7.   TAILINGS MANAGEMENT

7.5.1  

Rosh Pinah

The Rosh Pinah tailings dam is located 1.5km South and down gradient of the plant area. Slurry residue is currently pumped to the dam at a rate of approximately 80tph in either one of the two existing 180mm diameter steel or HDPE pipelines. It is estimated that the in-situ density of the tailings will be in the order of 1.5tpm3 therefore deposition on an annual basis will be approximately 660,000tpa or 440,000m3 p.a. based on a plant efficiency of approximately 94%.

The tailings dam layout is split into three compartments, two of which are located at the top surface of the dam at an elevation of 376.00 mamsl (24m high). The third compartment is an extensive tailings buttress located on the southern and south western flanks of the dam at an elevation of 362.00mamsl (18m high). All three compartments had elevated penstocks installed in 1998, before this time water was stored on top of the dam and allowed to either evaporate or seep into the sub surface sandy gravelly soils underlying the tailings dam. The elevated penstocks discharge into an unlined solution trench on the eastern side of the dam. The solution trench transport the decanted supernatant water to an unlined evaporation dam located immediately south of the tailings impoundment. There are currently no facilities in place to pump this water back to the plant for use in the process circuit.

The machine packed division wall between the two compartments located on the top of the tailings dam has been machine breached in several places with the objective of forming a single compartment with a total surface area of approximately 24,3Ha. The lower compartment has a current deposition surface area in the order of 14.2Ha. The overall area available to deposit the Rosh Pinah tailings is therefore 38,6Ha. The current rate of rise will be in the order of 1.25mpa if the total available deposition area is utilized. It is estimated that the closure rate of rise after five years using the entire surface area of the tailings dam to deposit tailings will be 1.35mpa. Both rates of rise are acceptable.

It is understood that tailings disposal will be outsourced to a contractor at the end of August. Preliminary discussions between mine management and the contractor would indicate that there is a suggestion to restrict the deposition of tailings for the next five years onto the southern buttress dam with the objective of bringing all compartments to the same elevation. If this option is pursued the rate of rise on the lower compartment will increase to 3,4mpa.

7.5.2  

Zincor

Zincor currently uses two disused gold tailings dams as disposal sites for their process waste products, namely solids and liquids arising from Zn production. These gold tailings dams are registered with the DME as Dam 7L3 and Dam 7L4. Dam 7L3 is situated closest to the Zincor process plant and receives both solid and liquid plant waste, whereas 7L4, which is situated about 2km from the plant is used solely as an evaporative facility for treated effluent. The solid waste products are basically chemical precipitate in the form of crystals and a fraction of the calcium that never leached. The crystals do change in size periodically. This means that there is almost a constant change in the material characteristics, the results of which are seen during routine deposition on 7L3.

7.5.3  

Chifeng

Chifeng recently constructed a new hazardous waste disposal facility. Construction has involved excavation of a pit and then lining the pit with a 2mm HDPE liner. Although, the liner was not properly keyed in during construction with the result that the liner has slumped, it appears that following the remedial work to repair the liner, the disposal site will be adequate for the disposal of residue generated. It must be noted that in terms of this assessment the slumping of the liner is not seen as a liability as it is currently being remediated from operating capital. There do not appear to be any boreholes around this site to monitor the efficiency of containment. These need to be implemented as part of a monitoring network. Currently, all waste generated on site is being hauled away by third parties who are processing the residues to remove the metals contained in the residue. The implication of this is that the residues are being stored on site until they are removed. This storage is potentially compounding the contamination of soils and groundwater at the plant.