POTENTIAL FOR RETROFITTING STD

Submarine tailings disposal (STD) systems have been retrofitted, desig ned, ol appear to be possible at several existing or abandoned coastal and island mines. At Atlas Copper Mine, the Philippines, the system i s somewhat different from the norm: a 500-m pipe pier, with a discharg e point just below the surface, extends offshore to 30-m water depth. Little environmental information is in the public domain, bur there ap pears to be some nearshore turbidity and deposition. A system was desi gned for the Toquepala and Cuajone mines, Peru, but was not implemente d. The discharge depth was to have been at 20 m to a sloping offshore bank, with low-oxygen water and sediments. The Marcopper Mine, the Phi lippines, elected for nearshore disposal, bur extended this by causewa y to surface discharge over deeper water. Reviews of potential STD sit es showed at least three locations with apparently suitable depth and slope close to shore. At Bougainville Copper Mine, Papua New Guinea, t he tailings disposal option was to a river with flow westward to the s ea. Nearshore deep water beyond a fringing reef in an easterly directi on was closer to the mine and could have been investigated for STD. Th e Jordan River Mine, Canada, in its most recent reopening (1972-74), i nstalled a tailings pipeline to discharge at 12-m depth to a nearshore depression. It blake repeatedly at this high wave energy site, which appeals unsuitable for an STD system. Screening criteria that can be a pplied in STD retrofit proposals include coastal accessibility and a c omplex of technical and geophysical factors allowing generation of a t ailings density current flowing coherently to a final deposition site.