Ash-flow tuffs and lava flows in the 

Mount Belknap caldera, Utah. 
USGS Research on Mineral Resources-1987 

Program and Abstracts 

Edited by Janet Somervi lie Sachs 

Third Annual V. E. McKelvey Forum on 

Mineral and Energy Resources 

U.S. Geological Survey Circular 995 
DEPARTMENT OF THE INTERIOR 

DONALD PAUL HODEL, Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Free on application to the Books and Open-File Reports Section, 

U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 
A society's wealth depends on the use it makes of raw materials, 

energy, and especially ingenuity. 

-V. E. McKelvey 

1916-1987 

Foreword 

The first two V. E. McKelvey Forums, in 1985 and 1986, were exceptionally well-attended by industrial, State and Federal government, and 

academic members of the earth science community. This participation 

resulted in many positive contributions to U.S. Geological Survey programs 

in mineral and energy resources. Through active exchanges of ideas between Geological Survey scientists and the people attending the Forums, 

we learned firsthand about the changing needs of the mineral and energy 

industries, and we found new ways to make significant improvements in 

our programs. 

The Forum is named for 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 Geological Survey. We were very fortunate to have Vince attend 

the first two Forums. The meeting is an annual event, and the subject matter alternates yearly between mineral and energy resources. Though the 

format of the meeting may change from year to year, the primary purpose 

will remain the same-to encourage direct communication between 

Geological Survey scientists and earth scientists in the industrial, academic, 

and government communities. 

Current programs in mineral-resource investigations at the Geological 

Survey include strategic and critical minerals, wilderness mineral evaluations, regional mineral assessments, and geochemical and geophysical 

research on new exploration techniques. The topics of papers at the 1987 

Forum span a very wide range of research; precious- and base-metal studies 

in ultramafic deposits in Alaska, geophysical research on disseminated gold 

deposits in Nevada, minerals in agriculture, isotopic research on mineral 

systems, nuclear borehole logging for critical metals, and the role of aqueous 

systems in the formation of mineral deposits are representative of the 95 

papers for the Forum. 

I am extremely pleased with the success of the two previous Forums, and 

I look forward to a highly useful and productive 1987 meeting. All of us 

at the Geological Survey welcome this opportunity to discuss our research 

with our colleagues in industry, academia, and government and to hear 

about ways we can better serve the mineral-resource needs of the public. 

v 

Dallas L. Peck 

Director 
PROGRAM CHAIRMEN 

(Semicolon indicates change in chairmanship) 

Technical Session 1 

Gary R. Winkler, Charles H. Thorman; Thomas G. 

Hildenbrand, David A. Lindsey 

Technical Session 2 

Byron R. Berger. Edwin H. McKee; Donald J. Grybeck, 

Frederick S. Fisher 

Technical Session 4 

Bruce R. Lipin, Lawrence J. Drew 
PROGRAM 

Tuesday Afternoon, March 10, 1987 

4:00 Registration (East Lobby) 

5:00 Ice-breaker/Cash Bar Mixer (East Lobby) 

Wednesday Morning, March 11, 1987-

Technical Session 1 

8:00 

8:10 

8:50 

9:00 

9:20 

9:40 

10:00 

10:20 

10:40 

11:00 

11:20 

11:40 

12:00 

Welcome and opening remarks (Dallas L. Peck and 

Robert M. Hamilton) 

Keynote Address: "International perspective on mineral resources" (Prof. Dr. Martin 0. C. Kursten, President, BGR, Hannover, Federal Republic of Germany) 

Overview of USGS mineral-resource program and 

activities (Glenn H. Allcott) 

Application of deposit models in U.S. Geological Survey programs (Dennis P. Cox and Donald A. Singer) 

Tectonic setting of some Cretaceous and Cenozoic 

structural and magmatic systems of the Western 

United States (Warren B. Hamilton) 

Post-Laramide magmatism in the U.S. Cordillera 

(Robert L. Christiansen) 

Coffee break 

The role of regional aeromagnetic and gravity data in 

mineral-resource investigations, southeastern 

Nevada (H. Richard Blank) 

Central San Juan caldera cluster, Colorado-New 

stratigraphic and structural interpretations and 

implications for mineralization {Peter W. Lipman 

and Marvin A. Lanphere) 

Quantitative analysis of fluid-inclusion gases-Applications to studies of ore deposits {Gary P. Landis, 

Albert H. Hofstra, David L. Leach, Jr., and Robert 

0. Rye) 

Sulfide solubilities in buffered systems at elevated 

pressures and temperatures and their depositional 

implications ( J. Julian Hemley, Gary L. Cygan, and 

William M. d 'Angelo) 40 Ar/39 Ar thermochronology of mineral depositsInformation on age, duration, number of episodes, 

and temperature of mineralization {Lawrence W. 

Snee) 

McKelvey Forum Luncheon {Harry A. Tourtelot, 

presiding) 

Welcome by Colorado State Geologist {John W. Rold) 

Luncheon Address: "The appropriate role of government in mineral-resource research" {Sen. Harrison 

H. Schmitt, Consultant, Albuquerque, NM) 

Wednesday Afternoon, March 11, 1987-

Technical Session 2 

2:00 New geochemical guides to Au-rich Co-Cu lodes in 

the Blackbird mining district, Lemhi County, Idaho 

(J. Thomas Nash and Gregory A. Hahn) 

2:20 Some features of the composition and distribution of 

geochemical types of placer gold in the KoyukukChandalar mining district, Alaska {Edwin L. Mosier, 

John B. Cathrall, John C. Antweiler, and Richard B. 

'fripp) 

2:40 Epithermal gold mineralization in the Republic of 

Palau (James J. Rytuba, William R. Miller, and 

Edwin H. McKee) 

VII 

3:00 

3:20 

"Mesothermal" gold-A metamorphic connection? 

(William J. Pickthorn, Richard J. Goldfarb, and David 

L. Leach, Jr.) 

Coffee break 

3:40 Ophiolites, metallogenic models, and terrane modelsInterrelations observed in the Arabian Shield and 

potential for "cryptic" mineralization {John S. 

Pallister) 

4:00 Geological setting of two sediment-hosted hydrothermal mineral localities in Escanaba Trough, Gorda 

Ridge (Janet L. Morton, William R. Normark, Mark 

L. Holmes, and Mitchell Lyle) 

4:20 The Red Dog Pb-Zn-Ag deposit, Alaska-An example 

of nonexhalative processes in the formation of 

syngenetic massive sulfides (Jeanine M. Schmidt 

and Robert A. Zierenberg) 

4:40 Comparative studies of modern and ancient sedimenthosted massive sulfides {Wayne C. Shanks III) 

Wednesday Evening, March 11, 1987-

Technical Session 3 

7:30-10:30 Seventy-four poster papers and authors, with kegs on 

tap 

Thursday Morning, March 12, 1987-

'Technical Session 4 

8:00 

8:20 

8:40 

9:00 

9:20 

9:40 

10:00 

11:30 

12:00 

Preliminary geophysical well-log analysis of the 

geothermal alteration of alluvial sediments in the 

Salton Sea basin, California {Frederick L. Paillet and 

Roger H. Morin) 

Mapping contact-metamorphic aureoles in Extremadura, Spain, using Landsat Thematic Mapper 

images (Lawrence C. Rowan, Carmen AntonPacheco, David W. Brickey, Marguerite J. Kingston, 

Alba Payas, Norma Vergo, and James K. Crowley) 

Neogene-Quaternary volcanism and mineralization in 

the Central Andes (George E. Ericksen, Robert L. 

Smith, and Robert P. Koeppen) 

Geographic information system requirements in 

mineral-resource assessment-Lessons learned 

through cooperative research (John L. Dwyer, Stanton H. Moll, Charles M. Trautwein, James E. Elliott, 

Robert C. Pearson, Walden P. Pratt, and J. Thomas 

Nash) 

Mineral-resource assessment process and results, 

Petersburg project area, southeastern Alaska {David 

A. Brew, Donald J. Grybeck, John B. Cathrall, Susan 

M. Karl, Richard D. Koch, David F. Barnes, Andrew 

Griscom, and Henry C. Berg) 

Coffee break 

Panel Discussion: "Future trends in mineral-resource 

research-Perspectives from government, industry, 

and academia" (Glenn H. Allcott, moderator; T S 

Ary, Robert C. Horton, Richard W. Hutchinson, 

William C. Kelly, Gregory E. McKelvey, and Larry D. 

Fellows, panelists) 

Concluding Address {Dr. Samuel S. Adams, Head, 

Geology and Geological Engineering Department, 

Colorado School of Mines, Golden, CO) 

Adjournment of Technical Sessions (Glenn H. Allcott) 
Thursday Afternoon, March 12, 1987-

Workshops and USGS Open-House 

1:30 Departure from Sheraton Denver Tech Center 

2:00 USGS Open House: Denver Federal Center, Lakewood 

Denver West Office Park, Golden 

Workshops: Microcomputer systems in geologic map 4:00 

compilation and drafting (Richard B. 

Taylor, Gary I. Selner, and Bruce R. 

Johnson) 

Fractal geometry-Concepts and application to geologic structure and mineralresource analysis {Christopher C. Barton) 

Conclusion of Forum 

Posters (Technical Session 3) 

[Initial number is booth number] 

I. Investigations of Mineralizing Processes and Mineralized Systems 

A. Studies Focused on Geochemistry and Mineralogy 

1. Sanford, R. F., Geochemistry of precious- and base-metal veins, 

Lake City area, Colorado 

2. Wanty, R. P., Fitzpatrick, J. J., and Goldhaber, M. B., 

Geochemical and crystallographic constraints on the formation of the vanadium-uranium ores of the Colorado Plateau 

3. Asher-Bolinder, Sigrid, and Whitney, Gene, Mechanism of 

lithium enrichment in the Popotosa Formation, Socorro 

County, New Mexico 

4. Hearn, P. P., Jr., Sutter, J. F., and Belkin, H. E., Authigenic Kfeldspar-An indicator of the geochronology and chemical 

evolution of mineralizing fluids in carbonate-hosted leadzinc deposits 

5. Church, S. E., Studies of lead isotopes in sulfide deposits from 

accreted terranes in the North American Cordillera 

6. Spirakis, C. S., and Heyl, A. V., A link among 34sulfur-rich 

pyrite in greenish-grey shales, ferric iron from smectite as 

it converts to illite, kinetics of sulfur redox reaction, and the 

genesis of Mississippi Valley-type deposits 

7. Philpotts, J. A., Kane, J. S., Aruscavage, P. J., Kirschenbaum, 

H., Johnson, R. G., Dorrzapf, A. F., Jr., Brown, Z., and Mee, 

J. S., Geochemical aspects of ocean-floor hydrothermal-vent 

fluids and massive sulfide chimneys from the southern Juan 

de Fuca Ridge 

8. Chaffee, M. A., Chemical zoning of mineral deposits as an 

exploration technique-The Red Mountain, Arizona, porphyry copper system 

9. Gray, Floyd, Page, N. J, and Moring, B. C., Petrology and 

platinum-group element variation in zoned ultramafic complexes, Klamath Mountains, Oregon and northern California 

10. Moring, B. C, Page, N. J, and Oscarson, R. L., Platinum-group 

element mineralogy of the Pole Corral podiform chromite 

deposit, Rattlesnake Creek terrane, northern California 

11. Zientek, M. L., and Oscarson, R. L., Textural association of 

platinum-group minerals from the J-M Reef, Stillwater Complex, Montana 

B. Studies Focused on Petrology and Field Relations 

12. Duffield, W. A., Relations between cassiterite-bearing veins 

and rhyolite layers, Black Range area, southwestern New 

Mexico 

13. Lan@, I. M., Nokleberg, W. J., Aleinikoff, J. N., and Church, 

S. E., Genesis and tectonic setting of volcanogenic massive 

sulfide deposits, eastern Alaska Range, Alaska 

14. Gamble, B. M., Gold veins of the Seward Peninsula, Alaska 

15. Tosdal, R. M. and Smith, D. B., Some characteristics of gneisshosted gold deposits of southeastern California 

16. Schmidt, R. G., Payas, Alba, Gumiel, Pablo, and D'Agostino, 

J. P., The Saxapahaw, North Carolina, gold occurrencesVJU 

Search for a deposit model and new remote sensing 

techniques 

17. Zierenberg,R. A., Koski,R. A., Shanks W. C., III, Seyfried, W. E., 

Jr., and Strickler M. D., Comparison of the Turner-Albright 

ophiolite-hosted massive sulfide, southwestern Oregon, to 

active hydrothermal deposits on the southern Juan de Fuca 

Ridge 

18. Bove, D. J., Han, Ken, and Rye, R. 0., Evolution of the Red 

Mountain alunite deposit, Lake City caldera, Colorado 

19. Clark, S. H. B., Potential for sedimentary exhalative base-metal 

deposits in Cambrian-Ordovician shelf carbonates of western 

Vermont and southern Quebec 

20. Ayuso, R. A., and Ratte, C. A., Epigenetic uranium mineralization in the Precambrian Mount Holly complex, Vermont 

21. Wenrich, K. J., Verbeek, E. R., Sutphin, H. B., Van Gosen, B. 

S., and Modreski, P. J., The Apex Mine, Utah-A Colorado 

Plateau-type solution-collapse breccia pipe 

22. Himmelberg, G. R., Loney, R. A., and Nabelek, P. I., 

Petrogenesis of gabbronorite at Yakobi and northwest 

Chichagof Islands, Alaska 

23. Bawiec, W. J., Zientek, M. L., and Attanasi, E. D., Threedimensional geologic model of the Mouat nickel-copper 

prospect, Stillwater Complex, Montana, and its application 

to mineral-resource assessment 

24. Larsen, C. E., and Force, E. R., A worldwide paleoclimatic 

model for Quaternary shoreline placer deposits of titanium 

minerals 

25. Sidder, G. B., Alteration and mineralization in the Monterrosas copper-iron deposit, Peru 

26. Breit, G. N., Meunier, J. D., Rowan, L. E., and Goldhaber, 

M. B., Alteration related to red bed copper mineralizing 

brines and other fault-controlled solutions in Lisbon Valley, 

Utah, and the Slick Rock district, Colorado 

27. Stollenwerk, K. G., and Eychaner, J. H., Neutralization of 

acidic ground water near Globe, Arizona 

C. Studies of Marine Systems 

28. Escowitz, E. C., and Grosz, A. E., Heavy minerals of the midAtlantic inner Continental Shelf 

29. Hein, J. R., Morgenson, L.A., Fleischman, Charlaine, Schwab, 

W. C., and Clague, D. A., Composition and distribution of 

cobalt-rich ferromanganese crusts from the Pacific 

30. Holmes, M. L., and Morton, J. L., Regional structure and 

distribution of hydrothermal activity within Escanaba 

Trough, southern Gorda Ridge 

31. Koski, R. A., Zierenberg, R. A., Kvenvolden, K. A., and Shanks, 

W. C., III, Mineralogy and chemistry of hydrothermal sulfide 

and petroleum deposits from Escanaba Trough, Gorda Ridge 

D. Studies Involving Microorganisms 

32. Lovley, D. R., Microbial transformations of iron minerals 

33. Repetski, J. E., Briskey, J. A., Armstrong, A. K., Smith, Fred, 
Wilbanks, Larry. and Tibbels, Dave, The application of conodonts to studies of Mississippi Valley-type ore depositsA preliminary assessment 

34. Robbins, E. I., LaBerge, G. L., and Schmidt, R. G., Evidence 

for iron-stripping and silica-stripping microorganisms in 

Precambrian granular and banded iron formations 

II. Mapping and Mineral-Resource Assessments 

35. Miller, F. K., National geologic mapping program 

36. Gair, J. E., Cannon, W. F., Peper, J. D., Cannon, S. S., and 

Martin, B. D., Appalachian metallogenic map 

37. Earhart, R. L., Metallogenic maps of massive sulfide occurrences in the Western United States 

38. Alminas, H. V., Tucker, R. E., Hopkins, R. T., Nishi, J. M., 

and Christian, R. P., A new tin-bearing base- and preciousmetal province in the U.S. Virgin Islands 

39. Miller, M. L. and Bundtzen, T. K., Geology and mineral 

resources of the Iditarod quadrangle, west-central Alaska 

40. Karl, S. M., Schmidt, J. M., Folger, Peter, Thompson, Bill, 

Long, Carl, Goldfarb, Richard, and Ellersieck, Inyo, Mineralresource assessment of the Baird Mountains quadrangle, 

western Brooks Range, Alaska 

41. Orris, G. J., Brem, G. F., Hardyman, R. F., John, D. A., Keith, 

W. J., Kleinhampl, F. J., Nash, J. T., Plouff, Donald, Silberling, N.J., Stewart, J. H., and Whitebread, D. H., Mineralresource assessment of the Tonopah 1 o x zo quadrangle 

42. Slack, John F., Mineral resource assessment of the Glens Falls 

1 o x zo quadrangle, New York, Vermont, and New 

Hampshire 

43. Watts, K. C., Jr., Geochemical exploration studies in the Glens 

Falls 1 o x 2 o quadrangle, New York, Vermont, and New 

Hampshire 

44. Page, N. J, Bagby, W. C., Case, J. E., Cox, D. P., Huber, D. 

F., Koeppen, R. P., Ludington, S. D., Marsh, S. P., Ponce, 

D. A., Schulz, K. J., and Singer, D. A., Mineral-resource 

assessment of Costa Rica 

45. Hosterman, J. W., Bentonite resources, cation-exchange 

capacity, mineralogy, and uses 

46. Lai, Tung-Ming, and Eberl, D. D., Ion-exchange fertilizer for 

the utilization of low-grade phosphate ores 

Ill. Geophysical Surveys and Other Geophysical 

Investigations 

47. Hoover, D. B., Smith, B. D., Grauch, V. J. S., and Podwysocki, 

M., Geophysical studies in the vicinity of the Getchell fault 

system, Humboldt County, Nevada 

49. Campbell, D. L., Labson, V. F., and Bisdorf, R. J., Geoelectric, gravity, and aeromagnetic studies in the Delta, Utah, 

quadrangle 

49. Flanigan, V. J., Senterfit, R. M., Mohr, Pam, and Wenrich, 

K. J., The geophysical character of solution-collapse breccia pipes on the Coconino Plateau of northern Arizona 

50. Williams, D. L., Stanley, W. D., and Labson, V. F., Preliminary 

results of geophysical studies near the Creede mining 

district, Colorado 

51. Phillips, J. D., and Daniels, D. L., Geophysical mapping of 

eastern U.S. early Mesozoic basins 

52. Friedman, J. D., and Mutschler, F. E., New geophysical, 

geochemical, and geologic investigations of northern 

Appalachian zinc-lead sulfide deposits of New York State 

53. Horton, Robert, and Long, Carl, Very low frequency aerial 

surveys applied to regional mineral assessment 

54. Kipp, K. L., Jr., Effect of topography on gas flow in 

unsaturated fractured rock-Numerical simulation 

IX 

55. Marron, D. C., Transport and flood-plain storage of metals 

associated with sediment downstream from Lead, South 

Dakota 

56. Mikesell, Jon, and Senftle, Frank, Nuclear borehole logging 

for critical metals 

57. Sherman, D. M., Electronic structures and spectra of 

minerals-Basic research to help the development of spectroscopic remote sensing and geophysical exploration 

techniques 

IV. Geochemical Investigations 

58. Morgan, J. W., Origin of platinum-group metals, gold, and 

rhenium in the Earth's mantle and the role of sulfide in 

mantle-crust partitioning 

59. Evans, H. T., Jr., Application of crystal chemistry to the 

geochemistry of vanadium 

60. Haas, J. L., Jr., Revision of the stability field of wustite and 

recommended standard oxygen potentials for the solid oxide 

buffers 

61. Krohn, M. D., New uses of ammonium in minerals in 

geochemistry 

62. Golightly, D. W., Montaser, A., Smith, B. L., and Dorrzapf, 

A. F., Jr., Spark-aerosol generation-A new technique for 

the direct analysis of geologic solids by inductively coupled 

plasma spectrometry 

63. Meier, A. L., and Lichte, F. E., Inductively coupled plasma 

mass spectrometry-Applications of a new technique in the 

study of mineral formation processes 

64. Tidball, R. R., Severson, R. C., McNeal, J. M., Briggs, P. H., 

and Kennedy, K. R., Trace-element source for contamination of agricultural drainage flowing into Kesterson National 

Wildlife Refuge, Merced County, California 

V. Information Systems 

65. Arndt, R. E., Johnson, T. L., and Ohlen, D. 0., U.S. Geological 

Survey's Federal Land Information System 

66. Dinardo, Thomas, Crane, Michael, and Ginnodo, K. L., 

CRIMS-Development of multiple automated mapping 

capabilities at Rocky Mountain Mapping Center, Denver, 

Colorado 

67. Alexander, Robert, and Dinardo, Thomas, Applications of 

digital mapping and geographic information systems to 

earthquake hazards reduction, Wasatch Front, Utah 

68. Selner, G. I., Taylor, R. B., and Johnson, B. R., Microcomputer systems for geologic map compilation and 

drafting 

69. Chavez, P. S., Jr., Schoonmaker, J. W., Jr., and Anderson, 

J. A., Digital mosaicking and merging of dissimilar data 

sets-GLORIA, magnetic, and bathymetric 

70. McCammon, R. B., PROSPECTOR 11-Towards a newer 

geo-logic 

71. Cox, D. P., Singer, D. A., and Barton, P. B., Geochemical 

anomalies and mineral-deposit models 

72. Bliss, J. D., Menzie, W. D., Orris, G. J., and Page, N. J, Mineral 

deposit density-A useful tool for mineral-resource 

assessment 

73. Medlin, A. L., Huber, D. F., Schruben, P. G., Mason, G. T., 

and Stoltz, M. L., Mineral Resources Data System-New 

techniques and applications for mineral-resources 

research 

74. Miller, B. M., An expert system for sedimentary basin 

analysis for assessment of mineral and energy 

resources 

Third Annual V. E. McKelvey Forum on Mineral and Energy Resources 

USGS Research on Minerals Resources-1987 

Programs and Abstracts 

Edited by Janet Somerville Sachs 

Applications of Digital Mapping and 

Geographic Information Systems to 

Earthquake Hazards Reduction, 

Wasatch Front, Utah 

Robert Alexander and Thomas Dinardo 

The U.S. Geological Survey is conducting experiments to determine the feasibility of applying digital 

map data bases and geographic information systems to earthquake hazards reduction in the Salt 

Lake City-Wasatch Front corridor, Utah. Preliminary 

work included input of geologic, hydrologic, and 

other map data relevant to the earthquake hazard 

within the Sugar House quadrangle, east-central 

Salt Lake County, UT. 

This 7.5-min quadrangle was the source of the 

digital line graph and digital elevation model data 

products to which all other data types were registered. More than two dozen types of data were 

entered into the project data base, including the surface trace of the Wasatch fault, potential liquefaction zones, predicted land stability during an 

earthquake, surface hydrologic features, topography, 

slope, flood zones, landslide and mudflow zones, 

land use, lifelines, and critical or response facilities, 

such as schools and hospitals. 

Preliminary analyses of the data bases include 

automated measuring and mapping of school locations and residential areas that coincide with highpotential earthquake hazard zones, lifelines crossing potential fault rupture zones, and undeveloped 

land that lies outside identified multihazard zones. 

Many other kinds of analyses can be performed on 

these and similar data sets, addressing scenarios 

that included preearthquake planning for response 

and recovery, loss estimation, and hazard mitigation 

through land use planning where the opportunity 

exists to guide new development away from the 

areas of greatest potential hazard. 

Recommendations are drawn from the Sugar 

House quadrangle experiments on how to apply 

digital technology to the development of a cooperative information management system in the impacted region. Through planned sharing of data and 

the use of appropriate data standards, such a system 

will assist in efficient implementation of earthquake 

hazard reduction measures. 

A New Tin-Bearing Base- and 

Precious-Metal Province in the U.S. 

Virgin Islands 

H. V. Alminas, R. E. Tucker, 1 R. T. Hopkins, J. M. 

Nishi, and R. P. Christian 

A regional geochemical study of the U.S. Virgin 

Islands (St. Thomas, St. John, and St. Croix) has 

delineated extensive areas with anomalous concentrations of Au, Ag, Te, Sb, Bi, As, Pb, Sn, Cu, Zn, 

and Ba. The anomalies appear to be structure 

related and transect all exposed rock types on the 

islands. 

The U.S. Virgin Islands are part of the northeastern portion of the Greater Antilles island arc and 

are located to the east of Puerto Rico. In addition 

to the main islands, about 50 smaller islands, which 

are concentrated mainly near St. Thomas and St. 

John, are within the study area. 

The most detailed geologic map of St. Thomas 

and St. John published to date is that produced by 

Donnelly (1966). As mapped by Donnelly, the two 

northern islands consist of island-arc-related 

Cretaceous and Tertiary volcanic, volcanoclastic, 

carbonate, and plutonic rocks. 

St. Croix was mapped by Whetten (1966), who indicated that the island is underlain by strongly 

folded Upper Cretaceous sedimentary rocks, which 

have undergone low-grade metamorphism, and by 

gently folded unmetamorphosedTertiary sedimentary rocks. Igneous intrusions of Late Cretaceous 

and early Tertiary age with contact metamorphic 

aureoles occur in the sedimentary rocks. 

1

Colorado School of Mines, Golden, CO. 
Outcrops, B-horizon soils, and stream sediments 

were sampled during the course of the geochemical 

study. In addition, heavy-mineral concentrates and 

oxalic acid leachates were derived from the soil and 

stream-sediment samples. Only the two derivative 

sample types were found to be effective in delineating the base- and precious-metal mineralization. 

Outcrop samples were effective in detecting the 

precious-metal assemblage. 

The most extensive anomalies are those of Ph, Sn, 

and Cu, which decrease in intensity and extent in 

the major islands in the order of St. Croix, St. John, 

and St. Thomas. Precious-metal anomalies on these 

islands show the reverse order. 

Scanning electron microscope, electron microprobe, and X-ray diffraction investigations indicate 

that, in the weathering environment, most of the 

Sn occurs as poorly crystallized cassiterite incorporating blebs of native Sn, native Ph, and euhedral 

crystals of a Sn-Cu alloy. Vugs filled with Sn 

chloride commonly occur within the native Sn and 

Ph blebs. Much of the Ph occurs in native form 

associated with chloride, carbonate, oxide, and sulfide forms. The Cu is found in native, oxide, 

chloride, silicate, and alloy forms. Most of the Au 

is found in native form with some occurrences of 

a Au-Ag telluride. The Ag is found in native telluride, chloride, sulfide, widespread iodide, and AuAg telluride forms. 

References Cited 

Donnelly, J. W., 1966, Geology of St. Thomas and St. John, 

U.S. Virgin Islands: Geological Society of America 

Memoir 98, p. 85-176. 

Whetten, J. D., 1966, Geology of St. Croix, U.S. Virgin 

Islands: Geological Society of America Memoir 98, p. 

177-239. 

U.S. Geological Survey's Federal 

Land Information System 

Raymond E. Arndt, Thomas L. Johnson, and 

Donald 0. Ohlen 

The U.S. Geological Survey is implementing the 

Federal Land Information System (FLIS), formerly 

called the Federal Mineral Land Information 

System. FLIS is a data base networking system 

which uses geographic information system technology to allow Federal policymakers and resource 

managers to evaluate more efficiently surface- and 

mineral-resource development issues at the 

national, State, and regional levels. 

2 

FLIS program activities are directed to users' 

needs, in that a geographic index of FLIS data 

sources with query capabilities will be made 

available. System outputs are tailored to user 

requests and include spatial display products and 

statistical summaries. Data conversion and networking capabilities are being developed and 

demonstrated for Federal lands in Alaska and New 

Mexico. The FLIS program has ongoing cooperative activities with other Federal agencies, 

including the Bureau of Land Management and the 

Bureau of Mines offices in those two States. 

The principal categories of data in use or being 

considered for use in FLIS statewide data bases are 

Federal ownership (surface and mineral reservations), restrictions to exploration and mining of 

federally owned minerals (legal and management 

withdrawals), mineral-resource potential and 

occurrence, surface-resource information (water, 

soils, land use and land cover, and terrain derivatives), and cartographic detail. At present, U.S. 

Geological Survey, Bureau of Land Management, 

and Bureau of Mines are the primary suppliers of 

data for these statewide data bases. 

Mechanism of Lithium Enrichment in 

the Popotosa Formation, 

Socorro County, New Mexico 

Sigrid Asher-Bolinder and Gene Whitney 

Sedimentation, Li geochemistry, and clay mineralogy combined to provide a source, a concentrator, 

and a trap for Li in tuffs of the Popotosa Formation, 

central New Mexico. These Li-rich tuffs (80-

3,850 ppm Li) occur in the closed-basin rocks of the 

Socorro paleobasin, a late Oligocene through 

Miocene precursor of the Rio Grande rift. The 7-

to 18-m.y.-old airfall and waterlain tuffs were erupted 

from postcaldera-resurgence vents near the paleobasin margin. Tuffs deposited in playa sediments 

are thicker, more zeolitic, and more Li rich than are 

tuffs deposited on alluvial flats. 

Li is leached preferentially from rhyolitic and 

dacitic volcanic glasses by fresh and alkaline ground 

waters. Li forms no salts in nature and has the 

lowest cation exchange capacity of the alkaline 

metals; however, it shows limited substitution for 

Mg in clay minerals. Airfall ashes have high porosity 

and permeability, which make them susceptible to 

leaching of Li and other cations by ground water 

flowing downbasin to the playa where evaporative 

concentration occurs. 
The thicknesses of the airfall portions of the playa 

tuffs correlate with their whole-rock lithium contents (r = 0.71, n = 13 samples), suggesting that 

thicker, hence, volumetrically larger, ashes were 

leached of more Li by ground waters moving 

through the tuffs to the basin center than were thinner ones. Thus, the source of Li in Popotosa tuffs 

may be the tuffs themselves. 

Li-rich playa tuffs consist of dioctahedral smectite, quartz, plagioclase, varying amounts of calcite 

and clinoptilolite, and traces of mordenite, gypsum, 

biotite, and dolomite. Li is contained in dioctahedral 

smectites, which have identical X-ray diffraction 

traces no matter what their Li content. When interlayer cations of high-Li smectites were exchanged 

for Sr, much of theCa, Na, and K were replaced by 

Sr. However, the Mg and Li values remained constant because they are structural elements of the 

octahedral layer. Cation exchange coefficients of the 

clay fractions range from 0.90 to 1.75 meq/g and are 

proportional to a clay fraction's Li content. Li + t 

occupies sites in the octahedral layer normally held 

by Al + 3 or Mg + 2 , leading to a net negative 

octahedral layer charge, balanced by the addition 

of Ca, Na, and K to the smectite interlayers. 

Whole-rock chemistries of high-Li playa tuffs are 

similar to those of their cogenetic volcanic flows 

except for Li and Mg enrichment and K depletion. 

Li is elevated as much as 58 times, and Mg is 10 

times higher in the tuffs than in the cogenetic flows. 

If Li in the tuffs was brought to the playa by groundwater dissolution and movementthrough the ashes, 

then why are calcium and sodium levels not 

elevated? and why do K values drop an order of 

magnitude in the playa facies, the center of 

evaporative concentration? Independent observation suggests that K in the flows was elevated by K 

metasomatism that did not affect the playa tuffs. 

However, the playa tuffs probably were enriched 

originally in Ca and Na by ground-water flow 

through the tuffs. Because those elements were not 

incorporated structurally into the dominant 

diagenetic phase smectite, their final concentrations 

were controlled by postdiagenetic events. Some Na 

Mount Baldy, a 12,082-tt peak in the Tushar Mountains of west-central Utah. It is within the 19-Ma Mount Belknap 

caldera and is composed of a lkali-rhyolite ash-flow tuffs and volcanic domes containing anomalous quantities of Mo, U, Be, and Li. Westward, beyond Mount Baldy, lie Beaver Valley and the Mineral Mountains along 

the eastern margin of the Basin and Range province. 

3 
and Ca and K presently are held as interlayer 

cations in the smectites; more of those cations may 

have been held as soluble salts in the tuffs, later 

removed by fresher waters introduced by intrabasin 

horsting, paleobasin breaching, and rainwater. 

A delicate balance between ground-water inflow 

and tuff leaching and evaporative concentration and 

incorporation of Li into neoforming smectite was 

maintained to achieve high structural Li values in 

these dioctahedral smectites. Paleobasin breaching 

occurred 4-7 m.y. ago; Li still in solution or in 

exchangeable sites would have been removed or 

replaced by other cations in fresher open-basin 

system waters. 

Epigenetic Uranium Mineralization in 

the Precambrian Mount Holly 

Complex 

Robert A. Ayuso and Charles A. Ratte1 

Epigenetic uranium-bearing veins and pegmatitic 

pods and lenses are disseminated widely in the Precambrian Mount Holly Complex in the Green 

Mountains in Vermont. These occurrences represent probably the largest bedrock uranium occurrences known in New England. Mineralized rocks 

at Okemo Mountain and Jamaica are on the eastern 

flank of the Green Mountains anticlinorium and may 

be related to the Taconic orogeny (about 440 m.y.) and 

to the Acadian orogeny (about 380 m.y.). 

Disseminated uranium mineralization is found in 

a wide variety of rock types ranging from feldspathic 

gneisses and pegmatite-rich rocks at Jamaica to 

cataclastically deformed rusty quartzites, schists, and 

calcsilicates at Okemo Mountain. In both areas, but 

especially the latter, a significant association exists 

between highly mineralized areas and quartz-tourmaline rocks. The veins are mineralogically simple 

and vary in width from about 10 em to a few meters. 

They contain uraninite, small amounts of brannerite, 

and uranophane as the important uranium-bearing 

minerals. At Okemo Mountain, uranium veins are 

hosted by epidote-chlorite-garnet-white micatourmaline-quartz rocks. Mineralized rocks are concentrated near shear zones in rusty quartzitic schists 

(epidote-tourmaline-magnetite-pyrite-hematitechlorite-white mica-quartz) and granitic gneisses 

(epidote-tourmaline-microcline-perthite-quartz). In 

the Jamaica area, the host rocks range from quartzitic and schistose rocks (garnet-chlorite-biotite-white 

1

Vermont State Geologist, Waterbury, VT 05676 . 

4 

mica-quartz), which are generally similar to those in 

Okemo Mountain, to thinly banded feldspathic 

gneisses (epidote-allanite-microcline-perthite-quartz) 

and pegmatite-rich gneisses (allanite-epidote-white 

mica-perthite-quartz). 

Bulk rock compositions of the mineralized units 

are highly variable. No strong correlations between 

uranium content and silica or between uranium and 

most other major elements are observed. High 

values for Fe20 3/Fe0 are found in many of the 

mineralized samples. Values for U 30 8 range from 

0.2 to 0.6 percent in the mineralized veins, and 

anomalous values as high as 22.0 percent have been 

recorded. Ratios of thorium to uranium vary from 

<0.01 to >10. Trace element variations are not 

related to the uranium content of the rocks. Total 

rare earth element (REE) content of the host rocks 

is widely variable and is relatively low (generally 

<300 ppm for total REE content, except in some 

samples where it is as high as 1,500 ppm). The most 

significant trace element covariation at Okemo 

Mountain is that for uranium and boron, which is 

in agreement with the observed association of 

mineralized veins and quartz-tourmaline rocks. 

The low total content of REE in the mineralized 

zones and their uncorrelated nature with respect 

to uranium argue against an origin of the widely 

disseminated mineralization by direct derivation 

from anatectic melts. The mineralized areas are best 

characterized as products of pegmatitic rocks 

remobilized by oxidized and boron-rich fluids 

formed in response to the Taconian and (or) Acadian orogenies. Migration of these fluids probably 

was controlled by the regional development of fractures and shear zones. 

Three-Dimensional Geologic Model 

of the Mouat Nickel-Copper Prospect, 

Stillwater Complex, Montana, and Its 

Application to Mineral-Resource 

Assessment 

W. J. Bawiec, M. L. Zientek, and E. D. Attanasi 

Deposits of magmatic Ni-Cu sulfides are concentrated near the base of the Stillwater Complex, an 

Archean mafic to ultramafic layered intrusion 

exposed on the northern edge of the Beartooth 

Mountains, MT. Extensive drilling and more limited 

underground development work, done largely by the 

Anaconda Minerals Company, has delineated the 

subsurface extent of one of these deposits in the 

Mountain View area, the Mouat Ni-Cu prospect. 
The three-dimensional interpretation of the geology 

of this deposit is based on 1:1200-scale surface mapping, 1:120- and 1:240-scale core logging of approximately 90,000 ft of core from 110 drill holes, 1:240-

scale arlit mapping, and Ni-Cu concentration data 

from the drill holes. Computer-generated graphics 

are used to illustrate the geology of this deposit. 

The three-dimensional structural interpretation 

of this area shows that the rocks of the Stillwater 

Complex are folded into a broad syncline cut by 

several generations of faults. The sulfides are concentrated at the lower contact of the Basal series 

with the underlying metasedimentary rocks and 

within very discontinuous, irregularly shaped 

Stillwater-associated sills and dikes that intrude the 

metasedimentary rocks. The base of the Stillwater 

Complex in this area shows considerable relief over 

short distances; as a result, the thickness of the 

Basal series ranges from 0 to over 450 ft. Metasedimentary rock xenoliths, the largest over 800 ft in 

length, occur within the Basal series and the 

Peridotite zone of the Ultramafic series. The oldest 

faults trend northeasterly and have near-vertical 

dips. These faults are cut by northwesterly trending, 

near-vertical faults showing left-lateral offset. The 

left-lateral northwesterly trending Verdigris fault, in 

turn, cuts all previous faults. Apparent offsets of 

these faults are less than 500 ft. Two high-angle 

reverse faults, the Lake and the Bluebird faults, show 

the greatest offset and truncate the Mouat deposit 

on the southwest and the northeast. 

As part of this study, several attempts were made 

to estimate the tonnage and grade of the explored 

part of the deposit. Because of the inclined attitude 

of the stratigraphy and increasing depth, the sulfide 

deposits in the deepest parts of the syncline were 

not evaluated. The sulfide accumulations at the base 

of the Basal series showed the greatest continuity; 

therefore, the grade and tonnage computations concentrated on rock units near this contact. Data on 

Cu and Ni concentrations were analyzed and 

examined in 25-ft intervals above the base of the 

Basal series and below the Basal series in the metasedimentary rock by using 25- x 25-ft and 100- x 100-

ft mining blocks. The intensity of faulting and the 

very irregular shape and distribution of mineralized 

footwall sills and dikes made it extremely difficult 

to use geostatistical methods. Therefore, conventional grade interpolation procedures were applied 

toNi and Cu data. Only two fault-bounded blocks 

contained sufficient data (number of drill holes or 

surface exposure of the contact) to credibly estimate 

grade-tonnage relations. One fault-bounded block 

lying directly west of the Verdigris fault contains 

5 

17.1 million-22.3 million short tons of ore having 

an average grade of 0.5 percent combined Ni and 

Cu. In a smaller fault-bounded block farther to the 

west, 2.4 million-5.3 million short tons of ore having an average grade of 0.5 percent combined Ni 

and Cu are thought to be present. 

Role of Regional Aeromagnetic and 

Gravity Data in Mineral-Resource 

Investigations, Southeastern Nevada 

H. Richard Blank 

Southeastern Nevada is a miogeosynclinal province that has undergone late Mesozoic compression 

followed by mid- to late-Cenozoic extension concommitant with calc-alkaline and bimodal magmatism. At least 50 percent of the bedrock is 

covered with surficial deposits. Because base- and 

precious-metal deposits here commonly are 

associated with plutons emplaced during tectonic 

modifications of the miogeosyncline, an important 

objective of mineral-resource evaluation is the 

delineation of concealed intrusive bodies and of 

regional structures that may impact the exploration 

rationale. For this task, use of recently compiled 

aeromagnetic and gravity maps can be of considerable benefit. 

Sources of strong magnetic anomalies include 

Cenozoic volcanic and Precambrian crystalline 

basement rocks as well as target plutons. However, 

the Precambrian basement and magnetically 

transparent Paleozoic carbonates generally have 

positive density contrasts, whereas the MesozoicCenozoic volcanic and sedimentary rocks have 

negative density contrasts, with respect to 

Mesozoic-Cenozoic plutons. Thus, gravity data used 

in conjunction with magnetic data serve as a powerful discriminator. 

Long-wavelength aeromagnetic anomalies 

primarily reflect topographic relief of the magnetic 

basement (whether it consists of Precambrian or 

younger rocks). Long-wavelength gravity anomalies 

record basement relief and carbonate surface relief, 

the latter dominated by Basin-Range faulting. Major 

discordances between aeromagnetic and gravity 

trends probably indicate that the terrane has been 

extended highly and that the magnetics "see 

through" suprajacent rocks and record structures 

of an autochthonous basement. Examples of magnetic basement that seems to bear no relation to 

Basin-Range structure are the Grant RangeRailroad Valley basement, believed to be associated, 
at least in part, with granitoid rocks of Mesozoic 

age, and the basement northeast of Las Vegas Valley, 

a possible decapitated core complex. 

In some places, potential field data suggest that 

the locus of igneous activity was confined to sites 

of modern intermontane basins, and it can be inferred that magma invaded high-level structural discontinuities of extensional origin. Large volcanotectonic structures, such as those of the Indian Peak 

caldera complex and the Caliente cauldron and 

their associated hypabyssal intrusions, have strong 

aeromagnetic and gravity signatures; the Pioche PbAg district apparently is truncated by Indian Peak 

ring faults and may extend to the east buried at considerable depth beneath alluvium and caldera infill volcanics. Elsewhere, it is possible to infer that 

mineralized plutons have shallow concealed extensions. Examples are granitic bodies in the Patterson Pass area of the Schell Creek Range, the pluton 

of the Freiburg district in the Worthington Mountains, and the Troy Canyon pluton of the Grant 

Range. 

Mineral Deposit Density-A Useful Tool 

for Mineral-Resource Assessment 

James D. Bliss, W. David Menzie, Greta J. Orris, 

and Norman J Page 

Mineral deposit density (MDD) is the number of 

deposits per unit area. When calculated for a single 

deposit type, such densities are hypothesized to be 

similar for large regions of comparable geology and 

thus provide a basis for mineral-resource assessment. This tool is particularly useful in the methodology developed for the Alaska Mineral Resource 

Assessment Program, which seeks to provide a 

quantitative, probabilistic estimate of the mineral 

endowment. Estimation of the mineral endowment 

includes (1) delineation of tracts permissive for the 

presence of deposit types that are known or 

suspected to occur within the map area, (2) use of 

descriptive and grade and tonnage models of these 

deposit types, and (3) estimation of the number of 

undiscovered deposits within identified tracts. Two 

basic approaches, standard statistical methods and 

expert judgment, have been used to estimate 

numbers of undiscovered deposits in tracts. MDD 

are basic data that can be used by either approach. 

Based on well-explored regions (that is, ones in 

which essentially all deposits of the type of interest 

have been found), the MDD for that specific deposit 

type can be derived. The development of MDD 

6 

depends on (1) insuring that deposits in the MDD 

are compatible with those in the grade and tonnage models and (2) establishing boundaries that 

contain all deposits in control regions by using concise operational rules based on geological, 

geochemical, and geophysical criteria that can be 

applied generally. MDD is computed for the control region by dividing the number of deposits by 

the size of the region. An initial estimate of the 

number of deposits that occur in a tract of land may 

be obtained by multiplying the MDD by the area of 

the tract. The estimate may then be adjusted to more 

precisely reflect specific geologic conditions in, and 

exploration history of, the tract by using either 

statistical models or expert opinion. 

