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At least 433 records · Page 24Linked to original sources
USGS1952

Stratigraphic sections of the Phosphoria formation in Idaho (third Idaho report)

The first of a series of reports giving detailed stratigraphic sections of the Phosphoria formation in the Western phosphate field as measured and described by the Geological Survey will soon be published as Circulars. Because of the needs of industry for many of these data during the 1951 field season, and in view of the unavoidable delays attendant on publication, the tabular data to be included in five of these Circulars have already been placed on open file in simple reproduction form (prepared by Ozalid from photographic negatives) and without explanatory text so that early use could be made of the data. The first four sets of tables, one each for the states of Montana, Idaho, Wyoming, and Utah, were released on open file on August 15, 1951, A second Idaho report was released on October 4, 1951. This report includes data of the same character but of samples from different localities and is the third report on samples from Idaho. The tables include name and location of section measured, brief description of geologic setting, acknowledgments for field and analytical work, abstract data on the sections (bed number, rock name, sample number, and thickness), and analytical data on the samples. The analytical data include reports on P 2 O 5 and acid insoluble for all samples and additional analyses, such as Al 2 O 3 , Fe 2 O 3 , and loss on ignition for selected samples. These reports are placed on open file at the offices of the Geological Survey in Washinton, D. C., Spokane, Washington, Salt Lake City, Utah, and Montpelier, Idaho, and at the offices of the Idaho Bureau of Mines and Geology, Moscow, Idaho, the Montana Bureau of Mines and Geology, Butte, Montana, the Wyoming Geological Survey, Laramie, Wyoming, and the University of Utah, Salt Lake City, Utah.

Idaho↗
USGS1961

Dacitic ash-flow sheet near Superior and Globe, Arizona

Remnants of a dacitic ash-flow sheet near Globe, Miama, and Superia, Arizona cover about 100 square miles; before erosion the area covered by the sheet was at least 400 square miles and perhaps as much as 1,500 square miles. Its maximum thickness is about 2,000 feet, its average thickness is about 500 feet, and its original volume was at least 40 cubic miles. It was erupted on an eroded surface with considerable relief. The main part of the deposit was thought by early workers to be a lava flow. Even after the distinctive character of welded tuffs and related rocks was discovered, the nature and origin of this deposit remained dubious because textures did not correspond to those in other welded tuff bodies. Yet a lava flow as silicic as this dacite would be viscous instead of spreading out as an extensive sheet. The purpose of this investigation has been to study the deposit, resolve the inconsistencies, and deduce its origin and history. Five stratigraphic zones are distinguished according to differences in the groundmass. From bottom to top the zones are basal tuff, vitrophyre, brown zone, gray zone, and white zone. The three upper zones are distinguished by colors on fresh surfaces, for each weathers to a similar shade of light reddish brown. Nonwelded basal tuff grades upward into the vitrophyre, which is a highly welded tuff. The brown and gray zones consist of highly welded tuff with a lithoidal groundmass. Degree of welding decreases progressively upward through the gray and the white zones, and the upper white zone is nonwelded. Textures are clearly outlined in the lower part of the brown zone, but upward they become more diffuse because of increasing devitrification. In the white zone, original textures are essentially obliterated, and the groundmass consists of spherulites and microcrystalline intergrowths. The chief groundmass minerals are cristobalite and sanidine, with lesser quartz and plagioclase. Phenocrysts comprise about 40 percent of the rock, and their relative proportions are fairly uniform. Almost three-fourths of the phenocrysts are plagioclase, one-tenth quartz, one-tenth biotite, and the remainder sanidine, magnetite, and hornblende, with accessory sphene, zircon, and appetite. Pumice fragments are nearly equidimensional near the top of the sheet, and downward they become progressively more flattened until they finally disappear. The zones and the pumice fragment flattening ration (ratio of length to height) provide means for recognizing several faults within the sheet. Twelve new chemical analyses are nearly uniform in composition. If named according to chemical composition, the rock would be a quartz latite, but when named according to phenocrysts, it is a dacite. From the field occurrence and the interpretation of relict textures, it is concluded that the deposit is an ash-flow sheet containing large amounts of welded tuff, and that it was emplaced by a type of nuee ardente instead of a lava flow or air-fall shower. The nature of zoning and trend of flattening ratios indicate a series of eruptions in rapid enough succession for the sheet to form a single cooling unit. Except in the lower part of the sheet, original textures were obscured by devitrification and crystallization during cooling. Nearly uniform mineralogy and chemistry suggest a single magnetic source. A nearly circular area, about 3? miles in diameter, of altered dacite and earlier volcanic rocks, bounded by intricately faulted and brecciated older rocks, may be the site of a caldera that represents the source of the eruptions.

