Fe-poor sphalerite 

deposited under lower temperature conditions 

whereby sea water and hydrothermal fluid mix 

above the discharge point. With continued sulfide 

deposition, the wall inhibits mixing of sea water 

and hydrothermal fluid. Inside the wall, the inten27 

Tube worms and crab at low-temperature vent on southern 

Juan de Fuca Ridge 

sifying hydrothermal system deposits a higher 

temperature assemblage of granular Fe-rich 

sphalerite, wurtzite, pyrite, and minor Cu-Fe 

sulfide. The zonation in wurtzite from Fe-rich cores 

to Fe-poor rims may result from a late-stage cooling of the hydrothermal fluid and (or) a change in 

fluid chemistry. The sulfide wall grows outward 

where a rupture in it permits the escape of hightemperature fluid and then deposition of a secondary shell over the breakthrough point. As temperature increases, earlier formed minerals dissolve, 

and Zn, Fe, and Pb migrate toward the outer sulfide wall. Tube worms flourished in the outer wall 

of type A samples, and abandoned tube structures 

served as conduits for the late-stage hydrothermal 

fluids. 

Type B sulfide samples are subrounded, 

spongy-textured fragments composed almost entirely of dendritic aggregates of pale Fe-poor colloform sphalerite and opaline silica This type of 

sulfide is deposited in open spaces by moderate- to 

low-temperature fluid discharging at a slow but 

variable rate; the fluid becomes increasingly oxidizing, resulting in late-stage deposition of 

hematite, barite, and sulfur. Type B samples show 

little evidence of burrowing animals. Active and 

inactive chimney samples recently collected by 

ALVIN are dominantly of type B sulfide. A single 

sample recovered in 1983 on the ANGUS camera 

sled is predominantly type B sulfide overprinted 

by late-stage type A mineralization. Additional 

dredged samples are coarse-grained sulfide with 

textures identical to those of recrystallized 

massive sulfide deposits. 

The dredged Zn-rich samples have high bulk 

concentrations of the chalcophile elements Ag, As, 
Cd, Tl, and Ge; however, Au is less than 0.1 ppm 

and Pt less than 0.005 ppm. 

GAS ANALYSIS OF ORE-FORMING FLUIDS 

G.P. Landis 

Precise analysis of the volatiles or gaseous 

fluids trapped in fluid inclusions during mineralization is used to determine physical and chemical 

parameters of metal transport and deposition and 

to better understand the environments of ore formation. Knowledge of the abundance of such gases 

as C02, CH4, S02, H2S, N2, 0 2, NH3, Ar, H2, and 

H20 in mineralizing fluids enables us to significantly refine ore-genesis models. The new mass 

spectrometer instrumentation developed for these 

analyses will also permit isotopic analyses of both 

stable isotopes (C, 0, S, H, N) and radiogenic isotopes (Ar, Ne, Xe, Kr, He) for very small samples 

extracted from fluid inclusions. 

Gas in fluid inclusions and other geologic materials is analyzed using a newly developed highperformance quadrupole mass spectrometer system, equipped with rods 30 em in length by 1.6 em 

in diameter, electromagnetically focused crossbeam ion source with dual iridium filaments, an 

off-axis electron multiplier (gain to 108

)/faraday 

cup collector, and 16K-data-point digital oscilloscope. A mass charge (m/e) range of 1-255 atomic 

mass units (AMU) is achieved, with at least unit 

resolution (10 percent valley), scan speeds of 100 s 

to 30 sf AMU, and a minimum detectable partial 

pressure of 8 X 10-15 mbar (8 ppb sensitivity). 

Instrument monitoring and control are completely 

computerized. FORTRAN- and MACRO-based 

software transfers data, makes computations, and 

produces tabulated analyses and graphical 

reports. 

Gas samples are liberated from host minerals 

either by mechanical crushing or by thermal 

decrepitation. Inlet sample gas pressures (to 10 

Torr) are monitored with a capacitance manometer, whereas the high vacuum attained by turbomolecular pumps ( < 10-9 Torr) is measured with 

standard Bayard-Alpert gauges. Inlet design includes a low volume internal resistive heating coil 

for work on small samples. An Nd-YAG (yttrium 

aluminum garnet) laser coupled through a microscope is being developed to enable opening individual inclusions for analysis while the sample is po28 

sitioned in the mass spectrometer high-vacuum 

inlet. Other features of the instrument include 

cryopump traps and charcoal traps, Zr-Al gettering alloys, a CuO finger, and an ion pump. 

Special applications of the gas analysis 

system that are progressing along with the final 

stages of instrument development include (1) 

study of complex H20-C02-CH4-N2-rich metamorphic fluids of upper greenschist facies rocks as 

possible ore-forming fluids in the Coeur d'Alene 

silver district, Idaho (with D.L. Leach), (2) evaluation of the importance of magmatic volatiles during comagmatic evolution and formation of Black 

Range (Taylor Creek) tin occurrences, New Mexico 

(with R.O. Rye and M.D. Wasserman), (3) assessment of the role of volatiles in the complex zonation and evolution of the Ta-bearing Harding 

pegmatite, northern New Mexico, (4) examination 

of organic components in the fluid inclusion gas 

from epigenetic sulfides in coal beds (with J .F. 

Whelan), and (5) development of data processing 

methods for quadrupole measurement of the carbon and oxygen isotope ratio of carbon dioxide 

fluid inclusions. By using appropriate collection 

procedures, inexpensive analytical methods for 

gas can be applied empirically to geochemical exploration for base- and precious-metal deposits. 

PRECIOUS AND BASE METAL MINERALIZATION 

IN THE COEUR D'ALENE DISTRICT, IDAHO, 

DURING PROTEROZOIC METAMORPHISM 

OF THE BELT BASIN 

David L. Leach, G. P. Landis, and Albert H. Hofstra 

Silver and lead-zinc-copper veins in the Coeur 

d'Alene district in northern Idaho occur in the 

most intensely and complexly deformed parts of 

the Proterozoic Belt Supergroup rocks. The rocks 

were regionally metamorphosed to upper greenschist facies during the late Precambrian, and this 

metamorphism, coincident with intense structural 

deformation, produced the vein mineralization. 

The veins were pathways for the escape of large 

volumes of metamorphic fluid and are believed to 

have formed along sites of hydraulic fracture or 

dilation of pre-existing fractures when fluid 

pressure exceeded load pressure. 

The ore is older than and clearly unrelated to 

the Gem stocks of Cretaceous age for the following 

reasons: (1) Coeur d'Alene veins do not cut the 
stocks but instead are sheared into them; (2) 

sulfide zoning is not present in veins about the 

stocks; (3) parts of veins within the contact aureole 

of the Gem stocks contain metamorphic garnet 

and biotite and recrystallized sulfide textures not 

observed outside the aureole; (4) Gem stocks are 

"dry" intrusions that have sharp contacts with 

Belt rocks, lack miarolitic cavities or pegmatitic 

textures, and lack abundant hydrous minerals and 

hydrothermal alteration; and (5) lead isotopes from 

the ore are radiogenic Precambrian lead, distinctly 

different from lead of the Cretaceous intrusions. 

Fluid-inclusion studies provide strong evidence that vein mineralization was produced by 

greenschist metamorphic fluids. These studies indicate that the temperature of the mineralizing 

fluid was about 350° C, the pressure was more 

than 1-2 kbar, and the salinity was 5-10 weight 

percent. Fluid compositions are dominated by 

H20, C02, CH4, N2, and NaCl. Some fluid inclusions rich in C02, N 2, or CH4 are believed to have 

trapped immiscible fluids present in the veins 

under metamorphic conditions. In addition to 

these components, other volatiles in the ore fluid 

represent refractory compounds of nitrogen and 

light-chain hydrocarbons that include alkenes, 

aliphatic nitriles, and primary ami des. Water present in the fluid inclusions is highly radiogenic and 

has variable strontium isotopic compositions (initial 87Sr/86Sr of > 1.000 to 1.420) that are characteristic of unhomogenized, greenschist-grade 

metamorphic fluids. 

Other evidence also supports the concept of 

mineralization by metamorphic fluids. (1) Veins occur along brittle fractures developed during major 

deformation of the rocks. (2) Veins having a vertical extent of as much as 8,000 feet do not show 

strong T-P gradients or mineral zones. (3) Extensive areas of hydrothermally altered rocks did not 

form. (4) Numerous veins of similar mineralogic 

and geologic character occur over a wide area in 

the region and yield similar fluid-inclusion T-P-X 

data. (5) Analysis of a coarse-grained sericite from 

a mineralized vein yielded a K-Ar age of 829 Ma, 

approximately coincident with the isotopic age for 

deformation, metamorphism, and uraninite vein 

mineralization. (6) The range in o34S of probable 

sulfur source(s) in the host rocks is approximately 

-6 to + 18 per mil, whereas that in vein sulfides 

reflects a narrower range indicative of sulfur 

isotope homogenization in the metamorphic fluid. 

The distribution of mineralization was con29 

trolled initially by stratigraphic permeability, producing disseminated replacement mineralization; 

later, when fracture permeability dominated the 

fluid flow dynamics, ore minerals were localized in 

major fractures or veins. Mechanisms for mineral 

deposition include changes in pH, /02, and other 

chemical parameters of the ore fluid by loss of 

volatiles, immiscibility in the H20-C02-NaCl 

system, and C02-CH4-H2 equilibria 

PARTIAL CHEMICAL EXTRACTIONS-THEIR 

APPLICATION TO GEOCHEMICAL EXPLORATION 

FOR ORE DEPOSITS IN THP 

TROPICAL ENVIRONMENT 

Robert E. learned, T. T. Chao, and 

Richard F. Sanzolone 

The objectives of our investigations were to 

determine the mode in which ore-related metals are 

bound in geochemical sample media of mineral dis· 

tricts of the tropical environment and the best use 

of that information in geochemical exploration. 

Accordingly, we applied partial chemical extraction procedures to determine the distribution of 

trace metals among the mineralogic and chemical 

phases that constitute several geochemical sample 

media of two porphyry copper districts in Puerto 

Rico. 

In saprolite, soil, and stream sediment of the 

districts, the secondary iron oxide phases bear the 

highest proportion of ore-related metals; silicate, 

sulfide, and organic phases bear substantially 

lower proportions. Moreover, the secondary oxide 

phases provide significantly stronger geochemical 

contrasts (anomaly-to-background ratios) than do 

other phases or the bulk media Only in unweathered rock (drill core) of the deposits is the sulfide 

phase an important bearer of ore-related elements. 

Distinctive patterns of apportionment of trace 

metals among phases thus characterize particular 

geochemical sample media of the district, and such 

patterns reflect the intensity of the chemical processes that attended the formation of respective 

media 

Partial chemical extraction procedures demonstrably have significant application to both the 

orientation and interpretive stages of geochemical 

exploration for metallic deposits in the tropical 

environment. 
METALS IN PLANTS-EXPLORA liON OF 

THE RED MOUNTAIN 

GOLD-BEARING STOCKWORK, 

YELLOW PINE DISTRICT, IDAHO 

B.F. Leonard, J.A. Erdman, and D.M. McKown 

New exploration targets for gold, molybdenum, tungsten, and tin are indicated by the 

systematic distribution of metals in soil and plants 

of the Red Mountain stockwork and its environs. 

The stockwork is built of countless quartz veins 

and veinlets, is extensively argillized, and contains 

sparsely disseminated gold, pyrite, arsenopyrite, 

pyrrhotite, fluorite, and other minerals. The 

stockwork developed along the outer ring-fracture 

zone of the Eocene Quartz Creek cauldron where 

subsidence strain, unrelieved by radial faulting, 

produced internal deformation and intense smallscale fracturing in rocks of the Idaho batholith. 

The stockwork crops out as a fault-bounded polygon 2, 700 ft (820 m) long and 2,000 ft (600 m) wide. 

It contains (underlies?) a large, virtually barren 

quartz body 1,350 ft (410 m) long and 350 ft 

(100m) wide. Deformed and shattered granite 

flanks and presumably underlies the stockwork, 

which may plunge southward beneath inclusionbearing granodiorite and alaskite of the Idaho 

batholith suite. Narrow dikes of rhyolite and latite 

radiate from two centers within the quartz body. 

Many dikes and small bosses of rhyolite and latite 

intrude stockwork and granite. The radial habit of 

some dikes and the high concentration of small intrusions within alteration zones of sericite and 

kaolinite suggest that a Tertiary porphyry is concealed beneath the mountain. Clay-mineral alteration zones mapped in residual soil extend far outward from the stockwork. Valleys filled with 

Quaternary deposits conceal the stockworkgranite complex on the east, north, and west. 

Metal anomalies in soil of a gridded area 

3,600 ft (1,100 m) by 8,400 ft (2,600 m) are mostly 

weak and small. In contrast, metal anomalies in 

plants are strong and large. Gold in ashed sapwood of Douglas-fir (Pseudotsuga menziesii) indicates a major Au anomaly, peak value 14.2 ppm, 

associated with granodiorite in an unexplored area 

south of the exposed stockwork. Locally, the Au 

anomaly is accompanied by a sizable tin anomaly, 

peak value 100 ppm, in Douglas-fir. Molybdenum 

concentrations in ashed leaf samples of beargrass 

(Xerophyllum tenax) indicate an extensive anoma30 

ly within a 2-mi-long (5-km-long) semielliptical belt 

in which Mo values exceed the median value, 

20 ppm. The maximum Mo concentration is 

500 ppm. Most of the belt occurs on valley fill, but 

the southern segment of it, near the major Au 

anomaly, is underlain mainly by granodiorite. 

Here, where beargrass is sparse, the peak value of 

Mo in beargrass drops to 70 ppm. Where beargrass is absent, ashed leaves of sedge (Carex 

geyeri) were used; these samples contain up to 100 

ppm Mo. An additional target for Mo is indicated 

by molybdenite from the inaccessible part of a 

prospect adit. The molybdenite, seen only in dump 

specimens, is in weakly silicified granite that may 

underlie part of the stockwork. The source of the 

molybdenite is hidden, and it is not indicated by 

geochemical data for samples of soil or plants. 

Just north of the major Au anomaly, in an area of 

float containing disseminated scheelite in weakly 

silicified granodiorite, 2-ppm values of W in beargrass coincide with a W anomaly in soil (peak 

value 22 ppm). Other areas characterized by 2 ppm 

W in beargrass are nearly coextensive with the 

Mo-in-beargrass anomalies that overlie Quaternary deposits of Quartz Creek valley. Some of the 

target areas for Au, Mo, W, and Sn have not been 

circumscribed by our sampling. The results suggest the presence of a concealed elliptical substructure that may be hoodlike and may contain more 

than one mineralized zone. 

MINERAL DEPOSIT MODELSTHEORY AND PRACTICE 

Steve Ludington and Paul Barton 

By the authority of the Organic Act of 1879, 

the USGS has the responsibility for ''classification 

of the public lands and examination of the ... 

mineral resources and products of the national domain." A vital tool used to fulfill this responsibility is the mineral deposit model. We define a model 

here as systematically arranged information that 

describes the essential attributes of a complex 

process or product. 

The uses of models may be classified as follows: (1) guidance of land-use planning, (2) estimation of potential commodity supplies or endowment, (3) support of prospecting, (4) education, and 

(5) guidance of research. 
Models may be grouped into subtypes such as 

(1) descriptive, (2) genetic, (3) probability-ofoccurrence, (4) grade/tonnage, and (5) quantitative 

process. Descriptive models together constitute a 

deposit classification and are a prerequisite for 

other types. Alone, they are most useful for research guidance and prospecting. Genetic models 

link the characteristics of descriptive models to 

underlying geologic processes and, because they 

are predictive, are extremely powerful for prospecting, as well as for education and research 

guidance. Probability-of-occurrence models result 

when numerical measures of importance are attached to descriptive characteristics in order to 

provide a numerical estimate of mineral potential. 

Implementation of these is in its infancy, but clearly they will be most useful for land planning and 

resource estimation. Grade/tonnage models use 

compilations of grade and tonnage information 

and allow assignments of probable value to be 

made. They are most useful for resource estimation and land-use planning. Quantitative process 

models result from the quantitative study of 

phenomena such as mass and energy transfer, and, 

at present, are used chiefly for research guidance 

and education. 

The generality of the USGS mandate results 

in a different approach from that of most other 

model users. In mineral exploration, for example, 

activity might progress from the identification of a 

commodity to selection of appropriate models, followed by their application to the goal of identifying new deposits. In contrast, the programs of the 

USGS approach models from a geographic context. Collection of geologic information precedes 

model selection. For example, in support of landuse planning, we are concerned with all commodities, and we build from the observations relating 

to a tract of land to a determination of mineral 

potential. Single attributes, such as "Secondary 

biotite is present,'' are generally ambiguous, 

although they may well suggest what additional 

observations might be made. Combinations of attributes are used to identify specific models, and 

new combinations may lead to new models. We are 

working to smooth and, where appropriate, to 

automate that identification. 

Fulfillment of our mission has two distinct 

parts: appropriate information about the earth 

must be generated and must be communicated to 

the public. The model effort promises to be a 

powerful contributor to both science and society. 

31 

EARLY AND MIDDLE CENOZOIC 

VOLCANIC SYNTHESIS 

Robert G. Luedke 

Maps for the middle and early Cenozoic volcanic centers (16-55 Ma) in the western conterminous United States are now being compiled in a 

manner similar to a series of seven maps showing 

the distribution, composition, and age of late 

Cenozoic volcanic centers (0-16 Ma) in the 

Western United States, Alaska, and Hawaii, 

which are published or in the process of publication (USGS Miscellaneous Investigations Series 

Maps I-1091). Those maps portray vent types, 

locations, and ages and major rock types and ages 

in the volcanic centers at the scale of 1:1,000,000; 

special larger scale maps show specific areas. That 

map series was designed primarily as a guide for 

exploration and evaluation of igneous-related 

geothermal resources but also serves as a base for 

evaluation of volcanic hazards and for studies of 

evolution of magmatic systems, related ore 

deposits, and general geology of volcanic rocks. 

For the new map series, most of the basic data 

have been accumulated for the Arizona-New Mexico-west Texas area; future work will cover all the 

conterminous Western States, within which a 

large number of the known mineral deposits are 

closely associated with or related to igneous 

centers. The rocks in these centers are being 

depicted in selected major rock compositions 

within arbitrarily established silica increments, in 

three age categories within the 16-55 Ma time 

frame, and as extrusive or intrusive types. The 

distribution of these volcanic-intrusive centers in 

the Western United States is known, but the quality and quantity of data varies. Also, the existing 

data are not on a map at a single scale and do not 

permit distinguishing the igneous rocks in a uniform manner throughout the region. 

Analysis of the temporal and spatial relations 

among igneous rock types, their tectonic relations, 

and their relation to ore deposits is fundamental to 

present and future progress in research on ore 

deposition, tectonism, and magmatism. Synthesis 

of the geological and geochemical data illustrated 

on this new series of maps will be used to produce 

models that will guide exploration for ore deposits 

and improve resource assessment. 
EXPERT SYSTEMS RESEARCH IN 

REGIONAL RESOURCE EVALUATION: 

EXPERIENCES IN THE APPLICATION OF 

MICROCOMPUTER TECHNOLOGIES 

Richard B. McCammon 

muPROSPECTOR, patterned after SRI's expert system PROSPECTOR, is designed to aid the 

geologist in evaluating the mineral resources 

within a given geographic area The central idea of 

the system is matching deposit models encoded by 

expert economic geologists against observations 

made by field geologists. muPROSPECTOR is a 

microcomputer-based system that can be applied 

to problems in regional mineral resource evaluation. To date, the knowledge base that has been 

incorporated in muPROSPECTOR consists of 

deposit models constructed as part of the mineral 

resource assessment in the Sherbrooke-Lewiston 

1 o X 2° quadrangles in New England. Included 

are models for volcanogenic massive sulfide, 

sediment-hosted lead-zinc-silver, tin greisen, porphyry copper, vein-type uranium, uraniferous 

peat, and tin-placer deposits. These models are 

represented in the knowledge base as a set of rules 

derived from recognition criteria developed for 

each deposit type. 

