Vista Gold Mt Todd PFS points towards use of ore sorting, fine grinding

Following extensive metallurgic test work carried out over the past year, Vista Gold looks like it has settled on a flowsheet for its Mt Todd gold project in the Northern Territory of Australia that includes ore sorting and the selection of the FLSmidth VXP mill as the preferred fine-grinding mill.

The company detailed this in an updated prefeasibility study (PFS) for the project, which factored in the results of metallurgical optimisation test work, a redesign of the fine grinding circuit, construction and ramp-up schedule changes and a comprehensive review of all aspects of the project.

The process improvements resulted in improved projected gold recovery and increased estimated gold production at Mt Todd, Vista Gold said.

According to the PFS, a 50,000 t/d operation at Mt Todd could see the operation produce 413,400 oz of gold over the life over the 13-year mine life at average all-in sustaining costs of $746/oz.

The estimated initial capital requirement came in at $826 million, with the project offering an after-tax net present value (5% discount) of $823 million at a $1,350/oz gold price and a $0.70=A$1.00 exchange rate.

In the company’s metallurgy, processing and infrastructure section, it detailed the processing side of Mt Todd, saying that recent metallurgic test programs had confirmed the efficiency of ore sorting across a broad range of head grades and the natural concentration of gold in the screen undersize material prior to sorting. The company carried out such test work at TOMRA Sorting Solutions in Germany, where two-stage (X-ray Transmission and laser) sorting tests were completed using production-sized and commercially available equipment.

It also said such test work had confirmed the efficiency of fine grinding and improved gold leach recoveries at an 80% passing grind size of 40 microns, in addition to the selection of the FLSmidth VXP mill as the preferred fine-grinding mill.

The company previously sent samples to Core Metallurgy Pty to obtain fine grinding data simulating grinding in the horizontal IsaMill and to the FLSmidth Minerals Testing and Research Center to obtain data simulating grinding in the vertical VXP Mill.