John C. Wiltshire

Major off-axis hydrothermal activity on the northern Gorda Ridge

The first hydrothermal field on the northern Gorda Ridge, the Sea Cliff hydrothermal field, was discovered and geologic controls of hydrothermal activity in the rift valley were investigated on a dive series using the DSV Sea Cliff. The Sea Cliff hydrothermal field was discovered where predicted at the intersection of axis-oblique and axis-parallel faults at the south end of a linear ridge at mid-depth (2700 m) on on the east wall. Preliminary mapping and sampling of the field reveal: a setting nested on nearly sediment-free fault blocks 300 m above the rift valley floor 2.6 km from the axis; a spectrum of venting types from seeps to black smokers; high conductive heat flow estimated to be equivalent to the convective flux of multiple black smokers through areas of the sea floor sealed by a caprock of clastic breccia primarily derived from basalt with siliceous cement and barite pore fillings; and a vent biota with Juan de Fuca Ridge affinities. These findings demonstrate the importance of off-axis hydrothermal activity and the role of the intersection of tectonic lineations in controlling hydrothermal sites at sea-floor spreading centers.

Manganese tailings: Useful properties suggest a potential for gas absorbent and ceramic materials

The proper disposal of material left over from marine ore processing poses a serious environmental problem. Areas in which these minerals are found have limited landfill capacity, and disposal at sea is considered to be damaging to the marine environment. Recycling tailings would help to solve this disposal problem and add to the economic benefits from marine mining operations. To this end, tailings typical of Mn‐ores have been characterized, gas adsorption measured, and a series of manganese borosilicate glasses and glazes have been developed from these materials. Over 300 different glasses and glazes have been successfully formed from melts in the temperature range of 1,100–1,300°C.

Hydrothermal activity on the Gorda Ridge

Near-bottom plumes of materials indicative of discharge of metal-rich hot springs were discovered at sites on the Gorda Ridge by a research team of government and university scientists on a cruise of the National Oceanic and Atmospheric Administration (NOAA) ship Surveyor during May 1985 as part of the NOAA Vents Program. The Gorda Ridge, off northern California and Oregon, is the only seafloor spreading center within the proclaimed 200-mile U.S. Exclusive Economic Zone (370 km wide) of the conterminous United States and is one of the last oceanic ridges to be explored for metal-rich hot springs. One reason for this neglect is that the Gorda Ridge is slow spreading, with half-rates ranging from 1.1 cm/yr in the southern portion to 2.2 cm/yr in the northern portion. Slow spreading centers have not been fully evaluated with regard to hydrothermal activity by many members of the research community, who have concentrated their attention on the faster spreading East Pacific Rise to the south and the Juan de Fuca Ridge to the north of the Gorda Ridge.

Ferromanganese crusts near Johnston Island : Geochemistry, stratigraphy and economic potential

The 200-mi exclusive economic zone (EEZ) around Johnston Island, 700 mi west of Hawaii, contains economically attractive concentrations of cobalt, nickel, platinum, and rare earth elements contained in manganese crusts on the surface of seafloor plateau areas. Detailed mineralogy and geochemistry reveal these deposits to be largely hydrogenous in origin although also containing elemental additions due to biological, weathering, hydrothermal, detrital, and diagenetic processes. The major mineralogical phase is vernadite (delta manganese dioxide) laid down in strataform crustal deposits. The most valuable metal, cobalt, shows concentrations highest in the upper layers of the crusts and decreasing with stratigraphic depth. Upcoming submersible dives will fully document the significance of this deposit.

The use of marine manganese tailings in industrial coatings applications

The disposal of tailings from a future manganese nodule or crust mining operation will be an environmental challenge. However, these manganese tailings can be used for a variety of beneficial uses. One of the major applications which shows great promise is in industrial coatings. Four areas of experimentation were undertaken. All experimental coatings were made by adding measured amounts of tailings to selected chemical carriers. The resulting mixtures were applied to wood, metal and concrete. Four kinds of coatings were tried: those for rust-resistance, termite resistance, antibiofouling and undercoating (including high temperature automotive undercoats). The coatings were applied by brush, roller and in one case sprayed. The coatings went on well and imparted a series of very useful qualities, including hardness, rust resistance and an even matte finish. The useful coatings properties can be traced back to the chemical composition of the tailings. These beneficial properties are derived from the highly oxidized state of the manganese, the chemical nature of manganese (which preferentially scavenges and tightly binds other elements), the small angular grain size of the particles, the metallic nature of the resulting coatings and the fact that manganese has a repelling effect on organisms.