Open-File Report↗
USGS1972

Surficial geology of the Mount Tom quadrangle, Massachusetts

Movement of the last ice sheet in the Mount Tom quadrangle was due south during time of major advance as indicated by striations, drumlins, and indicator stones. Erratics of the Belchertown Tonalite, derived from the northeast portion of the Easthampton quadrangle, have been carried southward a distance of at least 16 miles. The presence of tonalite boulders on the summit of Mount Tom, elevation 1,205 feet, testifies to uplift of erratics through a vertical distance of 1,000 feet. Three tills are recognized on the basis of color, grainsize parameters, and location: (1) a reddish-brown sandy till occurs west of the Holyoke Basalt ridge, (2) a brown silty till lies east of the basalt ridge, and (3) a grayish-brown till-with intermediate grain size occurs in the Easthampton quadrangle and the north-central portion of the Mount Tom quadrangle. The three tills are the same age and are equivalent to the upper till of southern New England. During deglaciation, readvance occurred from the northeast over a minimum distance of 3.5 miles in the southeast portion of the quadrangle. Evidence for readvance consists of (1) till over stratified drift, (2) southwest-oriented till fabrics on south-trending drumlins, (3) west-southwest-trending striations cutting south-trending striations, (4) southwest-oriented glaciotectonic structures, and (5) data from borings. West of the basalt ridge, northward retreat of an active ice margin was punctuated by four stillstands, during which outwash deltas were deposited in proglacial lakes. From oldest to youngest the deposits associated with the four stillstands are named: (1) Paper Mills delta, (2) Barnes delta, (3) Pomeroy Street delta, and (4) White Brook delta. East of the basalt ridge a series of small ice-contact deltas were deposited in high proglacial Lake Hitchcock, which expanded northward with the retreating ice margin. Deposition culminated along the upper east margin of the quadrangle with the formation of a large ice-contact delta named the Holyoke delta. Continued northward retreat of the ice margin both east and west of the basalt ridge permitted water of Lake Hitchcock to extend through the Holyoke Narrows and into the valleys of the Manhan River and Broad Brook in the north-central portion of the Mount Tom quadrangle. Drainage of Lake Hitchcock 10,700 years ago (Flint, 1956) initiated rapid downcutting by streams, as shown by numerous stream terraces along the Connecticut, Westfield, and Manhan Rivers, and along lesser tributaries.

Open-File Report↗
USGS1976

Laboratory manual: mineral X-ray diffraction data retrieval/plot computer program

The Mineral X-Ray Diffraction Data Retrieval/Plot Computer Program--XRDPLT (VanTrump and Hauff, 1976a) is used to retrieve and plot mineral X-ray diffraction data. The program operates on a file of mineral powder diffraction data (VanTrump and Hauff, 1976b) which contains two-theta or 'd' values, and intensities, chemical formula, mineral name, identification number, and mineral group code. XRDPLT is a machine-independent Fortran program which operates in time-sharing mode on a DEC System i0 computer and the Gerber plotter (Evenden, 1974). The program prompts the user to respond from a time-sharing terminal in a conversational format with the required input information. The program offers two major options: retrieval only; retrieval and plot. The first option retrieves mineral names, formulas, and groups from the file by identification number, by the mineral group code (a classification by chemistry or structure), or by searches based on the formula components. For example, it enables the user to search for minerals by major groups (i.e., feldspars, micas, amphiboles, oxides, phosphates, carbonates) by elemental composition (i.e., Fe, Cu, AI, Zn), or by a combination of these (i.e., all copper-bearing arsenates). The second option retrieves as the first, but also plots the retrieved 2-theta and intensity values as diagrammatic X-ray powder patterns on mylar sheets or overlays. These plots can be made using scale combinations compatible with chart recorder diffractograms and 114.59 mm powder camera films. The overlays are then used to separate or sieve out unrelated minerals until unknowns are matched and identified.

