A Free-Fall Corer for Rapid Reconnaissance Sampling of Fe-Mn Crusts and Other Consolidated Seafloor Deposits
Authors: Toth J.R. , Amerigian C.A. 
Published: October 2008

Current seabed sampling requirements of marine mining, petrologic, and other researchers studying deep seabed consolidated deposits are not met by existing technology. Analytical services Company (ASC) has undertaken the development of an untethered free-fall device for recovering discrete samples of consolidated deposits. This sampler utilizes percussion coring technology for sample recovery. A prototype sampler has been designed and fabricated and is currently undergoing an extensive series of shallow water drop tests. The results of these tests have been very successful and indicate a high probability of success for this project. Continued refinement of the sampler design and testing will continue with sea trials tentatively planned for late 1991. Future work includes the development of a coring device powered by hydrostatic pressure to replace the current percussion core gun.

INTRODUCTION

Current research on deep seabed consolidated deposits, including evaluation of Fe-Mn crusts and detailed petrologic studies of sea floor basalts, employs a wide variety of sophisticated reconnaissance imaging tools. Regional examination of deposits are performed using a range of acoustic mapping systems (GLORIA, Seabeam, sidescan sonar), with more detailed examinations conducted by near-bottom photography or video imaging. If budget allows, specific sites are visited by manned submersible. Few options, however, are available for collection of samples of consolidated material from the seabed for subsequent physical and chemical analysis.

Dredging has been the traditional sampling tool for hard rock and mineral deposits. Dredging methods have improved over the years, but dredges are inherently limited to recovering bulk material from a relatively large area and are highly biased toward recovery of loose rubble and material on local highs. As a result, recent workshops and reviews of research on marine minerals in the U.S. Exclusive Economic Zone (EEZ) (1,2,3,4,5) have recommended the development of tools especially designed for recovery of samples of hard minerals and other consolidated deposits as an important priority.

In response to this need, Analytical Services Company (ASC) is developing an untethered free-fall device for recovering discrete samples of seabed consolidated deposits. This device is being developed specifically for evaluating Fe-Mn crust deposits and fine-scale sampling of basalt in mid-ocean ridge and seamount environments. It will also be valuable in any application where surface samples of hard rock outcrops are desired.

BACKGROUND

In 1984 ASC became involved in the design and testing of marine percussion coring systems for recovering discrete samples of Fe-Mn crust and other seabed consolidated deposits. These systems utilize technology similar to that used by the oil industry in side-wall coring devices which recover samples from the walls of exploration drill holes. Samples are taken by firing short, hollow core barrels, using small explosive charges, into a variety of rock types. ASC's work culminated in the design and fabrication of a tethered, multiple-core sampling device that has been used to recover short cores from marine Fe-Mn crust deposits (6,7,8) and basalt glass from mid-ocean ridge outcrops (9).