In a normal consultation with muPROSPECTO R, the geologist is asked a series of questions 

relating to various pieces of evidence that might 

be present in an area Answers to these questions 

lead muPROSPECTOR to an evaluation of the 

mineral resources in the area. The evaluation consists of a probabilistic estimate for one or more 

deposits occurring in the area for each of the 

deposit types being considered and the reasons 

upon which the evaluation for each deposit type is 

based. At any time during the consultation, the 

geologist can ask muPROSPECTOR to summarize and make an evaluation based on the current 

information. The intent of the system is to provide 

the geologist with services equivalent to telephone 

access to a panel of experienced economic geologists, each an authority on a particular type of 

deposit. 

Experience with muPROSPECTOR has indicated that improvements in designing future expert systems for regional resource evaluation are 

needed in knowledge representation, reasoning 

mechanisms, and knowledge acquisition. Current 

limitations in knowledge representation are the 

result of insufficient expressiveness of the 

32 

language used to encode deposit models. Insufficient general knowledge of the geology of most of 

the models that have been constructed is also a 

major problem. What is needed are methods for 

matching observations volunteered by geologists 

about the general geologic, geochemical, and 

geophysical setting in an area with the attributes 

of existing models. With respect to reasoning 

mechanisms, control strategies are needed that 

take into account the more or less imperceptible 

grading of the characteristics of one deposit type 

into those of other deposit types. Current control 

strategies make restrictive assumptions about the 

interdependency of multiple sources of evidence 

and the manner in which they combine. With respect to knowledge acquisition, methods are 

needed for screening of data bases compiled for ore 

deposits, formulation of less-than-perfect models 

that others can subsequently modify easily, and 

computer-assisted instruction in deposit modeling. 

Future developments in muPROSPECTOR will 

require a close working relationship with economic 

and field geologists. 

APPLICATIONS OF THE MINERAL RESOURCES 

DATA SYSTEM AND THE INTERNATIONAL 

STRATEGIC MINERALS INVENTORY IN 

MINERAL-RESOURCE ASSESSMENTS 

BY REGION AND COMMODITY 

Antoinette L. Medlin, David M. Sutphin, and 

John H. DeYoung, Jr. 

From 1972 to 1982, the USGS developed the 

Computerized Resources Information Bank 

(CRIB). CRIB, a centralized data base, was initiated to meet the growing need for rapid access 

to data on mineral deposits and occurrences. 

Regional and commodity information was collected from geologists and commodity specialists 

at the USGS, other Federal agencies, and State 

geological agencies. In 1982, CRIB was used as 

the basis for establishing the Mineral Resources 

Data System (MRDS), which applies computerized data to mineral-resource assessments. 

MRDS contributes to several current USGS 

programs, including the Federal Mineral Land Information System (FMLIS), the Conterminous 

United States Mineral Assessment Program 

(CUSMAP), and the Alaska Mineral Resource 

Assessment Program (AMRAP). Data from 
MRDS are merged with digital boundary files in 

the FMLIS program to define areas with estimated potential for mineral resources. Effects of 

proposed land withdrawal and other existing or 

proposed limitations on mineral development can 

be graphically analyzed for selected areas. MRDS 

is a repository for data derived from CUSMAP 

and AMRAP studies and, when a new CUSMAP 

or AMRAP quadrangle is started, as a source of 

data for analysis to eliminate duplication of effort. 

MRDS includes the capability of storing data 

on mineral deposits and occurrences for use in 

deposit-type studies. Geodetically located information can be plotted in relation to digital data for 

area geology maps, regional terrane maps, geopolitical boundary maps, and other map bases that 

have been digitally recorded. Foreign and domestic data can be analyzed regionally and on a commodity basis in relation to known or suspected 

geologic features. 

One of the goals of the MRDS is to have data 

coverage by area and commodity for the major 

domestic and foreign deposits. One method to expand and improve the data for commodities was to 

use the existing cooperation with personnel involved in resource analysis in Canada and Germany. Initial planning sessions with members of 

earth-science and mineral-resource agencies in the 

United States, Canada, and Germany, and later 

South Africa, Australia, and the United Kingdom, 

led to the establishment of the International 

Strategic Minerals Inventory (ISMI) in November 

1981 to gather, analyze, and present information 

on major deposits of selected strategic mineral 

commodities. A basic premise is that, for many 

commodities, much of the current and near-future 

production is and will be from the few largest 

deposits. A data collection form for ISMI was 

designed and guidelines for data collection 

established. Participating countries agreed to a 

prototype phase of data collection with manganese, chromium, phosphate, and nickel as the subjects of initial study. In October 1983, work 

started on six additional commodities; these commodities and the country assigned as chief compiler are titanium-Australia, tungsten-Canada, 

graphite-Germany, vanadium-South Africa, 

cobalt-United Kingdom, and the platinum-group 

elements-United States. ISMI products include 

published circulars and data sets, including expert 

opinions on major deposits, which are a part of 

MRDS. 

33 

FISSION-TRACK DATING 

APPLIED TO MINERAL EXPLORA liON 

C.W. Naeser and Charles G. Cunningham 

Fission tracks are cylindrical zones of intense 

ionic disruption, which are formed in uraniumbearing solids by the passage of highly charged 

nuclei from the spontaneous fission of 238U. Once 

formed, these tracks are stable in most minerals at 

temperatures less than about 80° C. If the mineral 

is heated above a critical temperature, the tracks 

will disappear (anneal) as a function of time and 

temperature. For periods of geological time, the 

critical temperature for apatite is 120 ± 20° C; for 

zircon, it is 200 ± 30° C. Upon cooling these 

minerals will again begin to accumulate fission 

tracks. 

The partial to total resetting of fission-track 

ages of apatite and zircon in country rock around a 

mineralized area can be used to (1) locate a 

paleothermal anomaly, (2) determine the age of a 

paleothermal anomaly that may coincide with a 

mineralizing event, and (3) determine the direction 

toward the heat source. Two mining districts in 

Colorado have been studied, Rico and Gilman. 

Rico is a precious- and base-metal mining 

district. Sedimentary rocks throughout the 

district were intruded at 65 Ma by hornblende 

latite porphyry sills. Initial fission-track dating of 

a sill located about 6 km from the center of the 

district gave a reset age of 20 Ma for apatite and 

the age of intrusion of 65 Ma for zircon. Subsequent sampling and dating of sills closer to the 

mineralized area indicated the presence of a 

roughly concentric paleothermal anomaly with an 

age of about 5 Ma centered east of town. We interpret this to indicate the location of a large, unexposed, rhyolite stock of Pliocene age; the 

mineralization was caused by this stock, rather 

than by events associated with the intrusion of the 

Late Cretaceous monzonite stock exposed at the 

surface just west of the town. 

The ore body of the Eagle Mine, in the Gilman 

district, occurs as a manto deposit of sulfides that 

was deposited in a Paleozoic karst cave system in 

the Leadville Dolomite. Fragments of the Pando 

Porphyry (about 70 Ma) found in the cave floor 

breccia are surrounded by a sulfide-bearing 

matrix, indicating the age of the ore body must be 

younger than Late Cretaceous. A paleothermal 

anomaly defined by fission-track dating of apatite 
Fission tracks in apatite; large crystal is about 0.25 mm 

across 

and zircon circumscribes the ore body at the Eagle 

Mine, even though virtually no alteration of the 

country rock adjacent to the deposit is observed. 

Fission-track ages of apatite and zircon were 

determined for samples of the Pando Porphyry 

(present throughout the district), of the Precambrian rocks in the Eagle River Canyon 180 m 

below the ore body, and of Precambrian rocks 

sampled from cores drilled directly beneath the ore 

body. Apatite from a vug filling in the ore body 

was also dated. Preliminary stable-isotope and 

fluid-inclusion data suggest that the ore deposit 

was formed at temperatures in excess of 300 o C, 

well above the fission-track annealing temperature 

for both apatite and zircon. The fission-track 

results indicate that the age of the thermal anomaly is about 34 Ma and that a major paleothermal 

anomaly extends more than 1.5 km from the deposit. Zircon from the Pando Porphyry 0.5 km 

north of the Eagle Mine and apatite from the ore 

body have ages of 34.0 ± 1.5 Ma and 34.5 ± 

2.6 Ma, respectively. Zircon from the Pando Porphyry 1.5 km north of the Eagle Mine yields an 

age of about 45 Ma, indicating only partial resetting of the age by the thermal event that is 

associated spatially with the ore deposit. None of 

the ages from the Precambrian rocks below the 

deposit have been significantly reset. These data 

suggest that the source of the thermal anomaly 

was not directly beneath the deposit. 

34 

A MULTIDISCIPLINARY RESOURCE ASSESSMENT 

OF THE CHUGACH NATIONAL FOREST, ALASKA 

Steven W. Nelson 

The Chugach National Forest, a 9,000-mi2 

(23,000-km2

) area, is the second largest national 

forest in the United States and the largest national 

forest evaluated under the National Forest 

Wilderness Act. A multidisciplinary resource 

assessment was conducted between 1979 and 

1982. The largely reconnaissance-scale study by 

the U.S. Geological Survey included geologic mapping; regional aeromagnetic and gravity surveys; 

stream-sediment, panned-concentrate, bedrock, 

and organic-geochemistry studies (for hydrocarbons); and stable-isotope geochemistry and fluidinclusion studies of specific mineral deposits. Concurrently, the U.S. Bureau of Mines conducted 

mapping and geochemical and mineralogical 

studies of mines, prospects, and mineral occurrences. From these studies, 25 resource areas were 

identified. To facilitate land-planning decisions, 

these areas have been ranked, from most favorable 

to least favorable, for potential for additional 

resources of those commodities (Au, Cu, oil, coal) 

with a history of production in the study area 

The geology of the national forest is dominated by two major lithologic units, the Late Cretaceous Valdez Group and the Paleocene and (or) 

Eocene Orca Group. Both groups, separated by 

the Contact fault system, consist largely of metamorphosed to unmetamorphosed graywacke, siltstone, and shale. The Orca Group has traditionally 

been considered to be somewhat less metamorphosed than the Valdez Group and to be further 

distinguished from it by the presence of mafic 

volcanic rocks and local beds of conglomerate. Our 

mapping, however, has shown that these rock 

types are found in both groups. Sedimentary 

rocks, in part younger than the Orca Group, crop 

out in the southeastern part of the project area 

Plutonic rocks were emplaced in Eocene and 

Oligocene time. Most of the plutons are granitic in 

composition, but an early phase of the Oligocene 

plutons ranges in composition from quartz diorite 

to gabbro. 

Previous studies7 have suggested that the 

'Tysdal, R.G., and Case, J.E., 1982, Metalliferous mineral resource 

potential of the Seward and Blying Sound quadrangles, southern Alaska: 

U.S. Geological Survey Miscellaneous Field Studies Map MF-880-H, 

scale 1:250,000. 
w 

1.11 

Columbia Glacier entering Prince William Sound (tidewater), Chugach National Forest, and Chugach Mountains, southern Alaska 
Valdez and Orca Groups represent two different 

metallic mineral provinces. The Valdez Group is 

characterized by deposits worked for gold and the 

Orca Group by deposits worked for copper. This 

distinction is weakened by our study, which shows 

that the copper deposits appear to be related to 

mafic volcanism and are generally found in, or 

spatially related to, mafic volcanic rocks in both 

the Valdez and Orca Groups and that the goldbearing deposits occur in quartz fissure veins apparently hosted by various rock units. Gold, for 

example, is found in quartz veins that have been 

dated at 53 Ma, which cut Valdez Group sedimentary rocks, and in quartz veins cutting 34-Ma 

plutons. In these occurrences, the gold-bearing 

quartz veins occur along fractures and shears that 

cut across regional structure and fabric. Stableisotope studies suggest, at least for the older 

veins, that hot meteoric water leached the gold 

from the country rock. In the Orca Group, gold occurrences are restricted to quartz veins cutting 

sedimentary rocks near the 51-Ma McKinley Lake 

pluton and to quartz veins cutting greenstone in a 

few small areas. 

An estimated 264,000 oz. of gold have been 

recovered, from both lode and placer sources. During a 30-year period beginning in the 1900's, nearly 

206,400,000 lb. of copper, with minor amounts of 

gold and silver, were produced. Most of the ore 

was produced from four mines, though small 

amounts of copper were mined from at least 17 

other operations. The placer gold deposits are principally confined to the Kenai Peninsula area, 

although other occurrences have been identified in 

almost all of the metal-bearing resource potential 

areas. 

Extensive coal deposits occur in structurally 

complex Tertiary rocks in the Bering River area, 

and large tonnages of minable coal appear to be 

present. A total of about 20,000 tons of coal was 

produced intermittently in the early 1900's. The 

Katalla area has substantiated potential for oil 

and gas. The production of the field over a 30-year 

period was relatively small (154,000 bbl), and the 

complex structure and lack of suitable reservoir 

rocks in the area suggest that major fields are 

unlikely. 

36 

METALLOCENETIC HISTORY 

OF THE WRANGELLIA TERRANE, 

EASTERN ALASKA RANCE, ALASKA 

Warren J. Nokleberg and lan M. Lange 

Much of the southern part of the eastern 

Alaska Range, in the M t. Hayes, Gulkana, and 

Nabesna quadrangles, consists of the Wrangellia 

terrane, which exhibits a long and complicated 

stratigraphic and structural history and a long 

and complicated metallogenetic history. In the 

eastern Alaska Range, Wrangellia consists mainly 

of ( 1) a thick sequence of late Paleozoic island arc 

rocks, including submarine andesite flows, breccias, epiclastic rocks, volcanic graywacke, argillite, 

marble, and altered andesite and dacite porphyries, disconformably overlain by (2) Middle to 

Late Triassic Nikolai Greenstone, intruded by (3) 

cumulate mafic and ultramafic rocks probably 

comagmatic with the basalt flows of the Nikolai 

Greenstone, and disconformably overlain by (4) 

Late Triassic limestone. These and other terranes 

are unconformably overlain by Late Jurassic and 

Early Cretaceous flysch and intruded by isolated 

plutons of probable Late Jurassic and Early 

Cretaceous age. The Wrangellia terrane exhibits 

upper greenschist facies metamorphism with a 

weak cleavage or schistosity. 

Six principal types of mineral deposits and occurrences are found in Wrangellia in the eastern 

Alaska Range: (1) Small areas of sulfides, up to a 

few meters wide, with anomalous concentrations 

of Cu, Ph, Zn, Ag, and Au, occur in fracture zones 

and are disseminated in hydrothermally altered 

late Paleozoic volcanic rocks. Common sulfide 

minerals are chalcopyrite, bornite, sphalerite, and 

pyrite. (2) Pods and lenses of massive sulfides and 

skarn deposits containing chalcopyrite and pyrite 

with anomalous concentrations of Cu, Ag, and Au 

occur in marble and in hydrothermally altered 

volcanic rock adjacent to Permian andesite and 

dacite porphyries. Maximum dimensions are a few 

meters. (3) Local disseminated sulfides with 

anomalous concentrations of Cu, Ph, Zn, and Ag 

occur in hypabyssal Permian andesite and dacite 

porphyries. These porphyries are often propy-
Kennecott mill and tailings at base of Bonanza Ridge, Wrangell Mountains, southern Alaska 

litically altered, contain calcite and chalcopyrite 

veinlets, and are laced with disseminated chalcopyrite and pyrite. (4) Disseminated grains and 

lenses of Ni-bearing chromite occur in layers in 

cumulate mafic and ultramafic rock in extensive 

sills. (5) Disseminated sulfides with anomalous 

concentrations of Cu, Ag, and Au occur in various 

granitic plutonic rocks. These granitic rocks commonly contain very fine grained K-feldspar, 

quartz, secondary sericite, and pyrite, and minor 

chalcopyrite in fractures and isolated grains. (6) 

Sulfides with anomalous concentrations of Cu, Ag, 

and Au occur in quartz veins and associated altered Nikolai Greenstone and older metavolcanic 

rocks. The common sulfides are chalcopyrite, 

bornite, and pyrite. 

37 

Our preliminary accretionary terrane model 

relates the origin of these mineral deposits to the 

origin, migration, and accretion of Wrangellia. Initially, subduction formed a late Paleozoic island 

arc. During the early stages of the arc, disseminated and vein sulfide deposits formed in volcanic 

flows and associated rocks. Later, during the final 

stages of the island arc, sulfide deposits formed in 

skarn and volcanic rocks adjacent to shallow porphyries. Subsequent rifting during the Middle and 

Late Triassic resulted in submarine and subaerial 

extrusion of the Nikolai Greenstone and emplacement of associated cumulate mafic and ultramafic 

rock containing disseminated grains and lenses of 

chromite. In the Late Jurassic through Late Cretaceous, subduction and formation of an island arc 
along the leading edge of Wrangellia occurred during migration towards North America This 

resulted in intrusion of plutonic rocks containing 

disseminated and vein base-metal sulfides and in 

local skarn formation adjacent to granitic plutons. 

Finally, Wrangellia was accreted onto the western 

margin of North America during the middle or 

Late Cretaceous, resulting in regional greenschist 

facies metamorphism and deformation that culminated in formation of late-stage quartz sweat 

veins and altered areas with Cu-, Ag-, and Aubearing sulfides. This model may be an important 

predictive tool for mineral resource assessment 

and for discovery of new mineral deposits in 

Wrangellia throughout the North American 

Cordillera. 

SEDIMENT-HOSTED ORE DEPOSITS: 

GENETIC PROCESSES INFERRED FROM THE 

MINERALOGIC, CHEMICAL, AND ISOTOPIC 

COMPOSITION OF CLAY MINERALS 

H. Roy Northrop and Gene Whitney 

The characterization of mineralogic, chemical, 

and isotopic compositions of authigenic clay 

minerals enables recognition of the influence of 

sedimentary-basin-derived fluids on the genesis of 

sediment-hosted ore deposits. A case in point is 

the vanadium-uranium deposits hosted by the 

Morrison Formation (Upper Jurassic) in the Henry 

structural basin, Utah. There, an abrupt upper 

boundary and diffuse lower boundary of the 

vanadium-uranium mineralized interval occurs 

within an otherwise homogeneous sandstone body. 

The clay assemblage changes from authigenic 

kaolinite and smectite in barren rocks to 

vanadium-rich chlorite in the mineralized interval. 

The oxygen and deuterium isotopic compositions 

of these phases reflect the effects of a densitystabilized fluid interface between isotopically 

heavy brine (probably evolved from seawater) and 

isotopically light meteoric water. Isotope data in· 

dicate that vanadium-rich chlorite, the predomi· 

nant vanadium-ore mineral in the deposits, formed 

at and below this interface within the saline fluid. 

This vanadium chlorite grades into a vanadiumbearing mixed-layer chlorite-smectite in the unmineralized lateral extensions of the deposits; 

reflecting the planar geometry of the ore-forming 

environment. 

38 

Organic-matter-rich fluid inclusion in fluorite, Cave-in-Rock, 

Illinois 

A similar solution interface may have existed 

at the time of uranium mineralization in the 

100-m-thick sandstone sequence of the Westwater 

Canyon Member of the Morrison Formation in the 

San Juan Basin, New Mexico. However, after ore 

deposition, fluid migrations driven by basin subsidence have geochemically altered and redistributed some of the uranium deposits. One such 

alteration, involving the updip migration of warm 

(130° C) fluid from deeper in the basin, is defined 

by a systematic spatial zonation of neoformed 

chlorite and transformed illite-smectite within the 

Westwater sandstone. The proportion of illite in 

the mixed-layer illite-smectite is known to be 

related to potassium uptake, which is a function of 

temperature, time, and availability of potassium. 