Open-File Report↗
USGS1976

Earthquake prediction studies in Southern California: Research in progress, June 1976

The report of an uplift of the ground of up to 0.25 meters over at least 12,000 square kilometers of southern California (Castle, Church, and Elliott, 1976, Science, 192, pages 251-253) has increased significantly the interest in earthquake prediction studies in this region. A substantial increase in research is planned, particularly by the U.S. Geological Survey and its many contractors and by the California Division of Mines. The purpose of this report is to briefly summarize most of the work in progress to encourage communication among the wide variety of researchers and to assist all present or prospective researchers in this region to understand what work is underway and not yet published. Information in this report was collected primarily in response to a brief questionnaire. Some researchers did not respond and some may not have received copies of the questionnaire. Thus this report is not complete but we believe it summarizes the vast majority of research in progress. Any additions or corrections should be sent to the editor. The first name listed under each project is the person doing the most work on the project. The principal investigator, when not the first person on the list of names, is denoted by an asterick. Funding for the research listed comes primarily from the U.S. Geological Survey, National Science Foundation, and the State of California.

California↗
USGS1976

Mineral resources of Elko County, Nevada

Of the 66 named mining districts in Elko County, 56 have been productive of one or more of 19 different commodities: 11 metals--copper, gold, silver, lead, zinc, mercury, tungsten, manganese, iron, uranium, and antimony; 8 nonmetals--sand and gravel, stone, barite, diatomite, gems, oil shale, volcanic ash, and clay. In addition to the commodities produced, at least 5 others--beryllium, molybdenum, tin, phosphorite, and petroleum, occur in amounts sufficient to warrant exploration. The other districts have been explored, but no production has been recorded. Total value-when-sold of production recorded through 1969 was nearly $91 million; actual production was considerably greater, especially if sand and gravel, barite, and other nonmetallic products before 1953 are included. In value of metals produced, the five highest districts are Mountain City ($26 million), Tuscarora ($11 million), Jarbidge ($10 million), Aura ($6 million), and Railroad (nearly $5 million). The Rio Tinto copper mine in the Mountain City district yielded $21 million. Of the 17 districts that produced nonmetallic minerals, Bootstrap .is the largest producer, containing the Rossi mine, one of the two largest barite mines in the United States. Most of /he metals produced name from veins and replacement deposits in limestone or dolomite near granitic stocks; exceptions are manganese and mercury, which are not associated with known or inferred stocks; mercury is further excepted because it occurs in volcanic rocks, as do a few deposits of the major metals. The largest deposit--the Rio Tinto lode--was a combination of fissure filling and replacement along a bedding plane shear zone 150 ft wide and 1,200 ft long in carbonaceous shale of the Valmy Formation; this deposit is apparently older than the Mountain City stock and its mineralization may be related to Paleozoic mafic volcanism later than a major thrust fault, inferred to underlie the area at a depth of about 5,000 ft. Most of the nonmetallic minerals mined were sedimentary bedded deposits, but mica was mined from pegmatite deposits, and turquoise from both placer and hydrothermal deposits. The largest known reserves of metals (1973) are of porphyry copper in the Dolly Varden district and gold in the Bootstrap district. Reserves of barite also are presumed to be large. The greatest potential for future production of metals, notably copper and gold, appears to be in the known districts or extensions of them and peripheral to deposits that are related to known or concealed plutons and thrust faults. Potential resources in deposits too low in grade to be worked profitably at the present time include all commodities that have been produced and, in addition, known, deposits of beryllium, molybdenum, tin, and phosphorite. Speculative resources in undiscovered deposits may reasonably be predicted to include all known commodities as well as others that are unsuspected. Petroleum may yet be produced from the Elko Formation and geothermal energy from the Ruby Valley and Elko areas.

