This study is based on the concept of treating at Port Pirie 100,000 tons/year of non-upgraded willemite ore from Beltana with a zinc assay of 36.5%. The amount of granulated slag required in the process is the result of metallurgical considerations and was established as 60% ore/40% slag. The site chosen for this fuming plant was as near as practicable to the existing fuming plant at Port Pirie. This allows some interconnection of services and operations, but essentially confines this type of operation to one area of the BHAS works. The basic case, described in detail in this study, incorporates a number of important changes in process design when compared with the original fuming plant at Port Pirie. These changes are not only due to the differing feed material and product, but also due to experience gained by BHAS in their operation, and anticipated legislation concerning plant effluents. As well as presenting the design and cost estimate for the basic case, a number of variations to the process route have been investigated. These alternative routes show significant differences in capital and operating costs, which could have a large effect on their economic viability.