Key points
- Leg 3 of China’s Dayang Cruise 30 completed mid-depth drilling in the Southwest Indian Ridge polymetallic sulphide exploration area from 15 to 17 March.
- Three drilling operations covered a carbonate test area, an inactive sulphide area and a dead chimney area, recovering sulphides, carbonates and bedrock.
- The team used the Jinquzhe deep-hole drill rig, which works to 4,000 metres depth and drills up to 20 metres.
- Core recovery in the loose sulphides was low, with most samples being oxide and sulphide mixtures.
From 15 to 17 March, after three days and nights of hard work, leg 3 of China’s Dayang (Ocean) Cruise 30 completed as planned the mid-depth drilling survey tasks in China’s polymetallic sulphide exploration area on the Southwest Indian Ridge. Three drilling operations were carried out during the leg, in a carbonate test area, an inactive sulphide area, and the “dead chimney area” near China’s active hydrothermal field. Over several days of operations, the team used a mid-depth drill for the first time to drill in a sulphide area and successfully recovered sulphides, carbonates and the underlying bedrock, which is of major significance for studying the distribution of sulphides and their relationship with the surrounding wall rock, as well as the origin of the carbonates.
From 15 to 17 March, wind in the Southwest Indian Ocean contract area was force 4 to 5 with sea state 4. The Dayang Cruise 30 science team was greeted by good weather for seabed operations, and the team worked with the Jinquzhe (Enterpriser) deep-hole drill rig, a special-purpose piece of equipment for geological core drilling on the deep seabed. The Jinquzhe mainly comprises a communications and control system, the underwater drill unit itself, and the accompanying drill pipe and tooling. It can operate in water depths of up to 4,000 metres, is suited to hard seabed rock, can drill to a depth of 20 metres, and takes cores with a maximum diameter of 50 millimetres.
For three consecutive days, the Jinquzhe deep-hole drill rig operated on the seabed for more than ten hours a day. Deep-drilling team leader Zhong Lu said the seabed basalt causes considerable wear on the drill, and the recovered samples included many small fragments.
The terrain in the 17 March work area was relatively complex, and the mid-depth drilling team spent several hours selecting a landing position. Seabed video showed that the surroundings of the landing site were mostly sulphides. Drawing on the experience of the previous two days, the team therefore adopted a method of zero-speed pressurized deep drilling into the sulphide surface layer.
Assistant to the chief scientist Li Huaiming said that because the sulphides in this area are relatively loose, the core recovery rate was fairly low, and most of the samples collected were mixtures of oxides and sulphides. Encouragingly, this operation did recover some polymetallic sulphides.
Zhong Lu said China’s independently developed mid-to-deep-hole drill rig is a core sampling rig suited to relatively hard material. Sulphides, however, are complex in character, some loose, some brittle, some hard, which places high demands on the rig. Two problems remain to be solved in future: raising the sulphide sample recovery rate, and preventing recovered sulphide samples from being lost on the way up.
Chief scientist Tao Chunhui said this was the first time China had used mid-depth drilling to drill in a sulphide area, successfully recovering sulphides, carbonates and underlying bedrock, of major significance for studying sulphide distribution, the relationship between sulphides and wall rock, and carbonate genesis. It was also the first time China had obtained subsurface samples from its sulphide contract area, providing a technical reserve for future seabed sulphide exploration.
Over the three days, Zhong Lu led a mid-depth drilling team of Zang Long, Zhang Wei, Yuan Qingbo, Weng Lichun and Huo Hongqiang through gruelling work, with at most four hours of rest a day.
Before the drill went into the water, Zhong Lu checked the mid-depth drill from top to bottom again and again, and team members ran repeated circuit tests. When the screen showed the drill spinning at speed, smiles broke out on their faces.
During the fixed-point deep drilling, Captain Cao Yezheng personally conned the ship for more than ten hours at a stretch, with the chief officer, second officer and third officer standing rotating watches every day. Chief officer Xu Weiwei said drilling is like tying a stern anchor to the ship: if the ship drifts away, the drill string will deform, so the stern’s position must be held within a circle of 30 metres radius and the ship can move only 1 to 2 centimetres per second, with the officer of the watch glued to the display at all times, adjusting position promptly.
Three days of work beyond normal limits brought the team not only physical fatigue but also psychological pressure, because this was the first hole ever drilled in the Southwest Indian Ocean contract area. To the team’s satisfaction, they completed the deep-drilling task with distinction.