The proportion of illite layers in the illite-smectite 

increases both toward the center of the sandstone, 

perpendicular to bedding, and downdip toward the 

basin center, parallel to bedding, as does the abundance of pore-filling chlorite. The oxygen and 

hydrogen isotopic compositions of the illitesmectite vary as a function of the degree of illitization and of position within the basin, whereas the 

isotopic composition of the authigenic chlorite 

remains uniform. At 130° C and in a porous sandstone medium, the apparent limit on the illitization reaction responsible for the mineralogic 

zonation is the aqueous potassium content of the 
migrating fluid. The calculated isotopic composition of the illitizing fluid, and its apparently 

limited potassium content, are consistent with the 

chemistry of ''oilfield brines'' described in several 

midcontinent basins. The broad interest in petroleum occurrences and Mississippi Valley-type 

base-metal deposits, both of which have inferred 

genetic links to the migration of these evolved 

basin waters, attests to the importance of this 

type of geochemical reconstruction. 

ORGANIC MATTER ASSOCIATED WITH 

METAL ORES OF HYDROTHERMAL VENT ORIGIN 

William H. Orem, Patrick G. Hatcher, 

and Elliott C. Spiker 

The recently discovered active submarine 

hydrothermal systems associated with marine 

spreading centers are living laboratories for 

studies of metal ore genesis. Massive sulfides, apparently similar to those associated with 

ophiolites found on land, are currently being 

deposited around these hydrothermal systems. In 

addition, communities of large benthic siphonophores have been observed clustered about these 

submarine hydrothermal vents. The primary 

producers for these communities are apparently 

chemoautotrophic bacteria, which derive energy 

from catalyzing the oxidation of reduced sulfur 

species emanating from hydrothermal vents. 

Results of preliminary studies also indicate the 

presence of large amounts of particulate and 

dissolved organic matter associated with the high 

biological productivity around these vents. 

Organic matter may play a key role in the 

transport and deposition of metals in the deep sea 

In the case of ferromanganese oxide deposits, 

organic matter adsorbed onto active surfaces (such 

as basalts) may initiate the deposition of manganese (IV) oxides. In addition, organic matter adsorbed on the surfaces of metal oxide and sulfide 

deposits may inhibit their dissolution and oxidation, respectively. Organic-matter-metal-ion complexes may also facilitate transport of various 

metal ions to sites of metal oxide or sulfide deposition for incorporation in these deposits. 

We present here the results of a study on 

organic matter associated with massive sulfide 

deposits of known and presumed hydrothermal 

origin. The organic carbon contents of these ores 

39 

ranged from about 0.01 percent to nearly 4.0 percent. In these samples, higher carbon contents 

were associated with pyritic and chalcopyritic 

ores, while sphalerite-rich ores had much lower carbon contents. For example, a massive pyrite ore 

from the Galapagos spreading center contained 

3.0 percent organic carbon. The organic matter in 

this ore had a stable carbon isotope (o13C) value of 

-27.4 percent and a stable nitrogen isotope (o15N) 

value of +2.1 percent. These values are very 

distinctive compared to deep-ocean sedimentary 

organic matter but are similar to values observed 

in benthic organisms associated with active submarine hydrothermal vents. The molar C/N ratio 

of this sample (13.2) suggests a bacterial source for 

the organic matter associated with this metal ore. 

Solid-state 13C nuclear magnetic resonance (NMR) 

spectrum of the organic matter associated with 

the metal ore from the Galapagos spreading center 

has a predominantly paraffinic character, with a 

small aliphatic C-0 (that is, carbohydrate or ether) 

content and minor carboxyl or amide character. A 

small resonance due to aromatic carbon atoms was 

also observed in the spectrum. This spectrum 

resembled 13C NMR spectra of refractory organic 

matter isolated from Holocene marine sediments 

whose source is predominantly algal or microbial. 

The absence of a strong aliphatic C-0 and carboxyl 

or amide resonance in the spectrum suggests that 

the organic matter has been degraded by microbes 

during early diagenesis. 

The organic matter in these ores appears to be 

derived from chemoautotrophic bacterial production surrounding the vents. As the massive sulfide 

deposits form, the organic matter is incorporated 

in the matrix of the ore. Such high concentrations 

within the ore may play a key role in retarding oxidation of the metal sulfides. 

SEDIMENT DISPERSAL PATTERN IN THE 

EMERGED ATLANTIC COASTAL PLAIN 

(NEW JERSEY-GEORGIA) FROM 

EARLY CRETACEOUS TO HOLOCENE: 

A GUIDE TO POTENTIAL PLACER DEPOSITS 

James P. Owens 

Major depositional systems have been defined 

within the lithostratigraphic framework of the 

emerged Atlantic Coastal Plain. In general, delta 

and shelf deposits dominated before the Miocene; 
in the Neogene and Quaternary, barrier and backbarrier facies dominated. Grade and distribution 

of placer and other types of mineral deposits in the 

Atlantic Coastal Plain are controlled largely by 

these depositional systems. 

Placer deposits in the Coastal Plain are characterized by heavy minerals derived from igneous 

and metamorphic rocks. The most common 

opaque minerals are ilmenite and its weathering 

products. Magnetite, the other common iron oxide, 

is present in major concentrations only in upper 

Pleistocene and Holocene beds even though it is a 

major opaque mineral in the Piedmont rocks adjacent to the Coastal Plain. The most common nonopaque minerals are zircon, tourmaline, and rutile 

(ZTR); hornblende, epidote, and garnet (plus actinolite and tremolite, HEGAT); and staurolite, 

sillimanite, and kyanite (SSK). Chloritoid, monazite, and igneous apatite are locally abundant. 

Numerous other minerals are present, but these 

occur only in minor to trace amounts and are 

economically unimportant. 

Immature mineral assemblages are characterized by easily alterable non-opaques (HEGAT) and 

relatively fresh ilmenite and magnetite; mature 

mineral assemblages dominantly contain hard, 

chemically impervious non-opaques (ZTR) and 

weathered, iron-poor ilmenite. Maturity of placer 

mineral assemblages is a product of the 

mineralogy of the source rocks and the amount of 

physical and chemical alteration during and after 

deposition. The degree of maturity is thus linked 

to the depositional facies and the amount of time 

the sediment has remained in the emerged, actively oxidizing part of the Coastal Plain. 

One example of the relationship of environment and maturity is the commercial concentration of ilmenite found in barrier facies of Florida 

and New Jersey. In both regions, ilmenite is most 

abundant in the oldest barrier systems in the 

region and is associated with a limited non-opaque 

assemblage (ZTR dominant). In the younger barrier systems in both regions, the concentration of 

ilmenite decreases as the proportion of HEGAT 

minerals increases, hence reflecting a decrease in 

maturity. Whether this relationship is a function 

of differences in the source rocks or a reflection of 

time of residence in outcrop is still uncertain. 

Another example of the relationship of mineral concentration to depositional environment is 

the distribution of igneous phosphates, mainly 

monazite and less commonly apatite. Both min40 

erals are locally widespread in upper-delta-plain 

facies of the basal units of the Coastal Plain (Cretaceous), especially near the Fall Line. Apparently 

these minerals do not survive long transport or 

passage through the high-energy, nearshore 

marine environments because of their relative softness. Search for these minerals in potentially 

economic placers should be restricted to nonmarine, updip facies of the Coastal Plain. 

In the emerged Coastal Plain, stratigraphic 

units of the same age (time slices) have characteristic heavy-mineral assemblages, which can guide 

shallow subsurface investigation for economic 

placers. 

STUDIES OF ORE DEPOSITS IN THE EARLY 

MAGMATIC ENVIRONMENT: THE STILLWATER 

COMPLEX, MONTANA 

Norman J Page, W.J. Bawiec, R.J. Blakely, 

G.K. Czamanske, L.J. Drew, Michael P. Foose, 

R.L. Helz, M.D. Kleinkopf, Bruce R. Lipin, 

Patricia J. Loferski, J.H. Schuenemeyer, 

and M.L. Zientek 

The Stillwater Complex is a large Precambrian 

layered stratiform intrusion that crops out on the 

northern edge of the Beartooth Mountains in 

southwestern Montana and, as interpreted from 

geophysical studies, extends northward beneath 

the surface. A cooperative project composed of 

government, industry, and academic geoscientists 

has been investigating the Stillwater, in order to 

develop a detailed understanding of the genesis of 

the magmatic ore deposits it contains. The 2.7 to 

3.1 Ga intrusion is divided into three major stratigraphic units, each of which has its own characteristic mineralization: the Basal series, with 

disseminated to massive Cu-Ni-Fe sulfides; the 

Ultramafic series, with stratiform chromite 

deposits; and the Banded series, with platinumgroup elements (PGE) hosted in disseminated 

sulfide zones. 

Within the Basal series, detailed mineralogic 

and geochemical studies indicate that Fe-Cu-Ni 

sulfides result from intrusion of magma saturated 

with sulfide at the time of intrusion. This interpretation is supported by the presence of sulfiderich dikes of mafic norites. Sulfur isotopic and 

lithologic studies do not suggest contamination or 
Photomicrograph of reaction replacement texture in poikilitic chromite-olivine cumulate, 

Ultramafic zone, Stillwater Complex, Montana 

sulfur assimilation as the formative mechanism 

for these deposits. Cu-Ni concentration data and 

discriminant analysis can be used to map concentration units correlative with petrologicstratigraphic units. Investigations focused on the 

sills and dikes associated with the Basal series 

suggest that most of the fine-grained igneous 

rocks, previously interpreted to represent parental 

magma(s) of the complex, do not have compositions that could generate the rocks in the complex. 

Sills and dikes of gabbro-noritic composition with 

some textures apparently derived from rapid cooling occur immediately below the Basal series and 

are the most probable representatives of the 

parent magma of the complex. 

Within the Ultramafic series, detailed field, 

mineralogic, and geochemical studies focused on 

the chromite seams and the associated cumulates. 

Pegmatoids containing pyroxene, plagioclase, and 

lesser amounts of olivine, chromite, and biotite are 

closely associated with the chromite seams and 

may be above, below, or within the seam. These 

pegmatoids are commonly irregular and patchy 

and not everywhere stratiform, but they are 

always stratabound. This suggests a genetic relationship between chromite seams and the devel41 

opment of pegmatoids; pressure fluctuations may 

explain the origin of chromite seams. 

Within the Banded series, structural studies 

of sedimentary-like features and mineralogic and 

geochemical studies, particularly above and below 

the J-M Reef, have helped to unravel this complex 

series of rocks. Specifically, studies of structures 

including slumps, ramps, basins, and on-lap and 

off-lap of modal layers can be used to identify the 

larger primary basins in the Banded series that appear to be responsible for thickening and thinning 

of the mineralized zones. Recognition of mappable 

unconformities, combined with mineral composition and assemblage data, suggests successive 

additions of new magma to the Stillwater chamber. The hypothesis for origin of the platinumgroup element zones involves both features of 

sedimentary-like accumulating piles of crystals 

and interrelated changes in the chemical and 

physical properties of the parent magmas. 

The major types of mineralization exhibit 

similarities in mineralogy, chemistry, and structures; however, there are many differences in 

enrichment of metals, in their distribution, and in 

the relative importance of chemical and physical 

processes that may have produced the deposits. 
RECENT STUDIES OF THE 

DISTRIBUTION OF BACILLUS CEREUS 

NEAR SUBSURFACE GOLD DEPOSITS 

Nancy l. Parduhn, john R. Watterson, 

and Miles l. Silberman 

Results of several soil surveys in the vicinity 

of subsurface gold deposits show that an aerobic 

spore-forming soil bacterium, Bacillus cereus, 

often occurs in greater numbers or as a greater 

percentage of the Bacillus population in soils 

overlying mineralized bedrock than in adjacent, 

unmineralized terrain. 

In Clear Creek County, Colorado, the distribu· 

tion of B. cereus was studied in ten 01 and A1 soil 

horizon samples overlying gold veins. The veins 

are covered by 3-5 m of glacial overburden. B. 

cereus culture counts from both soil horizons are 

at least an order of magnitude higher in soils over 

the gold veins than in immediately adjacent soils. 

In a previous USGS study of soil geochemistry in 

this district, A1 soil horizons were found to be a 

far less effective sampling medium than 01 soil 

horizons (mull) for outlining gold veins in bedrock 

beneath the cover of glacial drift. The B. cereus 

assay appears equally effective in both soil 

horizons. 

Near Redding, California, soil traverses show 

elevated numbers of B. cereus displaced downslope 

from two greenstone-hosted gold veins, one ex· 

posed and one covered by 7-10 m of soil. Background counts of B. cereus in immediately adjacent soils are nil ( < 10 B. cereus/gram). 

Soils collected over the Hog Ranch disseminated gold deposit, located on the flank of a 

rhyolite flow-dome structure in Washoe County, 

Nevada, contain B. cereus populations one to two 

orders of magnitude higher than in adjacent unmineralized soils. 

Soils as much as several kilometers from the 

Dee disseminated gold deposit near Carlin, 

Nevada, contain large numbers of B. cereus, and it 

is not clear at present if these large numbers are 

associated with mineralization. However, among 

290 soil samples taken over the present pit 

area and in adjacent soils up to 8 km from the 

Dee deposit, the highest value (1,570,000 B. 

cereus/gram) occurred in a cluster of high samples 

(all > 100,000/gram) in soils developed on barren 

rock 100m above the deposit. 

42 

Gold crystals from a California placer; possibly nucleated 

around bacteria 

Soil samples from three other gold deposits 

have recently been collected and assayed: a Carlintype disseminated gold deposit, a disseminated 

gold deposit hosted in metamorphic rocks, and a 

disseminated gold breccia-pipe deposit, all covered 

by pediment. A relationship can be seen between 

B. cereus distributions and the location of 

mineralization in each case. 

Earlier studies of penicillin resistance in soil 

bacteria over two copper deposits indicated that 

B. cereus might thrive over many mineral 

deposits. Recent work indicates that the ability of 

B. cereus to resist antibiotics produced by metaltolerant fungi gives B. cereus an advantage in 

metalliferous soils. Studies of several different 

mineral deposit types that occur in a variety of 

lithologic and climatic settings indicate that the 

phenomenon is general and may have broad ap· 

plicability in geochemical exploration. 

The B. cereus assay has several advantages 

over conventional geochemical analysis: (1) B. 

cereus distributions are effective in glacial or 

pediment-covered terrain where geochemical techniques are of limited value. (2) The test is extremely rapid and inexpensive. On average, 50- 60 

samples a day can be processed. (3) Reproducibility of the technique is good (relative standard 

deviation = 10 percent). 
A COMPARISON OF LANDSAT THEMATIC 

MAPPER, MULTISPECTRAL SCANNER, AND 

AIRBORNE SENSORS FOR MAPPING THE 

DISTRIBUTION OF ALTERA liON MINERALS: 

EXAMPLES FROM THE 

SOUTHWESTERN UNITED STATES 

M.H. Podwysocki, M.S. Power, O.D. Jones, 

M.H. Koslow, and William E. Collins8 

Spaceborne geologic remote-sensing capabilities have progressed over the years from the 

relatively simple four-channel Landsat M ultispectral Scanner (MSS), which operates in the visible 

and near-infrared region and is capable of few 

mineralogic distinctions, to the present sevenchannel Landsat Thematic Mapper (TM), which 

has additional channels in the near- and midinfrared regions, allowing further mineralogic 

distinctions. Airborne spectroradiometers, precursors to future spaceborne systems, contain 64 or 

more narrow channels that can be used to identify 

individual species in some mineral groups. Data 

from these instruments were compared to determine their effectiveness for mapping hydrothermally altered rocks in Nevada and Utah study 

areas. These areas contain old mining districts 

noted for their past production of precious metals; 

the Nevada area is undergoing exploration for 

these and porphyry-type base-metal deposits. 

Hydrothermally altered volcanic rocks, which 

are indicators of potential mineralization, commonly contain such ferric-iron-bearing (limonitic) 

minerals as hematite, goethite, lepidocrocite, and 

jarosite. These minerals exhibit characteristic 

broad absorption bands in the visible and nearinfrared part of the electromagnetic spectrum that 

are detectable using either the MSS or TM sensors. However, limonite may form by processes 

unrelated to alteration. Hence, sole use of a 

limonite criterion in mapping alteration patterns 

may lead to inclusion of unaltered rocks. Conversely, bleached altered rocks lacking limonite will be 

excluded. 

Hydrothermally altered volcanic rocks also 

commonly contain minerals that have the hydroxyl anion bound in their lattice structures. 

These minerals, such as clays, micas, and hydrated 

sulfate minerals, exhibit narrow and often diagnostic absorption bands in the near-infrared part 

of the spectrum covered by TM. 

SColumbia University, New York, N.Y. 

43 

A comparison of band ratio images for the 

MSS and TM data shows significant differences in 

discrimination of altered from unaltered rocks. 

The MSS images depict most of the limonitic, 

hydrothermally altered rocks, on the basis of the 

characteristic signatures of limonite. However, the 

images also include many unaltered tuffs and 

plutonic rocks that display a limonitic signature. 

Also, dark sericitically altered volcanic rocks are 

not distinguished. Because of the additional bands 

in the near-infrared region, TM data can be used to 

distinguish limonitic unaltered from altered 

volcanic rocks and white unaltered from bleached 

argillized volcanic rocks. Also, dark sericitized 

volcanic rocks display a distinctive signature on 

the TM band ratio images. 

Airborne spectroradiometer data collected 

over another area were used to distinguish individual mineral species within the altered areas, 

on the basis of diagnostic absorption bands in the 

near-infrared part of the spectrum. Minerals 

distinguished in the study area include kaolinite, 

alunite, jarosite, gypsum, a mixed-layer clay, and 

some mixtures of these minerals. 

The progressive evolution of visible and nearinfrared sensor systems has provided the economic 

geologist with more detailed spectral information 

for a mineral exploration program. Anticipated 

results from airborne and spaceborne systems of 

the future suggest an even greater ability to 

distinguish mineral species. 

METAL CONCENTRATIONS IN 

MARINE BLACK SHALES 

Forrest G. Poole and George A. Desborough 

We have been studying metal concentrations 

in marine black shales of several Paleozoic rock 

units in the Ouachita orogen of west-central 

Arkansas, west Texas, and central Sonora (Mexico); the Antler and younger orogens of central and 

northern Nevada, central Idaho, and northeastern 

Washington; the Sevier orogen of southeastern 

Idaho and adjacent States; and the cratonic Big 

Snowy trough of central Montana. Most metals 

are indigenous in shales with a thermal history of 

< 100° C but are redistributed in shales with a 

thermal history of > 200 o C. Our studies include 

general mineralogy, concentration of metals, 
alteration by ground water and weathering, types 

of associated strata, and types and thermal 

maturity of organic matter. Initial studies have 

emphasized the potential for metal and hydrocarbon resources in low-temperature ( < 50 o C) 

organic-matter-rich anoxic mudstone deposits in 

order to establish the syngenetic concentration 

and residence of metals in sapropelic sediments. 

