Denver-based Vista Gold Corp has announced positive results for a new preliminary feasibility study for the development of the Batman deposit at the company’s wholly-owned Mt Todd gold project in Australia’s Northern Territory. The new study was managed by Tetra Tech, based in Golden, Colorado, and expands on a previously completed 2010 study. The latest study evaluates the viability of a 30,000 t/d processing facility and the optimised extraction of the identified mineral resource.Highlights include increased estimated reserves – up 103% from the previous study, an estimated 4.1 Moz of gold, and an average annual gold production of 240,000 oz/y over 14 years. The expected mining rate will be 29.5 Mt/y, with a waste to ore stripping ratio of 1.8.
Vista plans to extract ore from the mine using conventional open pit mining equipment and techniques. A waste mining fleet consisting of 180 t trucks and 21 m3 shovels has been selected to complement the 140 t truck and loader ore mining fleet. Vista would be the owner and operator of the mining fleets and expects to enter into maintenance and repair contracts for the major mining equipment. Ore will be mined in four pit development phases over the 14 year life. Waste rock will either be placed in a single waste dump or used for tailings embankment construction. Concurrent reclamation is planned for the lower benches of the dump.
In processing terms, Vista has tested and determined the expected ore hardness and then evaluated various combinations of equipment. The best combination of equipment has been identified as primary gyratory and secondary cone crushing followed by tertiary crushing with high pressure grinding rolls (HPGRs) and ball milling. The use of an HPGR is expected to result in a product which significantly improves the efficiency of the grinding circuit.
The proposed flow-sheet sees the slurried ore sized by cyclones, thickened, pre-aerated, and then leached in tanks prior to recovery in a hybrid carbon-in-pulp circuit. Gold will be stripped from the carbon and precipitated in an electro-winning cell prior to refining into dore bars.