118 » Marine Minerals: Exploring Our New Ocean Frontier 



• Bathymetric profiling yields detailed informa- 

 tion about water depth, and hence, of seabed 

 morphology. 



• Midrange side-looking sonars provide acous- 

 tic images similar to long-range sonars, but 

 of higher resolution. 



• Seismic reflection and refraction techniques ac- 

 quire information about the subsurface struc- 

 ture of the seabed. 



• Magnetic profiling is used to detect and char- 

 acterize the magnetic field. Magnetic traverses 

 may be used offshore to map sediments and 

 rocks containing magnetite and other iron-rich 

 minerals. 



• Gravity surveys are used to detect differences 

 in the density of rocks, leading to estimates of 

 crustal rock types and thicknesses. 



• Electrical techniques are used to study resis- 

 tivity, conductivity, electrochemical activity, 

 and other electrical properties of rocks. 



• Nuclear techniques furnish information about 

 the radioactive properties of some rocks. 



Many of these reconnaissance technologies are 

 also useful for more detailed studies of the seabed. 

 Most are towed through the water at speeds of from 

 1 to 10 knots. Hence, much information may be 

 gathered in relatively short periods of time. It is 

 often possible to use more than one sensor at a time, 

 thereby increasing exploration efficiency. Data sets 

 can be integrated, such that the combined data are 

 much more useful than information from any one 

 sensor alone. Generally, the major cost of offshore 

 reconnaissance is not the sensor itself, but the use 

 of the ship on which it is mounted. 



At still closer ranges, several other remote sens- 

 ing techniques and technologies become useful. 

 Short-range, higher frequency side-looking sonars 

 provide very high resolution of seafloor features at 

 a range of 100 meters (328 feet)' and less. At less 

 than about 50 meters in clear water, visual imag- 

 ing is often used. Photographs or videotapes may 

 be taken with cameras mounted on towed or low- 



'Many geophysical and geological measurements are commonly ex- 

 pressed in metric units. This convention will be retained in this chapter. 

 For selected measures, units in both metric and English systems will 

 be given. 



ered platforms or on either unmanned or manned 

 submersibles. Instruments for sampling the chem- 

 ical properties and temperature of near-bottom 

 water also may be carried aboard these platforms. 



Indirect methods of detection give way to direct 

 methods at the seabed. Only direct samples can pro- 

 vide information about the constituents of a deposit, 

 their relative abundance, concentration, grain size, 

 etc. Grab sampling, dredging, coring, and drilling 

 techniques have been developed to sample seabed 

 deposits, although technology for sampling consoli- 

 dated deposits lags behind that for sampling un- 

 consolidated sediments. If initial sampling of a 

 deposit is promising, a more detailed sampling pro- 

 gram may be carried out. In order to prove the 

 commercial value of a mineral occurrence, it may 

 be necessary to take thousands of samples. 



While some technology has been specifically de- 

 signed for minerals exploration, much technology 

 useful for this purpose has been borrowed from 

 technology originally designed for other purposes. 

 Some of the most sophisticated methods available 

 for exploration were developed initially for military 

 purposes. For instance, development of multi-beam 

 bathymetric systems by the U.S. Navy has proven 

 useful for civilian charting, oceanographic research, 

 and marine minerals exploration. Much technol- 

 ogy developed for military purposes is not imme- 

 diately available for civilian uses. Some technol- 

 ogies developed by the scientific community for 

 oceanographic research are also useful for minerals 

 exploration. 



Advances in technology usually generate inter- 

 est in finding applications to practical problems. 

 It is often cosdy to adapt technology for marine use. 

 When the military defines a need, the cost of de- 

 velopment of new technology is commonly less con- 

 strained than may be the case for the civilian sec- 

 tor. Conversely, although certain exploration 

 techniques (e.g., for sampling polymetallic sulfides) 

 are not yet very advanced, it does not necessarily 

 follow that the technical problems in research and 

 development are overwhelming. Identification ol 

 the need for new technology may be recent, and/or 

 the urgency to develop the technology, which might 

 be high for military use, may be relatively low for 

 civilian use. 