Open-File Report↗
USGS1976

Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Fairbanks Quadrangle, Alaska

For each mineral occurrence there is a page that gives the name of the occurrence; the mineral commodities present (listed alphabetically for metallic commodities and then for nonmetallic commodities); the mining district (Ransome and Kerns, 1954) in which the occurrence is located; the name of the 1:250,000-scale topographic quadrangle (Fairbanks); coordinates (as described by Cobb and Kachadoorian, 1961, p. 3-4); the metallic mineral resources map number (KF-410) and the occurrence number on that map if the occurrence is shown; and the latitude and longitude of the occurrence. These data, presented at the top of the page, are followed by a short, general summary of the published information on the occurrence. This is followed (continued on additional pages, if necessary) by more detailed summaries, arranged chronologically, of all references to the occurrence. Material in brackets is interpretive or explanatory and is not in the summarized reference.

Alaska↗
USGS1978

Stratigraphy of the Cache Formation (Pliocene and Pleistocene) in Clear Lake Basin, Lake County, California

Recent geologic mapping in the Clear Lake basin shows that the nonmarine Cache Formation can be subdivided into several members. New names are herein informally used for three distinct deposits called the B, L, and K members. The three members are geographically separate, except where the L member locally unconformably overlies the B member. This study of the Cache Formation provides a framework for understanding the late Cenozoic tectonic, geologic, and climatic histories of the Clear Lake, California, area. The B member is characterized by cross-stratified sandstone with interbedded reddish-brown conglomerate around the margins of the basin, and by gray sandstone and persistent, light-olive-gray conglomerate lower in the section, as it is exposed in the center of the basin. Minor amounts of basaltic tuff are present near the top of the B member in the Clear Lake basin. The B member has a maximum thickness of at least 1,500 m and represents dominantly fluvial and minor lacustrine deposition. This Blancan (Pliocene and early Pleistocene(?)) unit was deposited in a fault-controlled, subsiding basin. The L member is a heterogeneous deposit of pebble conglomerate, sandstone, siltstone, calcareous siltstone, limestone, tuff, and diatomite. This lacustrine unit has a maximum thickness of at least 130 m, and is mid-Pleistocene in age. The K member is composed of lacustrine sandstone and siltstone, and locally interbedded fluvial pebble conglomerate and sandstone. Several tuffs, including the tuff of Adobe Creek, an informally named marker bed, occur in the K member. The K member has a maximum thickness of at least 140 m and is mid-Pleistocene in age. The presence of fossil leaves and cones that represent growth during warm and cold climates indicate that the K member was deposited during both interglacial and glacial climatic conditions. The tuff of Adobe Creek of the K member has been recognized in water wells west and north of surface exposures of the K member. The B member is probably correlative with the Tehama Formation and is apparently unrelated to the sediment of Clear Lake. The L and K members intertongue with and are underlain by flows of the Clear Lake Volcanics. The L and K members are dominated by partly coeval lacustrine deposits that were possibly deposited in different subbasins of the same lake, and are possibly correlative with sediment concealed beneath Clear Lake.

California↗
USGS1979

Nebraska water-data programs, 1979

This report contains descriptions of 37 projects of the U.S. Geological Survey and of State agencies represented on the Nebraska Water Data-Coordination Committee. The descriptions include title, name of project leader, agency or agencies involved, statements of the problems and objectives, reports resulting from the project, and plans for 1979. Sources of water-related information are given with names, addresses, and telephone numbers. Also given is a list of selected, relatively recent publications pertaining to Nebraska. Appendices include current measuring sites for streamflow, water quality, and ground-water levels; an index to published streamflow records; a list of flood-prone area maps for Nebraska; and a list of communities participating in the Federal Insurance Administration (FIA) flood-insurance program. (Kosco-USGS)

