Gosowong Gold Mine Project
Improvement on sprayed concrete for ground support
Gosowong is owned and operated by PT Nusa Halmahera Minerals (PTNHM), an Indonesian company owned by Newcrest Mining Ltd (75%) and PT Aneka Tambang Tbk (25%). It is located on Halmahera Island, in the North Maluku Province of the Republic of Indonesia, approximately 2,450 kilometres northeast of the national capital, Jakarta. Gosowong commenced operations in 1999 and its primary products are gold and silver. The processing plant at Gosowong has the capacity to process 800,000 tonnes per year using a primary jaw crusher followed by SAG and ball mill circuits prior to final smelting of the gold/silver ore.
The Gosowong gold project has two main underground mines: Kencana and Toguraci. Conditions in the mines vary significantly throughout the underground workings. Kencana underground has zones of very soft and fractured rock with the potential for high deformation rates and drive squeezing. Toguraci underground generally has a more competent rock mass although the deeper parts of the mine experience high substrate temperatures associated with geothermal conditions (substrate surface temperature 60-70º C). Previously, the normal sprayed concrete mix design could not achieve 32 Mpa at 28 days or 1 Mpa in 1 hour as required by the design specifications due to the heat and application issues.
Master Builders Solutions was engaged to undertake a technical review of the shotcrete mix compatibility in conjunction with the raw materials and underground environmental conditions. A sprayed concrete solution from Master Builders Solutions was developed consisting of suitable admixtures combined with a tailored training package for operators, supervisors, and engineers. The improved product coupled with specific training requirements has benefited PT NHM, assisting operators to achieve a high quality sprayed concrete at design thicknesses (100mm) in a single pass. The shotcrete improvements have led to a more effective and efficient ground support system and a safer underground working environment.
The admixtures used in this project include:
- Internal curing agent - MasterRoc TCC 735 helps to achieve significantly stronger cured concrete strength in high-temperature environment.
- Hyperplasticizer - MasterGlenium SKY 8770 significantly improves workability even with poor quality sand.
- Hydration Densified silica fume - MasterRoc MS 610 helps to improve cohesiveness and workability of sprayed concrete mix Control Admixture, MasterRoc HCA 10 helps to maintain workability for long time periods.
- Alkali free accelerator - MasterRoc SA 167 significantly boosts early strength development, assisting with poor ground control and allowing mine production cycles to commence sooner.