Mitsubishi Heavy Industries Technical Review Vol. 50 No. 2 (June 2013)
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Development ofMining Element Engineering Test Machine forOperating in Seafloor Hydrothermal Deposits

SHINJI ISHIGURO*1

YOSHIAKI YAMAUCHI*2

HIROYUKI ODAKA*3

SEIGO AKIYAMA*4

Seafloor hydrothermal deposits (also referred as seafloor massive sulfide deposits, or SMSdeposits) are plentiful in the waters off of Japan. SMS deposits are promising mineral resources forresource-poor Japan. A joint venture of Mitsubishi Heavy Industry (MHI) (the representative of theJV), Kayaba System Machinery Co., Ltd., and Sumitomo Metal Mining Co., received an order of a
Mining element engineering test machine to collect technical data necessary to construct SMS
mining systems. The test machine was constructed in March 2012 and delivered to Japan Oil, Gasand Metals National Corporation (JOGMEC). We conducted an offshore examination with this testmachine to excavate an SMS deposit at the bottom of the sea in Okinawa’s waters in Nov. 2012 andsuccessfully collected the samples by using a slurry pump.

|1. Introduction
Japan has many SMS deposits in its exclusive economic zone (EEZ). It is estimated thatseveral deposits are located at economically feasible, relatively shallow water depths of approx.
1,000m-1,600m. SMS deposits are rich in copper, zinc, gold, and silver and also expected as
rare-metal resources. It is an urgent task for resource-poor Japan to develop the SMS deposits. In
order to commercialize these deposits, it is required to construct a pilot plant for an ocean
examination for actual proof.
Before constructing the pilot plant, we conducted a Mining element engineering test machinein order to collect technical data for mining unit.
Firstly we conducted element tests for an excavating device, a dredging device, and a crawlerdevice, and constructed a Mining element engineering test machine based on the test results. This
test machine was installed on the marine resource research vessel, Hakurei, to run on an actual
deposit in an offshore examination.
This report outlines the element tests (for the excavating device, dredging device, andcrawler device), construction of the Mining element engineering test machine, and the offshore
examination.

|2. Element tests
2.1(1)

Mining operations and mining heads
Mining system
In contrast with submarine fluid resources including oil and gas, SMS deposits arecommercially available only by excavating, collecting, refining heavy density ores fromdeep-sea areas, and then raising them to the sea surface and transporting them to the smelters.
SMS core sampling operations have been carried out on a trial basis, but large-scalecommercial mining with a mining system has not yet to be attempted because of the extreme
conditions of the deep sea.

*1 Chief Staff Manager, Ship & Ocean Business Department, Shipbuilding & Ocean Development*2 Deputy Manager, Ship & Ocean Business Department, Shipbuilding & Ocean Development*3 Kayaba System Machinary Co., LTD.
*4 Sumitomo Metal Mining Co., LTD.

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Figure 1 is a schematic view of the proposed mining system. This mining system
consists of a mining support vessel, a mining machine, a submerged pump unit, a riser pipe, etc.
The mining machine is remotely controlled with a controller on the support vessel through anumbilical cable. The mining machine collects and dredges ores. A submerged pump connectedwith the machine through a flexible pipe lifts the ores up to the support vessel through a riser
pipe. The recovered ores are stored in the hold of the mining support vessel and transported tothe smelters by another ships.

Figure 1

Proposed mining system

The mining system consists of a mining support vessel, a riser pipe, and a mining unit.

(2)

Mining operations and excavation cutting heads
SMS deposits are covered with breccia and sometimes with chimneys. Before main
excavation operations with a highly-efficient bench cut method, a pre-excavation is required toremove the breccia and chimneys. This approach needs two types of cutter heads; forpre-excavation and for main excavation operations. Consequently, it also needs two types ofmining machines; an auxiliary mining machine and a primary mining machine. Unlike onshore
mining operations where excavation and recovery are conducted separately, offshore mining
operations require a different approach for higher productivity and recovery rates. Specifically,excavation and dredging operations should be conducted simultaneously to reduce the mining
duration and costs associated with the equipment in the support vessel. Both mining machines
should use a cutter head that simultaneously serves excavation and dredging operations.
For main excavation operations, we selected drum cutters commonly used in mining orconstruction equipment, such as load cutters (as shown in Figure 2a). For pre-excavation
operations, we developed a multi-axis (4-axis) cutter to flexibly cut large breccia and chimneys,and effectively dredge them. A schematic view of the 4-axis cutter is shown in Figure 2b.