Open-File Report↗
USGS1979

Organic carbon content of Devonian shale sequence sampled in drill cuttings from eighteen wells in western Pennsylvania

This report contains results of organic carbon analyses performed by Rinehart Laboratories, Inc., Arvada, Colorado, under contract to the U.S. Geological Survey. The analytical method employs chemical (chromic acid) oxidation of an acid solution containing the rock residue. The detailed analytical specifications are contained in the Rinehart proposal in response to request for proposal 76-79 issued by the U.S. Geological Survey. The samples analyzed were furnished by John W. Hosterman, U.S. Geological Survey, Reston, Virginia, who has performed clay mineralogical analyses on splits of these same samples. In the following tabulation, samples are listed by the depth interval (in feet) over which the drill cuttings were collected. Organic carbon values are single determinations except where two values (duplicate analyses) are given. Each well is identified by county, well name, and API number. An estimate of the shallowest occurrence in the well of some named stratigraphic units has been inserted after the sample depth. These analyses were performed as a part of the U.S. Geological Survey Eastern Black Shales Program, which is being pursued in cooperation with the U.S. Department of Energy under the Eastern Gas Shales Project.

Pennsylvania↗
USGS1979

1980 water quality laboratory services catalog

The information in this catalog is provided to assist Water Resources Division personnel in the selection of analytical determinations, estimation of cost, calculation of sample volume requirements, identification of the necessary sample treatment, and selection of laboratory precision for samples to be submitted to Central Laboratories. The catalog contains 18 tables. Tables 1-4 are arranged alphabetically by constituent or schedule, and where available, include parameter name, unit of measurement, lab code or schedule code, applicable range and precision of the method, parameter code, method number and name, and a page index. Tables 1 and 2 list inorganic and organic constituents determined in water samples, table 3 provides information on determinations of chemical and physical properties of sediments, and table 4 lists biological determinations. Page references in these first four tables refer to the tables of determinations (tables 5 through 8) or to the tables of calculations (tables 9 through 12). Constituents that are found in more than one category are cross-referenced (e.g. nitrogen, organic is found in the inorganic table and is cross indexed in the organic table). Tables 13 through 16 list sample containers, sample preservations, and sample designations for each determination. Table 17 lists materials (bottles, preservatives, standardized solutions, and so forth) which may be purchased from the Central Laboratories. Table 18 lists agency codes which can be used to indicate the agency collecting or analyzing samples. Although the catalog is being released now, its effective date is September 11, 1979 to September 10, 1980. The early release is for program planning only.

Open-File Report↗
USGS1981

Western hemisphere strong-motion accelerograph station list, 1980

This list contains information on western hemisphere strong-motion stations that have been installed and are maintained by many different organizations. It contains information on all of those stations for which there is some data in the files of the USGS, but the list is incomplete even for stations in the United States. Since the stations being maintained are continuously changing, it is impossible to have complete information about all of the stations at any one time. The objective is to provide the community of persons who have an interest in strong-motion programs an indication of the current status of the networks in this part of the world. The USGS also maintains a computerized Strong Motion Information Retrieval System (SMIRS) which permits searching for various types of information about the strong motion stations, records, and events (Converse, 1978). In general, the information in SMIRS is more current than the information in this list. For convenience, the list has been arranged by country, north to south, alphabetically by states in the section for the United States, and then alphabetically by station name. Subsequent sections include a list by stations numbers, a cross-reference of obsolete station names, a cross-reference of station numbers as assigned by other agencies, and a cross-reference of three character designations for those that find that form of station designation useful. A list of the stations that were installed as required by a local building code or that are maintained by the owner of the facility appears in the Appendix. That list has not been updated since 1976 at which time the USGS stopped receiving information about new installations required by building codes.

