Source: International Dredging Review
Associated Minerals Corp. is operating a bucketwheel dredger at Green Cove Springs, Florida, south of Jacksonville. The dredge "Rocky Ford" digs a mineral-bearing sand containing rutile, zircon and ilmenite.
The dredge uses a 22-inch pump. A staff of 108 runs the dredge, the wet mill just behind the dredge, the dry mill on the company complex, and the office. The dredge operates three eight-hour shifts per day, 363 days a year. The dredge slowly digs its way through the deposit, which is on a Union Camp tree farm. The trees are harvested and the topsoil stripped and stockpiled ahead of the dredge. The bucketwheel digs black sand, leaving behind a pure white deposit, which is graded, covered with topsoil and planted in grass.
The mining site is about five miles from the headquarters building, down country roads, through the tree farm and into the clear-cut area where the dredge could be seen isolated in the pond it had made for itself. The dredge makes lateral passes 1,000 to 1,200 feet long, pulled by anchor wires.
The bucketwheel excavator digs along the bottom of the bank, caving in the bank in order to blend the mineral. With the bucketwheel it digs 900 to 1,200 tons per hour, which translates into 20,000 tons a day and seven million tons a year. AMC bought the 500 HP bucketwheel from Ellicott® Machine of Baltimore to replace a 1200 HP rotary cutterhead. The Ellicott® bucketwheel out-produces the previous excavator by more than 2:1 despite less than half the power consumption.
The material is pumped to the top of the four-story-high wet mill that follows the dredge, passing through a trommel that takes out the oversize, then through three sets of spirals that separate the heavy minerals to about an 85 percent concentrate. The mineral is stockpiled 4,800 feet away, pumped through six-inch polyethylene pipe using three 5X4" pumps. Trucks transport it to the dry mill where a combination of gravity and electrical processes separate the minerals.
The group operations manager explained that the deposit is the site of an ancient seashore where the ores were dropped in a huge crescent at a river mouth. The deposit is from one-fifth mile to one mile wide, 35 feet deep and contains 100 million tons of ore. The ancient seashore is now 15 miles inland.
Company literature puts the Florida operation's annual production at 30,000 tons of rutile, 35,000 tons of zircon and more than 60,000 tons of ilmenite, as well as smaller amounts of leucozene, monazite and staurolite. The quality of the mineral is very high, and the zircon is of a level of purity suitable for the more critical ceramic applications.
Associated Minerals is one of the largest mineral sands mining companies in the world. The company is a division of RGC Ltd. (Renison Goldfields).Reprinted from International Dredging Review