MDD for low-sulfide Au-quartz vein deposits in 

four large regions generally has similar values. This 

deposit type typically forms at moderate depth and 

temperatures in metasedimentary and metavolcanic 

rocks of predominantly greenschist facies on the 

flanks of batholithic complexes. Preliminary MD D's 

(deposit per square kilometer) for areas with lowsulfide Au-veins are 

1. Sierra Nevada Foothills, CA-4.6 x10-3, 

2. Klamath Mountains, CA-OR-4.3 x10-3 , 

3. Meguma Group of Nova Scotia, Canada-5.4 

x1o-3, and 

4. Victoria, Australia (for example, Bendigo, 

Ballarat)-5.0 x10-3 • 

Preliminary MDD's also have been developed for 

podiform chromite, silica-carbonate mercury, and 

bedded barite. MDD's for bedded barite deposits 

and low-sulfide Au veins are being used in the the 

mineral-resource assessments of the Tonopah 1 o x 

2 o quadrangle, Nevada, and the Wiseman 1 o x 3 o 

quadrangle, Brooks Range, AK, respectively. 

Evolution of the Red Mountain Alunite 

Deposit, Lake City Caldera, Colorado 

Dana J. Bove, Ken Hon, and R. 0. Rye 

The Red Mountain alunite deposit, one of the 

largest in the U.S. with 70 million metric tons of 

alunite, formed on the eastern margin of the 23.1-

Ma Lake City caldera. Several texturally and temporally distinct high-K dacite intrusions (63-65 percent Si02

) cut earlier postcaldera collapse high-K 

dacite lavas (63-66 percent Si02

) on Red Mountain. Almost all the rocks were alunitized late in the 

caldera cycle, and over one-half of the surface exposures display evidence of hydrothermal brecciation. 

Alunitization occurred in two large, roughly conical centers with roots extending more than 250m 
beneath the surface. Alunitized rocks change outward into argillized and propylitized postcollapse 

lavas and downward through argillic and potassic 

zones that are dominantly within dacite intrusions. 

Four 260- to 1,000-m drill holes intersect the area, 

but drill hole coverage does not permit direct observation of the transition between the alunite and 

argillized zones. Multiple stages of alunite are present and include (1) early fine to slightly coarser 

grained alunite replacing feldspar phenocrysts with 

quartz-pyrite alteration of the groundmass, (2) 

irregular flooding of alunite in groundmass and 

previously altered phenocrysts, and (3) late, 

fracture-controlled alunite veinlets. In argillically 

altered rocks, kaolinite overprints earlier sericite 

± pyrite. The potassic zone is defined by secondary 

K-feldspar ± biotite ± pyrite, which is overprinted 

by sericitic and kaolinitic alteration near the top 

of the zone. Weak "porphyry-type" mineralization 

with anomalous amounts of molybdenum (and 

minor molybdenite) occurs throughout a 1,000-m 

drill hole, with highest molybdenurn values (100-

300 ppm) in the zone of potassic alteration. Elevated 

concentrations of Cu, Pb, and Zn also were 

detected, but only rare, finely disseminated 

sphalerite and chalchopyrite could be identified. 

Mass balance calculations show large additions 

of sulfur from the hydrothermal system. This sulfur 

is present primarily as so3 within alunitized rocks 

and as FeS2 within the potassic and argillic zones. 

Al20 3 and K20 were removed during alunitization, 

and Sr was enriched due to the stabilization of a 

strontium-phosphate phase. Water was added to all 

the alteration zones as secondary hydrous alteration minerals. Potassium and rubidium were added 

to the potassic zone, and a slight gain in Al2 0 3 

was observed in kaolinite-altered rocks. Only Zr 

and Ti02 remained relatively immobile in the 

system. 

Hydrogen, oxygen, and sulfur stable isotope 

data constrain the origin of alunite and the source 

of fluids and sulfur. Each stage of alunite has 

distinctly different isotopic compositions as do different generations of pyrite. Stage 1 o34S SO 4 and 

o180 so4 values range from 6.9 to 10.7 per mil and 

6.0 to 9.7 per mil, respectively; Stage 2 values range 

from 19.7 to 27.2 per mil and 10.3 to 13.9 per mil, 

respectively; Stage 3 o3S04 values range from -3.3 

to -3.9 per mil. Pyrite, which is cogenetic with 

Stage 1 alunite, has o34S values ranging from -5.8 

to -8.7 per mil, while pyrite in the argillic 

assemblage has values of -1.0 to 2.1 per mil. 

Although interpretation is hampered by lack of 

experimental isotopic fractionation factors for 

7 

alunite in hydrothermal systems, the data suggest 

that Stage 1 alunite formed from sulfate derived 

from a magmatic sulfur source at temperatures 

above 350°C, and Stage 2 alunite formed from the 

same sulfur source at lower temperatures. In contrast, late Stage 3 alunite is probably of supergene 

origin or was derived from the surficial oxidation 

of H2S. 

We propose an origin for the Red Mountain 

alunite deposit where a large lateral influx of 

meteoric water from the adjacent resurgent dome 

of the Lake City caldera enters a zone of hot, dry 

rock above a dacite magma emanating large 

volumes of S02 and H2S gases. Fluid mixing 

occurred, creating an initially superheated acidic 

solution that permeated the overlying dome complex, and caused the formation of most of the 

alunite, periodicaly producing hydrothermal 

brecciation. 

Alteration Related to Red Bed Copper 

Mineralizing Brines and Other FaultControlled Solutions in Lisbon Valley, 

Utah, and the Slick Rock District, 

Colorado 

G. N. Breit, J. D. Meunier,1 E. L. Rowan, and M. B. 

Goldhaber 

Zones of red bed-type Cu enrichment along faults 

in Lisbon Valley, southeastern Utah, and the Slick 

Rock district, southwestern Colorado, were examined to evaluate the solutions responsible for the 

Cu mineralization. These fault-controlled fluids 

formed economic Cu deposits in the Cretaceous 

Dakota Sandstone along the Lisbon Valley fault and 

a zone of Cu enrichment in the Jurassic Morrison 

Formation along the structurally contiguous 

Dolores zone of faults. Fluid-inclusion studies of 

calcite in the fractures and isotopic and chemical 

studies of authigenic minerals in sandstones surrounding the faults indicate that three distinct solutions moved sequentially along the faults. These 

fluids not only formed the Cu deposits, but also 

precipitated calcite, barite, and dolomite and 

dissolved Fe oxides in zones up to 5 km from the 

faults. 

Calcite, barite, and Cu minerals precipitated from 

the earliest of the solutions. This water had a o180 

of about 0 per mil [Standard Mean Ocean Water 

(SMOW)], an average temperature of 95 °C, and 

a dissolved solid content greater than 8 weight 

1

CREGU, Nancy, France. 
percent N aCl equivalent. Fluid inclusions with different salinities indicate that this brine mixed with 

a dilute ground water during growth of the calcite. 

Collectively, the data suggest that the saline water 

was a connate water from the underlying Pennsylvanian Hermosa Formation. The Hermosa within the study area includes about 1,000 m of bedded 

evaporites. This saline water extracted copper from 

the Hermosa or from the red beds that occur between the evaporites and the Dakota and Morrison 

Formations. Interaction of the brines with the intervening clastic rocks is indicated by the Sr isotope 

composition of barite within the fault zones 

(

87Sr/86Sr of 0.7103). The Rb/Sr values of brines in 

the Hermosa are too low to account for the 87Sr/86Sr value of 0.7103. A likely source of Sr, in 

addition to the evaporites, are feldspars and clays 

in the clastic sediments. The extent of alteration by 

the brines is reflected by the decrease of 87Sr/86Sr 

in authigenic barite with increasing distance from 

The scanning electron microscope photograph of a 

12-J.Lm-long fluid inclusion in quartz from the Santa 

Rita porphyry copper deposit New Mexico. The 

inclusion contains a NaCI daughter mineral (cubic 

form). Various salts from the evaporated brine solution drape the NaCI crystal and form blebs around 

the opened inclusion. 

8 

the faults. The decrease in 87Sr/86Sr suggests mixing between Sr contained in the brines (0.7103) with 

Sr in the host sandstones (0.7080). 

Simultaneous with or shortly after the first brine, 

a second solution moved through the Dolores zone 

of faults. This water had an estimated 5180 of -8 

per mil (SMOW), which suggests that a component 

of the solution was meteoric water. As it moved 

through the sandstones, this solution precipitated 

dolomite. The solution also contained dissolved 

organic acids (probably derived from petroleum) 

that bleached red sandstones through which the 

solution passed. Flow of this solution was restricted 

to sandstones south of the Dolores zone of faults 

due to changes in permeability possibly related to 

the precipitation of calcite by the earlier brine. The 87Sr/86Sr of the dolomite is similar to the ratio in 

fracture-filling barite. The similar Sr isotope ratios 

and the 0 isotope compositions of the carbonate 

minerals indicate that this solution may have been 

a product of mixing between the earlier brine and 

the meteoric water described below. 

The final solution to move through the fractures 

was a very dilute ground water that precipitated 

calcite within the Dolores zone of faults. This solution herd a temperature of 50 oc and a 5180 near 

- 16 per mil (SMOW). 

These solutions were forced upward by Laramide 

tectonism when uplift of anticlines cored by the 

Hermosa evaporites expelled fluids along fractures. 

Waters with isotopic and chemical compositions 

similar to these solutions currently exist within the 

Hermosa and overlying units. 

Mineral-Resource Assessment Process 

and Results, Petersburg Project Area, 

Southeastern Alaska 

David A. Brew, Donald J. Grybeck, John B. 

Cathrall, Susan M. Karl, Richard D. Koch, David F. 

Barnes, A. Griscom, and Henry C. Berg1 

The Petersburg project region encompasses 16,300 

km2 and includes all the Petersburg, about one-third 

of the Port Alexander, and about one-tenth of the 

Sumdum 1:250,000-scale map areas, southeastern 

Alaska. Although the region contains only three 

mines that produced any commodities (barite, garnet, and gold), it contains a wide variety of metallic 

mineral occurrences and has long attracted the attention of prospectors and mineral exploration 

. companies. 

The mineral-resource assessment (MRA) was done 

by an expert panel of regional geologists, economic 

1

USGS retired. 
geologists, geochemists, and a geophysicist, who 

had participated collectively in 44 person-months 

of fieldwork between 1978 and 1982. In the course 

of the MRA process, 17 types of deposits were identified as being present and (or) geologically permissible, and, by using the procedures described 

below, 28 areas of interest were identified. 

The identification of the 28 areas was based on 

sequential data collection, data analysis, compilation, preliminary interpretation, and, finally, on the 

judgment of the expert panel. The information used 

came from the following sources: regional geology, 

economic geology, bedrock geochemistry, stream 

sediment geochemistry, panned concentrate geochemistry, geophysics:aeromagnetic, geophysics: 

gravity, geophysics:high-altitude aeroradiometric, 

geophysics:low-altitude aeroradiometric, and telegeology:Landsat and other high-altitude images. 

The basic data from all but one of these sources and 

a few preliminary interpretative maps were released. The most useful of the unreleased maps 

were (1) the interpretation of the geologic map showing the rock units and structural situations permissive for the 17 different types of deposits, (2) 

various stream sediment, panned concentrate, and 

bedrock geochemical maps depicting combinations 

of elements in various innovative ways, and (3) the 

preliminary aeromagnetic interpretation. 

The 28 areas of mineral resource interest were 

classified in four main categories, which have as a 

common factor permissive geology for a specific 

mineral-deposit type. The criteria for each category 

are 

1. A mine (with or without production); significant 

stream sediment, panned concentrate, and (or) 

bedrock geochemical anomalies; and both with 

and without significant geophysical anomalies; 

2. One or more prospects or metallic mineral occurrences; significant stream sediment, panned 

concentrate, and (or) bedrock geochemical 

anomalies; and both with and without significant geophysical anomalies; 

3. Significant stream sediment, panned concentrate, 

and (or) bedrock geochemical anomalies; and 

both with and without significant geophysical 

anomalies; and 

4. Significant geophysical anomalies. 

Only one of the three areas in Category 1 contains 

identified (inferred, paramarginal) resources. 

Undiscovered (hypothetical, submarginal) resources 

are contained in the other two areas in Category 1 

and in several of the areas in Category 2. The remaining areas have undiscovered (speculative) resources. 

The information available in the MRA process did 

9 

not justify applying statistical methods of estimating 

the number, size, and grade of the deposits that may 

be present in the region. 

Geoelectric, Gravity, and 

Aeromagnetic Studies in the Delta, 

Utah, Quadrangle 

David l. Campbell, Victor F. Labson, and 

Robert J. Bisdorf 

The Conterminous United States Mineral Assessment Program (CUSMAP) does integrated geologic, 

geophysical, and geochemical studies at 1:250,000 

scale to make mineral-resource assessments of 

selected 1 o x 2 o quadrangles. Work on the Delta, UT, 

quadrangle began in March 1986 and is scheduled 

to continue for 4 yr. Here, we report results to date 

from the geophysical part of the effort. 

Gravity and aeromagnetic data were compiled and 

used together with a preliminary geologic map to 

guide geoelectric work in the first field season. This 

geoelectric work consisted of 23 magnetotelluric 

(MT) soundings and 50 audiofrequency magnetotelluric (AMT) soundings. In addition, 139 directcurrent vertical electric soundings (VES) were used 

that had been made in the quadrangle earlier. All 

three methods show electrical resistivity versus 

depth under each site. MT soundings see deepest 

(often to more than 10 km depth) but take more time 

to make than the shallower AMT and VES soundings 

(1-2 MT soundings per day versus 3-6 AMT or VES 

soundings per day). MT and AMT soundings were 

made in conjunction with each other near Desert 

Mountain to investigate the depth and lateral extent 

of an inferred caldera and to the south of Whirlwind 

Valley to investigate a buried wishbone-shaped structure seen on the gravity map. VES were used to map 

thicknesses of sediments in the Thle Valley and northern Fish Springs Flat. Minor slingram and very 

low frequency geoelectric work also was begun in 

the historical Tintic mining district. 

Profiles made by contouring resistivities from 

sounding to sounding show that the Desert Mountain caldera contains up to 2 km of electrically conducting (<100-ohm-m) surficial material, probably 

water-saturated sedimentary and volcanic rocks. 

Many of the soundings show 10-30 m of very conductive (<20-ohm-m) surficial material, probably 

representing sediments shed from the Sheeprock 

and Simpson Ranges to the north and deposited in 

glacial Lake Bonneville. The profiles also show 

zones of 50- to 500-ohm-m material embedded in 
the caldera fill that may represent blocks of 

Paleozoic country rock that were brecciated and 

engulfed during Tertiary volcanic episodes. Such 

megabreccia zones appear from preliminary 

geologic mapping to characterize much of the 

Tin tic-Deep Creek volcanic belt. The outcropping 

central core of the Desert Mountain caldera consists largely of electrically resistive (>1,000 ohm-m) 

intrusive rocks; the sides of this core are steep and 

possibly fault bounded. 

Geoelectrical soundings can be used to further 

constrain gravity and magnetic models along 

selected profiles. Such a procedure was used to 

model a major fault of presumed Basin-Range age 

that the gravity map shows to be buried under 

Snake Valley midway between the Deep Creek and 

Fish Springs Ranges. 

Geophysical work in the first year of this study 

has added information on structural and lithologic 

settings in the Delta quadrangle but has not given 

any direct evidences of mineralization. The role of 

geophysics in the Delta CUSMAP study, for the 

most part, will be to define and investigate bedrock 

structures in the more than 50 percent of the 

quadrangle that is covered by lacustrine and alluvial 

sediments. 

Chemical Zoning of Mineral Deposits 

as an Exploration Technique-The 

Red Mountain, Arizona, Porphyry 

Copper System 

Maurice A. Chaffee 

The physical and chemical processes that produce 

a large hydrothermal mineral deposit (an economic 

or subeconomic enrichment of one or more minerals) or system (the deposit plus the surrounding 

rocks affected during the formation of the deposit) 

create chemical and mineralogical zones-areas 

that are enriched or depleted in various constituents-in these systems. This paper describes a 

chemical zoning study conducted at Red Mountain, 

about 80 km south of Thcson, AZ, where drilling 

to depths of more than 1,700 m has identified a 

remarkably complete porphyry Cu system. This 

system occurs within a gently dipping stack of 

predominantly felsic to intermediate volcanic rocks 

of Late Cretaceous to early Tertiary age that have 

been intruded by irregular bodies of porphyritic 

rocks. 

For this study, samples of drill core were collected 

at about 15-m intervals from seven drill holes that 

10 

comprise an east-west fence across the entire 

system. The samples were analyzed for 41 different 

elements. Evaluation of the spatial distributions of 

these elements indicates that chemical zoning is 

clearly present. This zoning of elements (for example, Mg and Li) can be used to help identify and correlate lithologic units. The zoning of elements or 

of ratios of elements also can be used to identify 

mineralogical and alteration zones; for example, Ba 

for barite, Co:Ni for pyrite, and Rb:Sr for advanced 

argillic alteration. Other elements (for example, Co, 

Mn, Ni, and Zn) can be used to identify the extent 

of chemical weathering. 

Three general areas of mineralization are recognized within the Red Mountain system. The deepest 

of the three consists of a chalcopyrite-pyrite deposit 

similar in configuration to the San ManuelKalamazoo, AZ, deposit. The limbs of this deposit 

converge to an apex about 800 m below the present 

surface. A deposit containing sparse hypogene 

enargite and extensive supergene chalcocite is present near the surface. Between these two deposits 

are roughly concentric zones for such elements as 

Ag, As, Cu, K, Mn, Sb, and Zn. Minerals typical of 

potassic and phyllic alteration zones in porphyry 

Cu systems are also present at Red Mountain. 

The distributions of the elements suggest that the 

Red Mountain system was formed in the following 

stages: (1) after deposition of the volcanic sequence, 

the top of the area was subjected to solutions that 

leached Ca and Na, (2) Fe was remobilized as part 

of an early "barrerr'' pyrite event, (3) solutions 

enriched in Ag, As, Au, B, Ba, Bi, Cd, Co, Cs, Cu, 

Hg, Li, K, Mo, Ph, Rb, S, Sb, Sn, Sr, Te, Tl, U, W, Zn, 

and possibly Mn moved upward and formed the 

deep chalcopyrite deposit, the upper enargite 

deposit, and the intermediate zones, (4) the enargite 

deposit, which was associated with advanced 

argillic alteration, was converted to a chalcocite 

blanket as a result of supergene enrichment, and 

(5) the area of the system was uplifted, eroded, and 

weathered. 

Anomalies of Ag, As, B, Ba, Bi, Hg, Mo, Ph, Sb, 

Sn, Te, and Tl are found in the outer fringes of this 

large system and are not strongly remobilized. As 

a result, any or all of the elements in this suite 

should be particularly useful in the search for deepseated porphyry Cu deposits such as that at Red 

Mountain. 

The recognition and understanding of chemical 

zoning can be a valuable technique in the search 

for new deposits, particularly deposits not exposed 

at the surface. Although this discussion emphasizes 

a zoned Cu system, the basic multielement chemical 
zoning concept developed here should be applicable 

to exploration for many other types of mineral 

deposits. 

Digital Mosaicking and Merging of 

Dissimilar Data Sets-GLORIA, 

Magnetic, and Bathymetric 

PatS. Chavez, Jr., James W. Schoonmaker, Jr., and 

Jeffery A. Anderson 

Data from the GLORIA (Geological Long-Range 

Inclined Asdic) digital imaging system have become 

an important component within the U.S. Geological 

Survey for offshore mapping. Digital processing 

techniques to correct the geometric and radiometric 

distortions inherent in the original data have been 

developed and are operational. Until recently, the 

processed results have been in long strips on trackline format that were film mosaicked into 2 o quadrangle areas for visual analysis. One disadvantage 

of film mosaics is that a new film mosaic must be 

made if a different type of enhancement or processed result is generated. Also, it is extremely difficult to digitally merge the sonar image data in 

track-line format with other types of data. To overcome these problems, procedures were developed 

to correct geometrically the individual long trackline strips of sonar image data to make digital 

mosaics of 2 o quadrangles. 

One of the major advantages of digital mosaicking over film mosaicking is that it allows the data, 

in quadrangle format, to be merged and combined 

with other image and nonimage data sets for digital 

analysis. In this project, we have merged the magnetic and bathymetric data, which were collected 

every 2 min at nadir locations during the GLORIA 

cruise, with the sonar image data. The magnetic and 

bathymetric data were converted first from vector 

to raster format with the same pixel size and geometric projection (Universal Transverse Mercator) 

as the sonar image data. A spatial filtering technique then was used to interpolate a surface 

through these data points. Special attention had to 

be given to the density and distribution of the data 

points (high density in the along-track direction and 

low density in the across-track direction). The 

resultant "image" products then were used individually and with the sonar image data for digital and 

visual analysis. The procedure for mosiacking the 

GLORIA sonar image data is more difficult than 

those required for other types of remotely sensed 

data, such as satellite images, because geometric 

11 

control is available only at nadir locations. Currently, no information exists about the pointing 

characteristics of the imaging system; that is, pitch, 

roll, yaw. As with other data sets, the geometric corrections for digital mosaicking involve the identification of control points and the generation of the 

transformation file using these control points and 

the actual resampling of the image file using the 

transformation. Because control points are available 

only at nadir locations, the first step becomes much 

more involved. The second step is straightforward 

and very similar, or identical, to those used on other 

remotely sensed data. Also, because of the radiometric quality of the sonar image data, especially 

at far-range locations, additional work is required 

to get an acceptable tone match between the various 

track lines. An interactive digital stenciling or 

feathering capability was developed to optimize this 

stage of the process, which is similar to the feathering technique used on film mosaics. 

Post-Laramide Magmatism in the U.S. 

Cordillera 

Robert L. Christiansen 

Three post-Laramide continental tectonomagmatic 

associations can be defined by the compositions, 

distributions, and tectonic settings of igneous rock 

suites. One is a classic arc, which produces predominantly basaltic to andesitic and subordinately 

dacitic to rhyolitic magmas in continental margin 

belts near active subduction zones. Another, generally more silicic, has few or no basalts but produces 

abundant andesites to rhyolites; compositionsbroadly calc-alkalic but more potassic than the arc 

suites-typically evolve from andesites to voluminous 

rhyolites, either in belts across interior regions of tectonic extension or near the coast in association with 

the migrating ends of a transform system. A third 

embraces basaltic, alkalic, and bimodal rhyolitebasalt suites, which occur in regions of tectonic rifting or in cratonic foreland zones adjacent to the 

andesite-rhyolite belts. Each association is 

characterized by different types of mineral deposits. 

Major contractional deformation ended in most of 

the U.S. Cordillera by 55-50 Ma. From 55 to 43 Ma, 

arc magmatism spanned from coastal Canada to central Oregon. Coeval basalts in coastal Washington 

and Oregon are oceanic in origin and were accreted 

to the continent later. The continental interior Challis 

andesite-rhyolite belt accompanied extension between the northern Cascades and the Rocky Mountain front in Montana and northwestern Wyoming, 
with voluminous ash-flow calderas in the central 

part. Contemporaneous alkalic centers evolved on 

the Great Plains of Montana, northern Wyoming, 

and northwestern South Dakota. In the southern 

Cordillera, arc magmatism was active in western 

Mexico; continental interior magmatism spanned 

northward into western Texas and southern New 

Mexico. 

From 43 to 3 7 Ma, arc magmatism persisted 

northward from central-western Oregon. Northern 

Cordilleran extension and magmatism stepped 

southward to the Tuscarora belt, reaching from central Oregon into northern Nevada and northwestern 

Utah; only minor activity continued in the Challis 

belt. In the southern Cordillera, continental interior 

andesites extended northward to central Colorado 

and westward to southeastern Arizona, with some 

voluminous rhyolites in southern New Mexico. 

From 37 to 21 Ma, the Cascade arc spanned from 

coastal Canada to northwestern Nevada. To the east, 

from central Oregon to northern Nevada, southern 

Idaho, and southwestern Montana, is the John DayLewis & Clark belt of relatively small bimodal 

trachyandesites and rhyolites. Voluminous andesiterhyolite magmatism jumped southward to a belt 

crossing central Nevada and splitting into two 

branches in western Utah; it produced voluminous 

ash-flow calderas, mainly after 34 Ma. Beginning 

about 28 Ma, major caldera activity moved to 

another belt overlapping this one on the south; 

activity continued until about 21 Ma. To the southeast, caldera-related eruptions occurred in Colorado 

and southwestern New Mexico between 34 and 

27 Ma; less voluminous andesite-rhyolite volcanism 

reached southeastern California by 35-32 Ma. By 

26-21 Ma, andesites to rhyolites erupted from 

Sonora to the southern Coast Ranges (now offset by 

the San Andreas fault), voluminous rhyolites 

erupted in southeastern Arizona, and mafic 

andesites and basalts became common in New Mexico and Colorado. Alkalic centers developed on the 

adjacent Cordilleran foreland and Colorado Plateau. 

Between 21 and 17 Ma, the continental margin 

arc became continuous except for a gap of 400 km 

in southeastern California, where subduction had 

ceased; part of this arc has been disrupted by later 

translation and rotation in southern California. 

Since 17 Ma, the arc has retreated northward with 

lengthening of the Pacific-North American 

transform system; andesites and rhyolites have 

erupted near the migrating Mendocino triple junction. Distributed extension to the east has been 

accompanied by basaltic and bimodal magmatism. 

Between 17 and 14 Ma, a linear rift from central 

12 

Nevada to western Idaho and eastern Washington 

erupted progressively more voluminous basalts 

northward. A 21- to 6-Ma belt of rhyolitic ash-flow 

calderas extended east-west across southern 

Nevada. During Basin and Range faulting since 14-

10 Ma, magmatism has concentrated toward the 

margins of extending regions. 

Studies of Lead Isotopes in Sulfide 

Deposits From Accreted Terranes in 

the North American Cordillera 

S. E. Church 

Recent studies of the composition of Ph in sulfide 

minerals from stratiform or sediment-hosted (SH) 

and from volcanogenic massive sulfide (VMS) 

bodies in accreted terranes in the North American 

Cordillera have shown that the primary source of 

Ph in these deposits is the crust. Specifically, the 

Ph isotope data indicate that the Ph in these sulfide 

systems reflects the interaction of the hydrothermal 

fluids with crustal sediments. In the case of SH 

deposits, Ph in the sulfide minerals reflects 

hydrothermal convection and deposition within the 

unconsolidated sediment pile. Ph from sulfide 

minerals in Cyprus-type VMS deposits represents 

hydrothermal convection within the oceanic crust 

and may reflect either a mantle-Ph composition or 

a mixture between mantle and sediment Ph. In contrast, the Ph isotope signature from Besshi- and 

Kuroko-type VMS deposits represents 

predominantly a crustal sediment Ph. Comparison 

of the average Ph isotope compositions found 

within the Devonian SH and VMS deposits in the 

Brooks Range differ significantly from that found 

in Devonian VMS deposits in the Alaska Range. 

Similarly, the isotopic composition of Ph in TriassicJurassic VMS deposits of the Klamath Mountains 

differs from VMS deposits of the same age found 

in southeastern Alaska. 

Variations in the average composition of Ph from 

calc-alkaline volcanic rocks (CAVR) from the active 

continental margin of the Pacific Basin also vary 

significantly. The studies of Ph isotopes in CAVR 

rocks has resulted in a general model that invokes 

admixing sediment Ph with melts derived from the 

subducted oceanic crust to form mixing arrays between the mantle and sediment-Ph compositions. 

Because the Ph isotope composition of the mantle 

and the crust are variable on a regional scale, valid 

interpretations of the Ph isotope data seem plausible only when comparisons are based on a regional 

geological model. Regional variations of the isotopic 
composition of Pb in modern oceanic sediments are 

reflected in CAVR from active volcanic arcs; for 

example, large variations have been found in the 

composition of Pb in CAVR's from the Cascade 

Range, the Lesser Antilles, and Japan and reflect the 

average composition of sediment Pb derived from 

the Western United States, the Brazilian craton, and 

the Asian craton, respectively, during Quaternary 

time. Thus, these rocks reflect the average composition of Pb in sediments derived from the present 

crustal geometry; sediment Pb, therefore, can be 

used to constrain models for accreted terranes 

because they accurately reflect the geometry of the 

rocks in the source. 

Studies of the isotopic composition of Pb from SH 

and VMS sulfide systems from the Western United 

States and Alaska indicate that Pb isotopes from 

deposits of the same age within a district are 

generally uniform and that the average composition 

of Pb from ores within the district can be used as 

a Pb isotope signature, or "fingerprint:' Similar work 

by Godwin and others (1982) also has shown regional 

variations of Pb isotopes from VMS deposits in the 

Canadian Cordillera. Regional variation between 

deposits of the same type and age within the North 

American Cordillera presumably reflects the average 

composition of Pb in sediments deposited in the 

sedimentary basin. Pb isotope data may be used to 

place limits on the extent of movement of accreted 

terranes in western North America. 

Reference Cited 

Godwin, C. 1., Sinclair, A. J., and Ryan, B. D., 1982, Lead 

isotope models for the genesis of carbonate-hosted ZnPb, shale-hosted Ba-Zn-Pb, and silver-rich deposits in 

the northern Canadian Cordillera: Economic Geology, 

v. 77' p. 82-94. 

Potential for Sedimentary Exhalative 

Base-Metal Deposits in CambrianOrdovician Shelf Carbonates of 

Western Vermont and Southern 

Quebec 

Sandra H. B. Clark 

Occurrences of sulfide minerals in the CambrianOrdovician carbonate-siliciclastic shelf terrane east 

of the Proterozoic basement of the Adirondack 

Mountains have been known at least since the 

1870's. The occurrences are near the line between 

the shelf sequence and the deeper water basinal 

13 

deposits to the east. Study of one of these occurrences at Lion Hill, which is about 3 mi north of 

Brandon, VT, resulted in a new interpretation of the 

genesis as sedimentary exhalative, analogous to the 

Irish carbonate-hosted zinc-lead deposits and 

indicated potential for additional deposits in the 

shelf sequence. Zinc-lead-copper mineralization at 

Lion Hill is primarily in the Lower Cambrian 

Monkton Quartzite, a mixed carbonate-siliciclastic 

tidal-flat sequence. Trace amounts of sulfide 

minerals also occur in the stratigraphically overlying Winooski Dolomite and underlying Dunham 

Dolomite. The Lion Hill deposit is on the overturned 

east limb of the Middlebury synclinorium, and host 

rocks are strongly deformed and metamorphosed 

to greenschist facies assemblages. The predominant 

ore mineral is sphalerite with smaller amounts of 

galena and chalcopyrite. Two mineralized zones that 

have been identified in drill core are along beddingschistosity planes and are elongate at about 

N. 70° W., which is approximately perpendicular to 

the fold axes. The two zones contain about 500,000 

tons of mineralized rock. The ore minerals occur 

predominantly as metamorphic segregations within 

schistosity surfaces, indicating pretectonic or, at the 

latest, syntectonic mineralization. Evidence for 

possible timing of mineralization relative to the 

deposition of host rocks comes from several 

sources. The association of layered magnetite iron 

formation with the lead-zinc mineralization suggests syngenetic deposition. Rarely preserved 

pretectonic textures indicative of mineralization 

during diagenesis include intergranular disseminated sulfides and dilatant fracture fillings by 

material, including sphalerite, that flowed in a 

plastic state. Discordant masses and veinlets indicate that some of the mineralization was epigenetic. 

The Lion Hill deposit differs from Mississippi 

Valley-type (MVT) deposits in scarcity of gangue 

minerals and lack of abundant open-space filling 

or evidence of paleokarst. Lead-isotope and fluidinclusion studies (Nora K. Foley, U.S. Geological 

Survey, written commun., 1986) also suggest that the 

Lion Hill deposits are more like the sedimentary 

exhalative zinc-lead deposits of Ireland, which are 

stratabound and stratiform, than MVT deposits. 

Overthickening of the Monkton Quartzite at Lion 

Hill and abrupt lithologic changes indicate possible crustal instability during sedimentation and 

synsedimentary faulting. Mineralizing fluids may 

have ascended along growth faults and deposited 

sulfides in unconsolidated sediments of a shallowwater marine environment. The escape of some 

metal-bearing fluids onto the seafloor could account 
for the associated iron formation. Forceful injection 

of fluids produced mineralized fractures and other 

locally discordant features. 

Applications of Deposit Models in U.S. 

Geological Survey Programs 

Dennis P. Cox and Donald A. Singer 

In 1986, the U.S. Geological Survey published 

Bulletin 1693, which contains 87 deposit model 

descriptions by 38 authors (Cox and Singer, 1986). 

These are derived from data on 3,900 individual 

deposits distributed in 111 countries. Tonnage and 

grade models for 60 of these types also are 

presented. Many of these models have been applied 

in domestic programs beginning with Alaska 

Mineral Resource Assessment in 1975 and internationally in Colombia in 1982. Currently, these 

models are finding increasing acceptance in the 

conterminous U.S. resource assessment programs 

and, in some (particularly Reno quadrangle), are 

being used in initial program planning stages. The 

deposit model framework is being used in the 

preparation of some commodity and regional 

resource reports for the Decade of North American 

Geology Series. In the Geological Survey's international program, deposit models are an integral part 

of resource assessment. Our collection of deposit 

models was adopted enthusiastically by the 

Geological Survey of Japan for use in their Deep 

Seated Resource Assessment Project, and Japanese 

geologists contributed important data for several 

deposit models. In Costa Rica, 14 models were 

applied in a 1:500,000-scale resource assessment; 

detailed field work was carried out on the characteristics of local epithermal gold deposits that were 

determined to be of the Sado type. In Papua New 

Guinea, a report has been prepared describing 

deposit models that are known or likely to be 

discovered in that country. These include a model 

for Lihir Island gold, a unique deposit type insofar 

as is presently known. 

Future applications include an assessment of tin 

resources based on deposit models being carried 

out by the International Strategic Minerals Inventory Working Group. In addition!, new models are 

being developed with special attention to nonmetallic deposits, and detailed subdivisions of some 

models, such as volcanogenic manganese, are being 

prepared. 

Reference Cited 

Cox, D. P., and Singer, D. A., eds., 1986, Mineral deposit 

models: U.S. Geological Survey Bulletin 1693, 379 p. 

Geochemists sampling organic-rich lower paleozoic carbonaceous limestones at the Horse Canyon 

disseminated gold deposit, Nevada. They are studying the thermal maturity of the organic material and 

its effect on the ore-forming process. 

14 
Geochemical Anomalies and 

Mineral-Deposit Models 

Dennis P. Cox, Donald A. Singer, and Paul B. Barton 

During the preparation of a compendium of 

mineral deposit models (Cox and Singer, 1986), we 

constructed a matrix relating 87 deposit types to 50 

chemical elements. In addition to providing the 

geochemical associations, the matrix contains a 

ranking of the frequency with which each anomalous element is associated with each deposit type. 

In this preliminary study, the assignments of 

numerical values to the occurrence frequency were 

based only on the experience of the three authors. 

The ranked matrix was subjected to factor analysis 

to examine how compatible it is with our intuitively 

held relations of geochemistry and mineralization 

processes. Factor analysis was used, first, to reveal 

relations among elements and, second, to reveal 

relations among deposit types. 

In the first analysis, each of the 50 elements was 

treated as a variable, and the 8 7 deposit types, as 

samples. Because of the high degree of similar 

affiliations among the 50 elements, a parsimonious 

grouping of elements into six factors reflects 50 percent of the variability among the elements (table 1). 

The elements are ordered by the strength of the correlation (factor loading) between element and factor. Multiple elements correlated with the factors 

suggest that not every element need be measured 

to reflect the factor. Note that the following factor 

group names, applied to the same factor numbers 

as table 1, are only for convenience and are not congruent with conventional geochemical usage-(1) 

Table 1 

FACTOR 1 FACTOR 2 FACTOR 3 

Ta Pb Ni 

Rb N;J PGE 

Cs Zn Cr 

Sn Cu Co 

w Au Mg 

Li ( M n) ( K) 

Nb (Te) 

Th (- N a) 

F ( K) 

Be 

REE 

B 

( u) 

I( Mo) 

lithophile group, (2) base- and precious-metal group, 

(3) siderophile group, (4) biogenic group, (5) chalcophile group, and (6) alkalic group. 

The second analysis examined the relations 

among deposit types by treating each of 80 deposit 

types as a variable and the 50 elements as samples. 

Alluvial and bauxite deposit types were excluded. 

Six factors (groups) were required to reflect 60 percent of the variability of deposit types shown by 

geochemical anomalies (table 2). Most base- and or 

precious-metal deposit types were associated with 

the first factor; the second factor contains deposit 

types associated with ultramafic rocks; the third factor has mostly iron or high Fe-bearing deposits; 

most Sn- and W-bearing deposits and Climax Mo 

are associated with the fourth factor; hot spring Au 

and Hg, Sb vein, and carbonate-hosted Au-Ag 

deposits are associated with the fifth factor; and 

phosphate- and U-bearing deposit types are associated with factor six. 

Sn polymetallic vein, porphyry Sn, and low-F porphyry Mo deposit types are associated with the first 

(base- and precious-metal) factor rather than the 

fourth (Sn-W vein, skarn, Climax Mo) deposit factor. This dichotomy for Sn and Mo results from the 

fact that the first group is associated with geochemically simple calc-alkaline rocks, whereas the 

second group is related to high-silica granite systems that contain a distinctive, highly evolved 

geochemical suite. Although Homestake Au-type 

deposits are associated predominantly with factor 

1, an association also exists with the fifth (hot 

spring) factor. 

In addition to being a powerful exploration tool, 

geochemistry offers a quick and relatively reliable 

FACTOR 4 FACTOR 5 FACTOR 6 

c Hg Zr 

Se Sb Ti 

u Tl Sr 

NH3 (Au) p 

v (As) (-As) 

(Ca) (Th) 

(Te) (REE) 

I'!} '=Secondar~ I 

15 
Table 2 

FACTOR 1 FACTOR 2 FACTOR 3 

Creede epithermal vein Dunitic Ni-Cu Algoma Fe 

Low sulfide Au-quartz vein Komatiitic Ni-Cu Superior Fe 

Porphyry Cu·Au Merensky Reef PGE Fe skarn 

Polymetallic veins Stillwater Ni-Cu Volcanic-hosted magnetite 

Polymetallic replacement Synorogenic·Synvolcanic Ni·Cu Bushveld Fe-Ti-V 

Cu skarn Limassol Forest Co-Ni Blackbird Co-Cu 

Replacement Mn Noril'sk Cu-Ni-PGE (Gold on flat faults) 

Zn·Pb skarn Alaskan Cr-Pt Olympic Dam Cu-U-Au 

Porphyry Cu Pediform chromite (Besshi massive sulfide) 

Porphyry Cu, skarn-related Bushveld Cr Stillwater Ni-Cu\ 

Sn-polymetallic vein Diamond pipes 

Porphyry Mo, low-F Lateritic Ni 

Comstock epithermal vein Carbonate-hosted asbestos 

Sado epithermal vein Serpentine-hosted asbestos 

Epithermal quartz-alunite Au Unconformity U-Au 

Sedimentary exhalative Zn·Pb Southeast Missouri Pb-Znl 

Homestake Au 

Porphyry Sn 

Volcanic-hosted Cu-As·Sb 

Au-Ag-Te veins 

Cyprus massive sulfide 

Epithermal Mn 

Kuroko massive sulfide 

Sandstone-hosted Pb·Zn 

Kipushi Cu-Pb-Zn 

Besshi massive sulfide 

Sediment-hosted Cu 

Southeast Missouri Pb·Zn 

(Sb veins) 

Basaltic Cu 

Volcanogenic Mn 

(Olympic Dam Cu·U·Au) 

(Blackbird Co-Cu) 

Gold on flat faults 

way to identify the general type of deposit at an 

early stage of exploration. This is our first attempt 

to generate a comprehensive compilation; subsequent efforts can be improved substantially by 

incorporation of additional input from experienced 

exploration geochemists. 

Reference Cited 

Cox, D.P., and Singer, D. A., eds., 1986, Mineral deposit 

models: U.S. Geological Survey Bulletin 1693, 379 p. 

CRIMS-Development of Multiple 

Automated Mapping Capabilities at 

the Rocky Mountain Mapping Center, 

Denver, Colorado 

Thomas Dinardo, Michael Crane, and 

K. lea Ginnodo 

The Rocky Mountain Mapping Center (RMMC), 

Denver, CO, is responsible for meeting the thematic 

cartography production requirements of the Central Region of the U.S. Geological Survey. Until 

recently, these production requirements dealt 

mainly with the traditional mapping efforts of the 

Geologic Division. Now, these requirements are 

being augmented by the needs of a number of other 

Survey programs including Wasatch Front Earthquake Hazards Reduction, Conterminous United 

States Mineral Assessment, National Water Quality 

16 

FACTOR 4 FACTOR 5 FACTOR 6 

W veins Almaden Hg Phosphate, upwelling type 

Sn greisen Hot-spring Hg Phosphate, warm current type 

Sn skarn Hot-spring Au·Ag Sandstone U 

W skam Sb veins Quartz pebble conglomerate Au·U 

Replacement Sn Carbonate-hosted Au-Ag Volcanoqenic U 

Climax Mo (Homestake Au) 

Rhyolite-hosted Sn Silica-carbonate Ho 

(Sn-polymetallic vein) 

Volcanoaenic U\ 

NOT ACCOUNTED FOR NOT INCLUDED 

Carbonatite Bauxite, laterite type 

Porphyry Cu-Mo Bauxite, karst type 

Sedimentary manganese Placer Au-PGE 

Bedded barite Placer PGE·AU 

Emerald vein Shoreline placer Ti 

Appalachian Zn Diamond placer 

1"1\" Secondarv Factor Alluvial olacer Sn 

Assessment, Regional Aquifer System Analysis, and 

Geographic Information System research and 

applications activities. 

To better meet these responsibilities, RMMC has 

developed a Central Region Integrated Mapping 

System (CRIMS). CRIMS is a software system that 

is designed to suppor!: the automated generation of 

thematic map products by providing interfaces to 

RMMC's array of high-accuracy cartographic plotting equipment. Input to CRIMS may derive from 

digital line graph files, Scitex scanning, and 

manually digitized data files. The development of 

CRIMS greatly enhances RMMC's digital thematic 

cartographic production capabilities and ability to 

respond to the requirements placed on it. 

Relations Between Cassiterite-Bearing 

Veins and Rhyolite Lavas, Black Range 

Area, Southwestern New Mexico 

Wendell A. Duffield 

Cassiterite-bearing veins cut late Oligocene 

rhyolite lava flows and domes in the Black Range 

area of southwestern New Mexico, and cassiteriterich placer deposits occur in streams that drain 

areas underlain by this rhyolite. Although bedrock 

and placer occurrences are too small and dispersed 

to have prompted much commercial production, the 

origin of the cassiterite has been the subject of many 

research projects during the past half century. These 

projects have focused on the cassiterite-bearing 
veins and have led to two theories for the origin of 

the Sn mineralization, one that postulates a direct 

genetic link between the veins and the host rhyolite 

and another that views the veins as the product of 

a hydrothermal event younger than and not directly 

related to the emplacement and cooling of the 

rhyolite lava. My ongoing study of the rhyolite 

emphasizes geochemical and physical aspects of 

volcanology and provides considerable evidence 

that the veins formed during cooling of newly 

emplaced lava and that the Sn came directly from 

such lava as it degassed and devitrified. 

Geologic mapping and isotopic geochronology 

indicate that a minimum of 30 km3 of rhyolite was 

emplaced over an area of about 300 km2 during 

half a million years or less. The rhyolite has a silica 

content of 77-78 percent and is essentially uniform 

in major-element composition throughout the lava 

field. Apparently, a large reservoir of homogeneous 

silicic magma underlay the region in late Oligocene 

time. Contents of Ba and Sr as low as 10 and 3 ppm, 

respectively, and of Th and Rb as high as 40 and 

460 ppm, respectively, attest to the highly 

chemically evolved character of the rhyolite magma. 

