Mining on the Pacific Rim
Japanese aggregate quarries differ from those in the United States in very subtle ways.
By Kerry Clines, Contributing Editor
Aggregate mining in Japan is pretty much the same as it is in the United States — blasting, loading, hauling, etc. — but there are subtle differences that make it unique. Those differences became quite apparent during a recent visit to the Ryoukami-Kougyou Co. quarry, located in a nature park in the mountains near Ogano in the Chichibu District, approximately two hours from Tokyo.
Ogano Quarry has been in operation since 1966 and employs 36 workers. It currently mines hard sandstone on 53 hectares of a 106-hectare (400+ acres) area available for mining.
Differences and challenges
One of the first things I noticed about this quarry was that it was upside down, so to speak. Most quarries found in the United States are holes in the ground with processing plants either down in the pit or above the pit at ground level. Ogano Quarry, however, is located on the side of a mountain. The aggregate is mined from the mountain and hauled down the mountain to the processing plant in the valley below.
Having a mine located on the side of a mountain presents an unusual challenge. The mountains in Japan are steep, so the benches are narrow — approximately 15 meters deep. The higher the benches are on the mountain, the narrower they become. Because of the narrow benches, Hidenori Kurihara, the mine manager, phased out the use of wheel loaders on the mountain and started using excavators for loading the haul trucks. Excavators are perfect for the narrow benches and steep terrain in the mountain quarry, because they can climb on top of the material to work, if necessary, and have a long reach, enabling them to load a truck without repositioning.
Another challenge quarry personnel encounter is the wear and tear on equipment caused by the rough terrain and the material being mined. The extremely hard sandstone (greywacke) at the quarry is very tough on buckets and ground-engaging tools, causing them to wear quickly.
The quarry also has to deal with the challenge of providing the same color material to the same customer. The rock comes in different shades of color depending on what area the material was mined from, and matching the colors can sometimes be a nightmare.
Blasting takes place every other day, followed by loading haul trucks. The operation is very efficient when it comes to loading. While the excavator is loading one haul truck, another is waiting, so loading time is very short. Once the material is loaded into the haul truck, it is taken down the 1.5-kilometer haul road to be processed. The quarry uses two different plants for processing material — a dry processing plant and a wash plant. The wash plant is used for those customers who prefer clean, washed stone; plus it helps control dust.
Material is usually run through the crushers three times. If a round-shaped rock is desired, the material is crushed a fourth time. The smallest rock produced at the quarry is 2.5 millimeters. “We usually make rocks a maximum of 40 millimeters in size,” Kurihara says. “We only make 80 or 85 millimeter rocks on request. The largest stone we make is a garden stone, usually 35 centimeters in size. We separate those stones depending on customer demand.”
When it comes to loadout, the quarry has no truck fleet of its own, so everything is loaded onto customer trucks. Silos are used for loading dry rock into customer highway trucks at the dry plant, and wheel loaders load the trucks at the wash plant. In keeping with the smaller size of most vehicles found in Japan when compared to their U.S. counterparts, customer highway aggregate trucks only hold 10 to 12 metric tons of material. However, a larger truck would have difficulty maneuvering on the tree-lined mountain roads leading into the quarry. The roads are beautiful, but narrow and winding, with occasional turnouts to allow customer trucks going in opposite directions to pass each other.
Ogano Quarry loads an average of 300 customer highway trucks per day. It processed and shipped 800,000 tons of stone last year, but is capable of producing 1 million tons annually. Approximately half of the stone produced is being used for concrete and water-permeable concrete for the walls of tunnels being built under Tokyo. Another 35 to 40 percent of the stone is used for road base. The rest is used for railroad ballast.
The quarry is expected to last another 15 to 20 years, at which time quarrying will move to the mountain on the other side of the valley and processing plant. “Only one side of the mountain is mined,” Kurihara says, “then it is replanted with cedar trees to bring the green back to the mountain.” The trees are expected to help with erosion control and prevent landslides, as well as return the mountain to a natural state.
The Shinto Shrine
On the way to the processing plant at Ogano Quarry, visitors will pass by a Shinto Shrine, which was designed and constructed by quarry personnel and built from materials found on site. The shrine is dedicated to the God of the Mountain and serves as a place for employees to pray for the safety of everyone working on the mountain.
“On the 17th of every month, all the workers come to the shrine,” says Hidenori Kurihara, mine manager. “We dedicate sacred rice wine to the God of the Mountain and pray for the safety of their work.”
Shinto is the native religion of Japan, or a way of living, that extends as far back as 500 B.C. Shintoism is the worship of invisible spiritual beings and powers, sometimes human or animal, but mostly having to do with nature and natural forces, such as rivers, trees, rocks, mountains, lightning, wind, etc. The shrines can be found all across the nation of Japan, especially in sacred and historical places, but also in non-secular locations like the quarry, as well as in homes.
Caterpillar 385C hydraulic excavators (2)
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