DENVER, July 24, 2017 /CNW/ -- Vista Gold Corp. (the "Company," "we" or "our") (NYSE MKT: VGZ) (TSX: VGZ) today announced the completion of the automated sorting tests on the coarse fractions of the four 5-tonne bulk samples from its Mt Todd gold project. The tests, completed at the facilities of Tomra Sorting Solutions near Hamburg, Germany, demonstrate that plus 5/8" (16 mm) product from the HPGR crusher can be efficiently sorted to separate the non-gold-bearing particles from the gold-bearing sulfides and quartz/calcite veining, at production rates.
The tests confirmed that, consistent with previous test work, 8-10% of the run-of-mine feed to the crushing circuit can be removed from the process stream prior to the grinding circuit. This is expected to reduce grinding circuit operating costs and provide a modest increase in grade to the grinding circuit. These results, combined with the favorable previously announced results of the HPGR crushing tests, provide support for key assumptions underlying the Company's decision to commence an update of the Mt Todd Preliminary Feasibility Study ("PFS").
Vista's President & CEO, Frederick H. Earnest, commented, "The application of this technology is not new to the mining sector and it is being used effectively where ores have distinct visual and/or density variations. Being present for the automated sorting of the bulk samples at production rates allowed us to observe the efficiency of this technology and its applicability to the Mt Todd gold project. The material balance results are consistent with previous test results and we expect to have assay results for the sorted material in August.
"With this phase of our metallurgical testing program complete, we are prepared to commence the grinding and leach recovery optimization testing once the samples are returned from Germany. The final results of this metallurgical testing program are expected to be available the middle of September. We have commenced the work of updating our PFS for the Mt Todd gold project, inclusive of flow sheet changes to integrate this sorting technology. We believe these changes will deliver a better technical project with improved economics."
Automated Sorting Test Results
The bulk sorting tests confirmed our ability to selectively remove particles known to have minerals associated with the presence of gold in the Batman deposit at production rates. The plus 5/8" (16 mm) material from the HPGR crushing/screening tests at Thyssen Krupp Industries was shipped to the facilities of Tomra Sorting Solutions. Three members of Vista's management/project development team were present to observe the tests, which were conducted in a standard production-size sorter with a 60 cm wide belt. Material from each of the four composites was sorted first using x-ray transmission ("XRT") to remove particles containing sulfide minerals and subsequently using lasers to remove particles containing quartz/calcite. The XRT sorting tests were conducted at three different sensitivity levels. The material balance results of the sorting tests are summarized in the following table.
| Plus 5/8" Fraction | Composite 1 | Composite 2 | Composite 3 | Composite 4 |
| XRT Sorted Material | 33-57% | 38-54% | 27-46% | 38-57% |
| Laser Sorted Material | 2.2-1.4% | 7.6-6.7% | 7.7-5.1% | 1.9-1.3% |
| Sorting Reject | 40-62% | 38-54% | 46-64% | 40-59% |
| Fraction of Total Composite | ||||
| Sorting Reject | 7.0-10.9% | 6.8-9.6% | 7.7-10.7% | 7.4-11.0% |
Each composite represents a different part of the Batman deposit with varying amounts of sulfide and quartz/calcite mineralization which provided the opportunity to sort material that represented: high grade core, low grade peripheral, average to high grade early production and average grade main deposit. The variation in the amount of material sorted by the XRT and laser sorting steps is a reflection of the relative mineral content and is not an indication of sorting efficiency. Upon receipt of assay results, the Company will determine the optimal settings, taking into consideration gold losses, grade of sorted product and total product rejected.
Based on the results of this testing, the Company plans to apply a different sorting recovery/waste reject factor to each of the different major mineralization styles in the deposit.
Commencement of Preliminary Feasibility Study Update
We believe that the Mt Todd gold project is a better gold project today as a result of the project optimization work completed over the last 12 months and we have commenced the work of updating the current PFS. As part of this work we intend to evaluate and include all appropriate production improvements and the most current economic factors. We believe the results of this study, when completed late this year or early next year, will demonstrate a technically improved project and provide an improved perspective of the value of the Mt Todd gold project at present gold prices.
Qualified Person
The scientific and technical information disclosed in this press release has been reviewed and approved by Mr. John Rozelle, Senior Vice President of Vista and a qualified person (as defined by Canadian National Instrument 43-101).
About Vista Gold Corp.
The Company is a well-funded gold project developer. Our principal asset is our flagship Mt Todd gold project in Northern Territory, Australia. Mt Todd is one of the largest undeveloped gold projects in Australia. For more information about our projects, including technical studies and resource estimates, please visit our website at www.vistagold.com.