Open-File Report↗
USGS1981

E-field ratio telluric survey near the Big Maria Mountains, Riverside County, California

The U.S. Geological Survey (USGS) under the Wilderness Act (Public Law 88-577) and the Federal Land Policy and Management Act (Public Law 94-579) has the responsibility, along with the U.S. Bureau of Mines, to survey certain areas in order to determine their mineral resource potential. This report presents results of three electric-field ratio telluric traverses conducted as part of the Bureau of Land Management Wilderness Program in the Big Maria Mountains, Riverside County, Calif. The telluric traverses were run on the southwest side of the Big Maria Mountains in an attempt to define the location of major buried faults near the eroded front of the range. E-field ratio tellurics is a descriptive name applied to the electrical exploration technique used in this survey. The telluric method refers to the measurement of the earth's electric field generated by induction from natural electromagnetic waves arriving at the surface. The E-field ratio telluric method uses a receiving array of three electrodes spaced equidistant and inline. This array is, in effect, two colinear dipoles sharing a common electrode. The potential difference across each dipole is then proportional to the component of the telluric field in the direction of the array. This configuration permits the measurement of the ratio of the telluric field at each dipole in the direction of the dipole line, and hence the name. The traverse data is extended by moving the three-electrode array forward one dipole length so that the forward electrode becomes the center electrode for the next ratio measurement. Electric-field data so obtained are proportional to the square root of the apparent resistivity of the earth at the location of the dipoles. However, because the apparent resistivity can be a function of the dipole direction, it is important to know the orientation of the dipoles with respect to major structures. Because the resistivity of fluid-saturated earth materials is largely dependent on the porosity of the rocks, the salinity of the pore fluid, and the presence of clays or similar material where surface conduction is high, alluvial fill, argillite and similar rocks tend to have low resistivities whereas igneous or high-grade metamorphic rocks have high resistivities. Variation in the electrical properties along a traverse may then be used to infer lithologic or structural changes.

California↗
USGS1983

Drainage-area data for Wisconsin streams

Drainage areas were determined for more than 7,000 sites in Wisconsin's 11 major river basins, including all named streams draining 5 or more square miles, and all unnamed streams draining 10 or more square miles. Also determined are drainage areas for gaging stations, sewage-treatment plants, dams, major highway crossings, and other sites where discharge measurements or water-quality data are available. Drainage areas were delineated on U.S. Geological Survey topographic maps. Drainage areas are shown in tabular form under six headings: station number; stream name, rank, and location; township, range, and section; county; type of site; and drainage area. Eleven major-river-basin maps show the location and station number of key sites.

Wisconsin↗
USGS1984

State hydrologic unit maps

A set of maps depicting approved boundaries of, and numerical codes for, river-basin units of the United States has been developed by the U.S. Geological Survey. These ' State Hydrologic Unit Maps ' are four-color maps that present information on drainage, culture, hydrography, and hydrologic boundaries and codes: (1) the 21 major water-resources regions and the 222 subregions designated by the U.S. Water Resources Council; (2) the 352 accounting units of the U.S. Geological Survey 's National Water Data Network; and (3) the 2,149 cataloging units of the U.S. Geological Survey 's Catalog of Information on Water Data. The maps are plotted on the Geological Survey State base-map series at a scale of 1:500,000 and, except for Alaska, depict hydrologic unit boundaries for all drainage basins greater than 700 mi squared (1,813 km squared). A complete list of all the hydrologic units, along with their drainage areas, their names, and the names of the States or outlying areas in which they reside, is contained in the report. These maps and associated codes provide a standardized base for use by water-resources organizations in locating, storing, retrieving, and exchanging hydrologic data. The Hydrologic Unit Codes shown on the maps have been approved as a Federal Information Processing Standard for use by the Federal establishment. (USGS)

Open-File Report↗
USGS1985

Drainage areas in the Big Sioux River basin in eastern South Dakota

The Big Sioux River basin of eastern South Dakota contains an important surface water supply and a sizeable aquifer system of major importance to the economy of South Dakota. The aquifers are complex, consisting of many small aquifers that are hydrologically associated with several large aquifers and the Big Sioux River. The complexity and interrelation of the surface water/groundwater systems has already created management problems. As development continues and increases, the problems will increase in number and complexity. To aid in planning for future development, an accurate determination of drainage areas for all basins, sub-basins, and noncontributing areas in the Big Sioux River basin is needed. All named stream basins, and all unnamed basins > 10 sq mi within the Big Sioux River basin in South Dakota are shown and are listed by stream name. Stream drainage basins in South Dakota were delineated by visual interpretation of contour information shown on U.S. Geological Survey 77-1/2 minute topographic maps. One table lists the drainage areas of major drainage basins in the Big Sioux River basin that do not have a total drainage area value > 10 sq mi. Another shows the drainage area above stream gaging stations in the Big Sioux River basin. (Lantz-PTT)

