Allied Nevada Gold Corp. (TSX:ANV)(NYSE Amex:ANV) has announced the metallurgical test results of 38 additional composite samples from its wholly owned Hycroft mine located near Winnemucca, Nevada.
The Company has compiled these additional results into its metallurgical model for milling oxide and sulfide mineralization. The model, which is now comprised of 137 composites including these new results, indicates average recoveries of 87% for gold and 82% for silver through a grind-flotation (to create a concentrate)-cyanidation of tailings circuit.
"We are confident that the ongoing positive test results indicate that we have completed a sufficient amount of testing to be comfortable with the flowsheet for the milling study," commented Scott Caldwell, President & CEO. "Management believes that, as we continue to optimize the metallurgical process, we should see improved metallurgical results for this project."
Bulk Sample Testing
Test work on the flotation concentrate from the first bulk sample (Brimstone mineralization) have shown:
- 30% gold and 83% silver recovery by direct cyanidation (leaching) of the flotation concentrate cleaned at a fine grind passing 325 mesh
- 85% gold and 75% silver from roasting followed by cyanidation of the calcine
- Optimization of the reagent scheme and energy requirements are expected to improve recoveries
- 98% gold and 93% silver from autoclaving followed by cyanidation
- Improved concentration ratio of 33:1
The results noted above have not been optimized for reagent requirements, particle grind size and, in the case of roasting, energy requirements. Management expects that further test work and optimization of the oxidation processes may improve recoveries.
Milling Feasibility Study – Metallurgical Testing Progress
Management estimates that approximately 70% of the required metallurgical testing has been completed for the initial milling feasibility study, expected mid-2011.
A master composite has been prepared representing the three largest mineralized domains, Brimstone, Vortex and Central. Concentrate produced from this master composite will be made available for external evaluation through existing oxidation plants.
Ongoing bond grindability test work continues to indicate a Bond Work Index of moderate ore hardness, which is typical of Nevada mineralization.
Further details of historical metallurgical test results are contained in the recently filed NI 43-101 compliant Amended and Restated Technical Report dated September 23, 2010 and filed with SEDAR.
Sulfide Concentrate Characteristics
The flotation concentrate has been found to be primarily pyrite and marcasite. This confirms past analysis on flotation testing. Mineralogical analysis shows that silver is contained, partly or fully, in the silver bearing minerals pyrargyrite, naumannite (a directly cyanide soluble silvtaer mineral) and selenian miargyrite. Additional mineralogical studies are ongoing to better define the silver bearing minerals.
Source: Allied Nevada Gold Corp.