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L.A. Morgenson

Publications and source records attributed to L.A. Morgenson.

4 recordsLinked to original sources
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↗
USGS1982

Uranium and thorium enrichment in rocks from the base of DSDP Hole 465A, Hess Rise, central North Pacific

Uranium and thorium are concentrated in Cretaceous limestone, chert, ash, basalt, and other rock types at Deep Sea Drilling Project Site 465 located on the southern Hess Rise in the central North Pacific. U concentrations, up to 194 ppm on a carbonate-free basis, are among the highest recorded for any deep-sea deposits. U was initially derived from seawater and concentrated by absorption on terrigenous (humic) organic matter in limestone in a shallow marine environment. U and Th were probably concentrated further by low-temperature hydrothermal fluids emanating from the basaltic basement. Mainly montmorillonite, an alteration product of basalt and ash, and organic matter in sedimentary rocks acted as hosts for U and Th. The unique combination of sediments rich in humic organic matter, abundant smectite in altered ash and basalt, and warm hydrothermal solutions provided the necessary conditions for migration and concentration of U and Th. To better understand the conditions limiting the migrating and concentration of U and Th, other rocks deposited during the ocean-wide Cretaceous anoxic events should be analyzed for these elements. ?? 1982.

Chemical Geology↗