Low-temperature mudstones studied include parts 

of the Ordovician Vinini Formation and Devonian 

Woodruff Formation of central and northern 

Nevada, Mississippian Heath Formation of central Montana, and Permian Phosphoria Formation 

of southeastern Idaho and adjacent States. Beds 

range in thickness from a few centimeters to 

several meters, and some of the thicker beds have 

been correlated throughout the region. Most of 

these metalliferous kerogen-rich shales have not 

previously been thoroughly examined for 

resources because rapid weathering and poor exposures preclude easy sampling of unoxidized 

rock, which is necessary to determine concentration and residence of indigenous metals. 

Shales with the highest organic-carbon (algalkerogen) content usually contain the highest concentrations of several metals, including silver, 

vanadium, zinc, chromium, nickel, and molybdenum. In areas of low-temperature thermal 

history, algal kerogen-rich beds commonly are oil 

shales. We have been concerned specifically with 

shales that (1) contain > 10 weight percent organic 

carbon and (2) have certain valuable metals, such 

as vanadium, molybdenum, nickel, and zinc, which 

have relatively high solubilities in seawater but 

were not derived from nearby hydrothermal or 

volcanogenic sources. In the Western United 

States, many low-temperature kerogenous marine 

black shales that exceed 10 weight percent organic 

carbon contain as much as 5,000 ppm vanadium, 

5,000 ppm molybdenum, 1,300 ppm nickel, 600 

ppm cobalt, 20 ppm silver, 11,700 ppm chromium, 

18,800 ppm zinc, 280 ppm cadmium, and 350 ppm 

selenium. Microscopic, electron microprobe, and 

X-ray diffraction studies of unaltered samples indicate that the principal residence of vanadium, 

molybdenum, and selenium is in organic matter; 

nickel is principally in marcasite and pyrite; 

chromium is in organic matter, mica, and iron 

sulfide minerals; and zinc and cadmium are in 

sphalerite. 

Post-depositional modifications such as diagenesis, elevated rock temperature, oxidation, and 

44 

fluid movement cause redistribution (enrichment 

or depletion) of indigenous metals both within the 

shale units and across unit boundaries. An important redistribution and concentration process may 

be episodic sediment dewatering and expulsion of 

geopressured metalliferous and petroliferous 

(including methane-bearing) warm brines from 

deeply buried basinal black shales. This pore-fluid 

expulsion could result in upward migration of 

metal- and hydrocarbon-bearing ore fluids through 

conduits into shallow basin-margin sedimenthosted repositories (for example, Mississippi 

Valley-type lead-zinc deposits). 

The total quantity of metals contained in 

black-shale deposits is enormous. Consideration of 

the usual parameters critical for resource development, such as grade, thickness, homogeneity, and 

tonnage, is difficult because these rocks are so fine 

grained that physical extraction and preconcentration of metalliferous phases have not so far been 

feasible. Necessary technological breakthroughs in 

extracting metals from kerogen-rich shales would 

enable the commercialization of many of these 

presently marginal and subeconomic metal deposits. Because the concentration of each metal is 

low relative to that of commercial ore, and because 

the most valuable metals are difficult to extract, 

the principal value of these shales will be based on 

the aggregate polymetallic assemblage and the 

hydrocarbon potential. 

SPECTRA OF MASSIVE SULFIDE GOSSAN 

AND FALSE GOSSAN IN THE NEAR INFRARED 

(800 nm TO 2500 nm) 

Gary L. Raines, Linda G. McGee, 

and Steven J. Sutley 

The near-infrared spectra of a suite of outcrop 

samples of massive sulfide gossans and false 

gossans representing three different weathering 

environments were measured and compared with 

X-ray, scanning electron microscope, and energy 

dispersive X -ray analyses. Gossans from a humid 

tropical environment and from an arid environment are represented. The gossans of the West 

Shasta massive sulfide district represent a 

weathering environment intermediate between 

these two extremes. In situ measurements of the 

near-infrared spectral properties of massive sulfide 

gossans have not been made. However, commer-
cially available field and airborne spectrometers 

are being used by the U.S. Geological Survey to 

map the distribution of minerals in hydrothermally altered areas in the Southwestern United States 

with spectral properties similar to those described 

below. 

On the basis of these spectral measurements, 

true gossans after massive sulfide deposits have 

spectra in the 800-2500 nm region that differ from 

spectra of false gossans. In humid tropical environments, highly leached, newly formed kaolin 

minerals occur in the gossan causing spectral differences near 1400 and 2200 nm. In arid environments, true gossans preserve talc and minor mica 

from the massive sulfide deposit; these minerals 

are not observed in false gossans. This results in 

spectral differences in the 2200 and 2300 nm 

region; in addition, true gossans generally have 

goethite spectral bands near 900 nm as opposed to 

hematite spectral bands near 850 nm for the false 

gossans. 

False gossans are not known in the West 

Shasta district. The main gossan type at the 

largest deposit, Iron Mountain, is a true gossan 

showing spectral features characteristic of 

goethite and diaspore, which has distinctive spectral features in the 1400-2500 nm region. The 

other gossan type shows the spectral features of 

goethite, but it contains a less leached mixture of 

kaolinite plus illite with different distinctive spectral features in the 1400-2500 nm region. These 

spectral differences define two groups of West 

Shasta gossans, inner gossans that are closely 

associated with large deposits and outer gossans 

that are associated with the margins of large 

deposits and with smaller massive sulfide 

deposits. 

THERMODYNAMIC PROPERTIES OF MINERALS 

Richard A. Robie, Bruce S. Hemingway, 

and John L. Haas, Jr. 

In order to help solve various problems in the 

geosciences, geologists have developed computerbased models using data of physical and chemical 

properties of rocks and minerals. The models used 

to calculate heat budgets or mass exchange between fluids and rock are based upon thermodynamic principles; therefore, the accuracy of the 

prediction will depend in part upon the accuracy of 

the thermodynamic data used for each mineral 

phase in the problem. As part of a coordinated effort to supply accurate data for heat budget 

calculations and mass transfer models, the U.S. 

Geological Survey supports the Thermodynamic 

Properties project and the National Center for the 

Thermodynamic Data of Minerals. 

The Thermodynamic Properties project operates several different types of calorimeters for 

measuring enthalpies (heats) of formation .1H of' 

heat capacities, C0 p, and entropies, so' between 5 

and 380 K and relative enthalpies, HoT-H o 298 up 

to 1300 K for the purpose of obtaining free energy 

values for minerals. We have recently undertaken 

a systematic study of the thermodynamic properties of the more common manganese minerals. 

Heat capacities and entropies have been determined for rhodochrosite (MnC03), hausmannite 

(Mn30 4), pyrolusite (Mn02), bixbyite (Mn203), and 

tephroite (Mn2Si04), with the intent of determining 

the stabilities of these phases with respect to 

temperature, pressure, and oxygen fugacity and 

thus furthering our understanding of the conditions of formation and the occurrence of manganese ore deposits. 

45 

At the National Center for the Thermodynamic Data of Minerals, we have developed an 

approach for evaluating published experimental 

data that uses the interrelations among the thermodynamic properties such as volume, heat 

capacity, entropy, enthalpy, Gibbs energy, equilibrium constants, and electrochemical potentials 

and a regression procedure for simultaneously fitting all properties for a group of chemically related 

compounds. The center has produced thermodynamic tables for the major mineral components 

of basalts and has determined the best values of 

the oxygen fugacity-temperature relations for the 

buffers of oxygen in the systems Fe-0, Ni-0, Cu-0, 

and Mn-0 and for the oxygen buffer assemblages 

quartz-fayalite-iron and quartz-fayalite-magnetite. 

In addition to developing thermodynamic 

data for minerals, the USGS has revised and updated the Larsen-Berman tables of optical properties of minerals (USGS Bulletin 1627, published 

1984) to reflect the additional knowledge since 

1934 when the last edition of this handbook was 

published. The center also supports the FordFleischer File of Mineralogical References. The 

file, dating back to 1916, contains more than 

100,000 citations related to composition, physical 

properties, crystallography, optics, che~cal reactions, and natural occurrences. 
IDENTIFICATION OF REGIONAL MINERAL 

RESOURCE TARGETS BY USING ORE DEPOSIT 

MODELS-TWO EXAMPLES FROM THE EASTERN 

U.S. EARLY MESOZOIC BASINS 

Gilpin R. Robinson, Jr., and David Gottfried 

Ore deposit models developed for diabasehosted massive sulfide deposits and sedimenthosted stratiform sulfide deposits can be applied 

to the Eastern U.S. early Mesozoic basins (EMB) 

to identify regional exploration targets. Significant ore deposits of these types are presently 

unknown in the EMB but are recognized in similar 

intracontinental rift-basin tectonic settings 

elsewhere. The models define regional targets by 

identifying types of associated deposits likely to 

be found in a given area and by providing criteria 

to locate favorable geologic-tectonic settings and 

to identify types of chemical transport, alteration, 

and fractionation associated with mineralization. 

Significant diabase-hosted sulfide deposits occur where basaltic magma is contaminated by 

favorable crustal material and forms an immiscible sulfide melt. In the EMB, tholeiitic diabase 

may host and conceal magmatic sulfide deposits of 

nickel, cobalt, copper, and platinum-group 

elements that formed in a similar manner to the 

deposits in the Noril'sk district (Siberia, U.S.S.R.), 

Insizwa Complex (Transkei, South Africa), or 

Duluth Complex (Minnesota, U.S.A.). Sulfide accumulations may occur in structural depressions 

at the base of diabase sheets or as sulfide disseminations in areas of abundant metasedimentary inclusions. Target areas for diabase-hosted 

sulfide mineralization in the EMB, defined by 

means of nickel, cobalt, and copper trace-element 

systematics, are diabase sheets with geochemical 

trends indicating sulfide fractionation. Additional 

features favorable for economic mineralization in 

diabase sheets exhibiting sulfide fractionation include diabase bodies with (1) sulfur isotopic 

signatures indicating contamination with crustal 

material and (2) sheet-like diabase bodies with 

cumulate zones, granophyric differentiates, and 

abundant metasedimentary inclusions. Our preliminary investigations have identified magma 

types in Connecticut, Virginia, North Carolina, 

and South Carolina that have trace-element geochemical trends consistent with sulfide fractionation and are thus favorable targets for exploration. 

Sediment-hosted stratiform sulfide deposits 

found in rift-basin settings are associated with 

lacustrine and restricted-basin marine sediments. 

Mineralization appears to be related to the 

transport of metal-bearing connate brines, either 

NORILSK-TYPE CUMULATE SULFIDES 

FAULT ZONE MINERALIZATION 

Pb - Zn- Ba VEINS 

URA IUM 

RED- BED COPPER 

URANIUM 

SEDIMENT- HOSTED STRATIFORM SULFIDES 

~DIABASE/ BASALT 

~ CONGLOMERATE a SANDSTONES 

- BLACK a GREEN SHALES 

~ SANDSTONE. SILTSTONES a SHALES 

FLUVIAL SEDIMENTS 

~SHALES a SILTSTONES 

MAGNETITE 

I 2 3 

0 

0SHEARED ROCKS MILES 

[2@ HORNFELS 

!551 PALEOZOIC LIMESTONE /DOLOMITE 

Schematic distribution of facies in the early Mesozoic basins in eastern North America showing some potential mineral 

resources (modified from C.E. Turner-Peterson, 1980, SEPM-Rocky Mountain Section, Short Course Notes) 

46 
through faults into the depositional basin or 

through the sediment pile. Favorable factors include (1) syndepositional-postdepositional faults, 

(2) lacustrine and marine sections with redox 

changes, (3) anomalous copper, lead, zinc, barium, 

boron, or silica mineralization, and (4) lead-zinccopper-barium vein occurrences. Occurrences of 

sandstone-hosted stratabound copper-silver 

mineralization and vein lead-zinc-copper-barium 

mineralization are widespread in the EMB and are 

believed to have formed from the transport of 

basinal brines to shallow sites of mineral deposition in the Jurassic to Early Cretaceous. Promising target areas for more extensive sedimenthosted stratiform mineralization include Jurassic 

lacustrine sections in the Hartford, Newark, and 

Culpeper basins and basal marine sections overlying buried Triassic basins in South Carolina, 

Georgia, and Florida. 

DEVELOPMENT OF DISSEMINATED GOLD 

DEPOSITS OF CORTEZ, HORSE CANYON, 

AND GOLD ACRES, NEVADA, AT THE END 

STAGE OF CALDERA-RELATED VOLCANISM 

James J. Rytuba 

The large disseminated gold deposits of Cortez, Gold Acres, and Horse Canyon, Nevada (total 

Au resource of 1.8 million oz.), are localized subparallel to and 4-6 km outside the margin of the 

Cortez caldera The caldera is an oval collapse 

structure, 16 km in maximum diameter, which 

resulted from the eruption of the 32.5±2-Ma 

Caetano Tuff. Collapse of the caldera was concurrent with eruption of the ash-flow tuff, resulting in 

the filling of the caldera with more than 1.5 km of 

tuff and interstratified collapse megabreccia The 

Caetano Tuff is a calc-alkaline rhyolite that is 

strongly zoned with respect to Hg, Rb, Sr, Nb, Zr, 

and Ba. Highest contents of Hg, Nb, and Rb occurred in the early phase of the eruption and indicate roofward enrichment of these elements in 

the magma chamber. Highest contents of Ba, Sr, 

and Zr occur in the late erupted tuff and indicate 

roofward depletion in the magma chamber. In contrast, the ore metals (Au, Ag, As, Sb, Tl, Cu, Ph, 

Zn) are not zoned in the tuff. Gold content is 

uniformly low, ranging from < 1 ppb to 1.3 ppb, 

and is similar to the gold content of other calcalkaline rhyolites. The contents of As, < 1.0-

2.4 ppm; Ph, 1.6-7.2 ppm; Zn, 23-57 ppm; Cu, 

47 

7.6-16 ppm; and Sb and Tl, < 1 ppm, are all similar 

to or lower than those reported for other calcalkaline rhyolites; only Hg, 0.5-3.1 ppm, is 

anomalously high. 

The gold deposits occur in the Roberts Mountains Formation of Silurian and Devonian age and 

the Wenban Limestone of Devonian age, which 

have been intruded by rhyolite porphyry dikes. 

The ore bodies consist of disseminations of gold, 

quartz, and pyrite and contain anomalous concentrations of As, Sb, and Tl. The Cortez ore bodies 

are localized adjacent to rhyolite porphyry dikes 

and have a strike and dip similar to those of the 

dikes. The ore bodies at Gold Acres and Horse 

Canyon are also, in part, localized by rhyolite porphyry dikes. Each deposit contains dikes that 

have Rb/Sr, Nb/Zr, and Ba/Sr ratios similar to 

those in the Caetano Tuff, indicating the intrusions and tuff are comagmatic. The original content of ore metals in the dikes was low and similar 

to that in the Caetano magma. Low levels of Au, 

As, and Sb, and locally Tl, Cu, and Ag, were introduced into the dikes during mineralization. Rb 

is depleted in the more intensely altered dikes, and 

K-Ar ages of biotite, 34.8±1.1 Ma, from Cortez 

dikes have been reset by the hydrothermal event. 

Although the age of the Caetano Tuff and mineralization fall within the analytical uncertainty of the 

K-Ar ages, the presence of mineralization in the 

outflow facies of the tuff and dikes indicates that 

the hydrothermal event occurred after caldera collapse and during the end stage of the caldera cycle. 

The magmatic event provided the heat for the 

hydrothermal systems but was not the source of 

the metals, as indicated by the low contents and 

absence of zoning of ore metals in the Caetano 

magma and the absence of anomalous Hg in the 

ore deposits even though the Caetano magma contained anomalously high Hg. 

HIGH-ALUMINA HYDROTHERMAL ALTERATION 

SYSTEMS AND THEIR ROLE IN MINERAL 

EXPLORATION, SOUTHEASTERN UNITED STATES 

R.G. Schmidt and T. L. Klein 

Large subvolcanic to solfataric hydrothermal 

systems characterized by an abundance of silica 

and high-alumina minerals (andalusite, pyrophyllite, topaz, dumortierite), very intense alteration of large volumes of rock, and profound 
changes in bulk composition are found at many 

localities worldwide and can be considered to be a 

subclass of porphyry-type alteration systems. Examples include Kounrad mine, Kazakhstan, 

U.S.S.R.; El Salvador mine, Chile; La Granja 

deposit, Peru; Island Copper mine, British Columbia, Canada; and Equity Silver silver-copper-gold 

mine, British Columbia. The alteration zones contain disseminated pyrite and traces to extractable 

quantities of gold, silver, copper, molybdenum, 

tin, and other metals. Fluorine, as topaz, is 

generally more abundant than boron, but tourmaline and (or) dumortierite is the abundant 

halogen mineral in some systems. Bismuth, 

arsenic, lead, and zinc are also commonly present. 

These systems are transitional to shallower 

solfataric and hot spring deposits and, with 

greater K-silicate alteration, into typical subvolcanic porphyry copper deposits. The presence 

of significant zones of high-alumina alteration 

within certain major porphyry-type deposits and 

prospects worldwide suggests that this type of 

alteration is a potentially useful exploration guide. 

Studies of several high-alumina deposits in metavolcanic rocks of the Carolina slate belt indicate 

similar alteration and metallogenic associations 

and suggest these deposits be seriously evaluated 

for their base- and precious-metal potential. 

The Carolina slate belt, extending from 

Georgia to Virginia, is a thick sequence of 

metamorphosed lava flows and volcaniclastic 

rocks that probably formed in a volcanic arc environment of late Precambrian to early Paleozoic 

age. These rocks probably formed in diverse environments including island arcs and continental 

margins. 

About 40 large bodies of high-alumina altered 

rocks have been identified within volcanic rocks of 

the slate belt. Ten to fifteen share many features of 

porphyry-type systems and consist of large, generally equidimensional alteration zones. The remainder have a tabular form. High-alumina minerals 

(pyrophyllite, andalusite, and sericite) have been 

mined in the slate belt from about 15 deposits of 

both types for industrial purposes, and four 

deposits are presently being mined. Former gold 

mines or gold prospects occur in at least three of 

the porphyry-like systems and adjacent to one of 

the tabular bodies. 

The equidimensional porphyry-like alteration 

systems in the Carolina slate belt are from one to 

several kilometers in diameter. Tilting and erosion 

permit us to get cross-sectional views into the 

systems over a vertical distance of perhaps as 

much as three kilometers. Alteration in these 

systems is dominated by intense silicification 

yielding a quartz granofels consisting of over 80 

percent quartz commonly accompanied by minor 

pyrophyllite (± topaz) and usually by pyrite. Pods 

of pyrophyllite, andalusite, and kaolinite occur 

locally within the highly silicified rocks or as 

peripheral alteration zones. The geochemical 

signature of these deposits is the suite Cu, Mo, Sn, 

B, and F, with sporadic As, Au, Bi, Li, Ph, and Zn. 

Some tabular deposits have little or no silicified 

rock in them, and most lack associated Sn or abundant F; each may have formed by intense hydrothermal alteration along shear zones, shallow 

solfataric processes, or alteration on the sea floor 

by ponding of hot, acidic and reducing brines. We 

assume that the tabular bodies are genetically 

related to the porphyry-like bodies, but data are 

lacking to document this connection. 

MULTIPLE EPISODES OF MINERALIZATION 

IN THE SOUTHERN TOQUIMA RANGE, 

NYE COUNTY, NEVADA 

Daniel R. Shawe 

The southern Toquima Range is a complex 

geologic terrane formed by multiple sedimentation, tectonism, igneous intrusion and extrusion, 

and mineralization. During Cambrian and Ordovician time, marine quartzite, silty and limy 

argillite, argillite, limestone, dolomite, and chert 

were deposited in a continental shelf-slope environment, and during Permian time clastic rocks were 

laid down. Geochemical data indicate that some 

Paleozoic units contain concentrations of metals 

possibly of submarine exhalative origin. Thrust 

faulting during Paleozoic and Mesozoic time 

stacked the Paleozoic sedimentary rocks into a 

sequence of thin thrust plates. The rocks were 

repeatedly intruded and mineralized near numerous igneous centers from the end of thrusting 

through most of the Tertiary. 