Sn content is 1-4 ppm in devitrified parts of the 

rhyolite (nearly the entire volume of lava), and other 

workers report values as high as 28 ppm in hydrated 

vitrophyre, material that may reflect more nearly the 

original Sn content of the magma. Thus, the 

devitrified rock is a possible source for the Sn in 

cassiterite; mass-balance calculations indicate that 

about 1-2 ppm of Sn in the rhyolite lava is 

equivalent to the Sn known in cassiterite of bedrock 

and placer occurrences. 

Bedrock cassiterite was deposited in such open 

spaces as vesicles and cooling joints, and nearly all 

of these occurrences are located in the outermost 

parts of lava flows, where steep gradients in 

temperature, vapor pressure, and vapor compositi.on favor mineral deposition in a cooling degassing lava. Other researchers report that fluid inclusions in cassiterite and associated vein minerals 

formed at 750-100°C, temperatures that reflect 

vap?r-dominated and hot-water mineralizing 

environments, and that coexisting cassiterite, bixbyite, and pseudobrookite lining vesicles in the 

outer zone of a lava flow were deposited from a 

vapor phase somewhat hotter than 500°C. These 

reports are consistent with the hypothesis that Sn 

deposition began immediately after emplacement 

of lava and continued during cooling to nearambient temperature. Two-feldspar geothermometry applied to phenocrysts in the lava suggests 

that preeruption magmatic temperature was about 

17 

815°C. Absence of Sn mineralization in an overlying ash-flow sheet of 40Ar/39Ar age identical to that 

of the lava also argues for Sn deposition during cooling of the host lava. All characteristics of the 

mineralization seem explicable through a direct 

genetic link between the cassiterite-bearing veins 

and their host rhyolite; one need not invoke a subsequent hydrothermal event. 

Geographic Information System 

Requirements in Mineral-Resource 

Assessment-Lessons Learned Through 

Cooperative Research 

John l. Dwyer,1 Stanton H. Moll, 1 Charles M. 

Trautwein, James E. Elliott, Robert C. Pearson, 

Walden P. Pratt, and J. Thomas Nash 

The Geologic and the National Mapping Divisions of the U.S. Geological Survey have been involved formally in cooperative research and 

development of computer-based geographic information systems (GIS's) applied to mineral-resource 

assessment objectives since 1982. Experience in the 

Conterminous United States Mineral Assessment 

Program (CUSMAP) projects including the Rolla, 

MO, Dillon, MT-ID, Butte, MT, and Tonopah, NV, 

1 o by 2 o quadrangles has resulted in the definition 

of processing requirements for geographically 

referenced geological, geophysical, geochemical, 

and mineral-resource data that are common to these 

studies. 

The diverse formats of data sets collected and 

compiled for regional mineral-resource assessments 

necessitate capabilities for digitally encoding and 

entering data into appropriate tabular, vector, and 

raster subsystems of the GIS. Although many of the 

required data sets are either available or can be provided in a digital format suitable for direct entry, 

their utility is largely dependent on the original 

intent and consequent preprocessing of the data. In 

this respect, special care must be taken to ensure 

that digital data type, encoding, and format will 

meet assessment objectives. 

Data processing within the GIS is directed 

primarily toward the development and application 

of models that can be used to describe spatially 

geological, geophysical, and geochemical environments either known or inferred to be associated 

with specific types of mineral deposits. Consequently, capabilities to analyze spatially, aggregate, 

1TGS Technology, Inc., Earth Resources Observation System Data Center, Sioux 

Falls, SD 57198. 
and display relations between data sets are principal processing requirements. To facilitate the 

development of these models within the GIS, interfaces must be developed among vector-, and raster-, 

and tabular-based processing subsystems to reformat resident data sets for comparative analyses and 

multivariate display of relations. 

Metallogenic Maps of Massive 

Sulfide Occurrences in the Western 

United States 

Robert L. Earhart 

Maps that show the distribution of volcanogenic 

massive sulfide occurrences and their host rocks 

are being compiled for the Western United States 

by teams of geologists from the U.S. Geological 

Survey, State Surveys, and industry. The maps are 

being published in the Geological Survey's 

Miscellaneous Field Studies map series, and, upon 

completion, the data will be combined to produce 

a Western United States metallogenic map of 

massive sulfide occurrences that shows the 

distribution of deposits with respect to tectonostratigraphic features. 

Each State map contains a summary text that 

discusses the geologic setting of the occurrences 

and an accompanying table that provides critical 

information about the localities shown on the map. 

Detailed information compiled in a dBase III format and published in a Geological Survey open-file 

report, further supplements map data and provides 

updated information for the Geological Survey 

Mineral Resource Data System. Some of the maps 

will be drafted digitally by using programs developed for the IBM PC and compatible microcomputers (Selner and others, 1986). The maps, 

along with the supplementary information, will 

provide detailed information on individual occurrences and an overview of massive sulfide distribution with respect to age, host lithologies, and 

regional and local tectonic frameworks. 

The metallogenic map of massive sulfide occurrences in Arizona (Donnelly and Conway, 1986) is 

an example of the State maps and related data 

bases. Massive sulfide deposits in Arizona have 

been the sources of important amounts of gold, 

silver, copper, and zinc. 

All known massive sulfide occurrences in 

Arizona formed between 1.7 and 1.8 b.y. Threefourths of the occurrences are clustered in volcanic 

and volcano sedimentary rocks of the Yavapai 

18 

Series in central and western Arizona. Most 

deposits are associated with felsic volcanic rock or 

were formed near contacts of mafic and felsic 

strata. The massive sulfides in nearly one-half the 

occurrences show a close spatial association with 

chemical sediments, including oxide facies iron formation and ferruginous chert. The compilation of 

data from the records of the massive sulfide occurrences in Arizona is utilized in plotting the distribution of rocks of appropriate age and lithology on 

the map. As a result, the State map delineates 

geologic terranes that may be favorable for new 

discoveries. 

References Cited 

Donnelly, Michael, and Conway, Clay, 1986, 

Metallogenic map of volcanogenic massive sulfide 

occurrences in Arizona, with contributions by Paul 

Handverger, edited by R. L. Earhart: U.S. Geological 

Survey Miscellaneous Field Investigation Map, MF1853B, 1:1,000,000 scale. 

Selner, G. I., Taylor, R. B., and Johnson, B. R., 1986, 

GSDRAW and GSMAP-Prototype programs for the 

IBM PC or compatible microcomputers to assist compilation and publication of geologic maps and illustrations: U.S. Geological Survey Open-File Report 86-

42, 40 p. 

Mineral Deposits in NeogeneQuaternary Eruptive Centers in the 

Central Andes 

George E. Ericksen, Robert L. Smith, and 

Robert P. Koeppen 

Eruptive centers, which include collapse calderas, 

composite cones, and flow-dome fields in the 

Neogene-Quaternary volcanic complex of the central Andean region of northwestern Argentina, 

western Bolivia, northern Chile, and southern Peru, 

are potential targets for hydrothermal mineral 

deposits. This volcanic complex extends over an 

area of about 300,000 km2 within a 1,000,000-km2

-

area that is one of the world's great mineral provinces. Because many deposits of Cu, Ph, Zn, Sn, W, 

Sb, Bi, Ag, and Au in this area are chiefly of prePliocene age, it had been believed that most of the 

Neogene-Quaternary volcanic rocks represented 

postmineralization cover. However, recent studies 

have shown that important metalliferous deposits 

as young as Pleistocene are associated with the 

eruptive centers. Mineral deposits in these centers 

were emplaced during the waning phases of 
volcanic activity, and available radiometric ages 

show that they were emplaced chiefly within an 

interval of not more than 1 m.y. after the major eruptive phase of the center. Our studies in the central 

Andes, beginning in 1978, have been focused on a 

better understanding of the relation between types 

of mineral deposits and the geochemistry of associated igneous rocks. We examined the possibility 

that some minor elements in igneous rocks might 

be utilized in exploration for tin deposits. Such 

stable minor elements as Ta, Th, Rb, and Hf are 

indicators of Sn-anomolous magmas. These 

magmas are widespread in the Bolivian tin belt but 

have not been found in the Chilean copper belt, suggesting that there may be real magmatic control of 

differences between types of mineralization. 

Epithermal Ag-Au deposits are by far the most 

economically important type of deposit associated 

with Neogene-Quaternary volcanic centers, chiefly 

collapse calderas, in the central Andes, and we 

believe that the potential for finding similar deposits 

in other eruptive centers is great. Other types of 

deposits present in the Neogene-Quaternary volcanic complex of the central Andes are (1) 

hydrothermal and exhalative Pb-Ag, Cu, Mn, and 

native S deposits and presumed magnetite-hematite 

flows in the upper parts of composite cones, (2) AgAu deposits associated with altered and brecciated 

porphyry stocks exposed in deeply eroded composite cones, (3) polymetallic Sn, Pb-Zn, and Ag-Au 

deposits associated with brecciated and hydrothermally altered porphyry stocks that are not 

associated with known volcanic landforms, (4) AgAu deposits in intensely altered volcanic rocks at 

sites of fossil geothermal spring systems, and (5) 

wood-tin veins and supergene U deposits in ashflow tuffs within and near collapse calderas. In 

addition, the volcanic rocks and associated thermal 

springs contain abundant water-soluble salts and 

are the chief sources of the widespread saline 

deposits of this region, which include major resources of Li and B. 

Heavy Minerals of the Mid-Atlantic 

Inner Continental Shelf 

Edward C. Escowitz and Andrew E. Grosz 

content in surficial sediments of particular geomorphic features, such as shore parallel shoals and submerged channels, has led to speculation of economic deposits. Analyses of vibracores, nominal 

length 5 m, now confirm the vertical continuity of 

high heavy-mineral concentrations offshore of Cape 

Charles, VA, and Cape May, NJ. 

Heavy-mineral (specific gravity > 2.96 gm/cm3) 

content for the surficial 6 m of sediment comprising Smith Island Shoal (approximately 20 km west 

of Cape Charles) has an average value greater than 

2.5 percent, whereas the upper 3 m exceeds 3.0 percent. In-situ economic heavy minerals at Smith 

Island Shoal have been estimated to be on the order 

of 106 metric tons using presently available vertical 

control. This estimate is based on the following 

assumptions: (1) 6 m thick, 10 km long, 3 km wide, 

equivalent deposit dimensions for rectangular solid 

estimate, (2) 50 percent of the seafloor volume is 

sediment, (3) 2.7 gm/cm3 average density of sediment, and (4) 1 percent of the deposit mass is 

economic heavy minerals. This estimate probably 

is conservative because deeper vertical control is 

likely to show deposit thickness exceeds 6 m, the 

length of the vibracore device used for this study 

(did not penetrate the deposit), and preliminary 

analysis of seismic reflection profiles indicates that 

deposit equivalent horizontal dimensions are likely 

to exceed those used for this estimate. 

Heavy-mineral concentration values for cores 

from an inner continental shelf study area offshore 

of Cape May have a maximum value of 5.1 percent 

for a 1.56-m vertical unit and exceed 3.0 percent for 

vertical units greater than 2 m at two other sites. 

Areas of high heavy-mineral concentration have a 

shore parallel trend but lie between Holocene 

shoals. High values also are associated with a relic 

channel approximately 25 km southeast of Cape 

May and were found to have a trend parallel to the 

recent channel between Cape May and Cape 

Henlopen, DE. 

Application of Crystal Chemistry to 

the Geochemistry of Vanadium 

Howard T. Evans, Jr. 

Vanadium ores generally are deposited under 

Economically valuable heavy-mineral assem- reducing conditions, in which trivalent vanadium 

blages have been identified in grab samples from behaves like trivalent iron; for example, in the titanithe mid-Atlantic inner continental shelf. Typically, ferous magnetite ores (for example, in South Africa) 

the heavy-mineral assemblages include ilmenite, vanadium does not occur as discrete minerals, but 

leucoxene (altered ilmenite), rutile, zircon, monazite, is present as a minor constituent in spinellike 

sillimanite, and staurolite. High heavy-mineral oxides (magnetite, coulsenite). When released from 

19 
such a state by hydrothermal or weathering action, 

vanadium displays a bewildering variety of reactions and forms numerous mineral phases because 

of its great sensitivity to two prominent 

environmental parameters, acidity and oxidation 

potential. To understand this behavior, it is 

necessary to follow the changes in the valence and 

structural states of the element. 

A simplified diagram (fig. 1) shows a field in 

which acidity varies on the abcissa and oxidation 

state on the ordinate. The appropriate environment 

for the occurrence of many vanadium minerals can 

be indicated qualitatively on the diagram. Most 

vanadium minerals are highly colored, and those 

with mixed valences are generally black. Proper 

location of such phases on the diagram often can 

be made only by crystal chemical techniques, 

including crystal structure analysis. 

High-temperature vein minerals form mostly in 

the upper left region of the diagram, where 

vanadium forms tetrahedral VO 4 

3

- groups similar 

to those of phosphate PO 4 

3- (vanadinite is isostructural with apatite). In the United States, a major 

source of vanadium is the mineralized sandstones 

of the Colorado Plateau, where a completely different, low-temperature, aqueous environment 

prevails and representatives from all parts of the 

diagram are found. The primary ore is mainly montroseite VO(OH), which is analogous to goethite 

FeO(OH), but, on exposure to air-laden ground 

water, vanadium passes up through the diagram to 

the top, where the mineral form depends on local 

acidity and other cations present. When vanadium 

and uranium become fully oxidized, they become 

bound together in the insoluble carnotite type of 

structure, which is a layer complex built from linear 

0-U-0 and double square pyramidal 0 3-V-02-V-03 

groups. The higher coordination state of the latter 

is typical of more acid environments. Without 

uranium, oxidized vanadates in acid medium form 

soluble, brightly colored polyvanadate salts 

(pascoite), which are leached rapidly. 

At the upper right of the diagram, there occurs 

an important group of mixed 4 + /5 + vanadium 

oxide minerals, which are analogous to a class of 

compounds known in solid state chemistry as 

"vanadium bronzes:' Several different structure 

motifs are known, but, generally, they consist of 

vo5 and vo6 groups joined into chains, which are 

linked laterally to form sheets, with large interlayer 

or channel spaces. Varying amounts of delocalized 

electrons in the chains are charge balanced by varying concentrations of interlayer cations. One structure is represented by hewettite with a layer composition V 3

0 8 , whose structure we have examined 

in some detail. Another type is straczekite with a 

V 20 5 layer~ A newly analyzed structure type is 

found in melanovanadite, which also has a V 20 5 

layer but with a structure completely different from 

that of straczekite. 

On the basis of crystal chemistry, we are able to 

classify rationally the 110 known vanadium mineral 

species and, on the diagram, to trace the course of 

weathering of the original montroseite ore from one 

species to the next as oxidation state rises and acidity swings either to alkaline or acid environments. 

Basic Neutral Acid 

w 5+ Vanadinite Rossite Carnotite Pascoite Hewettite 

u Oxidized 

Straczekite 

Sherwoodite Corvusite 

z 

<( 

..J 

<( 

> Melanovanadite 

~ 4+ Minasragrite Duttonite Paramontroseite 

::J 

i5 

<( Haggite z 

<( 

> 3+ Coulsenite Montroseite Karelianite Reduced 

9 8 7 6 5 4 

pH 

Figure 1. Approximate conditions of formation of some vanadium minerals in the valence-acidity field. 

20 
The Geophysical Character of 

Solution-Collapse Breccia Pipes on the 

Coconino Plateau of Northern Arizona 

Vincent J. Flanigan, R. Michael Senterfit, 

Pam Mohr, and Karen J. Wenrich 

The potential for economic mineral resources 

associated with solution-collapse breccia pipes has 

focused research on the nature and physical character of these geologic features. Numerous pipes are 

exposed on canyon walls, and occurrences of hundreds more are strongly suspected within the plateaus of northern Arizona. The pipes originated 

from solution caverns developed in the Mississippian Redwall Limestone accompanied with subsequent successive caving of younger Paleozoic rocks. 

High-grade U ore in association with potentially 

economic concentrations of Ag, Ph, Zn, Cu, Co, and 

Ni constitute the main mineral resources of these 

collapse breccia pipes. 

Based upon common surface expression and electrical characteristics, two physical models of breccia pipes are proposed for those pipes present on 

the Coconino Plateau. These two models are subsets 

of a basic geologic model and are related to the differences of character of the Kaibab Limestone collapse cone surrounding the throat of the breccia 

pipe. One model is a circular depression of 100 m 

or more in diameter at the center of a slight topographic high lying within an extended depressed 

area. An electrical cross section of this model suggests alternate conductive-resistive zones across the 

collapse cone, with the most conductive zone located over the throat of the pipe. At the surface of 

the Kaibab Limestone, the second model is quite 

similar to the first but differs in that the central area 

over the throat of the pipe is a small hill at the middle of a depression 500 m or more in diameter. An 

electrical cross section of the second model is very 

similar to the first model, except that the throat of 

the pipe is capped with a resistant plug of Kaibab 

Limestone. In the second model, the throat of the 

pipe apparently did not stope upwards through the 

Kaibab, but may have been covered by a circular 

block of relatively undisturbed Kaibab that later 

dropped into the underlying throat. Conductive 

zones outside of the central conductive zone or 

throat area probably are related to ring fracturing 

developed when the Kaibab plug dropped. Common 

physical features of the two models include circular 

drainage, concentrically inward-dipping strata, 

anomalous vegetation, and alteration of the exposed 

rocks by hydrothermal fluids. 

21 

New Geophysical, Geochemical, 

and Geological Investigations of 

Northern Appalachian Zinc-Lead 

Sulfide Deposits of New York State 

Jules D. Friedman and Felix E. Mutschler1 

Combined remote sensing geophysical, geological, 

and geochemical investigations of northern 

Appalachian ZnS-PbS deposits of the Shawangunk, 

NY, district have begun to answer old questions 

about the spatial distribution, tectonic control, 

mode, temperature, and age of origin of these 

orthoquartzite-hosted deposits. At the same time, 

our investigations also have raised new questions 

about their relation to Mississippi Valley-type (MVT) 

deposits and to similar sulfide deposits of Hercynian age along the Iapetus geosuture zone from 

Ireland to Scandinavia. 

The Shawangunk deposits are represented by 10 

or more small ore bodies and occurrences that we 

relocated, sampled, and analyzed in relation to 

Thematic Mapper, radar, aeromagnetic, and 

isostatic gravity maps. The mineralized bodies consist mostly of open-space and vein fillings in the 

Silurian Shawangunk Formation, the basal unit 

above the Taconian unconformity. The ZnS-PbS ore 

bodies and occurrences are localized along . the 

northeast-trending Shawangunk Mountain, a 

northwest-dipping monoclinal ridge marking the 

easternmost margin of the Silurian Salina sedimentary basin. The proximity of the basement in this 

area is evidenced by a northeast-trending aeromagnetic high and associated isostatic gravity low near 

Ellenville that might reflect a detached piece of 

faulted gneissic basement beneath the Taconian 

unconformity at a depth of a few kilometers. 

Most of the ore bodies and occurrences are 

located within a few kilometers of the exposed trace 

of the Taconian unconformity surface where it 

intersects N. 55-60° W.-striking fractures observed 

on optically and geodetically corrected radar 

mosaics. The deposits are marked by geochemical 

heavy-metal (Ph, Zn, Ni, Mn, Cu, and Co) anomalies 

reported by Moxham (1972) in overlying soils. 

Similar heavy-metal anomalies associated with 

radar lineaments of the same northwest-trending 

suite may indicate undiscovered mineralized bodies 

at depth. 

Preliminary geochemical analyses of the ore 

samples show as much as 220,000 ppb Hg content 

in Ellenville sphalerite and generally higher Ag, Fe, 

1

Eastern Washington University, Cheney, WA. 
Hg, Ti, and Nb and lower Cd content than other 

Appalachian and MVT deposits. 

Sulfide isotope statistics indicate that the 

sphalerite, chalcopyrite, and galena values are 

grouped closely around a mean of +24.37 o34S in 

relation to Canon Diablo troilite and provide significant information for our genetic model. 

The Shawangunk deposits have many similarities 

to other Appalachian and MVT ZnS-PbS deposits. 

All probably were emplaced by the migration along 

structural paths of connate brines from the interior 

of sedimentary basins to basin margins, but the 

Shawangunk deposits were formed at higher temperatures by lower salinity fluids as indicated by 

recent fluid-inclusion studies (J. S. Wilbur, Eastern 

Washington University, written comm., 1986) that 

suggest temperatures of ore deposition in the range 

of 150-265 oc in the Shawangunk district. 

In most MVT and Appalachian base-metal 

districts, the bulk of the ore is hosted by carbonate 

rock units. The Shawangunk deposits are hosted by 

orthoquartzite. A 400-m-thick, largely carbonate 

sequence of Silurian to Devonian age overlies the 

Shawangunk Formation. This sequence is covered 

by Quaternary deposits in the Rondout-Mamakating 

Valley on the western side of the Shawangunk ridge 

and could represent a host for related, but yet 

undiscovered, sulfide deposits in this area. 

Reference Cited 

Moxham, R. L., 1972, Geochemical reconnaissance of surficial materials in the vicinity of Shawangunk Mountain, New York: New York State Museum and Science 

Service Geological Survey Map and Chart Series, no. 

21, 20 p. 

Appalachian Metallogenic Map 

Jacob E. Gair, William F. Cannon, John D. Peper, 

Sallie I. Whitlow, Suzanne S. Cannon, and 

Beth D. Martin 

The Appalachian Metallogenic Map and accompanying information provide a systematic compendium of metallic mineral deposits on a new geologic 

base. The map illustrates major metallogenicgeologic relations and is expected to aid in making 

mineral-resource assessments and in identifying 

geologic features favorable for exploration. The map 

is a companion to maps being prepared with the 

same format and at the same scale, 1:1,000,000, by 

cooperating groups in the Canadian Appalachian 

provinces. All known deposits that have been mined 

are shown, as well as numerous prospects of record. 

22 

Deposits are represented by symbols depicting the 

geologic class, scaled to three ranges (large, 

moderate, small) of deposit size. Nine geologic 

classes of deposit and one "uncertain" category are 

shown, including stratabound concordant, stratabound discordant, vein, supergene residual, layered 

igneous, stockwork (pipe), placer, skarn, and 

pegmatite. Eighteen metallic commodities and two 

nonmetallic commodities, sulfur and fluorine, 

where these are associated closely with metallic 

commodities, are shown. The commodities are 

identified by color within deposit symbols. 

Deposits, which are numbered by State, are listed 

in an accompanying pamphlet along with the name 

of the deposit, if any, and additional information, 

including {1) chemical class of deposit, such as 

native metal, oxide, sulfide, and so forth, (2) ore 

characteristics, such as disseminated or massive, {3) 

genesis of the deposit, such as marine sedimentary 

or hydrothermal, and (4) host rock for mineralization, such as felsic volcanic or carbonate. Because 

crowding and overlapping of deposit symbols in 

many parts of the map would have resulted in 

obscuring one symbol by another, we could not 

include this additional information on the map. 

Some local areas of the map with excessive deposit 

"congestion" have been enlarged to a scale of 

1:500,000 to clarify deposit numbers. Much of the 

map and pamphlet information and references to 

literature is available in the U.S. Geological Survey 

Mineral Resources Data System (formerly the 

Computerized Resources Information Bank). 

The geologic map is modeled closely on the geologic base for the Metallogenic Map of Nova Scotia 

by Chatterjee {1983) and incorporates much new 

information from detailed mapping done during the 

last dozen years or so. The geologic features shown 

are those considered particularly significant for the 

formation (occurrence) of metallic mineral deposits. 

The principal feature is lithology, grouped according 

to volcanic or sedimentary, corresponding metamorphic, or igneous plutonic origin and as mafic-ultramafic bodies. Examples of some of these lithologies 

are dominantly felsic volcanic; dominantly coarse 

clastic sedimentary; dominantly carbonate sedimentary, granite, tonalite, gabbro (that is, igneous plutonic); and felsic (or mafic) paragneiss. The significant geologic features of the map also include a 

division of the stratified volcanic and sedimentary 

rocks into the following age units: Middle Proterozoic, Late Proterozoic and (or) Cambrian, Lower 

and Middle Cambrian, Cambro-Ordovician, Middle 

Ordovician-Devonian, Carboniferous, and TriassicJurassic. The plutonic rocks likewise are separated 
chronologically, in millions of years, into four 

groups-greater than 520, 52Q-440, 440-310, and less 

than 310. Specific radiometric ages of the larger 

plutons are shown on the map. Selected major unconformities, anticlinoria, synclinoria, domes, basins, 

and faults also are significant features of the map. 

Note. The map to be published will display 

geologic information by combinations of lines, patterns (for lithology), and colors (for age). In the 

preliminary version shown at the McKelvey Forum, 

lithologies and ages are shown by color on separate 

sheets. 

Reference Cited 

Chatterjee, A. K., 1983, Metallogenic map of the Province 

of Nova Scotia: Department of Mines and Energy, Nova 

Scotia, scale, 1:500,000. 

Gold Veins of the Seward Peninsula, 

Alaska 

Bruce M. Gamble 

Gold-bearing veins of the Seward Peninsula, AK, 

occur along high-angle faults in the Nome Group 

metamorphic rocks. The veins can be divided into 

two types-low and high sulfide. The low-sulfide 

type is more common and generally contains less 

than 3 percent arsenopyrite and (or) pyrite; galena, 

sphalerite, and scheelite occur locally. Quartz is the 

dominant gangue mineral, but plagioclase (albiteoligoclase) and (or) carbonate minerals (calcite, 

dolomite, ankerite) locally make up as much as 50 

percent of the veins. Minor amounts of chlorite, 

sericite, and clay minerals also may be present. The 

high-sulfide veins contain 20-80 percent stibnite 

and minor amounts of pyrite and arsenopyrite. 

Quartz is the dominant gangue mineral, but some 

sericite, calcite, and clay minerals are usually present. Veins at Bluff (83 km east of Nome) are 

unusual in that they contain as much as 60 percent 

arsenopyrite and lesser pyrite and stibnite. Again, 

quartz is the dominant gangue mineral; sericite and 

clay minerals are present in small amounts. 

Free gold (visible and microscopic) is rare in both 

vein types, which suggests that much of the Au may 

occur in sulfides. Au content of the veins varies 

widely. Grab samples from the low-sulfide veins 

show Au values ranging from 0 to 120 ppm. Those 

from the high-sulfide veins show values ranging 

from 0.5 to 40 ppm. Significant, but highly variable, 

amounts of As, Sb, Bi, Ag, W, Hg, Cu, Pb, and Zn 

are also present in the veins. 

23 

Veins range from 2 em to 4 m wide, but most are 

less than 50 em. More than one vein may be present in a single fault zone, and the wallrocks between 

the veins may carry low Au values. The veins at Big 

Hurrah (58 km northeast of Nome) are the largest 

on the Seward Peninsula. They range from 0.5 to 

4 m wide, and as many as four veins are present 

in a single fault zone. Approximately 810 kg (26,000 

oz) of gold was produced at the Big Hurrah Mine, 

primarily between 1903 and and 1907. 

Fluid inclusions in vein quartz from Big Hurrah 

contain C02 and CH4 (Read, 1985). A pressure 

estimate of 0.8 kbar, and temperature estimates 

ranging from 300 to 400 oc indicate emplacement 

after peak blueschist facies metamorphic conditions 

in Late Jurassic to Early Cretaceous time. Quartz 

from several veins on the Seward Peninsula yield 

o018 isotope values that range from + 10.2 to + 19.2 

(Gamble and others, 1985); these values are consistent with a metamorphic origin for the veins. 

Results obtained so far represent part of a ongoing 

study. Future work includes (1) obtaining additional 

measurements of fluid-inclusion compositions and 

homogenization temperatures, (2) K-Ar age determinations of suitable phases from several veins, (3) 

identification by X-ray of unknown phases, (4) assay 

of mineral separates, and (5) obtaining additional 

o018 isotope data. 

References Cited 

Gamble, B. M., Ashley, R. P., and Pickthorn, W. K., 1985, 

Preliminary study of lode gold deposits, Seward Peninsula, Alaska, in Bartsch-Winkler, Susan, ed., 1985, The 

United States Geological Survey in AlaskaAccomplishments in 1985: U.S. Geological Survey Circular 967, p. 27-29. 

Read, J. J., 1985, Gold-quartz vein deposition in an uplifted 

blueschist terrane, Seward Peninsula, Alaska [abs.]: 

Geological Society of America Abstracts with Programs, v. 17, no. 7, p. 696. 

Spark-Aerosol Generation-A New 

Technique for the Direct Analysis of 

Geologic Solids by Inductively 

Coupled Plasma Spectrometry 

D. W. Golightly, A. Montaser ,

1 B. L. Smith, and 

A. F. Dorrzapf, Jr. 

Aerosols generated by a unidirectional highvoltage spark are injected by flowing Ar into an Ar 

inductively coupled plasma (ICP). The particulates 

1

Departrnent of Chemistry, George Washington University, Washington, DC 20052. 
(size range: 0.1-100 JLm) produced by the spark are 

efficiently atomized, ionized, and excited to emit 

subsequently the characteristic radiations measured 

by a direct-reading polychromator. Nonconductive 

geologic materials are presented to the 4-mm pointto-plane spark gap, which requires electrical conductivity of both electrodes, in the form of a disk 

(25 mm diameter, 3 mm thick) that is formed in a 

die of a hydraulic press (39.5 MPa for 60 s) from a 

1:4 mixture of pulverized sample (-100 mesh) and 

Cu powder (-22 mesh). 

Spark erosion of material from the surface of the 

composite Cu disk is an erratic process. However, 

spectral line signals from analytes and matrix 

elements indicate that a pseudosteadystate condition is reached after 70-80 s of sparking. This situation, which persists for 10-20 s, provides an interval 

suitable for the necessary 5- to 10-s integrations of 

spectral line signals. Operating conditions, including the spark current (4.3 A) and break frequency 

(2 breaks per half cycle), delay interval (70s), plasma 

power (1.3 kW), observation height (20 mm), and 

injector gas flow rate (1 Llmin) were optimized by 

multiple-element sequential simplex optimization. 

The capabilities of this new technique for the 

generation of aerosols directly from the solid phase 

are illustrated by recent applications of the technique to the determinations of Ce, Co, Fe, Ni, P, and 

Ph in Co-rich ferromanganese nodules. The linerich spectra of Fe and Mn, which produced many 

spectral interferences, limited the number of elements that could be determined. For measurements 

that were feasible, the precision, based on six replicate determinations, ranged from 7 (Ce) to 14 percent (Fe) relative standard deviation. Because only 

two nodule standards (USGS-Nod-A-l, USGSNod-P-1) are available, the method of standard additions was used for these determinations. Also, the 

erratic sampling by the spark made necessary the 

use of the Mn(II) 257.6-nm line as an internal 

reference for all spectral measurements. Unlike conventional approaches, which require fusions or 

mixed-acid dissolutions of materials followed by 

pneumatic or ultrasonic nebulization of a solution 

Laboratory furnaces (cylindrical objects on laboratory bench) used to heat samples to estimate pressure and 

temperature conditions when mineral deposits formed. Here, a U.S. Geological Survey geologist places 

a sample in a cold-seal hydrothermal vessel that will be heated in one of the furnaces. 

24 
Scanning electron microscope photomicrograph of 

AgCI (cauliflower shape) developing from AgS 

(mottled) that is coating and impregnating a pyrite 

crystal. This crystal is from a pyrite-rich vein on St. 

Thomas, U.S. Virgin Islands. The vein also contains 

Au-Ag tellurides, Ag tellurides, Fe tellurides, native 

gold, and electrum. 

into the plasma, the spark aerosol generator provides a means for the direct introduction of sample into the ICP. This capability is expected to be 

particularly valuable in the analysis of mineral 

phases that are difficult to dissolve, such as beryl, 

cassiterite, chromite, rutile, and zircon. 

Petrology and Platinum-Group 

Element Variation in Zoned Ultramafic 

Complexes, Klamath Mountains, 

Oregon and Northern California 

Floyd Gray, Norman J Page, and Barry C. Moring 

Alaskan-type ultramafic-mafic complexes contain 

platinum-group element (PGE) resources, principally platinum, palladium, and minor rhodium. Some 

of the better known examples of these ultramaficmafic complexes occur in southeastern Alaska and 

British Columbia. Others are found in the Klamath 

Mountains of Oregon and northern California and 

the western Sierra Nevada in California. A detailed 

investigation of three postorogenic, Alaskan-type 

ultramafic-mafic complexes in the Klamath 

25 

Mountains was undertaken to develop a detailed 

understanding of the petrogenesis of the complexes 

and to characterize the PGE occurrences. 

Alaskan-type ultramafic-mafic complexes in the 

Klamath Mountains include the Lower Coon Mountain pluton and the intrusive suites at Tincup Peak 

and at Chanchelulla Peak. These rocks range in age 

from 142 to 163 Ma and intrude metasedimentary, 

metavolcanic, and ophiolitic cumulate ultramafic to 

gabbroic rocks that form part of the accreted 

oceanic terrane of the Klamath Mountain province. 

The Lower Coon Mountain pluton consists of 

layered clinopyroxene-rich lithologies occurring in 

chronological sequence, and the intrusive suite at 

Tincup Peak consists of a cogenetic sequence of 

wehrlite, clinopyroxenite, magnetite clinopyroxenite, feldspathic hornblende-magnetite clinopyroxenite, and dunite-olivine clinopyroxenite and a large 

component of pegmatitic hornblende gabbro. The 

ultramafic-mafic intrusive suite at Chanchelulla 

Peak, part of the Wildwood pluton, consists predominantly of clinopyroxenite, minor interlayered 

dunite, and wehrlite with minor hypabyssal gabbroic rocks. 

Clinopyroxene compositions in the three intrusive 

suites are calcium rich, range from Wo54_7-En45_1-

Fs0.19 to Wo44_9-En43_8-Fs11_

3, and resemble clinopyroxene with alkalic affinities. Olivine ranges from Fo72 

to Fo83, and plagioclase ranges from An68 to An96. 

Cyclic units of layered cumulus magnetite + spinel 

(± ilmenite) and coarse interstitial magnetite occur 

at Tincup Peak and Lower Coon Mountain. 

Characteristics of the rocks include (1) Rh contents up to nearly 1 ppb, (2) Ir and Ru contents of 

less than 100 and 20 ppb, respectively, (3) Pd contents that vary between rock units within intrusive 

suites and between the suites, and (4) relatively similar Pt contents among all units. Concentrations of 

Pd average 6.3 ppb at Lower Coon Mountain, 

13.7 ppb at Chanchelulla Peak, and 36.4 ppb at Tincup Peak. Individual rock units within each 

intrusive suite yield a Pt:(Pt + Pd) (Cohen-corrected 

abundance) that is greater in olivine-rich rocks than 

in clinopyroxenite and significantly greater than in 

gabbro, which suggests chemical fractionation of 

Pd within intrusive suites. 

All three intrusive suites contain disseminated 

sulfides, mainly pyrrhotite + pentlandite + chalcopyrite. Chalcopyrite and bornite at Tincup Peak 

are associated with disseminated nickel sulfides. 

The Chanchelulla Peak pluton also contains lenticular zones of disseminated to interstitial sulfides, 

mainly pyrrhotite, near its contact with sulfidebearing hornfelsic rocks. 
Sulfide minerals, the most significant collectors 

of PG E, exhibit similarities in occurrence, 

mineralogy, and chemistry; however, differences in 

their distribution and in the importance of chemical 

and physical processes that may have produced the 

sulfide occurrences are significant. 

Revision of the Stability Field of Wostite 

and Recommended Standard Oxygen 

Potentials for the Solid Oxide Buffers 

John L. Haas, Jr. 

From a detailed review of the published data for 

selected oxygen buffer assemblages, the composition Fe0.

9470 commonly associated with wustite 

was found to be metastable below 825 oc. The composition of wustite at the isobaric invariant temperature, 566(± 10) oc, is close to Fe0.

915(±o.oosP· The 

> 

- - 0.250 -I 

~ 

f= 

z 

L.U 

f-- 0 - 0.500 a.. 

-I 

~ 

u 

~ 

L.U - 0.750 

I 

u 

0 

a: 

fu 

~ - 1.000 L.U 

- 1.250 

250 500 750 

revised composition is consistent with the best 

observations of the phase stabilities in the stable 

region above and in the metastable region below 

566°C. The results are consistent with the 

experimental data in the much-cited classic study 

of Darken and Gurry (1945). The results are inconsistent with the extrapolations made by Darken and 

Gurry to temperatures below 1,100°C. Most phase 

diagrams for the system Fe-0 are based on Darken 

and Gurry's (1945) extrapolation of the stability 

limits of wlistite. The revised stability field is shifted 

systematically to higher excess 0 contents (more Fe 

vacancies) between 1,100 and 566°C. 

The standard 0 2 potentials of the 0 2 buffer 

assemblages, Fe-wustite, wustite-magnetite, Femagnetite, magnetite-hematite, quartz-fayalite-Fe, 

quartz-fayalite-magnetite, Ni-bunsenite, Cu-cuprite, 

and cuprite-tenorite were developed in the same 

review. The revised potentials are consistent with 

direct observations, indirect observations where 

1000 1250 1500 1750 2000 

TEMPERATURI: (K) 

Figure 1. Plots of the recommended standard 0 2 potentials relative to the ideal diatomic gas at 1 atm as 

a function of the absolute temperature. 

26 
one buffer assemblage is compared against another, 

indirect observations where H20:H2 or C02:CO 

were used to fix 0 2 potentials and volumes, densities, heat capacities, and entropies for each of the 

phases within the precisions for the observations. 

The recommended potentials relative to the ideal 

gas 0 2 at 1 atm, are shown in figure 1. Most of the 

buffer curves are nearly linear. However, the 

quartz-fayalite-magnetite and the magnetitehematite curves show pronounced curvature due 

to the heat effects associated with the magnetic 

anomalies in magnetite at 575°C and in hematite 

at 682 °C. The curvature in the other curves that 

include magnetite is not evident because wustite 

becomes unstable at nearly the same temperature 

as the magnetic anomaly in magnetite. 

Reference Cited 

Darken, L. S., and Gurry, R. W., 1945, The system ironoxygen, I, The wiistite field and related equilibria: 

American Chemical Society Journal, v. 67, p. 

1398-1412. 

Tectonic Setting of Some Cretaceous 

and Cenozoic Structural and 

Magmatic Systems of the Western 

United States 

Warren B. Hamilton 

Convergence of North American and eastern 

Pacific plates was slow during most of Cretaceous 

time; the subducting slab sank steeply below the 

advancing continent, and the magmatic arc was 

near the coast. Convergence was rapid during latest 

Cretaceous and early Paleogene time; the continent 

overrode the slab and was eroded against it, and the 

magmatic arc migrated far inland. Convergence 

slowed in late Paleogene time, and the slab again 

sank steeply. A strike-slip continental margin has 

evolved during the Neogene. 

Obliquely eroded crustal sections in arc batholiths 

show this crustal column to be typical-about 30 km 

depth, migmatites and granitic rocks of garnetamphibolite or low-pressure granulite facies; 25-

15 km, upper amphibolite facies migmatites and 

granitic rocks, many of them peraluminous, that 

crystallized from melts cooler and wetter than those 

either deeper or shallower; 15-4 km, crosscutting 

plutons of hornblende-biotite granitic rocks; 

4-0 km, calc-alkalic volcanic rocks, mostly as 

caldera complexes, ignimbrites, and voluminous ash 

27 

dispersed to mudstones and shales. 

Foreland thrusting of preexisting stratal wedges 

was synchronous with middle and Late Cretaceous 

arc magmatism. Gravitational spreading from the 

magmatically thickened zone may have driven the 

thrusting. 

When convergence was slow, accreted materials 

were metamorphosed at high pressure and low 

temperature beneath the leading part of the overriding continental plate, and some metamorphic 

rocks were cycled into melange above the sinking 

slab. During subsequent rapid convergence, 

accreted materials were underplated against tectonically eroded continental crust, beneath which 

they are now exposed. 

The western part of the continent was slowed by 

drag on the subducted slab during rapid convergence, and rotation of the Colorado Plateau 

relatively clockwise toward the continental interior 

produced Laramide Rocky Mountain crustal 

shortening. Laramide basement thrusts flatten 

downward into anastomosing zones of ductile shear 

that outline midcrust lenses. Midcrust shear zones 

of the same age outline analogous lenses exposed 

in south-central California. 

Severe intra-arc extension, orthogonal to the continental margin, affected magmatically heated Basin 

and Range crust during middle Tertiary slow convergence. Late Cenozoic oblique extension developed as the strike-slip continental margin evolved. 

Both regimes produced similar deformation. The 

middle crust was extended as lenses slid apart along 

ductile shear zones. The aggregate top__!.'detachment 

faults'~of these lenses increased in area as deep 

lenses emerged from beneath shallow ones. The 

brittle upper crust responded by block rotations. 

Range-sized fault blocks are allochthonous above 

the detachments, against which steeply rotated 

basin fills are truncated and new fill is deposited 

directly. Although some detachments surface as 

range-front faults, most originate at midcrustal 

depths. Some detachments remain active even after 

tectonic denudation has brought them to the surface, whereas others are broken by new steep faults 

related to deeper detachments. The lower crust is 

extended by more pervasive ductile flow. The Basin 

and Range Mohorovicic discontinuity has been 

remade magmatically. Similar extension affected 

Idaho and northeastern Washington during Eocene 

time. Neogene uplift of the Western United States 

largely records mantle heating, inferred to be due, 

in part, to asthenosphere diapirism consequent on 

extension and in part to conductive heating of subducted lithosphere. 
Authigenic K-Feldspar-An Indicator 

of the Geochronology and Chemical 

Evolution of Mineralizing Fluids in 

Carbonate-Hosted Lead-Zinc Deposits 

Paul P. Hearn, Jr., John F. Sutter, and 

Harvey E. Belkin 

Rocks containing abundant authigenic K-feldspar 

are now known to occur in clastic-rich zones of 

lower Paleozoic carbonate rocks throughout the 

Valley and Ridge province of the central and 

southern Appalachians, in correlative lithologies in 

western New England, and in the midcontinent 

area. Recent 40 Ar/39 Ar analyses, petrographic and 

fluid-inclusion studies, and geologic setting strongly 

suggest that the authigenic K-feldspar formed during the migration of basinal brines mobilized by 

orogenic activity and, thus, may provide useful 

information regarding the origin of nearby 

carbonate-hosted Pb-Zn mineralization. 

The authigenic K-feldspar in these rocks occurs 

most conspicuously as overgrowths on detrital Kfeldspar but is present in much larger quantities as 

a fine-grained matrix, which apparently is derived 

from the metasomatism of precursor clay minerals. 

Even assuming extensive volume reduction by compaction, mass-balance calculations indicate that the 

authigenic K-feldspar could not have formed by the 

diagenetic redistribution of components in an 

initial volume of sediment and pore water, but must 

have involved the movement of multiple pore 

volumes of fluid through these rocks. For four Kfeldspar separates from Cambrian rocks in the 

central and southern Appalachians, synthetic 40Ar/39Ar age spectra of authigenic K-feldspar 

overgrowths (made by subtracting a spectrum of 

detrital cores with overgrowths from a spectrum of 

cores chemically stripped of their overgrowths) 

yield Late Carboniferous to Early Permian ages 

(278-322 Ma). A single K-feldspar separate from the 

Bonneterre Dolomite (southeastern Missouri) also 

yields a late Paleozoic age (300 Ma). Fluid inclusions 

in quartz and K-feldspar overgrowths on detrital 

grains in unmineralized rocks from the central and 

southern Appalachians have homogenization 

temperatures from 100 to 200 oc and freezing-point 

depressions from -14 to -18.5°C (18-21 weight percent NaCl equivalent). The similarity of these fluid 

inclusions to those in nearby Mississippi Valley-type 

(MVT) ore deposits (Mascot-Jefferson City, 

Austinville-Ivanhoe, Friedensville) suggests that the 

authigenic K-feldspar and the ore deposits may be 

related genetically. This hypothesis is supported by 

28 

the recent discovery of authigenic K-feldspar 

intergrown with sulfide minerals in siliceous zones 

of MVT ore deposits in eastern Tennessee (MascotJefferson City) and eastern Pennsylvania 

(Friedensville ), and at four smaller stratabound PbZn deposits of indeterminate origin in New York, 

Vermont, and Quebec. 

