17:15 〜 19:15
[SCG51-P03] Onboard mini-core drilling of dredged rock samples: First operational attempt on Hakuho-maru KH-24-4 cruise
キーワード：船上ハードロック、ミニコア、岩石磁気、岩石物性
This study aims to establish an onboard mini-core sampling technique for preparing rock specimens suitable for magnetic and physical property measurements. Three main considerations motivated this approach: (1) the limited workspace available on research vessels, (2) the need to facilitate rapid and accurate decision-making among collaborating researchers during onboard sample partitioning, and (3) the requirement to efficiently conduct final sample preparation within limited time after the cruise. During the KH-24-6 cruise (October 12 to November 8, 2024), 27 dredge haul operations were conducted along the Marie Celeste Transform Fault, Central Indian Ridge, collecting basalt, dolerite, gabbro, and their altered varieties. A newly adapted mini-core drilling system with 25 mm and 35 mm diameter blades was used to extract 18 mm and 25 mm diameter cores from these rock samples.
Over a period of twelve days, 2–3 operators spent 2–6 hours per session and successfully shaped 142 mini-cores (total length 14,910 mm). While the system generally performed well, drilling harder rock samples required considerable effort. Steady onboard supply of water and electricity allowed for efficient long-duration drilling operations and the use of hoses to provide cooling water. However, drainage and cleanup posed challenges within ship interiors, suggesting that outdoor setups may be preferable. Hand-held drills made it difficult to maintain a straight drilling axis, indicating that a drill press may be advantageous for better core linearity, although it typically has lower rotational speed and may extend drilling time, especially for harder rocks. After the cruise, slicing the mini-cores into 2 cm cylindrical specimens (akin to cutting “Kintaro-ame” candy) produced about 250 samples in four hours, drastically reducing time compared with conventional methods.
In conclusion, onboard mini-core drilling offers notable advantages for maximizing limited research space and performing efficient sample partitioning. Further optimization—particularly balancing operator fatigue, drilling precision, and operation time—may be achieved through combining drill press and hand-held drilling approaches. Additional field testing, especially for very hard rock types, will help refine workflows concerning labor demands, workspace requirements, and overall efficiency. These findings are expected to support more effective rock sampling and streamlined collaborative research in future cruises.
Over a period of twelve days, 2–3 operators spent 2–6 hours per session and successfully shaped 142 mini-cores (total length 14,910 mm). While the system generally performed well, drilling harder rock samples required considerable effort. Steady onboard supply of water and electricity allowed for efficient long-duration drilling operations and the use of hoses to provide cooling water. However, drainage and cleanup posed challenges within ship interiors, suggesting that outdoor setups may be preferable. Hand-held drills made it difficult to maintain a straight drilling axis, indicating that a drill press may be advantageous for better core linearity, although it typically has lower rotational speed and may extend drilling time, especially for harder rocks. After the cruise, slicing the mini-cores into 2 cm cylindrical specimens (akin to cutting “Kintaro-ame” candy) produced about 250 samples in four hours, drastically reducing time compared with conventional methods.
In conclusion, onboard mini-core drilling offers notable advantages for maximizing limited research space and performing efficient sample partitioning. Further optimization—particularly balancing operator fatigue, drilling precision, and operation time—may be achieved through combining drill press and hand-held drilling approaches. Additional field testing, especially for very hard rock types, will help refine workflows concerning labor demands, workspace requirements, and overall efficiency. These findings are expected to support more effective rock sampling and streamlined collaborative research in future cruises.