Ann: Sorby Hills Definitive Feasibility Study, page-118

Does anyone think it's a bit weird The FS is being done on a different feed tonnes than the PFS? The whole idea of a PFS is to identify the single best option to develop for the FS. I suspect the economics for the PFS didn't stack up so the feed rate has been increased to improve the economics.
What should happen is the FS should be put back on hold and the PFS redone with a focus on increasing the plant feed rate.

In my view the relatively low feed grade, low lead price and high cost of operating in a remote area will mean this project will need to be as large a tonnage as possible for best economics. Hydro power is the big positive for this project as power costs are typically a high cost component of flotation plants because of the high cost of fine grinding.

A revised PFS should be done with an option for maximising the plant feed rate with the available Hydro power. Preconcentration of the ore should be examined using dense media separation (DMS) to reduce grinding costs and maximise the feed rate. DMS was used successfully at Mt Isa. SAG milling is inefficient compared to using High Pressure Grinding Rolls so the option of using HPGR in the circuit needs to be assessed. Argyle Diamonds had multiple HPGRs operating using hydro power so the technology was well proven in the area.

GR engineering will screw BML over by cutting normal design throughput safety margins, cutting costs on anything that can be cut regardless of how much it will hurt the operation. BML need to talk to operators that have been involved in commissioning and ramping up GR Engineering built plants to find out the design faults as GR dust off old design for flotation plants complete with all the design faults.