These findings agree with the conclusions of 

other workers that MVT mineralization in the central and southern Appalachians and the midcontinent region is related to the movement of basinal 

brines mobilized during late Paleozoic deformation 

along the Ouachita-Appalachian fold belt. Also, the 

apparent stability of K-feldspar in these ore fluids 

supports the contention that such fluids were not 

strongly acidic and implies that the metasomatism 

of clays may have been a more important source of 

metals than the dissolution of detrital K-feldspar. 

The results of this work suggest that the association of authigenic K-feldspar with sedimenthosted ore deposits may be more common than had 

been realized. Accordingly, this mineral phase 

promises to provide useful information regarding 

the time of migration and the chemical evolution 

of ore-forming fluids in a variety of geologic 

environments. 

Composition and Distribution of 

Cobalt-Rich Ferromanganese Crusts 

From the Pacific 

James R. Hein, lisa A. Morgenson, 

Charlaine Fleishman, William C Schwab, and 

David A. Clague 

We compiled data from the published literature 

and from unpublished U.S. Geological Survey files 

on the chemistry and distribution of Co-rich ferromanganese crusts in the Pacific. The U.S. 

Geological Survey collected samples from the 

Exclusive Economic Zone of the Hawaiian, 

Johnston, Palmyra, and Marshall Islands, as well as 

from the Gulf of Alaska Seamount province and the 

Lau Basin-Tonga Ridge area (table 1). 

Ferromanganese crusts coat most hard substrates 

on the flanks of seamounts, ridges, and plateaus. 

Crusts commonly average 2-4 em in thickness, are 

laminated, and may have well-defined outer and 

inner layers separated by a paper-thin layer of 

phosphorite. Growth rates vary between 2.5 and 

5 mm/m.y. Crusts generally are significantly 

younger than the substrates upon which they rest 

because the flanks of the seamounts and the ridges 

do not provide a mechanically stable environment 
Table 1. Average chemical composition for various elements of crusts from water depths less than 2,500 m 

from the Exclusive Economic Zone of the United States and other Pacific nations 

[All data are in weight percent. n, number of analyses for various elements. -, no data.] 

Areas n Mn Fe Co Ni Cu Pb Ti Si02 PzOs Fe/Mn 

Hawaii and Midway (on axis) ----- 2-38 24 16 0.91 0.45 0.05 1.1 7.9 0.73 

Hawaii and Midway (off axis) ---- 4-15 21 18 .60 .37 .10 0.18 1.3 16 1.0 .88 

Johnston Island ----------------- 12-40 22 17 .70 .43 .11 .17 1.3 12 1.2 .81 

Palmyra Atoll-Kingman Reef ------ 7-8 27 16 1.1 .51 .06 .17 1.1 5.5 1.9 .61 

Howland-Baker Islands1 - --------- 3 29 18 .99 .63 .08 .14 1.2 6.2 1.7 .64 

Marshall Islands ---------------- 55- 63 21 13 .74 .45 .08 .14 .9 4.4 1.5 .61 

Average central Pacific crusts - --- 34-167 22 15 .78 .44 .08 .16 1.1 6.3 1.5 .71 

Northern Mariana Islands 

(and Guam) ------------------- 6-7 12 16 .09 .13 .05 .07 1.41 

Western U.S. borderland --------- 2-5 19 16 .30 .30 .04 .15 .31 17 .95 

Gulf of Alaska Seamount 

Provinces -------------------- 3-6 26 18 .47 .44 .15 .17 .57 .98 .72 

Lau Basin (hydrothermal) ------ -- 2 46 .60 .007 .005 .02 .006 .005 .05 .01 

Tonga Ridge and Lau Basin 

(hydrogenous) ----------------- 6-9 16 20 .33 .22 .05 .16 1.0 1.0 1.26 

South China Sea2 --------------- 14 13 13 .13 .34 .04 .08 14 1.07 

Bonin Island area (Japan) -------- 1-10 21 13 .41 .55 .06 .12 .67 4.9 .82 .70 

French Polynesia --------------- 2-9 23 12 1.2 .60 .11 .26 1.0 6.5 .34 .56 

Average for Pacific 

hydrogenous crusts, all data ---- 56-319 22 15 .63 .44 .08 .16 .98 11 1.1 .81 

1Data provided by P. Halbach, Technical University of Clausthal. 2Data provided by H. R Kudrass, Bundesanstalt fur Geowissenschaften und Rohstoffe. 

for crust growth. Talus is coated with crusts about 

one-half as thick as crusts on rocks recovered from 

nearby outcrops. 

Cobalt contents of up to 2.5 weight percent have 

been measured, but average contents range up to 

1.1 percent. In addition, crusts are rich in Pt (to 

1.3 ppm), Ni (to 1.0 percent), and Ph, Ti, and Ce. 

Crusts are composed predominantly of o-Mn02 

and FeOOH II· Hp. Co, Ni, Ph, Pt, Ce, As, Mo, 

Cd, and Zn are correlated positively with the Mn 

phase, and Cu and Be, with the Fe phase. Fe, Cu, 

Be, K, Ce, AI, Ti, Si, and Ba increase in crusts 

with increasing depth of water, whereas Mn, Co, 

Ni, Ph, Mo, Cd, As, and Sr show the inverse 

relation. Many of these elements also show regional variations, including apparent changes with 

latitude. 

The metals in the crusts are derived from 

seawater. Once the first layer of ferromanganese 

oxide is deposited, the addition of metals to the 

oxide surface becomes autocatalytic. The relative 

amounts of oxide phases in the crusts may be determined by their ratios in colloidal floes in the surrounding seawater. The crusts rich in the strategic 

and economically important metals Co, Ni, Mn, and 

Pt occur in water depths of less than 2,500 m and 

lie beneath the 0-minimum zone where the Fe:Mn 

is small. Co and other metals are fixed in the crusts 

29 

Crew members securing lines on the submersible 

vessel Alvin after it surfaced following a U.S. Geological Survey research dive on the metal-sulfide deposits of the Juan de Fuca Ridge near Washington. 
by lattice substitution for Mn4 + in the Mn02 or by 

coprecipitation of Co oxide with Mn oxide. 

Important criteria that may characterize areas of 

thick Co-rich crusts include volcanoes and ridges 

shallower than 1,500-1,000 m, substrates older than 

about 20 Ma, areas of strong current activity, 

volcanic structures not capped by large modern 

atolls or reefs, a shallow and well-developed 0-

minimum zone, and slope stability and absence of 

local volcanism. 

Based on these criteria and high concentrations 

of Co, Ni, and Pt, areas of high economic potential 

can be outlined and include the Kiribati, Marshall, 

and Micronesia Island groups and Johnston and 

Kingman-Palmyra Islands. Seamounts in the continental borderlands and island arcs of the south and 

west Pacific have lower potential for Co-rich crusts. 

Sulfide Solubilities in Buffered Systems 

at Elevated Pressures and 

Temperatures and Their Depositional 

Implications 

J. J. Hemley, G. L. Cygan, and W. M. d~ngelo 

Experimental studies have been conducted on the 

solubility of Fe, Zn, Pb, and Cu sulfides in chloride 

solutions at elevated pressures and temperatures. 

The solutions were buffered in pH by quartz monzonite (that is, the assemblage K-feldsparmuscovite-quartz) and in 0 and S activities by 

assemblages in the Fe-S-0 or Fe-Cu-S-0 systems. 

Most experimentation was on the pyrite-pyrrhotitemagnetite buffer point. Temperature ranged from 

300 to 700°C, and pressure, from 0.5 to 2 kb. 

As expected, temperature and total chloride 

exhibit strong control on solubility, but total 

pressure proves to be of equal importance. At 400, 

500, and 600°C, Fe solubilities in a system at 1 kb 

total pressure and 1 m Cl and on the pyrrhotitepyrite-magnetite point were 1,000,150, 7,000,700, 

and 12,4001,000 ppm, respectively. At 500°C, 1 kb, 

and 2 m Cl, Fe was increased to about 20,000 ppm. 

At 500°C, 1 kb, 1 m Cl, and with sphalerite and 

galena also present, Zn and Pb solubilities were 

2,300 and 2,600 ppm, respectively, and Fe was 

reduced to 4,200 ppm. For the same system at 0.5 

kb, Fe, Zn, and Pb values were increased to 8,500, 

4,300, and 8,700 ppm, respectively, and, at 2 kb, they 

were decreased to 1,700, 800, and 1,200 ppm, 

respectively. Mo and Ag sulfides were also present 

in some of the runs, but concentrations were 

typically low, on the order of 10-100 ppm. 

30 

Although the solubility characteristics of only Fe, 

Zn, Pb, and Cu were dealt with to date in our study, 

the experimental results appear to have important 

applications to ore genesis in general. The changes 

with pressure are particularly important to oremineral transport. Metals could be transported without deposition over long distances on a decreasing 

pressure gradient so long as the decrease in temperature was not sufficient to significantly offset the 

pressure effect. Such a control would be approximated by a near-adiabatic cooling path, a condition 

probably fairly common geologically, especially in 

the more deep-seated hydrothermal systems. Deposition then could occur by way of several possible 

physical-chemical changes, such as an increase in 

pH, dilution of a brine, or a more extreme and abrupt 

drop in pressure or temperature. Competition between Fe and other base metals for chloride ligands 

is also important. On passing through Fe sulfide or 

Fe oxide-bearing rocks, mineralizing solutions carrying relatively high base metals and low Fe would 

dissolve Fe and deposit base metals, which would 

produce sulfide replacement and zoning relations 

that are characteristics of many sulfide ore bodies. 

The data also bear on the problem of original 

dissolution and entrainment of metals into the 

mineralizing fluid. In the adiabatic decompression 

path described, extensive leaching tends to occur in 

the beginning portion of the path; that is, close to 

the intrusive heat source. Maximum acquisition of 

metals, therefore, would tend to occur in a diffuse 

root zone of metasomatism well removed from the 

ore-body site, with maximum deposition high in the 

system where major perturbations in temperature, 

pressure, and chemistry are more likely to develop. 

The relative importance of orthomagmatic processes 

versus leaching at a heat source by externally derived 

fluids as the source of metals is yet to be established 

for most hydrothermal deposit types, but the processes delineated by the study apply regardless of 

the ultimate source of fluids or metals. 

Petrogenesis of Gabbronorite at 

Yakobi and Northwest Chichagof 

Islands, Alaska 

Glen R. Himmelberg, 1 Robert A. Loney, and 

Peter I. Nabelek2 

On Yakobi Island and at Mirror Harbor on the 

northwestern coast of Chichagof Island, gabbronorite 

1

U.S. Geological Survey and Department of Geology, University of Missouri, Columbia, MO. 2

Department of Geology, University of Missouri, Columbia, MO. 
occurs as irregular bodies, as much as 5.5 km in 

maximum dimension, mostly within a 40- to 43-Ma 

composite pluton consisting largely of tonalite. The 

gabbronorite is the host rock for a magmatic Ni-Cu 

sulfide deposit consisting dominantly of pyrrhotite, 

pentlandite, and chalcopyrite. The gabbronorite 

characteristically contains more orthopyroxene 

than augite, as well as a significant amount of hornblende. Rock types mapped as gabbronorite range 

from hornblende pyroxenite, through hornblendepyroxene gabbronorite, to quartz-bearing norite and 

gabbronorite. The tonalite pluton is composed of 

hornblende diorite, biotite-hornblende diorite, hornblende-quartz diorite, biotite-hornblende tonalite, 

and biotite granodiorite. Contacts between the types 

of gabbronorite are generally gradational on a scale 

of centimeters to meters, and those contacts between the gabbronorite and the tonalite pluton are 

gradational on a scale of meters to tens of meters. 

Rock textures, pyroxene-hornblende relations, and 

rock and mineral chemistry of the gabbronorite 

change systematically as the gabbronorite grades 

into the tonalite. The field, petrographic, and chemical data, including trace element abundances, of 

the gabbronoritic and tonalitic plutonic rocks can 

best be explained either by crystallization of gabbronorite from a tholeiitic magma with subsequent 

assimilation of tonalite that was simultaneously 

undergoing fractional crystallization or by fractional crystallization of a quartz diorite parent 

magma, which yielded the range of gabbronoritic 

and tonalitic plutonic rocks. 

Regional Structure and Distribution of 

Hydrothermal Activity Within Escanaba 

Trough, Southern Gorda Ridge 

Mark L. Holmes and Janet L. Morton 

The Gorda Ridge is a 300-km-long segment of the 

Pacific mid ocean ridge system located 2 50 km off 

the coast of northern California and southern 

Oregon. It is bounded on the north by the Blanco 

Fracture Zone and on the south by the Mendocino 

Ridge. This slow- to medium-spreading rate axis 

exhibits numerous morphological similarities to the 

slow-spreading mid-Atlantic Ridge and is unique in 

this respect among Pacific ridge crests. The axis of 

the Gorda Ridge is characterized by a deep (3,200-

3,800 m) axial valley flanked by steep ridges rising 

to depths of 2,000-2,500 m. The ridge is divided into 

three segments by right lateral offsets at lat 41 °37' 

N. and lat 42°26' N. 

31 

Escanaba Trough, which is the southernmost ridge 

segment, contains more than 500 m of Pleistocene 

turbidite and hemipelagic sediment derived primarily 

from the Gorda Fan. Seismic reflection studies conducted in September 1985 delineated at least five 

discrete volcanic centers (3-6 km in diameter and 

spaced along the trough axis at intervals of 15-20 km) 

that dome and pierce the sediment fill of Escanaba 

Trough. On GLORIA long-range side-scan imagery, 

these volcanic edifices appear as approximately circular areas of higher seafloor reflectivity. Heat-flow 

values exceeding 1,200 mW/m2 were measured over 

two of these intrusion zones. Dredge hauls and 

camera tows over two of these intrusive bodies at lat 

40°45' N. and lat 41 o N. recovered or photographed 

mudstone slabs, fresh basaltic glass, and many occurrences of polymetallic sulfide consisting of pyrrhotite, 

marcasite, sphalerite, galena, chalcopyrite, and barite. 

The hydrothermal activity appears to be confined to 

the axial parts of the central graben in the vicinity 

of the the volcanic intrusive centers. 

Geophysical Studies in the Vicinity of 

the Getchell Fault System, Humboldt 

County, Nevada 

D. B. Hoover, B. D. Smith, V. J. S. Grouch, and 

M. Podwysocki 

Interdisciplinary geophysical studies from 

regional to mine scale have been conducted along 

the Getchell trend of bulk-minable, disseminated Au 

deposits. This trend is defined by the Chimney, Getchell, Pinson, and Preble Au deposits, which generally are alined northeasterly for 20 mi along the 

eastern side of the Osgood Mountains, Humboldt 

County, NV. These deposits, related directly to the 

Getchell and associated faults, are presumed to have 

a common genesis. The Getchell trend and its Au 

deposits have been studied using gravity, magnetic, 

electromagnetic, induced polarization, radiometric, 

and remote sensing methods. 

Regional gravity and aeromagnetic data have been 

useful for identifying the area's major lithologic 

units and structures, some of which may indicate 

features associated with the genesis of the Au 

deposits. Cretaceous granodiorite of the Osgood 

Mountains pluton is well defined by a regional 

north-south aeromagnetic high. There are also 

northwest magnetic trends within the pluton. Detailed ground magnetic surveys show local magnetic 

highs associated with Cretaceous dikes and with 

skarns developed at the contact between the pluton 
and Paleozoic carbonate rocks. Regional gravity data 

define a northeast-trending high coincident with the 

Getchell Au trend that possibly reflects a deep crustal 

feature. 

Shallow and deep penetrating electromagnetic 

methods have been used to map conductive features 

in the Getchell trend. Near-surface conductive fault 

zones have been detected by Slingram and very low 

frequency methods. The deeper conductive expression of the Getchell fault system has been detected 

in 12 traverses using telluric profiling data supplemented with audiomagnetotelluric sounding data. 

A previously unknown fault zone under alluvial 

cover east of the main Getchell fault was discovered 

using the telluric method. 

Characterization of the electrical properties of 

rocks within the Getchell and Pinson areas has 

begun using spectral induced polarization methods. 

Results of in-situ and laboratory measurements 

indicate that the electrical signatures of mineralized 

rocks containing remobilized carbonaceous material 

are different from the signatures of unmineralized 

carbonaceous metasediments. Laboratory spectral 

reflectance measurements suggest that montmorillonite within the mineralized rock may be one source 

of the differences in electrical properties. These 

variations in electrical properties imply that complex 

resistivity surveys may be useful in detecting 

deposits within the Getchell trend. 

Ground radiometric measurements were evaluated 

for applicability to exploration because reported K 

metasomatism associated with disseminated Au 

deposits could cause radiometric anomalies. The erich zones of the Getchall fault are distinctly higher 

in U and K than the host carbonates. However, windblown detritus from the granodiorite obscures 

radiometric signatures in routine ground surveys. On 

the other hand, detailed surveys in open pits indicate 

that mine and borehole radiometric measurements 

may be practical in deposit evaluation. 

Remote sensing methods have been used to characterize various silica-bearing rocks, some of which 

are associated with disseminated Au deposits. 

Jasperoid replacements in carbonate rocks exhibit 

anomalous midinfrared reflectance spectra. X-ray 

analysis of these jasperoids shows that they are composed almost exclusively of quartz; however, they 

lack a characteristic double reflectance signature 

expected for quartz. The difference may be due to 

poor crystallinity of silica. With further study, jasperoids possibly might be detected unambiguously 

by midinfrared remote sensing methods. Identification of different silica-bearing rocks may lead to a 

rapid, cost-effective exploration tool for Au deposits. 

32 

Very Low Frequency Aerial Surveys 

Applied to Regional Mineral 

Assessment 

Robert Horton and Carl Long 

Combined aeromagnetic and very low frequency 

(VLF) aerial measurements were made as part of 

two U.S. Geological Survey Conterminous United 

States Mineral Assessment Program (CUSMAP) 

projects. The surveys, conducted from 1983 to 1986, 

include portions of the Glens Falls (Vermont and 

New Hampshire) and International Falls-Roseau 

(Minnesota) CUSMAPs. The aerial VLF method is 

an electromagnetic technique that responds to the 

electrical conductivity of near-surface geologic features; it is useful in mapping bedrock conductors, 

such as black slates, and in locating areas where 

conductive glacial overburden is thin or absent. In 

these two surveys, the primary objective of the VLF 

measurements was to contribute new structural, 

lithologic, and glacial deposit information that cannot be obtained from magnetic measurements. 

The VLF technique is based on measurement of 

the local electric and magnetic fields of a vertical 

polarized groundwave transmitted at 20-25 kHz by 

one of several VLF communication transmitters 

located worldwide. The Geological Survey's VLF 

aerial system measures the in-phase and quadrature 

parts of three components of the magnetic field and 

the quadrature part of the horizontal electrical field 

using the vertical electric field as a reference. 

Anomalies observed in the in-phase and quadrature 

parts of the magnetic field indicate lateral changes 

in conductivity. By assuming that the ground is 

homogeneous, the inverse of conductivity, "apparent resistivity;• may be calculated from the horizontal electric field. 

The eastern one-half of the Glens Falls CUSMAP 

was surveyed with an 800-m flight line spacing. In 

general, the geology of the area is comprised of a 

thick series of steeply dipping Paleozoic metasediments interspersed with volcanic and small igneous 

intrusive rocks. The VLF data show asymmetric and 

symmetric anomalies in the magnetic field that are 

continuous across several flight lines, which indicate conductive lithologic boundaries and structural 

features. Ground follow-up investigations identified 

conductive carbonaceous, graphitic, and sulfide 

zones that are coincident with the VLF aerial 

magnetic anomalies. Several of the conductive 

anomaly locations identified by this VLF survey suggest favorable ground for the occurrence of massive 

sulfide deposits. Some high-resistivity anomalies 
observed in the electric field data correlate with 

known intrusive units. Mineral deposits associated 

with intrusive bodies may occur in these resistive 

terrains. 

The western one-half of the International Falls and 

the eastern one-half of the Roseau CUSMAPs were 

surveyed with a 400-m flight line spacing. Here 

Precambrian bedrock terrain is covered partially by 

glacial overburden that makes geologic mapping 

dependent upon sparse outcrops and exploration 

drilling. The glacial tills contain conductive lake 

sediments that inhibit VLF mapping of buried bedrock features. However, the calculated apparent 

resistivity is useful in identifying areas with thin or 

no glacial cover. Low-resistivity background levels 

(<100 ohm-m) generally were produced by the glacial 

overburden. High-resistivity anomalies (>1,000 ohmm) usually correlate with high topographic areas that 

may contain outcrops or very thin overburden. However, high topographic areas that reflect low resistivities are caused by glacial moraines, filled valleys 

within bedrock outcrops, and possibly near-surface 

bedrock conductors. Low topographic areas that reflect high resistivities are caused by bedrock outcrops 

that have little or no surface expression or possibly 

sand and gravel deposits. The Minnesota VLF survey 

has identified possible sand and gravel deposits, new 

outcrops, and near-surface bedrock drilling targets 

that will benefit geologic mapping in the area. 

Bentonite Resources, Cation-Exchange 

Capacity, Mineralogy, and Uses 

John W. Hosterman 

Bentonite is defined as any material composed 

chiefly of the clay mineral, smectite, and whose 

physical properties are controlled by it. Fuller's earth 

is defined as any naturally occurring material that 

has a high absorptive capacity for liquids or gases. 

Most fuller's earth is produced from palygorskite and 

from bentonite. Ground silica, diatomaceous earth, 

talc, pyrophyllite, and kaolinite also are used to make 

fuller's earth, but they are not included here. 

The wide variety of physical properties of bentonite makes it suitable for many commercial utilizations and applications. The unique properties of bentonite make it an excellent ingredient in drilling 

muds where freshwater is present. Large amounts 

of bentonite are processed for bonding and pelletizing. The Na-bentonite is a swelling variety that is 

used for bonding foundry sand and pelletizing taconite iron ores. The Ca-bentonite is a nonswelling 

variety that is used in bonding foundry sand where 

33 

a high green strength is required. Other utilizations 

of bentonite include adhesives, animal feed, clarifying oils, fertilizer and pesticide carrier, sealer, and 

waste disposal. 

Most of the present commercial deposits of bentonite are from geologic units that are of Cretaceous 

or Tertiary age. The best grade Na-bentonite occurs 

in the Mowry Shale of Cretaceous age in Wyoming 

and Montana. The most abundant Ca-bentonite deposits are found in the Jackson and Claiborne 

Groups of Eocene age in Texas. No deposits of commercial bentonite have been found in rocks older 

than Mesozoic, and only one deposit of bentonite 

at Ash Meadows, NV, is believed to be Pleistocene 

in age. 

Bentonite production in the United States was 2.9 

million short tons in 1983. This is a major decrease 

from a production peak of 4.9 million short tons in 

1981; 65 percent of the bentonite production came 

from Wyoming, and the balance of the production 

came from nine other States. The resources of all 

grades of bentonite in the United States are 

undoubtedly large. Probably 800 million tons of bentonite are in Wyoming, Montana, and Texas. However, because of the continuous demand for Nabentonite over the last 75 yr, resources of this grade 

are rapidly declining. 

Mineral-Resource Assessment of the 

Baird Mountains Quadrangle, 

Western Brooks Range, Alaska 

Susan M. Karl, Jeanine M. Schmidt, Peter Folger, 

Bill Thompson, Carl Long, Richard Goldfarb, and 

lnyo Ellersieck 

Studies conducted for the Alaska Mineral Resource Assessment Program in the Baird Mountians 

quadrangle in northwestern Alaska included reconnaissance and local detailed geologic mapping, 

systematic rock, stream sediment, and heavy-mineral 

concentrate geochemical sampling and subsequent 

statistical analysis, detailed investigations of known 

and newly discovered mineral occurrences, and synthesis of geologic and geochemical data with 

regional gravity and aeromagnetic data. Additional 

techniques applied to resource evaluation undertaken during this study included analyzing insoluble residues from carbonate rocks and stream 

sediments from carbonate-dominated catchment 

basins and audiomagnetotelluric (AMT) profiling in 

tundra-covered terrain. 

The rocks in the Baird Mountains quadrangle, 

structurally complicated by regional folding and 
thrusting, consist mainly of Paleozoic marine carbonate, pelitic, and clastic rocks with minor amounts 

of nonmarine clastic rocks. Mafic and felsic volcanic 

and volcaniclastic rocks are intercalated locally with 

the Paleozoic sequences. Mesozoic marine sedimentary and mafic volcanic rocks overlie the Paleozoic 

rocks in the northwestern part of the quadrangle. 

Mixed metamorphic rocks and intermediate intrusive rocks of Precambrian age are tectonically 

interleaved with Paleozoic sedimentary and volcanic 

rocks in the northeastern part of the quadrangle. 

Polymetamorphosed pelitic schists dominate the 

southern part of the quadrangle. 

Previously known mineral occurrences in the 

Baird Mountains quadrangle include the carbonatehosted Omar Cu prospect, the Frost Pb-Zn-Ba 

occurrence, and placer Au from the Timber CreekKlery Creek area. During the course of this study, 

two new mineral occurrences were discovered-the 

Ahua, in the Kilyaktalik Peaks area, which consists 

of Ag mineralization hosted in silica-pyrite altered 

carbonaceous black shales, and the Powdermilk, in 

the Omar River area, which consists of stratabound 

Zn-Pb sulfide mineralization in bedded dolostones 

of possible Ordovician age. 

Profiles from modeled AMT data identified major 

structures and lithologic trends in poorly exposed 

areas and in the subsurface. Low resistivities in the 

Kilyaktalik Peaks area indicate potential for 

mineralization. 

Analyses of insoluble residues recovered from 

acid leaching of stream sediments broadened 

dispersion halos for base-metal elements in carbonate rocks by enhancing geochemical anomalies 

without affecting background concentrations and 

may prove to be an important exploration tool in 

areas of the Brooks Range underlain by carbonate 

rocks. 

Seven potential resource areas were defined by 

stream sediment values, bedrock geochemistry, and 

interpretation of R-mode factor analysis of heavymineral concentrate data-the Agashoshok-Eli River 

area with high Ag-Pb-Zn values (clastic rocks) and 

high Fe-Co-Cu-Ni values (carbonate and mafic 

rocks), the Squirrel and Omar Rivers area with high 

Ag, Pb, Zn, and Mo values (carbonate rocks), the 

Nakolikurok Creek area with high Fe-Co-Cu-Ni-Mn 

values (mixed carbonate and clastic rocks), the 

upper Tukpahlearik and Anaktok Creek area with 

high Fe-Co-Ni-Cu-Mo-Ag-Mn values (mixed 

metapelitic rocks, carbonate rocks, and carbonaceous slates), the Kilyaktalik Peaks area with very 

high values in Ag-Pb-Zn-Ba-Mo (carbonaceous 

shale, pelitic, and mixed clastic rocks), the Nanielik 

34 

Creek area with high Ag and base-metal values 

(pelitic, clastic, volcanic, carbonaceous, and carbonate rocks), and, finally, concentrate samples containing abundant scheelite plus occasional Au and 

(or) Ag may extend the known Klery Creek placer 

resource roughly 30 km to the northeast. 

Effect of Topography on Gas Flow in 

Unsaturated Fractured RockNumerical Simulation 

K. L. Kipp, Jr. 

Air flow in certain bore holes open to the 

unsaturated zone at Yucca Mountain, NV, cannot 

be accounted for completely by diurnal barometric 

pressure variations. This observation led to the 

hypothesis of thermally driven air circulation within the mountain that is affected by the topographic 

relief. An idealized numerical model was formulated to test the hypothesis that the seasonal variation of air temperature at the mountain surface 

coupled with the topographic relief causes a natural 

periodic air circulation through the unsaturated 

zone in the mountain. The model was based on the 

solution of finite-difference approximations to the 

coupled equations of flow of air saturated with 

water vapor, transport of heat, and transport of a 

solute tracer. The coupling occurs through the density, viscosity, and interstitial velocity terms. The 

vapor-saturated air was treated as an ideal gas, and 

the presence of water vapor was accounted for by 

use of a virtual temperature. The mountain is comprised of porous- and fractured-rock layers with a 

soil layer at the land surface and was approximated 

by two zones of porous media, one representing the 

rock and the other representing the soil. The simulation region was a two-dimensional vertical slice of 

rectangular shape, representing a slice part way 

through the mountain. The boundary conditions 

used were as follows: (1) along the upper part of the 

left side and along the top (mountainside and crest), 

specified pressure and temperature based on atmospheric conditions, (2) along the lower part of left 

side (below the mountainside), zero air flux and zero 

heat flux, (3) along the bottom (below the mountain 

base), no air flux and specified geothermal-heat flux, 

and (4) along the right side (symmetry plane), zero 

air flux and zero heat flux. The solute tracer was 

introduced by a steady flux along the mountainside. 

The initial conditions were the result of a steady 

state simulation of typical spring conditions. Then, 

the temperatures and pressures at land surface were 
varied seasonally. Simulations were advanced in 

time, until a periodic steady state was achieved for 

the air circulation and heat transport. 

The resulting air-velocity fields, temperature fields, 

tracer-plume configurations, and boundary fluxes 

indicated that the seasonal temperature variation at 

the land surface coupled with the topography indeed 

can induce atmospheric circulation through the 

mountain. In summer, air enters the mountain along 

the crest and leaves along the lower one-half of the 

mountainside. In winter, flow is reversed, but with 

a slightly slower rate. The temperature field is 

affected by the seasonal variations within 20 m of 

the land surface. The solute-tracer plume responds 

to the air-circulation pattern most markedly within 

40 m of the mountainside. In view of the feasibility 

of topographically affected air circulation through 

a mountain and the resulting potential for transport 

of consitituents in the vapor phase from within the 

mountain to the atmosphere, additional field and 

numerical simulation studies are in progress. 

Mineralogy and Chemistry of 

Hydrothermal Sulfide and Petroleum 

Deposits From Escanaba Trough, 

Gorda Ridge 

Randolph A. Koski, Robert A. Zierenberg, Keith A. 

Kvenvolden, and Wayne C. Shanks Ill 

In 1986, surveys with a towed camera system and 

the deep-ocean submersible Sea Cliff revealed that 

small conical chimneys and low semicontinuous 

mounds are widespread over the sediment surface 

at the SESCA (lat 40°45' N.; long 127°30' W.) and 

NESCA (lat 41 o N.; long 127°30' W.) sites in 

Escanaba Trough on the southern Gorda Ridge. 

Although active venting has not been observed, the 

recovery of hydrothermal deposits by dredge and 

submersible indicate recent hydrothermal discharge 

onto the seafloor. Samples dredged from Escanaba 

Trough include texturally homogeneous pyrrhotiterich massive sulfide with generally low base- and 

precious-metal content (Cu to 4 percent in some 

samples) and zoned polymetallic sulfide with high 

Zn (to 43 percent), Pb (to 8 percent), and Ag (to 

700 ppm) contents. The massive sulfide samples 

consist predominantly of pyrrhotite, sphalerite, 

galena, barite, cubic cubanite, chalcopyrite, tetrahedrite, and loellingite. Minor phases, identified by 

scanning electron microscopy, include argentite and 

native bismuth. The association of loellingite 

(FeAs2) and pyrrhotite indicates deposition from a 

35 

metal-poor and sulfur-deficient fluid that percolated 

through the underlying sediment. Barite-rich crusts 

on some pyrrhotitic massive sulfide samples have 

high Zn (to 17 percent), Ph (to 4 percent), Ag (to 

400 ppm), and Au (to 2 ppm). Massive talc deposits 

mantle some of the pyrrhotite-rich sulfide deposits 

at the SESCA site. 

Subsurface fluid flow and deposition is indicated 

by sulfide veinlets and the presence of abundant 

disseminated chlorite, talc, pyrite, and chalcopyrite 

in sediment cores. Samples of sediment with interlayered sulfide and mudstone breccia enclosed in 

a pyrrhotite-rich sulfide matrix have been dredged 

from the SESCA site. An altered sediment sample 

with interstitial sulfide contains high Ph (13.7 percent), as well as high Zn (7 percent), and Ag 

(340 ppm). The abundance of Ph in Escanaba 

Trough samples implies extensive interaction between hydrothermal fluids and the sediment at 

depth. 

A sample of sulfide-bearing turbiditic sediment 

also contains 5.6 percent interstitial asphaltic 

petroleum. This petroleum is composed of 44 percent polycyclic aromatic hydrocarbons, 2 percent 

aliphatic hydrocarbons, and 54 percent nonhydrocarbons. The extent of hydrocarbon aromatization 

and isomerization suggests rapid and intense thermal maturation due to interaction with hydrothermal fluid. Molecular markers, such as the 

dominance of odd-carbon-number alkanes, indicate 

that the petroleum source probably is continentally 

derived terrigenous plant matter in the Pleistocene 

and Holocene sediment that fills Escanaba Trough. 

New Uses of Ammonium Minerals in 

Geochemistry 

M. Dennis Krohn 

The ammonium ion (NH4) is known to replace K 

or other cations in several aluminosilicate and 

sulfate minerals, including feldspar (buddingtonite ), 

mica (tobellite), illite, and jarosite. Recent 

discoveries have added ammonioalunite and 

ammonioleucite to the list of natural ammonium 

minerals. Previously, ammonium minerals could 

not be identified in the field because they have no 

diagnostic optical properties and generally are 

recognized in X-ray diffraction by slight shifts in 

peak intensity and position from K-bearing analogs. 

Recent work at the U.S. Geological Survey has 

shown that ammonium minerals have diagnostic 

spectral properties in the near-infrared wavelength 
region and can be mapped readily in the field using 

ground-based or aerial sensors. Unlike chemical 

techniques, the specific mineralogy of the 

ammonium cation can be distinguished using the 

near-infrared spectral techniques. 

Research is underway to determine whether 

ammonium minerals have sufficiently specific 

geochemical affinities to be useful as an indicator 

of paleogeochemical conditions. Ammonium 

minerals occur in several economically important 

geologic environments including disseminated Au 

deposits, Hg-bearing hot springs deposits, sedimentary exhalative Pb-Zn-Ag deposits, oil shales, and 

anthracite coal beds. Based on field studies, the present working hypothesis is that the formation of 

ammonium minerals indicates the interaction of 

hydrothermal fluids and brines with organic matter within a restricted range of acidity and redox 

conditions. Such a hypothesis may. be considered 

as a type of organic aureole. Near-infrared reflectance techniques have been particularly successful 

in identifying ammonium-bearing minerals at hot 

springs deposits; such minerals generally show an 

enrichment of 10-100 times background values for 

ammonium. Distribution of ammonium-bearing 

minerals at these sites appears to be concentrated 

along fracture surfaces within hydrothermally 

altered rocks, which suggests some type of localization by hydrothermal fluids. The presence of pitted 

ammonia-alunite crystals and euhedral buddingtonite crystals at one site suggests at least two stages 

of crystallization. 

Several factors must be considered in applications 

using ammonium minerals. Lack of a host cation 

site for substitution limits the potential rock types 

where ammonium minerals can occur. Common 

minerals such as quartz, kaolinite, and calcite have 

no substitution site and cannot be considered. 

Opaque minerals in the rock may quench the spectral features and reduce the near-infrared detectability of ammonium-bearing minerals. Although 

concern has been expressed that ammonium 

minerals are not theoretically stable in an oxidizing environment, near-infrared studies have 

documented clearly ammonium-bearing minerals 

at the surface in rocks of Tertiary age in semiarid 

to temperate climates. In summary, the 

demonstrated detectability and relative stability of 

ammonium-bearing minerals combined with their 

occurrence in several economically important ore 

U.S. Geological Survey scientists performing induced polarization geophysical tests on sediment core (tube 

at left bottom) during a June 1985 cruise of the eastern U.S. seaboard. 

36 
U.S. Geological Survey mineralogist operating a calorimeter for measuring heat capacities of minerals at 

very low temperatures. These measurements are essential for calculating thermal stability of minerals of 

very high temperatures, thus increasing our understanding of how deposits of strategic minerals formed. 

deposit settings suggest that detection of 

ammonium minerals should be included in appropriate geochemical exploration programs. 

len-Exchange Fertilizer for the Utilization of Low-Grade Phosphate Ores 

Tung-Ming Lai and Dennis D. Eberl 

Nutrients are released to plants from phosphate 

rock when ammonium-saturated ion exchangers are 

present. The generalized reaction is 

Phosphate rock + NH4 exchanger 

= Ca exchanger + NH4 + + H2P04

- . 

The ion exchanger is a sink for Ca ions, thereby 

decreasing Ca activity in the soil solution and permitting further dissolution of the phosphate rock. 

This system offers the possibility of using low-grade 

phosphate ore as fertilizer, particularly if an ion 

exchanger, such as smectite, is present in the ore 

37 

and if the ion exchanger can be ammonium 

saturated. The system also makes N and Ca 

available to plants and can be regenerated by adding 

additional NH4 exchanger to soil-phosphate rock 

mixtures or by resaturating the ion exchanger with 

NH4 •. Only the NH4 exchanger needs to be added 

to soils that already contain phosphate compounds; 

by this method, phosphate that has been fixed as 

apatite in soils by the reaction of soluble phosphate 

fertilizer with the soil can be made available for 

uptake by plants. 

The rate of nutrient release can be adjusted by 

varying the ratio of exchanger to phosphate rock. 

Seedling uptake experiments indicate that the ionexchange fertilization system surpasses a soluble P 

system in P uptake by barley after several cuttings 

from the same pots. Preliminary results from 

greenhouse pot trials using sudangrass indicate that 

dry yields from the ion-exchange system are larger 

than those from a soluble P system. A new method 
that uses mixtures of OH- and H-saturated exchange 

resins has been developed for measuring P availability in soils that have been treated with the ionexchange system. 

Fertilization by ion exchange offers an alternative 

technology to the application of readily soluble and 

concentrated plant nutrients and may circumvent 

some of the problems associated with soluble 

fertilizers. 

Quantitative Analysis of Fluid-Inclusion 

Gases-Applications to Studies of Ore 

Deposits 

G. P. Landis, A. H. Hofstra, D. L. Leach, 

and R. 0. Rye 

Quantitative methods of fluid-inclusion gas 

analysis using a quadrupole mass spectrometer 

have been applied to the study of ores from the 

Coeur d'Alene district, Idaho; Mississippi Valleytype (MVT) deposits, Missouri, Arkansas, and 

Kansas; the Creede district, southern Colorado; and 

wood tin deposits, southern New Mexico. The 

chemistry of volatiles in ore and gangue mineral 

fluid inclusions helps characterize ore-forming 

fluids. Trends in volatile content and gas speciation, 

determined throughout the mineral parageneses, 

can be used to interpret the geochemical processes 

leading to ore formation. 

Analyses are obtained from samples previously 

studied by fluid-inclusion petrographic and microthermometric methods and constrained by a geologic framework. While under vacuum, inclusion 

gases are released either by mechanical crushing 

of host material or by thermal decrepitation. Controlled thermal ramp heating coupled with real-time 

multiple ion monitoring are used to profile gas release as a function of temperature. These profiles 

define discrete fluid-inclusion populations that can 

be distinguished from adsorbed-desorbed gas 

release, "matrix" gas, and the thermal decomposition of host minerals. Matrix gas collectively refers 

to the following sites of gas entrapment in the host 

mineral: submicrometer-sized fluid inclusions, domain boundaries, microstructures, crystal defects, 

and gas dissolved in the crystal. Chemical reactions 

of gases due to heating are evaluated easily. Sharply 

defined spikes representing sudden release of gas 

from single or multiple fluid inclusions are superimposed upon the thermal profiles. Quantitative 

analysis of these "bursts" permits detailed study of 

ore fluid chemistry at the level of individual fluid 

inclusions. Analyses of gas mixtures from discrete 

38 

fluid-inclusion populations tightly constrain ore 

genesis models. 

Gas data are quantified from the partial pressure 

of each gas determined in the mass spectrometer 

and the pressure-volume-temperature relations of 

the gas mixture in the inlet system. The following 

parameters are applied for each gas in a M x N 

matrix solution: ionization fragmentation, gas sensitivity, and kinetic adsorption-desorption on vacuum surfaces. Rapid, highly sensitive, and precise 

analyses are possible with a minimum detectable 

partial pressure of 8 x 10-15 mbar, a partial pressure sensitivity of 8 x 10-9 (that is, 8 ppb ), a maximum scan rate of 100 f.J-S per atomic mass unit 

(AMU), over a range of 0-255 AMU, and an electrometer dynamic range of five orders of magnitude. 

All instrument control is enabled by assembly and 

FORTRAN codes on a PDP 11/73 computer with 4 

MByte memory and 110 MByte Winchester disk 

capacity. Any gas species with major atomic mass 

unit peaks within the range of the instrument can 

be detected. The present system is calibrated for 32 

primary gases and light hydrocarbons, including 

H20, C02 , N2 , 0 2 , H2 , He, Ar, CH4 , H2S, S02 , N-0 

gases, NH3 , HF, and HCl, and common organics 

up to C6 • Total relative analytical precision of 1-3 

percent is typical. A separate gas chromatographmass spectrometer is used to identify more complex 

organic spectra. 

The following results are obtained from the above 

studies of ore systems: (1) Coeur d'Alene vein samples document the generation and evolution of ore 

fluids during metamorphism of the Belt basin. Fluid 

inclusions in Zn-rich veins contain greater concentrations of CH4 , short chain hydrocarbons, and N2 

than in younger Ag-rich veins in which C02 is 

dominant. Reduced fluids in.Zn-rich veins probably 

were derived from devolitalization reactions of 

sediments containing organic matter and NH4-

bearing phyllosilicates. Changes in P-T, f02 , and 

loss of volatiles by gas phase separation may have 

generated a more oxidized C02-rich fluid for the 

younger Ag veins. (2) The most abundant gases 

determined in samples from studied MVT's are 

C02 , N2 , and CH4 • The hydrocarbon content of 

these fluids is low (<0.1 mole percent) and consists 

largely of CH4 with traces of C2H6 • Water- and C02-

rich inclusions combine to yield bulk analyses of 

several mole percent C02 • The C02-rich (>20 mole 

percent) individual inclusions represent a period of 

local C02 effervescence during host rock dissolution and sulfide deposition. The thermal maturity 

and low concentration of hydrocarbons together 

with the high C02 content suggest that these 
ore-forming fluids are highly evolved basinal brines. 

(3) The gas studies of epithermal ores from the 

Creede district, combined with existing extensive 

detailed geologic and geochemical data, provide 

strong constraints on the sources of fluids and the 

role of mixing and boiling during ore deposition. The 

presence of variable amounts of organic gas species 

throughout the paragenesis points to a significant 

input from caldera moat sediments in the hydrothermal process. (4) The data from the Black Range tin 

occurrences confirm a magmatic origin for the ore 

fluids and permit study of the evolution of magmatic 

fluids during the period of ore deposition. 