Figure 2Excavation cutters

In the excavation operation we separately uses two-types cutter head. The main excavation
operation uses a drum cutter head. The pre-excavation operation uses a multi-axis cutter
head. Simultaneous excavating and dredging is possible with a single device, resulting in ahigher recovery rate. Peripheral excavation heads of the 4-axis cutter collect ores at thehead’s center. The vacuum head sucks the ores by a slurry transport method.

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A 4-axis cutter excavates the ground in a toric shape. The paired cutters of a 4-axix cutter
spin and rotate to collect the pulverized ore soil to the center of the cutter head. The pulverizedsoil is dredged with a vacuum head at the center of the cutter head. The vacuumed soil istransported to the test machine body through a slurry transportation method. A 2-axis head isalso available.

2.2

Element tests for excavating device

Based on the concept described in the Chapter 2.1, we selected a drum cutter and a 4-axis
cutter as the excavating heads to be used in the Mining element engineering test machine. Before
building the test machine, we conducted elemental tests for the excavating device with a drum
cutter and for the device with a 4-axis cutter.
In the element test for the drum cutter, we selected one for onshore earth-moving machines.
We assessed the basic performance, including excavation torque, reactive force, and soil volume
for four test samples: 20 MPa and 50 MPa concrete blocks, SMS deposit ore rocks, and serpentine
rocks. The test showed that the excavating device fitted with the drum cutter should generally
demonstrate the specifications and required performance as planned. The grain sizes of thepulverized samples were stable and controlled by changing excavation conditions.
In the element test for the 4-axis cutter, we fabricated an excavating device fitted with a4-axis cutter, assuming that it would be installed in the Mining element engineering test machine.
Figure 3 shows the situations of the element test for the 4-axis cutter.

Figure 3 Element test for the excavating device fitted with a 4-axiscutter
Paired excavation cutters rotate and spin, cutting the test sample in a toric-shape.
During actual mining operations, the excavated soil is collected to the center of thehead and sucked by the vacuum head placed at the center, transporting the slurryfrom the seafloor to the sea surface.

The test showed that the 4-axis cutter had an insufficient excavation capability of only 0.1 to
0.3 m3/h. The reason was because the limited hydraulic-pressure was split between the four drums,
resulting in poor performance of each drum. Then, we fabricated a 2-axis cutter to reduce thenumber of drums from four to two. We also increased the drum diameters and the peripheral
velocities.
Consequently, we modified the excavating device to test the 2-axis cutter. The cutter showedgood excavation capacity of 1.2 m3/h for the SMS sample. The device also excavated the serpentine
rocks (single axis compressive strength: 70 to 170 MPa) which overwhelmed the 4-axis cutter. Thiseffective modification significantly improved the excavating performance, and paved the way for
installing the excavating device into the test machine. The soil collection performance rivals the4-axis cutter. The grain size distribution of the pulverized soil was also stable.

2.3

Element test for dredging device

The main excavation operations require simultaneous excavation and dredging. Hence wefabricated a head by combining a dredging head with the excavation heads of both a drum cutter
and a 4-axis cutter. We conducted an element test in a test tank, and used two samples: crushedrocks and mud. The fabricated heads did not excavate but imitated only recovery of the test
samples to assess only their dredging performance.

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Figure 4 shows the assumed flow of the soil in the dredging head. The test confirmed thateach dredging head cleanly collect and transport all the crushed rocks in the slurry up to the rated
capacity of the slurry pump.

Figure 4 Element test for the dredging system (slurry flow by thedredging head (Imaging))
The crushed soil are gathered to the front of the dredge head by the spin and rotationof the cutter and vacuumed and slurry-transported by the slurry pump.

2.4

Element test for crawler device

SMS deposits are commonly covered with rugged terrain, and it is difficult for conventional
crawler devices to run on. Hence, we developed a suspended-style vehicle that is independentlysupported by four crawlers. The lengths and angles of the crawlers’ legs are adjustable to improve
the running performance on rugged terrain.
In the element test for the crawler device, we arranged a test-bed made of crushed rocks toassess the running performance on rugged terrain as well as the basic performance. Figure 5 showsthe element test for the crawler device.

