There are three types of embankment systems for handling tailings, upstream, downstream and centerline. The downstream construction needs coarse material and most gold operation rarely produces tailings with coarse particles. For this reason, tailings dam are constructed considering a mixture of upstream and downstream. The centerline procedure is an interesting option too.
An attractive and interesting consideration at the moment of selecting a tailings dam design is the cost and the upstream method is the best choice in this case. In this type of construction, the level of water is growing with the time and each portion of the dike is moving up so that the last dike is supported on the previous tailings dam. Obviously, the latter one is not well formed and creates a phreatic line near to the external surface. The system has a problem when there are intense rains due the drainage and resistance is affected by this condition. In other words, the phreatic surface has influence on dam stability. The system includes a hydrocyclone which is placed at the top of the pond so that the overflow (fine particles) is discharge in the pond and the underflow (coarse particles) forms part of the dikes to be erected. The dike may be erected 5 to 10 meters per year. Try to build higher dikes is not recommendable
The downstream construction system requires coarse particles and the classification performed by a hydrocyclone placed in the tailings dam is the source of coarse material because the hydrocyclone separate fine and coarse particles. When the gold recovery process needs fine liberation (e.g. cyanidation at 85% passing 75 microns) the method must be studied carefully. Under this consideration is a good alternative to employ waste rock material. The rocks may be part of the started dike. There are not restrictions for the raising rate. The main disadvantage of this method is the high cost of construction.
The third system is a good option for temporary tailings disposal. One condition very important to know is the plasticity of the material. Since the material has variable compaction or settling, the particles must have low plasticity in order to minimize failures. The height is influenced by the plasticity of the material and the cost of construction is in reasonable in comparison with the downstream method.
Upstream
Downstream
Centerline