Genesis and Tectonic Setting of 

Volcanogenic Massive Sulfide 

Deposits, Eastern Alaska Range, Alaska 

len M. Lange, Warren J. Nokleberg, 

John N. Aleinikoff, and Stanley E. Church 

A belt of volcanogenic massive sulfide deposits 

and occurrences extends for over 200 km along the 

northern flank of the eastern Alaska Range. The 

deposits occur in the Jarvis Creek Glacier subterrane, which forms the southern margin, and in the 

highest structural level of the Devonian and Mississippian Yukon-Tanana terrane. The deposits and 

enclosing metavolcanic and metasedimentary 

schists exhibit two periods of regional metamorphism and penetrative deformation-an older 

amphibolite facies event and a younger lower 

greenschist facies event. From west to east, the 

major districts are at Hayes Glacier, McGinnis 

Glacier, and Robertson River. 

The Hayes Glacier district contains the Miyaoka 

occurrence west of the glacier and several other 

occurrences east of the glacier. The occurrences 

strike west-northwest for about 10 km and consist 

of massive pyrite and pyrrhotite and minor chalcopyrite, sphalerite, and galena in south-dipping 

sulfide pods, lenses, and stringers that parallel the 

enclosing schists. Protoliths for the host rocks are 

mainly andesite and dacite tuffs and flows, shale, 

and marble, with lesser quartz-rich keratophyre 

flows and tuffs, volcanic graywacke, and siltstone. 

Selected samples contain up to 0.7 percent Pb, 0.5 

percent Zn, 0.9 percent Cu, 0.5 percent As, 0.5 percent Sn, 0.2 ppm Au, and 10 ppm Ag. 

To the east-southeast, the McGinnis Glacier 

district contains two occurrences about 1 km apart. 

The occurrences consist mainly of massive pyrite 

and pyrrhotite with lesser sphalerite, chalcopyrite, 

39 

and galena in highly deformed lenses and pods. Protoliths for the host rocks are mainly andesite flows 

and tuffs, shale, marl, and marble. Selected samples 

contain up to 0.3 percent Pb, 2.3 percent Zn, 0.3 percent Cu, 0.1 ppm Au, and 50 ppm Ag. 

Farther southeast, the Robertson River district 

contains about 10 or more occurrences in a 200-

km2 area. The occurrences consist of layers and 

zones of varying amounts of massive to disseminated pyrite, chalcopyrite, galena, sphalerite, and 

bornite. The layers and zones are generally conformable to layering in west-northwest-striking schists. 

Protoliths for the host rocks vary widely and include 

andesite, dacite, quartz keratophyre tuffs and flows, 

shale, quartzite, marl, and sparse marble. The occurrences are associated spatially with diorite or gabbro sills that exhibit only the younger lower greenschist facies metamorphism and deformation. 

Selected samples contain up to 1.5 percent Pb, 11 

percent Zn, 1.3 percent Cu, 0.5 percent As, 6 ppm 

Au, and 300 ppm Ag. 

Regionally, the sulfide occurrences are interpreted 

as Kuroko-type deposits that formed along the submarine volcanic part of a Devonian continental margin igneous arc. Deeper level portions of the arc are 

exposed in structurally lower levels of the YukonTanana terrane to the north and contain Devonian 

to Mississippian metamorphosed granodiorite and 

A U.S. Geological Survey geologist selecting analysis 

options of a cobalt-bearing mineral sample in this 

electron microprobe X-ray analyzer at the Survey 

laboratory in Reston, VA Detailed quantitative 

studies of elemental composition of polished rock 

surfaces are performed with a resolution of 4 p.m2 

(about 800,000 areas of that size would fit on a 

2-mm-sized pinhead). 
granite. U-Pb isotopic data on zircons from metavolcanic rocks hosting the sulfide occurrences 

indicate a 375-m.y. extrusive age. 207 Pb/204 Pb for 

sulfides from the three districts are similar and 

indicate Pb was derived, in part, from first cycle 

sediments eroded largely from Precambrian 

crystalline rocks. Radiogenic 207Pb/2°4Pb for feldspars in Devonian metavolcanic rocks are similar 

to those in sulfides and indicate incorporation of 

Precambrian (2.0-2.3 b.y., based on zircons) Pb into 

the Devonian magmas. A Precambrian crystalline 

source for quartz in metasedimentary rocks is indicated by locally abundant quartzite containing 2.3-

b.y. zircons. Pb isotope ratios from sulfides and 

igneous feldspars also suggest arc formation outside 

of Alaska. Intense Cretaceous greenschist facies 

metamorphism and penetrative deformation is 

indicated by reequilibration of U-Pb isotopic ratios 

and by metamorphic K-Ar hornblende, biotite, and 

muscovite ages of 110-115 m.y. The Cretaceous 

metamorphism and deformation is interpreted as 

representing the tectonic emplacement of the 

Yukon-Tanana terrane into proto-Alaska. 

A Worldwide Paleoclimatic Model for 

Quaternary Shore I i ne Placer Deposits 

of Titanium Minerals 

Curtis E. Larsen and Eric R. Force 

Titanium is extracted from marine placer deposits 

dominated by the mineral suite ilmenite-rutilezircon-monazite. The occurrence of this suite is 

dependent on a source terrane containing pelitic 

rocks of sillimanite or higher metamorphic grade. 

Through weathering and erosion, detrital grains of 

these heavy minerals are transported along fluvial 

systems to coastal regions. Wave action and longshore transport sort and concentrate them along 

active shorelines where they are deposited on the 

upper beach face by swash-backwash action. Later, 

heavy minerals may be moved inland by eolian 

transport to be stockpiled in coastal dunes. 

A warm, humid climate enriches this suite, as 

weathering removes unstable minerals, disaggregates composite grains, and upgrades the Ti02 

content of ilmenite by leaching of Fe. Detrital 

mineral grains inherit weathering from the regolith 

and older sedimentary hosts, and the in-situ weathering of Quaternary shoreline deposits is an 

important factor in determining the economic 

suitability of ilmenite from coastal placers. This is 

shown by mineralogic zonation within single 

deposits and by variation among coastal deposits 

40 

of different ages within a single area. Removal of 

Fe from FeTi03 through leaching reflects cumulative weathering of the placers. This, in turn, varies 

systematically with the age and latitude of the 

deposits in some well-known districts. 

In the Southeastern United States, for example, 

the southernmost sands from the oldest Quaternary 

shoreline deposits are the most weathered. These 

display a low percentage of unstable heavy minerals 

and a higher Ti02 content in altered ilmenite. The 

inverse condition holds for the southern hemisphere where the highest Ti02 contents are found 

in the more northerly of the older deposits of 

western Australia. On a worldwide basis, climate 

zones presently found between 35° N. and 35° S. 

appear to have been the most efficient in producing mineral assemblages beneficiated through 

weathering processes. Favorable source areas and 

coastal placers of the key mineral suite are present 

outside this zone, but the most valuable Quaternary 

coastal placers have weathered mineral suites and 

occur only within these latitudes. 

Source terrane determines the location of minerals of this suite, but the weathering history and 

latitudinal distribution define its economic significance. Thus, new resource areas may be highlighted 

along coastal zones with similar Quaternary sea-level 

histories and subtropical weathering regimes. 

The eastern coasts of South Africa and Mozambique, including the Richards Bay deposits, are analogs 

within this model, as is the southern coast of Brazil. 

The eastern coast of equatorial Africa shows source 

terranes and climatic regimes that suggest a favorable 

economic potential; however, Mauritania, on the arid 

northwestern African coast, has proper source terranes but lacks subtropical weathering. Its economic 

potential is demonstrably lower. The worldwide 

distribution of Quaternary placers containing titanium minerals indicates that studies of paleoclimate 

and contemporaneous weathering may provide 

models for pre-Quaternary deposits as well. 

Central San Juan Caldera Cluster, 

Colorado-New Stratigraphic and 

Structural Interpretations and Implications for Mineralization 

P. W. Lipman, M. A. Lanphere, R. L. Reynolds, 

J. G. Rosenbaum, and D. A. Sawyer 

In the 1950's, T. A. Steven and J. C. Ratte recognized calderas in the central San Juan Mountains 

of Colorado; known relations were summarized by 
Steven and Lipman (1976). New stratigraphic, structural, and petrologic data, supplemented by 40/

39 Ar 

dating and paleomagnetic data gathered in 1985-

86 now require several important reinterpretations. 

The outline and stratigraphy of the Bachelor 

caldera and related rocks have been refined (fig. 1); 

the caldera is more equant than previously 

recognized, and its core is farther south. A partly 

buried ridge of precaldera lavas, 20 km long, defines 

the composite west wall of the Bachelor and the 

LaGarita calderas. The northeastern topographic 

wall of the Bachelor caldera is defined by contacts 

between autochthonous Fish Canyon Tuff and 

rockslide debris of the same material. Other rocks, 

previously interpreted as lavas and ash-flow tuff 

interlayered with Bachelor caldera fill, are slide 

breccias from the caldera walls. Compositionally 

zoned Mammoth Mountain Tuff, previously considered to be a discrete ash-flow unit of uncertain 

source, is an upper part of the intracaldera 

Carpenter Ridge Tuff. The distribution of Mammoth 

Mountain indicates that early subsidence of the 

Bachelor caldera was greater near the margins than 

CENTRAL SAN JUAN 

CALDERA CLUSTER 

Hachured line: 

caldera wall 

10 15 KILOMETERS 

EXPLANATION 

CALDERAS 

L G, La Garita 

8, Bachelor 

C, Creede 

SL, San Luis 

C P, Cochetopa Park 

UNITS OF BACHELOR CALDERA 

lntracaldera tuff 

R, Rhyolitic 

0, Quartz latitic 

L, Landslide breccia 

F, Later caldera fill 

Figure 1. Geology of the central San Juan caldera 

cluster, showing details of the Bachelor caldera fill. 

41 

in the core, imparting a domical structure to the 

caldera floor during subsidence. 40/ 39 Ar dating has been crucial in showing that 

the Creede caldera (26.5 Ma) predates the San Luis 

caldera (26.0 Ma) (table 1), reversing the previously 

interpreted age sequence based largely on the more 

eroded form of the San Luis caldera. The San Luis 

caldera is probably more eroded than the Creede 

caldera simply because it is topographically higher. 

Stratigraphic relations locally confirm this relation 

where tuffs from the San Luis caldera overlie ringdome lavas (McKenzie Mountain flow) of the 

Creede caldera. Any tuffs from the San Luis caldera 

that once overlay sedimentary fill in the moat of the 

resurgent Creede caldera have been eroded 

completely. 

Fill of the San Luis caldera (Nelson Mountain 

Tuff) includes, in addition to a thick upper quartz 

latite, collapse breccias interleaved with altered and 

mineralized rhyolitic tuffs that previously were correlated with texturally and compositionally similar 

Carpenter Ridge Tuff within the Bachelor caldera. 

Postsubsidence lavas near the San Luis caldera are 

the youngest in the region, some perhaps as young 

as mineralization in the Creede district (about 

25 Maj. Some age and stratigraphic inconsistencies 

between the San Luis and the Cochetopa Park 

calderas require additional study. 

These in-progress interpretations have farreaching implications for the environment of 

associated ore deposition; for example, host rocks 

for precious-metal veins are not confined to fill of 

the Bachelor cadlera, as previously thought, but 

include fill of the younger San Luis caldera. 

Table 1. Calderas and ash-flow units 

Caldera Tuff unit Age (Ma) 

San Luis ---------- Nelson Mountain --- 25.9 

Rat Creek --------- 26.1 

Creede ------- Snowshoe Mountain 26.6 

Wason Park ------- 26.8 

Bachelor ---------- Carpenter Ridge ---- 27.3 

(includes Mammoth Mountain) 

LaGarita --------- Fish Canyon ------ 27.8 

Reference Cited 

Steven, T. A., and Lipman, P. W., 1976, Calderas of the San 

Juan volcanic field, southwestern Colorado: U.S. 

Geological Survey Professional Paper 958, 35 p. 
Microbial Transformations of Iron 

Minerals 

D. R. Lovley 

Microbially catalyzed reduction of Fe(III) was 

studied in sediments and, under more controlled 

conditions, in cultures. When Fe(III) was in the form 

of amorphic Fe(III) oxyhydroxide, Fe(III)-reducing 

microorganisms could oxidize completely nonrecalcitrant organic matter to C02 • These results 

demonstrated that the capacity for microorganisms 

to couple the oxidation of organic matter to Fe(III) 

reduction is much greater than generally considered. Fe(III)-reducing microorganisms in sediments 

and in culture readily reduced amorphic Fe(III) oxyhydroxide, even when the Fe(III) was adsorbed onto 

clay or when the Fe(III) was saturated with adsorbed organic matter or phosphate. Crystalline 

Steam emanating from a crack in the Main Terrace 

of the Steamboat Springs geothermal area near 

Reno, NV. This well-studied hot spring system contains 

significant concentrations of Au, Hg, As, Sb, Tl, and B. 

42 

Fe(III) oxides were reduced slowly, if at all. Most 

of the Fe(III) in fresh and brackish water sediments 

was also resistant to microbial reduction. These 

results may explain the preservation of Fe(III) in 

many deposits. In cultures of Fe(III)-reducing organisms, the reduction of amorphic Fe(III) oxyhydroxide resulted in the production of magnetite and 

siderite. This is the first report of biological magnetite production under strict anaerobic conditions. 

Surprisingly, Fe(III)-reducing organisms were unable to further reduce magnetite. These results suggest a potential mechanism for the accumulation 

and persistance of magnetite in some mineral formations. Studies on the interactions between Fe(III) 

reduction and sulfate reduction demonstrated that, 

when reactive Fe(III) forms, such as amorphic 

Fe(III) oxyhydroxide, are available, Fe(III)-reducing 

organisms prevent sulfate reduction by outcompeting sulfate-reducing organisms for organic matter. This result suggests that chemical reduction of 

reactive Fe(III) by sulfide may not be an important 

mechanism in the formation of iron-sulfur minerals 

in sediments because sulfide is produced after the 

production of Fe(II). These studies have demonstrated how an understanding of the factors that 

control the rate and extent of microbial processes 

can aid in evaluating the factors that influence the 

formation and dissolution of minerals. 

Transport and Flood-Plain Storage of 

Metals Associated With Sediment 

Downstream From Lead, South Dakota 

Donna C. Marron 

Between 1880 and 1977, about 90 million metric 

tons of finely milled mine tailings containing arsenopyrite and other metallic sulfides were discharged 

into Whitewood Creek near Lead, SD. Overbank 

deposition and meander migration have caused 

much of the sediment to be stored in the flood plain 

and on terraces along Whitewood Creek and downstream along the Belle Fourche River. This stored 

sediment contains greater than background concentrations of a variety of metals, particularly arsenic. 

The metal-contaminated sediments in the flood 

plains of Whitewood Creek and the Belle Fourche 

River contain as much as 0.6 percent arsenic; the 

arsenic concentrations of these sediments do not 

show a statistically significant decrease with increasing distance downstream from Lead. This lack 

of pattern apparently is caused by the overwhelming quantity of mine tailings that were discharged 
into the stream system yearly in relation to the quantity of "clean" sediment that was available in the 

stream system to dilute the contaminated sediments. In contrast, arsenic concentrations of 

stream-bed sediments collected in Whitewood 

Creek and the Belle Fourche River in 1985, 8 yr after 

the cessation of mine-tailings discharge, decrease 

systematically with increasing distance downstream from Lead (K. E. Goddard, U.S. Geological 

Survey, written commun., 1986). 

Metals analyses of different size fractions of contaminated flood-plain sediments show greater concentrations of metals in the finer sized fractions. 

In two samples from the flood plain of Whitewood 

Creek and two samples from the flood plain of the 

Belle Fourche River, arsenic concentrations in the 

greater than 64-~.tm fraction range from 60 to 95 percent of the arsenic concentrations of the 16- to 64-

~.tm fraction and from 17 to 41 percent of the arsenic 

concentrations of the less than 4-~.tm fraction. 

Arsenic concentrations obtained by a partial digestion procedure that is not effective for sulfide 

minerals were more than 70 percent of the arsenic 

concentrations obtained by using a total digestion 

procedure for 13 flood-plain sediment samples for 

which both types of data were obtained. This result 

indicates that much of the arsenic that is presently 

(1986) in the contaminated flood-plain sediments no 

longer occurs in association with the primary 

sulfide minerals that were the original source of the 

arsenic. 

Metal-contaminated sediment is stored in the 

flood plains of Whitewood Creek and the Belle 

Fourche River as point-bar deposits, overbank 

deposits, and deposits filling abandoned channels. 

Preliminary calculations of the quantity of metalcontaminated sediment stored on flood plains 

indicate that at least one-third of the mine tailings 

discharged into the river system presently are stored 

along about 120 km of the Belle Fourche River flood 

plain downstream of Lead. Measurements of 

meander-migration rates of channels in contaminated flood-plain areas indicate that the metal contaminated flood-plain deposits will continue to be 

a source of metals to adjacent streams for centuries. 

PROSPECTOR 11-Towards a Newer 

Geo-logic 

Richard B. McCammon 

One of the accomplishments of PROSPECTOR, 

a computer program developed in the mid-1970's, 

was to demonstrate the feasibility of encoding 

43 

expert knowledge in a way that would allow nonexperts to evaluate the mineral potential of an area. 

In experiments, nonexperts using PROSPECTOR 

performed at or near the level of expert economic 

geologists. Despite this success, PROSPECTOR has 

had little use in mineral-resource studies; mainly, 

this failure is attributed to (1) the high cost of maintaining and providing easy access to a complex computer program, (2) the feeling that the system was 

vulnerable to misapplication in the hands of an 

inexperienced operator, (3) the limited number of 

models in its repertory, and (4) its inability to deal 

with spatial relations. PROSPECTOR II, patterned 

after INTERNIST I, is designed to overcome these 

problems. 

The building block for PROSPECTOR II is the 

individual deposit model. For each model entered 

into the system, a model profile is constructed. The 

model profile consists of findings (observations), 

such as rock types, age, tectonic setting, mineralogy, 

alteration, and so forth, that have been reported to 

occur in association with known deposits considered to be instances of the model. Three variables 

are associated with each finding-an evoking 

strength, a frequency, and an import. The evoking 

strength answers the question, Given this finding, 

how strongly should I consider it to be specific to 

the ore-forming process attributed to the model? 

The frequency is an estimate of how often the finding is encountered in known deposits of the type 

represented by the model. The import, independent 

of the model, is the extent to which one is compelled 

to explain it at all. The evoking strengths, frequencies, and imports are expressed as numbers that 

represent a shorthand for judgmental information, 

inasmuch as the true quantitative information is 

unknown. Findings in the knowledge base are 

represented as numbers, such as age range; lists, 

such as mineralogy; or maps, such as anomaly patterns. In addition to model profiles, links between 

the models can be specified that express a predisposition of findings for one model with that of another. 

Solving problems in PROSPECTOR II results 

primarily from the application of two heuristic 

principles-the generation of hypotheses through 

a partitioning algorithm and the formation of conclusions about hypotheses, using such strategies as 

reasoning by exclusion. Initial positive and negative 

findings are entered by the user. The program 

retrieves the complete differential diagnosis from 

the knowledge base. For each model hypothesis, the 

following lists are maintained: (1) all positive findings explained by the model, (2) findings that might 

be associated with a model but are absent in the 
present instance, (3) findings not explained by the 

model, and (4) findings about which nothing is 

known in the present instance. A scoring system 

is used to rank the hypotheses in the differential 

diagnosis list. Hypotheses whose scores fall below 

a threshold number of points are discarded as unattractive. The sorted master differential diagnosis 

is used to identify a set of competitors to the topmost hypothesis. If no competitors are found, then 

the topmost hypothesis is accepted. Otherwise, a 

questioning strategy is pursued in an effort to "rule 

out" or "discriminate" among the set of competing 

hypotheses. Through questioning, a reduced set of 

plausible hypotheses and their relative scores are 

generated. The program recycles, all findings 

explained by the hypotheses being removed, and 

continues until all useful lines of questioning are 

exhausted. The interpretation based on all findings 

is presented to the user, along with an explanation 

of the line of reasoning that was followed. It is 

intended that PROSPECTOR II eventually will run 

on a microcomputer at the geologist's desk. 

Mineral Resources Data System-New 

Techniques and Applications for 

Mineral-Resources Research 

Antoinette l. Medlin, Donald F. Huber, 

Paul G. Schruben, George T. Mason, 

and Melissa l. Stoltz 

Changes in computer hardware and software 

available to the national Mineral Resources Data 

System (MRDS) are being used to extend and 

improve its capabilities to respond to U.S. Geological Survey, Federal, State, and public inquiries. 

Software developments in the field of spatial data 

handling and display have led to the integration of 

what are called Geographic Information System 

(GIS) techniques. These techniques provide the 

capability for a GIS user to select, summarize, and 

display, as maps or tables, the information associated with line and point features from data bases 

of spatial and attribute information. Currently, 

MRDS consists of over 84,000 spatially located data 

records with attributes for mineral deposits and 

occurrences in the United States and many foreign 

countries. 

In the past, a standard product from MRDS was 

a point location map with symbols representing a 

particular attribute from data records selected by 

user criteria. A current example of this type of map 

is the Glens Falls 1 o x 2 o study (Schruben and 

others, 1987). 

44 

Recent advancements in MRDS include developments in available data and software techniques. A 

number of files of digital line data for political, administrative, and geologic boundaries, all in geographic coordinates that can be displayed along with 

the point locations, have been acquired. MRDS has 

assembled information about these files into a data 

base, which provides an inventory of the currently 

available digital files, and has developed a plotting 

procedure for combining this data with MRDS data 

for GIS-like display or analysis. An option is also 

available for users to create their own digital line 

data files in the specified format and to plot them 

with MRDS data. Some of the available digital line 

files include national forest boundaries, wilderness 

boundaries, and the map by King and Beikman 

(1974). Examples of MRDS GIS-type applications 

have been prepared for Nevada, and commercially 

available GIS software is being tested. 

The MRDS data bases have been converted to a 

modern relational data base management system 

(DBMS) to take advantage of current software features. A compatible DBMS, Revelation, is available 

commercially for microcomputers, and a microbased version of MRDS, called MRDS-REV, has 

been developed to allow users to take advantage of 

the increased availability of personal computers. 

MRDS-REV has been used to enter and summarize 

the status of data available for areas in Alaska and 

Costa Rica. 

References Cited 

King, P. B., and Beikman, H. M., 1974, Geologic map of 

the United States: U.S. Geological Survey, scale 

1:2,500,000. 

Schruben, P. G., McBean, A., Nyahay, R. E., and Slack, 

J. F., in press, Mineral occurrences of the Glens Falls 

1 x 2 degree quadrangle, New York, Vermont, and New 

Hampshire: U.S. Geological Survey Miscellaneous 

Investigations Series Map. 

Inductively Coupled Plasma Mass 

Spectrometry-Applications of a New 

Technique in the Study of Mineral 

Formation Processes 

Allen l. Meier and Frederick E. Lichte 

Inductively coupled plasma mass spectrometry 

(ICP-MS) is a relatively new analytical technique that 

is extremely useful in studies of mineral formation 

processes. The high sensitivity and the low limits 

of detection (0.02-0.1 ng mL -1) of this technique are 
providing previously unobtainable information for 

the investigation of transport mechanisms and 

mobility of many elements in hydrothermal systems. 

We are investigating the use of ICP-MS to analyze 

geological samples of diverse types for a variety of 

geochemical applications. The analysis of fluids 

extracted from inclusions in galena, sphalerite, and 

hydrothermal dolomite from the midcontinent provides new information about the movement of the 

fluids that deposited the Mississippi Valley-type 

deposits. Investigations of fluid and vapor transport 

and the partitioning of base and precious metals 

between liquid and vapor phases in hydrothermal 

systems are being aided by the speed this technique 

provides in determining trace elements in water at 

the parts per billion level and below. The migration 

of metals through glacial overburden is being examined by simultaneously measuring trace concentrations of 20 or more elements in selective extracts 

of soil and till samples. The mobility of U through 

organic-rich material is being investigated by analyzing pore water and extracts from humic acids to 

determine U at the parts per billion level. The ability 

of the ICP-MS technique to determine individual 

isotopes rapidly, without the need for chemical 

separation, is permitting greater application of 

isotope ratio methods. Pb isotope measurements 

from galena and Fe- and Mn-oxide coatings of 

sediments are being used to assign buried mineralization to specific episodes of known mineralization having isotopically distinct Pb isotope signatures. The sensitivity of this technique to determine 

the Pt-group elements in Au beads following fire 

assay is aiding in the exploration for and understanding of the geochemistry of these important 

metals. The application of the isotope-dilution 

technique for determining Os and Re in molybdenite makes this technique extremely useful for 

studies concerning the distribution and abundance 

of these elements. A method developed to determine 

the rare earth elements in rocks and minerals, 

without the need for separation or preconcentration, is allowing greater use of these elements in 

petrogenetic studies. 

Nuclear Borehole Logging for Critical 

Metals 

Jon Mikesell and Frank Senftle 

In recent years, the United States has become 

increasingly dependent on foreign countries for its 

supply of critical metals such as Mn, V, and Cr. 

Recent political instability overseas is jeopardizing 

45 

our supply of these elements, and new methods 

must be investigated that will increase our potential to explore for deposits of these metals and to 

measure their concentrations at depth. 

One of the few techniques that is capable of this 

task within the narrow confines of a borehole is 

high-resolution gamma-ray spectroscopy. The U.S. 

Geological Survey has developed a borehole spectroscopy system that can be a valuable tool in 

exploration for critical metals; for example, quantitative logging for Mn in a borehole at about 

0.5 cm/s has been tested down to concentrations of 

0.2 percent Mn, and similar tests are currently in 

progress for V and Cr. An evaluation of the technique as applied to the other metals of possible 

strategic importance is considered. Thermal neutron activation and capture reactions are the only 

reactions that have sufficient sensitivity to be considered for exploration purposes. For the metals of 

industrial interest, the fast-neutron reaction cross 

sections are simply too small to yield the sensitivity 

needed for a practical exploration method using 

current state-of-the-art techniques. 

An Expert System for Sedimentary 

Basin Analysis for Assessment of 

Mineral and Energy Resources 

Betty M. Miller 

Most of the world's energy resources and many 

of its metals and mineral resources are derived from 

sedimentary rocks within the framework of a 

sedimentary basin. The exploration and assessment 

of such resources requires an understanding of their 

relation to the host strata, whether they are primary 

or postdepositional deposits. The most important 

product resulting from a "basin analysis" is the 

documentation of the paleogeographic evolution of 

a sedimentary basin. Basin analysis requires an 

understanding of many diverse geological specialties and an ability to assess the relation between 

varied types of evidence. 

The U.S. Geological Survey currently is involved 

in a research program to explore the feasibility of 

applying Expert Systems and knowledge acquisition techniques (specialties in the field of Artificial 

Intelligence) to the design and construction of a 

global system of sedimentary basin analysis. The 

first phase of a comprehensive expert systems 

approach includes the design and integration of 

regional geologic basin models and detailed basin 

analysis techniques into a computer system capable 

of incorporating large data files and graphic input 
and output. This basin analysis program also will 

access an integrated computer satellite system that 

will provide a suite of resource-assessment methods 

used to estimate the remaining undiscovered resources of a variety of energy and mineral commodities whose origins are within sedimentary 

basins. The primary objective in this first phase of 

the investigation is to design for the microcomputer 

a prototype expert system for basin analysis that 

will enable the geologist to understand and reconstruct the geologic evolution of a sedimentary basin 

and ultimately to assess its energy and mineral 

resources. 

The basic strategy uses expert systems techniques 

to design and develop a basin analysis program that 

will emphasize the evolution of a sedimentary basin 

through the documentation of its major components, as expressed by its stratigraphy, structural 

geology, and sedimentology. Previous work by the 

author on the design of sedimentary basin models, 

as a part of the muPETROL program (Miller, 1986) 

that uses expert systems techniques to classify 

world basins, is incorporated into the Basin 

Analysis Expert Systems Program (BA/ESP). The 

concepts used in muPETROL were the first phase 

toward analyzing the regional geologic framework 

and tectonic history which is preliminary to the 

detailed sedimentary basin analysis used in the 

BA/ESP program. 

Special efforts are being directed in the design of 

BA/ESP toward utilizing the capabilities of an 

expert system to access (1) a variety of available computer data bases (that is, well data bases, stratigraphic data files, log files, and so forth) and (2) 

satellite computer systems that perform various 

integrated tasks for geological interpretation and 

quantitative assessment of energy and mineral 

resources, such as the frequently noted "playanalysis system.'' 

The expert system, BA/ESP, will be used on an 

IBM-PC-XT/AT personal computer and run with the 

Knowledge Engineering System II, better known as 

the KESII expert systems program (by Software 

Architecture & Engineering, Inc.). This system 

would be available to the basin geologist who has 

access to a personal computer. 

Reference Cited 

Miller, B. M., 1986, Building an expert system helps 

classify sedimentary basins and assess petroleum 

resources: American Association of Petroleum 

Geologists, GEOBYTE, v. 1, no. 2, p. 44-50, 83-84. 

46 

National Geologic Mapping Program 

F. K. Miller 

The decline in geologic mapping and publication 

of geologic maps over the last two decades now is 

recognized widely in the geologic community. This 

increasing dearth of modern geologic maps has 

impacted the earth sciences and land use fields at 

all levels, but few areas as heavily as mineralresource exploration and research. Geologic maps 

are a primary data source for nearly all exploration 

programs and mineral-resource-related research. 

The immediate availability of a modern geologic 

map saves time and money and can be a significant 

factor in the success or failure of a project. 

To reverse the current decline in geologic mapping and to increase the rate of publication and versatility of geologic maps, the U.S. Geological Survey 

is establishing a vigorous National Geologic Mapping Program. The program is designed to rebuild 

the primary geologic map data base of the Nation 

and to supply pure and applied science researchers 

with basic geologic data. The program will increase 

new geologic mapping, provide a focal point to 

coordinate increased Federal, State, and academic 

mapping activities, and augment development of 

new mapping and publication technology. It will be 

conducted under four major components: Federal 

geologic mapping, Federal-State cooperative 

geologic mapping (COGEOMAP), geochronology 

and geologic processes, and modernizing mapping 

and map production technology. A fifth component, 

a university grants program, will be initiated when 

funds are available for this purpose. 

Geology and Mineral Resources of 

the lditarod Quadrangle, WestCentral Alaska 

Marti L. Miller and Thomas K. Bundtzen1 

In 1984, the U.S. Geological Survey and the Alaska 

Division of Geological and Geophysical Surveys 

[now the Alaska Division of Mining and Geology 

(ADMG)] began a 4-yr joint project to assess the 

mineral resources of the Iditarod Quadrangle. The 

ADMG had been conducting 1:63,360-scale geologic 

mapping and prospect evaluations within the 

quadrangle since 1977. In 1984, the Geological 

Survey began work on a more regional scale, and 

the two agencies merged their studies under the 

Alaska Mineral Resources Assessment Program. 

1

State of Alaska, Division of Geology and Geophysics, Fairbanks, AK. 
The Iditarod Quadrangle is largely underlain by 

interbedded sandstone, shale, and conglomerate of 

the late Early to Late Cretaceous Kuskokwim Group. 

These rocks form the core of the Kuskokwim Mountains, a dissected upland of accordant rounded 

ridges and broad sediment-filled lowlands. The 

Kuskokwim Group was deposited in a southwesttrending elongate basin. Deep water turbidite facies 

rocks dominate, but shallow shoreline facies rocks 

are also present. 

Late Cretaceous-early Tertiary volcanoplutonic 

complexes intrude and overlie the Kuskokwim 

Group. Five such complexes crop out within the 

quadrangle and form the highest and most rugged 

terrain. They consist of andesite and basalt that 

overlie or are in fault contact with monzonite 

plutons; locally, the plutons intrude and partially 

assimilate the comagmatic volcanic rocks. An extensive field of subaerial felsic to mafic volcanic rocks, 

coeval with the volcanoplutonic complexes, covers 

much of the western part of the quadrangle. 

Pre-Cretaceous rocks are exposed poorly. Precambrian to late Paleozoic basement rocks that represent parts of the Innoko, Ruby, and, possibly, 

Kilbuck terranes occur in a narrow northeastsouthwest-trending belt in the western one-half of 

the quadrangle. Radiometric data reveal that 

amphibolite-grade metamorphic rocks in the belt 

are some of the oldest rocks in Alaska. U-Pb age 

determinations indicate a protolith age of Early Proterozoic; Late Proterozoic and Cretaceous K-Ar age 

determinations suggest a complex metamorphic 

history for these amphibolite-grade lithologies. 

Ultramafic and gabbroic rocks correlative with 

Jurassic ophiolites of the Yukon-Koyukuk trend crop 

out in the northern part of the quadrangle. 

The Kuskokwim Group rocks have been deformed 

into a series of northeast-trending synclines and 

anticlines. High-angle faults parallel this fold structure, and emplacement of the plutons and volcanic 

rocks appears to be controlled by these faults. The 

Nixon-Iditarod fault, a major strike-slip transcurrent 

structural boundary in Alaska, bisects the 

quadrangle on a northeast-southwest diagonal. 

Mineral resources include Au, Ag, Hg, Sb, Sn, W, 

Cr, and Bi. A minimum of 1,600,000 oz of gold, 

240,000 oz of silver, 1,534 flasks of mercury, and a 

few hundred units of tungsten have been produced 

mainly from placer deposits since 1906. The Late 

Cretaceous-early Tertiary volcanoplutonic complexes and related dikes are the major sources of 

the hard-rock and heavy-mineral placer deposits. 

The mineral deposits are controlled structurally and 

occur in monzonitic plutons and associated 

47 

wallrocks. 

Placer gold continues to be the most economically 

significant mineral resource. The general formation 

of the placer gold deposits is best explained by 

mechanical erosion of gold-bearing hard-rock 

deposits. The present distribution of the gold is a 

result of several specific factors that include (l) 

structural controls, such as regional tilting or uplift, 

(2) geomorphic evolution of stream drainages in a 

periglacial environment, and (3) stream piracy, often 

a result of late Pleistocene glacial processes. Applying these factors may lead to the discovery of unexploited placer deposits. 

Origin of Platinum-Group Metals, 

Gold, and Rhenium in the Earth's 

Mantle and the Role of Sulfide in 

Mantle-Crust Partitioning 

John W. Morgan 

Trace-element analyses of highly siderophile 

elements, including platinum-group metals (PGM), 

Au, and Re, and chalocogens, including S, Se, and 

Te in spinel lherzolite xenoliths (SLX) of upper mantle origin suggest that these elements were introduced after formation of the core by an extraterrestrial influx during the first 600 m.y. of the Earth's 

history. The evidence is summarized as follows. 

Abundances of PGM in SLX are relatively constant 

worldwide, averaging 0.7 percent of those in Type 

I carbonaceous chondrite meteorites (C1). The PGM 

interelement ratios (for example, Os:Ir, Pd:Ir) are 

closely similar to those in C1. For Re and Au, 

absolute abundances are more variable, and both 

appear to be anticorrelated with the degree to which 

the SLX has been depleted by loss of a basaltic partial melt. In the least depleted SLX, however, 

Re:PGM and Au:PGM are close to C1, which implies 

that highly siderophile elements are present in 

undepleted upper mantle material in C1 (or 

"cosmic") proportions. This inference is confirmed 

by 1870s isotopic evidence from osmiridium of 

known age, which indicates a chondritic Os:Re of 

12 (by weight) in the mantle source. In SLX, Sand 

Se correlate strongly with Re, and abundances of 

these chalocogenic elements in undepleted mantle 

averaging 0.3 percent x C1 may be deduced. Thus, 

the average composition is depleted more than C1 

chondrites inS and Se (and Te?) relative to PGM, 

Re and Au, and the abundance pattern for siderophile elements and chalocogens closely matches the 

CM2 carbonaceous chondrites. The abundance 
pattern is also a reasonable match for that found 

in 3,900-m.y.-old Apollo 17 lunar impact breccias. 

It is well known that the Moon suffered intense 

bombardment during the first 600 m.y. of its 

existence, and the Earth cannot have escaped 

similar treatment, with the concommitant elemental enrichments. 

Systematic variations in the suite of SLX of abundances of S and Se with the degree of loss of partial melt suggest that primary basaltic liquid derived 

from a relatively undepleted mantle source should 

contain 1,040 ppm S and 300 ppb Se. These values 

are higher than those in most fresh oceanic basalt 

glasses, but the S abundance is in agreement with 

laboratory measurements of S solubility at upper 

mantle temperatures and pressures. Thus, about 20-

percent partial melting will remove totally the initial 

complement of 200 ppm S from undepleted mantle. In the absence of a free metallic iron phase, the 

highly siderophile elements are strongly 

chalcophile. Individual sulfide grains in a SLX from 

Kilbourne Hole, AZ, average 38 percent Fe, 23 percent Ni, 3 percent Cu, 2,300 ppm Co, 4.8 ppm Ir, 

6.4 ppm Os, and 1.4 ppm Au. Thus, most of the Ir, 

Os, and Au (as well as Cu) is contained in sulfides 

that constitute only 0.04 percent by weight of the 

rock. It seems likely that the relatively uniform 

abundances of PGM in SLX over a wide range of 

basalt depletion may be governed by "buffering" 

due to their high chalcophile affinities. Complete 

removal of a free sulfide phase by as much as 20-

percent partial melting may be a necessary precondition for removal of PGM from the mantle. 

Platinum-Group Element Mineralogy 

of the Pole Corral Pediform Chromite 

Deposit, Rattlesnake Creek Terrane, 

Northern California 

Barry C. Moring, Norman J Page, 

and R. l. Oscarson 

The Pole Corral deposit (Red Mountain group) 

was selected for mineralogic studies because it contained some of the highest platinum-group element 

(PGE) contents found in a geochemical survey of 

U.S. Geological Survey scientist collecting sediment from an active stream for geochemical sample to be 

used as part of the Walker lake 1 o x 2o CUSMAP geochemical evaluation. 

48 
280 podiform chromite deposits in California and 

Oregon. The deposit is located about 0.5 mi westsouthwest of Little Red Mountain, which is about 

7 mi (airline) southwest from the town of Beegum, 

CA. It occurs in serpentinized dunite hosted by 

serpentinized harzburgite, part of a disrupted 

ophiolite, in the fault-bounded Rattlesnake Creek 

terrane, which is a subdivision of the western 

Paleozoic and Triassic belt of the Klamath Mountains province. Chromitite crops out on the walls 

of a prospect pit and consists of 1- to 2-in.-thick 

layers in dunite, disrupted by faulting and shearing, 

with an aggregate length of about 40 ft. In 11 

samples of chromitite, Pd, Pt, Rh, Ir, and Ru contents range from 1 to 15, 35 to 2,530, 3 to 74, 70 to 

2,930, and 70 to 4,930 ppb, respectively, and average 

4.3, 271, 23, 999, and 1,909 ppb, respectively. The 

mineralogy also indicates Os is present. Increased 

PGE contents are not associated with increased Cu 

(maximum 7 ppm) or Ni (maximum 1,500 ppm) contents, which suggests that the chromitites are poor 

in base-metal sulfides. 

A back-scattered scanning electron microscope 

study of seven polished sections of chromitite from 

Pole Corral identified 24 grains of PG E minerals 

that were analyzed by qualitative methods. The 

grains ranged from about 2 to 20 m in diameter and 

occurred either as inclusions in chromite or at the 

boundary of chromite and serpentinized olivine 

crystals. Ten of the grains contained a single phase; 

the remainder contained multiple-phase grains (as 

many as four phases). Most of the grains consist of 

alloys. Ru-Fe alloy is the most common phase occurring as exsolution blebs and as single phase grains 

(found in 13 grains) in the chromitites. One grain 

of Ru-Fe alloy appears to be zoned with an Fe-rich 

core, and two grains have Os-rich rims. Alloys composed of various proportions of Os, Ir, and Ru occur 

in six grains and, within several of these, are 

domains enriched in Cr and Fe or composed of PtFe alloy. Four grains contain Pt-Fe alloys with 

variable contents of Ni and Cr(?). Au-Pd alloy forms 

one grain. Laurite (Ru, Ir, Os)S2 and compositions 

indicating the irarsite (Ir, Rh, Pt, Ru, Pd)AsS - osarsite (Os, Ru, Ir)AsS- ruarsite (Ru, Os, Ir)AsS group 

are the only sulfide or sulpharsenide PG E minerals 

identified. This mineralogy is similar to that of 

other podiform chromitites elsewhere in the world. 

Although the PGE contents of this chromitite and 

its mineralogy make an attractive exploration target, 

the tonnage distributions and PGE contents of 

podiform chromite deposits imply that these types 

of deposits will not contribute substantially to world 

PGE supply. 

49 

Geologic Setting of Two SedimentHosted Hydrothermal Mineral 

Localities in Escanaba Trough, 

Gorda Ridge 

Janet L. Morton, William R. Normark, 

Mark L. Holmes, and Mitchell Lyle1 

Escanaba Trough is a sediment-covered slowspreading (2.5 cm/yr) ridge segment at the southern 

end of the Gorda Ridge. Two large intrusive zones 

at lat 40°45' N.; long 127°30' W. (SESCA) and lat 

41 oN.; long 127°30' W. (NESCA) were mapped and 

sampled in July 1986 to determine their potential 

for hosting massive sulfide deposits. Detailed mapping of the SESCA site shows three hills less than 

1 km in diameter atop a low sediment-covered ridge. 

The hills are erosional remnants of sediment that 

has been uplifted as much as 100 m. The cores of 

the hills might be formed of basalt, although outcrops of basalt are rare at SESCA, and the crests 

of the hills are covered by at least several tens of 

meters of sediment. The hills are bounded by steep 

scarps and show abundant signs of recent slumping. The NESCA site is dominated by two major 

hills-one steep-sided, sediment-covered hill similar 

to the SESCA site and the other hill 3 km in 

diameter that has fresh basaltic pillow flows and 

sheet flows on the seafloor. Extensional basins 

extending north and south of the volcanic hill 

appear to be floored by large lava lakes with many 

collapse structures under a thin sediment cover. The 

extensional basins are bounded on the west by 

uplifted sediment-covered blocks. 

Many massive sulfide deposits, ranging in size up 

to 200 m across, were photographed and sampled 

at NESCA and SESCA. Major sulfide deposits are 

present around the base of the sediment-topped 

hills, apparently defining the original faults where 

uplift occurred, along sediment-covered fault scarps 

bounding the northern side of the volcanic hill at 

NESCA and along the sediment-covered slopes west 

of the extensional basins at NESCA. The larger 

deposits are partially eroded and sediment covered. 

Small isolated sulfide chimneys and mounds have 

grown on undisturbed sediment and indicate more 

recent diffuse hydrothermal flow through the sediment, perhaps above larger deposits contained 

within the sediment. Figure 1 schematically 

illustrates the distribution of major morphologic 

features and sampled hydrothermal deposits at 

NESCA and SESCA. 

1

0regon State University, Corvallis, OR. 
0 0 

2 KILOMETERS 

A 

2 KILOMETERS 

B 

50 

Figure 1. Distribution of major morphological features 

and sampled hydrothermal deposits. A NESCA. 8, 

SESCA. Hachured lines, major slopes; closed contours, hills; stipple, basalt outcrops; solid squares, 

dredges with massive sulfide; open squares, 

dredges with sulfide along veins or fractures; and 

solid circles, cores with massive sulfide. 

