tial. In addition, such indirect measurements as 
pressure and electric logging may be very helpful 
in evaluating fluid (oil and gas) potential, but 
direct measurements of recovered samples are 
required in most cases to evaluate the amount and 
quality of mineral deposits. 
Placer deposits and nodule deposits are easier to 
explore for than concealed sub-bottom bedrock 
deposits but still pose considerable difficulties. 
Placer deposits may not extend across the shore 
line, and in many cases, the beach separates 
environments containing different kinds of mineral 
occurrences. 
A great many samples must be taken to define a 
placer deposit. As with gold and diamonds, the 
best material is often in cracks and depressions in 
the bedrock and is difficult or impossible to reach. 
Placer or nodule mining in deep water requires 
relatively expensive equipment, and operating 
costs also are high, especially where sea state 
conditions are frequently unfavorable. 
The ratio of ore discoveries to targets explored 
may be as low as one in 1,000 onshore and may 
be even lower offshore. Exploration of the shelf 
for hard mineral deposits will be very speculative 
for the foreseeable future, and mineral explorers 
will require strong incentives to apply their energy 
and skill in an activity where good fortune will 
also be required. 
C. Exploration and Evaluation 
1. Types 
Mineral exploration in the ocean requires a 
sequence of activities, many similar to those on 
land. These include bathymetric, geophysical, and 
geological surveys, followed by sample analysis. 
2. Bathymetric 
Modern echo-sounders can, when used with 
shipboard recorders and underwater devices, deter- 
mine details of bottom relief to within one fathom 
in deep water and even more precisely in shallow 
water. Bottom contours, representing such fea- 
tures as submerged river channels (frequently a 
favorable location for placers), can be detected. 
Interpretation of echogram characteristics also 
helps to identify the type of sea bottom; i.e., rock, 
sand, or mud. Although side-looking sonar repre- 
sents a start towards more effective scanning of 
VI-182 
bottom profiles, much more highly developed 
devices and techniques will be needed. 
3. Geophysical 
Geophysical survey methods used on land have 
proved readily adaptable to the marine environ- 
ment. 
Magnetic anomalies discovered in marine sur- 
veys can indicate the major rock types, faults, and 
other structural features below the ocean floor. 
They also indicate the occurrence of magnetic 
ores. Marine magnetometers allow accurate meas- 
urements while under way. 
The gravity survey also is useful in locating 
anomalies. Marine gravimeters have been devel- 
oped recently for shipborne surveys and for use 
near the sea floor. While the accuracy of a ship 
mounted unit is an order of magnitude lower than 
that of analogous sea floor equipment, more data 
can be provided in less time. Gravity data is useful 
in broad reconnaissance studies for interpreting 
large subbottom structures. However, such data is 
best used together with the results of other 
geophysical data. 
Seismic surveys indicate structure, stratifica- 
tion, and sediment thicknesses. In addition, sub- 
merged beaches, which may contain placer concen- 
trations, may be indicated. Present sub-bottom 
profiling techniques, however, cannot evaluate 
mineral deposits. Sophisticated methods may be 
able to provide much higher resolution informa- 
tion including acoustic velocities, densities, and 
acoustic impedances, thereby helping to identify a 
particular material. 
Recently, electrical methods, such as measuring 
resistivity characteristics of rocks, radiometric 
techniques, and heat flow methods have been 
suggested as additional tools for detecting anom- 
alies. 
For more efficient exploration, mathematical 
search models have been used in laying out grids 
for geophysical surveys, sampling, drilling, and 
other exploration work.'® Efforts also have been 
made to apply computer techniques and mathema- 
tical models to the probability of finding minerals 
'© United Nations Economic and Social Council, “Re- 
sources of the Sea, Part One: Mineral Resources of the 
Sea Beyond the Continental Shelf,” Feb. 19, 1968, p. 44. 
