U.S. Geological Survey Marine-Minerals Research

The U.S. Exclusive Economic Zone is an area approximately one and two-thirds the size of the land area of the United States. In this frontier area, U.S. Geological Survey (USGS) research in marine minerals is aimed at three objectives: (1) defining geologic settings of potential mineral resources, (2) understanding the processes by which sea-floor nonliving resources form, and (3) estimating the resource potential. Potential resources of primary interest are cobalt-rich manganese sea-floor crusts, polymetallic sulfides in hydrothermal vent areas on the sea floor, and heavy-mineral placer deposits. Research activities include studies of manganese-crust samples from oceanographic-institution archives and a USGS research cruise through the central and southern Pacific. Preliminary results confirm that cobalt is concentrated by as much as 2.5 percent in the manganese crusts at water depths of 1,000-2,600 meters; further research on the precipitation processes and patterns of crust formation will be needed to understand the origin, occurrence patterns, and resource potential of these crusts. Research cruises have revealed a zone of polymetallic sulfide vent deposits a few hundred meters long in the Juan de Fuca spreading center. In September-October 1984, 15 ALVIN dives are scheduled for closeup study of the vent deposits, which will be compared with onshore massive-sulfide deposits. Other cruise data suggest that sulfides should be present in the sediment-filled axial trough of the Gorda Ridge.