Some Features on the Composition 

and Distribution of Geochemical 

Types of Placer Gold in the KoyukukChandalar Mining District, Alaska 

Elwin L. Mosier, John B. Cathrall, John C. Antweiler, 

and Richard B. Tripp 

The Koyukuk-Chandalar mining district of the 

Brooks Range mineral belt in north-central Alaska 

contains numerous placer Au deposits but few 

known lode Au sources. Au grains, collected from 

46 placer localities in the district, were analyzed for 

Ag and 37 trace elements utilizing direct currentarc optical emission spectroscopy. When possible, 

several measurements were made on each sample 

and averaged. Au content was determined by the 

summation of the 38 elements determined and subtracting from 100. Interpretation of results 

emphasize that the Au grains are almost invariably 

ternary (Au-Ag-Cu) alloys. The average Cu content 

is 0.040 percent, and the average Ag content and 

fineness [Au/(Au + Ag) x 1,000] are 10.5 percent and 

893 parts per thousand, respectively, for the 46 

placer localities. 

Geochemical studies of placer Au from the 

Koyukuk-Chandalar mining district reveal striking 

contrasts in the Ag and Cu content of placer Au that 

may have a direct relation to the depositional 

environments of the primary Au sources. Based on 

Ag and Cu content, five different geochemical types 

of placer Au can be identified ranging from Type 

1, which has high Ag content (21.2 weight percent) 

and low Cu content (0.007 weight percent), to Type 

5, which has low Ag content (6.00 weight percent) 

and high Cu content (0.276 weight percent). From 

Type 1 to Type 5 placer Au, Au, Cu, and Au:Ag 

values increase systematically, and Ag, Au:Cu, and 

Ag:Cu values decrease systematically. A regional 

plot of the placer Au types shows Type 1 placers 

occurring in the eastern portion of the district with 

Types 2-5 generally occurring in order westwardly 

across the district, suggesting a variation in the 

primary Au sources that possibly could reflect a gradient of increasing depositional depths for the primary Au sources from east to west. Phase relations 
for the ternary system of Ag, Cu, and Au show that 

higher Cu values correlate with high Au content. 

We hypothesize that the three elements probably 

were present in the ore-forming hydrothermal solutions and that phase relation for the three elements 

could be dependent upon the depositional environment. The 36 other trace elements determined in 

placer Au do not appear to correlate with the 

depositional environment of the primary Au source. 

A comparative study of Ag content with Au grain 

size disclosed that smaller grain sizes generally contained higher Ag content, which suggests that some 

Au and Ag has been dissolved and reprecipitated 

on Au nuclei and (or) other minute mineral grains. 

The source for accreted Au could be from weathering of auriferous minerals common in the Brooks 

Range mineral belt. Arsenopyrite, pyrite, scheelite, 

and galena may contain either finely divided Au or 

lattice Au and commonly are found in heavymineral concentrates from the alluvial placers. 

New Geochemical Guides to Au-Rich 

Co-Cu Lodes in the Blackbird Mining 

District, Lemhi County, Idaho 

J. Thomas Nash and Gregory A. Hahn1 

Au is a significant constituent of some lodes in 

the Blackbird mining district and could provide 

impetus for renewed mining of the Co-Cu ores. Au 

as native gold is present at grades in the range from 

about 0.5 to 20 g/t in siliceous exhalite layers that 

are also rich in cobaltite. The geologic association 

of Au with mafic volcaniclastic rocks and exhalite 

layers, and intimate paragenetic relation with CoAs-S minerals, and a distinctive geochemical 

signature [rich in Au, As, B, Bi, Co, Fe, Nb, and rare 

earth elements (REE)], provide a guide for 

evaluating sediment-hosted targets for similar Aurich zones. 

The Blackbird lodes are believed to be synsedimentary and related to volcanogenic processes 

operating in restricted parts of the Middle Proterozoic Yellowjacket Formation, not postmetamorphic hydrothermal veins as thought before 

geologic studies by Noranda Exploration, Inc., from 

1978 to 1982. All lodes are stratabound within the 

middle part of the Yellowjacket Formation, and Aurich ones are stratiform. The lodes are influenced 

by sedimentary features, such as growth faults, softsediment deformation, and dewatering structures, 

1

Noranda Exploration, Inc., Lakewood, CO 80215, now with Coca Mines, Inc., 

Denver, CO 80203. 

51 

and are associated closely with mafic tuffs and 

coeval dikes. Geochemistry of the lodes can be 

reconstructed reliably in time and space because 

metamorphism has caused only minor changes in 

rock fabric and chemistry and in ore mineralogy 

in areas of little deformation. 

All lodes are associated with tuffaceous rocks and 

dikes of alkali basalt composition. Beds judged to 

be tuffs are thinly bedded, contain 50-100 percent 

mafic silicates (biotite, garnet, chloritoid), and are 

locally rich in white mica. Chemically, these beds 

are rich in Fe (often more than 20 percent total as 

Fep3) and K (5-8 percent K20), as well as As-BiCo-Nb-Ti-Zr-REE. Au-rich Co-Cu lodes contain 

distinctive 1- to 10-cm-thick metachert layers, some 

of which contain abundant tourmaline and REEbearing phosphate minerals. Exploration is aided 

by visual recognition of beds rich in mafic silicates 

Figure 1. Photomicrograph of gold (bright, with scratches) with cobaltite and quartz from the Sunshine 

lode, Blackbird mining district, Idaho. The gold and 

cobalt minerals formed as a chemical sediment on 

the seafloor in association with basaltic volcanism 

in a process resembling a modern "black smoker." 
or metachert and is supplemented effectively by 

geochemical surveys for Co. 

Best Au grades are in layers that have abundant 

cobaltite or metachert. Assay data indicate a significant association with Co and As and an independence of Cu. Grades greater than 0.5 g/t appear to 

be in layers 1 m thick in the central and thickest part 

of the lode where highest concentrations of Si, Co, 

and As occur. Native gold grains range in size from 

<1 to 20 m. Most gold grains occur as inclusions 

in cobaltite, on cobaltite grain boundaries, or in 

microveinlets that cut cobaltite. Grains of gold <2 

Jtm in size also occur in quartz of metachert bands. 

Grain size of gold, which influences mill recovery, 

seems to be largest in lodes subjected to higher 

metamorphic grades. 

The association of Blackbird Co-Cu-Au lodes with 

mafic volcanic rocks at regional, district, and deposit scales provides an empirical exploration guide but 

also appears to explain many unusual geochemical 

features of these lodes. Other sediment-hosted Cu 

deposits generally lack associated Au, As, Bi, Co, 

Fe, and REE enrichments but, instead, are richer 

in Ag-Pb-Zn. The mafic rock association and geochemistry at Blackbird should be a useful guide to 

Au in Precambrian Fe-rich sedimentary rocks in 

which the paragenesis of gold generally is obscured 

by metamorphism. 

Mineral-Resource Assessment of the 

Tonopah 1° x 2° Quadrangle, Nevada 

Greta J. Orris, Gerald F. Brem, Richard F. Hardyman, 

David A. John, William J. Keith, Frank J. Kleinhampl, 

J. Thomas Nash, Donald Plouff, Norman J. Silberling, 

John H. Stewart, and Donald H. Whitebread 

The mineral-resource assessment of the Tonopah 

1° x 2 o quadrangle, Nevada, produced a quantitative, 

probabilistic estimate of the mineral endowment of 

the study area. The assessment process consisted of 

the following stages: (1) determination of appropriate 

descriptive and grade-tonnage models of deposit 

types that are known to occur, or may occur, within 

the study area, (2) delineation of areas permissive 

for the occurrence of the selected deposit types, and 

(3) estimation of the number of deposits by type that 

may occur within the delineated areas. 

Deposit types selected for evaluation in the 

Tonopah quadrangle include sediment-hosted (SH) 

disseminated Au-Ag, hot spring Au-Ag, epithermal 

Au-Ag vein, low-F porphyry Mo, porphyry Cu, 

polymetallic vein, polymetallic replacement deposits, 

bedded barite, simple Sb, and Fe, Cu, W, and Zn-Pb 

skarn deposits. Other deposit types known to occur 

52 

are placer Au, turquoise, and a variety of nonmetallic 

commodities including magnesite, perlite, and diatomite. As a first step in the delineation of tracts permissive for the occurrence of undiscovered deposits 

for the major deposit types, a list of favorable criteria 

was compiled for each deposit type with an emphasis on those characteristics identifiable at a regional 

scale, and known deposits were classified into appropriate deposit types. Many of the regional scale 

criteria were similar for different deposit types. 

Because permissive lithologies, geochemistry, alteration, and associated deposit types were not diagnostic for a single deposit type, many of the 

delineated areas contain groups of deposit types 

such as low-F porphyry Mo, W skarn, and polymetallic vein deposits or SH disseminated Au-Ag, 

epithermal Au-Ag vein, and simple Sb deposits. 

Adding to the complexity of delineating areas was 

the problem of determining what resources might 

underlie Tertiary and Quaternary cover of volcanic 

rocks and alluvium or relatively thin low-angle fault 

plates at depths of less than 1 km. 

Estimation of the number of undiscovered deposits was complicated by the problems of cover, Basin 

and Range physiography, and complex structural 

histories. For the SH disseminated Au-Ag, polymetallic vein, and epithermal Au-Ag vein deposit types, 

we estimated a 90-percent chance that one or more 

undiscovered deposits are present within the study 

area. In addition, it was estimated that there is a 50-

percent chance that at least one additional deposit 

is present for the following deposit types: polymetallic replacement, hot spring Au-Ag, low-F porphyry 

Mo, and W skarn. This assessment suggests a favorable environment for undiscovered deposits including deposit types such as bedded barite and turquoise, Cu and Zn-Pb skarn, and simple Sb deposits. 

Mineral-Resource Assessment of Costa 

Rica 

Norman J Page, W. C Bagby, J. E. Case, D. P. Cox, 

Donald F. Huber, Robert P. Koeppen, 

Stephen D. Ludington, S. P. Marsh, D. A. Ponce, 

Klaus J. Schulz, and D. A. Singer 

The U.S. Geological Survey, Direcci6n General de 

Geologfa, Minas, e Hidrocarburos, and the Universidad de Costa Rica undertook a nonfuel mineralresource assessment of Costa Rica in cooperation 

with the Los Alamos National Laboratory and 

funded by the U.S. Agency for International Development. It is based on evaluation of existing earth 

science data and new data gathered during 14 manmonths of field studies. 
To facilitate the resource assessment, rocks were 

grouped broadly on the geologic map. The oldest 

known rocks are Jurassic seafloor basalts, and the 

basement of the country is composed of oceanic 

crust formed in the Mesozoic, presumably as a result of the parting of the North and South American 

plates. This oceanic crust is overlain by Upper 

Cretaceous and Tertiary marine deposits that accumulated in a complex series of basins. A gravity 

profile, controlled by seismic refraction data, across 

Costa Rica suggests that the Pacific margin is composed of high-density stacked slices(?) of oceanic 

crust about 20-30 km thick, that a lower density 

crust increases in thickness to about 40 km below 

the central volcanic belt, and that crustal thickness 

is about 25 km along the Atlantic margin. As a result 

of interactions between the Caribbean and several 

Pacific plates, most of the country was uplifted during Miocene and later times to form the present 

mountainous isthmus. Uplift was accompanied by 

intense igneous activity related to subduction along 

the middle American trench. The resulting volcanic 

rocks cover more than one-half of Costa Rica. 

The Tertiary volcanic rocks of the "gold belt" are 

the coalesced products of numerous volcanic 

centers developed from about 23 to 1 Ma. Their evolution involved (1) deposition of lava flows interlayered with abundant volcanic fragmental rocks, (2) 

the deposition of the overlying volcanic unit from 

several volcanic centers and the emplacement of the 

Guacimal silicic intrusion, (3) widespread rhyolite 

magmatism and associated hydrothermal alteration, 

and (4) the unconformable deposition of the andesitic Monteverde Formation at a time of renewed 

volcanism in the Pliocene to Quaternary. The associated Au deposits consist of (1) Au, chalcopyrite, 

galena, sphalerite, and pyrite in quartz veins and 

stockworks hosted by intermediate and felsic volcanic rocks, (2) quartz, chlorite, and sericite alteration, and (3) quartz, adularia, kaolinite, rhodochrosite, and sparse barite forming gangue. Rhyolites 

appear to be the heat source for the hydrothermal 

systems. These epithermal precious-metal deposits 

are similar to a Sado-type epithermal model, which 

has a median Au grade of 6.0 g/t and median tonnage of 300,000 t. All available data on 319 deposits 

and occurrences of Au and other commodities were 

compiled by mineral-deposit type, verified by field 

observations where possible, and entered into a computer file. The plotted data show that the deposit 

types tend to cluster in areas of similar geology. 

The resource assessment consisted of (1) delineating domains according to the geologic environments that are permissive for Sado-type epithermal 

53 

veins, placer Au, porphyry Cu, volcanogenic Mn, 

podiform chromite, Cyprus-type massive sulfides, 

and bauxite, (2) characterizing undiscovered mineralization by analogy with tonnage and grade models, 

and (3) estimating the number of undiscovered deposits of each type within the delineated domains. 

Other deposit types, not delineated but present, include shoreline placer magnetite, polymetallic vein, 

Cu skarn, Zn-Pb skarn, and hot springS. Permissive 

geologic environments are also present for hot spring 

Au deposits and Au associated with alkalic volcanic 

rocks. Lateritic Ni deposits are unlikely. 

Preliminary Geophysical Well Log 

Analysis of the Geothermal Alteration 

of Alluvial Sediments in the Salton 

Sea Basin, California 

F. L. Paillet and R. H. Morin 

An extensive suite of geophysical well logs was 

obtained during the Salton Sea Scientific Drilling 

Project (SSSDP). These logs included conventional 

and research electric, acoustic, nuclear, temperature, and caliper logs for the uppermost 6,000 ft of 

borehole but were limited to natural gamma, epithermal neutron, deep induction, and temperature 

logs for the deeper interval (6,000-10,500 ft). A major 

limitation in the application of geophysical logging 

techniques to the SSSDP program was the effect of 

borehole conditions on the performance of logging 

equipment. The geophysical probes used during the 

SSSDP were designed to sample a 3-ft-diameter 

volume of the rock and borehole fluid environment, 

but damage to the borehole associated with the production of geothermal fluids resulted in hole 

enlargements much greater than 3 ft. Most of this 

damage occurred during initial attempts to control 

circulation before logs could be run in the borehole, 

so that geophysical logs were of little use in 

characterizing the production zones at depths 

below 6,000 ft. The difficulty in controlling circulation also resulted in logs being run at temperatures 

that ranged from 280 to 310°C, which caused the 

mechanical failure of the caliper tool. 

Analysis of geophysical logs for the upper part of 

the SSSDP borehole indicates that the logs provide 

information on the original lithology of the Salton 

Sea sediments. The nuclear, electric, and acoustic 

logs indicate variations in ratios of quartz to clay 

minerals in the sedimentary column that are related 

to variations in the depositional environment of the 

original sediments, such as alluvial fan, overbank 
splay, mudflat, and beach and dune sand deposits. 

In addition, the electric logs may indicate variations 

in pore-fluid chemistry that could be due to the generation of hydrothermal fluids in the sediments 

since they were deposited. Porosity logs indicate 

that primary porosity is very low throughout the 

sediments penetrated by the upper part of the 

SSSDP borehole; this supports the assumption that 

essentially all geothermal fluid production from the 

lower part of the borehole is derived from fractures. 

Conventional acoustic transit-time and acoustic 

waveform logs, vertical seismic profile (VSP) sections, and core samples for ultrasonic testing in the 

laboratory provide a unique opportunity to compare 

the dynamic properties of Salton Sea sediments at 

three different scales of investigation-0.5-2 in. for 

core samples, 1-3 ft for waveform logs, and 100-

500 ft for VSP data. Data from the waveform logs 

and laboratory and VSP-measured compressional 

velocities indicate that the acoustic transit times 

provided by the commercial acoustic logs are incorrect. Values that range from 100 to 150 p.s/ft on the 

log correspond to values that range from 65 to 

85 p.s/ft determined from waveform data. The large 

borehole diameter, dense drilling mud, and possible 

clay-mineral alteration in the vicinity of the borehole apparently affected the performance of conventional acoustic logging probes. Analysis of 

seismic velocities determined from acoustic waveform logs and laboratory tests of core samples 

indicates that progressive age and degree of alteration of sediments in the SSSDP borehole are 

associated with only minor changes in compressional velocity but major changes in shear velocity. 

These initial results support the hypothesis that the 

primary effect of geothermal alteration in the 

SSSDP borehole has been a decrease in the effective Poisson ratio of the sediments, from typical 

values for shaly sandstone that range from 0.28 to 

0.35 before alteration to values that range from 0.20 

to 0.25 after alteration. 

Ophiolites, Metallogenic Models, and 

Terrane Models- Interrelations 

Observed in the Arabian Shield and 

Potential for "Cryptic" Mineralization 

John 5. Pallister 

The Arabian Shield is now recognized as a mosaic of intraoceanic and continental microplates 

that were accreted during the Late Proterozoic. 

Considerable emphasis has been placed on the 

definition of exotic terranes and their internal 

54 

characteristics as a screen for efficient mineral 

exploration. In addition, ophiolitic rocks, which 

mark terrane boundaries in the Shield, are themselves targets for certain types of ore deposition. 

Based on reconnaissance field studies of the Arabian ophiolites, an intriguing mineral exploration 

target is serpentine-related Au and Co mineralization. Au deposits and prospects are concentrated 

along sutures (terrane boundaries) within the Arabian Shield. At several localities, deposits occur in 

quartz veins related to mafic-intermediate plutons 

that intrude serpentinized peridotites and carbonated or silicified serpentinite (listwanite or 

bibirite). This geologic setting, similar to that in the 

southern part of the Mother Lode system of the 

Sierra Nevada foothills of California, suggests that 

the Au may have been derived from the ultramafic 

rocks. 

The mineralized Bou Azzer ophiolite of Morocco 

has produced 50,000 tons of Co (4-8 percent of 

world production) since 1930 and provides a useful 

model for mineral exploration of the Arabian 

ophiolites. The Bou Azzer ophiolite is approximately the same age, is exposed in a similar tectonic setting, and has common internal characteristics. Bou 

Azzer Co (Ni-Fe) arsenide ore bodies occur in a 

quartz-carbonate gangue that is an alteration product of ophiolitic peridotite. The Bou Azzer metallogenic model, developed by Marc LeBlanc and 

coworkers, calls for Co concentration through three 

main stages-serpentinization of peridotite, which 

results in partitioning of Co and Ni into magnetite; 

weathering of serpentinite to yield Co and Ni 

enrichments in Mn-Fe hydroxides, serpentines, and 

bibirite and listwanite; and remobilization and concentration of Co (Ni-Fe) arsenides and accessory Cu, 

Mo, and Au, followed by reprecipitation along contacts with younger plutons and within latest PanAfrican age structures. 

A characteristic feature of the Arabian ophiolites 

is the conversion of serpentinite to listwanite and 

bibirite along bounding fault zones. Sutures of the 

eastern Shield are marked by belts of these carbonated and silicified serpentinites that extend for 

tens of kilometers. Listwanite and bibirite derived 

from the Arabian ophiolites are enriched locally in 

Cu, As, Co, and Ni. Ancient Au mines are found 

along contacts between altered serpentinite and 

younger intrusions, a setting where all three stages 

of the Bou Azzer model may be met. 

Most of the known metallic ore districts of Arabia 

were "rediscovered" in the 20th century with relative ease because of the presence of ancient workings. In contrast, Co and Ni deposits would not have 
been developed by ancient man, and tell-tale mine 

workings would not be present. Mineral exploration 

has progressed in the Arabian Shield to the point 

that significant new discoveries probably will be 

"cryptic;• either as buried deposits or of a type not 

formerly sought by the ancients (such as bauxite, 

Sn, W, and Co). Therefore, exploration based on 

mineralization models will become increasingly 

important. An obvious exploration target, based on 

the Bou Azzer model, is for Co and Ni associated 

with the very common listwanite and bibirite zones 

within the Late Proterozoic ophiolites. 

Geophysical Mapping of Eastern U.S. 

Early Mesozoic Basins 

Jeffrey D. Phillips and David L. Daniels 

Compilation of digital aeromagnetic and gravity 

data for 12 areas covering the exposed early Mesozoic basins of the Eastern United States is nearing 

completion. This compilation is being done as part 

of a multidisciplinary study focusing on ore-deposit 

models in failed rift environments. In 10 of the 12 

areas, Department of Defense gravity data files have 

been supplemented with newly collected gravity 

data and with gravity data from unpublished 

sources to yield sufficiently detailed coverage for 

preparation of complete Bouguer contour maps and 

bandpass filtered contour maps at a scale of 

1:125,000. Available gravity coverage in the southern 

Hartford basin, Connecticut, and the eastern 

Newark basin, New Jersey, is inadequate for compilation at this scale. In 9 of the 12 areas, data 

digitized from older aeromagnetic contour maps are 

being combined with newer digitally recorded 

aeromagnetic data to produce regional scale contour maps and computer-generated products, such 

as graytone aeromagnetic intensity maps. For three 

areas in central and southern Virginia, digital 

aeromagnetic coverage is inadequate for regional 

compilation. 

Model studies have been initiated using 2V2-D 

algorithms along selected gravity and magnetic profiles to test aspects of published geologic cross sections for the basins; for example, in the northern 

Hartford basin, Massachusetts, gravity and magnetic models suggest that the floor of the basin is 

uneven and probably offset along normal faults that 

are not mapped at the surface. In addition, the dip 

on the eastern border fault cannot be determined 

accurately from the gravity and magnetic data; it 

may be as great as 70° or as little as 50°, depending 

upon the geometry of a low-density Paleozoic gneiss 

55 

unit that apparently underlies the border fault. Outside the basin, the modeled configuration of a 

folded amphibolite layer, which is a magnetic 

marker bed within the Paleozoic section, agrees well 

with published geologic cross sections and supports 

the interpretation that the gneissic country rocks 

beneath and around the basin form continuous 

layers. 

Because of the association of economically important magnetite skarn deposits with Mesozoic 

diabase in the Gettysburg basin and uncertainty 

regarding the distribution of diabase at depth 

within the basin, a detailed gravity survey was completed recently in the Harrisburg, PA, area. Bowlshaped diabase sheets, which have a large positive 

density contrast with the enclosing Mesozoic 

sedimentary rocks, produce prominent positive 

gravity anomalies that can be used to estimate the 

thickness of the diabase sheets. Areas of maximum 

sheet thickness are readily apparent on the gravity 

map. These usually occur beneath the sedimentary 

cover rocks within the "rectangular" rings of exposed diabase. The Gettysburg, York Haven, and 

Quakertown sheets follow this pattern. The Morgantown diabase body, with its deep central gravity low, 

is an exception because it appears to have no significant thickness beyond its exposed rim. By delineating the areas of the Gettysburg basin that have 

significant thicknesses of diabase, the detailed 

gravity data place restrictions on the areas of the 

basin with high potential for undiscovered 

magnetite skarn deposits. 

Geochemical Aspects of Ocean-Floor 

Hydrothermal Vent Fluids and Massive 

Sulfide Chimneys From the Southern 

Juan de Fuca Ridge 

J. A. Philpotts, J. S. Kane, P. J. Aruscavage, 

H. Kirschenbaum, R. G. Johnson, A. F. Dorrzapf, Jr., 

Z. Brown, and J. S. Mee 

The U.S. Geological Survey is engaged in a 

multidisciplinary study of the southernmost segment of the Juan de Fuca (JDF) Ridge, an active 

spreading center located about 400 km off the coasts 

of Oregon, Washington, and British Columbia. In 

September and October 1984, hot springs and 

associated massive sulfide deposits were sampled 

in the central axial cleft of the ridge using the deepsea research submersible vehicle Alvin. The deposits have potential economic interest and provide 

general insight into the nature and genesis of 
massive sulfides. Our JDF geochemical investigation has focussed on the bulk chemical composition and coarse concentric zoning of 16 massive 

sulfide chimneys and on the composition of the 

hydrothermal fluids. We also are evaluating the 

capabilities of a number of analytical techniques 

based on analyses of JDF sulfides and a suite of 

sulfide standards. 

The JDF hydrothermal vent fluids, which were 

collected over a distance of 3.5 km along the ridge, 

show some small differences in composition. The 

fluids have the highest concentrations of many 

dissolved species yet reported for submarine hot 

springs. Relative concentrations are similar to those 

of fluids from 13 o N. on the East Pacific Rise (EPR); 

this compositional signature appears to differ from 

that of fluids from 21 oN., EPR, and the Galapagos 

spreading center. This dichotomy in chemistry may 

reflect largely the type and extent of alteration of 

the rocks with which the fluids are interacting. 

The JDF massive sulfide chimneys are composed 

predominantly of ZnS; FeS2 rims are common at 

some sites. Other phases include FeS, silica, 

anhydrite, and barite. Sulfate typically contributes 

less than 5 percent of total S. A unique chimney 

has a central orifice lined with isocubanite 

(CuFe 2S3 ) and a Mg-rich rim. However, Cu 

exceeds 1 percent in bulk materials from only four 

chimneys. Radial concentration variations of 

elements such as Cu, Ba, and Ph may contribute 

to understanding the preservation of ocean-floor 

sulfides, many of which are vulnerable to reaction 

with normal seawater. Among elements of potential economic interest, Zn averages 40 percent; Ph, 

0.15 percent; Cd, 0.1 percent; and Ag and Co, about 

200 ppm each in the JDF chimney sulfides. 

In preparing samples for analysis, acid dissolution of sulfides may result in incomplete recovery 

of elements such as Ph, Ba, Sr, and Ag, whereas 

roasting and fusion decomposition can result in 

loss of volatile elements. Additional flux helps to 

prevent sticking of high-Fe samples to graphite 

crucibles. Spectral and background interferences 

due to Zn, Fe, Cu, and so forth often dictate changes 

in analytical strategy. Further, silicate techniques 

may not be well calibrated for sulfides. Inductively 

Desert pavement that formed in the semiarid environment of central Nevada. Wind has removed fine material 

representing the original "matrix." Pebbles and cobbles are coated with iron and manganese oxides to 

produce the mottled pattern. 

56 
coupled plasma optical emiSSIOn spectroscopy 

appears to be the single most useful multielement 

technique for the analysis of sulfides. 

"Mesothermal" Gold-A Metamorphic 

Connection? 

W. J. Pickthorn, R. J. Goldfarb, and D. L. Leach 

Worldwide "mesothermal" gold-bearing vein 

deposits often are found in low- to moderate-grade 

metamorphic rocks, typically marine in origin, in 

tectonically disturbed or accreted terranes. In North 

America, deposits of this type frequently are located 

along the western margin of the Cordillera in the 

western Sierra Nevada, Klamath, and Siskiyou 

Mountains of California, western British Columbia, 

and along the Gulf of Alaska. The U.S. Geological 

Survey has undertaken a multidisciplinary study of 

mesothermal gold deposits in metamorphic rocks 

in Alaska to examine the genesis of this deposit type. 

The Cretaceous Valdez Group, a major component of the accreted Chugach terrane, south-central 

to southeastern Alaska, consists principally of tightly folded and metamorphosed graywacke and shale. 

Gold mineralization is found in small discontinuous 

quartz veins, pods, and stringers. These veins are 

emplaced along shear zones, faults, and joints that 

postdate accretion, deformation, and regional metamorphism. The veins are restricted to areas of 

greenschist facies metamorphism and show no consistent association with intrusive rocks. Wallrock 

alteration is generally absent. Fluid-inclusion analyses of gold-bearing quartz from throughout the 

Valdez Group yield minimum trapping pressures of 

1.5 kbar and corrected homogenization temperatures ranging from 260 to 330°C. Ore-forming fluids 

were of low salinity, with gas contents of up to 11 

mole percent. Analyses of the inclusion gas phase 

by Raman laser spectroscopy and quadrapole mass 

spectrometry indicate compositions ranging from 

pure C02 to mixtures dominated by CH4 and N2 • 

Stable isotope analyses of the quartz yielded o180 

values for the ore-forming fluid in the range from 

+ 6.5 to + 9.6 per mil. Analyses of hydrous ore-phase 

minerals indicates an ore-fluid oD of approximately 

-20 per mil. 

In southeastern Alaska, the Juneau gold belt 

extends for approximately 200 km along the western 

flank of the Coast Range batholith and coincides 

with the Coast Range megalineament. Approximately 7 5 percent of Alaska's total lode gold production was from this region, the majority from the 

Alaska-Juneau (A-J) Mine. Host rocks consist of 

57 

metamorphosed and deformed slate, phyllite, 

diorite, and greenstone. Stable isotope data (o180, 

+9.8 per mil; oD, -20 per mil) and fluid-inclusion 

pressure (F)-temperature (T) estimates (P, minimum 

1.5 kbar; T>200 °C) are very similar to the Valdez 

Group deposits, however the bulk fluid composition 

and the structural setting are quite different. Most 

fluid inclusions in samples studied from the A-J contained C02 contents in the range from 30 to 60 

mole percent with minor CH4 and N2• Evidence is 

good for boiling of the ore fluid. The A-J Mine is 

located along a major crustal structure, and the ore 

body consists of a 5.5-km-long by 100-m-wide zone 

of intense quartz veining; vein material often makes 

up more that 50 percent of the rock. Intense wallrock alteration also accompanies mineralization. 

The stable isotope, fluid inclusion, and inclusion 

gas chemistry data are consistent with those for 

fluids derived from metamorphic rocks during 

devolatilization reactions. We suggest that prograde 

metamorphism during accretion released the water 

and volatiles, which migrated into fractures in the 

previously metamorphosed rocks during a decrease 

in the confining lithostatic pressure. The relatively 

small veins in the Valdez Group rocks may represent a local fluid source, whereas the intense veining and alteration suggests a larger or deeper crustal 

source for the A-J ore fluid. Wall rock chemistry and 

varying redox conditions may have been important 

locally in controlling gold deposition. 

The Application of Conodonts to 

Studies of Mississippi Valley-Type Ore 

Deposits-A Preliminary Assessment 

John E. Repetski, Joseph A. Briskey, 

Augustus K. Armstrong, Fred Smith, 1 

Larry Wilbanks, 1 and Dave Tibbels1 

Conodonts are microfossils that are present in 

and easily recoverable from many Paleozoic and 

Triassic marine carbonate rocks that also are the 

host rocks for numerous Mississippi Valley-type 

(MVT) metallic ore deposits. Conodonts can be 

exploited in minerals exploration programs because 

(1) they are superb stratigraphic index fossils 

through most of their geologic range and, therefore, 

can be used to correlate strata, even in drilling programs, (2) their environmental preferences and 

limitations can aid in detailed facies reconstructions and basin analysis, and (3) their color alteration index (CAl) and variations in their surface 

1

Jersey Miniere Zinc Co., Gordonsville, TN 38563 . 
texture can place constraints on interpretations of 

the age and spatial distribution of ore bodies and 

on the temperature of diagenetic and ore-bearing 

solutions. 

Preliminary evaluation of Ordovician conodonts 

in the host rocks of zinc ore bodies in central Tennessee provides a case study for these developing 

techniques. Surface and subsurface sampling for 

conodonts is providing the biostratigraphic and 

paleoecologic framework that can be integrated 

with petrologic, diagenetic, and geochemical 

studies in progress on the surface, from cores, and 

underground in the mines. The regional CAl value 

of the host-rock formations in central Tennessee is 

about 1112. In a detailed traverse across an ore body 

in the Gordonsville Mine, central Tennessee district, 

CAl values range systematically from a low of 11/2 

to at least 2. Host rocks with the lower CAl values 

probably had relatively low initial permeability or 

were reduced in permeability during early (pre-ore) 

diagenesis, either or both of which would have 

largely isolated these rocks from the later orebearing hydrothermal solution(s). Furthermore, conodonts with corroded surfaces, where the etching 

cannot be attributed to processing techniques, are 

most common near the ore body, whereas vitreous 

noncorroded conodont elements are more common 

away from the body and presumably further from 

the etching effects of the ore-bearing fluids. 

As these preliminary observations are expanded 

upon and are correlated more closely with ongoing 

study of the petrology and geochemistry in these 

and other areas of MVT mineralization, conodonts 

may prove to be valuable new tools in minerals 

exploration. 

Evidence for Iron-Stripping and SilicaStripping Microorganisms in 

Precambrian Granular and Banded 

Iron Formations 

Eleanora I. Robbins, Gene L. LaBerge, 1 and 

Robert G. Schmidt 

Microscopic study of a combination of thin sections and acid residues from Archean and Proterozoic iron formations from North America 

(Gunflint, Ironwood, Palms, Biwabik, unnamed), 

Australia (Brockman, Warrawoona), and Greenland 

(lsua) has revealed abundant morphological and 

mineral evidence for previously unrecognized 

microfossils. The morphology of micrometer-sized 

1

Department of Geology, University of Wisconsin, Oshkosh, WI. 

58 

microstructures composed of hematite, magnetite, 

siderite, and chalcedonic spherules suggests the former presence of iron- and silica-stripping organisms. 

Different organisms may have been involved in 

deposition of the different colored layers of laminated iron formations. Black layers are composed 

of hematized rods, laths, and hollow tubes that may 

be morphlogical evidence for an iron-stripping 

sheathed bacterium much like modern Leptothrix 

ochracea or perhaps Gallionella ferruginea, both of 

which precipitate ferrihydrite on their sheaths. Dispersed with the rods in magnetic black layers are 

tiny magnetite crystals that suggest the former presence of magnetotactic bacteria much like Oceanospirillum. Red layers contain hematite spherules 

that may be morphological evidence for an ironstripping capsular bacterium much like microaerophilic Siderocapsa. White layers of chalcedonic 

spherules may be the remains of a silica-stripping 

photosynthetic chrysophyte. Silica is so pervasive 

in iron formation that silicic acid must have been 

a constituent of bottom muds. Silica bacteria much 

like Pseudomonas mirabilis or Bacillus siliceous may 

have played a part in the resolubilization of algal 

silica in the muds, but evaluation of the former 

presence of silica bacteria cannot be made on morphological grounds. Brown layers contain masses 

of globular siderite. Successive layers of globular 

siderite masses may be evidence for blooms of an 

iron-stripping bacterium or perhaps an alga. Putrefying bacteria may have played a part in the production of C02 and, therefore, of siderite in the bottom muds, but no unusual relict forms of putrefying 

bacteria remain. 

In certain granular rocks, internal globular microstructures are present within the granules. Such 

granules may be morphological evidence for coenobial masses of a capsular iron bacterium that 

shares properties with Siderocapsa; in species of 

modern Siderocapsa, coenobial colonies coalesce 

into macroscopic masses and fall to the bottom in 

response to adverse conditions in the water column. 

One variety of the Precambrian granules, reminiscent of Siderocapsa conorata, contains tens to hundreds of internal spherules; another variety, more 

like Siderocapsa eusphaera, contains thousands of 

internal spherules. 

The highly metamorphosed Early Archean Isua 

Iron-Formation apppears to contain two types of 

iron-walled microstructures. Rods of iron oxide 

appear similar to those of hematite in the younger 

iron formations; they may be morphological 

evidence for a sheath-forming iron bacterium much 

like Leptothrix. Also present are rounded, hematitic 
microstructures averaging 10 ~-tm that we have 

named Appelocysta treubii. Under the scanning 

electron microscope, they exhibit clavate to murate 

projections and appear to have plates and, perhaps, 

also sulcal grooves. Appelocysta may be the remains 

of a capsular iron bacterium as well as a thickwalled resting cyst of Isuasphaera. 

If this morphological evidence stands the test of 

chemical scrutiny, then iron formation may represent the successful attempt by iron-stripping 

bacteria to detoxify their environment of oxygen in 

Precambrian oceans. The role of silica-stripping 

organisms in the formation of these rocks is harder 

to discern; silica may have been deposited initially 

as frustules of siliceous algae, but, if so, the transformation from opal-A to opal-CT to quartz has 

destroyed most fine relict textures. 

Mapping Contact Metamorphic 

Aureoles in Extremadura, Spain, Using 

Landsat Thematic Mapper Images 

Lawrence C. Rowan, Carmen Anton-Pacheco, 1 

David W. Brickey, Marguerite J. Kingston, 

Alba Payas, 1 Norma Vergo, and James K. Crowley 

In the Extrema dura region of western Spain, Ag, 

Pb, Zn, and Sn deposits occur in the apices of late 

Hercynian granitic plutons and near the pluton contacts in late Proterozoic slate and metagraywacke 

that have been metamorphosed regionally to the 

greenschist facies. The plutons generally are well 

exposed and have distinctive geomorphological 

expression and vegetation; poor exposures of the 

metasedimentary host rocks and extensive cultivation, however, make delineation of the contact 

aureoles difficult. 

Landsat Thematic Mapper (TM) images have been 

used to distinguish soil developed on the contact 

metamorphic rocks from soil formed on the stratigraphically equivalent slate-metagraywacke sequence. The mineral constituents of these soils are 

similar, except that muscovite is more common in 

the contact metamorphic soil; carbonaceous 

material is common in both soils. Contact metamorphic soil have lower reflectance, especially in the 

1.6-m wavelength region (TM 5), and weaker Al-OH, 

Mg-OH, and Fe3+ absorption features than do 

spectra of the slate-metagraywacke soil. The lowreflectance and subdued absorption features 

exhibited by the contact metamorphic soil spectra 

1

Instituto Geologico y Minero de Espana, Rios Rosas 23, Madrid 28003, Spain. 

are attributed to the high absorption coefficient of 

the carbonaceous material caused by heating during emplacement of the granitic plutons. 

These spectral differences are evident in a TM 

4/3, 4/5, 3/1 color-composite image. Initially, this 

image was used to outline the contact aureoles, but 

digital classification of the TM data was necessary 

for generating internally consistent maps of the 

distribution of the exposed contact metamorphic 

soil. In an August 1984 TM scene of the Caceras 

area, the plowed vegetation-free fields were identified by their low TM 4/3 values. Then, ranges of 

TM 4/5 and 3/1 values were determined for selected 

plowed fields within and outside the contact 

aureoles; TM 5 produced results similar to TM 4/5. 

Field evaluation, supported by X-ray diffraction and 

petrographic studies, confirmed the presence of 

more extensive aureoles than shown in published 

geologic maps; few misclassified areas were noted. 

Additional plowed fields consisting of exposed contact metamorphic soil were mapped digitally in an 

August 1985 TM scene. 

59 

Subsequently, this approach was used to map two 

1-km-wide linear zones of contact metamorphosed 

rock and soil in the San Nicolas Sn-W mine area, 

which is located approximately 125 km southeast 

of the Caceras study area. Exposures of granite in 

the San Nicolas area are limited to a few altered 

granitic dikes in the mine and a small exposure of 

unaltered pegmatite-bearing granite in a quarry 

about 1.5 km west of the mine. The presence of 

coarsely crystalline biotite and beryl in the granite 

in the quarry and of contact metamorphosed slate 

up to 2.5 km from the nearest granite exposure suggests that only the apical part of a pluton is exposed 

in the quarry and that a larger shallowly buried 

body is probably present. 

These results indicate the potential application of 

TM image analysis to mineral exploration in 

lithologically similar areas that are cultivated in 

spite of poor rock exposures. 

Epithermal Gold Mineralization in the 

Republic of Palau 

James J. Rytuba, William R. Miller, and 

Edwin H. McKee 

The Republic of Palau, a U.S. Trust Territory, is 

located in the western Pacific and consists of more 

than 200 islands alined along the 350-km-long Palau 

trench-arc system. The largest island, Babelthaup, 

is composed principally of late Eocene(?) to early 
Miocene volcanic rocks. Basalts and basalticandesite flows and flow breccias of the late Eocene(?) 

Babelthaup Formation form the central and southeastern part of the island and are the oldest volcanic 

rocks in the arc. These volcanic rocks are characterized by high Ni (up to 190 ppm), Cr (up to 520 ppm), 

and Mg (up to 10.7 percent) concentrations and by 

low concentrations of the high-field-strength elements Zr ( s 40 ppm) and Ti02 (< 0.6 percent). This 

geochemistry indicates a boninitic affinity and a similarity to the oldest volcanism in the Yap, Mariana, 

and Bonin arc-trench systems north of Palau. 

Younger basaltic andesites to dacites of the Medorm 

Member of the Ngeremlengui Formation occur in 

the western part of Babelthaup and have a K-Ar age 

of 35.6±2.5 Ma. Basaltic andesites of the Arakabesan 

Member form several small islands south of Babelthaup and have a K-Ar age of 34.3 ± 1.5 Ma. These 

younger volcanics are characterized by low N i and 

Cr contents and by higher amounts of high-fieldstrength elements than the Babelthaup Formation 

and belong to the island-arc tholeiite series. 

Epithermal gold and base-metal mineralization 

occurred on the southeastern part of Babelthaup 

within basalt and basaltic andesite flows of the 

Babelthaup Formation. Mineralization consists of 

over 50 veins and silicified shear zones ranging in 

width from a few centimeters to several meters. The 

veins and shear zones have two preferred general 

orientations-north-northeast and north-northwest 

and are distributed over an area 1.5 by 1 km. Gold 

is present in all veins; channel samples across veins 

commonly contain 0.02-0.1 oz/ton. Te, Ag, Cu, and 

Zn are typically present in anomalously high concentrations in the veins. Sericite is present with 

quartz in the veins, and coarse crystals of epidote 

are locally present. Propylitic alteration is generally 

widespread in the country rock. Ore minerals 

include native gold, gold-silver-telluride, sphalerite, 

chalcopyrite, and, rarely, galena. 

Effective geochemical sampling media in Palau 

were found to be heavy-mineral concentrates from 

stream sediments and the -80-mesh fraction of sediment from mangrove coast and swamp environments. Heavy-mineral concentrates delineated the 

mineralized zone through mineralogy (presence of 

Au, CuFeS2, ZnS, PbS) and by the presence of 

strongly anomalous concentrations, in percent, of up 

to 0.07, Au; 1.5, Zn; 1.0, Cu; and 0.05, Ag. The -80-

mesh fraction of sediment from the intertidal zone 

within the mangrove coast and swamp environments 

surrounding the island of Babelthaup contains 

anomalous amounts of Au up to 100 ppb adjacent 

to the mineralized zone as compared with 1-2 ppb 

60 

outside the zone. Sampling of mangrove sediment 

combined with analysis of heavy-mineral concentrates provides an effective method for exploration 

for precious-metal resources in islands in the 

western Pacific. 

Geochemistry of Precious- and BaseMetal Veins, Lake City Area, Colorado 

Richard F. Sanford 

Silver-gold-lead-zinc-copper veins associated with 

the 28-Ma Uncompahgre and the 23-Ma Lake City 

nested calderas near Lake City, CO, show geochemical anomalies that vary with area and with stratigraphic position. Veins hosted by Uncompahgre 

caldera fill contain relatively high concentrations of 

Ag and Au, whereas those in Lake City caldera fill 

have moderate Ag and Au values. Base-metal contents vary widely in both groups of veins but tend 

to be higher in the Uncompahgre caldera. Gold is 

most concentrated in veins cutting the higher parts 

of Uncompahgre caldera fill, but Ag shows no similar stratigraphic control. Veins cutting Proterozoic 

granite adjacent to the two calderas have relatively 

high Au concentrations. Lead isotopic ratios of galena indicate similar groupings of veins. These variations reflect local control by source rock and conditions of deposition but not age of mineralization. 

Base and precious metals, as well as other trace 

elements, show several statistical associations that 

reflect the mineral content of the seven sets of veins. 

Groups 1 (Mo-Tl-Ba-As) and 2 (Mo-Li) are mainly 

within the Uncompahgre caldera; groups 3 (Cu-AsSb-Ag-Fe-Hg-Te-Bi-Pb), 4 (Zn-Cd-Pb-Cu-Bi-Au-Fe), and 

5 (U-Au-Te) are found in both calderas; and groups 

6 (Th-rare earth elements-P) and 7 (Be-In-Sn-Mn) are 

largely limited to the Lake City caldera. Group 1 

characterizes molybdenite-bearing quartz veins cutting Uncompahgre caldera fill in the southwestern 

part of the area. Group 2 reflects molybdenite(?) in 

veins of the Uncompahgre caldera in the northeastern part of the area. Group 3 reflects tetrahedrite 

(including Ag-, Sn-, and Te-rich varieties), tennantite, 

tellurides (for example, hessite), and minor basemetal minerals. This group includes the richest Ag 

ores. Group 4 elements are associated with low-grade 

base-metal ores consisting mainly of sphalerite, 

galena, chalcopyrite, pyrite, and minor tetrahedrite. 

