Abstract
A copper mine in Maluku Province, Indonesia, extracts the metal using a heap leach system and solvent extraction/electrowinning. Upon leaching maturity, the process leaves the heap leach dumps with residual materials containing pyrite, iron, and other unprocessed minerals. These residual materials are considered waste and uneconomic; moreover, high-contained pyrite material needs special treatment due to its acid rock generation capability.
The recent breakthrough in the nickel industry, the HPAL (High Pressured Acid Leaching) processing method, requires a significant amount of acid. Due to the high acid demand, the mine takes the opportunity to re-mine the spent pyrite residues from heap leach dumps and to produce sulphuric acid and other economic products such as iron pellets, base metals, and precious metals (copper, gold, and silver).
The implementation of this project poses several challenges for the mine. It necessitates a re-assessment of its resource and reserve estimation. With the production of multiple products, the mine must meet several 'ore' criteria. The presence of stacked heap leach materials and limited available spaces further complicates the blending process. This paper delves into the process and the challenges involved in estimating the reserve from the re-mining heap leach dump residues.