Three large granitic plutons intruded the 

Paleozoic rocks in Cretaceous time, probably near 

the close of regional thrust faulting, and later they 

were domed, metamorphosed, and mineralized. 

Base-metal sulfide-bearing skarn and tungstenbearing quartz veins were formed at places in and 

48 
near the plutons; production from them has been 

insignificant. The skarn deposits contain small 

amounts of gold. Economic silver deposits in 

Paleozoic rocks near Belmont may be related to 

nearby Cretaceous granite, though most of the 

silver possibly was introduced, or reworked from 

earlier deposits, during a Tertiary igneous event. 

In the Oligocene a granodiorite stock and a 

swarm of rhyolite and andesite dikes intruded the 

granite pluton and adjacent rocks east of Round 

Mountain; the intrusion was accompanied by tourmaline and base- and precious-metal sulfide mineralization of little economic interest. Concurrently, 

tungsten-bearing veins in granite near the Oligocene intrusive bodies were remineralized with 

base- and precious-metal sulfides. 

Near the end of the Oligocene and beginning of 

the Miocene, extensive volcanic activity commenced in the southern part of the Toquima 

Range. The Mount Jefferson and Manhattan 

calderas, and perhaps other unrecognized structures, collapsed during eruption of voluminous 

silicic ash-flow tuffs. Shortly after formation of the 

Manhattan caldera, a large stockwork and disseminated gold deposit was formed in rhyolitic ashflow tuff at Round Mountain about 5 km north of 

the caldera. The gold deposit at Round Mountain 

is one of the largest in the United States; it also 

contains significant amounts of silver. At about 

the same time, silver-gold mineralization occurred 

in rhyolitic ash-flow tuff at Jefferson, at the south 

margin of the Mount Jefferson caldera 

Later in Miocene time, extensive economic 

gold mineralization occurred in Cambrian phyllitic 

argillite, limestone, and quartzite in the Manhattan district, along the south margin of the 

Manhattan caldera. A possible igneous rock 

source has not been recognized, but it may be 

buried along the south margin of the caldera. 

Mercury deposits of probable late Tertiary age 

formed in several places near the margins of granitic plutons and peripheral to the Manhattan and 

Mount Jefferson calderas. Cinnabar was mined in 

and near granite bodies and from Paleozoic rocks 

in the east part of the Manhattan district. 

The Cretaceous, Oligocene, OligoceneMiocene, and Miocene mineralized systems in the 

southern Toquima Range are large, each covering 

several square kilometers, and the younger 

systems spatially overlap older ones. Geologic, 

geochemical, and lead-isotope data suggest that 

both derivation of metals from host rocks and 

49 

remineralization of older systems were important 

in forming the mineral deposits. Many geologic environments, including favorable host lithologies 

(highly fractured rocks of all kinds, organicmatter-rich carbonate and other sedimentary 

rocks), high- and low-angle faults, and caldera 

margins, are potential sites for large metal 

deposits such as porphyry copper-molybdenum 

systems, gold-bearing skarns, high-grade goldsilver lodes, Carlin-type gold deposits, and 

stockwork-disseminated gold-silver deposits in 

volcanic rocks. 

CHARACTERISTICS OF LODE-GOLD DEPOSITS 

IN THE PRINCE WILLIAM SOUND REGION, 

SOUTHERN ALASKA 

Miles L. Silberman and Dawn J. Madden 

Lode-gold deposits in low- to medium-grade 

metamorphosed, accreted sedimentary rocks are 

common and economically important throughout 

the world. Perhaps the best known examples of 

this deposit type are in the Klamath Mountains of 

northern California. Other occurrences are found 

in South Island (New Zealand), Papua New 

Guinea, southwestern Alaska, and parts of the 

Mother Lode Belts of central California Because 

of the importance of deposits of this type, we 

decided to study in detail one region where they occur in order to determine their mechanisms of formation and localization. The deposits near Prince 

William Sound, southern Alaska, are particularly 

suited for detailed study now, after ten years of 

regional and local geologic study, when a comprehensive regional picture is emerging. 

The deposits occur as narrow fissure veins 

emplaced along faults, fractures, and shears in 

metasedimentary rocks of the Upper Cretaceous 

Valdez Group in the Prince William Sound region. 

In some mining districts, the veins are peripheral 

to and cut small granitic stocks and plugs that intruded the metasedimentary rocks between 55 and 

50 Ma and again at 35 Ma. In other districts, the 

veins occur in metasedimentary host rocks that 

lack plutonic intrusions but contain small felsic to 

intermediate dikes, which are locally altered and 

cut by the veins. 

The veins consist of quartz and minor calcite; 

they contain generally low concentrations of 

sulfide minerals, predominantly arsenopyrite, and 
Prince William Sound and Chugach Mountains, July 1975 

associated pyrite, sphalerite, galena, and chalcopyrite. Native gold is the principal economic metal; 

past lode production is 131,000 ounces. Ag and As 

are the most common trace elements associated 

with the Au; variable amounts of Sb, Hg, Cu, Pb, 

Zn, and Ba are also present. Detailed elementdispersion studies at the Hope-Sunrise and Girdwood mining districts in the Chugach Mountains, 

west of Prince William Sound, indicate that the 

minor-element content of the veins reflects local 

variations in the metasedimentary host rocks. 

Plutonic rocks and dikes that are associated with 

gold mineralization have a characteristic REE pattern marked by strong depletion relative to chondrites and no Eu anomaly. In contrast, igneous 

rocks not associated with mineralization have 

nonuniform REE patterns. 

K-Ar ages of metamorphism, and of alteration 

associated with the gold-bearing veins, fall within 

the periods of granitic intrusion. Oxygen- and 

hydrogen-isotope ratios indicate that the veins 

were deposited by fluids with a strong meteoric 

50 

water component and a low water-to-rock ratio. 

Sulfur-isotope ratios suggest derivation of sulfur 

from the host rocks, probably by a process involving diffusion. The similarity of K-Ar ages of 

regional metamorphism, granitic intrusion, and 

mineralization suggests that these processes are 

related. The sulfur-isotope data and the similarity 

of vein and host-rock minor-element contents suggest that ore and related metals derive from the 

host rocks. These metals probably were leached by 

hot fluids largely of meteoric origin. The fluids 

were heated by a combination of metamorphism 

and granitic intrusion. 

From the isotopic and geochemical data, the 

processes that resulted in gold mineralization can 

be reconstructed as 

Accretion 

(60-55? Ma) 

Allochthonous terranes impinge on continental margin, 

penetrative deformation, folding, axial-plane cleavage, thickening of accreted wedge. 
Metamorphism 

(55-62 Ma) 

Intrusion 

(55-50 Ma) 

Uplift 

Mineralization 

(55-53 Ma) 

Heating of thickened wedge, 

high-grade metamorphism at 

depth, lower grade near surface. 

Generation of metamorphic 

fluids, which leach metals from 

wedge sediments. Formation of 

metamorphic segregation 

quartz veins. 

Migration of melts to shallow 

depth, and emplacement as 

plutons and dikes. Contact 

metamorphism, faulting. 

Uplift by thermal expansion, or 

loss of compression, opening of 

fractures, extensional shearing. 

Influx of meteoric water, mixing with metamorphic fluids as 

they ascend, deposition of 

quartz, calcite, metals in open 

fractures and shears. Late 

stages of process driven by heat 

of anatectic granites. 

METALLOGENY OF ARCHEAN AND 

PROTEROZOIC TERRANES IN THE 

LAKE SUPERIOR REGION 

P.K. Sims 

A tectonostratigraphic approach to metallogeny provides a framework within which to relate 

existing and possible undiscovered mineral deposits to their host terranes. 

Four major Precambrian tectonostratigraphic 

terranes have been delineated in the Lake Superior 

region of the United States and Canada. Two of 

these-an Archean greenstone-granite terrane 

(about 2,700 Ma) and an Archean gneiss terrane 

(3,550-2,600 Ma)-are partly covered by a 

continental-margin sequence of Early Proterozoic 

(about 2,000-1,900 Ma) miogeoclinal rocks assigned to the Marquette Range Supergroup and 

its equivalents in Minnesota. The third is an Early 

Proterozoic oceanic-arc assemblage-the Wisconsin magmatic terrane (about 1,900-1,800 Ma)-

51 

that mainly lacks an Archean basement. The 

fourth is a Middle Proterozoic (Keweenawan) rift 

assemblage-the Midcontinent rift system (1,100 

Ma). The two Archean terranes were tectonically 

joined in Late Archean time, and the Early Proterozoic oceanic-arc assemblage was accreted to 

the North American continent about 1,850 Ma, 

during the Penokean orogeny. The Midcontinent 

rift system is a major intracontinental rift that 

aborted before much crustal separation. 

Major known or potential ore deposits occur in 

all these terranes except the Archean gneiss. They 

can be grouped into two classes according to the 

tectonic environment in which they formed: islandarc crust and continental crust. 

In island-arc crust, four types of major 

mineral deposits exist, but only one is common to 

both the Early Proterozoic Wisconsin magmatic 

terrane and the Archean greenstone-granite terrane: volcanic-hosted Cu-Zn type massive sulfide 

deposits. The massive sulfide deposits in the 

Wisconsin magmatic terrane are in calc-alkaline 

volcanic rocks having island-arc chemical affinities; those in the Archean terrane apparently 

are mainly in felsic rocks of both tholeiitic and 

calc-alkaline affinities. The other deposits in 

island-arc crust-Algoma-type iron formations, 

ultramafic- and gabbro-hosted Cu-Ni deposits, and 

stratabound and intrusion-hosted Au depositsare virtually restricted to Archean rocks and, 

except for the iron formations, occur mainly in 

Canada. 

In continental crust, deposits in the Early Proterozoic epicratonic rocks are the vast Superiortype iron formations and the apparently subeconomic carbonate-hosted copper deposits. Major 

conglomerate-hosted uranium deposits occur in 

the Huronian Supergroup in the Lake Huron area 

of Canada, a continental-margin accumulation like 

the miogeoclinal sequence in the Lake Superior 

region. The Middle Proterozoic rocks of the Midcontinent rift system have deposits containing 

chalcophile elements, which ultimately were derived from magmas ascending from the mantle. 

The principal developed deposits are the famous 

volcanic- and sedimentary-hosted copper deposits 

on the Keweenawan Peninsula. A major resource 

for the future is the large, marginal-grade gabbrohosted Cu-Ni deposits of the Duluth Complex in 

northern Minnesota. 
SOME RECENT DEPOSIT MODELING EFFORTS 

D.A. Singer and D.P. Cox 

A compilation of 62 descriptive and 37 gradetonnage models, which was published in 1983, provides a starting point for a larger deposit modeling 

effort useful for resource assessment and exploration. The classification of deposits is empirical 

rather than genetic and is based on a study of wellknown deposits. Use of data from many deposits 

increases the robustness of the models, and emphasis on lithologic-tectonic associations allows 

the use of geology to indicate which resources are 

possible in a region. The deposit models make 

possible effective project design for assessments 

and exploration and provide a basis for quantitative assessments. 

Tonnages and average grades of well-explored 

deposits of each type are used to characterize 

grades and tonnages of undiscovered deposits in 

geologically similar settings. Variation of grade 

and tonnage within deposit types tends to be small 

compared with variation among deposit types. 

Graphical presentation of grade-tonnage models is 

particularly effective in showing differences 

among deposit types and the likelihood of occurrence of deposits having grades and tonnages 

above specified limits. 

Some additional benefits of this modeling effort have been the recognition that there are two 

types of podiform chromite deposits; one type, 

found in the cordillera, has a median size of 120 

tonnes, whereas podiform deposits in Turkey, the 

Philippines, and elsewhere have a median size of 

19,000 tonnes. Although the sample of deposits 

used in the larger type of podiform deposit is probably size-biased in favor of large deposits, the sample of deposits from the cordillera is not sizebiased, and statistically it is nearly impossible for 

the larger deposits from Turkey to have come from 

the same population as the smaller cordillera 

deposits. 

A recent analysis of 55 porphyry copper 

deposits that have reported grades for Cu, Mo, and 

Au demonstrates a continuum between (1) goldrich deposits emplaced at a median depth of 1 km, 

with a median size of 110 million tonnes and a 

median content of 2.6 percent magnetite in the 

potassic alteration zone, and (2) molybdenum-rich 

deposits emplaced at a median depth of 3.6 km, 

with a median size of 500 million tonnes and little 

52 

magnetite. Between these end members is an economically important group containing significant 

amounts of gold and molybdenum. 

TIN, MOLYBDENUM, AND OTHER METAL 

ELEMENTS IN SILICIC MAGMAS AND 

THEIR RELATION TO FLUORINE 

AND CHLORINE DISTRIBUTION 

Robert L. Smith 

Lithophilic metal elements, F, Cl, and probably H20, are commonly enriched in the tops of 

silicic magma chambers. Pyroclastic deposits from 

caldera-forming eruptions provide evidence that 

chemical gradients, spanning ten-fold enrichments 

of lithophilic elements and one hundred-fold depletions of refractory elements, may sometimes occur 

in the silicic magma reservoirs. The most fractionated liquids in these magmas contain the 

fewest phenocrysts and may be erupted in large 

volume, followed by more phenocryst-rich, less 

fractionated magma. 

Data from the Bandelier Tuff, New Mexico, 

show that the phenocrysts are in equilibrium at all 

levels with the liquid (glass) that surrounds them 

and thus are evidence that the phenocryst gradient was superimposed on a preexisting chemical 

gradient in the liquid. These highly fractionated, 

phenocryst-poor magmas preceded final solidification of the magma reservoir by more than one 

million years; the chemical gradients waxed and 

waned with alternating periods of repose and 

volcanic bleeding of the system. Thus, clearly, the 

timing of stock emplacement in such systems is 

critical to magmatic metal and volatile concentrations and may not be systematic. 

Geochemical studies of obsidians and volcanic 

systems like the Bandelier Tuff indicate that 

distribution patterns of metal elements are 

systematic and are strongly correlated with F and 

Cl distribution. For example, Sn and Mo are concentrated with F plus Cl in nonhydrated natural 

glasses, but Sn is also concentrated with F at very 

low Cl levels whereas Mo is not. The highest Mo 

concentrations (20 ppm) are found in Cl-rich 

peralkaline rhyolites, yet peralkaline magmas are 

not known to generate porphyry Mo deposits. 

Some other factors (probably H20) in subalkaline 

magmas (Mo < 10 ppm) control Mo release during 

stock emplacement and crystallization. Sn is 
enriched in all F -rich glasses but reaches highest 

concentrations in peraluminous compositions. The 

highest known Sn concentration(> 150 ppm) in an 

obsidian is found in the rare Macusanite glass 

from Peru. This glass also contains exceptionally 

high concentrations of Rb, Cs, Li, B, W, and F and 

exceptionally low concentrations of Zr, Hf, Th, 

Mo, Cl, and rare-earth elements. The glass has the 

composition of a lithium pegmatite, and the Sn 

concentration probably far exceeds that required 

for all other types of Sn deposits associated with 

silicic igneous rocks. Wood tins, including the socalled Mexican-type tins, probably require at least 

10 ppm Sn in the magma, but this threshold concentration may vary with fluid composition and 

rock permeability. 

Sn, Mo, F, and Cl are mobile during crystallization of rhyolitic and granitic rocks; hence their 

abundances are reliable indicators of initial 

magmatic concentrations only in unaltered glassy 

rocks. In crystallized silicic rocks, stable elements 

(Nb, Ta, Zr, Hf, Th, and Rb) may be used in 

various combinations to reconstruct approximate 

initial magmatic values for mobile elements and 

hence have potential for exploration. However, exploration strategies based on stable-element patterns require a knowledge of chemical variation as 

a function of tectonic environment. 

MINERAL RESOURCE ASSESSMENT OF THE 

SAN ISABEL NATIONAL FOREST, COLORADO; 

A PROTOTYPE FOR 1 :250,000-SCALE 

MULTIDISCIPLINARY ASSESSMENTS 

"FROM THE LITERATURE" 

Richard B. Taylor and John S. Dersch9 

This mineral resource assessment of the San 

Isabel National Forest is based entirely on 

published data and is a prototype of what may 

become a series of assessments that use available 

geologic, geochemical, and geophysical information. Land-use planning requires evaluation of the 

mineral resource potential of Federal lands at a 

rate exceeding the capacity, both budget and personnel, of the USGS to conduct field surveys. This 

study was undertaken to establish a methodology 

and to test the feasibility of "literature" assessments at a scale of 1:250,000, a scale chosen to 

best balance planning needs against the detail 

available from published information. The San Isa53 

bel National Forest covers 1,940 mi2 (4,970 km2

) 

in the southern Rocky Mountains and extends 

160 mi (260 km) south-southeast, from north of 

Leadville to south of the Spanish Peaks. It was selected for this study because of the diversity of its 

mineral deposits, which include a part of the Colorado Mineral Belt, and because the amount of information available is typical of that available for 

much of the Western United States. Responsibility for assessing locatable and leasable 

minerals was taken by the USGS, for salable 

minerals by the Forest Service; the project was 

conducted jointly, and information was shared 

throughout the work. 

The procedures used for this assessment were 

fundamentally similar to those of the initial phase 

of any mineral resource assessment project, except 

that the results have been published. Without 

fieldwork to obtain new data, the quality and 

nature of the assessment data inevitably vary 

from place to place. Procedures were as follows: 

( 1) Collection of available geologic maps and 

compilation of a coherent geologic map at 

1:250,000 from the disparate pieces. Maps published for the entire area (parts of the Leadville, 

Montrose, Pueblo, and Trinidad 1 o X 2° quadrangles) were supplemented by other maps, including those from graduate theses and recent 

mineral surveys of Wilderness Study Areas. 

(2) Collection of available geochemical and 

geophysical data and compilation of selected parts 

at a 1:250,000 scale. Sets of NURE (National 

Uranium Resource Evaluation) geochemical data 

were examined from the four stream-sediment 

surveys that covered the area, and 11 elements 

(Co, Cu, Cr, Fe, Mn, Ni, Ph, Sn, Th, U, and W) were 

selected as useful and analytically sufficiently 

reliable for assessment purposes. Plots of these 

elements were made for each of the four 1 o X 2 o 

sheets. Geochemical data from Wilderness surveys 

were examined but were not compiled at the scale 

of the San Isabel study. Regional gravity and 

aeromagnetic maps were collected for the entire 

area, and selected maps were reduced to 1:250,000 

scale. No attempt was made to recompile and 

recontour data. The surveys were made over two 

decades, and the diversity of the data was so great 

as to make the effort of integration and recontouring unwarranted. 

(3) Collection and examination of data on 

"JohnS. Dersch, U.S. Department of Interior, Forest Service. 
mineral deposits. This included study of published 

mine and district descriptions, computerized data 

files, and plotting of mine and prospect location information from ·1:24,000-scale topographic maps 

at 1:250,000 scale. 

(4) Construction of occurrence and genetic 

resource models, called "deposit types" in this 

report. The models are based on deposits both 

within and outside the forest. Each model was 

fine-tuned to local geology and to assessment data 

available for the area For example, the assessment models are restricted to analytical data 

available for the area because no opportunity was 

afforded either to collect new samples or to 

reanalyze existing samples. 

(5) Evaluation of the terrane within the forest 

boundaries and assignment of levels of mineral 

resource potential (and levels of certainty of 

assessment) to areas for specific commodities 

on the basis of specified deposit types. Seventeen 

deposit types were used in the San Isabel 

evaluation. 