Figure 5 Element test for the crawler device
This figure shows 4-crawler test-bed running on a wasteland made of crushed rock.

|3. Mining element engineering test machine
Mining element engineering test machine has a front-boom that swings to the right/left andmoves up/down. The boom has two types of cutters on its end: a drum cutter and 2-axis cutter. Theformer cuts the ground evenly. The latter cuts ground right in front of the machine and roughly cut
uneven ground. A dredging head is attached to each of the two heads. Consequently, a feature of
the test machine is that it simultaneously performs both excavation and dredging. The test machinewith the four crawlers runs on the seafloor, climb hills with up to an inclined angle of 35 degrees,and over steps up to 35 cm in height.

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Figure 6 shows a outline of Mining element engineering test machine.
Commercial mining machines will be a 1,000 kW-class underwater system weighing 120
metric tons. Although this test machine is only a 184 kW-class system weighing 20 metric tons, it
is still twice the size of general work class underwater ROVs (Remotely Operated Vehicles) andprovides sufficient heavy-duty performance.

Figure 6Mining element engineering test machine

A schematic view of Mining element engineering test machine fitted with a 2-axis cutter head

|4. Offshore examination
Mining element engineering test machine was installed on a marine resource research vessel,Hakurei, and an offshore examination was carried out in the waters off of Okinawa in Nov. 2012.
The test machine landed on a modest slope terrain with chimneys (from 2 to 5 m in height),
avoiding rough areas. The possible landing sites were very narrow because there were large (2 to 5m) and small (approx. 1 m) chimneys and chimney fragments in the test field.
Figure 7 shows the 2-axis cutter excavating these chimneys. This test machine collectedapprox. 25 kg SMS samples and stored them in the hold. The grain size distribution of the samples
was consistent with no grains over 50 mm, demonstrating stable excavation performance. Figure 8
shows the collected samples and grain size distribution.
Achievements on the offshore experiment and future tasks are described below.
(1) SMS sample recovery
We operated Mining element engineering test machine at an actual SMS deposit moundunder deep-sea conditions to assess its performance and behavior. This test machine
successfully cut the seafloor and chimneys and collected the SMS samples.
(2) Collection of operation data
We collected valuable operation data using this test machine on actual ore deposits on theseafloor. We successfully gained information which will be useful for constructing a future
pilot plant.
(3) Importance of assessing seafloor conditions
The target terrain of this offshore examination was covered with sedimentary layers. The
dust particles were disturbed and clouded the seawater when the test machine landed, obscuring
the seafloor. Breccia and small chimneys also created risky conditions. For safety reasons,several TV cameras and SONAR devices are essential to understand the conditions of the target
terrain and its surrounding area during the operations.

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Heavy-duty operation performanceCommercial mining machines, which are categorized as earth-moving machinery, shouldhave sufficient heavy-duty operation performance. They should also have sufficiently
protection and durability to withstand contact with breccia and mining targets.
(5) Excavation heads and mining target monitoring
Effective mining operations require the careful monitoring of the excavation cutting
heads and their surroundings. In this respect, multiple sensors to monitor head conditions aredesired.

Figure 7

Excavating chimney

The appearance of the 2-axis cutter head cutting
chimney.

Figure 8 Grain size distribution of the collected
SMS samples
This chart shows stable excavation/dredging performanceand no grains over 50 mm.

|5. Conclusion
We developed Mining element engineering test machine based on the element tests for theexcavating device, dredging device, and crawler device. In the offshore examination in November
2012, we successfully operated this test machine on the actual SMS mound deep underwater, andcollected the SMS samples. This offshore examination provides us with valuable operation data
and useful knowledge for constructing the future pilot plant.
We would like to express our appreciation to JOGMEC for their excellent support in theconstruction of Mining element engineering test machine.

References
1. Deep sea Mineral Exploration & Technology Division Metals Mining Technology Department JOGMEC ,The outline of action of JOGMEC for development of seafloor hydrothermal deposits and theinternational condition of mineral resources Mineral Resources Report (2011), p293
2. Masao Komatsu ,Shinji Ishiguro et.al, Feasibility study of seafloor hydrothermal deposit Mining system
The 22nd Ocean Engineering Symposium Japan , March 17-18, 2011 OEE22-05
3. Shinji Ishiguro et.al, The Outline of Mining element engineering test machine using 2-axis cutter anddrum cutter The Mining and Materials Processing Institute of Japan 2012(Akita)