Group 5 reflects uraninite, gold tellurides, and other 

tellurides and includes the most productive gold vein 

in the area. Group 6 characterizes thorite-monaziteapatite veinlets primarily from the Champion Mine 
in the Lake City caldera. Group 7 elements are in 

quartz veins having barite(?) casts. 

Lead isotope data from galena (Sanford and Ludwig, 1985) reveal that several separate hydrothermal 

cells with characteristic Pb isotope ratios operated 

in the area. The Pb isotopes from the Lake City 

caldera are relatively nonradiogenic (2°6Pb/204Pb0 = 

18.6 and less) compared to those from the Uncompahgre caldera (

206Pb/204/Pb = 18.6 to 19.0). Galena 

in veins cutting Proterozoic rocks is typically the 

most radiogenic (

206Pb/204Pb = 19.0 and higher). Local exceptions can be explained by hydrologic variations within several hydrothermal circulation cells. 

Geologic, geochemical, and radiometric evidence 

indicates multiple episodes of mineralization involving many local hydrothermal systems. Three 

broad groups of source rocks are suggested by the 

wallrock control on element and isotope distributions in the veins. Variations in the veins as a function of stratigraphy more likely indicate differences 

in conditions of transport and deposition. 

Reference Cited 

Sanford, R. F., and Ludwig, K. R., 1985, Lead isotopic 

evidence on the origin of hydrothermal veins, Lake City, 

Colorado: Geological Society of America, Abstracts 

with Programs, v. 17, p. 706. 

The Red Dog Pb-Zn-Ag Deposit, 

Alaska-An Example of Nonexhalative 

Processes in the Formation of 

Syngenetic Massive Sulfides 

Jeanine M. Schmidt and Robert A. Zierenberg 

The Red Dog shale-hosted massive sulfide (SHMS) 

deposit of the Noatak district, northwestern Alaska, 

contains 77 million tonnes of 17 percent Zn, 5 percent Pb, and 82 g/T Ag. The deposit is owned by 

the Northwest Alaska Native Corporation; their 

operating partner is Cominco American, Inc. The 

U.S. Geological Survey, in cooperation with Cominca, has a multiyear research effort underway to 

study regional and deposit geology. Detailed (1 in. 

= 10ft) mineralogic and textural logging of 12,000 

ft of core from the Main ore body has been completed, as has reconstruction of geologic sections 

and petrography. Sulfide and sulfate S isotopic and 

fluid-inclusion studies are to follow. 

The Red Dog deposit, hosted by siliceous black 

shale and chert of Carboniferous age, has a 

stratigraphic footwall that includes grey micrite and 

calcareous black shales and is overlain by barite and 

61 

variably baritic gray and green chert and shale of 

Pennsylvanian to Permian age. The deposit, which 

consists of imbricated sulfide sheets overlying 

Cretaceous sandstones, was disrupted by northward-directed thrusting during the Jurassic-Cretaceous Brooks Range orogeny. Massive sulfides and 

pervasively silicified rocks are relatively rigid compared to the enclosing shales, so that much of the 

deposit is undeformed internally and preserves 

many primary and early diagenetic features. 

Although Red Dog is classified as a SHMS 

deposit, it differs from other Pb-Zn deposits of the 

Noatak district and from other SHMS deposits 

worldwide. Silicified wallrocks and barite are common at Red Dog but minor in other Noatak district 

deposits. Silica and sphalerite are more abundant 

than Fe-sulfide phases. The aS34 values of Red Dog 

ores are near zero, and those from the nearby Lik 

deposit and many other SHMS have heavy (positive) 

aS34 values near contemporaneous seawater 

sulfate. Red Dog contains only rare laminated or 

bedded sulfides, is up to 150 m thick, and has no 

sediment interlayers or multiple sheets of sulfides. 

Much of the sulfide is semimassive with a "pseudobreccia" texture of remnant islands of an earlier 

generation silica sulfide, surrounded by irregular 

replacement fronts of later stages of mineralization; 

sulfide veining of sulfide is common. 

The earliest phases of mineralization, which are 

best preserved at the edges of the deposit, where 

mineralization was less intense, provide evidence for 

ore genesis. Diagenetic growth of barite in unconsolidated mud was common before sulfide deposition. Early and massive barite commonly are 

replaced by sulfides and (or) by silica. Much of the 

silica rock and siliceous massive sulfide formed by 

replacement of unconsolidated mud, which produced polyhedral aggregates of quartz with cores of 

inclusion-rimmed hexagonal growth zones. Stylolites 

are common in calcareous shales, barite, silica, and 

semimassive ores. 

Although many textures of the Red Dog deposit 

are the result of mineralization in unconsolidated 

sediment and below the sediment-water interface, 

other features suggest classic "exhalative" processes. 

Rarely preserved sedimentary structures indicate 

scour and resedimentation of sulfides. Tube-shaped 

trace fossils are interpreted as vent fauna that lived 

at or near the sediment-water interface during sulfide 

deposition. Subsurface mineralization at Red Dog 

may have contributed to the large size and high grade 

of the deposit because an overlying sediment and (or) 

silica cap effectively confined the hydrothermal fluid 

and prevented the loss of metals by dispersion in a 

buoyant plume. 
The Saxapahaw, North Carolina, 

Gold Occurrences-Search for a 

Deposit Model and New Remote 

Sensing Techniques 

R. G. Schmidt, Alba Payas, 1 Pablo Gumiel, 1 and 

J. P. D:Agostino 

Nonuniform distribution of gold within and near 

zones of intense siliceous high-alumina alteration 

near Saxapahaw, Alamance County, NC, suggests 

a model for gold mineralization that may be useful 

for exploration in the region. Remote sensing using 

Landsat Thematic Mapper (TM) data from forests 

and cultivated fields is proposed as a useful exploration tool. 

The Carolina slate belt is a complex of late Precambrian to Cambrian metamorphosed volcanosedimentary epiclastic and volcanic rocks extending 600 

km from central Georgia to southern Virginia. Near 

Saxapahaw, it is roughly 60 km wide and includes 

abundant dacitic crystal tuffs with lithic clasts. 

Three types of intrusive rocks have been distinguished within the study area; two of these were 

intruded before greenschist facies regional metamorphism. The complex quartz diorite pluton at 

Saxapahaw, an elliptical body 3 x 10 km, may have 

influenced gold distribution. From relict grains of 

unreequilibrated plagioclase, we interpret at least 

part of the pluton to be postmetamorphic. 

Intense siliceous premetamorphic high-alumina 

alteration is present in a very large northeast-trending zone intersected at right angles by the elongate 

quartz diorite pluton at Saxapahaw. The Snow 

Camp segment of the altered zone, southwest of the 

pluton, is 13 km long and several kilometers wide. 

Less well defined altered zones continue to the 

northeast of the pluton for 8 km. Within both segments, crystal tuffs have been converted to quartzsericite or quartz-paragonite rock and, where alteration was most intense, to highly siliceous masses 

depleted in Na, K, and Ca and containing pods of 

q uartz-pyrophy lli te-andal usite-pyrite, locally 

minable as ore-grade pyrophyllite rock. This alteration is commonly texture destructive and has trace 

concentrations of Cu, Mo, and Sn associated with it. 

Significant gold is restricted to sites 2-5 km distant on both sides from the pluton at Saxapahaw, 

which suggests that gold may have been introduced 

or remobilized by a hydrothermal system driven by 

the heat of the pluton. The most favorable environments for precipitation seem to have been present 

1Instituto de Geologico y Minero de Espaila, Rios Rosas 23, Madrid 28003, Spain. 

in siliceous sericite-bearing zones, but the paucity 

of gold in the southwestern part of the early 

siliceous high-alumina alteration system suggests 

that gold mineralization postdates that alteration 

event. We propose that introduction or mobilization 

of gold probably took place in preexisting altered 

zones and may even have been postmetamorphic 

and related to younger intrusive rocks. 

The study of Landsat TM data has permitted 

delineation of known and new areas of intense 

hydrothermal alteration. Spectrally anomalous soils 

in plowed fields have been correlated with potassic 

altered subvolcanic intrusive bodies. Deciduous 

forests in areas of intense hydrothermal alteration 

have a distinctive appearance on digitally processed 

falsecolor TM images. 

We suggest that spacial juxtapositions of large 

siliceous alteration zones and young plutonic 

bodies be identified because of their potential for 

62 

Stibiconite, Sbp6(0H), along a fracture in silicified 

Fa leozoic carbonaceous limestone from the Enfield 

Bell gold mine, Jerritt Canyon district. Nevada. 

Stibiconite is an alteration product of stibnite and 

is a good mineralogical indicator of the presence 

of antimony, which is commonly enriched in sedimentary-rock-hosted disseminated gold deposits. 
containing undiscovered gold deposits. TM and 

other Landsat-derived data have been particularly 

useful tools for finding areas of hydrothermal 

alteration. 

Microcomputer Systems for Geologic 

Map Compilation and Drafting 

Gary I. Selner, Richard B. Taylor, and 

Bruce R. Johnson 

. The advent of relatively inexpensive microcomputers and affordable high precision digitizers and 

plotters makes possible office-scale digital systems 

for aquisition, editing, and plotting of map data. 

GSDRAW and GSMAP (Selner and others, 1986) are 

programs for microcomputers that assist geologists 

and illustrators in compilation and publication 

drafting of geologic maps and illustrations. These 

programs attempt to do for geologic maps what 

digital word processing has done to facilitate composition and publication of text. As a set of practical "graphics programs" designed to produce geologic maps and other illustrations, they enable 

digital compilation of graphical elements, ease the 

process of modification in response to second 

thoughts and editorial comments, enable scale and 

projection changes, and lead from initial compilation to publication without redigitizing or redrafting. 

GSDRAW is based on storage of X.:Y coordinate 

data unique to each illustration, and GSMAP is 

based on storage of geodetic coordinates (latitudelongitude); otherwise, the two programs are very 

similar. GSDRAW is used for illustrations, cross sections, and maps where either latitude-longitude grid 

is not available or the use of a latitude-longitude 

system is not necessary. GSMAP is used for geologic maps using Universal Transverse Mercator or 

Lambert Conformal Conic map projections. A basic 

set of line types (such as thrust fault) and geologic 

symbols (such as strike and dip, foliation, lineation) 

has been included. Additional symbols can be 

added as needed by computer-oriented users. These 

programs are designed for plotter output. Screen 

graphics are used to assist digitizing and editing. 

GSDRAW and GSMAP have been designed for 

use on IBM PC and compatible microcomputers, 

plotters using Hewlett-Packard Graphic Language 

plot commands, and GTCO digitizers (modifications 

for other kinds of digitizers are relatively simple). 

Additional programs of interest to geologists that 

utilize the same hardware environment are either 

available or in the development process. The source 

63 

code and compiled versions are included with the 

open-file reports that document the programs. 

Reference Cited 

Selner, G. 1., Taylor, R. B., and Johnson, B. R., 1986, 

GSDRAW and GSMAP-Prototype programs for the 

IBM PC or compatible microcomputers to assist compilation and publication of geologic maps and illustrations: U.S. Geological Survey Open-File Report 86-

447A, B, 8 p . 

Comparative Studies of Modern and 

Ancient Sediment-Hosted Massive 

Sulfide Deposits 

Wayne C. Shanks Ill 

Sediment-hosted mafic volcanic-associated massive sulfide deposits are of economic interest because 

of their size and polymetallic nature, in some cases 

including relatively high precious-metal contents. 

Tectonic setting, local structure, depositional environment, metal and sulfur sources, and chemical 

state of the ore fluid and water column are factors 

that control ore formation. Metal and sulfur sources 

and ore fluid chemistry can be inferred from stable 

isotope studies of some ancient deposits, but, for 

highly deformed and metamorphosed deposits, 

study of modern analogs is of paramount 

importance. 

Guaymas Basin, formed by active rifting in the 

Gulf of California, is filled with several hundred 

meters of siliceous-calcareous biogenic sediment 

and interlayered turbidites. Diabase sills and dikes 

of midocean ridge basalt (MORB) affinity intrude 

the sedimentary sequence to within a few meters 

of the sediment-water interface. Seawater hydrothermal circulation surrounding the sills and dikes alters the sediments to greenschist facies assemblages 

and produces up to 312°C vent fluids. Hydrothermal 

mounds and elaborate "pagodalike" chimney structures are dominantly calcite, barite, anhydrite, pyrrhotite, marcasite, and silica; sphalerite, galena, and 

chalcopyrite are important "ore" minerals. Sulfur 

isotope values of sulfides range from -3.7 to +6.7 

per mil; ranges are smaller for each of three clusters 

of deposits related to separate diabase sills. Sulfide 

in the deposits is derived from the following 

sources: (1) basaltic sulfide with sulfur isotope 

values near 0 per mil, (2) sedimentary bacteriogenic 

sulfide with strongly negative values, and (3) isotopically heavy sulfide from hydrothermal reduction 
of seawater sulfate. Carbon isotope values of 

hydrothermal calcite ranges from -9.6 to + 14.0 per 

mil (Peedee belemnite), indicating 30- to 50-percent 

derivation from marine organic carbon in the sediment column. Oxygen isotope values of 7.3-10.8 per 

mil (Standard Mean Ocean Water) give temperatures from 214 to 31PC (for equilibrium isotopic 

exchange with 2.0 per mil water) in good agreement 

with measured vent temperatures. 

The newly discovered massive sulfide deposits on 

Gorda Ridge, within the Exclusive Economic Zone 

off northern California, occur in a somewhat different setting where basaltic volcanic domes penetrate to the seafloor through 0.5-1 km of sedimentary cover. Massive, extensive hydrothermal deposits 

rich in marcasite, pyrrhotite, barite, and talc flank 

and overlie the domes; some samples are extremely 

rich in Cu, Zn, Pb, and Ag. These deposits have 

Interpretive drawing of a 9-mm-high chimney from the 

Vent 1 site. southern Juan de Fuca Ridge, based on 

a photomosaic assembled from Alvin external 

photographs. Drawn by Calvin Fontaine. 

64 

little calcite or anhydrite due to lack of carbonate 

in the underlying sediments. Sulfur isotope values 

of sulfides (1-10 per mil) reflect only basaltic and 

seawater components; underlying sediments are not 

reducing and lack isotopically light biogenic 

sulfides. Large deposit extent may be related to the 

large thermal mass of the volcanic domes. 

Possible ancient analogs of the Guaymas and 

Gorda deposits include the Besshi and related 

deposits, Japan; Goldstream, British Columbia; and 

Ducktown, Gossan Lead, and Elizabeth in the U.S. 

Appalachians. The Elizabeth deposit and other 

deposits of the Vermont copper belt occur in 

intensely deformed and metamorphosed Ordovician(?) dominantly metapelitic rocks with minor 

metavolcanic rocks. The Elizabeth and Ely deposits, 

which occur in the noncalcareous Gile Mountain 

Formation, have sulfur isotope values ranging from 

4.3 to 9.4 per mil. The Gave and Cookville deposits, 

which are contained within the Standing Pond 

Volcanics, and Pike Hill, which is in the calcareous 

metapelites of the Waits River Formation, have 

sulfur isotopic values from 1.5 to 4.7 per mil. Standing Pond Volcanics, a thin extensive unit of MORE 

affinity, has disseminated sulfides with isotopic 

values from 0.5 to 1.6 per mil. Two- and threecomponent sulfur source models, as in the modern 

deposits, also may be applied to the massive sulfides 

of the Vermont copper belt. 

Electronic Structures and Spectra of 

Minerals-Basic Research To Help the 

Development of Spectroscopic 

Remote Sensing and Geophysical 

Exploration Techniques 

David M. Sherman 

Many exploration techniques that exploit the 

spectroscopic and other physical properties of 

minerals have been based largely on empirical 

grounds. To help develop new assessment techniques, however, we must know the physical basis 

for these properties. Such information is provided 

by the electronic structures of minerals. 

The electronic structure of a solid defines the 

energies and wavefunctions of its electronic and 

vibrational states. Transitions between such states 

give rise to the absorption bands observed in the 

infrared, visible, and near-ultraviolet spectra of 

minerals. Such spectra, in turn, are used in spectroscopic remote sensing techniques for the identification of minerals on the Earth's surface. The 

electronic structure of a solid also determines its 
magnetic and electrical properties and, ultimately, 

its chemical behavior. 

Of particular interest are the electronic structures 

of transition metal oxides, silicates, and sulfides. 

These phases cause absorption bands in the visible 

region of remotely sensed spectra and the electrical 

or magnetic anomalies observed with geophysical 

exploration techniques. These phenomena are a direct consequence of the partially occupied 3d electronic orbitals of transition-metal cations. The electronic structures of transition metal oxides and 

silicates are best obtained by using a "cluster molecular orbital" approach. Here, one calculates the 

electronic structure of a finite cluster of atoms that 

represents some structural unit of the crystal; for 

example, much of the electronic structures of Mn 

oxides can be understood in terms of the electronic 

structures of Mn06 clusters. Such clusters represent the Mn coordination polyhedron, and, from 

their electronic structures, we can interpret the 

ultraviolet and visible region spectra of manganese 

oxides and silicates. The reason that small clusters 

can often give an accurate description of the electronic structures of minerals is because in nonmetals, each electron tends to be localized to a single 

atom. This is in accordance with the partial ionic 

character of most transition metal oxides and 

silicates. 

In a number of minerals, however, the metal delectrons are not localized. When this happens, electrons can hop among different metal cations by way 

of thermally and optically activated processes. 

Optically activated electron hopping results in 

strong absorption bands in the visible spectral region of minerals and is responsible for the strong 

colors and pleochroism of numerous transition metal silicates. Thermally activated hopping (restricted 

to mixed valence minerals) can result in semiconduction as in magnetite. Indeed, probably all bulk 

electronic conduction with activation energies less 

than 1.0 eV in oxides and silicate minerals is due 

to thermally activated electron hopping. Understanding the nature of electron hopping in minerals, 

therefore, is important for understanding their electrical and spectroscopic properties. 

The research being done to address these problems consists of (1) electronic structure calculations 

on transition metal coordination polyhedra (for 

example, Fe06 , Mn06 clusters), (2) measurement 

and interpretation of the ultraviolet, visible, and 

near-infrared spectra of transition metal oxides and 

silicates, and (3) electronic structure calculations on 

larger clusters to understand the nature and 

mechanisms of electron hopping processes. 

65 

Alteration and Mineralization in the 

Monterrosas Copper-Iron Deposit, Peru 

Gary B. Sidder 

At the Monterrosas Mine, copper-iron ore is 

hosted by gabbro and diorite of the Late Cretaceous 

Coastal Batholith of central Peru. Chalcopyrite, pyrite, and magnetite in variable proportions, with 

gangue of actinolite, sodic scapolite, apatite, tourmaline, and quartz, form the vertical tabular ore 

body, which is about 430 m long, 3-20 m wide, and 

at least 110 m deep. Minor amounts of cubanite and 

pyrrhotite are present as blebs and as intergrowths 

with chalcopyrite in pyrite. The ore body contains 

1.9 million tons that average about 2 percent Cu. The 

grade of Cu ranges from 0.2 to 15 weight percent. 

Au (0.03 oz/ton), Ag (0.7 oz/ton), Co ( s 5,000 ppm), 

and Mo ( s 200 ppm) are present in recoverable 

quantities, and Ni ( s 200 ppm) and Ga ( s 200 ppm) 

occur in anomalously high concentrations. Fe, as 

massive magnetite, attains grades of 60 percent or 

more; however, it is not recovered. 

Alteration effects are widespread in gabbro and 

diorite and become more intense with increasing 

proximity to the ore zone. Secondary minerals, such 

as actinolite, sadie scapolite, epidotes, diopside, 

sphene, magnetite, chlorites, apatite, sericite, 

sulfides, and tourmaline, formed as late magmatic 

to hydrothermal replacements of the primary 

magmatic assemblage (labradorite-andesine, diopside, actinolitic hornblende, ilmenite, and apatite) 

and as fracture fillings. The abundance of alteration minerals decreases from >70 to <10 modal percent away from ore. Boundaries between the ore 

zone and altered gabbro-diorite wallrocks are 

indistinct. At the periphery of the ore body, a zone 

of finely to coarsely crystalline actinolite (;:: 5 em) 

that contains disseminated and stringer oxide and 

sulfide minerals is immediately adjacent to 

actinolitized gabbro-diorite wallrocks. This zone 

grades into one of massive magnetite that also hosts 

stringers and blebs of sulfides and actinolite; this, 

in turn, grades into a central zone that consists of 

massive sulfide with minor magnetite, actinolite, 

and other gangue. The size of the two outer zones 

may differ on either side of the high-grade sulfide 

zone, and the width of the ore zone changes along 

the strike. 

Metasomatic exchange of major and minor 

elements between hot saline fluids and gabbro and 

diorite characterizes the mineralization. Metasomatism involved the addition of FeOt, K20, and MgO 

and the ore-forming metals to the host rocks, with 
the accompanying depletion of Si02 , CaO, Nap, 

Ti02 , and, possibly, Al20 3 • These gains and losses 

define an alteration index that is correlative with 

the distance to ore, the intensity of alteration, and 

the concentration of Cu. The metal-enriched, saline 

(53+ to 43 weight percent NaCl), magmatic (o34S, 

1.6-3.3 per mil) hydrothermal (500 + to 350°C) fluid 

migrated into mineralized parts of gabbro and 

diorite along fractures. 

Textures, such as bent and broken crystals of 

plagioclase, a continuum from deuteric to hydrothermal alteration, and cross-cutting relations between ore and alteration minerals, indicate that 

mineralization was initiated during late magmatic 

crystallization of the gabbro and diorite magma. 

The proposed genetic model suggests that progressive crystallization of primary magmatic 

minerals resulted in the residual concentration and 

segregation of Fe, H20, Cl, P, and other volatiles 

and metals. Faults and fractures produced by 

magmatic pressures and (or) tectonism provided 

channelways for movement of the mineralizing 

fluids to depositional sites also within gabbro and 

diorite. Deposition of ore and alteration minerals 

resulted from decreases of temperature and acidity 

because of metasomatic reactions between the 

hydrothermal fluids and the early formed gabbrodiorite wallrocks. Thus, the Monterrosas deposit is 

similar to other amphibole-rich Cu-Fe deposits in 

Peru and Chile and resembles some skarnlike 

replacement deposits of Fe. 

Mineral-Resource Assessment of the 

Glens Falls 1 o x 2° Quadrangle, New 

York, Vermont, and New Hampshire 

John F. Slack 

A multidisciplinary study of the Glens Falls 1 o 

x 2 o quadrangle was carried out under the auspices 

of the U.S. Geological Survey Conterminous United 

Alvin after surfacing from a U.S. Geological Survey research dive. The research vessel is met by crew members 

in wet suits who will secure lines on the submersible vessel, which is owned by Woods Hole Oceanographic 

Institution and funded by the National Science Foundation, the Office of Naval Research, and the National 

Oceanographic and Atmospheric Administration. 

66 
States Mineral Assessment Program (CUSMAP) 

from 1982 through 1986. The overall mineralresource assessment is based on a variety of new 

data acquired during the CUSMAP project. Included are (1) geologic mapping, (2) regional 

geochemical sampling (principally panned concentrates), (3) magnetic, electromagnetic, and gravity 

surveys, (4) Landsat and radar lineament studies, 

(5) geobotanical remote sensing, (6) compilation of 

the locations of known mines, prospects, and 

mineral occurrences, and (7) topical studies of 

individual mineral deposits. 

The assessment reported here involves qualitative 

rather than quantitative methods of mineralresource appraisal. Lacking detailed grade and tonnage data for a variety of metal commodities and 

deposit types, a simplified technique of diagnostic 

and permissive recognition criteria is employed to 

assess mineral-resource potential. Three main 

criteria are used-favorable geology, geochemical 

anomalies, and known mineral occurrences. These 

criteria are integrated with applicable ore deposit 

models to evaluate potential for a variety of metallic 

mineral deposits; nonmetallic deposits, although 

important, are not considered. Areas with one 

recognition criterion are ranked as having low 

resource potential; areas with two or three criteria 

are assigned moderate or high resource potential, 

respectively. 

Metallic mineral resources in the Glens Falls 

quadrangle include previously known deposits and 

also several newly recognized deposit types. In the 

former category are (1) volcanogenic massive sulfides (Elizabeth, VT), (2) stratabound low-Ti magnetite deposits (Hammondville, NY), (3) discordant 

gold-quartz veins (Taggart, VT), (4) high-Ti magnetite 

deposits in anorthosite and gabbro (Moose Mountain, NY), (5) residual iron and (or) manganese 

deposits (Brandon, VT), (6) stratabound uranium 

deposits in Grenville basement rocks (Jamaica, VT), 

(7) small gold-rich pyrrhotite replacement deposits 

(Cuttingsville, VT), (8) uranium in Carboniferous 

two-mica granites (Sunapee, NH), and (9) small vein 

deposits containing a variety of metallic commodities (Holts Ledge, NH, Thetford, VT). 

Areas having moderate to high resource potential 

for previously unrecognized (in part, speculative) 

deposit types in the quadrangle include (1) volcanogenic gold in the volcanic belts of east-central 

Vermont and west-central New Hampshire, (2) 

porphyry-related gold associated with the alkaline 

intrusive complex (Cretaceous) at Cuttingsville, VT, 

(3) stockwork (or possibly Carlin-type) gold in black 

slates and limestones of the Taconic allochthons in 

67 

New York and Vermont, (4) sedimentary-exhalative 

(sedex-type) polymetallic sulfides in the Taconic 

allochthons, (5) vein- and (or) greisen-type tin-tungsten deposits associated with Devonian and (or) Carboniferous granitoid intrusions in western New 

Hampshire and parts of eastern Vermont, (6) tintungsten-molybdenum-fluorine in late (extensional) 

faults in the eastern Adirondacks, NY, and in western New Hampshire, (7) skarn-type tungsten deposits related to Devonian granitoids in eastern Vermont, (8) concentrations of rare earth elements 

associated with some of the stratabound (low-Ti) 

magnetite deposits of the eastern Adirondacks, (9) 

possible volcanogenic gold in aluminous, graphitic, 

and pyritic metasedimentary sequences of the 

eastern Adirondacks, (10) stratiform (Irish-type) 

lead-zinc-silver deposits in the early Paleozoic shelf 

sequence of western Vermont and eastern New 

York, and (11) uranium concentrations in peat in 

western New Hampshire and central Vermont. 

40ArJ39Ar Thermochronology of Mineral 

Deposits-Information on Age, Duration, Number of Episodes, and 

Temperature of Mineralization 

Lawrence W. Snee 

High-precision 40 Ar/39 Ar age-spectrum dating, a 

variant of the conventional K/Ar technique, is proving useful for solving some of the long-standing 

problems in economic geology, which have been, 

until recently, unresolvable. These problems include 

the age, duration, number of episodes, and temperature of mineralization. The method can provide 

mineral dates with very small analytical errors 

(rv0.25 percent), thus offering the level of precision 

needed for dating the episodes of mineralization 

and alteration of hydrothermal systems. This technique also provides information about the distribution of Ar in the mineral or "whole rock" analyzed, 

whether the material formed before, during, or after 

an alteration event. Even strongly altered wallrock 

minerals can often yield meaningful geochronological data. With advantages for high precision and 

application to altered or unaltered materials, questions of the actual duration of a mineralization event 

can be addressed. In many cases, 40 Ar/39 Ar agespectrum dates provide geothermometric, as well 

as geochronologic, information because such dates 

are actually determinations of the time and temperature at which a mineral closed to the diffusion of 

Ar. In this respect, 40 Ar/39 Ar data are unique in 

that they link temperature and time, providing a 
"thermochronology." These time-temperature data 

are fundamentally significant to the understanding 

of ore-forming processes. Two areas where this 

technique has provided valuable data are a Sn-W 

mine in Panasqueira, Portugal, and the central 

Idaho batholith. 

In a study of the Hercynian-aged Panasqueira 

Sn-W deposit, highly precise age differences were 

distinguished. Muscovite samples with an age difference as small as 2.2 Ma (0.7 percent of the 

mineralization age) are statistically distinct. 

Statistics are even better for comparison of multiple samples from separate events; that is, a difference of 0.9 Ma (0.3 percent) can be resolved. 

The total duration of thermal activity for the Sn and 

W ore-forming stages was at least 4.20 ± 5 Ma 

(1 u). Within that time-span, the age and duration 

of the first substage of the oxide-silicate stage, 

greisenization, and silica cap alteration, in that 

order, are resolvable. Minor Ar loss from all dated 

samples occurred during later reheating, probably 

during the later, longer lived pyrrhotite alteration 

stage. Studies of cross-cutting relations and fluidinclusion homogenization temperatures (Kelly 

and Rye, 1979) resulted in calibration of the Arretention temperature of muscovite. By combining 

the Ar retention temperature of muscovite with the 

age spectrum characteristics of the muscovite from 

a thermally complex area, constraints on the 

temperatures and relative durations of thermal 

episodes can be defined. 

In several mining districts in the central Idaho 

batholith a complex series of hydrothermal events 

occurred during the Cretaceous. High-precision 40 Ar/39 Ar age-spectrum dates that range from 78 

to 70 Ma were determined for muscovites and 

adularia from sulfide-bearing quartz veins with 

associated Au, W, Sb, Hg, Pb, and Ag. Even 

though Eocene hydrothermal activity has been 

considered important in this area, age spectra 

of muscovites and microclines collected near 

Eocene dikes, plutons, and volcanic centers 

indicate Cretaceous ages modified by partial 40 Ar 

loss incurred during post-Cretaceous events. 

Thus, after Cretaceous time, except in areas near 

intense Eocene thermal activity, the central Idaho 

batholith remained below 130°C (Ar-retention 

temperature of microcline). The ages of the quartzvein deposits are similar to emplacement and cooling ages of Cretaceous plutons. The 40 Ar/39 Ar data 

provide constraints for the cooling history of 

plutons and quartz veins and thus yield evidence 

for depth of formation and genesis of the mineral 

deposits. 

68 

Reference Cited 

Kelly, W. C., and Rye, R. 0., 1979, Geologic, fluid inclusion, and stable isotope studies of the tine-tungsten 

deposits of Panasqueira, Portugal: Economic Geology, 

v. 74, no. 8, p. 1721-1822. 

A Link Among 34Sulfur-Rich Pyrite in 

Greenish-Gray Shales, Ferric Iron 

From Smectite as It Converts to Illite, 

Kinetics of Sulfur Redox Reactions, 

and the Genesis of Mississippi ValleyType Deposits 

Charles S. Spirakis and Allen V. Heyl 

Theoretical arguments supported by chemical 

and isotopic data (Maynard, 1980) indicate that 

shales deposited during rapid sedimentation 

(shallow basin-margin environments) have low 

amounts of organic matter (<0.3 percent), are green 

to grey in color, and contain isotopically heavy S 

(up to + 29 per mil) in pyrite. The similarity of these 

isotope values to S isotope values in Mississippi 

Valley-type (MVT) deposits suggests that greenishgrey shales are a possible sulfur source. However, 

mobilization of S from pyrite requires oxidation. 

One of the few oxidizing agents of significant abundance in pyrite-bearing shales is ferric Fe, much of 

which is bound initially in smectite but is released 

as smectite converts to illite. The conversion reaction is triggered by heat in excess of about 80°C. 

Released ferric Fe initially will oxidize organic matter to produce organic acids and C02 ; in shales 

with a high ratio of smectite to organic matter, sufficient ferric Fe will remain after the oxidation of 

organic matter to oxidize S in pyrite. Kinetics 

indicate that, even to temperatures as high as about 

230°C (well above the regional temperatures around 

ore districts), the oxidation yields long-lived 

metastable concentrations of partly oxidized S 

species rather than sulfate. Addition of the partly 

oxidized S-hearing solution from shales to basinal 

solutions containing Pb and other metals can produce the mineralizing solutions. Experiments have 

shown that at temperatures of MVT sulfide mineralization, partly oxidized S species will be reduced 

quickly to sulfide by organic matter (a ubiquitous 

component of the deposits). Because reduction of 

partly oxidized S species in the mineralizing solution by organic matter at the sites of mineralization 

is rapid, sulfide S is produced without fractionation of isotopes. Therefore, precipitated sulfide 
minerals have isotopic values similar to the S 

isotopes in pyrite in greenish-grey shales. Although 

sulfate from evaporite minerals or from the oxidation of pyrite (IF sulfate, rather than partly oxidized 

species, were to form) would contain isotopically 

heavy S, the kinetic inhibition of sulfate reduction 

at temperatures of mineralization precludes sulfate 

reduction as a sulfide source-a constraint exacerbated by the requirement of near complete reduction of the S species to obtain the heavy S in the 

ores. 

The organic acid- and C02-bearing, but S-poor, 

solutions initially released during the clay conversion reaction may contribute to the presulfide-stage 

dissolution of carbonates associated with MVT deposits. The large quantities of Mg and Si released 

from the conversion of smectite to illite provide 

sources of these elements for the characteristic 

dolomitization and silicification of ore zones and 

solution pathways. 

The proposed scheme incorporates the relation 

between depositional environment and the chemical and isotopic character of shales with the 

chemistry of clay conversion reactions and with the 

kinetics of S redox reactions into a model that 

explains the genesis of the deposits as an aspect of 

the evolution of sedimentary basins. The model is 

consistent with the evidence for a single mineralizing solution (rather than mixing at the sites of 

mineralization) and with the evidence for reduction 

of a S species by organic matter at the sites of 

mineralization but is not constrained by the prohibitively slow reduction of sulfate. 

Reference Cited 

Maynard, J. B., 1980, Sulfur isotopes of iron sulfides in 

Devonian-Mississippian shales of the Appalachian 

Basin-Control by rate of sedimentation: American 

Journal of Science, v. 280, p. 772-786. 

Neutralization Of Acidic Ground 

Water Near Globe, Arizona 

Kenneth G. Stollenwerk and James H. Eychaner 

Acidic solutions related to mining and milling 

wide. The aquifer consists of alluvium and conglomerate derived from granite, schist, granite porphyry, and volcanic rocks and discharges about 

0.3 m3/s of water to a perennial stream. Sediment 

size ranges from clay to boulders, and calcareous 

cement content increases with age of sediment. 

This study was designed to evaluate the potential 

effects of the acidic plume on water quality 

downgradient from the plume and in the underlying freshwater aquifer. 

Maximum concentrations of selected constituents in the plume are 3,000 mg/L Fe(II), 200 mg/L 

Cu, 300 mg/L AI, and 16,400 mg/L dissolved solids; 

the minimum pH in the plume is 3.3. Using the 

geochemical computer program PHREEQE, solute 

speciation indicates that aqueous sulfate complexes 

in conjunction with low pH are responsible for the 

solubility of the metals. Adjacent uncontaminated 

water has trace concentrations of metals, as little 

as 400 mg/L dissolved solids, and neutral pH. 

Samples from 16 polyvinyl chloride-cased observation wells are representative of uncontaminated, 

contaminated, transition, and neutralized water. 

Chemical reactions with sediments and mixing 

with uncontaminated water neutralizes the acidic 

water. The reactions form a transition zone between contaminated and neutralized ground water 

where gypsum replaces calcite and most metals 

precipitate. Abundant gypsum crystals and 

sediments with ferric hydroxide coatings have been 

recovered from well cuttings. Although the most 

significant and rapid reactions involve carbonate 

minerals, alteration of igneous and metamorphic 

minerals collected from the plume indicates that 

they also affect solute composition. 

Solubility differences result in a chromatographic 

effect where more soluble elements have been 

transported a greater distance. Increased Mn and 

sulfate concentrations have been measured in the 

perennial streamflow leaving the study area, 81 km 

downvalley from the acidic plume. 

Trace-Element Source for Contamination of Agricultural Drainage Flowing 

Into Kesterson National Wildlife 

Refuge, Merced County, California 

processes are seeping into ground water in the R. R. Tidball, R. C. Severson, J. M. McNeal, 

Globe-Miami area of Arizona. As a result, a plume P. H. Briggs, and K. R. Kennedy 

of acidic ground water containing large concentrations of dissolved solids and metals is moving Agricultural drainage water derived from the San 

through the shallow aquifer system of the area. The Luis irrigation district, San Joaquin Valley, CA, is 

contaminant plume is about 17 km long and 600 m contaminated by Se that has caused high mortality 

69 
among nesting birds and aquatic life in Kesterson 

National Wildlife Refuge. Several hundred soil 

samples were collected in the irrigation district 

(Panoche Creek fan study area in fig. 1) and 

throughout the San Joaquin Valley to identify possible source areas for Se and other elements. All 

samples were analyzed for total concentrations of 

<> ~($) Panache Fan 

<o Study 

+ + 

+ 

+ 

+ 

COALINGA. 

+ 

ANTELOPE 

+ 

48 elements. Se and Hg anomalies were identified 

within the irrigation district with maximum values 

of 4.5 and 2.5 ppm, respectively. A second Se 

anomaly occurs in the Antelope Hills area in 

western Kern County, CA, with maximum values 

of 2.5 ppm, but this area is not a source for 

Kesterson. 

160" 

+ 

+ 

\P 

o~-s-

+ 

Percentile Se, ppm 

+ 

+ 

0 0.07 

10 .09 

30 . 11 

50 

70 

90 

95 

99 

+ 

. 13 

.18 

.36 

.59 

.88 

+38· 

+ 

+ 

+ 

40 

4) 

0 40 Ml ~IS':(, 

~----,--L-~----t---------r----~ I I 1 0~ 

40 0 40 KM 

+ + 

1Zfr 

MARICO 

FLAT 

+86· 

Figure 1. Map of total selenium at 0-30 em depth in soils of the San Joaquin Valley, CA. Gray scales delineate 

percentiles of the frequency distribution. 

70 
R-mode factor analysis showed associations of (1) 

Se with S, which reflect their common occurrence, 

(2) Ni, Mg, Cr, Co, Mn, and Fe, which indicate a 

serpentine source, and (3) C and Hg, which indicate 

that organic matter and Hg-rich sediments occur 

together. Hg is dispersed on the Panache Creek fan 

that probably originates from the New Idria Hg 

district. The present host for Se in the interfan area 

between Panache and Cantua Creeks appears to be 

mudflow-type deposits derived from adjacent finegrained sedimentary rocks. Se in a broad halo 

around the New Idria Hg district may have migrated 

into the surrounding sedimentary rocks. 

Some Characteristics of GneissHosted Gold Deposits of Southeastern 

California 

R. M. Tosdal and D. B. Smith 

In southeastern California, gneiss-hosted gold 

mineralization occurs at the American Girl and 

Padre Madre Mines in the Cargo Muchacho Mountains and at the Mesquite Mine and Black Mountain Prospect in the Chocolate Mountains. The style 

of gold mineralization is distinct from epithermal 

detachment fault-related gold deposits, such as at 

the nearby Picacho Mine. 

Two distinct amphibolite facies gneiss units host 

the gold deposits. The older unit consists of quartzofeldspathic gniess, which is derived from silicic 

volcanic and sedimentary protoliths; this unit is 

known locally as the Tumco Formation. Euhedral 

and embayed quartz and plagioclase blastophenocrysts suggest the protolith is composed, in part, of 

pyroclastic rocks or hypabyssal porphyry intrusive 

rocks. The younger gneiss unit consists of metamorphosed granitoids, ranging in composition from 

diorite to granite, that intruded the supracrustal 

rocks before and during(?) regional metamorphism. 

Granite gneiss is associated spatially with several 

of the mineralized zones; in these locations, the 

granite gneiss is structurally higher than the quartzofeldspathic gneiss. The gneiss units and mineralized zones share the same fabric and are intruded 

by late- and post-kinematic aplite and pegmatite. 

Discordant U-Pb zircon dates for both gneiss units 

indicate Jurassic ages for their protoliths. The 

pegmatites are undated but are related spatially to 

the granite gneiss. 

The gold occurs in shallowly dipping, tabular to 

lenticular bodies that are subparallel with the foliation. The bodies are along contacts between the two 

71 

gneiss units or entirely within the quartzofeldspathic gneiss. The gold is either disseminated or in 

siliceous zones composed of ptygmatically folded 

and boudinaged quartz-magnetite layers or veins. 

Metamorphic mineral assemblages and textures 

in the Cargo Muchacho district suggest two stages 

of synmetamorphic(?) hydrothermal alteration. The 

older assemblage is quartz + magnetite + biotite 

± hornblende ± K-feldspar ± sulfide minerals and 

always occurs in well-foliated gneiss. Locally, the 

younger assemblage is superposed on the older 

assemblage in the quartzofeldspathic gneiss. 

Aluminous minerals, such as muscovite, biotite, and 

kyanite, along with quartz, ilmenite, rutile, tourmaline, and rare accessory minerals, compose the 

younger assemblage. These rocks are schistose, 

where micaceous and granofelsic, but vuggy, where 

composed of kyanite and quartz. Late stage and 

postmineralization alteration and deformation 

features include pyrophyllite replacing kyanite; local 

brittle fractures filled with clay, chlorite, and carbonate minerals; and limonite replacing sulfides 

and magnetite. 

Geochemical anomalies from the mineralized 

areas are subdued and rather sporadic. Mineralized 

rocks in all areas have the following suite of 

elements in common: Au, Ag, As, Sb, Hg, W, Zn, 

and Te. In the Cargo Muchacho district, Cu, Bi, B, 

and F also are associated with gold mineralization. 

A variety of genetic models have been proposed 

for one or more of the gneiss-hosted gold deposits. 

These are (1) metamorphosed gold-bearing chemical 

sediments, (2) metamorphosed epithermal deposits, 

(3) epithermal mineralization related to mid-Tertiary 

detachment faults, (4) mesothermal mineralization 

related to granitic rocks, either a peraluminous 

granite at depth or the exposed gneissic granite, or 

(5) synmetamorphic and synplutonic hydrothermal 

mineralization related to the exposed gneissic 

granite, which is interpreted as a synmetamorphic 

intrusion. Insufficient data is available to prove any 

of these genetic models. 

Geochemical and Crystallographic 

Constraints on the Formation of the 

Vanadium-Uranium Ores of the 

Colorado Plateau 

Richard B. Wanty, Joan J. Fitzpatrick, and 

Martin B. Goldhaber 

The Colorado Plateau physiographic province 

contains many large deposits of V and U hosted in 

fluvial sandstones of the Salt Wash Sandstone 
Member of the Upper Jurassic Morrison Formation; 

the deposits also are enriched in Fe. Although the 

deposits have been mined principally for U, they are 

actually V deposits with secondary U; on the average, V is two to five times more abundant than U 

on a weight basis. The ores formed epigenetically 

as these elements were transported in moderately 

oxidizing low-temperature waters to chemically 

reduced rocks that contained detrital plant fragments. The ore-mineral assemblage consists of coffinite and uraninite, with associated V oxide, vanadiferous chlorite, and vanadiferous illite-smectite. Fe 

is present in the V-bearing phases. Because U, V, and 

Fe have redox-sensitive solubilities, the geochemistry of these elements was studied to determine 

specific chemical processes that formed the ore. 