(6) Publication of results, including text and 

1:250,000-scale geologic and mineral resource 

maps. The San Isabel study is reported in the 

publication listed at the end of this abstract. 

The credibility of an assessment "from the 

literature" relies in part on the adequacy of the 

literature and the time available for search, compilation, and interpretation and in part on the 

availability of geologists with experience in the 

area so that compiled data is interpreted as more 

than just words and numbers. 

Reference Cited 

Taylor, R. B., Stoneman, R. J., and Marsh, S. P., 1984, An 

assessment of the mineral resource potential of the San 

Isabel National Forest, south-central Colorado, with a section on salable minerals by J. S. Dersch, U.S. Department 

of Agriculture, Forest Service: U.S. Geological Survey 

Bulletin 1638, 42 p. 

PRELIMINARY RESULTS OF AN ALVIN DIVE 

PROGRAM ON ACTIVE HYDROTHERMAL VENTS 

AT THE SOUTHERN JUAN DE FUCA RIDGE 

USGS Juan de Fuca Study Group10 

In September 1984, the USGS Juan de Fuca 

Study Group conducted 8 ALVIN submersible 

dives to investigate hydrothermal activity on the 

54 

southern Juan de Fuca Ridge. Three primary vent 

sites along a 6-km segment of ridge were sampled 

and mapped. Traverses across the axial valley 

floor confirmed the general volcanic and tectonic 

features mapped by deep-towed photography in 

1983. From the inner valley walls to the axis, the 

1-km-wide, symmetric valley floor is characterized 

by the following sequence of volcanic features: 

smooth lobate sheetflows, lobate sheetflows with 

numerous small collapse pits, a subsided lava lake, 

and a 10- to 30-m-deep, 50-m-wide cleft along the 

center of the valley floor. Sonar images revealed 

that the central cleft is remarkably linear and continuous within the study area, although it is locally offset by a few tens of meters. 

Hydrothermal vents and associated fauna and 

(or) sulfide deposits were observed on all dives. All 

of the hydrothermal activity occurs within or at 

the margins of the central cleft. Features forming 

conduits for hydrothermal fluids include fractures 

along the base of the walls of the central cleft, 

basaltic pillars, and hollow lobate flows. Both lowtemperature, diffuse flow and high-temperature 

(maximum measured temperature 283 o C), blacksmoker chimneys were observed. Water samples 

from 9 vents have a minimum measured pH of 3.2 

and a maximum H2S in excess of 3 mmol/kg. 

Sulfide deposits occur as fields of chimneys and 

spires from 1 to 3 m high and 10 to 50 em in 

diameter. Some larger chimneys as much as 3 m in 

diameter and 9 m high were observed. The 

deposits are usually surrounded by a nearly continuous blanket of orange-brown hydrothermal 

sediment and (or) a white to yellow bacterial(?) 

mat. 

Recovered sulfide samples are predominantly 

the tops of chimneys or spires, which typically contain greater than 80 percent ZnS (determined by 

shipboard examination of hand specimens and 

limited microscopic inspection). The chimneys 

show crude concentric banding defined by colloform banded to dendritic sphalerite and have a 

porous texture. The concentric banding is accentuated by bands rich in one or more of the minerals 

pyrite, marcasite, anhydrite, wurtzite, chalcopyrite, and pyrrhotite. Less typical samples contain 

more abundant pyrite (up to 80 percent) intergrown with sphalerite and chalcopyrite or have interior conduits completely lined with chalcopyrite, 

10W.R. Normark, J.L. Morton, J.L. Bischoff, R. Brett, R.T. Holcomb, 

E.S. Kappel, R.A. Koski, S.L. Ross, W.C. Shanks III, J.F. Slack, K.L. 

von Damm, R.A. Zierenberg. 
/ 

~ 

Deep Submergence Research Vehicle ALVIN 

which is intergrown with sulfate and sphalerite 

toward the exterior. 

Benchmarks, consisting of floats with unique 

markings, were placed at each of the sampling 

sites. The benchmarks should allow us to observe 

physical changes in the deposits, both growth and 

dissolution, during subsequent deep-towed photographic or submersible work. 

MICROBIOLOGY OF SOIL DERIVED 

FROM A COPPER DEPOSIT 

John R. Watterson, Sarah S. Elliott, 

Nancy L. Parduhn, and David M. Updegraff 

Malachite, azurite, and other copper minerals 

are present in soils developed on a steeply dipping 

copper deposit of Eocene age, the Cotter Basin 

Prospect, Lewis and Clark County, Montana. For 

approximately 80 m across the deposit there are 

soils (some with > 1 percent Cu) inhabited only by 

55 

the "Montana silver plant," Eriogonum ovalifolium, sparse grasses, lichens, and soil microorganisms. A mixed forest flanks the deposit, but 

trees do not grow in the metal-rich soil, and conifers bordering the deposit are dwarfed and 

deformed. The large and abrupt geochemical gradients that exist here make this an excellent place 

to study the influence of natural high metal concentrations on the soil microflora 

A total of 28 samples was collected from the 

upper 10 em of soil in a traverse across the deposit; 

about half of the samples were located over the 

deposit, and half were from the forest on either 

side. Detailed chemical and microbiological 

studies on these soils over the last two years 

demonstrate that both the absolute number of 

viable, aerobic, spore-forming bacteria (mostly 

Bacillus species) and the penicillin resistance of 

these bacteria increase over the deposit. The 

bacteria responsible for this penicillin resistance 

were found to be B. cereus. Purified and identified 

B. cereus cultures from all but two traverse sites 
were tested for their relative resistance to the salts 

of 20 metals and 27 antibiotics. The pattern of antibiotic resistance defined the location of the 

deposit much more clearly than the pattern of 

resistance to any metal. 

Microfungi were also isolated from the soils 

over the deposit because certain species are known 

to produce penicillin and other antibiotics. A 

purified colony of the most prevalent soil fungus in 

the deposit area (a Penicillium sp.) was shown in 

bioassay tests to actively produce penicillin and 

other unidentified antibiotics. Bacillus populations over the deposit (predominantly B. cereus) 

showed little or no inhibition when grown with the 

Penicillium sp., whereas Bacillus populations 

away from the deposit were strongly inhibited. In 

addition, B. cereus isolates from over the deposit 

were found to be capable of normal germination 

and growth in ultrapure water with no other 

nutrient than mycelium tufts from the Penicillium 

sp. from the same site. B. cereus is the only known 

Bacillus sp. that can also "eat" microfungi, and 

this is why B. cereus is uniquely suited to live in 

this "toxic" metalliferous soil. Multiple antibiotic 

resistances are thus shown to be far more decisive 

criteria than metal resistances for the success of B. 

cereus over the deposit. 

PROCESSING OF LANDSAT IMAGERY TO MAP 

SURFACE MINERAL ALTERATION ON THE 

ALASKA PENINSULA, ALASKA 

Frederic H. Wilson and James E. York11 

Landsat images were digitally processed to 

facilitate assessment of the mineral resources of 

the Port Moller, Stepovak Bay, and Simeonof 

Island 1:250,000 quadrangles. Field mapping and 

assessment of these quadrangles were begun in 

1983 as part of the Alaska Mineral Resource 

Assessment Program (AMRAP). It was quickly 

realized that time and budget constraints would 

limit mapping coverage. Therefore, at the suggestion of Roger Ashley, we used existing Landsat 

multispectral scanner imagery to aid in locating 

surface alteration, which could be field checked or 

related to stream-sediment or hand-sample geochemical data. 

11J ames E. York, Technicolor Government Services Inc.; work performed under U.S. Geological Survey Contract Number 14-08-001-

20129. 

56 

Landsat imagery can delineate areas of surface alteration by emphasizing their particular 

spectral characteristics. Areas of primarily rock 

and soil were first separated from areas of vegetation, snow, and water by using a digital image of 

Landsat land cover classes prepared for another 

study. Using data from the rock and soil class, we 

tested various processing techniques, including 

contrast stretches, band ratios, classification 

based on spectral brightness, principal component 

transformations, and color transformations. The 

best delineation of known altered areas was obtained with a principal component transformation. 

This transformation is defined such that the first 

principal component contains the largest possible 

variance of the data Each succeeding principal 

component accounts for the largest possible remaining variance while remaining orthogonal to 

all previous principal components. 

Areas of known alteration were delineated 

when threshold values were exceeded in both the 

third and fourth principal components. This procedure also delineated other areas of potential surface alteration with spectral characteristics similar 

to the known altered areas. All areas of known and 

potential surface alteration were then digitally inserted into an image enhanced to show geomorphic 

variations for use in field checking. 

Field checks of the images indicated that most 

digitally selected areas corresponded well to areas 

of surface alteration. All areas of previously 

known surface alteration were visible on the image 

except where the area was in shadow. In addition, 

previously unknown areas of alteration were indicated. The field checking suggested that an important characteristic of the targeted areas was 

the presence of iron staining, which is associated 

with the most common form of surface alteration 

on the Alaska Peninsula 

Limitations of note are (1) the surface alteration must be exposed, though some vegetation 

cover will not significantly affect selection of an 

area; (2) shadowed areas tend to be masked and 

therefore not selected; (3) the surface alteration 

must cover at least one acre to be recognized as a 

single picture element (pixel), though intensely 

altered areas that are smaller may be selected; and 

(4) not all areas of surface alteration are mineralized and not all mineralized areas have this type 

of surface alteration. However, these Landsatderived images are extremely useful in the 

resource assessment and the early stages of evalu-
ation of an area. They allow rapid selection of areas 

that merit detailed field examination and geochemical sampling. 

MAHD ADH DHAHAB, A PROTEROZOIC 

EPITHERMAL PRECIOUS-METAL DEPOSIT, 

KINGDOM OF SAUDI ARABIA 

R.G. Worl and J.L. Doebrich 

Mahd adh Dhahab is the largest of the many 

ancient gold mines scattered throughout the Precambrian Shield of Saudi Arabia and is the only 

one with recent production. More than 2 million 

ounces of gold has been produced from the northern of two known ore zones during ancient and recent times. The southern ore zone, which is about 

the same size as the northern ore zone, was 

discovered by the USGS, was developed by Gold 

Fields-Mahd adh Dhahab, and is being prepared 

for production by PETROMIN. 

The two ore zones are in a north-trending zone 

of faults, altered rock, and metalliferous quartz 

veins and breccias approximately 1,200 ft (360 m) 

wide and 3,500 ft (1,100 m) long that cuts an eaststriking, north-dipping homoclinal sequence of 

volcanic, volcaniclastic, and epiclastic rocks of intermediate to felsic composition. Ore is localized 

where veins and breccias cut competent, coarsegrained, fragmental units directly below incompetent and impermeable fine-grained tuffaceous and 

fragmental units and near an epizonal rhyolite porphyry stock. Mineralization and alteration, except 

for early propylitization and silicification, is interpreted to have been caused by a single, large 

meteoric-water hydrothermal system, heated by 

the rhyolite, that was part of a larger, deeper 

magmatic-hydrothermal system. 

Primary ore is composed of abundant chalcopyrite, sphalerite, pyrite, and less abundant 

complex precious-metal minerals. Gold and silver 

occur mainly as inclusions in chalcopyrite and 

sphalerite and as minute grains of telluride 

minerals disseminated in chlorite bands of banded 

quartz-chlorite-hematite veins. The most common 

telluride minerals are petzite, hessite, and 

sylvanite. Free gold is present but not abundant. 

Reconnaissance study of abundant, minute fluid 

inclusions in quartz veins showed them to contain 

both low-density, vapor-rich fluids and liquid-rich 

fluids. Primary fluid inclusions yielded homogenization temperatures of 110-238 o C. Preliminary 

57 

isotopic analyses of sulfide minerals and quartz 

showed o34S values that range between 1.2 and 

6.3 per mil, a typical range for hydrothermal 

sulfide minerals derived from an igneous sulfur 

source. The sulfur-isotope data and the ore mineral 

assemblages together suggest a large sulfide 

system (porphyry?) at depth. The o1SO values of all 

stages of vein quartz throughout the area range 

between 8.5 and 11.1 per mil; these values indicate 

that the hydrothermal system consisted of 

dominantly meteoric water, which circulated in a 

single system uniform in temperature and o1

SO 

content throughout the area during the entire 

period of mineralization. 

Vein-related alteration, consisting of silicicsericitic-pyritic, chloritic, argillic, and silicic halos, 

was superimposed on broad zones of pervasive 

rhyolitic, silicic, potassic, and argillic alteration. 

Late pervasive propylitic alteration, superimposed 

on all alteration types, represents cooling and 

retrogression following contraction of the hydrothermal system. 

Geochemical, biogeochemical, and geophysical 

anomalies delineate the known ore bodies and suggest the presence of more ore zones in the area 

GENESIS OF METALLIFEROUS SEDIMENT IN THE 

ATLANTIS II DEEP, RED SEA 

Robert A. Zierenberg 

Genetic models of many massive sulfide 

deposits postulate deposition of metalliferous sediment by venting of high-salinity hydrothermal 

fluids onto the sea floor. The Atlantis II Deep, Red 

Sea, is a currently active modern example of such a 

process. Areal extent of the brine pool in the 

Atlantis II Deep exerts primary control on the 

distribution of metalliferous sediment. The presence of a density-stratified brine allows dispersion 

of metal-rich brine to all parts of the deep. Currently, the brine vented in the Southwest Basin 

rises to the density interface between the brine 

pool and overlying seawater and then flows laterally along the interface. The lower brine mass is 

isolated from oxygenated seawater, allowing basemetal sulfides to precipitate in areas far from the 

site of venting. Oxide minerals precipitate at the 

interface. 

The metalliferous sediments are composed primarily of intermixed and interlayered iron-rich 
clays, base-metal sulfides, and iron oxides, and less 

abundant sulfates and carbonates. The metalliferous sediments are extremely fine grained; interstitial water contents in the uppermost sediments 

are greater than 98 percent by weight. Sedimentation rates inside the brine pool are in excess of 

100 em per 1000 yr. High salinity, high temperature, and high trace-metal content of the brine 

produce a toxic environment, which ensures that 

the finely laminated sediments are not disturbed 

by bioturbation. 

In contrast, metalliferous sediment deposited 

in the area of active brine venting is highly disturbed; soft-sediment deformation features are common. Heterolithic and homolithic breccias occur, 

some of which are metalliferous turbidites dislodged by tectonic activity from steep graben walls 

flanking the deep. 

Influx of new brine causes further disruption, 

as well as deposition of epigenetic minerals in 

veins cutting unlithified metalliferous sediment. 

These veins provide a mineralogic record of the incoming hydrothermal fluid as it cools and mixes 

with interstitial brine. Smectites associated with 

the veins change from magnesium-rich saponites 

in the deepest veins to ferroan nontronites, which 

precipitate within the brine pool. Calculation of 

phase relations among smectite end members suggests that the change from magnesian saponite to 

ferroan nontronite results from cooling of the 

hydrothermal fluid. Temperatures calculated from 

oxygen isotopes in smectites range from 64 to 

242 o C and correlate with the Fe/(Fe+ Mg) ratio of 

the smectites, indicating that magnesium-rich 

smectite forms at higher temperature. Temperatures calculated from oxygen isotopes in coexisting anhydrite range from 184 to 264 o C. Anhydrite 1

SO temperatures correlate well with smectite 1SO 

temperatures for the samples formed at higher 

temperature, but it appears that anhydrite 1

SO 

does not maintain equilibrium as the hydrothermal fluid cools. Smectite 1

SO values provide the 

best data for determining the temperature of the 

hydrothermal fluid venting into the Atlantis II 

Deep. 

MINERAL RESOURCE PROGRAMS 

The following section contains extended 

abstracts that briefly explain the various Mineral 

Resource Programs. A detailed explanation of 

each program is presented at a poster session. The 

programs have the following goals: 

To assess the mineral resource potential of specific 

areas in the United States (particularly 

Federal lands) for resource management and 

Congressional action. 

To provide timely assessments of the Nation's 

mineral resources. Such information is important for foreign and domestic policy decisions 

and for long-range planning related to mineral 

supply. 

To identify new areas for exploration and develop 

new concepts of ore formation and distribution to increase our known mineral resources, 

particularly the strategic and critical 

minerals. 

To improve current methodology and develop new 

techniques for identifying and evaluating 

mineral resources and analyzing resource data 

more efficiently and more precisely. 

USGS mineral resource assessments are used in 

land-management decisions at all levels of government, from the Congress and the Executive 

Branch of the Federal Government to State and 

local governments. Resource and geoscience data 

generated through the programs provide basic 

information used for long-range planning for availability of nonfuel minerals on a national and international scale. 

AVAILABILITY AND APPLICATION OF NURE 

DATA SETS IN REGIONAL MINERAL SURVEY 

PROGRAMS OF THE U.S. GEOLOGICAL SURVEY 

Byron R. Berger, Thomas D. Fouch, 

Richard H. Godson, and Bruce F. Molnia 

58 

Comprehensive mineral resource surveys of 

public lands by the USGS and associated Federal 

agencies require the assembly of large amounts of 

geological, geochemical, and geophysical information. Because most of the readily apparent metallic 

and nonmetallic mineral deposits at and near the 

surface have been found, the identification of new 

resources deeper beneath the surface requires both 

adequate amounts of regional data and sophisticated interpretation techniques. In its mineral 

resource surveys, the USGS draws on all available 

published and unpublished data that pertain to 

mineral occurrences. The geochemical and geophysical data sets collected under the National 
Uranium Resource Evaluation (NURE) program 

of the U.S. Department of Energy (DOE) are examples of publicly available information that is being used in USGS programs. 

NURE data available from the USGS fall into 

six major categories: (1) geologic 1:250,000-scale 

quadrangle maps, (2) radiometric data from aerial 

surveys, (3) magnetic data from aerial surveys, (4) 

geochemical data from waters, rocks, and sediments, (5) radiometric data from borehole and 

NURE Drilling Program logging, and (6) evaluation data for resource estimates. These NURE 

data and related DOE publications are available in 

a variety of forms including map separates, openfile reports, and digital tapes. Digital geochemical 

and geophysical data are available from the 

USGS, EROS Data Center in Sioux Falls, South 

Dakota 57918. Publications and map separates are 

available from the USGS, Open-File Services Section, Western Distribution Branch, Denver, Colorado 80225. 

The NURE geochemical data are being used 

with multielement-association models based on 

analyses from the sampled mineralized and unmineralized rock exposures to investigate the 

regional geology and identify different mineral 

deposit types in western Montana These interpretive products can serve as regional evaluations 

for land-management planning purposes, for exploration, and for assessing mineral potential and 

can help define geologic structure. 

The NURE aeromagnetic data have been integrated with other airborne magnetic data to complete maps of large geographic areas such as the 

entire United States and the central midcontinent 

area These serve to elucidate structures, define 

trends in the crystalline basement rocks, and 

outline intrusive masses. 

A long-term comprehensive program is being 

formulated to examine the utility of the various 

types of NURE information in economic assessment of the Colorado Plateaus physiographic province. The relation of radiometric, magnetic, gravity, stream sediment, rock chemistry, and other 

NURE data to the region's known uranium 

deposits and geologic framework will be investigated. The Colorado Plateaus program of NURE 

data assessment and integration potentially involves study of NURE data generated under a 

variety of conditions and techniques in an area described by as many as 32 contiguous 1 o X 2 o maps 

in five States. Uranium deposits in the region exist 

59 

in a complex variety of geologic settings and were 

formed in several episodes of mineralization that 

range in age from late Paleozoic to Holocene. 

Results of these studies can be used to assess the 

utility of the various types of NURE data for 

assessment studies of other mineral deposits, to 

indicate new mineralized areas at the surface or in 

the subsurface, and to refine knowledge of the 

region's geologic framework. 

