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Positive interim met testing results for Vista Gold Corp.

Published by
Global Mining Review,

Yesterday, Vista Gold Corp. (Vista) announced that recent high pressure grinding roll (HPGR) crusher and ore sorting tests on high-grade samples confirm previous test results. The company also announced its plans to complete fine grinding and leaching tests in 1Q19 and to follow these results with updated preliminary feasibility study (PFS) economics in 2Q19.

Interim met testing results confirm benefits of ore sorting

Additional HPGR and ore sorting tests were completed on two, 2.5 t samples from Mt Todd's Batman deposit containing 1.39 and 1.70 grams of gold per tonne (g Au/t), respectively. This testing programme confirmed two important results:

  • HPGR crushing followed by screening results in increased concentration of gold in the fine fraction, and
  • the small amount of gold lost in the rejected material is proportionally lower when sorting higher-grade material.

As with previous tests, the samples were HPGR crushed at the facilities of thyssenkrupp Industrial Solutions in Germany and screened at 16 mm. The coarse material was sent to the facilities of Tomra Sorting Solutions in Germany, where two-stage (x-ray transmission and laser) sorting tests were completed using production-sized and commercially available equipment. 

Frederick H. Earnest, President and CEO of Vista Gold Corp. commented: "These tests confirm the value-adding benefit of ore sorting for the Mt Todd gold project and demonstrate lower gold losses with higher grade crusher feed.  We attribute these results to the favorable characteristics of the Batman deposit. Simply stated, the gold-containing sulfide minerals and quartz/calcite veining are more easily broken into small particles than the non-mineralised host rock. Where this breakage does not result in clean separation from the host rock in the first pass of HPGR crushing, the gold-bearing minerals are easily identified and separated in the ore sorting circuit.  These results complement our previously announced fine grinding and leaching test results (see 2 August 2018 press release) and we expect that these results will support additional improvements in the economics of the Mt Todd gold project when we complete the PFS economics expected in the second quarter of this year."


Met testing and PFS update schedule

The crushed and sorted samples have been transported to the facilities of Resource Development Inc., where sample preparation has been completed for assaying and additional fine grinding, leaching and tailings characterisation tests. Samples are being sent to Core Metallurgy Pty Ltd to obtain additional 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 VPX Mill.  Both tests will target a final product size of 38 - 45 microns and will generate a sufficient volume of material for subsequent leach tests. The fine grinding and leach tests are expected to be completed in the first quarter of 2019 with final results expected to be available in the second quarter of 2019.

The company has completed additional tailings characterisation tests and concluded that no material design changes are required to proceed to the economic analysis using a final grind size of 38 - 45 microns. At this time, the company anticipates announcing the results of an updated PFS in 2Q19.

Earnest added: "We expect the combination of the recently improved gold prices, weaker Australian dollar, and improved gold recovery to have a positive impact on the economics of the Mt Todd gold project. We anticipate that the planned testing programmes will confirm our ability to achieve a nearly constant tail grade at the target grind size, which has previously demonstrated gold recoveries better than 90% with no increase in process area power requirements."

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