The Globe and Mail

Go to the Globe and Mail homepage

Jump to main navigationJump to main content

Press release from Marketwire

Allied Nevada: Additional Metallurgical Test Results Continue to Confirm Milling Recoveries of 87.3% for Gold and 82.2% for Silver

Thursday, December 02, 2010

Allied Nevada: Additional Metallurgical Test Results Continue to Confirm Milling Recoveries of 87.3% for Gold and 82.2% for Silver06:30 EST Thursday, December 02, 2010RENO, NEVADA--(Marketwire - Dec. 2, 2010) - Allied Nevada Gold Corp. ("Allied Nevada" or the "Company") (TSX:ANV)(NYSE Amex:ANV) is pleased to announce that is has received additional metallurgical test results from 24 composite samples for its Hycroft mine located near Winnemucca, Nevada. The Company has compiled these new results in its metallurgical model for milling oxide and sulfide mineralization. The model, which is comprised of 99 composites including these new results, indicates average recoveries of 87.3% for gold and 82.2% for silver through a grind-flotation (to create a concentrate)-cyanidation of tailings circuit. Additional aqua regia tests confirm previous results indicating that flotation concentrate is very amenable to oxidation processes typically practiced within the industry, with recovery of 98.5% of the gold and 99.3% of the silver. "We are gaining more and more confidence as we continue to build the metallurgical model for the milling project," commented Scott Caldwell, President & CEO. "As we progress through the optimization of the metallurgical testing process and flow sheet development we expect to see gold and silver recoveries improve overall."Currently, 38 additional composite samples are being metallurgically tested using the grinding-flotation of the sulfides to create a concentrate and cyanidation of the tailings flow sheet. This test work continues to provide data for the milling metallurgical model. Master composites will be constructed by domain for optimization test work. Five one thousand (1,000) kilogram bulk samples have been obtained for pilot plant testing simulating the proposed milling-flotation-tail cyanidation flow sheet. Flotation concentrate will be evaluated using various oxidation processes including roasting and autoclaving. Material from each bulk sample will be submitted for comminution and grindability test work. The size and geometry of this deposit allow the flexibility to blend mill feed for optimum metallurgical performance such as gold and silver grades, sulfide content and ore hardness.Management estimates that approximately 60% of the required metallurgical testing has been completed for a milling feasibility study, expected mid-2011. Due to the very large size of the current mineral resource and the scope of the milling scenario, management intends to conduct sulfide test work on a significant number of composite samples, distributed throughout the deposit. Management believes that this level of test work will allow for final flow sheet and plant design and that this test work will be completed by mid-2011.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 Metallurgical Characteristics The goal of the sulfide metallurgical program is to provide information for the anticipated mill feasibility study, expected to be completed in the second half of 2011. All testing to date has been completed to a feasibility study standard.The previously announced results indicate:Sulfide mineralization is amenable to simple, conventional flotation technology. Coarse grind to 100 microns. Bond work index of 15.6 kWh/t, or equivalent to a moderate hardness. Sulfide sulfur content of the cleaner concentrate is approximately 25%. This level of sulfur has produced an exothermic reaction in pressure oxidation, roasting and smelting operations. This type of exothermic reaction will reduce the amount of energy required to operate these process plants, reducing overall process costs. Overall flotation concentration is in excess of 20:1. Direct relationship between recovery of sulfides and metals. Key sulfides are pyrite and marcasite (see Table). Flotation concentration is amenable to roasting, smelting or pressure oxidation. No metallurgical optimization test work has been completed for the variability tests. Composite Cleaner Flotation Concentrate MineralogyMineral ConstituentMineral Mass %Pyrite/Marcasite72.00 %Chalcopyrite0.13 %Arsenopyrite0.26 %Other Sulfides0.07 %Quartz16.60 %Feldspar3.15 %Clays2.01 %Micas4.15 %Other Silicates0.04 %Ti Oxides0.19 %Other Oxides0.04 %Native Sulfur0.25 %Sulfates1.04 %Carbonates0.01 %Ag Minerals0.01 %Other0.05 %Total100.00 %Multi-element analysis conducted on 154 holes drilled at Hycroft indicates that only trace amounts of mercury exist below 150 meters, predominantly where the sulfide mineralization occurs.Heap Leach Metallurgical Characteristics Current run-of-mine leach performance is consistent with historical gold recoveries of 56.6% and silver recoveries are averaging approximately 12% for a silver ounce to gold ounce production ratio of 2:1. The first crushing system became operational in the third quarter of 2010 and two additional crushers are expected to be added as more siliceous ore becomes available over the next 18 months. When combined with run-of-mine recoveries, crushing approximately 30% of the total current ore feed is expected to improve overall average recoveries to approximately 60% for gold and 14% for silver. The goal for oxide heap leach testing is to determine the optimum crush size for the oxide mineralization. Based upon the large size of the current oxide resource, management believes that additional column leach and grinding test work will be required on approximately 100 oxide composite samples. This test work is expected to be completed in the first half of 2011.Cautionary Statement Regarding Forward Looking InformationThis press release contains forward-looking statements within the meaning of the U.S. Securities Act of 1933 and the U.S. Securities Exchange Act of 1934 (and the equivalent under Canadian securities laws), that are intended to be covered by the safe harbor created by such sections. Such forward-looking statements include, without limitation, statements regarding the Company's expectations concerning the timing, results, indications, benefits of and resources needed for exploration, test work, the crushing systems and engineering assessments; management's expectations regarding recoveries, including the prospects for improving recoveries; expectations regarding potential growth and optimization opportunities; results of evaluation of underlying sulfide mineralization at Hycroft; results of evaluation of the benefits of crushing oxide mineralization; results of metallurgical testing on oxide and sulfide mineralization; reserve and resource estimates; and other statements that are not historical facts. Forward-looking statements address activities, events or developments that Allied Nevada expects or anticipates will or may occur in the future, and are based on current expectations and assumptions. Although Allied Nevada management believes that its expectations are based on reasonable assumptions, it can give no assurance that these expectations will prove correct. Important factors that could cause actual results to differ materially from those in the forward-looking statements include, among others, risks relating to uncertainties concerning reserve and resource estimates as well as those factors discussed in Allied Nevada's filings with the U.S. Securities and Exchange Commission (the "SEC") including Allied Nevada's latest Annual Report on Form 10-K and its other SEC filings (and Canadian filings) including, without limitation, its latest Quarterly Report on Form 10-Q. The Company does not intend to publicly update any forward-looking statements, whether as a result of new information, future events, or otherwise, except as may be required under applicable securities laws. The technical contents of this news release have been prepared under the supervision of Scott Wilson of Scott E. Wilson Consulting Inc., who is a Qualified Person as defined by National Instrument 43-101. Scott Wilson is an independent consultant for Allied Nevada and is the Qualified Person for Allied Nevada Gold Corp.Visit the Allied Nevada website at FURTHER INFORMATION PLEASE CONTACT: Scott CaldwellAllied Nevada Gold Corp.President & CEO(775) 358-4455ORTracey ThomAllied Nevada Gold Corp.Vice President, Investor Relations(416)