Open-File Report↗
USGS1986

Geological and geochemical data for seamounts and associated ferromanganese crusts in the Ratak Chain, Marshall Islands

In 1984, the U.S. Geological Survey (USGS) conducted a reconnaissance cruise L9-84-CP aboard the R/V S.P. LEE along the northern Ratak Ridge, Marshall Islands (Fig. 1). Preliminary geochemical results from the cruise show that ferromanganese crusts (Mn crusts) on the submarine slopes of seamounts, and islands may have potential for commercial exploitation (Schwab and others, 1985). In this report we present shipboard data and laboratory analyses for rock samples collected on cruise L9-84-CP. This report should supplement the reports of Schwab and Bailey (1985) and Schwab and others (1985). A total of 5410 km of 12-kHz and 3.5-kHz seismic-reflection data, and q O 730 km of 80-in 3 and 148-in 3 airgun seismic-reflection data were collected on cruise L9-84-CP (Schwab and Bailey, 1985). Eighteen sample stations were occupied; 13 dredge hauls and 3 box cores were collected (Table 1). These samples are available at the USGS Branch of Pacific Marine Geology offices in Menlo Park, California. Data presented in this report should encourage a more extensive field investigation and serious economic and technical evaluation of Mn crusts within the Marshall Islands area. Ferromanganese-oxide precipitates that encrust hard substrate on the submarine flanks of seamounts, guyots, atolls, islands, and linear volcanic ridges, have been known for several decades (Cronan, 1977; Frazer and Fisk, 1980) but were not studied in a systematic way until the West German MIDPAC expedition of 1981 (Halbach and others, 1982). Unlike abyssal ferromanganese nodules, Mn crusts contain higher concentrations of the economically attractive metals, cobalt and platinum (Toth, 1980; Craig and others, 1982; Halbach and others, 1984; Hein and others, 1985). Mn crusts are predominantly hydrogenous in origin, in contrast to abyssal ferromanganese nodules which also have a substantial diagenetic input (Halbach and others, 1981). In order for a Mn crust deposit to be economically attractive, it must be of high grade in recoverable metals, thick, and aerially extensive. During a 1984 workshop in Honolulu, East-West Center, engineers and geologists determined that Mn crusts must have an average thickness of 4 cm and a cobalt content greater than 0.8 percent of the dry weight (8000 ppm) to be considered for exploitation. The metals other than cobalt that are likely to be recovered from such a deposit include nickel, manganese, zinc, lead, phosphorous, and platinum. Preliminary chemical analyses of the Mn crusts collected during cruise L9-84-CP (Schwab and others, 1985) show that the average concentrations of metals within them are comparable with the mean metal contents of Mn crusts from the eastern Mid-Pacific Mountains and northern Line Islands Ridge, areas of high economic potential (Halbach and Manheim, 1984; Hein and others, 1985). Based on the extent of sea floor above 2400 m water depth and the age of the substrate, resource experts at the East- West Center in Honolulu placed the Marshall Islands as second in economic potential for Mn crusts as compared to the Mn crust resources within all other U.S. Pacific states, trust territories, and possessions (A.L. Clark, personal communication). Based on these and other geologic and oceanographic criteria, Hein and others (1986a) placed the Marshall Islands first with respect to U.S. interests. For convenience, several previously unnamed seamounts have been named (see Hein and others, 1986b), including Erikub Seamount, Utirik Seamount, Bikar Guyot, and Ratak Guyot. We use these names informally in this report.

Open-File Report↗