Valence-specific analyses for V and Fe in the ore 

show that V(III) is more abundant than the more 

oxidized forms. Approximately two-thirds of the Fe 

is in the ferric ( + 3) state in the oxide and clay minerals. X-ray diffraction analysis of the V oxides (heavy 

fractions, >2.89 gm/cm3

) from unoxidized samples 

stored under N2 show the presence of montroseite 

[(V,Fe)OOH] and the more oxidized paramontroseite 

(V02). The two phases were distinguished from 

each other on the basis of unit cell size and intensity differences between key reflections as indicated 

by the calculated intensity profiles for the two minerals. From a consideration of the diffraction 

characteristics of the paramontroseite, it appears that 

two generations are present-a good crystalline 

primary paramontroseite and a poorly crystalline 

oxidation product of primary montroseite. 

V and U together are soluble under moderately 

oxidizing conditions as vanadyl (V02+) or uranyl 

(U02 

2+) ions. Fe is soluble under reducing conditions but in the absence of dissolved sulfide. These 

elements may coexist in waters that are mildly 

oxidizing but anoxic; such a fluid probably transported the metals. V most likely was transported as 

V02 + or some complex thereof. Possible ions that 

may have complexed the V02 + include oxalate, 

fluoride, or carbonate. U probably was transported 

as uo2 2+' most likely in a complex with carbonate. 

Dissociation of the complexes occurred in response 

to changes in pH or ionic strength, or possibly by 

bacterial metabolism of organic ligands, within the 

host rocks. Once removed from their complexes, V 

and U were able to react with H2S, which was produced locally in the mineralizing zone by bacterial 

reduction of sulfate. The U was reduced and 

precipitated with silica in coffinite. The V02+ 

either hydrolyzed and precipitated as paramontroseite or was reduced by the H2

S to form V(III), 

72 

which precipitated as montroseite. Fe substituted 

in the V minerals because of its similar ionic size 

and charge. The fact that the Fe is mostly ferric 

indicates that the activity of H2S could not have 

been very high, although the presence of ore-stage 

pyrite indicates that at least some of the Fe was 

reduced. 

Geochemical Exploration Studies in 

the Glens Falls 1° x 2° Quadrangle, 

New York, Vermont, and New 

Hampshire 

Kenneth C WaHs, Jr. 

A regional geochemical survey of the Glens Falls 

1 o x 2 o quadrangle was completed recently as part 

of the mineral-resource assessment under the Conterminous United States Mineral Assessment Program. A total of 1,286 heavy-mineral concentrates 

from the active sediment channels of small streams 

were collected. These data were supplemented by 

the collection of other forms of geochemical data 

and by published ground- and surface-water data 

from the National Uranium Resource Evaluation 

Program. Data from the nonmagnetic fraction of the 

heavy-mineral concentrates have produced the most 

useful mineral-resource information and are the 

chief basis of the findings reported here, although 

the other data have been integrated into the 

interpretations. 

The Glens Falls area is separable into seven 

stratigraphic-tectonic areas composed of Precambrian and Paleozoic rocks with distinctive geologic 

history and somewhat dissimilar environments for 

the formation of mineral deposits. Several previously unrecognized zones of multielement anomalies 

of regional extent are shown to crosscut these terranes. These broad zones of anomalies evidently are 

related regionally to deep and shallow tectonic 

features and to specific lithostratigraphic units suggestive of stratabound metal occurrences. 

One regional set of northeast-trending zones of 

anomalous elements that includes Pb, Cu, Sn, and 

Ba transects tectonic-stratigraphic terranes and coincides with N. 60°-65° W. radar lineaments that 

other workers interpret as a deep-seated continental 

fracture system that is printed through cover rocks. 

Another regional zone has a geochemical signature of anomalous Sr, Ba, Nb, B, Fe, Pb, and Cu, is 

probably Mesozoic in age, trends east to west, and 

chemically overprints the geochemical signature of 

the older, regionally metamorphosed Precambrian 
and Paleozoic rocks. This geochemical overprint appears to be related to rifting, and hydrothermal activity accompanied by the emplacement of postkinematic, alkalic plutons of the White Mountain series 

that have potential for precious base and rare metal 

deposits. 

The regional geochemical data were interpreted in 

greater detail utilizing the following: (1) element 

associations and zonations determined by comparison of single-element map plots and R-mode factor 

analyses, (2) mineralogy of the samples, and (3) supplementary geochemical data. Interpretations were 

made by using ore-deposit models most appropriate 

to each of the geologic settings. 

R-mode factors that account for the most data variance, in order of decreasing contribution for the overall quadrangle, include (with the most strongly loaded elements in order) (1) V, Nb, Ti, B, Mn, Cr, Cu, 

Fe, and Mg-largely a rutile-tourmaline association, 

(2) La, Mg, Sc, Y, and B-an accessory mineral association that, at least in part, is related to pegmatites, 

(3) Ni, Co, As, Fe, and Cu-a pyrite-pyrrhotite association, (4) Sn, Pb, Sb, Ba, and Cu-a barite association 

chiefly found in the allochthonous, eugeosynclinal 

sequence of the Taconic Ranges, (5) Ca, Sr, Mn, and 

Co-a carbonate-oxide mineral association that, at 

least in part, is derived from zones of hydrothermal 

carbonization not related geographically to the distribution of the main calciferous lithologies, and (6) 

W, Bi, Mo, and Be-a scheelite association most 

typical of areas east of the Connecticut River where 

it is associated with domes and metavolcanics. 

Discrete areas of multielement anomalies probably are related to (1) the location of metavolcanic 

centers and proximal hydrothermal vent areas (Cu, 

Pb, B, Bi, W, As, Co, Fe, Sn, Ag, and Mo ), (2) zones 

in metasedimentary basins once occupied by anoxic 

seafloor depressions and hydrothermal vents (Pb, 

Zn, Cu, Ag, Sn, and Sb) that may grade laterally into 

oxidized facies equivalents characterized by anomalous Ba (barite) and Mn, and (3) areas of skarn and 

vein deposits associated with exposed plutons and 

concealed cusps (Cu, Pb, W, Bi, As, Co, and Mn). 

The Apex Mine, Utah-A Colorado 

Plateau-Type Solution-Collapse 

Breccia Pipe 

Karen J. Wenrich, Earl R. Verbeek, Hoyt B. Sutphin, 

Bradley S. Van Gosen, and Peter J. Modreski 

The Apex Mine, in southwestern Utah's Beaver 

Dam Mountains, is in the southern Basin and Range 

73 

province near the Colorado Plateau's western edge. 

Oxidized ore was mined intermittently from the 

Apex between 1884 and 1949 for Cu, Pb, Ag, and 

minor Zn and Au, as it was from numerous mines 

in the Grand Canyon area. Most of the old Grand 

Canyon Cu mines are in the oxidized zone of U- and 

base-metal-bearing breccia pipes that formed by collapse of overlying sedimentary rocks into solution 

caverns within the Mississippian Redwall Limestone. Most of the U ore occurs within the sandy 

breccia matrix formed by comminution of Pennsylvanian and Permian sedimentary rocks. Similarly, the Apex Mine is in a collapse breccia formed 

by solution, presumably of the underlying Red wall 

Limestone. In the past, this breccia was attributed 

to fault brecciation, but the following observations 

suggest instead that it formed by solution collapse: 

(1) the breccia clasts are polylithologic, are oriented 

nearly randomly, and range widely in size from pebbles to large slabs, (2) the breccia occurs in large, 

irregular masses whose shape and distribution bear 

no relation to fault position, (3) much of the breccia consists of a chaotic jumble of blocks in loose 

contact with large voids between individual blocks, 

and (4) individual clasts are not sheared, and the 

breccia exhibits no planar fabric suggestive of 

faulting. The faults, in fact, postdate this collapse 

breccia; in several places, masses of breccia have 

been brought into sharp fault contact against solid 

bedded limestone. 

Despite these similarities between the Plateau 

breccia pipes and the thoroughly oxidized Apex 

Mine in 1985, processing of Ge and Ga ore (averaging about 600 ppm Ge and 300 ppm Ga) began from 

the Apex, making it the world's first primary producer of these two metals. Similar concentrations 

of Ga and Ge are unknown in the Colorado Plateau 

U-bearing breccia pipes, although few samples have 

been analyzed for Ge. The only Ga concentrations 

found to exceed 100 ppm came from two samples 

from the Ridenour Mine, a U-rich breccia pipe on 

the Hualapai Indian Reservation. In addition toGa 

and Ge in the Apex Mine, Au is enriched within 

goethite- and jarosite-rich ore. Concentrations of Au 

in 7 of 21 samples from the breccia zone range between 8 and 33 ppm, suggesting that Au may be a 

viable byproduct from the Apex. Although such 

high Au concentrations are rare in the U-rich Colorado Plateau breccia pipes, they do occur in the 

oxidized zones of the Copper Mountain and the 

Chicken Mines (both on the north rim of the Grand 

Canyon). In both occurrences, and at the Apex mine, 

Au is associated with high Zn, specifically 

hemimorphite and smithsonite. 
A wide assortment of Cu, Pb, Zn and As minerals 

can be found at the Apex Mine. Along with minerals such as azurite, malachite, chrysocolla, 

brochantite, conichalcite, and aurichalcite (for 

which the Apex has long been popular with mineral 

collectors), other minerals identified by earlier 

workers and additional ones identified during this 

study are adamite, anglesite, cerussite, chalcopyrite, 

cobaltian adamite, covellite, cuprian adamite, 

cuprite, duftite, galena, goethite halloysite, hematite, 

hemimorphite, jarosite, plattnerite, plumbojarosite, 

and rosasite. Most of this mineral suite is similar 

to that of the Tsumeb solution-collapse breccia pipe 

in Namibia. In addition, the suite of base-metal 

elements is similar to that of the Colorado Plateau 

breccia pipes, and, although primary unoxidized 

ore minerals of these base metals, such as galena 

and chalcopyrite, are rare in the Apex Mine, they 

are present. 

Additional solution collapse breccia pipes have 

been identified in the Beaver Dam Mountains. 

Because breccia pipes on the Colorado Plateau tend 

to occur in clusters, there appears to be significant 

economic potential for more ore bodies similar to 

the Apex in this part of the Basin and Range. The 

major difference between ore bodies in the Beaver 

Dam Mountains and those on the Colorado Plateau 

is that the Apex type tends to be oxidized extensively and lacks U-bearing ore. The absence of Ubearing minerals may be due to (1) complete oxidation of the ore body during the Basin and Range 

faulting and tilting, such that any U minerals present would have been oxidized, dissolved, and transported away by oxidizing fluids, (2) the U-bearing 

fluids may not have migrated this far north, or (3) 

the hydrologic environment of the host rock in the 

Basin and Range may not have been favorable to U 

deposition during the Triassic. 

Preliminary Results of Geophysical 

Studies Near the Creede Mining 

District, Colorado 

David L. Williams, William D. Stanley, and 

Victor F. Labson 

Gravity, aeromagnetic, magnetotelluric (MT), and 

audiomagnetotelluric (AMT) surveys recently have 

been completed in the region around the Creede 

mining district, Colorado. The gravity and aeromagnetic surveys offer good coverage of the region, but 

MT coverage consists of a single reconnaissance 

profile in the southern part of the district. The AMT 

74 

survey was limited to the area of the northern moat 

of the Creede caldera. Only preliminary aeromagnetic maps are currently available. 

The region around Creede contains at least four 

large and diverse calderas of late Oligocene age 

known as the central San Juan caldera complex. 

Apparently, the calderas were emplaced through 

older volcanic rock overlying Precambrian basement and, in some instances, Mesozoic sedimentary rocks. The ash flows of the Bachelor and San 

Luis calderas and postcaldera lake sediments and 

volcaniclastics of the Creede Formation are the 

important host units of mineralization. 

In general, the caldera-generated ash-flow tuffs 

that make up most of the terrain have a strong remanent magnetizations. In places, these magnetizations are destroyed by high-temperature alteration, 

permitting aeromagnetic methods to detect such 

alteration zones. Intrusive rocks and the Creede Formation are typically less magnetic than unaltered 

ash-flow tuffs. The ash-flow tuffs have an average 

density of about 2.4 gm/cm3, whereas intrusive 

rocks generally are denser than 2.6 gm/cm3, and 

the Creede Formation is closer to 2.2 gm/cm3 • 

The gravity and regional aeromagnetic signatures 

of the individual calderas are diverse, with the La 

Garita caldera, oldest and largest of the group, showing gravity and magnetic highs. The Bachelor caldera, whose intracaldera ash-flow tuff hosts much 

of the Creede mineralization, has a slight gravity low 

and indefinite aeromagnetic signature. The Creede 

caldera is the most clearly delineated, with pro--

nounced gravity and magnetic highs. The anomalies 

for the Creede caldera define details of ash-flow tuff 

thickness and the resurgent Creede pluton. The San 

Luis caldera, youngest of the group, has a gravity 

high and a rather complex aeromagnetic signature. 

In addition to the regional aeromagnetic survey, 

a detailed helicopter aeromagnetic survey was 

flown over the mining district and preliminary 

maps show fine structures that may be identified 

with faults, veins, alteration zones, shallow intrusions, and breccia pipes. 

An AMT survey of the Creede Formation just 

south of the mining district was designed to map 

the thickness and lithology of the Creede Formation and was successful in achieving these goals. 

Fine-grained ashy lake sediment could be distinguished easily from coarser volcaniclastics and colluvium. Travertine bodies in the sediments als(] 

were detected easily. The reconnaissance MT profile extended from the Creede caldera moat acrosE 

the Bulldog Mountain region to the area between 

Nelson Mountain and the Equity Mine. Preliminary 
interpretations of the data reveal no major pluton 

underneath the mapped location of the Bachelor 

caldera crossed by the MT profile. However, a highly 

resistive body {3,000-12,000 ohm-m) detected north 

of Nelson Mountain at depths of 2-3 km is interpreted to represent a pluton, possibly associated 

with the southern edge of the San Luis caldera. The 

northern extent of this resistive body is not known 

because of the limited extent of the MT survey. 

Textural Association of PlatinumGroup Minerals From the J-M Reef, 

Stillwater Complex, Montana 

M. L. Zientek and R. L. Oscarson 

The mineralogy, grain size, and textural associations of platinum-group element (PGE) minerals 

have been determined for a sample collected from 

the J-M Reef of the Stillwater Complex, MT, by backscattered electron microscopy combined with qualitative and semiquantitative energy dispersive X-ray 

analysis. Approximately 160 PGE mineral grains 

were observed in the 5-cm2 area constituting this 

sample. At least 14 minerals are present and consist of Pd, Pt, and Rh sulfides; Pt and Pd tellurides; 

and Pt-Fe, Pt-Pd-Sn, Pd-Pb, Pd-Hg, Au-Pt-Pd alloys. 

Moncheite, Pd tellurides, and Pt-Fe alloy are the 

most common; michinerite, plumbopalladinite, and 

potarite, which have not been reported previously 

from the Stillwater Complex, are also present. Four 

distinct textural occurrences of these minerals are 

characterized by differing proportions of minerals 

and grain size. PG E minerals may occur as inclusions in base-metal sulfide (BMS), either totally surrounded by BMS or, more commonly, directly 

against the BMS-gangue contact. This is the textural 

occurrence most commonly described from the 

Merensky Reef, Bushveld Complex, South Africa. 

Fourteen percent of the observed grains fall in this 

category; moncheite and Pt-Fe alloy are most common in this group. The maximum dimension of all 

grains in this group averages 41~-tm. Associated with 

many PGE-mineral inclusions in BMS are PGE 

minerals included in the adjacent silicate gangue. 

This occurrence accounts for 10 percent of the 

grains and is dominated by moncheite. The grain 

size, which is much finer than those included in 

BMS, averages 4 ~-tm. Approximately 6 percent of 

the PG E minerals occur in chalcopyrite, which occurs in irregularly shaped clusters of grains included within bronzite. Pd tellurides dominate this 

occurrence, with an average grain size of 1.5 ~-tm. 

Most of the grains of PGE minerals (70 percent) 

occurred in discontinuous stringers or veinlets with 

or without BMS. Their mineralogy is dominated by 

Pd tellurides and a very high proportion of the 

phases observed other than moncheite. Au alloys, 

vysotskite, palladian pentlandite, and potarite are 

characteristic of these veinlets. Grain size, which is 

quite fine, averages 4 ~-tm. These veinlets probably 

represent the end product of the crystallization of 

a PG E-enriched immiscible sulfide liquid; serpentinization and associated veining postdate these 

veinlets. 

For this sample, PGE concentrations were estimated by summing the contribution to whole rock 

abundance made by each grain. Simple grain 

shapes (circles or rectangles) utilizing measured 

grain dimensions were used in these calculations. 

The calculated concentrations were 7 ppm Pd and 

55 ppm Pt. The actual concentrations, determined 

by combined fire assay-atomic absorption analysis, 

are 3 7 ppm Pd and 55 ppm Pt. 

PG E minerals account for all the Pt grade but only 

one-fifth of the Pd grade. The remaining Pd occurs 

in solid solution with pentlandite. The Pd content 

of previously analyzed J-M Reef pentlandites ranges 

from 1,870 to 13,600 ppm (Cabri and others, 1984). 

Semiquantitative analyses of pentlandite from the 

veinlets in this sample range from 3.5 to 8.7 weight 

percent Pd. 

Reference Cited 

Cabri, L. J., Blank, Herma, Goresy, A. E., Laflamme, J. H. 

G., Nobiling, Rainer, Sizgoric, M. B., and Traxel, Kurt, 

1984, Quantitative trace-element analyses of sulfides 

from Sudbury and Stillwater by proton microprobe: 

75 

Canadian Mineralogist, v. 22, p. 521-542. 

Comparison of the Turner-Albright 

Ophiolite-Hosted Massive Sulfide, 

Southwestern Oregon, to Active 

Hydrothermal Deposits on the 

Southern Juan de Fuca Ridge 

Robert A. Zierenberg, Randolph A. Koski, 

Wayne G. Shanks Ill, William E. Seyfried, Jr., 1 

and Michael D. Strickler2 

The Turner-Albright volcanogenic massive sulfide 

and associated altered volcanic rocks represent a 

well-preserved, relatively unmetamorphosed analog 

of the active seafloor hydrothermal systems developed at the southern Juan de Fuca spreading center. 

The deposit consists of several Cu-Zn-Ag-Au-Co-rich 

1

University of Minnesota, Minneapolis, MN. 2 Lithologic Resources, Grants Pass, OR. 
massive sulfide bodies in the lower part of the 

extrusive sequence of the Late Jurassic Josephine 

ophiolite. Basalt occurs as pillowed and massive 

flows, thick ponded lava lakes, talus, and hyaloclastite breccias. These basalts typically contain 

phenocrysts of fresh clinopyroxene; plagioclase, 

which is partially replaced by albite, chlorite, and 

pumpellyite; and titanomagnetite, which is altered 

totally to sphene and leucoxene. The formerly glassy 

groundmass of these rocks was metamorphosed 

beneath the seafloor to chlorite, pumpellyite, prehnite, and albite by circulation of heated seawater. 

A second, more primitive, lava series occurs as 

thick units of hyaloclastite breccia spatially 

associated with the sulfide horizons. These lavas 

contained phenocrysts of olivine, chromium spinel, 

and plagioclase and typically have plumose to dendritic relect quenched textures in the groundmass. 

However, these basalts have been altered hydrothermally by the ore-transporting fluids, and the leastaltered rocks are now essentially two component 

mixtures of Fe-rich chlorite and quartz. The 

chlorite-quartz rocks were altered at approximately 

350°C from a fluid depleted in Mg and enriched 

in 0180 by approximately 2 per mil, similar to 

hydrothermal fluids sampled at modern ridge crests. 

Increased alteration results in total replacement of 

the basalt by quartz. Intermediate stages of alteration often preserve the original volcanic textures. 

Typical sulfide intervals contain massive sulfide 

at the top and grade downward through semimassive sulfide to mineralized basalt. Much of the 

sulfide-bearing rock has fragmental textures. The 

down-hole decrease in sulfide content is accompanied by an increase in the proportion of altered 

volcanic fragments and a decrease in the degree of 

alteration of the fragments. Pyrite is the dominant 

sulfide, but sphalerite-rich intervals are common, 

especially at the tops of ore intercepts where 

primary growth banding often is preserved. Cu-rich 

zones show invasion and replacement of preexisting 

sulfides by chalcopyrite on all scales from entire 

core samples to individual color bands in sphalerite 

crystals. Sulfur isotope values for the sulfides are 

generally between 1 and 8 per mil. 

Only a small portion of the sulfides formed by 

true exhalative processes above the seawater-basalt 

interface; most formed below the seafloor from 

hydrothermal fluid that infiltrated and partially 

replaced basaltic hyaloclastite and talus breccia. The 

geologic setting and geochemical processes that led 

to the formation of the Turner-Albright deposit are 

similar to the active hydrothermal deposits forming 

at the southern Juan de Fuca Ridge, where only the 

upper Zn- and Ag-rich portion of the system is 

exposed for sampling by research submarines. 

The paleokarst, which formed in the Mississippian Redwall Limestone, is so extensive that many caves, such 

as this one along Diamond Creek, Al., were used during the Late Mississippian as passages by channels 

of the Surprise Canyon Formation. This 80- x 140-ft cave formed in the Thunder Springs Member of the 

Redwall with the top reaching into the Mooney Falls Member. Collapse of the overlying late Paleozoic 

sedimentary rocks into such caves formed breccia pipes, some of which were mineralized by U-bearing 

fluids about 200 Ma (age determined by Ken Ludwig). The extensive karst in the Redwall Limestone permitted considerable flushing of the soluble and fine-grained portions of the breccia pipes, such that total 

downdropping in some pipes exceeds 700 ft. This particular cave is an important part of the Hualapai 

Indian heritage. /l.s H. F. Dobyns and R. C. Euler stated in The Walapai People, "A cave in the steep north 

wall of Diamond Creek Canyon contained a rich deposit of red mineral pigment. Mixed with deer tailow, 

this pigment formed a fine face cream and body coating to protect skin against sunburn and cold. Its 

bright [red] color made it a very precious commodity that the Northeastern Pai sold in intertribal trade 

for good prices .... Mining was dangerous and difficult. Miners constructed tall ladders of notched logs 

to prop against the nearly vertical cliff wall so they could climb from the nearest ledge [shown at the 

bottom of the photograph as the sloping ledge of the Devonian Temple Butte Formation] up to the narrow 

opening into the cave." Research was funded by the Bureau of Indian Affairs in cooperation with the 

Hualapai Tribe. 

76 
n 
ORGANIZATION OF THE U.S. GEOLOGICAL SURVEY 

Office Name Telephone City 

Office of the Director 

Director Dallas L. Peck 703/648-7411 Reston 

Associate Director Doyle G. Frederick 703/648-7412 Reston 

Assistant Director for Research Bruce R. Doe 703/648-4453 Reston 

Assistant Director for Engineering Geology James F. Devine 703/648-4423 Reston 

Assistant Director for Administration Jack J. Stassi 703/648-7201 Reston 

Assistant Director for Programs Peter F. Bermel 703/648-4430 Reston 

Assistant Director for Intergovernmental Affairs John J. Dragonetti 703/648-442 7 Reston 

Chief, News Media Service Donovan B. Kelly 703/648-4459 Reston 

Assistant Director for Information Systems James E. Biesecker 703/648-7108 Reston 

National Mapping Division 

Chief Lowell E. Starr 703/648-5748 Reston 

Geologic Division 

Chief Geologist Robert M. Hamilton 703/648-6600 Reston 

Water Resources Division 

Chief Hydrologist Philip Cohen 703/648-5212 Reston 

ORGANIZATION OF THE GEOLOGIC DIVISION 

Office of the Chief Geologist 

Chief Geologist Robert M. Hamilton 703/648-6600 Reston 

Associate Chief Geologist William F. Cannon 703/648-6601 Reston 

Assistant Chief Geologist for Program Benjamin A. Morgan 703/648-6640 Reston 

Assistant Chief Geologist, Eastern Region Jack H. Medlin 703/648-6660 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 703/648-6100 Reston 

Chief, Branch of Alaskan Geology Donald J. Grybeck 907/786-7403 Anchorage 

Chief, Branch of Eastern Mineral Resources Bruce R. Lipin 703/648-6327 Reston 

Chief, Branch of Central Mineral Resources David A. Lindsey 303/236-5568 Denver 

Chief, Branch of Western Mineral Resources Edwin H. McKee 415/323-8111 Menlo Park 

Chief, Branch of Geochemistry Byron R. Berger 303/236-1800 Denver 

Chief, Branch of Resource Analysis Lawrence J. Drew 703/648-6125 Reston 

Chief, Branch of Geophysics Frank C. Frischknecht 303/236-1212 Denver 

Office of Energy and Marine Geology 

Chief Terry W. Offield 703/648-6470 Reston 

Chief, Branch of Petroleum Geology Dudley D. Rice 303/236-5711 Denver 

Chief, Branch of Coal Resources Harold J. Gluskoter 703/648-6401 Reston 

Chief, Branch of Sedimentary Processes Thomas D. Fouch 303/2 36-1644 Denver 

Chief, Branch of Pacific Marine Geology Monty A. Hampton 415/323-8111 Menlo Park 

Chief, Branch of Atlantic Marine Geology Robert B. Halley 617/548-8700 Woods Hole 

Office of Regional Geology 

Chief Eugene H. Roseboom 703/648-6960 Reston 

Chief, Branch of Eastern Regional Geology Gregory S. Gohn 703/648-6900 Reston 

Chief, Branch of Central Regional Geology Glen A. Izett 303/236-1250 Denver 

Chief, Branch of Western Regional Geology Robert 0. Castle 415/323-8111 Menlo Park 

Chief, Branch of Isotope Geology John N. Rosholt 303/236-7880 Denver 

Chief, Branch of Astrogeology Hugh H. Kieffer 602/52 7-7015 Flagstaff 

Chief Branch of Paleontology and Stratigraphy Richard Z. Poore 703/648-5288 Reston 

78 
Office Name 

Office of Earthquakes, Volcanoes, and Engineering 

Chief 

Chief, Branch of Engineering Seismology and 

Geology 

Chief, Branch of Global Seismology and 

Geomagnetism 

Chief, Branch of Seismology 

Chief, Branch of Geologic Risk Assessment 

Chief, Branch of Tectonophysics 

Chief, Branch of Igneous and Geotheranal 

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 

John R. Filson 

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 

79 

Telephone City 

703/648-6714 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 

703/648-6077 Reston 

703/648-6047 Reston 

U.S. Geological Survey 

345 Middlefield Road 

Menlo Park, CA 94025 

U.S. Geological Survey 

Quissett Campus, Building 13 

Woods Hole, MA 02543 
INDEX 

A 

Aleinikoff, J. N. (Branch of Isotope Geology)-------- 39 

Alexander, Robert (Research, Technology, and Applications 

Office, NMD) ------------------------------- 1 

Alminas, H. V. (Branch of Geochemistry)----------- 1 

Anderson, J. A. (Branch of Analysis, WRD) ---------- 11 

Anton-Pacheco, Carmen -----------------------59 

Antweiler, J. C. (Branch of Geochemistry)----------- 50 

Armstrong, A. K. (Branch of Western Mineral Resources) 57 

Arndt, R. E. (Branch of Applications, NMD) -------- 2 

Aruscavage, P. J. (Branch of Geochemistry)---------- 55 

Asher-Blinder, Sigrid (Branch of Sedimentary Processes) 2 

Attanasi, E. D. (Branch of Resource Analysis) -------- 4 

Ayuso, R. A. (Branch of Eastern Mineral Resources) ---- 4 

B 

Bagby, W. C. (Branch of Western Mineral Resources)--- 52 

Barnes, D. F. (Branch of Geophysics)------------ 8 

Barton, P. B. (Branch of Resource Analysis) --------- 15 

Bawiec, W. J. (Branch of Resource Analysis) --------- 4 

Belkin, H. E. (Branch of Resource Analysis) --------- 28 

Berg, H. C ---------------------------------- 8 

Bisdorf, R. J. (Branch of Geophysics)------------- 9 

Blank, H. R. (Branch of Geophysics) ----------------- 5 

Bliss, J. D. (Branch of Resource Analysis) ------------ 6 

Bove, D. J. (Branch of Sedimentary Processes) --------- 6 

Breit, G. N. (Branch of Sedimentary Processes) -------- 7 

Brem, G. F. (Branch of Western Mineral Resources) --- 52 

Brew, D. A. (Branch of Alaskan Geology)---------- 8 

Brickey, D. W. (Branch of Geophysics)------------ 59 

Briggs, P. H. (Branch of Geochemistry)------------- 59 

Briskey, J. A. (Branch of Western Mineral Resources)-- 57 

Brown, Z. (Branch of Geochemistry) -------------- 55 

Bundtzen, T. K ----------------------------- 46 

c 

Campbell, D. L. (Branch of Geophysics)------------ 9 

Cannon, S. S. (Branch of Eastern Mineral Resources) --- 22 

Cannon, W. F. (Office of Chief Geologist) ------------ 22 

Case, J. E. (Branch of Geophysics)----------------- 52 

Cathrall, J. B. (Branch of Geochemistry) ----------- 8, 50 

Chaffee, M. A. (Branch of Geochemistry) ------------- 10 

Chavez, P. S., Jr. (Branch of Applications, NMD) ------ 11 

Christian, R. P. (Branch of Central Mineral Resources) -- 1 

Christiansen, R. L. (Branch of Igneous and Geothermal 

Processes) --------------------------------- 11 

Church, S. E. (Branch of Geochemistry) --------- 12, 39 

Clague, D. A. (Branch of Pacific Marine Geology) ----- 28 

Clark, S. H. B. (Branch of Eastern Mineral Resources)-- 13 

Cox, D. P. (Branch of Resource Analysis)------ 14, 15, 52 

Crane, Michael (Research, Technology, and Applications 

Office, NMD) ------------------------------ 16 

Crowley, J. K. (Branch of Geophysics) ------------- 59 

Cygan, G. L. (Branch of Resource Analysis) -------- 30 

D 

D'Agostino, J. P. (Branch of Eastern Mineral Resources) 62 

d'Angelo, W. M. (Branch of Geochemistry)---------- 30 

Daniels, D. L. (Branch of Geophysics) ------------- 55 

Dinardo, Thomas (Research, Technology, and Applications 

Office, NMD) -------------------------- 1, 16 

Dorrzapf, A. F., Jr. (Branch of Geochemistry) ----- 23, 55 

80 

Duffield, W. A. (Branch of Igneous and Geothermal 

Processes)----------------------- 16 

Dwyer, J. L --------------------17 

E 

Earhart, R. L. (Branch of Central Mineral Resources) --- 18 

Eberl, D. D. (Branch of Regional Research, WRD) ---- 37 

Ellersieck, lnyo (Branch of Alaskan Geology) -------- 33 

Elliott, J. E. (Branch of Central Mineral Resources) --- 17 

Ericksen, G. E. (Branch of Eastern Mineral Resources) -- 18 

Escowitz, E. C. (Branch of Atlantic Marine Geology) -- 19 

Evans, H. T., Jr. (Branch of Igneous and Geothermal 

Processes) -------------------------- 19 

Eychaner, J. H. (Arizona Subdistrict Office, WRD) --- 69 

F 

Fitzpatrick, J. J. (Branch of Sedimentary Processes)---- 71 

Flanigan, V. J. (Branch of Geophysics)------------ 21 

Fleishman, Charlaine (Branch of Pacific Marine Geology) 28 

Folger, Peter (Branch of Geochemistry)---------- 33 

Force, E. R. (Branch of Eastern Mineral Resources) ---- 40 

Friedman, J.D. (Branch of Geophysics)---------- 21 

G 

Gair, J. E. (Branch of Eastern Mineral Resources) ----- 22 

Gamble, B. M. (Branch of Alaskan Geology)---------- 23 

Ginnodo, K. L. (Research, Technology, and Applications, 

Office, NMD) ---------------------------- 16 

Goldfarb, R. J. (Branch of Geochemistry) ------- 33, 57 

Goldhaber, M. B. (Branch of Sedimentary Processes)- 7, 71 

Golightly, D. W. (Branch of Geochemistry) ---------- 23 

Grauch, V. J. S. (Branch of Geophysics) ----------- 31 

Gray, Floyd (Branch of Western Mineral Resources)---- 25 

Griscom, A. (Branch of Geophysics) --------------- 8 

Grosz, A. E. (Branch of Eastern Mineral Resources) ---- 19 

Grybeck, D. J. (Branch of Alaskan Geology)--------- 8 

Gumiel, Pablo-------------------------- 62 

H 

Haas, J. 1., Jr. (Branch of Igneous and Geothermal Processes) 26 

Hahn, G. A --------------------------------51 

Hamilton, W. B. (Branch of Geophysics)---------- 27 

Hardyman, R. F. (Branch of Central Mineral Resources) 52 

Hearn, P. P., Jr. (Branch of Geochemistry) ------ 28 

Hein, J. R. (Branch of Pacific Marine Geology)-------- 28 

Hemley, J. J. (Branch of Resource Analysis)-------- 30 

Heyl, A. V. (Branch of Central Mineral Resources)---- 68 

Himmelberg, G. R --------------------30 

Hofstra, A. H. (Branch of Geochemistry) ---------- 38 

Holmes, M. L. (Branch of Pacific Marine Geology)-- 31, 49 

Hon, Ken (Branch of Igneous and Geothermal Processes) 6 

Hoover, D. B. (Branch of Central Mineral Resources)- 31 

Hopkins, R. T. (Branch of Geochemistry)---------- 1 

Horton, Robert (Branch of Geophysics) ------------ 32 

Hosterman, J. W. (Branch of Eastern Mineral Resources) 33 

Huber, D. F. (Branch of Resource Analysis)------ 44, 52 

J 

John, D. A. (Branch of Western Mineral Resources)-- 52 

Johnson, B. R. (Branch of Central Mineral Resources) -- 63 

Johnson, R. G. (Branch of Geochemistry)-------- 55 

Johnson, T. L. (Branch of Applications, NMD) ----- 2 
K 

Kane, J. S. (Branch of Geochemistry)------------ 55 

Karl, S. M. (Branch of Alaskan Geology) -------- 8, 33 

Keith, W. J. (Branch of Western Mineral Resources)--- 52 

Kennedy, K. R. (Branch of Geochemistry) ----------- 69 

Kingston, M. J. (Branch of Geophysics)---------- 59 

Kipp, K. L., Jr. (Branch of Regional Research, NMD) --- 34 

Kirschenbaum, H. (Branch of Geochemistry) -------- 55 

Kleinhampl, F. J. (Branch of Western Mineral Resources) 52 

Koch, R. D. (Branch of Alaskan Geology)--------- 8 

Koeppen, R. P. (Branch of Eastern Mineral Resources) 18, 52 

Koski, R. A. (Branch of Pacific Marine Geology) ---- 35, 75 

Krohn, M. D. (Branch of Geophysics)-------------- 35 

Kvenvolden, K. A. (Branch of Pacific Marine Geology)- 35 

L 

LaBerge G. L --------------------------58 

Labson V. F. (Branch of Geophysics)------------ 9, 74 

Lai, T.-M. (Branch of Regional Research, WRD) ---- 37 

Landis, G. P. (Branch of Central Mineral Resources)---- 38 

Lange, I. M. (Branch of Alaskan Geology) ----------- 39 

Lanphere, M. A. (Branch of Isotope Geology) ------ 40 

Larsen, C. E. (Branch of Eastern Mineral Resources) - 40 

Leach, D. L. (Branch of Geochemistry) -------- 38, 57 

Lichte, F. E. (Branch of Geochemistry)----------- 44 

Lipman, P. W. (Branch of Central Regional Geology) - 40 

Loney, R. A. (Branch of Alaskan Geology) ---------- 30 

Long, Carl (Branch of Geophysics) ------------ 32, 33 

Lovley, D. R. (Branch of Regional Research, WRD) ---- 42 

Ludington, S. D. (Branch of Resource Analysis)----- 52 

Lyle, Mitchell ---------------------------- 49 

M 

Marron, D. C. (Branch of Regional Research, WRD) --- 42 

Marsh, S. P. (Branch of Geochemistry)------------ 52 

Martin, B. D. (Branch of Eastern Mineral Resources)--- 22 

Mason, G. T. (Branch of Resource Analysis)--------- 44 

McCammon, R. B. (Branch of Resource Analysis) ----- 43 

McKee, E. H. (Branch of Western Mineral Resources) -- 59 

McNeal, J. M. (Branch of Geochemistry)---------- 69 

Medlin, A. L. (Branch of Resource Analysis) --------- 44 

Mee, J. S. (Branch of Geochemistry) ------------- 55 

Meier, A. L. (Branch of Geochemistry)------------ 44 

Menzie, W. D. (Branch of Resource Analysis)--------- 6 

Meunier, J. D ----------------------------- 7 

Mikesell, Jon (Branch of Isotope Geology) ---------- 45 

Miller, B. M. (Office of Chief Geologist) ---------- 45 

Miller, F. K. (Office of Regional Geology)--------- 46 

Miller, M. L. (Branch of Alaskan Geology)----------- 47 

Miller, W. R. (Branch of Geochemistry)----------- 59 

Modreski, P. J. (Branch of Central Mineral Resources) -- 73 

Mohr, Pam (Branch of Geophysics)--------------- 21 

Moll, S. H ------------------------ 17 

Montaser, A ---------------------------- 23 

Morgan, J. W. (Branch of Isotope Geology)--------- 47 

Morgenson, L. A. (Branch of Pacific Marine Geology) - 28 

Morin, R. H. (Branch of Regional Research, WRD) ---- 53 

Moring, B. C. {Branch of Resource Analysis) ------ 25, 48 

Morton, J. L. (Branch of Pacific Marine Geology) --- 31, 49 

Mosier, E. L. {Branch of Geochemistry)------------ 50 

Mutschler, F. E -------------------------- 21 

N 

Nabelek, P. I ---------------------------- 30 

Nash, J. T. (Branch of Geochemistry) ------- 17, 51, 52 

81 

Nishi, J. M. (Branch of Central Mineral Resources)----- 1 

Nokleberg, W. J. (Branch of Alaskan Geology)------ 39 

Normark, W. R. (Branch of Pacific Marine Geology)---- 49 

0 

Ohlen, D. 0. (Branch of Applications, NMD) -------- 2 

Orris, G. J. (Branch of Resource Analysis)------- 2, 52 

Oscarson, R. L. (Office of Chief Geologist, Western Region) 48, 

75 

p 

Page, N. J (Branch of Resource Analysis)---- 6, 25, 48, 52 

Paillet, F. L. (Branch of Regional Research, WRD) ---- 53 

Pallister, J. S. (Branch of Igneous and Geothermal Processes) 54 

Payas, Alba----------------------- 59,62 

Pearson, R. C. (Branch of Central Mineral Resources) - 17 

Peper, J. D. (Branch of Eastern Mineral Resources)--- 22 

Phillips, J. D. (Branch of Geophysics)------------ 55 

Phil potts, J. A. (Branch of Geochemistry) ----------- 55 

Pickthorn, W. J. (Branch of Western Mineral Resources) 57 

Plouff, Donald (Branch of Geophysics) ----------- 52 

Podwysocki, M. (Branch of Geophysics)------- 31 

Ponce, D. A. (Branch of Geophysics) ------------ 52 

Pratt, W. P. (Branch of Central Mineral Resources)----- 17 

R 

Ratte, C. A -------------------------- 4 

Repetski, J. E. (Branch of Paleontology and Stratigraphy) 57 

Reynolds, R. L. (Branch of Sedimentary Processes) ---- 40 

Robbins, E. I. (Branch of Coal Geology) ----------- 58 

Rosenbaum, J. G. (Branch of Geophysics)--------- 40 

Rowan, E. L. (Branch of Geochemistry)------------- 7 

Rowan, L. C. (Branch of Geophysics) ----------- 59 

Rye, R. 0. (Branch of Isotope Geology) --------- 6, 38 

Rytuba, J. J. (Branch of Western Mineral Resources)---- 59 

s 

Sanford, R. F. (Branch of Sedimentary Processes)--- 60 

Sawyer, D. A. (Branch of Central Mineral Resources)- 40 

Schmidt, J. M. (Branch of Alaskan Geology)------- 33, 61 

Schmidt, R. G. (Branch of Eastern Mineral Resources) 58, 62 

Schoonmaker, J. W., Jr. (Branch of Analysis, WRD) --- 11 

Schruben, P. G. (Branch of Resource Analysis)------- 44 

Schulz, K. J. (Branch of Eastern Mineral Resources -- 52 

Schwab, W. C. (Branch of Atlantic Marine Geology)--- 28 

Selner, G. I. (Office of Mineral Resources)------- 63 

Senftle, Frank (Branch of Isotope Geology) ------- 45 

Senterfit, R. M. (Branch of Geophysics)---------- 21 

Severson, R. C. (Branch of Geochemistry) --------- 69 

Seyfried, W. E., Jr ------------------------ 75 

Shanks, W. C., III (Branch of Eastern Mineral 

Resources) -------------------- 35, 63, 77 

Sherman, D. M. (Branch of Igneous and Geothermal 

Processes) ------------------------------ 64 

Sidder, G. B. (Branch of Western Mineral Resources)-- 65 

Silberling, N. J. (Branch of Paleontology and Stratigraphy) 52 

Singer, D. A. (Branch of Resource Analysis) ---- 14, 15, 52 

Slack, J. F. (Branch of Eastern Mineral Resources) --- 66 

Smith, B. D. (Branch of Geophysics)------------- 31 

Smith, B. L. (Branch of Geochemistry)----------- 23 

Smith, D. B. (Branch of Geochemistry)------------- 71 

Smith, Fred ---------------------- 57 

Smith, R. L. (Branch of Igneous and Geothermal Processes) 18 

Snee, L. W. (Branch of Central Mineral Resources)----- 67 
Spirakis, C. S. (Branch of Sedimentary Processes) ------ 68 

Stanley, W. D. (Branch of Geophysics) ---------------- 74 

Stewart, J. H. (Branch of Western Mineral Resources) -- 52 

Stollenwerk, K. G. (Branch of Regional Research, WRD) 69 

Stoltz, M. L. (Branch of Resource Analysis) ----------- 44 

Strickler, M. D ----------------------------------·-- 75 

Sutphin, H. B. (Branch of Resource Analysis) ---------- 73 

Sutter, J. F. (Branch of Sedimentary Processes)--------- 28 

T 

Taylor, R. B. (Office of Mineral Resources) ------------ 63 

Thompson, Bill (Branch of Alaskan Geology) ---------- 33 

Tibbels, Dave-------------------------------------- 57 

Tidball, R. R. (Branch of Geochemistry) --------------- 69 

Tosdal, R. M. (Branch of Western Mineral Resources) -- 71 

Trautwein, C. M. (Earth Resources Observation System Data 

Center, NMD) ---------------------------------- 17 

Tripp, R. B. (Branch of Geochemistry) --------------- 50 

Tucker, R. E ------------------------------------- 1 

v 

Van Gosen, B. S. (Branch of Sedimentary Processes)---- 73 

Verbeek, E. R. (Branch of Central Regional Geology) -- 73 

Verga, Norma (Branch of Geophysics)------------- 59 

w 

Wanty, R. B. (Branch of Sedimentary Processes) ------- 71 

Watts, K. C., Jr. (Branch of Geochemistry)------------ 72 

Wenrich, K. J. (Branch of Sedimentary Processes)--- 21, 73 

Whitebread, D. H. (Branch of Western Mineral Resources) 52 

Whitlow, S. I. (Branch of Eastern Mineral Resources)--- 22 

Whitney, Gene (Branch of Sedimentary Processes) ----- 2 

Wilbanks, Larry ------------------------------- 57 

Williams, D. L. (Branch of Geophysics) ------------- 74 

82 

z 

Zientek, M. L. (Branch of Western Mineral Resources) 4, 75 

Ziernberg, R. A. (Branch of Western Mineral 

Resources) ---------------------------- 35, 61, 75 

nU.S. G.P.O. 1987-181-407:40062