STRATEGIC AND CRITICAL MINERALS PROGRAM 

Alfred H. Chidester 

The Strategic and Critical Minerals Program 

provides a continuing assessment of the Nation's 

endowment of strategic minerals and a continuing 

analysis of world mineral resources, for the formulation of national minerals policy and the identification of secure sources of minerals that are 

critical to the security, industrial production, and 

economic well-being of the country and that are 

vulnerable to disruptions in supply. The program 

has three principal components: (1) commodity 

resource information and analysis, which includes 

acquiring, managing, and analyzing commodity 

data, applying empirical and genetic mineral 

deposit models to the analysis of commodity data, 

and developing grade and tonnage models of mineral deposits; (2) regional resource information and 

analysis, which includes developing resource 

analysis methodologies; and (3) basic research in 

support of the program's commodity and regional 

resource information and analysis responsibilities. 

Projects in support of the SCM Program are in 

the following categories: 

Commodity resource, in which about 50 commodity geologists keep track of major activities 

and developments in mining, exploration, and 

technology for about 95 commodities. 

Resource analysis methodology-research in techniques and methodologies for carrying out 

resource analysis. 

International resource assessment, in which 

resource assessment specialists and commodity geologists cooperate with foreign counterparts in assessing the mineral resources of a 

developing country. 

Metallogeny-studies of the relationship of 

mineral deposits to particular geologic 

terranes. 
Mineral deposits research-geologic research on 

the characteristics and genesis of selected 

strategic commodities, currently cobalt and 

tin. 

Research support-research on a wide variety of 

geological, geophysical, geochemical, petrologic, mineralogic, and isotopic subjects in 

support of the overall Strategic and Critical 

Minerals Program. 

Midcontinent program-a multidisciplinary study 

(geology, geochemistry, geophysics, geochronology, paleontology, isotope geology, and 

hydrogeology) of the Central United States, 

10 degrees in latitude by 12 degrees in 

longitude, aimed at assessing the mineral 

resources of the buried Precambrian basement 

and the overlying sedimentary rocks. 

Eastern Mesozoic basins-a multidisciplinary 

study of ten basins in the Eastern United 

States to develop deposit models for ore 

deposits in rift-basin and failed-rift environments, particularly for massive sulfides 

of the N oril 'sk type. 

Mineral resource data system (MRDS)-formerly 

known as Computerized Resource Information Base (CRIB), MRDS is a computer-based 

system designed to store, organize, and easily 

retrieve large amounts of mineral data It has 

become a reference tool for Federal, State, and 

industrial scientists seeking descriptive information on mineral localities in the United 

States and in many foreign countries. All data 

in MRDS are organized into records that 

define individual mines, mineral occurrences, 

districts, or regions. Presently, there are about 

72,000 records in the MRDS master file. 

International Strategic Minerals Inventory 

(ISMI)-a cooperative program between the 

United States, Canada, West Germany, Australia, South Africa, and the United Kingdom, 

to compile and report geologic, reserve, production, and trade information on major 

deposits of selected commodities. Deposit 

records for manganese, chromium, nickel, and 

phosphate have been completed, and summary reports for manganese, chromium, and 

phosphate have been published. Compilation 

of deposit records for vanadium, cobalt, 

tungsten, titanium, graphite, and the 

platinum-group elements is now underway. 

THE DEVELOPMENT OF 

ASSESSMENT TECHNIQUES PROGRAM 

Charles G. Cunningham 

The Development of Assessment Techniques 

(DAT) Program is a program of basic and applied 

research on the origin and the geological, 

geochemical, and geophysical expression of 

mineral deposit systems. The objectives are to 

develop concepts and techniques to improve the 

capability of identifying and evaluating mineral 

resources. To achieve these objectives, the program supports multidisciplinary field and laboratory studies directed toward understanding the 

processes by which mineral deposits form and 

developing new technology and models to assess 

the mineral resource potential in areas of concealed 

deposits. 

The studies are organized under the following 

major categories: 

Ore deposit models-Research that includes the 

acquisition and interpretation of fundamental 

geological, geochemical, and geophysical data 

to understand the processes by which deposits 

form and to identify the critical characteristics 

for their recognition. Syntheses of these data 

lead to empirical and genetic deposit models 

that improve the efficiency and effectiveness 

of resource assessments. This research includes multidisciplinary studies of disseminated gold and polymetallic sulfide deposits. 

Geochemical exploration techniques-Field and 

laboratory studies of the processes and products of primary and secondary geochemical 

dispersion of trace and minor elements within 

and surrounding ore deposits. These studies 

include (1) research on regional hydrologic and 

mechanical transport of trace and minor 

elements and on computational techniques for 

data evaluation and interpretation; (2) detailed 

topical investigations of geologic, hydrologic, 

biologic, and atmogeochemical processes and 

the relationship of these processes to geochemical dispersion; and (3) research on 

analytical methods for resource assessment 

and ore deposit research. This category supports the multidisciplinary group studying 

the role of organic material in the formation 

and detection of ore deposits. 

60 
Geophysical exploration techniques-Field and 

laboratory studies of the regional and detailed 

geophysical signatures of ore deposits. The 

studies include (1) research and development 

of new instrumentation, new analytical and 

computational methods, and a comprehensive 

set of computer programs for processing and 

interpreting gravity, magnetic, electrical, and 

electromagnetic data for evaluating ore 

deposits; (2) development and testing of 

remote-sensing techniques to discriminate 

geologic materials, to map altered rocks, and 

to detect structure, using thermal, multispectral, radar, and geobotanical data from 

satellite, aircraft, and ground measurements, 

for mineral resource assessment; and (3) study 

of petrophysical and spectral properties of 

minerals and rocks as an aid for identification 

of ore deposits in conjunction with other 

geophysical and remote-sensing techniques. 

District and deposit studies-Multidisciplinary 

studies of mineralized areas at regional, district, and deposit scales. Establishment of 

geologic syntheses and research on critical factors controlling ore deposition. 

Laboratory studies-Essential technical support 

for geological, geochemical, and geophysical 

research. Concepts and techniques developed 

or refined under this program are used in support of other programs including the 

A..M:RAP, CUSMAP, Mineral Resources of 

Public Lands, and Strategic and Critical Minerals Programs. This support function incorporates proven techniques and methodologies 

and provides a test ground for evaluating new 

technology for future use. 

THE CONTERMINOUS UNITED STATES 

MINERAL ASSESSMENT PROGRAM 

Gary C. Curtin 

Regional assessments of the mineral and 

energy potential of the conterminous United 

States are being made under the Conterminous 

United States Mineral Assessment Program 

(CUSMAP). This program is providing up-to-date, 

systematic assessments of areas that have identified resources or are thought to have potential 

for mineral occurrences, especially strategic and 

critical minerals. Under CUSMAP, 1:250,000-scale 

61 

quadrangles-areas of about 7,500 mP (20,000 

km2)-are assessed for their mineral and energy 

potential by integrating existing information, 

reevaluating known mineral occurrences, and acquiring new data through coordinated geologic, 

geochemical, geophysical, and related studies. The 

results of the assessments are published in folio 

format tailored to meet the needs of existing and 

potential users, such as industry, the public, Congress, other Federal agencies, and State and local 

governments. 

The primary goal of the program is to assess 

the mineral resource potential of 125 selected 

quadrangles during the next several decades. 

Priorities for selection of particular quadrangles 

have been based primarily on the known or 

perceived type and magnitude of their mineral 

potential. Priorities are also based on presence of 

areas, such as Forest Service and Bureau of Land 

Management lands, that are subject to both longterm planning and critical land-use decisions in the 

immediate future. Particular emphasis is placed on 

delineating areas that may contain concealed 

resources of known deposit types and on identifying environments for new types of deposits. Areas 

having potential for the occurrence of strategic 

and other mineral commodities such as cobalt, 

chromium, copper, gold, molybdenum, nickel, lead, 

lithium, tin, tungsten, zinc, and hydrocarbons 

have been identified and assessed during 

CUSMAP studies. 

To date, assessments of nine quadrangles 

have been completed (fig. 1) and the maps and 

reports describing their mineral potential have 

been published, together with maps showing their 

geologic, geochemical, and geophysical characteristics.12 Fieldwork in an additional seven quadrangles has been completed, and the folio reports 

are in preparation. Fieldwork is underway in eight 

quadrangles. The program has proven valuable in 

providing (1) an appropriate and effective base for 

tying mineral occurrenc-e and mining district data 

together on a regional basis, (2) a mineral data 

base for broader scale assessments in metallogenic 

provinces, and (3) a regional mineral resource 

framework for more detailed studies being made 

for Federal land-use and other critical policy decisions. Where appropriate, CUSMAP studies are 

12A listing of reports prepared under CUSMAP is available from the 

office of Mineral Resources, U.S. Geological Survey, 913 National 

Center, Reston, VA 22092; phone (703) 860-6561. 
0"1 

N 

mm 

§ 

Completed or scheduled for 

completion through 1985 

Quadrangles under study 

~ ~ Mineralized areas 

FIGURE I.-Status of systematic mineral resource assessments of conterminous United States 1:250,000-scale quadrangles. 
closely coordinated with those of other USGS programs that deal with mineral resources, in order to 

provide the most effective data for furthering our 

knowledge of the Nation's mineral resources. 

URANIUM AND THORIUM INVESTIGATIONS 

IN THE U.S. GEOLOGICAL SURVEY 

Thomas D. Fouch and Jennie L. Ridgley 

In 1984, the full responsibility for the geologic 

resources studies of uranium and thorium deposits 

was passed from the U.S. Department of Energy 

(DOE) to the USGS. The transfer of that responsibility has somewhat altered the USGS basic 

science program of uranium and thorium investigations to reflect the Survey's requirement to respond to the Nation's need for basic information 

on uranium and thorium geology and resources. 

As a result, the current goals of the USGS 

Uranium and Thorium research program are (1) to 

improve the understanding of the geologic habitat 

and distribution of identified domestic resources of 

uranium and thorium, (2) to apply this understanding to the development of regional guides to assess 

the undiscovered resources, and (3) to develop 

techniques for increasing the discovery rate and 

exploitation of economically recoverable nuclear 

raw materials. Attainment of these goals permits 

the USGS to advance the basic science of uranium 

and thorium geology, to provide information on 

undiscovered uranium and thorium endowment to 

the Energy Information Administration (E lA) of 

the DOE, and to assess the validity and utility of 

data sets and samples collected under the DOE's 

National Uranium Resource Evaluation (NURE) 

program. 

The Uranium and Thorium program concentrates much of its effort on topics or geographic 

areas where study results can be expected to affect 

estimates of undiscovered uranium and thorium 

endowment most significantly. Four major geographic and topical areas for new emphasis have 

been identified, and program resources are being 

focused in these areas. They are (1) surficial 

uranium deposits (SUDS) throughout the United 

States, (2) uranium in sedimentary breccia pipes of 

the southern Colorado Plateaus, (3) uranium in 

metamorphic rocks of the Piedmont physiographic 

province of the Eastern United States, and (4) 

uranium in sedimentary rocks of the northern 

Great Plains. These and other program geologic 

63 

research studies that are continuing in sedimentary, igneous, and metamorphic rocks in various 

parts of the United States will produce topical 

scientific products in the fields of radiogenic and 

stable isotopes, paleogroundwater movement, 

water-water and rock-water reactions, geochemical 

redox systems, and organic geochemical-metal 

deposit relations. 

The SUDS project has been examining uraniferous organic-matter-rich sediments in surficial environments in several Western, Rocky Mountain, 

and Northeastern States. These uraniferous 

sediments commonly are developed in mountain 

terrain underlain by granitic rocks. A Holocene 

boggy meadow in Washington State is currently 

being mined for uranium. Other surficial deposits 

of the Southwest United States and southwestern 

Great Plains are associated with caliche formation. 

In northern Arizona, Paleozoic formations 

contain breccia pipes filled with blocks of country 

rock (sandstone, shale, and limestone). Some pipes 

are mineralized with uranium, copper, cobalt, and 

precious metals. Mineralized pipes in the region 

contain small but rich uranium ore bodies, some of 

which are now the focus of mining activity. 

In Virginia, altered Paleozoic metamorphic 

rocks of the Piedmont province are locally rich in 

uranium minerals. Similar occurrences may exist 

elsewhere in the province where tectonic and mineralizing events seem comparable. 

USGS Uranium and Thorium program efforts, 

begun before 1984, will continue in the San Juan 

and other Rocky Mountain basins, in the Lake 

City caldera region of southwest Colorado, and 

through topical studies of world-class uranium 

deposits. 

MINERAL RESOURCES OF PUBLIC LANDS 

Gus H. Goudarzi and Susan M. Marcus 

The objectives of the Mineral Resources of 

Public Lands Program are to conduct mineral 

surveys to assess the mineral resource potential of 

those Forest Service lands that are included or are 

proposed for inclusion in the National Wilderness 

Preservation System and of those lands administered by the Bureau of Land Management for 

which a preliminary determination of wilderness 

suitability has been made (fig. 2). A mineral survey 

involves coordinated geologic, geochemical, and 
FOREST SERVICE NEEDS 

Wilderness type study - PL. 88-577 - 1 :50,000 scale 

Statutory requirements 1965-1984- PL. 88-577- 1:50,000 scale 

RPA. -PL. 93-378, 1974 NFMA. PL.-94-588, 1978- 1:250,000 scale 

About 220 million acres - 155 National Forests 

CJ 

1:250,000 1:50,000 

BUREAU OF LAND MANAGEMENT NEEDS 

Wilderness type study PL. 88-577 

Federal Land Pol icy and 

Management Act ( FLPMA) 

23.2 million acres -judged preliminarily 

suitable for wilderness 

ISA - Instant Study Areas 

COCA- California Desert Conservation Areas 

WSA - Wi 1 derness Study Areas 1 :50,000 

FIGURE 2.-U.S. Geological Survey Wilderness Mineral Surveys on lands managed by the Forest Service and the Bureau of Land 

Management. RPA, Forest and Rangeland Renewable Resources Planning Act of 1974; NFMA, National Forest Management 

Act of 1976. 

64 
geophysical studies, which provide data for estimating identified resources and the potential for 

the occurrence of undiscovered mineral resources 

in a designated area. Mineral resources of public 

lands are usually assessed through applying occurrence models to the geologic terranes of those 

lands. 

Principal products of a wilderness mineral 

survey are a mineral resource report and a mineral 

resource potential map at a scale that ranges from 

1:24,000 to 1:250,000, depending on the size of the 

area The data and interpretations used in the 

assessment of the mineral resource potential are 

published as Miscellaneous Field Studies (MF) 

maps, including geologic, geochemical, and geophysical maps, or as open-file reports. Where 

appropriate, a mines and prospect map is also 

prepared. 

Through this program, geologic maps at appropriate scales delineate rock units and structures that control known or potential mineral and 

energy resources. Geochemical surveys determine 

patterns of anomalous metal values indicative of 

concealed mineral deposits. Geophysical studies 

determine regional variations in magnetic, gravity, and electrical fields to identify geologic 

environments favorable for the occurrence of concealed mineral deposits. 

The recently published two-volume U.S. Geological Survey Professional Paper 1300 summarizes and presents the results of twenty years of 

mineral surveys on about 45 million acres of public 

lands, chiefly in the National Forests, in a form 

that decisionmakers will be able to use effectively 

in balancing wilderness preservation against mineral resource availability. These studies were made 

under the provisions of the Wilderness Act of 

1964, Public Law 88-577. 

U.S. Geological Survey Circular 901 describes 

the joint mineral surveys conducted by the USGS 

and U.S. Bureau of Mines of those public lands 

preliminarily recommended by the Bureau of Land 

Management as suitable for inclusion in the National Wilderness Preservation System. These 

studies are made under the provisions of the 

Federal Land Policy and Management Act of 

1976, Public Law 94-579. Thus far, studies have 

been completed on more than 3 million acres; 

about 10 million acres remain to be studied by 

1991. 

65 

References Cited 

Marsh, S.P., Kropschot, S.J., and Dickinson, R.J., eds., 1984, 

Wilderness mineral potential: U.S. Geological Survey Professional Paper 1300, 1183 p. 

Beikman, H.M., Hinkle, M.E., Frieders, Twila, Marcus, S.M., 

and Edwards, J .R., 1983, Mineral surveys by the Geological Survey and the Bureau of Mines of Bureau of Land 

Management Wilderness Study Areas: U.S. Geological 

Survey Circular 901, 28 p. 

FEDERAL MINERAL LAND 

INFORMATION SYSTEM 

Richard L. Kleckner 

The U.S. Geological Survey is developing the 

Federal Mineral Land Information System 

(FMLIS), which will allow land managers, policymakers, and others to rapidly retrieve, display, 

and analyze minerals information on Federal lands 

at regional, State, and National levels. This 

capability is being developed in order to input, 

manipulate, analyze, and output digital data 

through a geographic information system (GIS). A 

GIS is a tool for integrating and analyzing spatial 

data Functions within a GIS allow for changes in 

map scale and projection; data editing; registration and overlay; selection, retrieval, and display 

of data; tabulation of acreages; and measurement 

of distances. In an interactive environment, the 

user can rapidly analyze data, examine alternatives, and test hypotheses. 

The types of data to be analyzed in the Federal 

Mineral Land Information System include Federal 

surface ownership; subsurface mineral rights; 

restrictions to mineral development; identified 

mineral occurrences, mines, and deposits; and 

designations of mineral potential. Base cartographic data such as political boundaries, public 

land survey system, transportation, and hydrography provide a basis for locating and relating the 

FMLIS data. 

To move from a concept to an operational 

system requires research on data sources, data 

capture, GIS development, system maintenance, 

and coordination. Through 1985, the primary emphasis will be on developing the utility of the 

system and its ability to retrieve, display, and 

analyze minerals information on Federal lands. 
Specifically, the objectives of FMLIS are to (1) 

develop a GIS containing information on surface 

ownership, subsurface mineral rights, restrictions 

to mineral development, mineral occurrences, and 

designations of mineral potential for Federally 

owned or managed land, (2) develop procedures for 

accessing and analyzing data in the GIS in line 

with agency requirements, (3) establish agreements with appropriate Federal agencies for inputting and maintaining data in the GIS, and (4) 

implement procedures for an operational system 

by FY 1986. 

THE U.S. GEOLOGICAL SURVEY EEZ PROGRAM 

Terry W. Offield 

The Exclusive Economic Zone (EEZ) proclaimed by President Reagan in 1983 enlarges the 

Nation's offshore domain to about 3 billion acres. 

Extending to 200 nautical miles, much of this area 

is literally frontier, containing vast areas of Continental Shelf, Slope, and Rise and deep sea floor 

about which only the most rudimentary information exists. The EEZ is believed to have major 

energy and mineral resource potential. Estimates 

are that about one-third of the oil and gas yet to be 

discovered in the United States will be found in 

offshore areas. Potentially economic deposits include massive sulfide deposits found in ocean 

spreading centers, cobalt-rich manganese crusts 

on seamount surfaces, nearshore heavy-mineral 

placers, phosphorite, and sand and gravel. 

