Water depth 30-60 feet 



Type of coring equipment VIbracorer 



Number of cores in program 50 



Depth of penetration 20 feet 



Type of vessel 100- to 150-foot open deck work boat, 



twin screw equipped with A-frame 

 and double point mooring gear 



Mobilization/demobilization cost $25,000 



Vessel cost $50,000 (10 days at $5,000 per day; 



assumes 6 cores per day; 30% 

 downtime for weather) 



Coring equipment and operating crew . $30,000 (10 days at $3,000 per day) 



Contingency funds $25,000 



Total cost $130,000 



Cost per core $2,600 



^Costs do not include core analysis and program management. 

 SOURCE: Office of Tectinology Assessment, 1987. 



200 to 300 feet 



VIbracorer (equipped for deep water 



operation) 

 50 



20 feet 

 150- to 200-foot open deck work boat, 



twin screw, equipped with A-frame 



and double point mooring gear 

 $50,000 

 $160,000 (20 days at $8,000 per day; 



assumes 3 cores per day; 30% 



down time for weather) 

 $100,000 (20 days at $5,000 per day) 

 $25,000 



$335,000 

 $6,700 



applicable to technologies for sampling massive sul- 

 fides and cobalt crusts). The representativeness of 

 the sample is very important. A sample is repre- 

 sentative if what it contains can be repeatedly ob- 

 tained at the same site. In this regard, the size of 

 the sample is important. For example, for minerals 

 that occur in low concentrations (e.g. , precious me- 

 tals), a representative sample must be relatively 

 large. A representative sample for concentrated 

 heavy minerals may be much smaller. The depth of 

 sediment that a sampling tool is capable of penetrat- 

 ing also affects the representativeness of the sample. 



Undisturbed samples are particularly important 

 for studying the engineering properties and deposi- 

 tional history of a deposit. They are less important 

 for determining the constituents of a deposit. 



Other relevant factors affecting sampling per- 

 formance include: the time required to obtain a 

 sample; the ease of deploying, operating, and 

 retrieving the sampling device in rough seas; the 

 support vessel requirements; and the core storage 

 capability. Sampling tools that can sample quickly, 

 can continue to operate under adverse conditions, 

 and can be deployed from small ships are preferred 

 when the cost of sampling is a significant factor. 

 More often, the solution is a compromise among 

 these factors. 



Grab and Drag Sampling. — Grab sampling is 

 a simple and relatively inexpensive way of obtain- 

 ing a sample of the top few inches of the seafloor. 



With its mechanical jaws, a grab sampler can take 

 a bite of surficial sediment. However, a sample of 

 surficial sediment is not likely to be representative 

 of the deposit as a whole. Buried minerals may be 

 different from surface minerals, or, even if the 

 same, their abundance may be different. Moreover, 

 the sediments retrieved in a grab sample are dis- 

 turbed. Some of the finer particles may even es- 

 cape as the sample is being raised, particularly if 

 stones or debris prohibit the jaws from closing 

 properly. 



Notwithstanding their shortcomings, grab sam- 

 ples have helped geologists gain some knowledge 

 of possible heavy mineral concentrations along the 

 Eastern U.S. seaboard. However, grab samples 

 provide limited information and are not appropri- 

 ate for detailed, quantitative sampling of a mineral 

 occurrence. Drag sampling is similar to grab sam- 

 pling in that it is designed to retrieve only samples 

 from the surface. An additional limitation of this 

 type of sampling is that sample material is retrieved 

 all along the drag track and, therefore, sampling 

 is not representative of a specific site. 



Coring and Drilling Devices. — For more quan- 

 titative sampling, numerous types of coring or 

 drilling technologies have been developed. Impact 

 corers use gravity or some type of explosive mech- 

 anism to drive a core barrel a short distance into 

 sediment. Percussion drUling devices penetrate sedi- 

 ment by repeated pile driving action. Vibratory 