Mineralogy and geochemistry of ferromanganese crusts from Johnston Island EEZ

A total of 1360 kg of ferromanganese crust bearing samples were collected from 10 sites in the Karin Seamount Range and Kell Ridge of Johnston Island exclusive economic zone on a recent cruise of University of Hawaii research vessel Kaimikai-O-Kanaloa. Sixty eight ferromanganese crust samples and subsamples were analyzed mineralogically and chemically for 36 elements. The crusts are dominantly composed of vernadite (manganese dioxide). They are rich in Co (0.88%) and rare earth elements and poor in Cu (0.1%). They show a significant Ce anomaly and have a low Mn/Fe ratio. This is characteristic of marine hydrogenous Mn-Fe oxides. The rare earth element content of Johnston Island ferromanganese crusts is very close to the grades of land-based rare earth element deposits currently mined in China. There are two growth styles of crust. The first is as a spherical crust around loose debris. The second is as a sheet-like crust on the outcropping rock of the seamount. There are chemical and mineralogical differences between these two growth styles. The spherical crusts exhibit a smooth surface structure in the upper Mn-Fe layers. This upper area is chemically richer in Mn, Co, Ni, Ca and P than the lower part of the crust which is richer in Si and Al. The lower part has a rough surface structure. The sheet-like crust growth style exhibits a Co content which increases from the substrate to the crust surface. The compositional variation is mainly controlled by reaction between substrate and seawater. R-mode factor analysis was performed on the samples. Eighty percent of variance can be described by four factors. Factor 1, the trivalent rare earth element factor, with 36% of the variance is assumed to represent hydrogenous mineralization of Mn-Fe oxides, particularly incorporating rare earths. Factor 2 with 23% of the variance has a strong positive lending associated with Mn, Fe, Co, Ti and a strong negative loading associated with Ca and P. It is also a hydrogenetic meter and indicates an inverse relationship between ferromanganese oxides and calcium phosphate growth. Factor 3 with 13% of the variance has negative loadings on Ni, Cu, Cd, Mg and Zn. It may be a submarine weathering factor or indicate a hydrothermal input. Factor 4 with 7% of variance has strong positive loading for Si and Al. It is an aluminosilicate detrital mixing factor. Apart from scientific interest, the flat topography and high cobalt and rare earth content of this area make it an excellent candidate for potential mining in the next century.

Innovative tailings management for marine ferromanganese nodule and crust processing

Three factors have significantly increased the likelihood that manganese nodule and crust resources will be mined in the near future. These are (i) the legal clarification provided by the Law of the Sea Treaty now in full effect, (ii) the rapid economic growth in East Asia and (iii) the sharp rise in world cobalt prices. The Chinese Ocean Mining Company has announced plans to begin mining and is looking at joint venture possibilities with American companies. One of the major concerns with marine mining development is environmental. Current studies show 80% of the environmental effect to be associated with ore processing, particularly tailings disposal. New work indicates that tailings from proposed hydrometallurgical processing can be made into useful construction products. These include tiles, ceramics, coatings, resin castings for plumbing fixtures, additives to strengthen concrete, stack gas cleaners, rust-proofing and antibiofouling coverings. The economics of such a venture look favorable to the point that costs of tailings disposal should be zero or cash-generating on the basis of revenues from tailings products. This approach is an innovative strategy for tailings management and reduces potential environmental damage associated with marine mining.

Innovative Trends in Marine Management: Hawaii's Manganese Crust Work Group

In spite of tight funding, Hawaii has been the location of a number of innovative ocean technologies. These have been facilitated by the coordination of university researchers, industry representatives, Federal agencies, and State officials. An excellent example of this new trend in marine management is the recently formed Joint State-Federal Manganese Crust Work Group. Funded by the U.S. Department of the Interior, this group will oversee the writing of an EIS for a proposed manganese crust lease sale in the Hawaiian Archipelago and act as a forum for the consideration of the many complex issues surrounding ocean mining. The Work Groups success stems from its open dialogue with all concerned groups and its emphasis on an adequate research base.

Composition and Useful Properties of Tailings of Marine Manganese Nodules and Crusts

ABSTRACT Marine manganese nodules and crusts, when processed, yield tailings which may be utilized for environmental and economic benefit. The key to the reasonable and effective utilization of these tailings lies in making a systematic appraisal of their composition and properties. This article gives an introduction to the investigation of manganese tailings properties. The tailings have a high iron and/or manganese content, high surface area, high porosity, and fine grain size. Some tailings have a high rare earth element content which is valuable. They may also have high SO3, arsenic, and uranium contents which are harmful. Depending on the process used to produce the tailings, there will likely be some differences in chemical composition, mineral assemblages, surface area and adsorption capability, pore diameter and volume, density and pH. In assigning potentially beneficial applications for these tailings, these differences should be taken into account to optimize utilization.

Marine mineral tailings use in anticorrosive coatings

A new type of water-dispersive anticorrosive paint was prepared by using marine cobalt-rich crusts tailings which are the residue of cobalt-rich manganese crusts after the extraction of Co, Ni, Cu, Zn, Mn by acid leach. The first step making the paint is preparing the colored slurry by mixing the tailings (54.65%, mass) with water (40.78%) and some auxiliary materials (4.57%). The second step is mixing the colored slurry (40%) with a styrene-acrylate copolymer (40%), water (11.9%) and some auxiliary materials (8.1%). Test results indicate that the resistance to impact of the coating film is equal to or more than 490 Nmiddotcm, the resistance to saline water is more than 24 days. The tailings can provide both physical and chemical corrosion protection. With their fine particle size the tailings can be dispersed into the styrene-acrylate copolymer to form a uniform coating film with relatively high bonding strength on surfaces to be protected. With a high Fe2O3 content the tailings provide physical cladding. With a high content of Sr and other trace elements the tailings can react with corroded ferrite or with other corrosive materials, such as S04 2-, to form unreactive oxides or inert compounds. In this way, the tailings serve as chemical preservation agents. P2O5 contained within the tailings may combine with metallic elements or may react with polar groups in the styrene-acrylate copolymer to form stable complex compounds to keep corrosion from developing. Oxidizing and reducing properties of rare earth elements may accelerate the formation of a polymer network of coating molecules and shorten both the solidifying and film-forming times for the coating. The tailings also likely enhance the strength and water resistance of the resultant coatings.