The USGS marine-geology program is designed to acquire the information on geologic settings and history, geologic processes past and 

present, and resource occurrence or potential that 

will be needed for a national effort to explore and 

develop the EEZ. A first, major step, which will require many years, is the preparation of maps of the 

sea floor. Sidescan sonar image mosaics that 

already have been produced in preliminary form 

cover the conterminous Pacific EEZ from the edge 

of the shelf to 200 nautical miles. The images show 

the sea floor at 60-100 m. More than 100 new 

volcanos have been found, some as large and freshappearing as Mount St. Helens; the Juan de Fuca 

and Gorda spreading centers are seen in their entirety, along with the fracture zones that terminate them; major river courses meander down 

the slope and across the deep sea floor for hun66 

dreds of kilometers; ripple-like large-scale bedforms have been seen at water depths of more than 

3,500 m; and large subsea landslides have been 

delineated. Similar reconnaissance imaging of the 

EEZ around the continent will be done over the 

next few years, to be followed by surveys of the 

Hawaiian region and the EEZ around U.S.-related 

Pacific islands. Bathymetric mapping is underway 

through a cooperative agreement with the National Oceanic and Atmospheric Administration. 

Geophysical surveying and geologic mapping 

continue and will expand to cover the slope and 

rise and deep sea floor. Existing geophysical and 

geologic data will be compiled and interpreted. 

Other studies address the geologic processes that 

produced the rocks and their settings. Observations include sampling from shallow and deep drill 

holes as available, patterns of sedimentation and 

erosion both in modem environments and in the 

rock record, chemistry and petrology of the rocks 

of the seabed and below, comparison of rocks and 

structures in similar settings offshore and on land, 

and organic geochemical character of rocks and 

their environments to appraise the thermal 

maturation histories. Studies also focus on the 

geology and processes of resource formation and 

occurrence. Manganese crust samples from oceanographic institution archives are being collected 

and analyzed for cobalt, nickel, and trace elements; 

new surveys will probe the occurrence and origin 

of such crusts on mid-Pacific seamounts. Other 

studies focus on the geology of ocean spreading 

centers and the massive sulfide deposits that occur 

in such areas of interaction of seawater and new 

basaltic crust. These studies address questions of 

chemical and mineralogical differences between 

areas, processes of mineralization, comparison 

with ancient onshore deposits believed to be of 

similar origin, and resource potential. 

THE ALASKA MINERAL RESOURCES 

ASSESSMENT PROGRAM 

Gary R. Winkler 

AMRAP (Alaska Mineral Resources Assessment Program), the prototypic U.S. Geological 

Survey regional resource assessment program, 

enters its second decade with the continuing goal 

to provide comprehensive information on the mineral and energy resource endowment of Alaska to 
C'l 

........ 

-'--._ 

'------.________ 

---------

~',, ",;L_,"' I 

I 

_l44_\" -'r-- UNITED STATES ~-JO" I J 1..-<1 N H DEPARTMENT OF THE INTERIOR --6.1) GEOLOGICAL SURVEY 

O•c e ROCKY 

TOPOGRAPHIC 

MOUNTAIN MAPPING 

DIVISION 

C'EN1'~~ -1"" DENVER, COLORADO 

I --------------- ALASKA 

p A C F I C 

--------------------

EXPLANATION 

~ Folio published or in press 

at the end of 1984 

a 

Quadrangles in progress 

m 

Study begun in 1981 to meet 

requirements of ANTLCA 

~ Priority quadrangles tentatively 

scheduled to begin 1985 to 1990 

FIGURE 3.-Status of the Alaska Mineral Resources Assessment Program (AMRAP), February 1985, showing 1:250,000 quadrangles completed, in progress, or scheduled 

for study in the next five years. Regions of the State that are covered by summary mineral resource folios at scales of 1:600,000 to 1:1,000,000 are outlined by bold lines. 
the public, the private sector, the academic community, and those who are concerned with national mineral policy. The program is designed (1) 

to provide information to land management agencies for decisions regarding the classification and 

allocation of Alaska's Federal lands in response to 

mandates of the Alaska National Interest Lands 

Conservation Act (ANILCA); (2) to produce systematic, state-of-the-art geoscience information to 

the mineral and energy industries, Alaska natives, 

and other public and private interests concerned 

with exploration and development of Alaska's 

resources; and (3) to expand the general knowledge 

of Alaska's complex geological setting, much of 

which is known presently only in reconnaissance. 

In order to meet these broad objectives, 

AMRAP conducts four levels of study at progressively greater detail: Level 1, statewide compilations to identify the total mineral and energy 

resource base available for national needs; Level2, 

synoptic regional assessments of geologic provinces (scale, 1:1,000,000), with an analysis of probable sizes and grades of potential resources (fig. 3); 

Level 3, interdisciplinary studies of key 

1:250,000-scale quadrangles that are thought to 

have significant mineral or energy potential (fig. 

3); and Level 4, investigations of mineral districts 

and deposits, energy provinces, and technical 

topics that will aid in interpreting the setting and 

character of specific mineral or energy resources in 

Alaska 

The core of the program presently is Level 3 

studies. Fieldwork has been completed in 33 quadrangles, and complete folios (which include geologic, ·geochemical, and geophysical maps, a 

mineral and energy resource assessment, a summary circular, and derivative reports) are available 

for 19 of those quadrangles. Many individual folio 

components are available presently for the other 

14, and investigations continue in 16 quadrangles. 

68 

About 40 percent of the quadrangles intended for 

completion in the program are completed or are being studied. When key quadrangles in a large 

region or geological province have been completed 

(for example, the Seward Peninsula), a Level 2 synthesis is begun or updated. A regional mineral 

resource assessment for southeastern Alaska has 

been completed recently that has drawn upon new 

detailed Level 3 studies. A similar stage will be 

reached soon for the Alaska Peninsula, the Brooks 

Range, and the eastern part of southern Alaska 

(fig. 3). Synoptic mineral and energy resource 

assessments will provide up-to-date information 

on the potential for these regions and will show 

where additional information is needed. 

Level 4 research investigations always have 

been an integral part of AMRAP. These studies include a broad spectrum of topical or detailed 

geological mapping, geochemical and isotopic 

studies, chronostratigraphic and biostratigraphic 

interpretation, geophysical studies, and evaluation 

of specific mineral or energy resource occurrences 

or commodities. Work currently underway on 40 

projects will improve mineral deposit models, 

appraise specific resource potentials, and provide 

data that can directly aid exploration and 

development. 

Two approaches in Level 4 studies will be accelerated in the next few years. First, detailed and 

comprehensive occurrence studies have begun of 

large, high-grade districts, such as the Red Dog 

and affiliated deposits in the western Brooks 

Range, and districts that have unique features, 

such as the southern Ambler district in the 

southwestern Brooks Range, where the copperbase-metal deposits are rich in cobalt. Secondly, 

detailed multidisciplinary studies of strategic commodities, such as tin and chromium, have begun 

because knowledge of Alaska's large apparent 

resources will be important in the future. 
ORGANIZATION OF THE U.S. GEOLOGICAL SURVEY 

Office Name Telephone City 

Office of the Director 

Director Dallas L. Peck 703/860-7411 Reston 

Associate Director Doyle G. Frederick 703/860-7412 Reston 

Assistant Director for Research Bruce B. Hanshaw 703/860-7 488 Reston 

Assistant Director for Engineering Geology James F. Devine 703/860-7 491 Reston 

Assistant Director for Administration Edmund J. Grant 703/860-7201 Reston 

Assistant Director for Programs Peter F. Bermel 703/860-7 435 Reston 

Assistant Director for Intergovernmental 

Affairs John J. Dragonetti 703/860-7414 Reston 

Chief, Public Affairs Office Donovan B. Kelly 703/860-7 444 Reston 

Assistant Director for Information Systems James E. Biesecker 703/860-7108 Reston 

National Mapping Division 

Chief Rupert B. Southard 703/860-6231 Reston 

Geologic Division 

Chief Geologist Robert M. Hamilton 703/860-6531 Reston 

Water Resources Division 

Chief Hydrologist Philip Cohen 703/860-6921 Reston 

ORGANIZATION OF THE GEOLOGIC DIVISION 

Office of the Chief Geologist 

Chief Geologist Robert M. Hamilton 703/860-6531 Reston 

Associate Chief Geologist William C. Prinz 703/860-6532 Reston 

Assistant Chief Geologist for Program Benjamin A. Morgan 703/860-6584 Reston 

Assistant Chief Geologist, Eastern Region Bruce R. Doe 703/860-6631 Reston 

Assistant Chief Geologist, Central Region Harry A. Tourtelot 303/236-5438 Denver 

Assistant Chief Geologist, Western Region Carroll Ann Hodges 415/323-8111 Menlo Park 

Office of Mineral Resources 

Chief Glenn H. Allcott 703/860-6561 Reston 

Chief, Branch of Alaskan Geology Thomas P. Miller 907/786-7 403 Anchorage 

Chief, Branch of Eastern Mineral Resources Bruce R. Lipin 703/860-6913 Reston 

Chief, Branch of Central Mineral Resources Charles H. Thorman 303/236-5568 Denver 

Chief, Branch of Western Mineral Resources Edwin H. McKee 415/323-8111 Menlo Park 

Chief, Branch of Exploration Geochemistry Byron R. Berger 303/236-1800 Denver 

Chief, Branch of Resource Analysis Lawrence J. Drew 703/860-6446 Reston 

Chief, Branch of Analytical Chemistry Philip A. Baedecker 703/860-7246 Reston 

Chief, Branch of Geophysics Frank C. Frischknecht 303/236-1204 Denver 

Office of Energy and Marine Geology 

Chief Terry W. Offield 703/860-6431 Reston 

Chief, Branch of Oil and Gas Resources Dudley D. Rice 303/236-5 711 Denver 

Chief, Branch of Coal Resources Robert L. Rioux (Acting) 703/860-7734 Reston 

Chief, Branch of Energy Minerals Thomas D. Fouch 303/236-1644 Denver 

Chief, Branch of Pacific Marine Geology David G. Howell 415/323-8111 Menlo Park 

Chief, Branch of Atlantic Marine Geology William P. Dillon 617/548-8700 Woods Hole 

69 
Office 

Office of Regional Geology 

Chief 

Chief, Branch of Eastern Regional Geology 

Chief, Branch of Central Regional Geology 

Chief, Branch of Western Regional Geology 

Chief, Branch of Isotope Geology 

Chief, Branch of Astrogeology 

Chief, Branch of Paleontology and 

Stratigraphy 

Name 

Eugene H. Roseboom 

Gregory S. Gohn 

Robert B. Raup 

Desiree E. Stuart- Alexander 

Robert E. Zartman 

Gerald G. Schaber 

Richard Z. Poore 

Office of Earthquakes, Volcanoes, and Engineering 

Chief John R. Filson 

Chief, Branch of Engineering Seismology 

and Geology 

Chief, Branch of Global Seismology and 

Geomagnetism 

Chief, Branch of Seismology 

Chief, Branch of Engineering Geology and 

Tectonics 

Chief, Branch of Tectonophysics 

Chief, Branch of Igneous and Geothermal 

Processes 

Office of Scientific Publications 

Chief 

Office of International Geology 

Chief 

Addresses 

U.S. Geological Survey 

Reston, VA 22092 

U.S. Geological Survey 

Branch of Alaskan Geology 

4200 University Drive 

Anchorage, AK 99508-4667 

Thomas C. Hanks 

Robert P. Masse 

William L. Ellsworth 

Albert M. Rogers 

Wayne R. Thatcher 

L.J. Patrick Muffler 

John M. Aaron 

A. Thomas Ovenshine 

U.S. Geological Survey 

Box 25046 

Denver Federal Center 

Denver, CO 80225 

U.S. Geological Survey 

2255 North Gemini Drive 

Flagstaff, AZ 86001 

70 

Telephone City 

703/860-6411 Reston 

703/860-6404 Reston 

303/236-1259 Denver 

415/323-8111 Menlo Park 

303/236-7880 Denver 

602/527-7015 Flagstaff 

703/860-7289 Reston 

703/860-64 71 Reston 

415/323-8111 Menlo Park 

303/236-1510 Denver 

415/323-8111 Menlo Park 

303/236-1585 Denver 

415/323-8111 Menlo Park 

415/323-8111 Menlo Park 

703/860-6575 Reston 

703/860-6418 Reston 

U.S. Geological Survey 

345 Middlefield Road 

Menlo Park, CA 94025 

U.S. Geological Survey 

Quissett Campus, Building B 

Woods Hole, MA 02543 
INDEX OF AUTHORS 

Armstrong, Augustus K. ------------------------ 3 

Bagby, W.C. --------------------------------- 1 

Brurton,Paul---------------------------------- 30 

Bawiec, W.J. --------------------------------- 40 

Berger, Byron R. ------------------------------ 58 

Bischoff, James L. ----------------------------- 27 

Blakely, R.J. --------------------------------- 40 

Bodnar, Robert J. ----------------------------- 1 

Botbol, Joseph M. ----------------------------- 16 

Hove, D.J. ----------------------------------- 14 

Briskey, Joseph A ----------------------------- 3 

Campbell, David L. ---------------------------- 3 

Cannon, William F.---------------------------- 4 

Case,J.E.------------------------------------ 5 

Page 

Cathcart, James B. ---------------------------- 7 

Chao, T.T. ----------------------------------- 29 

Chidester, Alfred H. ---------------------------- 59 

Chou, I-Ming --------------------------------- 1 

Clague, David A ------------------------------ 8,27 

Cole, George P. ------------------------------- 3 

Collins, William E. ------------------------------ 43 

Connelly, Thomas J. --------------------------- 8 

Conway, Clay M. ------------------------------ 8 

Cox, D.P. ------------------------------------ 52 

Cunningham, Charles G. ------------------------ 3,33,60 

Curtin, Gary C. ------------------------------- 61 

Czamanske,G.K. ------------------------------40 

Dersch, John S. ------------------------------- 53 

Desborough, George A ------------------------- 43 

DeYoung, Jr., John H.-------------------------- 32 

Dingess, Paul R. ------------------------------ 3 

Doebrich, J.L. -------------------------------- 57 

Drew, L.J. ----------------------------------- 40 

du Bray, Edward A ---------------------------- 9 

Duval, Joseph S. ------------------------------ 3 

Dyni, John R. --------------------------------- 10 

Elliott, Sarah S. ------------------------------- 55 

Erdman,J.A.--------------------------------- 30 

Erickson, M.S. -------------------------------- 10 

Erickson, R.L. -------------------------------- 10 

Escowitz, Edward C. --------------------------- 16 

Flanigan, Vincent J. --------------------------- 11 

Foose, Michael P. ------------------------------ 12,40 

Force, Eric R. --------------------------------- 4 

Fouch, Thomas D. ----------------------------- 58,63 

Fournier, Robert 0. ---------------------------- 13 

Gair, Jacob E. -------------------------------- 14 

Gaylord, Walt B. ------------------------------ 3 

Gilbert, Raymond C. --------------------------- 3 

Godson, Richard H. ---------------------------- 58 

Goldfarb, R.J. -------------------------------- 1 

Gottfried, David ------------------------------ 46 

Goudarzi, Gus H. ------------------------------ 63 

Grauch, R.I. ---------------------------------- 14 

Grauch, V.J.S. -------------------------------- 14,15 

Grosz, Andrew E. ----------------------------- 16 

Grybeck, Donald J. ---------------------------- 17 

Haas, Jr., John L. ----------------------------- 45 

71 

Page 

Hall, Robert B. -------------------------------- 24 

Hall, Wayne---------------------------------- 19 

Hatch, Joseph R. ------------------------------ 20 

Hatcher, Patrick G. ---------------------------- 21,39 

Hathaway, John C. ---------------------------- 16 

Hearn, Jr., B. Carter --------------------------- 22 

Hein, James R. ------------------------------- 23 

He~.R.L.------------------------------------ 40 

Hemingway, Bruce S. -------------------------- 45 

Heyl, Allen V. -------------------------------- 20,24 

Hinkle, Margaret E. ---------------------------- 25 

Hofstra, Albert H. ----------------------------- 28 

Holmes, Mark -------------------------------- 8 

Hon, Ken ------------------------------------ 14 

Horton, Robert ------------------------------- 26 

Jones, O.D. ---------------------------------- 43 

King, J. David -------------------------------- 20 

Kleckner, Richard L. --------------------------- 65 

Klein, T.L. ----------------------------------- 47 

Kleinkopf, M.D. ------------------------------- 40 

Koski, Randolph A ---------------------------- 27 

Koslow, M.H. --------------------------------- 43 

Landis,G.P.---------------------------------- 28 

Lange, Ian M. -------------------------------- 36 

Leach, David L. ------------------------------- 28 

Learned, Robert E. ---------------------------- 29 

Leonard,B.F.--------------------------------- 30 

Lipin, Bruce R. ------------------------------- 40 

Loferski, Patricia J. ---------------------------- 40 

Long, Carl L. --------------------------------- 11 

Lopez, Ricardo -------------------------------- 16 

Ludington, Steve------------------------------ 19,30 

Luedke,RobertG.----------------------------- 31 

Madden, Dawn J. ------------------------------ 49 

Manheim, FrankT. ----------------------------23 

Marcus, Susan M. ----------------------------- 63 

McCammon, Richard B. ------------------------ 32 

McCarthy, J. Howard -------------------------- 25 

McGee, Elaine S. ------------------------------ 22 

McGee, Linda G. ------------------------------ 44 

McKown, D.M. ------------------------------- 30 

Medlin, Antoinette L. -------------------------- 32 

Molnia, Bruce F. ------------------------------ 58 

Mosier, E.L. ---------------------------------- 10 

Naeser, C.W. --------------------------------- 3,33 

Nelson, Steven W. ----------------------------- 17,34 

Nokleberg, Warren J. --------------------------- 36 

Northrop, H. Roy------------------------------ 38 

Offield, Terry W. ------------------------------ 66 

Orem, William H. ------------------------------ 39 

Owens, James P. ------------------------------ 39 

Page, Norman J ------------------------------- 19,40 

Parduhn, Nancy L. ---------------------------- 42,55 

Pickthorn, W.J. ------------------------------- 1 

Pitkin, James A ------------------------------ 3 

Podwysocki, M.H. ----------------------------- 43 

Poole, Forrest G. ------------------------------ 43 

Poppe, Laurence J. ---------------------------- 16 
Page 

Power, ~.S. ---------------------------------- 43 

Raines, Gary L. ------------------------------- 44 

Reynolds, R.L. -------------------------------- 14 

Ridgley, Jennie L. ----------------------------- 63 

Robie, Richard A. ----------------------------- 45 

Robinson, Jr., Gilpin R. ------------------------- 46 

Robison, Lori C. ------------------------------- 8 

Roedder, Edwin ------------------------------- 1 

Rytuba, James J. ------------------------------ 47 

Sanzolone, Richard F. -------------------------- 29 

Schmidt, R.G. -------------------------------- 47 

Schuenemeyer, J.H. ---------------------------- 40 

Shawe, Daniel R. ------------------------------ 48 

Silberman, ~iles L. ---------------------------- 42,49 

Sims, P.K. ----------------------------------- 51 

Singer, D.A. ---------------------------------- 52 

Smith, Bruce D. ------------------------------- 26 

Smith, RobertL. ------------------------------52 

72 

Page 

Spiker, Elliott C. ------------------------------ 39 

Steven, Thomas A. ---------------------------- 3 

Sutley, StevenJ. ------------------------------44 

Sutphin, David ~- ----------------------------- 32 

Taylor, Richard B. ----------------------------- 53 

Theodore, Ted G. ------------------------------ 19 

Updegraff, David ~- --------------------------- 55 

USGS Juan de Fuca Study Group----------------- 54 

Viets, J.G. ----------------------------------- 10 

Watterson, John R. ---------------------------- 42,55 

Whitney, Gene -------------------------------- 38 

Williams, S. Jeffress --------------------------- 16 

Wilson, Frederic H. ---------------------------- 56 

Winkler, Gary R. ------------------------------ 66 

Worl, R.G. ----------------------------------- 57 

York, James E. ------------------------------- 56 

Zientek, ~.L. --------------------------------- 40 

Zierenberg, Robert A. -------------------------- 27,57