Prewitt, JM & Puradyatmika, P 2012, 'Overburden stockpile revegetation techniques at PT Freeport Indonesia Grasberg Mine', in AB Fourie & M Tibbett (eds), Mine Closure 2012: Proceedings of the Seventh International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, pp. 493-505, https://doi.org/10.36487/ACG_rep/1208_43_Prewitt
(https://papers.acg.uwa.edu.au/p/1208_43_Prewitt/)
Abstract: PT Freeport Indonesia (PTFI) operates the Grasberg open pit mine in the Indonesian province of Papua producing copper and gold concentrate. The Grasberg pit began operation in 1989 and is currently planned to transition to an underground operation in 2017. By the time of the transition to underground operations, over three billion tonnes of overburden will have been placed in the overburden stockpiles surrounding the open pit. This paper briefly describes the layout of the stockpiles and processes in place to ensure geotechnical and geochemical stability of the stockpiles, but focuses on revegetation techniques for reclamation.
PTFI practices concurrent reclamation of overburden stockpiles as areas reach final configuration and has already reclaimed over 260 hectares of land surface area using native plants suitable to the alpine location. Reclamation plans, techniques and costs are covered by Five Year Reclamation Plans that are submitted to the government of Indonesia for approval. Progress is verified annually by Ministry of Energy and Mineral Resources (MEMR) inspectors. Successful completion of the planned revegetation is required to release the funds set aside based on the Five Year Reclamation Plans.
Plants, seeds and mosses are harvested from surrounding areas and prepared in a nursery operated at the mining area. A tissue culture technique to produce additional seeds and seedlings is also being trialled at Grasberg and is the subject of a separate paper at this conference. Transplanted plants and seedlings are allowed to acclimate to the alpine climate conditions in the nursery before being planted on the overburden stockpiles. A combination of organic compost, both produced onsite and purchased from offsite, and commercially available fertilisers are used to promote the plant growth. Soil availability is severely limited at the mine elevation and a limestone fines material is used as a soil substitute to allow placement of the plants, especially on the slopes. Overburden slopes are designed at 2H:1V overall with slope faces generally at angle of repose interspersed with flat benches. Transplanting on the slopes requires special techniques and training of personnel to ensure personnel safety as well as viability of the vegetation. In addition to transplanting, hydroseeding is used to assist in full vegetative coverage.
Monitoring of reclamation areas includes soil sampling, evaluation of erosion, plant viability surveys, and evaluation of biodiversity of flora and fauna. The biodiversity of reclaimed areas is compared to adjacent non-disturbed areas. Monitoring techniques used as well as some typical results are shown in the paper.